Adhesive, curable adhesive composition, adhesive sheet, and method for producing the same

Abstract

The present invention relates to an adhesive, a curable adhesive composition, an adhesive sheet, and a method for producing the same. The present invention provides an adhesive capable of exhibiting both low-temperature adhesiveness and high-temperature holding power, and an adhesive sheet obtained using the same. The adhesive of the present invention contains an acrylic base polymer. The acrylic base polymer contains an acrylic segment and a urethane segment. In the base polymer, the content of the urethane segment is 3 to 20 parts by weight, relative to 100 parts by weight of the acrylic segment. The adhesive sheet is obtained by coating the adhesive composition in layers and curing as necessary.

Description

[0001] This application is a divisional application of Chinese patent application filed on January 22, 2019, with application number 201910058330.9 and entitled "Adhesive, Curable Adhesive Composition, Adhesive Sheet and Method for Manufacturing the Same". Technical Field

[0002] This invention relates to adhesives and adhesive sheets. Furthermore, this invention relates to curable adhesive compositions applicable to the production of adhesive sheets, and methods for manufacturing adhesive sheets obtained using the adhesive compositions. Background Technology

[0003] Adhesive sheets are used in various applications such as joining, protecting, and decorating items. A representative example of adhesive sheets is acrylic adhesive sheets formed from adhesives with acrylic-based polymers as the main component. Acrylic adhesive sheets exhibit moderate wetting, cohesiveness, and adhesive properties, and also possess excellent weather resistance and heat resistance.

[0004] For acrylic adhesives, various properties, such as the glass transition temperature, can be adjusted by changing the types of monomers and the copolymerization ratio. Furthermore, the cohesive strength and adhesive properties can be improved by introducing crosslinking structures into the base polymer. For example, a crosslinking structure can be introduced into the polymer by reacting a polymer with reactive functional groups such as hydroxyl and carboxyl groups on its side chains with crosslinking agents such as isocyanates and epoxy resins. Additionally, polymers with crosslinking structures can be obtained by using polyfunctional monomers or oligomers having two or more polymerizable functional groups per molecule as copolymerizing components. Polyfunctional (meth)acrylates are commonly used as polyfunctional monomers and oligomers for introducing crosslinking structures into acrylic polymers.

[0005] By increasing the cohesiveness of the adhesive, the shear storage modulus increases. With the increase in shear storage modulus, the high-temperature adhesive holding force increases, exhibiting a tendency to suppress delamination of the joint even when a certain shear force is applied to the joint components at high temperatures. On the other hand, increasing the cohesiveness of the adhesive tends to decrease tackiness, sometimes resulting in insufficient adhesive force at low temperatures.

[0006] Patent Documents 1 and 2 disclose urethane adhesives obtained by copolymerizing urethane oligomers with acrylic monomers. Generally, urethane polymers have lower glass transition temperatures than acrylic polymers; therefore, urethane adhesives have the advantage of improved adhesion at low temperatures compared to acrylic adhesives.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2014 / 027788

[0010] Patent Document 2: International Publication No. 2016 / 002666 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] Mobile devices such as cell phones and smartphones, automobiles, and refrigeration and freezing equipment are used in a wide temperature range from low to high. Therefore, adhesives used for the bonding and surface decoration of components used in these devices require both excellent high-temperature retention and good low-temperature adhesion.

[0013] For acrylic adhesives, lowering the glass transition temperature of the polymer tends to improve adhesive properties at low temperatures. Furthermore, urethane adhesives disclosed in Patent Documents 1 and 2 have low glass transition temperatures and excellent adhesive properties at low temperatures.

[0014] For acrylic adhesives, as the glass transition temperature decreases, there is a tendency for the storage modulus to decrease and the adhesive holding power at high temperatures to decline. Urethane adhesives, which have low glass transition temperatures, also exhibit the same tendency, and their holding power at high temperatures cannot be considered sufficient. In other words, for conventional adhesives, there is a certain correlation between glass transition temperature and shear storage modulus, and it is not easy to achieve both low-temperature adhesiveness and high-temperature holding power.

[0015] In view of the above, the object of the present invention is to provide an adhesive that can combine low-temperature adhesiveness and high-temperature retention, and an adhesive sheet obtained by using the adhesive.

[0016] means for solving problems

[0017] The adhesive of the present invention contains an acrylic base polymer. The acrylic base polymer comprises acrylic segments and carbamate segments. In the base polymer, the content of carbamate segments is 3 to 20 parts by weight relative to 100 parts by weight of acrylic segments.

[0018] The weight-average molecular weight of the carbamate segments is preferably 3,000 to 50,000. The glass transition temperature of the carbamate segments is preferably below 0°C.

[0019] As urethane segments, urethane segments having polyether chains, polyester chains, polycarbonate chains, etc., are preferred. Urethane segments having polyether chains are obtained, for example, by reacting a polyether polyol with an isocyanate. Urethane segments having polyester chains are obtained, for example, by reacting a polyester polyol with an isocyanate. Urethane segments having polycarbonate chains, etc., are obtained, for example, by reacting a polycarbonate polyol with an isocyanate.

[0020] In the base polymer, acrylic segments and urethane segments are covalently bonded. In one embodiment, the acrylic base polymer has a structure obtained by crosslinking acrylic segments with urethane segments. The polymer obtained by crosslinking acrylic segments with urethane segments can be obtained, for example, by copolymerizing the monomer components constituting the acrylic segments with urethane (meth)acrylates having (meth)acryloyl groups at the ends.

[0021] The adhesive preferably contains 50% by weight or more of the aforementioned base polymer. The adhesive may contain components other than the aforementioned base polymer. For example, the adhesive may contain acrylic oligomers with a weight-average molecular weight of 1000 to 30000. The glass transition temperature of the adhesive is preferably -25°C to 0°C.

[0022] The adhesive described above can be formed by curing the curable adhesive composition using light curing, heat curing, or the like. In one embodiment, the curable adhesive composition comprises an acrylic monomer and / or a portion thereof as a polymer (acrylic prepolymer composition) and a urethane (meth)acrylate having a plurality of (meth)acryloyl groups. By curing the adhesive composition, the acrylic monomer contained in the prepolymer composition is polymerized with the urethane (meth)acrylate to obtain a base polymer in which a crosslinked structure formed by urethane segments is introduced onto the acrylic segments.

[0023] The content of urethane (meth)acrylate is preferably 3 to 20 parts by weight relative to 100 parts by weight of the total acrylic monomers and some of their polymers. The weight-average molecular weight of urethane (meth)acrylate is preferably 3,000 to 50,000. The glass transition temperature of urethane (meth)acrylate is preferably below 0°C.

[0024] The total content of acrylic monomers and a portion thereof in the adhesive composition is preferably 50% by weight or more. The adhesive composition may contain components other than acrylic monomers and a portion thereof, and urethane (meth)acrylates. The adhesive composition may contain acrylic oligomers with a weight average molecular weight of 1000 to 30000. The adhesive composition may contain a photopolymerization initiator and / or a thermal polymerization initiator. The adhesive composition is preferably a photocurable adhesive composition containing a photopolymerization initiator.

[0025] Furthermore, the present invention relates to an adhesive sheet obtained by forming the above-mentioned adhesive into a sheet shape. For example, this adhesive sheet can be formed by applying the above-mentioned curable adhesive composition in a layered manner onto a substrate and then curing the adhesive composition. As a curing method for the adhesive composition, light curing and heat curing are preferred.

[0026] Invention Effects

[0027] The adhesive of this invention, by having acrylic and urethane segments in a specified ratio in the base polymer, achieves both a low glass transition temperature and a high storage modulus. Therefore, the adhesive sheet of this invention exhibits excellent low-temperature adhesion and high-temperature adhesive retention, enabling highly reliable adhesion over a wide temperature range. Attached Figure Description

[0028] Figure 1 This is a cross-sectional view showing an example of the composition of an adhesive sheet with a release film.

[0029] Figure 2 This is a cross-sectional view showing an example of how the adhesive sheet is used.

[0030] Figure Labels

[0031] 5 Adhesive Sheets

[0032] 1, 2 release film

[0033] 10, 20 membrane substrates

[0034] 11, 21 Demolding layer

[0035] 3. Glued pieces Detailed Implementation

[0036] [Basic Polymers]

[0037] The adhesive of the present invention contains a base polymer comprising acrylic segments and urethane segments. In the base polymer, the content of urethane segments is 3 to 20 parts by weight, preferably 4 to 17 parts by weight, and more preferably 5 to 15 parts by weight, relative to 100 parts by weight of acrylic segments. By including acrylic segments and urethane segments, the glass transition temperature can be lowered without compromising the high-temperature adhesive holding power of the acrylic polymer, thereby improving low-temperature adhesiveness.

[0038] In the base polymer, acrylic segments and carbamate segments are covalently bonded. Examples of polymers in which acrylic and carbamate segments are covalently bonded include: block polymers where both segments form the main chain; graft polymers where one segment forms the main chain and another segment is bonded to the main chain to form a side chain; and crosslinked polymers where one segment is crosslinked with another. For graft polymers and crosslinked polymers, it is preferable that the acrylic segment is the main chain, and that carbamate segments, serving as side chains or crosslinking components, are bonded to the acrylic segment (acrylic polymer chain) that forms the main chain.

[0039] <Acrylic segments>

[0040] The acrylic segments contain alkyl (meth)acrylates as the main constituent monomers. It should be noted that, in this specification, "(meth)acrylate" refers to acrylic acid and / or methacrylic acid.

[0041] As alkyl (meth)acrylates, alkyl (meth)acrylates with alkyl groups having 1 to 20 carbon atoms are suitable. The alkyl group of the alkyl (meth)acrylate may have branches, and the alkyl (meth)acrylate may also have cyclic alkyl groups.

[0042] Specific examples of alkyl (meth)acrylates having chain-like alkyl groups include: methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and propyl (meth)acrylate. Nonyl acrylate, isononyl acrylate, decyl acrylate, isodecyl acrylate, undecyl acrylate, dodecyl acrylate, isotridecyl acrylate, tetradecyl acrylate, isotetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecanyl acrylate, octadecyl acrylate, isooctadecyl acrylate, nonadecanyl acrylate, etc.

[0043] Specific examples of alkyl (meth)acrylates having alicyclic alkyl groups include: cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, and other cycloalkyl (meth)acrylates; isobornyl (meth)acrylate and other (meth)acrylates having bicyclic aliphatic hydrocarbon rings; tetrahydrodicyclopentadienyl (meth)acrylate, tetrahydrodicyclopentadienyloxyethyl (meth)acrylate, tetrahydrotricyclopentadienyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, and other (meth)acrylates having three or more aliphatic hydrocarbon rings.

[0044] The amount of (meth)acrylate alkyl ester is preferably 50% by weight or more, more preferably 60% by weight or more, and even more preferably 70% by weight or more, relative to the total amount of monomer components constituting the acrylic segments. From the viewpoint of adjusting the glass transition temperature (Tg) of the acrylic segments to a suitable range, the amount of (meth)acrylate alkyl ester having a chain alkyl group having 4 to 10 carbon atoms is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight or more, relative to the total amount of monomer components constituting the acrylic segments.

[0045] It should be noted that the constituent components of the urethane segments (e.g., urethane (meth)acrylates) are not included in the monomer components constituting the acrylic segments. The same applies to graft polymers in which the acrylic segments are the main chain and have urethane grafted side chains, and to crosslinked polymers in which the acrylic segments are crosslinked via urethane segments, where the main chain structure includes terminal functional groups of the urethane segments.

[0046] Acrylic acid segments can contain hydroxyl-containing monomers and carboxyl-containing monomers as constituent monomer components.

[0047] Examples of hydroxyl-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-hydroxydodecyl (meth)acrylate, and methyl (4-hydroxymethylcyclohexyl)methacrylate, among other meth acrylates. Examples of carboxyl-containing monomers include: acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, and other acrylic monomers; itaconic acid, maleic acid, fumaric acid, and crotonic acid, among others.

[0048] Acrylic acid segments can contain nitrogen-containing monomers as constituent monomers. Examples of nitrogen-containing monomers include: N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazolium, and vinylpyridine. Vinyl monomers such as azoles, vinylmorpholine, (meth)acryloylmorpholine, N-vinylcarboxylic acid amides, and N-vinylcaprolactam; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile.

[0049] By incorporating highly polar monomers such as hydroxyl-containing monomers and carboxyl-containing monomers into acrylic segments, adhesives tend to exhibit improved cohesiveness and adhesive retention at high temperatures. The amount of highly polar monomers (the total of hydroxyl-containing monomers, carboxyl-containing monomers, and nitrogen-containing monomers) relative to the total amount of monomers constituting the acrylic segments is preferably 1% to 45% by weight, more preferably 5% to 40% by weight, and even more preferably 10% to 35% by weight.

[0050] Acrylic segments may include monomers other than those mentioned above, such as anhydride monomers, caprolactone adducts of (meth)acrylic acid, sulfonic acid monomers, phosphate monomers, vinyl acetate, vinyl propionate, styrene, α-methylstyrene, and other vinyl monomers; cyanoacrylic monomers such as acrylonitrile and methacrylonitrile; epoxy monomers such as glycidyl methacrylate; diol acrylate monomers such as polyethylene glycol methacrylate, polypropylene glycol methacrylate, methoxyethylene glycol methacrylate, and polypropylene glycol methacrylate; and acrylate monomers such as tetrahydrofurfuryl methacrylate, fluorinated (meth)acrylates, polysiloxane (meth)acrylates, and 2-methoxyethyl methacrylate.

[0051] Acrylic acid segments can contain polyfunctional monomers or oligomers. Polyfunctional compounds contain two or more polymerizable functional groups with unsaturated double bonds, such as (meth)acryloyl or vinyl groups, in one molecule. Examples of polyfunctional compounds 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, alkyl glycol di(meth)acrylate, tricyclodecanediethanol di(meth)acrylate, ethoxylated isocyanurate triacrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol di(meth)acrylate. Acrylates, 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, epoxy (meth)acrylate, butadiene (meth)acrylate, isoprene (meth)acrylate, etc.

[0052] By incorporating multifunctional monomers as constituent monomer components into acrylic segments, branched structures (crosslinked structures) are introduced onto the segments. As described later, in one embodiment of the adhesive of the present invention, a crosslinked structure formed by urethane segments is introduced onto the acrylic segments. In a base polymer having such a crosslinked structure, the low-temperature adhesive strength of the adhesive sometimes decreases when the amount of crosslinked structures formed by multifunctional monomer components other than urethane segments increases. Therefore, the amount of multifunctional compound is preferably 3% by weight or less, more preferably 1% by weight or less, further preferably 0.5% by weight or less, and particularly preferably 0.3% by weight or less, relative to the total amount of monomer components constituting the acrylic segments.

[0053] From the viewpoint of obtaining an adhesive with excellent low-temperature adhesion by lowering the glass transition temperature of the base polymer, the glass transition temperature of the acrylic segments is preferably below 0°C. On the other hand, from the viewpoint of improving adhesive retention at high temperatures, the glass transition temperature of the acrylic segments is preferably above -30°C, more preferably above -20°C, and even more preferably above -10°C. The glass transition temperature (Tg) of the acrylic segments can be determined from the peak temperature of the loss tangent (tanδ) of the polymer obtained by polymerizing the monomer components constituting the acrylic segments using dynamic viscoelasticity measurement (frequency: 1 Hz).

[0054] For basic polymers where acrylic and carbamate segments are bonded, it is difficult to determine the glass transition temperature (Tg) of the acrylic segment alone; therefore, evaluation based on theoretical Tg is sufficient. The glass transition temperature (Tg) of a homopolymer composed of acrylic segment monomers is... i and the weight fraction W of each monomer component i The theoretical Tg is calculated using the following Fox formula.

[0055] 1 / Tg=Σ(W i / Tg i )

[0056] Tg is the theoretical glass transition temperature (in K) of the polymer chain, expressed in W. i Tg represents the weight fraction (weight-based copolymerization ratio) of monomer component i constituting the chain segment. i The glass transition temperature (in K) of the homopolymer of monomer component i is given. The glass transition temperature of the homopolymer can be the value described in the 3rd edition of the Polymer Handbook (John Wiley & Sons, Inc., 1989). For homopolymers of monomers not described in the aforementioned literature, the Tg can be the peak temperature of the loss tangent (tanδ) obtained by dynamic viscoelasticity determination.

[0057] From the viewpoint of obtaining an adhesive with excellent low-temperature adhesion by lowering the glass transition temperature of the base polymer, the theoretical Tg of the acrylic segments is preferably 5°C or less, more preferably 0°C or less. On the other hand, from the viewpoint of improving adhesive retention at high temperatures, the theoretical Tg of the acrylic segments is preferably -50°C or more, more preferably -40°C or more, and even more preferably -20°C or more.

[0058] <Carbamate segments>

[0059] Carbamate segments are molecular chains containing carbamate bonds. Carbamate segments typically comprise polyurethane chains obtained by reacting diols with diisocyanates. From the viewpoint of obtaining adhesives that possess both low-temperature adhesion and high-temperature retention, the molecular weight of the polyurethane chains in the carbamate segments is preferably 3,000 to 50,000, more preferably 4,000 to 40,000, and even more preferably 5,000 to 30,000.

[0060] Examples of diols used to form polyurethane chains include: low molecular weight diols such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, and hexanediol; and high molecular weight polyols such as polyester polyols, polyether polyols, polycarbonate polyols, acrylic polyols, epoxy polyols, and caprolactone polyols.

[0061] Polyester polyols are polyesters with terminal hydroxyl groups, obtained by reacting a polyacid with a polyol in excess of the alcohol equivalent relative to the carboxylic acid equivalent. A combination of a dicarboxylic acid and a diol is preferred as the polyacid and polyol components constituting the polyester polyol.

[0062] Examples of dicarboxylic acids include: aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, tetradecanoic acid, and eicosanoic acid; and the anhydrides and lower alcohol esters of these dicarboxylic acids.

[0063] Examples of diols include: ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentylene glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, etc.

[0064] Polyether polyols are obtained by ring-opening addition polymerization of alkyl epoxides and polyols. Examples of alkyl epoxides include ethylene oxide, propylene oxide, butane oxide, phenyl ethylene oxide, and tetrahydrofuran. Examples of polyols include the aforementioned diols, glycerol, and trimethylolpropane.

[0065] Examples of polycarbonate polyols include: polycarbonate polyols obtained by polycondensation of a diol component with a carbonyl chloride; polycarbonate polyols obtained by transesterification condensation of a diol component with carbonate diesters such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, ethyl butyl carbonate, ethylene carbonate, propylene carbonate, diphenyl carbonate, and dibenzyl carbonate; copolymerized polycarbonate polyols obtained using two or more polyol components; and polycarbonates obtained by esterification of the above-mentioned polycarbonate polyols with carboxyl-containing compounds. Polyols; polycarbonate polyols obtained by etherification of the above-mentioned polycarbonate polyols with hydroxyl-containing compounds; polycarbonate polyols obtained by transesterification of the above-mentioned polycarbonate polyols with ester compounds; polycarbonate polyols obtained by transesterification of the above-mentioned polycarbonate polyols with hydroxyl-containing compounds; polyester polycarbonate polyols obtained by polycondensation of the above-mentioned polycarbonate polyols with dicarboxylic acid compounds; copolymer polyether polycarbonate polyols obtained by copolymerization of the above-mentioned polycarbonate polyols with epoxides, etc.

[0066] Polyacrylate polyols can be obtained by copolymerizing (meth)acrylates with monomers containing hydroxyl groups. Examples of monomers containing hydroxyl groups include: 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypentyl (meth)acrylate, and other hydroxyalkyl esters of (meth)acrylate; mono-esters of (meth)acrylate in polyols such as glycerol and trimethylolpropane; and N-hydroxymethyl (meth)acrylamide. Examples of (meth)acrylates include: methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

[0067] Polyacrylic acid polyols may contain monomer components other than those mentioned above as comonomers. Examples of comonomers other than those mentioned above include: unsaturated monocarboxylic acids such as (meth)acrylic acid; unsaturated dicarboxylic acids such as maleic acid and their anhydrides and monoesters or diesters; unsaturated nitriles such as (meth)acrylonitrile; unsaturated amides such as (meth)acrylamide and N-hydroxymethyl(meth)acrylamide; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether; α-olefins such as ethylene and propylene; halogenated α,β-unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene.

[0068] The diisocyanate used to form the polyurethane chain can be either an aromatic diisocyanate or an aliphatic diisocyanate. Examples of aromatic diisocyanates include: 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 2,2-bis(4-isocyanate-phenyl)propane, tetramethyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2-chloro-1,4-phenyl diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, phenylenediamine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl sulfoxide diisocyanate, 4,4'-diphenyl sulfone diisocyanate, and 4,4'-biphenyl diisocyanate. Examples of aliphatic diisocyanates include: butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis(isocyanate methyl)cyclohexane, and methylcyclohexane diisocyanate.

[0069] As diisocyanates, derivatives of isocyanate compounds can also be used. Examples of derivatives of isocyanate compounds include: dimers of polyisocyanates, trimers of isocyanates (isocyanurates), polymeric MDI, adducts with trimethylolpropane, biuret-modified compounds, urethane-modified compounds, urea-modified compounds, etc.

[0070] As a diisocyanate component, urethane prepolymers with isocyanate groups at the ends can also be used. By reacting a polyol with a polyisocyanate compound in an excess of the polyisocyanate compound, urethane prepolymers with isocyanate groups at the ends can be obtained.

[0071] By introducing functional groups capable of bonding with acrylic segments at the ends of polyurethane chains, covalent bonds can be formed between urethane and acrylic segments. For example, by using a polyurethane chain having functional groups capable of bonding with the ends of acrylic segments, block polymers having both acrylic and urethane segments can be obtained. By using a compound having a functional group at one end of the polyurethane chain capable of copolymerizing with monomer components constituting acrylic segments or capable of reacting with carboxyl groups, hydroxyl groups, or other functional groups contained in the side chains of acrylic segments, graft polymers in which urethane segments are bonded as side chains to acrylic segments (acrylic polymer chains as the main chain) can be obtained. By using a compound having functional groups at both ends of the polyurethane chain (or multiple ends if the polyurethane chain has branches) capable of copolymerizing with monomer components constituting acrylic segments or capable of reacting with carboxyl groups, hydroxyl groups, or other functional groups contained in the side chains of acrylic segments, cross-linked structures formed by urethane segments can be introduced onto the acrylic segments.

[0072] To obtain an acrylic-based polymer with a cross-linked structure formed by urethane segments, compounds having (meth)acryloyl groups at both ends of the polyurethane chain are preferred. For example, by copolymerizing the monomer component constituting the acrylic segments with a urethane di(meth)acrylate having (meth)acryloyl groups at both ends, a cross-linked structure formed by urethane segments can be introduced onto the acrylic segments. Uraffinate (meth)acrylates have the advantages of excellent compatibility with acrylic monomers and acrylic polymer chains, and the ability to easily and uniformly introduce cross-linking points onto the acrylic segments.

[0073] A urethane di(meth)acrylate with (meth)acryloyl groups at both ends can be obtained, for example, by using a (meth)acrylate compound with hydroxyl groups in addition to the diol component during the polymerization of polyurethane. From the viewpoint of controlling the chain length (molecular weight) of the urethane segment, it is preferable to synthesize an isocyanate-terminated polyurethane by reacting a diol with a diisocyanate in an isocyanate excess, then adding a (meth)acrylate compound with hydroxyl groups, and reacting the terminal isocyanate groups of the polyurethane with the hydroxyl groups of the (meth)acrylate compound.

[0074] Examples of (meth)acrylic acid compounds containing hydroxyl groups include: hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxymethylacrylamide, and hydroxyethylacrylamide.

[0075] To obtain isocyanate-terminated polyurethane, the diol component and the diisocyanate component are used in a manner where the NCO / OH (equivalent ratio) is preferably 1.1 to 2.0, more preferably 1.15 to 1.5. Alternatively, the diisocyanate component can be added after mixing and reacting approximately equal amounts of the diol component and the diisocyanate component.

[0076] As the urethane (meth)acrylate, commercially available products sold by companies such as Arakawa Chemical Industry, Shin-Nakamura Chemical Industry, Toa Synthetic, Kyoeisha Chemical, Nippon Kayaku, Nippon Synthetic Chemical Industry, Negami Kogyo, and DAICL-ALLNEX can be used. The weight-average molecular weight of the urethane (meth)acrylate is preferably 3,000 to 50,000, more preferably 4,000 to 40,000, and even more preferably 5,000 to 30,000.

[0077] The glass transition temperature of urethane (meth)acrylate is preferably below 0°C, more preferably below -10°C, further preferably below -30°C, and particularly preferably below -40°C. By using urethane (meth)acrylate with a low Tg, adhesives with excellent low-temperature adhesion can be obtained even when the cohesiveness of the base polymer is improved by introducing a cross-linking structure through urethane segments. The lower limit of the glass transition temperature of urethane (meth)acrylate is not particularly limited, but from the viewpoint of obtaining an adhesive with excellent high-temperature retention, it is preferably above -100°C, more preferably above -80°C, and further preferably above -60°C.

[0078] When multifunctional urethane (meth)acrylates such as urethane dimethacrylates are used to introduce cross-linked structures formed by urethane segments onto acrylic segments, the glass transition temperature of the urethane segments of the base polymer is approximately equal to that of the urethane (meth)acrylate.

[0079] <Preparation of Basic Polymers>

[0080] Polymers having acrylic and carbamate segments can be polymerized using various known methods. Using multifunctional carbamate (meth)acrylates such as dimethacrylate as constituents of the carbamate segments, and copolymerizing the monomeric components constituting the acrylic segments with the carbamate (meth)acrylates, an acrylic polymer is obtained in which a cross-linked structure formed by carbamate segments is introduced onto the acrylic segments.

[0081] The amount of urethane (meth)acrylate used is preferably 3 to 20 parts by weight, more preferably 4 to 25 parts by weight, and even more preferably 5 to 20 parts by weight, relative to 100 parts by weight of the monomer component used to form the acrylic segments. By setting the amount of urethane (meth)acrylate used within the above range, a base polymer with a urethane segment content within the aforementioned range can be prepared. If the urethane segment content is too low, there is a tendency for the adhesive's high-temperature holding power to decrease due to reduced cohesiveness of the base polymer. If the urethane segment content is too high, the viscosity decreases as the cohesiveness of the base polymer increases, and there is a tendency for reduced low-temperature adhesiveness.

[0082] Examples of polymerization methods include solution polymerization, photopolymerization, bulk polymerization, and emulsion polymerization. Considering the high reaction efficiency of free radical polymerization, solution polymerization or photopolymerization is preferred. Ethyl acetate, toluene, etc., can be used as solvents for solution polymerization.

[0083] Polymerization initiators, such as photopolymerization initiators and thermal polymerization initiators, can be used depending on the type of polymerization reaction. As photopolymerization initiators, benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-keto alcohol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzoyl-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators can be used. As thermal polymerization initiators, azo initiators, peroxide initiators, and redox initiators composed of peroxides and reducing agents (e.g., combinations of persulfate and sodium bisulfite, combinations of peroxide and sodium ascorbate, etc.) can be used.

[0084] During polymerization, chain transfer agents and polymerization inhibitors (polymerization inhibitors) can be used to adjust molecular weight, among other purposes. Examples of chain transfer agents include: α-thioglycerol, dodecyl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolic acid, 2,3-dimercapto-1-propanol, and other thiols; α-methylstyrene dimers, etc.

[0085] When preparing the basic polymer, depending on the bonding mode between the acrylic and urethane segments, the polymerization can be carried out in one step or in multiple steps, either by reacting all the monomer components constituting the acrylic segments with all the components constituting the urethane segments (e.g., urethane (meth)acrylate). For example, when obtaining a polymer with a cross-linked structure formed by urethane segments introduced onto the acrylic segments through multi-step polymerization, the following method is preferred: polymerizing the monofunctional monomers constituting the acrylic segments to form a prepolymer composition (prepolymerization); adding a polyfunctional compound such as urethane di(meth)acrylate to the slurry of the prepolymer composition; and polymerizing the prepolymer composition with the polyfunctional monomers (postpolymerization). The prepolymer composition is a partial polymer containing a polymer with a low degree of polymerization and unreacted monomers.

[0086] By prepolymerizing the constituent components of acrylic polymers, branch points (crosslinking points) formed by multifunctional compounds such as urethane di(meth)acrylate can be uniformly introduced into the acrylic segments. Alternatively, an adhesive sheet can be formed by postpolymerization on a substrate after coating a low molecular weight polymer or a mixture of a portion of the polymer and unpolymerized monomer components (adhesive composition) onto the substrate.

[0087] Low-polymerization-degree compositions, such as prepolymer compositions, have low viscosity and excellent coatability. Therefore, by following the method of post-polymerization on a substrate after coating an adhesive composition which is a mixture of a prepolymer composition and a multifunctional compound, the productivity of adhesive sheets can be improved and the thickness of the adhesive sheets can be made uniform.

[0088] Prepolymer compositions can be prepared, for example, by partially polymerizing (prepolymerizing) a composition (referred to as a "prepolymer forming composition") obtained by mixing monomeric components constituting acrylic segments with a polymerization initiator. The prepolymer forming composition may contain a multifunctional compound (a multifunctional monomer or a multifunctional oligomer). For example, the prepolymer forming composition may contain a portion of a multifunctional compound as a raw material for polymerizing, with the remaining multifunctional compound added after the prepolymer is polymerized and supplied for subsequent polymerization.

[0089] In addition to monomers and polymerization initiators, the composition for forming prepolymers may include chain transfer agents as needed. The polymerization method for the prepolymer is not particularly limited, but photopolymerization is preferred from the perspective of ease of adjusting the molecular weight (polymerization rate) of the prepolymer. There are no particular limitations on the polymerization initiators and chain transfer agents used for prepolymerization; for example, the photopolymerization initiators and chain transfer agents described above can be used.

[0090] There are no particular limitations on the polymerization rate of the prepolymer, but from the viewpoint of adjusting it to a viscosity suitable for coating on a substrate, 3% to 50% by weight is preferred, and more preferably 5% to 40% by weight. The polymerization rate of the prepolymer can be adjusted to the desired range by adjusting the type and amount of photoinitiator, the intensity of irradiation with active light such as UV light, and the irradiation time. It should be noted that the polymerization rate of the prepolymer is calculated from the weight before and after heating (drying) of the prepolymer composition at 130°C for 3 hours according to the following formula. In the case of prepolymerization by solution polymerization, the weight obtained by subtracting the amount of solvent from the total weight of the prepolymer composition is used as the weight before drying in the following formula, and the polymerization rate is calculated.

[0091] Polymerization rate (%) of prepolymer = (Weight after drying / Weight before drying) × 100

[0092] A curable adhesive composition is prepared by mixing polyfunctional urethane (meth)acrylate and, as needed, the remaining monomer components constituting the acrylic segments, polymerization initiators, chain transfer agents, and other additives into the above prepolymer composition. Then, post-polymerization is carried out to obtain a basic polymer in which a cross-linked structure formed by urethane segments is introduced into the acrylic segments.

[0093] There are no particular limitations on the polymerization initiators and chain transfer agents used for post-polymerization; for example, the photopolymerization initiators and chain transfer agents described above can be used. If the polymerization initiator used in prepolymerization remains in the prepolymer composition without deactivation, the addition of the polymerization initiator for post-polymerization can be omitted.

[0094] The polymerization method for post-polymerization is not particularly limited and can be the same as or different from that for the prepolymer. When the prepolymer is polymerized by photopolymerization, post-polymerization is also preferably carried out by photopolymerization. In particular, photopolymerization is suitable for preparing solvent-free adhesive compositions that are substantially free of solvents. The polymerization rate of the reaction product after post-polymerization is preferably 94% or more, more preferably 97% or more, and even more preferably 99% or more.

[0095] The post-polymerized base polymer has a large molecular weight and high viscosity, making it sometimes difficult to coat onto the substrate. Therefore, in the case of forming an adhesive sheet, as described later, it is preferable to prepare a curable adhesive composition comprising a prepolymer composition and a urethane (meth)acrylate, coat the adhesive composition onto the substrate in layers, and then perform post-polymerization.

[0096] [Adhesive Composition]

[0097] The adhesive of the present invention can be an adhesive composition that includes polymers other than the base polymer, oligomers, various additives, etc., in addition to the base polymer described above.

[0098] (Oligomers)

[0099] For purposes such as adjusting adhesive strength and viscosity, adhesive compositions may contain various oligomers. For example, oligomers with a weight-average molecular weight of about 1000 to about 30000 can be used as oligomers. Acrylic oligomers are preferred from the perspective of excellent compatibility with acrylic-based polymers.

[0100] Acrylic oligomers contain alkyl (meth)acrylates as the main constituent monomer component. Preferably, acrylic oligomers contain alkyl (meth)acrylates having chain-like alkyl groups ((meth)acrylate chain-like alkyl esters) and alkyl (meth)acrylates having alicyclic alkyl groups ((meth)acrylate alicyclic alkyl esters) as constituent monomer components. Specific examples of alkyl (meth)acrylate chain-like alkyl esters and alicyclic alkyl (meth)acrylate alicyclic alkyl esters are the same as those previously illustrated as constituent monomers of acrylic segments.

[0101] The glass transition temperature of acrylic oligomers is preferably 20°C or higher, more preferably 30°C or higher, and even more preferably 40°C or higher. By combining a low-Tg base polymer with a cross-linked structure formed from urethane segments with a high-Tg acrylic oligomer, there is a tendency to improve the high-temperature retention of the adhesive. There is no particular upper limit to the glass transition temperature of acrylic oligomers; it is typically 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. The glass transition temperature of the acrylic oligomers is calculated according to the aforementioned Fox formula.

[0102] Among the alkyl methacrylates exemplified, methyl methacrylate is preferred as a linear alkyl methacrylate, considering its high glass transition temperature and excellent compatibility with the base polymer. As an alicyclic alkyl methacrylate, tetrahydrodicyclopentadienyl acrylate, tetrahydrodicyclopentadienyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. That is, the acrylic oligomer preferably comprises one or more monomers selected from the group consisting of tetrahydrodicyclopentadienyl acrylate, tetrahydrodicyclopentadienyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate as constituent monomer components.

[0103] The amount of (meth)acrylate cycloalkyl esters is preferably 10% to 90% by weight, more preferably 20% to 80% by weight, and even more preferably 30% to 70% by weight, relative to the total amount of monomer components constituting the acrylic oligomer. The amount of (meth)acrylate chain alkyl esters is preferably 10% to 90% by weight, more preferably 20% to 80% by weight, and even more preferably 30% to 70% by weight, relative to the total amount of monomer components constituting the acrylic oligomer.

[0104] The weight-average molecular weight of the acrylic oligomer is preferably 1,000 to 30,000, more preferably 1,500 to 10,000, and even more preferably 2,000 to 8,000. By using acrylic oligomers with molecular weights in this range, there is a tendency to improve the adhesive strength and high-temperature retention properties of the adhesive.

[0105] Acrylic oligomers can be obtained by polymerizing the above-mentioned monomer components using various polymerization methods. Various polymerization initiators can be used when polymerizing acrylic oligomers. Additionally, chain transfer agents can be used to adjust the molecular weight.

[0106] When the adhesive composition contains oligomer components such as acrylic oligomers, the content of the oligomer component relative to 100 parts by weight of the base polymer is preferably 0.5 parts by weight to 20 parts by weight, more preferably 1 part by weight to 15 parts by weight, and even more preferably 2 parts by weight to 10 parts by weight. When the content of oligomers in the adhesive composition is within the above range, there is a tendency for improved adhesion at high temperatures and improved high-temperature retention.

[0107] (Silane coupling agent)

[0108] For the purpose of adjusting adhesive strength, a silane coupling agent can be added to the adhesive composition. When a silane coupling agent is added to the adhesive composition, the amount of silane coupling agent added is typically about 0.01 parts by weight to about 5.0 parts by weight, preferably about 0.03 parts by weight to about 2.0 parts by weight, relative to 100 parts by weight of the base polymer.

[0109] (Cross-linking agent)

[0110] The base polymer can have crosslinking structures other than the aforementioned multifunctional compounds, as needed. Crosslinking structures can be introduced into the base polymer by including a crosslinking agent in the adhesive composition. Examples of crosslinking agents include compounds that react with functional groups such as hydroxyl and carboxyl groups contained in the polymer. Specific examples of crosslinking agents include: isocyanate crosslinking agents, epoxy crosslinking agents, etc. Crosslinking agents such as zopyridine, carbodiimide, and metal chelate.

[0111] As mentioned above, when the amount of crosslinking structure formed by means of urethane segments increases, the low-temperature adhesive strength of the adhesive sometimes decreases. Therefore, the amount of crosslinking agent used relative to 100 parts by weight of the base polymer is preferably 3 parts by weight or less, more preferably 2 parts by weight or less, and even more preferably 1 part by weight or less.

[0112] (Other additives)

[0113] In addition to the components exemplified above, the adhesive composition may also include additives such as tackifiers, plasticizers, softeners, deterioration inhibitors, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents.

[0114] <Preparation of Adhesive Compositions>

[0115] By mixing the above-mentioned components with a solvent as needed, an adhesive composition can be prepared. When forming an adhesive sheet, the adhesive composition preferably has a viscosity suitable for application to a substrate (e.g., about 0.5 Pa·s to about 20 Pa·s). When the adhesive composition is a solution, the viscosity of the composition can be adjusted to an appropriate range by adjusting the molecular weight of the polymer, the concentration of the solids in the solution, etc.

[0116] The base polymers with cross-linked structures formed by urethane segments have large molecular weights and tend to have high solution viscosity. Furthermore, solvent-free adhesive compositions have high viscosity, making them sometimes difficult to coat onto substrates after the introduction of cross-linked structures. Therefore, in the case of forming adhesive sheets, it is preferable to prepare a curable adhesive composition comprising a prepolymer composition and urethane (meth)acrylate, coat the adhesive composition onto the substrate in a layered manner, and then perform post-polymerization.

[0117] As mentioned above, in addition to the prepolymer composition and urethane (meth)acrylate, the curable adhesive composition may also contain remaining monomer components constituting acrylic segments, polymerization initiators, chain transfer agents, and other additives. The curable adhesive composition may contain the aforementioned oligomers, silane coupling agents, crosslinking agents, etc.

[0118] By adjusting the polymerization rate of the prepolymer, the amount of urethane (meth)acrylate added, and the amount of oligomer added, the viscosity of the adhesive composition can be adjusted to an appropriate range. Thickening additives can be used in the adhesive composition for purposes such as adjusting viscosity.

[0119] [Adhesive sheet]

[0120] An adhesive sheet is formed by shaping the above-mentioned adhesive composition into a sheet. When using a curable adhesive composition, by applying the adhesive composition to a substrate and then performing post-polymerization on the substrate by heating, irradiation with active light, etc., an adhesive sheet containing an adhesive with a cross-linked structure formed by urethane segments introduced onto acrylic segments can be obtained.

[0121] The thickness of the adhesive sheet is not particularly limited and can be appropriately set according to the type of object being adhered to. For example, the thickness of the adhesive sheet is about 5 μm to about 500 μm. From the viewpoint of balancing adhesiveness to the object being adhered to and uniform thickness, the thickness of the adhesive sheet is preferably 10 μm to 400 μm, and more preferably 15 μm to 350 μm.

[0122] Various methods can be used for coating adhesive compositions onto substrates, including: roller coating, contact roller coating, gravure coating, reverse coating, roller brush coating, spraying, dip roller coating, doctor blade coating, doctor knife coating, air knife coating, curtain coating, die lip coating, and die-cutting machine coating.

[0123] When the adhesive composition is a solution, it is preferable to dry the solution after applying the adhesive composition. As a drying method, heat drying is preferred. The heat drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and particularly preferably 70°C to 170°C. The drying time can be appropriately chosen. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and particularly preferably 10 seconds to 10 minutes.

[0124] When the adhesive composition is photocurable, it is photocured by irradiating the adhesive composition applied to the substrate with active light. During photocuring, it is preferable to provide a protective sheet on the surface of the coating layer and irradiate the adhesive composition with active light while it is sandwiched between two sheets, thereby preventing polymerization inhibition caused by oxygen.

[0125] The selection of active light depends on the type of polymerizable components such as monomers, urethane (meth)acrylates, and photoinitiator; ultraviolet light and / or short-wavelength visible light are typically used. The cumulative intensity of the irradiated light is preferably approximately 100 mJ / cm². 2 ~ Approximately 5000 mJ / cm 2 As a light source for illumination, there are no particular limitations as long as it can illuminate light within a wavelength range that is sensitive to the photopolymerization initiator contained in the adhesive composition. LED light sources, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, etc., are preferred.

[0126] As the substrate and protective sheet used in the formation of the adhesive sheet, any suitable substrate can be used. The substrate and protective sheet can be a release film with a release layer on the contact surface with the adhesive sheet.

[0127] Figure 1 This is a cross-sectional view showing an example of the construction of an adhesive sheet with release films 1 and 2 temporarily attached to both sides of the adhesive sheet 5. The release films 1 and 2 are used to protect the surface of the adhesive sheet during the period before the adhesive sheet 5 is used to bond it to the substrate. As the release films 1 and 2, it is preferable to use release films that have release layers 11 and 21 on the surface of the film substrate 10 and 20 (the adhesive surface of the adhesive sheet 5).

[0128] As the film substrate for the release film, films containing various resin materials can be used. Examples of resin materials include: polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyarylate resins, and polyphenylene sulfide resins. Among these, polyester resins such as polyethylene terephthalate are particularly preferred.

[0129] The thickness of the film substrate is preferably 10 μm to 200 μm, more preferably 25 μm to 150 μm. When release films 1 and 2 are provided on both sides of the adhesive sheet 5, the thickness of release film 1 on one side and the thickness of release film 2 on the other side can be the same or different. When the release film is used as a substrate and an adhesive composition is coated on it, and then photocuring is performed by irradiating the adhesive composition with active light through the release film, it is preferable that the release film on the light-irradiated surface is transparent.

[0130] Materials used as release layers include: polysiloxane release agents, fluorinated release agents, long-chain alkyl release agents, fatty acid amide release agents, etc. The thickness of the release layer is typically about 10 nm to about 2000 nm. By changing the type of release agent and the thickness of the release layer, the peeling force of the release films 1 and 2 from the adhesive layer 5 can be adjusted.

[0131] The peeling force when peeling the first release film 1 from the adhesive sheet 5 can be the same as or different from the peeling force when peeling the second release film from the adhesive sheet 5. When the peeling forces are different, the workability is excellent when the release film 2 with a relatively smaller peeling force is first peeled from the adhesive sheet 5 and then bonded to the first substrate, and then the release film 1 with a relatively larger peeling force is peeled and then bonded to the second substrate.

[0132] As release films 1 and 2, they can be used directly as substrates or protective films when forming (coating) adhesive sheets, or they can be replaced with other release films after forming adhesive sheets.

[0133] Figure 2 This is a cross-sectional view showing an example of an adhesive sheet with a substrate, wherein a substrate sheet 3 is disposed on one surface of the adhesive sheet 5 and a release film 1 is temporarily attached to the other surface of the adhesive sheet 5. By peeling off the release film 1 temporarily attached to the surface of the adhesive sheet 5 and then attaching the exposed surface of the adhesive sheet 5 to the substrate, the substrate sheet can be attached to the surface of the substrate by means of the adhesive sheet 5. There are no particular limitations on the type of substrate sheet 3, which can be a transparent film, decorative film, glass substrate, etc.

[0134] In formation Figure 2 When the adhesive sheet with substrate shown is used, for example, it can be obtained from... Figure 1 The release film 2 on one side of the adhesive sheet with the release film shown is peeled off, and then the exposed surface of the adhesive sheet 5 is bonded to the substrate 3. The substrate 3 can be used as either a substrate or a protective film used in forming (coating) the adhesive sheet.

[0135] <Physical Properties of Adhesive Sheets>

[0136] The adhesive sheet of the present invention contains a polymer comprising acrylic segments and urethane segments as the base polymer constituting the adhesive, thus possessing both low-temperature adhesiveness and high-temperature adhesive retention.

[0137] For the adhesive sheet, in a high-temperature holding force test conducted at 100°C and a load of 1000g, it is preferable that it does not fall off the adhered material even after 2 hours. Furthermore, the peel force obtained from a 180° peel test conducted at 5°C and a peel speed of 300 mm / min is preferably 5 N / 10 mm or more, more preferably 6 N / 10 mm or more, and even more preferably 7 N / 10 mm or more.

[0138] From the viewpoint of improving low-temperature adhesive strength, the glass transition temperature of the adhesive sheet is preferably below 0°C. On the other hand, when the glass transition temperature is too low, there is a tendency for high-temperature holding strength to decrease. Therefore, the glass transition temperature of the adhesive sheet is preferably above -25°C, more preferably above -20°C, and even more preferably above -15°C. The glass transition temperature of the adhesive sheet is the peak temperature of the loss tangent (tanδ) obtained by dynamic viscoelasticity measurement (frequency: 1Hz).

[0139] From the perspective of improving high-temperature retention, the shear storage modulus G' of the adhesive sheet at 25°C is... 25℃Preferably, it is 0.05 MPa or higher, more preferably 0.10 MPa or higher, even more preferably 0.13 MPa or higher, and particularly preferably 0.15 MPa or higher. Additionally, the shear storage modulus G' of the adhesive sheet at a temperature of 80°C... 80℃ Preferably, it is 0.01 MPa or more, more preferably 0.03 MPa or more, and even more preferably 0.05 MPa or more.

[0140] From the perspective of adhesive holding force, G' 25℃ and G' 80℃ There is no specific upper limit. To ensure the adhesive sheet has adequate tack and wettability, G' 25℃ Preferably, the pressure is 3 MPa or less, more preferably 1 MPa or less, and even more preferably 0.5 MPa or less. From the same point of view, G' 80℃ Preferably, it is 0.3 MPa or less, and more preferably 0.25 MPa or less.

[0141] From the perspective of combining high-temperature retention and low-temperature adhesiveness, the glass transition temperature Tg (°C) and the shear storage modulus G' at 25°C of the adhesive sheet are important factors. 25℃ The product of (MPa) is preferably -1 or less, more preferably -3 or less, and even more preferably -4 or less.

[0142] [Uses of adhesive sheets]

[0143] The adhesive sheet of the present invention can be used for bonding various transparent and opaque components. There are no particular limitations on the types of materials to be bonded, including various resin materials, glass, metals, etc. In particular, because the adhesive sheet of the present invention possesses both low-temperature adhesive strength and high-temperature adhesive retention strength, it is suitable for bonding components in devices and the like, and for surface decoration, operating over a wide temperature range from low to high temperatures. Furthermore, the adhesive sheet of the present invention is also suitable for bonding image display devices such as liquid crystal display devices and organic EL display devices, and input devices such as touch panels.

[0144] [Example]

[0145] The present invention will now be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0146] [Preparation of acrylic oligomers]

[0147] 60 parts by weight of tetrahydrodicyclopentadienyl methacrylate (DCPMA), 40 parts by weight of methyl methacrylate (MMA), 3.5 parts by weight of α-thioglycerol as a chain transfer agent, and 100 parts by weight of toluene as a polymerization solvent were mixed and stirred at 70°C for 1 hour under a nitrogen atmosphere. Next, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator were added, and the reaction was carried out at 70°C for 2 hours, followed by a further increase to 80°C and a 2-hour reaction. The reaction mixture was then heated to 130°C, and the toluene, chain transfer agent, and unreacted monomers were dried to remove them, yielding a solid acrylic oligomer. The weight-average molecular weight of the acrylic oligomer was 5100.

[0148] [Example 1]

[0149] (polymerization of prepolymers)

[0150] The monomers used for prepolymer formation, namely 52.8 parts by weight of butyl acrylate (BA), 10.9 parts by weight of cyclohexyl acrylate (CHA), 9.7 parts by weight of N-vinyl-2-pyrrolidone (NVP), 14.8 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 11.8 parts by weight of isostearate acrylate (ISTA), as well as photopolymerization initiators (BASF's "Irgacure 184": 0.035 parts by weight and BASF's "Irgacure 651": 0.035 parts by weight), were combined and then polymerized by irradiation with ultraviolet light to achieve a viscosity (BH viscometer, rotor No. 5, 10 rpm, measurement temperature 30°C) of approximately 20 Pa·s, thereby obtaining a prepolymer composition (polymerization rate: approximately 9%).

[0151] (Preparation of photocurable adhesive compositions)

[0152] In the above prepolymer composition, 7 parts by weight of terminal acrylic modified polyether urethane ("UV-3300B" manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) and 3 parts by weight of terminal acrylic modified polyester urethane ("UV-3010B" manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) were added, along with 5 parts by weight of the above acrylic oligomer, 0.05 parts by weight of Irgacure 184 and 0.57 parts by weight of Irgacure 651 as photopolymerization initiators, 0.2 parts by weight of α-methylstyrene dimer ("Nofmer MSD" manufactured by Nippon Yu Co., Ltd.) as chain transfer agent, and 0.3 parts by weight of "KBM403" manufactured by Shin-Etsu Chemical Co., Ltd. as silane coupling agent. The mixtures were then uniformly mixed to prepare an adhesive composition.

[0153] (Making the adhesive sheet)

[0154] A photocurable adhesive composition is applied to a 50 μm thick polyethylene terephthalate (PET) film (MRF50, manufactured by Mitsubishi Chemical) with a polysiloxane-based release layer on its surface to form a coating layer with a thickness of 150 μm. A 38 μm thick PET film (MRF38, manufactured by Mitsubishi Chemical), with one side treated by polysiloxane release, is then laminated onto this coating layer. The irradiation intensity of the surface directly below the lamp is adjusted to reach 5 mW / cm². 2 The laminate was photocured by irradiating the 38μm thick PET film side with ultraviolet light for 300 seconds. Then, it was dried in a 90°C dryer for 2 minutes to evaporate residual monomers, resulting in an adhesive sheet with a thickness of 150μm.

[0155] [Examples 2-4, Comparative Examples 1-5]

[0156] Table 1 shows the variations in the monomer composition added during the polymerization of the prepolymer, as well as the types and amounts of polyfunctional compounds (urethane acrylates and / or polyfunctional acrylates), acrylic oligomers, photopolymerization initiators, chain transfer agents, and silane coupling agents added to the adhesive composition. Otherwise, the photocurable adhesive composition was prepared in the same manner as in Example 1, and coating, photocuring, and removal of residual monomers were performed on a substrate to obtain an adhesive sheet.

[0157] It should be noted that in Table 1, each component is represented by the following abbreviations.

[0158] <Acrylic monomers>

[0159] BA: Butyl acrylate

[0160] 2HEA: 2-Ethylhexyl acrylate

[0161] CHA: Cyclohexyl acrylate

[0162] NVP: N-vinyl-2-pyrrolidone

[0163] 4HBA: 4-Hydroxybutyl acrylate

[0164] ISTA: Isostearyl acrylate

[0165] INA: Isononyl acrylate

[0166] AA: Acrylic acid

[0167] 2MEA: 2-Methoxyethyl Acrylate

[0168] HEAA: Hydroxyethylacrylamide

[0169] <Carbamate acrylate>

[0170] UN-350: “ART-Resin UN-350” (a polyester urethane diacrylate with a weight average molecular weight of approximately 12,500 and a glass transition temperature of -57°C) manufactured by Nejo Kogyo Co., Ltd.

[0171] UV-3300B: "UV-3300B" (a polyether urethane diacrylate with a weight average molecular weight of approximately 12,000 and a glass transition temperature of -30°C) manufactured by Nippon Synthetic Chemical Industry Co., Ltd.

[0172] UV-3010B: "UV-3010B" (a polyester urethane diacrylate with a weight average molecular weight of approximately 11,000) manufactured by Nippon Synthetic Chemical Industry Co., Ltd.

[0173] UN-9200A: “ART-Resin UN-9200A” (a polycarbonate urethane diacrylate with a weight-average molecular weight of approximately 15,000 and a glass transition temperature of -27°C) manufactured by Genjo Industries, Ltd.

[0174] <Multifunctional acrylates>

[0175] HDDA: Hexanediol diacrylate

[0176] <Photopolymerization Initiator>

[0177] Irg651: Irgacure 651 (2,2-dimethoxy-1,2-diphenylethane-1-one)

[0178] Irg184: Irgacure 184 (1-hydroxycyclohexylphenyl ketone)

[0179] [evaluate]

[0180] <Weight-average molecular weight>

[0181] The weight-average molecular weight (Mw) of acrylic oligomers and urethane (meth)acrylates was determined using a GPC (gel permeation chromatography) apparatus (product name "HLC-8120GPC") manufactured by Tosoh Corporation. For the test samples, a 0.1 wt% solution of the base polymer was prepared by dissolving it in tetrahydrofuran and then filtering it through a 0.45 μm membrane filter. The GPC determination conditions are described below.

[0182] (Measurement conditions)

[0183] Column: Made by Tosoh Corporation, G7000HXL+GMHXL+GMHXL

[0184] Column dimensions: 7.8mm Φ x 30cm each (total column length: 90cm)

[0185] Column temperature: 40℃; Flow rate: 0.8 mL / min

[0186] Injection volume: 100μL

[0187] Eluent: Tetrahydrofuran

[0188] Detector: Differential refractometer (RI)

[0189] Standard sample: polystyrene

[0190] <Storage modulus and glass transition temperature of adhesive sheets>

[0191] An article with a thickness of approximately 1.5 mm, obtained by stacking 10 adhesive sheets, was used as the sample for testing. Dynamic viscoelasticity was measured using the Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific under the following conditions.

[0192] (Measurement conditions)

[0193] Deformation mode: Torsion

[0194] Measurement frequency: 1Hz

[0195] Heating rate: 5℃ / minute

[0196] Shape: parallel plate 7.9mmΦ

[0197] The shear storage modulus is determined by reading the storage modulus G' at each temperature from the measurement results. The temperature at which the loss tangent (tanδ) reaches its maximum (peak temperature) is taken as the glass transition temperature of the bonded sheet.

[0198] High Temperature Holding Power

[0199] The holding force of the adhesive sheet at 100°C was evaluated using a creep test according to JIS Z0237. A test sheet was prepared by peeling off one side of the release film from the adhesive sheet, bonding a 25 μm thick PET film, and cutting it into 10 mm wide pieces. The other side of the release film was peeled off and bonded to a bakelite board with an adhesive area of ​​10 mm wide and 20 mm long. It was held at 100°C for 30 minutes, then the bakelite board was lowered, and a load of 1000 g was applied to the free end of the test sheet (the portion not bonded to the bakelite board). Under the applied load, the test sheet was placed at 80°C for 2 hours, and the offset (in mm) from the initial bonding position was measured after 2 hours. For cases where the test sheet fell off within 2 hours (offset greater than 20 mm), the time until it fell off was recorded.

[0200] <Low-Temperature Adhesive Strength>

[0201] A clean acrylic resin board, cleaned by wiping it back and forth 10 times with a cloth soaked in isopropyl alcohol, was prepared as the substrate. A release film was peeled from one side of the adhesive sheet, and a 50 μm thick PET film was laminated and cut into pieces 10 mm wide × 100 mm long to create a test piece. The release film was then peeled from the other side of the test piece, pressed onto the substrate using a 5 kg roller, and held at 5°C for 30 minutes. The peel force was then measured by peeling the test piece from the acrylic resin board using a tensile testing machine at a tensile speed of 300 mm / min and a peel angle of 180°.

[0202] [Evaluation Results]

[0203] The composition and evaluation results of each adhesive sheet are shown in Table 1.

[0204] Table 1

[0205] Comparative Example 3, which incorporates a cross-linked structure formed by polyfunctional acrylates in the acrylic polymer chain, exhibits excellent high-temperature adhesive retention, but insufficient adhesive strength at 5°C. In Comparative Example 4, where a low Tg was achieved by adjusting the composition of the acrylic polymer chain, the adhesive strength at 5°C further decreased. In Comparative Example 5, where adhesion was improved by reducing the amount of polyfunctional acrylates introduced, the adhesive strength at 5°C increased, but the storage modulus was low and the high-temperature retention was poor. Based on these results, it can be concluded that for adhesive sheets using polymers with cross-linked structures introduced through polyfunctional acrylates, it is difficult to simultaneously achieve both low-temperature adhesiveness and high-temperature retention.

[0206] The adhesive sheets of Examples 1-3, which have introduced a cross-linked structure formed by urethane diacrylate onto the acrylic polymer chain, exhibit good high-temperature retention and 5°C adhesive strength, indicating that they can be used over a wide temperature range.

[0207] Compared to Comparative Example 1, which used 1 part by weight of urethane diacrylate, with a total of 100 parts by weight of monomer components constituting the acrylic polymer chain, the glass transition temperature increased and the storage modulus decreased compared to Examples 1 and 2. As a result, the high-temperature holding force decreased, and in the high-temperature holding force test, the test piece fell off immediately after the load was applied.

[0208] On the other hand, in Comparative Example 2, where the amount of urethane diacrylate used was set to 40 parts by weight, the glass transition temperature decreased and the storage modulus increased compared to Examples 1 and 2. Accompanyingly, a decrease in offset and an increase in high-temperature holding force were observed in the high-temperature holding test, but the adhesiveness at low temperatures became insufficient.

[0209] The results above show that by using a base polymer containing acrylic and carbamate segments and adjusting the amount of carbamate segments introduced, it is possible to achieve both low-temperature adhesive strength and high-temperature retention strength, which is difficult to achieve when using a base polymer with a cross-linked structure introduced through multifunctional acrylates.

Claims

1. An adhesive comprising an acrylic-based polymer, wherein, The acrylic-based polymer comprises acrylic segments and carbamate segments. The content of carbamate segments is 3 to 20 parts by weight relative to 100 parts by weight of the acrylic segments. The adhesive further comprises acrylic oligomers with a weight-average molecular weight of 1000 to 10000. The acrylic oligomers contain (meth)acrylates with three or more aliphatic hydrocarbon rings as monomer components. The content of the acrylic oligomer is 0.5 to 20 parts by weight relative to 100 parts by weight of the acrylic base polymer.

2. The adhesive as claimed in claim 1, wherein, The weight-average molecular weight of the carbamate segments is 3,000 to 50,000.

3. The adhesive as claimed in claim 1 or 2, wherein, The carbamate segments have one or more polymer chains selected from the group consisting of polyether chains, polyester chains and polycarbonate chains.

4. The adhesive as claimed in claim 1 or 2, wherein, The glass transition temperature of the carbamate segments is below 0°C.

5. The adhesive as claimed in claim 1 or 2, wherein, In the acrylic base polymer, the acrylic segments are crosslinked through the urethane segments.

6. The adhesive as claimed in claim 1 or 2, wherein, The adhesive contains more than 50% by weight of the acrylic-based polymer.

7. The adhesive as claimed in claim 1 or 2, wherein, The glass transition temperature of the adhesive is -25℃ to 0℃.

8. An adhesive sheet obtained by forming an adhesive according to any one of claims 1 to 7 into a sheet shape.

9. The adhesive sheet as claimed in claim 8, wherein, The shear storage modulus of the adhesive sheet at a temperature of 25°C is 0.15MPa~0.30MPa.

10. The adhesive sheet as claimed in claim 8 or 9, wherein, The product of the shear storage modulus (MPa) and the glass transition temperature (°C) of the adhesive sheet at a temperature of 25°C is below -1.

0.

11. An adhesive composition, which is a curable adhesive composition, wherein, The adhesive composition comprises acrylic monomers and / or a portion thereof, urethane (meth)acrylates, and acrylic oligomers with a weight average molecular weight of 1000 to 10000. The content of the urethane (meth)acrylate is 3 to 20 parts by weight relative to 100 parts by weight of the total acrylic monomers and some of their polymers. The acrylic oligomers contain (meth)acrylates with three or more aliphatic hydrocarbon rings as monomer components. The content of the acrylic oligomer is 0.5 to 20 parts by weight relative to a total of 100 parts by weight of the acrylic monomer and / or a portion thereof.

12. The adhesive composition of claim 11, wherein, The weight-average molecular weight of the urethane (meth)acrylate is 3,000 to 50,000.

13. The adhesive composition of claim 11 or 12, wherein, The glass transition temperature of the urethane (meth)acrylate is below 0°C.

14. The adhesive composition of claim 11 or 12, wherein, The adhesive composition also contains a photopolymerization initiator.

15. The adhesive composition of claim 11 or 12, wherein, The adhesive composition contains a total of 50% by weight or more of acrylic monomers and a portion of their polymers.

16. A method for manufacturing an adhesive sheet, wherein, The adhesive composition according to any one of claims 11 to 15 is applied in layers onto a substrate and then cured.

17. The method for manufacturing the adhesive sheet as described in claim 16, wherein, The curing process is photocuring.

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