Pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition

Abstract

To provide a pressure-sensitive adhesive composition for a decorative sheet, a decorative sheet, and a decorative structure, which are excellent in adhesive strength to low-polarity adherends, heat-resistant adhesive strength, heat-resistant retention, and cross-cut test (appearance of coating after molding) when used to decorate molded products. [Solution] The aforementioned problems are solved by a pressure-sensitive adhesive composition comprising a block copolymer (A) and an acrylic oligomer (B), wherein the block copolymer (A) contains a styrene-based elastomer (A1) having a soft block made of at least one of polybutadiene and polyisoprene, and a hard block made of a polymer of a vinyl aromatic compound, and the acrylic oligomer (B) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (b1) whose homopolymer has a glass transition temperature of 60°C or higher, and the weight-average molecular weight of the acrylic oligomer (B) is in the range of 5,000 to 200,000.

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition. [Background technology]

[0002] Because of their ease of handling, adhesive sheets with adhesive layers are widely used in a wide range of applications, including labeling and medical applications. The substrates used for adhesive sheets vary widely depending on the application, and may include high-polarity substrates such as stainless steel and polyester, as well as low-polarity substrates such as polyolefins. However, low-polarity substrates generally tend to be difficult to adhere to, and adhesives that can ensure adhesion to, for example, polyolefin-based resins are in demand. Furthermore, adhesives used in applications expected to be used in a variety of environments, such as marking films, window films, automotive components, and optical displays, require coating transparency, excellent coating appearance to prevent lifting or peeling at the adhesive interface between the adherend and the adhesive layer during processing, and excellent heat-resistant adhesion and heat retention to prevent peeling or misalignment even in high-temperature environments.

[0003] One example is an adhesive used to attach decorative sheets to substrates used to decorate the exterior surfaces of molded products such as automotive interior and exterior parts, keyboards, home appliances, smartphones, housing construction materials, furniture, musical instruments, and Shinkansen window frames. Decorating molded products using decorative sheets typically requires a heating process, so various durability properties are required in high-temperature environments. Furthermore, in recent years, there has been an increase in the use of polypropylene resin (hereinafter referred to as PP resin) as a substrate for decorative sheets, which has a low specific gravity and excellent thermoformability, so adhesion to PP resin is also required.

[0004] Patent Document 1 discloses a double-sided pressure-sensitive adhesive sheet for decorative molding, which contains an olefin-based elastomer having a block obtained by polymerizing a hydrogenated α-olefin and a block composed of a styrene-based polymer, a tackifying resin, an oil component, and a silane coupling agent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-139099 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors have conducted research and found that the pressure-sensitive adhesive composition described in Patent Document 1 does not exhibit satisfactory performance when used on PP resin, which is a low-polarity adherend.

[0007] That is, no pressure-sensitive adhesive composition has been developed to date that has excellent adhesive strength to low-polarity adherends, heat-resistant adhesive strength, and heat-resistant retention, and that has excellent coating film appearance after processing. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. The pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet according to the present invention have the following constitutions [1] to

[11] .

[0009] [1] A pressure-sensitive adhesive composition comprising a block copolymer (A) and an acrylic oligomer (B), wherein the block copolymer (A) contains a styrene-based elastomer (A1) having a soft block composed of at least one of polybutadiene and polyisoprene and a hard block composed of a polymer of a vinyl aromatic compound, and the acrylic oligomer (B) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (b1) whose homopolymer has a glass transition temperature of 60°C or higher, and the weight-average molecular weight of the acrylic oligomer (B) is in the range of 5,000 to 200,000.

[0010] [2] The pressure-sensitive adhesive composition according to [1], wherein the diblock ratio in 100% by mass of the block copolymer (A) is 10 to 80% by mass.

[0011] [3] The pressure-sensitive adhesive composition according to [1] or [2], wherein the glass transition temperature of the acrylic oligomer (B) is 30°C or higher but lower than 180°C.

[0012] [4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the (meth)acrylic monomer (b1) having a glass transition temperature of 60°C or higher in its homopolymer form is a (meth)acrylic monomer having a ring structure.

[0013] [5] The pressure-sensitive adhesive composition according to any one of [1] to [4], wherein the monomer mixture constituting the acrylic oligomer (B) further contains a monomer (b2) having a functional group.

[0014] [6] The pressure-sensitive adhesive composition according to [5], wherein the content of the functional group-containing monomer (b2) is 0.01 to 10 mass % relative to 100 mass % of the monomer mixture constituting the acrylic oligomer (B).

[0015] [7] The pressure-sensitive adhesive composition according to any one of [1] to [6], wherein the content of the acrylic oligomer (B) is 1 to 100 parts by mass per 100 parts by mass of the block copolymer (A).

[0016] [8] The pressure-sensitive adhesive composition according to any one of [1] to [7], further comprising 1 to 150 parts by mass of a tackifier resin (C) per 100 parts by mass of the block copolymer (A).

[0017] [9] The pressure-sensitive adhesive composition according to [8], wherein the tackifier resin (C) contains a hydrocarbon resin.

[0018]

[10] The pressure-sensitive adhesive composition according to [9], wherein the hydrocarbon resin contains at least one of an unhydrogenated aromatic petroleum resin and a hydrogenated aromatic petroleum resin.

[0019]

[11] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition according to any one of [1] to

[10] . [Effects of the Invention]

[0020] The present invention provides a pressure-sensitive adhesive composition that exhibits excellent adhesion to low-polarity adherends, heat-resistant adhesion, and heat-resistant retention, and that has excellent coating appearance after processing, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition. It has been discovered that when a pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing a predetermined block copolymer (A) and an acrylic oligomer (B), the composition exhibits excellent adhesion to low-polarity adherends, heat-resistant adhesion, and heat-resistant retention, and that the composition has excellent coating appearance after processing. DETAILED DESCRIPTION OF THE INVENTION

[0021] The pressure-sensitive adhesive composition of the present invention and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition will be described below, but the present invention is not limited thereto. In this specification, the term "(meth)acrylic monomer" refers to a (meth)acrylic acid ester, and the term "(meth)acrylic acid ester" includes an acrylic acid ester and a methacrylic acid ester. The term "(meth)acryloyl group" includes an acryloyl group and a methacryloyl group. The term "monomer" refers to a monomer having an ethylenically unsaturated group.

[0022] In this specification, a numerical range specified using "to" is intended to include the numerical values ​​before and after "to" as the range's lower and upper limits. Unless otherwise noted, the various components appearing in this specification may be used independently either alone or in combination of two or more. The weight average molecular weight (Mw) is a weight average molecular weight calculated in terms of polystyrene, determined by gel permeation chromatography (GPC). In the present invention, the terms "film" and "sheet" are not distinguished by thickness. In other words, the term "sheet" in this specification includes thin film-like materials, and the term "film" in this specification includes thick sheet-like materials. Furthermore, both "sheet" and "film" include laminates. Furthermore, the term "adherend" refers to a counterpart to which the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is attached.

[0023] <Adhesive composition> The pressure-sensitive adhesive composition of the present invention comprises a block copolymer (A) and an acrylic oligomer (B), wherein the block copolymer (A) contains a styrene-based elastomer (A1) having a soft block composed of at least one of polybutadiene and polyisoprene and a hard block composed of a polymer of a vinyl aromatic compound, and the acrylic oligomer (B) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (b1) whose homopolymer has a glass transition temperature of 60°C or higher, and wherein the weight-average molecular weight of the acrylic oligomer (B) is in the range of 5,000 to 200,000. Each component will be described below.

[0024] <Block copolymer (A)> The block copolymer (A) contains a styrene-based elastomer (A1) having a soft block made of at least one of polybutadiene and polyisoprene, and a hard block made of a polymer of a vinyl aromatic compound.

[0025] When the soft block constituting the styrene-based elastomer (A1) is (X) and the hard block is (Y), the molecular structure of the styrene-based elastomer (A1) may be linear, branched, radial, or any combination thereof. For example, it may be a block polymer having a structure such as XY (diblock), YXY (triblock), (YX-)n, or YXYXY (multiblock). Here, n is an integer of 2 or more.

[0026] The styrene-based elastomer (A1) is not particularly limited as long as it is a commonly used one. Examples include triblock polymers such as styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS), diblock polymers such as styrene-isoprene (SI), styrene-butadiene (SB), and styrene-(ethylene-butylene) (SEB), and hydrogenated block polymers such as styrene-(ethylene-propylene)-styrene (SEPS) and styrene-(ethylene-butylene)-styrene (SEBS). The inclusion of the styrene-based elastomer (A1) improves adhesive strength and heat-resistant retention. These can be used alone or in combination of two or more types.

[0027] Specific examples of the styrene-based elastomer (A1) include styrene-isoprene-styrene (SIS), such as Kraton's Kraton D series and Zeon's Quintac series, with those containing styrene-isoprene (SI) as the diblock component being preferred. Styrene-butylene-styrene (SBS), such as Kraton's Kraton D series and Asahi Kasei's Tufprene series, with those containing styrene-butylene (SB) as the diblock component being preferred. Styrene-(ethylene-butylene)-styrene (SEBS), such as Kraton's Kraton G series and Asahi Kasei's Tuftec series, with those containing styrene-(ethylene-butylene) (SEB) as the diblock component being preferred. Styrene-(ethylene-propylene)-styrene (SEPS), such as Kraton's Kraton G series and Kuraray's Septon series, with those containing styrene-(ethylene-propylene) (SEP) as the diblock component being preferred.

[0028] The block copolymer (A) may contain a block copolymer (A2) other than the styrene-based elastomer (A1). The block copolymer (A2) may be a thermoplastic block copolymer having a soft block (X) and a hard block (Y), such as a styrene-based elastomer other than (A1), an olefin-based elastomer, a polyester-based elastomer, a vinyl chloride resin-based elastomer, an acrylic elastomer, a urethane-based elastomer, or a polyamide-based elastomer. Among these, a styrene-based elastomer or an acrylic elastomer other than (A1) that is a block copolymer having a soft block mainly composed of structural units derived from a conjugated diene compound and a hard block mainly composed of structural units derived from a vinyl aromatic compound is preferred.

[0029] The compound other than (A1) that constitutes the soft block of the styrene-based elastomer is preferably a conjugated diene compound. Examples include isobutylene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadiene, and phenyl-1,3-butadiene. The soft block may be a conjugated diene compound in which the unsaturated bonds are partially or completely hydrogenated.

[0030] The compound other than (A1) constituting the hard block of the styrene-based elastomer is preferably a vinyl aromatic compound, such as α-methylstyrene, vinyltoluene, p-tert-butylstyrene, divinylbenzene, p-methylstyrene, or 1,1-diphenylstyrene, with styrene being more preferred because it provides good heat resistance retention.

[0031] The content of the other block copolymer (A2) is preferably less than 10% by mass relative to 100% by mass of the block copolymer (A). When the content of the other block copolymer is less than 10% by mass, good compatibility is easily obtained, and appropriate adhesive strength can be easily obtained.

[0032] The diblock ratio in 100% by mass of block copolymer (A) is preferably 10 to 80% by mass, more preferably 20 to 75% by mass, and even more preferably 30 to 70% by mass. By making the diblock ratio in 100% by mass of block copolymer (A) 10% by mass or more, the flexibility of the coating film is improved, and the adhesive strength and heat-resistant adhesive strength to olefin-based adherends are improved. By making the diblock ratio of block copolymer (A) 80% by mass or less, the cohesive strength of the coating film is improved, and the heat-resistant retention strength is improved. When block copolymer (A) contains multiple block copolymers with different diblock ratios, the diblock ratio in 100% by mass of block copolymer (A) is calculated as the sum of the products of the diblock ratios of each material and their contents. For example, when block copolymer (A) consists of 80 parts by mass of a block copolymer with a diblock ratio of 20% by mass and 20 parts by mass of a block copolymer with a diblock ratio of 60% by mass, the diblock ratio in 100% by mass of block copolymer (A) is calculated as 20 × 0.8 + 60 × 0.2 = 28% by mass.

[0033] The content of structural units derived from vinyl aromatic compounds in the block copolymer (A) is preferably 5 to 70% by mass, more preferably 10 to 50% by mass, based on 100% by mass of the block copolymer (A). By making the content of structural units derived from vinyl aromatic compounds in the block copolymer (A) 5% by mass or more, the cohesive strength of the coating film is improved and the heat resistance retention is better. By making the content of structural units derived from vinyl aromatic compounds in the block copolymer (A) 70% by mass or less, the flexibility of the coating film is improved and the adhesion to low-polarity materials such as PP resin is better. The content of structural units derived from vinyl aromatic compounds is determined by calculating the mass ratio of the vinyl aromatic compounds to the total mass of the block copolymer (A). When the vinyl aromatic compound is styrene, the content of structural units derived from vinyl aromatic compounds means the styrene content. The styrene content can be confirmed from the manufacturer's catalog values.

[0034] The weight-average molecular weight of the block copolymer (A) is preferably 10,000 to 500,000, more preferably 30,000 to 250,000. By making the weight-average molecular weight of the block copolymer (A) 10,000 or more, the cohesive strength of the coating film is improved and the heat resistance retention is better. By making the weight-average molecular weight of the block copolymer (A) 500,000 or less, the wettability to the adherend is improved and the adhesive strength to olefin-based adherends is better.

[0035] <Acrylic Oligomer (B)> The acrylic oligomer (B) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (b1) whose homopolymer has a glass transition temperature of 60°C or higher, and has a weight-average molecular weight in the range of 5,000 to 200,000. The monomer mixture constituting the acrylic oligomer (B) may contain, in addition to the acrylic monomer (b1), a monomer (b2) having a functional group, and other monomers other than (b1) and (b2). In this specification, a monomer having a functional group is classified as a monomer (b2) having a functional group even if the homopolymer has a glass transition temperature of 60°C or higher.

[0036] <(Meth)acrylic monomer (b1) having a homopolymer glass transition temperature of 60°C or higher> The (meth)acrylic monomer (b1) (hereinafter also referred to as monomer (b1)) having a homopolymer glass transition temperature of 60°C or higher contributes to wettability to low-polarity adherends and cohesive strength at high temperatures, i.e., adhesive strength and heat-resistant adhesive strength.

[0037] Examples of the (meth)acrylic monomer (b1) having a homopolymer glass transition temperature (Tg) of 60°C or higher include methyl methacrylate (MMA, Tg: 103°C), ethyl methacrylate (EMA, Tg: 65°C), isopropyl methacrylate (IPMA, Tg: 81°C), isobutyl methacrylate (IBMA, Tg: 67°C), tertiary butyl methacrylate (TBMA, Tg: 107°C), cyclohexyl methacrylate (CHMA, Tg: 66°C), isobornyl methacrylate (IBXMA, Tg: 180°C), and isobornyl acrylate (IBXA, Tg: 97°C). Among these, from the viewpoint of the balance between cohesive strength and wettability to low-polarity adherends, at least one selected from methyl methacrylate (MMA, Tg: 103°C), ethyl methacrylate (EMA, Tg: 65°C), cyclohexyl methacrylate (CHMA, Tg: 66°C), isobornyl methacrylate (IBXMA, Tg: 180°C), and isobornyl acrylate (IBXA, Tg: 97°C) is preferred as monomer (b1). From the viewpoint of further improving the balance between cohesive strength and wettability to low-polarity adherends, (meth)acrylic monomers having a ring structure, such as cyclohexyl methacrylate (CHMA, Tg: 66°C), isobornyl methacrylate (IBXMA, Tg: 180°C), and isobornyl acrylate (IBXA, Tg: 97°C), are more preferred.

[0038] The content of monomer (b1) is preferably 45% by mass or more and 99.99% by mass or less, more preferably 55% by mass or more and 99.5% by mass or less, and even more preferably 60% by mass or more and 99.5% by mass or less, based on 100% by mass of the monomer mixture constituting the acrylic oligomer (B). By setting the content of monomer (b1) to 40% by mass or more, based on 100% by mass of the monomer mixture constituting the acrylic oligomer (B), cohesive strength can be imparted, and by setting the content of monomer (b1) to 95% by mass or less, wettability to low-polarity adherends can be improved.

[0039] <Monomer having a functional group (b2)> The monomer (b2) having a functional group is not particularly limited as long as it has a functional group such as a hydroxy group, a carboxy group, an amino group, an amide group, or a glycidyl group. By including the functional group-containing monomer (b2) (hereinafter also referred to as "monomer (b2)"), the compatibility between the acrylic oligomer (B) and the block copolymer (A) tends to be less excessive, and therefore the acrylic oligomer (B) is appropriately localized on the surface of the adhesive layer when the adhesive layer is formed. When the acrylic oligomer (B) is appropriately localized on the surface of the adhesive layer, the wettability with the substrate is improved, resulting in excellent coating appearance after processing.

[0040] Examples of the monomer having a hydroxy group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0041] Examples of the monomer having a carboxy group include acrylic acid, methacrylic acid, and a monomer represented by the following formula (Formula 1). Formula 1 CH2=CR1-CO-O-(C2H4-COO-)nH Here, R1 represents hydrogen or a methyl group, and n represents an integer of 1 or more.

[0042] Examples of the monomer having an amino group include 2-(dimethylamino)methyl (meth)acrylate, 2-(diethylamino)ethyl (meth)acrylate, 3-(dimethylamino)propyl (meth)acrylate, and 2-(dimethylamino)dimethylaminoethyl (meth)acrylate.

[0043] Examples of the monomer having an amide group include N-vinyl lactams such as N-methylvinylpyrrolidone, N-vinylcaprolactam, N-vinylpyrrolidone, N-vinyl-2-pyrrolidone, and N-(meth)acryloylpyrrolidone; cyclic amides such as vinylmorpholine and (meth)acryloylmorpholine; N-vinylcarboxylic acid amides such as N-vinylformamide and N-vinylacetamide; and (meth)acrylamides such as (meth)acrylamide and substituted (meth)acrylamide.

[0044] Examples of the monomer having a glycidyl group include glycidyl (meth)acrylate.

[0045] Other monomers having functional groups include cyclic amines such as vinylpyridine, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, and vinyloxazole.

[0046] Among these, the monomer (b2) preferably contains at least one selected from the group consisting of a monomer having a hydroxy group, a monomer having an amino group, a monomer having a carboxy group, and a monomer having an amide group, from the viewpoints of compatibility and adhesion to the substrate. As the monomer having an amide group, (meth)acrylamides are preferred.

[0047] The content of monomer (b2) is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 8% by mass or less, and even more preferably 0.5% by mass or more and 5% by mass or less, based on 100% by mass of the monomer mixture constituting the acrylic oligomer (B). By setting the content of monomer (b2) to 0.01% by mass or more based on 100% by mass of the monomer mixture constituting the acrylic oligomer (B), adhesion to the substrate is improved and the coating film has an excellent appearance after processing, and by setting the content of monomer (b2) to 10% by mass or less, compatibility is improved and adhesive strength is improved.

[0048] <Other Monomers (b3)> The monomer mixture constituting the acrylic oligomer (B) may contain other monomers in addition to the monomers (b1) and (b2) as optional components, provided that the effects of the present invention are not impaired. Examples include (meth)acrylic monomers whose homopolymers have a glass transition temperature (Tg) of less than 60°C, vinyl monomers such as vinyl acetate and styrene, and the like. These may be used alone or in combination of two or more. Among these, examples of the monomer (b3) that can improve wettability to a low-polarity adherend include methyl acrylate (MA, Tg: 6°C), ethyl acrylate (EA, Tg: -27°C), butyl acrylate (BA, Tg: -54°C), isobutyl acrylate (IBA, Tg: -26°C), 2-ethylhexyl methacrylate (2EHMA, Tg: -10°C), n-butyl acrylate (n-BA, Tg: -57°C), 2-ethylhexyl acrylate (2EHA, Tg: -76°C), and n-octyl Preferred are (meth)acrylic monomers whose homopolymers have a glass transition temperature (Tg) of less than 60°C, such as acrylate (Tg: -80°C) and 2-octyl acrylate (Tg: -47°C), and at least one selected from the group consisting of ethyl acrylate (EA, Tg: -27°C), 2-ethylhexyl methacrylate (2EHMA, Tg: -10°C), and n-butyl acrylate (n-BA, Tg: -57°C) is preferred, with 2-ethylhexyl methacrylate (2EHMA, Tg: -10°C) being more preferred.

[0049] The content of the other monomer (b3) is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on 100% by mass of the monomer mixture constituting the acrylic oligomer (B). When the content of the other monomer (b3) is 45% by mass or less, based on 100% by mass of the monomer mixture constituting the acrylic oligomer (B), the adhesion to low-polarity adherends and the cohesive strength of the pressure-sensitive adhesive layer are improved, and appropriate adhesive strength can be easily obtained.

[0050] <Weight average molecular weight (Mw)> The weight-average molecular weight (Mw) of the acrylic oligomer (B) is in the range of 5,000 to 200,000, preferably in the range of 10,000 to 150,000, and more preferably in the range of 10,000 to 50,000. When the weight-average molecular weight (Mw) of the acrylic oligomer (B) is 5,000 or more, the pressure-sensitive adhesive composition can exhibit appropriate cohesive strength. Furthermore, when the weight-average molecular weight (Mw) of the acrylic oligomer (B) is 200,000 or less, the adhesive layer has good wettability with the adherend, and therefore adheres to the adherend with high adhesive strength, thereby enabling the adhesive layer to exhibit high adhesive strength.

[0051] The weight average molecular weight (Mw) of the acrylic oligomer (B) can be adjusted to a desired value by adjusting the reaction temperature, reaction time, type of organic solvent, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc.

[0052] <Glass transition temperature (Tg)> The glass transition temperature (Tg) of the acrylic oligomer (B) is preferably 30°C or higher and lower than 180°C, more preferably 55°C or higher and lower than 180°C, and even more preferably 70°C or higher and lower than 180°C. When the glass transition temperature (Tg) of the acrylic oligomer (B) is 30°C or higher and lower than 180°C, a decrease in viscoelasticity (i.e., a decrease in cohesive strength) due to high-temperature heating is suppressed. The pressure-sensitive adhesive layer can exhibit high heat-resistant retention by having appropriate viscoelasticity.

[0053] The glass transition temperature (Tg) of the acrylic oligomer (B) is a value obtained by converting the absolute temperature (K) calculated from the following formula 1 into Celsius temperature (°C). 1 / Tg=m1 / Tg1+m2 / Tg2+...+m(k-1) / Tg(k-1)+mk / Tg k (Equation 1)

[0054] In Formula 1, Tg1, Tg2, . . . , Tg(k-1), and Tgk respectively represent the glass transition temperatures (Tg) expressed in absolute temperature (K) when each monomer constituting the acrylic oligomer (B) is made into a homopolymer. m1, m2, . . . , m(k-1), and mk respectively represent the mole fractions of each monomer constituting the acrylic oligomer (B). m1+m2+···+m(k-1)+mk=1. Note that absolute temperature (K) can be converted to Celsius temperature (℃) by subtracting 273 from it, and Celsius temperature (℃) can be converted to absolute temperature (K) by adding 273 to it.

[0055] "Glass transition temperature (Tg) of a homopolymer" refers to the glass transition temperature (Tg) of a homopolymer produced by polymerizing the monomer alone. This can be obtained from information from the vendor of the monomer or from the values ​​listed in "Polymer Handbook 3rd Edition" (A Wiley-Interscience Publication, 1989).

[0056] The "glass transition temperatures (Tg) of homopolymers, expressed in Celsius degrees (°C)" are 180°C for isobornyl methacrylate (IBXMA), 97°C for isobornyl acrylate (IBXA), 103°C for methyl methacrylate (MMA), 65°C for ethyl methacrylate (EMA), 163°C for acrylic acid (AA), 18°C ​​for dimethylaminoethyl methacrylate (DM), 55°C for 2-hydroxyethyl methacrylate (HEMA), 100°C for styrene (St), and -10°C for 2-ethylhexyl methacrylate (2-EHMA).

[0057] The glass transition temperature (Tg) of the acrylic oligomer (B) can be appropriately adjusted, for example, by using a monomer having a different glass transition temperature (Tg) when made into a homopolymer.

[0058] The content of the acrylic oligomer (B) is preferably 1 to 100 parts by mass, more preferably 1 to 50 parts by mass, and even more preferably 1 to 30 parts by mass, per 100 parts by mass of the block copolymer (A). By using 1 part by mass or more of the acrylic oligomer (B) per 100 parts by mass of the block copolymer (A), the acrylic oligomer (B) is appropriately localized on the surface of the pressure-sensitive adhesive layer. The appropriate localization of the acrylic oligomer (B) on the surface of the pressure-sensitive adhesive layer improves wettability with the adherend, allowing the pressure-sensitive adhesive layer to adhere to the adherend with high adhesive strength. This allows the pressure-sensitive adhesive layer to exhibit high heat-resistant adhesive strength. Furthermore, when the content of the acrylic oligomer (B) is 100 parts by mass or less per 100 parts by mass of the block copolymer (A), the block copolymer (A) and the acrylic oligomer (B) maintain appropriate compatibility. This prevents, for example, a decrease in adhesive strength due to poor compatibility, and provides an excellent coating appearance after processing.

[0059] <Production of Acrylic Oligomer (B)> The acrylic oligomer (B) can be produced by polymerizing the acrylic monomer mixture. The polymerization can be carried out by known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization, but solution polymerization is preferred. Solvents used in solution polymerization are preferably, for example, acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone. The polymerization temperature is preferably a boiling point reaction at 60 to 120°C. The polymerization time is preferably about 5 to 12 hours.

[0060] The polymerization initiator used for the polymerization is preferably a radical polymerization initiator, and the radical polymerization initiator is generally a peroxide or an azo compound. Examples of peroxides include dialkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, and 2,5-di(t-butylperoxy)hexyne-3; Peroxyesters such as t-butyl peroxybenzoate, t-butyl peroxyacetate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; Peroxyketals such as 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and n-butyl-4,4-bis(t-butylperoxy)valerate; Hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, and 2,5-dimethylcyclohexane-2,5-dihydroperoxide; diacyl peroxides such as benzoyl peroxide, decanoyl peroxide, lauroyl peroxide, and 2,4-dichlorobenzoyl peroxide; Examples include peroxydicarbonates such as bis(t-butylcyclohexyl) peroxydicarbonate.

[0061] Examples of the azo compound include 2,2'-azobisbutyronitrile such as 2,2'-azobisisobutyronitrile (abbreviation: AIBN) and 2,2'-azobis(2-methylbutyronitrile); 2,2'-azobisvaleronitrile such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobispropionitriles such as 2,2'-azobis(2-hydroxymethylpropionitrile); Examples include 1,1'-azobis-1-alkanenitriles such as 1,1'-azobis(cyclohexane-1-carbonitrile).

[0062] The polymerization initiator is preferably used in an amount of 0.01 to 10 parts by mass, more preferably 0.1 to 2 parts by mass, based on 100 parts by mass of the monomer mixture.

[0063] After polymerizing the acrylic oligomer (B), the solvent may be appropriately evaporated to make the acrylic oligomer (B) solvent-free. To make the acrylic oligomer (B) solvent-free, the acrylic oligomer (B) solution may be heated above the boiling point of the solvent to evaporate the solvent, thereby obtaining a solvent-free acrylic oligomer (B). Vacuum equipment may be used to evaporate the solvent.

[0064] The present pressure-sensitive adhesive composition preferably further contains a tackifying resin (C) in addition to the block copolymer (A) and the acrylic oligomer (B).

[0065] <Tackifying resin (C)> Examples of the tackifying resin (C) include aliphatic petroleum resins (C5 petroleum resins), aromatic petroleum resins (C9 petroleum resins or styrene-based petroleum resins), alicyclic petroleum resins (dicyclopentadiene-based petroleum resins), aliphatic / aromatic copolymer petroleum resins, alicyclic / aromatic copolymer petroleum resins, aliphatic / alicyclic copolymer petroleum resins, hydrocarbon resins such as hydrogenated petroleum resins obtained by hydrogenating the above-mentioned petroleum resins, phenolic resins, modified phenolic resins, terpene phenolic resins, hydrogenated terpene phenolic resins, xylene phenolic resins, xylene resins, dicyclopentadiene-phenolic resins, phenol-modified petroleum resins, rosin ester resins, modified rosin ester resins, terpene resins, and hydrogenated terpene resins. These can be used alone or in combination of two or more. Among these, hydrocarbon resins, rosin ester resins, terpene phenol resins, and hydrogenated terpene phenol resins are preferred because they have good compatibility and can improve adhesion to low-polarity materials such as PP resins, with hydrocarbon resins and hydrogenated terpene phenol resins being more preferred, and hydrocarbon resins being even more preferred. Among hydrocarbon resins, it is particularly preferred to contain at least one of unhydrogenated aromatic petroleum resins and hydrogenated aromatic petroleum resins.

[0066] The tackifying resin (C) is not particularly limited as long as it is a commonly used one. For example, aromatic petroleum resins include the Endex series and Crystallex series from Eastman Co., Ltd. and the FTR series from Mitsui Chemicals Co., Ltd. For example, hydrogenated aromatic petroleum resins include the Alcon series from Arakawa Chemical Co., Ltd. and the Rigalite series from Eastman Co., Ltd.

[0067] The softening point of the tackifier resin (C) is preferably 80 to 160°C, more preferably 100 to 155°C. When the softening point of the tackifier resin (C) is within the above range, the cohesive strength of the coating film is improved, and an adhesive layer with better heat resistance retention can be obtained. The softening point in the present invention is determined by the ring and ball method, and indicates a value measured in accordance with JIS K 5902.

[0068] The content of the tackifier resin (C) is preferably 1 to 150 parts by mass, more preferably 10 to 150 parts by mass, and even more preferably 10 to 100 parts by mass, per 100 parts by mass of the block copolymer (A). By using 1 part by mass or more of the tackifier resin (C) per 100 parts by mass of the block copolymer (A), excellent heat resistance retention is achieved, and by using 150 parts by mass or less of the tackifier resin, excellent coating appearance can be maintained after processing.

[0069] In addition to the block copolymer (A), acrylic oligomer (B), and tackifier resin (C), the pressure-sensitive adhesive composition may contain, as necessary, any additives such as a solvent, other resins other than the block copolymer (A), a curing agent, a plasticizer, a silane coupling agent, a leveling agent, inorganic and / or organic fine particles, an ultraviolet absorber, a light stabilizer, an antioxidant, etc. The amounts of these additives added can be appropriately selected within a range that achieves the effects of the present invention.

[0070] Examples of other resins besides the block copolymer (A) include known thermoplastic resins, such as low-density polyethylene, ultra-low-density polyethylene, low-crystalline (amorphous) polyolefins, ionomer resins, ethylene copolymers such as ethylene-vinyl acetate copolymers, ethylene-(meth)acrylic acid copolymers, ethylene-(meth)acrylic acid ester-maleic anhydride copolymers, and ethylene-glycidyl methacrylate copolymers, as well as thermoplastic polyesters, polyamide-based resins such as polyamide-based copolymers, polyurethanes, polystyrene-based resins, cellophane, polyacrylonitrile, and polyvinyl chloride resins such as vinyl chloride-vinyl acetate copolymers. These resins may be used alone or in combination of two or more. The content of these other resins is preferably less than 10% by mass based on 100% by mass of the solid content of the pressure-sensitive adhesive composition. When the content of these resins is less than 10% by mass, good compatibility is easily achieved, and appropriate adhesive strength can be easily obtained.

[0071] The curing agent is preferably one that reacts with the functional groups in the acrylic oligomer (B) by heat or the like to form bonds. For example, one or more curing agents can be selected from known curing agents such as epoxy-based curing agents, isocyanate-based curing agents, oxazoline-based curing agents, aziridine-based curing agents, carbodiimide-based curing agents, metal chelate-based curing agents, and melamine-based curing agents, taking into consideration the reactivity with the functional groups of the acrylic oligomer (B) in the pressure-sensitive adhesive composition. However, it is preferable to include an isocyanate-based curing agent from the viewpoint of heat-resistant adhesive strength. The amount of the curing agent is preferably 0.1 to 5 parts by mass, more preferably 0.1 to 2 parts by mass, per 100 parts by mass of the acrylic oligomer (B).

[0072] <Method of manufacturing pressure-sensitive adhesive composition> A method for producing a pressure-sensitive adhesive composition will be described. However, the present invention is not limited to the following production method. The pressure-sensitive adhesive composition can be produced by dissolving the block copolymer (A), acrylic oligomer (B), and, if necessary, a tackifier resin (C), etc., in a solvent such as toluene, and mixing any additives. Alternatively, a method can be used in which pelletized rubber containing the block copolymer (A) is softened by heating, and then kneaded with the acrylic oligomer (B) and any additives using a stirrer, kneader, etc.

[0073] <Adhesive sheet> The pressure-sensitive adhesive sheet comprises a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition of the present invention.

[0074] The pressure-sensitive adhesive sheet of the present invention preferably has a configuration in which a release film is attached to at least one surface of the pressure-sensitive adhesive layer, specifically, a configuration in which release films are formed on both surfaces of the pressure-sensitive adhesive layer, or a configuration in which a release film is formed on one surface of the pressure-sensitive adhesive layer and a light-transmitting substrate is provided on the other surface of the pressure-sensitive adhesive, and the pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition of the present invention.

[0075] The thickness of the adhesive layer is preferably 2 to 1000 μm, more preferably 5 to 500 μm, still more preferably 10 to 100 μm, and most preferably 20 to 50 μm. The adhesive layer may be in the form of a single layer or a laminate of two or more layers.

[0076] Examples of the substrate include plastic films such as polyester (polyethylene terephthalate, polyethylene naphthalate), polycarbonate, polymethyl methacrylate, polyethylene, polypropylene, cyclic olefin, polyvinyl chloride, polyurethane, polyamide, and ethylene-vinyl acetate copolymer; inorganic materials such as glass plates; nonwoven fabrics; and paper.

[0077] When applying the pressure-sensitive adhesive composition to a substrate, a solvent may be added, and any suitable solvent can be used. Examples of solvents include methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, toluene, xylene, hexane, acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, n-propanol, and isopropanol. These organic solvents may be used alone or in combination of two or more. The viscosity of the pressure-sensitive adhesive composition can be adjusted by adding these organic solvents, or the viscosity can be reduced by heating the pressure-sensitive adhesive composition. From the viewpoint of solubility, propyl acetate, n-butyl acetate, isobutyl acetate, toluene, xylene, hexane, methyl ethyl ketone, and isopropanol are preferred, and propyl acetate, n-butyl acetate, isobutyl acetate, toluene, and hexane are more preferred.

[0078] The coating method is not particularly limited, and examples thereof include various coating methods using a Mayer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, spin coater, etc. The drying and curing method is also not particularly limited, and examples thereof include hot air drying, infrared rays, reduced pressure methods, and methods using active energy rays, but hot air or steam heating at 60 to 180°C is preferred from the viewpoint of outgassing resistance.

[0079] The pressure-sensitive adhesive composition of the present invention has excellent adhesive strength to low-polarity substrates, heat-resistant adhesive strength, and heat-resistant retention, and can impart an excellent coating film appearance in a cross-cut test, so the pressure-sensitive adhesive sheet of the present invention can be suitably used as a decorative sheet.

[0080] <Decorative sheet> The decorative sheet comprises a substrate and a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition. If necessary, the exposed surface of the pressure-sensitive adhesive layer can be covered with a release sheet. The release sheet is peeled off when the pressure-sensitive adhesive sheet is attached to an adherend. The substrate is not particularly limited, and examples thereof include plastic film, paper, and metal foil. The substrate may also be a laminated sheet in which one or more layers are laminated on at least one surface of the substrate. If necessary, the surface of the substrate on which the pressure-sensitive adhesive layer is to be formed may be subjected to an adhesion-enhancing treatment such as corona discharge treatment or application of an anchor coating agent. The release sheet is not particularly limited, and a known release sheet can be used, in which a known release treatment such as application of a release agent is applied to the surface of a substrate sheet such as a resin sheet or paper.

[0081] Examples of substrates used in decorative sheets include plastic films such as polyester (polyethylene terephthalate, polyethylene naphthalate), polycarbonate, polymethyl methacrylate, polyethylene, polypropylene, cyclic olefin, polyvinyl chloride, polyurethane, polyamide, and ethylene-vinyl acetate copolymer; inorganic materials such as glass plates; nonwoven fabrics; and paper.

[0082] <Release film> The release film is not particularly limited, but a transparent plastic substrate can be suitably used. Examples of materials for the transparent plastic substrate include polyesters such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate, triacetyl cellulose, polysulfone, polyarylate, and polycycloolefin. The plastic materials can be used alone or in combination of two or more.

[0083] Among the transparent plastic substrates described above, a transparent plastic substrate having excellent heat resistance, i.e., a transparent plastic substrate that is suppressed or prevented from deforming under severe conditions such as high temperature, high temperature and high humidity, etc. PET films or sheets are particularly suitable as the transparent plastic substrate.

[0084] The thickness of the transparent plastic substrate is not particularly limited, and is, for example, preferably 10 to 200 μm, more preferably 25 to 150 μm.

[0085] The decorative sheet using the pressure-sensitive adhesive composition can be suitably used for attachment to an adherend by vacuum forming or vacuum-pressure forming. Conventional known methods can be used for vacuum forming or vacuum-pressure forming.

[0086] <Method of manufacturing decorative sheet> A method for producing a decorative sheet having a pressure-sensitive adhesive layer made from the pressure-sensitive adhesive composition will now be described. However, conventionally known methods can be used as appropriate, and the present invention is not limited to the following production method. For example, when using a pressure-sensitive adhesive composition prepared by dissolving in a solvent, the pressure-sensitive adhesive composition diluted with a solvent is coated onto a sheet having a surface layer and a decorative layer formed thereon by knife coating, bar coating, blade coating, doctor coating, roll coating, cast coating, or the like to form a coating film. The sheet can then be heated and dried as needed to form a pressure-sensitive adhesive layer on the sheet. On the other hand, when using a pressure-sensitive adhesive composition prepared by a kneading method using heat, the pressure-sensitive adhesive layer can be formed on the sheet using a hot-melt coater, which can soften the pressure-sensitive adhesive composition by preheating. A decorative sheet having a pressure-sensitive adhesive layer made from the pressure-sensitive adhesive composition exhibits moderate adhesive strength at room temperature (e.g., 25°C) and excellent adhesiveness at high temperatures (e.g., 100 to 150°C), and can maintain these properties for long periods of time at high temperatures (e.g., 80°C for 7 days). Therefore, a decorative sheet having an adhesive layer made of the present adhesive composition can be suitably used for decorating the interior and exterior of aircraft, automobiles, building materials, nursing care and medical fields, electrical appliances, electronic components, smartphones, furniture, musical instruments, Shinkansen window frames, and the like, for example, by three-dimensional surface decoration (Threeimension Overlay Method: TOM molding), a type of vacuum and compressed air molding.

[0087] <Decorative structure and method for manufacturing the same> A decorative sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition can be attached to an adherend to form a decorative structure. The shape of the adherend is not particularly limited, and various shapes of adherends (e.g., three-dimensional molded products) can be used.

[0088] More specifically, the decorative structure may include, for example, a surface layer, a decorative layer, and a pressure-sensitive adhesive layer in this order. The surface layer is a layer that forms the surface of the decorated molded product, and any material conventionally known in the field of decorative sheets may be used as appropriate. The surface layer may be composed of various resins, such as acrylic resin, polyurethane, fluororesin, and polyvinyl chloride. The exposed surface of the surface layer may also be embossed. The decorative layer is used to decorate the object to be decorated, and various materials may be used depending on the intended use. The decorative layer may contain, for example, at least one resin selected from the group consisting of olefin-based resins, styrene-based resins, and vinyl chloride resins. The decorative layer may also optionally include other layers, such as a design layer, a bulk layer, and a bonding layer. The number of layers of the decorative sheet, the type, arrangement, thickness, etc. of each layer may be selected as appropriate and are not particularly limited. The adhesive layer is a layer for attaching a decorative sheet to an adherend (e.g., a molded product formed into a three-dimensional shape), and can be formed by drying the adhesive composition (e.g., after applying it to a substrate) or by crosslinking it by irradiating it with ultraviolet light, etc. [Example]

[0089] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." The blending amounts in the tables are in parts by mass, and amounts other than the solvent are calculated as non-volatile contents. Blank spaces in the tables indicate that no blending was performed. The weight average molecular weights of the block copolymer (A) and the acrylic oligomer (B) are measured by the following method.

[0090] <Measurement of weight average molecular weight (Mw)> The weight-average molecular weight (Mw) was measured by gel permeation chromatography (GPC). The instrument used was a GPC instrument manufactured by Shimadzu Corporation: an LC-GPC system "Prominence." The columns used were TSKgel α-M manufactured by Tosoh Corporation, with two columns connected in series. N,N-dimethylformamide (DMF) was used as the eluent, and measurements were carried out at 40°C. Mw was determined by conversion using polystyrene with a known Mw as the standard substance.

[0091] <Softening point measurement> The softening point of the tackifier resin (C) is determined by the ring and ball method (JIS K 5902) or by a published value such as a literature value or catalog value. If the published value is set as a temperature range, the average value of the lower and upper limits is used.

[0092] <Production Example of Acrylic Oligomer (B)> (Acrylic Oligomer (B-1)) Using a reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping tube, 100 parts of isobornyl methacrylate (IBXMA) as monomer (b1), 0.02 parts of 2,2-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 150 parts of methyl ethyl ketone as a solvent were charged into a reaction vessel and polymerized at 70°C for 5 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to obtain an acrylic oligomer solution (B-1) with a non-volatile content of 40.0±0.5%. The weight average molecular weight (Mw) of the resulting acrylic oligomer is shown in the table.

[0093] (Acrylic oligomers (B-2 to B-19), other oligomers (B'-1 to B'-4)) Acrylic oligomers (B-2 to B-19) and other oligomers (B'-1 to B'-4) were synthesized in the same manner as for the production of acrylic oligomer (B-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Table 1 and the amount of solvent was adjusted appropriately. The weight-average molecular weights and glass transition temperatures of the obtained oligomers are shown in Tables 1 to 3.

[0094] [Table 1]

[0095] [Table 2]

[0096] [Table 3]

[0097] Details of each monomer listed in Tables 1 to 3 above are as follows. "IBXMA": Isobornyl methacrylate (Tg of homopolymer: 180°C) "IBXA": Isobornyl acrylate (Tg of homopolymer: 97°C) "MMA": Methyl methacrylate (Tg of homopolymer: 103°C) "EMA": Ethyl methacrylate (Tg of homopolymer: 65°C) "AA": acrylic acid (Tg of homopolymer: 163°C) "DAM": 2-(dimethylamino)ethyl methacrylate (Tg of homopolymer: 18°C) "HEMA": 2-hydroxyethyl methacrylate (Tg of homopolymer: 55°C) "St": Styrene (Tg of homopolymer: 100°C) "2EHMA": 2-ethylhexyl methacrylate (Tg of homopolymer: -10°C)

[0098] <Preparation of Pressure-Sensitive Adhesive Composition> Example 1 100 parts of A1-3 (Kraton D1119, Kraton Corporation, styrene-isoprene-styrene (SIS) block polymer) as styrene-based elastomer (A1) and 10 parts of acrylic oligomer (B-1) were dissolved in toluene and stirred until homogenous, to obtain a pressure-sensitive adhesive composition with a solids concentration of 40% by mass. Stirring was carried out at 23°C for 3 hours. The solids content refers to the total of all components excluding toluene.

[0099] (Examples 2 to 33, Comparative Examples 1 to 4) As shown in Tables 4 to 6 and 8, pressure-sensitive adhesive compositions were obtained in the same manner as in Example 1, except that the types and amounts of the styrene elastomer (A1) and acrylic oligomer (B) were changed.

[0100] Example 34 100 parts of A1-3 (Kraton D1119, manufactured by Kraton Corporation, a styrene-isoprene-styrene (SIS) block polymer) as the styrene-based elastomer (A1), 10 parts of acrylic oligomer (B-17), and C-3 (Alcon P-140, manufactured by Arakawa Chemical Industries, a fully hydrogenated aromatic petroleum resin) as the tackifier resin (C) were dissolved in toluene and stirred until homogeneous, yielding a pressure-sensitive adhesive composition with a solids concentration of 40% by mass. Stirring was carried out at 23°C for 3 hours. The solids content refers to the total of all components excluding toluene.

[0101] (Examples 35 to 44, Comparative Example 5) As shown in Tables 7 and 8, pressure-sensitive adhesive compositions were obtained in the same manner as in Example 34, except that the types and amounts of the styrene-based elastomer (A1), acrylic oligomer (B), and tackifier resin (C) were changed.

[0102] [Table 4]

[0103] [Table 5]

[0104] [Table 6]

[0105] [Table 7]

[0106] [Table 8]

[0107] Details of the materials in Tables 4 to 8 are as follows:

[0108] (Block copolymer (A)) [Styrene-based elastomer (A1)] A1-1: Kraton D1160; manufactured by Kraton Corporation, styrene-isoprene-styrene (SIS) block polymer, Mw=117,000, styrene content 19% by mass, diblock ratio 0% by mass A1-2: Kraton D1161; manufactured by Kraton Corporation, styrene-isoprene-styrene (SIS) block polymer, Mw=220,000, styrene content 15% by mass, diblock ratio 10% by mass A1-3: Kraton D1119; Kraton Corporation, styrene-isoprene-styrene (SIS) block polymer, Mw=50,000, styrene content 22% by mass, diblock ratio 66% by mass A1-4: Kraton D1118, manufactured by Kraton Corporation, styrene-butadiene-styrene (SBS) block polymer, Mw=80,000, styrene content 33% by mass, diblock ratio 78% by mass A1-5: Kraton G1657; Kraton Corporation, styrene-ethylene-butylene-styrene (SEBS) block polymer, Mw=115,000, styrene content 13% by mass, diblock ratio 30% by mass A1-6: Septon 2063; manufactured by Asahi Kasei Corporation, styrene-ethylene-propylene-styrene (SEPS) block polymer, Mw=100,000, styrene content 13% by mass, diblock ratio 60% by mass [Other block copolymers (A2) other than (A1)] A2-1: Clarity LA2140; manufactured by Kuraray Co., Ltd. Polymethyl methacrylate (PMMA)-polybutyl acrylate (PBA)-PMMA block polymer, Mw=69,000, PMMA content 20% by mass, diblock ratio 0% by mass

[0109] (Tackifying resin (C)) C-1: YS Polyster TH130; manufactured by Yasuhara Chemical Co., Ltd., hydrogenated terpene phenolic resin, softening point 130°C C-2: YS Polyster T80; manufactured by Yasuhara Chemical Co., Ltd., terpene phenol resin, softening point 80°C C-3: Alcon P-140; Arakawa Chemical Co., Ltd., fully hydrogenated aromatic petroleum resin, softening point 140°C C-4: Endex 155; Eastman aromatic petroleum resin, softening point 153°C C-5: YS Polyster T160; manufactured by Yasuhara Chemical Co., Ltd., terpene phenol resin, softening point 160°C

[0110] (Preparation of adhesive sheet) The obtained adhesive composition was applied to a 38 μm thick polyethylene terephthalate release sheet using a comma coater so that the dried thickness would be 50 μm, and the sheet was dried for 2 minutes at 100° C. to obtain an adhesive sheet. Next, one side of a 100 μm thick polyethylene terephthalate film (hereinafter referred to as PET film, product name: A-4300, manufactured by Toyobo Co., Ltd.) was bonded to the adhesive surface of the adhesive sheet to prepare a laminate consisting of "release sheet / adhesive layer / PET film," and a test adhesive sheet was obtained.

[0111] <Evaluation of physical properties of pressure-sensitive adhesive composition> The adhesive strength of the resulting adhesive composition to a low-polarity adherend, heat-resistant adhesive strength, heat-resistant retention, and coating appearance after processing were evaluated by a cross-cut test using the following method.

[0112] <Adhesive strength> A test piece measuring 25 mm in width and 150 mm in length was cut out from the adhesive sheet prepared by the above method. The release sheet was peeled off from the cut decorative sheet, and the exposed adhesive layer was pressed onto a polypropylene (PP) plate as an adherend by moving a 2 kg pressure roller back and forth once to obtain a test piece. The test piece was left to stand in a thermostatic chamber at 23°C for 24 hours, and then the 180° angle peel strength (peel speed: 300 mm / min) of the test piece was measured in the thermostatic chamber at 23°C, and this was taken as the adhesive strength. [Evaluation criteria] ◎(Excellent): 20N / 25mm or more Good: 15N / 25mm or more, less than 20N / 25mm △ (Practical): 5N / 25mm or more, less than 15N / 25mm × (Not practical): Less than 5N / 25mm

[0113] <Heat-resistant adhesive strength> Test pieces were obtained in the same manner as in the evaluation of adhesive strength. The test pieces were then left to stand for 1 hour in a thermostatic chamber at 80°C, and the 180° angle peel strength (peel speed: 300 mm / min) of the test pieces was measured in an 80°C atmosphere to determine the heat-resistant adhesive strength. [Evaluation criteria] ◎(Excellent): 20N / 25mm or more Good: 15N / 25mm or more, less than 20N / 25mm △ (Practical): 5N / 25mm or more, less than 15N / 25mm × (Not practical): Less than 5N / 25mm

[0114] <Heat-resistance holding power> A test piece measuring 25 mm wide and 80 mm long was cut from the adhesive sheet prepared using the method described above. The release sheet was peeled off from the cut decorative sheet, and the exposed adhesive layer was then attached to a polypropylene (PP) plate as an adherend, with a bonding area of ​​25 mm x 25 mm, by pressing the adhesive layer back and forth once with a 1 kg pressure roller to obtain a test piece. The test piece was then left to stand in an 80°C atmosphere for 20 minutes, and then placed in an 80°C oven with a 1 kg load applied parallel to the adhesive layer surface. 24 hours after the load application began, the displacement (mm) from the original position was measured to evaluate heat resistance. [Evaluation criteria] ◎ (Excellent): 0mm (no deviation) 〇 (Good): Over 0mm and less than 5mm △ (Practical): 5mm or more, less than 25mm × (Not practical): 25mm or more

[0115] <Cross-cut test> The test laminate obtained above was attached to the frame of a TOM molding machine (NGF molding machine, manufactured by Fuse Vacuum Co., Ltd.), and a PP resin mortar cup with an inner diameter of 66 mm, an outer diameter of 70 mm, and a height of 38 mm was placed inside the frame. The PP resin mortar cup was then covered with the test laminate, resulting in a decorated structure. The top and curved surfaces of this decorated structure were cut crosswise with a cutter and left in an 80°C environment for 1000 hours. The presence or absence of lifting or peeling was visually inspected and evaluated according to the following criteria. [Evaluation criteria] ◎ (Excellent): No lifting or peeling is observed. ◯ (Good): At least one of lifting and peeling is observed, and the size or distance is 0.5 mm or less. △ (suitable for use): At least one of bubbling, lifting, and peeling is observed, and the size or distance is more than 0.5 mm and 1 mm or less. × (unsuitable for practical use): At least one of bubbling, lifting, and peeling is observed, and the size or distance is more than 1 mm and 1.5 mm or less.

[0116] The present invention is not limited to the above-described embodiments and examples, and appropriate design changes are possible without departing from the spirit of the present invention.

[0117] As shown in Examples 1 to 44 in Tables 4 to 7, the pressure-sensitive adhesive compositions of the present invention were excellent in adhesion to low-polarity adherends, heat-resistant adhesion, heat-resistant retention, and coating appearance after processing (cross-cut test).

[0118] On the other hand, the adhesive composition shown in Comparative Example 1 in Table 8 is an embodiment in which the block copolymer (A) does not contain the styrene-based elastomer (A1), and the adhesive strength and heat-resistant adhesive strength to low-polarity adherends were poor.

[0119] Furthermore, the adhesive compositions shown in Comparative Examples 2 and 3 in Table 8 did not contain a (meth)acrylic monomer (b1) whose homopolymer had a glass transition temperature of 60°C or higher, and exhibited poor adhesive strength and heat-resistant adhesive strength to low-polarity substrates in the cross-cut test.

[0120] In addition, the adhesive compositions shown in Comparative Examples 4 and 5 in Table 8 had a weight average molecular weight of the acrylic oligomer (B) outside the range of 5,000 to 200,000, and exhibited poor heat-resistant holding power, adhesive strength to low-polarity adherends, and heat-resistant adhesive strength. [Industrial Applicability]

[0121] The pressure-sensitive adhesive composition of the present invention has excellent adhesion to low-polarity adherends, heat-resistant adhesion, heat-resistant retention, and cross-cut test results (appearance of coating after molding), and therefore can be suitably used for decorating, for example, aircraft, automobiles, railways, interior and exterior building materials, the nursing and medical fields, and electrical appliances.

Claims

1. A pressure-sensitive adhesive composition comprising a block copolymer (A) and an acrylic oligomer (B), and optionally a tackifying resin (C), The block copolymer (A) contains a styrene-based elastomer (A1) having a soft block composed of at least one of polybutadiene and polyisoprene and a hard block composed of a polymer of a vinyl aromatic compound, the content of the styrene-based elastomer (A1) is 90 to 100% by mass based on 100% by mass of the block copolymer (A); The acrylic oligomer (B) is a copolymer of a monomer mixture containing a (meth)acrylic monomer (b1) having a glass transition temperature of 60°C or higher as a homopolymer, the content of the acrylic monomer (b1) is 45 to 100 mass% in 100 mass% of the monomer mixture constituting the acrylic oligomer (B); The weight average molecular weight of the acrylic oligomer (B) is in the range of 5,000 to 200,000; the glass transition temperature of the acrylic oligomer (B) is 30°C or higher and lower than 180°C; A pressure-sensitive adhesive composition, characterized in that the content of an acrylic oligomer (B) is 1 to 30 parts by mass relative to 100 parts by mass of a block copolymer (A), and the content of a tackifier resin (C) is 155 parts by mass or less.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the diblock ratio in 100% by mass of the block copolymer (A) is 10 to 80% by mass.

3. The pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic monomer (b1) having a glass transition temperature of 60°C or higher as a homopolymer is a (meth)acrylic monomer having a ring structure.

4. The pressure-sensitive adhesive composition according to claim 1 , wherein the monomer mixture constituting the acrylic oligomer (B) further contains a monomer (b2) having a functional group.

5. The pressure-sensitive adhesive composition according to claim 4, wherein the content of the monomer (b2) having a functional group is 0.01 to 10 mass% in 100 mass% of the monomer mixture constituting the acrylic oligomer (B).

6. The pressure-sensitive adhesive composition according to claim 1, comprising 1 to 150 parts by mass of the tackifier resin (C) per 100 parts by mass of the block copolymer (A).

7. The pressure-sensitive adhesive composition according to claim 6 , wherein the tackifier resin (C) comprises a hydrocarbon resin.

8. 8. The pressure-sensitive adhesive composition according to claim 7, wherein the hydrocarbon resin comprises at least one of an unhydrogenated aromatic petroleum resin and a hydrogenated aromatic petroleum resin.

9. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition according to any one of claims 1 to 8.

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