Water-dispersed adhesive composition and adhesive sheet

Abstract

The present invention provides a water-dispersed adhesive composition which is capable of improving water resistance. Provided is a water-dispersed adhesive composition which contains a base polymer, a water-dispersed tackifier resin, and a polyvinyl alcohol. The base polymer is an acrylic polymer that is obtained by emulsion polymerization of a monomer starting material. The polyvinyl alcohol has a saponification degree of 98 mol% or more and a weight average molecular weight of 25,000 to 80,000.

Description

Water-dispersible pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

[0001] The present invention relates to a water-dispersible PSA composition and a PSA sheet formed using the water-dispersible PSA composition. This application claims priority to Japanese Patent Application No. 2023-206970, filed December 7, 2023, the entire contents of which are incorporated herein by reference.

[0002] A water-dispersed PSA composition in the form of a PSA component dispersed in an aqueous medium (an emulsion-type PSA composition in which the PSA component is dispersed in an aqueous medium) is more desirable from the standpoint of environmental hygiene than a PSA composition in the form of a PSA component dissolved in an organic solvent (a solvent-type PSA composition). For this reason, PSA sheets made using the water-dispersed PSA composition are used in various fields in the form of double-sided tape and other forms. Patent documents 1 to 6 include technical documents relating to water-dispersed PSA compositions.

[0003] Japanese Patent Application Publication No. 2003-313525 Japanese Patent Application Publication No. 5-39468 Japanese Patent Application Publication No. 2013-129748 Japanese Patent Application Publication No. 2009-73897 Japanese Patent Application Publication No. 2009-13312 International Publication No. 2021 / 54215

[0004] A tackifier resin is sometimes blended into a PSA composition to improve adhesive performance. Since typical tackifier resins are water-insoluble, a tackifier resin emulsion dispersed in water (a water-dispersed tackifier resin) is preferably used as the tackifier resin added to the water-dispersed PSA composition. However, when a water-dispersed tackifier resin is added to a water-dispersed PSA composition, the water resistance (e.g., the ability to maintain adhesive strength when maintained under humid and hot conditions) of the PSA layer formed from the composition tends to decrease. For this reason, it has been difficult to improve water resistance while enhancing adhesive properties.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to provide a water-dispersible PSA composition capable of forming a PSA layer exhibiting improved water resistance. Another related object is to provide a PSA sheet comprising a PSA layer formed from the water-dispersible PSA composition.

[0006] The present inventors have found that, in an aqueous-dispersible pressure-sensitive adhesive composition containing an emulsion-polymerized acrylic polymer as a base polymer and a water-dispersible tackifier resin, adding polyvinyl alcohol having a high degree of saponification and a weight-average molecular weight within a specific range to the pressure-sensitive adhesive composition produces an effect of significantly improving the water resistance of an adhesive layer formed from the pressure-sensitive adhesive composition.

[0007] According to this specification, there is provided an aqueous-dispersed PSA composition comprising a base polymer, an aqueous-dispersed tackifier resin, and polyvinyl alcohol. Here, the base polymer is an acrylic polymer obtained by emulsion polymerization of monomer raw materials. The polyvinyl alcohol has a degree of saponification of 98 mol% or more and a weight-average molecular weight (Mw) of 25,000 to 80,000. By incorporating polyvinyl alcohol having a high degree of saponification and a weight-average molecular weight within the above range, it is easy to achieve an PSA layer that exhibits improved water resistance, even in a composition that includes an aqueous-dispersed tackifier resin.

[0008] In some embodiments, the content of the polyvinyl alcohol is 2 parts by weight or more and 6 parts by weight or less per 100 parts by weight of the base polymer. When the polyvinyl alcohol is contained in such a content, the effect of improving water resistance tends to be more suitably exhibited.

[0009] In some embodiments, the content of the water-dispersible tackifier resin is 5 to 60 parts by weight per 100 parts by weight of the base polymer. As the content of the water-dispersible tackifier resin increases, adhesive properties such as adhesive strength tend to improve. Furthermore, when the content of the water-dispersible tackifier resin is limited to the upper limit or less, a decrease in water resistance due to the addition of the water-dispersible tackifier resin is likely to be suppressed. A water-dispersible PSA composition having the above composition is likely to provide a PSA layer that favorably combines good water resistance and adhesive properties.

[0010] The acrylic polymer is preferably a polymer (emulsion polymer) of a monomer raw material containing more than 50 wt % of alkyl (meth)acrylate. A water-dispersible acrylic pressure-sensitive adhesive composition containing such an acrylic polymer as a base polymer is likely to provide a pressure-sensitive adhesive layer that exhibits good adhesive properties.

[0011] The present invention also provides a PSA sheet comprising a PSA layer formed from any of the water-dispersible PSA compositions disclosed herein. By virtue of having a PSA layer formed from the water-dispersible PSA composition, such a PSA sheet can exhibit good water resistance.

[0012] 1 is a schematic cross-sectional view illustrating a configuration of a pressure-sensitive adhesive sheet according to one embodiment.

[0013] Preferred embodiments of the present invention are described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings for carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic for the purpose of clearly explaining the present invention, and do not necessarily accurately represent the size or scale of the actual product provided.

[0014] In this specification, the term "adhesive" refers to a material that is in a soft solid (viscoelastic) state at temperatures around room temperature and has the property of adhering to an adherend under pressure. The adhesive referred to here is generally a material having a complex tensile modulus E ＊ (1Hz) <10 ７ dyne / cm ２ (typically, a material having the above properties at 25°C) The PSA in the technology disclosed herein can also be understood as the solid content (non-volatile content) of the PSA composition or a constituent of the PSA layer.

[0015] In this specification, "(meth)acryloyl" refers to acryloyl and methacryloyl in a comprehensive sense. Similarly, "(meth)acrylate" refers to acrylate and methacrylate in a comprehensive sense, and "(meth)acrylic" refers to acrylic and methacrylic in a comprehensive sense.

[0016] In this specification, the term "acrylic polymer" refers to a polymer containing more than 50% by weight of monomer units derived from an acrylic monomer as the monomer units constituting the polymer. The acrylic monomer refers to a monomer derived from a monomer having at least one (meth)acryloyl group per molecule.

[0017] In this specification, the term "water-dispersed" refers to a form in which at least a portion of the components are dispersed in water. For example, a "water-dispersed PSA composition" refers to a composition that contains a PSA composition and water, and in which at least a portion of the PSA composition is dispersed in water. The water-dispersed type also includes a suspended state and an emulsified state.

[0018] <Water-Dispersed Pressure-Sensitive Adhesive Composition> The pressure-sensitive adhesive composition disclosed herein is a water-dispersed (typically, aqueous emulsion) pressure-sensitive adhesive composition in which a pressure-sensitive adhesive component is dispersed in an aqueous medium. Here, the aqueous medium refers to a medium in which the solvent constituting the medium is water or a mixed solvent (aqueous solvent) containing water as the main component.

[0019] (Acrylic Polymer) The PSA composition disclosed herein is an acrylic PSA composition containing an acrylic polymer as a base polymer. Here, "base polymer" refers to the main component among the polymer components contained in the PSA composition (which may also be a PSA). Furthermore, in this specification, "main component" refers to a component contained in an amount of more than 50% by weight, unless otherwise specified. In a preferred embodiment, the acrylic PSA composition is an acrylic emulsion PSA composition containing a water-dispersible acrylic polymer. The water-dispersible acrylic polymer has an emulsion form in which the acrylic polymer is dispersed in water. Such an acrylic polymer preferably contains alkyl(meth)acrylate as the main monomer component (i.e., a component accounting for more than 50% by weight of the total amount of monomers constituting the acrylic polymer).

[0020] The acrylic polymer is preferably a polymer of a monomer raw material (monomer component) that contains, for example, an alkyl(meth)acrylate as a main monomer and may further contain a secondary monomer copolymerizable with the main monomer, where the main monomer is a component that accounts for more than 50% by weight of the monomer composition in the monomer raw material.

[0021] As the alkyl(meth)acrylate, for example, a compound represented by the following formula (1) can be suitably used: CH ２ = C(R １ ) COOR ２ (1) Here, R in the above formula (1) １ is a hydrogen atom or a methyl group. ２ is a chain alkyl group having 1 to 20 carbon atoms (hereinafter, this range of carbon atoms is referred to as "C １－２０From the viewpoint of the storage modulus of the adhesive, R ２ is C １－１４ alkyl(meth)acrylates in which R ２ is C １－１０ More preferred is alkyl(meth)acrylate, which is a chain alkyl group represented by the formula R ２ Alkyl (meth)acrylates in which is a butyl group or a 2-ethylhexyl group are particularly preferred.

[0022] R ２ is C １－２０ Examples of alkyl(meth)acrylates, which are chain alkyl groups, include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, s-butyl(meth)acrylate, pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, and isooctyl(meth)acrylate. Examples of alkyl (meth)acrylates include butyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These alkyl (meth)acrylates can be used alone or in combination of two or more. Preferred alkyl (meth)acrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

[0023] The technology disclosed herein is a method for preparing a polymerizable compound in which the monomer component is R ２ is C ４－１０Among the alkyl(meth)acrylates contained in the monomer component, R ２ is C ４－１０ This can be preferably implemented in an embodiment in which the total amount of alkyl (meth)acrylates, which are chain alkyl groups (typically the total amount of BA and 2EHA), accounts for 70% by weight or more (typically 80% by weight or more).

[0024] The alkyl(meth)acrylate is R ２ is C ４－１０ In the case where the alkyl (meth)acrylate (typically at least one of BA and 2EHA) is a chain alkyl group represented by the formula (1), other alkyl (meth)acrylates (R ２ is C ４ Less than or C １０ The total amount of alkyl(meth)acrylates (which are chain alkyl groups of more than 1000) in the monomer components constituting the acrylic polymer is preferably about 30% by weight or less (for example, 20% by weight or less, typically 15% by weight or less). From the viewpoint of obtaining the effect of the other alkyl(meth)acrylates, the total amount is preferably about 1% by weight or more (for example, 5% by weight or more, typically 10% by weight or more) in the monomer components. The other alkyl(meth)acrylates include alkyl(meth)acrylates of the formula (1) R ２ is C １－３ Preferably, alkyl(meth)acrylates, which are chain alkyl groups, are used. Specific examples thereof include methyl acrylate (MA), methyl methacrylate (MMA), and ethyl acrylate (EA). Among these, MA is more preferred.

[0025] A minor monomer copolymerizable with the alkyl (meth)acrylate main monomer can be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the acrylic polymer. Examples of the minor monomer include the following functional group-containing monomer components, which can be used singly or in combination of two or more: Carboxyl group-containing monomers: ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), and crotonic acid; ethylenically unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and citraconic acid, and their anhydrides (maleic anhydride, itaconic anhydride, etc.); Hydroxyl group-containing monomers: hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate; and unsaturated alcohols such as vinyl alcohol and allyl alcohol. Amide group-containing monomers: for example, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylolpropane(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide. Amino group-containing monomers: for example, aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, t-butylaminoethyl(meth)acrylate. Epoxy group-containing monomers: for example, glycidyl(meth)acrylate, methylglycidyl(meth)acrylate, allyl glycidyl ether. Cyano group-containing monomers: for example, acrylonitrile, methacrylonitrile. Keto group-containing monomers: for example, diacetone(meth)acrylamide, diacetone(meth)acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate, vinyl acetoacetate.Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-(meth)acryloylmorpholine.Alkoxysilyl group-containing monomers: for example, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane.

[0026] The functional group-containing monomers can be used alone or in combination of two or more. Among the functional group-containing monomers, carboxyl group-containing monomers, hydroxyl group-containing monomers, and cyano group-containing monomers are preferred, as they can favorably realize the introduction of crosslinking points and the improvement of cohesive strength as described above, and carboxyl group-containing monomers are more preferred. Among the carboxyl group-containing monomers, AA and MAA are preferred.

[0027] In a preferred embodiment, AA and MAA are used in combination as the functional group-containing monomer. A PSA composition containing an acrylic polymer with such a monomer composition (i.e., copolymer composition) can provide a PSA sheet with higher performance (e.g., better repulsion resistance). The weight ratio of AA to MAA (AA / MAA) can be, for example, in the range of approximately 0.1 to 10, more preferably approximately 0.3 or more (typically 0.5 or more), and more preferably approximately 5 or less (typically 4 or less). By having AA / MAA within the above range, there is a tendency for the effect of improving repulsion resistance to be sufficiently obtained, and furthermore, after the PSA sheet is produced, there is a tendency for the adhesive properties to have excellent stability over time.

[0028] In addition, it is preferable that an alkoxysilyl group-containing monomer is copolymerized with the acrylic polymer. The alkoxysilyl group-containing monomer is typically an ethylenically unsaturated monomer having at least one (preferably two or more, for example, two or three) alkoxysilyl group in one molecule, and specific examples thereof are as described above. The above alkoxysilyl group-containing monomers can be used alone or in combination of two or more. By copolymerizing the alkoxysilyl group-containing monomer, a crosslinked structure can be introduced into the pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition containing the acrylic polymer by a condensation reaction of silanol groups (silanol condensation).

[0029] When a functional group-containing monomer is copolymerized into an acrylic polymer, the proportion of the functional group-containing monomer in the total monomer components constituting the acrylic polymer is not particularly limited. Generally, from the viewpoint of achieving a good balance between cohesion and adhesion, the proportion of the functional group-containing monomer is preferably about 0.1 wt% or more (e.g., 0.5 wt% or more, typically 1 wt% or more). Furthermore, taking into account the adhesive effect of alkyl (meth)acrylate, it is preferably about 40 wt% or less (e.g., 30 wt% or less, typically 20 wt% or less). When a carboxyl group-containing monomer is copolymerized into an acrylic polymer, the proportion of the carboxyl group-containing monomer in the total monomer components is suitably 15 wt% or less from the viewpoint of improving water resistance, and may be, for example, 10 wt% or less, 5 wt% or less, or 3 wt% or less. Meanwhile, from the viewpoint of cohesion and the like, in some embodiments, the proportion may be, for example, 0.1 wt% or more, or 0.5 wt% or more. According to the technology disclosed herein, good water resistance can be achieved even in an embodiment in which the proportion of the carboxyl group-containing monomer in the total monomer components is 1% by weight or more, or 1.5% by weight or more. When an alkoxysilyl group-containing monomer is copolymerized with an acrylic polymer, the proportion of the alkoxysilyl group-containing monomer in the total monomer components is suitably 0.005% by weight or more (e.g., 0.01% by weight or more) and suitably 0.1% by weight or less (e.g., 0.03% by weight or less) of the total monomer components.

[0030] Furthermore, for the purpose of increasing the cohesive strength of the acrylic polymer, copolymerization components other than the above-mentioned minor monomers can be used. Examples of such copolymerization components include vinyl ester monomers such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene, substituted styrenes (α-methylstyrene, etc.) and vinyltoluene; cycloalkyl(meth)acrylates such as cyclohexyl(meth)acrylate, cyclopentyl(meth)acrylate and isobornyl(meth)acrylate; aryl(meth)acrylates (e.g., phenyl(meth)acrylate), aryloxyalkyl(meth)acrylates (e.g., phenoxyethyl(meth)acrylate), arylalkyl(meth)acrylates, and the like. aromatic ring-containing (meth)acrylates such as (meth)acrylates (for example, benzyl (meth)acrylate); olefin-based monomers such as ethylene, propylene, isoprene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether-based monomers such as methyl vinyl ether and ethyl vinyl ether; and the like.

[0031] Other examples of copolymerizable components other than the above-mentioned secondary monomers include monomers having multiple functional groups in one molecule. Examples of such polyfunctional monomers include 1,6-hexanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, glycerin di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, divinylbenzene, butyl di(meth)acrylate, hexyl di(meth)acrylate, and the like.

[0032] The amount of copolymerization components other than the above-mentioned secondary monomers may be appropriately selected depending on the purpose and application, and is not particularly limited. For example, it is preferably 10% by weight or less of the monomer composition of the acrylic polymer.

[0033] The acrylic polymer in the technology disclosed herein is suitably designed so that the glass transition temperature (Tg) of the polymer is −25° C. or lower (typically −75° C. or higher and −25° C. or lower). The Tg of the acrylic polymer may be preferably −35° C. or lower (e.g., −70° C. or higher and −35° C. or lower), more preferably −40° C. or lower (e.g., −70° C. or higher and −40° C. or lower). Setting the Tg of the acrylic polymer to the above-mentioned upper limit or lower is preferable from the viewpoint of improving adhesive strength. The Tg of the acrylic polymer can be adjusted by the type and amount ratio of the monomers used in synthesizing the polymer.

[0034] Here, the Tg of an acrylic polymer refers to the Tg calculated by Fox's formula based on the composition of the monomer components used in synthesizing the polymer. The Fox formula, as shown below, is a relationship between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer: 1 / Tg=Σ(Wi / Tgi) In the Fox formula, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature of a homopolymer of monomer i (unit: K).

[0035] The glass transition temperatures of the homopolymers used to calculate Tg are values ​​listed in publicly available documents. For example, for the monomers listed below, the following values ​​are used as the glass transition temperatures of the homopolymers of the monomers: 2-ethylhexyl acrylate -70°C n-butyl acrylate -55°C Methyl methacrylate 105°C Methyl acrylate 8°C Vinyl acetate 32°C Acrylic acid 106°C Methacrylic acid 228°C

[0036] For the glass transition temperatures of homopolymers of monomers other than those listed above, the values ​​given in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989) shall be used. When multiple values ​​are given in this document, the highest value shall be used.

[0037] For monomers for which the glass transition temperature of the homopolymer is not listed in the Polymer Handbook, the value obtained by the following measurement method will be used (see Japanese Patent Application Publication No. 2007-51271). Specifically, 100 parts by weight of the monomer, 0.2 parts by weight of azobisisobutyronitrile, and 200 parts by weight of ethyl acetate as a polymerization solvent are charged into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture is stirred for 1 hour while passing nitrogen gas through. After removing oxygen from the polymerization system in this manner, the temperature is raised to 63°C and the reaction is allowed to proceed for 10 hours. The mixture is then cooled to room temperature to obtain a homopolymer solution with a solids concentration of 33% by weight. This homopolymer solution is then cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. This test sample was punched out into a disk shape with a diameter of 7.9 mm, sandwiched between parallel plates, and subjected to a shear strain of 1 Hz using a viscoelasticity tester (ARES, manufactured by Rheometrics Corporation). Viscoelasticity was measured in a shear mode at a temperature range of −70 to 150°C and a heating rate of 5°C / min, and the peak top temperature of tan δ was taken as the Tg of the homopolymer.

[0038] In the technology disclosed herein, the acrylic polymer is produced by emulsion polymerization. That is, the acrylic polymer disclosed herein is a polymer (emulsion polymer) obtained by emulsion polymerization of a monomer raw material. The mode of emulsion polymerization is not particularly limited, and various monomer supply methods, polymerization conditions, materials used, etc. similar to those of conventionally known general emulsion polymerizations can be appropriately adopted. For example, as the monomer supply method, a batch charging method in which all the monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc. can be appropriately adopted. The monomer raw material may be added dropwise in the form of an aqueous emulsion. The polymerization temperature can be, for example, about 20°C or higher (usually 40°C or higher), and is suitably about 100°C or lower (usually 80°C or lower).

[0039] According to the emulsion polymerization, it is possible to prepare a polymerization liquid (acrylic polymer emulsion) in the form of an emulsion in which an acrylic polymer is dispersed in water. The water-dispersed PSA composition disclosed herein can be preferably produced using the polymerization liquid or a polymerization liquid that has been subjected to an appropriate post-treatment. Alternatively, an acrylic polymer may be synthesized using a polymerization method other than emulsion polymerization (e.g., solution polymerization, photopolymerization, bulk polymerization, etc.), and the polymer may be dispersed in water to prepare an acrylic polymer emulsion.

[0040] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method, for example, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, etc. azo-based initiators such as those listed above; persulfate-based initiators such as potassium persulfate and ammonium persulfate; peroxide-based initiators such as benzoyl peroxide, t-butyl hydroperoxide, and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; carbonyl-based initiators such as aromatic carbonyl compounds; and redox-based initiators such as a combination of a persulfate and sodium hydrogen sulfite, or a combination of a peroxide and sodium ascorbate. These polymerization initiators can be used alone or in combination of two or more.

[0041] From the viewpoint of water resistance, in some embodiments, it is preferable to use a polymerization initiator that is not a redox initiator. In particular, it is preferable not to use an ascorbic acid-based redox initiator as the polymerization initiator because ascorbic acid-based redox initiators can cause a decrease in water resistance.

[0042] The amount of the polymerization initiator used is not particularly limited as long as it is a normal amount, and can be selected, for example, from the range of about 0.005 parts by weight or more (preferably 0.01 parts by weight or more) to about 1 part by weight or less (preferably 0.8 parts by weight or less) per 100 parts by weight of the total monomer components.

[0043] During polymerization, a chain transfer agent (which may also be understood as a molecular weight regulator or polymerization degree regulator) may be used as needed. Examples of the chain transfer agent include mercaptans such as dodecyl mercaptan (dodecanethiol), lauryl mercaptan, glycidyl mercaptan, 2-mercaptoethanol, mercaptoacetic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol, as well as α-methylstyrene dimer. Such chain transfer agents may be used alone or in combination of two or more.

[0044] The amount of the chain transfer agent used can be about 0.001 part by weight or more (typically about 0.005 part by weight or more, for example, about 0.001 part by weight or more) relative to 100 parts by weight of the monomer components, and can be, for example, about 5 parts by weight or less (typically about 2 parts by weight or less, for example, about 1 part by weight or less). By setting the amount of the chain transfer agent used in an appropriate range, a desired polymerization rate can be obtained.

[0045] Emulsion polymerization of the monomer raw materials is usually carried out in the presence of a surfactant (emulsifier). The amount of surfactant used is not particularly limited. In consideration of polymerization stability and dispersion stability of the polymerization reaction product, the amount of surfactant used is usually 0.1 parts by weight or more, preferably 0.5 parts by weight or more, per 100 parts by weight of the monomer raw materials. From the viewpoint of achieving higher stability, it may be 1.0 parts by weight or more, or even 1.5 parts by weight or more. Furthermore, the amount of surfactant used may be, for example, 10 parts by weight or less, per 100 parts by weight of the monomer raw materials. On the other hand, from the viewpoint of improving water resistance, it is desirable to reduce the amount of surfactant used (especially non-reactive surfactant). From this viewpoint, the amount of surfactant used is usually preferably 5 parts by weight or less, or may be 4 parts by weight or less, 3 parts by weight or less, or 2.5 parts by weight or less, per 100 parts by weight of the monomer raw materials.

[0046] As the surfactant, known anionic surfactants, nonionic surfactants, cationic surfactants, etc. can be used. Usually, anionic or nonionic surfactants are preferred. Surfactants having a reactive functional group (typically a radically polymerizable functional group) may also be used. Hereinafter, surfactants having a reactive functional group will be referred to as reactive surfactants, and in contrast, general surfactants not having a reactive functional group will be referred to as non-reactive surfactants. The surfactants can be used alone or in combination of two or more.

[0047] Examples of non-reactive anionic surfactants include alkyl sulfates such as lauryl sulfate and octadecyl sulfate; fatty acid salts; alkylbenzenesulfonates such as nonylbenzenesulfonate and dodecylbenzenesulfonate; naphthalenesulfonates such as dodecylnaphthalenesulfonate; alkyldiphenyletherdisulfonates such as dodecyldiphenyletherdisulfonates; polyoxyethylene alkylether sulfates such as polyoxyethyleneoctadecylethersulfonate and polyoxyethylenelaurylethersulfonate; polyoxyethylene alkylphenylether sulfates such as polyoxyethylenelaurylphenylethersulfonate; polyoxyethylene styrenated phenylether sulfate; sulfosuccinates such as laurylsulfosuccinate and polyoxyethylenelaurylsulfosuccinate; polyoxyethylene alkylether phosphates; polyoxyethylene alkylether acetates; etc. When anionic surfactants form salts, these salts can be, for example, metal salts (preferably monovalent metal salts) such as sodium salts, potassium salts, calcium salts, magnesium salts, etc., ammonium salts, amine salts, etc.

[0048] Examples of non-reactive nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether; polyoxyethylene alkyl phenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether; sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monostearate and polyoxyethylene sorbitan monolaurate; polyoxyethylene glyceryl ether fatty acid esters; polyoxyethylene-polyoxypropylene block copolymers; and the like.

[0049] As the reactive surfactant, those having a polymerizable (typically radically polymerizable) functional group can be preferably used. For example, a reactive surfactant having a structure in which a radically polymerizable functional group is introduced into the anionic surfactant or nonionic surfactant as described above can be used. The type of radically polymerizable functional group is not particularly limited, and can be, for example, an alkenyl group, an acryloyl group, a methacryloyl group, a vinyl group, a vinyl ether group (vinyloxy group), an allyl ether group (allyloxy group), etc. Specific examples of the alkenyl group include a propenyl group and an isopropenyl group (CH ２ =C(CH ３ The concept of propenyl group here includes 1-propenyl group (CH ３ -CH=CH-) and 2-propenyl group (CH ２ =CH-CH ２ -; sometimes referred to as an allyl group.

[0050] Examples of anionic reactive surfactants include polyoxyethylene (allyloxymethyl) alkyl ether sulfates (e.g., ammonium salts), polyoxyethylene nonylpropenyl phenyl ether sulfates (e.g., ammonium salts), alkyl allyl sulfosuccinates (e.g., sodium salts), methacryloxy polyoxypropylene sulfates (e.g., sodium salts), polyoxyalkylene alkenyl ether sulfates (e.g., ammonium salts in which the alkenyl group terminates in an isopropenyl group).When anionic reactive surfactants form salts, the salts may be, for example, metal salts such as sodium salts, or non-metal salts such as ammonium salts or amine salts.Examples of nonionic reactive surfactants include polyoxyethylene nonylpropenyl phenyl ether.

[0051] Commercially available reactive surfactants include those manufactured by Daiichi Kogyo Seiyaku Co., Ltd. under the trade names "Aqualon HS-05," "Aqualon HS-10," "Aqualon HS-1025," "Aqualon HS-20," "Aqualon KH-10," "Aqualon KH-1025," "Aqualon KH-05," "Aqualon BC-0515," "Aqualon BC-10," "Aqualon BC-1025," "Aqualon BC-20," "Aqualon BC-2020," "Aqualon RN-20," "Aqualon RN-30," and "Aqualon RN-50." Examples of such products include "Aqualon AR-10," "Aqualon AR-20," "Aqualon AR-1025," and "Aqualon AR-2020," products manufactured by ADEKA Corporation under the trade names "ADEKA REASOAP SE-10N" and "ADEKA REASOAP SR-1025," products manufactured by Kao Corporation under the trade names "LATEMUL PD-104," "LATEMUL PD-420," "LATEMUL PD-430," and "LATEMUL PD-450," products manufactured by Sanyo Chemical Industries, Ltd. under the trade names "ELEMINOL JS-20" and "ELEMINOL RS-3000," and products manufactured by Nippon Nyukazai Co., Ltd. under the trade name "ANTOX MS-60."

[0052] From the viewpoint of improving water resistance, the surfactant used in the technology disclosed herein preferably contains a reactive surfactant. In other words, it is preferable that at least a portion of the surfactant used is a reactive surfactant. By emulsion polymerizing the monomer raw material in the presence of a reactive surfactant, the reactive surfactant can react and be incorporated into the acrylic polymer. Incorporation of the reactive surfactant into the acrylic polymer reduces the amount of free surfactant, thereby improving water resistance. Therefore, polymerization using a reactive surfactant can be advantageous for achieving both polymerization stability and the water resistance of a pressure-sensitive adhesive layer obtained from a pressure-sensitive adhesive composition containing the polymerized acrylic polymer. From the viewpoint of achieving better water resistance, the proportion of the reactive surfactant relative to the total weight of the surfactants used during emulsion polymerization can be 50 wt% or more, more preferably 70 wt% or more. For example, an embodiment in which only the reactive surfactant is used as the surfactant can be preferably adopted. Furthermore, the reactive surfactant incorporated into the acrylic polymer is restricted in its movement within the pressure-sensitive adhesive layer, making it less likely to bleed out onto the surface of the pressure-sensitive adhesive layer. This can also favorably contribute to improved water resistance. In this specification, "containing a reactive surfactant" refers to a concept that encompasses containing the reactive surfactant in a state after its reactive functional group (e.g., a radically polymerizable functional group) has reacted. The reactive surfactant in the technology disclosed herein is typically contained in the water-dispersible PSA composition or PSA layer in a form in which at least a portion of it is incorporated into the acrylic polymer as described above.

[0053] In some embodiments, anionic reactive surfactants are preferably used from the viewpoint of improving water resistance. When using nonionic reactive surfactants, more preferable results can be achieved by using them in combination with other surfactants, such as anionic reactive surfactants, anionic nonreactive surfactants, nonionic nonreactive surfactants, etc.

[0054] The weight average molecular weight (Mw) of the acrylic polymer is not particularly limited, and may be, for example, 10 × 10 ４ ~500 x 10 ４Here, the Mw of the acrylic polymer in this specification refers to the Mw of the tetrahydrofuran (THF) soluble portion (sol portion) of the acrylic polymer. The Mw of the acrylic polymer refers to a value calculated in terms of standard polystyrene based on GPC (gel permeation chromatography). From the viewpoint of improving adhesive properties, the Mw of the acrylic polymer is preferably 150 × 10 ４ Less than 100 × 10, more preferably ４ In addition, from the viewpoint of cohesion properties, the Mw of the acrylic polymer is preferably 20×10 or less. ４ More preferably, 30×10 ４ or more (for example, 40 x 10 ４ The weight average molecular weight (Mw) of the acrylic polymer is specifically measured by the method described in the examples below.

[0055] (Tackifying Resin) The water-dispersible PSA composition disclosed herein contains a tackifying resin, which allows the production of a PSA sheet that exhibits excellent adhesive properties (e.g., adhesive strength, repulsion resistance).

[0056] The tackifier resin is a water-dispersed tackifier resin (also referred to as a tackifier resin emulsion). That is, the water-dispersed PSA composition disclosed herein contains the tackifier resin in the form of an emulsion in which the tackifier resin is dispersed in water. For example, by mixing an aqueous emulsion of an acrylic polymer with an emulsion of the tackifier resin, a PSA composition containing these components in a desired ratio can be easily prepared. The tackifier resin emulsion used is preferably one that is substantially free of at least aromatic hydrocarbon solvents (more preferably, substantially free of aromatic hydrocarbon solvents and other organic solvents).

[0057] Examples of tackifying resins include rosin-based tackifying resins (including rosin derivative tackifying resins), petroleum-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, ketone-based tackifying resins, etc. These can be used alone or in combination of two or more.

[0058] Examples of the rosin-based tackifying resin include rosins such as gum rosin, wood rosin, and tall oil rosin, as well as stabilized rosins (e.g., stabilized rosins obtained by disproportionating or hydrogenating the above-mentioned rosins), polymerized rosins (e.g., polymers, typically dimers, of the above-mentioned rosins), and modified rosins (e.g., unsaturated acid-modified rosins modified with unsaturated acids such as maleic acid, fumaric acid, and (meth)acrylic acid). Examples of the rosin derivative tackifying resin include esters of the above-mentioned rosin-based resins (e.g., rosin esters such as stabilized rosin esters and polymerized rosin esters), phenol-modified rosin-based resins (phenol-modified rosins), and esters thereof (phenol-modified rosin esters). Examples of the petroleum-based tackifying resin include aliphatic petroleum resins, aromatic petroleum resins, copolymerized petroleum resins, alicyclic petroleum resins, and hydrogenated versions of these. Examples of the terpene-based tackifying resins include α-pinene resins, β-pinene resins, aromatic-modified terpene-based resins, terpene-phenol-based resins, etc. Examples of the ketone-based tackifying resins include ketone-based resins obtained by condensation of ketones (e.g., aliphatic ketones such as methyl ethyl ketone, methyl isobutyl ketone, and acetophenone; alicyclic ketones such as cyclohexanone and methylcyclohexanone) with formaldehyde, etc.

[0059] Examples of tackifying resins that can be preferably used in the technology disclosed herein include rosin-based tackifying resins and terpene-based tackifying resins. Suitable examples of rosin-based tackifying resins include stabilized rosin esters and polymerized rosin esters. Suitable examples of terpene-based tackifying resins include terpene phenol-based resins.

[0060] Such a tackifier resin emulsion may be prepared using a surfactant (emulsifier) ​​as needed. Surfactants that can be used in preparing the tackifier resin emulsion can be selected from one or more surfactants similar to those that can be used in preparing the acrylic polymer emulsion. Typically, anionic or nonionic surfactants are preferred. The surfactants used in preparing the acrylic polymer emulsion and the surfactants used in preparing the tackifier resin emulsion may be the same or different. For example, preferred embodiments include using an anionic surfactant in the preparation of both emulsions, using a nonionic surfactant in both emulsions, or using an anionic surfactant in one emulsion and a nonionic surfactant in the other. The amount of surfactant used is not particularly limited as long as it is an amount that allows the tackifier resin to be prepared into an emulsion. For example, the amount can be approximately 0.2 parts by weight or more (preferably 0.5 parts by weight or more) and approximately 10 parts by weight or less (preferably 5 parts by weight or less) per 100 parts by weight (solids basis) of the tackifier resin.

[0061] The softening point of the tackifier resin used is not particularly limited. From the viewpoint of improving cohesive strength, the softening point of the tackifier resin may be, for example, 80°C or higher, preferably 90°C or higher, or may be 100°C or higher, 120°C or higher, or 130°C or higher.

[0062] Although not particularly limited, in some embodiments, the tackifier resin in the technology disclosed herein may include a high-softening-point tackifier resin having a softening point of 140°C or higher. The softening point of the high-softening-point tackifier resin is preferably 145°C or higher, and may be, for example, 150°C or higher, 155°C or higher, 160°C or higher, or 165°C or higher. Use of the high-softening-point tackifier resin can favorably achieve both adhesion and cohesiveness. There is no particular upper limit for the softening point of the tackifier resin, but from the viewpoints of compatibility, low-temperature properties, etc., it is usually appropriate that the softening point be 200°C or lower, preferably 180°C or lower, and may be 175°C or lower.

[0063] The softening point of the tackifying resin is defined as the value measured based on the softening point test method (ring and ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at the lowest possible temperature and carefully filled into a ring placed on a flat metal plate, avoiding the formation of bubbles. After cooling, the raised portion of the ring, including the top edge, is cut off with a slightly heated knife. Next, a holder (ring stand) is placed in a glass container (heating bath) with a diameter of at least 85 mm and a height of at least 127 mm, and glycerin is poured into it to a depth of at least 90 mm. Next, a steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample are immersed in the glycerin without touching each other, and the glycerin temperature is maintained at 20°C ± 5°C for 15 minutes. Next, the steel ball is placed in the center of the surface of the sample in the ring and placed in its fixed position on the holder. Next, keeping the distance from the top of the ring to the glycerin surface at 50 mm, place a thermometer, align the center of the thermometer's mercury bulb with the center of the ring, and heat the container. The flame of the Bunsen burner used for heating should be aimed midway between the center of the bottom and the edge of the container, ensuring even heating. After heating begins and reaching 40°C, the rate of increase in bath temperature must be 5.0 ± 0.5°C per minute. The sample gradually softens, flows down the ring, and finally touches the bottom plate, at which point the temperature is read and considered the softening point. Two or more samples should be measured at the same time, and the average value should be used.

[0064] In order to optimally exert the effects of its use, the amount of tackifier resin used (based on solids content) is usually 1 part by weight or more per 100 parts by weight of acrylic polymer, preferably 3 parts by weight or more (e.g., 5 parts by weight or more), more preferably 10 parts by weight or more, and even more preferably 15 parts by weight or more. According to the technology disclosed herein, good water resistance can be achieved even in an embodiment in which 22 parts by weight or more (e.g., 25 parts by weight or more) of tackifier resin is contained per 100 parts by weight of acrylic polymer. Furthermore, in terms of cohesive strength, etc., the amount of tackifier resin used is usually 90 parts by weight or less per 100 parts by weight of acrylic polymer, preferably 60 parts by weight or less, more preferably 55 parts by weight or less.

[0065] When the aqueous PSA composition disclosed herein contains a high-softening point tackifying resin, the high-softening point tackifying resin may be used alone as the tackifying resin from the viewpoint of cohesive strength, etc. Furthermore, from the viewpoint of balancing various adhesive properties, in some embodiments, a high-softening point tackifying resin may be used in combination with a tackifying resin having a lower softening point (e.g., a tackifying resin having a softening point of 120°C or less, or 110°C or less). In such embodiments, the proportion of the high-softening point tackifying resin in the total tackifying resin used may be, for example, 20% by weight or more, 40% by weight or more, or 60% by weight or more. The proportion of the high-softening point tackifying resin may be, for example, 90% by weight or less, 80% by weight or less, or 70% by weight or less.

[0066] (Polyvinyl Alcohol) The water-dispersible PSA composition disclosed herein contains polyvinyl alcohol having a high degree of saponification and a specific weight-average molecular weight. In particular, by subsequently adding polyvinyl alcohol having the above-mentioned specific degree of saponification and weight-average molecular weight to an acrylic water-dispersible PSA composition containing a water-dispersible tackifier resin, the water resistance of a PSA layer formed from the water-dispersible PSA composition can be effectively improved.

[0067] The polyvinyl alcohol disclosed herein is a polymer containing a vinyl alcohol unit as a repeating unit. Here, the vinyl alcohol unit (hereinafter also referred to as "VA unit") is a polymer having the following chemical formula: -CH ２ The VA unit is, for example, a repeating unit (-CH ２ -CH(OCOCH ３ In some embodiments of the technology disclosed herein, polyvinyl alcohol obtained by saponifying polyvinyl acetate can be preferably used.

[0068] The degree of saponification (mol %) of such polyvinyl alcohol can be calculated by the following formula: Degree of saponification (mol %) = (number of hydroxyl groups) ÷ (number of hydroxyl groups + number of acetate groups) × 100 Specifically, the degree of saponification of polyvinyl alcohol is measured in accordance with JIS K 6726-1994.

[0069] The polyvinyl alcohol disclosed herein has a saponification degree of 98 mol% or more. When polyvinyl alcohol with a saponification degree of 98 mol% or more is used, when it is added to an aqueous PSA composition containing an aqueous PSA resin, the water resistance (e.g., the ability to maintain adhesive strength when maintained under humid and hot conditions) of the PSA layer formed from the aqueous PSA composition is likely to be improved. In some embodiments, the saponification degree of polyvinyl alcohol may be 98.3 mol% or more, or may be 98.5 mol% or more. In principle, the upper limit of the saponification degree of polyvinyl alcohol is 100 mol%. The polyvinyl alcohol disclosed herein may be what is called a fully saponified polyvinyl alcohol.

[0070] In some embodiments, the polyvinyl alcohol disclosed herein preferably has residual acetate groups uniformly distributed along the polymer chain of the polyvinyl alcohol. Polyvinyl alcohol having hydrophobic acetate groups uniformly distributed along the polymer chain tends to improve low-temperature viscosity stability in an aqueous solution.

[0071] In some embodiments, polyvinyl alcohol is added to the composition in the form of an aqueous solution dissolved in water. In such embodiments, the polyvinyl alcohol as a raw material is preferably in the form of particles. The particulate polyvinyl alcohol may be of various shapes and particle sizes, such as fine powder, granules, powder, and coarse particles, without any particular limitations. In some embodiments, the average particle diameter of the polyvinyl alcohol particles as a raw material is 1,000 μm or less. The use of polyvinyl alcohol particles with a small average particle diameter tends to improve the solubility in water and allows for uniform dispersion in the aqueous PSA composition, thereby contributing to improved water resistance of the aqueous PSA composition. From this perspective, the average particle diameter of the polyvinyl alcohol particles as a raw material is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 100 μm or less. The lower limit of the average particle diameter of the polyvinyl alcohol particles is not particularly limited, but from the viewpoint of handleability, it is preferably approximately 75 μm or more. Here, the average particle size of the polyvinyl alcohol particles can be the value of the major axis measured by optical microscope observation using a digital microscope in an environment of humidity 65% ​​RH and temperature 25°C.

[0072] In the technology disclosed herein, the weight average molecular weight (Mw) of polyvinyl alcohol is 2.5 × 10 ４ 8 x 10 or more ４ In this way, when polyvinyl alcohol having a weight-average molecular weight within a specific range is used, when it is added to an aqueous PSA composition containing an aqueous tackifier resin, the water resistance (e.g., the ability to maintain adhesive strength when maintained under humid and hot conditions) of the PSA layer formed from the aqueous PSA composition is likely to be improved. From the viewpoint of improving water resistance, the Mw of the polyvinyl alcohol is 2.7 × 10 ４ More preferably, it is 3.0 × 10 or more. ４ or more, 3.5 × 10 ４ or more, 4.0 × 10 ４ or more, 5.0 × 10 ４ or more, 5.5 × 10 ４From the viewpoint of improving water resistance, the Mw of polyvinyl alcohol is 8.0 × 10 ４ More preferably, it is less than 7.7 × 10 ４ It may be less than 7.5 × 10 ４ In particular, when polyvinyl alcohol having a high degree of saponification and a weight-average molecular weight within the above-mentioned specific range is used, when the polyvinyl alcohol is added to a water-dispersed PSA composition containing a water-dispersed tackifier resin, the water resistance of the PSA layer formed from the water-dispersed PSA composition is more likely to be improved.

[0073] The number average molecular weight (Mn) of polyvinyl alcohol is not particularly limited. In some preferred embodiments, the Mn of polyvinyl alcohol is 0.85×10 ４ or more, 0.95 × 10 ４ or more, 1.1 × 10 ４ or more, 1.2 × 10 ４ or more, 1.3 × 10 ４ In some preferred embodiments, the Mn of the polyvinyl alcohol is 4.1×10 ４ is less than or equal to 4.0 × 10 ４ It may be less than 3.8 × 10 ４ It may be less than 3.6 × 10 ４ It may be less than 3.5 × 10 ４ The following is also acceptable.

[0074] In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of various water-soluble polymers such as polyvinyl alcohol can be measured by gel permeation chromatography (GPC) (water-based, polyethylene glycol / polyethylene oxide equivalent). Specifically, they are measured by the method described in the Examples below.

[0075] Regarding the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polyvinyl alcohol polymer herein, which has reduced solubility in water due to a high molecular weight or the like, values ​​based on GPC using dimethylformamide (DMF) as an eluent (DMF-based, polystyrene equivalent) can be employed instead of the above-mentioned aqueous GPC measurement. Specifically, they are measured by the method described in the Examples below.

[0076] (Crosslinking Agent) The aqueous dispersion PSA composition used to form the PSA layer preferably contains a crosslinking agent as an optional component. The PSA layer in the technology disclosed herein may contain the crosslinking agent in a form after crosslinking reaction, a form before crosslinking reaction, a partially crosslinked form, an intermediate or composite form thereof, or the like. The crosslinking agent is typically contained in the PSA layer exclusively in a form after crosslinking reaction.

[0077] The type of crosslinking agent is not particularly limited, and crosslinking agents commonly used in the field of aqueous PSA compositions can be used. For example, a crosslinking agent selected from hydrazine-based crosslinking agents, epoxy-based crosslinking agents (such as polyethylene glycol diglycidyl ether), carbodiimide-based crosslinking agents (which may be hydrophilically treated), isocyanate-based (preferably aqueous-dispersible isocyanate-based) crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, metal chelate-based crosslinking agents, active methylol-based crosslinking agents, active alkoxymethyl-based crosslinking agents, silane coupling agents, etc. can be used. The crosslinking agents can be used alone or in combination of two or more. The amount of crosslinking agent used is not particularly limited, and is suitably, for example, approximately 10 parts by weight or less (e.g., approximately 0.005 to 10 parts by weight) per 100 parts by weight of the acrylic polymer, preferably approximately 5 parts by weight or less (0.01 to 5 parts by weight).

[0078] (Other Additives) In addition, from the viewpoint of easy releasability from the release liner, the aqueous dispersion PSA composition disclosed herein preferably contains a silicon compound (typically a silane coupling agent).As the silicon compound, one or more of alkylalkoxysilane compounds, vinyl group-containing silane compounds, epoxy group-containing silane compounds, styryl group-containing silane compounds, (meth)acryloyl group-containing silane compounds, amino group-containing silane compounds, ureido group-containing silane compounds, mercapto group-containing silane compounds, isocyanate group-containing silane compounds, and silyl group-containing sulfides can be used.Among these, alkylalkoxysilane compounds are preferred.The molecular weight of the silicon compound is suitably about 100 or more (e.g., 200 or more), and can be about 500 or less (e.g., 350 or less).

[0079] As the alkylalkoxysilane compound, any of alkyltrialkoxysilane, dialkyldialkoxysilane, trialkylmonoalkoxysilane, tetraalkoxysilane, and phenylalkoxysilane can be used. The alkyl includes both linear and cyclic alkyls. Specific examples of the above compounds include methyltrimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, n-hexyltrimethoxysilane, n-octyltrimethoxysilane, n-decyltrimethoxysilane, hexadecyltrimethoxysilane, methyltriethoxysilane, dimethoxydimethylsilane, diethoxydimethylsilane, cyclohexylmethyldimethoxysilane, methoxytrimethylsilane, octadecyldimethylmethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dimethoxydiphenylsilane, diphenylethoxymethylsilane, and dimethoxymethylphenylsilane. Among these, alkyltrialkoxysilanes are preferred.

[0080] The content of the silicon compound is preferably 0.005 parts by weight or more (e.g., 0.01 parts by weight or more, typically 0.03 parts by weight or more) relative to 100 parts by weight of the acrylic polymer from the viewpoint of fully exerting the effect of addition thereof. Also, from the viewpoint of storage stability, the content of the silicon compound is preferably less than 1.0 part by weight (e.g., 0.5 parts by weight or less, typically 0.3 parts by weight or less) relative to 100 parts by weight of the acrylic polymer.

[0081] The pressure-sensitive adhesive composition disclosed herein preferably contains a leveling agent from the viewpoint of wettability. When the pressure-sensitive adhesive composition contains a leveling agent, a thin coating film can be formed while suppressing the occurrence of defects when the pressure-sensitive adhesive composition is applied. The type of leveling agent is not particularly limited. Examples of leveling agents include "Surfynol 420" (acetylene glycol ethylene oxide surfactant, manufactured by Nissin Chemical Industry Co., Ltd.), "Pelex OT-P" (dialkyl sodium sulfosuccinate, manufactured by Kao Corporation), "Neocol P" (dialkyl sodium sulfosuccinate, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), "Neocol SW-C" (dialkyl sodium sulfosuccinate, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), "Nopco Wet 50" (sulfonic acid-based anionic surfactant, manufactured by San Nopco Ltd.), "SN Wet 126" (modified silicone / special polyether-based surfactant, manufactured by San Nopco Ltd.), "SN Wet FST2" (polyoxyalkyleneamine non-ionic wetting agent, manufactured by San Nopco Ltd.), "SN Wet S" (polyoxyalkyleneamine ether non-ionic wetting agent, manufactured by San Nopco Ltd.), and "SN Wet 125" (modified silicone-based surfactant, manufactured by San Nopco Ltd.). The leveling agents may be used alone or in combination of two or more.

[0082] The PSA composition disclosed herein may contain, as needed, an acid or base (such as aqueous ammonia) used for purposes such as pH adjustment. Examples of other optional components that may be incorporated into the PSA composition disclosed herein include viscosity modifiers, crosslinking aids, release modifiers, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, etc. These various additives can be conventionally known and can be used in the usual manner. Since they do not particularly characterize the present invention, detailed description thereof will be omitted.

[0083] In some embodiments, the aqueous PSA composition used to form the PSA layer can be prepared by mixing an aqueous dispersion of an acrylic polymer obtained by emulsion polymerization with an aqueous tackifier resin, polyvinyl alcohol, and other components (e.g., additives such as crosslinkers, leveling agents, thickeners, and neutralizers) that are used as needed. In a preferred embodiment, polyvinyl alcohol is added in the form of an aqueous solution to the aqueous dispersion of the acrylic polymer. The aqueous dispersion can be a polymerization reaction solution obtained by emulsion polymerization, or a polymerization reaction solution that has been subjected to treatments such as pH adjustment (e.g., neutralization), nonvolatile content adjustment, and viscosity adjustment as needed. Typically, the dispersion stability of the aqueous dispersion can be improved by adding a neutralizer such as aqueous ammonia to the polymerization reaction solution to adjust the pH to an appropriate range (e.g., a pH range of approximately 6 to 9).

[0084] Although not particularly limited, the nonvolatile content (NV) of the PSA composition can be, for example, about 20% by weight or more (typically about 30% by weight or more, preferably about 35% by weight or more) from the viewpoint of drying efficiency, etc., and can be about 75% by weight or less (typically about 70% by weight or less, preferably about 60% by weight or less) from the viewpoint of coatability, etc.

[0085] This specification provides a method for producing an aqueous PSA composition, including a polymerization step of emulsion-polymerizing a monomer raw material to obtain an aqueous dispersion of an acrylic polymer, and a compounding step of adding an aqueous tackifier resin and polyvinyl alcohol to the aqueous dispersion. As described above, a production method including a step of post-adding polyvinyl alcohol to an aqueous dispersion of an acrylic polymer makes it easy to produce an aqueous PSA composition that can improve the water resistance of the PSA layer. In the compounding step, additives such as a crosslinker, a leveling agent, a thickener, and a neutralizer can be further added as needed.

[0086] In the polymerization step for obtaining an aqueous dispersion of an acrylic polymer, a surfactant is typically used. As the surfactant used in the polymerization step for obtaining the aqueous dispersion of the acrylic polymer, a reactive surfactant can be preferably used from the viewpoint of improving water resistance, and an anionic reactive surfactant can be preferably used in particular. Furthermore, in the polymerization step for obtaining an aqueous dispersion of the acrylic polymer, a polymerization initiator may be used. From the viewpoint of improving water resistance, it is preferable to use a polymerization initiator that is not a redox initiator (for example, an ascorbic acid-based redox initiator).

[0087] In the blending step, the polyvinyl alcohol is preferably added in the form of an aqueous solution dissolved in water. From the viewpoints of viscosity and productivity, it is advantageous for the polyvinyl alcohol added in the blending step to be in the form of an aqueous solution with a high solids concentration. From these viewpoints, the polyvinyl alcohol added in the blending step is preferably an aqueous solution with a concentration of 5 to 15 wt %, and more preferably an aqueous solution with a concentration of 5 to 10 wt %. The aqueous polyvinyl alcohol solution used in the blending step can be prepared by adding polyvinyl alcohol (typically in the form of powder (particles)) as a raw material to a predetermined amount of water, heating the mixture to approximately 80°C, and stirring for about 30 minutes to 1 hour to dissolve the polyvinyl alcohol.

[0088] <Adhesive Sheet> (Structural Example of Adhesive Sheet) The adhesive sheet disclosed herein comprises an adhesive layer formed using the above-described aqueous adhesive composition. It may be a substrate-attached adhesive sheet having such an adhesive layer on one or both sides of a substrate (support), or it may be a substrate-less adhesive sheet in which the adhesive layer is supported on a release liner (which may also be understood as a substrate having a release surface). The concept of adhesive sheet here may include what are called adhesive tapes, adhesive labels, adhesive films, etc. The adhesive layer is typically formed continuously, but is not limited to such a form. For example, the adhesive layer may be formed in a regular or random pattern such as a dotted or striped pattern. The adhesive sheet may be in the form of a roll or a sheet. Alternatively, the adhesive sheet may be processed into various shapes.

[0089] The PSA sheet disclosed herein may be in the form of, for example, a double-sided PSA sheet having the cross-sectional structure schematically shown in Fig. 1 . This PSA sheet 1 comprises a substrate 15 and a first PSA layer 11 and a second PSA layer 12 supported on both sides of the substrate 15. More specifically, the first PSA layer 11 and the second PSA layer 12 are provided on a first surface 15A and a second surface 15B (both of which are non-releasable), respectively, of the substrate 15. Before use (before attachment to an adherend), the double-sided PSA sheet 1 may be in a spirally wound form, as shown in Fig. 1 , superimposed on a release liner 21, the front surface 21A and the back surface 21B of which are both release surfaces. In this form of double-sided PSA sheet 1, the surface of the second PSA layer 12 (second PSA surface 12A) is protected by the front surface 21A of the release liner 21, and the surface of the first PSA layer 11 (first PSA surface 11A) is protected by the back surface 21B of the release liner 21. Alternatively, the first adhesive surface 11A and the second adhesive surface 12A may each be protected by two independent release liners.

[0090] (Characteristics of Pressure-Sensitive Adhesive Sheet) The adhesive strength of the pressure-sensitive adhesive sheet (typically a double-sided pressure-sensitive adhesive sheet) disclosed herein is not particularly limited. A pressure-sensitive adhesive sheet according to a preferred embodiment may have a 180-degree peel strength (peeling strength from SUS plate) of, for example, 5 N / 20 mm or more after being attached to a stainless steel plate and maintained at 23°C and 50% RH for 30 minutes. Hereinafter, the peel strength from SUS plate after being maintained at 23°C and 50% RH for 30 minutes is also referred to as the "initial adhesive strength S0." Pressure-sensitive adhesive sheets exhibiting such characteristics are preferably used as highly adhesive pressure-sensitive adhesive sheets that firmly secure articles or components. The initial adhesive strength S0 is more preferably 7 N / 20 mm or more (e.g., 8 N / 20 mm or more), and even more preferably 9 N / 20 mm or more (e.g., 10 N / 20 mm or more, or even 11 N / 20 mm or more). When the pressure-sensitive adhesive sheet disclosed herein is a double-sided pressure-sensitive adhesive sheet, it is preferable that both adhesive surfaces exhibit the above-mentioned peel strength. The initial adhesive strength S0 is specifically measured by the method described in the Examples below. There is no particular upper limit to the initial adhesive strength S0, but from the viewpoint of balancing the adhesive properties, it may be, for example, 20 N / 20 mm or less, 19 N / 20 mm or less, or 18 N / 20 mm or less.

[0091] The technology disclosed herein can realize a pressure-sensitive adhesive sheet with improved water resistance. A pressure-sensitive adhesive sheet according to a preferred embodiment can have a 180-degree peel strength (peeling strength from SUS plate) of, for example, 4 N / 20 mm or more after being attached to a stainless steel plate and held for 24 hours under conditions of 60°C and 95% RH (hereinafter also referred to as humid and heat conditions). Hereinafter, the peel strength from SUS plate after being held for 24 hours under the humid and heat conditions is also referred to as the "adhesive strength Sw after aging under humid conditions." A pressure-sensitive adhesive sheet exhibiting such properties can achieve highly reliable bonding even in a humid environment (typically a high-temperature and high-humidity environment). Therefore, it can be preferably used as a pressure-sensitive adhesive sheet with high adhesive reliability. For example, it can be preferably used as a pressure-sensitive adhesive sheet that exhibits high adhesive reliability even in an environment where humidity may increase (for example, an environment where it may be exposed to an atmosphere where humidity changes). The adhesive strength Sw after aging under humid conditions is more preferably 5 N / 20 mm or more, and even more preferably 6 N / 20 mm or more (for example, 6.5 N / 20 mm or more, or even 7 N / 20 mm or more, or 8 N / 20 mm or more). When the PSA sheet disclosed herein is a double-sided PSA sheet, it is preferable that both adhesive surfaces exhibit the above-mentioned peel strength. The adhesive strength Sw after aging under humid conditions is specifically measured by the method described in the Examples below.

[0092] (Adhesive Strength Retention Rate) The technology disclosed herein tends to improve the water resistance of the adhesive layer and inhibit a decrease in adhesive strength when maintained under humid and hot conditions. In some preferred embodiments, the adhesive strength retention rate calculated by the following formula: Adhesive Strength Retention Rate (%) = (Adhesive Strength After Humidification and Aging Sw / Initial Adhesive Strength S0) × 100 is 50% or more, more preferably 55% or more, and even more preferably 60% or more. In some embodiments, the adhesive strength retention rate may be 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more. The upper limit of the adhesive strength retention rate is not particularly limited, but may be, for example, 130% or less.

[0093] The total thickness of the PSA sheet disclosed herein is not particularly limited. The total thickness of the PSA sheet can be, for example, 300 μm or less. Here, when the PSA sheet is a substrate-attached PSA sheet containing a substrate, the total thickness refers to the combined thickness of the substrate and the PSA layer. The total thickness of the PSA sheet does not include the thickness of the release liner. In a preferred embodiment, the total thickness is 200 μm or less (more preferably 100 μm or less). In some embodiments, the total thickness of the PSA sheet may be 50 μm or less, 40 μm or less, or 30 μm or less. The lower limit of the total thickness of the PSA sheet can be, for example, 3 μm or more, preferably 5 μm or more. In some embodiments, the total thickness of the PSA sheet may be 8 μm or more, 10 μm or more, or 15 μm or more.

[0094] <Adhesive Layer> The adhesive layer in the technology disclosed herein can be suitably formed by applying the above-described aqueous dispersion adhesive composition to a predetermined surface and drying or curing it. When applying (typically coating) the adhesive composition, a conventional coater (e.g., a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray coater, etc.) can be used. The thickness of the adhesive layer is not particularly limited, and is usually approximately 2 μm or more, preferably approximately 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Furthermore, the thickness of the adhesive layer is usually approximately 100 μm or less, preferably approximately 80 μm or less, and more preferably approximately 50 μm or less.

[0095] <Substrate> The substrate is not particularly limited, and examples thereof include porous materials such as plastic films, paper, cloth, and nonwoven fabrics, as well as appropriate thin sheets such as nets, foamed sheets, metal foils, and laminates thereof. From the viewpoint of improving processability, it is preferable to use a non-foamed thermoplastic film as the substrate.

[0096] The thermoplastic film preferably contains at least one resin selected from the group consisting of soft polyolefin resins, soft urethane resins, soft acrylic resins, soft polyester resins such as polybutylene terephthalate, and soft vinyl chloride resins. In some embodiments, the substrate is preferably a soft polyolefin resin sheet made of a soft polyolefin resin, a soft urethane resin sheet made of a soft urethane resin, a soft acrylic resin sheet made of a soft acrylic resin, a soft polyester resin sheet (soft polyester film) made of a soft polyester resin, or a soft vinyl chloride resin sheet made of a soft vinyl chloride resin.

[0097] Specific examples of thermoplastic films constituting the substrate include polyester resins such as polyethylene terephthalate and polybutylene terephthalate; olefin resin sheets made from EMMA (ethylene-methyl methacrylate copolymer) resin or EVA (ethylene-vinyl acetate copolymer) resin; polyethylene resin sheets made from one or more low-density polyethylenes, linear low-density polyethylenes containing α-olefin components, etc.; polyolefin resin sheets made from one or more olefin polymers such as propylene polymers (homogeneous, block, random), propylene polymers reactor-blended with rubber components, ethylene-propylene copolymers, propylene-α-olefin copolymers, and ethylene-propylene-α-olefin copolymers; vinyl chloride resin sheets, etc. The substrate disclosed herein may be formed by mixing two or more of the resins constituting these resin sheets.

[0098] For example, materials used in components of portable electronic devices are often required to be free of halogen substances, and therefore the base material preferably contains substantially no halogen substances.

[0099] Substrates according to other embodiments include nonwoven fabric substrates. For example, nonwoven fabrics made of natural fibers such as wood pulp, cotton, and hemp (e.g., Manila hemp); nonwoven fabrics made of chemical fibers (synthetic fibers) such as polyester fibers, rayon, vinylon, acetate fibers, polyvinyl alcohol (PVA) fibers, polyamide fibers, polyolefin fibers, and polyurethane fibers; and nonwoven fabrics made by combining two or more types of fibers of different materials; etc. can be used. Among these, nonwoven fabric substrates made of hemp (e.g., Manila hemp) are preferred. In this case, the amount of hemp contained in the nonwoven fabric is preferably 90% by weight or more, more preferably 95% by weight or more. Particularly preferably, a nonwoven fabric made essentially of hemp alone is used.

[0100] When a nonwoven fabric is used as the substrate, the basis weight is approximately 10 g / m ２ or more (for example, 13 g / m ２ or more), and is approximately 25 g / m ２ or less (e.g., 22 g / m ２ Preferably, a nonwoven fabric having a bulk density (which can be calculated by dividing the basis weight by the thickness) of about 0.25 g / cm3 can be used. ３ ~0.50 g / cm ３ Preferably, the range is within the range. Nonwoven fabrics having tensile strengths in both the machine direction (MD) and the transverse direction (TD) of approximately 8 N / 15 mm or more are preferred, nonwoven fabrics having an MD tensile strength of at least 12 N / 15 mm or more (e.g., 18 N / 15 mm or more, or even 24 N / 15 mm or more) are more preferred, and nonwoven fabrics having MD and TD tensile strengths of approximately 12 N / 15 mm or more (e.g., 16 N / 15 mm or more) are even more preferred. Nonwoven fabrics satisfying these tensile strengths are suitable for forming PSA sheets with excellent tensile strength.

[0101] Furthermore, in the manufacturing stage of a nonwoven fabric, polymers such as viscose, starch, cationic polymers (e.g., polyamide, amine, epichlorohydrin) may be used to improve the strength (e.g., tensile strength) of the nonwoven fabric. Such polymers (which can be understood as strength improvers for nonwoven fabrics) may be added at the papermaking stage of the nonwoven fabric (the stage of collecting fibers), or may be applied or impregnated after papermaking. Nonwoven fabrics made using such strength improvers are suitable for constructing PSA sheets with excellent tensile strength. Therefore, for example, in double-sided PSA sheets that are attached to recycled parts, the use of nonwoven fabrics made using the above-mentioned strength improvers is particularly effective.

[0102] The substrate may contain various additives, such as fillers (inorganic fillers, organic fillers, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, and colorants (pigments, dyes, etc.), as needed. The surface of the substrate (particularly the surface on which the pressure-sensitive adhesive layer is to be formed) may be subjected to a known or conventional surface treatment, such as corona discharge treatment, plasma treatment, or application of a primer. Such a surface treatment may be, for example, a treatment for improving the anchoring ability of the pressure-sensitive adhesive layer to the substrate.

[0103] The thickness of the substrate can be appropriately selected depending on the purpose, but is suitably approximately 200 μm or less, preferably 100 μm or less. A substrate with a limited thickness is particularly suitable for applications requiring a thin pressure-sensitive adhesive sheet. Furthermore, reducing the thickness of the substrate tends to improve the ability to conform to the surface shape (steps, etc.) of the adherend. The thickness of the substrate is usually suitably 1 μm or more, and may be 2 μm or more, 4 μm or more, and more preferably 10 μm or more. In some embodiments, the thickness of the substrate may be 20 μm or more, or may be 30 μm or more. Increasing the thickness of the substrate increases the strength of the substrate or pressure-sensitive adhesive sheet, and tends to improve handleability (processability) during production or use.

[0104] <Release Liner> The release liner that protects or supports the PSA layer (which may have both protective and supporting functions) is not particularly limited in terms of material or configuration, and an appropriate release liner can be selected and used from known release liners. For example, a release liner configured such that at least one surface of the substrate is subjected to a release treatment (typically, a release treatment layer formed by a release treatment agent is provided) can be suitably used. As the substrate (subject to release treatment) that constitutes this type of release liner, the same substrates as those described above as substrates that constitute PSA sheets (various plastic films, papers, cloths, rubber sheets, foam sheets, metal foils, composites thereof, etc.) can be appropriately selected and used. As the release treatment agent that forms the release treatment layer, known or conventional release treatment agents (for example, silicone-based, fluorine-based, long-chain alkyl-based, etc. release treatment agents) can be used. Alternatively, a low-adhesion substrate made of a fluorine-containing polymer (e.g., polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, chlorofluoroethylene-vinylidene fluoride copolymer, etc.) or a low-polarity polymer (e.g., an olefin resin such as polyethylene or polypropylene, etc.) may be used as a release liner without subjecting the surface of the substrate to a release treatment. Alternatively, such a low-adhesion substrate may be subjected to a release treatment on its surface and used as a release liner.

[0105] The thickness of the substrate and release treatment layer constituting the release liner is not particularly limited and can be appropriately selected depending on the purpose, etc. The total thickness of the release liner (the total thickness including the substrate and release treatment layer, in the case of a release liner configured to have a release treatment layer on the surface of the substrate) is, for example, preferably about 15 μm or more (typically about 15 μm to 500 μm), and more preferably about 25 μm to 500 μm.

[0106] <Method for producing a substrate-attached double-sided PSA sheet> In producing a substrate-attached double-sided PSA sheet, the method for providing PSA layers on one side and the other side of the substrate is not particularly limited. Typically, it is preferable to apply a method selected from the following to each of the one side and the other side: (1) a method in which an aqueous PSA composition is applied (typically coated) to a release liner and dried to form a PSA layer on the release liner, and then the PSA layer is attached to the substrate for transfer (lamination) (hereinafter also referred to as the "transfer method"); and (2) a method in which an aqueous PSA composition is applied (typically coated) directly to a substrate and dried (hereinafter also referred to as the "direct coating method" or "direct method"). For example, a double-sided PSA sheet may be produced by applying the transfer method to both sides of the substrate (transfer-transfer method), or a double-sided PSA sheet may be produced by applying the transfer method to one side of the substrate (typically the side on which the PSA layer is first provided) and the direct coating method to the other side (transfer-direct method).

[0107] <Applications> The pressure-sensitive adhesive sheet disclosed herein can easily maintain its adhesive strength (peel strength) to an adherend even when exposed to a high-temperature, high-humidity environment after being attached to the adherend. Taking advantage of these characteristics, the pressure-sensitive adhesive sheet disclosed herein can be preferably used in various products that can be used in environments requiring water resistance or moisture resistance, or in a form that is attached to components that constitute the products, for applications such as fixing, joining, molding, decorating, protecting, and supporting the products or components. In particular, it can be preferably used to fix the above-mentioned products or components. Examples of environments requiring water resistance or moisture resistance include environments where temperature and humidity change significantly (e.g., wet areas in homes, outdoors exposed to rain and wind, etc.). Examples of such products include home appliances, office automation equipment, vehicles (e.g., automobiles), housing equipment (including furniture and fixtures), and portable devices.

[0108] Examples of home appliances include televisions (CRT, LCD, plasma, OLED, etc.), DVD players and other AV equipment, microwave ovens, rice cookers, washing machines, washer-dryers, vacuum cleaners, refrigerators, freezers, kettles, air conditioners, dishwashers, air purifiers, lighting equipment, clocks, thermometers, PDAs (personal digital assistance), and landline telephones. Examples of office automation equipment include word processors, electronic dictionaries, desktop computers, laptops, CRT displays, LCD displays, OLED displays, printers, scanners, copiers, fax machines, and multifunction devices that have two or more of these functions. Examples of vehicles include automobiles and trains. Examples of home equipment (including furniture and fixtures) include baths, vanities, toilets, cupboards, bookshelves, tables, dressers, window glass, etc. Examples of portable devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices, digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, e-books, in-car information equipment, portable radios, portable televisions, portable printers, portable scanners, portable modems, and other portable electronic devices, as well as mechanical wristwatches, pocket watches, flashlights, hand mirrors, etc.

[0109] The matters disclosed in this specification include the following: [1] A water-dispersed PSA composition comprising a base polymer, a water-dispersed tackifier resin, and polyvinyl alcohol, wherein the base polymer is an acrylic polymer obtained by emulsion polymerization of a monomer raw material, and the polyvinyl alcohol has a saponification degree of 98 mol% or more and a weight-average molecular weight of 25,000 (2.5 × 10 ４ ) ~ 80,000 (8 x 10 ４). [2] The water-dispersed PSA composition according to [1] above, wherein the content of the polyvinyl alcohol is 2 parts by weight or more and 6 parts by weight or less, relative to 100 parts by weight of the base polymer. [3] The water-dispersed PSA composition according to [1] above or [2] above, wherein the content of the water-dispersed tackifier resin is 5 parts by weight or more and 60 parts by weight or less, relative to 100 parts by weight of the base polymer. [4] The water-dispersed PSA composition according to any one of [1] to [3] above, wherein the acrylic polymer is a polymer of a monomer raw material containing more than 50% by weight of alkyl (meth)acrylate. [5] The water-dispersed PSA composition according to any one of [1] to [4] above, wherein the water-dispersed tackifier resin comprises a tackifier resin having a softening point of 90°C or higher. [6] The aqueous dispersion pressure-sensitive adhesive composition according to any one of [1] to [5] above, which has a 180-degree peel strength of 7 N / 20 mm or more after being applied to a stainless steel plate and maintained at 23°C and 50% RH for 30 minutes. [7] The aqueous dispersion pressure-sensitive adhesive composition according to any one of [1] to [6] above, which has a 180-degree peel strength of 6.5 N / 20 mm or more after being applied to a stainless steel plate and maintained at 60°C and 95% RH for 24 hours. [8] The aqueous dispersion pressure-sensitive adhesive composition according to any one of [1] to [7] above, which has an adhesive strength retention rate of 50% or more, which is the ratio of the 180-degree peel strength after being applied to a stainless steel plate and maintained at 60°C and 95% RH for 24 hours to the 180-degree peel strength after being applied to a stainless steel plate and maintained at 23°C and 50% RH for 30 minutes. [9] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the water-dispersed pressure-sensitive adhesive composition according to any one of [1] to [8] above.

[10] The pressure-sensitive adhesive sheet according to [9] above, which is configured as a double-sided pressure-sensitive adhesive sheet comprising a substrate and, as the pressure-sensitive adhesive layers, a first pressure-sensitive adhesive layer disposed on one surface of the substrate and a second pressure-sensitive adhesive layer disposed on the other surface of the substrate.

[11] A method for producing a water-dispersed pressure-sensitive adhesive composition, comprising: a polymerization step of emulsion-polymerizing a monomer raw material to obtain an aqueous dispersion of an acrylic polymer; and a blending step of adding a water-dispersed tackifier resin and polyvinyl alcohol to the aqueous dispersion.

[12] A method for producing the water-dispersed PSA composition according to

[11] above, wherein a reactive surfactant (preferably an anionic reactive surfactant) is used in the polymerization step.

[13] A method for producing the water-dispersed PSA composition according to

[11] or

[12] above, wherein a polymerization initiator that is not a redox initiator is used in the polymerization step.

[14] A method for producing a PSA sheet, comprising the steps of obtaining a water-dispersed PSA composition by the production method according to any one of

[11] to

[13] above, and forming a PSA layer from the water-dispersed PSA composition.

[0110] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are based on weight unless otherwise specified. Furthermore, unless otherwise specified, the amount of each material used is based on the amount of active ingredient.

[0111] In the following examples, the Mw of acrylic polymers was measured by the following method. Specifically, the measurement target was dried at 130°C for 2 hours, and the resulting nonvolatile fraction was used as a measurement sample. The sample was immersed in THF at room temperature (typically 23°C) for 7 days to elute the soluble fraction. The insoluble fraction was then filtered off, and the filtrate was concentrated or diluted as necessary (it may be dried and then redissolved in THF) to prepare a THF solution containing an appropriate concentration of THF-soluble fraction (e.g., approximately 0.1 to 0.3 wt%; here, 0.2 wt%). This THF solution was filtered through a filter with an average pore size of 0.45 μm, and the filtrate (sample solution for molecular weight measurement) was used to determine the weight-average molecular weight relative to standard polystyrene using a gel permeation chromatography (GPC) apparatus. The GPC apparatus used was a Tosoh Corporation model "HLC-8120GPC." The measurement conditions were as follows: [GPC measurement conditions] Column: TSKgel GMH-H(S) Detector: differential refractometer Eluent: THF Flow rate: 0.6 mL / min Measurement temperature: 40°C Sample concentration: 0.2 wt% Sample solution injection amount: 100 μL

[0112] In the following examples, the Mw and Mn of various water-soluble polymers such as polyvinyl alcohol were measured by the following method: the sample to be measured was adjusted to a concentration of 0.1% by weight with an eluent, heated to 95°C for 30 minutes to dissolve, and then filtered using a 0.45 µm membrane filter. The resulting filtrate was subjected to aqueous GPC measurement under the following conditions using a GPC measurement device manufactured by Agilent Technologies, model number "1260Infinity." Analytical equipment: "1260 Infinity" manufactured by Agilent Technologies Column: TSKgel G6000PWXL + TSKgel G3000PWXL (connected in series) manufactured by Tosoh Corporation Column temperature: 40°C Eluent: aqueous sodium nitrate solution Flow rate: 0.8 mL / min Injection volume: 100 μL Detector: differential refractometer (RI) Standard samples: polyethylene glycol (PEG), polyethylene oxide (PEO)

[0113] In the following examples, for the Mw and Mn of polyvinyl alcohol whose solubility in water is reduced due to reasons such as high molecular weight, instead of the above-mentioned aqueous GPC measurement, values ​​based on GPC measurement using DMF as an eluent (DMF-based, polystyrene equivalent) were adopted. Specifically, the measurement object was adjusted to a concentration of 0.2 wt% with the eluent, heated and dissolved at 95 ° C. for 15 minutes, and then filtered using a 0.45 μm membrane filter. The obtained filtrate was subjected to DMF-based GPC measurement under the following conditions using an Agilent Technologies model "1200" as a GPC measurement device. Analytical equipment: "1200" manufactured by Agilent Technologies Column: TSKgel Super AWM-H + TSKgel Super AW4000 + TSKgel Super AW2500 (connected in series) manufactured by Tosoh Corporation Column temperature: 40°C Eluent: DMF (salt added) Flow rate: 0.4 mL / min Injection volume: 40 μL Detector: differential refractometer (RI) Standard sample: polystyrene (PS)

[0114] The polyvinyl alcohol and other water-soluble polymer materials used in the examples are as follows: PVA1: Polyvinyl alcohol (saponification degree 98.5 mol%, Mw: 3.5×10 ４ , Mn: 1.3 × 10 ４ PVA2: Polyvinyl alcohol (saponification degree 98.5 mol%, Mw: 5.3 × 10 ４ , Mn: 2.3 × 10 ４ PVA3: Polyvinyl alcohol (saponification degree 98.5 mol%, Mw: 6.3 × 10 ４ , Mn: 2.7 × 10 ４ PVA4: Polyvinyl alcohol (saponification degree 99.0 mol%, Mw: 7.5 × 10 ４ , Mn: 3.5 × 10 ４ PVA5: Polyvinyl alcohol (saponification degree 98.0 mol%, Mw: 1.9 × 10 ４ , Mn: 0.8 × 10 ４ PVA6: Polyvinyl alcohol (saponification degree 99.0 mol%, Mw: 9.1 × 10 ４ , Mn: 4.2 × 10 ４ PVA7: Polyvinyl alcohol (saponification degree 99.3 mol%, Mw: 11.5 × 10 ４ , Mn: 5.2 × 10 ４ PVA8: Polyvinyl alcohol (saponification degree 88.0 mol%, Mw: 1.5 × 10 ４ , Mn: 0.6 × 10 ４ PVA9: Polyvinyl alcohol (saponification degree 80.0 mol%, Mw: 6.4 × 10 ４ , Mn: 2.5 × 10 ４ PVA10: Polyvinyl alcohol (saponification degree 96.5 mol%, Mw: 6.4 × 10 ４ , Mn: 2.5 × 10 ４ PVA11: Polyvinyl alcohol (saponification degree 88.0 mol%, Mw: 5.5 × 10 ４ , Mn: 2.2 × 10 ４ PVA12: Polyvinyl alcohol (saponification degree 88.0 mol%, Mw: 6.6 × 10 ４ , Mn: 2.7 × 10 ４ ) PVP1: Polyvinylpyrrolidone (Mw: 5.0 × 10 ４) PVP2: Polyvinylpyrrolidone (Mw: 120.0 × 10 ４ ) PNVA1: Polyvinylamide (Mw: 5.0 × 10 ４ ) PNVA2: Polyvinylamide (Mw: 30.0 × 10 ４ ) XAM: xanthan gum polysaccharide hydrocolloid PEG1: polyethylene glycol (Mw: 0.1 × 10 ４ ) PEG2: polyethylene glycol (Mw: 50.0 × 10 ４ )

[0115] (Acrylic Polymer) 0.07 parts of a reactive surfactant (trade name "Aqualon KH-1025", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 61.1 parts of distilled water were placed in a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the atmosphere was replaced with nitrogen at 60° C. for 1 hour with stirring. Thereafter, 0.10 parts of a polymerization initiator (trade name "VA-057", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added thereto. To this mixture, 85 parts of 2-ethylhexyl acrylate (2EHA), 13 parts of methyl acrylate (MA), 1.25 parts of acrylic acid (AA), 0.75 parts of methacrylic acid (MAA), 0.025 parts of t-dodecanethiol (chain transfer agent), 0.02 parts of 3-methacryloxypropyltrimethoxysilane (trade name "KBM-503", manufactured by Shin-Etsu Chemical Co., Ltd.), and 1.93 parts of the reactive surfactant were emulsified in 28 parts of distilled water, and the resulting mixture was gradually added dropwise at 60°C over 4 hours to allow emulsion polymerization to proceed. After maintaining the mixture at 60°C for 3 hours, 0.05 parts of the polymerization initiator was added, and the mixture was further maintained at 60°C for 2 hours. The system was cooled to room temperature, and the pH was adjusted to 7 using 10% aqueous ammonia as a pH adjuster. In this manner, an aqueous dispersion of an acrylic polymer was prepared. The solid content of this acrylic polymer was 50.5%, and the sol weight average molecular weight (Mw) was 340,000.

[0116] (Preparation of Pressure-Sensitive Adhesive Composition) (Example 1) To the aqueous dispersion of the acrylic polymer, 55 parts of a tackifier resin (polymerized rosin ester, trade name "Tamanol E-200NT", manufactured by Arakawa Chemical Industries, Ltd., softening point 150°C) and 4 parts (solids content equivalent) of a 4% aqueous solution of polyvinyl alcohol (PVA1) were added, relative to 100 parts of the solids content of the aqueous dispersion. Furthermore, 1 part of a leveling agent (trade name "Pelex OT-P", manufactured by Kao Corporation) was further added. Thereafter, the pH was adjusted to 8 with 10% aqueous ammonia, and polyacrylic acid was added as a thickener to adjust the viscosity to 3 Pa s, thereby obtaining an aqueous-dispersible acrylic pressure-sensitive adhesive composition. Here, in this example, the viscosity adjustment was specifically performed by adding 0.25 parts of the polyacrylic acid (trade name "Aron B-500", non-volatile content 36%) relative to 100 parts of the acrylic polymer. The viscosity was measured using a BH-type viscometer with a rotor No. 2 at a rotation speed of 20 rpm, a liquid temperature of 25° C., and a measurement time of 1 minute. The nonvolatile content of the water-dispersible acrylic pressure-sensitive adhesive composition of this example was 38%.

[0117] (Formation of Pressure-Sensitive Adhesive Layer) The pressure-sensitive adhesive composition obtained as described above was applied to the silicone-treated surface of a 38 μm-thick polyethylene terephthalate (PET) release liner (trade name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) so that the thickness after drying would be 20 μm. Thereafter, the coating was dried by heating at 100° C. for 3 minutes to form a pressure-sensitive adhesive layer on the release liner.

[0118] (Preparation of double-sided pressure-sensitive adhesive sheet) One side (exposed side) of the pressure-sensitive adhesive layer was bonded to one side of a 12 μm PET film (Lumirror S10 #12). Next, the release liner was removed, and another pressure-sensitive adhesive layer was bonded to the other side of the PET film, to obtain a laminate with a total thickness of 52 μm having a structure of first pressure-sensitive adhesive layer / PET film / second pressure-sensitive adhesive layer. This laminate was treated in an autoclave under conditions of 50 ° C and 5 atm for 15 minutes, and then aged overnight in a dryer at 50 ° C to prepare a double-sided pressure-sensitive adhesive sheet according to this example.

[0119] (Examples 2 to 9, Comparative Examples 1 to 11) Double-sided PSA sheets of each example were obtained in the same manner as in Example 1, except that the tackifier resin content, thickener content, and PVA type and content were as shown in Tables 1 and 2. The non-volatile content of the water-dispersible acrylic PSA composition of each example was as shown in Tables 1 and 2.

[0120] (Comparative Examples 12 to 18) Double-sided PSA sheets of each example were obtained in the same manner as in Example 1, except that a water-soluble polymer shown in Table 3 was used instead of PVA1, and the tackifier resin content, thickener content, and water-soluble polymer content were set as shown in Table 3. The non-volatile content of the water-dispersible acrylic PSA composition of each example was as shown in Table 3.

[0121] [Peel Strength from SUS Plate] (Initial Adhesion Strength SO) The peel strength from SUS plate of each PSA sheet was measured as follows. That is, the release liner covering one side of the PSA sheet (double-sided PSA sheet) was peeled off, and the sheet was backed with a 25 μm thick polyethylene terephthalate (PET) film. This backed PSA sheet was cut to a size of 20 mm wide and 100 mm long to prepare a test piece. In an environment of 23°C and 50% RH, the test piece was pressure-bonded to a stainless steel plate (SUS304BA plate) as an adherend by rolling a 2 kg roller back and forth once. After holding this in an environment of 23°C and 50% RH for 30 minutes, the 180-degree peel strength [N / 20 mm] was measured using a tensile tester at a tensile speed of 300 mm / min in accordance with JIS Z0237. The measurement was performed three times (i.e., N = 3), and the average value was taken as the initial adhesive strength SO of the PSA sheet. The results are shown in the corresponding columns in Tables 1, 2 and 3. When measurements are performed on a single-sided PSA sheet, the backing with a film may be omitted.

[0122] (Adhesive Strength Sw after Aging under Humidity) A test piece was pressure-bonded to a stainless steel plate (SUS304BA plate) in the same manner as in the measurement of the initial adhesive strength S0. This was held under humid heat conditions of 60°C and 95% RH for 24 hours. Next, within 10 minutes of being transferred to an environment of 23°C and 50% RH, the 180-degree peel strength [N / 20 mm] was measured at a tensile speed of 300 mm / min using a tensile tester in accordance with JIS Z0237, in the same manner as in the measurement of the initial adhesive strength S0. The average value of three measurements (i.e., N = 3) was taken as the adhesive strength Sw of the PSA sheet after aging under humid conditions. The results are shown in the corresponding columns in Tables 1, 2, and 3. Note that when measuring a single-sided PSA sheet, the backing with a film may be omitted.

[0123] (Adhesive Strength Retention Rate) The maintenance of adhesive strength when maintained under humid and hot conditions was evaluated using the adhesive strength retention rate (%) calculated using the following formula: Adhesive Strength Retention Rate (%) = Adhesive Strength After Aging in Humidity Sw / Initial Adhesive Strength So × 100. The adhesive strength retention rate (%) obtained for the PSA sheets of each example is shown in the corresponding column in Tables 1, 2 and 3.

[0124]

[0125]

[0126]

[0127] As shown in Tables 1 to 3, the water resistance improver has a saponification degree of 98 mol% or more and a Mw of 2.5 × 10 ４ ~8 x 10 ４ It was confirmed that the PSA sheets of Examples 1 to 9, which used PVA1 to PVA4, had higher adhesive strength after aging under humid conditions and excellent adhesive strength retention, compared to the PSA sheet of Comparative Example 1, which did not use PVA, the PSA sheets of Comparative Examples 3 to 11, which used PVA3 to PVA12, which had a degree of saponification and / or Mw outside the above ranges, and the PSA sheets of Comparative Examples 12 to 18, which used various other water-soluble polymers instead of PVA. The PSA sheets of Comparative Examples 2 and 3, which did not use a tackifier resin, showed inferior initial adhesive strength compared to Examples 1 and 3, respectively.

[0128] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0129] REFERENCE SIGNS LIST 1 adhesive sheet 11 first adhesive layer 11A first adhesive surface 12 second adhesive layer 12A second adhesive surface 15 substrate (support) 21 release liner

Claims

1. A water-dispersible pressure-sensitive adhesive composition comprising a base polymer, a water-dispersible tackifier resin, and polyvinyl alcohol, wherein the base polymer is an acrylic polymer obtained by emulsion polymerization of a monomer raw material, and the polyvinyl alcohol has a degree of saponification of 98 mol% or more and a weight average molecular weight of 25,000 to 80,000.

2. The aqueous dispersion pressure-sensitive adhesive composition according to claim 1, wherein the content of the polyvinyl alcohol is 2 parts by weight or more and 6 parts by weight or less per 100 parts by weight of the base polymer.

3. The aqueous dispersion pressure-sensitive adhesive composition according to claim 1 or 2, wherein the content of the aqueous dispersion tackifier resin is 5 parts by weight or more and 60 parts by weight or less per 100 parts by weight of the base polymer.

4. The water-dispersible pressure-sensitive adhesive composition according to claim 1 or 2, wherein the acrylic polymer is a polymer of a monomer raw material containing more than 50% by weight of alkyl (meth)acrylate.

5. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the water-dispersible pressure-sensitive adhesive composition according to claim 1 or 2.

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