Interlayer sheet, interlayer sheet with release liner and optical laminate

Abstract

To provide an interlayer sheet that has flexibility fitted for tightly adhering and following to an adjacent member, and also has both of high refractive index and high transparency.SOLUTION: There is provided an interlayer sheet to be disposed between layers of a laminate in optical applications. The interlayer sheet includes a viscoelastic layer V1 having a refractive index n1 of 1.570 or more and a storage elastic modulus G'V1 at 25°C of 30-700 kPa. The interlayer sheet has a total light transmittance of 86% or more and a haze value of 1.0% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Generally, adhesives (also referred to as pressure-sensitive adhesives; the same applies hereinafter) are in a soft solid (viscoelastic) state at temperatures around room temperature and have the property of easily adhering to an adherend when pressure is applied. Utilizing these properties, adhesives are widely used for purposes such as joining, fixing, and protection in a variety of industrial fields, from home appliances to automobiles, various machines, electrical appliances, and electronic devices. One example of the use of adhesives is bonding polarizing films, retardation films, cover window components, and various other light-transmitting components to other components in displays such as liquid crystal displays and organic EL displays. Patent Documents 1 and 2 are examples of technical documents related to adhesives for optical components. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-169382 [Patent Document 2] Japanese Patent Application Publication No. 2017-128732 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Documents 1 and 2 propose a pressure-sensitive adhesive composition containing, as its main component, a (meth)acrylic acid ester polymer containing a monomer unit having multiple aromatic rings, and a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition. However, they do not disclose a specific pressure-sensitive adhesive that combines a refractive index of 1.570 or greater with flexibility. While a technique for increasing the refractive index by blending inorganic particles with a resin (e.g., inorganic particles such as zirconium oxide particles or titanium oxide particles) is known, pressure-sensitive adhesives containing inorganic particles have a trade-off between refractive index and adhesive properties (e.g., peel strength, flexibility, etc.), making their application to the pressure-sensitive adhesive field difficult. In particular, when blending inorganic particles into pressure-sensitive adhesives for optical applications, the impact on optical properties (e.g., total light transmittance, haze, etc.) must also be considered when considering improving the refractive index of an interlayer sheet used between layers of a laminate in optical applications. For example, when considering improving the refractive index of an interlayer sheet used between layers of a laminate in optical applications, it is necessary to achieve a high refractive index while balancing flexibility and high transparency, which allow the interlayer sheet to exhibit appropriate adhesion and deformation tracking capabilities to adjacent members.

[0005] The present invention was made in view of the above circumstances, and aims to provide an interlayer sheet that exhibits flexibility suitable for adhesion to and conformity with adjacent members, and that also has a high refractive index and high transparency. Another object of the present invention is to provide an interlayer sheet with a release liner that includes the above interlayer sheet. Another related object is to provide an optical laminate that includes the above interlayer sheet as a component. [Means for solving the problem]

[0006] According to this specification, an interlayer sheet is provided that is used by being disposed between layers of a laminate for optical applications. The interlayer sheet includes a viscoelastic layer V1 having a refractive index n1 of 1.570 or more. The interlayer sheet has a total light transmittance of 86% or more, a haze value of 1.0% or less, and a storage modulus G' at 25°C. V1 (hereinafter referred to as "storage modulus G' V1 The interlayer sheet has a high refractive index and a storage modulus G' of 30 kPa to 700 kPa.V1 Since the interlayer sheet V1 contains a viscoelastic layer V1 in which the viscosity (25) is suppressed to a certain level or less and is highly transparent, it is useful as an interlayer sheet for optical applications. In addition, since the interlayer sheet is pre-formed into a sheet shape, it can be easily placed in the desired location.

[0007] In some embodiments, the viscoelastic layer has a thickness of 5 μm or more, which is preferable because a viscoelastic layer having such a thickness can easily be laminated to an adjacent member with good adhesion by absorbing irregularities that may exist on the surface of the adjacent member.

[0008] The interlayer sheet according to some embodiments further includes a viscoelastic layer V2 laminated on the viscoelastic layer V1, wherein the storage modulus G' of the viscoelastic layer V2 at 25°C is V2 (hereinafter referred to as "storage modulus G' V2 (25)" is the storage modulus G' of the viscoelastic layer V1 at 25°C. V1 The interlayer sheet having such a configuration can be made more flexible due to the contribution of the viscoelastic layer V2.

[0009] 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 an interlayer sheet having such a configuration, the difference in refractive index between the viscoelastic layers V1 and V2 can be used to control the behavior of light passing through the interlayer sheet.

[0010] Furthermore, this specification provides an interlayer sheet with a release liner, comprising any one of the interlayer sheets disclosed herein and a release liner covering at least one surface of the interlayer sheet. The interlayer sheet disclosed herein is preferably produced, stored, distributed, processed, etc. in the form of an interlayer sheet with a release liner, at least one surface of which is protected by a release liner, and can be used in an embodiment in which the release liner is peeled off before lamination with an adjacent member.

[0011] This specification also provides an optical laminate comprising any one of the interlayer sheets disclosed herein and a resin film laminated on the interlayer sheet. In such an optical laminate, the advantages of the interlayer sheet disclosed herein, which combines a high refractive index, high transparency, and flexibility, can be favorably exhibited.

[0012] Appropriate combinations of the elements described in this specification may also be included within the scope of the invention for which patent protection is sought by this patent application. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a cross-sectional view schematically illustrating the configuration of an interlayer sheet according to one embodiment. [Figure 2] FIG. 10 is a cross-sectional view schematically showing the configuration of an interlayer sheet according to another embodiment. [Figure 3] FIG. 1 is a cross-sectional view schematically showing an optical laminate including an interlayer sheet according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present invention will be described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings on carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In the following drawings, components and parts having the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. The embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the actual product.

[0015] In this specification, the term "self-luminous element" refers to a light-emitting element whose luminance can be controlled by the value of the current flowing through it. The self-luminous element may be composed of a single element or an aggregate. Specific examples of the self-luminous element include, but are not limited to, a light-emitting diode (LED) and an organic electroluminescent (EL). When a light-emitting device is mentioned in this specification, the light-emitting device may include such a self-luminous element as a component. Examples of the light-emitting device include, but are not limited to, a light source module device (e.g., a surface light-emitting module) used for lighting and a display device formed with pixels.

[0016] This specification provides an interlayer sheet for use in optical applications by being disposed between layers of a laminate. The interlayer sheet includes at least a viscoelastic layer V1. The interlayer sheet may further include a viscoelastic layer V2 laminated on the viscoelastic layer V1. One or both of the viscoelastic layers V1 and V2 are typically pressure-sensitive adhesive layers formed from a pressure-sensitive adhesive. The interlayer sheet of this embodiment can be understood as a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer. Hereinafter, the interlayer sheet may be referred to as a pressure-sensitive adhesive sheet, the viscoelastic layer as a pressure-sensitive adhesive layer, the viscoelastic material as a pressure-sensitive adhesive, and the surface of the viscoelastic layer as a pressure-sensitive adhesive surface. Furthermore, the member on which the viscoelastic layer of the interlayer sheet disclosed herein is laminated may be referred to as an adherend of the interlayer sheet (pressure-sensitive adhesive sheet). In some embodiments, the interlayer sheet preferably has a pressure-sensitive adhesive surface formed from a pressure-sensitive adhesive layer V1.

[0017] <Example of interlayer sheet configuration> The interlayer sheet disclosed herein may be in the form of a substrate-attached PSA sheet having a PSA layer (for example, a single-layer PSA layer consisting of a viscoelastic layer V1, or a laminated PSA layer in which two or more PSA layers including a viscoelastic layer V1 and a viscoelastic layer V2 are laminated in direct contact) on one or both sides of a non-releasable substrate (support substrate), or may be in the form of a substrate-less PSA sheet (i.e., a PSA sheet without a non-releasable substrate; typically, a PSA sheet consisting of a PSA layer) in which the PSA layer is supported on a release liner. The concept of PSA sheet here may include what are called PSA tapes, PSA labels, PSA films, etc. The PSA sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be a PSA sheet processed into various shapes.

[0018] FIG. 1 shows an example of the structure of the interlayer sheet disclosed herein. This interlayer sheet (pressure-sensitive adhesive sheet) 1 is configured as a single-sided pressure-sensitive adhesive sheet (single-sided pressure-sensitive adhesive sheet) including a pressure-sensitive adhesive layer 10 having a first surface 10A that serves as the surface (adhesive surface) to be attached to an adherend, and a support substrate 20 laminated to a second surface 10B of the pressure-sensitive adhesive layer 10. The second surface 10B of the pressure-sensitive adhesive layer 10 is bonded to a first surface (non-releasable surface) 20A of the support substrate 20. A plastic film such as a polyester film can be used as the support substrate 20. The support substrate 20 may also be an optical film such as a polarizing plate. Before use (before attachment to an adherend), the pressure-sensitive adhesive sheet 1 can be in the form of a release-liner-attached pressure-sensitive adhesive sheet 50, in which the adhesive surface 10A is protected by a release liner 30, at least the pressure-sensitive adhesive layer side of which serves as a releasable surface (release surface), as shown in FIG. 1, for example. Alternatively, the second surface 20B of the support substrate 20 (the surface opposite to the first surface 20A, also referred to as the back surface) may be the release surface, and the adhesive surface 10A may be protected by being wound or laminated so that the adhesive surface 10A abuts against this second surface 20B. The adhesive layer 10 may have a single-layer structure consisting of a viscoelastic layer V1 as shown in FIG. 1, or may have a laminate structure in which two or more sub-adhesive layers with different compositions (for example, two sub-adhesive layers consisting of the viscoelastic layer V1 constituting the adhesive surface 10A and the viscoelastic layer V2 arranged on the support substrate 20 side) are laminated in direct contact (i.e., without being separated by a layer of non-adhesive material).

[0019] The interlayer sheet disclosed herein may be in the form of a substrate-less double-sided PSA sheet comprising a pressure-sensitive adhesive layer. As shown in FIG. 2, before use, the substrate-less double-sided PSA sheet 2 may be in a form in which the first surface (first adhesive surface) 10A and the second surface (second adhesive surface) 10B of the pressure-sensitive adhesive layer 10 are protected by release liners 31, 32, at least the PSA layer side of which is a releasable surface (release surface). Alternatively, the back surface of the release liner 31 (the surface opposite the PSA side) may be a release surface, and the adhesive surface 10B may be protected by being wound or laminated so that the adhesive surface 10B abuts against the back surface of the release liner 31. Such a substrate-less double-sided PSA sheet may be used, for example, by bonding a substrate (preferably a light-transmitting substrate, which may be an optical member such as an optical film) to at least one of the first and second adhesive surfaces. The pressure-sensitive adhesive layer 10 constituting the substrate-less double-sided pressure-sensitive adhesive sheet 2 shown in FIG. 2 has a laminated structure in which two sub-pressure-sensitive adhesive layers with different compositions are laminated in direct contact. Specifically, the pressure-sensitive adhesive layer 10 has a laminated structure (two-layer structure) consisting of a first viscoelastic layer (first pressure-sensitive adhesive layer, viscoelastic layer V1) 11 and a second viscoelastic layer (second pressure-sensitive adhesive layer, viscoelastic layer V2) 12. Alternatively, the interlayer sheet disclosed herein may be in the form of a substrate-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer with a single-layer structure (viscoelastic layer V1). An interlayer sheet in the form of such a laminated structure or a substrate-less double-sided pressure-sensitive adhesive sheet with a single-layer structure can be used, for example, as a component of an optical laminate in which optical members are laminated on each of the first and second adhesive surfaces.

[0020] The interlayer sheet disclosed herein may be a component of an optical laminate having an optical member bonded to at least one surface. For example, the interlayer sheet 1 shown in FIG. 1 may be a component of an optical laminate 100 having an optical member 70 laminated on a first surface 10A of a pressure-sensitive adhesive layer 10, as shown in FIG. 3. The optical member may be, for example, a glass plate, a resin film, a metal plate, or the like. The interlayer sheet 1 may be a component of the optical laminate by being disposed between the optical member 70 and a second optical member (not shown). Furthermore, in the interlayer sheet 1 shown in FIG. 1, when the support substrate 20 is an optical member such as an optical film, the interlayer sheet 1 may be understood as an optical laminate having an optical member laminated on a second surface 10B of the pressure-sensitive adhesive layer 10.

[0021] Furthermore, although not specifically shown, the interlayer sheet disclosed herein may be in the form of a substrate-attached double-sided adhesive pressure-sensitive adhesive sheet (substrate-attached double-sided pressure-sensitive adhesive sheet) that includes a support substrate having a non-releasable first and second surfaces, with a first pressure-sensitive adhesive layer fixedly laminated to the first surface and a second pressure-sensitive adhesive layer fixedly laminated to the second surface. An example of the configuration of such a substrate-attached double-sided pressure-sensitive adhesive sheet is the single-sided pressure-sensitive adhesive sheet 1 shown in FIG. 1 , in which the second surface 20B of the support substrate 20 is a non-releasable surface and a second pressure-sensitive adhesive layer is provided on the second surface 20B, the second surface of the second pressure-sensitive adhesive layer is bonded to the second surface 20B of the support substrate 20, and the first surface of the second pressure-sensitive adhesive layer (the surface opposite the second surface) forms the second adhesive surface of the substrate-attached double-sided pressure-sensitive adhesive sheet. The composition of the pressure-sensitive adhesive that constitutes the second pressure-sensitive adhesive layer may be the same as or different from the composition of the pressure-sensitive adhesive that constitutes the first pressure-sensitive adhesive layer. An interlayer sheet in the form of such a substrate-attached double-sided PSA sheet can be used, for example, as a component of an optical laminate in which optical members are laminated on each of the first and second adhesive surfaces. The substrate-attached double-sided PSA sheet before use can be in a form in which the first and second adhesive surfaces are protected by release liners, similar to the substrate-less double-sided PSA sheet described above.

[0022] <Characteristics of interlayer sheet> (refractive index) The interlayer sheet disclosed herein has a viscoelastic layer (adhesive layer) V1 having a refractive index n1 of 1.570 or higher. Such a viscoelastic layer V1 can be realized, 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 higher. The technology disclosed herein can provide an adhesive layer V1 having a refractive index of 1.570 or higher, an adhesive composition capable of forming the adhesive layer V1, and an interlayer sheet including the adhesive layer V1.

[0023] In this specification, the refractive index of a pressure-sensitive adhesive (viscoelastic material) refers to the refractive index of the surface (adhesive surface) of the pressure-sensitive adhesive. The refractive index of a pressure-sensitive adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) at a measurement wavelength of 589 nm and a measurement temperature of 25°C. As an Abbe refractometer, for example, the model "DR-M4" manufactured by ATAGO or an equivalent can be used. The measurement sample can be an adhesive layer made of the pressure-sensitive adhesive to be evaluated. Specifically, the refractive index of a pressure-sensitive adhesive can be measured by the method described in the Examples below. The refractive index of a pressure-sensitive adhesive can be adjusted, for example, by the composition of the pressure-sensitive adhesive (e.g., the composition of the monomer components constituting the base polymer, additives that may be used as needed, etc.).

[0024] In some embodiments, the refractive index of the pressure-sensitive adhesive layer V1 is advantageously greater than 1.570, preferably greater than 1.580, more preferably greater than 1.585, and even more preferably greater than 1.590 (e.g., greater than 1.595). A pressure-sensitive adhesive layer V1 having such a refractive index can effectively control the behavior of light passing through the pressure-sensitive adhesive layer V1 by utilizing the relative refractive index relationship between the pressure-sensitive adhesive layer V1 and an adjacent layer (which may be another viscoelastic layer (e.g., pressure-sensitive adhesive layer V2) included in the interlayer sheet, or the adherend onto which the pressure-sensitive adhesive layer V1 is laminated). In some embodiments of the technology disclosed herein, the refractive index of the pressure-sensitive adhesive layer V1 may be, for example, greater than or equal to 1.600, greater than or equal to 1.605, or greater than or equal to 1.610. The preferred upper limit of the refractive index of the pressure-sensitive adhesive layer V1 is not limited to a specific range because it may vary depending on the refractive index of the adjacent layer, etc. In some embodiments, the refractive index of the pressure-sensitive adhesive layer V1 may be, for example, 1.700 or less, 1.670 or less, or 1.650 or less, taking into consideration the balance between adhesive properties and transparency.

[0025] When the interlayer sheet disclosed herein is in the form of a double-sided PSA sheet (including both substrate-less double-sided PSA sheets and substrate-attached double-sided PSA sheets; the same applies hereinafter unless otherwise specified) with one side being a first adhesive side and the other side being a second adhesive side, and the first adhesive side is constituted by PSA layer V1, it is preferable that at least the first adhesive side of the PSA layer satisfy one of the refractive indices described above. The refractive index of the second adhesive side is not particularly limited.

[0026] In some embodiments, the refractive index n2 of the second adhesive surface may be approximately the same as the refractive index n1 of the first adhesive surface. More specifically, the absolute value of the difference in refractive index between the two adhesive surfaces, i.e., |n1-n2|, may be, for example, less than 0.05, or less than 0.03, or less than 0.01. The lower limit of |n1-n2| may be 0.00 or may be greater than 0.00. The relative relationship between the refractive indexes of the two adhesive surfaces may be n1>n2, and n1 <n2でもよく、n1=n2でもよい。

[0027] In some other embodiments, the difference between the refractive index n1 of the first adhesive surface of the interlayer sheet and the refractive index n2 of the second adhesive surface, i.e., n1-n2, may be, for example, greater than 0.00, may be 0.01 or greater, preferably 0.02 or greater, may be 0.03 or greater, may be 0.05 or greater, may be 0.10 or greater, may be 0.15 or greater, may be 0.20 or greater, or may be 0.25 or greater. The magnitude relationship between n1 and n2 may be reversed. The upper limit of n1-n2 is not particularly limited. In some embodiments, from the viewpoint of easily achieving a good balance between adhesive properties and transparency, n1-n2 may be, for example, 0.30 or less, 0.26 or less, 0.21 or less, 0.18 or less, or 0.16 or less. An interlayer sheet having different refractive indices between the first and second adhesive surfaces can be realized, for example, by laminating first and second adhesive layers having different refractive indices to a non-peelable supporting substrate in a substrate-attached double-sided adhesive sheet, or by making a substrate-less double-sided adhesive sheet have a laminated structure of two or more sub-adhesive layers in which the refractive index of the adhesive that makes up the first adhesive surface and the refractive index of the adhesive that makes up the second adhesive surface are different from each other in the laminated structure.

[0028] In some embodiments, the ratio (n1 / n2) of the refractive index n1 of the first adhesive surface to the refractive index n2 of the second adhesive surface may be, for example, greater than 1.00, may be approximately 1.01 or greater, suitably approximately 1.02 or greater, or may be approximately 1.03 or greater. In some embodiments, the ratio (n1 / n2) is advantageously approximately 1.05 or greater, preferably approximately 1.07 or greater, more preferably approximately 1.10 or greater, and may be approximately 1.11 or greater. The upper limit of the ratio (n1 / n2) is not particularly limited. In some embodiments, from the viewpoint of adhesive properties, transparency, and the like, the ratio (n1 / n2) may be, for example, approximately 1.20 or less, approximately 1.18 or less, approximately 1.16 or less, approximately 1.14 or less, or approximately 1.12 or less.

[0029] (storage modulus G') In the interlayer sheet (adhesive sheet) disclosed herein, the storage modulus G' (storage modulus G' V1(25)) is appropriately set depending on the purpose and mode of use, and is not limited to a specific range. V1 (25) can be, for example, in the range of about 30 kPa to 700 kPa. In some embodiments, from the viewpoint of ease of application to an 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 viewpoint of increasing the flexibility of the pressure-sensitive adhesive layer V1 at room temperature (e.g., 25°C) and facilitating adhesion to the adherend, the storage modulus G' V1 (25) is advantageously about 330 kPa or less, and preferably 300 kPa or less. In some embodiments where application property and flexibility in the room temperature range are more important, the storage modulus G' V1 (25) may be, for example, less than 270 kPa or less than 250 kPa, advantageously less than 200 kPa, preferably less than 180 kPa, and more preferably less than 160 kPa (e.g., less than 140 kPa). In some embodiments, the storage modulus G' V1 (25) may be less than 100 kPa or less than 90 kPa. V1 The lower limit of (25) is not particularly limited, but may be, for example, 30 kPa or more, 50 kPa or more, or 70 kPa or more from the viewpoint of processability, handling, etc. In some embodiments, in consideration of increasing the refractive index, the storage modulus G' V1 (25) may be 100 kPa or more, 150 kPa or more, 200 kPa or more, 250 kPa or more, or 300 kPa or more.

[0030] In the pressure-sensitive adhesive sheet disclosed herein, the storage modulus G' (storage modulus G' V1 (50)) is not particularly limited and may be, for example, less than 100 kPa. In some embodiments, the storage modulus G' V1The storage modulus G' (50) is suitably less than 60 kPa, preferably less than 40 kPa, and more preferably less than 38 kPa (for example, less than 36 kPa). V1 The pressure-sensitive adhesive layer V1 having a limited storage modulus G' can easily have improved adhesion to an adherend by applying moderate heating as necessary, thereby improving the adhesiveness to an adherend. V1 The lower limit of (50) is not particularly limited. In some embodiments, from the viewpoint of the heat resistance of the pressure-sensitive adhesive layer V1, the storage modulus G' V1 (50) may be, for example, 10 kPa or more, 15 kPa or more, 20 kPa or more, or 23 kPa or more.

[0031] In some embodiments of the interlayer sheet disclosed herein, the viscoelastic layer (adhesive layer) V1 satisfies the following conditions: (a) Storage modulus G' V1 (25) is 350 kPa or less (preferably less than 200 kPa, e.g., 180 kPa or less); and (b) Storage modulus G' V1 (50) is less than 60 kPa (preferably less than 50 kPa, more preferably less than 40 kPa, e.g., less than 38 kPa); It is preferable that at least one of the above conditions is satisfied. A pressure-sensitive adhesive layer V1 that satisfies at least the above condition (a) is preferred from the viewpoint of adhesion to an adherend and flexibility at room temperature (e.g., 25°C). An interlayer sheet having a pressure-sensitive adhesive layer V1 that satisfies at least the above condition (b) is preferred because its adhesion (adhesion) to an adherend can be easily improved by heating to a temperature slightly higher than room temperature. An interlayer sheet having a pressure-sensitive adhesive layer V1 that does not satisfy the above condition (a) but satisfies the above condition (b) has good reworkability (repositionability) at the initial stage of application at room temperature, and can be used as a thermally activated interlayer sheet that can effectively increase the peel strength from an adherend by heating to a temperature slightly higher than room temperature. The thermal activation may be performed by heating the interlayer sheet to a temperature slightly higher than room temperature when applying it to an adherend. The 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).

[0032] In some embodiments of the interlayer sheets disclosed herein, the storage modulus G' V1 (25) Storage modulus G' versus [kPa] V1 (50) [kPa] ratio, i.e., storage modulus ratio G' V1 (50) / G' V1 (25) is, for example, 70% or less, or may be 40% or less, 30% or less, or 20% or less. V1 (50) / G' V1 An interlayer sheet having a pressure-sensitive adhesive layer V1 with a small (25) is suitable for use as the above-mentioned heat-activatable interlayer sheet. V1 (50) / G' V1 The lower limit of (25) is not particularly limited. V1 (50) / G' V1 (25) is, for example, 5% or more, and from the viewpoint of the heat resistance of the interlayer sheet, is preferably 10% or more, may be 12% or more, or may be 15% or more.

[0033] Storage modulus G' V1 (25) and G' V1(50) can be obtained by dynamic viscoelasticity measurement, and G' V1 (50) / G' V1 (25) can be calculated. Dynamic viscoelasticity measurement can be performed by a conventional method using a commercially available dynamic viscoelasticity measuring device, for example, an ARES manufactured by TA Instruments or an equivalent, under the following measurement conditions. The sample to be measured is prepared by laminating the pressure-sensitive adhesive layer to be evaluated as necessary to a thickness of about 1.5 mm. [Measurement conditions] Deformation mode: Torsion Measurement frequency: 1Hz Heating rate: 5°C / min Shape: Parallel plate 7.9mmφ

[0034] Storage modulus G' of viscoelastic layer (adhesive layer) V1 V1 (25), G' V1 The (50) and storage modulus ratio can be adjusted by selecting the composition of the monomer components constituting the base polymer of the pressure-sensitive adhesive layer V1 (e.g., selecting the type and content of the monomer (m1)), selecting whether or not to use a crosslinking agent and the amount used, and selecting whether or not to use a refractive index improver or plasticizing material described below, and selecting the type and amount used). For example, by using, as the monomer (m1), in addition to a first monomer that is the main component of the monomer (m1), a relatively small amount of a second monomer having a chemical structure different from the first monomer in combination with the first monomer, the G' can be increased in comparison with the case where the first monomer is used alone as the monomer (m1). V1 (50) is made smaller, and G' V1 (50) / G' V1 (25) can be reduced.

[0035] When the PSA sheet disclosed herein is in the form of a double-sided PSA sheet having a first adhesive surface and a second adhesive surface (for example, a substrate-attached double-sided PSA sheet having a first PSA layer constituted by PSA layer V1 on a first surface of a substrate and a second PSA layer constituted by PSA layer V2 on a second surface of the substrate; a substrate-less double-sided PSA sheet having a laminate structure in which PSA layer V1 constituting the first adhesive surface and PSA layer V2 constituting the second adhesive surface are laminated without a non-adhesive substrate therebetween; a substrate-less double-sided PSA sheet having a single-layer structure in which one surface of PSA layer V1 is a first adhesive surface and the other surface of PSA layer V1 is a second adhesive surface; the same applies to other similar descriptions), the storage modulus G' described above can be used. V1 (25), G' V1 The storage modulus ratio (50) is applied to at least the pressure-sensitive adhesive layer constituting the first adhesive surface, and preferably to both the pressure-sensitive adhesive layer constituting the first adhesive surface and the pressure-sensitive adhesive layer constituting the second adhesive surface. The storage modulus G' of the pressure-sensitive adhesive layer constituting the first adhesive surface and the storage modulus G' of the pressure-sensitive adhesive layer constituting the second adhesive surface may be similar to or different from each other.

[0036] (Total light transmittance) The interlayer sheet disclosed herein includes a pressure-sensitive adhesive layer V1 having the above-described high refractive index, and the interlayer sheet has a total light transmittance of 86% or more. Such highly transparent interlayer sheets, with or without a substrate, are preferably used in applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of the adherend through the pressure-sensitive adhesive sheet. In some embodiments, the total light transmittance of the interlayer sheet is preferably 88% or more, more preferably 90% or more (e.g., greater than 90.0%), and may be 90.5% or more, 93% or more, or 95% or more. Theoretically, the upper limit of the total light transmittance is the value obtained by subtracting light loss due to reflection at the air interface (Fresnel loss) from 100%. In practice, it may be approximately 98% or less, approximately 96% or less, or approximately 95% or less. In some embodiments, taking into account the refractive index and adhesive properties, the total light transmittance of the interlayer sheet may be approximately 94% or less, approximately 93% or less, or approximately 92% or less. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. The transmittance meter used may be a product manufactured by Murakami Color Research Laboratory under the trade name "HAZEMETER HM-150" or an equivalent. 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, or the type and thickness of the substrate in a configuration that includes a substrate.

[0037] When the interlayer sheet disclosed herein is in the form of a substrate-attached double-sided PSA sheet in which a first PSA layer and a second PSA layer are fixedly laminated to a support substrate, and the first PSA layer is a layer constituted by PSA layer V1, it is sufficient that at least the first PSA layer satisfies any of the total light transmittances described above, and the total light transmittance of the second PSA layer is not particularly limited. In a use mode in which light passes through the PSA sheet in the thickness direction, it is preferable that the total light transmittance of the second PSA layer satisfies any of the total light transmittances of the first PSA layer described above. The relative relationship between the total light transmittances of the two PSA layers may be first PSA layer > second PSA layer, first PSA layer < second PSA layer, or first PSA layer = second PSA layer.

[0038] (Haze value) The interlayer sheet disclosed herein includes a pressure-sensitive adhesive layer V1 having the above-described high refractive index, and the haze value of the interlayer sheet is 1.0% or less. Such highly transparent interlayer sheets, with or without a substrate, are preferably used in applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of an adherend through the interlayer sheet. In some embodiments, the haze value of the interlayer sheet may be 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. There is no particular lower limit for the haze value of the interlayer sheet, and a lower haze value is preferable from the viewpoint of improving transparency. Meanwhile, in some embodiments, taking into consideration the refractive index and adhesive properties, the haze value of the interlayer sheet may be, for example, 0.05% or more, 0.1% or more, 0.2% or more, 0.3% or more, or 0.4% or more. These haze values ​​for the interlayer sheet can also be preferably applied to the haze value of a substrateless adhesive sheet (typically an adhesive sheet consisting of an adhesive layer) when the technology disclosed herein is implemented in the form of the adhesive sheet.

[0039] Here, the "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated onto a measurement object. It is also called the cloudiness value. The haze value can be expressed by the following formula: Th(%)=Td / Tt×100 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, thickness, etc. of the object to be measured.

[0040] When the interlayer sheet disclosed herein is in the form of a substrate-attached double-sided PSA sheet in which a first PSA layer and a second PSA layer are fixedly laminated to a support substrate, the interlayer sheet as a whole only needs to satisfy one of the haze values ​​described above, and the haze values ​​of the first PSA layer and the second PSA layer are not particularly limited. The relative haze values ​​of the two PSA layers may be first PSA layer > second PSA layer, first PSA layer < second PSA layer, or first PSA layer = second PSA layer. That is, the haze value of the first PSA layer and the haze value of the second PSA layer may be similar or different. The same applies to the haze value of each sub-adhesive layer when the interlayer sheet disclosed herein includes a PSA layer in which multiple sub-adhesive layers (e.g., PSA layer V1 and PSA layer V2) are directly laminated together.

[0041] (Surface smoothness of adhesive surface) In some embodiments of the interlayer sheet disclosed herein, it is preferable that the adhesive surface of the interlayer sheet (for example, the adhesive surface constituted by the adhesive layer V1) has high surface smoothness.

[0042] For example, the adhesive surface preferably has an arithmetic mean roughness Ra limited to a predetermined value or less. A configuration including an adhesive surface designed to have a low arithmetic mean roughness Ra is preferable from the viewpoint of optical homogeneity. By limiting the arithmetic mean roughness Ra, it is possible to effectively suppress the occurrence of brightness unevenness due to the surface condition of the adhesive layer, for example, in a usage mode in which light is extracted through the adhesive surface (such as an interlayer sheet arranged on the viewing side of the light-emitting element in a light-emitting device). A low arithmetic mean roughness Ra of the adhesive surface is also advantageous in suppressing optical distortion, which also contributes to improving 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 preferable that the arithmetic mean roughness Ra of at least the first adhesive surface be limited to a predetermined value or less, and it is more preferable that the arithmetic mean roughness Ra of both adhesive surfaces be limited to a predetermined value or less. High surface smoothness on each adhesive surface of the double-sided adhesive sheet can preferably achieve adhesion with excellent optical homogeneity.

[0043] In some embodiments, the arithmetic mean roughness Ra of the adhesive surface is preferably about 70 nm or less, more preferably about 65 nm or less, and even more preferably about 55 nm or less, and may be less than 50 nm, less than 45 nm, or less than 40 nm. From the viewpoint of production efficiency, etc., in some embodiments, the arithmetic mean roughness Ra of the adhesive surface may be, for example, about 10 nm or more, about 20 nm or more, or about 30 nm or more (e.g., about 40 nm or more). In an interlayer sheet having a first adhesive surface and a second adhesive surface, the arithmetic mean roughness Ra of the first adhesive surface and the arithmetic mean roughness Ra of the second adhesive surface may be similar or different.

[0044] Furthermore, for example, it is preferable that the maximum height Rz of the adhesive surface be limited to a predetermined value or less. A configuration including an adhesive surface designed to have a low maximum height Rz is preferable from the viewpoint of optical homogeneity. By limiting the maximum height Rz, for example, in a usage mode in which light is extracted through the adhesive surface as described above, it is possible to effectively suppress the occurrence of brightness unevenness due to the surface condition of the adhesive layer. A low maximum height Rz of the adhesive surface is also advantageous in suppressing 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 preferable that the maximum height Rz of at least the first adhesive surface be limited to a predetermined value or less, and it is more preferable that the maximum heights Rz of both adhesive surfaces be limited to a predetermined value or less. High surface smoothness on each adhesive surface of the double-sided adhesive sheet can favorably achieve adhesion with excellent optical homogeneity.

[0045] In some embodiments, the maximum height Rz of the adhesive surface is preferably approximately 600 nm or less, more preferably approximately 500 nm or less, even more preferably approximately 450 nm or less, and particularly preferably approximately 400 nm or less, and may be less than 350 nm, less than 300 nm, or less than 250 nm. From the viewpoint of production efficiency, in some embodiments, the maximum height Rz of the adhesive surface may be, for example, approximately 10 nm or more, approximately 50 nm or more, approximately 100 nm or more, or approximately 200 nm or more. In an interlayer sheet having a first adhesive surface and a second adhesive surface, the maximum height Rz of the first adhesive surface and the maximum height Rz of the second adhesive surface may be similar or different.

[0046] 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 that uses an optical interference method can be used, such as a 3D optical profiler (trade name "NewView7300", manufactured by ZYGO) or an equivalent. Specifically, the arithmetic mean roughness Ra and maximum height Rz can be measured by, for example, the following measurement method, or by setting the measurement operation and measurement conditions so as to obtain results equivalent to or corresponding to those obtained by the measurement method.

[0047] That is, the surface shape of the measurement sample is measured under the following conditions using a three-dimensional optical profiler (trade name "NewView7300", manufactured by ZYGO Corporation) in an environment of 23°C and 50% RH. The arithmetic surface roughness Ra is calculated from the measured data in accordance with JIS B 0601-2001. The maximum height Rz is calculated as the sum of the height Rp of the highest peak above the mean line of the roughness curve obtained by the above measurement (roughness curve) and the depth Rv of the deepest valley below the mean line. The measurement is performed five times (i.e., N=5), and the average value is used. The measurement sample can be prepared, for example, by cutting the pressure-sensitive adhesive layer to be measured or an interlayer sheet containing the pressure-sensitive adhesive layer to a size of about 150 mm in length and 50 mm in width. If the adhesive surface is protected with a release liner, the release liner is gently peeled off (for example, at a pulling speed of 300 mm / min and a peel angle of 180°) to expose the adhesive surface. It is desirable to allow the exposed adhesive surface to stand for about 30 minutes before measurement. [Measurement conditions] Measurement area: 5.62mm x 4.22mm (Objective lens: 2.5x, internal lens: 0.5x) Analysis mode: Remove: Cylinder Data Fill: ON(Max:25) Remove Spikes: ON (xRMS:1) Filter: OFF

[0048] The arithmetic mean roughness Ra and maximum height Rz of the adhesive surface can be adjusted by the composition and properties (viscosity, leveling ability, etc.) of the adhesive composition used to form the adhesive layer, and the properties of the surface (release surface) of the release liner that protects the adhesive surface.

[0049] (Water absorption rate) In some embodiments, the pressure-sensitive adhesive layer V1 preferably has a water absorption rate limited to a predetermined value or less. Limiting the water absorption rate of the pressure-sensitive adhesive layer V1 tends to suppress dimensional changes in the viscoelastic layer V1 due to fluctuations in the moisture content in the pressure-sensitive adhesive layer V1 (e.g., absorption and release of moisture, such as environmental humidity). This suppresses warping of the interlayer sheet or an optical laminate including the interlayer sheet, which is caused by a mismatch in dimensional changes between the pressure-sensitive adhesive layer V1 and its adjacent layer (which may be the pressure-sensitive adhesive layer V2, a supporting substrate, a release liner, an adherend, etc.). Suppressing fluctuations in the moisture content in the pressure-sensitive adhesive layer V1 is also preferable from the viewpoint of maintaining constant flatness, transparency, refractive index, etc. of the pressure-sensitive adhesive layer V1. Furthermore, an interlayer sheet having a pressure-sensitive adhesive layer V1 with low water absorption rate is less likely to occlude moisture, making it suitable as an interlayer sheet for use in components or products containing moisture-sensitive elements, such as organic electroluminescence (EL) elements.

[0050] In some embodiments, the water absorption rate of the pressure-sensitive adhesive layer V1 is suitably approximately 1.0% or less, preferably 0.7% or less, more preferably 0.5% or less (e.g., less than 0.5%), and may be 0.4% or less, 0.3% or less, or 0.2% or less. The lower limit of the water absorption rate of the pressure-sensitive adhesive layer V1 is not particularly limited, but from a practical standpoint, such as achieving compatibility with adhesive properties, it may 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 substrate-attached double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer, it is preferable that the water absorption rate of at least the first pressure-sensitive adhesive layer (preferably the pressure-sensitive adhesive layer V1) be limited to a predetermined value or less. From the standpoint of achieving greater effectiveness, it is more preferable that the water absorption rates of both the first and second pressure-sensitive adhesive layers be limited to a predetermined value or less.

[0051] The water absorption rate (also referred to as moisture content) of the pressure-sensitive adhesive layer is measured by the following method. [Moisture content measurement] The adhesive layer to be evaluated was placed on a 4 cm x 5 cm (area: 20 cm) sheet with two release liners placed on one side and the other side. 2 ) and the release liner on one side is removed and the specimen is attached to pre-weighed aluminum foil. Next, the release liner on the other side of the adhesive layer is removed, and the specimen is placed in a thermo-hygrostat chamber at a temperature of 60°C and a relative humidity of 90%, and then removed after 72 hours. After weighing the test specimen with the adhesive layer and aluminum foil laminated together, the moisture content is measured by Karl Fischer coulometric titration under the following conditions using a moisture meter (Mitsubishi Chemical Analytech Model CA-200) equipped with a thermal vaporizer (Mitsubishi Chemical Analytech Model VA-200). Anolyte: Aquamicron AKX (Mitsubishi Chemical) Catholyte: Aquamicron CXU (Mitsubishi Chemical) Heat evaporation temperature: 150℃

[0052] (gel fraction) The gel fraction of the viscoelastic layer V1 is appropriately set depending on the intended use, the mode of use, and the like, and is not limited to a specific range. The gel fraction is, for example, approximately 99% or less, and suitably approximately 97% or less. From the viewpoint of easily achieving both a high refractive index and adhesive properties, in some preferred embodiments, the gel fraction may be approximately 95% or less, more preferably approximately 92% or less (e.g., approximately 90% or less). A gel fraction that is not too high is also preferred from the viewpoint of properly conforming to irregularities that may exist on the adherend surface (e.g., an irregular structure provided for the purpose of improving the light extraction efficiency of a light-emitting device) and achieving good adhesion. In some embodiments, the gel fraction may be approximately 88% or less, approximately 75% or less, or approximately 65% ​​or less. Furthermore, from the viewpoint of imparting appropriate cohesiveness to the adhesive and appropriately exhibiting adhesive properties, the gel fraction is, for example, approximately 10% or more, suitably approximately 20% or more, and may be approximately 30% or more. From the viewpoint of deformation resistance of the viscoelastic layer V1 (preventing bubbles due to pressure extrusion or foreign matter entrapment, etc.), the gel fraction is preferably about 30% or more, more preferably about 40% or more, and may be about 45% or more, about 50% or more, about 65% or more, or about 75% or more. The gel fraction of the interlayer sheet (typically an interlayer sheet in the form of a substrate-less adhesive sheet) is also preferably within the range exemplified above. The gel fraction can be adjusted by the molecular weight, molecular structure, concentration, degree of crosslinking, etc. of the base polymer. The gel fraction is measured by the following method.

[0053] [Gel fraction measurement] A predetermined amount of sample (weight Wg1) is wrapped in a porous polytetrafluoroethylene membrane (weight Wg2) with an average pore size of 0.2 μm, and the opening is tied with string (weight Wg3). The porous polytetrafluoroethylene (PTFE) membrane is available from Nitto Denko Corporation under the trade name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent. The package is immersed in a sufficient amount of ethyl acetate and kept at room temperature (typically 23°C) for 7 days to allow only the sol component of the adhesive to elute out of the film, after which the package is taken out and the ethyl acetate adhering to the outer surface is wiped off, the package is dried at 130°C for 2 hours, and the weight of the package (Wg4) is measured. The gel fraction can be calculated by substituting each value into the following formula: Gel fraction (%) = [(Wg4 - Wg2 - Wg3) / Wg1] x 100

[0054] When the interlayer sheet disclosed herein is in the form of a double-sided pressure-sensitive adhesive sheet having a first adhesive surface and a second adhesive surface, with the first adhesive surface being composed of a pressure-sensitive adhesive layer V1 and the second adhesive surface being composed of a pressure-sensitive 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 may be similar or different. In some embodiments, the gel fraction of the viscoelastic layer V2 can be lower than the gel fraction of the viscoelastic layer V1. This configuration facilitates increasing the flexibility of the interlayer sheet due to the contribution of the viscoelastic layer V2, which has a relatively low gel fraction. This can provide an interlayer sheet that favorably achieves both a high refractive index of the viscoelastic layer V1 and flexibility of the interlayer sheet.

[0055] In some embodiments of the technology disclosed herein, the peak temperature of tan δ of the adhesive constituting the viscoelastic layer V1 is preferably approximately -50°C or higher and approximately 50°C or lower. Here, tan δ (loss tangent) of the adhesive refers to the ratio of the loss modulus G" to the storage modulus G' of the adhesive. In other words, tan δ = G" / G'. The tan δ of the adhesive is determined by sandwiching a disk-shaped adhesive sample approximately 2 mm thick and 7.9 mm in diameter between parallel plates and applying a shear strain at a frequency of 1 Hz using a viscoelasticity testing device, conducting a temperature dispersion test of the adhesive in shear mode under conditions of a measurement temperature range of -60°C to 60°C and a heating rate of 5°C / min, and using the storage modulus G' (Pa) and loss modulus G" (Pa) measured at that time, using the following formula: tan δ = G" / G'. The peak temperature of tan δ of the adhesive (hereinafter sometimes referred to as Tpeak) can be determined from the change in tan δ over the above temperature range. As the viscoelasticity testing device, an ARES manufactured by TA Instruments or an equivalent product can be used.

[0056] In some embodiments, the Tpeak of the viscoelastic layer V1 is advantageously 45°C or less or 35°C or less, preferably 30°C or less (e.g., 25°C or less), and may be 20°C or less, or 15°C or less. A PSA with a lower Tpeak tends to provide good initial adhesion and adhesion at room temperature. On the other hand, a PSA with a Tpeak that is not too low is preferred from the viewpoint of imparting appropriate cohesiveness to the PSA and tends to be suitable for achieving a high refractive index. From this viewpoint, in some embodiments, the PSA's Tpeak may be, for example, -40°C or more, -30°C or more, -20°C or more, -5°C or more, 5°C or more, 15°C or more, or even 25°C or more. A PSA with a relatively high Tpeak is preferably used in an embodiment in which, when attaching to an adherend, one or both of the PSA and the adherend are heated to a temperature slightly higher than room temperature, as necessary. The Tpeak of a pressure-sensitive adhesive can be adjusted by selecting the composition of the pressure-sensitive adhesive (for example, the composition of the monomer components that make up the base polymer, whether or not a refractive index enhancer or plasticizing material is used, and selecting the type and amount used). When the interlayer sheet disclosed herein is in the form of a double-sided pressure-sensitive adhesive sheet having a first adhesive surface and a second adhesive surface, the Tpeak of the above-mentioned pressure-sensitive adhesive is preferably applied to at least the pressure-sensitive adhesive layer (preferably the viscoelastic layer V1) constituting the first adhesive surface, and more preferably to both the pressure-sensitive adhesive layer constituting the first adhesive surface and the pressure-sensitive adhesive layer constituting the second adhesive surface. The Tpeak of the pressure-sensitive adhesive layer constituting the first adhesive surface and the Tpeak of the pressure-sensitive adhesive layer constituting the second adhesive surface may be similar to or different from each other.

[0057] <Viscoelastic layer V1> (base polymer) In the technology disclosed herein, the type of adhesive constituting the adhesive layer V1 is not particularly limited. The adhesive may contain, as an adhesive polymer (hereinafter also referred to as a "base polymer," meaning a structural polymer that forms the adhesive), one or more of various rubber-like polymers that can be used in the field of adhesives, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, and mixtures thereof), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine-based polymers. From the viewpoints of adhesive performance, cost, and the like, adhesives containing an acrylic polymer or a rubber polymer as a base polymer are preferably used. Among these, adhesives using an acrylic polymer as the base polymer (acrylic adhesives) are preferred. The technology disclosed herein is preferably implemented in an embodiment using an acrylic adhesive.

[0058] The following mainly describes interlayer sheets in which the adhesive layer V1 is composed of an acrylic adhesive, i.e., interlayer sheets having an acrylic adhesive layer, but it is not intended to limit the adhesive layer V1 in the interlayer sheets disclosed herein to an acrylic adhesive layer.

[0059] In this specification, the "base polymer" of a PSA refers to the main component of the rubbery polymer contained in the PSA, and is not to be construed in any other limiting sense. The rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, the "main component" refers to a component that accounts for more than 50% by weight, unless otherwise specified. In this specification, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer." Therefore, in this specification, an acrylic polymer is defined as a polymer containing a monomer unit derived from an acrylic monomer. A typical example of an acrylic polymer is a polymer in which the proportion of acrylic monomers in all monomers used in the synthesis of the acrylic polymer is more than 50% by weight (preferably more than 70% by weight, for example more than 90% by weight). In this specification, "(meth)acryloyl" refers collectively to acryloyl and methacryloyl. Similarly, "(meth)acrylate" refers collectively to acrylate and methacrylate, and "(meth)acrylic" refers collectively to acrylic and methacrylic. Therefore, the concept of an acrylic monomer as used herein can include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer).

[0060] (Acrylic polymer (A)) The interlayer sheet disclosed herein has a refractive index of 1.570 or more and a storage modulus G' at 25°C. V1This embodiment can be preferably implemented in an embodiment including an acrylic pressure-sensitive adhesive layer having a viscosity of 30 kPa to 700 kPa, a total light transmittance of 86% or more, and a haze value of 1.0% or less. The acrylic polymer serving as the base polymer of the acrylic pressure-sensitive adhesive layer preferably contains an aromatic ring-containing monomer (m1) as a monomer component constituting the acrylic polymer. That is, an acrylic polymer containing an aromatic ring-containing monomer (m1) as a monomer unit is preferred. Hereinafter, such an acrylic polymer will also be referred to as "acrylic polymer (A)." Hereinafter, the term "monomer component constituting the acrylic polymer" refers to a monomer that constitutes a repeating unit of the acrylic polymer in the pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition, regardless of whether the monomer component is contained in the pressure-sensitive adhesive composition in the form of a preformed polymer (which may be an oligomer) or an unpolymerized monomer. That is, the monomer component constituting the acrylic polymer may be contained in the pressure-sensitive adhesive composition in the form of a polymer, an unpolymerized monomer, or a partially polymerized monomer. In some embodiments, from the viewpoint of ease of preparation of the PSA composition, a PSA composition containing substantially all (e.g., 95 wt % or more, preferably 99 wt % or more) of the monomer components in the form of a polymer is preferred. A PSA composition containing substantially all of the monomer components in the form of a polymer is also preferred from the viewpoint of ease of forming an interlayer sheet with less distortion and warpage.

[0061] (Monomer (m1)) As the monomer (m1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule can be used. As the monomer (m1), one of such compounds can be used alone or two or more of them can be used in combination.

[0062] Examples of the ethylenically unsaturated group include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. From the viewpoint of polymerization reactivity, a (meth)acryloyl group is preferred, and from the viewpoints of flexibility and adhesiveness, an acryloyl group is more preferred. From the viewpoint of suppressing a decrease in the flexibility of the adhesive, a compound containing one ethylenically unsaturated group per molecule (i.e., a monofunctional monomer) is preferably used as the monomer (m1).

[0063] The number of aromatic rings contained in one molecule of the compound used as monomer (m1) may be 1 or 2 or more. The upper limit of the number of aromatic rings contained in 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 PSA, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, or may be 5 or less, 4 or less, 3 or less, or 2 or less.

[0064] The aromatic ring of the compound used as monomer (m1) may be, for example, a carbocyclic ring such as a benzene ring (which may be a benzene ring constituting a part of a biphenyl structure or a fluorene structure); a fused ring of a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, or a phenanthrene ring; or a heterocyclic 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. The heteroatom contained as a ring-constituting atom in the heterocyclic ring may be, for example, one or more selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatom constituting the heterocyclic ring may be one or both of nitrogen and sulfur. Monomer (m1) may have a structure in which one or more carbocyclic rings are fused with one or more heterocyclic rings, such as a dinaphthothiophene structure.

[0065] The aromatic ring (preferably a carbocyclic ring) may have one or more substituents on the ring-constituting atoms, or may have no substituents. When the aromatic ring has a substituent, examples of the substituent include, but are not limited to, an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (such as a fluorine atom, a chlorine atom, or a bromine atom), a hydroxyalkyl group, a hydroxyalkyloxy group, and a glycidyloxy group. In a carbon atom-containing substituent, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the aromatic ring may have no substituents on the ring-constituting atoms, or may have one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (such as a bromine atom). The term "the aromatic ring of the monomer (m1) has a substituent on its ring-constituting atom" refers to the aromatic ring having a substituent other than a substituent having an ethylenically unsaturated group.

[0066] The aromatic ring and the ethylenically unsaturated group may be bonded directly or via a linking group. The linking group may be, for example, an alkylene group, an oxyalkylene group, a poly(oxyalkylene) group, a phenyl group, an alkylphenyl group, an alkoxyphenyl group, a group in which one or more hydrogen atoms in these groups are substituted with hydroxyl groups (e.g., a hydroxyalkylene group), an oxy group (-O- group), a thiooxy group (-S- group), or the like. In some embodiments, aromatic ring-containing monomers having a structure in which the aromatic ring and the ethylenically unsaturated group are bonded directly or via a linking group selected from the group consisting of an alkylene group, an oxyalkylene group, and a poly(oxyalkylene) group are preferably used. The number of carbon atoms in the alkylene group and the oxyalkylene group is preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. The number of repeating oxyalkylene units in the poly(oxyalkylene) group may be, for example, 2 to 3.

[0067] Examples of compounds that can be preferably used as the monomer (m1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds can be used alone or in combination of two or more. One or more aromatic ring-containing (meth)acrylates and one or more aromatic ring-containing vinyl compounds can be used in combination.

[0068] The content of the monomer (m1) in the monomer components constituting the acrylic polymer (A) is not particularly limited and can be set so as to realize a pressure-sensitive adhesive layer that achieves 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.). In some embodiments, the content of the monomer (m1) in the monomer components may be, for example, 30% by weight or more, preferably 50% by weight or more, 60% by weight or more, or even 70% by weight or more. From the viewpoint of easily obtaining a higher refractive index, in some preferred embodiments, the content of the monomer (m1) may be, for example, more than 70% by weight, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or even 95% by weight or more. The upper limit of the content of the monomer (m1) in the monomer components is 100% by weight. From the viewpoint of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous for the content of the monomer (m1) to be less than 100% by weight, and for example, it is preferably approximately 99% by weight or less, more preferably 98% by weight or less, and may be 97% by weight or less, or may be 96% by weight or less. In some embodiments, the content of the monomer (m1) may be 93% by weight or less, 90% by weight or less, 80% by weight or less, or 75% by weight or less. In some embodiments in which adhesive properties and / or optical properties are more important, the content of the monomer (m1) in the monomer component may be 70% by weight or less, 60% by weight or less, or 45% by weight or less.

[0069] In some embodiments of the technology disclosed herein, a monomer having two or more aromatic rings (preferably carbon rings) in one molecule can be preferably used as the monomer (m1) because it is easy to achieve a high refractive index. Examples of a monomer having two or more aromatic rings in one molecule (hereinafter also referred to as a "monomer containing multiple aromatic rings") include a monomer having a structure in which two or more non-fused aromatic rings are bonded via a linking group, a monomer having a structure in which two or more non-fused aromatic rings are chemically bonded directly (i.e., without the intervention of other atoms), a monomer having a fused aromatic ring structure, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, and a monomer having a dibenzothiophene structure. The monomer containing multiple aromatic rings can be used alone or in combination of two or more.

[0070] The linking group may be, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (e.g., -O-(CH2) n - group, where n is 1 to 3, preferably 1), thiooxyalkylene groups (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), straight chain alkylene groups (i.e., -(CH2) n - group (where n is 1 to 6, preferably 1 to 3), the oxyalkylene group, the thiooxyalkylene group, and the linear alkylene group in which the alkylene group is partially or completely halogenated. From the viewpoint of the flexibility of the adhesive, suitable examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group, and a linear alkylene group. 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., m-phenoxybenzyl (meth)acrylate), thiophenoxybenzyl (meth)acrylate, benzyl benzyl (meth)acrylate, and the like.

[0071] The monomer having a structure in which two or more non-fused aromatic rings are directly chemically bonded can 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, biphenylmethyl (meth)acrylate, etc.

[0072] Examples of the monomer having the condensed aromatic ring structure include naphthalene ring-containing (meth)acrylate, anthracene ring-containing (meth)acrylate, vinyl group-containing naphthalene, vinyl group-containing anthracene, etc. Specific examples include 1-naphthylmethyl (meth)acrylate (also known as 1-naphthalenemethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate, etc.

[0073] Specific examples of the monomer having the fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene(meth)acrylate, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene(meth)acrylate, etc. Note that the monomer having the fluorene structure includes a structural portion in which two benzene rings are directly chemically bonded, and therefore is included in the concept of the monomer having a structure in which two or more non-fused aromatic rings are directly chemically bonded.

[0074] Examples of the monomer having the dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, and (meth)allyl group-containing dinaphthothiophene. Specific examples include (meth)acryloyloxymethyl dinaphthothiophene (for example, dinaphthothiophene having CHCH(R) at the 5th or 6th position of the dinaphthothiophene ring). 1 )C(O)OCH2- bonded compound. 1 is a hydrogen atom or a methyl group), (meth)acryloyloxyethyl dinaphthothiophene (for example, CHCH(R1 )C(O)OCH(CH3)- or CH2CH(R 1 )C(O)OCH2CH2- bonded compound. 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 5th or 6th position of a naphthothiophene ring), (meth)allyloxydinaphthothiophene, etc. Note that a monomer having a dinaphthothiophene structure is also included in the concept of a monomer having the above-mentioned fused aromatic ring structure because it contains a naphthalene structure or has a structure in which a thiophene ring and two naphthalene structures are fused together.

[0075] Examples of the monomer having the dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophene, vinyl group-containing dibenzothiophene, etc. Note that the monomer having the dibenzothiophene structure has a structure in which a thiophene ring and two benzene rings are fused, and therefore is included in the concept of the monomer having the fused aromatic ring structure. Note that neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-fused aromatic rings are directly chemically bonded.

[0076] As the monomer (m1) in the technology disclosed herein, a monomer having one aromatic ring (preferably a carbon ring) per molecule may be used. A monomer having one aromatic ring per molecule can be useful, for example, for improving the flexibility of the pressure-sensitive adhesive, adjusting the adhesive properties, improving the transparency, etc. In some embodiments, a monomer having one aromatic ring per molecule is preferably used in combination with a monomer containing multiple aromatic rings, from the viewpoint of improving the refractive index of the pressure-sensitive adhesive.

[0077] Examples of monomers having one aromatic ring in one molecule include carbon-containing aromatic ring (meth)acrylates such as benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxybutyl (meth)acrylate, cresyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and chlorobenzyl (meth)acrylate; 2-(4,6-dibromo-2-s-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, and 6- Examples of the aromatic ring-containing (meth)acrylate include bromine-substituted aromatic ring-containing (meth)acrylates such as (4,6-dibromo-2-s-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; carbon-containing aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; and compounds having a vinyl substituent on a heteroaromatic ring such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, and N-vinyloxazole.

[0078] Monomer (m1) may be a monomer having an oxyethylene chain interposed between the ethylenically unsaturated group and the aromatic ring in the various aromatic ring-containing monomers described above. Such a monomer having an oxyethylene chain interposed between the ethylenically unsaturated group and the aromatic ring can be understood as an ethoxylated product of the original monomer. The number of repeating oxyethylene units (-CHCHO-) in the 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, and phenoxydiethylene glycol di(meth)acrylate.

[0079] The content of the aromatic ring-containing monomer in the monomer (m1) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of easily realizing a pressure-sensitive adhesive having a higher refractive index, the content of the aromatic ring-containing monomer in the monomer (m1) may be, for example, 50% by weight or more, preferably 70% by weight or more, or 85% by weight or more, 90% by weight or more, or even 95% by weight or more. Substantially 100% by weight of the aromatic ring-containing monomer in the monomer (m1) may be. That is, only one or two or more aromatic ring-containing monomers may be used as the monomer (m1). Furthermore, in some embodiments, for example, taking into consideration the balance between a high refractive index and adhesive properties and / or optical properties, the content of the aromatic ring-containing monomer in the monomer (m1) may be less than 100% by weight, or may be 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less. In some embodiments, taking into consideration adhesive properties and / or optical properties, the content of the aromatic ring-containing monomer in the 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. The technology disclosed herein may also be implemented in an embodiment in which the aromatic ring-containing monomer content in the monomer (m1) is less than 5% by weight. The aromatic ring-containing monomer may not be used.

[0080] The content of the aromatic ring-containing monomer in the monomer components constituting the acrylic polymer is not particularly limited and can be set so as to realize a pressure-sensitive adhesive layer that satisfies 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 aromatic ring-containing monomer in the monomer components may be, for example, 3 wt% or more, 10 wt% or more, or 25 wt% or more. In some embodiments, to facilitate the realization of a pressure-sensitive adhesive having a higher refractive index, the content of the aromatic ring-containing monomer in the monomer components may be, for example, more than 35 wt%, preferably more than 50 wt%, more than 70 wt%, 75 wt% or more, 85 wt% or more, 90 wt% or more, or even 95 wt% or more. The content of the multiple aromatic ring monomer in the monomer component can be 100% by weight. However, from the viewpoint of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous to set it to less than 100% by weight, preferably approximately 99% by weight or less, more preferably 98% by weight or less, and may be 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, taking into consideration adhesive properties and / or optical properties, the content of the multiple aromatic ring 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 can also be implemented in an embodiment in which the content of the multiple aromatic ring monomer in the monomer component is less than 3% by weight.

[0081] In some embodiments of the technology disclosed herein, a high refractive index monomer may be preferably used as at least a portion of the monomer (m1). Here, "high refractive index monomer" refers to a monomer having a refractive index of, for example, about 1.510 or more, preferably about 1.530 or more, and more preferably about 1.550 or more. The upper limit of the refractive index of the high refractive index monomer is not particularly limited, but from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition and ease of achieving compatibility with flexibility suitable for a pressure-sensitive adhesive, it may 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 may be used alone or in combination of two or more. The refractive index of the monomer is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C. The Abbe refractometer may be an ATAGO DR-M4 model or an equivalent. If the manufacturer provides a nominal value for the refractive index at 25°C, that nominal value may be used.

[0082] As the high refractive index monomer, a compound having the corresponding refractive index can be appropriately selected from 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, Tg of homopolymer: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, Tg of homopolymer: 31°C), ethoxylated o-phenylphenol acrylate (number of repeating oxyethylene units: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, Tg of homopolymer: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, Tg of homopolymer: 2°C), and phenoxydiethylene glycol acrylate (refractive index: 1.510, Tg of homopolymer: 1.520). Examples of suitable dinaphthothiophene include, but are not limited to, 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), and 5-vinyl dinaphthothiophene (abbreviated as 5VDNT, refractive index: 1.793).

[0083] The content of the high refractive index monomer in the monomer (m1) (i.e., an aromatic ring-containing monomer having a refractive index of about 1.510 or more, preferably about 1.530 or more, more preferably about 1.550 or more) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of easily obtaining a higher refractive index, the content of the high refractive index monomer in the monomer (m1) may be, for example, 50% by weight or more, preferably 70% by weight or more, or 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (m1) may be the high refractive index monomer. In some embodiments, for example, from the viewpoint of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, the content of the high refractive index monomer in the 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, taking into account adhesive properties and / or optical properties, 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. The technology disclosed herein may also be implemented in an embodiment in which the content of the high refractive index monomer in the monomer component (m1) is less than 5% by weight. The high refractive index monomer need not be used.

[0084] The content of the high refractive index monomer in the monomer components constituting the acrylic polymer is not particularly limited and can be set so as to realize a pressure-sensitive adhesive layer that achieves 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 monomer components may be, for example, 3 wt% or more, 10 wt% or more, or 25 wt% or more. In some embodiments, from the viewpoint of easily realizing a pressure-sensitive adhesive having a higher refractive index, the content of the high refractive index monomer in the monomer components may be, for example, more than 35 wt%, preferably more than 50 wt%, more than 70 wt%, 75 wt% or more, 85 wt% or more, 90 wt% or more, or even 95 wt% or more. The content of the high refractive index monomer in the monomer component can be 100% by weight. However, from the viewpoint of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous to set it to less than 100% by weight, preferably 99% by weight or less, more preferably 98% by weight or less, and may be 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, taking into consideration adhesive properties 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 can also be implemented in an embodiment in which the content of the high refractive index monomer in the monomer component is less than 3% by weight.

[0085] 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 lower (preferably 5°C or lower or 0°C or lower, more preferably -10°C or lower, even more preferably -20°C or lower, for example -25°C or lower) is used as at least a portion of the monomer (m1). Increasing the content of the aromatic ring-containing monomer (m1) (particularly the aromatic ring-containing monomer (m1) corresponding to one or both of the above-mentioned multiple aromatic ring-containing monomer and high refractive index monomer) in the monomer components generally tends to increase the storage modulus G' of the PSA. However, by employing monomer L as part or all of the monomer (m1), the increase in storage modulus G' can be suppressed. This allows the refractive index to be improved while better maintaining flexibility suitable for a PSA. The lower limit of the Tg of monomer L is not particularly limited. In consideration of the balance with the refractive index-enhancing effect, in some embodiments, the Tg of monomer L may be, for example, -70°C or higher, -55°C or higher, or -45°C or higher. The monomer L can be used alone or in combination of two or more.

[0086] As the monomer L, a compound having the corresponding Tg can be appropriately selected from among the compounds encompassed by the concept of the aromatic ring-containing monomer (m1) disclosed herein (for example, the compounds and compound groups exemplified above). One suitable example of an aromatic ring-containing monomer that can be used as the monomer L is m-phenoxybenzyl acrylate (Tg of the homopolymer: -35°C). Another suitable example is phenoxydiethylene glycol acrylate (Tg of the homopolymer: -35°C).

[0087] The content of monomer L in monomer (m1) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of easily obtaining a PSA that achieves both a high refractive index and flexibility at a higher level, the content of monomer L in monomer (m1) may 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. Monomer (A1) may account for substantially 100% by weight of monomer L. In some embodiments, for example, from the viewpoint of achieving a good balance between flexibility suitable for a pressure-sensitive adhesive and a high refractive index, the content of monomer L 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, 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 need not be used.

[0088] The content of monomer L in the monomer components constituting the acrylic polymer may be, for example, 3 wt% or more, 10 wt% or more, or 25 wt% or more. In some embodiments, from the viewpoint of easily obtaining a PSA that combines a high refractive index and flexibility at a higher level, the content of monomer L in the monomer components may be, for example, more than 35 wt%, preferably more than 50 wt%, more than 70 wt%, 75 wt% or more, 85 wt% or more, 90 wt% or more, or even 95 wt% or more. The content of monomer L in the monomer components may be 100 wt%, but in consideration of the balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous to set it to less than 100 wt%, preferably approximately 99 wt% or less, more preferably 98 wt% or less, or 96 wt% or less, 95 wt% or less, 93 wt% or less, 90 wt% or less, 85 wt% or less, 80 wt% or less, or 75 wt% or less. In some embodiments, the content of monomer L in the monomer mixture 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 practiced in embodiments in which the content of monomer L in the monomer mixture is less than 3% by weight.

[0089] In some embodiments, the glass transition temperature Tg based on the composition of the monomer (m1) m1 From the viewpoint of flexibility of the adhesive, it is advantageous that the glass transition temperature Tg is about 20°C or less, preferably 10°C or less (for example, 5°C or less), more preferably 0°C or less, and even more preferably -10°C or less, and may be -20°C or less, or -25°C or less. m1 The lower limit of the glass transition temperature Tg is not particularly limited. m1 The glass transition temperature Tg may be, for example, −70° C. or higher, −55° C. or higher, or −45° C. or higher. m1is preferably -40°C or higher, -35°C or higher, -33°C or higher, -30°C or higher, or -25°C or higher, for example.

[0090] Here, the glass transition temperature Tg based on the composition of the monomer (m1) m1 The glass transition temperature (Tg) is calculated by the Fox formula (described later) based on the composition of only the monomer (m1) among the monomer components constituting the acrylic polymer. m1 The Tg and glass transition temperature Tg of the homopolymer of each aromatic ring-containing monomer used as the monomer (m1) can be calculated by applying the Fox formula described below to only the monomer (m1) among the monomer components constituting the acrylic polymer, and from the weight fraction of each aromatic ring-containing monomer in the total amount of the monomer (m1). In an embodiment in which only one type of monomer is used as the monomer (m1), the Tg and glass transition temperature Tg of the homopolymer of that monomer can be calculated. m1 is consistent with

[0091] In some embodiments, the aromatic ring-containing monomer (m1) can be a combination of monomer L (i.e., an aromatic ring-containing monomer 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, even more preferably -20°C or less, for example -25°C or less) and monomer H having a Tg higher than 10°C. The Tg of monomer H may be, for example, above 10°C, above 15°C, or above 20°C. By using monomer L and monomer H in combination, for example, in a configuration in which the content of aromatic ring-containing monomer (m1) in the monomer components is relatively high, it is possible to achieve a high refractive index and flexibility of the adhesive at a higher level. The ratio of the amounts of monomer L and monomer H used can be set so as to suitably exhibit such effects and is not particularly limited. For example, the Tg of any of the above-mentioned monomers having a glass transition temperature Tg m1 It is preferable to set the ratio of the amounts of the monomers L and H used so as to satisfy the following.

[0092] 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 composition in which the content of a compound containing a structure in which two or more non-fused aromatic rings are directly chemically bonded is less than 5 wt % (more preferably less than 3 wt %, and may even be 0 wt %) is preferred. Limiting the amount of the compound containing a structure in which two or more non-fused aromatic rings are directly chemically bonded in this way can be advantageous from the perspective of realizing a pressure-sensitive adhesive that balances flexibility, adhesiveness, and a high refractive index.

[0093] (Monomer (m2)) In some embodiments of the technology disclosed herein, the monomer components constituting the acrylic polymer may further contain a monomer (m2) in addition to the monomer (m1). The monomer (m2) is at least one of a monomer having a hydroxyl group (hydroxyl group-containing monomer) and a monomer having a carboxyl group (carboxyl group-containing monomer). The hydroxyl group-containing monomer is a compound having at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule. The carboxyl group-containing monomer is a compound having at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. The monomer (m2) can be useful for introducing crosslinking points into the acrylic polymer or imparting appropriate cohesiveness to the PSA. The monomer (m2) can be used alone or in combination of two or more types. The monomer (m2) is typically a monomer that does not contain an aromatic ring.

[0094] Examples of the ethylenically unsaturated group contained in the monomer (m2) include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. From the viewpoint of polymerization reactivity, a (meth)acryloyl group is preferred, and from the viewpoints of flexibility and adhesiveness, an acryloyl group is more preferred. From the viewpoint of suppressing a decrease in the flexibility of the adhesive, a compound containing one ethylenically unsaturated group per molecule (i.e., a monofunctional monomer) is preferably used as the monomer (m2).

[0095] Examples of hydroxyl group-containing monomers include, but are not limited to, 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. Preferred examples of hydroxyl group-containing monomers include 4-hydroxybutyl acrylate (Tg: −40° C.) and 2-hydroxyethyl acrylate (Tg: −15° C.). From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate, which has a lower Tg, is more preferred. In a preferred embodiment, 50% by weight or more (e.g., more than 50% by weight, more than 70% by weight, or more than 85% by weight) of the monomer (m2) may be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomers can be used alone or in combination of two or more.

[0096] In some embodiments in which a hydroxyl group-containing monomer is used as the monomer (m2), the hydroxyl group-containing monomer may be one or more selected from compounds not containing a methacryloyl group. Suitable examples of hydroxyl group-containing monomers not containing a methacryloyl group include the various hydroxyalkyl acrylates described above. For example, it is preferred that more than 50 wt%, more than 70 wt%, or more than 85 wt% of the hydroxyl group-containing monomers used as the monomer (m2) are hydroxyalkyl acrylates. The use of hydroxyalkyl acrylates allows the introduction of hydroxy groups into the acrylic polymer, which are useful for providing crosslinking points and imparting appropriate cohesion, and also makes it easier to obtain a PSA with good flexibility and adhesion at room temperature compared to using only the corresponding hydroxyalkyl methacrylate.

[0097] Examples of carboxyl group-containing monomers include, but are not limited to, acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, as well as itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Preferred examples of carboxyl group-containing monomers include acrylic acid and methacrylic acid. The carboxyl group-containing monomers may be used alone or in combination of two or more. Hydroxyl group-containing monomers and carboxyl group-containing monomers may be used in combination.

[0098] The content of monomer (m2) in the monomer components constituting the acrylic polymer is not particularly limited and can be set according to the purpose. In some embodiments, the content of the 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 usage effect, in some embodiments, the content of the monomer (A2) is preferably 1% by weight or more, or may be 2% by weight or more, or may be 4% by weight or more. The upper limit of the content of monomer (m2) in the monomer components is set so that the total content of the monomer (m2) and other monomers does not exceed 100% by weight. In some embodiments, the content of the monomer (m2) is suitably, for example, 30% by weight or less or 25% by weight or less. From the viewpoint of relatively increasing the content of monomer (m1) to facilitate a high refractive index, the content is preferably 20% by weight or less, more preferably 15% by weight or less, and may be less than 12% by weight, 10% by weight, or 7% by weight.

[0099] In embodiments in which a hydroxyl-containing monomer is used as monomer (m2), the content of the hydroxyl-containing monomer in the monomer component is not particularly limited and can be, for example, 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 is preferably 1% by weight or more of the monomer component, and may be 2% by weight or more, or even 4% by weight or more. The upper limit of the content of the hydroxyl-containing monomer in the monomer component is set so that the total content of other monomers does not exceed 100% by weight, and is suitably, for example, 30% by weight or less or 25% by weight or less. From the viewpoint of relatively increasing the content of monomer (m1) to facilitate a high refractive index, the upper limit is preferably 20% by weight or less, more preferably 15% by weight or less, and may be less than 12% by weight, 10% by weight or less, or even less than 7% by weight.

[0100] In embodiments using a carboxyl group-containing monomer as monomer (m2), the content of the carboxyl group-containing monomer in the monomer component is not particularly limited and can be, for example, 0.01 wt% or more (preferably 0.1 wt% or more, more preferably 0.3 wt% or more). In some embodiments, the content of the carboxyl group-containing monomer may be 1 wt% or more, 2 wt% or more, or even 4 wt% or more. The upper limit of the content of the carboxyl group-containing monomer in the monomer component is set so that the total amount of the carboxyl group-containing monomer and the amount of other monomers used does not exceed 100 wt%, and is suitably, for example, 30 wt% or less or 25 wt% or less. From the viewpoint of facilitating a high refractive index by relatively increasing the content of monomer (m1), the upper limit is preferably 20 wt% or less, more preferably 15 wt% or less, and may be less than 12 wt% or less than 10 wt%. In some embodiments, from the viewpoint of improving the flexibility of the PSA, the content of the carboxyl group-containing monomer is advantageously less than 7 wt%, preferably less than 5 wt%, or may be less than 3 wt%, less than 1 wt%, or may be less than 0.5 wt%. The technology disclosed herein can be preferably practiced, for example, in an embodiment in which only a hydroxyl group-containing monomer is used as the monomer (m2), i.e., an embodiment in which no carboxyl group-containing monomer is used.

[0101] The total content of monomer (m1) and monomer (m2) in the monomer components constituting the acrylic polymer may be, for example, 31% by weight or more, preferably 51% by weight or more, or 61% by weight or more, or 71% by weight or more. In some embodiments, the total content of monomer (m1) and monomer (m2) in the monomer components constituting the acrylic polymer may be, for example, 76% by weight or more, preferably 81% by weight or more, or 86% by weight or more, or 91% by weight or more, or 96% by weight or more, or 99% by weight or more, or even substantially 100% by weight, in order to facilitate the effects of these monomers to be favorably exhibited.

[0102] (monomer m3) The monomer components constituting the acrylic polymer may contain, as necessary, monomers other than the above-mentioned monomers (m1) and (m2). An example of such an optional component is alkyl(meth)acrylate (hereinafter also referred to as "monomer (m3)"). Monomer (m3) can be useful for adjusting the flexibility of the PSA and improving compatibility within the PSA.

[0103] The monomer (m3) may be a monomer having 1 to 20 carbon atoms (i.e., C 1-20 Alkyl (meth)acrylates having a linear or branched alkyl group at the ester terminal are preferably used. 1-20 Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate. , 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, and the like, but are not limited to these.

[0104] In some embodiments, an alkyl(meth)acrylate having a homopolymer Tg of −20° C. or lower (more preferably −40° C. or lower, e.g., −50° C. or lower) can be preferably used as at least a portion of the monomer (m3). Such an alkyl(meth)acrylate with a low Tg can be useful for improving the flexibility of the PSA. The lower limit of the Tg of the alkyl(meth)acrylate is not particularly limited, and may be, for example, −85° C. or higher, −75° C. or higher, −65° C. or higher, or −60° C. or higher. Specific examples of the low Tg alkyl(meth)acrylate include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), isononyl acrylate (iNA), and the like.

[0105] In some embodiments using the monomer (m3), from the viewpoint of flexibility, adhesiveness, etc., it is preferable that at least a portion of the monomer (m3) is an alkyl acrylate. For example, it is preferable 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) is an alkyl acrylate. It is also possible to use only one or more alkyl acrylates as the monomer (m3), without using any alkyl methacrylates.

[0106] In embodiments in which the monomer component includes an alkyl (meth)acrylate, the content of the alkyl (meth)acrylate in the monomer component can be set so as to appropriately achieve the intended effect. In some embodiments, the content of the alkyl (meth)acrylate may 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 alkyl (meth)acrylate may be, for example, 15% by weight or more, 30% by weight or more, or 45% by weight or more. The upper limit of the content of the monomer (m3) in the monomer component is set so that the total content together with the content of other monomers does not exceed 100% by weight, and may be, for example, less than 50% by weight. In some embodiments, the content of the monomer (m3) may be, for example, less than 35% by weight. Since alkyl (meth)acrylates generally have a relatively low refractive index, in order to increase the refractive index, it is advantageous to limit the content of the monomer (m3) in the monomer component and relatively increase the content of the monomer (m1). From this viewpoint, the content of the 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 may 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. The monomer (m3) may not be used substantially.

[0107] (Other monomers) The monomer components constituting the acrylic polymer may contain, as necessary, monomers other than the above-mentioned monomers (m1), (m2), and (m3) (hereinafter referred to as "other monomers"). The above-mentioned other monomers can be used for purposes such as adjusting the Tg of the acrylic polymer, adjusting the adhesive performance, and improving compatibility within the adhesive layer. The above-mentioned other monomers can be used alone or in combination of two or more.

[0108] Examples of the other monomers include monomers having functional groups other than hydroxyl groups and carboxyl groups (functional group-containing monomers). For example, examples of other monomers that can improve the cohesive strength and heat resistance of the adhesive include sulfonic acid group-containing monomers, phosphate group-containing monomers, and cyano group-containing monomers. Furthermore, examples of monomers that can introduce functional groups that can serve as crosslinking base points into acrylic polymers or that can contribute to improving peel strength and compatibility within the adhesive layer include amide group-containing monomers (e.g., (meth)acrylamide, N-methylol(meth)acrylamide, etc.), amino group-containing monomers (e.g., aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, etc.), monomers having nitrogen atom-containing rings (e.g., N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), imide group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, isocyanate group-containing monomers, and alkoxysilyl group-containing monomers. Incidentally, some of the monomers having a nitrogen atom-containing ring, such as N-vinyl-2-pyrrolidone, also fall under the category of amide group-containing monomers. The same applies to the relationship between the above-mentioned monomers having a nitrogen atom-containing ring and amino group-containing monomers.

[0109] Examples of other monomers that can be used in addition to the functional group-containing monomers 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 group-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether; etc. One 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, Tg of homopolymer: -67°C).

[0110] When the other monomers are used, their amount is not particularly limited and can be appropriately set within a range in which the total amount of the monomer components does not exceed 100% by weight. In some embodiments, from the viewpoint of easily achieving the refractive index-enhancing effect of the use of the monomer (m1), the content of the other monomers in the monomer components can be, for example, about 35% by weight or less, suitably about 25% by weight or less (e.g., 0 to 25% by weight), or may be about 20% by weight or less (e.g., 0 to 20% by weight), about 10% by weight or less, about 5% by weight or less, or, for example, about 1% by weight or less. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer components are substantially free of the other monomers.

[0111] In some embodiments, the monomer components constituting the acrylic polymer may be a composition in which the amount of methacryloyl group-containing monomer used is suppressed to a predetermined level or less. The amount of methacryloyl group-containing monomer used in the monomer components may be, for example, less than 5 wt %, less than 3 wt %, less than 1 wt %, or less than 0.5 wt %. Limiting the amount of methacryloyl group-containing monomer used in this manner may be advantageous from the perspective of realizing a pressure-sensitive adhesive that has a good balance between flexibility, adhesiveness, and a high refractive index. The monomer components constituting the acrylic polymer may be a composition that does not contain a methacryloyl group-containing monomer (for example, a composition consisting only of an acryloyl group-containing monomer).

[0112] In some embodiments, the monomer component constituting the base polymer (e.g., an acrylic polymer) of the viscoelastic layer V1 preferably contains a limited amount of carboxyl group-containing monomer to prevent coloration or discoloration (e.g., yellowing) of the viscoelastic layer V1. The amount of carboxyl group-containing monomer in the monomer component may be, for example, less than 1 wt %, preferably less than 0.5 wt %, more preferably less than 0.3 wt %, even less than 0.1 wt %, or even less than 0.05 wt %. Such a limited amount of carboxyl group-containing monomer is advantageous in preventing corrosion of metal materials that may be in contact with or adjacent to the viscoelastic layer V1 (e.g., metal wiring or metal films that may be present on an adherend). The interlayer sheet disclosed herein is preferably implemented in an embodiment in which the monomer component does not contain a carboxyl group-containing monomer. For the same reason, in some embodiments, the monomer components constituting the base polymer of the viscoelastic layer V1 preferably contain a limited amount of monomers having acidic functional groups (including carboxy groups, sulfonic acid groups, phosphate groups, etc.). The amount of the acidic functional group-containing monomer in the monomer components of such embodiments can be the same as the preferred amount of the carboxy group-containing monomer described above. The interlayer sheet disclosed herein can be preferably implemented in an embodiment in which the monomer components do not contain acidic group-containing monomers (i.e., an embodiment in which the base polymer of the viscoelastic layer V1 is acid-free).

[0113] (Base polymer glass transition temperature Tg T ) In some embodiments, the base polymer of the pressure-sensitive adhesive layer (e.g., an acrylic polymer) has a glass transition temperature Tg T The glass transition temperature Tg is suitably about 20°C or less, preferably about 10°C or less, more preferably 0°C or less, and may be -10°C or less, -20°C or less, -25°C or less, -28°C or less, or -30°C or less. TA low glass transition temperature Tg T may be, for example, -60°C or higher, and from the viewpoint of facilitating the high refractive index of the pressure-sensitive adhesive, is preferably -50°C or higher, more preferably higher than -45°C, may be higher than -40°C, may be higher than -35°C, may be higher than -25°C, may be -15°C or higher, or may be -5°C or higher.

[0114] Here, the glass transition temperature Tg of the polymer T Unless otherwise specified, the glass transition temperature (Tg) refers to the glass transition temperature calculated by the Fox equation based on the composition of the monomer components constituting the polymer. The Fox equation, as shown below, is a relational expression between the Tg of a copolymer and the glass transition temperature (Tgi) of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer. 1 / Tg=Σ(Wi / Tgi) In the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio by weight), and Tgi represents the glass transition temperature (unit: K) of the homopolymer of monomer i. The glass transition temperature of a homopolymer used to calculate Tg is the value described in publicly available sources such as "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). For monomers for which multiple values ​​are described in the Polymer Handbook, the highest value is used. If the Tg of a homopolymer is not described in publicly available sources, the value obtained by the measurement method described in JP 2007-51271 A is used.

[0115] (Method for preparing base polymer) In the technology disclosed herein, the method for obtaining the base polymer of the pressure-sensitive adhesive layer (for example, the acrylic polymer (A) composed of the above-mentioned monomer components) is not particularly limited, and known polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization can be appropriately used. In some embodiments, solution polymerization can be preferably used. The polymerization temperature during solution polymerization can be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, etc., and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0116] The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one solvent or a mixture of two or more solvents selected from aromatic compounds (typically aromatic hydrocarbons) such as toluene, acetate esters such as ethyl acetate, aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane, halogenated alkanes such as 1,2-dichloroethane, lower alcohols (for example, monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol, ethers such as tert-butyl methyl ether, and ketones such as methyl ethyl ketone can be used.

[0117] The initiator used for 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; and aromatic carbonyl compounds. Still other examples of polymerization initiators include redox-based initiators formed by combining a peroxide with a reducing agent. One polymerization initiator can be used alone, or two or more polymerization initiators can be used in combination. The amount of polymerization initiator used may be a typical amount, and can be selected, for example, from the range of approximately 0.005 to 1 part by weight (typically approximately 0.01 to 1 part by weight) per 100 parts by weight of the monomer components.

[0118] In the polymerization, various conventionally known chain transfer agents can be used as needed. For example, mercaptans such as n-dodecyl mercaptan, t-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 be used. Examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinolene; and styrenes such as α-methylstyrene and α-methylstyrene dimer. The chain transfer agents can be used alone or in combination of two or more. When a chain transfer agent is used, the amount used can be, for example, about 0.01 to 1 part by weight per 100 parts by weight of the monomer raw material.

[0119] The weight average molecular weight (Mw) of the base polymer is not particularly limited, and is, for example, about 10 × 10 4 ~500×10 4 From the viewpoint of adhesive performance, the Mw of the base polymer can be in the range of approximately 20×10 4 ~400×10 4 (More preferably, approximately 30×10 4 ~150×10 4 , for example, approximately 50×10 4 ~130×10 4 ) range is preferred.

[0120] Here, the Mw of the polymer can be determined in terms of polystyrene by gel permeation chromatography (GPC). Specifically, it can be determined by measuring under the following conditions using a GPC measuring device "HLC-8220GPC" (manufactured by Tosoh Corporation). [GPC measurement conditions] Sample concentration: 0.2 wt% (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40°C column: Sample column: 1 "TSKguardcolumn SuperHZ-H" + 2 "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: 1 tube of "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: polystyrene

[0121] (Refractive index enhancer) In some embodiments of the technology disclosed herein, the pressure-sensitive adhesive layer V1 (e.g., an acrylic pressure-sensitive adhesive layer) may contain a refractive index enhancer, if necessary, in addition to the base polymer. Herein, the term "refractive index enhancer" refers to a material that can increase the refractive index of the pressure-sensitive adhesive layer when used. A material having a higher refractive index than the pressure-sensitive adhesive layer containing the refractive index enhancer is preferably used as the refractive index enhancer. Furthermore, a material having a higher refractive index than the base polymer (e.g., acrylic polymer (A)) of the pressure-sensitive adhesive layer containing the refractive index enhancer is preferably used as the refractive index enhancer. Appropriate use of the refractive index enhancer can favorably achieve both a higher refractive index and practical adhesive performance. In some embodiments, the refractive index enhancer is preferably an organic material. The organic material used as the refractive index enhancer may be a polymer or a non-polymer. It may or may not have a polymerizable functional group. The refractive index enhancers may be used alone or in combination of two or more.

[0122] Refractive index improver (e.g., additive (H ROThe refractive index of the refractive index enhancer is not limited to a specific range and can be set within an appropriate range relative to the refractive index of the base polymer. The refractive index of the refractive index enhancer can be selected from a range of, for example, greater than 1.55, greater than 1.56, or greater than 1.57, and higher than the refractive index of the base polymer. From the viewpoint of increasing the refractive index of the adhesive, in some embodiments, the refractive index of the refractive index enhancer is advantageously 1.58 or higher, preferably 1.60 or higher, more preferably 1.63 or higher, and may be 1.65 or higher, 1.70 or higher, or 1.75 or higher. A refractive index enhancer with a higher refractive index can achieve the desired refractive index even with the use of a smaller amount of the refractive index enhancer. This is preferable from the viewpoint of suppressing deterioration of adhesive properties and optical properties. The upper limit of the refractive index of the refractive index enhancer is not particularly limited, but from the viewpoint of compatibility within the adhesive and ease of achieving both a high refractive index and flexibility suitable for the adhesive, it is, for example, 3.000 or less, or alternatively 2.500 or less, 2.000 or less, 1.950 or less, 1.900 or less, or 1.850 or less.

[0123] In some embodiments, a refractive index enhancer (e.g., an additive (H RO )) refractive index n b and the refractive index of the base polymer, n a The difference between b -n a (Hereinafter referred to as “Δn A "). ) is set to be greater than 0. In some embodiments, Δn A is, for example, 0.02 or more, and may be 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 By selecting a base polymer and a refractive index enhancer so that Δn is larger, the refractive index enhancing effect by using the refractive index enhancer tends to be higher. Also, from the viewpoint of compatibility in the pressure-sensitive adhesive layer, transparency of the pressure-sensitive adhesive layer, etc., in some embodiments, A may be, for example, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

[0124] In some embodiments, a refractive index enhancer (e.g., an additive (H RO )) refractive index n b and the refractive index n of the pressure-sensitive adhesive layer containing the refractive index enhancer T The difference between b -n T (Hereinafter referred to as “Δn B "). ) is set to be greater than 0. In some embodiments, Δn B is, for example, 0.02 or more, and may be 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 By selecting the composition of the pressure-sensitive adhesive layer and the refractive index enhancer so that Δn B may be, for example, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

[0125] The amount of refractive index enhancer used per 100 parts by weight of base polymer (when multiple types of refractive index enhancers are used, the total amount) is not particularly limited and can be set according to the purpose. From the viewpoint of increasing the refractive index of the adhesive, the amount of refractive index enhancer used per 100 parts by weight of base polymer can be, for example, 1 part by weight or more, advantageously 3 parts by weight or more, preferably 5 parts by weight or more, or may be 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or may be 20 parts by weight or more. In some embodiments, the amount of refractive index enhancer used per 100 parts by weight of base polymer can be, for example, 80 parts by weight or less, and from the viewpoint of achieving a good balance between increasing the refractive index of the adhesive and suppressing deterioration of adhesive properties and optical properties, it is advantageous to set it to 60 parts by weight or less, and preferably 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are more important, the amount of refractive index enhancer used per 100 parts by weight of 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 can also be preferably implemented in an embodiment where the amount of refractive index enhancer used per 100 parts by weight of base polymer in the adhesive layer is less than 1 part by weight, or where substantially no refractive index enhancer is used. Here, "substantially not used" means that the refractive index enhancer is not used, at least intentionally.

[0126] (Additives (H RO )) In some embodiments, an organic material having a higher refractive index than the base polymer may be preferably used as the refractive index improver. Hereinafter, such an organic material will be referred to as an "additive (H RO )" where the above "H RO " indicates that the material is an organic material with a high refractive index. The base polymer (e.g., an acrylic polymer, preferably an acrylic polymer (A)) and the additive (H ROBy using the additive (H) in combination, it is possible to realize a pressure-sensitive adhesive that more suitably balances the refractive index with adhesive properties (peel strength, flexibility, etc.) and / or optical properties (total light transmittance, haze value, etc.). RO The organic material used as the additive (H) may be a polymer or a non-polymer. It may or may not have a polymerizable functional group. RO ) can be used alone or in combination of two or more.

[0127] Additives (H RO The refractive index of the polymer is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C, just like the refractive index of the monomer. If the manufacturer provides a nominal value for the refractive index at 25°C, that nominal value can be used.

[0128] Additives (H RO The molecular weight of the organic material used as the additive (H) is not particularly limited and can be selected depending on the purpose. RO The molecular weight of the additive (H) can be selected, for example, from the range of 30,000 or less. RO ) is preferably a polymer or non-polymer having a lower molecular weight than the base polymer. From the viewpoint of achieving a good balance between the effect of increasing the refractive index and other properties (for example, optical properties such as flexibility and haze suitable for adhesives), in some embodiments, the additive (H RO The molecular weight of the additive (H) is suitably less than about 10,000, preferably less than 5,000, more preferably less than 3,000 (for example, less than 1,000), and may be less than 800, less than 600, less than 500, or less than 400. RO It is advantageous from the viewpoint of improving compatibility in the adhesive layer that the molecular weight of the additive (H) is not too large. RO The molecular weight of the additive (H) may be, for example, 130 or more, or 150 or more. RO ) is the molecular weight of the additive (H ROFrom the viewpoint of increasing the refractive index of the polymer, the molecular weight is preferably 170 or more, more preferably 200 or more, and may be 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 (for example, 1000 or more but less than 5000) is mixed with an additive (H RO ) can be used as Additives (H RO Regarding the molecular weight of the additive (H), for non-polymers or polymers with a low degree of polymerization (e.g., dimers to pentamers), the molecular weight calculated based on the chemical structure or the measured value using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS) can be used. RO If the polymer has a higher degree of polymerization, the weight average molecular weight (Mw) based on GPC performed under appropriate conditions can be used. If the manufacturer provides a nominal value for the molecular weight, that nominal value can be used.

[0129] Additives (H RO Examples of organic materials that can be selected for the organic compound include, but are not limited to, organic compounds having aromatic rings, organic compounds having heterocycles (which may be aromatic or non-aromatic heterocycles), and the like.

[0130] Additives (H RO The aromatic ring contained in the organic compound having an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") used as the monomer (m1) can be selected from the same aromatic rings contained in the compound used as the monomer (m2).

[0131] The aromatic ring may have one or more substituents on the ring-constituting atoms, or may have no substituents. When the aromatic ring has a substituent, examples of the substituent include, but are not limited to, an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (such as a fluorine atom, a chlorine atom, or a bromine atom), a hydroxyalkyl group, a hydroxyalkyloxy group, and a glycidyloxy group. In the case of a carbon atom-containing substituent, the number of carbon atoms contained in the substituent is, for example, 1 to 10, advantageously 1 to 6, preferably 1 to 4, and more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the aromatic ring may have no substituents on the ring-constituting atoms, or may have one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (such as a bromine atom).

[0132] Additives (H RO Examples of aromatic ring-containing compounds that can be used as the additive (H) include, but are not limited to, compounds that can be used as the monomer (m1); oligomers that contain, as a monomer unit, compounds that can be used as the monomer (m1); compounds in which, from a compound that can be used as the monomer (m1), a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring-constituting atom) or a portion of the group that constitutes an ethylenically unsaturated group is replaced with a hydrogen atom or a group that does not have an ethylenically unsaturated group (for example, a hydroxyl group, an amino group, a halogen atom, an alkyl group, an alkoxy group, a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group, etc.). RO), aromatic ring-containing monomers such as benzyl acrylate, m-phenoxybenzyl acrylate, 2-(o-phenylphenoxy)ethyl acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxypolyethylene glycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, the above-mentioned monomers having a fluorene structure, monomers having a dinaphthothiophene structure, and monomers having a dibenzothiophene structure; aromatic ring-containing compounds not having an ethylenically unsaturated group, such as 3-phenoxybenzyl alcohol, dinaphthothiophene and derivatives thereof (for example, compounds having a structure in which one or more substituents selected from hydroxyl groups, methanol groups, diethanol groups, glycidyl groups, etc. are bonded to a dinaphthothiophene ring); and the like. The aromatic ring-containing compound may also be an oligomer (preferably an oligomer having a molecular weight of about 5,000 or less, more preferably about 1,000 or less, for example, a low polymer of about 2 to 5) 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 with another monomer; or the like. As the other monomer, one or more monomers not having an aromatic ring may be used.

[0133] In some embodiments, the additive (H ROAs the compound (a), an organic compound having two or more aromatic rings in one molecule (hereinafter also referred to as a "multiple aromatic ring-containing compound") can be preferably used because it is easy to obtain a high refractive index effect. The multiple aromatic ring-containing compound may or may not have a polymerizable functional group such as an ethylenically unsaturated group. The multiple aromatic ring-containing compound may be a polymer or a non-polymer. The polymer may be an oligomer containing a multiple aromatic ring-containing monomer as a monomer unit (preferably an oligomer having a molecular weight of approximately 5,000 or less, more preferably approximately 1,000 or less, for example, a low polymer of about 2 to 5). The oligomer may be, for example: a homopolymer of a multiple aromatic ring-containing monomer; a copolymer of one or more multiple aromatic ring-containing monomers; a copolymer of one or more multiple aromatic ring-containing monomers with another monomer; or the like. The other monomer may be an aromatic ring-containing monomer that does not fall under the category of multiple aromatic ring-containing monomer, a monomer not having an aromatic ring, or a combination thereof.

[0134] 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, compounds having a dibenzothiophene structure, etc. The compounds containing multiple aromatic rings can be used alone or in combination of two or more.

[0135] Specific examples of the compound having the fluorene structure include the above-mentioned monomers having the fluorene structure, oligomers which are homopolymers or copolymers of such monomers, as well as 9,9-bisphenylfluorene and derivatives thereof, such as 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), and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (refractive index: 1.65).

[0136] Specific examples of the compound having the dinaphthothiophene structure include the above-mentioned monomers having the dinaphthothiophene structure, oligomers which are homopolymers or copolymers of such monomers, as well as hydroxyalkyldinaphthothiophenes such as dinaphthothiophene (refractive index: 1.808); 6-hydroxymethyldinaphthothiophene (refractive index: 1.766); dihydroxydinaphthothiophenes such as 2,12-dihydroxydinaphthothiophene (refractive index: 1.750); 2,12- Examples of such dinaphthothiophenes include dihydroxyalkyloxydinaphthothiophenes such as dihydroxyethyloxydinaphthothiophene (refractive index: 1.677); diglycidyloxydinaphthothiophenes such as 2,12-diglycidyloxydinaphthothiophene (refractive index: 1.723); and dinaphthothiophenes having two or more ethylenically unsaturated groups such as 2,12-diallyloxydinaphthothiophene (abbreviation: 2,12-DAODNT, refractive index: 1.729), and derivatives thereof.

[0137] Specific examples of the compound having the dibenzothiophene structure include the above-mentioned monomers having the dibenzothiophene structure, oligomers which are homopolymers or copolymers of such monomers, as well as dibenzothiophene (refractive index: 1.607), 4-dimethyldibenzothiophene (refractive index: 1.617), 4,6-dimethyldibenzothiophene (refractive index: 1.617), and the like.

[0138] Additives (H ROExamples of organic compounds having a heterocycle (hereinafter also referred to as heterocycle-containing organic compounds) that can be selected as the heterocycle-containing organic compound include thioepoxy compounds and compounds having a triazine ring. Examples of thioepoxy compounds include bis(2,3-epithiopropyl) disulfide and its polymer (refractive index: 1.74) described in Japanese Patent No. 3712653. Examples of compounds having a triazine ring include compounds having at least one triazine ring (e.g., 3 to 40, preferably 5 to 20) in one molecule. Note that, since the triazine ring is aromatic, compounds having a triazine ring are also included in the concept of the aromatic ring-containing compound, and compounds having multiple triazine rings are also included in the concept of the multiple aromatic ring-containing compound.

[0139] In some embodiments, the additive (H RO As the additive (H) having no ethylenically unsaturated group, a compound having no ethylenically unsaturated group can be preferably used. This can suppress deterioration of the pressure-sensitive adhesive composition due to heat or light (progression of gelation or decrease in leveling ability due to increase in viscosity) and improve storage stability. RO ) is used to RO In a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the ethylenically unsaturated group, or in a laminate including the pressure-sensitive adhesive sheet, it is also preferable from the viewpoint of suppressing dimensional changes and deformations (warping, waviness, etc.), optical distortion, etc., which are caused by the reaction of the ethylenically unsaturated group.

[0140] Additives (H RO In an embodiment in which an oligomer is used as the copolymerization initiator, the oligomer can be obtained by polymerizing the corresponding monomer components by a known method. When the oligomer is produced by radical polymerization, a polymerization initiator, a chain transfer agent, an emulsifier, etc. used in radical polymerization can be appropriately added to the monomer components to carry out polymerization. The polymerization initiator, chain transfer agent, emulsifier, etc. used in the radical polymerization are not particularly limited and can be appropriately selected and used. The weight-average molecular weight of the oligomer can be controlled by the amount of polymerization initiator and chain transfer agent used and the reaction conditions, and the amount used is appropriately adjusted depending on the type of these. Examples of the chain transfer agent include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, α-thioglycerol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. The chain transfer agent may be used alone or in combination of two or more. The amount of chain transfer agent used can be determined depending on the composition of the monomer components used in the synthesis of the oligomer, the type of chain transfer agent, and the like, so as to obtain an oligomer having a desired weight-average molecular weight. In some embodiments, the amount of chain transfer agent used per 100 parts by weight of the total amount of monomers used in the synthesis of the oligomer is suitably approximately 15 parts by weight or less, and may be 10 parts by weight or less, or even about 5 parts by weight or less. The lower limit of the amount of chain transfer agent used relative to 100 parts by weight of the total amount of monomers used in synthesizing the oligomer is not particularly limited, but 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.

[0141] Additives (H RO In the embodiment using the additive (H RO The amount of additive (H) used (when a plurality of compounds are used, the total amount thereof) is not particularly limited and can be set according to the purpose. From the viewpoint of increasing the refractive index of the adhesive, the amount of additive (H) used relative to 100 parts by weight of the base polymer is RO The amount of additive (H) used can be, for example, 1 part by weight or more, advantageously 3 parts by weight or more, preferably 5 parts by weight or more, even 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or even 20 parts by weight or more. In some embodiments, the amount of additive (H) used per 100 parts by weight of the base polymer is 1 part by weight or more. RO The amount of additive (H) used can be, for example, 80 parts by weight or less, and from the viewpoint of achieving a good balance between increasing the refractive index of the adhesive and suppressing deterioration of adhesive properties and optical properties, it is advantageous to set it to 60 parts by weight or less, and preferably to set it to 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are more important, the amount of additive (H) used relative to 100 parts by weight of the base polymer isRO The amount of ) used may be, 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.

[0142] (Plasticized material) In some embodiments of the interlayer sheet disclosed herein, the pressure-sensitive adhesive layer V1 may contain, in addition to the base polymer (e.g., acrylic polymer (A)) as described above, a plasticizing material having a lower molecular weight than the base polymer. The use of a plasticizing material can increase the flexibility of the pressure-sensitive adhesive layer V1, improving adhesion to the adherend and the flexibility and adaptability to deformation of the interlayer sheet as a whole. From the viewpoint of compatibility and transparency within the pressure-sensitive adhesive layer, organic materials can be preferably used as the plasticizing material. The plasticizing material may be the refractive index improver described above (e.g., the above-mentioned additive (H RO )) may also be a material that can be used as a

[0143] The molecular weight of the plasticizing material is not particularly limited as long as it is lower than that of the base polymer. In some embodiments, the molecular weight of the plasticizing material may be 30,000 or less, 25,000 or less, less than 10,000, preferably less than 5,000, more preferably less than 3,000 (e.g., less than 1,000), less than 800, less than 600, less than 500, or less than 400, from the viewpoint of easily exerting the plasticizing effect. A molecular weight of the plasticizing material that is not too large can be advantageous from the viewpoint of improving compatibility within the adhesive layer. In some embodiments, the molecular weight of the plasticizing material is suitably 130 or more, preferably 150 or more, 170 or more, 200 or more, 250 or more, or 300 or more, from the viewpoint of easily exerting a sufficient plasticizing effect. In some embodiments, the molecular weight of the plasticizing material may be 500 or more, 1,000 or more, or 2,000 or more. It is preferable that the molecular weight of the plasticizing material is not too low from the viewpoint of the heat resistance of the interlayer sheet and the prevention of contamination of the adherend.

[0144] Non-limiting examples of compounds that can be selected as plasticizing materials 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, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, a monomer having a dibenzothiophene structure, etc.); oligomers containing a compound that can be used as monomer (m1) as a monomer unit; and compounds in which the portion having an ethylenically unsaturated group in a compound that can be used as monomer (m1) has been removed and replaced with a hydrogen atom or a group not having an ethylenically unsaturated group (e.g., 3-phenoxybenzyl alcohol). To improve flexibility, oligomers containing a compound that can be used as monomer (m1) as a monomer unit may be copolymerized with a low Tg monomer such as n-butyl acrylate or 2-ethylhexyl acrylate. As the plasticizing material, one or more of known plasticizers (for example, phthalate esters, terephthalate esters, adipate esters, adipic acid polyesters, benzoic acid glycol esters, etc.) may be used.

[0145] In some embodiments, the plasticizing material may preferably be an organic material having a refractive index of about 1.50 or more (more preferably 1.53 or more). Specific examples of compounds that may be selected as the plasticizing material 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) Examples of suitable plasticizers include, but are not limited to, phenyl diphenyl phosphate (refractive index 1.56), trimethyl phenyl phosphate (refractive index 1.55), butyl benzyl phthalate (refractive index 1.54), rosin methyl ester (refractive index 1.53), alkyl benzyl phthalate (refractive index 1.53), butyl(phenylsulfonyl)amine (refractive index 1.53), trimethyl trimellitate (refractive index 1.52), benzyl phthalate (refractive index 1.52), 2-ethylhexyl diphenyl phosphate (refractive index 1.51), and tris(2,4-di-tert-butylphenyl) phosphite. From the standpoint of refractive index and compatibility, diethylene glycol dibenzoate is preferred. The upper limit of the refractive index of the plasticizer is not particularly limited and can be, for example, 3.00 or less. In some embodiments, from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition, compatibility within the pressure-sensitive adhesive, etc., the refractive index of the plasticizing material is suitably 2.50 or less, advantageously 2.00 or less, or may be 1.90 or less, 1.80 or less, or 1.70 or less. The refractive index of the plasticized material is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C, just like the refractive index of the monomer. If the manufacturer provides a nominal value for the refractive index at 25°C, that nominal value can be used.

[0146] In embodiments using a plasticizing material, the amount of plasticizing material used per 100 parts by weight of base polymer is not particularly limited and can be set according to the purpose. From the viewpoint of enhancing the plasticizing effect, the amount of plasticizing material used per 100 parts by weight of base polymer may be, for example, 0.1 parts by weight or more, or even 0.5 parts by weight or more. From the viewpoint of obtaining a higher plasticizing effect, it is preferably 1 part by weight or more, more preferably 3 parts by weight or more, or may be 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 even 20 parts by weight or more. Furthermore, from the viewpoint of achieving a good balance between increasing the refractive index of the adhesive and transparency and plasticizing effect, the amount of plasticizing material used per 100 parts by weight of base polymer is suitably approximately 100 parts by weight or less, preferably 80 parts by weight or less, more preferably 60 parts by weight or less, or may be 45 parts by weight or less, 35 parts by weight or less, or 25 parts by weight or less. In some embodiments where adhesive properties and optical properties are more important, the amount of plasticizing material used per 100 parts by weight of base polymer may be 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight or less.

[0147] (Leveling agent) In some embodiments, the PSA composition used to form the PSA layer (which may be the viscoelastic layer V1 and / or the viscoelastic layer V2) may contain a leveling agent as needed to improve the appearance of the PSA layer formed from the composition (e.g., to improve the uniformity of the thickness) or to improve the coatability of the PSA composition. Non-limiting examples of leveling agents include acrylic leveling agents, fluorine-based leveling agents, and silicone-based leveling agents. The leveling agent may be selected from commercially available leveling agents and used in the usual manner.

[0148] In some embodiments, the leveling agent can preferably be a polymer (hereinafter also referred to as "polymer (B)") that is a polymerization product of a monomer raw material (hereinafter also referred to as "monomer raw material B") containing a monomer having a polyorganosiloxane skeleton (hereinafter also referred to as "monomer S1") and an acrylic monomer. Polymer (B) can be said to be a copolymer of monomer S1 and an acrylic monomer. Polymer (B) can be used alone or in combination of two or more types.

[0149] Monomer S1 is not particularly limited, and any monomer containing a polyorganosiloxane skeleton can be used. Monomers having a structure with a polymerizable reactive group at one end can be preferably used as monomer S1. Among them, monomers S1 having a structure with a polymerizable reactive group at one end and no functional group at the other end that undergoes a crosslinking reaction with a base polymer (referring to the base polymer of the pressure-sensitive adhesive composition to which the leveling agent is blended, such as an acrylic polymer) can be preferably used. Commercially available products include, for example, single-end reactive silicone oils manufactured by Shin-Etsu Chemical Co., Ltd. (e.g., product numbers X-22-174ASX, X-22-2426, X-22-2475, KF-2012, etc.). Monomer S1 can be used alone or in combination of two or more types.

[0150] The functional group equivalent of the monomer S1 may be, for example, about 100 g / mol to 30,000 g / mol. In some preferred embodiments, the functional group equivalent is, for example, 500 g / mol or more, or may be 800 g / mol or more, 1,500 g / mol or more, or 2,000 g / mol or more. The functional group equivalent may 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 of the monomer S1 is within the above range, a good leveling effect is likely to be exhibited. When two or more types of monomers having different functional group equivalents are used as the monomer S1, the functional group equivalent of the monomer S1 can be the sum of the products of the functional group equivalents of each type of monomer and the weight fraction of the monomer.

[0151] Here, "functional group equivalent" means the weight of the main skeleton (e.g., polydimethylsiloxane) bonded to one functional group. The unit g / mol is calculated as 1 mol of functional group. The functional group equivalent of the monomer S1 can be calculated, for example, by nuclear magnetic resonance (NMR) analysis. 1 It can be calculated from the spectral intensity of H-NMR (proton NMR). 1 The functional group equivalent weight (g / mol) of monomer S1 was calculated based on the H-NMR spectrum intensity: 1 This can be done based on a general structural analysis method involving H-NMR spectrum analysis, and if necessary, by referring to the description in Japanese Patent No. 5951153. In the functional group equivalent of the monomer S1, the functional group refers to a polymerizable functional group (for example, an ethylenically unsaturated group such as a (meth)acryloyl group, a vinyl group, or an allyl group).

[0152] The content of monomer S1 in monomer raw material B is not limited to a specific range and can be any appropriate value within the range in which the desired effect is achieved using monomer S1. In some embodiments, the content of monomer S1 in monomer raw material B may be, for example, 5 to 60% by weight, 10 to 50% by weight, or 15 to 40% by weight.

[0153] In addition to the monomer S1, the monomer raw material B contains an acrylic monomer copolymerizable with the monomer S1. This can improve the compatibility of the polymer (B) in the pressure-sensitive adhesive layer. Examples of acrylic monomers that can be used for the monomer raw material B include alkyl acrylates. The term "alkyl" used here refers to a chain (including linear and branched) alkyl (group) and does not include the alicyclic hydrocarbon group described below. In some embodiments, the monomer raw material B contains (meth)acrylic acid C 4-12 Alkyl ester (preferably (meth)acrylic acid C4-10 Alkyl esters, such as (meth)acrylic acid C 6-10 In some other embodiments, the monomer feedstock B may contain at least one of methacrylic acid C 1-18 Alkyl ester (preferably methacrylic acid C 1-14 Alkyl esters, such as methacrylic acid C 1-10 Monomer raw material B may contain, as an acrylic monomer, one or more selected from the group consisting of methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA).

[0154] Other examples of the acrylic monomer include (meth)acrylic acid esters having an alicyclic hydrocarbon group. For example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, etc. can be used. It is not necessary to use a (meth)acrylic acid ester having an alicyclic hydrocarbon group.

[0155] The content of the (meth)acrylic acid alkyl ester and the (meth)acrylic acid ester having an alicyclic hydrocarbon group in the monomer raw material B may 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.

[0156] Other examples of monomers that can be contained in the monomer raw material B together with the monomer S1 include the carboxy 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, aminoalkyl (meth)acrylates, vinyl esters, vinyl ethers, olefins, (meth)acrylic acid esters having an aromatic hydrocarbon group, and halogen atom-containing (meth)acrylates, all of which are exemplified above as monomers that can be used in acrylic polymers.

[0157] The Mw of polymer (B) may be, for example, 5,000 or more, preferably 10,000 or more, or 15,000 or more. The Mw of polymer (B) may be, for example, 200,000 or less, preferably 100,000 or less, or 50,000 or less, or 30,000 or less. By setting the Mw of polymer (B) within an appropriate range, favorable compatibility and leveling properties can be exhibited.

[0158] The polymer (B) can be prepared, for example, by polymerizing the above-mentioned monomers by a known method such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, or photopolymerization. A chain transfer agent can be used as needed to adjust the molecular weight of polymer (B). Examples of the chain transfer agent include compounds having a mercapto group, such as t-dodecyl mercaptan, mercaptoethanol, and α-thioglycerol; thioglycolic acid esters, such as thioglycolic acid and methyl thioglycolate; and α-methylstyrene dimer. The amount of the chain transfer agent used is not particularly limited and can be appropriately determined so as to obtain polymer (B) having the desired molecular weight. In some embodiments, the amount of the chain transfer agent used relative to 100 parts by weight of the monomer may 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.

[0159] The amount of polymer (B) used relative to 100 parts by weight of base polymer (e.g., acrylic polymer) can be, for example, 0.001 parts by weight or more, and from the viewpoint of obtaining a higher effect of use, it may be 0.01 parts by weight or more, or may be 0.03 parts by weight or more. The amount of polymer (B) used may be, for example, 3 parts by weight or less, and from the viewpoint of reducing the influence on the refractive index, it is appropriate to set it to 1 part by weight or less, and it may be 0.5 parts by weight or less, or may be 0.1 parts by weight or less.

[0160] (Inorganic particles) The technology disclosed herein can be preferably implemented without substantially using inorganic particles as a refractive index enhancer. However, the use of inorganic particles as a refractive index enhancer is acceptable to the extent that it does not significantly impair the application effects of the technology disclosed herein. Examples of inorganic particles that can be used as a refractive index enhancer include inorganic particles composed of inorganic oxides (specifically, metal oxides) such as titania (titanium oxide, TiO), zirconia (zirconium oxide, ZrO), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, and niobium oxide (NbO, etc.). The average particle size (meaning the 50% volume average particle size determined by laser scattering and diffraction) of the inorganic particles can be selected, for example, from a range of approximately 10 nm to 100 nm. The refractive index of the inorganic particles is measured using a commercially available spectroscopic ellipsometer at a wavelength of 589 nm and a temperature of 23°C for a single layer film (with a film thickness that allows refractive index measurement) of the material constituting the inorganic particles. As the spectroscopic ellipsometer, for example, a product named "EC-400" (manufactured by J.A. Woolam) or an equivalent product can be used. When inorganic particles are used as a refractive index enhancer, the amount used is preferably less than 5 parts by weight, more preferably less than 1 part by weight, per 100 parts by weight of the base polymer. RO In the embodiment in which the inorganic particles are used, the amount of the inorganic particles used is, on a weight basis, RO ) is preferably used in an amount of not more than 2 times, more preferably not more than 1 time or not more than 0.5 times.

[0161] (Crosslinking agent) In the technology disclosed herein, the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer (which may be the viscoelastic layer V1 and / or the viscoelastic layer V2) may contain a crosslinking agent as needed for purposes such as adjusting the cohesive strength of the pressure-sensitive adhesive. Examples of crosslinking agents that can be used include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, melamine-based resins, and metal chelate-based crosslinking agents. Of these, isocyanate-based crosslinking agents are preferred. Other examples of crosslinking agents include monomers having two or more ethylenically unsaturated groups in one molecule, i.e., polyfunctional monomers. The crosslinking agents may be used alone or in combination of two or more.

[0162] As the isocyanate-based crosslinking agent, a bifunctional or higher isocyanate compound can be used, and examples thereof include 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-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate (XDI); and modified polyisocyanates obtained by modifying the above isocyanate compounds with an allophanate bond, biuret bond, isocyanurate bond, uretdione bond, urea bond, carbodiimide bond, uretonimine bond, oxadiazinetrione bond, or the like. Examples of commercially available products include Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, and Takenate D178N (all manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidur T80, Sumidur L, and 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 compounds can 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.

[0163] Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane. These may be used alone or in combination of two or more.

[0164] Examples of polyfunctional monomers 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, and 1,6-hexanediol di(meth)acrylate. acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, bisphenoxyethanol fluorene di(meth)acrylate, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butyldiol (meth)acrylate, hexyldiol di(meth)acrylate, etc. The polyfunctional monomers can be used alone or in combination of two or more.

[0165] When a crosslinking agent (which may be a polyfunctional monomer) is used, the amount used is not particularly limited and can be, for example, in the range of about 0.001 to 5.0 parts by weight per 100 parts by weight of the base polymer. From the viewpoint of improving the flexibility of the PSA, in some embodiments, the amount of crosslinking agent used per 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, and may be 1.0 part by weight or less, 0.5 parts by weight or less, or 0.2 parts by weight or less. Furthermore, from the viewpoint of appropriately exerting the effects of using the crosslinking agent, in some embodiments, the amount of crosslinking agent used per 100 parts by weight of the base polymer may 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.

[0166] A crosslinking catalyst may be used to promote the crosslinking reaction more effectively. Examples of the crosslinking catalyst include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, nursem ferric, butyltin oxide, and dioctyltin dilaurate. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of the crosslinking catalyst used is not particularly limited. The amount of the crosslinking catalyst used per 100 parts by weight of the base polymer can be, for example, in the range of approximately 0.0001 to 1 part by weight, preferably 0.001 to 0.5 parts by weight, taking into consideration the balance between the crosslinking reaction rate and the pot life of the pressure-sensitive adhesive composition.

[0167] The PSA composition may contain a compound that undergoes keto-enol tautomerization as a crosslinking retarder. This can extend the pot life of the PSA composition. For example, a compound that undergoes keto-enol tautomerization can be preferably used in a PSA composition containing an isocyanate-based crosslinking agent. Various β-dicarbonyl compounds can be used as the compound that undergoes keto-enol tautomerization. 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 tautomerization can be used alone or in combination of two or more. The amount of the compound that undergoes keto-enol tautomerization can be, for example, 0.1 to 20 parts by weight, alternatively 0.5 to 10 parts by weight, or alternatively 1 to 5 parts by weight, per 100 parts by weight of the base polymer.

[0168] (tackifier) The PSA layer (which may be the viscoelastic layer V1 and / or the viscoelastic layer V2) in the technology disclosed herein may contain a tackifier. Examples of tackifiers that can be used include 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 elastomer-based tackifier resins. These can be used alone or in combination of two or more. The amount of tackifier resin used is not particularly limited and can be set so as to achieve appropriate adhesive performance depending on the purpose and application. In some embodiments, from the viewpoints of refractive index and transparency, the amount of tackifier used is suitably 30 parts by weight or less, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, per 100 parts by weight of the base polymer of the PSA layer. The technology disclosed herein can be preferably implemented in an embodiment in which a tackifier is not used.

[0169] (Other additives) 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 that can be used in adhesive compositions, such as plasticizers, softeners, colorants, antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, preservatives, etc., to the extent that the effects of the present invention are not significantly impaired. As for such various additives, conventionally known ones can be used in the usual manner, and they do not particularly characterize the present invention, so detailed description thereof will be omitted.

[0170] (peel strength) In some embodiments of the interlayer sheet disclosed herein, the peel strength of the interlayer sheet to a glass plate is suitably about 1.0 N / 25 mm or more (e.g., 1.5 N / 25 mm or more), preferably 2 N / 25 mm or more, more preferably 3 N / 25 mm or more, and may be 4 N / 25 mm or more, 6 N / 25 mm or more, 8 N / 25 mm or more, 10 N / 25 mm or more, or 12 N / 25 mm or more. 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.

[0171] Here, the peel strength is determined by pressing the sheet to an alkali glass plate as an adherend, leaving it in an environment of 23°C and 50% RH for 30 minutes, then placing it in a pressure degassing apparatus (autoclave) and autoclaving it at a temperature of 50°C and a pressure of 0.5 MPa for 30 minutes, and leaving it in an atmosphere of 23°C and 50% RH for 24 hours, and then measuring the 180° peel adhesive strength under conditions of a peel angle of 180° and a pulling speed of 300 mm / min. If necessary, the interlayer sheet to be measured can be reinforced by attaching an appropriate backing material (e.g., a polyethylene terephthalate (PET) film with a thickness of about 25 μm to 50 μm). More specifically, the peel strength can be measured according to the method described in the Examples below. When the interlayer sheet disclosed herein is in the form of a double-sided pressure-sensitive adhesive sheet having a first adhesive surface and a second adhesive surface, in some embodiments, the above-mentioned peel strength is preferably applied to at least the first adhesive surface, and more preferably to both the first adhesive surface and the second adhesive surface. The peel strength of the first adhesive surface to a glass plate and the peel strength of the second adhesive surface to glass may be similar or different.

[0172] <Viscoelastic layer V2> In some preferred embodiments of the interlayer sheet disclosed herein, the interlayer sheet may further include, in addition to the viscoelastic layer V1, a viscoelastic layer (adhesive layer) V2 laminated on the viscoelastic layer V1. The viscoelastic layer V2 has a storage modulus G' at 25°C. V2 is the storage modulus G' of the viscoelastic layer V1 at 25°C. V1 It is preferable that G' is lower than V2 (twenty five) <G’ V1 The storage modulus G' is preferably (25). The interlayer sheet having such a configuration can be made more flexible by the contribution of the viscoelastic layer V2. V2 (25) is the storage modulus G' V1 By making the refractive index lower than (25), the interlayer sheet can preferably achieve both a high refractive index due to the viscoelastic layer V1 and flexibility due to the viscoelastic layer V2. By laminating the viscoelastic layer V2 on the viscoelastic layer V1, adhesion and flexibility are imparted, improving conformability to uneven surfaces and curved surfaces, and realizing an interlayer sheet that can be preferably applied to various device designs.

[0173] Storage modulus G' V2 (25) is not particularly limited and may be, for example, in the range of 1.0 kPa to 500 kPa. 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 (for example, 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 cohesiveness to the viscoelastic layer V2, in some embodiments, the storage modulus G' V2 (25) is suitably 5.0 kPa or more, preferably 10 kPa or more, may be 15 kPa or more, may be 25 kPa or more, may be 35 kPa or more, may be 60 kPa or more, or may be 80 kPa or more. From the viewpoint of easily realizing higher cohesive strength and adhesive properties, in some embodiments, the storage modulus G' V2 (25) may be 95 kPa or more, 110 kPa or more, or 140 kPa or more.

[0174] 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. An interlayer sheet having such a configuration can utilize the difference in refractive index between the viscoelastic layers V1 and V2 to control the behavior of light passing through the interlayer sheet. In such embodiments, 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, and may be, for example, within a range of about 1.35 to 1.55. In some embodiments, from the viewpoint of increasing the difference in refractive index from the refractive index n1 of the viscoelastic layer V1 and thereby enhancing the front brightness improvement effect described below, the refractive index n2 of the viscoelastic layer V2 is, for example, preferably 1.49 or less, more preferably 1.47 or less (e.g., 1.46 or less, or 1.45 or less), and may be 1.43 or less, 1.41 or less, or 1.40 or less. In addition, from the viewpoint of ease of material availability and compatibility with adhesive properties, in some embodiments, the refractive index n2 of the viscoelastic layer V2 may be, for example, 1.36 or more, 1.38 or more, 1.40 or more, or 1.42 or more.

[0175] The type of adhesive constituting the viscoelastic layer V2 is not particularly limited. The adhesive constituting the viscoelastic layer V2 may contain, as a base polymer, one or more of various rubber-like polymers that can be used in the field of adhesives, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, and mixtures thereof), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine-containing polymers. From the viewpoints of adhesive performance and cost, adhesives containing an acrylic polymer or a rubber polymer as a base polymer are preferably used. Among these, adhesives using an acrylic polymer as a base polymer (acrylic adhesives) are preferred. In an embodiment in which the viscoelastic layer V1 is an acrylic adhesive layer, from the viewpoint of adhesion between the viscoelastic layer V1 and the viscoelastic layer V2, a configuration in which the viscoelastic layer V2 is an acrylic adhesive layer is preferably used.

[0176] In some embodiments, the acrylic polymer is preferably, for example, a polymer of a monomer starting material that includes an alkyl (meth)acrylate and may further include another monomer (copolymerizable monomer) copolymerizable with the alkyl (meth)acrylate. The content of the alkyl (meth)acrylate in the monomer starting 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 also be a polymer of a monomer component that includes an alkyl (meth)acrylate as a main monomer and may further include the copolymerizable monomer as a secondary monomer. Here, the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition in the monomer starting material. More than 55% by weight or more than 60% by weight of the monomer composition may be alkyl (meth)acrylate.

[0177] As the alkyl(meth)acrylate, for example, a compound represented by the following formula (1) can be preferably used. CH2=C(R 1 )COOR 2 (1) Here, R in the above formula (1) 1is a hydrogen atom or a methyl group. 2 is a chain alkyl group having 1 to 20 carbon atoms (hereinafter, this range of carbon atoms is referred to as "C 1-20 From the viewpoint of the storage modulus of the adhesive, R 2 C 1-12 (For example, C 2-10 , typically C 4-8 The alkyl (meth)acrylates, which are chain alkyl groups of the above R 2 C 1-20 The alkyl(meth)acrylate, which is a chain alkyl group, can be used alone or in combination of two or more. Preferred alkyl(meth)acrylates include n-butyl acrylate and 2-ethylhexyl acrylate.

[0178] The copolymerizable monomer can be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the acrylic polymer. Examples of the copolymerizable monomer include one or more functional group-containing monomers, such as carboxyl group-containing monomers, hydroxyl group-containing monomers, acid anhydride group-containing monomers, amide group-containing monomers, amino group-containing monomers, nitrogen atom-containing ring-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. Other examples of copolymerizable monomers include vinyl ester-based monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, non-aromatic ring-containing (meth)acrylates, and alkoxy group-containing monomers. Specific examples include, but are not limited to, those monomers that can be used as the base polymer of the viscoelastic layer V1. For example, from the viewpoint of improving cohesive strength, an acrylic polymer copolymerized with a carboxyl group-containing monomer and / or a hydroxyl group-containing monomer is preferred as the copolymerizable monomer. Suitable examples of the carboxyl group-containing monomer include acrylic acid and methacrylic acid. Suitable examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate.

[0179] In some embodiments, a fluorine-containing monomer can be used as the copolymerizable monomer to lower the refractive index n2 of the pressure-sensitive adhesive layer V2. The content of the fluorine-containing monomer in the raw monomer material may be, for example, 10% by weight or more, 25% by weight or more, or 35% by weight or more. From the viewpoint of easily achieving a viscoelastic layer V2 with a lower refractive index, the content of the fluorine-containing monomer is preferably 40% by weight or more, more preferably 45% by weight or more, even more preferably 55% by weight or more, and may be 60% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or even 95% by weight or more. The upper limit of the content of the fluorine-containing monomer in the raw monomer material is not particularly limited and may be 100% by weight. In some embodiments, from the viewpoint of the cohesiveness of the viscoelastic layer V2, the content of the fluorine-containing 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 fluorine-containing monomers can be used alone or in combination of two or more.

[0180] As the fluorine-containing monomer, a fluorine-containing acrylic monomer can be preferably used. The fluorine-containing acrylic monomer is not particularly limited as long as it is an acrylic monomer having at least one fluorine atom in the molecule. For example, a fluorine-containing (meth)acrylic ester can be preferably used. Suitable examples of the fluorine-containing (meth)acrylic ester include those having a fluorinated hydrocarbon group at the ester terminal. Examples of the fluorinated hydrocarbon group include a fluorinated aliphatic hydrocarbon group, a fluorinated alicyclic hydrocarbon group, and a fluorinated aromatic hydrocarbon group. Suitable examples of the fluorinated hydrocarbon group include a fluorinated aliphatic hydrocarbon group. Examples of the fluorinated aliphatic hydrocarbon group include a fluorinated alkyl group. In the fluorinated aliphatic hydrocarbon group, the aliphatic hydrocarbon moiety may be linear or branched. In the fluorinated aliphatic hydrocarbon group, the fluorine atom may be bonded to any carbon atom in the aliphatic hydrocarbon group moiety. The number of fluorine atoms bonded to one carbon atom may be singular or plural. There is no particular limitation on the number of carbon atoms to which fluorine atoms are bonded.

[0181] In the fluorinated aliphatic hydrocarbon group (especially a fluorinated alkyl group), the number of carbon atoms in the hydrocarbon group moiety is not particularly limited. In some embodiments, in consideration of compatibility with other copolymerizable monomers, a fluorinated aliphatic hydrocarbon group having, for example, about 1 to 18 (preferably 1 to 12) carbon atoms is preferred. Specific examples of the fluorinated aliphatic hydrocarbon group include fluorinated methyl groups such as trifluoromethyl, difluoromethyl, and monofluoromethyl; and fluorinated ethyl 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. Examples of the fluorinated alkyl group having 3 or more carbon atoms include various fluorinated alkyl groups in which one or more fluorine atoms are bonded to one or more carbon atoms of the alkyl group moiety, similar to the fluorinated methyl group and fluorinated ethyl group exemplified above.

[0182] Examples of fluorinated alicyclic hydrocarbon groups include fluorinated cycloalkyl groups. As with the above-mentioned fluorinated aliphatic hydrocarbon groups, in fluorinated alicyclic hydrocarbon groups, the fluorine atom may be bonded to any carbon atom of the alicyclic hydrocarbon group, and the number of fluorine atoms bonded to one carbon atom may be either single or multiple. Furthermore, the number of carbon atoms to which fluorine atoms are bonded is not particularly limited. Examples of fluorinated alicyclic hydrocarbon groups include cyclohexyl groups having one fluorine atom, such as a 2-fluorocyclohexyl group, a 3-fluorocyclohexyl group, and a 4-fluorocyclohexyl group; cyclohexyl groups having two fluorine atoms, such as a 2,4-difluorocyclohexyl group and a 2,6-difluorocyclohexyl group; and cyclohexyl groups having three fluorine atoms, such as a 2,4,6-trifluorocyclohexyl group.

[0183] The fluorinated hydrocarbon group may or may not have a substituent. Such a substituent is not particularly limited, and examples thereof include hydrocarbon groups such as alkyl groups, alkoxy groups, hydroxy groups, carboxy groups, amino groups, nitro groups, cyano groups, and halogen atoms. The substituents may be used alone or in combination of two or more.

[0184] Examples of fluorine atom-containing (meth)acrylic acid esters [fluorinated (meth)acrylates] include fluorine atom-containing (meth)acrylic acid alkyl esters [fluorinated alkyl (meth)acrylates], fluorine atom-containing (meth)acrylic acid cycloalkyl esters [fluorinated cycloalkyl (meth)acrylates], and fluorine atom-containing (meth)acrylic acid aryl esters [fluorinated aryl (meth)acrylates].

[0185] As the fluorine atom-containing (meth)acrylic acid ester, a fluorinated alkyl (meth)acrylate (particularly a fluorinated alkyl acrylate) is preferred. Examples of fluorinated alkyl(meth)acrylates 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.).

[0186] The number of carbon atoms in the fluorinated alkyl group in the fluorinated alkyl (meth)acrylate is advantageously 3 or more, preferably 4 or more, more preferably 5 or more, even more preferably 6 or more or 7 or more, and particularly preferably 8 or more, from the viewpoint of refractive index lowering effect and flexibility. The number of carbon atoms in the fluorinated alkyl group is advantageously 18 or less, preferably 14 or less, more preferably 12 or less, and may be 10 or less or 9 or less, from the viewpoint of adhesive performance and the like. In some embodiments, the number of carbon atoms in the fluorinated alkyl group may be 7 or less or may be 5 or less. Furthermore, in some embodiments, the fluorine atom-containing (meth)acrylic acid ester is preferably a fluorinated alkyl (meth)acrylate in which fluorine is not bonded to the first carbon of the alkyl group. For example, a fluorinated alkyl (meth)acrylate in which fluorine is not bonded to either the first or second carbon of the alkyl group, such as 1H,1H,2H,2H-tridecafluorooctyl acrylate, can be preferably used.

[0187] In some embodiments of the interlayer sheet disclosed herein, the viscoelastic layer V2 is an acrylic pressure-sensitive adhesive layer, and the acrylic polymer serving as the base polymer of the pressure-sensitive adhesive may be a polymer of a monomer raw material containing at least the above-described fluorine-containing acrylic monomer (e.g., a fluorinated alkyl(meth)acrylate) and optionally further containing another monomer (copolymerizable monomer) copolymerizable with the fluorine-containing acrylic monomer. This monomer raw material may or may not contain an alkyl(meth)acrylate. The content of the fluorine-containing acrylic monomer in the monomer raw material may be, for example, 10% by weight or more, 25% by weight or more, or 35% by weight or more. From the viewpoint of easily achieving a viscoelastic layer V2 with a lower refractive index, the content of the fluorine-containing acrylic monomer is preferably 40% by weight or more, more preferably 45% by weight or more, even more preferably 55% by weight or more, and may be 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 fluorine-containing acrylic monomer in the monomer raw material is not particularly limited and may be 100% by weight. In some embodiments, from the viewpoint of the cohesion of the viscoelastic layer V2, the content of the fluorine-containing acrylic monomer is suitably 99.9% by weight or less, preferably 99.5% by weight or less, or may be 99% by weight or less, 97% by weight or less, or 92% by weight or less. The fluorine-containing acrylic monomer may be used alone or in combination of two or more.

[0188] The raw monomer material for preparing the base polymer of the viscoelastic layer V2 may contain a copolymerizable monomer in addition to a fluorine-containing acrylic monomer (e.g., a fluorinated alkyl (meth)acrylate). Examples of the copolymerizable monomer include one or more functional group-containing monomers, 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 (e.g., N-vinyl cyclic amides such as N-vinyl-2-pyrrolidone), sulfonic acid group-containing monomers, and phosphate group-containing monomers. Other examples of copolymerizable monomers include vinyl ester-based monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, non-aromatic ring-containing (meth)acrylates such as cycloalkyl (meth)acrylates and isobornyl (meth)acrylate, and alkoxy group-containing monomers. Specific examples include, but are not limited to, those monomers described above as being suitable for use as the base polymer of the viscoelastic layer V1. For example, from the viewpoint of improving cohesive strength, an acrylic polymer in which a carboxyl group-containing monomer and / or a hydroxyl group-containing monomer is copolymerized as the copolymerizable monomer is preferred.

[0189] In some preferred embodiments, the monomer raw material for preparing the base polymer of the viscoelastic layer V2 may contain a fluorine-containing monomer (e.g., a fluorine-containing acrylic monomer such as a fluorinated alkyl (meth)acrylate) and may further contain a hydroxyl group-containing monomer. The hydroxyl group-containing monomer may be useful for improving cohesion and introducing crosslinking points. Suitable examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate. 4-hydroxybutyl acrylate is more preferably used from the viewpoint of improving flexibility at room temperature. The content of the hydroxyl group-containing monomer in the monomer raw material is not particularly limited and may be, for example, 0.01 wt % or more (preferably 0.1 wt % or more, more preferably 0.5 wt % or more). In some embodiments, the content of the hydroxyl group-containing monomer may be 0.7 wt % or more, 0.9 wt % or more, or 1.5 wt % or more of the monomer raw material. The upper limit of the hydroxyl group-containing monomer content is not particularly limited and may be, for example, 15 wt % or less or 10 wt % or less. In some embodiments, from the viewpoint of achieving a low refractive index, the content of the hydroxyl group-containing monomer in the monomer raw material is suitably less than 10% by weight, preferably less than 5% by weight, or may be less than 3% by weight, less than 2.5% by weight, or less than 1.5% by weight.

[0190] In some embodiments, the monomer raw material for preparing the base polymer of the viscoelastic layer V2 preferably has a limited content of carboxyl group-containing monomers to prevent coloration or discoloration (e.g., yellowing) of the viscoelastic layer V2. The content of the carboxyl group-containing monomers in the monomer raw material may be, for example, less than 1 wt %, preferably less than 0.5 wt %, more preferably less than 0.3 wt %, and even more preferably less than 0.1 wt % (e.g., less than 0.05 wt %). Such a limited content of the carboxyl group-containing monomers is also advantageous from the viewpoint of preventing corrosion of metal materials that may be in contact with or adjacent to the viscoelastic layer V2 (e.g., metal wiring or metal films that may be present on an adherend). The interlayer sheet disclosed herein can be preferably implemented in an embodiment in which the monomer raw material does not contain a carboxyl group-containing monomer. For the same reason, in some embodiments, the monomer raw material for preparing the base polymer of the viscoelastic layer V2 preferably has a limited content of monomers having acidic functional groups (including carboxy groups, sulfonic acid groups, phosphate groups, etc.). The content of the acidic functional group-containing monomer in the monomer raw material in such embodiments can be the same as the preferred content of the carboxy group-containing monomer described above. The interlayer sheet disclosed herein can be preferably produced in an embodiment in which the monomer raw material does not contain an acidic group-containing monomer (i.e., an embodiment in which the base polymer of the viscoelastic layer V2 is acid-free).

[0191] The base polymer of the pressure-sensitive adhesive layer V2 can be prepared by appropriately employing a known polymerization method, similar to the base polymer of the pressure-sensitive adhesive layer V1. The weight-average molecular weight (Mw) of the base polymer is not particularly limited, and is, for example, about 10 × 10 4 ~500×10 4 may be in the range of approximately 20×10 4 ~200×10 4 In some embodiments, from the viewpoint of adhesion to the pressure-sensitive adhesive layer V1, the Mw of the base polymer of the pressure-sensitive adhesive layer V2 may be in the range of 150×10 4 It is appropriate that the value is less than 120 x 10 4Less than (e.g., 95 x 10 4 (less than 75 × 10 4 Less than 68 x 10 is also acceptable. 4 Less than 60 x 10 is also acceptable. 4 In some embodiments, from the viewpoint of the cohesion of the pressure-sensitive adhesive layer V2, the Mw of the base polymer may be, for example, 30×10 or less. 4 It may be 40 x 10 or more. 4 More than 50 x 10 4 In order to adjust the Mw, a conventionally known chain transfer agent can be used as necessary.

[0192] Although not particularly limited, from the viewpoint of adhesiveness, the Tg of the base polymer (e.g., acrylic polymer) of the pressure-sensitive adhesive layer V2 is advantageously about 0°C or lower, and preferably about -5°C or lower (e.g., about -15°C or lower, or -25°C or lower). From the viewpoint of the cohesive strength of the pressure-sensitive adhesive layer, the Tg of the base polymer of the pressure-sensitive adhesive layer V2 is about -75°C or higher, and 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 changing the monomer composition (i.e., the types and amount ratios of monomers used in synthesizing the polymer).

[0193] A known crosslinking agent may be used in the pressure-sensitive adhesive layer V2 as needed. Furthermore, a tackifier and other additives may be incorporated into the pressure-sensitive adhesive layer V2 as needed. The crosslinking agent and tackifier may be appropriately selected from those usable in the pressure-sensitive adhesive layer V1, and may be used in an appropriate amount.

[0194] In embodiments in which the PSA composition used to form the PSA layer V2 contains a crosslinking agent, for example, an isocyanate-based crosslinking agent may be preferably used as the crosslinking agent. In some embodiments, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the base polymer of the PSA composition may 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, from the viewpoint of, for example, adhesion to the PSA layer V1. Furthermore, in some embodiments, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the base polymer may 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, from the viewpoint of appropriately achieving the effects of using the crosslinking agent.

[0195] <Preparation of adhesive layer> In the interlayer sheet disclosed herein, the viscoelastic materials constituting each of the viscoelastic layers V1 and V2 may be adhesives obtained by curing a solvent-based, active energy ray-curable, water-dispersible, hot-melt, or other adhesive composition by drying, crosslinking, polymerization, cooling, or the like, i.e., a cured product of the adhesive composition. The adhesive composition may be cured using a single method (e.g., drying, crosslinking, polymerization, cooling, or the like), or two or more methods may be applied simultaneously or in multiple stages. For solvent-based adhesive compositions, the adhesive can typically be formed by drying (preferably further crosslinking) the composition. For active energy ray-curable adhesive compositions, the adhesive is typically formed by irradiating the composition with active energy rays to promote a polymerization reaction and / or a crosslinking reaction. When an active energy ray-curable adhesive composition requires drying, it is preferable to irradiate the composition with active energy rays after drying.

[0196] The viscoelastic layers V1 and V2 of the interlayer sheet disclosed herein can be formed by applying (e.g., coating) a pressure-sensitive adhesive composition to a suitable surface and then curing the composition. The pressure-sensitive adhesive composition can be applied using a conventional coater, such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, or spray coater.

[0197] In the interlayer sheet disclosed herein, either one or both of the viscoelastic layers V1 and V2 may be a pressure-sensitive adhesive layer having post-curing properties, or may be a pressure-sensitive adhesive layer not having post-curing properties. Here, a pressure-sensitive adhesive layer having post-curing properties refers to a pressure-sensitive adhesive layer that can be further cured by irradiation with heat or active energy rays (e.g., ultraviolet rays). Examples of pressure-sensitive adhesive layers having post-curing properties include pressure-sensitive adhesive layers having unreacted ethylenically unsaturated groups in the side chains of the base polymer, and pressure-sensitive adhesive layers containing unreacted polyfunctional monomers. In some embodiments, it is preferable that the pressure-sensitive adhesive layer not have post-curing properties. A pressure-sensitive adhesive layer not having post-curing properties does not undergo dimensional changes associated with the post-curing reaction (i.e., has good dimensional stability), and therefore is more likely to suppress warping of the pressure-sensitive adhesive sheet or the adherend to which the pressure-sensitive adhesive sheet is attached. The absence of dimensional changes (e.g., cure shrinkage) due to post-curing can also be advantageous from the perspective of suppressing optical distortion of the pressure-sensitive adhesive layer.

[0198] The thickness of the viscoelastic layer V1 is not particularly limited and can be, for example, 3 μm or more, preferably 5 μm or more. A viscoelastic layer V1 having a thickness of 5 μm or more is likely to provide good adhesive properties. Furthermore, a viscoelastic layer V1 of such a thickness easily absorbs irregularities that may exist on the surface of an adherend and adheres well to the adherend. A thickness of 5 μm or more is also preferred from the viewpoint of preventing coloring or color unevenness due to light interference. In some embodiments, the thickness of the viscoelastic layer V1 may be 10 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 85 μm or more. In some embodiments, the thickness of the viscoelastic layer V1 may be, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less. Not having too large a thickness of the viscoelastic layer V1 can be advantageous from the standpoint of, for example, thinning the interlayer sheet. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the thickness of the viscoelastic layer V1 is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm). In the case of an interlayer sheet having 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 similar to or different from each other. In an interlayer sheet in the form of a substrateless double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer, the thickness of the pressure-sensitive adhesive layer is the thickness of the interlayer sheet.

[0199] A pressure-sensitive adhesive layer having a laminated structure of pressure-sensitive adhesive layer V1 and pressure-sensitive adhesive layer V2 can be produced by, for example, forming pressure-sensitive adhesive layers V1 and V2 on a release surface (e.g., the release surface of a release liner) and then bonding their adhesive surfaces together; applying a pressure-sensitive adhesive composition for forming pressure-sensitive adhesive layer V2 onto pressure-sensitive adhesive layer V1 and then curing it; or conversely, applying a pressure-sensitive adhesive composition for forming pressure-sensitive adhesive layer V1 onto pressure-sensitive adhesive layer V2 and then curing it. When bonding the adhesive surfaces of pre-formed pressure-sensitive adhesive layers V1 and V2 together, a treatment to promote adhesion between the two pressure-sensitive adhesive layers may be performed, as necessary. Examples of such treatments include, but are not limited to, autoclaving and roll pressing.

[0200] <Supporting base material> The interlayer sheet (adhesive sheet) according to some embodiments may be in the form of a substrate-attached adhesive sheet having an adhesive layer on one or both sides of a support substrate. The material of the support substrate is not particularly limited and can be appropriately selected depending on the intended use and manner of use of the adhesive sheet. Non-limiting examples of substrates that can be used include plastic films such as polyolefin films primarily composed of polyolefins such as polypropylene (PP) or 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 made of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; woven and nonwoven fabrics made by spinning various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc.) alone or in combination; papers such as Japanese paper, fine paper, kraft paper, and crepe paper; and metal foils such as aluminum foil and copper foil. Substrates with a composite structure of these materials are also possible. Examples of such composite substrates include substrates having a structure in which a metal foil and the above-mentioned plastic film are laminated together, and plastic substrates reinforced with inorganic fibers such as glass cloth.

[0201] In some embodiments, various film substrates can be preferably used. The film substrate may be a porous substrate such as a foam film or a nonwoven fabric sheet, or a nonporous substrate, or a substrate having a structure in which a porous layer and a nonporous layer are laminated. In some embodiments, the film substrate preferably includes a base film that is an independently shape-retaining (self-supporting or independent) resin film. Here, the term "resin film" refers to a resin film that has a nonporous structure and typically contains substantially no air bubbles (void-free). Therefore, the resin film is a concept that is distinct from foam films and nonwoven fabrics. The resin film preferably includes an independently shape-retaining (self-supporting or independent) resin film. The resin film may have a single-layer structure or a multilayer structure of two or more layers (e.g., a three-layer structure).

[0202] Examples of materials constituting the resin film include polyester-based resins mainly composed of polyester, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefin-based resins mainly composed of polyolefin, such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; cellulose resins such as triacetyl cellulose; acetate-based resins; polysulfone-based resins; polyethersulfone-based resins; polycarbonate-based resins; polyamide (PA)-based resins such as nylon 6, nylon 66, and partially aromatic polyamide; and polyimide (PI)-based resins. Examples of suitable resins include transparent polyimide resins, polyamideimide (PAI), polyether ether ketone (PEEK), polyethersulfone (PES), cyclic polyolefin resins such as norbornene-based 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, polyphenylene sulfide (PPS) resins, polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), fluorine-based resins such as polytetrafluoroethylene (PTFE) and fluorinated polyimides, and the like.

[0203] The resin film may be formed using a resin material containing one of these resins alone, or may be formed using a resin material containing a blend of two or more of these resins. The resin film may be unstretched or stretched (for example, uniaxially or biaxially stretched). 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. are preferably used. Examples of resin films that are preferred from the standpoint of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. PET film and PPS film are particularly preferred from the standpoint of availability, etc., and PET film is particularly preferred.

[0204] The resin film may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, antiblocking agents, etc., as needed, provided that the effects of the present invention are not significantly impaired. The amount of additives added is not particularly limited and can be set appropriately depending on the application of the PSA sheet, etc.

[0205] The method for producing the resin film is not particularly limited, and any conventionally known resin film forming method such as extrusion molding, inflation molding, T-die casting, or calendar roll molding can be appropriately used.

[0206] The substrate may be substantially composed of such a base film. Alternatively, the substrate may include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include an optical property adjusting layer (e.g., a coloring layer, an anti-reflection layer), a printed layer or a laminate layer for imparting a desired appearance to the substrate, an antistatic layer, an undercoat layer, a release layer, or other surface treatment layer.

[0207] In some embodiments, a substrate having optical transparency (hereinafter also referred to as an optically transparent substrate) can be preferably used as the support substrate. This makes it possible to construct a substrate-attached pressure-sensitive adhesive sheet having optical transparency. The total light transmittance of the optically transparent substrate may be, for example, more than 50%, or may be 70% or more. In some preferred embodiments, the total light transmittance of the support substrate is 80% or more, more preferably 90% or more, and may even be 95% or more (e.g., 95 to 100%). The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. The transmittance meter used may be a product name "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or an equivalent. A suitable example of the optically transparent substrate is a resin film having optical transparency. The optically transparent substrate may also be an optical film.

[0208] The thickness of the substrate is not particularly limited and can be selected depending on the purpose and mode of use of the interlayer sheet. The thickness of the substrate may be, for example, 500 μm or less, and from the viewpoint of the handleability and processability of the interlayer sheet, it is preferably 300 μm or less, and may be 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, the ability to conform to the surface shape of the adherend tends to improve. Furthermore, from the viewpoint of handleability and processability, the thickness of the substrate may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

[0209] The surface of the substrate on which the pressure-sensitive adhesive layer (viscoelastic layer) is laminated may be subjected to conventional surface treatments, such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or the formation of an undercoat layer by applying a primer. Such surface treatments may be intended to improve the anchoring ability of the pressure-sensitive adhesive layer to the substrate. The composition of the primer used to form the undercoat layer is not particularly limited and can be appropriately selected from known primers. The thickness of the undercoat layer is not particularly limited, but is typically approximately 0.01 μm to 1 μm, preferably approximately 0.1 μm to 1 μm. Other treatments that may be applied to the substrate as needed include antistatic layer formation treatment, colored layer formation treatment, printing treatment, etc. These treatments may be applied alone or in combination.

[0210] When the interlayer sheet disclosed herein is in the form of a substrate-attached pressure-sensitive adhesive sheet, the thickness of the interlayer sheet may 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 viewpoint of handleability, the thickness of the interlayer sheet may be, for example, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more. The thickness of the interlayer sheet refers to the thickness of the portion that is attached to the adherend. For example, in the case of the interlayer sheet 1 having the configuration shown in Fig. 1, the thickness refers to the thickness from the first surface (adhesive surface) 10A of the pressure-sensitive adhesive layer to the second surface 20B of the support substrate, and does not include the thickness of the release liner 30.

[0211] <Interlayer sheet with release liner> The interlayer sheet (adhesive sheet) disclosed herein can be in the form of an adhesive product in which the surface (adhesive surface) of the adhesive layer is in contact with the release surface of a release liner. Thus, this specification provides an interlayer sheet with a release liner (adhesive product) comprising any of the interlayer sheets disclosed herein and a release liner having a release surface in contact with the adhesive surface of the interlayer sheet.

[0212] The release liner is not particularly limited, and examples thereof include a release liner having a release treatment layer on a release liner substrate such as a resin film or paper (which may be paper laminated with a resin such as polyethylene), and a release liner made of a resin film formed from a low-adhesion material such as a fluorine-based polymer (e.g., polytetrafluoroethylene) or a polyolefin-based resin (e.g., polyethylene, polypropylene). The release treatment layer may be formed by surface-treating the release liner substrate with a release treatment agent. The release treatment agent may be a 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 formed with a silicone-based release treatment agent may be preferably used. The thickness and method of forming the release treatment layer are not particularly limited, and can be set so as to exhibit appropriate releasability on the adhesive surface of the release liner.

[0213] In some embodiments, from the viewpoint of smoothness of the adhesive surface, a release liner (hereinafter also referred to as a release film) having a release treatment layer on a resin film (hereinafter also 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, a plastic film is typically a non-porous sheet, and is a concept that is distinguished from, for example, nonwoven fabrics (i.e., does not include nonwoven fabrics).

[0214] Examples of materials for the plastic film include 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; and 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. Release film substrates formed from one or a mixture of two or more of these resins can be used. Among these, a preferred release film substrate is a polyester resin film (e.g., a PET film) formed from a polyester resin.

[0215] The plastic film used as the release film substrate may be any of an unstretched film, a uniaxially stretched film, and a biaxially stretched film. The plastic film may have a single-layer structure or a multilayer structure including two or more sublayers. The plastic film may contain known additives that can be used in release film substrates for pressure-sensitive adhesive sheets, such as antioxidants, antiaging agents, heat stabilizers, light stabilizers, UV absorbers, colorants such as pigments and dyes, lubricants, fillers, antistatic agents, and nucleating agents. In a multilayer plastic film, each additive may be contained in all sublayers or only in some of the sublayers.

[0216] In some preferred embodiments, the release film substrate (typically a plastic film) preferably has a limited content of particles such as inorganic particles (e.g., pigments, lubricants, fillers, etc.) in the layer on the release surface side, or is substantially free of such particles. Here, "substantially free" means that the amount of particles (e.g., inorganic particles) in the layer is less than 1 wt %, preferably less than 0.1 wt % (e.g., 0 to 0.01 wt %). Release films equipped with such a release film substrate tend to have low arithmetic mean roughness Ra and maximum height Rz of the release surface. When the release film substrate (typically a plastic film) has a multilayer structure, the particle content in the layer on the release surface side can be 1 / 10 or less (e.g., 1 / 50 or less) of the particle content in layers other than the release surface side layer.

[0217] In an interlayer sheet with release liners having release liners on both the first adhesive surface and the second adhesive surface, the release liner placed on one adhesive surface (hereinafter also referred to as the one release liner) and the release liner placed on the other adhesive surface (hereinafter also referred to as the other release liner) may be made of the same material and have the same configuration, or may be made of different materials and have different configurations.

[0218] 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, the thickness of the release liner is suitably 20 μm or more, preferably 30 μm or more, and may be 35 μm or more, 40 μm or more, or 45 μm or more. Furthermore, from the viewpoint of the handleability of the release liner (e.g., ease of rolling), the thickness of the release liner is suitably 300 μm or less, preferably 250 μm or less, and may be 200 μm or less, 150 μm or less, or 130 μm or less. In some preferred embodiments, the thickness of the release liner is approximately 125 μm or less, may be approximately 115 μm or less, may be approximately 105 μm or less, may be approximately 90 μm or less, or may be approximately 70 μm or less. By setting the thickness of the release liner to a specified value or less, it is less likely to leave marks when rolled up, it can be removed more smoothly from the adhesive sheet, and it is more likely to achieve high surface smoothness on the adhesive surface after the release liner is removed.

[0219] In an interlayer sheet with release liners in an embodiment having one release liner and the other release liner, the thicknesses of the release liners may be the same or different. In some embodiments, from the viewpoint of ease of release, it is preferable that one release liner and the other release liner have different thicknesses. For example, it is preferable that the thickness of the thicker release liner is about 1.1 times or more (e.g., about 1.25 times or more; there is no particular upper limit, but for example, 5 times or less) the thickness of the thinner release liner.

[0220] (Arithmetic mean roughness Ra of adhesive surface) In some embodiments, the release liner (preferably a release film) preferably has an arithmetic mean roughness Ra of the adhesive surface limited to a predetermined value or less (e.g., approximately 100 nm or less, or even less than 50 nm) from the viewpoint of realizing an adhesive surface with high surface smoothness. In some embodiments, the arithmetic mean roughness Ra of the adhesive surface of the release liner is, for example, preferably approximately 30 nm or less, more preferably approximately 25 nm or less, and may be approximately 20 nm or less, or may be approximately 18 nm or less. Furthermore, from the viewpoint of ease of production and handling of the release liner, in some embodiments, the arithmetic mean roughness Ra may be, for example, approximately 5 nm or more, approximately 10 nm or more, or approximately 15 nm or more. In an interlayer sheet with release liners in which a release liner is disposed on each of the first and second adhesive surfaces, it is preferable that the adhesive surfaces of both release liners satisfy one of the arithmetic mean roughnesses Ra described above. The arithmetic mean roughnesses Ra of the adhesive surfaces of both release liners may be similar or different.

[0221] (Maximum height Rz of adhesive surface) In some embodiments, the release liner (preferably a release film) preferably has a maximum height Rz of 700 nm or less on the adhesive surface, from the viewpoint of realizing an adhesive surface with high surface smoothness. In some embodiments, the maximum height Rz of the adhesive surface of the release liner is preferably approximately 600 nm or less, and may be approximately 500 nm or less, approximately 400 nm or less, or approximately 300 nm or less. Furthermore, in terms of ease of production and handling of the release liner, in some embodiments, the maximum height Rz may be, for example, approximately 50 nm or more, approximately 80 nm or more, approximately 100 nm or more, approximately 200 nm or more, or approximately 300 nm or more. In an interlayer sheet with release liners in which a release liner is disposed on each of the first and second adhesive surfaces, it is preferable that the adhesive surfaces of both release liners satisfy one of the maximum heights Rz described above. The maximum heights Rz of the adhesive surfaces of both release liners may be similar or different.

[0222] (Surface texture on the back) The arithmetic mean roughness Ra and maximum height Rz of the back surface (opposite the pressure-sensitive adhesive layer) of the release liner (preferably a release film) are not particularly limited. From the viewpoint of productivity, etc., the arithmetic mean roughness Ra of the back surface of the release liner may be, for example, greater than 30 nm (e.g., greater than 35 nm, or even approximately 50 nm or greater). From the viewpoint of productivity, etc., the maximum height Rz of the back surface of the release liner may be, for example, greater than 400 nm (e.g., approximately 500 nm or greater) or greater than 800 nm (e.g., 1000 nm or greater).

[0223] The arithmetic mean roughness Ra and maximum height Rz of the release film surface can be adjusted by the selection of film material, molding method, surface treatment such as release treatment, etc. Examples include adjusting the smoothness of the layers that make up the release surface (anti-blocking layer, hard coat layer, oligomer prevention layer, etc.), reducing or eliminating the use of filler particles (particle-free) in the surface layer or release film substrate, and adjusting the stretching conditions.

[0224] The arithmetic mean roughness Ra and maximum height Rz of the surface of a release liner (preferably a release film) are measured using a non-contact surface roughness measuring device. A non-contact surface roughness measuring device employing an optical interference method, such as a 3D optical profiler (trade name "NewView7300" manufactured by ZYGO) or an equivalent, can be used. For example, a glass plate (a soda-lime glass plate manufactured by MATSUNAMI, 1.3 mm thick) can be attached to the surface of the release liner opposite the measurement surface with an adhesive, and the surface shape can be measured using a 3D optical profiler (trade name "NewView7300" manufactured by ZYGO) in an environment of 23°C and 50% RH.

[0225] <Application> The interlayer sheet disclosed herein can be attached to various adherends for use. The constituent material of the adherend (adherend material) is not particularly limited, but 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 these, and examples thereof include polyimide resins, acrylic resins, polyethernitrile resins, polyethersulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyetheretherketone resins, polyamide resins (so-called aramid resins, etc.), polyarylate resins, fluorine-based resins, etc. Examples of suitable materials include various resin materials (typically plastic materials) such as resin, polycarbonate resin, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, vinyl butyral polymers, liquid crystal polymers, and carbon materials such as graphene; metal oxides and mixtures thereof such as alumina, zirconia, titania, SiO2, ITO (indium tin oxide), and ATO (antimony-doped tin oxide); nitrides and composites thereof such as aluminum nitride, silicon nitride, titanium nitride, gallium nitride, and indium nitride; and inorganic materials such as alkali glass, alkali-free glass, quartz glass, borosilicate glass, and sapphire glass. The interlayer sheet disclosed herein can be used by being attached to a member (e.g., an optical member) whose surface is at least made of the above material.

[0226] The interlayer sheet disclosed herein can be used in an application mode that does not require heating to a temperature higher than room temperature (e.g., 20°C to 35°C) after lamination to an adherend. Furthermore, if acceptable depending on the constituent materials of the interlayer sheet (e.g., the material of the substrate) and the type of adherend, heat treatment may be performed at least at any time after lamination to the adherend, at the time of lamination, or before lamination. Heat treatment can be performed for purposes such as improving the adhesiveness of the pressure-sensitive adhesive to the adherend or promoting adhesion. The heat treatment temperature can be set appropriately to obtain the desired effect within an acceptable range depending on the constituent materials of the interlayer sheet and the type of adherend, taking into account the surface condition of the adherend, and may be, for example, about 100°C or less, 80°C or less, 60°C or less, or 50°C or less.

[0227] The member or material to which the interlayer sheet is attached or laminated (in the case of an interlayer sheet in the form of a double-sided pressure-sensitive adhesive sheet, at least one of the adherends) may be optically transparent. With such adherends, the advantages of the high transparency of the interlayer sheet disclosed herein are easily realized. The total light transmittance of the adherend may be, for example, greater than 50%, or even 70% or more. In some preferred embodiments, the total light transmittance of the adherend is 80% or more, more preferably 90% or more, and even more preferably 95% or more (e.g., 95 to 100%). The interlayer sheet disclosed herein is preferably used in an embodiment in which it is attached to or laminated on an adherend (e.g., an optical component) having a total light transmittance of a predetermined value or higher. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. The transmittance meter used may be a product called "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or an equivalent.

[0228] The refractive index of the adherend and the refractive index of the viscoelastic layer (e.g., viscoelastic layer V1, or in an embodiment having a viscoelastic layer V2, viscoelastic layer V2) disposed in contact with the adherend may be similar or different. For example, by increasing the refractive index of the viscoelastic layer (typically a pressure-sensitive adhesive layer) relative to the refractive index of the adherend, light incident on the pressure-sensitive adhesive layer from the adherend side at an angle equal to or smaller than the critical angle can be refracted toward the front, thereby increasing the front brightness. In this case, the refractive index of the adherend may be, for example, 1.55 or less, 1.50 or less, 1.48 or less, 1.45 or less, or even less than 1.45, or may be, for example, 1.10 or more, 1.20 or more, 1.30 or more, or 1.35 or more. Furthermore, an adherend having a refractive index relatively high relative to the pressure-sensitive adhesive layer can refract light incident on the adherend from the pressure-sensitive adhesive layer side toward the front, thereby increasing the front brightness. In this case, the refractive index of the adherend may be, for example, 1.60 or more, 1.65 or more, or 1.70 or more, or may be, for example, 3.00 or less, 2.50 or less, or 2.00 or less. On the other hand, by reducing the difference in refractive index between the pressure-sensitive adhesive layer and the adherend, light reflection at the interface can be suppressed. In this case, the refractive index of the adherend may be approximately 1.55 to 1.80, approximately 1.55 to 1.75, or approximately 1.60 to 1.70. The refractive index of the adherend can be measured in the same manner as the refractive index of the pressure-sensitive adhesive.

[0229] In some preferred embodiments, the adherend may have any of the refractive indices described above and any of the total light transmittances described above. In embodiments where the film is attached to or laminated on such an adherend, the effects of the technology disclosed herein are particularly favorably exhibited.

[0230] An example of a preferred application is an optical application. More specifically, the interlayer sheet disclosed herein can be preferably used as an optical pressure-sensitive adhesive sheet used for bonding optical members (for bonding optical members) or for manufacturing products (optical products) using the optical members.

[0231] The optical member refers to a member having optical properties (e.g., polarization, light refraction, light scattering, light reflectivity, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.). The optical member is not particularly limited as long as it has optical properties, and examples thereof include components constituting devices (optical devices) such as display devices (image display devices) and input devices, or components used in these devices, such as polarizing plates, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflection films, hard coat (HC) films, impact absorbing films, antifouling films, photochromic films, light control films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and further components in which these are laminated (these may be collectively referred to as "functional films"). The above-mentioned "plate" and "film" respectively include forms such as a plate, a film, and a sheet, and for example, "polarizing film" includes "polarizing plate" and "polarizing sheet", and "light guide plate" includes "light guide film" and "light guide sheet", etc. Furthermore, the above-mentioned "polarizing plate" includes a circular polarizing plate.

[0232] Examples of the display device include a liquid crystal display device, an organic EL (electroluminescence) display device, a micro LED (μLED), a mini LED (miniLED), a PDP (plasma display panel), electronic paper, etc. Examples of the input device include a touch panel, etc.

[0233] The optical member is not particularly limited, but examples thereof include members (e.g., sheet-, film-, or plate-shaped members) made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal thin film, etc. In this specification, the term "optical member" also includes members (such as design films, decorative films, and surface protection films) that serve to decorate or protect a display device or input device while maintaining its visibility.

[0234] The interlayer sheet disclosed herein can be used, for example, in a configuration in which it is disposed between an optical film, such as a film having one or more functions of light transmission, reflection, diffusion, waveguiding, focusing, and diffraction, or a fluorescent film, and another optical component (which may be another optical film), and is preferably used to bond the optical film to the other optical component. In particular, when bonding optical films having at least one function of light guiding, focusing, and diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, making this a preferred application of the technology disclosed herein. For example, a viscoelastic layer (adhesive layer) V1 can be preferably used as the bonding layer.

[0235] The viscoelastic layer (preferably a pressure-sensitive adhesive layer, e.g., a single-layer pressure-sensitive adhesive layer consisting of a viscoelastic layer V1, or a laminated pressure-sensitive adhesive layer consisting of two or more pressure-sensitive adhesive layers including a viscoelastic layer V1 and a viscoelastic layer V2 laminated in direct contact) of the interlayer sheet disclosed herein can be preferably used for bonding optical films such as light-guiding films, diffusion films, fluorescent films, color-tuning films, prism sheets, lenticular films, and microlens array films. In these applications, the trend toward miniaturization and high performance of optical components demands thinner films and improved light extraction efficiency. The viscoelastic layer (e.g., pressure-sensitive adhesive layer) of the interlayer sheet disclosed herein can be preferably used as a viscoelastic layer that can meet such demands. More specifically, for example, in bonding light-guiding films or diffusion films, adjusting the refractive index of the pressure-sensitive adhesive layer as a bonding layer (e.g., increasing the refractive index) can contribute to thinner films. In bonding fluorescent films, appropriately adjusting the refractive index difference between the fluorescent emitter and the pressure-sensitive adhesive can improve light extraction efficiency (which can also be understood as luminous efficiency). When bonding toning films, adjusting the refractive index of the adhesive appropriately to minimize the difference in refractive index between the adhesive and the toning pigment can reduce scattered components and contribute to improving light transmittance. When bonding prism sheets, lenticular films, microlens array films, etc., adjusting the refractive index of the adhesive appropriately can control light diffraction and contribute to improving brightness and / or viewing angle.

[0236] The interlayer sheet disclosed herein is preferably used in an embodiment in which it is attached to a high-refractive index adherend (which may be a high-refractive index layer, member, etc.), thereby suppressing interfacial reflection with the adherend. The interlayer sheet used in such an embodiment preferably has a small refractive index difference between the high-refractive index adherend and the pressure-sensitive adhesive layer (typically the viscoelastic layer V1) attached to the adherend, as described above, and high adhesion at the interface with the adherend. Furthermore, from the viewpoint of enhancing the uniformity of appearance, it is preferable that the pressure-sensitive adhesive layer has a highly uniform thickness, and for example, it is preferable that the adhesive surface has a high surface smoothness. When the high-refractive index adherend has a relatively small thickness (for example, 5 μm or less, 4 μm or less, or 2 μm or less), suppressing interfacial reflection is particularly meaningful from the viewpoint of suppressing coloring and color unevenness due to interference of reflected light. An example of such a usage mode is a mode in which, in a polarizing plate with a retardation layer that includes a polarizer, a first retardation layer, and a second retardation layer in this order, the film is used to bond the polarizer to the first retardation layer and / or the first retardation layer to the second retardation layer.

[0237] Furthermore, since the interlayer sheet disclosed herein includes a high-refractive index viscoelastic layer V1, it can be preferably used in an embodiment in which it is attached to a light-emitting layer of an optical semiconductor or the like (for example, a high-refractive index light-emitting layer mainly composed of inorganic materials). By reducing the difference in refractive index between the light-emitting layer and the viscoelastic layer V1, reflection at the interface therebetween can be suppressed, improving light extraction efficiency. The interlayer sheet used in such an embodiment preferably includes a high-refractive index adhesive layer as the viscoelastic layer V1. Furthermore, from the viewpoint of preventing deterioration of the self-luminous element due to moisture, it is preferable that the viscoelastic layer V1 has a low water absorption rate. From the viewpoint of improving brightness, it is preferable that the interlayer sheet has low coloration. This can also be advantageous from the viewpoint of suppressing unintentional coloration caused by the interlayer sheet.

[0238] 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 for a component facing the lens surface (e.g., a component having a surface shape corresponding to the lens surface), or a filling layer filled between the lens surface and the component in microlenses and other lens components (e.g., microlenses constituting a microlens array film or a lens component such as a microlens for a camera) used as components of cameras, light-emitting devices, etc. The viscoelastic layer V1 disclosed herein is suitable for achieving a high refractive index, and therefore can reduce the refractive index difference with a high-refractive-index lens (e.g., a lens made of a high-refractive-index resin or a lens having a surface layer made of a high-refractive-index resin) even when placed in contact with the lens. This is advantageous from the perspective of reducing the thickness of the lens and products incorporating the lens, and can also contribute 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 a lens resin, for example, by filling recesses or voids in an appropriate transparent component.

[0239] The mode of bonding optical members using the interlayer sheet disclosed herein is not particularly limited, and may include, for example, (1) bonding optical members to each other via the interlayer sheet disclosed herein, (2) bonding an optical member to a member other than an optical member via the interlayer sheet disclosed herein, or (3) bonding an optical member to an optical member or a member other than an optical member in which the interlayer sheet disclosed herein includes an optical member. In the mode (3), an interlayer sheet including an optical member may be, for example, an interlayer sheet whose support is an optical member (e.g., an optical film). Such an interlayer sheet including an optical member as a support may also be considered a pressure-sensitive adhesive optical member (e.g., a pressure-sensitive adhesive optical film). Furthermore, when the interlayer sheet disclosed herein is a pressure-sensitive adhesive sheet having a support and the functional film is used as the support, the interlayer sheet disclosed herein may also be considered a "pressure-sensitive adhesive functional film" having the pressure-sensitive adhesive layer disclosed herein on at least one side of the functional film.

[0240] As described above, the technology disclosed herein provides an optical laminate comprising the interlayer sheet disclosed herein and a member (e.g., a resin film such as an optical film) to which the interlayer sheet is attached. The member to which the interlayer sheet is attached may have the refractive index of the adherend material described above. Furthermore, the difference (refractive index difference) between the refractive index of the layer (e.g., viscoelastic layer V1) constituting the adhesive surface of the interlayer sheet and the refractive index of the member may be the refractive index difference between the adherend and the adhesive layer described above. The members constituting the laminate are as described above for the members, materials, and adherends, and therefore redundant explanations will not be repeated.

[0241] As will be understood from the above description and the following examples, the matters disclosed by this specification include the following. [1] A pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer, an adhesive surface formed by the adhesive layer; The pressure-sensitive adhesive layer has a refractive index of more than 1.570, a total light transmittance of 86% or more, and a haze value of 3.0% or less. [2] The pressure-sensitive adhesive sheet according to [1] above, wherein the pressure-sensitive adhesive layer has a thickness of 5 μm or more. [3] The pressure-sensitive adhesive sheet according to [1] or [2] above, which has a peel strength (adhesive strength) to a glass plate of 3 N / 25 mm or more. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the pressure-sensitive adhesive surface has an arithmetic mean roughness Ra of 100 nm or less. [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. [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, which is configured as a laminate including the pressure-sensitive adhesive layer and a light-transmitting substrate. [7] The pressure-sensitive adhesive sheet according to [6] above, wherein the light-transmitting substrate is a resin film. [8] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, which is a double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer. [9] The pressure-sensitive adhesive sheet according to any one of [1] to [8] above, a release liner disposed on the adhesive surface of the pressure-sensitive adhesive sheet; and A pressure-sensitive adhesive sheet with a release liner, comprising:

[10] A pressure-sensitive adhesive composition used to form a pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to any one of [1] to [8] above.

[0242]

[11] An acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit; The additive (H) is an organic material having a higher refractive index than the acrylic polymer (A). RO )and, A pressure-sensitive adhesive composition comprising:

[12] The above additives (H RO ) has a refractive index of 1.60 or more.

[13] The amount of the additive (H) relative to 100 parts by weight of the acrylic polymer (A). RO The pressure-sensitive adhesive composition according to the above

[11] or

[12] , wherein the content of the hydroxybenzoate is more than 0 parts by weight and not more than 60 parts by weight.

[14] The above additives (H RO The pressure-sensitive adhesive composition according to any one of the above

[11] to

[13] , wherein the compound (I) contains at least one compound selected from the group consisting of aromatic ring-containing compounds and heterocycle-containing compounds.

[15] The above additives (H RO The pressure-sensitive adhesive composition according to any one of the above

[11] to

[14] , which contains a compound having two or more aromatic rings in one molecule.

[16] The above additives (H RO ) is a compound having two or more aromatic rings in one molecule, (i) contains a structure in which two non-fused aromatic rings are directly chemically bonded; and (ii) containing a structure in which two aromatic rings are fused together; The pressure-sensitive adhesive composition according to

[15] above, comprising a compound that satisfies at least one of the following:

[17] The pressure-sensitive adhesive composition according to any one of

[11] to

[16] , 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.

[18] In the monomer components constituting the acrylic polymer (A), the content of the aromatic ring-containing monomer (m1) is more than 70% by weight and less than 100% by weight, The pressure-sensitive adhesive composition according to any one of the above

[11] to

[17] , wherein 50 wt % or more of the aromatic ring-containing monomers (m1) are monomers whose homopolymer has a glass transition temperature of 10°C or lower.

[19] The pressure-sensitive adhesive composition according to any one of

[11] to

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

[20] The pressure-sensitive adhesive composition according to any one of

[11] to

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

[21] A pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition according to any one of

[11] to

[20] above, which has a refractive index higher than 1.570.

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

[11] to

[20] above.

[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.

[0243]

[24] An interlayer sheet used by being disposed between layers of a laminate in optical applications, A viscoelastic layer V1 having a refractive index n1 of 1.570 or more; Total light transmittance is 86% or more; A haze value of 1.0% or less; and The storage modulus G' at 25°C is 30 kPa to 700 kPa; Meet the interlayer sheet.

[25] The interlayer sheet according to

[24] above, having a thickness of 5 μm or more.

[26] The interlayer sheet according to

[24] or

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

[27] The interlayer sheet according to

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

[28] The viscoelastic layer V2 is further laminated on the viscoelastic layer V1, Storage modulus G' of the viscoelastic layer V2 at 25°C V2 is the storage modulus G' of the viscoelastic layer V1 at 25°C V1 The interlayer sheet according to any one of the above

[24] to

[27] , wherein the thickness is lower than the thickness of the interlayer sheet.

[29] The interlayer sheet according to

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

[30] The interlayer sheet according to any one of

[24] to

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

[11] to

[18] above.

[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.

[32] The interlayer sheet according to any one of

[24] to

[31] above, a resin film laminated on the interlayer sheet; An optical laminate comprising:

[33] The interlayer sheet according to any one of

[24] to

[31] above, a release liner covering at least one surface of the interlayer sheet; an interlayer sheet with a release liner, comprising: [Example]

[0244] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to these specific examples. In the following description, "parts" and "%" representing amounts used and contents are by weight unless otherwise specified.

[0245] <Preparation of Acrylic Pressure-Sensitive Adhesive Composition C1> A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 95 parts of m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A," refractive index: 1.566, homopolymer Tg: -35°C; hereinafter abbreviated as "POB-A") as monomer components, 5 parts of 4-hydroxybutyl acrylate (4HBA), 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 100 parts of toluene as a polymerization solvent. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 60°C. The polymerization reaction was carried out for 6 hours to prepare a solution (50%) of acrylic polymer A1. The weight average molecular weight (Mw) of this acrylic polymer A1 was 500,000. The acrylic polymer A1 was obtained by polymerization of a Tg (i.e., Tg) based on the composition of the above monomer components. T ) is −35° C., and the Tg based on the composition of the aromatic ring-containing monomer (i.e., Tg m1 ) is -35℃. The above acrylic polymer A1 solution (50%) was diluted to 30% with ethyl acetate, and 334 parts of this solution (100 parts non-volatiles) was mixed with 10 parts (0.1 parts non-volatiles) of a 1% ethyl acetate solution of hexamethylene diisocyanate isocyanurate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 parts non-volatiles) of a 1% ethyl acetate solution of nursem ferric iron as a crosslinking catalyst, followed by stirring and mixing to prepare acrylic pressure-sensitive adhesive composition C1.

[0246] <Preparation of Acrylic Pressure-Sensitive Adhesive Composition C2> A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet, and condenser was charged with 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, hereafter abbreviated 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. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 60°C. The polymerization reaction was carried out for 6 hours to prepare a solution (50%) of acrylic polymer A2. The weight average molecular weight (Mw) of this acrylic polymer A2 was 500,000. A separable flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas inlet tube was charged with 20 parts of POB-A as monomer components, 80 parts of NMT-A, 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, and then nitrogen gas was introduced and the atmosphere was purged with nitrogen for approximately 1 hour while stirring. The flask was then heated to 70°C and reacted for 12 hours to yield an acrylic oligomer (oligomer B) with a weight-average molecular weight (Mw) of 4000 and a refractive index of 1.63. The above acrylic polymer A2 solution (50%) was diluted to 30% with ethyl acetate, and 334 parts of this solution (100 parts non-volatiles) were mixed with 20 parts of the above-prepared oligomer B, 10 parts (0.1 parts non-volatiles) 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 retarder, and 1 part (0.01 parts non-volatiles) of a 1% ethyl acetate solution of nursem ferric as a crosslinking catalyst, and the mixture was stirred to prepare acrylic pressure-sensitive adhesive composition C2.

[0247] <Preparation of Acrylic Pressure-Sensitive Adhesive Composition C3> A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet, and condenser was charged with 65 parts of 2-ethylhexyl acrylate as monomer components, 30 parts of 1H,1H,5H-octafluoropentyl acrylate (Osaka Organic Chemical Industry, Ltd., trade name: Biscoat 8F), 3 parts of N-vinyl-2-pyrrolidone (NVP, Nippon Shokubai), and 2 parts of 4HBA, 0.2 parts of AIBN as a polymerization initiator, and 200 parts of ethyl acetate as a polymerization solvent. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 60°C. The polymerization reaction was carried out for 9 hours to prepare a solution (33%) of acrylic polymer A3. The weight average molecular weight (Mw) of the acrylic polymer A3 was 550,000. The above solution (33%) of acrylic polymer A3 was diluted to 30% with ethyl acetate, and 10 parts (0.1 parts nonvolatile 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) was added as a crosslinking agent to 100 parts of nonvolatile content (solid content) and mixed with stirring to prepare acrylic pressure-sensitive adhesive composition C3.

[0248] <Production of interlayer sheet> (Example 1) The acrylic pressure-sensitive 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 pressure-sensitive adhesive layer. The silicone-treated surface of a PET film R2 (38 μm thick) that had been silicone-treated on one side was then bonded to the surface of the pressure-sensitive adhesive layer. In this way, a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer V1) was obtained in which both sides were protected by PET films (release liners) R1 and R2. Release liner R2 has a relatively light release property compared to release liner R1. The acrylic pressure-sensitive adhesive composition C3 prepared above was applied to the silicone-treated surface of a 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 10 μm thick pressure-sensitive adhesive layer V2. The silicone-treated surface of a PET film R2 (38 μm thick) that had been silicone-treated on one side was then bonded to the surface of the pressure-sensitive adhesive layer. In this way, a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer V2) was obtained in which both sides were protected by PET films (release liners) R1 and R2. The release liner R2 was peeled off from the pressure-sensitive adhesive layers V1 and V2, and the adhesive surfaces were bonded together and pressed with a hand roller. This laminate was autoclaved for 30 minutes at 50°C and 0.60 MPa, and then aged for 48 hours in a 50°C environment. In this way, an interlayer sheet (substrate-less double-sided pressure-sensitive adhesive sheet) consisting of a two-layer structure of pressure-sensitive adhesive layers V1 / V2 was obtained. The surface of this interlayer sheet was protected by two release liners R1.

[0249] (Example 2) An interlayer sheet (substrateless double-sided adhesive sheet) consisting of 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.

[0250] (Examples 3 to 5) In the same manner as in Example 1, single-layer pressure-sensitive adhesive layers each consisting of acrylic pressure-sensitive adhesive compositions C1 to C3 and having the thickness shown in Table 1 were prepared, and these were used as interlayer sheets according to Examples 3 to 5.

[0251] The obtained interlayer sheet was allowed to fully acclimate to an environment of 23°C and 50% RH, and then used for the following measurements and evaluations.

[0252] <Measurement and Evaluation (1)> (refractive index) The refractive index of each pressure-sensitive adhesive layer was measured using an Abbe refractometer (manufactured by ATAGO, model "DR-M4") at a measurement wavelength of 589 nm and a measurement temperature of 25° C. The results are shown in Table 1.

[0253] (storage modulus G') The pressure-sensitive adhesive layers of each example were laminated to a thickness of approximately 1.5 mm to prepare a measurement sample. Dynamic viscoelasticity measurements were carried out under the following conditions using an ARES manufactured by TA Instruments. The storage modulus G' at 25°C was read from the measurement results. The results are shown in Table 1. [Measurement conditions] Deformation mode: Torsion Measurement frequency: 1Hz Heating rate: 5°C / min Shape: Parallel plate 7.9mmφ

[0254] (Total light transmittance and haze value) The interlayer sheet according to each example was bonded to alkali-free glass (thickness 0.8-1.0 mm, total light transmittance 92%, haze 0.4%) to form a test piece, which was then measured for total light transmittance and haze using a haze meter (manufactured by Murakami Color Research Laboratory, trade name "HAZEMETER HM-150") at a measurement temperature of 23°C. 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.

[0255] (peel strength against glass plate) In a measurement environment of 23°C and 50% RH, the release liner was peeled from one side of the interlayer sheet according to 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 attached as a backing, followed by cutting to a size of 25 mm wide and 100 mm long to prepare a test piece. The release liner on the other side was peeled from the test piece, and the test piece was pressed against the surface of an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., 1.35 mm thick, blue plate with polished edges) as an adherend, using a 2 kg roller to make one reciprocating motion. This was left in the same 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, and then left for 24 hours in an atmosphere of 23°C and 50% RH. After that, the peel strength (adhesive strength) [N / 25 mm] was measured using a universal tension and compression tester in accordance with JIS Z 0237:2000 at a tension speed of 300 mm / min and a peel angle of 180°. The universal tension and compression tester used was a Minebea "Tension and Compression Tester, TG-1kN."

[0256] [Table 1]

[0257] As shown in Table 1, the interlayer sheets of Examples 1 to 4 have a refractive index n1 of 1.570 or more and a storage modulus G' V1 (25) contained a pressure-sensitive adhesive layer V1 with a strength of 700 kPa or less, and the interlayer sheet exhibited high transparency. These interlayer sheets exhibited practical peel strength suitable for bonding between layers of optical components.

[0258] <Evaluation of front brightness improvement effect> The interlayer sheet according to each example was attached to a white LED light source, and the light source was turned on in a darkroom environment for 30 minutes or more to stabilize it. Then, the front luminance of the part where the interlayer sheet was attached was measured using a spectroradiometer SR-UL1R (manufactured by Topcon Technohouse Corporation). Using the average value of the luminance measured three times, those that had a luminance improvement of 10% or more compared to the luminance of the light source without the interlayer sheet attached were evaluated as G (Good), and those that had a luminance improvement of less than 10% were evaluated as P (Poor).

[0259] [Table 2]

[0260] As shown in Table 2, the interlayer sheets of Examples 1 and 2, which have a laminated structure of a pressure-sensitive adhesive layer combining the low-refractive-index pressure-sensitive adhesive layer of Example 5 (pressure-sensitive adhesive layer V2) and the high-refractive-index pressure-sensitive adhesive layer of Examples 3 and 4 (pressure-sensitive adhesive layer V1), exhibited a front brightness improvement effect of 10% or more compared to when the interlayer sheet was not used. The interlayer sheets of Examples 3 to 5, which have a single-layer structure of the pressure-sensitive adhesive layer, did not exhibit an improvement in front brightness due to the interlayer sheet alone. The interlayer sheets of Examples 3 and 4 can be laminated to a member with a lower refractive index (e.g., a resin film) to improve the front brightness of the laminate. The interlayer sheet of Example 5 can be laminated to a member with a higher refractive index (e.g., a resin film) to improve the front brightness of the laminate.

[0261] <Preparation of Acrylic Pressure-Sensitive Adhesive Composition C4> A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 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. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 60°C, allowing the polymerization reaction to proceed for 6 hours, producing a solution (50%) of acrylic polymer A4. The Mw of this acrylic polymer A4 was 520,000. The above solution (50%) of acrylic polymer A4 was diluted to 30% with ethyl acetate, and 334 parts of this solution (100 parts non-volatile content) was mixed with 10 parts (0.1 parts non-volatile content) of a 1% ethyl acetate solution of Coronate HX as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 parts non-volatile content) of a 1% ethyl acetate solution of Nursem Ferric as a crosslinking catalyst, followed by stirring and mixing to prepare acrylic pressure-sensitive adhesive composition C4.

[0262] <Preparation of Acrylic Pressure-Sensitive Adhesive Composition C5> A solution of acrylic polymer A5 (50%) was prepared in the same manner as for the preparation of the solution of acrylic polymer A4, except that the composition (weight ratio) of the monomer components was changed to POB-A / ethyl carbitol acrylate (CBA) / 4HBA = 79 / 20 / 1. The Mw of this acrylic polymer A5 was 460,000. An acrylic pressure-sensitive adhesive composition C5 was prepared in the same manner as for the preparation of acrylic pressure-sensitive adhesive composition C4, except that the solution of acrylic polymer A5 was used instead of the solution of acrylic polymer A4.

[0263] <Preparation of Acrylic Pressure-Sensitive Adhesive Composition C6> A solution (50%) of acrylic polymer A6 was prepared in the same manner as the solution of acrylic polymer A4, except that the monomer composition (weight ratio) was changed to P2H-A / 4HBA = 99 / 1. In the above monomer composition, "P2H-A" refers to phenoxydiethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate P2H-A", refractive index: 1.510, Tg of homopolymer: -35°C). The Mw of this acrylic polymer A6 was 1,000,000. A solution (50%) of acrylic polymer A6 was diluted to 30% with ethyl acetate, and 334 parts of this solution (100 parts of nonvolatile matter) was mixed with an additive (H ROAcrylic adhesive composition C6 was prepared by adding 20 parts of 6-ethylacrylate-dinaphtho[2,1-b:1',2'-d]thiophene (6-acryloyloxyethyldinaphthothiophene, manufactured by Sugai Chemical Industry Co., Ltd., abbreviated as 6EDNTA, refractive index: 1.722) as a crosslinking agent, 10 parts (non-volatile content: 0.1 part) of a 1% ethyl acetate solution of Coronate HX as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (non-volatile content: 0.01 part) of a 1% ethyl acetate solution of Nursem Ferric as a crosslinking catalyst, and stirring and mixing them.

[0264] <Preparation of Acrylic Pressure-Sensitive Adhesive Composition C7> A solution (50%) of acrylic polymer A1 was diluted to 30% with ethyl acetate, and 334 parts of this solution (100 parts non-volatile content) was mixed with 10 parts of POB-A as an additive (plasticizing material), 10 parts (0.1 part non-volatile content) of a 1% ethyl acetate solution of Coronate HX as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 part non-volatile content) of a 1% ethyl acetate solution of Nursem Ferric as a crosslinking catalyst, followed by stirring to prepare acrylic pressure-sensitive adhesive composition C7.

[0265] <Preparation of Acrylic Pressure-Sensitive Adhesive Composition C8> Acrylic pressure-sensitive adhesive composition C8 was prepared in the same manner as in the preparation of acrylic pressure-sensitive adhesive composition C7, except that 10 parts of POB-A was changed to 10 parts of 3-phenoxybenzyl alcohol (manufactured by Tokyo Chemical Industry Co., Ltd., refractive index 1.59).

[0266] <Preparation of Acrylic Pressure-Sensitive Adhesive Composition C9> A solution (50%) of acrylic polymer A9 was prepared in the same manner as the solution of acrylic polymer A3, except that the composition (weight ratio) of the monomer components was changed to 2EHA / Viscoat 13F / 4HBA = 49 / 50 / 1. In the above-mentioned composition of the monomer components, "Viscoat 13F" represents 1H,1H,2H,2H-tridecafluorooctyl acrylate (manufactured by Osaka Organic Chemical Industry Ltd., trade name "Viscoat 13F"). The Mw of this acrylic polymer A9 was 550,000. An acrylic pressure-sensitive adhesive composition C9 was prepared in the same manner as the preparation of acrylic pressure-sensitive adhesive composition C3, except that a solution of acrylic polymer A9 was used instead of the solution of acrylic polymer A3.

[0267] <Production of interlayer sheet> (Examples 6-10) An interlayer sheet (substrateless double-sided adhesive sheet) consisting of a two-layer structure of adhesive layer V1 / adhesive layer 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 as shown in Table 3.

[0268] The interlayer sheets obtained in Examples 6 to 10 were thoroughly acclimatized to an environment of 23°C and 50% RH, and then the measurements and evaluations of each item were carried out in the same manner as in "Measurement and Evaluation (1)" above. The results are shown in Table 3.

[0269] [Table 3]

[0270] As shown in Table 3, the interlayer sheets of Examples 6 to 10 have a refractive index n1 of 1.570 or more and a storage modulus G' V1 (25) contained a pressure-sensitive adhesive layer V1 with a strength of 700 kPa or less, and the interlayer sheet exhibited high transparency. These interlayer sheets exhibited practical peel strength suitable for bonding between layers of optical components.

[0271] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0272] 1,2 Interlayer sheet (adhesive sheet) 10 Viscoelastic layer (adhesive layer, viscoelastic layer V1) 10A First surface (adhesive surface) 10B Second Surface 11 First viscoelastic layer (first adhesive layer, viscoelastic layer V1) 12 Second viscoelastic layer (second adhesive layer, viscoelastic layer V2) 20 Supporting base material 20A Page 1 20B 2nd side (back) 30, 31, 32 Release liner 50 Adhesive sheet with release liner (Interlayer sheet with release liner) 70 Optical Components 100 Optical laminate

Claims

1. An interlayer sheet to be placed between layers of a laminate for optical applications, Refractive index n １ is 1.570 or more, and the storage modulus G' at 25°C is V1 Viscoelastic layer V having a viscosity of 30 kPa to 700 kPa １ Including, An interlayer sheet having a total light transmittance of 86% or more and a haze value of 1.0% or less.

2. 2. The interlayer sheet according to claim 1, having a thickness of 5 μm or more.

3. The viscoelastic layer V １ The viscoelastic layer V is laminated on ２ further comprising The viscoelastic layer V ２ Storage modulus G' at 25 ° C. V2 is the viscoelastic layer V １ Storage modulus G' at 25 ° C. V1 The interlayer sheet according to claim 1 or 2, wherein the thickness is lower than 100 μm.

4. The viscoelastic layer V ２ Refractive index n ２ is the viscoelastic layer V １ Refractive index n １ The interlayer sheet of claim 3, wherein the thickness is lower than 100 μm.

5. The interlayer sheet according to any one of claims 1 to 4, a release liner covering at least one surface of the interlayer sheet; an interlayer sheet with a release liner, comprising:

6. The interlayer sheet according to any one of claims 1 to 4, a resin film laminated on the interlayer sheet; An optical laminate comprising:

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