Reinforcement film, method for manufacturing a device, and reinforcement method.

Abstract

To provide a reinforcement film capable of preventing an adhesive force from increasing with time after adhesion onto an adherend, and capable of being strongly adhered onto the adherend by photocuring the adhesive agent.SOLUTION: A reinforcement film (10) includes an adhesive layer (2) fastened and laminated on one principal surface of a film base material (1). The adhesive layer includes a photocurable composition containing an acrylic base polymer having a crosslinking structure, a photocuring agent, and a photoinitiator, and includes, as the photocuring agent, a polyfunctional (meth)acrylate having no urethane bond and an urethane (meth)acrylate. A content of the urethane (meth)acrylate is preferably 0.5 to 23 pts.mass, based on 100 pts.mass of the acrylic base polymer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a reinforcing film in which a film substrate and a photocurable adhesive layer are fixedly laminated. Furthermore, the present invention relates to a method for manufacturing a device to which a reinforcing film is bonded to the surface, and a reinforcing method for fixing and laminating a reinforcing film to the surface of an adherend. [Background technology]

[0002] Adhesive films are sometimes applied to the surfaces of optical devices such as displays and electronic devices for purposes such as surface protection and impact resistance. Typically, such adhesive films have an adhesive layer fixed to the main surface of the film substrate, and are bonded to the device surface via this adhesive layer.

[0003] By temporarily attaching an adhesive film to the surface of a device or device component before use, such as during assembly, processing, or transportation, damage or breakage to the adherend can be suppressed. Patent documents 1 and 2 disclose a reinforcing film comprising an adhesive layer made of a photocurable adhesive composition on a film substrate.

[0004] The adhesive of this reinforcing film is in a low-tack, temporary-adhesion state immediately after bonding to the substrate, making it easy to peel off. Therefore, rework from the substrate is possible, and the reinforcing film can also be selectively peeled off and removed from areas of the substrate that do not require reinforcement (non-reinforcement areas). The adhesive of the reinforcing film adheres firmly to the substrate through photocuring, resulting in a permanent bond of the film substrate to the surface of the substrate, making it usable as a reinforcing material for surface protection of devices, etc. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-41113 [Patent Document 1] Japanese Patent Publication No. 2020-2238 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] After a reinforcing film with a photocurable adhesive layer is bonded to a substrate, processes such as transport, inspection, and cutting are carried out before the adhesive layer is photocured. During this time, the reinforcing film is peeled off and removed from areas that are not to be reinforced, and the reinforcing film is peeled off and removed (rework) from products where bonding defects have occurred. The process from bonding the reinforcing film to the substrate to peeling it off takes several hours to several days.

[0007] Before the adhesive layer is photocured, the reinforcing film is temporarily attached to the substrate, but over time the adhesive strength to the substrate increases, and it may become difficult to peel the reinforcing film from the substrate. Patent documents 1 and 2 describe that light from fluorescent lamps or the like in the storage environment causes photocleavage of the photopolymerization initiator (photoradical generator), which promotes the photopolymerization reaction of the polyfunctional (meth)acrylate, which is a photocuring agent contained in the adhesive, and that this is one of the reasons for the increase in adhesive strength over time.

[0008] However, even when the reinforcing film is bonded to the substrate and stored in a light-shielded environment, the adhesive strength may increase approximately 24 hours after bonding. This suggests that there are factors other than light curing that contribute to the increase in adhesive strength over time.

[0009] Patent Document 1 describes increasing the amount of photocuring agent as one method to reduce the adhesive strength (initial adhesive strength) before photocuring of the adhesive. However, if the amount of photocuring agent is excessively high, although the initial adhesive strength may be reduced, the adhesive strength may not increase sufficiently after photocuring. In addition, if the amount of photocuring agent is excessively high, the photocuring agent is more likely to bleed out from the adhesive layer, causing contamination of the surface of the adherend.

[0010] In view of the above, an object of the present invention is to provide a reinforcing film including an adhesive layer that suppresses an increase in adhesive strength over time in a state where the film is adhered to an adherend and has appropriate adhesive strength to the adherend before and after photocuring. **Means for Solving the Problems**

[0011] As a result of studies by the inventors in view of the above problems, it has been found that by using a photocurable adhesive having a predetermined composition, an increase in adhesive strength over time in a state where the adhesive is adhered to an adherend is suppressed, and the present invention has been achieved.

[0012] The reinforcing film of the present invention includes an adhesive layer fixedly laminated on one main surface of a film base material. The adhesive layer is composed of a photocurable composition containing an acrylic-based polymer, a photocuring agent, and a photopolymerization initiator. The acrylic-based polymer contains, as monomer units, one or more selected from the group consisting of a hydroxy group-containing monomer and a carboxyl group-containing monomer, and a crosslinked structure is introduced by bonding of a crosslinking agent to the hydroxy group and / or carboxyl group of the base polymer.

[0013] In one embodiment, the acrylic-based polymer contains a carboxyl group-containing monomer as a monomer component. The acrylic-based polymer may have a crosslinked structure formed by bonding an epoxy-based crosslinking agent to a carboxyl group derived from the carboxyl group-containing monomer.

[0014] The photocurable composition constituting the adhesive layer contains, as a photocuring agent, a polyfunctional (meth)acrylate having no urethane bond and a urethane (meth)acrylate. The content of the urethane (meth)acrylate with respect to 100 parts by weight of the acrylic-based polymer is preferably 0.5 to 23 parts by weight. The content of the polyfunctional (meth)acrylate having no urethane bond with respect to 100 parts by weight of the acrylic-based polymer is preferably 4 to 40 parts by weight.

[0015] As a photoinitiator, urethane (meth)acrylate may have a functional group equivalent of the (meth)acryloyl group of 80 to 150 g / eq. The urethane (meth)acrylate may have four or more (meth)acryloyl groups in one molecule.

[0016] Specific examples of urethane (meth)acrylate include compounds in which the isocyanate group of diisocyanate and the hydroxy group of a (meth)acrylic compound having a hydroxy group form a urethane bond. Examples of diisocyanate include tolylene diisocyanate and hexamethylene diisocyanate. Examples of the (meth)acrylic compound having a hydroxy group include those having a pentaerythritol skeleton.

[0017] For the reinforcing film, it is preferable that the ratio F2 / F1 of the adhesive force F1 after 30 minutes and the adhesive force F2 after 24 hours when the adhesive layer is bonded to the polyimide film is 1.3 or less. When photocuring is performed 24 hours after the adhesive layer is bonded to the polyimide film, it is preferable that the ratio F4 / F2 of the adhesive force F4 and the adhesive force F2 before photocuring the adhesive layer is 10 or more.

[0018] After temporarily attaching the above-mentioned reinforcing film to the surface of the device as the adherend, a device with a reinforcing film can be obtained by photocuring the adhesive layer. After temporarily attaching the reinforcing film to the adherend and before photocuring the adhesive layer, the reinforcing film temporarily attached to the adherend may be cut, and the reinforcing film may be peeled off and removed from a part of the region on the adherend (non-reinforcing target region).

Advantages of the Invention

[0019] The reinforcing film of the present invention has an adhesive layer made of a photocurable composition, and the adhesive strength to the adherend is increased by photocuring the adhesive layer after bonding to the adherend. Before photocuring, the adhesive strength to the adherend is low, and the increase in adhesive strength over time after bonding the reinforcing film to the adherend is suppressed. Therefore, even after processes such as transportation, inspection, and cutting are carried out after bonding, the reinforcing film can be easily peeled off the adherend. [Brief explanation of the drawing]

[0020] [Figure 1] This is a cross-sectional view showing the laminated structure of the reinforcing film. [Figure 2] This is a cross-sectional view showing the laminated structure of the reinforcing film. [Figure 3] This is a cross-sectional view showing a device to which a reinforcing film has been attached. [Modes for carrying out the invention]

[0021] Figure 1 is a cross-sectional view showing one embodiment of a reinforcing film. The reinforcing film 10 comprises an adhesive layer 2 on one main surface of a film substrate 1. The adhesive layer 2 is fixedly laminated on one main surface of the film substrate 1. The adhesive layer 2 is a photocurable adhesive made of a photocurable composition, and hardens upon irradiation with active light such as ultraviolet light, increasing its adhesive strength to the adherend.

[0022] Figure 2 is a cross-sectional view of a reinforcing film with a release liner 5 temporarily attached to the main surface of the adhesive layer 2. Figure 3 is a cross-sectional view showing the reinforcing film 10 attached to the surface of the device 20.

[0023] 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 bonded to the surface of the device 20, thereby attaching the reinforcing film 10 to the surface of the device 20. In this state, the adhesive layer 2 is not yet photocured, and the reinforcing film 10 (adhesive layer 2) is temporarily attached to the device 20. By photocuring the adhesive layer 2, the adhesive strength at the interface between the device 20 and the adhesive layer 2 increases, and the device 20 and the reinforcing film 10 are fixed together.

[0024] "Adherence" refers to a state where two laminated layers are firmly bonded together, making separation at their interface impossible or difficult. "Temporary adhesion" refers to a state where the adhesive force between two laminated layers is weak, allowing them to be easily separated at their interface.

[0025] In the reinforcing film shown in Figure 2, the film substrate 1 and the adhesive layer 2 are fixed together, and the release liner 5 is temporarily attached to the adhesive layer 2. When the film substrate 1 and the release liner 5 are peeled apart, peeling occurs at the interface between the adhesive layer 2 and the release liner 5, and the state in which the adhesive layer 2 is fixed to the film substrate 1 is maintained. No adhesive remains on the release liner 5 after peeling.

[0026] In the device to which the reinforcing film 10 shown in Figure 3 is attached, the device 20 and the adhesive layer 2 are temporarily adhered before the adhesive layer 2 is photocured. When peeling the film substrate 1 from the device 20, peeling occurs at the interface between the adhesive layer 2 and the device 20, and the state in which the adhesive layer 2 is fixed on the film substrate 1 is maintained. Since no adhesive remains on the device 20, rework is easy. After the adhesive layer 2 is photocured, the adhesive strength between the adhesive layer 2 and the device 20 increases, making it difficult to peel the film 1 from the device 20, and peeling the two together may cause cohesive failure of the adhesive layer 2.

[0027] [Structure of the reinforcing film] <Film substrate> A plastic film is used as the film substrate 1. In order to fix the film substrate 1 and the adhesive layer 2, it is preferable that the surface of the film substrate 1 to which the adhesive layer 2 is attached is not treated with a release agent.

[0028] The thickness of the film substrate 1 is, for example, about 4 to 500 μm. From the viewpoint of reinforcing the device by providing rigidity and mitigating impact, the thickness of the film substrate 1 is preferably 12 μm or more, more preferably 30 μm or more, and even more preferably 45 μm or more. From the viewpoint of giving the reinforcing film flexibility and improving handling, the thickness of the film substrate 1 is preferably 300 μm or less, and more preferably 200 μm or less. From the viewpoint of achieving both mechanical strength and flexibility, the compressive strength of the film substrate 1 is 100 to 3000 kg / cm². 2 Preferably, 200-2900 kg / cm³ 2 More preferably, 300-2800 kg / cm² 2 More preferably, 400-2700 kg / cm² 2 That is particularly preferable.

[0029] Examples of plastic materials constituting the film substrate 1 include polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, and polyetheretherketone resins. In the case of reinforcing films for optical devices such as displays, the film substrate 1 is preferably a transparent film. Furthermore, when photocuring the adhesive layer 2 by irradiating it with active light from the film substrate 1 side, it is preferable that the film substrate 1 has transparency to the active light used to cure the adhesive layer. Polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate are preferably used because they possess both mechanical strength and transparency. When curing the adhesive layer by irradiating it with active light from the adherend side, it is sufficient that the adherend has transparency to the active light, and the film substrate 1 does not need to be transparent to the active light.

[0030] The surface of the film substrate 1 may be provided with functional coatings such as an easy-adhesion layer, a smooth-slip layer, a release layer, an antistatic layer, a hard coat layer, or an anti-reflective layer. As mentioned above, it is preferable that a release layer is not provided on the surface of the film substrate 1 to which the adhesive layer 2 is attached, in order to fix the film substrate 1 and the adhesive layer 2 together.

[0031] <Adhesive layer> The adhesive layer 2, which is fixedly laminated onto the film substrate 1, consists of a photocurable composition containing a base polymer, a photocuring agent, and a photopolymerization initiator. Before photocuring, the adhesive layer 2 has low adhesion to the adherend, such as devices and device components, making it easy to peel off. As the adhesive layer 2's adhesion to the adherend improves with photocuring, the reinforcing film is less likely to peel off the device surface even during device use, resulting in excellent adhesive reliability.

[0032] Photocurable adhesives hardly harden under typical storage conditions and harden upon irradiation with active light such as ultraviolet light. Therefore, the reinforcing film of the present invention has the advantage of allowing the timing of the hardening of the adhesive layer 2 to be arbitrarily set, and thus being able to flexibly respond to process lead times and the like.

[0033] When the reinforcing film is used in optical devices such as displays, the total light transmittance of the adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The haze of the adhesive layer 2 is preferably 2% or less, more preferably 1% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less.

[0034] (Base polymer) The base polymer is the main component of the adhesive composition and is the main factor that determines the adhesive strength of the adhesive layer. Because it has excellent optical transparency and adhesion, and because the adhesive strength and storage modulus can be easily controlled, the adhesive composition preferably contains an acrylic polymer as the base polymer, and it is preferable that 50% by weight or more of the adhesive composition is an acrylic polymer.

[0035] As the acrylic polymer, one containing an alkyl (meth)acrylate as the main monomer component is preferably used. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0036] As the alkyl (meth)acrylate ester, an alkyl (meth)acrylate ester having 1 to 20 carbon atoms in the alkyl group is preferably used. The alkyl (meth)acrylate ester may have branched alkyl groups or may have cyclic alkyl groups (alicyclic alkyl groups).

[0037] Specific examples of alkyl (meth)acrylate esters having a chain-like alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and (meth) Examples include nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0038] Specific examples of alkyl (meth)acrylates having an alicyclic alkyl group include cycloalkyl (meth)acrylates such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylates having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; and (meth)acrylates having three or more aliphatic hydrocarbon rings such as dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate. Alkyl (meth)acrylates having an alicyclic alkyl group may also have substituents on the ring, such as 3,3,5-trimethylcyclohexyl (meth)acrylate. Furthermore, the alkyl (meth)acrylate ester having an alicyclic alkyl group may also be a (meth)acrylate ester containing a fused ring of an alicyclic structure and a ring structure having an unsaturated bond, such as dicyclopentenyl (meth)acrylate.

[0039] The content of alkyl (meth)acrylate is preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 55% by weight or more, relative to the total amount of monomer components constituting the base polymer.

[0040] The acrylic base polymer preferably contains a monomer component having a crosslinkable functional group as a copolymerization component. Introducing a crosslinked structure into the base polymer improves cohesive strength, enhances the adhesive strength of the adhesive layer 2, and tends to reduce adhesive residue on the adherend during rework.

[0041] Examples of monomers having crosslinkable functional groups include hydroxyl group-containing monomers and carboxyl group-containing monomers. The hydroxyl group and carboxyl group of the base polymer serve as reaction sites with the crosslinking agent described later. For example, when using an isocyanate-based crosslinking agent, it is preferable to include a hydroxyl group-containing monomer as a copolymer component of the base polymer. When using an epoxy-based crosslinking agent, it is preferable to include a carboxyl group-containing monomer as a copolymer component of the base polymer.

[0042] Examples of monomers containing a hydroxyl group 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.

[0043] Examples of carboxyl group-containing monomers include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Among these, acrylic acid and methacrylic acid are preferred, with acrylic acid being particularly preferred, because they tend to improve adhesive strength and adhesive retention by increasing the cohesiveness of the adhesive.

[0044] When an acrylic base polymer contains a monomer containing a carboxyl group, the carboxyl group introduced into the base polymer can act as a crosslinking point with crosslinking agents such as epoxy crosslinking agents. Furthermore, when an acrylic base polymer contains a carboxyl group, the increase in adhesive strength over time of adhesives containing urethane (meth)acrylate as a photocuring agent tends to be suppressed.

[0045] The acrylic-based polymer preferably has a total amount of hydroxyl group-containing monomers and carboxyl group-containing monomers relative to the total amount of constituent monomer components of 1 to 30% by weight, more preferably 2 to 25% by weight, and even more preferably 3 to 20% by weight. In particular, the content of carboxyl group-containing monomers is preferably within the above range, and especially the content of acrylic acid or methacrylic acid is preferably within the above range.

[0046] The acrylic-based polymer may contain nitrogen-containing monomers as constituent monomer components, such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinyl carboxylic acid amides, and N-vinylcaprolactam.

[0047] The acrylic-based polymer may contain monomer components other than those listed above. For example, the acrylic-based polymer may contain vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphate group-containing monomers, acid anhydride group-containing monomers, and the like as monomer components.

[0048] The acrylic base polymer may be substantially nitrogen-free. The proportion of nitrogen in the constituent elements of the base polymer may be 0.1 mol% or less, 0.05 mol% or less, 0.01 mol% or less, 0.005 mol% or less, 0.001 mol% or less, or 0. By using a base polymer substantially nitrogen-free, the increase in the adhesive strength (initial adhesive strength) of the adhesive layer before photocuring when the adherend is subjected to surface activation treatment such as plasma treatment tends to be suppressed.

[0049] By not including nitrogen atom-containing monomers such as cyano group-containing monomers, lactam structure-containing monomers, amide group-containing monomers, morpholine ring-containing monomers, etc. as the constituent monomer components of the base polymer, a base polymer substantially free of nitrogen atoms can be obtained. When a crosslinked structure is introduced into the base polymer, it is only necessary that the polymer before the introduction of the crosslinked structure is substantially free of nitrogen atoms, and the crosslinking agent may contain nitrogen atoms. When the base polymer is substantially free of nitrogen atoms, from the viewpoint of enhancing the cohesiveness of the adhesive, it is preferable that the base polymer contains a carboxy group-containing monomer as a monomer component.

[0050] From the viewpoint of imparting excellent adhesiveness to the adhesive, the glass transition temperature of the acrylic-based base polymer is preferably -10°C or lower, more preferably -15°C or lower, and still more preferably -20°C or lower. The glass transition temperature of the acrylic-based base polymer may be -25°C or lower or -30°C or lower. The glass transition temperature of the acrylic-based base polymer is generally -100°C or higher, and may be -80°C or higher or -70°C or higher.

[0051] The glass transition temperature is the temperature (peak top temperature) at which the loss tangent tanδ in viscoelasticity measurement becomes maximum. Instead of the glass transition temperature by viscoelasticity measurement, the theoretical Tg may be applied. The theoretical Tg is the glass transition temperature Tg of the homopolymer of the constituent monomer components of the acrylic-based base polymer i and the weight fraction W of each monomer component i and is calculated by the following Fox's equation. 1 / Tg = Σ(W i / Tg i )

[0052] Tg is the glass transition temperature of the polymer (unit: K), W i is the weight fraction (copolymerization ratio based on weight) of the monomer component i constituting the segment, Tg iis the glass transition temperature (in K) of the homopolymer of monomer component i. The values ​​listed in the Polymer Handbook, 3rd edition (John Wiley & Sons, Inc., 1989) can be used as the glass transition temperature of homopolymers. For homopolymers of monomers not listed in the above literature, the peak top temperature of tanδ obtained by dynamic viscoelasticity measurement can be used.

[0053] When the base polymer contains high-Tg monomers as constituent monomer components, the cohesive strength of the adhesive is improved, resulting in excellent reworkability before photocuring and a tendency to exhibit high adhesive phosphorescence after photocuring. High-Tg monomers refer to monomers with a high glass transition temperature (Tg) of the homopolymer. Examples of monomers with a Tg of 40°C or higher for homopolymers include (meth)acrylic acid esters such as cyclohexyl methacrylate (Tg: 83°C), tetrahydrofurfuryl methacrylate (Tg: 60°C), dicyclopentanyl methacrylate (Tg: 175°C), dicyclopentanyl acrylate (Tg: 120°C), isobornyl methacrylate (Tg: 155°C), isobornyl acrylate (Tg: 97°C), methyl methacrylate (Tg: 105°C), 1-adamantyl methacrylate (Tg: 250°C), and 1-adamantyl acrylate (Tg: 153°C); and acid monomers such as methacrylic acid (Tg: 228°C) and acrylic acid (Tg: 106°C).

[0054] In acrylic base polymers, the content of monomers with a homopolymer Tg of 40°C or higher is preferably 1% by weight or more, more preferably 2% by weight or more, and even more preferably 3% by weight or more, relative to the total amount of constituent monomer components. In order to form an adhesive layer with appropriate hardness and excellent reworkability, it is preferable that the base polymer contains monomer components with a homopolymer Tg of 80°C or higher, and more preferably that it contains monomer components with a homopolymer Tg of 100°C or higher. In acrylic base polymers, the content of monomers with a homopolymer Tg of 100°C or higher relative to the total amount of constituent monomer components is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, even more preferably 1% by weight or more, and particularly preferably 2% by weight or more. On the other hand, from the viewpoint of giving the adhesive appropriate flexibility, the content of monomers with a homopolymer Tg of 40°C or higher is preferably 50% by weight or less, more preferably 40% by weight or less, even more preferably 30% by weight or less, and may also be 20% by weight or less or 10% by weight or less, relative to the total amount of constituent monomer components. From a similar viewpoint, the content of monomers with a Tg of 80°C or higher in the homopolymer is preferably 30% by weight or less, more preferably 25% by weight or less, even more preferably 20% by weight or less, and may also be 15% by weight or less, 10% by weight or less, or 5% by weight or less, based on the total amount of constituent monomer components.

[0055] Acrylic polymers as base polymers are obtained by polymerizing the above monomer components using various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization. Solution polymerization is preferred from the viewpoint of balancing properties such as adhesive strength and holding power of the adhesive, as well as cost. Ethyl acetate, toluene, etc. are used as solvents for solution polymerization. The solution concentration is usually about 20 to 80% by weight. Various known polymerization initiators such as azo-based and peroxide-based ones can be used for solution polymerization. Chain transfer agents may be used to adjust the molecular weight. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

[0056] 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. Note that when a cross-linked structure is introduced into the base polymer, the molecular weight of the base polymer refers to the molecular weight before the introduction of the cross-linked structure.

[0057] (Crosslinking agent) From the viewpoint of providing the adhesive with appropriate cohesive force to exhibit adhesive strength and ensuring the peelability of the adhesive layer from the adherend before photocuring, it is preferable to introduce a crosslinked structure into the base polymer. For example, a crosslinked structure can be introduced by adding a crosslinking agent to the solution after polymerization of the base polymer and heating as necessary. The crosslinking agent has two or more crosslinkable functional groups per molecule. The crosslinking agent may also have three or more crosslinkable functional groups per molecule.

[0058] Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. These crosslinking agents react with functional groups such as hydroxyl groups and carboxyl groups introduced into the base polymer to form a crosslinked structure. Isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they have high reactivity with the hydroxyl groups and carboxyl groups of the base polymer and facilitate the introduction of crosslinked structures.

[0059] As isocyanate crosslinking agents, polyisocyanates having two or more isocyanate groups in one molecule are used. Isocyanate crosslinking agents may also have three or more isocyanate groups in one molecule. Examples of isocyanate crosslinking agents include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; and trimethylolpropane / tri- Examples of isocyanate adducts include diisocyanate trimer adducts (e.g., Mitsui Chemicals' "Takenate D101E"), trimethylolpropane / hexamethylene diisocyanate trimer adducts (e.g., Tosoh's "Coronate HL"), xylylene diisocyanate trimethylolpropane adducts (e.g., Mitsui Chemicals' "Takenate D110N"), and hexamethylene diisocyanate isocyanurates (e.g., Tosoh's "Coronate HX").

[0060] 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 also have three or more or four or more epoxy groups in one molecule. The epoxy groups of the epoxy crosslinking agent may be glycidyl groups. Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipate ester, diglycidyl o-phthalate ester, triglycidyl-tris(2-hydroxyethyl) isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether. As epoxy crosslinking agents, commercially available products such as "Denacol" from Nagase ChemteX and "Tetrad X" and "Tetrad C" from Mitsubishi Gas Chemical may be used.

[0061] Even if the base polymer is substantially nitrogen-free, the crosslinking agent may contain nitrogen atoms. For example, a crosslinked structure may be introduced into a base polymer substantially nitrogen-free using an isocyanate crosslinking agent. When the base polymer is substantially nitrogen-free, using a crosslinking agent that does not contain nitrogen atoms, such as an epoxy crosslinking agent, tends to suppress the increase in initial adhesion due to surface activation treatments such as plasma treatment.

[0062] When a urethane (meth)acrylate is included as a photocuring agent, it is preferable that the acrylic base polymer has carboxyl groups derived from carboxyl group-containing monomers such as (meth)acrylic acid, and that an epoxy crosslinking agent is used as the crosslinking agent, from the viewpoint of increasing the cohesiveness of the adhesive and suppressing the increase in adhesive strength over time.

[0063] The amount of crosslinking agent used can be appropriately adjusted depending on the composition and molecular weight of the base polymer. The amount of crosslinking agent used is approximately 0.01 to 10 parts by weight per 100 parts by weight of the base polymer, preferably 0.1 to 5 parts by weight, more preferably 0.2 to 3 parts by weight, and even more preferably 0.3 to 2 parts by weight, and may also be 0.4 to 1.5 parts by weight or 0.5 to 1 part by weight.

[0064] A crosslinking catalyst may be used to promote the formation of crosslinked structures. Examples of crosslinking catalysts include organometallic compounds such as organometallic complexes (chelates), compounds of metals and alkoxy groups, and compounds of metals and acyloxy groups; as well as tertiary amines. In particular, organometallic compounds are preferred from the viewpoint of suppressing the progress of the crosslinking reaction in a solution state at room temperature and ensuring the pot life of the adhesive composition. Examples of metals in organometallic compounds include iron, tin, aluminum, zirconium, zinc, titanium, lead, and cobalt. The amount of crosslinking catalyst used is generally 0.5 parts by weight or less per 100 parts by weight of the acrylic base polymer.

[0065] (Photocuring agent) The adhesive composition constituting the adhesive layer 2 contains, in addition to the base polymer, a compound having two or more photopolymerizable functional groups in one molecule as a photocuring agent. The adhesive composition containing the photocuring agent is photocurable, and when photocuring is performed after bonding to the adherend, the adhesion strength to the adherend is improved.

[0066] As photopolymerizable functional groups, those having polymerizability by photoradical reactions are preferred, and as photocuring agents, compounds having two or more ethylenically unsaturated bonds in one molecule are preferred, and polyfunctional (meth)acrylates are preferred due to their high compatibility with acrylic-based polymers.

[0067] In this invention, a polyfunctional (meth)acrylate without urethane bonds and a polyfunctional (meth)acrylate having urethane bonds are used in combination as a photocuring agent. That is, the photocurable composition constituting the adhesive layer 2 includes a polyfunctional (meth)acrylate without urethane bonds and a polyfunctional (meth)acrylate having urethane bonds. Hereinafter, the polyfunctional (meth)acrylate having urethane bonds will be referred to as "urethane (meth)acrylate". In addition, the polyfunctional (meth)acrylate without urethane bonds may be simply referred to as "polyfunctional (meth)acrylate".

[0068] (Multifunctional (meth)acrylate) Examples of polyfunctional (meth)acrylates that do not have urethane bonds include compounds having (meth)acryloyl groups at both ends of a polyalkylene oxide chain, such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate; esters of polyols with (meth)acrylic acid, such as bisphenol A di(meth)acrylate, alkanediol di(meth)acrylate, glycerin di(meth)acrylate, glycerin tri(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, isocyanuric acid tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol poly(meth)acrylate; and epoxy (meth)acrylate.

[0069] Polyfunctional (meth)acrylates that do not have urethane bonds may be esters of alkylene oxide-modified polyols and (meth)acrylic acid. Examples of esters of alkylene oxide-modified polyols and (meth)acrylic acid include bisphenol A alkylene oxide-modified di(meth)acrylate, isocyanuric acid alkylene oxide-modified tri(meth)acrylate, trimethylolpropane alkylene oxide-modified tri(meth)acrylate, pentaerythritol alkylene oxide-modified di(meth)acrylate, pentaerythritol alkylene oxide-modified tri(meth)acrylate, and dipentaerythritol alkylene oxide-modified poly(meth)acrylate.

[0070] Among the above, polyfunctional (meth)acrylates that exhibit appropriate compatibility with acrylic-based polymers include compounds having (meth)acryloyl groups at both ends of a polyalkylene oxide chain, such as polyethylene glycol di(meth)acrylate and polypropylene glycol di(meth)acrylate, and esters of alkylene oxide-modified polyols and (meth)acrylic acid. The alkylene oxide is preferably (poly)ethylene oxide or (poly)propylene oxide, and the chain length (number of repeating units: n) of the alkylene oxide is preferably about 1 to 15.

[0071] From the viewpoint of compatibility with acrylic-based polymers, the molecular weight of the polyfunctional (meth)acrylate used as a photocuring agent is preferably 1500 or less, more preferably 1000 or less, even more preferably 500 or less, and particularly preferably 400 or less. From the viewpoint of achieving both compatibility with the base polymer and improved adhesion after photocuring, the functional group equivalent (g / eq) of the polyfunctional (meth)acrylate is preferably 500 or less, more preferably 400 or less, even more preferably 300 or less, and particularly preferably 200 or less. On the other hand, if the functional group equivalent of the polyfunctional (meth)acrylate is excessively small, the crosslinking point density of the adhesive layer after photocuring may increase, and the adhesion may decrease. Therefore, the functional group equivalent of the photocuring agent is preferably 80 or more, more preferably 100 or more, and even more preferably 120 or more.

[0072] The adhesion between the adhesive layer and the substrate before photocuring, and the adhesion between the adhesive layer and the substrate after photocuring, is influenced by the type of polyfunctional (meth)acrylate used as the photocuring agent. When polyfunctional (meth)acrylate with low compatibility with acrylic-based polymers is included, the polyfunctional (meth)acrylate tends to be concentrated near the adhesion interface with the substrate, resulting in a weaker adhesion between the adhesive layer and the substrate before photocuring. On the other hand, when polyfunctional (meth)acrylate with high compatibility with acrylic-based polymers is included, the adhesion between the adhesive layer and the substrate after photocuring tends to be stronger.

[0073] As a photocuring agent, two or more polyfunctional (meth)acrylates that do not have urethane bonds may be used in combination. For example, by using a polyfunctional (meth)acrylate with relatively low compatibility with acrylic-based polymers in combination with a polyfunctional (meth)acrylate with relatively high compatibility with acrylic-based polymers, a reinforcing film may be obtained that has lower adhesion to the substrate and is easy to peel off before photocuring, and higher adhesion to the substrate and is difficult to peel off after photocuring.

[0074] The compatibility between acrylic-based polymers and polyfunctional (meth)acrylates can be evaluated, for example, by the Hansen solubility parameter.

[0075] The Hansen solubility parameter (HSP) is calculated by subtracting the Hildebrand solubility parameter δ from the dispersion term δ. d , polarity term δ p , and hydrogen bond term δ h It is divided into three components and represented in three-dimensional space, δ 2 =δ d 2 +δ p 2 +δ h 2 The following relationship holds: Variance term δ d This is the effect due to dispersion forces, polar term δ p This is the effect due to the dipole force, and the hydrogen bond term δ hThis shows the effect due to hydrogen bonding forces. The distance Ra between two HSPs is the difference in dispersion terms Δδ between the two substances. d , difference of polarity terms Δδ p , and the difference Δδ of the hydrogen bonding term h Therefore, Ra = {4Δδ d 2 +Δδ p 2 +Δδ h 2} 1 / 2 It is represented by the formula, where a smaller Ra value indicates higher compatibility, and a larger Ra value indicates lower compatibility.

[0076] Detailed information on Hansen solubility parameters is provided in Charles M. Hansen's "Hansen Solubility Parameters: A Users Handbook" (CRC Press, 2007). For substances for which literature values ​​are unknown, calculations can be performed using the computer software Hansen Solubility Parameters in Practice (HSPiP).

[0077] Polyfunctional (meth)acrylates without urethane bonds tend to have a smaller HSP distance Ra (i.e., higher compatibility) with acrylic-based polymers the smaller the functional group equivalent of (meth)acryloyl groups, and a larger HSP distance Ra (i.e., lower compatibility) with acrylic-based polymers the larger the functional group equivalent of (meth)acryloyl groups.

[0078] From the viewpoint of increasing the adhesion strength of the adhesive to the substrate after photocuring, the HSP distance Ra between the polyfunctional (meth)acrylate without urethane bonds and the acrylic base polymer is preferably 7 or less, more preferably 5 or less, even more preferably 4 or less, and may also be 3 or less. On the other hand, from the viewpoint of decreasing the adhesion strength of the adhesive to the substrate before photocuring, the HSP distance Ra between the polyfunctional (meth)acrylate without urethane bonds and the acrylic base polymer is preferably 1.5 or more, more preferably 2 or more, even more preferably 3 or more, and may also be 4 or more, 5 or more, or 6 or more.

[0079] When using two or more polyfunctional (meth)acrylates that do not have urethane bonds in combination, it is preferable to use a polyfunctional (meth)acrylate with a small Ra (for example, Ra of 5 or less, 4 or less, or 3 or less) and relatively high compatibility with acrylic-based polymers, and a polyfunctional (meth)acrylate with a large Ra (for example, Ra of 4 or more, 5 or more, 6 or more, or 7 or more) and relatively low compatibility with acrylic-based polymers.

[0080] (Urethane (meth)acrylate) Urethane (meth)acrylate is a compound having one or more urethane bonds and two or more (meth)acryloyl groups in one molecule, preferably containing two or more urethane bonds in one molecule.

[0081] A urethane (meth)acrylate having two or more urethane bonds can be obtained, for example, by the reaction of a polyisocyanate with a (meth)acrylic compound having a hydroxyl group, where the isocyanate group of the polyisocyanate and the hydroxyl group of the (meth)acrylic compound bond to form a urethane bond.

[0082] The polyisocyanate may be an aromatic polyisocyanate, an alicyclic polyisocyanate, or an alicyclic polyisocyanate. Diisocyanate is preferred as the polyisocyanate.

[0083] Aromatic polyisocyanates include phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, toluidine diisocyanate, diphenyl ether diisocyanate, diphenyl diisocyanate, and naphthalene diisocyanate. Aliphatic polyisocyanates include butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate. Alicyclic polyisocyanates include cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis(isocyanate-methyl)cyclohexane, and methylcyclohexane diisocyanate.

[0084] Among these, aromatic polyisocyanates and aliphatic polyisocyanates are preferred. Tolylene diisocyanate (TDI) is particularly preferred as the aromatic polyisocyanate. The tolylene diisocyanate may be 2,4-tolylene diisosoanate, 2,6-tolylene diisocyanate, or a mixture of the two. Hexamethylene diisocyanate (HDI) is particularly preferred as the aliphatic polyisocyanate.

[0085] Examples of (meth)acrylic compounds having a hydroxyl group include compounds having one hydroxyl group and one (meth)acryloyl group, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxymethylacrylamide, and hydroxyethylacrylamide; and compounds having one hydroxyl group and two or more (meth)acryloyl groups, such as pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, trimethylolpropanedi(meth)acrylate, and isocyanuric acid di(meth)acrylate.

[0086] Among these, as (meth)acrylic compounds having a hydroxyl group, compounds having one hydroxyl group and two or more (meth)acryloyl groups are preferred, and among these, compounds having a pentaerythritol skeleton such as pentaerythritol tri(meth)acrylate and dipentaerythritol penta(meth)acrylate are particularly preferred.

[0087] The urethane (meth)acrylate obtained by the reaction of a diisocyanate with a (meth)acrylic compound having one hydroxyl group and two or more (meth)acryloyl groups in one molecule has two urethane bonds and four or more (meth)acryloyl groups in one molecule. The number of (meth)acryloyl groups in the urethane (meth)acrylate may be six or more, eight or more, twelve or fewer, or ten or fewer.

[0088] The above-mentioned urethane (meth)acrylate may be commercially available from companies such as Kyoeisha Chemical, Shin Nakamura Chemical, Negami Kogyo, Nippon Synthetic Chemical, Daicel Ornex, Showa Denko Materials, etc.

[0089] From the viewpoint of compatibility with acrylic-based polymers, the molecular weight of the urethane (meth)acrylate is preferably 1500 or less, more preferably 1300 or less, and may also be 1100 or less or 900 or less. On the other hand, from the viewpoint of suppressing the increase in adhesive strength to the adherend over time, the molecular weight of the urethane (meth)acrylate is preferably 500 or more, and may also be 600 or more or 700 or more.

[0090] From the viewpoint of achieving both suppression of the time-dependent increase in adhesive strength before photocuring and improvement of adhesive strength after photocuring, the functional group equivalent (g / eq) of the (meth)acryloyl group in the urethane (meth)acrylate is preferably 80 to 150, more preferably 100 to 135, and may also be 120 to 130.

[0091] (Content of photocuring agent) The amount of photocuring agent in the adhesive composition (total of polyfunctional (meth)acrylate without urethane bonds and urethane (meth)acrylate) is preferably 6 parts by weight or more, more preferably 8 parts by weight or more, even more preferably 10 parts by weight or more, and may be 12 parts by weight or more or 15 parts by weight or more, per 100 parts by weight of the base polymer. By setting the amount of photocuring agent within the above range, a reinforcing film is obtained that is easily peeled from the adherend before photocuring and can be firmly adhered to the adherend after photocuring.

[0092] The greater the amount of photocuring agent, the weaker the adhesion between the adhesive and the substrate before photocuring tends to be, resulting in better workability for rework and other processes. On the other hand, if the amount of photocuring agent is excessively large, the photocuring agent is prone to bleeding out, and when the reinforcing film is peeled off from the substrate, the bled-out components may transfer to the substrate, causing contamination. Also, if the amount of photocuring agent is excessively large, the viscosity of the adhesive after photocuring may be low, resulting in insufficient adhesion. For this reason, the amount of photocuring agent is preferably 50 parts by weight or less, more preferably 40 parts by weight or less, even more preferably 35 parts by weight or less, and may also be 30 parts by weight or less or 25 parts by weight or less, per 100 parts by weight of the base polymer.

[0093] By using both a polyfunctional (meth)acrylate without urethane bonds and a polyfunctional (meth)acrylate with urethane bonds as photocuring agents, the increase in adhesive strength to the substrate is suppressed even when the reinforcing film is left attached to the substrate for a long period of time, allowing the reinforcing film to be easily peeled off the substrate. Furthermore, when the adhesive is photocured, the adhesive strength to the substrate increases significantly, resulting in a strong bond between the reinforcing film and the substrate.

[0094] The greater the amount of urethane (meth)acrylate, the more likely it is that the increase in the adhesive strength of the adhesive to the substrate over time before photocuring will be suppressed. In particular, when the acrylic base polymer has carboxyl groups derived from a carboxyl group-containing monomer as a monomer component, the effect of suppressing the increase in adhesive strength over time by urethane (meth)acrylate tends to be more pronounced. It is thought that the carboxyl groups of the base polymer form hydrogen bonds with the urethane bond portion of the urethane (meth)acrylate, which enhances the cohesiveness of the adhesive and suppresses the wetting and spreading of the adhesive on the substrate surface, thus suppressing the increase in adhesive strength over time.

[0095] From the viewpoint of suppressing the increase in adhesive strength over time after the reinforcing film is bonded to the adherend, the content of urethane (meth)acrylate in the adhesive composition is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, even more preferably 1.5 parts by weight or more, and may be 2 parts by weight or more, per 100 parts by weight of the base polymer.

[0096] The inclusion of urethane (meth)acrylate as a photocuring agent suppresses the increase in adhesive strength over time, and also tends to decrease the adhesive strength of the adhesive to the substrate before photocuring. Urethane (meth)acrylate has the effect of increasing the cohesive force of acrylic-based polymers, and furthermore, the base polymer and urethane (meth)acrylate form hydrogen bonds. As a result, urethane (meth)acrylate is easily incorporated into the bulk portion of the adhesive layer, and consequently, polyfunctional (meth)acrylate without urethane bonds tends to be unevenly distributed near the surface (adhesive interface) of the adhesive layer, forming a weak boundary layer (WBL), which is considered to be one of the causes of the decrease in adhesive strength.

[0097] Urethane (meth)acrylate contributes to reducing the adhesive strength of the adhesive before photocuring and suppressing its increase over time, and facilitates the peeling of the reinforcing film from the adherend. However, if the urethane (meth)acrylate content is excessively high, the photocuring agent (polyfunctional (meth)acrylate and / or urethane (meth)acrylate without urethane bonds) is prone to bleeding out onto the surface of the adhesive layer (adhesion interface with the adherend), and the bleed-out components can contaminate the adherend. Furthermore, if the amount of urethane (meth)acrylate is excessively high, the increase in adhesive strength of the adhesive due to photocuring tends to be insufficient. Therefore, the urethane (meth)acrylate content is preferably 23 parts by weight or less, more preferably 20 parts by weight or less, even more preferably 15 parts by weight or less, and may also be 10 parts by weight or less, 7 parts by weight or less, or 5 parts by weight or less per 100 parts by weight of the base polymer.

[0098] As described above, the inclusion of urethane (meth)acrylate as a photocuring agent in the adhesive composition suppresses the increase in adhesive strength over time. However, if urethane (meth)acrylate is the only photocuring agent, the adhesive strength of the adhesive to the substrate before photocuring is high, making it difficult to peel the reinforcing film from the substrate. Furthermore, if urethane (meth)acrylate is the only photocuring agent, the adhesive strength to the substrate hardly increases even after photocuring.

[0099] The composition constituting the adhesive layer 2 uses both a polyfunctional (meth)acrylate without urethane bonds and a polyfunctional (meth)acrylate with urethane bonds as photocuring agents. As a result, the adhesive strength to the substrate is low before photocuring, and the increase in adhesive strength over time after bonding to the substrate is small, making it easy to peel off from the substrate. Furthermore, once the adhesive is photocured, the adhesive strength to the substrate increases significantly, and the reinforcing film adheres firmly to the substrate.

[0100] From the viewpoint of adjusting the adhesion between the adhesive layer and the adherend before and after photocuring to an appropriate range, the content of polyfunctional (meth)acrylate without urethane bonds in the adhesive composition is preferably 5 to 40 parts by weight, more preferably 10 to 35 parts by weight, even more preferably 15 to 30 parts by weight, and may be 18 to 27 parts by weight or 20 to 25 parts by weight per 100 parts by weight of the base polymer.

[0101] While the ratio of polyfunctional (meth)acrylate without urethane bonds to urethane (meth)acrylate in the photocuring agent is not particularly limited, it is preferable that the content of polyfunctional (meth)acrylate without urethane bonds is relatively high from the viewpoint of adjusting the adhesion strength with the substrate before and after photocuring to an appropriate range, and from the viewpoint of suppressing contamination of the substrate due to bleeding of the photocuring agent. The content of polyfunctional (meth)acrylate without urethane bonds is preferably 1 to 30 times, more preferably 1.5 to 25 times, even more preferably 2 to 20 times, and may also be 3 to 15 times, 4 to 13 times, or 5 to 10 times the content of urethane (meth)acrylate.

[0102] (Photopolymerization initiator) Photopolymerization initiators generate active species upon irradiation with active light, thereby accelerating the curing reaction of photocuring agents. It is preferable to use a photoradical polymerization initiator (photoradical generator) as the photopolymerization initiator.

[0103] Preferred photo-radical polymerization initiators are those that generate radicals upon irradiation with visible light or ultraviolet light with a wavelength shorter than 450 nm, and include hydroxyketones, benzyldimethylketals, aminoketones, acylphosphine oxides, benzophenones, and trichloromethyl group-containing triazine derivatives. Photo-polymerization initiators may be used alone or in combination of two or more.

[0104] The content of the photopolymerization initiator in the adhesive layer 2 is preferably 0.01 to 5 parts by weight, more preferably 0.02 to 3 parts by weight, and even more preferably 0.03 to 2 parts by weight, per 100 parts by weight of the base polymer. The content of the photopolymerization initiator in the adhesive layer 2 is preferably 0.02 to 20 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 7 parts by weight, per 100 parts by weight of the photocuring agent.

[0105] (Oligomer) The adhesive composition may contain an oligomer in addition to the base polymer. For example, the adhesive composition may contain an acrylic oligomer in addition to an acrylic base polymer. The oligomer used has a weight-average molecular weight of approximately 1,000 to 30,000. The acrylic oligomer contains an alkyl (meth)acrylate as its main constituent monomer component. From the viewpoint of increasing the adhesive strength of the adhesive layer 2 after photocuring, the glass transition temperature of the acrylic oligomer is preferably 40°C or higher, and more preferably 50°C or higher. The oligomer may contain crosslinkable functional groups, similar to the base polymer.

[0106] The oligomer content in the adhesive composition is not particularly limited. When the adhesive composition contains an acrylic oligomer in addition to an acrylic base polymer, the amount of oligomer per 100 parts by weight of the base polymer is preferably 0.1 to 20 parts by weight, and may be 0.3 to 10 parts by weight or 0.5 to 5 parts by weight.

[0107] (Other additives) In addition to the components exemplified above, the adhesive layer may also contain additives such as silane coupling agents, tackifiers, plasticizers, softeners, degradation inhibitors, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents, to the extent that they do not impair the properties of the present invention.

[0108] [Fabrication of reinforcing film] A reinforcing film is obtained by laminating a photocurable adhesive layer 2 onto a film substrate 1. The adhesive layer 2 may be formed directly on the film substrate 1, or an adhesive layer formed in sheet form on another substrate may be transferred onto the film substrate 1.

[0109] The above adhesive composition is applied to a substrate by methods such as roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, etc., and the solvent is dried and removed as necessary to form an adhesive layer. A suitable drying method can be used as appropriate. The heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and even more preferably 70°C to 170°C. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and even more preferably 10 seconds to 10 minutes.

[0110] The thickness of the adhesive layer 2 is, for example, about 1 to 300 μm. The greater the thickness of the adhesive layer 2, the better the adhesion to the substrate tends to be. On the other hand, if the thickness of the adhesive layer 2 is excessively large, the fluidity before photocuring may be high, making handling difficult. Therefore, the thickness of the adhesive layer 2 is preferably 3 to 100 μm, more preferably 5 to 50 μm, even more preferably 6 to 40 μm, and particularly preferably 8 to 30 μm. From the viewpoint of thinning, the thickness of the adhesive layer 2 may be 25 μm or less, 20 μm or less, or 18 μm or less.

[0111] If the adhesive composition contains a crosslinking agent, it is preferable to promote crosslinking by heating or aging simultaneously with or after the drying of the solvent. The heating temperature and heating time are set appropriately depending on 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. Heating to dry and remove the solvent may also serve as heating for crosslinking.

[0112] Even after a crosslinked structure is introduced into the polymer by a crosslinking agent, the photocuring agent remains unreacted. As a result, a photocurable adhesive layer 2 containing high molecular weight components and a photocuring agent is formed. When forming the adhesive layer 2 on a film substrate 1, it is preferable to attach a release liner 5 to the adhesive layer 2 for purposes such as protecting the adhesive layer 2. Crosslinking may also be performed after attaching the release liner 5 to the adhesive layer 2.

[0113] When forming the adhesive layer 2 on another substrate, a reinforcing film is obtained by transferring the adhesive layer 2 onto the film substrate 1 after the solvent has dried. The substrate used to form the adhesive layer may also be used as the release liner 5.

[0114] As the release liner 5, plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester film are preferably used. The thickness of the release liner is usually 3 to 200 μm, preferably about 10 to 100 μm. The contact surface of the release liner 5 with the adhesive layer 2 is preferably treated with a release agent such as silicone-based, fluorine-based, long-chain alkyl-based, or fatty acid amide-based, or silica powder. Because the surface of the release liner 5 is treated with a release agent, peeling occurs at the interface between the adhesive layer 2 and the release liner 5, and the state in which the adhesive layer 2 is fixed on the film substrate 1 is maintained. The release liner 5 may be treated with an antistatic treatment on either the treated surface or the untreated surface, or both. By treating the release liner 5 with an antistatic treatment, static charge can be suppressed when the release liner is peeled off the adhesive layer.

[0115] [Characteristics and Use of Reinforcement Film] The reinforcing film of the present invention is used by laminating it to a device or device component. The reinforcing film 10 has an adhesive layer 2 fixed to the film substrate 1, and before photocuring after lamination to the adherend, the adhesive strength to the adherend is low. Therefore, before photocuring, the reinforcing film can be easily peeled off the adherend.

[0116] The substrate to which the reinforcing film is laminated is not particularly limited and can include various electronic devices, optical devices and their components. Before laminating the reinforcing film, the surface of the substrate may be activated for purposes such as cleaning. Examples of surface activation treatments include plasma treatment, corona treatment, and glow discharge treatment.

[0117] By laminating a reinforcing film, appropriate rigidity is imparted, which is expected to improve handling and prevent damage. In the device manufacturing process, if a reinforcing film is laminated to work-in-progress, the reinforcing film may be laminated to the large work-in-progress before it is cut to the product size. In devices manufactured by a roll-to-roll process, the reinforcing film may also be laminated to the mother roll using a roll-to-roll method.

[0118] The reinforcing film may be bonded to the entire surface of the substrate, or it may be selectively bonded only to the areas requiring reinforcement (reinforcement target areas). Alternatively, the reinforcing film may be bonded to both the areas requiring reinforcement (reinforcement target areas) and the areas not requiring reinforcement (non-reinforcement target areas), and then the reinforcing film bonded to the non-reinforcement target areas may be cut and removed.

[0119] For example, after laminating a reinforcing film onto the mother roll of a device or work-in-progress using a roll-to-roll method, the mother roll with the laminated reinforcing film is cut and separated into individual products, and only the reinforcing film is cut by half-cutting to peel off the reinforcing film from the non-reinforced areas, thereby obtaining a device with the reinforcing film laminated to the reinforced areas. The cutting method is not particularly limited, and an appropriate cutting method such as a rotary cutter, a push-in blade (e.g., a die-cutting blade), or a laser cutter can be used.

[0120] If the adhesive has not yet been photocured, the reinforcing film is only temporarily attached to the surface of the substrate, and because the adhesive strength is low, the reinforcing film can be easily peeled off from the surface of the substrate. When peeling off the reinforcing film after it has been bonded to the substrate and processed by cutting or other means, or when peeling off the reinforcing film from a product with poor bonding (e.g., air trapped inside) (rework), it takes several hours to several days from the time the reinforcing film is bonded to the substrate until it can be peeled off. Even in such cases, the increase in adhesive strength over time is suppressed, and a low adhesive strength state is maintained, so the reinforcing film can be easily peeled off from the surface of the substrate.

[0121] From the viewpoint of facilitating peeling from the adherend, the adhesive strength F1 (initial adhesive strength) between the adhesive layer 2 and the adherend before photocuring is preferably 1 N / 25 mm or less, more preferably 0.5 N / 25 mm or less, even more preferably 0.3 N / 25 mm or less, and particularly preferably 0.1 N / 25 mm or less. From the viewpoint of preventing peeling of the reinforcing film during storage and handling, the initial adhesive strength F1 is preferably 0.005 N / 25 mm or more, and more preferably 0.01 N / 25 mm or more. The adhesive strength is determined by a peel test using a polyimide film as the adherend, at a tensile speed of 300 mm / min and a peel angle of 180°. Unless otherwise specified, the adhesive strength is measured at 25°C. The initial adhesive strength F1 is measured using a sample that has been left to stand at 25°C for 30 minutes after bonding.

[0122] After bonding the reinforcing film to the adherend and leaving it to stand at 25°C for 24 hours, the adhesive strength F2 is preferably 1 N / 25 mm or less, more preferably 0.5 N / 25 mm or less, even more preferably 0.3 N / 25 mm or less, and particularly preferably 0.1 N / 25 mm or less, similar to the initial adhesive strength F1 described above. As mentioned above, by using a combination of a polyfunctional (meth)acrylate without urethane bonds and a polyfunctional (meth)acrylate with urethane bonds as the photocuring agent, the increase in adhesive strength over time is suppressed.

[0123] The ratio F2 / F1 of the adhesive strength F1 after bonding the reinforcing film to the adherend and standing at 25°C for 30 minutes to the adhesive strength F2 after standing at 25°C for 24 hours is preferably 1.3 or less, more preferably 1.2 or less, even more preferably 1.1 or less, and may be less than 1. F2 / F1 is the rate of increase in adhesive strength over time, and an F2 / F1 of less than 1 means that the adhesive strength decreases over time. F2 / F1 is generally 0.5 or more, but may be 0.6 or more or 0.7 or more.

[0124] The increase in adhesive strength over time after bonding the reinforcing film to the substrate is thought to be due to the adhesive wetting and spreading across the surface of the substrate, improving the affinity between the substrate and the adhesive layer. As mentioned above, by including urethane (meth)acrylate as a photocuring agent in the adhesive composition, the increase in adhesive strength over time is suppressed, and the F2 / F1 ratio becomes smaller.

[0125] Even when peeling is performed several hours to several days after lamination, such as when the reinforcing film is bonded to a substrate, transported, cut, and visually inspected, and then the reinforcing film is removed from the non-reinforced area or rework is carried out, if F2 / F1 is within the above range, the reinforcing film can be easily peeled off the substrate, resulting in excellent work efficiency.

[0126] After the reinforcing film is bonded to the substrate, the adhesive layer 2 is photocured by irradiating it with active light. Ultraviolet light is preferred as the active light. The irradiation intensity and duration of the active light can be appropriately set according to the composition and thickness of the adhesive layer 2. The active light may be irradiated onto the adhesive layer 2 from either the film substrate 1 side or the substrate side, or from both sides.

[0127] As the adhesive layer is cured by light, the adhesive strength of the adhesive layer to the substrate increases. From the viewpoint of adhesive reliability during practical use of the device, the adhesive strength F4 between the adhesive layer 2 and the substrate after light curing is preferably 2N / 25mm or more, more preferably 3N / 25mm or more, even more preferably 5N / 25mm or more, and may be 7N / 25mm or more, 9N / 25mm or more, or 10N / 25mm or more. It is preferable that the adhesive layer of the reinforcing film after light curing has an adhesive strength within the above range to the polyimide film.

[0128] The adhesive strength F4 of the adhesive layer after photocuring is measured by a 180° peel test using a sample in which the reinforcing film is bonded to a polyimide film as the substrate, left to stand at 25°C for 24 hours, and then the adhesive is photocured.

[0129] The ratio F4 / F2 between the adhesive strength F2 after bonding the reinforcing film to the substrate and leaving it to stand at 25°C for 24 hours, and the adhesive strength F4 after photocuring following 24 hours of standing, is preferably 10 or more, more preferably 20 or more, and may be 30 or more, 50 or more, or 100 or more. F4 / F2 is the rate of increase in adhesive strength due to photocuring, and a larger F4 / F2 means that the adhesive is easily peeled off the substrate before photocuring, and can be firmly adhered to the substrate after photocuring.

[0130] The adhesive strength F4 measured using a sample obtained by laminating a reinforcing film to a polyimide film as the adherend, leaving it standing at 25°C for 24 hours, and then photocuring the adhesive, is preferably greater than the adhesive strength F3 measured using a sample obtained by leaving it standing at 25°C for 30 minutes after lamination and then photocuring the adhesive. When the composition constituting the adhesive layer 2 contains both a polyfunctional (meth)acrylate without urethane bonds and a polyfunctional (meth)acrylate with urethane bonds as a photocuring agent, F4 tends to be greater than F3.

[0131] F4 / F3 is preferably greater than 1, more preferably 1.1 or greater, and may be 1.2 or greater, 1.3 or greater, 1.4 or greater, or 1.5 or greater. An F4 / F3 greater than 1 means that if the substrate and the reinforcing film are bonded together and then photocured after a predetermined time, the adhesive strength after photocuring will be greater, and the substrate will be able to adhere more firmly. F4 / F3 is generally 10 or less, and may be 5 or less, 4 or less, or 3 or less.

[0132] The reinforcing film of the present invention has an adhesive layer 2 that is photocurable, and the curing timing can be arbitrarily set. Processing and rework of the reinforcing film can be performed at any time between the time the reinforcing film is attached to the substrate and the time the adhesive is photocured. As described above, by including both a polyfunctional (meth)acrylate without urethane bonds and a polyfunctional (meth)acrylate with urethane bonds in the adhesive layer as photocurable, the adhesive strength before and after photocuring is adjusted to an appropriate range, and the increase in adhesive strength over time after the reinforcing film is bonded to the substrate is suppressed. Therefore, even when removing the reinforcing film from the non-reinforced area or performing rework after the reinforcing film has been bonded to the substrate, the reinforcing film can be easily peeled off the substrate, allowing for flexible response to the lead time of the device manufacturing process.

[0133] By laminating the reinforcing film, the adherend is given appropriate rigidity, and stress is relieved and dispersed, thereby suppressing various defects that may occur during the manufacturing process, improving production efficiency, and increasing yield. After the adhesive layer is photocured, it exhibits high adhesion to the adherend, the reinforcing film is difficult to peel off from the device surface, and it has excellent adhesive reliability as well as high impact resistance. Therefore, even if the device is unexpectedly subjected to external forces during use after completion, such as dropping the device, placing heavy objects on the device, or being struck by flying objects, the reinforcing film prevents damage to the device. [Examples]

[0134] The present invention will be further explained with reference to the following examples, but it is not limited to these examples.

[0135] [Preparation of base polymer] <Base Polymer A> In a reaction vessel equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas inlet, 95 parts by weight of butyl acrylate (BA) and 5 parts by weight of acrylic acid (AA) were added as monomers, 0.2 parts by weight of azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and 233 parts by weight of ethyl acetate as a solvent. Nitrogen gas was then introduced, and the mixture was purged with nitrogen while stirring for approximately 1 hour. Subsequently, the mixture was heated to 60°C and reacted for 7 hours to obtain a solution of acrylic polymer A with a weight-average molecular weight of 600,000 and a copolymerization ratio of BA / AA = 95 / 5.

[0136] <Base Polymer B> A solution of acrylic base polymer B having a copolymerization ratio of 2EHA / AA = 95 / 5 was obtained in the same manner as the preparation of base polymer A, except that 2-ethylhexyl acrylate (2EHA) was used instead of butyl acrylate.

[0137] [Fabrication of reinforcing film] <Preparation of adhesive composition> Adhesive compositions with the compositions shown in Tables 1 and 2 were prepared by adding a crosslinking agent, a photocuring agent (polyfunctional compound), and a photopolymerization initiator to a solution of an acrylic polymer and mixing them uniformly. As the crosslinking agent, a tetrafunctional epoxy crosslinking agent ("Tetrad C" manufactured by Mitsubishi Gas Chemical Co., Ltd.) was added in the amounts shown in Tables 1 and 2. The type and amount of photocuring agent added were as shown in Tables 1 and 2. As the photopolymerization initiator, 0.3 parts by weight of "Omnirad 651" manufactured by IGM Resins was added per 100 parts by weight of the solids content of the acrylic polymer. Note that the amounts added in Tables 1 and 2 are the amounts added per 100 parts by weight of the base polymer (parts by weight of solids).

[0138] The details of the photocuring agents in Tables 1 and 2 are as follows, and the polyfunctional acrylate is a polyfunctional acrylate that does not contain urethane bonds. <Multifunctional acrylate> A200: Polyethylene glycol #200 (n=4) diacrylate (Shin Nakamura Chemical Industry Co., Ltd. "NK Ester A200", functional group equivalent: 154 g / eq) A400: Polyethylene glycol #400 (n=9) diacrylate (Shin Nakamura Chemical Industry Co., Ltd. "NK Ester A400", functional group equivalent: 254 g / eq) A600: Polyethylene glycol #600 (n=14) diacrylate ("NK Ester A600" manufactured by Shin Nakamura Chemical Industry, functional group equivalent 354 g / eq) M350: Trimethylolpropane EO-modified (n=1) triacrylate (Toagosei Co., Ltd. "Aronics M-350", functional group equivalent: 129 g / eq) DPH: Dipentaerythritol polyacrylate (a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate; manufactured by Shin Nakamura Chemical Industry Co., Ltd., "NK Ester A-DPH", functional group equivalent: 98 g / eq) <urethane acrylate> PET3A-HDI: Pentaerythritol triacrylate-hexamethylene diisocyanate adduct (Kyoeisha Chemical Co., Ltd. "UA-306H", functional group equivalent: 127) PET3A-TDI: Pentaerythritol triacrylate-tolylene diisocyanate adduct (Kyoeisha Chemical Co., Ltd. "UA-306T", functional group equivalent: 128) DPET5A-HDI: Dipentaerythritol pentaacrylate-hexamethylene diisocyanate adduct (Kyoeisha Chemical Co., Ltd. "UA-510HTF", functional group equivalent: 136)

[0139] <Application and crosslinking of adhesive solution> The above adhesive composition was applied using a fountain roll to a 75 μm thick polyethylene terephthalate (PET) film substrate (Toray's "Lumirror S10") that had not undergone surface treatment, so that the thickness after drying was 13 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated side of a release liner (a 25 μm thick polyethylene terephthalate film with a silicone release treatment on its surface) was bonded to the adhesive-coated surface. Subsequently, an aging treatment was performed in a 25°C atmosphere for 4 days to promote crosslinking, resulting in a reinforced film in which the adhesive sheet was fixedly laminated on the PET film substrate, and the release liner was temporarily attached on top of it.

[0140] [evaluation] <Adhesion strength to polyimide film> A 25 μm thick polyimide film (Ube Industries' "UPIREX S") was attached to a glass plate via double-sided adhesive tape (Nitto Denko's "No. 531") to obtain a polyimide film substrate for measurement. The release liner was peeled off from the surface of a reinforcing film cut to a width of 25 mm and a length of 100 mm, and this was bonded to the polyimide film substrate for measurement using a hand roller.

[0141] For each of the reinforcing films in the examples and comparative examples, the adhesive strength (180° peel strength) to the polyimide film was measured under the following four conditions. Condition 1: The reinforcing film was bonded to a polyimide film substrate, left to stand at room temperature (25°C) for 30 minutes, and then the adhesive strength F1 was measured. Condition 2: The reinforcing film was bonded to a polyimide film substrate, left to stand at room temperature for 24 hours, and then the adhesive strength F2 was measured. Condition 3: The reinforcing film is bonded to the polyimide film substrate, left to stand at room temperature for 30 minutes, then the adhesive is photocured, and the adhesive strength F3 is measured. Condition 4: The reinforcing film was bonded to the polyimide film substrate, left to stand at room temperature for 24 hours, then the adhesive was photocured, and the adhesive strength F4 was measured.

[0142] In conditions 3 and 4, the adhesive is photocured using an LED light source with a wavelength of 365 nm from the reinforcing film side (film substrate side) with an integrated light intensity of 1000 mJ / cm². 2 The test was conducted by irradiating with ultraviolet light. The adhesive strength was measured by a 180° peel test at a tensile speed of 300 mm / min, with the edges of the reinforcing film substrate held by a chuck.

[0143] From the measurement results, the rate of increase in adhesive strength (F2 / F1) after the adhesive was applied to the substrate and left to stand for 24 hours, and the rate of increase in adhesive strength due to photocuring (F4 / F2) after the adhesive was applied to the substrate and then photocured for 24 hours were calculated.

[0144] <Contamination of the adherend> Similar to condition 2 above, the reinforcing film was bonded to the polyimide film substrate and left to stand at room temperature for 24 hours before being peeled off the polyimide film substrate. The polyimide film substrate after peeling off the reinforcing film was visually observed in a bright environment and under fluorescent lighting in a dark room, and the presence or absence of contamination due to adhesive transfer to the polyimide film was evaluated according to the following criteria. A: No clouding is observed in either a light environment or a darkroom. B: No clouding is observed in a light environment, but slight clouding is observed in a dark room. C: Those in which cloudiness can be observed in a light environment. D: Polyimide film whose surface appears completely white in bright conditions.

[0145] The composition of the adhesive of the reinforcing films for each example and comparative example (type of base polymer, amount of crosslinking agent added, type and amount of photocuring agent added), as well as the evaluation results of adhesive strength and staining properties, are shown in Tables 1 and 2. Furthermore, for each of the acrylic base polymers A and B, and the four types of polyfunctional acrylates (A200, A400, A600, and M350), the HSP values ​​calculated by HSPiP, and the HSP distance Ra values ​​between the base polymer and the polyfunctional acrylate are shown in Table 3.

[0146] [Table 1]

[0147] [Table 2]

[0148] [Table 3]

[0149] In Comparative Examples 1-5, which contained only polyfunctional acrylate without urethane bonds as the photocuring agent, the F2 / F1 ratio was large, indicating that the adhesive strength increased over time after the reinforcing film was bonded to the substrate. In Comparative Examples 6 and 7, which contained only urethane (meth)acrylate as the photocuring agent, the F2 / F1 ratio was smaller compared to Comparative Examples 1-5, indicating that the increase in adhesive strength over time was suppressed. However, in Comparative Examples 6 and 7, the F4 / F2 ratio was small, and the adhesive strength to the substrate did not increase even after the adhesive was photocured.

[0150] In contrast, Examples 1 to 26, which include both polyfunctional acrylate without urethane bonds and urethane (meth)acrylate as photocuring agents, have an F2 / F1 ratio of less than 1, indicating that the adhesive strength decreases over time after the reinforcing film is bonded to the substrate. Furthermore, all of Examples 1 to 26 have a large F4 / F2 ratio, indicating that the reinforcing film can be firmly bonded to the substrate by photocuring the adhesive.

[0151] In Comparative Example 8, which had a high urethane (meth)acrylate content, the F2 / F1 ratio was small, similar to Comparative Examples 6 and 7, and the increase in adhesive strength over time was suppressed. However, the F4 / F2 ratio was small, and the adhesion strength to the substrate after photocuring of the adhesive was insufficient. In addition, in Comparative Example 8, significant contamination was observed on the substrate after peeling off the reinforcing film.

[0152] Comparative Example 4 is equivalent to replacing the urethane acrylate (number of acryloyl groups per molecule: 6) of Example 11 with DPH, which is a mixture of hexafunctional acrylate and pentafunctional acrylate, and Comparative Example 5 is equivalent to replacing the urethane acrylate of Example 20 with DPH. From the comparison between Example 11 and Comparative Example 4, and between Example 20 and Comparative Example 5, it can be seen that the inclusion of urethane (meth)acrylate in the photocuring agent contributes to suppressing the increase in adhesive strength over time.

[0153] Furthermore, Examples 11 and 20 showed higher F4 and F4 / F2 values ​​compared to Comparative Examples 4 and 5. These results indicate that by using a polyfunctional acrylate without urethane bonds and a urethane (meth)acrylate in combination as photocuring agents, the increase in adhesive strength of the adhesive before photocuring is suppressed over time, and the adhesive strength after photocuring is high, allowing the reinforcing film to adhere more firmly to the substrate.

[0154] Comparing Examples 1-3, which had different urethane acrylate contents, a tendency was observed for F1, F2, and F2 / F1 to decrease with increasing urethane acrylate content. These results indicate that urethane (meth)acrylate contributes to suppressing the increase in adhesive strength over time and reducing adhesive strength.

[0155] On the other hand, as the urethane acrylate content increased, the adhesive strengths F3 and F4 after photocuring tended to decrease. Furthermore, as the urethane acrylate content increased, the contamination of the adherend after peeling off the reinforcing film tended to worsen. From these results, and from the results of Comparative Example 8 above, it can be seen that when the urethane acrylate content is high, the urethane acrylate bleeds out to the surface of the adhesive layer and is more likely to transfer to the surface of the adherend, which can cause contamination.

[0156] Examples 7, 10, 14, and 15, like Example 1, contained 5 parts by weight of urethane acrylate, but their staining properties were "C". As shown in Table 3, A600 has a large HSP distance Ra and low compatibility with acrylic-based polymers. In Examples 7, 10, 14, and 15, which contained 10 parts by weight of A600, the low compatibility of the polyfunctional acrylate with the acrylic-based polymer was likely to bleed out to the surface of the adhesive layer, resulting in lower staining properties compared to the other examples.

[0157] On the other hand, since Examples 7, 10, 14, and 15 showed low adhesive strengths F1 and F2 before photocuring, it can be said that polyfunctional acrylates with low compatibility with acrylic-based polymers are useful for reducing adhesive strength (slight peeling).

[0158] Comparisons of Examples 1 and 4, Examples 6, 7 and 9, and Examples 13, 14 and 15 show that A600, with its large HSP distance Ra from the acrylic base polymer, contributes to the light peeling of the adhesive before photocuring.

[0159] These results indicate that, from the viewpoint of preventing contamination of the adherend, it is useful to use a polyfunctional acrylate with high compatibility with the base polymer (small HSP distance Ra), but from the viewpoint of light peeling, a polyfunctional acrylate with low compatibility with the base polymer (large HSP distance Ra) is useful. Furthermore, as shown in Examples 11, 12, 16-20, 23, and 24, by combining a polyfunctional (meth)acrylate with relatively high compatibility with the base polymer with a polyfunctional (meth)acrylate with relatively low compatibility with the base polymer, within a range where contamination does not decrease (bleed-out is unlikely to occur), it is possible to create a composition that satisfies all of the following: light peeling before photocuring, suppression of the increase in adhesive strength over time, prevention of contamination, and high adhesive strength after photocuring. [Explanation of symbols]

[0160] 1. Film substrate 2. Adhesive layer 10 Reinforcement film 5. Release Liner 20 Adherent

Claims

1. The film substrate comprises an adhesive layer fixedly laminated on one main surface of the film substrate. The adhesive layer comprises a photocurable composition containing an acrylic-based polymer, a photocuring agent having two or more photopolymerizable functional groups, and a photopolymerization initiator. The acrylic-based polymer contains one or more monomer components selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers, and a crosslinked structure is introduced into the acrylic-based polymer. The photocuring agent comprises a polyfunctional (meth)acrylate without urethane bonds and a urethane (meth)acrylate. The content of the polyfunctional (meth)acrylate without urethane bonds is 5 to 40 parts by weight per 100 parts by weight of the acrylic base polymer, and the content of the urethane (meth)acrylate is 0.5 to 23 parts by weight. Reinforcement film.

2. The reinforcing film according to claim 1, wherein the urethane (meth)acrylate has a functional group equivalent of 80 to 150 g / eq of (meth)acryloyl groups.

3. The reinforcing film according to claim 1 or 2, wherein the urethane (meth)acrylate has four or more (meth)acryloyl groups in one molecule.

4. The reinforcing film according to claim 1 or 2, wherein the urethane (meth)acrylate is a compound in which the isocyanate group of a diisocyanate and the hydroxyl group of a (meth)acrylic compound having a hydroxyl group form a urethane bond.

5. The reinforcing film according to claim 4, wherein the diisocyanate is tolylene diisocyanate or hexamethylene diisocyanate.

6. The reinforcing film according to claim 4, wherein the (meth)acrylic compound having a hydroxyl group has a pentaerythritol skeleton.

7. The reinforcing film according to claim 1 or 2, wherein the acrylic-based polymer contains a carboxyl group-containing monomer as a monomer component.

8. The reinforcing film according to claim 7, wherein the acrylic base polymer has a crosslinked structure formed by bonding an epoxy crosslinking agent to carboxyl groups derived from the carboxyl group-containing monomer.

9. Adhesion strength F 30 minutes after the adhesive layer is bonded to the polyimide film. １ The adhesive strength F after 24 hours following bonding the adhesive layer to the polyimide film is as follows: ２ F ２ / F １ The reinforcing film according to claim 1 or 2, wherein the ratio is 1.3 or less.

10. The adhesive strength F when the adhesive layer is bonded to the polyimide film and then photocured 24 hours later. ４ And the aforementioned adhesive force F ２ F ４ / F ２ The reinforcing film according to claim 9, wherein the number is 10 or more.

11. A method for manufacturing a device in which a reinforcing film is bonded to the surface, After temporarily attaching the adhesive layer of the reinforcing film according to claim 1 or 2 to the surface of the object to be adhered, A method for manufacturing a device, comprising irradiating the adhesive layer with an active light to photocur the adhesive layer, thereby increasing the adhesive strength between the reinforcing film and the adherend.

12. A method for manufacturing the device according to claim 11, wherein, after temporarily attaching the reinforcing film to the adherend, and before photocuring the adhesive layer, the reinforcing film temporarily attached to the adherend is cut and the reinforcing film is peeled off from a portion of the adherend.

13. A reinforcement method in which a reinforcing film is bonded to the surface of an object to be adhered, The adhesive layer of the reinforcing film according to claim 1 or 2 is temporarily attached to the surface of the adherend. A reinforcement method that increases the adhesive strength between the reinforcing film and the adherend by irradiating the adhesive layer with an active light to photocur the adhesive layer.

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