TWI855026B - Reinforcement film, device manufacturing method and reinforcement method - Google Patents

Abstract

The reinforcing film (10) of the present invention comprises a film substrate and an adhesive layer (2) fixedly laminated on one main surface of the film substrate. The adhesive layer comprises a photocurable composition. The photocurable composition constituting the adhesive layer comprises an acrylic base polymer, an acrylic oligomer, a photocurable agent, and a photopolymerization initiator. The acrylic oligomer comprises a carboxyl group and has a glass transition temperature of 0°C or above.

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 of fixing and laminating a reinforcing film on the surface of an adherend.

An adhesive film is sometimes attached to the surface of an optical device or electronic device such as a display for the purpose of surface protection or impact resistance. Such an adhesive film is usually formed by a laminate of an adhesive layer fixed on the main surface of a film substrate and attached to the device surface via the adhesive layer.

Before the device is assembled, processed, transported, etc., an adhesive film can be temporarily attached to the surface of the device or its components to prevent damage or destruction of the adherend. The adhesive film temporarily attached for the purpose of temporary surface protection is required to be easily peeled off from the adherend and not to leave adhesive residue on the adherend.

Patent document 1 discloses an adhesive film which is used for assembly, processing, transportation, etc. of a device and is also used in a state of being adhered to the surface of the device when the device is used. This adhesive film has the function of reinforcing the device by protecting the surface, dispersing the impact of the device, and imparting rigidity to the flexible device.

When an adhesive film is attached to an adherend, there is a possibility of poor attachment, such as bubbles being mixed in or the attachment position being offset. When poor attachment occurs, the following operation (secondary processing) is performed: the adhesive film is peeled off from the adherend and another adhesive film is attached. Adhesive films used as engineering materials are designed based on the premise of peeling off from the adherend, so they are easy to process secondary. On the other hand, reinforcing films based on permanent attachment are generally not assumed to be peeled off from the device but are firmly attached to the surface of the device, so they are difficult to process secondary.

Patent document 2 discloses an adhesive film having an adhesive layer designed to have low adhesiveness and increase adhesion over time just after bonding with an adherend. The adhesive that uses light or heat as a trigger to increase adhesion can arbitrarily set the time of adhesion increase caused by curing after bonding with an adherend. In addition, since the adhesion is small just after bonding (before the adhesion increase process), it is easy to peel off from the adherend and can be used as a reinforcing film with secondary processability. [Prior art document] [Patent document]

[Patent document 1] Japanese Patent Publication No. 2017-132977 [Patent document 2] International Publication No. 2015/163115

[The problem the invention is trying to solve]

Before attaching the reinforcing film to the surface of the adherend, the surface of the adherend may be subjected to a surface activation treatment such as plasma treatment or corona treatment for the purpose of cleaning the surface of the adherend. If the reinforcing film is attached to the surface of the adherend after the surface activation treatment, the adhesion force may be greatly increased compared to the case where the reinforcing film is attached to the adherend without the surface activation treatment, and it may be difficult to peel the reinforcing film from the adherend (secondary processing).

In view of this topic, the purpose of the present invention is to provide a reinforcing film that has low initial adhesion to the adherend even when the surface of the adherend is over-activated by plasma or the like, has excellent secondary processability, and can be firmly bonded to the adherend after the adhesion enhancement treatment. [Technical means to solve the problem]

In view of the above-mentioned problem, the inventors of the present invention and others conducted research and found that by using a photocurable adhesive with a specific composition, the difference in initial adhesion caused by the presence or absence of surface activation treatment of the adherend is smaller, the adherend also has excellent secondary processability for the surface activated adherend, and exhibits higher adhesion to the adherend after photocuring.

The reinforcing film of the present invention has an adhesive layer fixedly laminated on one main surface of the film substrate. The adhesive layer contains a photocurable composition containing a base polymer, an oligomer, a photocuring agent, and a photopolymerization initiator.

As the base polymer of the adhesive layer, an acrylic polymer can be used. The acrylic base polymer may be substantially free of nitrogen atoms. A crosslinking structure is preferably introduced into the base polymer. For example, the base polymer contains a hydroxyl-containing monomer and/or a carboxyl-containing monomer as a monomer unit, and a crosslinking structure is introduced by bonding a crosslinking agent such as a multifunctional isocyanate compound or a multifunctional epoxy compound to the functional groups.

As the oligomer, an acrylic oligomer having a weight average molecular weight of 1000 to 30000 and containing a carboxyl group can be used. By including the oligomer in the adhesive layer, even when the surface of the adherend is over-activated by plasma treatment or the like, the increase in the initial adhesion to the adherend can be suppressed, and after the adhesive layer is photocured, a higher adhesion to the activated adherend tends to be exhibited.

The gel fraction of the adhesive layer (photocurable composition) may be 50% or more. A crosslinking accelerator may be used when introducing the crosslinking structure. As the crosslinking accelerator, for example, an organic metal compound may be used.

The photocuring agent of the adhesive layer is, for example, a multifunctional (meth)acrylate, and the functional group equivalent of the photocuring agent is preferably about 100 to 500 g/eq.

After temporarily adhering the reinforcing film to the surface of the adherend, the adhesive layer is irradiated with active light to photo-cure the adhesive layer, thereby increasing the bonding strength between the reinforcing film and the adherend, thereby obtaining a device in which the reinforcing film is laminated on the surface of the adherend. When the adherend is a polyimide film, it is preferred that the bonding strength between the adhesive layer and the polyimide film is less than 1 N/25 mm before the adhesive layer is photo-cured (temporarily adhered state). The adherend may also be subjected to surface activation treatment such as plasma treatment before temporarily adhering the reinforcing film to the adherend. [Effect of the invention]

In the reinforcing film of the present invention, the adhesive layer contains a photocurable composition, and after being bonded to the adherend, the adhesive layer is photocured to increase the bonding strength to the adherend. Before the adhesive layer is photocured, the bonding strength to the adherend that has been over-activated by plasma treatment or the like is also small, so secondary processing is easy, and higher bonding strength is exhibited after photocuring.

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 substrate film 1. The adhesive layer 2 is a photocurable adhesive containing a photocurable composition, and is cured by irradiation with active light such as ultraviolet rays, thereby increasing the adhesion to the adherend.

Fig. 2 is a cross-sectional view showing a reinforcing film with a separator 5 temporarily adhered to the main surface of an adhesive layer 2. Fig. 3 is a cross-sectional view showing a state where a reinforcing film 10 is adhered and provided on the surface of a device 20.

The spacer 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, thereby attaching the reinforcing film 10 to the surface of the device 20. This state is a state where the adhesive layer 2 is 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 is increased, so that the device 20 and the reinforcing film 10 are fixed.

The so-called "fixed" refers to the state where two layers of the stack are firmly attached and it is impossible or difficult to peel them off at the interface. The so-called "tentative adhesion" refers to the state where the adhesion between two layers of the stack is relatively small and they can be easily peeled off at the interface.

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

In the device with the reinforcement film 10 attached as shown in FIG. 3, before the light curing of the adhesive layer 2, the device 20 and the adhesive layer 2 are temporarily adhered. If the film substrate 1 and the device 20 are peeled off, peeling occurs at the interface between the adhesive layer 2 and the device 20, and the state of the adhesive layer 2 being fixed on the film substrate 1 is maintained. Since no adhesive remains on the device 20, secondary processing is easy. After the light curing of the adhesive layer 2, since the adhesion between the adhesive layer 2 and the device 20 increases, it is difficult to peel the film 1 from the device 20. If the two are peeled off, there is a possibility that the cohesion of the adhesive layer 2 will be destroyed.

[Construction of reinforcing film] <Film substrate> A plastic film is used as the film substrate 1. In order to fix the film substrate 1 and the adhesive layer 2, it is preferred that the surface of the film substrate 1 to which the adhesive layer 2 is attached is not subjected to mold 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 shock mitigation, 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 thus 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 listed. In the reinforcing film for optical devices such as displays, the film substrate 1 is preferably a transparent film. In addition, when the adhesive layer 2 is photocured by irradiating active light from the side of the film substrate 1, the film substrate 1 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 can be used well. When the adhesive layer is cured by irradiating active light from the adherend side, the adherend only needs to be transparent to the active light, and the film substrate 1 may not be transparent 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 allow the film substrate 1 and the adhesive layer 2 to be fixed, it is preferred that the release layer is not provided on the surface of the film substrate 1 to which the adhesive layer 2 is attached.

<Adhesive layer> The adhesive layer 2 fixedly laminated on the film substrate 11 includes a photocurable composition containing a base polymer, a photocuring agent, and a photopolymerization initiator. Since the adhesive layer 2 has a weak bonding strength with the adherend such as the device or device parts before photocuring, it is easy to perform secondary processing. Since the bonding strength of the adhesive layer 2 with the adherend is improved by photocuring, the reinforcing film is not easy to peel off from the device surface when the device is used, and the bonding reliability is excellent.

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.

(Base polymer) The base polymer is the main component of the adhesive composition. From the perspective of setting the adhesive layer 2 before curing to an appropriate range of adhesion, it is preferred to introduce a cross-linked structure into the base polymer. The type of base polymer is not particularly limited, and an acrylic polymer, a silicone polymer, a urethane polymer, a rubber polymer, etc. can be appropriately selected. In particular, from the perspective of excellent optical transparency and adhesion, easy control of adhesion, and excellent compatibility with oligomers or photocuring agents, the adhesive composition preferably contains an acrylic polymer as the base polymer, and it is preferred that more than 50% by weight of the adhesive composition is an acrylic polymer.

As the acrylic polymer, a polymer containing an alkyl (meth)acrylate as a main monomer component can be preferably used. In addition, in this specification, the so-called "(meth)acrylic acid" means acrylic acid and/or methacrylic acid.

As the alkyl (meth)acrylate, an alkyl (meth)acrylate having an alkyl group with a carbon number of 1 to 20 can be preferably used. The alkyl group of the alkyl (meth)acrylate may be a straight chain or may have a branched chain. Examples of the alkyl (meth)acrylate 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, propyl (meth)acrylate, 1,2-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1,1-dimethoxy-1 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, aralkyl (meth)acrylate, and the like.

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

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 residual paste on the adherend during secondary processing tends to be reduced.

As monomers having a functional group capable of crosslinking, there can be listed hydroxyl-containing monomers or carboxyl-containing monomers. The hydroxyl group or carboxyl group of the base polymer becomes a reaction point with the crosslinking agent described below. For example, when an isocyanate-based crosslinking agent is used, it is preferred that a hydroxyl-containing monomer is contained as a copolymer component of the base polymer. When an epoxy-based crosslinking agent is used, it is preferred that a carboxyl-containing monomer is contained as a copolymer component of the base polymer.

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.

In the acrylic acid-based polymer, the total amount of the hydroxyl-containing monomer and the carboxyl-containing monomer is preferably 1 to 30% by weight, more preferably 2 to 25% by weight, and further preferably 3 to 20% by weight relative to the total amount of the constituent monomer components. It is particularly preferred that the content of the carboxyl-containing monomer is within the above range.

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 acrylic base polymer may also contain monomer components other than the above. For example, the acrylic base polymer may also contain vinyl ester monomers, aromatic vinyl monomers, epoxy-containing monomers, vinyl ether monomers, sulfone-containing monomers, phosphoric acid-containing monomers, acid anhydride-containing monomers, etc. as monomer components.

The base polymer may be one that does not substantially contain nitrogen atoms. The ratio of nitrogen in the constituent elements of the base polymer may be 0.1 mol% or less, 0.05 mol% or less, 0.01 mol% or less, 0.005 mol% or less, 0.001 mol% or less, or 0. By using a base polymer that does not substantially contain nitrogen atoms, there is a tendency to suppress the increase in the adhesion (initial adhesion) of the adhesive layer before light curing when the adherend is subjected to a surface activation treatment.

By not including nitrogen-containing monomers such as cyano-containing monomers, lactam-containing monomers, amide-containing monomers, and phenanthrene-containing monomers as constituent monomer components of the base polymer, a base polymer substantially free of 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 is substantially free of nitrogen atoms. When the base polymer substantially does not contain nitrogen atoms, from the viewpoint of improving the cohesiveness of the adhesive, the base polymer preferably contains a carboxyl-containing monomer as a monomer component.

The bonding properties of the adhesive before light curing are easily affected by the composition and molecular weight of the base polymer. The larger the molecular weight of the base polymer, the harder the adhesive tends to become. The weight average molecular weight of the acrylic base polymer is preferably 100,000 to 5 million, more preferably 300,000 to 3 million, and even more preferably 500,000 to 2 million. Furthermore, when a cross-linking structure is introduced into the base polymer, the molecular weight of the base polymer refers to the molecular weight before the cross-linking structure is introduced.

From the viewpoint of making the adhesive have appropriate softness, the glass transition temperature of the acrylic base polymer is preferably -10°C or lower, more preferably -15°C or lower, and further preferably -20°C or lower. The glass transition temperature of the acrylic base polymer may also be -25°C or lower or -30°C or lower. The glass transition temperature of the acrylic base polymer is usually -100°C or higher, and may also be -80°C or higher or -70°C or higher.

By making the base polymer contain a high Tg monomer as a constituent monomer component, the cohesive force of the adhesive is improved, the secondary processability before light curing is excellent, and higher bonding reliability is tended to be exhibited after light curing. The so-called high Tg monomer refers to a monomer with a higher glass transition temperature (Tg) of the homopolymer. Examples of monomers having a homopolymer Tg of 40°C or higher include (meth)acrylates such as cyclohexyl methacrylate (Tg: 66°C), tetrahydrofurfuryl methacrylate (Tg: 60°C), dicyclopentyl methacrylate (Tg: 175°C), dicyclopentyl acrylate (Tg: 120°C), isobutyl methacrylate (Tg: 173°C), isobutyl acrylate (Tg: 97°C), methyl methacrylate (Tg: 105°C), 1-adamantyl methacrylate (Tg: 250°C), and 1-adamantyl acrylate (Tg: 153°C); and acid monomers such as methacrylic acid (Tg: 228°C) and acrylic acid (Tg: 106°C).

In the acrylic base polymer, the content of monomers having a homopolymer Tg of 40°C or higher is preferably 1% by weight or higher, more preferably 2% by weight or higher, and further preferably 3% by weight or higher, relative to the total amount of the constituent monomer components. In order to form an adhesive layer having a moderate hardness and excellent secondary processability, the monomer components of the base polymer preferably include monomer components having a homopolymer Tg of 80°C or higher, and further preferably include monomer components having a homopolymer Tg of 100°C or higher. In the acrylic base polymer, the content of monomers having a homopolymer Tg of 100°C or higher is preferably 0.1% by weight or higher, more preferably 0.5% by weight or higher, further preferably 1% by weight or higher, and particularly preferably 2% by weight or higher. On the other hand, from the viewpoint of making the adhesive have appropriate softness, the content of the monomer having a Tg of 40°C or higher in the homopolymer is preferably 50% by weight or less, more preferably 40% by weight or less, further preferably 30% by weight or less, and may be 20% by weight or less or 10% by weight or less. From the same viewpoint, the content of the monomer having a Tg of 80°C or higher in the homopolymer is preferably 30% by weight or less, more preferably 25% by weight or less, further preferably 20% by weight or less, and may be 15% by weight or less, 10% by weight or less, or 5% by weight or less.

By polymerizing the above-mentioned monomer components using 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 the balance of the adhesive's adhesion, retention, and other properties, or cost, solution polymerization is preferred. As a solvent for solution polymerization, ethyl acetate, toluene, etc. are 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 be used. The reaction temperature is usually around 50 to 80°C, and the reaction time is usually around 1 to 8 hours.

(Oligomer) The adhesive composition may include an acrylic oligomer in addition to the acrylic base polymer. The acrylic oligomer contains an alkyl (meth)acrylate as a main monomer component and is a component having a weight average molecular weight less than that of the acrylic base polymer. The weight molecular weight of the acrylic oligomer is about 1,000 to 30,000, and may be more than 3,000, more than 5,000, or more than 7,000, and may be less than 25,000, less than 20,000, or less than 15,000.

As acrylic oligomers, those containing (meth) alkyl acrylate as a main monomer component can be preferably used. As the constituent monomer components of acrylic oligomers, the monomers exemplified above as monomer components constituting acrylic base polymers can be listed. The content of (meth) alkyl acrylate in the constituent monomer components of acrylic oligomers is preferably 40 wt % or more, more preferably 50 wt % or more, and further preferably 55 wt % or more, relative to the total amount of monomer components constituting the base polymer. From the viewpoint of increasing the glass transition temperature of the oligomer, it is preferred to contain a monomer having a homopolymer Tg of 40° C. or more as a monomer component. The oligomer having a carboxyl group contains a carboxyl group-containing monomer as a monomer component.

From the viewpoint of improving the adhesion of the adhesive layer 2 after light curing, the glass transition temperature of the acrylic oligomer is preferably 0°C or higher, more preferably 20°C or higher, and further preferably 30°C or higher. The glass transition temperature of the acrylic oligomer may also be 40°C or higher or 50°C or higher. The glass transition temperature of the acrylic oligomer is preferably higher than the glass transition temperature of the acrylic base polymer. The glass transition temperature of the acrylic oligomer is usually 200°C or lower, and may be 160°C or lower, 140°C or lower, or 120°C or lower.

The acrylic oligomer preferably has a carboxyl group. The acid value of the acrylic oligomer is, for example, about 10 to 800 mgKOH/g, and may also be 20 to 500 mgKOH/g, 30 to 300 mgKOH/g, or 40 to 200 mgKOH/g. By making the photocurable adhesive composition contain a high Tg oligomer containing a carboxyl group, there is a tendency to suppress the increase in the initial adhesion to the adherend even when the surface of the adherend is over-activated by plasma treatment or the like. In addition, by making the photocurable adhesive composition contain a high Tg oligomer containing a carboxyl group, there is a tendency for the adhesive after photocuring to show a higher adhesion to the activated adherend.

The acrylic oligomer and the acrylic base polymer may also contain a functional group capable of crosslinking. For example, when an epoxy crosslinking agent is used, if the acrylic oligomer has a carboxyl group, a crosslinking structure may be introduced through the reaction between the carboxyl group of the acrylic oligomer and the epoxy group of the crosslinking agent.

The acrylic oligomer may be substantially free of nitrogen atoms. The ratio of nitrogen in the constituent elements of the oligomer 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.

The acrylic oligomer can be obtained by polymerizing the above-mentioned monomer components using various polymerization methods. Various polymerization initiators can be used in the polymerization of the acrylic oligomer. In addition, a chain transfer agent can be used to adjust the molecular weight. As the acrylic oligomer having a carboxyl group, commercially available products such as the "ARUFON UC-3000" series manufactured by Toa Gosei can also be used.

The content of the acrylic oligomer in the adhesive composition is not particularly limited. From the viewpoint of adjusting the adhesion before and after photocuring to an appropriate range, the amount of the oligomer relative to 100 parts by weight of the base polymer is preferably 0.1 to 20 parts by weight, more preferably 0.2 to 10 parts by weight, and further preferably 0.3 to 5 parts by weight.

In acrylic adhesives, acrylic oligomers are sometimes used as adhesive agents. The amount of acrylic oligomers used as adhesive agents is often 20% by weight or more relative to 100 parts by weight of the base polymer. On the other hand, in the use of the present invention, the amount of acrylic oligomers can be a small amount. By using a small amount of acrylic oligomers, there is a tendency to suppress the increase in initial adhesion to the adherend that has been overactivated by plasma treatment or the like, and to increase the adhesion after photocuring. The amount of the oligomer relative to 100 parts by weight of the base polymer may be less than 4 parts by weight, less than 3 parts by weight, less than 2 parts by weight, or less than 1 part by weight.

(Crosslinking agent) From the perspective of giving the adhesive an appropriate cohesive force, it is preferred to introduce a crosslinking structure into the base polymer. For example, a crosslinking structure is introduced by adding a crosslinking agent to a solution of the base polymer after polymerization and heating the solution as necessary. 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.

As the crosslinking agent, there can be listed isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, metal chelate crosslinking agents, etc. These crosslinking agents react with functional groups such as hydroxyl groups or carboxyl groups introduced into the base polymer to form a crosslinking structure. In terms of high reactivity with hydroxyl groups or carboxyl groups of the base polymer and easy introduction of crosslinking structures, isocyanate crosslinking agents and epoxy crosslinking agents are preferred.

As the isocyanate crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule is 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-methylphenyl diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; trihydroxymethylpropane/methylphenyl diisocyanate trimer adducts (e.g., "Coronate L" manufactured by Tosoh), trihydroxymethylpropane/hexamethylene diisocyanate trimer adducts (e.g., "Coronate 1" 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 may 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 be a glycidyl group. Examples of epoxy crosslinking agents include: N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, Glyceryl 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 ChemteX, "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical can also be used.

Even when the base polymer does not substantially contain nitrogen atoms, the crosslinking agent may contain nitrogen atoms. For example, a crosslinking structure can be introduced into a base polymer that does not substantially contain nitrogen atoms by using an isocyanate crosslinking agent. When the base polymer does not substantially contain nitrogen atoms, the use of a crosslinking agent that does not contain nitrogen atoms, such as an epoxy crosslinking agent, tends to suppress the increase in initial adhesion caused by surface activation treatment such as plasma treatment.

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 0.01 to 10 parts by weight relative to 100 parts by weight of the base polymer, preferably 0.1 to 7 parts by weight, more preferably 0.2 to 6 parts by weight, and further preferably 0.3 to 5 parts by weight. In addition, the value obtained by dividing the amount of the crosslinking agent used relative to 100 parts by weight of the base polymer (parts by weight) by the functional group equivalent (g/eq) of the crosslinking agent is preferably 0.00015 to 0.11, more preferably 0.001 to 0.077, further preferably 0.003 to 0.055, and particularly preferably 0.0045 to 0.044. By using a larger amount of crosslinking agent than that of a common acrylic optical transparent adhesive for permanent bonding, the adhesive has an appropriate hardness, which tends to reduce the amount of adhesive residue on the adherend during secondary processing and improve the secondary processing properties.

(Crosslinking accelerator) The adhesive composition may contain a crosslinking accelerator in addition to the crosslinking agent. By using a crosslinking accelerator, the crosslinking reaction (introduction of the crosslinking structure into the base polymer) can be efficiently carried out. In addition, by using a crosslinking accelerator to introduce the crosslinking structure into the base polymer, the adherend whose surface is activated by the adhesive layer of the reinforcement film also tends to show a lower initial adhesion force.

As crosslinking promoters, organic metal compounds such as organic metal complexes (chelates), compounds of metals and alkoxy groups, and compounds of metals and acyloxy groups, as well as tertiary amines, etc. are listed. In particular, organic metal compounds are preferred from the perspective of inhibiting the crosslinking reaction in a solution state at room temperature and ensuring the shelf life of the adhesive composition. 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.

Examples of metals in organometallic compounds include iron, tin, aluminum, zirconium, zinc, titanium, lead, cobalt, and zinc.

As iron-based crosslinking promoters, there are: tri(acetylacetonate)iron, tri(hexane-2,4-dione)iron, tri(heptane-2,4-dione)iron, tri(heptane-3,5-dione)iron, tri(5-methylhexane-2,4-dione)iron, tri(octane-2,4-dione)iron, tri(6-methylheptane-2,4-dione)iron, tri(octane-2,4-dione)iron, tri(6-methylheptane-2,4-dione)iron, tri(5-methylhexane-2,4-dione)iron, tri(octane-2,4-dione)iron, tri(6-methylheptane-2,4-dione)iron, tri(heptane-3,5-dione)iron, tri(heptane-3,5-dione)iron, tri(heptane-2,4 ... Iron, tris(2,6-dimethylheptane-3,5-dione), iron, tris(nonane-2,4-dione), iron, tris(nonane-4,6-dione), iron, tris(2,2,6,6-tetramethylheptane-3,5-dione), iron, tris(tridecane-6,8-dione), iron, tris(1-phenylbutane-1,3-dione) Iron, tris(hexafluoroacetylacetone)iron, tris(ethyl acetylacetate)iron, tris(n-propyl acetylacetate)iron, tris(isopropyl acetylacetate)iron, tris(n-butyl acetylacetate)iron, tris(sec-butyl acetylacetate)iron, tris(tert-butyl acetylacetate)iron, tris(methyl propionyl acetate)iron, tris(ethyl propionyl acetate)iron, tris( Iron (n-propyl propionyl acetate), iron (isopropyl propionyl acetate), iron (n-butyl propionyl acetate), iron (sec-butyl propionyl acetate), iron (tert-butyl propionyl acetate), iron (benzyl acetoacetate), iron (dimethyl malonate), iron (diethyl malonate), iron (trimethoxide), iron (triethoxide), iron (triisopropoxide), etc.

As tin-based crosslinking promoters, there can be listed: dibutyltin dichloride, dibutyltin oxide, dibutyltin dibromide, dibutyltin maleate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin sulfide, tributyltin methoxide, tributyltin acetate, triethyltin ethoxide, tributyltin ethoxide, dioctyltin oxide, dioctyltin dilaurate, tributyltin chloride, tributyltin trichloroacetate, 2-ethyltin hexanoate, etc.

As aluminum-based crosslinking promoters, there can be listed: aluminum diisopropyl alcohol mono-second butoxide, aluminum second butoxide, aluminum isopropyl alcohol, aluminum ethoxide, aluminum ethyl acetate diisopropyl alcohol, aluminum triacetylacetate, aluminum alkyl acetylacetate diisopropyl alcohol, aluminum monoacetylacetone bis(ethyl acetate), aluminum triacetylacetone, and the like.

As the zirconium cross-linking promoter, there can be mentioned zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium tributyl monoacetonate, zirconium cycloalkanoate, zirconium propoxide, zirconium butoxide, and the like.

Examples of zinc-based crosslinking promoters include zinc cycloalkanoate and zinc 2-ethylhexanoate.

As titanium-based cross-linking promoters, there can be listed: dibutyl titanium dichloride, tetrabutyl titanium, tetraisopropyl titanium, tetraoctyl titanium, titanium trichloride butanol, titanium acetylacetonate, titanium tetraacetylacetonate, titanium ethyl acetylacetonate, titanium ammonium lactate, titanium triethanolamine, titanium diisopropyl diacetylacetonate, titanium isostearate, titanium diethanolamine, titanium aminoethylaminoethanol, etc.

As lead-based crosslinking promoters, lead oleate, lead 2-ethylhexanoate, lead benzoate, lead cycloalkanoate, etc. can be cited.

As the cobalt-based cross-linking accelerator, there can be mentioned cobalt 2-ethylhexanoate, cobalt benzoate, and the like.

The amount of the crosslinking accelerator used can be appropriately adjusted according to the type and amount of the crosslinking agent and the type of the crosslinking accelerator. The amount of the crosslinking accelerator used is generally about 0.001 to 2 parts by weight relative to 100 parts by weight of the base polymer.

When a crosslinking accelerator is used for an epoxy crosslinking agent, the amount of the crosslinking accelerator used is preferably 0.01 to 2.0 parts by weight relative to 100 parts by weight of the base polymer. For epoxy crosslinking agents, non-tin organic metals are preferably used as crosslinking accelerators. When a crosslinking accelerator is used for an isocyanate crosslinking agent, the amount of the crosslinking accelerator used is preferably 0.001 to 0.1 parts by weight.

The adhesive composition may also include a crosslinking retarder in addition to the crosslinking accelerator. By adding the crosslinking retarder, the crosslinking reaction in the solution state at room temperature can be inhibited, thereby extending the applicable period of the adhesive composition. 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 benzyl acetone; and alcohols such as tert-butyl alcohol. Among them, β-diketones are preferred, and acetylacetone is particularly preferred. The amount of the crosslinking delay agent used is about 0.1 to 30 parts by weight relative to 100 parts by weight of the total amount of the adhesive composition, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less.

(Photocuring agent) The adhesive composition constituting the adhesive layer 2 contains a photocuring agent in addition to the base polymer. If the adhesive layer 2 containing the photocurable adhesive composition is photocured after being attached to the adherend, the bonding strength with the adherend is improved.

The photocuring agent has two or more polymerizable functional groups in one molecule. As the polymerizable functional group, it is preferably one having polymerizability based on a photoradical reaction, and as the photocuring agent, it is preferably a compound having two or more ethylenic unsaturated bonds in one molecule. In addition, the photocuring agent is preferably a compound showing compatibility with the base polymer. In terms of showing appropriate compatibility with the base polymer, the photocuring agent is preferably a liquid at room temperature. By making the photocuring agent miscible with the base polymer and uniformly dispersing it in the composition, the contact area with the adherend can be ensured, and an adhesive layer 2 with high transparency can be formed. Furthermore, by making the base polymer and the photocuring agent exhibit appropriate compatibility, the cross-linked structure obtained by the photocuring agent can be easily introduced uniformly into the adhesive layer 2 after photocuring, thereby tending to appropriately increase the bonding force with the adherend.

The compatibility of the base polymer and the photocuring agent is mainly affected by the structure of the compound. The structure and compatibility of the compound can be evaluated, for example, by the Hansen solubility parameter. There is a tendency that the smaller the difference in the solubility parameters of the base polymer and the photocuring agent, the higher the compatibility becomes.

In terms of high compatibility with acrylic-based polymers, it is preferred to use a multifunctional (meth)acrylate as a photocuring agent. Examples of the multifunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, bisphenol A ethylene oxide-modified di(meth)acrylate, bisphenol A propylene oxide-modified di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and the like. Ester, trihydroxymethylpropane tri(meth)acrylate, di-trihydroxymethylpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, (meth)acrylate urethane, epoxy (meth)acrylate, butadiene (meth)acrylate, isoprene (meth)acrylate, etc. Among them, polyethylene glycol di(meth)acrylate or polypropylene glycol di(meth)acrylate is preferred, and polyethylene glycol di(meth)acrylate is particularly preferred, in terms of excellent compatibility with acrylic-based polymers. Two or more photocuring agents may be used in combination.

The compatibility between the base polymer and the photocuring agent is also affected by the molecular weight of the compound. There is a tendency that the smaller the molecular weight of the photocuring compound is, the higher the compatibility with the base polymer becomes. From the perspective of compatibility with the base polymer, the molecular weight of the photocuring agent is preferably 1500 or less, more preferably 1000 or less, further preferably 500 or less, and particularly preferably 400 or less.

From the viewpoint of high compatibility with the base polymer and improved adhesion after photocuring, the functional group equivalent (g/eq) of the photocuring agent is preferably 500 or less, more preferably 400 or less, further preferably 300 or less, and particularly preferably 200 or less. On the other hand, if the functional group equivalent of the photocuring agent 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 of the photocuring agent is preferably 80 or more, more preferably 100 or more, and further preferably 130 or more.

In the combination of acrylic base polymer and multifunctional acrylate photocuring agent, when the functional group equivalent weight of the photocuring agent is small, the interaction between the base polymer and the photocuring agent is strong, the initial adhesion is increased, and the secondary processability is reduced. From the perspective of maintaining the adhesion between the adhesive layer 2 and the adherend before photocuring within an appropriate range, it is also preferred that the functional group equivalent weight of the photocuring agent is within the above range.

The content of the photocuring agent in the adhesive composition is preferably 10 to 50 parts by weight relative to 100 parts by weight of the base polymer. By setting the amount of the photocuring agent to the above range, the adhesion between the adhesive layer and the adherend after photocuring can be adjusted to an appropriate range. The content of the photocuring agent is more preferably 15 to 45 parts by weight relative to 100 parts by weight of the base polymer, and further preferably 20 to 40 parts by weight.

(Photopolymerization initiator) Photopolymerization initiators generate active species by irradiation with active light and promote the curing reaction of photocuring agents. As photopolymerization initiators, photocation initiators (photoacid generators), photoradical initiators, photoanion initiators (photobase generators), etc. can be used according to the type of photocuring agent. When using ethylenically unsaturated compounds such as multifunctional acrylates as photocuring agents, it is preferred to use photoradical initiators as polymerization initiators.

The photo-radical initiator generates free radicals by irradiation with active light, and promotes the free radical polymerization reaction of the photocuring agent by transferring the free radicals from the photo-radical initiator to the photocuring agent. As the photo-radical 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, benzoyl dimethyl ketal, amino ketones, acyl phosphine oxides, benzophenones, and trichloromethyl-containing tris derivatives. The photo-radical initiator can be used alone or in combination of two or more.

When transparency is required for the adhesive layer 2, the photopolymerization initiator preferably has a low sensitivity to light with a wavelength longer than 400 nm (visible light). For example, a photopolymerization initiator having an absorption coefficient of 1×10 ² [mLg ^-1 cm ^-1 ] or less at a wavelength of 405 nm can be preferably used.

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 10 parts by weight, more preferably 0.05 to 7 parts by weight, and further preferably 0.1 to 5 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, 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.

[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 scraper coating, curtain coating, lip plate 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 used as appropriate. 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.

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, if the thickness of the adhesive layer 2 is too large, the fluidity before light curing is higher and the operation becomes difficult. Therefore, the thickness of the adhesive layer 2 is preferably 5 to 100 μm, more preferably 8 to 50 μm, further preferably 10 to 40 μm, and particularly preferably 13 to 30 μm.

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

By introducing a cross-linked structure into the base polymer, the gel fraction increases. The higher the gel fraction, the harder the adhesive is, and when the reinforcing film is peeled off from the adherend due to secondary processing, etc., the tendency of the adhesive residue to remain on the adherend can be suppressed. The gel fraction of the adhesive layer 2 before light curing is preferably 30% or more, more preferably 50% or more, further preferably 60% or more, and particularly preferably 65% or more. The gel fraction of the adhesive layer 2 before light curing can also be 70% or more or 75% or more.

Since the adhesive contains unreacted photocuring agent, the gel fraction of the adhesive layer 2 before photocuring is generally 90% or less. If the gel fraction of the adhesive layer 2 before photocuring is too large, the gripping force on the adherend is reduced and the initial adhesion becomes insufficient. Therefore, the gel fraction of the adhesive layer 2 before photocuring is preferably 85% or less, and more preferably 80% or less.

The gel fraction can be obtained as the insoluble matter in solvents such as ethyl acetate. Specifically, it is obtained as the weight fraction (unit: weight %) of the insoluble component of the adhesive layer after immersion in ethyl acetate at 23°C for 7 days relative to the sample before immersion. Generally speaking, the gel fraction of a polymer is equal to the degree of crosslinking. The more crosslinked parts in the polymer, the larger the gel fraction. Therefore, there is a tendency that the gel fraction becomes larger as the amount of crosslinking agent used (the content of crosslinking functional groups) increases. In addition, by using a crosslinking accelerator, the amount of unreacted functional groups of the crosslinking agent will decrease, so there is a tendency for the gel fraction to increase. In the adhesive layer 2 before photocuring, since the photocuring agent is in an unreacted state, the larger the amount of photocuring agent, the smaller the gel fraction becomes.

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 including the base polymer and the photocuring agent is formed. When the adhesive layer 2 is formed on the film substrate 1, it is preferred to attach a spacer 5 to the adhesive layer 2 for the purpose of protecting the adhesive layer 2. Alternatively, the crosslinking may be performed after attaching the spacer 5 to the adhesive layer 2.

When the adhesive layer 2 is formed on another substrate, the reinforcing film is obtained by transferring the adhesive layer 2 onto the film substrate 1 after drying the solvent. The substrate used for forming the adhesive layer can also be directly used as the spacer 5.

As the isolating member 5, a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, polyester film, etc. can be preferably used. The thickness of the isolating member is generally 3 to 200 μm, preferably about 10 to 100 μm. It is preferred that the contact surface of the isolating member 5 with the adhesive layer 2 is subjected to a mold release treatment using a mold release agent such as a polysilicone-based, fluorine-based, long-chain alkyl-based, or fatty amide-based release agent, or silicon dioxide powder, etc. By performing a mold release treatment on the surface of the isolating member 5, when the film substrate 1 and the isolating member 5 are peeled off, the state in which the adhesive layer 2 and the isolating member 5 are peeled off and the adhesive layer 2 is fixed on the film substrate 1 can be maintained.

[Use of reinforcing film] The reinforcing film of the present invention is used by being attached to a device or a component of a device. The adherend to which the reinforcing film is attached is not particularly limited, and various electronic devices, optical devices and their components can be listed. The reinforcing film can be attached to the entire surface of the adherend, or it can be selectively attached only to the portion that needs reinforcement. In addition, after the reinforcing film is attached to the entire surface of the adherend, the reinforcing film of the portion that does not need reinforcement can be cut off and the reinforcing film can be peeled off and removed. As long as the reinforcing film is temporarily attached to the surface of the adherend before the adhesive is photocured, the reinforcing film can be easily peeled off and removed from the surface of the adherend.

Since the reinforcing film is applied to give the appropriate rigidity, it is expected to improve the operability or prevent damage. In the manufacturing process of the device, when the reinforcing film is applied to the semi-finished product, the reinforcing film can be applied to the semi-finished product before it is cut into the product size. The reinforcing film can also be applied to the mother roll of the device manufactured by roll-to-roll processing in a roll-to-roll manner.

<Characteristics of the adhesive layer before light curing> In 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 light curing. Therefore, before light curing, the reinforcing film is easy to peel off from the adherend, and the secondary processing property is excellent. In addition, before light curing, the reinforcing film can be cut and the reinforcing film can be removed from a part of the surface of the adherend.

(Adhesion) From the perspective of facilitating peeling from the adherend and preventing the adhesive residue from remaining on the adherend after the reinforcing film is peeled off, the adhesion (initial adhesion) between the adhesive layer 2 and the adherend before photocuring is preferably 1 N/25 mm or less, more preferably 0.7 N/25 mm or less, and further preferably 0.5 N/25 mm or less. The adhesion between the adhesive layer 2 and the adherend before photocuring may also be 0.4 N/25 mm or less, 0.3 N/25 mm or less, or 0.2 N/25 mm or less. From the viewpoint of preventing the reinforcing film from peeling 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, and further preferably 0.03 N/25 mm or more. The initial adhesion may also be 0.05 N/25 mm or more, 0.07 N/25 mm or more, or 0.1 N/25 mm or more.

The reinforcing film preferably has a bonding strength to the polyimide film in the above range before the adhesive layer is photocured. In flexible display panels, flexible printed wiring boards (FPCs), devices integrating display panels and wiring boards, etc., flexible substrate materials are used, and polyimide films are generally used from the viewpoint of heat resistance or dimensional stability. The reinforcing film having the above bonding strength to the polyimide film as the substrate is easy to peel off before the adhesive is photocured, and has excellent bonding reliability after photocuring.

Before attaching the reinforcing film, the adherend such as the polyimide film on the device surface may be activated for cleaning. Examples of surface activation treatments include plasma treatment, corona treatment, and fluorescent discharge treatment. In particular, atmospheric pressure plasma treatment is preferred because it can be treated under atmospheric pressure and has a higher activation effect.

If the adherend is subjected to surface activation treatment, the adhesion between the adhesive layer 2 and the adherend before light curing tends to be higher than that without surface activation treatment. If the adhesion between the adhesive layer and the adherend before light curing is too strong, secondary processing may become difficult. Therefore, the adhesion between the adherend subjected to surface activation treatment and the adhesive layer before light curing is preferably less than 2 times the adhesion between the adherend not subjected to surface activation treatment and the adhesive layer before light curing, more preferably less than 1.5 times, further preferably less than 1.4 times, and may also be less than 1.3 times or less than 1.2 times.

In the present invention, by making the adhesive contain a high Tg oligomer containing a carboxyl group in addition to the base polymer, even when the adherend has been subjected to surface activation treatment, the adhesion force (initial adhesion force) of the adhesive layer before photocuring can be suppressed to a lower level. Therefore, even when the adherend such as a polyimide film has been subjected to surface activation treatment, secondary processing is as easy as when the surface activation treatment is not performed. In addition, by making the adhesive contain a high Tg oligomer containing a carboxyl group, there is a tendency for the adhesive after photocuring to show higher adhesion to the adherend subjected to surface activation treatment, and the adhesion reliability is excellent.

The reason why the addition of oligomers suppresses the increase in initial adhesion to the surface-activated adherend and improves the adhesion after light curing is not certain, but it is presumed to be related to the following situation: adding a small amount of oligomers will not significantly change the overall properties of the adhesive, but will change the properties of the adhesive interface with the adherend.

(Storage modulus) The shear storage modulus _G'i of the adhesive layer 2 at 25°C before light curing is preferably 1×10 ⁴ to 1.2×10 ⁵ Pa. The shear storage modulus (hereinafter simply referred to as "storage modulus") is obtained by reading the value at a specific temperature when measuring in the range of -50 to 150°C at a frequency of 1 Hz and 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 materials that exhibit viscoelastic properties such as adhesives, the storage modulus G' is used as an indicator of the degree of hardness. The storage modulus of the adhesive layer has a high correlation with the cohesive force, and there is a tendency that the higher the cohesive force of the adhesive, the greater the gripping force on the adherend. As long as the storage modulus of the adhesive layer 2 before light curing is 1×10 ⁴ Pa or more, the adhesive has sufficient hardness and cohesive force, so it is not easy to produce paste residues on the adherend when the reinforcing film is peeled off from the adherend. In addition, when the storage modulus of the adhesive layer 2 is large, the adhesive can be suppressed from overflowing from the end surface of the reinforcing film. As long as the storage modulus of the adhesive layer 2 before light curing is less than 1.2×10 ⁵ Pa, the adhesive layer 2 and the adherend can be easily peeled off at the interface, and it is not easy to cause coagulation and destruction of the adhesive layer or paste residue on the surface of the adherend during secondary processing.

From the viewpoint of improving the secondary processability of the reinforcing film and thereby suppressing the residual paste on the adherend during the secondary processing, the storage modulus _G'i of the adhesive layer 2 at 25°C before light curing is more preferably 3×10 ⁴ to 1×10 ⁵ Pa, and further preferably 4×10 ⁴ to 9.5×10 ⁴ Pa.

<Photocuring of adhesive layer> After the reinforcing film is attached to the adherend, the adhesive layer 2 is irradiated with active light to photocure 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 irradiation of the adhesive layer 2 with active light can be carried out from either the film substrate 1 side or the adherend side, or from both sides.

<Characteristics of the adhesive layer after photocuring> (Adhesion) From the perspective of adhesion reliability during practical use of the device, the adhesion between the adhesive layer 2 after photocuring and the adherend is preferably 2 N/25 mm or more, more preferably 3 N/25 mm or more, and further preferably 5 N/25 mm or more. The adhesion between the reinforcement film after the adhesive layer is photocured and the adherend may also be 6 N/25 mm or more, 8 N/25 mm or more, 10 N/25 mm or more, 13 N/25 mm or more, 15 N/25 mm or more, or 20 N/25 mm or more. The reinforcement film preferably has the adhesion within the above range to the polyimide film after the adhesive layer is photocured. The adhesion between the adhesive layer 2 and the adherend after photocuring is preferably 5 times or more, more preferably 10 times or more, greater than the adhesion between the adhesive layer 2 and the adherend before photocuring. The adhesion between the adhesive layer 2 and the adherend after photocuring may also be 20 times or more, 50 times or more, 80 times or more, 100 times or more, 120 times or more, or 140 times or more than the adhesion between the adhesive layer 2 and the adherend before photocuring.

As described above, by making the base polymer of the adhesive not contain nitrogen atoms, there is a tendency to suppress the increase in initial adhesion caused by the surface activation treatment of the adherend. On the other hand, when the adherend is subjected to surface activation treatment, there is a tendency for the adhesion between the adhesive layer 2 and the adherend after light curing to be greater than when the surface activation treatment of the adherend is not performed. In particular, by making the adhesive composition contain a high Tg oligomer containing a carboxyl group, there is a tendency to suppress the increase in initial adhesion caused by the surface activation treatment and increase the adhesion of the adhesive after light curing. That is, when using a reinforcing film having an adhesive layer with a specific composition, by performing a surface activation treatment such as plasma treatment on the adherend, the increase in initial adhesion force can be suppressed, secondary processability can be ensured, and higher adhesion force can be achieved after light curing, thereby obtaining a device with excellent adhesion reliability of the reinforcing film.

(Storage modulus) The storage modulus _G'f of the adhesive layer 2 at 25°C after light curing is preferably 1.0×10 ⁵ Pa or more. As long as the storage modulus of the adhesive layer 2 after light curing is 1.0×10 ⁵ Pa or more, the cohesive force increases, and the adhesion to the adherend is improved, and a higher adhesion reliability can be obtained. On the other hand, when the storage modulus is too large, the adhesive is difficult to wet and expand, and the contact area with the adherend becomes smaller. In addition, the stress dispersibility of the adhesive is reduced, so there is a tendency for the peeling force to be easily transmitted to the bonding interface, and the adhesion to the adherend is reduced. Therefore, the storage modulus _G'f of the adhesive layer 2 at 25°C after photocuring is preferably 2×10 ⁶ Pa or less. From the viewpoint of improving the bonding reliability of the reinforcing film after photocuring the adhesive layer, _G'f is more preferably 1.1×10 ⁵ to 1.2×10 ⁶ Pa, and further preferably 1.2×10 ⁵ to 1×10 ⁶ Pa.

The ratio of the storage modulus of the adhesive layer 2 at 25°C before and after photocuring, _G'f /G'i _, is preferably greater than 2. As long as _G'f is more than twice _G'i , the increase in G _' during photocuring can take into account both the secondary processability before photocuring and the bonding reliability after photocuring. _G'f / _G'i is more preferably greater than 4, further preferably greater than 8, and particularly preferably greater than 10. There is no particular upper limit to _G'f /G'i. When _G'f / _G'i is too large, it is easy to cause poor initial bonding due to small G' before photocuring, or reduce bonding reliability due to excessive G' after photocuring. Therefore, _G'f / _G'i is preferably less than 100, more preferably less than 40, further preferably less than 30, and particularly preferably less than 25.

The adherend with the reinforcement film may be subjected to an autoclave treatment for the purpose of improving the affinity of the laminated interface of multiple laminated components, or a heat treatment such as heat pressing for joining circuit components. When such a heat treatment is performed, it is preferred that the adhesive between the reinforcement film and the adherend does not flow from the end surface.

From the viewpoint of suppressing the overflow of the adhesive during high temperature heating, the storage modulus of the adhesive layer 2 after light curing at 100°C is preferably 5×10 ⁴ Pa or more, more preferably 8×10 ⁴ Pa or more, and further preferably 1×10 ⁵ Pa or more. From the viewpoint of preventing the overflow of the adhesive during heating and preventing the decrease in adhesion during heating, the storage modulus of the adhesive layer 2 after light curing at 100°C is preferably 60% or more of the storage modulus at 50°C, more preferably 65% or more, further preferably 70% or more, and particularly preferably 75% or more.

By bonding the reinforcing film, the semi-finished product as 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. In addition, since the reinforcing film is easy to peel off from the adherend before the adhesive layer is photocured even when the adherend has been subjected to surface activation treatment, it is also easy to perform secondary processing when lamination or poor bonding occurs. After the adhesive layer is photocured, it exhibits a higher bonding force to the adherend, and the reinforcing film is not easy to peel off from the device surface, and the bonding reliability is excellent. [Example]

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

[Example 1] <Polymerization of base polymer> 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 introduced, and nitrogen replacement was performed for about 1 hour while stirring. Thereafter, the mixture was heated to 60°C and reacted for 7 hours to obtain a solution of an acrylic polymer with a weight average molecular weight of 600,000.

<Preparation of adhesive composition> In the acrylic polymer solution, 1 part by weight of a carboxyl-containing acrylic oligomer ("ARUFON UC-3000" manufactured by Toa Gosei; weight average molecular weight: 10,000, glass transition temperature: 65°C, acid value: 74 mgKOH/g), 0.5 parts by weight of a tetrafunctional epoxy compound ("Tetrad C" manufactured by Mitsubishi Gas Chemical) as a crosslinking agent, 30 parts by weight of "NK Ester A200" (polyethylene glycol #200 (n=4) diacrylate; molecular weight 308, functional group equivalent 154 g/eq) manufactured by Shin-Nakamura Chemical Industry as a multifunctional acrylic monomer, and 0.1 parts by weight of a photopolymerization initiator ("Irgacure 651" manufactured by BASF) were added to prepare an adhesive composition.

<Adhesive composition coating and cross-linking> The adhesive composition was coated on a 75 μm thick polyethylene terephthalate film ("Lumirror S10" manufactured by Toray) without surface treatment using a slot roll so that the thickness after drying was 25 μm. The solvent was removed by drying at 130°C for 1 minute, and then the release-treated surface of the spacer (polyethylene terephthalate film with a thickness of 25 μm and subjected to silicone release treatment) was attached to the adhesive coating surface. Afterwards, an aging treatment was performed at 25° C. for 4 days to perform crosslinking, thereby obtaining a reinforcement film in which a photocurable adhesive sheet was fixedly laminated on the film substrate and a spacer was temporarily adhered thereon.

[Examples 2 and 3] In the preparation of the adhesive composition, the amount of acrylic oligomer added was changed as shown in Table 1, and the reinforcing film was prepared in the same manner as in Example 1.

[Example 4] In the preparation of the adhesive composition, an acrylic oligomer, a crosslinking agent, a multifunctional acrylic monomer, and a photopolymerization initiator are added to a solution of an acrylic polymer, and 0.2 parts by weight of zirconium tetraacetylacetonate (manufactured by Tokyo Chemical Industry) is added as a crosslinking promoter. In addition, 30 parts by weight of "NK ESTER A200" as a multifunctional acrylic monomer is added, and 5 parts by weight of "NK ESTER A600" (polyethylene glycol #600 (n=4) diacrylate; molecular weight 708, functional group equivalent 354 g/eq) manufactured by Shin-Nakamura Chemical is added. A reinforcing film is prepared in the same manner as in Example 1 except for these changes.

[Comparative Example 1] A reinforcing film was prepared in the same manner as in Example 1 except that no acrylic oligomer was added in the preparation of the adhesive composition.

[Comparative Examples 2 to 4] In the preparation of the adhesive composition, the type of acrylic oligomer was changed as shown in Table 1, and the reinforcing film was prepared in the same manner as in Example 4. The "UC-3510" used in Comparative Example 2 is a liquid acrylic oligomer containing a carboxyl group ("ARUFON UC-3510" manufactured by Toa Gosei, weight average molecular weight: 2000, glass transition temperature: -50°C, acid value: 70 mgKOH/g). The "UP-1190" used in Comparative Example 3 is a liquid acrylic oligomer without a carboxyl group ("ARUFON UP-1190" manufactured by Toa Gosei, weight average molecular weight: 3000, glass transition temperature: -77°C). The "oligomer A" used in Comparative Example 4 is an acrylic oligomer having a weight average molecular weight of 5100 and a glass transition temperature of 144° C. obtained by the following preparation example.

<Example of oligomer preparation> 60 parts by weight of dicyclopentyl methacrylate (DCPMA), 40 parts by weight of methyl methacrylate (MMA), 3.5 parts by weight of α-thioglycerol as a chain transfer agent, and 100 parts by weight of toluene as a polymerization solvent were mixed and stirred at 70°C for 1 hour under a nitrogen atmosphere. Then, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added and reacted at 70°C for 2 hours, and then the temperature was raised to 80°C and reacted for 2 hours. Thereafter, the reaction solution was heated to 130°C, toluene, chain transfer agent and unreacted monomers were dried and removed, and a solid oligomer A was obtained.

[Measurement of adhesion of polyimide film] <Adhesion before light curing> A polyimide film with a thickness of 12.5 μm ("Kapton 50EN" manufactured by DU PONT-TORAY) 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 isolation piece was peeled off from the surface of the reinforcement film cut to a width of 25 mm × a length of 100 mm, and then attached to the polyimide film substrate for measurement using a hand roller to prepare a sample for adhesion measurement (without plasma treatment).

While the polyimide 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 laminated to the polyimide film substrate for measurement after the plasma treatment using a hand roller to prepare a sample for adhesion measurement (with plasma treatment).

Using the test samples, the ends of the polyethylene terephthalate film of the reinforcement film were held by a chuck, and the 180° peeling test of the reinforcement film was performed at a tensile speed of 300 mm/min, and the peeling strength was measured. 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 after photocuring> A reinforcement film was attached to a polyimide film substrate (with and without plasma treatment), and then the adhesive layer was photocured by irradiating ultraviolet light with a cumulative light intensity of 4000 mJ/ ^cm2 from the reinforcement film side (PET film side) using a 365 nm LED (Light Emitting Diode) light source. The adhesion was measured by the 180° peel test in the same manner as above using the test sample.

The composition of the adhesive of each reinforcement film (type and addition amount of acrylic oligomer, type and addition amount of photocuring agent, addition amount of crosslinking promoter (zirconium tetraacetylacetonate)), the adhesion to the polyimide film before and after photocuring, the increase rate of adhesion before and after photocuring, and the increase rate of initial adhesion caused by plasma treatment (the ratio of adhesion before photocuring with plasma treatment to adhesion before photocuring without plasma treatment) are shown in Table 1. The addition amount in the composition of Table 1 is the addition amount (weight parts) relative to 100 weight parts of the base polymer.

[Table 1] Composition Follow-up Oligomer Light Hardener Crosslinking promoter No plasma treatment With plasma treatment Initial adhesion increase rate (times) Adhesion force (N/25 mm) Adhesion force increase rate (times) Adhesion force (N/25 mm) Adhesion force increase rate (times) Type Tg (℃) COOH quantity Type quantity quantity Before light hardening After light curing Before light hardening After light curing Embodiment 1 UC-3000 65 have 1 A200 30 - 0.14 12.2 85.3 0.17 26.0 156.3 1.17 Embodiment 2 UC-3000 65 have 0.5 A200 30 - 0.14 12.1 85.2 0.16 26.1 168.3 1.10 Embodiment 3 UC-3000 65 have 5 A200 30 - 0.21 13.9 66.1 0.23 28.3 121.9 1.11 Embodiment 4 UC-3000 65 have 0.5 A200/A600 30/5 0.2 0.06 4.3 71.8 0.08 12.0 150.0 1.33 Comparison Example 1 - A200 30 - 0.15 7.4 50.3 0.21 18.2 88.6 1.40 Comparison Example 2 UC-3510 -50 have 0.5 A200/A600 30/5 0.2 0.06 4.1 68.0 0.21 15.9 75.7 3.50 Comparison Example 3 UP-1190 -77 without 0.5 A200/A600 30/5 0.2 0.06 5.7 94.2 0.15 13.4 89.3 2.50 Comparison Example 4 Oligomer A 144 without 0.5 A200/A600 30/5 0.2 0.06 4.3 71.7 0.14 9.4 66.9 2.33

In any of the examples and comparative examples, when the reinforcing film was attached to a polyimide film substrate that had not been subjected to plasma treatment, the increase in adhesion before and after photocuring was less than 100 times. When the polyimide film substrate that had been subjected to plasma treatment was used as the adherend, in Examples 1 to 4, the adhesion increased to more than 120 times due to photocuring, and in Examples 1, 2, and 4, the increase in adhesion exceeded 150 times. On the other hand, in Comparative Example 1 in which the adhesive composition did not contain an oligomer, the increase in adhesion remained less than 90 times even when the polyimide film substrate that had been subjected to plasma treatment was used as the adherend. In Comparative Examples 2 and 3 in which low Tg oligomers were added and Comparative Example 4 in which a high Tg oligomer without a carboxyl group was added, the increase rate of the adhesive force before and after photocuring was also less than 90 times when the plasma-treated polyimide film was used as the adherend.

If we focus on the initial adhesion force (adhesion force before photocuring), the increase in initial adhesion force caused by plasma treatment in Examples 1 to 4 is relatively small. In contrast, the increase in initial adhesion force caused by plasma treatment in Comparative Examples 1 to 4 is relatively large, and in particular, the increase in initial adhesion force caused by plasma treatment in Comparative Examples 2 to 4 is more obvious.

Based on these results, it can be seen that the reinforcing film having a photocurable adhesive layer containing a high Tg oligomer containing a carboxyl group has a low initial adhesion to the adherend that has been activated by plasma treatment or the like, and has excellent secondary processability. After photocuring, it exhibits a high adhesion to the adherend and has excellent bonding reliability.

1: Film substrate 2: Adhesive layer 5: Isolation element 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 having a reinforcing film attached thereto.

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; the adhesive layer comprises a photocurable composition containing an acrylic base polymer, an acrylic oligomer with a weight average molecular weight of 1000-30000, a photocuring agent, and a photopolymerization initiator; and the acrylic oligomer comprises a carboxyl group and has a glass transition temperature of 0°C or above. As in claim 1, the reinforcing film, wherein 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 cross-linking structure is introduced by a cross-linking agent bonded to a hydroxyl group or a carboxyl group. As in claim 1, the reinforcing film, wherein the acrylic-based polymer contains carboxyl-containing monomers as monomer units, and a cross-linking structure is introduced by a cross-linking agent bonded to the carboxyl group. For example, in the reinforcing film of claim 2 or 3, the crosslinking agent is an epoxy crosslinking agent. For example, the reinforcing film of claim 2 or 3, wherein the gel fraction of the photocurable composition is 50% or more. A reinforcing film as claimed in any one of claims 1 to 3, wherein the acrylic-based polymer does not substantially contain nitrogen atoms. A reinforcing film as claimed in any one of claims 1 to 3, wherein the photocurable composition contains 0.1 to 20 parts by weight of the acrylic oligomer relative to 100 parts by weight of the acrylic base polymer. A reinforcing film as claimed in any one of claims 1 to 3, wherein the photocurable composition contains 10 to 50 parts by weight of the photocuring agent relative to 100 parts by weight of the base polymer. A reinforcing film as claimed in any one of claims 1 to 3, wherein the photocuring agent is a multifunctional (meth)acrylate. A reinforcing film as claimed in any one of claims 1 to 3, wherein the functional group equivalent of the above-mentioned photocuring agent is 100-500 g/eq. A reinforcing film as claimed in any one of claims 1 to 3, wherein the bonding strength between the adhesive layer and the polyimide film before light curing is less than 1N/25mm. A method for manufacturing a device having a reinforcing film attached to the surface thereof, wherein the adhesive layer of the reinforcing film as claimed in any one of claims 1 to 11 is temporarily adhered to the surface of an adherend, and then the adhesive layer is photocured by irradiating active light to the adhesive layer, thereby increasing the bonding strength between the reinforcing film and the adherend. A method for manufacturing a device as claimed in claim 12, wherein the surface activation treatment of the adherend is performed before temporarily bonding the reinforcing film. A method for manufacturing a device as claimed in claim 13, wherein the surface activation treatment is plasma treatment. A reinforcement method is a method for attaching a reinforcement film to the surface of an adherend. After the surface of the adherend is activated, the adhesive layer of the reinforcement film as claimed in any one of claims 1 to 11 is temporarily adhered to the surface of the adherend after activation, and the adhesive layer is irradiated with active light to photo-harden the adhesive layer, thereby increasing the bonding strength between the reinforcement film and the adherend.