Substrate-less double-sided adhesive tape

Abstract

To provide a substrate-less double-sided adhesive tape that has excellent adhesiveness at high temperatures and has excellent re-releasability at normal temperature.SOLUTION: A substrate-less double-sided adhesive tape of the invention includes an adhesive layer, a displacement occurred when a test of planar rebound resistance is conducted at a temperature of 180°C is 0.5 mm or less, and 180° peeling adhesive strength with respect to a SUS plate measured at a temperature of 23°C according to JIS Z0237:2009 is 12 N / 25 mm or less. The substrate-less double-sided adhesive tape has a thickness of 200 μm or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a substrate-less double-sided pressure-sensitive adhesive tape. [Background technology]

[0002] Conventionally, adhesive tapes having an adhesive layer made of an adhesive have been widely used to fix various parts in products such as electrical appliances, vehicles, houses, and building materials. As an adhesive, an adhesive containing an acrylic polymer mainly composed of a structural unit derived from acrylic (meth)acrylate such as 2-ethylhexyl acrylate or n-butyl acrylate is known (see, for example, Patent Documents 1 and 2). In addition, from the viewpoint of environmental consideration, it is desirable to separate and collect the double-sided adhesive tape used in the product when disposing of the product. For this reason, in order to easily peel the double-sided adhesive tape from the adherend, it is desirable for the double-sided adhesive tape to have removability. As a double-sided adhesive tape having removability, for example, a removable adhesive sheet described in Patent Document 3 is known as a conventional technology. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-021067 A [Patent Document 2] JP 2015-120876 A [Patent Document 3] JP 2009-24130 A Summary of the Invention [Problem to be solved by the invention]

[0004] Currently, automobiles are shifting to electric vehicles. Electric vehicles use parts that generate heat, such as motors, batteries, and power electronics parts, so double-sided adhesive tapes are often used in high-temperature environments. In addition, from an environmental perspective, it is desirable for double-sided adhesive tapes to be collected separately when electric vehicles are disposed of. For this reason, double-sided adhesive tapes used in electric vehicles are also required to be removably. However, when imparting removability to a double-sided adhesive sheet, the adhesive strength of the double-sided adhesive tape is usually reduced, resulting in a problem that the adhesive strength of the double-sided adhesive tape weakens in the high-temperature environments in which the double-sided adhesive tape is used in electric vehicles. Therefore, an object of the present invention is to provide a substrate-less double-sided pressure-sensitive adhesive tape that has excellent adhesive properties at high temperatures and also has excellent removability at room temperature. [Means for solving the problem]

[0005] As a result of intensive research, the present inventors have found that the above-mentioned problems can be solved by setting the displacement amount when a planar rebound resistance test is performed at a temperature of 180°C, the 180° peel adhesive strength against a SUS plate measured at a temperature of 23°C in accordance with JIS Z 0237:2009, and the thickness within a predetermined range, and have completed the present invention as described below. That is, the present invention provides the following [1] to [8]. [1] A substrate-less double-sided adhesive tape that has an adhesive layer, exhibits a displacement of 0.5 mm or less when tested for flat rebound resistance at 180°C, has a 180° peel adhesion strength against a stainless steel plate measured at 23°C in accordance with JIS Z 0237:2009 of 12 N / 25 mm or less, and has a thickness of 200 μm or less. [2] The substrate-less double-sided pressure-sensitive adhesive tape according to the above item [1], wherein the pressure-sensitive adhesive layer comprises an acrylic pressure-sensitive adhesive containing an acrylic polymer (A), the acrylic polymer (A) comprises a structural unit derived from butyl acrylate and a structural unit derived from acrylic acid, the content of the structural units derived from butyl acrylate in the acrylic polymer (A) being 80% by mass or more, and the content of the structural units derived from acrylic acid in the acrylic polymer (A) being 5% by mass or more. [3] The substrate-less double-sided pressure-sensitive adhesive tape according to [2] above, wherein the acrylic pressure-sensitive adhesive further contains a tackifier resin, and the content of the tackifier resin is 8 parts by mass or less per 100 parts by mass of the acrylic copolymer (A). [4] The substrate-less double-sided pressure-sensitive adhesive tape according to any one of [1] to [3] above, which has a 180° peel adhesion to a SUS plate of 5 N / 25 mm or more, measured at a temperature of 23°C in accordance with JIS Z 0237:2009. [5] The substrate-less double-sided pressure-sensitive adhesive tape according to any one of [1] to [4] above, which has a 180° peel adhesion to a SUS plate measured at a temperature of 80°C in accordance with JIS Z 0237:2009 of 17 N / 25 mm or more. [6] A substrate-less double-sided adhesive tape having an adhesive layer, a displacement of 0.5 mm or less when tested for flat rebound resistance at 180°C, and an interfacial peel mode when peeled at 180° from a stainless steel plate at 23°C in accordance with JIS Z 0237:2009, and a thickness of 200 μm or less. [7] The substrate-less double-sided adhesive tape according to the above item [6], which is attached to a SUS plate, left at a temperature of 80°C for 24 hours, and then peeled off at an angle of 180° from the SUS plate at a temperature of 23°C in accordance with JIS Z 0237:2009, exhibiting an interfacial peeling mode. [8] The substrate-less double-sided pressure-sensitive adhesive tape according to any one of the above [1] to [7], which is a substrate-less double-sided pressure-sensitive adhesive tape for vehicle interior parts. Effect of the Invention

[0006] According to the present invention, it is possible to provide a substrate-less double-sided pressure-sensitive adhesive tape that has excellent adhesion at high temperatures and also has excellent removability at room temperature. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a schematic diagram showing a method for testing the planar repulsion resistance of a substrate-less double-sided pressure-sensitive adhesive tape at high temperatures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Substrate-less double-sided adhesive tape of the first invention] The substrate-less double-sided adhesive tape of the first aspect of the present invention has an adhesive layer, and when tested for flat repulsion resistance at 180°C, the displacement is 0.5 mm or less, the 180° peel adhesion against a SUS plate measured at 23°C in accordance with JIS Z 0237:2009 is 12 N / 25 mm or less, and the thickness is 200 μm or less. This allows the substrate-less double-sided adhesive tape of the first aspect of the present invention to have excellent adhesion at high temperatures and excellent removability at room temperature. Note that the substrate-less double-sided adhesive tape of the first aspect of the present invention does not have a substrate.

[0009] (Displacement when testing for flat rebound resistance) In the substrate-less double-sided adhesive tape of the first invention of the present invention, the displacement amount when the flat repulsion resistance test is performed at a temperature of 180 ° C is 0.5 mm or less. If the displacement amount when the flat repulsion resistance test is performed at a temperature of 180 ° C is greater than 0.5 mm, the adhesive strength of the substrate-less double-sided adhesive tape may be insufficient when the substrate-less double-sided adhesive tape is used in a high-temperature environment such as an electric vehicle. From this viewpoint, in the substrate-less double-sided adhesive tape of the first invention of the present invention, the displacement amount when the flat repulsion resistance test is performed at a temperature of 180 ° C is preferably 0.3 mm or less, more preferably 0.1 mm or less. In the substrate-less double-sided adhesive tape of the first invention of the present invention, the lower limit of the range of the displacement amount when the flat repulsion resistance test is performed at a temperature of 180 ° C is usually 0.0 mm. Specifically, the displacement amount when the flat repulsion resistance test is performed at a temperature of 180 ° C can be measured by the method described in the Examples below. The amount of displacement when the flat surface repulsion resistance test is performed at a temperature of 180°C can be appropriately adjusted, for example, by the components constituting the acrylic polymer (A), more specifically, by the content ratio of the structural unit derived from butyl acrylate and the structural unit derived from acrylic acid in the pressure-sensitive adhesive layer. It can also be appropriately adjusted by the type and amount of the tackifier resin.

[0010] (180° peel adhesion measured at 23°C) In the substrate-less double-sided pressure-sensitive adhesive tape of the first aspect of the present invention, the 180° peel adhesion to a SUS (stainless steel: Steel Use Stainless) plate measured at a temperature of 23° C. in accordance with JIS Z 0237:2009 is 12 N / 25 mm or less. If the 180° peel adhesion to a SUS plate measured at a temperature of 23° C. in accordance with JIS Z 0237:2009 is greater than 12 N / 25 mm, the substrate-less double-sided pressure-sensitive adhesive tape cannot be easily peeled off from the adherend, and the recovery efficiency of the substrate-less double-sided pressure-sensitive adhesive tape is poor. From this viewpoint, in the substrate-less double-sided pressure-sensitive adhesive tape of the first aspect of the present invention, the 180° peel adhesion to a SUS plate measured at a temperature of 23° C. in accordance with JIS Z 0237:2009 is preferably 11 N / 25 mm or less, more preferably 10 N / 25 mm or less, even more preferably 9 N / 25 mm or less, and even more preferably 8 N / 25 mm or less. In addition, from the viewpoint of the adhesive strength of the substrate-less double-sided adhesive tape at room temperature, the substrate-less double-sided adhesive tape of the first invention of the present invention has a 180° peel adhesion against a SUS plate measured at a temperature of 23° C. according to JIS Z 0237:2009 of preferably 5 N / 25 mm or more, more preferably 6 N / 25 mm or more, and even more preferably 7 N / 25 mm or more. The 180° peel adhesion against a SUS plate measured at a temperature of 23° C. according to JIS Z 0237:2009 can be specifically measured by the method described in the Examples below. The 180° peel adhesion against a SUS plate measured at a temperature of 23° C. according to JIS Z 0237:2009 can be appropriately adjusted, for example, by the components constituting the acrylic polymer (A), and more specifically, can be adjusted by the content ratio of the structural unit derived from butyl acrylate and the structural unit derived from acrylic acid in the adhesive layer. It can also be appropriately adjusted by the type and amount of the tackifier resin.

[0011] (180° peel adhesion measured at 80℃) In the substrate-less double-sided pressure-sensitive adhesive tape of the first invention of the present invention, the 180° peel adhesion to a SUS plate measured at a temperature of 80° C. in accordance with JIS Z 0237:2009 is preferably 17 N / 25 mm or more. If the 180° peel adhesion to a SUS plate measured at a temperature of 23° C. in accordance with JIS Z 0237:2009 is 17 N / 25 mm or more, the adhesive strength of the substrate-less double-sided pressure-sensitive adhesive tape in a high temperature environment can be further increased. From this viewpoint, in the substrate-less double-sided pressure-sensitive adhesive tape of the first invention of the present invention, the 180° peel adhesion to a SUS plate measured at a temperature of 80° C. in accordance with JIS Z 0237:2009 is more preferably 17.5 N / 25 mm or more, even more preferably 18.0 N / 25 mm or more, even more preferably 18.5 N / 25 mm or more, and even more preferably 25 N / 25 mm or more. In the substrateless double-sided pressure-sensitive adhesive tape of the first invention of the present invention, the upper limit of the range of the 180° peel adhesion to a SUS plate measured at a temperature of 80° C. according to JIS Z 0237:2009 is not particularly limited, but is usually 50 N / 25 mm. Specifically, the 180° peel adhesion to a SUS plate measured at a temperature of 80° C. according to JIS Z 0237:2009 can be measured by the method described in the Examples below. The 180° peel adhesion to a SUS plate measured at a temperature of 80° C. according to JIS Z 0237:2009 can be appropriately adjusted, for example, by the components constituting the acrylic polymer (A), and more specifically, can be adjusted by the content ratio of the structural unit derived from butyl acrylate and the content ratio of the structural unit derived from acrylic acid in the pressure-sensitive adhesive layer. It can also be appropriately adjusted by the type and amount of the tackifier resin.

[0012] (Thickness) The thickness of the substrate-less double-sided adhesive tape of the first invention of the present invention is 200 μm or less. If the thickness of the substrate-less double-sided adhesive tape is greater than 200 μm, the substrate-less double-sided adhesive tape cannot be easily peeled off from the adherend, and the recovery efficiency of the substrate-less double-sided adhesive tape is poor. From this viewpoint, the thickness of the substrate-less double-sided adhesive tape of the first invention of the present invention is preferably 150 μm or less, more preferably 120 μm or less, even more preferably 100 μm or less, and even more preferably 70 μm or less. In addition, from the viewpoint of the adhesiveness of the substrate-less double-sided adhesive tape, the thickness of the substrate-less double-sided adhesive tape of the first invention of the present invention is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 25 μm or more, and even more preferably 40 μm or more.

[0013] (Acrylic adhesive) The pressure-sensitive adhesive layer in the substrate-less double-sided pressure-sensitive adhesive tape of the first aspect of the present invention contains an acrylic pressure-sensitive adhesive containing an acrylic polymer (A), which makes it easy to control the displacement amount when the substrate-less double-sided pressure-sensitive adhesive tape is subjected to a planar repulsion resistance test at a temperature of 180°C and the 180° peel adhesive strength against a SUS plate measured at a temperature of 23°C in accordance with JIS Z 0237:2009 within the above-mentioned ranges.

[0014] <Acrylic polymer (A)> The acrylic polymer (A) is obtained by polymerizing a monomer component containing at least an acrylic monomer. The acrylic polymer (A) is preferably a polymer having a polar group. The polar group is a functional group having active hydrogen and preferably capable of reacting with the crosslinking agent (B) described later, specifically, a carboxy group, a hydroxyl group, an amino group, etc. Among these functional groups, at least one selected from the group consisting of a carboxy group and a hydroxyl group is preferred, and it is more preferred to contain at least a carboxy group. The carboxy group and the hydroxyl group are highly reactive with the crosslinking agent (B) described later, and can easily form a crosslinked structure.

[0015] Specific examples of the acrylic polymer (A) include copolymers of (meth)acrylic acid alkyl ester monomer (A1) and polar group-containing monomer (A2), or copolymers of the above monomers (A1) and (A2) and monomer (A3) other than (A1) and (A2). Among these, copolymers of (meth)acrylic acid alkyl ester monomer (A1) and polar group-containing monomer (A2) are preferred. Incidentally, (meth)acrylate is used as a term meaning either or both of acrylate and methacrylate, and the same applies to other similar terms.

[0016] Examples of the (meth)acrylic acid alkyl ester monomer (A1) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isomyristyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc. Among these, n-butyl (meth)acrylate is preferred from the viewpoint of improving heat resistance. The monomer (A1) may be used alone or in combination of two or more kinds. Among the monomers (A1), from the viewpoint of improving heat resistance, alkyl (meth)acrylates in which the alkyl group has 1 to 12 carbon atoms are preferred, and alkyl acrylates in which the alkyl group has 2 to 8 carbon atoms are more preferred, for example, the alkyl acrylate in which the alkyl group has 2 to 8 carbon atoms is preferably 50 to 100 mass %, more preferably 70 to 100 mass %, and even more preferably 85 to 100 mass %, based on the total amount of the monomer (A1).

[0017] Among the polar group-containing monomers (A2), examples of monomers containing a carboxy group (hereinafter also referred to as "carboxy group-containing monomers (X1)") include acrylic acid, methacrylic acid, crotonic acid, etc. Among these, from the viewpoint of improving heat resistance, at least one selected from the group consisting of acrylic acid and methacrylic acid is preferred, and acrylic acid is more preferred. In addition, examples of the monomer containing a hydroxyl group among the polar group-containing monomers (A2) (hereinafter also referred to as "hydroxyl group-containing monomers (X2)") include (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate, and allyl alcohol. Among these, from the viewpoint of improving heat resistance, (meth)acrylates having a hydroxyl group are preferred, and 2-hydroxyethyl (meth)acrylate is more preferred. The polar group-containing monomer (A2) may be used alone or in combination of two or more kinds.

[0018] The polar group-containing monomer (A2) is preferably at least one selected from the group consisting of a carboxyl group-containing monomer (X1) and a hydroxyl group-containing monomer (X2), and more preferably contains at least a carboxyl group-containing monomer (X1). The at least one selected from the group consisting of a carboxyl group-containing monomer (X1) and a hydroxyl group-containing monomer (X2) is preferably at least one selected from the group consisting of acrylic acid, methacrylic acid, and 2-hydroxyethyl (meth)acrylate.

[0019] The monomer (A3) other than the above (A1) and (A2) is not particularly limited as long as it is copolymerizable with the monomers (A1) and (A2), and examples thereof include styrene derivatives such as styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, and divinylbenzene, compounds having a vinyl ester group such as vinyl acetate and vinyl propionate, N-vinylpyrrolidone, N-vinylmorpholine, (meth)acrylonitrile, N-cyclohexylmaleimide, N-phenylmaleimide, N-laurylmaleimide, N-benzylmaleimide, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, and tert-butyl vinyl ether. The monomer (A3) may be used alone or in combination of two or more kinds.

[0020] The amount of the monomer components used in the acrylic polymer (A) is preferably 80% by mass or more of the (meth)acrylic acid alkyl ester monomer (A1) and preferably 5% by mass or more of the polar group-containing monomer (A2) relative to the total amount of the monomer components. When the amount of the (meth)acrylic acid alkyl ester monomer (A1) and the amount of the polar group-containing monomer (A2) are within the above ranges, it becomes easy to set the displacement amount when a flat surface repulsion resistance test is performed at a temperature of 180°C in the substrateless double-sided pressure-sensitive adhesive tape and the 180° peel adhesive strength against a SUS plate measured at a temperature of 23°C in accordance with JIS Z 0237:2009 within the above ranges.

[0021] By using the monomer components for the acrylic polymer (A) in the above-mentioned amounts, the content of structural units derived from the (meth)acrylic acid alkyl ester monomer (A1) in the acrylic polymer (A) is 80 mass% or more, and the content of structural units derived from the polar group-containing monomer (A2) is 5 mass% or more. As described above, it is preferable to use butyl acrylate as the (meth)acrylic acid alkyl ester monomer (A1) and acrylic acid as the polar group-containing monomer (A2). Accordingly, it is preferable that the content of structural units derived from butyl acrylate in the acrylic polymer (A) is 80% by mass or more and the content of structural units derived from acrylic acid is 5% by mass or more.

[0022] From the above viewpoints, the amount of the monomer components used in the acrylic polymer (A) is, relative to the total monomer components, more preferably 80% by mass or more and 95% by mass or less of the (meth)acrylic acid alkyl ester monomer (A1), even more preferably 85% by mass or more and 93% by mass or less, still more preferably 88% by mass or more and 92% by mass or less, and more preferably 5% by mass or more and 20% by mass or less of the polar group-containing monomer (A2), even more preferably 7% by mass or more and 15% by mass or less, still more preferably 8% by mass or more and 12% by mass or less.

[0023] Therefore, the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer (A1) is more preferably 80% by mass to 95% by mass, even more preferably 85% by mass to 93% by mass, and even more preferably 88% by mass to 92% by mass. The content of the structural units derived from the polar group-containing monomer (A2) is more preferably 5% by mass to 20% by mass, even more preferably 7% by mass to 15% by mass, and even more preferably 8% by mass to 12% by mass.

[0024] In addition, the content of structural units derived from butyl acrylate in the acrylic polymer (A) is more preferably 80% by mass or more and 95% by mass or less, even more preferably 85% by mass or more and 93% by mass or less, and even more preferably 88% by mass or more and 92% by mass or less, and the content of structural units derived from acrylic acid is more preferably 5% by mass or more and 20% by mass or less, even more preferably 7% by mass or more and 15% by mass or less, and even more preferably 8% by mass or more and 12% by mass or less.

[0025] The amount of the monomer (A3) other than (A1) and (A2) used is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less, based on 100 parts by mass of the (meth)acrylic acid alkyl ester monomer (A1).

[0026] In order to improve the adhesive performance and heat resistance of the pressure-sensitive adhesive layer, the total amount of the monomer (A1) and the monomer (A2) in the total monomer components used in the acrylic polymer (A) is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, with the upper limit being 100% by mass.

[0027] The acrylic polymer (A) preferably has a weight average molecular weight (Mw) of 300,000 to 2,000,000, more preferably 500,000 to 2,000,000, even more preferably 500,000 to 1,500,000, and even more preferably 600,000 to 1,100,000. By setting the weight average molecular weight within the above range, the adhesive performance of the pressure-sensitive adhesive layer is improved and the heat resistance is easily improved. The weight average molecular weight can be adjusted by adjusting the polymerization conditions such as the amount of polymerization initiator used and the polymerization temperature, or by selecting the polymerization method. The weight average molecular weight is a weight average molecular weight measured by gel permeation chromatography (GPC) and converted into standard polystyrene. For example, the weight average molecular weight (Mw) can be measured using a gel permeation chromatograph (Waters, 2690 Separations Model). A sample is subjected to GPC measurement at a flow rate of 1 ml / min and a column temperature of 40° C. in the above-mentioned device, and the polystyrene-equivalent molecular weight of the polymer is measured to obtain the weight average molecular weight (Mw). A GPC KF-806L (Showa Denko KK) can be used as the column, and a differential refractometer can be used as the detector.

[0028] The acrylic polymer (A) is the main component of the acrylic pressure-sensitive adhesive and typically accounts for 50 mass % or more, preferably 55 to 98 mass %, and more preferably 60 to 95 mass %, of the total amount of the acrylic pressure-sensitive adhesive (based on non-volatile content).

[0029] The method for producing the acrylic polymer (A) is not particularly limited, and may be, for example, a method in which the above-mentioned monomer components are radically polymerized in the presence of a polymerization initiator. Examples of the polymerization method include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization, etc.

[0030] In the free radical polymerization method, the monomer components are polymerized in the presence of a polymerization initiator, such as an organic peroxide polymerization initiator or an azo polymerization initiator. Examples of the organic peroxide polymerization initiator include cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, stearoyl peroxide, o-chlorobenzoyl peroxide, acetyl peroxide, t-butyl hydroperoxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, 3,5,5-trimethylhexanoyl peroxide, t-butylperoxy-2-ethylhexanoate, and di-t-butyl peroxide.

[0031] Examples of the azo-based polymerization initiator include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1-azobis(cyclohexane-1-carbonitrile), 1-[(1-cyano-1-methylethyl)azo]formamide, 4 ,4'-Azobis(4-cyanovaleric acid), dimethyl-2,2'-azobis(2-methylpropionate), dimethyl-1,1'-azobis(1-cyclohexanecarboxylate), 2,2'-azobis{2-methyl-N-[1,1'-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2 ,2'-Azobis[N-(2-propenyl)-2-methylpropionamide], 2,2'-Azobis(N-butyl-2-methylpropionamide), 2,2'-Azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-Azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-Azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride 2,2'-azobis(2-(2-imidazolin-2-yl)propane) dihydrochloride, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate, 2,2'-azobis(1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2'-azobis(2,4,4-trimethylpentane), and the like. The polymerization initiator may be used alone or in combination of two or more kinds. The amount of the polymerization initiator used is preferably 0.01 to 10 parts by mass, and more preferably 0.05 to 2 parts by mass, based on 100 parts by mass of the monomer component.

[0032] When carrying out polymerization, in addition to the polymerization initiator, a chain transfer agent can be used. As the chain transfer agent, a thiol compound is preferable, and examples thereof include lauryl mercaptan, 2-mercaptoethanol, β-mercaptopropionic acid, octyl β-mercaptopropionate, methoxybutyl β-mercaptopropionate, trimethylolpropane tris(β-thiopropionate), butyl thioglycolate, propanethiols, butanethiols, and thiophosphites. The chain transfer agent may be used alone or in combination of two or more kinds. The amount of the chain transfer agent used is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 2 parts by mass, based on 100 parts by mass of the monomer component.

[0033] <Crosslinking agent (B)> The acrylic pressure-sensitive adhesive of the present invention preferably contains a crosslinking agent (B) in addition to the above-mentioned acrylic polymer (A). The crosslinking agent (B) is a component capable of crosslinking the pressure-sensitive adhesive layer, for example, by reacting with a polar group possessed by the acrylic polymer (A), and this makes it easier to increase the shear strength of the composite structure. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, a metal chelate-based crosslinking agent, etc. Among these, at least one selected from the group consisting of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent is preferred, and an isocyanate-based crosslinking agent is more preferred.

[0034] The isocyanate crosslinking agent is not particularly limited as long as it is a compound having two or more isocyanate groups in one molecule, and examples thereof include tolylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, 1,5-naphthalene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, xylylene diisocyanate, a tolylene diisocyanate adduct of trimethylolpropane, etc. Among these, tolylene diisocyanate and a tolylene diisocyanate adduct of trimethylolpropane are preferred. Commercially available isocyanate crosslinking agents include various polyisocyanate compounds such as Desmodur L75(C) (manufactured by Sumika Covestro), Coronate L-45E, and Coronate L-55E (manufactured by Tosoh Corporation); biuret polyisocyanate compounds such as Sumidur N (manufactured by Sumitomo Bayer Urethane Co., Ltd.); polyisocyanate compounds having an isocyanurate ring such as Desmodur IL and HL (manufactured by Bayer AG) and Coronate EH (manufactured by Nippon Polyurethane Co., Ltd.); and adduct polyisocyanate compounds such as Sumidur L (manufactured by Sumitomo Bayer Urethane Co., Ltd.), Coronate L, and Coronate HL (manufactured by Nippon Polyurethane Co., Ltd.).

[0035] The epoxy crosslinking agent is not particularly limited as long as it is a compound having two or more epoxy groups in one molecule, and examples thereof include diglycidyl aniline, diethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin diglycidyl ether, trimethylolpropane triglycidyl ether, 1,3-bis(N,N-diglycidylaminoethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-m-xylylenediamine. Commercially available epoxy crosslinking agents include, for example, E-AX and E-5C (manufactured by Soken Chemical Industries, Ltd.).

[0036] Examples of the aziridine crosslinking agent include N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide), trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), and trimethylolpropane-tri-β-(2-methylaziridine)propionate. Examples of the metal chelate crosslinking agent include chelate compounds in which the metal atom is aluminum, zirconium, titanium, zinc, iron, tin, etc., and aluminum chelates in which the central metal is aluminum are preferred. Commercially available products include Aluminum Chelate A and Aluminum Chelate M (manufactured by Kawaken Fine Chemicals Co., Ltd.). The crosslinking agent may be used alone or in combination of two or more kinds.

[0037] The content of the crosslinking agent (B) in the acrylic pressure-sensitive adhesive may be appropriately set according to the type of pressure-sensitive adhesive, and is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of the acrylic polymer (A). By setting the content of the crosslinking agent (B) to these lower limits or more, the adhesiveness of the pressure-sensitive adhesive layer to the fabric becomes good, and the above physical properties are easily improved. In addition, the upper limit of the content of the crosslinking agent (B) in the acrylic pressure-sensitive adhesive is not particularly limited, and is, for example, 20 parts by mass, preferably 15 parts by mass, relative to 100 parts by mass of the acrylic polymer (A).

[0038] <Tackifying resin (C)> The acrylic adhesive preferably contains a tackifier resin (C) in addition to the acrylic polymer (A) or the acrylic polymer (A) and the crosslinking agent (B). Examples of the tackifier resin (C) include rosin-based resins, rosin ester-based resins such as polymerized rosin ester resins, hydrogenated rosin-based resins, and other rosin-based tackifier resins, terpene-based resins such as terpene-based resins and terpene-phenol-based resins, coumarone-indene resins, alicyclic saturated hydrocarbon-based resins, C5-based petroleum resins, C9-based petroleum resins, and C5-C9 copolymerized petroleum resins. These tackifier resins may be used alone or in combination of two or more. Among these, from the viewpoint of heat resistance, rosin-based tackifier resins are preferred as the tackifier resin (C), rosin ester-based resins are more preferred, and polymerized rosin ester resins are even more preferred.

[0039] The softening point of the tackifier resin (C) is preferably 135°C or higher. When the softening point of the tackifier resin (C) is 135°C or higher, the heat resistance of the substrate-less double-sided pressure-sensitive adhesive tape can be further improved. From this viewpoint, the softening point of the tackifier is more preferably 140°C or higher, and even more preferably 145°C or higher. Furthermore, from the viewpoint of imparting suitable adhesive performance to the adhesive, the softening point of the tackifier resin is preferably 165°C or lower, more preferably 160°C or lower, and even more preferably 155°C or lower. The softening point can be measured in accordance with JIS K 2207.

[0040] The content of the tackifier resin (C) in the acrylic pressure-sensitive adhesive is, for example, 12 parts by mass or less, preferably 8 parts by mass or less, more preferably 7.5 parts by mass or less, relative to 100 parts by mass of the acrylic polymer (A). By making it equal to or less than the upper limit, the heat resistance of the substrate-less double-sided pressure-sensitive adhesive tape can be further improved. In addition, the content of the tackifier resin (C) in the acrylic pressure-sensitive adhesive is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, relative to 100 parts by mass of the acrylic polymer (A). By making it equal to or more than the lower limit, the adhesiveness of the substrate-less double-sided pressure-sensitive adhesive tape can be further improved.

[0041] The acrylic adhesive may be appropriately blended with additives that are blended into adhesives, such as fillers, antioxidants, UV protection agents, plasticizers, and viscosity adjusters, as long as the effects of the present invention are not impaired. The acrylic pressure-sensitive adhesive may be diluted with an organic solvent, etc. The dilution solvent may be the solvent used when synthesizing the acrylic polymer (A), or may be the solvent added after the synthesis of the acrylic polymer (A).

[0042] [Substrate-less double-sided adhesive tape of the second invention] The substrate-less double-sided adhesive tape of the second aspect of the present invention will be described below. Note that a description of the similarities to the substrate-less double-sided tape of the first aspect of the present invention will be omitted, and the differences from the substrate-less double-sided tape of the first aspect of the present invention will be mainly described. The substrate-less double-sided pressure-sensitive adhesive tape of the second aspect of the present invention has a pressure-sensitive adhesive layer, a displacement of 0.5 mm or less when tested for planar rebound resistance at 180° C., a peel mode of interfacial peeling when peeled at 180° from a SUS plate at 23° C. in accordance with JIS Z 0237: 2009, and a thickness of 200 μm or less. This allows the substrate-less double-sided pressure-sensitive adhesive tape of the second aspect of the present invention to have excellent adhesion at high temperatures and excellent removability at room temperature.

[0043] (Peeling mode when peeled at 180° at 23°C) In the substrate-less double-sided adhesive tape of the second invention of the present invention, the peeling mode when peeled off at 180° from a SUS plate at a temperature of 23° C. in accordance with JIS Z 0237:2009 is interfacial peeling. If the peeling mode is not interfacial peeling, for example, interlayer peeling occurs, making it difficult to separate the adhesive tape from the adherend, and the efficiency of recovery of the substrate-less double-sided adhesive tape may be reduced. The peeling mode when peeled off at 180° from a SUS plate at a temperature of 23° C. in accordance with JIS Z 0237:2009 can be measured by the method described in the Examples below. The peeling mode when peeled off at 180° from a SUS plate at a temperature of 23° C. in accordance with JIS Z 0237:2009 can be adjusted, for example, by the content ratio of the constituent unit derived from butyl acrylate and the content ratio of the constituent unit derived from acrylic acid in the adhesive layer.

[0044] (Peeling mode when attached to a SUS plate and left at 80℃ for 24 hours, then peeled off at 180° at 23℃) In the substrate-less double-sided adhesive tape of the second aspect of the present invention, it is preferable that the peeling mode is interfacial peeling when the tape is attached to a SUS plate and left at a temperature of 80° C. for 24 hours, and then peeled at 180° from the SUS plate at a temperature of 23° C. in accordance with JIS Z 0237:2009. If the peeling mode is interfacial peeling, the substrate-less double-sided adhesive tape attached to the adherend can be peeled off from the adherend with a weak force, which can further improve the efficiency of recovery of the substrate-less double-sided adhesive tape used for a long time in a high-temperature environment. The peeling mode when the tape is attached to a SUS plate and left at a temperature of 80° C. for 24 hours, and then peeled at 180° from the SUS plate at a temperature of 23° C. in accordance with JIS Z 0237:2009 can be measured by the method described in the Examples below. The peel mode when the pressure-sensitive adhesive layer is attached to a SUS plate and left at 80°C for 24 hours, and then peeled at 180° from the SUS plate at 23°C in accordance with JIS Z 0237:2009 can be adjusted, for example, by the content ratio of the structural unit derived from butyl acrylate and the content ratio of the structural unit derived from acrylic acid in the pressure-sensitive adhesive layer.

[0045] [Applications of substrate-less double-sided adhesive tape] The use of the substrate-less double-sided adhesive tape of the first and second inventions of the present invention is not particularly limited. The use of the substrate-less double-sided adhesive tape of the first and second inventions of the present invention includes, for example, vehicle interior parts, vehicle exterior parts, building materials, aviation interior parts, industrial equipment, heat dissipation material parts, train interior parts, etc. Among these uses, it is preferable to use it for vehicle interior parts. That is, the substrate-less double-sided adhesive tape of the first and second inventions of the present invention is preferably a substrate-less double-sided adhesive tape for vehicle interior parts. For example, it is preferable to use it for fixing vehicle interior parts. Examples of vehicle interior parts include, for example, in-vehicle panels such as ceiling panels, door panels, and instrument panels, in-vehicle heaters, car air conditioners, door trims, vibration-damping members, emblems, decorative films, and water-stopping members. The vehicle interior parts may be fixed to the vehicle, for example, via the substrate-less double-sided adhesive tape. The double-sided pressure-sensitive adhesive tape of the present invention is preferably used in high-temperature locations such as heaters, engine periphery, power source periphery, various electronic components, etc. The double-sided pressure-sensitive adhesive tape of the present invention has high heat resistance and can maintain good adhesive strength even when used in high-temperature locations.

[0046] [Method of manufacturing substrate-less double-sided adhesive tape] The method for producing the substrateless double-sided adhesive tape of the first and second inventions of the present invention is not particularly limited, and the tape can be produced by a conventionally known production method. For example, first, a pressure-sensitive adhesive composition diluted with an organic solvent or the like as necessary is prepared, the pressure-sensitive adhesive composition is applied to a support such as a release sheet, and the pressure-sensitive adhesive layer is formed by heating and drying as necessary. When the pressure-sensitive adhesive composition is applied to the release sheet, it is preferable to apply the composition to the release surface of the release sheet. Then, a release sheet is further attached to the surface of the pressure-sensitive adhesive layer on which the release sheet is not disposed, thereby obtaining the substrateless double-sided adhesive tape of the first and second inventions of the present invention sandwiched between two release sheets. EXAMPLES

[0047] The present invention will be described below with reference to examples, but the present invention is not limited to the scope of the examples.

[0048] [Evaluation method] For each of the Examples and Comparative Examples, the measurements and evaluations of the various physical properties were carried out as follows. <Thickness> The measurement was performed using a dial gauge.

[0049] <Displacement when testing for flat rebound resistance> FIG. 1 is a schematic diagram showing a method for testing the planar rebound resistance of an adhesive tape at high temperatures. As shown in FIG. 1, an aluminum plate (A) (width 25 mm × length 150 mm × thickness 0.5 mm) 6 and an aluminum plate (B) (width 25 mm × length 200 mm × thickness 2 mm) 5 were laminated using a substrate-less double-sided adhesive tape 1 cut to a width of 25 mm × length 150 mm. This laminate was pressed with a roller under a condition of 2 kg, and then left to stand for 24 hours to produce a test sample in which the aluminum plate (A) 6 and the aluminum plate (B) 5 were bonded together via the substrate-less double-sided adhesive tape 1. This test sample was sandwiched between a jig 7 with the aluminum plate (A) 6 facing up, and the width of the jig 7 was narrowed to 190 mm to warp the test sample into a bow shape, and the test sample was left to stand for 168 hours under a condition of 180 ° C. The height (displacement) of the floating of the substrate-less double-sided adhesive tape 1 in the test sample after standing for 168 hours was measured.

[0050] <180° peel adhesion measured at temperatures of 23℃ and 80℃> One side (the side not to be measured) of the substrate-less double-sided adhesive tape was lined with a 23 μm thick polyimide film, and then cut to a width of 25 mm × length of 75 mm to prepare a test piece. This test piece was placed on a SUS plate so that its adhesive layer (the side to be measured) faced the SUS plate, and then the test piece was laminated by rolling a 2 kg rubber roller back and forth once at a speed of 300 mm / min. After that, the test piece was aged at 23°C and 50% RH for 20 minutes to prepare a test sample. In accordance with JIS Z 0237:2009, this test sample was peeled in the 180° direction at 23°C and 80°C at a pulling speed of 300 mm / min, and the adhesive strength (N / 25 mm) was measured.

[0051] <Peeling mode when peeled at 180° at 23°C> The peeling mode of the test samples after peeling used in the evaluation of the 180° peel adhesion measured at a temperature of 23° C. described above was investigated. In addition, a test sample similar to the test sample used in the evaluation of 180° peel adhesion measured at 23°C above was left at 80°C for 24 hours, and the test sample was also evaluated for 180° peel adhesion measured at 23°C above to examine the peel mode. When peeling occurred at the interface between the SUS plate and the substrate-less double-sided adhesive tape, and no adhesive residue was left on the SUS plate, it was defined as "interface peeling." Here, "no adhesive residue" refers to the absence of adhesive components when visually observing the SUS plate. On the other hand, when adhesive components are present when visually observing the SUS plate, it is called "interlayer peeling."

[0052] <Evaluation of ease of disassembly at 23℃> Using the same test samples as those used in the evaluation of 180° peel adhesion measured at temperatures of 23°C and 80°C described above, a sensory test was conducted by peeling the substrate-less double-sided adhesive tape from the SUS plate. The evaluation criteria are as follows: ◯: No resistance was felt when peeling, and the substrate-less double-sided adhesive tape could be peeled off from the SUS plate with a small amount of force. △: Some resistance was felt when peeling, but strong force was not required to peel the substrate-less double-sided adhesive tape from the SUS plate. ×: Strong resistance was felt when peeling off, and strong force was required to peel the substrate-less double-sided adhesive tape from the SUS plate.

[0053] (Preparation of Acrylic Adhesive A) In a reaction vessel, 100 parts by mass of n-butyl acrylate and 11 parts by mass of acrylic acid were introduced to obtain a monomer component. The monomer component was dissolved in ethyl acetate, and 0.1 parts by mass of lauroyl peroxide was added as a polymerization initiator at the reflux point, and the mixture was refluxed at 70°C for 5 hours to obtain a solution of an acrylic polymer having a weight average molecular weight of 720,000.

[0054] Acrylic adhesive A was prepared by blending 7 parts by mass of a rosin-based resin (TF) (polymerized rosin ester resin, hydroxyl value 46, softening point 150°C, bio-derived carbon content 95% by mass) and 2.6 parts by mass of a crosslinking agent (isocyanate-based crosslinking agent) with 100 parts by mass (non-volatile content) of the above acrylic polymer (A)-containing solution.

[0055] (Preparation of Acrylic Adhesive B) Acrylic adhesive B was prepared by blending 100 parts by mass (based on non-volatile content) of acrylic adhesive 1 (manufactured by Otsuka Chemical Co., Ltd., product name "TERPLUS NS004") with 30 parts by mass of rosin resin (TF) (polymerized rosin ester resin, hydroxyl value 46, softening point 150°C, bio-derived carbon content 95% by mass) and 4.4 parts by mass of crosslinking agent (isocyanate-based crosslinking agent).

[0056] (Preparation of Acrylic Adhesive C) Ethyl acetate was added as a polymerization solvent into the reaction vessel, and after bubbling with nitrogen, the reaction vessel was heated while flowing in nitrogen to start reflux. Next, a polymerization initiator solution in which 0.1 parts by mass of azobisisobutyronitrile was diluted 10 times with ethyl acetate was added into the reaction vessel as a polymerization initiator, and 96.9 parts by mass of n-butyl acrylate (BA), 2.9 parts by mass of acrylic acid (AAc), and 0.2 parts by mass of 2-hydroxyethyl acrylate (HEA) were added dropwise over 2 hours. After the dropwise addition was completed, a polymerization initiator solution in which 0.1 parts by mass of azobisisobutyronitrile was diluted 10 times with ethyl acetate was added again into the reaction vessel as a polymerization initiator, and a polymerization reaction was carried out for 5 hours to obtain a polymer (X1)-containing solution. Acrylic adhesive C was prepared by mixing 14 parts by mass of rosin-based resin (TF) (polymerized rosin ester resin, hydroxyl value 46, softening point 150°C, bio-derived carbon content 95% by mass) and 1.4 parts by mass of crosslinking agent (isocyanate-based crosslinking agent) with 100 parts by mass (non-volatile content) of the above acrylic copolymer solution.

[0057] [Example 1] (Preparation of double-sided adhesive tape) Acrylic adhesive A was applied to a release sheet ("SLB-80WD" manufactured by Sumika Kakoshi Co., Ltd.) serving as a support, and the sheet was heated and dried at 110°C for 3 minutes. The sheet was then peeled off from the support to obtain a 50 μm thick substrateless double-sided adhesive tape consisting of a single adhesive layer formed from the acrylic adhesive.

[0058] [Example 2] The same procedure as in Example 1 was carried out, except that the thickness of the substrate-less double-sided adhesive tape was changed as shown in Table 1.

[0059] [Comparative Example 1] The same procedure as in Example 1 was repeated, except that the acrylic adhesive A was changed to the acrylic adhesive B.

[0060] [Comparative Examples 2 and 3] The same procedure as in Example 1 was repeated, except that the acrylic adhesive A was changed to the acrylic adhesive B, and the thickness of the substrate-less double-sided adhesive tape was changed as shown in Table 1.

[0061] [Comparative Example 4] The same procedure as in Example 1 was repeated, except that the acrylic pressure-sensitive adhesive A was changed to the acrylic pressure-sensitive adhesive C.

[0062] [Table 1]

[0063] The substrate-less double-sided pressure-sensitive adhesive tapes of Examples 1 and 2 had a displacement of 0.5 mm or less when tested for planar rebound resistance at 180° C., a 180° peel adhesive strength against a SUS plate measured at 23° C. in accordance with JIS Z 0237: 2009 of 12 N / 25 mm or less, and a thickness of 200 μm or less. Thus, the substrate-less double-sided pressure-sensitive adhesive tapes of Examples 1 and 2 had excellent adhesiveness at high temperatures and excellent removability at room temperature. The substrate-less double-sided adhesive tapes of Comparative Examples 1, 2, and 4 had a displacement of more than 0.5 mm when tested for flat surface repulsion resistance at a temperature of 180° C. Therefore, the substrate-less double-sided adhesive tapes of Comparative Examples 1, 2, and 4 had poor adhesion at high temperatures. The substrate-less double-sided adhesive tape of Comparative Example 3 had a displacement of more than 0.5 mm when tested for flat surface repulsion resistance at 180°C, and a 180° peel adhesive strength against a SUS plate measured at 23°C in accordance with JIS Z 0237:2009 of more than 12 N / 25 mm. Therefore, removability at room temperature was poor. [Explanation of symbols]

[0064] 1 adhesive tape 5 Aluminum plate (B) 6 Aluminum plate (A) 7 Jig

Claims

1. An adhesive layer is provided, The amount of displacement when tested for flat rebound resistance at a temperature of 180°C is 0.5 mm or less, The 180° peel adhesive strength against SUS plate measured at a temperature of 23°C in accordance with JIS Z 0237:2009 is 12 N / 25 mm or less, A substrate-less double-sided adhesive tape having a thickness of 200 μm or less.

2. the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive containing an acrylic polymer (A), The acrylic polymer (A) contains a structural unit derived from butyl acrylate and a structural unit derived from acrylic acid, the content of the structural unit derived from butyl acrylate in the acrylic polymer (A) is 80% by mass or more, The substrate-less double-sided pressure-sensitive adhesive tape according to claim 1 , wherein the acrylic polymer (A) contains the structural unit derived from acrylic acid in an amount of 5 mass % or more.

3. The acrylic adhesive further comprises a tackifying resin, The substrate-less double-sided pressure-sensitive adhesive tape according to claim 2 , wherein the content of the tackifier resin is 8 parts by mass or less per 100 parts by mass of the acrylic polymer (A).

4. The substrate-less double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 3, which has a 180° peel adhesive strength against an SUS plate measured at a temperature of 23°C in accordance with JIS Z 0237:2009 of 5 N / 25 mm or more.

5. The substrate-less double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 4, which has a 180° peel adhesive strength against an SUS plate, measured at a temperature of 80°C in accordance with JIS Z 0237:2009, of 17 N / 25 mm or more.

6. An adhesive layer is provided, The amount of displacement when tested for flat rebound resistance at a temperature of 180°C is 0.5 mm or less, When peeled at 180° from a SUS plate at a temperature of 23°C in accordance with JIS Z 0237:2009, the peel mode was interfacial peeling, A substrate-less double-sided adhesive tape having a thickness of 200 μm or less.

7. 7. The substrate-less double-sided pressure-sensitive adhesive tape according to claim 6, wherein the peel mode when the tape is attached to a stainless steel plate, left at a temperature of 80°C for 24 hours, and then peeled at an angle of 180° from the stainless steel plate at a temperature of 23°C in accordance with JIS Z 0237:2009 is interfacial peeling.

8. The substrate-less double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 7, which is a substrate-less double-sided pressure-sensitive adhesive tape for vehicle interior parts.

Images