JP7623808B2 - Photocurable pressure-sensitive adhesive composition, double-sided pressure-sensitive adhesive sheet and method for producing same, and optical device and method for producing same - Google Patents

Description

The present invention relates to a photocurable adhesive composition and a double-sided adhesive sheet formed from the photocurable adhesive composition. Furthermore, the present invention relates to an optical device including the double-sided adhesive sheet.

In optical devices, adhesive sheets are used to laminate components. For example, in liquid crystal display devices, optical films such as retardation films and polarizing plates are attached to both sides of a liquid crystal cell via adhesive sheets. In organic EL display devices, a circular polarizing plate is attached to the viewing surface of the organic EL cell via an adhesive sheet in order to prevent reflection of external light by the metal electrodes of the organic EL cell. In addition, optical components such as touch panel sensors and cover windows are attached to the surfaces of these image display devices via adhesive sheets.

It has been proposed to use a photocurable adhesive composition that cures when exposed to active light such as ultraviolet light as an adhesive sheet used for bonding components of an optical device. For example, Patent Document 1 shows an example in which a photopolymerization initiator is added to a monomer component, UV polymerization is performed in a solvent-free system, a multifunctional monomer and a photopolymerization initiator are added to the obtained low-polymerization polymer (partially polymerized product) to prepare a photocurable adhesive composition, which is applied to a substrate and then UV polymerization is performed again to obtain a transparent adhesive sheet. Patent Document 2 shows an example in which a solution containing a monomer component and a thermal polymerization initiator is heated to prepare a polymer solution by solution polymerization, an isocyanate-based crosslinking agent, a multifunctional monomer and a photopolymerization initiator are added to this solution to prepare a photocurable adhesive composition, which is applied to a substrate and then the solvent is removed by heating to obtain a transparent adhesive sheet. In this adhesive sheet, the multifunctional monomer is in an unreacted state, and when the adhesive sheet is bonded to an adherend and then irradiated with UV light, the storage modulus increases due to photopolymerization of the multifunctional monomer, thereby improving the adhesion reliability to the adherend.

JP 2011-74308 A JP 2014-227453 A

As shown in Patent Documents 1 and 2, a transparent adhesive sheet with a total light transmittance of 90% or more is generally used to bond components of an optical device. On the other hand, it is expected that an adhesive sheet that absorbs visible light will be used in an optical device for the purpose of controlling visibility, etc. An adhesive composition containing a colorant is used to prepare an adhesive sheet that absorbs visible light. The present invention aims to provide an adhesive composition that contains a colorant and is photocurable, and an adhesive sheet formed using the adhesive composition.

The adhesive composition of the present invention contains a polymer, a photopolymerizable compound, a photopolymerization initiator, and a colorant, and has photocurability. The colorant contained in the photocurable adhesive composition preferably has a maximum transmittance at wavelengths of 330 to 400 nm that is greater than the maximum transmittance at wavelengths of 400 to 700 nm. In addition, the colorant preferably has an average transmittance at wavelengths of 330 to 400 nm that is greater than the average transmittance at wavelengths of 400 to 700 nm. As the colorant, a pigment, dye, or the like is used.

The photopolymerization initiator preferably has at least one absorption maximum in the wavelength range of 330 to 400 nm. The polymer contained in the adhesive composition may be an acrylic polymer. The glass transition temperature of the polymer may be 0°C or lower. The adhesive composition may contain a crosslinking agent capable of crosslinking with the polymer. Examples of the crosslinking agent include an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent.

The double-sided adhesive sheet can be obtained by forming the above-mentioned adhesive composition into a sheet. The double-sided adhesive sheet may have a maximum transmittance at wavelengths of 330 to 400 nm that is greater than the maximum transmittance at wavelengths of 400 to 700 nm, and may have an average transmittance at wavelengths of 330 to 400 nm that is greater than the average transmittance at wavelengths of 400 to 700 nm. The average transmittance at wavelengths of 400 to 700 nm of the double-sided adhesive sheet may be 80% or less. The total light transmittance of the double-sided adhesive sheet may be 80% or less.

The thickness of the double-sided adhesive sheet is, for example, about 10 to 500 μm. The shear storage modulus of the double-sided adhesive sheet at a temperature of 25° C. may be 10 to 1000 kPa. The shear storage modulus of the double-sided adhesive sheet at a temperature of 85° C. may be 3 to 300 kPa.

The double-sided pressure-sensitive adhesive sheet of the first embodiment of the present invention is formed by applying the pressure-sensitive adhesive composition in a sheet form on a substrate, and irradiating the sheet-like coating film also provided on the substrate with ultraviolet light to photocure the photopolymerizable compound. That is, the double-sided pressure-sensitive adhesive sheet of the first embodiment is made of a photocured sheet-like molded product of the photocurable pressure-sensitive adhesive composition. The double-sided pressure-sensitive adhesive sheet of the first embodiment may have a non-volatile content of 90% or more.

The double-sided pressure-sensitive adhesive sheet of the second embodiment of the present invention is formed by applying the pressure-sensitive adhesive composition described above in the form of a sheet onto a substrate and removing the solvent as necessary. The double-sided pressure-sensitive adhesive sheet of the second embodiment is a photocurable pressure-sensitive adhesive sheet that contains a photopolymerizable compound in an unreacted state.

Double-sided pressure-sensitive adhesive sheets are used, for example, to bond multiple members (adherends) together in the formation of optical devices such as image display devices. A first adherend is bonded to a first main surface of the double-sided pressure-sensitive adhesive sheet, and a second adherend is bonded to the second main surface, thereby bonding the first adherend and the second adherend together via the double-sided pressure-sensitive adhesive sheet. If the double-sided pressure-sensitive adhesive sheet is photocurable, the double-sided pressure-sensitive adhesive sheet may be irradiated with ultraviolet light after bonding to the adherend to photocure the photopolymerizable compound.

A colored adhesive sheet can be obtained by using an adhesive composition containing a colorant. Because the colorant contained in the photocurable adhesive composition is UV-transparent, even when photocuring is performed by UV irradiation, curing inhibition is unlikely to occur and the polymerization rate can be increased.

FIG. 2 is a cross-sectional view showing an example of the configuration of a pressure-sensitive adhesive sheet with a release film. 1 is a transmission spectrum of a black colorant used in an example. 1 is a graph plotting the relationship between the amount of ultraviolet light irradiation and the non-volatile content of the pressure-sensitive adhesive sheet.

Figure 1 shows an adhesive sheet with release films, in which release films 1 and 2 are temporarily attached to both sides of a double-sided adhesive sheet 5. The double-sided adhesive sheet 5 is formed by forming an adhesive composition into a sheet. The adhesive composition is generally a viscous liquid that contains a polymer, and a double-sided adhesive sheet is obtained by applying the adhesive composition in a layer on a substrate and removing the solvent as necessary.

The double-sided pressure-sensitive adhesive sheet of the present invention is formed using a photocurable pressure-sensitive adhesive composition. The photocurable pressure-sensitive adhesive composition contains a photopolymerizable compound and a photopolymerization initiator in addition to a polymer. The double-sided pressure-sensitive adhesive sheet of the present invention is a colored pressure-sensitive adhesive sheet that absorbs visible light. A pressure-sensitive adhesive composition containing a colorant is used to form the colored pressure-sensitive adhesive sheet. That is, the photocurable pressure-sensitive adhesive composition used to form the double-sided pressure-sensitive adhesive sheet of the present invention contains a colorant in addition to a polymer, a photopolymerizable compound, and a photopolymerization initiator.

Double-sided pressure-sensitive adhesive sheets formed using a photocurable pressure-sensitive adhesive composition are broadly divided into a type in which photocuring is performed on the substrate (first form) and a type in which photocuring is not performed on the substrate, but rather after bonding to an adherend (second form).

[First Form]
The double-sided pressure-sensitive adhesive sheet of the first embodiment of the present invention is formed by applying a photocurable pressure-sensitive adhesive composition containing a polymer, a photopolymerizable compound, a photopolymerization initiator, and a colorant onto a substrate, and then photocuring the composition on the substrate.

<Adhesive composition>
(polymer)
Examples of the polymer contained in the pressure-sensitive adhesive composition include acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyvinyl ethers, vinyl acetate/vinyl chloride copolymers, modified polyolefins, epoxy-based, fluorine-based, and rubber-based polymers such as natural rubber and synthetic rubber. In particular, acrylic polymers are preferably used because they exhibit appropriate adhesive properties such as wettability, cohesiveness, and adhesiveness, and are also excellent in weather resistance and heat resistance.

The acrylic polymer contains an alkyl (meth)acrylate ester as the main monomer component. In this specification, "(meth)acrylic" means acrylic and/or methacrylic. The amount of the alkyl (meth)acrylate ester relative to the total amount of monomer components constituting the acrylic polymer is preferably 50% by weight or more, more preferably 55% by weight or more, and even more preferably 60% by weight or more.

As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms is preferably used. The (meth)acrylic acid alkyl ester may have a branched alkyl group or a cyclic alkyl group.

Specific examples of (meth)acrylic acid alkyl esters having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, and isooctyl (meth)acrylate. Examples of such acrylates include ethyl, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

Specific examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; and (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring such as dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

The acrylic polymer may contain polar group-containing monomers such as hydroxyl group-containing monomers, carboxy group-containing monomers, and nitrogen-containing monomers as constituent monomer components. When the acrylic polymer contains a polar group-containing monomer as a constituent monomer component, the cohesive strength of the adhesive tends to be increased and the adhesive strength tends to be improved. The amount of polar group-containing monomers (the total of the hydroxy group-containing monomers, carboxy group-containing monomers, and nitrogen-containing monomers) relative to the total amount of monomer components constituting the acrylic polymer is, for example, about 3 to 50% by weight, and may be 5 to 40% by weight or 10 to 30% by weight.

Examples of hydroxyl group-containing monomers include (meth)acrylic acid esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl (meth)acrylate. When a crosslinking structure is introduced into the polymer using an isocyanate crosslinking agent, the hydroxyl group can become a reaction point (crosslinking point) with the isocyanate group.

Examples of carboxyl group-containing monomers include acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, as well as itaconic acid, maleic acid, fumaric acid, and crotonic acid. When a crosslinking structure is introduced into the polymer using an epoxy crosslinking agent, the carboxyl group can become a reaction point (crosslinking point) with the epoxy group.

Nitrogen-containing monomers include vinyl monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinyl carboxylic acid amides, and N-vinylcaprolactam, as well as cyano group-containing monomers such as acrylonitrile and methacrylonitrile.

The acrylic polymer may contain, as monomer components other than those mentioned above, vinyl monomers such as acid anhydride group-containing monomers, caprolactone adducts of (meth)acrylic acid, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, vinyl acetate, vinyl propionate, styrene, and α-methylstyrene; epoxy group-containing monomers such as glycidyl (meth)acrylate; glycol-based acrylic ester monomers such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; acrylic ester monomers such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate, and 2-methoxyethyl (meth)acrylate.

The glass transition temperature (Tg) of the polymer contained in the pressure-sensitive adhesive composition is preferably 0° C. or lower. The glass transition temperature of the polymer may be −5° C. or lower, −10° C. or lower, or −15° C. or lower. The glass transition temperature of the polymer is the peak top temperature of the loss tangent (tan δ) measured by dynamic viscoelasticity measurement. When a crosslinked structure is introduced into the polymer, the glass transition temperature may be calculated based on the theoretical Tg from the composition of the polymer. The theoretical Tg is calculated from the glass transition temperature Tg _i of a homopolymer of the constituent monomer components of the polymer and the weight fraction W _i of each monomer component according to the following Fox formula.
1/Tg=Σ(W _i /Tg _i )

Tg is the glass transition temperature of the polymer (unit: K), W _i is the weight fraction (copolymerization ratio by weight) of the monomer component i constituting the polymer, and Tg _i is the glass transition temperature of a homopolymer of the monomer component i (unit: K). As the glass transition temperature of the homopolymer, the values described in Polymer Handbook, 3rd Edition (John Wiley & Sons, Inc., 1989) can be used. As the Tg of a homopolymer of a monomer not described in the above literature, the peak top temperature of tan δ measured by dynamic viscoelasticity measurement may be used.

The above monomer components are polymerized by various known methods to obtain a polymer. Although the polymerization method is not particularly limited, it is preferable to prepare the polymer by photopolymerization in the adhesive composition used to prepare the first type of double-sided adhesive sheet in which the adhesive composition is photocured on a substrate. Photopolymerization allows the preparation of a polymer without using a solvent, so that there is no need to dry and remove the solvent when forming the adhesive sheet, and a thick adhesive sheet can be formed uniformly.

In the preparation of a type of adhesive sheet in which the adhesive composition is photocured on a substrate, it is preferable to prepare a polymer (prepolymer) with a low degree of polymerization in which a portion of the monomer components remain unreacted. The composition (prepolymer forming composition) used to prepare the prepolymer preferably contains a photopolymerization initiator in addition to the monomer. The photopolymerization initiator may be appropriately selected according to the type of monomer. For example, a photoradical polymerization initiator is used for the polymerization of an acrylic polymer. Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators.

In the polymerization, a chain transfer agent or a polymerization inhibitor (polymerization retarder) may be used for the purpose of adjusting the molecular weight, etc. Examples of chain transfer agents include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol, and α-methylstyrene dimer.

The polymerization rate of the prepolymer is not particularly limited, but is preferably 3 to 50% by weight, more preferably 5 to 40% by weight, from the viewpoint of obtaining a viscosity suitable for application on a substrate. The polymerization rate of the prepolymer can be adjusted to a desired range by adjusting the type and amount of photopolymerization initiator, the irradiation intensity and irradiation time of active light such as UV light, etc. The polymerization rate of the prepolymer is the non-volatile content when heated at 130°C for 3 hours, and is calculated by the following formula. The polymerization rate (non-volatile content) of the pressure-sensitive adhesive sheet is also measured by the same method.
Polymerization rate (%) = weight after heating / weight before heating × 100

As described above, the photocurable adhesive composition used to form the colored adhesive sheet contains a polymer, a photopolymerizable compound, a photopolymerization initiator, and a colorant. For example, a photocurable adhesive composition can be obtained by adding a photopolymerizable compound, a photopolymerization initiator, and a colorant to a prepolymer. Instead of using a prepolymer, a low molecular weight polymer (oligomer) can be used, and the low molecular weight polymer can be mixed with a photopolymerizable compound, a photopolymerization initiator, and a colorant to prepare the adhesive composition.

(Photopolymerizable Compound)
The photopolymerizable compound contained in the pressure-sensitive adhesive composition has one or more photopolymerizable functional groups in one molecule. The photopolymerizable functional group may be any of radical polymerizable, cationic polymerizable, and anionic polymerizable, but a radical polymerizable functional group having an unsaturated double bond (ethylenically unsaturated group) is preferred because of its excellent reactivity.

A prepolymer contains a polymer and unreacted monomers, and the unreacted monomers retain photopolymerizability. Therefore, it is not necessary to add a photopolymerizable compound when preparing the pressure-sensitive adhesive composition. When a photopolymerizable compound is added to a prepolymer, the photopolymerizable compound added may be the same as or different from the monomer used in preparing the prepolymer.

When the polymer is an acrylic polymer, the compound added as the photopolymerizable compound is preferably a monomer or oligomer having a (meth)acryloyl group as a photopolymerizable functional group, since it has high compatibility with the polymer. The photopolymerizable compound may be a polyfunctional compound having two or more photopolymerizable functional groups in one molecule. Examples of photopolymerizable polyfunctional compounds include polyfunctional (meth)acrylates. Examples of polyfunctional (meth)acrylates include bifunctional poly ... functional (meth)acrylic acid esters; trifunctional (meth)acrylic acid esters such as pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ethoxylated isocyanuric acid tri(meth)acrylate; tetrafunctional (meth)acrylic acid esters such as ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and pentafunctional or higher (meth)acrylic acid esters such as dipentaerythritol penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate.

When a polyfunctional compound is used as the photopolymerizable compound, the amount of the polyfunctional compound used is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 25 parts by weight or less, relative to 100 parts by weight of the total amount of monomers (the total of the monomers used to prepare the prepolymer and the photopolymerizable compound added to the prepolymer). If the amount of the polyfunctional monomer used is excessively large, the adhesive sheet after photocuring may have low viscosity and poor adhesive strength. The amount of the polyfunctional compound used may be 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight or less. The amount of the polyfunctional monomer used may be 0, 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more.

(Photopolymerization initiator)
The photocurable pressure-sensitive adhesive composition contains a photopolymerization initiator. The photopolymerization initiator generates radicals, acids, bases, etc. by irradiation with active light such as ultraviolet rays, and can be appropriately selected according to the type of photopolymerizable compound. When the photopolymerizable compound is a compound having a (meth)acryloyl group (e.g., monofunctional or polyfunctional (meth)acrylate), it is preferable to use a photoradical polymerization initiator as the photopolymerization initiator. The photopolymerization initiator may be used alone or in a mixture of two or more kinds.

If the photopolymerization initiator used in preparing (polymerizing) the prepolymer remains in the prepolymer composition without being deactivated, the addition of the photopolymerization initiator may be omitted. When a photopolymerization initiator is added to the prepolymer composition, the photopolymerization initiator added may be the same as or different from the photopolymerization initiator used in preparing the prepolymer.

The photopolymerization initiator contained in the adhesive composition preferably has an absorption maximum in a wavelength region where light absorption by the colorant described below is small. Specifically, the photopolymerization initiator preferably has an absorption maximum in a wavelength region of 330 to 400 nm. By having the photopolymerization initiator have an absorption maximum in a region where light absorption by the colorant is small, the inhibition of curing by the colorant is suppressed, and the polymerization rate can be sufficiently increased by photocuring. Examples of photoradical polymerization initiators having an absorption maximum in a wavelength region of 330 to 400 nm include hydroxyketones, benzyl dimethyl ketals, aminoketones, acylphosphine oxides, benzophenones, trichloromethyl group-containing triazine derivatives, etc.

The content of the photopolymerization initiator in the photocurable adhesive composition is about 0.01 to 10 parts by weight, preferably about 0.05 to 5 parts by weight, per 100 parts by weight of the total amount of monomers (monomers used to prepare the prepolymer and photopolymerizable compounds added to the prepolymer).

(Coloring Agent)
The adhesive composition used to form the colored adhesive sheet contains a colorant. The colorant may be a dye or a pigment as long as it is soluble or dispersible in the adhesive composition. Pigments are preferred because they have high color expression even when added in small amounts.

The colorant used is one that absorbs visible light and is ultraviolet-transmitting. It is preferable that the colorant has a maximum transmittance at wavelengths of 330 to 400 nm that is greater than the maximum transmittance at wavelengths of 400 to 700 nm. It is also preferable that the colorant has an average transmittance at wavelengths of 330 to 400 nm that is greater than the average transmittance at wavelengths of 400 to 700 nm. The transmittance of the colorant is measured using a solution or dispersion diluted with an appropriate solvent or dispersion medium (an organic solvent with low absorption in the wavelength range of 330 to 700 nm) such as tetrahydrofuran (THF) so that the transmittance at a wavelength of 400 nm is about 50 to 60%.

Examples of UV-transmitting black pigments that absorb less UV light than they absorb visible light include Tokushiki's "9050BLACK" and "UVBK-0001." Examples of UV-transmitting black dyes include Orient Chemical Industry's "SOC-L-0123."

Carbon black and titanium black, which are commonly used as black colorants, have a higher UV absorption than visible light absorption (UV transmittance is lower than visible light transmittance). Therefore, when a colorant such as carbon black is added to a photocurable adhesive composition that is sensitive to UV, most of the UV irradiated for photocuring is absorbed by the colorant, the amount of light absorbed by the photopolymerization initiator is small, and photocuring takes time (the cumulative amount of light irradiation becomes large). In addition, when the adhesive sheet is thick, there is little UV light that reaches the surface opposite the light irradiated surface, so photocuring tends to be insufficient even with long-term light irradiation. In contrast, by using a colorant with a higher UV transmittance than visible light, it is possible to suppress curing inhibition caused by the colorant.

The content of the colorant in the photocurable adhesive composition is, for example, about 0.01 to 20 parts by weight per 100 parts by weight of the total amount of monomers, and may be set appropriately depending on the type of colorant, the color tone and light transmittance of the adhesive sheet, etc. The colorant may be added to the composition as a solution or dispersion in which it is dissolved or dispersed in an appropriate solvent.

(Other ingredients)
The photocurable adhesive composition may contain components other than the polymer, the photopolymerizable compound, the photopolymerization initiator, and the colorant. For example, a chain transfer agent may be contained for the purpose of adjusting the photocuring speed. In addition, an oligomer or a tackifier may be contained for the purpose of adjusting the viscosity of the adhesive composition or the adhesive strength of the adhesive sheet. As the oligomer, for example, one having a weight average molecular weight of about 1000 to 30000 is used. As the oligomer, an acrylic oligomer is preferable because it has excellent compatibility with acrylic polymers. The adhesive composition may contain additives such as a silane coupling agent, a plasticizer, a softener, an antidegradant, a filler, an antioxidant, a surfactant, and an antistatic agent.

<Preparation of double-sided adhesive sheet>
A photocurable adhesive composition containing a colorant is applied to a substrate in a sheet (layer), and the coating of the adhesive composition on the substrate is irradiated with ultraviolet light to perform photocuring, thereby obtaining a double-sided adhesive sheet. When performing photocuring, it is preferable to attach a cover sheet to the surface of the coating, and irradiate the adhesive composition with ultraviolet light while sandwiched between two sheets, thereby preventing polymerization inhibition due to oxygen. Before photocuring, the sheet-shaped coating may be heated for the purpose of removing the solvent or dispersion medium of the colorant. When removing the solvent or the like by heating, it is preferable to perform the removal before attaching the cover sheet.

Any suitable substrate may be used as the substrate and cover sheet used to form the double-sided adhesive sheet. The substrate and cover sheet may be a release film having a release layer on the surface that comes into contact with the double-sided adhesive sheet.

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

Methods for applying the adhesive composition onto a substrate include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating.

The thickness of the double-sided adhesive sheet is not particularly limited and may be set depending on the type and shape of the adherend. The thickness of the double-sided adhesive sheet is, for example, about 10 to 500 μm, and may be 20 μm or more, 30 μm or more, 40 μm or more, or 50 μm or more. As described above, since the colorant has UV transparency, even if the double-sided adhesive sheet is thick, it is possible to photocure the photocurable composition uniformly in the thickness direction. The thickness of the double-sided adhesive sheet may be 400 μm or less, 300 μm or less, 250 μm or less, or 200 μm or less.

By irradiating the adhesive composition applied in a layer on the substrate with ultraviolet light, active species are generated from the photopolymerization initiator, the photopolymerizable compound is polymerized, and as the polymerization rate increases (the amount of unreacted monomer decreases), the liquid adhesive composition becomes a solid (standardized) adhesive sheet. The light source for ultraviolet light irradiation is not particularly limited as long as it can irradiate light in the wavelength range to which the photopolymerization initiator contained in the adhesive composition is sensitive, and examples of the light source that can be used include an LED light source, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, and a xenon lamp.

The integrated light amount of the irradiated light is, for example, about 100 to 5000 mJ/ ^cm2 . The polymerization rate (non-volatile content) of the double-sided pressure-sensitive adhesive sheet made of the photocured product of the photocurable pressure-sensitive adhesive composition is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The polymerization rate may be 93% or more or 95% or more. In order to reduce the non-volatile content, the pressure-sensitive adhesive sheet may be heated to remove volatile content such as residual monomers, unreacted polymerization initiator, and solvent.

By laminating release films 1 and 2 to the surface of double-sided adhesive sheet 5, an adhesive sheet with release films is obtained, in which release films are temporarily attached to both sides, as shown in FIG. 1. The release films used as the substrate or cover sheet when forming the double-sided adhesive sheet may be used as release films 1 and 2 as they are.

When release films 1 and 2 are provided on both sides of the double-sided adhesive sheet 5, the thickness of one release film 1 and the thickness of the other release film 2 may be the same or different. The peeling force when peeling the release film temporarily attached to one side from the double-sided adhesive sheet 5 and the peeling force when peeling the release film temporarily attached to the other side from the double-sided adhesive sheet 5 may be the same or different. When the two peeling forces are different, the release film 2 (light release film) with a relatively small peeling force is peeled off from the double-sided adhesive sheet 5 first to be bonded to the first adherend, and the release film 1 (heavy release film) with a relatively large peeling force is peeled off to be bonded to the second adherend, which provides excellent workability.

<Characteristics of double-sided adhesive sheet>
The double-sided pressure-sensitive adhesive sheet containing the colorant has optical absorption in visible light. The total light transmittance of the double-sided pressure-sensitive adhesive sheet is, for example, 80% or less, and may be 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less.

As described above, the colorant used has a smaller ultraviolet absorption than visible light absorption. Therefore, the double-sided pressure-sensitive adhesive sheet has a smaller ultraviolet absorption than visible light absorption. Specifically, the maximum transmittance T _mUV of the pressure-sensitive adhesive sheet at wavelengths of 330 to 400 nm is preferably greater than the maximum transmittance T _mVIS of the pressure-sensitive adhesive sheet at wavelengths of 400 to 700 nm. In addition, the average transmittance T _aUV of the pressure-sensitive adhesive sheet at wavelengths of 330 to 400 nm is preferably greater than the average transmittance T _aVIS of the pressure-sensitive adhesive sheet at wavelengths of 400 to 700 nm.

The average transmittance T _aVIS of the double-sided pressure-sensitive adhesive sheet at a wavelength of 400 to 700 nm is, for example, 80% or less, and may be 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less. The average transmittance T _aUV of the double-sided pressure-sensitive adhesive sheet at a wavelength of 330 to 400 nm is preferably 5% or more, and may be 10% or more, 15% or more, 20% or more, or 25% or more. The difference T _aUV -T _aVIS between T _aUV and T _aVIS may be 3% or more, 5% or more, 8% or more, or 10% or more.

The double-sided pressure-sensitive adhesive sheet has a maximum transmittance _TmVIS in the wavelength range of 400 to 700 nm of, for example, 85% or less, and may be 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less. The double-sided pressure-sensitive adhesive sheet has a maximum transmittance _TmUV in the wavelength range of 330 to 400 nm of, preferably, 5% or more, and may be 10% or more, 15% or more, 20% or more, or 25% or more. The difference between _TmUV and _TmVIS , _TmUV -TmVIS _, may be 0.1% or more, 0.5% or more, 1% or more, or 1.5% or more.

The transmittance of the double-sided pressure-sensitive adhesive sheet may be adjusted according to the application or purpose. For example, when used as a light-shielding sealing member for an LED array, the average transmittance T _aVIS of the double-sided pressure-sensitive adhesive sheet at wavelengths of 400 to 700 nm is preferably 10% or less, and may be 7% or less or 5% or less. When the double-sided pressure-sensitive adhesive sheet is used for anti-reflection applications for OLEDs, T _aVIS is preferably 80% or less, and may be 78% or less or 75% or less. In either case, the maximum transmittance T _aUV of the double-sided pressure-sensitive adhesive sheet at wavelengths of 330 to 400 nm may be higher than T _aVIS .

The shear storage modulus G' _25°C of the adhesive sheet at a temperature of 25°C is, for example, about 10 to 1000 kPa, and may be 30 kPa or more, 50 kPa or more, 70 kPa or more, or 100 kPa or more, and may be 700 kPa or less, 500 kPa or less, 300 kPa or less, or 200 kPa or less. The shear storage modulus G' _85°C of the adhesive sheet at a temperature of 85°C is, for example, about 3 to 300 kPa, and may be 5 kPa or more, 7 kPa or more, or 10 kPa or more, and may be 200 kPa or less, 150 kPa or less, or 100 kPa or less. If the shear storage modulus of the adhesive sheet is within the above range, it is possible to achieve both appropriate flexibility and adhesiveness. The shear storage modulus is a value measured by dynamic viscoelasticity measurement at a frequency of 1 Hz.

[Second Form]
The double-sided pressure-sensitive adhesive sheet of the second embodiment of the present invention is a pressure-sensitive adhesive sheet of a type that does not undergo photocuring on a substrate, and is a photocurable pressure-sensitive adhesive composition formed into a sheet shape. The double-sided pressure-sensitive adhesive sheet of the second embodiment contains a photopolymerizable compound in an unreacted state, so that the pressure-sensitive adhesive sheet has photocurability.

<Adhesive composition>
The pressure-sensitive adhesive composition used to form the double-sided pressure-sensitive adhesive sheet of the second embodiment contains a polymer, a photopolymerizable compound, a photopolymerization initiator, and a colorant.

(polymer)
As the polymer contained in the pressure-sensitive adhesive composition, various polymers can be used as in the first embodiment, and an acrylic polymer is preferably used. The monomer components constituting the acrylic polymer are the same as in the first embodiment.

In order to introduce a crosslinked structure using a crosslinking agent described below, it is preferable that the monomer components constituting the polymer contain a hydroxyl group-containing monomer and/or a carboxyl group-containing monomer. For example, when an isocyanate-based crosslinking agent is used, it is preferable that the monomer component contains a hydroxyl group-containing monomer. When an epoxy-based crosslinking agent is used, it is preferable that the monomer component contains a carboxyl group-containing monomer.

In the second form, photocuring is not performed on the substrate, so that a solid (standard) adhesive sheet is formed, and a polymer with a relatively large molecular weight is used as the polymer contained in the photocurable adhesive composition. The weight-average molecular weight of the polymer is, for example, about 100,000 to 2,000,000.

Since high molecular weight polymers are solids, in order to apply the adhesive composition to a substrate, it is preferable that the adhesive composition is a solution in which the polymer is dissolved in an organic solvent. For example, a polymer solution can be obtained by solution polymerization of the monomer components. A polymer solution can also be prepared by dissolving a solid polymer in an organic solvent.

Ethyl acetate, toluene, etc. are generally used as the solvent for solution polymerization. The solution concentration is usually about 20 to 80% by weight. As the polymerization initiator, a thermal polymerization initiator such as an azo initiator, a peroxide initiator, or a redox initiator that combines a peroxide and a reducing agent (for example, a combination of persulfate and sodium hydrogen sulfite, or a combination of peroxide and sodium ascorbate) is preferably used. There is no particular restriction on the amount of the polymerization initiator used, but for example, it is preferably about 0.005 to 5 parts by weight, and more preferably about 0.02 to 3 parts by weight, per 100 parts by weight of the total amount of the monomer components that form the polymer.

(Photopolymerizable Compound)
In the second embodiment, the photopolymerizable compound contained in the pressure-sensitive adhesive composition is the same as that described above for the first embodiment, and a compound having one or more photopolymerizable functional groups is used.

(Photopolymerization initiator)
The photopolymerization initiator contained in the pressure-sensitive adhesive composition in the second embodiment is the same as that described above for the first embodiment, and preferably has an absorption maximum in the wavelength region of 330 to 400 nm. The amount of the photopolymerization initiator is about 0.01 to 10 parts by weight, and preferably about 0.05 to 5 parts by weight, based on 100 parts by weight of the polymer.

(Coloring Agent)
The colorant contained in the pressure-sensitive adhesive composition in the second embodiment is the same as that described above for the first embodiment, and preferably has a transmittance at wavelengths of 330 to 400 nm greater than the transmittance at wavelengths of 400 to 700 nm.

(Crosslinking Agent)
The second type of pressure-sensitive adhesive composition preferably contains a crosslinking agent capable of crosslinking with the polymer. Specific examples of the crosslinking agent for introducing a crosslinked structure into the polymer include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. Among them, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they have high reactivity with the hydroxyl group or carboxyl group of the polymer and are easy to introduce a crosslinked structure. These crosslinking agents react with functional groups such as hydroxyl groups and carboxyl groups introduced into the polymer to form a crosslinked structure.

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

As the epoxy-based crosslinking agent, a multifunctional epoxy compound having two or more epoxy groups in one molecule is used. The epoxy group of the epoxy-based crosslinking agent may be a glycidyl group. Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylene diamine, diglycidyl aniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether. As epoxy-based crosslinking agents, commercially available products such as "Denacol" manufactured by Nagase ChemteX and "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical may be used.

The amount of crosslinking agent is about 0.01 to 5 parts by weight, and may be 0.05 parts by weight or more, 0.1 parts by weight or more, or 0.2 parts by weight or more, or may be 3 parts by weight or less, 2 parts by weight or less, or 1 part by weight or less, based on 100 parts by weight of polymer.

(Other ingredients)
The pressure-sensitive adhesive composition of the second embodiment may contain, in addition to the above-mentioned components, an oligomer, a tackifier, a silane coupling agent, a chain transfer agent, a plasticizer, a softener, an antidegradant, a filler, an antioxidant, a surfactant, an antistatic agent, etc.

<Preparation of double-sided adhesive sheet>
The pressure-sensitive adhesive composition is applied onto a substrate, and the solvent is removed by drying as necessary to form a double-sided pressure-sensitive adhesive sheet on the substrate. As in the first embodiment, a release film is preferably used as the substrate.

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

After the solvent has dried, it is preferable to attach a cover sheet to protect the surface of the double-sided pressure-sensitive adhesive sheet. As the cover sheet, it is preferable to use a release film that has a release layer on the surface that comes into contact with the pressure-sensitive adhesive sheet, similar to the base film.

After applying the adhesive composition onto the substrate, a crosslinked structure is introduced into the polymer by heating as necessary. The heating temperature and heating time can be set appropriately depending on the type of crosslinking agent used, and are usually in the range of 20°C to 160°C and about 1 minute to 7 days. The heating for drying the solvent may also serve as the heating for crosslinking. The introduction of a crosslinked structure does not necessarily have to be accompanied by heating.

<Characteristics of double-sided adhesive sheet>
The double-sided pressure-sensitive adhesive sheet of the second embodiment preferably has the same thickness, light transmittance, and shear storage modulus as the double-sided pressure-sensitive adhesive sheet of the first embodiment. The double-sided pressure-sensitive adhesive sheet of the second embodiment does not undergo photocuring on the substrate, and therefore contains the photopolymerizable compound in an unreacted state. That is, the double-sided pressure-sensitive adhesive sheet of the second embodiment is a photocurable pressure-sensitive adhesive sheet containing a polymer, a photopolymerizable compound, a photopolymerization initiator, and a colorant.

After bonding the photocurable adhesive sheet to the adherend, it can be photocured by irradiating it with ultraviolet light. Photocuring can change the adhesive strength between the adhesive sheet and the adherend. For example, because the adhesive sheet is highly flexible before photocuring, it is possible to fill in the surface irregularities and steps of the adherend, and after photocuring, the adhesive strength and adhesive reliability to the adherend can be improved.

Ultraviolet rays are used as the actinic radiation for photocuring the adhesive sheet. As with the first form of adhesive sheet, the colorant has a higher transmittance for ultraviolet rays than for visible light, so even if the adhesive sheet is thick, inhibition of curing during photocuring can be suppressed.

The thickness of the double-sided adhesive sheet is not particularly limited and may be set depending on the type and shape of the adherend. The thickness of the double-sided adhesive sheet is, for example, about 10 to 500 μm, and may be 20 μm or more, 30 μm or more, 40 μm or more, or 50 μm or more. As described above, since the colorant is UV-transparent, curing inhibition is unlikely to occur, and process efficiency can be improved.

[Applications of adhesive sheets]
The double-sided pressure-sensitive adhesive sheet of the first and second forms can be used to bond various transparent and opaque members. The type of the adherend is not particularly limited, and examples thereof include various resin materials, glass, metal, and the like. The double-sided pressure-sensitive adhesive sheet is used, for example, to bond members of an optical device such as an image display device. Since the pressure-sensitive adhesive sheet is colored, it can have the effect of reducing the emission of scattered light and reflected light to the outside within the device, thereby improving visibility.

The double-sided adhesive sheet can be used as a sealing material or to fill spaces between components, and can also be used to seal optical semiconductor elements. Examples of optical semiconductor elements include light-emitting diodes (LEDs). For example, when an adhesive sheet is used to seal a micro LED array in which multiple LED elements are arranged in a tiled pattern, it is possible to seal multiple LEDs together because the adhesive sheet has excellent conformability to unevenness such as the gaps between the LEDs. In addition, the adhesive sheet reduces the scattering and reflection of visible light, so it is expected to have an effect of suppressing reduced visibility caused by scattering and reflection of light in the gaps between the LEDs.

If the double-sided adhesive sheet is photocurable, it may be photocured by irradiating it with ultraviolet light after bonding to the adherend. The adhesive sheet before photocuring is highly flexible and therefore has excellent conformability to irregularities such as the gaps between LEDs. By allowing the adhesive sheet to conform to the irregularities and then photocuring, improved adhesion reliability can be expected.

The double-sided pressure-sensitive adhesive sheet can also be used in a laminated, integrated state with other components. For example, an optical film such as a polarizing plate can be attached to one side of the double-sided pressure-sensitive adhesive sheet, and the sheet can be used in practical use as an optical film with a pressure-sensitive adhesive. A laminate in which an adherend is attached to each of the main surfaces of the double-sided pressure-sensitive adhesive sheet can also be used as a component of an optical device.

The double-sided adhesive sheet may be laminated with a material having ultraviolet absorbing properties. The ultraviolet absorbing layer may be a resin film, an adhesive layer, or the like. The ultraviolet absorbing layer may contain an ultraviolet absorbing agent. Examples of ultraviolet absorbing agents include benzotriazole-based ultraviolet absorbing agents, benzophenone-based ultraviolet absorbing agents, triazine ultraviolet absorbing agents, salicylate-based ultraviolet absorbing agents, and cyanoacrylate-based ultraviolet absorbing agents.

In order to protect components with low UV resistance, adhesive sheets and the like may be required to have UV shielding properties. Although an UV absorber can be added to the photocurable adhesive composition for forming the double-sided adhesive sheet 5, the UV absorber will absorb the UV rays used to photocure the adhesive, inhibiting photocuring and thus eliminating the significance of using a UV-transparent colorant. For this reason, it is preferable to block UV rays by laminating an UV absorbing layer on the double-sided adhesive sheet.

When laminating an ultraviolet absorbing layer after photocuring the adhesive composition, the ultraviolet absorbing layer may be laminated on one side of the double-sided adhesive sheet, or on both sides. When laminating an ultraviolet absorbing layer before photocuring the adhesive composition (e.g., a double-sided adhesive sheet of the second type), the ultraviolet absorbing layer may be laminated on one side, and ultraviolet light may be irradiated from the other side to photocure the adhesive.

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

[Evaluation method]
(Measurement of polymerization rate)
A predetermined amount (initial weight W1) of adhesive was collected from the adhesive layer and heated in an oven at 130°C for 2 hours in an aluminum cup (weight W2) whose weight had been measured in advance, and then removed and allowed to cool for 30 minutes in an atmosphere of 23°C and 50% RH. The weight after drying (W3) was then measured, and the polymerization rate (non-volatile content) was calculated using the following formula.
Polymerization rate (%) = 100 x (W3-W2)/W1

(Transmittance)
The release film on one side was peeled off from the adhesive sheet, and alkali-free glass was attached to the exposed surface. Thereafter, the release film on the other side was peeled off from the adhesive sheet to obtain a sample in which the adhesive sheet was attached to the alkali-free glass plate. Using this sample, the transmission spectrum of the evaluation sample was measured using a visible ultraviolet spectrophotometer (manufactured by Hitachi High-Technologies, product name "U-4100"). The transmittance of the adhesive sheet was determined by using the alkali-free glass (single unit) as the baseline and the ratio of the transmittance (amount of transmitted light) of the evaluation sample to the transmittance (amount of transmitted light) of the alkali-free glass. From the transmission spectrum of the adhesive sheet, the arithmetic average of the transmittance in the wavelength range of 400 to 700 nm and the arithmetic average of the transmittance in the wavelength range of 330 to 400 nm, as well as the maximum value of the transmittance in the wavelength range of 400 to 700 nm and the maximum value of the transmittance in the wavelength range of 330 to 400 nm were obtained. The transmission spectrum of the colorant was measured using a dispersion diluted to 0.1% by weight with THF as a sample in a quartz cell with an optical path length of 1 cm.

[Reference example: Preparation of transparent adhesive sheet]
(Polymerization of Prepolymer)
As monomer components for forming a prepolymer, 28.5 parts by weight of 2-ethylhexyl acrylate (2EHA), 28.5 parts by weight of isostearyl acrylate (ISTA), 22 parts by weight of isobornyl acrylate (IBHX), and 21 parts by weight of 4-hydroxybutyl acrylate (4HBA), as well as photopolymerization initiators (0.05 parts by weight of "Irgacure 184" manufactured by BASF, and 0.05 parts by weight of "Irgacure 651" manufactured by BASF) were blended and polymerized by irradiation with ultraviolet light to obtain a prepolymer composition A (polymerization rate 5 to 15%).

(Preparation of Pressure-Sensitive Adhesive Composition and Fabrication of Pressure-Sensitive Adhesive Sheet)
The prepolymer composition A was added with additional photopolymerization initiators (BASF's "Irgacure 184": 0.05 parts by weight, and BASF's "Irgacure 651": 0.05 parts by weight), and then degassed. This composition was applied to a 75 μm thick polyethylene terephthalate (PET) film (Mitsubishi Chemical's "Diafoil MRF75") having a silicone-based release layer on its surface as a substrate, and the photocurable adhesive composition was applied to the substrate to a thickness of 100 μm to form a coating layer. A 75 μm thick PET film (Mitsubishi Chemical's "Diafoil MRE75") with one side treated with silicone release was attached to the coating layer as a cover sheet. This laminate was photocured by irradiating it with ultraviolet light for 4 minutes from the cover sheet side using a black light adjusted so that the irradiation intensity on the irradiation surface directly under the lamp was 3.7 mW/ ^cm2 (cumulative irradiation amount: 880 mJ/ ^cm2 ), to obtain a transparent double-sided pressure-sensitive adhesive sheet with release films on both sides. The non-volatile content of the pressure-sensitive adhesive sheet was 98.0%.

[Comparative Example 1]
0.1 parts by weight of black dye ("VALIFAST BLACK 3810" manufactured by Orient Chemical Industries) and additional photopolymerization initiator were added to 100 parts by weight of the prepolymer composition prepared in the same manner as in Reference Example, and then degassing was performed. Using this composition, an attempt was made to prepare an adhesive sheet in the same manner as in Reference Example 1, but the composition was liquid after 4 minutes of ultraviolet irradiation, and an adhesive sheet could not be obtained.

[Comparative Example 2]
0.1 parts by weight of black dye ("VALIFAST BLACK 3810" manufactured by Orient Chemical Industry Co., Ltd.) was dissolved in 4 parts by weight of 2EHA to prepare a 20% solution. This solution was added to 100 parts by weight of a prepolymer composition prepared in the same manner as in Reference Example, and additional photopolymerization initiator was added, followed by degassing. An attempt was made to prepare an adhesive sheet using this composition, but as in Comparative Example 1, the composition was liquid after 4 minutes of ultraviolet irradiation, and no adhesive sheet was obtained.

[Example 1]
To 100 parts by weight of a prepolymer composition prepared in the same manner as in Reference Example, 0.5 parts by weight (0.1 parts by weight as black pigment) of a 20% dispersion of black pigment (Tokushiki's "9050BLACK") and additional photopolymerization initiator were added, and then degassing was performed. This composition was applied to a substrate to a thickness of 100 μm, and then heated at 80° C. for 1 minute to remove the dispersion medium. Thereafter, a cover sheet was attached, and an adhesive sheet was prepared in the same manner as in Reference Example 1. The non-volatile content of the adhesive sheet was 97.1%.

[Example 2]
(Polymerization of Prepolymer)
As monomer components for forming a prepolymer, 67 parts by weight of butyl acrylate (BA), 14 parts by weight of cyclohexyl acrylate (CHA), and 19 parts by weight of 4HBA, as well as photopolymerization initiators (0.09 parts by weight of BASF's "Irgacure 184" and 0.09 parts by weight of BASF's "Irgacure 651") were mixed and polymerized by irradiation with ultraviolet light to obtain prepolymer composition B (polymerization rate 5 to 15%).

(Preparation of Pressure-Sensitive Adhesive Composition)
To the above prepolymer composition B, 9 parts by weight of 2-hydroxyethyl acrylate (2HEA), 8 parts by weight of 4HBA, 0.02 parts by weight of dipentaerythritol hexaacrylate as a polyfunctional monomer, 0.35 parts by weight of 3-glycidoxypropyltrimethoxysilane ("KBM-403" manufactured by Shin-Etsu Silicones) as a silane coupling agent, 0.5 parts by weight of a photopolymerization initiator ("Irgacure 651" manufactured by BASF), and 4 parts by weight of a 20% dispersion of black pigment ("9050BLACK" manufactured by TOKUSHIKI) (0.8 parts by weight as black pigment) were added, mixed, and then degassed to prepare a photopolymerizable pressure-sensitive adhesive composition.

(Preparation of adhesive sheet)
An adhesive sheet was prepared in the same manner as in Reference Example 1, except that the above adhesive composition was used and the ultraviolet irradiation time was changed to 6 minutes and the cumulative irradiation amount to 1320 mJ/cm ² .

[Examples 3 and 4]
Except for changing the amount of black pigment added and the thickness of the adhesive sheet as shown in Table 1, adhesive sheets were prepared in the same manner as in Example 2.

[Example 5]
(Polymerization of Prepolymer)
As monomer components for forming a prepolymer, 36.5 parts by weight of lauryl acrylate (LA), 60 parts by weight of 2EHA, 2.5 parts by weight of N-vinylpyrrolidone (NVP), and 1 part by weight of 4HBA, as well as photopolymerization initiators (0.05 parts by weight of BASF's "Irgacure 184" and 0.05 parts by weight of BASF's "Irgacure 651") were mixed and polymerized by irradiation with ultraviolet light to obtain prepolymer composition C (polymerization rate 5 to 15%).

(Preparation of Pressure-Sensitive Adhesive Composition)
To the above prepolymer composition C, 0.08 parts by weight of 1,6-hexanediol diacrylate as a polyfunctional monomer, 0.3 parts by weight of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Silicones, product name "KBM-403") as a silane coupling agent, 0.3 parts by weight of a photopolymerization initiator (manufactured by BASF, "Irgacure 651"), and 4 parts by weight of a 20% dispersion of black pigment (manufactured by TOKUSHIKI, "9050BLACK") (0.8 parts by weight as black pigment) were added, mixed, and then degassed to prepare a photopolymerizable pressure-sensitive adhesive composition.

(Preparation of adhesive sheet)
An adhesive sheet was prepared in the same manner as in Reference Example 1, except that the above adhesive composition was used and the ultraviolet irradiation time was changed to 6 minutes and the cumulative irradiation amount to 1320 mJ/cm ² .

[Examples 6 and 7]
Except for changing the amount of black pigment added and the thickness of the adhesive sheet as shown in Table 1, adhesive sheets were prepared in the same manner as in Example 5.

[UV irradiation dose and polymerization rate]
For Reference Example 1, Comparative Example 1, Comparative Example 2, and Example 1, the UV irradiation time (accumulated irradiation amount) was changed to prepare pressure-sensitive adhesive sheets, and the relationship between the accumulated irradiation amount and the non-volatile content was examined. The results are shown in Figure 3. Note that for Comparative Example 2, the pressure-sensitive adhesive composition was liquid even after irradiating with UV rays for 10 minutes (2200 mJ/ ^cm2 ), and the non-volatile content of the pressure-sensitive adhesive sheet after irradiating with UV rays for 25 minutes (5500 mJ/ ^cm2 ) was 87.6%.

[Evaluation Results]
The transmission spectrum of the dispersion of the black pigment used in Examples 1 to 7 is shown in Figure 2. The types of prepolymers used in the preparation of the pressure-sensitive adhesive compositions of the above Reference Examples, Comparative Examples, and Examples, the types and amounts of colorants added, the thickness of the pressure-sensitive adhesive sheet, the non-volatile content of the pressure-sensitive adhesive sheet after irradiation with ultraviolet light, and the average transmittance and maximum transmittance calculated from the transmission spectrum of the pressure-sensitive adhesive sheet are shown in Table 1. The irradiation time of ultraviolet light was 4 minutes (cumulative irradiation amount 880 mJ/cm ² ) for Reference Example 1 and Example 1, 6 minutes (cumulative irradiation amount 1320 mJ/cm ² ) for Examples 2 to 7, and 7 minutes (cumulative irradiation amount 1540 mJ/cm ² ) for Comparative Example 1. The transmission spectrum was measured using a sample irradiated with ultraviolet light for 7 minutes for Comparative Example 1, and a sample irradiated with ultraviolet light for 25 minutes for Comparative Example 2.

The adhesive sheet of Reference Example 1, which does not contain a colorant, has a higher average transmittance of visible light (wavelength 400-700 nm) than the average transmittance of ultraviolet light (wavelength 330-400 nm), whereas in Examples 1-7, in which an ultraviolet-transmitting black pigment was added to the adhesive composition, the average transmittance of ultraviolet light was higher than the average transmittance of visible light. Furthermore, in Examples 1-7, the maximum transmittance of the ultraviolet region was higher than the maximum transmittance of the visible light region. On the other hand, in Comparative Examples 1 and 2, the average transmittance of ultraviolet light was lower than the average transmittance of visible light, and the maximum transmittance of the ultraviolet region was lower than the maximum average transmittance of the visible light region.

In Comparative Example 1, the colorant (dye) was not uniformly dissolved in the adhesive composition, so the measured transmittance was large. In Comparative Example 2, in which a colorant dissolved in a monomer (2EHA) was added in advance, the visible light transmittance was sufficiently reduced, but the ultraviolet light transmittance was also significantly reduced, and the adhesive was not sufficiently solidified even after 25 minutes (5500 mJ/cm ² ) of ultraviolet light irradiation. From these results, it can be seen that in Comparative Examples 1 and 2, the colorant absorbs ultraviolet light, so that the photocuring speed (photocuring efficiency) of the adhesive is significantly reduced.

From the results shown in Table 1 and Figure 3, it can be seen that Example 1 has sufficiently high photocurability compared to Comparative Examples 1 and 2. Furthermore, it can be seen that Examples 2 to 7 have low unreacted monomers and high photocurability even when the nonvolatile content is high, the colorant content is high, or the visible light transmittance is low, as in Example 1.

These results show that by preparing a photocurable adhesive composition using a colorant that absorbs less ultraviolet light than visible light, the inhibition of curing caused by the colorant is suppressed, and a colored double-sided adhesive sheet that absorbs visible light can be obtained with the same productivity as when no colorant is used.

When the pressure-sensitive adhesive sheets of the Reference Example and Examples 1 to 7 were attached to a stainless steel substrate and visually inspected, it was confirmed that the metallic luster of the stainless steel substrate was less and the reflectance was lower in Examples 1 to 7 than in the Reference Example. From these results, it is understood that pressure-sensitive adhesive sheets with low visible light transmittance can be applied as anti-reflection members for light-emitting elements, displays, and the like.

Claims (19)

A photocurable pressure-sensitive adhesive composition comprising a polymer, a photopolymerizable compound, a photopolymerization initiator, and a colorant,
The colorant has a maximum transmittance at wavelengths of 330 to 400 nm that is greater than the maximum transmittance at wavelengths of 400 to 700 nm. The photocurable pressure-sensitive adhesive composition according to claim 1 , wherein the colorant has an average transmittance at wavelengths of 330 to 400 nm that is greater than an average transmittance at wavelengths of 400 to 700 nm. 3. The photocurable pressure-sensitive adhesive composition according to claim 1 , wherein the photopolymerization initiator has at least one absorption maximum in a wavelength range of 330 to 400 nm. The photocurable pressure-sensitive adhesive composition according to any one of claims 1 to 3 , wherein the colorant is a pigment. The photocurable pressure-sensitive adhesive composition according to any one of claims 1 to 4 , wherein the polymer is an acrylic polymer. The photocurable pressure-sensitive adhesive composition according to any one of claims 1 to 5 , wherein the polymer has a glass transition temperature of 0°C or lower. The photocurable pressure-sensitive adhesive composition according to any one of claims 1 to 6 , further comprising a crosslinking agent capable of crosslinking with the polymer. A double-sided pressure-sensitive adhesive sheet which is a sheet-shaped product of the photocurable pressure-sensitive adhesive composition according to any one of claims 1 to 7 . A double-sided pressure-sensitive adhesive sheet comprising a photocured product of a sheet-shaped product of the photocurable pressure-sensitive adhesive composition according to any one of claims 1 to 7 . 10. The double-sided pressure-sensitive adhesive sheet according to claim 9 , having a non-volatile content of 90% by weight or more. The double-sided pressure-sensitive adhesive sheet according to any one of claims 8 to 10 , wherein the maximum transmittance at wavelengths of 330 to 400 nm is greater than the maximum transmittance at wavelengths of 400 to 700 nm. The double-sided pressure-sensitive adhesive sheet according to any one of claims 8 to 11 , wherein the average transmittance at wavelengths of 330 to 400 nm is greater than the average transmittance at wavelengths of 400 to 700 nm. The double-sided pressure-sensitive adhesive sheet according to any one of claims 8 to 12 , having a total light transmittance of 80% or less. The double-sided pressure-sensitive adhesive sheet according to any one of claims 8 to 13 , having a thickness of 10 to 500 µm. The double-sided pressure-sensitive adhesive sheet according to any one of claims 8 to 14 , having a shear storage modulus at a temperature of 25°C of 10 to 1000 kPa. The double-sided pressure-sensitive adhesive sheet according to any one of claims 8 to 15 , having a shear storage modulus at a temperature of 85°C of 3 to 300 kPa. A method for producing a photocurable adhesive composition according to any one of claims 1 to 7 , comprising applying the composition in the form of a sheet onto a substrate;
A method for producing a double-sided pressure-sensitive adhesive sheet, comprising irradiating a sheet-like coating film provided on a substrate with ultraviolet light to photocure the photopolymerizable compound. An optical device comprising a first adherend and a second adherend bonded together via the double-sided pressure-sensitive adhesive sheet according to any one of claims 8 to 16 . A method for producing an optical device in which a first adherend and a second adherend are bonded together via a double-sided pressure-sensitive adhesive sheet, comprising:
a first adherend and a second adherend are bonded to the first main surface and the second main surface of the double-sided pressure-sensitive adhesive sheet according to any one of claims 8 to 16 , respectively;
The double-sided pressure-sensitive adhesive sheet is irradiated with ultraviolet light to photocure the photopolymerizable compound.

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