Reinforcing film, device with reinforcing film and manufacturing method thereof

Abstract

The reinforcing film (10) is provided with an adhesive layer (2) that is adhesively laminated on one main surface of a film substrate (1). The adhesive layer is formed from a photocurable composition containing an acrylic base polymer having a cross-linked 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 300-30,000, and the amount of the polyol contained in the photocurable composition is preferably 5-60 parts by weight per 100 parts by weight of the acrylic base polymer.

Description

Technical Field

[0001] The present invention relates to a reinforcement film attached to a surface of a device and to a device having the reinforcement film and a method for manufacturing the device. Background Art

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

[0003] By temporarily bonding the adhesive film to the surface of the device or its components before use, such as during assembly, processing, and transportation of the device, damage or breakage of the adherend can be suppressed. Patent Documents 1 and 2 disclose a reinforcing film having an adhesive layer formed of a photocurable adhesive composition on a film substrate.

[0004] The reinforcing film has a high gel fraction of the adhesive and has low adhesion immediately after being attached to the adherend, so it is easy to peel off from the adherend. Therefore, it is possible to rework the adherend, and it is also possible to selectively peel off and remove the reinforcing film from the part of the adherend that does not need to be reinforced. The adhesive of the reinforcing film is firmly bonded to the adherend through photocuring, so that the film substrate is permanently bonded to the surface of the adherend, and can be used as a reinforcing material for surface protection of devices, etc.

[0005] In recent years, organic EL (Electro-Luminescence) panels using bendable substrates (flexible substrates) such as resin films have been put into practical use, and a bendable flexible display has been proposed. A foldable device is repeatedly bent at the same position. At the bent portion, compressive stress is applied to the inside and tensile stress is applied to the outside, strain is generated at the bent portion and its periphery, and sometimes the adhesive is peeled off from the adherend. Patent document 4 proposes the use of a photocurable adhesive as an adhesive for the reinforcing film of a foldable device, and the photocurable adhesive contains an acrylic base polymer with a low glass transition temperature.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2020-41113

[0009] Patent Document 2: Japanese Patent Application Publication No. 2020-134540

[0010] Patent Document 3: Japanese Patent Application Publication No. 2019-20726

[0011] Patent Document 4: International Publication No. 2022 / 050009 Summary of the invention

[0012] Problems to be solved by the invention

[0013] As described in Patent Document 3, foldable devices are easily charged because they use resin films as substrate materials, which sometimes causes electrostatic damage to the device caused by charging (static electricity). Patent Document 2 proposes to prevent the reinforcing film from being charged by providing an antistatic layer on the back side of the film substrate of the reinforcing film (the side opposite to the side where the adhesive layer is attached). However, since the back side of the substrate of the reinforcing film is separated from the adherend, it is difficult to properly suppress the device from being charged even if an antistatic layer is provided on the back side of the substrate.

[0014] In order to suppress the device from being charged, it is effective to make the adhesive layer provided in contact with the device contain an antistatic agent to reduce the resistance of the adhesive layer and make it have antistatic properties. However, even if an antistatic agent is added to the adhesive of the reinforcement film described in Patent Document 4, the adhesive is not sufficiently low in resistance. If the amount of the antistatic agent added is increased, the antistatic agent will seep out, causing a decrease in the bonding strength between the adhesive layer and the device and contamination of the device surface.

[0015] In view of the above circumstances, an object of the present invention is to provide a reinforcing film which is not easily peeled off due to a bending test, can be applied to a foldable device, and can contribute to the antistatic properties of the device.

[0016] Solutions for solving problems

[0017] The reinforcing film of the present invention comprises an adhesive layer laminated on one main surface of the film substrate. The adhesive layer is formed by a photocurable composition comprising an acrylic base polymer, a photocuring agent, a photopolymerization initiator, an antistatic agent and a polyol. The glass transition temperature of the acrylic base polymer is preferably below -40°C.

[0018] The number average molecular weight of the polyol contained in the photocurable composition is preferably 300 to 30,000. The amount of the polyol in the photocurable composition is preferably 5 to 60 parts by weight relative to 100 parts by weight of the acrylic base polymer. The polyol may be polypropylene glycol or polytetramethylene glycol. The polyol may be a diol type polypropylene glycol or a triol type polypropylene glycol.

[0019] The acrylic base polymer contains one or more monomer units selected from the group consisting of hydroxyl-containing monomers and carboxyl-containing monomers, and a crosslinking structure is introduced by bonding the hydroxyl group and / or carboxyl group of the acrylic base polymer with a crosslinking agent such as an isocyanate crosslinking agent or an epoxy crosslinking agent. The amount of the crosslinking agent may be about 0.03 to 2 parts by weight relative to 100 parts by weight of the acrylic polymer.

[0020] The photocurable composition constituting the 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. As the photocuring agent, for example, a multifunctional (meth)acrylate can be used. The multifunctional (meth)acrylate can be an alkylene oxide-modified multifunctional (meth)acrylate modified with an alkylene oxide such as ethylene oxide or propylene oxide.

[0021] The surface resistance of the adhesive layer is preferably 1×10 11 The shear storage modulus of the adhesive layer at -20°C after photocuring is preferably 1.0×10 4 ~1.0×10 6 Pa. The shear storage modulus of the adhesive layer at -20°C before photocuring can be 1.0×10 4 ~2.0×10 5 Pa. The shear storage modulus of the adhesive layer at 25°C before photocuring can be 5.0×10 3 ~1.0×10 5 Pa.

[0022] The adhesive strength of the adhesive layer to the polyimide film before photocuring is preferably 1 N / 25 mm or less. The adhesive strength of the adhesive layer to the polyimide film after photocuring is preferably 5 times or more of the adhesive strength of the adhesive layer to the polyimide film before photocuring.

[0023] By attaching the reinforcing film to the surface of the device and photocuring the adhesive layer, a device with a reinforcing film can be obtained. The device can be a bendable flexible device.

[0024] Effects of the Invention

[0025] In the reinforcing film of the present invention, the adhesive layer is formed of a photocurable composition, and the adhesive strength to the adherend is increased by photocuring the adhesive layer after bonding to the adherend. Since the adhesive strength to the adherend is low before photocuring, it is easy to peel off from the adherend.

[0026] The adhesive layer of the reinforcing film includes an antistatic agent and a polyol, and the resistance is reduced, so the charging of the adhesive layer itself is suppressed, and it also helps to prevent the adherend from being static. In addition, the adhesive layer includes a polyol, and the shear storage modulus is also low after photocuring, and the relaxation of stress strain is high. Therefore, even if the same part is repeatedly bent, the peeling of the adhesive layer at the bent part is also suppressed, and the bonding reliability is excellent. Therefore, the reinforcing film of the present invention is also suitable for foldable devices using a resin film substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a cross-sectional view showing the laminated structure of the reinforcing film.

[0028] Figure 2 It is a cross-sectional view showing the laminated structure of the reinforcing film.

[0029] Figure 3 It is a cross-sectional view showing a device to which a reinforcing film is attached. DETAILED DESCRIPTION

[0030] Figure 1 1 is a cross-sectional view showing an embodiment of a reinforcing film. The reinforcing film 10 has an adhesive layer 2 on one main surface of a film substrate 1. The adhesive layer 2 is laminated on one main surface of the film substrate 1. The adhesive layer 2 is a photocurable adhesive formed of a photocurable composition, and is cured by irradiation with active light such as ultraviolet rays, thereby increasing the bonding strength with the adherend.

[0031] Figure 2 It is a cross-sectional view of a reinforcing film in which a release liner 5 is temporarily bonded to the main surface of the pressure-sensitive adhesive layer 2 . Figure 3 It is a cross-sectional view showing a state where the reinforcing film 10 is attached to the surface of the device 20 .

[0032] The release liner 5 is peeled off from the surface of the adhesive layer 2, and the exposed surface of the adhesive layer 2 is attached to the surface of the device 20, thereby attaching the reinforcement film 10 to the surface of the device 20. In this state, the adhesive layer 2 is in a state before photocuring, and the reinforcement film 10 (adhesive layer 2) is temporarily attached to the device 20. By photocuring the adhesive layer 2, the adhesive force at the interface between the device 20 and the adhesive layer 2 is increased, and the device 20 and the reinforcement film 10 are bonded.

[0033] “Adhesion” refers to a state where two stacked layers are firmly bonded and cannot or are difficult to separate at the interface. “Temporary adhesion” refers to a state where the bonding force between two stacked layers is weak and they can be easily separated at the interface.

[0034] exist Figure 2In the reinforcement film shown, the film substrate 1 and the adhesive layer 2 are bonded, and the release liner 5 is temporarily bonded to the adhesive layer 2. When the film substrate 1 and the release liner 5 are peeled off, peeling occurs at the interface between the adhesive layer 2 and the release liner 5, and the adhesive layer 2 is maintained in a state of being bonded to the film substrate 1. No adhesive remains on the release liner 5 after peeling.

[0035] Figure 3 In the device with a reinforcing film shown, before the adhesive layer 2 is photocured, the device 20 and the adhesive layer 2 are in a temporary bonding state. When the film substrate 1 and the device 20 are peeled off, peeling occurs at the interface between the adhesive layer 2 and the device 20, so that the adhesive layer 2 is maintained in a state of being fixed to the film substrate 1. Since no adhesive remains on the device 20, it is easy to perform peeling operations such as rework and cutting. After the adhesive layer 2 is photocured, the adhesive force between the adhesive layer 2 and the device 20 increases and becomes a fixed state, so it is not easy to peel the film 1 from the device 20.

[0036] [Film base material]

[0037] A flexible plastic film is used as the film substrate 1 of the reinforcing film 10. In order to bond the film substrate 1 and the adhesive layer 2, it is preferred that the surface of the film substrate 1 on which the adhesive layer 2 is attached is not subjected to a release treatment.

[0038] The thickness of the film substrate is, for example, about 4 to 150 μm. From the viewpoint of strengthening the device by imparting rigidity, mitigating impact, etc., the thickness of the film substrate 1 is preferably 5 μm or more, more preferably 12 μm or more, further preferably 20 μm or more, and particularly preferably 25 μm or more. From the viewpoint of making the reinforced film flexible and foldable, the thickness of the film substrate 1 is preferably 125 μm or less, more preferably 100 μm or less. From the viewpoint of taking into account both mechanical strength and flexibility, the compressive strength of the film substrate 1 is preferably 100 to 3000 kg / cm 2 , more preferably 200 to 2900 kg / cm 2 , more preferably 300 to 2800 kg / cm 2 , particularly preferably 400 to 2700 kg / cm 2 .

[0039] As the plastic material constituting the film substrate 1, polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, polyetheretherketone, polyethersulfone, polyarylate resins, aromatic polyamide resins, etc. can be cited. In the reinforcing film for optical devices such as displays, the film substrate 1 is preferably a transparent film. In addition, in the case where the adhesive layer 2 is photocured by irradiating active light from the film substrate 1 side, the film substrate 1 preferably has transparency for the active light used in the curing of the adhesive layer. From the perspective of both mechanical strength and transparency, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, transparent polyimide, and transparent aromatic polyamide are preferably used. In the case of irradiating active light from the adherend side, as long as the adherend has transparency to the active light, the film substrate 1 may also be opaque to the active light.

[0040] Functional coatings such as an easy-adhesion layer, an easy-slip layer, a release layer, an antistatic layer, a hard coating layer, and an antireflection layer may also be provided on the surface of the film substrate 1. It should be noted that, as described above, in order to adhere the film substrate 1 to the adhesive layer 2, it is preferred that no release layer be provided on the surface of the film substrate 1 on which the adhesive layer 2 is attached. In the case where an antistatic layer is provided on the surface of the film substrate, it is preferred that an antistatic layer be provided on the surface of the film substrate 1 on which the adhesive layer 2 is attached from the viewpoint of reducing the surface resistance of the adhesive layer.

[0041] [Adhesive layer]

[0042] The adhesive layer 2 fixedly laminated on the film substrate 1 is formed of a photocurable composition. The photocurable composition constituting the adhesive layer 2 contains an acrylic base polymer, a photocuring agent, and a photopolymerization initiator, and further contains an antistatic agent and a polyol.

[0043] The adhesive layer 2 has a small adhesive force to adherends such as devices and device parts before photocuring, so it is easy to peel off. The adhesive layer 2 has improved adhesive force to the adherend through photocuring, so even when the device is used, the reinforcement film is not easy to peel off from the device surface, and the bonding reliability is excellent.

[0044] Photocurable adhesives are hardly cured under normal storage conditions, but are cured by irradiation with active light such as ultraviolet rays. Therefore, the reinforcing film of the present invention can arbitrarily set the curing timing of the adhesive layer 2, and has the advantage of being able to flexibly cope with the lead time of the process.

[0045] <Base polymer>

[0046] The base polymer is the main component of the adhesive composition and is the main factor determining the adhesive strength and storage modulus of the adhesive layer before photocuring. From the perspective of excellent optical transparency and adhesion, and easy control of adhesive strength and storage modulus, the adhesive composition preferably contains an acrylic polymer as the base polymer.

[0047] As the acrylic polymer, it is preferable to use a polymer containing an alkyl (meth)acrylate as a main monomer component. In addition, in this specification, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0048] As the alkyl (meth)acrylate, it is preferred to use an alkyl (meth)acrylate having an alkyl group with 1 to 20 carbon atoms. The alkyl group of the alkyl (meth)acrylate may be a straight chain or a branched chain. Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-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, nonyl (meth)acrylate, propylene (meth)acrylate, and tert-butyl (meth)acrylate. isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like.

[0049] Among the alkyl (meth)acrylates exemplified, from the viewpoint of reducing the shear storage modulus at low temperatures by lowering the Tg of the acrylic base polymer, thereby suppressing the peeling of the adhesive layer during repeated bending, alkyl (meth)acrylates C 1－9 The glass transition temperature of the homopolymer of the (meth)acrylic acid C having a glass transition temperature of -50°C or less as a homopolymer is preferably -50°C or less. 1－9Specific examples of the alkyl ester 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 them, butyl acrylate (BA) and 2-ethylhexyl acrylate are preferred.

[0050] From the perspective of lowering the Tg of the acrylic base polymer, 2-ethylhexyl acrylate (2EHA) is particularly preferred. If the monomer with the largest content (main monomer) in the constituent monomers of the acrylic base polymer is 2EHA, the glass transition temperature of the acrylic base polymer can be made below -60°C or below -65°C. On the other hand, in the adhesive composition, the polyol (details will be described below) acts as a plasticizer, so the shear storage modulus at low temperatures becomes smaller, which helps to improve the bonding reliability. Therefore, in the case where the adhesive composition contains a polyol, even if the glass transition temperature of the acrylic base polymer is around -50°C, sufficient bonding reliability can be ensured. From the perspective of improving adhesion and the compatibility of the acrylic base polymer with the polyol, the main monomer of the acrylic base polymer is particularly preferably butyl acrylate (BA).

[0051] The content of the alkyl (meth)acrylate is preferably 70% by weight or more, more preferably 80% by weight or more, and further 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, relative to the total amount of the monomer components constituting the acrylic base polymer. 1－9 The amount of the alkyl ester is within the above range, and more preferably the total amount of 2-ethylhexyl acrylate and butyl acrylate is within the above range. The amount of butyl acrylate may also be within the above range.

[0052] The acrylic acid base polymer preferably contains a monomer component having a crosslinkable functional group as a copolymer component. As monomers having a crosslinkable functional group, hydroxyl-containing monomers and carboxyl-containing monomers can be listed. The acrylic acid base polymer can have both hydroxyl-containing monomers and carboxyl-containing monomers as copolymer components, or can have only one of them as a copolymer component. There is a tendency that the cohesive force is improved and the peelability of the adhesive layer 2 before photocuring from the adherend is improved by introducing a crosslinking structure into the acrylic acid base polymer.

[0053] Examples of hydroxyl-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, and 4-(hydroxymethyl)cyclohexylmethyl (meth)acrylate. Among them, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred because they contribute greatly to improving the adhesive strength of the adhesive after photocuring.

[0054] Examples of the carboxyl group-containing monomer include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc. Among them, acrylic acid is particularly preferred because it contributes greatly to improving adhesive strength.

[0055] In the acrylic base polymer, the total amount of the hydroxyl group-containing monomer and the carboxyl group-containing monomer is preferably 0.5 to 15% by weight, more preferably 1 to 10% by weight, and further preferably 2 to 7% by weight relative to the total amount of the constituent monomer components. In the case where the acrylic base polymer contains a carboxyl group, the acrylic base polymer exhibits high compatibility with the polyol, so the acrylic base polymer preferably contains a carboxyl group-containing monomer such as (meth)acrylic acid as a constituent monomer component, and the content of the carboxyl group-containing monomer is preferably within the above range.

[0056] The acrylic base polymer may contain nitrogen-containing monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinylcarboxamides, and N-vinylcaprolactam as constituent monomer components.

[0057] The acrylic base polymer may contain monomer components other than those mentioned above. The acrylic base polymer may contain, for example, vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfonic group-containing monomers, phosphoric acid group-containing monomers, acid anhydride group-containing monomers, etc. as monomer components.

[0058] The acrylic acid base polymer before the cross-linking structure is introduced can be substantially free of nitrogen atoms. The ratio of nitrogen in the constituent elements of the acrylic acid base polymer can 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 acid base polymer substantially free of nitrogen atoms, when the adherend is subjected to surface activation treatment, there is a tendency that the adhesion (initial adhesion) of the adhesive layer before photocuring is suppressed. By not using nitrogen-containing monomers such as cyano-containing monomers, lactam-containing monomers, amide-containing monomers, and morpholine ring-containing monomers as constituent monomer components of the acrylic acid base polymer, an acrylic acid base polymer substantially free of nitrogen atoms can be obtained. Relative to the total amount of constituent monomer components of the acrylic acid base polymer, the amount of nitrogen-containing monomers can be 1 wt% or less, 0.5 wt% or less, 0.1 wt% or less, 0.05 wt% or less or 0.

[0059] The glass transition temperature of the acrylic base polymer is preferably below -40°C, and may be below -45°C. The glass transition temperature is the temperature (peak temperature) at which the loss tangent tanδ reaches a maximum value in the viscoelasticity measurement. By making the glass transition temperature sufficiently lower than the ambient temperature of the device, the shear storage modulus G' of the adhesive layer within the ambient temperature range is small, and peeling during repeated bending tends to be suppressed.

[0060] The theoretical Tg calculated by the Fox equation can be used instead of the glass transition temperature obtained by viscoelasticity measurement. The theoretical Tg is calculated by the following Fox equation from the glass transition temperature Tg of the homopolymer of the monomer component constituting the acrylic base polymer. i and the weight fraction W of each monomer component i to calculate.

[0061] 1 / Tg=Σ(W i / Tg i )

[0062] Tg is the glass transition temperature of the polymer chain (unit: K), W i is the weight fraction of monomer component i constituting the chain segment (copolymerization ratio based on weight), Tg i is the glass transition temperature of the homopolymer of monomer component i (unit: K). As the glass transition temperature of the homopolymer, the value described in the third edition of Polymer Handbook (John Wiley & Sons, Inc., 1989) can be used. The Tg of the homopolymer of the monomer not described in the above literature can be the peak temperature of tan δ obtained by dynamic viscoelasticity measurement.

[0063] The lower limit of the glass transition temperature of the acrylic base polymer is not particularly limited, and can generally be above -80°C, above -70°C, above -65°C, above -60°C, or above -55°C. From the viewpoint of reducing the shear storage modulus at low temperatures and suppressing peeling during repeated bending, the lower the glass transition temperature of the acrylic base polymer, the more preferred. In the case where the adhesive composition contains a polyol, even if the glass transition temperature of the acrylic base polymer is above -55°C, the adhesive after photocuring has excellent bonding reliability and can suppress peeling from the adherend during repeated bending at low temperatures.

[0064] The above-mentioned monomer components are polymerized by various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization to obtain an acrylic polymer as a base polymer. From the perspective of the balance of characteristics such as the adhesion and holding power of the adhesive, and the cost, solution polymerization is preferred. As a solvent for solution polymerization, ethyl acetate, toluene, etc. can be used. The solution concentration is usually about 20 to 80% by weight. As a polymerization initiator, various known polymerization initiators such as azo and peroxide can be used. In order to adjust the molecular weight, a chain transfer agent can be used. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

[0065] 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 crosslinking structure is introduced into the acrylic base polymer, the molecular weight of the acrylic base polymer refers to the molecular weight before the crosslinking structure is introduced.

[0066] <Cross-linking agent>

[0067] From the viewpoint of giving the adhesive a moderate cohesive force, exhibiting adhesive strength, and ensuring the peelability of the adhesive layer from the adherend before photocuring, it is preferred to introduce a crosslinking structure into the base polymer. For example, a crosslinking agent is added to a solution obtained by polymerizing an acrylic base polymer, and heating is performed as needed to introduce a crosslinking structure.

[0068] As the crosslinking agent, there can be cited isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, metal chelate crosslinking agents, etc. These crosslinking agents react with functional groups such as hydroxyl groups and carboxyl groups introduced into the acrylic base polymer to form a crosslinked structure. From the perspective of high reactivity with hydroxyl groups and carboxyl groups of the acrylic base polymer and easy introduction of a crosslinked structure, isocyanate crosslinking agents and epoxy crosslinking agents are preferred.

[0069] As described above, from the viewpoint of compatibility with polyols, the acrylic base polymer preferably has a carboxyl group derived from a carboxyl group-containing monomer such as acrylic acid. It is preferred to introduce a crosslinking structure into the acrylic base polymer having a carboxyl group using an epoxy crosslinking agent.

[0070] As the epoxy crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in one molecule is used. The epoxy crosslinking agent may be an epoxy crosslinking agent having 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 the epoxy crosslinking agent include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidyl aniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether. As the epoxy crosslinking agent, commercially available products such as "DENACOL" manufactured by Nagase ChemteX, and "TETRAD X" and "TETRAD C" manufactured by Mitsubishi Gas Chemical can also be used.

[0071] As the isocyanate-based crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule is used. 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-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; trimethylolpropane / toluene diisocyanate trimer adduct (e.g., "TAKENATE D101E" manufactured by Mitsui Chemicals), trimethylolpropane / hexamethylene diisocyanate trimer adduct (e.g., "Coronate HL" manufactured by Tosoh), trimethylolpropane adduct of xylylene diisocyanate (e.g., "TAKENATE D110N" manufactured by Mitsui Chemicals), isocyanurate of hexamethylene diisocyanate (e.g., "Coronate 100N" manufactured by Tosoh), and isocyanurate of toluene diisocyanate (e.g., "Coronate 100N" manufactured by Mitsui Chemicals). HX") and other isocyanate adducts.

[0072] The amount of the crosslinking agent used may be appropriately adjusted according to the composition and molecular weight of the acrylic base polymer. The amount of the crosslinking agent used is about 0.03 to 2 parts by weight, preferably 0.05 to 1 part by weight, more preferably 0.08 to 0.8 part by weight, and may also be 0.1 to 0.5 part by weight, relative to 100 parts by weight of the acrylic base polymer.

[0073] In order to promote the formation of a crosslinked structure, a crosslinking catalyst may be used. The amount of the crosslinking catalyst used is usually 0.5 parts by weight or less based on 100 parts by weight of the acrylic base polymer.

[0074] <Light curing agent>

[0075] The adhesive composition constituting the adhesive layer 2 contains a photocuring agent in addition to an acrylic base polymer. When the adhesive layer 2 composed of a photocurable adhesive composition is photocured after being attached to an adherend, the adhesive strength to the adherend is improved.

[0076] As the photocuring agent, a photocurable monomer or a photocurable oligomer can be used. As the photocuring agent, a compound having two or more ethylenically unsaturated bonds in one molecule is preferred. In addition, the photocuring agent is preferably a compound showing compatibility with an acrylic base polymer and a polyol. From the aspect of showing appropriate compatibility with an acrylic base polymer, the photocuring agent is preferably liquid at room temperature.

[0077] It is preferred to use a polyfunctional (meth)acrylate as the photocuring agent because of its high compatibility with the acrylic base polymer. The polyfunctional (meth)acrylate is typically an ester of a polyol and (meth)acrylic acid. Specific examples of the multifunctional (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, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate, isoprene (meth)acrylate, and the like.

[0078] The multifunctional (meth)acrylate may be an ester of a polyol modified with an alkylene oxide 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.

[0079] Specific examples of the alkylene oxide-modified multifunctional (meth)acrylate 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, pentaerythritol propylene oxide-modified tetra(meth)acrylate, and the like.

[0080] In the alkylene oxide-modified polyfunctional (meth)acrylate, 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 to an appropriate range.

[0081] The polyfunctional (meth)acrylate having an alkylene oxide chain (ether chain) has excellent compatibility with the acrylic base polymer and also has excellent compatibility with polyols such as polyethylene glycol and polypropylene glycol. In addition, the polyfunctional (meth)acrylate having an alkylene oxide chain can also contribute to lowering the resistance of the adhesive.

[0082] The compatibility of the base polymer and the photocuring agent is also affected by the molecular weight of the photocuring agent. There is a tendency that the smaller the molecular weight of the photocuring agent is, the higher the compatibility with the base polymer is. 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 also be 800 or less, 600 or less, 500 or less, or 400 or less.

[0083] In addition, there is a tendency that the smaller the functional group equivalent of the photocuring agent (i.e., the greater the number of functional groups per unit molecular weight), the higher the compatibility with the acrylic base polymer. From the viewpoint of compatibility with the acrylic base polymer, the functional group equivalent (g / eq) of the photocuring agent is preferably 80 to 500, more preferably 90 to 400, and may also be 100 to 300, 110 to 250, or 120 to 200.

[0084] The type and amount of the photocuring agent not only affects the adhesive force, but also the bulk properties of the adhesive. As long as the base polymer of the adhesive composition is the same, the shear storage modulus of the adhesive layer before photocuring will change little even if the type of the photocuring agent is different. On the other hand, if the content of the photocuring agent increases, the content of the base polymer in the composition will be relatively reduced, so the shear storage modulus of the adhesive layer before photocuring tends to become smaller.

[0085] There is a tendency that the smaller the functional group equivalent of the photocuring agent and the greater the content of the photocuring agent, the higher the crosslinking density based on photocuring, and therefore the shear storage modulus of the adhesive layer after photocuring is greater. In other words, there is a tendency that the greater the content of the photocuring agent, the smaller the shear storage modulus of the adhesive layer before photocuring, and the greater the shear storage modulus of the adhesive layer after photocuring.

[0086] From the viewpoint of improving the adhesive strength of the photocured adhesive and suppressing an excessive increase in the shear storage modulus, the content of the photocuring agent in the adhesive composition is preferably 3 to 40 parts by weight, more preferably 5 to 35 parts by weight, and may also 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.

[0087] Two or more photocuring agents may also be used in combination. When two or more photocuring agents are used in combination, the total amount of the photocuring agents is preferably within the above range. For example, by using a photocuring agent having relatively high compatibility with the acrylic base polymer and a photocuring agent having relatively low compatibility with the acrylic base polymer in combination, the initial adhesive force can be suppressed to a low level, and the shear storage modulus of the adhesive at room temperature after photocuring can be increased, and the properties of the adhesive layer before and after photocuring can be adjusted.

[0088] <Photopolymerization initiator>

[0089] The photopolymerization initiator generates active species by irradiation with active light rays, and promotes the curing reaction of the photocuring agent. As the photopolymerization initiator, a photocation initiator (photoacid generator), a photoradical initiator, a photoanion initiator (photobase generator), etc. are used according to the type of the photocuring agent. When a multifunctional acrylate is used as a photocuring agent, a photoradical initiator is preferably used. As the photoradical initiator, a photoradical generator that generates free radicals by cleavage by visible light or ultraviolet light with a wavelength shorter than 450nm is preferred, and hydroxy ketones, benzil dimethyl ketals, amino ketones, acyl phosphine oxides, benzophenones, trichloromethyl-containing triazine derivatives, etc. can be listed. The photoradical generator can be used alone or in combination of two or more.

[0090] The content of the photopolymerization initiator in the adhesive composition is preferably 0.001 to 5 parts by weight, more preferably 0.01 to 3 parts by weight, and further 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 adhesive composition is preferably 0.02 to 20 parts by weight, more preferably 0.05 to 10 parts by weight, and further preferably 0.1 to 7 parts by weight relative to 100 parts by weight of the photocuring agent.

[0091] <Antistatic Agent>

[0092] The adhesive composition contains an antistatic agent. When the adhesive contains an antistatic agent, the resistance of the adhesive layer can be reduced, the charge of the adhesive layer can be reduced, and the effect of suppressing the charge of the adherend can be imparted.

[0093] Examples of the antistatic agent include ionic compounds containing organic cations, alkali metal salts, ion-conductive polymers, ion-conductive fillers, conductive polymers, etc. Among them, ionic compounds containing organic cations and alkali metal salts are preferred because of their excellent compatibility with the acrylic base polymer.

[0094] The ionic compound containing an organic cation may be an ionic liquid which is liquid at room temperature, or may be an ionic solid which is solid at room temperature. The ionic compound containing an organic cation preferably consists of a fluorine organic anion or a fluorine inorganic anion and an onium cation.

[0095] Examples of the onium cation include nitrogen-containing onium cations, sulfur-containing onium cations (eg, trialkylsulfonium cations), phosphorus-containing onium cations (eg, tetraalkylphosphonium cations), and the like. Among them, nitrogen-containing onium cations are preferred.

[0096] Examples of the nitrogen-containing onium cation include pyridinium cation, pyrrolidinium cation, piperidinium cation, cations having a pyrroline skeleton, cations having a pyrrole skeleton, imidazolium cations, tetrahydropyrimidinium cations, dihydropyrimidinium cations, pyrazolium cations, pyrazolinium cations, and tetraalkylammonium cations.

[0097] The fluorinated organic anions constituting the ionic compound containing the organic cation may be completely fluorinated (perfluorinated) or partially fluorinated. As the fluorinated organic anions, perfluoroalkyl sulfonates, bis(fluorosulfonyl)imides, bis(perfluorinated alkanesulfonyl)imides, more specifically, for example, trifluoromethanesulfonates, pentafluoroethanesulfonates, heptafluoropropanesulfonates, nonafluorobutanesulfonates, bis(fluorosulfonyl)imides, bis(trifluoromethanesulfonyl)imides, etc. may be cited. As the fluorinated inorganic anions, hexafluorophosphoric acid, tetrafluoroboric acid, etc. may be cited.

[0098] The alkali metal salt is preferably composed of the above-mentioned fluorine organic anion or fluorine inorganic anion and an alkali metal cation. The alkali metal cation is Li + 、Na + or K + , among which Li + .

[0099] The content of the antistatic agent in the adhesive composition is about 0.01 to 3 parts by weight relative to 100 parts by weight of the acrylic base polymer, preferably 0.03 to 2 parts by weight, more preferably 0.05 to 1 part by weight, and further preferably 0.1 to 0.7 parts by weight. The content of the antistatic agent in the adhesive layer 2 is about 0.01 to 2% by weight, preferably 0.03 to 1% by weight, more preferably 0.05 to 0.7% by weight, further preferably 0.1 to 0.5% by weight, and may also be 0.15 to 0.4% by weight. If the amount of the antistatic agent is small, it is sometimes impossible to make the adhesive sufficiently low in resistance. When the amount of the antistatic agent is too much, it may become the cause of contamination and corrosion of the adherend due to the seepage of the antistatic agent, and the reduction of the adhesive force.

[0100] <Polyol>

[0101] The adhesive composition contains a polyol. By including a polyol in addition to an antistatic agent, the adhesive layer can be further reduced in resistance. In addition, by including a polyol in the adhesive composition, flexibility can be imparted to the adhesive layer, and peeling from the adherend can be suppressed when repeatedly bent at low temperatures.

[0102] Examples of the polyol include a polyol having two hydroxyl groups in one molecule (diol), a polyol having three hydroxyl groups in one molecule (triol), a polyol having four hydroxyl groups in one molecule (tetraol), a polyol having five hydroxyl groups in one molecule (pentaol), and a polyol having six hydroxyl groups in one molecule (hexaol).

[0103] As the polyol, a high molecular weight polyol is preferably used, and the number average molecular weight of the polyol is preferably 300 to 30000. When the molecular weight of the polyol is less than 300, the polyol is easy to ooze out on the surface of the adhesive layer, causing contamination of the adherend. When the molecular weight of the polyol is too large, the compatibility with the acrylic base polymer and the photocuring agent is low, and the transparency of the adhesive is sometimes reduced (causing white turbidity).

[0104] There is a tendency that the larger the molecular weight of the polyol is, the smaller the adhesive force of the adhesive layer 2 before photocuring to the adherend is, the larger the adhesive force after photocuring is, and the greater the rate of increase of the adhesive force before and after photocuring is. From the viewpoint of the adhesive properties of the adhesive layer before and after photocuring, the number average molecular weight of the polyol is preferably 400 or more, more preferably 500 or more, further preferably 700 or more, particularly preferably 1000 or more, and may also 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 also be 15000 or less or 12000 or less.

[0105] Examples of the high molecular weight polyol include polyether polyol, polyester polyol, polycarbonate polyol, caprolactone polyol, etc. Among them, polyether polyol is preferred because of its excellent compatibility with the acrylic base polymer and the photocuring agent.

[0106] Polyether polyols can be obtained by ring-opening addition polymerization of alkylene oxides and low molecular weight polyols. Examples of low molecular weight diols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, neopentyl glycol, pentylene glycol, 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, hydrogenated bisphenol F, etc. Examples of low molecular weight triols include glycerol and trimethylolpropane.

[0107] Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran (tetramethylene oxide), etc. A diol-type polyether polyol can be obtained by ring-opening addition polymerization of an alkylene oxide with a low molecular weight diol, and a triol-type polyether polyol can be obtained by ring-opening addition polymerization of ethylene oxide with a low molecular weight triol.

[0108] From the viewpoint of showing moderate compatibility with acrylic base polymers, the polyol is preferably liquid at room temperature. By using a polyol that is liquid at room temperature, the polyol easily acts as a plasticizer, and there is a tendency that the shear storage modulus of the adhesive before and after photocuring is reduced, and the peeling from the adherend is suppressed when repeatedly bent at low temperatures. From the viewpoint of improving the bending resistance of the adhesive force at low temperatures, the polyol is preferably a low freezing point. The freezing point of the polyol is preferably below 0°C, and may also be below -5°C, below -10°C, below -15°C, below -20°C, or below -25°C.

[0109] When the molecular weight of polyethylene glycol is 500 or more, it is solid at room temperature. On the other hand, the freezing point of polypropylene glycol and polytetramethylene glycol is lower than that of polyethylene glycol. For example, even if the molecular weight of polypropylene glycol is 10,000 or more, it is liquid at room temperature, and the shear storage modulus of the adhesive is greatly reduced. Therefore, as the polyol, polypropylene glycol or polytetramethylene glycol is preferred, among which diol-type polypropylene glycol or triol-type polypropylene glycol is preferred.

[0110] The content of the polyol in the adhesive composition is preferably 5 to 60 parts by weight relative to 100 parts by weight of the acrylic base polymer. If the amount of the polyol is too small, it is sometimes impossible to fully reduce the resistance of the adhesive. If the amount of the polyol is too much, it may become a cause of reduced adhesion of the adhesive and contamination of the adherend. The content of the polyol in the adhesive composition is more preferably 10 to 50 parts by weight relative to 100 parts by weight of the acrylic base polymer, and may also be 15 to 45 parts by weight, 20 to 40 parts by weight, or 25 to 35 parts by weight.

[0111] <Other ingredients>

[0112] As described above, the photocurable adhesive composition constituting the adhesive layer 2 contains an antistatic agent and a polyol in addition to the acrylic base polymer, the photocuring agent, and the photopolymerization initiator. The adhesive composition may contain components other than these.

[0113] For example, the adhesive composition may contain an oligomer having a molecular weight less than the base polymer. For example, in addition to the acrylic base polymer, the adhesive composition may also contain an acrylic oligomer having a weight average molecular weight of about 1,000 to 30,000. The acrylic oligomer contains (meth) alkyl acrylate as the main monomer component. From the viewpoint of improving the adhesive force of the adhesive layer 2 after photocuring, the glass transition temperature of the acrylic oligomer is preferably above 40°C, more preferably above 50°C. The acrylic oligomer may also contain a crosslinkable functional group like the acrylic base polymer.

[0114] In addition to the above components, the adhesive composition may contain additives such as silane coupling agents, tackifiers, plasticizers, softeners, anti-degradation agents, fillers, colorants, ultraviolet absorbers, antioxidants, and surfactants within a range that does not impair the characteristics of the present invention.

[0115] [Production of reinforcement film]

[0116] The reinforcement film is obtained by laminating the photocurable adhesive layer 2 on the film substrate 1. The adhesive layer 2 may be directly formed on the film substrate 1, or an adhesive layer formed in a sheet form on another substrate may be transferred to the film substrate 1.

[0117] By using roller coating, roller lick coating, gravure coating, reverse coating, roller brush, spray coating, dip roller coating, rod coating, blade coating, air knife coating, curtain coating, die lip coating, die coating, etc., the above-mentioned adhesive composition is applied to the substrate, and the solvent is dried and removed as needed to form an adhesive layer. As a drying method, an appropriate method can be appropriately adopted. The heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and 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 more preferably 10 seconds to 10 minutes.

[0118] When the adhesive composition contains a crosslinking agent, it is preferred to crosslink by heating or aging at the same time as the solvent drying or after the solvent drying. The heating temperature and heating time are appropriately set according to the type of crosslinking agent used, and crosslinking is usually carried out by heating for about 1 minute to 7 days in the range of 20°C to 160°C. The heating for drying and removing the solvent can also serve as the heating for crosslinking.

[0119] There is a tendency that the gel fraction will increase and the shear storage modulus of the adhesive layer 2 will increase by introducing a cross-linking structure into the acrylic base polymer. The higher the gel fraction of the adhesive before photocuring, the harder the adhesive is, and the more the tendency of the paste residue on the adherend can be suppressed when the reinforcing film is peeled off from the adherend due to rework or the like. The gel fraction of the adhesive layer 2 before photocuring (that is, the gel fraction of the photocurable composition constituting the adhesive layer) is preferably 25% or more, more preferably 30% or more, and may also be 35% or more, 40% or more, or 45% or more. On the other hand, when the gel fraction is too large, the shear storage modulus will increase and the relaxation of stress strain will decrease, so when using a flexible device, the adhesive may sometimes peel off at the bent portion. Therefore, the gel fraction of the adhesive layer 2 before photocuring is preferably 80% or less, and may also be 75% or less, 70% or less, or 65% or less.

[0120] The gel fraction can be obtained as the insoluble component in a solvent such as ethyl acetate, and specifically, as the weight fraction (unit: weight %) of the insoluble component after the adhesive layer is immersed in ethyl acetate at 23°C for 7 days 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 greater the gel fraction.

[0121] After the crosslinking structure is introduced into the polymer by the crosslinking agent, the photocuring agent also remains in an unreacted state. Therefore, the adhesive layer 2 contains an acrylic base polymer with a crosslinking structure introduced, a photocuring agent, a photopolymerization initiator, an antistatic agent, and a polyol. When the adhesive layer 2 is formed on the film substrate 1, it is preferred to attach a release liner 5 to the adhesive layer 2 for the purpose of protecting the adhesive layer 2. It is also possible to attach the release liner 5 to the adhesive layer 2 before crosslinking.

[0122] When the adhesive layer 2 is formed on another substrate, the solvent is dried and then the adhesive layer 2 is transferred to the film substrate 1 to obtain a reinforcement film. The substrate used for forming the adhesive layer can be used as the release liner 5 as it is.

[0123] As the release liner 5, a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, polyester film, etc. is preferably used. The thickness of the release liner is usually 3 to 200 μm, preferably about 10 to 100 μm. It is preferred that the contact surface of the release liner 5 with the adhesive layer 2 is subjected to a release treatment using a release agent such as a silicone, fluorine, long-chain alkyl or fatty acid amide, or silica powder. By subjecting the surface of the release liner 5 to a release treatment, when the film substrate 1 and the release liner 5 are peeled off, peeling occurs at the interface between the adhesive layer 2 and the release liner 5, and the adhesive layer 2 is maintained in a state of being adhered to the film substrate 1. As far as the release liner 5 is concerned, an antistatic treatment can be applied to either or both of the release-treated surface and the non-treated surface. By subjecting the release liner 5 to an antistatic treatment, the charge when the release liner is peeled off from the adhesive layer can be suppressed.

[0124] [Physical properties of adhesive layer]

[0125] The thickness of the adhesive layer 2 is, for example, about 1 to 300 μm. There is a tendency that the greater the thickness of the adhesive layer 2, the higher the adhesion to the adherend. On the other hand, when the thickness of the adhesive layer 2 is too large, the fluidity before photocuring is high, and it is sometimes difficult to handle. Therefore, the thickness of the adhesive layer 2 is preferably 3 to 100 μm, more preferably 5 to 50 μm, further preferably 6 to 40 μm, and particularly preferably 8 to 30 μm. From the viewpoint of thinning, the thickness of the adhesive layer 2 can be less than 25 μm, less than 20 μm, or less than 18 μm.

[0126] When the reinforcing film is used for an optical device such as a display, the total light transmittance of the adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. The haze of the adhesive layer 2 is preferably 2% or less, more preferably 1% or less, further preferably 0.7% or less, and particularly preferably 0.5% or less. As described above, by making the acrylic base polymer, the photocuring agent, and the polyol have appropriate compatibility, an adhesive layer in which the adhesive is not easily turbid and has a small haze can be formed.

[0127] The surface resistance of the adhesive layer 2 is preferably 1.0×10 11 Ω or less, more preferably 5.0×10 10 Ω or less, and can also be 3.0×10 10 Ω or less or 2.0×10 10 As described above, the adhesive composition contains an antistatic agent and a polyol, so that the resistance of the adhesive layer 2 can be reduced.

[0128] By making the adhesive layer 2 low-resistance, it is possible to suppress electrical damage to the adherend caused by static electricity when the reinforcement film is peeled off from the adherend. The adhesive layer 2 preferably has a surface resistance within the above range after photocuring. Normally, the surface resistance of the adhesive layer before and after photocuring hardly changes. The adhesive layer after photocuring has the above surface resistance, and the static electricity of the adherend to which the adhesive layer 2 is attached is removed by the adhesive layer 2, so that the adherend can be suppressed from being charged. Therefore, it is possible to suppress adverse conditions caused by static electricity, such as electrostatic damage in the device to which the reinforcement film is attached.

[0129] The shear storage modulus of the adhesive layer 2 before photocuring at 25°C is preferably 5.0×10 3 ~1.0×10 5 Pa. The shear storage modulus of the adhesive layer (hereinafter simply referred to as "storage modulus") is obtained by reading the value at a predetermined temperature when measuring at a frequency of 1 Hz in a range of -50 to 150°C at a heating rate of 5°C / min according to the method described in JIS K7244-1 "Plastics - Test methods for dynamic mechanical properties".

[0130] The storage modulus of the adhesive layer 2 before photocuring at 25°C is preferably 7.0×10 3 Pa or more, more preferably 9.0×10 3 Pa or more, and can also be 1.0×10 4 Pa or above or 1.5×10 4From the viewpoint of providing the adhesive layer with flexibility, the storage elastic modulus of the adhesive layer 2 at 25° C. before photocuring is preferably 7.0×10 4 Pa or less, more preferably 5.0×10 4 Pa or less, and can also be 4.0×10 4 Pa or less or 3.0×10 4 Below Pa.

[0131] From the same viewpoint as above, the storage modulus of the adhesive layer 2 at 60° C. before photocuring is preferably 5.0×10 3 ~8.0×10 4 Pa, more preferably 7.0×10 3 ~5.0×10 4 Pa, more preferably 8.0×10 3 ~4.0×10 4 Pa, or 1.0×10 4 Pa~3.0×10 4 Pa or 1.5×10 4 Pa~2.5×10 4 The storage modulus of the adhesive layer 2 at 60°C before photocuring is preferably 0.3 times or more of the storage modulus of the adhesive layer 2 at 25°C before photocuring, 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 60°C is usually 1.1 times or less of the storage modulus at 25°C, and may be 1.0 times or less or 0.9 times or less.

[0132] The storage modulus of the adhesive layer 2 before photocuring at -20°C is preferably 1.0×10 4 ~2.0×10 5 Pa, more preferably 1.5×10 4 ~1.0×10 5 Pa, can also be 2.0×10 4 ~7.0×10 4 Pa or 3.0×10 4 ~7.0×10 4 Pa. When the storage modulus of the pressure-sensitive adhesive layer at low temperature before photocuring is within the above range, the storage modulus of the pressure-sensitive adhesive layer after photocuring tends to be maintained low.

[0133] The storage modulus of the adhesive changes dramatically near the glass transition temperature of the base polymer. As described above, since the glass transition temperature of the base polymer is relatively low, an adhesive having a small storage modulus at low temperatures can be prepared. In addition, since the adhesive composition contains a high molecular weight polyol, the storage modulus at low temperatures tends to decrease. The storage modulus of the adhesive layer 2 at -20°C before photocuring is preferably less than 5 times the storage modulus of the adhesive layer 2 at 25°C before photocuring, more preferably less than 3 times, and may also be less than 2.5 times or less. The storage modulus at -20°C is generally more than 1.0 times the storage modulus at 25°C, and may also be more than 1.1 times, more than 1.3 times, or more than 1.5 times.

[0134] From the viewpoint of easy peeling from the adherend and preventing the generation of paste residue on the adherend after peeling the reinforcing film, the adhesive force between the adhesive layer 2 and the adherend before photocuring is preferably 1N / 25mm or less, more preferably 0.5N / 25mm or less, further preferably 0.3N / 25mm or less, and may also be 0.2N / 25mm or less or 0.1N / 25mm or less. From the viewpoint of preventing the peeling of the reinforcing film during storage and handling, the adhesive force between the adhesive layer 2 and the adherend before photocuring is preferably 0.01N / 25mm or more, more preferably 0.02N / 25mm or more, and may also be 0.03N / 25mm or more, 0.04N / 25mm or more, or 0.05N / 25mm or more.

[0135] The adhesive strength was determined by a peel test using a polyimide film as an adherend at a tensile speed of 300 mm / min and a peel angle of 180°. The adhesive strength is a value measured at 25° C. unless otherwise specified.

[0136] The storage modulus and adhesion of the 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. There is a tendency that the more the amount of crosslinking agent introduced, the higher the gel fraction, and the larger the storage modulus. There is a tendency that the more the amount of photocuring agent and polyol is, the smaller the content of the base polymer in the composition is relatively, and therefore the storage modulus is smaller.

[0137] In the case where the base polymer is not a completely compatible system with the photocuring agent and the polyol, the liquid photocuring agent will seep out on the surface, forming an adhesion barrier layer (weak boundary layer: Weak Boundary Layer; WBL) at the bonding interface with the adherend, and the liquid properties are enhanced. When the WBL is formed, the liquid properties of the surface (bonding interface) are enhanced while maintaining the bulk properties of the adhesive layer such as the storage modulus, resulting in a tendency for the adhesion to the adherend to decrease. It can be considered that in the case where the base polymer, the photocuring agent and the polyol show moderate compatibility to the extent that the transparency is not impaired, but it is not a completely compatible system, the adhesive layer before photocuring will form a WBL, thereby reducing the adhesion to the adherend.

[0138] When the adhesive layer 2 is photocured, the photocuring agent undergoes a curing reaction, the storage modulus increases, and the adhesive force to the adherend increases. The adhesive layer 2 preferably has a small storage modulus at low temperatures after photocuring.

[0139] The storage modulus of the adhesive layer after photocuring at -20°C is preferably 1.0×10 6 Pa or less, more preferably 5.0×10 6 Pa or less, more preferably 4.0×10 5 Pa or less, and can also be 3.0×10 5 Pa or less, 2.5×10 5 Pa or less or 2.0×10 5 Pa or less. Since the storage modulus of the adhesive layer 2 after photocuring is small at low temperature, the adhesive layer exhibits strain relaxation in a low temperature environment. Therefore, when the device with the reinforcement film attached is repeatedly bent or the bent state is maintained for a long time, the peeling of the adhesive layer at the bent portion can be suppressed.

[0140] On the other hand, if the storage modulus of the adhesive layer after photocuring is too small, the adhesive layer is prone to plastic deformation, and the adhesive layer may be peeled off from the adherend due to insufficient adhesive holding force. Therefore, the storage modulus of the adhesive layer after photocuring at -20°C is preferably 1.0×10 4 Pa or more, more preferably 3.0×10 4 Pa or more, more preferably 5.0×10 4 Pa or more, and can also be 7.0×10 4 Pa or above or 1.0×10 5 Pa or above.

[0141] The storage modulus of the adhesive layer at -20°C 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 of the adhesive layer at -20°C before photocuring. The storage modulus of the adhesive layer at -20°C after photocuring may also 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 of the adhesive layer at -20°C before photocuring.

[0142] The storage modulus of the 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 of the storage modulus of the adhesive layer at 25°C after photocuring. The storage modulus of the 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 of the storage modulus of the adhesive layer at 25°C before photocuring.

[0143] From the viewpoint of ensuring adhesiveness at room temperature and suppressing adhesive overflow from the end surface, the storage modulus of the adhesive layer after photocuring at 25°C is preferably 5.0×10 3 ~1.5×10 5 Pa, more preferably 1.0×10 4 ~1.0×10 5 Pa, more preferably 1.5×10 4 ~8.0×10 4 Pa, can also be 2.0×10 4 ~7.0×10 4 Pa or 3.0×10 4 ~5.0×10 4 Pa.

[0144] The storage modulus of the adhesive layer at 25°C after photocuring is preferably 7 times or less of the storage modulus of the adhesive layer before photocuring at 25°C, and may be 5 times or less, 4 times or less, or 3 times or less. The storage modulus of the adhesive layer at 25°C 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 of the adhesive layer before photocuring at 25°C.

[0145] From the same viewpoint as above, the storage modulus of the adhesive layer after photocuring at 60°C is preferably 5.0×10 3 ~1.0×10 5 Pa, more preferably 8.0×10 3 ~8.0×10 4 Pa, more preferably 1.0×10 4 ~6.0×10 4 Pa, can also be 2.0×10 4Pa~5.0×10 4 Pa or 2.5×10 4 Pa~4.5×10 4 Pa.

[0146] The storage modulus of the adhesive layer at 60°C after photocuring is preferably 0.3 times or more of the storage modulus of the adhesive layer at 25°C after photocuring, 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 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 of the storage modulus at 25°C.

[0147] The storage modulus of the adhesive layer at 60°C after photocuring is preferably 7 times or less of the storage modulus of the adhesive layer at 60°C before photocuring, and may be 5 times or less, 4 times or less, or 3 times or less. The storage modulus of the adhesive layer at 60°C 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 of the adhesive layer at 60°C before photocuring.

[0148] From the viewpoint of the reliability of adhesion during practical use of the device, the adhesive strength between the adhesive layer after photocuring and the adherend is preferably 1.5 N / 25 mm or more, and more preferably 2.0 N / 25 mm or more. From the viewpoint of suppressing the peeling of the adhesive when the flexible device is repeatedly bent at the same position, the adhesive strength between the adhesive layer after photocuring and the adherend can be 2.5 N / 25 mm or more or 3.0 N / 25 mm or more.

[0149] The adhesive force between the adhesive layer and the adherend after photocuring is preferably 5 times or more of the adhesive force between the adhesive layer and the adherend before photocuring, more preferably 10 times or more, further preferably 15 times or more, and may be 20 times or more, 30 times or more, or 50 times or more. As described above, by adjusting the type (compatibility with the base polymer) and the amount added of the photocuring agent and the polyol, the adhesive force (initial adhesive force) before photocuring can be suppressed to a low level, and the adhesive force of the adhesive after photocuring can be increased.

[0150] [Application of reinforcement film]

[0151] The reinforcing film of the present invention is used by being attached to a device or a component of the device. The adhesive layer 2 of the reinforcing film 10 is bonded to the film substrate 1, and the adhesive force to the adherend is small after being attached to the adherend and before being photocured. Therefore, the reinforcing film is easily peeled off from the adherend before photocuring.

[0152] The adherend to which the reinforcing film is adhered is not particularly limited, and various electronic devices, optical devices and their components can be listed. In one embodiment, the reinforcing film is adhered to the surface of a bendable flexible device. The bendable device has a hinge portion and can be bent with the hinge portion as the center. The bending angle can be set arbitrarily, and a 180° bend (fold) can be performed. In the case where the device is a display device, the reinforcing film can be adhered to the surface of the screen side, and the reinforcing film can also be adhered to the back side (housing). A flexible device that is configured to be bendable at a specified position such as a hinge portion is repeatedly bent and stretched at the same position when it is in use.

[0153] The reinforcement film can be attached to the entire surface of the adherend, or it can be selectively attached only to the portion that needs to be reinforced (reinforcement target area). In addition, after the reinforcement film is attached to the entire portion that needs to be reinforced (reinforcement target area) and the area that does not need to be reinforced (non-reinforcement target area), the reinforcement film attached to the non-reinforcement target area can be cut and removed. If the adhesive is before light curing, the reinforcement film is in a state of temporary adhesion to the surface of the adherend, so the reinforcement film can be easily peeled off from the surface of the adherend. It is also possible to attach a reinforcement film to the reinforcement target area and the non-reinforcement target area, selectively irradiate light to the reinforcement target area to photocure the adhesive, and then selectively peel off the reinforcement film in the non-reinforcement target area where the adhesive is not cured.

[0154] By attaching the reinforcing film, appropriate rigidity is imparted, so for thin components such as flexible devices, it is expected to improve handling and prevent damage. In the manufacturing process of the device, when the reinforcing film is attached to the semi-finished product, the reinforcing film can also be attached to the semi-finished product of a large size before being cut into product size. The reinforcing film can also be attached in a roll-to-roll manner on the mother roll of the device manufactured by the roll-to-roll process.

[0155] Before attaching the reinforcing film, the surface of the adherend may be activated for the purpose of cleaning. Examples of surface activation treatments include plasma treatment, corona treatment, glow discharge treatment, and the like. The adherend whose surface has been activated contains a large number of active groups such as hydroxyl, carbonyl, and carboxyl groups, and the bonding force is easily increased through 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 amic acid, terminal amino groups, or carboxyl groups (or carboxylic anhydride groups), etc., and the interaction with the polar functional groups of the base polymer is strong. Therefore, the initial bonding force is sometimes greatly increased due to the activation treatment.

[0156] If the initial adhesive force becomes too large, it may be difficult to perform peeling work such as rework. As described above, by making the base polymer substantially free of nitrogen atoms, it is possible to suppress excessive increase in the initial adhesive force to the adherend whose surface has been activated.

[0157] After the adherend is attached with a reinforcing film, the adhesive layer 2 is irradiated with active light to photocure the adhesive layer. As active light, there can be listed: ultraviolet rays, visible light, infrared rays, X-rays, α rays, β rays and γ rays. From the perspective of being able to inhibit the curing of the adhesive layer in the storage state and easy to cure, ultraviolet rays are preferred as active light. The irradiation intensity and irradiation time of the active light can be appropriately set according to the composition, thickness, etc. of the adhesive layer. The irradiation of the adhesive layer 2 with active light can be implemented from either side of the film substrate 1 side and the adherend side, or the irradiation of active light can be performed from both sides.

[0158] As described above, by laminating the reinforcing film of the present invention, the adherend is given appropriate rigidity, and the stress is relaxed and dispersed, thereby suppressing various undesirable situations that may occur in the manufacturing process, improving production efficiency, and improving the yield rate. The reinforcing film is easy to peel off from the adherend before the adhesive layer is photocured, so it is easy to rework in the case of lamination or poor lamination. In addition, it is also easy to perform processing such as selectively removing the reinforcing film from areas other than the reinforcement target area.

[0159] When the device is used after completion, even if an external force is accidentally applied due to the device being dropped, a heavy object being placed on the device, or a flying object colliding with the device, the device can be prevented from being damaged by the bonding reinforcement film. In addition, the reinforcement film is firmly bonded to the device after the adhesive is photocured, so even if it is used for a long time, the reinforcement film is not easy to peel off, and the reliability is excellent.

[0160] In a device with a reinforcing film in which the reinforcing film of the present invention is attached to a flexible device using a resin substrate, even when the device is repeatedly bent or kept in a bent state for a long time, the reinforcing film is not easily peeled off at the bent portion. Furthermore, static electricity of the resin substrate of the device can be removed by the adhesive layer, thereby suppressing adverse conditions such as electrostatic damage to the device caused by charging (static electricity).

[0161] Example

[0162] The present invention will be further described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0163] [Polymerization of acrylic acid-based polymer]

[0164] <Polymer A>

[0165] In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen inlet pipe, 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 were added, and nitrogen was introduced and nitrogen replacement was performed for about 1 hour while stirring. Then, the mixture was heated to 60° C. and reacted for 7 hours to obtain a solution of an acrylic polymer A having a weight average molecular weight (Mw) of 600,000.

[0166] <Polymer B, C>

[0167] The amount of monomer added was 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.

[0168] The ratio of added monomers of acrylic polymers A to C and the glass transition temperatures of the polymers are summarized in Table 1. The glass transition temperature was calculated from the ratio of added monomers based on the Fox equation.

[0169] BA: Butyl acrylate.

[0170] 2EHA: 2-ethylhexyl acrylate.

[0171] AA: Acrylic acid.

[0172] 2HEA: 2-Hydroxyethyl acrylate.

[0173] [Table 1]

[0174]

[0175] [Production of reinforcement film]

[0176] <Example 1>

[0177] (Preparation of Adhesive Composition)

[0178] To the solution of acrylic polymer A (based on 100 weight of the solid content of the polymer), 0.1 weight part of a tetrafunctional epoxy crosslinking agent (“TETRAD C” manufactured by Mitsubishi Gas Chemical) as a crosslinking agent, 0.2 weight part of zirconium tetraacetylacetonate (“ZC-150” manufactured by Matsumoto Fine Chemical) as a crosslinking catalyst, 20 weight parts of polyethylene glycol #600 diacrylate (“NK Ester A-600” manufactured by Shin-Nakamura Chemical Co., Ltd.) as a photocuring agent, 0.3 weight part of “Omnirad 651” manufactured by IGM Resins as a photopolymerization initiator, 0.2 weight part of 1-butyl-3-methylpyridinium bistrifluoromethanesulfonyl imide salt (“CIL-312” manufactured by Japan Carlit) as an antistatic agent, and 30 weight parts of polypropylene glycol (“PREMINOL S3011” manufactured by AGC) as a polyol were added and uniformly mixed to prepare an adhesive composition having the composition shown in Table 2.

[0179] (Coating and cross-linking of adhesive solution)

[0180] The adhesive composition was applied on a polyethylene terephthalate film having a thickness of 50 μm using a fountain roll in such a manner that the thickness after drying was 25 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated surface of a release liner (a polyethylene terephthalate film having a thickness of 25 μm, which was antistatically treated on both sides and silicone release-treated on one side) was attached to the applied surface of the adhesive. Then, an aging treatment was performed for 4 days in an atmosphere of 25°C, and cross-linking was performed to obtain a reinforcing film having a photocurable adhesive sheet laminated on a polyethylene terephthalate film substrate and a release liner temporarily bonded thereto.

[0181] <Comparative Example 1>

[0182] (Preparation of Adhesive Composition)

[0183] To the solution of acrylic polymer C (based on 100 weight of the solid content of the polymer), 0.25 weight parts of a trifunctional isocyanate crosslinking agent ("Coronate HX" manufactured by Tosoh) as a crosslinking agent and 0.25 weight parts of iron acetylacetonate ("Isocyanate" manufactured by Nippon Chemical Industry) as a crosslinking catalyst were added. Iron (III) "), 0.03 weight parts, trimethylolpropane EO modified (n = 1) triacrylate (Toagosei "ARONIX M-350") as a photocuring agent, 10 weight parts, IGM Resins "Omnirad 651" as a photopolymerization initiator, 0.3 weight parts, 1-butyl-3-methylpyridine bis trifluoromethanesulfonyl imide salt (Japan Carlit "CIL-312") as an antistatic agent, were uniformly mixed to prepare an adhesive composition with the composition shown in Table 2.

[0184] (Coating and cross-linking of adhesive solution)

[0185] Using the above-mentioned adhesive composition, coating and cross-linking were carried out in the same manner as in Example 1 to produce a reinforcing film.

[0186] <Examples 2 to 14, Comparative Examples 2 to 6>

[0187] The type of acrylic polymer, the type and amount of crosslinking agent, the type and amount of photocuring agent, the type and amount of antistatic agent, and the type and amount of polyol are changed as shown in Table 2 to prepare an adhesive composition. In Examples 2 to 11 and Comparative Examples 3 to 6, 0.2 parts by weight of zirconium tetraacetylacetonate is used as a crosslinking catalyst in the same manner as in Example 1, and in Comparative Example 2, 0.25 parts by weight of iron acetylacetonate is used as a crosslinking catalyst in the same manner as in Comparative Example 1. Using the adhesive composition of the composition shown in Table 2, coating and crosslinking are performed in the same manner as in Example 1 to prepare a reinforcement film. In Table 2, the amounts of crosslinking agent, photocuring agent, antistatic agent, and polyol are added in amounts relative to 100 parts by weight of the solid content of the acrylic polymer. The details of the crosslinking agent, photocuring agent, antistatic agent, and polyol are as follows.

[0188] (Crosslinking agent)

[0189] TC: N,N,N',N'-tetraglycidyl meta-xylylenediamine (tetrafunctional epoxy compound, "TETRAD C" manufactured by Mitsubishi Gas Chemical).

[0190] C-HX: isocyanurate of hexamethylene diisocyanate ("Coronate HX" manufactured by Tosoh).

[0191] (Light curing agent).

[0192] A200: polyethylene glycol #200 (n=4) diacrylate ("NK ESTER A200" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent: 151 g / eq).

[0193] A600: polyethylene glycol #600 (n=14) diacrylate ("NK ESTER A600" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent weight: 371 g / eq).

[0194] M350: trimethylolpropane EO-modified (n=1) triacrylate ("ARONIX M-350" manufactured by Toagosei Co., Ltd., functional group equivalent: 143 g / eq).

[0195] (Antistatic Agent)

[0196] CIL312: 1-Butyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide salt ("CIL-312" manufactured by Japan Carlit).

[0197] AS110: 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ("ELEXCEL AS-110" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0198] (Polyol)

[0199] S3011: polypropylene glycol, triol type ("PREMINOL S3011" manufactured by AGC, Mn=10000).

[0200] GP3000: polypropylene glycol, triol type ("SANNIX GP-3000" manufactured by Sanyo Chemical Industries, Ltd., Mn=3000).

[0201] GP1000: polypropylene glycol, triol type ("SANNIX GP-1000" manufactured by Sanyo Chemical Industries, Ltd., Mn=1000).

[0202] GP400: polypropylene glycol, triol type ("SANNIX GP-400" manufactured by Sanyo Chemical Industries, Ltd., Mn=400).

[0203] GP250: polypropylene glycol, triol type ("SANNIX GP-250" manufactured by Sanyo Chemical Industries, Ltd., Mn=250).

[0204] PP3000: polypropylene glycol, diol type ("SANNIX PP-3000" manufactured by Sanyo Chemical Industries, Ltd., Mn=3000).

[0205] PTGL3000: polytetramethylene glycol, triol type (“PTGL3000” manufactured by Hodogaya Chemical Industries, Ltd., Mn=3000).

[0206] <Example 15>

[0207] A film substrate having an antistatic layer of a conductive polymer (PEDOT / PSS) on one side of a polyethylene terephthalate film having a thickness of 50 μm was used, and an adhesive layer was formed on the antistatic layer-forming surface of the film substrate using the same adhesive composition as in Example 13. The antistatic layer (thickness 30 nm) was formed by the following method: (A) to (D) below were added to a water / ethanol mixed solvent having a weight ratio of 1 / 1, and stirred and mixed for about 20 minutes to prepare an antistatic treatment liquid having a solid content of about 0.4%, and the antistatic treatment liquid was applied to one side of the polyethylene terephthalate film using a rod coater, and heated at 130° C. for 2 minutes to dry it.

[0208] (A) 25% aqueous dispersion of a saturated copolyester resin as a binder ("Vylonal MD-1480" manufactured by Toyobo): 30 parts by weight in terms of solid content.

[0209] (B) As a binder, an aqueous dispersion of an acrylic resin prepared by emulsion polymerization of methyl methacrylate / butyl acrylate / hydroxyethyl methacrylate at a weight ratio of 85 / 10 / 5: 70 parts by weight in terms of solid content.

[0210] (C) An aqueous solution containing 0.5% of poly(3,4-ethylenedioxythiophene) and 0.8% of polystyrene sulfonate having a weight average molecular weight of 150,000 (manufactured by Bytron PHCStark) as a conductive polymer: 20 parts by weight in terms of solid content.

[0211] (D) Melamine-based crosslinking agent ("Sumimal M-50W" manufactured by Sumitomo Chemical): 5 parts by weight in terms of solid content.

[0212] [evaluate]

[0213] <Appearance>

[0214] The reinforcing film was visually observed, and a reinforcing film with white turbidity was evaluated as NG, and a transparent reinforcing film was evaluated as OK. For Comparative Example 2 in which white turbidity was observed, the subsequent evaluation was not performed.

[0215] <Surface resistance of adhesive layer>

[0216] The release liner was peeled off from the reinforcing film to expose the adhesive layer (before photocuring), and a probe ("Model 152P-2P" manufactured by TREK) was brought into contact with the surface of the adhesive layer under an environment of a temperature of 25°C and a relative humidity of 50%, and the surface resistance was measured using a resistivity meter ("Model 152-1" manufactured by TREK) under the conditions of an applied voltage of 10 V and a voltage application time of 10 seconds.

[0217] <Storage modulus>

[0218] On the release liner, the adhesive composition was coated and cross-linked in the same manner as above to prepare an adhesive sheet (before photocuring). The release liner was attached to the surface of the adhesive layer of the adhesive sheet before photocuring to isolate it from oxygen and irradiated with a 365nm LED lamp at 2000mJ / cm 2 The adhesive sheet before and after photocuring were laminated to prepare a test sample with a thickness of about 1.5 mm. The dynamic viscoelasticity was measured using the Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific under the following conditions, and the shear storage modulus G' values ​​were read at -20°C and 25°C.

[0219] (Measurement conditions)

[0220] Deformation mode: twist.

[0221] Measuring frequency: 1Hz.

[0222] Heating rate: 5°C / min.

[0223] Measuring temperature: -50~150℃.

[0224] Shape: parallel plate 8.0mmφ.

[0225] <Adhesion>

[0226] A polyimide film with a thickness of 25 μm ("Upilex 25S" manufactured by Ube Industries) was attached to a glass plate with a double-sided tape ("No. 531" manufactured by Nitto Denko) to obtain a polyimide film substrate for measurement. The release liner was peeled off from the surface of the reinforcing film cut into a width of 25 mm × a length of 100 mm, and it was attached to the polyimide film substrate for measurement with a hand roller to prepare a test sample before photocuring. The sample after photocuring the adhesive layer by irradiating ultraviolet rays from the reinforcing film side (PET film substrate side) of the test sample before photocuring was used as the test sample after photocuring. Using these test samples, the end of the film substrate of the reinforcing film was held with a chuck, and the reinforcing film was peeled 180° at a tensile speed of 300 mm / min, and the peel strength was measured.

[0227] <Bending test>

[0228] The release liner was peeled off from the surface of the reinforcing film, and a polyimide film ("Upilex 12.5SN" manufactured by Ube Industries) with a thickness of 12.5 μm was adhered to the surface of the adhesive layer using a hand roller. The laminate was cut into a size of 25 mm in width × 100 mm in length, and the adhesive layer was photocured by irradiating ultraviolet rays from the reinforcing film side (PET film substrate side) to obtain a test piece. Using a planar body unloaded U-shaped expansion and contraction testing machine (manufactured by YUASA SYSTEM), a bending fixture was installed on the short side of the test piece, and a repeated bending test was performed under the following conditions in a constant temperature bath at a temperature of -20°C or 25°C and a relative humidity of 50%, with the surface of the reinforcing film side (film substrate side) as the inner side. In the bent portion of the sample after the repeated bending test, those with no peeling or bulging between the reinforcing film and the adherend were evaluated as OK, and those with peeling or bulging observed between the reinforcing film and the adherend were evaluated as NG.

[0229] (Test conditions)

[0230] Bending radius: 3mm.

[0231] Bending angle: 180°.

[0232] Bending speed: 1 second / time.

[0233] Bending times: 200,000 times.

[0234] <Adherent contamination>

[0235] The release liner was peeled off from the surface of the reinforcement film, and a polyimide film (Ube Industries "Upilex25S") was attached to the surface of the adhesive layer using a hand roller. After standing 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 observed under a fluorescent light to confirm whether there was contamination. Those where contamination caused by attached matter was confirmed were evaluated as NG, and those where contamination was not confirmed were evaluated as OK.

[0236] Table 2 shows the composition of the adhesive of each reinforcement film and the evaluation results.

[0237] [Table 2]

[0238]

[0239] For Examples 1 to 11 in which the adhesive composition contains an antistatic agent and a polyol (triol type polypropylene glycol) in addition to the base polymer, the crosslinking agent, the photocuring agent and the photopolymerization initiator, the surface resistance of the adhesive is within 2×10 10 Ω or less, and no contamination of the adherend was observed. In addition, the adhesion to the polyimide film increased by more than 10 times through photocuring, and the shear storage modulus G' at -20°C after photocuring was 5×10 5Pa or less, no peeling of the adhesive layer was observed after repeated bending tests, showing good bonding reliability. Example 12 using diol-type polypropylene glycol as the polyol also had a low resistance adhesive as in Example 1, and good bonding reliability in the bending test.

[0240] In Example 13, which used an antistatic agent having a non-perfluorinated fluorinated organic anion, namely bis(fluorosulfonyl)imide, the surface resistance was lower than that of Example 1. In Example 13, the initial adhesive force was smaller than that of Example 1, and after photocuring, the adhesive force was as high as that of Example 1. In Example 15, which formed an adhesive layer on a substrate having an antistatic layer, the surface resistance of the adhesive layer was smaller than that of Example 13, and the storage modulus and adhesive force were the same as those of Example 13.

[0241] The adhesive of Example 14 using triol-type polytetramethylene glycol as the polyol has low resistance and good bonding reliability in the bending test, but the surface resistance shows a value greater than that of Example 13. By comparing Example 6 and Example 13 using polyols having the same molecular weight, it can be seen that polypropylene glycol contributes more to the lowering of resistance than polytetramethylene glycol.

[0242] In Comparative Example 3, in which the adhesive composition does not contain a polyol, the surface resistance of the adhesive is higher than that of Example 5, and the G' of the adhesive before and after photocuring also shows a higher value. In Comparative Example 3, the G' of the adhesive layer after photocuring at -20°C is large, so the adhesive layer peels off after the repeated bending test at -20°C, and the bonding reliability is poor. Comparative Example 4, in which the amount of the crosslinking agent is reduced to 0.1 parts by weight, is also the same as Comparative Example 3, and the G' of the adhesive layer after photocuring at -20°C is large, and the adhesive layer peels off after the repeated bending test at -20°C.

[0243] In Comparative Example 1 using polymer C having a low glass transition temperature, G' before and after photocuring was small, and no peeling of the adhesive layer due to the bending test was observed, but the surface resistance was large, and the resistance reduction effect by the antistatic agent was not observed.

[0244] These results show that the inclusion of a polyol in addition to the antistatic agent in the adhesive composition reduces the resistivity of the adhesive and imparts antistatic properties, and the polyol acts as a plasticizer to reduce G' at low temperatures, thereby improving the bonding reliability in the bending test.

[0245] In Comparative Example 2, in which 30 parts by weight of polyol was added to the composition of Comparative Example 1, the adhesive became cloudy. The cause of the cloudy state is believed to be that the polyol had low compatibility with other components of the adhesive composition.

[0246] In Example 11, which used M350 as a photocuring agent like Comparative Example 2, no turbidity was observed, so it is believed that in Comparative Example 2, the reason for the turbidity is that the compatibility of the acrylic base polymer and / or the crosslinking agent with the polyol is low. In Example 10, which used a combination of a low glass transition temperature polymer B with 2EHA as a main monomer component and an epoxy crosslinking agent, no turbidity was observed in the adhesive, so it is believed that in Comparative Example 2, the main reason for the reduced compatibility with the polyol is that the base polymer does not contain acrylic acid as a carboxyl group-containing monomer, but contains 2-hydroxyethyl acrylate as a hydroxyl group-containing monomer, and contains an isocyanate crosslinking agent. In other words, it is believed that in the example, since the base polymer contains a carboxyl group-containing monomer as a monomer component and a crosslinking structure is introduced by an epoxy crosslinking agent, the compatibility with the polyol is excellent, so the transparency of the adhesive is high.

[0247] It is known that 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. In addition, in Comparative Example 5, the surface resistance of the adhesive was higher than that of Examples 1, 3, 4, and 9, and even if the polyol was added in excess, the effect of reducing the resistance was not observed.

[0248] By comparing Examples 1, 3, 4, 9 and Comparative Example 5, the following tendency was observed: the greater the amount of polyol added, the smaller the adhesive strength of the adhesive before photocuring, and the greater the rate of increase in adhesive strength caused by photocuring. It is believed that in these examples, since the adhesive before photocuring forms WBL using polyol, the liquid properties of the surface of the adhesive layer (adhesive interface with the adherend) are enhanced, so the adhesive strength with the adherend becomes smaller, and it is believed that in Comparative Example 7, due to excessive formation of WBL, the polyol precipitated on the surface causes the adherend to be contaminated.

[0249] In Comparative Example 6 using a low molecular weight polyol, adherend contamination was observed similarly to Comparative Example 5. The reason for adherend contamination is believed to be that the low molecular weight polyol has little interaction with the base polymer and photocuring agent of the adhesive composition and is likely to bleed out on the surface of the adhesive layer.

[0250] In addition, in Comparative Example 6, compared with Examples 1, 6, 7, and 8, the adhesive force of the adhesive before photocuring is large, the adhesive force after photocuring is small, and the rate of increase of the adhesive force before and after photocuring is small. By comparing Examples 1, 6, 7, and 8 with Comparative Example 6, the following tendency can be observed: the larger the molecular weight of the polyol, the smaller the adhesive force of the adhesive before photocuring, the larger the adhesive force after photocuring, and the greater the rate of increase of the adhesive force before and after photocuring. It is believed that there is the following tendency: the low molecular weight polyol has a small effect as a WBL before the adhesive layer is photocured, and after the adhesive layer is photocured, it precipitates near the surface layer of the adhesive layer and acts as a WBL.

[0251] From the above results, it can be seen that the photocurable adhesive composition contains an antistatic agent and a polyol of a specified molecular weight, so that the adhesive has low resistance and antistatic properties, and has a low initial adhesive force, and shows excellent adhesive properties after photocuring. In addition, the shear storage modulus in the low temperature range is low, and the peeling of the adhesive during repeated bending is also suppressed.

[0252] Description of Reference Numerals

[0253] 1: film substrate; 2: adhesive layer; 10: reinforcing film; 5: release liner; 20: adherend.

Claims

1. A reinforcing film comprising a film substrate and an adhesive layer adhered to and laminated on one main surface of the film substrate, The adhesive layer is formed of a photocurable composition including an acrylic base polymer, a photocuring agent, a photopolymerization initiator, an antistatic agent, and a polyol. The acrylic base polymer contains one or more monomer units selected from the group consisting of a hydroxyl group-containing monomer and a carboxyl group-containing monomer, and a crosslinking structure is introduced into the acrylic base polymer. The number average molecular weight of the polyol is 300 to 30,000. The photocurable composition contains 5 to 60 parts by weight of the polyol based on 100 parts by weight of the acrylic base polymer.

2. The reinforcement film according to claim 1, wherein: The polyol is polypropylene glycol or polytetramethylene glycol.

3. The reinforcement film according to claim 1, wherein: The polyol is diol type polypropylene glycol or triol type polypropylene glycol.

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

5. The reinforcing film according to any one of claims 1 to 3, wherein The acrylic base polymer is a cross-linked polymer obtained by introducing a cross-linked structure using 0.03 to 2 parts by weight of a cross-linking agent based on 100 parts by weight of the polymer.

6. The reinforcement film according to claim 5, wherein: The acrylic base polymer contains a carboxyl group-containing monomer as a monomer unit, The cross-linking agent is an epoxy cross-linking agent.

7. The reinforcement film according to any one of claims 1 to 3, wherein The photocurable composition contains 3 to 40 parts by weight of the photocuring agent based on 100 parts by weight of the acrylic base polymer.

8. The reinforcement film according to any one of claims 1 to 3, wherein The photocuring agent is multifunctional (meth)acrylate.

9. The reinforcement film according to any one of claims 1 to 3, wherein The photocuring agent is a multifunctional (meth)acrylate containing an alkylene oxide chain.

10. The reinforcement film according to any one of claims 1 to 3, wherein The shear storage modulus of the adhesive layer at -20°C after photocuring is 1.0×10 4 ~1.0×10 6 Pa.

11. The reinforcement film according to any one of claims 1 to 3, wherein The shear storage modulus of the adhesive layer at -20°C before photocuring is 1.0×10 4 ~2.0×10 5 Pa, the shear storage modulus of the adhesive layer at 25°C before photocuring is 5.0×10 3 ~1.0×10 5 Pa.

12. The reinforcement film according to any one of claims 1 to 3, wherein The adhesive force of the adhesive layer to the polyimide film before photocuring is 1 N / 25 mm or less.

13. The reinforcement film according to any one of claims 1 to 3, wherein The adhesive force of the adhesive layer to the polyimide film after photocuring is more than 5 times the adhesive force of the adhesive layer to the polyimide film before photocuring.

14. The reinforcement film according to any one of claims 1 to 3, wherein The surface resistance of the adhesive layer is 1×10 11 Ω or less.

15. A method for manufacturing a device with a reinforcement film, wherein a reinforcement film is attached to the surface of a bendable device, wherein: The adhesive layer of the reinforcing film according to any one of claims 1 to 3 is attached to the surface of the bendable device, The adhesive layer is photocured.

16. A device with a reinforcement film, wherein the reinforcement film is attached to the surface of a bendable device, wherein: The reinforcing film comprises a film substrate and an adhesive layer adhered and laminated on one main surface of the film substrate. The adhesive layer is attached to the surface of the device. The adhesive layer is a photocured material obtained by photocuring a photocurable adhesive composition containing an acrylic base polymer and a photocuring agent, and contains an antistatic agent and a polyol having a number average molecular weight of 300 to 20,000. The acrylic base polymer contains one or more monomer units selected from the group consisting of a hydroxyl group-containing monomer and a carboxyl group-containing monomer, and a crosslinking structure is introduced into the acrylic base polymer. The shear storage modulus of the adhesive layer at -20°C is 1.0×10 4 ~1.0×10 6 Pa.

17. The device with a reinforcement film according to claim 16, wherein: The surface resistance of the adhesive layer is 1×10 11 Ω or less.

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