TW202444847A - Reinforcement film, device manufacturing method and reinforcement method - Google Patents

Abstract

The reinforcing film (10) of the present invention has an adhesive layer (2) fixedly laminated on one main surface of a film substrate (1). The adhesive layer comprises a photocurable composition containing an acrylic base polymer, a photocuring agent having two or more photopolymerizable functional groups, and a photopolymerization initiator. The acrylic base polymer comprises one or more monomer components selected from the group consisting of hydroxyl-containing monomers and carboxyl-containing monomers, and a crosslinking structure formed by a crosslinking agent bonded to hydroxyl and/or carboxyl groups is introduced. The surface resistance of the adhesive layer is 1×10 ¹⁵ Ω or more.

Description

Reinforcement film, device manufacturing method and reinforcement method

The present invention relates to a reinforcing film formed by fixing and laminating a film substrate and a photocurable adhesive layer. Furthermore, the present invention relates to a manufacturing method of a device having a reinforcing film attached to a surface, and a reinforcing method for fixing and laminating the reinforcing film on the surface of an adherend.

Adhesive films are sometimes attached to the surface of optical devices such as displays or electronic devices for the purpose of surface protection or impact resistance. Such adhesive films usually have an adhesive layer fixedly laminated on the main surface of the film substrate, and are attached to the device surface through the adhesive layer.

By temporarily adhering the adhesive film to the surface of the device or its components before use, such as during assembly, processing, and transportation of the device, damage or destruction of the adherend can be suppressed. Patent document 1 discloses a reinforcing film having an adhesive layer on a film substrate, wherein the adhesive layer comprises a photocurable adhesive composition.

The adhesive of the reinforcing film has low adhesion immediately after being bonded to the adherend, so it is easy to peel off from the adherend. Therefore, the adherend can be subjected to secondary processing, and the reinforcing film can also be selectively peeled off and removed from the parts of the adherend that do not need reinforcement. The adhesive of the reinforcing film is firmly bonded to the adherend by light curing, so that the film substrate is permanently bonded to the surface of the adherend, and can be used as a reinforcing material for surface protection of the device. [Prior technical literature] [Patent literature]

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

[The problem the invention is trying to solve]

The device having a reinforcing film having an adhesive layer fixed on a film substrate is easily charged because the substrate of the reinforcing film is a resin material. The charge (static electricity) of the substrate may leak to the electronic parts constituting the device and cause static electricity damage.

In view of the above situation, the purpose of the present invention is to provide a reinforcing film that can be peeled off immediately after being attached to an adherend, and can be firmly attached to an adherend by light-curing the adhesive after being attached to the adherend, and static electricity is not easily leaked to the adherend. [Technical means to solve the problem]

The reinforcing film of the present invention has an adhesive layer fixedly laminated on one main surface of the film substrate. The adhesive layer comprises a photocurable composition, and the photocurable composition comprises an acrylic base polymer, a photocuring agent, and a photopolymerization initiator. The acrylic base polymer contains one or more monomer units selected from the group consisting of hydroxyl-containing monomers and carboxyl-containing monomers, and a crosslinking structure is introduced by bonding the hydroxyl and/or carboxyl groups of the base polymer with the crosslinking agent.

The surface resistance of the adhesive layer is 1×10 ¹⁵ Ω or more. By making the adhesive constituting the reinforcement film have a high resistance, the leakage of static electricity from the resin film substrate to the inside of the device can be reduced, thereby suppressing the static electricity damage of the device. The surface free energy of the adhesive layer is preferably 20 mJ/m ² or less.

The photocurable composition constituting the adhesive layer contains 3 to 25 parts by weight of a photocuring agent relative to 100 parts by weight of the acrylic base polymer. As the photocuring agent, a multifunctional (meth)acrylate is preferred. The multifunctional (meth)acrylate may also be one having an alkylene oxide chain. As the photocuring agent, a multifunctional (meth)acrylate having an alkylene oxide chain and a urethane (meth)acrylate may also be included.

The acrylic-based polymer may also contain 50 to 99.5 parts by weight of an alkyl (meth)acrylate having an alkyl carbon number of 6 to 20, relative to 100 parts by weight of the total monomer components. The ratio of nitrogen in the constituent elements of the acrylic-based polymer may also be 0.1 mol % or less.

The shear storage modulus of the adhesive layer at 25°C before light curing may be 10 to 70 kPa. The shear storage modulus of the adhesive layer at 25°C after light curing may be 30 to 140 kPa.

The adhesion between the adhesive layer and the polyimide film before light curing can be less than 0.5 N/25 mm. The adhesion between the adhesive layer and the polyimide film after light curing can be more than 3 N/25 mm.

After the reinforcing film is attached and temporarily adhered to the surface of a device as an adherend, the adhesive layer is photocured to obtain a device with a reinforcing film. After the reinforcing film is temporarily adhered to the adherend and before the adhesive layer is photocured, the reinforcing film temporarily adhered to the adherend can be cut off and the reinforcing film can be peeled off and removed from a part of the adherend (non-reinforcement target area). In the device with a reinforcing film, the surface resistance of the adhesive layer is preferably 1×10 ¹⁵ Ω or more. [Effect of the invention]

In the reinforcing film of the present invention, the adhesive layer contains a photocurable composition, so that before the adhesive layer is photocured, the adhesive strength with the adherend is small and can be peeled off from the adherend, and after being attached to the adherend, the adhesive layer is photocured to increase the adhesive strength with the adherend. Since the adhesive layer of the reinforcing film has a high electrical resistance, it is possible to suppress electrostatic damage caused by static electricity leakage from the film substrate to the inside of the adherend.

FIG1 is a cross-sectional view showing an embodiment of a reinforcing film. The reinforcing film 10 has an adhesive layer 2 on one main surface of a film substrate 1. The adhesive layer 2 is fixedly laminated on one main surface of the film substrate 1. The adhesive layer 2 is a photocurable adhesive containing a photocurable composition, which is cured by irradiation with active light such as ultraviolet rays, thereby increasing the bonding strength with the adherend.

Fig. 2 is a cross-sectional view showing a reinforcing film with a peeling pad 5 temporarily attached to the main surface of the adhesive layer 2. Fig. 3 is a cross-sectional view showing a state where a reinforcing film 10 is attached to the surface of a device 20.

The peeling pad 5 is peeled off from the surface of the adhesive layer 2, and the exposed surface of the adhesive layer 2 is attached to the surface of the device 20, and the reinforcing film 10 is attached to the surface of the device 20. In this state, the adhesive layer 2 is in a state before light curing and the reinforcing film 10 (adhesive layer 2) is temporarily attached to the device 20. By light curing the adhesive layer 2, the bonding force at the interface between the device 20 and the adhesive layer 2 increases, and the device 20 and the reinforcing film 10 are fixed.

"Fixed" refers to the state where two layers of a laminate are firmly attached and cannot or are difficult to peel off at the interface. "Temporary adhesion" refers to the state where the adhesion between two layers of a laminate is relatively weak and can be easily peeled off at the interface.

In the reinforcement film shown in FIG2 , the film substrate 1 is fixed to the adhesive layer 2, and the peeling pad 5 is temporarily adhered to the adhesive layer 2. If the film substrate 1 and the peeling pad 5 are peeled off, peeling occurs at the interface between the adhesive layer 2 and the peeling pad 5, and the state in which the adhesive layer 2 is fixed to the film substrate 1 is maintained. No adhesive remains on the peeling pad 5 after peeling.

Regarding the device with the reinforcing film 10 attached as shown in FIG. 3, before the adhesive layer 2 is photocured, the device 20 and the adhesive layer 2 are in a temporarily adhered state. When the film substrate 1 is peeled off from the device 20, peeling occurs at the interface between the adhesive layer 2 and the device 20, and the state in which the adhesive layer 2 is fixed to the film substrate 1 is maintained. No adhesive remains on the device 20, so it is easy to perform secondary processing. After the adhesive layer 2 is photocured, the adhesion between the adhesive layer 2 and the device 20 increases, so it is difficult to peel the film 1 from the device 20. If the two are peeled off, the cohesion and destruction of the adhesive layer 2 may occur.

[Construction of the reinforcing film] ＜Film substrate＞ As the film substrate 1, a plastic film can be used. In order to fix the film substrate 1 and the adhesive layer 2, it is preferred that the surface of the film substrate 1 to which the adhesive layer 2 is attached is not subjected to release treatment.

The thickness of the film substrate is, for example, about 4 to 500 μm. From the perspective of reinforcing the device by imparting rigidity or buffering impact, the thickness of the film substrate 1 is preferably 12 μm or more, more preferably 30 μm or more, and further preferably 45 μm or more. From the perspective of making the reinforcing film flexible and improving operability, the thickness of the film substrate 1 is preferably 300 μm or less, and more preferably 200 μm or less. From the perspective of both mechanical strength and flexibility, the compressive strength of the film substrate 1 is preferably 100-3000 kg/cm ² , more preferably 200-2900 kg/cm ² , further preferably 300-2800 kg/cm ² , and particularly preferably 400-2700 kg/cm ² .

As the plastic material constituting the film substrate 1, polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, etc. can be cited. In the reinforcing film for optical devices such as displays, the film substrate is preferably a transparent film. In addition, when the adhesive layer 2 is photocured by irradiating active light from the film substrate 1 side, the film substrate is preferably transparent to the active light used for curing the adhesive layer. In terms of both mechanical strength and transparency, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate are preferably used. When the adhesive layer is cured by irradiating the adherend with active light from the adherend side, the adherend only needs to be transparent to the active light, and the film substrate 1 may be opaque to the active light.

Functional coatings such as an easy-adhesion layer, an easy-slip layer, a release layer, an antistatic layer, a hard coating layer, and an antireflection layer may also be provided on the surface of the film substrate 1. Furthermore, as described above, in order to fix the film substrate 1 and the adhesive layer 2, it is preferred that no release layer is provided on the surface of the film substrate 1 where the adhesive layer 2 is attached.

<Adhesive layer> The adhesive layer 2 fixedly laminated on the film substrate 1 includes a photocurable composition, which includes a base polymer, a photocuring agent, and a photopolymerization initiator. Before photocuring, the adhesive layer 2 has a weak adhesion to the adherend such as the device or device parts, so it is easy to peel off. The adhesive layer 2 has a stronger adhesion to the adherend by photocuring, so when the device is used, the reinforcing film is difficult to peel off from the device surface, and the adhesion reliability is excellent.

The light-curing adhesive hardly cures under normal storage conditions, but cures under irradiation with active light such as ultraviolet rays. Therefore, the reinforcing film of the present invention has the advantages of being able to arbitrarily set the curing time of the adhesive layer 2 and being able to flexibly cope with the preparation time of the steps.

The thickness of the adhesive layer 2 is, for example, about 1 to 300 μm. The thicker the adhesive layer 2 is, the better the adhesion to the adherend tends to be. On the other hand, when the thickness of the adhesive layer 2 is too large, the fluidity before photocuring is high, and it is sometimes difficult to operate. Therefore, the thickness of the adhesive layer 2 is preferably 3 to 100 μm, more preferably 5 to 50 μm, further preferably 6 to 40 μm, and particularly preferably 8 to 30 μm. From the perspective of thinning, the thickness of the adhesive layer 2 may also be less than 25 μm, less than 20 μm, or less than 18 μm.

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

The surface resistance of the adhesive layer 2 after light curing is 1×10 ¹⁵ Ω or more. Since the adhesive layer has a high resistance, when the film substrate 1 of the reinforcement film is charged, the adhesive layer 2 blocks static electricity, thereby preventing static electricity from leaking to the device 20 as the adherend and causing electrostatic damage.

The surface resistance of adhesive layer 2 is the value measured by bringing the probe of a high resistance resistivity meter into contact with the surface of the adhesive layer after light curing, under the conditions of applying a voltage of 1000V for 10 seconds. Generally speaking, the surface resistance of the adhesive layer is almost unchanged before and after light curing, so if the surface resistance of the adhesive layer before light curing is 1×10 ¹⁵ Ω or more, the surface resistance of the adhesive layer after light curing is also 1×10 ¹⁵ Ω or more.

The smaller the surface free energy of the adhesive layer 2, the smaller the degree of freedom of the molecules on the surface (interface with the adherend) (the molecules are less likely to move), and the surface resistance tends to increase. From the perspective of having high resistance, the surface free energy of the adhesive layer 2 after photocuring is preferably 20 mJ/m ² or less, more preferably 19 mJ/m ² or less, further preferably 18 mJ/m ² or less, and may also be 17 mJ/m ² or less, 16 mJ/m ² or less, or 15.5 mJ/m ² or less. From the perspective of suppressing contamination of the adherend due to the seepage of the constituents of the adhesive layer, the surface free energy of the adhesive layer is also preferably within the above range.

On the other hand, when the surface free energy of the adhesive is relatively small, the adhesive force of the adhesive layer before light curing is relatively large, and it tends to be difficult to peel the reinforcing film from the adherend. Therefore, the surface free energy of the adhesive layer 2 after light curing is preferably 12 mJ/ ^m2 or more, more preferably 13 mJ/m2 ^or more, further preferably 13.5 mJ/ ^m2 or more, and can also be 14 mJ/ ^m2 or more.

The surface resistance of the adhesive layer 2 is calculated by dropping two liquids (probe liquids) whose surface free energy dispersion term γ _d , polar term γ _p and hydrogen bond term γ _h are known on the surface of the light-cured adhesive layer, measuring the contact angles θ ₁ and θ ₂ relative to each liquid, and using the Owens-Wendt formula based on the values of the surface free energy dispersion term γ _d , polar term γ _p and hydrogen bond term γ _h of the probe liquid and the contact angle. In the measurement of the surface free energy of the adhesive layer, water and diiodomethane are used as probe liquids. The surface free energy of water is (γ _d ,γ _p ,γ _h )=(29.1,1.3,42.4), and the surface free energy of diiodomethane is (γ _d ,γ _p ,γ _h )=(46.8,4.0,0.0) (unit: mJ/m ² ).

The shear storage modulus (hereinafter referred to as "storage modulus") of the adhesive layer 2 before light curing at a temperature of 25°C is preferably 10 kPa or more, more preferably 15 kPa or more, further preferably 20 kPa or more, and may be 25 kPa or more or 30 kPa or more. The larger the storage modulus of the adhesive layer before light curing at room temperature, the better the processability such as cutting, and the more the residue of the adhesive on the adherend is suppressed when the reinforcing film is peeled off from the adherend.

On the other hand, if the storage modulus of the adhesive layer before light curing at room temperature is too large, the storage modulus of the adhesive layer after light curing also tends to increase, and the adhesion or impact resistance to the adherend is sometimes insufficient. Therefore, the storage modulus of the adhesive layer before light curing at a temperature of 25°C is preferably 70 kPa or less, more preferably 60 kPa or less, and further preferably 55 kPa or less, and can also be 50 kPa or less, 45 kPa or less, or 40 kPa or less.

The storage modulus of the adhesive layer is obtained by reading the value at a specific temperature when measuring at a frequency of 1 Hz, within the range of -70 to 150°C, 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". In this manual, unless otherwise specified, the storage modulus is the value at a temperature of 25°C.

From the perspective of achieving high adhesion to the adherend after photocuring, the storage modulus of the adhesive layer after photocuring at a temperature of 25°C is preferably 30 kPa or more, more preferably 35 kPa or more, and may be 40 kPa or more, 45 kPa or more, or 50 kPa or more. On the other hand, when the storage modulus after photocuring is too large, there is a tendency for insufficient adhesion to the adherend. In addition, the smaller the storage modulus of the adhesive layer after photocuring, the higher the impact mitigation effect (mitigation) generated by the adhesive layer 2, and the higher the impact resistance. Therefore, the storage modulus of the adhesive layer after light curing at a temperature of 25° C. is preferably 140 kPa or less, more preferably 120 kPa or less, further preferably 100 kPa or less, and may also be 90 kPa or less, 80 kPa or less, or 70 kPa or less.

Hereinafter, the preferred forms of the components of the photocurable composition constituting the adhesive layer 2 will be described in order.

(Base polymer) The base polymer is the main component of the adhesive composition and is the main factor that determines the adhesion of the adhesive layer. In terms of excellent optical transparency and adhesion and easy control of adhesion or storage modulus, the adhesive composition preferably contains an acrylic polymer as the base polymer, and preferably more than 50% by weight of the adhesive composition is an acrylic polymer.

As the acrylic polymer, one containing an alkyl (meth)acrylate as a main monomer component is preferably used. In the present specification, "(meth)acrylic acid" refers to acrylic acid and/or methacrylic acid.

As the alkyl (meth)acrylate, preferably used is an alkyl (meth)acrylate having an alkyl carbon number of 1 to 20. The alkyl (meth)acrylate may have a branched alkyl group or a cyclic alkyl group (alicyclic alkyl group).

Specific examples of the alkyl (meth)acrylate having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like.

Specific examples of the alkyl (meth)acrylate having an alicyclic alkyl group include: cycloalkyl (meth)acrylates such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylates having a dicyclic aliphatic hydrocarbon ring such as isobutyl (meth)acrylate; and (meth)acrylates having a tricyclic or more aliphatic hydrocarbon ring such as dicyclopentyl (meth)acrylate, dicyclopentyloxyethyl (meth)acrylate, tricyclopentyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate. The alkyl (meth)acrylate having an alicyclic alkyl group may be a (meth)acrylate having a substituent on the ring, such as 3,3,5-trimethylcyclohexyl (meth)acrylate. The alkyl (meth)acrylate having an alicyclic alkyl group may be a (meth)acrylate having a condensed ring of an alicyclic structure and a ring structure having an unsaturated bond, such as dicyclopentenyl (meth)acrylate.

The content of the alkyl (meth)acrylate is preferably 50 parts by weight or more, more preferably 60 parts by weight or more, and may be 70 parts by weight or more, 80 parts by weight or more, or 90 parts by weight or more, relative to 100 parts by weight of the total monomer components constituting the base polymer.

From the viewpoint of making the adhesive layer 2 have high resistance, the (meth)acrylic acid alkyl ester as the monomer component of the acrylic base polymer is preferably one having an alkyl carbon number of 6 or more. Since the volume of the alkyl group of the (meth)acrylic acid alkyl ester having an alkyl carbon number of 6 or more is large, the amount of (meth)acrylic group per unit volume of the base polymer is small, the surface free energy is small, and the resistance is easily increased.

From the viewpoint of lowering the glass transition temperature of the acrylic-based polymer and making the adhesive sheet have appropriate flexibility and adhesiveness, the alkyl group of the (meth)acrylic acid alkyl ester is preferably a chain alkyl group. The chain alkyl group may be a straight chain or a branched chain.

From the viewpoint of lowering the glass transition temperature of the acrylic-based polymer and making the adhesive sheet have appropriate flexibility, the alkyl (meth)acrylate preferably has a homopolymer glass transition temperature of -56°C or less, and preferably has an alkyl carbon number of 9 or less. Specific examples of the alkyl (meth)acrylate having an alkyl carbon number of 6 or more and a homopolymer glass transition temperature (Tg) of -56°C or less 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 the like. Among them, 2-ethylhexyl acrylate is particularly preferred because it contributes greatly to high resistance and has a low Tg, thereby being able to lower the storage modulus of the adhesive.

The content of the alkyl (meth)acrylate having an alkyl carbon number of 6 or more is preferably 50 parts by weight or more, more preferably 60 parts by weight or more, and may be 70 parts by weight or more, 75 parts by weight or more, 80 parts by weight or more, 85 parts by weight or more, or 90 parts by weight or more, relative to 100 parts by weight of the total monomer components constituting the base polymer. With respect to the acrylic base polymer, the amount of 2-ethylhexyl acrylate may also be within the above range relative to 100 parts by weight of the total monomer components.

The upper limit of the amount of the alkyl (meth)acrylate having an alkyl carbon number of 6 or more is not particularly limited. As described below, in order to introduce crosslinking points into the acrylic base polymer, a hydroxyl-containing monomer or a carboxyl-containing monomer is used as a copolymerization component of the acrylic base polymer. Therefore, the amount of the alkyl (meth)acrylate having an alkyl carbon number of 6 or more is preferably 99.5 parts by weight or less, more preferably 99 parts by weight or less, and may also be 98 parts by weight or less or 97 parts by weight or less, based on 100 parts by weight of the total amount of the monomer components constituting the base polymer.

The acrylic base polymer may contain two or more alkyl (meth)acrylates as monomer components. The two or more alkyl (meth)acrylates may contain one having an alkyl carbon number of 6 or more and one having an alkyl carbon number of 5 or less. The alkyl (meth)acrylate having an alkyl carbon number of 6 or more may contain one having an alkyl carbon number of 6 to 9 and one having an alkyl carbon number of 10 or more.

The acrylic base polymer preferably contains a monomer component having a crosslinking functional group as a copolymer component. By introducing a crosslinking structure into the base polymer, the cohesive force is improved, the adhesion of the adhesive layer 2 is improved, and the amount of adhesive residue on the adherend when the adhesive layer before light curing is peeled off from the adherend tends to be reduced.

Examples of monomers having a crosslinkable functional group include hydroxyl-containing monomers and carboxyl-containing monomers. The hydroxyl group or carboxyl group of the base polymer becomes a reaction site with the following crosslinking agent. For example, when an isocyanate crosslinking agent is used, it is preferred that the base polymer contains a hydroxyl-containing monomer as a copolymer component. When an epoxy crosslinking agent is used, it is preferred that the base polymer contains a carboxyl-containing monomer as a copolymer component.

Examples of the hydroxyl group-containing monomer 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. Examples of the carboxyl group-containing monomer include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

From the viewpoint of appropriately introducing a crosslinking structure based on a crosslinking agent such as an isocyanate crosslinking agent or an epoxy crosslinking agent, the total amount of the hydroxyl group-containing monomer and the carboxyl group-containing monomer is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and may also be 1.5 parts by weight or more, 2 parts by weight or more, 2.5 parts by weight or more, or 3 parts by weight or more, relative to 100 parts by weight of the total amount of the monomer components constituting the acrylic base polymer.

Since hydroxyl or carboxyl groups have high polarity, when the amount of hydroxyl-containing monomers or carboxyl-containing monomers in the monomer components of the acrylic base polymer is large, the resistance of the adhesive layer 2 tends to decrease. From the viewpoint of making the adhesive layer 2 have high resistance, the total amount of hydroxyl-containing monomers and carboxyl-containing monomers is preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and further preferably 15 parts by weight or less, and may also be 12 parts by weight or less, 10 parts by weight or less, or 8 parts by weight or less, relative to 100 parts by weight of the total amount of the monomer components of the acrylic base polymer.

The acrylic-based polymer may contain nitrogen-containing monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperidone, vinylpyrrolidone, vinylpyrrole, vinylimidazole, vinyloxazole, vinyloxaline, N-acryloyloxaline, N-vinylcarboxamides, and N-vinylcaprolactam as constituent monomer components.

The nitrogen-containing monomer has high polarity, so when the amount of the nitrogen-containing monomer in the monomer component of the acrylic base polymer is large, the resistance of the adhesive layer 2 tends to decrease. In addition, when the amount of the nitrogen-containing monomer is large, the adhesive layer 2 before photocuring tends to have improved adhesion to the adherend that has been subjected to surface activation treatment such as plasma treatment, and the reinforcing film tends to be difficult to peel off from the adherend.

Therefore, the acrylic-based polymer preferably has a smaller ratio of nitrogen-containing monomers in the monomer components. In addition, from the viewpoint of lowering the glass transition temperature of the acrylic-based polymer, it is also preferred that the amount of nitrogen-containing monomers is smaller. The amount of nitrogen-containing monomers is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and further preferably 3 parts by weight or less, and may also be 1 part by weight or less, 0.5 parts by weight or less, 0.1 parts by weight or less, or 0.05 parts by weight or less, relative to 100 parts by weight of the total amount of the monomer components of the acrylic-based polymer.

The acrylic-based polymer may not contain nitrogen-containing monomers as constituent monomer components. The acrylic-based polymer before the introduction of the cross-linked structure may not contain substantially nitrogen atoms. The ratio of nitrogen in the constituent elements of the acrylic-based polymer may be 0.1 mol% or less, 0.05 mol% or less, 0.01 mol% or less, 0.005 mol% or less, 0.001 mol% or less, or 0. By using an acrylic-based polymer that does not contain substantially nitrogen atoms, there is a tendency to suppress the increase in the adhesion (initial adhesion) of the adhesive sheet before light curing when the adherend is subjected to a surface activation treatment. By not using monomers containing nitrogen atoms as constituent monomer components, a polymer that does not contain substantially nitrogen atoms can be obtained. Furthermore, when a cross-linking structure is introduced into the base polymer, the cross-linking agent may contain nitrogen atoms as long as the polymer before the introduction of the cross-linking structure does not substantially contain nitrogen atoms.

The acrylic-based polymer may also contain monomer components other than those mentioned above. The acrylic-based polymer may also contain, for example, vinyl ester monomers, aromatic vinyl monomers, monomers containing epoxy groups, vinyl ether monomers, monomers containing sulfonic groups, monomers containing phosphoric acid groups, monomers containing acid anhydride groups, etc. as monomer components.

From the viewpoint of excellent adhesion of the adhesive, the glass transition temperature of the acrylic-based polymer is preferably below -40°C, more preferably below -50°C, further preferably below -55°C, and may be below -60°C or below -62°C. The glass transition temperature of the acrylic-based polymer is usually above -100°C, and may be above -80°C or above -70°C.

The glass transition temperature (Tg) is the temperature (peak temperature) at which the loss tangent tanδ reaches a maximum in the viscoelastic measurement. The theoretical glass transition temperature can also be used instead of the glass transition temperature obtained by viscoelastic measurement. The theoretical Tg is calculated using the following Fox formula based on the glass transition temperature Tg _i of the homopolymer of the monomer components constituting the acrylic base polymer and the weight fraction _Wi of each monomer component. 1/Tg=Σ( _Wi /Tg _i )

Tg is the theoretical glass transition temperature of the polymer (unit: K), _Wi is the weight fraction of monomer component i constituting the chain segment (copolymerization ratio based on weight), and Tg _i is the glass transition temperature of the homopolymer of monomer component i (unit: K). As the glass transition temperature of the homopolymer, the value listed in the Polymer Handbook 3rd edition (John Wiley & Sons, Inc., 1989) can be used. The glass transition temperature of the homopolymer of the monomer not listed in the above literature can be the peak temperature of tanδ obtained by dynamic viscoelastic measurement.

By polymerizing the above-mentioned monomer components by various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization, an acrylic polymer as a base polymer can be obtained. From the perspective of balancing the adhesive properties such as adhesion and retention or cost, solution polymerization is preferred. As a solvent for solution polymerization, ethyl acetate, toluene, etc. can be used. The solution concentration is usually around 20 to 80% by weight. As a polymerization initiator used for solution polymerization, various known ones such as azo series and peroxide series can be used. In order to adjust the molecular weight, a chain transfer agent can also be used. The reaction temperature is usually around 50 to 80°C, and the reaction time is usually around 1 to 8 hours.

The weight average molecular weight of the acrylic base polymer is preferably 200,000 to 3,000,000, more preferably 300,000 to 2,500,000, and may also be 400,000 to 2,000,000, or 500,000 to 1,800,000. Furthermore, when a cross-linked structure is introduced into the base polymer, the molecular weight of the base polymer refers to the molecular weight before the cross-linked structure is introduced.

(Crosslinking agent) From the perspective of giving the adhesive an appropriate cohesive force, it is preferable to introduce a crosslinking structure into the base polymer. For example, a crosslinking agent is added to a solution after the base polymer is polymerized, and heating is performed as necessary to introduce a crosslinking structure. The crosslinking agent has two or more crosslinking functional groups in one molecule. The crosslinking agent may also have three or more crosslinking functional groups in one molecule.

Examples of the crosslinking agent include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. These crosslinking agents react with functional groups such as hydroxyl groups or carboxyl groups introduced into the base polymer to form a crosslinking structure. Isocyanate crosslinking agents and epoxy crosslinking agents are preferred because they have a higher reactivity with the hydroxyl groups or carboxyl groups of the base polymer and can more easily introduce a crosslinking structure.

As the isocyanate crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule can be used. The isocyanate crosslinking agent may also have three or more isocyanate groups in one molecule. Examples of the isocyanate crosslinking agent include low-order aliphatic polyisocyanates such as butyl diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentyl diisocyanate, cyclohexyl diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; trihydroxymethylpropane/toluene diisocyanate trimer adducts (e.g., "Takenate D101E" manufactured by Mitsui Chemicals), trihydroxymethylpropane/hexamethylene diisocyanate trimer adducts (e.g., "Coronate D101E" manufactured by Tosoh); HL”), trihydroxymethylpropane adduct of xylylene diisocyanate (e.g., “Takenate D110N” manufactured by Mitsui Chemicals), isocyanurate of hexamethylene diisocyanate (e.g., “Coronate HX” manufactured by Tosoh), and the like.

As the epoxy crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in one molecule can be used. The epoxy crosslinking agent may also have three or more or four or more epoxy groups in one molecule. The epoxy group of the epoxy crosslinking agent may also be a glycidyl group. Examples of the epoxy crosslinking agent 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, ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trihydroxymethylpropane polyglycidyl ether, adipate diglycidyl ester, phthalate diglycidyl ester, tri(2-hydroxyethyl)isocyanuric acid triglycidyl ester, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, etc. As the epoxy-based crosslinking agent, commercially available products such as "DENACOL" manufactured by Nagase Chemicals, and "TETRAD X" and "TETRAD C" manufactured by Mitsubishi Gas Chemical can also be used.

As described above, when the base polymer does not substantially contain nitrogen atoms, the crosslinking agent may also contain nitrogen atoms. For example, an isocyanate crosslinking agent may also be used to introduce a crosslinking structure into a base polymer that does not substantially contain nitrogen atoms.

The amount of the crosslinking agent used can be appropriately adjusted according to the composition or molecular weight of the base polymer. The amount of the crosslinking agent used is about 0.1 to 5 parts by weight, preferably 0.15 to 3 parts by weight, more preferably 0.2 to 2 parts by weight, further preferably 0.25 to 1.5 parts by weight, and can also be 0.3 to 1 part by weight, 0.35 to 0.8 parts by weight, or 0.4 to 0.75 parts by weight, relative to 100 parts by weight of the acrylic base polymer.

The more the amount of crosslinking agent, the higher the crosslinking density of the base polymer, the adhesive layer before photocuring is given an appropriate hardness and the storage modulus increases, the processability such as cutting is improved, and the residue of the paste on the adherend when the reinforcing film is peeled off from the adherend tends to be suppressed. On the other hand, if the amount of crosslinking agent is too much, there is a situation where the adhesion to the adherend is not sufficiently increased even if the adhesive is photocured. If the amount of crosslinking agent is within the above range, the adhesive layer 2 has excellent processability and peelability from the adherend before photocuring, and can be firmly attached to the adherend after photocuring.

(Photocuring agent) The adhesive composition constituting the adhesive layer 2 contains, in addition to the base polymer, a compound having two or more photopolymerizable functional groups in one molecule as a photocuring agent. The adhesive composition containing the photocuring agent has photocuring properties, and if it is photocured after being attached to an adherend, the adhesion to the adherend is improved.

From the viewpoint of compatibility with the base polymer, the photocuring agent is preferably a liquid at room temperature. The photopolymerizable functional group of the photocuring agent is preferably polymerizable based on a photoradical reaction. As the photocuring agent, a compound having two or more ethylenic unsaturated bonds in one molecule is preferred, and from the viewpoint of showing appropriate compatibility with the acrylic base polymer, a multifunctional (meth)acrylate is preferred.

The multifunctional (meth)acrylate is typically an ester of a polyol and (meth)acrylic acid. Specific examples of the multifunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate and other polyalkylene glycol di(meth)acrylates, alkylene glycol di(meth)acrylates, tricyclodecanedimethanol di(meth)acrylate, isocyanuric acid di(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and the like. (meth)acrylate, trihydroxymethylpropane tri(meth)acrylate, di-trihydroxymethylpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate, isoprene (meth)acrylate, and the like.

The multifunctional (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 also be a polyalkylene oxide such as polyethylene glycol or polypropylene glycol.

Specific examples of the alkylene oxide-modified multifunctional (meth)acrylate include bisphenol A ethylene oxide-modified di(meth)acrylate, bisphenol A propylene oxide-modified di(meth)acrylate, trihydroxymethylpropane ethylene oxide-modified tri(meth)acrylate, trihydroxymethylpropane propylene oxide-modified tri(meth)acrylate, isocyanuric acid ethylene oxide-modified di(meth)acrylate, isocyanuric acid propylene oxide-modified di(meth)acrylate, isocyanuric acid ethylene oxide-modified tri(meth)acrylate, isocyanuric acid propylene oxide-modified tri(meth)acrylate, pentaerythritol ethylene oxide-modified tetra(meth)acrylate, pentaerythritol propylene oxide-modified tetra(meth)acrylate, and the like.

In the polyfunctional (meth)acrylate containing an alkylene oxide chain such as polyalkylene glycol di(meth)acrylate and alkylene oxide-modified polyfunctional (meth)acrylate, the alkylene oxide is preferably (poly)ethylene oxide or (poly)propylene oxide, and is particularly preferably (poly)ethylene oxide. The chain length n of the alkylene oxide (the number of repeating units of the alkylene oxide) is about 1 to 15. When a plurality of alkylene oxide chains are contained in one molecule, the average chain length n is preferably 1 to 15. The (average) chain length n of the alkylene oxide chain may be 12 or less, 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, or 3 or less. By adjusting the type and chain length of the alkylene oxide, the compatibility with the acrylic-based polymer can be adjusted to an appropriate range.

From the perspective of compatibility with acrylic base polymers, the molecular weight of the multifunctional (meth)acrylate used as a photocuring agent is preferably 1500 or less, more preferably 1000 or less, and may be 800 or less, 500 or less, or 400 or less. From the perspective of both compatibility with the base polymer and improved adhesion after photocuring, the functional group equivalent (g/eq) of the multifunctional (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 weight of the multifunctional (meth)acrylate is too small, the crosslinking point density of the adhesive layer after photocuring may increase, and the adhesion may decrease. Therefore, the functional group equivalent weight of the photocuring agent is preferably 80 or more, more preferably 100 or more, and may also be 120 or more or 130 or more.

The photocuring agent has the function of increasing the storage modulus of the adhesive by curing, thereby improving the adhesion to the adherend. The more the amount of photocuring agent, the greater the storage modulus of the adhesive layer after photocuring. From the viewpoint of sufficiently improving the adhesion between the adhesive layer and the adherend after photocuring, the content of the photocuring agent in the photocurable composition constituting the adhesive layer is preferably 2 parts by weight or more, more preferably 3 parts by weight or more, and further preferably 4 parts by weight or more, and may also be 5 parts by weight or more, 6 parts by weight or more, or 7 parts by weight or more.

In the adhesive layer before photocuring, the liquid photocuring agent reduces the cohesive force of the base polymer. Therefore, the more the amount of photocuring agent is, the smaller the storage modulus of the adhesive layer before photocuring is, and the less the adhesion to the adherend is. In most cases, the storage modulus of acrylic polymers whose main component is an alkyl (meth)acrylate with an alkyl carbon number of 6 or more is smaller than that of acrylic polymers whose main component is butyl acrylate. In a photocurable adhesive using an acrylic base polymer whose main component is an alkyl (meth)acrylate with an alkyl carbon number of 6 or more for the purpose of reducing resistance, if the amount of photocuring agent is increased, the storage modulus of the adhesive layer before photocuring is smaller, and the processability such as cutting is poor.

The more photocuring agents such as multifunctional (meth)acrylates are used, the greater the surface free energy of the adhesive layer is, and the lower the resistance tends to be. In particular, photocuring agents with alkylene oxide chains have a greater effect on lowering the resistance of the adhesive. In addition, if the amount of photocuring agent is excessive, the following situation may occur: the photocuring agent is easy to seep out of the adhesive layer before photocuring, and when the reinforcing film is peeled off from the adherend, the seeped components are transferred to the adherend and cause contamination.

From the viewpoints of increasing the resistivity of the adhesive layer, improving the processability of the adhesive layer before photocuring, or preventing contamination of the adherend, the content of the photocurable agent in the photocurable composition constituting the adhesive layer is preferably 35 parts by weight or less, more preferably 30 parts by weight or less, and further preferably 25 parts by weight or less, and may also be 20 parts by weight or less, 15 parts by weight or less, 12 parts by weight or less, 10 parts by weight or less, or 8 parts by weight or less, based on 100 parts by weight of the acrylic base polymer.

As described above, the photocuring agent has the function of reducing the adhesion of the adhesive layer to the adherend before photocuring to make it easier to peel off from the adherend, and improving the adhesion of the adhesive layer to the adherend after photocuring. In order to reduce the adhesion of the adhesive layer before photocuring and improve the adhesion of the adhesive layer after photocuring with a small amount of photocuring agent, it is preferred to use a multifunctional (meth)acrylate having an alkylene oxide chain as the photocuring agent.

Compared with multifunctional (meth)acrylates without epoxy chains, multifunctional (meth)acrylates with epoxy chains have lower compatibility with acrylic-based polymers and tend to be concentrated on the surface of the adhesive layer (near the interface with the adherend). When multifunctional (meth)acrylates with epoxy chains are included as photocuring agents, even if the amount is small, it is easy to form a weak boundary layer (WBL) by the photocuring agent being concentrated on the interface with the adherend.

If WBL is formed, the liquid properties of the surface (bonding interface) are enhanced while maintaining the overall properties of the adhesive layer, such as the storage modulus, so the bonding force with the adherend tends to decrease. Therefore, the storage modulus of the adhesive layer before photocuring is high, the processability such as cutting is excellent, and it is easy to peel off from the adherend. If the adhesive layer with WBL is formed by causing the photocuring agent to concentrate near the bonding interface with the adherend and photocuring is performed, the curing reaction of the photocuring agent is easy to proceed near the bonding interface where the density of the photocuring agent is high, so the bonding force is easy to improve. On the other hand, the storage modulus as an overall property tends to be suppressed from increasing.

Regarding multifunctional (meth)acrylates having alkylene oxide chains, the greater the average chain length n of the alkylene oxide chains, the lower the compatibility with the acrylic base polymer, and the tendency for the adhesion of the adhesive layer before photocuring to decrease. On the other hand, when the compatibility between the acrylic base polymer and the photocuring agent is too low, the liquid properties of the WBL formed on the surface of the adhesive layer are higher, the shearing of the photocuring agent is more difficult to maintain, and the seeping photocuring agent may cause contamination of the adherend. From the viewpoint of having appropriate compatibility with acrylic-based polymers, the average chain length n of the alkylene oxide chain in the multifunctional (meth)acrylate having an alkylene oxide chain is preferably 10 or less, more preferably 8 or less, further preferably 6 or less, and may also be 5 or less, 4 or less, or 3 or less.

As described above, in terms of being easy to form WBL by adding a small amount, a polyfunctional (meth)acrylate having an alkylene oxide chain and having two or more (meth)acrylic groups in one molecule is preferred as the photocuring agent. The polyfunctional (meth)acrylate having an alkylene oxide chain may also have three or more (meth)acrylic groups in one molecule.

When the photocuring agent has three or more (meth)acryl groups in one molecule, the adhesion of the adhesive layer is easily improved by photocuring. In addition, when a multifunctional acrylate having three or more (meth)acryl groups in one molecule is used, the storage modulus tends to increase by photocuring compared to the case of using a multifunctional acrylate having two (meth)acryl groups in one molecule.

As described above, by using an acrylic polymer having an alkyl (meth)acrylate having an alkyl carbon number of 6 or more as a main component of a monomer as a base polymer and using a multifunctional (meth)acrylate having an alkylene oxide chain as a photocuring agent, the amount of the photocuring agent used can be reduced, and a high-resistance adhesive layer can be formed. By using a multifunctional (meth)acrylate having an alkylene oxide chain as a photocuring agent, even if the amount of the photocuring agent added is small (for example, about 10 parts by weight or less relative to 100 parts by weight of the acrylic base polymer), it is easy to form a WBL at the interface with the adherend. If WBL is formed by a small amount of photocuring agent, the adhesive layer before photocuring has a high storage modulus, excellent processability such as cutting, and a small adhesion force, so it is easy to peel off from the adherend. On the other hand, the adhesive layer after photocuring can be firmly attached to the adherend, and the increase in storage modulus as an overall characteristic is suppressed, and the impact resistance is excellent.

Two or more photocuring agents may be used in combination. For example, as photocuring agents, two or more multifunctional (meth)acrylates having an alkylene oxide chain may be used, or a multifunctional (meth)acrylate having an alkylene oxide chain and a multifunctional (meth)acrylate without an alkylene oxide chain may be used. Furthermore, as photocuring agents, multifunctional (meth)acrylates having different functional groups (the number of (meth)acryloyl groups in one molecule) may be used. For example, in order to adjust the adhesion or storage modulus of the adhesive layer after photocuring, a bifunctional (meth)acrylate and a trifunctional or higher multifunctional (meth)acrylate may be used in combination as photocuring agents.

As the photocuring agent, multifunctional (meth)acrylates having an alkylene oxide chain and urethane (meth)acrylates can also be used. Urethane (meth)acrylates are compounds having one or more urethane bonds and two or more (meth)acrylic groups in one molecule, preferably two or more urethane bonds in one molecule. Urethane (meth)acrylates having two or more urethane bonds are obtained, for example, by the reaction of polyisocyanate and a (meth)acrylic compound having a hydroxyl group, where the isocyanate group of the polyisocyanate bonds with the hydroxyl group of the (meth)acrylic compound to form a urethane bond.

The polyisocyanate may be any one of an aromatic polyisocyanate, an alicyclic polyisocyanate, and an alicyclic polyisocyanate. Among them, aromatic polyisocyanates and aliphatic polyisocyanates are preferred. As the aromatic polyisocyanate, toluene diisocyanate (TDI) is particularly preferred. Toluene diisocyanate may be any one of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate, or a mixture thereof. As the aliphatic polyisocyanate, hexamethylene diisocyanate (HDI) is particularly preferred.

Examples of the (meth)acrylic compound having a hydroxyl group include compounds having one hydroxyl group and one (meth)acryl group, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxymethacrylamide, hydroxyethylacrylamide, and the like; and compounds having one hydroxyl group and two or more (meth)acryl groups, such as pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, trihydroxymethylpropane di(meth)acrylate, and isocyanuric acid di(meth)acrylate.

Among these, the (meth)acrylic compound having a hydroxyl group is preferably a compound having one hydroxyl group and two or more (meth)acryloyl groups, and specific examples thereof include compounds having a pentaerythritol skeleton such as pentaerythritol tri(meth)acrylate and dipentaerythritol penta(meth)acrylate.

The urethane (meth)acrylate obtained by the reaction of a diisocyanate with a (meth)acrylic acid compound having one hydroxyl group and two or more (meth)acrylic groups in one molecule has two urethane bonds and four or more (meth)acrylic groups in one molecule. The number of (meth)acrylic groups in the urethane (meth)acrylate may be 6 or more or 8 or less, or 12 or less or 10 or less.

As the urethane (meth)acrylate, commercially available products such as Kyoeisha Chemical, Shin-Nakamura Chemical, Negami Industry, Nippon Gosei Chemical, DAICEL-ALLNEX, and Showa Denko Materials can also be used.

From the perspective of compatibility with acrylic base polymers and the adjustment of the adhesion of the adhesive layer, the molecular weight of the urethane (meth) acrylate is preferably 500-1500, and may also be 600-1000, or 700-900. From the same perspective, the functional group equivalent (g/eq) of the (meth)acryl group of the urethane (meth) acrylate is preferably 80-200, and may also be 100-150, 110-140, or 120-130.

By including urethane (meth)acrylate in addition to the multifunctional (meth)acrylate without urethane bond as a photocuring agent, the adhesive layer before photocuring has a smaller adhesion, and the adhesive layer after photocuring tends to have an increased adhesion. As one reason, the urethane (meth)acrylate is considered to promote the formation of WBL by the multifunctional (meth)acrylate without urethane bond, especially the multifunctional (meth)acrylate having an alkylene oxide chain.

Urethane (meth)acrylate has the function of increasing the cohesive force of acrylic base polymer, and then the acrylic base polymer forms hydrogen bonds with urethane (meth)acrylate. Therefore, urethane (meth)acrylate is easily incorporated into the entire part of the adhesive layer. It is believed that if urethane (meth)acrylate is incorporated into the entire part of the adhesive layer, multifunctional (meth)acrylates without urethane bonds are easily segregated near the surface (bonding interface) of the adhesive layer, thereby promoting the formation of WBL.

When the photocurable composition constituting the adhesive layer contains urethane (meth)acrylate as a photocuring agent in addition to the multifunctional (meth)acrylate without urethane bond, the content of urethane (meth)acrylate is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, and may be 0.08 parts by weight or more or 0.1 parts by weight or more, based on 100 parts by weight of the acrylic base polymer.

When the content of urethane (meth) acrylate is too high, the photocuring agent (multifunctional (meth) acrylate and/or urethane (meth) acrylate without urethane bond) easily seeps out to the surface of the adhesive layer (the interface with the adherend), and the seeped out components may cause contamination of the adherend. Therefore, the content of urethane (meth) acrylate is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and further preferably 1 part by weight or less, and may also be 0.5 parts by weight or less, 0.4 parts by weight or less, 0.3 parts by weight or less, 0.25 parts by weight or less, or 0.2 parts by weight or less, relative to 100 parts by weight of the base polymer.

When the photocurable composition contains urethane (meth)acrylate as a photocuring agent in addition to the multifunctional (meth)acrylate without urethane bond, it is preferred that the content of the multifunctional (meth)acrylate without urethane bond is relatively large from the viewpoint of adjusting the adhesion to the adherend before and after photocuring to an appropriate range and suppressing the contamination of the adherend due to the seepage of the photocuring agent. The content of urethane (meth)acrylate is preferably 0.2 times or less, more preferably 0.1 times or less, and may also be 0.05 times or less, 0.03 times or less, or 0.02 times or less relative to the content of the multifunctional (meth)acrylate without urethane bond in terms of weight ratio. The content of the urethane (meth)acrylate may be 0.001 times or more, 0.005 times or more, 0.008 times or more, or 0.01 times or more relative to the content of the multifunctional (meth)acrylate having no urethane bond in terms of weight ratio.

(Photopolymerization initiator) The photopolymerization initiator generates active species by irradiation with active light, thereby promoting the curing reaction of the photocuring agent. As the photopolymerization initiator, depending on the type of the photocuring agent, photocation initiator (photoacid generator), photoradical polymerization initiator, photoanion initiator (photoalkalizer), etc. can be used. When using ethylenically unsaturated compounds such as multifunctional acrylates as photocuring agents, it is preferred to use photoradical polymerization initiators as polymerization initiators.

The photo-radical polymerization initiator generates free radicals by irradiation with active light, and the free radicals move from the photo-radical polymerization initiator to the photocuring agent, thereby promoting the free radical polymerization reaction of the photocuring agent. As the photo-radical polymerization initiator (photo-radical generator), it is preferred to generate free radicals by irradiation with visible light or ultraviolet light with a wavelength shorter than 450 nm, and examples thereof include: hydroxy ketones, benzyl dimethyl ketal, amino ketones, acyl phosphine oxides, benzophenones, trichloromethyl-containing tris derivatives, etc. The photo-radical polymerization initiator may be used alone or in combination of two or more.

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

(Other additives) In addition to the components listed above, the adhesive layer may also contain additives such as silane coupling agents, adhesion imparting agents, crosslinking promoters, crosslinking delayers, plasticizers, softeners, antioxidants, anti-degradation agents, fillers, colorants, ultraviolet absorbers, surfactants, antistatic agents, etc. within the range that does not impair the characteristics of the present invention.

As crosslinking promoters, there can be cited: organic metal complexes (chelates), compounds of metal and alkoxy, and compounds of metal and acyloxy, and other organic metal compounds; and tertiary amines, etc. From the perspective of suppressing the crosslinking reaction in the solution state at room temperature to ensure the shelf life of the adhesive composition, organic metal compounds are preferred. In addition, from the perspective of easily introducing a uniform crosslinking structure throughout the thickness direction of the adhesive layer, organic metal compounds that are liquid at room temperature are preferred as crosslinking promoters. Metals of organic metal compounds can be cited as iron, tin, aluminum, zirconium, zinc, titanium, lead, cobalt, zinc, etc.

Examples of the crosslinking retarder include β-ketoesters such as methyl acetylacetate, ethyl acetylacetate, octyl acetylacetate, oleyl acetylacetate, lauryl acetylacetate, and stearyl acetylacetate; β-diketones such as acetylacetone, 2,4-hexanedione, and benzoylacetone; and alcohols such as tert-butyl alcohol.

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

The adhesive composition is applied to the substrate by roller coating, contact roller coating, gravure coating, reverse coating, roller brush coating, spray coating, dip roller coating, rod coating, scraper coating, air knife coating, curtain coating, die lip coating, die nozzle coating, etc., and the solvent is dried and removed as needed to form an adhesive layer. As a drying method, an appropriate method can be appropriately adopted. The heating drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and further preferably 70°C to 170°C. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and further preferably 10 seconds to 10 minutes.

When the adhesive composition contains a crosslinking agent, it is preferred to perform crosslinking by heating or aging simultaneously with or after drying the solvent. The heating temperature or heating time can be appropriately set according to the type of crosslinking agent used. Crosslinking is usually performed by heating for about 1 minute to 7 days within the range of 20°C to 160°C. The heating used to dry and remove the solvent can also serve as the heating for crosslinking.

After the crosslinking structure is introduced into the polymer by the crosslinking agent, the photocuring agent also remains in an unreacted state. Therefore, a photocurable adhesive layer 2 containing a high molecular weight component and a photocuring agent is formed. When the adhesive layer 2 is formed on the film substrate 1, a peeling pad 5 is preferably attached to the adhesive layer 2 for the purpose of protecting the adhesive layer 2. Alternatively, the peeling pad 5 may be attached to the adhesive layer 2 before crosslinking.

When the adhesive layer 2 is formed on another substrate, the solvent is dried and then the adhesive layer 2 is transferred to the film substrate 1 to obtain a reinforcement film. The substrate used to form the adhesive layer can also be directly used as the peeling pad 5.

As the release pad 5, a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, polyester film, etc. is preferably used. The thickness of the release pad is usually 3 to 200 μm, preferably about 10 to 100 μm. For the contact surface of the release pad 5 with the adhesive layer 2, it is preferred to use a release agent such as a silicone-based, fluorine-based, long-chain alkyl-based, or fatty amide-based release agent, or silicon dioxide powder, etc. to perform a release treatment. By subjecting the surface of the peeling pad 5 to a release treatment, peeling occurs at the interface between the adhesive layer 2 and the peeling pad 5, and the adhesive layer 2 is fixed to the film substrate 1. The peeling pad 5 may be subjected to an antistatic treatment on either or both of the release-treated surface and the non-treated surface. By subjecting the peeling pad 5 to an antistatic treatment, it is possible to suppress the charge generated when the peeling pad is peeled from the adhesive layer.

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

The adherend to which the reinforcing film is to be attached is not particularly limited, and examples thereof include various electronic devices, optical devices and components thereof.

The reinforcing film can be applied to the entire surface of the adherend, or can be applied selectively to the portion that needs to be reinforced (reinforcement target area). In addition, the reinforcing film can be applied to the entire portion that needs to be reinforced (reinforcement target area) and the area that does not need to be reinforced (non-reinforcement target area), and then the reinforcing film applied to the non-reinforcement target area can be cut off and removed. If the adhesive is in the state of being temporarily adhered to the surface of the adherend before light curing, the reinforcing film can be easily peeled off from the surface of the adherend. Alternatively, a reinforcing film may be attached to a region to be reinforced and a region not to be reinforced, and after selectively irradiating the region to be reinforced with light to cure the adhesive by light, the reinforcing film in the region not to be reinforced where the adhesive has not been cured may be selectively peeled off and removed.

By attaching a reinforcing film, appropriate rigidity can be given, so it is expected that the workability can be improved or the damage prevention effect can be achieved. When attaching a reinforcing film to a semi-finished product in the manufacturing step of the device, the reinforcing film can also be attached to a large-sized semi-finished product before it is cut into product size. The reinforcing film can also be attached to the mother roll of the device manufactured by the roll-to-roll process in a roll-to-roll manner.

Before attaching the reinforcing film, the surface of the adherend may be activated for the purpose of cleaning. Examples of surface activation treatments include plasma treatment, corona treatment, and photoluminescence discharge treatment. The adherend whose surface has been activated contains a large number of active groups such as hydroxyl, carbonyl, and carboxyl groups, and the adhesion is easily increased through the intermolecular interaction with the polar functional groups of the base polymer of the adhesive. In particular, when the adherend is polyimide, the activation treatment activates the amide, the terminal amino group, or the carboxyl group (or carboxylic anhydride group), and the interaction with the polar functional groups of the base polymer is strengthened. Therefore, the initial adhesion is sometimes greatly increased by the activation treatment.

If the initial adhesion is too large, the reinforcement film attached to the non-reinforced area is sometimes difficult to peel off. As mentioned above, since the base polymer does not substantially contain nitrogen atoms, it is possible to suppress excessive increase in the initial adhesion to the adherend with the activated surface. The adhesion between the adherend with the activated surface and the adhesive layer before light curing is preferably 2.5 times or less of the adhesion between the adherend without the activated surface and the adhesive layer before light curing, more preferably 2 times or less, further preferably 1.5 times or less, and can also be 1.4 times or less or 1.3 times or less.

From the perspective of easy peeling from the adherend and preventing the paste residue from being left on the adherend after the reinforcing film is peeled off, the adhesion (initial adhesion) between the adhesive layer 2 and the adherend before light curing is preferably 0.5 N/25 mm or less, more preferably 0.3 N/25 mm or less, further preferably 0.25 N/25 mm or less, and may also be 0.2 N/25 mm or less or 0.15 N/25 mm or less. From the perspective of preventing the reinforcing film from being peeled off during storage or operation, the adhesion between the adhesive layer 2 and the adherend before light curing is preferably 0.005 N/25 mm or more, more preferably 0.01 N/25 mm or more.

Adhesion strength is determined by peeling test with polyimide film as adherend at a tensile speed of 300 mm/min and a peeling angle of 180°. Adhesion strength is measured at 25°C unless otherwise specified. Adhesion strength between adhesive layer and adherend before light curing is measured by using samples that were left at 25°C for 30 minutes after bonding.

As described above, from the viewpoint of improving processability or suppressing the paste residue when peeling from the adherend, the storage modulus of the adhesive layer 2 before photocuring at 25°C is preferably 10 kPa or more, more preferably 15 kPa or more, further preferably 20 kPa or more, and may be 25 kPa or more or 30 kPa or more. The storage modulus of the adhesive layer before photocuring depends on the composition of the base polymer, the amount of crosslinking agent introduced, and the content of the photocuring agent. There is a tendency that the storage modulus increases as the amount of crosslinking agent introduced increases. There is a tendency that the storage modulus decreases as the amount of photocuring agent increases.

After the reinforcing film is attached to the adherend, the adhesive layer 2 is irradiated with active light to photoharden the adhesive layer. Examples of active light include ultraviolet light, visible light, infrared light, X-rays, α-rays, β-rays, and γ-rays. Ultraviolet light is preferred as active light because it can inhibit the curing of the adhesive layer in storage and is easy to cure. The irradiation intensity or irradiation time of the active light can be appropriately set according to the composition or thickness of the adhesive layer. The active light irradiation of the adhesive layer 2 can be implemented from either the film substrate 1 side or the adherend side, or from both sides.

As the light cures, the adhesion of the adhesive layer to the adherend increases. From the perspective of adhesion reliability during actual use of the device, the adhesion between the adhesive layer 2 after light cure and the adherend is preferably 3 N/25 mm or more, more preferably 4 N/25 mm or more, and further preferably 5 N/25 mm or more, and may also be 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 reinforcing film preferably has an adhesion within the above range to the polyimide film after light cure.

The adhesion between the adhesive layer 2 and the adherend after light curing is preferably 5 times or more, more preferably 10 times or more, further preferably 30 times or more, and may be 50 times or more, 75 times or more, or 100 times or more. As described above, by adjusting the type (compatibility with the base polymer) and the amount of the photocuring agent, the adhesion before light curing (initial adhesion) can be suppressed to a lower level, and the adhesion of the adhesive after light curing can be increased.

As described above, from the perspective of giving the adhesive layer 2 an impact-mitigating effect, the storage modulus of the adhesive layer 2 after light curing at 25° C. is preferably 140 kPa or less, more preferably 120 kPa or less, further preferably 100 kPa or less, and may also be 90 kPa or less, 80 kPa or less, or 70 kPa or less.

The storage modulus of the adhesive layer after light curing at 25° C. is preferably 5 times or less, more preferably 3 times or less, and may be 2.5 times or less or 2 times or less of the storage modulus of the adhesive layer before light curing at 25° C.

From the viewpoint of suppressing the warping or damage of the adherend due to the curing and shrinkage of the adhesive when the adhesive layer is photocured while the adhesive layer is bonded to the adherend, the increase in the storage modulus of the adhesive layer 2 at 25°C due to photocuring is preferably 80 kPa or less, more preferably 50 kPa or less, further preferably 40 kPa or less, and may also be 30 kPa or less or 25 kPa or less.

The less the amount of crosslinking agent and the less the amount of photocuring agent, the less the storage modulus of the adhesive layer after photocuring tends to decrease, and the less the amount of photocuring agent, the less the increase in the storage modulus of the adhesive layer due to photocuring tends to decrease. In addition, by using a multifunctional (meth)acrylate having an alkylene oxide chain as a photocuring agent, the storage modulus of the adhesive layer can be suppressed from increasing due to photocuring, and the adhesion to the adherend can be improved.

As described above, by laminating the reinforcing film, the adherend can be given appropriate rigidity, and the stress can be relieved and dispersed, thereby suppressing various adverse conditions that may occur in the manufacturing steps, improving production efficiency, and improving yield. Since the reinforcing film is easy to peel off from the adherend before the adhesive layer is photocured, it is also easy to perform secondary processing when lamination or poor lamination occurs. In addition, it is also easier to selectively remove the reinforcing film from the area outside the reinforcement target area.

After the adhesive layer is photocured, it exhibits a higher adhesion to the adherend, and the reinforcement film is difficult to peel off from the device surface, with excellent adhesion reliability and high impact resistance. Therefore, during the use of the completed device, even if the device is accidentally subjected to external force due to the device falling, heavy objects being placed on the device, or flying objects colliding with the device, the reinforcement film can be attached to prevent the device from being damaged. [Example]

The following is further described with reference to embodiments, but the present invention is not limited to these embodiments.

[Preparation of base polymer] ＜Polymer A＞ In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen inlet tube, 95 parts by weight of butyl acrylate (BA) and 5 parts by weight of acrylic acid (AA) as monomers, 0.2 parts by weight of azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and 233 parts by weight of ethyl acetate as a solvent were added, and nitrogen was circulated, while stirring and nitrogen replacement was performed for about 1 hour. After that, it was heated to 60°C and reacted for 7 hours to obtain a solution of acrylic polymer A with a weight average molecular weight of 600,000.

<Polymer B~F> The amount of monomer added was changed as shown in Table 1. Other than that, the solutions of polymers B~F were obtained in the same manner as the polymerization of polymer A.

Table 1 lists the ratio of added monomers of acrylic polymers A to F, as well as the weight average molecular weight (Mw) and glass transition temperature (Tg) of the polymers. The glass transition temperature is calculated based on the Fox formula according to the ratio of added monomers. The weight average molecular weight (polystyrene conversion) is measured using GPC ("HLC-8220GPC" manufactured by Tosoh) under the following conditions. Sample concentration: 0.2 wt% (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: THF Flow rate: 0.6 mL/min Measurement temperature: 40°C Sample column: TSKguardcolumn SuperHZ-H (1 column) + TSKgel SuperHZM-H (2 columns) Reference column: TSKgel SuperH-RC (1 column)

In Table 1, monomers are recorded with the following abbreviations. BA:     Butyl acrylate 2EHA:      2-ethylhexyl acrylate MMA:       Methyl methacrylate LA:     Dodecyl acrylate 2HEA:      2-hydroxyethyl acrylate 4HBA:      4-hydroxybutyl acrylate AA:     Acrylic acid NVP:        N-vinylpyrrolidone

[Table 1] Monomer ratio (parts by weight) M Tg (℃) BA 2EHA MMA LA 2HEA 4HBA AA NVP Polymer A 95 - - - - - 5 - 600,000 -53 Polymer B - 96 - - 4 - - - 550,000 -68 Polymer C - 96 - - - - 4 - 550,000 -68 Polymer D - 90 - - - - 10 - 550,000 -65 Polymer E - 63 9 - - 13 - 15 800,000 -42 Polymer F 20 70 - 8 - 1 - 1 1,800,000 -63

[Preparation of reinforcing film] <Preparation of adhesive composition> A crosslinking agent, a multifunctional acrylate (without urethane bond) and a urethane acrylate as a photocuring agent, and a photopolymerization initiator were added to an acrylic polymer solution and mixed uniformly to prepare the adhesive compositions shown in Tables 2 to 4. As the base polymer, polymer B was used in samples 1 to 22, polymer C was used in samples 31 to 43, polymer D was used in samples 51 to 63, polymer F was used in samples 71 to 83, polymer A was used in samples 91 and 92, and polymer E was used in sample 96.

As a photopolymerization initiator, 0.3 parts by weight of "Omnirad 651" manufactured by IGM Resins was added relative to 100 parts by weight of the solid content of the acrylic polymer. The crosslinking agent and multifunctional acrylate were added in a manner to form the composition shown in Tables 2 to 4. The addition amounts in Tables 2 to 4 are relative to 100 parts by weight of the base polymer (parts by weight of the solid content). The details of the crosslinking agent and photocuring agent are described below.

(Crosslinking agent) T-C: N,N,N',N'-tetraglycidyl-m-phenylenediamine ("TETRAD C" manufactured by Mitsubishi Gas Chemical) C-HX: Isocyanurate of hexamethylene diisocyanate ("Coronate HX" manufactured by Tosoh) D110N: Trihydroxymethylpropane adduct of benzyl diisocyanate ("Takenate D110N" manufactured by Mitsui Chemicals)

(Multifunctional acrylate) A200: "NK Ester A200" manufactured by Shin-Nakamura Chemical Industry (polyethylene glycol #200 (n=4) diacrylate; molecular weight 308, functional group equivalent 154 g/eq) A600: "NK Ester A600" manufactured by Shin-Nakamura Chemical Industry (polyethylene glycol #600 (n=14) diacrylate; molecular weight 708, functional group equivalent 354 g/eq) M350: Trihydroxymethylpropane EO modified (n=1) triacrylate ("ARONIX M-350" manufactured by Toa Gosei, functional group equivalent 143 g/eq) APG700: APG700: Polypropylene glycol #700 (n=12) diacrylate; ("NK Ester APG700" manufactured by Shin-Nakamura Chemical Industry, functional group equivalent 404 g/eq) ADPHE: Ethoxylated dipentaerythritol polyacrylate ("NK Ester A-DPH-12E" manufactured by Shin-Nakamura Chemical Industry Co., Ltd., functional group equivalent of about 200 g/eq) TMPT: Trihydroxymethylpropane triacrylate ("NK Ester A-TMPT" manufactured by Shin-Nakamura Chemical Industry Co., Ltd., functional group equivalent of 99 g/eq) (Urethane acrylate) UA306: Pentaerythritol triacrylate-toluene diisocyanate adduct ("UA-306T" manufactured by Kyoeisha Chemical, functional group equivalent: 128 g/eq)

<Adhesive solution application and crosslinking> The adhesive composition was applied to a 75 μm thick polyethylene terephthalate film substrate ("DIAFOIL T100-75S" manufactured by Mitsubishi Chemical) without surface treatment using a slot roll so that the thickness after drying was 13 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated surface of a release pad (polyethylene terephthalate film with a thickness of 25 μm treated with silicone release) was attached to the adhesive-coated surface. Afterwards, the film was aged for 4 days at 25°C for crosslinking, and a reinforcement film was obtained in which an adhesive sheet was fixedly laminated on the film substrate and a peel-off pad was temporarily adhered thereon.

[Evaluation] ＜Adhesion to polyimide film＞ (Adhesion of adhesive layer before light curing) A polyimide film with a thickness of 25 μm ("Upilex 25S" manufactured by Ube Industries) was attached to a glass plate via a double-sided adhesive tape ("No.531" manufactured by Nitto Denko) to obtain a polyimide film substrate for measurement. The peel-off pad was peeled off from the surface of the reinforcement film cut into a width of 25 mm × a length of 100 mm, and then attached to the polyimide film substrate for measurement using a hand roller.

After the sample was left to stand at 25°C for 30 minutes, a 180° peeling test was performed at a tensile speed of 300 mm/min while holding the end of the film substrate of the reinforcing film with a clamp to measure the peeling strength (adhesion strength of the reinforcing film to the polyimide film that has not been treated with plasma).

While the polyimide film substrate for measurement was transported at a transport speed of 3 m/min, the surface of the polyimide film was plasma treated using a normal pressure plasma treatment machine at an electrode voltage of 160 V. A reinforcing film was attached to the plasma treated polyimide film using a hand roller, and the adhesion to the plasma treated polyimide film was measured by a 180° peel test in the same manner as above.

Based on the obtained results, the ratio of the bonding force in the case of plasma treatment to the bonding force in the case of no plasma treatment (the increase rate of bonding force caused by plasma treatment) was calculated.

(Adhesion of adhesive layer after photocuring) After the reinforcing film is attached to the polyimide film substrate for measurement (not treated with plasma), the adhesive layer is photocured by irradiating ultraviolet light with a cumulative light amount of 4000 mJ/ ^cm2 from the reinforcing film side (film substrate side) using a 365 nm LED light source. Using this test sample, the adhesion is measured by the 180° peel test in the same way as above.

Based on the obtained results, the ratio of the adhesion force after light curing to that before light curing (the increase rate of the adhesion force generated by light curing) was calculated.

<Storage modulus> On a peeling pad, the adhesive composition was applied and cross-linked in the same manner as above to prepare an adhesive sheet (before photocuring). A peeling pad was attached to the surface of the adhesive layer of the adhesive sheet before photocuring to isolate oxygen, and photocuring was performed by irradiating 4000 mJ/ ^cm2 of ultraviolet light using a 365 nm LED lamp. The adhesive sheet before photocuring and the adhesive sheet after photocuring were laminated to prepare a test sample with a thickness of about 1.5 mm, and a dynamic viscoelasticity measurement was performed using a rotational rheometer ("ADiscovery-HR2" manufactured by TA Instruments) under the following conditions to read the shear storage modulus G' at 25°C. (Measurement conditions) Deformation mode: Torsion Measurement frequency: 1 Hz Heating rate: 5°C/min Measurement temperature: -70～150°C Shape: Parallel plate 8.0 mm

<Surface resistance> Using a 365 nm LED light source, the adhesive layer was photocured by irradiating the substrate side of the reinforcing film with a cumulative light quantity of 4000 mJ/ ^cm2 of ultraviolet light. The peeling pad was peeled off from the surface of the photocured adhesive layer, and the surface resistance was measured by contacting the probe of a resistivity meter ("Hiresta-UX MCP-HT800" manufactured by Nittoseiko Analytech) with the surface of the adhesive layer at a temperature of 25°C and a relative humidity of 50% under the conditions of applying a voltage of 1000V for 10 seconds.

<Surface free energy> A 1.0 μL drop of probe liquid was dripped onto the surface of the photocured adhesive layer, and the contact angle was measured 500 milliseconds after the drop was added using an automatic contact angle meter ("CA-V" model manufactured by Kyowa Interface Science). Water and diiodomethane were used as probe liquids, and the surface free energy γ of the adhesive layer was calculated using the Owens-Wendt formula based on the surface free energy of each and the measured contact angle.

<Adhesive contamination> Remove the peel-off pad from the surface of the reinforcing film, and use a hand roller to adhere the polyimide film ("Upilex 25S" manufactured by Ube Industries) to the surface of the adhesive layer. After standing at 25°C for 30 minutes or more, peel the reinforcing film from the polyimide film and visually observe the surface of the polyimide film under a fluorescent light to check for contamination. Evaluate the contamination of the adherend according to the following criteria. A: No contamination was found in the sample peeled off after 24 hours of standing B: Contamination was found in the sample peeled off after 24 hours of standing, but no contamination was found in the sample peeled off after 30 minutes of standing C: Contamination was found in the sample peeled off after 30 minutes of standing

The composition of the adhesive of each reinforcement film (type of base polymer, type and amount of crosslinking agent, type and amount of photocuring agent) and the evaluation results are shown in Tables 2 to 4.

[Table 2] Sample No. Composition Adhesion force (N/25 mm) G'(kPa) Surface resistance (×10 ¹² Ω) γ (mJ/m ² ) Pollution polymer Crosslinking agent Light Hardener Before hardening After hardening Adhesion force increase rate (times) Before hardening After hardening Type Type quantity Multifunctional acrylate Urethane Acrylate Not plasma treated Plasma treated Adhesion force increase rate (times) Type quantity Type quantity 1 B C-HX 0.50 M350 8 UA306 0.05 0.15 0.16 1.06 11.5 75.3 26 41 ＞1000 14.8 A 2 B C-HX 0.50 M350 8 UA306 0.30 0.12 0.13 1.08 12.4 101 25 45 ＞1000 14.9 B 3 B C-HX 0.50 M350 8 UA306 1.00 0.11 0.12 1.06 11.7 106 twenty three 48 ＞1000 15.2 B 4 B C-HX 0.50 M350 8 UA306 3.00 0.11 0.12 1.16 12.6 118 twenty three 49 ＞1000 15.2 C 5 B C-HX 0.50 M350 8 UA306 0.15 0.12 0.15 1.22 12.2 100 25 45 ＞1000 14.9 A 6 B C-HX 0.50 A200 8 UA306 0.15 0.15 0.16 1.12 3.05 21.0 twenty two 39 ＞1000 15.1 A 7 B C-HX 0.50 A600 8 UA306 0.15 0.12 0.15 1.21 3.15 25.3 twenty four 36 ＞1000 15.5 C 8 B C-HX 0.50 APG700 8 UA306 0.15 0.14 0.19 1.33 4.23 30.2 twenty four 37 ＞1000 15.4 C 9 B C-HX 0.50 ADPHE 8 UA306 0.15 0.15 0.19 1.28 6.00 41.4 27 49 ＞1000 15.2 C 10 B C-HX 0.50 TMPT 8 UA306 0.15 0.83 0.89 1.07 1.08 1.3 twenty four 79 ＞1000 14.9 A 11 B C-HX 0.25 M350 8 UA306 0.15 0.20 0.31 1.55 15.3 76.8 17 37 ＞1000 15.3 A 12 B C-HX 0.75 M350 8 UA306 0.15 0.08 0.10 1.32 8.34 108 32 58 ＞1000 14.6 A 13 B C-HX 1.00 M350 8 UA306 0.15 0.05 0.08 1.45 5.13 98.7 40 63 ＞1000 14.1 A 14 B C-HX 1.25 M350 8 UA306 0.15 0.02 0.03 1.38 2.14 90.8 46 71 ＞1000 13.9 A 15 B C-HX 1.50 M350 8 UA306 0.15 0.02 0.02 1.10 0.44 21.4 53 78 ＞1000 13.9 A 16 B C-HX 0.50 M350 2 UA306 0.15 0.52 0.65 1.26 2.33 4.5 37 43 ＞1000 14.3 A 17 B C-HX 0.50 M350 5 UA306 0.15 0.19 0.24 1.30 7.09 38.3 33 44 ＞1000 14.7 A 18 B C-HX 0.50 M350 11 UA306 0.15 0.015 0.021 1.40 3.36 229 19 61 ＞1000 15.3 A 19 B C-HX 0.50 M350 14 UA306 0.15 0.007 0.008 1.20 1.05 153 16 78 ＞1000 15.6 B 20 B C-HX 0.50 M350 20 UA306 0.15 0.006 0.006 0.98 0.74 127 12 89 ＞1000 16.1 C twenty one B C-HX 0.50 M350 30 UA306 0.15 0.006 0.007 1.12 0.53 90.0 8 104 ＞1000 16.4 C twenty two B C-HX 0.50 M350 40 UA306 0.15 0.008 0.008 1.00 0.84 108 5 125 848 16.9 C

[Table 3] Sample No. Composition Adhesion force (N/25 mm) G'(kPa) Surface resistance (×10 ¹² Ω) γ (mJ/m ² ) Pollution polymer Crosslinking agent Light Hardener Before hardening After hardening Adhesion force increase rate (times) Before hardening After hardening Type Type quantity Multifunctional acrylate Urethane Acrylate Not plasma treated Plasma treated Adhesion force increase rate (times) Type quantity Type quantity 31 C TC 0.25 M350 8 UA306 0.15 0.26 0.43 1.65 14.8 57.6 29 55 ＞1000 15.1 A 32 C TC 0.50 M350 8 UA306 0.15 0.14 0.17 1.23 12.7 90.5 36 65 ＞1000 14.7 A 33 C TC 0.75 M350 8 UA306 0.15 0.10 0.12 1.23 8.28 87.1 41 72 ＞1000 14.4 A 34 C TC 1.00 M350 8 UA306 0.15 0.067 0.086 1.29 5.03 75.4 48 84 ＞1000 14.2 A 35 C TC 1.25 M350 8 UA306 0.15 0.046 0.064 1.38 2.77 60.2 53 87 ＞1000 14.1 A 36 C TC 1.50 M350 8 UA306 0.15 0.025 0.025 0.98 1.46 57.3 64 94 ＞1000 13.5 A 37 C TC 0.50 M350 2 UA306 0.15 0.76 0.92 1.21 2.47 3.3 47 55 ＞1000 14.1 A 38 C TC 0.50 M350 5 UA306 0.15 0.29 0.35 1.20 8.17 28.1 41 61 ＞1000 14.3 A 39 C TC 0.50 M350 11 UA306 0.15 0.081 0.11 1.35 10.0 123 29 77 ＞1000 15.1 A 40 C TC 0.50 M350 14 UA306 0.15 0.031 0.036 1.16 14.1 450 twenty three 96 ＞1000 15.5 B 41 C TC 0.50 M350 20 UA306 0.15 0.016 0.017 1.11 10.8 689 17 106 ＞1000 16.2 C 42 C TC 0.50 M350 30 UA306 0.15 0.012 0.012 1.03 2.33 198 13 118 ＞1000 16.5 C 43 C TC 0.50 M350 40 UA306 0.15 0.011 0.011 1.05 1.33 124 11 183 793 16.5 C 51 D TC 0.25 M350 8 UA306 0.15 0.57 0.92 1.61 22.5 39.3 37 76 ＞1000 14.8 A 52 D TC 0.50 M350 8 UA306 0.15 0.47 0.58 1.22 20.9 44.2 45 81 ＞1000 14.4 A 53 D TC 0.75 M350 8 UA306 0.15 0.40 0.45 1.11 16.6 41.2 52 88 ＞1000 14.2 A 54 D TC 1.00 M350 8 UA306 0.15 0.29 0.39 1.34 9.19 31.5 63 89 ＞1000 14.1 A 55 D TC 1.25 M350 8 UA306 0.15 0.19 0.27 1.41 5.13 26.7 71 94 ＞1000 13.8 A 56 D TC 1.50 M350 8 UA306 0.15 0.07 0.11 1.48 2.41 33.7 74 105 ＞1000 13.7 A 57 D TC 0.50 M350 2 UA306 0.15 0.96 1.17 1.22 2.33 2.4 59 65 ＞1000 14.1 A 58 D TC 0.50 M350 5 UA306 0.15 0.64 0.80 1.26 6.81 10.6 53 77 ＞1000 14.3 A 59 D TC 0.50 M350 11 UA306 0.15 0.32 0.33 1.05 22.7 71.54 38 98 ＞1000 14.8 A 60 D TC 0.50 M350 14 UA306 0.15 0.16 0.17 1.09 17.5 109.3 twenty four 111 ＞1000 14.8 B 61 D TC 0.50 M350 20 UA306 0.15 0.052 0.048 0.92 12.0 232 19 139 ＞1000 15.2 C 62 D TC 0.50 M350 30 UA306 0.15 0.025 0.030 1.24 2.72 111 17 164 ＞1000 15.7 C 63 D TC 0.50 M350 40 UA306 0.15 0.021 0.022 1.05 1.51 73.3 15 204 788 15.9 C

[Table 4] Sample No. Composition Adhesion force (N/25 mm) G'(kPa) Surface resistance (×10 ¹² Ω) γ (mJ/m ² ) Pollution polymer Crosslinking agent Light Hardener Before hardening After hardening Adhesion force increase rate (times) Before hardening After hardening Type Type quantity Multifunctional acrylate Urethane Acrylate Not plasma treated Plasma treated Adhesion force increase rate (times) Type quantity Type quantity 71 F C-HX 0.25 M350 8 UA306 0.15 0.36 0.77 2.14 16.6 46.2 twenty one 44 ＞1000 17.9 A 72 F C-HX 0.50 M350 8 UA306 0.15 0.26 0.57 2.21 13.7 52.8 25 47 ＞1000 17.8 A 73 F C-HX 0.75 M350 8 UA306 0.15 0.17 0.35 2.03 9.63 55.5 35 58 ＞1000 17.3 A 74 F C-HX 1.00 M350 8 UA306 0.15 0.10 0.20 2.07 4.93 50.8 42 67 ＞1000 17.2 A 75 F C-HX 1.25 M350 8 UA306 0.15 0.066 0.15 2.30 2.26 34.5 48 75 ＞1000 16.8 A 76 F C-HX 1.50 M350 8 UA306 0.15 0.031 0.10 3.06 0.66 20.9 57 83 ＞1000 16.4 A 77 F C-HX 0.50 M350 2 UA306 0.15 0.57 1.32 2.30 2.14 3.7 34 41 ＞1000 17.5 A 78 F C-HX 0.50 M350 5 UA306 0.15 0.33 0.77 2.36 5.86 17.9 31 45 ＞1000 17.4 A 79 F C-HX 0.50 M350 11 UA306 0.15 0.10 0.22 2.31 4.10 43.1 19 68 ＞1000 18.1 A 80 F C-HX 0.50 M350 14 UA306 0.15 0.048 0.16 3.33 1.85 38.6 17 72 ＞1000 18.2 B 81 F C-HX 0.50 M350 20 UA306 0.15 0.014 0.033 2.43 0.75 55.0 16 86 ＞1000 18.3 C 82 F C-HX 0.50 M350 30 UA306 0.15 0.011 0.032 3.00 0.53 49.1 10 99 ＞1000 18.4 C 83 F C-HX 0.50 M350 40 UA306 0.15 0.009 0.036 4.11 1.41 160 8 149 689 18.6 C 91 A TC 0.50 A200 30 - 0.15 0.20 1.35 5.39 36.4 50 189 590 24.8 A 92 A TC 0.50 A200 30 UA306 0.15 0.15 0.18 1.23 5.89 40.3 51 191 580 25.1 A 96 E D110N 1.50 A200 30 - 0.25 0.67 2.62 21.39 84.0 63 281 712 23.9 A

Regarding sample 91, which uses an adhesive composition prepared by mixing 30 parts by weight of a photocuring agent with respect to 100 parts by weight of polymer A, the surface free energy of the adhesive layer after photocuring exceeds 20 mJ/m ² and the electrical resistance is 10 ¹⁴ Ω level. The same is true for sample 96 using polymer E. Regarding sample 92, which has 0.15 parts by weight of urethane acrylate added as a photocuring agent, the adhesion of the adhesive layer after photocuring is slightly improved compared to sample 91, but other properties are not significantly different from those of sample 91.

For samples 21, 42, 62, and 82 in which 30 parts by weight of multifunctional acrylate and 0.15 parts by weight of urethane acrylate were blended with respect to polymers B, C, D, and E, the surface free energy of the adhesive layer after light curing was less than 20 mJ/m ² , and the resistance was greater than 1×10 ¹⁵ Ω, which was higher than that of samples 91, 92, and 96. On the other hand, for samples 22, 43, 63, and 83 in which the blending amount of multifunctional acrylate was changed to 40 parts by weight, the surface free energy of the adhesive layer after light curing was less than 20 mJ/m ² , but the resistance was in the order of 10 ¹⁴ Ω.

Regarding samples 91 and 92, since polymer A having butyl acrylate as a main component monomer has lower resistance than polymers B, C, D, and F having 2-ethylhexyl acrylate as a main component monomer, it is considered that the resistance of the adhesive layer is lower. Regarding sample 96, since polymer E contains a large amount of monomers with higher polarity as a constituent monomer component, it is considered that the resistance of the adhesive layer is lower.

In addition, polymer E contains NVP, a highly polar monomer containing nitrogen atoms, as a constituent monomer component, so the adhesive layer before light curing has improved adhesion to the plasma-treated polyimide film in sample 96. Regarding samples 71 to 85 using polymer F, the adhesion to the plasma-treated polyimide film is more than twice that to the non-plasma-treated polyimide film, and a tendency that the initial adhesion significantly increases by plasma treatment of the adherend is also observed.

For samples 22, 43, 63, and 83, the resistance of the adhesive layer is considered to be lower because the amount of the photocuring agent is larger. According to the comparison of samples 5, 16 to 22 using polymer B, samples 32, 37 to 43 using polymer C, samples 52, 57 to 63 using polymer D, and samples 72, 77 to 83 using polymer F, it is observed that the larger the amount of the photocuring agent, the greater the surface free energy of the adhesive layer.

Based on the above results, it can be seen that by using a low-resistance acrylic-based polymer and reducing the amount of photocuring agent, the surface free energy of the adhesive layer can be reduced and the resistance can be increased.

Furthermore, by comparing the samples made by changing the amount of photocuring agent with respect to the same base polymer, it was observed that the less the amount of photocuring agent was, the less likely it was to contaminate the adherend when the adhesive layer before photocuring was peeled off from the adherend. In addition to the viewpoint of high resistance, from the viewpoint of contamination resistance, it can be said that the less the amount of photocuring agent was, the better.

It was observed that the more the amount of photocuring agent was mixed, the smaller the adhesion of the adhesive layer to the polyimide film before photocuring, the greater the rate of increase of the adhesion caused by photocuring, and the adhesive layer after photocuring showed a tendency to have a higher adhesion. In addition, the more the amount of photocuring agent was mixed, the smaller the storage modulus of the adhesive layer before photocuring, the greater the rate of increase of the storage modulus caused by photocuring, and the greater the storage modulus of the adhesive layer after photocuring.

According to the comparison of samples 5, 11 to 15 using polymer B, samples 31 to 36 using polymer C, samples 51 to 56 using polymer D, and samples 71 to 76 using polymer F, it was observed that the more the amount of crosslinking agent was formulated, the weaker the adhesion of the adhesive layer before photocuring, and the greater the storage modulus of the adhesive layer before and after photocuring.

According to the results, it is known that by adjusting the amounts of the photocuring agent and the crosslinking agent, the adhesion and storage modulus of the adhesive layer before and after photocuring can be adjusted to a range suitable for use as a reinforcing film.

Regarding samples 5 to 10 using polymer B and changing the type of multifunctional acrylate as a photocuring agent, differences in properties were observed depending on the type of photocuring agent. Regarding sample 10 using TMPT as a photocuring agent without an ethylene oxide chain, the adhesive layer before photocuring had greater adhesion and the adhesive layer after photocuring had less adhesion than samples 5 to 9 using a photocuring agent containing an ethylene oxide chain. Since TMPT without ethylene oxide chains has a higher compatibility with acrylic polymers, it is difficult to form WBL. In contrast, multifunctional acrylates containing ethylene oxide chains have a lower compatibility with acrylic polymers than TMPT and are easy to form WBL. Therefore, it is believed that the initial adhesion is smaller and the increase rate of adhesion caused by light curing is higher.

Regarding samples 5 to 10, there was no significant difference in the storage modulus of the adhesive layer before light curing. However, the increase rate of the storage modulus caused by light curing was greater for samples 5, 9, and 10 using trifunctional or more multifunctional acrylates as the photocuring agent than for samples 6 to 8 using bifunctional acrylates, and the storage modulus of the adhesive layer after light curing increased. In particular, the increase in the storage modulus caused by light curing was more significant for sample 10 than for the other examples. As described above, since TMPT used as a photocuring agent in Sample 10 has a high compatibility with acrylic polymers and is difficult to form WBL, it is considered that it is easy to be incorporated into the entire part of the adhesive layer. The photocuring agent is uniformly cured in the thickness direction of the adhesive layer as a whole, so the storage modulus as an overall property is significantly increased.

Regarding samples 5, 6, and 10, it is difficult to contaminate the adherend when the adhesive layer before light curing is peeled off from the adherend, and the contamination resistance is excellent. On the other hand, regarding samples 7 to 9, the contamination resistance is poor. Regarding samples 7 to 9, since the chain length n of the ethylene oxide chain of the multifunctional acrylate as the light curing agent is relatively large, the compatibility with the acrylic base polymer is relatively low, so it is considered that the light curing agent easily permeates, resulting in contamination of the adherend.

For samples 5 to 9, there was no significant difference in the adhesion of the adhesive layer before photocuring, but the rate of increase in adhesion caused by photocuring was greater for sample 5 than for the other samples, and the adhesion of the adhesive layer increased after photocuring. The photocuring agent (M350) used in sample 5 is a trifunctional acrylate containing an ethylene oxide chain, which is easy to form WBL. After photocuring, the crosslinking density near the bonding interface increased, so it is believed that the adhesion increased after photocuring.

Regarding samples 1 to 5 using polymer B, 8 parts by weight of M350 as a multifunctional acrylate, and varying the amount of urethane acrylate, it was observed that the greater the amount of urethane acrylate, the less adhesion before photocuring. On the other hand, it was observed that the greater the amount of urethane acrylate, the more likely it is that the adherend will be contaminated by the adhesive layer before photocuring. Based on this result, it can be seen that by blending a small amount of urethane acrylate as a photocuring agent to a degree that does not contaminate the adherend in addition to blending a multifunctional acrylate that does not contain a urethane bond, a reinforcing film having a higher adhesion to the adherend after photocuring of the adhesive and excellent adhesion reliability can be obtained.

1: Film substrate 2: Adhesive layer 5: Peel-off pad 10: Reinforcement film 20: Adhesive

FIG1 is a cross-sectional view showing a laminated structure of a reinforcing film. FIG2 is a cross-sectional view showing a laminated structure of a reinforcing film. FIG3 is a cross-sectional view showing a device with a reinforcing film attached.

1: Membrane substrate

2: Adhesive layer

10: Reinforcement film

Claims (15)

A reinforcing film comprises a film substrate and an adhesive layer fixedly laminated on one main surface of the film substrate, wherein the adhesive layer comprises a photocurable composition containing an acrylic base polymer, a photocuring agent having two or more photopolymerizable functional groups, and a photopolymerization initiator, wherein the acrylic base polymer comprises one or more monomer components selected from the group consisting of hydroxyl-containing monomers and carboxyl-containing monomers, and a crosslinking structure formed by a crosslinking agent bonded to the hydroxyl group and/or the carboxyl group is introduced into the acrylic base polymer, and the surface resistance of the adhesive layer is 1×10 ¹⁵ Ω or more. As for the reinforcement film of claim 1, the surface free energy of the above-mentioned adhesive layer after light curing is less than 20 mJ/ ^m2 . The reinforcing film of claim 1, wherein the photocurable composition contains 3 to 25 parts by weight of the photocuring agent relative to 100 parts by weight of the acrylic base polymer. The reinforcing film of claim 1 comprises multifunctional (meth)acrylate as the photocuring agent. The reinforcing film of claim 1 comprises a multifunctional (meth)acrylate having an alkylene oxide chain as the photocuring agent. The reinforcing film of claim 1 comprises a multifunctional (meth)acrylate having an alkylene oxide chain and a urethane (meth)acrylate as the photocuring agent. The reinforcing film of claim 1, wherein the acrylic-based polymer comprises 50 to 99.5 parts by weight of an alkyl (meth)acrylate having an alkyl carbon number of 6 to 20, relative to 100 parts by weight of the total monomer components. The reinforcing film of claim 1, wherein the ratio of nitrogen in the constituent elements of the acrylic base polymer is less than 0.1 mol %. The reinforcing film of claim 1, wherein the shear storage modulus of the adhesive layer at 25°C before photocuring is 10 to 70 kPa. The reinforcing film of claim 1, wherein the shear storage modulus of the adhesive layer at 25° C. after light curing is 30 to 140 kPa. As in claim 1, the reinforcement film, wherein the bonding strength between the adhesive layer and the polyimide film before light curing is less than 0.5 N/25 mm. As in claim 1, the reinforcing film, wherein the adhesion between the adhesive layer and the polyimide film after light curing is 3 N/25 mm or more. A device with a reinforcing film is provided, wherein the reinforcing film is attached to the surface of the 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 attached to the surface of the device, the adhesive layer comprises a photocurable material formed by photocuring a photocurable adhesive composition containing an acrylic base polymer and a photocuring agent, the acrylic base polymer contains one or more selected from the group consisting of hydroxyl-containing monomers and carboxyl-containing monomers as monomer units, a cross-linked structure is introduced into the acrylic base polymer, and the surface resistance of the adhesive layer is 1×10 ¹⁵ Ω or more. A method for manufacturing a device with a reinforcing film, which is a method for manufacturing a device with a reinforcing film having a reinforcing film attached to a surface, The manufacturing method is to temporarily adhere the above-mentioned adhesive layer of the reinforcing film as any one of claims 1 to 12 to the surface of an adherend, and then irradiate the above-mentioned adhesive layer with active light to photoharden the above-mentioned adhesive layer, thereby increasing the bonding strength between the above-mentioned reinforcing film and the above-mentioned adherend. A reinforcement method is to adhere a reinforcement film to the surface of an adherend, The reinforcement method is to temporarily adhere the adhesive layer of the reinforcement film as in any one of claims 1 to 12 to the surface of the adherend, irradiate the adhesive layer with active light to photoharden the adhesive layer, thereby increasing the bonding strength between the reinforcement film and the adherend.