Adhesive sheet

Abstract

To provide an adhesive sheet which exhibits high adhesive force to an adherend having an oil content adhered to its surface.SOLUTION: There is provided an adhesive sheet 1A having at least an adhesive layer 11. The adhesive layer 11 contains a plasticizer. When an adhesive force (N / 25 mm) after 72 hours of adhesion to a melamine-coated surface is defined as AF1, and an adhesive force (N / 25 mm) after 72 hours of adhesion to an oil surface obtained by applying an engine oil, which is a 10W-30 mineral oil-based lubricant in SAE viscosity classification, in an amount of 2 g / m2 to the melamine-coated surface, is defined as AF2, a ratio (%) of AF2 to AF1 is 30% or more in the adhesive sheet 1A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet that can be used on an adherend having oily matter attached thereto. [Background technology]

[0002] Metals such as iron are prone to rust, so rust-preventive oils are usually applied to the surfaces of metal components made of these metals to prevent oxidation due to contact with air. In addition, when metals are industrially processed, processing oils, cutting oils, machine oils, press oils, etc. are used, and these oils often adhere to the surfaces of industrial metal components.

[0003] When an adhesive sheet such as an adhesive label is attached to such a metal member, sufficient adhesive strength cannot be obtained if oil remains on the surface of the metal member.

[0004] In order to solve the above problems, for example, Patent Document 1 discloses a block copolymer having a terminal polyaromatic vinyl block-polyconjugated diene block structure and a tackifier as the main components, and the initial storage modulus G' at 23°C is 5.1 × 10 4 ~1.0×10 6 Pa, and the storage modulus G' after adhesion to the oily surface is 5.0 × 10 4 ~9.9×10 5 The present invention discloses a pressure-sensitive adhesive composition for adhesion to oily surfaces, which has a storage modulus G' after adhesion to the oily surface that is smaller than the initial storage modulus G'. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-197629 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the pressure-sensitive adhesive composition for adhesion to oily surfaces of Patent Document 1 does not necessarily have sufficient adhesive strength to adherends having oily surfaces.

[0007] The present invention has been made in view of the above circumstances, and has as its object to provide a pressure-sensitive adhesive sheet that can exert high adhesive strength on adherends having oily surfaces. [Means for solving the problem]

[0008] In order to achieve the above object, first, the present invention provides a pressure-sensitive adhesive sheet having at least a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer containing a plasticizer, the adhesive strength (N / 25 mm) after 72 hours of application to a melamine-coated surface being AF1, and the melamine-coated surface being coated with 2 g / m of engine oil, which is a mineral oil-based lubricating oil having an SAE viscosity classification of 10W-30. 2 The adhesive sheet is characterized in that when the adhesive strength (N / 25 mm) after 72 hours of application to an oily surface when the amount of adhesive applied is 100 mg / ml, the ratio (%) of AF2 to AF1 is 30% or more (Invention 1).

[0009] In the above invention (Invention 1), the plasticizer contained in the adhesive layer absorbs oil adhering to the adherend, thereby improving the adhesiveness of the adhesive layer to the oily surface and enabling the adhesive layer to exhibit high adhesive strength to the oily surface. Specifically, as described above, the ratio of AF2 to AF1 can be made 30% or more, thereby reducing the degree of decrease in adhesive strength due to oil.

[0010] In the above invention (invention 1), it is preferable that the AF1 is 7N / 25mm or more (invention 2).

[0011] In the above inventions (Inventions 1 and 2), the adhesive constituting the adhesive layer is preferably an acrylic adhesive (Invention 3).

[0012] In the above inventions (Inventions 1 to 3), it is preferable that the pressure-sensitive adhesive layer does not contain a porous material as an oil absorbent (Invention 4).

[0013] In the above inventions (Inventions 2 to 4), it is preferable that the acrylic pressure-sensitive adhesive has a structure crosslinked with an isocyanate crosslinking agent (Invention 5).

[0014] In the above inventions (Inventions 1 to 5), the plasticizer is preferably a polyester-based plasticizer or a carboxylic acid ester-based plasticizer (Inventions 6 and 7).

[0015] In the above inventions (Inventions 1 to 7), it is preferable that the adhesive sheet comprises a substrate and the pressure-sensitive adhesive layer laminated on at least one surface of the substrate (Invention 8).

[0016] In the above inventions (Inventions 1 to 8), it is preferable that the label is to be attached to an oily surface (Invention 9). [Effects of the Invention]

[0017] The pressure-sensitive adhesive sheet according to the present invention can exert high adhesive strength to adherends having oily surfaces. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. [Figure 2] FIG. 4 is a cross-sectional view of a pressure-sensitive adhesive sheet according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described. [Adhesive sheet] The pressure-sensitive adhesive sheet according to this embodiment has at least a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer contains a plasticizer. The adhesive strength (N / 25 mm) after 72 hours of application to a melamine-coated surface is defined as AF1, and 2 g / m of engine oil, which is a mineral oil-based lubricant with an SAE viscosity classification of 10W-30, is applied to the melamine-coated surface. 2When the adhesive strength (N / 25 mm) after 72 hours of application to an oily surface is defined as AF2, it is preferable that the ratio (%) of AF2 to AF1 ((AF2 / AF1) x 100) is 30% or more.

[0020] Plasticizers used in pressure-sensitive adhesives are generally additives used to increase the flexibility and elasticity of pressure-sensitive adhesives. The inventors discovered that this plasticizer has the effect of absorbing oil, leading to the completion of the present invention. That is, the plasticizer contained in the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to this embodiment absorbs oil adhering to an adherend, thereby improving the adhesion of the pressure-sensitive adhesive layer to oily surfaces (surfaces of adherends to which oil has adhered), and enabling the pressure-sensitive adhesive layer to exhibit high adhesive strength to oily surfaces. Specifically, as described above, the ratio of AF2 to AF1 can be made 30% or more, thereby reducing the degree of decrease in adhesive strength due to oil.

[0021] Here, adhesive strength in this specification basically refers to adhesive strength measured by the 180° peel method in accordance with JIS Z0237:2009, where the measurement sample is 25 mm wide and 150 mm long, and the measurement sample is attached to the adherend using a 2 kg roller going back and forth once, left to stand for 30 minutes, and then left for a specified time (24 hours to 72 hours) under conditions of normal pressure, 23°C, and 50% RH, and then measured at a peel speed of 300 mm / min.

[0022] Examples of oils include hydrocarbons having 5 or more carbon atoms, fatty acids having 5 or more carbon atoms and their ester compounds (including fats and oils such as esters with polyhydric alcohols such as glycerin (e.g., triglycerides)), various silicone oils (e.g., methicone, cyclomethicone, etc.), etc. Oils also include mineral oils, synthetic oils, vegetable oils such as olive oil, sesame oil, and jojoba oil, animal oils such as fish oil and lard, and human sebum.

[0023] From the viewpoint of obtaining high oily surface adhesion, the ratio of AF2 to AF1 is preferably 34% or more, more preferably 37% or more, particularly preferably 40% or more, and even more preferably 43% or more. The upper limit of the ratio of AF2 to AF1 is not particularly limited, but is preferably 100% or less, particularly preferably 80% or less, and even more preferably 60% or less.

[0024] AF1 is preferably 7 N / 25 mm or more, more preferably 7.4 N / 25 mm or more, particularly preferably 7.8 N / 25 mm or more, and even more preferably 8.0 N / 25 mm or more. This ensures sufficient adhesive strength to the surface of an adherend that is not coated with oil. The upper limit of AF1 is preferably 30 N / 25 mm or less, more preferably 20 N / 25 mm or less, particularly preferably 15 N / 25 mm or less, and even more preferably 10 N / 25 mm or less. This allows for reworkability.

[0025] AF2 is preferably 1 N / 25 mm or more, more preferably 2 N / 25 mm or more, more preferably 2.5 N / 25 mm or more, particularly preferably 3 N / 25 mm or more, and even more preferably 3.5 N / 25 mm or more. This results in high adhesive strength to the surface of an adherend having oil attached thereto. The upper limit of AF2 is preferably 30 N / 25 mm or less, more preferably 20 N / 25 mm or less, particularly preferably 15 N / 25 mm or less, and even more preferably 10 N / 25 mm or less. This allows for reworkability.

[0026] In addition, in the pressure-sensitive adhesive sheet according to this embodiment, the adhesive strength (N / 25 mm) 24 hours after application to a melamine-coated surface is set to AF3, and engine oil, which is a mineral oil-based lubricating oil with an SAE viscosity classification of 10W-30, is applied to the melamine-coated surface at 2 g / m 2When the adhesive strength (N / 25 mm) after 24 hours of application to an oily surface is defined as AF4, the ratio (%) of AF4 to AF3 ((AF4 / AF3) x 100) is preferably 15% or more, more preferably 18% or more, particularly preferably 20% or more, and even more preferably 21% or more. This makes it easier to satisfy the above-mentioned physical properties, and allows the adhesive to exhibit relatively high adhesive strength to an oily surface even shortly after application (24 hours later). The upper limit of the ratio of AF4 to AF3 is not particularly limited, but is preferably 100% or less, particularly more preferably 60% or less, particularly preferably 40% or less, and even more preferably 30% or less.

[0027] AF3 is preferably 5 N / 25 mm or more, more preferably 6 N / 25 mm or more, particularly preferably 7 N / 25 mm or more, and even more preferably 7.5 N / 25 mm or more. This ensures sufficient adhesive strength to the surface of an adherend that is not coated with oil. The upper limit of AF3 is preferably 40 N / 25 mm or less, more preferably 30 N / 25 mm or less, particularly preferably 20 N / 25 mm or less, and even more preferably 15 N / 25 mm or less. This allows for reworkability.

[0028] AF4 is preferably 0.5 N / 25 mm or more, more preferably 0.8 N / 25 mm or more, more preferably 1.2 N / 25 mm or more, and particularly preferably 1.5 N / 25 mm or more. This ensures relatively high adhesive strength to oily surfaces even 24 hours after application. The upper limit of AF4 is preferably 40 N / 25 mm or less, more preferably 30 N / 25 mm or less, particularly preferably 20 N / 25 mm or less, even more preferably 10 N / 25 mm or less, and especially preferably 5 N / 25 mm or less. This allows for reworkability.

[0029] In this embodiment, the ratio of AF2 to AF1 (after 72 hours) is greater than the ratio of AF4 to AF3 (after 24 hours), and AF2 (after 72 hours) is greater than AF4 (after 24 hours). This indicates that the plasticizer absorbs oil over time, thereby improving the adhesion of the adhesive layer to the oily surface and, ultimately, the adhesive strength.

[0030] Examples of plasticizers in this embodiment include carboxylic acid ester plasticizers, phthalic acid ester plasticizers, phosphate ester plasticizers, adipate ester plasticizers, trimellitate ester plasticizers, polyester plasticizers, polyol plasticizers, epoxy plasticizers, and carbonate plasticizers. Among these, carboxylic acid ester plasticizers or polyester plasticizers are preferred from the viewpoint of obtaining high oily surface adhesion. In this embodiment, the plasticizers can be used alone or in combination of two or more.

[0031] Examples of carboxylic acid ester-based plasticizers include aliphatic carboxylic acid esters and aromatic carboxylic acid esters, with aliphatic carboxylic acid esters being preferred from the viewpoint of obtaining high adhesion to oily surfaces. Examples of aliphatic carboxylic acid esters include methyl acetylricinoleate, di-2-ethylhexyl adipate, di-2-ethylhexyl sebacate, adipic acid-propylene glycol polyester, and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate. Among these, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate is preferred from the viewpoint of obtaining higher adhesion to oily surfaces.

[0032] Examples of aromatic carboxylic acid esters include phthalate esters (also referred to as phthalate ester-based plasticizers) such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, di-2-ethylhexyl phthalate, dilauryl phthalate, distearyl phthalate, and diisononyl phthalate.

[0033] Examples of phosphate ester plasticizers include tricresyl phosphate, trioctyl phosphate, triphenyl phosphate, etc. Examples of adipate ester plasticizers include di-2-ethylhexyl adipate, diisononyl adipate, diisodecyl adipate, etc. Examples of trimellitate ester plasticizers include trioctyl trimellitate, triisononyl trimellitate, triisodecyl trimellitate, 2-ethylhexyl trimellitate, etc.

[0034] Examples of polyester plasticizers include adipic acid polyesters, phthalic acid polyesters, and sebacic acid polyesters, with adipic acid polyesters being preferred from the viewpoint of achieving high oily surface adhesion. The weight-average molecular weight of polyester plasticizers, particularly adipic acid polyesters, is preferably 500 to 10,000, more preferably 800 to 7,000, particularly preferably 1,200 to 5,000, and even more preferably 2,000 to 4,000. The weight-average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0035] Examples of polyol-based plasticizers include glycol-based plasticizers such as diethylene glycol dibenzoate, dipropylene glycol dibenzoate, triethylene glycol dibenzoate, triethylene glycol di-(2-ethylbutyrate), triethylene glycol di-(2-ethylhexoate), and dibutylmethylene bisthioglycolate; and glycerin-based plasticizers such as glycerol monoacetate, glycerol triacetate, and glycerol tributyrate.

[0036] Examples of epoxy plasticizers include epoxidized soybean oil, epoxidized linseed oil, epoxidized butyl stearate, diethylhexyl epoxyhexahydrophthalate, diisodecyl epoxyhexahydrophthalate, epoxy triglyceride, epoxidized octyl oleate, and epoxidized decyl oleate.

[0037] Examples of carbonate plasticizers include propylene carbonate and ethylene carbonate.

[0038] The adhesive constituting the adhesive layer of the adhesive sheet according to this embodiment may be any of an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, a rubber adhesive, a silicone adhesive, etc. The adhesive may be an emulsion type, a solvent type, or a solventless type, and may be a crosslinked type or a non-crosslinked type. Among these, an acrylic adhesive is preferred, as it is easy to obtain the above-mentioned physical properties.

[0039] The acrylic adhesive may be active energy ray-curable, non-active energy ray-curable, crosslinkable, non-crosslinkable, or a combination thereof. Among these, from the viewpoint of easily achieving the above-mentioned physical properties, non-active energy ray-curable acrylic adhesives are preferred, and crosslinkable non-active energy ray-curable acrylic adhesives are particularly preferred. From the viewpoint of the SDGs, the adhesive may be made of a material with a high biomass content, a recyclable or reusable material, or a recycled or reused material.

[0040] The adhesive constituting the adhesive layer in this embodiment preferably contains a (meth)acrylic acid ester polymer as the adhesive base, particularly preferably a crosslinked (meth)acrylic acid ester polymer, and more preferably has a structure in which the (meth)acrylic acid ester polymer is crosslinked with an isocyanate-based crosslinking agent. This makes it easier to satisfy the above-mentioned physical properties. In particular, when an isocyanate-based crosslinking agent is used, an adhesive that easily satisfies the above-mentioned adhesive properties can be formed.

[0041] In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the term "polymer" also includes the concept of "copolymer."

[0042] Specifically, the adhesive constituting the adhesive layer in this embodiment is preferably one obtained by crosslinking (preferably thermally crosslinking) an adhesive composition (hereinafter sometimes referred to as "adhesive composition P") containing a (meth)acrylic acid ester polymer (A), a crosslinking agent (B), and a plasticizer (C).

[0043] (1) Each ingredient (1-1) (Meth)acrylic acid ester polymer (A) The (meth)acrylic acid ester polymer (A) preferably contains a (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer. This allows the polymer to exhibit good adhesiveness. The alkyl group may be linear or branched.

[0044] From the viewpoint of adhesiveness, the (meth)acrylic acid alkyl ester is preferably a (meth)acrylic acid alkyl ester having an alkyl group containing 1 to 20 carbon atoms. Examples of (meth)acrylic acid alkyl esters having an alkyl group containing 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. Among these, from the viewpoint of further improving adhesiveness on oily surfaces, a (meth)acrylic acid ester having an alkyl group containing 1 to 8 carbon atoms is preferred, with methyl (meth)acrylate, n-butyl (meth)acrylate, or 2-ethylhexyl (meth)acrylate being particularly preferred, and n-butyl acrylate being even more preferred. These may be used alone or in combination of two or more.

[0045] The (meth)acrylic acid ester polymer (A) preferably contains 80 to 99.99 mass% of (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer, more preferably 88 to 99.9 mass%, particularly preferably 92 to 99.5 mass%, and even more preferably 96 to 99.2 mass%. This results in better adhesion to oily surfaces. In addition, other monomer components such as reactive group-containing monomers can be incorporated into the (meth)acrylic acid ester polymer (A) in suitable amounts.

[0046] The (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, a reactive group-containing monomer having, in the molecule, a reactive group that reacts with the crosslinking agent (B). The reactive group derived from the reactive group-containing monomer reacts with the crosslinking agent (B) to form a crosslinked structure (three-dimensional network structure), thereby obtaining a pressure-sensitive adhesive having the desired cohesive strength.

[0047] Preferred examples of the reactive group-containing monomer include a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), a monomer having a carboxyl group in the molecule (carboxyl group-containing monomer), a monomer having an amino group in the molecule (amino group-containing monomer), etc. Among these, from the viewpoint of properly dispersing the plasticizer (C) in the adhesive and making it easier to obtain the desired oily surface adhesion, a hydroxyl group-containing monomer or a carboxyl group-containing monomer that has excellent reactivity with the crosslinking agent (B) is preferred, and a carboxyl group-containing monomer is particularly preferred.

[0048] Examples of hydroxyl group-containing monomers include (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. These may be used alone or in combination of two or more.

[0049] Examples of carboxyl group-containing monomers include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferred in terms of the reactivity of the carboxyl group in the resulting (meth)acrylic acid ester polymer (A) with the crosslinking agent (B) and copolymerizability with other monomers. These may be used alone or in combination of two or more.

[0050] Examples of the amino group-containing monomer include aminoethyl (meth)acrylate, n-butylaminoethyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0051] The (meth)acrylic acid ester polymer (A) preferably contains 0.01 to 20 mass %, more preferably 0.1 to 12 mass %, particularly preferably 0.5 to 8 mass %, and even more preferably 0.8 to 4 mass % of reactive group-containing monomers as monomer units constituting the polymer. This allows a good crosslinked structure to be formed in the resulting pressure-sensitive adhesive, resulting in the desired cohesive strength. Furthermore, the plasticizer (C) is easily dispersed in the pressure-sensitive adhesive, making it easier to achieve the above-mentioned adhesive properties.

[0052] The (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. Examples of such monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used alone or in combination of two or more.

[0053] The (meth)acrylic acid ester polymer (A) is preferably a linear polymer, which is expected to facilitate entanglement of molecular chains and improve cohesive strength.

[0054] The (meth)acrylic acid ester polymer (A) is preferably a solution polymer obtained by solution polymerization. By using a solution polymer, a high molecular weight polymer can be easily obtained, and an improvement in cohesive strength can be expected. In addition, the plasticizer (C) can be easily dispersed. However, the (meth)acrylic acid ester polymer (A) may be polymerized without a solvent.

[0055] The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

[0056] The weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 100,000 to 3,000,000, more preferably 250,000 to 2,400,000, particularly preferably 400,000 to 1,600,000, further preferably 550,000 to 1,200,000, and most preferably 650,000 to 900,000. This results in better oil surface adhesion. In addition, the plasticizer (C) is easily dispersed, making it easier to achieve the above-mentioned physical properties.

[0057] In the pressure-sensitive adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used singly or in combination of two or more kinds.

[0058] The content of the (meth)acrylic acid ester polymer (A) in the pressure-sensitive adhesive composition P according to this embodiment is preferably 80 to 99.9 mass%, more preferably 85 to 99 mass%, particularly preferably 90 to 98.5 mass%, and even more preferably 92 to 98 mass%, which allows for good adhesive strength to be obtained.

[0059] (1-2) Crosslinking agent (B) The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) by heating the pressure-sensitive adhesive composition P or the like, and enables the formation of a favorable three-dimensional network structure, thereby improving the cohesive strength of the resulting pressure-sensitive adhesive.

[0060] The crosslinking agent (B) may be any agent that reacts with the reactive groups of the (meth)acrylic acid ester polymer (A), such as isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, and ammonium salt-based crosslinking agents. Among these, it is preferable to use an isocyanate-based crosslinking agent. Isocyanate-based crosslinking agents have excellent reactivity with the reactive groups of the (meth)acrylic acid ester polymer (A), and can easily obtain a pressure-sensitive adhesive structure that easily satisfies the aforementioned adhesive properties. Furthermore, in the resulting pressure-sensitive adhesive, the three-dimensional network structure formed by the (meth)acrylic acid ester polymer (A) and the isocyanate-based crosslinking agent easily coexists with the plasticizer (C) to an appropriate degree, which allows the pressure-sensitive adhesive to exhibit appropriate flexibility and oil absorbency. The crosslinking agent (B) can be used alone or in combination of two or more.

[0061] The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate; and biuret and isocyanurate forms thereof, as well as adducts thereof that are reaction products with low-molecular-weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among these, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate or trimethylolpropane-modified xylylene diisocyanate, are preferred from the viewpoint of reactivity with hydroxyl groups.

[0062] The content of the crosslinking agent (B) in the pressure-sensitive adhesive composition P is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, particularly preferably 0.3 to 2 parts by mass, and even more preferably 0.6 to 1 part by mass, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). This tends to result in favorable cohesive strength and adhesive strength of the resulting pressure-sensitive adhesive. In particular, in the resulting pressure-sensitive adhesive, the three-dimensional network structure formed by the (meth)acrylic acid ester polymer (A) and the crosslinking agent (B) tends to coexist appropriately with the plasticizer (C), and the pressure-sensitive adhesive tends to exhibit favorable flexibility and oil absorbency.

[0063] (1-3) Plasticizer (C) As the plasticizer (C), the above-mentioned ones can be used. The content of the plasticizer (C) in the adhesive composition P is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, particularly preferably 1.5 to 10 parts by mass, and even more preferably 3 to 6 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). This makes it easier to satisfy the above-mentioned physical properties, and improves oily surface adhesion.

[0064] (1-4) Various additives If desired, various additives commonly used in acrylic pressure-sensitive adhesives, such as antistatic agents, colorants, rust inhibitors, antioxidants, light stabilizers, ultraviolet absorbers, infrared absorbers, etc., can be added to the pressure-sensitive adhesive composition P. Note that polymerization solvents and dilution solvents described below are not included in the additives constituting the pressure-sensitive adhesive composition P.

[0065] Here, the adhesive composition P, and thus the adhesive layer, preferably does not contain a porous body as an oil absorbent. In this specification, "not containing a porous body as an oil absorbent" means "not substantially containing a porous body as an oil absorbent." Specifically, the content of the porous body in the adhesive layer is preferably 0.1% by mass or less, particularly preferably 0.01% by mass or less, and even more preferably 0.001% by mass or less. In the adhesive sheet according to this embodiment, high oil-surface adhesion can be achieved by the action of the plasticizer, even without containing the porous body. If the adhesive layer contains the porous body, not only is it economically disadvantageous, but it also has the disadvantages of reducing the adhesive strength and transparency of the adhesive. Furthermore, in the adhesive, most of the pores that exhibit the oil absorption properties of the porous body are covered by the material that constitutes the adhesive, making it difficult to fully exhibit the oil absorption performance of the porous body.

[0066] The porous body as the oil absorbent has a porosity of 10 to 80% by volume, an average particle size (secondary particle size; volume basis, measured by Coulter Counter particle size distribution method) of 0.1 to 30 μm, and is made of calcium silicate, calcium carbonate, diatomaceous earth, silica, alumina, montmorillonite, kaolin, glass, metal, salt, calcium lactate, lactose, dextrin, modified starch, porous starch, crystalline cellulose, methyl cellulose, a cellulose ether compound, or polyvinyl alcohol.

[0067] (2) Preparation of adhesive composition P The adhesive composition P can be produced by producing a (meth)acrylic acid ester polymer (A), mixing the obtained (meth)acrylic acid ester polymer (A) with a crosslinking agent (B) and a plasticizer (C), and adding additives, etc. as desired.

[0068] The (meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer using a conventional radical polymerization method. The polymerization of the (meth)acrylic acid ester polymer (A) is preferably carried out by a solution polymerization method, using a polymerization initiator as desired. However, the present invention is not limited to this, and the polymerization may be carried out without a solvent. Examples of polymerization solvents include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone, and two or more of them may be used in combination.

[0069] Examples of the polymerization initiator include azo compounds, organic peroxides, etc., and two or more of them may be used in combination. In the polymerization step, the weight average molecular weight of the resulting polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol.

[0070] Once the (meth)acrylic acid ester polymer (A) is obtained, the crosslinker (B), the plasticizer (C), and, if desired, additives, a dilution solvent, etc. are added to the solution of the (meth)acrylic acid ester polymer (A) and mixed thoroughly to obtain a solvent-diluted pressure-sensitive adhesive composition P (coating solution). Note that, when any of the above components is used in a solid state or when precipitation occurs when mixed with other components in an undiluted state, that component may be dissolved or diluted alone in a dilution solvent before being mixed with other components.

[0071] Examples of the dilution solvent include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosolve-based solvents such as ethyl cellosolve.

[0072] The concentration and viscosity of the coating solution prepared in this manner are not particularly limited as long as they are within a range that allows coating, and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted so that the concentration becomes 10 to 60 mass %. Note that the addition of a dilution solvent or the like is not a necessary condition for obtaining the coating solution, and as long as the adhesive composition P has a viscosity that allows coating, the addition of a dilution solvent is not necessary. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent for the (meth)acrylic acid ester polymer (A) itself serves as the dilution solvent.

[0073] (3) Formation of adhesive layer The adhesive layer in this embodiment preferably comprises an adhesive obtained by crosslinking (a coating layer of) the adhesive composition P. The crosslinking of the adhesive composition P can usually be carried out by a heat treatment. Note that this heat treatment can also serve as a drying treatment for volatilizing diluent solvents and the like from the coating layer of the adhesive composition P applied to the desired object.

[0074] The heating temperature for the heat treatment is preferably 50 to 150° C., particularly preferably 70 to 120° C. The heating time is preferably 10 seconds to 10 minutes, particularly preferably 50 seconds to 2 minutes.

[0075] After the heat treatment, if necessary, a curing period of about 1 to 2 weeks may be provided at room temperature (e.g., 23°C, 50% RH). If this curing period is required, the adhesive will be formed after the curing period has elapsed; if no curing period is required, the adhesive will be formed after the heat treatment has been completed.

[0076] The above heat treatment (and curing) crosslinks the (meth)acrylic acid ester polymer (A) via the crosslinking agent (B), thereby obtaining a pressure-sensitive adhesive.

[0077] (4) Thickness of the adhesive layer The thickness of the adhesive layer of the adhesive sheet according to this embodiment (measured in accordance with JIS K7130) is preferably 1 to 1000 μm, more preferably 5 to 600 μm, particularly preferably 10 to 200 μm, even more preferably 15 to 80 μm, and most preferably 20 to 40 μm, which makes it easier to obtain the aforementioned physical properties (oil surface adhesion).

[0078] (5)Specific configuration A specific configuration of an example of the pressure-sensitive adhesive sheet according to this embodiment is shown in FIG. 1 and FIG.

[0079] As shown in Figure 1, the adhesive sheet 1A of the first embodiment is composed of, from the bottom up, a release sheet 12, an adhesive layer 11 laminated on the release surface of the release sheet 12, and a substrate 13 laminated on the adhesive layer 11.

[0080] 2, the adhesive sheet 1B according to the second embodiment is composed of two release sheets 12a and 12b and an adhesive layer 11 sandwiched between the two release sheets 12a and 12b so as to be in contact with the release surfaces of the two release sheets 12a and 12b. In this specification, the release surface of a release sheet refers to the surface of the release sheet that has releasability, and includes both a surface that has been subjected to a release treatment and a surface that exhibits releasability even without being subjected to a release treatment.

[0081] In both pressure-sensitive adhesive sheets 1A and 1B, pressure-sensitive adhesive layer 11 is made of the above-mentioned pressure-sensitive adhesive layer (pressure-sensitive adhesive). Note that pressure-sensitive adhesive layer 11 may be formed as a single layer, or may be formed by laminating multiple layers.

[0082] There are no particular limitations on the substrate 13, and any substrate that is used as a substrate sheet for a normal pressure-sensitive adhesive sheet can be used. Examples of the plastic film include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefin films such as polyethylene and polypropylene; cellophane; diacetyl cellulose film; triacetyl cellulose film; acetyl cellulose butyrate film; polyvinyl chloride film; polyvinylidene chloride film; polyvinyl alcohol film; ethylene-vinyl acetate copolymer film; polystyrene film; polycarbonate film; polymethylpentene film; polysulfone film; polyether ether ketone film; polyether sulfone film; polyetherimide film; fluororesin film; polyamide film; acrylic resin film; polyurethane resin film; norbornene polymer film; cyclic olefin polymer film; cyclic conjugated diene polymer film; and vinyl alicyclic hydrocarbon polymer film, or a laminate film thereof; woven or nonwoven fabrics using fibers such as rayon, acrylic, or polyester; papers such as fine paper, glassine paper, impregnated paper, and coated paper; metal foils such as aluminum and copper; foams such as urethane foam and polyethylene foam; and laminates of two or more of these.

[0083] When the substrate 13 is a plastic film, it may contain various additives such as fillers, dyes, pigments, antioxidants, ultraviolet absorbers, light stabilizers, modifiers, antistatic agents, and the like.

[0084] Furthermore, when the substrate 13 is a plastic film, the surface on which the adhesive layer 11 is laminated or the surface on which the printing layer described below is provided may be subjected to a surface treatment such as a primer treatment, a corona treatment, or a plasma treatment in order to improve adhesion to those layers.

[0085] The substrate 13 may have a printed layer on one or both surfaces. When the substrate 13 is transparent, the printed layer may be provided on the adhesive layer 11 side of the substrate 13, or on the side opposite the adhesive layer 11. When the substrate 13 is opaque, the printed layer is preferably provided on the side opposite the adhesive layer 11 of the substrate 13. A printing coating layer or the like may be provided between the substrate 13 and the printed layer to improve adhesion between the substrate 13 and the printed layer. Furthermore, a coating layer to protect the printed layer may be provided on the side of the printed layer opposite the substrate 13.

[0086] The thickness of the substrate 13 varies depending on the type and application, but is usually preferably 10 to 300 μm, particularly preferably 20 to 200 μm, and further preferably 30 to 100 μm.

[0087] The release sheets 12, 12a, and 12b protect the adhesive layer 13 until the adhesive sheet 1 is used, and are peeled off when the adhesive sheet 1 (adhesive layer 11) is used.

[0088] Examples of the substrates constituting the release sheets 12, 12a, 12b include paper substrates such as glassine paper, coated paper, and fine paper, laminated paper in which resin such as polyethylene is laminated to these paper substrates, and plastic films such as polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene.

[0089] The release surface of the substrate (the surface in contact with the pressure-sensitive adhesive layer) is preferably subjected to a release treatment. Examples of release agents used in the release treatment include silicone-based, fluorine-based, long-chain alkyl-based, alkyd-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

[0090] From the perspective of the SDGs, the material that constitutes the release sheet may be a material with a high biomass content, a material that can be recycled or reused, or a recycled or reused material.

[0091] It is preferable that one of the release sheets 12a, 12b is a heavy release type release sheet with a high release strength, and the other is a light release type release sheet with a low release strength.

[0092] There are no particular restrictions on the thickness of the release sheets 12, 12a, 12b, but it is generally preferred that the thickness be 10 to 250 μm, and more preferably 20 to 150 μm.

[0093] (6) Manufacturing of adhesive sheets As an example of the production of a pressure-sensitive adhesive sheet according to this embodiment, the production of a pressure-sensitive adhesive sheet 1A or 1B using the pressure-sensitive adhesive composition P will be described.

[0094] To produce the pressure-sensitive adhesive sheet 1A, a coating solution of the pressure-sensitive adhesive composition P is preferably applied to the release surface of one of the release sheets 12, followed by heat treatment to thermally crosslink the pressure-sensitive adhesive composition P to form a coating layer, and then the substrate 13 is superimposed on the coating layer. If a curing period is required, a curing period is allowed, or if no curing period is required, the coating layer becomes the pressure-sensitive adhesive layer 11 as is. In this way, the pressure-sensitive adhesive sheet 1A is obtained. The conditions for the heat treatment and curing are as described above.

[0095] To produce the pressure-sensitive adhesive sheet 1B, a coating solution of the pressure-sensitive adhesive composition P is applied to the release surface of one of the release sheets 12a (or 12b), and a heat treatment is performed to thermally crosslink the pressure-sensitive adhesive composition P to form a coating layer. After that, the release surface of the other release sheet 12b (or 12a) is superimposed on the coating layer. If a curing period is required, a curing period is allowed, or if no curing period is required, the coating layer becomes the pressure-sensitive adhesive layer 11 as is. This results in the pressure-sensitive adhesive sheet 1B. The conditions for the heat treatment and curing are as described above.

[0096] The coating solution of the adhesive composition P can be applied by, for example, bar coating, knife coating, roll coating, blade coating, curtain coating, die coating, gravure coating, or the like.

[0097] (7) Uses of adhesive sheets The pressure-sensitive adhesive sheet according to this embodiment can be preferably used as a pressure-sensitive adhesive sheet to be attached to an adherend having oily matter or an adherend to which oily matter can be attached, and the type and material of the adherend are not particularly limited. Examples of the material of the adherend include metal, ceramics, plastic, glass, FRP, wood, stone, asphalt, concrete, and paints applied to the surfaces thereof. The types of oily matter are as described above. The pressure-sensitive adhesive sheet according to this embodiment can be particularly preferably used as a label to be attached to an oily surface.

[0098] The above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0099] For example, release sheet 12 in pressure-sensitive adhesive sheet 1A may be omitted, and either release sheet 12a or 12b in pressure-sensitive adhesive sheet 1B may be omitted.

[0100] In this specification, when it is written "X to Y" (X and Y are any numbers), it means "X or more and Y or less" unless otherwise specified, and also includes the meaning "preferably greater than X" or "preferably smaller than Y." Furthermore, when it is written "X or more" (X is any number), it means "preferably greater than X" unless otherwise specified, and when it is written "Y or less" (Y is any number), it also means "preferably smaller than Y" unless otherwise specified. [Example]

[0101] The present invention will be explained in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0102] Example 1 1. Preparation of (meth)acrylic acid ester polymer A (meth)acrylic acid ester polymer (A) was prepared by copolymerizing 99 parts by mass of n-butyl acrylate and 1 part by mass of acrylic acid by solution polymerization. The molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described below, and the weight average molecular weight (Mw) was found to be 700,000.

[0103] 2. Preparation of adhesive composition 100 parts by mass (solids equivalent; same below) of the (meth)acrylic acid ester polymer (A) obtained in the above step (1), 0.74 parts by mass of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., product name "Takenate D-101E") as the crosslinking agent (B), and 1.87 parts by mass of an adipic acid-based polyester (C1; manufactured by J-Plus, product name "D645", weight average molecular weight: 2200) as the plasticizer (C) were mixed, stirred thoroughly, and diluted with toluene to obtain a coating solution of the adhesive composition.

[0104] Here, the formulations (solid content equivalent) of the pressure-sensitive adhesive compositions when the (meth)acrylic acid ester polymer (A) is taken as 100 parts by mass (solid content equivalent) are shown in Table 1. Details of the abbreviations and the like shown in Table 1 are as follows. [Plasticizer (C)] C1: Adipic acid polyester (manufactured by J-Plus, product name "D645", weight average molecular weight: 2200) C2: 2,2,4-trimethyl-1,3-pentanediol diisobutyrate

[0105] 3. Manufacturing of adhesive sheets The obtained adhesive composition coating solution was applied with an applicator to the release-treated surface of a heavy-release type release sheet R1, one side of which had been treated with a silicone-based release agent for release of a polyethylene terephthalate film, and then heated at 100°C for 2 minutes to form a coating layer.

[0106] Next, the coating layer on the release sheet R1 obtained above was attached to a light-release type release sheet R2, which was a polyethylene terephthalate film with one side treated with a silicone-based release agent, so that the release-treated surface of the release sheet R2 was in contact with the coating layer, and the sheet was aged for 5 days under conditions of 23°C and 50% RH. In this way, an adhesive sheet having a 25 μm-thick adhesive layer, i.e., an adhesive sheet having a configuration of release sheet R2 / adhesive layer (thickness: 25 μm) / release sheet R1, was produced.

[0107] The thickness of the adhesive layer was measured in accordance with JIS K7130 using a constant pressure thickness measuring device (manufactured by Teclock Corporation, product name "PG-02") (the same applies hereinafter). Furthermore, it was confirmed that the release strength of release sheet R1 was greater than that of release sheet R2 in the obtained adhesive sheet.

[0108] Example 2 Pressure-sensitive adhesive sheets were produced in the same manner as in Example 1, except that the type and amount of plasticizer (C) was changed as shown in Table 1.

[0109] Comparative Example 1 An adhesive sheet was produced in the same manner as in Example 1, except that 3.73 parts by mass of hydrogenated petroleum resin (manufactured by Arakawa Chemical Industries, Ltd., product name "Arcon P-100") was used as a tackifier instead of plasticizer (C).

[0110] The weight average molecular weight (Mw) mentioned above is a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC) under the following conditions (GPC measurement). <Measurement conditions> GPC measuring device: Tosoh HLC-8020 GPC columns (passed in the following order): Tosoh Corporation TSK guard column HXL-H TSK gel GMHXL (×2) TSK gel G2000HXL Measurement solvent: tetrahydrofuran ·Measurement temperature: 40℃

[0111] [Test Example 1] (Measurement of adhesive strength) A melamine-coated plate (manufactured by Partec Co., Ltd., product name "SPCC-SD") was prepared, and the melamine-coated surface was used as the first adherend surface (non-oily surface).

[0112] Engine oil (manufactured by Monotaro Co., Ltd., product name "Engine Oil 10W-30 SP (API) CF Equivalent Mineral Oil"), which is a mineral oil-based lubricant with an SAE viscosity classification of 10W-30 and API (American Petroleum Institute) CF equivalent standard classification, was dropped onto the surface of the first adherend, and the dropped oil was spread using Bemcot (a registered trademark of Asahi Kasei Corporation) to obtain a thickness of 2 g / m. 2 The melamine coated surface with the oil (oily content) attached thereto was used as the second adherend surface (oily surface).

[0113] The release sheet R2 was peeled off from the pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was attached to one of the adhesive layers of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4360", thickness: 100 μm) having adhesive layers on both sides to obtain a release sheet R1 / adhesive layer / PET film laminate. This laminate was cut into a 25 mm wide, 150 mm long sample.

[0114] In an environment of 23°C and 50% RH, the release sheet R1 was peeled off from the sample, and the exposed adhesive layer was attached to the first adherend surface (non-oily surface) and the second adherend surface (oily surface), and then adhered by moving a 2 kg roller back and forth once. Then, the samples were left to stand for 30 minutes (taking into account the correction of misalignment during application).

[0115] After that, the samples were left in an environment of 23°C and 50% RH for 24 and 72 hours, and then the adhesive strength (N / 25 mm) was measured using a tensile tester (Tensilon, manufactured by Orientec Co., Ltd.) at a peel speed of 300 mm / min and a peel angle of 180 degrees. Measurements were conducted under conditions other than those described here in accordance with JIS Z0237:2009. When measuring adhesive strength to an oily surface (oily surface adhesive strength), the chart obtained has a certain width due to unevenness in the oil application. For this reason, the average adhesive strength obtained from the chart was taken as the oily surface adhesive strength (N / 25 mm).

[0116] Here, the adhesive strength after 72 hours on a non-oily surface is designated AF1, the adhesive strength after 72 hours on an oily surface is designated AF2, the adhesive strength after 24 hours on a non-oily surface is designated AF3, and the adhesive strength after 24 hours on an oily surface is designated AF4. The results are shown in Table 1.

[0117] From the measurement results obtained above, the ratio of AF2 to AF1 (%) ((AF2 / AF1) x 100) and the ratio of AF4 to AF3 (%) ((AF4 / AF3) x 100) were calculated. The results are shown in Table 1.

[0118] [Table 1]

[0119] As can be seen from Table 1, the adhesive sheets obtained in the examples had a high ratio (%) of AF2 to AF1 and a high ratio (%) of AF4 to AF3, and also had large values ​​for AF2 and AF4, indicating high adhesive strength to oily surfaces. [Industrial Applicability]

[0120] The pressure-sensitive adhesive sheet of the present invention can be suitably used, for example, as a label to be attached to an oily surface. [Explanation of symbols]

[0121] 1A, 1B...Adhesive sheet 11...Adhesive layer 12, 12a, 12b...Release sheet 13...Base material

Claims

1. A pressure-sensitive adhesive sheet having at least a pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer contains a plasticizer, The adhesive strength (N / 25 mm) after 72 hours of application to a melamine-coated surface is designated as AF1. The melamine coated surface was sprayed with 2 g / m of engine oil, which was a mineral oil-based lubricating oil with an SAE viscosity classification of 10W-30. ２ When the adhesive strength (N / 25 mm) after 72 hours on an oily surface is AF2, The ratio (%) of AF2 to AF1 is 30% or more. A pressure-sensitive adhesive sheet characterized by:

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the AF1 is 7 N / 25 mm or more.

3. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer is made of an acrylic pressure-sensitive adhesive.

4. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer does not contain a porous material as an oil absorbent.

5. 3. The pressure-sensitive adhesive sheet according to claim 2, wherein the acrylic pressure-sensitive adhesive has a structure crosslinked with an isocyanate crosslinking agent.

6. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the plasticizer is a polyester-based plasticizer.

7. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the plasticizer is a carboxylic acid ester plasticizer.

8. A substrate; the pressure-sensitive adhesive layer laminated on at least one surface side of the substrate; The adhesive sheet according to claim 1, characterized in that it comprises:

9. 9. The pressure-sensitive adhesive sheet according to claim 1, which is a label to be attached to an oily surface.

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