TW202000830A - Reinforcing film - Google Patents

Abstract

A reinforcing film (10) which comprises a film base (1) and a pressure-sensitive adhesive layer (2) tenaciously bonded to one main surface of the film base (1). The pressure-sensitive adhesive layer has been formed from a photocurable composition comprising a base polymer, a photocuring agent, a photo-radical initiator, and an antioxidant, the amounts of the photocuring agent, photo-radical initiator, and antioxidant being 10-50 parts by weight, 0.01-1 part by weight, and 0.01-2 parts by weight, respectively, per 100 parts by weight of the base polymer. In the reinforcing film of the present invention, the period from application to an adherend to an improvement in adhesive force can be set at will.

Description

Reinforcement membrane

The invention relates to a reinforcing film pasted on the surface of a device.

On the surface of an optical device such as a display or an electronic device, an adhesive film may be attached for surface protection or impact resistance. Such an adhesive film is usually fixed on the main surface of the film substrate with a build-up adhesive layer, and is adhered to the surface of the device through the adhesive layer.

In the state before assembly, processing, transportation, etc. of the device, it is possible to suppress the damage or damage of the adherend by temporarily sticking the adhesive film on the surface of the device or the component parts of the device. In this way, the temporarily adhered adhesive film can be easily peeled off from the adherend to temporarily protect the surface, and no paste remains on the adherend.

Patent Document 1 discloses an adhesive film which, in addition to device assembly, processing, transportation, etc., is used while the device is attached to the device surface without changing. Such an adhesive film has a function of reinforcing the device due to surface protection, dispersion of impact on the device, imparting rigidity to the flexible device, etc.

When attaching the adhesive film to the adherend, there may be a poor bonding such as the mixing of bubbles or the deviation of the sticking position. When a poor bonding occurs, the following operation (secondary processing) is carried out: the adhesive film is peeled off from the adherend and another adhesive film is bonded. Adhesive films used as engineering materials are designed on the premise of peeling from the adherend, so they are easy to reprocess. On the other hand, a reinforcing film that is premised on permanent adhesion generally does not assume peeling from the device but is firmly adhered to the surface of the device, so it is difficult to perform secondary processing.

Patent Document 2 discloses an adhesive sheet (adhesive layer) designed in such a manner that it has low adhesiveness immediately after being bonded to the adherend and then the force rises with time. The adhesive film with such an adhesive layer fixed on the film substrate is easily peeled off from the adhesive body immediately after being bonded to the adherend and firmly adheres to the adherend after a certain period of time, so it can be regarded as having It is used to reinforce the secondary processability. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2017-132977 [Patent Literature 2] WO2015/163115 Specification

[Problems to be solved by the invention]

Regarding the reinforcing film whose adhesive force with the adherend changes with time, it is difficult to say that the flexibility of the lead time of the step is sufficient. For example, a reinforcing film with an adhesive layer whose adhesive force rises with time must be inspected for a bonded state and a secondary process within a specific time after bonding with the adherend to before the adhesive force increases. In addition, when processing such as removing the reinforcing film from a part of the area after attaching the reinforcing film to the entire surface of the device or device parts, it is necessary to perform processing before the adhesive force rises.

In view of the above circumstances, the object of the present invention is to provide an easy secondary processing immediately after being bonded to the adherend, the time after the bonding with the adherend can be set arbitrarily until the adhesion force is improved, and the adhesion force can be improved by Reinforcement membrane firmly adhered to the adherend. [Technical means to solve the problem]

The reinforcing film of the present invention includes an adhesive layer fixedly deposited on one main surface of the film substrate. The adhesive layer includes a photo-curable composition containing a base polymer, a photo-hardener, a photo-radical initiator, and an antioxidant. The photocurable composition constituting the adhesive layer preferably contains 10 to 50 parts by weight of a photohardener, 0.01 to 1 part by weight of a photoradical initiator, and 0.01 to 2 parts by weight of an antioxidant with respect to 100 parts by weight of the base polymer. . The content of the antioxidant in the photocurable composition is preferably 0.2 to 5 times the content of the photo radical initiator.

From the viewpoint of suppressing the generation of free radicals from light radical initiators caused by light from fluorescent lamps, etc., as light radical initiators, it can be preferably used in the wavelength range of 310 nm to 355 nm, And the wavelengths longer than 360 nm do not show maximum absorption.

As the base polymer of the adhesive layer, for example, an acrylic polymer can be used. The acrylic polymer is preferably 5 to 50% by weight of a monomer component containing a homopolymer and having a glass transition temperature of 40° C. or higher.

The base polymer of the adhesive layer is preferably introduced with a cross-linked structure. For example, the base polymer contains a hydroxyl group-containing monomer and/or a carboxyl group-containing monomer as a monomer unit, and is introduced by bonding such functional groups with a cross-linking agent such as a polyfunctional isocyanate compound or a polyfunctional epoxy compound Cross-linked structure.

The light hardener of the adhesive layer is, for example, multifunctional (meth)acrylate. The functional group equivalent of the light hardener is preferably about 100 to 500 g/eq.

The reinforcing film preferably has an adhesive force with the polyimide film of 0.005 to 5 N/25 mm. After photocuring the adhesive layer, it is preferable that the adhesive force between the reinforcing film and the polyimide film is 6 N/25 mm or more. [Effect of invention]

The reinforcing film of the present invention includes the photocurable composition in the adhesive layer and photocuring the adhesive layer after being adhered to the adherend, thereby increasing the adhesion to the adherend. Since the adhesive force between the light-hardened body and the adherend is small, it is easy to perform secondary processing, and since the light-hardened material will show a higher adhesive force, it will help to reinforce the device and improve the reliability. The photohardenable adhesive can be arbitrarily set at the time of hardening after being attached to the adherend. In addition, the adhesive composition contains an antioxidant in addition to the base polymer, the light hardener, and the light radical initiator, thereby suppressing the light hardening reaction caused by light such as a fluorescent lamp in a storage environment. Therefore, the reinforcing film can be stored for a long time in a state before being bonded to the adherend, and after being bonded to the adherend and before photocuring. Therefore, the reinforcing film of the present invention has the advantage that it can flexibly cope with the preparation time of the steps.

Fig. 1 is a cross-sectional view showing an embodiment of a reinforcing film. The reinforcing film 10 includes an adhesive layer 2 on one main surface of the film base 1. The adhesive layer 2 is fixedly laminated on one main surface of the base film 1. The adhesive layer 2 is a photo-curable adhesive containing a photo-curable composition, and is cured by irradiation with active light such as ultraviolet rays, so that the adhesive force with the adherend increases.

FIG. 2 is a cross-sectional view of a reinforcing film with a spacer 5 temporarily adhered to the main surface of the adhesive layer 2. FIG. 3 is a cross-sectional view showing a state where the reinforcing film 10 is attached to the surface of the device 20.

The separator 5 is peeled off from the surface of the adhesive layer 2, and the exposed surface of the adhesive layer 2 is attached to the surface of the device 20, whereby the reinforcing film 10 is attached to the surface of the device 20. In this state, the adhesive layer 2 is in a state where the reinforcing film 10 (adhesive layer 2) is temporarily adhered to the device 20 before photocuring. By photohardening the adhesive layer 2, the adhesive force at the interface between the device 20 and the adhesive layer 2 increases, and the device 20 and the reinforcing film 10 are fixed.

The so-called "fixation" refers to a state where the two stacked layers are firmly adhered, impossible or difficult to peel at the interface between the two. The so-called "temporary adhesion" refers to a state where the adhesion between the two layers deposited is small and can be easily peeled off at the interface between the two.

In the reinforcing film shown in FIG. 2, the film substrate 1 is fixed to the adhesive layer 2, and the separator 5 is temporarily adhered to the adhesive layer 2. When the film substrate 1 and the separator 5 are peeled off, peeling occurs at the interface between the adhesive layer 2 and the separator 5, and the state where the adhesive layer 2 is fixed on the film substrate 1 is maintained. No adhesive remains on the separator 5 after peeling.

In the device shown in FIG. 3 where the reinforcing film 10 is attached, before the photocuring of the adhesive layer 2, the device 20 and the adhesive layer 2 are temporarily bonded. When the film substrate 1 and the device 20 are peeled off, peeling occurs at the interface between the adhesive layer 2 and the device 20, and the state where the adhesive layer 2 is fixed on the film substrate 1 is maintained. Since no adhesive remains on the device 20, secondary processing is easy. After the adhesive layer 2 is photohardened, the adhesion between the adhesive layer 2 and the device 20 increases, so it is difficult to peel off the film 1 from the device 20. If the two are peeled off, there may be agglomeration failure of the adhesive layer 2 .

[Film substrate] As the film base 1, a plastic film is used. In order to fix the film substrate 1 and the adhesive layer 2, it is preferable that the surface of the film substrate 1 on which the adhesive layer 2 is attached has not been subjected to release treatment.

The thickness of the film substrate is, for example, about 4 to 500 μm. From the viewpoint of reinforcing the device by imparting rigidity or impact relaxation, the thickness of the film substrate 1 is preferably 20 μm or more, more preferably 30 μm or more, and still more preferably 45 μm or more. From the viewpoint of making the reinforcing film flexible and improving operability, the thickness of the film substrate 1 is preferably 300 μm or less, and more preferably 200 μm or less. From the viewpoint of both mechanical strength and flexibility, the compressive strength of the film substrate 1 is preferably 100 to 3000 kg/cm ² , more preferably 200 to 2900 kg/cm ² , and further preferably 300 to 2800 kg /cm ² , particularly preferably 400-2700 kg/cm ² .

Examples of the plastic material constituting the film substrate 1 include polyester-based resins, polyolefin-based resins, cyclic polyolefin-based resins, polyamide-based resins, and polyimide-based resins. In the reinforcing film for optical devices such as displays, the film substrate 1 is preferably a transparent film. In addition, when the active light is irradiated from the film substrate 1 side to perform photo-curing of the adhesive layer 2, the film substrate 1 preferably has transparency to the active light used for curing the adhesive layer. In terms of having both mechanical strength and transparency, polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate can be used favorably. When the active light is irradiated from the side of the adherend, the adherend only needs to have transparency to the active light, and the film substrate 1 may be opaque to the active light.

On the surface of the film substrate 1, functional coatings such as an easy adhesion layer, an easy sliding layer, a release layer, an antistatic layer, a hard coating layer, and an antireflection layer can also be provided. In addition, as described above, in order to fix the film substrate 1 and the adhesive layer 2, it is preferable that no release layer is provided on the surface of the film substrate 1 where the adhesive layer 2 is attached.

[Adhesive layer] The adhesive layer 2 fixedly laminated on the film substrate 1 is a photo-curable composition containing a base polymer, a photo-hardener and a photo-radical initiator. When the reinforcing film is used in an optical device such as a display, the total light transmittance of the adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and still more preferably 90% or more. The haze of the adhesive layer 2 is preferably 2% or less, more preferably 1% or less, and further preferably 0.7% or less, particularly preferably 0.5% or less.

The adhesive layer 2 has a low adhesive force with the adherend before photo-hardening, so it is easy to perform secondary processing. When the adhesive layer 2 is irradiated with active light such as ultraviolet rays, free radicals are generated from the light radical initiator, and the adhesion with the adherend is improved by the radical polymerization reaction (photohardening) of the light hardener. Therefore, when the device is used, the reinforcing film is not easily peeled off from the device surface, and the reliability is excellent.

The light-curing adhesive is cured by irradiation with ultraviolet rays or the like. Therefore, the adhesive layer 2 containing the photo-curable adhesive composition has advantages such that the time of curing can be set arbitrarily, and the preparation time for the steps can be flexibly handled. On the other hand, before the use of the reinforcing film or the state where the reinforcing film is adhered to the adherend before photocuring, there is a free radical initiator due to light from a fluorescent lamp or the like in the storage environment The generation of free radicals.

Since the amount of free radicals generated by light such as fluorescent lamps is sufficiently smaller than the amount of free radicals generated by ultraviolet irradiation during light curing, even if placed under a fluorescent lamp for a short time, it will hardly undergo photohardening reaction. However, if the reinforcing film is stored under a fluorescent lamp for a long period of time, the cumulative amount of free radicals generated from the light radical initiator due to the light of the fluorescent lamp becomes large, and its influence cannot be ignored. Specifically, there is a case where the polymerization of the photo hardener is performed due to the free radicals generated from the photo radical initiator, and the adhesion of the adhesive increases, making it difficult for the reinforcing film to peel from the adherend. In addition, there may be a case where the photoradical initiator is deactivated due to long-term storage, and the photo hardening will not be performed even if it is irradiated with ultraviolet rays, and the adhesive force may not increase.

Regarding the reinforcing film of the present invention, the photocurable composition constituting the adhesive layer 2 contains an antioxidant in addition to the base polymer, the photohardener and the photoradical initiator. By using a photo radical initiator and an antioxidant together, even when the reinforcing film is stored under a fluorescent lamp for a long time, the change in the adhesive force is also small, and the adhesive force can be appropriately made during light irradiation rise.

<Composition of adhesive> Hereinafter, the preferred form will be described in order for each of the base polymer, the photo hardener, the photo radical initiator and the antioxidant constituting the photo hardenable composition.

(Base polymer) The base polymer is the main component of the adhesive composition. The type of base polymer is not particularly limited, and an acrylic polymer, a polysiloxane polymer, a urethane polymer, a rubber polymer, etc. may be appropriately selected. In particular, in terms of excellent optical transparency and adhesion, and easy control of adhesion, the adhesive composition preferably contains an acrylic polymer as a base polymer, and preferably 50 weight of the adhesive composition % Or more is acrylic polymer.

As the acrylic polymer, those containing alkyl (meth)acrylate as the main monomer component can be preferably used. In addition, in this specification, "(meth)acrylic acid" means acrylic acid and/or methacrylic acid.

As the (meth)acrylic acid alkyl ester, an alkyl (meth)acrylate having 1 to 20 carbon atoms of the alkyl group can be suitably used. The alkyl group of the (meth)acrylic acid alkyl ester may be straight chain or may have branched chain. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, (meth ) Second butyl acrylate, third butyl (meth) acrylate, amyl (meth) acrylate, isoamyl (meth) acrylate, neopentyl (meth) acrylate, hexyl (meth) acrylate , Heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, (meth) Isononyl acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, iso(meth)acrylate Tri (dodecyl) ester, myristyl (meth) acrylate, isotetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate Alkyl, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, (A Group) aralkyl acrylate, etc.

The content of the alkyl (meth)acrylate is preferably 40% by weight or more, more preferably 50% by weight or more, and further preferably 55% by weight or more with respect to the total amount of monomer components constituting the base polymer.

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 or a carboxyl group-containing monomer. The hydroxyl group or carboxyl group of the base polymer becomes a reaction point with the crosslinking agent described later. For example, when an isocyanate-based crosslinking agent is used, it is preferably a copolymerization component containing a hydroxyl group-containing monomer as a base polymer. When an epoxy-based crosslinking agent is used, it is preferably a copolymerization component containing a carboxyl group-containing monomer as a base polymer. Due to the introduction of the cross-linked structure in the base polymer, there is a tendency for the cohesive force to increase, the adhesive force of the adhesive layer 2 to increase, and the paste residue on the adherend during secondary processing to decrease.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate. Ester, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 4-(hydroxymethyl)cyclohexylmethyl (meth)acrylate Ester etc. Examples of carboxyl group-containing monomers include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, Butenoic acid and so on.

Regarding the acrylic base polymer, the total amount of the hydroxyl group-containing monomer and the carboxyl group-containing monomer is preferably 1 to 30% by weight, more preferably 3 to 25% by weight, and further preferably 5 ~20% by weight. It is particularly preferable that the content of the (meth)acrylate containing hydroxyl groups falls within the above range.

The acrylic base polymer preferably contains N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperidine, vinylpyrrolidone, vinyl Nitrogen-containing monomers such as pyrrole, vinylimidazole, vinyl oxazole, vinyl 𠰌olin, N-propenyl amide, N-vinyl carboxylic acid amides, N-vinyl caprolactam Monomer composition. The acrylic base polymer containing the nitrogen-containing monomer component exhibits moderate water absorption in a hot and humid environment and can suppress the localized water absorption of the adhesive. Therefore, it helps prevent localized whitening and local swelling of the adhesive layer. Stripping etc.

Regarding the acrylic base polymer, the content of the nitrogen-containing monomer relative to the total amount of constituent monomer components is preferably 1 to 30% by weight, more preferably 3 to 25% by weight, and still more preferably 5 to 20% by weight. The acrylic base polymer preferably contains N-vinylpyrrolidone as a nitrogen-containing monomer within the above range.

When the acrylic base polymer contains both a hydroxyl group-containing monomer and a nitrogen-containing monomer as monomer components, there is a tendency to improve the cohesive force and transparency of the adhesive. Regarding the acrylic base polymer, the total amount of the hydroxyl group-containing monomer and the nitrogen-containing monomer is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, and further preferably 15 ~35 wt%.

The acrylic base polymer may contain monomer components other than the above. The acrylic base polymer may also include, for example, cyano group-containing monomers, vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphoric acid group-containing monomers , Monomers containing acid anhydride groups, etc. as monomer components.

The adhesive properties of the adhesive before photohardening are easily affected by the composition and molecular weight of the base polymer. The larger the molecular weight of the base polymer, the harder the adhesive becomes. The weight average molecular weight of the acrylic base polymer is preferably 100,000 to 5 million, more preferably 300,000 to 3 million, and still more preferably 500,000 to 2 million. In addition, when a cross-linked structure is introduced into the base polymer, the molecular weight of the base polymer refers to the molecular weight before introduction of the cross-linked structure.

The higher the content of the high-Tg monomer component in the constituent components of the base polymer, the more the adhesive tends to become harder. In addition, the so-called high Tg monomer means a monomer having a high glass transition temperature (Tg) of the homopolymer. Examples of monomers having a homopolymer Tg of 40°C or higher include dicyclopentyl methacrylate (Tg: 175°C), dicyclopentyl acrylate (Tg: 120°C), and isomethacrylate (Tg: 173℃), isoacrylate (Tg: 97℃), methyl methacrylate (Tg: 105℃), 1-adamantyl methacrylate (Tg: 250℃), 1-adamantyl acrylate (Tg: 153°C) and other (meth)acrylic monomers; acrylamide (Tg: 145°C), dimethylacrylamide (Tg: 119°C), diethylacrylamide (Tg: 81°C), dimethylaminopropyl propyl acrylamide (Tg: 134° C), isopropyl acrylamide (Tg: 134° C), hydroxyethyl acrylamide (Tg: 98° C), etc. Vinyl monomer; N-vinylpyrrolidone (Tg: 54°C), etc.

Regarding the acrylic base polymer, the content of the monomer having a Tg of 40° C. or higher relative to the total amount of constituent monomer components is preferably 5 to 50% by weight, and more preferably 10 to 40% by weight. In order to form an adhesive layer with moderate hardness and excellent secondary processability, the monomer component of the base polymer is preferably a monomer component containing a homopolymer with a Tg of 80° C. or higher, and more preferably a homopolymer The Tg of the substance is a monomer component above 100°C. Regarding the acrylic base polymer, the content of the monomer having a Tg of 100° C. or higher relative to the total amount of constituent monomer components is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and further preferably 1 More than 3% by weight, particularly preferably more than 3% by weight. It is particularly preferable that the content of methyl methacrylate is in the above range.

The acrylic polymer as a base polymer can be obtained by polymerizing the above monomer components by various well-known methods such as solution polymerization, emulsion polymerization, and bulk polymerization. From the viewpoint of the balance of characteristics such as adhesive force and holding force of the adhesive, or cost, the solution polymerization method is preferred. As a solvent for solution polymerization, ethyl acetate, toluene, etc. are used. The concentration of the solution is usually about 20 to 80% by weight. As the polymerization initiator used in the solution polymerization, various known ones such as azo-based and peroxide-based can be used. In order to adjust the molecular weight, a chain transfer agent can be used. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

(Crosslinking agent) From the viewpoint of making the adhesive have moderate cohesion, it is preferable to introduce a cross-linked structure into the base polymer. For example, a cross-linking structure is introduced by adding a cross-linking agent to the solution after polymerizing the base polymer and heating as necessary. 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 chelates. Department of cross-linking agent. These crosslinking agents react with functional groups such as hydroxyl or carboxyl groups introduced into the base polymer to form a crosslinked structure. In terms of high reactivity with the hydroxyl group or carboxyl group of the base polymer and easy introduction of the cross-linked structure, isocyanate-based cross-linking agents and epoxy-based cross-linking agents are preferred.

As the isocyanate-based crosslinking agent, polyisocyanate having two or more isocyanate groups in one molecule is used. Examples of the isocyanate-based crosslinking agent include lower aliphatic polyisocyanates such as butylated diisocyanate and hexamethylene diisocyanate; cyclopentyl diisocyanate, cyclohexyl diisocyanate, and isophorone diisocyanate. Alicyclic isocyanates; 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate and other aromatic isocyanates; trimethylolpropane/toluene diisocyanate terpolymer plus Products (for example, "Coronate L" manufactured by Tosoh), trimethylolpropane/hexamethylene diisocyanate terpolymer adducts (for example, "Coronate HL" manufactured by Tosoh), xylylene diisocyanate Isocyanate adducts such as trimethylolpropane adducts (for example, "Takenate D110N" manufactured by Mitsui Chemicals, trimeric isocyanates for hexamethylene diisocyanate (for example, "Coronate HX" manufactured by Tosoh), etc.

As the epoxy-based crosslinking agent, a multifunctional epoxy compound having two or more epoxy groups in one molecule can be used. The epoxy group of the epoxy-based crosslinking agent may be a glycidyl group. Examples of the epoxy-based cross-linking agent include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, and 1,3-bis(N,N-di Glycidylaminomethyl) cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol Alcohol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, tri Hydroxymethylpropane polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, tris (2-hydroxyethyl) tripolyisocyanate triglycidyl ester, resorcinol diglycidyl Glycerin, bisphenol-S-diglycidyl ether, etc. 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 can also be used.

The amount of the cross-linking agent used may be appropriately adjusted according to the composition or molecular weight of the base polymer. The amount of the crosslinking agent used is about 0.1 to 10 parts by weight relative to 100 parts by weight of the base polymer, preferably 0.3 to 7 parts by weight, more preferably 0.5 to 5 parts by weight, and still more preferably 1 to 4 parts by weight. In addition, the amount of the cross-linking agent relative to 100 parts by weight of the base polymer (parts by weight) divided by the functional group equivalent (g/eq) of the cross-linking agent is preferably 0.00015 to 0.11, more preferably 0.001 to 0.077 It is further preferably 0.003 to 0.055, and particularly preferably 0.0045 to 0.044. By making the amount of cross-linking agent greater than that of ordinary acrylic optical transparent adhesives, the adhesive has a moderate hardness, and there is a reduction in paste residue on the adherend during secondary processing, and an improvement in secondary processing. tendency.

In order to promote the formation of cross-linked structures, cross-linked catalysts can also be used. For example, examples of the crosslinking catalyst of the isocyanate-based crosslinking agent include metals such as tetra-n-butyl titanate, tetraisopropyl titanate, iron(III) acetone, butyl tin oxide, and dioctyl tin dilaurate. System crosslinking catalyst (especially tin system crosslinking catalyst) and so on. The amount of crosslinking catalyst used is generally 0.05 parts by weight or less relative to 100 parts by weight of the base polymer.

(Photohardener) The adhesive composition constituting the adhesive layer 2 contains a light hardener in addition to the base polymer. If the adhesive layer 2 containing the photocurable adhesive composition is photohardened after being attached to the adherend, the adhesion with the adherend is increased.

As the light hardener, a compound having two or more ethylenically unsaturated bonds in one molecule is preferable. In addition, the light hardener is preferably a compound that exhibits compatibility with the base polymer. In terms of exhibiting moderate compatibility with the base polymer, the light hardener is preferably liquid at ordinary temperature. By making the photo hardener compatible with the base polymer and dispersing it uniformly in the composition, the contact area with the adherend can be ensured, and the adhesive layer 2 with high transparency can be formed. In addition, by showing a moderate compatibility between the base polymer and the light curing agent, the cross-linked structure is easily uniformly introduced into the adhesive layer 2 after the light curing, and the adhesion force with the adherend tends to rise appropriately .

The compatibility of the base polymer and the light hardener is mainly affected by the structure of the compound. The structure and compatibility of the compound can be evaluated by, for example, the Hansen solubility parameter. The smaller the difference between the solubility parameters of the base polymer and the light hardener, the higher the compatibility.

In terms of high compatibility with the acrylic base polymer, it is preferable to use a polyfunctional (meth)acrylate as a light hardener. Examples of polyfunctional (meth)acrylates include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, Bisphenol A ethylene oxide modified di(meth)acrylate, bisphenol A propylene oxide modified di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecane dimethanol Di(meth)acrylate, ethoxylated isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(methyl) ) Acrylate, di-trimethylolpropane tetra (meth) acrylate, ethoxylated pentaerythritol tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol poly (meth) acrylate, di Pentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, (meth)acrylate carbamate, epoxy (meth)acrylate, Butadiene (meth)acrylate, isoprene (meth)acrylate, etc. Among these, in terms of excellent compatibility with the acrylic base polymer, polyethylene glycol di(meth)acrylate or polypropylene glycol di(meth)acrylate is preferred, and polyglycol is particularly preferred. Ethylene glycol di(meth)acrylate.

The compatibility of the base polymer and the light hardener is also affected by the molecular weight of the compound. There is a tendency that the smaller the molecular weight of the photocurable compound, the higher the compatibility with the base polymer. From the viewpoint of compatibility with the base polymer, the molecular weight of the light hardener is preferably 1500 or less, more preferably 1000 or less, further preferably 500 or less, and particularly preferably 400 or less.

In the adhesive layer 2 before photohardening, the characteristics of the base polymer are the main dominating factors for adhesion. Therefore, as long as the base polymer of the adhesive composition is the same, even if the types of the light hardeners are different, the difference in the adhesive properties of the adhesive layer before the light hardening is also small. The type or content of the light hardener mainly affects the adhesion of the adhesive layer after light hardening. The smaller the functional group equivalent (ie, the greater the number of functional groups per unit molecular weight) and the greater the content of the light hardener, the more able to set the difference in adhesion force before and after light hardening.

From the viewpoint of having high compatibility with the base polymer and enhancing the adhesive strength after light curing, the functional group equivalent (g/eq) of the light hardener is preferably 500 or less, more preferably 400 or less, and further It is preferably 300 or less, and particularly preferably 200 or less. On the other hand, if the functional group equivalent of the light hardener is too small, there may be a case where the density of the crosslinking point of the adhesive layer after photohardening becomes high and the adhesiveness decreases. Therefore, the functional group equivalent of the light hardener is preferably 80 or more, more preferably 100 or more, and still more preferably 130 or more.

In the combination of the acrylic base polymer and the multifunctional acrylate light hardener, when the functional group equivalent of the light hardener is small, there is a tendency that the interaction between the base polymer and the light hardener is strong, and the initial stage Then the force rises. In the use of the present invention, there is a case where the excessive increase in the initial adhesive force causes a decrease in secondary processability. From the viewpoint of maintaining an appropriate range of the adhesive force between the adhesive layer 2 and the adherend before photohardening, it is also preferable that the functional group equivalent of the photohardener is within the above range.

The content of the light hardener in the adhesive composition is preferably 10-50 parts by weight relative to 100 parts by weight of the base polymer. By setting the formulation amount of the photo hardener to the above range, the adhesiveness between the adhesive layer and the adherend after photo hardening can be adjusted to an appropriate range. The content of the light hardener is more preferably 15 to 45 parts by weight relative to 100 parts by weight of the base polymer, and further preferably 20 to 40 parts by weight.

(Photo radical initiator) The photo radical initiator generates free radicals by the irradiation of active light, and promotes the radical polymerization reaction of the photo hardener by the radical transfer from the photo radical initiator to the photo hardener. As the photo radical initiator (photo radical generator), those that generate radicals by irradiation with visible light or ultraviolet rays with a wavelength shorter than 450 nm are preferred, and examples include hydroxyketones and benzoyl dimethyl acetal. Ketones, amino ketones, acyl phosphine oxides, benzophenones, trichloromethyl-containing derivatives, etc. The photo radical initiator may be used alone, or two or more kinds may be used in combination.

When transparency is required for the adhesive layer 2, the photo radical initiator is preferably less sensitive to light (visible light) with a wavelength longer than 400 nm. For example, the absorption coefficient at a wavelength of 405 nm can be preferably used It is a light radical initiator below 1×10 ² [mLg ^-1 cm ^-1 ]. In addition, if a light radical initiator with a small sensitivity to visible light is used, the amount of light radicals generated from the outer light in the storage environment is small, so the storage stability of the reinforcing film can be improved.

From the viewpoint of improving the storage stability of the reinforcing film, it is preferable to use a light radical initiator that does not show a large absorption at a wavelength longer than 360 nm. At wavelengths longer than 360 nm, it is shown that light-absorbing free radical initiators easily absorb ultraviolet light from fluorescent lamps (mainly mercury bright lines at 365 nm and 405 nm) to generate light radicals. If the maximum wavelength of light absorption of the light radical initiator is 360 nm or less, the amount of generated light radicals in the storage environment such as fluorescent lamps is small. Therefore, even when the reinforcing film is exposed to a fluorescent lamp for a long time, the effective concentration of the photo radical initiator can be maintained high. In addition, a small amount of free radicals generated by light in a storage environment such as a fluorescent lamp is trapped by an antioxidant, so that photopolymerization in the storage environment can be suppressed.

In order to improve the storage stability and enhance the adhesion to the adherend by light irradiation even after long-term storage, the light radical initiator included in the adhesive layer is preferably a maximum wavelength of light absorption of 355 Below nm. On the other hand, in order to improve the light curing efficiency by ultraviolet irradiation, the photo radical initiator preferably has a light absorption maximum at a wavelength longer than 310 nm. According to the above circumstances, in order to improve the storage stability of the reinforcing film, the light radical initiator included in the adhesive layer 2 preferably has no absorption maximum at a wavelength longer than 360 nm, and has a wavelength in the range of 310 to 355 nm Absorb the greatest. The absorption maximum wavelength of the optical radical initiator is more preferably 315 to 350 nm, and further preferably 320 to 340 nm.

The content of the photo radical initiator in the adhesive layer 2 is preferably 0.01 to 1 part by weight, more preferably 0.02 to 0.7 part by weight, and still more preferably 0.03 to 0.5 part by weight relative to 100 parts by weight of the base polymer. . The content of the photo radical initiator in the adhesive layer 2 is preferably 0.005 to 0.5 parts by weight, more preferably 0.01 to 0.4 parts by weight, and still more preferably 0.02 to 0.3 parts by weight relative to 100 parts by weight of the light hardener. . If the content of the photo radical initiator in the adhesive layer is too small, there may be cases where the photo hardening reaction does not sufficiently proceed even when irradiated with ultraviolet rays. If the content of the photo-radical initiator is too large, even if antioxidants are used in combination, the photo-hardening reaction will proceed in the storage environment, the adhesion with the adherend will increase, and the secondary processing of the reinforcing film will become Difficult situation.

(Antioxidants) Antioxidants have the effect of inhibiting the photohardening reaction of the reinforcing film in the storage environment. In addition to the photo-radical initiator, the composition containing an antioxidant may capture free radicals even when a small amount of photo-radicals are generated from the photo-radical initiator due to light from a fluorescent lamp or the like. Stable free radicals are generated, so the transfer of free radicals to the light hardener can be suppressed. Therefore, it is possible to suppress the light curing (radical polymerization reaction of the light hardener) caused by light from fluorescent lamps or the like.

Examples of antioxidants include amine antioxidants, sulfur antioxidants, phosphorus antioxidants, and phenol antioxidants.

Examples of sulfur-based antioxidants include: 3,3'-dilauric thiodipropionate, 3,3'-dimyristyl thiodipropionate, and 3,3'-thiodipropionate dihard Fatty esters, etc. Examples of the phosphorus-based antioxidant include triphenyl phosphite, diphenyl phosphite isodecyl, phenyl phosphite diisodecyl, and the like.

Examples of the amine-based antioxidants include monoalkyldiphenylamines such as monooctyldiphenylamine and monononyldiphenylamine; 4,4′-dibutyldiphenylamine and 4,4 '-Dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, 4, Dialkyldiphenylamines such as 4'-dinonyldiphenylamine; tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine Polyalkyl diphenylamines; α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthalene Naphthylamines such as amine, heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine, nonylphenyl-α-naphthylamine, etc.

Examples of phenolic antioxidants include 2,6-di-tert-butyl-p-cresol (dibutylhydroxytoluene; BHT), butylated hydroxyanisole, and 2,6-di-tert-butyl-4 -Monophenolic antioxidants such as ethylphenol, β-(3,5-di-tert-butyl-4-hydroxyphenyl) stearyl propionate; 2,2'-methylenebis(4-methyl -6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6- Third butyl phenol), 4,4'-butylene bis(3-methyl-6-third butyl phenol), 3,9-bis[1,1-dimethyl-2-[β-( 3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl] 2,4,8,10-tetraoxaspiro[5,5]undecane and other bisphenols Antioxidant; 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tri( 3,5-di-tert-butyl-4-hydroxybenzyl)benzene, tetra-(methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate ] Methane, bis[3,3'-bis-(4'-hydroxy-3'-third butylphenyl) butyric acid] glycol ester, 1,3,5-tris(3',5'-di Third butyl-4'-hydroxybenzyl)-S-tris-2,4,6-(1H,3H,5H) triketone, tocopherol and other polymer phenolic antioxidants.

From the viewpoint of suppressing photohardening caused by radicals generated from light radical initiators due to the light of fluorescent lamps and the like, among the antioxidants, amine-based antioxidants and phenol-based antioxidants are preferred As the role of free radical chain inhibitors, phenolic antioxidants having a hindered phenol structure are particularly preferred.

An antioxidant having a hindered phenol structure is one in which at least one of the carbon atoms adjacent to the carbon atom on the aromatic ring to which the OH group is bonded of phenol is bonded with a third butyl group having a larger steric hindrance. Examples of the antioxidant having a hindered phenol structure include dibutylhydroxytoluene (BHT) and pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (manufactured by BASF "Irganox 1010"), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate ("Irganox 1076" manufactured by BASF), 3,3',3' ',5,5',5''-hexatert-butyl-a,a',a''-(1,3,5-trimethylbenzene-2,4,6-triyl) tri-p-cresol ( "Irganox 1330" manufactured by BASF), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-tris-2,4,6(1H ,3H,5H)-trione ("Irganox 3114" manufactured by BASF), isocyanuric tris[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl ] Ester ("Irganox 3125" manufactured by BASF), pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] ("Adekastab AO-60" manufactured by ADEKA), 3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4 ,8,10-tetraoxaspiro[5.5]undecane ("Adekastab AO-80" manufactured by ADEKA), acrylic acid 2-[1-(2-hydroxy-3,5-di-third-pentylphenyl) Ethyl]-4,6-di-tert-amylphenyl ("Sumilizer GS" manufactured by Sumitomo Chemical), 2-tert-butyl-4-methyl-6-(2-hydroxy-3- Tributyl-5-methylbenzyl)phenyl ester ("Sumilizer GM" manufactured by Sumitomo Chemical), 2,2'-dimethyl-2,2'-(2,4,8,10-tetraoxy Heterospiro[5.5]undecane-3,9-diyl)dipropane-1,1'-diyl=bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl) Propionate] ("Sumilizer GA-80" manufactured by Sumitomo Chemical), 1,3,5-tris(3-hydroxy-4-tert-butyl-2,6-dimethylbenzyl)-1,3 ,5-三𠯤-2,4,6(1H,3H,5H)-trione ("Cyanox 1790" manufactured by Cytec), etc.

The content of the antioxidant in the adhesive layer 2 is preferably 0.01 to 2 parts by weight, more preferably 0.03 to 1 part by weight, further preferably 0.04 to 0.7 parts by weight, and particularly preferably 100 parts by weight of the base polymer. 0.05 to 0.5 parts by weight. The content of the antioxidant is preferably 0.2 to 5 times the content of the photo radical initiator, more preferably 0.3 to 3 times, and still more preferably 0.5 to 2 times.

(Combined effect of photo radical initiator and antioxidant) In a composition containing an antioxidant other than a photo radical initiator, even when a small amount of photo radicals are generated from the photo radical initiator due to light from a fluorescent lamp or the like, the antioxidant will be captured Free radicals generate stable free radicals. Therefore, the radical polymerization reaction caused by light from fluorescent lamps or the like can be suppressed. From the viewpoint of suppressing the polymerization reaction in the storage state of the reinforcing film, it is preferable that the content of the antioxidant is large. On the other hand, if the content of the antioxidant is too large, even if ultraviolet light is irradiated for photohardening, the antioxidant will capture most of the free radicals generated by the light, thus preventing the free radicals from the photo radical initiator to the photo hardener There is a case where the photo hardening is insufficient. Therefore, in order to suppress the photopolymerization in the storage environment and prevent the increase of the adhesive force, the photohardening reaction is appropriately performed during the light irradiation to increase the adhesive force, and the content of the antioxidant is preferably within the above range.

By using a photo radical initiator in combination with an antioxidant, the antioxidant captures free radicals generated by light from fluorescent lamps and the like, so it is possible to suppress the increase in adhesion caused by the photo-hardening reaction in the storage environment. Therefore, regardless of the type of photo radical initiator, the photohardening of the adhesive layer in the storage environment can be suppressed by the action of the antioxidant.

On the other hand, if a reinforcing film with an adhesive layer containing a photo radical initiator and an antioxidant is exposed to a fluorescent lamp for a long time, the photo radical initiator will be inactivated due to the inactivation of the photo radical initiator The effective concentration of the agent (the concentration of photo radical initiator capable of generating photo radicals) decreases. Therefore, even if ultraviolet irradiation is performed for photohardening, the amount of generated photo radicals is small, and the photohardening reaction may not proceed sufficiently.

The reinforcing film is preferably such that even after long-term storage, the adhesive is less likely to be photo-hardened by the light of a fluorescent lamp or the like in the storage environment, and a sufficient amount of free radicals are generated when light is irradiated. The free radical polymerization reaction with the adherend increases the adhesion. In order to sufficiently carry out the photo hardening reaction even after long-term storage, it is preferable to use a photo radical initiator with a small amount of free radical generation under a storage environment. Specifically, it is preferable to use a photo radical initiator as described above, which has an absorption maximum wavelength below 360 nm and is free of light caused by the mercury bright line of fluorescent lamps (especially at a wavelength of 365 nm). The amount of basis generation is small.

The amount of free radicals generated from the light radical initiator caused by the light of the fluorescent lamp can be irradiated with light at a wavelength of 365 nm at extremely low temperature as shown in the embodiment described later and use electron spin resonance (ESR) The method quantifies and evaluates the amount of free radicals. Since the radical derived from the photo-radical initiator has a very short life at normal temperature, it is suitable for extremely low temperature when evaluating the amount of radical generation.

(Other additives) In addition to the components exemplified above, the adhesive layer may also contain a silane coupling agent, an adhesion-imparting agent, a plasticizer, a softening agent, an anti-deterioration agent, a filler, a coloring agent, within a range that does not impair the characteristics of the present invention Additives such as ultraviolet absorbers, surfactants, antistatic agents.

[Production of Reinforcement Membrane] By stacking the photocurable adhesive layer 2 on the film substrate 1, a reinforcing film is obtained. The adhesive layer 2 may be formed directly on the film substrate 1, or the adhesive layer formed in a sheet shape on other substrates may be transferred to the film substrate 1.

By applying the above-mentioned adhesive composition by roll coating, contact roll coating, gravure coating, reverse coating, roll brush coating, spray coating, dip roll coating, bar coating, blade coating, air Knife coating, curtain coating, lip coating, die coating, etc. are applied to the substrate, and the solvent is dried and removed as necessary to form an adhesive layer. As a 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 still 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 still more preferably 10 seconds to 10 minutes.

The thickness of the adhesive layer 2 is, for example, about 1 to 300 μm. There is a tendency that the greater the thickness of the adhesive layer 2 is, the more the adhesion with the adherend will be improved. On the other hand, when the thickness of the adhesive layer 2 is too large, there are cases where the fluidity before photo-curing is high and the operation becomes difficult. Therefore, the thickness of the adhesive layer 2 is preferably 5 to 100 μm, more preferably 8 to 50 μm, still more preferably 10 to 40 μm, and particularly preferably 13 to 30 μm.

When the adhesive composition contains a crosslinking agent, it is preferable to perform crosslinking by heating or aging at the same time as the drying of the solvent or after the drying of the solvent. The heating temperature or heating time is appropriately set according to the type of crosslinking agent used, and is usually crosslinked by heating in the range of 20°C to 160°C by about 1 minute to 7 days. The heating used for drying and removing the solvent can also serve as the heating for crosslinking.

The introduction of a cross-linked structure into the base polymer increases the gel fraction. The higher the gel fraction, the harder the adhesive. When the reinforcement film is peeled off from the adherend due to secondary processing, etc., the tendency to remain in the paste of the adherend can be suppressed. The gel fraction of the adhesive layer 2 before photohardening is preferably 30% or more, more preferably 50% or more, and further preferably 60% or more, particularly preferably 65% or more. The gel fraction of the adhesive layer 2 before light curing can also be more than 70% or more than 75%.

Since the adhesive contains an unreacted photo hardener, the gel fraction of the adhesive layer 2 before photo hardening is generally 90% or less. If the gel fraction of the adhesive layer 2 before photohardening is too large, there may be a case where the holding power to the adherend decreases and the initial adhesive force becomes insufficient. Therefore, the gel fraction of the adhesive layer 2 before photohardening is preferably 85% or less, and more preferably 80% or less.

The gel fraction can be obtained in the form of insoluble matter in solvents such as ethyl acetate. Specifically, the insoluble content of the adhesive layer after immersing the adhesive layer in ethyl acetate at 23°C for 7 days relative to that before immersion The weight fraction of the sample (unit: weight %) is obtained by the method. Generally speaking, the gel fraction of the polymer is the same as the degree of crosslinking. The more crosslinked parts in the polymer, the greater the gel fraction becomes. In addition, the greater the amount of photohardener, the lower the gel fraction.

After the cross-linking structure is introduced into the polymer by the cross-linking agent, the light hardener also remains unreacted. Thus, a photo-curable adhesive layer 2 containing a base polymer and a photo-hardener is formed. In the case where the adhesive layer 2 is formed on the film substrate 1, it is preferable to attach a spacer 5 to the adhesive layer 2 for the purpose of protection of the adhesive layer 2 or the like. It is also possible to perform crosslinking after attaching the spacer 5 on the adhesive layer 2.

In the case where the adhesive layer 2 is formed on another substrate, the reinforcing film is obtained by transferring the adhesive layer 2 onto the film substrate 1 after drying the solvent. The substrate used for the formation of the adhesive layer can also be used as the spacer 5 directly.

As the separator 5, plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester films can be used favorably. The thickness of the separator is usually 3 to 200 μm, preferably about 10 to 100 μm. Preferably, the contact surface of the separator 5 and the adhesive layer 2 is implemented with a mold release agent such as polysilicon-based, fluorine-based, long-chain alkyl-based, or fatty amide-based, or silica powder. The demoulding process. By releasing the surface of the separator 5, when the film substrate 1 and the separator 5 are peeled off, they can be maintained at the interface between the adhesive layer 2 and the separator 5 to be peeled off and fixed on the film substrate 1 The state of the adhesive layer 2.

[Use of Reinforcement Membrane] The reinforcing film of the present invention is used by being attached to a device or device component. The reinforcing film 10 is fixed by the adhesive layer 2 and the film substrate 1, and after being attached to the adherend and before being hardened by light, the adhesion force to the adherend is small. Therefore, before photocuring, the reinforcing film is easily peeled off from the adherend, and the secondary processability is excellent. In addition, before photocuring, processing such as cutting the reinforcing film and removing the reinforcing film in a part of the surface of the adherend can also be easily performed.

The adherend for bonding the reinforcing film is not particularly limited, and various electronic devices, optical devices, and their constituent parts can be cited. The reinforcing film can be attached to the entire surface of the adherend, or it can be selectively attached only to the part that needs reinforcement. In addition, after the reinforcing film is attached to the entire surface of the adherend, the reinforcing film at a portion that does not need to be reinforced may be cut, and the reinforcing film may be peeled off and removed. If it is before photocuring, the reinforcing film is temporarily adhered to the surface of the adherend, so the reinforcing film can be easily peeled off from the surface of the adherend.

<Characteristics of the adhesive layer before light curing> (Adhesion) From the viewpoint of facilitating the peeling from the adherend and preventing the residual of the reinforcing film in the adherend after peeling, the adhesive force between the adhesive layer 2 and the adherend before photocuring is preferably 5 N /25 mm or less, more preferably 2 N/25 mm or less, and further preferably 1.3 N/25 mm or less. From the viewpoint of preventing the peeling of the reinforcing sheet during storage or handling, the adhesive force between the adhesive layer 2 and the adherend before photocuring is preferably 0.005 N/25 mm or more, more preferably 0.01 N/25 mm The above is more preferably 0.1 N/25 mm or more, and particularly preferably 0.3 N/25 mm or more.

The reinforcing film preferably has an adhesive force to the polyimide film in a state before photocuring the adhesive layer within the above range. For flexible display panels, flexible printed wiring boards (FPCs), devices integrating display panels and wiring boards, etc., flexible substrate materials are used, from the viewpoint of heat resistance or dimensional stability, Polyimide membranes are generally used. The adhesive layer has the above-mentioned adhesive force to the polyimide film as the substrate. The reinforcing film is easily peeled off before the photocuring of the adhesive, and the reliability after photocuring is excellent.

(Storage Modulus) The adhesive layer 2 preferably has a shear storage modulus G′ _i at 25° C. before light curing of 1×10 ⁴ to 1.2×10 ⁵ Pa. Shear storage modulus (hereinafter, only referred to as "storage modulus") is obtained by reading the method described in JIS K7244-1 "Plastics-Dynamic Mechanical Properties Test Method" at a frequency of 1 Hz under- The range of 50 to 150° C. is obtained as a value at a specific temperature when the temperature rise rate is 5° C./min.

In a substance that exhibits viscoelasticity like an adhesive, the storage modulus G'is used as an indicator of the degree of hardness. The storage modulus of the adhesive layer has a high correlation with the cohesive force, and there is a tendency that the higher the cohesive force of the adhesive, the greater the holding power of the adherend becomes. As long as the storage modulus of the adhesive layer 2 before photohardening is 1×10 ⁴ Pa or more, the adhesive has sufficient hardness and cohesive force, so when the reinforcing film is peeled from the adherend, it is not likely to be generated from the adherend Paste remains. In addition, when the storage modulus of the adhesive layer 2 is large, the adhesive can be prevented from overflowing from the end surface of the reinforcing film. As long as the storage modulus of the adhesive layer 2 before photohardening is 1.2×10 ⁵ Pa or less, it is easy to peel off at the interface between the adhesive layer 2 and the adherend, and it is not easy to cause adhesion when performing secondary processing The aggregation of the adhesive layer is destroyed or the paste remains on the surface of the adherend.

From the viewpoint of improving the secondary processability of the reinforcing sheet and suppressing the paste residue on the adherend during secondary processing, the storage modulus G′ _{i of the} adhesive layer 2 at 25° C. before light curing It is preferably 3×10 ⁴ to 1×10 ⁵ Pa, and more preferably 4×10 ⁴ to 9.5×10 ⁴ Pa.

＜Light curing of adhesive layer＞ After the reinforcing film is attached to the adherend, the adhesive layer 2 is irradiated with active light to harden the adhesive layer. Examples of the active rays include ultraviolet rays, visible rays, infrared rays, X rays, α rays, β rays, and γ rays. In terms of suppressing the hardening of the adhesive layer in the storage state and easily curing, the active light is preferably ultraviolet light. The irradiation intensity or irradiation time of the active light may be appropriately set according to the composition or thickness of the adhesive layer. The irradiation of the active light on the adhesive layer 2 can be performed from either side of the film substrate 1 side and the side of the adherend, or the irradiation of the active light can be performed from both sides.

<Characteristics of the adhesive layer after light curing> (Adhesion) From the viewpoint of practical reliability of the device, the adhesive force between the adhesive layer 2 and the adherend after photohardening is preferably 6 N/25 mm or more, more preferably 10 N/25 mm or more, and It is preferably 12 N/25 mm or more, and particularly preferably 14 N/25 mm or more. The reinforcing film is preferably an adhesive layer after photo-hardening that has an adhesion to the polyimide film in the above range. The adhesive force between the adhesive layer 2 and the adherend after photohardening is preferably more than 4 times the adhesive force between the adhesive layer 2 and the adherend before photohardening, more preferably 8 times and more preferably 10 More than times.

The adhesive layer 2 preferably has a storage modulus G′ _f at 25° C. after photocuring of 1.5×10 ⁵ Pa or more. If the storage modulus of the adhesive layer 2 after photohardening is 1.5×10 ⁵ Pa or more, as the cohesion increases, the adhesion with the adherend increases, and a higher adhesion reliability can be obtained. On the other hand, when the storage modulus is too large, the adhesive is difficult to wet and expand, and the contact area with the adherend becomes smaller. In addition, the stress dispersibility of the adhesive decreases, so there is a tendency that the peeling force easily propagates to the adhesive interface and the adhesive force with the adherend decreases. Therefore, the storage modulus G′ _f at 25° C. after photo-curing of the adhesive layer 2 is preferably 2×10 ⁶ Pa or less. To improve the adhesive layer so that the reinforcing sheet of the photohardenable Next viewpoint of reliability purposes, G _'f is more preferably ^{1.8 × 10 5 ~ 1.2 × 10} 6 Pa, and further preferably 2 × 10 ⁵ ~ 1 × 10 ⁶ Pa.

The ratio G′ _f /G′ _i of the storage modulus at 25° C. before and after the light curing of the adhesive layer 2 is preferably 2 or more. If G 'is _F G' _i of 2 times or more, the hardening caused by the light of the G 'of the increase is large, secondary processability can be both before and after photohardening of the photohardenable Next reliability. _G'f /G' _i is more preferably 4 or more, further preferably 8 or more, and particularly preferably 10 or more. G _'f / G' of the upper limit of _i is not particularly limited, to G _'f / G' of the case when _i is too large, easily lead to the front of the photo-curing by G 'is small and the initial cause of the failure and then, after the photohardening or because The G'is too large and the subsequent reliability decreases. Therefore, _G'f /G' _{i is} preferably 100 or less, more preferably 40 or less, and further preferably 30 or less, particularly preferably 25 or less.

The adherend after the reinforcement film is provided may be subjected to autoclave treatment for the purpose of improving the affinity of the lamination interface of a plurality of lamination members, or heat treatment such as thermocompression for circuit member joining. When performing such heat treatment, it is preferable that the adhesive between the reinforcing film and the adherend does not flow from the end surface.

From the viewpoint of suppressing the overflow of the adhesive during high-temperature heating, the storage modulus of the adhesive layer 2 after photocuring at 100°C is preferably 5×10 ⁴ Pa or more, more preferably 8×10 ⁴ Pa or more It is more preferably 1×10 ⁵ Pa or more. From the viewpoint of preventing the overflow of the adhesive during heating and preventing the reduction of the adhesive force during heating, the storage modulus of the adhesive layer 2 after light curing at 100°C is preferably the storage modulus at 50°C 60% or more, more preferably 65% or more, further preferably 70% or more, particularly preferably 75% or more.

[Use Form of Reinforcement Membrane] The reinforcing film of the present invention is used by being attached to the constituent members (semi-finished products) of various devices or completed devices. Since appropriate rigidity can be imparted by bonding the reinforcing film, it is expected to improve operability or prevent damage. In the manufacturing process of the device, when the reinforcement film is bonded to the semi-finished product, the reinforcement film may be bonded to the large semi-finished product before cutting to the size of the product. It is also possible to apply the reinforcing film on a roll-to-roll basis to the mother roll of a device manufactured by a roll-to-roll process.

As the device is highly integrated, compact, lightweight, and thin, the thickness of the components constituting the device tends to become smaller. Due to the thinning of the constituent members, it is easy to cause bending or curling due to stress or the like at the lamination interface. In addition, due to the reduction in thickness, it is easy to cause deflection due to its own weight. By attaching the reinforcing film, rigidity can be imparted to the adherend, so that bending, curling, and deflection caused by stress, dead weight, etc. can be suppressed, and operability is improved. Therefore, by attaching a reinforcement film to the semi-finished product in the manufacturing process of the device, it is possible to prevent defects or defects in the transportation or processing caused by the automated device.

In automatic conveyance, the contact between the semi-finished product to be conveyed and the conveying arm or pin is inevitable. In addition, there is a case where a semi-finished product is cut for adjustment of shape or removal of unnecessary parts. When the highly integrated, compact, lightweight and thin device comes into contact with the conveying device or is cut, it is easy to cause damage due to the local concentration of stress. In the manufacturing process of a device in which a plurality of components are laminated, not only the components are sequentially stacked, but also a part of the components or engineering materials are peeled off and removed from the semi-finished product. When the member is excessively thinned, stress may be locally concentrated at the peeling site and its vicinity to cause damage or dimensional change. Since the reinforcing film has the stress dispersibility obtained by the adhesive layer, it can be given appropriate rigidity by attaching the reinforcing film to the object to be transported and the object to be processed, and the stress can be relaxed and dispersed to suppress cracking. , Cracks, flaking, dimensional changes and other adverse conditions.

In this way, by attaching the reinforcing film of the present invention, moderate rigidity can be imparted to the semi-finished product as the adherend, and the stress can be relaxed and dispersed. Therefore, it is possible to suppress various defects that may occur in the manufacturing process. Increased production efficiency and improved yield. In addition, the reinforcement film is easier to peel from the adherend before photocuring the adhesive layer, so it is also easy to perform secondary processing in the case of lamination or occurrence of poor bonding.

In the reinforcing film of the present invention, the adhesive layer 2 is photocurable, and the time of curing can be set arbitrarily. The secondary processing or the processing of the reinforcing film can be performed at any time between after the adherend is placed on the reinforcing film and before the adhesive is photocured, so it can flexibly respond to the preparation time of the manufacturing steps of the device. As described above, since the adhesive layer contains antioxidants in addition to the light hardener and the light radical initiator, it is not easy to perform light hardening caused by light such as fluorescent lamps. Therefore, even in the case where the reinforcing film is attached to the adherend and stored for a long time, as long as it is before photocuring, the reinforcing film is easily peeled off from the adherend.

In the use of the completed device, when the external force is accidentally burdened due to the drop of the device, the placement of heavy goods on the device, the collision of flying objects on the device, etc., the reinforcement film can also be attached by And prevent the damage of the device. In addition, since the reinforcing film after photocuring the adhesive is firmly attached to the device, the reinforcing film is not likely to peel off during long-term use, and is excellent in reliability. [Example]

The following examples are further described, but the present invention is not limited to these examples.

[Production of Reinforcement Membrane] <polymerization of base polymer> 63 parts by weight of 2-ethylhexyl acrylate (2EHA) as monomers and 15 parts by weight of N-vinylpyrrolidone (NVP) were put into a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen introduction tube. 9 parts by weight of methyl methacrylate (MMA), 13 parts by weight of hydroxyethyl acrylate (HEA), 0.2 parts by weight of azobisisobutyronitrile as a thermal polymerization initiator, and 233 parts by weight of ethyl acetate as a solvent Nitrogen was added, and nitrogen was introduced, and nitrogen substitution was performed for about 1 hour while stirring. Thereafter, it was heated to 60°C and allowed to react for 7 hours to obtain a solution of an acrylic polymer having a weight average molecular weight (Mw) of 1.2 million.

<Preparation of adhesive composition> "Takenate D110N" (75% ethyl acetate solution of trimethylolpropane adduct of xylylene diisocyanate) manufactured by Mitsui Chemicals as a crosslinking agent is added to the acrylic polymer solution as multifunctional acrylic acid "A-200" (polyethylene glycol #200 (n=4) diacrylate; molecular weight 308, functional group equivalent 154 g/eq) manufactured by Shin Nakamura Chemical Industry, a monomer, photo radical initiator, And antioxidant and mixed uniformly to prepare an adhesive composition. The compounding amount (solid content) of the crosslinking agent was 2.5 parts by weight with respect to 100 parts by weight of the base polymer, and the compounding amount of the polyfunctional acrylic monomer was 30 parts by weight with respect to 100 parts by weight of the base polymer. As an antioxidant, pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] ("Irganox 1010" manufactured by BASF) was prepared in the amounts shown in Table 1. As photo radical initiators, the followings were prepared in the amounts shown in Table 1.

(Photo radical initiator) IRG184: 1-hydroxycyclohexyl phenyl ketone ("Irgacure 184" manufactured by BASF, absorption maximum wavelength: 246 nm, 280 nm, 333 nm) IRG651: 2,2-dimethoxy-1,2-diphenylethane-1-one ("Irgacure 651" manufactured by BASF, absorption maximum wavelength: 250 nm, 340 nm) IRG819: Bis(2,4,6-trimethylbenzyl)-phenylphosphine oxide ("Irgacure 819" manufactured by BASF, absorption maximum wavelength: 295 nm, 370 nm)

<Coating and crosslinking of adhesive solution> The above adhesive composition was applied to a 75 μm thick polyethylene terephthalate film (“Lumirror S10” manufactured by Toray) without surface treatment so that the thickness after drying became 25 μm using a grooved roller. Dry at 130°C for 1 minute to remove the solvent. Then, attach the separator to the coated surface of the adhesive (polyethylene terephthalate film with a thickness of 25 μm subjected to silicone release on the surface) The demolding surface. After that, aging treatment was carried out in an environment of 25°C for 4 days to allow crosslinking to proceed, and a reinforced film with a light-curing adhesive sheet laminated on the film substrate and a separator temporarily adhered thereto was obtained.

[Measurement of adhesive force] A polyimide film (“Kapton 50EN” manufactured by DU PONT-TORAY) with a thickness of 12.5 μm was attached to the glass plate via a double-sided tape (“No. 531” manufactured by Nitto Denko) to obtain Polyimide film substrate for measurement. The surface of the reinforcing film with a width of 25 mm×100 mm in length was cut off and the separator was peeled off and removed, and attached to the polyimide film substrate for measurement using a hand pressure roller as a test sample before light curing. Reinforce the film side (PET film side) of the test sample before photo-curing using an LED light source with a wavelength of 365 nm to irradiate ultraviolet light with a cumulative light amount of 400 mJ/cm ^{2 to} photo-harden the adhesive layer, and use the obtained as the test sample after photo-hardening . Using these test samples, the end of the polyethylene terephthalate film used as the reinforcing film was held by a chuck, the reinforcing film was peeled at 180° at a tensile speed of 300 mm/min, and the peel strength was measured.

<Evaluation of the adhesion of the reinforcing film after storage for a certain period of time> The reinforcing sheet was allowed to stand under a bright room at room temperature, and after 1 and 4 weeks, it was bonded to the polyimide film substrate for measurement. The test samples before and after photocuring were the same as above. The 180° peel strength was measured.

Table 1 shows the measurement results of the adhesive composition of each reinforcing film and the adhesion before and after light curing.

[Table 1]

Immediately after fabrication, the adhesion force of any sample was 0.2 to 0.4 N/25 mm before light hardening and could be easily peeled off from the adhesive body. After light hardening, the adhesion force rose to more than 15 N/25 mm, and The adherend adheres firmly.

In the sample 10 using an antioxidant-free adhesive, the adhesive force before photo-curing greatly increased in the sample after 4 weeks of storage, and it was difficult to peel from the adherend. On the other hand, in the sample 11 to which 0.1 parts by weight of antioxidant was added, the adhesion force before light curing slightly increased in the sample after 4 weeks of storage, but it was sufficiently peelable from the adherend. In addition, the adhesion force of the sample 11 after being stored for 4 weeks after photocuring was the same as that of the sample immediately after preparation.

In the samples 20 and 30 using the antioxidant-free adhesive, as in the sample 10, in the samples after 4 weeks of storage, a large increase in the adhesive force before photocuring was observed. In the samples 20 and 30 stored for 1 week, the adhesion force before light curing also increased to 10 N/25 mm or more. Samples 21 and 31 to which 0.1 parts by weight of antioxidants were added also had a lower adhesion before photo-curing in samples after storage for 1 week, and showed a higher adhesion after photo-curing.

From the comparison of the above results, it can be seen that by using a photo radical initiator and an antioxidant together, the following reinforcing film can be obtained, which even when stored under a fluorescent lamp for a long time, before being hardened by the adherend The secondary workability of peeling is also excellent, and exhibits high adhesion to the adherend by light curing.

After the sample 12 containing 0.5 parts by weight of the antioxidant was stored for 1 week, the rate of increase in the adhesive strength obtained by photocuring was reduced. After 4 weeks of storage, the adhesive strength hardly increased even after ultraviolet irradiation. The sample 13 to which 1 part by weight of the antioxidant was added was stored for 1 week, and the increase in adhesive force by ultraviolet irradiation was also insufficient. In the comparison of samples 21 to 23 and the comparison of samples 31 to 33, it can also be seen that as the amount of antioxidant added increases, even if ultraviolet irradiation is performed, the adhesive force tends not to increase.

From these results, it can be said that when the amount of the antioxidant added is large, it tends to be difficult to perform photo-curing as the storage time from the preparation sample becomes longer. It is considered that the reason is that as the storage time under the fluorescent lamp for preparing the sample becomes longer, the photo radical initiator is deactivated, and even if ultraviolet irradiation is performed, the amount of radical generation is also small.

If the storage time under a fluorescent lamp becomes longer and the effective concentration of the photo radical initiator decreases, the amount of free radicals generated during ultraviolet irradiation decreases. Antioxidants have the effect of trapping the free radicals generated from light radical initiators due to the light of fluorescent lamps and the like in the storage environment, and inhibiting the undesired light radical polymerization, but in the case of ultraviolet irradiation for photohardening, It also has the effect of capturing free radicals. Therefore, when the storage time under the fluorescent lamp becomes longer and the effective concentration of the photo radical initiator is lower, the free radicals captured by the antioxidants among the photo radicals generated from the photo radical initiator The higher the ratio, the lower the ratio of free radicals that contribute to photo radical polymerization. Since the greater the content of the antioxidant, the greater the polymerization inhibition effect (polymerization inhibition), it is considered that the photo-radical reaction of the photo-hardener is not easy to proceed even when irradiated with ultraviolet rays, and the adhesive force does not sufficiently increase.

From the above results, it can be seen that by appropriately adjusting the amount of antioxidants used in combination with the photo radical initiator, the following reinforcing film can be obtained: even when the storage time under a fluorescent lamp is long, the light is hardened The secondary workability before peeling off from the adherend is also excellent, and proper light curing by ultraviolet irradiation can achieve a high adhesion.

[Measurement and discussion of free radical concentration by electron spin resonance] In order to verify the radical generation amount of the photo radical initiator used in the above examples and the effect of the antioxidant, light was irradiated at an extremely low temperature, and the radical generation amount was evaluated by ESR.

The concentration is prepared for each of the systems using photo radical initiator alone (IRG184, IRG651 or IRG819), antioxidant alone (Irganox 1010), and photo radical initiator (Irg651 or Irg819) combined with antioxidant 0.2 mol/L ethyl acetate solution (the concentration of each is set to 0.2 mol/L in the combined system). Load 0.1 mL of the sample solution in an ESR sample tube (about 3.5 mmϕ quartz tube) and set it in the ESR cavity, and perform ESR measurement with light irradiation at a temperature of 40 K. The light irradiation lamp uses an ultra-high pressure mercury lamp (manufactured by Ushio), which cuts off short-wavelength light below 290 nm with a glass filter, and cuts off the hot wire with a water filter. The illuminance (wavelength 365 nm) measured on the front of the cavity was 18 mW/cm ² . The device and main measurement conditions are shown below.

Device: ESP350E (made by BRUKER) Attachment: HP5351B microwave frequency counter (manufactured by HEWLETT PACKARD) ER035M Gauss meter (made by BRUKER) ESR910 cryostat (made by BRUKER) Cavity: TM110, cylindrical Measuring temperature: 40 K Central magnetic field: 3385 G Magnetic field scanning width: 400 G Modulation: 100 kHz, 10 G Microwave: 9.49 GHz, 0.16 mW Scanning time: 83.89 seconds × 2 times Time constant: 327.68 milliseconds Data points: 1024

Based on the ESR spectra after 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes after the start of light irradiation, the amount of free radicals was quantified by a calibration curve method. For each sample, a graph obtained by plotting light irradiation time and radical concentration is shown in FIG. 4.

Observed on three kinds of photo radical initiators, Irgacure 819 (IRG819) showed the highest amount of free radicals. The reason is believed to be that: IRG819 shows a maximum absorption at a wavelength of 370 nm, and a high sensitivity to the irradiated light (wavelength 365 nm). Among Irgacure 184 (IRG184) and Irgacure 651 (IRG651), Irgacure 651 shows a larger amount of free radical generation.

It can be seen that there is a correlation between the amount of these free radicals generated and the change in the adhesive force before light curing when the sample 10, the sample 20, and the sample 30 are stored under fluorescent lamps. That is, Irgacure 184 is believed to have a relatively small amount of free radicals generated by light from fluorescent lamps. Therefore, sample 10 did not see an increase in adhesion before photohardening after being stored for 1 week. The sample 20 of Irgacure 651 and the sample 30 of Irgacure 819 have a relatively large amount of light radical generation caused by the light from the fluorescent lamp, so in the sample after 1 week of storage, the adhesion before light curing rise.

The antioxidant (Irganox 1010) showed a higher free radical concentration than the three photo-radical initiators. It is believed that the reason is that the stability of the free radicals generated from the antioxidant is higher, and the amount of free radicals disappears is smaller than that of the light radical initiator. Therefore, as the light irradiation time increases, the amount of free radicals accumulated in the system More.

The combined system of a photo radical initiator (IRG651 or IRG819) and an antioxidant shows a lower free radical concentration than when the antioxidant is used alone. Since the free radical concentration of the combined system is less than the sum of the case of using the photo radical initiator alone and the case of using the antioxidant alone, it is considered that the radical generated from the photo radical initiator is trapped by the antioxidant.

1‧‧‧membrane substrate 2‧‧‧Adhesive layer 5‧‧‧Parts 10‧‧‧Reinforcement membrane 20‧‧‧ Installation

FIG. 1 is a cross-sectional view showing the laminated structure of the reinforcing film. Fig. 2 is a cross-sectional view showing the laminated structure of the reinforcing film. FIG. 3 is a cross-sectional view showing a device provided with a reinforcement film. 4 is a graph showing the measurement results of the amount of free radicals generated by light irradiation at an extremely low temperature.

Claims (9)

A reinforcing film comprising a film substrate and an adhesive layer fixedly deposited on one of the main surfaces of the film substrate; and The adhesive layer includes a photo-curable composition containing a base polymer, a photo hardener, a photo radical initiator, and an antioxidant, and contains 10 to 50 parts by weight of the photo hardener with respect to 100 parts by weight of the base polymer. Parts, 0.01 to 1 part by weight of the photo radical initiator, and 0.01 to 2 parts by weight of the antioxidant. The reinforcing film according to claim 1, wherein the content of the antioxidant is 0.2 to 5 times the content of the photo radical initiator. The reinforced film according to claim 1 or 2, wherein the above-mentioned photo radical initiator has an absorption maximum in the range of wavelengths from 310 nm to 355 nm, and does not show an absorption maximum at wavelengths longer than 360 nm. The reinforcing membrane according to any one of claims 1 to 3, wherein the above-mentioned base polymer contains at least one kind selected from the group consisting of a hydroxyl group-containing monomer and a carboxyl group-containing monomer as a monomer unit, and Or a carboxyl-bonded cross-linking agent is introduced with a cross-linked structure. The reinforcing film according to any one of claims 1 to 4, which contains an acrylic polymer as the above-mentioned base polymer. The reinforcing film according to claim 5, wherein the acrylic polymer contains a homopolymer having a glass transition temperature of 40 to 50° C. or more and 5 to 50% by weight of the monomer component. The reinforcing film according to any one of claims 1 to 6, wherein the light hardener is a multifunctional (meth)acrylate. The reinforcing film according to any one of claims 1 to 7, wherein the functional group equivalent of the light hardener is 100 to 500 g/eq. The reinforcing film according to any one of claims 1 to 8, wherein the adhesive force between the adhesive layer and the polyimide film is 0.005 to 5 N/25 mm, and the adhesive layer is hardened with polyimide after photohardening The adhesion of the film is more than 6 N/25 mm.

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