Adhesive sheet

Abstract

Provided is an adhesive sheet that includes, in the given order, a resin film substrate, an undercoat layer, and an adhesive layer. The undercoat layer is provided on at least one surface of the resin film substrate and is in contact with the adhesive layer. In addition, the adhesive layer is formed from an adhesive composition containing a rubber-based latex and an aqueous crosslinking agent. The aqueous crosslinking agent includes an aqueous crosslinking agent having at least one functional group selected from among an oxazoline group, an isocyanate group and an epoxy group. Moreover, the undercoat layer includes a water-dispersible polymer having an oxazoline group.

Description

adhesive sheet

[0001] The present invention relates to a pressure-sensitive adhesive sheet. This application claims priority to Japanese Patent Application No. 2023-116983, filed on July 18, 2023, the entire contents of which are incorporated herein by reference.

[0002] Generally, pressure-sensitive adhesives (also referred to as pressure-sensitive adhesives; the same applies hereinafter) are 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, pressure-sensitive adhesives are widely used in various fields for purposes such as bonding, fixing, surface protection, masking, and marking, for example, in the form of a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on a substrate. Patent Document 1 is an example of a document disclosing this type of prior art. Patent Document 1 describes a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed on one side of a polyvinyl chloride film, the pressure-sensitive adhesive layer being formed from an aqueous pressure-sensitive adhesive composition containing rubber latex.

[0003] As a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on a substrate, one having a primer layer provided on the substrate is used. The provision of the primer layer improves the anchoring property of the pressure-sensitive adhesive layer to the substrate, and can suppress the occurrence of a problem (adhesive residue) in which adhesive residue remains on the surface of the adherend when the pressure-sensitive adhesive sheet is removed from the adherend. Patent documents disclosing such primer layers include Patent Documents 2 and 3. Patent Document 2 describes forming a primer layer made of an oxazoline group-containing acrylic polymer on one side of a polyethylene terephthalate film, and then forming an acrylic pressure-sensitive adhesive layer thereon. Patent Document 3 describes providing a primer layer made of a water-soluble oxazoline group-containing acrylic polymer between a polarizing film and an acrylic pressure-sensitive adhesive layer.

[0004] Japanese Patent No. 4676945 Japanese Patent Application Publication No. 2011-149002 Japanese Patent No. 4841267

[0005] In recent years, environmental considerations and efforts to eliminate the use of petroleum resources have led to calls for a reduction in the amount of organic solvents used. From this perspective, for example, even in the case of rubber-based pressure-sensitive adhesives, the use of aqueous pressure-sensitive adhesive compositions containing rubber latex is more desirable than solvent-based pressure-sensitive adhesive compositions in which the adhesive components are dissolved in an organic solvent. However, pressure-sensitive adhesives formed from pressure-sensitive adhesive compositions containing rubber latex, such as natural rubber latex, tend to have poorer anchoring properties to resin film substrates than pressure-sensitive adhesives formed from solvent-based pressure-sensitive adhesive compositions. In particular, when a polyolefin-based resin film is used as the resin film substrate, rubber latex-containing pressure-sensitive adhesive compositions tend to have poorer anchoring properties to the polyolefin-based resin film, which can result in adhesive residue being left behind when the pressure-sensitive adhesive sheet is removed from the adherend. For example, pressure-sensitive adhesive sheets used for surface protection of adherends are typically attached to the surface of the adherend, and after achieving their protective purpose, are usually peeled (removed) from the adherend. If a pressure-sensitive adhesive sheet used for such purposes does not have sufficient anchoring properties to the substrate, adhesive residue may be left behind when the sheet is removed from the adherend, which can contaminate the adherend, undesirably. Furthermore, adhesive sheets with poor anchoring properties of the adhesive layer may leave adhesive residue on the adherend surface during rework (reapplication). Rework refers to the process of peeling the adhesive sheet from the adherend and reapplication when the adhesive sheet is misaligned or the adhesive position is misaligned when applied to the adherend. Furthermore, if the adhesive layer does not have good anchoring properties, the adhesive layers may come into unintentional contact with each other during use of the adhesive sheet, and the adhesive layers may peel off from the substrate when attempting to peel them off. In such cases, the adhesive sheet can no longer be used as a product.

[0006] A known method for improving anchoring properties is to modify the substrate surface by corona discharge treatment or the like. However, corona discharge treatment does not produce the expected effect on rubber-based latex-containing pressure-sensitive adhesive compositions. Furthermore, the use of a primer containing an organic solvent goes against the trend toward eliminating organic solvents, thereby diminishing the significance of adopting a rubber-based latex-containing pressure-sensitive adhesive composition.

[0007] The present invention was created in view of the above circumstances, and aims to provide a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer formed using a rubber latex is well anchored to a resin film substrate without relying on organic solvents.

[0008] This specification provides a pressure-sensitive adhesive sheet having, in this order, a resin film substrate, an undercoat layer, and a pressure-sensitive adhesive layer. The undercoat layer is provided on at least one surface of the resin film substrate and is in contact with the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing a rubber latex and an aqueous crosslinking agent. The aqueous crosslinking agent contains an aqueous crosslinking agent having at least one functional group selected from an oxazoline group, an isocyanate group, and an epoxy group. The undercoat layer contains a water-dispersible polymer having an oxazoline group. By blending a pressure-sensitive adhesive composition containing a rubber latex with an aqueous crosslinking agent having a specific functional group to form a pressure-sensitive adhesive layer and using the water-dispersible polymer having an oxazoline group as a undercoat, the anchoring ability of the pressure-sensitive adhesive layer to the resin film substrate can be improved. This configuration allows for the realization of a pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer formed using a rubber latex is firmly anchored to the resin film without relying on organic solvents. The above-mentioned PSA sheets use substantially no organic solvents or use a reduced amount of organic solvents, which is desirable from the viewpoints of environmental hygiene and non-reliance on petroleum resources. In this specification, "anchoring ability" refers to the resistance to peeling of the PSA layer from the substrate, regardless of whether the substrate and the PSA layer are in direct contact with each other, in other words, the resistance to breakdown (anchoring breakdown) between the PSA layer and the substrate. Therefore, in this specification, the term "anchoring ability of the PSA layer to the substrate" or an equivalent expression is used even for a configuration in which a primer layer is present between the substrate and the PSA layer.

[0009] In some preferred embodiments, the resin film substrate is a polyolefin-based resin film substrate. While rubber-based latex-containing pressure-sensitive adhesive compositions have difficulty in providing anchoring properties to resin films, particularly polyolefin-based resin films, the technology disclosed herein makes it possible to firmly anchor the pressure-sensitive adhesive layer to the polyolefin-based resin film substrate by incorporating a specific aqueous crosslinking agent into the pressure-sensitive adhesive layer and using a water-dispersible polymer having an oxazoline group as an undercoat.

[0010] In some preferred embodiments, the glass transition temperature (Tg) of the water-dispersible polymer having an oxazoline group is 0° C. or lower. By using an oxazoline group-containing water-dispersible polymer having a low Tg as a primer, excellent anchoring properties are likely to be obtained.

[0011] In some preferred embodiments, the content of the aqueous crosslinking agent in the PSA layer is 0.1 parts by weight or more per 100 parts by weight of the rubber latex, based on the nonvolatile content. A PSA layer containing a predetermined amount or more of the aqueous crosslinking agent can adhere well to an undercoat layer containing a water-dispersible polymer having an oxazoline group, thereby exhibiting good anchoring properties. Furthermore, by containing a predetermined amount or more of the aqueous crosslinking agent, the PSA layer has appropriate cohesion and is less likely to leave adhesive residue.

[0012] In some embodiments, the thickness of the primer layer is 0.01 μm or more and 3 μm or less. By setting the thickness of the primer layer within this range, the effect of improving anchoring force due to the placement of the primer layer can be preferably exhibited.

[0013] In some embodiments, the rubber latex contains 50% by weight or more of natural rubber latex on a non-volatile basis. Natural rubber latex usually contains impurities such as proteins, making it difficult to achieve good anchoring properties for resin films such as polyolefin resin films. However, according to the technology disclosed herein, by incorporating a specific aqueous crosslinking agent into the PSA layer and using a water-dispersible polymer having an oxazoline group as an undercoat, it is possible to firmly anchor a PSA layer formed containing a rubber latex primarily composed of natural rubber latex to a resin film substrate.

[0014] The PSA sheet disclosed herein has a PSA layer that is well anchored to the resin film substrate, so that adhesive residue is unlikely to be left behind when peeled off from an adherend, making it suitable as a PSA sheet for surface protection that is attached to the surface of an adherend, achieves its protective purpose, and is then peeled off from the adherend.

[0015] 1 is a cross-sectional view schematically illustrating a pressure-sensitive adhesive sheet according to an embodiment.

[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 descriptions may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the pressure-sensitive adhesive sheet of the present invention that is actually provided as a product.

[0017] The concept of adhesive sheet as used herein may include those referred to as adhesive tape, adhesive label, adhesive film, etc. The adhesive layer is typically formed continuously, but is not limited to such a form, and may be an adhesive layer formed in a regular or random pattern such as a dotted or striped pattern. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be cut, punched, or otherwise processed into an appropriate shape depending on the application or mode of use.

[0018] As used herein, the term "adhesive" refers to a material that is in a soft solid (viscoelastic) state at temperatures around room temperature and that easily adheres to an adherend by pressure. The adhesive referred to here generally has 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] <Configuration example of pressure-sensitive adhesive sheet> The pressure-sensitive adhesive sheet disclosed herein is a pressure-sensitive adhesive sheet with a resin film substrate (support) having a pressure-sensitive adhesive layer on one or both sides of the resin film substrate, and has a resin film substrate, an undercoat layer, and a pressure-sensitive adhesive layer in this order. The undercoat layer is provided on at least one side of the resin film substrate and is in contact with the pressure-sensitive adhesive layer.

[0020] The configuration of a pressure-sensitive adhesive sheet according to one embodiment is shown schematically in Figure 1. This pressure-sensitive adhesive sheet 1 comprises a resin film substrate 10, an undercoat layer 30 provided on a first surface 10A of the resin film substrate 10, and a pressure-sensitive adhesive layer 20 disposed on the surface 30A of the undercoat layer 30, and is used by attaching the pressure-sensitive adhesive layer 20 to an adherend. The pressure-sensitive adhesive sheet 1 comprises the resin film substrate 10, the undercoat layer 30, and the pressure-sensitive adhesive layer 20, in this order, with the undercoat layer 30 disposed between the resin film substrate 10 and the pressure-sensitive adhesive layer 2. In addition, in the pressure-sensitive adhesive sheet 1, the other surface (back surface, second surface) 10B of the resin film substrate 10 is a surface having releasability (release surface). The PSA sheet 1 before use (i.e., before attachment to an adherend) may be in the form of a roll 50, as shown in FIG. 1 , in which the surface (adhesive surface) 20A of the PSA layer 20 is wound around a core (winding core) 52 in a roll shape so that the surface (adhesive surface) 20A abuts against the back surface 10B of the resin film substrate 10, thereby protecting the surface 20A. It may also be in the form of a roll without a core 52, i.e., a so-called coreless roll in which the PSA sheet 1 is wound alone. Alternatively, the PSA sheet 1 before use may be in the form of a roll, or may be in the form of a laminate in which sheet-like (discrete) PSA sheets are laminated such that the PSA layer surface of one PSA sheet abuts against the back surface of another PSA sheet, thereby protecting the adhesive surface 20A. Alternatively, the surface 20A of the PSA sheet 1 before use may be protected by a release liner, rather than by the back surface of the substrate constituting the PSA sheet.

[0021] In addition, when the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer on both sides of the resin film substrate, an undercoat layer can be provided on both sides (first side and second side) of the resin film substrate. When an undercoat layer is provided on both sides of the resin film substrate, the pressure-sensitive adhesive sheet has a first pressure-sensitive adhesive layer, a first undercoat layer, a resin film substrate, a second undercoat layer, and a second pressure-sensitive adhesive layer, in this order. Unless otherwise specified, the details described below regarding the pressure-sensitive adhesive layer apply independently to the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer in an embodiment in which the resin film substrate has a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on each side. Similarly, the details described below regarding the undercoat layer apply independently to the first undercoat layer and the second undercoat layer in an embodiment in which the resin film substrate has a first undercoat layer and a second undercoat layer on each side.

[0022] <Adhesive Layer> (Rubber Latex (A)) The adhesive layer is formed from a pressure-sensitive adhesive composition containing a rubber latex (A). As the rubber latex (A), either a natural rubber latex (A1) or a synthetic rubber latex (A2) can be used. Examples of the synthetic rubber latex (A2) include styrene-butadiene copolymer latex (SBR latex), nitrile rubber latex (NBR latex), and chloroprene latex. Such rubber latexes (A) may be used alone or in combination of two or more. The rubber latex refers to a dispersion in which a rubber polymer such as natural rubber or synthetic rubber is dispersed in water, and the natural rubber latex and synthetic rubber latex refer to dispersions in which natural rubber and synthetic rubber are dispersed in water, respectively.

[0023] In some embodiments, the PSA composition contains natural rubber latex (A1). PSA formed using natural rubber is likely to provide good adhesion to an adherend. On the other hand, because natural rubber latex (A1) usually contains impurities such as proteins, PSA layers formed using natural rubber latex (A1) are unlikely to provide good anchoring properties to resin films such as polyolefin resin films. However, the technology disclosed herein makes it possible to improve the anchoring properties of PSA layers formed using natural rubber latex (A1).

[0024] The natural rubber contained in the natural rubber latex (A1) may be, for example, depolymerized or non-depolymerized. The natural rubber may be unmodified natural rubber latex or modified natural rubber latex modified with, for example, an acrylic acid ester. Unmodified natural rubber latex and modified natural rubber latex may be used in combination. Although non-deproteinized natural rubber latex that has not been subjected to deproteinization treatment is usually used as the natural rubber latex (A1), deproteinized natural rubber latex that has been subjected to deproteinization treatment may also be used. The deproteinization treatment can be carried out by various known methods, such as a method using a protease. One type of natural rubber can be used alone, or two or more types can be used in combination.

[0025] In some preferred embodiments, unmodified natural rubber latex is used as the natural rubber latex (A1) from the viewpoints of adhesion, productivity, etc. In such embodiments, the proportion of unmodified natural rubber latex contained in the natural rubber latex (A1) is about 50% by weight or more (e.g., more than 50% by weight) based on the non-volatile content, and may be about 70% by weight or more, about 90% by weight or more, or about 95% by weight or more, and the natural rubber contained in the natural rubber latex (A1) may be substantially composed of unmodified natural rubber.

[0026] In this specification, the phrase "X is substantially composed of Y" means that the ratio of Y in X is 97% by weight or more and 100% by weight or less, and preferably 99% by weight or more and 100% by weight or less, and does not exclude the case where X unintentionally contains components other than Y.

[0027] In some preferred embodiments, a non-deproteinized natural rubber latex is used as the natural rubber latex (A1). By using a non-deproteinized natural rubber latex, the proteins in the natural rubber latex (A1) tend to react with the aqueous crosslinking agent (C), resulting in a high cohesive strength. In such embodiments, the proportion of non-deproteinized natural rubber latex in the natural rubber latex (A1) is approximately 50% by weight or more (e.g., more than 50% by weight) based on the non-volatile content, and may be approximately 70% by weight or more, approximately 90% by weight or more, or approximately 95% by weight or more. The natural rubber in the natural rubber latex (A1) may be substantially composed of non-deproteinized natural rubber. While not particularly limited, the amount of protein in the non-deproteinized natural rubber is approximately 0.2 to 0.7% by weight in terms of nitrogen content.

[0028] In an embodiment in which the rubber latex (A) contains natural rubber latex (A1), the proportion of the natural rubber latex (A1) contained in the rubber latex (A) is not particularly limited and may be, for example, about 10% by weight or more, or about 30% by weight or more, based on the non-volatile content. In some preferred embodiments, the proportion of the natural rubber latex (A1) contained in the rubber latex (A) is about 50% by weight or more (e.g., more than 50% by weight), about 70% by weight or more, about 90% by weight or more, or about 95% by weight or more, based on the non-volatile content, and the rubber latex (A) may be essentially composed of natural rubber latex (A1).

[0029] In some embodiments, the PSA composition contains a synthetic rubber latex (A2). PSA formed using the synthetic rubber latex (A2) tends to provide better anchoring properties to resin films and the like than PSA formed using a natural rubber latex (A1). As the synthetic rubber latex (A2), any commercially available latex for PSA applications can be used without particular limitation. Both unmodified synthetic rubber latex and modified (e.g., acid-modified) synthetic rubber latex can be used. The synthetic rubber can be used alone or in combination of two or more types.

[0030] In some preferred embodiments, the synthetic rubber latex (A2) is, for example, an acid-modified synthetic rubber latex obtained by acid-modifying various synthetic rubber latexes such as SBR latex, NBR latex, and chloroprene latex. By using an acid-modified synthetic rubber latex, the pressure-sensitive adhesive layer can adhere well to an undercoat layer containing an oxazoline group, as described below, and can improve anchoring properties to the resin film substrate. Furthermore, by using an acid-modified synthetic rubber latex, adhesion to adherends such as metal materials can be easily improved, and the cohesive strength of the pressure-sensitive adhesive layer can be improved by a crosslinking reaction with the aqueous crosslinking agent (C), as described below. As the acid-modified synthetic rubber latex, an acid-modified SBR latex is preferably used. As the acid-modified synthetic rubber latex, a synthetic rubber latex acid-modified by a known or conventional method may be used. For example, an acid-modified synthetic rubber latex can be obtained by modifying the synthetic rubber in the latex with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, or fumaric acid, or an anhydride of such an unsaturated carboxylic acid. Alternatively, a commercially available acid-modified synthetic rubber latex may be obtained and used. The acid-modified synthetic rubber may be used alone or in combination of two or more.

[0031] The presence or absence of acid modification of synthetic rubber latex can be confirmed by forming a film of the synthetic rubber latex and analyzing it by the ATR method (attenuated total reflection method) using FT-IR. As the analyzer, for example, a "Nicolet iS10" manufactured by Thermo Fisher Scientific Inc. or an equivalent product can be used.

[0032] In an embodiment in which the synthetic rubber latex (A2) contains an acid-modified synthetic rubber latex, the proportion of the acid-modified synthetic rubber latex contained in the synthetic rubber latex (A2) is not particularly limited and may be, for example, about 10% by weight or more, or about 30% by weight or more, based on the non-volatile content. In some preferred embodiments, from the viewpoint of effectively exhibiting the effects of the acid-modified synthetic rubber latex, the proportion of the acid-modified synthetic rubber latex contained in the synthetic rubber latex (A2) is about 50% by weight or more (e.g., more than 50% by weight), about 70% by weight or more, about 90% by weight or more, or about 95% by weight or more, based on the non-volatile content, and the synthetic rubber latex (A2) may be substantially composed of the acid-modified synthetic rubber latex.

[0033] The glass transition temperature (Tg) of the synthetic rubber (e.g., acid-modified synthetic rubber) contained in the synthetic rubber latex (A2) is not particularly limited. In some embodiments, from the viewpoint of improving adhesion, the Tg of the synthetic rubber is preferably about -10°C or lower, more preferably about -20°C or lower, even more preferably about -30°C or lower, even more preferably about -40°C or lower, and particularly preferably about -50°C or lower. In some embodiments, the lower limit of the Tg of the synthetic rubber is, for example, about -80°C or higher, or may be about -70°C or higher, or may be about -65°C or higher. For commercially available products, the manufacturer's nominal value may be used as the Tg of the synthetic rubber. When the manufacturer's nominal value is unknown or when the synthetic rubber is obtained by synthesis, analysis can be performed using a differential scanning calorimeter (DSC), and the Tg of the synthetic rubber can be confirmed from the temperature of the inflection point of the obtained calorimetric curve. As the DSC, a TA Instruments product name "Q2000" or an equivalent product can be used.

[0034] In an embodiment in which the rubber latex (A) contains a synthetic rubber latex (A2), the proportion of the synthetic rubber latex (A2) contained in the rubber latex (A) is not particularly limited and may be, for example, about 1% by weight or more, about 5% by weight or more, or about 10% by weight or more, based on the non-volatile content. In some embodiments, from the viewpoint of effectively exhibiting the effect of containing the synthetic rubber latex, the proportion of the synthetic rubber latex (A2) contained in the rubber latex (A) may be about 30% by weight or more, about 50% by weight or more (e.g., more than 50% by weight), about 70% by weight or more, about 90% by weight or more, or about 95% by weight or more, based on the non-volatile content, and the rubber latex (A) may be substantially composed of the synthetic rubber latex (A2). In some other embodiments, the proportion of the synthetic rubber latex (A2) contained in the rubber latex (A) may be about 90% by weight or less, about 70% by weight or less, about 50% by weight or less (e.g., less than 50% by weight), about 30% by weight or less, or about 10% by weight or less, based on the non-volatile content.

[0035] In some embodiments, the rubber latex (A) preferably contains a natural rubber latex (A1) and a synthetic rubber latex (A2). In such embodiments, the blending ratio of the natural rubber latex (A1) to the synthetic rubber latex (A2) is not particularly limited. The weight ratio (A1 / A2) of the natural rubber latex (A1) to the synthetic rubber latex (A2) may be, for example, 1 / 99 to 99 / 1, 10 / 90 to 99 / 1, or 30 / 70 to 99 / 1 based on the nonvolatile content.

[0036] In some preferred embodiments, the natural rubber latex (A1) and the synthetic rubber latex (A2) are contained in the PSA composition in a weight ratio (A1 / A2) of approximately 50 / 50 to 99 / 1 based on the nonvolatile content. The weight ratio (A1 / A2) may be 60 / 40 to 99 / 1. By incorporating a predetermined amount of synthetic rubber latex (A2) relative to the natural rubber latex (A1), the PSA composition retains the adhesive properties (e.g., adhesion) inherent to the natural rubber latex (A1), while effectively utilizing the effects of the synthetic rubber latex (A2), thereby achieving improved cohesive strength and anchoring properties. It is particularly preferred to use the natural rubber latex (A1) in combination with an acid-modified synthetic rubber latex as the synthetic rubber latex (A2). Although it is not intended to be particularly limited, it is considered that, when natural rubber latex (A1) is used alone, the reaction with the aqueous crosslinking agent (C) described below depends on the amount of protein in the natural rubber latex (A1), whereas by using an appropriate amount of acid-modified synthetic rubber latex (A2), the effect of the reaction with the aqueous crosslinking agent (C) (the effect based on the improvement of cohesive strength) can be stably exhibited.

[0037] In some preferred embodiments, from the viewpoint of improving adhesion, the weight ratio (A1 / A2) of the natural rubber latex (A1) to the synthetic rubber latex (A2) is more preferably about 70 / 30 or more, even more preferably 75 / 25 or more, even more preferably 80 / 20 or more, particularly preferably 85 / 15 or more, and may be 90 / 10 or more, or may be 95 / 5 or more, based on the nonvolatile content. In some embodiments, from the viewpoint of more effectively exhibiting the effect of containing the synthetic rubber, the weight ratio (A1 / A2) is 97 / 3 or less, may be 95 / 5 or less, 92 / 8 or less, 90 / 10 or less, or may be 80 / 20 or less, based on the nonvolatile content.

[0038] Although not particularly limited, in an embodiment in which a natural rubber latex (A1) and a synthetic rubber latex (A2) are used in combination as the rubber latex (A), the total proportion of the natural rubber latex (A1) and the synthetic rubber latex (A2) in the rubber latex (A) is preferably about 70% by weight or more, more preferably about 90% by weight or more, and even more preferably about 95% by weight or more, based on the non-volatile content. It is particularly preferable that the rubber latex (A) is substantially composed of the natural rubber latex (A1) and the synthetic rubber latex (A2), based on the non-volatile content.

[0039] (Tackifier (B)) In some embodiments, the PSA composition preferably contains a tackifier (B). Use of the tackifier (B) can improve the adhesiveness of the PSA layer. The tackifier (B) is typically blended in the PSA composition in the form of a tackifier emulsion from the viewpoint of compatibility. In this specification, the term "tackifier emulsion" refers to a dispersion in which a tackifier is dispersed in water. Examples of the tackifier (B) include petroleum-based tackifiers, rosin-based resins, rosin derivative resins, terpene-based resins, ketone-based resins, and xylene-based resins. The tackifier (B) can be used alone or in combination of two or more.

[0040] In some preferred embodiments, the PSA composition contains a petroleum-based tackifier emulsion as the tackifier (B). The petroleum-based tackifier emulsion (B) is highly compatible with the rubber-based latex (A), causes little contamination of the adherend, and can favorably improve the adhesiveness of the PSA layer. Examples of petroleum-based tackifiers contained in the petroleum-based tackifier emulsion include aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic / aromatic hydrocarbon resins, and hydrogenated versions of these. Examples of aliphatic hydrocarbon resins include homopolymers and copolymers of mainly C5 fractions (piperylene, isoprene, 2-methyl-2-butene, dicyclopentadiene, etc.) from petroleum naphtha cracking fractions, as well as hydrogenated versions of these (so-called C5 petroleum resins, etc.). Examples of aromatic hydrocarbon resins include homopolymers and copolymers of mainly C9 fractions (styrene, methylstyrene, indene, methylindene, coumarone, etc.) from petroleum naphtha cracked fractions, and hydrogenated products thereof (so-called C9 petroleum resins, etc.). Examples of aliphatic / aromatic hydrocarbon resins include copolymers of mainly C5 and C9 fractions from petroleum naphtha cracked fractions, and hydrogenated products thereof (so-called C5-C9 copolymer petroleum resins, etc.). Among these, aliphatic hydrocarbon resins and hydrogenated products of aliphatic / aromatic hydrocarbon resins are preferred, with aliphatic hydrocarbon resins being particularly preferred. The petroleum tackifiers can be used alone or in combination of two or more.

[0041] In an embodiment in which the PSA composition contains a petroleum-based tackifier emulsion as the tackifier (B), the proportion of the petroleum-based tackifier emulsion contained in the tackifier (B) is not particularly limited and may be, for example, about 10% by weight or more, or about 30% by weight or more, based on the non-volatile content. In some preferred embodiments, from the viewpoint of effectively exerting the action of the petroleum-based tackifier emulsion, the proportion of the petroleum-based tackifier emulsion contained in the tackifier (B) is about 50% by weight or more (e.g., more than 50% by weight), about 70% by weight or more, about 90% by weight or more, or about 95% by weight or more, based on the non-volatile content, and the tackifier (B) may be substantially composed of the petroleum-based tackifier emulsion.

[0042] In some other embodiments, the PSA composition contains a rosin-based tackifier emulsion as the tackifier (B). The rosin-based tackifier emulsion is well compatible with the rubber-based latex (A) and can improve the adhesiveness of the PSA layer. For example, it is well compatible with a PSA composition containing a synthetic rubber latex (A2) as the rubber-based latex (A), and can preferably exhibit an adhesiveness-improving effect. Examples of the rosin-based tackifier contained in the rosin-based tackifier emulsion include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; modified rosins obtained by modifying the unmodified rosins through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc.); and various other rosin derivatives. Examples of the rosin derivatives include rosin esters and rosin phenols. Examples of the rosin esters include rosin esters obtained by esterifying unmodified or modified rosin with a polyhydric alcohol; polyhydric alcohol esters of unsaturated fatty acid-modified rosin obtained by partially modifying unmodified or modified rosin with an unsaturated fatty acid (fumaric acid, maleic acid, etc.) and then esterifying; and polyhydric alcohol esters of unsaturated fatty acid-modified disproportionated rosin obtained by partially modifying unmodified or modified rosin with an unsaturated fatty acid, disproportionating it, and then esterifying it. Examples of the rosin phenols include those obtained by thermally polymerizing rosin by addition of phenols; and those obtained by esterifying the thermally polymerized product. The polyhydric alcohol used in the esterification is not particularly limited, and various known polyhydric alcohols such as diethylene glycol, glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, 1,2,4-butanetriol, and pentaerythritol can be used. The rosin-based tackifiers can be used alone or in combination of two or more.

[0043] The softening point of the tackifier (B) is not particularly limited, and for example, any suitable tackifier having a softening point in the range of approximately 60°C to 200°C can be used. In some embodiments, the softening point of the tackifier (B) may be approximately 180°C or less, approximately 160°C or less, or approximately 140°C or less. A tackifier (B) having a softening point of a predetermined value or less tends to produce a pressure-sensitive adhesive with good adhesion to the adherend. In some embodiments, the softening point of the tackifier (B) is approximately 70°C or more, approximately 80°C or more, or approximately 90°C or more. By using a tackifier (B) having a softening point of a predetermined value or more, it is possible to improve the resistance to adhesive transfer.

[0044] In some preferred embodiments, from the viewpoint of obtaining high adhesiveness, a tackifier having a softening point of 120°C or less (hereinafter, sometimes referred to as a "low-softening-point tackifier") is used as the tackifier (B). The use of a tackifier with a low softening point can also improve compatibility with rubber-based latex. The softening point of the low-softening-point tackifier is more preferably about 115°C or less, even more preferably about 110°C or less, particularly preferably about 105°C or less, and may be about 100°C or less. Furthermore, from the viewpoint of preventing adhesive transfer, the softening point of the low-softening-point tackifier is preferably about 60°C or more, more preferably about 80°C or more, even more preferably about 90°C or more, and may be about 95°C or more. Although not particularly limited, the petroleum-based tackifiers and rosin-based tackifiers are preferably used as the low-softening-point tackifier. Among these, the use of an aliphatic hydrocarbon resin is more preferable.The low softening point tackifier may be used alone or in combination of two or more.

[0045] In some embodiments, the tackifier (B) may or may not include one or more tackifiers having a softening point higher than 120°C (hereinafter, sometimes referred to as "high softening point tackifiers"). For example, the high softening point tackifier can be used in combination with the low softening point tackifier. Alternatively, the high softening point tackifier may be used alone as the tackifier (B).

[0046] In embodiments in which a low-softening point tackifier is used as the tackifier (B), the proportion of the low-softening point tackifier in the entire tackifier (B) is not particularly limited, and may be, for example, approximately 10% by weight or more, approximately 30% by weight or more, or approximately 50% by weight or more. In some preferred embodiments, from the viewpoint of effectively utilizing the effects of using the low-softening point tackifier, the proportion of the low-softening point tackifier in the entire tackifier (B) is more than 50% by weight, more preferably approximately 70% by weight or more, even more preferably approximately 90% by weight or more, and particularly preferably approximately 95% by weight or more. The tackifier (B) may be essentially composed of the low-softening point tackifier.

[0047] In this specification, the softening point of a petroleum-based tackifier is defined as a value measured according to the softening point test method (ring and ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at the lowest possible temperature and carefully filled into a ring placed on a flat metal plate, avoiding the formation of bubbles. After cooling, any raised portion of the ring, including the top edge, is cut off with a slightly heated knife. Next, a holder (ring stand) is placed in a glass container (heating bath) with a diameter of at least 85 mm and a height of at least 127 mm, and glycerin is poured in to a depth of at least 90 mm. Next, a steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample are immersed in the glycerin without touching each other, and the glycerin temperature is maintained at 20°C ± 5°C for 15 minutes. Next, the steel ball is placed in the center of the surface of the sample in the ring and placed in its fixed position on the holder. Next, maintain a distance of 50 mm from the top of the ring to the glycerin surface, place a thermometer, and heat the container with the center of the thermometer's mercury bulb at the same height as the center of the ring. The flame of the Bunsen burner used for heating should be aimed midway between the center of the bottom and the edge of the container, ensuring uniform heating. After heating begins and the temperature reaches 40°C, the rate of increase in the bath temperature must be 5.0 ± 0.5°C per minute. The sample gradually softens, flows down the ring, and finally touches the bottom plate, at which point the temperature is read and considered the softening point. Two or more samples should be measured at the same time, and the average value should be used.

[0048] Tackifier emulsions that can be used as the tackifier (B) can be prepared by appropriately employing known tackifying resin emulsification methods, or commercially available tackifier emulsions can be used. Examples of such emulsification methods include high-pressure emulsification and inversion emulsification. The high-pressure emulsification method can be carried out, for example, by adding water and a suitable emulsifier to a solution of a tackifier dissolved in a solvent (typically benzene, toluene, etc.), emulsifying the solution using a high-pressure emulsifier, and then removing the solvent (e.g., by vacuum distillation) as needed. Alternatively, a tackifier emulsion can be prepared substantially without using an organic solvent by heating the tackifier to above its softening point to a molten state, mixing the molten tackifier with water and a suitable emulsifier, and emulsifying the resulting mixture using a high-pressure emulsifier (solvent-free high-pressure emulsification method). The inversion emulsification method can be carried out, for example, by mixing a small amount of a solvent (benzene, toluene, etc.) with a tackifier, kneading in an appropriate emulsifier, and then gradually adding hot water to cause phase inversion emulsification to form an emulsion. Alternatively, a tackifier emulsion can be prepared without substantially using an organic solvent by raising the temperature of the tackifier to or above its softening point, kneading in an emulsifier, and gradually adding hot water to cause phase inversion emulsification (solvent-free phase inversion emulsification method).

[0049] The emulsifier used to emulsify the tackifier is not particularly limited, and can be appropriately selected from known emulsifiers. For example, anionic emulsifiers and nonionic emulsifiers can be used. Examples of anionic emulsifiers include alkyl sulfate-type anionic emulsifiers such as sodium lauryl sulfate, ammonium lauryl sulfate, and potassium lauryl sulfate; polyoxyethylene alkyl ether sulfate-type anionic emulsifiers such as sodium polyoxyethylene lauryl ether sulfate; polyoxyethylene alkyl phenyl ether sulfate-type anionic emulsifiers such as ammonium polyoxyethylene lauryl phenyl ether sulfate and sodium polyoxyethylene lauryl phenyl ether sulfate; sulfonate-type anionic emulsifiers such as sodium dodecylbenzenesulfonate; and sulfosuccinate-type anionic emulsifiers such as disodium lauryl sulfosuccinate and disodium polyoxyethylene lauryl sulfosuccinate. Examples of nonionic emulsifiers include polyoxyethylene alkyl ether-type nonionic emulsifiers such as polyoxyethylene lauryl ether; polyoxyethylene alkyl phenyl ether-type nonionic emulsifiers such as polyoxyethylene lauryl phenyl ether; polyoxyethylene fatty acid esters, polyoxyethylene polyoxypropylene block polymers; and the like. In some embodiments, a salt of a rosin may be used as the emulsifier. For example, from the viewpoints of ease of emulsification and stability over time of the emulsion, an ammonium salt of a rosin containing 50% by weight or more of dihydroabietic acid is preferably used.

[0050] Although not particularly limited, the emulsification of the tackifier is preferably carried out using the above-mentioned emulsifier in the presence of a protective colloid, such as a water-soluble salt of casein. The water-soluble salt of casein is not particularly limited, and is used in the form of an aqueous casein solution obtained by dissolving casein in an aqueous solution of a basic compound (sodium hydroxide, potassium hydroxide, ammonia, organic amines, etc.). For example, an aqueous ammonium casein solution is preferably used.

[0051] In an embodiment in which the PSA composition contains a tackifier (B), the content of the tackifier (B) in the PSA composition, and therefore in the PSA layer, is not particularly limited. For example, the content of the tackifier (B) relative to 100 parts by weight of the rubber latex (A) may be about 1 part by weight or more, about 10 parts by weight or more, or about 30 parts by weight or more, based on the nonvolatile content. From the viewpoint of obtaining higher adhesiveness, in some preferred embodiments, the content of the tackifier (B) relative to 100 parts by weight of the rubber latex (A) is about 50 parts by weight or more, more preferably about 55 parts by weight or more, even more preferably about 60 parts by weight or more, particularly preferably about 65 parts by weight or more, and may be about 70 parts by weight or more, about 80 parts by weight or more, or about 90 parts by weight or more, based on the nonvolatile content. In some embodiments, the content of the tackifier (B) relative to 100 parts by weight of the rubber latex (A) may be approximately 150 parts by weight or less, approximately 130 parts by weight or less, approximately 120 parts by weight or less, or approximately 110 parts by weight or less, based on the nonvolatile content. By appropriately limiting the content of the tackifier (B) within the above range, the tackifier (B) is easily compatible with the rubber latex (A), and good adhesive properties are easily obtained. In some preferred embodiments, the content of the tackifier (B) relative to 100 parts by weight of the rubber latex (A) may be approximately 100 parts by weight or less, approximately 95 parts by weight or less, approximately 90 parts by weight or less, approximately 85 parts by weight or less, approximately 80 parts by weight or less, or approximately 75 parts by weight or less, based on the nonvolatile content. By setting the content of tackifier (B) within the above range, it is possible to improve the releasability from the adherend while maintaining sufficient adhesiveness. For example, the decrease in cohesive strength of the pressure-sensitive adhesive layer is suppressed, and there is a tendency for the pressure-sensitive adhesive to have excellent properties of preventing adhesive residue and preventing contamination of the adherend after being peeled from the adherend. Furthermore, by limiting the amount of tackifier (B) used, it is possible to prevent the peel strength from the adherend from becoming excessively high, and it is possible to improve the workability when peeling from the adherend. For example, peeling defects such as tearing of the pressure-sensitive adhesive sheet during peeling are also easily prevented.

[0052] (Aqueous Crosslinking Agent (C)) The pressure-sensitive adhesive composition contains an aqueous crosslinking agent (C). Here, the term "aqueous crosslinking agent" encompasses both water-dispersible crosslinking agents and water-soluble crosslinking agents. The use of the aqueous crosslinking agent (C) can impart appropriate cohesive strength to the pressure-sensitive adhesive layer. The aqueous crosslinking agent (C) is preferably an aqueous crosslinking agent having at least one functional group selected from an oxazoline group, an isocyanate group, and an epoxy group. By blending the aqueous crosslinking agent having the specific functional group described above with a pressure-sensitive adhesive composition containing a rubber latex (A), the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition can adhere well to an undercoat layer containing an oxazoline group, as described below, and can improve anchoring to the resin film substrate. The aqueous crosslinking agent (C) can be an oxazoline-based crosslinking agent, an isocyanate-based crosslinking agent, or an epoxy-based crosslinking agent. The aqueous crosslinking agents (C) can be used singly or in combination of two or more.

[0053] As the oxazoline-based crosslinking agent, a compound having one or more oxazoline groups per molecule can be used. The oxazoline group may be any of a 2-oxazoline group, a 3-oxazoline group, and a 4-oxazoline group. An oxazoline-based crosslinking agent having a 2-oxazoline group can be preferably used. For example, a water-soluble copolymer or a water-dispersible copolymer obtained by copolymerizing an addition-polymerizable oxazoline such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, or 2-isopropenyl-5-ethyl-2-oxazoline with another monomer can be used as the oxazoline-based crosslinking agent. Both water-soluble and water-dispersible oxazoline-based crosslinking agents can be used, but water-soluble oxazoline-based crosslinking agents are preferred. Commercially available oxazoline crosslinking agents include, for example, trade names "Epocross WS-500," "Epocross WS-700," "Epocross K-2010E," "Epocross K-2020E," and "Epocross K-2035E," manufactured by Nippon Shokubai Co., Ltd.

[0054] Examples of isocyanate-based crosslinking agents that can be used include polyfunctional isocyanate compounds having two or more functionalities. Examples include aromatic isocyanates such as tolylene diisocyanate, xylene diisocyanate, polymethylene polyphenyl diisocyanate, tris(p-isocyanatophenyl)thiophosphate, and diphenylmethane diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate. Both water-soluble and water-dispersible isocyanate-based crosslinking agents can be used. As the isocyanate-based crosslinking agent, so-called blocked isocyanate-type isocyanate-based crosslinking agents in which the isocyanate group is blocked may also be used. Commercially available products include the "Burnoc DNW" series manufactured by DIC Corporation, the "Aquanate" series manufactured by Tosoh Corporation, the "Takenate WD" series manufactured by Mitsui Chemicals, Inc., and the "Elastron BN" series manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.

[0055] As the epoxy-based crosslinking agent, a compound having two or more epoxy groups per molecule can be used. Epoxy-based crosslinking agents having 3 to 5 epoxy groups per molecule are preferred. As the epoxy-based crosslinking agent, either water-soluble or water-dispersible types can be used, but water-soluble epoxy-based crosslinking agents are preferred. Specific examples of epoxy-based crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, (poly)ethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and the like. Examples of commercially available epoxy crosslinking agents include those manufactured by DIC Corporation under the trade name "Epiclon CR-5L" and those manufactured by Nagase ChemteX Corporation under the trade names "Denacol EX-313," "Denacol EX-512," "Denacol EX-810," "Denacol EX-821," "Denacol EX-830," and "Denacol EX-850."

[0056] In some preferred embodiments, at least one selected from an oxazoline-based crosslinking agent and an epoxy-based crosslinking agent is used as the aqueous crosslinking agent (C). Compared to, for example, an isocyanate-based crosslinking agent, oxazoline-based crosslinking agents and epoxy-based crosslinking agents have better stability in the pressure-sensitive adhesive composition and are advantageous in terms of productivity. Furthermore, oxazoline-based crosslinking agents and epoxy-based crosslinking agents tend to provide better adhesive transfer resistance. From this perspective, in some embodiments, the combined proportion of the oxazoline-based crosslinking agent and the epoxy-based crosslinking agent in the total amount of the aqueous crosslinking agent (C) contained in the pressure-sensitive adhesive composition may be approximately 10 wt% or more, approximately 30 wt% or more, or approximately 50 wt% or more, based on the nonvolatile content. In some preferred embodiments, the combined proportion of the oxazoline-based crosslinking agent and the epoxy-based crosslinking agent in the total amount of the aqueous crosslinking agent (C) is greater than 50 wt%, more preferably approximately 70 wt% or more, even more preferably approximately 90 wt% or more, and particularly preferably approximately 95 wt% or more, based on the nonvolatile content. The aqueous crosslinking agent (C) may be substantially composed of at least one selected from an oxazoline-based crosslinking agent and an epoxy-based crosslinking agent.

[0057] In some embodiments, it is particularly preferable to use an oxazoline-based crosslinking agent as the aqueous crosslinking agent (C). Oxazoline-based crosslinking agents can react at relatively low temperatures of around 80°C, so the desired adhesive properties are developed quickly and the adhesive properties have good stability over time. They are also suitable when there is a limit to the heating temperature during the preparation of an adhesive sheet, such as when using a polyolefin-based resin film. Oxazoline-based crosslinking agents are also advantageous in that they can efficiently increase the degree of crosslinking with a relatively small amount. Furthermore, adhesive layers formed using oxazoline-based crosslinking agents tend to have good processability. From this perspective, in some embodiments, the proportion of the oxazoline-based crosslinking agent in the total amount of the aqueous crosslinking agent (C) contained in the adhesive composition may be approximately 10 wt. % or more, approximately 30 wt. % or more, or approximately 50 wt. % or more, based on the nonvolatile content. In some preferred embodiments, the proportion of the oxazoline-based crosslinking agent in the total amount of the aqueous crosslinking agent (C) is more than 50% by weight, more preferably about 70% by weight or more, even more preferably about 90% by weight or more, and particularly preferably about 95% by weight or more, based on the nonvolatile content. The aqueous crosslinking agent (C) may be essentially composed of the oxazoline-based crosslinking agent.

[0058] In some embodiments, the aqueous crosslinking agent (C) preferably does not contain an isocyanate-based crosslinking agent or the amount of the isocyanate-based crosslinking agent used is limited. This can suppress the short pot life and gelation during storage caused by the inclusion of a relatively highly active isocyanate-based crosslinking agent, thereby improving productivity. From this perspective, in some embodiments, the proportion of the isocyanate-based crosslinking agent in the total amount of the aqueous crosslinking agent (C) contained in the pressure-sensitive adhesive composition may be approximately 50% by weight or less (e.g., less than 50% by weight), approximately 30% by weight or less, approximately 10% by weight or less, approximately 3% by weight or less, or approximately 1% by weight or less. The aqueous crosslinking agent (C) may be substantially free of an isocyanate-based crosslinking agent.

[0059] The pressure-sensitive adhesive composition may or may not contain, as the aqueous crosslinking agent (C), an aqueous crosslinking agent other than the aqueous crosslinking agent having at least one functional group selected from an oxazoline group, an isocyanate group, and an epoxy group, as long as the effect of the technology disclosed herein is not impaired. Examples of such other aqueous crosslinking agents include aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. The other aqueous crosslinking agents may be used alone or in combination of two or more.

[0060] The content of the aqueous crosslinking agent (C) in the PSA composition is not particularly limited and can be an appropriate amount that exhibits the desired anchoring improvement effect. In some embodiments, the content of the aqueous crosslinking agent (C) in the PSA composition, and therefore in the PSA layer, may be approximately 0.01 parts by weight or more per 100 parts by weight of the rubber latex (A), based on the nonvolatile content. In some preferred embodiments, the content of the aqueous crosslinking agent (C) is approximately 0.1 parts by weight or more, more preferably approximately 0.3 parts by weight or more, even more preferably approximately 0.5 parts by weight or more, even more preferably 0.8 parts by weight or more, particularly preferably 1.0 parts by weight or more, and may be approximately 2.0 parts by weight or more, 3.0 parts by weight or more, or 4.0 parts by weight or more, based on the nonvolatile content, per 100 parts by weight of the rubber latex (A). A PSA layer containing a predetermined amount or more of the aqueous crosslinking agent (C) can adhere well to an undercoat layer containing a water-dispersible polymer having an oxazoline group, thereby exhibiting good anchoring properties. Furthermore, by incorporating a predetermined amount or more of the aqueous crosslinking agent (C), the PSA layer has adequate cohesive strength and is less likely to leave adhesive residue. For example, when an acid-modified synthetic rubber latex is used as the rubber latex (A), the acid in the acid-modified synthetic rubber latex reacts well with the crosslinkable reactive groups of the aqueous crosslinking agent (C), resulting in a PSA layer with adequate cohesive strength and less likely to leave adhesive residue. Furthermore, in some embodiments, the content of the aqueous crosslinking agent (C) may be approximately 10 parts by weight or less, approximately 8 parts by weight or less, or approximately 6 parts by weight or less, based on the nonvolatile content, per 100 parts by weight of the rubber latex (A). By appropriately limiting the amount of the aqueous crosslinking agent (C) used, contamination of the adherend surface after removal of the PSA is easily prevented. In addition, the peel strength can be adjusted by using an appropriate amount of aqueous crosslinking agent (C). In some preferred embodiments, the content of the aqueous crosslinking agent (C) is about 5.0 parts by weight or less, or may be about 4.0 parts by weight or less, or may be about 3.5 parts by weight or less, or may be about 3.0 parts by weight or less, or may be about 2.5 parts by weight or less, or may be about 2.0 parts by weight or less, or may be about 1.5 parts by weight or less, based on the non-volatile content, relative to 100 parts by weight of the rubber latex (A). By setting the amount of the aqueous crosslinking agent (C) used within the above range, the peel strength can be suppressed and the releasability from the adherend can be improved.

[0061] (Laser beam absorbent) The pressure-sensitive adhesive layer may contain a laser beam absorbent as needed, or may not contain such a laser beam absorbent. By including a laser beam absorbent in the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer can be made into a laser beam absorbing layer, thereby improving the cutting ability with laser beam. As the laser beam absorbent that can be included in the pressure-sensitive adhesive layer, one or more types can be appropriately selected from the laser beam absorbents exemplified below. In an embodiment in which the pressure-sensitive adhesive layer contains a laser beam absorbent, the content of the laser beam absorbent in the pressure-sensitive adhesive layer is usually suitably 5 wt% or less, and from the viewpoint of adhesive performance, it is preferably 3 wt% or less, and may be 1 wt% or less. Alternatively, the technology disclosed herein can also be preferably implemented in an embodiment in which the pressure-sensitive adhesive layer does not substantially contain a laser beam absorbent.

[0062] (Antiaging Agent) The pressure-sensitive adhesive layer may contain an antioxidant, if necessary. The use of an antioxidant can improve the quality stability of the pressure-sensitive adhesive. The antioxidant may be used alone or in combination of two or more. Examples of antioxidants include phosphorus-based antioxidants, phenol-based antioxidants, hindered amine-based antioxidants, aromatic amine-based antioxidants, and sulfur-based antioxidants. Although not particularly limited, the amount of antioxidant contained in the pressure-sensitive adhesive layer may be, for example, approximately 20 parts by weight or less, typically 10 parts by weight or less, and may even be 5 parts by weight or less, based on the nonvolatile content, relative to 100 parts by weight of the rubber latex (A). Furthermore, the amount of the antioxidant may be, for example, 0.1 parts by weight or more, or may even be 0.5 parts by weight or more, or may even be 1 part by weight or more, based on the nonvolatile content, relative to 100 parts by weight of the rubber latex (A).

[0063] (Optional Components) The adhesive layer may contain various additives that can be used in the field of adhesives, such as viscosity adjusters (thickeners, etc.), leveling agents, dispersants, plasticizers, softeners, fillers, colorants such as pigments and dyes, light stabilizers, antioxidants, water-resistant agents, antifoaming agents, preservatives, and crosslinking aids, as needed. Dispersants that can function as protective colloids are preferred, and examples of usable dispersants include water-soluble polymers such as gelatin, polyvinyl alcohol, polyvinyl alcohol derivatives, water-soluble salts of cellulose, cellulose derivatives, and polyacrylic acid (salts) without hydrophobic side chains. The adhesive layer may also contain an emulsifier, as needed. Examples of such emulsifiers that can be used include those exemplified as emulsifiers that can be used to emulsify tackifier emulsions.

[0064] (Water-Dispersed Pressure-Sensitive Adhesive Composition) The PSA composition disclosed herein can be prepared using aqueous components as described above, which allows for the substantial use of no organic solvents or the use of reduced amounts of organic solvents. This is significant in terms of eliminating organic solvents and being environmentally friendly. The PSA composition can typically be implemented in the form of a water-dispersed PSA composition containing a rubber latex and an aqueous crosslinking agent. In this specification, the term "water-dispersed PSA composition" refers to a composition in which at least a portion of the PSA-forming components are dispersed in water. The term "water-dispersed" also includes suspended and emulsified states. Therefore, the concept of the water-dispersed PSA composition encompasses what are known as emulsion-type PSA compositions. The water-dispersed PSA composition contains water as a dispersion medium or solvent. The water-dispersed adhesive composition may also contain a liquid other than water, as necessary. The liquid other than water may be, for example, one or more selected from various organic solvents (e.g., lower alcohols) that are uniformly miscible with water. Typically, the proportion of water in the volatile components contained in the water-dispersed PSA composition is, for example, 90 wt % or more, and preferably 95 to 100 wt %. In this specification, a PSA (layer) formed from the water-dispersed PSA composition is also referred to as a water-dispersed PSA (layer).

[0065] It is preferable that the PSA composition (typically, a water-dispersed PSA composition) used to form the PSA layer is substantially free of organic solvents, from the viewpoints of environmental considerations and eliminating organic solvents. Here, "a PSA composition is substantially free of organic solvents" means that the amount of organic solvent in the PSA composition is less than 1 wt % (e.g., less than 0.1 wt %).

[0066] Although not particularly limited, in some embodiments, the PSA composition may have a composition in which the total amount of the rubber latex (A), the tackifier (B), and the aqueous crosslinker (C) accounts for 70 wt % or more of the total weight of the PSA composition based on nonvolatile content (i.e., the weight of the PSA layer constituted by this PSA). This allows the effects of containing the (A), (B), and (C) components to be optimally exhibited. In some preferred embodiments, the total amount of the (A), (B), and (C) components may be 80 wt % or more, 90 wt % or more (e.g., 90 to 100 wt %), or 95 wt % or more (e.g., 95 to 100 wt %) of the total weight of the PSA composition based on nonvolatile content. The PSA composition having the above composition allows the effects of the technology disclosed herein to be preferably realized.

[0067] (Formation of Pressure-Sensitive Adhesive Layer) The pressure-sensitive adhesive layer can be formed, for example, by applying (typically coating) any of the pressure-sensitive adhesive compositions disclosed herein to an undercoat layer provided on a resin film substrate or a release liner, and then drying the composition. A pressure-sensitive adhesive sheet can be produced by transferring the pressure-sensitive adhesive layer formed on the release liner to the surface of the undercoat layer on the resin film substrate. The pressure-sensitive adhesive composition can be applied using a known or conventional coater, such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, or spray coater. From the viewpoints of promoting the crosslinking reaction and improving production efficiency, the pressure-sensitive adhesive composition is preferably dried under heat. For example, a drying temperature of about 40 to 120°C, about 40 to 100°C, or about 40 to 80°C can be used. After drying the pressure-sensitive adhesive composition, aging may be performed, for example, within a range of about room temperature or higher and 60°C or lower, for the purposes of adjusting component migration within the pressure-sensitive adhesive layer, promoting the crosslinking reaction, and alleviating distortion that may exist within the pressure-sensitive adhesive sheet.

[0068] (Thickness of the Pressure-Sensitive Adhesive Layer) The thickness of the pressure-sensitive adhesive layer can be appropriately set so as to obtain appropriate adhesive performance depending on the application of the pressure-sensitive adhesive sheet, and is typically approximately 0.5 μm to 200 μm. From the viewpoint of improving adhesion to the adherend, in some preferred embodiments, the thickness of the pressure-sensitive adhesive layer may be, for example, 1.5 μm or more, 3 μm or more, 5 μm or more, 7 μm or more, or 10 μm or more. Furthermore, the thickness of the pressure-sensitive adhesive layer may be, for example, approximately 150 μm or less, or approximately 100 μm or less. By limiting the thickness of the pressure-sensitive adhesive layer, the pressure-sensitive adhesive sheet can be made thinner. Furthermore, limiting the thickness of the pressure-sensitive adhesive layer is also preferable in terms of preventing the occurrence of adhesive residue due to cohesive failure of the pressure-sensitive adhesive layer. In some preferred embodiments, the thickness of the pressure-sensitive adhesive layer is approximately 50 μm or less, 30 μm or less, 20 μm or less, 18 μm or less, 16 μm or less, or 15 μm or less. The small thickness of the adhesive layer as described above can be advantageous, for example, in terms of the speed and precision of laser processing in an adhesive sheet that can be used in a manner that is laser cut together with an adherend (workpiece).

[0069] <Resin Film Substrate> The PSA sheet contains a resin film as a substrate. PSA sheets having a resin film substrate can improve productivity, handling, processability, and the like. Furthermore, PSA sheets having a resin film substrate can have good removability from adherends. Here, "resin film" refers to a resin film with a non-porous structure that typically contains substantially no air bubbles (void-free). Therefore, the above-mentioned resin film is a concept that is distinguished from foam films and nonwoven fabrics. Examples of resin materials that constitute the resin film include, but are not limited to, polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); polyolefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, and polypropylene-polyethylene blend resin; and vinyl chloride resins (typically soft vinyl chloride resins), vinyl acetate resins, polyamide-based resins, and the like.

[0070] In some embodiments, from the viewpoint of various processability due to the flexibility of the resin film substrate, or, for example, from the viewpoint of the cuttability and non-contamination of the PSA sheet with a specific laser beam, a polyolefin resin film or a polyester resin film can be preferably used as the resin film. Among these, a polyolefin resin film is preferred from the viewpoint of conformability to the adherend, etc. PSA compositions containing rubber latex such as natural rubber latex tend to have reduced anchoring properties with respect to polyolefin resin film substrates, but the technology disclosed herein makes it possible to obtain good anchoring properties while enjoying the advantages of polyolefin resin films by using a polyolefin resin film substrate.

[0071] Here, a polyolefin-based resin film refers to a resin film whose main component is a polyolefin resin. In this specification, unless otherwise specified, the term "main component" refers to a component that accounts for more than 50% by weight. For example, a resin film whose main component is a polyolefin resin means that the resin film contains more than 50% by weight of the polyolefin resin. A suitable example of a polyolefin-based resin film is a resin film whose main component is a polyethylene (PE) resin and / or a polypropylene (PP) resin. The polyolefin-based resin film may contain PE resin and / or PP resin, and the total amount of PE resin and PP resin may account for more than 50% by weight of the polyolefin-based resin film, preferably 70% by weight or more, for example 85% by weight or more. In a resin film that contains PE resin but not PP resin, the total amount corresponds to the PE resin content.

[0072] The PE resin may be primarily composed of various polymers (ethylene-based polymers) containing ethylene as the main constituent monomer unit. It may also be a PE resin substantially composed of one or more ethylene-based polymers. The ethylene-based polymer may be a homopolymer of ethylene, or may be a copolymer (random copolymer, block copolymer, etc.) of ethylene as the main monomer with another α-olefin as a secondary monomer. Suitable examples of the α-olefin include α-olefins having 3 to 10 carbon atoms, such as propylene, 1-butene (which may be branched 1-butene), 1-hexene, 4-methyl-1-pentene, and 1-octene. For example, a PE resin primarily composed of an ethylene-based polymer copolymerized with the α-olefin as a secondary monomer at a ratio of 10% by weight or less (typically 5% by weight or less) may be preferably used.

[0073] The PE resin may also be a PE resin containing a copolymer of ethylene with a monomer (functional group-containing monomer) having another functional group in addition to the polymerizable functional group, or a PE resin in which such a functional group-containing monomer is copolymerized with an ethylene-based polymer. Examples of copolymers of ethylene and functional group-containing monomers include ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl methacrylate copolymer (EMMA), and ethylene-(meth)acrylic acid (i.e., acrylic acid and / or methacrylic acid) copolymers crosslinked with metal ions.

[0074] The density of the PE resin is not particularly limited. The concept of PE resin here includes high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE). In some embodiments, the density of the PE resin is, for example, 0.90 to 0.94 g / cm. ３ Preferred PE resins include LDPE and LLDPE.

[0075] The PP resin may be a polymer (propylene-based polymer) having propylene as the main constituent monomer unit, i.e., a polymer in which more than 50% by weight of all constituent monomer units is propylene as the main component. It may also be a PP resin substantially composed of one or more propylene-based polymers. The concept of propylene-based polymer here includes not only homopolypropylene, but also random copolymers (random polypropylenes) and block copolymers (block polypropylenes) of propylene and other monomers.

[0076] The first surface of the resin film substrate (i.e., the surface on which the pressure-sensitive adhesive layer is provided) may be subjected to an appropriate surface treatment, if necessary, to enhance adhesion to the undercoat layer. Examples of surface treatments for enhancing adhesion include corona discharge treatment, acid treatment, ultraviolet irradiation treatment, and plasma treatment.

[0077] In some preferred embodiments, the second surface of the resin film substrate is a release surface. The phrase "the second surface of the resin film substrate is a release surface" typically means that a pressure-sensitive adhesive sheet, with the surface (adhesive surface) of the pressure-sensitive adhesive layer provided on the first surface of the resin film substrate in contact with the release surface, can be peeled off without leaving any adhesive residue (residual pressure-sensitive adhesive) on the release surface.

[0078] In some embodiments, the resin composition constituting the second surface (hereinafter also referred to as "second surface-forming material") preferably contains a release agent. A resin film substrate having such a second surface can be understood as a resin film substrate having the release agent kneaded into at least the second surface. The second surface-forming material only needs to constitute the second surface of the resin film substrate; for example, it may constitute only the second surface side of the resin film substrate, or it may constitute the entire resin film substrate.

[0079] The second surface forming material may preferably be a resin composition containing at least a release agent and a resin material. Examples of the resin material include, but are not limited to, the various materials exemplified as the resin material constituting the resin film substrate, such as polyester resins such as PET and PBT; polyolefin resins such as PE, PP, ethylene-propylene copolymers, and PP-PE blend resins; and vinyl chloride resins (typically soft vinyl chloride resins), vinyl acetate resins, and polyamide resins.

[0080] Examples of release agents that can be used as a constituent component of the second-surface forming material (i.e., release agents for kneading into the second surface) include ethylene-vinyl alcohol copolymers, fatty acid amide-based additives, low-molecular-weight polyolefin waxes, long-chain alkyl-based additives, and silicone-based release agents. The release agents can be used alone or in appropriate combinations of two or more. It is preferable to select a release agent that has good miscibility with the resin component contained in the second-surface forming material.

[0081] Examples of the ethylene-vinyl alcohol copolymer include ethylene-vinyl alcohol copolymers obtained by saponifying a copolymer of ethylene with vinyl acetate, vinyl formate, vinyl propionate, or vinyl acetate. Examples of fatty acid amide additives include saturated fatty acid bisamides, unsaturated fatty acid bisamides, aromatic bisamides, and substituted ureas. More specific examples of fatty acid amide additives include N-stearyl-N'-stearamides such as methylene bisstearamide, ethylene bisstearamide, ethylene bisoleamide, N,N-dioleyl adipamide, and N-stearyl-N'-stearyl urea. These fatty acid amide additives may be used alone or in combination of two or more. Examples of low-molecular-weight polyolefin waxes that can be used include low-molecular-weight waxes such as polyethylene wax and polypropylene wax. As the long-chain alkyl additive, low-molecular-weight additives having alkyl chains, such as Peeloil (registered trademark) 1010 and Peeloil (registered trademark) 1010S (both manufactured by Ipposha Yushi Kogyo Co., Ltd.), can be appropriately used. Examples of silicone-based release agents include silylated polyolefins, silicone resins, silicone alkoxy oligomers, silicone oligomers, silicone master pellets, silicone rubber powders, and silicone emulsions. Examples of silylated polyolefins that can be used include silylated polyolefins prepared by the method shown in the examples of Japanese Patent Application Publication No. 2011-26448.

[0082] Suitable examples of the release agent to be kneaded into the second surface include the long-chain alkyl additives and silicone-based release agents. Of these, silicone-based release agents are particularly preferred. As the silicone-based release agent, silylated polyolefin is particularly preferred.

[0083] The content of the release agent in the second-surface-forming material is not particularly limited and can be, for example, about 0.01 to 80% by weight of the entire second-surface-forming material. In some embodiments, the content of the release agent in the second-surface-forming material may be, for example, 0.1% by weight or more, 0.3% by weight or more, 0.5% by weight or more, 0.7% by weight or more, or 1% by weight or more. From the viewpoint of compatibility with the resin material, the content of the release agent in the second-surface-forming material may be, for example, 70% by weight or less, 50% by weight or less, 30% by weight or less, or 10% by weight or less.

[0084] The resin film substrate may have a single layer structure or a multilayer structure of two or more layers. In some embodiments, a resin film substrate with a multilayer structure can be preferably used. A resin film substrate with a multilayer structure has the advantage that it is easy to differentiate the function and appearance between the first and second sides of the resin film substrate. In a resin film substrate with a multilayer structure, the types of resin materials constituting each layer may be the same or different. A resin film substrate with a multilayer structure may have, for example, a two-layer to five-layer structure, or may have a two-layer or three-layer structure. In other embodiments, the resin film substrate may have a single layer structure. A resin film substrate with a single layer structure can be advantageous in terms of the productivity and quality stability of the resin film substrate.

[0085] The molding method of the resin film substrate is not particularly limited, and conventionally known extrusion molding methods, such as inflation extrusion molding and cast molding, can be appropriately adopted. The resin film substrate may be unstretched, or may be stretched uniaxially or biaxially. A multilayer resin film substrate can be obtained by simultaneously molding resin compositions corresponding to each layer (for example, by multilayer inflation molding), by laminating each layer after molding, or by casting another layer on a previously molded layer, either alone or in combination.

[0086] In the pressure-sensitive adhesive sheet disclosed herein, the method of forming the second surface as a release surface preferably employs, but is not limited to, the method of forming the second surface of the resin film substrate using a second-surface-forming material containing a release agent in a resin composition, as described above. The second surface of the resin film substrate may be, for example, a release surface formed by applying a release treatment agent to a surface formed from a resin composition that does not contain a release agent. Such surface treatment can be carried out using, for example, a general silicone-based, long-chain alkyl-based, fluorine-based, or other release treatment agent. The surface formed from a resin composition containing a release agent (i.e., the surface into which the release agent has been incorporated) may also be further surface-treated by applying a release treatment agent.

[0087] The resin film substrate may contain a laser beam absorbent as needed. In some embodiments, the laser beam absorbent preferably contains a specific absorbent, which will be described later. A suitable example of a resin film substrate containing a laser beam absorbent is a resin film substrate containing a laser beam absorbing layer (which may contain the specific absorbent). In a resin film substrate with a multilayer structure, it is preferred that at least one layer is a laser beam absorbing layer containing a laser beam absorbent.

[0088] The laser light absorptivity of the resin film substrate including the laser light absorbing layer is not particularly limited, but can be set so that the laser light absorptivity of the pressure-sensitive adhesive sheet is 20% or more.In some embodiments, the laser light absorptivity of the resin film substrate may be, for example, 15% or more, usually 20% or more is appropriate, may be 25% or more, may be 30% or more, may be 45% or more, may be 60% or more, or may be 75% or more.The laser light absorptivity of the resin film substrate may be 100%, but in practice, it is preferably 95% or less, and may be 90% or less.In addition, the transmittance and reflectance of the resin film substrate can be appropriately selected from the same range as the transmittance and reflectance of the pressure-sensitive adhesive sheet described below.

[0089] The laser beam absorbent contained in the resin film substrate can be one type alone or two or more types in combination selected from the same laser beam absorbents exemplified below as usable in pressure-sensitive adhesive sheets. In an embodiment in which the laser beam absorbent contains a specific absorbent, the specific absorbent can be one type alone or two or more types in combination selected from the same laser beam absorbents exemplified below as usable in pressure-sensitive adhesive sheets. The ranges exemplified below for the laser beam absorbent content and the specific absorbent content in the resin film substrate can be applied, respectively.

[0090] The resin film substrate may contain any additives as needed, such as flame retardants, antistatic agents, light stabilizers (radical scavengers, ultraviolet absorbers, etc.), and antioxidants.

[0091] The thickness of the resin film substrate is not particularly limited and can be, for example, approximately 5 μm to 300 μm. From the viewpoint of the handleability of the resin film substrate or a pressure-sensitive adhesive sheet including the resin film substrate, in some preferred embodiments, the thickness of the resin film substrate may be, for example, 15 μm or more, 20 μm or more, 35 μm or more, 50 μm or more, or 75 μm or more. A pressure-sensitive adhesive sheet having a resin film substrate of a predetermined thickness can easily provide sufficient protection, for example, in applications involving the surface protection of an adherend. In some preferred embodiments, the thickness of the resin film substrate is, for example, 150 μm or less, 130 μm or less, 110 μm or less, or 90 μm or less. Reducing the thickness of the resin film substrate can be advantageous from the viewpoint of achieving a thinner pressure-sensitive adhesive sheet. Furthermore, reducing the thickness of the resin film substrate tends to improve the flexibility of the pressure-sensitive adhesive sheet and its ability to conform to the surface shape of the adherend. Furthermore, when applied to laser processing applications, limiting the thickness of the resin film substrate can improve the speed and precision of laser processing. In some other embodiments, the thickness of the resin film substrate may be 70 μm or less, 50 μm or less, or 40 μm or less.

[0092] In a resin film substrate containing a laser beam absorbing layer, the thickness of the laser beam absorbing layer (in a resin film substrate containing a plurality of laser beam absorbing layers, the total thickness of these layers) may be, for example, 3 μm or more, 5 μm or more, or 10 μm or more. From the viewpoint of the speed and precision of laser processing, in some embodiments, the thickness of the laser beam absorbing layer (in other words, the portion where the laser beam absorbent is disposed) of the entire thickness of the resin film substrate may be, for example, 20% or more, 50% or more, 70% or more, or 90% or more. Note that in a single-layer resin film substrate consisting of a laser beam absorbing layer or a resin film substrate consisting of a plurality of laser beam absorbent layers, the thickness of the laser beam absorbing layer accounts for 100% of the entire thickness of the substrate.

[0093] <Undercoat Layer> The PSA sheet includes an undercoat layer disposed on the PSA layer side surface of the resin film substrate. The undercoat layer is formed from an undercoat agent containing a water-dispersible polymer having an oxazoline group (oxazoline group-containing water-dispersible polymer). By disposing the undercoat layer between the resin film substrate and the PSA layer, the anchoring properties of the PSA layer formed from the PSA composition containing rubber latex (A) and aqueous crosslinking agent (C) can be effectively enhanced without relying on organic solvent-containing materials. Resistance to adhesive transfer can also be improved. Furthermore, by using a water-dispersible polymer as the undercoat agent, the undercoat layer can exhibit good water resistance and exhibit the desired performance against the rubber latex-containing PSA composition. Furthermore, the use of a water-dispersible polymer is preferable because it has less effect on the adhesive properties of the PSA layer disposed on the undercoat layer than a water-soluble polymer. The water-dispersible polymer refers to a polymer that is dispersible in water. An oxazoline group-containing polymer emulsion is typically used as the oxazoline group-containing water-dispersible polymer.

[0094] Examples of the oxazoline group-containing water-dispersible polymer include acrylic polymers and urethane polymers containing oxazoline groups in the side chain. Among these, the use of acrylic polymers having oxazoline groups is particularly preferred. The main chain of the acrylic polymer having oxazoline groups may be copolymerized with a monomer such as styrene.

[0095] The glass transition temperature (Tg) of the oxazoline group-containing water-dispersible polymer is not particularly limited. In some embodiments, the Tg of the oxazoline group-containing water-dispersible polymer may be approximately 50°C or lower, approximately 30°C or lower, or approximately 10°C or lower. In some preferred embodiments, from the viewpoint of improving the anchoring properties of the PSA layer, the Tg is preferably approximately 0°C or lower, more preferably approximately -20°C or lower, even more preferably approximately -30°C or lower, and even more preferably approximately -40°C or lower. An oxazoline group-containing water-dispersible polymer with a low Tg tends to facilitate application of a primer to a resin film (e.g., a polyolefin resin film) and to exhibit good film-forming properties. In some embodiments, the lower limit of the Tg of the oxazoline group-containing water-dispersible polymer is, for example, approximately -80°C or higher, may be approximately -70°C or higher, or may be approximately -60°C or higher. For commercially available products, the manufacturer's nominal value may be used as the Tg of the polymer. When the manufacturer's nominal value is unknown or when the polymer is synthesized, the Tg can be determined from the temperature of the inflection point of the obtained calorimetric curve by analysis using a differential scanning calorimeter (DSC). As the DSC, a product name "Q2000" manufactured by TA Instruments or an equivalent product can be used.

[0096] Although not particularly limited thereto, in some embodiments, the proportion of the oxazoline group-containing water-dispersible polymer in the undercoat layer is, for example, approximately 50% by weight or more (e.g., more than 50% by weight) based on the nonvolatile content, may be approximately 70% by weight or more, may be approximately 90% by weight or more, or may be approximately 95% by weight or more, and the undercoat layer may be essentially composed of the oxazoline group-containing water-dispersible polymer.

[0097] The primer may contain various additives such as surfactants, thickeners, stabilizers, antifoaming agents, colorants (pigments, dyes, etc.), etc., as needed.

[0098] Commercially available undercoat agents used to form the undercoat layer include those manufactured by Nippon Shokubai Co., Ltd. under the trade names "Epocross K-2010E," "Epocross K-2020E," and "Epocross K-2035E."

[0099] The undercoat agent can be formed by applying the undercoat agent directly to the surface of the resin film substrate using an applicator such as a wire bar, spray coater, fountain die coater, lip coater, closed edge die coater, gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, etc., and then drying the undercoat agent. The undercoat layer is typically formed continuously, but is not limited thereto, and may be formed in a regular or random pattern such as dots or stripes.

[0100] The thickness of the primer layer (after drying) is not particularly limited. In some embodiments, the thickness of the primer layer may be 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, 0.5 μm or more, or 1.0 μm or more. In some preferred embodiments, the thickness of the primer layer is 3 μm or less, 2 μm or less, or 1.5 μm or less. By setting the thickness of the primer layer within the above range, the anchoring force improvement effect due to the placement of the primer layer can be preferably exerted.

[0101] (Laser beam absorbent and laser beam absorbing layer) In some embodiments, the pressure-sensitive adhesive sheet contains a laser beam absorbent. By using a laser beam absorbent, the laser beam absorptivity of the pressure-sensitive adhesive sheet can be adjusted. As the laser beam absorbent, various materials that can increase the absorptivity of the laser beam used in processing (typically, the absorptivity at least at the dominant wavelength) can be preferably used. The type of laser beam absorbent contained in the pressure-sensitive adhesive sheet may be one type, or two or more types. In a pressure-sensitive adhesive sheet containing two or more types of laser beam absorbents, the laser beam absorbents may be used as a blend, or may be contained in different layers within the pressure-sensitive adhesive sheet.

[0102] In this specification, the term "laser beam absorbent" refers to a material that can exert an effect of increasing the laser beam absorption rate compared to when the laser beam absorbent is not used. In addition, in this specification, the term "specific absorbent" refers to the above-mentioned laser beam absorbent that has, as a constituent element, a metal with a specific heat of less than 900 J / kg·K and a thermal conductivity of less than 200 W / m·K. In this specification, a layer containing a laser beam absorbent (which may be a specific absorbent) may be referred to as a "laser beam absorbing layer."

[0103] Examples of laser beam absorbents that can be used in the adhesive sheet disclosed herein include metals such as aluminum, stainless steel, titanium, nickel, zirconium, tungsten, copper, silver, gold, zinc, molybdenum, chromium, and alloys that are mainly composed of these; metal compounds such as oxides of the above metals (for example, titanium oxide, aluminum oxide, etc.), nitrides, and carbides; carbon materials such as carbon black and carbon fiber; organic compounds such as phthalocyanine compounds, cyanine compounds, aminium compounds, naphthalocyanine compounds, naphthoquinone compounds, diimonium compounds, anthraquinone compounds, aromatic dithiol metal complexes (for example, nickel complexes); etc. In the laser beam absorbing layer that contains a laser beam absorbent in a resin composition, it is preferable to use a material that has a higher thermal decomposition temperature than the resin components that constitute the laser beam absorbing layer as the laser beam absorbent.

[0104] When a powdered laser beam absorbent is used, the shape of the particles constituting the powder is not particularly limited and may be, for example, flaky, spherical, needle-like, polyhedral, irregular, etc. Usually, a flaky, spherical, or needle-like laser beam absorbent can be preferably used. The average particle size of the laser beam absorbent is not particularly limited and may be, for example, 0.005 μm or more and 20 μm or less. From the viewpoint of dispersibility, usually, a laser beam absorbent having an average particle size of 10 μm or less or 5 μm or less can be preferably used. From the viewpoint of efficiently increasing the laser beam absorptance with a small amount of laser beam absorbent, in some embodiments, the average particle size of the laser beam absorbent may be, for example, 3 μm or less, 1 μm or less, 0.6 μm or less, 0.4 μm or less, or 0.3 μm or less. Furthermore, from the viewpoint of powder handling ease and ease of uniform dispersion, in some embodiments, the average particle size of the laser beam absorbent may be, for example, 0.008 μm or more, 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, 0.15 μm or more, or 0.2 μm or more. In this specification, unless otherwise specified, the term "average particle size" refers to the particle size at 50% of the cumulative value in the particle size distribution measured using a particle size distribution measuring device based on a laser scattering / diffraction method (50% volume average particle size).

[0105] In some embodiments, the laser light-absorbing layer may contain carbon black as the laser light-absorbing agent. For example, carbon black having an average particle size of 10 nm to 500 nm (more preferably 10 nm to 120 nm) may be used. Carbon black may be used alone or in combination with other laser light-absorbing agents.

[0106] In some embodiments, the laser beam absorbing layer may contain at least one of a metal powder and a metal compound powder as a laser beam absorbent. Such a laser beam absorbent is preferable because it can withstand heat generation accompanying absorption of the specific laser beam and appropriately maintain the property of absorbing the specific laser beam. Suitable examples of this type of laser beam absorbent include titanium oxide powder, aluminum oxide powder, and metallic aluminum powder.

[0107] The laser beam absorbing layer is typically a layer containing a laser beam absorbent in a resin component. Non-limiting examples of materials that can be used as such a resin component include, for example, polyester resins such as PET and PBT; polyolefin resins such as PE, PP, ethylene-propylene copolymers, and PP-PE blend resins; and vinyl chloride resins, vinyl acetate resins, polyamide resins, etc. The laser beam absorbing layer can be formed by molding a resin composition obtained by blending a laser beam absorbent with such a resin material into, typically, a film.

[0108] When a laser beam absorbent is used, the amount used is not particularly limited. In some embodiments, the amount of the laser beam absorbent used may be, for example, 0.01 wt % or more, 0.05 wt % or more, or 0.1 wt % or more of the laser beam absorbing layer containing the laser beam absorbent. Furthermore, from the viewpoint of reducing laser cutting residues and suppressing reflectance, in some embodiments, the content of the laser beam absorbent in the laser beam absorbing layer containing the laser beam absorbent may be, for example, 10 wt % or less, 5 wt % or less, 3 wt % or less, or 2 wt % or less.

[0109] In some embodiments, the pressure-sensitive adhesive sheet disclosed herein may preferably use, as the laser beam absorbent, a specific absorbent, i.e., a laser beam absorbent having as a constituent element a metal with a specific heat of less than 900 J / kg K and a thermal conductivity of less than 200 W / m K. The specific absorbent may be selected from the group consisting of: a simple metal of any one type satisfying the above specific heat and thermal conductivity; an alloy containing a metal of any one type satisfying the above specific heat and thermal conductivity in a proportion of more than 50 wt%, more than 70 wt%, or more than 90 wt%; an alloy containing two or more metals satisfying the above specific heat and thermal conductivity in a proportion of more than 50 wt%, more than 70 wt%, or more than 90 wt% in total; a metal compound containing a metal corresponding to such a simple metal or alloy as a constituent element; and the like. The specific absorbent referred to here includes, for example, iron, iron alloys (e.g., iron alloys containing at least one element selected from the group consisting of Cr, Ni, Si, W, Mn, and C), and metal compounds (iron-based compounds) containing, as a constituent element, a metal (iron-based metal) corresponding to the iron or iron alloy. As the iron-based compound, for example, an oxide of the iron-based metal (iron-based oxide) can be preferably used. Other examples of specific absorbents include Mn-based compounds containing, as a constituent element, a metal (Mn-based metal) corresponding to Mn or a Mn alloy, with Mn-based oxides being preferred. The specific absorbents can be used alone or in combination of two or more. In a pressure-sensitive adhesive sheet containing two or more types of specific absorbents, the specific absorbents may be used as a blend, or may be contained in different layers within the pressure-sensitive adhesive sheet.

[0110] Generally, the specific heat and thermal conductivity of a metal compound containing a metal as a constituent element tend to be smaller than those of a metal alone. Therefore, in some embodiments of the pressure-sensitive adhesive sheet disclosed herein, a metal compound containing a metal as a constituent element that satisfies the preferred specific heat and thermal conductivity disclosed herein can be preferably used as a specific absorbent. Metal compounds that can be used as specific absorbents can be, for example, oxides, sulfides, carbides, nitrides, hydroxides, oxyhydroxides, etc. of metals that satisfy the preferred specific heat and thermal conductivity disclosed herein. Other examples of metal compounds that can be used as specific absorbents include metal organic compounds (complexes, etc.) containing ions of the metal. From the viewpoint of withstanding the heat generated by absorbing specific laser light and appropriately maintaining the property of absorbing the specific laser light, oxides, sulfides, carbides, and nitrides of the above metals are preferred, and oxides are particularly preferred. Examples of the oxides include iron oxides (FeO, Fe ３ O ４ , Fe ２ O ３ etc.), manganese dioxide, titanium black, chromium oxide (CrO, Cr ２ O ３ Examples of the sulfides include, but are not limited to, iron sulfide, molybdenum sulfide, and the like.

[0111] When the PSA sheet disclosed herein contains a specific absorbent, the content of the specific absorbent is not particularly limited and can be appropriately selected, for example, from a range of 0.01 wt% to 20 wt% of the PSA sheet. In some embodiments, the content of the specific absorbent may be, for example, 0.05 wt% or more, 0.1 wt% or more, 0.3 wt% or more, 0.5 wt% or more, or 0.8 wt% or more. As the content of the specific absorbent increases, the absorption rate of the specific laser light tends to increase. On the other hand, if the content of the specific absorbent is too high, the energy of the absorbed specific laser light tends to diffuse in the surface direction, which may result in increased energy loss. From this perspective, the content of the specific absorbent is usually 15 wt% or less of the PSA sheet, preferably 10 wt% or less, more preferably 7 wt% or less, and may be 5 wt% or less or less than 5 wt%.

[0112] The PSA sheet disclosed herein may, in addition to the specific absorbent, optionally contain a laser beam absorbent other than the specific absorbent. Hereinafter, such auxiliary laser beam absorbents other than the specific absorbent are also referred to as "auxiliary absorbents." Auxiliary absorbents can be used, for example, to improve the absorbance of the PSA sheet, adjust the transmittance or reflectance, or adjust the appearance. Examples of auxiliary absorbents that can be used include metals such as aluminum, copper, silver, and gold; metal compounds such as oxides, nitrides, and carbides of the above metals; carbon black; and organic compounds such as phthalocyanine compounds, cyanine compounds, aminium compounds, naphthalocyanine compounds, naphthoquinone compounds, diimonium compounds, and anthraquinone compounds.

[0113] The amount of auxiliary absorber used is preferably less than 50% by weight of the total amount of laser light absorber contained in the pressure-sensitive adhesive sheet (i.e., the total amount of the specific absorber and auxiliary absorber), and may be less than 25%, less than 10%, or less than 5%. The pressure-sensitive adhesive sheet may also be substantially free of auxiliary absorbers. Here, "substantially free of auxiliary absorbers" means that auxiliary absorbers are not used at least intentionally. The total amount of laser light absorbers contained in the pressure-sensitive adhesive sheet is suitably 25% by weight or less of the pressure-sensitive adhesive sheet, and more preferably 20% by weight or less, 15% by weight or less, or 10% by weight or less.

[0114] When the PSA sheet disclosed herein contains a specific absorbent, the carbon black (CB) content of the PSA sheet is preferably less than 0.3 wt %, more preferably less than 0.1 wt %, even more preferably less than 0.05 wt %, and particularly preferably 0.02 wt % or less. Reducing the CB content tends to improve the non-contaminating properties of the PSA sheet. The PSA sheet may be substantially free of CB, i.e., a PSA sheet in which CB is not used at least intentionally. By containing a specific absorbent, the PSA sheet disclosed herein can efficiently process workpieces even without the use of CB or with the amount of CB limited as described above. Such a PSA sheet can advantageously achieve both improved workpiece processing efficiency and non-contaminating properties.

[0115] In some embodiments, a black metal compound may be preferably used as the specific absorbent. The use of a black metal compound can efficiently increase the laser light absorption rate of the pressure-sensitive adhesive sheet. This makes it possible to preferably achieve a pressure-sensitive adhesive sheet having the above-mentioned preferred laser light absorption rate even if CB is not used or the amount used is limited. The inventors' studies have surprisingly revealed that such black metal compounds, unlike CB, are less likely to produce black residue. Therefore, the use of a black metal compound can preferably achieve both improved workpiece processing efficiency and non-contamination.

[0116] Examples of black metal compounds include, but are not limited to, iron oxide, manganese dioxide, titanium black, chromium oxide, iron sulfide, molybdenum sulfide, etc. In terms of availability, iron oxide (e.g., FeO, Fe ３ O ４ Titanium black is a black particle having titanium atoms, and is preferably a black particle such as titanium oxynitride or low-order titanium oxide. Among these, iron oxide and titanium black are preferred as black metal compounds.

[0117] The content of the black metal compound in the pressure-sensitive adhesive sheet can be, for example, 0.05 wt% or more of the pressure-sensitive adhesive sheet, and from the viewpoint of improving the laser light absorption rate, it may be 0.1 wt% or more, 0.3 wt% or more, 0.5 wt% or more, or 0.8 wt% or more. Furthermore, from the viewpoint of reducing energy loss due to diffusion in the surface direction of the pressure-sensitive adhesive sheet, the content of the black metal compound is usually suitably 15 wt% or less of the pressure-sensitive adhesive sheet, preferably 10 wt% or less, more preferably 7 wt% or less, and may be 5 wt% or less or less than 5 wt%. Alternatively, the proportion of the black metal compound in the specific absorbent may be, for example, more than 50 wt%, may be 70 wt% or more, may be 90 wt% or more, or may be substantially 100 wt%.

[0118] (Thickness of the Pressure-Sensitive Adhesive Sheet) The thickness of the pressure-sensitive adhesive sheet is not particularly limited, and is typically approximately 10 μm to 500 μm. From the viewpoint of the handleability of the pressure-sensitive adhesive sheet, in some embodiments, the thickness of the pressure-sensitive adhesive sheet may be, for example, 20 μm or more, 25 μm or more, 40 μm or more, 55 μm or more, 70 μm or more, or 80 μm or more. In some embodiments, the thickness of the pressure-sensitive adhesive sheet may be, for example, 300 μm or less, 150 μm or less, 120 μm or less, or 100 μm or less. Pressure-sensitive adhesive sheets of the above thicknesses are preferably used for surface protection applications. Furthermore, when applying a pressure-sensitive adhesive sheet to laser processing applications, limiting the thickness of the pressure-sensitive adhesive sheet can improve the speed and precision of laser processing. In other embodiments, the thickness of the pressure-sensitive adhesive sheet may be 80 μm or less, 60 μm or less, or 50 μm or less. Pressure-sensitive adhesive sheets thinned as described above are preferably used for applications where thinness and weight reduction are desired.

[0119] <Characteristics of the Pressure-Sensitive Adhesive Sheet> Although not particularly limited, in embodiments in which the pressure-sensitive adhesive sheet is used for laser processing, the pressure-sensitive adhesive sheet preferably has a laser light absorptance of 20% or more in the wavelength range of the laser light used for processing (typically, the laser light absorptance at the main wavelength of the laser light). This laser light absorptance refers to the proportion of laser light actually absorbed by the pressure-sensitive adhesive sheet out of the laser light irradiated onto the pressure-sensitive adhesive sheet. A pressure-sensitive adhesive sheet with a laser light absorptance of 20% or more can efficiently absorb laser light. In some embodiments, the laser light absorptance of the pressure-sensitive adhesive sheet may be, for example, 25% or more, 30% or more, 45% or more, 60% or more, or 75% or more. The laser light absorptance of the pressure-sensitive adhesive sheet may be 100%, but in practice, 95% or less is preferable, and may be 90% or less.

[0120] In this specification, "laser light absorptance" refers to a value calculated from the transmittance T (%) and reflectance R (%) of a sample measured using a spectrophotometer (for example, a spectrophotometer manufactured by Hitachi High-Technologies Corporation, model "U-4100" or an equivalent), using the following formula (I): Absorbance A (%) = 100 (%) - T (%) - R (%) (I)

[0121] In this specification, for example, "laser light absorptance in the wavelength range of 900 nm to 1100 nm" refers to the minimum laser light absorptance in that wavelength range. Furthermore, unless otherwise specified, laser light absorptance in this specification refers to the laser light absorptance on the back surface of the adhesive sheet or substrate (the surface on the side irradiated with laser light, i.e., the surface opposite the surface attached to the workpiece).

[0122] The transmittance and reflectance of the pressure-sensitive adhesive sheet are not particularly limited. In some embodiments, the pressure-sensitive adhesive sheet may have a laser light transmittance of less than 70%, for example, less than 50%, at a wavelength at which the laser light absorption rate is minimum within the wavelength range of the laser light used for processing. In some embodiments, the pressure-sensitive adhesive sheet may have a laser light reflectance of less than 50%, for example, less than 40%, less than 20%, or less than 10%, at a wavelength at which the laser light absorption rate is minimum. A pressure-sensitive adhesive sheet that satisfies at least one of the above transmittance and the above reflectance (preferably both) is likely to have the preferred laser light absorbance disclosed herein.

[0123] <Applications> The applications of the PSA sheets disclosed herein are not particularly limited. They can be applied to various applications in which PSA sheets having a resin film substrate can be used, thereby contributing to reducing the amount of organic solvent used in such applications. The PSA sheets disclosed herein can be used, for example, for purposes such as fixing or joining components in various parts or products (e.g., for the purpose of semi-permanently fixing or joining). Furthermore, the PSA sheets disclosed herein have good anchoring properties of the PSA layer to the resin film substrate, so they are less likely to leave adhesive residue when peeled from the adherend. Therefore, they are suitable as PSA sheets for surface protection that are attached to the surface of an adherend and peeled from the adherend after achieving their protective purpose. For example, they can be used to protect the surfaces of components such as metal plates, painted plates, aluminum sashes, resin plates, decorative steel plates, vinyl chloride-laminated steel plates, and glass plates, optical films for liquid crystal displays such as polarizing films, optical components such as liquid crystal panels, and electronic components during transportation, processing, or curing. The PSA sheets disclosed herein are also suitable as packaging PSA sheets. PSA sheets used in packaging of textiles, paper, boxes, and other packaging materials are required to be able to be removed smoothly without leaving adhesive residue when the package is opened. The PSA sheets disclosed herein can be preferably used for such applications.

[0124] The adhesive sheet disclosed herein can be preferably used as one form of surface protection in a state where it is attached to a workpiece to be processed by various lasers and laser cut in conjunction with the laser processing of the workpiece. The laser light used for the laser processing is not particularly limited, and various conventionally known lasers can be used. For example, excimer lasers such as ArF excimer laser, KrF excimer laser, and XeCl excimer laser, solid-state lasers such as YAG laser, YLF laser, YVO4 laser, and titanium sapphire laser, semiconductor lasers (sometimes called diode lasers), fiber lasers, carbon dioxide lasers, etc. can be used. The type of laser processing performed on the workpiece with the adhesive sheet disclosed herein attached is not particularly limited, and can be, for example, cutting, drilling, cutting, engraving, etc.

[0125] The material of the workpiece is not particularly limited as long as it can be cut by laser light (e.g., laser light from a carbon dioxide laser or fiber laser). Examples of the material include metal or semimetal materials such as iron, iron alloys (carbon steel, stainless steel, chromium steel, nickel steel, etc.), aluminum, aluminum alloys, nickel, tungsten, copper, copper alloys, titanium, titanium alloys, and silicon; resin materials such as polyolefin resin, polycarbonate resin, and acrylic resin; ceramic materials such as alumina, silica, sapphire, silicon nitride, tantalum nitride, titanium carbide, silicon carbide, gallium nitride, and gypsum; glass materials such as aluminosilicate glass, soda-lime glass, soda-aluminosilicate glass, and quartz glass; cellulose-based materials such as paper, cardboard, wood, and plywood; and laminates and composites thereof. Suitable examples of the workpiece include metal materials such as iron, aluminum, copper, titanium, and alloys containing these metals as the main component (e.g., stainless steel). The shape of the workpiece is not particularly limited and may be plate-shaped, cylindrical, block-shaped, or the like. The adhesive sheet disclosed herein is preferable because it prevents lateral sliding even when it is attached to a metal plate as a workpiece and placed on top of it.

[0126] The adhesive sheet disclosed herein can be preferably used in such laser processing by adhering it to the surface of the workpiece on the side irradiated with laser light. Furthermore, for purposes such as protecting the surface of the workpiece before, during, or after laser processing, the adhesive sheet may be attached to the surface (back surface) opposite the side irradiated with laser light. The adhesive sheet disclosed herein can be preferably used in such laser processing using a short-wavelength laser with a dominant wavelength of 900 to 1100 nm. Examples of the short-wavelength laser that can be used include a fiber laser with a dominant wavelength of approximately 1050 nm and a diode laser with a dominant wavelength of approximately 950 nm.

[0127] The matters disclosed in this specification include the following: [1] A pressure-sensitive adhesive sheet having, in this order, a resin film substrate, an undercoat layer, and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing a rubber-based latex and an aqueous crosslinking agent, and the undercoat layer contains a water-dispersible polymer having an oxazoline group. [2] A pressure-sensitive adhesive sheet having, in this order, a resin film substrate, an undercoat layer, and a pressure-sensitive adhesive layer, wherein the undercoat layer is provided on at least one surface of the resin film substrate and is in contact with the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing a rubber-based latex and an aqueous crosslinking agent, the aqueous crosslinking agent contains an aqueous crosslinking agent having at least one functional group selected from an oxazoline group, an isocyanate group, and an epoxy group, and the undercoat layer contains a water-dispersible polymer having an oxazoline group. [3] The pressure-sensitive adhesive sheet according to [1] or [2] above, wherein the resin film substrate is a polyolefin-based resin film substrate. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the glass transition temperature of the water-dispersible polymer having an oxazoline group is 0°C or lower. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the content of the aqueous crosslinking agent in the pressure-sensitive adhesive layer is 0.1 parts by weight or more per 100 parts by weight of the rubber latex, based on non-volatile content. [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, wherein the thickness of the undercoat layer is 0.01 μm or more and 3 μm or less. [7] The pressure-sensitive adhesive sheet according to any one of [1] to [6] above, wherein the rubber latex contains natural rubber latex in a proportion of 50% by weight or more, based on non-volatile content. [8] The pressure-sensitive adhesive sheet according to any one of [1] to [7] above, wherein the pressure-sensitive adhesive sheet is used for protecting the surface of an adherend.

[0128] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to these specific examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0129] <Preparation of Tackifier Resin Emulsion> A resin solution was prepared by dissolving 100 parts of an aliphatic hydrocarbon resin (manufactured by ENEOS Corporation, trade name "T-REZ RB100," softening point 100°C) in 40 parts of toluene. Four parts of casein, 60 parts of water, and 28% aqueous ammonia were mixed, and the casein was heated and dissolved at 70°C to obtain an aqueous ammonia solution of casein. The amount of 28% aqueous ammonia used was 15 parts per 100 parts of casein. The aqueous ammonia solution of casein was cooled to 40°C, and 8 parts of an ammonium salt of hydrogenated rosin (containing 60% dihydroabietic acid) was added as an emulsifier and mixed to obtain an emulsifier-containing solution. The emulsifier-containing solution was then mixed with the resin solution and stirred for 1 hour at 800 rpm using a T.K. Homodisper (manufactured by Tokushu Kika Kogyo Co., Ltd.) to prepare a tackifier resin emulsion. The tackifier resin emulsion was prepared by adjusting the temperatures of the emulsifier-containing liquid and the resin solution to 40°C.

[0130] Example 1 Preparation of Pressure-Sensitive Adhesive Composition 70 parts of the tackifier resin emulsion obtained above, 2 parts of an antioxidant (manufactured by Seiko Chemical Co., Ltd., trade name "Nonflex CBP-E"), and 1 part of a water-soluble oxazoline crosslinking agent (manufactured by Nippon Shokubai Co., Ltd., trade name "Epocross WS-700") were added to 100 parts of natural rubber latex (available from Nomura Trading Co., Ltd., trade name "HYTEX HA", hereinafter sometimes abbreviated as "NR") on a non-volatile basis, and mixed to prepare a water-dispersible pressure-sensitive adhesive composition according to this example.

[0131] (Preparation of Pressure-Sensitive Adhesive Sheet) An oxazoline group-containing polymer emulsion (manufactured by Nippon Shokubai Co., Ltd., trade name "Epocross K-2010E", Tg -50°C) was applied with a wire bar #3 to a first surface of a polyethylene film (manufactured by Okura Kogyo Co., Ltd., product name "SHO Film", thickness 50 µm) serving as a resin film substrate, and then dried to form a primer layer (coating amount: 1.4 g / m on a non-volatile basis). ２ ) The pressure-sensitive adhesive composition was applied to the surface of the undercoat layer of the resin film substrate and dried to form a pressure-sensitive adhesive layer with a thickness of 12 μm. In this way, a pressure-sensitive adhesive sheet was obtained having an undercoat layer on the first surface of the resin film substrate and a pressure-sensitive adhesive layer on the undercoat layer.

[0132] Example 2 In the preparation of the pressure-sensitive adhesive composition of Example 1, a water-dispersible isocyanate-based crosslinking agent (manufactured by DIC Corporation, trade name "Burnoc DNW-6000") was used instead of the water-soluble oxazoline-based crosslinking agent. Otherwise, a pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1.

[0133] Example 3 In the preparation of the PSA composition of Example 1, 100 parts of natural rubber latex was replaced with 90 parts of the above natural rubber latex and 10 parts of acid-modified SBR latex (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol LX432M", Tg -55°C, hereinafter sometimes referred to as "SBR") on a non-volatile basis. Otherwise, a PSA sheet according to this example was obtained in the same manner as in Example 1.

[0134] Examples 4 to 5 In the preparation of the pressure-sensitive adhesive composition of Example 3, the amount of water-soluble oxazoline-based crosslinking agent was changed to 0.5 parts (Example 4) or 5 parts (Example 5) based on the nonvolatile content per 100 parts of the total amount of rubber latex. Otherwise, pressure-sensitive adhesive sheets according to each example were obtained in the same manner as in Example 3.

[0135] Example 6 In the preparation of the pressure-sensitive adhesive composition of Example 3, a water-soluble epoxy-based crosslinking agent (manufactured by Nagase ChemteX Corporation, product name "Denacol EX-313") was used instead of the water-soluble oxazoline-based crosslinking agent. Otherwise, a pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 3.

[0136] Example 7 An oxazoline group-containing polymer emulsion (manufactured by Nippon Shokubai Co., Ltd., trade name "Epocross K-2020E", Tg 0°C) was applied with a wire bar #3 to the first surface of a polyethylene film (manufactured by Okura Kogyo Co., Ltd., product name "SHO Film", thickness 50 μm) serving as a resin film substrate, and then dried to form a primer layer (coating amount: 1.4 g / m on a nonvolatile basis). ２ A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 2, except that this resin film substrate with an undercoat layer was used.

[0137] Example 8 A water-dispersible pressure-sensitive adhesive composition according to this example was prepared by mixing 100 parts, based on non-volatile content, of acid-modified SBR latex (manufactured by Nippon Zeon Co., Ltd., trade name "Nipol LX432M", Tg -55°C), 70 parts of rosin ester emulsion (manufactured by KRATON Corporation, trade name "AQUATACK 6085", softening point 82°C), 2 parts of an antioxidant (manufactured by Seiko Chemical Co., Ltd., trade name "Nonflex CBP-E"), and 1 part of a water-soluble oxazoline crosslinking agent (manufactured by Nippon Shokubai Co., Ltd., trade name "Epocross WS-700"). A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except that this pressure-sensitive adhesive composition was used.

[0138] Example 9 In the preparation of the pressure-sensitive adhesive sheet of Example 1, a pressure-sensitive adhesive composition was applied to a first surface of a polyethylene film (manufactured by Okura Kogyo Co., Ltd., product name "SHO Film", thickness 50 μm) serving as a resin film substrate, and the resulting film was dried to form a pressure-sensitive adhesive layer having a thickness of 12 μm. Otherwise, a pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1.

[0139] Example 10 In the preparation of the PSA sheet of Example 9, a corona discharge treatment was performed on a first surface of a polyethylene film (manufactured by Okura Kogyo Co., Ltd., product name "SHO Film", thickness 50 μm) serving as a resin film substrate, and then a PSA composition was applied to the corona discharge-treated surface and dried to form a PSA layer with a thickness of 12 μm. Otherwise, a PSA sheet according to this example was obtained in the same manner as in Example 9.

[0140] Example 11 In the production of the PSA sheet of Example 1, a polyester emulsion (manufactured by Toyobo MC Co., Ltd., trade name "Binalol MD-1100", Tg 40°C) was applied with a wire bar #3 to the first surface of a polyethylene film (manufactured by Okura Kogyo Co., Ltd., product name "SHO Film", thickness 50 μm) serving as a resin film substrate, and then dried to form an undercoat layer (coating amount: 1.4 g / m on a non-volatile basis). ２ A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 2, except that this resin film substrate with an undercoat layer was used.

[0141] Example 12 A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that no water-soluble oxazoline-based crosslinking agent was used. A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except that this pressure-sensitive adhesive composition was used.

[0142] Example 13 In the production of the PSA sheet of Example 1, a water-soluble oxazoline group-containing polymer (manufactured by Nippon Shokubai Co., Ltd., trade name "Epocross WS-700", Tg 50°C) was applied with a wire bar #3 to the first surface of a polyethylene film (manufactured by Okura Kogyo Co., Ltd., product name "SHO Film", thickness 50 µm) serving as a resin film substrate, and then dried to form an undercoat layer (coating amount: 1.4 g / m on a non-volatile basis). ２ A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except that this resin film substrate with an undercoat layer was used.

[0143] <Performance Evaluation> The adhesive sheets prepared above were evaluated for anchoring ability of the adhesive layer by the following method. The results are shown in Table 1.

[0144] (1) Finger Abrasion Test A pressure-sensitive adhesive sheet was cut into a width of 20 mm and fixed to an acrylic plate with the pressure-sensitive adhesive layer surface facing outward. A predetermined area (approximately 1 cm x 3 cm) on the surface of the pressure-sensitive adhesive layer was rubbed strongly with a finger with a constant force, and the number of rubs until peeling of the pressure-sensitive adhesive layer occurred was recorded. In addition, the degree of peeling of the pressure-sensitive adhesive layer after three rubs was visually observed and evaluated according to the following criteria: A: No peeling of the pressure-sensitive adhesive layer was observed. B: The peeled area of ​​the pressure-sensitive adhesive layer was 10% or less. C: The peeled area of ​​the pressure-sensitive adhesive layer was more than 10% and 50% or less. D: The peeled area of ​​the pressure-sensitive adhesive layer was more than 50%. In the finger abrasion test, a peeling evaluation of C or higher after three rubs was judged to be pass, and a peeling evaluation of D after three rubs was judged to be fail.

[0145] (2) Picking Test The adhesive sheet was cut into 20 mm widths, and the adhesive layer surfaces were bonded together using a hand roller. After one minute, the bonded adhesive layers were peeled off with a constant force. This picking operation, which consisted of bonding and peeling, was repeated, and the number of picking operations until peeling of the adhesive layer occurred was recorded. In addition, the degree of peeling of the adhesive layer after the third picking operation was visually observed and evaluated according to the following criteria. A: No peeling of the adhesive layer was observed. B: The peeled area of ​​the adhesive layer was 10% or less. C: The peeled area of ​​the adhesive layer was more than 10% and 50% or less. D: The peeled area of ​​the adhesive layer was more than 50%. In the above picking test, if the peeling evaluation after the third picking operation was C or higher, the sample was judged to have passed, and if the peeling evaluation after the third picking operation was D, the sample was judged to have failed.

[0146]

[0147] As shown in Table 1, the PSA sheets of Examples 1 to 8 have an undercoat layer formed from an oxazoline group-containing polymer emulsion between an PSA layer formed from a PSA composition containing rubber latex and a resin film substrate, and the PSA layer contains an oxazoline-based crosslinking agent, an isocyanate-based crosslinking agent, or an epoxy-based crosslinking agent as an aqueous crosslinking agent. The finger abrasion test and the picking test all passed. On the other hand, Example 9, which did not have an undercoat layer, Example 10, which underwent corona treatment instead of a primer, Example 11, which used a polyester-based primer, Example 12, which did not incorporate a crosslinking agent into the PSA layer, and Example 13, which used a water-soluble oxazoline group-containing polymer as a primer, all failed the finger abrasion test and the picking test. The above results show that a configuration comprising a resin film substrate, an undercoat layer, and a pressure-sensitive adhesive layer in this order, where the pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing a rubber latex and an aqueous crosslinking agent, where the aqueous crosslinking agent comprises an aqueous crosslinking agent having at least one functional group selected from an oxazoline group, an isocyanate group, and an epoxy group, and where the undercoat layer comprises a water-dispersible polymer having an oxazoline group, can provide good anchoring properties without relying on organic solvents.

[0148] 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.

[0149] REFERENCE SIGNS LIST 1 adhesive sheet 10 resin film substrate 10A first surface 10B second surface (back surface, release surface) 20 adhesive layer 20A surface (adhesive surface) 30 primer layer 30A surface (of primer layer)

Claims

1. A pressure-sensitive adhesive sheet having a resin film substrate, an undercoat layer, and an adhesive layer in this order, wherein the undercoat layer is provided on at least one surface of the resin film substrate and is in contact with the adhesive layer, the adhesive layer is formed from an adhesive composition containing a rubber-based latex and an aqueous crosslinking agent, the aqueous crosslinking agent comprises an aqueous crosslinking agent having at least one functional group selected from an oxazoline group, an isocyanate group, and an epoxy group, and the undercoat layer comprises a water-dispersible polymer having an oxazoline group.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the resin film substrate is a polyolefin-based resin film substrate.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the water-dispersible polymer having an oxazoline group has a glass transition temperature of 0°C or lower.

4. The adhesive sheet according to claim 1 or 2, wherein the content of the aqueous crosslinking agent in the adhesive layer is 0.1 parts by weight or more per 100 parts by weight of the rubber latex, based on the non-volatile content.

5. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the thickness of the undercoat layer is from 0.01 μm to 3 μm.

6. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the rubber-based latex contains natural rubber latex in an amount of 50% by weight or more based on the non-volatile content.

7. The pressure-sensitive adhesive sheet according to claim 1 or 2, which is used for protecting the surface of an adherend.

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