JP7675548B2 - Method for manufacturing adhesive sheet, reinforcing film, and device - Google Patents

Description

The present invention relates to an adhesive sheet made of a photocurable adhesive composition, and a reinforced film having the adhesive sheet on a film substrate. Furthermore, the present invention relates to a method for producing a device with a reinforced film, in which the reinforced film is bonded to the surface of an adherend.

Adhesive films are sometimes applied to the surfaces of optical devices such as displays and electronic devices for the purposes of surface protection, impact resistance, etc. Such adhesive films usually have an adhesive layer (adhesive sheet) fixed and laminated to the main surface of a film substrate, and are attached to the device surface via this adhesive sheet.

By temporarily attaching an adhesive film to the surface of a device or a device component before use, such as during device assembly, processing, or transportation, 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.

This reinforcing film can be peeled off from the adherend immediately after it is attached to the adherend because the adhesive has low adhesion. This allows the film to be reworked from the adherend, and also makes it possible to selectively peel off and remove the reinforcing film from locations on the adherend that do not require reinforcement. The adhesive of the reinforcing film firmly bonds to the adherend when photocured, so the film base material is permanently bonded to the surface of the adherend, making it usable as a reinforcing material for protecting the surface of devices, etc.

JP 2020-41113 A

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 placed in the display area of the display. For example, by placing an optical sensor on the back of an organic EL panel that serves as a display element, a configuration can be realized in which the optical sensor is located within the display area.

In this configuration, it has been pointed out that 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, considering the convenience of visual inspection and optical inspection by inspection equipment during the device manufacturing process, it is preferable that the adhesive sheet has a low haze.

In view of the above, the present invention aims to provide an adhesive sheet that has high haze in the final product when incorporated into a device without compromising inspectability during the device manufacturing process.

One aspect of the present invention is an adhesive sheet in which a photocurable adhesive composition is formed in a layer shape. The adhesive composition contains an acrylic-based polymer and a photocuring agent, and may further contain a photopolymerization initiator.

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 photocuring agent contains a multifunctional (meth)acrylate having 4 or more (meth)acryloyl groups in one molecule.

The content of the tetrafunctional or higher polyfunctional (meth)acrylate in the adhesive composition is preferably 7 parts by weight or more per 100 parts by weight of the acrylic base polymer.

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.

A further aspect of the present invention is a reinforcing film in which the above-mentioned adhesive sheet is fixedly laminated onto one main surface of a film substrate. After this sheet of reinforcing film is temporarily attached to the surface of an adherend, a device with the reinforcing film can be formed by photocuring the adhesive sheet. The adherend may be an organic EL panel.

The above-mentioned adhesive sheet has a small haze before photocuring, so even when attached to an adherend, the accuracy of optical inspection by visual inspection or imaging can be ensured. In addition, the adhesive sheet has a large haze after photocuring, so components such as optical sensors that are located behind the adhesive sheet are difficult to see (recognize) from the outer surface of the device.

FIG. 2 is a cross-sectional view showing the laminated structure of a pressure-sensitive adhesive sheet having release films on both sides. FIG. 2 is a cross-sectional view showing a laminated structure of a reinforcing film. 1 is a cross-sectional view showing an example of a laminated structure of a device to which a reinforcing film is attached. FIG.

Figure 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. Figure 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 that is cured by exposure to active light such as ultraviolet light, increasing the adhesive strength with the adherend.

Figure 3 is a cross-sectional view showing the 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 Figure 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 to 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.

"Fixed" 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.

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.

In the device with reinforcing film shown in FIG. 3, before the adhesive sheet 2 is photocured, the device 20 and the adhesive sheet 2 are in a temporary bonded state. 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 fixed 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 become fixed, making it 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.

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

Photocurable adhesives hardly cure in typical storage environments, but cure when exposed to active light such as ultraviolet light. Therefore, a reinforcing film in which an adhesive sheet 2 is fixedly laminated onto a film substrate 1 has the advantage that the timing of curing of the adhesive sheet 2 can be set as desired, allowing for flexible response to process lead times, etc.

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, even more 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.

The total light transmittance of adhesive sheets used in optical devices such as displays is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

If the adhesive sheet has a high haze, light scattering from the adhesive sheet may interfere with visual inspection or optical inspection by imaging during the device manufacturing process, resulting in reduced inspection accuracy. Therefore, from the viewpoint of ensuring 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 a final product such as a display, a high haze of the adhesive sheet can prevent components such as an optical sensor arranged behind the adhesive sheet from being visually recognized (recognized) by the 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.

The adhesive sheet of the present invention has low haze before photocuring, and the haze increases as a result of photocuring. Therefore, by carrying out an optical inspection before photocuring the adhesive sheet, the accuracy of the optical inspection can be improved. Furthermore, in the final product in which the adhesive sheet is photocured, the adhesive sheet has high haze, so that optical sensors and the like placed on the back surface are difficult for the user of the device to recognize.

The increase in haze of the adhesive sheet due to photocuring, i.e., the difference H ₁ -H ₀ between H ₁ of the adhesive sheet after photocuring and H ₀ 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.

<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.

(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.

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

As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid C _1-22 alkyl ester is preferably used, in which the carbon number of the alkyl group is 1 to 22. The (meth)acrylic acid alkyl ester may have an alkyl group that is branched or may have a cyclic alkyl group.

The acrylic base polymer preferably 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 higher the ratio of (meth)acrylic acid alkyl ester having a chain alkyl having 6 or more carbon atoms (hereinafter referred to as "C6 or more alkyl (meth)acrylate"), the higher the haze of the adhesive sheet after photocuring tends to be. The amount of C6 or more alkyl (meth)acrylate 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.

There is no particular upper limit to the amount of C6 or higher alkyl (meth)acrylate. As described below, in order to introduce crosslinking points 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.

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.

From the viewpoint of lowering the glass transition temperature of the acrylic base polymer and imparting appropriate flexibility to the 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), etc.

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, and 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, resulting in a significant increase in haze.

The constituent monomer components of the acrylic base polymer may contain two or more C6 or higher alkyl (meth)acrylates, and may contain a _C6-9 alkyl (meth)acrylate and a _C10-22 alkyl (meth)acrylate.

The constituent monomer components of the acrylic base polymer may include, in addition to C6 or higher alkyl (meth)acrylates, alkyl (meth)acrylate esters having an alkyl group with 5 or less carbon atoms, and alkyl (meth)acrylate esters having a cyclic alkyl group.

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.

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.

In addition to the above-mentioned (meth)acrylic acid alkyl ester, the acrylic base polymer preferably contains a monomer component having a crosslinkable functional group as a copolymerization component. 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.

Examples of hydroxy group-containing monomers 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 carboxy group-containing monomers include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc.

In the acrylic base polymer, the total amount of the hydroxyl group-containing monomer and the carboxyl 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.

The acrylic base polymer may contain nitrogen-containing monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinyl carboxylic acid amides, and N-vinylcaprolactam as constituent monomer components.

The acrylic base polymer may contain monomer components other than those mentioned above. The acrylic base polymer may contain, as monomer components, for example, vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphate group-containing monomers, acid anhydride group-containing monomers, etc.

The above monomer components are polymerized by various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization to obtain an acrylic polymer as the base polymer. From the viewpoint of the balance of adhesive strength, holding power, and other properties of the adhesive, as well as cost, the solution polymerization method is preferred. As the solvent for solution polymerization, ethyl acetate, toluene, methyl ethyl ketone, and the like 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.

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 crosslinked structure is introduced.

(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.

As the isocyanate-based crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule is used. Examples of polyisocyanate-based crosslinking agents 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, etc. Examples of isocyanate adducts include xylylene diisocyanate trimer adduct (e.g., Tosoh's "Coronate L"), trimethylolpropane/hexamethylene diisocyanate trimer adduct (e.g., Tosoh's "Coronate HL"), trimethylolpropane adduct of xylylene diisocyanate (e.g., Mitsui Chemicals' "Takenate D110N"), and isocyanurate of hexamethylene diisocyanate (e.g., Tosoh's "Coronate HX").

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-xylylene diamine, diglycidyl aniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether. As epoxy-based crosslinking agents, commercially available products such as "Denacol" manufactured by Nagase ChemteX and "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical may be used.

The amount of crosslinking agent used may be adjusted appropriately depending on the composition and molecular weight of the acrylic base polymer. The amount of 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, per 100 parts by weight of the acrylic base polymer.

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; as well as 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.

(Photocuring agent)
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.

As the photocuring agent, a polyfunctional (meth)acrylate having four or more (meth)acryloyl groups in one molecule is used. A representative polyfunctional (meth)acrylate is 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 an 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.

Specific examples of polyfunctional (meth)acrylates having 4 or more functionalities 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.

The multifunctional (meth)acrylate exhibits a suitable degree of compatibility with the acrylic base polymer, and has a small refractive index difference with the acrylic base polymer, so that the haze of the adhesive sheet before photocuring can be reduced. 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 larger the amount of multifunctional (meth)acrylate, the larger the increase in haze of the adhesive sheet due to photocuring (H ₁ -H ₀₎ tends to be.

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.

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 per 100 parts by weight of the acrylic base polymer, and may be 30 parts by weight or less or 25 parts by weight or less. The content of the photocuring agent other than the tetrafunctional or more polyfunctional (meth)acrylate is preferably 15 parts by weight or less per 100 parts by weight of the acrylic base polymer, 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.

(Photopolymerization initiator)
The 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, etc. The photopolymerization initiator may be used alone or in a mixture of two or more kinds.

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, per 100 parts by weight of the acrylic base polymer.

(Oligomer)
The adhesive composition may contain an oligomer in addition to the acrylic base polymer. For example, the adhesive composition may contain an acrylic oligomer in addition to the acrylic base polymer. The oligomer has a weight average molecular weight of about 1000 to 30000. 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 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.

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 per 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.

(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.

<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, etc., and the solvent is dried and removed as necessary to form an adhesive sheet. As the drying method, an appropriate method can 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.

When the 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.

The introduction of a crosslinked structure into the acrylic base polymer increases the gel fraction, 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 less adhesive remains on the adherend 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.

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. In general, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked parts in the polymer, the higher the gel fraction.

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 with release films temporarily attached to both sides, as shown in FIG. 1. Crosslinking may also be performed after the release film 52 is attached onto the adhesive sheet 2.

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 treated with a release agent such as a silicone-based, fluorine-based, long-chain alkyl-based, or fatty acid amide-based release agent, or with silica powder. The release films 51, 52 may be antistatically treated on either or both of the release-treated and non-treated surfaces. By treating the release films with an antistatic treatment, it is possible to suppress charging when the release films are peeled off from the adhesive sheet.

[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 handleability and damage prevention are expected for members with small thickness.

When attaching the film substrate 1 to a device or its component via the adhesive sheet 2, as shown in FIG. 2, a reinforcing film 10 in which an adhesive sheet is fixedly laminated onto the film substrate 1 may be prepared, and the adhesive sheet 2 of the reinforcing film 10 may be attached to the device or its component, and then the adhesive sheet 2 may be photocured.

<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 pressure-sensitive adhesive sheet 2 together, it is preferable that the surface of the film substrate 1 to which the pressure-sensitive adhesive sheet 2 is attached has not been subjected to a release treatment.

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 and 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 handling properties, the thickness of the film substrate 1 is preferably 300 μm or less, more preferably 200 μm or less.

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 active light from the film substrate 1 side, the film substrate 1 is preferably transparent to the active light used to cure the adhesive. Polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, transparent polyimide, transparent aramid, and polyether ether ketone are preferably used because they have both mechanical strength and transparency. When irradiating active light from the adherend side, it is sufficient that the adherend has transparency to active light, and the film substrate 1 does not need to be transparent to active light.

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, or an anti-reflection layer. In order to bond the film substrate 1 and the adhesive sheet 2 together, it is preferable that no release layer is provided on the surface of the film substrate 1 to which the adhesive sheet 2 is attached.

<Preparation of Reinforcement 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, from the adhesive sheet with release film shown in FIG. 1, the release film 52 temporarily attached to one side of the adhesive sheet 2 is peeled off, and the film substrate 1 is attached to the exposed surface of the adhesive sheet 2, so that the adhesive sheet 2 is fixedly laminated on the film substrate 1, as shown in FIG. 2, and a reinforcing film in which the release film is temporarily attached to the adhesive sheet 2 is obtained.

[Device with reinforcement 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.

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) in that order on a substrate, and is configured to extract light from the cathode side. A bottom-emission type organic EL panel has a cathode, an organic light-emitting layer, and an anode in that order on a transparent substrate, and is configured to extract light from the transparent substrate side. By using a flexible heat-resistant film such as a polyimide film as the substrate for the organic EL panel, it is possible to achieve a thin and flexible panel.

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

By attaching a reinforcing film, appropriate rigidity is imparted, which is expected to improve the handling properties and prevent damage to thin components such as organic EL panels that use flexible substrates. For example, a reinforcing film is attached to the flexible substrate on the back surface of the organic EL panel (the surface opposite the light extraction side). A reinforcing film may also be attached to the light extraction surface of the organic EL panel. The reinforcing film may also 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 electrodes.

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

From the viewpoint of being able to peel off from the adherend and preventing peeling during storage and handling, the adhesive strength between the 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, with a tensile speed of 300 mm/min and a peel angle of 180°. Unless otherwise specified, the adhesive strength is measured at 25°C.

As mentioned above, the haze of the 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 adhesive sheet 2 before photocuring is small, even after the reinforcing film is attached to the adherend, it does not interfere with optical inspection of the adherend, such as an organic EL panel, by visual inspection or imaging from the film substrate 1 side, and inspection accuracy can be maintained.

After laminating the reinforcing film to the adherend and, if necessary, performing optical inspection or removing the reinforcing film from the non-reinforced area, 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, since it can suppress the curing of the adhesive in a 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 adhesive sheet 2 may be irradiated with active light from either the film substrate 1 side or the adherend side, or from both sides.

As the photocuring proceeds, 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.

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 of the pressure-sensitive adhesive sheet H ₁ -H ₀ 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.

As described above, by bonding the reinforcing film, the adherend is given an appropriate rigidity and stress is alleviated and dispersed, thereby suppressing various defects that may occur during the manufacturing process, improving production efficiency, and improving yield. Furthermore, 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 bonding 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 bonded.

When the completed device is in use, even if an external force is suddenly applied due to dropping the device, placing a heavy object on the device, or being hit by a flying object, the reinforcing film attached to the device can prevent damage to the device. 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 with long-term use, and is highly reliable. In addition, since the adhesive sheet becomes highly hazy due to photocuring, optical sensors placed on the back of the reinforcing film are difficult to see from the outer surface of the device, and the device can also be suitably used in image display devices equipped with optical sensors such as fingerprint sensors in the display area of the display.

The following provides further explanation of the adhesive sheet with examples and comparative examples, but the present invention is not limited to these examples.

[Example 1]
<Preparation of Pressure-Sensitive Adhesive Composition>
Into 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.

0.1 parts by weight of hexamethylene diisocyanate isocyanurate (Tosoh's "Coronate HX") as a crosslinking agent, 0.02 parts by weight of iron acetylacetonate (Nihon Kagaku Sangyo's "Nacem Ferric") as a crosslinking catalyst, 10 parts by weight of dipentaerythritol polyacrylate (mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate; Shin-Nakamura Chemical Co., Ltd.'s "NK Ester A-DPH") as a photocuring agent, and 0.1 parts by weight of 2,2-dimethoxy-1,2-diphenylethan-1-one (IGM Resins' "Omnirad 651") as a photopolymerization initiator were added to the above acrylic polymer solution (100 parts by weight of polymer), and the mixture was mixed uniformly to obtain a pressure-sensitive adhesive composition.

<Preparation of adhesive sheet>
The above-mentioned 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 coating 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.

[Examples 2 to 7, Comparative Examples 1 to 7]
Except for changing the composition of the acrylic polymer monomer 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.

[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), which is a tetrafunctional epoxy compound, 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.

[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.

<Haze after photocuring>
The light release film was peeled off from the pressure-sensitive adhesive sheets of the Examples and Comparative Examples, the pressure-sensitive adhesive sheets were attached to a glass plate, and then the pressure-sensitive adhesive composition was photocured by irradiating the surface of the heavy release film with ultraviolet light at 2000 mJ/ ^cm2 from an LED light source with a wavelength of 365 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.

Table 1 shows the composition of the acrylic polymer in the adhesive composition of the examples and comparative examples, the type and amount of photocuring agent added, and the haze of the adhesive sheet before and after photocuring. In Table 1, the polymer composition is the weight ratio of the constituent monomers, and the amount of photocuring agent is the amount added per 100 parts by weight of the solid content of the acrylic polymer. Details of the monomers and photocuring agent are as follows.

<Monomer>
2EHA 2-Ethylhexyl acrylate BA Butyl acrylate 2HEA 2-Hydroxyethyl acrylate 4HBA 4-Hydroxybutyl acrylate AA Acrylic acid <Light hardener>
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.))

In Examples 1 to 8, in which a tetrafunctional or higher polyfunctional acrylate was used as the photocuring agent, the increase in haze H ₁ -H ₀ 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, H ₁ -H ₀ was less than 1%. Even in Comparative Examples 4 to 6, in which a small amount of tetrafunctional or higher acrylate was used, H ₁ -H ₀ was less than 1%. A comparison between Example 1 and Example 2, and a comparison between Example 3 and Example 4, shows that the greater the content of the tetrafunctional or higher polyfunctional acrylate in the pressure-sensitive adhesive composition, the greater the increase in haze of the pressure-sensitive adhesive sheet due to photocuring.

Comparing Example 2, Example 7, and Comparative Example 7, it was found 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 comparing Example 5 and Example 6. Comparing Example 8 with Comparative Examples 8 and 9, it was found that even when acrylic acid, a carboxyl group-containing monomer, was used as the copolymerization monomer component of the acrylic polymer and an epoxy-based crosslinking agent was used, the increase in haze due to photocuring was 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.

REFERENCE SIGNS LIST 1 film substrate 2 adhesive sheet 51, 52 release film 10 reinforcing film 20 adherend (organic EL panel)
100 Device with reinforcing film

Claims (6)

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 _H0 of 5% or less before photocuring and a haze _H1 of 6% or more after photocuring . The pressure-sensitive adhesive sheet according to claim 1 , wherein the photocurable pressure-sensitive adhesive composition further comprises a photopolymerization initiator. 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 hydroxyl group-containing monomers and carboxyl group-containing monomers, and a crosslinked structure is introduced into the acrylic base polymer. 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. 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. The method for manufacturing a device according to claim 5 , wherein the adherend is an organic EL panel.

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