Adhesive sheet, optical laminate, and image display device

Abstract

This adhesive sheet is formed from a photocurable adhesive composition that includes a monomer component M. The adhesive sheet includes inorganic particles and has a principal surface SA at which the concentration of the inorganic particles is equal to or less than the concentration CM of the inorganic particles at the center in the thickness direction of the adhesive sheet. The present invention provides an adhesive sheet that is formed from a photocurable adhesive composition, includes inorganic particles, and achieves a better balance between refractive index and adhesive force.

Description

Pressure-sensitive adhesive sheet, optical laminate and image display device

[0001] The present invention relates to a pressure-sensitive adhesive sheet, an optical laminate, and an image display device.

[0002] In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices), have rapidly become popular. Image display devices generally include an optical laminate including optical substrates such as a polarizing film and a retardation film. In an optical laminate including a plurality of optical substrates, a bonding layer is usually disposed between adjacent optical substrates to bond them together. One example of the bonding layer is a pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition.

[0003] Patent Document 1 discloses a thermosetting pressure-sensitive adhesive composition containing an acrylic polymer having a specific composition and weight-average molecular weight as a base polymer, inorganic particles, a plasticizer, and a silane coupling agent. Patent Document 2 discloses a technique for stably dispersing inorganic particles in a pressure-sensitive adhesive composition.

[0004] JP 2017-14376 A JP 2021-134322 A

[0005] To improve the surface brightness of an image display device, it is advantageous to use a pressure-sensitive adhesive sheet with a high refractive index. For example, by forming a pressure-sensitive adhesive sheet from a pressure-sensitive adhesive composition containing inorganic particles, it is possible to increase the refractive index of the pressure-sensitive adhesive sheet. However, according to the studies of the present inventors, when the pressure-sensitive adhesive composition is photocurable, there is room for improvement in the balance between the adhesive strength and the refractive index of a pressure-sensitive adhesive sheet containing inorganic particles.

[0006] An object of the present invention is to provide a pressure-sensitive adhesive sheet containing inorganic particles formed from a photocurable pressure-sensitive adhesive composition, which is suitable for improving the balance between refractive index and adhesive strength.

[0007] [1] A pressure-sensitive adhesive sheet according to an embodiment of the present invention is a pressure-sensitive adhesive sheet formed from a photocurable pressure-sensitive adhesive composition containing a monomer component M, the pressure-sensitive adhesive sheet containing inorganic particles, and a concentration C of the inorganic particles at the center in the thickness direction of the pressure-sensitive adhesive sheet. M[2] In the pressure-sensitive adhesive sheet described in the above [1], the pressure-sensitive adhesive sheet has a first main surface and a second main surface opposite to the first main surface, and of the first and second main surfaces, only the first main surface may be the main surface SA, and in this case, the concentration C of the inorganic particles in the first main surface may be S1 and the concentration C M The formula: (C S1 / C M )≦1.00, and the concentration C of the inorganic particles on the second main surface may satisfy the relationship shown by S2 and the concentration C M The formula: (C S2 / C M) ≧ 1.50. [3] In the pressure-sensitive adhesive sheet described in [2] above, the first main surface may be a surface to which the pressure-sensitive adhesive composition is irradiated with active energy rays during the formation of the pressure-sensitive adhesive sheet, and the second main surface may be a surface to which the pressure-sensitive adhesive composition is not irradiated with active energy rays during the formation of the pressure-sensitive adhesive sheet. [4] In the pressure-sensitive adhesive sheet described in [2] or [3] above, the refractive index n2 of the pressure-sensitive adhesive sheet when the second main surface is used as an evaluation surface may be higher than the refractive index n1 of the pressure-sensitive adhesive sheet when the first main surface is used as an evaluation surface. [5] In the pressure-sensitive adhesive sheet described in [4] above, the absolute value of the difference between the refractive index n1 and the refractive index n2 may be 0.02 or more. [6] In the pressure-sensitive adhesive sheet described in [4] or [5] above, the refractive index n1 may be 1.58 or more, and the refractive index n2 may be 1.61 or more. [7] In the pressure-sensitive adhesive sheet described in any one of [1] to [6] above, the reflectance of the pressure-sensitive adhesive sheet evaluated by the following evaluation method may be 8.1% or less. <Evaluation Method> A laminate is prepared in which an acrylic sheet with a refractive index of 1.49, the pressure-sensitive adhesive sheet with a thickness of 50 μm, and a sapphire glass sheet with a refractive index of 1.77 are laminated in this order. The first main surface of the pressure-sensitive adhesive sheet is in contact with the acrylic sheet. The second main surface of the pressure-sensitive adhesive sheet is in contact with the sapphire glass sheet. Next, the front reflectance of the laminate is measured using the SCI method with the sapphire glass sheet as the incident surface, and the obtained front reflectance is specified as the reflectance of the pressure-sensitive adhesive sheet. [8] In the pressure-sensitive adhesive sheet described in any one of [1] to [7] above, the inorganic particles may contain zirconium oxide. [9] In the pressure-sensitive adhesive sheet described in any one of [1] to [8] above, the content of the inorganic particles in the pressure-sensitive adhesive composition may be 40 parts by weight or more relative to 100 parts by weight of the total of the monomer component M and the inorganic particles.

[10] In the pressure-sensitive adhesive sheet according to any one of the above [1] to [9], the pressure-sensitive adhesive composition may contain an ultraviolet absorber.

[11] In the pressure-sensitive adhesive sheet described in

[10] above, the content of the ultraviolet absorber in the pressure-sensitive adhesive composition may be 1 to 5 parts by weight per 100 parts by weight of the total of the monomer component M and the inorganic particles.

[12] In the pressure-sensitive adhesive sheet described in any of [1] to

[11] above, the monomer component M may include a monomer a having a double bond-containing ring.

[13] In the pressure-sensitive adhesive sheet described in

[12] above, the double bond-containing ring may be an aromatic ring.

[14] In the pressure-sensitive adhesive sheet described in

[12] or

[13] above, the monomer a may include a (meth)acrylic monomer having the double bond-containing ring.

[15] In the pressure-sensitive adhesive sheet described in any of

[12] to

[14] above, the monomer a may include phenoxybenzyl acrylate.

[16] In the pressure-sensitive adhesive sheet described in any of

[12] to

[15] above, the content of the monomer a in the pressure-sensitive adhesive composition may be 40 parts by weight or more per 100 parts by weight of the total of the monomer component M and the inorganic particles.

[17] In the pressure-sensitive adhesive sheet according to any one of [1] to

[16] above, the pressure-sensitive adhesive composition may contain a polymer B having a weight-average molecular weight of 1,500 to 30,000.

[18] An optical laminate according to an embodiment of the present invention comprises the pressure-sensitive adhesive sheet according to any one of [1] to

[17] above and an optical film.

[19] An image display device according to an embodiment of the present invention comprises the optical laminate according to

[18] above.

[0008] According to an embodiment of the present invention, it is possible to provide a pressure-sensitive adhesive sheet containing inorganic particles formed from a photocurable pressure-sensitive adhesive composition, which is suitable for improving the balance between refractive index and adhesive strength.

[0009] FIG. 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a method for evaluating the dispersion state of inorganic particles in a pressure-sensitive adhesive sheet according to one embodiment of the present invention and the concentration of inorganic particles in the pressure-sensitive adhesive sheet. FIG. 3 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention.

[0010] [Terminology] In this specification, when the expression "weight" appears, it may be read as "mass," which is commonly used as an SI unit indicating weight, and vice versa.

[0011] In this specification, the expression "(meth)acrylic" means "acrylic and / or methacrylic", the expression "(meth)acrylate" means "acrylate and / or methacrylate", the expression "(meth)allyl" means "allyl and / or methallyl", and the expression "(meth)acrolein" means "acrolein and / or methacrolein".

[0012] In this specification, when the term "100 parts by weight of the total of the monomer component M and the inorganic particles" is used as a standard for the content of various components in the pressure-sensitive adhesive composition, it means the total amount of the monomer component M that is not partially polymerized and is contained in the pressure-sensitive adhesive composition, the monomer component M that is consumed for forming a partially polymerized product that may be contained in the pressure-sensitive adhesive composition, and the inorganic particles.

[0013] <<1. Pressure-sensitive adhesive sheet>> <<1-1. Pressure-sensitive adhesive sheet>> An example of a pressure-sensitive adhesive sheet according to an embodiment of the present invention is shown in FIG. 1. The pressure-sensitive adhesive sheet 1 in FIG. 1 is a pressure-sensitive adhesive sheet (hereinafter, sometimes referred to as a "photo-curable pressure-sensitive adhesive sheet") formed from a photo-curable pressure-sensitive adhesive composition (hereinafter, referred to as "pressure-sensitive adhesive composition A") containing a monomer component M. Photo-curable pressure-sensitive adhesive sheets usually contain a photopolymerization initiator. The pressure-sensitive adhesive sheet 1 contains inorganic particles. In the pressure-sensitive adhesive sheet 1, the concentration C of the inorganic particles 13 at the center M in the thickness direction is M The concentration of the inorganic particles 13 is equal to or smaller than the concentration C M is a region R having a thickness of 1 μm and centered at the center M of the thickness direction of the adhesive sheet 1. M The concentration of the inorganic particles 13 on the main surface SA can be specified as the concentration of the inorganic particles 13 in a region R that includes the main surface SA and has a thickness of 1 μm in the thickness direction of the pressure-sensitive adhesive sheet 1. SA The concentration of inorganic particles 13 in the evaluation region can be determined as the concentration of inorganic particles 13 in the evaluation region. The concentration of inorganic particles 13 in the evaluation region can be determined by analyzing a cross section in the thickness direction using transmission electron microscope energy dispersive X-ray spectroscopy (TEM-EDX). TEM-EDX allows the concentration of inorganic particles 13 to be determined as the ratio (I / C ratio) of the concentration of inorganic element I constituting the inorganic particles 13 (unit: atomic %) to the concentration of carbon C (unit: atomic %) in the evaluation region. An example of inorganic element I is zirconium constituting zirconium oxide particles. In this case, the concentration of inorganic particles 13 can be determined as the Zr / C ratio.

[0014] Photocurable pressure-sensitive adhesive sheets are generally formed by photocuring a coating layer of a pressure-sensitive adhesive composition by irradiating the coating layer with active energy rays such as ultraviolet light. However, according to the studies of the present inventors, when a pressure-sensitive adhesive composition containing inorganic particles is used, the adhesive strength of the pressure-sensitive adhesive sheet may be reduced more than expected based on the composition and curing conditions of the pressure-sensitive adhesive composition, and the degree of reduction is particularly large in photocurable pressure-sensitive adhesive compositions. Furthermore, according to the studies, it is presumed that the reduction in adhesive strength is due to the fact that photocuring tends to occur first in the center and its vicinity in the thickness direction of the coating layer, so that inorganic particles are pushed out from the first-cured portion and tend to gather on both main surfaces of the pressure-sensitive adhesive sheet. Since inorganic particles themselves usually do not have adhesive strength, the adhesive strength of the pressure-sensitive adhesive sheet may be reduced by inorganic particles gathering on the main surfaces.

[0015] In the pressure-sensitive adhesive sheet 1 according to the embodiment of the present invention, the distribution of the inorganic particles 13 in the thickness direction differs from that of the conventional photocurable pressure-sensitive adhesive sheet. Having a main surface SA with the same or lower concentration of inorganic particles 13 compared to the center M in the thickness direction can contribute to improving the balance between the refractive index and adhesive strength of the pressure-sensitive adhesive sheet 1. The concentration of inorganic particles 13 on the main surface SA may be lower than that on the center M in the thickness direction.

[0016] Of the two main surfaces of the pressure-sensitive adhesive sheet 1, only one may be the main surface SA, or both may be the main surface SA. Figures 1 and 2 show an example in which only one main surface is the main surface SA. In other words, the pressure-sensitive adhesive sheet 1 according to an embodiment of the present invention has a first main surface 11 and a second main surface 12 opposite the first main surface 11, and of the first and second main surfaces 11 and 12, only the first main surface 11 may be the main surface SA ( Figure 3 ). Furthermore, the pressure-sensitive adhesive sheet 1 according to an embodiment of the present invention has a first main surface 11 and a second main surface 12 opposite the first main surface 11, and both the first and second main surfaces 11 and 12 may be the main surface SA ( Figure 4 ). While Figures 3 and 4 show the concentration of inorganic particles 13 in the pressure-sensitive adhesive sheet 1 using shading, the illustrated shading is merely schematic and does not accurately represent the concentration in the actual pressure-sensitive adhesive sheet 1.

[0017] Concentration C of the inorganic particles 13 on the first main surface 11 S1is a region R that includes the first main surface 11 and has a thickness of 1 μm in the thickness direction of the pressure-sensitive adhesive sheet 1. S11 The concentration C of the inorganic particles 13 on the second main surface 12 can be determined by the above method. S2 , respectively, include the second main surface 12 and have a thickness of 1 μm in the thickness direction of the pressure-sensitive adhesive sheet 1. S12 The concentration of the inorganic particles 13 can be determined by the above method.

[0018] Regarding the pressure-sensitive adhesive sheet 1 of FIG. 3, the concentration C of the inorganic particles 13 on the first main surface 11 S1 and the concentration C of the inorganic particles 13 at the center M in the thickness direction M The formula: (C S1 / C M )≦1.00. S1 and concentration C M That is, (C S1 / C M ) <1.00, (C S1 / C M ) ≦0.90, (C S1 / C M ) ≦0.80, (C S1 / C M ) ≦0.75, (C S1 / C M ) ≦0.70, (C S1 / C M ) ≦0.65, (C S1 / C M ) ≦0.60, (C S1 / C M ) ≦0.55, (C S1 / C M ) ≦0.50, (C S1 / C M ) ≦0.45, (C S1 / C M ) ≦0.40, (C S1 / C M ) ≦0.35, (C S1 / C M ) ≦0.30, (C S1 / C M ) ≦0.25, and (C S1 / C M )≦0.20. S1 / C M The lower limit of ) is 0, and it may be 0.05 or more, or even 0.10 or more.

[0019] Regarding the pressure-sensitive adhesive sheet 1 of FIG. 3, the concentration C of the inorganic particles 13 on the second main surface 12 S2 and concentration C M The formula: (C S2 / C M )>1.00. S2 and concentration C M That is, (C S2 / C M ) ≧ 1.10, (C S2 / C M ) ≧ 1.25, (C S2 / C M ) ≧ 1.50, (C S2 / C M ) ≧ 1.75, (C S2 / C M ) ≧ 2.00, (C S2 / C M ) ≧ 2.10, (C S2 / C M ) ≧ 2.20, (C S2 / C M ) ≧ 2.30, (C S2 / C M ) ≧ 2.40, (C S2 / C M ) ≧ 2.50, (C S2 / C M ) ≧ 2.55, (C S2 / C M ) ≧ 2.60, (C S2 / C M ) ≧ 2.65, (C S2 / C M ) ≧ 2.70, (C S2 / C M ) ≧ 2.75, and (C S2 / C M ) ≧ 2.80. S2 / C M ) is, for example, 3.00 or less.

[0020] Concentration C of the adhesive sheet 1 in FIG. S1 and concentration C M , and concentration C S2and concentration C M can satisfy the relationship represented by any one of the above-mentioned formulas. For example, the concentration C S1 and concentration C M and the formula: (C S1 / C M ) ≦1.00, and the concentration C S2 and concentration C M and the formula: (C S2 / C M ) ≧1.50.

[0021] Regarding the pressure-sensitive adhesive sheet 1 of FIG. 4, the concentration C of the inorganic particles 13 on the first main surface 11 S1 and the concentration C of the inorganic particles 13 at the center M in the thickness direction M The concentration C exemplified for the adhesive sheet 1 in FIG. S1 and concentration C M The relationship shown in any of the equations may be satisfied.

[0022] Regarding the pressure-sensitive adhesive sheet 1 of FIG. 4, the concentration C of the inorganic particles 13 on the second main surface 12 S2 and concentration C M That is, (C S2 / C M ) ≦1.00, (C S2 / C M ) <1.00, (C S2 / C M ) ≦0.90, (C S2 / C M ) ≦0.80, (C S2 / C M ) ≦0.75, (C S2 / C M ) ≦0.70, (C S2 / C M ) ≦0.65, (C S2 / C M ) ≦0.60, (C S2 / C M ) ≦0.55, (C S2 / C M ) ≦0.50, (C S2 / C M ) ≦0.45, (C S2 / C M ) ≦0.40, (C S2 / CM ) ≦0.35, (C S2 / C M ) ≦0.30, (C S2 / C M ) ≦0.25, and (C S2 / C M )≦0.20. S2 / C M The lower limit of ) is 0, and it may be 0.05 or more, or even 0.10 or more.

[0023] Concentration C of the adhesive sheet 1 in FIG. S1 and concentration C M , and concentration C S2 and concentration C M can satisfy the relationship represented by any one of the above-mentioned formulas. S1 and concentration C M , and concentration C S2 and concentration C M may satisfy the relationship shown by the same formula.

[0024] The main surface SA can be formed, for example, by blending inorganic particles and an active energy ray absorber into the pressure-sensitive adhesive composition A that forms the pressure-sensitive adhesive sheet 1, and irradiating a coating layer of the pressure-sensitive adhesive composition A containing these with active energy rays. According to this method, the surface irradiated with active energy rays typically becomes the main surface SA. For example, in the pressure-sensitive adhesive sheet 1 shown in FIG. 3 , the first main surface 11 may be the surface irradiated with active energy rays to the pressure-sensitive adhesive composition A during the formation of the pressure-sensitive adhesive sheet 1, and the second main surface 12 may be the surface not irradiated with active energy rays to the pressure-sensitive adhesive composition A during the formation of the pressure-sensitive adhesive sheet 1. The irradiated and non-irradiated surfaces can be formed, for example, by irradiating only one side of the coating layer with active energy rays. Furthermore, by controlling the integrated light amount of active energy rays on both main surfaces of the coating layer for each main surface, it is also possible to irradiate both sides of the coating layer with active energy rays, while only the first main surface 11 is designated as the main surface SA.

[0025] 4, both the first main surface 11 and the second main surface 12 may be surfaces onto which the PSA composition A is irradiated with active energy rays during the formation of the PSA sheet 1. The two irradiated surfaces can be formed, for example, by irradiating both surfaces of the coating layer with active energy rays.

[0026] When the active energy rays are ultraviolet rays, the active energy ray absorber is typically an ultraviolet absorber (UVA).

[0027] The method for forming the main surface SA is not limited to the above example. The main surface SA may also be formed by other methods that can control the dispersion of the inorganic particles to be non-uniform in the thickness direction of the pressure-sensitive adhesive sheet 1, such as methods that utilize centrifugal force or gravity.

[0028] Whether the main surface of the adhesive sheet 1 is the surface irradiated with active energy rays or the surface not irradiated can be verified by focusing on features that could be differences that may arise between the irradiated surface and the non-irradiated surface, such as the fact that the irradiated surface usually has a structure in which inorganic particles 13 are buried from the outermost surface toward the interior of the adhesive sheet 1, compared to the non-irradiated surface; the fact that the peel force of the adhesive sheet 1 to the base sheet 31 and release liner 33 described below is usually greater on the irradiated surface than on the non-irradiated surface; or the fact that the refractive index of the main surface of an adhesive sheet 1 containing UVA is usually lower on the irradiated surface than on the non-irradiated surface.

[0029] Possible features of the adhesive sheet 1 of FIG. 3 will be described.

[0030] Concentration C of the inorganic particles 13 on the first main surface 11 S1 is the concentration C of the inorganic particles 13 on the second main surface 12 S2 The concentration C S2 Concentration C S1 Ratio C S1 / C S2is, for example, 0.90 or less, and may be less than 0.90, 0.75 or less, 0.50 or less, 0.45 or less, 0.40 or less, 0.35 or less, 0.30 or less, 0.25 or less, 0.20 or less, 0.17 or less, 0.15 or less, 0.12 or less, 0.10 or less, 0.090 or less, 0.080 or less, or even 0.075 or less. S1 / C S2 The lower limit of is more than 0, and may be 0.010 or more, 0.020 or more, 0.030 or more, or even 0.040 or more.

[0031] The inorganic particles 13 can contribute to increasing the refractive index of the adhesive sheet 1. The refractive index n2 of the adhesive sheet when the second main surface 12 is used as the evaluation surface may be greater than the refractive index n1 of the adhesive sheet 1 when the first main surface 11 is used as the evaluation surface.

[0032] In this specification, the refractive index of the pressure-sensitive adhesive sheet 1 refers to the refractive index of the surface of the pressure-sensitive adhesive sheet 1. The refractive index of the pressure-sensitive adhesive sheet 1 can be measured using a prism coupler under conditions of a measurement temperature of 25°C and a measurement wavelength of 594 nm. For pressure-sensitive adhesive sheets 1 with a thickness of less than 20 μm, measurement in the optical propagation mode is generally suitable. For pressure-sensitive adhesive sheets 1 with a thickness of 20 μm or more, measurement in the critical angle mode is generally suitable. A commercially available measuring device can be used as the prism coupler, and for example, a Model 2010 / M prism coupler manufactured by Metricon or an equivalent can be used.

[0033] The absolute value of the difference between the refractive index n1 and the refractive index n2 may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, or even 0.05 or more. In this case, the refractive index n2 may be larger than the refractive index n1. The upper limit of the absolute value of the difference is, for example, 0.20 or less.

[0034] The refractive index n1 is, for example, 1.55 or more, and may be 1.56 or more, 1.57 or more, 1.58 or more, 1.59 or more, 1.60 or more, or even 1.61 or more. The refractive index n2 is, for example, 1.59 or more, and may be 1.60 or more, 1.61 or more, 1.62 or more, 1.63 or more, 1.64 or more, or even 1.65 or more. In this case, the refractive index n2 may be larger than the refractive index n1. The pressure-sensitive adhesive sheet 1 may have both the refractive index n1 and the refractive index n2 selected from the above-mentioned multiple numerical ranges. For example, the refractive index n1 may be 1.58 or more, and the refractive index n2 may be 1.61 or more.

[0035] The pressure-sensitive adhesive sheet 1 can be combined with an optical substrate to form an optical laminate. Depending on the configuration of the optical laminate, it may be advantageous to have a difference between the refractive index n1 and the refractive index n2. For example, in an optical laminate in which a first optical substrate having a relatively high refractive index and a second optical substrate having a relatively low refractive index are laminated so as to sandwich the pressure-sensitive adhesive sheet 1, the main surface on the high refractive index side, for example, the second main surface 12 having the refractive index n2, faces the first optical substrate, and the main surface on the low refractive index side, for example, the first main surface 11 having the refractive index n1, faces the second optical substrate. By arranging the pressure-sensitive adhesive sheet 1 so that it faces the second optical substrate, reflection of light at the interface between each optical substrate and the pressure-sensitive adhesive sheet 1 can be suppressed. Suppression of reflection can result in a reduction in the front reflectance of the optical laminate. Reducing the front reflectance can contribute to, for example, improving the brightness of an image display device.

[0036] In view of the above, the reflectance of the pressure-sensitive adhesive sheet 1 evaluated by the following evaluation method may be 8.1% or less, 8.0% or less, 7.9% or less, or even 7.8% or less. <Evaluation Method> A laminate is prepared in which an acrylic sheet with a refractive index of 1.49, a 50 μm thick pressure-sensitive adhesive sheet 1, and a sapphire glass sheet with a refractive index of 1.77 are stacked in this order. The first main surface 11 of the pressure-sensitive adhesive sheet 1 is in contact with the acrylic sheet. The second main surface 12 of the pressure-sensitive adhesive sheet 1 is in contact with the sapphire glass sheet. Next, the front reflectance of the laminate is measured using the SCI method with the sapphire glass sheet as the incident surface, and the obtained front reflectance is identified as the reflectance of the pressure-sensitive adhesive sheet. The SCI method is well known to those skilled in the art as a method for measuring reflectance including specular reflection light.

[0037] Possible features of the adhesive sheet 1 of FIG. 4 will be described.

[0038] Concentration C of the inorganic particles 13 on the first main surface 11 S1 is the concentration C of the inorganic particles 13 on the second main surface 12 S2 The concentration C S2 Concentration C S1 Ratio C S1 / C S2 is 1 or close to 1. S1 / C S2 is, for example, 0.90 or more and 1.10 or less, 0.95 or more and 1.05 or less, 0.96 or more and 1.04 or less, 0.97 or more and 1.03 or less, 0.98 or more and 1.02 or less, or may be 0.99 or more and 1.01 or less.

[0039] The refractive index n1 of the pressure-sensitive adhesive sheet 1 when the first main surface 11 is used as the evaluation surface may be approximately equal to the refractive index n2 of the pressure-sensitive adhesive sheet when the second main surface 12 is used as the evaluation surface. This can be determined by the absolute value of the difference between the refractive index n1 and the refractive index n2 being 0 or close to 0. The absolute value of the difference may be less than 0.01.

[0040] The refractive index n1 and the refractive index n2 are, for example, 1.55 or more, and may be 1.56 or more, 1.57 or more, 1.58 or more, 1.59 or more, 1.60 or more, or even 1.61 or more. The refractive index n2 is, for example, 1.59 or more, and may be 1.60 or more, 1.61 or more, 1.62 or more, 1.63 or more, 1.64 or more, or even 1.65 or more. The pressure-sensitive adhesive sheet 1 can have both the refractive index n1 and the refractive index n2 selected from the above-mentioned multiple numerical ranges.

[0041] The common features of the adhesive sheets 1 of FIGS. 3 and 4 will be described.

[0042] The adhesive strength of the pressure-sensitive adhesive sheet 1 on the main surface SA, in terms of adhesive strength to alkali-free glass, may be, for example, 1.0 N / 25 mm or more, 1.5 N / 25 mm or more, 2.0 N / 25 mm or more, 2.5 N / 25 mm or more, 3.0 N / 25 mm or more, 3.5 N / 25 mm or more, 4.0 N / 25 mm or more, 4.5 N / 25 mm or more, 5.0 N / 25 mm or more, 5.5 N / 25 mm or more, 6.0 N / 25 mm or more, 6.5 N / 25 mm or more, 7.0 N / 25 mm or more, 7.5 N / 25 mm or more, or even 8.0 N / 25 mm or more. The upper limit of the adhesive strength is, for example, 50.0 N / 25 mm or less, and may be 40.0 N / 25 mm or less, 30.0 N / 25 mm or less, 25.0 N / 25 mm or less, 20.0 N / 25 mm or less, 15.0 N / 25 mm or less, or even 12.0 N / 25 mm or less. In some cases, the upper limit of the adhesive strength may be 10.0 N / 25 mm or less, 9.0 N / 25 mm or less, or even 8.0 N / 25 mm or less.

[0043] The adhesive strength can be determined by the following method. First, a laminate including a pressure-sensitive adhesive sheet 1 and a substrate is prepared under a measurement environment of 23°C and 50% RH. The substrate is not particularly limited as long as it can support the pressure-sensitive adhesive sheet 1 and does not substantially affect the adhesive strength measurement results. An example of the substrate is a polyethylene terephthalate film. Next, the laminate is cut into a strip measuring 100 mm in length and 25 mm in width to prepare a test piece. Next, the test piece is placed on alkali-free glass via the pressure-sensitive adhesive sheet 1, and a 2 kg roller is moved back and forth once to press them together. The alkali-free glass is glass that is substantially free of alkali components (alkali metal oxides). Specifically, the weight ratio of the alkali components in the glass is, for example, 1000 ppm or less, and even 500 ppm or less. The alkali-free glass is, for example, in the form of a plate and has a thickness of 0.5 mm or more.

[0044] After leaving this test piece under the above environment for 30 minutes, it is placed in a pressure degassing apparatus (autoclave) and autoclaved for 30 minutes under conditions of a temperature of 50°C and a pressure of 0.5 MPa. Next, it is left for 24 hours in an atmosphere of 23°C and 50% RH. Next, using a universal tension and compression tester, a peel test is performed to peel the test piece from the alkali-free glass at a peel rate of 300 mm / min and a peel angle of 180°. The force (peel strength) required to peel the test piece from the alkali-free glass is determined as the adhesive strength.

[0045] The pressure-sensitive adhesive sheet 1 may have a refractive index and adhesive strength selected from the above-mentioned ranges for the main surface SA. For example, the main surface SA may have a refractive index of 1.58 or more and an adhesive strength of 4.0 N / 25 mm or more. The main surface SA that may have a refractive index and adhesive strength within the above ranges is the first main surface 11 for the pressure-sensitive adhesive sheet 1 in Figure 3, and at least one main surface selected from the first main surface 11 and the second main surface 12 for the pressure-sensitive adhesive sheet 1 in Figure 4.

[0046] The gel fraction of the pressure-sensitive adhesive sheet 1 is, for example, 50% or more, and may be 75% or more, 80% or more, 85% or more, or even 90% or more.

[0047] The haze of the pressure-sensitive adhesive sheet 1 is, for example, 5.0% or less, and may be 3.0% or less, 2.0% or less, 1.7% or less, 1.5% or less, 1.2% or less, 1.0% or less, 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, or even 0.2% or less. The lower limit of the haze is not particularly limited and may be 0.1% or more. A low-haze pressure-sensitive adhesive sheet 1 is particularly suitable for use in optical laminates.

[0048] In this specification, haze refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated onto the pressure-sensitive adhesive sheet 1, which is the object to be measured. Haze can be calculated using the following formula: In the formula, Th is haze (%), Td is scattered light transmittance, and Tt is total light transmittance. Th (%) = Td / Tt x 100

[0049] The chromaticity of the adhesive sheet 1 is determined by the CIE1976 L standard defined in Japanese Industrial Standards (JIS) Z8781-4:2013. * , a * , b * Color space chromaticity b * The chromaticity b may be expressed as an absolute value of 2.0 or less. * The absolute value of chromaticity b may be 1.7 or less, 1.5 or less, 1.2 or less, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or even 0.5 or less. * The lower limit of the absolute value of chromaticity b of the pressure-sensitive adhesive sheet 1 is, for example, 0 or more, and may be 0.1 or more. * can be evaluated using a commercially available colorimeter capable of measurements in accordance with JIS Z8781-4:2013.

[0050] The thickness of the pressure-sensitive adhesive sheet 1 is, for example, 500 μm or less, and may be 250 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 30 μm or less, 25 μm or less, or even 20 μm or less. The lower limit of the thickness of the pressure-sensitive adhesive sheet 1 is, for example, 2 μm or more, and may be 5 μm or more. In some cases, the lower limit of the thickness of the pressure-sensitive adhesive sheet 1 may be 20 μm or more, or may be 30 μm or more. A preferred example of the thickness of the pressure-sensitive adhesive sheet 1 is 2 to 30 μm. Another preferred example of the thickness of the pressure-sensitive adhesive sheet 1 is 30 to 100 μm.

[0051] <1-2. Inorganic Particles> The pressure-sensitive adhesive sheet 1 contains inorganic particles. The inorganic particles can contribute to improving the refractive index of the pressure-sensitive adhesive sheet 1.

[0052] The inorganic particles are particles containing an inorganic substance containing an inorganic element I. However, the inorganic element I excludes non-metallic elements such as nitrogen, oxygen, fluorine, phosphorus, sulfur, chlorine, selenium, bromine, iodine, and rare gases. The inorganic substance may be an inorganic compound.

[0053] Preferred examples of inorganic element I are aluminum, magnesium, calcium, zinc, iron, copper, barium, tungsten and platinum. Inorganic element I may also be zirconium.

[0054] Examples of inorganic substances include metals and metal compounds. As inorganic particles, one or more types may be selected from metal compound particles and metal particles depending on the desired purpose, such as improving the refractive index. The metal compound particles may be metal oxide particles. Examples of materials constituting metal oxide particles include titanium oxide, zirconium oxide, cerium oxide, aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, and niobium oxide. The inorganic particles may be used alone or in combination of two or more types. The inorganic particles preferably contain zirconium oxide, and may be zirconium oxide particles composed essentially of zirconium oxide alone. The zirconium oxide particles can particularly contribute to increasing the refractive index of the pressure-sensitive adhesive sheet.

[0055] The material constituting the metal compound particles may be a metal hydroxide such as aluminum hydroxide, boehmite, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, copper hydroxide, barium hydroxide, basic magnesium carbonate, hydrotalcite, or a hydrated metal compound. Examples of the material constituting the metal particles are iron, zinc, tungsten, and platinum.

[0056] The material of the inorganic particles may be a high-entropy alloy in which multiple types of elements are mixed.

[0057] The inorganic particles may be surface-treated. One example of the surface treatment is hydrophobization. In this specification, it is preferable that the inorganic particles do not include carbon black particles.

[0058] The inorganic particles may contain a high refractive index material. The refractive index of the high refractive index material is, for example, 1.60 or more, and may be 1.70 or more, 1.80 or more, or even 2.00 or more. The upper limit of the refractive index of the high refractive index material is not particularly limited, and may be, for example, 3.00 or less, 2.80 or less, 2.50 or less, or even 2.20 or less. The refractive index of the material contained in the inorganic particles can be determined as the refractive index measured on a monolayer film of the material using a commercially available spectroscopic ellipsometer under conditions of 23°C and 549 nm. The spectroscopic ellipsometer may be, for example, an "EC-400" (manufactured by J.A. Woollam) or an equivalent.

[0059] The inorganic particles may be nanoparticles having an average particle size of less than 1 μm. The average particle size of the inorganic particles may be 100 nm or less. The average particle size may be 70 nm or less, 50 nm or less, 30 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 7 nm or less, 5 nm or less, or even 4 nm or less. The lower limit of the average particle size may be, for example, 1 nm or more, 1.5 nm or more, 2 nm or more, or even 2.5 nm or more. The average particle size can be specified as the median diameter (D50) in the particle size distribution measured by dynamic light scattering.

[0060] The content of inorganic particles in the pressure-sensitive adhesive sheet 1 can be within the range described in the description of the content of inorganic particles in the pressure-sensitive adhesive composition A (described below).

[0061] <1-3. Pressure-sensitive adhesive composition> <1-3-a. Content of inorganic particles> The pressure-sensitive adhesive composition A used to form the pressure-sensitive adhesive sheet 1 contains the monomer component M and usually also contains inorganic particles. The content of the inorganic particles in the pressure-sensitive adhesive composition A is, for example, 10 parts by weight or more, relative to 100 parts by weight of the total of the monomer component M and the inorganic particles (specifically, a mixture of the inorganic particles and the dispersant), and may be 20 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 36 parts by weight or more, 37 parts by weight or more, 38 parts by weight or more, 39 parts by weight or more, 40 parts by weight or more, 41 parts by weight or more, 42 parts by weight or more, 43 parts by weight or more, 44 parts by weight or more, 45 parts by weight or more, 46 parts by weight or more, 47 parts by weight or more, 48 parts by weight or more, 49 parts by weight or more, 50 parts by weight or more, 51 parts by weight or more, 52 parts by weight or more, 53 parts by weight or more, 54 parts by weight or more, 55 parts by weight or more, 56 parts by weight or more, 57 parts by weight or more, 58 parts by weight or more, 59 parts by weight or more, or even 60 parts by weight or more. The upper limit of the content is, for example, 90 parts by weight or less, and may be 80 parts by weight or less, 70 parts by weight or less, or even 60 parts by weight or less. The content is preferably 40 to 60 parts by weight.

[0062] <1-3-b. UVA> The pressure-sensitive adhesive composition A may contain UVA. The UVA can contribute to the formation of a pressure-sensitive adhesive sheet 1 by irradiating a coating layer of the pressure-sensitive adhesive composition A with ultraviolet light. When UVA is contained, the amount of ultraviolet light reaching the center of the coating layer in the thickness direction is reduced compared to when UVA is not contained. This is presumably to suppress the advance of photocuring at the center of the coating layer and delay photocuring compared to the vicinity of the main surface, which is the UV-irradiated surface, resulting in a dispersed state of inorganic particles forming the main surface SA. Furthermore, when the monomer component M contains the monomer a described below, UVA can also contribute to mitigating the effects of ultraviolet light on the monomer a and the structural units formed by polymerization of the monomer a. Monomer a is a monomer having a double-bond-containing ring, and since the double-bond-containing ring absorbs light in the short-wavelength region, it may have inferior ultraviolet resistance compared to (meth)acrylic monomers not containing a double-bond-containing ring.

[0063] Examples of UVAs include triazine-based UVAs, benzotriazole-based UVAs, benzophenone-based UVAs, oxybenzophenone-based UVAs, salicylic acid ester-based UVAs, and cyanoacrylate-based UVAs. Each UVA is a compound having a triazine skeleton, a benzotriazole skeleton, a benzophenone skeleton, an oxybenzophenone skeleton, a salicylic acid ester structure, and a cyanoacrylate structure, respectively. The UVA is preferably a triazine-based or benzotriazole-based UVA, and more preferably a benzotriazole-based UVA.

[0064] Examples of triazine-based UVAs include 2,4-bis-[{4-(4-ethylhexyloxy)-4-hydroxy}-phenyl]-6-(4-methoxyphenyl)-1,3,5-triazine (Tinosorb S, manufactured by BASF), 2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine (TINUVIN), 460, manufactured by BASF), reaction products of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl with [(C10-C16 (mainly C12-C13) alkyloxy)methyl]oxirane (TINUVIN 400, manufactured by BASF), 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-[3-(dodecyloxy)-2-hydroxypropoxy]phenol, 2-(2,4-dihydroxyphenyl)-1,3,5-triazin-2-yl Reaction products of 2-(4,6-diphenyl-1,3,5-triazine and (2-ethylhexyl)-glycidic acid ester (TINUVIN 405, manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol (TINUVIN 1577, manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]-phenol (ADK STAB LA46, manufactured by ADEKA), and 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine (TINUVIN 479, manufactured by BASF).

[0065] Examples of benzotriazole-based UVAs include 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (TINUVIN 928, manufactured by BASF), 2-(2H-1,2,3-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (TINUVIN 571, manufactured by BASF), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (TINUVIN PS, manufactured by BASF), ester compound of benzenepropanoic acid and 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy(C7-9 branched and linear alkyl) (TINUVIN 384-2, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (TINUVIN 900, manufactured by BASF), reaction product of methyl-3-(3-(2H-benzotriazol-2-yl)-5-t-butyl-4-hydroxyphenyl)propionate / polyethylene glycol 300 (TINUVIN 1130, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-p-cresol (TINUVIN P, manufactured by BASF), 2(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (TINUVIN 234, manufactured by BASF), 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol (TINUVIN 326, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (TINUVIN 328, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (TINUVIN 329, manufactured by BASF), -yl)-4-(1,1,3,3-tetramethylbutyl)phenol (TINUVIN 329, manufactured by BASF), reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate with polyethylene glycol 300 (TINUVIN 213, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (TINUVIN 571, manufactured by BASF), 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimido-methyl)-5-methylphenyl]benzotriazole (Sumisorb 250, manufactured by Sumitomo Chemical Co., Ltd.).

[0066] The UVA may be a liquid at 25° C. The UVA may be a benzotriazole-based UVA that is a liquid at 25° C.

[0067] The pressure-sensitive adhesive composition A may contain one or more UVAs.

[0068] The content of the UVA in the pressure-sensitive adhesive composition A is, for example, 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, 0.5 parts by weight or more, 0.6 parts by weight or more, 0.7 parts by weight or more, 0.8 parts by weight or more, 0.9 parts by weight or more, 1 part by weight or more, 1.1 parts by weight or more, 1.2 parts by weight or more, 1.3 parts by weight or more, 1.5 parts by weight or more, 1.8 parts by weight or more, 2 parts by weight or more, 2.5 parts by weight or more, or even 3 parts by weight or more, relative to 100 parts by weight of the total of the monomer component M and the inorganic particles. The upper limit of the content is not particularly limited, and may be, for example, 10 parts by weight or less, 8 parts by weight or less, 6 parts by weight or less, or even 5 parts by weight or less. The content of the UVA in the pressure-sensitive adhesive composition A may be 1 to 5 parts by weight, relative to 100 parts by weight of the total of the monomer component M and the inorganic particles.

[0069] When the pressure-sensitive adhesive composition A contains UVA, the light transmittance in the thickness direction of the pressure-sensitive adhesive sheet 1 may be 25% or less for light with a wavelength of 380 nm, and may be 20% or less, 18% or less, 16% or less, 15% or less, 13% or less, 11% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or even 1% or less. The lower limit of the transmittance is 0%. The light transmittance in the thickness direction of the pressure-sensitive adhesive sheet 1 can be evaluated using a commercially available transmittance meter.

[0070] <1-3-c. Monomer component M> The pressure-sensitive adhesive composition A contains a monomer component M. A portion of the monomer component M may be in the form of a partial polymer. The pressure-sensitive adhesive composition A is a photocurable pressure-sensitive adhesive composition that forms a pressure-sensitive adhesive sheet by irradiation with active energy rays. Being a photocurable type is particularly preferable in terms of environmental protection and sustainability, since the amount of energy required to form a pressure-sensitive adhesive sheet can be reduced compared to a thermosetting type that forms a pressure-sensitive adhesive sheet mainly using heat.

[0071] The content of the monomer component M relative to 100 parts by weight of the total of the monomer component M and the inorganic particles (specifically, a mixture of the inorganic particles and the dispersant) is, for example, 10 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 36 parts by weight or more, 37 parts by weight or more, 38 parts by weight or more, 39 parts by weight or more, 40 parts by weight or more, 41 parts by weight or more, 42 parts by weight or more, 43 parts by weight or more, 44 parts by weight or more, 45 parts by weight or more, 46 parts by weight or more, 47 parts by weight or more, 48 parts by weight or more, 49 parts by weight or more, 50 parts by weight or more, 51 parts by weight or more, 52 parts by weight or more, 53 parts by weight or more, 54 parts by weight or more, 55 parts by weight or more, 56 parts by weight or more, 57 parts by weight or more, 58 parts by weight or more, 59 parts by weight or more, or even 60 parts by weight or more. The upper limit of the content is, for example, 90 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, or even 60 parts by weight or less. The content is preferably 40 to 60 parts by weight.

[0072] [1-3-c1. Monomer a having a double bond-containing ring] The monomer component M may contain a monomer a having a double bond-containing ring. Monomer a can contribute to improving the refractive index of the pressure-sensitive adhesive sheet 1. In this specification, a double bond-containing ring refers to a ring in which at least one of the bonds constituting the ring is a double bond. Examples of double bonds include carbon-carbon double bonds, carbon-heteroatom double bonds, and heteroatom-heteroatom double bonds. Examples of heteroatoms include nitrogen, sulfur, and oxygen.

[0073] The number of double bonds in the double bond-containing ring is not particularly limited and may be, for example, 1 to 10, or 2 to 5. When the double bond-containing ring contains two or more double bonds, these double bonds may be conjugated or non-conjugated. The double bond-containing ring is preferably an aromatic ring.

[0074] The double bond-containing ring may be a carbocyclic ring. Examples of the carbocyclic ring include a benzene ring (which may be a benzene ring constituting a part of a biphenyl structure or a fluorene structure), a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, and a phenanthrene ring. The double bond-containing ring may be a heterocyclic ring (heterocyclic ring). Examples of the heterocyclic ring include a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, a pyrrole ring, a pyrazole ring, an imidazole ring, a triazole ring, an oxazole ring, an isoxazole ring, a thiazole ring, and a thiophene ring. Examples of heteroatoms that may be contained in the heterocyclic ring as ring-constituting atoms include at least one selected from the group consisting of nitrogen, sulfur, and oxygen. The heteroatom may be one or both of nitrogen and sulfur. The double bond-containing ring may be a fused ring. An example of the monomer a has a structure in which one or more carbocyclic rings and one or more heterocyclic rings are fused, such as a dinaphthothiophene structure.

[0075] The double bond-containing ring may have one or more substituents (excluding ethylenically unsaturated groups, which will be described later) on the ring-constituting atoms, or may have no substituents. Examples of the substituents include alkyl groups, alkoxy groups, aryloxy groups, hydroxyl groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl groups, hydroxyalkyloxy groups, and glycidyloxy groups. However, the substituents are not limited to the above examples. The substituents may contain carbon atoms, and in such cases, the number of carbon atoms contained in the substituent may be, for example, 1 to 4, 1 to 3, or even 1 to 2. One example of the double bond-containing ring has no substituents on the ring-constituting atoms. Another example of the double bond-containing ring has one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, and halogen atoms (e.g., bromine atoms) on the ring-constituting atoms.

[0076] In the monomer a, the number of double bond-containing rings contained in one molecule is, for example, 1, and may be 2 or more. The upper limit of the number of double bond-containing rings is not particularly limited and is, for example, 16 or less. The upper limit may be 12 or less, 8 or less, 6 or less, 5 or less, 4 or less, 3 or less, or even 2 or less.

[0077] In the monomer a, the double bond-containing ring is preferably located in a side chain. In other words, the monomer a preferably has at least one double bond-containing ring and at least one ethylenically unsaturated group in one molecule. As the monomer a, a compound having one ethylenically unsaturated group in one molecule (in other words, a monofunctional monomer) is preferably used.

[0078] Examples of ethylenically unsaturated groups are (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 adhesiveness, acryloyl groups are more preferred. In other words, monomer a preferably contains a (meth)acrylic monomer having a double bond-containing ring, and more preferably contains an acrylic monomer having a double bond-containing ring. Examples of (meth)acrylic monomers having a double bond-containing ring include aromatic ring-containing (meth)acrylates. Specific examples of aromatic ring-containing (meth)acrylates will be described later.

[0079] The double bond-containing ring and the ethylenically unsaturated group may be bonded directly or via a linking group. An example of the linking group includes one or more groups selected from the group consisting of alkylene groups, oxyalkylene groups, poly(oxyalkylene) groups, phenyl groups, alkylphenyl groups, alkoxyphenyl groups, groups in which one or more hydrogen atoms in these groups have been substituted with hydroxyl groups (e.g., hydroxyalkylene groups), oxy groups (-O-), and thiooxy groups (-S-). In one example of Monomer A, the double bond-containing ring and the ethylenically unsaturated group are bonded directly. In another example of Monomer A, the double bond-containing ring and the ethylenically unsaturated group are 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 oxyalkylene group that can be included in the linking group is, for example, 1 to 4, and may be 1 to 3, or even 1 to 2. The number of repeating oxyalkylene units in the poly(oxyalkylene) group that can be contained in the linking group is, for example, 1 to 8, and may be 1 to 6, 1 to 4, 1 to 3, 2 to 3, or even 1 to 2, 2, or 1.

[0080] Specific examples of the monomer a include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds may be used alone or in combination of two or more.

[0081] Monomer a may contain two or more aromatic rings (preferably carbon rings) in one molecule. A monomer having two or more aromatic rings and at least one ethylenically unsaturated group in one molecule (aromatic ring-containing monomer) can particularly contribute to increasing the refractive index of the PSA sheet.

[0082] Examples of the aromatic ring-containing monomer include a monomer having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, a monomer having a structure in which two or more non-condensed aromatic rings are directly bonded, a monomer having a condensed ring, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, and a monomer having a dibenzothiophene structure. Among these, a monomer having a structure in which two or more non-condensed aromatic rings are bonded via a linking group (for example, phenoxybenzyl (meth)acrylate described below) is preferably used.

[0083] The linking group may contain atoms such as P, Ge, Te, Se, N, S, and Si, and these atoms may be bonded to an oxygen atom. However, the linking group does not have to contain any of the above atoms. Examples of the linking group include an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (e.g., -O-(CH2) n -; n is 1 to 3, preferably 1), a thiooxyalkylene group (e.g., -S-(CH2) n -; n is 1 to 3, preferably 1), a straight chain alkylene group (-(CH2) n -; n is 1 to 6, preferably 1 to 3), and the above-mentioned oxyalkylene group, the above-mentioned thiooxyalkylene group, and the above-mentioned straight-chain alkylene group in which the alkylene group is partially or completely halogenated. The linking group may contain one or more types selected from the group consisting of an oxy group, a thiooxy group, an oxyalkylene group, and a straight-chain alkylene group. Specific examples of monomers having a structure in which two or more non-fused aromatic rings are bonded via a linking group include phenoxybenzyl (meth)acrylate, thiophenoxybenzyl (meth)acrylate, and benzyl benzyl (meth)acrylate.

[0084] Examples of the monomer having a structure in which two or more non-fused aromatic rings are directly bonded include biphenyl structure-containing (meth)acrylate, triphenyl structure-containing (meth)acrylate, and vinyl group-containing biphenyl. Specific examples include o-phenylphenol (meth)acrylate, biphenyl (meth)acrylate, and biphenylmethyl (meth)acrylate.

[0085] Examples of monomers having a condensed ring include naphthalene ring-containing (meth)acrylates, anthracene ring-containing (meth)acrylates, vinyl group-containing naphthalenes, and vinyl group-containing anthracenes. 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, and 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate.

[0086] Examples of monomers having a fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene(meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene(meth)acrylate. Note that, since monomers having a fluorene structure have a structure in which two benzene rings are directly bonded, they are included in the concept of monomers having a structure in which two or more non-fused aromatic rings are directly bonded.

[0087] Examples of the monomer having a dinaphthothiophene structure are (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, and (meth)allyl group-containing dinaphthothiophene. Specific examples include (meth)acryloyloxymethyl dinaphthothiophene (e.g., a compound having a structure in which a CHCH(R)C(O)OCH group is bonded to the 5th or 6th position of the dinaphthothiophene ring; R is a hydrogen atom or a methyl group), (meth)acryloyloxyethyl dinaphthothiophene (e.g., a compound having a structure in which a CHCH(R)C(O)OCH(CH) group or a CHCH(R)C(O)OCHCH group is bonded to the 5th or 6th position of the dinaphthothiophene ring; R is a hydrogen atom or a methyl group), vinyl dinaphthothiophene (e.g., a compound having a structure in which a vinyl group is bonded to the 5th or 6th position of the naphthothiophene ring), and (meth)allyloxy dinaphthothiophene. A monomer having a dinaphthothiophene structure is included in the concept of a monomer having a fused ring because it has a naphthalene structure and also has a structure in which a thiophene ring and two naphthalene structures are fused together.

[0088] Examples of monomers having a dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophenes and vinyl group-containing dibenzothiophenes. Note that, since monomers having a dibenzothiophene structure have a structure in which a thiophene ring and two benzene rings are fused, they are included in the concept of monomers having fused rings. Neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-fused aromatic rings are directly bonded.

[0089] Monomer a may be a monomer having one aromatic ring (preferably a carbon ring) and at least one ethylenically unsaturated group in one molecule (aromatic ring-single-containing monomer).

[0090] Examples of aromatic ring unit-containing monomers 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, and chlorobenzyl (meth)acrylate; 2-(4,6-dibromo-2-s-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, and 6-(4 bromine-substituted aromatic ring-containing (meth)acrylates such as 2,6-dibromo-4-isopropyl-2-(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-substituted aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; and compounds having a vinyl substituent on a heteroaromatic ring such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, and N-vinyloxazole.

[0091] Monomer a may have a structure in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the double bond-containing ring in the various monomers a described above. Monomers having this structure can be understood as ethoxylated products of the original monomers. The number of repeating oxyethylene units (—CHCHO—) in the oxyethylene chain is, for example, 1 to 8, and may be 1 to 6, 1 to 4, 1 to 3, or even 1 to 2, or even 1. Examples of monomer a that is an ethoxylated product include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate.

[0092] Monomer a may contain a high refractive index monomer. In this specification, the high refractive index monomer means a monomer having a refractive index of 1.51 or more, 1.53 or more, 1.55 or more, 1.56 or more, 1.57 or more, 1.58 or more, 1.59 or more, 1.60 or more, 1.61 or more, 1.62 or more, 1.63 or more, 1.64 or more, 1.65 or more, 1.66 or more, 1.67 or more, 1.68 or more, or even 1.69 or more. The upper limit of the refractive index of the high refractive index monomer is not particularly limited, and may be, for example, 3.00 or less, 2.50 or less, 2.00 or less, 1.90 or less, 1.80 or less, or even 1.70 or less. The high refractive index monomer may be used alone or in combination of two or more.

[0093] The refractive index of the monomer can be measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C. The Abbe refractometer may be a DR-M4 model manufactured by ATAGO or an equivalent (e.g., DR-M2 model). If the nominal value of the refractive index at 25°C is provided by the monomer manufacturer, etc., this nominal value can be used as the refractive index.

[0094] Examples of high refractive index monomers are phenoxybenzyl acrylate (refractive index 1.566), 1-naphthylmethyl acrylate (refractive index 1.595), ethoxylated o-phenylphenol acrylate (refractive index 1.578 when the number of repeating oxyethylene units is 1), benzyl acrylate (refractive index 1.519), phenoxyethyl acrylate (refractive index 1.517), phenoxydiethylene glycol acrylate (refractive index 1.510), 6-acryloyloxymethyldinaphthothiophene (refractive index 1.75), 6-methacryloyloxymethyldinaphthothiophene (refractive index 1.726), 5-acryloyloxyethyldinaphthothiophene (refractive index 1.786), 6-acryloyloxyethyldinaphthothiophene (refractive index 1.722), 6-vinyldinaphthothiophene (refractive index 1.802), and 5-vinyldinaphthothiophene (refractive index 1.793). However, the high refractive index monomer is not limited to the above examples. Monomer a preferably contains phenoxybenzyl acrylate as a high refractive index monomer.

[0095] The content of monomer a in the PSA composition A is, for example, 10 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 36 parts by weight or more, 37 parts by weight or more, 38 parts by weight or more, 39 parts by weight or more, 40 parts by weight or more, 41 parts by weight or more, 42 parts by weight or more, 43 parts by weight or more, 44 parts by weight or more, 45 parts by weight or more, 46 parts by weight or more, 47 parts by weight or more, 48 parts by weight or more, 49 parts by weight or more, 50 parts by weight or more, 51 parts by weight or more, 52 parts by weight or more, 53 parts by weight or more, 54 parts by weight or more, 55 parts by weight or more, 56 parts by weight or more, 57 parts by weight or more, 58 parts by weight or more, or even 59 parts by weight or more, relative to 100 parts by weight of the total of monomer component M and inorganic particles (specifically, a mixture of inorganic particles and a dispersant). The upper limit of the content may be, for example, 90 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, or even 60 parts by weight or less. The content is preferably 40 to 60 parts by weight.

[0096] [1-3-c2. Other Monomers] The monomer component M may contain other monomers in addition to the above-mentioned monomer a. One example of such other monomers is a hydroxyl group-containing monomer. The hydroxyl group-containing monomer has at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule. The monomer component M may contain one or more hydroxyl group-containing monomers.

[0097] Examples of the ethylenically unsaturated group are the same as those mentioned above in the description of monomer A. The hydroxyl group-containing monomer may be a (meth)acrylic monomer.

[0098] Examples of hydroxyl group-containing monomers include 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 acrylate. The hydroxyl group-containing monomer is preferably 4-hydroxybutyl (meth)acrylate. The content of the hydroxyl group-containing monomer in the monomer component M is, for example, 25% by weight or less, and may be 20% by weight or less, 15% by weight or less, 12% by weight or less, 10% by weight or less, 8% by weight or less, 7% by weight or less, 6% by weight or less, 5% by weight or less, 4% by weight or less, 3% by weight or less, or even 2% by weight or less. The lower limit of the content is, for example, 0.01% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or even 1% by weight or more. The monomer component M may not contain a hydroxyl group-containing monomer.

[0099] Another example of a monomer that can be contained in the monomer component M is a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms on the side chain. The number of carbon atoms in the alkyl group may be 7 or less, 6 or less, 5 or less, or even 4 or less. The alkyl group may be linear or branched. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, n-nonyl(meth)acrylate, isononyl(meth)acrylate, n-decyl(meth)acrylate, isodecyl(meth)acrylate, n-dodecyl(meth)acrylate (lauryl(meth)acrylate), n-tridecyl(meth)acrylate, n-tetradecyl(meth)acrylate, pentadecyl(meth)acrylate, hexadecyl(meth)acrylate, heptadecyl(meth)acrylate, and octadecyl(meth)acrylate. The (meth)acrylic acid alkyl ester may be n-butyl(meth)acrylate.

[0100] The content of the (meth)acrylic acid alkyl ester in the monomer component M is, for example, 25% by weight or less, and may be 20% by weight or less, 15% by weight or less, 10% by weight or less, 7% by weight or less, 5% by weight or less, or even 4% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or even 1% by weight or more. The monomer component M may not contain a (meth)acrylic acid alkyl ester.

[0101] Another example of a monomer that can be included in the monomer component M is an aliphatic ring-containing monomer. The aliphatic ring-containing monomer has at least one aliphatic ring and at least one ethylenically unsaturated group in one molecule. The aliphatic ring-containing monomer may be used alone or in combination of two or more types.

[0102] Examples of the ethylenically unsaturated group are the same as those mentioned above in the description of monomer A. The aliphatic ring-containing monomer may be a (meth)acrylic monomer.

[0103] Examples of the aliphatic ring-containing monomer include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, and adamantyl (meth)acrylate.

[0104] The content of the alicyclic monomer in the monomer component M is, for example, 25% by weight or less, and may be 20% by weight or less, 15% by weight or less, 10% by weight or less, 7% by weight or less, 5% by weight or less, or even 4% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or even 1% by weight or more. The monomer component M may not contain an alicyclic monomer.

[0105] Another example of a monomer that can be contained in the monomer component M is a carboxyl group-containing monomer. The carboxyl group-containing monomer that can be contained in the monomer component M has at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. The monomer component M may contain one or more types of carboxyl group-containing monomers.

[0106] Examples of the ethylenically unsaturated group are the same as those mentioned above in the description of monomer A. The carboxyl group-containing monomer may be a (meth)acrylic monomer.

[0107] Examples of carboxyl group-containing monomers are (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid and crotonic acid.

[0108] The content of the carboxyl group-containing monomer in the monomer component M is, for example, 10% by weight or less, and may be 7% by weight or less, 5% by weight or less, 3% by weight or less, or even 1% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or even 1% by weight or more. It is preferable that the monomer component M does not contain a carboxyl group-containing monomer.

[0109] Another example of a monomer that can be contained in the monomer component M is an ether group-containing monomer. The ether group-containing monomer that can be contained in the monomer component M has at least one ether group and at least one ethylenically unsaturated group in one molecule. The monomer component M may contain one or more types of ether group-containing monomers.

[0110] The ether group of the ether group-containing monomer is usually contained in a portion that becomes a side chain after polymerization. The side chain may be linear or branched. The ether group-containing monomer may have an oxyalkylene group, and the number of oxyalkylene groups in one molecule may be, for example, 1 to 30, 1 to 12, or even 1 to 5.

[0111] Examples of the oxyalkylene group include an oxymethylene group, an oxyethylene group, and an oxypropylene group. The ether group-containing monomer preferably has an oxyethylene group. The ether group-containing monomer having an oxyethylene group is represented, for example, by the following formula (1):

[0112] R in formula (1) 1 is a hydrogen atom or a methyl group. 2is a hydrocarbon group. In a preferred example, the hydrocarbon group is an alkyl group. The alkyl group may be linear or branched. Examples of the alkyl group are a methyl group and an ethyl group. In another example, the hydrocarbon group contains a carbon ring. Examples of the carbon ring are the same as those mentioned above in the description of the double bond-containing ring. An example of a hydrocarbon group containing a carbon ring is a phenyl group.

[0113] In formula (1), n ​​is an integer of 1 to 30, preferably an integer of 1 to 12, and may be an integer of 1 to 5.

[0114] Examples of ether group-containing monomers are 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, and methoxydipropylene glycol (meth)acrylate.

[0115] The content of the ether group-containing monomer in the monomer component M is, for example, 0.1% by weight or more, and may be 0.2% by weight or more, 0.3% by weight or more, 0.4% by weight or more, 0.5% by weight or more, 1% by weight or more, 2% by weight or more, 3% by weight or more, 4% by weight or more, or even 5% by weight or more. The upper limit of the content is, for example, 30% by weight or less, and may be 25% by weight or less, 20% by weight or less, 15% by weight or less, 14% by weight or less, 13% by weight or less, 12% by weight or less, 11% by weight or less, or even 10% by weight or less. The content is preferably 1 to 20% by weight.

[0116] The content of the other monomer relative to 100 parts by weight of the total of the monomer component M and the inorganic particles (specifically, a mixture of the inorganic particles and the dispersant) may be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 4 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, or even 1.5 parts by weight or less. The lower limit of the content 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 even 1 part by weight or more. The monomer component M may not contain other monomers.

[0117] The pressure-sensitive adhesive sheet 1 contains a polymer having structural units formed by polymerization of the monomers contained in the monomer component M.

[0118] The polymerization rate of the monomer component M in the pressure-sensitive adhesive sheet 1 is preferably 90% or more, and may be 95% or more, 98% or more, or even 99% or more.

[0119] <1-3-d. Partial Polymer> The PSA composition A may contain a partial polymer of the above-mentioned monomer component M. The partial polymer may be either a homopolymer or a copolymer. The partial polymer can contribute to the stable formation of a coating layer, which will be described later, by appropriately increasing the viscosity of the PSA composition A. Note that the PSA composition A does not necessarily contain a partial polymer.

[0120] The weight-average molecular weight of the partial polymer may be, for example, greater than 30,000, 50,000 or more, 100,000 or more, 500,000 or more, or even 1,000,000 or more. The upper limit of the weight-average molecular weight is not particularly limited, and may be, for example, 3,000,000 or less, or 2,000,000 or less. The weight-average molecular weight is measured by GPC (gel permeation chromatography) and calculated in polystyrene equivalent.

[0121] <1-3-e. Polymer B> The pressure-sensitive adhesive composition A may contain a polymer B having a weight-average molecular weight of 1,500 to 30,000. The polymer B can contribute to improving the adhesive strength of the pressure-sensitive adhesive sheet. The polymer B may function as a tackifier. In this specification, the polymer B may be referred to as an oligomer.

[0122] The weight average molecular weight of polymer B may be 25,000 or less, 20,000 or less, 18,000 or less, 16,000 or less, 15,000 or less, 13,000 or less, 10,000 or less, 8,000 or less, or even 6,000 or less. The lower limit of the weight average molecular weight is 1,500 or more, 2,000 or more, 2,500 or more, 3,000 or more, 3,500 or more, or even 4,000 or more. The weight average molecular weight may be 2,000 to 16,000, and preferably 4,000 to 16,000. The weight average molecular weight of polymer B can be determined by the method described above for the partial polymer of monomer component M.

[0123] Polymer B preferably contains a structural unit derived from monomer b having a double bond-containing ring. Polymer B containing a structural unit derived from monomer b can contribute to improving the refractive index of the pressure-sensitive adhesive sheet. Examples of monomer b include those mentioned above for monomer a. Monomer b may be the same as or different from monomer a.

[0124] In the monomer b, the double bond-containing ring is preferably an aromatic ring. The monomer b may contain two or more aromatic rings (preferably carbon rings) in one molecule, and preferably contains a monomer having two or more aromatic rings and at least one ethylenically unsaturated group in one molecule (aromatic ring-multiple-containing monomer). The monomer b particularly preferably contains phenoxybenzyl acrylate.

[0125] The content of the structural unit derived from monomer b in polymer B is, for example, 10% by weight or more, and may be 30% by weight or more, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, 97% by weight or more, 98% by weight or more, 99% by weight or more, or even 100% by weight. In some cases, the content may be 10% by weight or less, 5% by weight or less, or even 1% by weight or less. Polymer B may not contain any structural unit derived from monomer b.

[0126] Polymer B may contain a structural unit derived from a monomer other than the above-mentioned monomer b. Examples of the other monomer include those described above for monomer component M (hydroxyl group-containing monomers, (meth)acrylic acid alkyl esters having an alkyl group of 1 to 20 carbon atoms on the side chain, aliphatic ring-containing monomers, and carboxyl group-containing monomers).

[0127] The content of the structural unit derived from the hydroxyl group-containing monomer in polymer B is, for example, 25% by weight or less, and may be 20% by weight or less, 15% by weight or less, 12% by weight or less, 10% by weight or less, 8% by weight or less, 7% by weight or less, 6% by weight or less, 5% by weight or less, 4% by weight or less, 3% by weight or less, 2% by weight or less, or even 1% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, or even 0.5% by weight or more. Polymer B may not contain any structural unit derived from the hydroxyl group-containing monomer.

[0128] The content of structural units derived from a (meth)acrylic acid alkyl ester in polymer B may be, for example, 50% by weight or less, 40% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, 7% by weight or less, 5% by weight or less, or even 4% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or even 1% by weight or more. In some cases, the lower limit of the content may be 50% by weight or more. Polymer B may not contain structural units derived from a (meth)acrylic acid alkyl ester.

[0129] The content of the structural units derived from the alicyclic-containing monomer in the polymer B is, for example, 50% by weight or less, and may be 40% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, 7% by weight or less, 5% by weight or less, 4% by weight or less, 3% by weight or less, or even 2% by weight or less. The lower limit of the content is, for example, 0.01% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or even 1% by weight or more. In some cases, the lower limit of the content may be 50% by weight or more, 80% by weight or more, or even 90% by weight or more. The polymer B may not contain any structural units derived from the alicyclic-containing monomer.

[0130] The content of the structural unit derived from the carboxyl group-containing monomer in the polymer B is, for example, 10% by weight or less, and may be 7% by weight or less, 5% by weight or less, 3% by weight or less, or even 1% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or even 1% by weight or more. It is preferable that the polymer B does not contain any structural unit derived from the carboxyl group-containing monomer.

[0131] Another example of the other monomer is a nitrogen atom-containing monomer. The nitrogen atom-containing monomer refers to a monomer having at least one nitrogen atom in the molecule (in one molecule).

[0132] Examples of the nitrogen atom-containing monomer include N-vinyl cyclic amide, (meth)acrylamide, etc. The nitrogen atom-containing monomer may be used alone or in combination of two or more kinds.

[0133] Examples of N-vinyl cyclic amides include N-vinyl-2-pyrrolidone (NVP), N-vinyl-2-piperidone, N-vinyl-2-caprolactam, N-vinyl-3-morpholinone, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, and vinylmethyloxazolidinone. Examples of (meth)acrylamides include (meth)acrylamide, N-alkyl(meth)acrylamide, and N,N-dialkyl(meth)acrylamide. Examples of (meth)acrylamides also include various N-hydroxyalkyl(meth)acrylamides and N-alkoxyalkyl(meth)acrylamides.

[0134] Examples of nitrogen atom-containing monomers other than N-vinyl cyclic amides and (meth)acrylamides include amino group-containing monomers such as aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate; cyano group-containing monomers such as acrylonitrile and methacrylonitrile; (meth)acryloylmorpholine, N-vinylpiperazine, N-vinylpyrrole, N-vinylimidazole, N-vinylpyrazine, N-vinylmorpholine, N-vinylpyrazole, vinylpyridine, vinylpyrimidine, vinyloxazole, vinylisoxazole, vinylthiazole, vinylisothiazole, vinylpyridazine, (meth)acryloylpyrrolidone, (meth)acryloylpyrrolidine, (meth)acryloylpiperidine, N-methylvinyl heterocycle-containing monomers such as propylpyrrolidone; maleimide-based monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide; itaconimide-based monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-laurylitaconimide, and N-cyclohexylitaconimide; imide group-containing monomers such as succinimide-based monomers of N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, and N-(meth)acryloyl-8-oxyoctamethylenesuccinimide; and isocyanate group-containing monomers such as 2-(meth)acryloyloxyethylisocyanate.

[0135] The content of the constitutional unit derived from the nitrogen atom-containing monomer in polymer B is, for example, 25% by weight or less, and may be 20% by weight or less, 15% by weight or less, 12% by weight or less, 10% by weight or less, 8% by weight or less, 7% by weight or less, 6% by weight or less, 5% by weight or less, 4% by weight or less, 3% by weight or less, 2% by weight or less, or even 1% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, or even 0.5% by weight or more. Polymer B may not contain any constitutional unit derived from the nitrogen atom-containing monomer.

[0136] Another example of the other monomer is an ether group-containing monomer. The ether group-containing monomer has at least one ether group and at least one ethylenically unsaturated group in one molecule. The ether group-containing monomer may be used alone or in combination of two or more kinds.

[0137] Examples of the ethylenically unsaturated group are the same as those mentioned above in the description of monomer A. The ether group-containing monomer may be a (meth)acrylic monomer.

[0138] Examples of the ether group-containing monomer are 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and methoxydipropylene glycol (meth)acrylate. The ether group-containing monomer is preferably 2-(2-ethoxyethoxy)ethyl acrylate (CBA).

[0139] The content of the structural unit derived from the ether group-containing monomer in polymer B is, for example, 40% by weight or less, and may be 30% by weight or less, 25% by weight or less, 20% by weight or less, 15% by weight or less, 12% by weight or less, 10% by weight or less, 8% by weight or less, 7% by weight or less, 6% by weight or less, 5% by weight or less, 4% by weight or less, 3% by weight or less, 2% by weight or less, or even 1% by weight or less. The lower limit of the content may be, for example, 0.01% by weight or more, 0.1% by weight or more, or even 0.5% by weight or more. Polymer B may not contain any structural unit derived from the ether group-containing monomer.

[0140] Polymer B can be produced by known polymerization methods such as various radical polymerizations, including solution polymerization, radiation polymerization, bulk polymerization, emulsion polymerization, and polymerization under supercritical conditions. Examples of radiation that can be used for radiation polymerization include electron beams, UV rays, and microwaves. The resulting polymer B may be any of a random copolymer, a block copolymer, a graft copolymer, and the like.

[0141] The content of polymer B relative to 100 parts by weight of the total of monomer component M and inorganic particles (specifically, a mixture of inorganic particles and a dispersant) is, for example, 0.1 parts by weight or more, 0.5 parts by weight or more, 1 part by weight or more, 2 parts by weight or more, 3 parts by weight or more, 4 parts by weight or more, 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, 9 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or even 20 parts by weight or more. The upper limit of the content is, for example, 50 parts by weight or less, 40 parts by weight or less, 35 parts by weight or less, or even 30 parts by weight or less. The content is preferably 1 to 30 parts by weight, and more preferably 2 to 30 parts by weight.

[0142] The content of acidic groups (particularly COOH groups) in polymer B contained in pressure-sensitive adhesive sheet 1 is, for example, 0.1 wt % or less, 0.01 wt % or less, or even 0.001 wt % or less. Polymer B preferably contains substantially no acidic groups. The acidic group content can be measured, for example, by the following method. First, a sol component (non-crosslinked component) contained in pressure-sensitive adhesive sheet 1 is extracted using a solvent (e.g., toluene). A component (polymer B) having a weight-average molecular weight of 1,500 to 30,000 is separated using preparative GPC (gel permeation chromatography). This component is dried in an oven at 130°C for 2 hours to remove the solvent. The acidic group content can be determined by evaluating the dried component using infrared spectroscopy.

[0143] <1-3-f. Other Components> [1-3-f1. Dispersant] The PSA composition A may further contain a dispersant for inorganic particles. The dispersant is a component for sufficiently dispersing the inorganic particles in the PSA composition A. The dispersant is preferably in contact with the surfaces of the inorganic particles, and more preferably coats the surfaces of the inorganic particles.

[0144] An example of a dispersant is a compound having a hydrophilic portion and a hydrophobic portion in one molecule. The hydrophilic portion and the hydrophobic portion of the dispersant are presumed to exhibit relatively high affinity for the inorganic particles and the monomer component M, respectively. The dispersant may or may not have a polymerizable functional group such as an ethylenically unsaturated group.

[0145] The hydrophilic portion of the dispersant preferably has a hydrophilic group, such as an ether group or an ester group.

[0146] The hydrophilic portion of the dispersant preferably has a functional group F that exhibits adsorptivity or reactivity with inorganic particles. Examples of the functional group F include at least one selected from the group consisting of alkaline groups and acidic groups. Specific examples of the functional group F include a hydroxy group, a carboxy group, a nitrogen atom-containing group, a sulfur atom-containing group, a phosphorus atom-containing group, and a silicon atom-containing group. The number of functional groups F contained in one molecule of the dispersant may be 1, or may be 2 or more (for example, about 2 to 5). The types of the two or more functional groups F present in one molecule may be the same or different from each other.

[0147] The hydrophilic portion of the dispersant may have a chain structure, or may have a composite structure of a chain structure and a cyclic structure. The dispersant may include, for example, a structure in which a functional group F and a hydrophobic portion are linked via a chain structure; a structure in which a functional group F is located on a side chain of a chain structure whose one end is linked to the hydrophobic portion; or a structure in which a functional group F is not located on the other end of a chain structure whose one end is linked to the hydrophobic portion (for example, the other end of the chain structure is open). The dispersant may have two or more of the above structures.

[0148] The dispersant may be an aliphatic compound, for example, represented by the following formula (2):

[0149] In formula (2), R is an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, and more preferably an ethyl group. m is 1 to 10, preferably 2 to 8, and more preferably 3 to 7. n is 5 to 20, and preferably 8 to 12.

[0150] The dispersant may be an aromatic compound having an aromatic ring. Examples of the aromatic ring are the same as those mentioned above in the description of monomer a.

[0151] The dispersant may be selected from known surfactants. Examples of surfactants include anionic surfactants (carboxylic acid type, phosphate ester type, sulfate ester type, sulfonic acid type, etc.), nonionic surfactants, cationic surfactants, and amphoteric surfactants. The surfactant that can be used as the dispersant is preferably an anionic surfactant.

[0152] The content of the dispersant relative to 100 parts by weight of the inorganic particles is, for example, 0.1 parts by weight or more, 0.5 parts by weight or more, or even 1.0 part by weight or more. The upper limit of the content is, for example, 30 parts by weight or less, or may be 20 parts by weight or less.

[0153] [1-3-f2. Photopolymerization initiator] The pressure-sensitive adhesive composition A usually contains a photopolymerization initiator. The photopolymerization initiator may be a photoradical generator that generates radicals when exposed to visible light and / or ultraviolet light having a wavelength shorter than 450 nm.

[0154] Examples of the photopolymerization initiator include benzoin ethers such as benzoin methyl ether, benzoin isopropyl ether, and benzil dimethyl ketal; substituted benzoin ethers such as anisole methyl ether; substituted acetophenones such as 2,2-diethoxyacetophenone and 2,2-dimethoxy-2-phenylacetophenone; α-hydroxyalkylphenones such as 1-hydroxycyclohexyl-phenyl ketone; substituted alpha-ketol such as 2-methyl-2-hydroxypropiophenone; aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride; photoactive oximes such as 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime; and benzophenone compounds such as benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone, hydroxybenzophenone, acrylated benzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, and 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone. Thioxanthone compounds such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and 2,4-diethylthioxanthone; 2,4,6-trichloro-s-triazine, 2-phenyl-4,6-bis(trichloromethyl)-s-triazine, 2-(p-methoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine, and 2-(p-tolyl)-4,6-bis(trichloromethyl)-s-triazine , 2-piperonyl-4,6-bis(trichloromethyl)-s-triazine, 2,4-bis(trichloromethyl)-6-styryl-s-triazine, 2-(naphth-1-yl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-methoxy-naphth-1-yl)-4,6-bis(trichloromethyl)-s-triazine, 2,4-trichloromethyl-(piperonyl)-6-triazine, 2,4-trichloromethyl-(4'-methoxystyryl)-6-triazine and other triazine-based compounds;Oxime ester compounds such as 1,2-octanedione, 1-[4-(phenylthio)-, 2-(O-benzoyloxime)], O-(acetyl)-N-(1-phenyl-2-oxo-2-(4'-methoxy-naphthyl)ethylidene)hydroxylamine; phosphine compounds such as bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and 2,4,6-trimethylbenzoyldiphenylphosphine oxide; quinone compounds such as 9,10-phenanthrenequinone, camphorquinone, and ethylanthraquinone; borate compounds; carbazole compounds; imidazole compounds; and titanocene compounds. The pressure-sensitive adhesive composition A may contain one or more photopolymerization initiators.

[0155] Specific examples of the photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethan-1-one (Omnirad 651, manufactured by IGM Resins), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Omnirad 819, manufactured by IGM Resins), and 1-hydroxycyclohexyl phenyl ketone (Omnirad 184, manufactured by IGM Resins).

[0156] The content of the photopolymerization initiator relative to a total of 100 parts by weight of the monomer component M and the inorganic particles (specifically, a mixture of the inorganic particles and the dispersant) is, for example, 0.02 to 10 parts by weight, and may be 0.05 to 5 parts by weight, 0.1 to 3 parts by weight, or even 0.2 to 2 parts by weight.

[0157] [1-3-f3. Crosslinking Agent] The pressure-sensitive adhesive composition A may contain a crosslinking agent. An example of the crosslinking agent is a polyfunctional monomer having two or more polymerizable functional groups in one molecule. The polyfunctional monomer may be a (meth)acrylic monomer. Examples of the polyfunctional monomer are a monomer having two or more C=C bonds in one molecule, and a monomer having one or more C=C bonds and one or more polymerizable functional groups such as epoxy groups, aziridine groups, oxazoline groups, hydrazine groups, methylol groups, etc. in one molecule. The polyfunctional monomer is preferably a monomer having two or more C=C bonds in one molecule.

[0158] Examples of polyfunctional monomers include (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol diacrylate (N Polyfunctional acrylates (such as ester compounds of polyhydric alcohols and (meth)acrylic acid) such as 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and tetramethylolmethane tri(meth)acrylate; allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butyl di(meth)acrylate, and hexyl di(meth)acrylate. The polyfunctional monomer is preferably a polyfunctional acrylate, and more preferably trimethylolpropane tri(meth)acrylate, hexanediol di(meth)acrylate, or dipentaerythritol hexa(meth)acrylate.

[0159] The content of the crosslinking agent relative to 100 parts by weight of the total of the monomer component M and the inorganic particles (specifically, a mixture of the inorganic particles and the dispersant) may be, for example, 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or even 0.5 parts by weight or less. The lower limit of the content may be, for example, 0.01 parts by weight or more, 0.02 parts by weight or more, 0.03 parts by weight or more, 0.04 parts by weight or more, or even 0.05 parts by weight or more.

[0160] [1-3-f4. Silane Coupling Agent] The pressure-sensitive adhesive composition A may contain a silane coupling agent. Specific examples of the silane coupling agent include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-γ-aminopropyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane.

[0161] The content of the silane coupling agent relative to a total of 100 parts by weight of the monomer component M and the inorganic particles (specifically, a mixture of the inorganic particles and the dispersant) is, for example, 5 parts by weight or less, 3 parts by weight or less, 1 part by weight or less, 0.8 parts by weight or less, 0.5 parts by weight or less, 0.4 parts by weight or less, 0.3 parts by weight or less, 0.2 parts by weight or less, or even 0.1 parts by weight or less. The lower limit of the content is, for example, 0.01 parts by weight or more, or even 0.05 parts by weight or more. The pressure-sensitive adhesive composition A does not necessarily contain a silane coupling agent.

[0162] [1-3-f5. Antioxidant] The PSA composition A may contain an antioxidant. Examples of the antioxidant include phenol-based antioxidants, hindered phenol-based antioxidants, amine-based antioxidants, and phosphite-based antioxidants.

[0163] Examples of the phenolic antioxidants include monophenolic antioxidants, bisphenolic antioxidants, and polymeric phenolic antioxidants. Examples of the monophenolic antioxidants include 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, and stearin-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate. Examples of the bisphenol antioxidant are 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), and 3,9-bis[1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]2,4,8,10-tetraoxaspiro[5,5]undecane. Examples of the polymeric phenolic antioxidant are 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, bis[3,3'-bis-(4'-hydroxy-3'-t-butylphenyl)butyric acid]glycol ester, 1,3,5-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)-S-triazine-2,4,6-(1H,3H,5H)trione, and tocopherol.

[0164] The hindered phenolic antioxidant may have a structure in which a tertiary butyl group is bonded to at least one carbon atom adjacent to the carbon atom on the aromatic ring to which the phenolic OH group is bonded. Examples of the hindered phenolic antioxidant include dibutylhydroxytoluene (BHT); Irganox 1010, Irganox 1010FF, Irganox 1035, Irganox 1035FF, Irganox 1076, Irganox 1076FD, Irganox 1076DWJ, Irganox 1098, Irganox 109 ... Irganox 1135, Irganox 1330, Irganox 1726, Irganox 1425WL, Irganox 1520L, Irganox 245, Irganox 245FF, Irganox 259, Irganox 3114, Irganox 565 and Irganox 295 (all of which are trade names manufactured by BASF).

[0165] The amine antioxidant is preferably a hindered amine antioxidant. The hindered amine antioxidant may have at least one hindered piperazine group in one molecule. Examples of hindered amine antioxidants include Adeka STAB LA-63, Adeka STAB LA-63P, Adeka STAB LA-52, and Adeka STAB LA-57 (all of which are trade names, manufactured by ADEKA Corporation).

[0166] Examples of the phosphite antioxidants are triphenyl phosphite, diphenyl isodecyl phosphite, and phenyl diisodecyl phosphite; and Adeka STAB 2112, Adeka STAB 2112RG, Adeka STAB 1178, and Adeka STAB 3010 (all of which are trade names, manufactured by ADEKA Corporation).

[0167] The content of the antioxidant relative to a total of 100 parts by weight of the monomer component M and the inorganic particles (specifically, a mixture of the inorganic particles and the dispersant) is, for example, 5 parts by weight or less, 3 parts by weight or less, 1 part by weight or less, 0.8 parts by weight or less, or even 0.5 parts by weight or less. The lower limit of the content is, for example, 0.01 parts by weight or more, or even 0.05 parts by weight or more. The pressure-sensitive adhesive composition A does not necessarily contain an antioxidant.

[0168] [1-3-f6. Solvent] The content of the solvent in the PSA composition A is, for example, 5 wt % or less, and may be 4 wt % or less, 3 wt % or less, 2 wt % or less, 1 wt % or less, or even 0.5 wt % or less. The PSA composition A may be substantially free of a solvent. "Substantially free of a solvent" means that solvents derived from additives and the like are allowed at a content of, for example, 0.1 wt % or less, preferably 0.05 wt % or less, and more preferably 0.01 wt % or less.

[0169] [1-3-f7. Other Additives] The PSA composition A may contain additives other than those described above. Examples of the additives include a chain transfer agent, a viscosity modifier, a tackifier, a plasticizer, a softener, an antioxidant, a filler, a colorant, a surfactant, and an antistatic agent.

[0170] <1-3-g. Physical Properties> The viscosity of the pressure-sensitive adhesive composition A is preferably 5 to 150 poise at 25° C. The pressure-sensitive adhesive composition A having a viscosity in the above range is particularly suitable for forming a coating layer, which will be described later.

[0171] <1-3-h. Manufacturing method> The pressure-sensitive adhesive composition A can be prepared, for example, by the following method. First, a dispersion in which inorganic particles are dispersed in a solvent is prepared. This dispersion is mixed with a dispersant and at least a portion of the monomers contained in the monomer component M. The solvent is removed from the resulting mixture to prepare a dispersion containing inorganic particles, a dispersant, and a monomer. The method for removing the solvent from the mixture is not particularly limited, and methods such as removal under reduced pressure can be used. Next, the remaining monomers, polymer B, and additives such as a photopolymerization initiator are added to the dispersion and mixed. In this way, the pressure-sensitive adhesive composition A can be prepared.

[0172] <1-4. Method for producing a pressure-sensitive adhesive sheet> The pressure-sensitive adhesive sheet 1 can be formed from the pressure-sensitive adhesive composition A, for example, by irradiating a first laminate 30 comprising, in this order, a base sheet 31, a coating layer 32 containing the pressure-sensitive adhesive composition A, and a release liner 33 with active energy rays 34 (see FIG. 5 ). The coating layer 32 is irradiated with active energy rays 34 and cured to form the pressure-sensitive adhesive sheet 1. When the pressure-sensitive adhesive sheet 1 is formed by irradiating one side of the coating layer 32 with active energy rays 34, the irradiation is typically carried out from the side of the base sheet 31. In this case, the active energy rays 34 penetrate the base sheet 31 to reach the coating layer 32 and cure the coating layer 32. However, the irradiation with active energy rays 34 may also be carried out from the side of the release liner 33. When the pressure-sensitive adhesive sheet 1 is formed by irradiating both sides of the coating layer 32 with active energy rays 34, the irradiation is carried out from both the side of the release liner 33 and the side of the base sheet 31.

[0173] The formed PSA sheet 1 is sandwiched between the base sheet 31 and the release liner 33 until the release liner 33 is peeled off, and constitutes part of a second laminate 37. By peeling the release liner 33 from the second laminate 37, a third laminate 35 including the base sheet 31 and the PSA sheet 1 is obtained. In the third laminate 35, the surface of the PSA sheet 1 is exposed to the outside. An optical film can be laminated onto the exposed surface of the PSA sheet 1 directly or via another layer.

[0174] Examples of the active energy rays 34 include ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams, as well as visible light and ultraviolet light. The active energy rays 34 are preferably visible light or ultraviolet light having a wavelength shorter than 450 nm, and more preferably ultraviolet light. Hereinafter, visible light and ultraviolet light will be collectively referred to as "light."

[0175] The light may include light having a wavelength in the same region as the absorption wavelength of the photopolymerization initiator contained in the pressure-sensitive adhesive composition A. Light having a wavelength of 300 nm or less may be irradiated by filtering out short-wavelength light using a filter or the like. Filtering out short-wavelength light is suitable for suppressing deterioration of the base sheet 31 and / or the release liner 33 due to the active energy rays 34. The light source 38 of the active energy rays 34 is, for example, a light irradiation device equipped with an ultraviolet irradiation lamp. Examples of ultraviolet irradiation lamps include ultraviolet LEDs, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, microwave-excited mercury lamps, black light lamps, chemical lamps, germicidal lamps, low-pressure discharge mercury lamps, and excimer lasers. Two or more ultraviolet irradiation lamps may be combined.

[0176] The illuminance of the light irradiated onto the first laminate 30 (specifically, the coating layer 32) is, for example, 2.0 to 30 mW / cm 2 The illuminance is 2.5 mW / cm 2 Above, 3.0mW / cm 2 Above, 3.5mW / cm 2 Above, 4.0mW / cm 2 Above, 5.0mW / cm 2 Above, 6.0mW / cm 2 Above, 7.0mW / cm 2 Above, 8.0mW / cm 2 Above, 9.0mW / cm 2 or more, and even 10 mW / cm 2 The upper limit of the illuminance may be, for example, 25 mW / cm 2 less than 20 mW / cm 2 It may be the following:

[0177] The time for irradiating the first laminate 30 (specifically, the coating layer 32) with light is, for example, 10 to 1,000 seconds, and may be 60 seconds or more, 100 seconds or more, 150 seconds or more, or even 200 seconds or more. The upper limit of the time is, for example, 800 seconds or less, and may be 600 seconds or less, 500 seconds or less, 400 seconds or less, 300 seconds or less, or even 250 seconds or less. The light irradiation may be continuous or intermittent.

[0178] The integrated amount of light on the first laminate 30 (specifically, the coating layer 32) is, for example, 25 mJ / cm 2 or more, and 100 mJ / cm 2 Above, 500mJ / cm 2 Above, 1000mJ / cm 2 Above, 2000mJ / cm 2 Above, 2500mJ / cm 2 Above, 3000mJ / cm 2 Above, 5000mJ / cm 2 Above, 7500mJ / cm 2 or more, and even 10,000 mJ / cm 2 The upper limit of the integrated light amount is not particularly limited, and may be, for example, 30,000 mJ / cm 2 or less, and 25,000 mJ / cm 2 Below, 20000mJ / cm 2 Below, 18000 mJ / cm 2 It may be the following:

[0179] The light may be irradiated onto the first laminate 30 in multiple stages. The illuminance and / or the integrated amount of light in each stage may be the same or different from each other. Furthermore, the light source in each stage may be the same or different from each other.

[0180] An example of the substrate of the release liner 33 (hereinafter referred to as the "liner substrate") is a resin film. Examples of resins that can be contained in the liner substrate include polyesters such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyethersulfone, polycarbonate, polyamide, polyimide, polyolefin, (meth)acrylic resins, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl alcohol, polyarylate, and polyphenylene sulfide. The resin is preferably a polyester such as polyethylene terephthalate.

[0181] The release liner 33 may include a layer other than the liner substrate. The release liner 33 may include a release layer. The release liner 33 includes, for example, a liner substrate and a release layer formed on one surface of the liner substrate. This release liner 33 can be used so that the release layer faces the coating layer 32. The release layer is typically a cured layer of a release agent composition containing a release agent. Various release agents can be used as the release agent, such as silicone-based release agents, fluorine-based release agents, long-chain alkyl-based release agents, fatty acid amide-based release agents, and silica powder.

[0182] The release liner 33 may be in the form of a sheet or a continuous piece.

[0183] An example of the base sheet 31 is a resin film. Examples of the resin contained in the base sheet 31 are the same as the examples of the resin that can be contained in the liner base material.

[0184] The thickness of the base sheet 31 is, for example, 10 to 200 μm, and may be 25 to 150 μm.

[0185] The base sheet 31 may have a release layer on the surface facing the coating layer 32. Examples of the release layer that may be provided on the base sheet 31 are the same as the examples of the release layer that may be provided on the release liner 33. Both the release liner 33 and the base sheet 31 may have a release layer.

[0186] For the base sheet 31 , a sheet having a greater peel strength from the pressure-sensitive adhesive sheet 1 than the release liner 33 can usually be selected.

[0187] The base sheet 31 may be in the form of a sheet or a continuous sheet.

[0188] The first laminate 30 can be formed, for example, by forming a coating layer 32 on a base sheet 31 (or a release liner 33) and then placing the release liner 33 (or base sheet 31) on the formed coating layer 32. Alternatively, the first laminate 30 may be formed by applying the photocurable composition in a poured manner into the space between the base sheet 31 and the release liner 33, which are held at a predetermined distance so that their main surfaces face each other.

[0189] The coating layer 32 can be formed by various coating methods such as roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating.

[0190] The thickness of the coating layer 32 can be adjusted depending on the desired thickness of the PSA sheet 1, and may be, for example, 500 μm or less, 250 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 30 μm or less, 25 μm or less, or even 20 μm or less. The lower limit of the thickness of the coating layer 32 is, for example, 2 μm or more, and may be 5 μm or more.

[0191] The first laminate 30 may include a long base sheet 31, a long coating layer 32, and a long release liner 33, in other words, may be long. The long first laminate 30 can be obtained, for example, by forming the coating layer 32 between the base sheet 31 and the release liner 33 while conveying them after they have been unwound from a roll.

[0192] 2. Optical Laminate An example of an optical laminate according to an embodiment of the present invention is shown in Fig. 6. The optical laminate 20A in Fig. 6 includes a pressure-sensitive adhesive sheet 1 and an optical film 2. The pressure-sensitive adhesive sheet 1 and the optical film 2 are laminated to each other. The optical laminate 20A can be used as an optical film with a pressure-sensitive adhesive sheet.

[0193] Examples of the optical film 2 include a polarizing film, a retardation film, and a laminate film including a polarizing film and / or a retardation film. However, the optical film 2 is not limited to the above examples. The optical film 2 may also include a glass film.

[0194] The optical film 2 may be a polarizing film, and the pressure-sensitive adhesive sheet 1 may be in contact with the optical film 2 .

[0195] The polarizing film includes a polarizer. The polarizing film typically includes a polarizer and a protective film (transparent protective film). The protective film is disposed, for example, in contact with a main surface (the surface having the largest area) of the polarizer. The polarizer may be disposed between two protective films. The protective film may be disposed on at least one surface of the polarizer.

[0196] The polarizer is not particularly limited, and examples thereof include a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or an ethylene-vinyl acetate copolymer partially saponified film, which has been uniaxially stretched after adsorbing a dichroic substance such as iodine or a dichroic dye; a polyene-based oriented film such as a dehydrated polyvinyl alcohol or a dehydrochlorinated polyvinyl chloride; etc. A polarizer typically comprises a polyvinyl alcohol film (polyvinyl alcohol films include an ethylene-vinyl acetate copolymer partially saponified film) and a dichroic substance such as iodine.

[0197] The thickness of the polarizer is not particularly limited and may be, for example, 80 μm or less, 50 μm or less, 30 μm or less, 25 μm or less, or even 20 μm or less. The lower limit of the polarizer thickness is not particularly limited and may be, for example, 1 μm or more, 5 μm or more, 10 μm or more, or even 15 μm or more. A thin polarizer (for example, a thickness of 20 μm or less) is suppressed in dimensional change and can contribute to improving the durability of the optical laminate, particularly durability at high temperatures.

[0198] The material for the protective film may be, for example, a thermoplastic resin having excellent transparency, mechanical strength, thermal stability, moisture-blocking properties, isotropy, etc. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (norbornene-based resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The material for the protective film may be a thermosetting resin or an ultraviolet-curable resin such as a (meth)acrylic, urethane, acrylic urethane, epoxy, or silicone-based resin. When the polarizing film has two protective films, the materials of the two protective films may be the same or different. For example, a protective film made of a thermoplastic resin may be bonded to one main surface of the polarizer via an adhesive, and a protective film made of a thermosetting resin or an ultraviolet-curable resin may be bonded to the other main surface of the polarizer. The protective film may contain one or more optional additives, such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, color inhibitors, flame retardants, nucleating agents, antistatic agents, pigments, and colorants.

[0199] The thickness of the protective film can be determined as appropriate, but is generally about 10 to 200 μm in view of strength, workability such as handling, thinness, and the like.

[0200] The polarizer and the protective film are usually adhered to each other via an aqueous adhesive or the like. Examples of aqueous adhesives include isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl latex, aqueous polyurethane, and aqueous polyester. Examples of adhesives other than the above-mentioned adhesives include ultraviolet-curable adhesives and electron beam-curable adhesives. Electron beam-curable polarizing film adhesives exhibit suitable adhesiveness to various protective films. The adhesive may contain a metal compound filler.

[0201] In the polarizing film, a retardation film or the like can be formed on the polarizer instead of the protective film. Another protective film or a retardation film or the like can be further provided on the protective film.

[0202] The protective film may have a hard coat layer on the surface opposite to the surface bonded to the polarizer, and may also be subjected to treatments for purposes such as anti-reflection, anti-sticking, diffusion, and anti-glare.

[0203] The polarizing film may be a circular polarizing film.

[0204] The thickness of the polarizing film is, for example, 500 μm or less, and may be 300 μm or less, 200 μm or less, 100 μm or less, or even 60 μm or less. The lower limit of the thickness may be, for example, 10 μm or more, 25 μm or more, or even 40 μm or more.

[0205] The retardation film is a film having birefringence in the in-plane direction and / or the thickness direction, and is, for example, a stretched resin film or a film in which a liquid crystal material is oriented and fixed.

[0206] The retardation film may be a λ / 4 plate, a λ / 2 plate, an anti-reflection retardation film (see, for example, paragraphs 0221, 0222, and 0228 of JP 2012-133303 A), a viewing angle compensation retardation film (see, for example, paragraphs 0225 and 0226 of JP 2012-133303 A), or an inclined orientation retardation film for viewing angle compensation (see, for example, paragraph 0227 of JP 2012-133303 A). The retardation film is not limited to the above examples as long as it has birefringence in the in-plane direction and / or the thickness direction. There are also no limitations on the retardation value, arrangement angle, three-dimensional birefringence, whether the retardation film is single-layer or multi-layer, etc. of the retardation film. Known films can be used as the retardation film.

[0207] The thickness of the optical film 2 is, for example, 1 to 200 μm.

[0208] The optical film 2 may be a single layer or a laminated film composed of two or more layers. When the optical film 2 is a laminated film, the pressure-sensitive adhesive sheet 1 may be used to bond the layers together.

[0209] Another example of an optical laminate according to an embodiment of the present invention is shown in Figure 7. Optical laminate 20B in Figure 7 has a layered structure in which a release liner 3, a pressure-sensitive adhesive sheet 1, and an optical film 2 are layered in this order. By peeling off release liner 3, optical laminate 20B can be used as an optical film with a pressure-sensitive adhesive sheet.

[0210] The release liner 3 is typically a resin film. Examples of resins that make up the release liner 3 include polyesters such as polyethylene terephthalate (PET), polyolefins such as polyethylene and polypropylene, polycarbonate, acrylic, polystyrene, polyamide, and polyimide. The surface of the release liner 3 that comes into contact with the pressure-sensitive adhesive sheet 1 may be subjected to a release treatment. The release treatment is, for example, a treatment with a silicone compound. However, the release liner 3 is not limited to the above examples. The release liner 3 is peeled off when the optical laminate 20B is used, for example, when it is attached to the image forming layer.

[0211] Another example of an optical laminate according to an embodiment of the present invention is shown in Fig. 8. Optical laminate 20C in Fig. 8 has a layered structure in which a release liner 3, a pressure-sensitive adhesive sheet 4, a retardation film 2B, a pressure-sensitive adhesive sheet 1, and a polarizing film 2A are layered in this order. After peeling off release liner 3, optical laminate 20C can be used by being attached to, for example, an image-forming layer.

[0212] A known adhesive sheet can be used as the adhesive sheet 4. The adhesive sheet 1 may also be used as the adhesive sheet 4.

[0213] Another example of an optical laminate according to an embodiment of the present invention is shown in Fig. 9. Optical laminate 20D in Fig. 9 has a layered structure in which a release liner 3, a pressure-sensitive adhesive sheet 4, a retardation film 2B, a pressure-sensitive adhesive sheet 1, a polarizing film 2A, and a protective film 5 are layered in this order. After peeling off the release liner 3, optical laminate 20D can be used by being attached to, for example, an image-forming layer.

[0214] The protective film 5 has the function of protecting the optical film 2 (polarizing film 2A), which is the outermost layer, during distribution and storage of the optical laminate 20D and when the optical laminate 20D is incorporated into an image display device. The protective film 5 may also function as a window to the external space when incorporated into an image display device. The protective film 5 is typically a resin film. Examples of resins constituting the protective film 5 include polyesters such as PET, polyolefins such as polyethylene and polypropylene, acrylics, cycloolefins, polyimides, and polyamides, with polyesters being preferred. However, the protective film 5 is not limited to the above examples. The protective film 5 may be a glass film or a laminate film including a glass film. The protective film 5 may be subjected to surface treatments such as anti-glare, anti-reflection, and anti-static.

[0215] The protective film 5 may be bonded to the optical film 2 by any adhesive. Bonding by an adhesive sheet 1 is also possible.

[0216] The optical laminate may have any configuration as long as it includes the pressure-sensitive adhesive sheet 1 and the optical film 2 .

[0217] The pressure-sensitive adhesive sheet 1 can be disposed between any layers included in the optical laminate. In other words, the pressure-sensitive adhesive sheet 1 may be a so-called interlayer pressure-sensitive adhesive layer.

[0218] The optical laminate according to the embodiment of the present invention can be distributed and stored, for example, as a rolled body obtained by rolling up a strip-shaped optical laminate, or as a sheet-shaped optical laminate.

[0219] The optical laminate according to the embodiment of the present invention is typically used in an image display device, such as a liquid crystal display, an EL display such as an organic EL display, or an inorganic EL display.

[0220] 3. Image Display Device An example of an image display device according to an embodiment of the present invention is shown in FIG. 10. The image display device 21 of FIG. 10 has a layered structure in which a substrate 7, an image forming layer (e.g., an organic EL layer or a liquid crystal layer) 6, a pressure-sensitive adhesive sheet 4, a retardation film 2B, a pressure-sensitive adhesive sheet 1, a polarizing film 2A, and a protective film 5 are layered in this order. The image display device 21 has the optical laminate 20D of FIG. 9 (excluding the release liner 3). The image display device 21 may have the optical laminates 20A, 20B, and 20C of FIGS. 6 to 8 instead of the optical laminate 20D. The substrate 7 and the image forming layer 6 may have the same configurations as the substrate and the image forming layer, respectively, of known image display devices.

[0221] The image display device 21 in Fig. 10 may be an organic EL display or a liquid crystal display. However, the image display device 21 is not limited to this example. The image display device 21 may be an electroluminescence (EL) display, a plasma display (PD), a field emission display (FED), or the like. The image display device 21 may be used for home appliances, in-vehicle applications, public information displays (PID), and the like.

[0222] The image display device 21 may have any configuration as long as it includes the pressure-sensitive adhesive sheet 1 and / or the optical laminate 20 .

[0223] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0224] <Preparation of Dispersion D> [Synthesis of Dispersant d] 415 g (1 mol) of tristyrenated phenol and 1 g (0.018 mol) of potassium hydroxide were charged into an autoclave and mixed uniformly. The resulting reaction system was heated to 130 ° C., and 352 g (8 mol) of ethylene oxide (EO) was added dropwise. After the dropwise addition was completed, the pressure was maintained at 0.1 MPa at 130 ° C. and the mixture was aged for 1 hour to obtain an EO 8 mol adduct of tristyrenated phenol. Next, 767 g (1 mol) of the obtained EO 8 mol adduct of tristyrenated phenol and 152 g (1.3 mol) of sodium monochloroacetate were placed in a reactor and stirred to become uniform. Next, the reaction system was heated to 60 ° C. and 52 g of sodium hydroxide was added, followed by heating to 80 ° C. and aging for 3 hours. After aging, the mixture was cooled to 50 ° C., and 117 g (1.2 mol) of 98 wt% sulfuric acid was added dropwise at the same temperature to obtain a white suspension. The resulting suspension was washed with distilled water, and the solvent was removed by distillation under reduced pressure to obtain Dispersant d.

[0225] To 100 parts by weight of a methanol dispersion of zirconium oxide particles (manufactured by Sakai Chemical Industry Co., Ltd., grade name "SZR-M," average particle size (D50) based on dynamic light scattering: 3 nm, zirconium oxide particle concentration: 30 wt %), 1.5 parts by weight of the above-mentioned Dispersant d and 28.5 parts by weight of phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Industry Co., Ltd., trade name "Light Acrylate POB-A"; hereinafter referred to as "POB-A"), which is the monomer component M, were added and mixed. Next, the solvent was removed under reduced pressure using a rotary evaporator to obtain Dispersion D, a dispersion of zirconium oxide particles. Dispersion D contained zirconium oxide particles / Dispersant d / POB-A in a weight ratio of 50 / 2.5 / 47.5.

[0226] <Synthesis of Polymer B> A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 99 parts by weight of POB-A, 1 part by weight of 4-hydroxybutyl acrylate (4HBA), 0.30 parts by weight of 2,2'-azobisisobutyronitrile as a polymerization initiator, 3 parts by weight of 1-thioglycerol as a chain transfer agent, and 300 parts by weight of ethyl acetate. Nitrogen gas was introduced while maintaining the temperature at 70°C and stirring gently, and the mixture was thoroughly purged with nitrogen for at least 1 hour. The liquid temperature in the flask was then maintained at 72-74°C, and a polymerization reaction was carried out for 6 hours to prepare a solution of Polymer B. The solution was then heated at 90°C for 12 hours, and then subjected to reduced pressure treatment at 120°C for 3 hours to remove ethyl acetate. This yielded Polymer B, in which the amount of ethyl acetate detected by gas chromatography was less than 0.1 parts by weight. The weight-average molecular weight of Polymer B was 4,000.

[0227] [Weight-average molecular weight of polymer B] The weight-average molecular weight (Mw) of the obtained polymer B was measured by gel permeation chromatography (GPC). The measurement equipment and conditions were as follows: Analytical equipment: Alliance manufactured by Waters Column: TSKgel SuperHZM-H x 2 manufactured by Tosoh Column temperature: 40°C Eluent: THF Flow rate: 0.2 mL / min Injection volume: 30 μL Detector: Refractive index (RI) Standard sample: Polystyrene (PS) manufactured by Agilent

[0228] <Preparation of Pressure-Sensitive Adhesive Sheet> (Preparation of Pressure-Sensitive Adhesive Composition A1) 100 parts by weight of Dispersion D, 1.5 parts by weight of Tinuvin 571 (manufactured by BASF) as a UVA, 0.4 parts by weight of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (manufactured by IGM Resins, trade name "Omnirad 819") as a photopolymerization initiator, 0.025 parts by weight of 1,9-nonanediol diacrylate (NDDA) as a crosslinking agent, 0.5 parts by weight of Irganox 1010 (manufactured by BASF) as an antioxidant, and 0.3 parts by weight of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Silicones, trade name "KBM-403") as a silane coupling agent were mixed together. This gave a pressure-sensitive adhesive composition A1 of Example 1.

[0229] (Preparation of Pressure-Sensitive Adhesive Compositions A2 to A14) Pressure-Sensitive Adhesive Compositions A2 to A14 were obtained in the same manner as Pressure-Sensitive Adhesive Composition A1, except that the amount of Dispersion D, whether or not a further Monomer Component M was mixed and the type and amount of the mixed monomer component M if so, whether or not a UVA was mixed and the type and amount of the mixed monomer component M if so, the amount of the photopolymerization initiator, and whether or not a polymer B was mixed and the amount of the mixed polymer component B if so, were changed as shown in Table 1A below. Note that UVA was not mixed into Pressure-Sensitive Adhesive Compositions A9 to A14. Furthermore, Dispersion D was not mixed into Pressure-Sensitive Adhesive Compositions A13 to A14.

[0230]

[0231] The amounts (unit: parts by weight) of the zirconium oxide particles, dispersant d, and monomer component M (POB-A, MEA, 4HBA, and BA) in the PSA compositions A1 to A14 are shown in Table 1B below.

[0232]

[0233] The abbreviations in Tables 1A and 1B are as follows: POB-A: phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A") MEA: methoxyethyl acrylate 4HBA: 4-hydroxybutyl acrylate BA: n-butyl acrylate Tinuvin 571: benzotriazole-based UVA (manufactured by BASF Corporation, trade name "Tinuvin 571") Tinuvin 928: benzotriazole-based UVA (manufactured by BASF Corporation, trade name "Tinuvin 928") Omnirad 819: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (manufactured by IGM Resins Corporation, trade name "Omnirad 819") NDDA: 1,9-nonanediol diacrylate Irganox 1010: Hindered phenol-based antioxidant (manufactured by BASF, trade name "Irganox 1010") KBM-403: 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Silicones Co., Ltd., trade name "KBM-403")

[0234] [Preparation of Release Liner] 30 parts by weight of an addition reaction curable silicone (LTC761 containing a hexenyl group-containing polyorganosiloxane, a 30 wt% toluene solution, manufactured by Dow Corning Toray Co., Ltd.), 0.9 parts by weight of a release control agent (BY24-850 containing an unreactive silicone resin, manufactured by Dow Corning Toray Co., Ltd.), 2 parts by weight of a curing catalyst (SRX212 containing a platinum catalyst, manufactured by Dow Corning Toray Co., Ltd.), and a toluene / hexane mixed solvent (volume ratio 1:1) as a dilution solvent were mixed to obtain a silicone-based release agent composition. The concentration of silicone solids in the release agent composition was 1.0 wt%. Next, the release agent composition was applied with a wire bar to one side of a liner substrate (Lumirror XD500P, a polyester film, 75 μm thick), and heated at 130° C. for 1 minute to prepare a release liner having a release layer (thickness 60 nm) on one side.

[0235] [Preparation of Pressure-Sensitive Adhesive Sheet] (Example 1) A pressure-sensitive adhesive composition was applied to one side of a substrate sheet (PET separator, manufactured by Mitsubishi Plastics, MRF38) using an applicator to form a coating layer. Next, the above-mentioned release liner was placed on the formed coating layer to obtain a first laminate. The release liner was placed so that the release layer was in contact with the coating layer. Next, a light source with an illuminance of 2.5 mW / cm was applied from the substrate sheet side of the first laminate. 2 and an integrated light intensity of 2400 mJ / cm 2 The adhesive sheet was then irradiated with ultraviolet light from a black light source for 10 seconds. No ultraviolet light was irradiated from the release liner side. This photocured the coating layer, and the PSA sheet of Example 1 (thickness: 50 μm) sandwiched between the base sheet and the release liner was obtained. The illuminance of the light was measured using an illuminance meter (U0-T36T2, manufactured by Topcon Technohouse Co., Ltd.) near the surface of the base sheet where the ultraviolet light was incident.

[0236] (Examples 2 to 8, Comparative Examples 1 to 4, and Reference Examples 1 and 2) Pressure-sensitive adhesive sheets 1 of Examples 2 to 8, Comparative Examples 1 to 4, and Reference Examples 1 and 2 were obtained in the same manner as Example 1, except that the pressure-sensitive adhesive compositions shown in Table 2 below were used instead of pressure-sensitive adhesive composition A1. The pressure-sensitive adhesive sheets of Comparative Examples 1 to 4 did not contain UVA. The pressure-sensitive adhesive sheets of Reference Examples 1 and 2 did not contain inorganic particles or UVA.

[0237] <Evaluation> [Evaluation of inorganic particle concentration] The concentration C of inorganic particles on the first main surface, the second main surface and the center M of the pressure-sensitive adhesive sheet prepared above was measured. S1 , C S2 and C M was evaluated as the ratio of the zirconium concentration (unit: atomic %) to the carbon C concentration (unit: atomic %) in each evaluation region (Zr / C ratio) by the above-mentioned method using TEM-EDX (Hitachi High-Technologies Corporation, accelerating voltage 100 kV). S1 / C M and C S2 / C M is the C obtained by evaluation S1 , C S2 and C M The calculation was made from the above. The main surface of the pressure-sensitive adhesive sheet facing the base sheet (the surface irradiated with UVA in the above examples) was designated the first main surface, and the main surface of the pressure-sensitive adhesive sheet facing the release liner (the surface not irradiated with UVA in the above examples) was designated the second main surface. TEM-EDX was performed by rapidly freezing the pressure-sensitive adhesive sheet with liquid nitrogen and cutting out a section with a thickness of approximately 100 nm in a frozen atmosphere of -30°C using an ultramicrotome (Leica, UC7) as the test piece. The thickness of each evaluation area in the test piece was 1 μm, as described above. The width of each evaluation area in the test piece was 2 μm. The width of the evaluation area refers to the length of the evaluation area in the in-plane direction of the pressure-sensitive adhesive sheet.

[0238] [Evaluation of refractive index] For the pressure-sensitive adhesive sheets prepared above, the base sheet and release liner were peeled off to expose each of the main surfaces, and the refractive index was measured in critical angle mode using a prism coupler (manufactured by Metricon, model "2010M") at a measurement temperature of 25°C and a measurement wavelength of 594 nm. The main surface exposed by peeling off the base sheet was designated the first main surface, and the main surface exposed by peeling off the release liner was designated the second main surface.

[0239] [Evaluation of Light Transmittance @ 380 nm] The base sheet and release liner were peeled off from the pressure-sensitive adhesive sheet produced above, and each exposed main surface was covered with an alkali-free glass plate (thickness: 0.7 to 0.8 mm, total light transmittance: 92%, chromaticity: b *0.20) were bonded together to prepare a test specimen. This test specimen was left in an environment of 23°C and 50% RH for 30 minutes, and then placed in a pressure degassing apparatus (autoclave) and autoclaved for 30 minutes under conditions of a temperature of 50°C and a pressure of 0.5 MPa. Next, it was left in an atmosphere of 23°C and 50% RH for 24 hours. Next, in a measurement environment of 23°C, the light transmittance in the thickness direction of the test specimen for light with wavelengths of 300 nm to 800 nm was measured using an ultraviolet-visible-near-infrared spectrophotometer (UH4150, manufactured by Hitachi High-Technologies Corporation), and the light transmittance at a wavelength of 380 nm was determined from the measurement results.

[0240] [Evaluation of Reflectance] A laminate was prepared in which an acrylic sheet (thickness 2 μm) with a refractive index of 1.49, the above-prepared pressure-sensitive adhesive sheet (thickness 50 μm), and a sapphire glass sheet (thickness 0.5 μm) with a refractive index of 1.77 were laminated in this order. To prepare the laminate, the base sheet and release liner were peeled off from the pressure-sensitive adhesive sheet. Furthermore, the laminate was formed so that the main surface (first main surface) of the pressure-sensitive adhesive sheet exposed by peeling off the base sheet was in contact with the acrylic sheet, and the main surface (second main surface) of the pressure-sensitive adhesive sheet exposed by peeling off the release liner was in contact with the sapphire glass sheet. Next, the front reflectance of the laminate was measured using the SCI method with the sapphire glass sheet as the incident surface, and the obtained front reflectance was determined as the reflectance of the pressure-sensitive adhesive sheet. A spectrophotometer CM-2600d manufactured by Konica Minolta was used to measure the front reflectance.

[0241] [Evaluation of Adhesion Strength] Under a measurement environment of 23°C and 50% RH, the release liner was peeled from the pressure-sensitive adhesive sheet prepared above, and a polyethylene terephthalate film (thickness: 25 μm) was attached and backed. The resulting laminate was cut into a strip measuring 100 mm long x 25 mm wide to prepare a test piece. The substrate sheet was peeled from the test piece, and the test piece was placed on alkali-free glass (manufactured by Corning Incorporated, trade name "EG-XG", thickness: 0.7 mm), and the two were pressure-bonded by moving a 2 kg roller back and forth once.

[0242] After leaving this test piece under the above environment for 30 minutes, it was placed in a pressure degassing apparatus (autoclave) and autoclaved for 30 minutes under conditions of a temperature of 50°C and a pressure of 0.5 MPa. Next, it was left for 24 hours in an atmosphere of 23°C and 50% RH. Next, using a universal tension and compression tester (Shimadzu Corporation, Autograph SHIMAZU AGX-V 50N), the test piece was peeled from the alkali-free glass at a peel rate of 300 mm / min and a peel angle of 180°. At this time, the force (peel strength) required to peel the test piece from the alkali-free glass was determined as the adhesive strength.

[0243] The evaluation results are shown in Table 2 below.

[0244]

[0245] As shown in Table 2, the concentration C of inorganic particles at the center in the thickness direction of the pressure-sensitive adhesive sheet M The pressure-sensitive adhesive sheets of the examples having a main surface SA with an equal or lower concentration of inorganic particles were more suitable for improving the balance between refractive index and adhesive strength than the comparative examples having no main surface SA.

[0246] The pressure-sensitive adhesive sheet of the present invention can be used in image display devices such as EL displays and liquid crystal displays.

Claims

1. A pressure-sensitive adhesive sheet formed from a photocurable pressure-sensitive adhesive composition containing a monomer component M, which contains inorganic particles, and a concentration C of the inorganic particles at the center in the thickness direction of the pressure-sensitive adhesive sheet M a main surface SA in which the concentration of the inorganic particles is equal to or smaller than that of the main surface SA; 2. The pressure-sensitive adhesive sheet has a first main surface and a second main surface opposite to the first main surface, and of the first main surface and the second main surface, only the first main surface is the main surface SA, and a concentration C of the inorganic particles in the first main surface S1 and the concentration C M The formula: (C S1 / C M )≦1.00, and the concentration C of the inorganic particles on the second main surface satisfies the relationship represented by S2 and the concentration C M The formula: (C S2 / C M 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the relationship represented by the formula: ) ≥ 1.

50.

3. The adhesive sheet according to claim 2, wherein the first main surface is a surface onto which the adhesive composition is irradiated with active energy rays during the formation of the adhesive sheet, and the second main surface is a surface onto which the adhesive composition is not irradiated with active energy rays during the formation of the adhesive sheet.

4. An adhesive sheet as described in claim 2, wherein the refractive index n2 of the adhesive sheet when the second main surface is used as the evaluation surface is greater than the refractive index n1 of the adhesive sheet when the first main surface is used as the evaluation surface.

5. The pressure-sensitive adhesive sheet according to claim 4, wherein the absolute value of the difference between the refractive index n1 and the refractive index n2 is 0.02 or more.

6. The pressure-sensitive adhesive sheet according to claim 4, wherein the refractive index n1 is 1.58 or more, and the refractive index n2 is 1.61 or more.

7. The pressure-sensitive adhesive sheet according to claim 2, wherein the reflectance of the pressure-sensitive adhesive sheet evaluated by the following evaluation method is 8.1% or less. <Evaluation Method> A laminate is prepared in which an acrylic sheet with a refractive index of 1.49, the pressure-sensitive adhesive sheet with a thickness of 50 μm, and a sapphire glass sheet with a refractive index of 1.77 are laminated in this order. The first main surface of the pressure-sensitive adhesive sheet is in contact with the acrylic sheet. The second main surface of the pressure-sensitive adhesive sheet is in contact with the sapphire glass sheet. Next, the front reflectance of the laminate is measured using the SCI method with the sapphire glass sheet as the incident surface, and the obtained front reflectance is identified as the reflectance of the pressure-sensitive adhesive sheet.

8. The pressure-sensitive adhesive sheet according to claim 1, wherein the inorganic particles contain zirconium oxide.

9. The pressure-sensitive adhesive sheet according to claim 1, wherein the content of the inorganic particles in the pressure-sensitive adhesive composition is 40 parts by weight or more per 100 parts by weight of the total of the monomer component M and the inorganic particles.

10. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive composition contains an ultraviolet absorber.

11. The pressure-sensitive adhesive sheet according to claim 10, wherein the content of the ultraviolet absorber in the pressure-sensitive adhesive composition is 1 to 5 parts by weight per 100 parts by weight of the total of the monomer component M and the inorganic particles.

12. The pressure-sensitive adhesive sheet according to claim 1, wherein the monomer component M includes a monomer a having a double bond-containing ring.

13. The pressure-sensitive adhesive sheet according to claim 12, wherein the double bond-containing ring is an aromatic ring.

14. The pressure-sensitive adhesive sheet according to claim 12, wherein the monomer a includes a (meth)acrylic monomer having the double bond-containing ring.

15. The pressure-sensitive adhesive sheet according to claim 12, wherein the monomer a includes phenoxybenzyl acrylate.

16. The pressure-sensitive adhesive sheet according to claim 12, wherein the content of the monomer a in the pressure-sensitive adhesive composition is 40 parts by weight or more per 100 parts by weight of the total of the monomer component M and the inorganic particles.

17. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive composition contains polymer B having a weight-average molecular weight of 1,500 to 30,000.

18. An optical laminate comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 17 and an optical film.

19. An image display device comprising the optical laminate according to claim 18.

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