Adhesive sheet

Abstract

To provide an adhesive sheet that exhibits excellent impact resistance.SOLUTION: The present invention provides an adhesive sheet having an adhesive layer laminated on one or both surfaces of an impact-absorbing layer. The impact-absorbing layer and the adhesive layer each contain a polymer having a carboxyl group, and the impact-absorbing layer contains an organometallic complex compound. The content of the organometallic complex compound is 0.1 pt.wt. or more and 1.2 pts.wt. or less relative to 100 pts.wt. of a base polymer contained in the impact-absorbing layer.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. 2015-187263 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). To achieve good impact resistance, a means can be adopted in which an impact absorbing layer with impact absorbing capabilities is introduced into the adhesive sheet. For example, Patent Documents 1 and 2 describe adhesive sheets that employ a foam sheet as the impact absorbing layer and are constructed by laminating an adhesive layer on this foam 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.

[0005] Here, in a pressure-sensitive adhesive sheet formed by laminating a pressure-sensitive adhesive layer on an impact absorbing layer, if the adhesion at the interlayer interface between the impact absorbing layer and the pressure-sensitive adhesive layer is low, the impact resistance of the pressure-sensitive adhesive sheet is difficult to improve. That is, if the interlayer adhesion between the impact absorbing layer and the pressure-sensitive adhesive layer is low, when the pressure-sensitive adhesive sheet is fixedly attached to the adherend via the pressure-sensitive adhesive layer and an impact is applied to the pressure-sensitive adhesive sheet, the impact absorbing layer cannot withstand the tensile force generated by the deformation (typically elongation in the thickness direction) of the impact absorbing layer, and the impact absorbing layer may peel off from the pressure-sensitive adhesive layer. In this case, the pressure-sensitive adhesive sheet breaks before the impact absorbing ability inherent to the impact absorbing layer is fully exerted, and the impact resistance tends to decrease.

[0006] In order to increase the interlayer strength between the foam sheet and the pressure-sensitive adhesive layer, Patent Documents 1 and 2 describe subjecting the foam sheet to a surface treatment such as corona treatment. However, if the interlayer strength between the impact absorbing layer and the pressure-sensitive adhesive layer can be increased even without surface treatment of the impact absorbing layer, this would be advantageous because it would enable the provision of a pressure-sensitive adhesive sheet with excellent impact resistance by a simplified production method.

[0007] The present invention was created in view of the above circumstances, and has an object to provide a pressure-sensitive adhesive sheet that exhibits excellent impact resistance. [Means for solving the problem]

[0008] This specification provides a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer laminated on one or both sides of an impact absorbing layer. This configuration allows the impact absorbing layer and the pressure-sensitive adhesive layer to perform different functions, making it easy to achieve a pressure-sensitive adhesive sheet with a well-balanced combination of properties, such as adhesive properties and impact absorption. Here, both the impact absorbing layer and the pressure-sensitive adhesive layer contain a polymer having a carboxy group. The impact absorbing layer also contains an organometallic complex compound. The content of the organometallic complex compound is 0.1 to 1.2 parts by weight per 100 parts by weight of the base polymer contained in the impact absorbing layer. This configuration allows the polymers contained in the impact absorbing layer and the pressure-sensitive adhesive layer to be chemically bonded via the organometallic complex compound, thereby improving the interlayer strength between the impact absorbing layer and the pressure-sensitive adhesive layer. A pressure-sensitive adhesive sheet with sufficiently high interlayer strength between the impact absorbing layer and the pressure-sensitive adhesive layer can absorb the impact force without peeling between the impact absorbing layer and the pressure-sensitive adhesive layer when the pressure-sensitive adhesive sheet is subjected to an impact. Furthermore, the pressure-sensitive adhesive layer can subsequently deform after the impact absorbing layer deforms. When the impact absorbing layer and the pressure-sensitive adhesive layer can be deformed in a coordinated manner, the impact absorption time is prolonged and the impact resistance is easily improved.Furthermore, when the content of the organometallic complex compound is within the above range, the flexibility of the impact absorbing layer is easily controlled within a range suitable for exerting the impact absorption ability.With this configuration, the impact resistance of the pressure-sensitive adhesive sheet is easily improved.

[0009] In some embodiments, the impact absorbing layer contains an acrylic polymer and a styrene-based block copolymer. By including a styrene-based block copolymer, the impact absorbing layer is likely to be an elastomer layer with suitable flexibility. Having an elastomer layer with suitable flexibility contributes to improved impact absorption and improved interfacial adhesion between the impact absorbing layer and the pressure-sensitive adhesive layer. Furthermore, using an acrylic polymer in the impact absorbing layer contributes to improved interlayer strength, which tends to improve impact resistance. Furthermore, chemical resistance (the ability to withstand contact with chemicals and maintain adhesion) is likely to be improved.

[0010] In some embodiments, the pressure-sensitive adhesive layer is composed of an acrylic pressure-sensitive adhesive containing an acrylic polymer. This configuration tends to improve the interlayer strength and the peel strength from the adherend. Improved interlayer strength and peel strength from the adherend contribute to improved impact resistance of the pressure-sensitive adhesive sheet.

[0011] In some embodiments, the impact absorbing layer contains hollow particles. Impact absorbing layers containing hollow particles tend to deform favorably when an impact is applied, absorbing the impact. Therefore, this configuration tends to improve the impact resistance of the pressure-sensitive adhesive sheet. In addition, the use of hollow particles tends to reduce the viscosity during heat melting, making it easier to manufacture the impact absorbing layer using a hot melt method.

[0012] 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.

[0013] In some embodiments, the impact absorbing layer is formed from a hot melt composition. Such an impact absorbing layer is formed by molding in a heated molten state that is substantially free of organic solvents by pressing, coating, or the like, which is preferable from the viewpoints of productivity and reducing environmental impact.

[0014] The PSA sheets disclosed herein have excellent impact resistance and are therefore preferably used for joining components of portable electronic devices that require good impact resistance. Thus, 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. [Brief explanation of the drawings]

[0015] [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. [Figure 3] FIG. 2 is a diagram for schematically explaining a method for evaluating the impact peel strength of a pressure-sensitive adhesive sheet. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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.

[0017] In this specification, unless otherwise specified, the term "between layers" refers to the space between the impact absorbing layer (core layer) and the pressure-sensitive adhesive layer.

[0018] In this specification, the term "adhesive" refers to a material that is in a soft solid (viscoelastic) state at temperatures around room temperature and has the property of adhering to an adherend under pressure. The adhesive referred to here is generally a material having a complex tensile modulus E * (1Hz)<10 7 dyne / cm 2 The material may be a material having the properties satisfying the above (typically, a material having the above properties at 25°C).

[0019] In this specification, "(meth)acryloyl" refers to acryloyl and methacryloyl in a comprehensive sense. Similarly, "(meth)acrylate" refers to acrylate and methacrylate in a comprehensive sense, and "(meth)acrylic" refers to acrylic and methacrylic in a comprehensive sense.

[0020] In this specification, the term "acrylic polymer" refers to a polymer containing more than 50% by weight of monomer units derived from 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.

[0021] 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).

[0022] 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.

[0023] In this specification, the term "hot melt composition" refers to a composition used in a hot melt process. The term "hot melt process" refers to a method of forming a molded body (typically a sheet) by pressing, coating, or the like, a composition in a heated, molten state that is substantially free of organic solvents.

[0024] 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.

[0025] <Adhesive sheet composition> The pressure-sensitive adhesive sheet disclosed herein comprises an impact absorbing layer and a pressure-sensitive adhesive layer laminated on at least one surface of the impact absorbing layer. The concept of the pressure-sensitive adhesive sheet herein may include those referred to as pressure-sensitive adhesive tape, pressure-sensitive adhesive label, pressure-sensitive adhesive film, etc. The pressure-sensitive adhesive layer is typically formed continuously, but is not limited to such a form. For example, the pressure-sensitive adhesive layer may be formed in a regular or random pattern such as a dotted or striped pattern. The pressure-sensitive adhesive sheet may also be in the form of a roll or a sheet. Alternatively, the pressure-sensitive adhesive sheet may be processed into various shapes. The impact absorbing layer is disposed on the opposite side (inner side) of the pressure-sensitive adhesive layer from the adherend side (outer side). From the viewpoint of such layer arrangement, the "impact absorbing layer" may be referred to as the "core layer" in this specification.

[0026] The PSA sheet disclosed herein may be in the form of, for example, a single-sided PSA sheet having the cross-sectional structure schematically shown in Figure 1. This single-sided PSA sheet 1 is configured as a single-sided PSA sheet comprising an impact absorbing layer (core layer) 10 having a first side 10A and a second side 10B, and a PSA layer 21 provided on the first side 10A side. The PSA layer 21 is provided fixedly on the first side 10A side of the impact absorbing layer (core layer) 10, i.e., without the intention of separating the PSA layer 21 from the impact absorbing layer (core layer) 10. Before use, the PSA sheet 1 may be a component of a release-liner PSA sheet 100 in the form in which the surface (adhesive surface) 21A of the PSA layer 21 is protected by a release liner 31, at least the side facing the PSA layer 21 serving as a release surface, as shown in Figure 1. Alternatively, the release liner 31 may be omitted, and an impact absorbing layer (core layer) 10 having the second surface 10B as the release surface may be used, and the adhesive sheet 1 may be rolled up so that the adhesive surface 21A is in contact with the second surface (back surface) 10B of the impact absorbing layer (core layer) 10 and protected (in roll form).

[0027] 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 an impact absorbing layer (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 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 3 and wound into a spiral shape to form a release-liner PSA sheet in the form (roll form) in which the second adhesive surface 22A is protected by being in contact with the back surface of the release liner 31.

[0028] 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.

[0029] <Shock absorbing layer> The PSA sheet disclosed herein has an impact absorbing layer. As used herein, the term "impact absorbing layer" refers to a layer that, when an impact is applied to the PSA sheet, for example, by being dropped, converts the impact energy into other energy, such as deformation energy, thereby reducing the impact force acting on the entire PSA sheet. The impact absorbing layer typically has a maximum loss tangent tanδ in the temperature range of -40 to -10°C at a frequency of 1 Hz, and an initial modulus of elasticity of approximately 0.001 MPa as determined by a tensile test in a 23°C environment. In some preferred embodiments, the impact absorbing layer disclosed herein is a resin layer formed from a resin composition for forming an impact absorbing layer (hereinafter also referred to as a "core layer composition") that contains a base polymer, in order to provide the necessary flexibility for impact absorption.

[0030] The present inventors have focused particularly on improving the interlayer strength between the impact absorbing layer and the pressure-sensitive adhesive layer in order to improve the impact resistance of the pressure-sensitive adhesive sheet. As a result of extensive research, they have found that by incorporating a polymer having a carboxy group (hereinafter also referred to as "carboxy group-containing polymer A") into the impact absorbing layer and the pressure-sensitive adhesive layer, respectively, and further incorporating an organometallic complex compound into the impact absorbing layer, a crosslinking reaction between the layers can be induced to improve the interlayer strength, and as a result, the impact resistance of the pressure-sensitive adhesive sheet can be improved.

[0031] That is, the impact absorbing layer disclosed herein contains a carboxy group-containing polymer A (hereinafter, the carboxy group-containing polymer A contained in the impact absorbing layer will also be referred to as "carboxy group-containing polymer A1") and an organometallic complex compound.

[0032] (organometallic complex compounds) The impact absorbing layer disclosed herein contains an organometallic complex compound. Organometallic complex compounds are typically polyfunctional compounds in which a polyvalent metal atom is bonded (covalently or coordinately) to an organic compound (complexing agent). Such organometallic complex compounds function to crosslink and bond polar functional groups such as carboxyl groups and hydroxyl groups. From this perspective, the organometallic complex compound contained in the impact absorbing layer disclosed herein can also be understood as a metal complex crosslinking agent (or metal chelate crosslinking agent). By including an organometallic complex compound in the impact absorbing layer, carboxyl groups contained in the impact absorbing layer and the pressure-sensitive adhesive layer are chemically bonded via the organometallic complex compound contained in the impact absorbing layer, which facilitates improving the interlayer strength between the impact absorbing layer and the pressure-sensitive adhesive layer.

[0033] The impact absorbing layer in the technology disclosed herein may contain the organometallic complex compound in a form after crosslinking, a form before crosslinking, a partially crosslinked form, an intermediate or composite form thereof, etc. The organometallic complex compound is typically contained in the impact absorbing layer exclusively in the form after crosslinking.

[0034] The organometallic complex compound is preferably in a solid or powder state. In particular, when the impact absorbing layer disclosed herein is formed by a hot melt method involving blending materials at high temperatures, solid or powder additives reduce concerns about ignition and harm to the human body caused by volatile components compared to organic solvent dilution systems or liquid additives.

[0035] In the organometallic complex compound, examples of the polyvalent metal atom include elements of Group 2 of the periodic table, such as magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba); elements of Group 3 of the periodic table, such as scandium (Sc), yttrium (Y), lanthanoid elements [lanthanum (La), cerium (Ce), and the like], and actinoid elements [actinium (Ac), and the like]; elements of Group 4 of the periodic table, such as titanium (Ti) and zirconium (Zr); elements of Group 5 of the periodic table, such as vanadium (V), niobium (Nb), and tantalum (Ta); and elements of Group 6 of the periodic table, such as chromium (Cr). Group 6 elements of the periodic table, such as molybdenum (Mo), tungsten (W), etc.; Group 7 elements of the periodic table, such as manganese (Mn); Group 8 elements of the periodic table, such as iron (Fe); Group 9 elements of the periodic table, such as cobalt (Co); Group 10 elements of the periodic table, such as nickel (Ni), palladium (Pd), platinum (Pt); Group 11 elements of the periodic table, such as copper (Cu), silver (Ag), gold (Au); Group 12 elements of the periodic table, such as zinc (Zn); Group 13 elements of the periodic table, such as aluminum (Al), gallium (Ga), indium (In); and Group 14 elements of the periodic table, such as tin (Sn) and lead (Pb). In the organometallic complex compounds, the polyvalent metal atoms can be used alone or in combination of two or more. Aluminum, zirconium, and titanium are preferred as polyvalent metal atoms, with aluminum being particularly preferred.

[0036] Therefore, examples of the organometallic complex compound (metal complex crosslinking agent) that can be used include aluminum complex crosslinking agents, zirconium complex crosslinking agents, titanium complex crosslinking agents, chromium complex crosslinking agents, cobalt complex crosslinking agents, copper complex crosslinking agents, iron complex crosslinking agents, nickel complex crosslinking agents, vanadium complex crosslinking agents, zinc complex crosslinking agents, indium complex crosslinking agents, calcium complex crosslinking agents, magnesium complex crosslinking agents, manganese complex crosslinking agents, yttrium complex crosslinking agents, cerium complex crosslinking agents, strontium complex crosslinking agents, barium complex crosslinking agents, molybdenum complex crosslinking agents, lanthanum complex crosslinking agents, and tin complex crosslinking agents, and preferably aluminum complex crosslinking agents, zirconium complex crosslinking agents, and titanium complex crosslinking agents (more preferably aluminum complex crosslinking agents).

[0037] On the other hand, in the organometallic complex compound, the atom in the complexing agent that bonds to the polyvalent metal atom is not particularly limited, but an oxygen atom is preferred. Therefore, examples of the complexing agent include ester compounds, alcohol compounds, carboxylic acid compounds, ether compounds, and ketone compounds. More specifically, examples of the complexing agent include β-dicarbonyl compounds [e.g., β-diketones such as acetylacetone, 2,4-hexanedione, 2,4-heptanedione, 3,5-heptanedione, 2,4-octanedione, 3,5-octanedione, 2,4-nonanedione, 3,5-nonanedione, and 5-methyl-2,4-hexanedione; β-ketoesters (acetoacetate C), such as methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, isopropyl acetoacetate, butyl acetoacetate, isobutyl acetoacetate, s-butyl acetoacetate, t-butyl acetoacetate, 2-ethylhexyl acetoacetate, and dodecyl acetoacetate]. 1-20 alkyl esters, etc.; β-diesters such as diethyl malonate, etc.], and carbonyl compounds having a hydroxyl group or an amino group at the β-position (for example, diacetone alcohol, diacetone amine, salicylaldehyde, methyl salicylate, N-methyl salicylamide, etc.). The complexing agent may be used alone or in combination of two or more.

[0038] In some preferred embodiments, metal acetylacetonates (eg, aluminum tris(acetylacetonate)) may be employed as organometallic complex compounds.

[0039] When the organometallic complex compound is, for example, an aluminum complex-based crosslinking agent in which the polyvalent metal atom is aluminum, examples of the aluminum complex-based crosslinking agent include aluminum tris(acylacetonates) such as aluminum tris(acetylacetonate) and aluminum tris(propionylacetonate); aluminum tris(acetoacetic acid alkyl esters) such as aluminum tris(ethylacetoacetate) and aluminum tris(t-butylacetoacetate); aluminum mono(acetylacetonate)bis(ethylacetoacetate), aluminum mono(acetylacetonate)bis(isobutylacetoacetate), aluminum mono(acetylacetonate)bis(2-ethylhexylacetonate), Examples of suitable aluminum complex crosslinking agents include aluminum [(mono- or bis-)(acetylacetonate)] [(bis- or mono-)(acetoacetic acid alkyl ester)] such as aluminum mono(acetylacetonate)bis(dodecylacetoacetate); aluminum [(mono- or bis-)(acylacetonate)] aluminum [(di- or mono-)alcoholates] such as (acetylacetonate)aluminum diisopropylate and bis(acetylacetonate)aluminum monoisopropylate; and aluminum [(mono- or bis-)(acetoacetic acid alkyl ester)] aluminum [(di- or mono-)alcoholates] such as (ethylacetoacetate)aluminum diisopropylate and bis(ethylacetoacetate)aluminum monoisopropylate. Suitable aluminum complex crosslinking agents include aluminum tris(acetylacetonate) and aluminum tris(ethylacetoacetate).

[0040] Furthermore, examples of organometallic complex compounds (such as zirconium complex crosslinking agents and titanium complex crosslinking agents) other than aluminum complex crosslinking agents include those corresponding to the aluminum complex crosslinking agents exemplified above (for example, those in which the polyvalent metal atom of the aluminum complex crosslinking agents exemplified above is changed to zirconium, titanium, or the like).

[0041] The preferred content of the organometallic complex compound can be determined, for example, by the ratio relative to the base polymer contained in the impact absorbing layer, which will be described later. From the viewpoint of improving the interlayer strength between the impact absorbing layer and the pressure-sensitive adhesive layer, the content of the organometallic complex compound is preferably 0.1 parts by weight or more, more preferably 0.15 parts by weight or more, and even more preferably 0.2 parts by weight or more, relative to 100 parts by weight of the base polymer (e.g., a blend of an acrylic polymer and a styrene block copolymer) contained in the impact absorbing layer. In some embodiments, it may be 0.25 parts by weight or more, 0.3 parts by weight or more, 0.35 parts by weight or more, or even 0.4 parts by weight or more. If the content of the organometallic complex compound is too high, the elastic modulus of the impact absorbing layer may become too high, which may reduce the impact absorption ability of the impact absorbing layer. From this viewpoint, the content of the organometallic complex compound in the impact absorbing layer is preferably 1.2 parts by weight or less, more preferably 1.0 part by weight or less, per 100 parts by weight of the base polymer (e.g., a blend of an acrylic polymer and a styrene block copolymer) contained in the impact absorbing layer, and in some embodiments, it may be 0.8 parts by weight or less, or may be 0.6 parts by weight or less.

[0042] (base polymer) The impact absorbing layer disclosed herein contains one or more carboxy group-containing polymers A1. Other than the inclusion of the carboxy group-containing polymer A1, the polymer material contained in the impact absorbing layer is not particularly limited. In some embodiments, the impact absorbing layer contains 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 impact absorbing 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-based polymers. Here, when the impact absorbing layer contains two or more polymers as base polymers, it includes the case where a blend of the respective polymers is considered to be a single base polymer and the impact absorbing layer contains the base polymer.

[0043] (acrylic polymer) In some preferred embodiments, the impact absorbing layer includes an acrylic polymer as a base polymer. The acrylic polymer is preferably a polymer of a monomer raw material (monomer component) that includes, for example, an alkyl (meth)acrylate as a main monomer and may further include 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 carboxyl group (i.e., a carboxyl group-containing polymer A1).

[0044] 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 1-20 From 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.

[0045] R 2 C 1-20Examples 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).

[0046] The technology disclosed herein is a method for preparing a polymerizable compound in which the monomer component is R 2 C 4-10 Among 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). 4-10In 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).

[0047] 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.

[0048] 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.

[0049] The functional group-containing monomers can be used alone or in combination of two or more. Carboxy group-containing monomers, hydroxyl group-containing monomers, and cyano group-containing monomers are preferred because they can effectively introduce crosslinking points and improve cohesive strength. Among them, it is preferable to use a carboxy group-containing monomer from the viewpoint of introducing a carboxy group into the acrylic polymer and improving interlayer strength. Among the carboxy group-containing monomers, AA and MAA are preferred.

[0050] 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).

[0051] The acrylic polymer contained in the impact absorbing layer is preferably copolymerized with a carboxyl group-containing monomer. When the acrylic polymer is copolymerized with a carboxyl group-containing monomer, the proportion of the carboxyl group-containing monomer in the total monomer components is typically 0.1 wt% or more, preferably 1 wt% or more, more preferably 2 wt% or more, and even more preferably 3 wt% or more, and may be 3.5 wt% or more, 4 wt% or more, 4.5 wt% or more, or 4.8 wt% or more, from the viewpoint of impact absorption capacity and interlayer adhesion. The proportion of the carboxyl group-containing monomer in the total monomer components is preferably 15 wt% or less, for example, 10 wt% or less, 8 wt% or less, or 6 wt% or less.

[0052] 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.

[0053] 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.

[0054] 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).

[0055] 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.

[0056] 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.

[0057] 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℃

[0058] 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.

[0059] 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.

[0060] The method for obtaining the acrylic polymer used in the impact absorbing 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, etc. similar to those of conventionally known general suspension polymerization.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] (styrene-based block copolymer) In some preferred embodiments, the impact absorbing 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.

[0068] 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.

[0069] 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.

[0070] 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 impact absorbing 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.

[0071] The styrene content of the styrene block copolymer (typically, a hydrogenated styrene block copolymer; the same applies hereinafter) may be, for example, 5 to 40% by weight. From the viewpoint of the cohesion of the core layer, a styrene block copolymer having a styrene content of 10% by weight or more (more preferably, more than 10% by weight, e.g., 12% by weight or more) is usually preferred. From the viewpoint of interlaminar strength, the styrene content of the styrene 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, e.g., 18% by weight or less). From the viewpoint of obtaining high chemical resistance, a styrene block copolymer having a styrene content of 10 to 22% by weight can be preferably used.

[0072] (hollow particles) In some embodiments, the impact absorbing layer disclosed herein contains hollow particles. By including hollow particles in the impact absorbing layer, the impact absorption properties of the impact absorbing layer are likely to be improved. Furthermore, when the impact absorbing 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.

[0073] Here, hollow particles are spheres having a solid shell. From this perspective, a layer containing hollow particles is clearly distinguished from a so-called foam layer, 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.

[0074] 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.

[0075] The content of hollow particles is not particularly limited. In some preferred embodiments, the content of hollow particles in the impact absorbing 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 impact absorbing 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 impact absorbing 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 impact absorbing layer is within the above range, it is easy to form an impact absorbing layer with suitable impact absorbing capabilities. Furthermore, when the impact absorbing layer is formed by a hot melt method, the viscosity during heating and melting is likely to be suitable for coating.

[0076] (coloring agent) The impact absorbing 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 impact absorbing layer is preferably colored black.

[0077] Examples of black colorants that can be used to color the impact absorbing 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 standpoint of cost and availability. The amount of the black colorant used is not particularly limited. In some preferred embodiments, the content of the black colorant (e.g., carbon black) in the impact absorbing 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.

[0078] (Other crosslinkers) The composition for forming an impact absorbing layer used to form the impact absorbing layer may contain a crosslinking agent other than the organometallic complex compound (hereinafter also referred to as "other crosslinking agent"). The impact absorbing 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 impact absorbing layer exclusively in a form after crosslinking reaction.

[0079] The type of other 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 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 other crosslinking agents can be used alone or in combination of two or more. The amount of the other crosslinking agent used is not particularly limited, and is suitably, for example, approximately 10 parts by weight or less (e.g., approximately 0.005 to 10 parts by weight) per 100 parts by weight of the base polymer, and preferably approximately 5 parts by weight or less (0.01 to 5 parts by weight).

[0080] (tackifier) In some embodiments, the impact absorbing layer contains a tackifier (typically a tackifier resin). This makes it easier to obtain a PSA sheet that exhibits excellent interlayer strength. 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.

[0081] 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.

[0082] (Formation of shock absorbing layer) The impact absorbing layer disclosed herein can be formed from a core layer composition. The form of the core layer composition is not particularly limited, and can be, for example, a core layer composition in a form containing the components of the above-mentioned 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.

[0083] The impact absorbing layer disclosed herein can be formed from a core layer composition that is substantially free of organic solvents. Here, the core layer composition being 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.

[0084] The method for forming the impact absorbing layer (core layer) from the core layer composition is not particularly limited, and any known appropriate method can be used. For example, the impact absorbing layer can be formed by a hot melt method, a calendar method, a casting method, an inflation extrusion method, a T-die extrusion method, or the like. 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 a sheet (hot melt pressing method).

[0085] From the viewpoint of the storage stability of the core layer composition, it is preferable to form the impact absorbing layer from a solvent-free core layer composition. The impact absorbing layer disclosed herein may have a residual organic solvent content of less than 1000 ppm (the amount of organic solvent per 1 g of impact absorbing 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 impact absorbing 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.

[0086] (thickness of the shock absorbing layer) The thickness of the impact absorbing 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 impact absorbing 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. An impact absorbing layer having the above thickness tends to improve processability. In some preferred embodiments, the thickness of the impact absorbing 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 impact absorbing layer is suitably approximately 4 μm or more (e.g., 20 μm or more). The thickness of the impact absorbing 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 impact absorbing 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, may be 100 μm or more (for example, more than 100 μm), may be 120 μm or more, or may be 140 μm or more.When the thickness of the impact absorbing layer is increased, impact resistance tends to be improved.

[0087] <Adhesive layer> The pressure-sensitive adhesive sheet disclosed herein has a pressure-sensitive adhesive layer laminated on at least one surface of an impact absorbing layer. The pressure-sensitive adhesive layer disclosed herein contains one or more carboxy group-containing polymers A (hereinafter, the carboxy group-containing polymers A contained in the pressure-sensitive adhesive layer are also referred to as "carboxy group-containing polymers A2"). Here, the carboxy group-containing polymers A1 and A2 may be the same type of carboxy group-containing polymer A, or may be different types of carboxy group-containing polymers A.

[0088] (base polymer) In the technology disclosed herein, the type of adhesive constituting the adhesive layer is not particularly limited, except that it contains a carboxy group-containing polymer A2. 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-containing polymers. From the viewpoints of adhesive performance, cost, etc., adhesives containing an acrylic polymer or a rubber polymer as the base polymer are preferably used. Among these, adhesives using an acrylic polymer as the base polymer (acrylic adhesives) are preferred. The technology disclosed herein is preferably implemented in an embodiment using an acrylic adhesive.

[0089] 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.

[0090] 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.

[0091] (acrylic polymer) In some preferred embodiments, the pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer, and in some preferred embodiments, the acrylic polymer is a polymer having a carboxy group (i.e., carboxy group-containing polymer A2).

[0092] The acrylic polymer may be the same as the acrylic polymer that can be contained in the impact absorbing layer, and therefore a duplicated description will be omitted.

[0093] The acrylic polymer contained in the pressure-sensitive adhesive layer is preferably copolymerized with a carboxyl group-containing monomer. When a carboxyl group-containing monomer is copolymerized with the 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 1.5 wt% or more, from the viewpoint of improving interlayer strength. When emulsion polymerization is used to prepare the acrylic polymer contained in the pressure-sensitive adhesive layer, if the content of the carboxyl group-containing monomer is too low, the polymerization reaction tends to proceed less stably. From the viewpoint of adhesive properties such as adhesive 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. 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, from the viewpoint of impact resistance. When emulsion polymerization is used to prepare the acrylic polymer contained in the pressure-sensitive adhesive layer, if the content of the carboxyl group-containing monomer is too high, a homopolymer of the carboxyl group-containing monomer may be produced in water.

[0094] 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).

[0095] 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.

[0096] 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.

[0097] 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.

[0098] (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.

[0099] 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).

[0100] 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, viscosity modifiers, leveling agents, crosslinking aids, release modifiers, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), 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 as they do not particularly characterize the present invention.

[0101] (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.

[0102] (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.

[0103] (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 an impact-absorbing 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, generally, as the thickness of a pressure-sensitive adhesive layer decreases, impact resistance and adhesion to the adherend tend to decrease. However, according to the technology disclosed herein, sufficient impact resistance and adhesive strength can be achieved with a configuration having 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, may be 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 the impact-absorbing layer, the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may have the same thickness or different thicknesses.

[0104] <Method of manufacturing adhesive sheet> In producing a PSA sheet, the method for providing a PSA layer on one or both surfaces of an impact absorbing 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 impact absorbing 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 impact absorbing 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 impact absorbing layer (transfer-transfer method), or a double-sided PSA sheet may be produced by applying the transfer method to one surface of the impact absorbing layer (typically the surface on which the PSA layer is first applied) and the direct coating method to the other surface (transfer-direct method). Among 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 an impact absorbing layer, and then the laminate of the impact absorbing layer and the adhesive layer is aged to obtain an adhesive sheet.

[0105] <Application> The pressure-sensitive adhesive sheet disclosed herein has excellent impact resistance. Utilizing this characteristic, the pressure-sensitive adhesive sheet disclosed herein can be preferably used in various products requiring impact resistance or in a form attached to components constituting the products, for applications such as fixing, joining, molding, decorating, protecting, and supporting the products or components. In particular, it can be preferably used to fix the above-mentioned products or components. 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 sheet disclosed herein is suitable for such portable electronic devices.

[0106] 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.

[0107] The matters disclosed by this specification include the following: [1] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer laminated on one or both surfaces of an impact absorbing layer, the impact absorbing layer and the pressure-sensitive adhesive layer each contain a polymer having a carboxy group, The impact absorbing layer contains an organometallic complex compound, A pressure-sensitive adhesive sheet, wherein the content of the organometallic complex compound is 0.1 parts by weight or more and 1.2 parts by weight or less per 100 parts by weight of the base polymer contained in the impact absorbing layer. [2] The pressure-sensitive adhesive sheet according to [1] above, wherein the impact absorbing layer contains an acrylic polymer and a styrene block copolymer. [3] The pressure-sensitive adhesive sheet according to [1] or [2] above, wherein the pressure-sensitive adhesive layer is composed of an acrylic pressure-sensitive adhesive containing an acrylic polymer. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the impact absorbing layer contains hollow particles. [5] The pressure-sensitive adhesive sheet according to any one of the above [1] to [4], wherein the pressure-sensitive adhesive layer is formed from a water-dispersible pressure-sensitive adhesive composition. [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, wherein the impact absorbing layer is formed from a hot melt composition. [7] The pressure-sensitive adhesive sheet according to any one of [1] to [6] above, wherein the pressure-sensitive adhesive sheet is configured as a double-sided pressure-sensitive adhesive sheet in which a first pressure-sensitive adhesive layer is laminated on one side of the impact absorbing layer and a second pressure-sensitive adhesive layer is laminated on the other side of the impact absorbing layer. [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. [Example]

[0108] 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.

[0109] Example 1 (Formation of shock absorbing layer (core layer)) 65 parts of an acrylic polymer (trade name "NTK2", manufactured by Soken Chemical & Engineering Co., Ltd.) was coated with 5 parts of carbon black (trade name "Asahi CB#50", manufactured by Asahi Carbon Co., Ltd.) and 0.33 parts of hollow particles (trade name "Expancel 920DE40", manufactured by Akzo Nobel). The acrylic polymer (trade name "NTK2", manufactured by Soken Chemical & Engineering Co., Ltd.) used here is an acrylic polymer containing a carboxy group. In the above acrylic polymer, the proportion of the carboxy group-containing monomer in the total monomer components constituting the acrylic polymer was approximately 3 to 7 wt%. Using a benchtop kneader (manufactured by Xplore Instrument), the kneading temperature was set to 120°C and the rotation speed to 50 rpm. 35 parts of a styrene-ethylene-butylene-styrene block copolymer (SEBS, product name "Septon BIO SF902" manufactured by Kuraray Co., Ltd.), the entire amount of the acrylic polymer coated with carbon black and hollow particles obtained above, 0.25 parts of an aluminum chelate (product name "Orgatix AL-3215" manufactured by Matsumoto Fine Chemical Co., Ltd.) as an organometallic complex compound, and 20 parts of a tackifier (product name "SYLVALITE RE100S" manufactured by KRATON) were added in this order every minute. After adding the materials, the rotation speed was changed to 100 rpm, and the kneading was continued for 10 minutes. Thereafter, 0.25 parts of an epoxy crosslinking agent (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 2 minutes at a rotation speed of 100 rpm. After kneading, the materials were discharged from the kneader to obtain a kneaded product.

[0110] The resulting kneaded material was sandwiched between two 75 μm thick polyethylene terephthalate (PET) release liners (trade name "Diafoil MRF75", manufactured by Mitsubishi Chemical Corporation) together with a 160 μm thick metal spacer. The release liners with the kneaded material sandwiched between them were sandwiched between iron plates, placed on the iron plates of a press heated to 120°C, and preheated for 30 seconds. After preheating, the sheet was pressed twice at a pressure of 10 MPa for 30 seconds to obtain a 160 μm thick sheet, which served as the impact absorbing layer (core layer).

[0111] (Formation of adhesive layer) An acrylic emulsion pressure-sensitive adhesive (trade name "Polysol SE-4530", manufactured by Resonac Co., Ltd.) was applied to the silicone-treated surface of a 38 μm-thick polyethylene terephthalate (PET) release liner (trade name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) to a dry thickness of 20 μm. The adhesive was then dried by heating at 100°C for 3 minutes to form a pressure-sensitive adhesive layer on the release liner. The acrylic emulsion pressure-sensitive adhesive (trade name "Polysol SE-4530", manufactured by Resonac Co., Ltd.) used contained an acrylic polymer having a carboxy group. The proportion of the carboxy group-containing monomer in the total monomer components constituting the acrylic polymer was approximately 1 to 5 wt %.

[0112] (Preparation of double-sided adhesive sheets) One surface (exposed surface) of the pressure-sensitive adhesive layer was bonded to one surface of the core layer. Next, the release liner was removed, and another pressure-sensitive adhesive layer was bonded to the other surface of the core layer, yielding a laminate with a total thickness of 200 μm and a structure of first pressure-sensitive adhesive layer / core layer / second pressure-sensitive adhesive layer. This laminate was aged in a dryer at 80° C. for 96 hours to produce a double-sided pressure-sensitive adhesive sheet according to this example.

[0113] <Examples 2 and 3 and Comparative Examples 1 and 2> Double-sided PSA sheets according to each example were produced in the same manner as in Example 1, except that the amount of aluminum chelate used in forming the core layer A was changed as shown in Table 1.

[0114] An overview of each example is shown in Table 1.

[0115] [Impact resistance] The impact resistance of each of the resulting pressure-sensitive adhesive sheets was evaluated using the method schematically shown in Figure 3. Specifically, the pressure-sensitive adhesive sheet of each example was cut into a size of 1 cm x 1 cm to prepare measurement sample 3. The release liner on one side of measurement sample 3 was peeled off to expose the adhesive surface, and the adhesive surface was then bonded to the center of a 1.5 cm x 1.5 cm stainless steel (SUS304) jig 42. Next, the release liner on the other side of measurement sample 3 was peeled off to expose the adhesive surface, and the adhesive surface was then bonded to the center of an acrylic resin plate 44 measuring 6 cm x 5 cm as an adherend. With both sides of measurement sample 3 thus bonded to stainless steel jig 42 and acrylic resin plate 44, respectively, measurement sample 3 was left in an 80°C environment for 30 minutes. Thereafter, stainless steel jig 42 was attached to load cell 46 of an impact peel strength evaluation device with jig 42 facing up and acrylic resin plate 44 facing down. Next, a polycarbonate box-shaped plastic jig 48 with one open side was placed over the stainless steel jig 42 with the measurement sample 3 attached, and the plastic jig 48 was placed on the acrylic resin plate 44. The top surface of the plastic jig 48, i.e., the height of the outer top surface of the plastic jig 48 opposite the acrylic resin plate 44, was used as a reference point. A 510 g steel ball 50 was dropped vertically downward from a height of 30 cm from this point, and the steel ball 50 struck the outer top surface of the plastic jig 48. The stress applied to the measurement sample 3 at this time was measured using a recorder (trade name "Omniace" manufactured by A&D Co., Ltd.) attached to the load cell 46. For all of the measurement samples 3 measured in this example, the stress increased upon collision between the steel ball 50 and the plastic jig 48. After a brief change in stress was observed, the measurement sample 3 completely separated from the acrylic resin plate 44, and the measured stress returned to 0 (zero).

[0116] The maximum stress obtained in the above test was defined as the impact peel strength [unit: N / cm 2] was calculated. The higher the impact peel strength, the higher the impact resistance of the PSA sheet. The time from when stress begins to be applied to the measurement sample until the measurement sample breaks and the stress becomes 0 was defined as the impact absorption time (unit: μsec). The longer the impact absorption time, the better the impact resistance tends to be. Here, if the impact absorption time is sufficiently long, it is predicted that deformation of the impact absorbing layer (typically elongation in the thickness direction) and deformation of the PSA layer (typically elongation in the thickness direction) will occur in concert in that order.

[0117] In addition, the failure mode of the measured sample was observed after the impact test. Specifically, a photograph was taken of the fractured (peeled) surface of the measured sample after the test, and the photograph was analyzed to determine the percentage of the area of ​​the impact absorbing layer of the measured sample where cohesive failure had occurred, which was calculated as the cohesive failure rate [%]. A higher cohesive failure rate [%] indicates less fracture (peeling) occurred between the impact absorbing layer and the adhesive layer, suggesting relatively high interlayer strength. The evaluation results obtained are shown in Table 1.

[0118] [Table 1]

[0119] As shown in Table 1, the pressure-sensitive adhesive sheets of Examples 1 to 3, in which the impact absorbing layer contains an organometallic complex compound in a ratio of 0.1 to 1.2 parts by weight per 100 parts by weight of base polymer, exhibited higher impact peel strength and significantly longer impact absorption time than the pressure-sensitive adhesive sheets of Comparative Examples 1 and 2, which contained no organometallic complex compound or a higher amount than the above range. Furthermore, the cohesive failure rates after impact testing for the pressure-sensitive adhesive sheets of Examples 1 to 3 were all 100%, confirming that no failure occurred between the impact absorbing layer and the pressure-sensitive adhesive layer. This is thought to be due to improved interlayer strength.

[0120] 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]

[0121] 1 adhesive sheet 2 adhesive sheets 3 Measurement sample 10 core layer 21 Adhesive layer (first adhesive layer) 22 Second adhesive layer 31 Release liner 32 Release liner 42 Stainless steel jig 44 Acrylic resin plate 46 load cells 48 Plastic Jig 50 steel balls 100 adhesive sheets with release liner 200 adhesive sheet with release liner

Claims

1. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer laminated on one or both surfaces of an impact absorbing layer, the impact absorbing layer and the pressure-sensitive adhesive layer each contain a polymer having a carboxy group, the impact absorbing layer contains an organometallic complex compound, A pressure-sensitive adhesive sheet, wherein the content of the organometallic complex compound is 0.1 parts by weight or more and 1.2 parts by weight or less per 100 parts by weight of the base polymer contained in the impact absorbing layer.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the impact absorbing layer contains an acrylic polymer and a styrene block copolymer.

3. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive layer is made of an acrylic pressure-sensitive adhesive containing an acrylic polymer.

4. The pressure-sensitive adhesive sheet according to claim 1 , wherein the impact absorbing layer contains hollow particles.

5. 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.

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

7. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive sheet is configured as a double-sided pressure-sensitive adhesive sheet in which a first pressure-sensitive adhesive layer is laminated on one side of the impact absorbing layer and a second pressure-sensitive adhesive layer is laminated on the other side of the impact absorbing layer.

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

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