Interlayer sheets, interlayer sheets with release liners, and optical laminates

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 interlayer sheets, interlayer sheets with release liners, and optical laminates. [Background technology]

[0002] Generally, adhesives (also called pressure-sensitive adhesives; the same applies hereinafter) exhibit a soft solid (viscoelastic) state at temperatures around room temperature and have the property of easily adhering to a substrate under pressure. Taking advantage of this property, adhesives are widely used in various industrial fields, from home appliances to automobiles, various machinery, electrical equipment, and electronic devices, for purposes such as joining, fixing, and protection. One example of an application of adhesives is in display devices such as liquid crystal displays and organic EL displays, where polarizing films, phase difference films, cover window members, and various other light-transmitting members are joined to other members. Patent documents 1 and 2 are cited as technical documents relating to adhesives for optical components. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-169382 [Patent Document 2] Japanese Patent Publication No. 2017-128732 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Patent documents 1 and 2 propose an adhesive composition mainly composed of a (meth)acrylic acid ester polymer containing a monomer having multiple aromatic rings as a monomer unit, and an adhesive obtained by crosslinking the adhesive composition, but do not disclose a specific adhesive that combines a refractive index of 1.570 or higher with flexibility. On the other hand, there is a known technique for increasing the refractive index by blending particles made of inorganic materials with a high refractive index (for example, inorganic particles such as zirconium oxide particles or titanium oxide particles) into a resin, but adhesives containing inorganic particles have a trade-off relationship between refractive index and adhesive properties (e.g., peel strength, flexibility, etc.), making their application to the field of adhesives difficult. In particular, for adhesives for optical applications, it is necessary to consider the impact on optical properties (e.g., total light transmittance, haze, etc.) when blending inorganic particles. 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 increase the refractive index while balancing flexibility and high transparency that can exhibit appropriate adhesion and deformation-following properties to the member adjacent to the interlayer sheet.

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

[0006] This specification provides an interlayer sheet used in optical applications, which is placed between layers of a laminate. The interlayer sheet includes a viscoelastic layer V1 having a refractive index n1 of 1.570 or higher. The interlayer sheet has a total light transmittance of 86% or higher, a haze value of 1.0% or lower, and a storage modulus G' at 25°C. V1 (Hereafter, "storage modulus G' V1 (25) is sometimes written as ". The pressure is 30kPa to 700kPa. The above interlaminar sheet has a high refractive index while having a storage modulus G'V1 (25) contains a viscoelastic layer V1 in which the amount of (25) is suppressed to a certain level or less, and is highly transparent, making it useful as an interlayer sheet for optical applications. Furthermore, since the interlayer sheet is pre-formed into a sheet shape, it can be easily placed at the desired location.

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

[0008] Some embodiments of the interlayer sheet further include a viscoelastic layer V2 laminated on the viscoelastic layer V1. Here, the storage modulus G' of the viscoelastic layer V2 at 25°C. V2 (Hereafter, "storage modulus G' V2 (25) is sometimes written as "G' of the storage modulus of the viscoelastic layer V1 at 25°C". V1 Lower. Interlayer sheets with this configuration can be 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 behavior of light transmitted through the interlayer sheet can be controlled by utilizing the difference in refractive indices between the viscoelastic layers V1 and V2.

[0010] Furthermore, this specification provides an interlaminar sheet with a release liner, comprising any of the interlaminar sheets disclosed herein and a release liner covering at least one surface of the interlaminar sheet. The interlaminar sheets disclosed herein may be preferably used in a manner in which they are manufactured, stored, distributed, processed, etc., in the form of an interlaminar sheet with a release liner in which at least one surface is protected by the release liner, and the release liner is peeled off before lamination with adjacent members.

[0011] Furthermore, this specification provides an optical laminate comprising 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 having a high refractive index, high transparency, and flexibility can be preferably realized.

[0012] Furthermore, combinations of the elements described herein may also be included within the scope of the invention for which patent protection is sought in this patent application. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing the configuration of an interlayer sheet according to one embodiment. [Figure 2] This is a schematic cross-sectional view showing the configuration of an interlayer sheet according to another embodiment. [Figure 3] This is a schematic cross-sectional view showing an optical laminate including an interlayer sheet according to one embodiment. [Modes for carrying out the invention]

[0014] Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood by those skilled in the art based on the teachings on carrying out the invention described herein and the common technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed herein and the common technical knowledge in the art. In the following drawings, components and parts that perform the same function may be denoted by the same reference numeral and described accordingly, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic representations for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the size or scale of the actual product provided.

[0015] In this specification, "self-luminous element" means a light-emitting element whose luminescence can be controlled by the value of the current flowing through it. A self-luminous element may consist of a single element or an assembly of elements. Specific examples of self-luminous elements include, but are not limited to, light-emitting diodes (LEDs) and organic ELs. When a light-emitting device is referred to in this specification, the light-emitting device may include such self-luminous elements as components. Examples of the above-mentioned light-emitting devices include, but are not limited to, light source module devices used for illumination (e.g., planar light-emitting module) and display devices with pixels.

[0016] This specification provides an interlayer sheet used in optical applications, which is placed 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 adhesive layers composed of an adhesive. Such an interlayer sheet can be understood as an adhesive sheet having an adhesive layer. Hereinafter, the interlayer sheet may be referred to as an adhesive sheet, the viscoelastic layer as an adhesive layer, the viscoelastic material as an adhesive, and the surface of the viscoelastic layer as an adhesive surface. The member on which the viscoelastic layer of the interlayer sheet disclosed herein is laminated may be referred to as the adherend of the interlayer sheet (adhesive sheet). In some embodiments, it is preferable that the interlayer sheet has an adhesive surface composed of an adhesive layer V1.

[0017] <Example of interlayer sheet configuration> The interlayer sheets disclosed herein may be in the form of an adhesive sheet with a substrate, having an adhesive layer (for example, a single-layer adhesive layer consisting of a viscoelastic layer V1, or a laminated adhesive layer in which two or more adhesive layers including a viscoelastic layer V1 and a viscoelastic layer V2 are directly in contact and laminated) on one or both sides of a non-peelable substrate (supporting substrate), or they may be in the form of a substrate-less adhesive sheet (i.e., an adhesive sheet without a non-peelable substrate; typically an adhesive sheet consisting of an adhesive layer), such as in a form where the adhesive layer is held by a release liner. The concept of an adhesive sheet as used herein may include adhesive tapes, adhesive labels, adhesive films, etc. The adhesive sheets disclosed herein may be in the form of rolls, sheets, or even adhesive sheets processed into various shapes.

[0018] Figure 1 shows an example of the configuration of the interlayer sheet disclosed herein. This interlayer sheet (adhesive sheet) 1 is configured as a single-sided adhesive sheet (single-sided adhesive sheet) including an adhesive layer 10 whose first surface 10A is the surface that adheres to the substrate (adhesive surface), and a support substrate 20 laminated on the second surface 10B of the adhesive layer 10. The second surface 10B of the adhesive layer 10 is bonded to the first surface (non-peelable surface) 20A of the support substrate 20. As the support substrate 20, for example, a plastic film such as a polyester film may be used. The support substrate 20 may also be an optical film such as a polarizing plate. Before use (before adhesion to the substrate), the adhesive sheet 1 may be in the form of an adhesive sheet 50 with a release liner, where the adhesive surface 10A is protected by a release liner 30, at least on the side of the adhesive layer, which is a peelable surface (peel surface), as shown in Figure 1. Alternatively, the second surface 20B of the support substrate 20 (the surface opposite to the first surface 20A, also called the back surface) may be a release surface, and the adhesive surface 10A may be protected by being wound or laminated so that it comes into contact with this second surface 20B. The adhesive layer 10 may be a single-layer structure consisting of a viscoelastic layer V1 as shown in Figure 1, or it may be a laminated structure in which two or more sub-adhesive layers with different compositions (for example, two sub-adhesive layers, the viscoelastic layer V1 that constitutes the adhesive surface 10A and the viscoelastic layer V2 that is placed 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 adhesive sheet consisting of an adhesive layer. As shown in Figure 2, the substrate-less double-sided adhesive sheet 2 may be in a form in which, before use, the first surface (first adhesive surface) 10A and the second surface (second adhesive surface) 10B of the adhesive layer 10 are protected by release liners 31, 32, at least on the side facing the adhesive layer, which is a release surface. Alternatively, the back surface of the release liner 31 (the surface opposite to the adhesive side) may be a release surface, and the adhesive surfaces 10A and 10B may be protected by winding or laminating so that the adhesive surface 10B abuts against the back surface of the release liner 31. Such a substrate-less double-sided adhesive sheet can 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 adhesive surfaces of the first and second adhesive surfaces. The adhesive layer 10 constituting the substrate-less double-sided adhesive sheet 2 shown in Figure 2 has a laminated structure in which two sub-adhesive layers of different compositions are directly in contact and laminated. Specifically, the adhesive layer 10 is a laminated structure (two-layer structure) consisting of a first viscoelastic layer (first adhesive layer, viscoelastic layer V1) 11 and a second viscoelastic layer (second adhesive layer, viscoelastic layer V2) 12. Alternatively, the interlayer sheet disclosed herein may be in the form of a substrate-less double-sided adhesive sheet consisting of a single-layer adhesive layer (viscoelastic layer V1). Such an interlayer sheet in the form of a substrate-less double-sided adhesive sheet with a laminated structure or a single-layer structure can be used, for example, as a component of an optical laminate in which optical members are laminated on the first adhesive surface and the second adhesive surface, respectively.

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

[0021] Furthermore, the interlayer sheet disclosed herein may also be in the form of a double-sided adhesive sheet with a substrate (double-sided adhesive sheet with a substrate), comprising a support substrate having a non-peelable first surface and a second surface, with a first adhesive layer fixedly laminated on the first surface and a second adhesive layer fixedly laminated on the second surface. An example of such a double-sided adhesive sheet with a substrate is the single-sided adhesive sheet 1 shown in Figure 1, in which the second surface 20B of the support substrate 20 is a non-peelable surface and a second adhesive layer is provided on the second surface 20B, the second surface of the second adhesive layer is bonded to the second surface 20B of the support substrate 20, and the first surface of the second adhesive layer (the surface opposite to the second surface) is the second adhesive surface of the double-sided adhesive sheet with a substrate. The composition of the adhesive constituting the second adhesive layer may be the same as or different from the composition of the adhesive constituting the first adhesive layer. Such interlayer sheets in the form of a substrate-attached double-sided adhesive sheet can be used, for example, as a component of an optical laminate in which optical members are laminated on the first adhesive surface and the second adhesive surface, respectively. Before use, the substrate-attached double-sided adhesive sheet may be in a form in which the first adhesive surface and the second adhesive surface are protected by a release liner, similar to the substrate-less double-sided adhesive sheet described above.

[0022] <Characteristics of interlayer sheets> (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 constituting at least one surface (adhesive surface) of the viscoelastic layer with an adhesive (viscoelastic material) having a refractive index of 1.570 or higher. According to the technology disclosed herein, 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 containing the adhesive layer V1 can be provided.

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

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

[0025] The interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet (including both substrate-less double-sided adhesive sheets and substrate-attached double-sided adhesive sheets; the same applies hereinafter unless otherwise specified) in which one side is a first adhesive surface and the other side is a second adhesive surface, and when the first adhesive surface is composed of an adhesive layer V1, it is preferable that the adhesive layer satisfies at least one of the refractive indices described above for the first adhesive surface. The refractive index of the second adhesive surface 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 indices of 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 greater than 0.00. The relative relationship of the refractive indices of the two adhesive surfaces may be n1>n2, or 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 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 relative magnitudes of n1 and n2 may be reversed. There is no particular upper limit to n1-n2. 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, may be 0.26 or less, may be 0.21 or less, may be 0.18 or less, or may be 0.16 or less. An interlayer sheet with different refractive indices for the first and second adhesive surfaces can be realized, for example, in a double-sided adhesive sheet with a substrate, by laminating first and second adhesive layers with different refractive indices onto a non-peelable support substrate, or by creating a laminated structure of two or more sub-adhesive layers in a substrate-less double-sided adhesive sheet, and making the refractive indices of the adhesive constituting the first adhesive surface and the adhesive constituting the second adhesive surface different in this 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, approximately 1.01 or greater, preferably approximately 1.02 or greater, and may also be approximately 1.03 or greater. In some embodiments, the ratio (n1 / n2) may be advantageous to be approximately 1.05 or greater, preferably approximately 1.07 or greater, more preferably approximately 1.10 or greater, and may also be approximately 1.11 or greater. There is no particular upper limit to the ratio (n1 / n2). In some embodiments, from the viewpoint of adhesive properties, transparency, etc., 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, and approximately 1.12 or less.

[0029] (Storage modulus G') In the interlayer sheet (adhesive sheet) disclosed herein, the storage modulus G' of the viscoelastic layer (adhesive layer) V1 at 25°C (storage modulus G' V1(25) is appropriately set according to the purpose of use, usage mode, etc., and is not limited to a specific range. The storage elastic modulus G’ V1 (25) can be, for example, in the range of approximately 30 kPa to 700 kPa. In some embodiments, from the perspective of ease of attachment to the adherend, etc., the storage elastic modulus G’ V1 (25) is advantageously 600 kPa or less, preferably 500 kPa or less, and more preferably 400 kPa or less (for example, 350 kPa or less). In some embodiments, from the perspective of enhancing the flexibility of the adhesive layer V1 at room temperature (for example, 25 °C) and facilitating adhesion to the adherend, the storage elastic modulus G’ V1 (25) is advantageously 330 kPa or less, preferably 300 kPa or less. In some embodiments where the adhesion and flexibility at room temperature are more emphasized, the storage elastic 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 (for example, less than 140 kPa). In some embodiments, the storage elastic modulus G’ V1 (25) may be less than 100 kPa or less than 90 kPa. The storage elastic modulus G’ V1 (25) The lower limit is not particularly limited, but from the perspective of processability, handleability, etc., it may be, for example, 30 kPa or more, may be 50 kPa or more, or may be 70 kPa or more. In some embodiments, considering the increase in refractive index, the storage elastic modulus G’ V1 (25) may be 100 kPa or more, may be 150 kPa or more, may be 200 kPa or more, may be 250 kPa or more, or may be 300 kPa or more.

[0030] In the adhesive sheet disclosed herein, the storage elastic modulus G’ of the viscoelastic layer (adhesive layer) V1 at 50 °C (storage elastic modulus G’ V1 (50)) is not particularly limited and may be, for example, less than 100 kPa. In some embodiments, the storage elastic modulus G’ V1(50) is appropriately less than 60 kPa, preferably less than 40 kPa, and more preferably less than 38 kPa (e.g., less than 36 kPa). Thus, the storage modulus G' V1 The adhesive layer V1 with (50) restricted can be easily made to have better adhesion to the adherend by applying appropriate heating as needed, thereby improving adhesion to the adherend. Storage modulus G' V1 The lower limit of (50) is not particularly limited. In some embodiments, the storage modulus G' is chosen from the viewpoint of the heat resistance properties of the adhesive layer V1. 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 is provided for the following conditions: (a) Storage modulus G' V1 (25) is 350 kPa or less (preferably less than 200 kPa, for example 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, for example less than 38 kPa); It is preferable that at least one of the above conditions is met. An adhesive layer V1 that satisfies at least condition (a) above is preferred from the viewpoint of adhesion to the adherend and flexibility in the room temperature range (e.g., 25°C). An interlayer sheet having an adhesive layer V1 that satisfies at least condition (b) above is preferred because its adhesion to the adherend can be easily improved by heating it to a temperature slightly higher than room temperature. An interlayer sheet having an adhesive layer V1 that does not satisfy condition (a) above but satisfies condition (b) above can be used as a heat-activated type interlayer sheet that has good reworkability (repositionability) in the initial stages of application in the room temperature range and can effectively increase the peel strength from the adherend by heating it to a temperature slightly higher than room temperature. The above heat activation may be performed by heating the interlayer sheet to a temperature slightly higher than room temperature when applying it to the adherend. The above temperature slightly higher than room temperature is, for example, about 60°C or lower, and preferably about 55°C or lower (e.g., about 50°C or lower).

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

[0033] Storage modulus G' V1 (25) and G' V1(50) can be determined by dynamic viscoelasticity measurement, and from the result G' V1 (50) / G' V1 (25) can be calculated. Dynamic viscoelasticity measurement can be performed by a standard method using a commercially available dynamic viscoelasticity measuring device, for example, using ARES or an equivalent product manufactured by TA Instruments, under the following measurement conditions. As the sample for measurement, a sample prepared to a thickness of approximately 1.5 mm is used, by laminating the adhesive layer to be evaluated as needed. [Measurement conditions] Transformation mode: Twist 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 (50) and the storage modulus ratio can be adjusted by selecting the composition of the monomer components constituting the base polymer of the adhesive layer V1 (for example, selection of the type and content of monomer (m1)), selecting whether or not to use a crosslinking agent and the amount used, selecting whether or not to use a refractive index improver or plasticizing material, the type and amount used, etc. For example, as monomer (m1), in addition to the first monomer which is the main component of monomer (m1), a relatively small amount of a second monomer which has a different chemical structure from the first monomer is used in combination with the first monomer, thereby, in addition to the case when the first monomer is used alone as monomer (m1), G' V1 (50) Reduce the value, G' V1 (50) / G' V1 (25) may be reduced.

[0035] If the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface (for example, a double-sided adhesive sheet with a substrate having a first adhesive layer composed of an adhesive layer V1 on the first surface of the substrate and a second adhesive layer composed of an adhesive layer V2 on the second surface of the substrate, a substrate-less double-sided adhesive sheet with a laminated structure in which the adhesive layer V1 constituting the first adhesive surface and the adhesive layer V2 constituting the second adhesive surface are laminated without an intervening non-adhesive substrate, a substrate-less double-sided adhesive sheet with a single-layer structure in which one side of the adhesive layer V1 is the first adhesive surface and the other side of the adhesive layer V1 is the second adhesive surface, etc., the same applies to other similar descriptions), then the above-mentioned storage modulus G' V1 (25), G' V1 (50) and the storage modulus ratio are applied to at least the adhesive layer constituting the first adhesive surface, preferably to both the adhesive layer constituting the first adhesive surface and the adhesive layer constituting the second adhesive surface. The storage modulus G' of the adhesive layer constituting the first adhesive surface and the storage modulus G' of the adhesive layer constituting the second adhesive surface may be the same or different.

[0036] (Total light transmittance) The interlayer sheet disclosed herein includes an adhesive layer V1 having the high refractive index described above, and the total light transmittance of the interlayer sheet is 86% or more. Such a highly transparent interlayer sheet can be preferably applied to applications where high light transmittance is required (e.g., optical applications) or to applications where the adherend can be clearly seen through the adhesive sheet, with or without a substrate. 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%), may be 90.5% or more, may be 93% or more, or may be 95% or more. Theoretically, the upper limit of the total light transmittance is the value obtained by subtracting the light loss due to reflection at the air interface (Fresnel loss) from 100%, and in practice may be approximately 98% or less, approximately 96% or less, or approximately 95% or less. In some embodiments, considering 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. As the transmittance meter, the "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or an equivalent product is used. More specifically, for example, the total light transmittance of the interlayer sheet can be measured according to the embodiments described later. 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, the type and thickness of the substrate in the configuration including the substrate, etc.

[0037] The interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet with a substrate, in which a first adhesive layer and a second adhesive layer are fixedly laminated to a support substrate, and the first adhesive layer is a layer composed of adhesive layer V1. In this case, at least the first adhesive layer only needs to satisfy any of the above-described total light transmittances, and the total light transmittance of the second adhesive layer is not particularly limited. In usage modes in which light passes through in the thickness direction of the adhesive sheet, it is preferable that the total light transmittance of the second adhesive layer satisfies any of the above-described total light transmittances of the first adhesive layer. The relative relationship of the total light transmittances of the two adhesive layers may be first adhesive layer > second adhesive layer, first adhesive layer < second adhesive layer, or first adhesive layer = second adhesive layer.

[0038] (Haze value) The interlayer sheet disclosed herein includes an adhesive layer V1 having the high refractive index described above, and the haze value of the interlayer sheet is 1.0% or less. Such a highly transparent interlayer sheet can be preferably applied to applications where high light transmittance is required (e.g., optical applications) or to applications where the adherend can be clearly seen through the interlayer sheet, with or without a substrate. 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. The lower limit of the haze value of the interlayer sheet is not particularly limited, and from the viewpoint of improving transparency, a smaller haze value is preferable. On the other hand, in some embodiments, considering 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 interlayer sheets can also be preferably applied to the haze values ​​of adhesive sheets when the techniques disclosed herein are implemented in the form of substrate-less adhesive sheets (typically adhesive sheets consisting of an adhesive layer).

[0039] Here, "haze value" refers to the ratio of diffusely transmitted light to total transmitted light when visible light is shone on the object being measured. 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 and thickness of the material to be measured.

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

[0041] (Surface smoothness of the 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 composed of the adhesive layer V1) has high surface smoothness.

[0042] For example, it is preferable that the arithmetic mean roughness Ra of the adhesive surface is limited to a predetermined value or less. A configuration having 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 suppress the occurrence of brightness unevenness caused by the surface state of the adhesive layer in usage modes in which light is extracted through the adhesive surface (such as an interlayer sheet placed on the viewpoint side of the self-luminous element in a light-emitting device). A low arithmetic mean roughness Ra of the adhesive surface is also advantageous in suppressing optical distortion, and suppression of optical distortion also contributes to the improvement of optical homogeneity. When the interlayer adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, it is preferable that at least the arithmetic mean roughness Ra of the first adhesive surface is limited to a predetermined value or less, and it is more preferable that the arithmetic mean roughness Ra of both adhesive surfaces is limited to a predetermined value or less. By having high surface smoothness on each adhesive surface of the double-sided adhesive sheet, adhesion with excellent optical homogeneity can be preferably achieved.

[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, 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 (for example, 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 of the same magnitude or may be different.

[0044] Furthermore, for example, it is preferable that the maximum height Rz of the adhesive surface is limited to a predetermined value or less. A configuration having 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 usage embodiments where light is extracted through the adhesive surface as described above, it is possible to suppress the occurrence of brightness unevenness caused by 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 at least the maximum height Rz of the first adhesive surface is limited to a predetermined value or less, and it is more preferable that the maximum height Rz of both adhesive surfaces is limited to a predetermined value or less. By having high surface smoothness on each adhesive surface of the double-sided adhesive sheet, adhesion with excellent optical homogeneity can be preferably achieved.

[0045] In some embodiments, the maximum height Rz of the adhesive surface is preferably about 600 nm or less, more preferably about 500 nm or less, even more preferably about 450 nm or less, particularly preferably about 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, etc., in some embodiments, the maximum height Rz of the adhesive surface may be, for example, about 10 nm or more, about 50 nm or more, about 100 nm or more, or about 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 about the same 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. As the non-contact surface roughness measuring device, an optical interference surface roughness measuring device is used, for example, a 3D optical profiler (product name "NewView7300", manufactured by ZYGO) or an equivalent can be used. Specifically, the arithmetic mean roughness Ra and maximum height Rz can be measured, for example, by the following measurement method, or by setting the measurement operation and measurement conditions to obtain results equivalent to or corresponding to those obtained by the said measurement method.

[0047] Specifically, the surface shape of the sample to be measured is measured under the following conditions using a 3D optical profiler (product name "NewView7300", manufactured by ZYGO) 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 determined as the sum of the height Rp of the highest peak above the mean line of the roughness curve obtained from the above measurement and the depth Rv of the deepest valley below the mean line. The measurement is performed 5 times (i.e., N=5), and the average value is used. The above measurement sample can be prepared, for example, by cutting the adhesive layer to be measured or the interlayer sheet containing the adhesive layer to a size of approximately 150 mm in length and 50 mm in width. If the adhesive surface is protected by a release liner, the release liner should be gently peeled off (for example, under conditions of a tensile speed of 300 mm / min and a peeling angle of 180°) to expose the adhesive surface. It is desirable to allow the sample to stand for about 30 minutes after the adhesive surface is exposed before performing the 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 properties, etc.) of the adhesive composition used to form the adhesive layer, and the properties of the surface (release surface) of the release liner protecting the adhesive surface.

[0049] (Water absorption rate) In some embodiments, it is preferable that the adhesive layer V1 has a water absorption rate limited to a predetermined value or less. By limiting the water absorption rate of the adhesive layer V1, dimensional changes in the viscoelastic layer V1 due to fluctuations in the moisture content in the adhesive layer V1 (e.g., absorption and release of moisture such as humidity in the environment) tend to be suppressed. This makes it possible to suppress warping of the interlayer sheet or the optical laminate including the interlayer sheet caused by mismatches in dimensional changes between the adhesive layer V1 and adjacent layers (which may be adhesive layer V2, support substrate, release liner, adherend, etc.). Suppressing fluctuations in the moisture content in the adhesive layer V1 is also preferable from the viewpoint of maintaining constant flatness, transparency, refractive index, etc. of the adhesive layer V1. Furthermore, an interlayer sheet having an adhesive layer V1 with a low water absorption rate is less likely to absorb moisture, and is therefore suitable as an interlayer sheet used in components or products containing elements that are sensitive to moisture, such as organic EL elements.

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

[0051] The water absorption rate (also called moisture content) of the adhesive layer is measured by the following method. [Measurement of moisture content] The adhesive layer to be evaluated was placed on one side and the other side of the layer together with two release liners, measuring 4cm x 5cm (area: 20cm). 2 Cut the material to the specified size, remove the release liner from one side, and bond it to the pre-weighed aluminum foil. Next, remove the release liner from the other side of the adhesive layer, place it in a constant temperature and humidity chamber at 60°C and 90% relative humidity, and remove it after 72 hours. After weighing the test piece with the adhesive layer and aluminum foil laminated, measure the moisture content using a moisture meter (Mitsubishi Chemical Analytec CA-200) equipped with a heating vaporizer (Mitsubishi Chemical Analytec VA-200) by Karl Fischer coulometric titration under the following conditions. Anode liquid: Aquamicron AKX (manufactured by Mitsubishi Chemical) Cathodelibrium: Aquamicron CXU (manufactured by Mitsubishi Chemical) Heating vaporization temperature: 150℃

[0052] (Gel fraction) The gel fraction of the viscoelastic layer V1 is appropriately set according to the purpose and manner of use, and is not limited to a specific range. The gel fraction is, for example, approximately 99% or less, and approximately 97% or less is appropriate. From the viewpoint of suitably achieving both a high refractive index and adhesive properties, in some preferred embodiments, the gel fraction may be approximately 95% or less, and more preferably approximately 92% or less (for example, approximately 90% or less). A gel fraction that is not too high is also preferable from the viewpoint of appropriately following any irregularities that may exist on the surface of the adherend (for example, an uneven structure provided in a light-emitting device for the purpose of improving light extraction efficiency, etc.) and adhering well. 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 may be, for example, approximately 10% or more, approximately 20% or more is appropriate, and approximately 30% or more is also acceptable. From the viewpoint of deformation resistance of the viscoelastic layer V1 (prevention of bubbles due to pressure overflow or inclusion of foreign matter), the gel fraction is preferably approximately 30% or more, more preferably approximately 40% or more, and may also be approximately 45% or more, approximately 50% or more, approximately 65% ​​or more, or approximately 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] [Measurement of gel fraction] A predetermined amount of sample (weight Wg1) is wrapped in a drawstring-like shape with a porous polytetrafluoroethylene membrane (weight Wg2) having an average pore size of 0.2 μm, and the opening is tied with string (weight Wg3). As the porous polytetrafluoroethylene (PTFE) membrane, the product name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent product available from Nitto Denko Corporation is used. 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 leach out of the film. Then the package is removed, the ethyl acetate adhering to the outer surface is wiped off, and the package is dried at 130°C for 2 hours. The weight of the package (Wg4) is then measured. The gel fraction can be determined by substituting each value into the following formula. Gel fraction (%) = [(Wg4 - Wg2 - Wg3) / Wg1] × 100

[0054] The interlaminar sheet disclosed herein is a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, wherein the first adhesive surface is composed of an adhesive layer V1 and the second adhesive surface is composed of an adhesive layer V2. In this case, 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 the same or different. In some embodiments, the gel fraction of the viscoelastic layer V2 can be made lower than the gel fraction of the viscoelastic layer V1. With such a configuration, the flexibility of the interlaminar sheet can be easily increased due to the contribution of the viscoelastic layer V2, which has a relatively low gel fraction. This makes it possible to provide an interlaminar sheet that suitably achieves both a high refractive index of the viscoelastic layer V1 and flexibility of the interlaminar sheet.

[0055] In some embodiments of the technology disclosed herein, the peak temperature of the tanδ of the adhesive constituting the viscoelastic layer V1 is preferably approximately -50°C or higher, and also preferably approximately 50°C or lower. Here, the tanδ (loss tangent) of the adhesive refers to the ratio of the loss modulus G'' to the storage modulus G' of the adhesive. That is, tanδ = G'' / G'. The tanδ of the adhesive is determined by performing a temperature dispersion test of the adhesive in shear mode using a viscoelastic testing apparatus, sandwiching a disc-shaped adhesive sample with a thickness of approximately 2 mm and a diameter of 7.9 mm between parallel plates, and applying a shear strain at a frequency of 1 Hz, under the conditions of a measurement temperature range of -60°C to 60°C and a heating rate of 5°C / min. The storage modulus G' (Pa) and loss modulus G'' (Pa) at that time are obtained from the following equation: tanδ = G'' / G';. From the change in tanδ over the above temperature range, the peak temperature of the tanδ of the adhesive (hereinafter sometimes referred to as Tpeak) can be determined. For viscoelasticity testing, TA Instruments' ARES or equivalent can be used.

[0056] In some embodiments, the Tpeak of the viscoelastic layer V1 is advantageous to be 45°C or lower or 35°C or lower, preferably 30°C or lower (e.g., 25°C or lower), and may also be 20°C or lower, or 15°C or lower. Adhesives with lower Tpeaks tend to yield better initial adhesion and bonding in the room temperature range. On the other hand, a Tpeak that is not too low is preferable from the viewpoint of imparting appropriate cohesiveness to the adhesive and tends to be compatible with achieving a high refractive index. From this viewpoint, in some embodiments, the Tpeak of the adhesive may be, for example, -40°C or higher, -30°C or higher, -20°C or higher, -5°C or higher, 5°C or higher, 15°C or higher, and even 25°C or higher. Adhesives with relatively high Tpeaks can preferably be used in a manner in which, when attaching to an adherend, one or both of the adhesive and the adherend are heated to a temperature slightly higher than room temperature as needed. The Tpeak of the adhesive can be adjusted by selecting the composition of the adhesive (for example, the composition of the monomer components constituting the base polymer, the presence or absence of refractive index improvers and plasticizers, and the selection of their type and amount). When the interlayer sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, the above-described Tpeak of the adhesive is preferably applied to at least the adhesive layer constituting the first adhesive surface (preferably the viscoelastic layer V1), and more preferably to both the adhesive layer constituting the first adhesive surface and the adhesive layer constituting the second adhesive surface. The Tpeak of the adhesive layer constituting the first adhesive surface and the Tpeak of the adhesive layer constituting the second adhesive surface may be the same or different.

[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 one or more types of rubber-like polymers that can be used in the field of adhesives, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, mixtures thereof), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers, as the adhesive polymer (meaning the structural polymer that forms the adhesive, hereinafter also referred to as the "base polymer"). From the viewpoint of adhesive performance and cost, an adhesive containing an acrylic polymer or a rubber polymer as the base polymer is preferably used. Among these, an adhesive using an acrylic polymer as the base polymer (acrylic adhesive) is preferred. The technology disclosed herein is preferably implemented in a manner that uses an acrylic adhesive.

[0058] The following description will mainly focus on interlayer sheets in which the adhesive layer V1 is composed of an acrylic adhesive, i.e., interlayer sheets having an acrylic adhesive layer. However, the intention is not to limit the adhesive layer V1 in the interlayer sheets disclosed herein to an acrylic adhesive layer.

[0059] In this specification, the term "base polymer" of an adhesive refers to the main component of the rubbery polymer contained in the adhesive, and is not to be interpreted in any other way. The rubbery polymer refers to a polymer that exhibits rubber elasticity in the temperature range around room temperature. In addition, in this specification, unless otherwise specified, "main component" refers to a component that is present in an amount exceeding 50% by weight. Furthermore, in this specification, "acrylic polymer" refers to a polymer that contains monomer units derived from monomers having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. Hereinafter, monomers having at least one (meth)acryloyl group in one molecule will also be referred to as "acrylic monomers." Therefore, in this specification, acrylic polymers are defined as polymers that contain monomer units derived from acrylic monomers. A typical example of an acrylic polymer is a polymer in which the proportion of acrylic monomers among the total 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). Furthermore, in this specification, "(meth)acryloyl" comprehensively refers to acryloyl and methacryloyl. Similarly, "(meth)acrylate" comprehensively refers to acrylate and methacrylate, and "(meth)acrylic" comprehensively refers to acrylic and methacrylic. Therefore, the concept of acrylic monomers as used herein may encompass both monomers having an acryloyl group (acrylic monomers) and monomers having a methacryloyl group (methacrylic monomers).

[0060] (Acrylic polymer (A)) The interlayer sheets disclosed herein have a refractive index of 1.570 or higher and a storage modulus G' at 25°C. V1The invention can preferably be carried out in an embodiment that includes an acrylic adhesive layer having a pressure 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 that is the base polymer of the above acrylic 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, "monomer component constituting the acrylic polymer" means a monomer that constitutes a repeating unit of the acrylic polymer in the adhesive formed from the adhesive composition, regardless of whether it is included in the adhesive composition in the form of a pre-formed polymer (which may be an oligomer) or in the form of an unpolymerized monomer. That is, the monomer component constituting the acrylic polymer may be included in the adhesive composition in any of the forms of a polymer, unpolymerized or partially polymerized. From the viewpoint of ease of preparation of the adhesive composition, in some embodiments, an adhesive composition containing substantially all (for example, 95% by weight or more, preferably 99% by weight or more) of the monomer component in the form of a polymer is preferred. An adhesive composition containing substantially all of the monomer component in the form of a polymer is also preferred from the viewpoint of easily forming an interlayer sheet with less distortion and warping.

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

[0062] Examples of the ethylenically unsaturated groups mentioned above include (meth)acryloyl groups, vinyl groups, and (meth)allyl groups. From the viewpoint of polymerization reactivity, (meth)acryloyl groups are preferred, and from the viewpoint of flexibility and tackiness, acryloyl groups are more preferred. From the viewpoint of suppressing a decrease in the flexibility of the adhesive, a compound in which the number of ethylenically unsaturated groups in one molecule is 1 (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. There is no particular upper limit to the number of aromatic rings contained in monomer (m1), and it may be, for example, 16 or less. In some embodiments, from the viewpoint of ease of preparation of the acrylic polymer (A) and transparency of the adhesive, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, may be 5 or less, may be 4 or less, may be 3 or less, or may be 2 or less.

[0064] The aromatic ring of the compound used as monomer (m1) may be a carbon ring such as a benzene ring (which may be a benzene ring that constitutes part of a biphenyl or fluorene structure); a fused ring of a naphthalene ring, indene ring, azulene ring, anthracene ring, or phenanthrene ring; or a hetero ring such as a pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, pyrrole ring, pyrazole ring, imidazole ring, triazole ring, oxazole ring, isoxazole ring, thiazole ring, or thiophene ring. The heteroatoms included as ring constituent atoms in the above hetero ring may be one or more selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms constituting the above hetero ring may be nitrogen and sulfur, or both. Monomer (m1) may have a structure in which one or more carbon rings and one or more hetero rings are fused, such as a dinaphthothiophene structure.

[0065] The above aromatic ring (preferably a carbocyclic ring) may have one or more substituents on its ring constituent atoms, or it may not have substituents. If substituents are present, examples of such substituents include, but are not limited to, alkyl groups, alkoxy groups, aryloxy groups, hydroxyl groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl groups, hydroxyalkyloxy groups, glycidyloxy groups, etc. In substituents containing carbon atoms, the number of carbon atoms included 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 above aromatic ring may have no substituents on its ring constituent atoms, or it may be an aromatic ring having one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, and halogen atoms (e.g., bromine atoms). Note that when an aromatic ring of a monomer (m1) is said to have substituents on its ring constituent atoms, it means that the aromatic ring has substituents other than substituents having an ethylenically unsaturated group.

[0066] The aromatic ring and the ethylenically unsaturated group may be directly bonded or bonded via a linking group. The linking group may be a group comprising one or more structures selected from, for example, alkylene groups, oxyalkylene groups, poly(oxyalkylene) groups, phenyl groups, alkylphenyl groups, alkoxyphenyl groups, groups in which one or more hydrogen atoms are substituted with hydroxyl groups (e.g., hydroxyalkylene groups), oxy groups (-O- groups), thiooxy groups (-S- groups), etc. In some embodiments, aromatic ring-containing monomers may be preferred in which the aromatic ring and the ethylenically unsaturated group are directly bonded or bonded via a linking group selected from the group consisting of alkylene groups, oxyalkylene groups, and poly(oxyalkylene) groups. 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 monomers (m1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. Aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds can each be used individually or in combination of two or more. One or more aromatic ring-containing (meth)acrylates may be used in combination with one or more aromatic ring-containing vinyl compounds.

[0068] The content of monomer (m1) in the monomer component constituting the acrylic polymer (A) is not particularly limited and can be set to realize an adhesive layer that achieves both a 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 monomer (m1) in the monomer component may be, for example, 30% by weight or more, preferably 50% by weight or more, may be 60% by weight or more, or may be 70% by weight or more. From the viewpoint of easily obtaining a higher refractive index, in some preferred embodiments, the content of monomer (m1) may be, for example, more than 70% by weight, may be 75% by weight or more, may be 80% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. The upper limit of the content of monomer (m1) in the monomer component is 100% by weight. From the viewpoint of achieving a good balance between high refractive index and adhesive properties and / or optical properties, it is advantageous to have a monomer (m1) content of less than 100% by weight, for example, preferably about 99% by weight or less, more preferably 98% by weight or less, and may also be 97% by weight or less, or 96% by weight or less. In some embodiments, the monomer (m1) content 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 that place more emphasis on adhesive properties and / or optical properties, the monomer (m1) content 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, monomers (m1) having two or more aromatic rings (preferably carbocyclic rings) in one molecule can be preferably used because they easily provide a high refractive index effect. Examples of monomers having two or more aromatic rings in one molecule (hereinafter also referred to as "multiple aromatic ring-containing monomers") include monomers having a structure in which two or more non-condensed aromatic rings are linked via linking groups, monomers having a structure in which two or more non-condensed aromatic rings are chemically bonded directly (i.e., without the involvement of other atoms), monomers having a condensed aromatic ring structure, monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, and the like. Multiple aromatic ring-containing monomers can be used individually or in combination of two or more.

[0070] The above linking groups include, for example, oxy groups (-O-), thiooxy groups (-S-), and oxyalkylene groups (for example, -O-(CH2)). n - group, where n is 1 to 3, preferably 1), thiooxyalkylene group (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), linear alkylene group (i.e., -(CH2) n -Group (where n is 1 to 6, preferably 1 to 3), the above oxyalkylene group, the above thiooxyalkylene group, and the above linear alkylene group in which the alkylene group is partially halogenated or fully halogenated may be, etc. From the viewpoint of the flexibility of the adhesive, preferred examples of the above linking group include oxy group, thiooxy group, oxyalkylene group, and linear alkylene group. Specific examples of monomers having a structure in which two or more non-condensed aromatic rings are linked via a linking group include phenoxybenzyl(meth)acrylate (e.g., m-phenoxybenzyl(meth)acrylate), thiophenoxybenzyl(meth)acrylate, benzylbenzyl(meth)acrylate, etc.

[0071] Monomers having a structure in which two or more non-condensed aromatic rings are directly chemically bonded may include, for example, biphenyl structure-containing (meth)acrylate, triphenyl structure-containing (meth)acrylate, vinyl group-containing biphenyl, etc. Specific examples include o-phenylphenol (meth)acrylate and biphenylmethyl (meth)acrylate.

[0072] Examples of monomers having the above-mentioned 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 monomers having the above-mentioned fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene(meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene(meth)acrylate. Note that monomers having a fluorene structure include a structural portion in which two benzene rings are directly chemically bonded, and therefore are included in the concept of monomers having a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0074] Examples of monomers having the above-mentioned dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, (meth)allyl group-containing dinaphthothiophene, etc. A specific example is (meth)acryloyloxymethyl dinaphthothiophene (for example, CH2CH(R) at the 5th or 6th position of the dinaphthothiophene ring). 1 A compound with a structure in which C(O)OCH2- is bonded. Here, R 1 (These are a hydrogen atom or a methyl group.) (meth)acryloyloxyethyl dinaphthothiophene (for example, CH2CH(R) at the 5th or 6th position of the dinaphthothiophene ring)1 )C(O)OCH(CH3)- or CH2CH(R 1 A compound with a structure in which C(O)OCH2CH2- is bonded. Here, R 1 The group is a hydrogen atom or a methyl group. Examples include vinyl dinaphthothiophene (for example, a compound in which a vinyl group is bonded to the 5th or 6th position of the naphthothiophene ring), (meth)allyloxydinaphthothiophene, etc. Note that monomers having a dinaphthothiophene structure are also included in the concept of monomers having the above-mentioned condensed aromatic ring structure if they contain a naphthalene structure or if they have a structure in which a thiophene ring and two naphthalene structures are condensed.

[0075] Examples of monomers having the above-mentioned dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophene and vinyl group-containing dibenzothiophene. Since monomers having a dibenzothiophene structure have a structure in which a thiophene ring and two benzene rings are condensed, they are included in the concept of monomers having the above-mentioned condensed aromatic ring structure. Furthermore, neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0076] In the technologies disclosed herein, monomers (m1) may be monomers having one aromatic ring (preferably a carbocyclic ring) in one molecule. Monomers having one aromatic ring in one molecule can be useful, for example, for improving the flexibility of adhesives, adjusting adhesive properties, and improving transparency. In some embodiments, monomers having one aromatic ring in one molecule are preferably used in combination with monomers containing multiple aromatic rings from the viewpoint of improving the refractive index of the adhesive.

[0077] Examples of monomers having one aromatic ring in one molecule include carbon aromatic ring-containing (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, chlorobenzyl (meth)acrylate, etc.; 2-(4,6-dibromo-2-s-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, 6- Examples 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 aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; and compounds having vinyl substituents on heteroaromatic rings such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, and N-vinyloxazole.

[0078] As the monomer (m1), a monomer having a structure in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in the various aromatic ring-containing monomers described above may be used. A monomer in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in this manner can be understood as an ethoxylated product of the original monomer. The number of repeating oxyethylene units (-CH2CH2O-) in the above oxyethylene chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, for example, 1. Specific examples of ethoxylated aromatic ring-containing monomers include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol di(meth)acrylate, and the like.

[0079] The content of multiple aromatic ring-containing monomers 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 making it easier to realize adhesives with a higher refractive index, the content of multiple aromatic ring-containing monomers in monomer (m1) may be, for example, 50% by weight or more, preferably 70% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. Substantially 100% by weight of monomer (m1) may be multiple aromatic ring-containing monomers. That is, only one or more multiple aromatic ring-containing monomers may be used as monomer (m1). Also, in some embodiments, for example, considering the balance between high refractive index and adhesive properties and / or optical properties, the content of multiple aromatic ring-containing monomers in monomer (m1) may be less than 100% by weight, may be 98% by weight or less, may be 90% by weight or less, may be 80% by weight or less, or may be 65% by weight or less. In some embodiments, considering the adhesive properties and / or optical properties, the content of the multiple aromatic ring monomer in monomer (m1) may be 70% by weight or less, 50% by weight or less, 25% by weight or less, or 10% by weight or less. The techniques disclosed herein can also be carried out in embodiments in which the content of the multiple aromatic ring monomer in monomer (m1) is less than 5% by weight. The multiple aromatic ring monomer may not be used.

[0080] The content of multiple aromatic ring-containing monomers in the monomer components constituting the acrylic polymer is not particularly limited and can be set to realize an adhesive layer that achieves both a 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 multiple aromatic ring-containing monomers in the above monomer components may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of making it easier to realize an adhesive with a higher refractive index, the content of multiple aromatic ring-containing monomers in the above monomer components may be, for example, more than 35% by weight, preferably more than 50% by weight, may be more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. The content of the multiple aromatic ring-containing monomer in the above monomer component may be 100% by weight, but from the viewpoint of achieving a good balance between high refractive index and adhesive properties and / or optical properties, it is advantageous to have less than 100% by weight, preferably about 99% by weight or less, more preferably 98% by weight or less, and may also 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, considering the adhesive properties and / or optical properties, the content of the multiple aromatic ring-containing monomer in the above 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 embodiments in which the content of the multiple aromatic ring-containing monomer in the above monomer component is less than 3% by weight.

[0081] In some embodiments of the technology disclosed herein, high refractive index monomers may be preferably used as at least a portion of the monomer (m1). Here, "high refractive index monomer" refers to a monomer whose refractive index is, for example, approximately 1.510 or higher, preferably approximately 1.530 or higher, and more preferably approximately 1.550 or higher. 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 adhesive composition and ease of compatibility with flexibility suitable for an 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. High refractive index monomers can be used alone or in combination of two or more. The refractive index of the monomer is measured using an Abbe refractometer under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. An ATAGO DR-M4 or equivalent Abbe refractometer can be used. If the manufacturer provides a nominal refractive index value at 25°C, that nominal value may be used.

[0082] As the above-mentioned high refractive index monomer, compounds with the appropriate refractive index can be appropriately selected from among the compounds included in the concept of aromatic ring-containing monomer (m1) disclosed herein (for example, the compounds and groups of compounds exemplified above). Specific examples include m-phenoxybenzyl acrylate (refractive index: 1.566, homopolymer Tg: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, homopolymer Tg: 31°C), ethoxylated o-phenylphenol acrylate (number of oxyethylene unit repetitions: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, homopolymer Tg: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, homopolymer Tg: 2°C), and phenoxydiethylene glycol acrylate (refractive index: 1.510, homopolymer Examples 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 (abbreviation: 5VDNT, refractive index: 1.793).

[0083] The content of high refractive index monomers (i.e., aromatic ring-containing monomers having a refractive index of approximately 1.510 or higher, preferably approximately 1.530 or higher, and more preferably approximately 1.550 or higher) in monomer (m1) 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 high refractive index monomers in monomer (m1) may be, for example, 50% by weight or more, preferably 70% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. Substantially 100% by weight of monomer (m1) may be high refractive index monomers. Furthermore, in some embodiments, for example, from the viewpoint of achieving a good balance between 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, considering 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 can also be implemented in embodiments in which the content of the high refractive index monomer in the monomer component (m1) is less than 5% by weight. High refractive index monomers do not need to be used.

[0084] The content of high-refractive-index monomers in the monomer components constituting the acrylic polymer is not particularly limited and can be set to realize an 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 high-refractive-index monomers in the above monomer components may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of making it easier to realize an adhesive with a higher refractive index, the content of high-refractive-index monomers in the above monomer components may be, for example, more than 35% by weight, preferably more than 50% by weight, may be more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. The content of the high refractive index monomer in the above monomer component may be 100% by weight, but from the viewpoint of achieving a good balance between high refractive index and adhesive properties and / or optical properties, it is advantageous to have less than 100% by weight, preferably 99% by weight or less, more preferably 98% by weight or less, and may also 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, considering the adhesive properties and / or optical properties, the content of the high refractive index monomer in the above 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 embodiments in which the content of the high refractive index monomer in the above 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") is used as at least a portion of the monomer (m1), wherein the homopolymer Tg is 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). When the content of aromatic ring-containing monomer (m1) in the monomer component (in particular, aromatic ring-containing monomer (m1) that falls under one or both of the above-mentioned multiple aromatic ring-containing monomers and high refractive index monomers) is increased, the storage modulus G' of the adhesive generally tends to increase. However, by using monomer L as part or all of the monomer (m1), the increase in storage modulus G' can be suppressed. This makes it possible to improve the refractive index while better maintaining the flexibility suitable for an adhesive. The lower limit of the Tg of monomer L is not particularly limited. Considering the balance with the refractive index improvement 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. Monomer L can be used alone or in combination of two or more types.

[0086] As monomer L, a compound having the appropriate Tg can be appropriately selected from among the compounds (e.g., the compounds and groups of compounds exemplified above) that are included in the concept of aromatic ring-containing monomer (m1) disclosed herein. One preferred example of an aromatic ring-containing monomer that can be used as monomer L is m-phenoxybenzyl acrylate (homopolymer Tg: -35°C). Another preferred example is phenoxydiethylene glycol acrylate (homopolymer Tg: -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 making it easier to obtain an adhesive that achieves a higher level of both high refractive index and flexibility, 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 L may be substantially 100% by weight of monomer (A1). Furthermore, in some embodiments, from the viewpoint of achieving a good balance between flexibility and high refractive index suitable for use as an adhesive, for example, 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 embodiments in which the content of monomer L in monomer (m1) is less than 5% by weight. Monomer L may not be used at all.

[0088] The monomer L content in the monomer component constituting the acrylic polymer may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of making it easier to obtain an adhesive that achieves a higher level of both high refractive index and flexibility, the monomer L content in the monomer component may be, for example, more than 35% by weight, preferably more than 50% by weight, may be more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. The monomer L content in the above monomer component may be 100% by weight, but considering the balance between high refractive index and adhesive properties and / or optical properties, it is advantageous to have less than 100% by weight, preferably about 99% by weight or less, more preferably 98% by weight or less, may be 96% by weight or less, may be 95% by weight or less, may be 93% by weight or less, may be 90% by weight or less, may be 85% by weight or less, may be 80% by weight or less, or may be 75% by weight or less. In some embodiments, the content of monomer L 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 embodiments in which the content of monomer L in the monomer component is less than 3% by weight.

[0089] In some embodiments, the glass transition temperature Tg is determined by the composition of the monomer (m1). m1 From the viewpoint of the flexibility of the adhesive, it is advantageous for the temperature to be approximately 20°C or lower, preferably 10°C or lower (e.g., 5°C or lower), more preferably 0°C or lower, even more preferably -10°C or lower, and may also be -20°C or lower, or -25°C or lower. m1 The lower limit is not particularly limited. In some embodiments, considering the balance with the refractive index improvement effect, the glass transition temperature Tg m1 The glass transition temperature Tg may be, for example, -70°C or higher, -55°C or higher, or -45°C or higher. The technology disclosed herein relates to the glass transition temperature Tg m1The method can also be suitably implemented in embodiments where the temperature is, for example, -40°C or higher, -35°C or higher, -33°C or higher, -30°C or higher, or -25°C or higher.

[0090] Here, the glass transition temperature Tg is determined based on the composition of monomer (m1). m1 This refers to the glass transition temperature (Tg) determined by Fox's formula, described later, based on the composition of only the monomer (m1) among the monomer components constituting the acrylic polymer. m1 This can be calculated by applying Fox's formula, described later, to only the monomer (m1) among the monomer components constituting the acrylic polymer, and using the glass transition temperature of the homopolymer of each aromatic ring-containing monomer used as monomer (m1) and the weight fraction of each aromatic ring-containing monomer in relation to the total amount of monomer (m1). In the embodiment where only one type of monomer is used as monomer (m1), the Tg of the homopolymer of the monomer and the glass transition temperature Tg m1 This matches.

[0091] In some embodiments, the aromatic ring-containing monomer (m1) can be a combination of monomer L (i.e., an aromatic ring-containing monomer whose homopolymer Tg is 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) and monomer H whose Tg is 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 component is relatively high, a higher level of both high refractive index and flexibility of the adhesive can be achieved. The ratio of monomer L to monomer H used can be set so as to suitably exhibit such effects and is not particularly limited. For example, any of the above glass transition temperatures Tg m1 It is preferable to set the usage ratio of monomer L to monomer H so as to satisfy the following conditions.

[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-condensed aromatic rings are directly chemically bonded (e.g., a biphenyl structure). For example, an acrylic polymer composed of monomer components with a composition in which the content of a compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded is less than 5% by weight (more preferably less than 3% by weight, and may even be 0% by weight) is preferable. Limiting the amount of compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded in this way can be advantageous from the viewpoint of realizing an adhesive that balances flexibility, tackiness and high refractive index well.

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

[0094] Examples of ethylenically unsaturated groups in the monomer (m2) include (meth)acryloyl groups, vinyl groups, and (meth)allyl groups. From the viewpoint of polymerization reactivity, (meth)acryloyl groups are preferred, and from the viewpoint of flexibility and tackiness, acryloyl groups are more preferred. From the viewpoint of suppressing a decrease in the flexibility of the adhesive, a compound in which the number of ethylenically unsaturated groups in one molecule is 1 (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. Examples of hydroxyl group-containing monomers that can be preferably used 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 with a lower Tg is more preferred. In one preferred embodiment, 50% or more by weight (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. Hydroxyl group-containing monomers can be used individually or in combination of two or more.

[0096] In some embodiments using a hydroxyl group-containing monomer as the monomer (m2), the hydroxyl group-containing monomer may be one or more compounds selected from compounds that do not have a methacryloyl group. Suitable examples of hydroxyl group-containing monomers that do not have a methacryloyl group include the various hydroxyalkyl acrylates mentioned above. For example, it is preferable that more than 50%, 70%, or 85% by weight of the hydroxyl group-containing monomer used as the monomer (m2) is a hydroxyalkyl acrylate. The use of a hydroxyalkyl acrylate introduces hydroxyl groups into the acrylic polymer, which are useful for providing crosslinking points and imparting appropriate cohesiveness. Furthermore, it is easier to obtain an adhesive with better flexibility and tackiness 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. Examples of carboxyl group-containing monomers that can be preferably used include acrylic acid and methacrylic acid. Carboxylate group-containing monomers can be used individually or in combination of two or more. Hydroxyl group-containing monomers and carboxyl group-containing monomers may also be used in combination.

[0098] The content of monomer (m2) in the monomer component constituting the acrylic polymer is not particularly limited and can be set according to the purpose. In some embodiments, the content of monomer (m2) may 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 monomer (A2) is preferably 1% by weight or more, may be 2% by weight or more, or may be 4% by weight or more. The upper limit of the monomer (m2) content in the monomer component is set so that the total content with other monomers does not exceed 100% by weight. In some embodiments, the content of monomer (m2) is appropriately 30% by weight or less or 25% by weight or less, and from the viewpoint of making it easier to increase the refractive index by relatively increasing the content of monomer (m1), it is preferably 20% by weight or less, more preferably 15% by weight or less, may be less than 12% by weight, may be less than 10% by weight, or may be less than 7% by weight.

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

[0100] In embodiments where a carboxyl group-containing monomer is used as monomer (m2), the content of the carboxyl group-containing monomer in the monomer component is not particularly limited and may be, for example, 0.01% by weight or more (preferably 0.1% by weight or more, more preferably 0.3% by weight or more). In some embodiments, the content of the carboxyl group-containing monomer may be 1% by weight or more, 2% by weight or more, or 4% by weight 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 used with other monomers does not exceed 100% by weight, and is appropriately set to, for example, 30% by weight or less or 25% by weight or less. From the viewpoint of making it easier to increase the refractive index by relatively increasing the content of monomer (m1), it is preferably 20% by weight or less, more preferably 15% by weight or less, and may be less than 12% by weight or less than 10% by weight. In some embodiments, from the viewpoint of improving the flexibility of the adhesive, it is advantageous to have a content of less than 7% by weight of the carboxyl group-containing monomer, preferably less than 5% by weight, and may also be less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which only a hydroxyl group-containing monomer is used as the monomer (m2), that is, in an embodiment in which no carboxyl group-containing monomer is used.

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

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

[0103] As monomers (m3), those with 1 to 20 carbon atoms (i.e., C 1-20 Alkyl (meth)acrylates having a linear or branched alkyl group at the ester terminus 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. Examples include, but are not limited to, 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, and eicosyl (meth)acrylate.

[0104] In some embodiments, alkyl (meth)acrylates 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 low-Tg alkyl (meth)acrylates can help improve the flexibility of the adhesive. 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), and isononyl acrylate (iNA).

[0105] In some embodiments of using the monomer (m3), it is preferable that at least a portion of the monomer (m3) is an alkyl acrylate from the viewpoint of flexibility, tackiness, etc. 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) and not use alkyl methacrylate.

[0106] In embodiments where the monomer component includes alkyl (meth)acrylate, the content of alkyl (meth)acrylate in the monomer component can be set so that its effect is appropriately exhibited. In some embodiments, the content of 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 alkyl (meth)acrylate may be 15% by weight or more, 30% by weight or more, or 45% by weight or more. The upper limit of the monomer (m3) content in the monomer component is set so that the total content with other monomers does not exceed 100% by weight, and may be, for example, less than 50% by weight. In some embodiments, the monomer (m3) content may be, for example, less than 35% by weight. Generally, alkyl (meth)acrylate has a relatively low refractive index, so in order to increase the refractive index, it is advantageous to limit the content of monomer (m3) in the monomer component and relatively increase the content of monomer (m1). From this viewpoint, it is advantageous for the monomer (m3) content to be 24% by weight or less of the monomer component, preferably less than 23% by weight, more preferably less than 20% by weight, and may also 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 be substantially omitted.

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

[0108] Examples of other monomers mentioned above include monomers having functional groups other than hydroxyl and carboxyl groups (functional group-containing monomers). For example, other monomers that can improve the cohesive strength and heat resistance of adhesives include sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, and cyano group-containing monomers. Furthermore, monomers that can introduce functional groups that can act as crosslinking sites 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. Furthermore, some monomers containing nitrogen atom rings, such as N-vinyl-2-pyrrolidone, also fall under the category of amide group-containing monomers. The same applies to the relationship between monomers containing nitrogen atom rings and monomers containing amino groups.

[0109] Other monomers that can be used besides the above-mentioned 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; and others. One preferred example of other monomers that can be used for purposes such as improving the flexibility of adhesives is ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, homopolymer Tg: -67℃).

[0110] When using the above-mentioned other monomers, the amount used is not particularly limited and can be appropriately set within a range where the total amount of monomer components does not exceed 100% by weight. In some embodiments, from the viewpoint of making it easier to exhibit the refractive index improvement effect by using monomer (m1), the content of the above-mentioned other monomers in the monomer component can be, for example, approximately 35% by weight or less, and it is appropriate to be approximately 25% by weight or less (e.g., 0 to 25% by weight), approximately 20% by weight or less (e.g., 0 to 20% by weight), approximately 10% by weight or less, approximately 5% by weight or less, and for example, approximately 1% by weight or less. The technology disclosed herein can preferably be implemented in a manner in which the monomer component substantially does not contain the above-mentioned other monomers.

[0111] In some embodiments, the monomer components constituting the acrylic polymer may have a composition in which the amount of methacryloyl group-containing monomer used is limited to a predetermined level. The amount of methacryloyl group-containing monomer used in the monomer component may be, for example, less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. Limiting the amount of methacryloyl group-containing monomer used in this way may be advantageous from the viewpoint of realizing an adhesive that balances flexibility, tackiness, and high refractive index well. The monomer components constituting the acrylic polymer may also have a composition that does not contain methacryloyl group-containing monomer (for example, a composition consisting only of acryloyl group-containing monomer).

[0112] In some embodiments, the monomer component constituting the base polymer (e.g., acrylic polymer) of the viscoelastic layer V1 preferably has a limited amount of carboxyl group-containing monomer used, from the viewpoint of suppressing coloration or discoloration (e.g., yellowing) of the viscoelastic layer V1. The amount of carboxyl group-containing monomer used in the monomer component may be, for example, less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, may be less than 0.1% by weight, or less than 0.05% by weight. Limiting the amount of carboxyl group-containing monomer used in this way is also advantageous from the viewpoint of suppressing corrosion of metallic materials (e.g., metal wiring or metal films that may be present on the adherend) that may be in contact with or near the viscoelastic layer V1. The interlayer sheet disclosed herein may preferably be implemented in an embodiment in which the monomer component does not contain carboxyl group-containing monomer. For similar reasons, in some embodiments, it is preferable that the monomer component constituting the base polymer of the viscoelastic layer V1 has a limited amount of monomers having acidic functional groups (including carboxyl groups, sulfonic acid groups, phosphate groups, etc.). In such embodiments, the preferred amount of carboxyl group-containing monomers described above can be applied as the amount of acidic functional group-containing monomers used in the monomer component. The interlayer sheet disclosed herein can preferably be implemented in an embodiment in which the monomer component does not contain acidic group-containing monomers (i.e., an embodiment in which the base polymer of the viscoelastic layer V1 is acid-free).

[0113] (Glass transition temperature Tg of the base polymer) T ) In some embodiments, the base polymer of the adhesive layer (e.g., an acrylic polymer) has a glass transition temperature Tg based on the composition of the monomer components constituting the polymer. T However, it is appropriate for the temperature to be approximately 20°C or lower, preferably approximately 10°C or lower, more preferably 0°C or lower, and may also be -10°C or lower, -20°C or lower, -25°C or lower, -28°C or lower, or -30°C or lower. Glass transition temperature Tg TA low glass transition temperature (Tg) can be advantageous from the standpoint of improving the flexibility of the adhesive. T The temperature may be, for example, -60°C or higher, preferably -50°C or higher, more preferably above -45°C, may be above -40°C, may be above -35°C, may be above -25°C, may be above -15°C, or may be above -5°C.

[0114] Here, the glass transition temperature Tg of the polymer. T Unless otherwise specified, Tg refers to the glass transition temperature determined by Fox's formula based on the composition of the monomer components constituting the polymer. Fox's formula is a relationship between the Tg of a copolymer and the glass transition temperature Tgi of homopolymers obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below. 1 / Tg = Σ(Wi / Tgi) In the Fox equation above, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the homopolymer of monomer i (unit: K). For calculating the glass transition temperature (Tg) of homopolymers, the values ​​listed in publicly available materials such as the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. For monomers for which multiple values ​​are listed in the Polymer Handbook, the highest value shall be adopted. If the Tg of a homopolymer is not listed in publicly available materials, the value obtained by the measurement method described in Japanese Patent Publication No. 2007-51271 shall be used.

[0115] (Method for preparing the base polymer) In the technologies disclosed herein, the method for obtaining the base polymer of the adhesive layer (for example, an acrylic polymer (A) composed of the monomer components described above) is not particularly limited, and known polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization can be appropriately employed. In some embodiments, solution polymerization can be preferably employed. The polymerization temperature when performing solution polymerization can be appropriately selected depending on the type of monomer and solvent 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 used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, one solvent or a mixture of two or more solvents can be used, selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetic acid esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc.

[0117] The polymerization initiator can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and so on. Another example of polymerization initiators is a redox initiator, which is a combination of a peroxide and a reducing agent. Polymerization initiators can be used individually or in combination of two or more. The amount of polymerization initiator used can be the usual amount, for example, it can be selected from a range of approximately 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) per 100 parts by weight of monomer component.

[0118] For the polymerization described above, 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, chain transfer agents that do not contain sulfur atoms (non-sulfur chain transfer agents) may 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. Chain transfer agents can be used individually or in combination of two or more. When using a chain transfer agent, the amount used can be approximately 0.01 to 1 part by weight per 100 parts by weight of monomer raw material.

[0119] The weight-average molecular weight (Mw) of the base polymer is not particularly limited, for example, approximately 10 × 10 4 ~500×10 4 It can be in the range of . From the standpoint of adhesive performance, the Mw of the base polymer is approximately 20 × 10 4 ~400×10 4 (more preferably approximately 30 x 10 4 ~150×10 4 For example, approximately 50 x 10 4 ~130×10 4 It is preferable that it be within the range of ).

[0120] Here, the Mw of the polymer can be determined by converting it to polystyrene equivalent using gel permeation chromatography (GPC). Specifically, it can be determined by measuring using the "HLC-8220GPC" (manufactured by Tosoh Corporation) GPC measuring instrument under the following conditions. [GPC measurement conditions] Sample concentration: 0.2% by weight (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: Tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40℃ column: Sample columns: 1 x "TSKguardcolumn SuperHZ-H" + 2 x "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: Product name "TSKgel SuperH-RC" 1 piece (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: Polystyrene

[0121] (Refractive index improver) In some embodiments of the technology disclosed herein, the adhesive layer V1 (e.g., an acrylic adhesive layer) may contain, in addition to the base polymer, a refractive index improver as needed. Herein, a refractive index improver means a material that, when used, can increase the refractive index of the adhesive layer. Preferably, a material with a refractive index higher than that of the adhesive layer containing the refractive index improver may be used as the refractive index improver. Furthermore, preferably, a material with a refractive index higher than that of the base polymer (e.g., an acrylic polymer (A)) of the adhesive layer containing the refractive index improver may be used as the refractive index improver. By appropriately using a refractive index improver, a higher refractive index and practical adhesive performance can be suitably achieved. In some embodiments, the refractive index improver is preferably an organic material. The organic material used as the refractive index improver may be a polymer or a nonpolymer. It may also have polymerizable functional groups or not. The refractive index improver can be used alone or in combination of two or more types.

[0122] Refractive index improvers (for example, additives described later (H ROThe refractive index of the refractive index improver can be set to an appropriate range in relation to the refractive index of the base polymer, and is not limited to a specific range. The refractive index of the refractive index improver can be selected from a range that is, for example, greater than 1.55, greater than 1.56, or greater than 1.57, and is higher than the refractive index of the base polymer. From the viewpoint of increasing the refractive index of the adhesive, in some embodiments, it is advantageous for the refractive index improver to be 1.58 or higher, preferably 1.60 or higher, more preferably 1.63 or higher, and may also be 1.65 or higher, 1.70 or higher, or 1.75 or higher. With a refractive index improver with a higher refractive index, the desired refractive index can be achieved even with the use of a smaller amount of refractive index improver. This is preferable from the viewpoint of suppressing a decrease in adhesive properties and optical properties. There is no particular upper limit to the refractive index of the refractive index improver, but from the viewpoint of compatibility within the adhesive and ease of achieving both a high refractive index and flexibility suitable for the adhesive, for example it may be 3.000 or less, 2.500 or less, 2.000 or less, 1.950 or less, 1.900 or less, or 1.850 or less.

[0123] In some embodiments, a refractive index improver (for example, an additive (H) described later) RO )) refractive index n b and the refractive index n of the base polymer a The difference between, i.e., n b -n a (Hereinafter referred to as “Δn A It is also called ).) is set to be greater than 0. In some embodiments, Δn A For example, Δn can be 0.02 or greater, 0.05 or greater, 0.07 or greater, 0.10 or greater, 0.15 or greater, 0.20 or greater, or 0.25 or greater. A By selecting the base polymer and refractive index improver so that the ratio becomes larger, the refractive index improvement effect of the refractive index improver tends to increase. Furthermore, in some embodiments, from the viewpoint of compatibility within the adhesive layer and transparency of the adhesive layer, Δn A For example, it may be 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

[0124] In some embodiments, the refractive index of the refractive index improver (e.g., the additive (H RO )) is n b and the refractive index of the adhesive layer containing the refractive index improver is n T The difference between them, that is, n b -n T (hereinafter also referred to as "Δn B ").) is set to be greater than 0. In some embodiments, Δn B is, for example, 0.02 or more, may be 0.05 or more, may be 0.07 or more, may be 0.10 or more, may be 0.15 or more, may be 0.20 or more or 0.25 or more. By selecting the composition of the adhesive layer and the refractive index improver so that Δn B becomes larger, the refractive index improvement effect due to the use of the refractive index improver tends to be higher. Also, from the viewpoints of compatibility within the adhesive layer and transparency of the adhesive layer, etc., in some embodiments, Δn B may be, for example, 0.70 or less, may be 0.60 or less, may be 0.50 or less, may be 0.40 or less or 0.35 or less.

[0125] The amount of the refractive index improver used per 100 parts by weight of the base polymer (when using a plurality of types of refractive index improvers, 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 the refractive index improver used per 100 parts by weight of the base polymer can be, for example, 1 part by weight or more, preferably 3 parts by weight or more, more preferably 5 parts by weight or more, and may be 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more. Also, in some embodiments, the amount of the refractive index improver used per 100 parts by weight of the 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 the deterioration of the adhesive properties and optical properties, it is preferably 60 parts by weight or less, more preferably 45 parts by weight or less. In some embodiments that place more emphasis on the adhesive properties and optical properties, the amount of the refractive index improver used per 100 parts by weight of the base polymer may be, for example, 30 parts by weight or less, and may be 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 the refractive index improver used per 100 parts by weight of the base polymer in the adhesive layer is less than 1 part by weight or the refractive index improver is not substantially used. Here, not substantially used means not used at least intentionally.

[0126] (Additive (H RO )) In some embodiments, as the refractive index improver, an organic material having a higher refractive index than the base polymer can be preferably employed. Hereinafter, such an organic material may be referred to as "additive (H RO )". Here, the above "H RO " represents an organic material (Organic material) having a high refractive index (High Refractive index). The base polymer (for example, an acrylic polymer, preferably an acrylic polymer (A)) and the additive (H ROBy using a combination of ), an adhesive can be realized that more favorably balances refractive index and adhesive properties (peel strength, flexibility, etc.) and / or optical properties (total light transmittance, haze value, etc.). Additive (H RO The organic material used as an additive (H) may be a polymer or a nonpolymer. It may also have polymerizable functional groups or not. RO ) can be used individually or in combination of two or more types.

[0127] Additives (H RO The refractive index of ) is measured using an Abbe refractometer, similar to the refractive index of the monomer, under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. If the manufacturer or other source provides a nominal refractive index value at 25°C, that nominal value can be used.

[0128] Additives (H RO The molecular weight of the organic material used as an additive (H) is not particularly limited and can be selected according to the purpose. RO The molecular weight of the additive (H) can be selected from a range of, for example, 30,000 or less. RO The additive (H) is preferably a polymer or nonpolymer with 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 (e.g., flexibility suitable for adhesives, optical properties such as haze), in some embodiments, the additive (H) RO The molecular weight of the additive (H) is preferably less than 10,000, more preferably less than 5,000, more preferably less than 3,000 (e.g., less than 1,000), and may also be less than 800, less than 600, less than 500, or less than 400. RO The fact that the molecular weight of the additive (H) is not too large can be advantageous from the viewpoint of improving compatibility within the adhesive layer. RO The molecular weight of the additive (H) may be, for example, 130 or more, or 150 or more. In some embodiments, the additive (H RO The molecular weight of the additive (H ROFrom the viewpoint of increasing the refractive index of ), it is preferably 170 or higher, more preferably 200 or higher, and may also be 230 or higher, 250 or higher, 270 or higher, 500 or higher, 1000 or higher, and 2000 or higher. In some embodiments, a polymer with a molecular weight of about 1000 to 10000 (for example, 1000 or more and less than 5000) is used as an additive (H RO It can be used as ). Additives (H RO For nonpolymers or polymers with a low degree of polymerization (e.g., 2-5 mers), the molecular weight can be calculated based on the chemical structure, or measured using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS). 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 molecular weight, that nominal value can be used.

[0129] Additives (H RO Examples of organic materials that could be options include, but are not limited to, organic compounds having aromatic rings, organic compounds having heterocycles (which may be aromatic rings or non-aromatic heterocycles), etc.

[0130] Additives (H RO The aromatic ring of the above-mentioned organic compound having an aromatic ring (hereinafter also referred to as the "aromatic ring-containing compound") used as a monomer (m1) can be selected from those similar to the aromatic ring of the compound used as a monomer (m1).

[0131] The aromatic ring described above may have one or more substituents on its ring constituent atoms, or it may not have substituents. If substituents are present, examples of such substituents include, but are not limited to, alkyl groups, alkoxy groups, aryloxy groups, hydroxyl groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl groups, hydroxyalkyloxy groups, glycidyloxy groups, etc. In substituents containing carbon atoms, the number of carbon atoms in the substituent is, for example, 1 to 10, advantageously 1 to 6, preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the aromatic ring described above may have no substituents on its ring constituent atoms, or it may be an aromatic ring having one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, and halogen atoms (e.g., bromine atoms).

[0132] Additives (H RO Examples of aromatic ring-containing compounds that can be used as additives include, for example: compounds that can be used as monomers (m1); oligomers containing compounds that can be used as monomers (m1) as monomer units; compounds obtained by replacing a compound that can be used as monomer (m1) with a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring constituent atom) or a group that does not have a hydrogen atom or 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.); etc., but are not limited to these. Additives (H RONon-limiting specific examples of aromatic ring-containing compounds that can be used as ) include 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, monomers having the fluorene structure described above, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, etc.; aromatic ring-containing compounds that do not have an ethylenically unsaturated group, such as 3-phenoxybenzyl alcohol, dinaphthothiophene and its derivatives (for example, compounds in which one or more substituents selected from a hydroxyl group, methanol group, diethanol group, glycidyl group, etc. are attached to the dinaphthothiophene ring, one or more of which are hydroxyl groups, methanol groups, diethanol groups, glycidyl groups, etc.ethylenically unsaturated groups, one or more of which are aromatic ring-containing compounds; and the like. Furthermore, the aromatic ring-containing compound may be an oligomer containing such aromatic ring-containing monomers as monomer units (preferably an oligomer with a molecular weight of approximately 5000 or less, more preferably approximately 1000 or less; for example, a low polymer of about 2 to 5 units). The above oligomer may be, for example: a homopolymer of aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers and other monomers; etc. As the other monomers, one or more monomers without aromatic rings may be used.

[0133] In some embodiments, additive (H ROAs such, organic compounds having two or more aromatic rings in one molecule (hereinafter also referred to as "aromatic ring-containing compounds") can be preferably used because they easily provide a high refractive index effect. Aromatic ring-containing compounds may or may not have polymerizable functional groups such as ethylenically unsaturated groups. Furthermore, aromatic ring-containing compounds may be polymers or nonpolymers. The polymer may be an oligomer containing aromatic ring-containing monomers as monomer units (preferably an oligomer with a molecular weight of approximately 5000 or less, more preferably approximately 1000 or less; for example, a low polymer of about 2 to 5-mers). The oligomer may be, for example: a homopolymer of aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers and other monomers; etc. The other monomers may be aromatic ring-containing monomers that do not fall under the category of aromatic ring-containing monomers, monomers that do not have aromatic rings, or combinations thereof.

[0134] Non-limiting examples of compounds containing multiple aromatic rings include compounds having a structure in which two or more non-condensed aromatic rings are linked via linking groups, compounds having a structure in which two or more non-condensed aromatic rings are chemically bonded directly (i.e., without the involvement of other atoms), compounds having a condensed aromatic ring structure, compounds having a fluorene structure, compounds having a dinaphthothiophene structure, compounds having a dibenzothiophene structure, and so on. Compounds containing multiple aromatic rings can be used individually or in combination of two or more.

[0135] Specific examples of compounds having the above-mentioned fluorene structure include monomers having the fluorene structure described above, as well as oligomers which are homopolymers or copolymers of such monomers, and 9,9-bisphenylfluorene and its derivatives, 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 compounds having the above-mentioned dinaphthothiophene structure include monomers having the aforementioned dinaphthothiophene structure, oligomers which are homopolymers or copolymers of such monomers, as well as hydroxyalkyl dinaphthothiophenes such as dinaphthothiophene (refractive index: 1.808); 6-hydroxymethyl dinaphthothiophene (refractive index: 1.766); dihydroxydinaphthothiophenes such as 2,12-dihydroxydinaphthothiophene (refractive index: 1.750); and 2,12- Examples of dinaphthothiophenes and their derivatives include dihydroxyalkyl oxydinaphthothiophenes such as dihydroxethyloxydinaphthothiophene (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).

[0137] Specific examples of compounds having the above-mentioned dibenzothiophene structure include monomers having the aforementioned 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 heterocyclic organic compounds (hereinafter also referred to as heterocyclic organic compounds) that can be options include thioepoxy compounds and compounds having triazine rings. An example of a thioepoxy compound is bis(2,3-epithiopropyl) disulfide and its polymer (refractive index 1.74) described in Japanese Patent Publication No. 3712653. An example of a compound having a triazine ring is a compound having at least one triazine ring (for example, 3 to 40, preferably 5 to 20) in one molecule. Since triazine rings are aromatic, compounds having triazine rings are also included in the above concept of aromatic ring-containing compounds, and compounds having multiple triazine rings are also included in the above concept of compounds containing multiple aromatic rings.

[0139] In some embodiments, additive (H RO As the additive (H), compounds that do not have ethylenically unsaturated groups can be preferably used. This suppresses deterioration of the adhesive composition due to heat and light (progression of gelation and decrease in leveling properties due to increased viscosity), and improves storage stability. Additives that do not have ethylenically unsaturated groups (H RO ) adopting the additive (H RO Adhesive sheets having an adhesive layer containing ) and laminates containing said adhesive sheets are preferable from the viewpoint of suppressing dimensional changes and deformations (warping, undulation, etc.) and the occurrence of optical distortion caused by the reaction of ethylenically unsaturated groups.

[0140] Additives (H RO In embodiments where an oligomer is used as a polymer, the oligomer can be obtained by polymerizing the corresponding monomer component by a known method. When the oligomer is produced by radical polymerization, polymerization initiators, chain transfer agents, emulsifiers, etc. used in radical polymerization can be added to the monomer component as appropriate, and polymerization can be carried out. The polymerization initiators, chain transfer agents, emulsifiers, etc. used in radical polymerization are not particularly limited and can be selected and used as appropriate. 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 can be adjusted as appropriate depending on the type. Examples of the above-mentioned chain transfer agents 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 types. The amount of chain transfer agent used can be set to obtain an oligomer with a desired weight-average molecular weight, depending on the composition of the monomer components used in the synthesis of the oligomer and the type of chain transfer agent. In some embodiments, the amount of chain transfer agent used per 100 parts by weight of the total amount of monomer used in the synthesis of the oligomer is appropriately about 15 parts by weight or less, but may also be 10 parts by weight or less, or about 5 parts by weight or less. There is no particular lower limit to the amount of chain transfer agent used relative to 100 parts by weight of the total amount of monomer used in the synthesis of oligomers, but it 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] Additive (H RO In an embodiment using ), the additive (H) is used in proportion to 100 parts by weight of the base polymer. RO The amount of additive (H) used (total amount if multiple types of compounds are used) is not particularly limited and can be set according to the purpose. From the viewpoint of increasing the refractive index of the adhesive, the amount of additive (H) per 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, is advantageous to be 3 parts by weight or more, is preferably 5 parts by weight or more, may be 7 parts by weight or more, may be 10 parts by weight or more, may be 15 parts by weight or more, or may be 20 parts by weight or more. In some embodiments, the amount of additive (H) relative to 100 parts by weight of the base polymer is 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 the deterioration of adhesive properties and optical properties, it is advantageous to use 60 parts by weight or less, and preferably 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are given more importance, the amount of additive (H) per 100 parts by weight of the base polymer isRO The amount 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 adhesive layer V1 may include a plasticizer having a lower molecular weight than the base polymer (e.g., acrylic polymer (A)) as described above. The use of a plasticizer can increase the flexibility of the adhesive layer V1, improving adhesion to the adherend and the overall flexibility and conformability to deformation of the interlayer sheet. As the plasticizer, organic materials may be preferred from the viewpoint of compatibility and transparency within the adhesive layer. The plasticizer may include the refractive index improver (e.g., the additive (H) described above). RO It may also be a material that can be used as a substitute.

[0143] The molecular weight of the plasticizer is not particularly limited, as long as it is lower than that of the base polymer. In some embodiments, the molecular weight of the plasticizer 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), may be less than 800, less than 600, less than 500, or less than 400, from the viewpoint of facilitating the expression of the plasticizing effect. Having a molecular weight of the plasticizer 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 plasticizer is suitable to be 130 or more, preferably 150 or more, may be 170 or more, may be 200 or more, may be 250 or more, or may be 300 or more, from the viewpoint of facilitating the expression of a sufficient plasticizing effect. In some embodiments, the molecular weight of the plasticizer may be 500 or more, may be 1,000 or more, or may be 2,000 or more. Having a plasticizer with a molecular weight that is not too low is preferable from the viewpoint of the heat resistance of the interlayer sheet and the suppression 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 monomers (m1) (e.g., (meth)acrylates having aromatic rings such as benzyl, phenoxy, and naphthyl groups; monomers having a fluorene structure; monomers having a dinaphthothiophene structure; monomers having a dibenzothiophene structure, etc.); oligomers containing compounds that can be used as monomers (m1) as monomer units; and compounds with a structure obtained by removing the ethylenically unsaturated group portion from a compound that can be used as a monomer (m1) and replacing it with a hydrogen atom or a group that does not have an ethylenically unsaturated group (e.g., 3-phenoxybenzyl alcohol). From the viewpoint of improving flexibility, oligomers containing compounds that can be used as monomers (m1) as monomer units may be copolymerized with low-Tg monomers such as n-butyl acrylate or 2-ethylhexyl acrylate. As a plasticizing material, one or more known plasticizers (for example, phthalate esters, terephthalate esters, adipic acid esters, adipic acid polyesters, glycol benzoate esters, etc.) may be used.

[0145] In some embodiments, organic materials with a refractive index of approximately 1.50 or higher (more preferably 1.53 or higher) can be preferably used as the plasticizing material. Specific examples of compounds that can be selected as plasticizing materials include: diethylene glycol dibenzoate (refractive index 1.55), dipropylene glycol dibenzoate (refractive index 1.54), 3-phenoxytoluene (refractive index 1.57), 3-ethyl biphenyl (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), and 4-(tert-butyl) This includes, but is not limited to, phenyldiphenyl phosphate (refractive index 1.56), trimethylphenyl phosphate (refractive index 1.55), butylbenzyl phthalate (refractive index 1.54), rosin methyl ester (refractive index 1.53), alkylbenzyl phthalate (refractive index 1.53), butyl(phenylsulfonyl)amine (refractive index 1.53), trimethyltrimellitate (refractive index 1.52), benzyl phthalate (refractive index 1.52), 2-ethylhexyldiphenyl phosphate (refractive index 1.51), tris(2,4-di-tert-butylphenyl) phosphite, etc. From the viewpoint of refractive index and compatibility, for example, diethylene glycol dibenzoate can be preferably used. The upper limit of the refractive index of the plasticizing material is not particularly limited and may be, for example, 3.00 or less. In some embodiments, from the viewpoint of ease of preparation of the adhesive composition and compatibility within the adhesive, the refractive index of the plasticizing material is suitable to be 2.50 or less, advantageous to be 2.00 or less, may also be 1.90 or less, may also be 1.80 or less, or may also be 1.70 or less. The refractive index of the plasticizer is measured using an Abbe refractometer under the same conditions as the refractive index of the monomer, with a measurement wavelength of 589 nm and a measurement temperature of 25°C. If the manufacturer or other source provides a nominal refractive index value at 25°C, that nominal value may be used.

[0146] In embodiments using a plasticizing material, the amount of plasticizing material used per 100 parts by weight of the 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 the base polymer may be, for example, 0.1 parts by weight or more, or 0.5 parts by weight or more, and from the viewpoint of obtaining a higher plasticizing effect, it is preferable to be 1 part by weight or more, more preferably 3 parts by weight or more, and may also 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 20 parts by weight or more. Furthermore, from the viewpoint of achieving a good balance between high refractive index of the adhesive, transparency and plasticizing effect, it is appropriate to use approximately 100 parts by weight or less per 100 parts by weight of the base polymer, preferably 80 parts by weight or less, more preferably 60 parts by weight or less, and may also be 45 parts by weight or less, 35 parts by weight or less, or 25 parts by weight or less. In some embodiments where greater emphasis is placed on adhesive properties and optical properties, the amount of plasticizer 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 adhesive composition used to form the adhesive layer (which may be a viscoelastic layer V1 and / or a viscoelastic layer V2) may optionally contain a leveling agent for purposes such as improving the appearance of the adhesive layer formed from the composition (e.g., improving the uniformity of thickness) or improving the coatability of the adhesive composition. Non-limiting examples of leveling agents include acrylic leveling agents, fluorine leveling agents, and silicone leveling agents. The leveling agent can be selected appropriately from commercially available leveling agents and used by conventional methods.

[0148] In some embodiments, a polymer (hereinafter also referred to as "polymer (B)") which is a polymer 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 can preferably be used as the leveling agent. Polymer (B) can be described as 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. Preferably, monomer S1 has a structure having a polymerizable reactive group at one end. In particular, monomer S1 has a structure having a polymerizable reactive group at one end and no functional group at the other end that crosslinks with the base polymer (referring to the base polymer of the adhesive composition in which the leveling agent is formulated; for example, an acrylic polymer). Examples of commercially available products include Shin-Etsu Chemical Co., Ltd.'s single-end reactive silicone oils (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 monomer S1 may be, for example, around 100 g / mol to 30,000 g / mol. In some preferred embodiments, the functional group equivalent may be, for example, 500 g / mol or more, 800 g / mol or more, 1,500 g / mol or more, or 2,000 g / mol or more. Alternatively, 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 monomer S1 is within the above range, a good leveling effect is easily achieved. Furthermore, when using two or more monomers with different functional group equivalents as monomer S1, the functional group equivalent of monomer S1 can be the sum of the products of the functional group equivalent of each monomer and the weight fraction of that monomer.

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

[0152] The content of monomer S1 in monomer raw material B can be an appropriate value within the range in which the desired effect is achieved using monomer S1, and is not limited to a specific range. 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] Monomer raw material B includes monomer S1, as well as an acrylic monomer copolymerizable with monomer S1. This can improve the compatibility of polymer (B) within the adhesive layer. Examples of acrylic monomers that can be used in monomer raw material B include alkyl acrylates. Here, "alkyl" refers to a linear (including linear and branched) alkyl (group) and does not include the alicyclic hydrocarbon group described later. In some embodiments, monomer raw material B is (meth)acrylic acid C 4-12 Alkyl ester (preferably (meth)acrylate C)4-10 Alkyl esters, for example, (meth)acrylate C 6-10 It may contain at least one alkyl ester. In some other embodiments, monomer raw material B is methacrylate C 1-18 Alkyl ester (preferably C methacrylate) 1-14 Alkyl esters, for example, C methacrylate 1-10 It may contain at least one alkyl ester. Monomer raw material B may contain one or more acrylic monomers selected from, for example, methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA).

[0154] Other examples of the above-mentioned acrylic monomers include (meth)acrylic acid esters having alicyclic hydrocarbon groups. 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 (meth)acrylic acid esters having alicyclic hydrocarbon groups.

[0155] The content of the alkyl (meth)acrylate and the alicyclic hydrocarbon group-containing (meth)acrylate in 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 may be included in monomer raw material B along with monomer S1 include the carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, amide group-containing monomers, monomers having a nitrogen atom-containing ring, (meth)acrylate aminoalkyls, vinyl esters, vinyl ethers, olefins, (meth)acrylate esters having aromatic hydrocarbon groups, halogen atom-containing (meth)acrylates, etc., which 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, and may also be 15,000 or more. Alternatively, the Mw of polymer (B) may be, for example, 200,000 or less, preferably 100,000 or less, may also be 50,000 or less, and may also be 30,000 or less. By setting the Mw of polymer (B) within an appropriate range, suitable compatibility and leveling properties can be achieved.

[0158] Polymer (B) can be produced, for example, by polymerizing the above-mentioned monomers using known methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization. To adjust the molecular weight of polymer (B), a chain transfer agent may be used as needed. Examples of chain transfer agents that can be used 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 chain transfer agent used is not particularly limited and can be set as appropriate to obtain polymer (B) with the desired molecular weight. In some embodiments, the amount of chain transfer agent used per 100 parts by weight of 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 per 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 usage effect, it may be 0.01 parts by weight or more, or 0.03 parts by weight or more. Furthermore, the amount of polymer (B) used may be, for example, 3 parts by weight or less, and from the viewpoint of reducing the effect on the refractive index, it is appropriate to be 1 part by weight or less, and it may also be 0.5 parts by weight or less, or 0.1 parts by weight or less.

[0160] (Inorganic particles) The techniques disclosed herein can preferably be implemented in a manner that substantially does not use inorganic particles as refractive index improvers. However, the use of inorganic particles as refractive index improvers is permissible to the extent that it does not significantly impair the effectiveness of the techniques disclosed herein. Examples of inorganic particles that can be used as refractive index improvers include inorganic oxides (specifically metal oxides) such as titania (titanium oxide, TiO2), zirconia (zirconium oxide, ZrO2), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, and niobium oxide (Nb2O5, etc.). The average particle size of the above inorganic particles (referring to the 50% volume average particle diameter based on laser scattering and diffraction) can be selected from a range of approximately 10 nm to 100 nm, for example. The refractive index of the inorganic particles is measured on a single layer film of the material constituting the inorganic particles (a film thickness capable of refractive index measurement) using a commercially available spectroscopic ellipsometer under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 23°C. As a spectroscopic ellipsometer, for example, product name "EC-400" (manufactured by JA. Woolam) or an equivalent product is used. When inorganic particles are used as a refractive index improver, the amount used is preferably less than 5 parts by weight, and more preferably less than 1 part by weight, per 100 parts by weight of the base polymer. Additive (H RO In the manner in which the above inorganic particles are used, the amount of the above additive (H) is determined by weight. RO It is preferable to use no more than twice the amount of ) and more preferably one or less or 0.5 or less.

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

[0162] As isocyanate crosslinking agents, isocyanate compounds with two or more functions can be used, for example: aliphatic polyisocyanates such as trimethylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate (HDI), and dimer acid diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), and 1,3-bis(isocyanatomethyl)cyclohexane; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate (XDI); and polyisocyanate modified products obtained by modifying the above isocyanate compounds with allophanate bonds, biuret bonds, isocyanurate bonds, uretdione bonds, urea bonds, carbodiimide bonds, uretonimine bonds, oxadiazinetrione bonds, etc. Examples of commercially available products include the product names Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, Takenate D178N (all manufactured by Takeda Pharmaceutical Company Limited), Sumijoule T80, Sumijoule L, Desmodule N3400 (all manufactured by Sumika Bayer Urethane Co., Ltd.), Myrionate MR, Myrionate MT, Coronate L, Coronate HL, Coronate HX (all manufactured by Tosoh Corporation). Isocyanate compounds can be used individually or in combination of two or more. A bifunctional isocyanate compound may be used in combination with a trifunctional or higher isocyanate compound.

[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 can be used individually 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. Examples include 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, bisphenoxyethanol ful orange(meth)acrylate, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butyldiol(meth)acrylate, hexyldiol di(meth)acrylate, etc. Polyfunctional monomers can be used individually or in combination of two or more.

[0165] When using a crosslinking agent (which may be a polyfunctional monomer), the amount used is not particularly limited and can be in the range of approximately 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 adhesive, 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 also 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 exhibiting 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 more effectively advance the crosslinking reaction. Examples of crosslinking catalysts include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, ferric narcem, butyltin oxide, and dioctyltin dilaurate. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of crosslinking catalyst used is not particularly limited. The amount of crosslinking catalyst used per 100 parts by weight of base polymer can be in the range of approximately 0.0001 parts by weight to 1 part by weight, and preferably in the range of 0.001 parts by weight to 0.5 parts by weight, taking into consideration the balance between the speed of the crosslinking reaction and the length of the pot life of the adhesive composition.

[0167] The adhesive composition may contain a compound that induces keto-enol tautomerism as a crosslinking retarder. This can extend the pot life of the adhesive composition. For example, a compound that induces keto-enol tautomerism can be preferably used in an adhesive composition containing an isocyanate-based crosslinking agent. Various β-dicarbonyl compounds can be used as the compound that induces keto-enol tautomerism. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetate esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably used. The compound that induces keto-enol tautomerism can be used alone or in combination of two or more. The amount of the compound that induces keto-enol tautomerism can be, for example, 0.1 parts by weight to 20 parts by weight, 0.5 parts by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight, per 100 parts by weight of the base polymer.

[0168] (Adhesion agent) The adhesive layer (which may be a viscoelastic layer V1 and / or a viscoelastic layer V2) in the technology disclosed herein may contain a tackifier. Known tackifiers such as rosin-based tackifiers, terpene-based tackifiers, phenol-based tackifiers, hydrocarbon-based tackifiers, ketone-based tackifiers, polyamide-based tackifiers, epoxy-based tackifiers, and elastomer-based tackifiers can be used. These can be used individually or in combination of two or more. The amount of tackifier used is not particularly limited and can be set to achieve appropriate adhesive performance depending on the purpose and application. In some embodiments, from the viewpoint of refractive index and transparency, the amount of tackifier used is appropriately 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 adhesive layer. The technology disclosed herein can preferably be implemented in an embodiment that does not use a tackifier.

[0169] (Other additives) In the techniques disclosed herein, the adhesive composition used to form the adhesive layer (which may be a viscoelastic layer V1 and / or a viscoelastic layer V2) may optionally contain known additives that can be used in adhesive compositions, such as plasticizers, softeners, colorants, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, and preservatives, to the extent that the effects of the present invention are not significantly hindered. Such various additives can be conventionally used by ordinary methods and do not particularly characterize the present invention, so a detailed explanation is omitted.

[0170] (Peel strength) In some embodiments of the interlayer sheets disclosed herein, the peel strength of the interlayer sheet to the glass plate is appropriately approximately 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 also 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 material onto an alkali glass plate as the adherend, leaving it in an environment of 23°C and 50%RH for 30 minutes, then placing it in a pressurized degassing device (autoclave) and autoclaving it at a temperature of 50°C and a pressure of 0.5MPa for 30 minutes, and then leaving it in an atmosphere of 23°C and 50%RH for 24 hours, after which the adhesive strength is measured by peeling it off at a 180° angle and a tensile speed of 300 mm / min. For measurement, if necessary, an appropriate backing material (for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm to 50 μm) can be attached to the interlayer sheet to be measured to reinforce it. 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 adhesive sheet having a first adhesive surface and a second adhesive surface, in some embodiments, the peel strength described above is preferably applied to at least the first adhesive surface, and more preferably to both the first and second adhesive surfaces. The peel strength of the first adhesive surface to the glass plate and the peel strength of the second adhesive surface to the glass may be the same or different.

[0172] <Viscoelastic layer V2> In some preferred embodiments of the interlaminar sheet disclosed herein, the interlaminar sheet may further include, in addition to the viscoelastic layer V1 described above, a viscoelastic layer (adhesive layer) V2 laminated on the viscoelastic layer V1. The storage modulus G' at 25°C of the viscoelastic layer V2 is V2 However, the storage modulus G' of the viscoelastic layer V1 at 25°C V1 A lower value is preferable. That is, G' V2 (twenty five) <G’ V1 (25) is preferable. An interlayer sheet with such a configuration can be more flexible due to the contribution of the viscoelastic layer V2. Storage modulus G' V2 (25) Storage modulus G' V1 By making it lower than (25), it is possible to desirablely achieve both a high refractive index due to the viscoelastic layer V1 and flexibility due to the viscoelastic layer V2 in the interlayer sheet. By laminating the viscoelastic layer V2 onto the viscoelastic layer V1, adhesion and flexibility are provided, improving the ability to follow steps and curved surfaces, and an interlayer sheet that can be desirablely applied to a variety of device designs can be realized.

[0173] Storage modulus G' V2 (25) is not particularly limited and may be in the range of, for example, 1.0 kPa to 500 kPa. From the viewpoint of enhancing the effect of imparting flexibility and improving deformation followability by the viscoelastic layer V2, in some embodiments, the storage modulus G' V2(25) is appropriately 400 kPa or less, preferably 300 kPa or less, more preferably 200 kPa or less (e.g., 180 kPa or less, or 150 kPa), 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 appropriately 5.0 kPa or higher, preferably 10 kPa or higher, may be 15 kPa or higher, 25 kPa or higher, 35 kPa or higher, 60 kPa or higher, or 80 kPa or higher. From the viewpoint of making it easier to achieve higher cohesive force and adhesive properties, in some embodiments, the storage modulus G' V2 (25) may be 95 kPa or higher, 110 kPa or higher, or 140 kPa or higher.

[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. With an interlayer sheet having such a configuration, the behavior of light transmitted through the interlayer sheet can be controlled by utilizing the refractive index difference between the viscoelastic layers V1 and V2. 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 in the range of approximately 1.35 to 1.55. In some embodiments, from the viewpoint of increasing the refractive index difference with the refractive index n1 of the viscoelastic layer V1 to facilitate the front brightness improvement effect described later, the refractive index n2 of the viscoelastic layer V2 is preferably, for example, 1.49 or less, more preferably 1.47 or less (for example 1.46 or less, or 1.45 or less), and may also be 1.43 or less, 1.41 or less, or 1.40 or less. Furthermore, from the viewpoint of ease of obtaining materials and ease of compatibility with adhesive properties, in some embodiments, the refractive index n2 of the viscoelastic layer V2 may be, for example, 1.36 or higher, 1.38 or higher, 1.40 or higher, or 1.42 or higher.

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

[0176] In some embodiments, the acrylic polymer is preferably a polymer of a monomer raw material that contains, for example, an alkyl (meth)acrylate and may further contain other monomers copolymerizable with the alkyl (meth)acrylate (copolymerizable monomers). The content of the alkyl (meth)acrylate in the monomer raw material may be, for example, 10% by weight or more, 25% by weight or more, 35% by weight or more, or 45% by weight or more. The acrylic polymer may also be a polymer of a monomer component that contains alkyl (meth)acrylate as a main monomer and may further contain 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 raw 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, in equation (1) above, R 1R is a hydrogen atom or a methyl group. 2 A chain-like alkyl group having 1 to 20 carbon atoms (hereinafter, this range of carbon atoms will be referred to as "C") 1-20 It is sometimes expressed as ". ) From the viewpoint of the storage modulus of the adhesive, R 2 C 1-12 (For example C 2-10 Typically C 4-8 Alkyl (meth)acrylate, which is a chain-like alkyl group, is preferred. 2 C 1-20 Alkyl (meth)acrylates, which are chain-like alkyl groups, can be used individually or in combination of two or more. Preferred alkyl (meth)acrylates include n-butyl acrylate and 2-ethylhexyl acrylate.

[0178] The copolymerizable monomers described above can be useful for introducing crosslinking points into acrylic polymers or for enhancing the cohesive strength of acrylic polymers. Examples of copolymerizable monomers 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 nitrogen atom-containing rings, sulfonic acid group-containing monomers, and phosphate group-containing monomers. Other examples of copolymerizable monomers include vinyl ester 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 described above as monomers that can be used as the base polymer of the viscoelastic layer V1. For example, from the viewpoint of improving cohesive strength, acrylic polymers copolymerized with carboxyl group-containing monomers and / or hydroxyl group-containing monomers are preferred. Preferred examples of carboxyl group-containing monomers include acrylic acid and methacrylic acid. Preferred examples of hydroxyl group-containing monomers 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 adhesive layer V2. The content of the fluorine-containing 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 making it easier to realize a viscoelastic layer V2 with a higher 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 95% by weight or more. There is no particular upper limit to the content of the fluorine-containing monomer in the monomer raw material, 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 appropriate to be 99.9% by weight or less, preferably 99.5% or less, may be 99% by weight or less, may be 97% by weight or less, or may be 92% by weight or less. Fluorine-containing monomers can be used individually or in combination of two or more.

[0180] As the fluorine-containing monomer, fluorine-containing acrylic monomers can be suitably 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 its molecule. For example, fluorine-containing (meth)acrylic acid esters can be suitably used. A suitable example of a fluorine-containing (meth)acrylic acid ester is one having a fluorinated hydrocarbon group at its ester terminus. Examples of fluorinated hydrocarbon groups include fluorinated aliphatic hydrocarbon groups, fluorinated alicyclic hydrocarbon groups, and fluorinated aromatic hydrocarbon groups. Fluorinated aliphatic hydrocarbon groups are preferred as the fluorinated hydrocarbon group. Examples of fluorinated aliphatic hydrocarbon groups include fluorinated alkyl groups. In a fluorinated aliphatic hydrocarbon group, the aliphatic hydrocarbon moiety may be linear or branched. Furthermore, in a fluorinated aliphatic hydrocarbon group, the fluorine atom may be bonded to any carbon atom of the aliphatic hydrocarbon group moiety. The number of fluorine atoms bonded to a single carbon atom may be singular or multiple. The number of carbon atoms to which the fluorine atom is bonded is not particularly limited.

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

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

[0183] The fluorinated hydrocarbon group may or may not have substituents. Such substituents are not particularly limited and include, for example, hydrocarbon groups such as alkyl groups, alkoxy groups, hydroxyl groups, carboxyl groups, amino groups, nitro groups, cyano groups, halogen atoms, and the like. Substituents can be used individually or in combination of two or more.

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

[0185] As the fluorine atom-containing (meth)acrylic acid ester, fluorinated alkyl (meth)acrylates (especially fluorinated alkyl acrylates) are preferred. Examples of fluorinated alkyl (meth)acrylates include 2,2,2-trifluoroethyl acrylate (product name "Viscote 3F" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 2,2,3,3-tetrafluoropropyl acrylate (product name "Viscote 4F" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 1H,1H,5H-octafluoropentyl acrylate (product name "Viscote 8F" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 1H,1H,5H-octafluoropentyl methacrylate (product name "Viscote 8FM" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 2-(heptadecafluorononyl)ethyl acrylate (product name "FA-108" manufactured by Kyoeisha Chemical Co., Ltd.), and 1H,1H,2H,2H-tridecafluorooctyl acrylate (product name "Viscote 13F" manufactured by Osaka Organic Chemical Industry Co., Ltd.).

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

[0187] In some embodiments of the interlayer sheets disclosed herein, the viscoelastic layer V2 is an acrylic adhesive layer, and the acrylic polymer that is the base polymer of the adhesive may be a polymer of monomer raw materials that contains at least the above-mentioned fluorine-containing acrylic monomer (e.g., fluorinated alkyl (meth)acrylate) and may further contain other monomers copolymerizable with the fluorine-containing acrylic monomer (copolymerizable monomers). This monomer raw material may or may not contain alkyl (meth)acrylate. The content of the fluorine-containing acrylic monomer in the above 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 making it easier to realize 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, may be 60% by weight or more, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. The upper limit of the content of 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 cohesiveness of the viscoelastic layer V2, the content of the fluorine-containing acrylic monomer is suitable to be 99.9% by weight or less, preferably 99.5% or less, may be 99% by weight or less, may be 97% by weight or less, or may be 92% by weight or less. The fluorine-containing acrylic monomer can be used alone or in combination of two or more types.

[0188] The monomer raw material for preparing the base polymer of the viscoelastic layer V2 may be a composition that includes a copolymerizable monomer in addition to a fluorine-containing acrylic monomer (e.g., fluorinated alkyl (meth)acrylate). Examples of copolymerizable monomers 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 monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, non-aromatic ring-containing (meth)acrylates such as cycloalkyl (meth)acrylate and isobornyl (meth)acrylate, and alkoxy group-containing monomers. Specific examples of monomers that can be used as the base polymer of the viscoelastic layer V1 include, but are not limited to, those described above. For example, from the viewpoint of improving cohesive strength, acrylic polymers obtained by copolymerizing carboxyl group-containing monomers and / or hydroxyl group-containing monomers are preferred as the copolymerizable monomers.

[0189] In some preferred embodiments, the monomer raw material for preparing the base polymer of the viscoelastic layer V2 may be a composition containing a fluorine-containing monomer (e.g., a fluorine-containing acrylic monomer such as fluorinated alkyl (meth)acrylate) and further containing a hydroxyl group-containing monomer. The hydroxyl group-containing monomer can be useful for improving cohesive force and introducing crosslinking points. Preferred examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate. From the viewpoint of improving flexibility at room temperature, 4-hydroxybutyl acrylate may be more preferably used. The content of the hydroxyl group-containing monomer in the monomer raw material is not particularly limited and may 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 group-containing monomer may be 0.7% by weight or more, 0.9% by weight or more, or 1.5% by weight or more of the monomer raw material. The upper limit of the content of the hydroxyl group-containing monomer is not particularly limited and may be, for example, 15% by weight or less or 10% by weight or less. In some embodiments, from the viewpoint of lowering the refractive index, the content of the hydroxyl group-containing monomer in the above monomer raw material is suitable to be less than 10% by weight, preferably less than 5% by weight, may be less than 3% by weight, may be less than 2.5% by weight, or may be 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 from the viewpoint of suppressing coloration or discoloration (e.g., yellowing) of the viscoelastic layer V2. The content of carboxyl group-containing monomers in the above monomer raw material may be, for example, less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, and even more preferably less than 0.1% by weight (e.g., less than 0.05% by weight). Limiting the content of carboxyl group-containing monomers in this way is also advantageous from the viewpoint of suppressing corrosion of metallic materials (e.g., metal wiring or metal films that may be present on the adherend) that may be in contact with or near the viscoelastic layer V2. The interlayer sheet disclosed herein may preferably be implemented in an embodiment in which the above monomer raw material does not contain carboxyl group-containing monomers. For similar reasons, 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 carboxyl groups, sulfonic acid groups, phosphate groups, etc.). In such embodiments, the preferred content of carboxyl group-containing monomers described above can be applied as the content of acidic functional group-containing monomers in the monomer raw material. The interlayer sheet disclosed herein can preferably be implemented in an embodiment in which the monomer raw material does not contain acidic group-containing monomers (i.e., an embodiment in which the base polymer of the viscoelastic layer V2 is acid-free).

[0191] The base polymer of adhesive layer V2 can be prepared by appropriately employing known polymerization methods, similar to the base polymer of adhesive layer V1. The weight-average molecular weight (Mw) of the base polymer is not particularly limited, for example, approximately 10 × 10 4 ~500×10 4 It may be within the range of approximately 20 × 10 4 ~200×10 4 It may be within the range of . In some embodiments, from the viewpoint of adhesion to the adhesive layer V1, the Mw of the base polymer of the adhesive layer V2 is 150 × 10 4 The following is appropriate: 120 × 10 4(for example, 95 x 10) 4 The following is preferable: 75 × 10 4 The following is also acceptable: 68 × 10 4 The following is also acceptable: 60 x 10 4 The following is also acceptable. Furthermore, in some embodiments, from the viewpoint of the cohesiveness of the adhesive layer V2, the Mw of the base polymer is, for example, 30 × 10 4 The above is sufficient, 40 x 10 4 The above is also acceptable: 50 x 10 4 The above is also acceptable. Conventional chain transfer agents can be used as needed to prepare Mw.

[0192] While not particularly limited, from the viewpoint of adhesion, it is advantageous for the Tg of the base polymer (e.g., acrylic polymer) of the adhesive layer V2 to be approximately 0°C or lower, and preferably approximately -5°C or lower (e.g., approximately -15°C or lower, or -25°C or lower). Furthermore, from the viewpoint of cohesive force of the adhesive layer, the Tg of the base polymer of the adhesive layer V2 is approximately -75°C or higher, and preferably approximately -70°C or higher (e.g., -50°C or higher, and even more preferably -30°C or higher). The Tg of the base polymer can be adjusted by appropriately changing the monomer composition (i.e., the type and ratio of monomers used in the synthesis of the polymer).

[0193] A known crosslinking agent may be used in the adhesive layer V2 as needed. Furthermore, the adhesive layer V2 may contain tackifiers or other additives as needed. The crosslinking agent and tackifier can be appropriately selected from those that can be used in the adhesive layer V1, and used in appropriate amounts.

[0194] In embodiments where the adhesive composition used to form the adhesive layer V2 includes a crosslinking agent, an isocyanate-based crosslinking agent may be preferably used as the crosslinking agent. In some embodiments, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of the base polymer in the adhesive 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 adhesion to the adhesive layer V1, etc. Furthermore, from the viewpoint of appropriately exhibiting the effect of using the crosslinking agent, in some embodiments, the amount of 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.

[0195] <Preparation of the adhesive layer> In the interlayer sheet disclosed herein, the viscoelastic material constituting each of the viscoelastic layers V1 and V2 may be an adhesive obtained by curing an adhesive composition in the form of a solvent type, an active energy ray curable type, a water dispersion type, a hot melt type, etc., by drying, crosslinking, polymerization, cooling, etc., i.e., a cured product of the above adhesive composition. The curing means for the adhesive composition (e.g., drying, crosslinking, polymerization, cooling, etc.) may be applied by applying only one type, or two or more types simultaneously or in multiple stages. In the case of a solvent-type adhesive composition, the adhesive can typically be formed by drying (preferably further crosslinking) the composition. In the case of an active energy ray curable adhesive composition, the adhesive is typically formed by irradiating it with active energy rays to carry out polymerization and / or crosslinking reactions. If drying is necessary for an active energy ray curable adhesive composition, it is preferable to irradiate it with active energy rays after drying.

[0196] The viscoelastic layers V1 and V2 of the interlayer sheets disclosed herein can be formed by applying (e.g., coating) an adhesive composition to a suitable surface and then curing the composition. The application of the adhesive composition can be carried out using conventional coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, and spray coaters.

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

[0198] The thickness of the viscoelastic layer V1 is not particularly limited and can be, for example, 3 μm or more, and preferably 5 μm or more. A viscoelastic layer V1 with a thickness of 5 μm or more makes it easier to obtain good adhesive properties. Furthermore, a viscoelastic layer V1 of such thickness can absorb any irregularities that may exist on the surface of the adherend, making it easier to bond to the adherend with good adhesion. A thickness of 5 μm or more for the viscoelastic layer V1 is also preferable from the viewpoint of preventing discoloration and 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. Also, 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. Having a moderate thickness in the viscoelastic layer V1 can be advantageous from the viewpoint of thinning the interlayer sheet. The technology disclosed herein can preferably be implemented, for example, in a manner 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 the same or different. In the case of an interlayer sheet in the form of a substrate-less double-sided adhesive sheet consisting of an adhesive layer, the thickness of the adhesive layer becomes the thickness of the interlayer sheet.

[0199] An adhesive layer having a structure in which adhesive layer V1 and adhesive layer V2 are laminated can be formed by, for example, forming adhesive layers V1 and V2 on a release surface (e.g., the release surface of a release liner) and bonding their adhesive surfaces together, or by applying an adhesive composition for forming adhesive layer V2 onto adhesive layer V1 and curing it, or conversely, by applying an adhesive composition for forming adhesive layer V1 onto adhesive layer V2 and curing it, but is not limited to these methods. When bonding the adhesive surfaces of pre-formed adhesive layers V1 and V2 together, a treatment to promote adhesion between the two adhesive layers may be performed as needed. For example, autoclaving or roll pressing can be performed, but is not limited to these methods.

[0200] <Support substrate> The interlayer sheet (adhesive sheet) according to some embodiments may be in the form of an adhesive sheet with a substrate 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 according to the purpose of use and usage mode of the adhesive sheet, etc. Non-limiting examples of substrates that can be used include polyolefin films mainly composed of polyolefins such as polypropylene (PP) and ethylene-propylene copolymers, polyester films mainly composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), plastic films such as polyvinyl chloride films mainly composed of polyvinyl chloride; foam sheets made of foams such as polyurethane foams, polyethylene (PE) foams, and polychloroprene foams; various fibrous substances (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc., and can be).) woven fabrics and non-woven fabrics by single or blended spinning, etc.; papers such as Japanese paper, high-quality paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; etc. Substrates having a composite structure of these may also be used. Examples of such composite substrates include, for example, substrates having a structure in which a metal foil and the above plastic film are laminated, 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 non-woven fabric sheet, a non-porous substrate, or a substrate having a structure in which a porous layer and a non-porous layer are laminated. In some embodiments, as the film substrate, those containing an independently shape-maintainable (self-supporting or non-dependent) resin film as a base film can be preferably used. Here, the "resin film" means a resin film having a non-porous structure and typically substantially free of voids (voidless). Therefore, the resin film is a concept distinct from a foam film or a non-woven fabric. As the resin film, an independently shape-maintainable (self-supporting or non-dependent) one can be preferably used. The resin film may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure).

[0202] Materials that make up resin films include, for example, polyester resins mainly composed of polyester such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefin resins mainly composed of polyolefins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; cellulose resins such as triacetylcellulose; acetate resins; polysulfone resins; polyethersulfone resins; polycarbonate resins; polyamide (PA) resins such as nylon 6, nylon 66, and partially aromatic polyamides; and polyimide (PI) resins. Examples include resins, transparent polyimide resins, polyamide-imide (PAI), polyetheretherketone (PEEK), polyethersulfone (PES), norbornene-based resins and other cyclic polyolefin 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), polytetrafluoroethylene (PTFE), and fluorinated polyimide resins, among others.

[0203] The above-mentioned resin film may be formed using a resin material containing one of these resins alone, or it may be formed using a resin material blended with two or more of these resins. The above-mentioned resin film may be unoriented or oriented (e.g., uniaxially oriented or biaxially oriented). For example, PET film, PBT film, PEN film, unoriented polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, PP / PE blend film, etc., can be preferably used. Examples of resin films preferred from the viewpoint 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 viewpoint of availability, and PET film is preferred among them.

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

[0205] The method for manufacturing the resin film is not particularly limited. For example, conventionally known general resin film molding methods such as extrusion molding, inflation molding, T-die casting, and calender roll molding can be used as appropriate.

[0206] The above-mentioned substrate may be substantially composed of such a base film. Alternatively, the substrate may include auxiliary layers in addition to the base film. Examples of such auxiliary layers include optical property adjustment layers (e.g., coloring layers, anti-reflective layers), printing layers or lamination layers for imparting a desired appearance to the substrate, antistatic layers, undercoating layers, release layers, and other surface treatment layers.

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

[0208] The thickness of the substrate is not particularly limited and can be selected according to the purpose and manner of use of the interlayer sheet. The thickness of the substrate may be, for example, 500 μm or less, preferably 300 μm or less from the viewpoint of handling and processability of the interlayer sheet, and may also 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. Also, from the viewpoint of handling 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 adhesive layer (viscoelastic layer) is laminated may be subjected to conventionally known surface treatments as needed, such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or formation of an undercoat layer by applying an undercoat agent (primer). Such surface treatments may be performed to improve the anchoring ability of the 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 ones. The thickness of the undercoat layer is not particularly limited, but is usually appropriate at about 0.01 μm to 1 μm, and preferably at about 0.1 μm to 1 μm. Other treatments that may be applied to the substrate as needed include antistatic layer formation treatment, coloring layer formation treatment, and printing treatment. These treatments can be applied individually or in combination.

[0210] If the interlayer sheet disclosed herein is in the form of an adhesive sheet with a substrate, 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 handling and other factors, 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. Note that the thickness of the interlayer sheet refers to the thickness of the portion that is attached to the substrate. For example, in the interlayer sheet 1 with the configuration shown in Figure 1, it refers to the thickness from the first surface (adhesive surface) 10A of the 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 sheets (adhesive sheets) disclosed herein may take 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. Accordingly, 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 that contacts the adhesive surface of the interlayer sheet.

[0212] The release liner is not particularly limited, and for example, 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), or a release liner made of a resin film formed from a low-adhesion material such as a fluoropolymer (such as polytetrafluoroethylene) or a polyolefin resin (such as polyethylene or polypropylene) can be used. 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 fluoro-based release treatment agent, or molybdenum(IV) sulfide. In some embodiments, a release liner having a release treatment layer made of a silicone-based release treatment agent can be preferably used. The thickness and formation method of the release treatment layer are not particularly limited and can be set so that appropriate release properties are exhibited on the adhesive side 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 distinct from, for example, nonwoven fabrics (i.e., does not include nonwoven fabrics).

[0214] Examples of materials for the above-mentioned 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 copolymer, and ethylene-butene copolymer; cellulose resins such as triacetylcellulose; acetate resins; polysulfone resins; polyethersulfone resins; polycarbonate resins; polyamide resins; polyimide resins; norbornene resins; cyclic polyolefin 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. A release film substrate formed from one or more of these resins can be used. Among these, a polyester resin film (e.g., PET film) formed from a polyester resin is a preferred release film substrate.

[0215] The plastic film used as the release film substrate described above may be an unoriented film, a uniaxially oriented film, or a biaxially oriented film. Furthermore, 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 adhesive sheets, such as antioxidants, anti-aging 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 incorporated into all sublayers or into only some of the sublayers.

[0216] In some preferred embodiments, the release film substrate (typically a plastic film) may preferably have a limited content of particles such as inorganic particles (which may be pigments, lubricants, fillers, etc.) in the layer on the release side, or may be 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% by weight, preferably less than 0.1% by weight (e.g., 0 to 0.01% by weight). Release films with such a release film substrate tend to have a 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 side may be 1 / 10 or less (e.g., 1 / 50 or less) of the particle content in the layers other than the release side layer.

[0217] In an interlayer sheet with a release liner, having a release liner on a first adhesive surface and a second adhesive surface, the release liner placed on one adhesive surface (hereinafter also referred to as "the first 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 structure, or they may be made of different materials and have different structures.

[0218] The thickness of the release liner (preferably the release film) is not particularly limited and may 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 suitable to be 20 μm or more, preferably 30 μm or more, may be 35 μm or more, may be 40 μm or more, or may be 45 μm or more. Also, from the viewpoint of the handling of the release liner (e.g., ease of winding), the thickness of the release liner is suitable to be 300 μm or less, preferably 250 μm or less, may be 200 μm or less, may be 150 μm or less, or may be 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 below a predetermined value, winding marks are less likely to occur when the material is rolled up, removal from the adhesive sheet becomes smoother, and high surface smoothness can be easily obtained on the adhesive surface after the release liner has been removed.

[0219] In an interlayer sheet with a release liner, comprising 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 peelability and the like, 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 approximately 1.1 times or more (for example, approximately 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 the adhesive side surface) In some embodiments, it is preferable from the viewpoint of realizing an adhesive surface having high surface smoothness that the arithmetic mean roughness Ra of the surface on the adhesive side of the release liner (preferably a release film) is limited to a predetermined value or less (for example, approximately 100 nm or less, and more preferably less than 50 nm). In some embodiments, the arithmetic mean roughness Ra of the surface on the adhesive side of the release liner is preferably, for example, approximately 30 nm or less, more preferably approximately 25 nm or less, may be approximately 20 nm or less, or may be approximately 18 nm or less. Further, from the viewpoints of ease of manufacturing and handling of the release liner, in some embodiments, the arithmetic mean roughness Ra may be, for example, approximately 5 nm or more, may be approximately 10 nm or more, or may be approximately 15 nm or more. In an interlayer sheet with a release liner in which release liners are respectively disposed on the first adhesive surface and the second adhesive surface, it is preferable that the surfaces on the adhesive side of both release liners satisfy any of the above-described arithmetic mean roughnesses Ra. The arithmetic mean roughnesses Ra of the surfaces on the adhesive side of both release liners may be the same or different.

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

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

[0223] The arithmetic mean roughness Ra and maximum height Rz of the release film surface can be adjusted by selecting the film material, molding method, surface treatment such as release treatment, etc. For example, this can be done by adjusting the smoothness of the layers constituting the release surface (antiblocking layer, hard coat layer, oligomer prevention layer, etc.), reducing or eliminating (particle-free) filler particles 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 the release liner (preferably a release film) are measured using a non-contact surface roughness measuring device. As the non-contact surface roughness measuring device, an optical interference type surface roughness measuring device is used, for example, a 3D optical profiler (product name "NewView7300", manufactured by ZYGO) or an equivalent can be used. For example, a glass plate (soda-lime glass plate manufactured by MATSUNAMI, 1.3 mm thick) can be attached to the surface of the release liner opposite to the measurement surface with adhesive and fixed, and the surface shape can be measured using a 3D optical profiler (product name "NewView7300", manufactured by ZYGO) in an environment of 23°C and 50% RH.

[0225] <Application> The interlayer sheets disclosed herein can be used by laminating them to various adherends. The constituent materials of the adherends (adherend materials) are not particularly limited, but include, for example, 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, as well as, for example, 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 resins, etc. Examples of materials include various resin materials (typically plastics) such as resins, polycarbonate resins, cellulosic polymers such as diacetylcellulose and triacetylcellulose, 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 (antimond-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 sheets disclosed herein can be used by being attached to a component (e.g., an optical component) whose surface is at least made of the above materials.

[0226] The interlayer sheet disclosed herein can be used in a bonding manner that does not require heating to a temperature higher than room temperature (e.g., 20°C to 35°C) after bonding to the adherend. Furthermore, depending on the constituent materials of the interlayer sheet (e.g., the material of the substrate) and the type of adherend, a heat treatment may be performed at least one of the following times: after bonding to the adherend, at the time of bonding, or before bonding. The heat treatment can be performed for purposes such as improving the adhesion of the adhesive to the adherend or promoting adhesion. The heat treatment temperature can be set appropriately within an acceptable range depending on the constituent materials of the interlayer sheet and the type of adherend, taking into consideration the surface condition of the adherend, etc., in order to obtain the desired effect. For example, it may be around 100°C or lower, 80°C or lower, 60°C or lower, or 50°C or lower.

[0227] The member or material to which the interlayer sheet is to be attached or laminated (in the case of an interlayer sheet in the form of a double-sided adhesive sheet, at least one of the adherends) may be light-transmitting. With such an adherend, the advantage of the high transparency of the interlayer sheet disclosed herein is easily obtained. The total light transmittance of the adherend may be, for example, more than 50%, and may be 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., 95-100%). The interlayer sheet disclosed herein may be preferably used in a manner in which it is attached to or laminated to an adherend (e.g., an optical member) with 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. As the transmittance meter, the "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or an equivalent product is used.

[0228] The refractive index of the adherend and the refractive index of the viscoelastic layer (for example, viscoelastic layer V1, or viscoelastic layer V2 in a configuration having viscoelastic layer V2) placed in contact with the adherend may be the same or different. For example, by making the refractive index of the viscoelastic layer (typically an adhesive layer) relatively high compared to the refractive index of the adherend, light incident on the adhesive layer from the adherend side at an angle below the critical angle can be refracted toward the front, 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 less than 1.45, and may also be, for example, 1.10 or more, 1.20 or more, 1.30 or more, or 1.35 or more. Furthermore, using an adherend with a relatively high refractive index compared to the adhesive layer can refract light incident on the adherend from the 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 higher, 1.65 or higher, or 1.70 or higher, and may also be, for example, 3.00 or lower, 2.50 or lower, or 2.00 or lower. On the other hand, by reducing the refractive index difference between the adhesive layer and the adherend, light reflection at the interface can be suppressed. In this case, the refractive index of the adherend may be around 1.55 to 1.80, around 1.55 to 1.75, or around 1.60 to 1.70. The refractive index of the adherend can be measured in the same way as the refractive index of the adhesive.

[0229] In some preferred embodiments, the adherend may have any of the refractive indices and any of the total light transmittances described above. The effects of the techniques disclosed herein are particularly favorable in embodiments in which the material is attached to or laminated onto such an adherend.

[0230] One example of a preferred application is an optical application. More specifically, the interlayer sheet disclosed herein can be preferably used as an optical adhesive sheet for applications such as bonding optical components together (for bonding optical components) or for manufacturing products using the optical components (optical products).

[0231] The above-mentioned optical components refer to components that have optical properties (for example, polarization, refractiveness, scattering, reflectivity, transmission, absorption, diffraction, optical rotation, visibility, etc.). The above-mentioned optical components are not particularly limited as long as they have optical properties, but examples include components that make up devices (optical devices) such as display devices (image display devices) and input devices, or components used in such devices. Examples include polarizers, waveplates, phase difference plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflective films, hard coat (HC) films, shock-absorbing films, anti-fouling films, photochromic films, dimming films, transparent conductive films (ITO films), decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and even components in which these are laminated (these are sometimes collectively referred to as "functional films"). Furthermore, the terms "plate" and "film" above include forms such as plate-like, film-like, and sheet-like shapes, respectively. For example, "polarizing film" includes "polarizing plates" and "polarizing sheets," and "light guide plate" includes "light guide film" and "light guide sheet." In addition, the term "polarizing plate" above includes circular polarizing plates.

[0232] Examples of the above-mentioned display devices include liquid crystal displays, organic electroluminescent (EL) displays, micro-LEDs (μLEDs), mini-LEDs (miniLEDs), PDPs (plasma display panels), and electronic paper. Examples of the above-mentioned input devices include touch panels.

[0233] The optical components mentioned above are not particularly limited, but examples include components made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal thin films, etc. (for example, sheet-like, film-like, or plate-like components). In this specification, "optical components" also include components that serve a decorative or protective role while maintaining the visibility of display devices and input devices (such as design films, decorative films, and surface protection films).

[0234] The interlayer sheets disclosed herein can be used, for example, in a manner in which they are placed between an optical film, such as a film or fluorescent film having one or more functions such as light transmission, reflection, diffusion, guidance, focusing, or diffraction, and another optical component (which may be another optical film), and are preferably used to bond the optical film and the other optical component. In particular, in bonding optical films having at least one function of light guidance, focusing, or diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, and this may be 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 of the interlayer sheet disclosed herein (preferably an adhesive layer; for example, a single-layer adhesive layer consisting of a viscoelastic layer V1, or a laminated adhesive layer in which two or more adhesive layers including viscoelastic layer V1 and viscoelastic layer V2 are directly in contact and laminated) can be preferably used for bonding optical films such as light guide films, diffusion films, fluorescent films, color-tuning films, prism sheets, lenticular films, and microlens array films. In these applications, there is a demand for thinner designs and improved light extraction efficiency from the viewpoint of miniaturization and performance enhancement of optical components. The viscoelastic layer of the interlayer sheet disclosed herein can be preferably used as a viscoelastic layer (e.g., an adhesive layer) that can meet these demands. More specifically, for example, in bonding light guide films and diffusion films, thinning can be contributed to by adjusting the refractive index of the adhesive layer as a bonding layer (e.g., increasing the refractive index). In bonding fluorescent films, the light extraction efficiency (which can also be understood as luminous efficiency) can be improved by appropriately adjusting the refractive index difference between the fluorescent emitter and the adhesive. In bonding color-matching films, appropriately adjusting the refractive index of the adhesive to minimize the refractive index difference with the color-matching pigment can reduce scattering components and contribute to improved light transmittance. In bonding prism sheets, lenticular films, microlens array films, etc., appropriately adjusting the refractive index of the adhesive can control light diffraction and contribute to improved brightness and / or viewing angle.

[0236] The interlayer sheet disclosed herein is preferably used in a manner in which it is attached to a high refractive index adherend (which may be a high refractive index layer or component, etc.) to suppress interfacial reflection with the adherend. In such a manner, it is preferable that the interlayer sheet used has a small difference in refractive index between the high refractive index adherend and the adhesive layer (typically a viscoelastic layer V1) attached to the adherend, and has high adhesion at the interface with the adherend. Furthermore, from the viewpoint of improving the homogeneity of the appearance, it is preferable that the thickness of the adhesive layer is highly uniform, for example, that the surface smoothness of the adhesive surface is high. When the thickness of the high refractive index adherend is relatively small (for example, 5 μm or less, 4 μm or less, or 2 μm or less), suppressing reflection at the interface is particularly significant from the viewpoint of suppressing discoloration and color unevenness due to interference of reflected light. One example of such usage is a polarizing plate with a phase difference layer, which comprises a polarizer, a first phase difference layer, and a second phase difference layer in that order, and which is used for bonding the polarizer to the first phase difference layer and / or the first phase difference layer to the second phase difference layer.

[0237] Furthermore, since the interlayer sheet disclosed herein comprises a viscoelastic layer V1 with a high refractive index, it can preferably be used in a manner in which it is attached to an emissive layer such as an optical semiconductor (for example, a emissive layer with a high refractive index mainly composed of inorganic materials). By reducing the refractive index difference between the emissive layer and the viscoelastic layer V1, reflection at their interface can be suppressed, and the light extraction efficiency can be improved. In such a manner, the interlayer sheet preferably comprises a high refractive index adhesive layer as the viscoelastic layer V1. Also, from the viewpoint of preventing deterioration of the self-emissive element due to moisture, it is preferable that the water absorption rate of the viscoelastic layer V1 is low. From the viewpoint of improving brightness, it is preferable that the interlayer sheet has low coloration. This is also 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 in microlenses and other lens components (for example, microlenses constituting a microlens array film, or lens components such as camera microlenses) used as components of cameras, light-emitting devices, etc., as a coating layer covering the lens surface, a bonding layer with a component facing the lens surface (for example, a component having a surface shape corresponding to the lens surface), a filling layer filled between the lens surface and the component, etc. Since the viscoelastic layer V1 disclosed herein is suitable for increasing the refractive index, it can reduce the refractive index difference with a high refractive index lens (for example, 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 viewpoint of thinning the lens and the product equipped with 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 also be used as a lens resin itself, for example, in the form of being filled into a recess or void of a suitable transparent component.

[0239] The manner in which optical members are bonded using the interlayer sheet disclosed herein is not particularly limited, but for example, (1) the manner in which optical members are bonded to each other via the interlayer sheet disclosed herein, (2) the manner in which optical members are bonded to members other than optical members via the interlayer sheet disclosed herein, or (3) the manner in which the interlayer sheet disclosed herein includes an optical member and the interlayer sheet is bonded to an optical member or a member other than an optical member. In the embodiment of (3) above, the interlayer sheet including an optical member may be, for example, an interlayer sheet whose support is an optical member (e.g., an optical film). An interlayer sheet including an optical member as a support in this manner can also be understood as an adhesive optical member (e.g., an adhesive optical film). Furthermore, if the interlayer sheet disclosed herein is an adhesive sheet having a support, and the functional film is used as the support, the interlayer sheet disclosed herein can also be understood as an "adhesive functional film" having the adhesive layer disclosed herein on at least one side of the functional film.

[0240] Based on the above, the technology disclosed herein provides an optical laminate comprising an interlayer sheet disclosed herein and a member to which the interlayer sheet is attached (for example, a resin film such as an optical film). 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 constituting the adhesive surface of the interlayer sheet (for example, the viscoelastic layer V1) 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 as members, materials, and adherends, so we will not repeat any redundant explanations.

[0241] As can be understood from the above description and the following examples, the matters disclosed in this specification include the following: [1] An adhesive sheet containing an adhesive layer, Having an adhesive surface formed by the above adhesive layer, The above adhesive layer is an adhesive sheet having a refractive index greater than 1.570, a total light transmittance of 86% or more, and a haze value of 3.0% or less. [2] The adhesive sheet described in [1] above, wherein the adhesive layer has a thickness of 5 μm or more. [3] The adhesive sheet described in [1] or [2] above, wherein the peel strength (adhesion strength) to the glass plate is 3N / 25mm or more. [4] The adhesive surface is an adhesive sheet as described in any of [1] to [3] above, wherein the arithmetic mean roughness Ra is 100 nm or less. [5] The adhesive layer is an adhesive sheet according to any of [1] to [4] above, wherein the water absorption rate is 1.0% or less. [6] An adhesive sheet according to any one of [1] to [5] above, which is configured as a laminate including the adhesive layer and a light-transmitting substrate. [7] The adhesive sheet described in [6] above, wherein the light-transmitting substrate is a resin film. [8] An adhesive sheet according to any of [1] to [5] above, which is a double-sided adhesive sheet comprising the adhesive layer described above. [9] An adhesive sheet as described in any of [1] to [8] above, A release liner placed on the adhesive surface of the above adhesive sheet, Includes adhesive sheets with release liner.

[10] An adhesive composition used to form the adhesive layer of an adhesive sheet as described in any of [1] to [8] above.

[0242]

[11] An acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit, Additive (H) is an organic material with a higher refractive index than the acrylic polymer (A) mentioned above. RO )and, An adhesive composition containing the following:

[12] The above additive (H RO The adhesive composition described in

[11] above, wherein the refractive index of is 1.60 or greater.

[13] The above additive (H) per 100 parts by weight of the above acrylic polymer (A) RO The adhesive composition according to

[11] or

[12] above, wherein the content of ) is greater than 0 parts by weight and 60 parts by weight or less.

[14] The above additive (H RO The adhesive composition according to any one of

[11] to

[13] above, comprising at least one compound selected from the group consisting of aromatic ring-containing compounds and heterocycle-containing compounds.

[15] The above additive (H RO ) is an adhesive composition according to any one of

[11] to

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

[16] The above additive (H RO ) is a compound having two or more aromatic rings in one molecule, (i) including a structure in which two non-condensed aromatic rings are directly chemically bonded, (ii) A structure containing two aromatic rings fused together, The adhesive composition according to

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

[17] The adhesive composition according to any one of

[11] to

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

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

[11] to

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

[19] The adhesive composition according to any one of

[11] to

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

[20] An adhesive composition according to any one of

[11] to

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

[21] An adhesive formed from any of the adhesive compositions described in

[11] to

[20] above, wherein the refractive index is higher than 1.570.

[22] An adhesive sheet comprising an adhesive layer composed of an adhesive formed from any of the adhesive compositions described in

[11] to

[20] above.

[23] The adhesive sheet according to

[22] above, wherein the haze value of the adhesive layer is 1.0% or less.

[0243]

[24] An interlayer sheet used in optical applications, which is placed between layers of a laminate, It includes a viscoelastic layer V1 with a refractive index n1 of 1.570 or higher, and The total light transmittance is 86% or higher; The haze value is 1.0% or less; and, The storage modulus G' at 25°C is between 30 kPa and 700 kPa; An interlayer sheet that satisfies the requirements.

[25] The interlayer sheet described in

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

[26] The interlayer sheet according to

[24] or

[25] , wherein the viscoelastic layer V1 comprises 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] Further comprising a viscoelastic layer V2 laminated on the above viscoelastic layer V1, Storage modulus G' of the viscoelastic layer V2 at 25°C V2 The storage modulus G' of the viscoelastic layer V1 at 25°C is... V1 A lower interlayer sheet as described in any of

[24] to

[27] above.

[29] The interlayer sheet as described in

[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] , wherein the viscoelastic layer V1 is a layer formed from the adhesive composition described in any one of

[11] to

[18] above.

[31] The interlayer sheet according to any of

[24] to

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

[32] An interlayer sheet as described in any one of the above items

[24] to

[31] , A resin film laminated on the above interlayer sheet, An optical laminate containing [something].

[33] An interlayer sheet as described in any one of the above items

[24] to

[31] , A release liner covering at least one surface of the interlayer sheet, Interlayer sheets with release liners, including the above. [Examples]

[0244] The following describes several embodiments relating to the present invention, but the present invention is not intended to be limited to those examples shown. In the following description, "parts" and "%" used to express the amount used or content refer to weight unless otherwise specified.

[0245] <Preparation of acrylic adhesive composition C1> A four-necked 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℃; hereinafter abbreviated as "POB-A") and 5 parts of 4-hydroxybutyl acrylate (4HBA) as monomer components, 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 polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60℃ to prepare a 50% solution of acrylic polymer A1. The average molecular weight (Mw) of this acrylic polymer A1 was 500,000. The above acrylic polymer A1 has a Tg (i.e., Tg) based on the composition of the above monomer components. T ) is -35℃, and Tg (i.e., Tg) is based on the composition of aromatic ring-containing monomers. m1 The temperature is -35°C. A 50% solution of the above acrylic polymer A1 was diluted to 30% with ethyl acetate. To 334 parts of this solution (100 parts non-volatile), 10 parts (0.1 parts non-volatile) of a 1% ethyl acetate solution of hexamethylene diisocyanate isocyanurate (manufactured by Tosoh Corporation, trade name "Coronate HX", trifunctional isocyanate compound) was added as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 parts non-volatile) of a 1% ethyl acetate solution of ferric narcem as a crosslinking catalyst was added and stirred to prepare acrylic adhesive composition C1.

[0246] <Preparation of acrylic adhesive composition C2> In a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser, 72 parts of POB-A as monomer components, 23 parts of 1-naphthylmethyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate NMT-A", refractive index: 1.595, homopolymer Tg: 31°C; hereinafter abbreviated as "NMT-A"), 5 parts of 4HBA, 0.2 parts of AIBN as polymerization initiator, and 100 parts of toluene as polymerization solvent were charged. Nitrogen gas was introduced while gently stirring, and the polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60°C to prepare a 50% solution of acrylic polymer A2. The average molecular weight (Mw) of this acrylic polymer A2 was 500,000. In a separable flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas inlet tube, 20 parts of POB-A, 80 parts of NMT-A as monomer components, 0.2 parts of AIBN as a polymerization initiator, 3.5 parts of α-thioglycerol as a chain transfer agent, and 67 parts of methyl ethyl ketone were added. Then, nitrogen gas was introduced and the mixture was purged with nitrogen for approximately 1 hour while stirring. After that, the flask was heated to 70°C and reacted for 12 hours to obtain an acrylic oligomer (oligomer B) with a weight-average molecular weight (Mw) of 4000 and a refractive index of 1.63. A 50% solution of the above-mentioned acrylic polymer A2 was diluted to 30% with ethyl acetate. 334 parts of this solution (100 parts non-volatile content) were mixed with 20 parts of the oligomer B prepared above, 10 parts of a 1% ethyl acetate solution of hexamethylene diisocyanate isocyanurate (manufactured by Tosoh Corporation, trade name "Coronate HX", trifunctional isocyanate compound) as a crosslinking agent (0.1 parts non-volatile content), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric narcem as a crosslinking catalyst (0.01 parts non-volatile content). The mixture was stirred and mixed to prepare acrylic adhesive composition C2.

[0247] <Preparation of acrylic adhesive composition C3> A four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 65 parts 2-ethylhexyl acrylate, 30 parts 1H,1H,5H-octafluoropentyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., product name: Viscoat 8F), 3 parts N-vinyl-2-pyrrolidone (NVP, manufactured by Nippon Shokubai), and 2 parts 4HBA as monomer components, 0.2 parts AIBN as a polymerization initiator, and 200 parts ethyl acetate as a polymerization solvent. Nitrogen gas was introduced while gently stirring, and the polymerization reaction was carried out for 9 hours while maintaining the liquid temperature in the flask at around 60°C to prepare a 33% solution of acrylic polymer A3. The average polymerization molecular weight (Mw) of the above acrylic polymer A3 was 550,000. A 33% solution of the above acrylic polymer A3 was diluted to 30% with ethyl acetate. To 100 parts of the non-volatile content (solids), 10 parts of a 1% ethyl acetate solution of hexamethylene diisocyanate isocyanurate (manufactured by Tosoh Corporation, trade name "Coronate HX", trifunctional isocyanate compound) was added as a crosslinking agent (0.1 parts non-volatile content), and the mixture was stirred to prepare acrylic adhesive composition C3.

[0248] <Fabrication of interlayer sheets> (Example 1) The acrylic adhesive composition C1 prepared above was applied to the silicone-treated side of a polyethylene terephthalate (PET) film R1 (thickness 50 μm) with one side silicone-treated, and heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 25 μm. The silicone-treated side of a PET film R2 (thickness 38 μm) with one side silicone-treated was bonded to the surface of the adhesive layer. In this way, an adhesive layer (adhesive layer V1) was obtained in which both sides were protected by PET films (release liners) R1 and R2. The release liner R2 is relatively easier to peel than the release liner R1. Furthermore, the acrylic adhesive composition C3 prepared above was applied to the silicone-treated side of a PET film R1 (thickness 50 μm) with one side silicone-treated, and heated at 130°C for 2 minutes to form an adhesive layer V2 with a thickness of 10 μm. The silicone-treated side of a PET film R2 (thickness 38 μm) with one side silicone-treated was then bonded to the surface of the adhesive layer. In this way, an adhesive layer (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 adhesive layers V1 and V2, and the adhesive surfaces were bonded together and pressed with a hand roller. This laminate was then autoclaved at 50°C and 0.60 MPa for 30 minutes, followed by aging at 50°C for 48 hours. In this way, an interlayer sheet (substrate-less double-sided adhesive sheet) consisting of two adhesive layers V1 / V2 was obtained. The surface of this interlayer sheet is protected by two release liners R1.

[0249] (Example 2) An interlayer sheet (substrate-less double-sided adhesive sheet) consisting of two layers 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 3-5) In the same manner as in Example 1, single-layer adhesive layers were prepared, each consisting of one of the acrylic adhesive compositions C1 to C3 and having the thickness shown in Table 1, and these were used as interlayer sheets according to Examples 3 to 5.

[0251] The resulting interlayer sheets were allowed to acclimate sufficiently to an environment of 23°C and 50% RH before being used for the following measurements and evaluations.

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

[0253] (Storage modulus G') For each example, a sample was prepared by laminating adhesive layers to a thickness of approximately 1.5 mm. Dynamic viscoelasticity measurements were performed using an ARES system manufactured by TA Instruments under the following conditions. The storage modulus G' at 25°C was read from the measurement results. The results are shown in Table 1. [Measurement conditions] Transformation mode: Twist Measurement frequency: 1Hz Heating rate: 5°C / min Shape: Parallel plate 7.9mmφ

[0254] (Total light transmittance and haze value) Test specimens were prepared by laminating the interlayer sheet for each example onto alkali-free glass (thickness 0.8-1.0 mm, total light transmittance 92%, haze 0.4%). The total light transmittance and haze of the test specimens were measured using a haze meter (Murakami Color Technology Laboratory, product name "HAZEMETER HM-150") at a measurement environment of 23°C. The total light transmittance and haze values ​​of the interlayer sheet were obtained by subtracting the total light transmittance and haze of the alkali-free glass from the measured values. The results are shown in Table 1.

[0255] (Peel strength against glass plate) Under a measurement environment of 23°C and 50% RH, the release liner was peeled off from one side of the interlayer sheet for each example (in Examples 1 and 2, the surface of the adhesive layer formed from adhesive composition C3), a 50 μm thick PET film was bonded to the backing, and the sheet was cut to a size of 25 mm wide and 100 mm long to serve as a test specimen. The release liner was peeled off from the other side of the test specimen and pressed onto the surface of an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., 1.35 mm thick, blue plate with polished edge) using a 2 kg roller with one back-and-forth motion. The sample was left in the same environment for 30 minutes, then placed in a pressurized degassing device (autoclave) and autoclaved for 30 minutes at a temperature of 50°C and a pressure of 0.5 MPa. After that, it was left for 24 hours in an atmosphere of 23°C and 50% RH, and then the peel strength (adhesion) [N / 25mm] was measured using a universal tensile and compression tester in accordance with JIS Z 0237:2000, at a tensile speed of 300 mm / min and a peel angle of 180 degrees. The universal tensile and compression tester used was the "Tensile and Compression Tester, TG-1kN" manufactured by Minebea Co., Ltd.

[0256] [Table 1]

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

[0258] <Evaluation of the effect of improving frontal brightness> Each example's interlayer sheet was attached to a white LED light source, and the light source was stabilized by illuminating it in a darkroom environment for 30 minutes or more. Then, the frontal brightness of the area where the interlayer sheet was attached was measured using a spectroradiometer SR-UL1R (manufactured by Topcon Techno House Co., Ltd.). Using the average of three brightness measurements, samples showing a brightness improvement of 10% or more compared to the brightness of the light source without the interlayer sheet were evaluated as G (Good), and samples showing a brightness 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 adhesive layer combining the adhesive layer of Example 5 (adhesive layer V2) with the adhesive layer of Examples 3 and 4 (adhesive layer V1) with a low refractive index, showed a front brightness improvement effect of 10% or more compared to when the interlayer sheet was not used. In the interlayer sheets of Examples 3 to 5, where the adhesive layer of the interlayer sheet has a single-layer structure, no front brightness improvement effect was observed with the interlayer sheet alone. The interlayer sheets of Examples 3 and 4 can exhibit a front brightness improvement effect in the laminate with a member with a lower refractive index (e.g., a resin film) by laminating them with that member. The interlayer sheet of Example 5 can exhibit a front brightness improvement effect in the laminate with a member with a higher refractive index (e.g., a resin film) by laminating them with that member.

[0261] <Preparation of acrylic adhesive composition C4> A four-necked 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 polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60°C to prepare a 50% solution of acrylic polymer A4. The Mw of this acrylic polymer A4 was 520,000. A 50% solution of the above acrylic polymer A4 was diluted to 30% with ethyl acetate. To 334 parts of this solution (100 parts non-volatile content), 10 parts of a 1% ethyl acetate solution of Coronate HX as a crosslinking agent (0.1 parts non-volatile content), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of Narsem ferric as a crosslinking catalyst (0.01 parts non-volatile content) were added and stirred to prepare acrylic adhesive composition C4.

[0262] <Preparation of acrylic adhesive composition C5> A 50% solution of acrylic polymer A5 was prepared in the same manner as 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. Acrylic adhesive composition C5 was prepared in the same manner as the preparation of acrylic 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 adhesive composition C6> A 50% solution of acrylic polymer A6 was prepared in the same manner as the solution of acrylic polymer A4, except that the monomer component composition (weight ratio) was changed to P2H-A / 4HBA = 99 / 1. In the above monomer component composition, "P2H-A" represents phenoxydiethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate P2H-A", refractive index: 1.510, homopolymer Tg: -35℃). The Mw of this acrylic polymer A6 was 1 million. A 50% solution of acrylic polymer A6 is diluted to 30% with ethyl acetate, and 334 parts of this solution (100 parts non-volatile content) are 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-acryloyloxyethyl dinaphthothiophene, abbreviation: 6EDNTA, refractive index: 1.722, manufactured by Sugai Chemical Industry Co., Ltd.), 10 parts of a 1% ethyl acetate solution of Coronate HX as a crosslinking agent (0.1 parts non-volatile content), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of Narsem ferric as a crosslinking catalyst (0.01 parts non-volatile content), and stirring and mixing.

[0264] <Preparation of acrylic adhesive composition C7> A 50% solution of acrylic polymer A1 was diluted to 30% with ethyl acetate. To 334 parts of this solution (100 parts non-volatile content), 10 parts of POB-A as an additive (plasticizer), 10 parts of a 1% ethyl acetate solution of Coronate HX as a crosslinking agent (0.1 parts non-volatile content), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of Narsem ferric as a crosslinking catalyst (0.01 parts non-volatile content) were added and stirred to prepare acrylic adhesive composition C7.

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

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

[0267] <Fabrication of interlayer sheets> (Examples 6-10) An interlayer sheet (substrate-less 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] After allowing the interlayer sheets obtained in Examples 6-10 to acclimate sufficiently to an environment of 23°C and 50% RH, each item was measured and evaluated in the same manner as described 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 in Examples 6-10 have a refractive index n1 of 1.570 or higher and a storage modulus G' V1 (25) contained an adhesive layer V1 with a pressure of 700 kPa or less, and exhibited high transparency in the interlayer sheet. These interlayer sheets showed practical peel strength suitable for bonding between layers of optical components.

[0271] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. [Explanation of Symbols]

[0272] 1, 2 Interlayer sheet (adhesive sheet) 10. Viscoelastic layer (adhesive layer, viscoelastic layer V1) 10A First surface (adhesive side) 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 sheets with release liner (interlayer sheets with release liner) 70 Optical components 100 Optical laminate

Claims

1. An interlayer sheet used in optical applications, which is placed between layers of a laminate, Refractive index n １ The storage modulus G' at 25°C is 1.570 or higher. Ｖ１ Viscoelastic layer V has a pressure of 30 kPa to 700 kPa. １ Includes, The viscoelastic layer V1 contains an acrylic polymer as a base polymer, which includes a monomer containing multiple aromatic rings having two or more aromatic rings in one molecule, and a hydroxyalkyl acrylate as monomer units, and the monomer containing multiple aromatic rings is a monomer having a structure in which two or more non-condensed aromatic rings are linked via linking groups. In the monomer components constituting the acrylic polymer, the content of the monomer containing multiple aromatic rings is 70% by weight or more and 99% by weight or less, and the content of the hydroxyalkyl acrylate is 1% by weight or more and less than 7% by weight. An interlayer sheet having a total light transmittance of 86% or more and a haze value of 1.0% or less.

2. The interlayer sheet according to claim 1, wherein the thickness is 5 μm or more.

3. The viscoelastic layer V １ A viscoelastic layer V is laminated on top of it. ２ It further includes, The viscoelastic layer V ２ has a storage elastic modulus G' at 25°C Ｖ２ which is lower than that of the viscoelastic layer V １ at 25°C, and the interlayer sheet according to claim 1 or 2 Ｖ１ has a storage elastic modulus G' at 25°C

4. The viscoelastic layer V ２ refractive index n ２ The viscoelastic layer V １ refractive index n １ A lower interlayer sheet according to claim 3.

5. An interlayer sheet according to any one of claims 1 to 4, A release liner covering at least one surface of the interlayer sheet, Interlayer sheets with release liners, including the above.

6. An interlayer sheet according to any one of claims 1 to 4, A resin film laminated on the interlayer sheet, An optical laminate containing [something].

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