Adhesive sheet with release film and method for producing the same

Abstract

The adhesive sheet (1) with release film comprises a first release film (10) temporarily bonded to the first main surface of the photocurable adhesive sheet (50) and a second release film (20) temporarily bonded to the second main surface of the adhesive sheet. The adhesive sheet contains a photocurable acrylic polymer and a UV absorber. The first release layer (15) of the first release film is a fluorine-based release layer or a condensation-type silicone release layer. The adhesive sheet with release film is obtained, for example, by arranging a photocurable adhesive composition containing an acrylic monomer and / or a partial polymer of an acrylic monomer, a UV absorber, and a photopolymerization initiator in a layered manner between the first release film and the second release film, and irradiating light from the first release film side to photocuring the photocurable adhesive composition.

Description

Technical Field

[0001] The present invention relates to an adhesive sheet to which a release film is temporarily bonded and a method for producing the same. Background Art

[0002] In display devices such as liquid crystal displays and organic EL displays, and display input devices such as touch panels, transparent adhesive sheets are used to bond optical components. Transparent adhesive sheets are usually provided in the form of adhesive sheets with release films attached to both sides. When using an adhesive sheet, first peel off a release film (light release film) to expose one side of the adhesive sheet, and bond it to the first adherend, then peel off another release film (heavy release film), and bond the second adherend to the other side of the adhesive sheet.

[0003] From the viewpoint of suppressing the degradation of components caused by ultraviolet rays, sometimes the optical components used in display devices, input devices, etc. are required to have ultraviolet cut-off properties. For example, for organic EL displays, since the degradation of organic molecules constituting the light-emitting layer, etc., caused by ultraviolet rays, will have a significant impact on the display characteristics, high ultraviolet cut-off properties are required for the optical components arranged on the front surface of the element. In addition, with regard to the polarizing plates used in liquid crystal displays and organic EL displays, in order to prevent the degradation of the polarizer caused by ultraviolet rays (such as fading of iodine), ultraviolet cut-off properties are required for the optical components arranged on the surface closer to the front than the polarizer.

[0004] As a method for making an adhesive sheet have ultraviolet cutoff properties, a method of adding an ultraviolet absorber to an adhesive composition is known. For example, Patent Document 1 describes that an adhesive composition obtained by adding an ultraviolet absorber to a thermally polymerizable acrylic adhesive solution is coated into a film, and then heated and dried to obtain an adhesive sheet with ultraviolet cutoff properties. Patent Document 2 describes that a photocurable acrylic adhesive composition comprising a photocurable acrylic composition, a photopolymerization initiator, and an ultraviolet absorber is photocured in a state sandwiched between two release films to obtain a photocurable adhesive sheet with ultraviolet cutoff properties.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2013-75978

[0008] Patent Document 2: Japanese Patent Application Publication No. 2019-112505 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] Photocurable adhesive sheets generally do not require a solvent and are obtained by photocuring (photopolymerizing) a photocurable adhesive composition with substrate sheets attached to both sides thereof. Therefore, photocurable adhesive sheets have the advantages of being easy to increase in thickness and improving smoothness.

[0011] However, as also described in Patent Document 2, if a photocurable adhesive composition containing a UV absorber is irradiated with UV rays through a release film for photocuring, the peeling force between the release film on the light-irradiated side and the adhesive sheet after photocuring may increase significantly, making it difficult to peel off the release film when bonding to an adherend. Patent Document 2 proposes that the peeling force between the addition-type silicone release layer and the adhesive sheet can be reduced by adjusting the thickness of the addition-type silicone release layer, but it is not easy to sufficiently reduce the peeling force between the addition-type silicone release layer and the adhesive sheet after photocuring.

[0012] In view of the above problems, an object of the present invention is to provide a pressure-sensitive adhesive sheet with a release film which has ultraviolet light-cutting properties and good releasability from a release film.

[0013] Solutions for solving problems

[0014] The adhesive sheet with release film of the present invention comprises: a light-curable adhesive sheet having a first main surface and a second main surface, and a first release film temporarily bonded to the first main surface of the adhesive sheet. The first release film comprises a first release layer on a first film substrate, and the first release layer is in contact with the adhesive sheet. The adhesive sheet with release film may comprise a second release film temporarily bonded to the second main surface of the adhesive sheet. The adhesive sheet comprises a light-curable acrylic polymer and a UV absorber.

[0015] The first main surface of the adhesive sheet is the light irradiation surface when the photocurable adhesive composition is photocured. That is, the photocurable adhesive sheet is formed by irradiating the photocurable adhesive composition with light through the first release film. The first release layer of the first release film attached to the side of the photocurable adhesive composition to be irradiated with light is a fluorine-based release layer or a condensation-type silicone release layer. The second release layer of the second release film can be a non-fluorine-based addition-type silicone release layer.

[0016] The light transmittance of the adhesive sheet at a wavelength of 380 nm is preferably 50% or less. The adhesive sheet may contain 0.1 to 10 parts by weight of an ultraviolet absorber relative to 100 parts by weight of the acrylic polymer. The acrylic polymer of the adhesive sheet may contain a polyfunctional monomer component having two or more polymerizable functional groups in one molecule as a monomer component.

[0017] In a state where the first release layer of the first release film contacts the first main surface of the photocurable adhesive composition layer, the photocurable adhesive composition is irradiated with light from the first release film side, thereby obtaining an adhesive sheet with a release film. The photocurable adhesive composition comprises an acrylic material, an ultraviolet absorber and a photopolymerization initiator. As the acrylic material contained in the photocurable adhesive composition, an acrylic monomer and a partial polymer thereof can be cited. The acrylic material can include both an acrylic monomer and a partial polymer of an acrylic monomer.

[0018] In one embodiment, a laminate having a photocurable adhesive composition layer sandwiched between the first release film and the second release film is irradiated with light from the first release film side to photocuring the photocurable adhesive composition, thereby obtaining an adhesive sheet having release films bonded to both sides. In the adhesive sheet having release films bonded to both sides, the peeling force (peel strength) between the first release film and the adhesive sheet may be greater than the peeling force between the second release film and the adhesive sheet.

[0019] Effects of the Invention

[0020] The adhesive sheet with high visible light transmittance and UV cutoff is suitable for use as an optical adhesive sheet for display devices and display input devices requiring UV cutoff. The adhesive sheet with release film of the present invention can suppress excessive increase in the peeling force between the adhesive sheet and the first release film, so the peeling of the release film from the adhesive sheet and the lamination of the adhesive sheet to the adherend are excellent in operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a cross-sectional view showing the laminated structure of the pressure-sensitive adhesive sheet with a release film. DETAILED DESCRIPTION

[0022] The release film-attached pressure-sensitive adhesive sheet of the present invention comprises release films temporarily bonded to both surfaces of the pressure-sensitive adhesive sheet. “Temporarily bonded” means a state where the pressure-sensitive adhesive sheet is bonded in a releasable manner. Figure 1 It is a cross-sectional view of an adhesive sheet 1 with release films 10 and 20 bonded to both sides of an adhesive sheet 50. The adhesive sheet 50 is obtained by forming an adhesive into a sheet. The total light transmittance of the adhesive sheet 50 is preferably 85% or more, and more preferably 90% or more. The haze of the adhesive sheet is preferably 2% or less, and more preferably 1% or less. The total light transmittance and haze are measured using a haze meter in accordance with JIS K7136.

[0023] The adhesive sheet 50 is an acrylic adhesive containing a photocurable acrylic polymer. The acrylic adhesive sheet is formed by a photocurable adhesive, which is obtained by coating a photocurable adhesive composition containing a partial polymer (prepolymer) of an acrylic monomer and / or an acrylic polymer, and a photopolymerization initiator into a layer and photocuring it. In this specification, a "photocurable" adhesive refers to an adhesive that contains a compound containing a photopolymerizable functional group such as a vinyl group and a (meth)acryloyl group and can be photocured, and a "photocured" adhesive refers to an adhesive after the photocurable adhesive is photocured. It should be noted that when a part of the photopolymerizable compound remains in an unreacted form in the adhesive after the photocurable adhesive is polymerized, the adhesive is photocured and there is a case of photocurability.

[0024] [Photocurable adhesive composition]

[0025] The photocurable adhesive composition includes a photopolymerizable acrylic material, an ultraviolet absorber, and a photopolymerization initiator.

[0026] <Photopolymerizable acrylic material>

[0027] Examples of the photopolymerizable acrylic material contained in the photocurable adhesive composition include acrylic monomers and partial polymers (prepolymers) thereof.

[0028] (Monomer component)

[0029] As the acrylic monomer, a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 20 carbon atoms is preferably used. The alkyl group of the (meth)acrylic acid alkyl ester may have a branched chain. The content of the (meth)acrylic acid alkyl ester is preferably 40% by weight or more, more preferably 50% by weight or more, and further preferably 60% by weight or more relative to the total amount of the monomer components of the acrylic material.

[0030] In addition to the (meth)acrylic acid alkyl ester, a high polar monomer such as a hydroxyl-containing monomer and a nitrogen-containing monomer may be included as a copolymerization component. By making the acrylic polymer contain a high polar monomer unit, there is a tendency to increase the cohesive force of the adhesive, improve the adhesion of the adhesive sheet to the adherend, and suppress the turbidity of the adhesive in a high temperature and high humidity environment, thereby improving the transparency of the adhesive sheet.

[0031] Examples of the hydroxyl-containing monomer include 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 acrylate. The content of the hydroxyl-containing monomer is preferably 1 to 40% by weight, more preferably 3 to 30% by weight, and even more preferably 5 to 20% by weight relative to the total amount of the monomer components.

[0032] As the nitrogen-containing monomer, there can be cited vinyl monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylcarboxylic acid amides, and N-vinylcaprolactam; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile, etc. The nitrogen-containing monomer preferably has a cyclic structure containing a nitrogen atom, and lactam vinyl monomers such as N-vinylpyrrolidone are preferred. The content of the nitrogen-containing monomer is preferably 0.5 to 50% by weight, more preferably 1 to 40% by weight, and further preferably 3 to 30% by weight relative to the total amount of the monomer components.

[0033] As the copolymerizable monomer component, monomers other than the above, such as a carboxyl group-containing monomer, a cyclic ether group-containing monomer, and a silane-based monomer, may be contained.

[0034] The comonomer component may include a polyfunctional polymerizable compound having two or more polymerizable functional groups in one molecule. Examples of the polyfunctional polymerizable compound include compounds having two or more C=C bonds in one molecule; compounds having one C=C bond and having polymerizable functional groups such as epoxy, aziridine, oxazoline, hydrazine, hydroxymethyl, etc. Among them, polyfunctional polymerizable compounds having two or more C=C bonds in one molecule are preferred. The polyfunctional polymerizable compound may be present in the adhesive composition in the form of a monomer or an oligomer, or may be bonded to functional groups such as hydroxyl groups of the prepolymer component.

[0035] Examples of the polyfunctional polymerizable compound having two or more C=C bonds in one molecule include polyfunctional (meth)acrylates (ester compounds of polyols and (meth)acrylic acid) such as (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and tetramethylolmethane tri(meth)acrylate. The polyfunctional (meth)acrylate may be a compound having a (meth)acryloyl group at the end of a polymer chain such as epoxy (meth)acrylate, polyester (meth)acrylate, or urethane (meth)acrylate.

[0036] The amount of the multifunctional monomer used varies depending on its molecular weight, number of functional groups, etc., and is preferably 5% by weight or less, more preferably 3% by weight or less, and further preferably 2% by weight or less relative to the total amount of the monomer components. The amount of the multifunctional monomer used can be 0.001% by weight or more, 0.01% by weight or more, or 0.05% by weight or more relative to the total amount of the monomer components.

[0037] In the photocurable adhesive composition, the above-mentioned monomer component may exist in the form of a partial polymer (prepolymer). A prepolymer refers to a substance obtained by partially polymerizing a monomer component. By making the monomer component exist in the form of a prepolymer, the viscosity of the photocurable adhesive composition can be adjusted to a range suitable for coating on a support.

[0038] The prepolymer can be prepared by, for example, partially polymerizing a prepolymer-forming composition mixed with monomer components and a polymerization initiator. The prepolymer-forming composition may contain all monomer components constituting the acrylic polymer, or may contain only a portion of the monomers constituting the acrylic polymer. When the monomer components constituting the acrylic polymer include monofunctional monomers and polyfunctional monomers, the adhesive composition may be prepared by adding a polyfunctional monomer to a prepolymer composition obtained by partially polymerizing only the monofunctional monomers. By adding a polyfunctional monomer to a prepolymer composition obtained by partially polymerizing only the monofunctional monomers and performing post-polymerization, crosslinking points based on the polyfunctional monomers can be uniformly introduced into the polymer. It is also possible to make the prepolymer-forming composition contain a portion of the polyfunctional monomer components constituting the acrylic polymer, and add the remaining polyfunctional monomer components after the prepolymer is polymerized for post-polymerization.

[0039] The prepolymer may be prepared by two or more stages or three or more stages of polymerization. For example, only a monofunctional monomer may be prepolymerized, and then a polyfunctional monomer may be added for partial polymerization to prepare a prepolymer composition, and further monomer components may be added as needed for post-polymerization.

[0040] The polymerization method of the prepolymer is not particularly limited. From the viewpoint of adjusting the reaction time and setting the molecular weight (polymerization rate) of the prepolymer to the desired range, photopolymerization based on irradiation with active light such as ultraviolet rays is preferred. In the case of photopolymerization, the prepolymer forming composition preferably contains a photopolymerization initiator. Specific examples of the photopolymerization initiator are described below.

[0041] In the prepolymer forming composition, in addition to the monomer component and the polymerization initiator, a chain transfer agent may also be included as needed. The chain transfer agent has the following effects: the self-growing polymer chain accepts free radicals to stop the polymer chain extension, and the chain transfer agent after accepting the free radicals will attack the monomer and initiate polymerization again. By using a chain transfer agent, it is possible to suppress the excessive increase of the molecular weight without reducing the free radical concentration in the reaction system. As a chain transfer agent, thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, thioglycolic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol are suitable.

[0042] The polymerization rate of the prepolymer is not particularly limited, but is preferably 3 to 50%, more preferably 5 to 40%, from the viewpoint of setting a viscosity suitable for coating on a support. The polymerization rate of the prepolymer can be adjusted to the desired range by adjusting the type and amount of the photopolymerization initiator, the irradiation intensity / irradiation time of active light such as ultraviolet rays, etc. The polymerization rate is calculated using the following formula based on the weight before and after heating (drying) when the prepolymer composition is heated at 130°C for 3 hours. It should be noted that when partial polymerization is performed by solution polymerization, the value obtained by subtracting the amount of solvent from the total weight of the prepolymer composition is used as the weight before heating in the following formula to calculate the polymerization rate.

[0043] Polymerization rate (%) = 100 × (weight after heating / weight before heating)

[0044] <Preparation of Photocurable Adhesive Composition>

[0045] The photocurable adhesive composition is obtained by mixing the remaining monomer components, ultraviolet absorber, photopolymerization initiator and other additives into the above-mentioned photopolymerizable acrylic material (monomer and / or its partial polymer). The photocurable adhesive composition preferably contains the above-mentioned multifunctional monomer as the remaining monomer component.

[0046] <Ultraviolet light absorber>

[0047] Examples of the ultraviolet absorber include benzotriazole ultraviolet absorbers, benzophenone ultraviolet absorbers, triazine ultraviolet absorbers, salicylate ultraviolet absorbers, and cyanoacrylate ultraviolet absorbers. From the perspective of easily obtaining an acrylic adhesive having high ultraviolet absorbency, excellent compatibility with an acrylic polymer, and high transparency, triazine ultraviolet absorbers and benzotriazole ultraviolet absorbers are preferred, and among them, triazine ultraviolet absorbers containing a hydroxyl group and benzotriazole ultraviolet absorbers having one benzotriazole skeleton in one molecule are preferred.

[0048] As the ultraviolet absorber, commercial products can be used. Commercial products of triazine-based ultraviolet absorbers include a reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine-2-yl)-5-hydroxyphenyl and [(alkoxy)methyl]ethylene oxide ("TINUVIN 400" manufactured by BASF), a reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine and glycidyl acid (2-ethylhexyl) ester ("TINUVIN 405" manufactured by BASF), (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine ("TINUVIN 405" manufactured by BASF), and (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine ("TINUVIN 405" manufactured by BASF). 460”), 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[hexyloxy]-phenol (“TINUVIN 577” manufactured by BASF), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine (“TINUVIN 479” manufactured by BASF), 2,4-bis-[{4-(4-ethylhexyloxy)-4-hydroxy}-phenyl]-6-(4-methoxyphenyl)-1,3,5-triazine (“Tinosorb S” manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol (“ADK STAB LA-46” manufactured by ADEKA), and the like.

[0049] Examples of commercially available benzotriazole-based ultraviolet absorbers include 2-(2H-benzotriazole-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (“TINUVIN 928” manufactured by BASF), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (“TINUVIN PS” manufactured by BASF), 2-(2H-benzotriazole-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (“TINUVIN PS” manufactured by BASF), and 900”), 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (“TINUVIN 928” manufactured by BASF), 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (“TINUVIN 571” manufactured by BASF), 2-(2H-benzotriazol-2-yl)-p-cresol (“TINUVIN P” manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4-6-bis(1-methyl-1-phenylethyl)phenol (“TINUVIN 234” manufactured by BASF), 2-〔5-chloro(2H)-benzotriazol-2-yl〕-4-methyl-6-(tert-butyl)phenol (“TINUVIN 326”), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-amylphenol (“TINUVIN 328” manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (“TINUVIN 329” manufactured by BASF), ester compound of phenylpropionic acid and 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy (C7-9 side chain and linear alkyl) (“TINUVIN 384-2” manufactured by BASF), reaction product of methyl-3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate and polyethylene glycol (“TINUVIN 1 130”), reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl) propionate and polyethylene glycol 300 (“TINUVIN 213” manufactured by BASF), 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimidomethyl)-5-methylphenyl]benzotriazole (“Sumisorb 250” manufactured by Sumitomo Chemical Co., Ltd.), etc.

[0050] The content of the ultraviolet absorber in the photocurable adhesive composition is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 7 parts by weight, and further preferably 0.5 to 5 parts by weight relative to 100 parts by weight of the monomer component. By setting the content of the ultraviolet absorber to the above range, the reduction in transparency caused by the bleeding of the ultraviolet absorber can be suppressed, and the ultraviolet cutoff property of the adhesive sheet can be improved. In addition, if the content of the ultraviolet absorber is within the above range, the polymerization rate of the adhesive composition can be suppressed from decreasing.

[0051] <Photopolymerization Initiator>

[0052] The photocurable adhesive composition contains a photopolymerization initiator. The photopolymerization initiator is a photoradical generator that generates radicals by visible light or ultraviolet light having a wavelength shorter than 450 nm.

[0053] If the photocurable adhesive composition contains an ultraviolet absorber, part of the irradiation light for photocuring is absorbed by the ultraviolet absorber. From the viewpoint of promoting the generation of free radicals achieved by the cleavage of the photopolymerization initiator and increasing the polymerization rate, it is preferred to use a photopolymerization initiator that has sensitivity in a wavelength region where the absorption of the ultraviolet absorber is small. Specifically, the photopolymerization initiator preferably has sensitivity at a wavelength longer than 380 nm, and more preferably has sensitivity at a wavelength longer than 400 nm. It is preferred to use a photopolymerization initiator having an absorption coefficient of 1×10 at a wavelength of 405 nm. 2 [mLg -1 cm -1 The photopolymerization initiator having long-wavelength light sensitivity may be sensitive to light having a wavelength of 400 nm or less.

[0054] Specific examples of the photopolymerization initiator having photosensitivity at a wavelength of 400 nm or more include acylphosphine oxides such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide ("Lucirin TPO" manufactured by BASF), 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide ("Lucirin TPO-L" manufactured by BASF); aminoketones such as 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1 ("Irgacure 369" manufactured by BASF); bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide ("Irgacure 819" manufactured by BASF), 2,2-dimethoxy-1,2-diphenylethane-1-one ("Irgacure 651”), bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (“CGI403” manufactured by BASF), and the like.

[0055] As the photopolymerization initiator, a photopolymerization initiator having long-wavelength light sensitivity and a photopolymerization initiator not having long-wavelength light sensitivity (for example, a photopolymerization initiator having an absorption coefficient of less than 1×10 2 [mLg -1 cm -1 ] photopolymerization initiator).

[0056] Examples of the photopolymerization initiator that does not have long-wavelength light sensitivity include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, and titanocene-based photopolymerization initiators.

[0057] The content of the photopolymerization initiator in the photocurable adhesive composition is preferably 0.02 to 10 parts by weight, more preferably 0.05 to 5 parts by weight, relative to 100 parts by weight of the total monomer component and prepolymer component constituting the acrylic polymer. If the photopolymerization initiator is too little, the polymerization rate may be insufficient, and if the photopolymerization initiator is too much, the molecular weight of the polymer may be low, and the adhesive strength of the adhesive may be insufficient.

[0058] As described above, a photopolymerization initiator may also be used in the preparation of the prepolymer (partial polymerization). The photopolymerization initiator used in the partial polymerization may be the same as or different from the photopolymerization initiator added to the photocurable adhesive composition. In the case where the prepolymer-forming composition does not contain an ultraviolet absorber but is added after the partial polymerization, the photopolymerization initiator used in the partial polymerization may not have long-wavelength light sensitivity. The unreacted product of the photopolymerization initiator used in the partial polymerization may be directly used as the photopolymerization initiator in the photopolymerizable adhesive composition.

[0059] From the viewpoint of utilization efficiency of irradiated light, it is preferred that the prepolymer-forming composition does not contain an ultraviolet absorber, but that an ultraviolet absorber is added to the prepolymer composition after partial polymerization. For example, it is preferred that: a photopolymerization initiator without long-wavelength light sensitivity is used as a first-added polymerization initiator, partial polymerization is performed, an ultraviolet absorber and a photopolymerization initiator with long-wavelength light sensitivity are added as a post-added polymerization initiator to the partially polymerized composition to prepare a photocurable adhesive composition, the photocurable adhesive composition is applied in a layer on a substrate, and then post-polymerization is performed.

[0060] <Other ingredients>

[0061] The photocurable adhesive composition may contain a chain transfer agent. The chain transfer agent contained in the photocurable adhesive composition is not particularly limited, and for example, the above-mentioned chain transfer agents can be used.

[0062] The photocurable adhesive composition may contain various oligomers for the purpose of adjusting the adhesive strength and viscosity of the adhesive. As the oligomer, for example, an oligomer having a weight average molecular weight of about 1000 to 30000 may be used. As the oligomer, an acrylic oligomer is preferably used from the aspect of excellent compatibility with the acrylic polymer.

[0063] In addition to the above, the photocurable adhesive composition may also contain additives such as silane coupling agents, crosslinking agents, tackifiers, plasticizers, softeners, etc. In addition, the adhesive composition may contain additives such as anti-degradation agents, fillers, colorants, antioxidants, surfactants, antistatic agents, etc. within the range that does not impair the properties of the adhesive.

[0064] The photocurable adhesive composition preferably has a viscosity suitable for coating on a substrate (e.g., about 5 to 100 poise). The viscosity of the adhesive composition can be adjusted by, for example, the addition of various polymers such as tackifying additives, multifunctional monomers, etc., the polymerization rate of prepolymers, etc. The content of the acrylic monomer component (acrylic monomers and partial polymers of acrylic monomers) in the photocurable adhesive composition is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more.

[0065] [Formation of Adhesive Sheet]

[0066] The adhesive sheet can be obtained by coating the photocurable adhesive composition on a support or forming an adhesive composition layer between the support and the cover sheet, and irradiating the adhesive composition with active energy rays for photocuring. Examples of the coating method of the adhesive composition include roller coating, roller lick coating, gravure coating, reverse coating, roller brush, spray coating, dip roller coating, rod coating, knife coating, air knife coating, curtain coating, lip coating, and die coating.

[0067] The coating thickness of the photocurable adhesive composition (thickness of the adhesive sheet 50) is not particularly limited, and is, for example, about 10 to 500 μm. From the viewpoint of improving the ultraviolet absorbency based on the adhesive sheet, the thickness of the adhesive sheet is preferably 50 μm or more. The light transmittance of the adhesive sheet 50 at a wavelength of 380 nm is preferably 50% or less, more preferably 30% or less, further preferably 10% or less, and can be 5% or less or 3% or less.

[0068] The adhesive sheet is obtained by irradiating a laminate having a photocurable acrylic adhesive composition layer on a supporting substrate with ultraviolet rays and / or short-wavelength visible light for photocuring. When photocuring is performed by irradiating a laminate having a photocurable adhesive composition layer between a supporting substrate and a cover sheet, the light irradiation can be performed from any side of the supporting substrate side and the cover sheet side, or from both sides. As described in detail later, in the present invention, as a supporting substrate or a cover sheet attached to the light irradiation side of the adhesive sheet, a release film 10 having a predetermined release layer 15 is used.

[0069] From the viewpoint of increasing the curing speed, the light irradiation intensity is preferably 5 mW / cm 2 From the viewpoint of sufficiently increasing the molecular weight of the acrylic polymer after photocuring and ensuring the holding power at high temperature, the light irradiation intensity is preferably 20 mW / cm 2 the following.

[0070] The cumulative amount of irradiation light is preferably 100 to 5000 mJ / cm 2 The light source used for light irradiation is not particularly limited as long as it can irradiate light in a wavelength range to which the photopolymerization initiator contained in the adhesive composition has sensitivity, and preferably an LED light source, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a xenon lamp, etc. are used.

[0071] Most of the ultraviolet light irradiated to the photocurable adhesive composition containing the ultraviolet absorber is absorbed by the ultraviolet absorber. From the viewpoint of suppressing the low molecular weight caused by the temperature rise and improving the utilization efficiency and curing speed of the irradiated light, it is preferred to irradiate light in a wavelength region with small light absorption based on the ultraviolet absorber. From the aspect of less heat release from the light source and being able to irradiate light with a small wavelength amplitude, it is preferred to use an LED light source. When using an LED light source, the luminous peak wavelength is preferably above 350nm, and can be above 360nm, above 380nm or above 400nm.

[0072] The final polymerization rate of the monomer components in the photocured adhesive sheet is preferably 90% or more, more preferably 95% or more, and further preferably 98% or more. The gel fraction of the adhesive sheet is preferably 50% or more, more preferably 75% or more, and further preferably 85% or more.

[0073] [Release film]

[0074] As a supporting substrate for coating the adhesive composition and a cover sheet attached to the surface of the coating layer of the adhesive composition, a release film having a release layer on the contact surface with the coating layer (adhesive sheet) of the adhesive composition can be used. In the present invention, photocuring is performed in a state where a release film (first release film) 10 having a predetermined first release layer 15 is attached to the first main surface (light irradiation side) of the photocurable adhesive composition layer 55. A release film (second release film) 20 having a second release layer 25 is attached to the second main surface of the photocurable adhesive composition layer 55.

[0075] <Film substrate>

[0076] As the film substrates 11 and 21 of the release films 10 and 20, various transparent resin films are used. As the resin material, 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, polyphenylene sulfide resins, etc. can be listed. Among these, polyester resins such as polyethylene terephthalate are particularly preferred. The thickness of the film substrates 11 and 21 is preferably 10 to 200 μm, and more preferably 25 to 150 μm.

[0077] <Mold release layer>

[0078] As materials for the release layers 15 and 25, silicone resins, long-chain alkyl resins, fatty acid amide resins, etc. can be listed. These resins can contain fluorine atoms in the side chains of the polymer. For example, the silicone resin can be a fluorinated silicone resin containing fluorine atoms in the side chains.

[0079] The silicone-based release agent used for forming the silicone-based release layer can be roughly divided into a condensation-type silicone-based release agent and an addition-type silicone-based release agent, depending on the form of the curing reaction (crosslinking reaction) of the polyorganosiloxane as the main component.

[0080] In the formation of the addition type silicone release layer, a silicone resin composition of the type that is cured by addition reaction is used. The silicone resin composition of the type that is cured by addition reaction preferably comprises a polyorganosiloxane resin having alkenyl groups such as vinyl and hexenyl and a polyorganosiloxane compound (crosslinking agent) having a silane hydrogen group (SiH), and further comprises a curing catalyst (hydrosilylation catalyst). The silicone resin composition is heated to form a releasable coating (release layer) by utilizing the reaction (hydrosilylation reaction) of the alkenyl group of the polyorganosiloxane resin and the silane hydrogen group of the crosslinking agent.

[0081] Examples of polyorganosiloxanes include polyalkylalkylsiloxanes such as polydimethylsiloxane, polydiethylsiloxane, and polymethylethylsiloxane; polyalkylarylsiloxane; and poly(dimethylsiloxane-diethylsiloxane). Among these, polydimethylsiloxane is preferred. Polyorganosiloxanes may have various organic groups bonded to one Si atom.

[0082] The crosslinking agent is a polyorganosiloxane having a silyl hydrogen group, preferably having two or more silicon atoms having Si-H bonds in one molecule. The polyorganosiloxane having a silyl hydrogen group is preferably polymethyl hydrogen siloxane, poly(dimethylsiloxane-methyl hydrogen siloxane), silyl hydrogen group-terminated polydimethylsiloxane, or the like.

[0083] A commercially available product in which a polyorganosiloxane resin having an alkenyl group and a polyorganosiloxane compound having a silyl hydride group are pre-mixed may be used. Examples of commercially available products containing a polyorganosiloxane resin having an alkenyl group and a polyorganosiloxane compound having a silyl hydride group include "KS-847" and "X-62-2829" manufactured by Shin-Etsu Chemical Co., Ltd., and "SRX211", "LTC761" and "LTC300B" manufactured by Dow Corning Toray Co., Ltd.

[0084] As a catalyst for the addition reaction (hydrosilylation reaction), a platinum-based catalyst is preferable. Examples of the platinum-based catalyst include chloroplatinic acid, an olefin complex of platinum, and an olefin complex of chloroplatinic acid.

[0085] In forming the condensation type silicone release layer, a silicone resin composition that cures by condensation reaction is used. Examples of silicone resin compositions that cure by condensation reaction include polyorganosiloxane resins having silanol groups at molecular ends, polymethyl hydrogen siloxanes, cellulose derivatives, alkyd resins, and the like, and compositions that further include a curing catalyst.

[0086] As the polyorganosiloxane having a silanol group at a molecular terminal, an alkyl group such as a methyl group or an ethyl group, a phenyl group, etc. are preferably introduced as a side chain functional group (organic group). The condensed silicone-based resin composition may contain an alkoxy-containing polyorganosiloxane functioning as a crosslinking agent.

[0087] As a catalyst for the condensation reaction, an organic tin catalyst is preferable and examples of the organic tin catalyst include dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin dioctoate.

[0088] In the formation of the fluorine-based release layer, a resin composition containing a fluorine-based resin is used. The fluorine-based resin contains fluorine atoms in the side chain portion of the polymer, and specific examples thereof include fluorine-containing hydrocarbon resins such as polytetrafluoroethylene, fluorinated silicone resins, etc. From the viewpoint of the releasability of the self-adhesive sheet, fluorinated silicone resins are preferred.

[0089] The fluorinated silicone resin may be a curable type or a non-curable type. From the perspective of high adhesion to the film substrate and the ability to form a firm film, a curable fluorinated silicone resin (cured material of curable fluorinated silicone) is preferred. As a curable fluorinated silicone resin, an addition-type silicone is preferred. For example, a material obtained by replacing part or all of the alkyl groups of the side chains of the polyorganosiloxane in the above-mentioned addition-type silicone composition with fluorine atoms or fluoroalkyl groups can be used.

[0090] Commercially available products of curable fluorinated silicone resins include “KP-911” and “X-70-201S” manufactured by Shin-Etsu Chemical Co., Ltd., and “FS1265-300CS”, “FS1265-1000CS”, “FS1265-10000CS”, “BY24-900”, “BY24-903”, “Syl-off 3062”, and “Q2-7785” manufactured by Dow Corning Toray Co., Ltd.

[0091] The composition for forming the release layer (release agent composition) may contain an organic solvent in addition to the resin component. Examples of the organic solvent include hydrocarbon solvents such as cyclohexane, n-hexane, and n-heptane; aromatic solvents such as toluene and xylene; ester solvents such as ethyl acetate and methyl acetate; ketone solvents such as acetone and methyl ethyl ketone; and alcohol solvents such as methanol, ethanol, and butanol. The organic solvent may be a mixed solvent.

[0092] The release agent composition may contain various additives such as a filler, an antistatic agent, an antioxidant, a plasticizer, and a colorant as necessary.

[0093] The release layer is formed by applying the release agent composition to the film substrate, and performing heating and drying and curing reaction as required. As the coating method, roller coating, roller licking coating, gravure coating, reverse coating, roller brush, spray coating, dip roller coating, rod coating, knife coating, air knife coating, curtain coating, lip coating, die coating. As the heating and drying method, hot air drying can be listed. The conditions of hot air drying vary depending on the heat resistance of the substrate, usually about 80 to 150 ° C and about 10 seconds to 10 minutes. As required, for the purpose of promoting the curing reaction, active energy ray irradiation such as heat treatment and ultraviolet irradiation can be used in combination.

[0094] As described above, when the photocurable adhesive composition layer 55 is photocured, light is irradiated from the first release film 10 side. The first release layer 15 of the first release film 10 is preferably a fluorine-based release layer or a condensation-type silicone release layer. The silicone resin of the condensation-type silicone release layer can be fluorine-based or non-fluorine-based. When the first release layer 15 is a fluorine-based release layer or a condensation-type silicone release layer, there is a tendency for the peeling force from the photocurable adhesive sheet to become smaller than when a release film having a non-fluorine-based addition-type silicone release layer is used.

[0095] The second release layer 25 of the second release film 20 is not particularly limited, but is preferably a non-fluorine-based addition-type silicone release layer from the perspective of exhibiting a moderate release force. When the first release layer 15 of the first release film 10 (heavy release film) on the light irradiation side is a fluorine-based release layer or a condensation-type silicone release layer, and the second release layer 25 of the second release film 20 (light release film) on the opposite side is a non-fluorine-based addition-type silicone release layer, an adhesive sheet with a release film can be obtained in which the first release film 10 is easily peeled off from the photocurable adhesive layer 50, and the peeling force of the first release film and the peeling force of the second release film are moderately balanced.

[0096] [Releasability of release film and adhesive sheet]

[0097] In the adhesive sheet with a release film to which a release film is bonded on both sides of the adhesive sheet, usually, the peeling force of the adhesive sheet and a release film is relatively small compared to the peeling force of the adhesive sheet and another release film. When using an adhesive sheet, the release film (low release film) with low peeling force is peeled off from the adhesive sheet and fitted with the first adherend, and the release film (heavy release film) with relatively large peeling force is peeled off and fitted with the second adherend. By presetting the difference of the peeling force to the release film temporarily bonded to the surface and back of the adhesive sheet, so that when fitting with the first adherend, the light peeling film can be selectively peeled off, therefore, the operability of fitting can be improved.

[0098] In a photocurable adhesive sheet, the adhesive force of the adhesive is different before and after photocuring. Therefore, the adhesive properties of the adhesive sheet after photocuring are taken into consideration to adjust the adhesion (peelability) of the light release film and the heavy release film to the adhesive sheet. When the adhesive composition does not contain an ultraviolet absorber, the magnitude relationship between the peeling force of one release film and another release film does not change before and after photocuring. In contrast, when the photocurable adhesive composition contains an ultraviolet absorber, there is a tendency that the increase in the peeling force of the first release film 10 on the light irradiation side is significantly greater than the increase in the peeling force of the second release film 20 arranged on the opposite side.

[0099] Therefore, in the adhesive sheet with release film, the first release film 10 on the light irradiation side is preferably a heavy release film, and the second release film 20 on the opposite side is preferably a light release film. That is, the peeling force between the first release film 10 and the adhesive sheet 50 is preferably greater than the peeling force between the second release film 20 and the adhesive sheet 50.

[0100] As described above, the adhesive composition may be irradiated with light from either the supporting substrate side or the cover sheet side, or from both sides. When irradiating light from the supporting substrate side, the first release film 10 having the first release layer 15 may be used as the supporting substrate on which the adhesive composition is applied. When irradiating light from the cover sheet side, the first release film 10 having the first release layer 15 may be used as the cover sheet attached to the adhesive composition layer 55.

[0101] When irradiating light from both sides, the first release film may be used for either the supporting substrate or the cover sheet. A release film having a fluorine-based release layer or a condensed silicone release layer may be used for both the supporting substrate and the cover sheet. When irradiating light to both sides while conveying on a return track that reverses the conveying direction as described in Japanese Patent Application Laid-Open No. 2014-65754, it is preferred that the release film be used on the side that is first irradiated with light.

[0102] If the peeling force between the first release film 10 (heavy release film) and the adhesive sheet 50 is too large, when the first release film 10 is peeled off from the surface of the adhesive sheet 50 in a state where the adhesive sheet 50 is attached to the first adherend, the adhesive sheet may be deformed, whitened, or peeled off from the adherend. The peeling force (peel strength) between the adhesive sheet 50 and the first release film 10 after photocuring is preferably 0.1 to 1N / 50mm, more preferably 0.2 to 0.8N / 50mm, and further preferably 0.3 to 0.7N / 50mm. The peeling force between the release film and the adhesive sheet is a measured value obtained by a 180° peeling test at a tensile speed of 0.3m / min. As described above, when the release layer 15 of the first release film 10 is a fluorine-based release layer or a condensed silicone release layer, the excessive increase in the peeling force between the adhesive sheet 50 and the first release film 10 after photocuring can be suppressed.

[0103] The reason why the release strength of the release film on the light-irradiated side increases when the photocurable adhesive composition contains an ultraviolet absorber is not clear, but it is presumed to be related to the reaction between the unreacted reactive functional groups in the release layer and the compounds in the adhesive composition.

[0104] As mentioned above, most of the ultraviolet light irradiated to the photocurable adhesive composition containing ultraviolet light absorber is absorbed by the ultraviolet light absorber. If the ultraviolet light absorber absorbs light, light energy is converted into heat energy, and the temperature rises. Especially near the interface between the release layer of the release film on the light irradiation side and the adhesive composition layer, the light absorption amount based on the ultraviolet light absorber is large, so the temperature rises easily. If the temperature rises under light irradiation, it is easy to heat the reaction except the photocuring reaction. Therefore, it can be considered that: by the reaction of the unreacted thermally reactive functional groups in the release layer 15 and the compounds in the adhesive composition, etc., the bonding force (peeling force) will rise.

[0105] As shown in the reference example described later, if the release film whose peeling strength is increased by photocuring of the adhesive is temporarily peeled off from the adhesive sheet (the peeling strength at this time is set as the first peeling strength F1), and the same or the same type of release film is again attached to the adhesive sheet to perform a peeling test (the peeling strength at this time is set as the second peeling strength F2), the second peeling strength F2 becomes smaller than the first peeling strength F1. Therefore, it can also be considered that the formation of chemical bonds during photocuring is the reason why the bonding strength between the release layer and the adhesive layer becomes larger.

[0106] In the condensed silicone resin constituting the condensed silicone release layer, there are few or no functional groups with high thermal reactivity such as olefinic groups. Therefore, it can be considered that even if the temperature rises due to light absorption based on the ultraviolet absorber during photocuring, the reaction between the compounds in the adhesive composition layer 55 and the functional groups in the release layer 15 is not easy to occur, which can suppress the excessive increase of the peeling force.

[0107] The fluorine-based resin constituting the fluorine-based release layer has low surface free energy. Therefore, it is considered that the highly reactive functional groups in the adhesive composition have little interaction with the release layer, and chemical reactions at the interface are less likely to occur, which is related to the suppression of the increase in the release force.

[0108] As described above, the first peel strength F1 when peeling the first release film 10 from the photocurable adhesive sheet 50 is preferably 0.1 to 1 N / 50 mm. The second peel strength F2 when peeling the first release film 10 from the photocurable adhesive sheet 50 and reattaching the same or the same release film and peeling is preferably less than F1. F1 / F2 is preferably 3 or less. F1 / F2 is usually 0.5 or more. F1 / F2 is more preferably 0.7 to 2.5, and further preferably 0.8 to 2.0.

[0109] [Application of adhesive sheet]

[0110] The above-mentioned photocurable adhesive sheet has a high visible light transmittance and has ultraviolet cut-off properties, and therefore, can be suitably used as an optical adhesive for display devices and display input devices that require ultraviolet cut-off properties. As display devices, liquid crystal display devices, organic EL (electroluminescent) display devices, PDP (plasma display panel), electronic paper, etc. can be listed. As input devices, touch panels can be listed. In addition, the above-mentioned photocurable adhesive sheet can also be used for the bonding of display devices and input devices, and the bonding of transparent plates disposed on the surfaces of display devices and input devices.

[0111] When using an adhesive sheet with a release film with release films bonded to both sides, first, peel off the light release film (second release film 20) to expose the second main surface of the adhesive sheet 50, and bond it to the first adherend. Thereafter, peel off the heavy release film (first release film 10) to expose the first main surface of the adhesive sheet 50, and bond it to the second adherend. It can be bonded to the adherend after peeling off the release films on both sides. When the adhesive sheet has photocurability, the adhesive sheet after bonding to the adherend can be further irradiated with light. By further photocuring the adhesive sheet after bonding to the adherend, it is sometimes possible to improve the bonding reliability with the adherend.

[0112] Example

[0113] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0114] [Preparation of Adhesive Composition]

[0115] To a monomer mixture consisting of 78 parts by weight of 2-ethylhexyl acrylate (2EHA), 18 parts by weight of N-vinyl-2-pyrrolidone (NVP), and 4 parts by weight of 2-hydroxyethyl acrylate (HEA), 0.035 parts by weight of 1-hydroxycyclohexyl phenyl ketone ("Irgacure 184" manufactured by BASF) and 0.035 parts by weight of 2,2-dimethoxy-1,2-diphenylethane-1-one ("Irgacure 651" manufactured by BASF) as photopolymerization initiators were added. The composition was irradiated with ultraviolet rays and prepolymerized until the viscosity at room temperature reached about 20 Pa·s, thereby obtaining a prepolymer having a polymerization rate of about 8%.

[0116] To 100 parts by weight of the prepolymer composition, 2 parts by weight of polyester urethane diacrylate having a weight average molecular weight of 12,500 ("Art Resin UN-350" manufactured by Negami Industries), 5 parts by weight of an acrylic oligomer, 0.70 parts by weight of a UV absorber ("Tinosorb S" manufactured by BASF), 0.05 parts by weight of "Irgacure 184" manufactured by BASF as a photopolymerization initiator, 0.05 parts by weight of "Irgacure 651" manufactured by BASF, and 0.40 parts by weight of "Irgacure 819" manufactured by BASF, 0.07 parts by weight of α-methylstyrene dimer ("Nofmer MSD" manufactured by NOF Corporation) as a chain transfer agent, and 0.3 parts by weight of "KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd. as a silane coupling agent were added, and the mixture was uniformly mixed to prepare a photocurable adhesive composition. The acrylic oligomer used had dicyclopentanyl methacrylate and methyl methacrylate (MMA) as monomer components at a weight ratio of 60:40 and had a weight average molecular weight of 5100.

[0117] [Preparation of Release Film A]

[0118] 30 parts by weight of a non-fluorine-based addition-type silicone composition containing a polyorganosiloxane having a hexene group ("LTC761" manufactured by Dow Corning Toray Co., Ltd.), 0.9 parts by weight of a silicone dispersion ("BY 24-850" manufactured by Dow Corning Toray Co., Ltd.), and 2 parts by weight of a platinum catalyst for silicone curing ("SRX 212" manufactured by Dow Corning Toray Co., Ltd.) were diluted with a mixed solvent of toluene and hexane at a volume ratio of 1:1 to prepare a release agent solution. The solution was applied to one side of a biaxially stretched polyester film having a thickness of 75 μm, and heated in a hot air dryer at 130°C for 1 minute to prepare a release film A having a non-fluorine-based addition-type silicone release layer on one side of the polyester film.

[0119] [Comparative Example 1]

[0120] In Comparative Example 1, the supporting release film and the covering release film were the above-mentioned release film A. On the release layer forming surface of the supporting release film, the adhesive composition was applied with a thickness of 300 μm to form a coating layer, and the covering release film was attached to the surface of the coating layer to obtain a laminate. The irradiation intensity of the irradiation surface directly below the lamp reached 5 mW / cm 2 The laminate was irradiated with ultraviolet light from the side covered with the release film to perform photocuring, thereby obtaining a pressure-sensitive adhesive sheet having release films on both sides of the photocurable pressure-sensitive adhesive layer.

[0121] [Example 1]

[0122] As the cover release film, a release film having a fluorine-added silicone release layer on one side of a polyester film ("FSC6" manufactured by NIPPA) was used instead of the release film A. Otherwise, the same operation as in Comparative Example 1 was performed to obtain an adhesive sheet having release films on both sides of the photocurable adhesive layer.

[0123] [Example 2]

[0124] As the covering release film, a release film having a non-fluorine-based condensation-type silicone release layer on one side of the polyester film ("SR(S)" manufactured by NIPPA) was used instead of the release film A. Except for this, the same operation as in Comparative Example 1 was performed to obtain an adhesive sheet having release films on both sides of the photocurable adhesive layer.

[0125] [Reference Example 1]

[0126] In Comparative Example 1 and Examples 1 and 2, the coating layer was cured by ultraviolet irradiation from the opposite side, that is, the side supporting the release film, to obtain a pressure-sensitive adhesive sheet having release films on both sides of the photocurable pressure-sensitive adhesive layer.

[0127] [Evaluation of peelability]

[0128] <Peel Strength of Release Film>

[0129] The adhesive sheet with the release film was cut into 50 mm wide, and a 180° peel test was performed at a tensile speed of 0.3 m / min using a tensile tester at 23°C to measure the peel strength when the release film covering the adhesive sheet was peeled off. That is, for the samples of Comparative Example 1 and Examples 1 and 2, the peel strength of the release film on the light irradiation side was measured, and for Reference Example 1, the peel strength of the release film on the side opposite to the light irradiation side was measured.

[0130] [Evaluation results]

[0131] Table 1 shows the types of the cover release films of Examples and Comparative Examples and the results of measuring the peel strength of the cover release films.

[0132] [Table 1]

[0133]

[0134] When the adhesive was photocured by light irradiation from the side supporting the release film (reference example 1), no significant difference in the peel strength of the covering release film was observed using any release film. When light irradiation was performed from the side covering the release film, in comparative example 1, the peel strength exceeded 1N / 50mm, and a significant increase in the peel strength was observed. On the other hand, in Example 1 using a fluorine-based silicone release film and Example 2 using a condensed silicone release film, the peel strength increased compared to reference example 1, but the peel strength was still less than 0.5N / 50mm.

[0135] [Reference Example 2]

[0136] The supporting release film (light release film) was peeled off from the adhesive sheet with release film of the above-mentioned comparative example 1 (an example of using a non-fluorine-based addition-type silicone release film as a cover release film), and the adhesive sheet was attached to a glass plate. The cover release film (heavy release film) was peeled off from the sample, and a release film of the same type was attached to the adhesive sheet, and pressure was applied using a manual roller. A 5 cm wide scratch was made on the release film, and the peel strength was measured, and the result was 0.20 N / 50 mm.

[0137] Based on the comparison between Comparative Example 1 and Reference Examples 1 and 2, it can be considered that: in Comparative Example 1, the effect of increasing the adhesion between the release layer and the adhesive layer by irradiating light during the curing of the adhesive composition (for example, chemical bonds are generated by the reaction between the resin component of the release agent and the curing component in the adhesive) is large, and therefore the peel strength is increased.

[0138] On the other hand, it can be considered that: in Examples 1 and 2, the residual amount of curing reactive functional groups in the resin material constituting the release layer is small. Furthermore, in Example 1, the surface free energy of the release layer is small due to the introduction of fluorine. Therefore, the effect of increasing the adhesive force achieved by generating chemical bonds between the release layer and the adhesive layer is small, which can suppress the excessive increase in peel strength.

[0139] Description of Reference Numerals

[0140] 1: Adhesive sheet with release film

[0141] 10, 20: Release film

[0142] 11, 21: Film substrate

[0143] 15, 25: Release layer

Claims

1. A method for producing a pressure-sensitive adhesive sheet with a release film, wherein: The adhesive sheet with release film comprises: a photocurable adhesive sheet having a first main surface and a second main surface; a first release film temporarily bonded to the first main surface of the adhesive sheet; and a second release film temporarily bonded to the second main surface of the adhesive sheet. The manufacturing method comprises the following steps: A step of forming a laminated body in which a photocurable adhesive composition is provided in a layer between the first release film and the second release film, the photocurable adhesive composition comprising an acrylic monomer and / or a partial polymer of an acrylic monomer, an ultraviolet absorber, and a photopolymerization initiator; as well as a step of irradiating the photocurable adhesive composition between the first release film and the second release film with light from the first release film side to photocuring the photocurable adhesive composition; The first release film comprises a first release layer on a surface of a film substrate that contacts the photocurable adhesive composition. The second release film comprises a second release layer on a surface of the film substrate that contacts the photocurable adhesive composition. The first release layer is a fluorine-based release layer or a condensed silicone release layer.

2. The method for producing a pressure-sensitive adhesive sheet with a release film according to claim 1, wherein: The second release layer is a non-fluorine-based addition type silicone release layer.

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