Reinforcement film, device manufacturing method and reinforcing method

Abstract

A reinforcing film (10) comprises an adhesive agent layer (2) that is layered and fixed on one main surface of a film base material (1). The adhesive agent layer comprises a photocurable composition containing an acrylic base polymer having a crosslinked structure, a photocuring agent, and a photopolymerization initiator. The photocuring agent contains: a polyfunctional (meth)acrylate not having a urethane bond; and a urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton. The reinforcing film of the present invention does not easily get detached from an adherend even in a high-temperature and high-humidity environment.

Description

[Technical Field]

[0001] The present invention relates to a reinforced film having a film substrate and a photocurable pressure-sensitive adhesive layer bonded together. The present invention also relates to a method for producing a device having a surface to which the reinforced film is bonded, and a reinforcing method for bond-laminating a reinforced film to the surface of an adherend. [Background technology]

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

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

[0004] This reinforcing film has low adhesiveness immediately after application to the adherend, making it easy to peel off from the adherend. This allows for reworking from the adherend, and also allows for selective peeling and removal of the reinforcing film from areas of the adherend that do not require reinforcement. The adhesive of the reinforcing film firmly bonds to the adherend upon photocuring, leaving the film substrate permanently bonded to the surface of the adherend, making it usable as a reinforcing material for protecting the surface of devices, etc. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-41113 Summary of the Invention [Problem to be solved by the invention]

[0006] Although the adhesive of the reinforcing film disclosed in Patent Document 1 firmly adheres to the adherend after photocuring, in a high-temperature, high-humidity environment, the adhesive strength to the adherend decreases and the film may peel off from the adherend. In particular, in a foldable flexible display (foldable display), compressive stress is applied to the inside at the bent portion and tensile stress is applied to the outside, causing distortion at the bent portion and its surroundings. Therefore, when the adherend is a foldable display, peeling of the adhesive layer from the adherend at the bent portion and its surroundings is likely to occur in a high-temperature, high-humidity environment.

[0007] In view of the above, the present invention aims to provide a reinforcing film having a photocurable adhesive layer on a film substrate, in which the photocured adhesive layer has high adhesive strength to an adherend even in a high-temperature, high-humidity environment. [Means for solving the problem]

[0008] In view of the above problems, the inventors conducted research and found that by using a photocurable adhesive having a predetermined composition, the adhesive layer after photocuring can maintain high adhesive strength in a high-temperature, high-humidity environment, leading to the present invention.

[0009] The reinforcing film of the present invention includes a pressure-sensitive adhesive layer bonded to one main surface of a film substrate. The pressure-sensitive adhesive layer is made of a photocurable composition containing an acrylic base polymer, a photocuring agent, and a photopolymerization initiator. The acrylic base polymer contains, as a monomer unit, one or more monomers selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers, and a crosslinked structure is introduced.

[0010] The photocurable composition constituting the pressure-sensitive adhesive layer contains, as photocuring agents, a polyfunctional (meth)acrylate having no urethane bond and a urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton. In the photocurable composition, the amount of the polyfunctional (meth)acrylate having no urethane bond is preferably 3 to 40 parts by weight per 100 parts by weight of the acrylic base polymer, and the amount of the urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton is preferably 0.3 to 15 parts by weight per 100 parts by weight of the acrylic base polymer.

[0011] The polyfunctional (meth)acrylate having no urethane bond preferably contains an alkylene oxide chain. The polyfunctional (meth)acrylate having no urethane bond may have a functional group equivalent of a (meth)acryloyl group of 80 to 500 g / eq.

[0012] The urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton may have a functional group equivalent of a (meth)acryloyl group of 500 to 20,000 g / eq.

[0013] Before photocuring, the adhesive layer preferably has an adhesive strength F0 to a polyimide film of 1 N / 25 mm or less in an environment of 25°C and 50% relative humidity. After photocuring, the adhesive layer preferably has an adhesive strength F1 to a polyimide film of 5 N / 25 mm or more in an environment of 25°C and 50% relative humidity, and an adhesive strength F2 to a polyimide film of 4 N / 25 mm or more in an environment of 60°C and 93% relative humidity.

[0014] It is preferable that the adhesive layer after photocuring has a reduction rate ΔF of adhesive strength F2 in an environment of 60°C and 93% relative humidity, based on adhesive strength F1 in an environment of 25°C and 50% relative humidity, of 60% or less. ΔF(%)=100×(F1-F2) / F1

[0015] The above-mentioned reinforcing film is temporarily attached to the surface of a device as an adherend, and then the pressure-sensitive adhesive layer is photocured to obtain a device with the reinforcing film. The device may be a foldable flexible device, and the adherend (reinforcement target) of the reinforcing film may be a foldable image display element. The adherend may include a polyimide film.

[0016] After the reinforcing film is temporarily attached to the adherend, and before the adhesive layer is photocured, the reinforcing film temporarily attached to the adherend may be cut and peeled off and removed from a portion of the adherend (a non-reinforced area). [Effects of the Invention]

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

[0018] Since the adhesive layer of the reinforcing film contains a urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton as a photocuring agent, the adhesive layer after photocuring has high adhesive strength to the adherend even in a high-temperature, high-humidity environment. [Brief explanation of the drawings]

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

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

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

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

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

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

[0025] In the device with the reinforcement film 10 attached shown in FIG. 3, the device 20 and the adhesive layer 2 are in a temporarily bonded state before the adhesive layer 2 is photocured. When the film substrate 1 is peeled from the device 20, peeling occurs at the interface between the adhesive layer 2 and the device 20, and the adhesive layer 2 remains adhered to the film substrate 1. 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 reinforcement film 10 from the device 20, and peeling the two may cause cohesive failure of the adhesive layer 2.

[0026] [Structure of the reinforcing film] <Film substrate> A plastic film is used as the film substrate 1. In order to bond the film substrate 1 and the pressure-sensitive adhesive layer 2 together, it is preferable that the surface of the film substrate 1 to which the pressure-sensitive adhesive layer 2 is to be attached is not subjected to a release treatment.

[0027] The thickness of the film substrate 1 is, for example, about 4 to 500 μm. From the viewpoint of reinforcing the device by imparting rigidity and cushioning impact, the thickness of the film substrate 1 is preferably 12 μm or more, more preferably 30 μm or more, and even more preferably 45 μm or more. From the viewpoint of imparting flexibility to the reinforcing film and improving handleability, the thickness of the film substrate 1 is preferably 300 μm or less, 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 / cm 2 is preferred, and 200 to 2900 kg / cm 2 More preferably, 300 to 2800 kg / cm 2 is more preferably 400 to 2700 kg / cm 2 is particularly preferred.

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

[0029] The surface of the film substrate 1 may be provided with a functional coating such as an easy-adhesion layer, an easy-slip layer, a release layer, an antistatic layer, a hard coat layer, or an antireflection layer. As described above, in order to bond the film substrate 1 and the pressure-sensitive adhesive layer 2 together, it is preferable that no release layer is provided on the surface of the film substrate 1 to which the pressure-sensitive adhesive layer 2 is to be attached.

[0030] [Adhesive layer] The adhesive layer 2, which is adhered and laminated onto the film substrate 1, is made of a photocurable composition containing a base polymer, a photocuring agent, and a photopolymerization initiator. Before photocuring, the adhesive layer 2 has low adhesive strength to adherends such as devices and device components, making it easy to peel off. The adhesive layer 2's adhesive strength to adherends improves upon photocuring, making it difficult for the reinforcing film to peel off from the device surface even when the device is in use, resulting in excellent adhesive reliability.

[0031] Photocurable pressure-sensitive adhesives hardly cure under normal storage conditions, but cure when exposed to actinic rays such as ultraviolet light. Therefore, the reinforcing film of the present invention has the advantage that the timing of curing of the pressure-sensitive adhesive layer 2 can be set as desired, allowing for flexible adaptation to process lead times, etc.

[0032] When the reinforcing film is used in an optical device such as a display, the total light transmittance of the pressure-sensitive adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The haze of the pressure-sensitive adhesive layer 2 is preferably 2% or less, more preferably 1% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less.

[0033] (base polymer) The base polymer is the main component of the pressure-sensitive adhesive composition and is the main factor determining the adhesive strength of the pressure-sensitive adhesive layer, etc. Because of its excellent optical transparency and adhesive properties and ease of controlling adhesive strength, the pressure-sensitive adhesive composition preferably contains an acrylic polymer as the base polymer, and it is preferable that 50 wt % or more of the pressure-sensitive adhesive composition be an acrylic polymer.

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

[0035] As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 1 to 20 is preferably used. The (meth)acrylic acid alkyl ester may have a branched alkyl group or may have a cyclic alkyl group (alicyclic alkyl group).

[0036] Specific examples of the (meth)acrylic acid alkyl ester having a chain 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 of the acrylate 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, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0037] Specific examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; and (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring such as dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate. The (meth)acrylic acid alkyl esters having an alicyclic alkyl group may have a substituent on the ring, such as 3,3,5-trimethylcyclohexyl (meth)acrylate. The (meth)acrylic acid alkyl ester having an alicyclic alkyl group may also be a (meth)acrylic acid ester containing a condensed ring of an alicyclic structure and a ring structure having an unsaturated bond, such as dicyclopentenyl (meth)acrylate.

[0038] Among the exemplified (meth)acrylic acid alkyl esters, from the viewpoint of lowering the Tg of the base polymer, (meth)acrylic acid C 1-9 Alkyl esters are preferred, and (meth)acrylic acid C 4-9 Alkyl esters are preferred. The (meth)acrylic acid alkyl ester is preferably one whose homopolymer has a glass transition temperature of -50°C or lower. The glass transition temperature of the homopolymer of the (meth)acrylic acid alkyl ester is more preferably -55°C or lower, and even more preferably -60°C or lower. (Meth)acrylic acid C whose homopolymer has a glass transition temperature of -50°C or lower 1-9Specific examples of alkyl esters include 2-ethylhexyl acrylate (Tg: -70°C), n-hexyl acrylate (Tg: -65°C), n-octyl acrylate (Tg: -65°C), isononyl acrylate (Tg: -60°C), n-nonyl acrylate (Tg: -58°C), isooctyl acrylate (Tg: -58°C), butyl acrylate (Tg: -55°C), etc. Among these, butyl acrylate, 2-ethylhexyl acrylate, and n-octyl acrylate are preferred.

[0039] As the (meth)acrylic acid alkyl ester, (meth)acrylic acid C having an alkyl group with 1 to 9 carbon atoms 1-9 Alkyl ester and (meth)acrylic acid C in which the alkyl group has 10 to 20 carbon atoms 10-20 Alkyl esters may be used in combination. (Meth)acrylic acid C 10-20 Alkyl esters have a temperature range (plateau region) near Tg where the viscoelasticity is less dependent on temperature. Therefore, when an acrylic base polymer contains (meth)acrylic acid C as a monomer component, 1-9 In addition to alkyl esters, (meth)acrylic acid C 10-20 By including an alkyl ester, the temperature dependency of the storage modulus in the low temperature range is reduced, which may prevent warping of the adherend due to temperature changes and peeling of the reinforcing film from the adherend.

[0040] Since the temperature range of the plateau region is wide and the storage modulus in the plateau region is small, (meth)acrylic acid C 10-20 Among the chain alkyl esters, (meth)acrylic acid C 12-18 Alkyl esters are preferred. Among them, dodecyl (meth)acrylate and isostearyl (meth)acrylate are preferred, and dodecyl acrylate (also known as lauryl acrylate) is particularly preferred. As the (meth)acrylic acid alkyl ester, (meth)acrylic acid C 1-9 Alkyl ester and (meth)acrylic acid C 10-20 When alkyl esters are used in combination, a combination of 2-ethylhexyl acrylate or n-octyl acrylate with dodecyl acrylate is particularly preferred.

[0041] The content of the (meth)acrylic acid alkyl ester is preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 60% by weight or more, based on the total amount of monomer components constituting the base polymer.

[0042] The acrylic base polymer may contain two or more types of (meth)acrylic acid alkyl esters as monomer components. 6-9 Alkyl ester and (meth)acrylic acid C 10-20 When an alkyl ester is contained, the storage modulus of the pressure-sensitive adhesive at low temperatures tends to decrease.

[0043] As (meth)acrylic acid alkyl ester, (meth)acrylic acid C 6-9 Alkyl ester and (meth)acrylic acid C 10-20 When alkyl ester is contained, (meth)acrylic acid C is used for 100 parts by weight of the total amount of the constituent monomer components of the acrylic polymer. 6-9 The amount of alkyl ester is preferably 15 to 84 parts by weight, and (meth)acrylic acid C 10-20 The amount of alkyl ester is preferably 10 to 79 parts by weight. 6-9 The amount of the alkyl ester may be 20 to 70 parts by weight, 30 to 60 parts by weight, 35 to 55 parts by weight, or 40 to 50 parts by weight, and the amount of the (meth)acrylic acid C 10-20 The amount of alkyl ester may be 15 to 60 parts by weight, 20 to 50 parts by weight, 25 to 45 parts by weight, or 30 to 40 parts by weight.

[0044] The acrylic base polymer preferably contains a monomer component having a crosslinkable functional group as a copolymerization component. Examples of the monomer having a crosslinkable functional group include a hydroxy group-containing monomer and a carboxy group-containing monomer. The acrylic base polymer may contain both a hydroxy group-containing monomer and a carboxy group-containing monomer as copolymerization components, or may contain only one of them. The introduction of a crosslinked structure into the acrylic base polymer tends to improve the cohesive strength and the peelability of the pressure-sensitive adhesive layer 2 from the adherend before photocuring.

[0045] Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 4-(hydroxymethyl)cyclohexylmethyl (meth)acrylate, etc. Among these, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred because they contribute significantly to improving the adhesive strength of the pressure-sensitive adhesive after photocuring.

[0046] Examples of the carboxy group-containing monomer include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc. Among these, acrylic acid and methacrylic acid are preferred, with acrylic acid being particularly preferred, since they tend to increase the cohesiveness of the pressure-sensitive adhesive, thereby improving the adhesive strength and adhesive retention.

[0047] The amount of the monomer having a crosslinkable functional group (total amount of hydroxy group-containing monomer and carboxy group-containing monomer) relative to a total of 100 parts by weight of the constituent monomer components of the acrylic base polymer is preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight, and even more preferably 1.5 to 7 parts by weight.

[0048] The acrylic base polymer may contain, as a constituent monomer component, a nitrogen-containing monomer such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinylcarboxylic acid amides, or N-vinylcaprolactam.

[0049] The acrylic base polymer may contain, as a constituent monomer component, a (meth)acrylic acid ester having an alkylene oxide chain. The (meth)acrylic acid ester having an alkylene oxide chain is represented by the following general formula (1). CH2=CR 1 -COO-(R 2 -O) m -R 3 (1)

[0050] R in general formula (1) 1 is a hydrogen atom or a methyl group, and R 1 is a hydrogen atom, the compound of formula (1) is an acrylate, 1 Compounds of formula (1) where is a methyl group are methacrylates.

[0051] R in general formula (1) 2 is an alkylene group such as ethylene, propylene, or butylene, and -R 2 -O- is an alkylene oxide chain. -R 2 Specific examples of -O- include ethylene oxide (-CH2CH2-O-), propylene oxide (-CH(CH3)CH2-O-), and butylene oxide (-CH2CH2CH2CH2-O-).

[0052] In general formula (1), m is the number of repeating alkylene oxide units and is an integer of 1 or more. m is preferably 1 to 5. If m is too large, the (meth)acrylate compound represented by general formula (1) tends to act as a chain transfer agent, and the molecular weight of the acrylic base polymer as a polymer does not become sufficiently large, which may result in insufficient adhesive strength of the pressure-sensitive adhesive. 3 is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 20 carbon atoms. From the viewpoint of lowering the Tg of the acrylic base polymer and improving compatibility with the photocuring agent, R 3 is preferably an alkyl group having 1 to 3 carbon atoms, and a methyl group or an ethyl group is particularly preferred.

[0053] Specific examples of the compound represented by general formula (1) include methoxyethyl acrylate, phenoxyethyl acrylate, ethoxyethoxyethyl acrylate, and methoxytriethylene glycol acrylate.

[0054] The acrylic base polymer may contain other monomer components, such as vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphate group-containing monomers, and acid anhydride group-containing monomers.

[0055] From the viewpoint of imparting excellent adhesive properties to the PSA, the glass transition temperature of the acrylic base polymer is preferably −10° C. or lower, more preferably −15° C. or lower, and even more preferably −20° C. or lower. The glass transition temperature of the acrylic base polymer may be −25° C. or lower or −30° C. or lower. The glass transition temperature of the acrylic base polymer is generally −100° C. or higher, and may be −80° C. or higher or −70° C. or higher.

[0056] The glass transition temperature is the temperature (peak top temperature) at which the loss tangent tanδ in viscoelasticity measurement is maximized. Instead of the glass transition temperature determined by viscoelasticity measurement, the theoretical Tg calculated by the Fox formula may be used. The theoretical Tg is the glass transition temperature Tg of the homopolymer of the constituent monomer components of the acrylic base polymer. i and the weight fraction W of each monomer component i It is calculated using the following Fox formula: 1 / Tg=Σ(W i / Tg i )

[0057] Tg is the glass transition temperature of the polymer chain (unit: K), W i is the weight fraction of the monomer component i that constitutes the segment (copolymerization ratio by weight), Tg i is the glass transition temperature (unit: K) of the homopolymer of monomer component i. The glass transition temperature of the homopolymer can be determined from the values ​​listed in Polymer Handbook, 3rd Edition (John Wiley & Sons, Inc., 1989). For the Tg of a homopolymer of a monomer not listed in the above literature, the peak top temperature of tan δ measured by dynamic viscoelasticity measurement can be used.

[0058] The above monomer components are polymerized by various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization to obtain an acrylic polymer as a base polymer. Solution polymerization is preferred from the viewpoints of cost and the balance of adhesive strength, holding power, and other properties of the pressure-sensitive adhesive. Ethyl acetate, toluene, etc. are used as the solvent for solution polymerization. The solution concentration is usually about 20 to 80% by weight. Various known polymerization initiators such as azo-based and peroxide-based initiators can be used. A chain transfer agent may be used to adjust the molecular weight. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

[0059] The weight-average molecular weight of the acrylic base polymer is preferably 100,000 to 2,000,000, more preferably 200,000 to 1,500,000, and even more preferably 300,000 to 1,000,000. When a crosslinked structure is introduced into the acrylic base polymer, the molecular weight of the acrylic base polymer refers to the molecular weight before the introduction of the crosslinked structure.

[0060] (Crosslinking agent) It is preferable to introduce a crosslinked structure into the base polymer in order to provide the pressure-sensitive adhesive with an appropriate cohesive strength, thereby developing adhesive strength, and ensuring the peelability of the pressure-sensitive adhesive layer from the adherend before photocuring. For example, the crosslinked structure is introduced by adding a crosslinking agent to a solution obtained by polymerizing the base polymer and heating it 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.

[0061] Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. These crosslinking agents react with functional groups such as hydroxy groups and carboxy groups introduced into the acrylic base polymer to form a crosslinked structure. Isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they have high reactivity with the hydroxy groups and carboxy groups of the acrylic base polymer and allow for easy introduction of a crosslinked structure.

[0062] As the isocyanate-based crosslinking agent, a polyisocyanate having two or more isocyanate groups per molecule is used. The isocyanate-based crosslinking agent may be one having three or more isocyanate groups per molecule. Examples of the isocyanate-based crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate and xylylene diisocyanate; trimethylolpropane / trilene diisocyanate; Examples of suitable isocyanate crosslinking agents include isocyanate adducts such as a diisocyanate trimer adduct (e.g., "Takenate D101E" manufactured by Mitsui Chemicals), a trimethylolpropane / hexamethylene diisocyanate trimer adduct (e.g., "Coronate HL" manufactured by Tosoh), a trimethylolpropane adduct of xylylene diisocyanate (e.g., "Takenate D110N" manufactured by Mitsui Chemicals), and an isocyanurate of hexamethylene diisocyanate (e.g., "Coronate HX" manufactured by Tosoh). Examples of suitable isocyanate crosslinking agents include isocyanate compounds having a biuret group (e.g., "Duranate 24A-100" manufactured by Asahi Kasei) and isocyanate compounds having an allophanate group.

[0063] The epoxy crosslinking agent is a multifunctional epoxy compound having two or more epoxy groups in one molecule. The epoxy crosslinking agent may have three or more or four or more epoxy groups in one molecule. The epoxy group of the epoxy crosslinking agent may be a glycidyl group. Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether. As the epoxy-based crosslinking agent, commercially available products such as "Denacol" manufactured by Nagase ChemteX, and "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical may be used.

[0064] The amount of the crosslinking agent used may be adjusted appropriately depending on the composition, molecular weight, etc. of the acrylic base polymer. The amount of the crosslinking agent used is about 0.01 to 5 parts by weight, preferably 0.03 to 3 parts by weight, more preferably 0.05 to 1.0 part by weight, and may be 0.08 to 0.8 parts by weight or 0.1 to 0.5 parts by weight, relative to 100 parts by weight of the acrylic base polymer.

[0065] A crosslinking catalyst may be used to promote the formation of a crosslinked structure. Examples of crosslinking catalysts include organometallic compounds such as organometallic complexes (chelates), compounds of metals with alkoxy groups, and compounds of metals with acyloxy groups; and tertiary amines. Organometallic compounds are particularly 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 pressure-sensitive 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.

[0066] <Photocuring agent> The adhesive composition constituting the adhesive layer 2 contains, in addition to a base polymer, a compound having two or more photopolymerizable functional groups per molecule as a photocuring agent. An adhesive composition containing a photocuring agent has photocurability, and when photocuring is performed after lamination with an adherend, the adhesive strength with the adherend is improved.

[0067] The photopolymerizable functional group is preferably one that is polymerizable by a photoradical reaction, and the photocuring agent is preferably a compound having two or more ethylenically unsaturated bonds in one molecule, and polyfunctional (meth)acrylates are preferred because of their high compatibility with acrylic-based polymers.

[0068] In the present invention, a polyfunctional (meth)acrylate having no urethane bond and a polyfunctional (meth)acrylate having a urethane bond are used in combination as the photocuring agent. That is, the photocurable composition constituting the pressure-sensitive adhesive layer 2 contains a polyfunctional (meth)acrylate having no urethane bond and a polyfunctional (meth)acrylate having a urethane bond. Hereinafter, a polyfunctional (meth)acrylate having a urethane bond will be referred to as a "urethane (meth)acrylate." Furthermore, a polyfunctional (meth)acrylate having no urethane bond may be simply referred to as a "polyfunctional (meth)acrylate."

[0069] (Multifunctional (meth)acrylate) Examples of polyfunctional (meth)acrylates having no urethane bond 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; bisphenol A di(meth)acrylate, alkanediol di(meth)acrylate, glycerin di(meth)acrylate, glycerin tri(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, isocyanuric acid tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol acrylate, and the like. R Tall di(meth)acrylate, Pentaerythritol R Tetritol tri(meth)acrylate, Pentaerythritol R Examples include esters of polyol and (meth)acrylic acid, such as dipentaerythritol tetra(meth)acrylate and dipentaerythritol poly(meth)acrylate; and epoxy (meth)acrylate.

[0070] The polyfunctional (meth)acrylate having no urethane bond may be an ester of an alkylene oxide-modified polyol and (meth)acrylic acid. Examples of the ester of an alkylene oxide-modified polyol 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 acrylate, and the like. R Tall alkylene oxide modified di(meth)acrylate, pentaerythritol R Examples thereof include dipentaerythritol alkylene oxide modified tri(meth)acrylate and dipentaerythritol alkylene oxide modified poly(meth)acrylate.

[0071] Among the above, 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 are preferred as polyfunctional (meth)acrylates, as they exhibit suitable compatibility with acrylic base polymers. As the alkylene oxide, (poly)ethylene oxide or (poly)propylene oxide is preferred, and the chain length of the alkylene oxide (number of repeating units: n) is preferably about 1 to 15.

[0072] From the viewpoint of compatibility with the acrylic base polymer, the molecular weight of the polyfunctional (meth)acrylate used as the 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 adhesive strength 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, particularly preferably 200 or less, and may be 180 or less, 170 or less, or 160 or less. On the other hand, if the functional group equivalent of the polyfunctional (meth)acrylate is excessively small, the crosslinking density of the pressure-sensitive adhesive layer after photocuring may increase, resulting in reduced adhesiveness. Therefore, the functional group equivalent of the photocuring agent is preferably 80 or more, more preferably 100 or more, even more preferably 120 or more, and may be 130 or more, 140 or more, or 150 or more.

[0073] Two or more types of polyfunctional (meth)acrylates that do not have a urethane bond may be used in combination as the photocuring agent. For example, by using a polyfunctional (meth)acrylate that has relatively low compatibility with the acrylic base polymer in combination with a polyfunctional (meth)acrylate that has relatively high compatibility with the acrylic base polymer, a reinforcing film may be obtained that has a lower adhesive strength to the adherend and is easy to peel before photocuring, and a higher adhesive strength to the adherend and is difficult to peel after photocuring.

[0074] (urethane (meth)acrylate) The pressure-sensitive adhesive composition contains a urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton as a photocuring agent. By containing a urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton as a photocuring agent in addition to a polyfunctional (meth)acrylate having no urethane bond, the pressure-sensitive adhesive layer after photocuring tends to exhibit high adhesive strength to an adherend and to be prevented from decreasing in adhesive strength under high-temperature and high-humidity environments.

[0075] Here, "polyester" refers to polyester in the narrow sense, which means a polymer containing a carboxylic acid ester, i.e., a (-C-COO-) structural unit, which is a condensation structure of a carboxylic acid and an alcohol. "Polycarbonate" is a polymer containing a (-O-COO-) structural unit. Polycarbonate is a carbonate ester and is included in the broad sense of polyester.

[0076] A urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton can be obtained, for example, by reacting a polyisocyanate with a polyester polyol or a polycarbonate polyol to prepare a prepolymer having an isocyanate group at its terminal, and then bonding a (meth)acrylic compound having a hydroxy group to the isocyanate group at the terminal of the prepolymer. Alternatively, a urethane (meth)acrylate can be obtained by reacting a polyisocyanate with a (meth)acrylic compound having a hydroxy group, and then reacting the reaction product with a polyol.

[0077] Polyester polyols are polyesters having terminal hydroxyl groups, and are obtained by reacting a polybasic acid with a polyhydric alcohol so that the alcohol equivalent is in excess relative to the carboxylic acid equivalent. The polybasic acid component and polyhydric alcohol component that constitute the polyester polyol are typically a dibasic acid and a diol.

[0078] Examples of dibasic acid components include aromatic dicarboxylic acids such as orthophthalic acid, isophthalic acid, and terephthalic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, and octadecanedicarboxylic acid; and acid anhydrides and lower alcohol esters of these dicarboxylic acids.

[0079] Examples of diol components include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, and hydrogenated bisphenol F.

[0080] Commercially available polyester polyols include the "ETERNACOLL 3000" series manufactured by UBE and the "Nipporun" series manufactured by Tosoh.

[0081] Examples of polycarbonate polyols include polycarbonate polyols obtained by polycondensation of a diol component with phosgene; polycarbonate polyols obtained by transesterification of a diol component with a carbonate diester such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, ethylbutyl carbonate, ethylene carbonate, propylene carbonate, diphenyl carbonate, and dibenzyl carbonate; copolymer polycarbonate polyols obtained by combining two or more polyol components; polycarbonate polyols obtained by esterification of the above-mentioned various polycarbonate polyols with a carboxy group-containing compound; and various polycarbonate polyols obtained by esterification of the above-mentioned various polycarbonate polyols with a carboxy group-containing compound. Examples of the polycarbonate polyol include polycarbonate polyols obtained by etherifying a carbonate polyol with a hydroxyl group-containing compound; polycarbonate polyols obtained by transesterifying the above-mentioned various polycarbonate polyols with an ester compound; polycarbonate polyols obtained by transesterifying the above-mentioned various polycarbonate polyols with a hydroxyl group-containing compound; polyester-based polycarbonate polyols obtained by polycondensation of the above-mentioned various polycarbonate polyols with a dicarboxylic acid compound; and copolymerized polyether-based polycarbonate polyols obtained by copolymerizing the above-mentioned various polycarbonate polyols with an alkylene oxide.

[0082] Commercially available polycarbonate polyols include the "ETERNACOLL UH" series manufactured by UBE, the "BENEBIOL" series manufactured by Mitsubishi Chemical, and "DURANOL T5652" manufactured by Asahi Kasei.

[0083] The polyisocyanate may be any of an aromatic polyisocyanate, an alicyclic polyisocyanate, and an alicyclic polyisocyanate.

[0084] Aromatic polyisocyanates include phenylene diisocyanate and tolylene diisocyanate. SExamples of the polyisocyanate include butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate. Examples of the alicyclic polyisocyanate include cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and methylcyclohexane diisocyanate.

[0085] As the aromatic polyisocyanate, tolylene diisocyanate (TDI) is particularly preferred. Tolylene diisocyanate is 2,4-tolylene diisocyanate. S The polyisocyanate may be either 2,6-tolylene diisocyanate or 2,6-tolylene diisocyanate, or a mixture of the two. Hexamethylene diisocyanate (HDI) is particularly preferred as the aliphatic polyisocyanate. Isophorone diisocyanate (IPDI) is particularly preferred as the alicyclic polyisocyanate.

[0086] The polyisocyanate may be a trifunctional isocyanate having a cyanuric acid skeleton. Examples of the trifunctional isocyanate having a cyanuric acid skeleton include TDI trimer and HDI trimer. Alternatively, the polyisocyanate may be a polyisocyanate having a biuret group or an allophanate group.

[0087] Examples of the (meth)acrylic compound having a hydroxy group include compounds having one hydroxy group and one (meth)acryloyl group, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxymethyl acrylamide, and hydroxyethyl acrylamide; and compounds having one hydroxy group and two or more (meth)acryloyl groups, such as pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, trimethylolpropane di(meth)acrylate, and isocyanuric acid di(meth)acrylate.

[0088] By bonding an acrylic compound such as hydroxyethyl (meth)acrylate to an isocyanate-terminated prepolymer obtained by reacting a polyol with a diisocyanate, a bifunctional urethane (meth)acrylate having (meth)acryloyl groups at both ends can be obtained.

[0089] The urethane (meth)acrylate may have three or more (meth)acryloyl groups. For example, a trifunctional (or higher) urethane (meth)acrylate can be obtained by reacting a trifunctional isocyanate with a polyol and using an isocyanate-terminated prepolymer in which a diisocyanate is bonded to the end. Furthermore, a trifunctional (or higher) urethane (meth)acrylate can be obtained by using a compound having two or more (meth)acryloyl groups as a (meth)acrylic compound having a hydroxy group. Furthermore, a trifunctional (or higher) urethane (meth)acrylate can be obtained by using an isocyanate-terminated prepolymer obtained by reacting a trifunctional polyol with a diisocyanate.

[0090] The urethane (meth)acrylate may be commercially available from Kyoeisha Chemical, Shin-Nakamura Chemical, Negami Chemical Industries, Mitsubishi Chemical, Daicel Allnex, Resonac, or the like.

[0091] Two or more urethane (meth)acrylates may be used in combination as a photocuring agent. The urethane (meth)acrylate may be a mixture of urethane (meth)acrylates with different structures. For example, when a trifunctional isocyanate is reacted with an excess amount of polyol and a diisocyanate is bonded to the terminals to prepare a prepolymer, the diisocyanate bonds to both ends of the polyol that are not bonded to the trifunctional isocyanate, resulting in the production of a difunctional prepolymer as a by-product in addition to the trifunctional prepolymer. The reaction of this prepolymer composition with a (meth)acrylic compound having a hydroxy group produces a mixture of a trifunctional urethane (meth)acrylate and a difunctional urethane (meth)acrylate. A urethane (meth)acrylate having a polyester skeleton and a urethane (meth)acrylate having a polycarbonate skeleton may be used in combination as the urethane acrylate.

[0092] From the viewpoints of reducing initial adhesive strength, achieving high adhesive strength after photocuring, and maintaining adhesive strength in a high-temperature, high-humidity environment, the molecular weight of the urethane (meth)acrylate is preferably 1,000 to 50,000, more preferably 1,500 to 30,000, and may be 2,000 to 20,000, 2,500 to 15,000, or 3,000 to 10,000. The functional group equivalent (g / eq) of the (meth)acryloyl group of the urethane (meth)acrylate is preferably 500 to 20,000, more preferably 800 to 10,000, and even more preferably 1,000 to 7,000, and may be 1,200 to 5,000 or 1,500 to 4,000.

[0093] (Photocuring agent content) The content of the photocuring agent in the pressure-sensitive adhesive composition (total of the polyfunctional (meth)acrylate having no urethane bond and the urethane (meth)acrylate) is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, even more preferably 7 parts by weight or more, and may be 8 parts by weight or more or 10 parts by weight or more, relative to 100 parts by weight of the base polymer. By setting the amount of the photocuring agent in the above range, a reinforcing film is obtained that is easy to peel from the adherend before photocuring and that can be firmly adhered to the adherend after photocuring.

[0094] The greater the amount of photocuring agent, the weaker the adhesive strength between the adhesive and the adherend before photocuring, resulting in excellent peelability. On the other hand, if the amount of photocuring agent is excessively large, the photocuring agent is likely to bleed out, and when the reinforcing film is peeled from the adherend, the bleed-out components may transfer to the adherend, causing contamination. Furthermore, if the amount of photocuring agent is excessively large, the adhesive after photocuring tends to have low viscosity, insufficient adhesive strength and flexibility, and when applied to a foldable device, peeling is likely to occur at bent portions. Therefore, the content of the photocuring agent is preferably 50 parts by weight or less, more preferably 40 parts by weight or less, even more preferably 30 parts by weight or less, and may be 25 parts by weight or less, 20 parts by weight or less, or 15 parts by weight or less, per 100 parts by weight of the base polymer.

[0095] From the viewpoint of adjusting the adhesion between the pressure-sensitive adhesive layer and the adherend before and after photocuring to an appropriate range, the content of the polyfunctional (meth)acrylate not having a urethane bond in the pressure-sensitive adhesive composition is preferably 3 to 40 parts by weight, more preferably 5 to 30 parts by weight, and even more preferably 7 to 20 parts by weight, per 100 parts by weight of the base polymer.

[0096] From the viewpoint of suppressing a decrease in adhesive strength in a high-temperature, high-humidity environment, the content of the urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton in the pressure-sensitive adhesive composition is preferably 0.3 parts by weight or more, more preferably 0.5 parts by weight or more, even more preferably 0.8 parts by weight or more, and may be 1.0 parts by weight or more or 1.2 parts by weight or more, relative to 100 parts by weight of the base polymer.

[0097] Urethane (meth)acrylates having a polyester or polycarbonate skeleton contribute to increasing the adhesive strength of the pressure-sensitive adhesive layer after photocuring and maintaining the adhesive strength (suppressing a decrease in adhesive strength) in high-temperature, high-humidity environments, and also prevent peeling of the reinforcing film from the adherend. However, if the urethane (meth)acrylate content is excessively high, the adhesive layer may become cloudy due to reduced compatibility with the acrylic base polymer, or the photocuring agent may bleed out onto the surface of the pressure-sensitive adhesive layer (the adhesive interface with the adherend), causing contamination of the adherend. Furthermore, if the amount of urethane (meth)acrylate is excessively high, the increase in adhesive strength of the pressure-sensitive adhesive upon photocuring tends to be insufficient. Therefore, the content of urethane (meth)acrylates having a polyester or polycarbonate skeleton in the pressure-sensitive adhesive composition is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and may even be 7 parts by weight or less, or 5 parts by weight or less, per 100 parts by weight of the base polymer.

[0098] One of the presumed reasons why the use of urethane (meth)acrylates with a polyester or polycarbonate backbone as a photocuring agent prevents a decrease in adhesive strength in high-temperature, high-humidity environments is the formation of hydrogen bonds with the adherend and intermolecular interactions between carbonyl and nitrogen atoms. In urethane (meth)acrylates with a polyester or polycarbonate backbone, in addition to the urethane bond portion, the ester portion of the polyester or polycarbonate backbone (X-COO-: X is a carbon atom or oxygen atom) can form hydrogen bonds or intermolecular interactions with the material that constitutes the adherend (e.g., polyimide film).

[0099] In high-temperature, high-humidity environments, water easily penetrates the adhesive interface between the pressure-sensitive adhesive layer and the adherend, weakening the physical crosslinks between the two. This is thought to be one of the reasons for the decrease in adhesive strength. On the other hand, physical crosslinks formed by hydrogen bonds or intermolecular interactions between carbonyl and nitrogen atoms are not weakened by moisture penetration (the crosslinks are maintained). Urethane (meth)acrylates with a polyester or polycarbonate backbone have a higher number of ester bonds than urethane bonds, and a higher number of carbonyl groups than typical urethane (meth)acrylates with a polyether backbone. This leads to stronger hydrogen bonds with the adherend, which is thought to contribute to maintaining adhesive strength in high-temperature, high-humidity environments. Furthermore, when using urethane (meth)acrylates with a polycarbonate backbone, the adhesive layer exhibits higher adhesive strength with the adherend after photocuring than when using other urethane (meth)acrylates, and adhesive strength loss in high-temperature, high-humidity environments tends to be suppressed.

[0100] <Photopolymerization initiator> The photopolymerization initiator generates active species when irradiated with actinic rays, and promotes the curing reaction of the photocuring agent. As the photopolymerization initiator, it is preferable to use a photoradical polymerization initiator (photoradical generator).

[0101] The photoradical polymerization initiator is preferably one that generates radicals upon irradiation with visible light or ultraviolet light having a wavelength shorter than 450 nm, and examples thereof include hydroxyketones, benzyl dimethyl ketals, aminoketones, acylphosphine oxides, benzophenones, trichloromethyl group-containing triazine derivatives, etc. The photopolymerization initiators may be used alone or in combination of two or more.

[0102] The content of the photopolymerization initiator in the pressure-sensitive 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, relative to 100 parts by weight of the base polymer. The content of the photopolymerization initiator in the pressure-sensitive 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, relative to 100 parts by weight of the photocuring agent.

[0103] <Other ingredients> As described above, the photocurable pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer 2 contains an acrylic-based polymer, a photocuring agent, and a photopolymerization initiator. The pressure-sensitive adhesive composition may contain components other than these.

[0104] For example, the pressure-sensitive adhesive composition may contain an oligomer having a lower molecular weight than the base polymer. For example, the pressure-sensitive adhesive composition may contain, in addition to the acrylic base polymer, an oligomer having a weight-average molecular weight of about 1,000 to 30,000. of It may contain an acrylic oligomer.

[0105] The pressure-sensitive adhesive composition may contain an antistatic agent. When the pressure-sensitive adhesive contains an antistatic agent, the resistance of the pressure-sensitive adhesive layer is reduced, reducing the charge of the pressure-sensitive adhesive layer and also providing the effect of suppressing charge on the adherend. Examples of antistatic agents include ionic compounds containing organic cations, alkali metal salts, ion-conductive polymers, ion-conductive fillers, conductive polymers, etc. Among these, ionic compounds containing organic cations and alkali metal salts are preferred because of their excellent compatibility with acrylic-based polymers.

[0106] When the PSA composition contains an antistatic agent, the amount of the antistatic agent is about 0.01 to 3 parts by weight, preferably 0.03 to 2 parts by weight, more preferably 0.05 to 1 part by weight, and even more preferably 0.1 to 0.7 parts by weight, per 100 parts by weight of the acrylic base polymer. If the amount of antistatic agent is too small, the PSA may not be able to sufficiently reduce its resistance. If the amount of antistatic agent is too large, bleed-out of the antistatic agent may cause contamination or corrosion of the adherend, or a decrease in adhesive strength.

[0107] In addition to the above components, the pressure-sensitive adhesive composition may contain additives such as a silane coupling agent, a tackifier, a plasticizer, a softener, an anti-degradant, a filler, a colorant, an ultraviolet absorber, an antioxidant, and a surfactant, within a range that does not impair the properties of the present invention.

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

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

[0110] The thickness of the pressure-sensitive adhesive layer 2 is, for example, about 1 to 300 μm. The thicker the pressure-sensitive adhesive layer 2, the more the adhesive strength to the adherend tends to improve. On the other hand, if the pressure-sensitive adhesive layer 2 is excessively thick, the fluidity before photocuring may be high, making handling difficult. Therefore, the thickness of the pressure-sensitive adhesive layer 2 is preferably 3 to 100 μm, more preferably 5 to 50 μm, even more preferably 6 to 40 μm, and particularly preferably 8 to 30 μm. From the viewpoint of achieving a thinner thickness, the thickness of the pressure-sensitive adhesive layer 2 may be 25 μm or less, 20 μm or less, or 18 μm or less.

[0111] When the pressure-sensitive adhesive composition contains a crosslinking agent, it is preferable to promote crosslinking by heating or aging simultaneously with or after drying of the solvent. The heating temperature and heating time are appropriately set depending on the type of crosslinking agent used, and crosslinking is usually achieved by heating in the range of 20°C to 160°C for about 1 minute to 7 days. The heating for drying and removing the solvent may also serve as the heating for crosslinking.

[0112] Even after the crosslinking structure is introduced into the polymer by the crosslinking agent, the photocuring agent remains unreacted. Therefore, the pressure-sensitive adhesive layer 2 is made of a photocurable pressure-sensitive adhesive composition containing an acrylic-based polymer with a crosslinking structure introduced therein, a photocuring agent, and a photopolymerization initiator. When the pressure-sensitive adhesive layer 2 is formed on the film substrate 1, it is preferable to apply a release liner 5 onto the pressure-sensitive adhesive layer 2 for purposes such as protecting the pressure-sensitive adhesive layer 2. Crosslinking may be carried out after the release liner 5 is applied onto the pressure-sensitive adhesive layer 2.

[0113] When the pressure-sensitive adhesive layer 2 is formed on another substrate, the reinforcing film is obtained by transferring the pressure-sensitive adhesive layer 2 onto the film substrate 1 after drying the solvent. The substrate used to form the pressure-sensitive adhesive layer may be used as the release liner 5 as is.

[0114] As the release liner 5, a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, or polyester film is preferably used. The thickness of the release liner is typically 3 to 200 μm, preferably about 10 to 100 μm. The surface of the release liner 5 that comes into contact with the pressure-sensitive adhesive layer 2 is preferably treated with a release agent such as a silicone-based, fluorine-based, long-chain alkyl-based, or fatty acid amide-based release agent, or with silica powder or the like. By treating the surface of the release liner 5 with a release treatment, when the release liner 5 is peeled from the film substrate 1, peeling occurs at the interface between the pressure-sensitive adhesive layer 2 and the release liner 5, maintaining the pressure-sensitive adhesive layer 2 adhered to the film substrate 1. The release liner 5 may be antistatically treated on either or both of the release-treated and untreated surfaces. By treating the release liner 5 with an antistatic treatment, charging when the release liner is peeled from the pressure-sensitive adhesive layer can be suppressed.

[0115] [Characteristics of the reinforcing film and use of the reinforcing film] The reinforced film of the present invention is used by being attached to a device or a device component. The reinforced film 10 has a pressure-sensitive adhesive layer 2 fixed to a film substrate 1, and has low adhesive strength to the adherend after being attached to the adherend and before being photocured. Therefore, the reinforced film can be easily peeled from the adherend before being photocured.

[0116] The adherend to which the reinforcing film is attached is not particularly limited, and examples thereof include various electronic devices, optical devices, and their component parts. Before attaching the reinforcing film, the surface of the adherend may be subjected to an activation treatment for the purpose of cleaning, etc. Examples of surface activation treatment include plasma treatment, corona treatment, and glow discharge treatment.

[0117] By laminating a reinforcing film, appropriate rigidity is imparted, which is expected to improve the handleability and prevent breakage of thin members such as flexible devices. When a reinforcing film is laminated to a work-in-progress in the device manufacturing process, the reinforcing film may be laminated to a large-sized work-in-progress before it is cut to the product size. The reinforcing film may also be laminated roll-to-roll to a mother roll of a device manufactured by a roll-to-roll process.

[0118] The reinforcing film may be attached to the entire surface of the adherend, or may be selectively attached only to the area requiring reinforcement (area to be reinforced). Alternatively, the reinforcing film may be attached to the entire area requiring reinforcement (area to be reinforced) and the area not requiring reinforcement (area not to be reinforced), and then the reinforcing film attached to the area not requiring reinforcement may be cut and removed.

[0119] For example, a reinforcing film is laminated to a mother roll of a device or a work-in-progress thereof using a roll-to-roll method, and then the mother roll to which the reinforcing film is laminated is cut and separated into individual products. Only the reinforcing film is cut using a half cut, and the reinforcing film in the non-reinforced area is peeled off, thereby obtaining a device in which the reinforcing film is laminated to the area to be reinforced. The cutting method is not particularly limited, and any appropriate cutting method such as a rotary cutter, a push blade (e.g., a Thomson blade), or a laser cutter can be used.

[0120] Before the adhesive has been photocured, the reinforcing film is temporarily attached to the surface of the adherend and has a small adhesive strength, so the reinforcing film can be easily peeled off and removed from the surface of the adherend. The reinforcing film may be attached to the area to be reinforced and the area not to be reinforced, and the area to be reinforced may be selectively irradiated with light to photocure the adhesive, and then the reinforcing film in the area not to be reinforced, where the adhesive has not yet cured, may be selectively peeled off and removed.

[0121] From the viewpoint of facilitating peeling from the adherend and preventing adhesive residue on the adherend after peeling of the reinforcing film, the adhesive strength F0 between the pressure-sensitive adhesive layer 2 and the adherend before photocuring is preferably 1 N / 25 mm or less, more preferably 0.7 N / 25 mm or less, even more preferably 0.5 N / 25 mm or less, and may be 0.4 N / 25 mm or less, or 0.3 N / 25 mm or less. From the viewpoint of preventing peeling of the reinforcing film during storage or handling, the adhesive strength between the pressure-sensitive adhesive layer 2 and the adherend before photocuring is preferably 0.01 N / 25 mm or more, more preferably 0.02 N / 25 mm or more, and may be 0.03 N / 25 mm or more, 0.04 N / 25 mm or more, or 0.05 N / 25 mm or more.

[0122] Adhesion strength is measured by a peel test using a polyimide film as the adherend at a tensile speed of 300 mm / min and a peel angle of 180°. Unless otherwise specified, adhesion strength is measured at a temperature of 25°C and a relative humidity of 50%.

[0123] After laminating the reinforcing film to the adherend, the pressure-sensitive adhesive layer 2 is irradiated with actinic rays to photocure the pressure-sensitive adhesive layer. Ultraviolet rays are preferred as the actinic rays. The irradiation intensity and irradiation time of the actinic rays may be appropriately set depending on the composition and thickness of the pressure-sensitive adhesive layer 2. The pressure-sensitive adhesive layer 2 may be irradiated with actinic rays from either the film substrate 1 side or the adherend side, or may be irradiated with actinic rays from both sides.

[0124] When the pressure-sensitive adhesive layer 2 is photocured, the photocuring agent undergoes a curing reaction, increasing the adhesive strength with the adherend. From the viewpoint of adhesive reliability during practical use of the device, the adhesive strength F1 between the pressure-sensitive adhesive layer and the adherend after photocuring is preferably 5 N / 25 mm or more, more preferably 7 N / 25 mm or more, even more preferably 8 N / 25 mm or more, and may be 9 N / 25 mm or more or 10 N / 25 mm or more. In the reinforcing film, the pressure-sensitive adhesive layer after photocuring preferably has an adhesive strength to the polyimide film within the above range. The adhesive strength F1 between the pressure-sensitive adhesive layer and the adherend after photocuring is preferably 5 times or more, more preferably 10 times or more, even more preferably 15 times or more, and may be 20 times or more, 30 times or more, or 50 times or more, the adhesive strength F0 between the pressure-sensitive adhesive layer and the adherend before photocuring.

[0125] A sample obtained by laminating a reinforcing film to a polyimide film as an adherend and photocuring the pressure-sensitive adhesive layer preferably has an adhesive strength F2 between the photocured pressure-sensitive adhesive layer and the polyimide film of 4 N / 25 mm or more in a high-temperature, high-humidity environment of 60°C and 93% relative humidity. The adhesive strength F2 in a high-temperature, high-humidity environment is measured by leaving the sample at rest for 30 minutes in an environment of 60°C and 93% relative humidity, and then performing a 180° peel test in an environment of 60°C and 93% relative humidity.

[0126] If the adhesive strength F2 in a high-temperature, high-humidity environment is 4 N / 25 mm or more, peeling of the adhesive layer from the adherend can be suppressed even in locations where stress and strain are large within the device, such as bending locations of a foldable device. F2 is more preferably 5 N / 25 mm or more, even more preferably 6 N / 25 mm or more, and may be 7 N / 25 mm or more, 7.5 N / 25 mm or more, or 8 N / 25 mm or more.

[0127] A sample obtained by laminating a reinforcing film to a polyimide film as an adherend and photocuring the pressure-sensitive adhesive layer preferably exhibits a rate of decrease ΔF in adhesive strength of 60% or less in a high-temperature, high-humidity environment. ΔF(%)=100×(F1-F2) / F1

[0128] ΔF is the rate of decrease in adhesive strength F2 of the photocured adhesive layer in a high-temperature, high-humidity environment relative to adhesive strength F1 at room temperature, and the smaller the rate of decrease ΔF, the less adhesive strength is reduced in a high-temperature, high-humidity environment, and the more adhesive strength is maintained. ΔF is more preferably 50% or less, even more preferably 45% or less, and may be 40% or less.

[0129] As described above, when the pressure-sensitive adhesive composition contains a urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton as a photocuring agent, the adhesive strength of the photocured pressure-sensitive adhesive layer is prevented from decreasing in a high-temperature, high-humidity environment, which tends to reduce ΔF. Having a large F1 and a small ΔF results in a large adhesive strength F2 in a high-temperature, high-humidity environment, which reduces peeling of the reinforced film from the adherend, resulting in a device with a reinforced film that has excellent adhesive reliability.

[0130] The shear storage modulus of the adhesive layer after photocuring at -20°C is 5.0 x 10 5 Pa or less is preferable, and 3.0 × 10 5 Pa or less is more preferable, and 2.0×10 5 Pa or less is more preferable, and 1.5×10 5 Pa or less, 1.0×10 5 Pa or less or 9.0 x 10 4 The storage modulus of the pressure-sensitive adhesive layer 2 after photocuring is small at low temperatures, so that peeling of the pressure-sensitive adhesive layer at the bent portion can be suppressed even when the device to which the reinforced film is attached is repeatedly bent in a low-temperature environment or when the bent state is maintained for a long period of time. Therefore, a reinforced film having a pressure-sensitive adhesive layer with a small storage modulus at low temperatures can be suitably used for a foldable device.

[0131] In the reinforced film of the present invention, the pressure-sensitive adhesive layer 2 is photocurable, and the timing of curing can be set as desired. Processing of the reinforced film, such as processing and reworking, can be performed at any time between the time the reinforced film is attached to the adherend and the time the pressure-sensitive adhesive is photocured.

[0132] By laminating the reinforced film, the adherend is given appropriate rigidity and stress is alleviated and dispersed, thereby suppressing various defects that may occur in the manufacturing process, improving production efficiency, and improving yield. After photocuring, the pressure-sensitive adhesive layer exhibits high adhesive strength to the adherend, and maintains this high adhesive strength even in high-temperature, high-humidity environments. Therefore, in a device with a reinforced film in which the reinforced film of the present invention is laminated to a flexible device using a resin substrate, peeling of the reinforced film is unlikely to occur even at bending points, and the adhesive reliability is excellent. [Example]

[0133] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0134] [Polymerization of acrylic polymers] <Polymer A> A reaction vessel equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas inlet tube was charged with 96 parts by weight of 2-ethylhexyl acrylate (2EHA) and 4 parts by weight of 2-hydroxyethyl acrylate (2HEA) as monomers, 0.2 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 233 parts by weight of ethyl acetate as a solvent. Nitrogen gas was introduced and the mixture was purged with nitrogen for approximately 1 hour while stirring. The mixture was then heated to 60°C and reacted for 7 hours to obtain a solution of acrylic polymer A with a weight-average molecular weight (Mw) of 600,000.

[0135] <Polymers B and C> The amounts of the monomers charged were changed as shown in Table 1. Solutions of polymers B and C were obtained in the same manner as in the polymerization of polymer A except for the above.

[0136] <Polymer D> The amounts of the monomers charged were changed as shown in Table 1, the amount of the polymerization initiator (AIBN) was changed to 0.1 parts by weight, and the amount of the solvent (ethyl acetate) was changed to 200 parts by weight. A solution of polymer D was obtained in the same manner as in the polymerization of polymer A except for these changes.

[0137] The monomer ratios charged for acrylic polymers A to D and the weight average molecular weights (Mw) of the polymers are listed in Table 1. In Table 1, the monomers are abbreviated as follows: 2EHA: 2-ethylhexyl acrylate BA: Butyl acrylate NOAA: n-octyl acrylate LA: Lauryl acrylate AA: Acrylic acid 2HEA: 2-hydroxyethyl acrylate 4HBA: 4-hydroxybutyl acrylate MEA: Methoxyethyl acrylate

[0138] [Table 1]

[0139] [Preparation of reinforcing film] Example 1 (Preparation of Pressure-Sensitive Adhesive Composition) To a solution of acrylic polymer A (100% by weight of polymer solids), 0.1 parts by weight of a trifunctional isocyanate crosslinking agent (Tosoh's "Coronate HX") as a crosslinking agent, 0.02 parts by weight of iron acetylacetonate (Nihon Kagaku Sangyo's "Nacem Ferric") as a crosslinking catalyst, 0.3 parts by weight of IGM Resins' "Omnirad 651" as a photopolymerization initiator, and 0.2 parts by weight of 1-butyl-3-methylpyridinium bistrifluoromethanesulfonylimide (Nihon Carlit's "CIL-312") as an antistatic agent were added and mixed uniformly to prepare a pressure-sensitive adhesive composition.

[0140] (application of adhesive solution and cross-linking) The above-mentioned adhesive composition was applied to a 50 μm-thick polyethylene terephthalate film using a fountain roll so that the dried thickness would be 25 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated surface of a release liner (a 25 μm-thick polyethylene terephthalate film with antistatic treatment on both sides and silicone release treatment on one side) was attached to the adhesive-coated surface. Subsequently, aging treatment was performed for 4 days in an atmosphere at 25°C to promote crosslinking, resulting in a reinforced film in which a photocurable adhesive sheet was fixedly laminated onto a polyethylene terephthalate film substrate and a release liner was temporarily attached thereon.

[0141] <Example 2> (Preparation of Pressure-Sensitive Adhesive Composition) To a solution of acrylic polymer B (100% by weight as polymer solids), 0.5 parts by weight of a tetrafunctional epoxy crosslinker ("Tetrad C" manufactured by Mitsubishi Gas Chemical Company), 0.2 parts by weight of zirconium tetraacetylacetonate ("ZC-150" manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, the multifunctional acrylate and urethane acrylate shown in Table 2 as photocuring agents, 0.3 parts by weight of "Omnirad 651" manufactured by IGM Resins as a photopolymerization initiator, and 0.2 parts by weight of "CIL-312" manufactured by Nippon Carlit Co., Ltd. as an antistatic agent were added and mixed uniformly to prepare a pressure-sensitive adhesive composition.

[0142] (application of adhesive solution and cross-linking) Using the above pressure-sensitive adhesive composition, coating and crosslinking were carried out in the same manner as in Example 1 to prepare a reinforcing film.

[0143] Example 3 (Preparation of Pressure-Sensitive Adhesive Composition) To a solution of acrylic polymer C (100% by weight as polymer solids), 0.1 parts by weight of a trifunctional isocyanate crosslinking agent (Tosoh's "Coronate HX"), 0.02 parts by weight of Nippon Chemical Industry's "Nacem Ferric" as a crosslinking catalyst, the multifunctional acrylate and urethane acrylate shown in Table 2 as photocuring agents, 0.3 parts by weight of IGM Resins' "Omnirad 651" as a photopolymerization initiator, and 0.2 parts by weight of Nippon Carlit's "CIL-312" as an antistatic agent were added and mixed uniformly to prepare a pressure-sensitive adhesive composition.

[0144] (application of adhesive solution and cross-linking) Using the above pressure-sensitive adhesive composition, coating and crosslinking were carried out in the same manner as in Example 1 to prepare a reinforcing film.

[0145] <Examples 4 to 13, Comparative Examples 3 and 4> Pressure-sensitive adhesive compositions were prepared and reinforcing films were fabricated in the same manner as in Example 3, except that the type and amount of urethane acrylate used as the photocuring agent was changed as shown in Table 2. In Comparative Example 3, only a polyfunctional acrylate having no urethane bond was used as the photocuring agent, and no urethane acrylate was used.

[0146] <Examples 14 to 16> (Preparation of Pressure-Sensitive Adhesive Composition) A pressure-sensitive adhesive composition was prepared and a reinforcing film was produced in the same manner as in Example 2, except that acrylic polymer D was used instead of acrylic polymer B and the type and amount of photocuring agent added were changed as shown in Table 2.

[0147] <Comparative Example 1> A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that only a polyfunctional acrylate having no urethane bond was used as the photocuring agent, and no urethane acrylate was used, and a reinforcing film was produced.

[0148] <Comparative Example 2> A pressure-sensitive adhesive composition was prepared in the same manner as in Example 2, except that only a polyfunctional acrylate having no urethane bond was used as the photocuring agent, and no urethane acrylate was used, and a reinforcing film was produced from the prepared composition.

[0149] [Adhesion strength evaluation] A 25 μm-thick polyimide film (UBE "Upilex S") was attached to a glass plate using double-sided adhesive tape (Nitto Denko "No. 531") to obtain a polyimide film substrate for measurement. A 25 mm wide x 100 mm long piece of reinforced film was cut out, and the release liner was removed from the surface. The film was then attached to the polyimide film substrate for measurement using a hand roller.

[0150] This sample was left to stand for 30 minutes in an environment with a temperature of 25°C and a relative humidity of 50%, and then the edge of the PET film substrate of the reinforcing film was held with a chuck and a 180° peel test was performed at a pulling speed of 300 mm / min in an environment with a temperature of 25°C and a relative humidity of 50%, and the peel strength (adhesive strength F0 before photocuring) was measured.

[0151] Thirty minutes after laminating the reinforcing film to the polyimide film substrate for measurement, an LED light source with a wavelength of 365 nm was used from the reinforcing film side (PET film substrate side) with an integrated light intensity of 1000 mJ / cm 2 The pressure-sensitive adhesive layer was photocured by irradiating it with ultraviolet light of 180°. Using this test sample, a 180° peel test was carried out in the same manner as above, and the adhesive strength F1 after photocuring was measured.

[0152] In the same manner as described above, a test sample was prepared after photocuring the adhesive layer, and after leaving it to stand for 30 minutes in an environment of 60°C and 93% relative humidity, a 180° peel test was performed in an environment of 60°C and 93% relative humidity, and the adhesive strength F2 in a high-temperature, high-humidity environment was measured.

[0153] From the above adhesive strength measurements, the increase rate of adhesive strength before and after photocuring, F1 / F0, and the decrease rate of adhesive strength of the adhesive layer after photocuring in a high-temperature, high-humidity environment, ΔF (%) = 100 × (F1-F2) / F1, were calculated.

[0154] [Low temperature storage modulus] A pressure-sensitive adhesive composition was applied to a release liner and crosslinked in the same manner as in each of the above Examples and Comparative Examples to prepare a pressure-sensitive adhesive sheet (before photocuring). A release liner was attached to the surface of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet before photocuring to shield it from oxygen, and the sheet was exposed to 1000 mJ / cm irradiated with a 365 nm LED lamp. 2 The photocured adhesive sheets were stacked to prepare a measurement sample with a thickness of approximately 0.8 mm, and dynamic viscoelasticity measurements were performed under the following conditions using a rotational rheometer (TA Instruments "Discovery-HR2"), and the shear storage modulus G' at -20°C was read. (Measurement conditions) Deformation mode: Torsion Measurement frequency: 1Hz Heating rate: 5°C / min Measurement temperature: -50~150℃ Shape: Parallel plate 8.0mmφ

[0155] [Evaluation results] Table 2 shows the composition of the pressure-sensitive adhesive of the reinforcing films of the Examples and Comparative Examples (type of base polymer, type and amount of crosslinking agent, type and amount of photocuring agent), as well as the evaluation results of adhesive strength and storage modulus G' at -20°C. In Table 2, the amounts of crosslinking agent and photocuring agent are the amounts added per 100 parts by weight of the solid content of the acrylic polymer. Details of the crosslinking agent and photocuring agent are as follows:

[0156] <Crosslinking agent> TC: 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (tetrafunctional epoxy compound, "Tetrad C" manufactured by Mitsubishi Gas Chemical Company) C-HX: Isocyanurate of hexamethylene diisocyanate (Tosoh's "Coronate HX" 」 )

[0157] <Photocuring agent> (multifunctional acrylate) A200: Polyethylene glycol #200 (n=4) diacrylate ("NK Ester A-200" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent weight 151 g / eq) A600: Polyethylene glycol #600 (n=14) diacrylate ("NK Ester A-600" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent weight 371 g / eq) (urethane acrylate) UF-X9-83: Polycarbonate skeleton-containing urethane acrylate (Kyoeisha Chemical Company, "UF-X9-83", functional groups 2-3, weight-average molecular weight 8400) UF-X6-51: Polycarbonate skeleton-containing urethane acrylate (Kyoeisha Chemical Company, "UF-X6-51", functional groups 2-3, weight-average molecular weight 8400) UF-A7-52: Polycarbonate skeleton-containing urethane acrylate (Kyoeisha Chemical Company, "UF-A7-52," functional groups: 2, weight-average molecular weight: 5600) UF-H02: Polycarbonate skeleton-containing urethane acrylate (Kyoeisha Chemical's "UF-H02", functional group number 2, weight-average molecular weight 3000) UF-8001G(N): Polycarbonate skeleton-containing urethane acrylate (Kyoeisha Chemical Company, "UF-8001G(N)", functional groups: 2, weight-average molecular weight: 4500) UN-9000PEP: Polycarbonate-based urethane acrylate (Negami Chemical Industries, Ltd. "Art Resin UN-9000PEP", functional groups: 2, weight-average molecular weight: 5000) UN-9200A: Polycarbonate-based urethane acrylate (Negami Chemical Industries, Ltd. "Art Resin UN-9200A", functional groups: 2, weight-average molecular weight: 15,000) UF-3999BA: Polyester skeleton-containing urethane acrylate (Kyoeisha Chemical's "UF-3999BA", functional groups: 2, weight-average molecular weight: 15,000) UA-1138P: Polyether skeleton-containing urethane acrylate ("UA-1138P" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group number 2)

[0158] [Table 2]

[0159] In Comparative Examples 1 to 3, which contained only a polyfunctional acrylate without a urethane bond as a photocuring agent, the adhesive strength F1 of the pressure-sensitive adhesive after photocuring was smaller, and the adhesive strength F2 under a high-temperature, high-humidity environment was even smaller, compared to Examples 1 to 3. In Comparative Examples 1 to 3, the reduction rate ΔF of adhesive strength under a high-temperature, high-humidity environment was significantly greater than 60%.

[0160] Example 4, which contained a smaller amount of urethane acrylate (UF-X9-83) than Example 3, had a smaller F1 than Example 3, but the decrease rate ΔF of adhesive strength in a high-temperature, high-humidity environment was small at 24%, and adhesive strength F2 in a high-temperature, high-humidity environment was sufficiently larger than those of Comparative Examples 1 to 3. Examples 5 and 6, which contained a larger amount of urethane acrylate (UF-X9-83) than Example 3, had a small ΔF and showed high adhesive strength even in a high-temperature, high-humidity environment, similar to Example 3.

[0161] Examples 7 to 12, in which the type of urethane acrylate having a polycarbonate skeleton was changed, showed a small ΔF value and a high adhesive strength even in a high-temperature, high-humidity environment, similar to Example 3. ester In Example 13, which used a urethane acrylate (UF-3999BA) having a skeleton, the adhesive strength F1 after photocuring was smaller than in Examples 3, 7 to 12, but the decrease rate ΔF of adhesive strength in a high-temperature, high-humidity environment was small at 28%, and in a high-temperature, high-humidity environment, it showed high adhesive strength comparable to Examples 3, 7 to 12.

[0162] Examples 14 to 16, which used polymer D, exhibited excellent adhesive properties, similar to Examples 1 to 13. Furthermore, Examples 14 to 16 exhibited small storage moduli of the pressure-sensitive adhesive layer at low temperatures.

[0163] Comparative Example 4, which used a urethane acrylate containing a polyether skeleton (UA-1138P) as the photocuring agent, showed higher adhesive strength than Comparative Example 3, but ΔF exceeded 60%, and the adhesive strength F2 in a high-temperature, high-humidity environment was significantly lower than in Examples 3, 7 to 13, which used a urethane acrylate containing a polyester skeleton or polycarbonate skeleton as the photocuring agent.

[0164] From the above results, it can be seen that by using a urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton as a photocuring agent in addition to a multifunctional acrylate having no urethane bond, the adhesive layer after photocuring exhibits high adhesive strength to adherends such as polyimide films, has a small ΔF value, and maintains high adhesive strength even in high-temperature, high-humidity environments, thereby preventing the reinforcing film from peeling off from the adherend. [Explanation of symbols]

[0165] 1. Film substrate 2. Adhesive layer 10 Reinforcement film 5 Release liner 20 Adherent

Claims

1. A film substrate and a pressure-sensitive adhesive layer fixedly laminated on one main surface of the film substrate, The pressure-sensitive adhesive layer is a photocurable composition including an acrylic base polymer, a photocuring agent having two or more photopolymerizable functional groups, and a photopolymerization initiator; Before photocuring, the adhesive strength F 0 to a polyimide film is 1 N / 25 mm or less in an environment of a temperature of 25°C and a relative humidity of 50%; After photocuring, the adhesive strength F1 to a polyimide film is 5 N / 25 mm or more in an environment of a temperature of 25°C and a relative humidity of 50%, and the adhesive strength F2 to a polyimide film is 4 N / 25 mm or more in an environment of a temperature of 60°C and a relative humidity of 93%, the acrylic base polymer includes, as a monomer unit, one or more selected from the group consisting of a hydroxy group-containing monomer and a carboxy group-containing monomer, and a crosslinked structure is introduced into the acrylic base polymer; The photocuring agent includes a polyfunctional (meth)acrylate having no urethane bond, and a urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton. Reinforcement film.

2. The reinforcing film according to claim 1, wherein the photocurable composition contains 3 to 40 parts by weight of the polyfunctional (meth)acrylate having no urethane bond and 0.3 to 15 parts by weight of the urethane (meth)acrylate having a polyester skeleton or a polycarbonate skeleton, relative to 100 parts by weight of the acrylic base polymer.

3. The reinforcing film according to claim 1, wherein the urethane (meth)acrylate has a functional group equivalent of a (meth)acryloyl group of 500 to 20,000 g / eq.

4. The reinforced film according to claim 1 , wherein the polyfunctional (meth)acrylate having no urethane bond contains an alkylene oxide chain.

5. 2. The reinforcing film according to claim 1, wherein the polyfunctional (meth)acrylate having no urethane bond has a functional group equivalent of a (meth)acryloyl group of 80 to 500 g / eq.

6. Said F １ and the F ２ But 100 x (F １ -F ２ ) / F １ The reinforced film according to claim 1, wherein the film satisfies the following: ≦60.

7. A method for manufacturing a device having a reinforcing film bonded to a surface thereof, comprising: After the pressure-sensitive adhesive layer of the reinforcing film according to any one of claims 1 to 6 is temporarily attached to the surface of an adherend, A device manufacturing method comprising: irradiating the pressure-sensitive adhesive layer with active light rays to photocure the pressure-sensitive adhesive layer, thereby increasing the adhesive strength between the reinforcing film and the adherend.

8. The method for manufacturing a device described in claim 7, wherein after the reinforcing film is temporarily attached to the substrate, and before the adhesive layer is photocured, the reinforcing film temporarily attached to the substrate is cut, and the reinforcing film is peeled off and removed from a portion of the substrate.

9. The device manufacturing method according to claim 7 , wherein the adherend comprises a polyimide film, and the pressure-sensitive adhesive layer of the reinforcing film is attached to the polyimide film.

10. The method for manufacturing a device according to claim 7 , wherein the adherend is a foldable image display element.

11. A reinforcing method for laminating a reinforcing film to a surface of an adherend, comprising: The pressure-sensitive adhesive layer of the reinforcing film according to any one of claims 1 to 6 is temporarily attached to the surface of an adherend, A reinforcing method comprising irradiating the pressure-sensitive adhesive layer with active light rays to photocure the pressure-sensitive adhesive layer, thereby increasing the adhesive strength between the reinforcing film and the adherend.

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