adhesive sheet

Abstract

To provide an adhesive sheet which suppresses transition of a tackifier between layers in a multilayer adhesive sheet.SOLUTION: An adhesive sheet has a base material, a first adhesive layer and a second adhesive layer in this order, wherein content concentration (mass%) of a tackifier contained in the first adhesive layer is lower than content concentration (mass%) of a tackifier contained in the second adhesive layer, the glass transition temperature is 10°C or higher, and a block layer containing a resin selected from the group consisting of a polyester-based resin, an acrylic resin and a polyurethane-based resin as a main component is arranged between the first adhesive layer and the second adhesive layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet. [Background technology]

[0002] For various purposes, there are cases where a gradient is applied between the tackifier content in the PSA layer on the adherend side and the tackifier content in the PSA layer on the substrate side. For example, Patent Document 1 discloses a PSA sheet comprising a substrate, a tackifier-free PSA layer containing an acrylic polymer having a Tg of -10°C or less, and a tackifier-containing PSA layer containing a tackifier and one or more hydrocarbon polymers having a Tg of -10°C, with the aim of providing a PSA layer that exhibits good adhesion to polyolefin adherends and contains an acrylic polymer with a relatively low amount of tackifier. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2016-514184 Summary of the Invention [Problem to be solved by the invention]

[0004] In a laminate of pressure-sensitive adhesive layers having different tackifier contents as in Patent Document 1, if the tackifier migrates between layers, specifically, if the tackifier migrates from a layer with a high tackifier content to a layer with a low tackifier content due to a concentration gradient, the desired effect will not be achieved.

[0005] Therefore, an object of the present invention is to provide a multi-layered pressure-sensitive adhesive sheet that inhibits migration of a tackifier between layers. [Means for solving the problem]

[0006] The present invention is a pressure-sensitive adhesive sheet having a substrate, a first pressure-sensitive adhesive layer, and a second pressure-sensitive adhesive layer in this order, wherein the content concentration (mass %) of a tackifier contained in the first pressure-sensitive adhesive layer is lower than the content concentration (mass %) of a tackifier contained in the second pressure-sensitive adhesive layer, the first pressure-sensitive adhesive layer has a glass transition temperature of 10°C or higher, and a block layer containing as a main component a resin selected from the group consisting of polyester resins, acrylic resins, and polyurethane resins is disposed between the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer. [Effects of the Invention]

[0007] According to the pressure-sensitive adhesive sheet of the present invention, it is possible to inhibit the migration of a tackifier between layers in a multi-layer pressure-sensitive adhesive sheet. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing one embodiment of the pressure-sensitive adhesive sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention is a pressure-sensitive adhesive sheet having a substrate, a first pressure-sensitive adhesive layer, and a second pressure-sensitive adhesive layer in this order, wherein the content concentration (mass %) of a tackifier contained in the first pressure-sensitive adhesive layer is lower than the content concentration (mass %) of a tackifier contained in the second pressure-sensitive adhesive layer, the first pressure-sensitive adhesive layer has a glass transition temperature of 10°C or higher, and a block layer containing as a main component a resin selected from the group consisting of polyester resins, acrylic resins, and polyurethane resins is disposed between the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer.

[0010] In the present invention, a relatively large amount of tackifier is present in the second PSA layer (the application surface) that contacts the adherend. Tackifiers are incorporated, for example, to improve adhesion to low-polarity adherends. Therefore, by having a large amount of tackifier present on the PSA layer surface on the adherend side, it is possible to ensure high adhesion of the PSA sheet to low-polarity adherends while reducing the amount of tackifier used. However, the present inventors have discovered that simply incorporating a relatively large amount of tackifier on the adherend side makes it difficult to achieve the desired effect (e.g., lower adhesion to low-polarity adherends than expected). The inventors speculate that this is because, even if a large amount of tackifier is incorporated into the PSA layer on the adherend side during production, the tackifier diffuses due to a concentration gradient within the PSA layer, resulting in a lower tackifier concentration (mass %) on the PSA layer surface on the adherend side than the amount incorporated during production. Based on this speculation, the above problem was solved by providing a blocking layer to prevent the tackifier from migrating to the PSA layer on the substrate side. The above speculation does not limit the technical scope of the present invention.

[0011] In order to suppress migration of the tackifier, the blocking layer is mainly composed of a specific resin, i.e., a resin having a glass transition temperature of 10°C or higher and selected from the group consisting of polyester-based resins, acrylic-based resins, and polyurethane-based resins.

[0012] The present embodiment will be described in detail below.

[0013] In this specification, the range "X to Y" means "X or more and Y or less." Unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20 to 25°C) and a relative humidity of 45 to 55% RH. In this specification, "(meth)acrylic acid" refers to "acrylic acid or methacrylic acid," and "(meth)acrylate" refers to "acrylate or methacrylate."

[0014] The concept of a sheet includes things called tapes, labels, films, etc.

[0015] FIG. 1 is a cross-sectional schematic diagram showing one embodiment of the pressure-sensitive adhesive sheet of the present invention. Note that the drawings are exaggerated for ease of explanation, and the dimensional proportions of the components in the drawings may differ from the actual proportions. In FIG. 1, the pressure-sensitive adhesive sheet 10 is composed of a substrate 20, a first pressure-sensitive adhesive layer 30, a blocking layer 40, a second pressure-sensitive adhesive layer 50, and a release liner 60. The release liner 60 is formed to prevent dust and other foreign matter from adhering to the second pressure-sensitive adhesive layer until the pressure-sensitive adhesive sheet 10 is attached to an adherend. Therefore, the release liner 60 is peeled off when the sheet is attached to an adherend.

[0016] The second pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer that exhibits adhesiveness to an adherend when attached to the adherend. Therefore, the second pressure-sensitive adhesive layer becomes the outermost layer when attached (as described above, before attachment, the second pressure-sensitive adhesive layer is usually protected by a release liner). The second pressure-sensitive adhesive layer contains a relatively large amount of tackifier, for example, to ensure adhesiveness to low-polarity adherends. On the other hand, the first pressure-sensitive adhesive layer is disposed adjacent to, for example, a substrate, and therefore the tackifier concentration contained in the first pressure-sensitive adhesive layer may be lower than the tackifier concentration contained in the second pressure-sensitive adhesive layer.

[0017] In addition, in the embodiment of FIG. 1, the first pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer that is directly attached to the substrate, but is not limited to a form in which it is arranged adjacent to the substrate, and other functional layers such as an easy-adhesion layer or other pressure-sensitive adhesive layers may be arranged between the substrate and the first pressure-sensitive adhesive layer.

[0018] The structure of each layer constituting the pressure-sensitive adhesive sheet will be described below.

[0019] (First adhesive layer and second adhesive layer) The first adhesive layer and the second adhesive layer each contain an adhesive. Hereinafter, the adhesive contained in the first adhesive layer will be referred to as the first adhesive, and the adhesive contained in the second layer will be referred to as the second adhesive. The first adhesive and the second adhesive will also be collectively referred to as adhesives.

[0020] The adhesive is not particularly limited, and may be an acrylic adhesive, a rubber adhesive, a silicone adhesive, a urethane adhesive, a polyester adhesive, etc. The adhesives may be used alone or in combination of two or more.

[0021] The first adhesive and the second adhesive may be the same or different.

[0022] The content of the first adhesive in the first adhesive layer is not particularly limited, but is preferably 70% by mass or more (upper limit 100% by mass), and may be 75% by mass or more, 80% by mass or more, 85% by mass or more, or 90% by mass or more.

[0023] The content of the adhesive in the second adhesive layer is not particularly limited, but is preferably 60 to 99.9% by mass, more preferably 70 to 99% by mass, even more preferably 75 to 98% by mass, and particularly preferably 80 to 95% by mass.

[0024] The second adhesive is preferably a rubber-based adhesive and / or an acrylic-based adhesive, more preferably an acrylic-based adhesive, because the adhesive strength improving effect of adding a tackifier is more easily achieved. Also, the first adhesive is preferably the same as the second adhesive, and in this respect, the (first and second) adhesives are preferably a rubber-based adhesive and / or an acrylic-based adhesive, more preferably an acrylic-based adhesive.

[0025] The acrylic polymer constituting the acrylic pressure-sensitive adhesive is formed by using a (meth)acrylic acid alkyl ester as the main monomer component, and optionally a monomer copolymerizable with the (meth)acrylic acid alkyl ester (copolymerizable monomer). Here, the main component refers to 50% by mass or more (up to 100% by mass) of the monomers, and the content of the (meth)acrylic acid alkyl ester relative to the total monomers is, in order of preference, 65% by mass or more, 85% by mass or more, and 90% by mass or more.

[0026] Examples of (meth)acrylic acid alkyl esters include 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. These may be used alone or in combination of two or more.

[0027] Examples of copolymerizable monomers copolymerizable with (meth)acrylic acid alkyl esters include carboxyl group-containing monomers or anhydrides thereof, such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid; hydroxyl group-containing monomers, such as hydroxyalkyl (meth)acrylates (2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, and glycerin dimethacrylate; amide group-containing monomers, such as (meth)acrylamide, N-vinylpyrrolidone, and N,N-dimethylacrylamide; amino group-containing monomers, such as aminoethyl (meth)acrylate and (meth)acryloylmorpholine; aromatic vinyl compounds, such as styrene and substituted styrene; cyano group-containing monomers, such as acrylonitrile; vinyl esters, such as vinyl acetate; and diketo group-containing monomers, such as diacetone acrylamide and acetoacetoxymethyl acrylate. These may be used alone or in combination of two or more. The amount of copolymerizable monomers copolymerizable with these alkyl (meth)acrylates is preferably 10% by mass or less based on the total amount of monomers.

[0028] From the viewpoint of improving adhesiveness, it is preferable to include a carboxyl group-containing monomer as a copolymerizable monomer copolymerizable with a (meth)acrylic acid alkyl ester. Examples of the carboxyl group-containing monomer include (meth)acrylic acid, maleic acid, maleic anhydride, fumaric acid, fumaric anhydride, crotonic acid, itaconic acid, itaconic anhydride, myristoleic acid, palmitoleic acid, and oleic acid. The content of the carboxyl group-containing monomer in the monomer mixture used in producing the acrylic polymer is preferably 0.1 to 5 mass%, more preferably 0.3 to 3 mass%.

[0029] The weight average molecular weight of the acrylic polymer is not particularly limited, and is, for example, 100,000 to 5,000,000.

[0030] The method for producing the acrylic polymer is not particularly limited, and conventionally known methods such as solution polymerization using a polymerization initiator, emulsion polymerization, suspension polymerization, reverse-phase suspension polymerization, thin-film polymerization, and spray polymerization can be used. In addition to the method of initiating polymerization using a polymerization initiator, a method of initiating polymerization by irradiation with radiation, electron beams, ultraviolet rays, or the like can also be employed. Among these, emulsion polymerization is preferred because it further enhances the effects of the present invention. That is, in a preferred embodiment of the present invention, the acrylic polymer is an emulsion polymer.

[0031] An example of the emulsion polymerization method is a method in which an emulsifier and a polymerization initiator are added to a monomer mixture containing the above-mentioned monomers, and emulsion polymerization is carried out.

[0032] In emulsion polymerization, from the viewpoint of polymerization stability, it is preferable that the emulsifier (or a part of the emulsifier) ​​is dissolved in the monomer mixture or that the monomer mixture is made into an O / W emulsion in advance.

[0033] The procedure for carrying out emulsion polymerization may be, for example, the following methods (1) to (3). (1) The entire amount of the monomer mixture, emulsifier, water, etc. is charged, the temperature is raised, and the polymerization initiator dissolved in water is added dropwise or in portions to carry out polymerization. (2) Water, an emulsifier, and a portion of the monomer mixture are charged into a reaction vessel, and the temperature is raised. Then, a polymerization initiator dissolved in water is added dropwise or in portions to proceed with the polymerization reaction. Then, the remaining monomer mixture is added dropwise or in portions to continue the polymerization. (3) A polymerization initiator dissolved in water is placed in a reaction vessel, and after the temperature is raised, an emulsion consisting of a monomer mixture, an emulsifier, and water is added dropwise or in portions to carry out polymerization.

[0034] The emulsifier is not particularly limited, but from the viewpoint of improving the dispersion stability of the emulsion polymer, anionic emulsifiers or nonionic emulsifiers are preferred, and anionic emulsifiers are more preferred.

[0035] Examples of anionic emulsifiers include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, allyl alkyl sulfosuccinate salt, etc. Examples of nonionic emulsifiers include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, etc. These emulsifiers may be used alone or in combination of two or more.

[0036] The amount of emulsifier added is preferably 0.5 to 12 parts by mass, more preferably 0.8 to 8 parts by mass, and even more preferably 1 to 6 parts by mass, per 100 parts by mass of the monomer mixture, from the viewpoint of stability of the emulsion polymerization reaction and prevention of deterioration of physical properties due to remaining unreacted emulsifier.

[0037] The emulsifier may be added directly to a solution prepared by adding water to the monomer mixture, or may be added in advance to a polymerization vessel, or both may be used.

[0038] The polymerization initiator may be either water-soluble or oil-soluble. Examples include azo compounds such as 2,2'-azobis(2-methylpropionamidine) dihydrochloride and 2,2'-azobis(2-amidinopropane) dihydrochloride; persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; and peroxides such as benzoyl peroxide, t-butyl hydroperoxide, and hydrogen peroxide. Redox initiators such as a combination of a persulfate and sodium bisulfite or a combination of a peroxide and sodium ascorbate may also be used. The polymerization initiators may be used alone or in combination of two or more. Among these, persulfates or redox initiators are preferred from the viewpoint of excellent polymerization stability.

[0039] The amount of the polymerization initiator added is preferably 0.01 to 6 parts by mass, more preferably 0.03 to 4 parts by mass, and even more preferably 0.05 to 2 parts by mass, relative to 100 parts by mass of the monomer mixture, from the viewpoint of accelerating the polymerization rate.

[0040] The polymerization initiator may be added to the reaction vessel in advance, may be added immediately before the start of polymerization, may be added in multiple batches after the start of polymerization, may be added to the monomer mixture in advance, or may be added to an emulsion of the monomer mixture after preparing the emulsion.

[0041] During emulsion polymerization, a known chain transfer agent or pH buffer may be further added.

[0042] The water used in emulsion polymerization is preferably ion-exchanged water, and the amount of water used is preferably 30 to 400 parts by mass, more preferably 35 to 200 parts by mass, and even more preferably 40 to 150 parts by mass, per 100 parts by mass of the monomer mixture.

[0043] The emulsion polymer dispersion obtained by emulsion polymerization may be further adjusted to a pH of 5 to 9 (preferably pH 6 to 8.5) by adding aqueous ammonia, various water-soluble amines, or aqueous alkali solutions such as aqueous sodium hydroxide and aqueous potassium hydroxide.

[0044] The solid content concentration of the emulsion polymer dispersion is preferably 10 to 80 mass %, more preferably 25 to 70 mass %, and even more preferably 45 to 65 mass %.

[0045] The emulsion polymer has an emulsion shape (particulate shape) in which the emulsion polymer is dispersed. In this case, the average particle size of the emulsion polymer is preferably 50 to 500 nm, more preferably 100 to 300 nm. Here, the average particle size of the emulsion polymer is a volume-based median size measured by a laser diffraction dispersion method.

[0046] Examples of rubber-based pressure-sensitive adhesives include natural rubber, modified natural rubber obtained by graft polymerizing natural rubber with one or more monomers selected from (meth)acrylic acid alkyl esters, styrene, and (meth)acrylonitrile, diene-based homopolymers such as polybutadiene, polyisoprene, and polychloroprene, diene-based copolymers such as polystyrene-polybutadiene and polystyrene-polyisoprene, styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, urethane rubber, polyisobutylene-based resins, and polybutene resins.

[0047] The content concentration (mass %) of the tackifier contained in the first pressure-sensitive adhesive layer is lower than the content concentration (mass %) of the tackifier contained in the second pressure-sensitive adhesive layer.

[0048] Specifically, the content concentration (mass %) of the tackifier contained in the first adhesive layer is preferably 1 / 2 or less, and more preferably 1 / 10 or less, of the content concentration (mass %) of the tackifier contained in the second adhesive layer.

[0049] Since the amount of tackifier added to the PSA layer can be reduced, the concentration (% by mass) of tackifier contained in the first PSA layer is preferably 10% by mass or less (lower limit: 0% by mass), more preferably 5% by mass or less (lower limit: 0% by mass), and even more preferably 3% by mass or less (lower limit: 0% by mass). Even when no tackifier is added to the first PSA composition, it is difficult to avoid a small amount of tackifier migrating from the second PSA layer, and therefore the content of tackifier in the first PSA layer tends to be higher than the amount of tackifier added to the first PSA composition.

[0050] In consideration of adhesive performance to adherends (particularly low-polarity adherends), the content concentration (% by mass) of the tackifier in the second pressure-sensitive adhesive layer is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. In consideration of compatibility with the pressure-sensitive adhesive, the content concentration (% by mass) of the tackifier in the second pressure-sensitive adhesive layer is preferably 40% by mass or less, and more preferably 30% by mass or less, in the pressure-sensitive adhesive layer.

[0051] The tackifier concentration (mass %) in the adhesive layer can be measured by using Fourier transform infrared spectroscopy (FT-IR) and checking the intensity of the peak attributable to the tackifier in the spectrum of the adhesive layer.

[0052] The tackifier contained in each pressure-sensitive adhesive layer is not particularly limited, and examples include alicyclic petroleum resins, terpene resins, rosin resins, styrene resins, etc. In a preferred embodiment, from the viewpoint of compatibility with pressure-sensitive adhesives (particularly acrylic pressure-sensitive adhesives and rubber pressure-sensitive adhesives), the tackifier contained in the second pressure-sensitive adhesive layer is at least one selected from the group consisting of alicyclic petroleum resins, terpene resins, and rosin resins.

[0053] Petroleum resins are obtained by polymerizing, by known methods, diolefins and monoolefins in the fraction of cracked oil, a by-product of the production of ethylene by steam cracking petroleum. C5 petroleum resins are made from C5 fractions such as isoprene, 1,3-pentadiene, cyclopentene, and cyclopentadiene, while C9 petroleum resins are made from C9 fractions such as styrene, vinyltoluene, α-methylstyrene, indene, alkylindene, and dicyclopentadiene.

[0054] Examples of alicyclic petroleum resins include alicyclic hydrocarbon resins obtained by cyclodimerizing C5 petroleum resins and then polymerizing them; polymers of cyclic diene compounds (cyclopentadiene, dicyclopentadiene, ethylidene norbornene, dipentene, ethylidene bicycloheptene, vinylcycloheptene, tetrahydroindene, vinylcyclohexene, limonene, etc.) or hydrogenated products thereof; and alicyclic hydrocarbon resins obtained by hydrogenating the aromatic rings of C9 petroleum resins or C5 / C9 resins.

[0055] The alicyclic petroleum resin may be a commercially available product, and examples of commercially available products include the Alcon (registered trademark) series (Alcon (registered trademark) P-90, P-100, P-115, P-125, P-140, M-90, M-100, M-115, M-135 (all manufactured by Arakawa Chemical Industries, Ltd.)), the Quintone (registered trademark) series (Quintone (registered trademark) 1105, 1325, 1340, TD-401, 1500, 1525L, 1920, 2940, etc. (all manufactured by Zeon Corporation), and the like.

[0056] The alicyclic petroleum resins may be used alone or in combination of two or more.

[0057] Examples of the terpene resin include terpene resin, terpene phenol resin, aromatic modified terpene resin, and hydrogenated terpene phenol resin obtained by hydrogenating these resins, among which terpene resin and terpene phenol resin are preferred.

[0058] Commercially available terpene resins may be used. Examples of terpene resins include YS Resin (registered trademark) PX1250, PX1150, PX1000, PX800, PX1150N, and PX300N (all manufactured by Yasuhara Chemical Co., Ltd.). Examples of terpene phenol resins include YS Polystar (registered trademark) U130, U115, T160, T145, T130, T115, T100, T80, T30, S145, G150, G125, N125, K125, and TH130 (all manufactured by Yasuhara Chemical Co., Ltd.). Examples of aromatic modified terpene resins include YS Resin (registered trademark) TO125, TO115, TO105, and TO85 (all manufactured by Yasuhara Chemical Co., Ltd.). Examples of hydrogenated terpene phenol resins include YS Polystar (registered trademark) UH115 (all manufactured by Yasuhara Chemical Co., Ltd.).

[0059] The terpene resins may be used alone or in combination of two or more kinds.

[0060] Examples of rosin-based resins include natural rosin, rosin ester, hydrogenated rosin, hydrogenated rosin ester, polymerized rosin, polymerized rosin ester, and disproportionated rosin ester. Commercially available products may be used. The rosin-based resins may be used alone or in combination of two or more.

[0061] The method of adding the tackifier is not particularly limited. For example, in a preferred embodiment in which an acrylic polymer is obtained by emulsion polymerization, examples include: (1) a method in which a tackifier is added to a monomer mixture, an emulsifier, water, etc. before the start of polymerization, and then the monomer is polymerized; (2) a method in which a tackifier emulsion is prepared using a tackifier, an emulsifier, water, etc., and the like, and the emulsion is used to blend the tackifier into a pressure-sensitive adhesive composition; etc. The emulsifier used above can be any of the emulsifiers described in the section on emulsion polymerization of acrylic polymers.

[0062] Each PSA layer is formed from a PSA composition containing a PSA, a tackifier, and other additives. In another preferred embodiment of the present invention, the first PSA layer is formed from a first PSA composition, and the second PSA layer is formed from a second PSA composition, and the concentration (mass %) of the tackifier contained in the first PSA composition is lower than the concentration (mass %) of the tackifier contained in the second PSA layer-forming composition.

[0063] Since the amount of tackifier added in the pressure-sensitive adhesive layer can be reduced, the content concentration (mass %) of the tackifier contained in the first pressure-sensitive adhesive composition is preferably 10 mass % or less (lower limit 0 mass %), more preferably 5 mass % or less (lower limit 0 mass %), even more preferably 3 mass % or less (lower limit 0 mass %), particularly preferably 1 mass % or less, and most preferably 0 mass %.

[0064] Furthermore, in consideration of adhesive performance to adherends (particularly low-polarity adherends), the content concentration (% by mass) of the tackifier in the second pressure-sensitive adhesive composition is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. In consideration of compatibility with the pressure-sensitive adhesive, the content concentration (% by mass) of the tackifier in the second pressure-sensitive adhesive layer is preferably 40% by mass or less, and more preferably 30% by mass or less, in the pressure-sensitive adhesive layer.

[0065] The concentration (mass %) of the tackifier contained in the first PSA composition is lower than the concentration (mass %) of the tackifier contained in the second PSA composition.

[0066] Specifically, the content concentration (mass%) of the tackifier contained in the first pressure-sensitive adhesive composition is preferably 1 / 2 or less, and more preferably 1 / 10 or less, of the content concentration (mass%) of the tackifier contained in the second pressure-sensitive adhesive composition.

[0067] The pressure-sensitive adhesive composition for forming each pressure-sensitive adhesive layer may contain a crosslinking agent. Known crosslinking agents can be used as the crosslinking agent. Examples include, but are not limited to, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, metal chelate-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, carbodiimide-based crosslinking agents, and hydrazine-based crosslinking agents. A pressure-sensitive adhesive composition that does not contain a crosslinking agent is also suitable.

[0068] The crosslinking agent may be used alone or in the form of a mixture of two or more kinds.

[0069] When a crosslinking agent is added, the amount of the crosslinking agent added is preferably 0.1 to 10 parts by mass, and more preferably 0.3 to 5 parts by mass, per 100 parts by mass of the acrylic polymer, when the composition contains an acrylic polymer, for example.

[0070] The PSA composition may further contain other additives known in the art, such as fillers, pigments, UV absorbers, wetting agents, preservatives, etc. Examples of fillers include zinc oxide, silica, calcium carbonate, etc.

[0071] The thickness of each pressure-sensitive adhesive layer (film thickness after drying) is usually 5 to 100 μm, preferably 5 to 50 μm. The thicknesses of the pressure-sensitive adhesive layers may be different or the same. For example, by making the second pressure-sensitive adhesive layer thinner than the first pressure-sensitive adhesive layer, the amount of tackifier used can be reduced.

[0072] (Block layer) The block layer contains a resin as a main component, which means that the main component accounts for 50% by mass or more (up to 100% by mass) of the block layer, preferably 75% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0073] The glass transition temperature of the resin contained in the block layer is 10°C or higher. A glass transition temperature of 10°C or higher suppresses the migration of the tackifier contained in each pressure-sensitive adhesive layer, thereby suppressing migration of the tackifier. From the viewpoint of suppressing migration, the glass transition temperature is preferably 25°C or higher, more preferably 50°C or higher. Furthermore, the glass transition temperature is preferably 100°C or lower, more preferably 80°C or lower. The glass transition temperature can be measured in accordance with JIS K 7121-2012. Specifically, the glass transition temperature can be measured using a differential scanning calorimeter "DSC Q2000" manufactured by TA Instruments Japan Co., Ltd. under conditions of a nitrogen atmosphere, a measurement temperature range of -50 to 150°C, and a heating rate of 10°C / min.

[0074] The resin contained in the block layer may be one type alone or two or more types in combination. When the block layer contains two or more types of resin, the glass transition temperature of the mixed resins is the glass transition temperature of the resin contained in the block layer.

[0075] The resin contained in the block layer is selected from the group consisting of polyester-based resins, acrylic-based resins, and polyurethane-based resins. These resins have poor compatibility with tackifiers and can inhibit the penetration of the tackifier into the block layer. Furthermore, block layers using these resins also have good adhesion to the pressure-sensitive adhesive layer. Of these, in terms of the effects of the present invention, it is preferable that the resin contained in the block layer is a polyester-based resin. These resins may be used alone or in combination of two or more.

[0076] The polyester resin is a polymer having an ester bond in the main chain, which is formed by copolymerizing a polyol as a monomer with a polycarboxylic acid and / or a carboxylic acid anhydride (also referred to as a "carboxylic acid component" in this embodiment).

[0077] Specific examples of the polyol include polyether polyols such as diethylene glycol, dipropylene glycol, triethylene glycol, and polyethylene glycol, polyester polyols, ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-pentanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanediol, 2,2,4-trimethyl-1,3-pentanediol, glycerin, glycerin monoallyl ether, trimethylolethane, trimethylolpropane, and pentaerythritol.

[0078] Specific examples of the carboxylic acid component include polycarboxylic acids such as malonic acid, phthalic acid, terephthalic acid, isophthalic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, succinic acid, glutaric acid, hexachloroendomethylenetetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, endomethylenehexahydrophthalic acid, adipic acid, sebacic acid, azelaic acid, dimer acid, decadicarboxylic acid, cyclohexanedicarboxylic acid, trimellitic acid, pyromellitic acid, trimesic acid, and cyclopentanedicarboxylic acid, and anhydrides of these polycarboxylic acids.

[0079] The combination of these polyol and carboxylic acid components is not limited.

[0080] Furthermore, the polyester-based resin may be modified, such as a urethane-modified polyester. Specific examples of urethane-modified polyesters include polymers (polyester urethanes) obtained by reacting various polyisocyanate compounds with polyester polyols having hydroxyl groups at the terminals of polymers obtained by condensation polymerization of the above-mentioned polyols and carboxylic acid components. In this embodiment, resin materials having ester bonds in the main chain, such as polyesters and urethane-modified polyesters, are referred to as polyester-based resins.

[0081] The polyester resin may be water-based.

[0082] "Aqueous polyester resin" refers to a polyester resin that can be dissolved in an aqueous solvent to form an aqueous solution, or a polyester resin that can be dispersed as an emulsion in an aqueous solvent to form an aqueous dispersion. The use of such an "aqueous" polyester resin makes it possible to reduce the amount of volatile organic compounds emitted during coating. Here, an aqueous solvent refers to one that contains 60% by mass or more of water (up to 100% by mass), preferably 70% by mass or more, more preferably 85% by mass or more, and most preferably 95% by mass or more.

[0083] Components other than water contained in the aqueous solvent include water-soluble organic solvents, such as methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, dimethylformamide, methyl cellosolve, tetrahydrofuran, and ethylene glycol mono-t-butyl ether.

[0084] In one embodiment of the present invention, in order to prepare an aqueous dispersion in which the aqueous polyester resin is dispersed as an emulsion in water, a small amount of an emulsifier, a surfactant, or the like may be used within a range that does not impair the effects of the present invention.

[0085] However, low-molecular-weight components such as emulsifiers and surfactants may be localized in the block layer, resulting in reduced adhesiveness and reduced interlayer adhesion. From the viewpoint of suppressing this phenomenon, in one embodiment of the present invention, the aqueous polyester resin is preferably a self-emulsifying aqueous polyester resin (for example, a self-emulsifying water-dispersible polyester resin).

[0086] If the resin is a self-emulsifying aqueous polyester resin, it is possible to form an emulsion without using low-molecular-weight components such as emulsifiers or surfactants, which cause a decrease in interlayer adhesion, and therefore the interlayer adhesion of the resulting PSA sheet can be further improved. Note that "self-emulsifying" means that some kind of hydrophilic group is chemically introduced into the resin skeleton, and the resin itself has emulsifying ability, without the need for the addition of an emulsifier or surfactant.

[0087] The hydroxyl value of the polyester resin is preferably 2 mgKOH / g or more, more preferably 4 mgKOH / g or more, even more preferably 6 mgKOH / g or more, and particularly preferably 8 mgKOH / g or more. When the hydroxyl value is equal to or greater than the above-mentioned lower limit, migration of the tackifier can be further reduced. The hydroxyl value of the polyester resin is a value measured in accordance with JIS K 0070-1992. The upper limit of the hydroxyl value of the polyester resin is, for example, 30 mgKOH / g or less.

[0088] In the case of an aqueous polyester resin, the number average molecular weight (Mn) is preferably 1,000 to 30,000, more preferably 3,000 to 25,000, and even more preferably 5,000 to 20,000, from the viewpoint of improving solubility or dispersibility in water and interlayer adhesion with a pressure-sensitive adhesive layer or the like.

[0089] In the present invention, the number average molecular weight (Mn) is a value calculated as a standard polystyrene as measured by gel permeation chromatography (GPC), and specifically, is a value measured according to the method described below.

[0090] Number average molecular weight (Mn) Measurements are carried out using a gel permeation chromatograph (manufactured by Tosoh Corporation, product name "HLC-8320") under the conditions below, and the values ​​measured are converted into standard polystyrene equivalents. Columns: "TSK guard column super HH", "TSK gel super HM-H (x2)", "TSK gel super H2000" (all manufactured by Tosoh Corporation) Column temperature: 40℃ Developing solvent: tetrahydrofuran ·Flow rate: 1.0mL / min The acrylic resin is preferably a resin formed by using a (meth)acrylic acid alkyl ester as the main monomer component and, if necessary, a monomer copolymerizable with the (meth)acrylic acid alkyl ester (copolymerizable monomer). Here, the main component refers to 50% by mass or more (up to 100% by mass) of the monomers, and the content of the (meth)acrylic acid alkyl ester relative to the total monomers is, in order of preference, 65% by mass or more, 85% by mass or more, and 90% by mass or more.

[0091] Examples of (meth)acrylic acid alkyl esters include 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. These may be used alone or in combination of two or more. In order to increase the glass transition temperature of the acrylic resin to 10°C or higher, it is a preferred embodiment that the (meth)acrylic acid alkyl ester contains a monomer whose homopolymer has a high glass transition temperature. Examples of monomers that produce homopolymers with high glass transition temperatures include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, cyclohexyl acrylate, and stearyl acrylate, and these monomers may be contained in a total amount of, for example, 40 to 80 mass% of the total amount of (meth)acrylic acid alkyl esters. However, other (meth)acrylic acid alkyl esters may be contained as long as the glass transition temperature of the acrylic resin is 10°C or higher.

[0092] Examples of copolymerizable monomers copolymerizable with (meth)acrylic acid alkyl esters include carboxyl group-containing monomers or anhydrides thereof, such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid; hydroxyl group-containing monomers, such as hydroxyalkyl (meth)acrylates (2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, and glycerin dimethacrylate; amide group-containing monomers, such as acrylamide, methacrylamide, N-vinylpyrrolidone, and N,N-dimethylacrylamide; amino group-containing monomers, such as aminoethyl (meth)acrylate and (meth)acryloylmorpholine; aromatic vinyl compounds, such as styrene and substituted styrene; cyano group-containing monomers, such as acrylonitrile; vinyl esters, such as vinyl acetate; and diketo group-containing monomers, such as diacetone acrylamide and acetoacetoxymethyl acrylate. These may be used alone or in combination of two or more.

[0093] In the present invention, a copolymerizable monomer copolymerizable with a (meth)acrylic acid alkyl ester may be selected so that the glass transition temperature is 10°C or higher. Among these, from the viewpoint of increasing the polarity of the acrylic resin and making it more difficult for the tackifier to migrate, it is preferable to use a carboxyl group-containing monomer, a hydroxyl group-containing monomer, an amide group-containing monomer, or an amino group-containing monomer. The content of the copolymerizable monomer copolymerizable with a (meth)acrylic acid alkyl ester is, for example, 0.05 to 5.0 mass% based on the total amount of monomers.

[0094] The acrylic resin may be in the form of a water dispersion.

[0095] The aqueous dispersion of the acrylic resin is in the form of an emulsion dispersed in an aqueous solvent. The use of such an aqueous dispersion can reduce the amount of volatile organic compounds emitted during coating.

[0096] The form of the aqueous dispersion dispersed as an emulsion in an aqueous solvent is the same as that of the emulsion polymer produced by emulsion polymerization as explained in the section on pressure-sensitive adhesives.

[0097] In the case of an aqueous acrylic resin, the number average molecular weight (Mn) is preferably 3,000 to 500,000, more preferably 5,000 to 200,000, and even more preferably 10,000 to 100,000, from the viewpoint of improving solubility or dispersibility in water and interlayer adhesion with a pressure-sensitive adhesive layer, etc.

[0098] The acrylic resin may be a polymer obtained by crosslinking a polymer obtained by polymerizing a monomer component with a crosslinking agent. Examples of the crosslinking agent include those exemplified in the section on the pressure-sensitive adhesive layer.

[0099] The polyurethane resin can be produced by reacting a polyol such as polyester polyol, polyether polyol, or polycarbonate polyol with a polyfunctional isocyanate compound.

[0100] Polyester polyols can be synthesized from, for example, an acid component such as polycarboxylic acid and a glycol component or a polyol component. Examples of polyester polyols include those obtained by reacting an acid component such as terephthalic acid, adipic acid, azelaic acid, sebacic acid, phthalic anhydride, isophthalic acid, or trimellitic acid with a glycol component such as 3-methyl-1,5-pentanediol or propylene glycol, or a polyol component such as glycerin, trimethylolpropane, or pentaerythritol. Examples of polyester polyols include polyester polyols obtained by ring-opening polymerization of lactones such as polycaprolactone, poly(β-methyl-γ-valerolactone), and polyvalerolactone. The molecular weight of the polyester polyol is preferably 1,000 to 6,000.

[0101] As the polyether polyol, for example, a polyalkylene glycol adduct of a polyhydric alcohol is preferably used. Examples of the polyhydric alcohol include aliphatic dihydric alcohols such as ethylene glycol, propylene glycol, 1,4-butylene glycol (tetramethylene glycol), and neopentyl glycol; glycerin, trioxyisobutane, 1,2,3-butanetriol, 1,2,3-pentanetriol, 2-methyl-1,2,3-propanetriol, 2-methyl-2,3,4-butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl-3,4,5-heptanetriol, 2,4-dimethylaminopropanol, and the like. Examples of the polyether polyol include trihydric alcohols such as ethyl-2,3,4-pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4-butanetriol, 1,2,4-pentanetriol, and trimethylolpropane; tetrahydric alcohols such as erythritol, pentaerythritol, 1,2,3,4-pentanetetraol, 2,3,4,5-hexanetetraol, 1,2,3,5-pentanetetraol, and 1,3,4,5-hexanetetraol; pentahydric alcohols such as adonitol, arabitol, and xylitol; and hexahydric alcohols such as sorbitol, mannitol, and iditol. The molecular weight of the polyether polyol is preferably 1,000 to 6,000.

[0102] The polycarbonate polyol preferably used is, for example, one obtained by reacting a polyol monomer such as a diol with a carbonate such as ethylene carbonate or dimethyl carbonate. Examples of the polyol monomer include the above-mentioned polyhydric alcohols; polyol monomers having an alicyclic structure such as 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanediol, 1,3-cyclopentanediol, 1,4-cycloheptanediol, 2,5-bis(hydroxymethyl)-1,4-dioxane, 2,7-norbornanediol, tetrahydrofuran dimethanol, 1,4-bis(hydroxyethoxy)cyclohexane, and isosorbide; and aromatic polyol monomers such as 1,4-benzenedimethanol, 1,3-benzenedimethanol, 1,2-benzenedimethanol, 4,4'-naphthalenedimethanol, and 3,4'-naphthalenedimethanol.

[0103] Examples of polyfunctional isocyanate compounds include hexamethylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and trimethylolpropane / tolylene diisocyanate trimer adduct.

[0104] In order to adjust the molecular weight of the polyurethane resin, a chain extender may be used during production of the polyurethane resin. Examples of the chain extender include polyamines such as ethylenediamine and 1,4-tetramethylenediamine, polyols such as ethylene glycol and propylene glycol, and polyalkylene glycols such as polyethylene glycol.

[0105] The polyurethane resin may be in the form of a water dispersion.

[0106] Aqueous dispersions of polyurethane resins are prepared by dispersing polyurethane obtained by reacting a polyisocyanate component with a polyol component in water, optionally chain-extending in the presence of a chain extender, which is a low-molecular-weight compound having two or more active hydrogens, such as a diol or diamine, and then stably dispersing or dissolving the polyurethane in water. Examples of aqueous dispersions include polyurethane dispersions in which hydrophilic groups or hydrophilic segments are added to a urethane resin to self-disperse it, polyurethane emulsions in which a hydrophobic urethane resin is forcibly emulsified with a surfactant, and water-soluble urethane resins dissolved in water. Self-dispersed polyurethane dispersions are particularly preferred. The polyurethane resin is not particularly limited, and those prepared using conventional water-based polyurethane resin techniques, such as the acetone method or prepolymer method, can be used.

[0107] In the case of an aqueous urethane resin, the number average molecular weight (Mn) is preferably 10,000 to 200,000, more preferably 30,000 to 150,000, from the viewpoint of improving solubility or dispersibility in water and interlayer adhesion with a pressure-sensitive adhesive layer, etc.

[0108] The thickness of the blocking layer is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. The blocking layer is intended to suppress the migration of the tackifier, so it does not require the same mechanical properties as the substrate. Therefore, it is preferable that the blocking layer be as thin as possible as long as it can suppress the migration of the tackifier. From the viewpoint of achieving the desired effect, the thickness of the blocking layer is preferably 0.1 μm or more, and more preferably 0.5 μm or more.

[0109] (base material) The substrate is not particularly limited, and various substrates used as support substrates for pressure-sensitive adhesive sheets can be used.The substrate can be a resin substrate; so-called synthetic paper made of resin; metal foil such as copper, aluminum, stainless steel, or the like; composite sheet substrate made by laminating a metal foil and a plastic film; vapor-deposited foil substrate made by vapor-depositing aluminum, silica, or the like; nonwoven fabric substrate; or paper substrate such as high-quality paper, kraft paper, glassine paper, art paper, coated paper, heat-sensitive coloring paper, or moisture-proof paper.Among these, the substrate is preferably a resin substrate, synthetic paper, or paper substrate. Examples of resins that constitute a suitable resin substrate include polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polystyrene, polycarbonate, polymethylpentene, polysulfone, polyether ether ketone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyimide, fluororesin, polyamide, acrylic resin, norbornene-based resin, and cycloolefin resin.

[0110] In this embodiment, since the amount of tackifier in the pressure-sensitive adhesive layer on the substrate side is relatively low, the substrate is preferably a substrate other than a low-polarity substrate. Specific examples include polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Among these, the substrate is preferably polyethylene terephthalate because of its high mechanical strength and excellent heat resistance.

[0111] The thickness of the substrate is not particularly limited, but from the viewpoint of mechanical properties, it is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more, and from the viewpoint of thinning, it is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0112] (Release liner) The release liner is a component that protects the pressure-sensitive adhesive layer and prevents a decrease in adhesiveness. The release liner is peeled off from the pressure-sensitive adhesive sheet when the sheet is attached to an adherend. Therefore, the pressure-sensitive adhesive sheet of the present invention also includes a sheet that does not have a release liner.

[0113] The release liner is not particularly limited, but examples thereof include paper such as fine paper, glassine paper, clay-coated paper, and polyethylene-laminated paper; polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; and plastic films such as polyolefin films such as polypropylene and polyethylene.

[0114] The thickness of the release liner is usually about 10 to 400 μm. The surface of the release liner may be provided with a layer of a release agent made of silicone or the like to improve the releasability of the pressure-sensitive adhesive layer. When such a layer is provided, the thickness of the layer is usually about 0.01 to 5 μm.

[0115] (Manufacturing method) The method for producing the pressure-sensitive adhesive sheet of the present invention is not particularly limited, but examples include: (1) a method in which a second pressure-sensitive adhesive layer-forming composition (pressure-sensitive adhesive composition) is applied onto a release liner to form a second pressure-sensitive adhesive layer, then a block layer-forming composition is applied onto the pressure-sensitive adhesive layer to form a block layer, and then a first pressure-sensitive adhesive layer-forming composition (pressure-sensitive adhesive composition) is applied onto the block layer to form a first pressure-sensitive adhesive layer, and then the first pressure-sensitive adhesive layer is laminated to a resin substrate; and (2) a method in which a second pressure-sensitive adhesive layer-forming composition, a block layer-forming composition, and then the first pressure-sensitive adhesive layer-forming composition are laminated onto a release liner in multiple layers to form a second pressure-sensitive adhesive layer, a block layer, and a first pressure-sensitive adhesive layer, and then the resin substrate is laminated to the first pressure-sensitive adhesive layer.

[0116] The method for applying the pressure-sensitive adhesive composition to the release liner or the blocking layer is not particularly limited, and the composition can be applied using a known application device such as a roll coater, a knife coater, an air knife coater, a bar coater, a blade coater, a slot die coater, or a lip coater.

[0117] Furthermore, by using a continuous coating device such as a die coater, a slide curtain coater, or a slide bead coater, the second pressure-sensitive adhesive layer-forming composition, the block layer-forming composition, and further the first pressure-sensitive adhesive layer-forming composition can be coated in multiple layers.

[0118] <Method of applying pressure-sensitive adhesive sheets to low-polarity substrates> The pressure-sensitive adhesive sheet of this embodiment is suitable for use on low-polarity adherends.

[0119] Therefore, another embodiment of the present invention is a method of applying the pressure-sensitive adhesive sheet of the first or second embodiment to an adherend with low polarity.

[0120] Here, examples of low polarity adherends include polyolefin resins such as polypropylene and polyethylene.

[0121] The adhesive strength to a low-polarity adherend is preferably 5 N / 25 mm or more. The adhesive strength is measured for each adherend by the method described in the Examples. [Example]

[0122] The effects of the present invention will be explained using the following examples and comparative examples. In the examples, the units "parts" and "%" are sometimes used, but unless otherwise specified, they represent "parts by mass" or "% by mass." Unless otherwise specified, each operation is carried out at room temperature (25°C).

[0123] Example 1 (1) Preparation of the composition for forming the second pressure-sensitive adhesive layer A mixture of 125 parts by weight of ion-exchanged water, 3 parts by weight of anionic reactive emulsifier "Latemul S-180A" (manufactured by Kao Corporation), 0.3 parts by weight of dibasic sodium phosphate, 0.5 parts by weight of ammonium persulfate, 42 parts by weight of 2-ethylhexyl acrylate, 53 parts by weight of n-butyl acrylate, 3 parts by weight of acrylic acid, 2 parts by weight of diacetone acrylamide, and 18 parts by weight of tackifier "YS Polystar N-125" (manufactured by Yasuhara Chemical Co., Ltd., terpene phenol type) was emulsified using a high-pressure homogenizer to prepare an emulsion with an average particle size of 250 nm. Next, this emulsion was heated at 80 ° C for 8 hours to undergo emulsion polymerization, and an acrylic resin emulsion was obtained.

[0124] 0.45 parts by weight of adipic acid hydrazide was added to 100 parts by mass (solid content) of the acrylic resin emulsion obtained above to prepare an acrylic emulsion-type pressure-sensitive adhesive. The average particle size of this acrylic emulsion-type pressure-sensitive adhesive was 180 nm.

[0125] (2) Preparation of the first adhesive layer-forming composition A first composition for forming a pressure-sensitive adhesive layer was obtained in the same manner as in (1) Preparation of a second composition for forming a pressure-sensitive adhesive layer, except that no tackifier was added.

[0126] (3) Creating adhesive sheets A release liner (silicone-coated glassine paper) was coated with a second adhesive layer-forming composition, a water-dispersible polyester resin solution (Vylonal MD-1200 (Toyobo Co., Ltd.), solids content 34% by mass, polyester resin: hydroxyl value 6 mgKOH / g, number average molecular weight 15,000, Tg 67°C, self-emulsifying type) as a block layer-forming composition, and the first adhesive layer-forming composition using a slide curtain coater. The coating was then dried at 100°C for 1 minute to obtain a laminate of a second adhesive layer (10 μm thick), a block layer (1 μm thick), and a first adhesive layer (10 μm thick) on the release liner.

[0127] A polyethylene terephthalate film (thickness: 50 μm) was attached as a substrate to the surface of the first pressure-sensitive adhesive layer of the laminate to obtain a pressure-sensitive adhesive sheet.

[0128] Example 2 An adhesive sheet was obtained in the same manner as in Example 1, except that the water-dispersible polyester resin solution used in Example 1 was changed to a water-dispersible polyester resin solution (Vylonal MD-1500 (manufactured by Toyobo Co., Ltd.), solid content 30 mass%, polyester resin: hydroxyl value 14 mg KOH / g, number average molecular weight 8,000, Tg 77°C, self-emulsifying type).

[0129] Example 3 An adhesive sheet was obtained in the same manner as in Example 1, except that the water-dispersed polyester resin solution in Example 1 was changed to a water-dispersed acrylic resin solution (solid content 30 mass%, acrylic resin: monomer composition: methyl methacrylate / n-butyl acrylate / acrylic acid = 64.0 / 35.4 / 0.6 (mass ratio), number average molecular weight 30,000, Tg 28°C).

[0130] (Comparative Example 1) An adhesive sheet was obtained in the same manner as in Example 1, except that the water-dispersible polyester resin solution in Example 1 was changed to a water-dispersible polyester resin solution (Vylonal MD-1985 (manufactured by Toyobo Co., Ltd.), solid content 27 mass%, polyester resin: hydroxyl value 4 mg KOH / g, number average molecular weight 25,000, Tg -20°C).

[0131] (Comparative Example 2) An adhesive sheet was obtained in the same manner as in Example 1, except that no blocking layer was provided.

[0132] (Evaluation method 1: Evaluation of tackifier migration) The surface of the second adhesive layer was measured by FT-IR immediately after production of the adhesive sheet and 7 days after production. The degree of migration was evaluated according to the following evaluation criteria based on the reduction in the peak attributable to the tackifier. Note that for those rated as ◎, ○, or △, the reduction in the peak attributable to the tackifier was less than 30%, and therefore the amount of tackifier that had migrated to the first adhesive layer was also less than 30%, and therefore the concentration of tackifier contained in the first adhesive layer of the adhesive sheet 7 days after production was lower than the concentration of tackifier contained in the second adhesive layer.

[0133] ◎: The reduction in the peak due to the tackifier was less than 10% ○: The reduction in the peak derived from the tackifier was 10% or more and less than 20% △: The reduction in the peak due to the tackifier was 20% or more but less than 30% ×: The amount of reduction in the peak derived from the tackifier was 30% or more (Evaluation method 2: Evaluation of adhesion between the blocking layer and the adhesive layer) The second adhesive layer surface was rubbed with a finger to check for peeling of the adhesive layer, and the result was evaluated according to the following evaluation criteria. The results are shown in Table 1.

[0134] ◎: No peeling occurred between the second adhesive layer and the block layer ○: Slight peeling occurred between the second adhesive layer and the block layer (Evaluation method 3: Adhesion) The pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples were left standing under standard conditions (23°C, 50% RH) for 7 days, the release liner was peeled off, and the pressure-sensitive adhesive layer was attached to a polyethylene plate. The sheet was then left standing under standard conditions for 30 minutes, after which the adhesive strength was measured. Specifically, the sheet was peeled off in a 180° direction at a test speed of 300 mm / min using a tensile tester, and the adhesive strength was measured. The numerical values ​​were converted to peel force per 25 mm of sheet width (N / 25 mm). The results are shown in Table 1.

[0135] [Table 1]

[0136] From the above results, it can be seen that the pressure-sensitive adhesive sheets of the examples suppress the migration of the tackifier and also have excellent adhesion. [Explanation of symbols]

[0137] 10 adhesive sheet 20 Base material 30 First adhesive layer 40 Block Layer 50 Second adhesive layer 60 Release Liner

Claims

1. A pressure-sensitive adhesive sheet having a substrate, a first pressure-sensitive adhesive layer, and a second pressure-sensitive adhesive layer in this order, a content concentration (mass%) of a tackifier contained in the first pressure-sensitive adhesive layer is lower than a content concentration (mass%) of a tackifier contained in the second pressure-sensitive adhesive layer; A pressure-sensitive adhesive sheet comprising a block layer disposed between the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer, the block layer having a glass transition temperature of 25°C or higher and containing as a main component a resin selected from the group consisting of polyester resins and acrylic resins.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive contained in the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is a rubber-based pressure-sensitive adhesive and / or an acrylic-based pressure-sensitive adhesive.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the tackifier contained in the second pressure-sensitive adhesive layer is at least one selected from the group consisting of alicyclic petroleum resins, terpene resins, and rosin resins.

4. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the blocking layer has a thickness of 5 µm or less.

Images