JP7743228B2 - Adhesive composition and adhesive processed product - Google Patents

Description

The present invention relates to an adhesive composition and an adhesive processed product.

Pressure-sensitive adhesives (also known as pressure-sensitive adhesives) are easy to use and have adhesive properties to a variety of substrates, including plastics, paper, metal, and glass. Therefore, they are widely used as adhesive layers in adhesive-treated products such as tapes, labels, sheets, and double-sided tapes. The compositions used in these pressure-sensitive adhesives (adhesive compositions) typically have acrylic resins or styrene resins (such as styrene-based block copolymers) as the base polymer.

In particular, adhesive compositions with acrylic resin as the base polymer are known to have excellent transparency and excellent adhesion to polar substrates such as paper, metal, and glass.

On the other hand, as electronic devices and other devices become thinner, there is a growing demand for thinner double-sided tapes used to bond internal components. Therefore, adhesive compositions are required to have sufficient adhesiveness and adhesion even when used in thin adhesive layers.

In response to the above requirements, a method has been proposed in which a tackifying resin such as a rosin-based resin, a terpene-based resin, or a petroleum-based resin is added to an acrylic adhesive composition to further enhance the adhesiveness of the adhesive composition. For example, Patent Document 1 describes that adding a tackifying resin that has low compatibility with (meth)acrylic polymers, such as a rosin-based resin, to an acrylic adhesive composition can ensure that the adhesive strength is exhibited at both room temperature and high temperatures. Patent Document 1 also describes that the tackifying resin is added so that the haze value of the adhesive composition when formed into a film is 15 to 95%.

Japanese Unexamined Patent Publication No. 16882/1982

Patent Document 1 states that the addition of a tackifying resin such as the rosin-based resin can further increase the adhesiveness of the adhesive composition. However, as noted in Patent Document 1, adding the tackifying resin reduces the transparency of the adhesive composition.

The present invention was made in consideration of the above circumstances, and aims to provide an adhesive composition that has sufficient adhesiveness even in a thin film and can produce an adhesive layer with high transparency, as well as an adhesive processed product having an adhesive layer obtained from the adhesive composition.

That is, the present invention provides the following pressure-sensitive adhesive composition.
A pressure-sensitive adhesive composition comprising 47 parts by mass or more and 99 parts by mass or less of a (meth)acrylic resin (A), 0.5 parts by mass or more and 50 parts by mass or less of a (co)polymer (B) different from the (meth)acrylic resin (A), and 0.5 parts by mass or more and 3 parts by mass or less of a crosslinking agent (C) (wherein the total content of the (meth)acrylic resin (A), the (co)polymer (B), and the crosslinking agent (C) is taken as 100 parts by mass), wherein the (meth)acrylic resin (A) satisfies the following requirements (A-1) and (A-2), and the (co)polymer (B) satisfies all of the following requirements (B-1) to (B-5).
(A-1) Contains a structural unit derived from a (meth)acrylate having an alkyl group having 1 to 12 carbon atoms, and a structural unit derived from a (meth)acrylate containing a hydroxyl group.
(A-2) The glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) is in the range of −80° C. or higher and 0° C. or lower.
(B-1) The (co)polymer (B) contains structural units derived from isopropenyltoluene in an amount of 20 mol % or more based on the total amount of structural units of the (co)polymer (B).
(B-2) The softening point measured in accordance with JIS K2207 is in the range of 80°C or higher and 120°C or lower.
(B-3) The glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) is in the range of 30° C. or higher and 70° C. or lower.
(B-4) The number average molecular weight (Mn) is in the range of 750 or more and 1200 or less, the z average molecular weight (Mz) is in the range of 2000 or more and 3000 or less, and the polydispersity (Mw/Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is in the range of 1.5 or more and 1.8 or less, as measured by gel permeation chromatography (GPC) in terms of polystyrene.
(B-5) The solubility parameter is 9.80 (cal/cm ³ ) ^1/2 or less.

The present invention also provides the following adhesive processed products.
An adhesive processed product has an adhesive layer obtained from the above adhesive composition, and is a tape, a label, a sheet or a double-sided tape.

The adhesive composition of the present invention makes it possible to obtain an adhesive layer that has sufficient adhesiveness even in a thin film and is highly transparent. Furthermore, adhesive processed products having an adhesive layer obtained from this adhesive composition can be used for a variety of purposes.

1 is a graph showing the relationship between the total light transmittance of the adhesive processed products of Examples 1 and 2 and Comparative Examples 1 to 7 and the adhesive strength of the adhesive layer of the adhesive processed products.

One embodiment of the present invention relates to an adhesive composition containing a (meth)acrylic resin (A) that satisfies specific requirements, a (co)polymer (B) that satisfies specific requirements, and a crosslinking agent (C). In this specification, (meth)acrylic means "acrylic, methacrylic, or both," (meth)acrylate means "acrylate, methacrylate, or both," and (co)polymer means "homopolymer, copolymer, or both."

[(Meth)acrylic resin (A)]
The (meth)acrylic resin (A) is a (co)polymer of an acrylic monomer or a methacrylic monomer.

The (meth)acrylic resin (A) satisfies the following requirements (A-1) and (A-2).
(A-1) Contains a structural unit derived from a (meth)acrylate having an alkyl group having 1 to 12 carbon atoms, and a structural unit derived from a (meth)acrylate containing a hydroxyl group.
(A-2) The glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) is in the range of −80° C. or higher and 0° C. or lower.

(Regarding requirement (A-1))
Requirement (A-1) is a requirement for enhancing the adhesiveness of the adhesive composition according to this embodiment.

Specifically, when the (meth)acrylic resin (A) contains a structural unit derived from a (meth)acrylate having an alkyl group having 1 to 12 carbon atoms, the glass transition temperature (Tg) of the (meth)acrylic resin (A) becomes 0°C or lower, and the adhesiveness of the adhesive composition is further enhanced.

From the above perspective, the (meth)acrylate having an alkyl group with 1 to 12 carbon atoms is preferably a (meth)acrylate having an alkyl group with 1 to 10 carbon atoms, and more preferably a (meth)acrylate having an alkyl group with 2 to 8 carbon atoms. The alkyl group may be linear or branched.

Examples of (meth)acrylates having an alkyl group having 1 to 12 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, and lauryl (meth)acrylate.

The amount of structural units derived from a (meth)acrylate having an alkyl group having 1 to 12 carbon atoms relative to the total amount of structural units in the (meth)acrylic resin (A) is preferably 50 mol% to 99 mol%, more preferably 55 mol% to 95 mol%, and even more preferably 60 mol% to 90 mol%.

Furthermore, when the (meth)acrylic resin (A) contains structural units derived from a (meth)acrylate containing a hydroxyl group, the number of crosslinking points by the crosslinking agent (C) increases, which increases the crosslinking density of the adhesive composition and makes it easier to achieve a high molecular weight. With such an adhesive composition, the entanglement between the polymers becomes stronger, making it less likely for the adhesive properties to decrease when pressed together.

A (meth)acrylate containing a hydroxyl group may have only one hydroxyl group in its molecule, or two or more hydroxyl groups. Examples of the above-mentioned (meth)acrylate containing a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and N-methylol (meth)acrylamide. Of these, from the above-mentioned viewpoint, hydroxyethyl (meth)acrylate is preferred as the above-mentioned (meth)acrylate containing a hydroxyl group.

The content of the structural units derived from the above-mentioned hydroxyl group-containing (meth)acrylate relative to the total amount of structural units in the (meth)acrylic resin (A) is preferably 0.1 mol % or more and 5 mol % or less, more preferably 0.2 mol % or more and 3 mol % or less, and even more preferably 0.3 mol % or more and 2 mol % or less.

In addition, the (meth)acrylic resin (A) may further contain structural units derived from a monomer (or oligomer) polymerizable with the (meth)acrylate having an alkyl group with 1 to 12 carbon atoms or the (meth)acrylate containing a hydroxyl group, as long as the purpose and effects of this embodiment are not impaired. Examples of such monomers include monomers (or oligomers) that can react with the crosslinking agent (C) to form a crosslinked structure, and vinyl-based monomers (or oligomers). Examples of monomers that can form a crosslinked structure include (meth)acrylic acid and (meth)acrylamide. On the other hand, examples of vinyl-based monomers include styrene and vinyl acetate.

(Regarding requirement (A-2))
Requirement (A-2) is a requirement for enabling the adhesive composition according to this embodiment to exhibit its adhesiveness suitably over a wider temperature range.

Specifically, if the (meth)acrylic resin (A) is a copolymer having a glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) in the range of -80°C or higher and 0°C or lower, the adhesive composition formed into a thin-film adhesive layer can exhibit adhesiveness over a wide temperature range. From the above perspective, the (meth)acrylic resin (A) preferably has a glass transition temperature (Tg) in the range of -70°C or higher and -5°C or lower, and more preferably in the range of -60°C or higher and -10°C or lower.

The glass transition temperature (Tg) of the (meth)acrylic resin (A) can be adjusted by the type and ratio of the (meth)acrylate having an alkyl group with 1 to 12 carbon atoms or the (meth)acrylate containing a hydroxyl group used when polymerizing the (meth)acrylic resin (A).

In the present embodiment, the glass transition temperature (Tg) of the (meth)acrylic resin (A) can be calculated from a theoretical value obtained by the following FOX formula.
1/Tg=W1/Tg1+W2/Tg2+...+Wn/Tgn
(In the formula, Tg is the glass transition temperature (K) of the acrylic resin (A), W1, W2, ..., Wn are the weight fractions of each monomer, and Tg1, Tg2, ..., Tgn are the glass transition temperatures of the homopolymers of each monomer.)
The glass transition temperature of the homopolymer used in the above calculation can be a value given in the literature.

(synthesis method)
The (meth)acrylic resin (A) satisfying the above requirements (A-1) and (A-2) can be obtained by synthesizing the monomers (or oligomers) that form the structural units by a known polymerization method. The polymerization method is not particularly limited as long as it is a radical polymerization method including bulk polymerization, solution polymerization, suspension polymerization, and the like. Among these, solution polymerization is preferred from the viewpoint of ease of controlling the glass transition temperature (Tg) and other properties of the (meth)acrylic resin (A).

A polymerization initiator may be used during polymerization. Examples of such polymerization initiators include dicumyl peroxide, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, 1,1-bis(t-butylperoxy)cyclohexane, α,α'-azobisisobutyronitrile, acetyl peroxide, t-butyl peroxypivalate, t-butyl hydroperoxide, cumene hydroperoxide, t-hexyl peroxypivalate, 2,2'-azobis-(2,4-dimethylvaleronitrile), lauryl peroxide, t-butyl peroxyneohexanoate, di-t-butyl peroxide, azodicyclohexylcarbonitrile, α,α-dimethyl azodiisobutyrate, succinic acid peroxide, dicumene peroxide, and dichlorobenzoyl peroxide.

Examples of solvents used in the above solution polymerization include ethyl acetate, butyl acetate, benzene, toluene, xylene, cyclohexane, and methyl ethyl ketone.

[(Co)polymer (B)]
The (co)polymer (B) is a (co)polymer different from the (meth)acrylic resin (A) and satisfies all of the following requirements (B-1) to (B-5):

(B-1) The (co)polymer (B) contains structural units derived from isopropenyltoluene in an amount of 20 mol % or more based on the total amount of structural units of the (co)polymer (B).
(B-2) The softening point measured in accordance with JIS K2207 is in the range of 80°C or higher and 120°C or lower.
(B-3) The glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) is in the range of 30° C. or higher and 70° C. or lower.
(B-4) The number average molecular weight (Mn) is in the range of 750 or more and 1200 or less, the z average molecular weight (Mz) is in the range of 2000 or more and 3000 or less, and the polydispersity (Mw/Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is in the range of 1.5 or more and 1.8 or less, as measured by gel permeation chromatography (GPC) in terms of polystyrene.
(B-5) The solubility parameter is 9.80 (cal/cm ³ ) ^1/2 or less.

(Regarding requirement (B-1))
Requirement (B-1) is a requirement for increasing the adhesiveness of the adhesive composition of this embodiment without decreasing the transparency.

Specifically, when (co)polymer (B) contains structural units derived from isopropenyl toluene (including isotopes of o-isopropenyl toluene, m-isopropenyl toluene, and p-isopropenyl toluene) in an amount of 20 mol% or more relative to the total amount of its structural units, the solubility parameter (SP value) of (co)polymer (B) becomes close to the SP value (8.6 to 9.1) of (meth)acrylic resin (A). Therefore, it is believed that (meth)acrylic resin (A) and (co)polymer (B) become more compatible, and (co)polymer (B) becomes more easily finely dispersed in (meth)acrylic resin (A).

The content of structural units derived from isopropenyl toluene relative to the total amount of structural units in (co)polymer (B) is preferably 30 mol% or more, more preferably 45 mol% or more, and even more preferably 60 mol% or more. There is no particular upper limit to the content of structural units derived from isopropenyl toluene, but as described below, the (co)polymer (B) preferably contains 10 mol% or more of structures derived from monomers consisting of unsaturated aliphatic hydrocarbon compounds having 4 or 5 carbon atoms. Therefore, the amount of structural units derived from isopropenyl toluene is preferably 90 mol% or less, more preferably 89 mol% or less, and even more preferably 88 mol% or less.

(Regarding requirement (B-2))
Requirement (B-2) is a requirement for adjusting the viscosity of the pressure-sensitive adhesive composition of the present embodiment to a desired range.

Specifically, when the softening point of the (co)polymer (B) measured by a differential scanning calorimeter (DSC) is in the range of 80°C or higher and 120°C or lower, it is easy to adjust the viscosity of the adhesive composition to an appropriate range. In other words, it becomes easier to apply the adhesive composition to a substrate. From the above viewpoint, the softening point of the (co)polymer (B) is preferably 85°C or higher and 115°C or lower, more preferably 90°C or higher and 110°C or lower, and even more preferably 95°C or higher and 105°C or lower.

The softening point of (co)polymer (B) can be adjusted by the type of copolymerized monomer, molecular weight, molecular weight distribution, etc.

(Regarding requirement (B-3))
Requirement (B-3) is a requirement for adjusting both the transparency and adhesiveness within suitable ranges while increasing the heat resistance of the adhesive composition of this embodiment.

Specifically, when the glass transition temperature (Tg) of (co)polymer (B) measured in accordance with JIS K2207 is 30°C or higher, the heat resistance of the adhesive composition is further improved. Furthermore, when the glass transition temperature (Tg) of (co)polymer (B) is 70°C or lower, both the transparency and adhesiveness of the adhesive composition tend to fall within suitable ranges. From the above viewpoints, the glass transition temperature (Tg) of (co)polymer (B) is preferably 35°C or higher and 65°C or lower, more preferably 40°C or higher and 60°C or lower, and even more preferably 45°C or higher and 55°C or lower.

The glass transition temperature (Tg) of the (co)polymer (B) can be adjusted by the type of copolymerized monomer, molecular weight, molecular weight distribution, etc.

In the present invention, the glass transition temperature (Tg) of the (co)polymer (B) can be calculated from the theoretical value obtained using the above-mentioned FOX formula.

(Regarding requirement (B-4))
Requirement (B-4) is a requirement for increasing the adhesiveness of the adhesive composition according to this embodiment without decreasing the transparency.

Specifically, (co)polymer (B) has a polystyrene-equivalent number-average molecular weight (Mn) of 750 to 1200, a z-average molecular weight (Mz) of 2000 to 3000, and a dispersity (Mw/Mn), which is the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), of 1.5 to 1.8, as measured by gel permeation chromatography (GPC). A number-average molecular weight (Mn) within this range prevents a decrease in adhesiveness. Furthermore, a z-average molecular weight (Mz) within this range maintains transparency. Furthermore, a dispersity (Mw/Mn) within this range improves adhesiveness.

The number average molecular weight (Mn) of the (co)polymer (B) is preferably 780 or more and 1,180 or less, more preferably 800 or more and 1,150 or less, and even more preferably 850 or more and 1,100 or less.

Furthermore, the z-average molecular weight (Mz) of the (co)polymer (B) is preferably 2,050 or more and 2,800 or less, and more preferably 2,100 or more and 2,500 or less.

Furthermore, the dispersity (Mw/Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the (co)polymer (B), is preferably 1.51 or more and 1.7 or less, more preferably 1.52 or more and 1.6 or less.

The number average molecular weight (Mn), z-average molecular weight (Mz), and dispersity (Mw/Mn), which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of the (co)polymer (B), can be adjusted within the above ranges by adjusting the type of monomer to be copolymerized or by performing vacuum distillation, etc.

(Regarding Requirement (B-5)) Requirement (B-5) is a requirement for improving the transparency of the pressure-sensitive adhesive composition of the present embodiment.

Specifically, when the solubility parameter of the (co)polymer (B) is 9.80 (cal/cm ³ ) ^1/2 or less, the solubility parameter is close to that of the (meth)acrylic resin (A). This results in very good compatibility between the (meth)acrylic resin (A) and the (co)polymer (B), and the (co)polymer (B) in the (meth)acrylic resin (A) is difficult to visually recognize. In other words, the transparency of the pressure-sensitive adhesive composition is good. The solubility parameter of the (co)polymer (B) is preferably 9.50 (cal/cm ³ ) ^1/2 or more and 9.79 (cal/cm ³ ) ^1/2 or less, more preferably 9.56 (cal/cm ³ ) ^1/2 or more and 9.78 (cal/cm ³ ) ^1/2 or less.

The solubility parameters of the (co)polymer (B) and (meth)acrylic resin (A) are determined by the Fedors formula. The Fedors formula is a calculation formula for calculating the SP value from cohesive energy density, molar volume (molar molecular volume), etc., and is described in "A Method for Estimating Both the Solubility Parameters and Molar Volumes of Liquids" by R. F. Fedors (POLYMER ENGINEERING AND SCIENCE, published February 1974, Vol. 14, No. 2, pp. 147-152). In other words, the SP value calculated by the Fedors formula is a calculated value determined by the molecular structure of the compound.

The solubility parameter can be adjusted by the type, combination, and ratio of the structural units that make up the (co)polymer (B).

(Other requirements)
The (co)polymer (B) preferably further satisfies the following (B-6).

(B-6) Contains structural units derived from unsaturated aliphatic hydrocarbon compounds having 4 or 5 carbon atoms in an amount of 10 mol % to 30 mol % based on the total amount of all structural units in (co)polymer (B).

When (co)polymer (B) has a structural unit derived from an unsaturated aliphatic hydrocarbon compound having 4 or 5 carbon atoms, (co)polymer (B) can be crosslinked, making it easier for the z-average molecular weight to fall within the above-mentioned range.

On the other hand, if the amount of structural units derived from unsaturated aliphatic hydrocarbon compounds having 4 or 5 carbon atoms is 30 mol% or less, the amount of isopropyl toluene in the (co)polymer (B) becomes sufficiently large, resulting in good transparency of the pressure-sensitive adhesive composition as described above.

Examples of unsaturated aliphatic hydrocarbon compounds having 4 or 5 carbon atoms include C4 fractions and _C5 fractions, which are by-produced during petroleum refining and cracking and contain unsaturated aliphatic hydrocarbon compounds having 4 or ₅ carbon atoms as their main components.

The _C4 fraction and _C5 fraction are fractions whose boiling point range under normal pressure is usually −15 to +45° C. The _C4 fraction and _C5 fraction contain unsaturated aliphatic hydrocarbon compounds such as 1-butene, isobutene, 2-butene, 1,3-butadiene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 2-pentene, isoprene, 1,3-pentadiene, and cyclopentadiene.

The _C4 fraction and _C5 fraction may be petroleum fractions including light oil fractions including gas fractions produced as a by-product during atmospheric distillation (topping) of crude oil or the like in refineries, similar light oil fractions produced as a by-product in petroleum cracking or reforming treatment processes, and light oil fractions including gas obtained in petroleum naphtha cracking or the like in petrochemical plants, and may be used as they are, or may be used as desired fractions after being subjected to distillation, extraction or other treatment.

The content of structural units derived from unsaturated aliphatic hydrocarbon compounds having 4 or 5 carbon atoms relative to the total amount of structural units in (co)polymer (B) is more preferably 10 mol% or more and 30 mol% or less, even more preferably 11 mol% or more and 25 mol% or less, and particularly preferably 12 mol% or more and 20 mol% or less.

(For other monomers)
The (co)polymer (B) may, as necessary, contain a structural unit derived from a monomer other than the above-mentioned isopropenyl toluene or unsaturated hydrocarbon compound having 4 or 5 carbon atoms. Copolymerization of isopropenyl toluene and an unsaturated hydrocarbon compound having 4 or 5 carbon atoms with a monomer other than these makes it easy to adjust the softening point, glass transition temperature (Tg), etc. of the (co)polymer (B).

Examples of monomers other than those mentioned above include vinyl aromatic compounds and unsaturated aliphatic hydrocarbon compounds with carbon atoms other than 4 or 5.

Examples of the vinyl aromatic compound include styrene-based monomers such as substituted styrene having a substituent on the aromatic ring and substituted α-methylstyrene having a substituent on the aromatic ring. Examples of the substituent on the aromatic ring include alkyl groups having 1 to 20 carbon atoms, alkoxy groups having 1 to 20 carbon atoms, aryl groups having 6 to 20 carbon atoms, and halogen atoms. The vinyl aromatic compound may have one of the above substituents on the aromatic ring, or two or more of the above substituents on the aromatic ring.

Specific examples of the substituted styrenes include methylstyrene (excluding α-methylstyrene), ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, and 3,4-dichlorostyrene.

(synthesis method)
The (co)polymer (B) can be obtained by synthesizing isopropenyl toluene, an unsaturated hydrocarbon compound having 4 or 5 carbon atoms, other monomers, etc., by a known polymerization method. The polymerization is preferably cationic polymerization, and more preferably carried out in the presence of a Friedel-Crafts catalyst.

The Friedel-Crafts catalyst is not particularly limited as long as it is a known Friedel-Crafts catalyst, including aluminum chloride, aluminum bromide, dichloromonoethylaluminum, titanium tetrachloride, tin tetrachloride, boron trifluoride, and various complexes such as boron trifluoride ether complexes and phenol complexes. Of these, boron trifluoride phenol complexes are preferred. The amount of the Friedel-Crafts catalyst used can be 0.05 to 5 parts by mass, and preferably 0.1 to 2 parts by mass, per 100 parts by mass of the total raw material monomers.

From the standpoint of removing the heat of reaction generated during the polymerization reaction, suppressing the viscosity of the reaction solution, and adjusting the molecular weight, it is preferable to carry out the polymerization reaction using a solvent so that the concentration of the raw material monomer is approximately 10 to 60% by mass. Examples of such solvents include aliphatic hydrocarbons such as pentane, hexane, heptane, and octane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclohexane; and aromatic hydrocarbons such as toluene, xylene, ethylbenzene, and mesitylene. These solvents may be used alone or in combination.

The polymerization can be carried out in a reactor by polymerizing the raw material monomers in the solvent in the presence of the catalyst. The polymerization can be carried out in a single stage, but is preferably carried out in multiple stages. The polymerization temperature varies depending on the raw material composition and the target molecular weight range, but is preferably -50 to +50°C. The reaction time is preferably 10 minutes to 10 hours. After the polymerization is complete, the catalyst is decomposed using a basic aqueous solution or a basic compound containing an alcohol such as methanol, followed by washing with water. Unreacted raw materials and solvent are removed by stripping or distillation to obtain the desired (co)polymer (B).

The unreacted raw materials and solvents can be removed by, for example, concentration procedures that utilize the difference in vapor pressure between substances, including atmospheric distillation, reduced-pressure distillation, and steam distillation, as well as concentration methods that utilize differences in molecular size or affinity for packing materials such as silica gel, including open columns and flash columns. Of these, reduced-pressure distillation is preferred from the standpoint of suppressing thermal decomposition and increasing concentration efficiency. The range of reduced pressure is not particularly limited. On the other hand, from the standpoint of suppressing thermal decomposition of the (co)polymer (B), the heating temperature is preferably 250°C or less, more preferably 230°C or less, and even more preferably 210°C or less.

[Crosslinking agent (C)]
The crosslinking agent (C) is not particularly limited as long as it can crosslink the (meth)acrylic resin (A) and further increase the adhesiveness of the adhesive composition according to this embodiment.

Examples of crosslinking agents (C) include epoxy compounds such as sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, neopentyl glycol diglycidyl ether, and resorcinol diglycidyl ether; isocyanate compounds such as tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate triadduct of trimethylolpropane, and polyisocyanates; trimethylol Examples of crosslinking agents (C) include aziridine compounds such as trimethylolpropane-tri-β-aziridinylpropionate, tetramethylolmethane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide), N,N'-toluene-2,4-bis(1-aziridinecarboxamide), and trimethylolpropane-tri-β-(2-methylaziridine)propionate; and melamine compounds such as hexamethoxymethylolmelamine. The crosslinking agent (C) may be used singly or in combination.

It is preferable that the crosslinking agent (C) be blended so that the number of functional groups in the crosslinking agent (C) that can bond with the (meth)acrylic resin (A) (when the crosslinking agent (C) contains a blocked isocyanate, this includes the number of functional groups generated by dissociation of the blocking agent) does not exceed the number of functional groups in the (meth)acrylic resin (A). However, if new functional groups are generated by the crosslinking reaction or if the crosslinking reaction proceeds slowly, a larger amount may be blended.

[Content ratio]
The pressure-sensitive adhesive composition according to this embodiment contains 47 to 99 parts by mass of a (meth)acrylic resin (A), 0.5 to 50 parts by mass of a (co)polymer (B), and 0.5 to 3 parts by mass of a crosslinking agent (C), where the total content of the (meth)acrylic resin (A), the (co)polymer (B), and the crosslinking agent (C) is 100 parts by mass.

When the content of the (meth)acrylic resin (A) is 47 parts by mass or more, a relatively large amount of the (meth)acrylic resin (A) is contained in the adhesive composition, and the adhesive composition is likely to form a crosslinked structure. As a result, the adhesive composition has a high molecular weight, and the adhesiveness is less likely to decrease when the adhesive is bonded. On the other hand, when the content of the (meth)acrylic resin (A) is 99 parts by mass or less, sufficient amounts of the (co)polymer (B) and crosslinking agent (C) are contained in the adhesive composition. Therefore, the adhesiveness of the adhesive composition is likely to be good. The content of the (meth)acrylic resin (A) is preferably 57.2 parts by mass or more and 94 parts by mass or less, and more preferably 62.5 parts by mass or more and 88.5 parts by mass or less.

When the content of the (co)polymer (B) is 0.5 parts by mass or more, the adhesiveness of the pressure-sensitive adhesive composition is enhanced. On the other hand, when the content of the (co)polymer (B) is 50 parts by mass or less, the transparency of the pressure-sensitive adhesive composition is enhanced. From the above viewpoints, the content of the (co)polymer (B) is preferably 5 parts by mass or more and 40 parts by mass or less, and more preferably 10 parts by mass or more and 35 parts by mass or less.

When the content of the crosslinking agent (C) is 0.5 parts by mass or more, the adhesive composition tends to aggregate appropriately, and the adhesive composition is less likely to remain on the surface of the adherend after peeling. When the content of the crosslinking agent (C) is 3 parts by mass or less, the adhesive composition contains sufficient amounts of (meth)acrylic resin (A) and (co)polymer (B), and therefore tends to have good adhesive properties. The content of the crosslinking agent (C) is preferably 1 part by mass or more and 2.8 parts by mass or less, and more preferably 1.5 parts by mass or more and 2.5 parts by mass or less.

It is preferable that the adhesive composition according to this embodiment is substantially free of rosin resin or terpene resin. Rosin resin or terpene resin will discolor or color the adhesive composition. To prevent the above-mentioned coloration, hydrogenated resins made by hydrogenating rosin resin or terpene resin are sometimes used in adhesive compositions, but these tend to reduce the adhesive's holding power. Furthermore, because rosin resin or terpene resin has an acid value, there is a risk that applying an adhesive composition containing these to metal may corrode the metal.

The term "substantially free" means that the content of rosin resin or terpene resin relative to the total mass of the adhesive composition is 0.1 mass% or less.

[Manufacturing method]
The adhesive composition according to this embodiment can be prepared by mixing the above-mentioned (meth)acrylic resin (A), (co)polymer (B), and crosslinking agent (C) in amounts corresponding to the above-mentioned contents, together with an optionally used solvent.

Examples of such solvents include ethyl acetate, butyl acetate, benzene, toluene, xylene, cyclohexane, and methyl ethyl ketone.

[Application]
The adhesive composition according to this embodiment can be used in various applications requiring adhesiveness as adhesive processed products such as tapes, labels, sheets, and double-sided tapes.

The shape of the adhesive processed product is not particularly limited, but it can be configured, for example, to have a substrate and an adhesive layer obtained from the above-mentioned adhesive composition. The adhesive layer may have a substrate on both sides.

The thickness of the adhesive layer is not particularly limited, but from the viewpoint of imparting the desired adhesiveness to the adhesive processed product and minimizing the impact on the productivity of the adhesive processed product, it is preferably 5 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, and even more preferably 10 μm or more and 30 μm or less. The above-mentioned adhesive composition can exhibit sufficient adhesiveness even in a thin film. Therefore, for example, sufficient adhesive strength can be obtained even if the thickness of the adhesive layer is 30 μm or less.

The type of substrate is not particularly limited, and may be a resin film, a metal film, or the like. The shape of the substrate is also not particularly limited, and may be flat or have a three-dimensional structure, and is selected appropriately depending on the application. There are also no particular restrictions on its transparency, but as mentioned above, the pressure-sensitive adhesive composition has excellent transparency. Therefore, pressure-sensitive adhesive products can be used in applications where transparency is required, and in such cases, it is preferable that the substrate also has excellent transparency.

For example, if transparency is required for an adhesive product, the total light transmittance of the adhesive product measured in accordance with JIS K7361 is preferably 87% or higher. In such applications, it is preferable to use a transparent PET film or the like as the substrate.

Furthermore, when the adhesive-processed product is attached to an SUS substrate via the adhesive layer, the adhesive strength measured by a 180° peel test is preferably 9 N/25 mm or more, more preferably 10 N/25 mm or more, and even more preferably 10.5 N/25 mm or more.

The above-mentioned adhesive processed product can be produced by applying the above-mentioned adhesive composition to the surface of a substrate and drying the applied adhesive composition to crosslink each component.

The coating method is not particularly limited, and can be any known method such as a roll coater, reverse roll coater, gravure roll, bar coater, comma coater, or die coater. The drying conditions are also not particularly limited, and drying at 80 to 200°C for 10 seconds to 10 minutes is preferred, and drying at 80 to 170°C for 15 seconds to 5 minutes is more preferred.

The present invention will be explained below using examples and comparative examples, but the present invention is not limited to the following examples in any way.

[Measurement of physical properties]
<Structural unit content>
The content (mol %) of the structural units in the (co)polymers (B1) to (B8) was determined by analyzing the ¹³ C-NMR spectrum measured under the following conditions.
Apparatus: AVANCEIII cryo-500 type nuclear magnetic resonance apparatus manufactured by Bruker Biospin Measurement nucleus: ¹³ C (125 MHz)
Measurement mode: Single pulse proton broadband decoupling Pulse width: 45° (5.00 μsec)
Number of points: 64k
Measurement range: 250 ppm (-55 to 195 ppm)
Repeat time: 5.5 seconds Number of times of accumulation: 128 Measurement solvent: orthodichlorobenzene/benzene-d ₆ (4/1 (volume ratio))
Sample concentration: 60 mg/0.6 mL
Measurement temperature: 120℃
Window function: exponential (BF: 1.0 Hz)
Chemical shift reference: δδ signal 29.73 ppm

<Softening point>
The softening points of the (co)polymers (B1) to (B8) were measured by the ring and ball method in accordance with JIS K2207.

<Glass transition temperature (Tg)>
The glass transition temperatures (Tg) of the (meth)acrylic resin (A) and the (co)polymers (B1) to (B8) were determined by sealing these resins in a simple hermetic pan and raising the temperature from −100° C. to 200° C. at a rate of 10° C./min under a nitrogen stream, and analyzing the DSC curves in accordance with JIS K7121.

<Number Average Molecular Weight (Mn), Z Average Molecular Weight (Mz), Weight Average Molecular Weight (Mw/Mn), and Content of Compounds with a Molecular Weight of 400 or Less>
The number average molecular weight (Mn), weight average molecular weight (Mw), z-average molecular weight (Mz), and molecular weight distribution (Mw/Mn) of the (meth)acrylic resin (A) and the (co)polymers (B1) to (B8) were determined by GPC measurement. The measurement was carried out under the following conditions. The number average molecular weight (Mn), weight average molecular weight (Mw), and z-average molecular weight (Mz) were then determined from a calibration curve using commercially available monodisperse standard polystyrene, and Mw/Mn was calculated.
Apparatus: GPC HLC-8320 (manufactured by Tosoh Corporation)
Solvent: tetrahydrofuran Column: TSKgel G7000 x 1, TSKgel G4000 x 2, TSKgel G2000 x 1 (all manufactured by Tosoh Corporation)
Flow rate: 1.0 ml/min Sample: 20 mg/mL tetrahydrofuran solution Temperature: 40°C

<Solubility parameter (SP value)>
The solubility parameters of the (co)polymers (B1) to (B8) were calculated using the Fedors formula. The Fedors formula is a formula for calculating the SP value from cohesive energy density, molar volume (molar molecular volume), and the like, and is described in "A Method for Estimating Both the Solubility Parameters and Molar Volumes of Liquids" by R. F. Fedors (POLYMER ENGINEERING AND SCIENCE, published February 1974, Vol. 14, No. 2, pp. 147-152). In other words, the SP value calculated using the Fedors formula is a calculated value determined by the molecular structure of the compound.

[Synthesis of (meth)acrylic resin (A)]
The (meth)acrylic resin (A) was synthesized using the following monomers.

2-Ethylhexyl acrylate (2EHA)
Ethyl acrylate (EA)
Vinyl acetate (VA)
Acrylic acid (AA)
Hydroxyethyl acrylate (HEA)

(Synthesis of (meth)acrylic resin (A1))
A temperature-controllable reactor equipped with a stirrer was charged with 350 parts by weight of ethyl acetate as a polymerization solvent and 40 parts by weight of toluene, and the mixture was purged with nitrogen and heated. After heating to 75 ° C., a solution containing 316 parts by weight of 2EHA, 43 parts by weight of EA, 50 parts by weight of VA, 9 parts by weight of AA, 2 parts by weight of HEA, and 2 parts by weight of benzoyl peroxide as a polymerization initiator was continuously added to the reactor and reacted for 5 hours. After 5 hours, the mixture was diluted with 120 parts by weight of toluene to obtain an ethyl acetate/toluene solution containing a (meth)acrylic resin (A1) with a solids content of 45%.

The glass transition temperature (Tg) of the (meth)acrylic resin (A1) obtained by volatilizing the solvent from the resulting solution was measured and found to be -60°C.

[Synthesis of (co)polymer (B)]
(Co)polymers (B1) to (B8) were prepared as follows. Table 1 shows the composition, softening point, glass transition temperature (Tg), number average molecular weight (Mn), z-average molecular weight (Mz), dispersity (Mw/Mn), which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), and solubility parameter. In Table ₁ , "IPT" stands for isopropenyl toluene, and C5 stands for a _C5 fraction obtained by thermal cracking of petroleum naphtha. The _C5 fraction mainly contains unsaturated aliphatic hydrocarbon compounds having 5 carbon atoms.

(Synthesis of (co)polymer (B1))
A mixture of isopropenyltoluene, a _C5 fraction obtained by thermal cracking of petroleum naphtha, and dehydrated and purified toluene (total monomer/toluene = 1/1 (volume ratio)), and a boron trifluoride phenolate complex (1.7 times phenol equivalent) diluted 10 times with dehydrated and purified toluene were continuously fed into the first plate of a 1270 ml capacity autoclave equipped with a stirring blade, and a polymerization reaction was carried out at 5°C. The mass ratio of isopropenyltoluene to _C5 fraction (isopropenyltoluene/ _C5 fraction) was 71/29, the feed rate of the mixture of monomer and toluene was 1.0 liter/hour, and the feed rate of the diluted catalyst was 116 milliliters/hour.

The reaction mixture was transferred to a second-stage autoclave, where the polymerization reaction was continued at 5°C. When the total residence time in the first and second-stage autoclaves reached 2 hours, the reaction mixture was continuously discharged from the autoclaves. When the residence time reached three times the normal residence time, 1 liter of the reaction mixture was sampled to terminate the polymerization reaction. After the polymerization was completed, a 1N aqueous NaOH solution was added to the sampled reaction mixture to deash the catalyst residue. The resulting reaction mixture was washed five times with a large amount of water, and the solvent and unreacted monomers were then removed under reduced pressure using an evaporator to obtain (co)polymer (B1), a copolymer of isopropenyl toluene and _C5 fraction. The (co)polymer (B1) had a content of structural units derived from isopropenyl toluene of 87 mol%, a softening point of 95°C, a glass transition temperature (Tg) of 42°C, a number average molecular weight (Mn) of 890, a z-average molecular weight (Mz) of 2120, a polydispersity (Mw/Mn) which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of 1.55, and a solubility parameter of 9.77 (cal/ ^cm3 ) ^1/2 .

(Synthesis of (co)polymer (B2))
(Co)polymer (B2), a copolymer of isopropenyltoluene and _C5 fraction, was obtained by the same method as in the synthesis of (co)polymer (B1), except that the mass ratio of isopropenyltoluene to _C5 fraction (isopropenyltoluene/ _C5 fraction) was 56/44 and the feed rate of the diluted catalyst was 84 mL/hour. (Co)polymer (B2) had a content of structural units derived from isopropenyltoluene of 88 mol%, a softening point of 105°C, a glass transition temperature (Tg) of 50°C, a number average molecular weight (Mn) of 1050, a z-average molecular weight (Mz) of 2380, a polydispersity (Mw/Mn) which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of 1.54, and a solubility parameter of 9.78 (cal/ ^cm3 ) ^1/2 .

(Synthesis of (co)polymer (B3))
The (co)polymer (B3), a copolymer of isopropenyltoluene and _C5 fraction, was obtained by the same method as in the synthesis of (co)polymer (B1), except that the mass ratio of isopropenyltoluene to _C5 fraction (isopropenyltoluene/ _C5 fraction) was 90/10 and the feed rate of the diluted catalyst was 105 mL/hour. The (co)polymer (B3) had a content of structural units derived from isopropenyltoluene of 96 mol%, a softening point of 97°C, a glass transition temperature (Tg) of 41°C, a number average molecular weight (Mn) of 710, a z-average molecular weight (Mz) of 1510, a polydispersity (Mw/Mn) which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of 1.45, and a solubility parameter of 9.86 (cal/ ^cm3 ) ^1/2 .

(Synthesis of (co)polymer (B4))
The (co)polymer (B4), a copolymer of isopropenyltoluene and _C5 fraction, was obtained by the same method as in the synthesis of (co)polymer (B1), except that the mass ratio of isopropenyltoluene to _C5 fraction (isopropenyltoluene/ _C5 fraction) was 90/10 and the feed rate of the diluted catalyst was 56 mL/hour. The (co)polymer (B4) had a content of structural units derived from isopropenyltoluene of 96 mol%, a softening point of 124°C, a glass transition temperature (Tg) of 62°C, a number average molecular weight (Mn) of 1,140, a z-average molecular weight (Mz) of 3,100, a polydispersity (Mw/Mn), which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), of 1.74, and a solubility parameter of 9.86 (cal/ ^cm3 ) ^1/2 .

(Synthesis of Polymer (B5))
(Co)polymer (B5), a homopolymer of isopropenyl toluene, was obtained in the same manner as in the synthesis of (co)polymer (B1), except that the _C5 fraction obtained by thermal cracking of petroleum naphtha was not fed and the feed rate of the diluted catalyst was 105 mL/hour. (Co)polymer (B5) had a content of structural units derived from isopropenyl toluene of 100 mol%, a softening point of 100°C, a glass transition temperature (Tg) of 45°C, a number average molecular weight (Mn) of 760, a z-average molecular weight (Mz) of 1700, a polydispersity (Mw/Mn), which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), of 1.50, and a solubility parameter of 9.90 (cal/ ^cm3 ) ^1/2 .

(Synthesis of (co)polymer (B6))
(Co)polymer (B6), a homopolymer of isopropenyl toluene, was obtained in the same manner as in the synthesis of (co)polymer (B5), except that the supply rate of the diluted catalyst was 82 mL/hour. The (co)polymer (B6) had a content of structural units derived from isopropenyl toluene of 100 mol%, a softening point of 118°C, a glass transition temperature (Tg) of 62°C, a number average molecular weight (Mn) of 980, a z-average molecular weight (Mz) of 2910, a polydispersity (Mw/Mn) which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of 1.80, and a solubility parameter of 9.90 (cal/ ^cm3 ) ^1/2 .

(Synthesis of (co)polymer (B7))
(Co)polymer (B7), a homopolymer of isopropenyl toluene, was obtained in the same manner as in the synthesis of (co)polymer (B5), except that the supply rate of the diluted catalyst was 68 mL/hour. The (co)polymer (B7) had a content of structural units derived from isopropenyl toluene of 100 mol%, a softening point of 133°C, a glass transition temperature (Tg) of 72°C, a number average molecular weight (Mn) of 1,110, a z-average molecular weight (Mz) of 3,510, a polydispersity (Mw/Mn) which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of 1.89, and a solubility parameter of 9.90 (cal/ ^cm3 ) ^1/2 .

(Synthesis of (co)polymer (B8))
(Co)polymer (B8), a homopolymer of isopropenyl toluene, was obtained in the same manner as in the synthesis of (co)polymer (B5), except that the supply rate of the diluted catalyst was 53 mL/hour. The (co)polymer (B8) had a content of structural units derived from isopropenyl toluene of 100 mol%, a softening point of 145°C, a glass transition temperature (Tg) of 78°C, a number average molecular weight (Mn) of 1520, a z-average molecular weight (Mz) of 4740, a polydispersity (Mw/Mn) which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of 1.99, and a solubility parameter of 9.90 (cal/ ^cm3 ) ^1/2 .

[Crosslinking agent (C)]
As the crosslinking agent (C1), Takenate D-101E (an isocyanate compound, "Takenate" is a registered trademark of Mitsui Chemicals, Inc.) manufactured by Mitsui Chemicals, Inc. was used.

[Production and evaluation of adhesive processed products]
The ethyl acetate/toluene solution containing the (meth)acrylic resin (A1), any one of the (co)polymers (B1) to (B8), and the crosslinking agent (C) were mixed at room temperature so that the ratio of the (meth)acrylic resin (A1), any one of the (co)polymers (B1) to (B8), and the crosslinking agent (C) contained in the solution was the mass ratio shown in Table 2, thereby obtaining an ethyl acetate/toluene solution of a pressure-sensitive adhesive composition.

The resulting ethyl acetate/toluene solution of the adhesive composition was applied to release paper so that the film thickness after drying would be 10-50 μm. After drying at 100°C for 10 minutes, a 25 μm PET film was pressed onto the coated surface to produce an adhesive sheet. The adhesive composition was then left to stand at 50°C for 3 days to allow sufficient crosslinking.

<Measurement of total light transmittance>
The release paper of the adhesive sheet, whose adhesive layer had a thickness of 50 μm, was peeled off to expose the adhesive layer, and a 25 μm-thick PET film was pressed onto the exposed adhesive layer to obtain a test piece. The test piece had a configuration of PET film/adhesive layer/PET film = 25 μm/50 μm/25 μm. The total light transmittance of the test piece was then measured in accordance with JIS K7361.

<Measurement of adhesive strength>
The pressure-sensitive adhesive sheet, with an adhesive layer thickness of 30 μm, was cut into a width of 25 mm and a length of 150 mm to prepare a test piece. The release paper was peeled off from the test piece to expose the adhesive layer, and the exposed adhesive layer was brought into contact with a stainless steel plate (SUS) in an atmosphere of 23°C, and the test piece was pressure-bonded by rolling a 2 kg rubber roll back and forth twice. After leaving it for 20 minutes, the 180° peel strength was measured at a speed of 300 mm/min in accordance with JIS Z0237.

The formulation of the adhesive composition that constitutes the prepared adhesive processed products, as well as the total light transmittance and adhesive strength of the adhesive layer of the adhesive processed products, are shown in Table 2. Furthermore, the relationship between total light transmittance and adhesive strength for Examples 1 and 2 and Comparative Examples 1 to 7 is shown in Figure 1.

As shown in Table 2 and Figure 1, the adhesive compositions (Examples 1 and 2) containing a (co)polymer (B) that satisfies all of the requirements (B-1) to (B-5) had both higher adhesive strength and transparency than the adhesive compositions (Comparative Examples 2 to 7) containing a (co)polymer (B) that did not satisfy any of the requirements (B-1) to (B-5). Furthermore, when no (co)polymer (B) was included (Comparative Example 1), the adhesive strength was very low.

The present invention provides an adhesive composition that is both highly transparent and highly adhesive. The present invention can be particularly suitably implemented in a variety of applications where transparency of the adhesive composition is required.

Claims (5)

47 parts by mass or more and 99 parts by mass or less of a (meth)acrylic resin (A);
0.5 parts by mass or more and 50 parts by mass or less of a (co)polymer (B) different from the (meth)acrylic resin (A);
0.5 parts by mass or more and 3 parts by mass or less of a crosslinking agent (C);
(wherein the total content of the (meth)acrylic resin (A), the (co)polymer (B), and the crosslinking agent (C) is 100 parts by mass),
The (meth)acrylic resin (A) satisfies the following requirements (A-1) and (A-2), and
The (co)polymer (B) satisfies all of the following requirements (B-1) to (B- 6 ):
Adhesive composition.
(A-1) Contains a structural unit derived from a (meth)acrylate having an alkyl group having 1 to 12 carbon atoms, and a structural unit derived from a (meth)acrylate containing a hydroxyl group.
(A-2) The glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) is in the range of −80° C. or higher and 0° C. or lower.
(B-1) The (co)polymer (B) contains structural units derived from isopropenyltoluene in an amount of 20 mol % or more based on the total amount of structural units of the (co)polymer (B).
(B-2) The softening point measured in accordance with JIS K2207 is in the range of 80°C or higher and 120°C or lower.
(B-3) The glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) is in the range of 30° C. or higher and 70° C. or lower.
(B-4) The number average molecular weight (Mn) is in the range of 750 or more and 1200 or less, the z average molecular weight (Mz) is in the range of 2000 or more and 3000 or less, and the polydispersity (Mw/Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is in the range of 1.5 or more and 1.8 or less, as measured by gel permeation chromatography (GPC) in terms of polystyrene.
(B-5) The solubility parameter is 9.80 (cal/cm ³ ) ^1/2 or less.
(B-6) The (co)polymer (B) contains structural units derived from an unsaturated aliphatic hydrocarbon compound having 4 or 5 carbon atoms in an amount of 10 mol % to 30 mol % based on the total amount of all structural units. A pressure-sensitive adhesive layer obtained from the pressure-sensitive adhesive composition according to claim 1 ,
a tape, label, sheet or double-sided tape;
Adhesive processed products. The thickness of the adhesive layer is 5 μm or more and 50 μm or less.
The adhesive processed product according to claim 2 . The total light transmittance measured in accordance with JIS K7361 is 87% or more.
The adhesive processed product according to claim 2 or 3 . When attached to an SUS substrate via the adhesive layer, the adhesive strength measured by a 180° peel test is 10 N/25 mm or more.
The adhesive processed product according to any one of claims 2 to 4 .