Adhesive composition and adhesive sheet

Abstract

Provided is an adhesive composition comprising: a rubber-based latex containing an acid-modified synthetic rubber latex at 50 wt% or more in terms of non-volatile content; and a rosin-based tackifier emulsion as a tackifier. In this adhesive composition, the glass transition temperature of an acid-modified synthetic rubber contained in the acid-modified synthetic rubber latex is -20°C or lower. The rosin-based tackifier contained in the rosin-based tackifier emulsion has a softening point of 140°C or lower.

Description

Pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

[0001] The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet. This application claims priority to Japanese Patent Application No. 2023-116984, filed on July 18, 2023, the entire contents of which are incorporated herein by reference.

[0002] Generally, 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 under pressure. Utilizing this property, adhesives are widely used in various fields for purposes such as bonding, fixing, surface protection, masking, and marking, for example, in the form of adhesive sheets having an adhesive layer on a substrate. For example, Patent Document 1 is a technical document relating to an adhesive sheet that can be used for surface protection during laser processing. Patent Document 2 is a technical document relating to an aqueous adhesive composition containing a rubber latex and a tackifying resin emulsion.

[0003] Japanese Patent No. 7058096 Japanese Patent No. 4676945

[0004] Pressure-sensitive adhesive sheets may be required to have various properties depending on their intended use, the context of use, and the like. For example, in applications where a pressure-sensitive adhesive sheet is attached to an adherend and exposed to a high-speed peel load, the pressure-sensitive adhesive sheet is required to have a peel strength (high-speed peel strength) that prevents lifting or peeling from the adherend under such high-speed peel load. One example of an application requiring such high-speed peel strength is laser processing. Laser processing is a technique for processing various materials using laser light, such as cutting or drilling, and uses, for example, a carbon dioxide laser with a dominant wavelength of approximately 9.3 μm to 10.6 μm or a short-wavelength laser with a dominant wavelength of approximately 0.9 μm to 1.1 μm. One example of laser processing is a mode in which a pressure-sensitive adhesive sheet is attached as an auxiliary material to an adherend (a workpiece), which is a workpiece to be processed, and laser light is irradiated onto the workpiece to laser-process the pressure-sensitive adhesive sheet and the workpiece. Pressure-sensitive adhesive sheets that can be used in such a mode preferably have a high-speed peel strength suitable for suppressing lifting or peeling due to the assist gas supplied during laser processing.

[0005] In particular, by using a short-wavelength laser beam with a dominant wavelength of approximately 0.9 μm to 1.1 μm, the energy required for processing can be efficiently applied to the workpiece. This can be advantageous from the perspective of increasing processing speed and fine processing. On the other hand, processing using a short-wavelength laser tends to require a high assist gas pressure to increase the processing speed. For this reason, it is particularly desirable for adhesive sheets intended for processing using a short-wavelength laser to have a certain level of high-speed peel strength in order to prevent the occurrence of an incident in which such high-pressure assist gas gets between the sheet and the workpiece and causes the sheet to lift off the workpiece.

[0006] In addition, adhesive sheets may be required to have resistance to peeling under a low-speed peel load, i.e., a predetermined low-speed peel strength. For example, a workpiece that has been cut or otherwise processed using the above-mentioned laser light may then be subjected to post-processing such as bending or drilling. In this case, the adhesive sheet attached as an auxiliary material for laser processing remains attached to the workpiece after laser processing and continues to be used in the post-processing. In this case, if the low-speed peel strength of the adhesive sheet is too low, it may not be able to withstand the bending, pulling, etc., that occurs during the post-processing, and there is a concern that the adhesive sheet may peel off. For this reason, it is desirable for adhesive sheets used in laser processing to have a low-speed peel strength of a certain level or higher in order to prevent peeling during the post-processing.

[0007] On the other hand, adhesive sheets used for surface protection of adherends are attached to the surface of the adherend, and after achieving their protective purpose, are usually peeled off (re-peeled) from the adherend. Therefore, adhesive sheets used for such purposes must have a peel strength to the adherend limited to a range that allows re-peeling. Furthermore, when re-peeled from the adherend, it is desirable that there is no problem of adhesive residue remaining on the adherend surface (glue residue), and that the sheet be peeled off without contaminating the adherend. It is also desirable that adhesive sheets used for surface protection during laser processing do not leave adhesive residue or contaminate the sheet when peeled off after processing, including laser processing.

[0008] Recently, there has been a demand for a reduction in the amount of organic solvents used, due to environmental considerations and the need to eliminate the use of petroleum resources. From this perspective, for example, even with rubber-based PSAs, it is more desirable to use an aqueous PSA composition containing a rubber latex than a solvent-based PSA composition in which the PSA component is dissolved in an organic solvent. However, PSA compositions containing natural rubber latex tend to lack mechanical stability (mechanical stability) against mechanical shear (shear force). When the PSA composition lacks mechanical stability, aggregates are likely to form due to the mechanical shear applied during delivery by a gear pump or coating by a roll coater. The formation of such aggregates can reduce the commercial value (e.g., appearance quality) of PSA sheets produced using the PSA composition.

[0009] The mechanical stability of natural rubber latex-containing PSA compositions can be improved by using protective colloids, emulsifiers, or dispersants, as proposed in, for example, Patent Document 2. However, such additives can adversely affect adhesive properties. For example, the inclusion of additives such as emulsifiers can cause a decrease in peel strength, e.g., high-speed peel strength. Furthermore, PSAs containing such additives tend to have reduced anchoring properties to substrates such as resin films, potentially leaving adhesive residue when removing the PSA sheet from the adherend. In particular, PSAs formed from rubber latex-containing PSA compositions tend to lack anchoring properties to polyolefin-based resin film substrates. While anchoring properties to the substrate can be improved by providing a primer layer on the substrate, sufficient adhesive residue prevention may still not be achieved. Furthermore, additives such as emulsifiers contained in PSAs can bleed out and contaminate the adherend surface.

[0010] The present invention was made in view of the above circumstances, and aims to provide a rubber-based latex-containing pressure-sensitive adhesive composition that has good mechanical stability, and is capable of forming a pressure-sensitive adhesive that has good high-speed peel strength and is excellent in preventing adhesive transfer and preventing contamination of adherends. Another related aim is to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition.

[0011] According to this specification, a pressure-sensitive adhesive composition is provided that includes a rubber latex containing 50% or more by weight of acid-modified synthetic rubber latex, based on the nonvolatile content, and a rosin-based tackifier emulsion as a tackifier. In this pressure-sensitive adhesive composition, the acid-modified synthetic rubber contained in the acid-modified synthetic rubber latex has a glass transition temperature of −20°C or lower. Furthermore, the rosin-based tackifier contained in the rosin-based tackifier emulsion has a softening point of 140°C or lower. With a pressure-sensitive adhesive composition having the above configuration, good mechanical stability can be achieved due to the use of rubber latex. Furthermore, a pressure-sensitive adhesive can be formed that has good high-speed peel strength and is less likely to leave adhesive residue or stain on the adherend surface upon peeling. That is, good high-speed peel strength and excellent resistance to adhesive residue and adherend staining can be achieved simultaneously. The pressure-sensitive adhesive composition can be obtained from a rubber latex and a rosin-based tackifier emulsion without relying on organic solvents. Therefore, it is possible to substantially eliminate the use of organic solvents or reduce the amount of organic solvent used. This is significant in terms of eliminating organic solvents and being environmentally friendly.

[0012] In some preferred embodiments, the PSA composition contains an acid-modified styrene-butadiene copolymer latex as the acid-modified synthetic rubber latex. The technology disclosed herein is preferably carried out in an embodiment using an acid-modified styrene-butadiene copolymer latex.

[0013] In some preferred embodiments, the content of the tackifier is 50 parts by weight or more and 100 parts by weight or less based on the nonvolatile content of the rubber latex. By setting the content of the tackifier within this range, it is possible to preferably achieve excellent resistance to adhesive transfer and staining of the adherend while maintaining good high-speed peel strength.

[0014] In some embodiments, the PSA composition does not contain a crosslinking agent, or contains the crosslinking agent in an amount of 5 parts by weight or less per 100 parts by weight of the rubber latex, based on the nonvolatile content. By setting the content of the crosslinking agent within the above range, the PSA layer obtained has good high-speed peel strength and suitable cohesive strength, and is likely to exhibit excellent resistance to adhesive transfer and contamination of the adherend.

[0015] The present specification also provides a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of any of the pressure-sensitive adhesive compositions disclosed herein and a substrate supporting the pressure-sensitive adhesive layer. A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition disclosed herein has good high-speed peel strength due to the pressure-sensitive adhesive layer formed with good mechanical stability, and is less likely to leave adhesive residue or stain the adherend surface upon peeling.

[0016] In some embodiments, the PSA sheet has a primer layer disposed between the substrate and the PSA layer. By disposing the primer layer between the substrate and the PSA layer, the anchoring properties of the PSA layer can be increased, thereby improving the resistance to adhesive transfer. In this specification, "anchoring properties" 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 (anchor breakdown) between the PSA layer and the substrate. Therefore, in this specification, the term "anchoring properties of the PSA layer to the substrate" or an equivalent expression is used not only to refer to the anchoring properties of the PSA layer to the substrate in a configuration in which the substrate and the PSA layer are in contact with each other, but also to a configuration in which a primer layer is present between the substrate and the PSA layer.

[0017] In some embodiments, the PSA sheet comprises a polyolefin resin film as the substrate. PSA sheets comprising a polyolefin resin film substrate are suitable for applications involving laser cutting, specifically laser processing, because, for example, when cut with laser light, the cutting width is easily controlled and cut edges with good shape precision are easily formed. Furthermore, for example, while aqueous PSA compositions generally tend to have reduced anchoring properties to polyolefin resin film substrates, providing a primer layer on the surface of the polyolefin resin film substrate can enhance the anchoring properties of the PSA layer and improve adhesive transfer resistance.

[0018] In some preferred embodiments, the undercoat layer contains a polymer having an oxazoline group. By using an oxazoline group-containing polymer as a material for the undercoat layer, the anchoring strength of the PSA layer formed by containing a rubber latex is improved, and more excellent resistance to adhesive transfer is likely to be obtained.

[0019] The PSA sheet disclosed herein is less likely to leave adhesive residue or stain when peeled off from an adherend, and is therefore suitable as a PSA sheet for surface protection that is attached to the surface of an adherend, achieves its protective purpose, and then peeled off from the adherend.

[0020] The pressure-sensitive adhesive sheet disclosed herein has good high-speed peel strength, and therefore is less likely to lift or peel from the adherend due to assist gas pressure, even when attached to an object to be processed (adherend) and then cut together with the object using laser light. Therefore, the pressure-sensitive adhesive sheet disclosed herein can be preferably used as a laser processing pressure-sensitive adhesive sheet that is cut using laser light (e.g., laser light such as a carbon dioxide laser or a short-wavelength laser). The pressure-sensitive adhesive sheet is particularly suitable as a laser processing pressure-sensitive adhesive sheet that is cut using a short-wavelength laser light (hereinafter also referred to as "specific laser light") with a dominant wavelength in the range of 900 nm to 1100 nm. A suitable example of the laser processing application is to protect the surface of a metal plate during laser processing of the metal plate.

[0021] Fig. 2 is a cross-sectional view schematically showing a pressure-sensitive adhesive sheet according to one embodiment;Fig. 3 is a cross-sectional view schematically showing a pressure-sensitive adhesive sheet according to another embodiment;Fig. 4 is a cross-sectional view schematically showing a pressure-sensitive adhesive sheet according to another embodiment.

[0022] 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.

[0023] 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.

[0024] 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 ２The material may be a material having the properties satisfying the above (typically, a material having the above properties at 25°C).

[0025] <Adhesive Composition> (Rubber Latex (A)) The adhesive composition disclosed herein contains a rubber latex (A). The rubber latex (A) contains 50% by weight or more of an acid-modified synthetic rubber latex based on the nonvolatile content. The glass transition temperature (Tg) of the acid-modified synthetic rubber contained in the acid-modified synthetic rubber latex is −20° C. or lower. The term “rubber latex” refers to a dispersion in which a rubber polymer such as an acid-modified synthetic rubber is dispersed in water, and the term “acid-modified synthetic rubber latex” refers to a dispersion in which an acid-modified synthetic rubber is dispersed in water. By using an acid-modified synthetic rubber latex as the rubber latex (A), better mechanical stability can be achieved compared to compositions using natural rubber latex. In addition, in embodiments in which an adhesive layer is formed on a substrate, the acid modification can improve anchoring properties to the substrate and the primer layer on the substrate. Furthermore, the improved cohesive strength and anchoring properties of the adhesive due to the acid modification make it less likely to leave adhesive residue on the adherend surface upon peeling. For example, PSA's formed using acid-modified synthetic rubber latex are more likely to provide anchoring properties to resin films and the like than PSA's formed using natural rubber latex or synthetic rubber that is not acid-modified. Furthermore, by using an acid-modified synthetic rubber with a Tg of −20° C. or lower, adhesion to adherends such as metal materials can be improved, and high-speed peel strength in particular can be improved. Furthermore, other additives such as tackifiers are more easily compatible, and contamination of the adherend surface tends to be suppressed.

[0026] In some preferred embodiments, from the viewpoint of improving mechanical stability and anchoring property, the proportion of the acid-modified synthetic rubber latex in the rubber latex (A) is about 60% by weight or more, more preferably about 70% by weight or more, even more preferably about 80% by weight or more, even 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 acid-modified synthetic rubber latex. For example, additives such as emulsifiers that may be contained in natural rubber latex can bleed out and cause contamination of the surface of the adherend, so increasing the proportion of the acid-modified synthetic rubber latex is advantageous in terms of preventing contamination of the adherend. In some other embodiments, from the viewpoint of effectively obtaining the effect of blending a rubber polymer other than the acid-modified synthetic rubber latex (specifically, natural rubber or non-acid-modified synthetic rubber), the proportion of the acid-modified synthetic rubber latex contained in the rubber latex (A) may be about 90% by weight or less, about 80% by weight or less, or 70% by weight or less based on the non-volatile content.

[0027] 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.

[0028] In some preferred embodiments, the Tg of the acid-modified synthetic rubber contained in the acid-modified synthetic rubber latex is approximately -30°C or lower, more preferably approximately -40°C or lower, and even more preferably approximately -50°C or lower, from the viewpoints of improving high-speed peel strength and reducing contamination of the adherend surface. Furthermore, in some embodiments, the lower limit of the Tg of the acid-modified synthetic rubber is, for example, approximately -80°C or higher, and may be approximately -70°C or higher, or may be approximately -65°C or higher. For commercially available products, the manufacturer's nominal value may be used as the Tg of the acid-modified synthetic rubber. When the manufacturer's nominal value is unknown or when 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 a DSC, a "Q2000" product manufactured by TA Instruments or an equivalent can be used.

[0029] Examples of acid-modified synthetic rubber latex include those obtained by acid-modifying various synthetic rubber latexes, such as styrene-butadiene copolymer latex (SBR latex), nitrile rubber latex (NBR latex), and chloroprene latex. Among these, it is preferable to use acid-modified SBR latex as the acid-modified synthetic rubber latex. The acid-modified synthetic rubber latex may be a synthetic rubber latex acid-modified by a known or conventional method. For example, the 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 product may be obtained as the acid-modified synthetic rubber latex. The acid-modified synthetic rubber may be used alone or in combination of two or more.

[0030] 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.

[0031] In some embodiments, the rubber latex (A) may or may not contain a rubber polymer other than the acid-modified synthetic rubber latex (e.g., natural rubber latex, non-acid-modified synthetic rubber). Examples of other rubber latexes containing such rubber polymers include natural rubber latex and non-acid-modified synthetic rubber latex. The other rubber latexes can be used singly or in combination of two or more. For example, using a predetermined amount of natural rubber latex as the other rubber latex can improve peel strength. Furthermore, in a use mode in which a pressure-sensitive adhesive sheet is attached to a workpiece (adherend) and then laser processing is performed on the workpiece, using natural rubber as a pressure-sensitive adhesive component can easily produce a pressure-sensitive adhesive that can suppress lifting or peeling of the pressure-sensitive adhesive sheet due to assist gas pressure, even if the time until laser processing is shortened. Note that natural rubber latex refers to a dispersion in which natural rubber is dispersed in water.

[0032] The natural rubber contained in the natural rubber latex may be, for example, depolymerized or non-depolymerized. Furthermore, 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. Furthermore, although non-deproteinized natural rubber latex that has not been subjected to deproteinization treatment is usually used as the natural rubber latex, 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. Natural rubbers can be used singly or in combination of two or more.

[0033] In some embodiments, unmodified natural rubber latex is used as the natural rubber latex from the viewpoints of adhesion, productivity, etc. In such embodiments, the proportion of unmodified natural rubber latex contained in the natural rubber latex 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, and the natural rubber contained in the natural rubber latex may be substantially composed of unmodified natural rubber.

[0034] In some embodiments, non-deproteinized natural rubber latex is used as the natural rubber latex. The use of non-deproteinized natural rubber latex tends to facilitate the attainment of high cohesive strength. In such embodiments, the proportion of non-deproteinized natural rubber latex contained in the natural rubber latex 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, and the natural rubber contained in the natural rubber latex may be substantially composed of non-deproteinized natural rubber. While not particularly limited, the amount of protein in non-deproteinized natural rubber is approximately 0.2 to 0.7% by weight in terms of nitrogen content.

[0035] (Tackifier (B)) The pressure-sensitive adhesive composition contains a rosin-based tackifier emulsion as the tackifier (B). The rosin-based tackifier contained in the rosin-based tackifier emulsion has a softening point of 140°C or lower. The rosin-based tackifier emulsion refers to a dispersion in which a rosin ester as a tackifier is dispersed in water. An emulsion containing a rosin-based tackifier having a softening point of 140°C or lower is well compatible with the acid-modified synthetic rubber latex, reduces contamination of the adherend, and can improve the adhesiveness of the pressure-sensitive adhesive layer. The rosin-based tackifier emulsions can be used alone or in combination of two or more.

[0036] Examples of the rosin-based tackifier include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; modified rosins (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins) obtained by modifying the unmodified rosin through hydrogenation, disproportionation, polymerization, or the like; 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 it; and polyhydric alcohol esters of unsaturated fatty acid-modified disproportionated rosin obtained by partially modifying unmodified or modified rosin with an unsaturated fatty acid, followed by disproportionation and then esterifying it. Examples of the rosin phenols include those obtained by thermally polymerizing rosins with phenols after addition; and those obtained by esterifying the thermal polymers. 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. Of these, rosin esters are preferably used as rosin-based tackifiers. One type of rosin-based tackifier can be used alone, or two or more types can be used in combination.

[0037] In some preferred embodiments, from the viewpoints of improving compatibility and improving high-speed peel strength, the rosin-based tackifier used has a softening point of about 130° C. or less. The softening point of the rosin-based tackifier is more preferably about 120° C. or less, even more preferably about 110° C. or less, even more preferably about 100° C. or less, and particularly preferably about 90° C. or less. Furthermore, from the viewpoints of preventing adhesive residue and adherend contamination, the softening point of the rosin-based tackifier is preferably about 60° C. or more, more preferably about 70° C. or more, even more preferably about 80° C. or more, and may be about 90° C. or more.

[0038] In this specification, the softening point of a 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.

[0039] The PSA composition may or may not contain a tackifier other than a rosin-based tackifier having a softening point of 140°C or less, as long as the effects of the technology disclosed herein are not impaired. Examples of such other tackifiers include rosin-based tackifiers having a softening point higher than 140°C, petroleum-based tackifiers (e.g., aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic / aromatic hydrocarbon resins, and hydrogenated versions of these), terpene-based resins, ketone-based resins, xylene-based resins, etc. The above-mentioned other tackifiers may be used alone or in combination of two or more.

[0040] In some embodiments, the proportion of the rosin-based tackifier having a softening point of 140°C or less in the total amount of tackifier (B) contained in the PSA composition may be approximately 50% by weight or more, preferably approximately 70% by weight or more, more preferably approximately 80% by weight or more, even more preferably approximately 90% by weight or more, and particularly preferably approximately 95% by weight or more. It is particularly preferred that the tackifier (B) contained in the PSA composition is substantially composed of a rosin-based tackifier having a softening point of 140°C or less.

[0041] The rosin-based tackifier emulsion and other tackifier emulsions that can be used as the tackifier (B) can be prepared by appropriately employing a known tackifying resin emulsification method, or a commercially available tackifier emulsion 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 an appropriate 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 solution with water and an appropriate 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).

[0042] 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.

[0043] 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.

[0044] The content of the tackifier (B) (preferably a rosin-based tackifier with a softening point of 140°C or less; the same applies hereinafter) in the PSA composition is not particularly limited, and can be an appropriate amount that provides the desired high-speed peel strength, resistance to adhesive transfer, and resistance to contamination of the adherend. In some embodiments, the content of the tackifier (B) per 100 parts by weight of the rubber latex (A) may be more than 30 parts by weight, for example, approximately 40 parts by weight or more, based on the nonvolatile content. By using a predetermined amount or more of the tackifier (B) (preferably a rosin-based tackifier with a softening point of 140°C or less), good high-speed peel strength is easily obtained, and the low-speed peel strength can also be adjusted to the desired range. From the viewpoint of obtaining high 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, even more preferably about 65 parts by weight or more, particularly preferably about 70 parts by weight or more, and may be about 80 parts by weight or more, or may be about 90 parts by weight or more, based on the non-volatile content. Also, in some embodiments, the content of the tackifier (B) relative to 100 parts by weight of the rubber latex (A) may be about 150 parts by weight or less, about 130 parts by weight or less, about 120 parts by weight or less, or about 110 parts by weight or less, based on the non-volatile 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 (e.g., high-speed peel strength) can be easily obtained. Furthermore, the adhesive can be easily released from the adherend. In some preferred embodiments, the content of the tackifier (B) per 100 parts by weight of the rubber latex (A) is approximately 100 parts by weight or less, or may be 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 limiting the content of the tackifier (B) within the above range, the adhesive can have sufficient adhesion while improving the releasability from the adherend. For example, the decrease in cohesive strength of the adhesive layer is suppressed, and the adhesive tends to have excellent resistance to adhesive residue and contamination of the adherend after peeling from the adherend.

[0045] In some embodiments, the PSA composition may have a composition in which the total amount of the rubber latex (A) and the tackifier (B) 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) and (B) components to be optimally exhibited. In some preferred embodiments, the total amount of the (A) and (B) 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. PSA compositions having the above composition allow the effects of the technology disclosed herein to be preferably realized.

[0046] (Crosslinking Agent (C)) The PSA composition may or may not contain a crosslinking agent (C). In some embodiments, the PSA composition preferably contains a crosslinking agent (C). The use of a crosslinking agent (C) can improve anchoring properties. In embodiments in which the PSA composition is applied to a PSA sheet having a substrate, the inclusion of a crosslinking agent facilitates good anchoring properties to the substrate or the undercoat layer on the substrate. Furthermore, the use of a crosslinking agent imparts appropriate cohesive strength to the resulting PSA layer, thereby suppressing the occurrence of adhesive residue. This effect is believed to be achieved by a good reaction between the acid in the acid-modified synthetic rubber latex and the crosslinkable reactive groups of the crosslinking agent. The technology disclosed herein is not limited to the above interpretation. An aqueous crosslinking agent is preferably used as the crosslinking agent (C). The use of an aqueous crosslinking agent is also beneficial in terms of eliminating organic solvents and being environmentally friendly. The term "aqueous crosslinking agent" encompasses both water-dispersible crosslinking agents and water-soluble crosslinking agents.

[0047] Examples of the crosslinking agent (C) that can be used include isocyanate-based crosslinking agents, oxazoline-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. The crosslinking agent (C) can be used singly or in combination of two or more. Among these, it is preferable to use an aqueous crosslinking agent having at least one functional group selected from an oxazoline group, an isocyanate group, and an epoxy group as the crosslinking agent (C). In other words, oxazoline-based crosslinking agents, isocyanate-based crosslinking agents, and epoxy-based crosslinking agents are preferably used as the crosslinking agent (C). Blending an aqueous crosslinking agent having the specific functional group described above into a pressure-sensitive adhesive composition containing a rubber latex (A) can further improve anchoring properties to substrates such as resin films. While not particularly limited, oxazoline-based crosslinking agents, isocyanate-based crosslinking agents, and epoxy-based crosslinking agents can provide good adhesion to, for example, an undercoat layer containing a polymer having an oxazoline group, thereby exhibiting excellent anchoring properties.

[0048] 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.

[0049] 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.

[0050] 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."

[0051] Examples of the aziridine crosslinking agent include trimethylolpropane tris[3-(1-aziridinyl)propionate], trimethylolpropane tris[3-(1-(2-methyl)aziridinylpropionate)], etc. Commercially available aziridine crosslinking agents include, for example, trade names "ChemiTite PZ-33" and "ChemiTite DZ-22E" manufactured by Nippon Shokubai Co., Ltd.

[0052] The carbodiimide crosslinking agent may be a low molecular weight compound or a high molecular weight compound having two or more carbodiimide groups. Commercially available carbodiimide crosslinking agents include, for example, the Carbodilite V series (aqueous solution type) manufactured by Nisshinbo, such as "Carbodilite V-02," "Carbodilite V-02-L2," and "Carbodilite V-04," and the Carbodilite E series (aqueous dispersion type) such as "Carbodilite E-01," "Carbodilite E-02," and "Carbodilite E-04."

[0053] In some preferred embodiments, at least one selected from an oxazoline-based crosslinking agent and an epoxy-based crosslinking agent is used as the 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, making them advantageous in terms of productivity. Furthermore, oxazoline-based crosslinking agents and epoxy-based crosslinking agents are likely to provide excellent adhesive transfer resistance. In embodiments in which the pressure-sensitive adhesive composition is applied to a pressure-sensitive adhesive sheet having a substrate, the presence of the oxazoline-based crosslinking agent or epoxy-based crosslinking agent can improve the anchoring ability of the pressure-sensitive adhesive layer to the substrate or undercoat layer. From this perspective, in some embodiments, the combined proportion of the oxazoline-based crosslinking agent and the epoxy-based crosslinking agent to the total amount of 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 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 crosslinking agent (C) may essentially consist of at least one selected from the oxazoline-based crosslinking agent and the epoxy-based crosslinking agent.

[0054] In some embodiments, it is particularly preferable to use an oxazoline-based crosslinking agent as the 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 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 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 non-volatile content. The crosslinking agent (C) may be essentially composed of the oxazoline-based crosslinking agent.

[0055] In some embodiments, it is preferable that the crosslinking agent (C) does not contain an isocyanate-based crosslinking agent or that the amount of isocyanate-based crosslinking agent used is limited. This can suppress the short pot life and gelation during storage that are 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 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 crosslinking agent (C) may be substantially free of an isocyanate-based crosslinking agent.

[0056] In embodiments in which the PSA composition contains a crosslinking agent (C), the content of the crosslinking agent (C) in the PSA composition is not particularly limited and can be an appropriate amount that satisfies both high-speed peel strength, adhesive transfer prevention, and adherend contamination prevention. In some embodiments, the content of the crosslinking agent (C) in the PSA composition 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 crosslinking agent (C) is approximately 0.1 parts by weight or more per 100 parts by weight of the rubber latex (A) based on the nonvolatile content, 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. By incorporating a predetermined amount or more of the crosslinking agent (C), the resulting pressure-sensitive adhesive layer has suitable cohesive strength and anchoring properties, and is likely to achieve excellent resistance to adhesive transfer and contamination of the adherend. Furthermore, in some embodiments, the content of the crosslinking agent (C) may be 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 crosslinking agent (C) used, the peel strength can be adjusted to a preferred range, and good high-speed peel strength can be easily obtained. Furthermore, contamination of the adherend surface after removal of the pressure-sensitive adhesive is likely to be prevented. From the viewpoint of achieving a better balance between high-speed peel strength, prevention of adhesive transfer, and prevention of contamination of the adherend, in some preferred embodiments, the content of the crosslinking agent (C) relative to 100 parts by weight of the rubber latex (A) is approximately 5.0 parts by weight or less, more preferably approximately 4.0 parts by weight or less, even more preferably approximately 3.5 parts by weight or less, still more preferably approximately 3.0 parts by weight or less, still more preferably approximately 2.5 parts by weight or less, particularly preferably approximately 2.0 parts by weight or less, and may be approximately 1.5 parts by weight or less, based on the non-volatile content.In addition, in an embodiment in which the PSA composition does not contain the crosslinking agent (C) or the amount of the crosslinking agent (C) is limited, the content of the crosslinking agent (C) relative to 100 parts by weight of the rubber latex (A) can be less than 1.0 part by weight, for example, less than 0.3 part by weight, or less than 0.1 part by weight, based on the non-volatile content, and the PSA composition may be substantially free of the crosslinking agent (C).

[0057] (Laser beam absorbent) The pressure-sensitive adhesive composition 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 composition, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition can be made 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 composition, one or more types can be appropriately selected from the laser beam absorbents exemplified below. In an embodiment in which the pressure-sensitive adhesive composition contains a laser beam absorbent, the content of the laser beam absorbent in the pressure-sensitive adhesive composition is typically suitably 5 wt % or less, based on the non-volatile content, 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 composition, and thus the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition, does not substantially contain a laser beam absorbent.

[0058] (Antiaging Agent) The pressure-sensitive adhesive composition 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 composition 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).

[0059] (Optional Components) The PSA composition may contain, as needed, various additives that can be used in the field of PSA compositions (typically, aqueous PSA compositions), such as viscosity modifiers (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. The dispersant is preferably one that can function as a protective colloid, 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 PSA composition may also contain, as needed, an emulsifier. Examples of such emulsifiers that can be used include those exemplified as emulsifiers that can be used to emulsify tackifier emulsions.

[0060] In some embodiments, the PSA composition may have a composition in which the total amount of the rubber latex (A), tackifier (B), and 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. PSA compositions having the above composition allow the effects of the technology disclosed herein to be preferably realized.

[0061] (Water-Dispersed Pressure-Sensitive Adhesive Composition) The PSA composition disclosed herein can be prepared using aqueous components as described above, thereby substantially eliminating the use of organic solvents or enabling 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 an acid-modified synthetic rubber latex and a rosin-based tackifier emulsion. 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 PSA composition may 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. Generally, the proportion of water in the volatile components contained in the water-dispersed pressure-sensitive adhesive composition is, for example, 90% by weight or more, and preferably 95 to 100% by weight.

[0062] In some embodiments, from the viewpoint of environmental considerations and eliminating organic solvents, it is preferable that the PSA composition (typically, a water-dispersible PSA composition) is substantially free of organic solvents. Here, "a PSA composition 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 %).

[0063] <Pressure-Sensitive Adhesive> This specification provides a pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition disclosed herein. The pressure-sensitive adhesive may be a pressure-sensitive adhesive obtained by curing the pressure-sensitive adhesive composition by drying, crosslinking, cooling, or the like, i.e., a cured product of the pressure-sensitive adhesive composition. The curing method (e.g., drying, crosslinking, cooling, etc.) of the pressure-sensitive adhesive composition may be a single curing method, or multiple methods may be applied simultaneously or in multiple stages. In this specification, a pressure-sensitive adhesive formed from a water-dispersed pressure-sensitive adhesive composition is also referred to as a water-dispersed pressure-sensitive adhesive.

[0064] <Pressure-Sensitive Adhesive Sheet> (Configuration Example) This specification provides a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from any one of the pressure-sensitive adhesive compositions disclosed herein. The pressure-sensitive adhesive sheet may be a substrate-attached pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer on one or both sides of a sheet-like substrate (support), or may be a substrate-less pressure-sensitive adhesive sheet (i.e., a pressure-sensitive adhesive sheet without a non-releasable substrate) having the pressure-sensitive adhesive layer provided on a release liner, for example.

[0065] The configuration of a pressure-sensitive adhesive sheet according to one embodiment is shown schematically in FIG. 1 . This pressure-sensitive adhesive sheet 1 comprises a substrate 10, an undercoat layer 30 provided on a first surface 10A of the substrate 10, and a pressure-sensitive adhesive layer 20 disposed on the surface 30A of the undercoat layer 30. The pressure-sensitive adhesive layer 20 is attached to an adherend for use. The undercoat layer 30 is in contact with the pressure-sensitive adhesive layer 20. In the pressure-sensitive adhesive sheet 1, the other surface (back surface, second surface) 10B of the substrate 10 is a releasable surface (release surface). Before use (i.e., before attachment to an adherend), the pressure-sensitive adhesive sheet 1 may be in the form of a roll 50, as shown in FIG. 1 , wound around a core 52 such that the surface (adhesive surface) 20A of the pressure-sensitive adhesive layer 20 abuts the back surface 10B of the substrate 10, thereby protecting the surface 20A. Alternatively, the pressure-sensitive adhesive sheet 1 may be in the form of a roll without a core 52, i.e., a so-called coreless roll in which the pressure-sensitive adhesive 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 with the PSA layer surface of one PSA sheet abutting against the back surface of another PSA sheet, thereby protecting the PSA surface 20A. Alternatively, the PSA 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.

[0066] The pressure-sensitive adhesive sheet may have, for example, a cross-sectional structure as schematically shown in FIG. 2 . In the pressure-sensitive adhesive sheet 2 shown in FIG. 2 , the substrate 10 includes a back layer 11 constituting the other surface (second surface) 10B of the substrate 10, and a support layer 12 disposed inside the back layer 11 (the side on which the pressure-sensitive adhesive layer 20 is provided). In this embodiment, the substrate 10 is made of a resin film. The back layer 11 is made of a resin composition containing a release agent, thereby making the surface of the back layer 11 (which also serves as the second surface 10B of the substrate 10) a release surface. The support layer 12 may be a layer made of a resin composition that does not contain a release agent, or may be a layer made of a resin composition that contains a release agent. In the pressure-sensitive adhesive sheet 2 shown in FIG. 2 , the substrate 10 has a two-layer structure consisting of the back layer 11 and the support layer 12, but the structure of the substrate 10 is not limited to a two-layer structure.

[0067] The pressure-sensitive adhesive sheet 3 shown in Fig. 3 is a modified example of the pressure-sensitive adhesive sheet 2 shown in Fig. 2, and differs from the pressure-sensitive adhesive sheet 2 in that it does not have an undercoat layer. Specifically, the pressure-sensitive adhesive sheet 3 comprises a substrate 10 and a pressure-sensitive adhesive layer 20 provided on one surface (first surface) 10A of the substrate 10. The substrate 10 includes a backing layer 11 that constitutes the other surface (second surface) 10B of the substrate 10, and a support layer 12 that is disposed on the inner side of the backing layer 11 (the side on which the pressure-sensitive adhesive layer 20 is provided). In the configuration shown in Fig. 3, from the viewpoint of the anchoring ability of the pressure-sensitive adhesive layer 20 to the substrate 10, it is preferable that the support layer 12 be a layer made of a resin composition that does not contain a release agent.

[0068] (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 a substrate, an undercoat layer provided on the substrate, or a release liner, and then drying the composition. 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 heating. 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 may be further aged, for example, at a temperature between room temperature and about 60°C, 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. In the case of a substrate-attached pressure-sensitive adhesive sheet, the pressure-sensitive adhesive layer may be formed by applying the pressure-sensitive adhesive composition directly to the substrate, or the pressure-sensitive adhesive layer formed on a release liner may be transferred to the substrate.

[0069] 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. The thickness of the pressure-sensitive adhesive layer 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. Limiting the thickness of the pressure-sensitive adhesive layer allows for a thinner pressure-sensitive adhesive sheet. Limiting the thickness of the pressure-sensitive adhesive layer is also preferable in terms of preventing 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).

[0070] (Substrate) In some embodiments, the PSA sheet may be in the form of a substrate-attached PSA sheet having a PSA layer on one or both sides of a substrate (support substrate). A PSA sheet having a substrate can improve productivity, handling, processability, etc. Furthermore, a PSA sheet having a substrate can have good removability from an adherend. The material of the substrate is not particularly limited and can be appropriately selected depending on the intended use and mode of use of the PSA sheet. Non-limiting examples of usable substrate materials include various resin films, foam sheets, woven and nonwoven fabrics made of various fibrous materials, either alone or in a blend, paper, metal foil, etc. Substrates having a composite configuration of these may also be used.

[0071] In some embodiments, the PSA sheet includes a resin film as a substrate. Here, "resin film" refers to a resin film that has a non-porous structure and typically contains substantially no air bubbles (void-free). Therefore, the resin film is a concept that is distinct 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 copolymers, and polypropylene-polyethylene blend resins; and vinyl chloride resins (typically soft vinyl chloride resins), vinyl acetate resins, and polyamide-based resins.

[0072] In some embodiments, from the viewpoint of various processability due to the flexibility of the substrate, or, for example, from the viewpoint of the cuttability and non-contamination of the PSA sheet with a specific laser beam, a polyolefin-based resin film or a polyester-based resin film can be preferably used as the resin film. Among these, a polyolefin-based resin film is preferred from the viewpoint of conformability to the adherend, etc. Generally, aqueous PSA compositions tend to have reduced anchoring properties when used with a polyolefin-based resin film substrate. However, according to the technology disclosed herein, by using a polyolefin-based resin film substrate, it is possible to obtain good anchoring properties and, therefore, prevention of adhesive transfer while enjoying the advantages of a polyolefin-based resin film.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] The first surface of the 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 pressure-sensitive adhesive layer and the undercoat layer. Examples of surface treatments to enhance adhesion include corona discharge treatment, acid treatment, ultraviolet irradiation treatment, and plasma treatment.

[0079] In some preferred embodiments, the second surface of the substrate is a release surface. "The second surface of the substrate is a release surface" typically means that a PSA sheet, with the surface (adhesive surface) of the PSA layer provided on the first surface of the substrate in contact with the release surface, can be peeled off without leaving any adhesive residue (residual adhesive) on the release surface.

[0080] 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 substrate having such a second surface can be understood as a 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 substrate, and may, for example, constitute only the second surface side of the substrate, or may constitute the entire substrate.

[0081] As the second surface forming material, a resin composition containing at least a release agent and a resin material can be preferably used. Examples of the resin material include, but are not limited to, the various materials exemplified as the resin material constituting the resin film as the 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] The substrate may have a single layer structure or a multilayer structure of two or more layers. In some embodiments, a substrate with a multilayer structure may be preferably employed. A 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 substrate. In a substrate with a multilayer structure, the types of materials (e.g., resin materials) constituting each layer may be the same or different. A substrate with a multilayer structure may have, for example, a two- to five-layer structure, or may have a two- or three-layer structure. In other embodiments, the substrate may have a single layer structure. A substrate with a single layer structure may be advantageous in terms of the productivity and quality stability of the substrate.

[0087] The method for forming the substrate (e.g., a resin film substrate) is not particularly limited, and a conventionally known extrusion molding method, such as inflation extrusion molding or cast molding, can be appropriately adopted. The substrate may be unstretched or may be stretched uniaxially or biaxially. A multilayer substrate can be obtained by simultaneously molding resin compositions corresponding to each layer (e.g., 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.

[0088] In some preferred embodiments, the substrate may be a substrate with a multilayer structure of two or more layers, including a back layer formed from the second-surface-forming material described above and a support layer disposed inside the back layer (i.e., closer to the first surface). Hereinafter, the resin composition (i.e., the second-surface-forming material) that forms the back layer in a substrate of this configuration may be referred to as the "back-layer-forming material." As with the second-surface-forming material described above, a resin composition containing a release agent may be preferably used as the back-layer-forming material. The back-layer-forming material may be, for example, a resin composition containing at least a release agent and a resin material. The release agent that can be used as a component of the back-layer-forming material, the content of the release agent in the back-layer-forming material, and examples of resin materials that can be used as a component of the back-layer-forming material are the same as those for the second-surface-forming material described above, and therefore, redundant explanations will be omitted.

[0089] The support layer may be a layer formed from a resin composition. Hereinafter, the resin composition forming the support layer may be referred to as the "support layer-forming material." Resin components that can be used as constituents of the support layer-forming material include, but are not limited to, polyester resins, polyolefin resins, vinyl chloride resins, vinyl acetate resins, polyamide-based resins, and the like, similar to the resin materials constituting the resin film described above. The support layer-forming material may contain one type selected from such resin materials alone, or an appropriate combination of two or more types. The support layer-forming material may not contain a release agent similar to that used in the second-surface-forming material, or it may contain a release agent. In an embodiment in which one surface of the support layer also serves as the first surface of the substrate, the support layer-forming material preferably does not contain a release agent, from the viewpoint of improving the anchoring ability of the pressure-sensitive adhesive layer to the support layer. The resin material constituting the back layer-forming material and the resin material constituting the support layer-forming material may be the same or different. From the viewpoint of adhesion between the back layer and the support layer, in some embodiments, the resin material constituting the back layer-forming material may preferably be the same type of resin as the resin material constituting the support layer-forming material.

[0090] A substrate including a back layer and a support layer disposed therein can be obtained, for example, by laminating a support layer-forming material and a back layer-forming material by co-extrusion molding. The support layer-forming material may be co-extruded with the back layer-forming material in the form of a pre-formed base resin film. The number of layers to be laminated in each of the layers is not particularly limited, and the back layer and the support layer may each be a single layer, or may have a multi-layer laminate structure as needed.

[0091] The co-extrusion molding may be any method commonly used for producing films, sheets, etc., and is not particularly limited. Specifically, a multi-layer structure having two, three, four or more layers may be formed, and for example, an inflation method, a co-extrusion T-die method, etc. may be used. The use of these co-extrusion molding methods is preferable in terms of cost and productivity.

[0092] 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 substrate using a second-surface-forming material containing a release agent in a resin composition, as described above. The second surface of the 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, or fluorine-based 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.

[0093] The 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 substrate containing a laser beam absorbent is a substrate containing a laser beam absorbing layer (which may contain a specific absorbent). In a substrate with a multilayer structure, it is preferable that at least one layer is a laser beam absorbing layer containing a laser beam absorbent. For example, in an embodiment in which the substrate contains a backing layer and a support layer, it is preferable that at least one of the backing layer and the support layer (for example, both) contains a laser beam absorbent.

[0094] The laser light absorptivity of the substrate containing 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 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 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 substrate can be appropriately selected from the same range as the transmittance and reflectance of the pressure-sensitive adhesive sheet described below.

[0095] The laser beam absorbent contained in the 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 substrate can be applied, respectively.

[0096] The substrate may contain any additives as needed, such as flame retardants, antistatic agents, light stabilizers (radical scavengers, ultraviolet absorbers, etc.), antioxidants, etc.

[0097] The thickness of the substrate is not particularly limited and can be, for example, approximately 5 μm to 300 μm. From the viewpoint of the handleability of the substrate or a pressure-sensitive adhesive sheet including the substrate, in some preferred embodiments, the thickness of the 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 substrate with a predetermined thickness is likely to provide sufficient protection, for example, in applications for protecting the surface of an adherend. In some preferred embodiments, the thickness of the 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 substrate can be advantageous from the viewpoint of achieving a thinner pressure-sensitive adhesive sheet. Furthermore, reducing the thickness of the 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 used in laser processing applications, limiting the thickness of the substrate can improve the speed and precision of laser processing. In some other embodiments, the thickness of the substrate may be 70 μm or less, 50 μm or less, or 40 μm or less.

[0098] In a substrate including a back layer (preferably a back layer made of a resin composition containing a release agent) and a support layer, the thickness of the back layer (if the back layer has a laminated structure, the total thickness of these layers) is not particularly limited. From the viewpoint of easily forming a back layer with little thickness unevenness, the thickness of the back layer is advantageously, for example, 1 μm or more, and may be 3 μm or more, or 5 μm or more. The technology disclosed herein can also be suitably implemented in the form of a pressure-sensitive adhesive sheet including a substrate in which the back layer has a thickness of more than 7 μm, more than 10 μm, more than 15 μm, more than 20 μm, or more than 25 μm. The upper limit of the thickness of the back layer is not particularly limited, as long as it is less than the thickness of the entire substrate including the back layer. The thickness of the back layer of the entire thickness of the substrate can be, for example, 1% or more, 3% or more, 5% or more, or 8% or more, or, for example, 95% or less, 70% or less, 50% or less, 20% or less, or 15% or less. The thickness of the back surface layer can be, for example, 60 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, 10 μm or less, etc., depending on the thickness of the entire substrate. Reducing the thickness of the back surface layer can be advantageous from the viewpoint of making the PSA sheet thinner.

[0099] From the viewpoints of suppressing unevenness in the thickness of the support layer and of the ease of handling of a preformed resin film when the support layer is used, the thickness of the support layer is usually 5 μm or more, preferably 10 μm or more, and may be 25 μm or more, 40 μm or more, or 60 μm or more. The upper limit of the thickness of the support layer is not particularly limited, and it is sufficient if it is less than the thickness of the entire substrate including the back layer.

[0100] In a substrate including a laser beam absorbing layer, the thickness of the laser beam absorbing layer (in a substrate including 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 substrate may be, for example, 20% or more, 50% or more, 70% or more, or 90% or more. Note that in a single-layer substrate consisting of a laser beam absorbing layer or a 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.

[0101] (Undercoat Layer) In some preferred embodiments, the PSA sheet includes an undercoat layer disposed on the PSA layer-side surface of the substrate (typically a resin film substrate). By disposing the undercoat layer between the substrate and the PSA layer, the anchoring properties of the PSA layer can be enhanced, improving adhesive transfer resistance. For example, in embodiments using a polyolefin resin film as the substrate, the anchoring properties of the PSA layer can be improved by providing an undercoat layer on the surface of the polyolefin resin film substrate, which is difficult to achieve anchoring properties. The undercoat layer-forming material (undercoat agent, also referred to as a primer) can be a known or conventional undercoat agent capable of improving the anchoring properties of the rubber-based PSA layer. For example, the undercoat layer can contain one or more resin materials selected from urethane resins, polyester resins, acrylic resins, polyamide resins, and rubbers such as natural rubber and synthetic rubber, either alone or in combination. Furthermore, undercoat agents containing epoxy or isocyanate functional groups can also be used.

[0102] In some preferred embodiments, the undercoat layer is formed from an undercoat agent containing at least a compound containing an oxazoline group. The oxazoline group-containing compound is preferably a polymer containing an oxazoline group, such as an acrylic polymer or a urethane polymer containing an oxazoline group in its side chain. Among these, the use of an acrylic polymer having an oxazoline group is particularly preferred. The main chain of the acrylic polymer having an oxazoline group may be copolymerized with a monomer such as styrene. By incorporating an oxazoline group into the undercoat layer, the anchoring properties of the pressure-sensitive adhesive layer containing the acid-modified synthetic rubber can be effectively improved, making it easier to achieve better adhesive transfer resistance.

[0103] Furthermore, from the viewpoint of environmental considerations and eliminating the use of organic solvents, it is preferable to use an aqueous material as the undercoat agent. As the aqueous material, either a water-dispersed type (aqueous emulsion) or a water-soluble type can be used. Considering the water resistance and performance retention of the undercoat layer, and the influence on the adhesive properties of the adhesive layer provided on the undercoat layer, it is preferable to use an aqueous dispersion type undercoat agent. A suitable example of such an aqueous dispersion type undercoat agent is an oxazoline group-containing polymer emulsion.

[0104] The glass transition temperature (Tg) of the polymer (preferably an oxazoline group-containing polymer) that can be used as an undercoating agent is not particularly limited. In some embodiments, the Tg of the 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 pressure-sensitive adhesive 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. Polymers with low Tg tend to make it easier to apply the undercoating agent to resin films (e.g., polyolefin resin films) and to have good film-forming properties. Furthermore, in some embodiments, the lower limit of the Tg of the 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.

[0105] Although not particularly limited, in some embodiments, the proportion of the polymer (preferably the oxazoline group-containing 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 polymer.

[0106] The primer may contain various additives such as surfactants, thickeners, stabilizers, antifoaming agents, colorants (pigments, dyes, etc.), etc., as needed.

[0107] 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."

[0108] The primer can be formed by applying the primer directly to the surface of the 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 primer. The primer 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.

[0109] The thickness of the primer layer (after drying) is not particularly limited. In some embodiments, it 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 effect of improving anchoring force due to the placement of the primer layer can be preferably exerted.

[0110] (Laser beam absorbent and laser beam absorbing layer) In some preferred 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.

[0111] 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."

[0112] 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.

[0113] 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).

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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%.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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%.

[0127] (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.

[0128] <Characteristics of the Pressure-Sensitive Adhesive Sheet> (High-Speed ​​Peel Strength) The pressure-sensitive adhesive sheet disclosed herein preferably has a high-speed peel strength of 3.0 N / 10 mm or more when attached to a stainless steel (SUS) plate at a tensile speed of 30 m / min under an environment of 23°C and 50% RH one week later. Pressure-sensitive adhesive sheets having the above-mentioned high-speed peel strength are less likely to lift or peel from the adherend under high-speed peel loads, for example. For example, when the pressure-sensitive adhesive sheet is used for laser processing, lift or peeling caused by the assist gas supplied during laser processing can be suppressed. Although not particularly limited, a tensile speed of 30 m / min in the above-mentioned high-speed peel strength measurement is a measurement condition that corresponds well to the situation in which an assist gas is sprayed onto the pressure-sensitive adhesive sheet attached to the workpiece when the workpiece is processed with a short-wavelength laser beam, for example. If the adhesive sheet is lifted by the assist gas supplied during laser processing (typically, partial peeling occurs due to the assist gas penetrating the adhesive interface between the workpiece and the adhesive sheet due to its wind pressure from the cut portion caused by the laser light), the adhesive sheet will be exposed to heat in a state where it is no longer fixed to the workpiece (bonded by the adhesive), resulting in increased thermal shrinkage, which can lead to inconveniences such as the surface of the workpiece becoming more easily exposed on both sides of the cut portion. An adhesive sheet having a high-speed peel strength of 3.0 N / 10 mm or more can effectively prevent the adhesive sheet from lifting during cutting. In some preferred embodiments, the high-speed peel strength of the adhesive sheet is 3.5 N / 10 mm or more, more preferably 4.0 N / 10 mm or more, even more preferably 4.5 N / 10 mm or more, even more preferably 5.0 N / 10 mm or more, even more preferably 5.5 N / 10 mm or more, and particularly preferably 6.0 N / 10 mm or more.

[0129] Although not particularly limited, the upper limit of the high-speed peel strength can be, for example, approximately 15 N / 10 mm or less, and may be approximately 12 N / 10 mm or less. By limiting the high-speed peel strength, a removable PSA sheet can be obtained. From the viewpoint of obtaining good removability, in some preferred embodiments, the high-speed peel strength is 10 N / 10 mm or less, or may be 9.0 N / 10 mm or less, 8.0 N / 10 mm or less, or 7.0 N / 10 mm or less. By setting the high-speed peel strength to a predetermined value or less within the above range, the workload when peeling the PSA sheet from the adherend is reduced, and peeling defects such as tearing of the PSA sheet during peeling can be prevented.

[0130] (Slow-Speed ​​Peel Strength) Although not particularly limited, the low-speed peel strength of the pressure-sensitive adhesive sheet is preferably 3.0 N / 10 mm or less when measured at a tensile speed of 0.3 m / min one week after being attached to a stainless steel (SUS) plate under an environment of 23°C and 50% RH. A pressure-sensitive adhesive sheet having the above low-speed peel strength can have good removability. In some preferred embodiments, the low-speed peel strength may be 2.5 N / 10 mm or less, 2.0 N / 10 mm or less, or 1.5 N / 10 mm or less. By setting the low-speed peel strength to a predetermined value or less, for example, it is possible to reduce the effort required to peel off a pressure-sensitive adhesive sheet that has been attached to an adherend and is no longer needed, thereby improving workability. In addition, suppressing the low-speed peel strength is also significant from the viewpoint of preventing adhesive residue from remaining on the surface of the adherend after the pressure-sensitive adhesive sheet is peeled off.

[0131] Furthermore, the low-speed peel strength of the pressure-sensitive adhesive sheet is preferably 0.5 N / 10 mm or more. A pressure-sensitive adhesive sheet with a high low-speed peel strength adheres well to the adherend and is less likely to peel off. For example, when the pressure-sensitive adhesive sheet is used for surface protection during processing such as laser processing, peeling of the pressure-sensitive adhesive sheet during processing steps such as bending and drilling (which may be post-processing after laser processing) tends to be effectively suppressed. From the viewpoint of achieving a higher effect, in some preferred embodiments, the low-speed peel strength of the pressure-sensitive adhesive sheet is, for example, 1.0 N / 10 mm or more, or may be 1.5 N / 10 mm or more, or may be 2.0 N / 10 mm or more.

[0132] More specifically, the high-speed peel strength and low-speed peel strength are measured by the method described in the Examples below.

[0133] (Laser light absorption characteristics) 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 absorptivity of 20% or more in the wavelength range of the laser light used for processing (typically, the laser light absorptivity at the main wavelength of the laser light). This laser light absorptivity 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 absorptivity of 20% or more can efficiently absorb laser light. In some embodiments, the laser light absorptivity 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 absorptivity of the pressure-sensitive adhesive sheet may be 100%, but in practice it is preferably 95% or less, and may be 90% or less.

[0134] 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)

[0135] 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).

[0136] 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.

[0137] <Applications> The applications of the pressure-sensitive adhesive sheets disclosed herein are not particularly limited. Taking advantage of the advantages of combining good high-speed peel strength with good adhesive residue prevention and adherend contamination prevention, the pressure-sensitive adhesive sheets disclosed herein can be used in a variety of applications. For example, they can be suitably used as surface protective materials (which can also be understood as surface-protective pressure-sensitive adhesive sheets). The surface protective materials are attached to the surface of an adherend, and after achieving their protective purpose, are peeled from the adherend. Particularly preferred are pressure-sensitive adhesive sheets that can be peeled from the adherend again without leaving adhesive residue or contaminating the adherend. The pressure-sensitive adhesive sheets disclosed herein can be used, for example, 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 pressure-sensitive adhesive sheets disclosed herein are also suitable as packaging pressure-sensitive adhesive sheets. PSA sheets used for packaging with packaging materials such as textiles, paper, boxes, etc. are required to have a peel strength that prevents peeling at a certain high speed, and may also be required 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] The matters disclosed by this specification include the following. [1] A pressure-sensitive adhesive composition comprising: a rubber latex containing, on a non-volatile basis, 50% by weight or more of an acid-modified synthetic rubber latex; and a rosin-based tackifier emulsion as a tackifier, wherein the glass transition temperature of the acid-modified synthetic rubber contained in the acid-modified synthetic rubber latex is -20°C or lower, and the softening point of the rosin-based tackifier contained in the rosin-based tackifier emulsion is 140°C or lower. [2] The pressure-sensitive adhesive composition according to [1] above, comprising an acid-modified styrene-butadiene copolymer latex as the acid-modified synthetic rubber latex. [3] The pressure-sensitive adhesive composition according to [1] or [2] above, wherein the content of the tackifier is 50 parts by weight or more and 100 parts by weight or less per 100 parts by weight of the rubber latex on a non-volatile basis. [4] The pressure-sensitive adhesive composition according to any one of [1] to [3] above, which does not contain a crosslinking agent or contains the crosslinking agent in an amount of 5 parts by weight or less per 100 parts by weight of the rubber latex, based on the non-volatile content. [5] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition according to any one of [1] to [4] above, and a substrate supporting the pressure-sensitive adhesive layer. [6] The pressure-sensitive adhesive sheet according to [5] above, in which an undercoat layer is disposed between the substrate and the pressure-sensitive adhesive layer. [7] The pressure-sensitive adhesive sheet according to [6] above, in which the substrate is a polyolefin resin film. [8] The pressure-sensitive adhesive sheet according to [6] or [7] above, in which the undercoat layer contains a polymer having an oxazoline group. [9] The pressure-sensitive adhesive sheet according to any one of [6] to [8] above, which is used for protecting the surface of an adherend.

[10] The pressure-sensitive adhesive sheet according to any one of [6] to [9] above, which is used by being cut with laser light having a dominant wavelength of 900 nm to 1100 nm.

[0142] 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.

[0143] Example 1 Preparation of Pressure-Sensitive Adhesive Composition 100 parts, on a non-volatile basis, of acid-modified SBR latex (manufactured by Zeon Corporation, trade name "Nipol LX432M", Tg -55°C, hereinafter sometimes referred to as "acid-modified SBR-A") were mixed with 70 parts of a rosin ester emulsion (manufactured by Kraton Corporation, trade name "AQUATACK 6085", softening point 82°C, hereinafter sometimes referred to as "rosin-based Em-A") as a tackifier, 2 parts of an antioxidant (manufactured by Seiko Chemical Co., Ltd., trade name "Nonflex CBP-E"), and 1 part of a water-soluble oxazoline-based crosslinking agent (manufactured by Nippon Shokubai Co., Ltd., trade name "Epocross WS-700") to prepare a water-dispersible pressure-sensitive adhesive composition according to this example.

[0144] (Preparation of Resin Film Substrate) Fe in Polyolefin ３ O ４ A black master batch (hereinafter referred to as Fe ３ O ４ A support layer-forming material consisting of 3 parts LDPE (low-density polyethylene, manufactured by Tosoh Corporation, trade name "Petrothene 186R") and a back layer-forming material consisting of 94 parts of the support layer-forming material and 6 parts of a silylated polyolefin masterbatch were co-extruded by inflation molding at a die temperature of 180°C to form a film, resulting in a two-layer resin film consisting of a support layer and a back layer. The total thickness of this resin film was 80 μm, of which the back layer was 8 μm thick. The silylated polyolefin masterbatch contained approximately 30% silylated polyolefin (prepared by the method described in the examples of Japanese Patent Application Publication No. 2011-26448) as a silicone-based release agent and approximately 70% PE resin. The content of the silicone-based release agent in the back layer-forming material was 1.8%. The resin film obtained in this manner is referred to as PE in Table 1.

[0145] (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 to the first surface (support layer side) of the resin film obtained above using a wire bar #3, and then dried to form an undercoat 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 and dried to form a pressure-sensitive adhesive layer having a thickness of 12 μm. In this way, a pressure-sensitive adhesive sheet was obtained, which had a undercoat layer on a first surface of a resin film as a substrate, a pressure-sensitive adhesive layer on the undercoat layer, and the second surface of the substrate served as a release surface.

[0146] Examples 2 to 13 PSA sheets according to each example were obtained in the same manner as in Example 1, except that in the preparation of the PSA composition, the type of rubber latex (natural rubber latex and acid-modified SBR latex), the weight ratio (based on non-volatile content), the type of tackifier, the amount of tackifier, the type of crosslinker, and the amount of crosslinker were changed as shown in Table 1. As the acid-modified SBR-B in Table 1, an acid-modified SBR latex (manufactured by DIC Corporation, trade name "Luckstar 5215A", Tg -60°C) was used. As the natural rubber latex, a trade name "HYTEX HA" (available from Nomura Trading Co., Ltd.) was used. As the rosin-based Em-B in Table 1, a rosin ester emulsion (trade name "Hariestar SK-218NS", softening point 100°C) manufactured by Harima Chemicals Co., Ltd. was used. The isocyanate crosslinking agent used was a water-dispersible isocyanate crosslinking agent (manufactured by DIC Corporation under the trade name "Burnoc DNW-6000"), and the epoxy crosslinking agent used was a water-soluble epoxy crosslinking agent (manufactured by Nagase ChemteX Corporation under the trade name "Denacol EX-810").

[0147] Example 14 In the preparation of the pressure-sensitive adhesive sheet of Example 1, the first surface (the surface on the support layer side) of the resin film was subjected to a corona discharge treatment, and then the pressure-sensitive adhesive composition was applied to the corona-discharge-treated surface and dried to form a pressure-sensitive adhesive layer having a thickness of 12 μm.

[0148] <Example 15> A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except that a 40 μm thick polypropylene film (manufactured by Futamura Chemical Co., Ltd., product name "FOA", indicated as "PP" in Table 1) was used as the substrate.

[0149] Example 16 In the preparation of the pressure-sensitive adhesive composition of Example 1, SBR latex (manufactured by Nippon Zeon Co., Ltd., product name "Nipol LX110", Tg -47°C, not acid-modified) was used instead of the acid-modified SBR-A. Otherwise, a pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1.

[0150] Example 17 In the preparation of the pressure-sensitive adhesive composition of Example 1, an acid-modified SBR latex (manufactured by Nippon Zeon Co., Ltd., product name "Nipol LX421", Tg -18°C, hereinafter sometimes referred to as "acid-modified SBR-C") was used instead of the acid-modified SBR-A. Otherwise, a pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1.

[0151] Example 18 In the preparation of the PSA composition of Example 1, a petroleum-based tackifier emulsion was used as the tackifier instead of the rosin-based Em-A. A PSA sheet according to this example was obtained in the same manner as in Example 1 except for the above. The petroleum-based tackifier emulsion was prepared by the following method. A resin solution was obtained 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. Furthermore, 4 parts of casein, 60 parts of water, and 28% aqueous ammonia were mixed, and the casein was heated to 70°C to dissolve, thereby obtaining an aqueous ammonia solution of casein. The amount of 28% aqueous ammonia used was 15 parts per 100 parts of casein. The casein ammonia solution was cooled to 40°C, and 8 parts of ammonium salt of hydrogenated rosin (60% dihydroabietic acid) was added as an emulsifier and mixed to obtain an emulsifier-containing liquid. The emulsifier-containing liquid was then mixed with the resin solution and stirred at 800 rpm for 1 hour using a T.K. Homodisper manufactured by Tokushu Kika Kogyo Co., Ltd. to prepare a petroleum-based tackifier emulsion. The petroleum-based tackifier emulsion was prepared by adjusting the temperatures of the emulsifier-containing liquid and resin solution to 40°C.

[0152] Example 19 In the preparation of the pressure-sensitive adhesive composition of Example 1, a rosin ester emulsion (trade name "Tamanol E-200NT", softening point 150°C, hereinafter sometimes referred to as "rosin-based Em-C") manufactured by Arakawa Chemical Industries, Ltd. was used as the tackifier instead of the rosin-based Em-A. Otherwise, a pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1.

[0153] Example 20 In the preparation of the PSA composition of Example 1, natural rubber latex (available from Nomura Trading Co., Ltd., product name "HYTEX HA") was used instead of the acid-modified SBR-A. Otherwise, a PSA sheet according to this example was obtained in the same manner as in Example 1.

[0154] <Performance Evaluation> A sample of an appropriate size was cut out from the pressure-sensitive adhesive sheet prepared above, and the following items were evaluated. The results are shown in Table 1.

[0155] (1) Low-speed peel strength The pressure-sensitive adhesive sheet according to each example is cut into a strip of 10 mm wide and 100 mm long to prepare a test piece.Under the standard environment of 23 ° C and 50% RH, the adhesive surface of the test piece is pressed against a stainless steel plate (SUS304BA plate) as an adherend with a 2 kg rubber roller according to JIS Z0237:2000, by rolling it back and forth once, to obtain a measurement sample.After leaving this measurement sample under the same standard environment for 1 week, under the standard environment, using a universal tensile tester, the peel strength (low-speed peel strength) [N / 10 mm] is measured under the conditions of a pulling speed of 0.3 m / min and a peel angle of 180 degrees.

[0156] (2) High-speed peel strength The pressure-sensitive adhesive sheet according to each example was cut into a strip of 10 mm wide and 100 mm long to prepare a test piece. Under a standard environment of 23 ° C and 50% RH, the adhesive surface of the test piece was pressed against a stainless steel plate (SUS304BA plate) as an adherend with a 2 kg rubber roller according to JIS Z0237:2000, by rolling it back and forth once to obtain a measurement sample. After leaving this measurement sample under the same standard environment for 1 week, under the same standard environment, a universal tensile tester was used to measure the peel strength (high-speed peel strength) [N / 10 mm] under the conditions of a tensile speed of 30 m / min and a peel angle of 180 degrees. If the high-speed peel strength is 3 N / 10 mm or more, it is determined that the test piece has good high-speed peel strength.

[0157] In measuring the peel strength, a universal tension-compression tester (device name "Tension-compression tester, TCM-1kNB" manufactured by Minebea Co., Ltd.) was used as the tensile tester. The stainless steel plate (SUS304BA plate) used as the adherend was cleaned by the method specified in JIS Z0237:2000.

[0158] (3) Staining / Adhesive Residue Evaluation The adherend surface after the high-speed peel test was photographed, the contrast adjusted as necessary, and the image was binarized using image analysis software (ImageJ). After peeling the adhesive sheet, the percentage of the area of ​​staining (transfer of adhesive components) and adhesive residue (cohesive failure of the adhesive) (adhesive residue staining area) observed on the adherend was measured within a 10 mm x 10 cm area of ​​the surface (adhesive residue staining area) and evaluated according to the following criteria: A: Neither adhesive residue nor staining was observed (adhesive residue staining area: 0%), or adhesive residue and staining were observed but the adhesive residue staining area percentage was 10% or less. B: Adhesive residue and staining were observed, and the adhesive residue staining area percentage was more than 10% and 30% or less. C: Adhesive residue and staining were observed, and the adhesive residue staining area percentage was more than 30% and 80% or less. D: Adhesive residue and staining were observed, and the adhesive residue staining area percentage was greater than 80%. A or B was judged as passing, and C or D was judged as failing.

[0159] (3) Evaluation of anchoring property (3-1) Finger abrasion test A 20 mm wide piece of PSA sheet according to each example was cut out and fixed to an acrylic plate with the PSA layer surface facing outward. A predetermined area (approximately 1 cm × 3 cm) on the PSA layer surface was rubbed strongly with a finger at a constant force 50 times, and the number of rubs until the PSA layer peeled off was recorded.

[0160] (3-2) Picking test The PSA sheet according to each example was cut into a width of 20 mm, and the surfaces of the PSA layers were bonded together with a hand roller. After one minute had passed, the bonded PSA layers were peeled off with a constant force. This picking operation, which consisted of bonding and peeling, was repeated 10 times, and the number of picking operations until the PSA layer peeled off was recorded.

[0161] (4) Mechanical Stability Evaluation After adjusting the nonvolatile content of the PSA composition according to each example to 40%, the rate of occurrence of aggregates was determined using a Marlon stability tester according to the following formula: Rate of occurrence of aggregates [%] = (aggregates / initial solid content) x 100. The Marlon stability tester conditions were a load of 10 kg, a rotation speed of 2000 rpm, and a shear time of 5 minutes. A test in which the rate of occurrence of aggregates was 0.5% or less was judged to pass.

[0162]

[0163] As shown in Table 1, the PSA compositions of Examples 1 to 15 were formed from PSA compositions in which the rubber latex contained, on a nonvolatile basis, 50% by weight or more of an acid-modified synthetic rubber latex with a Tg of −20°C or lower, and further contained a rosin-based tackifier emulsion with a softening point of 140°C or lower. PSA sheets containing such PSA compositions had high-speed peel strengths of 3 N / 10 mm or higher and passed the staining and adhesive residue evaluations. The PSA compositions of each of the above examples also had good mechanical stability. On the other hand, Example 16, which used a synthetic rubber latex that was not acid-modified; Example 17, which used an acid-modified synthetic rubber with a Tg higher than −20°C; Example 18, which used a petroleum-based tackifier; and Example 19, which used a rosin-based tackifier with a softening point higher than 140°C, all had low high-speed peel strengths and failed the staining and adhesive residue evaluations. Furthermore, Example 20, which used natural rubber as the rubber latex, had poor mechanical stability. The above results show that a pressure-sensitive adhesive composition containing a rubber latex containing 50% by weight or more of acid-modified synthetic rubber latex on a non-volatile basis and a rosin-based tackifier emulsion as a tackifier, in which the glass transition temperature of the acid-modified synthetic rubber is -20°C or lower and the softening point of the rosin-based tackifier is 140°C or lower, can form a pressure-sensitive adhesive that has good mechanical stability, good high-speed peel strength, and excellent resistance to adhesive residue and contamination of the adherend, even with a composition that uses a rubber latex that is preferable from the standpoint of organic solvent-free and environmental hygiene.

[0164] 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.

[0165] REFERENCE SIGNS LIST 1, 2, 3 Pressure-sensitive adhesive sheet 10 Substrate 10A First surface 10B Second surface (back surface, release surface) 11 Back surface layer 12 Support layer 20 Pressure-sensitive adhesive layer 20A Surface (adhesive surface) 30 Primer layer 30A Surface (of primer layer)

Claims

1. A pressure-sensitive adhesive composition comprising: a rubber-based latex containing, on a non-volatile basis, 50% by weight or more of acid-modified synthetic rubber latex; and a rosin-based tackifier emulsion as a tackifier; wherein the glass transition temperature of the acid-modified synthetic rubber contained in the acid-modified synthetic rubber latex is -20°C or lower; and the softening point of the rosin-based tackifier contained in the rosin-based tackifier emulsion is 140°C or lower.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the acid-modified synthetic rubber latex comprises an acid-modified styrene-butadiene copolymer latex.

3. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the content of the tackifier is 50 parts by weight or more and 100 parts by weight or less based on the non-volatile content, per 100 parts by weight of the rubber latex.

4. The pressure-sensitive adhesive composition according to claim 1 or 2, which does not contain a crosslinking agent or contains said crosslinking agent in an amount of 5 parts by weight or less per 100 parts by weight of said rubber latex, based on the non-volatile content.

5. An adhesive sheet comprising an adhesive layer made of the adhesive composition according to claim 1 or 2, and a substrate supporting the adhesive layer.

6. The pressure-sensitive adhesive sheet according to claim 5, wherein an undercoat layer is disposed between the substrate and the pressure-sensitive adhesive layer.

7. The pressure-sensitive adhesive sheet according to claim 6, comprising a polyolefin resin film as the substrate.

8. The pressure-sensitive adhesive sheet according to claim 6, wherein the undercoat layer contains a polymer having an oxazoline group.

9. The pressure-sensitive adhesive sheet according to claim 5, which is used for protecting the surface of an adherend.

10. The pressure-sensitive adhesive sheet according to claim 5, which is used by being cut with a laser beam having a dominant wavelength of 900 nm to 1100 nm.

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