Adhesive sheet

Abstract

To provide an adhesive sheet that can be applied to a wide range of manufacturing processes and exhibits excellent chemical resistance.SOLUTION: An adhesive sheet comprising a core layer and an adhesive layer laminated on one or both surfaces of the core layer, wherein the core layer contains a polymer having a carbonyl group, and the adhesive layer contains a hydrazide compound.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Generally, adhesives (also called pressure-sensitive adhesives; the same applies hereinafter) are in a soft solid (viscoelastic) state at temperatures around room temperature, and have the property of easily adhering to an adherend when pressure is applied. Utilizing this property, 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 multilayer adhesive sheets such as substrate-attached adhesive tapes having an adhesive layer on a supporting substrate. Patent documents 1 and 2 are cited as technical documents relating to this type of adhesive sheet. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-71863 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-14665 Summary of the Invention [Problem to be solved by the invention]

[0004] Adhesive sheets used for bonding components in portable electronic devices that are at risk of being dropped are required to have the ability to withstand impacts such as dropping and maintain their bonding (hereinafter also referred to as impact resistance). For example, Patent Document 1 attempts to improve impact resistance by incorporating an impact-absorbing foam sheet into the adhesive sheet. In this type of adhesive sheet, the foam sheet deforms when an impact is applied, thereby absorbing the impact and improving the impact resistance of the adhesive sheet. In such multilayer adhesive sheets having multiple layers, improving the adhesion at the interface between each layer is an important point in improving performance such as impact resistance.

[0005] Furthermore, adhesive sheets used for bonding components in electronic devices are required to maintain bonding when exposed to chemicals (hereinafter also referred to as chemical resistance). Chemicals that come into contact with an adhesive sheet penetrate primarily through the interfaces of each layer, causing the layers to swell and potentially reducing the adhesion between the layers. Therefore, in order to improve chemical resistance, it is effective to improve the adhesion at the interfaces of each layer in addition to improving the resistance of the layers themselves to chemicals.

[0006] Regarding interlayer adhesion, for example, Patent Document 2 addresses the use of a polymer containing acidic groups in a pressure-sensitive adhesive layer, and coating the pressure-sensitive adhesive layer with a composition containing an amino-group-containing polymer to form an adjacent layer, thereby increasing interlayer adhesion through the interaction (chemical bond) between the acidic and amino groups. However, the technology described in Patent Document 2 requires a step of directly coating the composition for forming the adjacent layer on the pressure-sensitive adhesive layer when producing a multilayer pressure-sensitive adhesive sheet, which limits the freedom of selection of a pressure-sensitive adhesive sheet production method. Furthermore, there is still room for improvement in terms of improving the chemical resistance of each layer.

[0007] The present invention was created in view of the above circumstances, and has an object to provide a pressure-sensitive adhesive sheet that is applicable to various production methods and has high chemical resistance. [Means for solving the problem]

[0008] The inventors have discovered that chemical resistance can be improved by adopting a configuration in which a core layer and an adhesive layer are laminated together, the core layer containing a polymer having a carbonyl group, and the adhesive layer containing a hydrazide compound.

[0009] According to this specification, a pressure-sensitive adhesive sheet is provided that includes a core layer and a pressure-sensitive adhesive layer laminated on one or both sides of the core layer. The core layer contains a polymer having a carbonyl group. The pressure-sensitive adhesive layer also contains a hydrazide compound. With this configuration, the hydrazide compound contained in the pressure-sensitive adhesive layer migrates into the core layer and reacts with the carbonyl group of the polymer having a carbonyl group to form a ketohydrazide crosslink. As crosslinking of the polymer contained in the core layer progresses in this manner, the chemical resistance of the pressure-sensitive adhesive sheet tends to improve. Furthermore, with this configuration, even if a manufacturing method is applied in which the core layer and the pressure-sensitive adhesive layer are separately prepared and then bonded together to produce a pressure-sensitive adhesive sheet, the ketohydrazide crosslinking reaction of the polymer in the core layer proceeds smoothly, and the chemical resistance of the resulting pressure-sensitive adhesive sheet tends to improve. Therefore, a pressure-sensitive adhesive sheet with the above configuration tends to have a high degree of freedom in selecting a manufacturing method.

[0010] In some embodiments, the maximum stress of the core layer measured in a tensile test conducted at a temperature of 23°C and a tensile speed of 50 mm / min is 1.0 MPa or less. The maximum stress here refers to the maximum stress measured from the start of tension to breakage in the tensile test. The maximum stress is an indicator of the hardness of the core layer, and the smaller the maximum stress, the softer the core layer tends to be. A configuration including a core layer with a maximum stress of 1.0 MPa or less tends to improve adhesion between the core layer and the pressure-sensitive adhesive layer, and also tends to improve chemical resistance and impact resistance.

[0011] In some embodiments, the PSA sheet has an adhesive strength retention rate after alcohol immersion of 80% or more. Here, the adhesive strength retention rate after alcohol immersion [%] is calculated from the ratio of the adhesive strength after alcohol immersion F1 [N / 5mm] to the initial peel strength F0 [N / 5mm] (F1 / F0 × 100). The initial peel strength F0 [N / 5mm] is the peel strength measured under conditions of a tensile speed of 300 mm / min and a peel angle of 180° for a 5 mm wide PSA sheet attached to a stainless steel plate as an adherend. Furthermore, the adhesive strength after alcohol immersion F1 [N / 5mm] is the peel strength measured under conditions of a tensile speed of 300 mm / min and a peel angle of 180° after immersing a 5 mm wide PSA sheet attached to a stainless steel plate as an adherend in a test solution prepared by mixing isopropyl alcohol and water in a weight ratio of 30:70 for 4 days under an environment of 60°C. When the adhesive strength retention rate after alcohol immersion required as described above is equal to or greater than the above lower limit, a PSA sheet with excellent chemical resistance is easily achieved.

[0012] In some embodiments, the core layer comprises a blend of an acrylic polymer and a styrene-based block copolymer. By including a styrene-based block copolymer in the core layer, it is easy to achieve a core layer with suitable softness. This is advantageous for improving the adhesion at the interface between the core layer and the pressure-sensitive adhesive layer, contributing to improved chemical resistance. Furthermore, by including an acrylic polymer in the core layer, it is easy to improve interlayer strength and chemical resistance.

[0013] In some embodiments, the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive. This configuration tends to improve at least one of the interlayer strength between the pressure-sensitive adhesive layer and the core layer and the peel strength from the adherend. Improved interlayer strength also tends to contribute to improved chemical resistance and impact resistance of the pressure-sensitive adhesive sheet.

[0014] In some embodiments, the core layer is formed from a hot-melt composition, which can be formed by coating in a heated, molten state that is substantially free of organic solvents, and is therefore preferable from the standpoints of productivity and reducing environmental impact.

[0015] In some embodiments, the PSA layer is formed from a water-dispersed PSA composition (specifically, an aqueous dispersion of a PSA layer-forming material such as a polymer). In other words, in some embodiments, the PSA constituting the PSA layer is a water-dispersed PSA (emulsion PSA). With this configuration, the PSA layer can be produced substantially without using an organic solvent, thereby realizing a PSA sheet with low environmental impact.

[0016] The PSA sheets disclosed herein tend to have excellent chemical resistance and excellent impact resistance, and are therefore preferably used for joining components of portable electronic devices that require good chemical resistance and impact resistance. Therefore, this specification provides a portable electronic device that uses any of the PSA sheets disclosed herein, in other words, a portable electronic device that includes the PSA sheet.

[0017] The technology disclosed herein provides a method for producing a pressure-sensitive adhesive sheet. The method includes forming a core layer from a hot-melt composition, forming a pressure-sensitive adhesive layer from a water-dispersed pressure-sensitive adhesive composition, and laminating the pressure-sensitive adhesive layer on one or both surfaces of the core layer. The hot-melt composition includes an acrylic polymer A obtained by suspension polymerization of a monomer component including a monomer having a carbonyl group. The water-dispersed pressure-sensitive adhesive composition includes an acrylic polymer B obtained by emulsion polymerization of the monomer component, and a hydrazide compound. This method allows at least a portion of the hydrazide compound contained in the pressure-sensitive adhesive composition to migrate to the core layer, forming ketohydrazide crosslinks in the core layer, making it easy to obtain a pressure-sensitive adhesive sheet with improved chemical resistance. Furthermore, the method allows a pressure-sensitive adhesive sheet to be produced substantially without using organic solvents, thereby realizing a pressure-sensitive adhesive sheet with low environmental impact. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional view illustrating a configuration of a pressure-sensitive adhesive sheet according to one embodiment. [Figure 2]FIG. 4 is a schematic cross-sectional view showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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.

[0020] In this specification, the term "interlayer" in terms such as "interlayer strength" and "interlayer adhesion" refers to the space between the core layer and the pressure-sensitive adhesive layer unless otherwise specified.

[0021] In this specification, the term "carbonyl group" does not include a carboxy group (-COOH) contained in a carboxylic acid. A typical example of a "carbonyl group" in this specification is a ketone (R 1 -CO-R 2 ) (sometimes referred to as a "keto group" or "ketone group") and the -C(=O)- moiety in aldehyde (R-CHO) (sometimes referred to as an "aldehyde group").

[0022] 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).

[0023] 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.

[0024] In this specification, the term "acrylic polymer" refers to a polymer containing more than 50% by weight of monomer units derived from an acrylic monomer as the monomer units constituting the polymer. The acrylic monomer refers to a monomer derived from a monomer having at least one (meth)acryloyl group in one molecule.

[0025] In this specification, "styrene-based block copolymer" refers to a polymer having at least one styrene block. The styrene block refers to a segment in which styrene is the main monomer. A segment consisting essentially of styrene is a typical example of the styrene block referred to here. In this specification, "hydrogenated styrene-based block copolymer" refers to a styrene-based block copolymer containing a hydrogenated product in which at least a portion has been hydrogenated (hydrogen atoms have been added). Furthermore, "styrene-ethylene-butylene-styrene block copolymer" refers to a polymer in which at least a portion of the double bonds of a styrene-butadiene block copolymer have been hydrogenated. Here, "styrene-butadiene block copolymer" refers to a polymer having at least one styrene block and at least one butadiene block (a segment in which butadiene is the main monomer).

[0026] In this specification, the "styrene content" of a styrene block copolymer (including hydrogenated styrene block copolymers) refers to the weight ratio of the styrene component to the total weight of the block copolymer. The styrene content can be measured by NMR (nuclear magnetic resonance spectroscopy). The proportion of diblock units in a styrene-based block copolymer (hereinafter sometimes referred to as the "diblock unit ratio" or "diblock ratio") is determined by the following method. Specifically, the styrene-based block copolymer is dissolved in tetrahydrofuran (THF), and high-performance liquid chromatography is performed using two liquid chromatography columns (GS5000H and G4000H, manufactured by Tosoh Corporation) connected in series (a total of four columns, two columns each) at a temperature of 40°C and a flow rate of 1 mL / min, using THF as the mobile phase. The peak area corresponding to the diblock unit is measured from the resulting chart. The diblock unit ratio is then determined by calculating the percentage of the peak area corresponding to the diblock unit relative to the total peak area.

[0027] In this specification, the term "hot melt composition" refers to a composition used in a hot melt process, which is a method of forming a molded product such as a sheet by pressing, coating, or the like, a composition in a heated, molten state that is substantially free of organic solvents.

[0028] In this specification, the term "water-dispersed" refers to a form in which at least a portion of the components are dispersed in water. For example, a "water-dispersed PSA composition" refers to a composition that contains a PSA composition and water, and in which at least a portion of the PSA composition is dispersed in water. The water-dispersed type also includes a suspended state and an emulsified state.

[0029] <Adhesive sheet composition> The pressure-sensitive adhesive sheet disclosed herein has a core layer and a pressure-sensitive adhesive layer laminated on at least one surface of the core layer. The concept of pressure-sensitive adhesive sheet here may include what are called pressure-sensitive adhesive tapes, pressure-sensitive adhesive labels, pressure-sensitive adhesive films, 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.

[0030] The pressure-sensitive adhesive sheet disclosed herein may be in the form of, for example, a single-sided pressure-sensitive adhesive sheet having a cross-sectional structure schematically shown in FIG. 1. This pressure-sensitive adhesive sheet 1 is configured as a single-sided pressure-sensitive adhesive sheet comprising a core layer 10 having a first surface 10A and a second surface 10B, and a pressure-sensitive adhesive layer 21 provided on the first surface 10A side of the core layer 10. The pressure-sensitive adhesive layer 21 is fixedly provided on the first surface 10A side of the core layer 10, i.e., without the intention of separating the pressure-sensitive adhesive layer 21 from the core layer 10. As shown in FIG. 1, the pressure-sensitive adhesive sheet 1 before use may be a component of a release-liner-attached pressure-sensitive adhesive sheet 100 in a form in which the surface (adhesive surface) 21A of the pressure-sensitive adhesive layer 21 is protected by a release liner 31, at least the side facing the pressure-sensitive adhesive layer 21 being a release surface. Alternatively, the release liner 31 may be omitted, and the core layer 10 may be used, with the second surface 10B being a release surface, and the pressure-sensitive adhesive sheet 1 may be rolled up to protect the adhesive surface 21A by abutting against the second surface (back surface) 10B of the core layer 10.

[0031] Furthermore, 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 Figure 2. This PSA sheet 2 is configured as a double-sided PSA sheet comprising a core layer 10 having a first surface 10A and a second surface 10B, a first PSA layer 21 fixedly provided on the first surface 10A side, and a second PSA layer 22 fixedly provided on the second surface 10B side. As shown in Figure 2, the PSA sheet 2 before use may be a component of a release-liner PSA sheet 200 in a form in which the surface (first adhesive surface) 21A of the first PSA layer 21 and the surface (second adhesive surface) 22A of the second PSA layer 22 are protected by release liners 31, 32. Alternatively, the release liner 32 may be omitted, and a release liner 31 having release surfaces on both sides may be used, which may be superimposed on the PSA sheet 2 and wound into a spiral shape to form a release-liner PSA sheet in a form in which the second adhesive surface 22A is protected by contacting the back surface of the release liner 31 (roll form).

[0032] The release liner may be a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, or a release liner made of a low-adhesion material such as a polyolefin resin (e.g., polyethylene or polypropylene) or a fluorine-based resin. The release treatment layer may be formed by surface treating the liner substrate with a release agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. In the field of electronic devices, a release liner having a release treatment layer on the surface of a resin film or a release liner made of a low-adhesion material is preferred from the viewpoint of avoiding the generation of paper dust.

[0033] The present inventors discovered that the chemical resistance of a pressure-sensitive adhesive sheet can be improved by including a polymer having a carbonyl group in the core layer and further including a hydrazide compound in the pressure-sensitive adhesive layer, and thus completed the present invention.

[0034] <Core layer> The PSA sheets disclosed herein have a core layer. Although not particularly limited, in some embodiments, the core layer disclosed herein may be an elastomer layer that has the ability to absorb impact forces when an impact is applied to the PSA sheet. From this perspective, in some embodiments, the core layer disclosed herein can be rephrased as an impact-absorbing layer.

[0035] The core layer disclosed herein contains a polymer having a carbonyl group (hereinafter also referred to as a "carbonyl group-containing polymer"). In some preferred embodiments, the core layer is an elastomer layer formed from a resin composition (hereinafter also referred to as a "core layer composition") containing the carbonyl group-containing polymer as a base polymer.

[0036] (base polymer) The core layer disclosed herein comprises one or more carbonyl group-containing polymers. Other than the carbonyl group-containing polymer, the polymer material contained in the core layer is not particularly limited. In some embodiments, the core layer comprises a polymer material that can be used in the field of pressure-sensitive adhesives as the base polymer (i.e., a component that accounts for more than 50% by weight of the polymer components). The base polymer contained in the core layer can be one or more of various rubber-like polymers, such as acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine-containing polymers. Here, "the core layer comprising two or more polymers as base polymers" includes the core layer containing a blend of the individual polymers, which is considered to be a single base polymer.

[0037] (acrylic polymer) In some preferred embodiments, the core layer contains an acrylic polymer as a base polymer. 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. In some preferred embodiments, the acrylic polymer is a polymer having a carbonyl group (i.e., a carbonyl group-containing polymer).

[0038] As the alkyl(meth)acrylate, for example, a compound represented by the following formula (1) can be suitably used. CH2=C(R 1 )COOR 2 (1) Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. 2 is a chain alkyl group having 1 to 20 carbon atoms (hereinafter, this range of carbon atoms is referred to as "C 1-20From the viewpoint of the storage modulus of the adhesive, R 2 C 1-14 alkyl(meth)acrylates, which are chain alkyl groups of the formula R 2 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.

[0039] R 2 C 1-20 Examples of alkyl(meth)acrylates, which are chain alkyl groups, include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, s-butyl(meth)acrylate, pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, and isooctyl(meth)acrylate. Examples of alkyl (meth)acrylates include butyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These alkyl (meth)acrylates can be used alone or in combination of two or more. Preferred alkyl (meth)acrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

[0040] The technology disclosed herein is a method for preparing a polymerizable compound in which the monomer component is R 2 C 4-10Among the alkyl (meth)acrylates contained in the monomer component, R 2 C 4-10 Alkyl (meth)acrylate (C 4-10 This method can be preferably implemented 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 an embodiment in which a chain alkyl (meth)acrylate is used, the proportion of 2EHA is not particularly limited, and can be determined by the above C 4-10 In the chain alkyl (meth)acrylate, it is suitable that the amount is more than 50% by weight, and from the viewpoint of impact resistance, it 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).

[0041] The alkyl(meth)acrylate is R 2 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 less than C4 or C 10 The total amount of alkyl(meth)acrylates (which are chain alkyl groups of more than 1000 carbon atoms) 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 those represented by the formula (1) R 2 C 1-3 Preferably, alkyl(meth)acrylates, which are chain alkyl groups, are used. Specific examples include methyl acrylate (MA), methyl methacrylate (MMA), and ethyl acrylate (EA). Of these, MA is more preferred.

[0042] The secondary monomer copolymerizable with the alkyl (meth)acrylate main monomer can be useful for introducing crosslinking points into the acrylic polymer and for increasing the cohesive strength of the acrylic polymer. As the secondary monomer, for example, the following functional group-containing monomer components can be used alone or in combination of two or more: Carboxy group-containing monomers: for example, 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: for example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate; 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. Monomers having an epoxy group: for example, glycidyl (meth)acrylate, methyl glycidyl (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, 3-(meth)acryloxypropylmethyldiethoxysilane.

[0043] The functional group-containing monomers can be used alone or in combination of two or more. In some preferred embodiments, a keto group-containing monomer is preferably used from the viewpoint of introducing a carbonyl group into the acrylic polymer. Among the keto group-containing monomers, monomers having a -COCH group (e.g., a -CHCOCH group) in the molecule, such as diacetone (meth)acrylamide and diacetone (meth)acrylate, are preferred, and diacetone acrylamide (DAAM) is particularly preferred.

[0044] In some embodiments, carboxyl group-containing monomers, hydroxyl group-containing monomers, and cyano group-containing monomers may also be preferably used because they can effectively introduce crosslinking points and improve cohesion. Of the carboxyl group-containing monomers, AA and MAA are preferred.

[0045] 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. Generally, in order to achieve a good balance between cohesive strength and adhesiveness, the proportion of the functional group-containing monomer is preferably about 0.1% by weight or more (e.g., 0.5% by weight or more, typically 1% by weight or more). Furthermore, in consideration of the adhesive effect of alkyl (meth)acrylate, the proportion of the functional group-containing monomer in the total monomer components is preferably about 40% by weight or less (e.g., 30% by weight or less, typically 20% by weight or less).

[0046] When a keto group-containing monomer is copolymerized with an acrylic polymer, the proportion of the keto group-containing monomer in the total monomer components is typically 0.05 wt% or more, preferably 0.1 wt% or more, more preferably 0.3 wt% or more, and even more preferably 0.5 wt% or more, and may be 0.6 wt% or more, 0.7 wt% or more, 0.8 wt% or more, or 0.9 wt% or more. As the proportion of the keto group-containing monomer increases, the number of reaction sites available for reaction with the hydrazino group of the hydrazide compound contained in the adhesive layer increases, facilitating the formation of ketohydrazide crosslinks. A core layer formed with ketohydrazide crosslinks is less susceptible to swelling upon contact with chemicals, making it easier to achieve a pressure-sensitive adhesive sheet with improved chemical resistance. On the other hand, if there are too many crosslinks with the hydrazide compound, the core layer becomes too hard, which can reduce interlayer adhesion and reduce chemical resistance. From this viewpoint, the proportion of the keto group-containing monomer in the total monomer components is suitably 10% by weight or less, and may be, for example, 5% by weight or less (less than 5% by weight), 4% by weight or less, 3% by weight or less, 2% by weight or less, 1.5% by weight or less, or 1.2% by weight or less.

[0047] 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 usually 0.5% by weight or more, preferably 1% by weight or more, more preferably 2% by weight or more, and even more preferably 3% by weight or more, and may be 4% by weight or more, 5% by weight or more, 6% by weight or more, or 7% by weight or more. The proportion of the carboxyl group-containing monomer in the total monomer components is suitably 15% by weight or less, and may be, for example, 10% by weight or less, 8% by weight or less, or 6% by weight or less.

[0048] 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. Examples of the monomer include aromatic ring-containing (meth)acrylates such as (meth)acrylates (e.g., 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; and vinyl ether-based monomers such as methyl vinyl ether and ethyl vinyl ether.

[0049] 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.

[0050] 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).

[0051] The acrylic polymer in the technology disclosed herein is suitably designed so that the glass transition temperature (Tg) of the polymer is −25° C. or lower (typically −75° C. or higher and −25° C. or lower). The Tg of the acrylic polymer may be preferably −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). Impact resistance tends to be improved by using an acrylic polymer with a low Tg. In addition, 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.

[0052] Here, the Tg of an acrylic polymer refers to the Tg calculated by the Fox equation based on the composition of the monomer components used in the synthesis of the polymer. The Fox equation, as shown below, is a relational expression 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 above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio by weight), and Tgi represents the glass transition temperature (unit: K) of the homopolymer of monomer i.

[0053] The glass transition temperature of the homopolymer used to calculate Tg is determined based on the value described in the publicly available literature. For example, for the following monomers, the following values ​​are used as the glass transition temperatures of the homopolymers of the monomers: 2-Ethylhexyl acrylate -70℃ n-Butyl acrylate -55℃ Methyl methacrylate 105℃ Methyl acrylate 8℃ Vinyl acetate 32℃ Acrylic acid 106℃ Methacrylic acid 228℃

[0054] 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. If multiple values ​​are given in this document, the highest value shall be used.

[0055] 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 the polymerization solvent were charged into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture was stirred for 1 hour while passing nitrogen gas through. After removing oxygen from the polymerization system in this manner, the temperature was raised to 63°C and the reaction was continued for 10 hours. The mixture was then cooled to room temperature to obtain a homopolymer solution with a solids concentration of 33% by weight. This homopolymer solution was then cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) approximately 2 mm thick. This test sample was punched out into a disk 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). Viscoelasticity was measured in shear mode at a temperature range of -70 to 150°C and a heating rate of 5°C / min. The peak top temperature of tan δ was taken as the Tg of the homopolymer.

[0056] The method for obtaining the acrylic polymer used in the core layer 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 adopted. A preferred polymerization method is suspension polymerization. The mode of suspension polymerization is not particularly limited, and it can be carried out by appropriately adopting various monomer supply methods, polymerization conditions, materials used, and the like, similar to those of conventionally known general suspension polymerization.

[0057] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method, such as 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. Examples of suitable initiators include, but are not limited to, azo initiators such as potassium persulfate and ammonium persulfate; peroxide initiators such as benzoyl peroxide, t-butyl hydroperoxide, and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; carbonyl initiators such as aromatic carbonyl compounds; and redox 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.

[0058] 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) relative to 100 parts by weight of the total monomer components.

[0059] 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 chain transfer agents include mercaptans such as dodecyl mercaptan (also known as dodecanethiol or lauryl mercaptan), glycidyl mercaptan, 2-mercaptoethanol, mercaptoacetic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol, as well as α-methylstyrene dimer. These chain transfer agents may be used alone or in combination of two or more.

[0060] 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 0.01 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 within an appropriate range, a desired polymerization rate can be obtained.

[0061] A dispersant (such as a surfactant) can be used as needed for the suspension polymerization of the monomer raw material. The dispersant is not particularly limited, but preferred examples include water-soluble polymers such as polyvinyl alcohol, polyacrylic acid, gelatin, starch, cellulose ethers (such as carboxymethyl cellulose and hydroxyethyl cellulose), sodium polyacrylate, and polyvinylpyrrolidone. The dispersants may be used alone or in combination of two or more.

[0062] The amount of the dispersant used is usually preferably 5 parts by weight or less, or may be 4 parts by weight or less, 3 parts by weight or less, or 2 parts by weight or less, based on 100 parts by weight of the monomer component.

[0063] (styrene-based block copolymer) In some preferred embodiments, the core layer contains a styrene-based block copolymer as a base polymer. This configuration tends to result in an elastomer layer with appropriate flexibility. The styrene-based block copolymer is a block copolymer of a monovinyl-substituted aromatic compound and a conjugated diene compound. The monovinyl-substituted aromatic compound refers to a compound in which one vinyl-containing functional group is bonded to an aromatic ring. A typical example of the aromatic ring is a benzene ring (which may be a benzene ring substituted with a non-vinyl-containing functional group (e.g., an alkyl group)). Specific examples of the monovinyl-substituted aromatic compound include styrene, α-methylstyrene, vinyltoluene, and vinylxylene. Specific examples of the conjugated diene compound include 1,3-butadiene, isoprene, and farnesene. These block copolymers can be used alone or in combination.

[0064] The A segment (hard segment) in the styrene-based block copolymer preferably has a copolymerization ratio of the monovinyl-substituted aromatic compound (two or more types may be used in combination) of 70% by weight or more (more preferably 90% by weight or more, and may be substantially 100% by weight). The B segment (soft segment) in the styrene-based block copolymer preferably has a copolymerization ratio of the conjugated diene compound (two or more types may be used in combination) of 70% by weight or more (more preferably 90% by weight or more, and may be substantially 100% by weight). Such a block copolymer can realize a pressure-sensitive adhesive sheet with higher performance.

[0065] The styrene-based block copolymer may be in the form of a diblock copolymer, a triblock copolymer, a radial copolymer, a mixture thereof, or the like. In the triblock copolymer or the radial copolymer, it is preferable that an A segment (e.g., a styrene block) is disposed at the end of the polymer chain. This is because the A segments disposed at the end of the polymer chain tend to gather together to form domains, which form a pseudo-crosslinked structure and improve the cohesion of the PSA. In the technology disclosed herein, from the viewpoint of interlayer strength, a styrene-based block copolymer having a diblock ratio of 30% by weight or more (more preferably 40% by weight or more, even more preferably 50% by weight or more, particularly preferably 60% by weight or more, typically 65% ​​by weight or more) can be preferably used. From the viewpoint of interlayer strength, a block copolymer having a diblock ratio of 70% by weight or more is particularly preferred. Furthermore, from the viewpoint of cohesion properties, etc., a block copolymer having a diblock ratio of 90% by weight or less (more preferably 85% by weight or less, for example, 80% by weight or less) can be preferably used. For example, a block copolymer having a diblock ratio of 60 to 85% by weight is preferred, and one having a diblock ratio of 70 to 85% by weight (for example, 70 to 80% by weight) is more preferred.

[0066] The pressure-sensitive adhesive composition disclosed herein contains, as the styrene-based block copolymer, a hydrogenated styrene-based block copolymer in which at least a portion of the styrene-based block copolymer is hydrogenated. In the technology disclosed herein, the proportion of the hydrogenated styrene-based block copolymer in the styrene-based block copolymer contained in the core layer is preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more. In some preferred embodiments, substantially all (e.g., 95 to 100% by weight) of the styrene-based block copolymer is a hydrogenated styrene-based block copolymer.

[0067] The styrene content of the styrene-based block copolymer (including hydrogenated styrene-based block copolymers; the same applies hereinafter) may be, for example, 5 to 40% by weight. From the viewpoint of the cohesiveness of the core layer, a styrene-based block copolymer having a styrene content of 10% by weight or more (more preferably more than 10% by weight, for example, 12% by weight or more) is usually preferred. From the viewpoint of interlayer strength, the styrene content of the styrene-based block copolymer is preferably 35% by weight or less (typically 30% by weight or less, more preferably 25% by weight or less), and particularly preferably 22% by weight or less (typically less than 20% by weight, for example, 18% by weight or less). From the viewpoint of obtaining high chemical resistance, a styrene-based block copolymer having a styrene content of 10 to 22% by weight can be preferably used.

[0068] (hollow particles) In some embodiments, the core layer disclosed herein contains hollow particles. The inclusion of hollow particles in the core layer tends to improve the impact absorption of the core layer. Furthermore, when the core layer is formed by a hot melt method, the use of hollow particles tends to make the viscosity of the composition during heating and melting suitable for coating.

[0069] Here, hollow particles are spheres with a solid shell. From this perspective, a layer containing hollow particles is clearly distinguished from a so-called foam sheet, which does not have a solid shell around the cell structure. Hollow particles can be classified as inorganic hollow particles, organic hollow particles, etc., depending on the material constituting the shell. Examples of inorganic hollow particles include glass hollow particles such as hollow glass balloons, hollow particles made of metal compounds such as hollow alumina balloons, and porcelain hollow particles such as hollow ceramic balloons. Examples of organic hollow particles include resin hollow particles such as acrylic resins. In the technology disclosed herein, organic hollow particles are preferably used from the viewpoint of impact absorption.

[0070] In some preferred embodiments, the hollow particles may be pre-expanded thermally-expandable microcapsules, which are spheres formed with a thermoplastic resin shell encapsulating a liquid gas and are formed by thermal expansion due to the evaporation of the liquid gas. The pre-expanded thermally-expandable microcapsules may be hollow particles having a shell made of a copolymer of vinylidene chloride, acrylonitrile, methyl methacrylate, or the like. In some embodiments, the hollow particles have an average particle size of approximately 30 to 90 μm, for example, 30 to 60 μm. The hollow particles may be used singly or in combination of two or more types.

[0071] The content of hollow particles is not particularly limited. In some preferred embodiments, the content of hollow particles in the core layer is 0.05% by weight or more, more preferably 0.1% by weight or more, and even more preferably 0.15% by weight or more. The content of hollow particles in the core layer may be 0.2% by weight or more, 0.25% by weight or more, or 0.3% by weight or more. The content of hollow particles in the core layer is usually suitably 1.5% by weight or less, and may be 1.0% by weight or less, 0.8% by weight or less, 0.5% by weight or less, or 0.4% by weight or less. When the content of hollow particles in the core layer is within the above range, it is easy to form a core layer with suitable impact absorption capabilities. Furthermore, when the core layer is formed by a hot melt method, the viscosity during heating and melting is likely to be suitable for coating.

[0072] (coloring agent) The core layer in the technology disclosed herein may be colored. For this coloring, known organic or inorganic colorants can be used alone or in appropriate combination of two or more. For example, when the pressure-sensitive adhesive sheet disclosed herein is used for light-shielding purposes, the core layer is preferably colored black.

[0073] Examples of black colorants that can be used to color the core layer black include carbon black (furnace black, channel black, acetylene black, thermal black, lamp black, etc.), graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite (non-magnetic ferrite, magnetic ferrite, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complexes, composite oxide-based black pigments, and anthraquinone-based organic black pigments. Carbon black is a preferred black colorant from the standpoints of cost and availability. The amount of black colorant used is not particularly limited. In some preferred embodiments, the content of the black colorant (e.g., carbon black) in the core layer is 0.5% by weight or more, and may be 1% by weight or more, 2% by weight or more, 3% by weight or more, or 4% by weight or more. The upper limit of the content of the black colorant (for example, carbon black) is not particularly limited, but is suitably, for example, 10% by weight or less, and may be 7% by weight or less, or 6% by weight or less.

[0074] (Other crosslinkers) The core layer composition used to form the core layer may contain a crosslinking agent. The core 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 core layer exclusively in a form after crosslinking reaction.

[0075] 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 complex-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 in the core layer composition is not particularly limited, and is suitably, for example, approximately 10 parts by weight or less (e.g., approximately 0.005 to 10 parts by weight) per 100 parts by weight of the base polymer, and preferably approximately 5 parts by weight or less (0.01 to 5 parts by weight).

[0076] The adhesive sheet disclosed herein is characterized in that a pressure-sensitive adhesive layer containing a hydrazide compound is laminated on the surface of a core layer containing a polymer having a carbonyl group, causing the hydrazide compound to migrate across the layer to the core layer and form ketohydrazide crosslinks in the core layer. If the core layer composition already contains a hydrazine-based crosslinking agent, crosslinking will proceed prior to the formation of the core layer, increasing the viscosity of the composition and making it difficult to apply to hot-melt processes, etc. From this perspective, in some embodiments, the amount of hydrazine-based crosslinking agent used in the core layer composition is less than 0.005 parts by weight per 100 parts by weight of the base polymer. Preferably, the core layer composition is substantially free of hydrazine-based crosslinking agents.

[0077] (tackifier) In some embodiments, the core layer contains a tackifier (typically a tackifier resin). This makes it easier to obtain a PSA sheet that exhibits excellent interlayer adhesion. Examples of tackifiers 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.

[0078] The core layer composition disclosed herein may contain, as needed, an acid or base (such as aqueous ammonia) used for purposes such as pH adjustment. Examples of other optional components that may be incorporated into the core layer composition disclosed herein include viscosity modifiers, leveling agents, crosslinking aids, release modifiers, plasticizers, softeners, fillers, colorants (such as pigments and dyes), antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, and preservatives. Conventionally known additives can be used in the usual manner for these various additives, and detailed description thereof will be omitted because they do not particularly characterize the present invention.

[0079] (Formation of the core layer) The core layer disclosed herein is formed from a core layer composition. The form of the core layer composition is not particularly limited, and may be, for example, a core layer composition in a form containing the components having the above-described composition in an organic solvent (solvent-type), a core layer composition in a form in which the components are dispersed in an aqueous solvent (water-dispersed type, typically aqueous emulsion type), or a hot-melt type core layer composition.

[0080] The core layer disclosed herein can be formed from a core layer composition that is substantially free of organic solvents. Here, the fact that the core layer composition is substantially free of organic solvents (also referred to as solvent-free) means that the amount of organic solvent in the core layer composition is less than 1% by weight (e.g., less than 0.1% by weight). Such a core layer composition can be a hot-melt core layer composition. Hot-melt core layer compositions can be applied in a heated, molten state that is substantially free of organic solvents, making them preferable from the standpoints of productivity and reducing environmental impact.

[0081] The method for forming the core layer from the core layer composition is not particularly limited, and any known appropriate method can be used. For example, the core layer can be formed by a hot melt method, a calendar method, a casting method, an inflation extrusion method, a T-die extrusion method, etc. Among these, it is preferable to use the hot melt method, particularly a method in which the core layer composition in a heated and molten state is pressed with a press to form it into a sheet (hot melt pressing method).

[0082] From the viewpoint of the storage stability of the core layer composition, it is preferable to form the core layer from a solvent-free core layer composition. The core layer disclosed herein may have a residual organic solvent content of less than 1000 ppm (the amount of organic solvent per gram of core layer is less than 1000 μg (i.e., less than 1000 μg / 1 g)). In such a substantially solvent-free (typically hot-melt) configuration, the effects of the technology disclosed herein can be preferably realized. In some embodiments, the residual organic solvent content in the core layer may be, for example, less than 900 ppm, less than 800 ppm, less than 700 ppm, less than 600 ppm, less than 500 ppm, less than 400 ppm, less than 300 ppm, less than 200 ppm, or less than 100 ppm.

[0083] (Core layer thickness) The thickness of the core layer is not particularly limited and can be appropriately set depending on the strength, flexibility, and intended use of the pressure-sensitive adhesive sheet. From the viewpoint of thinning, the thickness of the core layer can be, for example, about 1000 μm or less, and may be 750 μm or less, 500 μm or less, or 400 μm or less. A core layer having the above thickness tends to improve processability. In some preferred embodiments, the thickness of the core layer may be approximately 300 μm or less, 250 μm or less, 200 μm or less, or 160 μm or less. The thickness of the core layer is suitably approximately 4 μm or more (e.g., 20 μm or more). The thickness of the core layer may be, for example, 30 μm or more, 40 μm or more, or 50 μm or more. In some embodiments, from the viewpoint of impact resistance, the thickness of the core layer is advantageously, for example, 55 μm or more or more than 55 μm, preferably 60 μm or more, may be 80 μm or more, 100 μm or more (e.g., more than 100 μm), 120 μm or more, or may be 140 μm or more. As the thickness of the core layer increases, impact resistance tends to improve.

[0084] (Characteristics of the core layer) From the viewpoint of improving interlayer adhesion and chemical resistance, it is preferable that the core layer has flexibility within an appropriate range. The maximum stress measured in a tensile test can be used as an index of the flexibility (hardness or softness) of the core layer. The maximum stress here refers to the maximum value of stress observed from the start of tension to break in the tensile test. In general, the maximum stress of a measurement sample that does not have a yield point can match the stress at break (breaking stress). Furthermore, the maximum stress of a measurement sample that has a yield point may not match the breaking stress.

[0085] In some preferred embodiments, the core layer has a maximum stress of 1.0 MPa or less, as measured in a tensile test conducted at a temperature of 23°C and a tensile speed of 50 mm / min. A core layer exhibiting a maximum stress in this range is relatively flexible and tends to have improved interlayer adhesion and chemical resistance. From this perspective, the maximum stress is more preferably less than 1.0 MPa, even more preferably less than 0.9 MPa, and particularly preferably less than 0.8 MPa. In some embodiments, the maximum stress may be 0.7 MPa or less, 0.65 MPa or less, or 0.6 MPa or less.

[0086] The lower limit of the maximum stress of the core layer is not particularly limited. If the core layer is too soft, it may swell when it comes into contact with chemicals, which may result in a decrease in chemical resistance. From this perspective, the maximum stress is preferably 0.45 MPa or more, more preferably 0.50 MPa or more, and particularly preferably 0.55 MPa or more.

[0087] Here, the sample for measuring the maximum stress of the core layer was Core Layer A before the core layer and the adhesive layer were bonded together. pre The preferred range of the maximum stress of the core layer is the maximum stress of the core layer A after the pressure-sensitive adhesive layer is laminated on the core layer. after Core layer A obtained using as a measurement sample After In some preferred embodiments, the core layer A disclosed herein may also be applied to a maximum stress of 1000 kJ / cm. pre Maximum stress and core layer A after The difference in maximum stress between the core layer A and thepre The maximum stress of the core layer is within ±5% of the maximum stress of the core layer. Specifically, the maximum stress of the core layer can be measured by the method described in the examples below.

[0088] <Adhesive layer> The pressure-sensitive adhesive sheet disclosed herein has a pressure-sensitive adhesive layer laminated on at least one surface of a core layer. The pressure-sensitive adhesive layer disclosed herein contains a hydrazide compound.

[0089] (hydrazide compounds) The hydrazide compounds disclosed herein include those that are understood to be hydrazine-based crosslinkers. In some embodiments, the hydrazide compound may be any of various hydrazide compounds having two or more (e.g., about 2 to 4, typically two) hydrazino groups (-NHNH) in the molecule (e.g., an acid hydrazide compound having a structural moiety represented by -CONHNH). Examples of such hydrazide compounds include saturated dicarboxylic acid dihydrazides such as oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, and sebacic acid dihydrazide; and unsaturated dicarboxylic acid dihydrazides such as maleic acid dihydrazide, fumaric acid dihydrazide, and itaconic acid dihydrazide. A single hydrazide compound selected from these compounds may be used alone, or two or more may be used in combination. Among these, glutaric acid dihydrazide, adipic acid dihydrazide, and pimelic acid dihydrazide are preferred. Although not particularly limited, from the viewpoints of reactivity and ease of handling, hydrazide compounds having a formula weight per hydrazino group of approximately 70 to 100 can be preferably used. For example, adipic acid dihydrazide (ADH) can be preferably used.

[0090] Such a hydrazide compound (hydrazine-based crosslinking agent) can typically be used by adding it to an aqueous dispersion of an acrylic polymer. For example, an aqueous dispersion of an acrylic polymer obtained by emulsion polymerization of the above-mentioned monomer raw materials can be prepared, and a hydrazine-based crosslinking agent can be added and mixed thereto. The manner in which the hydrazine-based crosslinking agent is added is not particularly limited. For example, the hydrazine-based crosslinking agent may be added as is (typically in a solid form, e.g., powder form), or may be added as a hydrazine-based crosslinking agent solution (e.g., an aqueous solution) in which the hydrazine-based crosslinking agent is dissolved in a suitable solvent, or may be added in the form of an aqueous dispersion (e.g., an emulsion) in which the hydrazine-based crosslinking agent or a solution thereof in an organic solvent is dispersed in water.

[0091] (base polymer) In the technology disclosed herein, the type of adhesive constituting the adhesive layer is not particularly limited. The adhesive may contain, as an adhesive polymer (hereinafter also referred to as "base polymer"), one or more of various rubber-like polymers that can be used in the field of adhesives, such as acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine-based polymers. From the viewpoints of adhesive performance, cost, etc., adhesives containing acrylic polymers or rubber polymers as the base polymer are preferably used. Among these, adhesives using acrylic polymers as the base polymer (acrylic adhesives) are preferred. The technology disclosed herein is preferably implemented in an embodiment using an acrylic adhesive.

[0092] The following description will mainly focus on adhesive layers made of acrylic adhesives, i.e., adhesive sheets having acrylic adhesive layers, but it is not intended to limit the adhesive layers of the adhesive sheets disclosed herein to those made of acrylic adhesives.

[0093] The "base polymer" of a pressure-sensitive adhesive refers to the main component of the rubber-like polymer contained in the pressure-sensitive adhesive, and is not to be construed in any other limiting sense. The rubber-like polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature.

[0094] (acrylic polymer) In some preferred embodiments, the pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer. The monomer components constituting the acrylic polymer can be the same as the examples specifically cited as the monomer components that can be used in the core layer.

[0095] When a carboxyl group-containing monomer is copolymerized with an acrylic polymer, the proportion of the carboxyl group-containing monomer in the total amount of monomer components constituting the acrylic polymer is typically 0.5 wt% or more, preferably 1 wt% or more, and may be 1.2 wt% or more, from the viewpoint of improving interlaminar strength. The proportion of the carboxyl group-containing monomer in the total amount of the monomer components is preferably 15 wt% or less, and may be, for example, 10 wt% or less, from the viewpoint of adhesive properties such as adhesive strength. In some embodiments, the proportion of the carboxyl group-containing monomer in the total amount of the monomer components is preferably 5 wt% or less, and may be 3 wt% or less.

[0096] The method for obtaining an acrylic polymer is not particularly limited, and various polymerization methods known as methods for synthesizing 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, and the like 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, and the like can be appropriately employed. The monomer raw materials may be added dropwise in the form of an aqueous emulsion. The polymerization temperature can be, for example, about 20°C or higher (usually 40°C or higher), and is suitably about 100°C or lower (usually 80°C or lower).

[0097] 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 polymerization liquid that has been subjected to an appropriate post-treatment. Alternatively, an acrylic polymer emulsion may be prepared by synthesizing an acrylic polymer using a polymerization method other than emulsion polymerization (e.g., solution polymerization, photopolymerization, bulk polymerization, etc.) and dispersing the polymer in water. Generally, good processability tends to be obtained by using an acrylic polymer emulsion designed to have a relatively high molecular weight.

[0098] Emulsion polymerization of the monomer raw materials is usually carried out in the presence of a surfactant (emulsifier). The amount of surfactant used is not particularly limited. In consideration of polymerization stability and dispersion stability of the polymerization reaction product, the amount of surfactant used is usually 0.1 parts by weight or more, preferably 0.5 parts by weight or more, per 100 parts by weight of the monomer raw materials. From the viewpoint of achieving even higher stability, it may be 1.0 parts by weight or more, or even 1.5 parts by weight or more. Furthermore, the amount of surfactant used may be, for example, 10 parts by weight or less per 100 parts by weight of the monomer raw materials. On the other hand, from the viewpoint of adhesive properties, it is desirable to limit the amount of surfactant used (especially non-reactive surfactants). 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.

[0099] As the surfactant, known anionic surfactants, nonionic surfactants, cationic surfactants, etc. can be used. Usually, anionic or nonionic surfactants are preferred. The surfactants can be used alone or in combination of two or more.

[0100] 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.

[0101] 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.

[0102] As the reactive surfactant, those having a polymerizable (typically radically polymerizable) functional group can be preferably used. For example, reactive surfactants having a structure in which a radically polymerizable functional group is introduced into the anionic surfactant or nonionic surfactant 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 alkenyl groups include a propenyl group and an isopropenyl group (CH═C(CH)—). The concept of a propenyl group here includes a 1-propenyl group (CH—CH═CH—) and a 2-propenyl group (CH═CH—CH—; sometimes referred to as an allyl group).

[0103] 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), methacryloxypolyoxypropylene sulfates (e.g., sodium salts), polyoxyalkylene alkenyl ether sulfates (e.g., ammonium salts in which the alkenyl group ends at an isopropenyl group), etc. 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.

[0104] Commercially available reactive surfactants include those manufactured by Daiichi Kogyo Seiyaku Co., Ltd. under the trade names "Aqualon HS-05," "Aqualon HS-10," "Aqualon HS-1025," "Aqualon HS-20," "Aqualon KH-10," "Aqualon KH-1025," "Aqualon KH-05," "Aqualon BC-0515," "Aqualon BC-10," "Aqualon BC-1025," "Aqualon BC-20," "Aqualon BC-2020," "Aqualon RN-20," "Aqualon RN-30," and "Aqualon RN-50." Examples include "Aqualon AR-10," "Aqualon AR-20," "Aqualon AR-1025," and "Aqualon AR-2020," ADEKA Corporation product names "ADEKA REASOAP SE-10N" and "ADEKA REASOAP SR-1025," Kao Corporation product names "Latemul PD-104," "Latemul PD-420," "Latemul PD-430," and "Latemul PD-450," Sanyo Chemical Industry Co., Ltd. product names "Eleminol JS-20" and "Eleminol RS-3000," and Nippon Nyukazai Co., Ltd. product name "Antox MS-60."

[0105] In view of emulsification performance and the like, an anionic reactive surfactant may be preferably used in some embodiments. When a nonionic reactive surfactant is used, more preferable results can be achieved by using it in combination with other surfactants, such as an anionic reactive surfactant, an anionic non-reactive surfactant, or a nonionic non-reactive surfactant.

[0106] In embodiments using a surfactant, the surfactant preferably contains a reactive surfactant from the viewpoint of adhesive properties. In other words, at least a portion of the surfactant used is preferably 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.

[0107] (tackifying resin) In some preferred embodiments, the PSA layer contains a tackifying resin. This makes it easier to obtain a PSA sheet that exhibits excellent adhesive properties (e.g., adhesive strength and repulsion resistance). Examples of tackifying resins include rosin-based tackifying resins (including rosin derivative tackifying resins), petroleum-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, and ketone-based tackifying resins. These can be used alone or in combination of two or more.

[0108] 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 such an 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).

[0109] The PSA compositions disclosed herein may contain, as needed, an acid or base (such as aqueous ammonia) used for purposes such as pH adjustment. Examples of other optional components that may be incorporated into the PSA compositions disclosed herein include crosslinkers other than hydrazine-based crosslinkers, viscosity modifiers, leveling agents, crosslinking aids, release modifiers, thickeners, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, and preservatives. These various additives can be conventionally known and can be used in the usual way. Since they do not particularly characterize the present invention, detailed description of them will be omitted.

[0110] (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 exposure to active energy rays such as ultraviolet light 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 having a pressure-sensitive adhesive layer formed from a water-dispersed (typically, aqueous emulsion) pressure-sensitive adhesive composition in which a pressure-sensitive adhesive component is dispersed in an aqueous medium.

[0111] (Formation of 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 coating) 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.

[0112] (Adhesive layer thickness) The thickness of the pressure-sensitive adhesive layer is not particularly limited, and a configuration having a pressure-sensitive adhesive layer with an appropriate thickness, for example, in the range of 0.1 to 500 μm, can be adopted depending on the application and intended use. In embodiments where the pressure-sensitive adhesive sheet is a double-sided pressure-sensitive adhesive sheet in which pressure-sensitive adhesive layers are laminated on both sides of a core layer, the thickness of the pressure-sensitive adhesive layer referred to here refers to the thickness of the pressure-sensitive adhesive layer on one side. In some embodiments, to avoid the pressure-sensitive adhesive sheet becoming excessively thick, the thickness of the pressure-sensitive adhesive layer is typically approximately 100 μm or less, preferably approximately 70 μm or less, more preferably approximately 60 μm or less, and even more preferably approximately 50 μm or less. The thickness of the pressure-sensitive adhesive layer can be approximately 35 μm or less, for example, approximately 30 μm or less. A pressure-sensitive adhesive layer with a limited thickness can effectively meet demands for thinner and lighter products. Furthermore, while a thinner pressure-sensitive adhesive layer generally tends to reduce impact resistance and adhesion to the adherend, the technology disclosed herein makes it possible to achieve sufficient impact resistance and adhesive strength with a pressure-sensitive adhesive layer of limited thickness. From the viewpoint of adhesion to the adherend, the lower limit of the thickness of the pressure-sensitive adhesive layer is, in some embodiments, suitably approximately 0.5 μm or more, may be approximately 1 μm or more, and is advantageously approximately 3 μm or more, preferably approximately 10 μm or more, more preferably approximately 12 μm or more (e.g., greater than 12 μm), and even more preferably approximately 15 μm or more, for example, approximately 18 μm or more. In a double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on each side of a core layer, the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may have the same thickness or different thicknesses.

[0113] <Method of manufacturing adhesive sheet> In producing a PSA sheet, the method for providing a PSA layer on one or both surfaces of a core layer is not particularly limited. Generally, it is preferable to use one of the following methods: (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 core layer for transfer (lamination) (hereinafter also referred to as the "transfer method"); and (2) a method in which a PSA composition is directly applied (typically coated) to the core 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 surfaces of the core layer (transfer-transfer method), or a double-sided PSA sheet may be produced by applying the transfer method to one surface of the core layer (typically the surface on which the PSA layer is first applied) and the direct coating method to the other surface (transfer-direct method). Of these, the transfer method (or transfer-transfer method) is preferred from the viewpoint of being able to form each layer independently. A method is preferably employed in which an adhesive layer is transferred onto one or both surfaces of a core layer, and then the laminate of the core layer and the adhesive layer is aged to obtain an adhesive sheet.

[0114] <Characteristics of adhesive sheets> In some embodiments, the pressure-sensitive adhesive sheet has an adhesive strength retention rate of 50% or more when immersed in an alcohol solution (adhesive strength retention rate after immersion in alcohol), and such a pressure-sensitive adhesive sheet is likely to have excellent performance in terms of withstanding chemicals (e.g., alcohol-based solvents) and maintaining adhesion. Here, the adhesive strength retention rate after alcohol immersion [%] is calculated from the ratio (F1 / F0 × 100) of the adhesive strength F1 [N / 5mm] after alcohol immersion to the initial peel strength F0 [N / 5mm] of the adhesive sheet. The initial peel strength F0 [N / 5mm] refers to the peel strength measured for a 5mm wide adhesive sheet attached to a stainless steel plate as an adherend at a tensile speed of 300mm / min and a peel angle of 180°, i.e., the peel strength before alcohol immersion. The adhesive strength F1 [N / 5mm] after alcohol immersion refers to the peel strength measured for a 5mm wide adhesive sheet attached to a stainless steel plate as an adherend at a 60°C environment for 4 days in a test solution prepared by mixing isopropyl alcohol and water in a weight ratio of 30:70, and then at a tensile speed of 300mm / min and a peel angle of 180°, i.e., the peel strength after alcohol immersion. The adhesive strength retention rate after alcohol immersion can be measured specifically by the method described in the Examples. A high adhesive strength retention rate after alcohol immersion means that the decrease in peel strength due to alcohol immersion is suitably suppressed.

[0115] In some preferred embodiments, the adhesive strength retention rate after alcohol immersion is 80% or more, more preferably 85% or more, and even more preferably 90% or more. There are no particular limitations on the upper limit of the adhesive strength retention rate after alcohol immersion. The adhesive strength retention rate after alcohol immersion is usually 110% or less, and may be 100% or less.

[0116] <Application> The pressure-sensitive adhesive sheets disclosed herein have excellent chemical resistance. Furthermore, the pressure-sensitive adhesive sheets disclosed herein tend to have excellent impact resistance. Taking advantage of these characteristics, the pressure-sensitive adhesive sheets disclosed herein can be preferably used in various products requiring chemical resistance and impact resistance, or in a form where they are attached to components constituting such products, for applications such as fixing, joining, molding, decorating, protecting, and supporting the products or components. In particular, they can be preferably used to fix the above-mentioned products or components. For example, portable electronic devices are at risk of being dropped due to their usage, and pressure-sensitive adhesive sheets used in portable electronic devices may be required to have impact resistance. The double-sided pressure-sensitive adhesive sheets disclosed herein are suitable for such portable electronic devices.

[0117] 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, etc.), 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, "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.

[0118] The matters disclosed by this specification include the following: [1] A pressure-sensitive adhesive sheet comprising a core layer and a pressure-sensitive adhesive layer laminated on one or both surfaces of the core layer, the core layer contains a polymer having a carbonyl group, The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer contains a hydrazide compound. [2] The pressure-sensitive adhesive sheet according to [1] above, wherein the core layer has a maximum stress of 1.0 MPa or less, as measured in a tensile test carried out under conditions of a temperature of 23°C and a tensile speed of 50 mm / min. [3] The pressure-sensitive adhesive sheet according to [1] or [2] above, which has an adhesive strength retention rate of 80% or more after immersion in alcohol; Here, the adhesive strength retention rate [%] after alcohol immersion is calculated from the ratio of the adhesive strength F1 [N / 5mm] after alcohol immersion to the initial peel strength F0 [N / 5mm] (F1 / F0 × 100), The initial peel strength F0 [N / 5mm] is the peel strength measured under the conditions of a 5mm wide adhesive sheet attached to a stainless steel plate as an adherend, at a pulling rate of 300mm / min and a peel angle of 180 degrees, The adhesive strength after alcohol immersion F1 [N / 5mm] is the peel strength measured under the conditions of a pulling speed of 300mm / min and a peel angle of 180 degrees after a 5mm wide adhesive sheet attached to a stainless steel plate as an adherend is immersed in a test liquid made by mixing isopropyl alcohol and water in a weight ratio of 30:70 in an environment of 60°C for 4 days. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the core layer contains a blend of an acrylic polymer and a styrene block copolymer. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive. [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, wherein the core layer is formed from a hot-melt composition. [7] The pressure-sensitive adhesive sheet according to any one of the above [1] to [6], wherein the pressure-sensitive adhesive layer is formed from a water-dispersible pressure-sensitive adhesive composition. [8] The pressure-sensitive adhesive sheet according to any one of [1] to [7] above, which is used to fix components in a portable electronic device. [9] Forming a core layer from a hot melt composition; forming a pressure-sensitive adhesive layer from the water-dispersible pressure-sensitive adhesive composition; and A method for producing a pressure-sensitive adhesive sheet, comprising laminating the pressure-sensitive adhesive layer on one or both surfaces of the core layer, The hot melt composition contains an acrylic polymer A obtained by suspension polymerization of a monomer component including a monomer having a carbonyl group, The water-dispersible pressure-sensitive adhesive composition comprises an acrylic polymer B obtained by emulsion polymerization of a monomer component, and a hydrazide compound. [Example]

[0119] 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 by weight unless otherwise specified.

[0120] <Example 1> <Formation of core layer A> 1.1 Preparation of acrylic polymer A(1) 91.5 parts of butyl acrylate (BA), 7.5 parts of methacrylic acid (MAA), 1 part of diacetone acrylamide (DAAM), 0.10 parts of polymerization initiator (AIBN), and 0.05 parts of t-dodecanethiol (chain transfer agent) were placed in a container and dissolved at room temperature to obtain mixed solution A. 500 parts of distilled water and 1 part of dispersion stabilizer (trade name "Metolose 60SH-50", manufactured by Shin-Etsu Chemical Co., Ltd.) were added to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and dissolved. While stirring at 300 rpm with a stirring blade, the mixed solution A was added, and nitrogen substitution was performed for 1 hour. While continuing stirring, the reaction system was heated to 60°C, and suspension polymerization was allowed to proceed while maintaining the temperature constant for 3 hours. Next, the reaction system was heated to 75°C, and aging was allowed to proceed while maintaining the temperature constant for 3 hours, after which it was cooled to room temperature. The reaction product was subjected to solid-liquid separation, thoroughly washed with water, and then dried at 40° C. for 24 hours using a dryer to obtain a bulk acrylic polymer A(1).

[0121] 1.2 Preparation of Mixture A Styrenic block copolymer (trade name "Septon BIO-SF902", manufactured by Kuraray Co., Ltd.) 35 parts, the acrylic polymer A (1) 65 parts, tackifier (trade name "SYLVALITE RE100S", manufactured by Kraton Corporation) 20 parts, carbon black (trade name "Asahi CB # 50", manufactured by Asahi Carbon Co., Ltd.) 5 parts, hollow particles (trade name "Expancel 920DE40", manufactured by Akzo Nobel) 0.33 parts, was added to a circulation kneader (a benchtop kneader manufactured by Xplore Instrument Co., Ltd.) equipped with a conical screw and kneaded at 120 ° C. and 100 rpm for 10 minutes. Then, 0.25 parts of an epoxy crosslinker (trade name "Denacol Ex411", manufactured by Nagase ChemteX Corporation) and 0.013 parts of an imidazole catalyst (trade name "IBMI12", manufactured by Mitsubishi Chemical Corporation) were added and kneaded for a further 5 minutes to obtain a mixture A.

[0122] 1.3 Formation of core layer (elastomer layer) A Mixture A was sandwiched between two 75 μm thick polyethylene terephthalate (PET) release liners (trade name "Diafoil MRF75", manufactured by Mitsubishi Chemical Corporation) and press-molded at 120°C and 5 MPa to form a 160 μm thick core layer (elastomer layer) A.

[0123] <Formation of Pressure-Sensitive Adhesive Layer B> 2.1 Preparation of acrylic polymer B A reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser was charged with 96.5 parts of distilled water and 0.8 parts of a surfactant (trade name "Aqualon KH1025" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and the mixture was purged with nitrogen at 25°C for 1 hour while stirring. The temperature inside the reaction vessel was then raised to 80°C. Next, 41 parts of 2-ethylhexyl acrylate (2EHA), 34 parts of butyl acrylate (BA), 23 parts of methyl methacrylate (MMA), 0.7 parts of acrylic acid (AA), 0.54 parts of methacrylic acid (MAA), 0.05 parts of a chain transfer agent (t-dodecanethiol manufactured by Wako Pure Chemical Industries, Ltd.), and 3.2 parts of a surfactant (trade name "Aqualon KH1025" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were emulsified in 100 parts of distilled water to prepare emulsion B. 3% of the total amount of the prepared emulsion B was added to the reaction vessel, and 0.025 parts of a polymerization initiator (ammonium peroxodisulfate (APS), manufactured by Kishida Chemical Co., Ltd.) was added and allowed to react for 30 minutes. Thereafter, 0.02 parts of the polymerization initiator were added every 30 minutes until the total amount reached 0.1 parts, while the remaining emulsion (97% of the total amount) was added dropwise over 3.5 hours to carry out polymerization. An aging reaction was further carried out at 80°C for 2 hours to prepare an aqueous dispersion of acrylic polymer B. The solids concentration of this acrylic polymer B was 50%.

[0124] 2.2 Preparation of Pressure-Sensitive Adhesive Composition B To the aqueous dispersion of acrylic polymer B, 1 part of adipic acid dihydrazide (ADH) as a crosslinking agent and 1 part of a thickener (trade name "Aron B-500", manufactured by Toagosei Co., Ltd.) were added relative to 100 parts of the solid content of the aqueous dispersion. Thereafter, the pH was adjusted to 7 with 10% aqueous ammonia to prepare PSA composition B.

[0125] 2.3 Formation of adhesive layer B The pressure-sensitive adhesive composition B obtained as described above was applied to the silicone-treated surface of a 75 μm-thick polyethylene terephthalate (PET) release liner (trade name "Diafoil MRF75", manufactured by Mitsubishi Chemical Corporation) so that the thickness after drying would be 20 μm. The resulting coating was then heated and dried at 100° C. for 3 minutes to form a pressure-sensitive adhesive layer B on the release liner.

[0126] 3. Preparation of double-sided adhesive sheets One surface (exposed surface) of the pressure-sensitive adhesive layer B was bonded to one surface of the core layer A. Next, the release liner was removed, and another pressure-sensitive adhesive layer B was bonded to the other surface of the core layer A, yielding a laminate with a total thickness of 200 μm having a structure of first pressure-sensitive adhesive layer B / core layer A / second pressure-sensitive adhesive layer B. This laminate was aged for 7 days in a dryer at 50° C. to produce a double-sided pressure-sensitive adhesive sheet according to this example.

[0127] <Examples 2-6> Table 1 shows an overview of the acrylic polymer A (specifically, acrylic polymers A(0), A(1), A(3), and A(5)). An overview of each example is shown in Table 2. Double-sided PSA sheets according to each example were produced in the same manner as in Example 1, except that the composition of the acrylic polymer A used in forming the core layer A and / or the presence or absence of ADH as a crosslinking agent in forming the PSA layer B were as shown in Table 2.

[0128] [Table 1]

[0129] [Table 2]

[0130] <Flexibility evaluation of core layer A> [Tensile test] The core layer A of each example (the core layer A before being attached to the adhesive layer B) was cut to a width of 2 cm and a length of 3 cm to prepare a test piece, and the long side was rolled up to prepare a rod-shaped test piece with a length of 3 cm. The test piece was subjected to a tensile test using a tensile tester under conditions of 23°C and 50% RH, with a chuck distance of 10 mm and a tensile speed of 50 mm / min, and the maximum stress [MPa] was measured. The maximum stress [MPa] was calculated by multiplying the maximum value [N] of the load observed from the start of the tensile test until the test piece broke by the cross-sectional area [mm 2The tensile strength was calculated by dividing the tensile strength by the tensile strength. A universal tension and compression tester (model name "AUTOGRAPH", manufactured by Shimadzu Corporation) was used as the tensile tester. The results obtained are shown in the corresponding columns in Table 2. If the core layer A to be measured cannot be wound into a rod shape, the core layer A shall be punched out into a No. 1 dumbbell shape (10 mm width, conforming to JIS K 6251) and used as a test piece, and a tensile test similar to that described above shall be carried out to measure the maximum stress [MPa].

[0131] <Chemical resistance> [Initial peel strength F0] A primer (product name "N-200NT", manufactured by 3M) was applied to the surface of a 50 μm-thick PET film to prepare a backing film. In an environment of 23°C and 50% RH, the primer-coated surface of the backing PET film was attached to one adhesive surface of a double-sided PSA sheet according to each example to form a backing, and the backing was cut to a size of 5 mm wide and 60 mm long to prepare a measurement sample. In the same environment, a primer (product name "N-200NT", manufactured by 3M) was applied to the surface of a stainless steel plate (SUS304BA plate) as an adherend, and the adhesive surface (surface to be measured) of the prepared measurement sample was pressed against the primer-coated surface of the stainless steel plate (SUS304BA plate) by rolling a 2 kg roller back and forth once, and the resultant was left in an environment of 23°C for 24 hours. Then, in an environment of 23°C and 50% RH, the peel strength (initial peel strength F0) [N / 5mm] was measured using a tensile tester in accordance with JIS Z 0237: 2000 under the conditions of a pulling speed of 300 mm / min and a peel angle of 180°. The tensile tester used was an "AUTOGRAPH" model manufactured by Shimadzu Corporation.

[0132] [Peel strength after immersion in alcohol F1] In the same manner as in the measurement of the initial peel strength F0, a 5 mm wide, 60 mm long measurement sample (adhesive sheet) backed with a PET film was prepared using the double-sided PSA sheet according to each example. The adhesive surface (surface to be measured) of the measurement sample was pressed against the surface of a stainless steel plate (SUS304BA plate) by rolling a 2 kg roller back and forth once, and the sample was left in an environment at 23 °C for 24 hours. Isopropyl alcohol (IPA) and water were mixed in a container at a weight ratio of IPA:water = 30:70, and this was used as the test liquid (30% IPA aqueous solution) for the immersion test. The stainless steel plate with the measurement sample attached was immersed in the container containing the test liquid so that the measurement sample and stainless steel plate were completely immersed in the test liquid, and the container was placed in a thermostatic chamber maintained at 60 °C. The measurement sample attached to the stainless steel plate in this way was immersed in the test liquid for 4 days in an environment at 60 °C, after which the measurement sample and stainless steel plate were removed, the adhering test liquid was wiped off with a cloth, and the sample was left in the open air for 3 hours to dry. Then, using a tensile tester, the peel strength F1 [N / 5 mm] after alcohol immersion was measured under the same conditions as in the measurement of the initial peel strength F0.

[0133] Using the obtained initial peel strength F0 and peel strength F1 after alcohol immersion, the peel strength retention rate [%] was calculated according to the following formula: peel strength retention rate [%] = (F1 / F0) × 100. A higher peel strength retention rate indicates higher chemical resistance (specifically, alcohol resistance). The peel strength retention rate [%] obtained for the double-sided PSA sheets of each example is shown in Table 2.

[0134] As shown in Table 2, the adhesive sheets of Examples 1 to 3, which have a core layer A containing any of the acrylic polymers A(1), A(3), and A(5) using diacetone acrylamide (DAAM) as the monomer, and an adhesive layer B containing a hydrazide compound (ADH), were confirmed to have higher adhesive strength retention and chemical resistance than the adhesive sheets of Examples 4 and 6, in which the core layer A does not contain a polymer having a carbonyl group, and the adhesive sheets of Examples 5 and 6, in which the adhesive layer B does not contain a hydrazide compound.

[0135] 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. [Explanation of symbols]

[0136] 1 adhesive sheet 2 adhesive sheets 10 core layer 21 Adhesive layer (first adhesive layer) 22 Second adhesive layer 31 Release liner 32 Release liner 100 adhesive sheets with release liner 200 adhesive sheet with release liner

Claims

1. A pressure-sensitive adhesive sheet comprising a core layer and a pressure-sensitive adhesive layer laminated on one or both surfaces of the core layer, the core layer contains a polymer having a carbonyl group, The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer contains a hydrazide compound.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the core layer has a maximum stress of 1.0 MPa or less as measured in a tensile test carried out at a tensile speed of 50 mm / min in an environment of 23°C.

3. 3. The pressure-sensitive adhesive sheet according to claim 1 or 2, which has an adhesive strength retention rate of 80% or more after immersion in alcohol; Here, the adhesive strength retention rate [%] after alcohol immersion is determined from the ratio of the adhesive strength F1 [N / 5 mm] after alcohol immersion to the initial peel strength F0 [N / 5 mm] (F1 / F0 × 100), The initial peel strength F0 [N / 5 mm] is the peel strength measured under conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees for a 5 mm wide pressure-sensitive adhesive sheet attached to a stainless steel plate as an adherend, The adhesive strength F1 [N / 5 mm] after alcohol immersion is a peel strength measured under conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees after a 5 mm wide adhesive sheet attached to a stainless steel plate as an adherend is immersed in a test liquid prepared by mixing isopropyl alcohol and water in a weight ratio of 30:70 in an environment of 60°C for 4 days.

4. The pressure-sensitive adhesive sheet according to claim 1 , wherein the core layer comprises a blend of an acrylic polymer and a styrene-based block copolymer.

5. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive layer comprises an acrylic pressure-sensitive adhesive.

6. The pressure-sensitive adhesive sheet according to claim 1 , wherein the core layer is formed from a hot-melt composition.

7. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive layer is formed from a water-dispersible pressure-sensitive adhesive composition.

8. The pressure-sensitive adhesive sheet according to claim 1 or 2, which is used to fix components in a portable electronic device.

9. forming a core layer from a hot melt composition; forming a pressure-sensitive adhesive layer from the water-dispersible pressure-sensitive adhesive composition; and A method for producing a pressure-sensitive adhesive sheet, comprising laminating the pressure-sensitive adhesive layer on one or both surfaces of the core layer, The hot melt composition contains an acrylic polymer A obtained by suspension polymerization of a monomer component including a monomer having a carbonyl group, The method for producing a pressure-sensitive adhesive sheet, wherein the water-dispersed pressure-sensitive adhesive composition comprises an acrylic polymer B obtained by emulsion polymerization of a monomer component, and a hydrazide compound.

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