Adhesive sheet, polarizing plate with adhesive, image display apparatus and its manufacturing method

Abstract

The adhesive sheet (21) is composed of an adhesive composition including an acrylic base polymer and a UV absorber. The light transmittance of the adhesive sheet at a wavelength of 380 nm is preferably 5% or less. The monomer component constituting the acrylic base polymer preferably has a small amount of polar monomers, such as hydroxyl group-containing monomers, carboxyl group-containing monomers, and nitrogen atom-containing monomers.

Description

Technology Field

[0001] The present invention relates to an adhesive sheet and an adhesive-equipped polarizing plate used in the formation of an image display device, an image display device, and a method for manufacturing the same. Background Technology

[0002] Liquid crystal displays and organic EL displays are widely used as various image display devices such as mobile phones, smartphones, car navigation devices, personal computer monitors, and televisions. In liquid crystal displays, a polarizer is placed on the visible side surface of the liquid crystal cell based on its display principle. In self-emissive display devices such as organic EL, a circular polarizer (a stack of a polarizer and a quarter-wave plate) is placed on the visible side surface of the cell to suppress the external light from being reflected from the metal electrode (cathode) and appearing as a mirror.

[0003] On the viewing side surface of the image display device, a front transparent plate (also called a "cover window"), such as a transparent resin plate or a glass plate, is provided for the purpose of preventing damage to the image display panel due to impact from the outer surface. The cover window is bonded with a polarizing plate placed on the viewing side surface of the image display panel by interposing an adhesive sheet.

[0004] As for polarizers, a laminated configuration in which a transparent protective film is bonded to both sides of a polarizer is common, but from the perspective of thinning or making image display devices flexible, a configuration in which the transparent protective film on one or both sides of the polarizer is omitted has been proposed. For example, Patent Document 1 discloses a configuration in which a cover window is bonded by interposing an adhesive sheet placed in contact with the polarizer. Prior art literature

[0005] International Publication No. 2017 / 216886 The problem to be solved

[0006] It has been found that an image display device in which a cover window is bonded by an adhesive sheet provided in contact with the visible surface of a polarizer has durability issues, such as the polarizer being prone to yellowing during weathering tests or fading during humidification durability tests. Furthermore, if the composition of the adhesive placed in contact with the polarizer is adjusted to increase durability, the reliability of the adhesion tends to decrease. Taking these problems into account, the present invention aims to provide an adhesive sheet capable of forming an image display device that contributes to thinning, is resistant to discoloration of the polarizer or delamination between the polarizer and the cover window, and possesses excellent durability. means of solving the problem

[0007] One embodiment of the present invention is an adhesive sheet used for bonding a polarizer made of a polyvinyl alcohol-based film containing iodine and a cover window of an image display device. The adhesive sheet is composed of an adhesive composition comprising an acrylic base polymer and a UV absorber, and is disposed in contact with the polarizer. The light transmittance of the adhesive sheet at a wavelength of 380 nm is preferably 5% or less.

[0008] The acrylic base polymer included in the adhesive composition preferably has a nitrogen-containing monomer content of 5 parts by weight or less, a hydroxyl group-containing monomer content of 0.1 to 8 parts by weight, and a carboxyl group-containing monomer content of 1 part by weight or less, based on a total of 100 parts by weight of monomer components.

[0009] The acrylic base polymer may contain 20 to 75 parts by weight of a high Tg monomer that does not contain any hydroxyl groups, carboxyl groups, or nitrogen atoms, and has a glass transition temperature of 10°C or higher, based on 100 parts by weight of the total monomer components. The high Tg monomer may be a (meth)acrylic acid ester having an alicyclic structure.

[0010] The acrylic base polymer may contain 20 to 79 parts by weight of (meth)acrylate alkyl ester having a glass transition temperature of -40°C or lower, based on 100 parts by weight of the total monomer components.

[0011] The acrylic base polymer may have a crosslinked structure formed by a thermal crosslinking agent.

[0012] The adhesive composition constituting the adhesive sheet may include a photopolymerizable polyfunctional compound having two or more photopolymerizable functional groups in one molecule and a photopolymerization initiator.

[0013] One embodiment of the present invention is an adhesive-equipped polarizing plate comprising a polyvinyl alcohol-based film containing iodine, wherein the adhesive sheet is disposed in contact with the first main surface of a polarizer having a first main surface and a second main surface. The adhesive-equipped polarizing plate may further comprise an adhesive sheet on the second main surface side of the polarizer. The adhesive sheet disposed on the second main surface side of the polarizer may be in contact with the second main surface of the polarizer, or may be laminated with another layer interposed on the second main surface of the polarizer.

[0014] One embodiment of the present invention is an image display device comprising, in this order, a second adhesive sheet, a polarizer made of a polyvinyl alcohol-based film containing iodine, a first adhesive sheet, and a cover window on the surface of an image display cell, wherein the first adhesive sheet is the adhesive sheet and is disposed in contact with the polarizer.

[0015] When the adhesive composition constituting the adhesive sheet includes a photopolymerizable polyfunctional compound and a photopolymerization initiator, in forming an image display device, after bonding a polarizer and a cover window with the first adhesive sheet interposed therebetween, the adhesive composition may be photocured by irradiating an active light from the cover window side. Effects of the invention

[0016] An image display device having an adhesive sheet of an embodiment of the present invention placed in contact with the visible side surface of a polarizer suppresses discoloration or fading of the polarizer caused by external ultraviolet rays, heating, humidity, etc., and has excellent durability and interlayer adhesion reliability. Brief explanation of the drawing

[0017] FIG. 1 is a cross-sectional view schematically illustrating one embodiment of an image display device. Figure 2 is a cross-sectional view illustrating one form of a polarizing plate equipped with an adhesive. Figure 3 is a cross-sectional view illustrating one form of a polarizing plate equipped with an adhesive. Specific details for implementing the invention

[0018] One embodiment of the present invention is an adhesive sheet disposed in contact with the visible side surface of a polarizer in an image display device, and is used for bonding a polarizer and a cover window.

[0019] FIG. 1 is a cross-sectional view illustrating one form of an image display device having a cover window on the visible side surface. The image display device (100) has a polarizing plate (10) bonded to the surface of an image display cell (60) by interposing an adhesive sheet (22), and has a cover window (70) bonded to the polarizing plate (10) by interposing an adhesive sheet (21) of an embodiment of the present invention.

[0020] The polarizing plate (10) comprises a polarizer (11) made of a polyvinyl alcohol-based film containing iodine. In the polyvinyl alcohol-based polarizer containing iodine, the polymer chains of polyvinyl alcohol and polyiodide ions (I3 - and I5 - The polymer chains form a complex, and as the polymer chains are oriented in a predetermined direction, the polyiodide ions are oriented and exhibit polarization performance.

[0021] A suitable optical layer (15) may be provided on the second main surface (the side facing the image display cell (60)) of the polarizer (11). On the first main surface (the side facing the viewer) of the polarizer (11), an adhesive sheet (21) of an embodiment of the present invention is disposed in contact with the polarizer (11). By disposing of the adhesive sheet (21) on the side facing the polarizer (11) without interposing another optical layer, the image display device can be made thinner or more flexible.

[0022] [Adhesive Sheet]

[0023] Base Polymer

[0024] The adhesive composition constituting the adhesive sheet (21) contains an acrylic base polymer. The acrylic base polymer contains (meth)acrylate alkyl ester as a main constituent monomer component. In addition, in this specification, "(meth)acrylate" means acrylic and / or methacrylate.

[0025] As for the (meth)acrylate alkyl ester, an (meth)acrylate alkyl ester having 1 to 20 carbon atoms in the alkyl group is suitably used. The (meth)acrylate alkyl ester may have a branched alkyl group or a cyclic alkyl group (alicyclic alkyl group).

[0026] Specific examples of (meth)acrylate alkyl esters having a chain alkyl group include (meth)acrylate methyl, (meth)acrylate ethyl, (meth)acrylate 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 octyl, (meth)acrylate isooctyl, (meth)acrylate nonyl, (meth)acrylate isononyl, (meth)acrylate decyl, (meth)acrylate isodecyl, (meth)acrylate undecyl, (meth)acrylate dodecyl. Examples include (meth)acrylate isododecyl, (meth)acrylate tetradecyl, (meth)acrylate isotetradecyl, (meth)acrylate pentadecyl, (meth)acrylate cetyl, (meth)acrylate heptadecyl, (meth)acrylate octadecyl, (meth)acrylate isooctadecyl, (meth)acrylate nonadecyl, (meth)acrylate eicosyl, etc.

[0027] Specific examples of (meth)acrylate alkyl esters having a dicyclic alkyl group include (meth)acrylate cycloalkyl esters such as (meth)acrylate cyclopentyl, (meth)acrylate cyclohexyl, (meth)acrylate cycloheptyl, (meth)acrylate cyclooctyl, etc.; (meth)acrylate esters having a bicyclic aliphatic hydrocarbon group such as (meth)acrylate isobornyl, etc.; Examples of (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings include dicyclofentanyl (meth)acrylate, dicyclofentanyloxyethyl (meth)acrylate, tricyclofentanyl (meth)acrylate, 1-adamanthyl (meth)acrylate, 2-methyl-2-adamanthyl (meth)acrylate, and 2-ethyl-2-adamanthyl (meth)acrylate. An alkyl (meth)acrylic acid ester having a ring-like alkyl group may have a substituent on a ring such as 3,3,5-trimethylcyclohexyl (meth)acrylate. Additionally, an alkyl (meth)acrylic acid ester having a ring-like alkyl group may be a (meth)acrylic acid ester containing a condensed ring of a ring structure having an unsaturated bond with a ring-like structure, such as dicyclofentanyl (meth)acrylate.

[0028] The amount of (meth)acrylate alkyl ester per 100 parts by weight of the total monomer component constituting the acrylic base polymer is preferably 60 parts by weight or more, more preferably 70 parts by weight or more, even more preferably 80 parts by weight or more, and may be 85 parts by weight or more, 90 parts by weight or more, or 92 parts by weight or more.

[0029] It is preferable that the acrylic base polymer contains an acrylic monomer having crosslinkable functional groups as a copolymer monomer component. By having crosslinkable functional groups in the base polymer, the base polymer can react with a crosslinking agent to increase the cohesive strength of the adhesive and improve adhesive reliability.

[0030] Examples of acrylic monomers having crosslinkable functional groups include hydroxyl group-containing monomers and carboxyl group-containing monomers. For instance, when an isocyanate-based crosslinking agent is used, a crosslinked structure is introduced through the reaction between the hydroxyl group and the isocyanate group. When an epoxy-based crosslinking agent is used, a crosslinked structure is introduced through the reaction between the carboxyl group and the epoxy group. As described below, from the perspective of making the adhesive acid-free, it is preferable to use a hydroxyl group-containing monomer as a copolymer component of the base polymer and to introduce a crosslinked structure using an isocyanate-based crosslinking agent. When the base polymer contains a hydroxyl group-containing monomer as a monomer component, the crosslinkability of the base polymer increases, and the clouding of the adhesive under high temperature and high humidity environments tends to be suppressed, resulting in a highly transparent adhesive.

[0031] Examples of hydroxyl group-containing monomers include (meth)acrylic acid 2-hydroxyethyl, (meth)acrylic acid 2-hydroxypropyl, (meth)acrylic acid 4-hydroxybutyl, (meth)acrylic acid 6-hydroxyhexyl, (meth)acrylic acid 8-hydroxyoctyl, (meth)acrylic acid 10-hydroxydecyl, (meth)acrylic acid 12-hydroxylauryl, and (meth)acrylic acid esters such as (4-hydroxymethylcyclohexyl)-methylacrylate. Among these, 2-hydroxyethyl acrylic acid (Tg of homopolymer: -15°C) and 4-hydroxybutyl acrylic acid (Tg of homopolymer: -32°C) are preferred because they contribute significantly to improving adhesion and can also suppress clouding of the adhesive sheet under high humidity environments.

[0032] The amount of hydroxyl group-containing monomer per 100 parts by weight of the total monomer components constituting the acrylic base polymer is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, more preferably 0.8 parts by weight or more, and may be 1 part by weight or more, 1.5 parts by weight or more, or 2 parts by weight or more. By increasing the amount of hydroxyl group-containing monomer, the unreacted functional groups of the crosslinking agent are reduced, so the degree of crosslinking can be increased with a small amount of crosslinking agent, thereby improving adhesion reliability.

[0033] Meanwhile, if the amount of hydroxyl group-containing monomer in the base polymer is excessively large, the hydrophilicity and moisture permeability of the adhesive sheet increase along with the increase in polarity of the polymer, and the polarizer (11) placed in contact with the adhesive sheet (21) is prone to fading under high temperature and high humidity conditions. When the hydrophilicity and moisture permeability of the adhesive sheet are high, moisture from the external environment is prone to reaching the polarizer, and it is thought that the disturbance of the orientation of the polymer chains constituting the polarizer due to moisture, or the detachment of polyiodide ions from the polymer chains, is a factor in the fading of the polarizer. The amount of hydroxyl group-containing monomer per 100 parts by weight of the total monomer component constituting the acrylic base polymer is preferably 8 parts by weight or less, more preferably 7 parts by weight or less, and may be 6 parts by weight or less or 5 parts by weight or less.

[0034] The acrylic base polymer may include monomer components other than those mentioned above. As monomer components, the acrylic base polymer may include, for example, vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, etc.

[0035] The acrylic base polymer may include a nitrogen-containing monomer as a monomer component. Examples of nitrogen-containing monomers include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylcarboxylic acid amides, N-vinylcaprolactam, acrylonitrile, methacrylonitrile, etc.

[0036] When an acrylic base polymer includes a nitrogen-containing monomer as a monomer component, the cohesive strength is improved and the adhesive reliability tends to increase. On the other hand, as the amount of nitrogen-containing monomer in the base polymer included in the adhesive increases, the polarizer (11) placed in contact with the adhesive sheet (21) is prone to fading. Since nitrogen atoms are easily coordinated to iodine, if the amount of nitrogen atoms included in the base polymer of the adhesive sheet increases, it is thought that one of the factors causing the polarizer to fade is that the iodine fixed to the polymer chain of the polarizer is coordinated with the nitrogen atoms of the adhesive and detached from the polymer chain. The amount of nitrogen-containing monomer per 100 parts by weight of the total monomer component constituting the acrylic base polymer is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and may be 1 part by weight or less, 0.5 parts by weight or less, 0.1 parts by weight or less, or 0.05 parts by weight or less. The acrylic base polymer may not include nitrogen-containing monomers as monomer components.

[0037] If the acid component contained in the adhesive sheet migrates to the polarizer, it can promote the hydrolysis of polyvinyl alcohol and cause the polarizer to deteriorate. Therefore, it is desirable for the adhesive sheet (21) to have a low content of organic acid monomers (free organic acids), such as (meth)acrylic acid. In thermosetting or photocuring polymers, the presence of unreacted residual monomers is inevitable. Therefore, in order to reduce the acid monomer content in the adhesive sheet, it is desirable to reduce the amount of organic acid monomer components, such as (meth)acrylic acid, in the monomer components constituting the base polymer. The content of carboxyl group-containing monomers relative to the total amount of constituent monomer components of the acrylic base polymer is preferably 1 part by weight or less, more preferably 0.5 parts by weight or less, and even more preferably 0.1 parts by weight or less. It is desirable for the acrylic base polymer not to contain carboxyl group-containing monomers as monomer components.

[0038] In order to suppress fading of the polarizer (11) in a high temperature and high humidity environment, it is preferable that the base polymer constituting the adhesive sheet (21) placed in contact with the polarizer (11) be of low polarity. In order to lower the polarity of the base polymer, it is preferable that the content of polar monomers, such as nitrogen-containing monomers, hydroxyl group-containing monomers, and carboxyl group-containing monomers, be small as constituent monomer components. The content of polar monomers per 100 parts by weight of the total constituent monomer components of the acrylic base polymer is preferably 12 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 8 parts by weight or less, and may be 6 parts by weight or less or 5 parts by weight or less.

[0039] The acrylic base polymer does not need to include polar monomers as constituent monomer components. However, from the perspective of introducing a crosslinked structure to the base polymer using a thermal crosslinking agent such as an isocyanate-based crosslinking agent, it is preferable to include at least 0.1 parts by weight of polar monomers, such as hydroxyl group-containing monomers. The content of polar monomers relative to 100 parts by weight of the total constituent monomer components of the acrylic base polymer is more preferably 0.5 parts by weight or more, more preferably 0.8 parts by weight or more, and may be 1 part by weight or more, 1.5 parts by weight or more, or 2 parts by weight or more.

[0040] In order to increase the cohesive strength of an acrylic base polymer with a low content of polar monomer components and to increase adhesive reliability, it is desirable that the acrylic base polymer include, as constituent monomer components, a high Tg monomer that does not contain hydroxyl groups, carboxyl groups, and nitrogen atoms, and also has a glass transition temperature of 10°C or higher.

[0041] As high-Tg monomers that do not contain polar groups, styrene (Tg: 80°C), methyl methacrylate (Tg: 105°C), cyclohexyl acrylate (Tg: 15°C), cyclohexyl methacrylate (Tg: 66°C), 3,3,5-trimethylcyclohexyl acrylate (Tg: 52°C), dicyclofentanyl methacrylate (Tg: 175°C), dicyclofentanyl acrylate (Tg: 120°C), dicyclofentanyl acrylate (Tg: 120°C), isobornyl methacrylate (Tg: 173°C), isobornyl acrylate (Tg: 97°C), 1-adamantyl methacrylate (Tg: 250°C), 1-adamantyl acrylate (Tg: 153°C), etc. Examples may be provided. Among these high-Tg monomers, acrylic acid esters are preferred because they exhibit excellent copolymerization with the low-Tg monomer (lower alkyl acrylic acid ester) described later. Additionally, since both acrylic acid esters and methacrylic acid esters can exhibit high Tg, (meth)acrylic acid esters having an alicyclic structure are preferred as high-Tg monomers, and among them, acrylic acid esters having an alicyclic structure such as cyclohexyl acrylate, dicyclofentanyl acrylate, dicyclopentenyl acrylate, isobornyl acrylate, and 1-adamantyl acrylate are preferred. For high-Tg monomers, the glass transition temperature of the homopolymer may be 13°C or higher or 15°C or higher.

[0042] From the perspective of increasing the adhesive reliability of the adhesive sheet, the content of a high-Tg monomer that does not contain polar groups, based on 100 parts by weight of the total constituent monomer components of the acrylic base polymer, is preferably 20 parts by weight or more, more preferably 25 parts by weight or more, and even more preferably 30 parts by weight or more. On the other hand, if the content of the high-Tg monomer is excessively large, the glass transition temperature of the base polymer increases, and the adhesiveness or impact resistance at low temperatures may decrease. Therefore, based on 100 parts by weight of the total constituent monomer components of the acrylic base polymer, the content of a high-Tg monomer that does not contain polar groups is preferably 75 parts by weight or less, more preferably 70 parts by weight or less, and may be 65 parts by weight or less, 60 parts by weight or less, 55 parts by weight or less, or 50 parts by weight or less.

[0043] From the perspective of achieving compatibility between the adhesive reliability of the adhesive sheet and adhesiveness or impact resistance at low temperatures, the glass transition temperature of the acrylic base polymer is preferably -50 to 10°C, more preferably -45 to 5°C, and even more preferably -40 to 0°C. The glass transition temperature of the acrylic base polymer can be calculated based on the theoretical Tg. The theoretical Tg is the glass transition temperature Tg of the homopolymer of the constituent monomer components of the base polymer. i Wow, the weight fraction W of each monomer component i From, it is calculated by the following Fox formula.

[0044] 1 / Tg=Σ(W i / Tg i )

[0045] Tg is the glass transition temperature of the base polymer (unit: K), W i is the weight fraction of monomer component i constituting the base polymer (copolymerization ratio based on weight), Tg iTg is the glass transition temperature (unit: K) of the homopolymer of monomer component i. As the glass transition temperature of the homopolymer, the values ​​listed in the Polymer Handbook, 3rd edition (John Wiley & Sons, Inc., 1989) may be adopted. For the Tg of the homopolymer of monomers not listed in the above literature, the peak top temperature of the loss tangent (tanδ) obtained by dynamic viscoelasticity measurement may be adopted.

[0046] In order to keep the glass transition temperature of an acrylic base polymer containing 20 parts by weight or more of a high-Tg monomer as a monomer component within the above range, it is preferable that the acrylic base polymer includes a low-Tg monomer as a monomer component, wherein the glass transition temperature of the homopolymer is -40°C or lower. Examples of low-Tg monomers include chain-shaped alkyl esters of acrylic acid such as 2-ethylhexyl acrylate (Tg: -70°C), n-hexyl acrylate (Tg: -65°C), n-octyl acrylate (Tg: -65°C), isononyl acrylate (Tg: -60°C), n-nonyl acrylate (Tg: -58°C), isooctyl acrylate (Tg: -58°C), and butyl acrylate (Tg: -55°C). Among these, butyl acrylate and 2-ethylhexyl acrylate are particularly preferred.

[0047] The content of (meth)acrylate alkyl ester, having a glass transition temperature of -40°C or lower, relative to 100 parts by weight of the total constituent monomer components of the acrylic base polymer, is preferably 20 to 79 parts by weight, more preferably 25 to 70 parts by weight, and may be 30 to 65 parts by weight.

[0048] An acrylic base polymer is obtained by polymerizing the above monomer components using various known methods, such as solution polymerization, emulsion polymerization, or bulk polymerization. From the perspective of the balance of properties such as adhesive strength and holding power, as well as cost, the solution polymerization method is suitable. Generally, ethyl acetate, toluene, etc., are used as solvents for solution polymerization. The solution concentration is typically about 20 to 80 weight%. As a polymerization initiator, thermal polymerization initiators such as azo-based initiators, peroxide-based initiators, or redox-based initiators combining peroxide and a reducing agent (e.g., a combination of persulfate and sodium bisulfite, or a combination of peroxide and sodium ascorbate) are preferably used. Although the amount of polymerization initiator used is not particularly limited, for example, about 0.005 to 5 weight parts per 100 weight parts of the total monomer components forming the base polymer is preferable, and about 0.02 to 3 weight parts is more preferable.

[0049] A chain transfer agent may be used to adjust the molecular weight of the base polymer. The chain transfer agent can absorb radicals from the growing polymer chain to stop the elongation of the polymer, and at the same time, the chain transfer agent that absorbed the radicals can attack the monomer to restart polymerization. Therefore, by using a chain transfer agent, the increase in the molecular weight of the base polymer can be suppressed without lowering the radical concentration in the reaction system. Thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolic acid, and 2,3-dimercapto-1-propanol are suitably used as chain transfer agents.

[0050] Although the amount of chain transfer agent used is not particularly limited, if the amount of chain transfer agent used is excessively large, the molecular weight of the base polymer decreases, and the processability and dimensional stability of the adhesive sheet before photocuring may decrease. Therefore, the amount of chain transfer agent used is preferably 1 part by weight or less, more preferably 0.3 parts by weight or less, even more preferably 0.15 parts by weight or less, and particularly preferably 0.1 parts by weight or less, based on 100 parts by weight of the total amount of monomer components constituting the base polymer.

[0051] The weight average molecular weight of the acrylic base polymer is preferably 100,000 to 3 million, more preferably 250,000 to 2 million, and even more preferably 500,000 to 1.5 million. In addition, when a cross-linked structure is introduced into the acrylic base polymer, the molecular weight of the base polymer refers to the molecular weight before the introduction of the cross-linked structure.

[0052] <Cross-linked structure of base polymer>

[0053] It is preferable that the acrylic base polymer has a cross-linked structure. As a method for introducing a cross-linked structure into the base polymer, generally, (1) a method of reacting the base polymer with the cross-linked agent by adding a cross-linked agent after polymerizing a base polymer having functional groups that can react with the cross-linked agent; and (2) a method of introducing a branched structure (cross-linked structure) into the polymer chain by including a photopolymerizable polyfunctional compound in the polymerization component of the base polymer.

[0054] In the adhesive composition constituting the adhesive sheet (21) that is placed in contact with the polarizer (11), it is preferable that the acrylic base polymer has a cross-linked structure introduced by the method of (1) above. The adhesive composition constituting the adhesive sheet (21) may include a photopolymerizable polyfunctional compound and a photopolymerization initiator, and the cross-linked structure of (2) above may be introduced by performing photocuring after bonding the adhesive sheet (21) and the cover window (70). That is, in the adhesive composition constituting the adhesive sheet (21), it is preferable that the base polymer has a cross-linked structure by a (thermal)crosslinking agent such as an isocyanate-based crosslinking agent, and it may also be possible to introduce a cross-linked structure by a photopolymerizable polyfunctional compound (photocrosslinking agent) by photocuring.

[0055] <Adhesive Composition>

[0056] An adhesive composition is prepared by mixing a crosslinking agent, a photopolymerizable polyfunctional compound, a photopolymerization initiator, and, if necessary, oligomers or various additives with an acrylic base polymer. The adhesive composition preferably has a viscosity suitable for application onto a substrate (e.g., about 0.5 to 20 Pa·s). By adjusting the molecular weight of the base polymer, the amount of the photopolymerizable polyfunctional compound added, and the composition, molecular weight, and amount added of other components (e.g., oligomers), the viscosity of the adhesive composition can be set to an appropriate range. Thickening additives may be used for the purpose of adjusting viscosity.

[0057] (UV absorber)

[0058] It is preferable that the adhesive sheet (21) has ultraviolet absorption properties. In a polarizing plate in which a transparent protective film is provided on the viewing side surface of the polarizer, the transparent protective film generally has ultraviolet absorption properties, thereby suppressing the deterioration of the polarizer caused by ultraviolet rays incident from outside the display device. On the other hand, in a configuration where the adhesive sheet (21) is placed in contact with the viewing side surface of the polarizer (11), since a transparent protective film is not provided on the viewing side of the polarizer, the adhesive sheet (21) is made to have ultraviolet absorption properties, thereby suppressing photodeterioration of the polarizer (11) caused by ultraviolet rays (e.g., structural change of polyiodide ions (I5) - from I3 - It is desirable to prevent color change of the polarizer accompanying changes in etc.

[0059] In order to provide the adhesive sheet (21) with ultraviolet absorption properties, it is preferable that the adhesive composition includes an ultraviolet absorber. Examples of ultraviolet absorbers include benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, triazine-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers. Triazine-based ultraviolet absorbers and benzotriazole-based ultraviolet absorbers are preferred because they have high ultraviolet absorption properties, excellent compatibility with acrylic polymers, and are easy to obtain a highly transparent acrylic adhesive. Among these, triazine-based ultraviolet absorbers containing hydroxyl groups and benzotriazole-based ultraviolet absorbers having one benzotriazole backbone in one molecule are preferred.

[0060] Commercially available products may be used as UV absorbers. Commercially available triazine-based UV absorbers include the reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine-2-yl)-5-hydroxyphenyl and [(alkyloxy)methyl]oxirane (BASF “TINUVIN 400”), the reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine and (2-ethylhexyl)-glycidic acid ester (BASF “TINUVIN 405”), (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine (BASF “TINUVIN 460”), Examples include 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[(hexyl)oxy]-phenol (BASF “TINUVIN 577”), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine (BASF “TINUVIN 479”), 5,5'-bis(2-ethylhexyloxy)-2,2'-[6-(4-methoxyphenyl)-1,3,5-triazine-2,4-diyl]diphenol (BASF “Tinosorb S”), 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]-phenol (ADEKA “ADK STAB LA-46”), etc. It is possible.

[0061] Commercially available benzotriazole-based UV absorbers include 2-(2H-benzotriazole-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF “TINUVIN 928”), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (BASF “TINUVIN PS”), 2-(2H-benzotriazole-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (BASF “TINUVIN 900”), 2-(2H-benzotriazole-2-yl)-6-dodecyl-4-methylphenol (BASF “TINUVIN 571”), and 2-(2H-benzotriazole-2-yl)-p-cresol (BASF “TINUVIN P”). 2-(2H-benzotriazole-2-yl)-4-6-bis(1-methyl-1-phenylethyl)phenol (BASF “TINUVIN 234”), 2-[5-chloro(2H)-benzotriazole-2-yl]-4-methyl-6-(tert-butyl)phenol (BASF “TINUVIN 326”), 2-(2H-benzotriazole-2-yl)-4,6-di-tert-pentylphenol (BASF “TINUVIN 328”), 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF “TINUVIN 329”), benzenepropanoic acid and 3-(2H-benzotriazole-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy(C7-9 side chain) Examples include ester compounds of (and straight-chain alkyl) (BASF “TINUVIN 384-2”), reaction product of methyl-3-(3-(2H-benzotriazole-2-yl)-5-t-butyl-4-hydroxyphenyl)propionate and polyethylene glycol (BASF “TINUVIN 1 130”), reaction product of methyl-3-(3-(2H-benzotriazole-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate and polyethylene glycol 300 (BASF “TINUVIN 213”), 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimidomethyl)-5-methylphenyl]benzotriazole (Sumitomo Chemical “Sumisorb 250”), etc.

[0062] When the adhesive composition contains an ultraviolet absorber, the content of the ultraviolet absorber per 100 parts by weight of the acrylic base polymer is approximately 0.05 to 10 parts by weight, preferably 0.1 to 5 parts by weight, and more preferably 0.3 to 3 parts by weight. By keeping the content of the ultraviolet absorber within the above range, the decrease in transparency caused by the bleed-out of the ultraviolet absorber is suppressed, and the adhesive sheet (21) is provided with ultraviolet shielding properties, thereby suppressing photodegradation of the polarizer caused by ultraviolet rays from the outside.

[0063] (Crosslinking agent)

[0064] As mentioned above, it is preferable for the acrylic base polymer to have a cross-linked structure. A cross-linked structure is introduced into the base polymer by adding a cross-linking agent to the adhesive composition and heating as necessary. To distinguish it from cross-linked structures introduced by photopolymerizable polyfunctional compounds, cross-linking by isocyanate-based cross-linking agents, etc., is sometimes described as "thermal cross-linking," but the introduction of a cross-linked structure by a cross-linking agent does not necessarily involve heating. By introducing a thermal cross-linked structure into the acrylic base polymer, the cohesiveness of the adhesive sheet increases, and adhesiveness tends to improve.

[0065] Examples of crosslinking agents include compounds that react with functional groups, such as hydroxyl groups, contained in the base polymer. Specific examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred due to their high reactivity with the hydroxyl groups of the base polymer and the ease of introducing a crosslinked structure.

[0066] As isocyanate-based crosslinking agents, polyisocyanates having two or more isocyanate groups in one molecule are used. Examples of isocyanate-based crosslinking agents include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; Examples of isocyanate adducts include trimethylolpropane / tolylene diisocyanate trimer adducts (e.g., the solvent "Coronate L"), trimethylolpropane / hexamethylene diisocyanate trimer adducts (e.g., the solvent "Coronate HL"), trimethylolpropane adducts of xylylene diisocyanate (e.g., Mitsui Chemicals' "Takenate D110N"), and isocyanurate adducts of hexamethylene diisocyanate (e.g., the solvent "Coronate HX").

[0067] By adjusting the amount of crosslinking agent added, the cohesiveness or adhesive strength of the adhesive can be adjusted. The amount of crosslinking agent added is preferably 0.01 to 1 weight part per 100 weight parts of base polymer, more preferably 0.05 to 0.7 weight parts, and even more preferably 0.1 to 0.5 weight parts.

[0068] (Photopolymerizable polyfunctional compound)

[0069] In order to make the adhesive sheet photocurable, it is preferable that the adhesive composition include a photopolymerizable polyfunctional compound. The photopolymerizable polyfunctional compound has two or more photopolymerizable functional groups in one molecule. The photopolymerizable functional groups may be radical polymerizable, cationic polymerizable, or anionic polymerizable, but radical polymerizable functional groups having an unsaturated double bond (ethylenically unsaturated group) are preferred due to their excellent reactivity. As for the photopolymerizable polyfunctional compound, a polyfunctional (meth)acrylate is preferred due to its high compatibility with an acrylic base polymer, and a polyfunctional acrylate is particularly preferred due to its high photoradical reactivity.

[0070] As polyfunctional (meth)acrylates, difunctional (meth)acrylic acid esters such as hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, bisphenol A ethylene oxide modified di(meth)acrylate, bisphenol A propylene oxide modified di(meth)acrylate, alkanediold di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, pentaerythritol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and glycerin di(meth)acrylate; Examples include trifunctional (meth)acrylic acid esters such as pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ethoxylated isocyanuric acid tri(meth)acrylate; tetrafunctional (meth)acrylic acid esters such as ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and quintally or more functional (meth)acrylic acid esters such as dipentaerythritol penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate.

[0071] From the perspective of increasing the adhesive reliability of the adhesive sheet after photocuring, the molecular weight of the photopolymerizable polyfunctional compound is preferably 1,500 or less, and more preferably 1,000 or less. The functional group equivalent (g / eq) of the polyfunctional compound is preferably 50 to 500, more preferably 70 to 300, and even more preferably 80 to 200. In terms of exhibiting suitable compatibility with the base polymer, the photopolymerizable polyfunctional compound is preferably liquid at room temperature.

[0072] The content of the photopolymerizable multifunctional compound in the adhesive composition is preferably 0.3 to 15 parts by weight per 100 parts by weight of the acrylic base polymer, more preferably 0.5 to 10 parts by weight, and even more preferably 1 to 5 parts by weight. If the content of the photopolymerizable multifunctional compound is low, the adhesive reliability of the adhesive sheet after photocuring tends to be insufficient. On the other hand, if the content of the photopolymerizable multifunctional compound is excessively high, the proportion of the base polymer in the adhesive sheet (adhesive composition) before photocuring decreases, and the processability or dimensional stability of the adhesive sheet may decrease. In addition, if the content of the photopolymerizable multifunctional compound is excessively high, the adhesive sheet after photocuring becomes hard, and the adhesive strength or impact resistance of the adhesive sheet (21) at low temperatures may become insufficient.

[0073] (Photopolymerization initiator)

[0074] A photocurable adhesive composition comprising a photopolymerizable polyfunctional compound preferably includes a photopolymerization initiator. Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, etc. The content of the photopolymerization initiator in the adhesive composition is preferably 0.01 to 5 parts by weight per 100 parts by weight of the base polymer, and more preferably 0.05 to 3 parts by weight.

[0075] (Oligomer)

[0076] The adhesive composition may include various oligomers for the purpose of adjusting the adhesive strength or viscosity of the adhesive sheet. As for the oligomer, for example, one having a weight-average molecular weight of about 1,000 to 30,000 is used. As for the oligomer, an acrylic oligomer is preferred due to its excellent compatibility with an acrylic base polymer.

[0077] The acrylic oligomer contains (meth)acrylate alkyl esters as the main constituent monomer components. Among these, it is preferable to include (meth)acrylate alkyl esters having chain-like alkyl groups (chain-like alkyl (meth)acrylates) and (meth)acrylate alkyl esters having alicyclic alkyl groups (alicyclic alkyl (meth)acrylates) as constituent monomer components. Specific examples of chain-like alkyl (meth)acrylates and alicyclic alkyl (meth)acrylates are as previously exemplified as constituent monomers of the acrylic base polymer.

[0078] The glass transition temperature of the acrylic oligomer is preferably 20°C or higher, more preferably 50°C or higher, even more preferably 80°C or higher, and particularly preferably 100°C or higher. By using a low-Tg base polymer with a cross-linked structure and a high-Tg acrylic oligomer in combination, the adhesive strength of the adhesive sheet tends to improve. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, but generally it is 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. The glass transition temperature of the acrylic oligomer is calculated by the aforementioned Fox formula.

[0079] Among the alkyl (meth)acrylate esters exemplified, methyl methacrylate is preferred as a chain alkyl (meth)acrylate due to its high glass transition temperature and excellent compatibility with the base polymer. As a dicyclic alkyl (meth)acrylate, dicyclofentanyl acrylate, dicyclofentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. That is, the acrylic oligomer preferably comprises, as constituent monomer components, one or more selected from the group consisting of dicyclofentanyl acrylate, dicyclofentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate.

[0080] The amount of alicyclic alkyl (meth)acrylate relative to the total amount of monomer components constituting the acrylic oligomer is preferably 10 to 90 weight%, more preferably 20 to 80 weight%, and even more preferably 30 to 70 weight%. The amount of chain-like alkyl (meth)acrylate relative to the total amount of monomer components constituting the acrylic oligomer is preferably 10 to 90 weight%, more preferably 20 to 80 weight%, and even more preferably 30 to 70 weight%.

[0081] The weight average molecular weight of the acrylic oligomer is preferably 1,000 to 30,000, more preferably 1,500 to 10,000, and even more preferably 2,000 to 8,000. By using an acrylic oligomer having a molecular weight within this range, the adhesive strength or adhesive retention support of the adhesive sheet tends to be improved.

[0082] Acrylic oligomers are obtained by polymerizing the above monomer components by various polymerization methods. Various polymerization initiators may be used during the polymerization of acrylic oligomers. Additionally, chain transfer agents may be used for the purpose of adjusting the molecular weight.

[0083] When an oligomer component, such as an acrylic oligomer, is included in the adhesive composition, the content thereof is preferably 0.1 to 10 parts by weight and more preferably 0.2 to 5 parts by weight per 100 parts by weight of the base polymer. When the content of the oligomer in the adhesive composition is within the above range, an improvement in adhesion can be expected.

[0084] (Silanic coupling agent)

[0085] A silane coupling agent may be added to the adhesive composition for the purpose of adjusting adhesive strength, etc. When a silane coupling agent is added to the adhesive composition, the amount added is typically about 0.01 to 5.0 parts by weight per 100 parts by weight of base polymer, and preferably about 0.03 to 2.0 parts by weight.

[0086] (Antioxidant)

[0087] The adhesive composition may include an antioxidant. By including an antioxidant, the reaction or deterioration of the curable component caused by heat or light in the storage or usage environment of the adhesive composition or adhesive sheet can be suppressed. Examples of antioxidants include amine-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, and phenol-based antioxidants. Among these, it is preferable for them to act as radical chain inhibitors, such as amine-based antioxidants and phenol-based antioxidants, and phenol-based antioxidants having a hindered phenol structure are particularly preferred.

[0088] An antioxidant having a hindered phenol structure is one in which a group with high steric hindrance, such as a tert-butyl group, is bonded to at least one of the carbon atoms adjacent to the carbon atom on the aromatic ring to which the OH group of phenol is bonded. As antioxidants having a hindered phenol structure, dibutylhydroxytoluene (BHT), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (BASF “Irganox 1010”), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (BASF “Irganox 1076”), 3,3’,3”,5,5’,5”-hexa-tert-butyl-a,a’,a”-(mesitylene-2,4,6-toluyl)tri-p-cresol (BASF “Irganox 1330”), 1,3,5-Tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (BASF “Irganox 3114”), isocyanuric acid tris[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl](BASF “Irganox 3125”), pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate](ADEKA “ADEKASTAP AO-60”), 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane (ADEKA "AdekaStab AO-80"), 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl (Sumitomo Chemicals "Smilizer GS"), 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl (Sumitomo Chemicals "Smilizer GM"), 2,2'-dimethyl-2,2'-(2,4,8,10-tetraoxaspiro[5.Examples include 5] Undecane-3,9-diyl)dipropane-1,1'-diyl=bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propanoate] (Sumitomo Chemicals "Smilizer GA-80"), 1,3,5-tris(3-hydroxy-4-tert-butyl-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (Cytec "Cyanox 1790").

[0089] When the adhesive composition includes an antioxidant, from the perspective of suppressing unwanted curing reactions or deterioration, the content of the antioxidant is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, even more preferably 0.1 parts by weight or more, and may be 0.3 parts by weight or more or 0.5 parts by weight or more, per 100 parts by weight of the acrylic base polymer. On the other hand, if the content of the antioxidant is excessively high, it may cause inhibition of curing when the adhesive sheet is photocured. Therefore, the content of the antioxidant is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and even more preferably 3 parts by weight or less, per 100 parts by weight of the acrylic base polymer.

[0090] (Other additives)

[0091] In addition to each component exemplified above, the adhesive composition may include additives such as chain transfer agents, tackifiers, plasticizers, softeners, deterioration inhibitors, fillers, colorants, surfactants, and antistatic agents.

[0092] [Adhesive Sheet]

[0093] An adhesive sheet is formed on a substrate by applying an adhesive composition onto the substrate and, if necessary, drying and removing the solvent. Any suitable substrate is used for forming the adhesive sheet. The substrate may be a release film having a release layer on the surface of a resin film.

[0094] Examples of resin materials for the release film include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyarylate resins, and polyphenylene sulfide resins. Among these, polyester resins such as polyethylene terephthalate are particularly preferred. The thickness of the release film is preferably 10 to 200 μm, and more preferably 25 to 150 μm. Examples of materials for the release layer include silicone-based release agents, fluorine-based release agents, long-chain alkyl-based release agents, and fatty acid amide-based release agents. The thickness of the release layer is generally about 10 to 2000 nm.

[0095] Various methods such as roll coat, kiss roll coat, gravure coat, reverse coat, roll brush, spray coat, dip roll coat, bar coat, knife coat, air knife coat, curtain coat, rip coat, and die coater are used as methods for applying an adhesive composition onto a substrate.

[0096] When the adhesive composition contains a solvent, it is preferable to dry the solvent after applying the adhesive composition onto a substrate. As a drying method, an appropriate method may be employed depending on the purpose. The heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and particularly preferably 70°C to 170°C. An appropriately suitable drying time may be employed. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and particularly preferably 10 seconds to 10 minutes.

[0097] After drying the solvent, it is desirable to install a cover sheet to protect the surface of the adhesive sheet. As the cover sheet, it is preferable to use a release film that has a release layer on the contact surface with the adhesive sheet, similar to the base film.

[0098] After applying the adhesive composition onto a substrate, heating is performed as needed to introduce a crosslinked structure into the base polymer. The heating temperature and heating time can be appropriately set according to the type of crosslinking agent used, and are typically in the range of 20°C to 160°C for 1 minute to 7 days. Heating for drying the solvent may also serve as heating for crosslinking. As mentioned above, the introduction of the crosslinked structure does not necessarily involve heating.

[0099] A crosslinking catalyst may be used to promote the formation of a crosslinked structure. For example, as crosslinking catalysts for isocyanate-based crosslinking agents, metal-based crosslinking catalysts (especially tin-based crosslinking catalysts) such as tetra-n-butyl titanate, tetraisopropyl titanate, ferric nasem, butyl tin oxide, dioctyl tin dilaurate, and dibutyl tin dilaurate can be used.

[0100] By bonding a release film to the surface of an adhesive sheet, an adhesive sheet with release films attached to both sides is obtained. The substrate or cover sheet used during the formation of the adhesive sheet may also serve as the release film.

[0101] When release films are provided on both sides of the adhesive sheet, the thickness of one release film and the thickness of the other release film may be the same or different. The peeling force when peeling off the release film attached to one side of the adhesive sheet and the peeling force when peeling off the release film attached to the other side of the adhesive sheet may be the same or different.

[0102] The thickness of the adhesive sheet (21) used for bonding the polarizer (11) and the cover window (70) is preferably 30 μm or more, more preferably 40 μm or more, and even more preferably 50 μm or more. By increasing the thickness of the adhesive sheet (21), impact resistance tends to increase. Additionally, if the cover window (70) has a printing step due to decorative printing, the adhesive sheet (21) may be made to have step absorption properties. Although the upper limit of the thickness of the adhesive sheet (21) is not particularly limited, from the perspective of the productivity of the adhesive sheet, it is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 250 μm or less.

[0103] The total light transmittance of the adhesive sheet (21) is preferably 85% or more, and more preferably 90% or more. The haze of the adhesive sheet is preferably 1.5% or less, and more preferably 1% or less.

[0104] The light transmittance of the adhesive sheet (21) at a wavelength of 380 nm is preferably 5% or less, more preferably 4% or less, and may be 3% or less. By increasing the ultraviolet shielding properties of the adhesive sheet (21), photodegradation such as yellowing of the polarizer (11) caused by ultraviolet rays incident from the outside can be suppressed. As described above, by including an ultraviolet absorber in the adhesive composition, the adhesive sheet (21) can be made to have ultraviolet absorption properties while maintaining the transparency of visible light.

[0105] [Polarizing plate]

[0106] Polarizer

[0107] The polarizing plate (10) includes a polarizer (11). The polarizer (11) is a polyvinyl alcohol-based film containing iodine. As a material for the polyvinyl alcohol-based film applied to the polarizer, polyvinyl alcohol or a derivative thereof is used. As derivatives of polyvinyl alcohol, examples include polyvinyl formal, polyvinyl acetal, etc., as well as olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, or their alkyl esters, acrylamide, etc., may be used. Polyvinyl alcohol with a degree of polymerization of about 1,000 to 10,000 and a degree of saponification of about 80 to 100 mol% is generally used.

[0108] A polarizer is obtained by performing iodine dyeing and stretching treatment on a polyvinyl alcohol-based film. The thickness of the polarizer is preferably about 1 to 50 μm. As a polarizer, a thin polarizer with a thickness of 10 μm or less may be used. Examples of thin polarizers include those described in Japanese Patent Publication No. Sho 51-069644, Japanese Patent Publication No. 2000-338329, WO2010 / 100917, Japanese Patent No. 4691205, and Japanese Patent No. 4751481. Such a thin polarizer is obtained, for example, by a manufacturing method comprising a process of stretching a polyvinyl alcohol-based resin layer and a stretching resin substrate into a laminated state and a process of iodine dyeing.

[0109] Optical layer

[0110] An optical layer is not provided on the first main surface (the side facing the viewer) of the polarizer (11), and an adhesive sheet (21) is provided in contact with the polarizer (11) as described above. The polarizing plate (10) may consist only of the polarizer (11), or a suitable optical layer (15) may be disposed on the second main surface (the side facing the image display cell (60)) of the polarizer (11).

[0111] The optical layer (15) may be a transparent protective film for protecting the polarizer (11), an optical compensation layer for the purpose of expanding the viewing angle, or a quarter-wave plate for forming a circular polarizer together with the polarizer (11). The optical layer (15) may have the function of a transparent protective film and the function of a phase difference plate.

[0112] As a material constituting the optical layer (15), for example, a resin material having excellent transparency, mechanical strength, and thermal stability may be used. Specific examples of such resin materials include cellulose-based resins such as triacetylcellulose, polyester-based resins, polyethersulfone-based resins, polysulfone-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyolefin-based resins, (meth)acrylic-based resins, cyclic polyolefin-based resins (norbornene-based resins), polyarylate-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, and mixtures thereof. The optical layer (15) may be a liquid crystal material. For example, as the optical layer (15), a liquid crystal layer in which liquid crystal molecules are oriented in a predetermined direction may be used.

[0113] The optical layer (15) may be in direct contact with the second main surface of the polarizer (11), or may be bonded by interposing a suitable adhesive layer. The optical layer (15) may be a laminate of two or more layers. For example, the optical layer (15) may be a laminate of two or more films, a laminate in which a liquid crystal layer is provided on a film substrate, or a laminate in which two or more liquid crystal layers are stacked. The optical layer (15) may include an alignment layer for aligning liquid crystal molecules in a predetermined direction.

[0114] [Adhesive-equipped polarizing plate]

[0115] The adhesive sheet (21) may be provided as an adhesive-equipped polarizing plate (81) integrally laminated with the polarizing plate (10), as shown in FIG. 2. In the adhesive-equipped polarizing plate, the adhesive sheet (21) is disposed in contact with the first main surface of the polarizer (11). In FIG. 2, an optical layer (15) is provided on the second main surface of the polarizer (11), but as described above, the polarizing plate (10) does not have to have an optical layer on the second main surface of the polarizer.

[0116] The method of attaching the adhesive sheet (21) on the first main surface of the polarizer (11) is not particularly limited. An adhesive sheet (21) prepared on a substrate in advance may be bonded onto the polarizer (11), or the adhesive sheet (21) may be formed using the polarizer (11) as a substrate.

[0117] In the adhesive-equipped polarizing plate (81), it is preferable that a release film (41) be peelably adhered to the adhesive sheet (21). The release film has the function of protecting the exposed surface of the adhesive sheet (21) until the adhesive sheet (21) is bonded to the cover window (70). The substrate used during the formation (coating) of the adhesive sheet may be used as is as the release film (41) on the adhesive sheet (21).

[0118] As shown in FIG. 3, the polarizing plate equipped with an adhesive may be a double-sided adhesive polarizing plate having an adhesive sheet (21) in contact with a polarizer (11) on the viewing side surface of the polarizing plate (10) and another adhesive sheet (22) on the other side of the polarizing plate. It is preferable that a release film (42) be peelably adhered to the adhesive sheet (22).

[0119] In the adhesive-equipped polarizing plate (81) illustrated in FIG. 3, the polarizing plate (10) has an optical layer (15) on the second main surface of the polarizer (11), and an adhesive sheet (22) is disposed on the optical layer (15). The adhesive sheet (22) may be laminated in contact with the polarizer (11) without interposing another layer on the second main surface of the polarizer (11).

[0120] In this way, by using a polarizing plate equipped with double adhesive, in which an adhesive layer is pre-attached to both sides of the polarizing plate (10), the process of attaching a polarizing plate to the surface of an image display cell and then attaching a separate adhesive sheet on the polarizing plate can be omitted, thereby simplifying the manufacturing process of the image display device.

[0121] The adhesive sheet (22) is used for bonding the polarizing plate (10) and the image display cell (60). The thickness of the adhesive sheet (22) is preferably 3 μm to 30 μm, more preferably 5 μm to 27 μm, and even more preferably 10 μm to 25 μm. Various adhesives used for bonding the polarizing plate and the image display cell can be used as the adhesive sheet (22). An acrylic adhesive is preferably used as the adhesive constituting the adhesive sheet (22).

[0122] [Image display device]

[0123] As illustrated in FIG. 1, the image display device (100) is provided with a cover window (70) bonded to the viewing side of the polarizing plate (10) via an adhesive sheet (21). On the other side of the polarizing plate (10), an image display cell (60), such as a liquid crystal cell or an organic EL cell, is bonded via an adhesive sheet (22). The image display cell (60) may be foldable.

[0124] As the cover window (70), a transparent plate having suitable mechanical strength and thickness is used. As such a transparent plate, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate, is used. If the image display cell (60) is foldable, the cover window (70) may also be foldable. The cover window may be a plurality of transparent films laminated with an adhesive or adhesive interposed therein, or it may be equipped with a touch panel sensor. As the touch panel sensor, any type of touch panel, such as a resistive type, a capacitive type, an optical type, or an ultrasonic type, is used.

[0125] The order of bonding the polarizing plate (10) and the cover window (70) by the adhesive sheet (21), and bonding the adhesive sheet (22) and the image display cell (60) is not particularly limited. As described above, an adhesive-equipped polarizing plate with an adhesive sheet attached to the surface of the polarizing plate in advance may be used.

[0126] After bonding the polarizing plate (10) and the cover window (70) with an adhesive sheet (21) interposed therebetween, degassing may be performed to remove bubbles near the bonding interface or the printing step. Suitable methods such as heating, pressurizing, or depressurizing may be employed as degassing methods. For example, bonding may be performed under reduced pressure and heating to suppress the incorporation of bubbles, and then, to suppress delay bubbles, heating and pressurizing may be performed simultaneously by autoclave treatment, etc.

[0127] When the adhesive sheet (21) is made of a photocurable adhesive composition, photocuring of the adhesive composition is performed after the polarizing plate (10) and the cover window (70) are bonded. By irradiating light, the polymerization reaction of the photopolymerizable polyfunctional compound proceeds, and consequently, the adhesive reliability of the adhesive sheet is increased.

[0128] The amount of light irradiated during photocuring is not particularly limited as long as it is within a range where the adhesive sheet can be photocured, for example, an integrated amount of light of about 50 to 10,000 mJ / cm². Light irradiation on the adhesive sheet (21) may be performed from either the polarizer (10) side or the cover window (70) side, but from the perspective of preventing deterioration of the polarizer (11) due to ultraviolet rays, it is preferable to irradiate ultraviolet rays from the cover window (70) side. If the adhesive sheet (21) has ultraviolet shielding properties, even if ultraviolet rays are irradiated for photocuring of the adhesive sheet (21), most of the ultraviolet rays are absorbed by the adhesive sheet (21), so the amount of ultraviolet rays irradiated to the polarizer can be reduced.

[0129] In the image display device (100), the adhesive sheet (21) placed in contact with the viewing side of the polarizer (11) has the composition described above. Therefore, even when the image display device is exposed to a high temperature and high humidity environment or exposed to external light for a long time, deterioration such as fading or yellowing of the polarizer is suppressed, and the adhesive reliability between the polarizing plate (10) and the cover window (70) is excellent.

[0130] <Example>

[0131] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0132] [Production of adhesive sheets 1 to 14]

[0133] Polymerization of base polymer

[0134] Monomer components (total 100 parts by weight) in the proportions shown in Table 1 and azobisisobutyronitrile (AIBN) as a thermal polymerization initiator were introduced together with 233 parts by weight of ethyl acetate, stirred for 1 hour under a nitrogen atmosphere at 23°C, and then nitrogen was substituted. Afterward, the reaction was carried out at 56°C for 5 hours, followed by a reaction at 70°C for 3 hours to prepare an acrylic base polymer solution.

[0135] In Table 1, monomers are listed by the following abbreviations.

[0136] BA: Butyl acrylate

[0137] CHA: Cyclohexyl acrylate

[0138] IBXA: Isobornyl acrylate

[0139] DCPA: Dicyclopenthenyl acrylate

[0140] 4HBA: 4-hydroxybutyl acrylate

[0141] NVP: N-vinyl-2-pyrrolidone

[0142] AM: Acrylamide

[0143] HEAA: Hydroxyethylacrylamide

[0144] <Preparation of Photocurable Adhesive Composition>

[0145] A photocurable adhesive composition was prepared by adding the following post-addition components in the amounts shown in Table 1 to 100 parts by weight of the base polymer to the acrylic base polymer solution obtained above, and then mixing uniformly.

[0146] Isocyanate-based crosslinking agent: Trimethylolpropane adduct of xylylene diisocyanate (Mitsui Chemicals "Takenate D110N")

[0147] Polyfunctional Acrylate: Dipentaerythritol Hexacrylate (DPHA)

[0148] Silane coupling agent: 3-Glycidoxypropyltrimethoxysilane (Shin-Etsu Kagaku High School "KBM-403")

[0149] Antioxidant: Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate](BASF “Irganox 1010”)

[0150] Photopolymerization initiator: 2,2-dimethoxy-2-phenylacetophenone (IGM Resins "Omnirad 651")

[0151] UV absorber: 5,5'-Bis(2-ethylhexyloxy)-2,2'-[6-(4-methoxyphenyl)-1,3,5-triazine-2,4-diyl]diphenol (BASF "Tinosorb S")

[0152] Production of adhesive sheets

[0153] The above photocurable adhesive composition was applied onto a release film (a polyethylene terephthalate film having a silicone-based release layer on one side), heated at 100°C for 3 minutes to remove the solvent, and then another release film was bonded to the surface. This laminate was aged for 3 days under an atmosphere of 25°C to promote crosslinking, and an adhesive sheet with release films attached to both sides was obtained.

[0154] [Adhesive Sheet A]

[0155] In a reaction vessel equipped with a thermometer, a stirrer, a cooler, and a nitrogen gas inlet tube, 99 parts by weight of butyl acrylate and 1 part by weight of 4-hydroxybutyl acrylate as monomer components, and 0.2 parts by weight of AIBN as a thermal polymerization initiator were added together with 233 parts by weight of ethyl acetate, stirred for 1 hour under a nitrogen atmosphere at 23°C, and then nitrogen purging was performed. Afterward, the reaction was carried out at 60°C for 5 hours to obtain a solution of an acrylic base polymer having a weight average molecular weight (Mw) of 1.1 million. To this base polymer solution, 0.8 parts by weight of trimethylolpropanetolylene diisocyanate (Nippon Polyurethane High School “Coronate L”) as an isocyanate-based crosslinking agent and 0.1 parts by weight of a silane coupling agent (Shin-Etsu Kagaku High School “KBM403”) were added and then uniformly mixed to prepare an adhesive composition solution.

[0156] The adhesive composition was applied onto a release film such that the thickness after drying was 20 μm, and after drying at 100°C for 3 minutes to remove the solvent, another release film was bonded to the surface. This laminate was aged for 2 days under an atmosphere of 50°C to promote crosslinking, and an adhesive sheet A with release films attached to both sides was obtained.

[0157] [Evaluation of Adhesive Sheets 1 to 14]

[0158] UV transmittance

[0159] One release film was peeled off from the surface of the adhesive sheet and bonded to an alkali-free glass plate, and then the other release film was peeled off to prepare a sample for measurement. The transmittance spectrum was measured using a visible ultraviolet spectrophotometer, and the transmittance at a wavelength of 380 nm was read.

[0160] <Adhesion Reliability>

[0161] A polarizer made of an iodine-impregnated stretched polyvinyl alcohol film with a thickness of 25 μm was bonded onto an alkali-free glass plate by interposing adhesive sheets 1 to 14. On top of this, an aluminum foil was bonded by interposing adhesive sheet A, and then ultraviolet light with an integrated light intensity of 3000 mJ / cm² was irradiated from the alkali-free glass plate side using a metal halide lamp (300 mW / cm²) to cure the adhesive and produce an evaluation sample.

[0162] A moisture-resistant heat test was conducted by holding the evaluation sample in a constant temperature and humidity chamber at a temperature of 85°C and a relative humidity of 85% for 100 hours. After the test, a 10 cm × 10 cm area of ​​the sample was observed using a digital microscope with a magnification of 20x to check for the presence or absence of bubbles. It was classified as OK if no bubbles with a diameter of 20 µm or larger were detected, and NG if one or more bubbles with a diameter of 20 µm or larger were detected.

[0163] <Fading and Weather Resistance>

[0164] A polarizer made of an iodine-impregnated stretched polyvinyl alcohol film with a thickness of 25 μm was bonded onto a first alkali-free glass plate with adhesive sheet A interposed thereon. After bonding a second alkali-free glass plate with adhesive sheets 1 to 14 interposed thereon, ultraviolet light with an integrated light intensity of 3000 mJ / cm² was irradiated from the second alkali-free glass plate side with a metal halide lamp (300 mW / cm²) to cure the adhesive and produce an evaluation sample.

[0165] (Moisture resistance)

[0166] A sample for evaluation was held in a constant temperature and humidity chamber at a temperature of 85°C and a relative humidity of 85% for 100 hours to conduct a heat resistance test. The difference ΔT = T1 - T0 between the transmittance T0 at a wavelength of 550 nm before the test and the transmittance T1 at a wavelength of 550 nm after the test was calculated.

[0167] (Weather resistance)

[0168] The evaluation sample was mounted on a fixing jig to prevent light from being incident from the first alkali-free glass plate side, and a weathering fade test was conducted using a UV fade meter (Suga Shikenki “U48AU”) by irradiating light from a carbon arc lamp from the second alkali-free glass plate side for 100 hours under conditions of a temperature of 40°C, relative humidity of 20%, and a radiation intensity (integrated illuminance of 300 to 700 nm) of 500 ± 50 W / m². b of the transmitted light of the sample before the test * 0 and b of the transmitted light of the sample after the test * Difference of 1 Δb * =b * 1-b * 0 was obtained. Also, b * b is the chromaticity index of the CIE1976 color space. * ...and the sample was loaded onto the backlight and measured.

[0169] The composition and evaluation results of the adhesive for each adhesive sheet are shown in Table 1.

[0170]

[0171] In the example using Composition 3, which does not contain a UV absorber, Δb in the sample after the weathering test * The increase was significant, and the polarizer had yellowed. From the comparison between Composition 2 and Composition 3, it can be seen that the adhesive sheet includes a UV absorber, thereby improving weather resistance and suppressing the yellowing of the polarizer.

[0172] In the sample using Composition 7, which contains 8 parts by weight of NVP among 100 parts by weight of monomer components constituting the base polymer, the change in transmittance ΔT before and after the humid heat resistance test was large, and the humid heat resistance was insufficient. The same was true for Composition 8, which contains 8 parts by weight of AM, and Composition 9, which contains 8 parts by weight of HEAA. In comparison of Compositions 2, 6, and 7, there was a tendency for ΔT to decrease as the amount of NVP decreased. From these results, it can be seen that by reducing the amount of nitrogen atom-containing monomers in the monomer components constituting the base polymer, the humid heat resistance is improved and the fading of the polarizer can be suppressed.

[0173] When comparing compositions 2, 10, 11, and 12, in which the amount of 4HBA in the monomer component constituting the base polymer is different, it was observed that ΔT tended to decrease as the amount of 4HBA decreased. From these results, it can be seen that by reducing the amount of hydroxyl group-containing monomer in the monomer component constituting the base polymer, the resistance to heat and humidity is improved and the fading of the polarizer can be suppressed.

[0174] The sample using Composition 1, in which the amount of CHA in the monomer component constituting the base polymer was 15 parts by weight, showed insufficient adhesive reliability compared to the sample using Composition 2, in which the amount of CHA was 30 parts by weight. The samples using Compositions 13 and 14, in which the proportion of CHA was increased, showed sufficient adhesive reliability. In addition, Example 4, using IBXA instead of CHA, and Example 5, using DCPA, also showed sufficient adhesive reliability. From these results, it can be seen that by increasing the proportion of high-Tg monomers in the monomer component constituting the base polymer, the adhesive sheet exhibits excellent adhesive reliability even when the proportion of nitrogen atom-containing monomers or hydroxyl group-containing monomers is small. Explanation of the symbols

[0175] 10: Polarizer 11: Polarizer 15: Optical layer 21, 22: Adhesive sheet 81, 82: Polarizing plates equipped with adhesive 60: Image display cell 70: Cover Window 100: Image display device

Claims

Claim 1 A polarizing plate equipped with an adhesive, comprising: a polarizer having a first main surface and a second main surface and made of a polyvinyl alcohol-based film containing iodine; and a first adhesive sheet disposed in contact with the first main surface of the polarizer, wherein the first adhesive sheet is made of an adhesive composition comprising an acrylic base polymer and a UV absorber, and the acrylic base polymer contains 20 to 75 parts by weight of a high Tg monomer having a glass transition temperature of 10°C or higher, wherein the amount of nitrogen-containing monomer is 5 parts by weight or less per 100 parts by weight of the total monomer components, and does not contain any hydroxyl groups, carboxyl groups, or nitrogen atoms. Claim 2 In claim 1, the first adhesive sheet is a polarizing plate equipped with an adhesive having a light transmittance of 5% or less at a wavelength of 380 nm. Claim 3 delete Claim 4 A polarizing plate equipped with an adhesive according to claim 1 or 2, wherein the acrylic base polymer has a content of 0.1 to 8 parts by weight of a hydroxyl group-containing monomer per 100 parts by weight of the total monomer components. Claim 5 A polarizing plate equipped with an adhesive according to claim 1 or 2, wherein the acrylic base polymer has a content of 1 part by weight or less of a carboxyl group-containing monomer per 100 parts by weight of the total monomer components. Claim 6 delete Claim 7 A polarizing plate equipped with an adhesive, wherein the high Tg monomer is a (meth)acrylic acid ester having a cycloaliphatic structure in claim 1 or 2. Claim 8 A polarizing plate equipped with an adhesive according to claim 1 or 2, wherein the acrylic base polymer contains 20 to 79 parts by weight of an (meth)acrylate alkyl ester having a glass transition temperature of -40°C or lower, based on a total of 100 parts by weight of monomer components. Claim 9 A polarizing plate equipped with an adhesive, wherein, in claim 1 or 2, the acrylic base polymer has a crosslinked structure formed by a thermal crosslinking agent. Claim 10 A polarizing plate equipped with an adhesive according to claim 1 or 2, wherein the adhesive composition comprises a photopolymerizable polyfunctional compound having two or more photopolymerizable functional groups in one molecule and a photopolymerization initiator. Claim 11 delete Claim 12 An adhesive-equipped polarizing plate according to claim 1 or 2, further comprising a second adhesive sheet on the second main side of the polarizer. Claim 13 In claim 12, the adhesive-equipped polarizing plate in which the second adhesive sheet is laminated in contact with the second main surface of the polarizer. Claim 14 In claim 12, the adhesive-equipped polarizing plate in which the second adhesive sheet is laminated with another layer interposed on the second main surface of the polarizer. Claim 15 An image display device comprising, in this order, a second adhesive sheet, a polarizer made of a polyvinyl alcohol-based film containing iodine, a first adhesive sheet, and a cover window on the surface of an image display cell, wherein the first adhesive sheet is composed of an adhesive composition comprising an acrylic base polymer and a UV absorber, and the acrylic base polymer contains 20 to 75 parts by weight of a high Tg monomer in which the amount of nitrogen-containing monomer is 5 parts by weight or less, does not contain hydroxyl groups, carboxyl groups, and nitrogen atoms, and the glass transition temperature of the homopolymer is 10°C or higher, based on a total of 100 parts by weight of monomer components, and the glass transition temperature of the homopolymer is 10°C or higher. Claim 16 A method for manufacturing an image display device, wherein the image display device comprises, in order, a second adhesive sheet, a polarizer made of a polyvinyl alcohol-based film containing iodine, a first adhesive sheet in contact with the polarizer, and a cover window on the surface of an image display cell, wherein the first adhesive sheet is composed of an adhesive composition comprising an acrylic base polymer, a photopolymerizable polyfunctional compound having two or more photopolymerizable functional groups in one molecule, a photopolymerization initiator, and an ultraviolet absorber, wherein the acrylic base polymer contains 20 to 75 parts by weight of a high Tg monomer in which the amount of nitrogen-containing monomer is 5 parts by weight or less, does not contain hydroxyl groups, carboxyl groups, and nitrogen atoms, and the glass transition temperature of the homopolymer is 10°C or higher, and wherein the polarizer and the cover window are bonded with the first adhesive sheet interposed therebetween, and then an active light is irradiated from the cover window side to photocur the adhesive composition.

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