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

Abstract

The present invention provides a reinforcing film that is easily peelable immediately after bonding to an adherend, can be firmly bonded to an adherend by photocuring the adhesive after bonding, and has a low shear storage modulus at low temperatures and an adhesive layer with low resistance. [Solution] The reinforcing film (10) comprises an adhesive layer (2) fixedly laminated on one main surface of a film substrate (1). The adhesive layer consists of a photocurable composition comprising an acrylic base polymer having a crosslinked structure, a photocuring agent, and a photopolymerization initiator. The acrylic base polymer includes, as constituent monomers, alkyl (meth)acrylate esters having a chain-like alkyl group with 3 to 6 carbon atoms, alkyl (meth)acrylate esters having a chain-like alkyl group with 7 to 9 carbon atoms, and (meth)acrylate esters having an alkylene oxide chain, and further comprises one or more selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers.

Description

[Technical Field]

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

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

[0003] By temporarily attaching an adhesive film to the surface of a device or device component in a pre-use state such as during assembly, processing, or transportation, damage or breakage of the adherend can be suppressed. Patent Document 1 discloses a reinforcing film comprising an adhesive layer on a film substrate, the adhesive layer being made of a photocurable adhesive composition containing a base polymer and a polyfunctional acrylate as a photocuring agent.

[0004] This reinforcing film has a high gel fraction in its adhesive, resulting in low tackiness immediately after bonding to the substrate, making it easy to peel off. Therefore, rework from the substrate is possible, and the reinforcing film can be selectively peeled off from areas of the substrate where reinforcement is not needed. The adhesive of the reinforcing film adheres firmly to the substrate through photocuring, resulting in a permanent bond of the film substrate to the substrate's surface. This allows it to be used as a reinforcing material for surface protection of devices, etc.

[0005] In recent years, organic EL panels using foldable substrates (flexible substrates) such as resin films have been put into practical use, and foldable devices (foldable devices) have also been put into practical use. In Patent Document 2, as an adhesive for the reinforcing film of a foldable device, by using a photocurable adhesive containing an acrylic-based polymer with a low glass transition temperature, it is proposed to suppress peeling of the adhesive layer at the bending portion of the foldable device.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In foldable devices, since resin films such as polyimide are used as the substrate material of the display element, they are easily charged, and there may be a problem of electrostatic breakdown of the device due to charging (static electricity). In order to suppress the charging of the device to which the reinforcing film is bonded, it is effective to make the adhesive layer have antistatic properties by reducing the resistance of the adhesive layer by containing an antistatic agent in the adhesive layer provided in contact with the device. However, even if an antistatic agent is added to the adhesive of the reinforcing film described in Patent Document 2, the adhesive is not sufficiently reduced in resistance, and when the addition amount of the antistatic agent is increased, the antistatic agent bleeds out, causing a decrease in the adhesive force between the adhesive layer and the device and contamination of the device surface.

[0008] In view of the above, an object of the present invention is to provide a reinforcing film that has a small adhesive force and is easily peeled immediately after being bonded to an adherend, can be firmly bonded to the adherend by photocuring the adhesive after being bonded to the adherend, has a small shear storage modulus at low temperature, and has a low-resistance adhesive layer. [Means for solving the problem]

[0009] The reinforcing film of the present invention comprises an adhesive layer fixedly laminated on one main surface of a film substrate. The adhesive layer consists of a photocurable composition comprising an acrylic-based polymer, a photocuring agent, and a photopolymerization initiator. The photocurable composition constituting the adhesive layer may further contain an antistatic agent.

[0010] The acrylic-based polymer contains, as constituent monomers, one or more selected from the group consisting of alkyl (meth)acrylate esters having a chain-like alkyl group, (meth)acrylate esters having an alkylene oxide chain, and monomers containing a hydroxyl group and a carboxyl group. A crosslinked structure is introduced into the acrylic-based polymer.

[0011] (Meth)acrylic acid esters having alkylene oxide chains as constituent monomers of acrylic-based polymers are compounds represented by general formula (1). CH2=CR 1 -COO-(R 2 -O) m -R 3 (1)

[0012] R 1 R is a hydrogen atom or a methyl group. 2 R is an alkylene group having 2 to 4 carbon atoms, which may have branches. m is an integer from 6 to 15. 3 These are a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

[0013] The acrylic-based polymer contains 60 to 93 parts by weight of an alkyl (meth)acrylate having a chain-like alkyl group and 6 to 20 parts by weight of an (meth)acrylate represented by the above general formula (1), per 100 parts by weight of the total constituent monomers. Preferably, the acrylic-based polymer further contains 1 to 20 parts by weight of a hydroxyl group-containing monomer as a constituent monomer.

[0014] The alkyl (meth)acrylate ester having a chain-like alkyl group as a constituent monomer of the acrylic base polymer preferably includes those with a chain-like alkyl group having 3 to 6 carbon atoms and those with a chain-like alkyl group having 7 to 9 carbon atoms. The acrylic base polymer may contain 10 to 30 parts by weight of alkyl (meth)acrylate ester having a chain-like alkyl group having 3 to 6 carbon atoms and 50 to 80 parts by weight of alkyl (meth)acrylate ester having a chain-like alkyl group having 7 to 9 carbon atoms, per 100 parts by weight of the total constituent monomers.

[0015] The alkyl (meth)acrylate ester having a chain-like alkyl group as a constituent monomer of the acrylic-based polymer may have a molar average number of carbon atoms of 5 or more and less than 9. The acrylic-based polymer may also have n-octyl acrylate as the most abundant monomer (main monomer) among its constituent monomers.

[0016] The adhesive layer preferably has a shear storage modulus of 100 kPa or less at -20°C after photocuring. The surface resistance of the adhesive layer is 1 × 10⁻⁶. 11 A value of Ω or less is preferable.

[0017] Preferably, the adhesive layer has an adhesive strength of 3 N / 25 mm or less to the polyimide film before photocuring. Preferably, the adhesive layer has an adhesive strength of 6 N / 25 mm or more to the polyimide film after photocuring.

[0018] A device with a reinforcing film is obtained by laminating the above-mentioned reinforcing film onto the surface of the device and photocuring the adhesive layer. The device may be a flexible device that can be bent. [Effects of the Invention]

[0019] The reinforcing film of the present invention has an adhesive layer made of a photocurable composition, and the adhesive strength to the adherend is increased by photocuring the adhesive layer after adhesion to the adherend. Before photocuring, the adhesive strength to the adherend is low, so it is easy to peel off from the adherend.

[0020] The acrylic-based polymer constituting the adhesive layer of the reinforcing film has a predetermined composition, which suppresses static charge buildup in the adhesive layer and contributes to preventing static charge buildup on the adherend. Furthermore, because the adhesive layer has a low shear storage modulus at low temperatures and excellent stress relaxation properties, peeling of the adhesive layer at the bending point is suppressed even when the same bending point is repeatedly subjected to, resulting in excellent adhesive reliability. For this reason, the reinforcing film of the present invention can be suitably used in foldable devices using resin film substrates. [Brief explanation of the drawing]

[0021] [Figure 1] This is a cross-sectional view showing the laminated structure of the reinforcing film. [Figure 2] This is a cross-sectional view showing the laminated structure of the reinforcing film. [Figure 3] This is a cross-sectional view showing a device to which a reinforcing film has been attached. [Modes for carrying out the invention]

[0022] Figure 1 is a cross-sectional view showing one embodiment of a reinforcing film. The reinforcing film 10 comprises an adhesive layer 2 on one main surface of a film substrate 1. The adhesive layer 2 is fixedly laminated on one main surface of the film substrate 1. The adhesive layer 2 is a photocurable adhesive made of a photocurable composition, and hardens upon irradiation with active light such as ultraviolet light, increasing the adhesive strength to the adherend.

[0023] Figure 2 is a cross-sectional view of a reinforcing film with a release liner 5 temporarily attached to the main surface of the adhesive layer 2. Figure 3 is a cross-sectional view showing the reinforcing film 10 attached to the surface of the device 20.

[0024] The release liner 5 is peeled off from the surface of the adhesive layer 2, and the exposed surface of the adhesive layer 2 is bonded to the surface of the device 20, thereby attaching the reinforcing film 10 to the surface of the device 20. In this state, the adhesive layer 2 is not yet photocured, and the reinforcing film 10 (adhesive layer 2) is temporarily attached to the device 20. By photocuring the adhesive layer 2, the adhesive strength at the interface between the device 20 and the adhesive layer 2 increases, and the device 20 and the reinforcing film 10 are fixed together.

[0025] "Adherence" refers to a state where two laminated layers are firmly bonded together, making separation at their interface impossible or difficult. "Temporary adhesion" refers to a state where the adhesive force between two laminated layers is weak, allowing them to be easily separated at their interface.

[0026] In the reinforcing film shown in Figure 2, the film substrate 1 and the adhesive layer 2 are fixed together, and the release liner 5 is temporarily attached to the adhesive layer 2. When the film substrate 1 and the release liner 5 are peeled apart, peeling occurs at the interface between the adhesive layer 2 and the release liner 5, and the state in which the adhesive layer 2 is fixed to the film substrate 1 is maintained. No adhesive remains on the release liner 5 after peeling.

[0027] In the device with the reinforcing film shown in Figure 3, the device 20 and the adhesive layer 2 are temporarily adhered before the adhesive layer 2 is photocured. When the film substrate 1 and the device 20 are peeled apart, the peeling occurs at the interface between the adhesive layer 2 and the device 20, so the adhesive layer 2 remains fixed to the film substrate 1. Since 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, and they become fixed, making it difficult to peel the reinforcing film 10 from the device 20.

[0028] [Film substrate] A flexible plastic film is used as the film base material 1 of the reinforcing film 10. In order to fix the film base material 1 and the adhesive layer 2, it is preferable that the surface of the film base material 1 to which the adhesive layer 2 is attached is not treated with a release agent.

[0029] The thickness of the film substrate is, for example, about 4 to 150 μm. From the perspective of reinforcing the device by imparting rigidity and shock mitigation, etc., the thickness of the film substrate 1 is preferably 5 μm or more, more preferably 12 μm or more, still more preferably 20 μm or more, and particularly preferably 25 μm or more. From the perspective of making the reinforcing film flexible and foldable, the thickness of the film substrate 1 is preferably 125 μm or less, more preferably 100 μm or less. From the perspective of achieving both mechanical strength and flexibility, the compressive strength of the film substrate 1 is preferably 100 to 3000 kg / cm 2 is preferred, 200 to 2900 kg / cm 2 is more preferred, 300 to 2800 kg / cm 2 is still more preferred, 400 to 2700 kg / cm 2 is particularly preferred.

[0030] Examples of the plastic material constituting the film substrate 1 include polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, polyether ether ketone, polyether sulfone, polyarylate resins, aramid resins, etc. In the reinforcing film for optical devices such as displays, the film substrate 1 is preferably a transparent film. Further, when irradiating the adhesive layer 2 with active light from the film substrate 1 side to perform photocuring of the adhesive layer, the film substrate 1 preferably has transparency with respect to the active light used for curing the adhesive layer. Because it has both mechanical strength and transparency, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, transparent polyimide, and transparent aramid are preferably used. When irradiating active light from the adherend side, it is only necessary that the adherend has transparency with respect to the active light, and the film substrate 1 does not necessarily have to be transparent to the active light.

[0031] The surface of the film substrate 1 may be provided with functional coatings such as an easy-adhesion layer, a smooth-slip layer, a release layer, an antistatic layer, a hard coat layer, or an anti-reflective layer. As mentioned above, it is preferable that a release layer is not provided on the surface of the film substrate 1 to which the adhesive layer 2 is attached, in order to fix the film substrate 1 and the adhesive layer 2 together.

[0032] [Adhesive layer] The adhesive layer 2, which is fixedly laminated onto the film substrate 1, is made of a photocurable composition. The photocurable composition constituting the adhesive layer 2 includes an acrylic-based polymer, a photocuring agent, and a photopolymerization initiator.

[0033] Before photocuring, the adhesive layer 2 has low adhesion to the adherend, such as the device or device components, making it easy to peel off. As the adhesive layer 2 is photocured, its adhesion to the adherend improves, making it difficult for the reinforcing film to peel off the device surface even during device use, resulting in excellent adhesive reliability.

[0034] Photocurable adhesives hardly harden under typical storage conditions and harden upon irradiation with active light such as ultraviolet light. Therefore, the reinforcing film of the present invention has the advantage of allowing the timing of the hardening of the adhesive layer 2 to be arbitrarily set, and thus being able to flexibly respond to process lead times and the like.

[0035] <Base polymer> The base polymer is the main component of the adhesive composition and is the key element that determines various properties of the adhesive layer, such as adhesive strength and shear storage modulus. In this invention, an acrylic polymer is used as the base polymer of the adhesive. Acrylic polymers have excellent optical transparency and adhesion, and their adhesive strength and shear storage modulus are easily controllable.

[0036] The acrylic-based polymer contains an alkyl (meth)acrylate as a monomer component. The acrylic-based polymer used in the present invention is a copolymer containing, in addition to an alkyl (meth)acrylate, an alkylene oxide chain-containing (meth)acrylate ester and a monomer having a crosslinkable functional group as monomer components. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0037] ((meth)acrylate alkyl ester) As the alkyl (meth)acrylate ester, alkyl (meth)acrylate esters having 1 to 20 carbon atoms in the alkyl group are preferably used. From the viewpoint of suppressing peeling of the adhesive layer when repeatedly bent by lowering the glass transition temperature of the acrylic base polymer and reducing the shear storage modulus, the alkyl group of the alkyl (meth)acrylate ester is preferably a linear alkyl group. The linear alkyl group may be linear or branched.

[0038] Examples of alkyl (meth)acrylates having a chain-like alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and (meth) Examples include nonyl acrylate, isononyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate, isotridecyl methacrylate, tetradecyl methacrylate, isotetradecyl methacrylate, pentadecyl methacrylate, cetyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, isooctadyl methacrylate, nonadecyl methacrylate, and eicosyl methacrylate.

[0039] Among the example alkyl (meth)acrylate esters, from the viewpoint of lowering the glass transition temperature of the acrylic-based polymer, (meth)acrylate C 1-9 Alkyl esters are preferred, and those with a homopolymer glass transition temperature of -50°C or lower are preferred. The glass transition temperature of the (meth)acrylate alkyl ester homopolymer is more preferably -55°C or lower, and even more preferably -60°C or lower. (meth)acrylate C with a homopolymer 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), and butyl acrylate (Tg: -55°C). Among these, alkyl (meth)acrylates having a chain-like alkyl group with 7 to 9 carbon atoms, such as 2-ethylhexyl acrylate, n-heptyl acrylate, and n-octyl acrylate, are preferred because they can reduce the shear storage modulus around -20°C, and n-octyl acrylate is particularly preferred.

[0040] (Meth)acrylate alkyl esters include (meth)acrylate C, where the number of carbon atoms in the chain alkyl group is 7 to 9. 7-9 Alkyl esters and (meth)acrylic acid C, in which the chain alkyl group has 3 to 6 carbon atoms. 3-6 Alkyl esters may be used in combination. Generally, (meth)acrylate C 3-6 Alkyl esters are (meth)acrylate C 7-9 Compared to alkyl esters, homopolymers have a higher Tg. On the other hand, acrylic-based polymers use (meth)acrylate C as a monomer component. 7-9 In addition to alkyl esters, (meth)acrylate C 3-6 The inclusion of alkyl esters makes it easier to control the adhesive strength of the adhesive layer before and after photocuring within an appropriate range. (meth)acrylate C 3-6 Among alkyl esters, butyl acrylate and n-hexyl acrylate are preferred due to their low Tg of homopolymer, with butyl acrylate being particularly preferred.

[0041] (Meth)acrylic acid esters having alkylene oxide chains) (Meth)acrylic acid esters having an alkylene oxide chain are esters of (meth)acrylic acid and an alcohol having an alkylene oxide chain, and are compounds represented by the following general formula (1). CH2=CR 1 -COO-(R2 -O) m -R 3 (1)

[0042] R in general formula (1) 1 R is a hydrogen atom or a methyl group, 1 Compounds of formula (1) in which is a hydrogen atom are acrylates, R 1 Compounds of formula (1) in which is a methyl group are methacrylates. From the viewpoint of lowering the Tg of acrylic-based polymers, 1 It is preferable that it is a hydrogen atom.

[0043] R in general formula (1) 2 is an alkylene group having 2 to 4 carbon atoms, which may have branches, and -R 2 -O- is an alkylene oxide chain. 2 The fact that the carbon number is 2 to 4 helps to reduce the resistance of the adhesive. 2 Alkylene oxide-R with 2 to 4 carbon atoms 2 Specific examples of -O- include ethylene oxide (-CH2CH2-O-), propylene oxide (-CH(CH3)CH2-O-), and butylene oxide (-CH2CH2CH2CH2-O-). From the perspective of reducing the resistance of adhesives, R 2 It is particularly preferable that it be ethylene oxide.

[0044] In general formula (1), m is the number of repeating alkylene oxide units (chain length) and is an integer between 6 and 15. A number of repeating alkylene oxide units m of 6 or more reduces the resistance of the adhesive. If m is excessively large, it may inhibit polymer polymerization or reduce the adhesive strength of the adhesive.

[0045] R 3 R 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 acrylic-based polymers and improving compatibility with photocuring agents, 3 The group is preferably an alkyl group having 1 to 3 carbon atoms, and a methyl group or an ethyl group is particularly preferred.

[0046] Specific examples of compounds represented by general formula (1) include methoxypolypropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethoxypolypropylene glycol (meth)acrylate, and ethoxypolyethylene glycol (meth)acrylate. Among these, methoxypolyethylene glycol acrylate is particularly preferred from the viewpoint of reducing resistance.

[0047] From the viewpoint of achieving both low resistance and adhesive properties, the number of repeats m of the alkylene oxide in general formula (1) is preferably 6 to 13, and more preferably 7 to 12.

[0048] (Monomers having crosslinkable functional groups) Monomers having crosslinkable functional groups are specifically hydroxyl group-containing monomers and carboxyl group-containing monomers. The acrylic-based polymer may have both hydroxyl group-containing monomers and carboxyl group-containing monomers as monomer components, or it may have only one of them. The introduction of a crosslinked structure into the acrylic-based polymer tends to improve cohesive strength and the peelability of the adhesive layer 2 from the adherend before photocuring.

[0049] Examples of hydroxyl 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, and 4-(hydroxymethyl)cyclohexylmethyl (meth)acrylate. Among these, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred because they contribute significantly to improving the adhesive strength of the adhesive after photocuring.

[0050] Examples of carboxyl group-containing monomers include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Among these, acrylic acid is particularly preferred because it contributes significantly to improving adhesive strength.

[0051] (Monomer ratio) The acrylic-based polymer preferably contains 60 to 93 parts by weight of alkyl (meth)acrylate having a chain-like alkyl group and 6 to 20 parts by weight of alkylene oxide chain (meth)acrylate ester, per 100 parts by weight of the total constituent monomers.

[0052] (Meth)acrylic acid esters having alkylene oxide chains are components that contribute to improving the compatibility between the base polymer and the photocuring agent and to reducing the resistance of the adhesive. The higher the proportion in the acrylic base polymer, the lower the resistance of the adhesive layer tends to be. The amount of (meth)acrylic acid ester having alkylene oxide chains is more preferably 7 to 15 parts by weight, and may be 8 to 13 parts by weight, per 100 parts by weight of the total constituent monomers of the acrylic base polymer.

[0053] The higher the proportion of (meth)acrylic acid esters containing alkylene oxide chains, the lower the adhesive resistance tends to be. However, if the proportion of (meth)acrylic acid esters containing alkylene oxide chains becomes excessively high, it may become difficult to control the adhesive strength of the adhesive layer before and after photocuring.

[0054] From the viewpoint of lowering the glass transition temperature of the acrylic-based polymer, the amount of (meth)acrylate alkyl ester having a chain-like alkyl group is preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be 75 parts by weight or more or 80 parts by weight or more, based on 100 parts by weight of the total constituent monomers of the acrylic-based polymer.

[0055] On the other hand, as the proportion of alkyl (meth)acrylate increases, the proportion of (meth)acrylate having an alkylene oxide chain relatively decreases, and the effect of reducing resistance may not be fully exhibited. The amount of alkyl (meth)acrylate having a chain-like alkyl group is preferably 92 parts by weight or less, more preferably 90 parts by weight or less, and may be 87 parts by weight or less or 85 parts by weight or less, based on 100 parts by weight of the total constituent monomers of the acrylic base polymer.

[0056] As mentioned above, from the viewpoint of achieving both a low Tg of acrylic-based polymers and control of adhesive strength, (meth)acrylate C is used as an alkyl ester having a chain-like alkyl group. 7-9 Alkyl esters and (meth)acrylate C 3-6 It is preferable to use alkyl esters in combination.

[0057] The most abundant monomer (main monomer) in acrylic-based polymers is (meth)acrylic acid C, which has a chain-like alkyl group with 7 to 9 carbon atoms. 7-9 It is preferably an alkyl ester, and more preferably an alkyl (meth)acrylate ester having a chain-like alkyl group with 8 carbon atoms. As the alkyl (meth)acrylate ester having a chain-like alkyl group with 8 carbon atoms, 2-ethylhexyl acrylate and n-octyl acrylate are preferred, and among these, n-octyl acrylate is particularly preferred.

[0058] (meth)acrylic acid C, per 100 parts by weight of the total constituent monomers of the acrylic-based polymer 7-9 The amount of alkyl ester is preferably 50 to 80 parts by weight, more preferably 55 to 75 parts by weight, and may also be 58 to 70 parts by weight or 60 to 68 parts by weight. In particular, the amount of alkyl (meth)acrylate having a chain alkyl group with 8 carbon atoms is preferably within the above range, and the amount of n-octyl acrylate is particularly preferably within the above range.

[0059] From the perspective of controlling adhesive strength, (meth)acrylic acid C3-6 Among alkyl esters, butyl acrylate is particularly preferred. (meth)acrylate C is used per 100 parts by weight of the total constituent monomers of the acrylic base polymer. 4-6 The amount of alkyl ester is preferably 10 to 30 parts by weight, more preferably 13 to 27 parts by weight, and may also be 15 to 25 parts by weight or 17 to 23 parts by weight.

[0060] The (meth)acrylate alkyl ester having a chain-like alkyl group as a constituent monomer of the acrylic-based polymer may have a molar average number of carbon atoms of the alkyl group of 5 or more and less than 9. The molar average number of carbon atoms is calculated by multiplying the number of moles of each (meth)acrylate alkyl ester by the number of carbon atoms of the alkyl group, summing the results, and dividing the obtained value by the total number of moles of (meth)acrylate alkyl ester.

[0061] When the molar average number of carbon atoms in the alkyl group of the alkyl (meth)acrylate is 5 or more, the glass transition temperature of the acrylic base polymer tends to be low, and the low-temperature shear storage modulus tends to be low. The larger the molar average number of carbon atoms in the alkyl group of the alkyl (meth)acrylate, the higher the hydrophobicity of the acrylic base polymer tends to be, and when the molar average number of carbon atoms in the alkyl group is 9 or more, the increase in adhesive strength due to photocuring tends to be insufficient. The molar average number of carbon atoms in the alkyl group of the alkyl (meth)acrylate is more preferably 5.5 or more and less than 8, even more preferably 6 or more and less than 8, and may be 7.5 or less or 7.0 or less.

[0062] The amount of monomers having crosslinkable functional groups (total amount of hydroxyl group-containing monomers and carboxyl group-containing monomers) relative to 100 parts by weight of the total constituent monomers of the acrylic-based polymer is preferably 0.5 to 25 parts by weight, more preferably 1 to 20 parts by weight, even more preferably 3 to 18 parts by weight, and may also be 5 to 15 parts by weight or 8 to 12 parts by weight.

[0063] When an acrylic base polymer contains hydroxyl groups, the shape recovery of the adhesive layer tends to be high. Therefore, it is preferable that the acrylic base polymer contains hydroxyl group-containing monomers as constituent monomer components, and it is preferable that the content of hydroxyl group-containing monomers is within the above range. Furthermore, the greater the amount of hydroxyl group-containing monomers, the lower the resistance of the adhesive layer tends to be. From the viewpoint of adhesive strength and low resistance, it is particularly preferable that the amount of hydroxyl group-containing monomers per 100 parts by weight of the total constituent monomers of the acrylic base polymer be 8 parts by weight or more.

[0064] (Other monomers) Acrylic-based polymers may contain monomers other than those listed above as constituent monomers. Examples of monomers other than those listed above include nitrogen-containing monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinyl carboxylic acid amides, and N-vinylcaprolactam. Other monomers include 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.

[0065] (Glass transition temperature) The glass transition temperature of the acrylic-based polymer is preferably -40°C or lower, more preferably -45°C or lower, and may be -50°C or lower or -55°C or lower. A glass transition temperature sufficiently lower than the ambient temperature of the device results in a low shear storage modulus of the adhesive layer within the ambient temperature range, which tends to suppress peeling during repeated bending. The lower limit of the glass transition temperature of the acrylic-based polymer is not particularly limited, but is generally -80°C or higher, and may be -75°C or higher or -70°C or higher.

[0066] The glass transition temperature is the temperature at which the loss tangent tanδ in viscoelastic measurements is maximized (peak top temperature). Instead of the glass transition temperature obtained by viscoelastic measurements, the theoretical Tg calculated by Fox's equation may be applied. The theoretical Tg is the glass transition temperature Tg of the homopolymer of the constituent monomer components of an acrylic-based polymer. i And the weight fraction W of each monomer component i Therefore, it is calculated using the following Fox formula. 1 / Tg = Σ(W i / Tg i )

[0067] Tg is the glass transition temperature of the polymer chain (unit: K), W i This is the weight fraction (weight-based copolymerization ratio) of monomer component i that constitutes the segment, Tg i is the glass transition temperature (in K) of the homopolymer of monomer component i. The values ​​listed in the Polymer Handbook, 3rd edition (John Wiley & Sons, Inc., 1989) can be used as the glass transition temperature of homopolymers. For homopolymers of monomers not listed in the above literature, the peak top temperature of tanδ obtained by dynamic viscoelasticity measurement can be used.

[0068] (Polymerization of acrylic polymers) Acrylic polymers as base polymers are obtained by polymerizing the above monomer components using various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization. Solution polymerization is preferred from the viewpoint of balancing properties such as adhesive strength and holding power of the adhesive, as well as cost. Ethyl acetate, toluene, etc. are used as solvents for solution polymerization. The solution concentration is usually about 20 to 80% by weight. Various known polymerization initiators such as azo-based and peroxide-based ones can be used. Chain transfer agents may be used to adjust the molecular weight. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

[0069] The weight-average molecular weight of the acrylic-based polymer is preferably 100,000 to 2,000,000, more preferably 200,000 to 1,500,000, and even more preferably 300,000 to 1,000,000. Note that when a cross-linked structure is introduced into the acrylic-based polymer, the molecular weight of the acrylic-based polymer refers to the molecular weight before the introduction of the cross-linked structure.

[0070] <Crosslinking agent> From the viewpoint of providing the adhesive with appropriate cohesive force to exhibit adhesive strength and ensuring the peelability of the adhesive layer from the adherend before photocuring, it is preferable to introduce a crosslinked structure into the acrylic base polymer. For example, a crosslinked structure can be introduced by adding a crosslinking agent to the solution after polymerization of the acrylic base polymer and heating as necessary. The crosslinking agent has two or more crosslinkable functional groups per molecule. The crosslinking agent may also have three or more crosslinkable functional groups per molecule.

[0071] Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. These crosslinking agents react with functional groups such as hydroxyl groups and carboxyl groups introduced into the 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 hydroxyl groups and carboxyl groups of the acrylic base polymer and facilitate the introduction of crosslinked structures. Isocyanate-based crosslinking agents are preferred when the acrylic base polymer has hydroxyl groups as crosslinkable functional groups, and epoxy-based crosslinking agents are preferred when the acrylic base polymer has carboxyl groups as crosslinkable functional groups.

[0072] As isocyanate crosslinking agents, polyisocyanates having two or more isocyanate groups in one molecule are used. Isocyanate crosslinking agents may also have three or more isocyanate groups in one molecule. Examples of isocyanate crosslinking agents include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate (e.g., Asahi Kasei's "Duranate D101"); 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; trimethyl Examples of isocyanate adducts include rollpropane / tolylene diisocyanate trimer adducts (e.g., Mitsui Chemicals' "Takenate D101E"), trimethylolpropane / hexamethylene diisocyanate trimer adducts (e.g., Tosoh's "Coronate HL"), trimethylolpropane adducts of xylylene diisocyanate (e.g., Mitsui Chemicals' "Takenate D110N"), and isocyanurates of hexamethylene diisocyanate (e.g., Tosoh's "Coronate HX"). As isocyanate crosslinking agents, isocyanate compounds having biuret groups (e.g., Asahi Kasei's "Duranate 24A-100") or isocyanate compounds having allophanate groups may be used, and various urethane prepolymers can also be used.

[0073] As the epoxy crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in one molecule is used. The epoxy crosslinking agent may also have three or more or four or more epoxy groups in one molecule. The epoxy groups of the epoxy crosslinking agent may be glycidyl groups. Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipate ester, diglycidyl o-phthalate ester, triglycidyl-tris(2-hydroxyethyl) isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether. As epoxy crosslinking agents, commercially available products such as "Denacol" from Nagase ChemteX and "Tetrad X" and "Tetrad C" from Mitsubishi Gas Chemical may be used.

[0074] The amount of crosslinking agent used can be appropriately adjusted depending on the composition and molecular weight of the acrylic base polymer. The amount of crosslinking agent used is approximately 0.005 to 5 parts by weight per 100 parts by weight of the acrylic base polymer, but may also be 0.01 to 3 parts by weight, 0.015 to 1 part by weight, or 0.02 to 0.5 parts by weight.

[0075] A crosslinking catalyst may be used to promote the formation of crosslinked structures. Examples of crosslinking catalysts include organometallic compounds such as organometallic complexes (chelates), compounds of metals and alkoxy groups, and compounds of metals and acyloxy groups; as well as tertiary amines. In particular, organometallic compounds are preferred from the viewpoint of suppressing the progress of the crosslinking reaction in a solution state at room temperature and ensuring the pot life of the adhesive composition. Examples of metals in organometallic compounds include iron, tin, aluminum, zirconium, zinc, titanium, lead, and cobalt. The amount of crosslinking catalyst used is generally 0.1 parts by weight or less per 100 parts by weight of the acrylic base polymer.

[0076] <Photocuring agent> The adhesive composition constituting the adhesive layer 2 contains an acrylic-based polymer, as well as a compound having a photopolymerizable functional group as a photocuring agent. The adhesive composition containing the photocuring agent is photocurable, and when photocuring is performed after bonding to the substrate, the adhesion strength to the substrate is improved.

[0077] As the photopolymerizable functional group, an ethylenically unsaturated bond is preferred, and among these, a (meth)acryloyl group is preferred. The photocuring agent may have one photopolymerizable functional group or two or more photopolymerizable functional groups. A monofunctional photocuring agent having one photopolymerizable functional group and a polyfunctional photocuring agent having two or more photopolymerizable functional groups may be used in combination.

[0078] From the viewpoint of increasing the adhesive strength of the adhesive by photocuring, the adhesive composition preferably contains a polyfunctional photocuring agent. A polyfunctional (meth)acrylate is preferred as the polyfunctional photocuring agent. A typical polyfunctional (meth)acrylate is an ester of a polyol and (meth)acrylic acid. Specific examples of polyfunctional (meth)acrylates include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, isocyanuric acid di(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and trimeth Examples include tyrolpropane tri(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, pentaerythritoltetra(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, isoprene(meth)acrylate, etc.

[0079] The polyfunctional (meth)acrylate may be an ester of an alkylene oxide-modified polyol and (meth)acrylic acid. Examples of alkylene oxides include ethylene oxide (EO) and propylene oxide (PO). The alkylene oxide may also be a polyalkylene oxide such as polyethylene glycol or polypropylene glycol.

[0080] 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, isocyanurate ethylene oxide-modified di(meth)acrylate, isocyanurate propylene oxide-modified di(meth)acrylate, isocyanurate ethylene oxide-modified tri(meth)acrylate, isocyanurate propylene oxide-modified tri(meth)acrylate, pentaerythritol ethylene oxide-modified tetra(meth)acrylate, and pentaerythritol propylene oxide-modified tetra(meth)acrylate.

[0081] From the viewpoint of compatibility with acrylic-based polymers and reducing the resistance of the adhesive, polyfunctional (meth)acrylates (polyfunctional (meth)acrylates having alkylene oxide chains) are preferred. From the viewpoint of achieving both compatibility with acrylic-based polymers and improved adhesion after photocuring, the functional group equivalent (g / eq) of the polyfunctional (meth)acrylate is preferably 500 or less, more preferably 400 or less, and may be 300 or less, 250 or less, 200 or less, 180 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 point density of the adhesive layer after photocuring increases, which can lead to a higher shear storage modulus and reduced adhesion in the low-temperature range. Therefore, the functional group equivalent of the photocuring agent is preferably 80 or more, more preferably 100 or more, and may be 120 or more or 130 or more.

[0082] The acrylic-based polymer exhibits increased polarity due to the inclusion of (meth)acrylic acid esters having alkylene oxide chains as monomer components, thus demonstrating compatibility with polyfunctional (meth)acrylates also containing alkylene oxide chains. Furthermore, the inclusion of alkylene oxide chains in both the acrylic-based polymer and the photocuring agent tends to reduce the adhesive resistance.

[0083] The compatibility with photocuring agents containing alkylene oxide chains can be adjusted by adjusting the ratio of (meth)acrylic acid esters having alkylene oxide chains in the constituent monomer components of the acrylic base polymer. If the acrylic base polymer has a polarity such that it is not completely compatible with the photocuring agent ((meth)acrylic acid esters having alkylene oxide chains), the photocuring agent tends to be unevenly distributed on the surface of the adhesive layer (near the adhesive interface with the adherend), and even with a small amount of photocuring agent, the uneven distribution of the photocuring agent at the adhesive interface with the adherend can easily form a weak boundary layer (WBL).

[0084] When WBL (Wall-Based Bloc) is formed, the liquid properties of the surface (adhesive interface) become stronger while retaining bulk properties such as the shear storage modulus of the adhesive layer, which tends to reduce the adhesive strength to the adherend. Therefore, the adhesive layer is easily peeled off the adherend before photocuring. When an adhesive layer in which WBL has been formed, with the photocuring agent unevenly distributed near the adhesive interface with the adherend, is photocured, the curing reaction of the photocuring agent proceeds more easily near the adhesive interface where the density of the photocuring agent is high, thus improving the adhesive strength. In addition, when WBL is formed, the increase in the shear storage modulus, a bulk property, due to photocuring tends to be suppressed, making it highly applicable to foldable devices.

[0085] The smaller the functional group equivalent of the polyfunctional photocuring agent and the higher its content, the higher the crosslinking density due to photocuring, which tends to increase the shear storage modulus of the adhesive layer after photocuring. From the viewpoint of increasing the adhesive strength of the adhesive after photocuring while suppressing an excessive increase in the shear storage modulus, the content of the polyfunctional photocuring agent in the adhesive composition is preferably 1 to 25 parts by weight, more preferably 3 to 20 parts by weight, and may also be 4 to 17 parts by weight or 5 to 15 parts by weight, per 100 parts by weight of the acrylic base polymer. As described above, by adjusting the compatibility between the acrylic base polymer and the photocuring agent, if WBL is formed on the surface (adhesive interface) of the adhesive layer, the adhesive strength can be easily increased by photocuring even with a small amount of photocuring agent, and high adhesive strength can be achieved.

[0086] Monofunctional photocuring agents having a single photopolymerizable functional group include various alkyl (meth)acrylates and oligomers such as urethane (meth)acrylates. Using a monofunctional photocuring agent in addition to a polyfunctional photocuring agent such as a polyfunctional (meth)acrylate tends to reduce the adhesive strength of the adhesive before photocuring. Furthermore, the combined use of a monofunctional photocuring agent tends to increase the distance between crosslinking points after photocuring, thus reducing the shear storage modulus at low temperatures.

[0087] From the viewpoint of increasing the distance between crosslinking points and reducing the shear storage modulus of the adhesive layer at low temperatures after photocuring, a monofunctional photocuring agent with a molecular weight of 1000 or more is preferred. From the viewpoint of compatibility with acrylic-based polymers, the weight-average molecular weight of the oligomer used as a monofunctional photocuring agent is preferably 1000 to 30000, more preferably 1500 to 20000, and may also be 2000 to 15000. From the viewpoint of reducing the adhesive strength of the adhesive before photocuring and improving the adhesive strength of the adhesive layer after photocuring, urethane (meth)acrylate is preferred as the oligomer.

[0088] When a polyfunctional photocuring agent and a monofunctional photocuring agent are used in combination, the content of the monofunctional photocuring agent is preferably 1 to 45 parts by weight, more preferably 3 to 40 parts by weight, and may also be 4 to 35 parts by weight or 5 to 30 parts by weight per 100 parts by weight of the acrylic base polymer. When a polyfunctional photocuring agent and a monofunctional photocuring agent are used in combination, the total amount of the photocuring agent is preferably 3 to 50 parts by weight, and may also be 5 to 40 parts by weight, 7 to 35 parts by weight, 10 to 30 parts by weight or 15 to 25 parts by weight per 100 parts by weight of the acrylic base polymer.

[0089] <Photopolymerization initiator> Photopolymerization initiators generate active species upon irradiation with active light, thereby accelerating the curing reaction of photocuring agents. Depending on the type of photocuring agent, photocationic initiators (photoacid generators), photoradical initiators, photoanionic initiators (photobase generators), etc., are used as photopolymerization initiators. When a polyfunctional acrylate is used as the photocuring agent, it is preferable to use a photoradical initiator. As photoradical initiators, photoradical generators that cleave and generate radicals upon irradiation with visible light or ultraviolet light with a wavelength shorter than 450 nm are preferred, and examples include hydroxyketones, benzyldimethylketals, aminoketones, acylphosphine oxides, benzophenones, and trichloromethyl group-containing triazine derivatives. Photoradical generators may be used alone or in mixtures of two or more types.

[0090] The content of the photopolymerization initiator in the adhesive composition is preferably 0.001 to 5 parts by weight, more preferably 0.01 to 3 parts by weight, and even more preferably 0.03 to 1 part by weight, per 100 parts by weight of the acrylic base polymer. The content of the photopolymerization initiator in the adhesive composition is preferably 0.02 to 20 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 7 parts by weight, per 100 parts by weight of the total photocuring agent.

[0091] <Antistatic agent> The photocurable adhesive composition constituting the adhesive layer 2 preferably contains an antistatic agent. By including an antistatic agent in the adhesive, the adhesive layer's resistance is reduced, thereby decreasing the charge buildup of the adhesive layer, and also providing an effect that suppresses the charge buildup of the adherend.

[0092] Examples of antistatic agents include ionic compounds containing organic cations, alkali metal salts, ion-conducting polymers, ion-conducting fillers, and conductive polymers. Among these, ionic compounds containing organic cations and alkali metal salts are preferred due to their excellent compatibility with acrylic-based polymers.

[0093] The ionic compound containing the organic cation may be an ionic liquid, which is liquid at room temperature, or an ionic solid, which is solid at room temperature. Preferably, the ionic compound containing the organic cation is composed of an organic anion or a fluoroinorganic anion and an onium cation. The organic anion may be a fluoroorganic anion containing a fluorine atom, or an organic anion that does not contain a fluorine atom.

[0094] Examples of onium cations include nitrogen-containing onium cations, sulfur-containing onium cations (e.g., trialkylsulfonium cations), and phosphorus-containing onium cations (e.g., tetraalkylphosphonium cations). Among these, nitrogen-containing onium cations are preferred.

[0095] Examples of nitrogen-containing onium cations include pyridinium cations, pyrrolidinium cations, piperidinium cations, cations having a pyrroline skeleton, cations having a pyrrole skeleton, imidazolium cations, tetrahydropyrimidinium cations, dihydropyrimidinium cations, pyrazolium cations, pyrazolinium cations, and tetraalkylammonium cations.

[0096] Fluoroorganic anions constituting ionic compounds containing organic cations may be fully fluorinated (perfluorinated) or partially fluorinated. Examples of fluoroorganic anions include perfluoroalkyl sulfonates, bis(fluorosulfonyl)imides, and bis(perfluoroalkanesulfonyl)imides. More specifically, examples include trifluoromethanesulfonate, pentafluoroethanesulfonate, heptafluoropropanesulfonate, nonafluorobutanesulfonate, bis(fluorosulfonyl)imides, and bis(trifluoromethanesulfonyl)imides. Examples of organic anions that do not contain fluorine atoms include sulfonate anions such as p-toluenesulfonate, borate anions, and dicyanamide anions. Examples of fluoroinorganic anions include hexafluorophosphate and tetrafluoroboric acid.

[0097] The alkali metal salt is preferably composed of the above-mentioned organic anion or fluoroinorganic anion and an alkali metal cation. The alkali metal cation is Li + kaNa + or K + And among them Li + It is preferable.

[0098] The amount of antistatic agent in the adhesive composition is preferably about 0.01 to 3 parts by weight per 100 parts by weight of the acrylic base polymer, but may also be 0.03 to 2 parts by weight, 0.05 to 1 part by weight, or 0.1 to 0.7 parts by weight. If the amount of antistatic agent is too small, the adhesive may not be sufficiently low-resistance. If the amount of antistatic agent is too large, it may cause contamination or corrosion of the adherend due to the antistatic agent bleeding out, and a decrease in adhesive strength.

[0099] As described above, the acrylic base polymer of the adhesive composition contains a (meth)acrylic acid ester having an alkylene oxide chain as a monomer component, which reduces its resistance. Therefore, even with a small amount of antistatic agent added, the adhesive's resistance can be reduced. This allows for the provision of an adhesive layer with low surface resistance and excellent antistatic properties while suppressing problems such as bleed-out of the antistatic agent.

[0100] <Other ingredients> As described above, the photocurable adhesive composition constituting the adhesive layer 2 preferably comprises an acrylic-based polymer, a photocuring agent, and a photopolymerization initiator, and further preferably an antistatic agent. In addition to these components, the adhesive composition may also contain additives such as silane coupling agents, tackifiers, plasticizers, softeners, degradation inhibitors, fillers, colorants, UV absorbers, antioxidants, and surfactants, to the extent that they do not impair the properties of the present invention.

[0101] [Fabrication of reinforcing film] A reinforcing film is obtained by laminating a photocurable adhesive layer 2 onto a film substrate 1. The adhesive layer 2 may be formed directly on the film substrate 1, or an adhesive layer formed in sheet form on another substrate may be transferred onto the film substrate 1.

[0102] The above adhesive composition is applied to a substrate by methods such as roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, etc., and the solvent is dried and removed as necessary to form an adhesive layer. A suitable drying method can be used as appropriate. The heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and even more preferably 70°C to 170°C. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and even more preferably 10 seconds to 10 minutes.

[0103] If the adhesive composition contains a crosslinking agent, it is preferable to promote crosslinking by heating or aging simultaneously with or after the drying of the solvent. The heating temperature and heating time are set appropriately depending on the type of crosslinking agent used, and crosslinking is usually carried out by heating for about 1 minute to 7 days in the range of 20°C to 160°C. Heating to dry and remove the solvent may also serve as heating for crosslinking.

[0104] Even after a crosslinked structure is introduced into the polymer by a crosslinking agent, the photocuring agent remains unreacted. Therefore, the adhesive layer 2 contains an acrylic-based polymer with a crosslinked structure, a photocuring agent, and a photopolymerization initiator. When forming the adhesive layer 2 on a film substrate 1, it is preferable to attach a release liner 5 to the adhesive layer 2 for purposes such as protecting the adhesive layer 2. Crosslinking may also be performed after attaching the release liner 5 to the adhesive layer 2.

[0105] When forming the adhesive layer 2 on another substrate, a reinforcing film is obtained by transferring the adhesive layer 2 onto the film substrate 1 after the solvent has dried. The substrate used to form the adhesive layer may also be used as the release liner 5.

[0106] As the release liner 5, plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester film are preferably used. The thickness of the release liner is usually 3 to 200 μm, preferably about 10 to 100 μm. The contact surface of the release liner 5 with the adhesive layer 2 is preferably treated with a release agent such as silicone, fluorine, long-chain alkyl, or fatty acid amide, or silica powder. Because the surface of the release liner 5 is treated with a release agent, when the release liner 5 is peeled off from the film substrate 1, peeling occurs at the interface between the adhesive layer 2 and the release liner 5, and the state in which the adhesive layer 2 is fixed on the film substrate 1 is maintained. The release liner 5 may have an antistatic treatment applied to either the release-treated surface or the untreated surface, or both. By applying an antistatic treatment to the release liner 5, static charge can be suppressed when the release liner is peeled off from the adhesive layer.

[0107] [Physical properties of the adhesive layer] The thickness of the adhesive layer 2 is, for example, about 1 to 300 μm. The greater the thickness of the adhesive layer 2, the better the adhesion to the substrate tends to be. On the other hand, if the thickness of the adhesive layer 2 is excessively large, the fluidity before photocuring may be high, making handling difficult. Therefore, the thickness of the adhesive layer 2 is preferably 3 to 100 μm, more preferably 5 to 50 μm, even more preferably 6 to 40 μm, and particularly preferably 8 to 30 μm. From the viewpoint of thinning, the thickness of the adhesive layer 2 may be 25 μm or less, 20 μm or less, or 18 μm or less.

[0108] When the reinforcing film is used in optical devices such as displays, the total light transmittance of the adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The haze of the adhesive layer 2 is preferably 2% or less, more preferably 1% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less.

[0109] The adhesive layer 2 is preferably one whose adhesive strength to the adherend increases upon photocuring, and which has a low shear storage modulus at low temperatures (hereinafter simply referred to as "storage modulus") even after photocuring. The storage modulus of the adhesive is determined by reading the value at a predetermined temperature when measured at a frequency of 1 Hz and a heating rate of 5°C / min in the range of -70 to 100°C, in accordance with the method described in JIS K7244-1 "Plastics - Test methods for dynamic mechanical properties".

[0110] The storage modulus of the adhesive layer at -20°C after photocuring is preferably 100 kPa or less, more preferably 95 kPa or less, and even more preferably 90 kPa or less. Because the storage modulus of the adhesive layer 2 at low temperatures after photocuring is low, the adhesive layer exhibits strain relaxation properties in low-temperature environments. Therefore, 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, peeling of the adhesive layer at the bending point can be suppressed.

[0111] On the other hand, if the storage modulus of the adhesive layer after photocuring is excessively low, the adhesive layer is prone to plastic deformation, and the adhesive layer may peel off from the adherend due to insufficient adhesive strength. Therefore, the storage modulus of the adhesive layer at -20°C after photocuring is preferably 10 kPa or higher, more preferably 20 kPa or higher, even more preferably 30 kPa or higher, and may also be 40 kPa or higher, 50 kPa or higher, 60 kPa or higher, 65 kPa or higher, or 70 kPa or higher.

[0112] From the viewpoint of facilitating peeling from the adherend and preventing adhesive residue from remaining on the adherend after peeling off the reinforcing film, the adhesive strength between the adhesive layer and the adherend before photocuring is preferably 3N / 25mm or less, more preferably 2.5N / 25mm or less, and may also be 2N / 25mm or less, 1.5N / 25mm or less, or 1N / 25mm or less. From the viewpoint of preventing peeling of the reinforcing film during storage and handling, the adhesive strength between the adhesive layer and the adherend before photocuring is preferably 0.01N / 25mm or more, more preferably 0.02N / 25mm or more, and may also be 0.03N / 25mm or more, 0.04N / 25mm or more, or 0.05N / 25mm or more.

[0113] When the adhesive layer 2 is photocured, the photocuring agent undergoes a curing reaction, increasing the adhesive strength to the adherend. As mentioned above, it is preferable that the adhesive layer 2 has a low storage modulus at low temperatures after photocuring. From the viewpoint of adhesive reliability during practical use of the device, the adhesive strength between the photocured adhesive layer and the adherend is preferably 6N / 25mm or higher, more preferably 6.5N / 25mm or higher, and may also be 7N / 25mm or higher.

[0114] The adhesive strength between the adhesive layer after photocuring and the adherend is preferably at least twice, more preferably at least three times, and may be 3.5 times, 4 times, 4.5 times, or 5 times or more than the adhesive strength between the adhesive layer and the adherend before photocuring.

[0115] Adhesion strength is determined by a peel test using polyimide film as the substrate, at a tensile speed of 300 mm / min and a peel angle of 180°. Unless otherwise specified, adhesion strength is measured at 25°C.

[0116] The surface resistance of the adhesive layer 2 is 1.0 × 10⁻⁶. 11 Preferably less than Ω, 7.0 × 10 10 Ω or less, 5.0×10 10 Ω or less, 4.0×10 10 Less than or equal to Ω, or 3.0 × 10⁻⁶ 10The resistance may be less than or equal to Ω. As described above, the adhesive layer 2 can be made less resistive by including an (meth)acrylic acid ester having an alkylene oxide chain as a monomer component in the acrylic base polymer constituting the adhesive composition.

[0117] The low resistance of the adhesive layer 2 suppresses electrical damage to the adherend due to static electricity when the reinforcing film is peeled off from the adherend. It is preferable that the surface resistance of the adhesive layer 2 remains within the above range even after photocuring. Generally, the surface resistance of the adhesive layer hardly changes before and after photocuring. Because the adhesive layer after photocuring has the above surface resistance, static electricity of the adherend to which the adhesive layer 2 is bonded is removed via the adhesive layer 2, thereby suppressing the charging of the adherend. Therefore, it is possible to suppress problems caused by static electricity, such as electrostatic discharge damage, in devices to which the reinforcing film is bonded.

[0118] [Use of reinforcing film] The reinforcing film of the present invention is used by laminating it to a device or device component. The reinforcing film 10 has an adhesive layer 2 fixed to the film substrate 1, and before photocuring after lamination to the adherend, the adhesive strength to the adherend is low. Therefore, before photocuring, the reinforcing film can be easily peeled off the adherend.

[0119] The substrate to which the reinforcing film is bonded is not particularly limited and can include various electronic devices, optical devices and their components. In one embodiment, the reinforcing film is bonded to the surface of a bendable flexible device such as a foldable device or a rollable device. A foldable device has a hinge and can be folded around this hinge. If the device is a display device, the reinforcing film may be bonded to the screen side surface or to the back side (housing). In a flexible device that is configured to bend at a predetermined location such as a hinge, bending and stretching are repeatedly performed at the same location during use.

[0120] The reinforcing film may be bonded to the entire surface of the substrate, or it may be selectively bonded only to the areas requiring reinforcement (reinforcement target areas). Alternatively, the reinforcing film may be bonded to both the areas requiring reinforcement (reinforcement target areas) and the areas not requiring reinforcement (non-reinforcement target areas), and then the reinforcing film bonded to the non-reinforcement target areas may be cut and removed. If the adhesive has not yet been photocured, the reinforcing film is only temporarily attached to the surface of the substrate, and can therefore be easily peeled off and removed from the surface of the substrate. Alternatively, the reinforcing film may be bonded to the reinforcement target areas and the non-reinforcement target areas, and then the adhesive in the reinforcement target areas may be selectively irradiated with light to photocur the adhesive, after which the reinforcing film in the non-reinforcement target areas, where the adhesive has not yet cured, may be selectively peeled off and removed.

[0121] By laminating a reinforcing film, appropriate rigidity is imparted, which is expected to improve handling and prevent damage to thin components such as flexible devices. In the device manufacturing process, if a reinforcing film is laminated to work-in-progress, the reinforcing film may be laminated to the large work-in-progress before it is cut to product size. In devices manufactured by a roll-to-roll process, the reinforcing film may also be laminated to the mother roll using a roll-to-roll method.

[0122] After the reinforcing film is bonded to the substrate, the adhesive layer 2 is photocured by irradiating it with active light. Examples of active light include ultraviolet light, visible light, infrared light, X-rays, alpha rays, beta rays, and gamma rays. Ultraviolet light is preferred as the active light because it can suppress hardening of the adhesive layer during storage and is easy to cure. The irradiation intensity and duration of the active light can be appropriately set according to the composition and thickness of the adhesive layer. Irradiation of the adhesive layer 2 with active light may be performed from either the film substrate 1 side or the substrate side, or from both sides.

[0123] As described above, by laminating the reinforcing film of the present invention, appropriate rigidity is imparted to the adherend, and stress is relieved and dispersed, thereby suppressing various defects that may occur in the manufacturing process, improving production efficiency, and improving yield. The reinforcing film is easily peeled off from the adherend before the adhesive layer is photocured, so rework is easy even if lamination or bonding defects occur. Furthermore, processing such as selectively removing the reinforcing film from areas other than the reinforcement target area is also easy.

[0124] During use of the completed device, even if the device is unexpectedly subjected to external forces such as being dropped, having heavy objects placed on it, or being struck by flying objects, the reinforcement film prevents damage to the device. Furthermore, because the reinforcement film adheres firmly to the device after the adhesive has been photocured, it is less likely to peel off even after long-term use, resulting in superior reliability.

[0125] In a device with a reinforced film, where the reinforcing film of the present invention is laminated to a flexible device using a resin substrate, deformation such as wrinkles in the reinforcing film at the bending point and peeling of the reinforcing film from the device are unlikely to occur even when repeatedly bending and extending, or when the bent state is maintained for a long period of time, demonstrating excellent adhesive reliability. Furthermore, since the adhesive layer has low resistance and can remove static electricity from the resin substrate of the device via the adhesive layer, malfunctions such as electrostatic discharge damage to the device caused by static charge can be suppressed. [Examples]

[0126] The present invention will be further explained below with reference to examples and comparative examples, but it is not limited to these examples.

[0127] [Preparation of adhesive layer and reinforcing film] <Polymerization of acrylic polymers> In a reaction vessel equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas inlet tube, 100 parts by weight of monomers in the weight ratios shown in Table 1, 0.065 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 150 parts by weight of ethyl acetate as a solvent were added. Nitrogen gas was then introduced, and the mixture was purged with nitrogen while stirring for approximately 1 hour. Subsequently, the mixture was heated to 57°C and reacted for 6 hours to obtain solutions of acrylic polymers A to E. <Preparation of adhesive composition> To a solution of acrylic polymer (100 parts by weight as polymer solids), 0.025 parts by weight of a bifunctional isocyanate crosslinking agent (Asahi Kasei's "Duranate D101") was added as a crosslinking agent, 0.05 parts by weight of iron acetylacetonate (Nippon Chemical Industries' "Nasem Ferric") was added as a crosslinking catalyst, 7.5 parts by weight of trimethylolpropane EO-modified (n=1) triacrylate (Toagosei's "Aronics M-350") and 9.0 parts by weight of monofunctional urethane acrylate with a weight-average molecular weight of 10000 (AGC's "U-Fine LD-301") were added as photocuring agents, 0.3 parts by weight of IGM Resins' "Omnirad 651" was added as a photopolymerization initiator, and 1-ethyl-3-methylimidazolium bisfluorosulfonylimide (Daiichi Kogyo Seiyaku's "Elexel") was added as an antistatic agent. 0.3 parts by weight of AS-110 was added and uniformly mixed to prepare an adhesive composition.

[0128] <Preparation of reinforcing film> The above adhesive composition was applied to a 50 μm thick polyethylene terephthalate film using an applicator to a dry thickness of 18 μm. After drying at 130°C for 3 minutes to remove the solvent, the release-treated side of a release liner (a 38 μm thick polyethylene terephthalate film with both sides treated with antistatic agents and one side with a silicone release agent) was bonded to the adhesive-coated surface. Subsequently, an aging treatment was performed in a 50°C atmosphere for 3 days to promote crosslinking, resulting in a reinforced film in which a photocurable adhesive sheet was fixedly laminated on the polyethylene terephthalate film substrate, with the release liner temporarily attached on top.

[0129] [evaluation] The following evaluations were performed on the reinforcing film obtained above.

[0130] <Adhesive strength> A 25 μm thick polyimide film (UBE "UPIREX 25S") was attached to a SUS plate via double-sided adhesive tape (Nitto Denko "No. 531") to obtain a polyimide film substrate for measurement. The release liner was peeled off from the surface of a reinforcing film cut to a width of 25 mm x length of 100 mm, and it was bonded to the polyimide film substrate for measurement using a hand roller to obtain a test sample before photocuring. The adhesive layer of the test sample before photocuring was photocured by irradiating it with ultraviolet light from the reinforcing film side (PET film substrate side) to obtain a test sample after photocuring. Using a Shimadzu "Autograph AGX-V2", the end of the film substrate of the reinforcing film in the test sample was held with a chuck, and the reinforcing film was peeled 180° at a tensile speed of 300 mm / min to measure the peel strength.

[0131] <Surface resistance> The release liner was peeled off the reinforcing film to expose the adhesive layer (before photocuring). Under conditions of 25°C and 50% relative humidity, the surface resistance was measured by contacting the probe of a resistivity meter ("Highresta UP MCP-HT450" manufactured by Nitto Seiko Analytech) to the surface of the adhesive layer with an applied voltage of 10V and a voltage application time of 10 seconds.

[0132] <Storage modulus> Adhesive compositions were applied and crosslinked onto the release liner in the same manner as in each of the above examples and comparative examples to prepare adhesive sheets (before photocuring). A release liner was attached to the surface of the adhesive layer of the adhesive sheet before photocuring to block oxygen, and 1000 mJ / cm² was exposed to light using a 365 nm LED lamp. 2 The adhesive sheets were photocured by irradiation with ultraviolet light. After photocuring, the adhesive sheets were stacked to prepare a sample with a thickness of approximately 0.8 mm for measurement. Dynamic viscoelasticity measurements were performed using a dynamic viscoelasticity analyzer (TA Instruments "ARES-G2") under the following conditions, and the value of the shear storage modulus G' at -20°C was read. Transformation mode: Twist Measurement frequency: 1Hz Heating rate: 5°C / min Measurement temperature: -70~100℃ Shape: Parallel plate 8.0mmφ

[0133] [Evaluation Results] Table 1 shows the composition of the acrylic-based polymer adhesive used in the reinforcing films of the examples and comparative examples, as well as the evaluation results of the reinforcing films. In Table 1, monomers are indicated by the following abbreviations.

[0134] <Monomer> BA: Butyl acrylate 2EHA: 2-Ethylhexyl acrylate NOAA: n-octyl acrylate LA: Lauryl acrylate 4HBA: 4-hydroxybutyl acrylate MPE: Methoxypolyethylene glycol (m≒9) acrylate (Osaka Organic Chemical Industry Co., Ltd. "MPE400A", average molecular weight 470) CBA: Ethyl carbitol acrylate (Osaka Organic Chemical Industry Co., Ltd. "Viscoat #190", molecular weight 188)

[0135] [Table 1]

[0136] The reinforcing films of Examples 1 and 2, using polymers A and B containing 10 parts by weight of MPE having an average chain length m of approximately 9, exhibited low surface resistance, an adhesive strength of 3 N / 25 mm or less before photocuring, an adhesive strength of 6 N / 25 mm or more after photocuring, and a low storage modulus G' of the adhesive layer at low temperatures (-20°C) after photocuring, demonstrating excellent properties for foldable device applications.

[0137] In Comparative Example 1, which used polymer C with an MPE ratio of 5 parts by weight, the surface resistance of the adhesive layer was significantly higher compared to Examples 1 and 2. In Comparative Example 3, which used polymer E containing CBA with an ethylene oxide chain length of 2, the adhesive layer exhibited high resistance, similar to Comparative Example 1. Furthermore, Comparative Example 3 had high adhesive strength in the adhesive layer before photocuring and poor peelability. These results indicate that the inclusion of (meth)acrylic acid esters having alkylene oxides with a long chain length m as constituent monomers in acrylic-based polymers reduces the resistance of the adhesive and also contributes to reducing the adhesive strength of the adhesive layer before photocuring.

[0138] Comparative Example 2, which used polymer D containing 38 parts by weight of lauryl acrylate (an acrylic acid ester having an alkyl group with 12 carbon atoms), had a low storage modulus at low temperatures, but the increase in adhesive strength due to photocuring was insufficient compared to Examples 1 and 2.

[0139] From these results, it can be seen that a photocurable adhesive composition containing an acrylic-based polymer having a predetermined composition has low resistance and antistatic properties, low initial adhesive strength, excellent adhesive properties after photocuring, and a low storage modulus in the low-temperature range, making it suitable as a reinforcing film for foldable devices. [Explanation of Symbols]

[0140] 1. Film substrate 2. Adhesive layer 10 Reinforcement film 5. Release Liner 20 Adherent

Claims

1. The film substrate comprises an adhesive layer fixedly laminated on one main surface of the film substrate, The adhesive layer comprises a photocurable composition containing an acrylic-based polymer, a photocuring agent which is a compound having one or more photopolymerizable functional groups, and a photopolymerization initiator. The acrylic-based polymer contains, per 100 parts by weight of the total constituent monomers, 10 to 30 parts by weight of an alkyl (meth)acrylate having a chain alkyl group having 3 to 6 carbon atoms, 50 to 80 parts by weight of an alkyl (meth)acrylate having a chain alkyl group having 7 to 9 carbon atoms, and 6 to 20 parts by weight of an alkyl (meth)acrylate represented by the following general formula (1), and further contains one or more constituent monomers selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers. The aforementioned acrylic-based polymer has a cross-linked structure introduced into it. Reinforcement film: CH ２ =CR １ -COO-(R ２ -O) ｍ -R ３ (1) In general formula (1), R １ is a hydrogen atom or a methyl group, R ２ This is an alkylene group having 2 to 4 carbon atoms, which may have branches. m is an integer between 6 and 15. R ３ This is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

2. The reinforcing film according to claim 1, wherein the acrylic-based polymer contains 1 to 20 parts by weight of a hydroxyl group-containing monomer per 100 parts by weight of the total constituent monomers.

3. The reinforcing film according to claim 1, wherein the acrylic-based polymer has n-octyl acrylic acid as the most abundant monomer among its constituent monomers.

4. The reinforcing film according to claim 1, wherein the photocurable composition further comprises an antistatic agent.

5. The reinforcing film according to claim 1, wherein the adhesive layer has a shear storage modulus of 100 kPa or less at -20°C after photocuring.

6. The reinforcing film according to claim 1, wherein the adhesive layer has an adhesive strength of 3 N / 25 mm or less to the polyimide film before photocuring.

7. The reinforcing film according to claim 1, wherein the adhesive layer has an adhesive strength of 6 N / 25 mm or more to the polyimide film after photocuring.

8. The surface resistance of the adhesive layer is 1×10 １１ Ω or less, the reinforcing film according to claim 1.

9. A device with a reinforcing film, wherein a reinforcing film is attached to the surface of a foldable device, The reinforcing film comprises a film substrate and an adhesive layer fixedly laminated on one main surface of the film substrate. The adhesive layer is bonded to the surface of the device. The adhesive layer is made of a photocured product obtained by photocuring a photocurable adhesive composition containing an acrylic-based polymer, a photocuring agent which is a compound having one or more photopolymerizable functional groups, and a photopolymerization initiator. The acrylic-based polymer contains, per 100 parts by weight of the total constituent monomers, 10 to 30 parts by weight of an alkyl (meth)acrylate having a chain alkyl group having 3 to 6 carbon atoms, 50 to 80 parts by weight of an alkyl (meth)acrylate having a chain alkyl group having 7 to 9 carbon atoms, and 6 to 20 parts by weight of an alkyl (meth)acrylate represented by the following general formula (1), and further contains one or more constituent monomers selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers. The aforementioned acrylic-based polymer has a cross-linked structure introduced into it. Devices with reinforcing film: CH ２ =CR １ -COO-(R ２ -O) ｍ -R ３ (1) In general formula (1), R １ is a hydrogen atom or a methyl group, R ２ This is an alkylene group having 2 to 4 carbon atoms, which may have branches. m is an integer between 6 and 15. R ３ This is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

10. The device with a reinforcing film according to claim 9, wherein the adhesive layer has a shear storage modulus of 100 kPa or less at -20°C.

11. A method for manufacturing a device with a reinforcing film, wherein a reinforcing film is attached to the surface of a foldable device, The adhesive layer of the reinforcing film according to any one of claims 1 to 8 is bonded to the surface of a foldable device. The adhesive layer is photocured. A method for manufacturing a device with a reinforcing film.

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