Adhesive composition and adhesive layer

Abstract

To provide an optical adhesive composition that exhibits superior refractive index and high adhesive durability at high temperatures.SOLUTION: An adhesive composition comprising a (meth)acrylic polymer having structural units derived from a hydroxyl group-containing (meth)acrylic monomer and structural units derived from a transition metal element-containing (meth)acrylic monomer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition. [Background technology]

[0002] Display devices have a structure in which multiple optical components, such as optical films and image display elements, are laminated together. Pressure-sensitive adhesive layers are sometimes used to laminate the optical components together, and these pressure-sensitive adhesive layers are required to have properties such as excellent transparency so as not to interfere with the visibility of the displayed image. Furthermore, components with a high refractive index are sometimes used as the optical components. When a pressure-sensitive adhesive layer is laminated onto an optical component with a high refractive index, a difference in refractive index between the optical component and the pressure-sensitive adhesive layer occurs, which can result in a decrease in the brightness of the displayed image due to light loss. Therefore, the pressure-sensitive adhesive layer is required to have a high refractive index.

[0003] Patent Document 1 describes an acrylic adhesive containing an ethylenically unsaturated monomer, acrylic acid, and zirconium carboxyl ethyl acrylate or phenoxyethyl acrylate. This acrylic adhesive has basic adhesive properties suitable for display applications, as well as a high refractive index and transparency, and is said to prevent a decrease in the brightness of displayed images due to light loss by reducing the difference in refractive index with the display film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent Publication No. 10-2012-0012706 Summary of the Invention [Problem to be solved by the invention]

[0005] Display devices are often placed under high-temperature conditions, and the adhesive layer must have high-temperature durability. However, conventional high-refractive-index acrylic adhesives are insufficient in both refractive index and high-temperature durability.

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having excellent refractive index and high-temperature adhesive durability. [Means for solving the problem]

[0007] The present invention provides the following aspects. [1] A pressure-sensitive adhesive composition comprising a (meth)acrylic polymer having a structural unit derived from a hydroxyl group-containing (meth)acrylic monomer and a structural unit derived from a transition metal element-containing (meth)acrylic monomer.

[0008] [2] The pressure-sensitive adhesive composition of aspect 1, wherein the content of structural units derived from hydroxyl group-containing (meth)acrylic monomers relative to all structural units constituting the (meth)acrylic polymer is 0.8% by mass or more and 15% by mass or less, preferably 2% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 6% by mass or less.

[0009] [3] The pressure-sensitive adhesive composition of aspect 1 or 2, wherein the content of structural units derived from a transition metal element-containing (meth)acrylic monomer relative to all structural units constituting the (meth)acrylic polymer is 0.05% by mass or more and 8.5% by mass or less, preferably 0.5% by mass or more and 5% by mass or less, and more preferably 0.9% by mass or more and 4.7% by mass or less.

[0010] [4] The pressure-sensitive adhesive composition of any one of Aspects 1 to 3, wherein the (meth)acrylic polymer has a weight-average molecular weight of 850,000 or more and 5,000,000 or less, preferably 900,000 or more and 3,500,000 or less, and more preferably 1,000,000 or more and 3,200,000 or less.

[0011] [5] The pressure-sensitive adhesive composition of any one of Aspects 1 to 4, further comprising, as a viscosity adjusting component, at least one (meth)acrylic monomer and a polymerization initiator.

[0012] [6] The pressure-sensitive adhesive composition according to any one of Aspects 1 to 5, which is an optical pressure-sensitive adhesive composition.

[0013] [7] A pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of any one of embodiments 1 to 6.

[0014] [8] The pressure-sensitive adhesive layer of embodiment 7, wherein the pressure-sensitive adhesive layer has a gel fraction of 70% or more and 96% or less, preferably 75% or more and 90% or less, and more preferably 80% or more and 87% or less.

[0015] [9] The pressure-sensitive adhesive layer of aspect 7 or 8, wherein the pressure-sensitive adhesive layer has a refractive index of 1.47 or greater and 1.68 or less, preferably 1.49 or greater and 1.64 or less, and more preferably 1.53 or greater and 1.61 or less.

[0016]

[10] A pressure-sensitive adhesive sheet comprising a substrate and, on a main surface of the substrate, a pressure-sensitive adhesive layer according to any one of embodiments 7 to 9. [Effects of the Invention]

[0017] According to the present invention, there is provided a pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive layer having excellent refractive index and high-temperature adhesive durability. By using the pressure-sensitive adhesive composition of the present invention, a pressure-sensitive adhesive layer having excellent refractive index and high-temperature adhesive durability can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail, but the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the spirit of the present invention. Furthermore, when multiple upper and lower limit values ​​are specified for a specific parameter, any upper and lower limit values ​​can be combined to form a suitable numerical range.

[0019] <(Meth)acrylic polymer> The pressure-sensitive adhesive composition of the present invention contains a (meth)acrylic polymer. The (meth)acrylic polymer contains a structural unit derived from a transition metal-containing (meth)acrylic monomer and a structural unit derived from a hydroxyl group-containing (meth)acrylic monomer. In this specification, "(meth)acrylic" means at least one selected from the group consisting of acrylic and methacrylic. The same applies to "(meth)acrylate" and "(meth)acryloyl".

[0020] The (meth)acrylic polymer contains a structural unit derived from a transition metal-containing (meth)acrylic monomer. Transition metals include metallic elements from Groups 4 to 11 in the periodic table. Such transition metals can form complexes with the (meth)acrylic monomer to form a polyfunctional (meth)acrylic complex compound. Polymerization of a raw material mixture containing the polyfunctional (meth)acrylic complex compound causes the (meth)acrylic polymer to undergo intrapolymer crosslinking and interpolymer crosslinking, increasing the crosslink density of the (meth)acrylic polymer. Because the (meth)acrylic polymer contains a transition metal with a high refractive index and has a high crosslink density, the refractive index of a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition containing the polymer increases. Furthermore, the (meth)acrylic polymer contains a polyfunctional (meth)acrylic complex compound, which increases the cohesive strength, thereby improving the high-temperature durability of the pressure-sensitive adhesive layer.

[0021] Examples of transition metal-containing (meth)acrylic monomers that can be used include zirconium (meth)acrylate, zirconyl di(meth)acrylate, zirconium butoxide (meth)acrylate, zirconium carboxyethyl (meth)acrylate, hafnium (meth)acrylate, hafnium butoxide (meth)acrylate, hafnium oxide di(meth)acrylate, and hafnium carboxyethyl (meth)acrylate.

[0022] Among the above, from the viewpoint of increasing the refractive index of the (meth)acrylic polymer and improving its high-temperature durability, formula [H2C=CHCOOCH2CH2COO- ]4Zr 4+ Zirconium carboxyethyl acrylate represented by the formula [H2C=CHCOOCH2CH2COO - ]4Hf 4+ It is preferred to use hafnium carboxyethyl acrylate represented by the formula: or a combination of both.

[0023] From the viewpoint of achieving both refractive index and durability, the content of the structural units derived from the transition metal-containing (meth)acrylic monomer is, for example, 0.05% by mass or more and 8.5% by mass or less, preferably 0.5% by mass or more and 5% by mass or less, and more preferably 0.9% by mass or more and 4.7% by mass or less, based on all structural units constituting the (meth)acrylic polymer.

[0024] The (meth)acrylic polymer contains structural units derived from hydroxyl group-containing (meth)acrylic monomers. The inclusion of structural units derived from hydroxyl group-containing (meth)acrylic monomers increases the cohesive strength and crosslink density between the (meth)acrylic polymers through hydrogen bonding. As a result, the refractive index and high-temperature adhesive durability of the resulting pressure-sensitive adhesive layer are improved.

[0025] Examples of hydroxyl group-containing (meth)acrylic monomers that can be used include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-(2-hydroxyethoxy)ethyl (meth)acrylate, 2- or 3-chloro-2-hydroxypropyl (meth)acrylate, diethylene glycol mono(meth)acrylate, and 4-hydroxyphenyl (meth)acrylate. Among these, hydroxyalkyl (meth)acrylates having 1 to 5 carbon atoms in the alkyl moiety are preferred, and those having 2 to 4 carbon atoms in the alkyl moiety are more preferred.

[0026] Of the above, it is particularly preferable to use 4-hydroxybutyl acrylate, 4-hydroxyphenyl acrylate, and 2-hydroxyethyl acrylate from the viewpoint of polymerizability, refractive index, and high-temperature durability of the adhesive layer.

[0027] From the viewpoint of achieving both the refractive index and high-temperature durability of the adhesive layer, the content of the structural units derived from the hydroxyl group-containing (meth)acrylic monomer is, for example, 0.8% by mass or more and 15% by mass or less, preferably 2% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 6% by mass or less, based on all structural units constituting the (meth)acrylic polymer.

[0028] The (meth)acrylic polymer preferably contains a structural unit derived from an aromatic ring-containing (meth)acrylic monomer. Examples of aromatic rings include a benzene ring, a naphthalene ring, and a biphenyl ring. By containing a structural unit derived from an aromatic ring-containing (meth)acrylic monomer, the refractive index of the pressure-sensitive adhesive layer is improved. Furthermore, since aromatic ring-containing (meth)acrylic monomers have a high glass transition temperature, by containing a structural unit derived from an aromatic ring-containing (meth)acrylic monomer, the glass transition temperature of the (meth)acrylic polymer is increased, thereby improving the high-temperature durability of the pressure-sensitive adhesive layer.

[0029] Examples of aromatic ring-containing (meth)acrylic monomers that can be used include those having a benzene ring, such as benzyl (meth)acrylate, phenyl (meth)acrylate, 2-phenylethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, phenoxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 4-hydroxyphenyl (meth)acrylate, and 4-benzoylphenyl (meth)acrylate; those having a naphthalene ring, such as 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl (meth)acrylate, and 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate; and those having a biphenyl ring, such as biphenyl (meth)acrylate and 2-(2-biphenylyloxy)ethyl acrylate.

[0030] Of these, it is preferable to use 4-hydroxyphenyl acrylate and 4-benzoylphenyl acrylate from the viewpoint of polymerizability, and the refractive index and durability of the adhesive layer.

[0031] The content of the structural units derived from aromatic ring-containing (meth)acrylic monomers is, for example, 0.5% by mass or more and 19% by mass or less, preferably 1.0% by mass or more and 5% by mass or less, and more preferably 1.5% by mass or more and 3% by mass or less, based on all structural units constituting the (meth)acrylic polymer, from the viewpoint of the refractive index and high-temperature durability of the pressure-sensitive adhesive layer. Note that a (meth)acrylic monomer containing both a hydroxyl group and an aromatic ring in the molecule is treated as both a hydroxyl group-containing (meth)acrylic monomer and an aromatic ring-containing (meth)acrylic monomer.

[0032] The (meth)acrylic polymer preferably contains a structural unit derived from a (meth)acrylic acid alkyl ester having, for example, an alkyl group having 1 to 24 carbon atoms, preferably 4 to 10 carbon atoms. The alkyl group of the (meth)acrylic acid alkyl ester may be linear, branched, or cyclic. By using a (meth)acrylic polymer containing a structural unit derived from a (meth)acrylic acid alkyl ester, it becomes easier to obtain a pressure-sensitive adhesive layer that has good adhesion to optical members.

[0033] Examples of the (meth)acrylic acid alkyl esters include propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, tridecyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, dodecyl (meth)acrylate, hexadecyl acrylate, docosyl (meth)acrylate, cyclohexyl (meth)acrylate, etc. The above (meth)acrylic acid alkyl esters may be used alone or in combination of two or more.

[0034] Of the above, it is preferable to use butyl acrylate, n-octyl acrylate, or isononyl acrylate from the viewpoint of increasing the cohesive strength of the (meth)acrylic polymer and from the viewpoint of adhesion to optical members.

[0035] The content of the structural units derived from the (meth)acrylic acid alkyl ester is, for example, 55% by mass or more and 95% by mass or less, preferably 70% by mass or more and 93% by mass or less, and more preferably 80% by mass or more and 90% by mass or less, based on all structural units constituting the (meth)acrylic polymer, from the viewpoint of adhesion of the pressure-sensitive adhesive layer to optical components and high-temperature durability.

[0036] The (meth)acrylic polymer may contain structural units derived from an ethylenically unsaturated carboxylic acid such as (meth)acrylic acid, crotonic acid, maleic acid, itaconic acid, citraconic acid, or β-carboxyethyl (meth)acrylate. The inclusion of structural units derived from an ethylenically unsaturated carboxylic acid increases the cohesive strength and crosslink density between the (meth)acrylic polymers due to hydrogen bonding. This improves the refractive index and high-temperature adhesive durability of the resulting pressure-sensitive adhesive layer.

[0037] The content of the structural units derived from ethylenically unsaturated carboxylic acid is, for example, 10% by mass or less, preferably 0.2% by mass or more and 8% by mass or less, and more preferably 5% by mass or more and 7% by mass or less, based on all structural units constituting the (meth)acrylic polymer, from the viewpoint of adhesion of the pressure-sensitive adhesive layer to optical components and high-temperature durability.

[0038] A (meth)acrylic polymer can be produced by polymerizing a (meth)acrylic monomer. A known polymerization method can be used to polymerize the (meth)acrylic monomer. For example, a raw material mixture containing a (meth)acrylic monomer and an initiator can be irradiated with active energy rays such as ultraviolet light, or the raw material mixture can be heated to polymerize the (meth)acrylic monomer. From the viewpoints that polymerization can be carried out without using an organic solvent and that the polymer can be produced in a short time, it is preferable to polymerize the (meth)acrylic polymer by irradiating the raw material mixture with active energy rays. Examples of active energy rays include ultraviolet light and electron beams, and ultraviolet light is preferred. The (meth)acrylic monomer contained in the raw material mixture becomes a structural unit of the (meth)acrylic polymer.

[0039] The raw material mixture contains a polymerization initiator. The type of polymerization initiator is selected to match the polymerization method of the raw material mixture. Polymerization initiators include photopolymerization initiators and thermal polymerization initiators.

[0040] Examples of the photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone, (2,4-cyclopentadien-1-yl)[(1-methylethyl)benzene]-Fe(II) hexafluorophosphate, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, a mixture of oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and oxy-phenyl-acetic acid 2-[2-hydroxy-ethoxy]-ethyl ester, benzil dimethyl ketal, and 1-hydroxycyclohexyl phenyl ketone.

[0041] Examples of the thermal polymerization initiator include azo compounds, organic peroxides, inorganic peroxides, etc. Examples of the azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane].

[0042] Examples of organic peroxides include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxypivalate, (3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, and diacetyl peroxide.

[0043] Examples of inorganic peroxides include potassium persulfate, ammonium persulfate, and hydrogen peroxide.

[0044] Among the above, from the viewpoint of increasing the polymerization rate of the (meth)acrylic monomer and the polymerization rate of the (meth)acrylic polymer, it is preferable to use a photopolymerization initiator, and it is particularly preferable to use 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methylpropiophenone.

[0045] The content of the polymerization initiator is, for example, 0.1% by mass or more and 10% by mass or less, preferably 1% by mass or more and 8% by mass or less, and more preferably 2% by mass or more and 7% by mass or less, based on the total amount of (meth)acrylic monomers contained in the raw material mixture.

[0046] The (meth)acrylic polymer has a weight-average molecular weight (Mw) of, for example, 850,000 to 5,000,000, preferably 900,000 to 3,500,000, and more preferably 1,000,000 to 3,200,000. The weight-average molecular weight of the methacrylic polymer can be determined using gel permeation chromatography (GPC). In this case, polystyrene is used as a standard substance for converting the weight-average molecular weight.

[0047] <Adhesive composition> The pressure-sensitive adhesive composition can be prepared by mixing the (meth)acrylic polymer, viscosity adjusting component, polymerization initiator, additives, etc. in accordance with a conventional method.

[0048] The viscosity adjusting component is a component that adjusts the viscosity of the (meth)acrylic polymer to lower it, thereby enabling or facilitating the process of forming it into a PSA sheet. The type and content of the viscosity adjusting component are adjusted so as not to adversely affect the properties of the (meth)acrylic polymer other than viscosity, particularly the refractive index and adhesiveness.

[0049] Examples of viscosity adjusting components include volatile organic solvents, and mixtures of monomers and polymerization initiators, etc. Among these, mixtures of monomers and polymerization initiators are preferred as viscosity adjusting components because they do not need to be dried after forming the pressure-sensitive adhesive layer and there is no risk of volatile substances foaming within the pressure-sensitive adhesive layer.

[0050] As the viscosity adjusting component monomer, the above-mentioned (meth)acrylic monomers can be used.

[0051] Among these, the inclusion of a hydroxyl group-containing (meth)acrylic monomer can improve the adhesion of the pressure-sensitive adhesive layer due to hydrogen bonding between the pressure-sensitive adhesive layer and the optical component, and the inclusion of a (meth)acrylic acid alkyl ester improves the coatability of the pressure-sensitive adhesive composition and improves the uniformity of the pressure-sensitive adhesive layer, making them preferred as viscosity-adjusting components.

[0052] Hydroxyl group-containing (meth)acrylic monomers preferred as viscosity adjusting components include 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, etc. Of these, 4-hydroxybutyl acrylate and 2-hydroxyethyl acrylate are preferred.

[0053] (Meth)acrylic acid alkyl esters preferred as viscosity adjusting components include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, cyclohexyl acrylate, hexyl acrylate, dodecyl acrylate, hexadecyl acrylate, n-octyl (meth)acrylate, isononyl (meth)acrylate, etc. In addition, the hydrogen atom of the alkyl group of the (meth)acrylic acid alkyl ester may be substituted with an alkoxy group, such as 2-methoxyethyl acrylate.

[0054] When a hydroxyl group-containing (meth)acrylic monomer is contained as a viscosity adjusting component, the type of the hydroxyl group-containing (meth)acrylic monomer that serves as a constituent unit of the (meth)acrylic polymer may be the same as or different from that of the hydroxyl group-containing (meth)acrylic monomer.Furthermore, when a (meth)acrylic acid alkyl ester monomer is contained as a viscosity adjusting component, the type of the (meth)acrylic acid alkyl ester monomer that serves as a constituent unit of the (meth)acrylic polymer may be the same as or different from that of the (meth)acrylic acid alkyl ester monomer.

[0055] The content of the monomer is, for example, 3% by mass to 30% by mass, preferably 4% by mass to 25% by mass, and more preferably 5% by mass to 20% by mass, based on the pressure-sensitive adhesive composition.

[0056] If the content of the monomer in the pressure-sensitive adhesive composition is less than 3% by mass, the viscosity of the pressure-sensitive adhesive composition will be too high, making it difficult to form it into a layer of uniform thickness, and if it exceeds 30% by mass, the viscosity of the pressure-sensitive adhesive composition will be too low, making it difficult to form it into a layer of sufficient thickness.

[0057] From the viewpoint of durability and adhesion of the pressure-sensitive adhesive layer, the content of the hydroxyl group-containing (meth)acrylic monomer is, for example, 3% by mass or more and 74% by mass or less, preferably 10% by mass or more and 70% by mass or less, and more preferably 15% by mass or more and 65% by mass or less, based on the total amount of the monomers.

[0058] The polymerization initiator contained in the PSA composition can be the same as or different from the polymerization initiator contained in the raw material mixture for the (meth)acrylic polymer.

[0059] The content of the polymerization initiator is, for example, 0.05% by mass to 10% by mass, preferably 1% by mass to 6% by mass, and more preferably 1.5% by mass to 4% by mass, based on the pressure-sensitive adhesive composition.

[0060] If the content of the polymerization initiator in the pressure-sensitive adhesive composition is less than 0.05% by mass, the polymerization initiation property may decrease, whereas if it exceeds 10% by mass, the durability of the pressure-sensitive adhesive layer may decrease.

[0061] The pressure-sensitive adhesive composition may contain additives such as a crosslinking agent, a silane coupling agent, a crosslinking catalyst, a weather stabilizer, a tackifier, a plasticizer, a softener, a dye, a pigment, an inorganic filler, light-scattering fine particles, an antistatic agent such as an ionic compound, etc. The type and content of the additive are adjusted so as not to adversely affect the properties of the (meth)acrylic polymer, in particular the refractive index and adhesiveness.

[0062] Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an amine-based crosslinking agent, a melamine-based crosslinking agent, an aziridine-based crosslinking agent, a hydrazine-based crosslinking agent, an aldehyde-based crosslinking agent, an oxazoline-based crosslinking agent, a metal alkoxide-based crosslinking agent, a metal chelate-based crosslinking agent, a metal salt-based crosslinking agent, and an ammonium salt-based crosslinking agent.

[0063] Examples of the silane coupling agent include an organosilicon compound having at least one alkoxysilyl group in the molecule. Silicon compounds containing polymerizable unsaturated groups, such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; Silicon compounds having an epoxy structure, such as 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane; Amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane; 3-chloropropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, or a condensate of at least one of these with an alkyl group-containing silicon compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, or ethyltrimethoxysilane etc.

[0064] <Adhesive sheet (C)> The pressure-sensitive adhesive composition can be formed into a layer by applying it to a substrate and drying it as needed. Examples of methods for applying the pressure-sensitive adhesive composition or its organic solvent dilution include bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

[0065] When the pressure-sensitive adhesive composition contains a mixture of a (meth)acrylic monomer and a polymerization initiator in addition to a (meth)acrylic polymer, the pressure-sensitive adhesive composition applied to the substrate is subjected to an active energy ray irradiation treatment or a heat treatment, etc., to polymerize the monomer. The pressure-sensitive adhesive composition formed into a layer on the main surface of the substrate is thereby cured to form a pressure-sensitive adhesive layer. In this way, a pressure-sensitive adhesive sheet including a substrate and a pressure-sensitive adhesive layer is produced. Examples of active energy rays include ultraviolet rays and electron beams, and ultraviolet rays are preferred.

[0066] The thickness of the pressure-sensitive adhesive layer is, for example, 1 μm to 100 μm, preferably 2 μm to 80 μm, more preferably 3 μm to 60 μm, and even more preferably 5 μm to 30 μm. If the thickness of the pressure-sensitive adhesive sheet is less than 1 μm, the adhesiveness may decrease, and if it exceeds 100 μm, the transparency may decrease.

[0067] From the viewpoint of high-temperature durability of the pressure-sensitive adhesive layer, the gel fraction of the pressure-sensitive adhesive layer is, for example, 70% to 96%, preferably 75% to 90%, and more preferably 80% to 87%. The gel fraction of the pressure-sensitive adhesive layer can be adjusted, for example, by the type of (meth)acrylic polymer contained in the pressure-sensitive adhesive composition (e.g., the type and content of structural units derived from a hydroxyl group-containing (meth)acrylic polymer, or the type and content of structural units derived from an ethylenically unsaturated carboxylic acid), the amount of initiator and crosslinker contained in the pressure-sensitive adhesive composition, and the UV light intensity and temperature when the pressure-sensitive adhesive composition is cured to form the pressure-sensitive adhesive layer. The gel fraction can be measured by the method described in the Examples below.

[0068] The refractive index of the pressure-sensitive adhesive layer is, for example, 1.47 or more and 1.68 or less, preferably 1.49 or more and 1.64 or less, and more preferably 1.53 or more and 1.61 or less. This can sometimes happen.

[0069] The haze value of the pressure-sensitive adhesive layer is, for example, 2.3% or less, preferably 0.2% to 1.9%, and more preferably 0.24% to 1.5%. If the haze of the pressure-sensitive adhesive layer exceeds 2.3%, light loss due to scattering increases, which may reduce the visibility of the displayed image. [Example]

[0070] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to these examples. Comparative Example 5 is a specific example corresponding to Example 1 of Patent Document 1.

[0071] <Performance evaluation method> The adhesive layers of the examples and comparative examples were subjected to characteristic tests by the following methods.

[0072] (1) Transparency assessment The release film was peeled off from the pressure-sensitive adhesive sheet obtained in the following Examples and Comparative Examples, and the sheet was attached to a glass slide to obtain a test sample having a pressure-sensitive adhesive layer / glass slide configuration. The haze value (%) of this test sample was measured in accordance with JIS K-7136 using a reflectance / transmittance meter (HR-100 (product name), manufactured by Murakami Color Research Laboratory Co., Ltd.). The haze value of the pressure-sensitive adhesive layer was determined by subtracting the haze value of the glass slide alone (0.2%) from the haze value.

[0073] [Transparency Evaluation Criteria] A (Excellent): Haze value is 2% or less B (Poor): Haze value exceeds 2%

[0074] (2) Refractive index evaluation The release film was peeled off from the pressure-sensitive adhesive sheet obtained in the following Examples and Comparative Examples, and the pressure-sensitive adhesive layer was attached to a measurement plate. The pressure-sensitive adhesive layer was irradiated with sodium D-line in an atmosphere of 25°C, and the refractive index was measured using an Abbe refractometer (NAR-1T (trade name), manufactured by ATAGO Co., Ltd.).

[0075] [Refractive index evaluation standard] A (Excellent): The refractive index of the adhesive layer exceeds 1.65 B (Good): The refractive index of the adhesive layer is 1.48 or more and 1.65 or less C (poor): The refractive index of the adhesive layer is less than 1.48

[0076] (3) Measurement of weight average molecular weight (Mw) The weight average molecular weight (Mw, polystyrene equivalent) of the (meth)acrylic polymer described below was determined by the following size exclusion chromatography (SEC) using tetrahydrofuran as the mobile phase.

[0077] Specifically, the (meth)acrylic polymer to be measured was dissolved in tetrahydrofuran at a concentration of approximately 0.05% by mass, and 10 μL of the solution was injected into the SEC. The mobile phase was run at a flow rate of 1.0 mL / min. The column used was PLgel MIXED-B (trade name) manufactured by Polymer Laboratories. The detector used was a UV-VIS detector, Agilent GPC (trade name).

[0078] (4) Thickness measurement The thickness was measured using a contact type film thickness measuring device (Nikon Corporation, "ZC-101").

[0079] (5) Measurement of gel fraction The pressure-sensitive adhesive sheets obtained in the following Examples and Comparative Examples were cut into pieces 80 mm wide x 80 mm long, and the pressure-sensitive adhesive layers contained in the cut-out pressure-sensitive adhesive sheets were used as samples. The samples were wrapped in a polyester mesh (mesh size 200), and their masses were weighed using a precision balance. The mass of the sample alone, M1, was calculated by subtracting the mass of the mesh alone from the weighed mass. Next, the pressure-sensitive adhesive layer wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 72 hours, and the sample was removed (hereinafter, the removed sample is referred to as the "sample after immersion"). The immersed sample was air-dried for 24 hours in an environment at a temperature of 23°C and a relative humidity of 50%, and then further dried in an oven at 120°C for 4 hours, after which its mass was weighed using a precision balance. The mass of the sample alone, M2, was calculated by subtracting the mass of the mesh alone from the weighed mass. The gel fraction was determined from the mass M1 and the mass M2 according to the following formula.

[0080] Gel fraction [%] = (M2 / M1) × 100

[0081] (6) High temperature adhesive durability (80℃) One release film of the adhesive sheet obtained in the following Examples and Comparative Examples was peeled off, and a 50 μm-thick PET film was attached to obtain a laminate having a PET film / adhesive layer / release film configuration. This laminate was cut into a 100 mm wide x 100 mm long piece, and the release film was peeled off to obtain a PET film / adhesive layer configuration (this configuration may also be referred to as Test Piece A), which was then attached to a non-alkali glass (10 inch size) via the adhesive layer.

[0082] This sample was subjected to pressure bonding in an autoclave (50°C, 0.5 MPa atmosphere) for approximately 20 minutes, and then held under constant temperature and humidity conditions (23°C, 50% RH) for 4 hours to prepare an evaluation sample. The evaluation sample consisted of test piece A (PET film / adhesive layer) / alkali-free glass. After storing the evaluation sample in an environment at a temperature of 80°C for 100 hours, the presence or absence of peeling at the corners of test piece A was visually inspected and judged according to the following criteria.

[0083] [High temperature adhesive durability evaluation criteria] A (Excellent): Peeling is observed between the adhesive layer and the glass in an area less than 0.5 mm from the corner. B (Good): Peeling is observed between the adhesive layer and the glass in an area 0.5 mm or more but less than 1 mm from the corner. C (Poor): Peeling is observed between the adhesive layer and the glass in an area 1 mm or more from the corner.

[0084] <Examples 1 to 8 and Comparative Examples 1 to 4> 1. Preparation of (meth)acrylic polymers A1 to A12 A 1-liter reaction vessel equipped with a cooling device was prepared. A mixture of the monomer components shown in Table 1 in the amounts shown in Table 1 was added to the reactor while refluxing nitrogen gas. Next, while stirring the mixture, nitrogen gas was refluxed into the reactor for 1 hour to remove oxygen, and then the temperature of the mixture was raised to 60°C. While maintaining the temperature at 60°C, the photopolymerization initiators shown in Table 1 were added in the amounts shown in Table 1. The polymerization reaction was carried out by irradiating the mixture with a UV lamp (10 mW) while stirring, yielding (meth)acrylic polymers A1 to A13. The amounts of the monomer components shown in Table 1 represent the mass percentages (mass%) based on the total mass of the monomer components, and the amounts of the photopolymerization initiators represent the mass percentages (mass%) based on the total mass of the monomer components. The weight-average molecular weights (Mw) of the (meth)acrylic polymers A1 to A12 are shown in Table 1.

[0085] 2. Preparation of Pressure-Sensitive Adhesive Compositions B1 to B12 Pressure-sensitive adhesive compositions B1 to B13 were prepared by mixing the (meth)acrylic polymer, monomer component, transition metal component, photopolymerization initiator, and curing agent shown in Table 2 in the amounts shown in Table 2. The blending amounts shown in Table 2 indicate mass percentages (mass %) based on the total mass of the mixed components.

[0086] 3. Preparation of adhesive sheets C1 to C12 Pressure-sensitive adhesive compositions B1 to B12 were applied to the release-treated surface of release film A (polyethylene terephthalate film coated with a silicone release agent) so that the thickness of the pressure-sensitive adhesive layer was as shown in Table 2. Release film B (polyethylene terephthalate film coated with a silicone release agent) was laminated on the coating layer so that the release-treated surface was in contact with the coating layer, and then UV irradiation was performed to produce pressure-sensitive adhesive sheets C1 to C12 having a layer structure of release film A / pressure-sensitive adhesive layer / release film B. The UV irradiation conditions were an integrated light dose of 400 mJ / cm2 2 , illuminance is 1.8mW / cm 2 (UVV standard). Property tests were carried out using the pressure-sensitive adhesive layers of the obtained pressure-sensitive adhesive sheets C1 to C13. The evaluation results of the properties are shown in Table 4.

[0087] <Comparative Example 5> (corresponding to Example 1 of Patent Document 1) 1. Preparation of (meth)acrylic polymer A13 A 1-L reaction vessel equipped with a cooling device was prepared. While refluxing nitrogen gas, a mixture of 125 g of ethyl acetate and 25 g of methanol as solvents, the monomer components shown in Table 1, and a thermal polymerization initiator in the amounts shown in Table 1 (total amount of monomer components and thermal polymerization initiator: 100 g) was added to the reactor. Next, while stirring the mixture, nitrogen gas was refluxed through the reactor for 1 hour to remove oxygen, and then the temperature of the mixture was raised to 70°C. The reaction was allowed to proceed for 5 hours while maintaining the temperature at 70°C, yielding (meth)acrylic polymer A13. The amounts of the monomer components shown in Table 1 represent the mass percentage (mass%) based on the total mass of the monomer components, and the amount of the photopolymerization initiator represents the mass percentage (mass%) based on the total mass of the monomer components. The weight-average molecular weight (Mw) of (meth)acrylic polymer A13 is shown in Table 1.

[0088] 2. Preparation of Pressure-Sensitive Adhesive Composition B13 A pressure-sensitive adhesive composition B13 was prepared by mixing the (meth)acrylic polymer A13 and a methylaziridine derivative (NeoCryl CX-100) as a curing agent in the amounts shown in Table 2. The blending amounts shown in Table 2 indicate mass percentages (mass%) based on the total mass of the (meth)acrylic polymer and curing agent. The mass percentages of the (meth)acrylic polymer shown in Table 2 are the amounts of the active ingredients.

[0089] 3. Preparation of adhesive sheet C13 PSA composition B13 was applied to the release-treated surface of release film A (polyethylene terephthalate film coated with a silicone release agent) and dried at 80°C for 1 minute. Release film B (polyethylene terephthalate film coated with a silicone release agent) was then laminated on top of it so that the release-treated surface was in contact with the coating layer, producing PSA sheet C13 having a layer structure of release film A / pressure-sensitive adhesive layer / release film B. The thickness of the pressure-sensitive adhesive layer is as shown in Table 2. The property evaluation results are shown in Table 3.

[0090] [Table 1]

[0091] [Table 2]

[0092] The meanings of the abbreviations in Tables 1 and 2 are as follows:

[0093] (Hydroxyl group-containing (meth)acrylic monomer) 4-HPMA: 4-hydroxyphenyl methacrylate (obtained from Tokyo Chemical Industry Co., Ltd.) 4-HBA: 4-hydroxybutyl acrylate (obtained from Tokyo Chemical Industry Co., Ltd.)

[0094] (Transition metal-containing (meth)acrylic monomer) ZrCEA: Zirconium carboxyethyl acrylate (obtained from Sigma Aldrich) HfCEA: Hafnium carboxyethyl acrylate (obtained from Sigma Aldrich)

[0095] ((Meth)acrylic acid alkyl ester) BA: butyl acrylate (obtained from Tokyo Chemical Industry Co., Ltd.) OA: n-octyl acrylate (obtained from Tokyo Chemical Industry Co., Ltd.) 2-EHA: 2-ethylhexyl acrylate (obtained from Tokyo Chemical Industry Co., Ltd.)

[0096] (Aromatic ring-containing (meth)acrylic monomer) 4-BPMA: 4-benzoylphenyl methacrylate (obtained from Tokyo Chemical Industry Co., Ltd.) AA: acrylic acid

[0097] (Photopolymerization initiator) Omnirad 184: 1-hydroxycyclohexyl phenyl ketone (obtained from IGM Resins BV)

[0098] (thermal polymerization initiator) AIBN: 2,2'-azoisobutyronitrile (obtained from Tokyo Chemical Industry Co., Ltd.)

[0099] (hardening agent) NeoCryl CX-100: methylaziridine derivative (MAZ) (obtained from DSM Neoresin)

[0100] (transition metal component) ZrO2: Zirconia (obtained from Tokyo Chemical Industry Co., Ltd.)

[0101] [Table 3]

Claims

1. A pressure-sensitive adhesive composition comprising a (meth)acrylic polymer having a structural unit derived from a hydroxyl group-containing (meth)acrylic monomer and a structural unit derived from a transition metal element-containing (meth)acrylic monomer.

2. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the content of structural units derived from a hydroxyl group-containing (meth)acrylic monomer relative to all structural units constituting the (meth)acrylic polymer is 0.8% by mass or more and 15% by mass or less.

3. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the content of structural units derived from a transition metal element-containing (meth)acrylic monomer relative to all structural units constituting the (meth)acrylic polymer is 0.05% by mass or more and 8.5% by mass or less.

4. The pressure-sensitive adhesive composition according to claim 1 , wherein the (meth)acrylic polymer has a weight-average molecular weight of 850,000 or more and 5,000,000 or less.

5. The pressure-sensitive adhesive composition according to claim 1, further comprising at least one (meth)acrylic monomer and a polymerization initiator as viscosity adjusting components.

6. The pressure-sensitive adhesive composition according to claim 1 , which is an optical pressure-sensitive adhesive composition.

7. A pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 6.

8. The pressure-sensitive adhesive layer according to claim 7 , wherein the pressure-sensitive adhesive layer has a gel fraction of 70% or more and 96% or less.

9. The pressure-sensitive adhesive layer according to claim 7 , wherein the pressure-sensitive adhesive layer has a refractive index of 1.47 or more and 1.68 or less.

10. A pressure-sensitive adhesive sheet comprising a substrate and the pressure-sensitive adhesive layer according to claim 7 on a main surface of the substrate.

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