JP2024069115A - Adhesive sheet, adhesive and adhesive composition - Google Patents

Abstract

To provide an adhesive sheet which has adhesive force applicable to various base materials under ordinary temperature, can maintain adhesive force between an ordinary temperature region and a low temperature region, and moreover can exhibit strong adhesive force even in an ultralow temperature region of -10°C or lower.SOLUTION: An adhesive sheet has a base material, and an adhesive layer formed on any one surface of the base material, and is used at -10°C or lower, wherein the adhesive layer contains an acrylic resin (A) having a degree of dispersion of 5 or less, and a peak temperature of tanδ obtained by dynamic viscoelasticity measurement is 0°C or lower.SELECTED DRAWING: None

Description

The present invention relates to an adhesive sheet, and more specifically, to an adhesive sheet that can be used not only in the normal temperature range, but also in the ultra-low temperature range of -10°C or less, such as for adhesive tapes for frozen foods. The present invention also relates to an adhesive contained in the adhesive layer of the adhesive sheet, and an adhesive composition that constitutes the adhesive.

Conventionally, adhesive sheets such as single-sided adhesive tape and double-sided adhesive tape have been used to fix various components. In particular, strong adhesive strength is often required when fixing heavy objects or when firmly fixing components. On the other hand, there is a problem that adhesive strength is extremely reduced in low-temperature environments such as cold regions and freezers where the temperature is below freezing, especially in the ultra-low temperature range of -10°C or less, compared to normal temperature ranges. Therefore, there has been a demand for adhesive sheets that can maintain strong adhesive strength even in the ultra-low temperature range of -10°C or less. As an adhesive for use in such low temperature ranges, Patent Document 1 discloses an emulsion-type adhesive containing two types of tackifier resins with different softening points, with the aim of improving the low-temperature adhesiveness and curved surface application of the adhesive sheet. Patent Document 2 also discloses an adhesive sheet having an adhesive layer with a predetermined adhesive strength on one side of a label substrate having a porous layer.

JP 2007-186589 A JP 2020-56804 A

However, when the adhesive sheet described in Patent Document 1 is used, although adhesive strength and curved surface adhesion are exhibited at low temperatures of around 5°C, a decrease in adhesive strength is observed in applications requiring even stronger adhesive strength and at ultra-low temperatures of -10°C or below, and this is not satisfactory.
On the other hand, although Patent Document 2 has excellent curved surface application properties for porous substrates, the substrates are limited, and therefore it is not suitable for PET substrates or polyolefin substrates that do not have a porous structure, and is not satisfactory.
Therefore, an object of the present invention is to provide an adhesive sheet that has adhesive strength applicable to various substrates at room temperature, and that can maintain its adhesive strength from room temperature to low temperatures, and even exhibit strong adhesive strength even in the ultra-low temperature range of -10°C or below.

The inventors have discovered that in a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on one side of a variety of base material layers, the pressure-sensitive adhesive layer contains an acrylic resin (A) with a polydispersity of 5 or less, and the peak temperature of tan δ obtained by dynamic viscoelasticity measurement is 0°C or less, making it possible to use the sheet not only in room temperature environments, but also in ultra-low temperature environments of -10°C or less.

That is, the present invention includes the following aspects.
Aspect (1) of the present invention is a pressure-sensitive adhesive sheet having a substrate and a pressure-sensitive adhesive layer formed on either one surface of the substrate, the pressure-sensitive adhesive sheet being used at −10° C. or lower, the pressure-sensitive adhesive layer containing an acrylic resin (A) having a degree of dispersion of 5 or less, and having a peak temperature of tan δ obtained by dynamic viscoelasticity measurement of 0° C. or less.

In aspect (2) of the present invention, in the pressure-sensitive adhesive sheet of aspect (1), the tan δ peak temperature is -10°C or lower.

In aspect (3) of the present invention, in the pressure-sensitive adhesive sheet of aspect (1) or (2), the acrylic resin (A) has a structural unit derived from a carboxyl group-containing monomer.

In aspect (4) of the present invention, in the pressure-sensitive adhesive sheet of any one of aspects (1) to (3), the acrylic resin (A) is obtained by polymerization in an organic solvent.

In aspect (5) of the present invention, in the pressure-sensitive adhesive sheet of any one of aspects (1) to (4), the gel fraction of the pressure-sensitive adhesive layer is 20 to 95% by weight.

Aspect (6) of the present invention is an adhesive contained in the adhesive layer in the adhesive sheet of any one of aspects (1) to (5).

Aspect (7) of the present invention is an adhesive composition that constitutes the adhesive of aspect (6).

Aspect (8) of the present invention is a pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer obtained by curing a pressure-sensitive adhesive composition containing an acrylic resin laminated on either one surface of the substrate,
The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer has an adhesive strength represented by the following formula (1):
Formula (1)
180° peel strength > 5N/25mm
(For SUS304BA plate, peeling temperature: -15°C, peeling speed: 300mm/min)

In the present invention, "an adhesive sheet used at -10°C or below" means that the adhesive sheet is temporarily or permanently placed in an environment of -10°C or below, i.e., the use temperature of the adhesive sheet is -10°C or below. In addition, in this specification, "ultra-low temperature range" means -10°C or below, particularly -15°C or below, and even -30°C, with the lower limit temperature usually being -50°C. "Normal temperature range" means 5 to 35°C, preferably 15 to 25°C.

The "adhesive sheet" of the present invention is a laminate having at least a substrate and an adhesive layer formed on one side of the substrate, and conceptually includes, for example, an adhesive film and an adhesive tape. Furthermore, the substrate of the present invention is not particularly limited in terms of material, shape, or size.

The adhesive sheet of the present invention has adhesive strength that can be applied to various substrates at room temperature, and can maintain its adhesive strength from room temperature to low temperatures, and can even exhibit strong adhesive strength at ultra-low temperatures of -10°C or below.

Hereinafter, embodiments for carrying out the present invention will be described in detail, but the present invention is not limited to these.
In the present invention, "(meth)acrylic" means acrylic or methacrylic, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylate" means acrylate or methacrylate, respectively.

<<Adhesive sheet>>
The pressure-sensitive adhesive sheet of the present invention has a substrate and a pressure-sensitive adhesive layer formed on either side of the substrate, and the pressure-sensitive adhesive layer contains an acrylic resin (A). The acrylic resin (A) will be described below.

<Acrylic resin (A)>
The acrylic resin (A) is a resin having a structural unit derived from at least one (meth)acrylic monomer and obtained by polymerizing a polymerization component containing at least one (meth)acrylic monomer. The acrylic resin (A) is obtained, for example, by polymerizing a polymerization component containing a (meth)acrylic monomer as a main component and, in some cases, various other polymerizable monomers.

The phrase "mainly composed of" a (meth)acrylic monomer means that the (meth)acrylic monomer is generally contained in an amount of 40% by weight or more, preferably 50% by weight or more, and more preferably 60% by weight or more of the total polymerizable components. The upper limit of the (meth)acrylic monomer content is 100% by weight.

The above (meth)acrylic monomers include, for example, (meth)acrylic acid or a derivative thereof, (meth)acrylamide or a derivative thereof, etc. Specific examples include alkyl group-containing (meth)acrylates (a1), functional group-containing (meth)acrylates (a2), etc.

Among the above (meth)acrylic acid or derivatives thereof, examples of the alkyl group-containing (meth)acrylate (a1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, 2-methyl-2-nitropropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, t-pentyl (meth)acrylate, 3-pentyl (meth)acrylate, 2,2-dimethylbutyl (meth)acrylate, n-hexyl (meth)acrylate, cetyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 4-methyl-2-propylpentyl (meth)acrylate, and n-octadecyl (meth)acrylate.
The alkyl group in the alkyl group-containing (meth)acrylate (a1) generally has 1 to 20 carbon atoms, preferably 2 to 14 carbon atoms, more preferably 4 to 12 carbon atoms, and particularly preferably 4 to 8 carbon atoms.

The functional group-containing (meth)acrylate (a2) is preferably a functional group-containing monomer containing at least one monomer selected from the group consisting of hydroxyl group-containing (meth)acrylates and carboxyl group-containing (meth)acrylates.
Examples of hydroxyl group-containing (meth)acrylates include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate; [4-(hydroxymethyl)cyclohexyl]methyl acrylate, cyclohexanedimethanol mono(meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. Among these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoints of copolymerizability and versatility.
Examples of the carboxyl group-containing (meth)acrylate include (meth)acrylic acid, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl hexahydrophthalic acid, 2-acryloyloxyethyl phthalic acid, etc. Among these, (meth)acrylic acid is preferred from the viewpoints of copolymerizability and versatility.

Among these functional group-containing (meth)acrylates, carboxyl group-containing (meth)acrylates are preferred, and (meth)acrylic acid is particularly preferred, in that they provide better adhesion to the substrate and are easier to increase adhesive strength at ultra-low temperatures.

Other examples of the derivatives of (meth)acrylic acid include, for example,
cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate and cyclopentyl (meth)acrylate; aralkyl (meth)acrylates such as benzyl (meth)acrylate;
(meth)acrylates containing a biphenyloxy structure, such as biphenyloxyethyl (meth)acrylate;
Polycyclic (meth)acrylates such as 2-isobornyl (meth)acrylate, 2-norbornylmethyl (meth)acrylate, 5-norbornen-2-yl-methyl (meth)acrylate, 3-methyl-2-norbornylmethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and dicyclopentanyl (meth)acrylate;
alkoxy group- or phenoxy group-containing (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxymethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethyl carbitol (meth)acrylate, phenoxyethyl (meth)acrylate, and alkylphenoxypolyethylene glycol (meth)acrylate;
etc.

Other examples include epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate glycidyl ether;
Halogen-containing (meth)acrylates such as 2,2,2-trifluoroethyl (meth)acrylate, 2,2,2-trifluoroethylethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropentyl (meth)acrylate, heptadecafluorodecyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate;
Alkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate;
oxetane group-containing (meth)acrylates such as 3-oxetanylmethyl (meth)acrylate, 3-methyl-oxetanylmethyl (meth)acrylate, 3-ethyl-oxetanylmethyl (meth)acrylate, 3-butyl-oxetanylmethyl (meth)acrylate, and 3-hexyl-oxetanylmethyl (meth)acrylate;
etc.

Examples of the (meth)acrylamide derivatives include
N-alkyl group-containing (meth)acrylamide derivatives, such as N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and N-hexyl(meth)acrylamide;
N-hydroxyalkyl group-containing (meth)acrylamide derivatives, such as N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, and N-methylol-N-propane (meth)acrylamide;
N-aminoalkyl group-containing (meth)acrylamide derivatives, such as aminomethyl(meth)acrylamide and aminoethyl(meth)acrylamide;
N-alkoxy group-containing (meth)acrylamide derivatives such as N-methoxymethyl(meth)acrylamide and N-ethoxymethyl(meth)acrylamide;
N-mercaptoalkyl group-containing (meth)acrylamide derivatives, such as mercaptomethyl(meth)acrylamide and mercaptoethyl(meth)acrylamide;
Heterocycle-containing (meth)acrylamide derivatives such as N-acryloylmorpholine, N-acryloylpiperidine, N-methacryloylpiperidine, and N-acryloylpyrrolidine:
etc.

The above (meth)acrylic monomers may be used alone or in combination of two or more.

In particular, the content of the alkyl group-containing (meth)acrylate (a1) is preferably 40% by weight or more, more preferably 60% by weight or more, based on the total polymerized components of the acrylic resin (A). The upper limit of the content of the alkyl group-containing (meth)acrylate (a1) is 100% by weight.

The content of the functional group-containing (meth)acrylate (a2) is preferably 0.01 to 30% by weight, more preferably 0.1 to 15% by weight, and particularly preferably 0.5 to 10% by weight, based on the total polymerizable components in the acrylic resin (A). If the amount of the functional group-containing (meth)acrylate (a2) is too small, the cohesive strength of the adhesive when formed tends to decrease, whereas if the amount is too large, the tan δ peak temperature of the adhesive layer increases, the adhesive strength at ultra-low temperatures tends to decrease, the storage stability of the adhesive tends to decrease, and the pot life tends to be shortened.

In particular, the content of the hydroxyl group-containing (meth)acrylate is preferably 0 to 25% by weight, more preferably 0 to 15% by weight, and particularly preferably 0 to 5% by weight. If the content is too high, the pot life tends to be shortened and the tan δ peak temperature of the pressure-sensitive adhesive layer tends to be easily increased.
The content of the carboxyl group-containing (meth)acrylate is preferably 0.01 to 25% by weight, more preferably 0.1 to 20% by weight, and particularly preferably 0.5 to 15% by weight. If the amount of carboxyl groups is too large, the glass transition temperature of the acrylic resin (A) increases, and the adhesiveness decreases, tending to reduce the adhesive strength at ultra-low temperatures. If the amount of carboxyl groups is too small, the crosslinking of the acrylic resin (A) does not proceed easily, and aging takes time, and the cohesive strength tends to decrease.

The acrylic resin (A) may contain, as a polymerization component, a polymerizable monomer other than the (meth)acrylic monomer (hereinafter referred to as "other polymerizable monomer").
Examples of the other polymerizable monomers include
Unsaturated carboxylic acids such as crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, acrylamido-N-glycolic acid, and cinnamic acid;
Vinyl carboxylate ester monomers such as vinyl acetate, vinyl propionate, vinyl stearate, and vinyl benzoate;
Monomers containing an aromatic ring, such as styrene and α-methylstyrene;
Examples of the monomer include acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, dialkyl itaconate, dialkyl fumarate, allyl alcohol, acrylic chloride, methyl vinyl ketone, allyl trimethyl ammonium chloride, dimethyl allyl vinyl ketone, etc. Among these, one type may be used alone, or two or more types may be used in combination.

The content of the other polymerizable monomer is preferably 0 to 50% by weight, more preferably 0 to 25% by weight, and particularly preferably 0 to 10% by weight, based on the total polymerizable components in the acrylic resin (A).

[Method for producing acrylic resin (A)]
The method for producing the acrylic resin (A) can employ the above-mentioned copolymerization components, and conventionally known methods such as solution radical polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. For example, a method of mixing or dropping a copolymerization component and a polymerization initiator, which are appropriately selected from monomers, into an organic solvent, and polymerizing under a predetermined polymerization condition can be mentioned. Among them, solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is more preferred in that the acrylic resin (A) can be obtained stably. In emulsion polymerization, the emulsifier remains in the system even after the pressure-sensitive adhesive layer is formed, so that the emulsifier may migrate to the adherend when the adherend is applied for a long period of time or depending on the storage environment.

Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane; esters such as ethyl acetate and butyl acetate; aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. These organic solvents may be used alone or in combination of two or more.

Among these organic solvents, in terms of ease of polymerization reaction, chain transfer effect, ease of drying during coating of the pressure-sensitive adhesive composition, and safety, esters such as ethyl acetate and butyl acetate, and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone are preferred, and ethyl acetate is particularly preferred. One selected from these may be used alone, or two or more may be used in combination.
The amount of the organic solvent used is usually 10 to 900 parts by weight based on 100 parts by weight of the copolymerization components.

Examples of polymerization initiators used in such solution radical polymerization include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(methylpropionic acid), etc., which are ordinary radical polymerization initiators; organic peroxides such as benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, etc.; and the like, which can be appropriately selected and used according to the monomer to be used. These polymerization initiators may be used alone or in combination of two or more kinds.
The amount of the polymerization initiator used is usually 0.01 to 5 parts by weight based on 100 parts by weight of the copolymerization components.

In this way, the acrylic resin (A) used in the present invention is obtained.

[Physical Properties of Acrylic Resin (A)]
The weight average molecular weight (Mw) of the acrylic resin (A) obtained as described above is preferably 100,000 or more, more preferably 100,000 to 1,500,000, particularly preferably 150,000 to 1,000,000, and even more preferably 200,000 to 800,000. If the weight average molecular weight is too small, the cohesive force tends to be insufficient and the adhesiveness tends to decrease. If the weight average molecular weight is too large, the viscosity tends to be too high, which tends to increase scaling during polymerization and decrease handleability.

The dispersity of the acrylic resin (A) [weight average molecular weight (Mw)/number average molecular weight (Mn)] is 5 or less, preferably 4.5 or less, more preferably 4 or less, particularly preferably 3.5 or less, even more preferably 3 or less, and especially preferably 2.5 or less. If the dispersity is too high, the adhesive strength in the ultra-low temperature range tends to decrease. The lower limit of the dispersity is usually 1.
The dispersity of the acrylic resin (A) can be easily reduced by using living polymerization such as living radical polymerization, living anionic polymerization, living cationic polymerization, etc. Also, it can be reduced by using normal solution radical polymerization by shortening the reaction time or reducing the amount or number of additions of the radical polymerization initiator.

The weight average molecular weight of the acrylic resin (A) is a weight average molecular weight converted to standard polystyrene molecular weight, and can be measured by connecting three columns in series: Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 ⁷ , separation range: 100 to 2 × 10 ⁷ , theoretical plate number: 10,000 plates / column, packing material: styrene-divinylbenzene copolymer, packing particle size: 10 μm) to a high performance liquid chromatograph (manufactured by Japan Waters, "Waters 2695 (main body)" and "Waters 2414 (detector)"), and the number average molecular weight can also be measured by the same method. The degree of dispersion can be determined from the measured values of the weight average molecular weight and the number average molecular weight.

The glass transition temperature (Tg) of the acrylic resin (A) is preferably -85°C or higher, more preferably -80 to 20°C, particularly preferably -75 to 0°C, even more preferably -70 to -10°C, and especially preferably -65 to -30°C. If the glass transition temperature is too low, the cohesive strength and adhesive strength of the adhesive layer tend to decrease, and if it is too high, the adhesive strength in the ultra-low temperature range tends to decrease.

Ｔｇ：重合体のガラス転移温度（Ｋ）
Ｔga：モノマーＡのホモポリマーのガラス転移温度（Ｋ）Ｗａ：モノマーＡの重量分率
Ｔgb：モノマーＢのホモポリマーのガラス転移温度（Ｋ）Ｗｂ：モノマーＢの重量分率
Ｔgn：モノマーＮのホモポリマーのガラス転移温度（Ｋ）Ｗｎ：モノマーＮの重量分率
（Ｗａ＋Ｗｂ＋・・・＋Ｗｎ＝１） The glass transition temperature is calculated by the following Fox formula.

Tg: glass transition temperature of the polymer (K)
Tga: Glass transition temperature (K) of homopolymer of monomer A Wa: Weight fraction of monomer A Tgb: Glass transition temperature (K) of homopolymer of monomer B Wb: Weight fraction of monomer B Tgn: Glass transition temperature (K) of homopolymer of monomer N Wn: Weight fraction of monomer N (Wa + Wb + ... + Wn = 1)

That is, it is a value calculated by applying the glass transition temperature and weight fraction of the homopolymer polymerized from each of the monomers constituting the acrylic resin (A) to the Fox formula.
The glass transition temperature of the homopolymer polymerized from the monomers constituting the acrylic resin (A) is usually measured by a differential scanning calorimeter (DSC) and can be measured by a method in accordance with JIS K7121-1987 or JIS K 6240.

Since the acrylic resin (A) is the main component of the adhesive composition, the content of the acrylic resin (A) is preferably 50% by weight or more, more preferably 60 to 98% by weight, particularly preferably 70 to 95% by weight, and even more preferably 75 to 93% by weight, relative to the adhesive composition. Outside this range, the effects of the present invention tend to be difficult to achieve.

<Crosslinking Agent (B)>
The pressure-sensitive adhesive sheet of the present invention is generally produced by applying a pressure-sensitive adhesive composition containing the above-mentioned acrylic resin (A) to either one side of a substrate, and crosslinking the composition to form a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive. Therefore, the pressure-sensitive adhesive composition used in the present invention preferably contains a crosslinking agent (B) in addition to the above-mentioned acrylic resin (A).
The crosslinking agent (B) is preferred in that it improves the elastic modulus when the pressure-sensitive adhesive is formed, prevents migration of components contained in the substrate or adherend, and improves durability.

The crosslinking agent (B) is a compound that reacts with a functional group in the acrylic resin (A) to form a crosslinked structure, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, amine-based crosslinking agents, metal chelate-based crosslinking agents, etc. Among these, it is preferable to use an isocyanate-based crosslinking agent or an epoxy-based crosslinking agent, and in particular, an isocyanate-based crosslinking agent is preferable, in terms of improving adhesion to an adherend and excellent reactivity with the acrylic resin (A).
The crosslinking agent (B) may be used alone or in combination of two or more kinds.

Examples of the isocyanate crosslinking agent include aromatic isocyanate compounds, alicyclic isocyanate compounds, and aliphatic isocyanate compounds.
Examples of the aromatic isocyanate compounds include tolylene diisocyanate compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate; xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate; diphenylmethane compounds such as diphenylmethane-4,4-diisocyanate; and naphthalene diisocyanate compounds such as 1,5-naphthalene diisocyanate.
Examples of the alicyclic isocyanate compounds include isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane, and norbornane diisocyanate.
Examples of the aliphatic isocyanate compounds include hexamethylene diisocyanate and trimethylhexamethylene diisocyanate.
Further, examples of the isocyanate compounds include adducts, biuret compounds, and isocyanurates (isocyanate compounds containing an isocyanurate skeleton).

Among these isocyanate-based crosslinking agents, tolylene diisocyanate-based compounds are preferred in terms of pot life and durability, xylylene diisocyanate-based compounds and isocyanurate skeleton-containing isocyanate-based compounds are preferred in terms of shortening the aging time, and aromatic ring-free isocyanate-based compounds are preferred in terms of yellowing resistance. Specific examples of these preferred isocyanate-based crosslinking agents include, for example, an adduct of at least one isocyanate-based compound selected from the group consisting of tolylene diisocyanate, xylylene diisocyanate, and hexamethylene diisocyanate with trimethylolpropane, and an isocyanurate of at least one isocyanate-based compound selected from the group consisting of tolylene diisocyanate, xylylene diisocyanate, and hexamethylene diisocyanate with trimethylolpropane, and these adducts and isocyanurates are preferred in terms of excellent balance between durability, pot life, and crosslinking speed.

Examples of the epoxy crosslinking agent include bisphenol A-epichlorohydrin type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, diglycerol polyglycidyl ether, etc.

Examples of the aziridine-based crosslinking agent include tetramethylolmethane-tri-β-aziridinyl propionate, trimethylolpropane-tri-β-aziridinyl propionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide), etc.

Examples of the melamine-based crosslinking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, melamine resins, etc.

Examples of the aldehyde crosslinking agents include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

Examples of the amine-based crosslinking agent include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, polyamides, etc.

Examples of the metal chelate crosslinking agent include coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium with ligands such as acetylacetone and acetoacetyl ester.

When a crosslinking agent (B) is used, its content is preferably 0.005 to 30 parts by weight, more preferably 0.01 to 10 parts by weight, particularly preferably 0.03 to 5 parts by weight, and even more preferably 0.05 to 3 parts by weight, per 100 parts by weight (solid content) of the acrylic resin (A). If the content is too low, it tends to be difficult to obtain the effect of improving durability, while if the content is too high, the stress relaxation property decreases, making the adherend substrate more likely to warp or requiring long-term aging.

<Optional ingredients>
In addition to the above-mentioned components, the pressure-sensitive adhesive composition of the present invention may contain various additives as optional components.The optional components include, for example, conductive agents such as carbon and metal; inorganic fillers such as metal particles and glass particles; tackifiers such as urethane resins, rosin, rosin esters, hydrogenated rosin esters, aliphatic petroleum resins, alicyclic petroleum resins, and styrene resins; fillers; antioxidants; ultraviolet absorbers; silane coupling agents; crosslinking accelerators such as ionic compounds, peroxides, and urethane catalysts; crosslinking retarders such as acetylacetone; and various other additives.These may be used alone or in combination of two or more.

In addition to the above optional components, the adhesive composition used in the present invention may also contain impurities contained in the raw materials for producing the components of the adhesive composition, as long as the effects of the present invention are not impaired.

The adhesive composition of the present invention can be made into an adhesive by crosslinking the acrylic resin (A). In addition, by laminating an adhesive layer containing this adhesive on a substrate such as a plastic film, a laminate having a substrate/adhesive layer laminate structure can be obtained. Furthermore, by laminating this adhesive layer on an adherend, a laminate having an adherend/adhesive layer laminate structure can be obtained. In the following, the substrate and adherend are collectively referred to as "members".

<Adhesive Layer>
In the present invention, the pressure-sensitive adhesive layer has a peak temperature of tan δ obtained by dynamic viscoelasticity measurement of 0° C. or lower, preferably −10° C. or lower, more preferably −15° C. or lower, particularly preferably −20° C. or lower, and even more preferably −25° C. or lower.
The peak temperature of tan δ can be lowered by lowering the glass transition temperature of the acrylic resin (A), reducing the amount of crosslinking agent blended, or blending a plasticizer.

The method for measuring the peak temperature of tan δ obtained by dynamic viscoelasticity measurement is as follows. Using a dynamic viscoelasticity device, dynamic viscoelasticity measurement is performed under the following conditions: adhesive jig: 20 mm diameter parallel plate, distortion: 0.1%, frequency: 1 Hz, heating rate: 3°C/min, measurement temperature: -100°C to 150°C. The temperature at the peak top (peak temperature) can be measured by reading the value of tan δ from the obtained viscoelasticity curve.

The adhesive sheet of the present invention may be a single-sided adhesive sheet in which an adhesive layer is laminated to a substrate, or a substrate-less double-sided adhesive sheet in which separators (release sheets) are laminated to both sides of the adhesive layer. From the standpoint of ease of handling, however, a single-sided adhesive sheet is preferred.

Methods for producing pressure-sensitive adhesive sheets include, for example, coating a substrate with a pressure-sensitive adhesive composition, drying the composition, attaching a substrate or a separator, and performing an aging treatment by aging at room temperature (unheated state) or aging under heating. In addition, a substrate-less double-sided pressure-sensitive adhesive sheet can be produced by coating a separator with a pressure-sensitive adhesive composition, drying the composition, attaching another separator with a different peel strength to the separator, and performing an aging treatment.

The aging treatment is a process carried out to chemically crosslink the acrylic resin (A) and the crosslinking agent (B) to give the adhesive an appropriate level of adhesiveness. The aging conditions are, for example, a temperature that is usually between room temperature (20±10°C) and 40°C, and a time that is usually between 1 and 30 days. Specific examples include conditions such as 1 to 20 days at 23°C and 1 to 7 days at 40°C.

When applying the pressure-sensitive adhesive composition, it is preferable to dilute the pressure-sensitive adhesive composition with a solvent before application, and the solid content concentration is preferably 5 to 65% by weight, more preferably 20 to 55% by weight.
The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition. For example, ester-based solvents such as methyl acetate, ethyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol-based solvents such as methanol, ethanol, and propyl alcohol; etc. can be used. Among these, ethyl acetate is preferably used in terms of solubility, drying property, and price.

The viscosity of the diluted adhesive composition is preferably 500 to 15,000 mPa·s/25°C, and more preferably 1,000 to 10,000 mPa·s/25°C. If the viscosity is too low and a component with a high specific gravity is used, the component will tend to settle, and the concentration of the component in the adhesive composition will tend to be non-uniform.

Examples of methods for applying the pressure-sensitive adhesive composition include roll coating, die coating, gravure coating, comma coating, and screen printing.

The thickness of the adhesive layer in the adhesive sheet is preferably 5 to 250 μm, more preferably 10 to 150 μm, and even more preferably 15 to 100 μm. If the adhesive layer is too thin, the thickness precision and adhesive strength tend to decrease, and if the adhesive layer is too thick, the adhesive layer tends to protrude from the edges when the adhesive sheet is rolled.

The gel fraction of the adhesive layer is preferably 1% by weight or more and less than 99% by weight, more preferably 20 to 95% by weight, particularly preferably 15 to 93% by weight, and even more preferably 30 to 90% by weight, in terms of adhesion to the member and temporary application properties before curing. If the gel fraction of the adhesive layer is too high, the tack of the adhesive layer becomes small, and sufficient adhesion to the adherend interface cannot be obtained, tending to reduce the adhesive strength. If the gel fraction is too low, the cohesive strength of the adhesive layer tends to be insufficient, and the holding power and removability tend to decrease. The lower limit of the gel fraction is usually 0% by weight.

The gel fraction is an indication of the degree of crosslinking (degree of hardening) and is calculated, for example, by the following method. First, the adhesive is picked from an adhesive sheet in which an adhesive layer is laminated on the surface of a substrate, and the adhesive is wrapped in a 200-mesh SUS wire mesh and immersed in ethyl acetate adjusted to 23°C for 24 hours. The weight of the adhesive layer is measured before and after immersion in ethyl acetate, and the difference between the two weights is taken as the weight of the insoluble adhesive components remaining in the wire mesh. The gel fraction is the weight percentage of the insoluble adhesive components remaining in the wire mesh relative to the weight of the adhesive layer before immersion in ethyl acetate.

<Adhesive strength>
In the pressure-sensitive adhesive sheet of the present invention, the pressure-sensitive adhesive layer preferably has the following adhesive strength: In other words, the pressure-sensitive adhesive sheet of the present invention is a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer obtained by curing a pressure-sensitive adhesive composition containing an acrylic resin is laminated on either one surface of a substrate, and the pressure-sensitive adhesive layer preferably has an adhesive strength represented by the following formula (1).
Formula (1)
180° peel strength ≧5N/25mm
(For SUS304BA plate, peeling temperature: -15°C, peeling speed: 300mm/min)

When measuring the above adhesive strength, first, a pressure-sensitive adhesive composition containing the acrylic resin (A) is prepared by the above-mentioned method.
Next, the adhesive composition containing the acrylic resin (A) is applied to a 38 μm-thick light release silicone separator (manufactured by Mitsui Chemicals Tocello, Inc., "SP-PET01 38BU") using an applicator so that the thickness after drying is 25 μm, and then dried at 100° C. for 3 minutes to form an adhesive layer. After bonding a substrate to the surface of the adhesive layer, aging is performed at 40° C. for 3 days to produce an adhesive sheet with the substrate (a laminate of light release silicone separator/adhesive layer/substrate).

After cutting the adhesive sheet with the substrate prepared above into a width of 25 mm, the light release silicone separator is peeled off and the adhesive layer side is attached to a SUS304BA plate by rolling a 2 kg roller back and forth twice in a 23°C x 50% RH environment. After leaving it to stand for 30 minutes in a -15°C environment, the 180° peel strength (unit: N/25 mm) is measured in a -15°C environment at a speed of 300 mm/min using an AUTO Graph AG-X Plus (manufactured by Shimadzu Corporation).

The adhesive strength of the above formula (1) is 5 N/25 mm or more, preferably 10 N/25 mm or more, and particularly preferably 15 N/25 mm or more. The upper limit is usually 50 N/25 mm.
As a method for adjusting the adhesive strength to the above range, a method of curing the adhesive composition containing the above-mentioned acrylic resin (A) can be mentioned.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are by weight.
In the following examples, the weight average molecular weight, dispersity, glass transition temperature and other physical properties of the acrylic resins were measured according to the methods described above.
First, prior to the examples, the following components were prepared.

<Acrylic resin (A)>
[Preparation of acrylic resin (A-1)]
Into a reactor equipped with a temperature controller, a thermometer, a stirrer, a dropping funnel and a reflux condenser, 95 parts of n-butyl acrylate (a1), 5 parts of acrylic acid (a2), 13 parts of ethyl acetate, 42 parts of acetone and 0.013 parts of 2,2'-azobisisobutyronitrile (AIBN (thermal polymerization initiator)) as a polymerization catalyst were charged and heated with stirring. The reaction was started when the internal temperature reached its peak top. 0.5 hours after the start of the reaction, a mixed solution of 30 parts of ethyl acetate and 0.013 parts of AIBN was added dropwise over 1 hour. Further, 1.75 hours after the start of the reaction, 30 parts of ethyl acetate was added dropwise over 1 hour, and the reaction was terminated 3.25 hours after the start of the reaction, thereby obtaining an acrylic resin (A-1) solution [glass transition temperature -50.3°C, resin content 18.0%, viscosity 8,000 mPa s (25°C), weight average molecular weight (Mw) 2,023,000, Mw/Mn 3.21].

[Preparation of acrylic resin (A-2)]
Into a reactor equipped with a temperature controller, a thermometer, a stirrer, a dropping funnel, and a reflux condenser, 46 parts of 2-ethylhexyl acrylate (a1), 45.9 parts of n-butyl acrylate (a1), 8 parts of acrylic acid (a2), 0.1 parts of 2-hydroxyethyl methacrylate (a2), 10 parts of ethyl acetate, 40 parts of acetone, and 0.013 parts of AIBN were charged, and the temperature was raised with stirring. The reaction was started when the internal temperature reached its peak top, and 0.5 hours after the start of the reaction, a mixed solution of 30 parts of ethyl acetate and 0.013 parts of AIBN was added dropwise over 1 hour. Further, 1.75 hours after the start of the reaction, 30 parts of ethyl acetate was added dropwise over 1 hour, and the reaction was terminated 3.25 hours after the start of the reaction, thereby obtaining an acrylic resin (A-2) solution [glass transition temperature -54.9°C, resin content 23.4%, viscosity 23,600 mPa s (25°C), weight average molecular weight (Mw) 1,739,000, Mw/Mn 3.39].

[Preparation of acrylic resin (A-3)]
Into a reactor equipped with a temperature controller, a thermometer, a stirrer, a dropping funnel, and a reflux condenser, 0.10 parts of NTAc (RAFT-NTAc: manufactured by Nippon Terpene Chemical Co., Ltd.) as a RAFT agent, 46 parts of 2-ethylhexyl acrylate (a1), 45.9 parts of n-butyl acrylate (a1), 8 parts of acrylic acid (a2), 0.1 parts of 2-hydroxyethyl methacrylate (a2), 25 parts of ethyl acetate, 25 parts of acetone, and 0.05 parts of AIBN were charged, and the temperature was raised to reflux with stirring. The reaction was started when the internal temperature stabilized, and 1.5 hours and 3 hours after the start of the reaction, 6.8 parts of ethyl acetate and 0.05 parts of AIBN were added. Furthermore, 4.5 hours after the start of the reaction, 30 g of ethyl acetate and 0.1 parts of AIBN were added dropwise over 1 hour, and the reaction was terminated 7 hours after the start of the reaction, thereby obtaining an acrylic resin (A-3) solution obtained by living radical polymerization [glass transition temperature -54.9°C, resin content 42.6%, viscosity 2,800 mPa s (25°C), weight average molecular weight (Mw) 357,000, Mw/Mn 1.72].

[Preparation of acrylic resin (A-4)]
In a reactor equipped with a temperature controller, a thermometer, a stirrer, a dropping funnel and a reflux condenser, 70 parts of ethyl acetate and 0.06 parts of AIBN were charged, and the temperature was raised to reflux while stirring. When the internal temperature was stabilized, a mixture of 46 parts of 2-ethylhexyl acrylate (a1), 45.9 parts of n-butyl acrylate (a1), 8 parts of acrylic acid (a2), and 0.1 parts of 2-hydroxyethyl methacrylate (a2) was added dropwise over 2 hours as copolymerization components, and reacted under reflux. Next, 8.3 parts of toluene and 0.06 parts of AIBN were added 3 hours after the start of the reaction, and the reaction was terminated 5.5 hours after the start of the reaction, to obtain an acrylic resin (A-4) solution [glass transition temperature -54.9 ° C, resin content 38.0%, viscosity 2,500 mPa · s (25 ° C), weight average molecular weight (Mw) 560,000, Mw / Mn 4.45].

[Preparation of Acrylic Resin (A'-1)]
In a reactor equipped with a temperature controller, a thermometer, a stirrer, a dropping funnel and a reflux condenser, 70 parts of ethyl acetate and 0.04 parts of AIBN were charged, and the temperature was raised to reflux while stirring. When the internal temperature was stabilized, a mixture of 91.9 parts of n-butyl acrylate (a1), 0.1 parts of 2-hydroxyethyl methacrylate (a2) and 8 parts of acrylic acid (a2) was added dropwise over 2 hours as copolymerization components and reacted under reflux. Then, 13.3 parts of toluene and 0.08 parts of AIBN were added 3 hours after the start of the reaction, and the reaction was terminated 5.5 hours after the start of the reaction to obtain an acrylic resin (A'-1) solution [glass transition temperature -47.3 ° C, resin content 35.0%, viscosity 7,000 mPa · s (25 ° C), weight average molecular weight (Mw) 877,000, Mw / Mn 5.80].

[Preparation of Acrylic Resin (A'-2)]
A reactor equipped with a temperature controller, a thermometer, a stirrer, a dropping funnel, and a reflux condenser was charged with 75 parts of ethyl acetate, and the temperature was raised to reflux with stirring. When the internal temperature became stable, a mixture of 70 parts of n-butyl acrylate (a1), 20 parts of methyl methacrylate, 9.9 parts of acrylic acid (a2), 0.1 part of 2-hydroxyethyl methacrylate (a2), 3.75 parts of ethyl acetate, and 0.035 parts of AIBN was added dropwise as copolymerization components over a period of 2 hours, and the mixture was allowed to react under reflux. Next, 3 hours after the start of the reaction, 7.5 parts of ethyl acetate and 0.04 parts of AIBN were added, and 5 hours after the start of the reaction, 7.5 parts of ethyl acetate and 0.04 parts of AIBN were added, and the reaction was terminated 7 hours after the start of the reaction (polymerization rate: approximately 99%), to obtain an acrylic resin (A'-2) solution [glass transition temperature: -23.3°C, resin content: 38.6%, viscosity: 8,500 mPa·s (25°C), weight average molecular weight (Mw): 456,000, Mw/Mn: 3.09].

Details of the obtained acrylic resins (A-1) to (A-4) and (A'-1) to (A'-2) are shown in Table 1.
The alphanumeric characters in Table 1 represent the following monomers.
BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate Aac: acrylic acid HEMA: 2-hydroxyethyl methacrylate MMA: methyl methacrylate

<Crosslinking Agent (B)>
(B-1): Takenate D101E (isocyanate-based crosslinking agent: manufactured by Mitsui Chemicals, Inc.)

<Other Components (C)>
(C-1): Super Ester A100 (rosin-based tackifier: manufactured by Arakawa Chemical Industries, Ltd.)

<Examples 1 to 6 and Comparative Examples 1 to 3>
The above components were mixed according to Table 2 below, and the solid content was adjusted to a range of 30 to 60% using ethyl acetate to obtain a pressure-sensitive adhesive composition.

The resulting adhesive composition was used to prepare an adhesive sheet according to the procedure described below. The adhesive sheet was then used to evaluate the gel fraction and adhesive strength at room temperature, low temperature, and ultra-low temperature, as described below.
The evaluation methods and evaluation criteria for each item are as follows. The results are also shown in Table 2 below.

<Preparation of adhesive sheet>
The adhesive composition was applied to a 38 μm thick light release silicone separator (manufactured by Mitsui Chemicals Tocello, Inc., "SP-PET01 38BU") using an applicator so that the thickness after drying would be 25 μm, and dried at 100° C. for 3 minutes to form an adhesive layer. A substrate as shown in Table 2 was attached to the surface of the adhesive layer, and then aging was carried out at 40° C. for 3 days to produce an adhesive sheet with the substrate (a laminate of light release silicone separator/adhesive layer/substrate).

[Gel fraction]
Only the adhesive layer was taken out from the 5 cm x 5 cm adhesive sheet, sandwiched between SUS 200 mesh, immersed in ethyl acetate, and left to stand for 24 hours at 23°C. After standing, it was taken out and the ethyl acetate was completely evaporated using a dryer. The gel fraction was calculated from the weight before and after immersion using the following formula, and evaluated according to the following criteria.
Gel fraction=[Weight of adhesive layer (before immersion)−Weight of SUS mesh]/[Weight of adhesive layer (after immersion)−Weight of SUS mesh]×100
(Evaluation criteria)
◯: 15% or more, 95% or less △: 5% or more, less than 15% or more than 95% ×: Less than 5%

[Adhesive strength at 23°C]
The adhesive sheet with the substrate prepared above was cut into a width of 25 mm, the light release silicone separator was peeled off, and the adhesive layer side was attached to a SUS304BA plate by rolling a 2 kg roller twice in a 23°C x 50% RH environment. After leaving it to stand for 30 minutes in the same environment, the 180° peel strength (unit: N/25 mm) was measured in the same environment at a speed of 300 mm/min using an AUTO Graph AG-X Plus (manufactured by Shimadzu Corporation) and evaluated according to the following criteria.
(Evaluation criteria)
◎: 20N/25mm or more 〇: 10N/25mm or more, less than 20N/25mm △: 5N/25mm or more, less than 10N/25mm ×: Less than 5N/25mm

[Adhesive strength at 0°C]
The adhesive sheet with the substrate prepared above was cut into a width of 25 mm, the light release silicone separator was peeled off, and the adhesive layer side was attached to a SUS304BA plate by rolling a 2 kg roller twice in a 23°C x 50% RH environment. After leaving it to stand for 30 minutes in a 0°C environment, the 180° peel strength (unit: N/25 mm) was measured in a 0°C environment at a speed of 300 mm/min using an AUTO Graph AG-X Plus (manufactured by Shimadzu Corporation) and evaluated according to the following criteria.
(Evaluation criteria)
◎: 20N/25mm or more 〇: 10N/25mm or more, less than 20N/25mm △: 5N/25mm or more, less than 10N/25mm ×: Less than 5N/25mm

[Adhesive strength at -15°C]
The adhesive sheet with the substrate prepared above was cut into a width of 25 mm, the light release silicone separator was peeled off, and the adhesive layer side was attached to a SUS304BA plate by rolling a 2 kg roller twice in a 23°C x 50% RH environment. After leaving it to stand for 30 minutes in a -15°C environment, the 180° peel strength (unit: N/25 mm) was measured at a speed of 300 mm/min in a -15°C environment using an AUTO Graph AG-X Plus (manufactured by Shimadzu Corporation) and evaluated according to the following criteria.
(Evaluation criteria)
◎: 20N/25mm or more 〇: 10N/25mm or more, less than 20N/25mm △: 5N/25mm or more, less than 10N/25mm ×: Less than 5N/25mm

Yupo paper/80: Yupotac (registered trademark) SGS-80 Thickness: 80 μm (manufactured by Yupo Corporation)
PET/100: Lumirror (registered trademark) T-60 Thickness: 100 μm (manufactured by Toray Industries, Inc.)

As shown in Table 2, in the pressure-sensitive adhesive sheets of Examples 1 to 6, the dispersity of the acrylic resin (A) was 5 or less, and the peak temperature of tan δ of the pressure-sensitive adhesive layer was 0°C or less. Therefore, it can be seen that the pressure-sensitive adhesive sheets have excellent adhesive strength against both the Yupo paper and PET substrates from room temperature to the ultra-low temperature range of -15°C.
On the other hand, in the pressure-sensitive adhesive sheets of Comparative Examples 1 to 3 in which the dispersity of the acrylic resin (A) exceeds 5 or the peak temperature of tan δ of the pressure-sensitive adhesive layer exceeds 0°C, the adhesive strength is excellent in the room temperature range, but the adhesive strength decreases rapidly in the temperature range below 0°C, and the object of the present invention could not be achieved.

The adhesive sheet of the present invention has excellent adhesive strength from room temperature to ultra-low temperature range of -10°C or less, so it can be used for various adhesive applications, such as building materials, curing, medical use, and packaging, and is particularly useful as an adhesive sheet for labels for pharmaceuticals that require freezing and for use in cold regions.

Claims (8)

A pressure-sensitive adhesive sheet having a substrate and a pressure-sensitive adhesive layer formed on either one surface of the substrate, the pressure-sensitive adhesive sheet being usable at temperatures of -10°C or lower,
The pressure-sensitive adhesive layer comprises an acrylic resin (A) having a degree of dispersion of 5 or less, and the pressure-sensitive adhesive sheet has a peak temperature of tan δ obtained by dynamic viscoelasticity measurement of 0° C. or less. The pressure-sensitive adhesive sheet according to claim 1, wherein the tan δ peak temperature is -10°C or lower. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the acrylic resin (A) has a structural unit derived from a carboxyl group-containing monomer. The adhesive sheet according to claim 1 or 2, wherein the acrylic resin (A) is obtained by polymerization in an organic solvent. The adhesive sheet according to claim 1 or 2, wherein the gel fraction of the adhesive layer is 20 to 95% by weight. An adhesive contained in the adhesive layer of the adhesive sheet according to claim 1 or 2. An adhesive composition constituting the adhesive according to claim 6. A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer obtained by curing a pressure-sensitive adhesive composition containing an acrylic resin laminated on either one surface of the substrate,
The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer has an adhesive strength represented by the following formula (1):
Formula (1)
180° peel strength > 5N/25mm
(For SUS304BA plate, peeling temperature: -15°C, peeling speed: 300mm/min)