Optical adhesive sheet and release liner-attached optical adhesive sheet

Abstract

This adhesive sheet (10) has an adhesive surface (11) and an adhesive surface (12) on the opposite side from the adhesive surface (11). The maximum height Sz of the adhesive surfaces (11, 12) is 500 nm or less. The haze H150(%) at 150% elongation and the haze H0(%) at non-elongation of the adhesive sheet (10) satisfy |H150-H0| ≤ 1.0.

Description

Optical adhesive sheets and optical adhesive sheets with release liner

[0001] The present invention relates to an optical pressure-sensitive adhesive sheet and an optical pressure-sensitive adhesive sheet with a release liner.

[0002] A display panel has a laminated structure including elements such as a pixel panel, a polarizing film, a touch panel, and a cover film. In the manufacturing process of such a display panel, for example, an optically transparent adhesive sheet (optical adhesive sheet) is used to bond the elements included in the laminated structure. The optical adhesive sheet is manufactured, for example, in the form of an adhesive sheet with a release liner, in which both sides of the sheet are covered with release liners.

[0003] Meanwhile, development of stretchable display panels is progressing, for example, for tablet terminals. A stretchable display panel is a display panel that can be repeatedly deformed (stretched, kneaded, folded, etc.). In a stretchable display panel, each element in a laminated structure is manufactured to be repeatedly deformable. A thin optical adhesive sheet is used to bond such elements. Optical adhesive sheets for flexible devices such as stretchable display panels are described, for example, in Patent Document 1 listed below.

[0004] Japanese Patent Application Laid-Open No. 2018-111754

[0005] Optical adhesive sheets for display panels are required to have small defects caused by unevenness on the surface of the adhesive sheet (surface unevenness defects) so that they do not affect the displayed image on the display panel. However, at deformed portions of optical adhesive sheets for flexible devices, the surface unevenness defects are stretched and enlarged due to the deformation. Therefore, optical adhesive sheets for flexible devices are required to have even smaller surface unevenness defects than conventional optical adhesive sheets for display panels.

[0006] In addition, optical adhesive sheets for display panels are required to have low haze so as not to affect the image displayed on the display panel. Optical adhesive sheets for flexible devices are required to have low haze both in an undeformed state and in a deformed state. However, even if conventional optical adhesive sheets are transparent in a stationary state (in a state where they are in their natural length without deformation), depending on the monomer composition of the polymer components (polymers, oligomers) in the adhesive sheet and the compatibility between the polymer components and additives (low molecular weight components), components such as additives may aggregate in a deformed state, causing an increase in haze.

[0007] The present invention provides an optical pressure-sensitive adhesive sheet and an optical pressure-sensitive adhesive sheet with a release liner that are suitable for flexible device applications.

[0008] The present invention [1] is an optical adhesive sheet having a first adhesive surface and a second adhesive surface opposite to the first adhesive surface, wherein the maximum height Sz of the first adhesive surface and the second adhesive surface is 500 nm or less, and the haze H at 150% elongation is 150 (%) and unstretched haze H ０ (%) is |H 150 -H ０ |≦1.0.

[0009] The present invention [2] is the haze H ０ The optical pressure-sensitive adhesive sheet according to the above [1], wherein the viscosity is 2.0% or less.

[0010] The present invention [3] is a method for measuring the yield strain Y in the first tensile test under the conditions of 23°C and a tensile speed of 10 mm / min. １ The optical pressure-sensitive adhesive sheet according to the above [1] or [2], wherein the optical resistance is 150% or more.

[0011] The present invention [4] is characterized in that the yield strain Y in the second tensile test is measured at 23°C and a tensile speed of 1500 mm / min. ２ The optical pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the optical pressure-sensitive adhesive sheet has a refractive index of 150% or more.

[0012] The present invention [5] is a method for measuring the strain stress S after the first third tensile test under the conditions of 23°C, a tensile speed of 200 mm / min, and an elongation length of 150%.１ and after the tenth third tensile test, the strain stress S １０ and the stress S １ The stress S １０ The optical pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the ratio is 0.5 or more.

[0013] The present invention [6] is an optical adhesive sheet with a release liner, comprising the optical adhesive sheet described in any one of [1] to [5] above, a first release liner releasably contacting the first adhesive surface, and a second release liner releasably contacting the second adhesive surface.

[0014] The present invention [7] includes an optical adhesive sheet with release liner described in [6] above, in which the maximum height Sz of the surface of the first release liner facing the optical adhesive sheet is 2000 nm or less, and the maximum height Sz of the surface of the second release liner facing the optical adhesive sheet is 2000 nm or less.

[0015] As described above, the optical adhesive sheet of the present invention has a maximum height Sz of 500 nm or less on the first adhesive surface and the second adhesive surface. The adhesive surface of the optical adhesive sheet in the flexible device has a high smoothness of a maximum height Sz of 500 nm or less, which is suitable for suppressing the occurrence of large surface irregularity defects not only in the non-deformed part of the adhesive sheet but also in the deformed part. In addition, as described above, the optical adhesive sheet has a haze H 150 (%) and unstretched haze H ０ (%) is |H 150 -H ０ |≦1.0 is satisfied. This is suitable for suppressing an increase in haze in the deformed portion of the optical pressure-sensitive adhesive sheet when the flexible device including the optical pressure-sensitive adhesive sheet is deformed. Therefore, the optical pressure-sensitive adhesive sheet is suitable for suppressing the occurrence of large surface irregularity defects and suppressing an increase in haze. Such an optical pressure-sensitive adhesive sheet is suitable for flexible device applications.

[0016] The optical pressure-sensitive adhesive sheet with release liner of the present invention comprises the optical pressure-sensitive adhesive sheet as described above, and is therefore suitable for flexible device applications as a supply material for the optical pressure-sensitive adhesive sheet.

[0017] 1 is a cross-sectional schematic diagram of an optical pressure-sensitive adhesive sheet with a release liner according to one embodiment of the present invention.

[0018] As shown in Figure 1, a pressure-sensitive adhesive sheet 10 as one embodiment of the optical pressure-sensitive adhesive sheet of the present invention has a sheet shape of a predetermined thickness and extends in a direction (plane direction) perpendicular to the thickness direction. The pressure-sensitive adhesive sheet 10 has an adhesive surface 11 (first adhesive surface) and an adhesive surface 12 (second adhesive surface) opposite to the adhesive surface 11. Figure 1 shows a state in which release liners 20, 30 are bonded to the adhesive surfaces 11, 12 of the pressure-sensitive adhesive sheet 10. The release liner 20 is disposed on the adhesive surface 11. The release liner 30 is disposed on the adhesive surface 12. That is, the pressure-sensitive adhesive sheet X with a release liner shown in Figure 1 comprises the release liner 20, the pressure-sensitive adhesive sheet 10, and the release liner 30, arranged in that order in the thickness direction H. The pressure-sensitive adhesive sheet X with a release liner is one embodiment of the optical pressure-sensitive adhesive sheet with a release liner of the present invention.

[0019] The adhesive sheet 10 has a maximum height Sz of 500 nm or less on the adhesive surfaces 11 and 12, and a haze H 150 (%) and unstretched haze H ０ (%) is |H 150 -H ０ |≦1.0. The maximum height Sz is a parameter relating to the surface texture based on ISO 25178-2:2012. The method for measuring the maximum height Sz is as described later in the examples. ０ is the haze when the adhesive sheet 10 is not stretched or deformed. 150 is the haze when the adhesive sheet 10 is stretched in one direction by 150% of its length. ０ and Hayes H. 150 The method for measuring is as described below in the examples.

[0020] As described above, the adhesive sheet 10 has a maximum height Sz of 500 nm or less on the adhesive surfaces 11, 12. Having high smoothness with a maximum height Sz of 500 nm or less on the adhesive surfaces 11, 12 of the adhesive sheet 10 in a flexible device is suitable for suppressing the occurrence of large surface irregularity defects not only in non-deformed portions of the adhesive sheet 10 but also in deformed portions. The present inventors have discovered that the maximum height Sz is useful as an indicator for suppressing surface irregularity defects in adhesive sheets 10 for flexible device applications. The present invention is based on this discovery.

[0021] In addition, as described above, the pressure-sensitive adhesive sheet 10 has a haze H 150 (%) and unstretched haze H ０ (%) is |H 150 -H ０ |≦1.0 is satisfied. This is suitable for suppressing an increase in haze in the deformed portion of the pressure-sensitive adhesive sheet 10 when the flexible device including the pressure-sensitive adhesive sheet 10 is deformed.

[0022] Therefore, the pressure-sensitive adhesive sheet 10 is suitable for suppressing the occurrence of large surface irregularity defects and suppressing an increase in haze. Such a pressure-sensitive adhesive sheet 10 is suitable for use in flexible devices.

[0023] The release liner-attached pressure-sensitive adhesive sheet X includes the pressure-sensitive adhesive sheet 10 as described above, and is therefore suitable for flexible device applications as a supply material for optical pressure-sensitive adhesive sheets.

[0024] The maximum height Sz of the PSA sheet 10 is preferably 400 nm or less, more preferably 300 nm or less, from the viewpoint of suppressing the above-mentioned surface irregularity defects. The maximum height Sz of the PSA sheet 10 is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 150 nm or more, from the viewpoint of preventing blocking in the roll-form PSA sheet 10. That is, from the viewpoint of simultaneously suppressing the above-mentioned surface irregularity defects and preventing the above-mentioned blocking, the maximum height Sz of the PSA sheet 10 is preferably 50 to 500 nm, more preferably 100 to 400 nm, and even more preferably 150 to 300 nm. Examples of methods for adjusting the maximum height Sz of the PSA sheet 10 include adjusting the surface roughness, such as the maximum height Sz, of the release surfaces 21, 31 (contacting the PSA sheet 10) of the release liners 20, 30. Examples of methods for adjusting the surface roughness of the release surfaces 21, 31 include adjusting the surface roughness of the coating film when a release treatment agent is applied to the liner substrate described below.

[0025] Haze H of adhesive sheet 10 ０ From the viewpoint of ensuring the transparency required for the pressure-sensitive adhesive sheet 10, the haze H of the pressure-sensitive adhesive sheet 10 is preferably 2.0% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and even more preferably 0.25% or less. ０ is, for example, 0.0% or more. ０ From the viewpoint of ensuring the transparency required for the pressure-sensitive adhesive sheet 10, the haze H of the pressure-sensitive adhesive sheet 10 is preferably 0.0 to 2.0%, more preferably 0.0 to 1.0%, even more preferably 0.0 to 0.5%, and even more preferably 0.0 to 0.25%. ０ can be measured using a haze meter in accordance with JIS K7136:2000 (Haze H 150 The same applies to (1) and (2). Examples of haze meters include "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and "HM-150N" manufactured by Murakami Color Research Laboratory Co., Ltd. ０ The specific method for measuring the haze H is as described later in the examples. ０Examples of methods for adjusting the haze H include selecting the type of base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight, adjusting the degree of crosslinking, and adjusting the blending amount. ０ Examples of methods for adjusting the haze H include selecting the type of components other than the base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight, and adjusting the blending amount. 150 The same is true for .

[0026] Haze H of adhesive sheet 10 150 From the viewpoint of ensuring the required transparency when the pressure-sensitive adhesive sheet 10 is stretched, the haze H of the pressure-sensitive adhesive sheet 10 is preferably 2.0% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and even more preferably 0.25% or less. 150 is, for example, 0.0% or more. 150 From the viewpoint of ensuring the required transparency when the pressure-sensitive adhesive sheet 10 is stretched, the haze H is preferably 0.0 to 2.0%, more preferably 0.0 to 1.0%, even more preferably 0.0 to 0.5%, and even more preferably 0.0 to 0.25%. 150 The specific method for measuring is as described below in the examples.

[0027] The pressure-sensitive adhesive sheet 10 has a yield strain Y １ The method of the first tensile test is specifically as described later in the examples. １ is preferably 150% or more, more preferably 160% or more, and even more preferably 170% or more, from the viewpoint of ensuring flexibility in the pressure-sensitive adhesive sheet 10 to follow deformation of the adherend in the low-speed range. １ is preferably 200% or less, more preferably 190% or less, and even more preferably 180% or less, from the viewpoint of ensuring the restorability (shape restorability) when the pressure-sensitive adhesive sheet 10 returns to its original shape after being stretched. １ From the viewpoint of achieving both the flexibility and the shape recovery, the yield strain Y is preferably 150 to 200%, more preferably 160 to 190%, and even more preferably 170 to 180%.１ The method for adjusting the viscosity may include, for example, selecting the types of components constituting the pressure-sensitive adhesive sheet 10 and adjusting the amounts of the components.

[0028] In the second tensile test at 23°C and a tensile speed of 1500 mm / min, the pressure-sensitive adhesive sheet 10 had a yield strain Y ２ The method of the second tensile test is specifically as described later in the examples. ２ From the viewpoint of ensuring flexibility in the pressure-sensitive adhesive sheet 10 to follow deformation of the adherend in the high-speed range, the yield strain Y is preferably 150% or more, more preferably 170% or more, and even more preferably 180% or more. ２ From the viewpoint of ensuring the shape recovery of the pressure-sensitive adhesive sheet 10 after stretching, the yield strain Y is preferably 220% or less, more preferably 210% or less, and even more preferably 200% or less. ２ From the viewpoint of achieving both the flexibility and the shape recovery, the yield strain Y is preferably 150 to 220%, more preferably 170 to 210%, and even more preferably 180 to 200%. ２ The method for adjusting the viscosity may include, for example, selecting the types of components constituting the pressure-sensitive adhesive sheet 10 and adjusting the amounts of the components.

[0029] The pressure-sensitive adhesive sheet 10 had a strain stress S after the first third tensile test under the conditions of 23°C, a tensile speed of 20 cm / min, and an elongation length of 150%. １ and after the tenth third tensile test, the strain stress S １０ The third tensile test method and stress S １ ,S １０ The specific method for measuring the initial stress S of the pressure-sensitive adhesive sheet will be described later in the Examples. １ Stress S after repeated deformation １０ The ratio (S １０ / S １ ) is an index of the elastic recovery of the shape of the pressure-sensitive adhesive sheet after repeated deformation. １０ / S １From the viewpoint of ensuring the above-mentioned elastic recovery of the pressure-sensitive adhesive sheet 10, the ratio (S １０ / S １ From the viewpoint of ensuring the flexibility of the pressure-sensitive adhesive sheet 10, the ratio (S １０ / S １ ) is preferably 0.5 to 1.2, more preferably 0.6 to 1.0, and even more preferably 0.65 to 0.95, from the viewpoint of ensuring both the elastic recovery property and flexibility of the pressure-sensitive adhesive sheet 10.

[0030] Stress S of the adhesive sheet 10 １ From the viewpoint of ensuring the above-mentioned elastic recovery of the pressure-sensitive adhesive sheet 10, the stress S of the pressure-sensitive adhesive sheet 10 is preferably 0.100 MPa or more, more preferably 0.120 MPa or more, and even more preferably 0.150 MPa or more. １ In order to ensure the stress relaxation properties required for flexible device applications in the pressure-sensitive adhesive sheet 10, the stress S １ From the viewpoint of achieving both the elastic recovery property and the stress relaxation property of the pressure-sensitive adhesive sheet 10, the stress S of the pressure-sensitive adhesive sheet 10 is preferably 0.100 to 0.215 MPa, more preferably 0.120 to 0.210 MPa, and even more preferably 0.150 to 0.205 MPa. １ Examples of methods for adjusting the stress S include adjusting the monomer composition of the base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight, adjusting the blending amount, and adjusting the degree of crosslinking. １０ The same applies to

[0031] Stress S of the adhesive sheet 10 １０ From the viewpoint of ensuring the elastic recovery of the pressure-sensitive adhesive sheet 10 after repeated deformation, the stress S of the pressure-sensitive adhesive sheet 10 is preferably 0.070 MPa or more, more preferably 0.080 MPa or more, and even more preferably 0.090 MPa or more. １０is preferably 0.215 MPa or less, more preferably 0.210 MPa or less, and even more preferably 0.205 MPa or less, from the viewpoint of ensuring the stress relaxation properties of the pressure-sensitive adhesive sheet 10 after repeated deformation. １０ From the viewpoint of achieving both elastic recovery and stress relaxation properties of the pressure-sensitive adhesive sheet 10 after repeated deformation, the stress is preferably 0.070 to 0.215 MPa, more preferably 0.080 to 0.210 MPa, and even more preferably 0.090 to 0.205 MPa.

[0032] The pressure-sensitive adhesive sheet 10 is a sheet-like pressure-sensitive adhesive formed from a pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet 10 (pressure-sensitive adhesive composition) includes a base polymer. The base polymer is preferably a polymer (photopolymerized polymer) obtained by photopolymerization of a polymerizable component such as a monomer component. Photopolymerization is a polymerization method in which a polymerization reaction of a polymerizable component is promoted by irradiation with active energy rays such as ultraviolet rays.

[0033] Examples of base polymers include acrylic polymers, polyurethane polymers, polyamide polymers, and polyvinyl ether polymers. The base polymers may be used alone or in combination of two or more. From the viewpoint of ensuring good adhesiveness and transparency in the pressure-sensitive adhesive sheet 10, the base polymer is preferably an acrylic polymer. The acrylic polymer is a copolymer of monomer components containing 50% or more by mass of (meth)acrylic acid ester. "(Meth)acrylic" refers to acrylic and / or methacrylic.

[0034] In this embodiment, the acrylic polymer is a polymer obtained by photopolymerization of a polymerizable component including a monofunctional monomer and a polyfunctional polymerizable compound as a crosslinking agent. The acrylic polymer is, for example, a polymer obtained by photopolymerization of a partial polymer obtained by photopolymerization of a monofunctional monomer (a mixture of a polymer of the monofunctional monomer and an unreacted monofunctional monomer) and a polyfunctional polymerizable compound.

[0035] Such acrylic polymers include a photopolymerized polymer (first photopolymerized polymer) having a photocrosslinked structure. The photocrosslinked structure is a structure in which linear chain structures formed by units derived from monofunctional monomers are crosslinked by units derived from a crosslinking agent. The base polymer may also include a photopolymerized polymer (second photopolymerized polymer) that does not have such a photocrosslinked structure. The second photopolymerized polymer is a polymer of a monofunctional monomer.

[0036] The monofunctional monomer preferably includes a monofunctional (meth)acrylic acid alkyl ester, and more preferably includes a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms. The (meth)acrylic acid alkyl ester may have a linear or branched alkyl group, or may have a cyclic alkyl group (alicyclic alkyl group).

[0037] Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, Examples include nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (i.e., (meth)acrylate laurate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

[0038] Examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid alkyl esters having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid alkyl esters having a tricyclic or higher aliphatic hydrocarbon ring. Examples of (meth)acrylic acid cycloalkyl esters include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having three or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0039] The monofunctional (meth)acrylic acid alkyl ester may be used alone or in combination of two or more kinds. The monofunctional (meth)acrylic acid alkyl ester is preferably an acrylic acid alkyl ester having an alkyl group having 3 to 12 carbon atoms, and more preferably at least one selected from the group consisting of n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), acrylate laurate (LA), and cyclohexyl acrylate (CHA).

[0040] The proportion of the (meth)acrylic acid alkyl ester in the monofunctional monomer is preferably 68 to 99% by mass, more preferably 70 to 85% by mass, and even more preferably 72 to 78% by mass. The proportion of the (meth)acrylic acid alkyl ester in the monofunctional monomer is preferably 68% by mass or more, more preferably 70% by mass or more, and even more preferably 72% by mass or more. When the proportion of the (meth)acrylic acid alkyl ester is equal to or greater than the above-mentioned lower limit, the adhesive sheet 10 can appropriately exhibit basic properties such as adhesiveness. Furthermore, the proportion of the monofunctional (meth)acrylic acid alkyl ester in the monofunctional monomer is preferably 99% by mass or less, more preferably 85% by mass or less, and even more preferably 78% by mass or less. When the proportion of the (meth)acrylic acid alkyl ester is equal to or less than the above-mentioned upper limit, the proportion of the polar group-containing monomer in the base polymer, as described below, can be ensured.

[0041] The monofunctional monomer may include a copolymerizable monomer copolymerizable with the (meth)acrylic acid alkyl ester. Examples of the copolymerizable monomer include polar group-containing monomers. Examples of the polar group-containing monomer include hydroxy group-containing monomers, monomers having a nitrogen atom-containing ring, and carboxy group-containing monomers. The copolymerizable monomers may be used alone or in combination of two or more. The polar group-containing monomer is useful for modifying the acrylic polymer, such as ensuring the cohesive strength of the acrylic polymer. The polar group-containing monomer is preferably at least one selected from the group consisting of hydroxy group-containing monomers and monomers having a nitrogen atom-containing ring.

[0042] Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate. The hydroxy group-containing monomer is preferably at least one selected from the group consisting of 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA).

[0043] The proportion of the hydroxy group-containing monomer in the monofunctional monomer is preferably 1 to 30% by mass, more preferably 5 to 28% by mass, and even more preferably 8 to 25% by mass. The proportion of the hydroxy group-containing monomer in the monofunctional monomer is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more. When this proportion of the hydroxy group-containing monomer is equal to or greater than the above-mentioned lower limit, the cohesive strength of the PSA sheet 10 can be ensured, and the adhesive strength of the PSA sheet 10 to the adherend can be ensured. Furthermore, the proportion of the hydroxy group-containing monomer in the monomer components is preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 25% by mass or less. When this proportion of the hydroxy group-containing monomer is equal to or less than the above-mentioned upper limit, the polarity of the acrylic polymer (which is related to the compatibility of the acrylic polymer with various additive components in the PSA sheet 10) can be appropriately adjusted.

[0044] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and acryloylmorpholine. The monomer having a nitrogen atom-containing ring is preferably N-vinyl-2-pyrrolidone (NVP).

[0045] The proportion of the monomer having a nitrogen atom-containing ring in the monofunctional monomer is preferably 1 to 30% by mass, more preferably 5 to 25% by mass, and even more preferably 10 to 20% by mass. The proportion of the monomer having a nitrogen atom-containing ring in the monofunctional monomer is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. When this proportion of the monomer having a nitrogen atom-containing ring is equal to or greater than the above-mentioned lower limit, the cohesive strength of the PSA sheet 10 can be ensured, and the adhesive strength of the PSA sheet 10 to the adherend can be ensured. Furthermore, the proportion of the monomer having a nitrogen atom-containing ring in the monofunctional monomer is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. When this proportion of the monomer having a nitrogen atom-containing ring is equal to or less than the above-mentioned upper limit, the glass transition temperature of the acrylic polymer can be appropriately adjusted, and the polarity of the acrylic polymer (related to the compatibility of the acrylic polymer with various additive components in the PSA sheet 10) can be appropriately adjusted.

[0046] Examples of carboxy group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0047] The proportion of the carboxyl group-containing monomer in the monofunctional monomer is preferably 0 to 3 mass %, more preferably 0 to 1 mass %, even more preferably 0 to 0.5 mass %, even more preferably 0 to 0.1 mass %, and particularly preferably 0.0 mass %, from the viewpoint of suppressing acid corrosion on the adherend of the pressure-sensitive adhesive sheet 10.

[0048] The monofunctional monomer may contain other copolymerizable monomers, such as acid anhydride monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds.

[0049] Examples of polyfunctional polymerizable compounds (crosslinking agents) include polyfunctional monomers containing two or more ethylenically unsaturated double bonds in one molecule. Examples of polyfunctional monomers include polyfunctional (meth)acrylates. Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher polyfunctional (meth)acrylates.

[0050] Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol dimethacrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, stearic acid-modified pentaerythritol di(meth)acrylate, dicyclopentenyl diacrylate, di(meth)acryloyl isocyanurate, and ethoxylated bisphenol A diacrylate (BPAEODE).

[0051] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

[0052] Examples of tetrafunctional or higher polyfunctional (meth)acrylates include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol pentaacrylate, and dipentaerythritol hexa(meth)acrylate.

[0053] The polyfunctional polymerizable compound may be used alone or in combination of two or more kinds. The polyfunctional polymerizable compound is preferably at least one selected from the group consisting of 1,6-hexanediol diacrylate (HDDA) and dipentaerythritol hexaacrylate (DPHA).

[0054] The amount of the polyfunctional polymerizable compound in the polymerizable component is preferably 0.01 to 2 parts by mass, more preferably 0.05 to 1.5 parts by mass, and even more preferably 0.1 to 1 part by mass, per 100 parts by mass of the monofunctional monomer. The amount of the polyfunctional polymerizable compound in the polymerizable component is preferably 0.01 part by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 part by mass or more, per 100 parts by mass of the monofunctional monomer. When the amount of the polyfunctional polymerizable compound is equal to or greater than the above-mentioned lower limit, the cohesive strength of the pressure-sensitive adhesive sheet 10 is increased, thereby improving the adhesive reliability after being laminated to an adherend. The amount of the polyfunctional polymerizable compound in the polymerizable component is preferably 2 parts by mass or less, more preferably 1.5 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of the monofunctional monomer. When the amount of the polyfunctional polymerizable compound is equal to or less than the above-mentioned upper limit, the flexibility of the pressure-sensitive adhesive sheet 10 is easily ensured.

[0055] In this embodiment, the acrylic polymer is formed by photopolymerization of the polymerizable components. The polymerizable components (including a monofunctional monomer and a multifunctional polymerizable compound as a crosslinker) may be polymerized in one step or in multiple steps. In the multistep polymerization method, a monofunctional monomer is first polymerized to prepare a prepolymer composition containing a partial polymer (a mixture of a polymer of the monofunctional monomer and unreacted monofunctional monomer) (preliminary polymerization). Next, a multifunctional polymerizable compound as a crosslinker is added to the prepolymer composition, and then a polymerization reaction is allowed to proceed in a reaction system containing the partial polymer and the multifunctional polymerizable compound (main polymerization). A photopolymerization initiator may be used in the photopolymerization.

[0056] Examples of the photopolymerization initiator include a radical photopolymerization initiator, a cationic photopolymerization initiator, and an anionic photopolymerization initiator.

[0057] Examples of the radical photopolymerization initiator include an acylphosphine oxide photopolymerization initiator, a benzoin ether photopolymerization initiator, an acetophenone photopolymerization initiator, and an α-ketol photopolymerization initiator.

[0058] Examples of acylphosphine oxide photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Examples of benzoin ether photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-1,2-diphenylethan-1-one. Examples of acetophenone photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. The photopolymerization initiators may be used alone or in combination. The photopolymerization initiator is preferably at least one selected from the group consisting of 2,2-dimethoxy-1,2-diphenylethan-1-one and 1-hydroxycyclohexyl phenyl ketone.

[0059] The amount of photopolymerization initiator is preferably 0.03 to 0.5 parts by mass, more preferably 0.06 to 0.3 parts by mass, and even more preferably 0.08 to 0.2 parts by mass, per 100 parts by mass of the polymerizable component. The amount of photopolymerization initiator is preferably 0.03 parts by mass or more, more preferably 0.06 parts by mass or more, and even more preferably 0.08 parts by mass or more, per 100 parts by mass of the polymerizable component. When the amount of photopolymerization initiator is equal to or greater than the above-mentioned lower limit, a crosslinked network with sufficient crosslinking density is formed in the acrylic polymer, thereby ensuring the adhesive strength of the pressure-sensitive adhesive sheet 10. The amount of photopolymerization initiator is preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and even more preferably 0.2 parts by mass or less, per 100 parts by mass of the polymerizable component. When the amount of photopolymerization initiator is equal to or less than the above-mentioned upper limit, cohesive failure of the adhesive surface of the pressure-sensitive adhesive sheet 10 can be suppressed when the pressure-sensitive adhesive sheet 10 is peeled from the adherend. When the acrylic polymer is photopolymerized by prepolymerization and main polymerization, a photopolymerization initiator may be added after the prepolymerization and during the main polymerization.

[0060] From the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10, the weight-average molecular weight of the base polymer is preferably 100,000 to 5,000,000, more preferably 300,000 to 3,000,000, and even more preferably 500,000 to 2,000,000. The weight-average molecular weight of the base polymer is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more. When the weight-average molecular weight of the base polymer is equal to or greater than the above-mentioned lower limit, the cohesive strength of the pressure-sensitive adhesive sheet 10 can be ensured. The weight-average molecular weight of the base polymer is preferably 5,000,000 or less, more preferably 3,000,000 or less, and even more preferably 2,000,000 or less. When the weight-average molecular weight of the base polymer is equal to or less than the above-mentioned upper limit, the flexibility of the pressure-sensitive adhesive sheet 10 can be ensured. The weight-average molecular weight of the acrylic polymer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0061] From the viewpoint of ensuring the flexibility of the base polymer, the glass transition temperature (Tg) of the base polymer is preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. The glass transition temperature is, for example, -80°C or higher. That is, the glass transition temperature of the base polymer is preferably -80°C to 0°C, more preferably -80°C to -10°C, and even more preferably -80°C to -20°C.

[0062] The glass transition temperature of the base polymer may be determined using the theoretical glass transition temperature (Tg) calculated based on the Fox formula below. The Fox formula is a relationship between the glass transition temperature (Tg) of a polymer and the glass transition temperature (Tgi) of a homopolymer of the monomers constituting the polymer. In the Fox formula below, Tg represents the glass transition temperature (°C) of the polymer, Wi represents the weight fraction of the monomer i constituting the polymer, and Tgi represents the glass transition temperature (°C) of the homopolymer formed from the monomer i. Literature values ​​can be used for the glass transition temperature of the homopolymer. For example, the "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) lists the glass transition temperatures of various homopolymers. Meanwhile, the glass transition temperature of a homopolymer of a monomer can also be determined using the method specifically described in JP 2007-51271 A.

[0063] Fox's formula: 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0064] The base polymer content in the pressure-sensitive adhesive sheet 10 is preferably 80 to 99.9% by mass, more preferably 85 to 99.5% by mass, and even more preferably 90 to 99.0% by mass. The base polymer content in the pressure-sensitive adhesive sheet 10 is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. When the base polymer content is equal to or greater than the above-mentioned lower limit, basic properties such as adhesiveness can be appropriately exhibited in the pressure-sensitive adhesive sheet 10. The base polymer content in the pressure-sensitive adhesive sheet 10 is, for example, 99.9% by mass or less, 99.5% by mass or less, or 99.0% by mass or less.

[0065] The pressure-sensitive adhesive sheet 10 may contain other components, such as an oligomer, a silane coupling agent, an ultraviolet absorber, an antioxidant, a surfactant, and a rust inhibitor.

[0066] The release liner 20 has a release surface 21 on the side facing the pressure-sensitive adhesive sheet 10. The release liner 20 releasably contacts the pressure-sensitive adhesive surface 11 of the pressure-sensitive adhesive sheet 10 on the release surface 21 side. In this embodiment, the release liner 20 is a heavy release liner that requires a greater force to be peeled from the pressure-sensitive adhesive sheet 10 than the release liner 30.

[0067] Examples of the release liner 20 include a release liner in which the release surface 21 is formed on a liner substrate by a release treatment layer, and a release liner formed from a low-adhesion material. Examples of liner substrates include resin films and paper. Examples of resins for resin films include polyester resins and polycarbonate resins. Examples of polyester resins include polyethylene terephthalate (PET) and polybutylene terephthalate. The release layer can be formed by surface treating the liner substrate with a release treatment agent. Examples of release treatment agents include silicone release treatment agents, long-chain alkyl release treatment agents, and fluorine release treatment agents. Examples of low-adhesion materials include polyolefin resins and fluorine-based polymers. Examples of polyolefin resins include polyethylene, polypropylene, and cycloolefin polymer (COP). Examples of fluorine-based polymers include polytetrafluoroethylene.

[0068] The maximum height Sz of the release surface 21 is preferably 2000 nm or less, more preferably 1800 nm or less, and even more preferably 1700 nm or less, from the viewpoint of reducing the maximum height Sz of the adhesive surface 11 of the PSA sheet 10. The maximum height Sz of the release surface 21 is preferably 1000 nm or more, more preferably 1200 nm or more, and even more preferably 1300 nm or more, from the viewpoint of suppressing unintended peeling of the release liner 20 from the PSA sheet 10. The maximum height Sz of the release surface 21 is preferably 1000 to 2000 nm, more preferably 1200 to 1800 nm, and even more preferably 1300 to 1700 nm, from the viewpoint of achieving both a reduction in the maximum height Sz of the adhesive surface 11 and the suppression of peeling of the release liner 20. Examples of methods for adjusting the maximum height Sz of the release surface 21 include adjusting the surface roughness of the coating film when a release treatment agent is applied to the liner substrate described below (the same applies to the maximum height Sz of the release surface 31 of the release liner 30).

[0069] The release liner 30 has a release surface 31 on the side facing the pressure-sensitive adhesive sheet 10. The release liner 30 releasably contacts the pressure-sensitive adhesive surface 12 of the pressure-sensitive adhesive sheet 10 on the release surface 31 side. In this embodiment, the release liner 30 is a light release liner that requires less force to be peeled from the pressure-sensitive adhesive sheet 10 than the release liner 20.

[0070] Examples of the release liner 30 include a release liner having a release-treated layer on the surface of a liner substrate and a release liner made of a low-adhesion material. The material of the release liner 30 is specifically the same as the material described above for the release liner 20.

[0071] The maximum height Sz of the release surface 31 is preferably 2000 nm or less, more preferably 1800 nm or less, and even more preferably 1700 nm or less, from the viewpoint of reducing the maximum height Sz of the adhesive surface 12 of the PSA sheet 10. The maximum height Sz of the release surface 31 is preferably 1000 nm or more, more preferably 1200 nm or more, and even more preferably 1300 nm or more, from the viewpoint of suppressing unintended peeling of the release liner 30 from the PSA sheet 10. The maximum height Sz of the release surface 31 is preferably 1000 to 2000 nm, more preferably 1200 to 1800 nm, and even more preferably 1300 to 1700 nm, from the viewpoint of achieving both a reduction in the maximum height Sz of the adhesive surface 12 and the suppression of peeling of the release liner 30.

[0072] The pressure-sensitive adhesive sheet 10 can be produced, for example, as follows.

[0073] First, a prepolymer composition is prepared. Specifically, a mixture (liquid) containing the monofunctional monomer for forming the base polymer and a photopolymerization initiator is prepared. Next, the mixture is irradiated with ultraviolet light to photopolymerize a portion of the monofunctional monomer in the mixture, thereby obtaining a prepolymer composition. Examples of light sources for ultraviolet irradiation include ultraviolet LED lights, black light lamps, high-pressure mercury lamps, and metal halide lamps. In the ultraviolet irradiation, the illuminance is, for example, 5 to 200 mW / cm. ２ The cumulative irradiation amount is, for example, 100 to 5000 mJ / cm ２ The ultraviolet irradiation is preferably continued until the viscosity of the composition reaches approximately 15 to 25 Pa·s. This viscosity is measured using a Brookfield viscometer with a No. 5 rotor at a rotor rotation speed of 10 rpm and a temperature of 30°C. The prepolymer composition contains a photopolymerized product of a monofunctional monomer and an unreacted monofunctional monomer (residual monomer). The prepolymer composition does not contain a solvent.

[0074] Next, a multifunctional polymerizable compound (crosslinking agent) and, if necessary, other components are added to the prepolymer composition to prepare a pressure-sensitive adhesive composition. Examples of other components include an oligomer, an additional photopolymerization initiator, a silane coupling agent, an antioxidant, and a rust inhibitor. This pressure-sensitive adhesive composition does not contain a solvent. That is, the pressure-sensitive adhesive composition prepared in this step is a solventless pressure-sensitive adhesive composition.

[0075] Next, a pressure-sensitive adhesive composition is applied to release surface 21 of release liner 20 to form a coating film, and then release surface 31 of release liner 30 is bonded to the coating film on release liner 20. Examples of methods for applying the pressure-sensitive adhesive composition include 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.

[0076] Next, the coating film between the release liners 20 and 30 is irradiated with ultraviolet light to photocure the coating film, forming a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer formation process). The UV irradiation causes a polymerization reaction in the coating film in a reaction system containing the residual monomer and the polyfunctional polymerizable compound, forming a first photopolymerized polymer having a photocrosslinked structure. The pressure-sensitive adhesive layer may then be dried by heating. The drying temperature is, for example, 80°C to 150°C. The drying time is, for example, 30 seconds to 10 minutes. The drying process allows unreacted monomers in the pressure-sensitive adhesive layer to be volatilized and removed. Having a maximum height Sz of 2000 nm or less for the release surfaces 21 and 31 is suitable for forming a pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet 10) between the release surfaces 21 and 31 with highly smooth adhesive surfaces 11 and 12.

[0077] In this manner, it is possible to produce a PSA sheet 10 whose adhesive surfaces 11, 12 are covered and protected by release liners 20, 30. That is, it is possible to produce a PSA sheet X with release liners. Release liners 20, 30 are peeled off from PSA sheet 10 as needed when using PSA sheet 10.

[0078] The pressure-sensitive adhesive sheet 10 can be formed from a solvent-free pressure-sensitive adhesive composition. Such a pressure-sensitive adhesive sheet 10 is suitable for reducing the environmental load. That is, a pressure-sensitive adhesive sheet 10 formed from a solvent-free pressure-sensitive adhesive composition is environmentally friendly and preferable from the viewpoint of sustainable development.

[0079] The thickness of the pressure-sensitive adhesive sheet 10 is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more, from the viewpoint of ensuring sufficient adhesiveness to the adherend. The thickness of the pressure-sensitive adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less, from the viewpoint of ease of handling and thinning of the pressure-sensitive adhesive sheet 10. The thickness of the pressure-sensitive adhesive sheet 10 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 100 μm, from the viewpoint of achieving both the above-mentioned adhesiveness and the above-mentioned ease of handling and thinning.

[0080] The pressure-sensitive adhesive sheet 10 is, for example, an optical pressure-sensitive adhesive sheet arranged at a light passage location in a flexible device. Flexible devices include flexible display panels. Flexible display panels include foldable display panels, rollable display panels, and stretchable display panels. A flexible display panel is a display panel that can be repeatedly folded. A rollable display panel is a display panel that can be repeatedly rolled up. A stretchable display panel is a display panel that can be repeatedly deformed (stretched, twisted, folded, etc.). A flexible display panel has a laminated structure including elements such as a pixel panel, a polarizing film, a touch panel, and a cover film. The pressure-sensitive adhesive sheet 10 is used, for example, to bond elements included in the laminated structure during the manufacturing process of a flexible display panel.

[0081] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. The specific numerical values ​​of the blending amounts (contents), physical property values, parameters, etc. described below can be substituted with the upper limits (numerical values ​​defined as "equal to or less than") or lower limits (numerical values ​​defined as "equal to or more than") of the corresponding blending amounts (contents), physical property values, parameters, etc. described in the above-mentioned "Description of the Invention."

[0082] Preparation of First Heavy Release Liner A first release treatment agent solution with a silicone solids concentration of 1.25% by mass was prepared by mixing 80 parts by mass of a silicone release treatment agent (product name "KE-3703", a 28.5% by mass toluene solution of an addition-type silicone release treatment agent containing a polyorganosiloxane having hexenyl groups in the molecule and a polyorganosiloxane crosslinker having hydrosilyl groups in the molecule, manufactured by Shin-Etsu Chemical Co., Ltd.), 20 parts by mass of a silicone release control agent (product name "KS-3800", manufactured by Shin-Etsu Chemical Co., Ltd.), 3.0 parts by mass of a platinum catalyst for silicone curing (product name "CAT-PL-50T", manufactured by Shin-Etsu Chemical Co., Ltd.), and a solvent. The solvent was a mixed solvent of toluene and hexane in a volume ratio of 1:1.

[0083] Next, a first polyethylene terephthalate (PET) film (thickness: 75 μm, maximum surface height Sz: 1480 nm) serving as a substrate film was subjected to a release treatment. Specifically, the first release treatment agent solution was first applied to one side of the substrate film to form a coating film. A wire bar #9 was used for application. The amount of coating was 0.1 g / m2 in terms of solid content. ２ Next, the coating film on the substrate film was dried by heating at 130°C for 1 minute using a hot air dryer, thereby forming a silicone release layer on the substrate film.

[0084] In this manner, a first heavy-duty release liner (substrate film / release layer) was produced. The maximum height Sz of the surface of the first heavy-duty release liner on the release layer side was 1504 nm.

[0085] <Preparation of Secondary Release Liner> A secondary release liner (substrate film / release layer) was prepared in the same manner as the primary release liner, except for the following: A second PET film (thickness 75 μm, maximum surface height Sz 3460 nm) was used as the substrate film. The maximum surface height Sz of the secondary release liner on the release layer side was 3320 nm.

[0086] <Preparation of First Light Release Liner> A second release treatment agent solution with a silicone solids concentration of 1.0% by mass was prepared by mixing 100 parts by mass of a silicone release treatment agent (product name "KS-847T", a 30% toluene solution of vinyl group-containing addition type silicone, manufactured by Shin-Etsu Chemical Co., Ltd.), 3.0 parts by mass of a platinum catalyst for silicone curing (product name "CAT-PL-50T", manufactured by Shin-Etsu Chemical Co., Ltd.), 15,000 parts by mass of toluene as a solvent, and 1,500 parts by mass of normal hexane.

[0087] Next, a first PET film (75 μm thick, 1480 nm maximum surface height) was subjected to a release treatment. Specifically, the second release treatment agent solution was applied to one side of the base film to form a coating film. A wire bar #9 was used for application. The amount of coating was 0.1 g / m2 in terms of solid content. ２ Next, the coating film on the substrate film was dried by heating at 130°C for 1 minute using a hot air dryer, thereby forming a silicone release layer on the substrate film.

[0088] In this manner, a first light release liner (substrate film / release layer) was produced. The maximum height Sz of the surface of the first light release liner on the release layer side was 1680 nm.

[0089] <Preparation of Second Light Release Liner> A second light release liner (substrate film / release layer) was prepared in the same manner as the first light release liner, except that a second PET film (thickness 75 μm, maximum surface height Sz 3460 nm) was used as the substrate film. The maximum surface height Sz of the release layer side of the second light release liner was 3730 nm.

[0090] Example 1 Preparation of Pressure-Sensitive Adhesive Composition First, a mixture containing 75 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of 2-hydroxyethyl acrylate (HEA), 15 parts by mass of N-vinyl-2-pyrrolidone (NVP), 0.05 parts by mass of a first photopolymerization initiator (trade name "Omnirad 184", 1-hydroxycyclohexyl-phenyl-ketone, manufactured by BASF Corporation), and 0.05 parts by mass of a second photopolymerization initiator (trade name "Omnirad 651", 2,2-dimethoxy-1,2-diphenylethan-1-one, manufactured by BASF Corporation) was irradiated with ultraviolet light (polymerization reaction) to obtain a prepolymer composition (polymerization rate: approximately 10%) (the prepolymer composition contained unreacted monomer components). Next, 100 parts by mass of the prepolymer composition and 0.3 parts by mass of 1,6-hexanediol diacrylate (HDDA) (product name "A-HD-N", manufactured by Shin-Nakamura Chemical Co., Ltd.) as a first crosslinking agent were mixed to obtain a first pressure-sensitive adhesive composition.

[0091] <Formation of Pressure-Sensitive Adhesive Layer> First, a first pressure-sensitive adhesive composition was applied to a first heavy-duty release liner to form a coating film. The coating film was formed on the silicone release layer of the first heavy-duty release liner. Next, the silicone release layer side of the first light-duty release liner was laminated to the coating film on the first heavy-duty release liner (lamination step). Next, ultraviolet light was irradiated onto the coating film through the first light-duty release liner to cure the coating film, forming a transparent first pressure-sensitive adhesive layer with a thickness of 100 μm. For ultraviolet irradiation, a black light was used as the irradiation light source, and the irradiation intensity was 5 mW / cm. ２ It was decided.

[0092] In this manner, a PSA sheet with release liner of Example 1 (first heavy release liner / adhesive sheet (first PSA layer) / second light release liner) was prepared.

[0093] [Example 2, Comparative Examples 1 to 3] Each of the release-liner-equipped PSA sheets of the Examples and Comparative Examples was produced in the same manner as the release-liner-equipped PSA sheet of Example 1, except that the monomer composition of the base polymer and the formulation of the crosslinking agent were changed as shown in Table 1, and that the release liner shown in Table 1 was used.

[0094] <Maximum height Sz> The maximum heights Sz of the first adhesive surface and the second adhesive surface of each release-lined adhesive sheet of the Examples and Comparative Examples were measured. The first adhesive surface is the adhesive surface that contacts the heavy release liner. The second adhesive surface is the adhesive surface that contacts the light release liner.

[0095] Specifically, a release-liner-attached PSA sheet piece of a predetermined size was first cut out from a release-liner-attached PSA sheet. Next, the light release liner was peeled off from the PSA sheet of the sheet piece, and the exposed adhesive surface (second adhesive surface) was attached to a glass slide (manufactured by Matsunami Glass Co., Ltd.). The heavy release liner was then peeled off from the PSA sheet on the glass slide, and the exposed adhesive surface (first adhesive surface) was observed and imaged using a three-dimensional optical interference optical microscope (product name "ContourX-200", manufactured by Bruker) (first observation). The observation was performed in USI mode, using a 10x magnification objective lens and a 0.55x magnification internal lens, and the maximum height Sz was determined from an observation image with a measurement area of ​​1.3 mm x 1.5 mm (maximum height Sz is the sum of the maximum peak height Sp and the maximum valley depth Sv. These are parameters based on ISO 25178-2:2012). The maximum height Sz was also measured under the same conditions for the second adhesive surface of another piece of PSA sheet cut out from the same PSA sheet with release liner. The larger of the maximum heights Sz measured for the first and second adhesive surfaces is shown in Table 1 as the maximum height Sz (nm) of the adhesive surface.

[0096] Meanwhile, the maximum height Sz of the surface on the silicone release layer side was measured for each of the first heavy release liner, the second heavy release liner, the first light release liner, and the second light release liner. Specifically, the release layer surface of the release liner was first observed and photographed using the optical microscope described above (second observation). The conditions for the second observation were the same as those for the first observation. Next, the maximum height Sz (nm) was determined from the observed image (measurement area 1.3 mm × 1.5 mm). The results are shown in Table 1.

[0097] <Haze> The unstretched haze H of each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples was measured as follows. ０ was measured.

[0098] First, a sample for haze measurement was prepared. Specifically, a release-liner adhesive sheet piece (5 mm wide x 5 mm long) was cut out from the release-liner adhesive sheet. Next, the light release liner was peeled off from the adhesive sheet of the sheet piece. Next, the exposed surface of the adhesive sheet was attached to a glass slide (manufactured by Matsunami Glass Co., Ltd.). Next, the heavy release liner was peeled off from the adhesive sheet on the glass slide. This yielded a sample for haze measurement.

[0099] Next, the haze of the sample was measured in accordance with JIS K7136:2000 using a haze meter "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd. In this measurement, the measurement results obtained by measuring only the glass slide under the same conditions were used as the baseline. The haze (%) of each pressure-sensitive adhesive sheet was calculated based on the haze H ０ The values ​​are shown in Table 1.

[0100] On the other hand, for each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples, the haze H ０ The haze H at 150% elongation was measured in the same manner as 150 In preparing a sample for haze measurement, both release liners were peeled off from a piece of PSA sheet with release liners (width 5 mm × length 5 mm), and then the PSA sheet was stretched in the length direction to 150% of its original length and then attached to a glass slide.

[0101] The measurement results are shown in haze H at 150% elongation. 150 The values ​​are shown in Table 1. 150 and Hayes H. ０ The absolute value of the difference ΔH (= |H 150 -H ０ |) values ​​are also shown in Table 1.

[0102] <Tensile Test> The following first tensile test was carried out on each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples.

[0103] Specifically, the required number of test pieces were first prepared for each PSA sheet. In preparing the test pieces, a release-liner PSA sheet piece (40 mm wide x 40 mm long) was first cut out from a release-liner PSA sheet. Next, one release liner was peeled off from the sheet piece, and the PSA sheet piece was then rolled lengthwise onto the other release liner, taking care to avoid trapping air bubbles, to form a cylindrical shape (cylinder height 40 mm). In this way, a cylindrical PSA sheet piece was obtained as a test piece.

[0104] Next, a tensile test was performed on the test piece using a Tensilon type tensile tester (product name "Autograph AG-50NX plus" manufactured by Shimadzu Corporation) in an environment of 23°C and relative humidity of 50% (first tensile test). In this tensile test, the initial chuck distance was 10 mm, the tensile speed was 10 mm / min, and the test piece (cylindrical adhesive sheet piece) was pulled in the height direction of the cylindrical shape until it broke. The strain at the time of breakage (yield point) of the test piece in the first tensile test was referred to as the yield strain Y. １ The yield strain is shown as a percentage in Table 1. The yield strain is the initial length L of the test piece in the tensile direction in the tensile test. ０ The ratio of the elongation length ΔL of the test piece at the time when the test piece broke to the elongation length ΔL (ΔL / L ０ The elongation length ΔL is the initial length L of the test piece. ０ This is the amount of expansion from

[0105] A second tensile test was also carried out on another test piece of each PSA sheet of the Examples and Comparative Examples. The second tensile test was the same as the first tensile test, except that the tensile speed was changed from 10 mm / min to 1500 mm / min. The strain at break of the test piece in the second tensile test was defined as the yield strain Y ２ The results are shown in Table 1 as percentages.

[0106] On the other hand, for other test pieces of each pressure-sensitive adhesive sheet of the Examples and Comparative Examples, the stress generated in the test piece was measured while the following steps 1 to 3 were sequentially performed, and one cycle was repeated 10 times to examine the stress retention. The stress at the end of step 1 of the first cycle was defined as stress S １ The stress at the end of step 2 of the 10th cycle is shown in Table 1. １０ The stress S is shown in Table 1.１ Stress S １０ The ratio (S １０ / S １ ) are also shown in Table 1.

[0107] Step 1: In an environment of 23°C and 50% relative humidity, the test piece was pulled to an elongation length of 150% using a tensile tester (Autograph AG-50NX plus) (third tensile test). In this tensile test, the initial chuck distance was 10 mm, the pulling speed was 20 cm / min, and the test piece (cylindrical PSA sheet piece) was pulled in the height direction of the cylinder.

[0108] Step 2: The specimen was held at 150% elongation for 300 seconds.

[0109] Step 3: The specimen was returned to its original length (0% elongation).

[0110] The adhesive sheets of Comparative Examples 1 to 3 each had a maximum height Sz of the adhesive surface that greatly exceeded 500 nm. In such adhesive sheets, surface irregularities on the adhesive surface become larger when the adhesive sheet is stretched. Such adhesive sheets are not suitable for flexible device applications. The adhesive sheet of Comparative Example 3 had a haze H 150 and the haze H when not stretched ０ The difference between the ratio (S １０ / S １ ) was less than 60%, and the stress retention was low. Such a pressure-sensitive adhesive sheet is also not suitable for flexible device applications.

[0111] In contrast, the pressure-sensitive adhesive sheets of the Examples had a maximum height Sz of the adhesive surface of 500 nm or less, and the above-mentioned haze difference ΔH was 1.0%. Such pressure-sensitive adhesive sheets are suitable for use in flexible devices in suppressing the occurrence of large surface irregularity defects and suppressing an increase in haze. In addition, the pressure-sensitive adhesive sheets of the Examples had a ratio (S １０ / S １ ) significantly exceeded 60%, and the stress retention was high.

[0112]

[0113] The above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be interpreted as limiting. Modifications of the present invention that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0114] The optical pressure-sensitive adhesive sheet and the optical pressure-sensitive adhesive sheet with a release liner of the present invention are suitably used, for example, in the production of display panels.

[0115] X: Pressure-sensitive adhesive sheet with release liner H: Thickness direction 10: Pressure-sensitive adhesive sheet 11: Adhesive surface (first adhesive surface) 12: Adhesive surface (second adhesive surface) 20: Release liner (first release liner) 21: Release surface 30: Release liner (second release liner) 31: Release surface

Claims

1. An optical adhesive sheet having a first adhesive surface and a second adhesive surface opposite to the first adhesive surface, wherein the maximum height Sz of the first adhesive surface and the second adhesive surface is 500 nm or less, and the haze H at 150% elongation is 150 (%) and haze H when not stretched ０ (%) is |H 150 -H ０ An optical adhesive sheet that satisfies |≦1.

0.

2. Hayes H ０ The optical adhesive sheet according to claim 1 , wherein the optical adhesive sheet has a refractive index of 2.0% or less.

3. Yield strain Y in the first tensile test at 23°C and a tensile speed of 10 mm / min １ The optical pressure-sensitive adhesive sheet according to claim 1 , wherein the optical coefficient of curvature is 150% or more.

4. Yield strain Y in the second tensile test at 23°C and a tensile speed of 1500 mm / min ２ The optical pressure-sensitive adhesive sheet according to claim 1 , wherein the optical coefficient of curvature is 150% or more.

5. After the first third tensile test under the conditions of 23° C., tensile speed 20 cm / min and elongation length 150%, the strain stress S １ and after the tenth third tensile test, the strain stress S １０ and the stress S １ The stress S １０ The optical adhesive sheet according to claim 1 , wherein the ratio is 0.5 or more.

6. An optical adhesive sheet with a release liner, comprising: an optical adhesive sheet according to any one of claims 1 to 5; a first release liner releasably contacting the first adhesive surface; and a second release liner releasably contacting the second adhesive surface.

7. An optical adhesive sheet with release liner as described in claim 6, wherein the maximum height Sz of the surface of the first release liner facing the optical adhesive sheet is 2000 nm or less, and the maximum height Sz of the surface of the second release liner facing the optical adhesive sheet is 2000 nm or less.

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