Adhesive sheet

Abstract

To provide a releasable adhesive sheet which utilizes biomass in an adhesive layer while exhibiting superior releasability and superior adhesion between the adhesive layer and a substrate.SOLUTION: An adhesive sheet of the present invention includes a substrate and a releasable adhesive layer provided on one surface side of the substrate. The adhesive layer comprises a crosslinked product of a biomass-based emulsion adhesive crosslinked by an epoxy crosslinking agent. It is preferable that the epoxy crosslinking agent is glycerol polyglycidyl ether.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an adhesive sheet.

Background Art

[0002] A re-peelable adhesive sheet (re-peelable adhesive sheet) that can be peeled relatively easily after being attached to an adherend is easy to handle and is used for various labels and the like (see, for example, Patent Document 1).

[0003] Conventionally, an organic solvent-based adhesive composition has been used as an adhesive composition for forming an adhesive layer of an adhesive sheet. However, there has been a problem that the organic solvent volatilizes during coating. In addition, there has also been a problem that a small amount of the organic solvent remains in the adhesive layer of the adhesive sheet.

[0004] On the other hand, an emulsion-type adhesive composition is superior to an organic solvent-type adhesive composition in terms of environmental aspects, safety aspects, and hygiene aspects.

[0005] Therefore, in recent years, an emulsion-type adhesive composition has been frequently used as an adhesive composition for forming an adhesive layer of an adhesive sheet (see, for example, Patent Document 2).

[0006] In recent years, environmental problems such as global warming have been emphasized, and regulations on suppressing the emission of greenhouse gases such as carbon dioxide have been strengthened. From such a viewpoint, an adhesive sheet has been proposed that can reduce the amount of fossil resource-based materials used and reduce the amount of greenhouse gas emissions during incineration or the like by blending plant-derived components or the like.

[0007] However, in the re-peelable adhesive sheet, when the biomass degree of the adhesive layer is increased, there has been a problem that the re-peelability and the adhesion of the adhesive layer to the substrate are deteriorated.

[0008] In addition, many adherends to which the pressure-sensitive adhesive sheet is to be attached have curved surfaces. Therefore, there is also a demand for a pressure-sensitive adhesive sheet that is particularly excellent in adhesiveness to curved surfaces.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] An object of the present invention is to provide a pressure-sensitive adhesive sheet that is excellent in re-peelability and adhesion between the pressure-sensitive adhesive layer and the base material while utilizing biomass in the pressure-sensitive adhesive layer in a re-peelable pressure-sensitive adhesive sheet.

Means for Solving the Problems

[0011] Such an object is achieved by the present invention described in the following (1) to (5). (1) A base material and, a re-peelable pressure-sensitive adhesive layer provided on one surface side of the base material, wherein the pressure-sensitive adhesive layer contains a crosslinked product of a biomass-based emulsion-type pressure-sensitive adhesive crosslinked with an epoxy-based crosslinking agent.

[0012] (2) The pressure-sensitive adhesive sheet according to (1) above, wherein the epoxy-based crosslinking agent is glycerol polyglycidyl ether.

[0013] (3) The pressure-sensitive adhesive sheet according to (1) or (2) above, wherein the functional group blocking rate of the emulsion-type pressure-sensitive adhesive is 10 mol% or more and 50 mol% or less.

[0014] (4) The pressure-sensitive adhesive sheet according to any one of (1) to (3) above, wherein the ratio of the epoxy-based crosslinking agent to 100 parts by mass of the emulsion-type pressure-sensitive adhesive in the pressure-sensitive adhesive layer is 0.2 parts by mass or more and 1.0 part by mass or less.

[0015] (5) The pressure-sensitive adhesive sheet according to any one of (1) to (4) above, which is attached to the curved surface portion of an adherend having a curved surface.

Advantages of the Invention

[0016] According to the present invention, in a re-peelable pressure-sensitive adhesive sheet, it is possible to provide a pressure-sensitive adhesive sheet that is excellent in re-peelability and adhesion between the pressure-sensitive adhesive layer and the base material while utilizing biomass in the pressure-sensitive adhesive layer.

Brief Description of the Drawings

[0017]

Figure 1

Modes for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0019] [1] Pressure-sensitive adhesive sheet FIG. 1 is a cross-sectional view showing a configuration example of the pressure-sensitive adhesive sheet of the present invention. The pressure-sensitive adhesive sheet 1 has a base material 10 and a re-peelable pressure-sensitive adhesive layer 20 provided on one surface side of the base material 10. And the pressure-sensitive adhesive layer 20 contains a crosslinked product of a biomass-based emulsion-type pressure-sensitive adhesive crosslinked with an epoxy-based crosslinking agent.

[0020] The pressure-sensitive adhesive sheet 1 is adhered so as to cover at least a part of the surface of the adherend. In this specification, the concept of "sheet" shall include the concept of film.

[0021] According to this adhesive sheet 1, since the adhesive layer 20 contains a biomass-based adhesive, the environmental load can be reduced.

[0022] In this specification, the biomass-based adhesive refers to an adhesive in which components derived from organisms (hereinafter also referred to as "biomass materials") are blended.

[0023] Biomass materials such as components derived from plants release carbon dioxide, which is a greenhouse gas, by combustion or the like. However, this carbon dioxide can typically be traced back to what was absorbed from the atmosphere by photosynthesis during the growth process of plants, so it does not substantially contribute to the increase in carbon dioxide in the atmosphere. That is, biomass materials can be regarded as carbon-neutral materials that do not substantially cause an increase or decrease in carbon through circulation in the global environment over a relatively short period of time.

[0024] And because the biomass material is a carbon-neutral material, the adhesive sheet 1 that incorporates the biomass material and reduces the usage amount of fossil resource-based materials has a reduced carbon dioxide emission amount derived from fossil resource-based materials during incineration or the like. In other words, the carbon dioxide emission amount derived from materials that are difficult to recycle in a relatively short period of time is reduced, and the greenhouse gas emission amount during incineration or the like is reduced.

[0025] Also, according to this adhesive sheet 1, since the adhesive layer 20 contains a crosslinked product of an adhesive crosslinked with an epoxy-based crosslinking agent, the crosslinked product forms a suitable network structure within the adhesive layer 20, thereby suitably improving the cohesive force of the adhesive layer 20 and enabling it to have an appropriate adhesive force.

[0026] As a result, the adhesive sheet 1 has improved adhesion between the adhesive layer 20 and the base material 10 and is excellent in re-peelability.

[0027] In addition, in the adhesive sheet 1, an emulsion-type adhesive, which is a non-solvent-based adhesive, is used as the adhesive. Therefore, it is possible to reduce the emission amount of volatile organic compounds (VOCs) during the production of the adhesive sheet 1, and it is also possible to reduce the residual solvent amount of the product after production.

[0028] Therefore, in this adhesive sheet 1, while increasing the biomass degree of the adhesive layer 20 to reduce the environmental load, the releasability and the adhesion between the adhesive layer 20 and the base material 10 are excellent. In addition, the adhesive sheet 1 is also excellent in conformability to a curved surface.

[0029] On the other hand, when the above conditions are not satisfied, satisfactory results cannot be obtained. For example, even if the adhesive layer contains a crosslinked product of a biomass-based emulsion-type adhesive crosslinked with a crosslinking agent, if the crosslinking agent is not an epoxy-based crosslinking agent but a crosslinking agent other than the epoxy-based crosslinking agent, the adhesive strength increases and the releasability decreases after a certain number of days have passed after sticking.

[0030] [1-1] Base material Examples of the base material 10 included in the adhesive sheet 1 include papers, synthetic papers, synthetic resin films, and the like. Note that the base material 10 may be a single layer or a multilayer formed by laminating two or more layers.

[0031] Examples of the papers used as the base material 10 include kraft paper, fine paper, art paper, coated paper, cast-coated paper, foil paper, thermal paper, thermal transfer paper, and the like.

[0032] Examples of the synthetic papers used as the base material 10 include synthetic papers composed of resins such as polypropylene, polystyrene, polyethylene, and polyester.

[0033] Note that even if a paper base material is used in the adhesive sheet 1, since the adhesive sheet 1 has excellent releasability, breakage of the paper base material hardly occurs when the adhesive sheet 1 is peeled from the adherend.

[0034] Examples of the resin constituting the synthetic resin film used as the base material 10 include polyolefin resins such as polyethylene and polypropylene; vinyl resins such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polystyrene; acrylonitrile-butadiene-styrene copolymer; cellulose triacetate; polycarbonate; urethane resins such as polyurethane and acrylic-modified polyurethane; polymethylpentene; polysulfone; polyetheretherketone; polyethersulfone; polyphenylene sulfide; polyimide resins such as polyetherimide and polyimide; polyamide resins; acrylic resins; fluorine-based resins, etc.

[0035] Among these, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene, and acrylonitrile-butadiene-styrene copolymer are preferred.

[0036] Here, the resin constituting the synthetic resin film is preferably a recycled resin. Thereby, the environmental load can be more effectively reduced.

[0037] Examples of the recycled resin include recycled polyethylene terephthalate (PET), etc.

[0038] Also, a metallic tone gloss layer such as aluminum vapor deposition or tin vapor deposition may be provided on either one surface of the synthetic resin film.

[0039] Note that the synthetic resin film may contain various additives. Examples of such additives include ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, slip agents, antiblocking agents, fillers, colorants, etc.

[0040] The thickness of the base material 10 is appropriately set according to the application, but is preferably 5 μm or more and 1000 μm or less, more preferably 10 μm or more and 700 μm or less, and even more preferably 20 μm or more and 500 μm. As a result, the adhesive sheet 1 has particularly excellent handleability.

[0041] In addition, in the adhesive sheet 1, from the viewpoint of improving the adhesion of ink or the like during printing, an easy-adhesion layer or the like may be further provided on the surface of the base material 10 opposite to the adhesive layer 20. The printing method for the adhesive sheet 1 is not particularly limited, and examples include flexographic printing, gravure printing, offset printing, screen printing, inkjet printing, digital printing, laser printing, and the like.

[0042] [1-2] Adhesive layer The adhesive layer 20 is the part that comes into contact with and bonds to the adherend when the adhesive sheet 1 is adhered to the adherend.

[0043] As described above, the adhesive layer 20 is a re-peelable adhesive layer and includes a crosslinked product of an emulsion-type adhesive crosslinked with an epoxy-based crosslinking agent.

[0044] Also, as described above, the adhesive layer 20 contains a biomass-based adhesive in which a plant-derived component is blended.

[0045] Examples of the plant-derived component include (meth)acrylic acid alkyl esters obtained by esterifying alcohols made from vegetable oils (e.g., palm oil, coconut oil, rosin), rice bran, corn cobs, cotton, pulp, seeds, etc., and polymers obtained by polymerizing using at least a part of the monomers.

[0046] [1-2-1] Emulsion-type adhesive The emulsion-type pressure-sensitive adhesive is a pressure-sensitive adhesive formed using an adhesive composition that is an emulsion containing an adhesive component or a precursor thereof as a dispersed phase. Usually, the emulsion-type pressure-sensitive adhesive itself that constitutes the pressure-sensitive adhesive layer 20 hardly contains the dispersion medium component of the adhesive composition. Even when it contains the dispersion medium component of the adhesive composition, the component does not function as a dispersion medium.

[0047] The adhesive composition is preferably an aqueous emulsion containing an acrylic copolymer.

[0048] The emulsion-type pressure-sensitive adhesive can be obtained, for example, by emulsion-polymerizing a monomer mixture containing an alkyl (meth)acrylate having an alkyl group with 4 to 12 carbon atoms, a carboxyl group-containing unsaturated monomer, a carbonyl group-containing unsaturated monomer, and, if necessary, other unsaturated monomers. In this specification, the term "(meth)acrylic acid" is a concept that includes both "acrylic acid" and "methacrylic acid". The same applies to "(meth)acrylate", "(meth)acrylo", and "(meth)allyl" described later.

[0049] Examples of the alkyl (meth)acrylate having an alkyl group with 4 to 12 carbon atoms include n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, isooctyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, isoundecyl (meth)acrylate, dodecyl (meth)acrylate, isododecyl (meth)acrylate, etc. One or more selected from these can be used in combination. Among them, n-octyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl acrylate are preferred.

[0050] Examples of the carboxyl group-containing unsaturated monomer include acrylic acid, acrylic acid dimer, methacrylic acid, crotonic acid, itaconic acid, maleic acid, etc., and one or more selected from these can be used in combination. Among them, acrylic acid and methacrylic acid are preferred.

[0051] Furthermore, examples of other unsaturated monomers include (meth)acrylic acid alkyl esters having an alkyl group with 1 to 3 carbon atoms such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, etc., and (meth)acrylic acid alkyl esters having an alkyl group with 13 or more carbon atoms such as tridecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, etc., dimethylaminoethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, methoxy triethylene glycol (meth)acrylate, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, etc.

[0052] In addition to the above, as the unsaturated monomer, a functional group-containing unsaturated monomer, for example, a hydroxyl group-containing unsaturated monomer, an epoxy group-containing unsaturated monomer, an alkoxysilyl group-containing unsaturated monomer, an unsaturated monomer containing an amide group or a methylol group, a polyfunctional unsaturated monomer, etc. may be used.

[0053] Examples of the hydroxyl group-containing unsaturated monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, etc.

[0054] Examples of the unsaturated monomer containing an amide group or a methylol group include acrylamide, methacrylamide, N-methylol acrylamide, butoxy N-methylol acrylamide, etc.

[0055] The pressure-sensitive adhesive sheet 1 may use a biomass-based material for at least a part of the constituent monomers of the polymer that constitutes the emulsion-type pressure-sensitive adhesive in the pressure-sensitive adhesive layer 20. However, as the biomass-based monomer, it is preferable to use n-octyl (meth) acrylate.

[0056] Thereby, an acrylic copolymer having a low glass transition temperature, flexibility, and suitable adhesive strength can be obtained, and characteristics with a good balance between adhesive strength and re-peelability can be obtained in the pressure-sensitive adhesive layer 20.

[0057] The content of n-octyl (meth) acrylate is preferably 50% by mass or more and 80% by mass or less, more preferably 55% by mass or more and 75% by mass or less, and even more preferably 60% by mass or more and 70% by mass or less, based on the total amount of the monomer components constituting the acrylic copolymer contained in the pressure-sensitive adhesive layer 20. Thereby, the above-described effects can be made more remarkable.

[0058] However, since biomass materials are expensive, in order to suppress the raw material cost while increasing the proportion of biomass materials, in addition to n-octyl (meth) acrylate, 2-ethylhexyl acrylate is preferably used in combination as a monomer of the acrylic copolymer.

[0059] In addition, by using 2-ethylhexyl acrylate, an acrylic copolymer having properties similar to those obtained when using n-octyl (meth) acrylate, in other words, having a low glass transition temperature, flexibility, and suitable adhesive strength can be obtained.

[0060] In particular, by using n-octyl (meth) acrylate and 2-ethylhexyl acrylate in combination, the balance between the adhesive strength and re-peelability of the pressure-sensitive adhesive layer 20 as described above can be made particularly excellent, and the raw material cost can be suitably suppressed.

[0061] The content rate of 2-ethylhexyl acrylate is preferably 5% by mass or more and 20% by mass or less, more preferably 7% by mass or more and 18% by mass or less, and still more preferably 10% by mass or more and 15% by mass or less, based on the total amount of the monomer components constituting the acrylic copolymer contained in the pressure-sensitive adhesive layer 20. Thereby, the above-described effects can be made more remarkable.

[0062] With respect to the total amount of the monomer components constituting the acrylic copolymer contained in the pressure-sensitive adhesive layer 20, When the content rate of n-octyl (meth) acrylate is X1 [% by mass] and the content rate of 2-ethylhexyl acrylate is X2 [% by mass], it preferably satisfies the relationship of 0.10 ≤ X2 / X1 ≤ 0.20, more preferably satisfies the relationship of 0.12 ≤ X2 / X1 ≤ 0.19, and still more preferably satisfies the relationship of 0.13 ≤ X2 / X1 ≤ 0.18. Thereby, the above-described effects can be made more remarkable.

[0063] In the adhesive sheet 1, it is preferable to use acrylic acid as the functional group-containing monomer constituting the emulsion-type pressure-sensitive adhesive in the pressure-sensitive adhesive layer 20.

[0064] The carboxyl group possessed by acrylic acid can react with an epoxy-based crosslinking agent during aging after the formation of the pressure-sensitive adhesive layer 20, and a more suitable network structure can be formed within the pressure-sensitive adhesive layer 20.

[0065] Thereby, the balance of the re-peelability of the adhesive sheet 1, the adhesion between the pressure-sensitive adhesive layer 20 and the base material 10, and the curvature adhesiveness can be made more suitable.

[0066] The content rate of acrylic acid is preferably 0.5% by mass or more and 5.0% by mass or less, more preferably 0.7% by mass or more and 3.0% by mass or less, and still more preferably 0.8% by mass or more and 2.0% by mass or less, based on the total amount of the monomer components constituting the acrylic copolymer contained in the pressure-sensitive adhesive layer 20. This can make the above-described effects more remarkable.

[0067] The method for producing the emulsion-type pressure-sensitive adhesive is not particularly limited. For example, it can be preferably produced by adding an emulsifier and a polymerization initiator to a monomer mixture containing the above-described monomers and performing emulsion polymerization.

[0068] In the emulsion polymerization, from the viewpoint of polymerization stability, it is preferable that the monomer mixture dissolves the emulsifier (or a part of the emulsifier) in the monomer mixture or is previously in the state of an O / W-type emulsion.

[0069] The content of the emulsion-type pressure-sensitive adhesive in the pressure-sensitive adhesive layer 20 is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less.

[0070] If the content of the emulsion-type pressure-sensitive adhesive in the pressure-sensitive adhesive layer 20 is less than the lower limit value, the adhesion of the pressure-sensitive adhesive layer 20 to the base material 10 and the adhesion of the pressure-sensitive adhesive sheet 1 to the adherend may decrease. On the other hand, if the content of the emulsion-type pressure-sensitive adhesive in the pressure-sensitive adhesive layer 20 exceeds the upper limit value, the adhesion of the pressure-sensitive adhesive layer 20 to the adherend becomes too high, and when the pressure-sensitive adhesive sheet 1 is peeled off from the adherend, a part of the pressure-sensitive adhesive layer 20 may remain on the adherend.

[0071] The average particle diameter of the emulsion-type pressure-sensitive adhesive in the pressure-sensitive adhesive layer 20 is preferably 80 nm or more and 1000 nm or less, more preferably 200 nm or more and 800 nm or less, and even more preferably 300 nm or more and 600 nm or less.

[0072] If the average particle diameter of the emulsion-type pressure-sensitive adhesive is less than the lower limit value, the adhesion of the pressure-sensitive adhesive layer 20 to the adherend becomes too high, and when the pressure-sensitive adhesive sheet 1 is peeled off from the adherend, a part of the pressure-sensitive adhesive layer 20 may remain on the adherend. On the other hand, if the average particle diameter of the emulsion-type pressure-sensitive adhesive exceeds the upper limit value, the adhesion of the pressure-sensitive adhesive layer 20 to the base material 10 may decrease, or the adhesiveness of the pressure-sensitive adhesive sheet 1 to the adherend may decrease. In addition, in this specification, the "average particle diameter" refers to the volume-based average particle diameter.

[0073] [1-2-2] Epoxy crosslinking agent The epoxy crosslinking agent is a component that can crosslink the emulsion-type pressure-sensitive adhesive by heating and seasoning the pressure-sensitive adhesive composition and can favorably form a crosslinked structure of a three-dimensional network structure. Thereby, the pressure-sensitive adhesive layer 20 has a predetermined cohesive force and is excellent in mechanical strength, adhesion to the base material 10, and re-peelability. In particular, the adhesiveness to a curved surface is good.

[0074] The epoxy crosslinking agent is preferably a compound having two or more epoxy groups or glycidyl groups in one molecule.

[0075] Examples of such epoxy crosslinking agents include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and the like. The epoxy crosslinking agent may be used alone or in combination of two or more.

[0076] Among them, as the epoxy crosslinking agent, it is preferable to use sorbitol polyglycidyl ether and glycerol polyglycidyl ether, and it is more preferable to use glycerol polyglycidyl ether.

[0077] As a result, in the adhesive layer 20, a three-dimensional network structure can be more suitably formed, and the adhesion to the base material 10 and the peelability can be made more excellent. In particular, by using glycerol polyglycidyl ether as the epoxy-based crosslinking agent, the curvature adhesion can be made excellent.

[0078] In addition, in this specification, glycerol polyglycidyl ether has one glycerol and a plurality of glycidyl ethers, and has the general formula C3H5O3H 3-n (C3H5O) n (n is 2 or 3), and is distinguished from polyglycerol polyglycidyl ether and diglycerol polyglycidyl ether.

[0079] The functional groups of the emulsion-type adhesive are preferably blocked by the epoxy groups or glycidyl groups of the epoxy-based crosslinking agent.

[0080] The functional group blocking rate of the emulsion-type adhesive is preferably 10 mol% or more and 50 mol% or less, more preferably 20 mol% or more and 40 mol% or less, and even more preferably 25 mol% or more and 35 mol% or less.

[0081] As a result, the peelability from the adherend of the adhesive sheet 1 can be made more excellent, and the contamination of the adherend by the adhesive can be more suitably prevented.

[0082] On the other hand, when the functional group blocking rate is less than the lower limit value, the adherend may be contaminated by the adhesive because the adhesion to the adherend increases due to the interaction between the functional group in the functional group-containing unsaturated monomer and the adherend. On the other hand, when the functional group blocking rate exceeds the upper limit value, the adherend may be contaminated because the epoxy-based crosslinking agent that has not undergone the crosslinking reaction remains on the adherend.

[0083] In addition, in this specification, the functional group blocking rate can be determined as the mol% of the epoxy group or glycidyl group of the epoxy-based crosslinking agent with respect to the functional group of the acrylic copolymer constituting the emulsion-type adhesive.

[0084] The ratio of the epoxy-based crosslinking agent to 100 parts by mass of the emulsion-type adhesive in the adhesive layer 20 is preferably 0.2 parts by mass or more and 1.0 part by mass or less, more preferably 0.4 parts by mass or more and 0.8 part by mass or less, and even more preferably 0.5 parts by mass or more and 0.7 part by mass or less.

[0085] As a result, the adhesive layer 20 can have more appropriate cohesive force, and the re-peelability and the adhesion of the adhesive layer 20 to the base material 10 can be made more excellent. In particular, the exudation resistance of the adhesive layer 20 and the curved surface adhesiveness of the adhesive sheet 1 can be made excellent.

[0086] On the other hand, if the amount of the epoxy-based crosslinking agent is less than the above lower limit value, the cohesive force of the adhesive may be insufficient, and the exudation resistance of the adhesive layer 20 may decrease. On the other hand, if the amount of the epoxy-based crosslinking agent exceeds the above upper limit value, the wettability of the adhesive layer 20 may decrease, and the curved surface adhesiveness may decrease.

[0087] The biomass degree of the adhesive layer 20 is preferably 10% or more and 60% or less, more preferably 20% or more and 55% or less, and even more preferably 30% or more and 50% or less.

[0088] As a result, while more suitably reducing the environmental load, the adhesive force of the adhesive layer 20 can be made more suitable, and for example, more excellent curved surface adhesiveness can be exhibited.

[0089] On the other hand, if the biomass degree of the adhesive layer 20 is less than the above lower limit value, the effect of reducing the environmental load will decrease. Further, if the biomass degree of the adhesive layer 20 exceeds the above upper limit value, the curved surface adhesiveness is likely to decrease.

[0090] Here, in this specification, the biomass content refers to the ratio (mass %) of carbon derived from biomass and is measured according to ASTM D6866-22. The biomass content of the adhesive layer can be calculated by multiplying the biomass content of the (meth)acrylic acid alkyl ester derived from biomass by its mass % in the solid content of the adhesive composition.

[0091] The gel fraction of the adhesive layer 20 is preferably 40% or more and 90% or less, more preferably 44% or more and 80% or less, and even more preferably 48% or more and 72% or less.

[0092] Thereby, the exudation resistance and the adhesiveness to a curved surface of the adhesive layer 20 can be made more excellent.

[0093] On the other hand, when the gel fraction of the adhesive layer 20 is less than the above lower limit value, the cohesive force of the adhesive layer 20 is insufficient, and when the adhesive sheet 1 is attached to the curved surface portion of the adherend, bleeding of the adhesive or the components constituting the adhesive from the sheet end is likely to occur. Further, when the gel fraction of the adhesive layer 20 exceeds the above upper limit value, the flexibility of the adhesive layer 20 decreases, and floating and peeling are likely to occur at the interface between the adhesive layer 20 and the adherend when attached to the curved surface portion of the adherend.

[0094] In this specification, the gel fraction of the crosslinked product of the emulsion-type adhesive means the value measured by the method described in the examples below.

[0095] In addition to the components described above, other components may be blended in the adhesive composition as necessary.

[0096] Examples of other components include a dispersant, an antioxidant, a polymerization initiator, an ultraviolet absorber, a light stabilizer, a heat stabilizer, a softening agent, a silane coupling agent, a filler, a colorant, an antistatic agent, etc., and one or more selected from these can be used in combination.

[0097] The thickness of the adhesive layer 20 is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less.

[0098] Thereby, the adhesive force of the adhesive sheet 1 to the adherend is more favorably exhibited, and the workability when the adhesive sheet 1 is attached to the adherend or when the adhesive sheet 1 is peeled from the adherend becomes more excellent.

[0099] [1-3] Release liner The surface layer of the adhesive layer 20 of the unused adhesive sheet 1 is preferably covered with a release liner 30 as shown in FIG. 1.

[0100] Thereby, the adhesive layer 20 before being attached to the adherend can be suitably protected, and the unused adhesive sheet 1 becomes easy to handle.

[0101] The release liner 30 has releasability with respect to the adhesive layer 20. And the release liner 30 has a function of protecting the adhesive layer 20, at least when the adhesive sheet 1 is stored. Note that when the adhesive sheet 1 is attached to the adherend, the release liner 30 is in a state of being peeled from the adhesive layer 20.

[0102] Examples of the constituent material of the release liner 30 include various plastics such as paper such as kraft paper, fine paper, and glassine paper, polyesters such as polyethylene terephthalate (PET), polyolefins such as polyethylene and polypropylene, and metals. One or more selected from these can be used in combination.

[0103] The release liner 30 may be subjected to a release treatment. Examples of the release treatment agent used for the release treatment include silicone, olefin-based resin, isoprene-based resin, butadiene-based resin, long-chain alkyl-based resin, alkyd-based resin, and the like.

[0104] The thickness of the release liner 30 is not particularly limited, but is preferably 10 μm or more and 150 μm or less, and more preferably 20 μm or more and 140 μm or less.

[0105] [2] Applications of the pressure-sensitive adhesive sheet The pressure-sensitive adhesive sheet 1 is excellent in the adhesion between the base material 10 and the pressure-sensitive adhesive layer 20, has an appropriate adhesive force, and is also excellent in re-peelability from the adherend. Thereby, even when the adherend is a container or a package having a curved surface, the floating and peeling of the pressure-sensitive adhesive sheet 1 can be suppressed, and the pressure-sensitive adhesive sheet 1 can be suitably attached. Further, when the pressure-sensitive adhesive sheet 1 is re-peeled, peeling at the interface between the pressure-sensitive adhesive layer 20 and the base material 10 and adhesive residue on the adherend are preferably suppressed.

[0106] In the pressure-sensitive adhesive sheet 1, by blending a plant-derived component into the pressure-sensitive adhesive layer 20, the biomass degree of the pressure-sensitive adhesive layer 20 is increased, and the amount of use of fossil resource-based materials is relatively reduced. Therefore, in the pressure-sensitive adhesive layer 20, the proportion of carbon-neutral materials that do not substantially cause an increase in carbon dioxide in the atmosphere during incineration or the like can be increased, and the proportion of materials that are difficult to regenerate in a relatively short period like fossil resource-based materials can be reduced. Therefore, it also has the advantage of reducing the emission amount of carbon dioxide, which is a greenhouse gas, during incineration or the like.

[0107] Further, in the pressure-sensitive adhesive sheet 1, since the pressure-sensitive adhesive layer 20 is formed from an emulsion-type pressure-sensitive adhesive composition, it is also excellent in terms of safety, hygiene, and the environment.

[0108] The pressure-sensitive adhesive sheet 1 is preferably used by being attached to the curved surface portion of an adherend having a curved surface because it is particularly excellent in curved surface adhesiveness.

[0109] Specifically, the adhesive sheet 1 can be suitably used, for example, as a display label or an attention-catching label (attention seal, pop label, pop sheet, etc.) for adherends having a curved surface, such as containers for beverages (e.g., PET bottles, etc.), containers for foods (e.g., egg cases, etc.), packaging, stationery, cosmetic containers, containers for kitchen utensils, and containers for bath supplies.

[0110] In addition, the adhesive sheet 1 can also be suitably used as various labels such as labels for OA equipment, price tag seals, labels for shipping cardboard boxes, labels for electronic devices, and logistics management labels.

[0111] [3] Method for manufacturing the adhesive sheet The adhesive sheet 1 can be manufactured by any method. For example, it can be suitably manufactured using a method comprising a first step of manufacturing an adhesive composition containing an emulsion-type adhesive and an epoxy-based crosslinking agent, a second step of applying the adhesive composition to the base material 10, and a third step of crosslinking the adhesive composition applied on the base material 10.

[0112] [3-1] First step In the first step, an adhesive composition is manufactured by mixing an emulsion-type adhesive and an epoxy-based crosslinking agent.

[0113] [3-2] Second step In the second step, the adhesive composition is applied to one surface side of the base material 10.

[0114] This step can be performed, for example, by applying the adhesive composition to the surface of the base material 10.

[0115] In addition, this step can be suitably performed, for example, by applying the adhesive composition on the release liner 30, drying it for a predetermined time, and then transferring the adhesive composition applied on the release liner 30 to one surface of the base material 10.

[0116] The method of applying the pressure-sensitive adhesive composition to the base material 10 or the release liner 30 is not particularly limited. For example, it can be applied using known coating apparatuses such as a roll coater, a knife coater, an air knife coater, a bar coater, a blade coater, a slot die coater, a lip coater, a gravure coater, etc.

[0117] [3-3] The Third Step In the third step, the emulsion-type pressure-sensitive adhesive is crosslinked to form the pressure-sensitive adhesive layer 20. The crosslinking of the emulsion-type pressure-sensitive adhesive can be carried out by heat treatment. This heat treatment can also be combined with the drying treatment after the application of the pressure-sensitive adhesive composition.

[0118] The temperature of the heat treatment is preferably 50°C or higher and 150°C or lower, more preferably 70°C or higher and 120°C or lower. Also, the time of the heat treatment is preferably 10 seconds or longer and 10 minutes or shorter, more preferably 50 seconds or longer and 2 minutes or shorter. Thereby, the crosslinking reaction can proceed suitably.

[0119] After the heat treatment, if necessary, a seasoning period of about one to two weeks at room temperature (for example, 23°C, 50% RH) may be provided. When this seasoning period is necessary, the pressure-sensitive adhesive layer 20 is formed after the expiration of the seasoning period, and when the seasoning period is not necessary, the pressure-sensitive adhesive layer 20 is formed after the completion of the heat treatment.

[0120] By the above heat treatment (and seasoning), the emulsion-type pressure-sensitive adhesive is sufficiently crosslinked via the epoxy-based crosslinking agent. The pressure-sensitive adhesive layer 20 thus obtained has excellent cohesive force.

[0121] By the method as described above, the pressure-sensitive adhesive layer 20 can be formed on the surface of the base material 10 to obtain the adhesive sheet 1.

[0122] In addition, by using an emulsion-type adhesive that is non-solvent-based as the adhesive, it is possible to reduce the emissions of volatile organic compounds (VOCs) during the production of the adhesive sheet, and also to reduce the amount of residual solvent in the product after production.

[0123] As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited thereto.

[0124] For example, the adhesive sheet according to the present invention may further include a configuration other than those described above. For example, the adhesive sheet according to the present invention may include a coating layer (e.g., a coating layer for printing, etc.) or an intermediate layer.

[0125] Also, the adhesive sheet of the present invention may be manufactured by any method and is not limited to being manufactured by the method described in the above-described embodiments.

Examples

[0126] Hereinafter, the present invention will be described in detail based on specific examples, but the present invention is not limited thereto. For the processes and measurements in the following examples where the temperature conditions are not shown, they were carried out at room temperature (23°C).

[0127] [4] Production of Adhesive Sheet (Example 1) (Synthesis of Emulsion of Acrylic Copolymer) Based on a total of 100 parts by mass (solid content ratio) of a monomer mixture consisting of n-octyl acrylate (biomass content 72%): 64 parts by mass, 2-ethylhexyl acrylate: 10 parts by mass, n-butyl acrylate: 5 parts by mass, methyl methacrylate: 20 parts by mass, and acrylic acid: 1 part by mass, 4 parts by mass (solid content ratio) of sodium polyoxyethylene alkyl ether sulfate as an anionic emulsifier and 56 parts by mass of ion-exchanged water were added, mixed, and emulsified to prepare an emulsion.

[0128] Next, 28 parts by mass of ion-exchanged water was added into a reactor equipped with a thermometer, a stirrer, a dropping device, a reflux condenser, and a nitrogen inlet tube. Nitrogen was sealed in, and the temperature inside the reactor was raised to 80 °C and maintained at 80 °C. As a polymerization initiator, 2 parts by mass of an aqueous ammonium persulfate solution with a concentration of 10% by mass (solid content ratio: 0.2 part by mass) was added. Immediately after that, the above emulsion was continuously dropped over 4 hours for emulsion polymerization. In parallel, 4 parts by mass of an aqueous ammonium persulfate solution with a concentration of 5% by mass (solid content ratio: 0.2 part by mass) was dropped.

[0129] After the dropping was completed, it was aged at 80 °C for 4 hours, then cooled to room temperature (23 °C), neutralized by adding aqueous ammonia, and further ion-exchanged water was added to obtain a solution of an acrylic copolymer emulsion.

[0130] (Preparation of Emulsion-Type Adhesive Composition) To 100 parts by mass of the acrylic copolymer emulsion solution obtained as described above, 0.7 part by mass of glycerol polyglycidyl ether as an epoxy-based crosslinking agent was mixed and stirred to prepare an emulsion-type adhesive composition.

[0131] (Manufacture of Adhesive Sheet) The emulsion-type adhesive composition prepared as described above was applied onto the release-treated surface of a release liner using a roll knife coater and dried to form an adhesive layer with a thickness of 20 μm.

[0132] Next, a synthetic paper with a thickness of 45 μm (trade name: Yupo for Tape (registered trademark) SKS45, manufactured by Yupo Corporation) was laminated onto the surface of the formed adhesive layer to manufacture an adhesive sheet.

[0133] In the adhesive sheet thus obtained, the biomass degree of the adhesive layer was 46%, and the functional group blocking rate of the emulsion-type adhesive was 35%.

[0134] (Example 2) In the preparation of the emulsion-type pressure-sensitive adhesive composition, an emulsion-type pressure-sensitive adhesive composition was prepared and a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that 0.9 part by mass of sorbitol polyglycidyl ether was used as the epoxy-based crosslinking agent instead of glycerol polyglycidyl ether.

[0135] (Examples 3 to 5) In the preparation of the emulsion-type pressure-sensitive adhesive composition, an emulsion-type pressure-sensitive adhesive composition was prepared and a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that the addition amount of the epoxy-based crosslinking agent was changed as shown in Table 1.

[0136] (Comparative Example 1) In the preparation of the emulsion-type pressure-sensitive adhesive composition, an emulsion-type pressure-sensitive adhesive composition was prepared and a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that 1.7 parts by mass of a carbodiimide-based crosslinking agent was used instead of the epoxy-based crosslinking agent.

[0137] (Comparative Example 2) A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that a solvent-based re-peelable pressure-sensitive adhesive was used instead of the emulsion-type pressure-sensitive adhesive.

[0138] [5] Evaluation The following evaluations were performed on the pressure-sensitive adhesive sheets of the above Examples and Comparative Examples.

[0139] [5-1] Adhesive strength (adhesive strength after 24 hours, adhesive strength after 3 days of acceleration) The measurement was carried out in accordance with the measurement of the 180° peel adhesive strength of JIS Z0237. Specifically, the pressure-sensitive adhesive sheets of the above Examples and Comparative Examples were cut into a width of 25 mm, pasted on a SUS304 steel plate, and roll-pressed once back and forth with a roller having a mass of 2000 g.

[0140] Then, after standing still for 24 hours in an environment of 23°C and 50% RH, the pressure-sensitive adhesive sheet with the paper substrate was peeled off from the SUS304 steel plate at a peeling speed of 300 mm / min, and the adhesive strength after 24 hours was measured.

[0141] After sticking, the sheet was left standing for 3 days in an environment of 60°C and 95% RH (relative humidity), and then in an environment of 23°C and 50% RH, the adhesive sheet with the paper base material was peeled off from the SUS304 steel plate at a peeling rate of 300 mm / min to measure the adhesion over time.

[0142] [5-2] Measurement of gel fraction The adhesive sheets of the respective examples and comparative examples were cut into a size of 80 mm × 80 mm, the adhesive layer was wrapped with a polyester mesh (mesh size 200), its mass was weighed with a precision balance, and the mass of only the adhesive was calculated by subtracting the mass of the mesh alone and the mass of the base material. The mass at this time was designated as M1.

[0143] Next, the adhesive sheet wrapped with the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 3 days. Then, the adhesive was taken out, air-dried for 24 hours in an environment of a temperature of 23°C and a relative humidity of 50%, and further dried in an oven at 80°C for 12 hours. After drying, its mass was weighed with a precision balance, and the mass of only the adhesive was calculated by subtracting the mass of the mesh alone and the mass of the base material. The mass at this time was designated as M2. The gel fraction (%) is represented by (M2 / M1) × 100.

[0144] [5-3] Adhesion to the base material The release liner was peeled off from the adhesive sheets of the respective examples and comparative examples, and a cross cut (30 mm × 30 mm) was made in the adhesive layer with a cutter knife. Then, the adhesive layer at the cut portion was rubbed with the pulp of the finger to confirm the degree of detachment of the adhesive layer, and the adhesion to the base material was evaluated according to the following criteria.

[0145] ○... The adhesive layer does not detach from the base material and maintains good adhesion. △... A part of the adhesive layer detaches from the base material, but a certain degree of adhesion is maintained. ×... The entire adhesive layer detaches from the base material, and the adhesion is insufficient.

[0146] [5-4] Curvature adhesion The base material of the pressure-sensitive adhesive sheet in each of the above examples and comparative examples was changed to synthetic paper with a thickness of 80 μm (product name: Yupotack (registered trademark) base paper SGS80, manufactured by Yupo Corporation), and cut into 25 mm × 40 mm under the environment of 23 °C and 50% RH to obtain test pieces. These test pieces were attached to a round bar adherend made of polyethylene (PE) with a diameter of 15 mmφ so that the long side direction wound around the outer circumference. After standing for 3 days from the attachment, the peeling condition in the long side direction was measured.

[0147] [5-5] Resistance to seepage The pressure-sensitive adhesive sheets in each of the above examples and comparative examples were cut into 20 mm × 100 mm, and in an environment of 60 °C, a load of 0.42 KN / cm 2 was applied over 24 hours, and then in an environment of 23 °C and 50% RH, the seepage length (mm) of the adhesive layer on the long side was measured.

[0148] [5-6] Re-peelability The pressure-sensitive adhesive sheets in each of the above examples and comparative examples were cut into 30 mm × 50 mm under the environment of 23 °C and 50% RH to obtain test pieces. These test pieces were attached to an adherend (SUS306 steel plate). After standing for 7 days in an environment of 60 °C and 95% RH, it was returned to an environment of 23 °C and 50% RH, and after standing for 1 day, it was used as a test sample. It was peeled off by hand at speeds of 0.3 m / min (low speed) and 30 m / min (high speed), and the peeling state was observed.

[0149] If: Peeling occurs at the interface between the adhesive layer and the adherend, and no adhesive layer remains on the adherend. G: There is contamination or cloudiness on the adherend These results are summarized in Table 1. In Table 1, the addition amount of the cross-linking agent indicates the amount of the cross-linking agent added per 100 parts by mass of the emulsion solution of the acrylic copolymer in parts by mass.

[0150]

Table 1

[0151] As is apparent from Table 1, excellent results were obtained with the pressure-sensitive adhesive sheet of the present invention. Further, it was confirmed that the pressure-sensitive adhesive sheet of the present invention has sufficient adhesion, re-peelability, and curved surface adhesiveness between the pressure-sensitive adhesive layer and the base material. In contrast, satisfactory results were not obtained in the comparative examples.

[0152] In addition, in the production of the pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet was produced and evaluated in the same manner as in the above examples, except that the functional group blocking rate of the emulsion-type pressure-sensitive adhesive was variously changed in the range of 10% or more and 50% or less. As a result, good results similar to the above were obtained.

Explanation of reference numerals

[0153] 1... Pressure-sensitive adhesive sheet 10... Base material 20... Pressure-sensitive adhesive layer 30... Release liner

Claims

1. A base material, and a re-peelable pressure-sensitive adhesive layer provided on one surface side of the base material, wherein the pressure-sensitive adhesive layer contains a crosslinked product of a biomass-based emulsion pressure-sensitive adhesive crosslinked with an epoxy-based crosslinking agent. The pressure-sensitive adhesive sheet is characterized by this.

2. The pressure-sensitive adhesive sheet according to Claim 1, wherein the epoxy-based crosslinking agent is glycerol polyglycidyl ether.

3. The pressure-sensitive adhesive sheet according to Claim 1, wherein the functional group blocking rate of the emulsion pressure-sensitive adhesive is 10 mol% or more and 50 mol% or less.

4. The pressure-sensitive adhesive sheet according to Claim 1 or 2, wherein the ratio of the epoxy-based crosslinking agent to 100 parts by mass of the emulsion pressure-sensitive adhesive in the pressure-sensitive adhesive layer is 0.2 parts by mass or more and 1.0 part by mass or less.

5. The pressure-sensitive adhesive sheet according to Claim 1 or 2, which is attached to the curved surface portion of an adherend having a curved surface.

Images