Adhesive and adhesive sheet

Abstract

To provide an adhesive and an adhesive sheet allowing recycling with water.SOLUTION: An adhesive containing a cyclodextrin compound, the adhesive exhibiting a gel fraction of less than 50% after immersion in pure water for 72 hours and exhibiting a weight loss of less than 10% when heated at 100°C for 1 hour. Preferably, the adhesive is an acrylic adhesive. Preferably, it contains an acrylic polymer obtained by copolymerizing an acrylic monomer with a cyclodextrin compound having a polymerizable group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water-recyclable adhesive and adhesive sheet. [Background technology]

[0002] In recent years, there has been an increasing demand for the creation of a recycling-based society, and there is a growing demand for recyclability of various products and materials.

[0003] Recently, novel materials using cyclodextrin monomers have been proposed. Specifically, Patent Document 1 proposes a polymer material containing a crosslinked polymer crosslinked by the interaction between a host group and a guest group, in which the host group is a monovalent group obtained by removing one hydrogen atom or one hydroxyl group from cyclodextrin, and the crosslinked polymer contains a predetermined repeating structural unit.

[0004] Furthermore, Patent Document 2 proposes an inclusion complex formed from a host group of a host group-containing monomer and a guest group of a guest group-containing monomer, in which the host group-containing monomer is a cyclodextrin monomer derivative having a (meth)acryloyl group, and the guest group-containing monomer is a predetermined monomer having a vinyl group. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6636610 [Patent Document 2] Patent No. 6239043 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above-mentioned background, it is desirable that the adhesive in the adhesive sheet can also be recycled. However, Patent Documents 1 and 2 do not describe the adhesive in the adhesive sheet, nor do they mention recyclability at all.

[0007] When recycling adhesives, it is more desirable from the environmental and health perspectives to use water rather than an organic solvent to dissolve the adhesive layer of the adhesive sheet.

[0008] The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that can be recycled with water. [Means for solving the problem]

[0009] To achieve the above object, first, the present invention provides an adhesive containing a cyclodextrin compound, characterized in that the gel fraction after immersion in pure water for 72 hours is less than 50% and the weight loss when heated at 100°C for 1 hour is less than 10% (Invention 1).

[0010] The adhesive according to the above invention (Invention 1) contains a cyclodextrin compound, and the gel fraction WG is less than 50%, which gives the adhesive excellent solubility in water and makes it possible to recycle the adhesive with water. Furthermore, the weight loss is less than 10%, which gives the adhesive excellent heat-resistant adhesiveness and prevents a decrease in adhesive strength after heating. Therefore, even if the adhesive dissolved in water is re-formed into an adhesive layer, it can still exhibit good adhesive strength.

[0011] In the above invention (Invention 1), it is preferable that the pressure-sensitive adhesive is molded to a thickness of 500 μm and a width of 10 mm, and when stretched to the breaking elongation at a measuring length of 20 mm and a tensile speed of 200 mm / min under an environment of 23°C and 50% RH, the maximum stress is 1 MPa or more (Invention 2).

[0012] In the above inventions (Inventions 1 and 2), it is preferable that the adhesive strength of an 80 μm thick, 25 mm wide adhesive layer made of the adhesive to soda lime glass is 0.1 N / 25 mm or more (Invention 3).

[0013] In the above inventions (Inventions 1 to 3), the cyclodextrin compound preferably has a polymerizable group (Invention 4).

[0014] In the above inventions (inventions 1 to 4), an acrylic pressure-sensitive adhesive is preferred (invention 5).

[0015] In the above inventions (Inventions 4 and 5), it is preferable to contain an acrylic polymer obtained by copolymerizing an acrylic monomer with the cyclodextrin compound (Invention 6).

[0016] Secondly, the present invention provides an adhesive sheet having at least an adhesive layer, characterized in that the adhesive constituting the adhesive layer is the adhesive described above (Inventions 1 to 6) (Invention 7).

[0017] In the above invention (Invention 7), it is preferable that the adhesive sheet has two release sheets, and the adhesive layer is sandwiched between the release sheets so as to contact the release surfaces of the two release sheets (Invention 8). [Effects of the Invention]

[0018] The pressure-sensitive adhesive according to the present invention can be recycled with water, and the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to the present invention can be recycled with water. [Brief explanation of the drawings]

[0019] [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

[0020] Hereinafter, an embodiment of the present invention will be described. [Adhesive] The pressure-sensitive adhesive according to one embodiment of the present invention contains a cyclodextrin compound, and preferably has a gel fraction (hereinafter sometimes referred to as "gel fraction WG") of less than 50% after immersion in pure water for 72 hours. Furthermore, it is preferable that the weight loss when heated at 100°C for 1 hour is less than 10%. The method for measuring the gel fraction WG in this specification is as shown in the test examples described later. Furthermore, the method for measuring the weight loss in this specification is also as shown in the test examples described later.

[0021] The adhesive according to the present embodiment contains a cyclodextrin compound, and the gel fraction WG is less than 50%, which provides excellent solubility in water and allows the adhesive to be recycled in water. Furthermore, the weight loss is less than 10%, which provides the adhesive with excellent heat-resistant adhesiveness and suppresses a decrease in adhesive strength after heating. Therefore, even if the adhesive dissolved in water is re-formed into an adhesive layer, it can still exhibit good adhesive strength. Specifically, by immersing the adhesive according to the present embodiment (an adhesive sheet comprising an adhesive layer made of the adhesive and a substrate) in water, the adhesive dissolves in the water and falls off from the substrate, etc. The adhesive dissolved in water can be applied, heated, dried, and re-formed into an adhesive layer, allowing it to be reused with good adhesive strength.

[0022] The water in which the adhesive (layer) is dissolved during recycling is not particularly limited, but examples thereof include pure water, ultrapure water, deionized water, distilled water, purified water, tap water, etc. Among these, it is preferable to use pure water or ultrapure water from the viewpoint of obtaining a recycled adhesive with few impurities.

[0023] From the viewpoint of water solubility, the gel fraction WG of the pressure-sensitive adhesive according to this embodiment is preferably 40% or less, more preferably 30% or less, particularly preferably 20% or less, even more preferably 12% or less, and of these, preferably 6% or less. On the other hand, from the viewpoint of cohesive strength, the gel fraction WG of the pressure-sensitive adhesive according to this embodiment is preferably 0% or more, more preferably 0.1% or more.

[0024] From the viewpoint of recyclability, the weight loss of the pressure-sensitive adhesive according to the present embodiment is preferably 9% or less, more preferably 8% or less, particularly preferably 7% or less, and even more preferably 6.5% or less, and preferably 0% or more, more preferably 0.1% or more.

[0025] When the pressure-sensitive adhesive according to the present embodiment is molded to a thickness of 500 μm and a width of 10 mm and stretched to the breaking elongation at a measurement length of 20 mm and a tensile speed of 200 mm / min under an environment of 23°C and 50% RH, the maximum stress is preferably 1 MPa or more. This makes it easier to exhibit excellent holding power. From this viewpoint, the maximum stress is more preferably 3 to 100 MPa, particularly preferably 5 to 75 MPa, and even more preferably 6 to 50 MPa or more, and of these, preferably 7 to 40 MPa. Details of the tensile test for measuring the maximum stress in this specification are as shown in the test examples described later.

[0026] The adhesive strength of an 80 μm thick, 25 mm wide adhesive layer made of the adhesive according to this embodiment to soda lime glass is preferably 0.1 N / 25 mm or more, more preferably 0.3 to 50 N / 25 mm, particularly preferably 0.4 to 25 N / 25 mm, even more preferably 0.5 to 10 N / 25 mm, and of these, preferably 0.6 to 5 N / 25 mm. When the lower limit of the adhesive strength is within the above range, the desired adhesive durability and excellent holding power are easily obtained. Furthermore, when the upper limit of the adhesive strength is within the above range, good reworkability is obtained.

[0027] Here, the adhesive strength in this specification basically refers to the adhesive strength measured by the 180-degree peel method in accordance with JIS Z0237:2009, and the measurement sample is 25 mm wide and 100 mm long, and the measurement sample is attached to the adherend and pressurized at 0.5 MPa and 50°C for 20 minutes, and then left to stand for 24 hours under conditions of normal pressure, 23°C, and 50% RH, and then measured at a peel speed of 300 mm / min.

[0028] The pressure-sensitive adhesive according to the present embodiment contains a cyclodextrin compound. The cyclodextrin compound in this specification may be cyclodextrin itself, a cyclodextrin having a substituent (a cyclodextrin derivative), or a cyclodextrin or cyclodextrin derivative incorporated into a polymer (a polymer having cyclodextrin or a cyclodextrin derivative as a constituent monomer). Among the above, it is preferable that the pressure-sensitive adhesive according to the present embodiment contains a polymer having cyclodextrin or a cyclodextrin derivative as a constituent monomer, since this easily satisfies the above-mentioned physical properties.

[0029] The pressure-sensitive adhesive according to the present embodiment is preferably a solvent-free pressure-sensitive adhesive. Furthermore, the pressure-sensitive adhesive according to the present embodiment is preferably an acrylic pressure-sensitive adhesive, and more preferably a solvent-free acrylic pressure-sensitive adhesive.

[0030] The adhesive according to the present embodiment preferably contains a polymer having a main chain formed by copolymerizing an acrylic monomer and a cyclodextrin compound having a polymerizable group, or contains an acrylic polymer and a cyclodextrin or a cyclodextrin derivative, and more preferably contains a polymer having a main chain formed by copolymerizing an acrylic monomer and a cyclodextrin compound having a polymerizable group. Such a composition makes it easier to satisfy the above-mentioned physical properties, and improves the recyclability of the adhesive in water.

[0031] The pressure-sensitive adhesive according to the present embodiment preferably does not contain low-molecular-weight guest molecules that can be included in the cyclodextrin compound. In this specification, "inclusion" refers to the phenomenon in which a guest molecule is incorporated into the cavity of a host molecule (cyclodextrin compound). In addition, "low-molecular-weight guest molecules" in this specification refer to molecules that can be included in a cyclodextrin compound, including those that have not yet been included. Examples of such guest molecules include n-butyl acrylate, styrene, octyl acrylate, and dodecyl acrylate for α-cyclodextrin compounds, n-butyl acrylate, t-butyl acrylate, styrene, adamantyl acrylate, and isobornyl acrylate for β-cyclodextrin compounds, and octyl acrylate and dodecyl acrylate for γ-cyclodextrin compounds.

[0032] In this specification, the phrase "the PSA does not contain low-molecular-weight guest molecules that can be included in a cyclodextrin compound" means that the PSA does not substantially contain any low-molecular-weight guest molecules. Specifically, the PSA is allowed to contain guest molecules in an amount of 1 mol or less, preferably 0.1 mol or less, particularly preferably 0.01 mol or less, and even more preferably 0.001 mol or less, per 100 mol of the total amount of acrylic monomers. For example, the monomers listed above may be used as acrylic monomers. These monomers basically become polymers upon polymerization and do not become low-molecular-weight guest molecules that can be included in a cyclodextrin compound. However, they may remain in small amounts after polymerization, and are therefore defined as above.

[0033] The polymer having a main chain obtained by copolymerizing the above-mentioned acrylic monomer with a cyclodextrin compound having a polymerizable group preferably does not have a branched structure, which makes it possible to prevent the resulting PSA from becoming too dense and to easily satisfy the gel fraction WG mentioned above.

[0034] The adhesive of this embodiment preferably contains, as a main polymer, an acrylic polymer (P) obtained by copolymerizing the acrylic monomer (A) and the polymerizable cyclodextrin compound (Bp) using an acrylic monomer (A), a cyclodextrin compound having a polymerizable group (hereinafter sometimes referred to as a "polymerizable cyclodextrin compound") (Bp), and preferably further a photopolymerization initiator (C).

[0035] 1. Each ingredient (1) Acrylic Monomer (A) The acrylic monomer (A) in this embodiment is preferably a monofunctional acrylic monomer, which allows the resulting polymer to have no branched structure and makes it easier to satisfy the gel fraction WG described above.

[0036] In the pressure-sensitive adhesive according to this embodiment, the acrylic monomer (A) may be used alone or in combination of two or more. The acrylic monomer (A) preferably first contains a monomer containing a carboxy group in the molecule (carboxy group-containing monomer). By using the carboxy group-containing monomer, the resulting polymer becomes hydrophilic, making it easier to satisfy the above-mentioned physical properties. The carboxy group-containing monomer may be used alone or in combination of two or more.

[0037] 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 from the viewpoint of more easily satisfying the above-mentioned physical properties. These may be used alone or in combination of two or more.

[0038] The content of the carboxyl group-containing monomer in the acrylic monomer (A) is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, particularly preferably 70 to 100 mass%, and even more preferably 80 to 100 mass%, which brings the above-mentioned physical properties into more preferable ranges.

[0039] Secondly, the acrylic monomer (A) preferably contains a monomer containing a nitrogen atom in the molecule (nitrogen atom-containing monomer). By using the nitrogen atom-containing monomer, the adhesive has high cohesive strength, and the above-mentioned physical properties are easily satisfied. The nitrogen atom-containing monomer may be used alone or in combination of two or more.

[0040] Examples of the nitrogen atom-containing monomer include a monomer having an amino group, a monomer having an amide group, and a monomer having a nitrogen-containing heterocycle. Among these, a monomer having an amide group is preferred from the viewpoint of easily satisfying the above-mentioned physical properties. Furthermore, from the viewpoint of increasing the degree of freedom of the portion derived from the nitrogen atom-containing monomer in the higher-order structure of the pressure-sensitive adhesive formed, it is preferable that the nitrogen atom-containing monomer does not contain a reactive unsaturated double bond group other than one polymerizable group used in polymerization to form the acrylic polymer (P). The nitrogen atom-containing monomer may be used alone or in combination of two or more types.

[0041] Examples of monomers having an amide group include (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-tert-butyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-phenyl(meth)acrylamide, N-(n-butoxymethyl)(meth)acrylamide, dimethylaminopropyl(meth)acrylamide, and N-vinylcaprolactam. Among these, N,N-diethyl(meth)acrylamide is preferred, and N,N-diethylacrylamide is particularly preferred. In this specification, (meth)acryl means both acrylic and methacrylic. The same applies to other similar terms.

[0042] The content of the nitrogen atom-containing monomer (particularly the monomer having an amide group) in the acrylic monomer (A) is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, particularly preferably 70 to 100 mass%, and even more preferably 80 to 100 mass%, which brings the above-mentioned physical properties into more preferable ranges.

[0043] The acrylic monomer (A) preferably contains a monomer having a cyclic structure in addition to the above monomers, because the use of such a monomer results in high cohesive strength due to interaction with the cyclodextrin compound in the polymer.

[0044] Examples of monomers having a cyclic structure include (meth)acrylic acid esters such as (meth)acrylic acid esters having an alicyclic structure, (meth)acrylic acid esters having an aromatic ring structure, (meth)acrylic acid esters having a heterocyclic structure, and (meth)acrylic acid esters having an adamantane skeleton. Specific examples include cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, (meth)acrylic acid imide, phenoxyethyl (meth)acrylate, (meth)acrylic acid imide, adamantyl (meth)acrylate, and derivatives thereof.

[0045] Among these, (meth)acrylic acid esters having an adamantane skeleton are preferred from the viewpoint of obtaining high cohesive strength. Specifically, adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, etc. are preferred, and among them, 2-ethyl-2-adamantyl (meth)acrylate is preferred, and 2-ethyl-2-adamantyl acrylate is particularly preferred from the viewpoint of radical polymerizability and interaction with a cyclodextrin compound.

[0046] When the acrylic monomer (A) contains a monomer having a cyclic structure, the content of the monomer having a cyclic structure is preferably 0.01 to 20 mol, more preferably 0.1 to 10 mol, particularly preferably 0.5 to 8 mol, and even more preferably 1 to 6 mol, per 100 mol of the main monomer (carboxyl group-containing monomer / nitrogen atom-containing monomer), which brings the above-mentioned physical properties into more preferable ranges.

[0047] The acrylic monomer (A) may contain an acrylic monomer other than the above-mentioned monomers, for example, a (meth)acrylic acid alkyl ester having 1 to 20 carbon atoms.

[0048] The content of the component derived from the acrylic monomer (A) in the pressure-sensitive adhesive according to this embodiment is preferably 50 to 99.99 mass%, more preferably 65 to 99.9 mass%, particularly preferably 80 to 99.5 mass%, and even more preferably 90 to 99.0 mass%, which brings the above-mentioned physical properties into more preferable ranges.

[0049] (2) Polymerizable cyclodextrin compound (Bp) In this embodiment, the cyclodextrin portion of the polymerizable cyclodextrin compound (Bp) is preferably α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin, and among these, β-cyclodextrin is preferred from the viewpoint of easily satisfying the above-mentioned physical properties.

[0050] The polymerizable cyclodextrin compound (Bp) in this embodiment preferably has a polymerizable group, and the polymerizable group is a group in which a portion of the hydroxyl groups present in the cyclodextrin is substituted. Furthermore, the polymerizable cyclodextrin compound (Bp) in this embodiment preferably exhibits hydrophilicity from the viewpoint of water recycling. Therefore, it is preferable that the hydroxyl groups present in the cyclodextrin remain as they are, except for those substituted with the polymerizable group.

[0051] The polymerizable group of the polymerizable cyclodextrin compound (Bp) is not particularly limited as long as it can polymerize with the acryloyl group of the acrylic monomer (A), but is preferably a group containing a polymerizable unsaturated double bond, and more preferably an ethylenically unsaturated group. Specifically, a (meth)acryloyl group, a vinyl group, an allyl group, or the like is preferred, and a (meth)acryloyl group is particularly preferred. The (meth)acryloyl group may also be a functional group derived from (meth)acrylamide. That is, the polymerizable cyclodextrin compound (Bp) is preferably modified with (meth)acrylamide.

[0052] The polymerizable cyclodextrin compound (Bp) preferably has one polymerizable group per cyclodextrin molecule, which allows the copolymer of the acrylic monomer (A) and the polymerizable cyclodextrin compound (Bp) to have no branched structure, making it easier to satisfy the gel fraction WG described above.

[0053] From the above viewpoint, the content of the cyclodextrin compound having two or more polymerizable groups per molecule in the pressure-sensitive adhesive is preferably low, specifically, 0.1% by mass or less is preferable, particularly 0.01% by mass or less is preferable, and further preferably 0.001% by mass or less is preferable.

[0054] The polymerizable cyclodextrin compound (Bp) in this embodiment is preferably a compound represented by the following formula (1). [ka] (R in the above formula (1) 1 represents a hydrogen atom or a methyl group. 2 represents O, NH, a hydrocarbon containing O, a hydrocarbon containing NH, or a hydrocarbon containing O and NH. CD represents α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, or a derivative thereof.

[0055] Examples of the "hydrocarbon containing NH" mentioned above, assuming that the right side is bonded to CD, include -CH2-NH-CH2-, -NH-CH2-O-CH2-, -O-CH2-NH-CH2-, -CH2-NH-CH2-O-, -O-CH2-NH-CH2-O-, -CH2-O-CO-NH-CH2-O-, -CH2-O-CO-NH-C2H4-O-, etc. Among the above, -NH-CH2-O-CH2- is particularly preferred from the viewpoint of easily satisfying the above-mentioned physical properties.

[0056] CD in the above formula (1) is preferably β-cyclodextrin with a remaining hydroxyl group.

[0057] The weight-average molecular weight (Mw) of the polymerizable cyclodextrin compound (Bp) is preferably 100 to 5000, more preferably 200 to 4000, particularly preferably 600 to 3500, and even more preferably 800 to 3000. This makes it easier to satisfy the above-mentioned physical properties and improves water recycling properties. The weight-average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0058] The content of the polymerizable cyclodextrin compound (Bp)-derived component in the PSA according to the present embodiment (total amount of polymerizable cyclodextrin compound (Bp) used during PSA production) is, in terms of a molar ratio relative to 100 mol of the main acrylic monomer (A), preferably 0.01 to 10, more preferably 0.05 to 8, particularly preferably 0.1 to 6, even more preferably 0.2 to 4, and most preferably 0.4 to 2. This makes it easier to satisfy the above-mentioned physical properties, and the resulting PSA has better water recyclability.

[0059] (3) Photopolymerization initiator (C) When ultraviolet light is used as the active energy ray for copolymerizing the acrylic monomer (A) with the polymerizable cyclodextrin compound (Bp) or for polymerizing the acrylic monomer (A), it is preferable to further use a photopolymerization initiator (C) in producing the adhesive. This allows the acrylic monomer (A) to be copolymerized efficiently without remaining in the adhesive, and also reduces the polymerization and curing time and the exposure dose of the active energy ray.

[0060] Examples of such photopolymerization initiators (C) include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzophenone, p-phenylbenzophenone, Examples of the benzophenone include 4,4'-diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethyl ketal, acetophenone dimethyl ketal, p-dimethylaminobenzoic acid ester, oligo[2-hydroxy-2-methyl-1[4-(1-methylvinyl)phenyl]propanone], 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, etc. These may be used alone or in combination of two or more.

[0061] The amount of photopolymerization initiator (C) used is preferably 0.001 to 10, more preferably 0.01 to 1, and even more preferably 0.02 to 0.5, particularly preferably 0.05 to 0.3, and even more preferably 0.1 to 0.2, in terms of a molar ratio relative to 100 mol of the main acrylic monomer (A). This makes it easier for the resulting pressure-sensitive adhesive to satisfy the aforementioned physical properties.

[0062] (4) Polyhydric alcohol The pressure-sensitive adhesive according to the present embodiment preferably contains a polyhydric alcohol in addition to the acrylic polymer (P) obtained from the above components. The moisture-retaining effect of the polyhydric alcohol allows the pressure-sensitive adhesive to be stored for a long period of time.

[0063] Examples of polyhydric alcohols include dihydric alcohols, trihydric alcohols, and tetrahydric or higher polyhydric alcohols. Examples of dihydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, and neopentyl glycol. Examples of trihydric alcohols include glycerin, trimethylolethane, and trimethylolpropane. Examples of tetrahydric or higher polyhydric alcohols include diglycerin, triglycerin, pentaerythritol, dipentaerythritol, mannitol, and sorbitol. Among the above, glycerin is particularly preferred due to its excellent moisture-retaining properties. One type of polyhydric alcohol may be used alone, or two or more types may be used in combination.

[0064] When the pressure-sensitive adhesive according to the present embodiment contains a polyhydric alcohol, the amount thereof is preferably 10 to 500 parts by mass, more preferably 30 to 300 parts by mass, particularly preferably 50 to 200 parts by mass, and even more preferably 70 to 100 parts by mass, relative to 100 parts by mass of the acrylic polymer (P).

[0065] (5) Other ingredients If desired, the pressure-sensitive adhesive according to this embodiment may contain various additives commonly used in acrylic pressure-sensitive adhesives, such as a silane coupling agent, an anti-rust agent, an ultraviolet absorber, an infrared absorber, an antistatic agent, a tackifier, an antioxidant, a light stabilizer, a softener, a refractive index modifier, a colorant, a filler, etc. The pressure-sensitive adhesive according to this embodiment may also contain a non-polymerizable cyclodextrin compound.

[0066] 2. Manufacturing method The acrylic polymer (P), which is the main polymer of the pressure-sensitive adhesive according to the present embodiment, is preferably produced by copolymerizing an acrylic monomer (A) with a polymerizable cyclodextrin compound (Bp), and particularly preferably by copolymerization without a solvent. Specifically, it is preferably produced by the following method.

[0067] The first manufacturing method is a method in which the acrylic monomer (A) and the polymerizable cyclodextrin compound (Bp) are cured all at once. When forming a pressure-sensitive adhesive layer, a mixed liquid containing the entire amount of the acrylic monomer (A), the entire amount of the polymerizable cyclodextrin compound (Bp), and optionally a photopolymerization initiator (C) and the like is applied to a desired object and cured to form a pressure-sensitive adhesive layer.

[0068] The mixed liquid can be cured by irradiation with active energy rays or by heat treatment, and is preferably cured by irradiation with active energy rays.

[0069] The active energy ray refers to an electromagnetic wave or a charged particle beam that has an energy quantum, and specific examples thereof include ultraviolet rays, electron beams, etc. Among active energy rays, ultraviolet rays are particularly preferred because they are easy to handle.

[0070] The ultraviolet irradiation can be performed using a high-pressure mercury lamp, a Heraeus H lamp, a xenon lamp, or the like, and the amount of ultraviolet irradiation is set to an illuminance of 50 to 1000 mW / cm. 2 The light intensity is preferably 50 to 10,000 mJ / cm 2 is preferably 100 to 7000 mJ / cm 2 More preferably, it is 200 to 4000 mJ / cm 2 On the other hand, the electron beam irradiation can be carried out by an electron beam accelerator or the like, and the irradiation dose of the electron beam is preferably 10 to 1000 krad.

[0071] The heating temperature for the heat treatment is preferably 60 to 150° C., and particularly preferably 80 to 120° C. The heating time for the heat treatment is preferably 10 seconds to 10 minutes, and particularly preferably 30 seconds to 5 minutes. This heat treatment can also serve as a drying treatment after application of the mixed liquid.

[0072] In producing the acrylic polymer (P), the heat treatment may be followed by irradiation with active energy rays, or both treatments may be carried out simultaneously.

[0073] The second production method includes at least the steps of curing a polymerizable cyclodextrin compound (Bp) to obtain a primary cured product (syrup), mixing an acrylic monomer (A), the polymerizable cyclodextrin compound (Bp), and the primary cured product to obtain a secondary mixture, and curing the secondary mixture to obtain a secondary cured product. In the step of obtaining the primary cured product, preferably, a primary mixture containing the acrylic monomer (A) together with the polymerizable cyclodextrin compound (Bp) is cured.

[0074] To form a pressure-sensitive adhesive layer, a primary mixture containing a predetermined amount of polymerizable cyclodextrin compound (Bp) and, optionally, predetermined amounts of acrylic monomer (A), photopolymerization initiator (C), etc. is first prepared, and the primary mixture is cured to form a primary cured product (syrup). Next, the remaining amount of acrylic monomer (A), the remaining amount of polymerizable cyclodextrin compound (Bp), the primary cured product, and, optionally, photopolymerization initiator (C), etc. are mixed to obtain a secondary mixture (secondary mixed liquid). This secondary mixture (secondary mixed liquid) is applied to the desired object and cured to form a pressure-sensitive adhesive layer.

[0075] The amount of the polymerizable cyclodextrin compound (Bp) to be blended when the primary mixture is prepared is preferably 1 mol% or more, more preferably 5 mol% or more, particularly preferably 15 mol% or more, and even more preferably 30 mol% or more, and the upper limit is preferably 100 mol% or less, based on the total amount (100 mol%) of the polymerizable cyclodextrin compound (Bp). The amount of the acrylic monomer (A) to be blended when the primary mixture is prepared is preferably 0 to 80 mol%, particularly preferably 10 to 60 mol%, and even more preferably 20 to 50 mol%, based on the total amount (100 mol%) of the acrylic monomer (A).

[0076] The method for curing the primary mixture and the secondary mixture is the same as in the first manufacturing method described above, except that in curing the primary mixture, the amount of ultraviolet light irradiation is set to an illuminance of 50 to 1000 mW / cm 2 The light intensity is preferably 200 to 10,000 mJ / cm 2 is preferably 500 to 8000 mJ / cm 2 In addition, in curing the secondary mixture, the amount of ultraviolet light to be irradiated is preferably 50 to 1000 mW / cm. 2 The light intensity is preferably 200 to 20,000 mJ / cm 2 is preferably 500 to 10,000 mJ / cm 2 It is particularly preferred that:

[0077] The third production method includes a step of curing one or more acrylic monomers (A) to obtain a primary cured product, a step of mixing at least a polymerizable cyclodextrin compound (Bp) and the primary cured product to obtain a secondary mixture, and a step of curing the secondary mixture to obtain a secondary cured product. In the step of obtaining the secondary mixture, the acrylic monomer (A) is preferably mixed with the polymerizable cyclodextrin compound (Bp) and the primary cured product to obtain a secondary mixture.

[0078] When forming a pressure-sensitive adhesive layer, a primary mixture containing a predetermined amount of acrylic monomer (A) and, optionally, a photopolymerization initiator (C) and the like is first prepared. In the third manufacturing method, the polymerizable cyclodextrin compound (Bp) is not added at this time. The primary mixture is then cured to form a primary cured product (syrup). Next, the remaining amount of acrylic monomer (A), the polymerizable cyclodextrin compound (Bp), the primary cured product, and, optionally, a photopolymerization initiator (C) and the like are mixed to obtain a secondary mixture (secondary mixed liquid). This secondary mixture (secondary mixed liquid) is applied to a desired object and cured to form a pressure-sensitive adhesive layer.

[0079] The amount of the acrylic monomer (A) to be blended when preparing the primary mixture is preferably 5 to 80 mol %, more preferably 10 to 60 mol %, and even more preferably 20 to 50 mol %, relative to the total amount (100 mol %) of the acrylic monomer (A).

[0080] The method for curing the primary mixture and the secondary mixture is the same as in the second manufacturing method described above.

[0081] When the pressure-sensitive adhesive according to the present embodiment contains components other than the acrylic polymer (P), such as a polyhydric alcohol or additives, it can be produced by mixing the acrylic polymer (P) prepared as described above with a polyhydric alcohol and, if desired, adding additives, etc. The pressure-sensitive adhesive can also be diluted with water to achieve a viscosity suitable for application.

[0082] [Adhesive sheet] The pressure-sensitive adhesive sheet according to one embodiment of the present invention comprises at least a pressure-sensitive adhesive layer, and preferably has a release sheet laminated on one or both sides of the pressure-sensitive adhesive layer. Specific configurations of examples of pressure-sensitive adhesive sheets according to this embodiment are shown in Figures 1 and 2.

[0083] 1. Configuration 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.

[0084] 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.

[0085] In both pressure-sensitive adhesive sheets 1A and 1B, pressure-sensitive adhesive layer 11 is made of the pressure-sensitive adhesive described above. The thickness of pressure-sensitive adhesive layer 11 (measured in accordance with JIS K7130) is determined appropriately depending on the intended use of pressure-sensitive adhesive sheet 1A or 1B, but is preferably 1 μm or more, more preferably 3 μm or more, particularly preferably 5 μm or more, even more preferably 10 μm or more, and most preferably 15 μm or more. This allows for good high-temperature lamination. The thickness of pressure-sensitive adhesive layer 11 is preferably 3000 μm or less, more preferably 1000 μm or less, particularly preferably 600 μm or less, even more preferably 100 μm or less, and most preferably 50 μm or less. This improves the water solubility of pressure-sensitive adhesive layer 11 and improves the water recyclability of the pressure-sensitive adhesive. Note that pressure-sensitive adhesive layer 11 may be formed as a single layer or as a laminate of multiple layers.

[0086] 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.

[0087] The substrate 13 may be a desired optical member, such as a polarizing plate (polarizing film), a polarizer, a retardation plate (retardation film), a viewing angle compensation film, a brightness enhancement film, a contrast enhancement film, a liquid crystal polymer film, a diffusion film, or a semi-transmissive reflective film.

[0088] 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.

[0089] The release sheets 12, 12a, and 12b protect the adhesive layer 11 until the adhesive sheet 1 is used, and are peeled off when the adhesive sheet 1 (adhesive layer 11) is used.

[0090] Examples of materials that can be used as the release sheets 12, 12a, and 12b include polyethylene films, polypropylene films, polybutene films, polybutadiene films, polymethylpentene films, polyvinyl chloride films, vinyl chloride copolymer films, polyethylene terephthalate films, polyethylene naphthalate films, polybutylene terephthalate films, polyurethane films, ethylene vinyl acetate films, ionomer resin films, ethylene-(meth)acrylic acid copolymer films, ethylene-(meth)acrylic acid ester copolymer films, polystyrene films, polycarbonate films, polyimide films, and fluororesin films. Crosslinked films of these materials can also be used. Furthermore, laminated films of these materials can also be used.

[0091] The release surfaces of the release sheets 12, 12a, and 12b (particularly the surfaces that come into contact with the pressure-sensitive adhesive layer 11) are preferably subjected to a release treatment. Examples of release agents used for the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents. It is preferable that one of the release sheets 12a and 12b be a heavy-release type release sheet with a high release strength, and the other be 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 it be 20 to 200 μm, and more preferably 30 to 120 μm.

[0093] 2. Manufacturing method To produce the pressure-sensitive adhesive sheet 1A, the aforementioned mixed liquid or secondary mixed liquid is preferably applied to the release surface of release sheet 12 to form a coating layer, and then substrate 13 is laminated on the coating layer, and the coating layer is cured to form pressure-sensitive adhesive layer 11. Alternatively, the aforementioned mixed liquid or secondary mixed liquid is applied to one surface of substrate 13 to form a coating layer, and then the release surface of release sheet 12 is laminated on the coating layer, and the coating layer is cured to form pressure-sensitive adhesive layer 11. The curing conditions are as described above.

[0094] In addition, to manufacture the above-mentioned adhesive sheet 1B, the above-mentioned mixed liquid or secondary mixed liquid is applied to the release surface of one of the release sheets 12a (or 12b) to form a coating layer, and then the release surface of the other release sheet 12b (or 12a) is superimposed on the coating layer, and then the coating layer is cured to form the adhesive layer 11.

[0095] The mixed solution or the secondary mixed solution can be applied by, for example, bar coating, knife coating, roll coating, blade coating, die coating, gravure coating, or the like.

[0096] 3. Physical Properties (1) Heat-resistant adhesiveness The adhesive layer of the adhesive sheet (PET film / adhesive layer) according to this embodiment is attached to soda lime glass, pressurized at 0.5 MPa and 50°C for 20 minutes, and then left to stand for 24 hours under normal pressure, 23°C, and 50% RH to prepare a sample.

[0097] The adhesive strength of the adhesive sheet in the above sample (peel speed 300 mm / min, 180° peel) is defined as the initial adhesive strength (N / 25 mm).

[0098] Meanwhile, the above sample is heated at 100°C for 1 hour. Then, it is left for 24 hours under conditions of 23°C and 50% RH. The adhesive strength of the resulting pressure-sensitive adhesive sheet after heating (peel speed 300mm / min, 180° peel) is defined as the adhesive strength after heating (N / 25mm).

[0099] In the pressure-sensitive adhesive sheet according to this embodiment, the rate of change in adhesive strength (%) calculated by the following formula is preferably 20% or more, particularly preferably 50% or more, and even more preferably 100% or more. This means that the pressure-sensitive adhesive sheet according to this embodiment has excellent heat-resistant adhesive properties. In this case, even if the pressure-sensitive adhesive dissolved in water is re-formed into a pressure-sensitive adhesive layer, it can still exhibit good adhesive strength. From the viewpoint of achieving both heat-resistant adhesiveness and holding power, the rate of change in adhesive strength (%) is preferably 2000% or less, more preferably 1500% or less, particularly preferably 1000% or less, and even more preferably 700% or less. Adhesive strength change rate (%) = (adhesive strength after heating / initial adhesive strength) x 100

[0100] (2) Water-recycling adhesive The adhesive layer of the adhesive sheet (PET film / adhesive layer) according to this embodiment is attached to soda lime glass, pressurized at 0.5 MPa and 50°C for 20 minutes, and then left to stand for 24 hours under normal pressure, 23°C, and 50% RH to prepare a sample.

[0101] The adhesive strength of the adhesive sheet in the above sample (peel speed 300 mm / min, 180° peel) is defined as the initial adhesive strength (N / 25 mm).

[0102] Meanwhile, the sample was immersed in pure water for 24 hours to dissolve the adhesive. The aqueous solution containing the dissolved adhesive was concentrated to a viscosity suitable for coating, after which the adhesive layer was reformed on a release sheet, and a substrate (PET film) was laminated to produce an adhesive sheet (PET film / reformed adhesive layer) similar to the original adhesive sheet. The sample was then left for 24 hours under conditions of 23°C and 50% RH. The adhesive strength of the resulting adhesive sheet with the reformed adhesive layer (peel speed 300 mm / min, 180° peel) was taken as the adhesive strength after reformation (N / 25 mm).

[0103] In the pressure-sensitive adhesive sheet according to this embodiment, the adhesive strength change rate (%) calculated by the following formula is preferably 50% or more, particularly preferably 75% or more, and even more preferably 100% or more. As a result, the pressure-sensitive adhesive sheet according to this embodiment can maintain high adhesive strength even when the pressure-sensitive adhesive layer is dissolved in water and then reformed, and can be said to have excellent water-recycling adhesiveness. From the viewpoint of achieving both water-recycling adhesiveness and holding power, the adhesive strength change rate (%) is preferably 400% or less, more preferably 300% or less, particularly preferably 200% or less, and even more preferably 150% or less. Adhesive strength change rate (%) = (adhesive strength after reformation / initial adhesive strength) x 100

[0104] (3) Holding power When the adhesive layer of the adhesive sheet (PET film / adhesive layer) according to this embodiment is applied to soda-lime glass and left at 40°C for 15 minutes, and then subjected to a holding power test in accordance with JIS Z0237:2009, the amount of deviation under the conditions of a test temperature of 40°C, an application area of ​​25mm x 25mm, a load of 9.8N, and a holding time of 3 hours is preferably 22mm or less, more preferably 19mm or less, particularly preferably 17mm or less, and even more preferably 15mm or less. This indicates that the adhesive sheet has excellent holding power. Details of the holding power test in this specification are as shown in the test examples described below.

[0105] 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.

[0106] 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.

[0107] 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]

[0108] 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.

[0109] [Production Example 1] As the polymerizable cyclodextrin compound (Bp), a polymerizable β-cyclodextrin compound represented by the following formula (2) was produced by the same procedure as in Production Example 1 (βCDAAm) of JP 2020-143220 A. [ka]

[0110] Example 1 1. Preparation of adhesive composition coating solution Acrylic acid as the acrylic monomer (A), the polymerizable β-cyclodextrin compound (Bp) produced in Production Example 1, and 1-hydroxycyclohexyl phenyl ketone as the photopolymerization initiator (C) were mixed in the molar ratios shown in Table 1 and thoroughly stirred to obtain a mixed solution.

[0111] 2. Manufacturing of adhesive sheets The mixture obtained in step 1 above was applied with a knife coater to the release-treated surface of a heavy release type release sheet R1, which was a polyethylene terephthalate film with one side treated with a silicone-based release agent.

[0112] Next, the coating layer on the release sheet R1 obtained above was bonded 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.

[0113] The coating layer was then cured by irradiating it with active energy rays (ultraviolet rays; UV) through the release sheet R2 under the following conditions to form an 80 μm thick adhesive layer. In this way, an adhesive sheet consisting of release sheet R2 / adhesive layer (thickness: 80 μm) / release sheet R1 was produced. The adhesive layer was composed of an acrylic polymer (P) obtained by polymerizing an acrylic monomer (A) and a polymerizable β-cyclodextrin compound (Bp).

[0114] <Activated energy ray irradiation conditions> -High pressure mercury lamp used ·Illuminance 200mW / cm 2 ,Light intensity 2000mJ / cm 2 The UV illuminance and light intensity meter used is the "UVPF-A1" manufactured by Eye Graphics.

[0115] 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, when the release sheets were peeled from the adhesive layers of the obtained adhesive sheets, the peel strength of release sheet R1 was greater than that of release sheet R2.

[0116] [Examples 2 to 6, Comparative Examples 1 to 5] Pressure-sensitive adhesive sheets were produced in the same manner as in Example 1, except that the type and amount of acrylic monomer (A), the amount of polymerizable cyclodextrin compound (Bp), and the amount of photopolymerization initiator (C) were changed as shown in Table 1. In Examples 2, 3, 5, and 6, glycerin was further blended in the amount shown in Table 1 (parts by mass relative to 100 parts by mass of acrylic polymer), and in Comparative Examples 3 to 5, pure water was further blended in the amount shown in Table 1 (same as above).

[0117] Details of the abbreviations and other information listed in Table 1 are as follows: [Acrylic Monomer (A)] AAc: acrylic acid DEAAm: N,N-diethylacrylamide EtAdA: 2-ethyl-2-adamantyl acrylate HDA: 1,6-hexanediol diacrylate

[0118] [Test Example 1] (Measurement of gel fraction WG) The pressure-sensitive adhesive sheets produced in the examples and comparative examples were cut to a size of 80 mm x 80 mm, the pressure-sensitive adhesive layer was wrapped in a polyester mesh (mesh size 200), and the mass was weighed on a precision balance. The mass of the mesh alone was subtracted to calculate the mass of the pressure-sensitive adhesive alone. This mass was designated M1.

[0119] Next, the adhesive wrapped in the polyester mesh was immersed in pure water at room temperature (23°C) for 72 hours. The adhesive was then removed and air-dried for 24 hours in an environment with a temperature of 23°C and a relative humidity of 50%, and then dried in an oven at 80°C for 12 hours. After drying, the mass was weighed using a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. This mass was designated M2. The gel fraction (%) was expressed as (M2 / M1) x 100. This gave the gel fraction (WG) of the adhesive (gel fraction after immersion in pure water for 72 hours). The results are shown in Table 2.

[0120] Test Example 2 (Weight Loss Measurement) The pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples were left to stand for 24 hours in an environment at a temperature of 23°C and a relative humidity of 50%. Thereafter, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet was measured for the rate of weight loss from the initial weight (thermal weight loss rate = weight loss; %) when heated at 100°C for 1 hour using a thermogravimetric analyzer (TGA; Shimadzu Corporation, product name "DTA-60"). The results are shown in Table 2.

[0121] [Test Example 3] (Tensile test) The adhesive layers of the pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples were laminated in multiple layers to a total thickness of 500 μm, and then a sample measuring 10 mm wide x 75 mm long was cut out. The sample was placed in a tensile tester (manufactured by Orientec Co., Ltd., product name "Tensilon") so that the sample measurement area was 10 mm wide x 25 mm long (in the elongation direction), and elongated at a tensile speed of 200 mm / min using the tensile tester in an environment of 23°C and 50% RH. The sample was elongated until it broke, and the maximum stress (MPa) at that time was measured. The results are shown in Table 2.

[0122] [Test Example 4] (Measurement of adhesive strength) 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 an easy-adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4360", thickness: 100 μm) having an easy-adhesion layer to obtain a release sheet R1 / adhesive layer / PET film laminate. The resulting laminate was cut into a width of 25 mm and a length of 100 mm.

[0123] The release sheet R1 was peeled from the laminate under an environment of 23°C and 50% RH, and the exposed adhesive layer was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.). It was then pressurized for 20 minutes at 0.5 MPa and 50°C in an autoclave manufactured by Kurihara Manufacturing Co., Ltd. The sample was then left for 24 hours under conditions of 23°C and 50% RH, and this was used as a sample. The adhesive strength (initial adhesive strength; N / 25 mm) was measured using a tensile tester (manufactured by Orientec Co., Ltd., product name "Tensilon") at a peel rate of 300 mm / min and a peel angle of 180°. Measurements were conducted under conditions other than those described here in accordance with JIS Z0237:2022. The results are shown in Table 2.

[0124] [Test Example 5] (Evaluation of heat-resistant adhesiveness) The adhesive strength measured in Test Example 4 is defined as the initial adhesive strength (N / 25 mm). The sample prepared in Test Example 4 was heated in an oven at 100°C for 1 hour, and then left to stand for 24 hours under conditions of 23°C and 50% RH. The adhesive strength of the resulting pressure-sensitive adhesive sheet after heating was measured in the same manner as in Test Example 4. This was designated as the post-heating adhesive strength (N / 25 mm).

[0125] The adhesive strength change rate (%) was calculated from the above initial adhesive strength and the measured adhesive strength after heating according to the following formula. Adhesive strength change rate (%) = (adhesive strength after heating / initial adhesive strength) x 100

[0126] The heat-resistant adhesive property was then evaluated based on the calculated rate of change in adhesive strength according to the following criteria. The results are shown in Table 2. ○…Adhesive strength change rate is 50% or more △: Adhesive strength change rate is less than 50%, 20% or more ×…Adhesive strength change rate is less than 20%

[0127] [Test Example 6] (Evaluation of Water Recycle Adhesion) The adhesive strength measured in Test Example 4 is defined as the initial adhesive strength (N / 25 mm). The sample prepared in Test Example 4 was immersed in pure water for 24 hours to dissolve the adhesive. The aqueous solution containing the dissolved adhesive was concentrated to a viscosity suitable for coating and then applied to the release surface of Release Sheet R1. The solution was then dried by heating at 90°C for 5 minutes to reform an adhesive layer (80 μm). This adhesive layer was bonded to the adhesive layer of a PET film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4360", thickness: 100 μm) having an adhesive layer. In Comparative Examples 3 and 5, the adhesive layer could not be reformed.

[0128] The release sheet R1 was peeled from the pressure-sensitive adhesive layer under an environment of 23°C and 50% RH, and the exposed pressure-sensitive adhesive layer was attached to soda-lime glass (manufactured by Nippon Sheet Glass Co., Ltd.), and then pressurized in an autoclave manufactured by Kurihara Manufacturing Co., Ltd. at 0.5 MPa and 50°C for 20 minutes. The sample was then left to stand under conditions of 23°C and 50% RH for 24 hours, and this was used as a sample. The adhesive strength of this sample was measured in the same manner as in Test Example 4. This was taken as the adhesive strength after reformation (N / 25 mm).

[0129] The adhesive strength change rate (%) was calculated from the above initial adhesive strength and the measured adhesive strength after reforming according to the following formula. Adhesive strength change rate (%) = (adhesive strength after reformation / initial adhesive strength) x 100

[0130] The adhesive strength was then evaluated based on the calculated adhesive strength change rate, according to the following criteria. The results are shown in Table 2. ◎...Adhesive strength change rate is 100% or more ○…Adhesive strength change rate is less than 100%, 50% or more ×: Adhesive strength change rate is less than 50% or re-forming is not possible

[0131] [Test Example 7] (Holding Power Test) The holding power of the adhesive sheets was measured in accordance with JIS Z0237:2009, except for the procedures described below. The release sheet R2 was peeled off from the adhesive sheets produced in the Examples and Comparative Examples, and the exposed adhesive layer was attached to an easy-adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4360", thickness: 100 μm) having an easy-adhesion layer, to obtain a release sheet R1 / adhesive layer / PET film laminate. The resulting laminate was cut to a width of 25 mm and a length of 125 mm.

[0132] Next, the release sheet R1 was peeled off from the laminate, and this was used as a sample. Only the 25 mm × 25 mm portion of the exposed adhesive layer of the sample was attached to a soda lime glass plate (manufactured by Nippon Sheet Glass Co., Ltd.). The soda lime glass plate was then placed perpendicular to the ground so that the sample was hanging from the soda lime glass plate, and left at 40 ° C for 15 minutes. Thereafter, the sample was left at 40 ° C for 3 hours while applying a load of 9.8 N, and the amount of displacement (mm) of the sample after 3 hours was measured.

[0133] Based on the amount of displacement measured above and whether or not the device fell, the holding power was evaluated according to the following criteria. The results are shown in Table 2. ◎...Misalignment is 20mm or less 〇: Misalignment is over 20mm and no fall occurs ×…Falled

[0134] [Table 1]

[0135] [Table 2]

[0136] As can be seen from Table 2, the adhesive sheets (adhesives) produced in the examples had excellent heat-resistant adhesive properties and water-recyclable adhesive properties, and could be recycled with water and reused as adhesive sheets. [Industrial Applicability]

[0137] The pressure-sensitive adhesive and pressure-sensitive adhesive sheet according to the present invention are suitable for applications requiring recyclability. [Explanation of symbols]

[0138] 1A, 1B...Adhesive sheet 11...Adhesive layer 12, 12a, 12b...Release sheet 13...Base material

Claims

1. A pressure-sensitive adhesive containing a cyclodextrin compound, The gel fraction after immersion in pure water for 72 hours is less than 50%; Weight loss when heated at 100°C for 1 hour is less than 10% A pressure-sensitive adhesive characterized by:

2. The adhesive according to claim 1, characterized in that the maximum stress when the adhesive is molded into a thickness of 500 μm and a width of 10 mm and stretched to the breaking elongation at a measuring length of 20 mm and a tensile speed of 200 mm / min under an environment of 23°C and 50% RH is 1 MPa or more.

3. 2. The adhesive according to claim 1, wherein an adhesive layer made of the adhesive and having a thickness of 80 μm and a width of 25 mm has an adhesive strength to soda lime glass of 0.1 N / 25 mm or more.

4. 2. The pressure-sensitive adhesive according to claim 1, wherein the cyclodextrin compound has a polymerizable group.

5. 2. The adhesive according to claim 1, which is an acrylic adhesive.

6. 5. The pressure-sensitive adhesive according to claim 4, comprising an acrylic polymer obtained by copolymerizing an acrylic monomer with the cyclodextrin compound.

7. A pressure-sensitive adhesive sheet having at least a pressure-sensitive adhesive layer, The adhesive constituting the adhesive layer is the adhesive according to any one of claims 1 to 6. A pressure-sensitive adhesive sheet characterized by:

8. The pressure-sensitive adhesive sheet has two release sheets, The pressure-sensitive adhesive layer is sandwiched between the two release sheets so as to be in contact with the release surfaces of the two release sheets. The adhesive sheet according to claim 7 .

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