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

Abstract

Provided is a reinforcing film which is easy to peel off directly after bonding with an adherend, which can be firmly adhered to the adherend by photocuring an adhesive after bonding with the adherend, and which is not susceptible to peeling due to a bending test. This reinforcing film (10) comprises an adhesive layer (2) fixedly layered on one principal surface of a film base material (1). The adhesive layer is composed of a photocurable composition containing a photocuring agent and an acrylic base polymer having a crosslinked structure. After photocuring, the adhesive layer preferably has a shear storage modulus at -20°C of 1.0 × 104 to 5.0 × 105 Pa, and a shear storage modulus at 25°C of 8.0 × 103 to 5.0 × 105 Pa.

Description

[Technical Field]

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

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

[0003] By temporarily attaching an adhesive film to the surface of a device or a device component before use, such as during device assembly, processing, transportation, etc., it is possible to prevent the adherend from being scratched or damaged. Patent 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 a high gel fraction of adhesive and 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, permanently bonding the film substrate to the surface of the adherend, making it usable as a reinforcing material for protecting the surface of devices, etc.

[0005] In recent years, organic EL panels using bendable substrates (flexible substrates) such as resin films have been put to practical use, and bendable flexible displays have been proposed. A foldable flexible display (foldable display) is repeatedly bent at the same location. At the bent portion, compressive stress is applied to the inside and tensile stress is applied to the outside, causing distortion at the bent portion and its surroundings, which may result in peeling of the adhesive from the adherend. Patent Document 2 proposes using a soft adhesive sheet to bond components in a foldable display to mitigate stress distortion at the bent portion (e.g., Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-41113 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-45213 [Patent Document 3] Japanese Patent Application Publication No. 2017-119801 Summary of the Invention [Problem to be solved by the invention]

[0007] When the reinforcing film proposed in Patent Document 1 is applied to a flexible device, peeling may occur at the bent portion because the adhesive is hard after photocuring. In particular, the flexibility and adhesive holding strength of the adhesive are low at low temperatures, so when a bending test is performed at low temperatures, the adhesive is likely to peel from the adherend at the bent portion. The adhesive sheets described in Patent Documents 2 and 3 are prevented from peeling from the adherend when repeatedly bent in a low-temperature environment, but the adhesive is not photocurable and shows high adhesion immediately after being attached to the adherend, making them difficult to peel or process.

[0008] In view of the above, the present invention aims to provide a reinforcing film that is easy to peel off immediately after being attached to an adherend, can be firmly adhered to the adherend by photocuring the adhesive after being attached to the adherend, and is less likely to peel off during a bending test. [Means for solving the problem]

[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-based polymer and a photocuring agent. The glass transition temperature of the acrylic-based polymer is preferably −45° C. or lower.

[0010] The acrylic base polymer contains, as monomer units, a hydroxyl group-containing monomer and a carboxyl group-containing monomer. Shi base The crosslinking agent may be an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, or another such crosslinking agent, which is bonded to the hydroxyl and / or carboxyl groups of the base polymer to introduce a crosslinked structure. The amount of the crosslinking agent may be about 0.05 to 1 part by weight per 100 parts by weight of the acrylic polymer.

[0011] The photocurable composition constituting the pressure-sensitive adhesive layer preferably contains 3 to 30 parts by weight of a photocuring agent per 100 parts by weight of the acrylic base polymer. For example, a polyfunctional (meth)acrylate is used as the photocuring agent. The polyfunctional (meth)acrylate may be an alkylene oxide-modified polyfunctional (meth)acrylate modified with an alkylene oxide such as ethylene oxide or propylene oxide. The functional group equivalent of the photocuring agent is, for example, about 80 to 300 g / eq.

[0012] After photocuring, the adhesive layer had a shear storage modulus of 1.0 × 10 at -20°C. 4 ~5.0×10 5 The shear storage modulus of the pressure-sensitive adhesive layer after photocuring at 25°C is preferably 8.0 × 10 3 ~5.0×10 5 Pa is preferred.

[0013] The shear storage modulus of the adhesive layer at -20°C before photocuring is 1.0 x 10 4 ~5.0×10 5 The shear storage modulus of the pressure-sensitive adhesive layer at 25°C before photocuring is preferably 5.0 × 10 3 ~1.0×10 4 Pa is preferred.

[0014] The shear storage modulus at 25°C of the pressure-sensitive adhesive layer after photocuring is preferably 1.2 to 7 times the shear storage modulus at 25°C of the pressure-sensitive adhesive layer before photocuring. The shear storage modulus at -20°C of the pressure-sensitive adhesive layer after photocuring is preferably 1.2 to 7 times the shear storage modulus at -20°C of the pressure-sensitive adhesive layer before photocuring.

[0015] The reinforcing film is attached to the surface of the device, and the pressure-sensitive adhesive layer is photocured to obtain a device with the reinforcing film. The device may be a flexible device that can be bent. [Effects of the Invention]

[0016] The reinforcing film of the present invention has a pressure-sensitive adhesive layer made of a photocurable composition, and by photocuring the pressure-sensitive adhesive layer after adhering to the adherend, the adhesive strength with the adherend is increased. Because the adhesive strength with the adherend is low before photocuring, the reinforcing film is easily peeled from the adherend. Even after photocuring, the pressure-sensitive adhesive layer of the reinforcing film has a low storage modulus and high stress-strain relaxation properties. Therefore, even when a foldable device is repeatedly bent at the same location, peeling of the pressure-sensitive adhesive layer at the bent location is suppressed, resulting in excellent adhesion reliability. [Brief explanation of the drawings]

[0017] [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. [Figure 4]FIG. 10 is a cross-sectional view showing a folded state of the device to which the reinforcing film is attached. DETAILED DESCRIPTION OF THE INVENTION

[0018] 1 is a cross-sectional view showing one embodiment of a reinforced film. Reinforced film 10 has a pressure-sensitive adhesive layer 2 on one main surface of a film substrate 1. The pressure-sensitive adhesive layer 2 is fixedly laminated on one main surface of the film substrate 1. The pressure-sensitive adhesive layer 2 is a photocurable pressure-sensitive adhesive made from a photocurable composition, and is cured by irradiation with actinic rays such as ultraviolet light, thereby increasing the adhesive strength with the adherend.

[0019] Fig. 2 is a cross-sectional view of a reinforced film in which a separator 5 is temporarily attached onto the main surface of a pressure-sensitive adhesive layer 2. Fig. 3 is a cross-sectional view of a device 100 with a reinforced film in which a reinforced film 10 is attached to the surface of a foldable device 20. Fig. 4 is a cross-sectional view showing a state in which the device is folded around a hinge 25.

[0020] The separator 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.

[0021] "Adhesion" 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 it easy to separate them at their interface.

[0022] In the reinforced film shown in Fig. 2, the film substrate 1 and the pressure-sensitive adhesive layer 2 are bonded together, and the separator 5 is temporarily bonded to the pressure-sensitive adhesive layer 2. When the film substrate 1 and the separator 5 are peeled apart, peeling occurs at the interface between the pressure-sensitive adhesive layer 2 and the separator 5, and the pressure-sensitive adhesive layer 2 remains bonded to the film substrate 1. No pressure-sensitive adhesive remains on the separator 5 after peeling.

[0023] In the device with a reinforcing film shown in FIG. 3, the device 20 and the adhesive layer 2 are temporarily attached to each other before the adhesive layer 2 is photocured. When the film substrate 1 and the device 20 are peeled off, the peeling occurs at the interface between the adhesive layer 2 and the device 20, so the adhesive layer 2 remains adhered to the film substrate 1. Because no adhesive remains on the device 20, peeling operations such as rework and cutting are easy. After the adhesive layer 2 is photocured, the adhesive strength between the adhesive layer 2 and the device 20 increases, resulting in a fixed state, making it difficult to peel the film 1 from the device 20.

[0024] [Film base material] A flexible plastic film is used as the film substrate 1 of the reinforcing film 10. In order to bond the film substrate 1 and the pressure-sensitive adhesive layer 2 together, it is preferable that the surface of the film substrate 1 to which the pressure-sensitive adhesive layer 2 is to be attached is not subjected to a release treatment.

[0025] The thickness of the film substrate is, for example, about 4 to 150 μm. From the viewpoint of reinforcing the device by imparting rigidity and cushioning impact, the thickness of the film substrate 1 is preferably 5 μm or more, more preferably 12 μm or more, even more preferably 20 μm or more, and particularly preferably 25 μm or more. From the viewpoint of imparting flexibility to the reinforcing film so that it can be folded, the thickness of the film substrate 1 is preferably 125 μm or less, more preferably 100 μm or less. From the viewpoint of achieving both mechanical strength and flexibility, the compressive strength of the film substrate 1 is 100 to 3000 kg / cm 2 is preferred, and 200 to 2900 kg / cm 2 More preferably, 300 to 2800 kg / cm 2 is more preferably 400 to 2700 kg / cm 2 is particularly preferred.

[0026] Examples of plastic materials constituting the film substrate 1 include polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, polyether ether ketone, polyethersulfone, polyarylate resins, and aramid resins. In a reinforcement film for an optical device such as a display, the film substrate 1 is preferably a transparent film. Furthermore, when photocuring of the pressure-sensitive adhesive layer 2 is performed by irradiating actinic rays from the film substrate 1 side, the film substrate 1 is preferably transparent to the actinic rays used to cure the pressure-sensitive adhesive layer. Polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, transparent polyimides, and transparent aramids are preferably used because they combine mechanical strength and transparency. When irradiating actinic rays from the adherend side, the adherend only needs to be transparent to the actinic rays, and the film substrate 1 does not need to be transparent to the actinic rays.

[0027] 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.

[0028] [Adhesive layer] The adhesive layer 2, which is fixedly laminated on the film substrate 1, is made of a photocurable composition containing a base polymer and a photocuring agent. Before photocuring, the adhesive layer 2 has low adhesive strength to adherends such as devices and device components, and is therefore easy to peel off. The adhesive layer 2 has improved adhesive strength to adherends upon photocuring, so the reinforcing film is less likely to peel off from the device surface even when the device is in use, resulting in excellent adhesive reliability.

[0029] Photocurable pressure-sensitive adhesives hardly cure under normal storage conditions, but cure when exposed to actinic rays such as ultraviolet rays. Therefore, the reinforcing film of the present invention has the advantage that the timing of curing of the pressure-sensitive adhesive layer 2 can be set as desired, allowing for flexible adaptation to process lead times, etc.

[0030] 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.

[0031] 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.

[0032] It is preferable that the adhesive strength of the pressure-sensitive adhesive layer 2 with the adherend increases upon photocuring and that the shear storage modulus (hereinafter simply referred to as "storage modulus") at low temperatures is small even after photocuring. The storage modulus of the pressure-sensitive adhesive is determined by reading the value at a predetermined temperature when measured at a frequency of 1 Hz, in the range of -50 to 150°C, and at a heating rate of 5°C / min, in accordance with the method described in JIS K7244-1 "Plastics - Test methods for dynamic mechanical properties."

[0033] The storage modulus of the adhesive layer after photocuring at -20°C is 5.0 × 10 5 Pa or less is preferable, and 4.0 × 10 5 Pa or less is more preferable, and 3.0 × 10 5 Pa or less is more preferable, and 2.5×10 5 Pa or less or 2.0 x 105 The storage modulus at low temperatures of the pressure-sensitive adhesive layer 2 after photocuring is small, and therefore the pressure-sensitive adhesive layer exhibits strain relaxation properties in a low-temperature environment, and therefore peeling of the pressure-sensitive adhesive layer at the bent portion can be suppressed even when the device to which the reinforcing film is bonded is repeatedly bent or when the bent state is maintained for a long period of time.

[0034] On the other hand, if the storage modulus of the pressure-sensitive adhesive layer after photocuring is excessively small, the pressure-sensitive adhesive layer is prone to plastic deformation, and the pressure-sensitive adhesive layer may peel off from the adherend due to insufficient adhesive holding power. Therefore, the storage modulus of the pressure-sensitive adhesive layer after photocuring at -20°C should be 1.0 × 10 4 Pa or more is preferable, 2.0 × 10 4 Pa or more is more preferable, 3.00 × 10 4 Pa or more is more preferable, and 4.0 × 10 4 Pa or more, 5.0×10 4 Pa or higher, 6.0×10 4 Pa or higher, 7.0×10 4 Pa or above or 8.0 x 10 4 It may be more than Pa.

[0035] To ensure adhesion at room temperature and to prevent the adhesive layer from protruding from the edges, the storage modulus of the adhesive layer at 25°C after photocuring is set to 8.0 × 10 3 ~1.5×10 5 Pa is preferred, 1.0 x 10 4 ~1.0×10 5 Pa is more preferable, 1.5 × 10 4 ~8.0×10 4 Pa is more preferable, and 2.0×10 4 ~6.0×10 4 It may be Pa.

[0036] The pressure-sensitive adhesive layer 2 is not particularly limited in composition as long as it contains a base polymer and a photocuring agent and the adhesive strength to the adherend is increased by photocuring. From the viewpoint of increasing the efficiency of curing by irradiation with actinic rays, the pressure-sensitive adhesive composition (photocurable composition) constituting the pressure-sensitive adhesive layer 2 preferably contains a photopolymerization initiator.

[0037] (base polymer) The base polymer is the main component of the pressure-sensitive adhesive composition and is the main factor determining the adhesive strength and storage modulus of the pressure-sensitive adhesive layer before photocuring. The pressure-sensitive adhesive composition preferably contains an acrylic polymer as the base polymer, and preferably 50 wt % or more of the pressure-sensitive adhesive composition is an acrylic polymer, because it has excellent optical transparency and adhesiveness and is easy to control the adhesive strength and storage modulus.

[0038] 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.

[0039] As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is preferably used. The alkyl group of the (meth)acrylic acid alkyl ester may be linear or branched. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and non-methyl (meth)acrylate. Examples thereof include isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0040] 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 those having a glass transition temperature of -50°C or lower are preferred. The glass transition temperature of the homopolymer of (meth)acrylic acid alkyl ester is more preferably -55°C or lower, and even more preferably -60°C or lower. (Meth)acrylic acid C having a glass transition temperature of -50°C or lower is preferred. 1-9 Specific 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 and 2-ethylhexyl acrylate are preferred, with 2-ethylhexyl acrylate being particularly preferred due to its low Tg.

[0041] The content of the (meth)acrylic acid alkyl ester is preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 85% by weight or more, and may be 90% by weight or more, 93% by weight or more, or 95% by weight or more, based on the total amount of the monomer components constituting the base polymer. 1-9 The amount of alkyl ester is preferably in the above range, and the total amount of 2-ethylhexyl acrylate and butyl acrylate is more preferably in the above range. The amount of 2-ethylhexyl acrylate may also be in the above range.

[0042] The acrylic base polymer preferably contains a monomer component having a crosslinkable functional group as a copolymerization component. Examples of the monomer having a crosslinkable functional group include a hydroxyl group-containing monomer and a carboxyl group-containing monomer. The base polymer may contain both a hydroxyl group-containing monomer and a carboxyl group-containing monomer as copolymerization components, or only one of them. The introduction of a crosslinked structure into the base polymer tends to improve the cohesive strength and the releasability of the pressure-sensitive adhesive layer 2 from the adherend before photocuring.

[0043] 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 (Tg: -15°C) and 4-hydroxybutyl acrylate (Tg: -32°C) are preferred because they contribute significantly to improving the adhesive strength of the pressure-sensitive adhesive after photocuring and have low Tg values ​​for the homopolymers.

[0044] Examples of the carboxy group-containing monomer include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl phthalic acid, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

[0045] The total amount of the hydroxy group-containing monomer and the carboxy group-containing monomer relative to the total amount of the constituent monomer components of the acrylic base polymer is preferably 0.5 to 15 wt%, more preferably 1 to 10 wt%, and even more preferably 2 to 7 wt%. When a crosslinked structure is introduced into the acrylic base polymer using an isocyanate crosslinking agent, the content of the hydroxy group-containing (meth)acrylic acid ester such as 2-hydroxyethyl (meth)acrylate or 4-hydroxypropyl (meth)acrylate is preferably within the above range.

[0046] 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.

[0047] 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.

[0048] The base polymer before the introduction of a crosslinked structure may be substantially free of nitrogen atoms. The proportion of nitrogen in the constituent elements of the base polymer may be 0.1 mol% or less, 0.05 mol% or less, 0.01 mol% or less, 0.005 mol% or less, 0.001 mol% or less, or 0.001 mol% or less. Using a base polymer substantially free of nitrogen atoms tends to suppress an increase in the adhesive strength (initial adhesive strength) of the pressure-sensitive adhesive layer before photocuring when the adherend is subjected to a surface activation treatment. By not using nitrogen-atom-containing monomers such as cyano group-containing monomers, lactam structure-containing monomers, amide group-containing monomers, and morpholine ring-containing monomers as the constituent monomer components of the base polymer, a base polymer substantially free of nitrogen atoms can be obtained. The amount of nitrogen-containing monomer relative to the total amount of the constituent monomer components of the acrylic base polymer may be 1 wt% or less, 0.5 wt% or less, 0.1 wt% or less, 0.05 wt% or less, or 0.

[0049] The glass transition temperature of the acrylic base polymer is preferably −45° C. or lower, more preferably −50° C. or lower, even more preferably −55° C. or lower, particularly preferably −60° C. or lower, and may be −63° C. or lower or −65° C. or lower. There are no particular restrictions on the lower limit of the glass transition temperature of the acrylic base polymer, but it is generally −80° C. or higher, and may be −75° C. or higher or −70° C. or higher.

[0050] The glass transition temperature is the temperature (peak top temperature) at which the loss tangent tanδ in viscoelasticity measurement is maximized. When the glass transition temperature is sufficiently lower than the ambient temperature of the device, the storage modulus G' of the adhesive layer within the ambient temperature range of the device tends to be small, and peeling during repeated bending tends to be suppressed.

[0051] 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 )

[0052] 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.

[0053] 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.

[0054] 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 base polymer, the molecular weight of the base polymer refers to the molecular weight before the introduction of the crosslinked structure.

[0055] (Crosslinking agent) In order to provide the pressure-sensitive adhesive with adequate cohesive strength, develop adhesive strength, and ensure the adhesive layer can be easily peeled from the adherend before photocuring, it is preferable to introduce a crosslinked structure into the base polymer. For example, a crosslinked structure can be introduced by adding a crosslinking agent to a solution obtained after polymerizing the base polymer and heating the solution as needed. 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 base polymer to form a crosslinked structure. Isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they are highly reactive with the hydroxy groups and carboxy groups of the base polymer and facilitate the introduction of a crosslinked structure.

[0056] The isocyanate crosslinking agent used is a polyisocyanate having two or more isocyanate groups in one molecule. Examples of the polyisocyanate 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 Examples of isocyanate adducts include a xylylene diisocyanate trimer adduct (e.g., "Coronate L" manufactured by Tosoh), a trimethylolpropane / hexamethylene diisocyanate trimer adduct (e.g., "Coronate HL" manufactured by Tosoh), a trimethylolpropane adduct of xylylene diisocyanate (e.g., "Takenate D110N" manufactured by Mitsui Chemicals), and an isocyanurate of hexamethylene diisocyanate (e.g., "Coronate HX" manufactured by Tosoh).

[0057] The 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.

[0058] The amount of the crosslinking agent used may be adjusted appropriately depending on the composition, molecular weight, etc. of the base polymer. The amount of the crosslinking agent used is about 0.03 to 2 parts by weight, preferably 0.05 to 1 part by weight, more preferably 0.08 to 0.8 parts by weight, and even more preferably 0.1 to 0.5 parts by weight, relative to 100 parts by weight of the base polymer.

[0059] A crosslinking catalyst may be used to promote the formation of a crosslinked structure. For example, crosslinking catalysts for isocyanate-based crosslinking agents include metal-based crosslinking catalysts (especially tin-based crosslinking catalysts) such as tetra-n-butyl titanate, tetraisopropyl titanate, nursem ferric, butyltin oxide, dioctyltin dilaurate, and dibutyltin dilaurate. The amount of crosslinking catalyst used is generally 0.1 parts by weight or less per 100 parts by weight of the base polymer.

[0060] (light curing agent) The pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer 2 contains a photocuring agent in addition to a base polymer. When the pressure-sensitive adhesive layer 2 made of a photocurable pressure-sensitive adhesive composition is photocured after being attached to an adherend, the adhesive strength to the adherend is improved.

[0061] As the photocuring agent, a photocurable monomer or a photocurable oligomer is used. As the photocuring agent, a compound having two or more ethylenically unsaturated bonds in one molecule is preferred. Furthermore, as the photocuring agent, a compound showing compatibility with the base polymer is preferred. In order to show appropriate compatibility with the base polymer, the photocuring agent is preferably a liquid at room temperature.

[0062] It is preferable to use a polyfunctional (meth)acrylate as the photocuring agent because it has high compatibility with the acrylic base polymer. A typical example of the polyfunctional (meth)acrylate is an ester of a polyol and (meth)acrylic acid. Specific examples of the polyfunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, isocyanuric acid di(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and trimethylolpropanediol di(meth)acrylate. Examples of the acrylate include ethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate, and isoprene (meth)acrylate.

[0063] The polyfunctional (meth)acrylate may be an ester of an alkylene oxide-modified polyol and (meth)acrylic acid. Examples of the alkylene oxide include ethylene oxide (EO) and propylene oxide (PO). The alkylene oxide may be a polyalkylene oxide such as polyethylene glycol or polypropylene glycol. The chain length n of the alkylene oxide is approximately 1 to 10. By adjusting the type and chain length of the alkylene oxide, the compatibility with the acrylic base polymer can be adjusted to an appropriate range.

[0064] Specific examples of alkylene oxide-modified polyfunctional (meth)acrylates include bisphenol A ethylene oxide-modified di(meth)acrylate, bisphenol A propylene oxide-modified di(meth)acrylate, trimethylolpropane ethylene oxide-modified tri(meth)acrylate, trimethylolpropane propylene oxide-modified tri(meth)acrylate, isocyanuric acid ethylene oxide-modified di(meth)acrylate, isocyanuric acid propylene oxide-modified di(meth)acrylate, isocyanuric acid ethylene oxide-modified tri(meth)acrylate, isocyanuric acid propylene oxide-modified tri(meth)acrylate, pentaerythritol ethylene oxide-modified tetra(meth)acrylate, and pentaerythritol propylene oxide-modified tetra(meth)acrylate.

[0065] The polyfunctional (meth)acrylate may be a metal (meth)acrylate such as zinc (meth)acrylate, magnesium (meth)acrylate, calcium (meth)acrylate, barium (meth)acrylate, strontium (meth)acrylate, nickel (meth)acrylate, copper (meth)acrylate, or aluminum (meth)acrylate.

[0066] The compatibility between the base polymer and the photocuring agent also depends on the molecular weight of the photocuring agent. The smaller the molecular weight of the photocuring agent, the higher the compatibility with the base polymer tends to be. From the viewpoint of compatibility with the base polymer, the molecular weight of the photocuring agent is preferably 1500 or less, more preferably 1000 or less, and may be 800 or less, 600 or less, 500 or less, 450 or less, or 400 or less.

[0067] Furthermore, the smaller the functional group equivalent weight of the photocuring agent (i.e., the greater the number of functional groups per unit molecular weight), the higher the compatibility with the base polymer tends to be. From the viewpoint of compatibility with the base polymer, the functional group equivalent weight (g / eq) of the photocuring agent is preferably 80 to 300, more preferably 90 to 200, and even more preferably 100 to 170, and may be 110 to 160 or 120 to 150.

[0068] If the base polymer and photocuring agent are not completely compatible, the liquid photocuring agent will bleed out to the surface, forming a weak boundary layer (WBL) at the adhesive interface with the adherend, strengthening the liquid properties. When a WBL is formed, the adhesive layer retains its bulk properties, such as storage modulus, while the liquid properties of the surface (adhesive interface) become stronger, which tends to weaken the adhesive strength with the adherend.

[0069] When the base polymer and photocuring agent are moderately compatible but not completely compatible, a WBL is formed in the adhesive layer before photocuring, resulting in low initial adhesive strength and easy peeling from the adherend. On the other hand, after photocuring, the liquid properties of the photocuring agent disappear and a photocrosslinked structure is uniformly introduced into the adhesive layer, significantly improving adhesive strength with the adherend.

[0070] The compatibility between the base polymer and the photocuring agent is mainly affected by the structure of the compound. The structure and compatibility of the compound can be evaluated, for example, by the Hansen solubility parameter (HSP). The Hansen solubility parameter (HSP) is calculated by multiplying the Hildebrand solubility parameter δ by the dispersion term δ. d , polarity term δ p , and the hydrogen bond term δ h and expressed in three-dimensional space, and δ 2 =δ d 2 +δ p 2 +δ h 2 The following relationship holds: Dispersion term δ d is the effect of dispersion forces, and the polar term δ p is the effect of dipole-dipole forces, and the hydrogen bond term δ h indicates the effect of hydrogen bonding. The HSP distance Ra of two substances is the difference in dispersion terms between the two substances, Δδ d , the difference in polar terms Δδ p , and the difference in hydrogen bond terms Δδ h From this, Ra={4Δδ d 2 +Δδ p 2 +Δδ h2} 1 / 2 The smaller the Ra, the higher the compatibility, and the larger the Ra, the lower the compatibility.

[0071] Details of Hansen solubility parameters are given in Hansen Solubility Parameters: A Users Handbook (CRC Press, 2007) by Charles M. Hansen, and for substances for which literature values ​​are unknown, they can be calculated using computer software Hansen Solubility Parameters in Practice (HSPiP).

[0072] As mentioned above, acrylic base polymers with low glass transition temperatures have a high proportion of (meth)acrylic acid esters, such as 2-ethylhexyl acrylate, in their constituent monomer components, and a low proportion of highly polar monomers, such as hydroxyl-group-containing monomers, carboxyl-group-containing monomers, and nitrogen-containing monomers. When using a base polymer with a low glass transition temperature and low polarity, the HSP distance Ra between the base polymer and the photocuring agent can be adjusted within an appropriate range by using a multifunctional (meth)acrylate incorporating an alkylene oxide, such as ethylene oxide or propylene oxide, as the photocuring agent. The longer the chain length n of the alkylene oxide in the alkylene oxide-modified multifunctional (meth)acrylate, the larger the HSP distance Ra tends to be.

[0073] If the HSP distance Ra between the base polymer and the photocuring agent is excessively large, although the initial adhesive strength is low, contamination due to bleed-out of the photocuring agent may occur, and the increase in adhesive strength due to photocuring may be insufficient. Therefore, the chain length n of the alkylene oxide is preferably 1 to 5, more preferably 1 to 3. For example, when the photocuring agent is trimethylolpropane ethylene oxide-modified triacrylate, the chain length n of ethylene oxide (EO) attached to each of the three methylol groups of trimethylolpropane is preferably 1 or 2. A pressure-sensitive adhesive containing a low-Tg acrylic base polymer whose main constituent monomer is 2-ethylhexyl acrylate and trimethylolpropane EO-modified triacrylate whose chain length n is 1 or 2 exhibits low initial adhesive strength and high adhesive strength to the adherend after photocuring. From the viewpoint of suppressing bleed-out of the photocuring agent to the surface of the pressure-sensitive adhesive layer, the chain length n of EO is particularly preferably 1.

[0074] The type and amount of photocuring agent affect not only the adhesive strength but also the bulk properties of the adhesive. If the base polymer of the adhesive composition is the same, the change in the storage modulus of the adhesive layer before photocuring is small even if the type of photocuring agent is different. On the other hand, as the content of the photocuring agent increases, the content of the base polymer in the composition becomes relatively smaller, and the storage modulus of the adhesive layer before photocuring tends to decrease.

[0075] The smaller the functional group equivalent weight of the photocuring agent and the greater the content of the photocuring agent, the higher the crosslink density due to photocuring, and therefore the greater the storage modulus of the pressure-sensitive adhesive layer after photocuring. That is, the greater the content of the photocuring agent, the smaller the storage modulus of the pressure-sensitive adhesive layer before photocuring and the greater the storage modulus of the pressure-sensitive adhesive layer after photocuring.

[0076] From the viewpoint of increasing the adhesive strength of the pressure-sensitive adhesive after photocuring while suppressing an excessive increase in storage modulus, the content of the photo-curing agent in the pressure-sensitive adhesive composition is preferably 3 to 30 parts by weight, more preferably 5 to 20 parts by weight, and may be 6 to 15 parts by weight or 7 to 12 parts by weight, relative to 100 parts by weight of the base polymer.

[0077] Two or more types of photocuring agents may be used in combination. When two or more types of photocuring agents are used in combination, the total amount of the photocuring agents is preferably within the above range. For example, by using a photocuring agent having a relatively high compatibility with the base polymer in combination with a photocuring agent having a relatively low compatibility with the base polymer, it is possible to adjust the properties of the pressure-sensitive adhesive layer before and after photocuring, such as increasing the storage modulus of the pressure-sensitive adhesive at room temperature after photocuring while keeping the initial adhesive strength low.

[0078] (Photopolymerization initiator) The pressure-sensitive adhesive composition preferably contains a photopolymerization initiator. The photopolymerization initiator generates active species upon irradiation with actinic rays and promotes the curing reaction of the photocuring agent. As the photopolymerization initiator, a photocationic initiator (photoacid generator), a photoradical initiator, a photoanionic initiator (photobase generator), etc. are used depending on the type of photocuring agent, etc. When a polyfunctional acrylate is used as the photocuring agent, it is preferable to use a photoradical initiator. As the photoradical initiator, a photoradical generator that is cleaved by visible light or ultraviolet light having a wavelength shorter than 450 nm to generate radicals is preferred, and examples of the photoradical initiator include hydroxyketones, benzyl dimethyl ketals, aminoketones, acylphosphine oxides, benzophenones, and trichloromethyl group-containing triazine derivatives. The photoradical generators may be used alone or in combination of two or more.

[0079] When transparency is required for the pressure-sensitive adhesive layer 2, the photopolymerization initiator (photoradical generator) preferably has low sensitivity to light (visible light) with a wavelength longer than 400 nm. For example, the photopolymerization initiator (photoradical generator) preferably has an absorption coefficient of 1×10 at a wavelength of 405 nm. 2 [mLg -1 cm -1 Furthermore, if a photopolymerization initiator having a low sensitivity to visible light is used, the photopolymerization initiator is less likely to be cleaved due to external light in the storage environment, and the storage stability of the reinforcing film can be improved.

[0080] The content of the photopolymerization initiator in the pressure-sensitive adhesive composition is preferably 0.001 to 5 parts by weight, more preferably 0.01 to 3 parts by weight, and even more preferably 0.03 to 1 part by weight, relative to 100 parts by weight of the base polymer.

[0081] (oligomer) The pressure-sensitive adhesive composition may contain an oligomer in addition to the base polymer. For example, the pressure-sensitive adhesive composition may contain an acrylic oligomer in addition to the acrylic base polymer. The oligomer used has a weight-average molecular weight of about 1,000 to 30,000. The acrylic oligomer contains a (meth)acrylic acid alkyl ester as a main constituent monomer component. From the viewpoint of increasing the adhesive strength of the pressure-sensitive adhesive layer 2 after photocuring, the glass transition temperature of the acrylic oligomer is preferably 40°C or higher, more preferably 50°C or higher. The oligomer may contain a crosslinkable functional group, similar to the base polymer.

[0082] The content of the oligomer in the pressure-sensitive adhesive composition is not particularly limited. When the pressure-sensitive adhesive composition contains an acrylic oligomer in addition to an acrylic base polymer, the amount of the oligomer relative to 100 parts by weight of the base polymer is preferably 0.1 to 20 parts by weight, more preferably 0.3 to 10 parts by weight, and even more preferably 0.5 to 5 parts by weight, from the viewpoint of adjusting the adhesive strength within an appropriate range.

[0083] (Other additives) In addition to the components exemplified above, the adhesive layer 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, a surfactant, and an antistatic agent, within a range that does not impair the properties of the present invention.

[0084] [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.

[0085] 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.

[0086] 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.

[0087] The introduction of a crosslinked structure into the base polymer increases the gel fraction, which tends to increase the storage modulus of the adhesive layer 2. The higher the gel fraction of the adhesive before photocuring, the harder the adhesive is, and the less adhesive residue tends to be left on the adherend when the reinforcing film is peeled from the adherend during rework or the like. The gel fraction of the adhesive layer 2 before photocuring (i.e., the gel fraction of the photocurable composition constituting the adhesive layer) is preferably 25% or more, more preferably 30% or more, and may be 35% or more, 40% or more, or 45% or more. On the other hand, if the gel fraction is excessively high, the storage modulus increases and stress-strain relaxation is poor, which may cause the adhesive to peel off at bent portions when a flexible device is used. Therefore, the gel fraction of the adhesive layer 2 before photocuring is preferably 80% or less, more preferably 75% or less, even more preferably 70% or less, and may be 65% or less.

[0088] The gel fraction can be determined as the insoluble content in a solvent such as ethyl acetate, and specifically, it is determined as the weight fraction (unit: wt%) of the insoluble content after immersing the pressure-sensitive adhesive layer in ethyl acetate for 7 days at 23°C relative to the sample before immersion. Generally, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked parts in the polymer, the higher the gel fraction.

[0089] Even after the crosslinking structure is introduced into the polymer by the crosslinking agent, the photocuring agent remains unreacted. Therefore, a photocurable pressure-sensitive adhesive layer 2 containing a base polymer and a photocuring agent is formed. When the pressure-sensitive adhesive layer 2 is formed on the film substrate 1, it is preferable to provide a separator 5 on the pressure-sensitive adhesive layer 2 for the purpose of protecting the pressure-sensitive adhesive layer 2, etc. Crosslinking may be performed after providing the separator 5 on the pressure-sensitive adhesive layer 2.

[0090] When the pressure-sensitive adhesive layer 2 is formed on another substrate, the solvent is dried, and then the pressure-sensitive adhesive layer 2 is transferred onto the film substrate 1 to obtain a reinforcing film. The substrate used to form the pressure-sensitive adhesive layer may be used as the separator 5 as is.

[0091] As the separator 5, a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, or polyester film is preferably used. The thickness of the separator is usually 3 to 200 μm, preferably about 10 to 100 μm. The surface of the separator 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. By treating the surface of the separator 5 with a release treatment, when the film substrate 1 and the separator 5 are peeled from each other, peeling occurs at the interface between the pressure-sensitive adhesive layer 2 and the separator 5, and the pressure-sensitive adhesive layer 2 remains adhered to the film substrate 1. The separator 5 may be antistatically treated on either or both of the release-treated and non-treated surfaces. By treating the separator 5 with an antistatic treatment, charging when the separator is peeled from the pressure-sensitive adhesive layer can be suppressed.

[0092] [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 an adhesive layer 2 fixed to a film substrate 1, and after being attached to the adherend and before being photocured, the adhesive strength to the adherend is low. Therefore, the reinforced film can be easily peeled from the adherend before being photocured.

[0093] The adherend to which the reinforced film is attached is not particularly limited, and examples thereof include various electronic devices, optical devices, and their components. In one embodiment, the reinforced film is attached to the surface of a foldable flexible device. The foldable device has a hinge portion 25 as shown in FIG. 3 and can be folded around this hinge portion. The folding angle can be set arbitrarily, and the device may be bent (folded) 180° as shown in FIG. 4. Note that in FIG. 4, the device is folded so that the adhesive surface of the reinforced film 10 faces inward, but the device may also be bent so that the reinforced film 10 faces outward. When the device is a display device, the reinforced film may be attached to the screen-side surface or the back side (housing). As shown in FIGS. 3 and 4, a flexible device configured to be bendable at a predetermined location, such as the hinge portion 25, repeatedly bends and stretches at the same location during use.

[0094] The reinforcing film may be attached to the entire surface of the adherend, or may be selectively attached only to the area requiring reinforcement (reinforcement target area). Alternatively, the reinforcing film may be attached to the entire area requiring reinforcement (reinforcement target area) and the area not requiring reinforcement (non-reinforcement target area), and then the reinforcing film attached to the non-reinforcement target area may be cut and removed. Before the adhesive is photocured, the reinforcing film is temporarily attached to the surface of the adherend, so it can be easily peeled and removed from the surface of the adherend. The reinforcing film may be attached to the area requiring reinforcement and the area not requiring reinforcement, and the area requiring reinforcement may be selectively irradiated with light to photocure the adhesive, and then the reinforcing film may be selectively peeled and removed from the non-reinforcement target area where the adhesive is not cured.

[0095] 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.

[0096] Before laminating the reinforcing film, the surface of the adherend may be subjected to an activation treatment for the purpose of cleaning, etc. Examples of the surface activation treatment include plasma treatment, corona treatment, and glow discharge treatment. The adherend whose surface has been activated is free of hydroxyl groups, carbonyl groups, carboxyl groups, and the like. Shi base These adhesives contain many active groups such as amide acid, terminal amino groups, and carboxyl groups (or carboxylic anhydride groups), which interact strongly with the polar functional groups of the base polymer of the adhesive, and thus adhesive strength is likely to increase. In particular, when the adherend is a polyimide, activation treatment can significantly increase the initial adhesive strength due to the activation of amide acid, terminal amino groups, and carboxyl groups (or carboxylic anhydride groups), which interact strongly with the polar functional groups of the base polymer.

[0097] If the initial adhesive strength is excessively high, peeling operations such as reworking may become difficult. As described above, since the base polymer is substantially free of nitrogen atoms, an excessive increase in the initial adhesive strength to an adherend whose surface has been subjected to an activation treatment can be suppressed.

[0098] To facilitate peeling from the adherend and prevent adhesive residue on the adherend after peeling the reinforcement film, the adhesive strength between the pressure-sensitive adhesive layer 2 and the adherend before photocuring is preferably 1 N / 25 mm or less, more preferably 0.5 N / 25 mm or less, even more preferably 0.3 N / 25 mm or less, and may be 0.1 N / 25 mm or less, or even 0.05 N / 25 mm or less. To prevent peeling of the reinforcement film during storage or handling, the adhesive strength between the pressure-sensitive adhesive layer 2 and the adherend before photocuring is preferably 0.005 N / 25 mm or more, more preferably 0.01 N / 25 mm or more. The adhesive 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, the adhesive strength is measured at 25°C.

[0099] The storage modulus of the pressure-sensitive adhesive layer 2 at 25°C before photocuring was 5.0 × 10 3 ~1.0×10 5 From the viewpoint of suppressing adhesive residue on the adherend when the reinforcing film is peeled from the adherend, the storage modulus of the pressure-sensitive adhesive layer 2 at 25°C before photocuring is preferably 7.0 × 10 3 Pa or higher is preferable, 9.0 × 10 3 Pa or more is more preferable, and 1.0×10 4 Pa or 1.5 x 10 4 In order to provide flexibility to the pressure-sensitive adhesive layer, the storage modulus of the pressure-sensitive adhesive layer 2 at 25°C before photocuring may be 7.0 × 10 Pa or more. 4 Pa or less is preferable, and 5.0 × 10 4 Pa or less is more preferable, and 4.0 × 10 4 Pa or less or 3.0 x 10 4 It may be less than Pa.

[0100] The storage modulus of the pressure-sensitive adhesive layer 2 at −20° C. before photocuring was 1.0×10 4 ~2.0×10 5 Pa is preferred, 2.0 x 10 4 ~1.0×10 5 Pa is more preferred, 3.0 × 10 4 ~9.0×10 4 Pa or 4.0 x 104 ~9.0×10 4 It may be Pa. When the storage modulus at low temperature of the pressure-sensitive adhesive layer before photocuring is within the above range, the storage modulus of the pressure-sensitive adhesive layer tends to be maintained low even after photocuring.

[0101] The storage modulus of the pressure-sensitive adhesive layer before photocuring depends on the composition of the base polymer, the amount of crosslinking agent introduced, the content of the photocuring agent, etc. The greater the amount of crosslinking agent introduced, the higher the gel fraction and the greater the storage modulus. The greater the amount of photocuring agent, the smaller the content of the base polymer in the composition, so the smaller the storage modulus tends to be.

[0102] The storage modulus of the PSA changes rapidly near the glass transition temperature of the base polymer. As described above, when the glass transition temperature of the base polymer is sufficiently lower than -20°C, a PSA with a low storage modulus at low temperatures can be prepared. The storage modulus of the PSA layer at -20°C before photocuring is preferably 7 times or less, more preferably 5 times or less, and may be 4 times or less, 3.5 times or less, or 3 times or less than the storage modulus at 25°C. The storage modulus of the PSA layer at -20°C before photocuring may be 1.5 times or more, 1.8 times or more, or 2.0 times or more than the storage modulus at 25°C.

[0103] After laminating the reinforcing film to the adherend, the pressure-sensitive adhesive layer 2 is irradiated with actinic rays to photocure the pressure-sensitive adhesive layer. Examples of actinic rays include ultraviolet light, visible light, infrared light, X-rays, α-rays, β-rays, and γ-rays. Ultraviolet light is preferred as the actinic rays because it can inhibit curing of the pressure-sensitive adhesive layer during storage and facilitates curing. The irradiation intensity and irradiation time of the actinic rays may be appropriately set depending on the composition, thickness, etc. of the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer 2 may be irradiated with actinic rays from either the film substrate 1 side or the adherend side, or may be irradiated with actinic rays from both sides.

[0104] As the photocuring proceeds, the storage modulus of the pressure-sensitive adhesive layer increases, and the adhesive strength to the adherend also increases. From the viewpoint of adhesive reliability during practical use of the device, the adhesive strength between the pressure-sensitive adhesive layer 2 and the adherend after photocuring is preferably 2 N / 25 mm or more, and more preferably 2.5 N / 25 mm or more. From the viewpoint of suppressing peeling of the adhesive when the flexible device is repeatedly bent at the same location, the adhesive strength between the pressure-sensitive adhesive layer 2 and the adherend after photocuring may be 3 N / 25 mm or more, 4 N / 25 mm or more, 5 N / 25 mm or more, 6 N / 25 mm or more, 7 N / 25 mm or more, 8 N / 25 mm or more, 9 N / 25 mm or more, or 10 N / 25 mm or more. The adhesive strength between the pressure-sensitive adhesive layer 2 and the adherend after photocuring is preferably 10 times or more, more preferably 30 times or more, and may be 50 times or more, 100 times or more, or 200 times or more, of the adhesive strength between the pressure-sensitive adhesive layer 2 and the adherend before photocuring. As mentioned above, by adjusting the type of photocuring agent (compatibility with the base polymer) and the amount added, it is possible to keep the adhesive strength before photocuring (initial adhesive strength) low and increase the adhesive strength of the adhesive after photocuring.

[0105] As described above, the pressure-sensitive adhesive layer 2 after photocuring has a storage modulus of 1.0 × 10 at −20° C. 4 ~5.0×10 5 Pa, and the storage modulus at 25°C is 8.0 × 10 3 ~1.5×10 5 It is preferable that the storage modulus of the pressure-sensitive adhesive layer after photocuring is low in the low temperature range, which tends to prevent peeling of the pressure-sensitive adhesive layer when repeatedly bent at low temperatures.

[0106] The storage modulus of the pressure-sensitive adhesive layer at −20° C. after photocuring is preferably 7 times or less, more preferably 5 times or less, and may be 4 times or less, 3.5 times or less, or 3 times or less, the storage modulus at 25° C. The storage modulus of the pressure-sensitive adhesive layer at −20° C. before photocuring may be 1.5 times or more, 1.8 times or more, or 2.0 times or more the storage modulus at 25° C.

[0107] The storage modulus at −20° C. of the pressure-sensitive adhesive layer after photocuring is preferably 7 times or less, and may be 5 times or less, 4 times or less, or 3.5 times or less, of the storage modulus at −20° C. of the pressure-sensitive adhesive layer before photocuring. The storage modulus at −20° C. of the pressure-sensitive adhesive layer after photocuring may be 1.1 times or more, 1.3 times or more, 1.5 times or more, or 1.7 times or more of the storage modulus at −20° C. of the pressure-sensitive adhesive layer before photocuring.

[0108] The storage modulus at 25°C of the pressure-sensitive adhesive layer after photocuring is preferably 7 times or less, and may be 5 times or less, 4 times or less, or 3.5 times or less, of the storage modulus at 25°C of the pressure-sensitive adhesive layer before photocuring. The storage modulus at -20°C of the pressure-sensitive adhesive layer after photocuring may be 1.1 times or more, 1.3 times or more, 1.5 times or more, or 1.7 times or more of the storage modulus at -20°C of the pressure-sensitive adhesive layer before photocuring.

[0109] As described above, by applying the reinforced film of the present invention to the adherend, appropriate rigidity is imparted and stress is alleviated and dispersed, thereby suppressing various defects that may occur in the manufacturing process, improving production efficiency, and improving yield. Furthermore, since the reinforced film is easily peeled from the adherend before the pressure-sensitive adhesive layer is photocured, rework is easy even if lamination or adhesion defects occur. Furthermore, processing such as selectively removing the reinforced film from areas other than the area to be reinforced is also easy.

[0110] During use of the completed device, even if an external force is suddenly applied due to the device being dropped, a heavy object being placed on the device, or a flying object hitting the device, the reinforcing film attached thereto can prevent damage to the device. Furthermore, since the reinforcing film firmly adheres to the device after the adhesive is photocured, the reinforcing film is less likely to peel off even during long-term use, providing excellent reliability. Furthermore, since the adhesive layer of the reinforcing film has a low storage modulus even at low temperatures, peeling of the adhesive at bent portions is less likely to occur, even when used in flexible devices, demonstrating excellent adhesion reliability. [Example]

[0111] 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.

[0112] [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 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 550,000.

[0113] <Polymers B to I> The amounts of the monomers charged were changed as shown in Table 1. Solutions of polymers B to I were obtained in the same manner as in the polymerization of polymer A except for the above.

[0114] The monomer ratios used and the glass transition temperatures of the acrylic polymers A to I are listed in Table 1. The glass transition temperatures were calculated from the monomer ratios used based on the Fox formula. 2EHA 2-Ethylhexyl Acrylate BA Butyl Acrylate MMA Methyl methacrylate NVP N-Vinylpyrrolidone 2HEA 2-hydroxyethyl acrylate 4HBA 4-hydroxybutyl acrylate AA acrylic acid β-CEA 2-carboxyethyl acrylate HOA-MS 2-Acryloyloxyethyl succinate

[0115] [Table 1]

[0116] [Preparation of reinforcing film] <Preparation of Pressure-Sensitive Adhesive Composition> A crosslinking agent and a photocuring agent were added to the acrylic polymer solution and mixed uniformly to prepare the pressure-sensitive adhesive compositions shown in Table 2. The amounts of crosslinking agent and photocuring agent in Table 2 are the amounts added per 100 parts by weight of the solid content of the base polymer. Details of the crosslinking agent and photocuring agent are as follows. In Examples 7 to 9, two types of photocuring agents were used, and the amounts of each photocuring agent are shown in Table 2.

[0117] (Crosslinking agent) Takenate D110N: 75% ethyl acetate solution of xylylene diisocyanate trimethylolpropane adduct (Mitsui Chemicals "Takenate D110N") C-HX: Isocyanurate of hexamethylene diisocyanate (Tosoh's "Coronate HX") TC: N,N,N',N'-tetraglycidyl-m-xylylenediamine (tetrafunctional epoxy compound, "Tetrad C" manufactured by Mitsubishi Gas Chemical Company)

[0118] (light curing agent) M350: Trimethylolpropane EO-modified (n=1) triacrylate (Toagosei "Aronix M-350", functional group equivalent weight 144g / eq) M360: Trimethylolpropane EO-modified (n=2) triacrylate (Toagosei "Aronix M-360", functional group equivalent weight 186g / eq) M310: Trimethylolpropane PO-modified (n=1) triacrylate (Toagosei "Aronix M-310", functional group equivalent weight 158g / eq) M321: Trimethylolpropane PO-modified (n=2) triacrylate (Toagosei "Aronix M-321", functional group equivalent weight 200g / eq) APG700: Polypropylene glycol #700 (n = 12) diacrylate ("NK Ester APG700" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent weight 404 g / eq) A200: Polyethylene glycol #200 (n=4) diacrylate ("NK Ester A200" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent weight 154 g / eq) TMPT: Trimethylolpropane triacrylate ("NK Ester TMPT" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent weight 99 g / eq) ZnAc: Zinc acrylate (manufactured by Nisshoku Technofine, functional group equivalent weight 104g / eq)

[0119] (Photopolymerization initiator) In addition to the examples shown in Table 2, 0.2 parts by weight of 2,2-dimethoxy-1,2-diphenylethan-1-one (manufactured by IGM Resins under the brand name "Omnirad 651") was added as a photopolymerization initiator relative to 100 parts by weight of the solid content of the base polymer in Examples 1 to 18 and Comparative Examples 1 to 3, 7, and 8. In Comparative Examples 4 to 6, 0.1 parts by weight of 1-hydroxycyclohexyl phenyl ketone (manufactured by IGM Resins under the brand name "Omnirad 184") was added as a photopolymerization initiator relative to 100 parts by weight of the solid content of the base polymer.

[0120] <Application of adhesive solution and crosslinking> The above-mentioned adhesive composition was applied to an untreated transparent film substrate using a fountain roll so that the dried thickness would be 13 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated surface of a separator (a 25 μm-thick polyethylene terephthalate film with one side treated with silicone release and both sides treated with antistatic agents) was attached to the adhesive-coated surface. Subsequently, aging treatment was performed for 4 days in a 25°C atmosphere to promote crosslinking, resulting in a reinforced film in which a photocurable adhesive sheet was fixedly laminated onto the transparent film substrate and a separator was temporarily attached thereon. In Examples 1 to 5, 7 to 18, and Comparative Examples 1 to 8, a 75 μm-thick polyethylene terephthalate film ("Lumirror S10" manufactured by Toray Industries, Inc.) was used as the transparent film substrate. In Example 6, a 50 μm-thick ultraviolet-transmitting transparent polyimide film ("Neoprim S-100" manufactured by Mitsubishi Gas Chemical Company, Inc.) was used as the transparent film substrate.

[0121] [evaluation] <Storage modulus> The adhesive composition was applied to the separator and crosslinked in the same manner as above to prepare an adhesive sheet (before photocuring). A separator was attached to the surface of the adhesive layer of the adhesive sheet before photocuring to isolate it from oxygen, and the sheet was exposed to 2000 mJ / cm 2 of light from a 365 nm LED lamp. 2 The adhesive sheet was photocured by irradiating it with ultraviolet light of 1000 kJ / cm2. The adhesive sheet before photocuring and the adhesive sheet after photocuring were laminated to prepare a measurement sample with a thickness of approximately 1.5 mm. Dynamic viscoelasticity measurements were performed under the following conditions using an Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific, and the shear storage modulus G' values ​​at -20°C and 25°C were read. (Measurement conditions) Deformation mode: Torsion Measurement frequency: 1Hz Heating rate: 5°C / min Measurement temperature: -50~150℃ Shape: Parallel plate 8.0mmφ

[0122] <Adhesive strength> A 12.5 μm-thick polyimide film (Toray DuPont "Kapton 50EN") was attached to a glass plate using double-sided adhesive tape (Nitto Denko "No. 531") to prepare a polyimide film substrate for measurement. The separator was peeled off from the surface of a 25 mm wide x 100 mm long cut-out reinforced film, and the film was then attached to the polyimide film substrate for measurement using a hand roller. This prepared the test sample before photocuring. The pre-photocured test sample was prepared by photocuring the adhesive layer by irradiating the reinforced film side (PET film substrate side) of the pre-photocured test sample with UV light. Using these test samples, the edge of the reinforced film substrate was held with a chuck and the reinforced film was peeled 180° at a pulling speed of 300 mm / min to measure peel strength.

[0123] <Bending test> The separator was peeled off from the surface of the reinforcement film, and a polyimide film (Toray DuPont "Kapton 50EN") was laminated to the surface of the adhesive layer using a hand roller. This laminate was cut into a size of 25 mm wide x 100 mm long, and the adhesive layer was photocured by irradiating the reinforcement film side (PET film substrate side) with UV light to obtain test specimens. Using a planar no-load U-shaped stretch tester (Yuasa System Co., Ltd.), a bending jig was attached to the short edge of the test specimen. Repeated bending tests were performed under the following conditions in a thermostatic chamber at a temperature of -20°C or 25°C and a relative humidity of 50%, with the reinforcement film side (film substrate side) facing inward. After the repeated bending test, the specimens were rated as "OK" if there was no peeling or lifting between the reinforcement film and the substrate; those that showed peeling or lifting were rated as "NG." (Test conditions) Bending radius: 3 mm Bending angle: 180° Bending speed: 1 second / time Number of bends: 200,000

[0124] Table 2 shows the composition of the adhesive for each reinforcing film, the shear storage modulus G' and adhesive strength of the adhesive layer before and after photocuring, and the evaluation results of the bending test.

[0125] [Table 2]

[0126] In Comparative Example 2, in which Polymer F, which has a glass transition temperature of -34°C, was used as the base polymer, the storage modulus at -20°C was large both before and after photocuring of the pressure-sensitive adhesive layer, and peeling of the pressure-sensitive adhesive layer was observed after repeated bending tests. In Comparative Example 3, in which the type of crosslinking agent was changed and the amount of crosslinking material and photocuring agent were reduced, the storage modulus of the pressure-sensitive adhesive layer was smaller than in Comparative Example 2, but the storage modulus at -20°C was still large, and peeling of the pressure-sensitive adhesive layer was observed after repeated bending tests. In the other Comparative Examples, the storage modulus at -20°C was also large, and peeling of the pressure-sensitive adhesive layer was observed after repeated bending tests.

[0127] On the other hand, in Examples 1 to 18 in which the storage modulus of the photocured adhesive layer at −20° C. was small, no peeling of the adhesive layer was observed after the repeated bending test, and good adhesion reliability was demonstrated.

[0128] A comparison of Examples 1 to 3 with Comparative Example 7 reveals that the smaller the amount of isocyanate crosslinking agent, the smaller the storage modulus of the pressure-sensitive adhesive layer before and after photocuring tends to be. In Examples 14 to 16, in which a crosslinked structure using an epoxy-based crosslinking agent was introduced into base polymers G, H, and I having carboxy groups, the adhesive strength before photocuring was small and the adhesive strength after photocuring was high, similar to Examples 2 and 12, which used an isocyanate-based crosslinking agent. A comparison of Examples 4 to 6 reveals that the larger the amount of photocuring agent, the smaller the initial adhesive strength tends to be.

[0129] Comparing Examples 2, 10, 11, 17, and 18 with Comparative Example 8, when the type of photocuring agent was changed, there was no significant difference in the storage modulus of the adhesive layer before photocuring, but differences were observed in the initial adhesive strength. Furthermore, in these examples, differences were also observed in the adhesive strength and storage modulus of the adhesive after photocuring. Among these examples, Example 2, which used M350 as the photocuring agent, exhibited low initial adhesive strength and high adhesive strength after photocuring, demonstrating excellent properties.

[0130] In Comparative Example 8, which used only trimethylolpropane triacrylate (TMPT) as the photocuring agent, the increase in adhesive strength before and after photocuring was small, but the storage modulus of the adhesive layer at -20°C after photocuring increased significantly, and peeling was observed after the flex test. On the other hand, in Examples 7 and 8, which used a combination of TMPT and M350 as the photocuring agents, the increase in storage modulus at -20°C after photocuring was small, and the adhesive layer after photocuring exhibited excellent adhesive properties.

[0131] These results show that not only the composition of the base polymer, but also the type and amount of crosslinker and the type and amount of photocuring agent significantly affect the properties of the adhesive layer before and after photocuring. In particular, when the type of photocuring agent was changed, the change in the physical properties of the adhesive layer before and after photocuring was significant. The compatibility between the base polymer and the photocuring agent changes as the photocuring agent structure changes, and when the two show adequate compatibility, the adhesive exhibits low initial adhesive strength and excellent adhesive properties after photocuring, as well as a low storage modulus at low temperatures, which prevents the adhesive from peeling even when repeatedly flexed.

Claims

1. A film substrate and a pressure-sensitive adhesive layer fixedly laminated on one main surface of the film substrate, the pressure-sensitive adhesive layer is made of a photocurable composition containing an acrylic-based polymer and a photocuring agent; the acrylic base polymer contains, as a monomer unit, one or more monomer units selected from the group consisting of a hydroxy group-containing monomer and a carboxy group-containing monomer, and has a glass transition temperature of −55° C. or lower; The acrylic base polymer is a crosslinked polymer into which a crosslinked structure has been introduced using 0.05 to 1 part by weight of a crosslinking agent relative to 100 parts by weight of the polymer; The photocuring agent contains an alkylene oxide-modified polyfunctional (meth)acrylate having a (poly)alkylene oxide chain with 1 to 5 repeating units of alkylene oxide, After photocuring, the pressure-sensitive adhesive layer has a shear storage modulus of 1.0×10 at −20° C. ４ ~5.0 x 10 ５ Pa, and the shear storage modulus at 25°C is 8.0 × 10 ３ ~1.5 x 10 ５ Pa, Reinforcement film.

2. 2. The reinforcing film according to claim 1, wherein the photocurable composition contains 3 to 30 parts by weight of the photocuring agent relative to 100 parts by weight of the acrylic base polymer.

3. 3. The reinforcing film according to claim 1, wherein the photocuring agent has a functional group equivalent of 80 to 300 g / eq.

4. The reinforcing film according to any one of claims 1 to 3, wherein the crosslinking agent is an isocyanate-based crosslinking agent or an epoxy-based crosslinking agent.

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

6. The pressure-sensitive adhesive layer has a shear storage modulus at 25 ° C. after photocuring that is 1.2 to 7 times the shear storage modulus at 25 ° C. before photocuring. The reinforced film according to any one of claims 1 to 5.

7. The pressure-sensitive adhesive layer has a shear storage modulus at −20 ° C. after photocuring that is 1.2 to 7 times the shear storage modulus at −20 ° C. before photocuring. The reinforced film according to any one of claims 1 to 6.

8. A device with a reinforcing film, in which a reinforcing film is attached to the surface of a foldable device, The reinforcing film includes a film substrate and a pressure-sensitive adhesive layer fixedly laminated on one main surface of the film substrate, the pressure-sensitive adhesive layer is attached to a device surface, the pressure-sensitive adhesive layer is made of a photocured product obtained by photocuring a photocurable pressure-sensitive adhesive composition containing an acrylic base polymer and a photocuring agent; In the photocurable pressure-sensitive adhesive composition, the acrylic base polymer contains, as a monomer unit, one or more monomer units selected from the group consisting of a hydroxy group-containing monomer and a carboxy group-containing monomer, and has a glass transition temperature of −55° C. or lower; The acrylic base polymer is a crosslinked polymer into which a crosslinked structure has been introduced using 0.05 to 1 part by weight of a crosslinking agent relative to 100 parts by weight of the polymer; The photocuring agent contains an alkylene oxide-modified polyfunctional (meth)acrylate having a (poly)alkylene oxide chain with 1 to 5 repeating units of alkylene oxide, The pressure-sensitive adhesive layer has a shear storage modulus of 1.0×10 at −20° C. ４ ~5.0 x 10 ５ Pa, and the shear storage modulus at 25°C is 8.0 × 10 ３ ~5.0 x 10 ５ Pa, Device with reinforced film.

9. A method for manufacturing a device with a reinforcing film in which a reinforcing film is attached to a surface of a foldable device, comprising: The pressure-sensitive adhesive layer of the reinforcing film according to any one of claims 1 to 7 is attached to a surface of a foldable device, photocuring the pressure-sensitive adhesive layer; A method for manufacturing a device with a reinforcing film.

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