Reinforcement film, device with reinforcement film, and method for manufacturing the same

Abstract

A reinforcing film (10) comprises an adhesive layer (2) that is layered and fixed on one main surface of a film base material (1). The adhesive layer is composed of a photocurable composition containing an acrylic base polymer having a crosslinked structure, a photocuring agent, a photopolymerization initiator, an antistatic agent, and a polyol. The number average molecular weight of the polyol contained in the photocurable composition is preferably 300 to 30,000, and the amount of polyol in the photocurable composition is preferably 5 to 60 parts by weight per 100 parts by weight of the acrylic base polymer.

Description

[Technical Field]

[0001] The present invention relates to a reinforcing film to be attached to the surface of a device, and further to a device including the reinforcing film and a method for manufacturing the same. [Background technology]

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

[0003] By temporarily attaching an adhesive film to the surface of a device or a device component before use, such as during device assembly, processing, transportation, etc., it is possible to prevent the adherend from being scratched or damaged. Patent Documents 1 and 2 disclose reinforcing films that have an adhesive layer made of a photocurable adhesive composition on a film substrate.

[0004] This reinforcing film has a high gel fraction and low adhesiveness immediately after application to the adherend, making it easy to remove from the adherend. This allows for reworking from the adherend, and also allows for selective peeling and removal of the reinforcing film from areas of the adherend that do not require reinforcement. The reinforcing film's adhesive firmly bonds to the adherend upon photocuring, permanently bonding the film substrate to the adherend's surface, making it usable as a reinforcing material for protecting the surface of devices, etc.

[0005] In recent years, organic EL panels using foldable substrates (flexible substrates) such as resin films have been put to practical use, and foldable flexible displays have been proposed. Foldable devices are repeatedly bent at the same location. At the bent portion, compressive stress is applied to the inside and tensile stress to the outside, causing distortion at the bent portion and its surroundings, which may result in peeling of the adhesive from the adherend. Patent Document 4 proposes using a photocurable adhesive containing an acrylic-based polymer with a low glass transition temperature as the adhesive for the reinforcing film of a foldable device. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-41113 [Patent Document 2] Japanese Patent Publication No. 2020-134540 [Patent Document 3] Japanese Patent Application Publication No. 2019-20726 [Patent Document 4] International Publication No. 2022 / 050009 Summary of the Invention [Problem to be solved by the invention]

[0007] As described in Patent Document 3, foldable devices use a resin film as the substrate material, which is prone to charging and can cause problems with electrostatic breakdown of the device due to charging (static electricity). Patent Document 2 proposes preventing charging of the reinforced film by providing an antistatic layer on the back surface of the film substrate of the reinforced film (the surface opposite to the surface to which the adhesive layer is attached). However, because the back surface of the reinforced film substrate is separated from the adherend, it is difficult to adequately suppress charging of the device even if an antistatic layer is provided on the back surface of the substrate.

[0008] In order to suppress static electricity in a device, it is effective to incorporate an antistatic agent into the pressure-sensitive adhesive layer provided in contact with the device, thereby lowering the resistance of the pressure-sensitive adhesive layer and providing antistatic properties. However, even when an antistatic agent is added to the pressure-sensitive adhesive of the reinforcing film described in Patent Document 4, the resistance of the pressure-sensitive adhesive is not sufficiently reduced, and increasing the amount of antistatic agent added causes the antistatic agent to bleed out, which reduces the adhesive strength between the pressure-sensitive adhesive layer and the device and causes contamination of the device surface.

[0009] In view of the above, an object of the present invention is to provide a reinforcing film that is less likely to peel off during a bending test, is applicable to a foldable device, and can contribute to preventing static electricity in the device. [Means for solving the problem]

[0010] The reinforcing film of the present invention includes a pressure-sensitive adhesive layer bonded to one main surface of a film substrate. The pressure-sensitive adhesive layer is made of a photocurable composition containing an acrylic-based polymer, a photocuring agent, a photopolymerization initiator, an antistatic agent, and a polyol. The glass transition temperature of the acrylic-based polymer is preferably −40° C. or lower.

[0011] The number average molecular weight of the polyol contained in the photocurable composition is preferably 300 to 30,000. The amount of polyol in the photocurable composition is preferably 5 to 60 parts by weight per 100 parts by weight of the acrylic base polymer. The polyol may be polypropylene glycol or polytetramethylene glycol. The polyol may be diol or triol polypropylene glycol.

[0012] The acrylic base polymer contains, as a monomer unit, one or more monomers selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers, and a crosslinking agent such as an isocyanate crosslinking agent or an epoxy crosslinking agent is bonded to the hydroxyl group and / or carboxyl group of the acrylic base polymer to introduce a crosslinked structure. The amount of the crosslinking agent may be about 0.03 to 2 parts by weight per 100 parts by weight of the acrylic polymer.

[0013] The photocurable composition constituting the pressure-sensitive adhesive layer preferably contains 3 to 40 parts by weight of a photocuring agent relative to 100 parts by weight of the acrylic base polymer. For example, a polyfunctional (meth)acrylate is used as the photocuring agent. The polyfunctional (meth)acrylate may be an alkylene oxide-modified polyfunctional (meth)acrylate modified with an alkylene oxide such as ethylene oxide or propylene oxide.

[0014] The surface resistance of the adhesive layer is 1 x 10 11 The pressure-sensitive adhesive layer preferably has a shear storage modulus of 1.0×10 Ω or less at −20° C. after photocuring. 4 ~1.0×10 6 The pressure-sensitive adhesive layer preferably has a shear storage modulus of 1.0×10 Pa at −20° C. before photocuring. 4 ~2.0×10 5 The pressure-sensitive adhesive layer may have a shear storage modulus of 5.0×10 Pa at 25°C before photocuring. 3 ~1.0×10 5 It may be Pa.

[0015] The adhesive layer preferably has an adhesive strength to the polyimide film of 1 N / 25 mm or less before photocuring, and the adhesive strength to the polyimide film after photocuring is preferably at least five times the adhesive strength to the polyimide film before photocuring.

[0016] The reinforcing film is attached to the surface of the device, and the pressure-sensitive adhesive layer is photocured to obtain a device with the reinforcing film. The device may be a flexible device that can be bent. [Effects of the Invention]

[0017] The reinforcing film of the present invention has a pressure-sensitive adhesive layer made of a photocurable composition, and the adhesive strength to the adherend is increased by photocuring the pressure-sensitive adhesive layer after adhesion to the adherend. Because the adhesive strength to the adherend is low before photocuring, the reinforcing film can be easily peeled off from the adherend.

[0018] The pressure-sensitive adhesive layer of the reinforcing film contains an antistatic agent and a polyol, which reduces the resistance, thereby suppressing the charging of the pressure-sensitive adhesive layer itself and contributing to the prevention of charging of the adherend.In addition, since the pressure-sensitive adhesive layer contains a polyol, the shear storage modulus is low even after photocuring, and the stress-strain relaxation is high.Even when repeatedly bent at the same location, peeling of the pressure-sensitive adhesive layer at the bent location is suppressed, and the adhesive reliability is excellent.Therefore, the reinforcing film of the present invention can also be suitably used for foldable devices using a resin film substrate. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is a cross-sectional view showing a laminated structure of a reinforcing film. [Figure 2] FIG. 2 is a cross-sectional view showing a laminated structure of a reinforcing film. [Figure 3] FIG. 10 is a cross-sectional view showing a device to which a reinforcing film is attached. DETAILED DESCRIPTION OF THE INVENTION

[0020] 1 is a cross-sectional view showing one embodiment of a reinforced film. Reinforced film 10 has a pressure-sensitive adhesive layer 2 on one main surface of a film substrate 1. The pressure-sensitive adhesive layer 2 is fixedly laminated on one main surface of the film substrate 1. The pressure-sensitive adhesive layer 2 is a photocurable pressure-sensitive adhesive made from a photocurable composition, and is cured by irradiation with actinic rays such as ultraviolet light, thereby increasing the adhesive strength with the adherend.

[0021] Fig. 2 is a cross-sectional view of a reinforced film having a release liner 5 temporarily attached onto the main surface of a pressure-sensitive adhesive layer 2. Fig. 3 is a cross-sectional view showing a state in which a reinforced film 10 is attached to the surface of a device 20.

[0022] The release liner 5 is peeled off and removed 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, thereby attaching the reinforcement film 10 to the surface of the device 20. In this state, the adhesive layer 2 has not yet been photocured, and the reinforcement film 10 (adhesive layer 2) is temporarily attached to the device 20. By photocuring the adhesive layer 2, the adhesive strength at the interface between the device 20 and the adhesive layer 2 increases, and the device 20 and the reinforcement film 10 are fixed together.

[0023] "Fixed" means that the two laminated layers are firmly bonded together, making it difficult or impossible to separate them at their interface. "Temporary adhesion" means that the adhesive strength between the two laminated layers is weak, making them easy to separate at their interface.

[0024] In the reinforced film shown in Figure 2, film substrate 1 and pressure-sensitive adhesive layer 2 are bonded together, and release liner 5 is temporarily attached to pressure-sensitive adhesive layer 2. When film substrate 1 and release liner 5 are peeled apart, peeling occurs at the interface between pressure-sensitive adhesive layer 2 and release liner 5, and the pressure-sensitive adhesive layer 2 remains bonded to film substrate 1. No pressure-sensitive adhesive remains on release liner 5 after peeling.

[0025] In the device with a reinforcing film shown in FIG. 3, the device 20 and the adhesive layer 2 are temporarily bonded together before the adhesive layer 2 is photocured. When the film substrate 1 and the device 20 are peeled apart, the peeling occurs at the interface between the adhesive layer 2 and the device 20, so the adhesive layer 2 remains adhered to the film substrate 1. Because no adhesive remains on the device 20, peeling operations such as rework and cutting are easy. After the adhesive layer 2 is photocured, the adhesive strength between the adhesive layer 2 and the device 20 increases, resulting in a fixed state, making it difficult to peel the film 1 from the device 20.

[0026] [Film base material] 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 layer 2 together, it is preferable that the surface of the film substrate 1 to which the pressure-sensitive adhesive layer 2 is to be attached is not subjected to a release treatment.

[0027] The thickness of the film substrate is, for example, about 4 to 150 μm. From the viewpoint of reinforcing the device by imparting rigidity and cushioning impact, the thickness of the film substrate 1 is preferably 5 μm or more, more preferably 12 μm or more, even more preferably 20 μm or more, and particularly preferably 25 μm or more. From the viewpoint of imparting flexibility to the reinforcing film so that it can be folded, the thickness of the film substrate 1 is preferably 125 μm or less, more preferably 100 μm or less. From the viewpoint of achieving both mechanical strength and flexibility, the compressive strength of the film substrate 1 is 100 to 3000 kg / cm 2 is preferred, and 200 to 2900 kg / cm 2 More preferably, 300 to 2800 kg / cm 2 is more preferably 400 to 2700 kg / cm 2 is particularly preferred.

[0028] Examples of plastic materials constituting the film substrate 1 include polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, polyether ether ketone, polyethersulfone, polyarylate resins, and aramid resins. In a reinforcement film for an optical device such as a display, the film substrate 1 is preferably a transparent film. Furthermore, when photocuring of the pressure-sensitive adhesive layer 2 is performed by irradiating actinic rays from the film substrate 1 side, the film substrate 1 is preferably transparent to the actinic rays used to cure the pressure-sensitive adhesive layer. Polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, transparent polyimides, and transparent aramids are preferably used because they combine mechanical strength and transparency. When irradiating actinic rays from the adherend side, the adherend only needs to be transparent to the actinic rays, and the film substrate 1 does not need to be transparent to the actinic rays.

[0029] 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 antireflection layer. As mentioned above, in order to bond the film substrate 1 and the pressure-sensitive adhesive layer 2 together, it is preferable that no release layer is provided on the surface of the film substrate 1 on which the pressure-sensitive adhesive layer 2 is to be applied. When an antistatic layer is provided on the surface of the film substrate, it is preferable that the antistatic layer is provided on the surface of the film substrate 1 on which the pressure-sensitive adhesive layer 2 is to be applied, from the viewpoint of reducing the surface resistance of the pressure-sensitive adhesive layer.

[0030] [Adhesive layer] The pressure-sensitive adhesive layer 2, which is fixedly laminated on the film substrate 1, is made of a photocurable composition. The photocurable composition constituting the pressure-sensitive adhesive layer 2 contains an acrylic-based polymer, a photocuring agent, and a photopolymerization initiator, and further contains an antistatic agent and a polyol.

[0031] Before photocuring, the adhesive layer 2 has low adhesive strength to adherends such as devices and device components, and is therefore easy to peel off. Since the adhesive strength to adherends of the adhesive layer 2 improves upon photocuring, the reinforcing film is less likely to peel off from the device surface even when the device is in use, and adhesive reliability is excellent.

[0032] Photocurable pressure-sensitive adhesives hardly cure under normal storage conditions, but cure when exposed to actinic rays such as ultraviolet rays. Therefore, the reinforcing film of the present invention has the advantage that the timing of curing of the pressure-sensitive adhesive layer 2 can be set as desired, allowing for flexible adaptation to process lead times, etc.

[0033] <Base polymer> The base polymer is the main component of the pressure-sensitive adhesive composition and is the main factor determining the adhesive strength and storage modulus of the pressure-sensitive adhesive layer before photocuring. The pressure-sensitive adhesive composition preferably contains an acrylic polymer as the base polymer because it has excellent optical transparency and adhesiveness and is easy to control the adhesive strength and storage modulus.

[0034] The acrylic polymer preferably contains an alkyl (meth)acrylate ester as a main monomer component. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0035] As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is preferably used. The alkyl group of the (meth)acrylic acid alkyl ester may be linear or branched. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and non-methyl (meth)acrylate. Examples thereof include 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, and eicosyl (meth)acrylate.

[0036] Among the exemplified (meth)acrylic acid alkyl esters, (meth)acrylic acid C is preferred from the viewpoint of suppressing peeling of the adhesive layer when repeatedly bent by lowering the Tg of the acrylic base polymer and reducing the shear storage modulus at low temperatures. 1-9 Alkyl esters are preferred, and those having a glass transition temperature of the homopolymer of -50°C or lower are preferred. (Meth)acrylic acid C having a glass transition temperature of the homopolymer of -50°C or lower 1-9Specific examples of alkyl esters 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), butyl acrylate (Tg: -55°C), etc. Among these, butyl acrylate (BA) and 2-ethylhexyl acrylate are preferred.

[0037] From the viewpoint of lowering the Tg of the acrylic base polymer, 2-ethylhexyl acrylate (2EHA) is particularly preferred. If 2EHA is the monomer (main monomer) most abundant among the constituent monomers of the acrylic base polymer, the glass transition temperature of the acrylic base polymer can be set to −60°C or lower, or −65°C or lower. Meanwhile, in the pressure-sensitive adhesive composition, the polyol (described in detail below) acts as a plasticizer, reducing the shear storage modulus at low temperatures and contributing to improved adhesive reliability. Therefore, when the pressure-sensitive adhesive composition contains a polyol, sufficient adhesive reliability can be ensured even if the glass transition temperature of the acrylic base polymer is approximately −50°C. From the viewpoints of improved adhesion and compatibility between the acrylic base polymer and the polyol, it is particularly preferred that the main monomer of the acrylic base polymer is butyl acrylate (BA).

[0038] The content of the (meth)acrylic acid alkyl ester is preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 85% by weight or more, and may be 90% by weight or more, 93% by weight or more, or 95% by weight or more, based on the total amount of the monomer components constituting the acrylic base polymer. 1-9 The amount of alkyl ester is preferably within the above range, and the total of 2-ethylhexyl acrylate and butyl acrylate is more preferably within the above range, and the amount of butyl acrylate may also be within the above range.

[0039] 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 hydroxy group-containing monomer and a carboxy group-containing monomer. The acrylic base polymer may contain both a hydroxy group-containing monomer and a carboxy group-containing monomer as copolymerization components, or may contain only one of them. The introduction of a crosslinked structure into the acrylic base polymer tends to improve the cohesive strength and the peelability of the pressure-sensitive adhesive layer 2 from the adherend before photocuring.

[0040] 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. Among these, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred because they contribute significantly to improving the adhesive strength of the pressure-sensitive adhesive after photocuring.

[0041] Examples of the carboxy group-containing monomer include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc. Among these, acrylic acid is particularly preferred because it contributes greatly to improving adhesive strength.

[0042] The acrylic base polymer preferably contains 0.5 to 15% by weight of the hydroxy group-containing monomer and carboxy group-containing monomer, more preferably 1 to 10% by weight, and even more preferably 2 to 7% by weight, of the total amount of constituent monomer components. When the acrylic base polymer contains a carboxy group, the acrylic base polymer and polyol exhibit high compatibility, so the acrylic base polymer preferably contains a carboxy group-containing monomer such as (meth)acrylic acid as a constituent monomer component, and the content of the carboxy group-containing monomer is preferably within the above range.

[0043] The acrylic base polymer may contain, as a constituent monomer component, a nitrogen-containing monomer such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinylcarboxylic acid amides, or N-vinylcaprolactam.

[0044] The acrylic base polymer may contain other monomer components, such as vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphate group-containing monomers, and acid anhydride group-containing monomers.

[0045] The acrylic base polymer before the introduction of a crosslinking structure may be substantially free of nitrogen atoms. The proportion of nitrogen in the constituent elements of the acrylic base polymer may be 0.1 mol% or less, 0.05 mol% or less, 0.01 mol% or less, 0.005 mol% or less, 0.001 mol% or less, or 0. By using an acrylic base polymer that is substantially free of nitrogen atoms, an increase in the adhesive strength (initial adhesive strength) of the pressure-sensitive adhesive layer before photocuring tends to be suppressed when the adherend is subjected to a surface activation treatment. By not using nitrogen-atom-containing monomers such as cyano group-containing monomers, lactam structure-containing monomers, amide group-containing monomers, and morpholine ring-containing monomers as the constituent monomer components of the acrylic base polymer, an acrylic base polymer that is substantially free of nitrogen atoms can be obtained. The amount of nitrogen-containing monomers relative to the total amount of the constituent monomer components of the acrylic base polymer may be 1 wt% or less, 0.5 wt% or less, 0.1 wt% or less, 0.05 wt% or less, or 0.

[0046] The glass transition temperature of the acrylic base polymer is preferably -40°C or lower, and may be -45°C or lower. The glass transition temperature is the temperature (peak top temperature) at which the loss tangent tanδ in viscoelasticity measurement is maximized. When the glass transition temperature is sufficiently lower than the ambient temperature of the device, the shear storage modulus G' of the pressure-sensitive adhesive layer within the ambient temperature range of the device tends to be small, and peeling during repeated bending tends to be suppressed.

[0047] Instead of the glass transition temperature determined by viscoelasticity measurement, the theoretical Tg calculated by the Fox formula may be used. The theoretical Tg is the glass transition temperature Tg of the homopolymer of the constituent monomer components of the acrylic base polymer. i and the weight fraction W of each monomer component i It is calculated using the following Fox formula: 1 / Tg=Σ(W i / Tg i )

[0048] Tg is the glass transition temperature of the polymer chain (unit: K), W iis the weight fraction of the monomer component i that constitutes the segment (copolymerization ratio by weight), Tg i is the glass transition temperature (unit: K) of the homopolymer of monomer component i. The glass transition temperature of the homopolymer can be determined from the values ​​listed in Polymer Handbook, 3rd Edition (John Wiley & Sons, Inc., 1989). For the Tg of a homopolymer of a monomer not listed in the above literature, the peak top temperature of tan δ measured by dynamic viscoelasticity measurement can be used.

[0049] The lower limit of the glass transition temperature of the acrylic base polymer is not particularly limited, but is generally −80° C. or higher, and may be −70° C. or higher, −65° C. or higher, −60° C. or higher, or −55° C. or higher. From the viewpoint of reducing the shear storage modulus at low temperatures and suppressing peeling during repeated flexing, the lower the glass transition temperature of the acrylic base polymer, the more preferable, but when the pressure-sensitive adhesive composition contains a polyol, even if the glass transition temperature of the acrylic base polymer is −55° C. or higher, the pressure-sensitive adhesive after photocuring will have excellent adhesive reliability and will be able to suppress peeling from the adherend during repeated flexing at low temperatures.

[0050] 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 a base polymer. Solution polymerization is preferred from the viewpoints of cost and the balance of adhesive strength, holding power, and other properties of the pressure-sensitive adhesive. Ethyl acetate, toluene, etc. are used as the solvent for solution polymerization. The solution concentration is usually about 20 to 80% by weight. Various known polymerization initiators 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.

[0051] 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 acrylic base polymer refers to the molecular weight before the introduction of the crosslinked structure.

[0052] <Crosslinking agent> From the viewpoints of imparting an appropriate cohesive strength to the pressure-sensitive adhesive, thereby enabling the pressure-sensitive adhesive layer to exhibit adhesive strength, and ensuring the peelability of the pressure-sensitive adhesive layer from the adherend before photocuring, it is preferable that a crosslinked structure be introduced into the base polymer. For example, the crosslinked structure is introduced by adding a crosslinking agent to a solution obtained after polymerization of an acrylic base polymer, and then heating the solution as necessary.

[0053] Examples of crosslinking agents 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 hydroxy groups and carboxy groups introduced into the acrylic base polymer to form a crosslinked structure. Isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they have high reactivity with the hydroxy groups and carboxy groups of the acrylic base polymer and allow for easy introduction of a crosslinked structure.

[0054] As described above, from the viewpoint of compatibility with polyols, the acrylic base polymer preferably has a carboxy group derived from a carboxy group-containing monomer such as acrylic acid. A crosslinked structure is preferably introduced into the acrylic base polymer having a carboxy group using an epoxy crosslinking agent.

[0055] The epoxy crosslinking agent is a multifunctional epoxy compound having two or more epoxy groups in one molecule. The epoxy crosslinking agent may have three or more or four or more epoxy groups in one molecule. The epoxy group of the epoxy crosslinking agent may be a glycidyl group. Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether. As the epoxy-based crosslinking agent, commercially available products such as "Denacol" manufactured by Nagase ChemteX, and "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical may be used.

[0056] The isocyanate crosslinking agent is a polyisocyanate having two or more isocyanate groups in one molecule. Examples of the isocyanate crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate and xylylene diisocyanate; trimethylolpropane / trilene diisocyanate; Examples of the isocyanate adduct include a diisocyanate trimer adduct (e.g., "Takenate D101E" manufactured by Mitsui Chemicals), a trimethylolpropane / hexamethylene diisocyanate trimer adduct (e.g., "Coronate HL" manufactured by Tosoh), a trimethylolpropane adduct of xylylene diisocyanate (e.g., "Takenate D110N" manufactured by Mitsui Chemicals), and an isocyanurate of hexamethylene diisocyanate (e.g., "Coronate HX" manufactured by Tosoh).

[0057] The amount of crosslinking agent used may be adjusted appropriately depending on the composition, molecular weight, etc. 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, relative to 100 parts by weight of the acrylic base polymer.

[0058] A crosslinking catalyst may be used to promote the formation of a crosslinked structure. 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.

[0059] <Photocuring agent> The pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer 2 contains a photocuring agent in addition to an acrylic base polymer. When the pressure-sensitive adhesive layer 2 made of a photocurable pressure-sensitive adhesive composition is photocured after being attached to an adherend, the adhesive strength to the adherend is improved.

[0060] As the photocuring agent, a photocurable monomer or a photocurable oligomer is used. As the photocuring agent, a compound having two or more ethylenically unsaturated bonds in one molecule is preferred. Furthermore, as the photocuring agent, a compound showing compatibility with the acrylic base polymer and the polyol is preferred. Since the photocuring agent shows moderate compatibility with the acrylic base polymer, it is preferred that the photocuring agent be liquid at room temperature.

[0061] It is preferable to use a polyfunctional (meth)acrylate as the photocuring agent because it has high compatibility with the acrylic base polymer. A typical example of the polyfunctional (meth)acrylate is an ester of a polyol and (meth)acrylic acid. Specific examples of the polyfunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, isocyanuric acid di(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and trimethylolpropanediol di(meth)acrylate. Examples of the acrylate include ethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate, and isoprene (meth)acrylate.

[0062] The polyfunctional (meth)acrylate may be an ester of an alkylene oxide-modified polyol and (meth)acrylic acid. Examples of the alkylene oxide include ethylene oxide (EO) and propylene oxide (PO). The alkylene oxide may be a polyalkylene oxide such as polyethylene glycol or polypropylene glycol.

[0063] Specific examples of alkylene oxide-modified polyfunctional (meth)acrylates include bisphenol A ethylene oxide-modified di(meth)acrylate, bisphenol A propylene oxide-modified di(meth)acrylate, trimethylolpropane ethylene oxide-modified tri(meth)acrylate, trimethylolpropane propylene oxide-modified tri(meth)acrylate, isocyanuric acid ethylene oxide-modified di(meth)acrylate, isocyanuric acid propylene oxide-modified di(meth)acrylate, isocyanuric acid ethylene oxide-modified tri(meth)acrylate, isocyanuric acid propylene oxide-modified tri(meth)acrylate, pentaerythritol ethylene oxide-modified tetra(meth)acrylate, and pentaerythritol propylene oxide-modified tetra(meth)acrylate.

[0064] In alkylene oxide-modified polyfunctional (meth)acrylates, the chain length n of the alkylene oxide is about 1 to 10. By adjusting the type and chain length of the alkylene oxide, the compatibility with the acrylic base polymer can be adjusted within an appropriate range.

[0065] Multifunctional (meth)acrylates having alkylene oxide chains (ether chains) have excellent compatibility with acrylic base polymers, as well as with polyols such as polyethylene glycol and polypropylene glycol, and can also contribute to lowering the resistance of pressure-sensitive adhesives.

[0066] The compatibility between the base polymer and the photocuring agent also depends on the molecular weight of the photocuring agent. The smaller the molecular weight of the photocuring agent, the higher the compatibility with the base polymer tends to be. From the viewpoint of compatibility with the acrylic base polymer, the molecular weight of the photocuring agent is preferably 1500 or less, more preferably 1000 or less, and may be 800 or less, 600 or less, 500 or less, or 400 or less.

[0067] Furthermore, the smaller the functional group equivalent weight of the photocuring agent (i.e., the greater the number of functional groups per unit molecular weight), the higher the compatibility with the acrylic-based polymer. From the viewpoint of compatibility with the acrylic-based polymer, the functional group equivalent weight (g / eq) of the photocuring agent is preferably 80 to 500, more preferably 90 to 400, and may be 100 to 300, 110 to 250, or 120 to 200.

[0068] The type and amount of photocuring agent affect not only the adhesive strength but also the bulk properties of the adhesive. If the base polymer of the adhesive composition is the same, the change in the shear storage modulus of the adhesive layer before photocuring is small even if the type of photocuring agent is different. On the other hand, as the content of the photocuring agent increases, the content of the base polymer in the composition becomes relatively smaller, which tends to decrease the shear storage modulus of the adhesive layer before photocuring.

[0069] The smaller the functional group equivalent weight of the photocuring agent and the greater the content of the photocuring agent, the higher the crosslinking density due to photocuring, and therefore the greater the shear storage modulus of the pressure-sensitive adhesive layer after photocuring. That is, the greater the content of the photocuring agent, the smaller the shear storage modulus of the pressure-sensitive adhesive layer before photocuring and the greater the shear storage modulus of the pressure-sensitive adhesive layer after photocuring.

[0070] From the viewpoint of increasing the adhesive strength of the pressure-sensitive adhesive after photocuring while suppressing an excessive increase in the shear storage modulus, the content of the photo-curing agent in the pressure-sensitive adhesive composition is preferably 3 to 40 parts by weight, more preferably 5 to 35 parts by weight, and may be 7 to 30 parts by weight or 10 to 25 parts by weight, relative to 100 parts by weight of the acrylic base polymer.

[0071] Two or more types of photocuring agents may be used in combination. When two or more types of photocuring agents are used in combination, it is preferable that the total amount of the photocuring agents is within the above range. For example, by using a photocuring agent having relatively high compatibility with the acrylic base polymer in combination with a photocuring agent having relatively low compatibility with the acrylic base polymer, it is possible to adjust the properties of the pressure-sensitive adhesive layer before and after photocuring, such as increasing the shear storage modulus at room temperature of the pressure-sensitive adhesive after photocuring while keeping the initial adhesive strength low.

[0072] <Photopolymerization initiator> Photopolymerization initiators generate active species upon irradiation with actinic rays and promote the curing reaction of the photocuring agent. Photopolymerization initiators include photocationic initiators (photoacid generators), photoradical initiators, and photoanionic initiators (photobase generators), depending on the type of photocuring agent. When a polyfunctional acrylate is used as the photocuring agent, it is preferable to use a photoradical initiator. Photoradical initiators are preferably photoradical generators that are cleaved by visible light or ultraviolet light with a wavelength shorter than 450 nm to generate radicals, and examples of such photoradical initiators include hydroxyketones, benzyl dimethyl ketals, aminoketones, acylphosphine oxides, benzophenones, and trichloromethyl group-containing triazine derivatives. The photoradical generators may be used alone or in combination of two or more.

[0073] The content of the photopolymerization initiator in the pressure-sensitive adhesive composition is preferably 0.001 to 5 parts by weight, more preferably 0.01 to 3 parts by weight, and even more preferably 0.03 to 1 part by weight, relative to 100 parts by weight of the acrylic base polymer. The content of the photopolymerization initiator in the pressure-sensitive adhesive composition is preferably 0.02 to 20 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 7 parts by weight, relative to 100 parts by weight of the photocuring agent.

[0074] <Antistatic agent> The PSA composition contains an antistatic agent. When the PSA contains an antistatic agent, the PSA layer has a low resistance, reducing static electricity in the PSA layer and also providing the effect of suppressing static electricity on the adherend.

[0075] Examples of antistatic agents include ionic compounds containing organic cations, alkali metal salts, ion-conductive polymers, ion-conductive fillers, conductive polymers, etc. Among these, ionic compounds containing organic cations and alkali metal salts are preferred because of their excellent compatibility with acrylic-based polymers.

[0076] The ionic compound containing an organic cation may be an ionic liquid that is a liquid at room temperature or an ionic solid that is a solid at room temperature. The ionic compound containing an organic cation is preferably composed of a fluoroorganic anion or a fluoroinorganic anion and an onium cation.

[0077] Examples of the onium cation include nitrogen-containing onium cations, sulfur-containing onium cations (for example, trialkylsulfonium cations), phosphorus-containing onium cations (for example, tetraalkylphosphonium cations), etc. Among these, nitrogen-containing onium cations are preferred.

[0078] Examples of nitrogen-containing onium cations include pyridinium cations, pyrrolidinium cations, piperidinium cations, cations having a pyrroline skeleton, cations having a pyrrole skeleton, imidazolium cations, tetrahydropyrimidinium cations, dihydropyrimidinium cations, pyrazolium cations, pyrazolinium cations, and tetraalkylammonium cations.

[0079] The fluoroorganic anion constituting the ionic compound containing an organic cation may be completely fluorinated (perfluorinated) or partially fluorinated. Examples of the fluoroorganic anion include perfluoroalkylsulfonate, bis(fluorosulfonyl)imide, and bis(perfluoroalkanesulfonyl)imide. More specifically, examples include trifluoromethanesulfonate, pentafluoroethanesulfonate, heptafluoropropanesulfonate, nonafluorobutanesulfonate, bis(fluorosulfonyl)imide, and bis(trifluoromethanesulfonyl)imide. Examples of the fluoroinorganic anion include hexafluorophosphate and tetrafluoroboric acid.

[0080] The alkali metal salt preferably comprises the above-mentioned fluoroorganic or fluoroinorganic anion and an alkali metal cation. The alkali metal cation is Li + , Na +or K + Among them, Li + is preferred.

[0081] The content of the antistatic agent in the pressure-sensitive adhesive composition is approximately 0.01 to 3 parts by weight, preferably 0.03 to 2 parts by weight, more preferably 0.05 to 1 part by weight, and even more preferably 0.1 to 0.7 parts by weight, per 100 parts by weight of the acrylic base polymer. The content of the antistatic agent in the pressure-sensitive adhesive layer 2 is approximately 0.01 to 2% by weight, preferably 0.03 to 1% by weight, more preferably 0.05 to 0.7% by weight, and even more preferably 0.1 to 0.5% by weight, and may be 0.15 to 0.4% by weight. If the amount of antistatic agent is too small, the resistance of the pressure-sensitive adhesive may not be sufficiently reduced. If the amount of antistatic agent is too large, bleed-out of the antistatic agent may cause contamination or corrosion of the adherend, or a decrease in adhesive strength.

[0082] <Polyol> The pressure-sensitive adhesive composition contains a polyol. When the pressure-sensitive adhesive contains a polyol in addition to an antistatic agent, the resistance of the pressure-sensitive adhesive layer is further reduced. Furthermore, when the pressure-sensitive adhesive composition contains a polyol, flexibility is imparted to the pressure-sensitive adhesive layer, and peeling from the adherend when repeatedly bent at low temperatures can be suppressed.

[0083] Examples of polyols include polyols (diols) having two hydroxy groups per molecule, polyols (triols) having three hydroxy groups per molecule, polyols (tetraols) having four hydroxy groups per molecule, polyols (pentaols) having five hydroxy groups per molecule, and polyols (hexaols) having six hydroxy groups per molecule.

[0084] The polyol is preferably a high molecular weight polyol, and the number average molecular weight of the polyol is preferably 300 to 30,000. If the molecular weight of the polyol is less than 300, the polyol is likely to bleed out onto the surface of the adhesive layer, causing contamination of the adherend. If the molecular weight of the polyol is excessively large, the compatibility with the acrylic base polymer and the photocuring agent is low, and the transparency of the adhesive may decrease (become cloudy).

[0085] The larger the molecular weight of the polyol, the smaller the adhesive strength of the pressure-sensitive adhesive layer 2 to the adherend before photocuring, the larger the adhesive strength after photocuring, and the larger the rate of increase in adhesive strength before and after photocuring. From the viewpoint of the adhesive properties of the pressure-sensitive adhesive layer before and after photocuring, the number-average molecular weight of the polyol is preferably 400 or more, more preferably 500 or more, even more preferably 700 or more, particularly preferably 1000 or more, and may be 2000 or more, 3000 or more, 4000 or more, or 5000 or more. From the viewpoint of compatibility, the number-average molecular weight of the polyol is preferably 25000 or less, more preferably 20000 or less, and may be 15000 or less, or 12000 or less.

[0086] Examples of high molecular weight polyols include polyether polyols, polyester polyols, polycarbonate polyols, caprolactone polyols, etc. Among these, polyether polyols are preferred because of their excellent compatibility with the acrylic base polymer and the photocuring agent.

[0087] Polyether polyols can be obtained by ring-opening addition polymerization of alkylene oxides with low-molecular-weight polyols. Examples of low-molecular-weight diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, and hydrogenated bisphenol F. Examples of low-molecular-weight triols include glycerin and trimethylolpropane.

[0088] Examples of alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran (tetramethylene oxide), etc. Diol-type polyether polyols can be obtained by ring-opening addition polymerization of alkylene oxides to low-molecular-weight diols, and triol-type polyether polyols can be obtained by ring-opening addition polymerization of ethylene oxide to low-molecular-weight triols.

[0089] The polyol is preferably a liquid at room temperature because it exhibits adequate compatibility with the acrylic base polymer. By using a polyol that is a liquid at room temperature, the polyol is more likely to act as a plasticizer, reducing the shear storage modulus of the pressure-sensitive adhesive before and after photocuring, and tending to suppress peeling from the adherend when repeatedly flexed at low temperatures. From the viewpoint of improving the flex resistance of the adhesive strength at low temperatures, the polyol preferably has a low freezing point. The freezing point of the polyol is preferably 0°C or lower, and may be -5°C or lower, -10°C or lower, -15°C or lower, -20°C or lower, or -25°C or lower.

[0090] Polyethylene glycol is solid at room temperature when its molecular weight is 500 or more. On the other hand, polypropylene glycol and polytetramethylene glycol have a lower freezing point than polyethylene glycol. For example, polypropylene glycol is liquid at room temperature even when its molecular weight is 10,000 or more, and has a significant effect of reducing the shear storage modulus of the adhesive. Therefore, polypropylene glycol or polytetramethylene glycol is preferred as the polyol, and diol-type or triol-type polypropylene glycol is particularly preferred.

[0091] The content of polyol in the PSA composition is preferably 5 to 60 parts by weight per 100 parts by weight of the acrylic base polymer. If the amount of polyol is too small, the resistance of the PSA may not be sufficiently reduced. If the amount of polyol is too large, it may cause a decrease in the adhesive strength of the PSA or contamination of the adherend. The content of polyol in the PSA composition is more preferably 10 to 50 parts by weight, and may be 15 to 45 parts by weight, 20 to 40 parts by weight, or 25 to 35 parts by weight per 100 parts by weight of the acrylic base polymer.

[0092] <Other ingredients> As described above, the photocurable pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer 2 contains an antistatic agent and a polyol in addition to an acrylic-based polymer, a photocuring agent and a photopolymerization initiator. The pressure-sensitive adhesive composition may contain components other than these.

[0093] For example, the pressure-sensitive adhesive composition may contain an oligomer having a lower molecular weight than the base polymer. For example, the pressure-sensitive adhesive composition may contain, in addition to the acrylic base polymer, an acrylic oligomer having a weight-average molecular weight of about 1,000 to 30,000. The acrylic oligomer contains a (meth)acrylic acid alkyl ester as a main constituent monomer component. From the viewpoint of increasing the adhesive strength of the pressure-sensitive adhesive layer 2 after photocuring, the glass transition temperature of the acrylic oligomer is preferably 40°C or higher, more preferably 50°C or higher. The acrylic oligomer may contain a crosslinkable functional group, similar to the acrylic base polymer.

[0094] In addition to the above components, the pressure-sensitive adhesive composition may contain additives such as a silane coupling agent, a tackifier, a plasticizer, a softener, an anti-degradant, a filler, a colorant, an ultraviolet absorber, an antioxidant, and a surfactant, within a range that does not impair the properties of the present invention.

[0095] [Preparation of reinforcing film] A reinforcing film is obtained by laminating a photocurable pressure-sensitive adhesive layer 2 on a film substrate 1. The pressure-sensitive adhesive layer 2 may be formed directly on the film substrate 1, or a pressure-sensitive adhesive layer formed in sheet form on another substrate may be transferred onto the film substrate 1.

[0096] The pressure-sensitive adhesive composition is applied to a substrate by roll coating, kiss roll coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, or the like, and the solvent is dried and removed as necessary to form a pressure-sensitive adhesive layer. A suitable drying 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.

[0097] When the pressure-sensitive adhesive composition contains a crosslinking agent, it is preferable to promote 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 achieved 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.

[0098] The introduction of a crosslinked structure into the acrylic-based polymer increases the gel fraction, which tends to increase the shear storage modulus of the adhesive layer 2. The higher the gel fraction of the adhesive before photocuring, the harder the adhesive becomes, and the less adhesive residue tends to be left on the adherend when the reinforcing film is peeled from the adherend during rework or other processes. The gel fraction of the adhesive layer 2 before photocuring (i.e., the gel fraction of the photocurable composition constituting the adhesive layer) 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 high, the shear storage modulus increases and stress-strain relaxation is poor, which may result in peeling of the adhesive at bent portions during use of a flexible device. Therefore, the gel fraction of the adhesive layer 2 before photocuring is preferably 80% or less, and may be 75% or less, 70% or less, or 65% or less.

[0099] The gel fraction can be determined as the insoluble content in a solvent such as ethyl acetate, and specifically, it is determined as the weight fraction (unit: wt%) of the insoluble content after immersing the pressure-sensitive adhesive layer in ethyl acetate for 7 days at 23°C relative to the sample before immersion. Generally, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked parts in the polymer, the higher the gel fraction.

[0100] Even after the crosslinking structure is introduced into the polymer by the crosslinking agent, the photocuring agent remains unreacted. Therefore, the pressure-sensitive adhesive layer 2 contains an acrylic base polymer with a crosslinked structure introduced therein, a photocuring agent, a photopolymerization initiator, an antistatic agent, and a polyol. When the pressure-sensitive adhesive layer 2 is formed on the film substrate 1, it is preferable to apply a release liner 5 onto the pressure-sensitive adhesive layer 2 for purposes such as protecting the pressure-sensitive adhesive layer 2. Crosslinking may be carried out after the release liner 5 is applied onto the pressure-sensitive adhesive layer 2.

[0101] When the pressure-sensitive adhesive layer 2 is formed on another substrate, the reinforcing film is obtained by transferring the pressure-sensitive adhesive layer 2 onto the film substrate 1 after drying the solvent. The substrate used to form the pressure-sensitive adhesive layer may be used as the release liner 5 as is.

[0102] As the release liner 5, a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, or polyester film is preferably used. The thickness of the release liner is typically 3 to 200 μm, preferably about 10 to 100 μm. The surface of the release liner 5 that comes into contact with the pressure-sensitive adhesive layer 2 is 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 or the like. By treating the surface of the release liner 5 with a release treatment, when the release liner 5 is peeled from the film substrate 1, peeling occurs at the interface between the pressure-sensitive adhesive layer 2 and the release liner 5, maintaining the pressure-sensitive adhesive layer 2 adhered to the film substrate 1. The release liner 5 may be antistatically treated on either or both of the release-treated and untreated surfaces. By treating the release liner 5 with an antistatic treatment, charging when the release liner is peeled from the pressure-sensitive adhesive layer can be suppressed.

[0103] [Physical properties of adhesive layer] The thickness of the pressure-sensitive adhesive layer 2 is, for example, about 1 to 300 μm. The thicker the pressure-sensitive adhesive layer 2, the more the adhesive strength to the adherend tends to improve. On the other hand, if the pressure-sensitive adhesive layer 2 is excessively thick, the fluidity before photocuring may be high, making handling difficult. Therefore, the thickness of the pressure-sensitive adhesive layer 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 achieving a thinner thickness, the thickness of the pressure-sensitive adhesive layer 2 may be 25 μm or less, 20 μm or less, or 18 μm or less.

[0104] When the reinforcing film is used in an optical device such as a display, the total light transmittance of the pressure-sensitive adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The haze of the pressure-sensitive adhesive layer 2 is preferably 2% or less, more preferably 1% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less. As described above, the acrylic base polymer, the photocuring agent, and the polyol have appropriate compatibility, which makes it difficult for the pressure-sensitive adhesive to become cloudy, and a pressure-sensitive adhesive layer with low haze is formed.

[0105] The surface resistance of the adhesive layer 2 is 1.0×10 11 Ω or less is preferable, 5.0×10 10 Ω or less is more preferable, and 3.0×10 10 Ω or less or 2.0 x 10 10 It may be Ω or less. As described above, the pressure-sensitive adhesive composition contains an antistatic agent and a polyol, so that the pressure-sensitive adhesive layer 2 can have a low resistance.

[0106] The low resistance of the pressure-sensitive adhesive layer 2 can suppress electrical damage to the adherend due to static electricity, etc., when the reinforcing film is peeled off from the adherend. The pressure-sensitive adhesive layer 2 preferably has a surface resistance within the above range even after photocuring. Generally, the surface resistance of the pressure-sensitive adhesive layer changes very little before and after photocuring. When the pressure-sensitive adhesive layer after photocuring has the above surface resistance, static electricity on the adherend to which the pressure-sensitive adhesive layer 2 is attached is removed via the pressure-sensitive adhesive layer 2, thereby suppressing charging of the adherend. Therefore, problems caused by static electricity, such as electrostatic breakdown, in devices to which the reinforcing film is attached can be suppressed.

[0107] The shear storage modulus of the adhesive layer 2 at 25°C before photocuring is 5.0 × 10 3 ~1.0×10 5 It is preferably 1 Pa. The shear storage modulus of the pressure-sensitive adhesive layer (hereinafter simply referred to as "storage modulus") is determined in accordance with the method described in JIS K7244-1 "Plastics - Test methods for dynamic mechanical properties" by reading the value at a predetermined temperature when measurement is performed at a frequency of 1 Hz in the range of -50 to 150°C at a heating rate of 5°C / min.

[0108] From the viewpoints of improving the processability of the adhesive layer, suppressing the adhesive from protruding from the edge of the reinforcing film, and preventing contamination of the adherend due to adhesive residue when the reinforcing film is peeled from the adherend, the storage modulus of the adhesive layer 2 at 25°C before photocuring is set to 7.0 × 10 3 Pa or higher is preferable, 9.0 × 10 3 Pa or more is more preferable, and 1.0×10 4 Pa or 1.5 x 10 4In order to provide flexibility to the pressure-sensitive adhesive layer, the storage modulus of the pressure-sensitive adhesive layer 2 at 25°C before photocuring may be 7.0 × 10 Pa or more. 4 Pa or less is preferable, and 5.0 × 10 4 Pa or less is more preferable, and 4.0 × 10 4 Pa or less or 3.0 x 10 4 It may be less than Pa.

[0109] From the same viewpoint as above, the storage modulus of the pressure-sensitive adhesive layer 2 at 60°C before photocuring is 5.0 × 10 3 ~8.0×10 4 Pa is preferred, 7.0 x 10 3 ~5.0×10 4 Pa is more preferable, 8.0 × 10 3 ~4.0×10 4 Pa is more preferable, and 1.0×10 4 Pa ~ 3.0 × 10 4 Pa or 1.5 x 10 4 Pa~2.5×10 4 The storage modulus at 60°C of the pressure-sensitive adhesive layer 2 before photocuring is preferably 0.3 times or more, more preferably 0.5 times or more, and may be 0.6 times or more or 0.7 times or more, the storage modulus at 25°C. The storage modulus at 60°C is generally 1.1 times or less, and may be 1.0 times or less, or 0.9 times or less, the storage modulus at 25°C.

[0110] The storage modulus of the pressure-sensitive adhesive layer 2 at −20° C. before photocuring was 1.0×10 4 ~2.0×10 5 Pa is preferred, 1.5 x 10 4 ~1.0×10 5 Pa is more preferred, 2.0 x 10 4 ~7.0×10 4 Pa or 3.0 x 10 4 ~7.0×10 4 It may be Pa. When the storage modulus at low temperature of the pressure-sensitive adhesive layer before photocuring is within the above range, the storage modulus of the pressure-sensitive adhesive layer tends to be maintained low even after photocuring.

[0111] The storage modulus of a pressure-sensitive adhesive changes rapidly near the glass transition temperature of the base polymer. As described above, a pressure-sensitive adhesive with a low storage modulus at low temperatures can be prepared by using a base polymer with a low glass transition temperature. Furthermore, the pressure-sensitive adhesive composition containing a high-molecular-weight polyol tends to have a low storage modulus at low temperatures. The storage modulus of the pressure-sensitive adhesive layer 2 at -20°C before photocuring is preferably 5 times or less, more preferably 3 times or less, and may be 2.5 times or less or 2 times or less, of the storage modulus at 25°C. The storage modulus at -20°C is generally 1.0 times or more, and may be 1.1 times or more, 1.3 times or more, or 1.5 times or more, of the storage modulus at 25°C.

[0112] From the viewpoint of facilitating peeling from the adherend and preventing adhesive residue on the adherend after peeling of the reinforcing film, the adhesive strength between the pressure-sensitive adhesive layer 2 and the adherend before photocuring is preferably 1 N / 25 mm or less, more preferably 0.5 N / 25 mm or less, even more preferably 0.3 N / 25 mm or less, and may be 0.2 N / 25 mm or less, or 0.1 N / 25 mm or less. From the viewpoint of preventing peeling of the reinforcing film during storage or handling, the adhesive strength between the pressure-sensitive adhesive layer 2 and the adherend before photocuring is preferably 0.01 N / 25 mm or more, more preferably 0.02 N / 25 mm or more, and may be 0.03 N / 25 mm or more, 0.04 N / 25 mm or more, or 0.05 N / 25 mm or more.

[0113] Adhesion strength is measured by a peel test using a polyimide film as the adherend at a tensile speed of 300 mm / min and a peel angle of 180°. Unless otherwise specified, adhesion strength is measured at 25°C.

[0114] The storage modulus and adhesive strength of the pressure-sensitive adhesive layer before photocuring depend on the composition of the base polymer, the amount of crosslinking agent introduced, the type and content of the photocuring agent and polyol, etc. The greater the amount of crosslinking agent introduced, the higher the gel fraction and the greater the storage modulus. The greater the amount of photocuring agent and polyol, the smaller the content of the base polymer in the composition, so the smaller the storage modulus tends to be.

[0115] If the base polymer, photocuring agent, and polyol are not completely miscible, the liquid photocuring agent bleeds out to the surface, forming a weak boundary layer (WBL) at the adhesive interface with the adherend, strengthening its liquid properties. When a WBL is formed, the adhesive layer retains its bulk properties, such as storage modulus, while the liquid properties of the surface (adhesive interface) become stronger, tending to weaken the adhesive strength with the adherend. If the base polymer, photocuring agent, and polyol are moderately miscible enough to maintain transparency but are not completely miscible, the WBL will form in the adhesive layer before photocuring, weakening its adhesive strength with the adherend.

[0116] When the pressure-sensitive adhesive layer 2 is photocured, the photocuring agent undergoes a curing reaction, increasing the storage modulus and the adhesive strength to the adherend. It is preferable that the pressure-sensitive adhesive layer 2 has a small storage modulus at low temperatures even after photocuring.

[0117] The storage modulus of the adhesive layer after photocuring at -20°C is 1.0 × 10 6 Pa or less is preferable, and 5.0 × 10 6 Pa or less is more preferable, and 4.0 × 10 5 Pa or less is more preferable, and 3.0 × 10 5 Pa or less, 2.5×10 5 Pa or less or 2.0 x 10 5 The pressure-sensitive adhesive layer 2 after photocuring may have a small storage modulus at low temperatures, and therefore exhibits strain relaxation properties in a low-temperature environment, thereby preventing peeling of the pressure-sensitive adhesive layer at the bent portion even when the device to which the reinforcing film is bonded is repeatedly bent or when the bent state is maintained for a long period of time.

[0118] On the other hand, if the storage modulus of the pressure-sensitive adhesive layer after photocuring is excessively small, the pressure-sensitive adhesive layer is prone to plastic deformation, and the pressure-sensitive adhesive layer may peel off from the adherend due to insufficient adhesive holding power. Therefore, the storage modulus of the pressure-sensitive adhesive layer after photocuring at -20°C should be 1.0 × 10 4 Pa or more is preferable, 3.0 × 10 4 Pa or more is more preferable, 5.0 × 104 Pa or more is more preferable, and 7.0 × 10 4 Pa or 1.0 x 10 5 It may be more than Pa.

[0119] The storage modulus at −20° C. of the pressure-sensitive adhesive layer after photocuring is preferably 13 times or less, more preferably 10 times or less, and may be 7 times or less, 5 times or less, or 4.5 times or less, of the storage modulus at −20° C. of the pressure-sensitive adhesive layer before photocuring. The storage modulus at −20° C. of the pressure-sensitive adhesive layer after photocuring may be 1.1 times or more, 1.5 times or more, 2.0 times or more, or 2.5 times or more of the storage modulus at −20° C. of the pressure-sensitive adhesive layer before photocuring.

[0120] The storage modulus of the pressure-sensitive adhesive layer at −20° C. after photocuring is preferably 7 times or less, more preferably 5 times or less, and may be 4.5 times or less or 4 times or less than the storage modulus at 25° C. The storage modulus of the pressure-sensitive adhesive layer at −20° C. before photocuring may be 1.5 times or more, 2.0 times or more, or 2.5 times or more than the storage modulus at 25° C.

[0121] To ensure adhesion at room temperature and to prevent the adhesive from protruding from the edge, the storage modulus of the adhesive layer after photocuring at 25°C is set to 5.0 × 10 3 ~1.5×10 5 Pa is preferred, 1.0 x 10 4 ~1.0×10 5 Pa is more preferable, 1.5 × 10 4 ~8.0×10 4 Pa is more preferable, and 2.0×10 4 ~7.0×10 4 Pa or 3.0 x 10 4 ~5.0×10 4 It may be Pa.

[0122] The storage modulus at 25°C of the pressure-sensitive adhesive layer after photocuring is preferably 7 times or less, and may be 5 times or less, 4 times or less, or 3 times or less, the storage modulus at 25°C of the pressure-sensitive adhesive layer before photocuring. The storage modulus at 25°C of the pressure-sensitive adhesive layer after photocuring may be 1.1 times or more, 1.3 times or more, 1.5 times or more, or 1.7 times or more, the storage modulus at 25°C of the pressure-sensitive adhesive layer before photocuring.

[0123] From the same viewpoint as above, the storage modulus of the adhesive layer after photocuring at 60°C is 5.0 × 10 3 ~1.0×10 5 Pa is preferred, 8.0 x 10 3 ~8.0×10 4 Pa is more preferable, and 1.0 × 10 4 ~6.0×10 4 Pa is more preferable, and 2.0×10 4 Pa ~ 5.0 × 10 4 Pa or 2.5 x 10 4 Pa ~ 4.5 × 10 4 It may be Pa.

[0124] The storage modulus of the pressure-sensitive adhesive layer after photocuring at 60°C is preferably 0.3 times or more, more preferably 0.5 times or more, and may be 0.6 times or more or 0.7 times or more, the storage modulus at 25°C. The storage modulus at 60°C may be 1.1 times or less, 1.0 times or less, 0.9 times or less, or 0.8 times or less the storage modulus at 25°C.

[0125] The storage modulus at 60°C of the pressure-sensitive adhesive layer after photocuring is preferably 7 times or less, and may be 5 times or less, 4 times or less, or 3 times or less, of the storage modulus at 60°C of the pressure-sensitive adhesive layer before photocuring. The storage modulus at 60°C of the pressure-sensitive adhesive layer after photocuring may be 1.1 times or more, 1.3 times or more, 1.5 times or more, or 1.7 times or more of the storage modulus at 60°C of the pressure-sensitive adhesive layer before photocuring.

[0126] From the viewpoint of adhesive reliability during practical use of the device, the adhesive strength between the adhesive layer and the adherend after photocuring is preferably 1.5 N / 25 mm or more, more preferably 2.0 N / 25 mm or more. From the viewpoint of suppressing peeling of the adhesive when the flexible device is repeatedly bent at the same location, the adhesive strength between the adhesive layer and the adherend after photocuring may be 2.5 N / 25 mm or more or 3.0 N / 25 mm or more.

[0127] The adhesive strength between the pressure-sensitive adhesive layer and the adherend after photocuring is preferably at least 5 times, more preferably at least 10 times, even more preferably at least 15 times, and may be at least 20 times, at least 30 times, or at least 50 times the adhesive strength between the pressure-sensitive adhesive layer and the adherend before photocuring. As described above, by adjusting the types (compatibility with the base polymer) and amounts of the photocuring agent and polyol, it is possible to keep the adhesive strength before photocuring (initial adhesive strength) low and increase the adhesive strength of the pressure-sensitive adhesive after photocuring.

[0128] [Use of reinforcing film] The reinforced film of the present invention is used by being attached to a device or a device component. The reinforced film 10 has a pressure-sensitive adhesive layer 2 fixed to a film substrate 1, and has low adhesive strength to the adherend after being attached to the adherend and before being photocured. Therefore, the reinforced film can be easily peeled from the adherend before being photocured.

[0129] The adherend to which the reinforced film is attached is not particularly limited, and examples thereof include various electronic devices, optical devices, and their component parts. In one embodiment, the reinforced film is attached to the surface of a foldable flexible device. The foldable device has a hinge portion and can be folded around this hinge portion. The folding angle can be set arbitrarily, and the device may be bent (folded) by 180°. When the device is a display device, the reinforced film may be attached to the surface on the screen side, or to the back side (housing). A flexible device that is configured to be bendable at a predetermined location such as a hinge portion repeatedly bends and stretches at the same location when in use.

[0130] The reinforcing film may be attached to the entire surface of the adherend, or may be selectively attached only to the areas requiring reinforcement (reinforcement target areas). Alternatively, the reinforcing film may be attached to the entire areas requiring reinforcement (reinforcement target areas) and the areas not requiring reinforcement (non-reinforcement target areas), and then the reinforcing film attached to the non-reinforcement target areas may be cut and removed. Before the adhesive is photocured, the reinforcing film is temporarily attached to the surface of the adherend, so it can be easily peeled and removed from the surface of the adherend. The reinforcing film may be attached to the areas requiring reinforcement and the areas not requiring reinforcement, and the areas requiring reinforcement may be selectively irradiated with light to photocure the adhesive, and then the reinforcing film may be selectively peeled and removed from the non-reinforcement target areas where the adhesive is not yet cured.

[0131] By laminating a reinforcing film, appropriate rigidity is imparted, which is expected to improve the handleability and prevent breakage of thin members such as flexible devices. 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 also be laminated roll-to-roll to a mother roll of a device manufactured by a roll-to-roll process.

[0132] 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. An adherend whose surface has been activated contains many active groups such as hydroxyl groups, carbonyl groups, and carboxyl groups, which tend to increase adhesive strength due to intermolecular interactions with the polar functional groups of the base polymer of the adhesive. In particular, when the adherend is a polyimide, the activation treatment activates amide acids, terminal amino groups, carboxyl groups (or carboxylic anhydride groups), etc., which interact strongly with the polar functional groups of the base polymer, and therefore the activation treatment may significantly increase the initial adhesive strength.

[0133] If the initial adhesive strength is excessively high, it may be difficult to perform peeling operations such as rework. As described above, since the base polymer is substantially free of nitrogen atoms, an excessive increase in the initial adhesive strength to an adherend whose surface has been activated can be suppressed.

[0134] After laminating the reinforcing film to the adherend, the pressure-sensitive adhesive layer 2 is irradiated with actinic rays to photocure the pressure-sensitive adhesive layer. Examples of actinic rays include ultraviolet light, visible light, infrared light, X-rays, α-rays, β-rays, and γ-rays. Ultraviolet light is preferred as the actinic rays because it can inhibit curing of the pressure-sensitive adhesive layer during storage and facilitates curing. The irradiation intensity and irradiation time of the actinic rays may be appropriately set depending on the composition, thickness, etc. of the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer 2 may be irradiated with actinic rays from either the film substrate 1 side or the adherend side, or may be irradiated with actinic rays from both sides.

[0135] As described above, by applying the reinforced film of the present invention to an adherend, appropriate rigidity is imparted and stress is alleviated and dispersed, thereby suppressing various defects that may occur in the manufacturing process, improving production efficiency, and improving yield. Because the reinforced film is easily peeled from the adherend before photocuring the pressure-sensitive adhesive layer, rework is easy even if lamination or adhesion defects occur. Furthermore, processing such as selectively removing the reinforced film from areas other than the area to be reinforced is also easy.

[0136] When the completed device is in use, the reinforcing film prevents damage to the device even if an external force is suddenly applied due to the device being dropped, a heavy object being placed on the device, the device being hit by a flying object, etc. Furthermore, because the reinforcing film is firmly adhered to the device after the adhesive is photocured, the reinforcing film is unlikely to peel off even during long-term use, providing excellent reliability.

[0137] In a device with a reinforced film of the present invention, which is formed by bonding the reinforced film to a flexible device using a resin substrate, the reinforced film is unlikely to peel off at the bent portion even when the device is repeatedly bent or maintained in a bent state for a long period of time. Furthermore, since static electricity on the resin substrate of the device can be removed via the pressure-sensitive adhesive layer, problems such as electrostatic breakdown of the device caused by charging (static electricity) can be suppressed. [Example]

[0138] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0139] [Polymerization of acrylic polymers] <Polymer A> A reaction vessel equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas inlet tube was charged with 95 parts by weight of butyl acrylate (BA) and 5 parts by weight of acrylic acid (AA) as monomers, 0.2 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 233 parts by weight of ethyl acetate as a solvent. Nitrogen gas was introduced and the mixture was purged with nitrogen for approximately 1 hour while stirring. The mixture was then heated to 60°C and reacted for 7 hours to obtain a solution of acrylic polymer A with a weight-average molecular weight (Mw) of 600,000.

[0140] <Polymers B and C> The amounts of the monomers charged were changed as shown in Table 1. Solutions of polymers B and C were obtained in the same manner as in the polymerization of polymer A except for the above.

[0141] The monomer ratios used for acrylic polymers A to C and the glass transition temperatures of the polymers are listed in Table 1. The glass transition temperatures were calculated from the monomer ratios used based on Fox's formula. BA: Butyl acrylate 2EHA: 2-ethylhexyl acrylate AA: Acrylic acid 2HEA: 2-hydroxyethyl acrylate

[0142] [Table 1]

[0143] [Preparation of reinforcing film] Example 1 (Preparation of Pressure-Sensitive Adhesive Composition) To a solution of acrylic polymer A (100% by weight as solids of the polymer), 0.1 parts by weight of a tetrafunctional epoxy crosslinking agent (Mitsubishi Gas Chemical Company, Ltd., "Tetrad C") as a crosslinking agent, 0.2 parts by weight of zirconium tetraacetylacetonate (Matsumoto Fine Chemical Co., Ltd., "ZC-150") as a crosslinking catalyst, 20 parts by weight of polyethylene glycol #600 diacrylate (Shin-Nakamura Chemical Co., Ltd., "NK Ester A-600") as a photocuring agent, 0.3 parts by weight of IGM Resins' "Omnirad 651" as a photopolymerization initiator, 0.2 parts by weight of 1-butyl-3-methylpyridinium bistrifluoromethanesulfonylimide (Nippon Carlit Co., Ltd., "CIL-312") as an antistatic agent, and 30 parts by weight of polypropylene glycol (AGC's "Preminol S3011") as a polyol were added and mixed uniformly to prepare a pressure-sensitive adhesive composition having the composition shown in Table 2.

[0144] (application of adhesive solution and cross-linking) The above-mentioned adhesive composition was applied to a 50 μm-thick polyethylene terephthalate film using a fountain roll so that the dried thickness would be 25 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated surface of a release liner (a 25 μm-thick polyethylene terephthalate film with antistatic treatment on both sides and silicone release treatment on one side) was attached to the adhesive-coated surface. Subsequently, aging treatment was performed for 4 days in an atmosphere at 25°C to promote crosslinking, resulting in a reinforced film in which a photocurable adhesive sheet was fixedly laminated onto a polyethylene terephthalate film substrate and a release liner was temporarily attached thereon.

[0145] <Comparative Example 1> (Preparation of Pressure-Sensitive Adhesive Composition) A solution of acrylic polymer C (100% by weight of polymer solids) was mixed with 0.25 parts by weight of a trifunctional isocyanate crosslinking agent (Tosoh's "Coronate HX") as a crosslinking agent, 0.03 parts by weight of iron acetylacetonate (Nippon Chemical Industry's "Nacem Ferric") as a crosslinking catalyst, 10 parts by weight of trimethylolpropane EO-modified (n = 1) triacrylate (Toagosei's "Aronix M-350") as a photocuring agent, 0.3 parts by weight of IGM Resins' "Omnirad 651" as a photopolymerization initiator, and 0.2 parts by weight of 1-butyl-3-methylpyridinium bistrifluoromethanesulfonylimide (Nippon Carlit's "CIL-312") as an antistatic agent. The adhesive composition shown in Table 2 was prepared by adding the mixture.

[0146] (application of adhesive solution and cross-linking) Using the above pressure-sensitive adhesive composition, coating and crosslinking were carried out in the same manner as in Example 1 to prepare a reinforcing film.

[0147] <Examples 2 to 14 and Comparative Examples 2 to 6> Pressure-sensitive adhesive compositions were prepared by changing the type of acrylic polymer, the type and amount of crosslinking agent, the type and amount of photocuring agent, the type of antistatic agent, and the type and amount of polyol as shown in Table 2. In Examples 2 to 11 and Comparative Examples 3 to 6, 0.2 parts by weight of zirconium tetraacetylacetonate was used as the crosslinking catalyst, as in Example 1, and in Comparative Example 2, 0.25 parts by weight of iron acetylacetonate was used as the crosslinking catalyst, as in Comparative Example 1. Using pressure-sensitive adhesive compositions having the compositions shown in Table 2, coating and crosslinking were carried out in the same manner as in Example 1 to prepare reinforcing films. In Table 2, the amounts of crosslinking agent, photocuring agent, antistatic agent, and polyol are the amounts added per 100 parts by weight of the solid content of the acrylic polymer. Details of the crosslinking agent, photocuring agent, antistatic agent, and polyol are as follows:

[0148] (Crosslinking agent) TC: N,N,N',N'-tetraglycidyl-m-xylylenediamine (tetrafunctional epoxy compound, "Tetrad C" manufactured by Mitsubishi Gas Chemical Company) C-HX: Isocyanurate of hexamethylene diisocyanate (Tosoh's "Coronate HX")

[0149] (light curing agent) A200: Polyethylene glycol #200 (n = 4) diacrylate ("NK Ester A200" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent weight 151 g / eq) A600: Polyethylene glycol #600 (n=14) diacrylate ("NK Ester A600" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent weight 371 g / eq) M350: Trimethylolpropane EO-modified (n=1) triacrylate (Toagosei "Aronix M-350", functional group equivalent weight 143g / eq)

[0150] (antistatic agent) CIL312: 1-butyl-3-methylpyridinium bistrifluoromethanesulfonylimide ("CIL-312" manufactured by Nippon Carlit) AS110: 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (Dai-ichi Kogyo Seiyaku "Elexcel AS-110")

[0151] (Polyol) S3011: Polypropylene glycol, triol type (AGC "Preminol S-3011", Mn=10000) GP3000: Polypropylene glycol, triol type (Sanyo Chemical Industries, Ltd. "Sannyx GP-3000", Mn=3000) GP1000: Polypropylene glycol, triol type (Sanyo Chemical Industries, Ltd. "Sannyx GP-1000", Mn=1000) GP400: Polypropylene glycol, triol type (Sanyo Chemical Industries, Ltd. "Sannyx GP-400", Mn=400) GP250: Polypropylene glycol, triol type (Sanyo Chemical Industries, Ltd. "Sannyx GP-250", Mn=250) PP3000: Polypropylene glycol, diol type (Sanyo Chemical Industries, Ltd. "Sannyx PP-3000", Mn=3000) PTGL3000: Polytetramethylene glycol, triol type (Hodogaya Chemical Co., Ltd. "PTGL3000", Mn=3000)

[0152] Example 15 A film substrate having an antistatic layer of a conductive polymer (PEDOT / PSS) on one side of a 50 μm-thick polyethylene terephthalate film was used, and a pressure-sensitive adhesive layer was formed on the antistatic layer-forming surface of the film substrate using the same pressure-sensitive adhesive composition as in Example 13. The antistatic layer (30 nm thick) was formed by adding the following components (A) to (D) to a water / ethanol mixed solvent in a weight ratio of 1:1, stirring and mixing for about 20 minutes to prepare an antistatic treatment solution with a solids content of about 0.4%. This solution was then applied to one side of the polyethylene terephthalate film using a bar coater, and the film was then dried by heating at 130°C for 2 minutes.

[0153] (A) As a binder, a 25% aqueous dispersion of saturated copolymer polyester resin ("Binalol MD-1480" manufactured by Toyobo): 30 parts by weight in terms of solid content (B) As a binder, an aqueous dispersion of an acrylic resin obtained by emulsion polymerization of methyl methacrylate / butyl acrylate / hydroxyethyl methacrylate in a weight ratio of 85 / 10 / 5: 70 parts by weight in terms of solid content (C) Aqueous solution containing 0.5% poly(3,4-ethylenedioxythiophene) and 0.8% polystyrene sulfonate having a weight-average molecular weight of 150,000 as a conductive polymer (manufactured by Bytron PHC Stark): 20 parts by weight of solid content (D) Melamine-based crosslinking agent (Sumitomo Chemical's "Sumimal M-50W"): 5 parts by weight in solid content

[0154] [evaluation] <Appearance> The reinforcing film was visually observed, and those that were cloudy were rated as NG, and those that were transparent were rated as OK. For Comparative Example 2 in which cloudiness was observed, further evaluation was not carried out.

[0155] <Surface resistance of adhesive layer> The release liner was peeled off from the reinforcing film to expose the adhesive layer (before photocuring). A probe (TREK Model 152P-2P) was brought into contact with the surface of the adhesive layer in an environment of 25°C and 50% relative humidity, and the surface resistance was measured using a resistivity meter (TREK Model 152-1) at an applied voltage of 10 V for a voltage application time of 10 seconds.

[0156] <Storage modulus> The adhesive composition was applied to the release liner and crosslinked in the same manner as above to prepare an adhesive sheet (before photocuring). A release liner was attached to the surface of the adhesive layer of the adhesive sheet before photocuring to shield it from oxygen, and the adhesive sheet was exposed to 2000 mJ / cm 2 of a 365 nm LED lamp. 2 The adhesive sheet before and after photo-curing were laminated to prepare a measurement sample with a thickness of approximately 1.5 mm. Dynamic viscoelasticity measurements were performed under the following conditions using an Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific, and the shear storage modulus G' values ​​were read at -20°C and 25°C. (Measurement conditions) Deformation mode: Torsion Measurement frequency: 1Hz Heating rate: 5°C / min Measurement temperature: -50~150℃ Shape: Parallel plate 8.0mmφ

[0157] <Adhesive strength> A 25 μm-thick polyimide film (Ube Industries, "Upilex 25S") was attached to a glass plate using double-sided adhesive tape (Nitto Denko, "No. 531") to obtain a polyimide film substrate for measurement. The release liner was peeled off from the surface of a reinforced film cut into a 25 mm wide x 100 mm long piece, and the piece was then attached to the polyimide film substrate for measurement using a hand roller to prepare a pre-photocuring test sample. The pre-photocuring test sample was then photocured by irradiating the reinforced film side (PET film substrate side) with ultraviolet light to photocure the adhesive layer, thereby preparing a post-photocuring test sample. Using these test samples, the edge of the film substrate of the reinforced film was held with a chuck and the reinforced film was peeled 180° at a pulling rate of 300 mm / min to measure peel strength.

[0158] <Bending test> The release liner was peeled off from the surface of the reinforced film, and a 12.5 μm-thick polyimide film (Ube Industries, "Upilex 12.5SN") was laminated to the surface of the adhesive layer using a hand roller. This laminate was cut into a 25 mm wide x 100 mm long piece, and the adhesive layer was photocured by irradiating the reinforced film side (PET film substrate side) with UV light to obtain a test specimen. Using a planar no-load U-shaped stretch tester (Yuasa System Co., Ltd.), a bending jig was attached to the short edge of the test specimen. Repeated bending tests were performed under the following conditions in a thermostatic chamber at -20°C or 25°C and 50% relative humidity, with the reinforced film side (film substrate side) facing inward. After the repeated bending test, the specimens were rated as "OK" if there was no peeling or lifting between the reinforced film and the substrate, and "NG" if there was peeling or lifting. (Test conditions) Bending radius: 3 mm Bending angle: 180° Bending speed: 1 second / time Number of bends: 200,000

[0159] <Stainability of adherends> The release liner was peeled off from the surface of the reinforcement film, and a polyimide film (Ube Industries' "Upilex 25S") was laminated to the surface of the adhesive layer using a hand roller. After leaving it to stand at 25°C for 30 minutes, the reinforcement film was peeled off from the polyimide film, and the surface of the polyimide film was visually inspected under fluorescent light to check for contamination. Those that were found to be contaminated by adhesive matter were rated as NG, and those that were not were rated as OK.

[0160] The composition of the adhesive for each reinforcing film and the evaluation results are shown in Table 2.

[0161] [Table 2]

[0162] In Examples 1 to 11, the pressure-sensitive adhesive composition contains an antistatic agent and a polyol (triol-type polypropylene glycol) in addition to a base polymer, a crosslinking agent, a photocuring agent, and a photopolymerization initiator, and the surface resistance of the pressure-sensitive adhesive is 2×10 10 The adhesive strength to the polyimide film increased by more than 10 times after photocuring, and the shear storage modulus G' at -20°C after photocuring was 5 x 10 5 The adhesive strength was below 1 Pa, and no peeling of the adhesive layer was observed after repeated bending tests, demonstrating good adhesive reliability. In Example 12, which used diol-type polypropylene glycol as the polyol, the adhesive had low resistance, similar to Example 1, and also showed good adhesive reliability in the bending test.

[0163] Example 13, which used an antistatic agent having bis(fluorosulfonyl)imide, a non-perfluorinated organic fluoroanion, had a reduced surface resistance compared to Example 1. Example 13 had a lower initial adhesive strength compared to Example 1, but after photocuring, showed high adhesive strength equivalent to that of Example 1. Example 15, in which a pressure-sensitive adhesive layer was formed on a substrate having an antistatic layer, had a lower surface resistance of the pressure-sensitive adhesive layer compared to Example 13, and the storage modulus and adhesive strength were similar to those of Example 13.

[0164] In Example 14, which used triol-type polytetramethylene glycol as the polyol, the pressure-sensitive adhesive had low resistance and good adhesion reliability in the bending test, but showed a higher surface resistance value than Example 13. A comparison of Example 6 and Example 13, which used polyols with equivalent molecular weights, shows that polypropylene glycol contributes more to reducing resistance than polytetramethylene glycol.

[0165] In Comparative Example 3, in which the pressure-sensitive adhesive composition did not contain a polyol, the surface resistance of the pressure-sensitive adhesive was higher than in Example 5, and the G' values ​​of the pressure-sensitive adhesive before and after photocuring were also high. In Comparative Example 3, the G' value of the pressure-sensitive adhesive layer after photocuring was large at -20°C, and the pressure-sensitive adhesive layer peeled off after repeated bending tests at -20°C, indicating poor adhesion reliability. In Comparative Example 4, in which the amount of crosslinker was reduced to 0.1 parts by weight, the G' value of the pressure-sensitive adhesive layer after photocuring was large at -20°C, and the pressure-sensitive adhesive layer peeled off after repeated bending tests at -20°C, similar to Comparative Example 3.

[0166] In Comparative Example 1, which used polymer C with a low glass transition temperature, G' before and after photocuring was small, and no peeling of the adhesive layer was observed during the bending test, but the surface resistance was high, and no resistance-reducing effect of the antistatic agent was observed.

[0167] These results show that when the adhesive composition contains a polyol in addition to an antistatic agent, the resistivity of the adhesive is reduced, imparting antistatic properties, and the polyol acts as a plasticizer, reducing G' at low temperatures, thereby improving adhesion reliability in bending tests.

[0168] In Comparative Example 2, in which 30 parts by weight of polyol was added to the composition of Comparative Example 1, the PSA became cloudy. The cloudiness is thought to be due to the low compatibility of the polyol with other components of the PSA composition.

[0169] In Example 11, which used M350 as the photocuring agent, as in Comparative Example 2, no clouding was observed. Therefore, in Comparative Example 2, the clouding is believed to be due to poor compatibility between the acrylic base polymer and / or crosslinker and the polyol. In Example 10, which used a combination of a low-glass transition temperature polymer B containing 2EHA as the main monomer component and an epoxy-based crosslinker, no clouding of the adhesive was observed. Therefore, in Comparative Example 2, the base polymer does not contain the carboxyl group-containing monomer acrylic acid, but contains the hydroxyl group-containing monomer 2-hydroxyethyl acrylate, and contains an isocyanate crosslinker. In other words, in the Examples, the base polymer contains a carboxyl group-containing monomer as a monomer component, and a crosslinked structure is introduced by the epoxy-based crosslinker, which results in excellent compatibility with the polyol, and therefore, the adhesive has high transparency.

[0170] In Comparative Example 5, in which the amount of polyol added was increased compared to Examples 1, 3, 4, and 9, the surface of the polyimide film was contaminated after the reinforcing film was peeled off. Furthermore, in Comparative Example 5, the surface resistance of the PSA was higher than in Examples 1, 3, 4, and 9, and it was found that adding an excess amount of polyol did not have the effect of reducing resistance.

[0171] A comparison of Examples 1, 3, 4, and 9 with Comparative Example 5 showed a tendency that the greater the amount of polyol added, the smaller the adhesive strength of the pressure-sensitive adhesive before photocuring and the greater the rate of increase in adhesive strength due to photocuring. In these examples, it is thought that WBL was formed by the polyol in the pressure-sensitive adhesive before photocuring, and that the liquid properties of the surface of the pressure-sensitive adhesive layer (the adhesive interface with the adherend) became stronger, thereby reducing the adhesive strength with the adherend. In Comparative Example 7, excessive WBL was formed, and the polyol precipitated on the surface is thought to have caused contamination of the adherend.

[0172] In Comparative Example 6, in which a low molecular weight polyol was used, contamination of the adherend was observed, as in Comparative Example 5. The low molecular weight polyol has little interaction with the base polymer and photocuring agent of the pressure-sensitive adhesive composition, and is likely to bleed out onto the surface of the pressure-sensitive adhesive layer, which is thought to be the cause of the contamination of the adherend.

[0173] Furthermore, in Comparative Example 6, the adhesive strength of the adhesive before photocuring was greater, the adhesive strength after photocuring was smaller, and the rate of increase in adhesive strength before and after photocuring was smaller compared to Examples 1, 6, 7, and 8. Comparing Examples 1, 6, 7, and 8 with Comparative Example 6, it was observed that the larger the molecular weight of the polyol, the smaller the adhesive strength of the adhesive before photocuring, the larger the adhesive strength after photocuring, and the larger the rate of increase in adhesive strength before and after photocuring. It is thought that low-molecular-weight polyols have little effect as WBLs before photocuring the adhesive layer, but tend to precipitate near the surface of the adhesive layer after photocuring and act as WBLs.

[0174] The above results show that when the photocurable adhesive composition contains an antistatic agent and a polyol of a specified molecular weight, the adhesive has low resistance and antistatic properties, has low initial adhesive strength, and exhibits excellent adhesive properties after photocuring.Furthermore, the shear storage modulus in the low temperature range is low, and peeling of the adhesive is suppressed even when repeatedly bent. [Explanation of symbols]

[0175] 1. Film substrate 2. Adhesive layer 10 Reinforcement film 5 Release liner 20 Adherent

Claims

1. A film substrate and a pressure-sensitive adhesive layer fixedly laminated on one main surface of the film substrate, the pressure-sensitive adhesive layer is made of a photocurable composition containing an acrylic-based polymer, a photocuring agent, a photopolymerization initiator, an antistatic agent, and a polyol; the acrylic base polymer contains a carboxyl group-containing monomer as a monomer unit, and a crosslinked structure is introduced using 0.03 to 2 parts by weight of an epoxy crosslinking agent per 100 parts by weight of the polymer; The polyol has a number average molecular weight of 300 to 30,000, The photocurable composition contains 5 to 60 parts by weight of the polyol relative to 100 parts by weight of the acrylic base polymer. Reinforcement film.

2. The reinforced film of claim 1 , wherein the polyol is polypropylene glycol or polytetramethylene glycol.

3. The reinforced film according to claim 1 , wherein the polyol is a diol or triol polypropylene glycol.

4. The reinforced film according to any one of claims 1 to 3, wherein the acrylic base polymer has a glass transition temperature of -40°C or lower.

5. 4. The reinforcing film according to claim 1, wherein the photocurable composition contains 3 to 40 parts by weight of the photocuring agent relative to 100 parts by weight of the acrylic base polymer.

6. The reinforcing film according to any one of claims 1 to 3, wherein the photocuring agent is a polyfunctional (meth)acrylate.

7. The reinforcing film according to any one of claims 1 to 3, wherein the photocuring agent is a polyfunctional (meth)acrylate containing an alkylene oxide chain.

8. After photocuring, the pressure-sensitive adhesive layer has a shear storage modulus of 1.0×10 at −20° C. ４ ~1.0 x 10 ６ The reinforcing film according to any one of claims 1 to 3, wherein Pa.

9. The pressure-sensitive adhesive layer has a shear storage modulus of 1.0×10 at −20° C. before photocuring. ４ ~2.0 x 10 ５ Pa, and the shear storage modulus at 25°C is 5.0 × 10 ３ ~1.0 x 10 ５ The reinforcing film according to any one of claims 1 to 3, wherein Pa.

10. The reinforcing film according to any one of claims 1 to 3, wherein the adhesive layer has an adhesive strength to a polyimide film of 1 N / 25 mm or less before photocuring.

11. The reinforcing film according to any one of claims 1 to 3, wherein the adhesive strength of the pressure-sensitive adhesive layer to the polyimide film after photocuring is at least five times the adhesive strength of the pressure-sensitive adhesive layer to the polyimide film before photocuring.

12. The surface resistance of the pressure-sensitive adhesive layer is 1×10 １１ The reinforcing film according to any one of claims 1 to 3, having a stiffness of Ω or less.

13. A method for manufacturing a device with a reinforcing film in which a reinforcing film is attached to a surface of a foldable device, comprising: The pressure-sensitive adhesive layer of the reinforcing film according to any one of claims 1 to 3 is attached to a surface of a foldable device, photocuring the pressure-sensitive adhesive layer; A method for manufacturing a device with a reinforcing film.

14. A device with a reinforcing film, in which a reinforcing film is attached to the surface of a foldable device, The reinforcing film includes a film substrate and a pressure-sensitive adhesive layer fixedly laminated on one main surface of the film substrate, the pressure-sensitive adhesive layer is attached to a device surface, the pressure-sensitive adhesive layer is a photocured product obtained by photocuring a photocurable pressure-sensitive adhesive composition containing an acrylic-based polymer and a photocuring agent, and further contains an antistatic agent and a polyol having a number average molecular weight of 300 to 20,000; the acrylic base polymer contains a carboxyl group-containing monomer as a monomer unit, and a crosslinked structure is introduced using 0.03 to 2 parts by weight of an epoxy crosslinking agent per 100 parts by weight of the polymer; The pressure-sensitive adhesive layer has a shear storage modulus of 1.0×10 at −20° C. ４ ~1.0 x 10 ６ Pa, Device with reinforced film.

15. The surface resistance of the pressure-sensitive adhesive layer is 1×10 １１ The device with the reinforced film according to claim 14, having a resistance of Ω or less.

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