Interlayer sheet, interlayer sheet with release liner, and optical laminate

Abstract

Provided is an interlayer sheet for use in optical applications and disposed between layers of a laminate. The interlayer sheet comprises a material having a refractive index n1 of 1.570 or greater and a storage elastic modulus G' at 25°C. V1 The viscoelastic layer V1 has a viscosity of 30 kPa to 700 kPa. The interlayer sheet has a total light transmittance of 86% or more and a haze value of 1.0% or less.

Description

Technical Field

[0001] The present invention relates to an interlayer sheet, an interlayer sheet with a release liner, and an optical laminate.

[0002] This application claims priority based on Japanese Patent Application No. 2020-052408 filed on March 24, 2020, Japanese Patent Application No. 2020-166429 filed on September 30, 2020, and Japanese Patent Application No. 2021-049063 filed on March 23, 2021, the entire contents of which are incorporated herein by reference. Background Art

[0003] Generally, adhesives (also called pressure-sensitive adhesives. The same applies hereinafter) have the property of being in a soft solid (viscoelastic) state in a temperature range near room temperature and being easily adhered to the adherend by pressure. Taking advantage of this property, adhesives are widely used in various industrial fields ranging from home appliances to automobiles, various machines, electrical devices, electronic devices, etc. for the purposes of bonding, fixing, and protection. As an example of the use of adhesives, there can be cited the use of bonding polarizing films, phase difference films, cover window components, and other various light-transmitting components to other components in display devices such as liquid crystal display devices and organic EL display devices. As technical documents related to adhesives for optical components, Patent Documents 1 and 2 can be cited.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-169382

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2017-128732 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] Patent documents 1 and 2 propose an adhesive composition with a (meth) acrylate polymer as the main component and an adhesive cross-linked with the adhesive composition, wherein the (meth) acrylate polymer contains a monomer having multiple aromatic rings as a monomer unit, but there is no disclosure of a specific adhesive having a refractive index of 1.570 or more and softness. On the other hand, it is also known to mix particles (such as inorganic particles such as zirconium oxide particles and titanium oxide particles) formed by an inorganic material with a high refractive index in a resin to increase the refractive index, but the refractive index and adhesive properties (such as peel strength, softness, etc.) of the adhesive mixed with inorganic particles are in a trade-off relationship, so it is difficult to apply to the field of adhesives. In particular, for adhesives for optical applications, it is also necessary to consider the impact on optical properties (such as total light transmittance, haze, etc.) when mixing inorganic particles. For example, in optical applications, when studying the refractive index improvement of the interlayer sheet used between the layers of the stack, it is required to obtain a balance of appropriate adhesion, deformation followability and high transparency for the components adjacent to the interlayer sheet, and to achieve a high refractive index.

[0010] The present invention has been developed in light of the above-mentioned circumstances, and its object is to provide an interlayer sheet that exhibits flexibility suitable for adhesion and conformability to adjacent components, and that combines a high refractive index with high transparency. Another object of the present invention is to provide an interlayer sheet with a release liner comprising the interlayer sheet. A further related object is to provide an optical layered body comprising the interlayer sheet as a component.

[0011] Solutions for solving problems

[0012] According to this specification, an interlayer sheet for use in optical applications and disposed between layers of a laminate is provided. The interlayer sheet comprises a viscoelastic layer V1 having a refractive index n1 of 1.570 or greater. The interlayer sheet has a total light transmittance of 86% or greater, a haze value of 1.0% or less, and a storage modulus G' at 25°C of V1 (hereinafter sometimes referred to as "storage modulus G' V1 (25)".) is 30kPa to 700kPa. The above interlayer sheet contains a high refractive index and a storage modulus G' V1 (25) The viscoelastic layer V1 is suppressed to below a certain level and is highly transparent, so it is useful as an interlayer sheet for optical applications. In addition, the interlayer sheet is pre-formed into a sheet shape, so it can be easily arranged at a desired location.

[0013] In some embodiments, the viscoelastic layer has a thickness of 5 μm or greater. A viscoelastic layer having such a thickness is preferred because it can easily be laminated on an adjacent member with good adhesion by absorbing irregularities that may exist on the surface of the member.

[0014] Some embodiments of the interlayer sheet further include a viscoelastic layer V2 laminated on the viscoelastic layer V1. Here, the storage modulus G' of the viscoelastic layer V2 at 25°C is V2 (hereinafter sometimes referred to as "storage modulus G' V2 (25)".) is lower than the storage modulus G' of the viscoelastic layer V1 at 25°C V1 The interlayer sheet having such a structure can have further improved flexibility due to the contribution of the viscoelastic layer V2.

[0015] In some embodiments, the refractive index n2 of the viscoelastic layer V2 is lower than the refractive index n1 of the viscoelastic layer V1. With the interlayer sheet having such a configuration, the behavior of light passing through the interlayer sheet can be controlled by utilizing the refractive index difference between the viscoelastic layers V1 and V2.

[0016] Furthermore, according to this specification, a release-linered interlayer sheet is provided, comprising any of the interlayer sheets disclosed herein and a release liner covering at least one surface of the interlayer sheet. The interlayer sheet disclosed herein can be preferably used in the following manner: manufacturing, storing, distributing, processing, etc., as such an interlayer sheet with a release liner, wherein at least one surface is protected by the release liner, and the release liner is removed before lamination with adjacent components.

[0017] Furthermore, the specification provides an optical layered body comprising any of the interlayer sheets disclosed herein and a resin film laminated on the interlayer sheet. In this optical layered body, the advantages of the interlayer sheet disclosed herein, which combines a high refractive index with high transparency and flexibility, can be advantageously utilized.

[0018] It should be noted that the technical solutions formed by appropriately combining the elements described in this specification may also be included in the scope of protection required by this patent application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a cross-sectional view schematically showing the structure of an interlayer sheet according to one embodiment.

[0020] Figure 2 This is a cross-sectional view schematically showing the structure of an interlayer sheet according to another embodiment.

[0021] Figure 3 This is a cross-sectional view schematically showing an optical laminate including an interlayer sheet according to one embodiment. DETAILED DESCRIPTION

[0022] The following describes preferred embodiments of the present invention. Matters necessary for implementing the present invention, other than those specifically mentioned in this specification, will be understood by those skilled in the art based on the teachings of implementing the invention described in this specification and common knowledge at the time of application. The present invention can be implemented based on the disclosures in this specification and common knowledge in the art.

[0023] It should be noted that in the following drawings, components / parts having the same function are sometimes described with the same reference numerals, and repeated descriptions are sometimes omitted or simplified. In addition, the embodiments described in the drawings are schematic for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the dimensions or scale of the actual product provided.

[0024] In this specification, a self-luminous element refers to a light-emitting element that can control the brightness of the light by the value of the current flowing. The self-luminous element can be composed of a single body or an aggregate. Specific examples of self-luminous elements include light-emitting diodes (LEDs) and organic ELs, but are not limited to them. When a light-emitting device is mentioned in this specification, the light-emitting device may include such a self-luminous element as a constituent element. Examples of the above-mentioned light-emitting devices include light source module devices used as lighting (such as a planar light-emitting body module) and display devices forming pixels, but are not limited to them.

[0025] According to the specification, an interlayer sheet for use in optical applications and arranged between layers of a laminate is provided. The interlayer sheet at least comprises a viscoelastic layer V1. The interlayer sheet may further comprise a viscoelastic layer V2 laminated on the viscoelastic layer V1. One or both of the viscoelastic layers V1 and V2 are typically adhesive layers composed of an adhesive. The interlayer sheet of this type can be understood as an adhesive sheet having an adhesive layer. Hereinafter, the interlayer sheet may be referred to as an adhesive sheet, the viscoelastic layer may be referred to as an adhesive layer, the viscoelastic material may be referred to as an adhesive, and the surface of the viscoelastic layer may be referred to as an adhesive surface. In addition, the component on which the viscoelastic layer of the interlayer sheet disclosed herein is laminated may sometimes be referred to as the adherend of the interlayer sheet (adhesive sheet). In some embodiments, the interlayer sheet preferably has an adhesive surface composed of an adhesive layer V1.

[0026] <Example of Interlayer Sheet Configuration>

[0027] The interlayer sheet disclosed herein may be in the form of an adhesive sheet with a substrate having an adhesive layer (for example, an adhesive layer of a single-layer structure formed by a viscoelastic layer V1, or an adhesive layer of a laminated structure in which two or more adhesive layers comprising a viscoelastic layer V1 and a viscoelastic layer V2 are directly in contact and laminated) on one or both sides of a non-peelable substrate (supporting substrate), or in the form of an adhesive sheet without a substrate (that is, an adhesive sheet without a non-peelable substrate. Typically, an adhesive sheet formed by an adhesive layer) in which the adhesive layer is retained on a release liner. The concept of adhesive sheet mentioned here may include objects referred to as adhesive tapes, adhesive labels, adhesive films, etc. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be an adhesive sheet further processed into various shapes.

[0028] An example of the structure of the interlayer sheet disclosed herein is shown in Figure 1 . The interlayer sheet (adhesive sheet) 1 is constructed in the form of a single-sided adhesive sheet (single-sided adhesive sheet), and the single-sided adhesive sheet comprises: an adhesive layer 10 whose first surface 10A becomes the adhesive surface (adhesive surface) to be adhered to the adherend, and a supporting substrate 20 laminated on the second surface 10B of the adhesive layer 10. The second surface 10B of the adhesive layer 10 is bonded to the first surface (non-peelable surface) 20A of the supporting substrate 20. As the supporting substrate 20, for example, a plastic film such as a polyester film can be used. The supporting substrate 20 can be, for example, an optical film such as a polarizing plate. The adhesive sheet 1 before use (before being adhered to the adherend) can be, for example, as Figure 1 As shown in FIG. 1 , the adhesive sheet 50 with a release liner is in the form of an adhesive surface 10A protected by a release liner 30 whose at least the adhesive layer side serves as a releasable surface (release surface). Alternatively, the second surface 20B of the supporting substrate 20 (the surface on the opposite side to the first surface 20A, also referred to as the back surface) serves as a release surface, and the adhesive surface 10A is protected by being wound or laminated in a manner such that the adhesive surface 10A abuts against the second surface 20B. The adhesive layer 10 may be as follows: Figure 1 As shown, the structure is a single layer formed by the viscoelastic layer V1, but it can also be a stacked structure in which two or more sub-adhesive layers with different compositions (for example, the viscoelastic layer V1 constituting the adhesive surface 10A and the viscoelastic layer V2 arranged on the supporting substrate 20 side) are in direct contact (that is, not separated by a layer of non-adhesive material) and stacked.

[0029] The interlayer sheet disclosed herein may also be in the form of a double-sided adhesive sheet without a substrate formed by an adhesive layer. Figure 2As shown, the substrate-free double-sided adhesive sheet 2 can be in the following form: before use, the first surface (first adhesive surface) 10A and the second surface (second adhesive surface) 10B of the adhesive layer 10 are protected by release liners 31 and 32, at least the adhesive layer side of which serves as a releasable surface (release surface). Alternatively, it can be in the form of a back surface (the surface on the opposite side from the adhesive side) of the release liner 31 serving as a release surface, and the adhesive surfaces 10A and 10B are protected by being wound or laminated in a manner such that the adhesive surface 10B abuts against the back surface of the release liner 31. Such a substrate-free double-sided adhesive sheet can be used, for example, by bonding a substrate (preferably a light-transmitting substrate, for example, an optical component such as an optical film) to at least one of the first adhesive surface and the second adhesive surface.

[0030] constitute Figure 2 The adhesive layer 10 of the substrate-free double-sided adhesive sheet 2 shown has a laminated structure in which two sub-adhesive layers of different compositions are in direct contact and laminated. Specifically, the adhesive layer 10 is a laminated structure (double-layer structure) formed by a first viscoelastic layer (first adhesive layer, viscoelastic layer V1) 11 and a second viscoelastic layer (second adhesive layer, viscoelastic layer V2) 12. Alternatively, the interlayer sheet disclosed herein can also be in the form of a substrate-free double-sided adhesive sheet formed by an adhesive layer (viscoelastic layer V1) of a single-layer structure. This interlayer sheet in the form of a substrate-free double-sided adhesive sheet of a laminated structure or a single-layer structure can be used, for example, as a constituent element of an optical laminate in which optical components are laminated on the first adhesive surface and the second adhesive surface.

[0031] The interlayer sheet disclosed herein may be a component of an optical laminate having an optical member bonded to at least one surface. Figure 1 The interlayer sheet 1 shown may be as follows Figure 3 As shown in FIG. 1 , an optical laminate 100 is formed by laminating an optical component 70 on the first surface 10A of the adhesive layer 10. The optical component may be, for example, a glass plate, a resin film, a metal plate, etc. The interlayer sheet 1 may also become a component of the optical laminate by being arranged between the optical component 70 and a second optical component not shown. Figure 1 In the interlayer sheet 1 shown, when the supporting substrate 20 is an optical member such as an optical film, the interlayer sheet 1 can be understood as an optical laminate in which the optical member is laminated on the second surface 10B of the pressure-sensitive adhesive layer 10 .

[0032] In addition, although not specifically shown in the figure, the interlayer sheet disclosed herein may also be in the form of a double-sided adhesive sheet with a substrate (double-sided adhesive sheet with a substrate), wherein the double-sided adhesive sheet with a substrate comprises a supporting substrate having a first side and a second side with non-releasable properties, a first adhesive layer fixedly laminated on the first side, and a second adhesive layer fixedly laminated on the second side. As examples of the configuration of such a double-sided adhesive sheet with a substrate, the following forms can be cited: Figure 1 In the single-sided adhesive sheet 1 shown, the second surface 20B of the supporting substrate 20 is a non-peelable surface and a second adhesive layer is provided on the second surface 20B. The second surface of the second adhesive layer is bonded to the second surface 20B of the supporting substrate 20, and the first surface of the second adhesive layer (the surface on the opposite side to the second surface) becomes the second adhesive surface of the double-sided adhesive sheet with substrate. The composition of the adhesive constituting the second adhesive layer may be the same as or different from the composition of the adhesive constituting the first adhesive layer. The interlayer sheet in the form of a double-sided adhesive sheet with substrate can be used as a constituent element of an optical laminate in which optical components are respectively stacked on the first adhesive surface and the second adhesive surface. As for the double-sided adhesive sheet with substrate before use, similarly to the above-mentioned double-sided adhesive sheet without substrate, it can be a form in which the first adhesive surface and the second adhesive surface are protected by a release liner.

[0033] <Characteristics of Interlayer Sheet>

[0034] (Refractive Index)

[0035] The interlayer sheet disclosed herein comprises a viscoelastic layer (adhesive layer) V1 having a refractive index n1 of 1.570 or greater. This viscoelastic layer V1 can be achieved, for example, by forming at least one surface (adhesive surface) of the viscoelastic layer with an adhesive (viscoelastic material) having a refractive index of 1.570 or greater. The technology disclosed herein provides an adhesive layer V1 having a refractive index of 1.570 or greater, an adhesive composition capable of forming the adhesive layer V1, and an interlayer sheet comprising the adhesive layer V1.

[0036] It should be noted that, in this specification, the refractive index of the adhesive (viscoelastic material) refers to the refractive index of the surface (adhesive surface) of the adhesive. The refractive index of the adhesive can be measured using a commercially available refractometer (Abbe refractometer) at a measuring wavelength of 589 nm and a measuring temperature of 25°C. As an Abbe refractometer, for example, the model "DR-M4" manufactured by ATAGO or its equivalent can be used. As a measurement sample, an adhesive layer formed by the adhesive of the evaluation object can be used. Specifically, the refractive index of the adhesive can be measured by the method described in the examples below. The refractive index of the adhesive can be adjusted, for example, by the composition of the adhesive (for example, the composition of the monomer components constituting the base polymer, additives that can be used as needed, etc.).

[0037] In some embodiments, it is advantageous for the refractive index of the adhesive layer V1 to be higher than 1.570, preferably 1.580 or higher, more preferably 1.585 or higher, and still more preferably 1.590 or higher (e.g., 1.595 or higher). With the adhesive layer V1 having such a refractive index, by virtue of the relative refractive index relationship between the adhesive layer V1 and the adjacent layer (which may be another viscoelastic layer contained in the interlayer sheet (e.g., the adhesive layer V2), or the adherend to which the adhesive layer V1 is laminated), the behavior of light passing through the adhesive layer V1 can be effectively controlled. In some embodiments of the technology disclosed herein, the refractive index of the adhesive layer V1 can be, for example, 1.600 or higher, or higher than 1.600, 1.605 or higher, or higher than 1.605, or 1.610 or higher, or higher than 1.610. The preferred upper limit of the refractive index of the adhesive layer V1 can vary depending on the refractive index of the adjacent layer, etc., and thus is not limited to a specific range. In some embodiments, taking into account the balance with the adhesive properties and transparency, the refractive index of the adhesive layer V1 can be, for example, 1.700 or lower, 1.670 or lower, or 1.650 or lower.

[0038] When the interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface on one side and a second adhesive surface on the other side (including both a substrate-free double-sided adhesive sheet and a double-sided adhesive sheet with a substrate. The same shall apply hereinafter unless otherwise specified), and when the first adhesive surface is constituted by the adhesive layer V1, it is preferred that at least the first adhesive surface of the adhesive layer satisfies any of the above refractive indices. There is no particular limitation on the refractive index of the second adhesive surface.

[0039] In some embodiments, the refractive index n2 of the second adhesive surface can be approximately the same as the refractive index n1 of the first adhesive surface. More specifically, the absolute value of the difference in refractive indices between the two adhesive surfaces, i.e., |n1 - n2|, can be, for example, less than 0.05, or less than 0.03, or less than 0.01. The lower limit of |n1 - n2| can be 0.00, or greater than 0.00. The relative relationship between the refractive indices of the two adhesive surfaces can be n1 > n2, n1 < n2, or n1 = n2.

[0040] In other embodiments, the difference between the refractive index n1 of the first bonding surface of the interlayer sheet and the refractive index n2 of the second bonding surface, i.e., n1-n2, can be, for example, greater than 0.00, can be 0.01 or greater, preferably 0.02 or greater, can be 0.03 or greater, can be 0.05 or greater, can be 0.10 or greater, can be 0.15 or greater, can be 0.20 or greater, or can be 0.25 or greater. The magnitude relationship between n1 and n2 can also be reversed. There is no particular upper limit on n1-n2. In some embodiments, from the perspective of easily balancing adhesion properties and transparency, n1-n2 can be, for example, less than 0.30, less than 0.26, less than 0.21, less than 0.18, or less than 0.16. An interlayer sheet having different refractive indices on the first adhesive surface and the second adhesive surface can be realized, for example, by laminating the first and second adhesive layers having different refractive indices on a non-peelable supporting substrate in a double-sided adhesive sheet with a substrate; or making the double-sided adhesive sheet without a substrate a laminated structure of two or more sub-adhesive layers, in which the refractive index of the adhesive constituting the first adhesive surface is different from the refractive index of the adhesive constituting the second adhesive surface.

[0041] In some ways, the ratio (n1 / n2) of the refractive index n1 of the 1st bonding surface and the refractive index n2 of the 2nd bonding surface, for example, can be greater than 1.00, can be about more than 1.01, is suitable for about more than 1.02, and can also be about more than 1.03. In some ways, it is advantageous to be about more than 1.05 than (n1 / n2), is preferably about more than 1.07, more preferably about more than 1.10, and can also be about more than 1.11. There is no particular restriction on the upper limit of (n1 / n2). In some ways, from the viewpoints such as bonding characteristics, transparency, the ratio (n1 / n2), for example, can be about below 1.20, can be about below 1.18, can be about below 1.16, can be about below 1.14, and can also be about below 1.12.

[0042] (Storage modulus G')

[0043] In the interlayer sheet (adhesive sheet) disclosed herein, the storage modulus G' (storage modulus G') of the viscoelastic layer (adhesive layer) V1 at 25°C is V1 (25)) can be appropriately set according to the purpose of use, usage mode, etc., and is not limited to a specific range. Storage modulus G' V1 (25) For example, it can be in the range of about 30 kPa to 700 kPa. In some embodiments, from the perspective of ease of attachment to the adherend, the storage modulus G' V1(25) is advantageously about 600 kPa or less, preferably 500 kPa or less, and more preferably 400 kPa or less (e.g., 350 kPa or less). In some embodiments, from the perspective of improving the flexibility of the adhesive layer V1 at room temperature (e.g., 25°C) so that it can easily adhere to the adherend, the storage modulus G' is V1 (25) is advantageously below about 330 kPa, preferably below 300 kPa. In some embodiments where the adhesiveness and softness at room temperature are more important, the storage modulus G' V1 (25) For example, it can be lower than 270 kPa or lower than 250 kPa, and it is advantageous to be lower than 200 kPa, preferably lower than 180 kPa, and more preferably lower than 160 kPa (for example, lower than 140 kPa). In some embodiments, the storage modulus G' V1 (25) can be lower than 100 kPa or lower than 90 kPa. Storage modulus G' V1 The lower limit of (25) is not particularly limited. From the perspective of processability and handling, it can be, for example, 30 kPa or more, 50 kPa or more, or 70 kPa or more. In some embodiments, considering the high refractive index, the storage modulus G' V1 (25) It can be 100 kPa or more, 150 kPa or more, 200 kPa or more, 250 kPa or more, or 300 kPa or more.

[0044] In the PSA sheet disclosed herein, the storage modulus G' (storage modulus G') of the viscoelastic layer (PSA layer) V1 at 50°C is V1 (50)) is not particularly limited, and can be, for example, less than 100 kPa. In some embodiments, the storage modulus G' V1 (50) It is appropriate to be lower than 60 kPa, preferably lower than 40 kPa, more preferably lower than 38 kPa (e.g. lower than 36 kPa). This limits the storage modulus G' V1 The adhesive layer V1 of (50) can be heated appropriately as needed to easily improve the adhesion to the adherend, thereby improving the adhesion to the adherend. Storage modulus G' V1 There is no particular restriction on the lower limit of (50). In some embodiments, from the perspective of heat resistance of the adhesive layer V1, the storage modulus G' V1 (50) For example, it may be 10 kPa or more, 15 kPa or more, 20 kPa or more, or 23 kPa or more.

[0045] In some aspects of the interlayer sheet disclosed herein, the viscoelastic layer (adhesive layer) V1 preferably satisfies at least one of the following conditions:

[0046] (a) Storage modulus G' V1 (25) 350 kPa or less (preferably less than 200 kPa, for example, 180 kPa or less); and

[0047] (b) Storage modulus G' V1 (50) less than 60 kPa (preferably less than 50 kPa, more preferably less than 40 kPa, for example less than 38 kPa).

[0048] An adhesive layer V1 that satisfies at least the above-mentioned condition (a) is preferred from the viewpoint of adhesion and flexibility to the adherend in the room temperature region (e.g., 25°C). An interlayer sheet having an adhesive layer V1 that satisfies at least the above-mentioned condition (b) is preferred because it can easily improve adhesion (adhesion) to the adherend by heating to a temperature slightly higher than room temperature. An interlayer sheet having an adhesive layer V1 that does not satisfy the above-mentioned condition (a) but satisfies the above-mentioned condition (b) has good reworkability (re-stickability) at the initial stage of pasting in the room temperature region and can be used as a heat-activated interlayer sheet that can effectively improve the peel strength from the adherend by heating to a temperature slightly higher than room temperature. The above-mentioned heat activation can be performed by heating the interlayer sheet to a temperature slightly higher than room temperature when pasting to the adherend. The above-mentioned temperature slightly higher than room temperature is, for example, about 60°C or lower, preferably about 55°C or lower (e.g., about 50°C or lower).

[0049] In some aspects of the interlayer sheet disclosed herein, the storage modulus G' V1 (50)[kPa] relative to storage modulus G' V1 (25) [kPa] ratio, i.e. storage modulus ratio G' V1 (50) / G' V1 (25) For example, it can be 70% or less, 40% or less, 30% or less, or 20% or less. V1 (50) / G' V1 (25) The interlayer sheet with a small adhesive layer V1 is suitable for use as the above-mentioned heat-activated interlayer sheet. G' V1 (50) / G' V1 There is no particular restriction on the lower limit of (25). V1 (50) / G' V1 (25) For example, it is 5% or more. From the viewpoint of the heat resistance of the interlayer sheet, it is preferably 10% or more, and may be 12% or more, or may be 15% or more.

[0050] Storage modulus G' V1 (25) and G' V1 (50) can be obtained by dynamic viscoelasticity measurement, and G' can be calculated based on the results.V1 (50) / G' V1 (25) Dynamic viscoelasticity measurement can be performed by conventional methods using a commercially available dynamic viscoelasticity measuring apparatus, such as ARES manufactured by TA Instruments or its equivalent, under the following measurement conditions. As a sample for measurement, a sample prepared by laminating the adhesive layer of the evaluation object as needed to a thickness of about 1.5 mm is used.

[0051] [Measurement conditions]

[0052] Deformation Mode: Twist

[0053] Measuring frequency: 1Hz

[0054] Heating rate: 5℃ / min

[0055] Shape: Parallel Plate

[0056] Storage modulus G' of viscoelastic layer (adhesive layer) V1 V1 (25), G' V1 (50) and the storage modulus ratio can be adjusted by selecting the composition of the monomer components of the base polymer constituting the adhesive layer V1 (for example, the type and content of the monomer (m1)), whether a cross-linking agent is used and the amount of use, whether a refractive index enhancer and a plasticizer are used, the type and amount of use, etc. For example, as the monomer (m1), on the basis of using the first monomer as the main component of the monomer (m1), by using a second monomer having a chemical structure different from that of the first monomer in combination with the first monomer in a smaller amount, it is possible to reduce G' on the basis of using the first monomer alone as the monomer (m1). V1 (50) Reduce G' V1 (50) / G' V1 (25).

[0057] When the PSA sheet disclosed herein is a double-sided PSA sheet having a first adhesive surface and a second adhesive surface (for example, a double-sided PSA sheet with a substrate having a first adhesive layer composed of an adhesive layer V1 on the first surface of the substrate and a second adhesive layer composed of an adhesive layer V2 on the second surface of the substrate; a double-sided PSA sheet with a laminated structure in which the adhesive layer V1 constituting the first adhesive surface and the adhesive layer V2 constituting the second adhesive surface are laminated without a non-adhesive substrate interposed therebetween; a double-sided PSA sheet with a single-layer structure in which one surface of the adhesive layer V1 serves as the first adhesive surface and the other surface of the adhesive layer V1 serves as the second adhesive surface, etc. The same applies to other similar descriptions), the storage modulus G' is V1 (25), G' V1(50) and the storage modulus ratio can be applied to at least the adhesive layer constituting the first adhesive surface, and preferably to both the adhesive layer constituting the first adhesive surface and the adhesive layer constituting the second adhesive surface. The storage modulus G' of the adhesive layer constituting the first adhesive surface and the storage modulus G' of the adhesive layer constituting the second adhesive surface can be of the same magnitude or different.

[0058] (Total light transmittance)

[0059] The interlayer sheet disclosed herein comprises the above-mentioned adhesive layer V1 having a high refractive index, and the total light transmittance of the interlayer sheet is 86% or more. For such an interlayer sheet with high transparency, a structure with a substrate or a structure without a substrate can be preferably used in applications requiring high light transmittance (such as optical applications) and applications requiring good visual recognition of the performance of the adherend through the adhesive sheet. In some embodiments, the total light transmittance of the interlayer sheet is preferably 88% or more, more preferably 90% or more (for example, higher than 90.0%), can be 90.5% or more, can be 93% or more, or can be 95% or more. The upper limit of the total light transmittance is theoretically the value obtained by subtracting the light loss (Fresnel loss) caused by reflection generated at the air interface from 100%, and in practice it can be about 98% or less, about 96% or less, or about 95% or less. In some embodiments, taking into account the refractive index and adhesive properties, the total light transmittance of the interlayer sheet can be about 94% or less, about 93% or less, or about 92% or less. Total light transmittance is measured in accordance with JIS K7136:2000 using a commercially available transmittance meter. A transmittance meter, such as the "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or an equivalent, can be used. More specifically, the total light transmittance of the interlayer sheet can be measured, for example, according to the examples described below. The total light transmittance of the interlayer sheet can be adjusted, for example, by selecting the composition and thickness of the viscoelastic layer contained in the interlayer sheet, and the type and thickness of the substrate in the configuration including the substrate.

[0060] The interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet with a substrate in which a first adhesive layer and a second adhesive layer are fixedly laminated on a supporting substrate, and when the first adhesive layer is a layer consisting of an adhesive layer V1, at least the first adhesive layer satisfies any of the above-mentioned total light transmittances, and the total light transmittance of the second adhesive layer is not particularly limited. In the use mode in which light passes through the thickness direction of the adhesive sheet, it is preferred that the total light transmittance of the second adhesive layer satisfies any of the total light transmittances of the first adhesive layer. The relative relationship of the total light transmittances of the two adhesive layers can be 1st adhesive layer > 2nd adhesive layer, 1st adhesive layer < 2nd adhesive layer, or 1st adhesive layer = 2nd adhesive layer.

[0061] (Haze value)

[0062] The interlayer sheet disclosed herein comprises the above-mentioned adhesive layer V1 having a high refractive index, and the haze value of the interlayer sheet is 1.0% or less. For such an interlayer sheet with high transparency, a structure with a substrate or a structure without a substrate can be preferably applied to applications requiring high light transmittance (such as optical applications) and applications requiring good visual recognition of the performance of the adherend through the interlayer sheet. In some embodiments, the haze value of the interlayer sheet can be less than 0.9%, less than 0.8%, less than 0.5%, or less than 0.3%. There is no particular restriction on the lower limit of the haze value of the interlayer sheet. From the perspective of improving transparency, the smaller the haze value, the more preferred. On the other hand, in some embodiments, taking into account the refractive index and adhesive properties, the haze value of the interlayer sheet can be, for example, more than 0.05%, more than 0.1%, more than 0.2%, more than 0.3%, or more than 0.4%. These haze values related to the interlayer sheet can also be preferably applied to the haze value of the PSA sheet when the technology disclosed herein is implemented in the form of a PSA sheet without a substrate (typically, a PSA sheet formed of a PSA layer).

[0063] Here, "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when the object being measured is irradiated with visible light. It is also called the haze value. The haze value can be expressed using the following formula.

[0064] Th (%) = Td / Tt × 100

[0065] In the above formula, Th is the haze value (%), Td is the scattered light transmittance, and Tt is the total light transmittance. The haze value can be measured according to the method described in the Examples below. The haze value can be adjusted, for example, by selecting the composition and thickness of the measurement object.

[0066] When the interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet with a substrate in which the first adhesive layer and the second adhesive layer are fixedly laminated on a supporting substrate, the interlayer sheet as a whole can satisfy any of the above-mentioned haze values, and there is no particular restriction on the haze values of the first adhesive layer and the second adhesive layer. The relative relationship of the haze values of the two adhesive layers can be 1st adhesive layer>2nd adhesive layer, 1st adhesive layer<2nd adhesive layer, or 1st adhesive layer=2nd adhesive layer. That is, the haze value of the first adhesive layer and the haze value of the second adhesive layer can be of the same degree or different. The same applies to the haze value of each sub-adhesive layer when the interlayer sheet disclosed herein comprises an adhesive layer formed by directly laminating a plurality of sub-adhesive layers (for example, adhesive layer V1 and adhesive layer V2).

[0067] (Surface smoothness of adhesive surface)

[0068] In some aspects of the interlayer sheet disclosed herein, the adhesive surface of the interlayer sheet (eg, the adhesive surface composed of the adhesive layer V1) preferably has high surface smoothness.

[0069] For example, the arithmetic mean roughness Ra of the above-mentioned adhesive surface is preferably limited to below a specified value. It is preferred from the viewpoint of optical homogeneity to have a structure with an adhesive surface designed to have a low arithmetic mean roughness Ra. By limiting the arithmetic mean roughness Ra, for example, in a mode of use in which light is extracted through the above-mentioned adhesive surface (an interlayer sheet configured closer to the viewpoint side than the self-luminous element in a light-emitting device), it is possible to exert an effect of suppressing the uneven brightness caused by the surface state of the adhesive layer. When the arithmetic mean roughness Ra of the adhesive surface is low, it is also advantageous to suppress optical distortion, and the suppression of optical distortion also contributes to the improvement of optical homogeneity. When the interlayer adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, it is preferred that the arithmetic mean roughness Ra of at least the first adhesive surface is limited to below a specified value, and more preferably the arithmetic mean roughness Ra of both adhesive surfaces is limited to below a specified value. By making each adhesive surface of the double-sided adhesive sheet have high surface smoothness, it is possible to preferably achieve bonding with excellent optical homogeneity.

[0070] In some embodiments, the arithmetic mean roughness Ra of the bonding surface is preferably about 70 nm or less, more preferably about 65 nm or less, further preferably about 55 nm or less, and can be less than 50 nm, less than 45 nm, or less than 40 nm. From the viewpoint of production efficiency, in some embodiments, the arithmetic mean roughness Ra of the bonding surface can be, for example, about 10 nm or more, about 20 nm or more, or about 30 nm or more (for example, about 40 nm or more). In the interlayer sheet having the first bonding surface and the second bonding surface, the arithmetic mean roughness Ra of the first bonding surface and the arithmetic mean roughness Ra of the second bonding surface can be the same or different.

[0071] In addition, for example, the maximum height Rz of the above-mentioned adhesive surface is preferably limited to below a specified value. It is preferred to have an adhesive surface designed to have a low maximum height Rz from the viewpoint of optical homogeneity. By limiting the maximum height Rz, for example, in the use method of extracting light through the above-mentioned adhesive surface as described above, it is possible to exert an effect of suppressing the uneven brightness caused by the surface state of the adhesive layer. When the maximum height Rz of the adhesive surface is low, it is also beneficial to suppress optical distortion. When the interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, it is preferred that at least the maximum height Rz of the first adhesive surface is limited to below a specified value, and more preferably the maximum height Rz of both adhesive surfaces is limited to below a specified value. By making each adhesive surface of the double-sided adhesive sheet have high surface smoothness, it is possible to preferably achieve bonding with excellent optical homogeneity.

[0072] In some ways, the maximum height Rz of the bonding surface is preferably about 600nm or less, more preferably about 500nm or less, further preferably about 450nm or less, particularly preferably about 400nm or less, can be lower than 350nm, can be lower than 300nm, also can be lower than 250nm. From viewpoints such as production efficiency, in some ways, the maximum height Rz of the bonding surface can for example be about 10nm or more, can be about 50nm or more, can be about 100nm or more, also can be about 200nm or more. In the interlayer sheet of the mode with the 1st bonding surface and the 2nd bonding surface, the maximum height Rz of the 1st bonding surface can be the same degree as the maximum height Rz of the 2nd bonding surface, or can be different.

[0073] The arithmetic mean roughness Ra and maximum height Rz of the adhesive surface are measured using a non-contact surface roughness measuring device. A non-contact surface roughness measuring device using an optical interference method can be used, for example, a three-dimensional optical profiler (trade name "NewView7300", manufactured by ZYGO) or its equivalent. Specifically, the arithmetic mean roughness Ra and maximum height Rz can be measured, for example, using the following measurement method or by setting the measurement operation and measurement conditions in a manner that yields results equivalent to or corresponding to those obtained using this measurement method.

[0074] Specifically, the surface profile of the sample for measurement was measured under the following conditions using a three-dimensional optical profiler (trade name "NewView7300", manufactured by ZYGO Corporation) at 23°C and 50% RH. The arithmetic surface roughness Ra was calculated based on the measured data in accordance with JIS B0601-2001. The maximum height Rz was determined by calculating the sum of the height Rp of the highest peak above the mean line of the roughness curve and the depth Rv of the deepest valley below the mean line, for the data obtained from the above measurement (roughness curve). The measurement was performed five times (i.e., N = 5), and the average value was used.

[0075] The sample for measurement can be prepared, for example, by cutting the adhesive layer or interlayer sheet containing the adhesive layer to be measured into a size of approximately 150 mm in length and 50 mm in width. If the adhesive surface is protected by a release liner, the release liner is gently peeled off (for example, at a tensile speed of 300 mm / min and a peel angle of 180°) to expose the adhesive surface. It is ideal to wait for approximately 30 minutes after the adhesive surface is exposed before measurement.

[0076] [Measurement conditions]

[0077] Measuring area: 5.62mm×4.22mm

[0078] (Objective lens: 2.5x, internal lens: 0.5x)

[0079] Parsing mode:

[0080] Remove: Cylinder

[0081] DataFill: ON (Max: 25)

[0082] RemoveSpikes: ON (xRMS: 1)

[0083] Filter: OFF

[0084] The arithmetic mean roughness Ra and maximum height Rz of the adhesive surface can be adjusted by the composition and properties (viscosity, leveling properties, etc.) of the adhesive composition used to form the adhesive layer, the properties of the surface (release surface) of the release liner protecting the adhesive surface, etc.

[0085] (Water absorption)

[0086] In some embodiments, the water absorption of the adhesive layer V1 is preferably limited to a specified value or less. By limiting the water absorption of the adhesive layer V1, there is a tendency to suppress the dimensional change of the viscoelastic layer V1 caused by the change in the amount of water in the adhesive layer V1 (for example, the absorption and release of water such as moisture in the environment). As a result, the warping of the interlayer sheet or the optical laminate containing the interlayer sheet caused by the inconsistency of the dimensional change between the adhesive layer V1 and the adjacent layer (which may be the adhesive layer V2, the supporting substrate, the release liner, the adherend, etc.) can be suppressed. From the perspective of maintaining the flatness, transparency, refractive index, etc. of the adhesive layer V1 at a certain level, it is also preferred to suppress the change in the amount of water in the adhesive layer V1. In addition, the interlayer sheet having an adhesive layer V1 with a low water absorption is not easy to absorb water, and is therefore suitable as an interlayer sheet used in components or products such as organic EL elements that contain elements that hate water.

[0087] In some embodiments, the water absorption rate of the adhesive layer V1 is appropriately about 1.0% or less, preferably 0.7% or less, more preferably 0.5% or less (for example, less than 0.5%), and can be 0.4% or less, 0.3% or less, or 0.2% or less. There is no particular restriction on the lower limit of the water absorption rate of the adhesive layer V1. From a practical point of view such as taking into account the adhesive properties, it can be, for example, 0.01% or more, 0.05% or more, 0.1% or more, 0.15% or more, or 0.25% or more. When the interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet with a substrate having a first adhesive layer and a second adhesive layer, it is preferred that the water absorption rate of at least the first adhesive layer (preferably the adhesive layer V1) is limited to a specified value or less. From the viewpoint of obtaining a higher effect, it is more preferred that the water absorption rates of both the first and second adhesive layers be limited to a specified value or less.

[0088] The water absorption rate (also referred to as moisture content) of the pressure-sensitive adhesive layer is measured by the following method.

[0089] [Determination of moisture content]

[0090] The pressure-sensitive adhesive layer to be evaluated, together with two release liners placed on one side and the other side thereof, was cut into a 4 cm × 5 cm (area: 20 cm 2 ) size, remove the release liner from one surface, and laminate to a pre-weighed aluminum foil. Next, remove the release liner from the other side of the adhesive layer, place in a constant temperature and humidity chamber at 60°C and 90% relative humidity, and remove after 72 hours. The test piece, consisting of the adhesive layer and aluminum foil laminate, was weighed and then measured for moisture content using a moisture meter (Mitsubishi Chemical Analytech CA-200) equipped with a heated vaporizer (Mitsubishi Chemical Analytech VA-200) using Karl Fischer coulometric titration under the following conditions.

[0091] Anolyte: AQUAMICRON AKX (Mitsubishi Chemical)

[0092] Catholyte: AQUAMICRON CXU (Mitsubishi Chemical)

[0093] Heating gasification temperature: 150℃

[0094] (Gel fraction)

[0095] The gel fraction of the viscoelastic layer V1 is appropriately set according to the purpose of use, the mode of use, etc., and is not limited to a specific range. The gel fraction is, for example, about 99% or less, and about 97% or less is appropriate. From the perspective of easily and appropriately balancing a high refractive index and adhesive properties, in some preferred embodiments, the gel fraction is about 95% or less, and can more preferably be about 92% or less (for example, about 90% or less). From the perspective of appropriately following the unevenness that may exist on the surface of the adherend (for example, the uneven structure provided in a light-emitting device for the purpose of improving light extraction efficiency) and achieving good adhesion, it is also preferred that the gel fraction is not too high. In some embodiments, the gel fraction can be about 88% or less, about 75% or less, or about 65% or less. In addition, from the perspective of imparting moderate cohesion to the adhesive and appropriately exhibiting adhesive properties, the gel fraction is, for example, about 10% or more, about 20% or more is appropriate, and can also be about 30% or more. From the perspective of deformation resistance of the viscoelastic layer V1 (preventing overflow due to pressure, bubbles caused by the intrusion of foreign matter, etc.), the gel fraction is preferably at least approximately 30%, more preferably at least approximately 40%, and can be at least approximately 45%, at least approximately 50%, at least approximately 65%, or at least approximately 75%. The gel fraction of the interlayer sheet (typically an interlayer sheet in the form of a substrate-free PSA sheet) is also preferably within the ranges exemplified above. The gel fraction can be adjusted by adjusting the molecular weight, molecular structure, concentration, and degree of crosslinking of the base polymer. The gel fraction is measured by the following method.

[0096] [Measurement of gel fraction]

[0097] A predetermined amount of sample (weight Wg1) was wrapped in a purse-shaped porous polytetrafluoroethylene membrane (weight Wg2) with an average pore size of 0.2 μm, and the opening was tied with a kite string (weight Wg3). The porous polytetrafluoroethylene (PTFE) membrane used was "NITOFLON (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm), available from Nitto Denko Corporation, or an equivalent.

[0098] The package is immersed in a sufficient amount of ethyl acetate and maintained at room temperature (typically 23°C) for 7 days to allow only the sol component of the adhesive to elute outside the film. The package is then removed and the ethyl acetate adhering to the outer surface is wiped off. The package is then dried at 130°C for 2 hours, and the weight of the package (Wg4) is measured. The gel fraction is calculated by substituting the values into the following formula.

[0099] Gel fraction (%) = [(Wg4-Wg2-Wg3) / Wg1] × 100

[0100] When the interlayer sheet disclosed herein is a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, and the first adhesive surface is composed of an adhesive layer V1 and the second adhesive surface is composed of an adhesive layer V2, the gel fraction of the viscoelastic layer V1 constituting the first adhesive surface and the gel fraction of the viscoelastic layer V2 constituting the second adhesive surface can be of the same or different magnitude. In some embodiments, the gel fraction of the viscoelastic layer V2 can be lower than that of the viscoelastic layer V1. This configuration facilitates improving the flexibility of the interlayer sheet through the contribution of the relatively low gel fraction of the viscoelastic layer V2. This allows for the provision of an interlayer sheet that optimally combines the high refractive index of the viscoelastic layer V1 with the flexibility of the interlayer sheet.

[0101] In some aspects of the technology disclosed herein, the peak temperature of tan δ of the adhesive constituting the viscoelastic layer V1 is preferably above approximately -50°C, and preferably below approximately 50°C. Here, tan δ (loss tangent) of an adhesive refers to the ratio of the loss modulus G" to the storage modulus G' of the adhesive. Specifically, tan δ = G" / G'. The tan δ of an adhesive can be determined by clamping a disk-shaped adhesive sample approximately 2 mm thick and 7.9 mm in diameter between parallel plates. Using a viscoelasticity testing apparatus, a temperature dispersion test is conducted in shear mode over a measurement temperature range of -60°C to 60°C and a heating rate of 5°C / minute while applying shear strain at a frequency of 1 Hz. The storage modulus G' (Pa) and loss modulus G" (Pa) at this temperature are then used to determine the peak temperature of tan δ (sometimes referred to as Tpeak) of the adhesive. The change in tan δ within this temperature range can be used to determine the peak temperature of tan δ (sometimes referred to as Tpeak). As a viscoelasticity tester, ARES manufactured by TA Instruments or an equivalent thereof can be used.

[0102] In some embodiments, it is advantageous for the viscoelastic layer V1 to have a Tpeak of 45°C or below or 35°C, preferably below 30°C (e.g., below 25°C), below 20°C, or below 15°C. With an adhesive having a lower Tpeak, it tends to be easier to obtain good initial adhesion and tightness in the room temperature region. On the other hand, from the perspective of imparting moderate cohesion to the adhesive, it is preferred that the Tpeak of the adhesive is not too low, as it tends to be suitable for achieving a high refractive index. From this perspective, in some embodiments, the Tpeak of the adhesive is, for example, above -40°C, above -30°C, above -20°C, above -5°C, above 5°C, above 15°C, or even above 25°C. An adhesive with a higher Tpeak can be preferably used in a method in which one or both of the adhesive and the adherend are heated to a temperature slightly higher than room temperature as needed when attaching the adhesive to the adherend. The Tpeak of the adhesive can be adjusted by selecting the composition of the adhesive (for example, the composition of the monomer components constituting the base polymer, the use of a refractive index enhancer or a plasticizer, and the selection of the type and amount of the plasticizer).

[0103] When the interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, the Tpeak of the adhesive is preferably applied to at least the adhesive layer (preferably the viscoelastic layer V1) constituting the first adhesive surface, and more preferably to both the adhesive layer constituting the first adhesive surface and the adhesive layer constituting the second adhesive surface. The Tpeak of the adhesive layer constituting the first adhesive surface and the Tpeak of the adhesive layer constituting the second adhesive surface may be of the same magnitude or different.

[0104] <Viscoelastic Layer V1>

[0105] (Base polymer)

[0106] In the technology disclosed herein, the type of adhesive constituting the adhesive layer V1 is not particularly limited. The above-mentioned adhesive can be one or more of various rubber-like polymers such as acrylic polymers, rubber polymers (such as natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, fluorine polymers, etc. that can be used in the field of adhesives as adhesives as adhesives (meaning a structural polymer that gives the adhesive shape, hereinafter also referred to as a "base polymer"). From the viewpoints of adhesive performance, cost, etc., it is preferred to use an adhesive containing an acrylic polymer or a rubber polymer as a base polymer. Among them, an adhesive with an acrylic polymer as the base polymer (acrylic adhesive) is preferred. The technology disclosed herein is preferably implemented in a manner using an acrylic adhesive.

[0107] The following description will focus on an interlayer sheet in which the adhesive layer V1 is composed of an acrylic adhesive, that is, an interlayer sheet having an acrylic adhesive layer. However, the adhesive layer V1 in the interlayer sheet disclosed herein is not limited to an acrylic adhesive layer.

[0108] It should be noted that, in this specification, the term "base polymer" of an adhesive refers to the main component of the rubbery polymer contained in the adhesive, and is not intended to be limiting in any other sense. The rubbery polymer is a polymer that exhibits rubber elasticity in a temperature range near room temperature. Furthermore, in this specification, "main component" refers to a component contained in an amount exceeding 50% by weight, unless otherwise specified.

[0109] In this specification, an "acrylic polymer" refers to a polymer comprising, as monomer units constituting the polymer, monomer units derived from a monomer having at least one (meth)acryloyl group per molecule. Hereinafter, a monomer having at least one (meth)acryloyl group per molecule will also be referred to as an "acrylic monomer." Therefore, an acrylic polymer in this specification is defined as a polymer comprising monomer units derived from an acrylic monomer. Typical examples of acrylic polymers include polymers in which the ratio of acrylic monomers in the total monomers used to synthesize the acrylic polymer is greater than 50% by weight (preferably greater than 70% by weight, for example, greater than 90% by weight).

[0110] In this specification, "(meth)acryloyl" refers to both acryloyl and methacryloyl. Similarly, "(meth)acrylate" refers to both acrylate and methacrylate, and "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid. Therefore, the term "acrylic monomer" as used herein encompasses both monomers having an acryloyl group (acrylic monomer) and monomers having a methacryloyl group (methacrylic monomer).

[0111] (Acrylic polymer (A))

[0112] The interlayer sheet disclosed herein may preferably have a refractive index of 1.570 or higher, a storage modulus G' at 25°C, V1The acrylic adhesive layer is implemented in the form of an acrylic adhesive layer having a pressure drop of 30kPa to 700kPa, a total light transmittance of 86% or more, and a haze value of 1.0% or less. For the acrylic polymer serving as the base polymer of the acrylic adhesive layer, a polymer containing an aromatic ring-containing monomer (m1) as a monomer component constituting the acrylic polymer is preferred. That is, an acrylic polymer containing an aromatic ring-containing monomer (m1) as a monomer unit is preferred. The acrylic polymer will also be referred to as "acrylic polymer (A)" hereinafter. Here, in this specification, "monomer component constituting the acrylic polymer" refers to a monomer constituting a repeating unit of the acrylic polymer in the adhesive formed by the adhesive composition, regardless of whether it is contained in the adhesive composition in the form of a pre-formed polymer (which may be an oligomer) or in the form of an unpolymerized monomer. That is, the monomer component constituting the acrylic polymer may be contained in the above-mentioned adhesive composition in any form of a polymer, an unpolymerized polymer, or a partially polymerized polymer. From the perspective of ease of preparation of the adhesive composition, in some embodiments, an adhesive composition containing substantially all (e.g., 95% by weight or more, preferably 99% by weight or more) of the monomer components as a polymer is preferred. An adhesive composition containing substantially all of the monomer components as a polymer is also preferred from the perspective of easily forming an interlayer sheet with minimal deformation and warping.

[0113] (monomer (m1))

[0114] As the monomer (m1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule is used. As the monomer (m1), one of these compounds may be used alone or in combination of two or more.

[0115] Examples of the ethylenically unsaturated group include (meth)acryloyl, vinyl, and (meth)allyl groups. From the perspective of polymerization reactivity, a (meth)acryloyl group is preferred, while from the perspective of flexibility and adhesiveness, an acryloyl group is more preferred. From the perspective of suppressing a decrease in the flexibility of the adhesive, a compound having one ethylenically unsaturated group per molecule (i.e., a monofunctional monomer) is preferably used as the monomer (m1).

[0116] The number of aromatic rings contained in one molecule of the compound used as the monomer (m1) may be 1 or 2 or more. The upper limit of the number of aromatic rings contained in the monomer (m1) is not particularly limited, and may be, for example, 16 or less. In some embodiments, from the viewpoint of ease of preparation of the acrylic polymer (A) and transparency of the adhesive, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less.

[0117] The aromatic ring possessed by the compound used as monomer (m1) may be, for example, a benzene ring (which may be a benzene ring constituting a part of a biphenyl structure or a fluorene structure); a condensed ring of a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, or a phenanthrene ring; a carbon ring such as a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, a pyrrole ring, a pyrazole ring, an imidazole ring, a triazole ring, an oxazole ring, an isoxazole ring, a thiazole ring, or a thiophene ring; or a heterocyclic ring. The heteroatoms contained as ring atoms in the above heterocyclic ring may be, for example, one or more selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms constituting the above heterocyclic ring may be one or both of nitrogen and sulfur. Monomer (m1) may also have a structure such as a dinaphthothiophene structure in which one or more carbon rings are condensed with one or more heterocyclic rings.

[0118] The above-mentioned aromatic ring (preferably a carbon ring) may have one or more substituents on the ring-forming atoms, or may not have a substituent. When having a substituent, examples of the substituent include alkyl, alkoxy, aryloxy, hydroxyl, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl, hydroxyalkyloxy, glycidoxy, etc., but are not limited to these. In the substituent containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, for example, it can be 1 or 2. In some aspects, the above-mentioned aromatic ring may be an aromatic ring that has no substituent on the ring-forming atoms, or has one or more substituents selected from the group consisting of alkyl, alkoxy and halogen atoms (such as bromine atoms). It should be noted that the aromatic ring possessed by the monomer (m1) having a substituent on its ring-forming atoms means that the aromatic ring has a substituent other than a substituent containing an ethylenically unsaturated group.

[0119] The aromatic ring and the ethylenically unsaturated group may be directly bonded or bonded via a linking group. The linking group may be, for example, a group comprising one or more structures selected from alkylene, oxyalkylene, poly(oxyalkylene) groups, phenyl, alkylphenyl, alkoxyphenyl, a group in which one or more hydrogen atoms in these groups are substituted by hydroxyl groups (for example, hydroxyalkylene), oxy (-O- group), thiooxy (-S- group), etc. In some embodiments, it is preferred to use an aromatic ring-containing monomer having a structure in which the aromatic ring is directly bonded to the ethylenically unsaturated group or bonded via a linking group selected from the group consisting of alkylene, oxyalkylene and poly(oxyalkylene) groups. The number of carbon atoms in the alkylene and oxyalkylene groups is preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. The number of repetitions of the oxyalkylene unit in the poly(oxyalkylene) group may be, for example, 2 to 3.

[0120] Examples of compounds that can be preferably used as monomer (m1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. Aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds can be used alone or in combination of two or more. Alternatively, one or more aromatic ring-containing (meth)acrylates and one or more aromatic ring-containing vinyl compounds can be used in combination.

[0121] The content of the monomer (m1) in the monomer component constituting the acrylic polymer (A) is not particularly limited and can be set in a manner that allows for achieving an adhesive layer having both the desired refractive index and adhesive properties (such as peel strength, flexibility, etc.) and / or optical properties (such as total light transmittance, haze value, etc.). In some embodiments, the content of the monomer (m1) in the above-mentioned monomer component can be, for example, 30% by weight or more, preferably 50% by weight or more, can be 60% by weight or more, or can be 70% by weight or more. From the viewpoint of easily obtaining a higher refractive index, in some preferred embodiments, the content of the above-mentioned monomer (m1) is, for example, higher than 70% by weight, can be 75% by weight or more, can be 80% by weight or more, can be 85% by weight or more, can be 90% by weight or more, or can be 95% by weight or more. The upper limit of the content of the monomer (m1) in the above-mentioned monomer component is 100% by weight. From the perspective of achieving a good balance between high refractive index and adhesive properties and / or optical properties, it is advantageous to set the content of the above-mentioned monomer (m1) to less than 100 weight %, for example, preferably about 99 weight % or less, more preferably 98 weight % or less, 97 weight % or less, or 96 weight % or less. In some embodiments, the content of the above-mentioned monomer (m1) can be 93 weight % or less, 90 weight % or less, 80 weight % or less, or 75 weight % or less. In some embodiments in which adhesive properties and / or optical properties are given greater importance, the content of the above-mentioned monomer (m1) in the above-mentioned monomer component can be 70 weight % or less, 60 weight % or less, or 45 weight % or less.

[0122] In some embodiments of the technology disclosed herein, as monomer (m1), a monomer having two or more aromatic rings (preferably a carbocyclic ring) in one molecule can be preferably used from the perspective of easily obtaining a high refractive index-enhancing effect. Examples of monomers having two or more aromatic rings in one molecule (hereinafter also referred to as "monomers containing multiple aromatic rings") include: monomers having a structure in which two or more non-fused aromatic rings are bonded via a linking group, monomers having a structure in which two or more non-fused aromatic rings are directly (i.e., without the aid of other atoms) chemically bonded, monomers having a fused aromatic ring structure, monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, and the like. Monomers containing multiple aromatic rings can be used alone or in combination of two or more.

[0123] The linking group may be, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (e.g., -O-(CH2) n -alkyl, where n is 1 to 3, preferably 1), thiooxyalkylene (e.g. -S-(CH2) n -alkyl, where n is 1 to 3, preferably 1), straight chain alkylene (i.e. -(CH2) n - alkyl, where n is 1 to 6, preferably 1 to 3), groups in which the alkylene groups in the above-mentioned oxyalkylene groups, the above-mentioned thiooxyalkylene groups, and the above-mentioned linear alkylene groups are partially or completely halogenated, etc. From the perspective of the flexibility of the adhesive, suitable examples of the above-mentioned linking group include oxy groups, thiooxy groups, oxyalkylene groups, and linear alkylene groups. Specific examples of monomers having a structure in which two or more non-condensed aromatic rings are bonded via a linking group include phenoxybenzyl (meth)acrylate (e.g., p-phenoxybenzyl (meth)acrylate), thiophenoxybenzyl (meth)acrylate, and benzylbenzyl (meth)acrylate.

[0124] The monomer having a structure in which two or more non-fused aromatic rings are directly chemically bonded may be, for example, a biphenyl structure-containing (meth)acrylate, a triphenyl structure-containing (meth)acrylate, a vinyl group-containing biphenyl, etc. Specific examples include o-phenylphenol (meth)acrylate and biphenyl methyl (meth)acrylate.

[0125] Examples of the monomer having a fused aromatic ring structure include naphthalene ring-containing (meth)acrylates, anthracene ring-containing (meth)acrylates, vinyl-containing naphthalene, and vinyl-containing anthracene. Specific examples include 1-naphthylmethyl (meth)acrylate (also known as 1-naphthylmethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthylethyl (meth)acrylate, 2-naphthyloxyethyl acrylate, and 2-(4-methoxy-1-naphthyloxy)ethyl (meth)acrylate.

[0126] Specific examples of the monomer having a fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene(meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene(meth)acrylate. It should be noted that the monomer having a fluorene structure includes a structural portion in which two benzene rings are directly chemically bonded, and is therefore included in the concept of the monomer having a structure in which two or more non-fused aromatic rings are directly chemically bonded.

[0127] Examples of the monomer having a dinaphthothiophene structure include dinaphthothiophene containing a (meth)acryloyl group, dinaphthothiophene containing a vinyl group, and dinaphthothiophene containing a (meth)allyl group. Specific examples include (meth)acryloyloxymethyl dinaphthothiophene (e.g., CH2CH(R) bonded to the 5- or 6-position of the dinaphthothiophene ring). 1 )C(O)OCH2- structure compound. Here, R 1 is a hydrogen atom or a methyl group. ), (meth)acryloyloxyethyl dinaphthothiophene (for example, CH2CH(R) is bonded to the 5-position or 6-position of the dinaphthothiophene ring) 1 )C(O)OCH(CH3)- or CH2CH(R 1 )C(O)OCH2CH2- structure compound. Here, R 1 is a hydrogen atom or a methyl group. ), vinyl dinaphthothiophene (for example, a compound having a structure in which a vinyl group is bonded to the 5-position or 6-position of the naphthothiophene ring), (methyl)allyloxy dinaphthothiophene, etc. It should be noted that the monomer having a dinaphthothiophene structure is included in the concept of the monomer having a fused aromatic ring structure because it contains a naphthalene structure and also has a structure in which a thiophene ring is fused with two naphthalene structures.

[0128] Examples of the monomer having a dibenzothiophene structure include (meth)acryloyl-containing dibenzothiophene and vinyl-containing dibenzothiophene. It should be noted that the monomer having a dibenzothiophene structure is included in the concept of the monomer having a fused aromatic ring structure because it has a structure in which a thiophene ring is fused with two benzene rings.

[0129] It should be noted that neither the dinaphthothiophene structure nor the dibenzothiophene structure belongs to a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0130] As the monomer (m1) in the technology disclosed herein, a monomer having one aromatic ring (preferably a carbocyclic ring) in one molecule may also be used. A monomer having one aromatic ring in one molecule can, for example, contribute to improving the flexibility of the adhesive, adjusting the adhesive properties, improving the transparency, etc. In some embodiments, from the perspective of improving the refractive index of the adhesive, a monomer having one aromatic ring in one molecule is preferably used in combination with a monomer containing multiple aromatic rings.

[0131] Examples of monomers having one aromatic ring in one molecule include (meth)acrylates containing a carbon aromatic ring, such as benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxybutyl (meth)acrylate, cresol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and chlorobenzyl (meth)acrylate; (meth)acrylates containing a carbon aromatic ring, such as 2-(4,6-dibromo-2-sec-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, and 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate. (Meth)acrylates containing bromine-substituted aromatic rings, such as 6-(4,6-dibromo-2-sec-butylphenoxy)hexyl (meth)acrylate, 6-(4,6-dibromo-2-isopropylphenoxy)hexyl (meth)acrylate, 2,6-dibromo-4-nonylphenyl acrylate, and 2,6-dibromo-4-dodecylphenyl acrylate; vinyl compounds containing carbon aromatic rings, such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; compounds having vinyl substituents on heteroaromatic rings, such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, and N-vinyloxazole; etc.

[0132] As monomer (m1), a monomer having a structure in which an oxyethylene chain is sandwiched between the ethylenically unsaturated group and the aromatic ring among the various aromatic ring-containing monomers described above can also be used. Such a monomer having an oxyethylene chain sandwiched between the ethylenically unsaturated group and the aromatic ring can be understood as an ethoxylate of the original monomer. The number of repetitions of the oxyethylene unit (-CH2CH2O-) in the above-mentioned oxyethylene chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, for example 1. Specific examples of ethoxylated aromatic ring-containing monomers include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol di(meth)acrylate, and the like.

[0133] The content of the monomer containing multiple aromatic rings in the monomer (m1) is not particularly limited, and can be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, from the perspective of easily achieving an adhesive with a higher refractive index, the content of the monomer containing multiple aromatic rings in the monomer (m1) can be, for example, 50% by weight or more, preferably 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. It is also possible that substantially 100% by weight of the monomer (m1) is a monomer containing multiple aromatic rings. That is, as monomer (m1), only one or two or more monomers containing multiple aromatic rings can be used. In addition, in some embodiments, for example, considering the balance between high refractive index and adhesive properties and / or optical properties, the content of the monomer containing multiple aromatic rings in the monomer (m1) can be less than 100% by weight, can be less than 98% by weight, can be less than 90% by weight, can be less than 80% by weight, or can be less than 65% by weight. In some embodiments, the content of the monomer containing multiple aromatic rings in monomer (m1) may be 70% by weight or less, 50% by weight or less, 25% by weight or less, or 10% by weight or less, taking into account adhesive and / or optical properties. The technology disclosed herein may also be implemented in an embodiment in which the content of the monomer containing multiple aromatic rings in monomer (m1) is less than 5% by weight. It is also possible to omit the monomer containing multiple aromatic rings.

[0134] The content of the monomer containing multiple aromatic rings in the monomer components constituting the acrylic polymer is not particularly limited and can be set in a manner that can achieve an adhesive layer that takes into account the desired refractive index and adhesive properties (such as peel strength, flexibility, etc.) and / or optical properties (such as total light transmittance, haze value, etc.). The content of the monomer containing multiple aromatic rings in the above-mentioned monomer components can be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of easily achieving an adhesive with a higher refractive index, the content of the monomer containing multiple aromatic rings in the above-mentioned monomer components can be, for example, higher than 35% by weight, preferably higher than 50% by weight, higher than 70% by weight, higher than 75% by weight, higher than 85% by weight, higher than 90% by weight, or higher than 95% by weight. The content of the monomer containing multiple aromatic rings in the monomer component can be 100% by weight, but from the perspective of achieving a good balance between a high refractive index and adhesive and / or optical properties, it is advantageous to set it below 100% by weight. It is preferably about 99% by weight or less, more preferably 98% by weight or less, 96% by weight or less, 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or even 75% by weight or less. In some embodiments, considering adhesive and / or optical properties, the content of the monomer containing multiple aromatic rings in the monomer component can be 70% by weight or less, 50% by weight or less, 25% by weight or less, 15% by weight or less, or even 5% by weight or less. The technology disclosed herein can also be implemented in an embodiment in which the content of the monomer containing multiple aromatic rings in the monomer component is less than 3% by weight.

[0135] In some embodiments of the technology disclosed herein, a high refractive index monomer can be preferably used as at least a part of the monomer (m1). Here, "high refractive index monomer" refers to a monomer whose refractive index is, for example, about 1.510 or more, preferably about 1.530 or more, and more preferably about 1.550 or more. There is no particular limit on the upper limit of the refractive index of the high refractive index monomer. From the perspective of the ease of preparation of the adhesive composition and the ease of taking into account the flexibility of being suitable as an adhesive, it can be, for example, 3.000 or less, 2.500 or less, 2.000 or less, 1.900 or less, 1.800 or less, or 1.700 or less. The high refractive index monomer can be used alone or in combination of two or more.

[0136] The refractive index of the monomer is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C. The Abbe refractometer can be the "DR-M4" manufactured by ATAGO or an equivalent. If a nominal value of the refractive index at 25°C is provided by the manufacturer, that nominal value can be used.

[0137] As the high refractive index monomer, a substance having a suitable refractive index can be appropriately adopted from the compounds included in the concept of the aromatic ring-containing monomer (m1) disclosed herein (for example, the compounds and compound groups exemplified above). Specific examples include m-phenoxybenzyl acrylate (refractive index: 1.566, homopolymer Tg: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, homopolymer Tg: 31°C), ethoxylated o-phenylphenol acrylate (number of repetitions of oxyethylene units: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, homopolymer Tg: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, homopolymer Tg: 2°C), phenoxydiethylene glycol acrylate (refractive index: 1.510, homopolymer Tg: 31°C). g: -35 ° C), 6-acryloyloxymethyl dinaphthothiophene (6MDNTA, refractive index: 1.75), 6-methacryloyloxymethyl dinaphthothiophene (6MDNTMA, refractive index: 1.726), 5-acryloyloxyethyl dinaphthothiophene (5EDNTA, refractive index: 1.786), 6-acryloyloxyethyl dinaphthothiophene (6EDNTA, refractive index: 1.722), 6-vinyl dinaphthothiophene (6VDNT, refractive index: 1.802), 5-vinyl dinaphthothiophene (abbreviation: 5VDNT, refractive index: 1.793), etc., but are not limited to these.

[0138] The content of the high-refractive-index monomer (i.e., a monomer containing an aromatic ring having a refractive index of about 1.510 or greater, preferably about 1.530 or greater, and more preferably about 1.550 or greater) in monomer (m1) is not particularly limited, and may be, for example, 5% by weight or greater, 25% by weight or greater, 35% by weight or greater, or 40% by weight or greater. In some embodiments, from the perspective of easily obtaining a higher refractive index, the content of the high-refractive-index monomer in monomer (m1) may be, for example, 50% by weight or greater, preferably 70% by weight or greater, 85% by weight or greater, 90% by weight or greater, or 95% by weight or greater. Substantially 100% by weight of monomer (m1) may be the high-refractive-index monomer. In some embodiments, from the perspective of achieving a good balance between the high refractive index and adhesive properties and / or optical properties, the content of the high-refractive-index monomer in monomer (m1) may be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less. In some embodiments, the content of the high refractive index monomer in the monomer (m1) may be 70% by weight or less, 50% by weight or less, 25% by weight or less, 15% by weight or less, or 10% by weight or less, taking into account the adhesive properties and / or optical properties. The technology disclosed herein may also be implemented in a manner in which the content of the high refractive index monomer in the monomer component (m1) is less than 5% by weight. It is also possible not to use a high refractive index monomer.

[0139] The content of the high refractive index monomer in the monomer component constituting the acrylic polymer is not particularly limited and can be set in a manner that allows for achieving an adhesive layer having both the desired refractive index and adhesive properties (e.g., peel strength, flexibility, etc.) and / or optical properties (e.g., total light transmittance, haze value, etc.). The content of the high refractive index monomer in the above-mentioned monomer component can be, for example, more than 3 wt %, more than 10 wt %, or more than 25 wt %. In some embodiments, from the viewpoint of easily achieving an adhesive having a higher refractive index, the content of the high refractive index monomer in the above-mentioned monomer component can be, for example, higher than 35 wt %, preferably higher than 50 wt %, higher than 70 wt %, more than 75 wt %, more than 85 wt %, more than 90 wt %, or more than 95 wt %. The content of the high-refractive index monomer in the monomer component may be 100% by weight, but from the perspective of achieving a good balance between the high refractive index and adhesive and / or optical properties, it is advantageous to set it to less than 100% by weight. It is preferably 99% by weight or less, more preferably 98% by weight or less, 96% by weight or less, 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less. In some embodiments, considering adhesive and / or optical properties, the content of the high-refractive index monomer in the monomer component may be 70% by weight or less, 50% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein may also be implemented in a manner where the content of the high-refractive index monomer in the monomer component is less than 3% by weight.

[0140] In some preferred embodiments of the technology disclosed herein, an aromatic ring-containing monomer (hereinafter sometimes referred to as "monomer L") having a homopolymer Tg of 10°C or less (preferably 5°C or less or 0°C or less, more preferably -10°C or less, further preferably -20°C or less, for example -25°C or less) is used as at least a part of the monomer (m1). If the content of the aromatic ring-containing monomer (m1) in the monomer component (especially the aromatic ring-containing monomer (m1) equivalent to one or both of the above-mentioned monomer containing multiple aromatic rings and the high refractive index monomer) is increased, the storage modulus G' of the adhesive generally tends to increase. By using monomer L as part or all of the monomer (m1), the increase in the storage modulus G' can be suppressed. In this way, the flexibility suitable for the adhesive can be better maintained and the refractive index can be increased. The lower limit of the Tg of monomer L is not particularly limited. Taking into account the balance with the refractive index improvement effect, in some embodiments, the Tg of monomer L can be, for example, above -70°C, above -55°C, or above -45°C. The monomer L can be used alone or in combination of two or more.

[0141] As monomer L, a substance having a suitable Tg can be appropriately adopted from among the compounds encompassed by the concept of the aromatic ring-containing monomer (m1) disclosed herein (e.g., the compounds and compound groups exemplified above). A suitable example of an aromatic ring-containing monomer that can be used as monomer L is m-phenoxybenzyl acrylate (homopolymer Tg: -35°C). Another suitable example is phenoxydiethylene glycol acrylate (homopolymer Tg: -35°C).

[0142] The content of monomer L in monomer (m1) is not particularly limited, and for example, it can be 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, from the perspective of easily obtaining an adhesive that combines high refractive index and flexibility at a higher level, the content of monomer L in monomer (m1) can be, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. It is also possible that substantially 100% by weight of monomer (A1) is monomer L. In addition, in some embodiments, for example, from the perspective of achieving a good balance between flexibility and high refractive index suitable for use as an adhesive, the content of monomer L in monomer (m1) can be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, 70% by weight or less, 50% by weight or less, 25% by weight or less, or 10% by weight or less. The technology disclosed herein can also be implemented in an embodiment in which the content of monomer L in monomer (m1) is less than 5% by weight. Monomer L may not be used.

[0143] The content of monomer L in the monomer component constituting the acrylic polymer can be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the perspective of easily obtaining an adhesive that achieves both a high refractive index and flexibility at a higher level, the content of monomer L in the monomer component can be, for example, greater than 35% by weight, preferably greater than 50% by weight, greater than 70% by weight, greater than 75% by weight, greater than 85% by weight, greater than 90% by weight, or greater than 95% by weight. The content of monomer L in the above monomer component can be 100% by weight, but considering the balance between the high refractive index and the adhesive and / or optical properties, it is advantageous to set it below 100% by weight, preferably about 99% by weight or less, more preferably 98% by weight or less, 96% by weight or less, 95% by weight or less, 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less. In some embodiments, the content of monomer L in the monomer composition can be 70% by weight or less, 50% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein can also be practiced in an embodiment in which the content of monomer L in the monomer composition is less than 3% by weight.

[0144] In some embodiments, from the viewpoint of the flexibility of the adhesive, the glass transition temperature Tg of the composition of the monomer (m1) is m1 It is advantageous to be about 20°C or less, preferably 10°C or less (e.g., 5°C or less), more preferably 0°C or less, further preferably -10°C or less, and may be -20°C or less, or may be -25°C or less. Glass transition temperature Tg m1 There is no particular lower limit. Considering the balance with the refractive index improvement effect, in some embodiments, the glass transition temperature Tg m1 For example, it can be -70°C or higher, -55°C or higher, or -45°C or higher. The technology disclosed herein can also be used as a glass transition temperature Tg m1 The temperature is preferably -40°C or higher, -35°C or higher, -33°C or higher, -30°C or higher, or -25°C or higher.

[0145] Here, the glass transition temperature Tg based on the composition of the monomer (m1) is m1 It means Tg determined by the Fox equation described below based on the composition of only the monomer (m1) among the monomer components constituting the acrylic polymer. m1The following Fox formula can be applied to only the monomer (m1) among the monomer components constituting the acrylic polymer, and the glass transition temperature of the homopolymer of each aromatic ring-containing monomer used as the monomer (m1) and the weight fraction of each aromatic ring-containing monomer in the total amount of the monomer (m1) can be used to calculate the glass transition temperature. In the embodiment in which only one monomer is used as the monomer (m1), the Tg of the homopolymer of the monomer and the glass transition temperature Tg m1 consistent.

[0146] In some embodiments, as an aromatic ring-containing monomer (m1), a monomer L (i.e., a monomer containing an aromatic ring whose homopolymer has a Tg of 10°C or less, preferably 5°C or less or 0°C or less, more preferably -10°C or less, further preferably -20°C or less, for example -25°C or less) and a monomer H having a Tg higher than 10°C can be used in combination. The Tg of monomer H can be, for example, higher than 10°C, higher than 15°C, or higher than 20°C. By combining monomer L and monomer H, for example, in a configuration in which the content of the aromatic ring-containing monomer (m1) in the monomer component is relatively high, it is possible to achieve both high refractive index and softness of the adhesive at a higher level. The usage ratio of monomer L to monomer H can be set in a manner that suitably exhibits the effect, and is not particularly limited. For example, it is preferred to satisfy any of the above-mentioned glass transition temperatures Tg m1 The usage ratio of monomer L and monomer H is set in a certain manner.

[0147] In some embodiments, the aromatic ring-containing monomer (m1) can be preferably selected from compounds that do not contain a structure in which two or more non-fused aromatic rings are directly chemically bonded (e.g., a biphenyl structure). For example, an acrylic polymer composed of monomer components having a content of less than 5% by weight (more preferably less than 3% by weight, and may be 0% by weight) of compounds containing a structure in which two or more non-fused aromatic rings are directly chemically bonded can be advantageous. From the perspective of achieving an adhesive that achieves a good balance between flexibility, adhesiveness, and a high refractive index, limiting the amount of compounds containing a structure in which two or more non-fused aromatic rings are directly chemically bonded can be advantageous.

[0148] (Single unit (m2))

[0149] In some embodiments of the technology disclosed herein, the monomer component constituting the acrylic polymer may further contain a monomer (m2) on the basis of the above-mentioned monomer (m1). The above-mentioned monomer (m2) is a monomer belonging to at least one of a monomer having a hydroxyl group (hydroxyl-containing monomer) and a monomer having a carboxyl group (carboxyl-containing monomer). The above-mentioned hydroxyl-containing monomer is a compound having at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule. The above-mentioned carboxyl-containing monomer is a compound containing at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. Monomer (m2) can be used to help introduce crosslinking points into the acrylic polymer or to impart moderate cohesion to the adhesive. Monomer (m2) can be used alone or in combination of two or more. Monomer (m2) is typically a monomer that does not contain an aromatic ring.

[0150] Examples of the ethylenically unsaturated group possessed by the monomer (m2) include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. From the perspective of polymerization reactivity, a (meth)acryloyl group is preferred, and from the perspective of flexibility and adhesiveness, an acryloyl group is more preferred. From the perspective of suppressing a decrease in the flexibility of the adhesive, a compound having one ethylenically unsaturated group per molecule (i.e., a monofunctional monomer) is preferably used as the monomer (m2).

[0151] Examples of hydroxyl-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate, but are not limited thereto. Examples of preferably used hydroxyl-containing monomers include 4-hydroxybutyl acrylate (Tg: -40°C) and 2-hydroxyethyl acrylate (Tg: -15°C). From the perspective of improving flexibility in the room temperature region, 4-hydroxybutyl acrylate having a lower Tg is more preferred. In a preferred embodiment, 50% by weight or more (e.g., greater than 50% by weight, greater than 70% by weight, or greater than 85% by weight) of monomer (m2) may be 4-hydroxybutyl acrylate. The hydroxyl-containing monomers may be used alone or in combination of two or more.

[0152] In some embodiments of using a hydroxyl-containing monomer as monomer (m2), the hydroxyl-containing monomer may be one or more selected from compounds that do not have a methacryloyl group. Suitable examples of hydroxyl-containing monomers that do not have a methacryloyl group include the various hydroxyalkyl acrylates described above. For example, it is preferred that more than 50% by weight, more than 70% by weight, or more than 85% by weight of the hydroxyl-containing monomer used as monomer (m2) be hydroxyalkyl acrylate. By using hydroxyalkyl acrylate, hydroxyl groups that help provide crosslinking points and impart moderate cohesiveness can be introduced into the acrylic polymer, and compared to the case of using only the corresponding hydroxyalkyl methacrylate, it is easier to obtain an adhesive with good flexibility and adhesion in the room temperature range.

[0153] As the example of carboxyl-containing monomers, acrylic acid monomers such as (meth) acrylic acid, (meth) carboxyethyl acrylate, (meth) carboxypentyl acrylate and itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid etc. can be listed, but are not limited to these. As the example of carboxyl-containing monomers that can be preferably used, acrylic acid and methacrylic acid can be listed. Carboxyl-containing monomers can be used alone or in combination of two or more. Hydroxyl-containing monomers and carboxyl-containing monomers can also be used in combination.

[0154] The content of the monomer (m2) in the monomer component constituting the acrylic polymer is not particularly limited and can be set according to the purpose. In some embodiments, the content of the above-mentioned monomer (m2) can be, for example, 0.01% by weight or more, 0.1% by weight or more, or 0.5% by weight or more. From the viewpoint of obtaining a higher effect of use, in some embodiments, the content of the above-mentioned monomer (A2) is preferably set to 1% by weight or more, can be set to 2% by weight or more, or can be set to 4% by weight or more. The upper limit of the content of the monomer (m2) in the monomer component is set in such a way that the total content of the monomer (m2) and the content of other monomers does not exceed 100% by weight. In some embodiments, it is appropriate to set the content of the above-mentioned monomer (m2) to, for example, 30% by weight or less or 25% by weight or less. From the viewpoint of relatively increasing the content of the monomer (m1) and making it easier to obtain a high refractive index, it is preferably set to 20% by weight or less, more preferably set to 15% by weight or less, can be lower than 12% by weight, can be lower than 10% by weight, or can be lower than 7% by weight.

[0155] In the method of using a hydroxyl-containing monomer as a monomer (m2), the content of the hydroxyl-containing monomer in the monomer component is not particularly limited, for example, it can be 0.01 weight % or more (preferably 0.1 weight % or more, more preferably 0.5 weight % or more). In some methods, the content of the above-mentioned hydroxyl-containing monomer is preferably set to 1 weight % or more of the above-mentioned monomer component, can be set to 2 weight % or more, and can also be set to 4 weight % or more. The upper limit of the content of the hydroxyl-containing monomer in the monomer component is set in a manner that the total amount of the content of the hydroxyl-containing monomer with other monomers does not exceed 100 weight %, for example, it is appropriate to set it to 30 weight % or less or 25 weight % or less. From the viewpoint of making the content of monomer (m1) relatively increase and making it easy to increase the refractive index, it is preferably set to 20 weight % or less, more preferably set to 15 weight % or less, can be lower than 12 weight %, can be lower than 10 weight %, and can be lower than 7 weight %.

[0156] In the mode of using carboxyl group-containing monomer as monomer (m2), the content of the carboxyl group-containing monomer in monomer component is not particularly limited, for example, can be more than 0.01 % by weight (preferably more than 0.1 % by weight, more preferably more than 0.3 % by weight). In some ways, the content of above-mentioned carboxyl group-containing monomer can be set as more than 1 % by weight, can be set as more than 2 % by weight, also can be set as more than 4 % by weight. The upper limit of the content of the carboxyl group-containing monomer in monomer component is set in the mode that the total of the usage amount with other monomers is no more than 100 % by weight, for example, it is appropriate to be set as below 30 % by weight or below 25 % by weight, from making the content of monomer (m1) relatively increase and making high refractive index easy viewpoint, preferably be set as below 20 % by weight, more preferably be set as below 15 % by weight, can be lower than 12 % by weight, also can be lower than 10 % by weight. In some ways, from the viewpoint that the flexibility of adhesive improves, it is favourable that the content of above-mentioned carboxyl group-containing monomer is set as lower than 7 % by weight, preferably be set as lower than 5 % by weight, can be set as lower than 3 % by weight, can be set as lower than 1 % by weight, also can be set as lower than 0.5 % by weight. The technique disclosed herein can be preferably implemented, for example, in an embodiment using only a hydroxyl group-containing monomer as the monomer (m2), that is, in an embodiment not using a carboxyl group-containing monomer.

[0157] The total content of the monomers (m1) and (m2) in the monomer components constituting the acrylic polymer may be, for example, 31% by weight or more, preferably 51% by weight or more, 61% by weight or more, or 71% by weight or more. In some embodiments, from the perspective of easily and appropriately exerting the effects of these monomers, the total content of the monomers (m1) and (m2) in the monomer components constituting the acrylic polymer may be, for example, 76% by weight or more, preferably 81% by weight or more, 86% by weight or more, 91% by weight or more, 96% by weight or more, 99% by weight or more, or substantially 100% by weight.

[0158] (Single m3)

[0159] The monomer components constituting the acrylic polymer may also include monomers other than the above-mentioned monomers (m1) and (m2), as needed. An example of such an optional component is an alkyl (meth)acrylate (hereinafter also referred to as "monomer (m3)"). Monomer (m3) can help adjust the flexibility of the adhesive and improve the compatibility within the adhesive.

[0160] As the monomer (m3), preferably used is a monomer having 1 to 20 carbon atoms at the ester terminal (ie, C 1-20 (meth)acrylates containing a linear or branched alkyl group. 1-20 Specific examples of the alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and nonyl (meth)acrylate. , isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, etc., but are not limited to these.

[0161] In some embodiments, it is preferred to use an alkyl (meth)acrylate whose homopolymer has a Tg of -20°C or less (more preferably -40°C or less, for example -50°C or less) as at least a part of the monomer (m3). This low-Tg alkyl (meth)acrylate can help improve the flexibility of the adhesive. The lower limit of the Tg of the above-mentioned alkyl (meth)acrylate is not particularly limited, for example, it can be above -85°C, above -75°C, above -65°C, or above -60°C. Specific examples of the above-mentioned low-Tg alkyl (meth)acrylate include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), and isononyl acrylate (iNA).

[0162] In some embodiments using monomer (m3), from the perspectives of flexibility, adhesiveness, etc., it is preferred that at least a portion of the monomer (m3) be an alkyl acrylate. For example, it is preferred that 50% by weight or more (more preferably 75% by weight or more, and even more preferably 90% by weight or more) of the monomer (m3) be an alkyl acrylate. Alternatively, one or more alkyl acrylates may be used as monomer (m3), without using an alkyl methacrylate.

[0163] In the embodiment in which the monomer component includes an alkyl (meth)acrylate, the content of the alkyl (meth)acrylate in the monomer component can be set in a manner that appropriately exerts its use effect. In some embodiments, the content of the above-mentioned alkyl (meth)acrylate can be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. In some embodiments, the content of the above-mentioned alkyl (meth)acrylate can be 15% by weight or more, 30% by weight or more, or 45% by weight or more. The upper limit of the content of monomer (m3) in the monomer component is set in a manner such that the total content of the monomer (m3) and the content of other monomers does not exceed 100% by weight, for example, it can be less than 50% by weight. In some embodiments, the content of the above-mentioned monomer (m3) can be, for example, less than 35% by weight. Generally, the refractive index of alkyl (meth)acrylate is low. Therefore, in order to achieve a high refractive index, it is advantageous to limit the content of monomer (m3) in the monomer component and increase the content of monomer (m1) relatively. From this viewpoint, the content of monomer (m3) is advantageously 24% by weight or less of the monomer components, preferably less than 23% by weight, more preferably less than 20% by weight, and can be less than 17% by weight, less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. Substantially no monomer (m3) may be used.

[0164] (Other monomers)

[0165] The monomer components constituting the acrylic polymer may contain monomers other than the above-mentioned monomers (m1), (m2), and (m3) (hereinafter referred to as "other monomers") as needed. These other monomers can be used, for example, to adjust the Tg of the acrylic polymer, adjust the adhesive properties, improve compatibility within the adhesive layer, etc. These other monomers can be used alone or in combination of two or more.

[0166] As examples of the above-mentioned other monomers, monomers having functional groups other than hydroxyl and carboxyl groups (functional group-containing monomers) can be listed. For example, as other monomers that can improve the cohesion and heat resistance of the adhesive, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, etc. can be listed. In addition, as monomers that can introduce functional groups that can become crosslinking bases into acrylic polymers, or contribute to the improvement of peel strength and the improvement of compatibility in the adhesive layer, amide group-containing monomers (such as (methyl) acrylamide, N-hydroxymethyl (methyl) acrylamide, etc.), amino group-containing monomers (such as (methyl) acrylate, (methyl) acrylate N, N-dimethylaminoethyl ester, etc.), monomers with nitrogen-containing rings (such as N-vinyl-2-pyrrolidone, N-(methyl) acryloyl morpholine, etc.), imide group-containing monomers, epoxy group-containing monomers, ketone group-containing monomers, isocyanate group-containing monomers, alkoxysilyl group-containing monomers, etc. can be listed. It should be noted that among the monomers having a nitrogen atom-containing ring, for example, N-vinyl-2-pyrrolidone is also an amide group-containing monomer. The same applies to the relationship between the above-mentioned monomers having a nitrogen atom-containing ring and amino group-containing monomers.

[0167] Examples of other monomers that can be used in addition to the functional group-containing monomers mentioned above include vinyl ester monomers such as vinyl acetate; non-aromatic ring-containing (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; olefin monomers such as ethylene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride; alkoxy-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate; and vinyl ether monomers such as methyl vinyl ether. A suitable example of other monomers that can be used for purposes such as improving the flexibility of the adhesive is ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, homopolymer Tg: -67°C).

[0168] When using the above-mentioned other monomers, their usage is not particularly limited and can be appropriately set within the range that the total amount of the monomer component does not exceed 100% by weight. In some embodiments, from the viewpoint of easily exerting the refractive index improvement effect brought about by the use of monomer (m1), the content of the above-mentioned other monomers in the monomer component can be, for example, set to about 35% by weight or less, and it is appropriate to set it to about 25% by weight or less (for example, 0 to 25% by weight), it can be about 20% by weight or less (for example, 0 to 20% by weight), it can be about 10% by weight or less, it can be about 5% by weight or less, or it can be, for example, about 1% by weight or less. The technology disclosed herein can preferably be implemented in a manner that the monomer component does not substantially contain the above-mentioned other monomers.

[0169] In some embodiments, the monomer components that make up the acrylic polymer can be a composition in which the amount of methacryloyl-containing monomers is suppressed to a specified level or less. The amount of methacryloyl-containing monomers in the monomer components can be, for example, less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. This limitation in the amount of methacryloyl-containing monomers can be advantageous from the perspective of achieving an adhesive that achieves a well-balanced balance of flexibility, adhesion, and a high refractive index. The monomer components that make up the acrylic polymer can also be a composition that does not contain methacryloyl-containing monomers (e.g., a composition that contains only acryloyl-containing monomers).

[0170] In some embodiments, the amount of carboxyl-containing monomers used in the monomeric components of the base polymer (e.g., acrylic polymer) constituting the viscoelastic layer V1 is preferably limited to prevent coloration or discoloration (e.g., yellowing) of the viscoelastic layer V1. The amount of carboxyl-containing monomers used in the monomeric components may be, for example, less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, less than 0.1% by weight, or even less than 0.05% by weight. Limiting the amount of carboxyl-containing monomers in this manner is also advantageous from the perspective of inhibiting corrosion of metal materials that may be disposed in contact with or in proximity to the viscoelastic layer V1 (e.g., metal wiring, metal films, etc. that may be present on an adherend). The interlayer sheet disclosed herein may preferably be implemented in a manner where the monomeric components do not contain carboxyl-containing monomers.

[0171] For similar reasons, in some embodiments, the monomer components of the base polymer constituting the viscoelastic layer V1 preferably limit the amount of monomers containing acidic functional groups (including sulfonic acid groups, phosphoric acid groups, etc. in addition to carboxyl groups). The preferred amounts of acidic functional group-containing monomers used in the monomer components of this embodiment can be applied to the aforementioned preferred amounts of carboxyl group-containing monomers. The interlayer sheet disclosed herein can preferably be implemented in an embodiment in which the monomer components do not contain acidic group-containing monomers (i.e., the base polymer of the viscoelastic layer V1 is acid-free).

[0172] (Glass transition temperature Tg of base polymer T )

[0173] In some embodiments, the base polymer (eg, acrylic polymer) of the adhesive layer has a glass transition temperature (Tg) based on the composition of the monomer components constituting the polymer. T It is suitable to be about 20°C or less, preferably about 10°C or less, more preferably 0°C or less, and can be -10°C or less, -20°C or less, -25°C or less, -28°C or less, or -30°C or less. Glass transition temperature Tg T When the temperature is low, it is advantageous from the viewpoint of improving the flexibility of the adhesive.T For example, it can be above -60°C, preferably above -50°C, more preferably above -45°C, from the viewpoint of facilitating the high refractive index of the adhesive, and can be above -40°C, above -35°C, above -25°C, above -15°C, or above -5°C.

[0174] Here, the glass transition temperature Tg of the polymer T Unless otherwise specified, the glass transition temperature is determined using the Fox equation based on the composition of the monomer components constituting the polymer. The Fox equation, shown below, represents the relationship between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer formed by homopolymerization of the monomers constituting the copolymer.

[0175] 1 / Tg=Σ(Wi / Tgi)

[0176] In the above Fox formula, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio based on weight), and Tgi represents the glass transition temperature of the homopolymer of monomer i (unit: K).

[0177] As the glass transition temperature of the homopolymer used to calculate Tg, the value described in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) and other known materials are used. For monomers for which multiple values are described in the above-mentioned Polymer Handbook, the highest value is used. If the Tg of the homopolymer is not described in the known materials, the value obtained by the measurement method described in Japanese Patent Application Publication No. 2007-51271 is used.

[0178] (Method for preparing base polymer)

[0179] In the technology disclosed herein, the method for obtaining the base polymer of the adhesive layer (for example, the acrylic polymer (A) composed of the monomer components described above) is not particularly limited, and known polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization can be appropriately adopted. In some embodiments, solution polymerization can be preferably adopted. The polymerization temperature during solution polymerization can be appropriately selected according to the types of monomers and solvents used, the type of polymerization initiator, etc., and can be set to, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0180] The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one solvent selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetates such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (e.g., monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; or a mixed solvent of two or more thereof can be used.

[0181] The initiator used in the polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; etc. Further examples of polymerization initiators include redox-based initiators based on a combination of a peroxide and a reducing agent. The polymerization initiator can be used alone or in combination of two or more. The amount of the polymerization initiator used may be a conventional amount, for example, it can be selected from a range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) relative to 100 parts by weight of the monomer component.

[0182] In the above-mentioned polymerization, various conventionally known chain transfer agents can be used as needed. For example, thiols such as n-dodecyl mercaptan, tert-dodecyl mercaptan, thioglycolic acid, and α-thioglycerol can be used. Alternatively, a chain transfer agent that does not contain a sulfur atom (non-sulfur chain transfer agent) can also be used. Examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenes such as α-pinene and terpinolene; styrenes such as α-methylstyrene and α-methylstyrene dimer; etc. Chain transfer agents can be used alone or in combination of two or more. When using a chain transfer agent, the amount used can be, for example, about 0.01 to 1 part by weight relative to 100 parts by weight of the monomer raw material.

[0183] The weight average molecular weight (Mw) of the base polymer is not particularly limited, and may be, for example, approximately 10×10 4 ~500×10 4 From the viewpoint of adhesive performance, the Mw of the base polymer is preferably about 20×10 4 ~400×10 4 (More preferably, about 30×10 4 ~150×10 4 , for example, about 50×10 4 ~130×10 4) range.

[0184] Here, the Mw of the polymer can be determined by gel permeation chromatography (GPC) in terms of polystyrene. Specifically, it can be determined by measuring using a GPC measuring apparatus with the trade name "HLC-8220GPC" (manufactured by Tosoh Corporation) under the following conditions.

[0185] [GPC measurement conditions]

[0186] Sample concentration: 0.2 wt% (tetrahydrofuran solution)

[0187] Sample injection volume: 10 μL

[0188] Eluent: tetrahydrofuran (THF)

[0189] Flow rate: 0.6 mL / min

[0190] Column temperature (measurement temperature): 40°C

[0191] column:

[0192] Sample column: 1 product name "TSKguardcolumnSuperHZ-H" + 2 products brand name "TSKgelSuperHZM-H" (manufactured by Tosoh Corporation)

[0193] Reference column: 1 product name "TSKgelSuperH-RC" (manufactured by Tosoh Corporation)

[0194] Detector: Differential Refractometer (RI)

[0195] Standard sample: polystyrene

[0196] (Refractive Index Enhancer)

[0197] In some embodiments of the technology disclosed herein, the adhesive layer V1 (e.g., an acrylic adhesive layer) may contain a refractive index enhancer as needed in addition to the base polymer. Here, in this specification, a refractive index enhancer refers to a material that can increase the refractive index of the adhesive layer through its use. As a refractive index enhancer, a material having a higher refractive index than the refractive index of the adhesive layer containing the refractive index enhancer can be preferably used. In addition, as a refractive index enhancer, a material having a higher refractive index than the base polymer (e.g., acrylic polymer (A)) of the adhesive layer containing the refractive index enhancer can be preferably used. Through the appropriate use of the refractive index enhancer, a higher refractive index and practical adhesive performance can be appropriately taken into account. In some embodiments, the refractive index enhancer is preferably an organic material. The organic material used as the refractive index enhancer can be a polymer or a non-polymer. In addition, it can have a polymerizable functional group or not. The refractive index enhancer can be used alone or in combination of two or more.

[0198] Refractive index enhancer (e.g., additives described below (H RO )) can be set to an appropriate range by the relative relationship with the refractive index of the base polymer, and is therefore not limited to a specific range. The refractive index of the refractive index enhancer can be selected from a range that is higher than 1.55, higher than 1.56 or higher than 1.57, and higher than the refractive index of the base polymer. From the perspective of high refractive index of the adhesive, in some embodiments, it is advantageous for the refractive index of the refractive index enhancer to be higher than 1.58, preferably higher than 1.60, more preferably higher than 1.63, higher than 1.65, higher than 1.70, or higher than 1.75. By utilizing a refractive index enhancer with a higher refractive index, the target refractive index can be achieved by using a smaller amount of refractive index enhancer. This is preferred from the perspective of suppressing the reduction of adhesive properties and optical properties. The upper limit of the refractive index of the refractive index enhancer is not particularly limited. From the viewpoints of compatibility within the adhesive, ease of achieving a high refractive index and flexibility suitable for an adhesive, it may be, for example, 3.000 or less, 2.500 or less, 2.000 or less, 1.950 or less, 1.900 or less, or 1.850 or less.

[0199] In some embodiments, the refractive index enhancer (e.g., the additive (H RO ))'s refractive index n b The refractive index n of the base polymer a The difference, that is, n b -n a (hereinafter also referred to as "Δn A ”.) is set to be greater than 0. In some embodiments, Δn AFor example, it can be 0.02 or more, 0.05 or more, 0.07 or more, 0.10 or more, 0.15 or more, 0.20 or more, or 0.25 or more. A The larger the refractive index, the higher the refractive index improvement effect due to the use of the refractive index enhancer. In addition, from the perspective of compatibility within the adhesive layer, transparency of the adhesive layer, etc., in some embodiments, Δn A For example, it may be 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

[0200] In some embodiments, the refractive index enhancer (e.g., the additive (H RO ))'s refractive index n b The refractive index n of the adhesive layer containing the refractive index enhancer is T The difference, that is, n b -n T (hereinafter also referred to as "Δn B ”.) is set to be greater than 0. In some embodiments, Δn B For example, Δn is 0.02 or more, 0.05 or more, 0.07 or more, 0.10 or more, 0.15 or more, 0.20 or more, or 0.25 or more. B The larger the refractive index, the higher the refractive index improvement effect due to the use of the refractive index enhancer. In addition, from the perspective of compatibility within the adhesive layer, transparency of the adhesive layer, etc., in some embodiments, Δn B For example, it may be 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

[0201] The amount of refractive index enhancer relative to 100 parts by weight of base polymer (their total amount when using multiple refractive index enhancers) is not particularly limited and can be set according to purpose. From the viewpoint of the high refractive index of adhesive, the amount of refractive index enhancer relative to 100 parts by weight of base polymer can, for example, be set to more than 1 part by weight, and it is advantageous to be set to more than 3 parts by weight, and is preferably set to more than 5 parts by weight, can be more than 7 parts by weight, can be more than 10 parts by weight, can be more than 15 parts by weight, and can also be more than 20 parts by weight. In addition, in some ways, the amount of refractive index enhancer relative to 100 parts by weight of base polymer can, for example, be set to less than 80 parts by weight, and from the viewpoint of well-balancedly taking into account the high refractive index of adhesive and the reduction suppression of bonding characteristics and optical characteristics, it is advantageous to be set to less than 60 parts by weight, and is preferably set to less than 45 parts by weight. In some embodiments where adhesive and optical properties are prioritized, the amount of the refractive index enhancer used relative to 100 parts by weight of the base polymer may be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, 5 parts by weight or less, or 3 parts by weight or less. The technology disclosed herein may also be preferably implemented in an embodiment where the amount of the refractive index enhancer used relative to 100 parts by weight of the base polymer in the adhesive layer is less than 1 part by weight, or where substantially no refractive index enhancer is used. Here, "substantially no" means at least not intentionally used.

[0202] (Additives (H RO ))

[0203] In some embodiments, as a refractive index enhancer, an organic material having a higher refractive index than the base polymer may be preferably used. Hereinafter, such an organic material may be referred to as an "additive (H RO )". Here, the above "H RO " represents an organic material with a high refractive index. By combining a base polymer (such as an acrylic polymer, preferably an acrylic polymer (A)) with an additive (H RO ), it is possible to realize an adhesive that more appropriately takes into account the refractive index and adhesive properties (peel strength, softness, etc.) and / or optical properties (total light transmittance, haze value, etc.). RO ) can be a polymer or a non-polymer. In addition, it can have a polymerizable functional group or not. RO ) can be used alone or in combination of two or more.

[0204] Additives (H ROThe refractive index of the monomer is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25° C., similarly to the refractive index of the monomer. If a nominal value of the refractive index at 25° C. is provided by the manufacturer, the nominal value may be used.

[0205] As an additive (H RO ) The molecular weight of the organic material used is not particularly limited and can be selected according to the purpose. RO ) can be selected from the range of 30,000 or less. RO ) is preferably a polymer or non-polymer having a molecular weight lower than that of the base polymer. From the perspective of achieving a good balance between the effect of high refractive index and other properties (such as flexibility suitable for adhesives, optical properties such as haze), in some embodiments, the additive (H RO ) is suitably less than about 10,000, preferably less than 5,000, more preferably less than 3,000 (e.g., less than 1,000), and may be less than 800, less than 600, less than 500, or less than 400. The additive (H RO ) is not too large, it may be advantageous from the viewpoint of improving the compatibility within the adhesive layer. RO ) can be, for example, 130 or more, or 150 or more. In some embodiments, the additive (H RO ) from the viewpoint of increasing the refractive index, the additive (H RO ) preferably has a molecular weight of 170 or more, more preferably 200 or more, 230 or more, 250 or more, 270 or more, 500 or more, 1000 or more, or 2000 or more. In some embodiments, a polymer having a molecular weight of about 1000 to 10000 (e.g., 1000 or more and less than 5000) can be used as the additive (H RO ).

[0206] As an additive (H RO ) molecular weight. For non-polymers or polymers with a low degree of polymerization (e.g., 2-5 polymers), the molecular weight calculated based on the chemical structure or the value measured by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) can be used. Additives (H RO ) is a polymer with a higher degree of polymerization, the weight average molecular weight (Mw) based on GPC performed under appropriate conditions can be used. When a nominal value of molecular weight is provided by a manufacturer, the nominal value can be adopted.

[0207] Can be an additive (H ROExamples of the organic material that can be selected from the group consisting of: an organic compound having an aromatic ring, an organic compound having a heterocyclic ring (which may be an aromatic ring or a non-aromatic heterocyclic ring), etc., but are not limited to these.

[0208] As an additive (H RO The aromatic ring possessed by the above-mentioned organic compound having an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") used in the present invention can be selected from the same aromatic rings as the aromatic ring possessed by the compound used as the monomer (m1).

[0209] The above-mentioned aromatic ring may have one or more substituents on the ring-forming atoms, or may not have a substituent. When there is a substituent, examples of the substituent include alkyl, alkoxy, aryloxy, hydroxyl, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl, hydroxyalkyloxy, glycidoxy, etc., but are not limited to these. In the substituent containing carbon atoms, the number of carbon atoms contained in the substituent is, for example, 1 to 10, advantageously 1 to 6, preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. In some embodiments, the above-mentioned aromatic ring may be an aromatic ring that has no substituent on the ring-forming atoms, or has one or more substituents selected from the group consisting of alkyl, alkoxy and halogen atoms (such as bromine atoms).

[0210] As an additive (H RO Examples of aromatic ring-containing compounds include: compounds that can be used as monomers (m1); oligomers containing compounds that can be used as monomers (m1) as monomer units; compounds having a structure in which a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring-forming atom) or a portion of the group that constitutes an ethylenically unsaturated group is removed from the compound that can be used as a monomer (m1) and replaced with a hydrogen atom or a group that does not have an ethylenically unsaturated group (such as a hydroxyl group, an amino group, a halogen atom, an alkyl group, an alkoxy group, a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidoxy group, etc.); etc., but are not limited to these. Can be used as an additive (H RONon-limiting examples of aromatic ring-containing compounds include: benzyl acrylate, m-phenoxybenzyl acrylate, 2-(o-phenylphenoxy)ethyl acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxypolyethylene glycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, and other aromatic ring-containing monomers such as the aforementioned monomers having a fluorene structure, a dinaphthothiophene structure, and a dibenzothiophene structure; and aromatic ring-containing compounds without ethylenically unsaturated groups, such as 3-phenoxybenzyl alcohol, dinaphthothiophene, and its derivatives (e.g., compounds having a structure in which one or more substituents selected from the group consisting of hydroxyl, carbinol, diethanol, and glycidyl groups are bonded to the dinaphthothiophene ring). Furthermore, the aromatic ring-containing compound may be an oligomer (preferably an oligomer having a molecular weight of approximately 5,000 or less, more preferably approximately 1,000 or less, such as a dimer to pentamer) containing such an aromatic ring-containing monomer as a monomer unit. The oligomer may be, for example, a homopolymer of an aromatic ring-containing monomer; a copolymer of one or more aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers and other monomers; etc. As the other monomer, one or more monomers not containing an aromatic ring may be used.

[0211] In some embodiments, as an additive (H RO ), from the perspective of easily obtaining a high refractive index-enhancing effect, an organic compound having two or more aromatic rings in one molecule (hereinafter also referred to as "a compound containing multiple aromatic rings") can be preferably used. The compound containing multiple aromatic rings may or may not have a polymerizable functional group such as an ethylenically unsaturated group. In addition, the compound containing multiple aromatic rings may be a polymer or a non-polymer. In addition, the above-mentioned polymer may be an oligomer containing a monomer containing multiple aromatic rings as a monomer unit (preferably an oligomer having a molecular weight of about 5000 or less, more preferably about 1000 or less. For example, an oligomer of about 2 to 5 polymers). The above-mentioned oligomer may be, for example: a homopolymer of a monomer containing multiple aromatic rings; a copolymer of one or more monomers containing multiple aromatic rings; a copolymer of one or more monomers containing multiple aromatic rings and other monomers; etc. The above-mentioned other monomers may be an aromatic ring-containing monomer that does not belong to the monomer containing multiple aromatic rings, or a monomer without an aromatic ring, or a combination thereof.

[0212] Non-limiting examples of compounds containing multiple aromatic rings include compounds having a structure in which two or more non-fused aromatic rings are bonded via a linking group, compounds having a structure in which two or more non-fused aromatic rings are chemically bonded directly (i.e., not via other atoms), compounds having a fused aromatic ring structure, compounds having a fluorene structure, compounds having a dinaphthothiophene structure, and compounds having a dibenzothiophene structure. Compounds containing multiple aromatic rings may be used alone or in combination of two or more.

[0213] Specific examples of the above-mentioned compounds having a fluorene structure include, in addition to the above-mentioned monomers having a fluorene structure and oligomers as homopolymers or copolymers of the monomers, 9,9-bis(4-hydroxyphenyl)fluorene (refractive index: 1.68), 9,9-bis(4-aminophenyl)fluorene (refractive index: 1.73), 9,9-bis(4-hydroxy-3-methylphenyl)fluorene (refractive index: 1.68), 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (refractive index: 1.65), and other 9,9-bisphenylfluorene and its derivatives.

[0214] Specific examples of the compound having a dinaphthothiophene structure include, in addition to the monomer having a dinaphthothiophene structure and an oligomer as a homopolymer or copolymer of the monomer, dinaphthothiophene (refractive index: 1.808); hydroxyalkyl dinaphthothiophenes such as 6-hydroxymethyl dinaphthothiophene (refractive index: 1.766); dihydroxy dinaphthothiophenes such as 2,12-dihydroxy dinaphthothiophene (refractive index: 1.750); 2,12-dihydroxy dinaphthothiophene (refractive index: 1.766); Dihydroxyalkyloxy dinaphthothiophene such as hydroxyethyloxy dinaphthothiophene (refractive index: 1.677); diglycidyloxy dinaphthothiophene such as 2,12-diglycidyloxy dinaphthothiophene (refractive index 1.723); dinaphthothiophene having two or more ethylenically unsaturated groups such as 2,12-diallyloxy dinaphthothiophene (abbreviation: 2,12-DAODNT, refractive index 1.729); and other dinaphthothiophenes and their derivatives.

[0215] Specific examples of the above-mentioned compounds having a dibenzothiophene structure include, in addition to the above-mentioned monomers having a dibenzothiophene structure and oligomers which are homopolymers or copolymers of the monomers, dibenzothiophene (refractive index: 1.607), 4-dimethyldibenzothiophene (refractive index: 1.617), 4,6-dimethyldibenzothiophene (refractive index: 1.617), etc.

[0216] As an additive (H RO) as an option and having a heterocyclic ring (hereinafter also referred to as a heterocyclic ring-containing organic compound) include thioepoxy compounds, compounds having a triazine ring, and the like. Examples of thioepoxy compounds include bis(2,3-epithiopropyl)disulfide and its polymer (refractive index 1.74) described in Japanese Patent Gazette No. 3712653. Examples of compounds having a triazine ring include compounds having at least one triazine ring (for example, 3 to 40, preferably 5 to 20) in one molecule. It should be noted that the triazine ring has aromatic properties, and therefore compounds having a triazine ring are also included in the concept of the above-mentioned aromatic ring-containing compound. In addition, compounds having multiple triazine rings are also included in the concept of the above-mentioned aromatic ring-containing compound.

[0217] In some embodiments, as an additive (H RO ), it is preferable to use a compound without an ethylenically unsaturated group. This can inhibit the deterioration of the adhesive composition caused by heat and light (the leveling property is reduced due to the progress of gelation and the increase in viscosity) and improve storage stability. RO From the viewpoint of suppressing dimensional change, deformation (warping, undulation, etc.), and generation of optical distortion caused by the reaction of ethylenically unsaturated groups, it is also preferable to use an additive (H) having no ethylenically unsaturated groups. RO ).

[0218] When using oligomers as additives (H RO ) in the manner of, the oligomer can be obtained by polymerizing the corresponding monomer components using a known method. When the above-mentioned oligomer is produced by free radical polymerization, a polymerization initiator, chain transfer agent, emulsifier, etc. for free radical polymerization can be appropriately added to the above-mentioned monomer components to carry out polymerization. The above-mentioned polymerization initiator, chain transfer agent, emulsifier, etc. for free radical polymerization are not particularly limited and can be appropriately selected and used. It should be noted that the weight-average molecular weight of the oligomer can be controlled by the amount of the polymerization initiator and chain transfer agent used and the reaction conditions, and their amount can be appropriately adjusted according to their types.

[0219] Examples of the chain transfer agent include lauryl mercaptan, glycidyl mercaptan, thioglycolic acid, 2-mercaptoethanol, α-thioglycerol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. One chain transfer agent may be used alone or in combination of two or more. The amount of the chain transfer agent used may be set so as to obtain an oligomer with a desired weight average molecular weight, based on the composition of the monomer components used in the synthesis of the oligomer, the type of chain transfer agent, and the like. In some embodiments, it is appropriate to set the amount of the chain transfer agent used to be approximately 15 parts by weight or less, 10 parts by weight or less, or approximately 5 parts by weight or less, relative to 100 parts by weight of the total amount of the monomers used in the synthesis of the oligomer. The lower limit of the amount of the chain transfer agent used is not particularly limited, and may be, for example, 0.01 parts by weight or more, 0.1 parts by weight or more, 0.5 parts by weight or more, or 1 part by weight or more, relative to 100 parts by weight of the total amount of the monomers used in the synthesis of the oligomer.

[0220] When using additives (H RO ) as a refractive index enhancer, the additive (H RO ) relative to 100 parts by weight of the base polymer (the total amount thereof when multiple compounds are used) is not particularly limited and can be set according to the purpose. From the viewpoint of increasing the refractive index of the adhesive, the additive (H RO ) can be used in an amount of, for example, 1 part by weight or more relative to 100 parts by weight of the base polymer, and it is advantageous to use 3 parts by weight or more, preferably 5 parts by weight or more, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more. In some embodiments, the additive (H RO ) can be used in an amount of, for example, 80 parts by weight or less relative to 100 parts by weight of the base polymer. From the perspective of achieving a good balance between the high refractive index of the adhesive and the suppression of the decrease in adhesive properties and optical properties, it is advantageous to use 60 parts by weight or less, and preferably 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are given greater emphasis, the additive (H RO ) can be used in an amount of, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less relative to 100 parts by weight of the base polymer.

[0221] (Plasticized material)

[0222] In some embodiments of the interlayer sheet disclosed herein, the adhesive layer V1 may contain, in addition to the base polymer (e.g., acrylic polymer (A)) as described above, a plasticizer having a molecular weight lower than that of the base polymer. The use of the plasticizer can improve the flexibility of the adhesive layer V1, the adhesion to the adherend, the flexibility of the interlayer sheet as a whole, and the ability to follow deformation. As the plasticizer, organic materials can be preferably used from the viewpoint of compatibility and transparency within the adhesive layer. The plasticizer can be a material that can also be used as the above-mentioned refractive index enhancer (e.g., the above-mentioned additive (H RO )) materials.

[0223] The molecular weight of plasticizing material is lower than base polymer, is not particularly limited. In some ways, from the viewpoint of easily showing plasticizing effect, the molecular weight of plasticizing material can be less than 30000, can be less than 25000, can be less than 10000, preferably less than 5000, more preferably less than 3000 (such as less than 1000), can be less than 800, can be less than 600, can be less than 500, also can be less than 400. When the molecular weight of plasticizing material is not too large, from the viewpoints such as the compatibility improvement in the adhesive layer, it can be advantageous. In addition, in some ways, from the viewpoint of easily playing sufficient plasticizing effect, the molecular weight of plasticizing material is appropriate for more than 130, is preferably more than 150, can be more than 170, can be more than 200, can be more than 250, also can be more than 300. In some ways, the molecular weight of plasticizing material can be more than 500, can be more than 1000, also can be more than 2000. It is preferable that the molecular weight of the plasticizer is not too low from the viewpoint of heat resistance of the interlayer sheet and suppression of contamination of the adherend.

[0224] Non-limiting examples of compounds that can be selected as plasticizers include: compounds that can be used as monomer (m1) (e.g., (meth)acrylates having an aromatic ring such as a benzyl group, a phenoxy group, or a naphthyl group, monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, etc.); oligomers containing compounds that can be used as monomer (m1) as monomer units; compounds having a structure in which an ethylenically unsaturated group in a compound that can be used as monomer (m1) is removed and replaced with a hydrogen atom or a group without an ethylenically unsaturated group (e.g., 3-phenoxybenzyl alcohol); etc. From the perspective of improving flexibility, oligomers containing compounds that can be used as monomer (m1) as monomer units may be copolymerized with a low Tg monomer such as n-butyl acrylate or 2-ethylhexyl acrylate. As the plasticizing material, one or more known plasticizers (for example, phthalate-based plasticizers, terephthalate-based plasticizers, adipate-based plasticizers, adipic acid-based polyesters, benzoic acid glycol esters, etc.) can be used.

[0225] In some embodiments, as a plasticizer, an organic material having a refractive index of about 1.50 or more (more preferably 1.53 or more) can be preferably used. Specific examples of compounds that can be selected as plasticizers include: diethylene glycol dibenzoate (refractive index 1.55), dipropylene glycol dibenzoate (refractive index 1.54), 3-phenoxytoluene (refractive index 1.57), 3-ethylbiphenyl (refractive index 1.59), 3-methoxybiphenyl (refractive index 1.61), 4-methoxybiphenyl (refractive index 1.57), polyethylene glycol dibenzoate, 3-phenoxybenzyl alcohol (refractive index 1.59), triphenyl phosphate (refractive index 1.56), benzyl benzoate (refractive index 1.57), 4-(tert-butyl) ) phenyl diphenyl phosphate (refractive index 1.56), trimethylphenyl phosphate (refractive index 1.55), butylbenzyl phthalate (refractive index 1.54), rosin methyl ester (refractive index 1.53), alkylbenzyl phthalate (refractive index 1.53), butyl (benzenesulfonyl) amide (refractive index 1.53), trimethyl trimellitate (refractive index 1.52), benzyl phthalate (refractive index 1.52), 2-ethylhexyl diphenyl phosphate (refractive index 1.51), tris (2,4-di-tert-butylphenyl phosphite), etc., but are not limited to these. From the viewpoint of refractive index and compatibility, for example, diethylene glycol dibenzoate can be preferably used. The upper limit of the refractive index of the plasticizer is not particularly limited, for example, it can be 3.00 or less. In some embodiments, from the perspective of ease of preparation of the adhesive composition, compatibility within the adhesive, etc., the refractive index of the plasticizer is appropriately 2.50 or less, advantageously 2.00 or less, and can be 1.90 or less, 1.80 or less, or 1.70 or less.

[0226] The refractive index of the plasticizer is measured, similarly to the refractive index of the monomer, using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25° C. If a nominal value of the refractive index at 25° C. is provided by the manufacturer, that nominal value may be used.

[0227] In the mode of using plasticizing material, the usage amount of plasticizing material relative to 100 parts by weight of base polymer is not particularly limited and can be set according to purpose. From the viewpoint of improving plasticizing effect, the usage amount of plasticizing material relative to 100 parts by weight of base polymer can be, for example, more than 0.1 parts by weight, or more than 0.5 parts by weight. From the viewpoint of obtaining higher plasticizing effect, it is preferably set to more than 1 part by weight, more preferably set to more than 3 parts by weight, more preferably set to more than 5 parts by weight, more preferably set to more than 7 parts by weight, more preferably set to more than 10 parts by weight, more preferably set to more than 15 parts by weight, or more than 20 parts by weight. In addition, from the viewpoint of taking into account the high refractive index and transparency of adhesive and plasticizing effect well in a balanced manner, it is appropriate that the usage amount of plasticizing material relative to 100 parts by weight of base polymer is set to about 100 parts by weight or less, preferably set to less than 80 parts by weight, more preferably set to less than 60 parts by weight, more preferably set to less than 45 parts by weight, more preferably set to less than 35 parts by weight, or less than 25 parts by weight. In some embodiments where adhesive properties and optical properties are more important, the amount of the plasticizer used may be 15 parts by weight or less, 10 parts by weight or less, or even 5 parts by weight or less relative to 100 parts by weight of the base polymer.

[0228] (Leveling agent)

[0229] In some embodiments, the adhesive composition used to form the adhesive layer (which may be the viscoelastic layer V1 and / or the viscoelastic layer V2) may contain a leveling agent as needed for purposes such as improving the appearance of the adhesive layer formed from the composition (e.g., improving thickness uniformity) and improving the coating properties of the adhesive composition. Non-limiting examples of leveling agents include acrylic leveling agents, fluorine leveling agents, and silicone leveling agents. For example, a suitable leveling agent can be selected from commercially available leveling agents and used using conventional methods.

[0230] In some embodiments, the leveling agent may preferably be a polymer (hereinafter referred to as "polymer (B)") comprising a monomer having a polyorganosiloxane skeleton (hereinafter referred to as "monomer S1") and a monomer raw material of an acrylic monomer (hereinafter referred to as "monomer raw material B"). Polymer (B) may be a copolymer of monomer S1 and an acrylic monomer. One polymer (B) may be used alone or in combination of two or more.

[0231] As monomer S1, there is no particular limitation, and any monomer containing a polyorganosiloxane skeleton can be used. As monomer S1, a monomer having a structure with a polymerizable reaction group at one end can be preferably used. Among them, monomer S1 having a structure with a polymerizable reaction group at one end and not having a functional group that can undergo a cross-linking reaction with a base polymer (referring to the base polymer of the adhesive composition to be compounded with the leveling agent. For example, an acrylic polymer) can be preferably used. As a commercially available product, for example, single-end reactive silicone oils (such as product numbers such as X-22-174ASX, X-22-2426, X-22-2475, and KF-2012) manufactured by Shin-Etsu Chemical Co., Ltd. can be listed. Monomer S1 can be used alone or in combination of two or more.

[0232] The functional group equivalent weight of monomer S1 can be, for example, about 100 g / mol to 30,000 g / mol. In some preferred embodiments, the functional group equivalent weight is, for example, 500 g / mol or more, 800 g / mol or more, 1,500 g / mol or more, or 2,000 g / mol or more. In addition, the functional group equivalent weight can be, for example, 20,000 g / mol or less, less than 10,000 g / mol, 7,000 g / mol or less, or 5,500 g / mol or less. When the functional group equivalent weight of monomer S1 is within the above range, a good leveling effect is easily achieved.

[0233] When two or more monomers having different functional group equivalents are used as monomer S1, the functional group equivalent of monomer S1 may be the sum of the products of the functional group equivalents of the various monomers and the weight fractions of the monomers.

[0234] Here, "functional group equivalent weight" refers to the weight of the main skeleton (e.g., polydimethylsiloxane) to which each functional group is bonded. The unit of notation is g / mol, which is converted to 1 mol of functional groups. The functional group equivalent weight of monomer S1 can be calculated, for example, based on nuclear magnetic resonance (NMR) analysis. 1 It is calculated based on the spectral intensity of H-NMR (proton NMR). 1 The functional group equivalent (g / mol) of monomer S1 can be calculated based on the H-NMR spectrum intensity. 1 Conventional structural analysis techniques in H-NMR spectrum analysis are performed with reference to Japanese Patent No. 5951153. In the functional group equivalent of monomer S1, the functional group refers to a polymerizable functional group (e.g., ethylenically unsaturated groups such as (meth)acryloyl, vinyl, and allyl).

[0235] The content of monomer S1 in the monomer feed B can be an appropriate value within the range in which the desired effect of using the monomer S1 is achieved, and is not limited to a specific range. In some embodiments, the content of monomer S1 in the monomer feed B can be, for example, 5 to 60% by weight, 10 to 50% by weight, or 15 to 40% by weight.

[0236] In addition to monomer S1, monomer raw material B also contains an acrylic monomer that can be copolymerized with monomer S1. As a result, the compatibility of the polymer (B) in the adhesive layer can be improved. As acrylic monomers that can be used for monomer raw material B, for example, alkyl acrylates can be listed. The "alkyl" mentioned here refers to a chain (including straight chain and branched) alkyl (group), excluding the alicyclic hydrocarbon group described later. In some embodiments, monomer raw material B may contain (meth)acrylic acid C 4-12 Alkyl ester (preferably (meth) acrylic acid C 4-10 Alkyl esters, such as (meth) acrylic acid C 6-10 In some other embodiments, the monomer raw material B may include methacrylic acid C 1-18 Alkyl ester (preferably methacrylic acid C 1-14 Alkyl esters, such as methacrylate C 1-10 The monomer raw material B may contain, for example, one or more selected from methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA) as acrylic monomers.

[0237] Other examples of the acrylic monomer include (meth)acrylates having an alicyclic hydrocarbon group. For example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentyl (meth)acrylate, and 1-adamantyl (meth)acrylate can be used. (Meth)acrylates having an alicyclic hydrocarbon group do not necessarily need to be used.

[0238] The content of the above-mentioned alkyl (meth)acrylate and the above-mentioned (meth)acrylate having an alicyclic hydrocarbon group in the monomer raw material B can be, for example, 10% by weight or more and 95% by weight or less, 20% by weight or more and 95% by weight or less, 30% by weight or more and 90% by weight or less, 40% by weight or more and 90% by weight or less, or 50% by weight or more and 85% by weight or less.

[0239] Other examples of monomers that can be included in the monomer raw material B together with monomer S1 include: carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, amide group-containing monomers, monomers having a nitrogen atom-containing ring, (meth)acrylic acid aminoalkyl esters, vinyl esters, vinyl ethers, olefins, (meth)acrylates having aromatic hydrocarbon groups, halogen atom-containing (meth)acrylates, etc., which are listed above as monomers that can be used in acrylic polymers.

[0240] The Mw of the polymer (B) may be, for example, 5000 or more, preferably 10000 or more, or 15000 or more. Furthermore, the Mw of the polymer (B) may be, for example, 200000 or less, preferably 100000 or less, or 50000 or less, or 30000 or less. By setting the Mw of the polymer (B) within an appropriate range, suitable compatibility and leveling properties can be achieved.

[0241] The polymer (B) can be produced by polymerizing the above-mentioned monomers by a known method such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, or photopolymerization.

[0242] In order to adjust the molecular weight of the polymer (B), a chain transfer agent can be used as needed. Examples of chain transfer agents include compounds having a thiol group, such as n-dodecyl mercaptan, mercaptoethanol, and α-thioglycerol; thioglycolates such as thioglycolic acid and methyl thioglycolate; α-methylstyrene dimer; etc. The amount of the chain transfer agent used is not particularly limited and can be appropriately set to obtain a polymer (B) with a desired molecular weight. In some embodiments, the amount of the chain transfer agent used relative to 100 parts by weight of the monomer can be, for example, 0.1 to 5 parts by weight, 0.2 to 3 parts by weight, or 0.5 to 2 parts by weight.

[0243] The amount of polymer (B) used relative to 100 parts by weight of the base polymer (e.g., acrylic polymer) can be, for example, 0.001 parts by weight or more. To achieve a higher effect, it can be 0.01 parts by weight or more, or even 0.03 parts by weight or more. Furthermore, the amount of polymer (B) used can be, for example, 3 parts by weight or less. To reduce the effect on the refractive index, it is preferably 1 part by weight or less. It can also be 0.5 parts by weight or less, or even 0.1 parts by weight or less.

[0244] (Inorganic particles)

[0245] The technology disclosed herein can preferably be implemented in a manner that substantially does not use inorganic particles as a refractive index enhancer. Of course, it is permissible to use inorganic particles as a refractive index enhancer within the limit of not significantly impairing the application effect of the technology disclosed herein. Examples of inorganic particles that can be used as refractive index enhancers include inorganic particles composed of inorganic oxides (specifically, metal oxides) such as titanium oxide (titanium oxide, TiO2), zirconium oxide (zirconium oxide, ZrO2), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, and niobium oxide (Nb2O5, etc.). The average particle size of the above-mentioned inorganic particles (referring to the 50% volume average particle size based on the laser scattering / diffraction method) can be selected from the range of about 10nm to 100nm. It should be noted that the refractive index of the inorganic particles is measured using a commercially available spectroscopic ellipsometer at a measuring wavelength of 589nm and a measuring temperature of 23°C for a single layer film of the material constituting the inorganic particles (set to a film thickness at which the refractive index can be measured). As a spectroscopic ellipsometer, for example, the product name "EC-400" (manufactured by JA. Woolam Co., Ltd.) or its equivalent can be used. When using inorganic particles as a refractive index enhancer, the amount used is preferably less than 5 parts by weight, more preferably less than 1 part by weight, relative to 100 parts by weight of the base polymer. RO ) in the embodiment, the amount of the inorganic particles used is preferably set to the amount of the additive (H RO ) is less than 2 times the amount used, more preferably less than 1 time or less than 0.5 times.

[0246] (cross-linking agent)

[0247] In the technology disclosed herein, for the adhesive composition for forming the adhesive layer (which can be the viscoelastic layer V1 and / or the viscoelastic layer V2), a cross-linking agent can be contained as needed for purposes such as adjusting the cohesive force of the adhesive. As the cross-linking agent, there can be used isocyanate cross-linking agents, epoxy cross-linking agents, aziridine cross-linking agents, oxazoline cross-linking agents, melamine resins, metal chelate cross-linking agents, and other cross-linking agents known in the field of adhesives. Among them, isocyanate cross-linking agents can be preferably used. As other examples of cross-linking agents, monomers having two or more ethylenically unsaturated groups in one molecule, i.e., multifunctional monomers, can be listed. The cross-linking agent can be used alone or in combination of two or more.

[0248] As the isocyanate cross-linking agent, a difunctional or higher-functional isocyanate compound can be used, for example, aliphatic polyisocyanates such as trimethylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate (HDI), and dimer acid diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), and 1,3-bis(isocyanatomethyl)cyclohexane; aromatic isocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate (XDI); polyisocyanate modified products obtained by modifying the above-mentioned isocyanate compounds with an allophanate bond, a biuret bond, an isocyanurate bond, a uretdione bond, a urea bond, a carbodiimide bond, a uretonimine bond, an oxadiazinetrione bond, etc.; and the like. Examples of commercially available products include Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, Takenate D178N (all manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidur T80, Sumidur L, Desmodur N3400 (all manufactured by Sumika Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, and Coronate HX (all manufactured by Tosoh Corporation). The isocyanate compound may be used alone or in combination of two or more. A bifunctional isocyanate compound and a trifunctional or higher isocyanate compound may also be used in combination.

[0249] Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane. These can be used alone or in combination of two or more.

[0250] Examples of the polyfunctional monomer include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, bisphenoxyethanolfluorene di(meth)acrylate, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butyl glycol (meth)acrylate, and hexyl glycol di(meth)acrylate. The polyfunctional monomers can be used alone or in combination of two or more.

[0251] The amount used when using a cross-linking agent (which can be a multifunctional monomer) is not particularly limited, and for example, it can be set in the range of about 0.001 to 5.0 parts by weight relative to 100 parts by weight of the base polymer. From the viewpoint of improving the flexibility of the adhesive, in some embodiments, the amount of the cross-linking agent used relative to 100 parts by weight of the base polymer is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, can be 1.0 parts by weight or less, can be 0.5 parts by weight or less, or can be 0.2 parts by weight or less. In addition, from the viewpoint of appropriately exerting the effect of the use of the cross-linking agent, in some embodiments, the amount of the cross-linking agent used relative to 100 parts by weight of the base polymer can be, for example, 0.005 parts by weight or more, can be 0.01 parts by weight or more, can be 0.05 parts by weight or more, or can be 0.08 parts by weight or more.

[0252] In order to carry out the cross-linking reaction more effectively, a cross-linking catalyst can also be used. Examples of cross-linking catalysts include tetra-n-butyl titanate, tetraisopropyl titanate, iron acetylacetonate ( Metal-based crosslinking catalysts such as tin (Iron III), butyl tin oxide, and dioctyltin dilaurate are also available. Among them, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of the crosslinking catalyst used is not particularly limited. Considering the balance between the speed of the crosslinking reaction and the pot life of the adhesive composition, the amount of the crosslinking catalyst used can be, for example, in the range of approximately 0.0001 parts by weight to 1 part by weight, preferably in the range of 0.001 parts by weight to 0.5 parts by weight, relative to 100 parts by weight of the base polymer.

[0253] The adhesive composition may contain a compound that undergoes keto-enol tautomerism as a crosslinking retarder. Thus, the effect of extending the pot life of the adhesive composition can be achieved. For example, in an adhesive composition containing an isocyanate-based crosslinking agent, a compound that undergoes keto-enol tautomerism can be preferably utilized. As a compound that undergoes keto-enol tautomerism, various β-dicarbonyl compounds can be used. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetic esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably used. The compound that undergoes keto-enol tautomerism can be used alone or in combination of two or more. The amount of the compound that undergoes keto-enol tautomerism used can be, for example, 0.1 parts by weight or more and 20 parts by weight or less, 0.5 parts by weight or more and 10 parts by weight or less, or 1 part by weight or more and 5 parts by weight or less relative to 100 parts by weight of the base polymer.

[0254] (Thickener)

[0255] The adhesive layer (which can be viscoelastic layer V1 and / or viscoelastic layer V2) in the technology disclosed herein may contain a tackifier. As a tackifier, known tackifier resins such as rosin-based tackifier resins, terpene-based tackifier resins, phenol-based tackifier resins, hydrocarbon-based tackifier resins, ketone-based tackifier resins, polyamide-based tackifier resins, epoxy-based tackifier resins, and elastic system tackifier resins can be used. These can be used alone or in combination with more than two kinds. The usage amount of the tackifier resin is not particularly limited and can be set to give play to appropriate adhesive properties according to the purpose and use. In some embodiments, from the viewpoint of refractive index and transparency, it is appropriate for the usage amount of the tackifier to be set to less than 30 parts by weight relative to 100 parts by weight of the base polymer of the adhesive layer, preferably to be set to less than 10 parts by weight, and more preferably to be set to less than 5 parts by weight. The technology disclosed herein can preferably be implemented without using a tackifier.

[0256] (Other additives)

[0257] In the technology disclosed herein, the adhesive composition used to form the adhesive layer (which may be the viscoelastic layer V1 and / or the viscoelastic layer V2) may contain, as necessary, known additives for use in adhesive compositions, such as plasticizers, softeners, colorants, antistatic agents, anti-aging agents, UV absorbers, antioxidants, light stabilizers, and preservatives, as long as they do not significantly impair the effects of the present invention. These various additives can be conventionally used, and since they do not particularly contribute to the characterization of the present invention, detailed descriptions thereof will be omitted.

[0258] (Peel Strength)

[0259] In some embodiments of the interlayer sheet disclosed herein, the interlayer sheet preferably has a peel strength of about 1.0 N / 25 mm or greater (e.g., 1.5 N / 25 mm or greater), preferably 2 N / 25 mm or greater, more preferably 3 N / 25 mm or greater, and may be 4 N / 25 mm or greater, 6 N / 25 mm or greater, 8 N / 25 mm or greater, 10 N / 25 mm or greater, or 12 N / 25 mm or greater. The upper limit of the peel strength is not particularly limited, and may be, for example, 30 N / 25 mm or less, 25 N / 25 mm or less, or 20 N / 25 mm or less.

[0260] Here, the above-mentioned peel strength can be grasped as follows: press-bonded to an alkaline glass plate as an adherend, placed in an environment of 23°C and 50% RH for 30 minutes, then placed in a pressurized degassing device (autoclave), and autoclaved for 30 minutes under the conditions of a temperature of 50°C and a pressure of 0.5 MPa. After further placing in an atmosphere of 23°C and 50% RH for 24 hours, the 180° peeling adhesive force is measured under the conditions of a peeling angle of 180 degrees and a tensile speed of 300 mm / min. During the measurement, if necessary, an appropriate lining material (for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm to about 50 μm) can be attached to the interlayer sheet of the measurement object for reinforcement. Specifically, the peel strength can be measured according to the method described in the examples below.

[0261] When the interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, in some embodiments, the above-described peel strength preferably applies to at least the first adhesive surface, and more preferably applies to both the first and second adhesive surfaces. The peel strength of the first adhesive surface against the glass plate and the peel strength of the second adhesive surface against the glass plate may be of the same level or different.

[0262] <Viscoelastic Layer V2>

[0263] In some preferred embodiments of the interlayer sheet disclosed herein, the interlayer sheet may further comprise a viscoelastic layer (adhesive layer) V2 laminated on the viscoelastic layer V1 in addition to the viscoelastic layer V1. The viscoelastic layer V2 preferably has a storage modulus G' at 25°C of V2 Lower than the storage modulus G' of the viscoelastic layer V1 at 25°C V1 That is, G' is preferred V2 (25) <G’ V1 (25) The interlayer sheet of this structure can make the softness more excellent by the contribution of the viscoelastic layer V2. V2 (25) lower than the storage modulus G' V1(25) In the interlayer sheet, the high refractive index of the viscoelastic layer V1 and the softness of the viscoelastic layer V2 can be preferably achieved. By laminating the viscoelastic layer V2 on the viscoelastic layer V1, adhesion and softness are imparted, thereby improving the ability to follow height differences and curved surfaces, thereby achieving an interlayer sheet that can be preferably used in various device designs.

[0264] Storage modulus G' V2 (25) is not particularly limited, and may be, for example, in the range of 1.0 kPa to 500 kPa. From the perspective of improving the effect of imparting flexibility based on the viscoelastic layer V2 and improving the followability to deformation, in some embodiments, the storage modulus G' V2 (25) is suitably 400 kPa or less, preferably 300 kPa or less, more preferably 200 kPa or less (e.g., 180 kPa or less, or 150 kPa or less), and may be 120 kPa or less, 90 kPa or less, or 70 kPa or less. In addition, from the viewpoint of imparting appropriate cohesion to the viscoelastic layer V2, in some embodiments, the storage modulus G' V2 (25) is preferably 5.0 kPa or more, preferably 10 kPa or more, 15 kPa or more, 25 kPa or more, 35 kPa or more, 60 kPa or more, or 80 kPa or more. From the perspective of easily achieving higher cohesion and adhesive properties, in some embodiments, the storage modulus G' V2 (25) It can be 95 kPa or more, 110 kPa or more, or 140 kPa or more.

[0265] In some embodiments, the refractive index n2 of the viscoelastic layer (adhesive layer) V2 is lower than the refractive index n1 of the viscoelastic layer (adhesive layer) V1. With an interlayer sheet having this configuration, the difference in refractive indices between the viscoelastic layers V1 and V2 can be used to control the behavior of light passing through the interlayer sheet. In this embodiment, the refractive index n2 of the adhesive layer V2 is not particularly limited as long as it is lower than the refractive index n1 of the adhesive layer V1. For example, it can be within a range of approximately 1.35 to 1.55. In some embodiments, to increase the refractive index difference with the refractive index n1 of the viscoelastic layer V1 and thereby enhance the front brightness enhancement effect described below, the refractive index n2 of the viscoelastic layer V2 is preferably, for example, 1.49 or less, more preferably 1.47 or less (e.g., 1.46 or less, or 1.45 or less), and can be 1.43 or less, 1.41 or less, or even 1.40 or less. In addition, from the perspective of ease of material acquisition and ease of achieving both adhesive properties, in some embodiments, the refractive index n2 of the viscoelastic layer V2 can be, for example, 1.36 or greater, 1.38 or greater, 1.40 or greater, or 1.42 or greater.

[0266] The type of adhesive constituting the viscoelastic layer V2 is not particularly limited. The adhesive constituting the viscoelastic layer V2 can be an adhesive comprising one or more of various rubber-like polymers such as acrylic acid polymers, rubber polymers (such as natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, fluorine polymers, etc., which are usable in the field of adhesives, as a base polymer. From the viewpoints of adhesive performance and cost, an adhesive comprising an acrylic acid polymer or a rubber polymer as a base polymer can be preferably adopted. Among them, an adhesive (acrylic acid adhesive) with an acrylic acid polymer as a base polymer is preferably adopted. In the case where the viscoelastic layer V1 is an acrylic acid adhesive layer, from the viewpoint of the adhesion between the viscoelastic layer V1 and the viscoelastic layer V2, the viscoelastic layer V2 can be preferably configured as an acrylic acid adhesive layer.

[0267] In some embodiments, the acrylic polymer is preferably a polymer of a monomer raw material that contains an alkyl (meth)acrylate and may further contain other monomers (co-monomers) copolymerizable with the alkyl (meth)acrylate. The content of the alkyl (meth)acrylate in the monomer raw material may be, for example, 10% by weight or more, 25% by weight or more, 35% by weight or more, or 45% by weight or more. The acrylic polymer may be a polymer of a monomer component that contains an alkyl (meth)acrylate as a main monomer and may further contain the co-monomer as a secondary monomer. Here, the main monomer refers to a component that occupies more than 50% by weight of the monomer composition in the monomer raw material. Alternatively, more than 55% by weight or more than 60% by weight of the monomer composition may be an alkyl (meth)acrylate.

[0268] As the (meth)acrylate, for example, a compound represented by the following formula (1) can be preferably used.

[0269] CH2=C(R 1 )COOR 2 (1)

[0270] Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. 2 A chain alkyl group having 1 to 20 carbon atoms (hereinafter, this range of carbon atoms may be represented as "C 1-20 From the viewpoint of storage modulus of the adhesive, R 2 C 1-12 (For example, C 2-10 , typically C 4-8) chain alkyl (meth)acrylate. 2 C 1-20 The (meth)acrylic acid alkyl ester having a chain alkyl group may be used alone or in combination of two or more. Preferred examples of the (meth)acrylic acid alkyl ester include n-butyl acrylate and 2-ethylhexyl acrylate.

[0271] The above-mentioned copolymerizable monomers can help introduce crosslinking points into the acrylic polymer or improve the cohesion of the acrylic polymer. As the above-mentioned copolymerizable monomers, for example, one or more monomers containing functional groups such as carboxyl group-containing monomers, hydroxyl group-containing monomers, acid anhydride group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a nitrogen atom-containing ring, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers can be used. Other examples of copolymerizable monomers include vinyl ester monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, (meth)acrylates containing non-aromatic rings, and alkoxy group-containing monomers. As specific examples, the above-mentioned substances that can be used as monomers for the base polymer of the viscoelastic layer V1 can be listed, but are not limited to these. For example, from the perspective of improving cohesion, acrylic polymers copolymerized with carboxyl group-containing monomers and / or hydroxyl group-containing monomers as the above-mentioned copolymerizable monomers are preferred. Suitable examples of carboxyl group-containing monomers include acrylic acid and methacrylic acid. Preferred examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate.

[0272] In some embodiments, a fluorinated monomer may be used as the copolymerizable monomer to lower the refractive index n2 of the adhesive layer V2. The content of the fluorinated monomer in the monomer raw material may be, for example, 10% by weight or greater, 25% by weight or greater, or 35% by weight or greater. To facilitate achieving a viscoelastic layer V2 with a lower refractive index, the content of the fluorinated monomer is preferably 40% by weight or greater, more preferably 45% by weight or greater, even more preferably 55% by weight or greater, 60% by weight or greater, 75% by weight or greater, 85% by weight or greater, 90% by weight or greater, or 95% by weight or greater. The upper limit of the content of the fluorinated monomer in the monomer raw material is not particularly limited and may be 100% by weight. In some embodiments, from the perspective of the cohesion of the viscoelastic layer V2, a fluorinated monomer content of 99.9% by weight or less is appropriate, preferably 99.5% or less, 99% by weight or less, 97% by weight or less, or 92% by weight or less. Fluorinated monomers may be used alone or in combination of two or more.

[0273] As the fluorine-containing monomer, a fluorine-containing acrylic monomer can be suitably used. As the fluorine-containing acrylic monomer, there is no particular limitation as long as it is an acrylic monomer having at least one fluorine atom in the molecule. For example, fluorine-containing (meth)acrylate can be suitably used. As suitable examples of fluorine-containing (meth)acrylate, substances having a fluorinated hydrocarbon group at the ester end can be listed. As fluorinated hydrocarbon groups, for example, fluorinated aliphatic hydrocarbon groups, fluorinated alicyclic hydrocarbon groups, fluorinated aromatic hydrocarbon groups, etc. can be listed. As fluorinated hydrocarbon groups, fluorinated aliphatic hydrocarbon groups are suitable. As fluorinated aliphatic hydrocarbon groups, fluorinated alkyl groups can be listed. In the fluorinated aliphatic hydrocarbon group, the aliphatic hydrocarbon portion can be linear or branched. In addition, in the fluorinated aliphatic hydrocarbon group, the fluorine atom can be bonded to any carbon atom in the aliphatic hydrocarbon portion. The fluorine atom bonded to one carbon atom can be single or multiple. The number of carbon atoms bonded with fluorine atoms is not particularly limited.

[0274] In the fluoroaliphatic hydrocarbon group (including fluoroalkyl), the number of carbon atoms in the hydrocarbon portion is not particularly limited. In some embodiments, considering the compatibility with other copolymerizable monomers, a fluoroaliphatic hydrocarbon group having a carbon number of, for example, 1 to 18 (preferably 1 to 12) is preferred. Specific examples of the fluoroaliphatic hydrocarbon group include fluoromethyl groups such as trifluoromethyl, difluoromethyl, and monofluoromethyl; fluoroethyl groups such as pentafluoroethyl, 1,1,2,2-tetrafluoroethyl, 1,2,2,2-tetrafluoroethyl, 1,1,2-trifluoroethyl, 1,2,2-trifluoroethyl, 2,2,2-trifluoroethyl, 1,1-difluoroethyl, 1,2-difluoroethyl, 2,2-difluoroethyl, 1-monofluoroethyl, and 2-monofluoroethyl; and the like. Examples of the fluoroalkyl group having 3 or more carbon atoms include various fluoroalkyl groups in which a single or multiple fluorine atoms are bonded to any one or more carbon atoms in the alkyl portion, similar to the fluoromethyl group and fluoroethyl group exemplified above.

[0275] As fluorinated alicyclic hydrocarbon groups, fluorinated cycloalkyl groups and the like can be cited. Similar to the above-mentioned fluorinated aliphatic hydrocarbon groups, in the fluorinated alicyclic hydrocarbon group, the fluorine atom can be bonded to any carbon atom of the alicyclic hydrocarbon group, and the fluorine atoms bonded to one carbon atom can be single or multiple. Furthermore, there is no particular restriction on the number of carbon atoms bonded with fluorine atoms. Fluorinated alicyclic hydrocarbon groups include, for example: cyclohexyl groups having one fluorine atom, such as 2-fluorocyclohexyl, 3-fluorocyclohexyl, and 4-fluorocyclohexyl; cyclohexyl groups having two fluorine atoms, such as 2,4-difluorocyclohexyl and 2,6-difluorocyclohexyl; cyclohexyl groups having three fluorine atoms, such as 2,4,6-trifluorocyclohexyl, etc.

[0276] The fluoroalkyl group may or may not have a substituent. Such a substituent is not particularly limited, and examples thereof include hydrocarbon groups such as an alkyl group, an alkoxy group, a hydroxyl group, a carboxyl group, an amino group, a nitro group, a cyano group, and a halogen atom. The substituent may be used alone or in combination of two or more.

[0277] Examples of the fluorine-containing (meth)acrylates [fluoro(meth)acrylates] include fluorine-containing alkyl (meth)acrylates [fluoroalkyl (meth)acrylates], fluorine-containing cycloalkyl (meth)acrylates [fluorocycloalkyl (meth)acrylates], and fluorine-containing aryl (meth)acrylates [fluoroaryl (meth)acrylates].

[0278] As the fluorine-containing (meth)acrylate, fluoroalkyl (meth)acrylate (particularly fluoroalkyl acrylate) is suitable. Examples of the fluoroalkyl (meth)acrylate include 2,2,2-trifluoroethyl acrylate (trade name “Viscoat 3F” manufactured by Osaka Organic Chemical Industry Co., Ltd.), 2,2,3,3-tetrafluoropropyl acrylate (trade name “Viscoat 4F” manufactured by Osaka Organic Chemical Industry Co., Ltd.), 1H,1H,5H-octafluoropentyl acrylate (trade name “Viscoat 8F” manufactured by Osaka Organic Chemical Industry Co., Ltd.), 1H,1H,5H-octafluoropentyl methacrylate (trade name “Viscoat 8FM” manufactured by Osaka Organic Chemical Industry Co., Ltd.), 2-(heptadecafluorononyl)ethyl acrylate (trade name “FA-108” manufactured by Kyoeisha Chemical Co., Ltd.), and 1H,1H,2H,2H-tridecafluorooctyl acrylate (trade name “Viscoat 13F” manufactured by Osaka Organic Chemical Industry Co., Ltd.).

[0279] From the viewpoints of low refractive index effect, flexibility, etc., it is advantageous that the number of carbon atoms of the fluoroalkyl group in the fluoroalkyl (meth)acrylate is 3 or more, preferably 4 or more, more preferably 5 or more, further preferably 6 or more or 7 or more, and particularly preferably 8 or more. From the viewpoints of adhesive properties, it is advantageous that the number of carbon atoms of the above-mentioned fluoroalkyl group is 18 or less, preferably 14 or less, more preferably 12 or less, and can be 10 or less or 9 or less. In some embodiments, the number of carbon atoms of the above-mentioned fluoroalkyl group can be 7 or less or 5 or less. In addition, in some embodiments, as the fluorine-containing (meth)acrylate, a fluoroalkyl (meth)acrylate in which fluorine is not bonded to the carbon at the 1-position of the alkyl group is preferred. For example, a fluoroalkyl (meth)acrylate in which fluorine is not bonded to the carbon at the 1-position and the carbon at the 2-position of the alkyl group, such as 1H,1H,2H,2H-tridecafluorooctyl acrylate, can be preferably used.

[0280] In some embodiments of the interlayer sheet disclosed herein, the viscoelastic layer V2 is an acrylic adhesive layer. The acrylic polymer serving as the base polymer of the adhesive can be a polymer of a monomer raw material comprising at least the fluorinated acrylic monomer described above (e.g., a fluoroalkyl (meth)acrylate) and further comprising another monomer copolymerizable with the fluorinated acrylic monomer (a copolymerizable monomer). The monomer raw material may or may not contain an alkyl (meth)acrylate. The content of the fluorinated acrylic monomer in the monomer raw material can be, for example, 10% by weight or more, 25% by weight or more, or 35% by weight or more. To facilitate achieving a viscoelastic layer V2 with a lower refractive index, the content of the fluorinated acrylic monomer is preferably 40% by weight or more, more preferably 45% by weight or more, further preferably 55% by weight or more, 60% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The upper limit of the content of the fluorinated acrylic monomer in the monomer raw material is not particularly limited and can be 100% by weight. In some embodiments, from the perspective of the cohesion of the viscoelastic layer V2, the content of the fluorinated acrylic monomer is suitably 99.9% by weight or less, preferably 99.5% by weight or less, and may be 99% by weight or less, 97% by weight or less, or 92% by weight or less. The fluorinated acrylic monomer may be used alone or in combination of two or more.

[0281] The monomer raw materials used to prepare the base polymer of the viscoelastic layer V2 can include a copolymerizable monomer in addition to a fluorine-containing acrylic monomer (e.g., a fluoroalkyl (meth)acrylate). Examples of such copolymerizable monomers include one or more monomers containing functional groups, such as carboxyl group-containing monomers, hydroxyl group-containing monomers, acid anhydride group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers containing nitrogen-containing rings (e.g., N-vinyl cyclic amides such as N-vinyl-2-pyrrolidone), sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. Other examples of copolymerizable monomers include vinyl ester monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, cycloalkyl (meth)acrylates, non-aromatic ring-containing (meth)acrylates such as isobornyl (meth)acrylate, and alkoxy group-containing monomers. Specific examples include, but are not limited to, the above-mentioned monomers that can be used as the base polymer of the viscoelastic layer V1. For example, from the viewpoint of improving cohesive force, an acrylic polymer obtained by copolymerizing a carboxyl group-containing monomer and / or a hydroxyl group-containing monomer as the copolymerizable monomer is preferred.

[0282] In some preferred embodiments, the monomer raw material for preparing the base polymer of the viscoelastic layer V2 may be a composition containing a fluorine-containing monomer (e.g., a fluorine-containing acrylic monomer such as fluoroalkyl (meth)acrylate) and a hydroxyl-containing monomer. Hydroxyl-containing monomers can contribute to the improvement of cohesion, the introduction of crosslinking points, etc. Suitable examples of hydroxyl-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate. From the perspective of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate can be more preferably used. The content of the hydroxyl-containing monomer in the monomer raw material is not particularly limited, and for example, it can be 0.01% by weight or more (preferably 0.1% by weight or more, more preferably 0.5% by weight or more). In some embodiments, the content of the hydroxyl-containing monomer can be 0.7% by weight or more, 0.9% by weight or more, or 1.5% by weight or more of the monomer raw material. The upper limit of the content of the hydroxyl-containing monomer is not particularly limited, and for example, it can be 15% by weight or less or 10% by weight or less. In some embodiments, from the perspective of lowering the refractive index, the content of the hydroxyl group-containing monomer in the above-mentioned monomer raw material is appropriately less than 10 weight %, preferably less than 5 weight %, can be less than 3 weight %, can be less than 2.5 weight %, and can also be less than 1.5 weight %.

[0283] In some embodiments, from the perspective of suppressing coloration or discoloration (e.g., yellowing) of the viscoelastic layer V2, the monomer raw material used to prepare the base polymer of the viscoelastic layer V2 preferably limits the content of carboxyl-containing monomers. The content of carboxyl-containing monomers in the above-mentioned monomer raw material can be, for example, less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, and even more preferably less than 0.1% by weight (e.g., less than 0.05% by weight). From the perspective of suppressing corrosion of metal materials that may be arranged in contact with or close to the viscoelastic layer V2 (e.g., metal wiring, metal films, etc. that may be present on the adherend), limiting the content of carboxyl-containing monomers in this way is also advantageous. The interlayer sheet disclosed herein can preferably be implemented in a manner in which the above-mentioned monomer raw material does not contain carboxyl-containing monomers.

[0284] For similar reasons, in some embodiments, the monomer raw materials used to prepare the base polymer of the viscoelastic layer V2 preferably limit the content of monomers containing acidic functional groups (including sulfonic acid groups, phosphoric acid groups, etc. in addition to carboxyl groups). The preferred content of acidic functional group-containing monomers in the monomer components of this embodiment can be applied to the aforementioned preferred content of carboxyl group-containing monomers. The interlayer sheet disclosed herein can preferably be implemented in an embodiment in which the monomer raw materials do not contain acidic group-containing monomers (i.e., the base polymer of the viscoelastic layer V2 is acid-free).

[0285] The base polymer of the adhesive layer V2 can be prepared by a known polymerization method as the base polymer of the adhesive layer V1. The weight average molecular weight (Mw) of the base polymer is not particularly limited, and can be, for example, about 10×10 4 ~500×10 4 The range can also be about 20×10 4 ~200×10 4 In some embodiments, from the viewpoint of adhesion to the adhesive layer V1, the Mw of the base polymer of the adhesive layer V2 is 150×10 4 The following are suitable, preferably 120×10 4 Below (for example 95×10 4 Below), can be 75×10 4 Below, it can be 68×10 4 Below, it can also be 60×10 4 In some embodiments, from the viewpoint of the cohesiveness of the adhesive layer V2, the Mw of the base polymer may be, for example, 30×10 4 Above, it can be 40×10 4 Above, it can also be 50×10 4 To adjust Mw, a conventionally known chain transfer agent can be used as needed.

[0286] Although not particularly limited, from the perspective of adhesiveness, the Tg of the base polymer (e.g., acrylic polymer) of the adhesive layer V2 is advantageously about 0°C or lower, preferably about -5°C or lower (e.g., about -15°C or lower, or -25°C or lower). Furthermore, from the perspective of the cohesive force of the adhesive layer, the Tg of the base polymer of the adhesive layer V2 is about -75°C or higher, preferably about -70°C or higher (e.g., -50°C or higher, or even -30°C or higher). The Tg of the base polymer can be adjusted by appropriately varying the monomer composition (i.e., the types and amounts of the monomers used in the synthesis of the polymer).

[0287] In the adhesive layer V2, a known crosslinking agent can be used as needed. In addition, the adhesive layer V2 can contain other additives such as a tackifier as needed. The crosslinking agent and the tackifier can be appropriately selected from the same substances as those that can be used for the adhesive layer V1 and used in an appropriate amount.

[0288] In embodiments where the adhesive composition used to form adhesive layer V2 includes a crosslinking agent, an isocyanate crosslinking agent can be preferably used as the crosslinking agent. In some embodiments, from the perspective of adhesion to adhesive layer V1, the amount of the isocyanate crosslinking agent used relative to 100 parts by weight of the base polymer of the adhesive composition can be, for example, less than 0.5 parts by weight, less than 0.3 parts by weight, less than 0.2 parts by weight, or less than 0.15 parts by weight. In addition, from the perspective of appropriately utilizing the effect of the crosslinking agent, in some embodiments, the amount of the isocyanate crosslinking agent used relative to 100 parts by weight of the base polymer can be, for example, 0.005 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.08 parts by weight or more.

[0289] <Preparation of Adhesive Layer>

[0290] In the interlayer sheet disclosed herein, the viscoelastic materials constituting each of the viscoelastic layers V1 and V2 can be adhesives obtained by curing adhesive compositions in the form of solvent-based, active energy ray-curable, water-dispersible, hot-melt, etc. by drying, cross-linking, polymerization, cooling, etc., i.e., cured products of the above-mentioned adhesive compositions. The curing means (e.g., drying, cross-linking, polymerization, cooling, etc.) of the adhesive composition can be applied only to one type, or two or more types can be applied simultaneously or in multiple stages. For solvent-based adhesive compositions, the composition can typically be dried (preferably further cross-linked) to form an adhesive. For active energy ray-curable adhesive compositions, the adhesive is typically formed by performing a polymerization reaction and / or a cross-linking reaction by irradiating active energy rays. In the case where the active energy ray-curable adhesive composition needs to be dried, it is advisable to irradiate active energy rays after drying.

[0291] The viscoelastic layers V1 and V2 of the interlayer sheet disclosed herein can be formed by applying (e.g., coating) an adhesive composition to a suitable surface and then curing the composition. Application of the adhesive composition can be carried out using conventional coating machines such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, and spray coaters.

[0292] In the interlayer sheet disclosed herein, any one or both of the viscoelastic layers V1 and V2 may be an adhesive layer having post-curing properties, or an adhesive layer not having post-curing properties. Here, an adhesive layer having post-curing properties refers to an adhesive layer that can be further cured by irradiation with heat or active energy rays (such as ultraviolet rays). As examples of adhesive layers having post-curing properties, adhesive layers having unreacted ethylenically unsaturated groups in the side chains of the base polymer and adhesive layers containing unreacted multifunctional monomers can be cited. In some embodiments, the adhesive layer preferably does not have post-curing properties. An adhesive layer that does not have post-curing properties does not produce dimensional changes associated with post-curing reactions (i.e., good dimensional stability), and therefore easily suppresses warping of the adhesive sheet or the adherend to which the adhesive sheet is attached. When dimensional changes (such as curing shrinkage) caused by post-curing are not produced, it can also be advantageous from the perspective of suppressing optical distortion of the adhesive layer.

[0293] The thickness of the viscoelastic layer V1 is not particularly limited, but can be, for example, 3 μm or greater, preferably 5 μm or greater. A viscoelastic layer V1 with a thickness of 5 μm or greater facilitates excellent adhesive properties. Furthermore, a viscoelastic layer V1 of this thickness easily absorbs any surface irregularities that may exist on the adherend, allowing for good adhesion to the adherend. To prevent coloration and unevenness caused by light interference, a viscoelastic layer V1 thickness of 5 μm or greater is also preferred. In some embodiments, the viscoelastic layer V1 may have a thickness of 10 μm or greater, 20 μm or greater, 30 μm or greater, 50 μm or greater, 70 μm or greater, or 85 μm or greater. Furthermore, in some embodiments, the viscoelastic layer V1 may have a thickness of, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less. A viscoelastic layer V1 that is not excessively thick can be advantageous for reducing the thickness of the interlayer sheet. The technology disclosed herein can be preferably implemented, for example, with the thickness of the viscoelastic layer V1 being in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm). In the case of an interlayer sheet comprising a viscoelastic layer V1 and a viscoelastic layer V2, the thickness of the viscoelastic layer V2 can be selected from the same range as the thickness of the viscoelastic layer V1 exemplified above. The thicknesses of the viscoelastic layer V1 and the viscoelastic layer V2 may be approximately the same or different. For an interlayer sheet in the form of a substrate-less double-sided PSA sheet formed of an adhesive layer, the thickness of the adhesive layer is the thickness of the interlayer sheet.

[0294] The adhesive layer formed by laminating the adhesive layer V1 and the adhesive layer V2 can be formed by, for example: forming the adhesive layers V1 and V2 on a releasable surface (such as the release surface of a release liner) and attaching their adhesive surfaces to each other; applying the adhesive composition for forming the adhesive layer V2 to the adhesive layer V1 and curing it; conversely applying the adhesive composition for forming the adhesive layer V1 to the adhesive layer V2 and curing it; etc., but are not limited to these. When the adhesive surfaces of the pre-formed adhesive layers V1 and V2 are attached to each other, a treatment to promote the close adhesion of the two adhesive layers can be performed as needed. For example, autoclave treatment, roller pressing treatment, etc. can be performed, but are not limited to these.

[0295] <Supporting Base Material>

[0296] Some interlayer sheets (adhesive sheets) can be in the form of adhesive sheets with a substrate, wherein the adhesive layer is provided on one or both sides of the supporting substrate. The material of the supporting substrate is not particularly limited and can be appropriately selected according to the intended use and usage of the adhesive sheet. Non-limiting examples of usable substrates include polyolefin films primarily composed of polyolefins such as polypropylene (PP) and ethylene-propylene copolymers; polyester films primarily composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); and polyvinyl chloride films primarily composed of polyvinyl chloride; foam sheets formed from foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; woven and nonwoven fabrics made from various fibrous materials (including natural fibers such as linen and cotton, synthetic fibers such as polyester and vinylon, and semi-synthetic fibers such as acetate) either alone or in blends; paper such as Japanese paper, high-quality paper, kraft paper, and crepe paper; and metal foils such as aluminum foil and copper foil. Composite substrates of these materials are also possible. Examples of such composite substrates include laminated metal foils and the aforementioned plastic films, and plastic substrates reinforced with inorganic fibers such as glass cloth.

[0297] In some embodiments, various film substrates can be preferably used. The above-mentioned film substrate can be a porous substrate such as a foam film, a non-woven fabric sheet, etc., or a non-porous substrate, or a substrate having a structure in which a porous layer and a non-porous layer are stacked. In some embodiments, as the above-mentioned film substrate, a substrate comprising a resin film that can independently maintain a shape (self-supporting or non-dependent) as a base film can be preferably used. Here, "resin film" refers to a non-porous structure, typically a resin film that is substantially free of bubbles (non-porous). Therefore, the above-mentioned resin film is a concept different from foam film and non-woven fabric. As the above-mentioned resin film, a film that can independently maintain a shape (self-supporting or non-dependent) can be preferably used. The above-mentioned resin film can be a single-layer structure, or a multilayer structure (for example, a 3-layer structure) of more than two layers.

[0298] Examples of the material constituting the resin film include polyester resins mainly composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefin resins mainly composed of polyolefins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymers, and ethylene-butene copolymers; cellulose resins such as triacetyl cellulose; acetate resins; polysulfone resins; polyethersulfone resins; polycarbonate resins; polyamide (PA) resins such as nylon 6, nylon 66, and partially aromatic polyamides; and polyimide ( Cyclic polyolefin resins such as polyimide (PI)-based resins, transparent polyimide resins, polyamideimide (PAI), polyetheretherketone (PEEK), polyethersulfone (PES), norbornene-based resins, (meth)acrylic resins, polyvinyl chloride-based resins, polyvinylidene chloride-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, ethylene-vinyl acetate copolymer resins, ethylene-vinyl alcohol copolymer resins, polyarylate-based resins, polyphenylene sulfide (PPS)-based resins, polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), polytetrafluoroethylene (PTFE), fluorinated polyimide and other fluorine-based resins, etc.

[0299] The above-mentioned resin film can be the film formed by the resin material that uses the independent resin that comprises 1 such resin, and can also be the film formed by the resin material that uses 2 or more blends.The above-mentioned resin film can be unstretched, and can also be stretched (such as uniaxial stretching or biaxial stretching).For example, PET film, PBT film, PEN film, unstretched polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, PP / PE blend film etc. can be preferably used.From the viewpoint of intensity, dimensional stability, as the example of preferred resin film, PET film, PEN film, PPS film and PEEK film can be enumerated.From the viewpoints such as obtaining ease, PET film and PPS film are particularly preferably used, wherein preferred PET film.

[0300] The resin film may be blended with known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, lubricants, and antiblocking agents as needed, within a range that does not significantly impair the effects of the present invention. The amount of the additives blended is not particularly limited and may be appropriately determined depending on the intended use of the adhesive sheet.

[0301] The method for producing the resin film is not particularly limited, and for example, conventionally known general resin film forming methods such as extrusion molding, inflation molding, T-die casting, and calendar roll molding can be appropriately employed.

[0302] The substrate may be substantially composed of such a base film. Alternatively, the substrate may further include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include an optical property adjustment layer (e.g., a coloring layer, an antireflection layer), a printed layer for imparting a desired appearance to the substrate, a laminating layer, an antistatic layer, a primer layer, a release layer, and other surface treatment layers.

[0303] In some embodiments, as a supporting substrate, a substrate having light transmittance (hereinafter also referred to as a light transmittance substrate) can be preferably used. Thus, a light-transmitting adhesive sheet with a substrate can be formed. The total light transmittance of the light-transmitting substrate can be, for example, higher than 50%, or can be 70% or more. In some preferred embodiments, the total light transmittance of the supporting substrate is 80% or more, more preferably 90% or more, or can be 95% or more (for example, 95-100%). The above-mentioned total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K7136:2000. As a transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Technology Research Institute or its equivalent is used. As a suitable example of the above-mentioned light-transmitting substrate, a light-transmitting resin film can be listed. The above-mentioned light-transmitting substrate can be an optical film.

[0304] The thickness of the substrate is not particularly limited and can be selected based on the intended use and method of use of the interlayer sheet. The thickness of the substrate can be, for example, 500 μm or less. From the perspective of the handleability and processability of the interlayer sheet, it is preferably 300 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, or 10 μm or less. As the thickness of the substrate decreases, there is a tendency for the substrate to better conform to the surface shape of the adherend. In addition, from the perspective of handleability and processability, the thickness of the substrate can be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

[0305] For the surface of one side of the laminated adhesive layer (viscoelastic layer) in the substrate, corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, the formation of the primer based on the coating of the primer (primer) and other previously known surface treatments can be implemented as needed. Such surface treatment can be a treatment for improving the anchoring property of the adhesive layer to the substrate. The composition of the primer used in the formation of the primer is not particularly limited and can be appropriately selected from the known compositions. The thickness of the primer is not particularly limited and is generally about 0.01 μm to 1 μm, preferably about 0.1 μm to 1 μm. As other treatments that can be implemented on the substrate as needed, antistatic layer formation treatment, coloring layer formation treatment, printing treatment, etc. can be listed. These treatments can be applied alone or in combination.

[0306] When the interlayer sheet disclosed herein is in the form of a pressure-sensitive adhesive sheet with a substrate, the thickness of the interlayer sheet can be, for example, 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, 75 μm or less, or 50 μm or less. Furthermore, from the perspective of handling, the thickness of the interlayer sheet can be, for example, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more.

[0307] It should be noted that the thickness of the interlayer sheet refers to the thickness of the portion that is attached to the adherend. Figure 1 The interlayer sheet 1 of the structure shown refers to the thickness from the first surface (adhesive surface) 10A of the pressure-sensitive adhesive layer to the second surface 20B of the supporting substrate, and does not include the thickness of the release liner 30 .

[0308] <Interlayer Sheet with Release Liner>

[0309] The interlayer sheet (PSA sheet) disclosed herein can be in the form of a PSA product in which the surface (adhesive surface) of the PSA layer is brought into contact with the release surface of a release liner. Therefore, according to this specification, a release-liner-attached interlayer sheet (PSA product) is provided, comprising: any interlayer sheet disclosed herein; and a release liner having a release surface that contacts the adhesive surface of the interlayer sheet.

[0310] There are no particular limitations on the release liner, and for example, a release liner having a release treatment layer on a release liner substrate such as a resin film, paper (which may be paper laminated with a resin such as polyethylene), or a release liner comprising a resin film formed from a low-adhesion material such as a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin-based resin (polyethylene, polypropylene, etc.) can be used. The release treatment layer can be a layer formed by surface-treating the release liner substrate with a release treatment agent. The release treatment agent can be a well-known release treatment agent such as a silicone-based release treatment agent, a long-chain alkyl-based release treatment agent, a fluorine-based release treatment agent, or molybdenum (IV) sulfide. In some embodiments, a release liner having a release treatment layer based on a silicone-based release treatment agent can be preferably used. The thickness and formation method of the release treatment layer are not particularly limited and can be set in a manner that exhibits appropriate releasability on the adhesive side surface of the release liner.

[0311] In some embodiments, from the perspective of smoothness of the adhesive surface, a release liner (hereinafter referred to as a release film) having a release treatment layer on a resin film (hereinafter referred to as a release film substrate) as a release liner substrate can be preferably used. Various plastic films can be used as the release film substrate. In this specification, the plastic film is typically a non-porous sheet, which is a concept that distinguishes it from, for example, non-woven fabrics (i.e., non-woven fabrics are not included).

[0312] As the material of the above-mentioned plastic film, for example, polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), polyolefin resins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymers, and ethylene-butene copolymers, cellulose resins such as triacetyl cellulose, acetate resins, polysulfone resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, cyclic polyolefin resins such as norbornene resins, (meth) acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, ethylene-vinyl acetate copolymer resins, ethylene-vinyl alcohol copolymer resins, polyarylate resins, and polyphenylene sulfide resins can be cited. A release film substrate formed of any one of these resins or a mixture of two or more thereof can be used. Among them, a polyester resin film (such as a PET film) formed of a polyester resin can be cited as a preferred release film substrate.

[0313] The plastic film used as the release film substrate may be an unstretched film, a uniaxially stretched film, or a biaxially stretched film. Furthermore, the plastic film may be a single-layer structure or a multilayer structure comprising two or more sublayers. The plastic film may contain known additives that can be used in release film substrates of adhesive sheets, such as antioxidants, ageing agents, heat stabilizers, light stabilizers, ultraviolet absorbers, pigments, dyes, and other colorants, lubricants, fillers, antistatic agents, and nucleating agents. In a multilayer plastic film, each additive may be incorporated into all sublayers or only into a portion of the sublayers.

[0314] In some preferred embodiments, as the above-mentioned release film substrate (typically a plastic film), a substrate in which the content of particles such as inorganic particles (for example, pigments, lubricants, fillers, etc.) in the layer on the release surface side is limited, or substantially does not contain such particles can be preferably used. Here, substantially not containing means that the amount of particles (for example, inorganic particles) in the layer is less than 1% by weight, preferably less than 0.1% by weight (for example, 0 to 0.01% by weight). A release film having such a release film substrate tends to have a low arithmetic mean roughness Ra and a low maximum height Rz of the release surface. When the above-mentioned release film substrate (typically a plastic film) includes a multilayer structure, the particle content in the layer on the release surface side can be less than 1 / 10 (for example, less than 1 / 50) of the particle content in the layer other than the release surface side layer.

[0315] For an interlayer sheet with a release liner having a release liner on each of the first and second adhesive surfaces, the release liner arranged on one adhesive surface (hereinafter referred to as one release liner) and the release liner arranged on the other adhesive surface (hereinafter referred to as the other release liner) may have the same material and structure, or may have different materials and structures.

[0316] The thickness of the release liner (preferably a release film) is not particularly limited, and can be, for example, about 10 μm to 500 μm. From the viewpoint of the strength and dimensional stability of the release liner, it is appropriate that the thickness of the release liner is 20 μm or more, preferably 30 μm or more, 35 μm or more, 40 μm or more, or 45 μm or more. In addition, from the viewpoint of the handleability of the release liner (for example, ease of winding), it is appropriate that the thickness of the release liner is 300 μm or less, preferably 250 μm or less, 200 μm or less, 150 μm or less, or 130 μm or less. In some preferred embodiments, the thickness of the release liner is about 125 μm or less, about 115 μm or less, about 105 μm or less, about 90 μm or less, or about 70 μm or less. By setting the thickness of the release liner to a predetermined value or less, winding marks are less likely to form when rolled, and removal from the adhesive sheet becomes smoother, making it easier to obtain a high surface smoothness on the adhesive surface after the release liner is removed.

[0317] In a release-lined interlayer sheet comprising one release liner and another release liner, the thicknesses of these release liners may be the same or different. In some embodiments, from the perspective of peeling workability, it is preferred that one release liner and the other release liner have different thicknesses. For example, the thickness of the thicker release liner is preferably at least about 1.1 times the thickness of the thinner release liner (e.g., at least about 1.25 times; the upper limit is not particularly limited, but is, for example, 5 times or less).

[0318] (Arithmetic mean roughness Ra of the bonding surface)

[0319] In some ways, from the viewpoint of realizing the adhesive face with high surface smoothness, the arithmetic mean roughness Ra of the preferred adhesive face side surface of release liner (preferably release film) is limited to below the specified value (for example, below about 100nm, and then lower than 50nm). In some ways, the arithmetic mean roughness Ra of the adhesive face side surface of release liner is for example preferably below about 30nm, more preferably below about 25nm, can be below about 20nm, also can be below about 18nm. In addition, from the viewpoints such as ease of manufacture, handleability of release liner, in some ways, above-mentioned arithmetic mean roughness Ra can for example be more than about 5nm, can be more than about 10nm, also can be more than about 15nm. For the interlayer sheet with release liner of the form of being respectively configured with release liner on the 1st adhesive face and the 2nd adhesive face, the adhesive face side surface of preferred two release liners all satisfies above-mentioned arbitrary arithmetic mean roughness Ra. The arithmetic mean roughness Ra of the adhesive face side surface of two release liners can be the same degree, also can be different.

[0320] (Maximum height Rz of the bonding surface)

[0321] In some ways, from the viewpoint of realizing the adhesive face with high surface smoothness, the maximum height Rz of the preferred adhesive face side surface of release liner (preferably peeling film) is below 700nm. In some ways, the maximum height Rz of the adhesive face side surface of release liner is preferably below about 600nm, can be below about 500nm, can be below about 400nm, also can be below about 300nm. In addition, from the viewpoints such as manufacturing ease, handleability of release liner, in some ways, above-mentioned maximum height Rz for example can be more than about 50nm, can be more than about 80nm, can be more than about 100nm, can be more than about 200nm, also can be more than about 300nm. For the interlayer sheet of the band release liner of the form that is respectively configured with release liner on the 1st adhesive face and the 2nd adhesive face, the adhesive face side surface of preferred two release liners all satisfies above-mentioned arbitrary maximum height Rz. The maximum height Rz of the adhesive face side surface of two release liners can be the same degree, also can be different.

[0322] (Surface texture of the back side)

[0323] The arithmetic mean roughness Ra and the maximum height Rz of the back side (opposite side of the adhesive layer) of the release liner (preferably a release film) are not particularly limited. From the perspective of productivity, the arithmetic mean roughness Ra of the back side of the release liner can be, for example, higher than 30 nm (e.g., higher than 35 nm, or even higher than about 50 nm). From the perspective of productivity, the maximum height Rz of the back side of the release liner can be, for example, higher than 400 nm (e.g., higher than about 500 nm), or higher than 800 nm (e.g., higher than 1000 nm).

[0324] The arithmetic mean roughness Ra and maximum height Rz of the release film surface can be adjusted by selecting the film material, forming method, and surface treatment such as release treatment. Examples of these include adjusting the smoothness of the layers constituting the release surface (such as the anti-blocking layer, hard coat layer, and oligomer barrier layer); reducing or eliminating filler particles in the surface layer or release film substrate (e.g., eliminating particles); and adjusting other stretching conditions.

[0325] The arithmetic mean roughness Ra and maximum height Rz of the release liner (preferably a release film) surface are measured using a non-contact surface roughness measuring device. A non-contact surface roughness measuring device employing an optical interference method can be used, such as a three-dimensional optical profilometer (trade name "NewView7300", manufactured by ZYGO) or its equivalent. For example, a glass plate (soda-lime glass plate, 1.3 mm thick, manufactured by MATSUNAMI) can be attached to the surface opposite to the measurement surface of the release liner using an adhesive and fixed, and the surface profile can be measured using a three-dimensional optical profilometer (trade name "NewView7300", manufactured by ZYGO) in an environment of 23°C and 50% RH.

[0326] <Purpose>

[0327] The interlayer sheet disclosed herein can be used by being attached to various adherends. The constituent materials of the above-mentioned adherends (adherend materials) are not particularly limited, and examples thereof include: metal materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, indium, zinc, etc., or alloys containing two or more of them, such as polyimide resins, acrylic resins, polyether nitrile resins, polyether sulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyether ether ketone resins, polyamide resins (so-called aramid resins, etc.), polyarylate resins, fluorine-based resins. Various resin materials (typically plastic materials) such as resins, polycarbonate resins, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, vinyl butyral polymers, liquid crystal polymers, and carbon materials such as graphene; metal oxides such as aluminum oxide, zirconium oxide, titanium oxide, SiO2, ITO (indium tin oxide), and ATO (antimony-doped tin oxide), and mixtures thereof; nitrides such as aluminum nitride, silicon nitride, titanium nitride, gallium nitride, and indium nitride, and composites thereof; and inorganic materials such as alkaline glass, alkali-free glass, quartz glass, borosilicate glass, and sapphire glass. The interlayer sheet disclosed herein can be bonded to a member (e.g., an optical member) at least the surface of which is composed of the above materials.

[0328] The interlayer sheet disclosed herein can be used in a pasting manner without the need for heating to a temperature higher than room temperature (e.g., 20°C to 35°C) after being attached to an adherend. In addition, depending on the constituent material of the interlayer sheet (e.g., the material of the substrate) and the type of adherend, if permitted, a heat treatment may be performed at least at any time after attachment to the adherend, at the time of attachment, and before attachment. The heat treatment may be performed for the purpose of improving the adhesion of the adhesive to the adherend, promoting adhesion, etc. Regarding the heat treatment temperature, depending on the constituent material of the interlayer sheet, the type of adherend, and within the permitted range, it may be appropriately set to obtain the desired effect in consideration of the surface state of the adherend, for example, it may be around 100°C or below, it may be below 80°C, it may be below 60°C, or it may be below 50°C.

[0329] The components or materials to which the interlayer sheet is attached or stacked (for the interlayer sheet in the form of a double-sided adhesive sheet, at least one of the adherends) may be light-transmitting. In such adherends, the advantage of the interlayer sheet disclosed herein being highly transparent can be easily obtained. The total light transmittance of the adherend may be, for example, higher than 50%, or may be higher than 70%. In some preferred embodiments, the total light transmittance of the adherend is higher than 80%. It is more preferably higher than 90%, and further preferably higher than 95% (for example, 95 to 100%). The interlayer sheet disclosed herein can be preferably used in a manner of being attached or stacked on an adherend (for example, an optical component) having a total light transmittance higher than a specified value. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K7136:2000. As a transmittance meter, "HAZEMETER HM-150" manufactured by Murakami Color Technology Research Institute or its equivalent is used.

[0330] The refractive index of the adherend and the refractive index of the viscoelastic layer (e.g., viscoelastic layer V1, or in a form having a viscoelastic layer V2, viscoelastic layer V2) disposed in contact with the adherend may be of the same degree or different. For example, by increasing the refractive index of the viscoelastic layer (typically the adhesive layer) relative to the refractive index of the adherend, light incident on the adhesive layer from the adherend side at an angle below the critical angle can be refracted toward the front side, thereby increasing the front brightness. In this case, the refractive index of the adherend can be, for example, less than 1.55, less than 1.50, less than 1.48, less than 1.45, or less than 1.45. Alternatively, it can be, for example, greater than 1.10, greater than 1.20, greater than 1.30, or greater than 1.35. Furthermore, by using an adherend with a relatively high refractive index compared to the adhesive layer, light incident on the adherend from the adhesive layer side can be refracted toward the front side, thereby increasing the front brightness. At this time, the refractive index of the adherend can be, for example, 1.60 or more, 1.65 or more, or 1.70 or more. In addition, for example, it can be 3.00 or less, or 2.50 or less, or 2.00 or less. On the other hand, by reducing the refractive index difference between the adhesive layer and the adherend, light reflection at the interface can be suppressed. At this time, the refractive index of the adherend can be about 1.55 to 1.80, about 1.55 to 1.75, or about 1.60 to 1.70. The refractive index of the adherend can be measured by the same method as the refractive index of the adhesive.

[0331] In some preferred embodiments, the adherend may have any of the aforementioned refractive indices and any of the aforementioned total light transmittances. When the adherend is attached or laminated to such an adherend, the effects of the technology disclosed herein can be particularly preferably exerted.

[0332] As an example of a preferred application, optical applications can be cited. More specifically, for example, as an optical adhesive sheet for use in bonding optical components (optical component bonding) or in manufacturing products using such optical components (optical products), the interlayer sheet disclosed herein can be preferably used.

[0333] The above-mentioned optical component refers to a component having optical properties (such as polarization, light refraction, light scattering, light reflectivity, light transmittance, light absorption, light diffraction, optical rotation, visual recognition, etc.). As the above-mentioned optical component, as long as it is a component with optical properties, there is no particular limitation, for example, components constituting devices (optical devices) such as display devices (image display devices) and input devices or components used in these devices can be listed, for example, polarizing plates, wavelength plates, phase difference plates, optical compensation films, brightness improvement films, light guide plates, reflective films, anti-reflection films, hard coating (HC) films, impact absorbing films, antifouling films, photochromic films, dimming films, transparent conductive films (ITO films), appearance films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, further laminated with these components (sometimes collectively referred to as "functional films".) etc. It should be noted that the above-mentioned "plate" and "film" each include forms such as plate, film, and sheet. For example, "polarizing film" includes "polarizing plate," "polarizer," and the like, and "light guide plate" includes "light guide film," "light guide sheet," and the like. Furthermore, the above-mentioned "polarizing plate" includes a circularly polarizing plate.

[0334] Examples of the display device include liquid crystal display devices, organic EL (electroluminescence) display devices, micro LEDs (μLEDs), mini LEDs (miniLEDs), PDPs (plasma display panels), and electronic paper. Examples of the input device include touch panels.

[0335] The optical components are not particularly limited, and examples thereof include components formed from glass, acrylic resins, polycarbonate, polyethylene terephthalate, metal films, etc. (e.g., sheet-shaped, film-shaped, or plate-shaped components). It should be noted that the term "optical component" as used in this specification also includes components that maintain the visual recognition of display devices and input devices and perform decorative and protective functions (e.g., appearance films, decorative films, surface protection films, etc.).

[0336] The interlayer sheet disclosed herein can be used, for example, between an optical film such as a film having one or more functions of light transmission, reflection, diffusion, waveguiding, light collection, or diffraction, or a fluorescent film, and another optical component (which may be another optical film). It is preferably used to join these optical films to these other optical components. In joining optical films having at least one of the functions of light waveguiding, light collection, or diffraction, it is ideal for the entire bonding layer to have a high refractive index, making it a preferred application of the technology disclosed herein. For example, a viscoelastic layer (adhesive layer) V1 can be preferably used as the bonding layer.

[0337] The viscoelastic layer of the interlayer sheet disclosed herein (preferably an adhesive layer. For example, an adhesive layer of a single-layer structure formed by a viscoelastic layer V1, or an adhesive layer of a laminated structure formed by directly contacting and laminating two or more adhesive layers including a viscoelastic layer V1 and a viscoelastic layer V2) can be preferably used for, for example, joining optical films such as light-guiding films, diffusion films, fluorescent films, color-adjusting films, prism films, lens-shaped films, and microlens array films. In these applications, from the perspective of the trend of miniaturization and high performance of optical components, thinning and improvement of light extraction efficiency are required. As a viscoelastic layer (such as an adhesive layer) that can meet this demand, the viscoelastic layer of the interlayer sheet disclosed herein can be preferably utilized. In more detail, for example, in the joining of light-guiding films and diffusion films, by adjusting the refractive index of the adhesive layer as a bonding layer (for example, increasing the refractive index), thinning can be contributed. In the joining of fluorescent films, by appropriately adjusting the refractive index difference between the fluorescent light-emitting body and the adhesive, the light extraction efficiency (which can also be grasped as the luminous efficiency) can be improved. When bonding toning films, appropriately adjusting the adhesive's refractive index to minimize the difference in refractive index with the toning pigment can reduce scattering components and contribute to improved light transmittance. When bonding prisms, lenticular films, microlens array films, etc., appropriately adjusting the adhesive's refractive index can control light diffraction and contribute to improved brightness and / or viewing angle.

[0338] The interlayer sheet disclosed herein is preferably used in a manner of being pasted to an adherend with a high refractive index (which may be a layer, component, etc. with a high refractive index), and can suppress interface reflection with the above-mentioned adherend. As described above, the interlayer sheet used in this manner preferably has a small refractive index difference between the adherend with a high refractive index and the adhesive layer (typically a viscoelastic layer V1) pasted thereto, and has high adhesion to the interface with the adherend. In addition, from the viewpoint of improving the homogeneity of the appearance, the thickness uniformity of the adhesive layer is preferably high, for example, the surface smoothness of the adhesive surface is preferably high. In the case where the thickness of the adherend with a high refractive index is small (for example, less than 5 μm, less than 4 μm, or less than 2 μm), it is particularly meaningful to suppress reflection at the interface from the viewpoint of suppressing coloring and color unevenness caused by interference of reflected light. As an example of such usage, there can be listed: in a polarizing plate with a phase difference layer which sequentially comprises a polarizer, a first phase difference layer and a second phase difference layer, a method for joining the polarizer to the first phase difference layer and / or joining the first phase difference layer to the second phase difference layer.

[0339] In addition, the interlayer sheet disclosed herein has a viscoelastic layer V1 with a high refractive index, and therefore can be preferably used in a manner of being adhered to a light-emitting layer (for example, a high-refractive light-emitting layer mainly composed of inorganic materials) of an optical semiconductor or the like. By reducing the refractive index difference between the light-emitting layer and the viscoelastic layer V1, it is possible to suppress reflection at their interface and improve light extraction efficiency. The interlayer sheet used in this manner preferably has an adhesive layer with a high refractive index as the viscoelastic layer V1. In addition, from the viewpoint of preventing the degradation of the self-luminous element due to moisture in advance, the water absorption rate of the viscoelastic layer V1 is preferably low. From the viewpoint of improving brightness, the interlayer sheet is preferably low in coloration. This can also be advantageous from the viewpoint of suppressing unintentional coloration caused by the interlayer sheet.

[0340] The viscoelastic layer V1 of the interlayer sheet disclosed herein can be preferably used as a coating layer covering the lens surface, a bonding layer to a component opposing the lens surface (e.g., a component having a surface shape corresponding to the lens surface), or a filling layer between the lens surface and the component, in microlenses and other lens components (e.g., microlenses constituting microlens array films, camera microlenses, etc.) used as components in cameras, light-emitting devices, etc. The viscoelastic layer V1 disclosed herein is suitable for increasing the refractive index, and thus, even when placed in contact with a high-refractive-index lens (e.g., a lens composed of a high-refractive-index resin, or a lens having a surface layer made of a high-refractive-index resin), it can reduce the refractive index difference with the lens. This is advantageous from the perspective of reducing the thickness of the lens and products incorporating the lens, and also contributes to suppressing aberrations and improving the Abbe number. In the technology disclosed herein, the viscoelastic material constituting the viscoelastic layer V1 can itself be used as the lens resin, for example, by filling a recess or void in a suitable transparent component.

[0341] There is no particular limitation on the method of bonding optical components using the interlayer sheet disclosed herein. For example, it can be (1) a method of bonding optical components to each other with the help of the interlayer sheet disclosed herein, (2) a method of bonding optical components to components other than optical components with the help of the interlayer sheet disclosed herein, or (3) a method in which the interlayer sheet disclosed herein is in a form containing optical components and the interlayer sheet is bonded to optical components or components other than optical components. It should be noted that in the above-mentioned method (3), the interlayer sheet in a form containing optical components can be, for example, an interlayer sheet whose support is an optical component (such as an optical film). This interlayer sheet in a form containing an optical component as a support can also be understood as an adhesive type optical component (such as an adhesive type optical film). In addition, when the interlayer sheet disclosed herein is an adhesive sheet of a type having a support, and the above-mentioned functional film is used as the above-mentioned support, the interlayer sheet disclosed herein can also be understood as an "adhesive type functional film" having an adhesive layer disclosed herein on at least one side of the functional film.

[0342] As described above, according to the technology disclosed herein, an optical laminate is provided, comprising the interlayer sheet disclosed herein and a component (e.g., a resin film such as an optical film) to which the interlayer sheet is adhered. The component to which the interlayer sheet is adhered may have the refractive index of the adherend material described above. In addition, the difference in refractive index between the layer (e.g., viscoelastic layer V1) constituting the adhesive surface of the interlayer sheet and the component (refractive index difference) may be the refractive index difference between the adherend and the adhesive layer described above. The components constituting the laminate are the same as those described above for the components, materials, and adherends, and therefore will not be repeated.

[0343] It will be understood from the above description and the following embodiments that the matters disclosed by this specification include the following contents.

[0344] [1] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer,

[0345] It has an adhesive surface consisting of the above adhesive layer,

[0346] The adhesive layer has a refractive index higher than 1.570, a total light transmittance higher than 86%, and a haze value lower than 3.0%.

[0347] [2] The adhesive sheet according to [1] above, wherein the adhesive layer has a thickness of 5 μm or more.

[0348] [3] The adhesive sheet according to [1] or [2] above, wherein the peel strength (adhesive force) to a glass plate is 3 N / 25 mm or more.

[0349] [4] The adhesive sheet according to any one of [1] to [3] above, wherein the adhesive surface has an arithmetic mean roughness Ra of 100 nm or less.

[0350] [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the pressure-sensitive adhesive layer has a water absorption rate of 1.0% or less.

[0351] [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, which is constituted as a laminate comprising the pressure-sensitive adhesive layer and a light-transmitting substrate.

[0352] [7] The adhesive sheet according to [6] above, wherein the light-transmitting substrate is a resin film.

[0353] [8] The PSA sheet according to any one of [1] to [5] above, which is a double-sided adhesive PSA sheet formed of the PSA layer.

[0354] [9] A pressure-sensitive adhesive sheet with a release liner, comprising:

[0355] The adhesive sheet according to any one of [1] to [8] above, and

[0356] A release liner is placed on the adhesive surface of the adhesive sheet.

[0357]

[10] An adhesive composition for forming an adhesive layer of the adhesive sheet according to any one of [1] to [8] above.

[0358]

[11] An adhesive composition comprising:

[0359] an acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit; and

[0360] Additives (H RO ), which is an organic material having a higher refractive index than the above-mentioned acrylic polymer (A).

[0361]

[12] The adhesive composition according to

[11] above, wherein the additive (H RO ) has a refractive index of 1.60 or more.

[0362]

[13] The adhesive composition according to

[11] or

[12] , wherein the additive (H RO ) is higher than 0 parts by weight and is 60 parts by weight or less.

[0363]

[14] The adhesive composition according to any one of

[11] to

[13] above, wherein the additive (H RO ) contains at least one compound selected from the group consisting of aromatic ring-containing compounds and heterocyclic ring-containing compounds.

[0364]

[15] The adhesive composition according to any one of

[11] to

[14] above, wherein the additive (H RO ) includes compounds having two or more aromatic rings in one molecule.

[0365]

[16] The adhesive composition according to

[15] above, wherein the additive (H RO ) contains a compound satisfying at least one of the following as the compound having two or more aromatic rings in one molecule:

[0366] (i) a structure comprising two non-fused aromatic rings directly chemically bonded together; and

[0367] (ii) A structure comprising two fused aromatic rings.

[0368]

[17] The adhesive composition according to any one of

[11] to

[16] above, wherein the content of the aromatic ring-containing monomer (m1) in the monomer components constituting the acrylic polymer (A) is 50% by weight or more.

[0369]

[18] The adhesive composition according to any one of

[11] to

[17] above, wherein the content of the aromatic ring-containing monomer (m1) in the monomer components constituting the acrylic polymer (A) is higher than 70% by weight and lower than 100% by weight,

[0370] 50% by weight or more of the aromatic ring-containing monomer (m1) is a monomer having a homopolymer glass transition temperature of 10°C or lower.

[0371]

[19] The adhesive composition according to any one of

[11] to

[18] above, wherein the monomer components constituting the acrylic polymer (A) further contain a monomer (m2) having at least one of a hydroxyl group and a carboxyl group.

[0372]

[20] The adhesive composition according to any one of

[11] to

[18] above, which is used to form the adhesive layer of the adhesive sheet according to any one of [1] to [8] above.

[0373]

[21] An adhesive comprising the adhesive composition according to any one of

[11] to

[20] above, wherein the adhesive has a refractive index higher than 1.570.

[0374]

[22] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer comprising a pressure-sensitive adhesive, wherein the pressure-sensitive adhesive is formed from the pressure-sensitive adhesive composition according to any one of

[11] to

[20] above.

[0375]

[23] The pressure-sensitive adhesive sheet according to

[22] above, wherein the pressure-sensitive adhesive layer has a haze value of 1.0% or less.

[0376]

[24] An interlayer sheet used for optical applications and arranged between layers of a laminate.

[0377] It comprises a viscoelastic layer V1 having a refractive index n1 of 1.570 or more, and

[0378] The interlayer sheet satisfies: a total light transmittance of more than 86%;

[0379] A haze value of 1.0% or less; and

[0380] The storage modulus G' at 25°C is 30 kPa to 700 kPa.

[0381]

[25] The interlayer sheet according to

[24] above, wherein the thickness is 5 μm or more.

[0382]

[26] The interlayer sheet according to

[24] or

[25] , wherein the viscoelastic layer V1 contains a main polymer and a plasticizer having a molecular weight lower than that of the main polymer.

[0383]

[27] The interlayer sheet according to

[26] above, wherein the weight average molecular weight of the plasticizer is 30,000 or less.

[0384]

[28] The interlayer sheet according to any one of

[24] to

[27] , further comprising a viscoelastic layer V2 laminated on the viscoelastic layer V1.

[0385] The storage modulus G' of the viscoelastic layer V2 at 25°C V2 Lower than the storage modulus G' of the viscoelastic layer V1 at 25°C V1 .

[0386]

[29] The interlayer sheet according to

[28] above, wherein the refractive index n2 of the viscoelastic layer V2 is lower than the refractive index n1 of the viscoelastic layer V1.

[0387]

[30] The interlayer sheet according to any one of

[24] to

[29] above, wherein the viscoelastic layer V1 is a layer formed from the adhesive composition according to any one of

[11] to

[18] above.

[0388]

[31] The interlayer sheet according to any one of

[24] to

[29] above, wherein the viscoelastic layer V1 is the adhesive layer in the adhesive sheet according to any one of [1] to [5] above.

[0389]

[32] An optical laminate comprising:

[0390] The interlayer sheet according to any one of

[24] to

[31] above, and

[0391] A resin film laminated on the above-mentioned interlayer sheet.

[0392]

[33] An interlayer sheet with a release liner, comprising:

[0393] The interlayer sheet according to any one of

[24] to

[31] above, and

[0394] A release liner covering at least one surface of the interlayer sheet.

[0395] Example

[0396] The following describes some embodiments of the present invention, but it is not intended to limit the present invention to the scope shown in these specific examples. It should be noted that in the following description, "parts" and "%" indicating the amount and content are by weight unless otherwise specified.

[0397] <Preparation of Acrylic Adhesive Composition C1>

[0398] In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube and a condenser, 95 parts of m-phenoxybenzyl acrylate (produced by Kyoeisha Chemical Co., Ltd., trade name "LIGHT ACRYLATE POB-A", refractive index: 1.566, homopolymer Tg: -35°C. hereinafter referred to as "POB-A") and 5 parts of 4-hydroxybutyl acrylate (4HBA) as a monomer component, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 100 parts of toluene as a polymerization solvent were added. While slowly stirring, nitrogen was introduced and the liquid temperature in the flask was maintained at 60°C for 6 hours to carry out a polymerization reaction to prepare a solution (50%) of acrylic polymer A1. The weight average molecular weight (Mw) of the acrylic polymer A1 is 500,000. The Tg (i.e., Tg T ) is -35 ° C, based on the Tg of the composition of the monomer containing an aromatic ring (ie Tg m1 ) is -35℃.

[0399] The solution (50%) of the acrylic polymer A1 was diluted to 30% with ethyl acetate. To 334 parts of the solution (100 parts of non-volatile components), 10 parts (0.1 parts of non-volatile components) of a 1% ethyl acetate solution of an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retardant, and iron acetylacetonate ( 1 part of a 1% ethyl acetate solution of Iron III (0.01 part of non-volatile matter) was added and stirred to prepare an acrylic adhesive composition C1.

[0400] <Preparation of Acrylic Adhesive Composition C2>

[0401] In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, and a condenser, 72 parts of POB-A as monomer components, 23 parts of 1-naphthylmethyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "LIGHT ACRYLATE NMT-A," refractive index: 1.595, homopolymer Tg: 31°C, hereinafter referred to as "NMT-A"), 5 parts of 4HBA, 0.2 parts of AIBN as a polymerization initiator, and 100 parts of toluene as a polymerization solvent were placed. While slowly stirring and introducing nitrogen, a polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at approximately 60°C to prepare a solution (50%) of acrylic polymer A2. The weight-average molecular weight (Mw) of this acrylic polymer A2 was 500,000.

[0402] In a separable flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet tube, 20 parts of POB-A and 80 parts of NMT-A as monomer components, 0.2 parts of AIBN as a polymerization initiator, 3.5 parts of α-thioglycerol as a chain transfer agent, and 67 parts of methyl ethyl ketone were placed. Nitrogen was then introduced and the atmosphere was replaced with nitrogen for approximately one hour while stirring. The flask was then heated to 70°C and reacted for 12 hours to obtain an acrylic oligomer (oligomer B) having a weight-average molecular weight (Mw) of 4,000 and a refractive index of 1.63.

[0403] The solution (50%) of the acrylic polymer A2 was diluted to 30% with ethyl acetate, and to 334 parts of the solution (100 parts of non-volatile components) were added 20 parts of the oligomer B prepared above, 10 parts of a 1% ethyl acetate solution of an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent (0.1 parts of non-volatile components), 2 parts of acetylacetone as a crosslinking retarder, and ferric acetylacetonate ( 1 part of a 1% ethyl acetate solution of Iron III (0.01 part of non-volatile matter) was added and stirred to prepare an acrylic adhesive composition C2.

[0404] <Preparation of Acrylic Adhesive Composition C3>

[0405] In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, and a condenser, 65 parts of 2-ethylhexyl acrylate, 30 parts of 1H,1H,5H-octafluoropentyl acrylate (trade name: Viscoat 8F, manufactured by Osaka Organic Chemical Industry Co., Ltd.), 3 parts of N-vinyl-2-pyrrolidone (NVP, manufactured by Nippon Shokubai), 2 parts of 4HBA, 0.2 parts of AIBN as a polymerization initiator, and 200 parts of ethyl acetate as a polymerization solvent were placed. A polymerization reaction was carried out for 9 hours while slowly stirring and introducing nitrogen. The temperature in the flask was maintained at approximately 60°C, thereby preparing a solution of acrylic polymer A3 (33%). The weight-average molecular weight (Mw) of acrylic polymer A3 was 550,000.

[0406] The above-mentioned solution (33%) of acrylic polymer A3 was diluted to 30% with ethyl acetate, and 10 parts (0.1 parts of non-volatile content) of a 1% ethyl acetate solution of an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent was added to 100 parts of the non-volatile content (solid content), followed by stirring and mixing to prepare an acrylic adhesive composition C3.

[0407] <Preparation of interlayer sheet>

[0408] (Example 1)

[0409] The acrylic adhesive composition C1 prepared above was applied to the silicone-treated surface of a polyethylene terephthalate (PET) film R1 (50 μm thick) that had been silicone-treated on one side, and heated at 130°C for 2 minutes to form a 25 μm thick adhesive layer. The silicone-treated surface of a PET film R2 (38 μm thick) that had been silicone-treated on one side was attached to the surface of the adhesive layer. This operation resulted in an adhesive layer (adhesive layer V1) protected on both sides by PET films (release liners) R1 and R2. It should be noted that the release liner R2 is relatively easy to release compared to the release liner R1.

[0410] Separately, the acrylic adhesive composition C3 prepared above was applied to the silicone-treated surface of a PET film R1 (50 μm thick) with a silicone treatment on one side, and heated at 130°C for 2 minutes to form a 10 μm thick adhesive layer V2. The silicone-treated surface of a PET film R2 (38 μm thick) with a silicone treatment on one side was laminated to the adhesive layer. This produced an adhesive layer (adhesive layer V2) protected on both sides by the PET films (release liners) R1 and R2.

[0411] The release liner R2 was removed from the adhesive layers V1 and V2, and the adhesive surfaces were brought together and pressed using a hand roller. The laminate was then autoclaved at 50°C and 0.60 MPa for 30 minutes, followed by aging at 50°C for 48 hours. This procedure yielded an interlayer sheet (substrate-less double-sided adhesive sheet) with a two-layer structure of adhesive layers V1 / V2. The surfaces of the interlayer sheet were protected by two release liners R1.

[0412] (Example 2)

[0413] An interlayer sheet (substrateless double-sided adhesive sheet) having a two-layer structure of adhesive layers V1 / V2 was obtained in the same manner as in Example 1 except that the type of adhesive composition used to form adhesive layers V1 and V2 and the thickness of each adhesive layer were changed as shown in Table 1.

[0414] (Examples 3~5)

[0415] In the same manner as in Example 1, single-layer adhesive layers each consisting of acrylic adhesive compositions C1 to C3 and having the thickness shown in Table 1 were prepared as interlayer sheets of Examples 3 to 5.

[0416] The obtained interlayer sheet was fully acclimatized in an environment of 23° C. and 50% RH and then used for the following measurements and evaluations.

[0417] <Measurement and Evaluation (1)>

[0418] (Refractive Index)

[0419] The refractive index of each pressure-sensitive adhesive layer was measured using an Abbe refractometer (manufactured by ATAGO Corporation, model "DR-M4") at a measurement wavelength of 589 nm and a measurement temperature of 25° C. The results are shown in Table 1.

[0420] (Storage modulus G')

[0421] The adhesive layers of each example were stacked to a thickness of approximately 1.5 mm, and these were used as measurement samples. Dynamic viscoelasticity measurements were performed using ARES manufactured by TA Instruments under the following conditions. The storage modulus G' at 25°C was read from the measurement results. The results are shown in Table 1.

[0422] [Measurement conditions]

[0423] Deformation Mode: Twist

[0424] Measuring frequency: 1Hz

[0425] Heating rate: 5℃ / min

[0426] Shape: Parallel Plate

[0427] (Total transmittance and haze value)

[0428] Using a test piece obtained by laminating the interlayer sheet of each example to alkali-free glass (thickness 0.8-1.0 mm, total light transmittance 92%, haze 0.4%), the total light transmittance and haze of the test piece were measured under a measurement environment of 23°C using a haze meter (trade name "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory). The total light transmittance and haze of the alkali-free glass were subtracted from the measured values to obtain the total light transmittance and haze values of the interlayer sheet. The results are shown in Table 1.

[0429] (Peel strength to glass plate)

[0430] Under a measurement environment of 23°C and 50% RH, the release liner was removed from one surface of the interlayer sheet of each example (the surface of the adhesive layer formed from Adhesive Composition C3 in Examples 1 and 2), and a 50 μm thick PET film was laminated for lining. The resulting sheet was then cut into a size of 25 mm wide and 100 mm long to prepare a test piece. The release liner on the other surface of the test piece was removed, and the sheet was then press-bonded to the surface of an alkali glass plate (manufactured by Matsunami Glass Industries, Ltd., 1.35 mm thick, blue-edged) as the adherend using a 2 kg roller with one reciprocating motion. The samples were placed in this environment for 30 minutes, then placed in a pressure degassing apparatus (autoclave) and autoclaved for 30 minutes at a temperature of 50°C and a pressure of 0.5 MPa. After further placing in an atmosphere of 23°C and 50% RH for 24 hours, the peel strength (adhesive force) [N / 25mm] was measured using a universal tensile-compression tester in accordance with JIS Z 0237:2000 at a tensile speed of 300 mm / min and a peel angle of 180 degrees. A "Tensile-Compression Tester, TG-1kN" manufactured by Minebea was used as the universal tensile-compression tester.

[0431] [Table 1]

[0432] Table 1

[0433]

[0434] C1: POB-A / 4HBA (95 / 5)

[0435] C2: POB-A / NMT-A / 4HBA (72 / 23 / 5) 100 parts + oligomer B 20 parts

[0436] C3: 2EHA / Viscoat 8F / NVP / 4HBA(65 / 30 / 3 / 2)

[0437] As shown in Table 1, the interlayer sheets of Examples 1 to 4 have a refractive index n1 of 1.570 or more, a storage modulus G' V1(25) The pressure-sensitive adhesive layer V1 has a pressure-sensitive adhesive strength of 700 kPa or less, and the interlayer sheet exhibits high transparency. These interlayer sheets exhibit a practical peel strength suitable for interlayer bonding of optical components.

[0438] <Evaluation of the front brightness improvement effect>

[0439] Each interlayer sheet was attached to a white LED light source. The light source was illuminated in a darkroom for at least 30 minutes to stabilize. The frontal brightness of the area where the interlayer sheet was attached was measured using a spectroradiometer SR-UL1R (manufactured by TOPCONTECHNOHOUSE CORPORATION). The average of the three measurements was used, and a rating of G (Good) was given for a brightness improvement of 10% or more compared to the brightness of the light source without the interlayer sheet attached, and P (Poor) was given for a brightness improvement of less than 10%.

[0440] [Table 2]

[0441] Table 2

[0442] example 1 2 3 4 5 Front brightness improvement effect G G P P P

[0443] As shown in Table 2, the interlayer sheets of Examples 1 and 2, which have an adhesive layer having a laminated structure of a combination of the adhesive layer of Example 5 (adhesive layer V2) with a low refractive index and the adhesive layer of Examples 3 and 4 (adhesive layer V1) with a high refractive index, were confirmed to have a front brightness improvement effect of more than 10% compared to the case where no interlayer sheet was used. For the interlayer sheets of Examples 3 to 5 in which the adhesive layer of the interlayer sheet was a single-layer structure, no front brightness improvement effect was confirmed by the interlayer sheet alone. It should be noted that the interlayer sheets of Examples 3 and 4 can exert an effect of improving the front brightness in the laminated body with a component with a lower refractive index (such as a resin film). In addition, the interlayer sheet of Example 5 can exert an effect of improving the front brightness in the laminated body with a component with a higher refractive index (such as a resin film) by laminating it.

[0444] <Preparation of Acrylic Adhesive Composition C4>

[0445] In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, and a condenser, 79 parts of POB-A as monomer components, 20 parts of n-butyl acrylate (BA), 1 part of 4HBA, 0.2 parts of AIBN as a polymerization initiator, and 100 parts of toluene as a polymerization solvent were placed. While slowly stirring and introducing nitrogen, a polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at approximately 60°C to prepare a solution of acrylic polymer A4 (50%). The Mw of this acrylic polymer A4 was 520,000.

[0446] The solution (50%) of the acrylic polymer A4 was diluted to 30% with ethyl acetate. To 334 parts of the solution (100 parts of non-volatile components), 10 parts of a 1% ethyl acetate solution of Coronate HX (0.1 parts of non-volatile components) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and iron acetylacetonate ( 1 part of a 1% ethyl acetate solution of Iron III (0.01 part of non-volatile matter) was added and stirred to prepare an acrylic adhesive composition C4.

[0447] <Preparation of Acrylic Adhesive Composition C5>

[0448] A 50% solution of acrylic polymer A5 was prepared in the same manner as for the solution of acrylic polymer A4, except that the monomer composition (weight ratio) was changed to POB-A / ethyl carbitol acrylate (CBA) / 4HBA = 79 / 20 / 1. The Mw of this acrylic polymer A5 was 460,000. Acrylic adhesive composition C5 was prepared in the same manner as for the preparation of acrylic adhesive composition C4, except that the solution of acrylic polymer A5 was used in place of the solution of acrylic polymer A4.

[0449] <Preparation of Acrylic Adhesive Composition C6>

[0450] A 50% solution of acrylic polymer A6 was prepared in the same manner as for the solution of acrylic polymer A4, except that the monomer composition (weight ratio) was changed to P2H-A / 4HBA = 99 / 1. "P2H-A" in the above monomer composition represents phenoxydiethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "LIGHTACRYLATE P2H-A," refractive index: 1.510, homopolymer Tg: -35°C). The Mw of this acrylic polymer A6 was 1,000,000.

[0451] A solution of acrylic polymer A6 (50%) was diluted to 30% with ethyl acetate, and to this solution (100 parts of non-volatile components) was added an additive (H RO ) 20 parts of 6-ethylacrylate-dinaphtho[2,1-b:1',2'-d]thiophene (6-acryloyloxyethyldinaphthothiophene, No.: 6EDNTA, refractive index: 1.722, manufactured by Sugai Chemical IND.CO.,LTD.), 10 parts of a 1% ethyl acetate solution of Coronate HX as a crosslinking agent (0.1 parts of non-volatile components), 2 parts of acetylacetone as a crosslinking retardant, and iron acetylacetonate as a crosslinking catalyst ( 1 part of a 1% ethyl acetate solution of Iron III (0.01 part of non-volatile matter) was added and stirred to prepare an acrylic adhesive composition C6.

[0452] <Preparation of Acrylic Adhesive Composition C7>

[0453] A solution (50%) of acrylic polymer A1 was diluted to 30% with ethyl acetate, and 10 parts of POB-A as an additive (plasticizer), 10 parts of a 1% ethyl acetate solution of Coronate HX as a crosslinking agent (0.1 parts of non-volatile components), 2 parts of acetylacetone as a crosslinking retarder, and ferric acetylacetonate as a crosslinking catalyst were added to 334 parts of the solution (100 parts of non-volatile components). 1 part of a 1% ethyl acetate solution of Iron III (0.01 part of non-volatile matter) was added and stirred to prepare an acrylic adhesive composition C7.

[0454] <Preparation of Acrylic Adhesive Composition C8>

[0455] Acrylic adhesive composition C8 was prepared in the same manner as in the preparation of acrylic adhesive composition C7, except that 10 parts of POB-A was replaced with 10 parts of 3-phenoxybenzyl alcohol (manufactured by Tokyo Chemical Industry Co., Ltd., refractive index 1.59).

[0456] <Preparation of Acrylic Adhesive Composition C9>

[0457] A solution of acrylic polymer A9 (50%) was prepared in the same manner as for the solution of acrylic polymer A3, except that the monomer composition (weight ratio) was changed to 2EHA / Viscoat 13F / 4HBA = 49 / 50 / 1. "Viscoat 13F" in the above monomer composition represents 1H,1H,2H,2H-tridecafluorooctyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat 13F"). The Mw of this acrylic polymer A9 was 550,000. Acrylic adhesive composition C9 was prepared in the same manner as for the preparation of acrylic adhesive composition C3, except that the solution of acrylic polymer A9 was used in place of the solution of acrylic polymer A3.

[0458] <Preparation of interlayer sheet>

[0459] (Examples 6~10)

[0460] The types of adhesive compositions used to form adhesive layers V1 and V2 and the thicknesses of each adhesive layer were set as shown in Table 3. In addition, an interlayer sheet (substrate-free double-sided adhesive sheet) formed by a two-layer structure of adhesive layer V1 / adhesive layer V2 was obtained in the same manner as in Example 1.

[0461] After the interlayer sheets obtained in Examples 6 to 10 were fully acclimated in an environment of 23° C. and 50% RH, the various items were measured and evaluated in the same manner as in the above “Measurement and Evaluation (1)”.

[0462] [Table 3]

[0463] Table 3

[0464]

[0465] C4: POB-A / BA / 4HBA (79 / 20 / 1)

[0466] C5: POB-A / CBA / 4HBA (79 / 20 / 1)

[0467] C6: P2H-A / 4HBA (99 / 1) 1C 0 parts + 6EDNTA 20 parts

[0468] C7: 100 parts of POB-A / 4HBA (95 / 5) + 10 parts of POB-A

[0469] C8: 100 parts of POB-A / 4HBA (95 / 5) + 10 parts of 3-phenoxybenzyl alcohol

[0470] C9:2EHA / Viscoat13F / 4HBA(49 / 50 / 1)

[0471] As shown in Table 3, the interlayer sheets of Examples 6 to 10 have a refractive index n1 of 1.570 or more, a storage modulus G' V1 (25) The pressure-sensitive adhesive layer V1 has a pressure-sensitive adhesive strength of 700 kPa or less, and the interlayer sheet exhibits high transparency. These interlayer sheets exhibit a practical peel strength suitable for interlayer bonding of optical components.

[0472] While the specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The embodiments described in the claims include various modifications and alterations of the specific examples described above.

[0473] Description of Reference Numerals

[0474] 1.2 Interlayer sheet (adhesive sheet)

[0475] 10 Viscoelastic layer (adhesive layer, viscoelastic layer V1)

[0476] 10A 1st surface (adhesive surface)

[0477] 10B Surface 2

[0478] 11. First viscoelastic layer (first adhesive layer, viscoelastic layer V1)

[0479] 12 Second viscoelastic layer (second adhesive layer, viscoelastic layer V2)

[0480] 20 Supporting substrate

[0481] 20A Side 1

[0482] 20B Side 2 (Back)

[0483] 30, 31, 32 release liner

[0484] 50 Adhesive sheet with release liner (interlayer sheet with release liner)

[0485] 70 optical components

[0486] 100 Optical laminate

Claims

1. An interlayer sheet used for placement between layers of a laminate in optical applications. The refractive index n1 is 1.570 or more, and the storage modulus G' at 25°C is V1 A viscoelastic layer V1 having a viscosity of 30 kPa to 700 kPa, wherein the viscoelastic layer V1 comprises an acrylic polymer as a base polymer, the acrylic polymer containing an aromatic ring-containing monomer as a monomer unit, and the content of the aromatic ring-containing monomer in the monomer components constituting the acrylic polymer is 50% by weight or more and 96% by weight or less, The interlayer sheet further includes a viscoelastic layer V2 laminated on the viscoelastic layer V1, and the storage modulus G' of the viscoelastic layer V2 at 25°C is V2 Lower than the storage modulus G' of the viscoelastic layer V1 at 25°C V1 , the refractive index n2 of the viscoelastic layer V2 is lower than the refractive index n1 of the viscoelastic layer V1, The interlayer sheet has a total light transmittance of 90% or more and a haze value of 0.56% or less. 2 . The interlayer sheet according to claim 1 , having a thickness of 5 μm or more.

3. An interlayer sheet with a release liner, comprising: The interlayer sheet according to claim 1 or 2, and A release liner covers at least one surface of the interlayer sheet.

4. An optical laminate comprising: The interlayer sheet according to claim 1 or 2, and A resin film laminated on the interlayer sheet.

Images