Adhesive sheet

Abstract

Provided is an adhesive sheet that is provided with a substrate of a vinyl chloride resin film containing a plasticizer, and an adhesive layer on the substrate of the vinyl chloride resin film. In this adhesive sheet, the total amount of a nonionic surfactant in the substrate of the vinyl chloride resin film and in the adhesive layer is 1-150 parts by weight with respect to 100 parts by weight of a base polymer in the adhesive layer.

Description

Pressure-sensitive adhesive sheet

[0001] The present invention relates to a pressure-sensitive adhesive sheet. The present application claims priority based on Japanese Patent Application No. 2025-039466 filed on March 12, 2025, the entire content of which is incorporated herein by reference.

[0002] A pressure-sensitive adhesive sheet may be used as a protective material for protecting the surface of an article. For example, a pressure-sensitive adhesive sheet with a base material is known as a protective sheet for protecting the surface of a workpiece such as a metal plate. The pressure-sensitive adhesive sheet is bonded to the surface of a workpiece to protect the surface of the workpiece during storage, transportation, processing and the like of the workpiece. As a base material for such a pressure-sensitive adhesive sheet, a film-shaped base material mainly composed of vinyl chloride resin (PVC base material) is suitably used because it has high tensile strength and the like. Techniques related to such pressure-sensitive adhesive sheets are described, for example, in Patent Document 1 below.

[0003] Japanese Patent Application Laid-Open No. 2015-187245

[0004] In the pressure-sensitive adhesive sheet disclosed in Patent Document 1, a predetermined plasticizer is blended into the PVC base material to impart flexibility to the base material. Patent Document 1 specifically describes a pressure-sensitive adhesive sheet produced by a method in which a toluene solution containing a base polymer or the like is applied onto such a base material to form a coating film, and then the coating film is dried to form a pressure-sensitive adhesive layer. In a pressure-sensitive adhesive sheet with a PVC base material, when sufficient flexibility is imparted to the PVC base material, the property of following deformation during processing of a workpiece that is an adherend (followability) is ensured.

[0005] However, plasticizers in PVC substrates tend to migrate to the adhesive layer on the substrate by diffusion. When the amount of plasticizer in the PVC substrate decreases due to this migration, the substrate loses flexibility and hardens. If the flexibility of the PVC substrate of the adhesive sheet (protective sheet) on the surface of the workpiece is excessively low, tearing or lifting (partial peeling from the surface of the workpiece) may occur in the adhesive sheet during processing of the workpiece. The adhesive sheet used as a protective sheet is required to suppress the occurrence of such tearing and lifting (requirements for processing characteristics). Furthermore, it is required that no residue or discoloration of the adhesive sheet components is observed on the surface of the workpiece after the adhesive sheet (protective sheet) has been peeled off (requirements for low contamination).

[0006] The present invention was conceived under the circumstances described above, and aims to provide an adhesive sheet suitable for achieving good processing characteristics and low contamination as a protective sheet with a polyvinyl chloride resin film substrate.

[0007] The adhesive sheet provided in this specification comprises a vinyl chloride resin film substrate containing a plasticizer and an adhesive layer on the vinyl chloride resin film substrate. The total amount of nonionic surfactant in the vinyl chloride resin film substrate and the adhesive layer is 1 part by weight or more and 150 parts by weight or less per 100 parts by weight of the base polymer in the adhesive layer. An adhesive sheet with such a configuration is suitable for achieving good processing characteristics and low contamination as a protective sheet by having at least a portion of the nonionic surfactant present in the vinyl chloride resin film substrate. Specifically, it is as follows:

[0008] An adhesive sheet with the above configuration can be manufactured, for example, by forming an adhesive layer containing a predetermined amount of nonionic surfactant on a polyvinyl chloride resin film substrate containing a plasticizer. This method allows for the subsequent addition of a nonionic surfactant to a properly manufactured polyvinyl chloride resin film substrate (PVC substrate). That is, the nonionic surfactant migrates from the adhesive layer containing the nonionic surfactant to the PVC substrate. The inventors have found that such a nonionic surfactant can compensate for the diffusion and migration of the plasticizer from the PVC substrate to the adhesive layer, thereby exhibiting a softening effect on the PVC substrate. The present invention is based on this finding. In the adhesive sheet with the above configuration, the total amount of nonionic surfactant being 1 part by weight or more is suitable for suppressing the hardening of the PVC substrate caused by plasticizer migration. Suppressing the hardening of the PVC substrate helps ensure the flexibility of the substrate, thus helping to achieve the above-mentioned processing characteristics for a protective sheet. In addition, having a total amount of nonionic surfactant of 150 parts by weight or less is suitable for suppressing the nonionic surfactant in the adhesive layer from bleeding out from the adhesive surface of the adhesive layer. Such suppression of bleeding out helps to achieve the aforementioned low-stain properties for the protective sheet. These processing characteristics and low-stain properties are specifically shown in the examples and comparative examples described below. Therefore, the adhesive sheet with the above configuration is suitable for achieving good processing characteristics and low-stain properties as a protective sheet with a PVC substrate.

[0009] In some preferred embodiments, the base polymer is an acrylic polymer or a rubber polymer. Such a configuration is preferred for ensuring adhesion to the protective sheet.

[0010] In some preferred embodiments, the acrylic polymer is a polymer of monomer components containing acrylonitrile. Such a configuration is preferred for ensuring the cohesive force of the adhesive layer. It is also preferred for ensuring compatibility between the acrylic polymer and the nonionic surfactant in the adhesive layer.

[0011] In some preferred embodiments, the nonionic surfactant has an HLB (Hydrophile-Lipophile Balance) value of 5 to 20. An HLB value of 5 or higher for the nonionic surfactant is preferable in ensuring good coatability when applying the adhesive composition containing the nonionic surfactant onto a vinyl chloride resin film substrate during the manufacturing process of the adhesive sheet with the above configuration. An HLB value of 20 or lower for the nonionic surfactant is preferable in suppressing the bleed-out of the nonionic surfactant from the adhesive surface of the adhesive layer when the nonionic surfactant is included in the adhesive layer.

[0012] In some preferred embodiments, the nonionic surfactant has a number-average molecular weight (Mn) of 100 to 2500. Having an Mn of 100 or more for the nonionic surfactant is preferable in suppressing the volatilization of the nonionic surfactant (e.g., volatilization from the adhesive composition) during the manufacturing process of the adhesive sheet with the above configuration. Having an Mn of 2500 or less for the nonionic surfactant is preferable in ensuring the mobility and diffusion of the nonionic surfactant in the adhesive layer and the vinyl chloride resin film substrate, thereby achieving the complementary migration by the nonionic surfactant described above.

[0013] In some preferred embodiments, the vinyl chloride resin film substrate has a thickness of 30 to 200 μm. A thickness of 30 μm or more for the vinyl chloride resin film substrate is preferable for ensuring its function as a protective material in the adhesive sheet. A thickness of 200 μm or less for the vinyl chloride resin film substrate is preferable for ensuring ease of processing the adhesive sheet (such as external shaping using a press machine).

[0014] In some preferred embodiments, the adhesive layer has a thickness of 1 to 30 μm. A thickness of 1 μm or more is preferable for ensuring the adhesive strength of the adhesive layer. A thickness of 30 μm or less is preferable for ensuring the ease of processing the adhesive sheet.

[0015] In some preferred embodiments, the adhesive layer is a dried and solidified layer of a water-dispersible adhesive composition or a dried and solidified layer of a solvent-type adhesive composition. The configuration in which the adhesive layer is a dried and solidified layer of a water-dispersible adhesive composition is particularly preferred from the viewpoint of reducing environmental impact. The water-dispersible adhesive composition preferably contains an aqueous solvent, the base polymer dispersed in the aqueous solvent, and the nonionic surfactant as an additive component to the aqueous solvent and the base polymer.

[0016] In some preferred embodiments, it is a protective sheet for protecting the surface of an object to be adhered to. An adhesive sheet having the above configuration that can enjoy the above-described effects is suitable for use, for example, as a protective sheet for protecting the surface of an object to be processed.

[0017] The ratio of the amount of nonionic surfactant in the vinyl chloride resin film substrate to the total amount of nonionic surfactant in the vinyl chloride resin film substrate and the adhesive layer is 50% to 99%. This configuration is suitable for achieving both the above-mentioned processing characteristics and low contamination properties for a protective sheet in an adhesive sheet with a vinyl chloride resin film substrate.

[0018] This is a schematic cross-sectional view of an adhesive sheet according to one embodiment of the present invention.

[0019] Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood by those skilled in the art based on the teachings on carrying out the invention described herein and the common technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed herein and the common technical knowledge in the art.

[0020] In this specification, "acrylic monomer" means a monomer having at least one (meth)acryloyl group in one molecule. In this specification, "(meth)acryloyl" comprehensively means acryloyl and methacryloyl. Similarly, "(meth)acrylate" comprehensively means acrylate and methacrylate, and "(meth)acrylic" comprehensively means acrylic and methacrylic.

[0021] Figure 1 is a schematic cross-sectional view of an adhesive sheet X, which is one embodiment of the present invention. The adhesive sheet X comprises a PVC substrate 10 and an adhesive layer 20. The PVC substrate 10 is a film-like substrate mainly composed of polyvinyl chloride resin, and has a first surface 11 and a second surface 12 opposite to the first surface 11. The adhesive layer 20 is located on the second surface 12 of the PVC substrate 10. The adhesive layer 20 has a first surface 21 that is in contact with the PVC substrate 10 and a second surface 22 opposite to the first surface 21. The second surface 22 is the adhesive surface of the adhesive sheet X or adhesive layer 20. The first surface 11 of the PVC substrate 10 is the back surface of the adhesive sheet X, located opposite to the second surface 22. Such an adhesive sheet X may be a single-sheet adhesive sheet or a long adhesive sheet (adhesive tape). The second surface 22 (adhesive surface) of the adhesive sheet X may also be covered with a release liner. The adhesive sheet X, which serves as the adhesive tape, may have a first surface 11, which is the back surface, as the release surface, and may be wound in a roll shape.

[0022] In this embodiment, the PVC contained in the PVC substrate 10 is a polymer in which vinyl chloride is the main monomer (a monomer that accounts for, for example, more than 50% by weight of the monomer component). The PVC may be a homopolymer of vinyl chloride or a copolymer of vinyl chloride and other monomers (comonomers). Examples of comonomers include vinylidene chloride, olefins, carboxyl group-containing monomers or their acid anhydrides, (meth)acrylic acid esters, vinyl ester monomers, and styrene monomers. Examples of olefins include ethylene and propylene. Examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Examples of (meth)acrylic acid esters include esters of alkyl alcohols or cycloalkyl alcohols having about 1 to 10 carbon atoms and (meth)acrylic acid. Examples of vinyl ester monomers include vinyl acetate and vinyl propionate. Examples of styrene monomers include styrene, substituted styrene (α-methylstyrene, etc.), and vinyltoluene. In the above copolymer, the copolymerization ratio of vinyl chloride is preferably 70% by weight or more, more preferably 90% by weight or more. PVC is synthesized, for example, by suspension polymerization.

[0023] From the viewpoint of ensuring the strength of the PVC substrate 10, the average degree of polymerization of the PVC is preferably 600 or more, more preferably 800 or more, and even more preferably 1000 or more. From the viewpoint of ensuring the flexibility of the PVC substrate 10, the average degree of polymerization of the PVC is preferably 1800 or less, more preferably 1500 or less, and even more preferably 1200 or less.

[0024] From the viewpoint of fully exhibiting the properties of PVC in the PVC substrate 10, the PVC content is preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 75% by weight or more. The higher the PVC content of the PVC substrate 10, the higher the abrasion resistance of the PVC substrate 10 tends to be. From the viewpoint of ensuring the flexibility of the PVC substrate 10, the PVC content is preferably 90% by weight or less, more preferably 85% by weight or less, and even more preferably 80% by weight or less.

[0025] The PVC substrate 10 contains a plasticizer. Various materials known to exhibit a plasticizing effect on PVC can be used as the plasticizer without particular limitation. Examples include higher alkyl esters of polybasic acids, polyesters of polycarboxylic acids and polyhydric alcohols, and phosphate esters (such as tricresyl phosphate). Examples of higher alkyl esters of polybasic acids include phthalate esters, adipic acid esters, and trimellitic acid esters.

[0026] Examples of phthalate esters include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisodecyl phthalate, diundecyl phthalate, ditridecyl phthalate, bis(2-ethylhexyl) terephthalate (dioctyl terephthalate: DOTP), and bis(2-ethylhexyl) isophthalate.

[0027] Examples of adipate esters include dibutyl adipate, diisobutyl adipate, di-2-ethylhexyl adipate, diisononyl adipate, and diisodecyl adipate.

[0028] Examples of trimellitic acid esters include tri-2-ethylhexyl trimellitic acid, trin-octyl trimellitic acid, trin-decyl trimellitic acid, triisononyl trimellitic acid, and triisodecyl trimellitic acid ester.

[0029] As the polyester (polyester plasticizer) mentioned above, for example, polyester compounds obtained from polycarboxylic acids such as succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, citric acid, phthalic acid, isophthalic acid, terephthalic acid, and trimellitic acid, and polyhydric alcohols such as (poly)ethylene glycol (here, "(poly)ethylene glycol" comprehensively refers to ethylene glycol and polyethylene glycol; the same applies hereinafter), (poly)propylene glycol, (poly)butylene glycol, (poly)hexanediol, (poly)neopentyl glycol, and polyvinyl alcohol can be used. As the polycarboxylic acid, aliphatic dicarboxylic acids having 4 to 12 carbon atoms (typically 6 to 10) are preferred, and adipic acid and sebacic acid are preferred examples. In particular, adipic acid is desirable in terms of versatility and cost. The polyhydric alcohols mentioned above are preferably aliphatic diols having 2 to 10 carbon atoms, and preferred examples include ethylene glycol and butylene glycol (e.g., 1,3-butanediol, 1,4-butanediol).

[0030] The molecular weight of the plasticizer is preferably 250 or more, more preferably 300 or more, and even more preferably 350 or more. The larger the plasticizer, the greater the effect of weakening the interaction between PVCs in the PVC substrate 10 (resulting in a greater flexibility of the PVC substrate 10), and the greater the effect of suppressing diffusion migration from the PVC substrate 10 to the adhesive layer 20. The molecular weight of the plasticizer is, for example, 1500 or less, 1000 or less, or 800 or less.

[0031] The present invention can preferably be implemented in a manner that uses a PVC substrate 10 containing a plasticizer having a relatively small molecular weight (for polymer plasticizers such as the polyester-based plasticizers mentioned above, for example, the number-average molecular weight Mn). That is, the effects of the present invention described later are better demonstrated when the PVC substrate 10 contains a plasticizer with a relatively small molecular weight. The molecular weight of the relatively small plasticizer is, for example, 10,000 or less, 5,000 or less, or 1,500 or less.

[0032] From the viewpoint of fully exhibiting the properties of the plasticizer in the PVC substrate 10, the plasticizer content is preferably 10% by weight or more, more preferably 15% by weight or more, and even more preferably 20% by weight or more. The higher the plasticizer content of the PVC substrate 10, the more flexible the PVC substrate 10 tends to be. From the viewpoint of ensuring the strength of the PVC substrate 10, the plasticizer content is preferably 40% by weight or less, more preferably 30% by weight or less, and even more preferably 25% by weight or less.

[0033] In this embodiment, the PVC substrate 10 contains a nonionic surfactant. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene fatty acid esters, glycol fatty acid esters (such as propylene glycol monostearate), glycerin fatty acid esters, and sorbitan fatty acid esters.

[0034] Examples of polyoxyethylene alkyl ethers include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene cetostearyl ether, and polyoxyethylene behenyl ether.

[0035] Examples of polyoxyethylene polyoxypropylene alkyl ethers include polyoxyethylene polyoxypropylene cetyl ether and polyoxyethylene polyoxypropylene cetyl ether.

[0036] Examples of polyoxyethylene fatty acid esters include diethylene glycol laurate, polyethylene glycol monolaurate, polyethylene glycol monostearate, and polyethylene glycol monoisostearate.

[0037] Examples of glycerin fatty acid esters include glyceryl stearate, glyceryl isostearate, glyceryl oleate, and glyceryl behenate.

[0038] Examples of sorbitan fatty acid esters include sorbitan laurate, sorbitan palmitate, sorbitan stearate, sorbitan isostearate, sorbitan oleate, sorbitan sesquistearate, sorbitan sesquiisostearate, sorbitan sesquioleate, sorbitan trioleate, and sorbitan tristearate.

[0039] From the viewpoint of softening the PVC base material 10, the content of the nonionic surfactant in the PVC base material 10 is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, still more preferably 1.0% by weight or more, even more preferably 1.5% by weight or more, and even more preferably 2.0% by weight or more. From the viewpoint of securing the strength of the PVC base material 10, the content of the nonionic surfactant in the PVC base material 10 is preferably 5.0% by weight or less, more preferably 4.7% by weight or less, and still more preferably 4.5% by weight or less.

[0040] The PVC base material 10 may contain other components besides PVC, a plasticizer, and a nonionic surfactant. Examples of said other components include resins other than PVC, stabilizers, colorants, antistatic agents, and ultraviolet absorbers.

[0041] The thickness of the PVC base material 10 is, for example, 20 µm or more. From the viewpoint of securing the strength of the PVC base material 10, the thickness is preferably 30 µm or more, more preferably 50 µm or more, and still more preferably 70 µm or more. The thickness of the PVC base material 10 is, for example, 300 µm or less. From the viewpoint of conformability to an adherend during processing of the adherend, the thickness is preferably 200 µm or less, more preferably 120 µm or less, and still more preferably 90 µm or less.

[0042] The maximum elongation (elongation at break) of the PVC base material 10 measured in accordance with JIS K 7127 (1999) is preferably 100% or more, more preferably 150% or more, and still more preferably 200% or more, from the viewpoint of conformability to an adherend during processing of the adherend. The maximum elongation of the PVC base material 10 is, for example, 1000% or less.

[0043] The PVC substrate 10 can be produced, for example, by molding a molten PVC-containing composition into a film. In the present embodiment, the PVC-containing composition contains the above-described PVC and a plasticizer, and optionally contains the other components described above. In some embodiments, from the viewpoint of suitable film molding (sheet formation), it is preferable that the PVC-containing composition does not contain a surfactant such as a nonionic surfactant. Examples of the molding method include calender molding, casting molding, and inflation molding.

[0044] The PVC substrate 10 may have a release layer (not shown) on the first surface 11. In the present embodiment, the release layer is a layer formed from a release treatment agent. The release treatment agent contains, for example, a release agent and a resin. Examples of the release agent include silicone-based release agents, fluorine-based release agents, and long-chain alkyl-based release agents. Examples of the resin in the release treatment agent include (meth)acrylic polymers and ethylene-vinyl acetate copolymers. A release treatment agent (release layer) containing a silicone-based release agent and a (meth)acrylic polymer is preferable because it has good compatibility with the base of the PVC substrate 10. For example, the release layer can be formed by applying a release treatment agent to the first surface 11 of the PVC substrate 10 to form a coating film, and then drying the coating film. The thickness of such a release layer is, for example, 0.3 µm or more, preferably 0.7 µm or more, more preferably 1.0 µm or more, and for example, 3.0 µm or less, preferably 2.0 µm or less, more preferably 1.5 µm or less.

[0045] The second surface 12 on the pressure-sensitive adhesive layer 20 side of the PVC substrate 10 may be subjected to surface treatment. Examples of the surface treatment include corona discharge treatment, plasma treatment, ozone exposure, flame exposure, ultraviolet irradiation treatment, acid treatment, alkali treatment, and application of a primer. The surface treatment may be a treatment for improving the adhesion between the PVC substrate 10 and the pressure-sensitive adhesive layer 20.

[0046] The adhesive layer 20 is a layer containing an adhesive (pressure-sensitive adhesive) that exhibits viscoelasticity in the temperature range near room temperature. The adhesive is a component that gives the adhesive properties to the adhesive layer 20. Examples of adhesives include acrylic polymers, rubber polymers, polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers. An acrylic polymer is a polymer that contains monomer units derived from monomers having at least one (meth)acryloyl group in one molecule (acrylic monomers) in its polymer structure, and is typically a polymer that contains monomer units derived from acrylic monomers in a proportion of more than 50% by weight.

[0047] The adhesive layer 20 preferably contains an acrylic polymer or a rubber polymer as a base polymer. The base polymer is the main component of the adhesive in the adhesive layer 20, and refers to the component that accounts for more than 50% by weight of the adhesive in the adhesive layer 20.

[0048] Acrylic polymers are preferably polymers of monomer components mainly composed of alkyl (meth)acrylates. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isopropyl (meth)acrylate. Octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, etc. １－２０Alkyl esters are one example. In particular, (meth)acrylic acid C ２－１４ Alkyl esters are preferred, and (meth)acrylic acid C ２－１０ Alkyl esters are more preferred. Among alkyl esters of (meth)acrylate, butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are particularly preferred. １－２０ " and other "C Ｘ－Ｙ The notation " means that the number of carbon atoms is between X and Y, and (meth)acrylic acid C Ｘ－Ｙ Alkyl esters refer to alkyl (meth)acrylate esters having an alkyl group with X to Y carbon atoms at the ester terminus.

[0049] The proportion of (meth)acrylate alkyl ester in the total amount of monomer components forming the acrylic polymer is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more, from the viewpoint of adhesion and cohesiveness of the adhesive layer 20.

[0050] The monomer components for forming the acrylic polymer may include copolymerizable monomers that can copolymerize with alkyl (meth)acrylate esters. Examples of such copolymerizable monomers include carboxyl group-containing monomers, hydroxyl group-containing monomers, monomers having nitrogen atom-containing rings, cyano group-containing monomers, silane monomers, sulfo group-containing monomers, and glycidyl group-containing monomers. Copolymerizable monomers may be used alone or in combination of two or more types.

[0051] Examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. From the viewpoint of ensuring the tackiness of the adhesive layer 20, the monomer components preferably include carboxyl group-containing monomers, and more preferably include at least one selected from the group consisting of acrylic acid and methacrylic acid.

[0052] The proportion of carboxyl group-containing monomers in the above monomer component is preferably 0.5% by weight or more, more preferably 1% by weight or more, and even more preferably 1.5% by weight or more, from the viewpoint of introducing crosslinking points into the acrylic polymer and ensuring the cohesive force of the adhesive layer 20. The proportion of carboxyl group-containing monomers in the monomer component is preferably 5% by weight or less, more preferably 3% by weight or less, and even more preferably 2% by weight or less, from the viewpoint of avoiding the risk of corrosion of the adherend by acid.

[0053] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate.

[0054] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholindione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and acryloylmorpholine.

[0055] Examples of cyano group-containing monomers include acrylonitrile and methacrylonitrile. The monomer component preferably contains acrylonitrile. That is, the acrylic polymer is preferably a polymer of monomer components containing acrylonitrile. Such a configuration is preferable for ensuring the cohesive force of the adhesive layer 20. Furthermore, the inclusion of acrylonitrile as a constituent monomer in the acrylic polymer is also preferable for ensuring compatibility between the acrylic polymer and the nonionic surfactant described later.

[0056] The proportion of cyano group-containing monomers in the above monomer components is preferably 5% by weight or more, more preferably 8% by weight or more, and even more preferably 10% by weight or more, from the viewpoint of ensuring the cohesive force of the adhesive layer 20. The proportion of cyano group-containing monomers in the monomer components is preferably 30% by weight or less, more preferably 25% by weight or less, and even more preferably 20% by weight or less, from the viewpoint of ensuring the proportion of other monomers.

[0057] Examples of silane monomers include monomers having an alkoxysilyl group, such as 3-methacrylateoxypropyltrimethoxysilane and 3-acrylooxypropyltrimethoxysilane. Examples of sulfo group-containing monomers include styrene sulfonic acid, allyl sulfonic acid, sodium vinyl sulfonate, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid. Examples of phosphate group-containing monomers include 2-hydroxyethylacryloyl phosphate. Examples of glycidyl group-containing monomers include glycidyl (meth)acrylate and 2-ethylglycidyl ether (meth)acrylate.

[0058] As polymerization methods for acrylic polymers, appropriate methods such as thermal polymerization (typically carried out in the presence of a thermal polymerization initiator), including emulsion polymerization, solution polymerization, and bulk polymerization; photopolymerization (typically carried out in the presence of a photopolymerization initiator), which is performed by irradiation with light such as ultraviolet light; and radiation polymerization (typically carried out by irradiation with radiation such as beta rays and gamma rays) can be appropriately employed. Two or more polymerization methods may also be combined (for example, in steps).

[0059] When the acrylic polymer is an emulsion-type acrylic polymer (acrylic polymer emulsion), the emulsion-type acrylic polymer may be an acrylic polymer prepared by polymerization methods other than emulsion polymerization (such as solution polymerization), which is then emulsified using an emulsifier as needed. However, it is preferable to use an acrylic polymer prepared by emulsion polymerization.

[0060] Polymerization methods for acrylic polymers include general one-step polymerization, continuous dropwise polymerization, and segmented dropwise polymerization. Any of these methods may be used, or multiple polymerization methods may be combined. Furthermore, the polymerization reaction may be carried out in steps; for example, polymerization may be carried out once, and then further polymerization may be carried out by adding monomer components.

[0061] When preparing acrylic polymers by emulsion polymerization, one or more known emulsifiers can be used in combination during polymerization. In particular, it is preferable to use a reactive emulsifier that has a group capable of copolymerizing with (meth)acrylic acid ester (for example, a group containing an ethylenically unsaturated bond site). Since the reactive emulsifier is bonded to the molecular chains in the adhesive composition (especially the molecular chains of the acrylic polymer), the precipitation and migration of the emulsifier on the surface of the adhesive layer are suppressed or prevented, and a decrease in adhesive strength and contamination of the adherend by the emulsifier can be effectively suppressed or prevented. Therefore, it is preferable that the emulsion-type acrylic polymer used in the technology disclosed herein is prepared by emulsion polymerization of monomer components in the presence of a reactive emulsifier.

[0062] Reactive emulsifiers can be any emulsifier that has emulsifying properties and a group that can copolymerize with (meth)acrylic acid esters. Examples include anionic emulsifiers such as sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium polyoxyethylene alkyl sulfosuccinate; and nonionic anionic emulsifiers such as sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium polyoxyethylene alkyl sulfosuccinate. Reactive emulsifiers have a form in which a radically polymerizable functional group (radical reactive group) such as a propenyl group or an allyl ether group is introduced (or is equivalent to such a form). The above reactive emulsifiers can be used individually or in combination of two or more.

[0063] Furthermore, there are no particular restrictions on emulsifiers other than the reactive emulsifiers mentioned above (non-reactive emulsifiers), and they can be appropriately selected from known emulsifiers. Specific examples of non-reactive emulsifiers include anionic emulsifiers such as sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium polyoxyethylene alkyl sulfosuccinate; nonionic emulsifiers such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, and polyoxyethylene polyoxypropylene block polymer; and nonionic anionic emulsifiers such as sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium polyoxyethylene alkyl sulfosuccinate. These non-reactive emulsifiers can be used individually or in combination of two or more.

[0064] The amount of emulsifier (especially reactive emulsifier) ​​used is not limited to a specific range, as the amount is appropriately selected depending on the emulsion. However, it is generally appropriate to use 0.1 to 5 parts by weight (preferably 1 to 3 parts by weight) per 100 parts by weight of monomer mixture.

[0065] Furthermore, polymerization initiators and chain transfer agents may be used during polymerization to obtain acrylic polymers (preferably emulsion-type acrylic polymers). The polymerization initiators and chain transfer agents are not particularly limited and can be appropriately selected and used from known ones. Examples of polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylpropionamidine) disulfide, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonnitrile), 2,2'-azobis(2,4,4-trimethylpentane), dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis[2-methyl-N-(phenylmethyl)-propionamidine]dihydrochloride, and 2,2'-azobis[2-(3,4,5,6-tetrahydropyrimidine-2-yl)propane]di Examples of polymerization initiators include azo-based polymerization initiators such as hydrochloride and 2,2'-azobis[2-(2-imidazolin-2-yl)propane]; persulfate-based polymerization initiators such as potassium persulfate and ammonium persulfate; peroxide-based polymerization initiators such as benzoyl peroxide, hydrogen peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclododecane, 3,3,5-trimethylcyclohexanoyl peroxide, and t-butylperoxypivalate; and redox-based polymerization initiators composed of persulfates and sodium bisulfite. Polymerization initiators can be used individually or in combination of two or more. The amount of polymerization initiator used is not particularly limited and can be appropriately selected depending on the polymerization method, polymerization reactivity, type and proportion of monomer components, type of polymerization initiator, etc. For example, it can be appropriately selected from the range of 0.005 to 1 part by weight per 100 parts by weight of monomer mixture.

[0066] Furthermore, as a chain transfer agent, one or more selected from, for example, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimethylcapto-1-propanol, etc., may be used.

[0067] A crosslinking agent may be used in the adhesive layer 20. Examples of crosslinking agents include oxazoline-based crosslinking agents, melamine-based crosslinking agents, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, aziridine-based crosslinking agents, and metal chelate-based crosslinking agents. The crosslinking agent can be used alone or in combination of two or more types.

[0068] As an oxazoline crosslinking agent, any agent having one or more oxazoline groups in one molecule can be used without particular limitation. When the adhesive layer 20 is formed from the water-dispersible adhesive composition described below, an oxazoline crosslinking agent that is soluble or dispersible in water is preferred. The oxazoline group may be any of 2-oxazoline, 3-oxazoline, or 4-oxazoline groups. Usually, an oxazoline crosslinking agent having a 2-oxazoline group can be preferably used. For example, a water-soluble copolymer or water-dispersible copolymer obtained by copolymerizing an addition-polymerizable oxazoline such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, or 2-isopropenyl-5-ethyl-2-oxazoline with another monomer can be used as an oxazoline crosslinking agent. Examples of commercially available oxazoline crosslinking agents include those manufactured by Nippon Shokubai Co., Ltd., such as "Epocross WS-500," "Epocross WS-700," "Epocross K-2010E," "Epocross K-2020E," and "Epocross K-2030E."

[0069] From the viewpoint of imparting appropriate cohesiveness to the adhesive layer and obtaining good non-stick residue, it is preferable that the amount of oxazoline crosslinking agent used be such that the amount of oxazoline groups per equivalent of carboxyl groups in the base polymer is 0.1 equivalent or more, preferably 0.15 equivalent or more, more preferably 0.2 equivalent or more, for example 0.3 equivalent or more. Furthermore, from the viewpoint of obtaining good low-contamination properties, it is preferable that the amount of oxazoline crosslinking agent used be such that the amount of oxazoline groups per equivalent of carboxyl groups in the base polymer is 5 equivalents or less, preferably 3 equivalents or less, more preferably 2 equivalents or less, for example 0.7 equivalents or less (typically 0.5 equivalents or less).

[0070] Examples of melamine-based crosslinking agents include hexamethylol melamine, butylated melamine resin, and butanol-modified melamine formaldehyde resin. The amount of melamine-based crosslinking agent used is preferably 3 to 24 parts by weight, more preferably 5 to 18 parts by weight, and even more preferably 7 to 14 parts by weight, per 100 parts by weight of the base polymer.

[0071] As an isocyanate-based crosslinking agent, any agent having two or more isocyanate groups per molecule can be used without particular limitation. The isocyanate groups in the above-mentioned isocyanate-based crosslinking agent may form isocyanate regenerating functional groups (blocked isocyanates) in which the isocyanate groups are temporarily protected by a protecting group, for example, by treatment with a blocking agent. The isocyanate-based crosslinking agent can be used alone or in combination of two or more types.

[0072] Examples of isocyanate-based crosslinking agents include aromatic polyisocyanates such as tolylene diisocyanate and xylene diisocyanate; aliphatic isocyanates such as isophorone diisocyanate; alicyclic polyisocyanates such as hexamethylene diisocyanate; and more specifically, lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic polyisocyanates such as dichloropentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic diisocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and polymethylene polyphenyl diisocyanate; and trimethylolpropane / tolylene diisocyanate trimer adducts (such as "Coronate L" manufactured by Tosoh Corporation). Examples include isocyanate adducts such as trimethylolpropane / hexamethylene diisocyanate trimer adducts (manufactured by Tosoh Corporation, trade name "Coronate HL", etc.) and isocynurate derivatives of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", etc.); polyisocyanates such as polyether polyisocyanates and polyester polyisocyanates; adducts of these polyisocyanates with polyols; and polyfunctionalized polyisocyanates obtained by isocyanurate bonds, biuret bonds, allophanate bonds, etc.

[0073] When the adhesive layer 20 is formed from the water-dispersible adhesive composition described below, an isocyanate-based crosslinking agent that is soluble or dispersible in water is preferred. For example, water-soluble, water-dispersible, or self-emulsifying isocyanate-based crosslinking agents can be preferably used. Examples of commercially available isocyanate-based crosslinking agents (aqueous isocyanate-based crosslinking agents) include the following products from DIC Corporation: "Barnock DNW-5000", "Barnock DNW-5010", "Barnock DNW-5100", "Barnock DNW-5200", "Barnock DNW-5500", and "Barnock DNW-6000"; and the following products from Nippon Polyurethane Industry Co., Ltd.: "Aquanate 100", "Aquanate 105", "Aquanate 110", "Aquanate 120", "Aquanate 130", "Aquanate 200", and "Aquanate Examples include "T210"; Mitsui Chemicals Polyurethane Co., Ltd.'s product names "Takenate WD-220", "Takenate WD-240", "Takenate WD-720", "Takenate WD-725", "Takenate WD-726", "Takenate WD-730", "Takenate WB-700", "Takenate WB-720", and "Takenate WB-920"; Daiichi Kogyo Seiyaku Co., Ltd.'s product names "Elastron BN-04", "Elastron BN-11", "Elastron BN-27", "Elastron BN-69", and "Elastron BN-77"; etc.

[0074] As an epoxy crosslinking agent, any agent having two or more epoxy groups in one molecule can be used without particular limitation. Epoxy crosslinking agents having three to five epoxy groups in one molecule are preferred. Epoxy crosslinking agents can be used individually or in combination of two or more. Epoxy crosslinking agents that are soluble or dispersible in water are preferred. Specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy crosslinking agents include "TETRAD-X" and "TETRAD-C" from Mitsubishi Gas Chemical Company, "Epiclon CR-5L" from DIC Corporation, "Denacol EX-512" from Nagase ChemteX Corporation, and "TEPIC-G" from Nissan Chemical Industries, Ltd.

[0075] Examples of the rubber polymers mentioned above include natural rubber and synthetic rubber. As for natural rubber, any known material that can be used in adhesive compositions can be used without particular limitation. The term "natural rubber" here is not limited to unmodified natural rubber, but encompasses modified natural rubber, for example, that has been modified with acrylic acid esters. Unmodified natural rubber and modified natural rubber may be used in combination. Examples of synthetic rubbers include styrene-butadiene rubber (SBR), styrene-isoprene rubber, and chloroprene rubber. These synthetic rubbers may be unmodified or modified (e.g., carboxylated). The rubber polymers can be used individually or in combination of two or more.

[0076] When the adhesive layer 20 contains a rubber polymer, the adhesive layer 20 is preferably a rubber adhesive layer formed from a water-dispersible rubber adhesive composition obtained by blending a rubber latex with a tackifying resin and other additives as needed. The rubber latex may be a dispersion of various known rubber polymers in water. Both natural rubber latex and synthetic rubber latex can be used. As the natural rubber latex, any known material that can be used in an adhesive composition can be used without particular limitation. The term "natural rubber latex" here is not limited to unmodified natural rubber latex, but includes modified natural rubber latex, for example, that has been modified with an acrylic acid ester. Unmodified natural rubber latex and modified natural rubber latex may be used in combination. As the synthetic rubber latex, any known material that can be used in an adhesive composition can be used without particular limitation. Preferred examples include styrene-butadiene rubber latex (SBR latex), styrene-isoprene rubber latex, and chloroprene rubber latex. The synthetic rubber contained in these synthetic rubber latexes may be unmodified or modified (e.g., carboxylated). The rubber latexes can be used individually or in combination of two or more types.

[0077] The adhesive layer 20 preferably contains a nonionic surfactant. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene fatty acid esters, glycol fatty acid esters, glycerin fatty acid esters, and sorbitan fatty acid esters. Specific examples of these are the same as those described above for the nonionic surfactant in the PVC substrate 10.

[0078] The number-average molecular weight (Mn) of the nonionic surfactant is preferably 100 or more, more preferably 150 or more, more preferably 200 or more, and more preferably 230 or more. This configuration is preferable in suppressing the volatilization of the nonionic surfactant (for example, volatilization from the adhesive composition) during the manufacturing process of the adhesive sheet X described later. Furthermore, the larger the Mn of the nonionic surfactant, the more suppressed the bleed-out of the nonionic surfactant from the second surface 22 (adhesive surface) of the adhesive layer 20 tends to be. This suppression of bleed-out helps ensure low contamination in the adhesive sheet X. The Mn of the nonionic surfactant is preferably 2500 or less, more preferably 2300 or less, and even more preferably 2200 or less. The smaller the Mn of the nonionic surfactant, the more mobile the nonionic surfactant tends to be in the PVC substrate 10 and the adhesive layer 20. The high mobility of nonionic surfactants helps to compensate for the diffusion and migration of plasticizers from the PVC substrate 10 to the adhesive layer 20 by allowing the nonionic surfactants to change their distribution within the PVC substrate 10 and the adhesive layer 20 (for example, migration from the adhesive layer 20 to the PVC substrate 10), and therefore helps to exert a softening effect on the PVC substrate 10.

[0079] The HLB value of the nonionic surfactant is, for example, 3 or higher, preferably 5 or higher, more preferably 8 or higher, more preferably 11 or higher, and more preferably 12 or higher. Such a configuration is preferable for ensuring good coatability when applying an adhesive composition containing a nonionic surfactant onto a PVC substrate 10 in the manufacturing process of the adhesive sheet X described later. The HLB value of the nonionic surfactant is typically 20 or lower, preferably 18 or lower, more preferably 16 or lower, and more preferably 14 or lower. Such a configuration is preferable for suppressing the bleed-out of the nonionic surfactant from the second surface 22 (adhesive surface) when the adhesive layer 20 contains a nonionic surfactant. In this specification, HLB is the Hydrodrophile-Lipophile Balance by Griffin, a value that represents the degree of affinity of a surfactant to water and oil, and is expressed as a numerical value between 0 and 20 representing the ratio of hydrophilicity to lipophilicity. The definition of HLB is, for example, W. C. Griffin: J. Soc. As described in Cosmetic Chemists, 1,311 (1949).

[0080] The amount of nonionic surfactant in the adhesive layer 20 is preferably 0.1 parts by weight or more, more preferably 1 part by weight or more, more preferably 3 parts by weight or more, more preferably 5 parts by weight or more, and more preferably 10 parts by weight or more, per 100 parts by weight of the base polymer in the adhesive layer 20, from the viewpoint of ensuring the transfer amount of nonionic surfactant to the PVC substrate 10 and thereby making the PVC substrate 10 more flexible. The amount of nonionic surfactant in the PVC substrate 10 in the adhesive sheet X is preferably 100 parts by weight or less, more preferably 90 parts by weight or less, and even more preferably 80 parts by weight or less, per 100 parts by weight of the base polymer in the adhesive layer 20, from the viewpoint of suppressing bleed-out from the second surface 22 of the adhesive layer 20.

[0081] The adhesive layer 20 may contain a tackifying resin in addition to the base polymer and the like described above. As the tackifying resin, a suitable one can be selected from various known tackifying resins. For example, one or more can be selected from various tackifying resins such as rosin resins, petroleum resins, terpene resins, phenolic resins, coumarone indene resins, and ketone resins. In embodiments in which the adhesive layer is formed from a water-dispersible adhesive composition, a tackifying resin emulsion is preferably used as the tackifying resin.

[0082] The adhesive layer 20 may contain, as needed, various additives common in the field of adhesives, such as viscosity modifiers (thickeners, etc.), leveling agents, softeners, fillers, colorants such as pigments and dyes, light stabilizers, anti-aging agents, antioxidants, water-resistant agents, antistatic agents, foaming agents, defoaming agents, and preservatives.

[0083] The thickness of the adhesive layer 20 is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 8 μm or more, from the viewpoint of ensuring the adhesive strength of the adhesive layer 20. The thickness of the adhesive layer 20 is, for example, 50 μm or less, and from the viewpoint of ensuring the ease of processing of the adhesive sheet X and making it easier to suppress the total thickness of the adhesive sheet, it is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less.

[0084] In the adhesive sheet X, the content of nonionic surfactant in the PVC substrate 10 and the adhesive layer 20 is 1 part by weight or more per 100 parts by weight of the base polymer in the adhesive layer 20, preferably 4 parts by weight or more, more preferably 9 parts by weight or more, more preferably 14 parts by weight or more, more preferably 18 parts by weight or more, and more preferably 25 parts by weight or more. This configuration is suitable for suppressing the hardening of the PVC substrate 10 caused by plasticizer migration by having a nonionic surfactant in the PVC substrate 10. In the adhesive sheet X, suppressing the hardening of the PVC substrate 10 helps to ensure the flexibility of the PVC substrate 10, and thus helps to achieve the above-mentioned processing characteristics for the protective sheet.

[0085] In the adhesive sheet X, the content of nonionic surfactant in the PVC substrate 10 and the adhesive layer 20 is 150 parts by weight or less per 100 parts by weight of the base polymer in the adhesive layer 20, preferably 130 parts by weight or less, more preferably 110 parts by weight or less, and even more preferably 100 parts by weight or less, and may be 95 parts by weight or less, 85 parts by weight or less, or 75 parts by weight or less. Such a configuration is suitable for suppressing the nonionic surfactant in the adhesive layer 20 from bleeding out from the second surface 22 (adhesive surface) of the adhesive layer 20. Such suppression of bleeding out helps to achieve the aforementioned low contamination properties for the protective sheet in the adhesive sheet X.

[0086] As described above, adhesive sheet X is suitable for achieving good processing characteristics and low contamination as a protective sheet with a PVC base material. Such adhesive sheet X is useful as a protective sheet for protecting the surface of metal plates and other materials that are to be processed. Processing includes drawing, bending, and punching.

[0087] In the adhesive sheet X, the ratio of the amount of nonionic surfactant in the PVC substrate 10 to the total amount of nonionic surfactant in the PVC substrate 10 and the adhesive layer 20 is, for example, 10% or more, may be 20% by weight or more, or 30% by weight or more. In some embodiments, the ratio of the amount of nonionic surfactant in the PVC substrate is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more, from the viewpoint of ensuring the flexibility of the PVC substrate 10. Also, the ratio of the amount of nonionic surfactant in the PVC substrate 10 is, for example, 100% or less (typically less than 100%), preferably 99% or less, and more preferably 98% or less. Such a configuration is suitable for suppressing the hardening of the PVC substrate 10 caused by plasticizer migration. In the adhesive sheet X, suppressing the hardening of the PVC substrate 10 helps to ensure the flexibility of the PVC substrate 10, and thus helps to achieve the above-mentioned processing characteristics for the protective sheet.

[0088] The adhesive sheet X described above can be manufactured, for example, by forming an adhesive layer 20 on a PVC substrate 10. For example, it can be formed by applying an adhesive composition for forming the adhesive layer 20 onto the PVC substrate 10 to form a coating film, and then drying and solidifying (curing if necessary) the coating film. Examples of application methods include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating.

[0089] When the adhesive composition is a water-dispersible adhesive composition, it preferably contains an aqueous solvent, a base polymer dispersed in the aqueous solvent, a nonionic surfactant as an additive to the aqueous solvent and base polymer, and other components (such as a crosslinking agent) as needed. The aqueous solvent refers to water, or a mixed solvent having water as the main component (a component present in more than 50% by weight). The solvents other than water constituting this mixed solvent may be one or more selected from various organic solvents (such as lower alcohols) that can be uniformly mixed with water. The proportion of water in the aqueous solvent is typically 90% by weight or more, preferably 95 to 100% by weight. The base polymer for the water-dispersible adhesive composition is preferably a polymer synthesized by emulsion polymerization. The water-dispersible adhesive composition may also be prepared by adding a nonionic surfactant and other components as needed to the reaction solution (polymer emulsion) after emulsion polymerization. Furthermore, when a rubber-based polymer is used as the base polymer, the water-dispersible adhesive composition may be the rubber-based latex described above.

[0090] When the adhesive composition is a solvent-type adhesive composition, it preferably contains a solvent, a base polymer, a nonionic surfactant as an additive to the solvent and base polymer, and other components (such as a crosslinking agent) as needed. Examples of solvents include toluene and ethyl acetate. The base polymer for the solvent-type adhesive composition is preferably a polymer synthesized by solution polymerization. The solvent-type adhesive composition may also be prepared by adding a nonionic surfactant and other components as needed to the reaction solution after solution polymerization.

[0091] The adhesive layer 20 is preferably an adhesive layer formed from the above-described water-dispersible adhesive composition, or an adhesive layer formed from the above-described solvent-type adhesive composition. That is, the adhesive layer 20 is preferably a dried and solidified layer of a water-dispersible adhesive composition or a dried and solidified layer of a solvent-type adhesive composition. The dried and solidified layer of the adhesive composition includes the coating film of the adhesive composition that has dried, and the layer in which a crosslinking reaction by a crosslinking agent has progressed after drying.

[0092] The matters disclosed in this specification include: (1) an adhesive sheet comprising a vinyl chloride resin film substrate containing a plasticizer, and an adhesive layer on the vinyl chloride resin film substrate, wherein the total amount of nonionic surfactant in the vinyl chloride resin film substrate and the adhesive layer is 1 part by weight or more and 150 parts by weight or less per 100 parts by weight of the base polymer in the adhesive layer. (2) the adhesive sheet according to (1), wherein the base polymer is an acrylic polymer or a rubber polymer. (3) the adhesive sheet according to (2), wherein the acrylic polymer is a polymer of monomer components containing acrylonitrile. (4) the adhesive sheet according to any one of (1) to (3), wherein the plasticizer is at least one selected from the group consisting of phthalates, adipicates, and trimelliticates. [5] The adhesive sheet according to any one of [1] to [4] above, wherein the phthalate ester is at least one selected from the group consisting of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisodecyl phthalate, diundecyl phthalate, ditridecyl phthalate, bis(2-ethylhexyl) terephthalate, and bis(2-ethylhexyl) isophthalate. [6] The adhesive sheet according to any one of [1] to [5] above, wherein the nonionic surfactant has an HLB value of 5 to 20. [7] The adhesive sheet according to any one of [1] to [6] above, wherein the nonionic surfactant has a number average molecular weight of 100 to 2500. [8] The adhesive sheet according to any one of [1] to [7] above, wherein the nonionic surfactant is at least one selected from the group consisting of polyoxyethylene alkyl ether, polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene fatty acid ester, glycol fatty acid ester, glycerin fatty acid ester, and sorbitan fatty acid ester. [9] The adhesive sheet according to any one of [1] to [8] above, wherein the vinyl chloride resin film substrate has a thickness of 30 to 200 μm.

[10] The adhesive sheet according to any one of [1] to [9] above, wherein the adhesive layer has a thickness of 1 to 30 μm.

[11] The adhesive sheet according to any one of [1] to

[10] above, wherein the adhesive layer is a dried and solidified layer of a water-dispersible adhesive composition or a dried and solidified layer of a solvent-type adhesive composition.

[12] The adhesive sheet according to any one of [1] to

[11] above, wherein the water-dispersible adhesive composition contains an aqueous solvent, the base polymer dispersed in the aqueous solvent, and the nonionic surfactant as an additive component to the aqueous solvent and the base polymer.

[13] The adhesive sheet according to any one of [1] to

[12] above, which is a protective sheet for protecting the surface of an adherend.

[14] The adhesive sheet according to any one of [1] to

[13] above, wherein the ratio of the amount of nonionic surfactant in the vinyl chloride resin film substrate to the total amount of nonionic surfactant in the vinyl chloride resin film substrate and the adhesive layer is 50% to 99%.

[0093] The following describes several experimental examples related to the present invention, but the present invention is not intended to be limited to these specific examples. In the following description, "parts" and "%" used to express amounts and content are based on weight unless otherwise specified. Also, unless otherwise specified, the amount of each material used is based on the amount of active ingredient.

[0094] <Emulsion Polymerization of Acrylic Polymers> First, a mixture containing 85 parts n-butyl acrylate (BA), 15 parts acrylonitrile (AN), 2 parts acrylic acid (AA), 2 parts polyoxyethylene-1-(allyloxymethyl) alkyl ether ammonium sulfate (trade name "Aqualon KH-1025", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a reactive emulsifier, and 150 parts water was stirred in a homomixer while introducing nitrogen gas into the mixture to prepare a monomer emulsion. Next, the monomer emulsion was heated to 50°C in a reaction vessel equipped with a reflux condenser, nitrogen introduction tube, thermometer, and stirring device, while stirring under a nitrogen atmosphere. Next, 0.03 parts of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (trade name "V-50", manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added to the monomer emulsion in the reaction vessel. The emulsion polymerization reaction was then carried out for 5 hours while maintaining the temperature of the monomer emulsion at around 50°C. After the resulting reaction mixture was cooled to room temperature, the pH of the mixture was adjusted to approximately 8 by adding 10% ammonium water. In this manner, a polymer emulsion containing an acrylic polymer (emulsion-based acrylic polymer) was obtained.

[0095] <Solution polymerization of acrylic polymers> In a reaction vessel equipped with a reflux condenser, nitrogen inlet tube, thermometer, and stirring device, a mixture containing 85 parts BA, 15 parts AN, 2 parts AA, 0.2 parts 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and toluene as a polymerization solvent was stirred at 60°C for 3 hours under a nitrogen atmosphere (solution polymerization). The reaction mixture was then aged at 70°C for 3 hours. In this manner, a toluene solution of an acrylic polymer (solvent-based acrylic polymer) was obtained.

[0096] <Rubber-based polymer> Styrene-butadiene rubber (SBR) latex (product name "NipoL LX209", manufactured by Nippon Zeon Co., Ltd.) was prepared as the rubber-based polymer.

[0097] <Vinyl Chloride Resin Film Substrate> A vinyl chloride resin film substrate (PVC substrate) with a thickness of 70 μm was prepared from a raw material mixture consisting of vinyl chloride resin and a plasticizer by calendering. As the vinyl chloride resin, PVC with an average degree of polymerization of 1050 was used. As the plasticizer, bis(2-ethylhexyl) terephthalate (molecular weight 391), a DOTP plasticizer manufactured by J-Plus Co., Ltd., was used. The plasticizer content of the raw material mixture was 20%.

[0098] <Strip Treatment Solution> First, 70 parts of methyl methacrylate (MMA), 30 parts of BA, and 10 parts of hydroxyethyl acrylate (HEA) were polymerized in a toluene solution to obtain an acrylic copolymer. Next, 60 parts of silicone resin (product name "KS-723A", manufactured by Shin-Etsu Chemical Co., Ltd.), 40 parts of silicone resin (product name "KS-723B", manufactured by Shin-Etsu Chemical Co., Ltd.), 50 parts of the above acrylic copolymer, and 10 parts of tin-based catalyst (product name "Cat-PS3", manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed in solution. This obtained a stripping treatment solution (stripping agent).

[0099] [Example 1] First, the above-mentioned release treatment liquid was applied to one side of the PVC substrate to form a coating film, and then the coating film was dried to form a release layer with a thickness of 1.0 μm (arithmetic mean surface roughness Ra: 0.5 μm). Meanwhile, to the above-mentioned polymer emulsion, 50 parts of a nonionic surfactant and 2 parts of an oxazoline crosslinking agent (product name "Epocross WS-500", manufactured by Nippon Shokubai Co., Ltd.) were added and mixed to prepare a water-dispersible adhesive composition. Next, the water-dispersible adhesive composition was applied to the other side of the PVC substrate (with the release layer) to form a coating film, and then the coating film was dried at 80°C for 120 seconds to form an adhesive layer with a thickness of 10 μm. Polyoxyethylene lauryl ether (product name "Emulgen 102KG", Mn: 230, HLB value: 6.3, manufactured by Kao Corporation) was used as the nonionic surfactant. As described above, the adhesive sheet of Example 1 (adhesive sheet with PVC substrate) was prepared.

[0100] [Examples 2-16, Comparative Examples 1, 2] Except for changing the type and amount of nonionic surfactant incorporated into the water-dispersible adhesive composition for forming the adhesive layer, as shown in Table 1, the adhesive sheets of Examples 2-16 and Comparative Examples 1, 2 were prepared in the same manner as the adhesive sheet of Example 1.

[0101] [Example 17] First, a release layer with a thickness of 1.0 μm was formed on one side of the PVC substrate as described above in Example 1. Meanwhile, to the toluene solution of the acrylic polymer, 50 parts of a nonionic surfactant and 10 parts of a melamine crosslinking agent (trade name "Amidia J82060N", butanol-modified melamine formaldehyde resin, manufactured by DIC Corporation) were added and mixed to prepare a solvent-type adhesive composition. Next, the solvent-type adhesive composition was applied to the other side of the PVC substrate (with the release layer) to form a coating film, and then the coating film was dried at 130°C for 90 seconds to form an adhesive layer with a thickness of 10 μm. Polyethylene glycol monolaurate (trade name "Emanon 1112", Mn: 670, HLB value: 13.7, manufactured by Kao Corporation) was used as the nonionic surfactant. As described above, the adhesive sheet of Example 17 (adhesive sheet with PVC substrate) was prepared.

[0102] [Example 18] First, a release layer with a thickness of 1.0 μm was formed on one side of the PVC substrate as described above in Example 1. Meanwhile, a water-dispersible adhesive composition was prepared by adding 50 parts of a nonionic surfactant and 2 parts of an oxazoline crosslinking agent (Epocross WS-500) per 100 parts of the rubber polymer contained therein to the styrene-butadiene rubber latex and mixing. Next, the water-dispersible adhesive composition was applied to the other side of the PVC substrate (with the release layer) to form a coating film, and then the coating film was dried at 75°C for 120 seconds to form an adhesive layer with a thickness of 10 μm. Polyethylene glycol monolaurate (trade name "Emanon 1112") was used as the nonionic surfactant. In this manner, the adhesive sheet of Example 18 (adhesive sheet with PVC substrate) was prepared.

[0103] [Comparative Examples 3-5] The adhesive sheets of Comparative Examples 3-5 were prepared in the same manner as the adhesive sheet of Example 1, except that an ionic surfactant (Comparative Example 3), a hydrophobic polymer (Comparative Example 4), or a tackifying resin (Comparative Example 5) was added to the water-dispersible adhesive composition for forming the adhesive layer, instead of a nonionic surfactant. The ionic surfactant used in Comparative Example 3 was 50 parts of polyoxyethylene lauryl ether sodium sulfate (trade name "Emal 20C", manufactured by Kao Corporation) per 100 parts of acrylic polymer. The hydrophobic polymer used in Comparative Example 4 was a polybutene derivative (trade name "Emawet 30E", manufactured by NOF Corporation). The tackifying resin used in Comparative Example 5 was a rosinphenol resin (trade name "Tamanol E200NT", manufactured by Arakawa Chemical Industries, Ltd.).

[0104] [Comparative Example 6] The adhesive sheet of Comparative Example 6 was prepared in the same manner as the adhesive sheet of Example 17, except that a nonionic surfactant was not added to the water-dispersible adhesive composition for forming the adhesive layer.

[0105] [Comparative Example 7] The adhesive sheet of Comparative Example 7 was prepared in the same manner as the adhesive sheet of Example 18, except that a nonionic surfactant was not included in the water-dispersible adhesive composition for forming the adhesive layer.

[0106] [Comparative Examples 8 and 9] An attempt was made to produce an adhesive sheet in the same manner as the adhesive sheet of Example 1, except that 50 parts (Comparative Example 8) or 5 parts (Comparative Example 9) of bis(2-ethylhexyl) terephthalate (DOTP manufactured by J-Plus Co., Ltd.), an ionic surfactant, were added to the water-dispersible adhesive composition for forming the adhesive layer, instead of 50 parts of the nonionic surfactant. However, the ionic surfactant did not dissolve completely in the adhesive layer, and an adhesive sheet could not be properly produced.

[0107] <Young's Modulus> The Young's modulus of each adhesive sheet in Examples 1 to 18 and Comparative Examples 1 to 7 was investigated as follows.

[0108] First, a sample piece (150 mm long x 10 mm wide) was cut from the adhesive sheet. Next, the sample piece was subjected to a tensile test using a Tensilon-type tensile testing machine (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) at 25°C and 50% relative humidity, and the tensile stress generated during the pulling process was measured. This yielded a stress-strain curve (S-S curve). In this tensile test, the initial chuck distance was set to 50 mm, the sample piece was pulled in the length direction, and the tensile speed was set to 300 mm / min. The rate of change in stress between the elongation of 1.0 mm and 2.0 mm in this tensile test was determined as Young's modulus (MPa). The results are shown in Table 1.

[0109] <Processing Characteristics> The processing characteristics of each adhesive sheet in Examples 1 to 18 and Comparative Examples 1 to 7 during the processing of the adherend were investigated as follows.

[0110] First, a sample sheet (100 mm square) was cut from the adhesive sheet. Next, the adhesive side of the sample sheet was attached to one side of a 0.4 mm thick stainless steel plate (SUS304BA, 100 mm square). Then, using a press machine (AIDA 60t press machine), a jig was pressed into the stainless steel plate from the sample sheet side to obtain a bento-shaped press-molded body (deep drawing). This press-molded body has a bottomed rectangular tube (main body) that is 40 mm square and has a deep draw of 15 mm, and a folded side edge with a width of 15 mm from the opening periphery, with the sample sheet attached to the inside of the rectangular tube and on the sides. Next, the press-molded body was left for 24 hours in an environment of 23°C and 50% relative humidity. After this, the presence and extent of tears or lifting (partial peeling) of the sample sheet (adhesive sheet) on the press-molded body were checked by visual inspection. Furthermore, after peeling and removing the sample sheet from the press-molded body, the presence or absence of dents on the surface of the molded body was visually inspected. A "Superior" rating was given if the adhesive sheet showed no tears, no lifting in the rectangular tube covering area, no lifting in the side areas, and no dents on the press-molded body. A "Good" rating was given if the adhesive sheet showed no tears or lifting in the rectangular tube covering area, no dents on the press-molded body, and if lifting occurred in the side areas of the adhesive sheet but the area percentage of such lifting was kept below 40%. A "Acceptable" (practical) rating was given if the adhesive sheet showed no tears or lifting in the rectangular tube covering area, no dents on the press-molded body, and lifting occurred in the side areas of the adhesive sheet by 40% or more (area percentage). A "Poor" (unpractical) rating was given if the adhesive sheet showed tears, lifting in the rectangular tube covering area, or dents on the press-molded body. The results are shown in Table 1.

[0111] <Low Contamination Properties> The low contamination properties of each adhesive sheet in Examples 1 to 18 and Comparative Examples 1 to 7 were investigated as follows.

[0112] First, using a sample sheet (100 mm square) cut from an adhesive sheet, a deep drawing process was performed in the same manner as described above for evaluating processing characteristics, to obtain a bento-shaped press-molded body. Next, the press-molded body was left for 7 days in an environment of 23°C and 50% relative humidity. Then, the adhesive sheet was peeled off the press-molded body. After this, the presence or absence of contamination on the surface of the press-molded body was checked by visual inspection. If no contamination was found, it was evaluated as "excellent," and if contamination was found, it was evaluated as "poor."

[0113] <Distribution rate of nonionic surfactant to substrate> For each adhesive sheet in Examples 1 to 18 and Comparative Examples 1 to 7, the distribution rate of nonionic surfactant to substrate was investigated as follows.

[0114] First, the adhesive sheet was left for one month at 23°C and 50% relative humidity. Next, a predetermined amount (approximately 0.2 g) of substrate material was taken from the adhesive sheet. Then, the substrate material was immersed in chloroform and left for 24 hours to extract the substrate into a solution. Next, acetonitrile was added to the solution, and the solution was filtered through a membrane filter (pore size 0.2 μm). Next, the solution was diluted to prepare a sample solution. Next, the amount of nonionic surfactant in the sample solution was measured using a high-performance liquid chromatography-mass spectrometry (LC / MS) instrument (Thermo Fisher Scientific "UltiMate3000 / LTQ Orbitrap XL"). Based on the concentration, the substrate distribution ratio of the nonionic surfactant was determined. The substrate distribution ratio (%) of the nonionic surfactant can be calculated by dividing the amount of nonionic surfactant in the substrate by the total amount of nonionic surfactant in the substrate and adhesive layer. The total amount of nonionic surfactant can be calculated based on the amount of nonionic surfactant incorporated into the adhesive layer.

[0115]

[0116]

[0117] As shown in Table 1, in the adhesive sheets of Examples 1 to 18, where the total amount of nonionic surfactant in the PVC substrate and adhesive layer was 1 part by weight or more and 150 parts by weight or less per 100 parts by weight of the base polymer in the adhesive layer, both processing characteristics and low staining properties were achieved. In contrast, in the adhesive sheets of Comparative Examples 1 to 7, where the total amount of nonionic surfactant was 0 parts by weight or more than 150 parts by weight per 100 parts by weight of the base polymer in the adhesive layer, both processing characteristics and low staining properties were not achieved. In Comparative Examples 3 to 5, adhesive sheets were prepared by incorporating an ionic surfactant (Comparative Example 3), a hydrophobic polymer (Comparative Example 4), or a tackifying resin (Comparative Example 5) into the adhesive layer instead of a nonionic surfactant, but the effect of achieving both processing characteristics and low staining properties was not obtained. In the case of Comparative Example 3, it is thought that the compatibility of the ionic surfactant with the emulsion-type acrylic polymer in the adhesive layer was not sufficient.

[0118] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above.

[0119] X Adhesive sheet 10 PVC base material 11 First side 12 Second side 20 Adhesive layer 21 First side 22 Second side (adhesive side)

Claims

1. An adhesive sheet comprising a vinyl chloride resin film substrate containing a plasticizer, and an adhesive layer on the vinyl chloride resin film substrate, wherein the total amount of nonionic surfactant in the vinyl chloride resin film substrate and the adhesive layer is 1 part by weight or more and 150 parts by weight or less per 100 parts by weight of the base polymer in the adhesive layer.

2. The adhesive sheet according to claim 1, wherein the base polymer is an acrylic polymer or a rubber polymer.

3. The adhesive sheet according to claim 2, wherein the acrylic polymer is a polymer of monomer components containing acrylonitrile.

4. The adhesive sheet according to claim 1, wherein the nonionic surfactant has an HLB value of 5 to 20.

5. The adhesive sheet according to claim 1, wherein the nonionic surfactant has a number average molecular weight of 100 to 2500.

6. The adhesive sheet according to claim 1, wherein the vinyl chloride resin film substrate has a thickness of 30 to 200 μm.

7. The adhesive sheet according to claim 1, wherein the adhesive layer has a thickness of 1 to 30 μm.

8. The adhesive sheet according to claim 1, wherein the adhesive layer is a dried and solidified layer of a water-dispersible adhesive composition or a dried and solidified layer of a solvent-type adhesive composition.

9. The adhesive sheet according to claim 8, wherein the water-dispersible adhesive composition comprises an aqueous solvent, the base polymer dispersed in the aqueous solvent, and the nonionic surfactant as an additive component to the aqueous solvent and the base polymer.

10. The adhesive sheet according to claim 1, which is a protective sheet for protecting the surface of an object to be adhered to.

11. The adhesive sheet according to any one of claims 1 to 10, wherein the ratio of the amount of nonionic surfactant in the vinyl chloride resin film substrate to the total amount of nonionic surfactant in the vinyl chloride resin film substrate and the adhesive layer is 50% to 99%.

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