Hot-melt adhesive composition and adhesive sheet

Abstract

Provided is a hot-melt adhesive composition that has a low viscosity when heated and melted and that can form an adhesive layer as appropriate. Provided is a hot-melt adhesive composition containing a base polymer. The base polymer contains an acrylic polymer A and an acrylic polymer B. The acrylic polymer A is a polymer of a monomer component in which a (meth)acrylic monomer A having an alkyl group with 4 or more and 8 or less carbon atoms is a main component. The acrylic polymer B is a polymer of a monomer component in which a (meth)acrylic monomer B having an alkyl group with 9 or more and 12 or less carbon atoms is a main component. The content of the acrylic polymer B is 10% by weight or more and 90% by weight or less, based on 100% by weight of the total amount of the acrylic polymer A and the acrylic polymer B in the base polymer.

Description

Technical Field

[0001] This invention relates to hot-melt adhesive compositions. It also relates to adhesive sheets comprising an adhesive layer formed from a hot-melt adhesive composition. This application claims priority to Japanese Patent Application No. 2021-14456, filed February 1, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0002] Adhesives (also known as pressure-sensitive adhesives, hereinafter the same) are typically soft solids (viscoelastics) in a temperature range near room temperature, possessing the property of easily bonding to substrates using pressure. Taking full advantage of these properties, adhesives are widely used in various industries, from household appliances to automobiles and office automation equipment, as a bonding method with good workability and high bonding reliability.

[0003] Adhesives are typically formed into a thin film using an adhesive composition and used as an adhesive sheet containing this thin film adhesive (adhesive layer). In manufacturing such adhesive sheets, adhesive compositions in the form of solvent solutions such as toluene solutions are usually used, and the adhesive layer is formed by coating the solvent solution onto a suitable surface. However, in recent years, due to environmental protection requirements that limit the use of solvents, the use of solvent-free hot-melt adhesive compositions in the formation of adhesive layers has been investigated. Patent Document 1 is cited as a relevant technical document for such hot-melt adhesive compositions.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-147655 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Hot-melt adhesive compositions are typically formed into a thin film by extrusion from a die of an extruder while heated and molten, thus forming an adhesive layer. If the viscosity of the molten hot-melt adhesive composition is too high, it becomes difficult to extrude from the die, resulting in reduced thickness uniformity and poor appearance of the adhesive layer. In particular, from the viewpoint of adhesive properties, the viscosity of the adhesive composition tends to be high when using a high molecular weight polymer as the base polymer. Therefore, it is advantageous to obtain a hot-melt adhesive composition with a molten viscosity low enough for extrusion molding.

[0009] The present invention was made in view of the above circumstances, and its object is to provide a hot-melt adhesive composition with low viscosity in the molten state that can suitably form an adhesive layer. Another object of the present invention is to provide an adhesive sheet obtained using the above-described hot-melt adhesive composition.

[0010] Solution for solving the problem

[0011] According to this specification, a hot-melt adhesive composition comprising a base polymer is provided. The base polymer comprises acrylic polymer A and acrylic polymer B. Here, acrylic polymer A is a polymer whose main component is a (meth)acrylic monomer A having an alkyl group having 4 or more but less than 8 carbon atoms. Acrylic polymer B is a polymer whose main component is a (meth)acrylic monomer B having an alkyl group having 9 or more but less than 12 carbon atoms. When the total amount of acrylic polymer A and acrylic polymer B in the base polymer is set to 100% by weight, the content of acrylic polymer B is 10% by weight or more and 90% by weight or less.

[0012] The hot-melt adhesive composition has a suitablely low viscosity when heated and melted, and therefore, when used for example in extrusion molding, it can be used to form an adhesive layer appropriately.

[0013] In a preferred embodiment, the (meth)acrylate monomer A is an alkyl (meth)acrylate having an alkyl group with 4 or more but less than 8 carbon atoms at the ester terminus. In another preferred embodiment, the (meth)acrylate monomer B is an alkyl (meth)acrylate having an alkyl group with 9 or more but less than 12 carbon atoms at the ester terminus. According to the adhesive composition comprising acrylic polymer A and acrylic polymer B as base polymers, it is easy to simultaneously achieve improved adhesive properties (e.g., adhesion and holding power) and low viscosity in the molten state, wherein acrylic polymer A and acrylic polymer B are monomeric polymers with these monomers as main components.

[0014] In a preferred embodiment of the technology disclosed herein, the weight-average molecular weight (Mw) of the aforementioned acrylic polymer A is 75 × 10⁻⁶. 4 Above and 120×10 4 Below. Additionally, in another preferred embodiment of the technology disclosed herein, the weight-average molecular weight (Mw) of the aforementioned acrylic polymer B is 75 × 10⁻⁶. 4 Above and 120×10 4Generally, if the Mw of the base polymer contained in a hot-melt adhesive composition is high, there is a tendency for the viscosity of the adhesive composition in the molten state to become high, making it difficult to form an adhesive layer appropriately by extrusion molding in the molten state; or, the uniformity of the thickness of the formed adhesive layer decreases, or poor appearance easily occurs. According to the present invention, the viscosity of the adhesive composition is appropriately lowered when heated and melted. Therefore, even if the Mw of acrylic polymer A and acrylic polymer B contained in the base polymer are both above the aforementioned specified values, the viscosity of the adhesive composition in the molten state will be appropriately lowered, making it easier to form an adhesive layer appropriately. Furthermore, from the viewpoint of adhesive properties, the Mw of acrylic polymer A and acrylic polymer B are preferably below the aforementioned upper limit value.

[0015] In a preferred embodiment of the technology disclosed herein, the hot-melt adhesive composition has a shear viscosity of 7000 Pa·s or less at 130°C. With a hot-melt adhesive composition having a shear viscosity of 7000 Pa·s or less at 130°C, the viscosity in the molten state is readily available for extrusion molding, thus facilitating the formation of an adhesive layer.

[0016] In a preferred embodiment of the technology disclosed herein, the hot-melt adhesive composition further comprises a crosslinking agent. According to this hot-melt adhesive composition, there is a tendency to suitably adjust the cohesive strength, enabling the formation of an adhesive layer with excellent adhesive properties. In a preferred embodiment, the crosslinking agent is an isocyanate-based crosslinking agent.

[0017] According to this specification, an adhesive sheet having an adhesive layer formed from any adhesive composition disclosed herein is provided. With this configuration, an adhesive sheet that exhibits both improved thickness uniformity and appearance, as well as good adhesive properties (e.g., adhesion and holding power), is readily obtained. Furthermore, the adhesive sheet of this configuration is solvent-free, thus easily reducing environmental impact.

[0018] It should be noted that the appropriate combination of the above features is also included in the claims that are claimed by this patent application. Attached Figure Description

[0019] Figure 1 This is a cross-sectional view schematically illustrating one example of the composition of an adhesive sheet.

[0020] Figure 2 This is a cross-sectional view schematically showing another example of the composition of the adhesive sheet. Detailed Implementation

[0021] The following describes suitable embodiments of the present invention. It should be noted that those skilled in the art will understand that matters other than those specifically mentioned in this specification, and matters necessary for implementing the present invention, are based on the implications of implementing the invention described in this specification and common technical knowledge at the time of application. The present invention can be implemented based on the disclosure in this specification and common technical knowledge in the field. Furthermore, in the following drawings, components / parts that perform the same function are sometimes labeled with the same symbols, and sometimes repeated descriptions are omitted or simplified. Additionally, the embodiments described in the drawings are schematic for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the dimensions or scale of the actual product provided.

[0022] <Adhesive Composition>

[0023] The adhesive compositions disclosed herein are hot-melt adhesive compositions. Herein, in this specification, "hot-melt adhesive composition" means an adhesive composition used in a hot-melt (hot-melting) manner when forming an adhesive layer. Typically, a hot-melt adhesive composition is a solvent-free adhesive composition that is substantially solvent-free. In this specification, "solvent-free" or "substantially solvent-free" means that the solvent content in the total adhesive composition is 1% by weight or less, more preferably 0.1% by weight or less, and even more preferably 0.01% by weight or less, including the case where the solvent content is 0% by weight. In this specification, hot-melt adhesive composition is sometimes abbreviated as "adhesive composition".

[0024] (Basic Polymer)

[0025] The adhesive compositions disclosed herein comprise a base polymer. The type of base polymer is not particularly limited. For example, the adhesive compositions disclosed herein may comprise one or more of the following polymers that exhibit rubber elasticity at room temperature: acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, fluoropolymers, etc., which are considered as base polymers (i.e., components comprising 50% by weight or more of the polymer composition). Here, "the adhesive composition comprises two or more polymers as base polymers" means that a mixture in which the polymers are blended is considered as one base polymer, including cases where the base polymer is present.

[0026] The adhesive compositions disclosed herein are preferably implemented in such a manner that more than 50% by weight of the aforementioned monomeric components are (meth)acrylic monomers. The adhesive compositions disclosed herein are preferably adhesive compositions comprising an acrylic polymer as the base polymer, i.e., acrylic adhesive compositions. In some preferred embodiments of the adhesive composition, more than 70%, more than 80%, or more than 90% by weight of the polymeric component contained in the composition may be acrylic polymers. More than 95% by weight or more than 98% by weight of the aforementioned polymeric component may be acrylic polymers.

[0027] It should be noted that, in this specification, "acrylic polymer" refers to a polymer whose polymer structure contains monomer units derived from (meth)acrylic monomers, typically referring to polymers containing monomer units derived from (meth)acrylic monomers in a proportion exceeding 50% by weight. Furthermore, in this specification, a (meth)acrylic monomer refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl group" means including both acryloyl and methacryloyl groups. Therefore, the concept of (meth)acrylic monomers here can include both monomers having an acryloyl group (acrylic monomers) and monomers having a methacryloyl group (methacrylic monomers). Similarly, in this specification, "(meth)acrylic acid" means including both acrylic acid and methacrylic acid, and "(meth)acrylate" means including both acrylates and methyl acrylates.

[0028] In a preferred embodiment of the technology disclosed herein, the adhesive composition comprises an acrylic polymer as a base polymer, said acrylic polymer being a monomeric component with (meth)acrylic monomers as the main component. Here, in this specification, "main component" refers to a component contained in an amount exceeding 50% by weight. The content of the "main component" in the monomeric component is preferably 85% by weight or more, more preferably 90% by weight or more, further preferably 92% by weight or more, and particularly preferably 95% by weight or more.

[0029] The adhesive composition disclosed herein is characterized in that it comprises at least two or more acrylic polymers as the base polymer. By using a base polymer based on this composition, it is easy to achieve a good balance of various properties, such as improved adhesive properties and reduced viscosity in the molten state. In the disclosed technology, the base polymer comprises at least acrylic polymer A and acrylic polymer B. Here, acrylic polymer A is a polymer with (meth)acrylate monomer A as the main component. Additionally, acrylic polymer B is a polymer with (meth)acrylate monomer B as the main component. By using a base polymer based on this composition, it is easy to simultaneously achieve both good adhesive properties (e.g., adhesive strength and holding power) and reduced viscosity upon heating and melting.

[0030] (Acrylic polymer A)

[0031] In the technology disclosed herein, the base polymer comprises an acrylic polymer A, which is a polymer of monomeric components having an alkyl (meth)acrylate monomer A having 4 or more and 8 or fewer carbon atoms as the main component. In a preferred embodiment of the technology disclosed herein, the aforementioned alkyl (meth)acrylate monomer A is an alkyl (meth)acrylate ester having an alkyl group having 4 or more and 8 or fewer carbon atoms at the ester terminus. Hereinafter, alkyl (meth)acrylate esters having an alkyl group having X or more and Y or fewer carbon atoms at the ester terminus are sometimes referred to as "(meth)acrylate C". X-Y Alkyl ester. In the (meth)acrylic acid monomer A, (meth)acrylic acid C... 4-8 In the case of alkyl esters, (meth)acrylic acid C 4-8 C in alkyl esters 4-8 The structure of the alkyl group is not particularly limited; both straight-chain and branched structures are acceptable. As (meth)acrylic acid monomer A, this (meth)acrylic acid C... 4-8 Alkyl esters can be used alone or in combination of two or more. As a suitable example of the aforementioned acrylic polymer A, an example containing (meth)acrylic acid C can be cited. 4-8 An acrylic polymer in which at least one of the alkyl esters is a monomer unit.

[0032] (meth)acrylic acid C having a straight-chain alkyl group at the ester terminus 4-8 Alkyl esters include n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, and n-octyl (meth)acrylate. Additionally, (meth)acrylate C-terminus... 4-8Alkyl esters, such as tert-butyl (meth)acrylate, isobutyl (meth)acrylate, isoamyl (meth)acrylate, tert-amyl (meth)acrylate, neopentyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate. The techniques disclosed herein preferably include a (meth)acrylate monomer A comprising a component selected from acrylic acid C. 4-8 One or more of the alkyl esters are preferably implemented. As acrylic acid C 4-8 Suitable examples of alkyl esters include n-butyl acrylate, 2-ethylhexyl acrylate, and isooctyl acrylate. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are preferred.

[0033] The content of (meth)acrylic monomer A in the monomer component constituting the above-mentioned acrylic polymer A is, for example, more than 50% by weight, preferably 85% by weight or more, more preferably 90% by weight or more, further preferably 92% by weight or more, and particularly preferably 95% by weight or more.

[0034] The monomer units constituting acrylic polymer A include, as needed, other secondary monomers (copolymeric monomers) capable of copolymerizing with (meth)acrylic monomer A, in addition to the main component (meth)acrylic monomer A. Monomers having functional groups (e.g., carboxyl, hydroxyl, amide, etc.) can be suitably used as secondary monomers capable of copolymerizing with (meth)acrylic monomer A. Monomers containing functional groups can play a role in introducing crosslinking sites into acrylic polymer A or in improving the cohesiveness of acrylic polymer A, and consequently, the base polymer.

[0035] As the aforementioned secondary monomers, for example, one type of monomer containing a functional group can be used alone or in combination of two or more types.

[0036] Hydroxyl-containing monomers: for example, hydroxyalkyl esters of methacrylates such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, and (4-hydroxymethylcyclohexyl)methyl acrylate; unsaturated alcohols such as vinyl alcohols and allyl alcohols; ether compounds such as 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, and diethylene glycol monovinyl ether.

[0037] Carboxyl-containing monomers: for example, olefinic unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), crotonic acid, and isocrotonic acid; olefinic unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid.

[0038] Monomers containing anhydride groups: for example, maleic anhydride and itaconic anhydride.

[0039] Monomers having a ring containing a nitrogen atom: for example, N-vinyl-2-pyrrolidone, methyl-N-vinylpyrrolidone, vinylpyridine, vinylpyrazine, vinylpyrimidine, N-vinylpiperidone, N-vinylpiperazine, N-vinylpyrrole, N-vinylimidazolium, N-vinyloxazole, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, N-(meth)acryloylmorpholine, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, etc.

[0040] Amide-containing monomers: for example, (meth)acrylamide; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, N,N-di(tert-butyl)(meth)acrylamide, etc.; N-alkyl(meth)acrylamides such as N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, N-n-butyl(meth)acrylamide; N-vinylcarboxylic acid amides such as N-vinylacetamide; monomers having hydroxyl and amide groups, such as N-(2-hydroxyethyl)(methyl)acrylamide. Acrylamide, N-(2-hydroxypropyl)(methyl)acrylamide, N-(1-hydroxypropyl)(methyl)acrylamide, N-(3-hydroxypropyl)(methyl)acrylamide, N-(2-hydroxybutyl)(methyl)acrylamide, N-(3-hydroxybutyl)(methyl)acrylamide, N-(4-hydroxybutyl)(methyl)acrylamide and other N-hydroxyalkyl(methyl)acrylamides; monomers having alkoxy and amide groups, such as N-methoxymethyl(methyl)acrylamide, N-methoxyethyl(methyl)acrylamide, N-butoxymethyl(methyl)acrylamide and other N-alkoxyalkyl(methyl)acrylamides; N,N-dialkylaminoalkyl(methyl)acrylamides such as N,N-dimethylaminopropyl(methyl)acrylamide and other N,N-dialkylaminoalkyl(methyl)acrylamides.

[0041] Amino-containing monomers: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and tert-butylaminoethyl (meth)acrylate.

[0042] Monomers having a succinimide backbone: for example, N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, N-(meth)acryloyl-8-oxyhexamethylenesuccinimide, etc.

[0043] Maleimides: For example, N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, etc.

[0044] Itaconimides: For example, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, N-laurylitaconimide, etc.

[0045] Epoxy monomers: for example, glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, allyl glycidyl ether.

[0046] Cyano-containing monomers: for example, acrylonitrile, methacrylonitrile.

[0047] Ketone-containing monomers: for example, diacetone (meth)acrylamide, diacetone (meth)acrylate, vinyl ketone, vinyl ethyl ketone, allyl acetoacetate, vinyl acetoacetate.

[0048] Alkoxysilyl monomers: for example, alkoxysilyl-containing (meth)acrylates such as 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloyloxypropylmethyldimethoxysilane, 3-(meth)acryloyloxypropylmethyldiethoxysilane, vinyl compounds such as vinyltrimethoxysilane, etc.

[0049] Monomers containing sulfonic acid or phosphoric acid groups: for example, styrene sulfonic acid, allyl sulfonic acid, sodium vinyl sulfonate, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamide propanesulfonic acid, (meth)acrylate sulfonyl propane, (meth)acryloyloxynaphthalene sulfonic acid, 2-hydroxyethylacryloyl phosphate, etc.

[0050] Monomers containing isocyanate groups: for example, ethyl 2-isocyanate of (meth)acrylate, (meth)acryloyl isocyanate, and m-isopropenyl-α,α-dimethylbenzyl isocyanate.

[0051] When using monomers containing functional groups as described above, there is no particular limitation on their amount; generally, 0.01% by weight or more of the total monomer components constituting acrylic polymer A is suitable. From the viewpoint of better utilizing the effects of using monomers containing functional groups, the amount of monomers containing functional groups can be set to 0.1% by weight or more of the total monomer components, and can be set to 1% by weight or more. Furthermore, the amount of monomers containing functional groups can be set to 50% by weight or less of the total monomer components, preferably 15% by weight or less, more preferably 10% by weight or less, further preferably 8% by weight or less, and particularly preferably 5% by weight or less. This prevents the cohesive force of the adhesive from becoming too high, and improves the adhesion to the bonded objects.

[0052] The adhesive composition disclosed herein is preferably implemented such that the monomer components constituting the acrylic polymer A include (meth)acrylate monomer A, and also include one or both of acrylic acid and a hydroxyl-containing monomer. As the hydroxyl-containing monomer, hydroxyalkyl (meth)acrylate is preferably used. Particularly preferred are hydroxyethyl acrylate (HEA), hydroxybutyl acrylate (4HBA), and other hydroxyl-containing acrylic monomers. 1-4 Alkyl esters.

[0053] In the preparation of acrylic polymer A, the monomer raw materials may also include secondary monomers other than the functionalized monomers mentioned above, in order to improve the cohesive strength of acrylic polymer A.

[0054] As specific, non-limiting examples of the aforementioned sub-monomers, the following monomers can be listed.

[0055] Alkoxy monomers: for example, alkoxyalkyl esters of methacrylates such as 2-methoxyethyl acrylate, 3-methoxypropyl acrylate, and 2-ethoxyethyl acrylate; methoxyalkyl glycol methacrylates, methoxy polyethylene glycol methacrylates, methoxy polypropylene glycol methacrylates, and alkoxy(poly)alkylene glycol methacrylates.

[0056] Vinyl esters: such as vinyl acetate, vinyl propionate, etc.

[0057] Vinyl ethers: For example, vinyl alkyl ethers such as methyl vinyl ether and ethyl vinyl ether.

[0058] Aromatic vinyl compounds: for example, styrene, α-methylstyrene, vinyltoluene, etc.

[0059] Olefins: such as ethylene, butadiene, isoprene, isobutene, etc.

[0060] (Meth)acrylates containing alicyclic hydrocarbon groups: for example, cyclopentyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, dicyclopentyl methacrylate, adamantane methacrylate, etc.

[0061] (Meth)acrylates containing aromatic rings: for example, aryl methacrylates such as phenyl methacrylate, aryl methacrylates such as phenoxyethyl methacrylate, and arylalkyl methacrylates such as benzyl methacrylate.

[0062] In addition, there are heterocyclic (meth)acrylates such as tetrahydrofurfuryl methacrylate, halogenated monomers such as vinyl chloride and fluorine-containing (meth)acrylates, organosilicon (meth)acrylates and monomers containing organosiloxane chains, and (meth)acrylates obtained from terpene compound derivative alcohols.

[0063] Such other secondary monomers can be used alone or in combination of two or more. The amount of the above-mentioned secondary monomers can be appropriately selected according to the purpose and use, without particular limitation. For example, it is preferably less than 20% by weight of all monomer raw materials of acrylic polymer A (e.g., 2 to 20% by weight, typically 3 to 10% by weight).

[0064] In a preferred embodiment of the technology disclosed herein, the adhesive composition comprises, as a base polymer, one or more acrylic polymers selected from acrylic polymer A. From the viewpoint of adjusting adhesive properties, the base polymer preferably comprises two or more acrylic polymers selected from acrylic polymer A. Furthermore, from the viewpoint of simplifying composition, the base polymer preferably comprises one acrylic polymer selected from acrylic polymer A.

[0065] (Acrylic polymer B)

[0066] In the technology disclosed herein, the base polymer, in addition to comprising acrylic polymer A, also comprises a polymer of monomeric components, namely acrylic polymer B, which is described below as having (meth)acrylic monomer B as the main component.

[0067] (Meth)acrylate monomer B is a (meth)acrylate monomer having an alkyl group having 9 or more and 12 or fewer carbon atoms. In a preferred embodiment of the technology disclosed herein, the aforementioned (meth)acrylate monomer B is an alkyl (meth)acrylate ester having an alkyl group having 9 or more and 12 or fewer carbon atoms at the ester terminus. When (meth)acrylate monomer B is (meth)acrylate C... 9-12 In the case of alkyl esters, (meth)acrylic acid C 9-12 C in alkyl esters 9-12The structure of the alkyl group is not particularly limited; both straight-chain and branched alkyl groups can be used. As (meth)acrylic acid monomer B, this (meth)acrylic acid C... 9-12 Alkyl esters can be used alone or in combination of two or more.

[0068] (meth)acrylic acid C having a straight-chain alkyl group at the ester terminus 9-12 Alkyl esters include, for example, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, and n-dodecyl (meth)acrylate (or lauryl (meth)acrylate). Additionally, (meth)acrylate C-terminus... 9-12 Alkyl esters, such as isononyl (meth)acrylate, isodecanyl (meth)acrylate, 2-propylheptyl (meth)acrylate, isoundecyl (meth)acrylate, and isododecyl (meth)acrylate. The techniques disclosed herein can be used with (meth)acrylate monomer B comprising acrylic acid C. 9-12 One or more of the alkyl esters are preferably implemented. As acrylic acid C 9-12 Suitable examples of alkyl esters include isononyl acrylate, isodecanyl acrylate, and n-dodecyl acrylate (or lauryl acrylate).

[0069] The content of (meth)acrylic monomer B in the monomer component constituting the above-mentioned acrylic polymer B is, for example, more than 50% by weight, preferably 85% by weight or more, more preferably 90% by weight or more, further preferably 92% by weight or more, and particularly preferably 95% by weight or more.

[0070] The monomer units constituting acrylic polymer B, in addition to the main component (meth)acrylate monomer B, may also include other secondary monomers (copolymeric monomers) capable of copolymerizing with (meth)acrylate monomer B, as needed. As secondary monomers capable of copolymerizing with (meth)acrylate monomer B, monomers having functional groups (e.g., carboxyl, hydroxyl, amide, etc.) may be suitably used. Monomers containing functional groups can play a role in introducing crosslinking sites into acrylic polymer B or in improving the cohesive strength of acrylic polymer B, and consequently the base polymer.

[0071] As the aforementioned secondary monomer, the same monomer as other secondary monomers capable of copolymerizing with the aforementioned (meth)acrylic monomer A can be used. Specific examples of secondary monomers that can be used as raw materials for acrylic polymer B include monomers that are the same as those capable of being used as raw materials for acrylic polymer A.

[0072] When using monomers containing functional groups as described above, there is no particular limitation on their amount; generally, 0.01% by weight or more of the total monomer content constituting acrylic polymer B is suitable. From the viewpoint of better utilizing the effects of using monomers containing functional groups, the amount of monomers containing functional groups can be set to 0.1% by weight or more of the total monomer content, and can be set to 1% by weight or more. Furthermore, the amount of monomers containing functional groups can be set to 50% by weight or less of the total monomer content, preferably 15% by weight or less, more preferably 10% by weight or less, further preferably 8% by weight or less, and particularly preferably 5% by weight or less. This prevents the cohesive force of the adhesive from becoming too high, and improves the adhesion to the bonded objects.

[0073] The adhesive composition disclosed herein is preferably implemented such that the monomer components constituting the acrylic polymer B include (meth)acrylate monomer B, and also include one or both of acrylic acid and hydroxyl-containing monomers. As the hydroxyl-containing monomer, hydroxyalkyl (meth)acrylate is preferably used. Particularly preferred are hydroxyethyl acrylate (HEA), hydroxybutyl acrylate (4HBA), and other hydroxyacrylate monomers. 1-4 Alkyl esters.

[0074] In the preparation of acrylic polymer B, the monomer raw materials may include secondary monomers other than the functionalized monomers mentioned above, for the purpose of improving the cohesive strength of acrylic polymer B. These secondary monomers can be the same monomers used in the preparation of acrylic polymer A. One such secondary monomer may be used alone, or two or more may be used in combination. The amount of these secondary monomers is not particularly limited, as long as it is appropriately selected according to the purpose and application; for example, it is preferably set to 20% by weight or less (e.g., 2 to 20% by weight, typically 3 to 10% by weight) of the total monomer raw materials of acrylic polymer B.

[0075] In a preferred embodiment of the technology disclosed herein, the adhesive composition comprises, as a base polymer, one or more polymers selected from acrylic polymers B. From the viewpoint of adjusting adhesive properties and viscosity in the molten state, the base polymer preferably comprises two or more acrylic polymers selected from acrylic polymers B. Furthermore, from the viewpoint of simplifying the composition, the base polymer preferably comprises one acrylic polymer selected from acrylic polymers B.

[0076] In a preferred embodiment of the technology disclosed herein, the base polymer included in the adhesive composition is a mixture of acrylic polymer A and acrylic polymer B. In other words, in the technology disclosed herein, the base polymer of the adhesive composition can be a mixture obtained by blending one or more acrylic polymers selected from acrylic polymer A with one or more acrylic polymers selected from acrylic polymer B. From the viewpoint of simplifying composition, in one embodiment of the technology disclosed herein, the base polymer can be a mixture of two or more acrylic polymers selected from acrylic polymer A and one acrylic polymer selected from acrylic polymer B, or a mixture of one acrylic polymer selected from acrylic polymer A and two or more acrylic polymers selected from acrylic polymer B, or a mixture of one acrylic polymer selected from acrylic polymer A and one acrylic polymer selected from acrylic polymer B. Here, the type of acrylic polymer can be distinguished according to the type, proportion, arrangement, etc., of the monomer units constituting the acrylic polymer, and the weight-average molecular weight of the polymer.

[0077] In the technology disclosed herein, when the total amount of acrylic polymer A and acrylic polymer B in the base polymer is set to 100% by weight, the content of acrylic polymer B (i.e., the proportion of acrylic polymer B in the total of acrylic polymer A and acrylic polymer B) is preferably 10% by weight or more. More preferably, the content of acrylic polymer B is 20% by weight or more, and even more preferably 30% by weight or more. In a preferred embodiment, the content of acrylic polymer B can be 40% by weight or more, 45% by weight or more, or 50% by weight or more. There is a tendency that the more the content of acrylic polymer B becomes relative to the content of acrylic polymer A, the more appropriately the viscosity of the adhesive composition will decrease in the molten state upon heating.

[0078] Furthermore, in the technology disclosed herein, when the total amount of acrylic polymer A and acrylic polymer B in the base polymer is set to 100% by weight, the content of acrylic polymer B is preferably 90% by weight or less, more preferably 80% by weight or less, and even more preferably 70% by weight or less. In a preferred embodiment, the content of the acrylic polymer B may be 60% by weight or less, 55% by weight or less, or 50% by weight or less. There is a tendency that the more the content of acrylic polymer A becomes relative to the content of acrylic polymer B, the more the adhesive properties (e.g., adhesive strength or holding power) will be improved.

[0079] It should be noted that when the base polymer contains two or more acrylic polymers A, the content of acrylic polymer A mentioned above represents the total amount of each acrylic polymer A. Similarly, when the base polymer contains two or more acrylic polymers B, the content of acrylic polymer B mentioned above represents the total amount of each acrylic polymer B.

[0080] (Other acrylic polymers)

[0081] In the technology disclosed herein, the adhesive composition may include, as the base polymer, other acrylic polymers besides acrylic polymer A and acrylic polymer B. Examples of other acrylic polymers include (meth)acrylic acid C. 2-3 Alkyl esters, (meth)acrylic acid C 13-18 Polymers with alkyl esters as the main monomer component. As (meth)acrylic acid C 2-3 Alkyl esters, examples of which include ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate, are alkyl esters. As a C-type alkyl ester... 13-18 Alkyl esters, examples of which include (meth)acrylate tridecyl ester, (meth)acrylate tetradecyl ester, (meth)acrylate pentadecyl ester, (meth)acrylate hexadecyl ester, (meth)acrylate heptadecanyl ester, (meth)acrylate octadecyl ester, (meth)acrylate isotriadecyl ester, (meth)acrylate isotetradecyl ester, (meth)acrylate isopentadecanyl ester, (meth)acrylate isohexadecyl ester, (meth)acrylate isoheptadecanyl ester, (meth)acrylate isostearyl ester, etc. The techniques disclosed herein can be suitably implemented in a manner where the base polymer substantially does not contain any acrylic polymers other than acrylic polymer A and acrylic polymer B.

[0082] There are no particular limitations on the method for polymerizing the monomer feedstock. Various polymerization methods known as methods for synthesizing acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization, can be appropriately employed. For example, solution polymerization is preferred. As for the monomer supply method during solution polymerization, suitable methods include one-time supply of all monomer feedstock, continuous supply (dropwise addition), and batch supply (dropwise addition). The solvent used in solution polymerization (polymerization solvent) can be appropriately selected from existing known organic solvents. For example, any one solvent selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); esters such as ethyl acetate and butyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc., or a mixture of two or more solvents can be used. The polymerization temperature can be appropriately selected based on the type of monomer and solvent used, the type of polymerization initiator, etc., for example, it can be around 20℃ to 120℃ (typically 40℃ to 80℃). According to solution polymerization, a polymerization reaction solution in which the polymer of the monomer raw material is dissolved in the polymerization solvent can be obtained. The adhesive composition used in the formation of the adhesive layer can preferably be manufactured using the above-mentioned polymerization reaction solution.

[0083] During polymerization, depending on the polymerization method and process, known or commonly used thermal polymerization initiators and photopolymerization initiators can be used. Examples of thermal polymerization initiators include azo-based initiators, peroxide-based initiators, redox initiators composed of peroxides and reducing agents, and substituted ethane initiators. Examples of photopolymerization initiators include α-ketool-based photoinitiators, acetophenone-based photoinitiators, benzoin ether-based photoinitiators, ketal-based photoinitiators, aromatic sulfonyl chloride-based photoinitiators, photoactive oxime-based photoinitiators, benzophenone-based photoinitiators, thioxanone-based photoinitiators, and acylphosphine oxide-based photoinitiators. One polymerization initiator can be used alone or in combination of two or more.

[0084] The amount of polymerization initiator used is the usual amount, for example, it can be selected from about 0.005 to 1 part by weight (typically 0.01 to 1 part by weight) relative to 100 parts by weight of all monomer raw materials.

[0085] The adhesive composition disclosed herein may, as needed, further include polymers other than acrylic polymers as secondary polymers. Examples of suitable secondary polymers include various polymers other than acrylic polymers that may be included in the adhesive layer. When the adhesive composition disclosed herein includes secondary polymers in addition to acrylic polymers, it is preferable that the content of the secondary polymer is less than 100 parts by weight relative to 100 parts by weight of the acrylic polymer, preferably 50 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 10 parts by weight or less. The content of the secondary polymer relative to 100 parts by weight of the acrylic polymer may be 5 parts by weight or less, or 1 part by weight or less. The technique disclosed herein is preferably implemented, for example, in such a way that 99.5% to 100% by weight of the polymer included in the adhesive composition is an acrylic polymer.

[0086] The molecular weight of acrylic polymer A is not particularly limited and can be set to an appropriate range according to the required performance. The weight-average molecular weight (Mw) of acrylic polymer A is approximately 5 × 10⁻⁶. 4 The above is suitable, and appropriate selection and use are recommended, with approximately 75×10 being the preferred size. 4 The above, and more preferably, is about 80×10 4 The above, and further optimized, is approximately 85×10 4 The above (e.g., approximately 90×10) 4 The above-mentioned substances. According to the technology disclosed herein, in order to achieve an adhesive composition with appropriately low viscosity even when heated and melted, an adhesive composition in which an acrylic polymer A having a Mw of at least the aforementioned specified value can be readily and suitably formed into an adhesive layer. The upper limit of the Mw of the acrylic polymer A is not particularly limited, but is approximately 150 × 10⁻⁶. 4 The following are suitable, preferably approximately 120×10 4 The following, more preferably, is approximately 115 × 10 4 The following (e.g., approximately 110×10) 4 (See below). By keeping the Mw of the acrylic polymer A within the above range, the elastic modulus of the adhesive can be easily adjusted to a preferred range, and good cohesion can be easily achieved.

[0087] The molecular weight of acrylic polymer B is not particularly limited and can be set to an appropriate range according to the required performance. The weight-average molecular weight (Mw) of acrylic polymer B is approximately 5 × 10⁻⁶. 4 The above is suitable, and appropriate selection and use are recommended, with approximately 75×10 being the preferred size. 4 The above, and more preferably, is about 80×10 4 The above, and further optimized, is approximately 85×10 4 The above (e.g., approximately 90×10)4 The above-mentioned substances. According to the technology disclosed herein, in order to achieve an adhesive composition with appropriately low viscosity even when heated and melted, an adhesive composition in which an acrylic polymer B having a Mw of at least the aforementioned specified value can be readily and suitably formed into an adhesive layer. The upper limit of the Mw of the acrylic polymer B is not particularly limited, but is approximately 150 × 10⁻⁶. 4 The following are suitable, preferably approximately 120×10 4 The following, more preferably, is approximately 115 × 10 4 The following (e.g., approximately 110×10) 4 (See below). By keeping the Mw of the acrylic polymer B within the above range, the elastic modulus of the adhesive can be easily adjusted to a preferred range, and good cohesive strength can be easily achieved.

[0088] It should be noted that, here, the Mw of the polymer (e.g., acrylic polymer A, acrylic polymer B, etc.) refers to the polystyrene conversion value determined by gel permeation chromatography (GPC). As the GPC measuring apparatus, for example, the HLC-8220 manufactured by Tosoh Corporation can be used. Specifically, the Mw of the base polymer can be determined using the method described in the examples below.

[0089] (glass transition temperature (Tg))

[0090] The acrylic polymer A included in the adhesive composition disclosed herein can be set, for example, so that its glass transition temperature (Tg), calculated based on the composition of the monomers constituting acrylic polymer A, is less than 0°C. Similarly, the acrylic polymer B included in the adhesive composition disclosed herein can be set, for example, so that its glass transition temperature (Tg), calculated based on the composition of the monomers constituting acrylic polymer B, is less than 0°C. Here, Tg calculated based on the composition of the monomers refers to Tg obtained using the Fox formula based on the composition of the monomers. As shown below, the Fox formula is a relationship between the Tg of the copolymer and the glass transition temperature Tgi of the homopolymer obtained by homopolymerizing the monomers constituting the copolymer.

[0091] 1 / Tg=Σ(Wi / Tgi)

[0092] In the above Fox formula, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the homopolymer of monomer i (unit: K).

[0093] The glass transition temperature of the homopolymer used in the Tg calculation is the value recorded in known sources. Specifically, values ​​from the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) can be used. For monomers for which multiple values ​​are recorded in the aforementioned Polymer Handbook, the highest value is adopted. For the glass transition temperature of homopolymers of monomers not recorded in the aforementioned Polymer Handbook, values ​​obtained using the measurement method described in Japanese Patent Application Publication No. 2007-51271 can be used.

[0094] The Tg calculated based on the composition of the aforementioned monomer components can be considered as the Tg of the polymer containing those monomer components. The Tg of the acrylic polymer A calculated in this way is preferably below -10°C, but can be below -20°C, below -30°C, or below -40°C. If the Tg is lower than this, there is a tendency for improved adhesion to the adhered materials. In several embodiments, the Tg of the acrylic polymer A can be below -50°C, below -55°C, or below -60°C. The lower limit of the Tg of the acrylic polymer A is not particularly limited; from the viewpoint of material availability and improved cohesion of the adhesive layer, a Tg of -80°C or higher is generally suitable, and preferably above -70°C.

[0095] The Tg of acrylic polymer B is preferably below 150°C, but can be below 50°C, below 30°C, or below 10°C. Lowering the Tg tends to improve the adhesion to the adhered materials. In several embodiments, the Tg of acrylic polymer B can be below -20°C, below -35°C, or below -50°C. The lower limit of the Tg of acrylic polymer B is not particularly limited; from the viewpoint of material availability and improved cohesion of the adhesive layer, a Tg of -80°C or higher is generally suitable, and preferably above -70°C. In several embodiments, the Tg of acrylic polymer B can be above -20°C, above -10°C, or above 0°C.

[0096] (Viscosity)

[0097] In the technology disclosed herein, the viscosity of the adhesive composition is not particularly limited. The shear viscosity of the adhesive composition at 130°C is preferably 7000 Pa·s or less, more preferably 6800 Pa·s or less, and even more preferably 6700 Pa·s or less. Furthermore, from the viewpoint of ease of extrusion molding of the adhesive layer, a shear viscosity of the adhesive composition at 130°C is generally suitable to be 500 Pa·s or more, preferably 1000 Pa·s or more (e.g., 1500 Pa·s or more). The shear viscosity of the adhesive composition at 130°C can be measured using the method described in the examples below.

[0098] It should be noted that, when measuring the shear viscosity of the adhesive composition, the adhesive composition used for the measurement is preferably free of crosslinking agents. Hereinafter, the adhesive composition free of crosslinking agents will also be referred to as adhesive composition PL. If the shear viscosity of adhesive composition PL at 130°C is within the above range, then adhesive composition PL, or an adhesive composition obtained by adding a crosslinking agent to adhesive composition PL, can be used for extrusion molding to suitably form an adhesive layer.

[0099] The adhesive compositions disclosed herein may include tackifiers. There are no particular limitations on the tackifier; examples include rosin-based tackifiers, terpene-based tackifiers, phenol-based tackifiers, hydrocarbon-based tackifiers, ketone-based tackifiers, polyamide-based tackifiers, epoxy-based tackifiers, and elastic system tackifiers. Tackifiers may be used alone or in combination of two or more.

[0100] As rosin-based tackifiers, examples include unmodified rosins (raw rosin) such as resin rosin, wood rosin, and tall oil rosin; modified rosins that have been modified through polymerization, disproportionation, hydrogenation, etc. (polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, partially hydrogenated rosin, rosin with other chemical modifications, etc.); and various rosin derivatives.

[0101] As one example of the aforementioned rosin derivatives, rosin phenolic resins can be obtained by adding phenol to rosin (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst and then thermally polymerizing it.

[0102] Rosin ester resins include rosin ester compounds obtained by esterifying unmodified rosin with alcohols (unmodified rosin esters), polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, and partially hydrogenated rosin; and rosin ester compounds obtained by esterifying modified rosin with alcohols (polymerized rosin esters, stabilized rosin esters, disproportionated rosin esters, fully hydrogenated rosin esters, partially hydrogenated rosin esters, etc.).

[0103] Unsaturated fatty acid modified rosin resins are obtained by modifying unmodified rosin and modified rosin (polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, partially hydrogenated rosin, etc.) with unsaturated fatty acids.

[0104] Unsaturated fatty acid modified rosin ester resin is obtained by modifying rosin ester resin with unsaturated fatty acids.

[0105] Rosin alcohol resins are obtained by reducing the carboxyl groups in unmodified rosin, modified rosin (polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, partially hydrogenated rosin, etc.), unsaturated fatty acid modified rosin resins, and unsaturated fatty acid modified rosin ester resins.

[0106] Metal salts of rosin-based resins (especially rosin ester resins), including unmodified rosin, modified rosin, and various rosin derivatives; etc.

[0107] Examples of terpene-based tackifiers include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers, as well as modified terpene resins obtained by modifying these terpene resins (phenol modification, aromatic modification, hydrogenation modification, hydrocarbon modification, etc.) (e.g., terpene phenol resins, styrene-modified terpene resins, aromatic-modified terpene resins, hydrogenated terpene resins, etc.).

[0108] Examples of phenolic tackifiers include condensates of various phenols (e.g., phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcinol, etc.) with formaldehyde (e.g., alkylphenol resins, xylene-formaldehyde resins, etc.), methyl phenolic resins obtained by reacting the above phenols with formaldehyde using an alkaline catalyst, and phenolic varnishes obtained by reacting the above phenols with formaldehyde using an acid catalyst.

[0109] Examples of hydrocarbon-based thickeners include aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (such as styrene-olefin copolymers), aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone-indene resins, and various other hydrocarbon-based resins.

[0110] (Cross-linking agent)

[0111] In a preferred embodiment of the technology disclosed herein, the adhesive composition further comprises a crosslinking agent. There is no particular limitation on the crosslinking agent, and various crosslinking agents can be used. Examples of crosslinking agents disclosed herein include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, melamine-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, hydrazine-based crosslinking agents, and amine-based crosslinking agents. They can be used alone or in combination of two or more.

[0112] As isocyanate-based crosslinking agents, multifunctional isocyanate compounds with two or more functions can be used. Examples include aromatic isocyanates such as toluene diisocyanate, xylene diisocyanate, polymethylene polyphenyl diisocyanate, tris(p-isocyanate phenyl)thiophosphate, and diphenylmethane diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate. Commercially available examples include trimethylolpropane / toluene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate L"), trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate HL"), and isocyanurate derivatives of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX"), etc.

[0113] As an epoxy-based crosslinking agent, epoxy-based crosslinking agents having two or more epoxy groups per molecule can be used without limitation. Preferably, epoxy-based crosslinking agents having three to five epoxy groups per molecule are used. Specific examples of epoxy-based crosslinking agents include N,N,N',N'-tetraglycidylm-phenylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy crosslinking agents include those manufactured by Mitsubishi Gas Chemical Co., Ltd. under the trade names "TETRAD-X" and "TETRAD-C", manufactured by DIC under the trade name "EPICLON CR-5L", manufactured by Nagase ChemteX Corporation under the trade names "DENACOLEX-512", "DENACOL EX-411", and "DENACOL EX-321", and manufactured by Nissan Chemical Industries Co., Ltd. under the trade name "TEPIC-G".

[0114] The amount of crosslinking agent is not particularly limited and can be appropriately set in a way that achieves the desired effect. From the viewpoint of adhesion and bonding reliability, the amount of crosslinking agent relative to 100 parts by weight of the base polymer is generally suitable to be about 15 parts by weight or less, preferably about 12 parts by weight or less, more preferably about 10 parts by weight or less, and can be less than 7 parts by weight or less than 5 parts by weight. There is no particular limitation on the lower limit of the amount of crosslinking agent. From the viewpoint of improving adhesive performance, the amount of crosslinking agent relative to 100 parts by weight of the base polymer is generally suitable to be 0.01 parts by weight or more, preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, further preferably 0.2 parts by weight or more, and can be 0.5 parts by weight or more, 1 part by weight or more, or 1.5 parts by weight or more.

[0115] To more effectively carry out the reaction of any of the aforementioned crosslinking agents, a crosslinking catalyst can be used. As a crosslinking catalyst, tin-based catalysts (especially dioctyltin dilaurate) and amine-based catalysts (e.g., 1-isobutyl-2-methylimidazole) are preferred. There is no particular limitation on the amount of crosslinking catalyst used; for example, it can be about 0.0001 parts by weight to 1 part by weight relative to 100 parts by weight of the base polymer.

[0116] (Multifunctional monomer)

[0117] The adhesive compositions disclosed herein can be prepared using multifunctional monomers as needed. Multifunctional monomers, by replacing or in combination with crosslinking agents as described above, can help to regulate cohesion and other objectives. Examples of multifunctional monomers include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, allyl methacrylate, vinyl methacrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butanediol (meth)acrylate, and hexanediol di(meth)acrylate. Preferred multifunctional monomers include trimethylolpropane tri(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. One multifunctional monomer may be used alone or in combination of two or more. The amount of multifunctional monomer used varies depending on its molecular weight, number of functional groups, etc., and is generally suitable in the range of about 0.01 parts by weight to 3.0 parts by weight relative to 100 parts by weight of the base polymer. The adhesive compositions disclosed herein are preferably implemented in a manner that substantially does not contain multifunctional monomers.

[0118] Furthermore, to the extent that it does not significantly impair the effects of the present invention, the adhesive compositions disclosed herein may, as needed, include leveling agents, plasticizers, softeners, colorants (dyes, pigments, etc.), antistatic agents, antioxidants, ultraviolet absorbers, antioxidants, light stabilizers, preservatives, and other known additives that can be used in adhesives.

[0119] <Formation of Adhesive Layer>

[0120] The adhesive layer of the adhesive sheet disclosed herein can be an adhesive layer formed from a hot-melt adhesive composition comprising a base polymer (e.g., a mixture of acrylic polymer A and acrylic polymer B), and may contain any other arbitrary components as needed. The adhesive composition disclosed herein is molded in a heated molten state, and subsequently, an adhesive layer is formed by a curing process.

[0121] The method for molding the hot-melt adhesive composition disclosed herein into a film (or sheet) is not particularly limited and can be carried out by any known suitable method. The adhesive composition disclosed herein can be molded, for example, by calendering, casting, blow extrusion, T-die extrusion, etc. For example, when molding the adhesive composition disclosed herein into a film by melt extrusion, the adhesive composition is heated to a relatively high temperature (typically about 90–110°C, for example, about 100°C) and is in a highly fluid molten state. Then, the molten adhesive composition is extruded from the die of an extruder to form a film. The adhesive composition molded into a film is then left at a lower temperature (typically about 30–50°C, for example, about 40°C) for a certain period of time (typically 12 hours or more, for example, 24 hours or more) to cure it and form an adhesive layer with suitable adhesive properties.

[0122] In the adhesive sheet disclosed herein, the thickness of the adhesive layer is not particularly limited and can be appropriately selected according to the purpose. Generally, a thickness of about 5 to 1000 μm is suitable, and from the viewpoint of adhesion, it is preferably about 10 μm or more (e.g., 15 μm or more, typically 25 μm or more), preferably 750 μm or less, more preferably 500 μm or less, and even more preferably about 400 μm or less (e.g., 300 μm or less, typically 200 μm or less).

[0123] <Example of adhesive sheet composition>

[0124] According to the technology disclosed herein, an adhesive sheet having the aforementioned adhesive layer is provided. The adhesive layer typically constitutes at least one surface of the adhesive sheet. The adhesive sheet can be a substrate-supported adhesive sheet having an adhesive layer on one or both sides of a substrate (support), or it can be a substrate-free adhesive sheet (substrate-free adhesive sheet).

[0125] The concept of adhesive sheet as used herein can include terms such as adhesive tape, adhesive label, adhesive film, etc. Furthermore, the adhesive sheet provided in this specification can be in roller form or in single sheet form. Alternatively, it can be an adhesive sheet further processed into various shapes and forms.

[0126] Figure 1 and Figure 2 This is a diagram illustrating a suitable configuration example of the adhesive sheet disclosed herein. Figure 1 The adhesive sheet 1 shown has the following configuration: one surface (first adhesive surface) 21A and the other surface (second adhesive surface) 21B of the substrate-free adhesive layer 21 are respectively protected by release liner 31, 32 which at least the adhesive layer side serves as the release surface. Figure 2The adhesive sheet 2 shown has a configuration in which one surface (first adhesive surface) 21A of the adhesive layer 21 is protected by a release liner 31 on both sides, which are called release surfaces. When it is wound up, the other surface (second adhesive surface) 21B of the adhesive layer 21 contacts the back side of the release liner 31, thereby forming a configuration in which the other side 21B is also protected by the release liner 31.

[0127] Double-sided adhesive sheets, whether substrate-free or with a substrate, can be used as single-sided adhesive sheets with a substrate by attaching a non-peelable substrate to one adhesive surface.

[0128] For example Figure 1 , 2 As shown, the adhesive sheet before use (before being pasted onto the substrate) can be in the form of an adhesive sheet with a release liner protecting the adhesive surface. There are no particular limitations on the release liner; for example, a release liner with a surface treated for release, such as a resin film or paper, or a release liner formed from a low-adhesion material such as a fluoropolymer (polytetrafluoroethylene, etc.) or a polyolefin resin (polyethylene, polypropylene, etc.) can be used. The release treatment can, for example, use silicone-based or long-chain alkyl-based release agents. In some embodiments, a resin film with a release treatment is preferred as the release liner.

[0129] When the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, the adhesive constituting the first adhesive surface (first adhesive) and the adhesive constituting the second adhesive surface (second adhesive) may optionally have the same composition or different compositions. A substrate-free double-sided adhesive sheet with different compositions for the first and second adhesive surfaces can be achieved, for example, by directly (without the aid of a substrate) laminating two or more adhesive layers with different compositions into a multilayer adhesive layer structure.

[0130] <Substrate>

[0131] In adhesive sheets with substrates of single-sided or double-sided adhesive types, the substrate serving as the supporting (base) adhesive layer can be various sheet-like substrates such as resin film, paper, cloth, rubber sheet, foam sheet, metal foil, and composites thereof. The aforementioned substrate can be a single layer or a laminate of the same or different types of substrates. It should be noted that, in this specification, a single layer refers to a layer composed of the same composition, including the form of multiple layers composed of the same composition stacked together.

[0132] In a preferred embodiment, a substrate (resin film substrate) with resin sheets as the main constituent element can be used. Examples of resins constituting the substrate include, for instance, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-low-density polyethylene, random copolymer polypropylene, block copolymer polypropylene, homopolymer polypropylene, polybutene, polymethylpentene, ethylene-vinyl acetate copolymer (EVA), ionomers, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid (random, alternating) copolymer, ethylene-butene copolymer, ethylene-hexene copolymer, and other polyolefin resins; polyurethane; polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate, and polybutylene terephthalate (PBT); polycarbonate; polyimide; polyetheretherketone; polyetherimide; polyamides such as aramid and fully aromatic polyamides; polyphenyl sulfide; fluoropolymers; polyvinyl chloride; polyvinylidene chloride; cellulose resins; silicone resins; etc. The aforementioned resins can be used alone or in combination of two or more to form the entirety or part of the substrate (e.g., any layer in a substrate with two or more laminated structures).

[0133] The substrate can be mixed with various additives as needed, such as fillers (inorganic fillers, organic fillers, etc.), antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, and colorants (pigments, dyes, etc.).

[0134] The aforementioned substrate can be manufactured using any suitable method. For example, it can be manufactured using known methods such as calendering, casting, blow extrusion, and T-die extrusion. Alternatively, it can be manufactured by stretching as needed.

[0135] To improve adhesion to and retention of the adhesive layer, physical treatments such as corona discharge, plasma treatment, sanding, ozone exposure, flame exposure, high-voltage electric shock exposure, and ionization radiation treatment can be applied to the adhesive layer side surface of the substrate; chemical treatments such as acid treatment, alkali treatment, and chromic acid treatment can be applied; and easy-to-bond treatments based on the coating agent (primer) can be used; and other known or conventional surface treatments can be applied. Additionally, to impart antistatic properties, a conductive vapor-deposited layer containing metals, alloys, or their oxides can be formed on the substrate surface.

[0136] In some preferred embodiments, a primer layer is formed on the adhesive layer side surface of the substrate. In other words, a primer layer can be disposed between the substrate and the adhesive layer. There are no particular limitations on the primer layer forming material; one or more of the following can be used: urethane (polyisocyanate) resins, polyester resins, acrylic resins, polyamide resins, melamine resins, olefin resins, polystyrene resins, epoxy resins, phenolic resins, isocyanurate resins, and polyvinyl acetate resins. When an acrylic adhesive layer is formed on a resin film substrate by a primer layer, polyester, urethane, or acrylic primer layers are preferred. When an acrylic adhesive layer is formed on a polyester substrate such as PET film by a primer layer, a polyester primer layer is particularly preferred. The thickness of the primer layer is not particularly limited and is typically in the range of about 0.1 μm to 10 μm (e.g., 0.1 μm to 3 μm, typically 0.1 μm to 1 μm). The primer layer can be formed using a known or conventional coating machine such as a gravure roller coater or a reverse roller coater.

[0137] The adhesive sheet disclosed herein is a single-sided adhesive sheet with an adhesive layer on one side of the substrate. Alternatively, the non-adhesive layer side (back side) of the substrate can be peeled off using a release agent (back side treatment agent). There are no particular limitations on the back side treatment agent that can be used to form the back side treatment layer; other known or conventional treatment agents such as silicone-based, fluorine-based, and long-chain alkyl-based back side treatment agents can be used depending on the purpose and application.

[0138] The thickness of the substrate is not particularly limited and can be appropriately selected depending on the purpose, typically ranging from about 2μm to 800μm. From the viewpoint of processability and operability of the adhesive sheet, a substrate thickness of 5μm or more is suitable, preferably 10μm or more, 20μm or more, 30μm or more, or 40μm or more. Furthermore, from the viewpoint of flexibility, a substrate thickness of 300μm or less is typically suitable, preferably 200μm or less, 150μm or less, 125μm or less, 80μm or less, or 60μm or less.

[0139] The total thickness of the adhesive sheet disclosed herein (which may include an adhesive layer and a substrate, but excluding a release liner) is not particularly limited, and a range of about 10 μm to 1200 μm is suitable. Considering adhesion and operability, the total thickness of the adhesive sheet is preferably in the range of about 15 μm to 300 μm, more preferably in the range of about 20 μm to 200 μm.

[0140] The adhesive strength of the adhesive sheet disclosed herein is not particularly limited. For example, under conditions of a peel angle of 180 degrees, a stretching speed of 300 mm / min, and an environment of 23°C and 50% RH, a peel strength of 1 N / 20 mm or more when peeling an adhesive sheet cut to a width of 20 mm and a length of 100 mm from a stainless steel sheet (SUS304BA sheet) as the adherend is generally suitable, preferably 4 N / 20 mm or more, more preferably 4.5 N / 20 mm or more, and particularly preferably 5 N / 20 mm or more. The upper limit of the peel strength is not particularly limited, but from the viewpoint of suppressing cohesive failure of the adhesive layer, it is preferably 10 N / 20 mm or less. Specifically, the peel strength (adhesive force) of the adhesive sheet can be measured using the method described in the examples below.

[0141] The holding force of the adhesive sheet disclosed herein is not particularly limited. For example, a test sample is prepared by attaching an adhesive sheet cut to a width of 10 mm and a length of 100 mm to a bakelite board (phenolic resin board) as the substrate with an adhesive length of 20 mm, such that the length direction of the test sample is vertical. A load of 500 g is applied to the free end of the test sample, and it is placed at 40°C for 60 minutes. In the above-mentioned holding force test, the test sample preferably does not fall off the bakelite board. Specifically, the holding force of the adhesive sheet can be measured using the method described in the examples described later.

[0142] Example

[0143] The following describes several embodiments related to the present invention, but this does not mean that the present invention is not limited to the contents shown in these embodiments. It should be noted that in the following description, "parts" and "%" are weight bases unless otherwise specified.

[0144] (Preparation of polymer A1)

[0145] In a reaction vessel equipped with a Liebig condenser, nitrogen inlet pipe, thermometer, dropping funnel, and stirrer, 100 parts of n-butyl acrylate (BA) and 5 parts of acrylic acid (AA) as monomer raw materials, and 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as polymerization initiator, were added to toluene as polymerization solvent. Following nitrogen reflux at room temperature for 1 hour, the mixture was heated to 60°C for 5 hours for solution polymerization, and then further subjected to solution polymerization at 80°C for 2 hours to prepare a solution of polymer A1.

[0146] (Preparation of polymer A2)

[0147] Instead of 100 parts of n-butyl acrylate (BA) as a monomer raw material, 100 parts of 2-ethylhexyl acrylate (2EHA) are used. Otherwise, a solution of polymer A2 is prepared using the same method as that used for polymer A1.

[0148] (Preparation of polymer B1)

[0149] Instead of 100 parts of n-butyl acrylate (BA) as a monomer raw material, 100 parts of isononyl acrylate (INA) are used. Otherwise, a solution of polymer B1 is prepared using the same method as that used for polymer A1.

[0150] (Preparation of polymer B2)

[0151] Instead of 100 parts of n-butyl acrylate (BA) as a monomer raw material, 100 parts of lauryl acrylate (LA) are used. Otherwise, a solution of polymer B2 is prepared using the same method as that used for polymer A1.

[0152] The weight-average molecular weight (Mw) of polymers A1, A2, B1, and B2 prepared above was determined using the following apparatus and measurement conditions.

[0153] Device: Tosoh Corporation, HCL-8220

[0154] Separation column: Tosoh Corporation, GMHHR-H(20)

[0155] Detector: Differential refraction detector

[0156] Solvent: THF

[0157] Flow rate: 0.5 mL / min

[0158] Measurement conditions: column temperature 40℃

[0159] Table 1 shows the content of materials used in the preparation of polymers A1, A2, B1 and B2, and also shows the weight-average molecular weight of each polymer as measured by the above method.

[0160] [Table 1]

[0161] Table 1

[0162]

[0163] <Example 1>

[0164] (Preparation of the adhesive composition)

[0165] Adhesive composition PL was prepared by mixing solutions of polymer A2 and polymer B1, with polymer A2 comprising 90 parts by weight and polymer B1 comprising 10 parts by weight. Two parts of an isocyanate-based crosslinking agent (trimethylolpropane / toluene diisocyanate trimer adduct, manufactured by Tosoh Corporation, trade name "CORONATE L", solids concentration of 75% by weight) were added to the adhesive composition PL, and toluene was removed by vacuum drying to obtain the hot-melt adhesive composition of Example 1.

[0166] <Examples 2-6, Comparative Examples 1-5>

[0167] The types and amounts of polymers used were varied as shown in Tables 2-4. Otherwise, the hot melt adhesive compositions of each example were obtained using the same method as in Example 1.

[0168] [Determination of Adhesive Strength]

[0169] Using an extruder, the hot-melt adhesive compositions prepared in each example were heated and melted at approximately 100°C and sprayed onto a 25μm thick PET substrate, thereby producing an adhesive sheet with a 50μm thick adhesive layer laminated on the PET substrate. The produced adhesive sheet was cut into dimensions of 20mm width and 100mm length as samples for testing adhesive strength (peel strength). At 23°C and 50% RH, a 2kg rubber roller was used to press the adhesive surface of the test sample against a stainless steel plate (SUS304BA plate) as the adherend. After being placed at 50°C for 2 hours, the peel strength (adhesive force) [N / 20mm] was measured at 23°C and 50% RH using a tensile testing machine according to JIS Z0237:2000, with a peel angle of 180 degrees and a tensile speed of 300mm / min. The tensile testing machine used was a Shimadzu AG-IS triple tensile testing machine. As a tensile testing machine, in addition to the aforementioned testing machines, equivalent products can be used. The test results are shown in the corresponding columns of Tables 2 to 4.

[0170] It should be noted that in the adhesive strength test of the adhesive sheets made using the hot melt adhesive compositions of Comparative Examples 3 and 5, cohesive failure of the adhesive layer occurred.

[0171] [Measurement of holding power]

[0172] Using an extruder, the hot-melt adhesive compositions prepared in each example were heated and melted at approximately 100°C and sprayed onto a 25μm thick PET substrate, thereby producing an adhesive sheet with a 50μm thick adhesive layer laminated on the PET substrate. The produced adhesive sheet was cut into dimensions of 10mm width and 100mm length as samples for holding force testing. At 23°C and 50% RH, a 2kg roller was reciprocated once, and the adhesive surface of the above-mentioned test sample was adhered to a bakelite board (phenolic resin board) as the substrate with an adhesive area of ​​10mm width and 20mm length. The substrate with the test sample thus adhered was then hung at 40°C with the length direction of the test sample perpendicular to the vertical direction, and left for 30 minutes. Next, a 500g load was applied to the free end of the above-mentioned test sample, and the sample was left at 40°C for 60 minutes under this load, according to JIS Z0237. After 60 minutes, the offset distance [mm] of the test sample from its initial pasting position was measured. It should be noted that if the test sample falls from the bakelite board after 60 minutes, the result is evaluated as "fall". A creep testing machine (model: TG83-001) manufactured by Imada Corporation was used as the testing apparatus. The measurement results are shown in the corresponding columns of Tables 2-4.

[0173] [Determination of Shear Viscosity]

[0174] The adhesive composition PL prepared in each example before the addition of the crosslinking agent was coated onto a separator (manufactured by Mitsubishi Chemical Corporation, product name MRF-38) and dried. It was then peeled off from the separator, resulting in a sheet with a thickness of approximately 50 μm. Multiple sheets were stacked to create a sheet slightly thicker than 0.5 mm, which was used as the sample for shear viscosity measurement. For the above-mentioned sample, a Thermo Ficher RheoStress 6000 rheometer was used as the measuring device. The shear viscosity [Pa·s] was measured under the following conditions: a measuring temperature of 130 °C, a measuring speed of 0.1 (1 / second), a measuring interval of 0.5 mm, and a measuring terminal of P8 CSJ (measuring surface: Φ8 plate). The measurement results are shown in the corresponding columns of Tables 2–4.

[0175] [Table 2]

[0176] Table 2

[0177]

[0178] [Table 3]

[0179] Table 3

[0180]

[0181] *1In the adhesive strength test of Comparative Example 3, the adhesive layer underwent cohesive failure.

[0182] [Table 4]

[0183] Table 4

[0184]

[0185] *2 In the adhesive strength test of Comparative Example 5, the adhesive layer underwent cohesive failure.

[0186] The results shown in Table 2 clearly demonstrate that, in systems containing polymer A2 and polymer B1 as base polymers, the adhesive compositions of Examples 1 to 3, in which the content of polymer B1 in the base polymer is 10% by weight or more and 90% by weight or less, have lower shear viscosity compared to the adhesive composition of Comparative Example 1, in which the content of polymer B1 is 5% by weight, and are superior in one or both of adhesive strength and holding power compared to the adhesive composition of Comparative Example 2, in which the content of polymer B1 is 95% by weight.

[0187] The results shown in Tables 3 and 4 also exhibit the same trend. Specifically, in systems containing polymers A2 and B2 as base polymers, the adhesive compositions of Examples 4 and 5, with polymer B2 content of 10% or 50% by weight, show superior adhesive properties (adhesive strength and / or holding power) compared to the adhesive composition of Comparative Example 3, with polymer B2 content of 95% by weight. Furthermore, in systems containing polymers A1 and B2 as base polymers, the adhesive composition of Example 6, with polymer B2 content of 10% by weight, exhibits lower shear viscosity and superior holding power compared to the adhesive composition of Comparative Example 4, with polymer B2 content of 5% by weight, and superior adhesive properties (adhesive strength and / or holding power) compared to the adhesive composition of Comparative Example 5, with polymer A1 content of 5% by weight. The shear viscosity of the adhesive compositions of Examples 1-6 is within a range suitable for extrusion molding. On the other hand, the adhesive compositions of Comparative Examples 3 and 5 showed cohesive failure in the adhesive layer during the adhesive strength test.

[0188] The specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations to the specific examples described above.

[0189] Explanation of reference numerals in the attached figures

[0190] 1, 2 adhesive sheets

[0191] 21 Adhesive layer

[0192] 21A First Adhesive Surface

[0193] 21B Second Adhesive Surface

[0194] 31, 32 Peeling gaskets

Claims

1. A hot-melt adhesive composition comprising a base polymer, The base polymers consist only of acrylic polymer A and acrylic polymer B. Here, the acrylic polymer A is a polymer whose main component is a (meth)acrylic monomer A having an alkyl group with 4 or more but less than 8 carbon atoms. The acrylic polymer A further comprises one or both of acrylic acid and hydroxyl-containing monomers as monomeric components. The acrylic polymer B is a polymer whose main component is a (meth)acrylic acid monomer B having an alkyl group having 9 or more but less than 12 carbon atoms. The acrylic polymer B also contains one or both of acrylic acid and hydroxyl-containing monomers as monomer components. When the total amount of acrylic polymer A and acrylic polymer B in the base polymer is set to 100% by weight, the content of acrylic polymer B is 10% by weight or more and 90% by weight or less, and the weight-average molecular weight of acrylic polymer A is 75 × 10⁻⁶. 4 Above and 120×10 4 the following, The weight-average molecular weight of the acrylic polymer B is 75 × 10⁻⁶. 4 Above and 120×10 4 the following, The main component refers to the component contained in a content of more than 50% by weight. The hot melt adhesive composition also includes a crosslinking agent.

2. The hot-melt adhesive composition according to claim 1, wherein the shear viscosity at 130°C is 7000 Pa. Below s.

3. The hot melt adhesive composition according to claim 1, wherein, The crosslinking agent is an isocyanate-based crosslinking agent.

4. An adhesive sheet comprising an adhesive layer formed using the hot-melt adhesive composition according to any one of claims 1 to 3.

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