Pressure-sensitive adhesive composition for decorative sheet, decorative sheet, and decorative structure

Abstract

To provide a pressure-sensitive adhesive composition for a decorative sheet, which is excellent in adhesion to a low-polarity adherend, heat-resistant adhesion, heat-resistant holding power, and transparency / moldability (coating appearance after molding) in decoration of a molded article, and to provide a decorative sheet and a decorative structure.SOLUTION: The problem is solved by a pressure-sensitive adhesive composition for a decorative sheet containing a block copolymer (A) and a tackifier resin (B), the pressure-sensitive adhesive composition containing a styrene-based elastomer (a- 1) 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 tackifier resin (B) having a softening point of 125 to 200 °C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition for a decorative sheet, a decorative sheet, and a decorative structure. [Background technology]

[0002] Decorating the exterior surfaces of molded products such as automobile interior and exterior parts, keyboards, home appliances, smartphones, housing materials, furniture, musical instruments, and Shinkansen window frames with decorative films (decorative sheets) is a common method for improving the appearance of these products. Known methods for decorating three-dimensional molded products with decorative sheets include insert molding, in-mold molding, vacuum forming, and vacuum-compressed air forming.

[0003] The insert molding method is a method of producing a decorated molded product by first forming a decorative sheet into a predetermined shape and inserting it into a mold, then injecting heated molten resin into the mold under pressure and cooling and solidifying it to integrate the decorative sheet and the molded product. The in-mold molding method is a method of producing a decorated molded product by placing a film with a printed design in the mold via a release layer, injecting heated molten resin, cooling and solidifying it, and then peeling off the film to transfer the design. In this way, with the insert molding and in-mold molding methods, the molded product is decorated at the same time as it is formed, and the design is formed on the exterior surface of the molded product.

[0004] On the other hand, vacuum forming is a method in which a decorative sheet is softened by applying heat, and the air between the decorative sheet and the molded product is removed from the molded product side, creating a vacuum-like state and adhering the decorative sheet to the molded product. Vacuum pressure forming is a method in which a vacuum-like state is similarly created, and then air pressure is applied from the decorative sheet side above the molded product to adhere the decorative sheet to the molded product. Thus, vacuum forming and vacuum pressure forming are methods of decorating a molded product by laminating a decorative sheet at room temperature after the molded product is completed and then heating it. In other words, because the decorative sheet is applied to the exterior surface of the molded product in a separate process from the molding of the molded product, a single machine can be used to apply the decorative sheet to molded products of various shapes. Furthermore, vacuum forming and vacuum pressure forming are widely used because they enable continuous coating from the front to the back of the molded product at the edge, i.e., wrap-around coating, which is difficult to achieve with in-mold molding and other methods.

[0005] Compared to acrylonitrile-butadiene-styrene resin (hereinafter referred to as ABS resin), which is commonly used as an adherend material, polypropylene resin (hereinafter referred to as PP resin) has a low specific gravity and excellent thermoformability. For this reason, in recent years, PP resin has been increasingly used as an adherend to reduce weight and improve processability. Adhesives are used to attach decorative sheets to adherends, and there is a growing need for adhesives that can bond decorative sheets to low-polarity materials such as PP resin.

[0006] 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 compound 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]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2020-139099 Summary of the Invention [Problem to be solved by the invention]

[0008] Typically, when decorative sheets are attached to molded products using vacuum or vacuum-pressure forming, the molded products are expected to be used in a variety of environments. Therefore, heat-resistance retention is also important, preventing poor appearance, such as lifting or peeling at the adhesive interface with the adhesive layer, even in high-temperature environments. Since PP resin is a low-polarity material and therefore difficult to bond to, ensuring these properties presents a challenge. Furthermore, high transparency is becoming increasingly important from the perspective of design, and there is a demand for adhesive compositions for decorative sheets that can satisfy these various performance requirements in a well-balanced manner.

[0009] The inventors have conducted studies 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.

[0010] In other words, no pressure-sensitive adhesive composition for decorative sheets has been developed to date that can impart adhesive strength to low-polarity adherends, heat-resistant adhesive strength, heat-resistant retention, an appearance with excellent transparency, and excellent moldability when decorating molded articles. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. The pressure-sensitive adhesive composition for decorative sheets, the decorative sheet, and the decorative structure according to the present invention have the following constitutions [1] to [9].

[0012] [1] A pressure-sensitive adhesive composition for decorative sheets, comprising a block copolymer (A) and a tackifier resin (B), wherein the block copolymer (A) contains a styrene-based elastomer (A-1), and the styrene-based elastomer (A-1) has 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 softening point of the tackifier resin (B) is 125 to 200°C.

[0013] [2] The pressure-sensitive adhesive composition for decorative sheets according to [1], wherein the diblock ratio in 100% by mass of the block copolymer (A) is 10 to 80% by mass.

[0014] [3] The pressure-sensitive adhesive composition for decorative sheets according to [1] or [2], wherein the block copolymer (A) further comprises a styrene-based elastomer (A-2) having a soft block consisting of at least one of hydrogenated polybutadiene and hydrogenated polyisoprene, and a hard block consisting of a polymer of a vinyl aromatic compound.

[0015] [4] The pressure-sensitive adhesive composition for decorative sheets according to [3], which contains 0.1 to 20 mass % of a styrene-based elastomer (A-2) based on 100 mass % of the block copolymer (A).

[0016] [5] The pressure-sensitive adhesive composition for decorative sheets according to any one of [1] to [4], wherein the tackifier resin (B) contains a hydrocarbon resin.

[0017] [6] The pressure-sensitive adhesive composition for decorative sheets according to [5], wherein the hydrocarbon resin contains at least one of an aromatic petroleum resin and a hydrogenated aromatic petroleum resin.

[0018] [7] The pressure-sensitive adhesive composition for decorative sheets according to any one of [1] to [6], which is used for attachment to an adherend by vacuum forming or vacuum-pressure forming.

[0019] [8] A decorative sheet comprising a substrate and an adhesive layer made of the adhesive composition for decorative sheets according to any one of [1] to [7].

[0020] [9] A decorative structure comprising an adherend and the decorative sheet according to [8]. [Effects of the Invention]

[0021] The present invention makes it possible to provide a pressure-sensitive adhesive composition for decorative sheets, a decorative sheet, and a decorative structure that can impart excellent adhesion to low-polarity adherends, heat-resistant adhesion, heat-resistant retention, and an appearance with excellent transparency and excellent formability when decorating molded articles. It has been discovered that when an adhesive layer is formed from a pressure-sensitive adhesive composition containing a predetermined block copolymer (A) and a tackifier resin (B), it is possible to impart excellent adhesion to low-polarity adherends, heat-resistant adhesion, and heat-resistant retention, an appearance with excellent transparency, and excellent formability when decorating molded articles. DETAILED DESCRIPTION OF THE INVENTION

[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 term "sheet" refers to a flexible laminate, and includes thin laminates called "films."

[0023] <Adhesive composition for decorative sheets> The adhesive composition for decorative sheets of the present invention (hereinafter sometimes abbreviated as adhesive composition) comprises a block copolymer (A) and a tackifier resin (B), wherein the block copolymer (A) contains a styrene-based elastomer (A-1) 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 wherein the softening point of the tackifier resin (B) is 125 to 200°C.

[0024] <Block copolymer (A)> The block copolymer (A) is a thermoplastic block copolymer having a soft block (X) and a hard block (Y), and examples thereof include styrene-based elastomers, olefin-based elastomers, polyester-based elastomers, vinyl chloride resin-based elastomers, acrylic elastomers, urethane-based elastomers, polyamide-based elastomers, etc. Among these, styrene-based elastomers, which are block copolymers 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, are preferred.

[0025] The molecular structure of the block copolymer (A) 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 (radial), or YXYXY (multiblock), where n is an integer of 1 or greater. Among these, diblock structures, triblock structures, and combinations thereof are preferred, as they provide good adhesive strength, heat-resistant retention, and moldability.

[0026] The compound constituting the soft block is preferably a conjugated diene compound. Examples include butadiene, isoprene, 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.

[0027] The compound constituting the hard block is preferably a vinyl aromatic compound, such as styrene, α-methylstyrene, vinyltoluene, p-tertiary butylstyrene, divinylbenzene, p-methylstyrene, or 1,1-diphenylstyrene, and among these, styrene is more preferred because it provides good heat resistance retention.

[0028] 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.

[0029] 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.

[0030] 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 further improved. By making the weight-average molecular weight of the block copolymer (A) 500,000 or less, the viscosity can be reduced and the moldability can be further improved.

[0031] The block copolymer (A) contains a styrene-based elastomer (A-1) 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 styrene-based elastomer (A-1) is not particularly limited as long as it is a commonly used elastomer, but styrene-isoprene-styrene (SIS) block polymers and styrene-butadiene-styrene (SBS) block polymers are preferred. Specific examples include Kraton's Kraton D series and Zeon's Quintac series. The styrene-based elastomer (A-1) has a structural unit derived from a conjugated diene compound that contains a double bond of an unsaturated carbon, which enhances the wettability of the adhesive and allows it to exhibit excellent adhesion to low-polarity materials such as PP resin.

[0032] The content of the styrene elastomer (A-1) in 100% by mass of the block copolymer (A) is preferably 60 to 100% by mass, more preferably 80 to 100% by mass. By making the content of the styrene elastomer (A-1) in 100% by mass of the block copolymer (A) 60% or more, the adhesive strength to low-polarity materials such as PP resin and heat resistance retention are improved.

[0033] The block copolymer (A) preferably further contains a styrene-based elastomer (A-2) having a soft block composed of at least one of hydrogenated polybutadiene and hydrogenated polyisoprene and a hard block composed of a polymer of a vinyl aromatic compound. The styrene-based elastomer (A-2) is a hydrogenated product of the styrene-based elastomer (A-1) and may be fully or partially hydrogenated. That is, even if the soft block contains at least one of polybutadiene and polyisoprene, if it contains at least one of hydrogenated polybutadiene and hydrogenated polyisoprene, it is classified as a styrene-based elastomer (A-2). The styrene-based elastomer (A-2) is not particularly limited as long as it is a commonly used elastomer, but styrene-ethylene-butylene-styrene (SEBS) block polymers and styrene-ethylene-propylene-styrene (SEPS) block polymers are preferred. Specific examples include Kraton's Kraton G series and Asahi Kasei's Tuftec series. The styrene-based elastomer (A-2) is used to impart cohesive strength to the coating film, improving its heat-resistant retention.

[0034] The content of the styrene elastomer (A-2) in 100% by mass of the block copolymer (A) is preferably 0.1 to 20% by mass, more preferably 0.1 to 10% by mass, and even more preferably 2 to 5% by mass. By setting the content of the styrene elastomer (A-2) to 0.1% by mass or more, the cohesive strength of the coating film is improved and the heat resistance retention is further improved, and by setting the content of the styrene elastomer (A-2) to 20% by mass or less, an appearance with excellent transparency can be imparted.

[0035] The block copolymer (A) may contain other block copolymers in addition to the styrene-based elastomers (A-1) and (A-2). The content of the other block copolymers is preferably less than 10% by mass relative to 100% by mass of the block copolymer (A). If the content of the other block copolymers is less than 10% by mass, good compatibility and appropriate adhesive strength can be easily obtained.

[0036] <Tackifying resin (B)> The tackifier resin (B) is not particularly limited as long as it has a softening point of 125 to 200°C. Examples include aliphatic petroleum resins (C5 petroleum resins), aromatic petroleum resins (C9 petroleum resins or styrene petroleum resins), alicyclic petroleum resins (dicyclopentadiene 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, 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 may be used alone or in combination of two or more. Among these, hydrocarbon resins, rosin ester resins, and terpene phenol resins are preferred because they have good compatibility and can improve adhesion to low-polarity materials such as PP resins, and among these, hydrocarbon resins are more preferred, with aromatic petroleum resins and hydrogenated aromatic petroleum resins being even more preferred. Note that aromatic petroleum resins refer to non-hydrogenated aromatic petroleum resins and exclude hydrogenated aromatic petroleum resins.

[0037] The tackifying resin (B) 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.

[0038] The softening point of the tackifier resin (B) is 125 to 200°C, preferably 135 to 160°C. When the softening point of the tackifier resin (B) 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 K5601-2-2.

[0039] The content of the tackifier resin (B) is preferably 5 to 200 parts by mass, more preferably 20 to 150 parts by mass, and even more preferably 40 to 100 parts by mass, per 100 parts by mass of the block copolymer (A). By using 5 parts by mass or more of the tackifier resin (B) per 100 parts by mass of the block copolymer (A), excellent adhesion to low-polarity materials such as PP resin is achieved, and by using 200 parts by mass or less of the tackifier resin, moldability can be maintained.

[0040] In addition to the block copolymer (A) and the tackifying resin (B), the pressure-sensitive adhesive composition may contain, as necessary, any additives such as a solvent, other resins other than the block copolymer (A), 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 in which the effects of the present invention can be obtained.

[0041] 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.

[0042] 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, methyl ethyl ketone, and isopropanol are preferably used, and n-butyl acetate, isobutyl acetate, and toluene are more preferably used.

[0043] <Method of manufacturing pressure-sensitive adhesive composition> A method for producing a pressure-sensitive adhesive composition will now 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) and the tackifier resin (B) 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 tackifier resin (B) and any additives using a stirrer, kneader, or the like.

[0044] <Decorative sheet> The pressure-sensitive adhesive composition of the present invention described above is used for decorative sheets. The decorative sheet of the present invention (hereinafter also referred to as the present decorative sheet) comprises a substrate and an adhesive layer made of the present pressure-sensitive adhesive composition. If necessary, the exposed surface of the 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 resin sheets, paper, and metal foils. The substrate may also be a laminate 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 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 known release sheets 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.

[0045] 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.

[0046] The decorative sheet using the pressure-sensitive adhesive composition is used for attachment to an adherend by vacuum forming or vacuum-pressure forming, and conventionally known vacuum forming or vacuum-pressure forming methods can be used as appropriate.

[0047] <Method of manufacturing decorative sheet> A method for producing the decorative sheet having an adhesive layer will now be described. However, conventionally known methods can be used as appropriate, and the present invention is not limited to the following manufacturing 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 an adhesive layer. On the other hand, when using a pressure-sensitive adhesive composition prepared by a kneading method using heat, a hot-melt coater, which can soften the pressure-sensitive adhesive composition by preheating, can be used to form an adhesive layer on the sheet. If the block copolymer (A) contained in the composition requires crosslinking by active energy rays, the composition can be coated on the sheet and then irradiated with active energy rays to form an adhesive layer (crosslinked product) on the sheet. In this case, for example, a belt-conveyor type ultraviolet irradiation device can be used to irradiate the pressure-sensitive adhesive composition coated on the sheet with ultraviolet light to obtain an adhesive layer. The ultraviolet irradiation dose can be, for example, 500 mJ / cm. 2 More than 5000mJ / cm 2 The decorative sheet has moderate adhesive strength at room temperature (e.g., 25°C), excellent adhesiveness when bonded at high temperatures (e.g., 100 to 150°C), and can maintain its properties at high temperatures for long periods (e.g., 7 days at 80°C). Therefore, the decorative sheet can be suitably used for decorating the interior and exterior of aircraft, automobiles, and building materials, the nursing and medical fields, electrical appliances, electronic components, smartphones, furniture, musical instruments, and Shinkansen window frames and walls, using three-dimensional surface decoration (Three-Dimensional Overlay Method: TOM molding), a type of vacuum and pressure forming.

[0048] <Decorative structure and method for manufacturing the same> The decorated structure according to the present invention (hereinafter also referred to as the present structure) comprises an adherend and a decorative sheet. It can be formed by attaching the decorative sheet to the adherend using the present pressure-sensitive adhesive composition. The adherend is not particularly limited, and various shapes of objects (for example, three-dimensional molded products) can be used.

[0049] More specifically, the decorative structure may include, for example, a surface layer, a decorative layer, and an adhesive layer in this order. The surface layer is the 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]

[0050] The present invention will be explained in more detail below with reference to Production Examples and Examples. However, the present invention is not limited to the following Examples. Hereinafter, "parts" means "parts by mass" and "%" means "% by mass." The blending amounts of raw materials (excluding solvents) shown in the following Examples and Tables are calculated on a non-volatile basis.

[0051] [Measurement of weight-average molecular weight] The weight average molecular weight (Mw) was measured by gel permeation chromatography (GPC) under the following conditions. Note that Mw is a polystyrene equivalent value. Measurement equipment: GPC equipment "SHODEX GPC-101" manufactured by Shoko Science Co., Ltd. Column: KF-G 4A / KF-805 / KF-803 / KF-802 Temperature: 40℃ Eluent: tetrahydrofuran (THF) Flow rate: 1.0mL / min Detector: RI (differential refractometer)

[0052] [Softening point measurement] The softening point of tackifier resin (B) 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.

[0053] Example 1 (Preparation of Pressure-Sensitive Adhesive Composition) 100 parts by weight of Kraton D1119 (a styrene-isoprene-styrene (SIS) block polymer manufactured by Kraton) as the styrene-based elastomer (A-1), 40 parts by weight of YS Polystar T130 (a terpene phenol resin manufactured by Yasuhara Chemical Co., Ltd.) as the tackifier resin (B), and 1 part by weight of Irganox 1010 (an antioxidant manufactured by BASF) as the additive were dissolved in toluene and stirred until homogeneous, to obtain a pressure-sensitive adhesive composition with a solids concentration of 45% by weight. The mixture was stirred at 23°C for 3 hours. The solids content refers to the total of all components excluding toluene.

[0054] (Examples 2 to 13, 19, and 21) A pressure-sensitive adhesive composition was obtained in the same manner as in Example 1 using the composition shown in Table 1.

[0055] (Examples 14 to 18, 20) A pressure-sensitive adhesive composition was obtained in the same manner as in Example 1, except that Kraton G1657 (a styrene-ethylene-butylene-styrene (SEBS) block polymer manufactured by Kraton Corporation) was added as the styrene-based elastomer (A-2) in addition to the styrene-based elastomer (A-1) in the amounts shown in Table 2.

[0056] (Comparative Example 1) An adhesive composition was obtained in the same manner as in Example 1, except that 100 parts by mass of Septon 2063 (Asahi Kasei Corporation, styrene-ethylene propylene-styrene (SEPS) block polymer) was added as the styrene-based elastomer (A-2), 70 parts by mass of Alcon P140 (Arakawa Chemical Industries, Ltd., fully hydrogenated aromatic petroleum resin) was added as the tackifying resin (B), and 1 part by mass of Irganox 1010 (BASF, antioxidant) was added as an additive.

[0057] (Comparative Example 2) As shown in Table 1, a pressure-sensitive adhesive composition was obtained in the same manner as in Comparative Example 1, except that tackifier resin (B) was not used and the tackifier resin other than (B) was changed to FTR8100 (a copolymer of styrene-based monomers, manufactured by Mitsui Chemicals, Inc.).

[0058] (Production of decorative sheets) The resulting adhesive composition was applied to the release-treated surface of a polyethylene terephthalate (PET) film (38 μm thick) with one side treated for release, so that the dry thickness would be 50 μm. After drying at 105°C for 2 minutes, the composition was attached to the untreated surface of a 50 μm thick PET film to produce a decorative sheet.

[0059] <Evaluation of physical properties of pressure-sensitive adhesive composition> The adhesive strength to low-polarity adherends, heat-resistant adhesive strength, heat-resistant retention, and transparency and moldability (appearance of coating after molding) of the resulting adhesive compositions were evaluated by the following methods.

[0060] <Adhesive strength> A test piece measuring 25 mm in width and 150 mm in length was cut out from the decorative sheet produced by the above method. The release sheet was peeled off from the cut-out 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): 15N / 25mm or more Good: 10N / 25mm or more, less than 15N / 25mm △ (Practical): 1N / 25mm or more, less than 10N / 25mm × (Not practical): Less than 1N / 25mm

[0061] <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): 10N / 25mm or more Good: 3N / 25mm or more, less than 10N / 25mm △ (Practical): 1N / 25mm or more, less than 3N / 25mm × (Not practical): Less than 1N / 25mm

[0062] <Heat-resistance holding power> A test piece measuring 25 mm wide and 80 mm long was cut from the decorative 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. 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

[0063] <Transparency and moldability (appearance of coating after molding)> The decorative sheet prepared by the above method 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 decorative sheet to obtain a decorated structure. The appearance of the coating film after molding was evaluated based on the following evaluation criteria. [Evaluation criteria] ◎ (Excellent): The decorative sheet is transparent and no lifting or peeling is observed. 〇 (Good): The decorative sheet is transparent, but there is slight lifting or peeling only at the edges. △ (Practical): The decorative sheet is transparent, but there is some lifting or peeling in some areas other than the edges. × (Not practical): The decorative sheet is opaque or peels off over the entire surface

[0064] [Table 1]

[0065] [Table 2]

[0066] The details of the materials in Tables 1 and 2 are as follows:

[0067] (Styrene-based elastomer (A-1)) Kraton D1160: Kraton Corporation, styrene-isoprene-styrene (SIS) block polymer, Mw = 117,000, styrene content 19% by mass, diblock ratio 0% by mass Kraton D1161: Kraton Corporation, styrene-isoprene-styrene (SIS) block polymer, Mw = 220,000, styrene content 15% by mass, diblock ratio 10% by mass. Kraton D1119: Kraton Corporation, styrene-isoprene-styrene (SIS) block polymer, Mw=50,000, styrene content 22% by mass, diblock ratio 66% by mass 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

[0068] (Styrene-based elastomer (A-2)) Kraton G1657: Kraton Corporation, styrene-ethylene-butylene-styrene (SEBS) block polymer, Mw=115,000, styrene content 13% by mass, diblock ratio 30% by mass. Septon 2063: Asahi Kasei Corporation, styrene-ethylene-propylene-styrene (SEPS) block polymer, Mw=100,000, styrene content 13% by mass, diblock ratio 60% by mass

[0069] (tackifying resin) YS Polyster T130: Terpene phenol resin manufactured by Yasuhara Chemical Co., Ltd., softening point 130°C YS Polyster T160: Terpene phenol resin manufactured by Yasuhara Chemical Co., Ltd., softening point 160°C Alcon P-125: Arakawa Chemical Co., Ltd., fully hydrogenated aromatic petroleum resin, softening point 125°C Alcon P-140: Arakawa Chemical Co., Ltd., fully hydrogenated aromatic petroleum resin, softening point 140°C Endex 155: Eastman aromatic petroleum resin, softening point 153°C FTR8100: Mitsui Chemicals, aromatic petroleum resin, softening point 100°C

[0070] (additives) Irganox 1010: BASF hindered phenolic antioxidant

[0071] 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.

[0072] As shown in Examples 1 to 21 in Tables 1 and 2, the pressure-sensitive adhesive compositions of the present invention were excellent in adhesion to low-polarity adherends, heat-resistant adhesion, heat-resistant retention, and transparency and moldability (appearance of the coating after molding).

[0073] On the other hand, the pressure-sensitive adhesive composition shown in Comparative Example 1 in Table 2 does not contain a styrene-based elastomer (A-1) having a soft block consisting of at least one of polybutadiene and polyisoprene and a hard block consisting of a polymer of a vinyl aromatic compound, and the heat resistance retention was not practical.

[0074] The adhesive composition shown in Comparative Example 2 in Table 2 did not contain a tackifier resin (B) having a softening point of 125 to 200°C, and the heat-resistant adhesive strength and heat-resistant retention were not practically usable. [Industrial Applicability]

[0075] The pressure-sensitive adhesive composition of the present invention has excellent adhesion to low-polarity substrates, heat-resistant adhesion, heat-resistant retention, and transparency and moldability (appearance of the coating after molding), and is therefore suitable for use in the decoration of, for example, aircraft, automobiles, railways, interior and exterior building materials, the nursing and medical fields, and electrical appliances. Its applications are not particularly limited, but are preferably used for automobile interior and exterior parts, home appliances, smartphones, and housing building materials, more preferably for automobile interior and exterior parts and housing building materials, and particularly preferably for automobile interior and exterior parts. Furthermore, known methods for decoration using decorative sheets include insert molding, in-mold molding, vacuum forming, and vacuum-pressure forming. Although not particularly limited, vacuum forming and vacuum-pressure forming are particularly preferred.

Claims

1. A pressure-sensitive adhesive composition for decorative sheets, comprising a block copolymer (A) and a tackifier resin (B), The block copolymer (A) contains a styrene-based elastomer (A-1), The styrene-based elastomer (A-1) has 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, A pressure-sensitive adhesive composition for decorative sheets, wherein the softening point of the tackifier resin (B) is 125 to 200°C.

2. 2. The pressure-sensitive adhesive composition for decorative sheets 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 for decorative sheets according to claim 1, wherein the block copolymer (A) further comprises a styrene-based elastomer (A-2) having a soft block consisting of at least one of hydrogenated polybutadiene and hydrogenated polyisoprene, and a hard block consisting of a polymer of a vinyl aromatic compound.

4. 4. The pressure-sensitive adhesive composition for decorative sheets according to claim 3, wherein the block copolymer (A) contains 100% by mass of the styrene elastomer (A-2) in an amount of 0.1 to 20% by mass.

5. 2. The adhesive composition for decorative sheets according to claim 1, wherein the tackifier resin (B) comprises a hydrocarbon resin.

6. 6. The pressure-sensitive adhesive composition for decorative sheets according to claim 5, wherein the hydrocarbon resin comprises at least one of an aromatic petroleum resin and a hydrogenated aromatic petroleum resin.

7. The adhesive composition for decorative sheets according to any one of claims 1 to 6, which is used for attachment to an adherend by vacuum forming or vacuum-pressure forming.

8. A decorative sheet comprising a substrate and an adhesive layer made of the adhesive composition for decorative sheets according to claim 7.

9. A decorative structure comprising an adherend and the decorative sheet according to claim 8.

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