KR20240012452A - Adhesive composition, adhesive sheet, optical laminate, and image display device - Google Patents

Abstract

The provided adhesive composition contains a (meth)acrylic polymer (A) as a main component and further contains a crosslinking agent (B). When a pressure-sensitive adhesive sheet is formed using the pressure-sensitive adhesive composition, the gel fraction G _2h of the pressure-sensitive adhesive sheet at 2 hours from the time point T ₀ of forming the pressure-sensitive adhesive sheet is less than 60% by weight, and 24 hours after the time point T ₀ The gel fraction G _24h of the adhesive sheet at the time is 60% by weight or more. This pressure-sensitive adhesive composition is suitable for forming a pressure-sensitive adhesive sheet that can suppress dimensional changes in the optical film included in the optical laminate and also ensures durability.

Description

Adhesive composition, adhesive sheet, optical laminate, and image display device

The present invention relates to an adhesive composition, an adhesive sheet, an optical laminate, and an image display device.

In recent years, image display devices represented by liquid crystal displays and electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices) have spread rapidly. These various image display devices usually have a laminated structure of an optical laminated body including an image forming layer such as a liquid crystal layer or an EL emitting layer, and an optical film and an adhesive sheet. The adhesive sheet is mainly used for bonding between films included in an optical laminate or for bonding an image forming layer to an optical laminate. Examples of optical films include a polarizing plate, a retardation film, and a polarizing plate with a retardation film in which the polarizing plate and the retardation film are integrated. Patent Document 1 discloses an example of an optical laminated body.

Japanese Patent Publication No. 2008-031214 Japanese Patent Publication No. 2009-98665

Excessive changes in the dimensions of the optical film due to temperature changes cause light leakage and color unevenness in the image display device. Light leakage and color unevenness are particularly likely to occur in an image display device that uses a polarizing plate with a retardation film and has a relatively large size. Additionally, image display devices with narrowly designed frames (bezels) (narrow frames) are becoming widespread, and suppression of dimensional changes is becoming increasingly important. In order to suppress dimensional changes, it is conceivable to increase the elastic modulus of the adhesive sheet included in the optical laminate. However, simply increasing the elastic modulus may reduce the durability of the adhesive sheet and make it unable to keep up with changes in dimensions.

The purpose of the present invention is to provide a pressure-sensitive adhesive composition suitable for forming a pressure-sensitive adhesive sheet that can suppress dimensional changes in an optical film included in an optical laminate and also ensures durability.

The present invention,

It is an adhesive composition containing (meth)acrylic polymer (A) as a main component,

Further comprising a cross-linking agent (B),

When an adhesive sheet is formed with the adhesive composition,

The gel fraction G _2h of the adhesive sheet at the time point 2 hours after forming the adhesive sheet T ₀ is less than 60% by weight,

Provided is a pressure-sensitive adhesive composition in which the gel fraction G _24h of the pressure-sensitive adhesive sheet at 24 hours from the time point T ₀ is 60% by weight or more.

In another aspect, the present invention:

An adhesive sheet formed from the adhesive composition of the present invention is provided.

In another aspect, the present invention:

An optical laminate including the adhesive sheet of the present invention and an optical film is provided.

In another aspect, the present invention:

An image display device including the optical laminate of the present invention is provided.

The adhesive composition according to the present invention is suitable for forming an adhesive sheet that can suppress dimensional changes in the optical film included in the optical laminate and also ensures durability.

1 is a cross-sectional view schematically showing an example of the adhesive sheet of the present invention.
Figure 2 is a cross-sectional view schematically showing an example of the optical laminated body of the present invention.
Figure 3 is a cross-sectional view schematically showing an example of the optical laminated body of the present invention.
Figure 4 is a cross-sectional view schematically showing an example of the optical laminate of the present invention.
Figure 5 is a cross-sectional view schematically showing an example of the optical laminate of the present invention.
Fig. 6 is a cross-sectional view schematically showing an example of the image display device of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below.

In this specification, “(meth)acrylic” means acrylic and methacryl. In addition, “(meth)acrylate” means acrylate and methacrylate.

[Adhesive composition]

The adhesive composition (I) of this embodiment contains a (meth)acrylic polymer (A) and a crosslinking agent (B). The (meth)acrylic polymer (A) is contained in the adhesive composition (I) as the main component. In other words, the adhesive composition (I) is an acrylic adhesive composition. The main ingredient refers to the ingredient with the highest content in the composition. The content rate of the main component is, for example, 50% by weight or more, and may be 60% by weight or more, 70% by weight or more, 73% by weight or more, and further may be 75% by weight or more.

When a pressure-sensitive adhesive sheet is formed from the pressure-sensitive adhesive composition (I), the gel fraction G _2h of the pressure-sensitive adhesive sheet at the time of 2 hours from T ₀ when the pressure-sensitive adhesive sheet is formed is less than 60% by weight. Additionally, the gel fraction G _24h of the adhesive sheet at 24 hours from time point T ₀ is 60% by weight or more. The above range of the gel fraction G _2h means that the crosslinking reaction when forming a pressure-sensitive adhesive sheet with the pressure-sensitive adhesive composition (I) proceeds relatively slowly in the initial stage from T ₀ until 2 hours have elapsed. The suppressed crosslinking rate in the initial stage increases the uniformity of the crosslinked structure in the adhesive sheet, and the increased uniformity contributes to improving the durability of the adhesive sheet. In addition, the fact that the gel fraction G _24h is in the above range contributes to suppressing dimensional change in the optical film included in the optical laminate.

Gel fraction G _2h is 55% by weight or less, less than 55% by weight, 50% by weight or less, 47% by weight or less, 45% by weight or less, less than 45% by weight, 40% by weight or less, 35% by weight or less, 30% by weight or less. , 25% by weight or less, 20% by weight or less, 15% by weight or less, 14% by weight or less, 13% by weight or less, and further 12% by weight or less. The lower limit of the gel fraction G _2h is, for example, 2 weight% or more, 4 weight% or more, 5 weight% or more, 7 weight% or more, 8 weight% or more, 9 weight% or more, 9.5 weight% or more, and further 9.7 weight%. It may be % or more.

The gel fraction G _24h may be 65% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 90% by weight or more, 92% by weight or more, and further 94% by weight or more. The upper limit of the gel fraction G _24h is, for example, 99% by weight or less, and may be 98% by weight or less, 97% by weight or less, and further 96% by weight or less.

The ratio G _24h /G _2h of the gel fraction G _24h to the gel fraction G 2h is, for example, 2 or more, and _may be 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, and even 8 or more. The upper limit of the ratio G _24h / G _2h is, for example, 48 or less, and may be 45 or less, 40 or less, 35 or less, 30 or less, 25 or less, 20 or less, 15 or less, 10 or less, and further may be 9.7 or less.

The gel fraction G ₀ of the adhesive sheet immediately after the point in time T ₀ of forming the adhesive sheet may be 3% by weight or more and 50% by weight or less. Immediately after is typically within 10 minutes from time T ₀ , and may be within 5 minutes. The upper limit of the gel fraction G ₀ is 45% by weight or less, 40% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, 8% by weight or less. % or less, 6 weight% or less, and further 5 weight% or less.

The ratio G _2h /G ₀ of the gel fraction G _2h to the gel fraction G ₀ is, for example, less than 20, less than 15, less than 10, less than 6, less than 5, less than 4, less than 3, less than 2.5, less than 2.4, Furthermore, it may be 2.3 or less. The lower limit of the ratio G _2h /G ₀ is, for example, 1 or more, and may be greater than 1, 1.1 or more, 1.2 or more, 1.5 or more, 1.7 or more, 2 or more, and further 2.1 or more.

The gel fraction G _7d of the adhesive sheet at 7 days from time T ₀ may be 90% by weight or more, 91% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, and further 95% by weight. It may be % or more. The upper limit of G _7d is, for example, 99.5% by weight or less, and may be 99% by weight or less, and further may be 98% by weight or less.

The ratio G _7d /G _24h of the gel fraction G _7d to the gel fraction G _24h is, for example, 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, 1.1 or less, 1.07 or less, 1.05 or less, 1.03 or less, and further 1.02 or less. You can continue. The ratio G _7d /G _24h is, for example, 1 or more.

The time point T ₀ at which the adhesive sheet is formed is the time when the formation of the adhesive sheet is completed, and can be specifically determined depending on the form of the adhesive composition (I). For solvent-type and emulsion-type adhesive compositions (I), the time point T ₀ is the time when the coating film containing the adhesive composition (I) applied on the base film is dried by heating and then reaches room temperature by natural cooling. It can be determined as: Drying conditions (temperature and time) are, for example, 90°C and 100 seconds. Room temperature is 20 to 25°C. However, the time point T ₀ can be determined by the time when 25°C is reached. As the base film, various resin films such as polyethylene terephthalate (PET) film can be used. For the active energy ray curing type (photo curing type), the time point T ₀ can be determined as the time when the progress of photo curing is completed by irradiation of the active energy ray to the coating film containing the adhesive composition (I). The photocurable coating film contains a monomer (group) that becomes the (meth)acrylic polymer (A) by polymerization, a crosslinking agent (B), and, if necessary, a partial polymerization of the monomer (group), a polymerization initiator, additives, and solvents. It may be a coating film of the mixture. For both the solvent type and the photocurable type, the thickness of the coating film when determining the time point T ₀ is, for example, a thickness at which the thickness of the formed adhesive sheet is 50 μm.

The gel fraction at each time point can be evaluated as follows. First, approximately 0.2 g is scraped from the adhesive sheet at each time point to obtain a small piece. Next, the obtained small piece was wrapped with a stretched porous polytetrafluoroethylene film (NTF1122, manufactured by Nitto Denko, average pore diameter 0.2 μm) and tied with a string to obtain a test piece. Next, the weight A of the obtained test piece is measured. Weight A is the total weight of the small pieces of the adhesive sheet, the stretched porous membrane, and the lead string. The total weight B of the stretched porous membrane and yarn used is measured in advance. Next, the test piece is immersed in a container with an internal volume of 50 mL filled with ethyl acetate and left to stand at 23°C for one week. After standing, the test piece is taken out from the container, dried in a dryer set at 130°C for 2 hours, and then the weight C of the test piece is measured. From the measured weight A, weight B, and weight C, the gel fraction is calculated by the formula: gel fraction (% by weight) = (C-B)/(A-B) x 100 (%).

Gel fractions G ₀ , G _2h , G _24h and G _7d are, for example, the glass transition temperature (Tg) and composition of the base polymer included in the adhesive composition; Type and mixing amount of crosslinking agent; Types and mixing amounts of additives such as tackifiers; And it varies based on various factors such as drying (curing) conditions for forming an adhesive sheet with an adhesive composition.

[(meth)acrylic polymer (A)]

The (meth)acrylic polymer (A) preferably has as its main unit a structural unit derived from a (meth)acrylic monomer (A1) having an alkyl group of 1 to 30 carbon atoms in the side chain. The alkyl group may be linear or may have branches. The (meth)acrylic polymer (A) may have one or two or more types of structural units derived from the (meth)acrylic monomer (A1). Examples of (meth)acrylic monomer (A1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, and t-butyl (meth)acrylate. Acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth) Acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl(meth)acrylate, n-dodecyl(meth)acrylate (lauryl(meth)acrylate), n-tridecyl(meth)acrylate and n-tetradecyl(meth)acrylate. It is acrylate. In this specification, the “main unit” refers to, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more of the total structural units of the polymer. It means the unit that occupies.

The (meth)acrylic polymer (A) may have a structural unit derived from a (meth)acrylic monomer (A1) having a long-chain alkyl group in the side chain. An example of the monomer (A1) is n-dodecyl (meth)acrylate (lauryl (meth)acrylate). In this specification, “long-chain alkyl group” means an alkyl group having 6 to 30 carbon atoms.

The (meth)acrylic polymer (A) may have a structural unit derived from a (meth)acrylic monomer (A1) whose glass transition temperature (Tg) is in the range of -70 to -20°C when used as a homopolymer. An example of the monomer (A1) is n-butylacrylate.

The (meth)acrylic polymer (A) may have structural units other than those derived from the (meth)acrylic monomer (A1). The structural unit is derived from a monomer (A2) copolymerizable with a (meth)acrylic monomer (A1). The (meth)acrylic polymer (A) may have one type or two or more types of the structural unit.

An example of the monomer (A2) is an aromatic ring-containing monomer. The aromatic ring-containing monomer may be an aromatic ring-containing (meth)acrylic monomer. Examples of aromatic ring-containing monomers include phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, and ethylene oxide-modified nonylphenol (meth)acrylate. ester, hydroxyethylated β-naphthol (meth)acrylate and biphenyl (meth)acrylate. The content of structural units derived from aromatic ring-containing monomers in the (meth)acrylic polymer (A) is, for example, 0 to 50% by weight, 1 to 30% by weight, 5 to 25% by weight, and 8 to 20% by weight. , 10 to 18 weight%, and further may be 12 to 16 weight%. When the compounding amount of the crosslinking agent (B) in the adhesive composition (I) increases, self-polymers of the crosslinking agent (B) may be formed. The fact that the (meth)acrylic polymer (A) has a structural unit derived from an aromatic ring-containing monomer improves the compatibility of the (meth)acrylic polymer (A) with the crosslinking agent (B) and its self-polymer. Improvement of compatibility can contribute to improving the uniformity of the adhesive sheet by, for example, suppressing precipitation of the self-polymer.

Another example of monomer (A2) is a hydroxyl group-containing monomer. The hydroxyl group-containing monomer may be a hydroxyl group-containing (meth)acrylic monomer. Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate. , hydroxyalkyl (meth)acrylates such as 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate, and (4-hydride) Roxymethylcyclohexyl)-methyl acrylate. Additionally, hydroxyl groups can react with various crosslinking agents. From the viewpoint of improving the uniformity of the crosslinked structure to be formed, the content of structural units derived from hydroxyl group-containing monomers in the (meth)acrylic polymer (A) may be 1% by weight or less, 0.5% by weight or less, and further 0.1% by weight. It may be less than or equal to 0% by weight (not including the structural unit).

The monomer (A2) may be a carboxyl group-containing monomer, an amino group-containing monomer, or an amide group-containing monomer. Examples of carboxyl group-containing monomers are (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of amino group-containing monomers are N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate. Examples of amide group-containing monomers include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropylacrylamide, and N-methyl(meth)acrylamide. Acrylamide, N-butyl (meth)acrylamide, N-hexyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methylol-N-propane (meth)acrylamide, aminomethyl (meth) Acrylamide-based monomers such as acrylamide, aminoethyl (meth)acrylamide, mercaptomethyl (meth)acrylamide, and mercaptoethyl (meth)acrylamide; N-acryloyl heterocyclic monomers such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, and N-(meth)acryloylpyrrolidine; and N-vinyl group-containing lactam monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam. By having the (meth)acrylic polymer (A) having a structural unit derived from a carboxyl group-containing monomer, especially acrylic acid, for example, the self-polymerization of the crosslinking agent (B) can be increased. The improvement of the self-polymerization of the crosslinking agent (B) can contribute to suppressing peeling of the adhesive sheet in a humidified environment and stabilizing the physical properties of the adhesive sheet in systems with a high content of the crosslinking agent (B).

The monomer (A2) may be a polyfunctional monomer. Examples of polyfunctional monomers include hexanediol di(meth)acrylate (1,6-hexanediol di(meth)acrylate), butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (Poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth) Acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, epoxy acrylate, polyester acrylate and urethane acrylate. multifunctional acrylates such as; And it is divinylbenzene. Multifunctional acrylates are preferably 1,6-hexanediol diacrylate and dipentaerythritol hexa(meth)acrylate.

The total content of structural units derived from carboxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, and polyfunctional monomers in the (meth)acrylic polymer (A) is preferably 20% by weight or less, and more preferably It is 10% by weight or less, more preferably 8% by weight or less. When the (meth)acrylic polymer (A) has the structural unit, the total content is, for example, 0.01% by weight or more, and may be 0.05% by weight or more. The (meth)acrylic polymer (A) does not need to contain structural units derived from polyfunctional monomers.

Examples of other monomers (A2) include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, ( (meth)acrylic acid alkoxyalkyl esters such as 3-ethoxypropyl (meth)acrylic acid, 4-methoxybutyl (meth)acrylic acid, and 4-ethoxybutyl (meth)acrylic acid; Epoxy group-containing monomers such as glycidyl (meth)acrylate and methyl glycidyl (meth)acrylate; monomers containing sulfonic acid groups such as sodium vinyl sulfonate; Monomer containing a phosphate group; (meth)acrylic acid esters having an alicyclic hydrocarbon group such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; Vinyl esters such as vinyl acetate and vinyl propionate; Aromatic vinyl compounds such as styrene and vinyl toluene; olefins or dienes such as ethylene, propylene, butadiene, isoprene, and isobutylene; Vinyl ethers such as vinyl alkyl ether; And it is vinyl chloride.

The total content of structural units derived from the other monomers (A2) in the (meth)acrylic polymer (A) is, for example, 30% by weight or less, may be 10% by weight or less, or 0% by weight (the composition (not including units) is preferred.

The (meth)acrylic polymer (A) can be formed by polymerizing one or two or more types of monomers described above by a known method. You may polymerize a monomer and a partially polymerized product of the monomer. Polymerization can be performed, for example, by solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, or active energy ray polymerization. Solution polymerization and active energy ray polymerization are preferred because they can form a pressure-sensitive adhesive sheet with excellent optical transparency. Polymerization is preferably carried out while avoiding contact between the monomer and/or partial polymer and oxygen. For this purpose, polymerization is carried out, for example, in an inert gas atmosphere such as nitrogen, or in a state where oxygen is blocked by a resin film, etc. can be hired. The (meth)acrylic polymer (A) to be formed may be any form such as a random copolymer, a block copolymer, or a graft copolymer.

The polymerization system that forms the (meth)acrylic polymer (A) may contain one type or two or more types of polymerization initiators. The type of polymerization initiator can be selected depending on the polymerization reaction, and may be, for example, a thermal polymerization initiator or a photopolymerization initiator.

Solvents used in solution polymerization include, for example, esters such as ethyl acetate and n-butyl acetate; Aromatic hydrocarbons such as toluene and benzene; Aliphatic hydrocarbons such as n-hexane and n-heptane; Alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; Ketones such as methyl ethyl ketone and methyl isobutyl ketone. However, the solvent is not limited to the above examples. The solvent may be a mixed solvent of two or more solvents.

Polymerization initiators used in solution polymerization include, for example, azo-based polymerization initiators, peroxide-based polymerization initiators, and redox-based polymerization initiators. Peroxide-based polymerization initiators include, for example, dibenzoyl peroxide and t-butyl permaleate. Among them, the azo-based polymerization initiator disclosed in Japanese Patent Application Laid-Open No. 2002-69411 is preferable. The azo-based polymerization initiator is, for example, 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2- Methyl propionic acid) dimethyl, 4,4'-azobis-4-cyanovaleric acid. However, the polymerization initiator is not limited to the above examples. The amount of the azo polymerization initiator used is, for example, 0.05 to 0.5 parts by weight, and may be 0.1 to 0.3 parts by weight, based on 100 parts by weight of the total amount of monomers.

Active energy rays used in active energy ray polymerization include, for example, ionizing radiation such as α-rays, β-rays, γ-rays, neutron beams, and electron beams, and ultraviolet rays. As for the active energy ray, ultraviolet rays are preferable. Polymerization by irradiation of ultraviolet rays is also called photopolymerization. The polymerization system of active energy ray polymerization typically contains a photopolymerization initiator. The polymerization conditions for active energy polymerization are not limited as long as the (meth)acrylic polymer (A) is formed.

Photopolymerization initiators include, for example, 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, and benzyl-based photopolymerization. Initiator, benzophenone-based photopolymerization initiator, ketal-based photopolymerization initiator, and thioxanthone-based photopolymerization initiator. However, the photopolymerization initiator is not limited to the above examples.

Benzoin ether-based photopolymerization initiators include, for example, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-1,2-di. Phenylethan-1-one, anisole methyl ether. Acetophenone-based photopolymerization initiators include, for example, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, 4 -(t-Butyl)dichloroacetophenone. The α-ketol-based photopolymerization initiator is, for example, 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. The aromatic sulfonyl chloride-based photopolymerization initiator is, for example, 2-naphthalenesulfonyl chloride. A photoactive oxime-based photopolymerization initiator is, for example, 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. The benzoin-based photopolymerization initiator is, for example, benzoin. The benzyl-based photopolymerization initiator is, for example, benzyl. Benzophenone-based photopolymerization initiators include, for example, benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. The ketal-based photopolymerization initiator is, for example, benzyldimethyl ketal. Thioxanthone-based photopolymerization initiators include, for example, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, and 2,4-diiso Propylthioxanthone and dodecylthioxanthone.

The amount of the photopolymerization initiator used is, for example, 0.01 to 1 part by weight, and may be 0.05 to 0.5 parts by weight, based on 100 parts by weight of the total amount of monomers.

The weight average molecular weight (Mw) of the (meth)acrylic polymer (A) is, for example, 1 million to 2.8 million, and may be 1.2 million or more, and further 1.4 million or more, from the viewpoint of durability and heat resistance of the adhesive sheet. The weight average molecular weight (Mw) of polymers and oligomers in this specification is a value (polystyrene conversion) based on measurement by GPC (gel permeation chromatography).

The content of the (meth)acrylic polymer (A) in the adhesive composition (I), in terms of solid content, is, for example, 50% by weight or more, and may be 60% by weight or more, 70% by weight or more, and further may be 80% by weight or more. The upper limit of the content rate is, for example, 99% by weight or less, and may be 97% by weight or less, 95% by weight or less, 93% by weight or less, and further 90% by weight or less.

[Cross-linking agent (B)]

The crosslinking agent (B) is typically a polyfunctional crosslinking agent having two or more crosslinking reactive groups per molecule. The crosslinking agent (B) may be a trifunctional or higher crosslinking agent having 3 or more crosslinking reactive groups per molecule. The upper limit of the number of crosslinking reactive groups per molecule is, for example, 5.

The crosslinking agent (B) is, for example, an isocyanate-based crosslinking agent. The isocyanate-based crosslinking agent contains an isocyanate group as a crosslinking reactive group. The isocyanate-based crosslinking agent (B) may be an aromatic isocyanate compound, an alicyclic isocyanate compound, or an aliphatic isocyanate compound.

Examples of aromatic isocyanate compounds that can be used in the crosslinking agent (B) include phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4' -Diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, and xylylene diisocyanate. .

Examples of alicyclic isocyanate compounds that can be used in the crosslinking agent (B) include 1,3-cyclopentene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, and hydrogenated diisocyanate. These are diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated tetramethylxylylene diisocyanate.

Examples of aliphatic isocyanate compounds that can be used in the crosslinking agent (B) include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, and 1,3-butylene diisocyanate. , dodecamethylene diisocyanate and 2,4,4-trimethylhexamethylene diisocyanate.

The crosslinking agent (B) may be a derivative of the above isocyanate compound. Examples of derivatives include multimers (dimers, trimers, pentamers, etc.), adducts (adducts) obtained by addition to polyhydric alcohols such as trimethylolpropane, urea-modified products, biuret-modified products, and allophanate-modified products. It is a urethane prepolymer obtained by adding polyol, isocyanurate modified product, carbodiimide modified product, and polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, and polyisoprene polyol.

The crosslinking agent (B) is preferably an aromatic isocyanate compound and its derivatives, and more preferably is tolylene diisocyanate and its derivatives (in other words, tolylene diisocyanate-based (TDI-based) crosslinking agent). The TDI-based crosslinking agent has superior reaction uniformity compared to xylylene diisocyanate and its derivatives (in other words, xylylene diisocyanate-based (XDI-based) crosslinking agent). An example of a TDI-based crosslinking agent is an adduct of tolylene diisocyanate and a polyfunctional alcohol, and a more specific example is a trimethylolpropane/tolylene diisocyanate trimer adduct.

A commercial product can be used as the crosslinking agent (B). Examples of commercial products include Millionate MT, Millionate MTL, Millionate MR-200, Millionate MR-400, Coronate L, Coronate HL, and Coronate HX (above, coating agents: all brand names), And Takenate D-102, Takenate D-103, Takenate D-110N, Takenate D-120N, Takenate D-140N, Takenate D-160N, Takenate D-165N, Takenate D-170HN, Takenate These are Nate D-178N, Takenate 500, and Takenate 600 (above, manufactured by Mitsui Chemicals; all are brand names). As the crosslinking agent (B), Coronate L, Takenate D-102, and Takenate D-103 (all trimethylolpropane/tolylene diisocyanate trimer adducts) can be preferably used.

The compounding amount of the crosslinking agent (B) in the adhesive composition (I) is, for example, 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, and 8 parts by weight, based on 100 parts by weight of the (meth)acrylic polymer (A). It may be more than 100 parts by weight, more than 9 parts by weight, more than 10 parts by weight, more than 10 parts by weight, and even more than 11 parts by weight. The upper limit of the mixing amount is, for example, 30 parts by weight or less, 28 parts by weight or less, 25 parts by weight or less, 23 parts by weight or less, 20 parts by weight or less, 19 parts by weight or less, 18 parts by weight or less, and even 15 parts by weight or less. do. The pressure-sensitive adhesive composition (I) whose blending amount is within the above range is suitable for forming a pressure-sensitive adhesive sheet with an increased elastic modulus.

According to examination by the present inventors, when the compounding amount reaches the above range, the crosslinking agents (B) react with each other during formation of the adhesive sheet, and self-polymers of the crosslinking agent (B) are easily formed. The formation of the self-polymer contributes to the formation of an adhesive sheet that can suppress dimensional changes in the optical film by increasing the cohesive force of the adhesive sheet. Additionally, in the pressure-sensitive adhesive composition (I) in which the gelation rate in the initial stage is suppressed, precipitation of the self-polymer in the formed pressure-sensitive adhesive sheet is suppressed, thereby improving the uniformity of the pressure-sensitive adhesive sheet.

The adhesive sheet formed from the adhesive composition (I) may have an interpenetrating network (IPN) structure of a crosslinked product of the (meth)acrylic polymer (A) and the self-polymer of the crosslinking agent (B). The IPN structure is suitable for improving the durability of the adhesive sheet.

Other examples of the crosslinking agent (B) are peroxide-based crosslinking agents, epoxy-based crosslinking agents, imine-based crosslinking agents, and polyfunctional metal chelates. However, the crosslinking agent (B) is preferably an isocyanate type. When the pressure-sensitive adhesive composition (I) contains a crosslinking agent (B) other than an isocyanate type, the total mixing amount is preferably 0.1 to 5 parts by weight, and 0.1 to 3 parts by weight, based on 100 parts by weight of the (meth)acrylic polymer (A). Parts by weight, 0.1 to 2 parts by weight, and 0.1 to 1 parts by weight are more preferable in that order. The adhesive composition (I) does not need to contain a crosslinking agent (B) other than an isocyanate type, for example, an epoxy type crosslinking agent.

[(meth)acrylic oligomer]

The adhesive composition (I) may further contain a (meth)acrylic oligomer (D).

The (meth)acrylic oligomer (D) may have the same composition as the (meth)acrylic polymer (A) described above except that the weight average molecular weight (Mw) is different. The weight average molecular weight (Mw) of the (meth)acrylic oligomer (D) is, for example, 1000 or more, and may be 2000 or more, 3000 or more, and further may be 4000 or more. The upper limit of the weight average molecular weight (Mw) of the (meth)acrylic oligomer is, for example, 30,000 or less, and may be 15,000 or less, 10,000 or less, and further may be 7,000 or less.

The (meth)acrylic oligomer (D) has, for example, one or two or more types of structural units derived from the following monomers: methyl (meth)acrylate, ethyl (meth)acrylate, and propyl (meth). Acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate , isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl ( Alkyl (meth)acrylates such as meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate. rate; esters of (meth)acrylic acid and alicyclic alcohol, such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclofentanyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from terpene compound derivative alcohols.

The (meth)acrylic oligomer (D) preferably has a structural unit derived from a (meth)acrylic monomer having a relatively bulky structure. In this case, the adhesiveness of the adhesive sheet can be further improved. Examples of the acrylic monomer include alkyl (meth)acrylates having an alkyl group with a branched structure, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohol, such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclofentanyl (meth)acrylate; These are aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate. The monomer preferably has a cyclic structure, and more preferably has two or more cyclic structures. In addition, when irradiating ultraviolet rays during polymerization of the (meth)acrylic oligomer (D) and/or during formation of the adhesive sheet, it is difficult to inhibit the progress of polymerization and/or formation, so the monomer has an unsaturated bond. It is preferable not to have one, and for example, an alkyl (meth)acrylate having an alkyl group having a branched structure, or an ester of (meth)acrylic acid and an alicyclic alcohol can be used.

Specific examples of the (meth)acrylic oligomer (D) include copolymers of butylacrylate, methyl acrylate, and acrylic acid, copolymers of cyclohexyl methacrylate and isobutyl methacrylate, and cyclohexyl methacrylate and isobornyl. Copolymer of methacrylate, copolymer of cyclohexyl methacrylate and acryloylmorpholine, copolymer of cyclohexyl methacrylate and diethylacrylamide, copolymer of 1-adamantyl acrylate and methyl methacrylate. Polymer, copolymer of dicyclopentanyl methacrylate and isobornyl methacrylate, dicyclopentanyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, isobornyl acrylate and cyclofentanyl methacrylate. A copolymer of at least one type selected from methyl methacrylate, a homopolymer of dicyclopentanyl acrylate, a homopolymer of 1-adamantyl methacrylate, and a homopolymer of 1-adamantyl acrylate.

To polymerize the (meth)acrylic oligomer (D), the method for polymerizing the (meth)acrylic polymer (A) described above can be adopted.

When the adhesive composition (I) contains a (meth)acrylic oligomer (D), the compounding amount is, for example, 70 parts by weight or less, and 50 parts by weight or less, with respect to 100 parts by weight of the (meth)acrylic polymer (A). , furthermore, it may be 40 parts by weight or less. The lower limit of the compounding amount is, for example, 1 part by weight or more, and may be 2 parts by weight or more, and further may be 3 parts by weight or more, with respect to 100 parts by weight of the (meth)acrylic polymer (A). The adhesive composition (I) does not need to contain the (meth)acrylic oligomer (D).

[additive]

The adhesive composition (I) may contain other additives. Examples of additives include silane coupling agents, polyfunctional alcohols, colorants such as pigments and dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, rework enhancers, softeners, antioxidants, anti-aging agents, light stabilizers, These are powders, particles, and thin substances such as ultraviolet absorbers, polymerization inhibitors, antistatic agents (alkali metal salts of ionic compounds, ionic liquids, ionic solids, etc.), inorganic fillers, organic fillers, and metal powders. The additive can be blended in an amount of, for example, 10 parts by weight or less, preferably 5 parts by weight or less, and more preferably 1 part by weight or less, with respect to 100 parts by weight of the (meth)acrylic polymer (A).

Examples of silane coupling agents include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl). ) Silane coupling agents containing epoxy groups such as ethyltrimethoxysilane; 3-Aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine and N -Amino group-containing silane coupling agents such as phenyl-γ-aminopropyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and silane coupling agents containing isocyanate groups such as 3-isocyanate propyltriethoxysilane.

When the adhesive composition (I) contains a silane coupling agent, the compounding amount is, for example, 5 parts by weight or less, 3 parts by weight or less, and 1 part by weight or less, with respect to 100 parts by weight of the (meth)acrylic polymer (A). , it may be 0.5 part by weight or less, 0.2 part by weight or less, 0.1 part by weight or less, and further 0.05 part by weight or less. The adhesive composition (I) does not need to contain a silane coupling agent.

The adhesive composition (I) may contain polyfunctional alcohol. The molecular weight of the polyfunctional alcohol is, for example, 240 or less, and may be 230 or less, 220 or less, 210 or less, 200 or less, 190 or less, 180 or less, 170 or less, 160 or less, and further 150 or less. The lower limit of the molecular weight is, for example, 60 or more, and may be 80 or more, 90 or more, and further may be 100 or more.

Examples of polyfunctional alcohols include alkylene glycols such as ethylene glycol and propylene glycol, and polymers thereof; Ether glycols such as diethylene glycol and polymers thereof; trimethylolethane; trimethylolpropane; glycerin; and sugar alcohols such as pentaerythritol and sorbitol. The polyfunctional alcohol is preferably trimethylolpropane, glycerin, diethylene glycol and polymers thereof, and is more preferably trimethylolpropane.

Polyfunctional alcohol may be trifunctional or more. Examples of trifunctional polyfunctional alcohols are trimethylolpropane and glycerin.

The polyfunctional alcohol does not need to have a reactive group other than a hydroxyl group that is reactive with the crosslinking agent (B). The reactive group is, for example, at least one selected from an amino group, a carboxyl group, and an epoxy group, and is especially an amino group.

The compounding amount of the polyfunctional alcohol in the adhesive composition (I) is, for example, 0.5 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the (meth)acrylic polymer (A). The upper limit of the mixing amount may be 15 parts by weight or less, 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 4 parts by weight or less, and further 3 parts by weight or less.

The adhesive composition (I) does not need to contain a crosslinking accelerator such as a catalyst. Examples of crosslinking accelerators are polyethers, polyether polyols, and phosphoric acid esters having a reactive group with reactivity with the crosslinking agent (B). The reactive group is, for example, at least one selected from a hydroxyl group, an amino group, a carboxyl group, and an epoxy group, and is particularly a hydroxyl group or an amino group. The adhesive composition (I) does not need to contain a polyether polyol having an amino group, and does not need to contain a phosphoric acid ester having a hydroxyl group.

The form of the adhesive composition (I) is, for example, emulsion type, solvent type (solution type), active energy ray curing type (photocuring type), and heat melt type (hot melt type). From the viewpoint of forming a more durable adhesive sheet, the adhesive composition (I) may be of a solvent type. The solvent-type adhesive composition (I) does not need to contain a photocuring agent such as an ultraviolet curing agent.

[Adhesive sheet]

An example of the adhesive sheet of this embodiment is shown in Fig. 1. The pressure-sensitive adhesive sheet 1 in FIG. 1 is formed from the pressure-sensitive adhesive composition (I). The adhesive sheet 1 contains, for example, a crosslinked product of (meth)acrylic polymer (A). The adhesive sheet 1 can be formed from the adhesive composition (I) as follows.

For the solvent type, for example, the adhesive composition (I) or a mixture of the adhesive composition (I) and the solvent is applied to a base film to form a coating film, and the formed coating film is dried to form the adhesive sheet 1. The pressure-sensitive adhesive composition (I) is thermally cured by heat during drying. For the active energy ray curing type (photocuring type), for example, a monomer (group) that becomes a (meth)acrylic polymer (A) by polymerization, a crosslinking agent (B), and, if necessary, a partial polymerization of the monomer (group), A mixture of polymerization initiator, oligomer (D), additive, and solvent is applied to a base film, and active energy rays are irradiated to form the adhesive sheet 1. Before irradiation with active energy rays, the solvent may be removed by drying. The base film may be a film (release film) in which a peeling treatment has been performed on the applied surface.

The adhesive sheet 1 formed on the base film can be transferred to any layer. Additionally, the base film may be an optical film, and in this case, an optical laminated body containing the adhesive sheet 1 and the optical film is obtained.

For application to the base film, a known method can be adopted. Application includes, for example, 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, lip coat, extrusion by die coater, etc. It can be done by court.

For the solvent type, the drying temperature after application is, for example, 40 to 200°C. The drying temperature may be 160°C or lower, 150°C or lower, 130°C or lower, 120°C or lower, and further may be 100°C or lower. By setting the drying temperature to 130°C or lower, 120°C or lower, and further 100°C or lower, the adhesive sheet 1 with more excellent durability can be obtained. In other words, the adhesive sheet (1) may be obtained by drying the coating film of the adhesive composition (I) at a temperature of 130°C or lower, 120°C or lower, and further at 100°C or lower. The drying time is, for example, 5 seconds to 20 minutes, and may be 5 seconds to 10 minutes, and may also be 10 seconds to 5 minutes. For the active energy ray curable type, the drying temperature and drying time when drying after application may be within the above range.

The composition and mixture applied to the base film preferably have a viscosity suitable for handling and coating. For this reason, for the active energy ray curable type, it is preferable that the mixture to be applied contains a partial polymerization of a monomer (group).

In one example of a release film, the application surface is peeled off using a silicone compound.

The thickness of the adhesive sheet 1 is, for example, 1 to 200 μm, and may be 5 to 150 μm, or further 10 to 100 μm.

The storage modulus G' (25°C) of the adhesive sheet 1 is, for example, 0.15 MPa or more, 0.2 MPa or more, 0.25 MPa or more, 0.3 MPa or more, 0.4 MPa or more, 0.5 MPa or more, 0.6 MPa or more, and 0.7 MPa. Above, 0.8 MPa or more, 0.9 MPa or more, 1.0 MPa or more, and further may be 1.1 MPa or more. The upper limit of the storage elastic modulus G' (25°C) is, for example, 5 MPa or less, and may be 3.0 MPa or less, 2.5 MPa or less, and further may be 2.0 MPa or less. The pressure-sensitive adhesive sheet 1 with a storage elastic modulus G' in the above range is more suitable for suppressing dimensional changes in the optical film.

The storage elastic modulus (25°C) of the adhesive sheet 1 can be evaluated by the following method. First, prepare a sample for measurement made of the material constituting the adhesive sheet (1). The shape of the sample for measurement is disk-shaped. The sample for measurement has a bottom diameter of 8 mm and a thickness of 2 mm. The sample for measurement may be a laminate in which a plurality of adhesive sheets 1 are laminated and punched into a disk shape. Next, dynamic viscoelasticity measurement is performed on the measurement sample. For dynamic viscoelasticity measurement, for example, ARES-G2 manufactured by TA Instruments can be used. From the results of the dynamic viscoelasticity measurement, the storage modulus G' of the adhesive sheet 1 at 25°C can be specified. Additionally, the conditions for dynamic viscoelasticity measurement are as follows.

·Measuring conditions

Frequency: 1Hz

Deformation Mode: Torsion

Measurement temperature: -70℃ to 150℃

Temperature increase rate: 5℃/min

The adhesive sheet 1 can be used for optical purposes, for example. The adhesive sheet 1 may be used in an optical laminate and/or an image display device. The adhesive sheet 1 is suitable for use in image display devices that particularly require suppression of dimensional changes with respect to optical films, such as image display devices with narrow frames or image display devices with a relatively large screen size. . By use in such an image display device, peeling of the film included in the optical laminated body is suppressed, for example.

[Optical laminate]

An example of the optical laminated body of this embodiment is shown in FIG. 2. The optical laminate 10A in FIG. 2 includes an adhesive sheet 1 and an optical film 2. The adhesive sheet 1 and the optical film 2 are laminated on each other. The optical laminate 10A can be used as an optical film with an adhesive sheet.

Examples of the optical film 2 are a polarizer, a retardation film, and a laminated film including a polarizer and/or a retardation film. However, the optical film 2 is not limited to the above example. The optical film 2 may contain a glass film.

The polarizing plate includes a polarizer. A polarizer protective film may be bonded to at least one side of the polarizer. Any adhesive or adhesive can be used to bond the polarizer and the polarizer protective film. The adhesive sheet 1 may be used for bonding. The polarizer is typically a polyvinyl alcohol (PVA) film in which iodine is oriented by stretching, such as air stretching (dry stretching) or boric acid water stretching.

The retardation film is a film that has birefringence in the in-plane direction and/or the thickness direction. The retardation film is, for example, a stretched resin film or a film obtained by aligning and fixing a liquid crystal material.

The retardation film includes a λ/4 plate, a λ/2 plate, an anti-reflection retardation film (e.g., see paragraphs 0221, 0222, and 0228 of Japanese Patent Application Laid-Open No. 2012-133303), and a retardation film for viewing angle compensation (e.g., Refer to paragraphs 0225 and 0226 of Japanese Patent Application Laid-Open No. 2012-133303), or an inclined orientation retardation film for viewing angle compensation (for example, see paragraph 0227 of Japanese Patent Application Laid-Open No. 2012-133303). The retardation film is not limited to the above examples as long as it has birefringence in the in-plane direction and/or the thickness direction. There is no limitation on the retardation value, arrangement angle, three-dimensional birefringence, whether it is a single layer or a multilayer, etc., of the retardation film. As the retardation film, a known film can be used.

The thickness of the optical film 2 is, for example, 1 to 200 μm. The thickness of the optical film 2, which is a polarizing plate, is, for example, 1 to 150 μm, and may be 100 μm or less, 75 μm or less, 50 μm or less, 20 μm or less, and further 15 μm or less. The lower limit of the thickness may be 10 μm or more, 20 μm or more, 50 μm or more, 75 μm or more, and further 100 μm or more.

The optical film 2 may be a single layer or a laminated film composed of two or more layers. When the optical film 2 is a laminated film, the adhesive sheet 1 may be used to bond each layer.

Another example of the optical laminated body of this embodiment is shown in FIG. 3. The optical laminate 10B in FIG. 3 has a laminated structure in which the release liner 3, the adhesive sheet 1, and the optical film 2 are laminated in this order. The optical laminate 10B can be used as an optical film with an adhesive sheet by peeling off the release liner 3.

The release liner 3 is typically a resin film. Examples of the resin constituting the release liner 3 are polyester such as polyethylene terephthalate (PET), polyolefin such as polyethylene and polypropylene, polycarbonate, acrylic, polystyrene, polyamide, and polyimide. The surface of the release liner 3 that is in contact with the adhesive sheet 1 may be subjected to a release treatment. The peeling treatment is, for example, treatment with a silicone compound. However, the release liner 3 is not limited to the above examples. The release liner 3 is peeled off when the optical laminate 10B is used, for example, when attached to the image forming layer.

Another example of the optical laminated body of this embodiment is shown in FIG. 4. The optical laminate 10C in FIG. 4 has a laminated structure in which the release liner 3, the adhesive sheet 1, the retardation film 2A, the interlayer adhesive 4, and the polarizing plate 2B are laminated in this order. The optical laminate 10C can be used by peeling off the release liner 3 and then attaching it to an image forming layer, for example.

As the interlayer adhesive 4, a known adhesive can be used. The adhesive sheet (1) may be used for the interlayer adhesive (4).

Another example of the optical laminated body of this embodiment is shown in FIG. 5. The optical laminate 10D in FIG. 5 includes a release liner 3, an adhesive sheet 1, a retardation film 2A, an interlayer adhesive 4, a polarizing plate 2B, and a protective film 5 laminated in this order. It has a layered structure. The optical laminate 10D can be used by, for example, attaching it to an image forming layer after peeling off the release liner.

The protective film 5 is the outermost layer, the optical film 2 (polarizing plate 2B), during distribution and storage of the optical laminated body 10D and in the state in which the optical laminated body 10D is built into the image display device. It has the function of protecting. Additionally, the protective film 5 may function as a window to external space when built into an image display device. The protective film 5 is typically a resin film. The resin constituting the protective film 5 is, for example, polyester such as PET, polyolefin such as polyethylene and polypropylene, acrylic, cycloolefin, polyimide, and polyamide, with polyester being preferred. However, the protective film 5 is not limited to the above example. The protective film 5 may be a glass film or a laminated film containing a glass film. The protective film 5 may be subjected to surface treatment such as anti-glare, anti-reflection, or anti-static treatment.

The protective film 5 may be bonded to the optical film 2 with any adhesive. Bonding using the adhesive sheet 1 is also possible.

The optical laminated body of this embodiment can be distributed and stored, for example, as a wound body obtained by winding a strip-shaped optical laminated body or as a sheet-shaped optical laminated body.

The optical laminated body of this embodiment is typically used in an image display device. Image display devices are, for example, EL displays such as liquid crystal displays, organic EL displays, and inorganic EL displays.

[Embodiment of image display device]

An example of the image display device of this embodiment is shown in FIG. 6. The image display device 11 in FIG. 6 includes a substrate 7, an image forming layer (for example, an organic EL layer or a liquid crystal layer) 6, an adhesive sheet 1, a retardation film 2A, and an interlayer adhesive 4. , the polarizing plate 2B and the protective film 5 are stacked in this order. The image display device 11 has the optical laminated bodies 10A, 10B, 10C, and 10D of FIGS. 2 to 5 (except the release liner 3). The substrate 7 and the image forming layer 6 may have the same configuration as the substrate and image forming layer provided in a known image display device, respectively.

The image display device 11 in FIG. 6 may be an organic EL display or a liquid crystal display. However, the image display device 11 is not limited to this example. The image display device 11 may be an electroluminescence (EL) display, a plasma display (PD), a field emission display (FED), or the like. The image display device 11 may be used for home appliance applications, vehicle-mounted applications, public information display (PID) applications, etc.

The image display device of this embodiment can have any configuration as long as it is provided with the optical laminated body of this embodiment.

Example

Hereinafter, the present invention will be described in more detail through examples. The present invention is not limited to the examples shown below.

First, the evaluation method of the (meth)acrylic polymer and adhesive sheet produced in Examples and Comparative Examples is shown.

[Weight average molecular weight (Mw)]

The weight average molecular weight (Mw) of the (meth)acrylic polymer was evaluated by GPC under the following conditions.

·Analysis device: Waters, Acquity APC

Column: Dosoje, G7000HXL+GMHXL+GMHXL

·Column temperature: 40℃

Eluent: Tetrahydrofuran (acid added)

·Flow rate: 0.8mL/min

·Injection volume: 100μL

Detector: Differential refractometer (RI)

·Standard sample: made by Agilent, polystyrene (PS)

[Gel fraction G ₀ , G _2h , G _24h , G _7d ]

The gel fractions G ₀ , G _2h , G _24h , and G _7d when a pressure-sensitive adhesive sheet was formed from the pressure-sensitive adhesive composition were evaluated by the method described above. However, PET film was used as the base film. Application of the adhesive composition to the base film was performed at room temperature (25°C) using a coater. The thickness of the coating film formed on the base film was adjusted so that the thickness of the adhesive sheet after drying was 50 μm. The drying conditions for the coating film when determining the time point T ₀ at which the adhesive sheet was formed were 90°C and 100 seconds. The atmosphere in which the pressure-sensitive adhesive sheet was left for natural cooling after drying and after time point _T0 was set to 25°C and 50% RH. The fact that the temperature of the coated film after drying returned to room temperature through natural cooling (in other words, it became usable as an adhesive sheet) was confirmed by measuring the surface temperature of the film with an infrared radiation thermometer. Evaluation of the gel fraction G ₀ was performed on the adhesive sheet 5 minutes after the time point T ₀ .

[Storage modulus G' (25℃)]

The storage elastic modulus G' (25°C) of the adhesive sheet was evaluated by the method described above. However, the sample for measurement was prepared by punching the laminate obtained by overlapping the produced adhesive sheets (7 days or more had elapsed from time T ₀ ) into a disk shape. ARES-G2 manufactured by TA Instruments was used to measure the dynamic viscoelasticity of the measurement sample.

[Humidification Durability]

The humidification durability (corresponding to an accelerated durability test) of the adhesive sheet was evaluated by the following method. First, a circularly polarizing plate with an adhesive sheet was formed in which each adhesive sheet produced in Examples and Comparative Examples (seven days or more from time point T ₀ ) was provided on one exposed surface. Next, the circularly polarizing plate was fixed to the surface of a glass plate (Eagle XG, manufactured by Corning) via the adhesive sheet. The circularly polarizing plate was fixed in an atmosphere of 23°C and 50% RH. Subsequently, after treatment in an autoclave at 50°C and 5 atm (absolute pressure) for 15 minutes, left to cool to 23°C to stabilize bonding of the circularly polarizing plate to the glass plate, heating at 60°C and 95% RH It was left in a humidified atmosphere for 500 hours. After leaving, it was returned to an atmosphere of 23°C and 50% RH, it was visually confirmed whether the circularly polarizing plate peeled off from the glass plate or foaming occurred between the glass plate and the circularly polarizing plate, and the humidification durability was evaluated as follows.

A: No apparent changes such as foaming or peeling are observed.

B: At the end, some individual peeling or foaming is seen, but it is within the range of no problem in practical terms.

C: At the end, continuous peeling or foaming is slightly visible, but is within a range that is not problematic for practical use.

D: Significant peeling or foaming is seen at the ends, which poses a practical problem.

Hereinafter, a method of forming a circularly polarizing plate with an adhesive sheet used for evaluation of humidification durability is shown.

<Production of polarizer P1>

(Production of polarizer)

A long polyvinyl alcohol (PVA)-based resin film (manufactured by Kuraray, product name “PE3000”, thickness 30 ㎛) is stretched uniaxially in the longitudinal direction (total stretching ratio 5.9 times) using a roll stretching machine, while simultaneously stretching the resin. Each treatment of swelling, dyeing, crosslinking, washing, and drying was performed on the film in order to produce a polarizer with a thickness of 12 μm. In the swelling treatment, the resin film was stretched 2.2 times while being treated with pure water at 20°C. In the dyeing treatment, the resin film was stretched 1.4 times while being treated with an aqueous solution at 30°C containing iodine and potassium iodide in a weight ratio of 1:7. The iodine concentration in the aqueous solution was adjusted so that the single transmittance of the polarizer to be produced was 45.0%. For the crosslinking treatment, a two-step process was adopted. In the first stage crosslinking treatment, the resin film was stretched 1.2 times while being treated with an aqueous solution of boric acid and potassium iodide at 40°C. The boric acid content in the aqueous solution used in the first step crosslinking treatment was 5.0% by weight, and the potassium iodide content was 3.0% by weight. In the second stage crosslinking treatment, the resin film was stretched 1.6 times while being treated with an aqueous solution of boric acid and potassium iodide at 65°C. The boric acid content in the aqueous solution used in the second stage crosslinking treatment was 4.3% by weight, and the potassium iodide content was 5.0% by weight. For the washing treatment, a 20°C aqueous potassium iodide solution was used. The content of potassium iodide in the aqueous solution used in the washing treatment was 2.6% by weight. The drying treatment was performed under drying conditions of 70°C and 5 minutes.

(Production of polarizer P1)

A triacetylcellulose (TAC) film (manufactured by Konica Minolta, product name “KC2UA”, thickness 25 μm) was bonded to each main surface of the above-produced polarizer using a polyvinyl alcohol-based adhesive. However, in the TAC film bonded to one main surface, a hard coat (7 μm thick) was formed on the main surface opposite to the polarizer side. In this way, polarizing plate P1 having the structure of protective layer with hard coat/polarizer/protective layer (without hard coat) was obtained.

<Production of phase contrast film R1>

(Production of the first retardation film)

26.2 parts by weight of isosorbide (ISB), 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF) 100.5 parts by weight, 1,4-cyclohexanedimethanol (1,4-CHDM) ) 10.7 parts by weight, 105.1 parts by weight of diphenyl carbonate (DPC), and 0.591 parts by weight of cesium carbonate (0.2% by weight aqueous solution) as a catalyst were added to a reaction vessel and dissolved in a nitrogen atmosphere (about 15 minutes). At this time, the temperature of the heating medium in the reaction vessel was set to 150°C, and stirring was performed as necessary. Next, the pressure in the reaction vessel was reduced to 13.3 kPa, and the temperature of the heating medium was raised to 190°C over 1 hour. The phenol generated with the increase in the temperature of the heating medium was discharged out of the reaction vessel (the same applies hereinafter). Next, the temperature inside the reaction vessel was maintained at 190°C for 15 minutes, and then the pressure inside the reaction vessel was changed to 6.67 kPa, and the temperature of the heating medium was raised to 230°C over 15 minutes. At the point when the stirring torque of the stirrer provided in the reaction vessel began to increase, the temperature of the heating medium was raised to 250°C in 8 minutes, and the pressure in the reaction vessel was set to 0.200 kPa or less. After reaching a predetermined stirring torque, the reaction was terminated, and the resulting reactant was extruded into water and pelletized. In this way, a polycarbonate resin having a composition of BHEPF/ISB/1,4-CHDM=47.4 mol%/37.1 mol%/15.5 mol% was obtained. The glass transition temperature of the obtained polycarbonate resin was 136.6°C, and the reduced viscosity was 0.395 dL/g.

After vacuum drying the produced polycarbonate resin pellets at 80°C for 5 hours, a single screw extruder (made by Isuzu Kakoki, screw diameter 25 mm, cylinder set temperature 220°C), T die (width 200 mm, set temperature 220°C), An elongated resin film with a thickness of 120 μm was obtained using a film forming apparatus equipped with a cooling roll (set temperature 120 to 130° C.) and a winder. Next, the obtained resin film was stretched in the width direction using a tenter stretching machine at a stretching temperature of 137 to 139°C and a stretching ratio of 2.5 times, to obtain a first retardation film.

(Production of the second retardation film)

20 parts by weight of a side-chain liquid crystal polymer (weight average molecular weight 5000) represented by the following general formula (I) (where 65 and 35 are mol% of each structural unit), a polymerizable liquid crystal (BASF) exhibiting a nematic liquid crystal phase 80 parts by weight of the product, brand name "PaliocolorLC242") and 5 parts by weight of a photopolymerization initiator (manufactured by Chiba Specialty Chemicals, brand name "Irgacure 907") were dissolved in 200 parts by weight of cyclopentanone to prepare a liquid crystal coating liquid. Next, the prepared liquid crystal coating liquid was applied to the surface of the base film, a norbornene-based resin film (manufactured by Nippon Zeon, brand name “Zeonex”) using a bar coater, and then heated and dried at 80°C for 4 minutes to form a coating film. The liquid crystals contained in were oriented. Next, the coating film was cured by irradiation of ultraviolet rays, and a liquid crystal solidified layer (thickness 0.58 μm), which is a second retardation film, was formed on the base film. The in-plane phase difference Re of the liquid crystal frozen layer for light with a wavelength of 550 nm is 0 nm, the phase difference Rth in the thickness direction is -71 nm (nx = 1.5326, ny = 1.5326, nz = 1.6550), and the liquid crystal frozen layer has nz > nx = ny. It showed refractive index characteristics.

(Production of phase contrast film R1)

One side of the first retardation film produced above and the liquid crystal solidification layer of the second retardation film were bonded through an adhesive to produce retardation film R1.

<Production of circular polarizer with adhesive sheet>

(Production of interlayer adhesive)

A four-necked flask equipped with a stirring blade, thermometer, nitrogen gas introduction tube, and condenser contained 79.9 parts by weight of butylacrylate, 15 parts by weight of benzyl acrylate, 5 parts by weight of acrylic acid, and 0.1 part by weight of 4-hydroxybutylacrylate. The monomer mixture was added. Next, to 100 parts by weight of the monomer mixture, 0.1 part by weight of 2,2'-azoisobutyronitrile was added together with ethyl acetate as a polymerization initiator, and nitrogen gas was introduced while gently stirring to purge the inside of the flask with nitrogen. The liquid temperature in the flask was maintained at around 55°C, and the polymerization reaction proceeded for 7 hours. Next, ethyl acetate was added to the obtained reaction liquid to adjust the solid content concentration to 30% by weight, and a solution of the (meth)acrylic polymer used in the interlayer adhesive was obtained. The weight average molecular weight of the obtained polymer was 2.2 million.

Next, to the solution of the obtained (meth)acrylic polymer, 0.5 parts by weight of trimethylolpropane/tolylene diisocyanate trimer adduct (coating agent, brand name "Coronate L"), peroxide type, based on 100 parts by weight of solid content of the solution. 0.1 parts by weight of benzoyl peroxide as a cross-linking agent, 0.2 parts by weight of an epoxy group-containing silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., product name “KBM-403), and 0.5 parts by weight of a polyether compound having a reactive silyl group (Kanekase, Cyryl SAT10). The parts were mixed to obtain an adhesive composition PSA1 used as an interlayer adhesive for bonding the polarizing plate P1 and the retardation film R1.

(Production of polarizer with interlayer adhesive layer)

After drying, the prepared adhesive composition PSA1 was applied to the peeling surface of a 38-μm-thick polyethylene terephthalate (PET) film (Mitsubishi Chemical Polyester Film, MRF38), which is a peeling film whose peeling surface was subjected to silicone treatment. It was applied to a layer thickness of 12 μm and dried at 155°C for 1 minute to form an interlayer adhesive layer. Next, the formed interlayer adhesive layer was transferred to the protective layer (without hard coat) side of the polarizing plate P1, and a polarizing plate with an interlayer adhesive layer was obtained.

(Production of circular polarizer with adhesive sheet)

Each adhesive sheet produced in the Examples and Comparative Examples (7 days from time point T ₀ (those that had elapsed above) were transferred from the release film and attached. Next, the above-produced polarizing plate with an interlayer adhesive layer was attached to the first retardation film side of the retardation film R1 via the interlayer adhesive layer, thereby obtaining a circularly polarizing plate with an adhesive sheet. The attachment of the retardation film R1 and the polarizing plate with the interlayer adhesive layer was carried out so that the angle between the slow axis of the first retardation film and the absorption axis of the polarizer was 45 degrees in the counterclockwise direction when viewed from the side of the first retardation film.

Next, the manufacturing method of each adhesive sheet of Examples and Comparative Examples will be described.

The correspondence between the abbreviated names or names shown in the following description and the compounds are as follows.

BA: n-butylacrylate

BzA: Benzyl acrylate

AA: Acrylic acid

HBA: 4-hydroxybutylacrylate

AIBN: 2,2'-azobisisobutyronitrile

C/L: Trimethylolpropane/tolylene diisocyanate trimer adduct (isocyanate-based crosslinking agent; dosing agent, Coronate L)

Peroxide: Benzoyl peroxide (Nippon Yushi Co., Ltd., Kniper BMT)

TetradC: 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (multifunctional epoxy-based crosslinker; Mitsubishi Gas Chemical Co., Ltd., Tetrad C)

KBM403: 3-glycidoxypropyltriethoxysilane (silane coupling agent; manufactured by Shin-Etsu Chemical Co., Ltd., KBM403)

TMP: Trimethylolpropane

EDP: ethylenediamine/propylene oxide tetramer adduct (polyether polyol-based crosslinking accelerator; manufactured by ADEKA, EDP-300)

[Production of (meth)acrylic polymer (A)]

(Synthesis Example 1)

79.9 parts by weight of BA, 15.0 parts by weight of BzA, 5.0 parts by weight of AA, and 0.1 part by weight of HBA were added to a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas introduction tube, and condenser. Next, 0.1 parts by weight of AIBN was added as a polymerization initiator to 100 parts by weight of the mixture of BA, BzA, AA, and HBA, and nitrogen gas was introduced while gently stirring to purge the inside of the flask with nitrogen, and then the liquid temperature in the flask was adjusted to 55°C. The polymerization reaction was maintained for 7 hours. Next, ethyl acetate was added to the obtained reaction liquid to adjust the solid content concentration to 12% by weight, and a solution of (meth)acrylic polymer (A-1) was obtained. The weight average molecular weight (Mw) of the (meth)acrylic polymer (A-1) was 2.2 million.

(Synthesis Example 2)

A solution of (meth)acrylic polymer (A-2) was obtained in the same manner as in Synthesis Example 1, except that the monomers used were changed to 94.9 parts by weight, 5.0 parts by weight of AA, and 0.1 parts by weight of HBA. The weight average molecular weight (Mw) of the (meth)acrylic polymer (A-2) was 2.2 million.

The types and amounts of monomers and polymerization initiators used in Synthesis Examples 1 and 2, and the weight average molecular weight (Mw) of the obtained polymer are summarized in Table 1 below.

[Production of adhesive composition and adhesive sheet]

(Examples 1 to 7, Comparative Examples 1 and 2)

As shown in Table 2 below, a crosslinking agent and the like were mixed with 100 parts by weight of the solid content of the (meth)acrylic polymer (A) to obtain a solvent-type adhesive composition.

Next, the obtained pressure-sensitive adhesive composition was applied to the peeling surface of a 38-μm-thick PET film (Mitsubishi Chemical Polyester Film, MRF38), which is a peeling film whose peeling surface was subjected to silicone treatment, and then heated to 90°C (Example) It was dried for 100 seconds in an air-circulating constant temperature oven set at 5, 60,110°C) to form adhesive sheets (15 μm thick) of Examples 1 to 7 and Comparative Examples 1 and 2. A fountain coater was used to apply the adhesive composition. The evaluation results of each produced adhesive sheet are shown in Table 3 below. Also, for Examples 5 and 6, the drying conditions for evaluating each gel fraction were the above-mentioned 90°C and 100 seconds.

As shown in Table 3, the pressure-sensitive adhesive sheets of the Examples in which the gel fraction G _2h is less than 60% by weight and the G _24h is 60% by weight or more are suitable for suppressing dimensional changes compared to the pressure-sensitive adhesive sheets of the Comparative Examples. , showed high durability.

Industrial applicability

According to the adhesive composition of the present invention, an adhesive sheet used in, for example, an image display device can be formed.

Claims (15)

It is an adhesive composition containing (meth)acrylic polymer (A) as a main component,
Further comprising a cross-linking agent (B),
When an adhesive sheet is formed with the adhesive composition,
The gel fraction G _2h of the adhesive sheet at the time point 2 hours after forming the adhesive sheet T ₀ is less than 60% by weight,
A pressure-sensitive adhesive composition in which the gel fraction G _24h of the pressure-sensitive adhesive sheet at 24 hours from the time point T ₀ is 60% by weight or more. The pressure-sensitive adhesive composition according to claim 1, wherein the ratio G _24h /G _{2h of the gel fraction G 24h to} the gel fraction G _2h is 2 or more. The adhesive composition according to claim 1 or 2, wherein the gel fraction G ₀ of the adhesive sheet immediately after the time T ₀ is 3% by weight or more and 50% by weight or less. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the gel fraction G _7d of the pressure-sensitive adhesive sheet at 7 days from the time point T ₀ is 90% by weight or more. The adhesive composition according to any one of claims 1 to 4, which is of solvent type. The pressure-sensitive adhesive composition according to any one of claims 1 to 5, wherein the crosslinking agent (B) is an isocyanate type. The pressure-sensitive adhesive composition according to any one of claims 1 to 5, wherein the crosslinking agent (B) is a tolylene diisocyanate type. The adhesive composition according to any one of claims 1 to 7, wherein the crosslinking agent (B) is trifunctional or higher. The pressure-sensitive adhesive composition according to any one of claims 1 to 8, wherein a compounding amount of the crosslinking agent (B) is 5 parts by weight or more with respect to 100 parts by weight of the (meth)acrylic polymer (A). The adhesive composition according to any one of claims 1 to 9, wherein the (meth)acrylic polymer (A) contains a structural unit derived from an aromatic ring-containing monomer. The adhesive composition according to any one of claims 1 to 10, wherein the (meth)acrylic polymer (A) contains a structural unit derived from a hydroxyl group-containing monomer at a content of 1% by weight or less. An adhesive sheet formed from the adhesive composition according to any one of claims 1 to 11. The adhesive sheet according to claim 12, wherein the storage modulus G' at 25°C is 0.4 MPa or more. An optical laminate comprising the adhesive sheet according to claim 12 or 13 and an optical film. An image display device comprising the optical laminate according to claim 14.

Images