Double-sided adhesive sheet

Abstract

Provided is a double-sided adhesive sheet having a first adhesive layer, an intermediate layer, and a second adhesive layer in this order. The double-sided adhesive sheet has a total thickness of 100 μm or less. The intermediate layer contains a water-dispersible silicone elastomer and a non-silicone resin.

Description

double-sided adhesive sheet

[0001] The present invention relates to a double-sided pressure-sensitive adhesive sheet. This application claims priority to Japanese Patent Application No. 2023-103211, filed on June 23, 2023, the entire contents of which are incorporated herein by reference.

[0002] Generally, pressure-sensitive adhesives (also referred to as pressure-sensitive adhesives; the same applies hereinafter) are soft solids (viscoelastic bodies) at temperatures around room temperature and have the property of easily adhering to an adherend when pressure is applied. Taking advantage of this property, pressure-sensitive adhesives are widely used for purposes such as joining and fixing components in smartphones and other portable electronic devices, for example, in the form of double-sided adhesive sheets (double-sided adhesive sheets) in which both the first and second surfaces are adhesive. Patent documents related to double-sided adhesive sheets include Patent Documents 1 to 3.

[0003] Japanese Patent Application Publication No. 2023-008802 Japanese Patent Application Publication No. 2020-128454 Japanese Patent Application Publication No. 2017-510696

[0004] Patent Document 1 discloses a double-sided pressure-sensitive adhesive sheet (without a substrate) comprising a pressure-sensitive adhesive layer, which contains a specific filler and has specific properties, resulting in excellent impact resistance and reworkability (see paragraph 0008, etc.). Patent Document 2 discloses a double-sided pressure-sensitive adhesive tape that exhibits excellent impact resistance by including a pressure-sensitive adhesive layer laminate comprising two or more pressure-sensitive adhesive layers each containing a low-polarity filler (see claim 1, paragraph 0015, etc.). However, when a filler is incorporated into the pressure-sensitive adhesive layer that constitutes the adhesive surface (the surface that is attached to the adherend), as in Patent Documents 1 and 2, the adhesive performance is easily affected by the influence of the filler, and the influence of the filler tends to become greater as the pressure-sensitive adhesive layer becomes thinner. For example, pressure-sensitive adhesive sheets used in portable electronic devices tend to become thinner due to demands for smaller and lighter portable electronic devices. However, when a filler is incorporated into the pressure-sensitive adhesive layer that constitutes the adhesive surface, it is difficult to achieve both a sufficient level of thinness and impact resistance. On the other hand, Patent Document 3 relates to a double-sided tape for touchscreens that has excellent impact resistance and waterproofing, and discloses a double-sided tape for touchscreens that has an impact-resistant pillar layer containing impact-resistant pillars including hollow microparticles formed on the upper surface of a substrate layer, and has first and second adhesive layers on the upper surface of the impact-resistant pillar layer and the lower surface of the substrate layer (Claim 1, Paragraph 0008, etc.). However, the technology described in Patent Document 3 assumes that the impact-resistant pillar layer containing hollow microparticles has a certain thickness or more (Paragraph 0036), and requires a substrate layer separate from the impact-resistant pillar layer, so it is unsuitable for aiming for further thinning to a total thickness of 100 μm or less while obtaining the desired impact resistance.

[0005] The present invention was created in view of the above circumstances, and has an object to provide a double-sided PSA sheet that exhibits improved impact resistance despite having a total thickness of 100 μm or less.

[0006] According to this specification, a double-sided PSA sheet is provided having a first PSA layer, an intermediate layer, and a second PSA layer, in that order. This double-sided PSA sheet has a total thickness of 100 μm or less. The intermediate layer contains a water-dispersible silicone elastomer and a non-silicone resin. A double-sided PSA sheet having the above configuration can exhibit improved impact resistance despite its thin total thickness of 100 μm or less.

[0007] According to the technology disclosed herein, by appropriately setting the content of the water-dispersible silicone elastomer in the intermediate layer that does not constitute the adhesive surface, it is possible to achieve the desired impact resistance improvement effect in a double-sided PSA sheet whose total thickness is limited to 100 μm or less. In some preferred embodiments, the content of the water-dispersible silicone elastomer in the intermediate layer can be in the range of 5 parts by weight to 300 parts by weight per 100 parts by weight of the polymer component contained in the non-silicone resin.

[0008] In some preferred embodiments, the intermediate layer contains a polyurethane resin, a urethane acrylic resin, an acrylic resin, a rubber, a polyolefin resin, or a blend thereof as the non-silicone resin. By providing an intermediate layer containing any of the above materials as the non-silicone resin used in combination with a water-dispersible silicone elastomer, it is possible to preferably realize a double-sided PSA sheet that exhibits good impact resistance despite its thin thickness.

[0009] In some preferred embodiments of the double-sided PSA sheet, the thickness ratio of the intermediate layer to the total thickness is within the range of 10% to 80%. By having the thickness ratio within this range, a good balance can be achieved between the impact resistance provided by the adhesiveness of the first and second PSA layers and the impact resistance provided by the intermediate layer containing the water-dispersible silicone elastomer, making it possible to preferably realize a double-sided PSA sheet that exhibits good impact resistance despite its thin thickness.

[0010] In some preferred embodiments, the intermediate layer is formed from a water-dispersible material. By using a water-dispersible material (specifically, an aqueous dispersion of an intermediate layer-forming material containing at least a water-dispersible silicone elastomer and a non-silicone resin) as the intermediate layer-forming material, it is possible to prevent or suppress component migration between the intermediate layer and the PSA layer.

[0011] In some preferred embodiments, the intermediate layer is formed from a water-dispersible material, and the first and second PSA layers are both formed from water-dispersible PSA compositions, which can more effectively prevent interlayer component migration over time.

[0012] In some preferred embodiments, the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are both acrylic pressure-sensitive adhesive layers containing an acrylic polymer. The technology disclosed herein is preferably implemented in an embodiment using an acrylic pressure-sensitive adhesive. From the viewpoint of impact resistance, an acrylic polymer having a glass transition temperature (Tg) of −25° C. or lower is preferably used as the acrylic polymer.

[0013] Some preferred embodiments of the double-sided PSA sheet have an impact resistance of 0.30 J or greater as measured by an impact test using a DuPont impact tester. The technology disclosed herein makes it possible to realize a double-sided PSA sheet that exhibits an impact resistance of 0.30 J or greater despite having a total thickness of 100 μm or less.

[0014] The double-sided PSA sheets disclosed herein can exhibit improved impact resistance despite their thin thickness, and are therefore preferably used for joining components of portable electronic devices that are becoming smaller and lighter and require good impact resistance, and can exhibit good impact resistance when the portable electronic device is dropped, etc. Therefore, this specification provides a portable electronic device that uses any of the double-sided PSA sheets disclosed herein, in other words, a portable electronic device that includes the PSA sheet.

[0015] Appropriate combinations of the elements described in this specification may also be included within the scope of the invention for which patent protection is sought by this patent application.

[0016] 1 is a schematic cross-sectional view illustrating a configuration of a double-sided pressure-sensitive adhesive sheet according to one embodiment.

[0017] 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.

[0018] 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 The material may be a material having the properties satisfying the above (typically, a material having the above properties at 25°C).

[0019] 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.

[0020] In this specification, the term "acrylic polymer" refers to a polymer containing more than 50% by weight of monomer units derived from acrylic monomers as the monomer units constituting the polymer. The acrylic monomer refers to a monomer having at least one (meth)acryloyl group per molecule. Therefore, the term "acrylic monomer" encompasses both monomers having at least one acryloyl group per molecule and monomers having at least one methacryloyl group per molecule.

[0021] In this specification, "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 containing a PSA composition and water, with at least a portion of the PSA composition dispersed in water. The water-dispersed type also includes suspended and emulsified states. However, the term "water-dispersed silicone elastomer" refers to a silicone elastomer derived from a silicone elastomer aqueous dispersion containing a silicone elastomer and water, with at least a portion of the silicone elastomer dispersed in water.

[0022] <Configuration of Double-Sided Pressure-Sensitive Adhesive Sheet> The double-sided pressure-sensitive adhesive sheet disclosed herein has a first pressure-sensitive adhesive layer, an intermediate layer, and a second pressure-sensitive adhesive layer, in this order. The concept of pressure-sensitive adhesive sheet herein may include those referred to as pressure-sensitive adhesive tape, pressure-sensitive adhesive label, pressure-sensitive adhesive film, etc. The pressure-sensitive adhesive layer is typically formed continuously, but is not limited to such a form. For example, the pressure-sensitive adhesive layer may be formed in a regular or random pattern such as a dotted or striped pattern. The pressure-sensitive adhesive sheet may be in the form of a roll or a sheet. Alternatively, the pressure-sensitive adhesive sheet may be processed into various shapes.

[0023] 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 double-sided PSA sheet 1 includes an intermediate layer 15 and a first PSA layer 11 and a second PSA layer 12 supported on either side of the intermediate layer 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 intermediate layer 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 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.

[0024] The double-sided PSA sheet disclosed herein has a total thickness (including the PSA layer and intermediate layer, but excluding the release liner) of 100 μm or less. A double-sided PSA sheet limited to a total thickness of 100 μm or less can effectively meet the demand for thinner and lighter products (e.g., portable electronic devices) to which the double-sided PSA sheet is applied. In some embodiments, from the viewpoint of thinning, the total thickness of the double-sided PSA sheet is preferably approximately 90 μm or less, more preferably approximately 80 μm or less, and may be approximately 75 μm or less, or may be approximately 70 μm or less (e.g., 65 μm or less). In other embodiments, the total thickness of the double-sided PSA sheet may be approximately 60 μm or less, approximately 50 μm or less, or may be approximately 40 μm or less (e.g., 35 μm or less). According to the technology disclosed herein, in a configuration in which the total thickness of the double-sided PSA sheet is limited as described above, excellent impact resistance improvement effects can be achieved by incorporating a water-dispersible silicone elastomer into the intermediate layer. The lower limit of the total thickness of the double-sided PSA sheet is not particularly limited, and may be, for example, approximately 5 μm or more. From the viewpoint of impact resistance, it is advantageous to make it approximately 10 μm or more, and it is preferably approximately 15 μm or more, and it may be approximately 20 μm or more, approximately 25 μm or more, approximately 30 μm or more, approximately 35 μm or more, approximately 45 μm or more, or approximately 60 μm or more. According to the technology disclosed herein, a double-sided PSA sheet having a total thickness within the above range can effectively improve impact resistance while maintaining good adhesive properties.

[0025] <First Pressure-Sensitive Adhesive Layer and Second Pressure-Sensitive Adhesive Layer> (Base Polymer) In the technology disclosed herein, the type of pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited. The pressure-sensitive adhesive may contain, as a base polymer, one or more of various rubber-like polymers that can be used in the field of pressure-sensitive adhesives, such as acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, polyamide polymers, and fluorine-based polymers.

[0026] The "base polymer" of a pressure-sensitive adhesive refers to the main component of the rubbery polymer contained in the pressure-sensitive adhesive, and is not to be construed in any other limiting sense. The rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, the term "main component" refers to a component that accounts for more than 50% by weight, unless otherwise specified.

[0027] (Acrylic Polymer) In some preferred embodiments, the pressure-sensitive adhesive layer (used to encompass the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer; the same applies hereinafter unless otherwise specified) contains an acrylic polymer as a base polymer.

[0028] 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. Here, the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition in the monomer raw material. The monomer raw material may also contain a material derived from a renewable organic resource (biomass material) or a monomer having a structural moiety derived from biomass (e.g., a linear alkyl group).

[0029] 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 １－２０ From 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.

[0030] 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, n-octyl(meth)acrylate, 2-octyl(meth)acrylate, Examples of alkyl (meth)acrylates include acrylate, isooctyl (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).

[0031] The technology disclosed herein is a method for preparing a polymerizable compound in which the monomer component is R ２ is C ４－１０ Among the alkyl(meth)acrylates contained in the monomer component, R ２ is C ４－１０ alkyl (meth)acrylate (C ４－１０This method can be preferably carried out in an embodiment in which the total amount of the chain alkyl (meth)acrylates (typically the total amount of BA and 2EHA) is 70% by weight or more (typically 80% by weight or more). ４－１０ In the embodiment in which a chain alkyl (meth)acrylate is used, the proportion of 2EHA is not particularly limited, and ４－１０ In the chain alkyl (meth)acrylate, the content is suitably more than 50% by weight, and from the viewpoint of impact resistance, the content is preferably 70% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more (for example, 95 to 100% by weight).

[0032] 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.

[0033] 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.

[0034] 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.

[0035] In some preferred embodiments, 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, even more preferably 0.5 or more, and particularly preferably 1.0 or more (e.g., greater than 1.0). Furthermore, the weight ratio (AA / MAA) is 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 after the PSA sheet is produced, there is a tendency for the adhesive properties to have excellent stability over time.

[0036] 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).

[0037] When a functional group-containing monomer is copolymerized with an acrylic polymer, the proportion of the functional group-containing monomer in the total monomer components constituting the acrylic polymer is not particularly limited. Usually, 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 (for example, 0.5 wt% or more, typically 1 wt% or more). In addition, taking into account the adhesive effect of alkyl (meth)acrylate, it is preferably about 40 wt% or less (for example, 30 wt% or less, typically 20 wt% or less).

[0038] When a carboxyl group-containing monomer is copolymerized with an acrylic polymer, the proportion of the carboxyl group-containing monomer in the total monomer components is suitably 15% by weight or less, for example, 10% by weight or less, from the viewpoint of adhesive properties such as adhesive strength. In some preferred embodiments, the proportion of the carboxyl group-containing monomer in the total monomer components is 5% by weight or less, or may be 3% by weight or less, from the viewpoint of impact resistance. On the other hand, in some embodiments, the proportion may be, for example, 0.1% by weight or more, or may be 0.5% by weight or more, from the viewpoint of cohesion and the like. The technology disclosed herein can be preferably implemented 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The amount of copolymerization components other than the above-mentioned secondary monomers is not particularly limited and may be appropriately selected depending on the purpose and application. For example, the amount is preferably 10% by weight or less of the monomer composition of the acrylic polymer, may be 3% by weight or less, or may be less than 1% by weight (for example, 0% by weight or more and less than 1% by weight).

[0043] In the technology disclosed herein, the acrylic polymer used as the base polymer of the pressure-sensitive adhesive layer 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 preferably be −40°C or lower (e.g., −70°C or higher and −40°C or lower), more preferably −50°C or lower (typically −70°C or higher and −50°C or lower). Use of an acrylic polymer with a low Tg tends to improve impact resistance. Furthermore, setting the Tg of the acrylic polymer to the above-mentioned upper limit or lower is also preferable from the viewpoint of improving adhesive strength and adhesion to the intermediate layer. The Tg of the acrylic polymer can be adjusted by the type and amount ratio of monomers used in synthesizing the polymer.

[0044] 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).

[0045] 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

[0046] 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.

[0047] 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 JP 2007-51271 A). 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.

[0048] The method for obtaining an acrylic polymer is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. An example of a polymerization method that can be preferably employed is emulsion polymerization. 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 employed. For example, as the monomer supply method, a batch charging method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc. can be appropriately employed. The monomer raw materials may be added dropwise in the form of an aqueous emulsion (emulsified liquid). 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).

[0049] 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. For example, a water-dispersed PSA composition can be preferably produced using the polymerization liquid or a product obtained by subjecting the polymerization liquid to 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Emulsion polymerization of the monomer raw material 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 material. 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 material. On the other hand, from the viewpoint of adhesive properties, it is desirable to limit 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, and may be 4 parts by weight or less, 3 parts by weight or less, or 2.5 parts by weight or less.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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," "Aqualon RN-50," and Examples of such products include Aqualon AR-10, Aqualon AR-20, Aqualon AR-1025, and Aqualon AR-2020, ADEKA Corporation products under the trade names Adeka Reasop SE-10N and Adeka Reasop SR-1025, Kao Corporation products under the trade names Latemul PD-104, Latemul PD-420, Latemul PD-430, and Latemul PD-450, Sanyo Chemical Industries, Ltd. products under the trade names Eleminol JS-20 and Eleminol RS-3000, and Nippon Nyukazai Co., Ltd. product under the trade name Antox MS-60.

[0061] In some embodiments, an anionic reactive surfactant may be preferably used from the viewpoint of emulsification performance, etc. When a nonionic reactive surfactant is used, more preferable results may be achieved by using it in combination with another surfactant, for example, an anionic reactive surfactant, an anionic nonreactive surfactant, a nonionic nonreactive surfactant, etc.

[0062] In embodiments using a surfactant, the surfactant preferably contains a reactive surfactant from the viewpoint of adhesive properties. 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 materials 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. The reactive surfactant incorporated into the acrylic polymer is restricted in its movement within the adhesive layer, making it less likely to bleed out to the surface of the adhesive layer. Therefore, polymerization using a reactive surfactant can be advantageous for achieving both polymerization stability and the adhesive properties of the adhesive layer obtained from the adhesive composition containing the polymerized acrylic polymer. To achieve better adhesive properties, the proportion of the reactive surfactant in 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 using only the reactive surfactant as the surfactant can be preferably adopted. In this specification, "containing a reactive surfactant" refers to the concept of 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-dispersed PSA composition or PSA layer in a form in which at least a portion of the surfactant is incorporated into the acrylic polymer as described above.

[0063] 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 ４ Here, the Mw of the acrylic polymer refers to the Mw of the ethyl acetate 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 or less, more preferably 100 x 10 ４In 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 or more).

[0064] (Polymer Having Hydrolyzable Silyl Groups) In some embodiments of the double-sided PSA sheet disclosed herein, the PSA layer is preferably formed from a PSA composition containing a polymer having a hydrolyzable silyl group (hereinafter also referred to as a hydrolyzable silyl group-containing polymer). In the case of a PSA layer formed from a water-dispersible PSA composition, the hydrolyzable silyl group may be in a pre-hydrolyzed form, a post-hydrolyzed form, or an intermediate form (partially hydrolyzed form) in the water-dispersible PSA composition. Typically, the majority of the hydrolyzable silyl groups contained in the water-dispersible PSA composition are in a post-hydrolyzed form. By containing hydrolyzable silyl groups in the form of a hydrolyzable silyl group-containing polymer (e.g., a hydrolyzable silyl group-containing acrylic polymer) in the PSA composition, migration of the hydrolyzable silyl groups or silanol groups generated by hydrolysis into adjacent layers is prevented or suppressed, allowing for precise control of the degree of crosslinking in the PSA layer formed from the composition. The hydrolyzable silyl group-containing polymer can also be useful for improving adhesion between the PSA layer and the intermediate layer.

[0065] Representative examples of the hydrolyzable silyl group include a trialkoxysilyl group and a dialkoxysilyl group. Examples of the trialkoxysilyl group include a group represented by the general formula: -SiR １１ R １２ R １３ ; where R １１ , R １２ and R １３are each independently selected from alkoxy groups having 1 to 4 carbon atoms (preferably 1 to 3, more preferably 1 to 2). Specific examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, and an isopropoxy group, and preferred examples from the viewpoint of hydrolysis reactivity include a methoxy group and an ethoxy group. Suitable examples of the trialkoxysilyl group include a trimethoxysilyl group and a triethoxysilyl group. From the viewpoint of hydrolysis reactivity and the like, a trimethoxysilyl group can be preferably used in some embodiments. Furthermore, from the viewpoint of the storage stability of the PSA composition and the dispersion stability in the case of a water-dispersible PSA composition, a triethoxysilyl group can be preferably used in some embodiments.

[0066] Examples of dialkoxysilyl groups include those represented by the general formula: -SiR ２１ R １２ R １３ an alkyldialkoxysilyl group represented by the formula: ２１ is an alkyl group having 1 to 4 carbon atoms (preferably 1 to 3, more preferably 1 to 2), and R １２ and R １３ are each independently selected from alkoxy groups having 1 to 4 carbon atoms (preferably 1 to 3, more preferably 1 to 2). Specific examples of alkyl groups having 1 to 4 carbon atoms include methyl, ethyl, propyl, and isopropyl groups. From the viewpoint of ease of reaction of silanol groups generated from the alkoxy groups, preferred examples include methyl and ethyl groups, with methyl being more preferred. Specific examples of alkoxy groups having 1 to 4 carbon atoms include methoxy, ethoxy, propoxy, and isopropoxy groups. From the viewpoint of hydrolysis reactivity, preferred examples include methoxy and ethoxy groups. Suitable examples of the dialkoxysilyl groups include methyldimethoxysilyl and methyldiethoxysilyl groups.

[0067] In the polymer having a hydrolyzable silyl group, the type of hydrolyzable silyl group that the polymer has may be one type or two or more types.In some embodiments, from the viewpoint of uniformly progressing the hydrolysis reaction and the reaction of silanol groups, a polymer containing only one type of hydrolyzable silyl group can be preferably used.In addition, the pressure-sensitive adhesive composition may contain only one type of polymer having a hydrolyzable silyl group, or may contain two or more types.The embodiment containing only one type of polymer having a hydrolyzable silyl group can be advantageous from the viewpoint of easily adjusting the degree of intralayer crosslinking and / or interlayer crosslinking due to the reaction of silanol groups.

[0068] Methods for obtaining a polymer having a hydrolyzable silyl group include, for example, (a) a method in which a hydrolyzable silyl group-containing monomer having a hydrolyzable silyl group and a polymerizable functional group (for example, a radically polymerizable functional group such as an ethylenically unsaturated group) in the molecule is used, and the hydrolyzable silyl group-containing monomer is copolymerized with another monomer; (b) a method in which a hydrolyzable silyl group-containing compound having a hydrolyzable silyl group and a reactive functional group X in the molecule and a primary polymer having a functional group Y that reacts with the reactive functional group X are used, and the functional group Y in the primary polymer is reacted with the reactive functional group X in the hydrolyzable silyl group-containing compound; and other known methods can be appropriately employed for preparation.

[0069] In some embodiments, a method using a silane coupling agent can be preferably adopted as a method for obtaining a polymer having a hydrolyzable silyl group. By using a silane coupling agent, a polymer having a hydrolyzable silyl group derived from the silane coupling agent can be obtained. The silane coupling agent is a compound having a hydrolyzable silyl group and a reactive functional group in the molecule. Examples of the reactive functional group include ethylenically unsaturated groups such as acryloyl, methacryloyl, vinyl, and styryl groups. From the viewpoint of polymerization reactivity, preferred ethylenically unsaturated groups include acryloyl and methacryloyl groups. The above method (a) can be preferably carried out in an embodiment in which a silane coupling agent having a hydrolyzable silyl group and an ethylenically unsaturated group in the molecule is used as the hydrolyzable silyl group-containing monomer.

[0070] Other examples of the reactive functional group include an epoxy group, an amino group, a ureido group, an isocyanate group, and a mercapto group. The isocyanate group may form an isocyanurate structure. The method (b) above can be preferably carried out in an embodiment in which a silane coupling agent having such a reactive functional group (reactive functional group X) is used as the hydrolyzable silyl group-containing compound. Examples of combinations of the reactive functional group X and the functional group Y include, but are not limited to, a combination of an epoxy group and a carboxy group, a combination of an epoxy group and an amino group (listed in the order of reactive functional group X, functional group Y; the same applies below), a combination of an amino group and a carboxy group, a combination of an amino group and an epoxy group, a combination of an amino group and an isocyanate group, a combination of an isocyanate group and a hydroxyl group, a combination of an isocyanate group and a carboxy group, and a combination of an isocyanate group and an amino group.

[0071] Non-limiting specific examples of silane coupling agents that can be used to prepare a polymer having a hydrolyzable silyl group (for example, a hydrolyzable silyl group-containing acrylic polymer) include (meth)acryloyl group-containing silane coupling agents such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; vinyl group-containing silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane; styryl group-containing silane coupling agents such as styryltrimethoxysilane; epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. coupling agents; for example, silane coupling agents containing an isocyanate group (which may form an isocyanurate structure), such as 3-isocyanatepropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate; amino group-containing silane coupling agents, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine; ureido group-containing silane coupling agents, such as 3-ureidopropyltrialkoxysilane; mercapto group-containing silane coupling agents, such as 3-mercaptopropyltrimethoxysilane, 2-mercaptopropylmethyldimethoxysilane; and the like.

[0072] In the polymer that has the hydrolyzable silyl group derived from silane coupling agent, the amount of silane coupling agent used is appropriately set so as to obtain desired effect.In some embodiments, the amount of silane coupling agent used in the polymer that has the hydrolyzable silyl group derived from silane coupling agent can be for example 0.001 parts by weight or more with respect to 100 parts by weight of polymer forming components other than silane coupling agent, from the viewpoint of obtaining higher use effect, it is usually appropriate to be 0.005 parts by weight or more, it is advantageous to be 0.01 parts by weight or more, it is preferably 0.02 parts by weight or more or 0.03 parts by weight or more, it is more preferably 0.05 parts by weight or more or 0.08 parts by weight or more, it can be 0.1 parts by weight or more, it can be 0.2 parts by weight or more, it can be 0.3 parts by weight or more or 0.5 parts by weight or more. In some embodiments, the amount of the silane coupling agent used can be, for example, 5.0 parts by weight or less per 100 parts by weight of the polymer-forming components other than the silane coupling agent. From the viewpoints of the storage stability of the PSA composition and the stability of the dispersion state over time in the case of a water-dispersed PSA composition, it is usually appropriate to use 3.0 parts by weight or less, advantageously 2.0 parts by weight or less, preferably 1.5 parts by weight or less, more preferably 1.0 part by weight or less, or alternatively 0.8 parts by weight or less, 0.5 parts by weight or less, 0.3 parts by weight or less, 0.2 parts by weight or less, or 0.1 parts by weight or less.

[0073] In some embodiments, the hydrolyzable silyl group-containing polymer (e.g., a hydrolyzable silyl group-containing acrylic polymer) contained in the pressure-sensitive adhesive composition is preferably the base polymer of the pressure-sensitive adhesive layer formed from the composition. For example, it is preferred that more than 50 wt% (more preferably 65 wt% or more, even more preferably 75 wt% or more, e.g., 85 wt% or more) of the polymer components contained in the pressure-sensitive adhesive composition be hydrolyzable silyl group-containing polymer. The content of the hydrolyzable silyl group-containing polymer in the polymer components contained in the pressure-sensitive adhesive composition may be 100 wt%, or may be less than 100 wt%, 99.5 wt% or less, or 99 wt% or less, from the viewpoint of obtaining the effects of using other polymers used as needed (e.g., adjusting the viscosity and coatability of the pressure-sensitive adhesive composition, adjusting adhesive performance, etc.).

[0074] (Tackifier Resin) In some preferred embodiments, the PSA layer contains a tackifier resin. This makes it easier to obtain a PSA sheet that exhibits excellent adhesive properties (e.g., adhesive strength, repulsion resistance). Examples of tackifier resins include rosin-based tackifier resins (including rosin derivative tackifier resins), petroleum-based tackifier resins, terpene-based tackifier resins, phenol-based tackifier resins, and ketone-based tackifier resins. These can be used alone or in combination of two or more.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] Although not particularly limited, in some embodiments, the tackifier resin 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.

[0079] 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.

[0080] In an embodiment in which the PSA layer is formed from a water-dispersed PSA composition, it is preferable to use a water-dispersed tackifier resin (also referred to as a tackifier resin emulsion) as the tackifier resin. In this embodiment, the water-dispersed PSA composition 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, it is possible to easily prepare a PSA composition containing these components in a desired ratio. It is preferable to use a tackifier resin emulsion that is at least substantially free of aromatic hydrocarbon solvents (more preferably, substantially free of aromatic hydrocarbon solvents and other organic solvents).

[0081] 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.

[0082] In order to optimally utilize the effects of its use, the amount of tackifier resin used (based on solids content) is typically 1 part by weight or more per 100 parts by weight of base polymer (e.g., acrylic polymer), preferably 3 parts by weight or more (e.g., 5 parts by weight or more), more preferably 12 parts by weight or more, and even more preferably 16 parts by weight or more. According to the technology disclosed herein, good adhesive properties can be achieved in an embodiment containing 22 parts by weight or more (e.g., 25 parts by weight or more) of tackifier resin per 100 parts by weight of base polymer. Furthermore, in terms of cohesive strength, etc., the amount of tackifier resin used is typically 90 parts by weight or less per 100 parts by weight of base polymer, preferably 70 parts by weight or less, more preferably 55 parts by weight or less, and even more preferably 50 parts by weight or less (e.g., 45 parts by weight or less, typically 40 parts by weight or less).

[0083] When the PSA layer disclosed herein contains a high-softening point tackifier resin, from the viewpoint of cohesive strength, etc., it is possible to use only the high-softening point tackifier resin as the tackifier resin. Furthermore, from the viewpoint of balancing various adhesive properties, in some embodiments, a high-softening point tackifier resin can be used in combination with a tackifier resin having a lower softening point (e.g., a tackifier 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 tackifier resin in the total tackifier 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 tackifier resin may be, for example, 90% by weight or less, 80% by weight or less, or 70% by weight or less. Limiting the amount of the high-softening point tackifier resin used to a predetermined amount or less can be advantageous in terms of impact resistance.

[0084] (Polyacrylic Acid) In some embodiments, the PSA layer may contain polyacrylic acid. For example, by adding an appropriate amount of polyacrylic acid having an appropriate number average molecular weight to an acrylic water-dispersible PSA composition, the water resistance of the PSA layer formed from the water-dispersible PSA composition can be improved.

[0085] The molecular weight of the polyacrylic acid is not particularly limited, and for example, the number average molecular weight (Mn) is 2000 or more and 550 × 10 ４ The following polyacrylic acids can be used: In some preferred embodiments, the Mn of the polyacrylic acid is 3000 or more and 500×10 ４ or less, or 5000 or more, 500 x 10 ４ When the Mn of the polyacrylic acid is high, the effect of improving water resistance tends to be more easily exhibited. From this viewpoint, the Mn of the polyacrylic acid is 1 × 10 ４ or more (e.g., 5 x 10 ４ or more), and more preferably 10 × 10 ４ or more, and more preferably 15×10 ４ That is 20 x 10 ４ On the other hand, if the Mn of the polyacrylic acid is too high, the addition of the polyacrylic acid will cause a sudden increase in the viscosity of the PSA composition (specifically, the water-dispersed PSA composition), which may lead to problems such as a decrease in coatability, and it may become difficult to incorporate an amount of polyacrylic acid suitable for improving water resistance. From this viewpoint, the Mn of the polyacrylic acid is 400×10 ４ It is preferable that the value is equal to or less than 300×10 ４ or less, and more preferably 200×10 ４ In one embodiment of the technology disclosed herein, the Mn of the polyacrylic acid is 150×10 ４ It may be less than or equal to 100×10 ４ It may be 75×10 or less. ４ It may be 50×10 or less. ４ Less than 35 x 10 ４ The following is also acceptable.

[0086] In this specification, the number average molecular weight (Mn) refers to a value calculated as a standard polyethylene glycol / polyethylene oxide, measured by GPC.

[0087] In embodiments using polyacrylic acid, the amount of polyacrylic acid used can be set so that the effects of its addition are optimally exhibited. In some embodiments, polyacrylic acid is used in an amount of 0.3 parts by weight or more and 7 parts by weight or less per 100 parts by weight of base polymer. The amount of polyacrylic acid per 100 parts by weight of base polymer is more preferably 0.4 parts by weight or more, and even more preferably 0.5 parts by weight or more. In some embodiments, the amount of polyacrylic acid per 100 parts by weight of base polymer may be 1 part by weight or more, or even 1.5 parts by weight or more. Furthermore, from the viewpoint of coatability and forming a PSA layer with good surface condition, the amount of polyacrylic acid per 100 parts by weight of base polymer is more preferably 6 parts by weight or less, and even more preferably 5 parts by weight or less (e.g., 4.5 parts by weight or less). In one embodiment of the technology disclosed herein, the amount of polyacrylic acid per 100 parts by weight of base polymer may be 4.25 parts by weight or less, or even 4 parts by weight or less.

[0088] (Crosslinking Agent) The pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer may contain a crosslinking agent as an optional component. The pressure-sensitive adhesive 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 pressure-sensitive adhesive layer exclusively in a form after crosslinking reaction.

[0089] The type of crosslinking agent is not particularly limited, and can be appropriately selected from, for example, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, and amine-based crosslinking agents. Both oil-soluble and water-soluble crosslinking agents 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 approximately 10 parts by weight or less (e.g., approximately 0.005 to 10 parts by weight) per 100 parts by weight of the base polymer (e.g., an acrylic polymer), and preferably approximately 5 parts by weight or less (0.01 to 5 parts by weight). The technology disclosed herein can be preferably implemented in an embodiment using a pressure-sensitive adhesive composition that does not contain a crosslinking agent.

[0090] (Silicon Compound) In addition, from the viewpoint of easy releasability from the release liner, the pressure-sensitive adhesive layer may contain 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, silyl group-containing sulfides, etc. can be used.Among them, alkylalkoxysilane compounds are preferred.The molecular weight of the silicon compound is suitably about 100 or more (for example, 200 or more), and can be about 500 or less (for example, 350 or less).

[0091] 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.

[0092] In order to fully exert the effect of the addition, the content of the silicon compound is preferably 0.005 parts by weight or more (for example, 0.01 parts by weight or more, typically 0.03 parts by weight or more) relative to 100 parts by weight of the base polymer (for example, an acrylic polymer). In addition, in order to improve storage stability, the content of the silicon compound is preferably less than 1.0 part by weight (for example, 0.5 parts by weight or less, typically 0.3 parts by weight or less) relative to 100 parts by weight of the base polymer.

[0093] (Other Additive Components) In the technology disclosed herein, the adhesive composition used to form the adhesive layer may contain, as necessary, 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 adhesive composition disclosed herein include viscosity modifiers, leveling agents, crosslinking aids, release modifiers, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, preservatives, etc. As for such various additives, conventionally known ones can be used in the usual manner, and as they do not particularly characterize the present invention, detailed description thereof will be omitted.

[0094] (Pressure-Sensitive Adhesive Composition) The pressure-sensitive adhesive layer (layer comprising a pressure-sensitive adhesive) disclosed herein may be a pressure-sensitive adhesive layer formed from an aqueous pressure-sensitive adhesive composition, a solvent-based pressure-sensitive adhesive composition, a hot-melt pressure-sensitive adhesive composition, or an active energy ray-curable pressure-sensitive adhesive composition that cures upon irradiation with active energy rays such as ultraviolet rays or electron beams. The aqueous pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive (a pressure-sensitive adhesive layer-forming component) in a medium (aqueous medium) primarily composed of water, and typically includes what is referred to as a water-dispersed pressure-sensitive adhesive composition (a composition in which at least a portion of the pressure-sensitive adhesive is dispersed in an aqueous medium). Here, the aqueous medium refers to water or a mixed solvent or dispersion medium (aqueous solvent or aqueous dispersion medium) primarily composed of water. Furthermore, the solvent-based pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive in an organic solvent. The organic solvent contained in the solvent-based pressure-sensitive adhesive composition may be one or more of the organic solvents (e.g., toluene, ethyl acetate, etc.) that can be used in the solution polymerization described above, without any particular limitation. The technology disclosed herein can be preferably implemented in an embodiment comprising a PSA layer formed from a water-dispersed (typically, aqueous emulsion) PSA composition in which a PSA component is dispersed in an aqueous medium.

[0095] (Formation of Pressure-Sensitive Adhesive Layer) The pressure-sensitive adhesive layer in the technology disclosed herein can be suitably formed by applying the above-mentioned pressure-sensitive adhesive composition to a predetermined surface and drying or curing it. When applying (typically applying) the pressure-sensitive 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.

[0096] (Thickness of the Pressure-Sensitive Adhesive Layer) The thickness of the pressure-sensitive adhesive layer can be set so that the total thickness of the double-sided pressure-sensitive adhesive sheet is 100 μm or less. The first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may have the same thickness or different thicknesses. The thicknesses of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are each independently typically set to approximately 2 μm or more. From the viewpoint of adhesive properties such as impact resistance, adhesive strength, and repulsion resistance, the thickness is preferably approximately 5 μm or more, more preferably 8 μm or more, even more preferably 10 μm or more, and may even be 15 μm or more (e.g., 18 μm or more). The thicknesses of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer can each independently be set to, for example, approximately 45 μm or less. From the viewpoint of thinning, the thickness is preferably 35 μm or less, advantageously 30 μm or less, preferably approximately 25 μm or less, and more preferably 22 μm or less (e.g., 20 μm or less). Pressure-sensitive adhesive layers with limited thickness can effectively meet demands for thinness and weight reduction. In some embodiments where thinner thickness is important, the thickness of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may each independently be 16 μm or less, 14 μm or less, or 12 μm or less.

[0097] <Intermediate Layer> The double-sided PSA sheet disclosed herein includes an intermediate layer between the first and second PSA layers, the intermediate layer containing a water-dispersible silicone elastomer and a non-silicone resin. In a thin double-sided PSA sheet with a total thickness of 100 μm, by including a water-dispersible silicone elastomer in the intermediate layer that does not constitute the adhesive surface, it is possible to increase impact absorption while minimizing the effect on adhesive performance (e.g., adhesion to an adherend), and effectively improve the impact resistance of the double-sided PSA sheet.

[0098] The intermediate layer in the technology disclosed herein can be preferably formed using an intermediate layer-forming composition containing a silicone elastomer aqueous dispersion in which a silicone elastomer is dispersed in water in particulate form and a non-silicone resin. From the standpoint of ease of mixing the silicone elastomer aqueous dispersion with the non-silicone resin, the intermediate layer-forming composition is preferably in the form of an aqueous dispersion material in which at least a portion of the intermediate layer-forming material containing a water-dispersible silicone elastomer and a non-silicone resin (preferably a water-dispersible non-silicone resin) is dispersed in water. By using an aqueous dispersion material (specifically, an aqueous dispersion of an intermediate layer-forming material containing at least a water-dispersible silicone elastomer and a non-silicone resin) as the intermediate layer-forming material, component migration that may occur between the adhesive layer and the adhesive layer can be prevented or suppressed. Low interlayer component migration means that the adhesive sheet is less likely to experience changes in its properties over time due to component migration. In thin adhesive sheets with a total thickness of 100 μm or less, such as those disclosed herein, even slight component migration can have a significant impact on various properties, such as adhesive properties, making it practically important to prevent or suppress interlayer component migration. In some preferred embodiments of the double-sided PSA sheet, the intermediate layer is formed from a water-dispersible material, and at least one of the first and second PSA layers (preferably both) is formed from a water-dispersible PSA composition. This configuration makes it possible to more effectively prevent or inhibit component migration between the PSA layer and the intermediate layer. The reduced interlayer component migration means that the double-sided PSA sheet is less likely to experience changes in its properties over time due to component migration, which is preferable in practice.

[0099] From the viewpoint of adhesion to the pressure-sensitive adhesive layer, the intermediate layer is preferably a non-foamed layer (typically, a non-foamed resin layer). In this specification, the term "non-foamed layer" refers to a substantially non-porous layer, and is a concept that is distinguished from so-called nonwoven fabrics and woven fabrics (i.e., a concept that excludes nonwoven fabrics and woven fabrics). The non-foamed resin layer refers to a resin layer that has not been intentionally treated to form a foam. Specifically, the non-foamed resin layer may be a resin layer having an expansion ratio of less than 1.1 times (for example, less than 1.05 times, typically less than 1.01 times).

[0100] (Water-dispersible silicone elastomer) The silicone elastomer in the water-dispersible silicone elastomer that constitutes the intermediate layer is not particularly limited, and examples thereof include those that contain one or more of polysiloxanes such as polydialkylsiloxanes such as polydimethylsiloxane; polydicycloalkylsiloxanes such as polydicyclohexylsiloxane; polyalkylcycloalkylsiloxanes such as polymethylcyclohexylsiloxane; polydialkyl-dicycloalkylsiloxanes such as polydimethyl-dicycloalkylsiloxane; polydialkyl-alkylcycloalkylsiloxanes such as polydimethyl-methylcyclohexylsiloxane; polydiarylsiloxanes such as polydiphenylsiloxane; polyalkylarylsiloxanes such as polymethylphenylsiloxane; polydialkyl-diarylsiloxanes such as polydimethyl-diphenylsiloxane; polydialkyl-alkylarylsiloxanes such as polydimethyl-methylphenylsiloxane; and polydiaryl-alkylarylsiloxanes such as polydiphenyl-methylphenylsiloxane. From the viewpoint of flexibility, silicone elastomers primarily composed of polydialkylsiloxane are preferred, and silicone elastomers primarily composed of polydimethylsiloxane are particularly preferred. The polysiloxane constituting the silicone elastomer is usually preferably crosslinked. The silicone elastomer may have a reactive functional group such as an epoxy group, an amino group, a mercapto group, or a carboxy group, or a radically polymerizable functional group such as a (meth)acryloyl group or a vinyl group. The reactive functional group may be a reactive functional group capable of reacting with a functional group contained in a non-silicone resin, as described below. This can contribute to improving the impact resistance of the double-sided PSA sheet by improving the cohesion of the intermediate layer containing the water-dispersible silicone elastomer. A suitable example of a combination of a functional group contained in a non-silicone resin and a functional group contained in a silicone elastomer is a combination of a carboxy group and an epoxy group.

[0101] The silicone elastomers are preferably in the form of aqueous dispersions of the silicone elastomers, and can be used alone or in combination to prepare the intermediate layer. Each silicone elastomer aqueous dispersion may contain only one type of silicone elastomer particle, or two or more types. The silicone elastomer aqueous dispersion may be prepared by a known method, a commercially available product, or a commercially available product that has been subjected to an optional treatment (e.g., a treatment to introduce functional groups into the silicone elastomer). Silicone elastomer aqueous dispersions are commercially available from Dow-Toray Industries, Inc., Shin-Etsu Chemical Co., Ltd., and others. Specific examples include Dow-Toray Industries, Inc.'s products under the trade names "DOWSIL 33 Additive" and "DOWSIL BY 29-119," and Shin-Etsu Chemical Co., Ltd.'s products under the trade names "KM-9729" and "X-52-1133." In addition to the silicone elastomer and water, the silicone elastomer aqueous dispersion may contain additives such as surfactants, as needed.

[0102] From the viewpoint of thinning the double-sided PSA sheet, the average particle size of the silicone elastomer is suitably less than 10 μm, advantageously 8 μm or less, preferably 7 μm or less, more preferably 6 μm or less, and may be 5 μm or less (e.g., less than 5 μm), or may be 4 μm or less. Furthermore, the average particle size of the silicone elastomer may be, for example, 0.05 μm or more. From the viewpoint of impact resistance, etc., it is advantageously 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more (e.g., more than 1 μm), and may be 2 μm or more, or may be 3 μm or more. When a commercially available silicone elastomer aqueous dispersion is used as the average particle size of the silicone elastomer, the nominal value of the commercially available product (the value provided in the product information) can be used. When the nominal value is unknown, or when a non-commercially available silicone elastomer aqueous dispersion is used, the median diameter (d ５０ ) can be adopted.

[0103] In some embodiments, the water-dispersible silicone elastomer contained in the intermediate layer is preferably a particle having a particle shape that is substantially free of voids, from the viewpoints of ease of preparation of the intermediate layer-forming composition (e.g., an intermediate layer-forming composition in the form of a water-dispersible material), impact resistance, durability, quality stability, ease of thinning of the intermediate layer, etc. Here, particles having a particle shape that is substantially free of voids are a concept that is distinct from so-called porous particles or hollow particles, and typically refer to particles in which the volume ratio of voids to the apparent volume of the particle is 10% or less (preferably 5% or less, more preferably 3% or less, for example 1% or less).

[0104] The content of the water-dispersible silicone elastomer in the intermediate layer is not particularly limited and can be appropriately set so as to obtain the desired impact resistance improvement effect. The content of the water-dispersible silicone elastomer in the intermediate layer can be, for example, within a range of 0.1% to 95% by weight of the entire intermediate layer. In some embodiments, from the viewpoint of impact resistance (e.g., the impact absorption ability of the intermediate layer), the content of the water-dispersible silicone elastomer in the intermediate layer is suitably approximately 0.5% by weight or more, preferably 1% by weight or more, more preferably 3% by weight or more, and may be 5% by weight or more, or even 7% by weight or more (e.g., 9% by weight or more). In other embodiments (e.g., embodiments in which the non-silicone resin includes a polyurethane resin), the content of the water-dispersible silicone elastomer in the intermediate layer may be, for example, 10% by weight or more, or even 15% by weight or more (e.g., 17% by weight or more). In some preferred embodiments, the content of the water-dispersible silicone elastomer in the intermediate layer is, for example, 20% by weight or more, more preferably 25% by weight or more or 30% by weight or more (e.g., more than 30% by weight), even more preferably 35% by weight or more, and may be 40% by weight or more, 45% by weight or more, or even 50% by weight or more. Furthermore, from the viewpoints of the film-forming properties and cohesiveness of the intermediate layer and the anchoring properties of the pressure-sensitive adhesive layer, the content of the water-dispersible silicone elastomer in the intermediate layer is suitably 90% by weight or less, preferably 85% by weight or less, and more preferably 80% by weight or less. In some preferred embodiments, the content of the water-dispersible silicone elastomer in the intermediate layer is, for example, 75% by weight or less, more preferably 70% by weight or less, and may be 65% by weight or less, 60% by weight or less, or 55% by weight or less. In some other embodiments (e.g., embodiments in which the non-silicone resin includes an acrylic resin), the content of the water-dispersible silicone elastomer in the intermediate layer may be, for example, 45% by weight or less, 40% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less.

[0105] (Non-Silicone Resin) As the non-silicone resin constituting the intermediate layer, various non-silicone resin materials capable of forming (forming) an intermediate layer containing a water-dispersible silicone elastomer can be used. Non-limiting examples of non-silicone resin materials include polyurethane resins; polyolefin resins; acrylic resins such as acrylic copolymers; vinyl chloride resins (PVC) such as flexible polyvinyl chloride; blends and hybrids (also referred to as composites) of the above resins; and the like. A preferred example of a hybrid of the above resins is a urethane-acrylic hybrid resin. A preferred example of a blend of the above resins is a urethane-acrylic blend resin. The material constituting the intermediate layer may be rubbers (including those generally referred to as rubber and thermoplastic elastomers). One or more suitable materials can be selected and used from the above materials. In some embodiments, the non-silicone resin material contained in the intermediate layer may be a polyurethane resin, a urethane-acrylic resin (a concept that includes urethane-acrylic hybrid resins and urethane-acrylic blend resins), an acrylic resin, rubbers, a polyolefin resin, or a blend thereof. Among these, polyurethane resins, urethane acrylic resins, and acrylic resins are preferred.

[0106] In some preferred embodiments, the intermediate layer is formed containing a polyurethane-based resin. An intermediate layer containing a water-dispersible silicone elastomer and a polyurethane-based resin can be preferably obtained by selecting and using one or more appropriate polyurethane-based resins (specifically, water-dispersible polyurethane-based resins). Furthermore, an intermediate layer containing a polyurethane-based resin, for example, in an embodiment in which an acrylic pressure-sensitive adhesive layer is laminated, is likely to achieve good anchoring properties, is less likely to break anchor upon impact, and is likely to achieve excellent impact resistance. Here, the polyurethane-based resin is a polymer compound synthesized by polyaddition reaction of a polyol (e.g., a diol) and a polyisocyanate (e.g., a diisocyanate) in an appropriate ratio. As the polyurethane-based resin, any of ether-based polyurethanes, ester-based polyurethanes, and carbonate-based polyurethanes can be used. Among these, ester-based polyurethanes are preferred.

[0107] The polyol is not particularly limited, and one or more suitable polyols can be selected from various diols, polyester polyols, polyether polyols, carbonate diols, etc. Specific examples of polyols include diols such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, polytetramethylene ether glycol (PTMG), polyethylene glycol, and polypropylene glycol; polyester polyols which are polycondensates of the above diols and dicarboxylic acids (e.g., adipic acid, azelaic acid, sebacic acid, and dimer acid); and carbonate diols such as polyalkylene carbonate diols. The above diols and dicarboxylic acids may be biologically derived materials (biomass materials). In the case of a polymer polyol (e.g., PTMG), its number average molecular weight (Mn) may be, for example, 10,000 or less, and from the viewpoints of reactivity and handleability, it is preferably 5,000 or less, and may be 3,000 or less, 2,000 or less, or 1,000 or less. Furthermore, the Mn of the polymer polyol may be, for example, 200 or more, 400 or more, 600 or more, 800 or more, or 1,000 or more. The Mn of the polymer polyol can be measured by GPC as a value converted into a standard polyethylene glycol / polyethylene oxide. When a nominal value of the number average molecular weight is provided by a manufacturer, etc., this value can be used.

[0108] The polyisocyanate is not particularly limited, and one or more suitable polyisocyanates may be selected from aromatic, aliphatic, and alicyclic diisocyanates, and polymers of these diisocyanates (e.g., dimers and trimers), and the like, and may be used. Specific examples of polyisocyanates include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, butane-1,4-diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, methylcyclohexane diisocyanate, and m-tetramethylxylylene diisocyanate.

[0109] In the synthesis of polyurethane resins, the NCO / OH ratio is appropriately set so as to obtain the desired structure and mechanical properties. In some embodiments, the NCO / OH equivalent ratio (hereinafter referred to as "NCO / OH ratio") may be, for example, about 0.8 or more and 3.0 or less, or may be greater than 1.0 (e.g., 1.1 or more) and 2.5 or less, or may be 1.1 or more and 2.0 or less, or may be 1.1 or more and 1.5 or less.

[0110] In addition to the polyol and polyisocyanate, other copolymerization components (e.g., carboxylic acid) may be incorporated into the polyurethane resin. The proportion of the other copolymerization components is preferably less than 10% by weight (e.g., 0 to 3% by weight) of the polyurethane resin.

[0111] The polyurethane resin (preferably a water-dispersible polyurethane resin) used in the composition for forming the intermediate layer may be synthesized by a known method, or a commercially available product may be obtained and used. Examples of such commercially available products include "U-coat DA-100" (trade name) manufactured by Sanyo Chemical Industry Co., Ltd., "ADEKA BONTITAR HUX" series (trade name) manufactured by ADEKA Corporation, and "SUPERFLEX" series (trade name) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. In some embodiments, a hydrolyzable silyl group-containing urethane polymer, which will be described later, may be preferably used as the urethane resin constituting the intermediate layer.

[0112] In some embodiments, the intermediate layer may be composed of a urethane acrylic resin. Examples of urethane acrylic resins (preferably, water-dispersible urethane acrylic resins) used to form the intermediate layer include reaction products of acrylic polymers having two or more hydroxyl groups (specifically, polyol-type acrylic copolymers) with isocyanate compounds; copolymers of radically polymerizable urethane polymers having ethylenically unsaturated groups at both ends with acrylic monomers (e.g., acrylic monomers containing alkyl(meth)acrylate as a main component); and resins containing urethane(meth)acrylate polymers. Examples of urethane(meth)acrylate polymers include polymers containing structural units derived from urethane(meth)acrylate. Urethane(meth)acrylate refers to a compound having a urethane bond and a (meth)acryloyl group in one molecule, and such compounds can be used without particular limitations. Urethane(meth)acrylates can be used alone or in combination of two or more. Urethane(meth)acrylate polymers can be synthesized by known methods. Furthermore, various commercially available urethane (meth)acrylates can be used as the urethane (meth)acrylate. The urethane acrylic resin may be a urethane-acrylic hybrid. Examples of the urethane-acrylic hybrid include a water-dispersed urethane-acrylic hybrid obtained by seed polymerization of a (meth)acrylic monomer using a urethane polymer constituting a urethane polymer aqueous dispersion (which may be a urethane polymer aqueous dispersion obtained by synthesizing a urethane polymer in an acrylic monomer and dispersing the resulting urethane polymer together with the acrylic monomer in water). The weight ratio of the urethane component to the acrylic component in the urethane acrylic resin (urethane / acrylic ratio) is not particularly limited and may be, for example, within a range of 5 / 95 to 95 / 5, 10 / 90 to 90 / 10, or 80 / 20 to 20 / 80.In some preferred embodiments, the urethane / acrylic ratio may be, for example, within a range of 5 / 90 to 70 / 30, within a range of 10 / 90 to 60 / 40, or within a range of 20 / 80 to 50 / 50. In some embodiments, a urethane acrylic resin including a urethane acrylic polymer having a hydrolyzable silyl group, as described below, may be preferably used as the non-silicone resin constituting the intermediate layer.

[0113] The monomer component used as the acrylic component can be appropriately selected from various monomers similar to the monomer components of the acrylic polymer that can be contained in the pressure-sensitive adhesive layer described above. For example, the monomer component may include at least an alkyl(meth)acrylate and may also include other monomers copolymerizable with the alkyl(meth)acrylate (e.g., a carboxyl group-containing monomer, a hydroxyl group-containing monomer, a monomer having an alkoxysilyl group, etc.). The alkyl(meth)acrylate can preferably be a compound represented by the above-mentioned formula (1) (which may be a compound having an alkyl group derived from biomass). In some embodiments, the content of the alkyl(meth)acrylate in the monomer components constituting the acrylic polymer can be appropriately set with reference to the examples of the content of the alkyl(meth)acrylate in the monomer components of the acrylic polymer that can be contained in the pressure-sensitive adhesive layer described above. The same applies to the amount of the other monomers used.

[0114] In some embodiments, the monomer component used as the acrylic component is selected from the group consisting of R ２ is C １－２ Alkyl (meth)acrylate (i.e., C １－２ It is preferable that the copolymer contains alkyl (meth)acrylate. １－２ The alkyl (meth)acrylate may be used alone or in combination of two or more. For example, the monomer component preferably contains at least one of MMA and MA, and more preferably contains at least MMA. １－２The content of alkyl (meth)acrylate can be, for example, 5% by weight or more, 15% by weight or more, 25% by weight or more, 35% by weight or more, 45% by weight or more, 50% by weight or more, more than 50% by weight, or 55% by weight or more. １－２ The content of alkyl (meth)acrylate can be, for example, 85% by weight or less, 75% by weight or less, or 65% by weight or less.

[0115] In some embodiments, the monomer component used as the acrylic component may be selected from the group consisting of R in formula (1) and R in formula (1) from the viewpoint of flexibility, impact resistance, etc. of the intermediate layer. ２ is C ３－９ It is possible to include alkyl (meth)acrylate, which is a chain alkyl group of the formula C. ３－９ Examples of the chain alkyl (meth)acrylate are the same as those of the acrylic polymer that can be contained in the pressure-sensitive adhesive layer, and therefore, redundant descriptions will be omitted. ３－９ The chain alkyl (meth)acrylates can be used alone or in combination of two or more. ３－９ The content of the chain alkyl (meth)acrylate can be, for example, 5% by weight or more, 15% by weight or more, or 25% by weight or more. ３－９ The content of the chain alkyl (meth)acrylate can be, for example, 70% by weight or less, 60% by weight or less, 50% by weight or less, or 40% by weight or less. １－２ Alkyl (meth)acrylate and C ３－９ It may also contain a chain alkyl (meth)acrylate in combination.

[0116] In some embodiments, the monomer component used as the acrylic component suitably has a Tg of −30° C. or higher (typically −30° C. or higher and 40° C. or lower) calculated based on the composition of the monomer component using the Fox formula. From the viewpoints of the strength of the intermediate layer and the handleability of the PSA sheet, the Tg based on the composition of the acrylic component is preferably −20° C. or higher, more preferably −10° C. or higher, and even more preferably −5° C. or higher; for example, it may be 0° C. or higher, 5° C. or higher, 10° C. or higher, or 15° C. or higher, 20° C. or higher, 25° C. or higher, or 30° C. or higher. Furthermore, in some embodiments, from the viewpoints of flexibility, impact resistance, etc., the Tg based on the composition of the monomer component is suitably 60° C. or higher, advantageously 50° C. or lower, preferably 45° C. or lower, more preferably 40° C. or lower, and may be 35° C. or lower, or may be 30° C. or lower. The Tg based on the composition of the above monomer components can be determined in the same manner as for the acrylic polymer that can be contained in the pressure-sensitive adhesive layer, except that the Fox equation is applied to only the monomer components used as the above acrylic component.

[0117] The urethane component in the urethane acrylic resin can be appropriately selected from, for example, the various polyols and polyisocyanates exemplified above as materials (which may be biomass materials) that can be used in the synthesis of the polyurethane resin. The polyurethane formed from such a urethane component can be any of ether-based polyurethane, ester-based polyurethane, and carbonate-based polyurethane. In some embodiments, the polyurethane can be an ether-based polyurethane or an ester-based polyurethane. From the viewpoint of flexibility and impact resistance, ether-based polyurethane is more preferable. The NCO / OH ratio of the urethane component is not particularly limited and can be, for example, 0.8 or more and 3.0 or less. In some embodiments, the NCO / OH ratio can be, for example, greater than 1.0 (e.g., 1.1 or more), 1.2 or more, 1.3 or more, or 1.4 or more, from the viewpoint of ease of synthesis of the urethane acrylic polymer. In addition, in some embodiments, the NCO / OH ratio can be, for example, 2.5 or less, 2.0 or less, or 1.8 or less.

[0118] In some other embodiments, the intermediate layer may be formed containing an acrylic resin. The acrylic polymer contained in the acrylic resin (preferably, a water-dispersible acrylic resin) used to form the intermediate layer may be a homopolymer or a copolymer (random copolymer, block copolymer, graft copolymer, etc.). Acrylic resins also include those known as acrylic rubber. The acrylic resin may be used alone as a non-silicone resin, or may be used as a non-silicone resin in the form of a blend or hybrid with a polyurethane resin. Any acrylic resin having properties suitable for use as an intermediate layer material may be used without particular limitation. For example, it may be synthesized by a known or conventional method, or a commercially available product may be used. In some embodiments, the monomer component of the acrylic polymer contained in the acrylic resin may be appropriately selected from various monomers (which may have a biomass-derived alkyl group) similar to the monomer components of the acrylic polymer that may be contained in the above-mentioned pressure-sensitive adhesive layer. For example, an acrylic resin containing an acrylic polymer having a hydrolyzable silyl group, as described below, may be preferably used as the non-silicone resin constituting the intermediate layer.

[0119] In some other embodiments, the intermediate layer may be formed containing a polyolefin-based resin. By selecting and using one or more suitable polyolefin-based resins (preferably water-dispersible polyolefin-based resins), an intermediate layer containing a water-dispersible silicone elastomer and a polyolefin-based resin can be obtained. The polyolefin-based resin may be, for example, an α-olefin homopolymer, a copolymer of two or more α-olefins, or a copolymer of one or more α-olefins with other vinyl monomers. Specific examples include polyethylene (PE), polypropylene (PP), poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymers such as ethylene-propylene rubber (EPR), ethylene-propylene-butene copolymers, ethylene-butene copolymers, ethylene-vinyl alcohol copolymers, and ethylene-ethyl acrylate copolymers. Both low-density (LD) polyolefins and high-density (HD) polyolefins can be used. The polyolefin-based resin may be an ionomer. Examples of commercially available polyolefin resins include the "Chemipearl" series manufactured by Mitsui Chemicals, Inc.

[0120] In some other embodiments, the intermediate layer may be formed containing non-silicone rubbers. By selecting and using one or more rubbers (preferably water-dispersible rubbers, also known as latex), an intermediate layer containing a water-dispersible silicone elastomer and rubbers can be obtained. Examples of rubbers include styrene-based copolymers (typically styrene-based elastomers) such as styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-ethylene-butylene copolymer, styrene-ethylene-propylene copolymer, styrene-butadiene-styrene copolymer, styrene-isoprene-styrene copolymer, and modified products thereof. Examples of commercially available rubbers include the "Nipol" series manufactured by Nippon Zeon Corporation.

[0121] When the composition for forming an intermediate layer is in the form of a water-dispersible material, the water-dispersible material may contain a surfactant for the purposes of dispersibility, dispersion stability, etc. of the material, or may be substantially free of a surfactant. Here, "the water-dispersible material is substantially free of a surfactant" means that a surfactant is not intentionally used, and for example, the content of surfactant in the water-dispersible material is less than 0.1 wt % (e.g., less than 0.01 wt % or less than 0.001 wt %) based on the solid content. In an embodiment in which the water-dispersible material contains a surfactant, the surfactant can be appropriately selected, for example, from those exemplified in relation to the pressure-sensitive adhesive layer.

[0122] In some embodiments, any of the above-described types of non-silicone resins may be non-silicone resins containing a polymer having a hydrolyzable silyl group (a hydrolyzable silyl group-containing polymer). The meaning of the hydrolyzable silyl group in the hydrolyzable silyl group-containing polymer, the form of the hydrolyzable silyl group in the aqueous dispersion composition for forming an intermediate layer when the composition for forming an intermediate layer is aqueous dispersion-type, and examples of the hydrolyzable silyl group (including representative examples, specific examples, and preferred examples) are the same as those for the hydrolyzable silyl group-containing polymer contained in the pressure-sensitive adhesive composition, and therefore a redundant description will be omitted. Suitable examples of the polymer having a hydrolyzable silyl group include, for example, an acrylic polymer having a hydrolyzable silyl group, a urethane acrylic polymer having a hydrolyzable silyl group, a urethane (meth)acrylate having a hydrolyzable silyl group, and a urethane-acrylic hybrid. Such an intermediate layer exhibits moderate cohesion due to the silanol groups generated from the hydrolyzable silyl group-containing polymer forming a crosslinked structure within the intermediate layer, which can contribute to improved impact resistance by suppressing cohesive failure of the intermediate layer in impact resistance measurements. Furthermore, the silanol groups can form a crosslinked structure between the intermediate layer and the pressure-sensitive adhesive layer adjacent to it, which can contribute to improving impact resistance by improving interlayer adhesion between the intermediate layer and the pressure-sensitive adhesive layer.

[0123] In the embodiment that the hydrolyzable silyl group in the polymer that has hydrolyzable silyl group is derived from silane coupling agent, the amount of the silane coupling agent used is appropriately set so as to obtain desired effect.In some embodiments, the amount of the silane coupling agent used in the polymer that has above-mentioned hydrolyzable silyl group can be for example 0.001 parts by weight or more with respect to 100 parts by weight of polymer-forming components other than silane coupling agent, and from the viewpoint of better exhibiting the effect of improving the adhesion between intermediate layer and pressure-sensitive adhesive layer, it is usually appropriate to be 0.005 parts by weight or more, be advantageous to be 0.01 parts by weight or more, be preferably 0.02 parts by weight or more or 0.03 parts by weight or more, be more preferably 0.05 parts by weight or more or 0.08 parts by weight or more, can be 0.1 parts by weight or more, can be 0.2 parts by weight or more, can be 0.3 parts by weight or more or 0.5 parts by weight or more. In addition, in some embodiments, the amount of the silane coupling agent used can be, for example, 5.0 parts by weight or less per 100 parts by weight of the polymer-forming components other than the silane coupling agent. From the viewpoint of the storage stability of the composition for forming an intermediate layer (for example, the stability of the dispersed state over time), it is usually appropriate to use 3.0 parts by weight or less, and it is advantageous to use 2.0 parts by weight or less, preferably 1.5 parts by weight or less, more preferably 1.0 part by weight or less, and may be 0.8 parts by weight or less, 0.5 parts by weight or less, 0.3 parts by weight or less, 0.2 parts by weight or less, or 0.1 parts by weight or less.

[0124] In some embodiments, the hydrolyzable silyl group-containing polymer contained in the intermediate layer-forming composition is preferably the base polymer of the intermediate layer formed from the intermediate layer-forming composition. For example, it is preferred that more than 50% by weight (more preferably 65% ​​by weight or more, even more preferably 75% by weight or more, for example 85% by weight or more) of the polymer components contained in the intermediate layer-forming composition be hydrolyzable silyl group-containing polymer. The content of the hydrolyzable silyl group-containing polymer in the polymer components contained in the intermediate layer-forming composition may be 100% by weight, or may be less than 100% by weight (99.5% by weight or less, 99% by weight or less, etc.) from the viewpoint of obtaining the effects of using other polymers used as needed (for example, adjusting the viscosity and coatability of the intermediate layer-forming composition, adjusting the adhesive performance, etc.).

[0125] The content of the non-silicone resin in the intermediate layer is not particularly limited and can be appropriately set within a range in which the total content of the non-silicone resin and the water-dispersible silicone elastomer does not exceed 100% by weight. The content of the non-silicone resin in the intermediate layer can be, for example, within a range of 5% to 99.9% by weight of the entire intermediate layer. In some embodiments, from the viewpoint of easily exhibiting the effect of improving impact resistance (e.g., the impact absorption properties of the intermediate layer) provided by the water-dispersible silicone elastomer, the content of the non-silicone resin in the intermediate layer is suitably approximately 99.5% by weight or less, preferably 99% by weight or less, more preferably 97% by weight or less, and may be 95% by weight or less, or may be 93% by weight or less (e.g., 91% by weight or less). In other embodiments (e.g., embodiments in which the non-silicone resin includes a polyurethane resin), the content of the non-silicone resin in the intermediate layer may be, for example, 90% by weight or less, or may be 85% by weight or less (e.g., 83% by weight or less). In some preferred embodiments, the content of the non-silicone resin in the intermediate layer is, for example, 80% by weight or less, more preferably 75% by weight or less or 70% by weight or less, even more preferably 65% ​​by weight or less, and may be 60% by weight or less, 55% by weight or less, or even 50% by weight or less. Furthermore, from the viewpoint of the film-forming properties and cohesiveness of the intermediate layer, the anchoring properties of the pressure-sensitive adhesive layer, etc., the content of the non-silicone resin in the intermediate layer is suitably 10% by weight or more, preferably 15% by weight or more, and more preferably 20% by weight or more. In some preferred embodiments, the content of the non-silicone resin in the intermediate layer is, for example, 25% by weight or more, more preferably 30% by weight or more, may be 35% by weight or more, may be 40% by weight or more, or may be 45% by weight or more. In some other embodiments (e.g., embodiments in which the non-silicone resin includes an acrylic resin), the content of the non-silicone resin in the intermediate layer may be, for example, 55% by weight or more, 60% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, or 85% by weight or more.

[0126] The content of the water-dispersible silicone elastomer relative to 100 parts by weight of the polymer component contained in the non-silicone resin is not particularly limited and can be appropriately set so as to obtain the desired impact resistance improvement effect. The content of the water-dispersible silicone elastomer may be, for example, within a range of 0.5 to 500 parts by weight (preferably 5 to 300 parts by weight) relative to 100 parts by weight of the polymer component contained in the non-silicone resin. In some embodiments, from the viewpoint of impact resistance (e.g., impact absorption by the intermediate layer), the content of the water-dispersible silicone elastomer relative to 100 parts by weight of the polymer component contained in the non-silicone resin is suitably approximately 1 part by weight or more, preferably 3 parts by weight or more, more preferably 5 parts by weight or more, and may be 10 parts by weight or more (e.g., more than 10 parts by weight), or even 15 parts by weight or more. In some other embodiments (for example, embodiments in which the non-silicone resin includes a polyurethane resin), the content of the water-dispersible silicone elastomer relative to 100 parts by weight of the polymer component contained in the non-silicone resin may be, for example, 20 parts by weight or more, preferably 30 parts by weight or more (e.g., more than 30 parts by weight), more preferably 40 parts by weight or more or 50 parts by weight or more, may be 70 parts by weight or more, may be 90 parts by weight or more, or may be 100 parts by weight or more. Furthermore, from the viewpoints of the film-forming ability and cohesiveness of the intermediate layer and the anchoring ability of the pressure-sensitive adhesive layer, the content of the water-dispersible silicone elastomer in the intermediate layer is suitably 400 parts by weight or less, preferably 300 parts by weight or less, more preferably 250 parts by weight or less, may be 200 parts by weight or less, may be 180 parts by weight or less, may be 150 parts by weight or less, or 120 parts by weight or less, may be 100 parts by weight or less, or may be 80 parts by weight or less, relative to 100 parts by weight of the polymer component of the non-silicone resin. In some other embodiments (for example, embodiments in which the non-silicone resin includes an acrylic resin), the content of the water-dispersible silicone elastomer relative to 100 parts by weight of the polymer component included in the non-silicone resin may be, for example, 75 parts by weight or less, 50 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less, or 15 parts by weight or less.

[0127] In some embodiments, the intermediate layer may contain particles other than water-dispersible silicone elastomers as filler particles. Both organic and inorganic materials can be used as filler particles, and inorganic materials such as metal filler particles, metal oxide fillers such as silica, metal hydroxide filler particles, and carbonates such as calcium carbonate are preferably used. The filler particles can be used alone or in combination of two or more. From the viewpoint of dispersibility in the resin, the filler particles are preferably added in the form of an aqueous dispersion. The particle size of the filler particles is not particularly limited, and fillers of an appropriate size can be used depending on the thickness and dispersibility of the intermediate layer to which the filler particles are added.

[0128] In embodiments in which the intermediate layer contains filler particles, the content of the filler particles is not particularly limited. From the viewpoint of effectively exhibiting the effect of adding the filler particles, the amount of the filler particles is, for example, 1 part by weight or more, suitably 10 parts by weight or more, or even 20 parts by weight or more, or even 30 parts by weight or more, per 100 parts by weight of the non-silicone-based resin contained in the intermediate layer. The upper limit of the amount of the filler particles is, for example, less than 100 parts by weight, suitably about 70 parts by weight or less, per 100 parts by weight of the resin. In other embodiments, the content of the filler particles in the intermediate layer is, for example, less than 30 parts by weight, or even less than 10 parts by weight, per 100 parts by weight of the non-silicone-based resin contained in the intermediate layer. The intermediate layer disclosed herein may be substantially free of filler particles.

[0129] The intermediate layer may contain various additives, such as leveling agents, thickeners, antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, colorants (pigments, dyes, etc., such as carbon black), and preservatives, as necessary. The surface of the intermediate layer (particularly the surface on which the pressure-sensitive adhesive layer is provided) 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 substrate anchoring ability of the pressure-sensitive adhesive layer. When the intermediate layer contains a polyurethane resin, its high surface energy allows it to achieve good anchoring ability even without the above-mentioned surface treatment.

[0130] The intermediate layer may have a single layer structure, or a multi-layer structure of two, three, or more layers. For example, the intermediate layer may be substantially composed of a resin layer formed from a resin composition (preferably a water-dispersible resin composition) containing a water-dispersible silicone elastomer and a non-silicone resin. In addition to the resin layer, the intermediate layer may also include an auxiliary layer (typically, a layer substantially free of a water-dispersible silicone elastomer). The auxiliary layer may be, for example, a decorative layer such as a printing layer, an antistatic layer, an undercoat layer, or the like.

[0131] The method for producing the intermediate layer is not particularly limited, and any conventionally known film forming method may be appropriately adopted. For example, the intermediate layer can be suitably formed by applying a composition for forming the intermediate layer (preferably a composition in the form of a water-dispersible material) to a predetermined surface (e.g., a release surface, the surface of a previously formed pressure-sensitive adhesive layer, the surface of a coating film of the pressure-sensitive adhesive composition, etc.) and curing it by means of drying or the like.

[0132] The thickness of the intermediate layer may be, for example, approximately 1 μm or more, typically 2 μm or more, advantageously 3 μm or more, preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 9 μm or more. According to the technology disclosed herein, by setting the thickness of the intermediate layer at a predetermined value or more, it is possible to achieve excellent impact resistance while obtaining good handleability (e.g., productivity and processability). From this perspective, in some embodiments, the thickness of the intermediate layer may be, for example, 10 μm or more, 15 μm or more, 18 μm or more, or 22 μm or more. Furthermore, from the viewpoint of reducing the thickness of the double-sided pressure-sensitive adhesive sheet, the thickness of the intermediate layer is generally suitably approximately 90 μm or less, advantageously 70 μm or less, preferably 50 μm or less, more preferably 45 μm or less or 40 μm or less, and may be 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 12 μm or less, or 10 μm or less.

[0133] In some embodiments, the thickness of the intermediate layer is set so that the thickness ratio of the intermediate layer to the total thickness of the double-sided PSA sheet is within the range of 10% to 80%. Having a thickness ratio within this range allows for a good balance between the impact resistance provided by the adhesive properties of the first and second PSA layers (e.g., adhesion to the adherend, adhesion to the intermediate layer) and the impact resistance provided by the intermediate layer containing the water-dispersible silicone elastomer, thereby achieving a double-sided PSA sheet that exhibits good impact resistance despite its thin thickness. In some preferred embodiments, the thickness ratio of the intermediate layer may be, for example, 15% or more, 20% or more, 25% or more, 35% or more, 40% or more, or 45% or more. By setting the thickness ratio of the intermediate layer relatively high, the impact resistance improvement effect due to the impact absorption properties of the intermediate layer can be better exhibited. In some embodiments, the thickness ratio of the intermediate layer is preferably 70% or less, more preferably 65% ​​or less, and may be 60% or less, 55% or less, 50% or less, 45% or less, or 40% or less. By setting the thickness ratio of the intermediate layer relatively low, the first and second adhesive layers in a thin double-sided adhesive sheet can exhibit good adhesion, and a decrease in impact resistance due to peeling at the interface with the adherend or at the interface between the adhesive layer and the intermediate layer can be suitably suppressed.

[0134] In some embodiments of the double-sided PSA sheet disclosed herein, the intermediate layer preferably contains a water-dispersible silicone elastomer as described above, while the first and second PSA layers are substantially free of the water-dispersible silicone elastomer. Here, "substantially" means that the water-dispersible silicone elastomer is not contained, at least intentionally. For example, this refers to the content of the water-dispersible silicone elastomer in each PSA layer being less than 0.05% by weight (e.g., less than 0.01% by weight or less than 0.001% by weight), and includes cases where neither PSA layer contains a water-dispersible silicone elastomer. By having the first and second PSA layers constituting the surface (adhesive surface) of the double-sided PSA sheet be substantially free of the water-dispersible silicone elastomer, it is possible to avoid the influence of the water-dispersible silicone elastomer on adhesive performance while enjoying the improved impact resistance that comes from including the water-dispersible silicone elastomer in the intermediate layer.

[0135] <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-based 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 subject to a release treatment on its surface and used as a release liner. Materials derived from living organisms (biomass materials), or recyclable or recycled materials (also referred to as recycled materials) may be used as constituent materials of the release liner.

[0136] 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.

[0137] <Method for producing double-sided PSA sheet> In producing a double-sided PSA sheet, the method for providing PSA layers on one side and the other side of the intermediate layer is not particularly limited. Typically, it is preferable to apply a method selected from the following to each of the one and other sides: (1) a method in which a 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 intermediate layer to transfer (laminate) it (hereinafter also referred to as the "transfer method"); and (2) a method in which a PSA composition is directly applied (typically coated) to the intermediate layer 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 intermediate layer (transfer-transfer method), or a double-sided PSA sheet may be produced by applying the transfer method to one side of the intermediate layer (typically the side on which the PSA layer is first provided) and the direct coating method to the other side (transfer-direct method). Furthermore, (3) a method (also referred to as simultaneous coating) can be adopted in which a first PSA composition (e.g., a PSA composition for forming a first PSA layer) is applied to a release liner, an intermediate layer-forming material (e.g., an aqueous dispersion of a resin) is applied thereon, and a second PSA composition (e.g., a PSA composition for forming a second PSA layer) is then applied thereon, and the entire layer is then dried or cured. This method allows the entire layer to be subjected to a single curing treatment, such as drying, which is advantageous in terms of productivity. The technology disclosed herein uses an aqueous dispersion material as the intermediate layer-forming material, which makes it difficult for the layers to become mixed (regions where components of one layer have penetrated into the other layer). This makes it possible to produce a PSA sheet by simultaneous coating, in which the materials for forming the first PSA layer, intermediate layer, and second PSA layer are successively applied. Various methods and conditions that make it difficult for mixed layers to occur can be selected for the simultaneous coating method and conditions.

[0138] <Characteristics of the double-sided PSA sheet> Although not particularly limited, the double-sided PSA sheet disclosed herein, when configured with a total thickness of 100 μm or less (preferably 80 μm or less, more preferably 70 μm or less, for example 65 μm or less), preferably has an impact resistance of approximately 0.30 J or more, more preferably approximately 0.40 J or more, and even more preferably approximately 0.50 J or more, as measured by an impact test using a DuPont impact tester. In some preferred embodiments, the double-sided PSA sheet, when configured with a total thickness of 100 μm or less (preferably 80 μm or less, more preferably 70 μm or less, for example 65 μm or less), may exhibit an impact resistance of approximately 0.70 J or more, approximately 1.00 J or more, approximately 1.20 J or more, or 1.30 J or more (for example 1.40 J or more). The upper limit of the impact resistance is not particularly limited. In some embodiments, taking into consideration ease of thinning, the impact resistance may be, for example, not more than 5.00 J, not more than 4.00 J, or not more than 3.00 J. More specifically, the impact resistance is measured by the method described in the examples below.

[0139] In some embodiments of the double-sided PSA sheet disclosed herein, the impact resistance [J] of the double-sided PSA sheet is suitably improved by 30% or more (impact resistance improvement rate) relative to the impact resistance [J] of a double-sided PSA sheet (hereinafter also referred to as a control sample) having the same composition and configuration except that the intermediate layer does not contain a water-dispersible silicone elastomer. It is preferably 40% or more, more preferably 50% or more, and even more preferably 70% or more. In some preferred embodiments, the impact resistance improvement rate may be, for example, 100% or more, 200% or more, 300% or more, 350% or more, 400% or more, or 450% or more. There is no particular upper limit to the impact resistance improvement rate, and a higher rate is more desirable from the perspective of improving impact resistance. In some embodiments, from the perspective of practical aspects such as cost and productivity, the impact resistance improvement rate may be, for example, 5000% or less, 3000% or less, or 1000% or less.

[0140] The impact resistance improvement rate is the impact resistance improvement rate of the double-sided PSA sheet to be evaluated (i.e., the double-sided PSA sheet having an intermediate layer containing a water-dispersible silicone elastomer) in E １ [J] and the impact resistance of the above control sample were measured using E ０ Based on [J], it is calculated by the following formula: Impact resistance E ０ , E １ As described above, is measured by an impact test using a DuPont impact tester, and more specifically, is measured by the method described in the Examples below. Impact resistance improvement rate [%] = (E １ -E ０ ) / E ０ ×100

[0141] The adhesive strength of the double-sided PSA sheet disclosed herein is not particularly limited. In some embodiments, the double-sided PSA sheet 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 held at 23°C and 50% RH for 30 minutes. A double-sided PSA sheet exhibiting such properties is preferably used as a highly adhesive double-sided PSA sheet that firmly secures articles or components. The peel strength from SUS plate is preferably 6 N / 20 mm or more, and may be 7 N / 20 mm or more. In some preferred embodiments, the peel strength from SUS plate is 8 N / 20 mm or more, more preferably 10 N / 20 mm or more, even more preferably 12 N / 20 mm or more, particularly preferably 14 N / 20 mm or more, and may even be 16 N / 20 mm or more. The upper limit of the peel strength from SUS plate is not particularly limited, and may be approximately 30 N / 20 mm or less (e.g., 25 N / 20 mm or less). In a double-sided pressure-sensitive adhesive sheet having pressure-sensitive adhesive surfaces on both sides, the peel strength from SUS plate on each side may be the same or different.

[0142] The peel strength of a double-sided PSA sheet from a SUS plate is measured as follows. Specifically, the release liner covering one side of the double-sided PSA sheet is peeled off, and the sheet is backed with a 25 μm thick polyethylene terephthalate (PET) film. The backed PSA sheet is cut to a size of 20 mm wide and 100 mm long to prepare a test piece. Under an environment of 23°C and 50% RH, the test piece is pressure-bonded to a stainless steel plate (SUS304BA plate) as an adherend by rolling a 2 kg roller back and forth once. After holding the test piece under an environment of 23°C and 50% RH for 30 minutes, the 180° peel strength [N / 20 mm] is measured using a tensile tester at a tensile speed of 300 mm / min in accordance with JIS Z0237. The measurement is performed three times (i.e., N=3), and the average value is used as the peel strength of the PSA sheet from a SUS plate.

[0143] <Applications> The double-sided PSA sheets disclosed herein can exhibit improved impact resistance despite their thin thickness. Taking advantage of these characteristics, the double-sided PSA sheets disclosed herein can be preferably used in various products that are desirably thin and require impact 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, they can be preferably used for fixing the above products or components. For example, there is a strong demand for portable electronic devices to be smaller and lighter, and PSA sheets for portable electronic devices are desirably thin. Furthermore, portable electronic devices are at risk of being dropped due to their usage, and PSA sheets used in portable electronic devices may be required to have impact resistance. The double-sided PSA sheets disclosed herein are suitable for such portable electronic devices.

[0144] Non-limiting examples of the portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear devices worn on the wrist like a wristwatch, modular devices worn on a part of the body with a clip or strap, eyewear devices including eyeglasses (monocular and binocular, including head-mounted devices), clothing devices attached to shirts, socks, hats, etc. as accessories, earwear devices attached to the ears like earphones), 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 devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, the term "portable" does not simply mean that the device is portable, but rather means that the device has a level of portability that allows an individual (average adult) to carry it relatively easily.

[0145] The present specification discloses the following: [1] A double-sided PSA sheet having a first PSA layer, an intermediate layer, and a second PSA layer in this order, the double-sided PSA sheet having a total thickness of 100 μm or less, the intermediate layer containing a water-dispersible silicone elastomer and a non-silicone resin. [2] The double-sided PSA sheet according to [1] above, in which the content of the water-dispersible silicone elastomer in the intermediate layer is 5 parts by weight or more and 300 parts by weight or less per 100 parts by weight of the polymer component contained in the non-silicone resin. [3] The double-sided PSA sheet according to [1] or [2] above, in which the intermediate layer contains, as the non-silicone resin, a polyurethane resin, a urethane acrylic resin, an acrylic resin, rubbers, a polyolefin resin, or a blend thereof. [4] The double-sided PSA sheet according to any of [1] to [3] above, in which the thickness ratio of the intermediate layer to the total thickness is within the range of 10% to 80%. [5] The double-sided pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the intermediate layer is formed from a water-dispersible material, and the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are both formed from water-dispersible pressure-sensitive adhesive compositions. [6] The double-sided pressure-sensitive adhesive sheet according to any one of [1] to [5] above, wherein the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are both acrylic pressure-sensitive adhesive layers containing an acrylic polymer. [7] The double-sided pressure-sensitive adhesive sheet according to [6] above, wherein the acrylic polymer has a glass transition temperature of -25°C or lower. [8] The double-sided pressure-sensitive adhesive sheet according to any one of [1] to [7] above, wherein the impact resistance measured by an impact test using a DuPont impact tester is 0.30 J or greater. [9] The double-sided pressure-sensitive adhesive sheet according to any one of [1] to [8] above, which is used to fix components in a portable electronic device.

[0146] 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, the amount of each material used is based on solid content unless otherwise specified.

[0147] Example 1 Preparation of 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 emulsion polymerization was allowed to proceed while gradually adding dropwise thereto at 60°C over 4 hours. 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 solids concentration of this acrylic polymer was 50.5%, and the sol weight-average molecular weight (Mw) was 340,000. The sol weight-average molecular weight (Mw) was determined by GPC, as described above, for the soluble component (sol component) eluted by drying an aqueous dispersion of the acrylic polymer at 100° C. for 3 minutes and then immersing it in ethyl acetate.

[0148] (Preparation of Pressure-Sensitive Adhesive Composition) To the aqueous dispersion of the acrylic polymer, 30 parts of a tackifier resin (polymerized rosin ester, trade name "Tamanol E-200NT", manufactured by Arakawa Chemical Industries, Ltd., softening point 150°C) were added relative to 100 parts of the solid content of the aqueous dispersion, and 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 to prepare a pressure-sensitive adhesive composition.

[0149] (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 19 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.

[0150] (Formation of Intermediate Layer) To an aqueous dispersion of polyurethane resin (polyester skeleton) (trade name "ADEKA BONTITAR HUX-380" manufactured by ADEKA Corporation), 100 parts by solids of an aqueous dispersion A of a silicone elastomer (trade name "DOWSIL 33 Additive" manufactured by Dow-Toray Industries, Inc., an aqueous dispersion of epoxy group-containing silicone elastomer particles, average particle size 3 μm; hereinafter, the silicone elastomer may also be referred to as "Filler A") were added and mixed with stirring, relative to 100 parts solids of the aqueous dispersion. Next, a thickener (trade name "ADEKA NOL UH-541VF" manufactured by ADEKA Corporation) was added so that the viscosity of the coating liquid after addition was 3.0 Pa s, and 1 part of a leveling agent (trade name "PELEX OT-P" manufactured by Kao Corporation) was further added. The obtained coating liquid (composition for forming an intermediate layer) was applied to the silicone-treated surface of a 38 μm PET release liner (product name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) so that the thickness after drying would be 12 μm, and the coating was dried by heating at 100°C for 3 minutes to produce the intermediate layer (intermediate layer film) according to this example.

[0151] (Preparation of double-sided PSA sheet) One side (exposed side) of the PSA layer was bonded to one side of the intermediate layer. Next, the release liner was removed, and another PSA layer was bonded to the other side of the intermediate layer to obtain a laminate having a first PSA layer / intermediate layer / second PSA layer structure with a total thickness of 50 μm. 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 produce a double-sided PSA sheet according to this example.

[0152] Examples 2 to 7 An intermediate layer according to each example was obtained in the same manner as in Example 1, except that the thickness of the intermediate layer was changed as shown in Table 1 and the amount of Filler A used per 100 parts of polyurethane was changed as shown in Table 1. A double-sided PSA sheet according to each example was produced in the same manner as in Example 1, except that the obtained intermediate layer was used.

[0153] Example 8 An intermediate layer was obtained in the same manner as in Example 4, except that the aqueous dispersion A of silicone elastomer used to prepare the intermediate layer in Example 4 was changed to an aqueous dispersion B of silicone elastomer (product name "DOWSIL BY 29-119", manufactured by Dow-Toray Industries, Inc., aqueous dispersion of silicone elastomer particles, average particle size 4 μm; hereinafter, the silicone elastomer is also referred to as "filler B"). A double-sided PSA sheet according to this example was produced in the same manner as in Example 1, except that the obtained intermediate layer was used.

[0154] Example 9 (Formation of Intermediate Layer) A reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser was charged with 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, and the mixture was purged with nitrogen at 60°C for 1 hour with stirring. Then, 0.10 parts of a polymerization initiator (trade name "VA-057", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. An emulsion of 85 parts of 2EHA, 13 parts of MA, 1.25 parts of AA, 0.75 parts of MAA, 0.025 parts of t-dodecanethiol, 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 in 28 parts of distilled water was gradually added dropwise to the mixture at 60°C over 4 hours to allow emulsion polymerization to proceed. After further maintaining the temperature 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 to prepare an aqueous dispersion of an acrylic polymer (solids concentration 50.5%). To this aqueous dispersion of the acrylic polymer, 30 parts of a tackifier resin (trade name "Tamanol E-200NT", manufactured by Arakawa Chemical Industries, Ltd.) were added per 100 parts of the acrylic polymer, and 1 part of a leveling agent (trade name "Pelex OT-P", manufactured by Kao Corporation) was further added. The pH was then adjusted to 8 using 10% aqueous ammonia to obtain an aqueous dispersion of an acrylic resin for forming an intermediate layer. To the aqueous dispersion of the acrylic resin, 10 parts of the aqueous dispersion A of the silicone elastomer (filler A) were added based on solids per 100 parts of the acrylic polymer, and the mixture was stirred and mixed. The obtained coating liquid (composition for forming an intermediate layer) was applied to the silicone-treated surface of a 38 μm PET release liner (product name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) so that the thickness after drying would be 25 μm, and the coating was dried by heating at 100°C for 3 minutes to produce the intermediate layer (intermediate layer film) according to this example.

[0155] (Preparation of Double-Sided Pressure-Sensitive Adhesive Sheet) A double-sided pressure-sensitive adhesive sheet according to this example was prepared in the same manner as in Example 1, except that the intermediate layer obtained above was used.

[0156] Example 10 An intermediate layer according to this example was obtained in the same manner as in Example 9, except that the amount of Filler A used relative to 100 parts of acrylic polymer was changed as shown in Table 1. A double-sided PSA sheet according to this example was produced in the same manner as in Example 1, except that this intermediate layer was used.

[0157] Example 11 (Formation of Intermediate Layer) 116 g of polytetramethylene ether glycol (trade name "PTMG1000", manufactured by Mitsubishi Chemical Corporation) was placed in a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and 333.3 g of acrylic monomer (106.1 g of n-butyl acrylate (BA), 212.2 g of methyl methacrylate (MMA), and 15 g of acrylic acid (AA)) was added and dissolved, followed by nitrogen substitution with stirring for approximately 1 hour. The system was heated in a water bath set at 65°C, and after confirming that the temperature of the solution in the reaction vessel had reached 65°C, 33.9 g of 1,3-bis(isocyanatomethyl)cyclohexane (H6-XDI, manufactured by Mitsui Chemicals, Inc.) was added (NCO / OH ratio = 1.5). After confirming that the solution was generating heat, the temperature was maintained by cooling. After the heat generation subsided, 12 mg of dibutyltin(IV) dilaurate (Wako Pure Chemical Industries, Ltd.) was added and the mixture was allowed to react at 65°C for 2 hours. Next, 16.8 g of 4-hydroxybutyl acrylate (4HBA) was added and the mixture was allowed to react for another 2 hours, after which the system was cooled. In this way, a urethane / acrylic monomer mixed solution containing a urethane polymer having an acryloyl group derived from 4HBA introduced therein and an acrylic monomer was obtained.

[0158] To 200 g of the obtained urethane / acrylic monomer mixed solution, 6 g (3 parts per 100 parts of the mixed solution) of a reactive surfactant (trade name "Aqualon KH-1025", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was added on a solids basis and mixed. Distilled water was added to this mixture in an amount such that the concentration of the urethane / acrylic monomer mixed solution became 45%, and then 0.2 g (0.1 part per 100 parts of the mixed solution) of 3-methacryloxypropyltrimethoxysilane (silane coupling agent, trade name "KBM-503", manufactured by Shin-Etsu Chemical Co., Ltd.) was added. The mixture was emulsified using a high-speed emulsifying disperser (Homomixer, manufactured by Primix Corporation) and further subjected to a micronization treatment using a wet micronization device (Starburst Mini, manufactured by Sugino Machine Co., Ltd.) to obtain a median diameter (d ５０ An emulsion having a median diameter (d ) of less than 500 nm was obtained. ５０ ) was measured using a particle size distribution measuring device based on the laser diffraction / scattering method.

[0159] 400 g of the resulting emulsion was 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 for approximately 2 hours while stirring. The system was heated in a water bath set to 60°C, and 120 mg of a polymerization initiator (product name "VA-057", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. The reaction was carried out for 5 hours while maintaining the temperature of the contents of the reaction vessel at 60°C, and then the system was cooled to obtain an aqueous dispersion of a urethane acrylic polymer copolymerized with 3-methacryloxypropyltrimethoxysilane.

[0160] To the aqueous dispersion of the urethane acrylic polymer, 10 parts of the aqueous dispersion A of the silicone elastomer (filler A) were added based on the solids content per 100 parts of the aqueous dispersion, and the mixture was stirred and mixed. The pH was then adjusted to 8 with 10% aqueous ammonia. The resulting coating liquid (intermediate layer-forming composition) was applied to the silicone-treated surface of a 38 μm PET release liner (product name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) to a dry thickness of 25 μm, and the coating was dried by heating at 100° C. for 3 minutes to produce the intermediate layer (intermediate layer film) according to this example.

[0161] (Preparation of Double-Sided Pressure-Sensitive Adhesive Sheet) A double-sided pressure-sensitive adhesive sheet according to this example was prepared in the same manner as in Example 1, except that the intermediate layer obtained above was used.

[0162] Example 12 An intermediate layer according to this example was obtained in the same manner as in Example 11, except that the amount of Filler A used relative to 100 parts of urethane acrylic polymer was changed as shown in Table 1. A double-sided PSA sheet according to this example was produced in the same manner as in Example 1, except that this intermediate layer was used.

[0163] Example 13 A double-sided PSA sheet according to this example was produced in the same manner as in Example 4, except that the thickness of the first PSA layer and the thickness of the second PSA layer were changed as shown in Table 1.

[0164] Examples 14 to 16 An intermediate layer according to each example was obtained in the same manner as in Examples 1, 2, and 7, except that Filler A was not used. A double-sided PSA sheet according to each example was produced in the same manner as in Example 1, except that the obtained intermediate layer was used.

[0165] Example 17 An intermediate layer was obtained in the same manner as in Example 4, except that the aqueous dispersion A of silicone elastomer used to prepare the intermediate layer in Example 4 was changed to an aqueous dispersion of silica particles (product name "Snowtex ST-50T", manufactured by Nissan Chemical Industries, Ltd.; hereinafter, the silica particles are also referred to as "Filler C"). A double-sided PSA sheet according to this example was produced in the same manner as in Example 1, except that the obtained intermediate layer was used.

[0166] Examples 18 and 19 An intermediate layer according to each example was obtained in the same manner as in Examples 9 and 13, respectively, except that Filler A was not used. A double-sided PSA sheet according to each example was produced in the same manner as in Example 1, except that the obtained intermediate layer was used.

[0167] <Evaluation> A double-sided PSA sheet whose adhesive surface was protected by a release liner was punched into a frame shape with a width of 2 mm and an outer diameter of 24.5 mm square to obtain a frame-shaped PSA sheet. In addition, a stainless steel plate (SUS304BA) with a thickness of 2 mm and an outer diameter of 50 mm square with a 20 mm square hole in the center, and a square stainless steel plate (SUS304BA) with a thickness of 3 mm and a 25 mm square were prepared. The frame-shaped PSA sheet with the release liner removed was placed between the two stainless steel plates so that the two stainless steel plates and the frame-shaped PSA sheet were arranged point-symmetrically from the center (so that the frame-shaped PSA sheet surrounded the hole in the perforated stainless steel plate), and pressure-bonded under conditions of 62 N and 10 seconds with uniform pressure, and then left to stand at 80 ° C for 30 minutes, and then returned to 23 ° C overnight. This was used as a test specimen. A cylindrical measurement stage measuring 50 mm in length, 49 mm in outer diameter, and 43 mm in inner diameter was placed on the base of a DuPont impact tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.). The test specimen was placed on the measurement stage, with a square stainless steel plate (non-perforated stainless steel plate) facing downward, in a point-symmetrical arrangement relative to the center of the measurement stage. The upper perforated stainless steel plate of the test specimen was supported on the measurement stage, and the lower square stainless steel plate was attached to the perforated stainless steel plate by the frame-shaped adhesive sheet and positioned so as to enter the hollow portion of the measurement stage. A stainless steel impact core with a tip radius of 3.1 mm was placed on the test specimen (specifically, on the lower square stainless steel plate), and the weight was dropped onto the impact core (shooting mold) at 23 °C and 50% RH under the following conditions (weight and drop height). That is, the weight of the falling weight and the height of the drop were changed in 50 mm increments from 50 mm to 500 mm with a weight of 50 g, in 50 mm increments from 300 mm to 500 mm with a weight of 100 g, in 50 mm increments from 350 mm to 500 mm with a weight of 150 g, in 50 mm increments from 350 mm to 500 mm with a weight of 200 g, in 50 mm increments from 400 mm to 500 mm with a weight of 200 g, and in 50 mm increments from 350 mm to 500 mm with a weight of 300 g, so that the energy increased until peeling occurred. In this case, the test was not repeated for energy that had already been measured, and the load and height were set so that the energy would not overlap. The integrated energy up to the condition just before peeling was taken as the impact absorption energy (J).The energy was calculated from the load x height. The measurement was carried out five times (i.e., N=5), and the average value was used as the evaluation result of the impact resistance.

[0168] The outline of each example and the evaluation results are shown in Tables 1 and 2.

[0169]

[0170]

[0171] As shown in Tables 1 and 2, the double-sided PSA sheets of Examples 1 to 13, which had an intermediate layer containing a water-dispersible silicone elastomer and a non-silicone resin, all exhibited good impact resistance in impact tests, despite having a total thickness of 100 μm or less. Furthermore, for example, the double-sided PSA sheet of Example 13 exhibited an impact resistance improvement rate of 389% relative to the PSA sheet of Example 19, which corresponds to the control sample, demonstrating excellent impact resistance improvement. The double-sided PSA sheets of Examples 1 to 10 also exhibited an impact resistance improvement of 40% or more relative to their respective control samples. Meanwhile, the impact resistance of the double-sided PSA sheets of Examples 14 to 16 and Examples 18 to 19, which used intermediate layers that did not contain a water-dispersible silicone elastomer, was clearly lower than that of the corresponding double-sided PSA sheets (double-sided PSA sheets with the same composition and configuration except for the inclusion of a water-dispersible silicone elastomer in the intermediate layer). Furthermore, the double-sided PSA sheet of Example 17, in which the water-dispersible silicone elastomer in the intermediate layer of Example 4 was replaced with silica particles, exhibited lower impact resistance compared to the double-sided PSA sheet of Example 15.

[0172] 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.

[0173] REFERENCE SIGNS LIST 1 double-sided adhesive sheet 11 first adhesive layer 11A first adhesive surface 12 second adhesive layer 12A second adhesive surface 15 intermediate layer 21 release liner

Claims

1. A double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer, an intermediate layer, and a second pressure-sensitive adhesive layer in that order, the sheet having a total thickness of 100 μm or less, the intermediate layer containing a water-dispersible silicone elastomer and a non-silicone resin.

2. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the content of the water-dispersible silicone elastomer in the intermediate layer is 5 parts by weight or more and 300 parts by weight or less per 100 parts by weight of the polymer component contained in the non-silicone resin.

3. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the intermediate layer contains, as the non-silicone resin, a polyurethane resin, a urethane acrylic resin, an acrylic resin, rubbers, a polyolefin resin, or a blend thereof.

4. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the thickness ratio of said intermediate layer to said total thickness is within the range of 10% to 80%.

5. The double-sided adhesive sheet according to claim 1 or 2, wherein the intermediate layer is formed from a water-dispersible material, and the first adhesive layer and the second adhesive layer are both formed from a water-dispersible adhesive composition.

6. The double-sided adhesive sheet according to claim 1 or 2, wherein the first adhesive layer and the second adhesive layer are both acrylic adhesive layers containing an acrylic polymer.

7. The double-sided pressure-sensitive adhesive sheet according to claim 6, wherein the glass transition temperature of the acrylic polymer is −25° C. or lower.

8. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, which has an impact resistance of 0.30 J or more as measured by an impact test using a DuPont impact tester.

9. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, which is used to fasten components in a portable electronic device.

Images