Reinforced film

Abstract

Provided is a reinforced film which is easy to rework immediately after bonding to an adherend, can be firmly bonded to the adherend, and can be arbitrarily set until the adhesive strength increases after bonding to the adherend. The reinforcing film (10) is provided with an adhesive layer (2) which is fixedly laminated on one main surface of a film substrate (1). The adhesive layer is formed from a photocurable composition containing a base polymer, a photocuring agent, a photoradical initiator, and an ultraviolet absorber. The photoradical initiator preferably has a maximum absorption in the wavelength range of 310 nm to 370 nm.

Description

[0001] This application is a divisional application of the application with the application date of January 31, 2020, application number 202080013960.5, and invention name "Reinforced Film". Technical Field

[0002] The present invention relates to a reinforced film attached to the surface of a device. Background Art

[0003] On the surface of optical devices such as displays and electronic devices, an adhesive film is sometimes pasted for purposes such as surface protection and imparting impact resistance. Such an adhesive film usually has an adhesive layer laminated on the main surface of a film substrate and is attached to the device surface by means of this adhesive layer.

[0004] In the state before use such as device assembly, processing, and transportation, by temporarily pasting an adhesive film on the surface of the device or device components, damage and breakage of the adherend can be suppressed. Thus, the adhesive film temporarily pasted for temporary surface protection is required to be easily peeled off from the adherend and no residual adhesive is generated on the adherend.

[0005] Patent Document 1 discloses an adhesive film that is used in a state of being attached to the device surface not only during device assembly, processing, transportation, etc., but also during device use. Such an adhesive film not only protects the surface but also has functions of dispersing impact on the device and imparting rigidity to a flexible device to enhance the device.

[0006] When an adhesive film is attached to an adherend, sometimes adhesion defects such as air bubble entrapment and deviation of the attachment position occur. In the case of adhesion defects, an operation of peeling the adhesive film from the adherend and attaching another adhesive film (rework) is performed. Since the adhesive film used as an engineering material is designed on the premise of being peeled off from the adherend, it is easy to rework. On the other hand, a reinforced film designed for permanent bonding is generally not supposed to be peeled off from the device but is firmly bonded to the device surface, so it is difficult to rework.

[0007] Patent Document 2 discloses an adhesive film having an adhesive layer, which is designed to have low adhesiveness immediately after being attached to the adherend and its adhesive force increases with time. Patent Document 3 discloses an adhesive film having a photocurable adhesive layer on the surface of a hard coating film. Since these adhesive films are easily peeled off from the adherend immediately after being attached to the adherend and their adhesive force increases with time, heat, light energy, etc., and they are firmly bonded to the adherend, they can be used as a reinforced film with reworkability.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-132977

[0011] Patent Document 2: WO 2015 / 163115

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 2015-217530 Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] When using an adhesive whose adhesive force to an adherend changes over time to obtain a reinforced film, after the reinforced film is adhered to the adherend, it is necessary to perform inspection of the adhered state, rework, etc. within a specified time until the adhesive force increases. In addition, when the reinforced film is adhered to the entire surface of a device or a device component and then a process such as removing the reinforced film from a part of the region is performed, the process needs to be performed within the period until the adhesive force increases. Therefore, an adhesive film whose adhesive force changes over time is not sufficiently flexible in terms of the lead time for the process.

[0015] On the other hand, a photocurable adhesive can arbitrarily set the timing of curing after being adhered to an adherend and can flexibly respond to the lead time of the process. However, if a reinforced film having a photocurable adhesive is adhered to an adherend and a semi-finished product in a state before the photocuring of the adhesive is stored for a long time, the adhesive force to the adherend will increase even without light irradiation for curing, and it may be difficult to peel the reinforced film from the adherend. In view of this problem, an object of the present invention is to provide a reinforced film that is less likely to cause a change in the adhesive force of a photocurable adhesive over time even when a semi-finished product in a state adhered to an adherend is stored for a long time.

[0016] Means for Solving the Problems

[0017] The reinforced film of the present invention has an adhesive layer fixed on one main surface of a film substrate. The adhesive layer is formed of a photocurable composition containing a base polymer, a photo-curing agent, a photo-radical initiator, and an ultraviolet absorber. The photocurable composition constituting the adhesive layer preferably contains 0.1 to 10 parts by weight of an ultraviolet absorber with respect to 100 parts by weight of the base polymer. Examples of the ultraviolet absorber include triazine compounds.

[0018] From the viewpoint of suppressing the generation of radicals by the photo-radical initiator due to light from a fluorescent lamp or the like, as the photo-radical initiator, a photo-radical initiator having a maximum absorption in the wavelength range of 310 nm to 370 nm and not showing a maximum absorption at a long wavelength greater than 380 nm is preferably used.

[0019] The light transmittance of the adhesive layer at a wavelength of 350 nm is, for example, about 3 to 70%. The light transmittance of the reinforced film as a laminate of the adhesive layer and the thin film substrate at a wavelength of 350 nm is, for example, about 3 to 70%. The light transmittance of the adhesive layer at the maximum absorption wavelength of the photoinitiator is preferably about 3 to 70%. The light transmittance of the reinforced film at the maximum absorption wavelength of the photoinitiator is preferably about 3 to 70%.

[0020] As the base polymer of the adhesive layer, an acrylic polymer can be used, for example. It is preferable that a crosslinked structure is introduced into the base polymer of the adhesive layer. For example, the base polymer contains a hydroxyl group-containing monomer and / or a carboxyl group-containing monomer as monomer units, and a crosslinking agent such as a polyfunctional isocyanate compound or a polyfunctional epoxy compound is bonded to these functional groups, thereby introducing a crosslinked structure.

[0021] The photocuring agent of the adhesive layer is, for example, a polyfunctional (meth)acrylate. The functional group equivalent of the photocuring agent is preferably about 100 to 500 g / eq.

[0022] Preferably, the adhesive strength of the reinforced film after photocuring the adhesive layer with the polyimide film is 5 times or more the adhesive strength of the reinforced film before photocuring the adhesive layer with the polyimide film.

[0023] Effects of the Invention

[0024] The reinforced film of the present invention is formed of a photocurable composition for the adhesive layer, and after bonding to an adherend, the adhesive layer is photocured, thereby increasing the adhesive strength with the adherend. Since the adhesive strength with the adherend before photocuring is small and it is easy to rework, a high adhesive strength is exhibited after photocuring. The adhesive composition can suppress the photocuring reaction caused by light from a fluorescent lamp or the like in the storage environment by further containing an ultraviolet absorber on the basis of the base polymer, the photocuring agent, and the photoinitiator. Therefore, the reinforced film can be stored for a long time before bonding to the adherend and in the state before photocuring after bonding to the adherend, and can flexibly cope with the lead time of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a cross-sectional view showing the laminated structure of the reinforced film.

[0026] Figure 2 It is a cross-sectional view showing the laminated structure of the reinforced film.

[0027] Figure 3 It is a cross-sectional view showing an apparatus to which the reinforced film is attached. DETAILED DESCRIPTION

[0028] Figure 1It is a cross-sectional view showing an embodiment of the reinforcing film. The reinforcing film 10 has an adhesive layer 2 on one main surface of the 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 formed from a photocurable composition, and is cured by irradiation with active light such as ultraviolet rays, and the bonding strength with the adherend increases.

[0029] Figure 2 It is a cross-sectional view of the reinforcing film in which a release film 5 is temporarily adhered to the main surface of the adhesive layer 2. Figure 3 It is a cross-sectional view showing a state in which the reinforcing film 10 is attached to the surface of the device 20.

[0030] The release film 5 is peeled off from the surface of the adhesive layer 2, and the exposed surface of the adhesive layer 2 is adhered to the surface of the device 20, whereby the reinforcing film 10 is attached to the surface of the device 20. In this state, the adhesive layer 2 is before photocuring, and the reinforcing film 10 (adhesive layer 2) is temporarily adhered to the device 20. By photocuring the adhesive layer 2, the adhesive 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.

[0031] "Fixing" means a state in which two laminated layers are firmly bonded and it is impossible or difficult to peel at the interface between the two. "Temporary adhesion" means a state in which the adhesive force between two laminated layers is small and it is easy to peel at the interface between the two.

[0032] Figure 2 In the shown reinforcing film, the film substrate 1 and the adhesive layer 2 are fixed, and the release film 5 is temporarily adhered to the adhesive layer 2. If the film substrate 1 and the release film 5 are peeled off, peeling will occur at the interface between the adhesive layer 2 and the release film 5, and the state where the adhesive layer 2 is fixed to the film substrate 1 is maintained. No adhesive remains on the peeled release film 5.

[0033] For Figure 3 Regarding the device with the reinforcing film 10 attached as shown, the device 20 and the adhesive layer 2 are in a temporarily adhered state before the adhesive layer 2 is photocured. If the film substrate 1 and the device 20 are peeled off, peeling will occur at the interface between the adhesive layer 2 and the device 20, and the state where the adhesive layer 2 is fixed to the film substrate 1 is maintained. Since no adhesive remains on the device 20, rework is easy. After the adhesive layer 2 is photocured, the adhesive force between the adhesive layer 2 and the device 20 increases, so it is difficult to peel the film substrate 1 from the device 20. If the two are peeled, cohesive failure of the adhesive layer 2 sometimes occurs.

[0034] [Film substrate]

[0035] As the film substrate 1, a plastic film can be used. In order to fix the film substrate 1 to the adhesive layer 2, it is preferable not to apply a release treatment to the surface of the film substrate 1 where the adhesive layer 2 is provided.

[0036] The thickness of the film substrate is about 4 to 500 μm, for example. From the perspective of enhancing the equipment by imparting rigidity, cushioning impact, etc., the thickness of the film substrate 1 is preferably 12 μm or more, more preferably 30 μm, and further preferably 45 μm or more. From the perspective of making the reinforced film flexible and improving operability, the thickness of the film substrate 1 is preferably 300 μm or less, more preferably 200 μm or less. From the perspective of balancing 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 , particularly preferably 400 - 2700 kg / cm 2 .

[0037] Examples of the plastic material constituting the film substrate 1 include polyester resins, polyolefin resins, cyclic olefin resins, polyamide resins, polyimide resins, etc. In the reinforced 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 film substrate 1 side, it is preferable that the film substrate 1 is transparent to the active light used in the curing of the adhesive layer. Considering both mechanical strength and transparency, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate can be suitably used.

[0038] When transparency is required for the reinforced film (for example, in optical applications such as displays), the total light transmittance of the film substrate 1 is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. The haze of the film substrate 1 is preferably 2% or less, more preferably 1% or less, further preferably 0.7% or less, and particularly preferably 0.5% or less. When the adhesive layer 2 is cured by irradiating active light from the film substrate 1 side, the film substrate 1 preferably has little absorption of active light. For example, when the adhesive layer 2 is cured by irradiating ultraviolet light from the film substrate 1 side, the light transmittance of the film substrate 1 at a wavelength of 350 nm is preferably 20% or more, more preferably 30% or more. The light transmittance of the film substrate 1 at a wavelength of 350 nm can be 40% or more, 50% or more, 60% or more, or 70% or more. When the adhesive layer is cured by irradiating active light from the adherend side, it is only necessary that the adherend is transparent to the active light, and the film substrate 1 can be opaque to the active light.

[0039] On the surface of the thin film substrate 1, functional coatings such as an easy-bonding layer, an easy-sliding layer, a release layer, an antistatic layer, a hard coating, and an antireflection layer can be provided. It should be noted that, as described above, in order to fix the thin film substrate 1 to the adhesive layer 2, it is preferred not to provide a release layer on the surface of the thin film substrate 1 where the adhesive layer 2 is attached.

[0040] [Adhesive layer]

[0041] The adhesive layer 2 laminated on the thin film substrate 1 is a photocurable composition containing a base polymer, a photocuring agent, and a photo radical initiator. When the reinforced film is used for optical devices such as displays, the total light transmittance of the adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and 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.

[0042] Since the adhesive force between the adhesive layer 2 and the adherend is small before photocuring, it is easy to rework. If the adhesive layer 2 is irradiated with active light such as ultraviolet light, free radicals are generated by the photo radical initiator, and the adhesive force between the adhesive layer 2 and the adherend is increased through the radical polymerization reaction (photocuring) of the photocuring agent. Therefore, when the device is used, the reinforced film is not easily peeled off from the surface of the device, and the bonding reliability is excellent.

[0043] The photocurable adhesive is cured by irradiation with ultraviolet light or the like. Therefore, the curing timing of the adhesive layer 2 formed from the photocurable adhesive composition can be arbitrarily set, and it has the advantage of being able to flexibly respond to the lead time of the process. On the other hand, before the reinforced film is used, or in the state before photocuring after the reinforced film is adhered to the adherend, sometimes free radicals are generated by the light from a fluorescent lamp or the like in the storage environment.

[0044] The amount of free radicals generated by the light from a fluorescent lamp or the like is small enough compared to the amount of free radicals generated by the ultraviolet irradiation during photocuring. Therefore, even if the reinforced film is placed under a fluorescent lamp for a short time, the photocuring reaction hardly proceeds. However, if the reinforced film is stored under a fluorescent lamp for a long time, the cumulative amount of free radicals generated by the light from the fluorescent lamp and generated by the photo radical initiator increases, and sometimes its influence can no longer be ignored. Specifically, due to the free radicals generated by the photo radical initiator, the polymerization of the photocuring agent proceeds and the adhesive force of the adhesive increases, and sometimes it is difficult to peel the reinforced film from the adherend.

[0045] The photocurable composition constituting the adhesive layer 2 of the reinforcing film of the present invention further contains an ultraviolet absorber on the basis of a base polymer, a photocuring agent, and a photo radical initiator. By adding an ultraviolet absorber that absorbs light (ultraviolet light) in a wavelength region overlapping with the light absorption band (excitation wavelength) of the photo radical initiator, even when the reinforcing film is stored under a fluorescent lamp for a long time, the change in adhesive force is small, and the adhesive force can be appropriately increased during light irradiation.

[0046] <Composition of the adhesive>

[0047] Hereinafter, preferred embodiments of each of the base polymer, photocuring agent, photo radical initiator, and ultraviolet absorber constituting the photocurable composition will be described in turn.

[0048] (Base polymer)

[0049] The base polymer is the main constituent of the adhesive composition. The type of the base polymer is not particularly limited, and an acrylic polymer, a silicone polymer, a urethane polymer, a rubber polymer, etc. may be appropriately selected. In particular, from the viewpoints of excellent optical transparency and adhesiveness and easy control of adhesiveness, the adhesive composition preferably contains an acrylic polymer as the base polymer, and preferably 50% by weight or more of the adhesive composition is an acrylic polymer.

[0050] As the acrylic polymer, a substance containing (meth)acrylic acid alkyl ester as the main monomer component is preferably used. It should be noted that in this specification, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0051] As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group can be suitably used. The alkyl group of the (meth)acrylic acid alkyl ester can be linear or branched. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, 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, aralkyl (meth)acrylate, and the like.

[0052] The content of the (meth)acrylic acid alkyl ester is preferably 40% by weight or more, more preferably 50% by weight or more, and further preferably 55% by weight or more based on the total amount of the monomer components constituting the base polymer.

[0053] The acrylic base polymer preferably contains a monomer component having a crosslinkable functional group as a copolymer component. Examples of the monomer having a crosslinkable functional group include a hydroxyl group-containing monomer and a carboxyl group-containing monomer. The hydroxyl group and carboxyl group of the base polymer will become reaction sites with the crosslinking agent described later. For example, in the case of using an isocyanate-based crosslinking agent, it is preferable to contain a hydroxyl group-containing monomer as a copolymer component of the base polymer. In the case of using an epoxy-based crosslinking agent, it is preferable to contain a carboxyl group-containing monomer as a copolymer component of the base polymer. By introducing a crosslinked structure into the base polymer, the cohesive force is increased, the adhesive force of the adhesive layer 2 is increased, and there is a tendency that the residual glue on the adherend is reduced during rework.

[0054] Examples of the hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 4-(hydroxymethyl)cyclohexylmethyl (meth)acrylate, etc. Examples of the carboxyl group-containing monomers include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc.

[0055] For the acrylic base polymer, the total amount of the hydroxy group-containing monomer and the carboxyl group-containing monomer is preferably 1 to 30% by weight, more preferably 3 to 25% by weight, and still more preferably 5 to 20% by weight, relative to the total amount of the constituent monomer components. The content of the (meth)acrylate containing a hydroxy group is particularly preferably within the above range.

[0056] The acrylic base polymer may contain nitrogen-containing monomers such as N-vinylpyrrolidone, N-methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acrylmorpholine, N-vinylcarboxylic acid amides, N-vinylcaprolactam, etc. as the constituent monomer components.

[0057] The acrylic base polymer may contain monomer components other than those described above. The acrylic base polymer may contain, for example, cyano group-containing monomers, vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphoric acid group-containing monomers, acid anhydride group-containing monomers, etc. as the monomer components.

[0058] The adhesive properties of the adhesive before photocuring are easily affected by the constituent components and molecular weight of the base polymer. There is a tendency that the larger the molecular weight of the base polymer, the harder the adhesive. The weight average molecular weight of the acrylic base polymer is preferably 100,000 to 5,000,000, more preferably 300,000 to 3,000,000, and still more preferably 500,000 to 2,000,000. It should be noted that in the case where a crosslinked structure is introduced into the base polymer, the molecular weight of the base polymer refers to the molecular weight before the introduction of the crosslinked structure.

[0059] There is a tendency that the higher the content of the high-Tg monomer component in the basic polymer composition, the harder the adhesive. It should be noted that the high-Tg monomer refers to a monomer with a high glass transition temperature (Tg) of the homopolymer. As monomers with a Tg of the homopolymer of 40 °C or higher, examples include: dicyclopentanyl methacrylate (Tg: 175 °C), dicyclopentanyl acrylate (Tg: 120 °C), isobornyl methacrylate (Tg: 173 °C), isobornyl acrylate (Tg: 97 °C), methyl methacrylate (Tg: 105 °C), 1-adamantyl methacrylate (Tg: 250 °C), 1-adamantyl acrylate (Tg: 153 °C), etc. (meth)acrylic acid monomers; acryloylmorpholine (Tg: 145 °C), dimethylacrylamide (Tg: 119 °C), diethylacrylamide (Tg: 81 °C), dimethylaminopropylacrylamide (Tg: 134 °C), isopropylacrylamide (Tg: 134 °C), 2-hydroxyethylacrylamide (Tg: 98 °C), etc. vinyl monomers containing an amide group; methacrylic acid (Tg: 228 °C), acrylic acid (Tg: 106 °C), etc. acid monomers; N-vinylpyrrolidone (Tg: 54 °C), etc.

[0060] For acrylic acid-based basic polymers, relative to the total amount of the constituent monomer components, the content of monomers with a Tg of the homopolymer of 40 °C or higher is preferably 1 to 50% by weight, more preferably 3 to 40% by weight. In order to form an adhesive layer with appropriate hardness and excellent reworkability, as the monomer component of the basic polymer, it is preferably to contain a monomer component with a Tg of the homopolymer of 80 °C or higher, and more preferably to contain a monomer component with a Tg of the homopolymer of 100 °C or higher. For acrylic acid-based basic polymers, relative to the total amount of the constituent monomer components, the content of monomers with a Tg of the homopolymer of 100 °C or higher is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, further preferably 1% by weight or more, and particularly preferably 3% by weight or more.

[0061] By polymerizing the above monomer components using various known methods such as solution polymerization, emulsion polymerization, bulk polymerization, etc., an acrylic acid-based polymer as the basic polymer can be obtained. From the perspectives of the balance of properties such as the adhesive force and holding force of the adhesive, cost, etc., the solution polymerization method is preferred. As the solvent for solution polymerization, ethyl acetate, toluene, etc. can be used. The solution concentration is usually about 20 to 80% by weight. As the polymerization initiator for solution polymerization, various known substances such as azo compounds and peroxides can be used. A chain transfer agent can also be used to adjust the molecular weight. The reaction temperature is usually about 50 to 80 °C, and the reaction time is usually about 1 to 8 hours.

[0062] (Crosslinking agent)

[0063] From the perspective of imparting appropriate cohesion to the adhesive, it is preferable to introduce a crosslinked structure into the base polymer. For example, a crosslinking agent is added to the solution after polymerization of the base polymer, and heating is carried out as required to introduce the crosslinked structure. Examples of the crosslinking agent include 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 and carboxyl groups introduced into the base polymer to form a crosslinked structure. From the perspective of high reactivity with the hydroxyl groups and carboxyl groups of the base polymer and easy introduction of the crosslinked structure, isocyanate crosslinking agents and epoxy crosslinking agents are preferred.

[0064] As the isocyanate crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule can be used. Examples of the isocyanate crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; trimethylolpropane / toluene diisocyanate trimer adduct (e.g., "Coronate L" manufactured by Tosoh Corporation), trimethylolpropane / hexamethylene diisocyanate trimer adduct (e.g., "Coronate HL" manufactured by Tosoh Corporation), trimethylolpropane adduct of xylylene diisocyanate (e.g., "Takenate D110N" manufactured by Mitsui Chemicals, Inc.), isocyanurate form of hexamethylene diisocyanate (e.g., "Coronate HX" manufactured by Tosoh Corporation), and other isocyanate adducts.

[0065] As an epoxy crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in one molecule can be used. The epoxy group of the epoxy crosslinking agent may be a glycidyl group. Examples of the epoxy crosslinking agent include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, dehydrated sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, diethyl adipate diglycidyl ester, phthalic acid diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, etc. As the epoxy crosslinking agent, commercially available products such as "Denacol" manufactured by Nagase ChemteX Corporation, "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical Company, Inc. can be used.

[0066] The amount of the crosslinking agent can be appropriately adjusted according to the composition, molecular weight, etc. of the base polymer. With respect to 100 parts by weight of the base polymer, the amount of the crosslinking agent is about 0.01 to 10 parts by weight, 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 (parts by weight) of the crosslinking agent with respect to 100 parts by weight of the base polymer 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 making the amount of the crosslinking agent larger than that of a conventional acrylic optical transparent adhesive for permanent bonding and making the adhesive have an appropriate hardness, there is a tendency that the residual adhesive on the adherend is reduced during rework and the reworkability is improved.

[0067] In order to promote the formation of the crosslinked structure, a crosslinking catalyst can be used. Examples of the crosslinking catalyst include organic metals such as tetra-n-butyl titanate, tetra-isopropyl titanate, iron acetylacetonate, butyltin oxide, dioctyltin dilaurate, dibutyltin dilaurate, etc. Generally, with respect to 100 parts by weight of the base polymer, the amount of the crosslinking catalyst is 1 part by weight or less.

[0068] (Photoinitiator)

[0069] The adhesive composition constituting the adhesive layer 2 further contains a photoinitiator on the basis of the base polymer. If the adhesive layer 2 formed from the photocurable adhesive composition is photocured after being bonded to the adherend, the adhesive force between the adhesive layer 2 and the adherend will increase.

[0070] As the photoinitiator, a compound having two or more ethylenically unsaturated bonds in one molecule is preferred. In addition, the photoinitiator is preferably a compound that shows compatibility with the base polymer. From the perspective of showing moderate compatibility with the base polymer, the photoinitiator is preferably a substance that is liquid at room temperature. By making the photoinitiator compatible with the base polymer and uniformly dispersed in the composition, the contact area with the adherend can be ensured, and an adhesive layer 2 with high transparency can be formed. In addition, by making the base polymer and the photoinitiator show moderate compatibility, it is easy to uniformly introduce a crosslinked structure based on the photoinitiator into the photocured adhesive layer 2, and there is a tendency for the adhesive force between the adhesive layer 2 and the adherend to increase appropriately.

[0071] The compatibility between the base polymer and the photoinitiator is mainly affected by the compound structure. The structure and compatibility of the compound can be evaluated by, for example, the Hansen solubility parameter, and there is a tendency that the smaller the difference in the solubility parameters between the base polymer and the photoinitiator, the higher the compatibility.

[0072] From the perspective of high compatibility with acrylic base polymers, polyfunctional (meth)acrylates are preferably used as photoinitiators. Examples of polyfunctional (meth)acrylates 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, alkane diol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, di(trimethylolpropane) 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, urethane (meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate, isoprene (meth)acrylate, etc. Among these, polyethylene glycol di(meth)acrylate or polypropylene glycol di(meth)acrylate is preferred from the perspective of excellent compatibility with acrylic base polymers, and polyethylene glycol di(meth)acrylate is particularly preferred.

[0073] The compatibility between the base polymer and the photoinitiator is also affected by the molecular weight of the compound. There is a tendency that the smaller the molecular weight of the photocurable compound, the higher the compatibility with the base polymer. From the perspective of compatibility with the base polymer, the molecular weight of the photoinitiator is preferably 1500 or less, more preferably 1000 or less, still more preferably 500 or less, and particularly preferably 400 or less.

[0074] In the adhesive layer 2 before photocuring, the properties of the base polymer are the main determinants of adhesiveness. Therefore, if the base polymers of the adhesive compositions are the same, even if the types of photoinitiators are different, the differences in the adhesive properties of the adhesive layer before photocuring are small. The type and content of the photoinitiator mainly affect the adhesive strength of the adhesive layer after photocuring. The smaller the functional group equivalent (i.e., the more the number of functional groups per unit molecular weight on average) and the larger the content of the photoinitiator, the more the difference in adhesive strength can be formed before and after photocuring.

[0075] From the perspective of high compatibility with the base polymer and increasing the adhesive strength after photocuring, the functional group equivalent (g / eq) of the photoinitiator is preferably 500 or less, more preferably 400 or less, still more preferably 300 or less, and particularly preferably 200 or less. On the other hand, if the functional group equivalent of the photoinitiator is too small, sometimes the crosslinking point density of the adhesive layer after photocuring will increase and the adhesiveness will decrease. Therefore, the functional group equivalent of the photoinitiator is preferably 80 or more, more preferably 100 or more, still more preferably 130 or more.

[0076] In the combination of an acrylic base polymer and a polyfunctional acrylate photoinitiator, when the functional group equivalent of the photoinitiator is small, the interaction between the base polymer and the photoinitiator is strong, and there is a tendency for the initial adhesive strength to increase. In the use of the present invention, there are cases where an excessive increase in the initial adhesive strength leads to a decrease in reworkability. From the perspective of maintaining the adhesive strength between the adhesive layer 2 before photocuring and the adherend within an appropriate range, it is also preferred that the functional group equivalent of the photoinitiator is within the above range.

[0077] Relative to 100 parts by weight of the base polymer, the content of the photoinitiator in the adhesive composition is preferably 10 to 50 parts by weight. By making the blending amount of the photoinitiator within the above range, the adhesiveness between the adhesive layer after photocuring and the adherend can be adjusted to an appropriate range. The content of the photoinitiator is more preferably 15 to 45 parts by weight, and still more preferably 20 to 40 parts by weight, relative to 100 parts by weight of the base polymer.

[0078] (Photo radical initiator)

[0079] A photo radical initiator generates radicals upon irradiation with actinic light, and promotes the radical polymerization reaction of a photo-curing agent by the migration of radicals from the photo radical initiator to the photo-curing agent. As the photo radical initiator (photo radical generator), a substance that generates radicals upon irradiation with visible light or ultraviolet light having a wavelength of less than 450 nm is preferred, and examples thereof include hydroxy ketones, benzyl dimethyl ketals, amino ketones, acylphosphine oxides, benzophenones, triazine derivatives containing a trichloromethyl group, and the like. The photo radical initiator can be used alone or in combination of two or more.

[0080] In the case where transparency is required for the adhesive layer 2, the photo radical initiator preferably has low sensitivity to light (visible light) having a wavelength greater than 400 nm. For example, a photo radical initiator having an extinction coefficient at a wavelength of 405 nm of 1×10 2 [mLg -1 cm -1 or less is preferably used. In addition, if a photo radical initiator having low sensitivity to visible light is used, the amount of radicals generated by external light in the storage environment is small, and thus the storage stability of the reinforcing film can be improved.

[0081] From the viewpoint of improving the storage stability of the reinforcing film, a photo radical initiator that does not exhibit maximum absorption at a wavelength greater than 380 nm is preferably used. A photo radical initiator that exhibits maximum absorption at a wavelength greater than 380 nm easily absorbs light from a fluorescent lamp (mainly the mercury bright line at 405 nm) to generate photo radicals. If the maximum wavelength of light absorption of the photo radical initiator is 370 nm or less, the amount of radicals generated by light in the storage environment such as a fluorescent lamp is small. Therefore, even when the reinforcing film is exposed to a fluorescent lamp for a long time, a high effective concentration of the photo radical initiator can be maintained. In addition, from the viewpoint of suppressing the generation of photo radicals caused by ultraviolet rays from a fluorescent lamp (mainly the mercury bright line at a wavelength of 365 nm) and improving the storage stability of the reinforcing film, the photo radical initiator is preferably a substance that does not exhibit maximum absorption at a wavelength greater than 360 nm.

[0082] In order to achieve high storage stability and enable the adhesive force with the adherend to be increased by light irradiation even after long-term storage, the maximum wavelength of light absorption of the photoinitiator contained in the adhesive layer is preferably 370 nm or less, more preferably 355 nm or less. On the other hand, in order to improve the photocuring efficiency based on ultraviolet irradiation, the photoinitiator preferably has a maximum light absorption at a wavelength greater than 310 nm. In summary, in order to improve the storage stability of the reinforcing film, the photoinitiator contained in the adhesive layer 2 is preferably a substance that does not have a maximum absorption at a wavelength greater than 380 nm and has a maximum absorption in the wavelength range of 310 to 370 nm, more preferably a substance that does not have a maximum absorption at a wavelength greater than 360 nm and has a maximum absorption in the wavelength range of 310 to 355 nm. The maximum absorption wavelength of the photoinitiator is further preferably 315 to 350 nm, particularly preferably 320 to 345 nm.

[0083] The content of the photoinitiator in the adhesive layer 2 is preferably 0.01 to 1 part by weight, more preferably 0.02 to 0.7 part by weight, and further preferably 0.03 to 0.5 part by weight, based on 100 parts by weight of the base polymer. The content of the photoinitiator in the adhesive layer 2 is preferably 0.005 to 0.5 part by weight, more preferably 0.01 to 0.4 part by weight, and further preferably 0.02 to 0.3 part by weight, based on 100 parts by weight of the photocuring agent. If the content of the photoinitiator in the adhesive layer is too small, the photocuring reaction may not proceed sufficiently even when irradiated with ultraviolet light. If the content of the photoinitiator is too large, the adhesive force is likely to increase due to the photocuring reaction in the storage environment even when a UV absorber is added, and sometimes it may be difficult to rework the reinforcing film.

[0084] (UV absorber)

[0085] The UV absorber has the effect of suppressing the photocuring reaction in the storage environment of the reinforcing film. For a composition containing a UV inhibitor in addition to the photoinitiator, even when irradiated with light having a wavelength to which the photoinitiator is sensitive from a fluorescent lamp or the like, since the amount of light absorption by the UV absorber is large, the amount of light absorbed by the photoinitiator is relatively reduced. Therefore, the generation of free radicals can be suppressed, and photocuring (radical polymerization reaction of the photocuring agent) caused by light from a fluorescent lamp or the like can be suppressed.

[0086] Examples of the ultraviolet absorber include benzotriazole ultraviolet absorbers, benzophenone ultraviolet absorbers, triazine ultraviolet absorbers, salicylate ultraviolet absorbers, cyanoacrylate ultraviolet absorbers, and the like. From the viewpoint of high absorbability of long-wavelength ultraviolet rays with wavelengths of 320 to 400 nm and excellent compatibility with the base polymer and the photoinitiator, triazine ultraviolet absorbers are preferred. Among the triazine ultraviolet absorbers, triazine ultraviolet absorbers containing a hydroxyl group are preferred, and hydroxyphenyltriazine ultraviolet absorbers are particularly preferred.

[0087] As the ultraviolet absorber, commercially available products can be used. Examples of the commercially available products of triazine ultraviolet absorbers include the reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl and [(alkoxy)methyl]oxirane ("TINUVIN 400" manufactured by BASF), the reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine and (2-ethylhexyl)-glycidate ("TINUVIN 405" manufactured by BASF), (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine ("TINUVIN460" manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol ("TINUVIN577" manufactured by BASF), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine ("TINUVIN 479" manufactured by BASF), and the like.

[0088] The content of the ultraviolet absorber in the adhesive layer 2 is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the base polymer. The content of the ultraviolet absorber can be 0.3 parts by weight or more, 0.5 parts by weight or more, 1 part by weight or more, 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 with respect to 100 parts by weight of the base polymer. The content of the ultraviolet absorber can be 9 parts by weight or less, 8 parts by weight or less, 7 parts by weight or less, 6 parts by weight or less, or 5 parts by weight or less with respect to 100 parts by weight of the base polymer. The content of the ultraviolet absorber can be 5 times or more, 10 times or more, 30 times or more, or 50 times or more with respect to the content of the photo-radical initiator. The content of the ultraviolet absorber can be 5000 times or less, 3000 times or less, 1000 times or less, 500 times or less, 300 times or less, or 100 times or less with respect to the content of the photo-radical initiator.

[0089] From the perspective of suppressing the polymerization reaction of the inhibition-enhanced film in the storage state, it is preferable that the content of the ultraviolet absorber is relatively large. On the other hand, if the content of the ultraviolet absorber is too large, even when ultraviolet irradiation is carried out for photocuring, most of the excitation light will be absorbed by the ultraviolet absorber, and the amount of light absorbed by the photoinitiator will decrease. Therefore, the generation of free radicals may be hindered, and even when ultraviolet light is irradiated, the curing may be insufficient. Therefore, in order to suppress the increase in adhesion caused by the reaction in the storage environment and appropriately carry out the photocuring reaction during light irradiation to increase the adhesion, it is preferable that the content of the ultraviolet absorber is within the above range.

[0090] In order to suppress photocuring (free radical polymerization reaction of the photoinitiator) caused by light from a fluorescent lamp or the like, it is preferable that the absorption wavelength of the ultraviolet absorber overlaps with the light absorption band (excitation wavelength) of the photoinitiator. The light transmittance of the adhesive layer containing the ultraviolet absorber at the maximum absorption wavelength of the photoinitiator is preferably 70% or less, more preferably 65% or less, and further preferably 60% or less. As the addition amount of the ultraviolet absorber increases, the light transmittance of the adhesive layer at the maximum absorption wavelength of the photoinitiator decreases. The light transmittance of the adhesive layer at the maximum absorption wavelength of the photoinitiator is more preferably 50% or less, and further preferably 40% or less. The light transmittance of the adhesive layer at the maximum absorption wavelength of the photoinitiator can be 35% or less, 30% or less, 25% or less, or 20% or less.

[0091] On the other hand, when the light transmittance of the adhesive layer at the maximum absorption wavelength of the photoinitiator is too small, the amount of light absorbed by the ultraviolet absorber is large, and even when ultraviolet light is irradiated for photocuring, the amount of light absorbed by the photoinitiator is small. Therefore, the amount of generated free radicals is small, and sometimes the photocuring of the adhesive may not proceed sufficiently, or the time required for photocuring becomes long and the curing efficiency decreases. Therefore, the light transmittance of the adhesive layer at the maximum absorption wavelength of the photoinitiator is preferably 3% or more, more preferably 4% or more, and further preferably 5% or more. The light transmittance of the adhesive layer at the maximum absorption wavelength of the photoinitiator can be 7% or more, 10% or more, 13% or more, or 15% or more.

[0092] By adjusting the type and / or addition amount of the ultraviolet absorber according to the type (maximum absorption wavelength) of the photoinitiator, the light transmittance of the adhesive layer at the maximum absorption wavelength of the photoinitiator can be adjusted to the above range. When the photoinitiator has multiple maximum absorptions, it is preferable that the light transmittance of the adhesive layer at the maximum absorption wavelength closest to 365 nm (mercury bright line of the fluorescent lamp) is within the above range.

[0093] As described above, the photo radical initiator is preferably a substance having a maximum absorption in the wavelength range of 310 to 370 nm. When the photo radical initiator has a maximum absorption in the wavelength range of 310 to 370 nm, the light transmittance of the adhesive layer at the maximum absorption wavelength in this wavelength range is preferably in the above range.

[0094] In addition, from the perspective of suppressing the photocuring of the adhesive caused by light in a storage environment such as a fluorescent lamp regardless of the maximum absorption wavelength of the photo radical initiator and ensuring the curing efficiency during light irradiation, the light transmittance of the adhesive layer at a wavelength of 350 nm is preferably 3 to 70%, more preferably 4 to 65%, and further preferably 5 to 60%. The light transmittance of the adhesive layer at a wavelength of 350 nm can be 50% or less, 40% or less, 35% or less, 30% or less, 25% or less, or 20% or less. The light transmittance of the adhesive layer at a wavelength of 350 nm can be 7% or more, 10% or more, 13% or more, or 15% or more.

[0095] (Other additives)

[0096] In addition to the components exemplified above, the adhesive layer may also contain additives such as silane coupling agents, tackifiers, plasticizers, softeners, antioxidants, anti-degradants, fillers, colorants, surfactants, antistatic agents, etc. within the range that does not impair the characteristics of the present invention.

[0097] [Production of Reinforcing Film]

[0098] A reinforcing film can be obtained by laminating a photocurable adhesive layer 2 on a film substrate 1. The adhesive layer 2 can be directly formed on the film substrate 1, or an adhesive layer formed in a sheet shape on another substrate can be transferred to the film substrate 1.

[0099] The above adhesive composition is applied to a substrate by roll coating, roll licking coating, gravure coating, reverse coating, roll brushing, spraying, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, etc., and the solvent is removed by drying as needed to form an adhesive layer. As the drying method, a suitable 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.

[0100] The thickness of the adhesive layer 2 is, for example, about 1 to 300 μm. There is a tendency that the greater the thickness of the adhesive layer 2, the higher the adhesiveness to the adherend. On the other hand, when the thickness of the adhesive layer 2 is too large, the fluidity before photocuring is high, and it may be difficult to operate. 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.

[0101] When the adhesive composition contains a crosslinking agent, it is preferable to carry out crosslinking by heating or curing simultaneously with or after the drying of the solvent. The heating temperature and heating time can be appropriately set according to the type of crosslinking agent used. Generally, crosslinking is carried out by heating in the range of 20°C to 160°C for about 1 minute to 7 days. The heating for drying and removing the solvent can also serve as the heating for crosslinking.

[0102] By introducing a crosslinked structure into the base polymer, the gel fraction increases. There is a tendency that the higher the gel fraction, the harder the adhesive, and when peeling the reinforcing film from the adherend due to rework or the like, the residual adhesive on the adherend is inhibited. The gel fraction of the adhesive layer 2 before photocuring 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 photocuring can be 70% or more or 75% or more.

[0103] Since the adhesive contains unreacted photocuring agent, the gel fraction of the adhesive layer 2 before photocuring is generally 90% or less. When the gel fraction of the adhesive layer 2 before photocuring is too large, the anchoring force to the adherend sometimes decreases and the initial adhesiveness is insufficient. Therefore, the gel fraction of the adhesive layer 2 before photocuring is preferably 85% or less, more preferably 80% or less.

[0104] The gel fraction can be determined in the form of an insoluble component with respect to a solvent such as ethyl acetate. Specifically, it can be determined in the form of the weight fraction (unit: wt%) of the insoluble component after immersing the adhesive layer in ethyl acetate at 23°C for 7 days relative to the weight of the sample before immersion. Generally, the gel fraction of a polymer is equal to the crosslinking degree, and the more crosslinked parts in the polymer, the greater the gel fraction. In addition, the more the amount of the photocuring agent, the smaller the gel fraction.

[0105] After introducing a crosslinked structure into the polymer by the crosslinking agent, the photocuring agent also remains in an unreacted state. Therefore, a photocurable adhesive layer 2 containing a base polymer and a photocuring agent is formed. When the adhesive layer 2 is formed on the thin film substrate 1, for the purpose of protecting the adhesive layer 2 and the like, it is preferable to attach a release film 5 on the adhesive layer 2. Crosslinking can also be carried out after attaching the release film 5 on the adhesive layer 2.

[0106] When the adhesive layer 2 is formed on other substrates, after drying the solvent, the adhesive layer 2 is transferred onto the thin film substrate 1, whereby a reinforced film can be obtained. The substrate used to form the adhesive layer can also be directly used as the release film 5.

[0107] As the release film 5, plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester films are preferably used. The thickness of the release film is generally 3 to 200 μm, preferably about 10 to 100 μm. It is preferable to perform a release treatment on the contact surface between the release film 5 and the adhesive layer 2 using a release agent such as a silicone-based, fluorine-based, long-chain alkyl-based, or fatty acid amide-based agent or silica powder. By performing a release treatment on the surface of the release film 5, when the thin film substrate 1 and the release film 5 are peeled off, peeling occurs at the interface between the adhesive layer 2 and the release film 5, maintaining the state where the adhesive layer 2 adheres to the thin film substrate 1.

[0108] The reinforced film for optical applications such as displays preferably has high visible light transparency. The total light transmittance of the reinforced film 10 is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. The haze of the thin film substrate 1 of the reinforced film 10 is preferably 2% or less, more preferably 1% or less, further preferably 0.7% or less, and particularly preferably 0.5% or less.

[0109] The light transmittance of the reinforced film 10 with the adhesive layer 2 fixedly laminated on the thin film substrate 1 at a wavelength of 350 nm is preferably 3 to 70%. The light transmittance of the reinforced film 10 at a wavelength of 350 nm is more preferably 4 to 65%, and further preferably 5 to 60%. The light transmittance of the reinforced film 10 at a wavelength of 350 nm can be 50% or less, 40% or less, 35% or less, 30% or less, 25% or less, or 20% or less. The light transmittance of the reinforced film 10 at a wavelength of 350 nm can be 7% or more, 10% or more, 13% or more, or 15% or more.

[0110] When the photoinitiator contained in the adhesive layer 2 has a maximum absorption in the wavelength range of 310 to 370 nm, the light transmittance of the reinforced film 10 at the maximum absorption wavelength is preferably 3 to 70%, more preferably 4 to 65%, and further preferably 5 to 60%. The light transmittance of the reinforced film 10 at the maximum absorption wavelength of the photoinitiator can be 50% or less, 40% or less, 35% or less, 30% or less, 25% or less, or 20% or less. The light transmittance of the reinforced film 10 at the maximum absorption wavelength of the photoinitiator can be 7% or more, 10% or more, 13% or more, or 15% or more.

[0111] As described above, by making the light transmittance of the thin film substrate 1 and the adhesive layer 2 within a specified range, the reinforced film 10 having the light transmittance within the above range can be obtained. Specifically, from the perspective of improving the photocuring efficiency of the adhesive layer 2, the thin film substrate 1 is preferably a substance having transmittance to near ultraviolet rays. On the other hand, from the perspective of suppressing the photocuring of the adhesive layer 2 in the storage state, it is preferable to add an ultraviolet absorber to the adhesive layer 2 to make it have ultraviolet absorptivity.

[0112] [Use of Reinforced Film]

[0113] The reinforced film of the present invention is used by being adhered to a device or a component constituting the device. The adhesive layer 2 of the reinforced film 10 is fixed to the thin film substrate 1, and the adhesive force to the adherend is small after being adhered to the adherend and before photocuring. Therefore, it is easy to peel the reinforced film from the adherend before photocuring, and the reworkability is excellent. In addition, before photocuring, processing such as cutting the reinforced film and removing the reinforced film from a part of the surface of the adherend can be easily performed.

[0114] The adherend to which the reinforced film is adhered is not particularly limited, and various electronic devices, optical devices, and their components can be cited. The reinforced film can be adhered to the entire surface of the adherend, or can be selectively adhered only to the part that needs to be strengthened. In addition, after adhering the reinforced film to the entire surface of the adherend, the reinforced film at the part that does not need to be strengthened can be cut and peeled off. As long as it is before photocuring, the reinforced film is in a state of being temporarily adhered to the surface of the adherend, so it can be easily peeled off from the surface of the adherend.

[0115] [Properties of Adhesive Layer before Photocuring]

[0116] (Adhesive Force)

[0117] From the perspective of being easily peeled off from the adherend and preventing residual glue on the adherend after peeling off the reinforced film, the adhesive force between the adhesive layer 2 before photocuring and the adherend is preferably 5 N / 25 mm or less, more preferably 3 N / 25 mm or less, and further preferably 2 N / 25 mm or less. The adhesive force between the adhesive layer 2 before photocuring and the adherend can be 1.5 N / 25 mm or less or 1 N / 25 mm or less. From the perspective of preventing the reinforced film from peeling off during storage and operation, the adhesive force between the adhesive layer 2 before photocuring and the adherend is preferably 0.005 N / 25 mm or more, more preferably 0.01 N / 25 mm or more, further preferably 0.02 N / 25 mm or more, and particularly preferably 0.03 N / 25 mm or more.

[0118] Regarding the reinforcing film, preferably, in the state before the adhesive layer is photocured, its adhesive force relative to the polyimide film is within the above range. In flexible display panels, flexible printed circuit boards (FPCs), devices integrating display panels and circuit boards, etc., polyimide films are generally used from the perspectives of being able to use flexible substrate materials, heat resistance, and dimensional stability. For the reinforcing film in which the adhesive layer has the above adhesive force relative to the polyimide film as the substrate, it is easy to peel before the adhesive layer is photocured, and has excellent bonding reliability after photocuring.

[0119] (Storage modulus)

[0120] The shear storage modulus G' of the adhesive layer 2 at 25°C before photocuring i is preferably 1×10 4 ~1.2×10 5 Pa. The shear storage modulus (hereinafter simply referred to as "storage modulus") can be obtained as follows: According to the method described in JIS K7244-1 "Plastics - Test Methods for Dynamic Mechanical Properties", it is measured at a heating rate of 5°C / minute in the range of -50 to 150°C under the condition of a frequency of 1 Hz, and the value at the specified temperature at this time is read to obtain it.

[0121] In substances such as adhesives that exhibit viscoelasticity, the storage modulus G' is used as an index indicating the degree of hardness. There is a high correlation between the storage modulus of the adhesive layer and the cohesive force, and there is a tendency that the higher the cohesive force of the adhesive, the greater the anchoring force on the adherend. When the storage modulus of the adhesive layer 2 before photocuring is 1×10 4 Pa or more, the adhesive has sufficient hardness and cohesive force, so when peeling the reinforcing film from the adherend, it is not easy to generate residual glue on the adherend. In addition, when the storage modulus of the adhesive layer 2 is large, the seepage of the adhesive from the end face of the reinforcing film can be suppressed. When the storage modulus of the adhesive layer 2 before photocuring is 1.2×10 5 Pa or less, it is easy to peel at the interface between the adhesive layer 2 and the adherend, and even in the case of rework, cohesive failure of the adhesive layer and residual glue on the surface of the adherend are not likely to occur.

[0122] From the perspective of improving the reworkability of the reinforcing sheet and suppressing residual glue on the adherend during rework, the storage modulus G' of the adhesive layer 2 at 25°C before photocuring i is more preferably 3×10 4 ~1×10 5 Pa, and further preferably 4×10 4 ~9.5×10 4 Pa.

[0123] <Photocuring of the Adhesive Layer>

[0124] After the reinforcing film is adhered to the adherend, actinic light is irradiated onto the adhesive layer 2 to photocure the adhesive layer. Examples of the actinic light include ultraviolet rays, visible light, infrared rays, X-rays, α-rays, β-rays, and γ-rays. From the viewpoints of suppressing the curing of the adhesive layer in the storage state and facilitating curing, ultraviolet rays are preferably used as the actinic light. The irradiation intensity and irradiation time of the actinic light can be appropriately set according to the composition, thickness, etc. of the adhesive layer. The actinic light can be irradiated from either one of the film base material 1 side and the adherend side, or the actinic light can be irradiated from both sides.

[0125] <Properties of the photocured adhesive layer>

[0126] (Adhesive force)

[0127] From the viewpoint of the bonding reliability during actual use of the device, the adhesive force between the photocured adhesive layer 2 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 adhesive force between the reinforcing film after photocuring the adhesive layer and the adherend can be 6 N / 25 mm or more, 8 N / 25 mm or more, 10 N / 25 mm or more, 12 N / 25 mm or more, or 13 N / 25 mm or more. It is preferred that the photocured adhesive layer of the reinforcing film has an adhesive force within the above range with respect to the polyimide film. The adhesive force between the photocured adhesive layer 2 and the adherend is preferably 5 times or more, more preferably 8 times or more, and further preferably 10 times or more the adhesive force between the adhesive layer 2 before photocuring and the adherend. The adhesive force between the photocured adhesive layer and the adherend can be 20 times or more, 30 times or more, 40 times or more, or 50 times or more the adhesive force between the adhesive layer before photocuring and the adherend.

[0128] The storage modulus G' of the adhesive layer 2 at 25°C after photocuring f is preferably 1.5×10 5 Pa or more. When the storage modulus of the photocured adhesive layer 2 is 1.5×10 5 Pa or more, the adhesive force with the adherend increases as the cohesive force increases, and high bonding reliability can be obtained. On the other hand, when the storage modulus is too large, it is difficult for the adhesive to wet and spread, and the contact area with the adherend becomes smaller. In addition, since the stress dispersion of the adhesive decreases, there is a tendency that the peeling force easily propagates at the bonding interface and the adhesive force with the adherend decreases. Therefore, the storage modulus G' of the adhesive layer 2 at 25°C after photocuring f is preferably 2×10 6 Pa or less. From the viewpoint of improving the bonding reliability of the reinforcing sheet after photocuring the adhesive layer, G' fMore preferably, it is 1.1×10 5 ~1.2×10 6 Pa, and further preferably 1.2×10 5 ~1×10 6 Pa.

[0129] The ratio G’ of the storage modulus of the adhesive layer 2 at 25°C before and after photocuring f / G’ i is preferably 2 or more. G’ f is when it is 2 times or more of G’ i , the increase in G’ brought about by photocuring is large, and the reworkability before photocuring and the bonding reliability after photocuring can be taken into account. G’ f / G’ i is more preferably 4 or more, further preferably 8 or more, and particularly preferably 10 or more. G’ f / G’ i The upper limit of is not particularly limited, but when G’ f / G’ i is too large, it is likely to cause initial bonding defects due to the small G’ before photocuring, or a decrease in bonding reliability due to the excessive G’ after photocuring. Therefore, G’ f / G’ i is preferably 100 or less, more preferably 40 or less, further preferably 30 or less, and particularly preferably 25 or less.

[0130] For the adherend with the reinforcing film attached, sometimes autoclave treatment for the purpose of improving the affinity of the lamination interface of multiple laminated members, heat pressing for circuit member bonding, etc. are carried out. When carrying out such heat treatment, it is preferable that the adhesive between the reinforcing film and the adherend does not flow out from the end face.

[0131] From the perspective of suppressing the exudation of the adhesive during high-temperature heating, the storage modulus of the photocured adhesive layer 2 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 perspective of preventing the exudation of the adhesive during heating and also preventing the decrease in the adhesive force during heating, the storage modulus of the photocured adhesive layer 2 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.

[0132] [Usage form of the reinforcing film]

[0133] The reinforcing film of the present invention is used by being attached to the constituent members (semi-finished products) of various devices and the completed devices. By attaching the reinforcing film, appropriate rigidity can be imparted, so that an improvement in operability and an anti-breakage effect can be expected. In the manufacturing process of a device, when attaching the reinforcing film to a semi-finished product, the reinforcing film can also be attached to a large-sized semi-finished product before being cut into the product size. The reinforcing film can also be attached in a roll-to-roll manner to the master roll of a device manufactured by a roll-to-roll process.

[0134] With the increasing integration, miniaturization, light weight, and thinness of devices, there is a tendency for the thickness of the constituent members of the devices to become smaller. Due to the thinning of the constituent members, bending and curling caused by stress at the lamination interface are likely to occur. In addition, due to the thinning, deflection caused by self-weight is likely to occur. By attaching the reinforcing film, rigidity can be imparted to the adherend, so that bending, curling, deflection, etc. caused by stress, self-weight, etc. can be suppressed, and the operability is improved. Therefore, by attaching the reinforcing film to a semi-finished product in the manufacturing process of a device, defects and adverse conditions during transfer and processing by an automated device can be prevented.

[0135] During automatic transfer, the semi-finished product to be transferred inevitably comes into contact with transfer arms, pins, etc. In addition, in order to adjust the shape and remove unnecessary parts, cutting processing of the semi-finished product is sometimes performed. In highly integrated, miniaturized, light-weight, and thin devices, breakage due to local stress concentration is likely to occur during contact with transfer devices, etc. and cutting processing. In the manufacturing process of a device composed of multiple laminated members, sometimes not only are the members laminated in sequence, but also a part of the member, process materials, etc. are peeled off from the semi-finished product. In the case of thinning of the member, stress sometimes locally concentrates at the peeling site and its vicinity, resulting in breakage and dimensional changes. Since the reinforcing film has stress dispersibility brought about by the adhesive layer, by attaching the reinforcing film to the object to be transferred and the object to be processed, appropriate rigidity can be imparted, and the stress can be relaxed / dispersed, so that adverse conditions such as cracks, cracking, peeling, and dimensional changes can be suppressed.

[0136] In this way, by attaching the reinforcing film of the present invention, appropriate rigidity can be imparted to the semi-finished product as the adherend, and the stress can be relaxed / dispersed, so that various adverse conditions that may occur in the manufacturing process can be suppressed, the production efficiency can be improved, and the yield can be improved. In addition, since the reinforcing film is easily peeled off from the adherend before the adhesive layer is photocured, rework is also easy in the case of lamination and attachment defects.

[0137] The adhesive layer 2 of the reinforcing film of the present invention is photocurable, and the curing timing can be arbitrarily set. Since rework, processing of the reinforcing film, etc. can be carried out at any time during the period from when the reinforcing film is attached to the adherend to when the adhesive is photocured, it is possible to flexibly cope with the lead time of the equipment manufacturing process. As described above, since the adhesive layer contains an ultraviolet absorber in addition to a photoinitiator and a photo-radical initiator, photocuring caused by light from a fluorescent lamp or the like is not likely to occur. Therefore, even when stored for a long time with the reinforcing film attached to the adherend, as long as it is before photocuring, the reinforcing film can be easily peeled off from the adherend, and it is possible to flexibly cope with the lead time of the process, etc.

[0138] Examples

[0139] Examples are listed below for further illustration, but the present invention is not limited to these examples.

[0140] [Examples 1 to 4 and Comparative Example 1]

[0141] <Preparation of Adhesive Composition>

[0142] 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) as a monomer, 5 parts by weight of acrylic acid (AA), 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 charged, nitrogen was introduced, and nitrogen replacement was carried out for about 1 hour while stirring. Then, it was heated to 60 °C and reacted for 7 hours to obtain a solution of an acrylic polymer having a weight average molecular weight of 600,000.

[0143] In the solution of the acrylic polymer, 0.5 part by weight of a tetrafunctional epoxy compound (Tetrad C manufactured by Mitsubishi Gas Chemical Company, Inc.) as a crosslinking agent, 30 parts by weight of NKEster A200 (polyethylene glycol #200 (n = 4) diacrylate; molecular weight 308, functional group equivalent 154 g / eq) manufactured by Shin-Nakamura Chemical Co., Ltd. as a polyfunctional acrylic monomer, and 1 part by weight of a photoinitiator (Irgacure651 manufactured by BASF; maximum absorption wavelengths: 250 nm, 340 nm) were added. Further, in Examples 1 to 4, a triazine-based ultraviolet absorber (TINUVIN 405 manufactured by BASF) was added in the amounts shown in Table 1 and mixed uniformly to prepare an adhesive composition.

[0144] <Coating and Crosslinking of Adhesive Composition>

[0145] On a polyethylene terephthalate film with a thickness of 75 μm (LUMIRROR S10 manufactured by Toray Industries, Inc.) without surface treatment, the above adhesive composition was coated using a fountain roll so that the dried thickness reached 25 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated surface of a release film (a polyethylene terephthalate film with a thickness of 25 μm whose surface was silicone release-treated) was adhered to the coated surface of the adhesive. Then, a curing treatment was carried out for 4 days in an atmosphere of 25°C to cause crosslinking, obtaining a reinforced film in which a photocurable adhesive sheet was fixedly laminated on a film substrate and a release film was temporarily adhered thereto.

[0146] [Examples 5 to 8 and Comparative Example 2]

[0147] [Preparation of Adhesive Composition]

[0148] In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet tube, 63 parts by weight of 2-ethylhexyl acrylate (2EHA) as a monomer, 9 parts by weight of methyl methacrylate (MMA), 13 parts by weight of 2-hydroxyethyl acrylate (HEA), 15 parts by weight of N-vinylpyrrolidone (NVP), 0.2 part by weight of AIBN as a thermal polymerization initiator, and 233 parts by weight of ethyl acetate as a solvent were charged, nitrogen was introduced, and nitrogen replacement was carried out with stirring for about 1 hour. Then, it was heated to 60°C and reacted for 7 hours to obtain a solution of an acrylic polymer having a weight average molecular weight of 1.2 million.

[0149] [Preparation of Adhesive Composition]

[0150] To the acrylic polymer solution, a 75% ethyl acetate solution (Takenate D110N manufactured by Mitsui Chemicals, Inc.) of a trimethylolpropane adduct of benzenedimethyl diisocyanate, which is a crosslinking agent, in an amount of 2.5 parts by weight based on solid content, 30 parts by weight of "NK Ester APG700" (polypropylene glycol #700 (n = 12) diacrylate; molecular weight 808, functional group equivalent 404 g / eq) manufactured by Shin-Nakamura Chemical Co., Ltd. as a polyfunctional acrylic monomer, and 1 part by weight of a photopolymerization initiator (Irgacure 184 manufactured by BASF; maximum absorption wavelengths: 246 nm, 280 nm, 333 nm) were added. Further, in Examples 5 to 8, a triazine-based ultraviolet absorber (TINUVIN 405 manufactured by BASF) was added in the amounts shown in Table 1 and mixed uniformly to prepare an adhesive composition.

[0151] [Coating and Crosslinking of Adhesive Composition]

[0152] In the same manner as in the above Examples 1 to 4 and Comparative Example 1, the adhesive composition was coated, heat-dried, and crosslinked to produce a reinforced film in which a photocurable adhesive sheet was fixedly laminated on a film substrate and a release film was temporarily pasted thereon.

[0153] [Measurement of Adhesive Force]

[0154] A polyimide film with a thickness of 12.5 μm (Kapton 50EN manufactured by DU PONT-TORAY Co., Ltd.) was adhered to a glass plate with a double-sided adhesive tape (No. 531 manufactured by Nitto Denko Corporation) to obtain a polyimide film substrate for measurement. The release film was peeled off from the surface of the reinforced film cut into a width of 25 mm × a length of 100 mm, and it was adhered to the polyimide film substrate for measurement with a hand roller to obtain a test sample before photocuring. From the side of the reinforced film (PET film side) of the test sample before photocuring, ultraviolet rays with an accumulated light amount of 4000 mJ / cm 2 were irradiated using an LED light source with a wavelength of 365 nm to photocure the adhesive layer, and the resulting sample was used as a test sample after photocuring. Using these test samples, the end of the polyethylene terephthalate film of the reinforced film was held with a jig, and a 180° peel test of the reinforced film was performed at a tensile speed of 300 mm / min to measure the peel strength.

[0155] [Evaluation of the Adhesive Force of the Reinforced Film 4 Weeks after Self-Adhesion]

[0156] The reinforced sheet was adhered to the polyimide film substrate for measurement and left standing for 4 weeks in a bright environment at a temperature of 23°C and an illuminance of 620 lux from a fluorescent lamp, and then the peel strength was measured.

[0157] The composition of the adhesive of each reinforced film and the measurement results of the adhesive force before and after photocuring and the adhesive force after standing for 4 weeks (before photocuring) are shown in Table 1.

[0158] [Table 1]

[0159]

[0160] In any of the Examples and Comparative Examples, the adhesive force was 0.4 N / 25 mm or less immediately after being adhered to the polyimide film substrate, and it could be easily peeled off from the polyimide film. In addition, when photocuring was performed immediately after adhesion, the adhesive force increased and it was firmly adhered to the polyimide film substrate.

[0161] In any of the examples and comparative examples, an increase in adhesive force was observed 4 weeks after bonding to the polyimide film substrate. In Comparative Examples 1 and 2 where no ultraviolet absorber was added, the adhesive force after 4 weeks increased to more than 30 times the adhesive force just after bonding, making it difficult to peel from the polyimide film substrate.

[0162] Compared with Comparative Example 1, Examples 1 to 4 to which an ultraviolet absorber was added had a smaller increase rate of adhesive force after 4 weeks. The more the amount of ultraviolet absorber added, the more the increase in adhesive force was suppressed. The same trend was also observed in the comparison between Comparative Example 2 and Examples 5 to 8. From these results, it can be seen that by adding an ultraviolet absorber, the photocuring of the adhesive in a bright room environment can be suppressed.

[0163] Compared with Examples 3, 4 and Comparative Example 1, the adhesive force after photocuring decreased in Examples 1 and 2. Compared with Examples 6 to 8 and Comparative Example 1, the adhesive force after photocuring decreased in Example 5. From these results, it can be considered that when the amount of ultraviolet absorber added increases, as the light absorption amount of the ultraviolet absorber increases, the excitation light absorbed by the photoinitiator (free radical initiator) decreases, so the photocuring of the adhesive can be suppressed.

Claims

1. An enhanced film, which comprises a film substrate and an adhesive layer fixedly laminated on one main surface of the film substrate. The adhesive layer is formed from a photocurable composition containing a base polymer, a photo-curing agent, a photo-radical initiator, and an ultraviolet absorber.

2. The enhanced film according to claim 1, wherein, the photo-radical initiator has a maximum absorption in the wavelength range of 310 nm to 370 nm.

3. The enhanced film according to claim 2, wherein, the photo-radical initiator does not show a maximum absorption at a wavelength greater than 380 nm.

4. The enhanced film according to claim 2 or 3, wherein, The absorption coefficient of the photo radical initiator at a wavelength of 405 nm is 1×10 2 [mLg -1 cm -1 or less.

5. The enhanced film according to any one of claims 2 to 4, wherein, at the maximum absorption wavelength within the wavelength range of 310 to 370 nm of the photo-radical initiator, the light transmittance of the adhesive layer is 3 to 70%.

6. The enhanced film according to any one of claims 2 to 5, wherein, at the maximum absorption wavelength within the wavelength range of 310 to 370 nm of the photo-radical initiator, the light transmittance is 3 to 70%.

7. The enhanced film according to any one of claims 1 to 6, wherein, the light transmittance of the adhesive layer at 350 nm is 3 to 70%.

8. The enhanced film according to any one of claims 1 to 7, which has a light transmittance of 3 to 70% at 350 nm.

9. The enhanced film according to any one of claims 1 to 8, wherein, the photocurable composition contains 10 to 50 parts by weight of the photo-curing agent relative to 100 parts by weight of the base polymer.

10. The enhanced film according to any one of claims 1 to 9, wherein, the photocurable composition contains 0.01 to 1 part by weight of the photo-radical initiator and 0.1 to 10 parts by weight of the ultraviolet absorber relative to 100 parts by weight of the base polymer.

11. The enhanced film according to any one of claims 1 to 10, wherein, the ultraviolet absorber is a triazine compound.

12. The enhanced film according to any one of claims 1 to 11, wherein, the gel fraction of the photocurable composition is 60% or more.

13. The enhanced film according to any one of claims 1 to 12, wherein, the base polymer contains one or more selected from the group consisting of a hydroxyl group-containing monomer and a carboxyl group-containing monomer as monomer units, and has a crosslinked structure introduced by a crosslinking agent bonded to a hydroxyl group or a carboxyl group.

14. The enhanced film according to any one of claims 1 to 13, wherein, an acrylic polymer is contained as the base polymer.

15. The enhanced film according to any one of claims 1 to 14, wherein, the photo-curing agent is a polyfunctional (meth)acrylate.

16. The enhanced film according to any one of claims 1 to 15, wherein, the functional group equivalent of the photo-curing agent is 100 to 500 g / eq.

17. The enhanced film according to any one of claims 1 to 16, wherein, The adhesion force of the cured adhesive layer to the polyimide film is more than 5 times that of the uncured adhesive layer to the polyimide film.

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