WO2024247886A1 - 補強フィルム、補強フィルム付きデバイスおよびその製造方法 - Google Patents

補強フィルム、補強フィルム付きデバイスおよびその製造方法 Download PDF

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WO2024247886A1
WO2024247886A1 PCT/JP2024/019040 JP2024019040W WO2024247886A1 WO 2024247886 A1 WO2024247886 A1 WO 2024247886A1 JP 2024019040 W JP2024019040 W JP 2024019040W WO 2024247886 A1 WO2024247886 A1 WO 2024247886A1
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meth
adhesive layer
weight
acrylate
photocuring
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PCT/JP2024/019040
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English (en)
French (fr)
Japanese (ja)
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賢一 片岡
真宏 井川
和弘 阿部
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日東電工株式会社
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B32B27/26—Layered products comprising a layer of synthetic resin characterised by the use of special additives using curing agents
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J11/00—Features of adhesives not provided for in group C09J9/00, e.g. additives
    • C09J11/02—Non-macromolecular additives
    • C09J11/06—Non-macromolecular additives organic
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
    • C09J133/04—Homopolymers or copolymers of esters
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J4/00—Adhesives based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; adhesives, based on monomers of macromolecular compounds of groups C09J183/00 - C09J183/16
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J7/00—Adhesives in the form of films or foils
    • C09J7/30—Adhesives in the form of films or foils characterised by the adhesive composition
    • C09J7/38—Pressure-sensitive adhesives [PSA]
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements

Definitions

  • the present invention relates to a reinforcing film that is applied to the surface of a device. Furthermore, the present invention relates to a device equipped with a reinforcing film and a method for manufacturing the same.
  • Adhesive films are sometimes applied to the surfaces of optical devices such as displays and electronic devices for the purposes of surface protection, impact resistance, etc.
  • Such adhesive films usually have an adhesive layer fixedly laminated to the main surface of a film substrate, and are attached to the device surface via this adhesive layer.
  • Patent Documents 1 and 2 disclose a reinforcing film that has an adhesive layer made of a photocurable adhesive composition on a film substrate.
  • This reinforcing film has a high gel fraction in the adhesive and has low adhesion immediately after application to the adherend, making it easy to peel off from the adherend. This allows for rework from the adherend, and also makes it possible to selectively peel off the reinforcing film from areas of the adherend that do not require reinforcement.
  • the adhesive in the reinforcing film adheres firmly to the adherend when photocured, so the film base material is permanently bonded to the surface of the adherend, making it usable as a reinforcing material for protecting the surfaces of devices, etc.
  • R 1 is a hydrogen atom or a methyl group
  • the compound of the formula (1) in which R 1 is a hydrogen atom is an acrylate
  • the compound of the formula (1) in which R 1 is a methyl group is a methacrylate. From the viewpoint of lowering the Tg of the acrylic base polymer, it is preferable that R 1 is a hydrogen atom.
  • R 2 is an alkylene group having 2 to 4 carbon atoms which may have a branch, and -R 2 -O- is an alkylene oxide chain.
  • R 2 has 2 to 4 carbon atoms, the resistance of the adhesive is reduced and the compatibility between the acrylic base polymer and the photocuring agent is improved.
  • alkylene oxide -R 2 -O- in which R 2 has 2 to 4 carbon atoms include ethylene oxide (-CH 2 CH 2 -O-), propylene oxide (-CH(CH 3 )CH 2 -O-), and butylene oxide (-CH 2 CH 2 CH 2 CH 2 -O-).
  • m is the number of repeating alkylene oxide units and is an integer from 1 to 5.
  • m is the number of repeating alkylene oxide units and is an integer from 1 to 5.
  • a high molecular weight for example, a weight average molecular weight of 100,000 or more.
  • the (meth)acrylate compound represented by general formula (1) tends to act as a chain transfer agent, so the molecular weight of the acrylic base polymer as a polymer does not become sufficiently large, and the adhesive strength of the adhesive may be insufficient.
  • compounds represented by general formula (1) include methoxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, ethoxyethoxyethyl (meth)acrylate, methoxydipropylene glycol (meth)acrylate, and methoxytriethylene glycol (meth)acrylate.
  • methoxyethyl acrylate glass transition temperature of homopolymer: -50°C is particularly preferred.
  • 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, and 4-(hydroxymethyl)cyclohexylmethyl (meth)acrylate.
  • 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred because they contribute greatly to improving the adhesive strength of the adhesive after photocuring.
  • the amount of the (meth)acrylic acid alkyl ester is preferably 40 parts by weight or more, more preferably 50 parts by weight or more, even more preferably 60 parts by weight or more, and may be 65 parts by weight or more, 70 parts by weight or more, 75 parts by weight or more, or 80 parts by weight or more, relative to 100 parts by weight of the total of the constituent monomer components of the acrylic base polymer.
  • the amount of the (meth)acrylic acid alkyl ester having an alkyl group with 6 or more carbon atoms is preferably in the above-mentioned range, the amount of the (meth)acrylic acid C6-9 alkyl ester may be in the above-mentioned range, the total of 2-ethylhexyl acrylate, n-heptyl acrylate, and n-octyl acrylate may be in the above-mentioned range, and the amount of n-octyl acrylate may be in the above-mentioned range.
  • the amount of the (meth)acrylic acid C 6-9 alkyl ester is preferably 15 to 84 parts by weight, and the amount of the (meth)acrylic acid C 10-20 alkyl ester is preferably 10 to 79 parts by weight, relative to 100 parts by weight of the total amount of the constituent monomer components of the acrylic polymer.
  • the amount of the (meth)acrylic acid C 6-9 alkyl ester may be 20 to 70 parts by weight, 30 to 60 parts by weight, 35 to 55 parts by weight, or 40 to 50 parts by weight, and the amount of the (meth)acrylic acid C 10-20 alkyl ester may be 15 to 60 parts by weight, 20 to 50 parts by weight, 25 to 45 parts by weight, or 30 to 40 parts by weight.
  • the acrylic base polymer may contain a monomer other than the above as a constituent monomer component.
  • the monomer other than the above include nitrogen-containing monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinylcarboxylic acid amides, and N-vinylcaprolactam.
  • the other monomers include vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphoric acid group-containing monomers, and acid anhydride group-containing monomers.
  • the glass transition temperature of the acrylic base polymer is preferably -40°C or lower, more preferably -45°C or lower, and may be -50°C or lower or -55°C or lower.
  • the lower limit of the glass transition temperature of the acrylic base polymer is not particularly limited, but is generally -80°C or higher, and may be -75°C or higher or -70°C or higher.
  • the glass transition temperature is the temperature (peak top temperature) at which the loss tangent tan ⁇ in viscoelasticity measurement is maximized.
  • the theoretical Tg calculated by Fox's formula may be applied.
  • Tg is the glass transition temperature (unit: K) of the polymer chain
  • W i is the weight fraction (copolymerization ratio based on weight) of the monomer component i constituting the segment
  • Tg i is the glass transition temperature (unit: K) of a homopolymer of the monomer component i.
  • the glass transition temperature of the homopolymer the values described in Polymer Handbook, 3rd Edition (John Wiley & Sons, Inc., 1989) can be used.
  • the peak top temperature of tan ⁇ measured by dynamic viscoelasticity measurement may be used.
  • the weight average molecular weight of the acrylic base polymer is preferably 100,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, and may be 300,000 or more, 400,000 or more, or 500,000 or more.
  • the number of repeating units of the alkylene oxide of the (meth)acrylic acid ester having an alkylene oxide chain m in general formula (1)
  • the action of the monomer as a chain transfer agent is small, and therefore a high molecular weight acrylic polymer can be easily obtained.
  • the weight average molecular weight of the acrylic base polymer is preferably 2 million or less, more preferably 1.5 million or less, even more preferably 1.2 million or less, and may be 1 million or less or 900,000 or less.
  • a crosslinked structure is introduced into the acrylic base polymer, but the molecular weight of the acrylic base polymer refers to the molecular weight before the crosslinked structure is introduced.
  • a crosslinked structure is introduced into the base polymer.
  • the crosslinked structure is introduced by adding a crosslinking agent to a solution obtained by polymerizing an acrylic base polymer, and heating the solution as necessary.
  • Crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. These crosslinking agents react with functional groups such as hydroxyl groups and carboxyl groups introduced into the acrylic-based polymer to form a crosslinked structure. Isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they are highly reactive with the hydroxyl groups and carboxyl groups of the acrylic-based polymer and allow easy introduction of crosslinked structures. When the acrylic-based polymer has hydroxyl groups as crosslinkable functional groups, isocyanate-based crosslinking agents are preferred, and when the acrylic-based polymer has carboxyl groups as crosslinkable functional groups, epoxy-based crosslinking agents are preferred.
  • the isocyanate-based crosslinking agent a polyisocyanate having two or more isocyanate groups per molecule is used.
  • the isocyanate-based crosslinking agent may have three or more isocyanate groups per molecule.
  • Examples of the isocyanate-based crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; trimethylolpropane/trile diisocyanate; and the like.
  • isocyanate adducts examples include a diisocyanate trimer adduct (e.g., Mitsui Chemicals' "Takenate D101E"), a trimethylolpropane/hexamethylene diisocyanate trimer adduct (e.g., Tosoh's "Coronate HL”), a xylylene diisocyanate trimethylolpropane adduct (e.g., Mitsui Chemicals' "Takenate D110N”), and a hexamethylene diisocyanate isocyanurate (e.g., Tosoh's "Coronate HX").
  • a diisocyanate trimer adduct e.g., Mitsui Chemicals' "Takenate D101E
  • a trimethylolpropane/hexamethylene diisocyanate trimer adduct e.g., Tosoh's "Coronate HL
  • the epoxy crosslinking agent a multifunctional epoxy compound having two or more epoxy groups in one molecule is used.
  • the epoxy crosslinking agent may have three or more or four or more epoxy groups in one molecule.
  • the epoxy group of the epoxy crosslinking agent may be a glycidyl group.
  • epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylene diamine, diglycidyl aniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl este
  • the amount of crosslinking agent used may be adjusted appropriately depending on the composition and molecular weight of the acrylic base polymer.
  • the amount of crosslinking agent used is about 0.01 to 5 parts by weight, preferably 0.03 to 3 parts by weight, more preferably 0.05 to 1 part by weight, and may be 0.08 to 0.8 parts by weight or 0.1 to 0.5 parts by weight, per 100 parts by weight of the acrylic base polymer.
  • a crosslinking catalyst may be used to promote the formation of a crosslinked structure.
  • crosslinking catalysts include organometallic compounds such as organometallic complexes (chelates), compounds of metals and alkoxy groups, and compounds of metals and acyloxy groups; as well as tertiary amines.
  • organometallic compounds are preferred from the viewpoint of suppressing the progress of the crosslinking reaction in a solution state at room temperature and ensuring the pot life of the adhesive composition.
  • metals in organometallic compounds include iron, tin, aluminum, zirconium, zinc, titanium, lead, and cobalt.
  • the amount of crosslinking catalyst used is generally 0.5 parts by weight or less per 100 parts by weight of the acrylic base polymer.
  • the adhesive composition constituting the adhesive layer 2 contains, in addition to the base polymer, a compound having two or more photopolymerizable functional groups in one molecule as a photocuring agent.
  • the adhesive composition containing the photocuring agent has photocurability, and when photocuring is performed after lamination with an adherend, the adhesive strength with the adherend is improved.
  • the photopolymerizable functional group is preferably one that has the polymerizability due to a photoradical reaction
  • the photocuring agent is preferably a compound that has two or more ethylenically unsaturated bonds in one molecule, and polyfunctional (meth)acrylates are preferred because of their high compatibility with acrylic-based polymers.
  • a polyfunctional (meth)acrylate is an ester of a polyol and (meth)acrylic acid.
  • polyfunctional (meth)acrylates include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, isocyanuric acid di(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and trimethylol di(meth)acrylate.
  • acrylates examples include thyrolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate, and isoprene (meth)acrylate.
  • the polyfunctional (meth)acrylate may be an ester of an alkylene oxide-modified polyol and (meth)acrylic acid.
  • alkylene oxide examples include ethylene oxide (EO) and propylene oxide (PO).
  • EO ethylene oxide
  • PO propylene oxide
  • the alkylene oxide may be a polyalkylene oxide such as polyethylene glycol or polypropylene glycol.
  • alkylene oxide modified polyfunctional (meth)acrylates include bisphenol A ethylene oxide modified di(meth)acrylate, bisphenol A propylene oxide modified di(meth)acrylate, trimethylolpropane ethylene oxide modified tri(meth)acrylate, trimethylolpropane propylene oxide modified tri(meth)acrylate, isocyanuric acid ethylene oxide modified di(meth)acrylate, isocyanuric acid propylene oxide modified di(meth)acrylate, isocyanuric acid ethylene oxide modified tri(meth)acrylate, isocyanuric acid propylene oxide modified tri(meth)acrylate, pentaerythritol ethylene oxide modified tetra(meth)acrylate, pentaerythritol propylene oxide modified tetra(meth)acrylate, etc.
  • the alkylene oxide is preferably (poly)ethylene oxide or (poly)propylene oxide, and particularly preferably (poly)ethylene oxide.
  • the chain length of the alkylene oxide (the number of repeating units of the alkylene oxide) n is about 1 to 15.
  • the average chain length n is preferably 1 to 15.
  • the (average) chain length n of the alkylene oxide chain may be 12 or less, 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, or 3 or less.
  • the molecular weight of the polyfunctional (meth)acrylate as the photocuring agent is preferably 1500 or less, more preferably 1000 or less, and may be 800 or less, 500 or less, or 400 or less.
  • the functional group equivalent (g/eq) of the polyfunctional (meth)acrylate is preferably 500 or less, more preferably 400 or less, and may be 300 or less, 250 or less, 200 or less, 180 or less, or 160 or less.
  • the functional group equivalent of the polyfunctional (meth)acrylate is preferably 80 or more, more preferably 100 or more, and may be 120 or more or 130 or more.
  • polyfunctional (meth)acrylates have excellent compatibility with acrylic-based polymers.
  • polyfunctional (meth)acrylates with alkylene oxide chains have higher polarity than polyfunctional (meth)acrylates without alkylene oxide chains, and therefore have lower compatibility with acrylic polymers, particularly with acrylic polymers with a small amount of polar functional groups.
  • (Meth)acrylic acid alkyl esters with an alkyl group having 6 or more carbon atoms have a relatively small volume ratio of alkylene oxide chains compared to (meth)acrylic acid alkyl esters with a small alkyl group carbon number (such as butyl acrylate, where the alkyl group has 4 carbon atoms), and therefore have low polarity.
  • the acrylic base polymer contains, as a monomer component, a (meth)acrylic acid ester having an alkylene oxide chain in addition to a (meth)acrylic acid alkyl ester whose alkyl group has 6 or more carbon atoms, which increases the polarity and makes the adhesive compatible with multifunctional (meth)acrylates having alkylene oxide chains.
  • the adhesive tends to have low resistance because both the acrylic base polymer and the photocuring agent contain alkylene oxide chains.
  • the ratio of (meth)acrylic acid esters with alkylene oxide chains in the constituent monomer components of the acrylic base polymer it is possible to adjust the compatibility with the light curing agent with an alkylene oxide chain. As mentioned above, if there is no (meth)acrylic acid ester with an alkylene oxide chain, or if the ratio of (meth)acrylic acid esters with alkylene oxide chains is low, the compatibility with the light curing agent is low, which can cause the light curing agent to bleed out.
  • the acrylic base polymer has a polarity such that it is not completely compatible with the photocuring agent (a (meth)acrylic acid ester having an alkylene oxide chain)
  • the photocuring agent will tend to be unevenly distributed on the surface of the adhesive layer (near the adhesive interface with the adherend), and even if the amount of photocuring agent used is small, the photocuring agent unevenly distributed at the adhesive interface with the adherend will tend to form an adhesion-inhibiting layer (Weak Boundary Layer; WBL).
  • the adhesive layer When a WBL is formed, the adhesive layer retains its bulk properties such as storage modulus while the liquid properties of the surface (adhesive interface) become stronger, which tends to reduce the adhesive strength with the adherend. Therefore, the adhesive layer before photocuring is easy to peel off from the adherend.
  • an adhesive layer in which a WBL has been formed with the photocuring agent unevenly distributed near the adhesive interface with the adherend is photocured, the curing reaction of the photocuring agent is likely to proceed near the adhesive interface where the density of the photocuring agent is high, which tends to improve the adhesive strength.
  • the increase in the storage modulus, which is a bulk property, due to photocuring tends to be suppressed, making it highly applicable to foldable devices.
  • the content of the photocuring agent in the adhesive composition is preferably 3 to 25 parts by weight, more preferably 5 to 20 parts by weight, and may be 8 to 17 parts by weight or 10 to 15 parts by weight, per 100 parts by weight of the acrylic base polymer.
  • a polyfunctional (meth)acrylate having an alkylene oxide chain and a urethane (meth)acrylate may be used.
  • the urethane (meth)acrylate is a compound having one or more urethane bonds and two or more (meth)acryloyl groups in one molecule, and preferably contains two or more urethane bonds in one molecule.
  • the urethane (meth)acrylate having two or more urethane bonds can be obtained, for example, by reacting a polyisocyanate with a (meth)acrylic compound having a hydroxyl group, and the isocyanate group of the polyisocyanate and the hydroxyl group of the (meth)acrylic compound are bonded to form a urethane bond.
  • the urethane (meth)acrylate having two or more urethane bonds can also be obtained by reacting a polyisocyanate with a polyol to prepare a prepolymer having an isocyanate group at the end, and then bonding a (meth)acrylic compound having a hydroxyl group to the isocyanate group at the end of the prepolymer.
  • a urethane (meth)acrylate having two or more urethane bonds can be obtained by reacting a polyisocyanate with a (meth)acrylic compound having a hydroxy group, and then reacting the reaction product with a polyol.
  • the polyisocyanate may be any of aromatic polyisocyanates, alicyclic polyisocyanates, and cycloaliphatic polyisocyanates.
  • aromatic polyisocyanate tolylene diisocyanate (TDI) is particularly preferred.
  • tolylene diisocyanate 2,4-tolylene diisocyanate or 2,6-tolylene diisocyanate may be used, or a mixture of the two.
  • aliphatic polyisocyanate hexamethylene diisocyanate (HDI) is particularly preferred.
  • isophorone diisocyanate (IPDI) is particularly preferred.
  • Examples of (meth)acrylic compounds having a hydroxy group include compounds having one hydroxy group and one (meth)acryloyl group, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxymethylacrylamide, and hydroxyethylacrylamide; and compounds having one hydroxy group and two or more (meth)acryloyl groups, such as pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, trimethylolpropane di(meth)acrylate, and isocyanuric acid di(meth)acrylate.
  • one (meth)acryloyl group such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate
  • a urethane (meth)acrylate obtained by reacting a diisocyanate with a (meth)acrylic compound having one hydroxy group and two or more (meth)acryloyl groups in one molecule has two urethane bonds and four or more (meth)acryloyl groups in one molecule.
  • the number of (meth)acryloyl groups in the urethane (meth)acrylate may be six or more, eight or more, or twelve or ten or less.
  • urethane (meth)acrylates may be commercially available from Kyoeisha Chemical, Shin-Nakamura Chemical, Negami Chemical Industries, Mitsubishi Chemical, Daicel-Allnex, Resonac, etc.
  • urethane (meth)acrylate By including urethane (meth)acrylate as the photocuring agent in addition to a multifunctional (meth)acrylate that does not have a urethane bond, the adhesive strength of the adhesive layer before photocuring may be low and the adhesive strength of the adhesive layer after photocuring may be high.
  • urethane (meth)acrylate promotes the formation of WBL by multifunctional (meth)acrylates that do not have a urethane bond, particularly multifunctional (meth)acrylates that have an alkylene oxide chain.
  • the photocurable composition constituting the adhesive layer contains, as a photocuring agent, a urethane (meth)acrylate in addition to a polyfunctional (meth)acrylate that does not have a urethane bond
  • the content of the urethane (meth)acrylate is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, and may be 0.08 parts by weight or more or 0.1 parts by weight or more, per 100 parts by weight of the acrylic base polymer.
  • the photopolymerization initiator generates active species by irradiation with active light rays, and promotes the curing reaction of the photocuring agent.
  • a photocation initiator photoacid generator
  • a photoradical initiator photobase generator
  • photobase generator photoanion initiator
  • the content of the photopolymerization initiator in the adhesive composition is preferably 0.001 to 5 parts by weight, more preferably 0.01 to 3 parts by weight, and even more preferably 0.03 to 1 part by weight, per 100 parts by weight of the acrylic base polymer.
  • the content of the photopolymerization initiator in the adhesive composition is preferably 0.02 to 20 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 7 parts by weight, per 100 parts by weight of the photocuring agent.
  • the pressure-sensitive adhesive composition contains an antistatic agent.
  • the resistance of the pressure-sensitive adhesive layer is reduced, reducing the static electricity of the pressure-sensitive adhesive layer and providing the effect of suppressing static electricity on the adherend.
  • the ionic compound containing an organic cation may be an ionic liquid that is liquid at room temperature, or an ionic solid that is solid at room temperature.
  • the ionic compound containing an organic cation is preferably composed of an organic anion or a fluoroinorganic anion and an onium cation.
  • the organic anion may be a fluoroorganic anion that contains a fluorine atom, or an organic anion that does not contain a fluorine atom.
  • onium cations examples include nitrogen-containing onium cations, sulfur-containing onium cations (e.g., trialkylsulfonium cations), phosphorus-containing onium cations (e.g., tetraalkylphosphonium cations), etc. Among these, nitrogen-containing onium cations are preferred.
  • nitrogen-containing onium cations include pyridinium cations, pyrrolidinium cations, piperidinium cations, cations having a pyrroline skeleton, cations having a pyrrole skeleton, imidazolium cations, tetrahydropyrimidinium cations, dihydropyrimidinium cations, pyrazolium cations, pyrazolinium cations, and tetraalkylammonium cations.
  • the fluoro organic anion constituting the ionic compound containing an organic cation may be completely fluorinated (perfluorinated) or partially fluorinated.
  • fluoro organic anions include perfluoroalkylsulfonates, bis(fluorosulfonyl)imides, and bis(perfluoroalkanesulfonyl)imides. More specifically, for example, trifluoromethanesulfonate, pentafluoroethanesulfonate, heptafluoropropanesulfonate, nonafluorobutanesulfonate, bis(fluorosulfonyl)imides, and bis(trifluoromethanesulfonyl)imides.
  • organic anions that do not contain fluorine atoms include sulfonate anions such as p-toluenesulfonate, borate anions, and dicyanamide anions.
  • fluoro inorganic anions include hexafluorophosphate and tetrafluoroboric acid.
  • the alkali metal salt preferably comprises the above organic anion or fluoroinorganic anion and an alkali metal cation, which is Li + , Na + or K + , with Li + being preferred.
  • the content of the antistatic agent in the adhesive composition is about 0.01 to 3 parts by weight, preferably 0.03 to 2 parts by weight, more preferably 0.05 to 1 part by weight, and even more preferably 0.1 to 0.7 parts by weight, based on 100 parts by weight of the acrylic base polymer.
  • the content of the antistatic agent in the adhesive layer 2 is about 0.01 to 2% by weight, preferably 0.03 to 1% by weight, more preferably 0.05 to 0.7% by weight, and even more preferably 0.1 to 0.5% by weight, and may be 0.15 to 0.4% by weight. If the amount of the antistatic agent is small, the adhesive may not be sufficiently low-resistance. If the amount of the antistatic agent is excessively large, it may cause contamination or corrosion of the adherend due to bleed-out of the antistatic agent, or a decrease in adhesive strength.
  • the acrylic base polymer of the adhesive composition contains a (meth)acrylic acid ester having an alkylene oxide chain as a monomer component, the resistance of the adhesive can be reduced, even if only a small amount of antistatic agent is added. Therefore, it is possible to provide an adhesive layer that has low surface resistance and excellent antistatic properties while suppressing problems such as bleed-out of the antistatic agent.
  • the photocurable pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer 2 contains an acrylic-based polymer, a photocuring agent, a photopolymerization initiator, and an antistatic agent.
  • the pressure-sensitive adhesive composition may contain components other than these.
  • the adhesive composition may contain an oligomer having a lower molecular weight than the base polymer.
  • the adhesive composition may contain, in addition to the acrylic base polymer, an acrylic oligomer having a weight average molecular weight of about 1000 to 30000.
  • the acrylic oligomer contains an alkyl (meth)acrylate ester as the main monomer component.
  • the glass transition temperature of the acrylic oligomer is preferably 40°C or higher, more preferably 50°C or higher.
  • the acrylic oligomer may contain a crosslinkable functional group like the acrylic base polymer.
  • the adhesive composition may contain additives such as silane coupling agents, tackifiers, plasticizers, softeners, anti-degradants, fillers, colorants, UV absorbers, antioxidants, and surfactants, to the extent that the properties of the present invention are not impaired.
  • additives such as silane coupling agents, tackifiers, plasticizers, softeners, anti-degradants, fillers, colorants, UV absorbers, antioxidants, and surfactants, to the extent that the properties of the present invention are not impaired.
  • Additives may be used to reduce the resistance of the adhesive or to adjust the compatibility between the acrylic base polymer and the photocuring agent.
  • polyether polyols such as polyethylene glycol and polypropylene glycol tends to reduce the resistance of the adhesive.
  • low molecular weight additives such as polyols do not contribute to the photocuring of the adhesive and remain as liquid components even after the adhesive is photocured. Therefore, if the amount of low molecular weight additives is large, the gel fraction of the adhesive after photocuring is small, the adhesive layer is prone to plastic deformation, and the strain recovery rate tends to decrease.
  • the amount of additives is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 5 parts by weight or less, and may be 3 parts by weight or less, 2 parts by weight or less, or 1 part by weight or less, relative to 100 parts by weight of the acrylic base polymer.
  • the total amount of the acrylic base polymer, crosslinking agent and photocuring agent relative to the total solid content of the adhesive composition is preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 93% by weight or more, and may be 95% by weight or more, 97% by weight or more or 98% by weight or more.
  • a reinforcing film is obtained by laminating a photocurable pressure-sensitive adhesive layer 2 on a film substrate 1.
  • the pressure-sensitive adhesive layer 2 may be formed directly on the film substrate 1, or a pressure-sensitive adhesive layer formed in a sheet form on another substrate may be transferred onto the film substrate 1.
  • the above adhesive composition is applied to a substrate by roll coating, kiss roll coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, or the like, and the solvent is dried and removed as necessary to form an adhesive layer.
  • the drying method any appropriate method may be adopted.
  • the heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and even more preferably 70°C to 170°C.
  • the drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and even more preferably 10 seconds to 10 minutes.
  • the adhesive composition contains a crosslinking agent
  • the heating temperature and heating time are set appropriately depending on the type of crosslinking agent used, and crosslinking is usually achieved by heating for about 1 minute to 7 days at a temperature in the range of 20°C to 160°C.
  • the heating for drying and removing the solvent may also serve as the heating for crosslinking.
  • the introduction of a crosslinked structure into the acrylic-based polymer increases the gel fraction and the storage modulus of the adhesive layer 2 tends to increase.
  • the higher the gel fraction of the adhesive before photocuring the harder the adhesive is, and the less adhesive remains on the adherend when the reinforcing film is peeled off from the adherend by rework or the like.
  • the gel fraction of the adhesive layer 2 before photocuring i.e., the gel fraction of the photocurable composition constituting the adhesive layer
  • the gel fraction of the adhesive layer 2 before photocuring is preferably 80% or less, and may be 75% or less, 70% or less, or 65% or less.
  • the gel fraction can be determined as the insoluble portion in a solvent such as ethyl acetate. Specifically, it is determined as the weight fraction (unit: weight %) of the insoluble portion after immersing the adhesive layer in ethyl acetate at 23°C for 7 days relative to the sample before immersion.
  • the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked parts in the polymer, the higher the gel fraction.
  • the adhesive layer 2 contains an acrylic base polymer with a crosslinking structure introduced, a photocuring agent, a photopolymerization initiator, and an antistatic agent.
  • a release liner 5 onto the adhesive layer 2 for the purpose of protecting the adhesive layer 2, etc.
  • Crosslinking may be performed after attaching the release liner 5 onto the adhesive layer 2.
  • the reinforcing film is obtained by transferring the adhesive layer 2 onto the film substrate 1 after drying the solvent.
  • the substrate used to form the adhesive layer may be used as the release liner 5 as is.
  • a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, or polyester film is preferably used.
  • the thickness of the release liner is usually 3 to 200 ⁇ m, and preferably about 10 to 100 ⁇ m.
  • the surface of the release liner 5 that comes into contact with the adhesive layer 2 is preferably treated with a release agent such as a silicone-based, fluorine-based, long-chain alkyl-based, or fatty acid amide-based release agent, or with silica powder or the like.
  • the release liner 5 may be treated with an antistatic treatment on either or both of the release-treated surface and the non-treated surface. By treating the release liner 5 with an antistatic treatment, it is possible to suppress charging when the release liner is peeled from the adhesive layer.
  • the thickness of the pressure-sensitive adhesive layer 2 is, for example, about 1 to 300 ⁇ m.
  • the thickness of the pressure-sensitive adhesive layer 2 is preferably 3 to 100 ⁇ m, more preferably 5 to 50 ⁇ m, even more preferably 6 to 40 ⁇ m, and particularly preferably 8 to 30 ⁇ m. From the viewpoint of thinning, the thickness of the pressure-sensitive adhesive layer 2 may be 25 ⁇ m or less, 20 ⁇ m or less, or 18 ⁇ m or less.
  • the total light transmittance of the adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.
  • the haze of the adhesive layer 2 is preferably 2% or less, more preferably 1% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less.
  • the surface resistance of the pressure-sensitive adhesive layer 2 is preferably 5.0 ⁇ 10 ⁇ or less, more preferably 1.0 ⁇ 10 ⁇ or less, and may be 7.0 ⁇ 10 ⁇ or less, 5.0 ⁇ 10 ⁇ or less, or 3.0 ⁇ 10 ⁇ or less.
  • the pressure-sensitive adhesive composition contains an antistatic agent, and the acrylic base polymer further contains a (meth)acrylic acid ester having an alkylene oxide chain as a monomer component, thereby making it possible to reduce the resistance of the pressure-sensitive adhesive layer 2.
  • the low resistance of the adhesive layer 2 can suppress electrical damage to the adherend caused by static electricity, etc., when the reinforcing film is peeled off from the adherend.
  • the adhesive layer 2 preferably has a surface resistance in the above range even after photocuring. In general, the surface resistance of the adhesive layer changes very little before and after photocuring. Since the adhesive layer after photocuring has the above surface resistance, static electricity on the adherend to which the adhesive layer 2 is attached is removed via the adhesive layer 2, so charging of the adherend can be suppressed. Therefore, defects caused by static electricity, such as electrostatic breakdown, in devices to which the reinforcing film is attached can be suppressed.
  • the shear storage modulus of the pressure-sensitive adhesive layer 2 at 25° C. before photocuring is preferably 5.0 ⁇ 10 3 to 1.0 ⁇ 10 5 Pa.
  • the shear storage modulus of the pressure-sensitive adhesive layer (hereinafter simply referred to as "storage modulus") is determined by reading the value at a predetermined temperature when measured at a temperature rise rate of 5° C./min in the range of -50 to 150° C. under a condition of a frequency of 1 Hz in accordance with the method described in JIS K7244-1 "Plastics - Test methods for dynamic mechanical properties".
  • the storage modulus of the pressure-sensitive adhesive layer 2 at 25° C. before photocuring is preferably 7.0 ⁇ 10 3 Pa or more, more preferably 9.0 ⁇ 10 3 Pa or more, and may be 1.0 ⁇ 10 4 Pa or more or 1.5 ⁇ 10 4 Pa or more.
  • the storage modulus of the pressure-sensitive adhesive layer 2 at 25° C. before photocuring is preferably 7.0 ⁇ 10 4 Pa or less, more preferably 5.0 ⁇ 10 4 Pa or less, and may be 4.0 ⁇ 10 4 Pa or less or 3.0 ⁇ 10 4 Pa or less.
  • the storage modulus of the pressure-sensitive adhesive layer 2 at ⁇ 20° C. before photocuring is preferably 1.0 ⁇ 10 4 to 2.0 ⁇ 10 5 Pa, more preferably 1.5 ⁇ 10 4 to 1.0 ⁇ 10 5 Pa, and may be 2.0 ⁇ 10 4 to 7.0 ⁇ 10 4 Pa or 3.0 ⁇ 10 4 to 7.0 ⁇ 10 4 Pa.
  • the storage modulus at low temperature of the pressure-sensitive adhesive layer before photocuring is within the above range, the storage modulus of the pressure-sensitive adhesive layer tends to be maintained low even after photocuring.
  • the photocuring agent undergoes a curing reaction, increasing the storage modulus and the adhesive strength with the adherend. It is preferable that the adhesive layer 2 has a small storage modulus at low temperatures even after photocuring.
  • the storage modulus of the pressure-sensitive adhesive layer after photocuring at ⁇ 20° C. is preferably not more than 5.0 ⁇ 10 5 Pa, more preferably not more than 3.0 ⁇ 10 5 Pa, even more preferably not more than 2.0 ⁇ 10 5 Pa, and may be not more than 1.5 ⁇ 10 5 Pa or not more than 1.0 ⁇ 10 5 Pa. Since the storage modulus of the pressure-sensitive adhesive layer 2 after photocuring is small at low temperatures, the pressure-sensitive adhesive layer exhibits strain relaxation properties in a low-temperature environment, and therefore peeling of the pressure-sensitive adhesive layer at the bending portion can be suppressed even when the device to which the reinforcing film is bonded is repeatedly bent or when the bent state is maintained for a long period of time.
  • the acrylic base polymer contains n-octyl acrylate as a monomer component, a plateau region of storage modulus (region where the temperature dependence of storage modulus is small) exists in the low temperature region around -20°C, making it easier to obtain an adhesive with a small storage modulus at -20°C.
  • the storage modulus of the pressure-sensitive adhesive layer after photocuring is preferably 1.0 x 10 4 Pa or more, more preferably 3.0 x 10 4 Pa or more, and may be 5.0 x 10 4 Pa or more or 7.0 x 10 4 Pa or more.
  • the strain recovery rate of the pressure-sensitive adhesive layer at a temperature of 60° C. is preferably 85% or more, more preferably 90% or more, even more preferably 91% or more, and may be 92% or more.
  • the strain recovery rate is calculated by the following formula from the maximum strain S1 when a shear stress of 2 kPa is applied to the pressure-sensitive adhesive layer for 10 minutes using a rotational rheometer, and then the stress is released and left to stand for 10 minutes to recover the strain, and the minimum strain S2 when the stress is released.
  • Strain recovery rate (%) 100 ⁇ (S 1 - S 2 ) / S 1
  • the strain recovery rate is an index showing the extent to which the adhesive layer will return to its original shape when stress is applied to it to cause deformation (distorted state) and then released; the closer to 100%, the higher the shape recovery rate. If the strain recovery rate is within the above range, when the foldable device is held in a folded state (a state in which the adhesive layer is subjected to elongation strain) and then the device is returned to an extended state and the stress on the adhesive layer is released, the adhesive layer will easily restore its shape, making it less likely to develop wrinkles or other deformations.
  • the adhesive strength 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, even more preferably 0.5 N/25 mm or less, and may be 0.4 N/25 mm or less, or 0.3 N/25 mm or less.
  • the adhesive strength between the adhesive layer 2 and the adherend before photocuring is preferably 0.01 N/25 mm or more, more preferably 0.02 N/25 mm or more, and may be 0.03 N/25 mm or more, 0.04 N/25 mm or more, or 0.05 N/25 mm or more.
  • Adhesive strength is determined by a peel test using a polyimide film as the adherend, with a tensile speed of 300 mm/min and a peel angle of 180°. Unless otherwise specified, adhesive strength is measured at 25°C.
  • the adhesive strength between the adhesive layer and the adherend after photocuring is preferably 5 N/25 mm or more, more preferably 7 N/25 mm or more, even more preferably 8 N/25 mm or more, and may be 9 N/25 mm or more or 10 N/25 mm or more.
  • the adhesive strength between the adhesive layer and the adherend after photocuring is preferably at least 5 times, more preferably at least 10 times, even more preferably at least 15 times, and may be at least 20 times, at least 30 times, or at least 50 times, of the adhesive strength between the adhesive layer and the adherend before photocuring.
  • the adhesive strength before photocuring initial adhesive strength
  • the reinforcing film of the present invention is used by being attached to a device or a device component.
  • the reinforcing film 10 has the pressure-sensitive adhesive layer 2 fixed to the film substrate 1, and has a low adhesive strength to the adherend before being photocured after being attached to the adherend. Therefore, the reinforcing film is easy to peel off from the adherend before being photocured.
  • the adherend to which the reinforcing film is attached is not particularly limited, and examples include various electronic devices, optical devices, and their components.
  • the reinforcing film is attached to the surface of a foldable flexible device.
  • the foldable device has a hinge portion and can be folded around this hinge portion. The folding angle can be set as desired, and the device may be bent (folded) at 180°.
  • the reinforcing film may be attached to the surface on the screen side, or the reinforcing film may be attached to the back side (housing).
  • a flexible device that is configured to be bendable at a predetermined location such as a hinge portion, bending and stretching are repeated at the same location when in use.
  • the reinforcing film may be attached to the entire surface of the adherend, or may be selectively attached only to the areas requiring reinforcement (areas to be reinforced). Alternatively, the reinforcing film may be attached to the entire areas requiring reinforcement (areas to be reinforced) and areas not requiring reinforcement (areas not to be reinforced), and then the reinforcing film attached to the areas not requiring reinforcement may be cut and removed. If the adhesive has not yet been photocured, the reinforcing film is in a state where it is temporarily attached to the surface of the adherend, so that it can be easily peeled off and removed from the surface of the adherend.
  • the reinforcing film may be attached to the areas to be reinforced and areas not requiring reinforcement, and the areas to be reinforced may be selectively irradiated with light to photocur the adhesive, and then the reinforcing film may be selectively peeled off and removed from the non-reinforced areas where the adhesive is not yet cured.
  • the reinforcing film By laminating the reinforcing film, appropriate rigidity is imparted, which is expected to improve the handling properties and prevent damage to thin components such as flexible devices.
  • the reinforcing film When the reinforcing film is laminated to a work-in-progress during the device manufacturing process, the reinforcing film may be laminated to a large-sized work-in-progress before it is cut to the product size.
  • the reinforcing film may also be laminated roll-to-roll to the mother roll of a device manufactured by a roll-to-roll process.
  • the adhesive layer 2 is irradiated with active light rays to photocure the adhesive layer.
  • active light rays include ultraviolet light, visible light, infrared light, X-rays, alpha rays, beta rays, and gamma rays.
  • Ultraviolet light is preferred as the active light rays because it can suppress hardening of the adhesive layer during storage and is easy to harden.
  • the irradiation intensity and irradiation time of the active light rays may be set appropriately depending on the composition and thickness of the adhesive layer.
  • the adhesive layer 2 may be irradiated with active light rays from either the film substrate 1 side or the adherend side, or from both sides.
  • the adherend is given an appropriate rigidity and stress is alleviated and dispersed, thereby suppressing various defects that may occur during the manufacturing process, improving production efficiency, and improving yield.
  • the reinforcing film Before the adhesive layer is photocured, the reinforcing film can be easily peeled off from the adherend, so rework is easy even if lamination or lamination defects occur.
  • processing such as selectively removing the reinforcing film from areas other than those to be reinforced is also easy.
  • the reinforcing film attached to the device can prevent damage to the device.
  • the reinforcing film is firmly attached to the device after the adhesive is photocured, the reinforcing film is unlikely to peel off even with long-term use, providing excellent reliability.
  • the reinforced film is unlikely to peel off at the bent portion even when the device is repeatedly bent or when the bent state is maintained for a long time. Furthermore, even when the device is extended after being bent for a long time, the adhesive layer has a high strain recovery rate and high shape recovery, so deformation such as wrinkles is unlikely to occur. Furthermore, the adhesive layer has low resistance and static electricity can be removed from the resin substrate of the device through the adhesive layer, so defects such as electrostatic damage to the device caused by charging (static electricity) can be suppressed.
  • Example 1 Preparation of Reinforcement Film
  • a trifunctional isocyanate-based crosslinking agent Tosoh's "Coronate HX" as a crosslinking agent
  • 0.02 parts by weight of iron acetylacetonate Nihon Kagaku Sangyo's "Nacem Ferric" as a crosslinking catalyst
  • the multifunctional acrylate and urethane acrylate shown in Table 1 as photocuring agents
  • 0.2 parts by weight of 1-butyl-3-methylpyridinium bistrifluoromethanesulfonylimide Nahon Carlit's "CIL-312"
  • the above adhesive composition was applied to a polyethylene terephthalate film having a thickness of 50 ⁇ m using a fountain roll so that the thickness after drying was 25 ⁇ m. After drying at 130 ° C for 1 minute to remove the solvent, the release-treated surface of a release liner (a polyethylene terephthalate film having a thickness of 25 ⁇ m, both sides of which were antistatically treated and one side of which was silicone release-treated) was attached to the adhesive-coated surface.
  • a release liner a polyethylene terephthalate film having a thickness of 25 ⁇ m, both sides of which were antistatically treated and one side of which was silicone release-treated
  • aging treatment was performed for 4 days in an atmosphere of 25 ° C to promote crosslinking, and a reinforcing film was obtained in which a photocurable adhesive sheet was fixed and laminated on a polyethylene terephthalate film substrate and a release liner was temporarily attached thereon.
  • Example 3 A pressure-sensitive adhesive composition was prepared in the same manner as in Example 2, except that 0.2 parts by weight of antistatic agent B was used instead of antistatic agent A, and a reinforcing film was produced.
  • Example 12 Preparation of Pressure-Sensitive Adhesive Composition
  • acrylic polymer H 100 weight percent as polymer solids
  • a tetrafunctional epoxy crosslinking agent (“Tetrad C” manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a crosslinking agent
  • zirconium tetraacetylacetonate (“ZC-150” manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst
  • ZC-150 zirconium tetraacetylacetonate
  • the multifunctional acrylate and urethane acrylate shown in Table 1 as photocuring agents 0.3 parts by weight of "Omnirad 651” manufactured by IGM Resins as a photopolymerization initiator, and 0.2 parts by weight of "CIL-312” manufactured by Nippon Carlit Co., Ltd. as an antistatic agent were added and mixed uniformly to prepare a pressure-sensitive adhesive composition.
  • ⁇ Surface resistance> The release liner was peeled off from the reinforcing film to expose the pressure-sensitive adhesive layer (before photocuring).
  • a probe (Model 152P-2P, manufactured by TREK) was brought into contact with the surface of the pressure-sensitive adhesive layer in an environment of a temperature of 25° C. and a relative humidity of 50%, and the surface resistance was measured using a resistivity meter (Model 152-1, manufactured by TREK) under conditions of an applied voltage of 10 V and a voltage application time of 10 seconds.
  • the adhesive composition was applied and crosslinked in the same manner as in each of the above examples and comparative examples to prepare an adhesive sheet (before photocuring).
  • a release liner was attached to the surface of the adhesive layer of the adhesive sheet before photocuring to isolate it from oxygen, and 1000 mJ/ cm2 of ultraviolet light was irradiated from a 365 nm LED lamp to photocure it.
  • the photocured adhesive sheets were laminated to prepare a measurement sample with a thickness of about 0.8 mm, and a dynamic viscoelasticity measurement was performed under the following conditions using a rotational rheometer ("Discovery-HR2" manufactured by TA Instruments), and the value of the shear storage modulus G' at -20 ° C was read. (Measurement conditions) Deformation mode: Torsion Measurement frequency: 1 Hz Heating rate: 5°C/min Measurement temperature: -50 to 150°C Shape: Parallel plate 8.0mm ⁇
  • a polyimide film having a thickness of 25 ⁇ m (UBE's "Upilex 25S") was attached to a glass plate via a double-sided adhesive tape (Nitto Denko's "No. 531”) to obtain a polyimide film substrate for measurement.
  • the release liner was peeled off and removed from the surface of the reinforced film cut to a width of 25 mm x length of 100 mm, and the film was attached to the polyimide film substrate for measurement using a hand roller to obtain a test sample before photocuring.
  • the test sample before photocuring was irradiated with ultraviolet light from the reinforced film side (PET film substrate side) to photocur the adhesive layer, thereby obtaining a test sample after photocuring.
  • the end of the film substrate of the reinforced film was held with a chuck, and the reinforced film was peeled at 180° at a pulling speed of 300 mm/min, and the peel strength was measured.
  • the release liner was peeled off from the surface of the reinforcing film, and a polyimide film ("Upilex 25S" manufactured by UBE) was attached to the surface of the adhesive layer using a hand roller. After standing at 25°C for 30 minutes, the reinforcing film was peeled off from the polyimide film, and the surface of the polyimide film was visually inspected under a fluorescent lamp to confirm the presence or absence of contamination. Those that were found to be contaminated by attached matter were rated as x, and those that were not found to be contaminated were rated as ⁇ .
  • compositions of the adhesives of the reinforcing films of the examples and comparative examples (the composition and weight average molecular weight Mw of the acrylic polymer, the amount of the photocuring agent, the crosslinking agent, the antistatic agent, and the added amount of PPG) and the evaluation results of the adhesive strength are shown in Tables 1 and 2.
  • the amount of each component is the amount added per 100 parts by weight of the solid content of the acrylic polymer, and in all examples, the amount of the antistatic agent is 0.2 parts by weight.
  • Details of the constituent monomers of the acrylic polymer, the crosslinking agent, and the photocuring agent are as follows:
  • T-C 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (a tetrafunctional epoxy compound, "Tetrad C” manufactured by Mitsubishi Gas Chemical Company)
  • C/HX Isocyanurate of hexamethylene diisocyanate ("Coronate HX" manufactured by Tosoh)
  • UA Polycarbonate skeleton-containing urethane acrylate (Kyoeisha Chemical's "UF-X9-83", functional group number 2-3, weight
  • Antistatic Agent 1-butyl-3-methylpyridinium bistrifluoromethanesulfonylimide ("CIL-312" manufactured by Nippon Carlit)
  • Antistatic agent B 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (abbreviation: EMI-FSI)
  • Antistatic agent C 1-ethyl-3-methylimidazolium dicyanamide (abbreviation: EMI-N(CN) 2 )
  • Comparative Example 6 which used an adhesive containing polymer O, whose main monomer component is butyl acrylate (BA), and 30 parts by weight of a photocuring agent (A200), had a large storage modulus G' at -20°C after photocuring, and was poor in flexibility.
  • Comparative Example 7 which used 10 parts by weight of a photocuring agent (A600) with a long chain length and 30 parts by weight of PPG to reduce resistance, had an adhesive layer that achieved both a low storage modulus and low resistance, but had a reduced strain recovery rate.
  • Comparative Example 1 which used polymer J, whose main monomer component was 2-ethylhexyl acrylate (2EHA), which has a lower glass transition temperature than butyl acrylate, to reduce the storage modulus, the compatibility between the polymer and the light hardener was low, and the liquid light hardener leaked out.
  • Comparative Example 2 which used polymer K, whose main monomer component was n-octyl acrylate (NOAA). 2EHA and NOAA have lower polarity than BA, so it is believed that the low compatibility between the acrylic polymer and the light hardener containing an alkylene oxide chain is the cause of the leakage.
  • Comparative Example 8 which used an adhesive in which 10 parts by weight of PPG was added to the composition of Comparative Example 1, no seepage of the photocuring agent was observed as in Comparative Example 1, but the surface of the polyimide film was contaminated after the reinforcing film was peeled off.
  • the PPG acted as a compatibilizer to suppress the seepage of the photocuring agent, but the photocuring agent and/or PPG were not sufficiently compatible in the composition, and it is believed that the bled-out components were the cause of contamination of the adherend.
  • Example 1 where Polymer A containing methoxyethyl acrylate (MEA) as a monomer component was used instead of Polymer J in Comparative Example 1, G' was as small as in Comparative Example 8, and no seepage of the photocuring agent or contamination of the adherend due to bleed-out was observed.
  • the adhesive layer in Example 1 had a high strain recovery rate of 93%, and combined low G', low resistance, and high recovery.
  • Example 2 instead of polymer K in Comparative Example 2, polymers B to G containing methoxyethyl acrylate (MEA) as a monomer component were used in Examples 2, 4 to 10, which also had low G', low resistance and high recovery, just like Example 1, and the same was true for Example 3, in which the type of antistatic agent was changed.
  • Example 3 had a smaller surface resistance than Example 2, and it can be seen that antistatic agent B (EMI-FSI) exhibited superior antistatic properties.
  • MEA methoxyethyl acrylate
  • the acrylic polymer contained MEA, an acrylic acid ester containing an alkylene oxide chain, as a constituent monomer, which is thought to have increased the polarity of the polymer, improved the compatibility between the acrylic polymer and the photocuring agent, and suppressed the seepage of the photocuring agent.
  • Examples 1 to 10 showed a high strain recovery rate because the adhesive layer after photocuring did not contain low molecular weight components such as PPG.
  • Example 11 which used polymer H containing ethoxyethoxyethyl acrylate (EEEA) as a monomer component, also showed excellent properties, similar to Examples 1 to 10.
  • Example 12 which used polymer I containing acrylic acid as a monomer component, showed excellent properties, but the strain recovery rate was smaller than that of Examples 1 to 11.
  • Examples 13 to 16 which used 2-ethylhexyl acrylate (2EHA), a C8 alkyl ester, and lauryl acrylate (LA), a C12 alkyl ester, as the (meth)acrylic acid alkyl ester monomer component, showed higher adhesive strength after photocuring and lower surface resistance, and thus exhibited superior properties, as compared with Example 12.
  • a comparison between Example 13 and Example 14, and a comparison between Example 15 and Example 16 shows that antistatic agent C (EMI-N(CN) 2 ), which does not contain fluorine atoms, exhibits antistatic properties equal to or greater than those of antistatic agent B (EMI-FSI).
  • Comparative Example 3 which used polymer L with a weight-average molecular weight of 60,000, had low surface resistance and excellent antistatic properties, but the adhesive strength did not increase sufficiently even after photocuring, and the adhesive strength of the adhesive layer after photocuring was insufficient.
  • Methoxypolyethylene glycol acrylate (AM90G) used as a monomer component of polymer L has an excellent resistance-lowering effect due to the long chain length of the polyethylene glycol, but it acts as a chain transfer agent during polymerization of the polymer, which is thought to prevent the molecular weight of the polymer from increasing sufficiently.
  • Comparative Example 4 which used polymer M, in which the proportion of MEA in the constituent monomer components of the acrylic polymer was 4%, had a small G' and a large strain recovery rate, but the surface resistance was large and the antistatic properties were insufficient.
  • Comparative Example 5 which used Polymer N, in which the proportion of MEA in the constituent monomer components of the acrylic polymer was 60%, had high adhesive strength of the adhesive layer before photocuring and poor easy peelability. Furthermore, in Comparative Example 5, the adhesive strength did not increase sufficiently even after photocuring, and the adhesive strength of the adhesive layer after photocuring was insufficient. In Comparative Example 5, the proportion of acrylic acid ester containing an alkylene oxide chain in the monomer components constituting the acrylic polymer was high, which excessively increased the compatibility between the acrylic polymer and the photocuring agent, making it difficult for the photocuring agent to act as a WBL, and it is believed that this resulted in a large initial adhesive strength.
  • a photocurable adhesive composition containing an acrylic-based polymer with a specified composition has low resistance and antistatic properties, low initial adhesive strength, and excellent adhesive properties after photocuring. It also has a low storage modulus in the low temperature range and a high strain recovery rate, making it suitable as a reinforcing film for foldable devices.

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PCT/JP2024/019040 2023-05-29 2024-05-23 補強フィルム、補強フィルム付きデバイスおよびその製造方法 WO2024247886A1 (ja)

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