Method for manufacturing adhesive sheet, reinforcing film, and device

Abstract

To provide a photocurable adhesive sheet having high haze in a final product assembled in a device without deteriorating detectability in a manufacturing step of a device.SOLUTION: An adhesive sheet (2) is formed by layering an adhesive composition containing an acrylic base polymer and a polyfunctional (meth)acrylate having 4 or more (meth)acryloyl groups in one molecule as a photocuring agent. The acrylic base polymer contains 70 wt.% or more of a (meth)acrylic acid alkyl ester in which the alkyl group is a chain alkyl having 6 or more carbon atoms, based on a total amount of the constituent monomer components. A content of the tetra- or higher polyfunctional (meth)acrylate in the adhesive composition is preferably 7 pts.mass or more with respect to 100 pts.mass of the acrylic base polymer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet made of a photocurable pressure-sensitive adhesive composition, and a reinforced film having the pressure-sensitive adhesive sheet on a film substrate. The present invention further relates to a method for producing a device with a reinforced film by bonding the reinforced film to the surface of an adherend. [Background technology]

[0002] An adhesive film may be attached to the surface of an optical device such as a display or an electronic device for the purpose of surface protection, imparting impact resistance, etc. Such an adhesive film usually has an adhesive layer (adhesive sheet) fixed and laminated on the main surface of a film substrate, and is attached to the device surface via this adhesive sheet.

[0003] By temporarily attaching an adhesive film to the surface of a device or a device component before use, such as during device assembly, processing, transportation, etc., it is possible to prevent the adherend from being scratched or damaged. Patent Document 1 discloses a reinforcing film that includes an adhesive sheet made of a photocurable adhesive composition on a film substrate.

[0004] This reinforcing film can be peeled off from the adherend immediately after bonding because the adhesive has low adhesion. Therefore, it can be reworked from the adherend, and it is also possible to selectively peel off and remove the reinforcing film from a location on the adherend that does not require reinforcement. The adhesive of the reinforcing film is firmly bonded to the adherend by photocuring, so the film base material is permanently bonded to the surface of the adherend, and it can be used as a reinforcing material that protects the surface of devices. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-41113 A Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, displays have become increasingly bezel-less, and a configuration has been proposed in which an optical sensor such as a fingerprint sensor is disposed in the display area of ​​the display. For example, by disposing an optical sensor on the back surface of an organic EL panel as a display element, a configuration having an optical sensor within the display area can be realized.

[0007] It has been pointed out that in this configuration, when the screen is viewed in a bright place, components such as the optical sensor arranged on the back side of the image display panel are visible (identifiable). By arranging a high haze adhesive sheet on the back side of the image display panel (between the image display panel and the optical sensor), the visibility (identification) of the optical sensor from the display surface can be reduced. On the other hand, in consideration of the convenience of visual inspection and optical inspection by an inspection device in the device manufacturing process, it is preferable that the adhesive sheet has a low haze.

[0008] In view of the above, an object of the present invention is to provide a pressure-sensitive adhesive sheet that has high haze in the final product incorporated into a device without reducing inspectability during the device manufacturing process. [Means for solving the problem]

[0009] One aspect of the present invention is a pressure-sensitive adhesive sheet having a layer of a photocurable pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition contains an acrylic base polymer and a photocuring agent, and may further contain a photopolymerization initiator.

[0010] The acrylic base polymer contains 70% by weight or more of (meth)acrylic acid alkyl ester, the alkyl group of which is a chain alkyl having 6 or more carbon atoms, relative to the total amount of the constituent monomer components. The light hardener contains a multifunctional (meth)acrylate having 4 or more (meth)acryloyl groups in one molecule.

[0011] The content of the tetrafunctional or higher polyfunctional (meth)acrylate in the pressure-sensitive adhesive composition is preferably 7 parts by weight or more based on 100 parts by weight of the acrylic base polymer.

[0012] The difference H1-H0 between the haze H1 of the pressure-sensitive adhesive sheet after photocuring and the haze H0 before photocuring is preferably 1.0% or more. The haze H0 of the pressure-sensitive adhesive sheet before photocuring is preferably less than 6%, and may be 5% or less. The haze H1 of the pressure-sensitive adhesive sheet after photocuring is preferably 3% or more, and may be 5% or more or 6% or more.

[0013] Another embodiment of the present invention is a reinforced film having the above-mentioned pressure-sensitive adhesive sheet fixedly laminated on one main surface of a film substrate. The reinforced film sheet is temporarily attached to the surface of an adherend, and then the pressure-sensitive adhesive sheet is photocured to form a device with the reinforced film. The adherend may be an organic electroluminescence panel. Effect of the Invention

[0014] The above-mentioned pressure-sensitive adhesive sheet has a small haze before photocuring, so that the accuracy of optical inspection by visual inspection or imaging can be ensured even when the sheet is attached to an adherend. In addition, the pressure-sensitive adhesive sheet has a large haze after photocuring, so that components such as an optical sensor arranged on the back side of the pressure-sensitive adhesive sheet are difficult to see (recognize) from the outer surface of the device. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a cross-sectional view showing the laminated structure of a pressure-sensitive adhesive sheet having release films on both sides. [Diagram 2] FIG. 2 is a cross-sectional view showing a laminated structure of a reinforcing film. [Diagram 3] 1 is a cross-sectional view showing an example of a laminated structure of a device to which a reinforcing film is attached. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Fig. 1 is a cross-sectional view showing an adhesive sheet with release films, in which release films 51, 52 are temporarily attached to both sides of an adhesive sheet 2. Fig. 2 is a cross-sectional view of a reinforcing film, in which an adhesive sheet 2 is fixedly laminated onto one main surface of a film substrate 1, and a release film 52 is temporarily attached onto the adhesive sheet 2. The adhesive sheet 2 is a layer of a photocurable adhesive composition, which is cured by irradiation with active light such as ultraviolet light, thereby increasing the adhesive strength with the adherend.

[0017] 3 is a cross-sectional view showing a state in which the reinforcing film 10 is attached to the surface of the device 20. The release film 51 is peeled off and removed from the surface of the adhesive sheet 2 of the reinforcing film shown in FIG. 2, and the exposed surface of the adhesive sheet 2 is attached to the surface of the device 20, thereby attaching the reinforcing film 10 to the surface of the device 20. In this state, the adhesive sheet 2 has not yet been photocured, and the reinforcing film 10 (adhesive sheet 2) is temporarily attached onto the device 20. By photocuring the adhesive sheet 2, the adhesive force at the interface between the device 20 and the adhesive sheet 2 increases, and the reinforcing film 10 is fixed to the surface of the device 20.

[0018] "Adhesion" means that the two laminated layers are firmly bonded together, making it difficult or impossible to peel them apart at their interface. "Temporary adhesion" means that the adhesive strength between the two laminated layers is weak, making them easy to peel apart at their interface.

[0019] In the adhesive sheet shown in Fig. 1, release films 51, 52 are temporarily attached to both sides of the adhesive sheet 2, and the release films 51, 52 can be easily peeled off from the surface of the adhesive sheet 2. In the reinforcing film shown in Fig. 2, the film substrate 1 and the adhesive sheet 2 are adhered to each other, and the release film 51 is temporarily attached to the adhesive sheet 2. When the film substrate 1 and the release film 51 are peeled off, peeling occurs at the interface between the adhesive sheet 2 and the release film 51, and the adhesive sheet 2 remains adhered to the film substrate 1. No adhesive remains on the release film 51 after peeling.

[0020] In the device with reinforcing film shown in Fig. 3, the device 20 and the adhesive sheet 2 are in a temporary bonded state before the adhesive sheet 2 is photocured. When the film substrate 1 and the device 20 are peeled off, the peeling occurs at the interface between the adhesive sheet 2 and the device 20, so the adhesive sheet 2 remains in a bonded state on the film substrate 1. After the adhesive sheet 2 is photocured, the adhesive strength between the adhesive sheet 2 and the device 20 increases and they are in a bonded state, so it is difficult to peel the film substrate 1 from the device 20, and peeling the two off may cause cohesive failure of the adhesive sheet 2.

[0021] [Adhesive sheet] The adhesive sheet 2 is made of a photocurable composition containing a base polymer and a photocuring agent. Before photocuring, the adhesive sheet 2 has low adhesive strength with an adherend such as a device or device part, and is therefore peelable from the adherend. The adhesive sheet 2 has excellent adhesive reliability because its adhesive strength with the adherend is improved by photocuring.

[0022] Photocurable adhesives hardly cure in normal storage environments, but cure when exposed to active light such as ultraviolet light. Therefore, the reinforcing film in which the adhesive sheet 2 is fixedly laminated onto the film substrate 1 has the advantage that the timing of curing the adhesive sheet 2 can be set as desired, and it can flexibly respond to process lead times, etc.

[0023] The thickness of the adhesive sheet 2 is, for example, about 1 to 300 μm. The thicker the adhesive sheet 2, the more the adhesiveness to the adherend tends to improve. On the other hand, if the adhesive sheet 2 is too thick, the fluidity before photocuring is high, and handling may become difficult. Therefore, the thickness of the adhesive sheet 2 is preferably 3 to 100 μm, more preferably 5 to 50 μm, further preferably 6 to 40 μm, and particularly preferably 8 to 30 μm. From the viewpoint of thinning, the thickness of the adhesive sheet 2 may be 25 μm or less, 20 μm or less, or 18 μm or less.

[0024] The total light transmittance of a pressure-sensitive adhesive sheet used in an optical device such as a display is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0025] When the haze of the adhesive sheet is high, light scattering in the adhesive sheet may hinder the inspection during visual inspection or optical inspection by imaging in the manufacturing process of the device, and the inspection accuracy may decrease. Therefore, from the viewpoint of ensuring the inspection accuracy, the haze of the adhesive sheet is preferably less than 6%, and may be 5% or less, 4% or less, or 3% or less. On the other hand, in the final product such as a display, a high haze of the adhesive sheet can suppress a member such as an optical sensor arranged on the back side of the adhesive sheet from being visually recognized (recognized) by a user. From this viewpoint, the haze of the adhesive sheet is preferably 3% or more, more preferably 5% or more, even more preferably 6% or more, and may be 7% or more, 8% or more, 9% or more, or 10% or more.

[0026] The adhesive sheet of the present invention has a low haze before photocuring, and the haze increases due to photocuring. Therefore, by performing an optical inspection before photocuring the adhesive sheet, the accuracy of the optical inspection is improved. In addition, in the final product in which the adhesive sheet is photocured, the haze of the adhesive sheet is high, so that the optical sensor and the like arranged on the back surface are difficult to be recognized by the user of the device.

[0027] The increase in haze of the adhesive sheet due to photocuring, i.e., the difference H1-H0 between H1 of the adhesive sheet after photocuring and H0 of the adhesive sheet before photocuring, is preferably 1.0% or more, more preferably 1.5% or more, and may be 2.0% or more, 2.5% or more, 3.0% or more, 4.0% or more, or 5.0% or more. The upper limit of the increase in haze is not particularly limited, but is generally 30% or less, and may be 20% or less, or 15% or less.

[0028] <Adhesive composition> The adhesive composition constituting the adhesive sheet 2 contains a base polymer and a photocuring agent, and has photocurability. As described below, when the adhesive composition contains a specific base polymer and a photocuring agent, an adhesive sheet with a large increase in haze due to photocuring can be obtained. From the viewpoint of increasing the efficiency of photocuring, the adhesive composition (photocurable composition) constituting the adhesive sheet 2 preferably contains a photopolymerization initiator.

[0029] (Base polymer) The base polymer is the main component of the pressure-sensitive adhesive composition and is the main factor that determines various properties of the pressure-sensitive adhesive sheet, such as adhesive strength, etc. Since the adhesive strength, etc. can be easily controlled, the pressure-sensitive adhesive composition preferably contains an acrylic polymer as the base polymer, and it is preferable that 50 wt % or more of the pressure-sensitive adhesive composition is an acrylic polymer.

[0030] The acrylic base polymer contains an alkyl (meth)acrylate ester as a main monomer component. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0031] As the (meth)acrylic acid alkyl ester, there may be mentioned (meth)acrylic acid C having an alkyl group having 1 to 22 carbon atoms. 1-22 An alkyl ester is preferably used. The (meth)acrylic acid alkyl ester may have a branched alkyl group or a cyclic alkyl group.

[0032] The acrylic base polymer preferably contains 70% by weight or more of (meth)acrylic acid alkyl esters in which the alkyl group is a chain alkyl having 6 or more carbon atoms, based on the total amount of the constituent monomer components. The higher the ratio of (meth)acrylic acid alkyl esters having a chain alkyl having 6 or more carbon atoms (hereinafter referred to as "C6 or more alkyl (meth)acrylates"), the higher the haze of the adhesive sheet after photocuring tends to be. The amount of C6 or more alkyl (meth)acrylates is more preferably 75% by weight or more, even more preferably 80% by weight or more, and may be 85% by weight or more, 90% by weight or more, 93% by weight or more, or 95% by weight or more, based on the total amount of the constituent monomer components.

[0033] The upper limit of the amount of C6 or higher alkyl (meth)acrylate is not particularly limited. As described later, in order to introduce a crosslinking point into the acrylic base polymer, it is preferable to use a hydroxyl group-containing monomer or a carboxyl group-containing monomer, and the amount of C6 or higher alkyl (meth)acrylate is preferably 99.5% by weight or less, more preferably 99% by weight or less, and may be 98% by weight or less, or 97% by weight or less, based on the total amount of the constituent monomer components of the acrylic base polymer.

[0034] The chain alkyl group of the C6 or higher alkyl (meth)acrylate may be linear or branched. Specific examples of C6 or higher alkyl (meth)acrylates include hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (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, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and docosyl acrylate.

[0035] From the viewpoint of lowering the glass transition temperature of the acrylic base polymer and imparting appropriate flexibility to the pressure-sensitive adhesive sheet, the number of carbon atoms in the chain alkyl group in the C6 or higher alkyl (meth)acrylate is preferably 9 or less. Specific examples of C6 or higher alkyl (meth)acrylates with low Tg include 2-ethylhexyl acrylate (Tg: -70°C), n-hexyl acrylate (Tg: -65°C), n-octyl acrylate (Tg: -65°C), isononyl acrylate (Tg: -60°C), n-nonyl acrylate (Tg: -58°C), isooctyl acrylate (Tg: -58°C), and the like.

[0036] As mentioned above, the chain alkyl group in the C6 or higher alkyl (meth)acrylate may have a branch. When the alkyl group has a large carbon number or has a branched structure, the molecular volume is large, so when the adhesive is photocured with a photocuring agent having a large number of functional groups, a domain with a large volume is likely to be formed, and the increase in haze is considered to be significant.

[0037] The monomer components constituting the acrylic base polymer may contain two or more C6 or higher alkyl (meth)acrylates, and (meth)acrylic acid C 6-9 Alkyl esters and (meth)acrylic acid C 10-22 It may also contain alkyl esters.

[0038] The monomer components constituting the acrylic base polymer may include, in addition to C6 or higher alkyl (meth)acrylate, an alkyl (meth)acrylate ester having an alkyl group with 5 or less carbon atoms, or an alkyl (meth)acrylate ester having a cyclic alkyl group.

[0039] Specific examples of (meth)acrylic acid alkyl esters having an alkyl group having 5 or less carbon atoms 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, and neopentyl (meth)acrylate.

[0040] 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.

[0041] The acrylic base polymer preferably contains, as a copolymerization component, a monomer component having a crosslinkable functional group in addition to the above-mentioned (meth)acrylic acid alkyl ester. Examples of the monomer having a crosslinkable functional group include a hydroxyl group-containing monomer and a carboxyl group-containing monomer. The acrylic base polymer may have both a hydroxyl group-containing monomer and a carboxyl group-containing monomer as copolymerization components, or may have only one of them. The introduction of a crosslinked structure into the acrylic base polymer tends to improve the cohesive force and the peelability of the pressure-sensitive adhesive sheet 2 from the adherend before photocuring.

[0042] Examples of the hydroxy group-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, 4-(hydroxymethyl)cyclohexylmethyl (meth)acrylate, etc. Examples of the carboxy group-containing monomer include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc.

[0043] In the acrylic base polymer, the total amount of the hydroxy group-containing monomer and the carboxy group-containing monomer relative to the total amount of the constituent monomer components is preferably 0.5 to 20% by weight, more preferably 1 to 15% by weight, and may be 1.5 to 10% by weight.

[0044] The acrylic base polymer may contain, as a constituent monomer component, a nitrogen-containing monomer such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinylcarboxylic acid amides, or N-vinylcaprolactam.

[0045] The acrylic base polymer may contain a monomer component other than the above. The acrylic base polymer may contain, as a monomer component, for example, a vinyl ester monomer, an aromatic vinyl monomer, an epoxy group-containing monomer, a vinyl ether monomer, a sulfo group-containing monomer, a phosphoric acid group-containing monomer, an acid anhydride group-containing monomer, etc.

[0046] The monomer components are polymerized by various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization to obtain an acrylic polymer as a base polymer. From the viewpoint of the balance of properties such as adhesive strength and holding power of the pressure-sensitive adhesive, and from the viewpoint of cost, the solution polymerization method is preferred. As the solvent for solution polymerization, ethyl acetate, toluene, methyl ethyl ketone, etc. are used. The solution concentration is usually about 20 to 80% by weight. As the polymerization initiator, various known ones such as azo-based and peroxide-based initiators can be used. A chain transfer agent may be used to adjust the molecular weight. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

[0047] The weight average molecular weight of the acrylic base polymer is preferably 100,000 to 2,000,000, more preferably 200,000 to 1,500,000, and even more preferably 300,000 to 1,000,000. When a crosslinked structure is introduced into the acrylic base polymer, the molecular weight of the base polymer refers to the molecular weight before the introduction of the crosslinked structure.

[0048] (Crosslinking agent) In order to provide the adhesive with an appropriate cohesive force, develop adhesive strength, and ensure the peelability of the adhesive sheet from the adherend before photocuring, it is preferable that a crosslinking structure is introduced into the acrylic base polymer. For example, a crosslinking agent is added to the solution after polymerization of the acrylic base polymer, and the solution is heated as necessary to introduce a crosslinking structure. Examples of the crosslinking agent 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. These crosslinking agents react with functional groups such as hydroxyl groups and carboxyl groups introduced into the acrylic base polymer to form a crosslinking structure. Isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they are highly reactive with the hydroxyl groups and carboxyl groups of the acrylic base polymer and are easy to introduce a crosslinking structure.

[0049] As the isocyanate crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule is used. Examples of the polyisocyanate 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 diisocyanate, ... 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"), trimethylolpropane adducts of xylylene diisocyanate (e.g., Mitsui Chemicals' "Takenate D110N"), and isocyanurate of hexamethylene diisocyanate (e.g., Tosoh's "Coronate HX").

[0050] As the epoxy crosslinking agent, a multifunctional epoxy compound having two or more epoxy groups in one molecule is used. The epoxy crosslinking agent may have three or more or four or more epoxy groups in one molecule. The epoxy group of the epoxy crosslinking agent may be a glycidyl group. Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, 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 the epoxy-based crosslinking agent, commercially available products such as "Denacol" manufactured by Nagase ChemteX, and "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical may be used.

[0051] The amount of the crosslinking agent used may be adjusted appropriately depending on the composition and molecular weight of the acrylic base polymer, etc. The amount of the crosslinking agent used is about 0.03 to 2 parts by weight, preferably 0.05 to 1 part by weight, more preferably 0.08 to 0.8 parts by weight, and may be 0.1 to 0.5 parts by weight, relative to 100 parts by weight of the acrylic base polymer.

[0052] A crosslinking catalyst may be used to promote the formation of a crosslinked structure. Examples of the crosslinking catalyst include organometallic compounds such as organometallic complexes (chelates), compounds of metals and alkoxy groups, and compounds of metals and acyloxy groups; and tertiary amines. In particular, organometallic compounds are preferred from the viewpoint of suppressing the progress of the crosslinking reaction in a solution state at room temperature and ensuring the pot life of the adhesive composition. Examples of metals in organometallic compounds include iron, tin, aluminum, zirconium, zinc, titanium, lead, and cobalt. The amount of the crosslinking catalyst used is generally 0.5 parts by weight or less per 100 parts by weight of the acrylic base polymer.

[0053] (Light hardener) The adhesive composition constituting the adhesive sheet 2 contains a photocuring agent in addition to an acrylic base polymer. When the adhesive sheet 2 made of a photocurable adhesive composition is photocured after being attached to an adherend, the adhesive strength with the adherend is improved.

[0054] As the photocuring agent, a polyfunctional (meth)acrylate having four or more (meth)acryloyl groups in one molecule is used. The polyfunctional (meth)acrylate is typically an ester of a polyol and (meth)acrylic acid. From the viewpoint of compatibility with the acrylic base polymer, the molecular weight of the photocuring agent is preferably 2000 or less, more preferably 1000 or less, and may be 800 or less or 600 or less. From the viewpoint of providing the adhesive with appropriate cohesiveness after photocuring to enhance adhesion, the functional group equivalent of the photocuring agent (i.e., the molecular weight per (meth)acryloyl group) is preferably 60 to 200, more preferably 70 to 150, and may be 75 to 130 or 80 to 120.

[0055] Specific examples of polyfunctional (meth)acrylates having 4 or more functional groups include tetramethylolmethane tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ditrimethylolpropane penta(meth)acrylate, ditrimethylolpropane hexa(meth)acrylate, pentasritol tetra(meth)acrylate, ethoxylated pentasritol tetra(meth)acrylate, propoxylated pentasritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc. Two or more types of polyfunctional (meth)acrylates may be used in combination.

[0056] Multifunctional (meth)acrylates exhibit moderate compatibility with acrylic base polymers and have a small refractive index difference with the acrylic base polymers, so they can reduce the haze of the adhesive sheet before photocuring. In addition, by using a tetrafunctional or higher multifunctional (meth)acrylate as a photocuring agent, the haze of the adhesive sheet after photocuring tends to increase, and the greater the amount of multifunctional (meth)acrylate, the greater the increase in haze H1-H0 of the adhesive sheet due to photocuring tends to be.

[0057] The amount of the polyfunctional (meth)acrylate having 4 or more functional groups in the adhesive composition is preferably 7 parts by weight or more, more preferably 8 parts by weight or more, even more preferably 10 parts by weight or more, and may be 13 parts by weight or more or 15 parts by weight or more, relative to 100 parts by weight of the acrylic base polymer. The amount of the polyfunctional (meth)acrylate having 4 or more functional groups in the adhesive composition is not particularly limited, but if the amount of the photocuring agent is excessively large, the haze of the adhesive sheet before photocuring may increase. In addition, if the amount of the photocuring agent is excessively large, the adhesive strength and flexibility of the adhesive sheet after photocuring may be insufficient. Therefore, the amount of the polyfunctional (meth)acrylate having 4 or more functional groups in the adhesive composition is preferably 40 parts by weight or less, more preferably 35 parts by weight or less, even more preferably 30 parts by weight or less, and may be 25 parts by weight or less, relative to 100 parts by weight of the acrylic base polymer.

[0058] The adhesive composition may contain, as a photocuring agent, a trifunctional or less (meth)acrylate or other photocurable monomer or oligomer in addition to a tetrafunctional or more polyfunctional (meth)acrylate. When the adhesive composition contains a tetrafunctional or more polyfunctional (meth)acrylate as a photocuring agent, the total amount of the photocuring agent (the total of the tetrafunctional or more polyfunctional (meth)acrylate and other photocuring agent) is preferably 40 parts by weight or less, and may be 30 parts by weight or less or 25 parts by weight or less, relative to 100 parts by weight of the acrylic base polymer. The content of the photocuring agent other than the tetrafunctional or more polyfunctional (meth)acrylate is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and may be 5 parts by weight or less, 3 parts by weight or less, or 1 part by weight or less, relative to 100 parts by weight of the acrylic base polymer.

[0059] (Photopolymerization initiator) The pressure-sensitive adhesive composition preferably contains a photopolymerization initiator. The photopolymerization initiator generates active species by irradiation with active light rays, and promotes the curing reaction of the photocuring agent. When a polyfunctional (meth)acrylate is used as the photocuring agent, it is preferable to use a photoradical polymerization initiator. As the photoradical polymerization initiator, a photoradical generator that is cleaved by visible light or ultraviolet light having a wavelength shorter than 450 nm to generate radicals is preferable, and examples of the photoradical polymerization initiator include hydroxyketones, benzyl dimethyl ketals, aminoketones, acylphosphine oxides, benzophenones, trichloromethyl group-containing triazine derivatives, and the like. The photopolymerization initiator may be used alone or in a mixture of two or more kinds.

[0060] The content of the photopolymerization initiator in the pressure-sensitive adhesive composition is about 0.001 to 5 parts by weight, and may be 0.01 to 3 parts by weight, or 0.03 to 1 part by weight, based on 100 parts by weight of the acrylic base polymer.

[0061] (Oligomer) The pressure-sensitive adhesive composition may contain an oligomer in addition to the acrylic base polymer. For example, the pressure-sensitive adhesive composition may contain an acrylic oligomer in addition to the acrylic base polymer. The oligomer used has a weight-average molecular weight of about 1,000 to 30,000. The acrylic oligomer contains a (meth)acrylic acid alkyl ester as a main constituent monomer component. From the viewpoint of increasing the adhesive strength of the pressure-sensitive adhesive sheet 2 after photocuring, the glass transition temperature of the acrylic oligomer is preferably 40° C. or higher, more preferably 50° C. or higher. The oligomer may contain a crosslinkable functional group like the acrylic base polymer.

[0062] The content of the oligomer in the pressure-sensitive adhesive composition is not particularly limited. When the pressure-sensitive adhesive composition contains an acrylic oligomer in addition to an acrylic base polymer, the amount of the oligomer relative to 100 parts by weight of the acrylic base polymer is preferably 0.1 to 20 parts by weight, more preferably 0.3 to 10 parts by weight, and even more preferably 0.5 to 5 parts by weight, from the viewpoint of adjusting the adhesive strength within an appropriate range.

[0063] (Other additives) In addition to the above-exemplified components, the pressure-sensitive adhesive composition may contain additives such as a silane coupling agent, a tackifier, a plasticizer, a softener, an anti-degradation agent, a filler, a colorant, an ultraviolet absorber, an antioxidant, a surfactant, and an antistatic agent, within a range that does not impair the properties of the present invention.

[0064] <Formation of adhesive sheet> The above-mentioned adhesive composition is applied to a substrate by roll coating, kiss roll coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, or the like, and the solvent is dried and removed as necessary to form an adhesive sheet. As the drying method, an appropriate method may be adopted as appropriate. The heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and even more preferably 70°C to 170°C. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and even more preferably 10 seconds to 10 minutes.

[0065] When the pressure-sensitive adhesive composition contains a crosslinking agent, it is preferable to proceed with crosslinking by heating or aging simultaneously with or after drying of the solvent. The heating temperature and heating time are appropriately set depending on the type of crosslinking agent used, and crosslinking is usually performed by heating in the range of 20°C to 160°C for about 1 minute to 7 days. The heating for drying and removing the solvent may also serve as the heating for crosslinking.

[0066] By introducing a crosslinked structure into the acrylic base polymer, the gel fraction increases, and the storage modulus of the adhesive sheet 2 tends to increase. The higher the gel fraction of the adhesive before photocuring, the harder the adhesive is, and the more likely it is that adhesive residue on the adherend is suppressed when the reinforcing film is peeled off from the adherend by rework or the like. The gel fraction of the adhesive sheet 2 before photocuring (i.e., the gel fraction of the photocurable composition constituting the adhesive sheet) is preferably 25% or more, more preferably 30% or more, and may be 35% or more, 40% or more, or 45% or more. On the other hand, if the gel fraction is excessively large, the adhesive strength and flexibility may decrease. Therefore, the gel fraction of the adhesive sheet 2 before photocuring is preferably 80% or less, and may be 75% or less, or 70% or less.

[0067] The gel fraction can be determined as the insoluble portion in a solvent such as ethyl acetate, specifically, it is determined as the weight fraction (unit: weight %) of the insoluble portion after immersing the pressure-sensitive adhesive sheet in ethyl acetate for 7 days at 23° C. relative to the sample before immersion. Generally, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked portions in the polymer, the higher the gel fraction.

[0068] The substrate used to form the adhesive sheet is not particularly limited. For example, an adhesive composition is applied onto a release film 51, and after performing solvent removal and crosslinking as necessary, a release film 52 is attached to obtain an adhesive sheet having release films temporarily attached to both sides as shown in FIG. 1. Crosslinking may be performed after the release film 52 is attached onto the adhesive sheet 2.

[0069] As the release films 51, 52, plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester films are preferably used. The thickness of the release film is usually 3 to 200 μm, and preferably about 10 to 100 μm. The surfaces of the release films 51, 52 that come into contact with the adhesive sheet 2 are preferably subjected to a release treatment using a release agent such as a silicone-based, fluorine-based, long-chain alkyl-based, or fatty acid amide-based agent, or silica powder. The release films 51, 52 may be subjected to an antistatic treatment on either or both of the release-treated surface and the non-treated surface. By subjecting the release film to an antistatic treatment, it is possible to suppress the charge when the release film is peeled off from the adhesive sheet.

[0070] [Reinforcing film] The above-mentioned pressure-sensitive adhesive sheet is used for bonding various members. In one embodiment, the pressure-sensitive adhesive sheet 2 is used for bonding a flexible plastic film substrate to the surface of various devices or their constituent members. By bonding a flexible plastic film to the surface of a device or its constituent member, appropriate rigidity is imparted, and therefore, effects such as improved handling and damage prevention are expected for members with small thickness.

[0071] When attaching a film substrate 1 to a device or a component thereof via an adhesive sheet 2, a reinforcing film 10 having an adhesive sheet adhered and laminated onto the film substrate 1 may be prepared as shown in FIG. 2, and the adhesive sheet 2 of the reinforcing film 10 may be attached to the device or a component thereof, and then the adhesive sheet 2 may be photocured.

[0072] <Film substrate> A flexible plastic film is used as the film substrate 1 of the reinforcing film 10. In order to bond the film substrate 1 and the adhesive sheet 2 together, it is preferable that the surface of the film substrate 1 to which the adhesive sheet 2 is attached has not been subjected to a release treatment.

[0073] The thickness of the film substrate 1 is, for example, about 4 to 500 μm. From the viewpoint of reinforcing the device by imparting rigidity or cushioning impact, the thickness of the film substrate 1 is preferably 12 μm or more, more preferably 20 μm or more, and may be 30 μm or more, 40 μm or more, or 45 μm or more. From the viewpoint of imparting flexibility to the reinforcing film and improving handleability, the thickness of the film substrate 1 is preferably 300 μm or less, more preferably 200 μm or less.

[0074] Examples of plastic materials constituting the film substrate 1 include polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, polyether ether ketone, polyether sulfone, polyarylate resins, and aramid resins. In a reinforcing film for an optical device such as a display, the film substrate 1 is preferably a transparent film. In addition, when the adhesive sheet 2 is photocured by irradiating the film substrate 1 with active light rays from the film substrate 1 side, the film substrate 1 is preferably transparent to the active light rays used to cure the adhesive. Since they have both mechanical strength and transparency, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, transparent polyimide, transparent aramid, and polyether ether ketone are preferably used. When irradiating active light rays from the adherend side, the adherend only needs to have transparency to the active light rays, and the film substrate 1 does not need to be transparent to the active light rays.

[0075] The surface of the film substrate 1 may be provided with a functional coating such as an easy-adhesion layer, an easy-slip layer, a release layer, an antistatic layer, a hard coat layer, an antireflection layer, etc. In order to bond the film substrate 1 and the pressure-sensitive adhesive sheet 2, it is preferable that no release layer is provided on the surface of the film substrate 1 to which the pressure-sensitive adhesive sheet 2 is attached.

[0076] <Preparation of reinforcing film> A reinforcing film is obtained by laminating a photocurable adhesive sheet 2 on a film substrate 1. The adhesive sheet 2 may be formed directly on the film substrate 1, or an adhesive sheet formed on a release film may be transferred onto the film substrate 1. For example, by peeling off the release film 52 temporarily attached to one side of the adhesive sheet 2 from the adhesive sheet with release film shown in FIG. 1 and laminating the film substrate 1 to the exposed surface of the adhesive sheet 2, the adhesive sheet 2 is fixedly laminated on the film substrate 1 as shown in FIG. 2, and a reinforcing film in which a release film is temporarily attached to the adhesive sheet 2 is obtained.

[0077] [Device with stiffening film] The above-mentioned reinforcing film of the present invention is used by being attached to a device or a device component. The adherend to which the reinforcing film is attached is not particularly limited, and examples thereof include various electronic devices, optical devices and their components.

[0078] In one embodiment, the adherend to which the reinforcing film is attached is an organic EL panel. The organic EL panel may be either a top-emission type or a bottom-emission type. A top-emission type organic EL panel has an anode (metal electrode), an organic light-emitting layer, and a cathode (transparent electrode) on a substrate in this order, and has a configuration in which light is extracted from the cathode side. A bottom-emission type organic EL panel has a cathode, an organic light-emitting layer, and an anode on a transparent substrate in this order, and has a configuration in which light is extracted from the transparent substrate side. By using a flexible heat-resistant film such as a polyimide film as the substrate of the organic EL panel, it is possible to realize a thin and flexible panel.

[0079] The reinforcing film may be attached to the entire surface of the adherend, or may be selectively attached only to the portion requiring reinforcement (reinforcement target area). Alternatively, the reinforcing film may be attached to the entire portion requiring reinforcement (reinforcement target area) and the portion not requiring reinforcement (non-reinforcement target area), and then the reinforcing film attached to the non-reinforcement target area may be cut and removed. If the adhesive has not yet been photocured, the reinforcing film is in a state of being temporarily attached to the surface of the adherend, and therefore the reinforcing film can be peeled off and removed from the surface of the adherend. The reinforcing film may be attached to the reinforcement target area and the non-reinforcement target area, light may be selectively irradiated to the reinforcement target area to photocur the adhesive, and then the reinforcing film in the non-reinforcement target area where the adhesive is not yet cured may be selectively peeled off and removed.

[0080] By attaching the reinforcing film, appropriate rigidity is imparted, and therefore, effects such as improved handling and prevention of damage are expected for thin members such as organic EL panels using flexible substrates. For example, the reinforcing film is attached to the flexible substrate on the back surface (opposite side to the light extraction side) of the organic EL panel. The reinforcing film may be attached to the light extraction surface of the organic EL panel. The reinforcing film may be attached to something other than the substrate of the organic EL panel, for example, the reinforcing film may be attached to a sealant that seals the organic light-emitting layer and the electrodes.

[0081] In the device manufacturing process, when the reinforcing film is laminated to a work in progress, the reinforcing film may be laminated to a large-sized work in progress before being cut to the product size. The reinforcing film may be laminated to a mother roll of a device manufactured by a roll-to-roll process by roll-to-roll. Before laminating the reinforcing film, the surface of the adherend may be subjected to an activation treatment for the purpose of cleaning or the like. Examples of the surface activation treatment include plasma treatment, corona treatment, and glow discharge treatment.

[0082] From the viewpoint of being peelable from the adherend and preventing peeling during storage or handling, the adhesive strength between the pressure-sensitive adhesive sheet 2 and the adherend before photocuring is preferably about 0.005 to 1 N / 25 mm. The adhesive strength is determined by a peel test using a polyimide film as the adherend at a tensile speed of 300 mm / min and a peel angle of 180°. Unless otherwise specified, the adhesive strength is measured at 25°C.

[0083] As described above, the haze of the pressure-sensitive adhesive sheet 2 before photocuring is preferably less than 6%, and may be 5% or less, 4% or less, or 3% or less. Since the haze of the pressure-sensitive adhesive sheet 2 before photocuring is small, even after a reinforcing film is attached to an adherend, it does not interfere with optical inspection of an adherend such as an organic EL panel by visual inspection or imaging from the film substrate 1 side, and inspection accuracy can be maintained.

[0084] The reinforcing film is attached to the adherend, and if necessary, optical inspection or removal of the reinforcing film from the non-reinforcement target area is performed. Then, the adhesive sheet 2 is irradiated with active light to photocure the adhesive. Examples of active light include ultraviolet light, visible light, infrared light, X-rays, α-rays, β-rays, and γ-rays. UV light is preferred as the active light because it can suppress the curing of the adhesive in the storage state and is easy to cure. The irradiation intensity and irradiation time of the active light may be appropriately set according to the composition and thickness of the adhesive. The active light may be irradiated to the adhesive sheet 2 from either the film substrate 1 side or the adherend side, or from both sides.

[0085] As the adhesive sheet 2 is photocured, the adhesive strength of the adhesive sheet 2 to the adherend increases. The adhesive strength between the adhesive sheet 2 and the adherend after photocuring is preferably 2 N / 25 mm or more, and more preferably 2.5 N / 25 mm or more. The adhesive strength between the adhesive sheet 2 and the adherend after photocuring is preferably 5 times or more the adhesive strength between the adhesive sheet 2 and the adherend before photocuring.

[0086] As described above, the haze of the pressure-sensitive adhesive sheet 2 increases due to photocuring. The haze of the pressure-sensitive adhesive sheet 2 after photocuring is preferably 3% or more, more preferably 5% or more, even more preferably 6% or more, and may be 7% or more, 8% or more, 9% or more, or 10% or more. The increase in haze H1-H0 of the pressure-sensitive adhesive sheet due to photocuring is preferably 1.0% or more, more preferably 1.5% or more, and may be 2.0% or more, 2.5% or more, 3.0% or more, 4.0% or more, or 5.0% or more, and may be 30% or less, 20% or less, or 15% or less.

[0087] As described above, by laminating the reinforcing film, appropriate rigidity is imparted to the adherend, and stress is alleviated and dispersed, thereby suppressing various defects that may occur in the manufacturing process, improving production efficiency, and improving yield. In addition, since the reinforcing film can be peeled off from the adherend before the adhesive is photocured, rework is possible in the event of lamination or lamination defects, and processing such as selectively removing the reinforcing film from areas other than the area to be reinforced is also possible. Furthermore, since the adhesive sheet has low haze before photocuring, the accuracy of visual and imaging inspection can be ensured even when the reinforcing film is laminated.

[0088] When the completed device is used, even if an external force is suddenly applied due to dropping the device, placing a heavy object on the device, or collision of a flying object with the device, the reinforcing film is attached to the device, so that the device can be prevented from being damaged. In addition, since the reinforcing film is firmly attached to the device after the adhesive is photocured, the reinforcing film is unlikely to peel off even in long-term use, and is highly reliable. In addition, since the adhesive sheet has a high haze due to photocuring, optical sensors and the like arranged on the back surface of the reinforcing film are difficult to see from the outer surface of the device, the device can also be suitably used for image display devices equipped with optical sensors such as fingerprint sensors in the display area of ​​the display. EXAMPLES

[0089] The pressure-sensitive adhesive sheet will be further described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0090] [Example 1] <Preparation of Pressure-Sensitive Adhesive Composition> In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen gas inlet tube, 96.2 parts by weight of 2-ethylhexyl acrylate (2EHA) and 3.8 parts by weight of 2-hydroxyethyl acrylate (2HEA) as monomers, 0.2 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 156 parts by weight of ethyl acetate as a solvent were charged, and nitrogen gas was introduced and nitrogen substitution was performed for about 1 hour while stirring. After that, the mixture was heated to 60°C and reacted for 7 hours to obtain a solution of an acrylic polymer with a weight average molecular weight (Mw) of 600,000.

[0091] To the above acrylic polymer solution (100 parts by weight of polymer), 0.1 parts by weight of an isocyanurate of hexamethylene diisocyanate ("Coronate HX" manufactured by Tosoh) as a crosslinking agent, 0.02 parts by weight of iron acetylacetonate ("Nacem Ferric" manufactured by Nippon Kagaku Sangyo) as a crosslinking catalyst, 10 parts by weight of dipentaerythritol polyacrylate (a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate; "NK Ester A-DPH" manufactured by Shin-Nakamura Chemical Co., Ltd.) as a photocuring agent, and 0.1 parts by weight of 2,2-dimethoxy-1,2-diphenylethan-1-one ("Omnirad651" manufactured by IGM Resins) as a photopolymerization initiator were added and mixed uniformly to obtain a pressure-sensitive adhesive composition.

[0092] <Preparation of adhesive sheet> The above adhesive composition was applied to a silicone release-treated 75 μm thick polyethylene terephthalate film (heavy release film) so that the thickness after drying was 20 μm. After drying at 130° C. for 1 minute to remove the solvent, the release-treated surface of a 50 μm thick polyethylene terephthalate film (light release film) whose surface was silicone release-treated was attached to the adhesive-coated surface. Then, aging treatment was performed for 4 days in an atmosphere of 25° C. to promote crosslinking, and an adhesive sheet with release films temporarily attached to both sides was obtained.

[0093] [Examples 2 to 7, Comparative Examples 1 to 7] Except for changing the monomer composition of the acrylic polymer and the type and amount of the photocuring agent added as shown in Table 1, pressure-sensitive adhesive compositions were prepared and pressure-sensitive adhesive sheets were produced in the same manner as in Example 1.

[0094] [Example 8, Comparative Examples 8 and 9] The composition of the acrylic polymer monomer, and the type and amount of the photocuring agent added were changed as shown in Table 1. In addition, 0.1 parts by weight of N,N,N',N'-tetraglycidyl-m-xylylenediamine (tetrafunctional epoxy compound, "Tetrad C" manufactured by Mitsubishi Gas Chemical Company) was added as a crosslinking agent instead of the isocyanate-based crosslinking agent, and no crosslinking catalyst was added. Aside from these changes, a pressure-sensitive adhesive composition was prepared and a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1.

[0095] [evaluation] <Haze before photocuring> The release film (light release film) on one side of the adhesive sheet of each of the examples and comparative examples was peeled off, the adhesive sheet was attached to a glass plate, and then the release film (heavy release film) on the other side was peeled off to prepare a sample for haze measurement. Using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., "NDH-5000"), light was irradiated from the adhesive sheet side to measure the haze H0 of the adhesive sheet before photocuring in accordance with JIS K7136.

[0096] <Haze after photocuring> The light release film was peeled off from the pressure-sensitive adhesive sheets of the Examples and Comparative Examples, and the pressure-sensitive adhesive sheets were attached to a glass plate. Then, the sheet was irradiated with 2000 mJ / cm 2 from an LED light source with a wavelength of 365 nm from the surface with the heavy release film. 2 The pressure-sensitive adhesive composition was photocured by irradiating it with ultraviolet light of 1000 nm. Thereafter, the heavy release film was peeled off, and the surface of the pressure-sensitive adhesive sheet was irradiated with light to measure the haze H1 of the pressure-sensitive adhesive sheet before photocuring.

[0097] The acrylic polymer compositions of the pressure-sensitive adhesive compositions of the Examples and Comparative Examples, the types and amounts of photocuring agents added, and the haze of the pressure-sensitive adhesive sheets before and after photocuring are shown in Table 1. In Table 1, the polymer compositions are the weight ratios of the constituent monomers, and the amounts of the photocuring agents are the amounts added per 100 parts by weight of the solid content of the acrylic polymer. Details of the monomers and photocuring agents are as follows:

[0098] <Monomer> 2EHA 2-Ethylhexyl acrylate BA Butyl Acrylate 2HEA 2-Hydroxyethyl acrylate 4HBA 4-Hydroxybutyl acrylate AA Acrylic Acid <Light curing agent> DPH Dipentaerythritol polyacrylate (Refractive index: 1.489, Viscosity: 7500 mPa·s (25°C)) TMMT Pentaerythritol tetraacrylate (Refractive index: 1.480, Viscosity: 215 mPa·s (40°C)) HDN 1,6-Hexanediol diacrylate (Refractive index: 1.456, Viscosity: 6 mPa·s (25°C)) DCP Tricyclodecane dimethanol diacrylate (Refractive index: 1.503, Viscosity: 135 mPa·s (25°C)) TMPT Trimethylolpropane Triacrylate (Refractive index: 1.474, Viscosity: 105 mPa·s (25°C))

[0099] [Table 1]

[0100] In Examples 1 to 8, in which a tetrafunctional or higher polyfunctional acrylate was used as the photocuring agent, the increase in haze H1-H0 due to photocuring of the pressure-sensitive adhesive sheet was 1% or more, whereas in Comparative Examples 1 and 2, in which a bifunctional acrylate was used, and in Comparative Example 3, in which a trifunctional acrylate was used, H1-H0 was less than 1%. Even in Comparative Examples 4 to 6, in which a small amount of tetrafunctional or higher acrylate was used, H1-H0 was less than 1%. A comparison between Example 1 and Example 2, and a comparison between Example 3 and Example 4, shows that the increase in haze of the pressure-sensitive adhesive sheet due to photocuring increases as the content of the tetrafunctional or higher polyfunctional acrylate in the pressure-sensitive adhesive composition increases.

[0101] A comparison between Example 2, Example 7, and Comparative Example 7 shows that the higher the ratio of 2EHA (C8 alkyl acrylate) in the monomer components constituting the acrylic polymer, the greater the increase in haze due to photocuring. A similar tendency was also seen in a comparison between Example 5 and Example 6. A comparison between Example 8 and Comparative Examples 8 and 9 shows that even when acrylic acid, a carboxyl group-containing monomer, is used as the copolymerization monomer component of the acrylic polymer and an epoxy-based crosslinking agent is used, the increase in haze due to photocuring is greater by using a (meth)acrylic acid alkyl ester having an alkyl group with a large carbon number as the main monomer component constituting the base polymer. [Explanation of symbols]

[0102] 1 Film substrate 2 Adhesive Sheet 51,52 Release film 10 Reinforcement film 20 Substrate (organic EL panel) 100 Device with reinforcement film

Claims

1. A pressure-sensitive adhesive sheet having a layer of a photocurable pressure-sensitive adhesive composition comprising an acrylic-based polymer and a photocuring agent, In the photocurable pressure-sensitive adhesive composition, The acrylic base polymer contains 70% by weight or more of (meth)acrylic acid alkyl ester, the alkyl group of which is a chain alkyl having 6 or more carbon atoms, based on the total amount of the constituent monomer components; the photocuring agent contains a polyfunctional (meth)acrylate having four or more (meth)acryloyl groups in one molecule, The composition contains 7 parts by weight or more of the polyfunctional (meth)acrylate relative to 100 parts by weight of the acrylic base polymer, A pressure-sensitive adhesive sheet having a haze H 0 of 5% or less before photocuring and a haze H 1 of 6% or more after photocuring.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the photocurable pressure-sensitive adhesive composition further comprises a photopolymerization initiator.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the acrylic base polymer contains, as a constituent monomer component, one or more monomers selected from the group consisting of hydroxy group-containing monomers and carboxy group-containing monomers, and a crosslinked structure is introduced into the acrylic base polymer.

4. A reinforcing film comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 3 adhered and laminated to one main surface of a film substrate.

5. A method for manufacturing a device having a reinforcing film bonded to a surface thereof, comprising the steps of: After the pressure-sensitive adhesive sheet of the reinforcing film according to claim 4 is temporarily attached to the surface of an adherend, A method for manufacturing a device, comprising photocuring the pressure-sensitive adhesive sheet.

6. The method for manufacturing a device according to claim 5 , wherein the adherend is an organic EL panel.

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