Adhesive sheet with release sheet

Abstract

To provide an adhesive sheet with a non-silicone-based release sheet having release sheet detachability comparable with a case when a silicone-based release sheet is used.SOLUTION: There is provided an adhesive sheet with a release sheet, comprising an adhesive sheet having an adhesive layer and a non-silicone release sheet disposed on a surface of the adhesive layer. The adhesive layer contains an acrylic polymer. The acrylic polymer is a polymer of a monomer component including an alkyl (meth)acrylate (m1) having an alkyl group having 6 to 17 carbon atoms at an ester terminal, wherein the alkyl group having 6 to 17 carbon atoms is a linear alkyl group or a branched alkyl group having one branch carbon atom.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[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 when pressure is applied. Utilizing these properties, adhesives are widely used in the form of adhesive sheets for purposes such as joining parts and protecting surfaces. For example, adhesive sheets having an adhesive layer on one surface of a substrate are preferably used as surface protection sheets to prevent damage (scratches, stains, corrosion, etc.) to the surface of various items when they are processed or transported. Such adhesive sheets can be distributed, stored, and processed with the adhesive surface protected by a release sheet before use. Patent Document 1 is an example of a prior art document disclosing this type of conventional technology. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-224811 Summary of the Invention [Problem to be solved by the invention]

[0004] Silicone-based release sheets, which have excellent light release properties, are widely used as release sheets for pressure-sensitive adhesive sheets (see, for example, Patent Document 1). However, depending on the usage and application of the pressure-sensitive adhesive sheet, the use of silicone-based release sheets may not be desirable. For example, when a pressure-sensitive adhesive sheet is used to protect the surface of an optical component, the silicone material contained in the silicone-based release sheet may be transferred from the release surface of the release sheet to the adhesive surface and even to the adherend, potentially changing the surface properties of the adherend after the pressure-sensitive adhesive sheet is peeled and removed. Furthermore, depending on the application location of the pressure-sensitive adhesive sheet, such as inside precision equipment, it may be desirable to avoid the use of silicone materials that can generate siloxane gas. In such cases, non-silicone release sheets, such as release sheets having a release treatment layer formed with a release treatment agent other than a silicone material (non-silicone release treatment agent), are used. However, these non-silicone release sheets tend to be less easily releasable from the adhesive surface (release sheet releasability) than silicone-based release sheets, resulting in reduced releasability.

[0005] The present invention was created in consideration of the above circumstances, and aims to provide a pressure-sensitive adhesive sheet with a non-silicone release sheet that has release sheet releasability that is comparable to that of a silicone release sheet. [Means for solving the problem]

[0006] According to this specification, there is provided a pressure-sensitive adhesive sheet with a release sheet, comprising a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer and a non-silicone release sheet disposed on the surface of the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer contains an acrylic polymer. The acrylic polymer is a polymer of a monomer component containing an alkyl (meth)acrylate (m1) having an alkyl group having 6 to 17 carbon atoms at the ester terminal. Here, the alkyl group having 6 to 17 carbon atoms is a linear alkyl group or a branched alkyl group having one branch carbon atom. By using a pressure-sensitive adhesive containing an acrylic polymer with the above structure, it is possible to obtain a pressure-sensitive adhesive sheet that has release sheet releasability comparable to that obtained when a silicone-based release sheet is used, even when a non-silicone release sheet is used.

[0007] In some preferred embodiments, the alkyl (meth)acrylate (m1) includes at least one selected from n-heptyl acrylate and n-octyl acrylate. By using at least one selected from n-heptyl acrylate and n-octyl acrylate as a monomer component of the acrylic polymer, the effects of the technology disclosed herein are preferably exhibited.

[0008] In some embodiments, the monomer component includes a monomer (m2) having a hydroxyl group. By using a monomer having a hydroxyl group, the side chain of the acrylic polymer has a hydroxyl group. Such a hydroxyl group can serve as a crosslinking point when a crosslinking agent such as an isocyanate-based or epoxy-based crosslinking agent is used.

[0009] In some preferred embodiments, the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent. In embodiments using an isocyanate-based crosslinking agent as the crosslinking agent, the techniques disclosed herein are preferably implemented.

[0010] In some embodiments, the pressure-sensitive adhesive layer contains a zirconium-containing compound. The use of a zirconium-containing compound as a catalyst facilitates both the aging (typically crosslinking reaction) of the pressure-sensitive adhesive layer and a long pot life. The use of a zirconium-based catalyst is also desirable from the perspective of reducing environmental impact. Furthermore, the use of a zirconium-containing compound as a catalyst facilitates the formation of a colorless pressure-sensitive adhesive. This can be an advantageous feature when the pressure-sensitive adhesive sheet is used for optical applications.

[0011] In some preferred embodiments, the non-silicone release sheet has a release sheet substrate and a non-silicone release treatment layer provided on at least one surface of the release sheet substrate. The non-silicone release treatment layer is formed from a material containing a long-chain alkyl release treatment agent. In embodiments where a release sheet having a release treatment layer containing a long-chain alkyl release treatment agent is used as the non-silicone release sheet, the desired light releasability can be preferably obtained.

[0012] In some embodiments, the PSA sheet has a substrate and the PSA layer disposed on at least one surface of the substrate. Such a substrate-attached PSA sheet is excellent in processability and handling, and can be preferably used, for example, as a surface protection film that is removed (peeled) from an adherend after use.

[0013] The adhesive surface of the pressure-sensitive adhesive sheet disclosed herein is protected by a release sheet, so the adhesive surface is kept smooth and can be uniformly attached to the adherend. Furthermore, by using a non-silicone release sheet as the release sheet, contamination of the adherend by silicone materials does not occur. This can be an advantageous feature, for example, in optical applications where specific optical properties are required. Therefore, the pressure-sensitive adhesive sheet disclosed herein is preferably used for optical applications, specifically, in a form where it is attached to an optical component.

[0014] Furthermore, the pressure-sensitive adhesive sheet disclosed herein is suitable, for example, as a surface protection film. After being attached to an object to be protected, the surface protection film is usually peeled off (re-peeled off) from the object to be protected once its protection purpose has been achieved. Since such a surface protection film is required not to alter the object to be protected before and after protection of the object, it can be advantageous to use a non-silicone pressure-sensitive adhesive sheet with a release sheet that does not cause contamination of the silicone material on the surface of the object to be protected after peeling and removal. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet with a release sheet according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will be 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 on 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. In the following drawings, components and parts having the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. The embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the actual product.

[0017] In this specification, the term "adhesive" refers to a material that, as mentioned above, is in a soft solid (viscoelastic) state at temperatures around room temperature and has the property of easily adhering to an adherend by pressure. The adhesive referred to here is generally a material having a complex tensile modulus E as defined in "CA Dahlquist, "Adhesion: Fundamentals and Practice", McLaren & Sons (1966), p. 143". *(1Hz)<10 7 dyne / cm 2 The material may be a material having the properties satisfying the above (typically, a material having the above properties at 25°C).

[0018] In this specification, biomass-derived carbon refers to carbon (renewable carbon) derived from biomass materials, i.e., materials derived from renewable organic resources. The biomass materials typically refer to materials derived from biological resources (typically, plants that perform photosynthesis) that can be sustainably reproduced in the presence of sunlight, water, and carbon dioxide. Therefore, materials derived from fossil resources that are depleted through use after mining (fossil resource-based materials) are excluded from the concept of biomass materials used here. The biomass carbon ratio of the pressure-sensitive adhesive (layer) and pressure-sensitive adhesive sheet, i.e., the proportion of biomass-derived carbon in the total carbon contained in the pressure-sensitive adhesive (layer) and pressure-sensitive adhesive sheet, can be estimated from the content of the carbon isotope with mass number 14 measured in accordance with ASTM D6866.

[0019] <Configuration example of adhesive sheet with release sheet> The pressure-sensitive adhesive sheet with release sheet disclosed herein comprises a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer and a non-silicone release sheet disposed on the surface of the pressure-sensitive adhesive layer. 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 non-releasable substrate (support substrate), or may be a substrate-less pressure-sensitive adhesive sheet (i.e., a pressure-sensitive adhesive sheet without a non-releasable substrate) in which the pressure-sensitive adhesive layer is held by a release sheet. Hereinafter, the support substrate may be simply referred to as "substrate." The concept of pressure-sensitive adhesive sheet here may include those referred to as pressure-sensitive adhesive tape, pressure-sensitive adhesive label, pressure-sensitive adhesive film, etc. The pressure-sensitive adhesive sheet may be in the form of a roll or sheets. It may also be a pressure-sensitive adhesive sheet processed into various shapes.

[0020] The structure of a pressure-sensitive adhesive sheet with a release sheet according to one embodiment is shown schematically in FIG. 1. This pressure-sensitive adhesive sheet 100 with a release sheet includes a pressure-sensitive adhesive sheet 1 having a pressure-sensitive adhesive layer 21 and a release sheet 31 laminated on the surface (adhesive surface) 21A of the pressure-sensitive adhesive layer 21. The pressure-sensitive adhesive sheet 1 is configured as a substrate-attached single-sided pressure-sensitive adhesive sheet comprising a sheet-like support substrate (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, and a pressure-sensitive adhesive layer 21 provided on the first surface 10A side of the support substrate 10. The pressure-sensitive adhesive layer 21 is provided fixedly on the first surface 10A side of the support substrate 10, i.e., without any intention to separate the pressure-sensitive adhesive layer 21 from the support substrate 10. Such a single-sided adhesive pressure-sensitive adhesive sheet 1 is suitable as a surface protection film, the adhesive surface of which is attached to the surface of an adherend (a target to be protected, for example, an optical component such as a polarizing plate). Before use, the adhesive sheet 1 has the form of an adhesive sheet 100 with a release sheet, and the surface (adhesive surface) 21A of the adhesive layer 21 is protected by a release sheet 31, at least the side facing the adhesive layer 21 being the release surface.

[0021] <Adhesive layer> (acrylic polymer) The pressure-sensitive adhesive layer disclosed herein contains an acrylic polymer. The pressure-sensitive adhesive layer is typically a pressure-sensitive adhesive layer having an acrylic polymer as the base polymer. Such a pressure-sensitive adhesive layer is also called an acrylic pressure-sensitive adhesive layer. The base polymer refers to the main component of the rubber-like polymer (a polymer that exhibits rubber elasticity in a temperature range around room temperature) contained in the pressure-sensitive adhesive layer. In this specification, unless otherwise specified, the term "main component" refers to a component contained in an amount of more than 50% by weight. Furthermore, the following explanations regarding the components that may be contained in the pressure-sensitive adhesive and the pressure-sensitive adhesive layer are also applicable to the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive (layer) unless otherwise specified.

[0022] In this specification, the term "acrylic polymer" refers to a polymer derived from a monomer component containing more than 50% by weight of a (meth)acrylic monomer. The content of the (meth)acrylic monomer in the monomer component is preferably 70% by weight or more, and may be 80% by weight or more. In some embodiments, the content of the (meth)acrylic monomer in the monomer component may be 90% by weight or more, 95% by weight or more, or even 100% by weight. Meanwhile, in consideration of the balance of adhesive properties, in some embodiments, the proportion of the (meth)acrylic monomer in the entire monomer component may be, for example, less than 99% by weight, less than 95% by weight, or less than 93% by weight.

[0023] In this specification, "(meth)acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl" refers to acryloyl and methacryloyl in a comprehensive sense. Similarly, "(meth)acrylate" refers to acrylate and methacrylate in a comprehensive sense, and "(meth)acrylic" refers to acrylic and methacrylic in a comprehensive sense. Therefore, the concept of a (meth)acrylic monomer here can include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer).

[0024] The acrylic polymer typically uses a polymer of a monomer raw material containing one or more linear alkyl (meth)acrylates as the main monomer and, optionally, one or more secondary monomers copolymerizable with the main monomer. The main monomer refers to a component that accounts for more than 50% by weight of the total monomer components. The linear alkyl (meth)acrylate refers to an alkyl (meth)acrylate having a linear alkyl group at the ester terminal. The linear alkyl group encompasses both linear and branched alkyl groups and does not include cyclic alkyl groups known as alicyclic. The secondary monomer refers to a monomer component other than the linear alkyl (meth)acrylate used as the main monomer, including functional group-containing monomers such as hydroxyl group-containing monomers and carboxy group-containing monomers, as described below, and other copolymerizable monomers. In this specification, the secondary monomer refers to a monomer component other than the alkyl (meth)acrylate (m1) and other linear alkyl (meth)acrylates among the monomer components.

[0025] The acrylic polymer used in the technology disclosed herein contains an alkyl(meth)acrylate (m1) having a specific chemical structure as a monomer component. Specifically, the alkyl(meth)acrylate (m1) has an alkyl group having 6 to 17 carbon atoms at the ester terminal, and the alkyl group having 6 to 17 carbon atoms is either a linear alkyl group or a branched alkyl group having one carbon atom in the branch (also referred to as a branch or branching group). A pressure-sensitive adhesive containing an acrylic polymer with the above structure can achieve release sheet releasability comparable to that of a silicone-based release sheet, even when a non-silicone-based release sheet is used. The reason for this is not particularly limited, but the results of the examples described below suggest that the acrylic polymer synthesized using the alkyl(meth)acrylate (m1) as a monomer component has a relatively long, linear or low-branched alkyl group in the side chain of the acrylic polymer. It is believed that such side-chain alkyl groups contribute to the easy release properties of non-silicone-based release sheets. The alkyl (meth)acrylate (m1) is contained as at least a part of the main monomer (chain alkyl (meth)acrylate) in the monomer components of the acrylic polymer. Hereinafter, a chain alkyl (meth)acrylate having a chain alkyl group with a carbon number of X at the ester terminal will be referred to as C X In the case of alkyl (meth)acrylate (for example, a chain alkyl (meth)acrylate having a chain alkyl group having 6 to 17 carbon atoms at the ester terminal), C 6-17 It is sometimes called alkyl (meth)acrylate.

[0026] The alkyl(meth)acrylate (m1) can also be represented by the following formula (1). CH2=C(R 1 )COOR 2 (1) Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. 2is an alkyl group having 6 to 17 carbon atoms, and is either a linear alkyl group or a branched alkyl group having one carbon atom in the branch. The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate (m1) is preferably 7 or more, and may be 8 or more, 9 or more, 10 or more, or 12 or more, from the viewpoint of easy releasability from non-silicone release sheets. The greater the number of carbon atoms in the alkyl group, the more effectively the effects and properties of the alkyl group having a long chain are likely to be exhibited. Furthermore, from the viewpoints of adhesive formability, adhesive properties, aging speed, etc., the number of carbon atoms is preferably 14 or less, more preferably 12 or less, even more preferably 10 or less, and particularly preferably 8 or less (for example, 7 or 8).

[0027] C used as alkyl (meth)acrylate (m1) 6-17 Specific examples of linear alkyl (meth)acrylates include n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-pentadecyl (meth)acrylate, n-hexadecyl (meth)acrylate, and n-heptadecyl (meth)acrylate. 6-17Specific examples of branched alkyl (meth)acrylates include methylheptyl (meth)acrylates such as 2-octyl (meth)acrylate and isooctyl acrylate, methyloctyl (meth)acrylate, methylnonyl (meth)acrylate, methyldecyl (meth)acrylate, methyldodecyl (meth)acrylate, methyltridecyl (meth)acrylate, methyltetradecyl (meth)acrylate, methylpenta(meth)acrylate, and methylhexadecyl (meth)acrylate. The alkyl (meth)acrylate (m1) can be used alone or in combination of two or more. Although not particularly limited, in some embodiments, alkyl acrylates are preferably used as the alkyl (meth)acrylate (m1).

[0028] In some embodiments, C 6-17 A linear alkyl (meth)acrylate is preferably used. Among them, as the alkyl (meth)acrylate (m1), n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, and n-dodecyl (meth)acrylate are more preferred, and n-heptyl (meth)acrylate and n-octyl (meth)acrylate are even more preferred.

[0029] C 6-17 As the branched alkyl(meth)acrylate, either an isoalkyl(meth)acrylate having an isoalkyl group in which a methyl group is branched at the carbon immediately before the end of the branched alkyl group, or a branched alkyl(meth)acrylate having a non-isobranched alkyl group in which a methyl group is branched at the carbon two or more carbons before the end of the branched alkyl group, such as 2-octyl(meth)acrylate, can be used. In some embodiments, however, a branched alkyl(meth)acrylate having a non-isobranched alkyl group in which the side chain terminal of the acrylic polymer is a relatively long linear alkyl group is preferred. For example, a C 6-17 Branched alkyl (meth)acrylates can be preferably used.

[0030] The proportion of the alkyl (meth)acrylate (m1) in the entire monomer components is determined depending on the intended use, required properties, and the like. In some embodiments, the proportion of the alkyl (meth)acrylate (m1) in the entire monomer components may be, for example, 10% by weight or more, suitably 30% by weight or more. In some preferred embodiments, it is 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, or even 85% by weight or more, particularly preferably 90% by weight or more, or even 92% by weight or more, or even 95% by weight or more. By increasing the amount of the alkyl (meth)acrylate (m1) used, the properties based on the alkyl (meth)acrylate (m1) can be effectively expressed. On the other hand, from the viewpoint of copolymerizing functional group-containing monomers that serve as crosslinking points, the proportion of the alkyl (meth)acrylate (m1) in the entire monomer components may be, for example, less than 99% by weight, or even less than 98% by weight, or even less than 97% by weight. In some other embodiments, the upper limit of the proportion of the alkyl (meth)acrylate (m1) in the total monomer components may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), from the viewpoint of obtaining the effect of using other monomers.

[0031] In some embodiments, the proportion of the alkyl (meth)acrylate (m1) in the total chain alkyl (meth)acrylates contained in the monomer components of the acrylic polymer may be, for example, 10% by weight or more, suitably 30% by weight or more. In some preferred embodiments, it is 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, and may be 95% by weight or more, or even 99% by weight or more. By increasing the amount of alkyl (meth)acrylate (m1) used, the properties based on the alkyl (meth)acrylate (m1) can be effectively expressed. In some embodiments, an acrylic polymer having a monomer composition containing only alkyl (meth)acrylate (m1) as the chain alkyl (meth)acrylate is used. Therefore, the upper limit of the proportion of alkyl (meth)acrylate (m1) in the total chain alkyl (meth)acrylate is 100% by weight. In some other embodiments, the proportion of the alkyl (meth)acrylate (m1) in the total amount of the chain alkyl (meth)acrylate may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), from the viewpoint of obtaining the effect of using a chain alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1).

[0032] In some preferred embodiments, the alkyl (meth)acrylate (m1) is 7-12 Linear alkyl (meth)acrylates are used. Among them, C 7-8 It is more preferable to use a linear alkyl (meth)acrylate. 7-12 Linear alkyl (meth)acrylate (more preferably C 7-8The proportion of the linear alkyl (meth)acrylate may be, for example, 10% by weight or more, suitably 30% by weight or more, and in some preferred embodiments, 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, or even 85% by weight or more, particularly preferably 90% by weight or more, or even 92% by weight or more, or even 95% by weight or more. In addition, the proportion of C in the total monomer components may be 7-12 Linear alkyl (meth)acrylate (more preferably C 7-8 The proportion of the linear alkyl (meth)acrylate may be, for example, less than 99% by weight, less than 98% by weight, or less than 97% by weight. 7-12 Linear alkyl (meth)acrylate (more preferably C 7-8 The upper limit of the proportion of the linear alkyl (meth)acrylate may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (for example, less than 50% by weight) from the viewpoint of obtaining the effect of using other monomers.

[0033] In some preferred embodiments, n-heptyl (meth)acrylate is used as the alkyl (meth)acrylate (m1). By using n-heptyl (meth)acrylate, the effects of the technology disclosed herein can be particularly favorably exhibited. Among them, n-heptyl acrylate is particularly preferable from the viewpoint of adhesive properties.

[0034] The proportion of n-heptyl (meth)acrylate in the total monomer components is determined depending on the intended use, required properties, etc. In some embodiments, the proportion of n-heptyl (meth)acrylate in the total monomer components may be, for example, 10% by weight or more, and suitably 30% by weight or more. In some preferred embodiments, it is 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, or even 85% by weight or more, particularly preferably 90% by weight or more, or even 92% by weight or more, or even 95% by weight or more. By increasing the amount of n-heptyl (meth)acrylate used, the effect of its use can be effectively exhibited. On the other hand, from the viewpoint of copolymerizing functional group-containing monomers that serve as crosslinking points, the proportion of n-heptyl (meth)acrylate in the total monomer components may be, for example, less than 99% by weight, or even less than 98% by weight, or even less than 97% by weight. In some other embodiments, the proportion of n-heptyl (meth)acrylate in the total monomer components may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), from the viewpoint of obtaining the effects of using various monomers other than n-heptyl (meth)acrylate.

[0035] In some embodiments, the proportion of n-heptyl(meth)acrylate in the total chain alkyl(meth)acrylates contained in the monomer components of the acrylic polymer may be, for example, 10% by weight or more, suitably 30% by weight or more. In some preferred embodiments, it is 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, even 95% by weight or more, or even 99% by weight or more. By increasing the amount of n-heptyl(meth)acrylate used, the effects of its use can be effectively exhibited. The technology disclosed herein is preferably implemented in an embodiment using an acrylic polymer whose monomer composition contains only n-heptyl(meth)acrylate as the chain alkyl(meth)acrylate. Therefore, the upper limit of the proportion of n-heptyl(meth)acrylate in the total chain alkyl(meth)acrylates is 100% by weight. In some other embodiments, the proportion of n-heptyl(meth)acrylate in the total amount of the chain alkyl(meth)acrylates may be 95% by weight or less, 75% by weight or less, 60% by weight or less, or 50% by weight or less (e.g., less than 50% by weight), from the viewpoint of obtaining the effect of using other chain alkyl(meth)acrylates.

[0036] In some embodiments, the monomer components constituting the acrylic polymer may contain a chain alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1) within the range that does not significantly impair the effects of the invention. Examples of the chain alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1) include C 1-5 Alkyl (meth)acrylate, alkyl group with 18 or more carbon atoms 18+ Alkyl (meth)acrylate, alkyl group with branched group having 2 or more carbon atoms 6-17 Branched alkyl (meth)acrylates can be used alone or in combination of two or more. 1-5Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, and isopentyl (meth)acrylate. 18+ Specific examples of alkyl(meth)acrylate include octadecyl(meth)acrylate, nonadecyl(meth)acrylate, and eicosyl(meth)acrylate. 6-17 Specific examples of branched alkyl (meth)acrylates include 2-ethylhexyl (meth)acrylate.

[0037] The proportion of the chain alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1) in the monomer components is not particularly limited, and may be, for example, approximately 50% by weight or less (e.g., less than 50% by weight), 30% by weight or less, 10% by weight or less, or 1% by weight or less. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer components are substantially free of chain alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1). In an embodiment in which the monomer components contain a chain alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1), the proportion of the chain alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1) in the monomer components may be, for example, 1% by weight or more, 10% by weight or more, or 30% by weight or more.

[0038] In this specification, the term "monomer components substantially free of monomer A (e.g., a chain alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1))" means that the monomer A is not used at least intentionally, and it is acceptable for the monomer A to be unintentionally included in an amount of, for example, about 0.1% by weight or less.

[0039] In some embodiments, the monomer component may contain, as the linear alkyl (meth)acrylate, an alkyl (meth)acrylate having a biomass-derived alkyl group at the ester terminal (hereinafter also referred to as "biomass linear alkyl (meth)acrylate"). In recent years, environmental issues such as global warming have become a focus of attention, and there is a demand for reducing the amount of fossil resource-based materials used, such as petroleum. Under these circumstances, there is also a demand in the field of pressure-sensitive adhesives for reducing the amount of fossil resource-based materials used. By using a biomass linear alkyl (meth)acrylate, it is possible to suitably realize an acrylic pressure-sensitive adhesive composition that takes into consideration reduced dependence on fossil resource-based materials.

[0040] The biomass linear alkyl (meth)acrylate is not particularly limited, and may be, for example, an ester of a biomass-derived alkanol and biomass-derived or non-biomass-derived (meth)acrylic acid. Examples of biomass-derived alkanols include biomass ethanol and alkanols derived from plant materials such as palm oil, palm kernel oil, coconut oil, and castor oil. When the biomass-derived alkanol has three or more carbon atoms, the alkanol may be linear or branched. In some embodiments, an ester of a biomass-derived alkanol and non-biomass-derived (meth)acrylic acid is used as the biomass linear alkyl (meth)acrylate used in the synthesis of an acrylic polymer. In such a biomass linear alkyl (meth)acrylate, the greater the number of carbon atoms in the alkanol, the higher the ratio of biomass-derived carbon atoms to the total carbon atoms contained in the biomass linear alkyl (meth)acrylate, i.e., the higher the biomass carbon ratio of the linear alkyl (meth)acrylate. Therefore, in the above-mentioned biomass linear alkyl (meth)acrylate, it is desirable that the linear alkyl group derived from biomass has a large number of carbon atoms in order to reduce dependence on fossil resource-based materials. On the other hand, if the linear alkyl group constituting the linear alkyl (meth)acrylate has too many carbon atoms, it tends to be difficult to obtain adhesive properties such as adhesive strength, and it may also be disadvantageous in terms of productivity, such as synthesis, handling, and cost. In an embodiment in which an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid is used as the biomass linear alkyl (meth)acrylate, it is desirable to use a material that achieves a good balance between adhesive properties and reduced dependence on fossil resource-based materials (more specifically, the biomass carbon ratio of the above-mentioned linear alkyl (meth)acrylate).

[0041] In the technology disclosed herein, a biomass linear alkyl (meth)acrylate can be used for both the alkyl (meth)acrylate (m1) and the linear alkyl (meth)acrylate other than the alkyl (meth)acrylate (m1). In embodiments in which two or more compounds are used as the linear alkyl (meth)acrylate used in the synthesis of an acrylic polymer, at least a portion of them (e.g., one or two, or all, i.e., all) can be biomass linear alkyl (meth)acrylates. In some preferred embodiments, by using a biomass linear alkyl (meth)acrylate as the alkyl (meth)acrylate (m1), the effects of the technology disclosed herein can be preferably achieved while reducing dependence on fossil resource-based materials.

[0042] From the viewpoints of adhesive formability, adhesive properties, and aging speed, the number of carbon atoms in the alkyl group of the biomass linear alkyl (meth)acrylate is preferably 14 or less, more preferably 12 or less, even more preferably 10 or less, and particularly preferably 8 or less (e.g., 7 or 8). Furthermore, the number of carbon atoms is preferably 7 or more. For example, in an embodiment in which an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid is used as the biomass linear alkyl (meth)acrylate, the biomass carbon ratio of the synthesized acrylic polymer can be increased by increasing the number of carbon atoms in the alkyl group.

[0043] In some preferred embodiments, n-heptyl(meth)acrylate having an n-heptyl group derived from biomass (hereinafter also referred to as "biomass heptyl(meth)acrylate") is used as the alkyl(meth)acrylate (m1). By using biomass heptyl(meth)acrylate, the effects of the technology disclosed herein can be particularly favorably exhibited while reducing dependence on fossil resource-based materials. Among these, biomass heptyl acrylate is particularly preferred from the viewpoint of adhesive properties.

[0044] In some embodiments, the proportion of biomass linear alkyl (meth)acrylate (e.g., biomass n-heptyl (meth)acrylate) in the total linear alkyl (meth)acrylate used as a monomer component of the acrylic polymer may be, for example, 1% by weight or more, suitably 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more (e.g., more than 50% by weight), and may be 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or even 99% by weight or more. Increasing the proportion of biomass linear alkyl (meth)acrylate used can improve the biomass carbon ratio of the acrylic polymer while effectively achieving the effects of its use. The technology disclosed herein can be preferably implemented in an embodiment using an acrylic polymer with a monomer composition containing only biomass linear alkyl (meth)acrylate as the linear alkyl (meth)acrylate. Therefore, the upper limit of the proportion of the biomass chain alkyl (meth)acrylate in the total chain alkyl (meth)acrylate is 100% by weight. In some other embodiments, the proportion of the biomass chain alkyl (meth)acrylate in the total chain alkyl (meth)acrylate may be 95% by weight or less, 70% by weight or less, 50% by weight or less (e.g., less than 50% by weight), 30% by weight or less, 10% by weight or less, or 1% by weight or less.

[0045] In some embodiments, the monomer components of the acrylic polymer preferably contain a monomer (m2) having a hydroxyl group. The hydroxyl group-containing monomer (m2) is included in the monomer components as the aforementioned secondary monomer. By using the hydroxyl group-containing monomer (m2), the side chain of the acrylic polymer has a hydroxyl group. Such a hydroxyl group can serve as a crosslinking point when using a crosslinking agent such as an isocyanate-based or epoxy-based crosslinking agent. The hydroxyl group-containing monomer (m2) can be used alone or in combination of two or more types.

[0046] The length of the hydroxyl-containing side chain of the hydroxyl-containing monomer (m2) is not particularly limited. The carbon number of the hydroxyl-containing side chain of the hydroxyl-containing monomer (m2) may be, for example, 2 or more, preferably 3 or more. Here, the hydroxyl-containing side chain of the hydroxyl-containing monomer (m2) refers to, for example, a chain structure bonded to a (meth)acryloyl group in the case of a hydroxyl-containing (meth)acrylic monomer. By using a hydroxyl-containing monomer (m2) having a hydroxyl group in a side chain with a relatively long carbon number, the hydroxyl group serving as the crosslinking point and the crosslinking agent are brought into close proximity, which is thought to result in rapid aging (crosslinking reaction). Furthermore, by appropriately setting the length of the side chain of the hydroxyl-containing monomer (m2) based on the relationship with the chain length of the alkyl group of the alkyl (meth)acrylate (m1), the crosslinking reaction can be appropriately controlled, thereby achieving both favorable crosslinking reaction progress and a practical pot life. The hydroxyl-containing monomer (m2) may be derived from biomass or non-biomass.

[0047] As the hydroxyl group-containing monomer (m2), a hydroxyl group-containing (meth)acrylic monomer is preferably used. Specific examples of the hydroxyl group-containing (meth)acrylic monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate; and hydroxyalkyl (meth)acrylamides such as N-hydroxypropyl (meth)acrylamide and N-hydroxybutyl (meth)acrylamide. Among these, hydroxyalkyl (meth)acrylates are preferred, and 4-hydroxybutyl (meth)acrylate is more preferred. The hydroxyl group-containing (meth)acrylic monomers may be used alone or in combination of two or more.

[0048] In some preferred embodiments, a (meth)acrylic monomer having a hydroxyalkyl group having 3 or more carbon atoms is used as the hydroxyl group-containing (meth)acrylic monomer. Among these, hydroxyalkyl (meth)acrylates having a hydroxyalkyl group having 3 or more carbon atoms at the ester terminal are more preferred, and among these, compounds in which the alkyl group constituting the hydroxyalkyl group is linear are even more preferred. The number of carbon atoms in the hydroxyalkyl group of the hydroxyalkyl (meth)acrylate is, for example, 3 to 10, preferably 4 to 10, and may be 4 to 8 or 4 to 6.

[0049] In embodiments using a hydroxyl group-containing monomer (m2), the content of the hydroxyl group-containing monomer (m2) in the monomer components can be appropriately set depending on the intended use, required properties, etc. In some embodiments, the content of the hydroxyl group-containing monomer (m2) is, for example, 0.01 wt% or more of the total monomer components, and may be 0.1 wt% or more, and suitably greater than 0.5 wt%. In some preferred embodiments, it may be 1 wt% or more (e.g., greater than 1 wt%), 2 wt% or more, or even 3 wt% or more. In some embodiments, the content of the hydroxyl group-containing monomer (m2) in the total monomer components may be, for example, less than 15 wt%, and suitably 10 wt% or less. In some preferred embodiments, it may be 8 wt% or less, 6 wt% or less, or 5 wt% or less. Using an appropriate amount of the hydroxyl group-containing monomer (m2) within the above range improves cohesive strength and facilitates adjustment to favorable removably adhesive strength, making it easier to form a PSA suitable for, for example, removably surface protection applications.

[0050] Although not particularly limited, in some embodiments, the proportion of the hydroxyl group-containing monomer (m2) in the minor monomers used as the monomer components of the acrylic polymer is 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more, from the viewpoint of effectively exhibiting the effect of copolymerizing the hydroxyl group-containing monomer (m2). For example, it may be 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more (e.g., 99.9% by weight or more). The upper limit of the proportion of the hydroxyl group-containing monomer (m2) in the total copolymerizable monomers is 100% by weight, and may be, for example, 95% by weight or less.

[0051] In some embodiments, the monomer component of the acrylic polymer may contain a monomer having a carboxy group as a secondary monomer. By using a carboxy group-containing monomer, the side chain of the acrylic polymer has a carboxy group. Such a carboxy group can serve as a crosslinking point when using a crosslinking agent such as an epoxy crosslinking agent. By using a carboxy group-containing monomer, a pressure-sensitive adhesive having appropriate cohesive strength can be easily obtained. The carboxy group-containing monomer can be used alone or in combination of two or more types.

[0052] Examples of carboxyl group-containing monomers include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, 2-(meth)acryloyloxyethyl tetrahydrophthalic acid, crotonic acid, and isocrotonic acid; and ethylenically unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid. The carboxyl group-containing monomer may also be a monomer having a metal salt (e.g., an alkali metal salt) of a carboxyl group. As the carboxy group-containing monomer, a carboxy group-containing (meth)acrylic monomer is preferably used. The above carboxy group-containing (meth)acrylic monomers can be used alone or in combination of two or more.

[0053] In an embodiment using a carboxyl group-containing monomer, the length of the side chain having a carboxyl group in the monomer is not particularly limited. The number of carbon atoms in the carboxyl group-containing side chain of the carboxyl group-containing monomer may be, for example, 1 or more, or 2 or more, and preferably 3 or more. For example, one or more (meth)acrylic monomers having a carboxyl group with 3 or more carbon atoms can be selected and used from the Light Ester series or Light Acrylate series available from Kyoeisha Chemical Co., Ltd. Specific examples include products under the trade names "Light Ester HO-MS(N)" (2-methacryloyloxyethyl succinic acid) and "HOA-MPE(N)" (2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid).

[0054] In some embodiments, the amount of carboxyl group-containing monomer used in the monomer component forming the acrylic polymer is, for example, less than 10 wt%, or may be less than 8 wt%, or less than 5 wt%, or less than 3 wt%, or less than 1 wt%, or less than 0.5 wt%, or less than 0.3 wt%, or less than 0.1 wt%. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer component is substantially free of carboxyl group-containing monomer. By limiting the amount of carboxyl group-containing monomer used or eliminating its use, it is easy to adjust the adhesive strength to an appropriate range that allows for re-removal, and it is easy to form a pressure-sensitive adhesive suitable for, for example, re-removable surface protection applications.

[0055] The monomer components forming the acrylic polymer may contain other copolymerizable monomers copolymerizable with the alkyl(meth)acrylate (m1). The other copolymerizable monomers are defined as copolymerizable monomers different from the alkyl(meth)acrylate (m1), chain alkyl(meth)acrylates other than the alkyl(meth)acrylate (m1), the hydroxyl group-containing monomer (m2), and the carboxy group-containing monomer. Non-limiting examples of other copolymerizable monomers include functional group-containing monomers such as acid anhydride group-containing monomers, sulfonic acid group- or phosphoric acid group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, amide group-containing monomers such as (meth)acrylamide and N,N-dimethyl(meth)acrylamide, amino group-containing monomers such as aminoethyl(meth)acrylate and N,N-dimethylaminoethyl(meth)acrylate, monomers having a nitrogen atom-containing ring such as N-vinyl-2-pyrrolidone and N-(meth)acryloylmorpholine, imide group-containing monomers, and the like, vinyl ester monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, cyclohexyl(meth)acrylate, cyclopentyl(meth)acrylate, isopropyl alcohol, etc. Examples of the copolymerizable monomer include cycloalkyl (meth)acrylates such as bornyl (meth)acrylate, aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate), olefinic monomers, chlorine-containing monomers, isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate, alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, and vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether. The other copolymerizable monomers can be used alone or in combination of two or more.

[0056] The monomer components constituting the acrylic polymer may or may not contain the other copolymerizable monomers. The amount of the other copolymerizable monomers is not particularly limited and may be appropriately selected depending on the purpose and application. The content of the other copolymerizable monomers in the monomer components is, for example, suitably less than 30% by weight, preferably less than 10% by weight, more preferably less than 8% by weight, more preferably less than 5% by weight, and may be less than 3% by weight (e.g., less than 1% by weight). The technology disclosed herein can be preferably implemented in an embodiment in which the monomer components are substantially free of other copolymerizable monomers.

[0057] The biomass carbon ratio of the monomer components constituting the acrylic polymer (the biomass carbon ratio of the acrylic polymer) may be, for example, 1% or more, suitably 10% or more, preferably 30% or more, more preferably 50% or more (e.g., more than 50%), may be 70% or more, may be 80% or more, or may be 90% to 100%. By designing in this way, an acrylic pressure-sensitive adhesive that takes into consideration reduced dependence on fossil resource-based materials can be obtained.

[0058] The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization can be preferably employed. The adoption of solution polymerization can be advantageous from the viewpoints of transparency, adhesive performance, and the like. The monomer supply method for solution polymerization can be appropriately adopted, such as a batch charging method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, or a divided supply (dropping) method. The polymerization temperature for solution polymerization can be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, and the like, and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0059] The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents (toluene, ethyl acetate, etc.). The initiator used in polymerization can be appropriately selected from conventionally known polymerization initiators (for example, azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN), peroxide-based initiators, etc.) depending on the type of polymerization method. The amount of polymerization initiator used may be a normal amount, and can be selected, for example, from the range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) per 100 parts by weight of the monomer components.

[0060] Although not particularly limited, the weight average molecular weight (Mw) of the acrylic polymer is usually about 10 × 10 4 It is suitable that the Mw of the acrylic polymer is 30×10 or more. A PSA exhibiting good cohesive strength is easily obtained by using an acrylic polymer having such Mw. In some embodiments, the Mw of the acrylic polymer is, for example, 30×10 4 It is appropriate that the density is equal to or greater than 50×10 4 That's 70 x 10 4 By setting the Mw of the acrylic polymer to a predetermined value or more, the cohesive strength of the pressure-sensitive adhesive is improved, and it is easy to prevent adhesive residue from being left on the surface of the adherend. Furthermore, from the viewpoint of adhesion to the adherend, the Mw of the acrylic polymer is usually about 500 × 10 4 It is appropriate that the value is less than 300 × 10 4 It may be less than 100 x 10 4 Less than (e.g., 100 x 10 4 It may be less than that. By setting the Mw to a predetermined value or less, the PSA tends to have appropriate fluidity and to easily obtain wettability (adhesion) to the adherend. For example, in surface protection applications, good wettability means that the surface protection film will not peel off from the adherend during use and can preferably fulfill its protective function. For acrylic polymers obtained by solution polymerization, it is particularly significant that the Mw is in the above-mentioned preferred range.

[0061] The Mw of the acrylic polymer can be measured by gel permeation chromatography (GPC) and calculated as a value converted into standard polystyrene. Specifically, it can be measured using a GPC measuring device (trade name: "HLC-8220GPC" manufactured by Tosoh Corporation) under the following conditions. The same applies to the examples described below. [GPC measurement conditions] Sample concentration: 0.2 wt% (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40°C column: Sample column: 1 "TSKguardcolumn SuperHZ-H" + 2 "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: 1 tube of "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: polystyrene

[0062] (Crosslinking agent) In some embodiments, the pressure-sensitive adhesive layer contains a crosslinking agent. The crosslinking agent can be useful for increasing the cohesive strength of the pressure-sensitive adhesive. The crosslinking agent can be selected from various crosslinking agents known in the field of pressure-sensitive adhesives. Examples of such crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, and amine-based crosslinking agents. The crosslinking agents can be used alone or in combination of two or more. The crosslinking agent may be derived from biomass or non-biomass.

[0063] The amount of crosslinking agent used is not particularly limited. The amount of crosslinking agent used can be selected, for example, from the range of 0.1 to 20 parts by weight per 100 parts by weight of the acrylic polymer. From the viewpoint of achieving a good balance between improved cohesive strength and adhesion to the adherend, the amount of crosslinking agent used per 100 parts by weight of the acrylic polymer is usually preferably 10 parts by weight or less, but may also be 8 parts by weight or less, or 6 parts by weight or less, and is suitably 0.5 parts by weight or more, or may even be 1 part by weight or more. By using an amount of crosslinking agent within an appropriate range, the cohesive strength of the pressure-sensitive adhesive can be increased, adhesive residue on the adherend can be prevented, and adhesion to the adherend can be obtained.

[0064] In some embodiments, the pressure-sensitive adhesive layer preferably contains an isocyanate-based crosslinking agent. The isocyanate-based crosslinking agent may be used alone or in combination of two or more. The isocyanate-based crosslinking agent may be derived from biomass or non-biomass. The isocyanate-based crosslinking agent may also be used in combination with other crosslinking agents, such as epoxy-based crosslinking agents.

[0065] As the isocyanate-based crosslinking agent, a polyisocyanate-based crosslinking agent having two or more isocyanate groups per molecule is preferably used. The number of isocyanate groups per molecule of the polyisocyanate-based crosslinking agent is preferably 2 to 10, for example, 2 to 4, and typically 2 or 3. Examples of the polyisocyanate-based crosslinking agent include aromatic polyisocyanates such as tolylene diisocyanate and xylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic polyisocyanates such as hexamethylene diisocyanate. More specifically, for example, lower aliphatic polyisocyanates such as butylene diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate; alicyclic polyisocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic diisocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and polymethylene polyphenyl diisocyanate; trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate L"), trimethylolpropane / hexamethyldiisocyanate, and the like. Examples of suitable polyisocyanate adducts include isocyanate adducts such as a trimer adduct of samethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HL"), an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX"), and an isocyanurate of pentamethylene diisocyanate (manufactured by Mitsui Chemicals, Inc., trade name "Stabio D-370N"); polyisocyanates such as polyether polyisocyanate and polyester polyisocyanate; adducts of these polyisocyanates with polyols; and polyisocyanates obtained by multifunctionalizing these polyisocyanates with isocyanurate bonds, biuret bonds, allophanate bonds, etc. For example, in applications where transparency is required for the pressure-sensitive adhesive, it is preferable to use aliphatic diisocyanates such as pentamethylene diisocyanate and hexamethylene diisocyanate, or isocyanurates of such aliphatic diisocyanates.In an embodiment in which an isocyanate-based crosslinking agent is used, the proportion of aliphatic polyisocyanates (aliphatic diisocyanates, isocyanurates of aliphatic diisocyanates, etc.) in the total amount of the isocyanate-based crosslinking agent is, for example, preferably more than 50% by weight, may be 70% by weight or more, or may be 90% by weight or more (for example, 95 to 100% by weight).

[0066] When an isocyanate-based crosslinking agent is used, the amount used may be, for example, approximately 0.1 parts by weight or more, 0.5 parts by weight or more, 1.0 parts by weight or more, or more than 1.5 parts by weight, per 100 parts by weight of the acrylic polymer. From the viewpoint of obtaining a higher effect of use, in some preferred embodiments, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the acrylic polymer is, for example, 2.0 parts by weight or more (e.g., more than 2.0 parts by weight), more preferably 2.5 parts by weight or more, 3.0 parts by weight or more, or even 3.5 parts by weight or more. Furthermore, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the acrylic polymer is usually suitably 20 parts by weight or less, may be 10 parts by weight or less, may be 8 parts by weight or less, or may be 6 parts by weight or less. In some preferred embodiments, the amount of the isocyanate-based crosslinking agent used is 5 parts by weight or less (e.g., less than 5 parts by weight), or may be 4.5 parts by weight or less (e.g., less than 4.0 parts by weight). By using an appropriate amount of the isocyanate crosslinking agent, the cohesive strength of the adhesive can be increased, adhesive residue on the adherend can be prevented, and adhesion to the adherend can be obtained. Furthermore, by limiting the amount of the isocyanate crosslinking agent used, a transparent adhesive can be easily formed.

[0067] Although not particularly limited, the technology disclosed herein can be preferably implemented in an embodiment having a pressure-sensitive adhesive layer containing an acrylic polymer and a crosslinking agent. In some embodiments, the combined amount (total amount) of the acrylic polymer and crosslinking agent in the pressure-sensitive adhesive layer is suitably from about 85% by weight to about 100% by weight, preferably about 90% by weight or more (e.g., more than 90% by weight), and may be about 95% by weight or more, about 98% by weight or more, or about 99% by weight or more (e.g., more than 99% by weight). In the above-mentioned pressure-sensitive adhesive composition, the amount of optional additives used is limited. This is preferable from the viewpoint of preventing contamination of the adherend by optional additives (e.g., low-molecular-weight components).

[0068] (catalyst) The pressure-sensitive adhesive layer preferably contains a catalyst. The use of a catalyst efficiently promotes the curing reaction of the pressure-sensitive adhesive composition (typically, the crosslinking reaction of the crosslinking agent described above), making it easier to achieve stable adhesion from an early stage after the production of the pressure-sensitive adhesive sheet. The catalyst is also referred to as a crosslinking catalyst. Examples of catalysts include tin (Sn)-containing compounds (tin-based catalysts), zirconium (Zr)-containing compounds (zirconium-based catalysts), titanium (Ti)-containing compounds (titanium-based catalysts), hafnium (Hf)-containing compounds (hafnium-based catalysts), iron (Fe)-containing compounds (iron-based catalysts), aluminum (Al)-containing compounds (aluminum-based catalysts), zinc (Zn)-containing compounds (zinc-based catalysts), and bismuth (Bi)-containing compounds (bismuth-based catalysts). These are typically organic compounds containing a metal in the active center and are also referred to as organometallic catalysts. The catalysts can be used alone or in combination of two or more.

[0069] In some preferred embodiments, a compound containing a Group 4 element is used as a catalyst. The use of a Group 4 element-containing compound as a catalyst allows for rapid aging and a sufficient pot life. The use of a Group 4 element-containing compound allows for a favorable catalyst addition effect without the use of tin-based catalysts, which have been widely used due to their high catalytic activity, thereby enabling the production of a pressure-sensitive adhesive that takes environmental impact and safety into consideration. Furthermore, Group 4 element-containing compounds tend to cause less hue change, such as discoloration, than other catalysts such as iron-based catalysts. Therefore, for example, in applications where transparency and optical properties are required for the pressure-sensitive adhesive, the use of a Group 4 element-containing compound as a catalyst is preferred. Furthermore, the use of an appropriate Group 4 element-containing compound can effectively suppress contamination of the adherend surface. The Group 4 element-containing compounds can be used alone or in combination of two or more. As the Group 4 element-containing compound, any of zirconium-containing compounds (zirconium-based catalysts), titanium-containing compounds (titanium-based catalysts), and hafnium-containing compounds (hafnium-based catalysts) can be used, with zirconium-containing compounds being preferred. A pressure-sensitive adhesive having excellent transparency can be preferably obtained by using a zirconium-containing compound.

[0070] The zirconium-containing compound (organic zirconium-containing compound), which is a suitable example of the catalyst, is not particularly limited and examples thereof include zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium ethylacetoacetate, zirconium octylate compounds, etc. More specifically, zirconium alkoxides such as tetraethoxyzirconium, tetra-n-propoxyzirconium, tetra-i-propoxyzirconium, tetra-n-butoxyzirconium (normal butyl zirconate), tetra-i-butoxyzirconium, tetra-sec-butoxyzirconium, and tetra-t-butoxyzirconium; triethoxy mono(acetylacetonate)zirconium, tri-n-propoxy mono(acetylacetonate)zirconium; Tri-i-propoxy mono(acetylacetonate)zirconium, Tri-n-butoxy mono(acetylacetonate)zirconium, Tri-sec-butoxy mono(acetylacetonate)zirconium, Tri-t-butoxy mono(acetylacetonate)zirconium, Diethoxy bis(acetylacetonate)zirconium, Di-n-propoxy bis(acetylacetonate)zirconium, Di-i-propoxy bis(acetylacetonate)zirconium, Di -n-Butoxy bis(acetylacetonate)zirconium, di-sec-butoxy bis(acetylacetonate)zirconium, di-t-butoxy bis(acetylacetonate)zirconium, monoethoxy tris(acetylacetonate)zirconium, mono-n-propoxy tris(acetylacetonate)zirconium, mono-i-propoxy tris(acetylacetonate)zirconium, mono-n-butoxy tris(acetylacetonate)zirconium , mono-sec-butoxy tris(acetylacetonate)zirconium, mono-t-butoxy tris(acetylacetonate)zirconium, tetrakis(acetylacetonate)zirconium, triethoxy mono(ethylacetoacetate)zirconium, tri-n-propoxy mono(ethylacetoacetate)zirconium, tri-i-propoxy mono(ethylacetoacetate)zirconium, tri-n-butoxy mono(ethylacetoacetate)zirconium,Tri-sec-butoxy mono(ethylacetoacetate)zirconium, Tri-t-butoxy mono(ethylacetoacetate)zirconium, Diethoxy bis(ethylacetoacetate)zirconium, Di-n-propoxy bis(ethylacetoacetate)zirconium, Di-i-propoxy bis(ethylacetoacetate)zirconium, Di-n-butoxy bis(ethylacetoacetate)zirconium, Di-sec-butoxy bis(ethylacetoacetate)zirconium, Di-t-butoxy bis(ethylacetoacetate)zirconium, Monoethoxy tris(ethylacetoacetate)zirconium , zirconium chelates such as mono-n-propoxy tris(ethylacetoacetate)zirconium, mono-i-propoxy tris(ethylacetoacetate)zirconium, mono-n-butoxy tris(ethylacetoacetate)zirconium, mono-sec-butoxy tris(ethylacetoacetate)zirconium, mono-t-butoxy tris(ethylacetoacetate)zirconium, tetrakis(ethylacetoacetate)zirconium, mono(acetylacetonato)tris(ethylacetoacetate)zirconium, bis(acetylacetonato)bis(ethylacetoacetate)zirconium, and tris(acetylacetonato)mono(ethylacetoacetate)zirconium; and the like. The above zirconium-containing compounds can be used alone or in combination of two or more.

[0071] The titanium-containing compound (organic titanium-containing compound) is not particularly limited, and examples thereof include tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetraoctyl titanate, titanium acetylacetonate, titanium tetraacetylacetonate, and titanium ethylacetoacetate. More specifically, examples thereof include tetraethoxytitanium, tetra-n-propoxytitanium, tetra-i-propoxytitanium, tetra-n-butoxytitanium, tetra-n-butoxytitanium dimer, tetra-i-butoxytitanium, tetra-sec-butoxytitanium, tetra-t-butoxytitanium, titanium di-2-ethylhexyloxybis(2-ethyl-3-hydroxyhexyloxide), titanium lactate, titanium lactate ammonium salt, and titanium diisopropoxybis(triethoxy) ... Nolaminate), tetrakis(2-ethylhexyloxy)titanium, titanium-i-propoxyoctylene glycolate, di-i-propoxy bis(acetylacetonato)titanium, propanedioxytitanium bis(ethylacetoacetate), tri-n-butoxytitanium monostearate, di-i-propoxytitanium distearate, titanium stearate, di-i-propoxytitanium diisostearate, (2-n-butoxycarbonylbenzoyloxy)tri Butoxy titanium, di-n-butoxy bis(triethanolaminato) titanium, triethoxy mono(acetylacetonate) titanium, tri-n-propoxy mono(acetylacetonate) titanium, tri-i-propoxy mono(acetylacetonate) titanium, tri-n-butoxy mono(acetylacetonate) titanium, tri-sec-butoxy mono(acetylacetonate) titanium, tri-t-butoxy mono(acetylacetonate) titanium, diethoxy bi bis(acetylacetonate)titanium, di-n-propoxy bis(acetylacetonate)titanium, di-n-butoxy bis(acetylacetonate)titanium, di-sec-butoxy bis(acetylacetonate)titanium, di-t-butoxy bis(acetylacetonate)titanium, monoethoxy tris(acetylacetonate)titanium, mono-n-propoxy tris(acetylacetonate)titanium, mono-i-propoxy tris(acetylacetonate)titanium,Mono-n-butoxy tris(acetylacetonate)titanium, mono-sec-butoxy tris(acetylacetonate)titanium, mono-t-butoxy tris(acetylacetonate)titanium, tetrakis(acetylacetonate)titanium, triethoxy mono(ethylacetoacetate)titanium, tri-n-propoxy mono(ethylacetoacetate)titanium, tri-i-propoxy mono(ethylacetoacetate)titanium, tri-n-butoxy mono(ethylacetoacetate)titanium, tri-sec-butoxy mono(ethylacetoacetate)titanium, tri-t-butoxy mono(ethylacetoacetate)titanium, diethoxy bis(ethylacetoacetate)titanium, di-n-propoxy bis(ethylacetoacetate)titanium, di-i-propoxy bis(ethylacetoacetate)titanium, di-n-butoxy bis(ethylacetoacetate) Examples of the titanium acetylacetonate include titanium di-sec-butoxy bis(ethylacetoacetate), titanium di-t-butoxy bis(ethylacetoacetate), titanium monoethoxy tris(ethylacetoacetate), titanium mono-n-propoxy tris(ethylacetoacetate), titanium mono-i-propoxy tris(ethylacetoacetate), titanium mono-n-butoxy tris(ethylacetoacetate), titanium mono-sec-butoxy tris(ethylacetoacetate), titanium mono-t-butoxy tris(ethylacetoacetate), titanium tetrakis(ethylacetoacetate), titanium mono(acetylacetonate)tris(ethylacetoacetate), titanium bis(acetylacetonate)bis(ethylacetoacetate), and titanium tris(acetylacetonate)mono(ethylacetoacetate). The titanium-containing compounds can be used alone or in combination of two or more.

[0072] As the hafnium-containing compound (organic hafnium-containing compound), compounds in which the zirconium or titanium of the zirconium-containing compound and titanium-containing compound is replaced with hafnium are used. Examples thereof include hafnium tetraacetylacetonate; hafnium pentanedionate; hafnium alkoxides such as tetramethoxyhafnium, tetraethoxyhafnium, tetrabutoxyhafnium, and tetrapentoxyhafnium; etc. The hafnium-containing compound can be used alone or in combination of two or more.

[0073] Other examples of catalysts include tin-containing compounds (organotin-containing compounds) such as dioctyltin dilaurate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin diacetylacetonate, tetra-n-butyltin, trimethyltin hydroxide, and butyltin oxide; aluminum-containing compounds (organoaluminum-containing compounds) such as aluminum sec-butoxide, aluminum trisacetylacetonate, aluminum bisethylacetoacetate, and aluminum trisethylacetoacetate; and iron-containing compounds (organic iron-containing compounds) such as ferric nursem.

[0074] In some embodiments, the catalyst used in the adhesive layer does not contain a tin-containing compound. The technology disclosed herein does not exclude the use of tin-based catalysts, but it can achieve the desired catalyst addition effects (fast aging and sufficient pot life) without using tin-based catalysts, which have been widely used due to their high catalytic activity. By refraining from using tin-based catalysts, an adhesive can be obtained that takes into consideration environmental impact and safety.

[0075] The amount of catalyst used is not particularly limited. The amount of catalyst used can be, for example, approximately 0.0001 parts by weight or more, suitably approximately 0.001 parts by weight or more, and may be approximately 0.005 parts by weight or more (e.g., 0.01 parts by weight or more) per 100 parts by weight of the acrylic polymer. In some preferred embodiments, the amount of catalyst used per 100 parts by weight of the acrylic polymer is approximately 0.02 parts by weight or more, and may be approximately 0.03 parts by weight or more. Using the catalyst within the above range tends to facilitate the formation of a PSA with good release sheet releasability. Furthermore, the amount of catalyst used can be, for example, approximately 1 part by weight or less, or may be approximately 0.5 parts by weight or less, suitably approximately 0.1 parts by weight or less, and may be approximately 0.05 parts by weight or less, per 100 parts by weight of the acrylic polymer. The crosslinking reaction rate can be adjusted by using an appropriate amount of catalyst. Furthermore, limiting the amount of catalyst used can suppress catalyst-induced contamination of the adherend.

[0076] (Other ingredients) Furthermore, the pressure-sensitive adhesive layer composition used to form the pressure-sensitive adhesive layer may optionally contain a compound that undergoes keto-enol tautomerization as a crosslinking retarder. For example, a compound that undergoes keto-enol tautomerization may be preferably used in a pressure-sensitive adhesive composition containing an isocyanate-based crosslinking agent. This may result in an effect of extending the pot life of the pressure-sensitive adhesive composition. Various β-dicarbonyl compounds may be used as the compound that undergoes keto-enol tautomerization. Specific examples include β-diketones such as acetylacetone and 2,4-hexanedione; acetoacetate esters such as methyl acetoacetate and ethyl acetoacetate; propionyl acetate esters such as ethyl propionyl acetate; isobutyryl acetate esters such as ethyl isobutyryl acetate; and malonate esters such as methyl malonate and ethyl malonate. Among these, acetylacetone and acetoacetate esters are particularly preferred. The compounds that undergo keto-enol tautomerization may be used alone or in combination of two or more.

[0077] The amount of the compound that undergoes keto-enol tautomerization used may be, for example, 1 part by weight or more, suitably 5 parts by weight or more, and may be, for example, 15 parts by weight or more, relative to 100 parts by weight of the acrylic polymer contained in the PSA composition. In some embodiments, from the viewpoint of obtaining a sufficient pot life, the amount of the compound that undergoes keto-enol tautomerization used may be, for example, 30 parts by weight or more, 60 parts by weight or more, or even 120 parts by weight or more, relative to 100 parts by weight of the acrylic polymer contained in the PSA composition. Furthermore, the amount may be, for example, 200 parts by weight or less, suitably 180 parts by weight or less, and may be, for example, 160 parts by weight or less, or may be 140 parts by weight or less.

[0078] The pressure-sensitive adhesive layer may further contain various conventional additives as needed. Examples of such additives include surface lubricants, leveling agents, tackifying resins, release modifiers (such as surfactants), plasticizers, softeners, fillers, colorants (such as pigments and dyes), antistatic agents, antioxidants, preservatives, light stabilizers, UV absorbers, polymerization inhibitors, and silane coupling agents. The content of these optional additives may be appropriately determined depending on the intended use. The amount of the optional additives used is, for example, less than 10 parts by weight, preferably approximately 3 parts by weight or less, per 100 parts by weight of the acrylic polymer. In some preferred embodiments, the amount is approximately 1 part by weight or less (e.g., less than 1 part by weight), even 0.5 parts by weight or less, 0.3 parts by weight or less, or even 0.1 parts by weight or less (e.g., less than 0.1 parts by weight). Limiting the amount of optional additives (e.g., low-molecular-weight components such as release modifiers and antistatic agents) can prevent contamination of the adherend caused by the optional additives. From a similar viewpoint, the proportion of the acrylic polymer in the adhesive layer is suitably 80% by weight or more, preferably 85% by weight or more, more preferably 90% by weight or more (for example, 90% by weight or more and 99.9% by weight or less), and may be 95% by weight or more.

[0079] (Method for forming pressure-sensitive adhesive layer) The form of the PSA composition used to form the PSA layer is not particularly limited, and preferred are aqueous PSA compositions, solvent-based PSA compositions, and the like. Here, the term "aqueous PSA composition" refers to a PSA composition containing a PSA (a PSA layer-forming component) in a solvent (aqueous solvent) primarily composed of water. A typical example is a water-dispersed PSA composition in which the PSA is dispersed in water. Furthermore, the term "solvent-based PSA composition" refers to a PSA composition containing a PSA in an organic solvent. The organic solvent contained in the solvent-based PSA composition can be one or more of the organic solvents (e.g., toluene and ethyl acetate) that can be used in the solution polymerization described above, without particular limitation. From the viewpoint of adhesive properties, etc., the technology disclosed herein can be preferably implemented in an embodiment in which a PSA layer is formed from a solvent-based PSA composition. In an embodiment in which a solvent-based PSA layer is formed from a solvent-based PSA composition, the effects of the technology disclosed herein are preferably realized.

[0080] Formation of a pressure-sensitive adhesive (layer) from a pressure-sensitive adhesive composition can be carried out by a conventionally known method. For example, in the case of a substrate-less double-sided pressure-sensitive adhesive sheet, a pressure-sensitive adhesive composition can be applied to a surface (release surface) having releasability, and then the pressure-sensitive adhesive composition is cured to form a pressure-sensitive adhesive layer (a layer made of a pressure-sensitive adhesive) on the surface, thereby forming a pressure-sensitive adhesive sheet. In the case of a pressure-sensitive adhesive sheet with a substrate, a method (direct method) in which a pressure-sensitive adhesive composition is directly applied (typically coated) to the substrate and cured to form a pressure-sensitive adhesive layer can be preferably employed. Alternatively, a method (transfer method) in which a pressure-sensitive adhesive composition is applied to a surface (release surface) having releasability and cured to form a pressure-sensitive adhesive layer on the surface, and then the pressure-sensitive adhesive layer can be transferred to the substrate. The release surface can be the surface of a release sheet, the back surface of a release-treated substrate, or the like. The pressure-sensitive adhesive composition can be cured by subjecting the pressure-sensitive adhesive composition to a curing treatment such as drying, crosslinking, polymerization, or cooling. Two or more curing treatments can be carried out simultaneously or in stages.

[0081] The pressure-sensitive adhesive composition can be applied using a known or commonly used coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a die coater, a bar coater, a knife coater, a spray coater, etc. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation, curtain coating, or the like. From the viewpoints of promoting the crosslinking reaction, improving production efficiency, etc., the pressure-sensitive adhesive composition is preferably dried under heating. The drying temperature can be, for example, about 40 to 150° C., and is usually preferably about 60 to 130° C. After drying the pressure-sensitive adhesive composition, aging may be further carried out 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 substrate or pressure-sensitive adhesive layer, etc.

[0082] (Thickness) Although not particularly limited, the thickness of the pressure-sensitive adhesive layer is, for example, approximately 1 μm or more, and preferably approximately 3 μm or more (for example, approximately 5 μm or more). From the viewpoint of adhesion to the adherend, the thickness is preferably approximately 10 μm or more, more preferably approximately 14 μm or more, and even more preferably approximately 17 μm or more. The thickness can be, for example, approximately 100 μm or less, and is suitably approximately 50 μm or less (for example, approximately 30 μm or less), preferably approximately 25 μm or less. A pressure-sensitive adhesive layer having the above thickness is suitable as a pressure-sensitive adhesive layer for surface protection films.

[0083] (gel fraction) Although not particularly limited, the gel fraction of the pressure-sensitive adhesive layer is preferably 70% or more. A pressure-sensitive adhesive with a gel fraction of 70% or more is less likely to suffer deformation or damage, such as dents, due to external forces, for example, during production, and is less likely to undergo changes in appearance. Such a pressure-sensitive adhesive is likely to form a pressure-sensitive adhesive sheet with a smooth surface, and is preferable because it enables high-precision inspection, for example, when forming a transparent pressure-sensitive adhesive sheet and inspecting an adherend through the pressure-sensitive adhesive sheet. Furthermore, setting the gel fraction high makes it easier to form a pressure-sensitive adhesive with excellent removability. From this perspective, the gel fraction is more preferably greater than 80%, and may be greater than 85% (e.g., 90% or more), 92% or more, or 94% or more (e.g., 95% or more). The gel fraction may be 100%, but from the viewpoint of adhesion to an adherend, it may be, for example, less than 99% or less than 95% (e.g., 94% or less).

[0084] The gel fraction of the adhesive layer is measured using the following method. W1g of the adhesive layer is removed and wrapped in a porous PTFE (polytetrafluoroethylene) sheet to create a sample. The sample is placed in a glass bottle, immersed in an ethyl acetate solution, and left to stand for 7 days, after which the sample is removed and dried at 130°C for 2 hours. The dried sample is weighed, and the weight of the porous PTFE sheet is subtracted from this to determine the dried weight of the adhesive, W2g. W1 and W2 are substituted into the following formula to calculate the gel fraction [%]. Gel fraction [%] = (W2 / W1) × 100 As the porous PTFE sheet, a product under the trade name "TEMISH" manufactured by Nitto Denko Corporation or an equivalent product can be used.

[0085] (biomass carbon ratio) In some embodiments, the PSA layer contains a biomass-derived material, and the biomass carbon ratio thereof may be equal to or greater than a predetermined value. The biomass carbon ratio of the PSA layer is, for example, 1% or greater, and may be 10% or greater, preferably 30% or greater, and more preferably 50% or greater. A high biomass carbon ratio in a PSA means that the amount of fossil resource-based materials, such as petroleum, used is reduced. From this perspective, a higher biomass carbon ratio in a PSA is preferable. For example, the biomass carbon ratio of the PSA layer may be 55% or greater, 60% or greater, 70% or greater, 75% or greater, 80% or greater, or even greater than 80%. The upper limit of the biomass carbon ratio is 100% by definition, but may be 99% or less. From the perspective of material availability, it may be 95% or less or 90% or less. From the perspective of easily exhibiting good adhesive performance, in some embodiments, the biomass carbon ratio of the PSA layer may be, for example, 90% or less, 85% or less, or 80% or less.

[0086] <Base material> The material of the support substrate used as the support for the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and for example, a resin film can be preferably used. The resin film can be formed from various resin materials into a film shape. The resin material is preferably one that can form a resin film excellent in one or more of the following properties: transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, etc. For example, a resin film composed of a resin material whose main component (i.e., a component contained in more than 50 wt%) is polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate; celluloses such as diacetyl cellulose and triacetyl cellulose; polycarbonates; acrylic polymers such as polymethyl methacrylate; etc. can be preferably used as the substrate. Other examples of resin materials constituting the resin film include those primarily composed of styrene-based polymers such as polystyrene and acrylonitrile-styrene copolymer; polyolefins such as polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, and ethylene-propylene copolymer; polyvinyl chlorides; and polyamides such as nylon 6, nylon 6,6, and aromatic polyamides. Alternatively, a resin film composed of a resin material primarily composed of polyimides, polysulfones, polyethersulfones, polyetheretherketones, polyphenylene sulfides, fluorine-based resins, polyvinyl alcohols, polyvinyl acetates, polyvinylidene chlorides, polyvinyl butyrals, polyarylates, polyoxymethylenes, epoxy resins, etc. may be used as the substrate. The resin material constituting the resin film may be a blend of two or more of these materials.

[0087] In this specification, the term "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, nonwoven fabrics, and woven fabrics.

[0088] Other examples of substrates include foam sheets made of foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; woven and nonwoven fabrics made by spinning various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, and semi-synthetic fibers such as acetate), either alone or in combination; papers such as Japanese paper, fine paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; and glass. Substrates having a composite structure of these materials may also be used. Examples of substrates with such composite structures include substrates having a structure in which metal foil and the above-mentioned plastic film are laminated together, and plastic sheets reinforced with inorganic fibers such as glass cloth.

[0089] The substrate may be formed from a biomass-derived material or a non-biomass-derived material. From the viewpoint of producing a PSA sheet that takes into consideration reduced dependence on fossil resource-based materials, a biomass-derived substrate material (typically a resin film) is preferably used.

[0090] The substrate may also be formed using a recyclable material or a recycled material (also referred to as a recycled material). Resin films are preferably used as such recycled materials. Resin films (for example, polyester films such as PET films) are recyclable, so regardless of whether plant-derived materials are used, by reusing used resin films, sustainable reproduction is possible and the environmental burden can be reduced. Such recyclable resin films or recycled resin films are also referred to as recycled films. The recycled materials (for example, recycled films) may be formed from biomass-derived materials or non-biomass-derived materials.

[0091] In some preferred embodiments, the substrate is a resin film (polyester resin film) formed from a resin (polyester resin) containing polyester as the main component (a component contained in an amount of more than 50% by weight). For example, a resin film in which the polyester is primarily PET (PET film) or a resin film in which the polyester is primarily PEN (PEN film) can be preferably used.

[0092] The substrate may have a single layer structure or a multilayer structure. Therefore, the resin film that can be used as the substrate may also have a single layer structure or a multilayer structure of two or more layers (for example, a three-layer structure). A resin film with a single layer structure can be preferably used as the substrate.

[0093] The substrate (typically a resin film) may contain various additives, such as antioxidants, antiaging agents, heat stabilizers, light stabilizers, ultraviolet absorbers, antistatic components, plasticizers, colorants (pigments, dyes, etc.), and fillers, as needed.

[0094] The surface of the substrate facing the pressure-sensitive adhesive layer may be subjected to a surface treatment such as chromate treatment, ozone exposure, flame exposure, high-voltage shock exposure, or ionizing radiation treatment. Such a surface treatment may be, for example, a treatment to enhance adhesion between the substrate and the pressure-sensitive adhesive layer. In some embodiments, the surface of the substrate facing the pressure-sensitive adhesive layer may be subjected to a primer treatment. In some embodiments, the back surface of the substrate may be subjected to a hard coat treatment. This improves the scratch resistance of the back surface of the substrate, and when the pressure-sensitive adhesive sheet is used as a protective sheet, it may exhibit better protective performance. In other embodiments, the substrate may be subjected to an antistatic treatment to suppress the generation of static electricity. The substrate may also be subjected to various treatments such as antifouling, antifingerprint, antiglare, and antireflection.

[0095] The thickness of the substrate can be appropriately selected taking into consideration the use, purpose, and usage form of the pressure-sensitive adhesive sheet. From the viewpoint of workability such as strength and handleability, a substrate having a thickness of approximately 10 μm or more is appropriate, and this thickness is preferably approximately 20 μm or more, and more preferably approximately 30 μm or more (e.g., 35 μm or more). Furthermore, from the viewpoint of cost, etc., the thickness of the substrate is appropriately approximately 200 μm or less, preferably approximately 150 μm or less, more preferably approximately 100 μm or less, and even more preferably approximately 75 μm or less (e.g., 50 μm or less). Substrates having the above thickness are suitable as substrates for surface protection films, for example.

[0096] <Release sheet> The release sheet used in the release-sheeted PSA sheet disclosed herein is a non-silicone release sheet. Non-silicone release sheets are used to protect the adhesive surface of PSA sheets before use during distribution, storage, processing, etc., in applications where the use of silicone-based release sheets is undesirable, and can also be used to form PSA layers and produce PSA sheets. In this specification, "release sheet" is also referred to as a release sheet, and includes what are called release films and release liners. Furthermore, "non-silicone release sheet" refers to a release sheet in which at least the surface (release surface) facing the PSA sheet is made of a material that does not contain a silicone material. For example, the entire release sheet may be made of a material that does not contain a silicone material. Examples of non-silicone release sheets include release sheets having a release treatment layer formed with a release treatment agent other than a silicone material (non-silicone release treatment agent).

[0097] Examples of non-silicone release sheets that can be used include release sheets having a release-treated layer on the surface of a substrate such as a resin film or paper, fluorine-based release sheets having a single-layer or multi-layer structure made from a fluorine-based polymer (polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, chlorofluoroethylene-vinylidene fluoride copolymer, etc.), and polyolefin-based release sheets having a single-layer or multi-layer structure made from a polyolefin-based resin (polyethylene, polypropylene, etc.).

[0098] In some embodiments, the non-silicone release sheet has a release sheet substrate and a non-silicone release treatment layer provided on at least one surface of the release sheet substrate. Here, "release sheet substrate" refers to the substrate used to form the release sheet, i.e., the release sheet substrate, and is used for the purpose of distinguishing it from the aforementioned PSA sheet substrate, but is not otherwise particularly limited. Various plastic films can be used as the release sheet substrate. In this specification, the term "plastic film" typically refers to a non-porous sheet, and is a concept that is distinguished from, for example, nonwoven fabric (i.e., does not include nonwoven fabric). As the substrate, a resin film with a non-porous structure that is typically substantially bubble-free (void-free) can be preferably used. The resin film may have a single-layer structure or a multi-layer structure of two or more layers (e.g., a three-layer structure).

[0099] Examples of materials for the plastic film include polyolefin resins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); polyvinyl chloride resins; polyvinylidene chloride resins; polyvinyl alcohol resins; ethylene-vinyl acetate copolymer resins; ethylene-vinyl alcohol copolymer resins; cellulose resins such as triacetyl cellulose; acetate resins; polycarbonate resins; and polyamide resins. Release sheet substrates formed from one or a mixture of two or more of these resins may also be used. Among these, a preferred release sheet substrate is a polyester resin film (e.g., a PET film) formed from a polyester resin. As with the substrate of the pressure-sensitive adhesive sheet, those formed from biomass-derived materials and recycled materials (e.g., recycled films) may be preferably used as the release sheet substrate.

[0100] The plastic film used as the release sheet substrate may be any of an unstretched film, a uniaxially stretched film, and a biaxially stretched film. The plastic film may have a single-layer structure or a multilayer structure including two or more sublayers. The plastic film may contain known additives that can be used in substrates, such as antioxidants, antiaging agents, heat stabilizers, light stabilizers, UV absorbers, colorants such as pigments and dyes, lubricants, fillers, plasticizers, antistatic agents, slip agents, antiblocking agents, and nucleating agents. In a multilayer plastic film, each additive may be contained in all or only some of the sublayers.

[0101] In some embodiments, the non-silicone release treatment layer disposed on the release sheet substrate is a release treatment layer that does not contain a silicone material, and may be, for example, a release treatment layer formed from a non-silicone release treatment agent such as a long-chain alkyl release treatment agent, an aliphatic carboxylic acid ester release treatment agent, a fluorine-based release treatment agent, or a molybdenum sulfide release treatment agent. Although not particularly limited, a release treatment layer formed from at least one selected from a long-chain alkyl release treatment agent and an aliphatic carboxylic acid ester release treatment agent is preferred as the non-silicone release treatment layer, as it is easy to form a release treatment layer that is free of coating unevenness and whitening. Of these, a release treatment layer formed from a material containing a long-chain alkyl release treatment agent is particularly preferred, as it is easy to obtain excellent light releasability.

[0102] The long-chain alkyl-based release treatment agent used contains a long-chain alkyl group-containing compound having a linear or branched alkyl group with 6 or more carbon atoms. The carbon number of the alkyl group in the long-chain alkyl group-containing compound is preferably 8 or more, more preferably 12 or more. Examples of the alkyl group include octyl, decyl, lauryl, octadecyl, and behenyl. Examples of the long-chain alkyl group-containing compound include various long-chain alkyl group-containing polymeric compounds, long-chain alkyl group-containing amine compounds, long-chain alkyl group-containing ether compounds, and long-chain alkyl group-containing quaternary ammonium salts. From the viewpoints of heat resistance and stain resistance, long-chain alkyl group-containing polymeric compounds are preferred. Furthermore, from the viewpoint of effectively achieving water repellency with a small amount of use, polymeric compounds having a long-chain alkyl group in the side chain are more preferred. The long-chain alkyl group-containing compounds can be used alone or in combination of two or more.

[0103] Examples of polymeric compounds having a long-chain alkyl group in the side chain include acrylic polymers obtained by polymerizing a monomer component containing an alkyl(meth)acrylate having an alkyl group with 6 or more carbon atoms, and polymers obtained by reacting a polymer having a reactive group with an alkyl group-containing compound capable of reacting with the reactive group. Examples of the reactive group include a hydroxyl group, an amino group, a carboxyl group, and an acid anhydride. Examples of compounds having these reactive groups include polyvinyl alcohol, butyral resin, ethylene-vinyl alcohol resin, polyethyleneimine, polyethyleneamine, reactive group-containing polyester resin, and reactive group-containing poly(meth)acrylic resin. Among these, acrylic polymers, polyvinyl alcohol, butyral resin, and ethylene-vinyl alcohol resin are preferred from the viewpoints of easy releasability and ease of handling.

[0104] Examples of alkyl group-containing compounds reactive with the reactive group and used in the reaction with the polymer having the reactive group include long-chain alkyl group-containing isocyanates such as octyl isocyanate, decyl isocyanate, lauryl isocyanate, octadecyl isocyanate, and behenyl isocyanate; long-chain alkyl group-containing acid chlorides such as octyl chloride, decyl chloride, lauryl chloride, octadecyl chloride, and behenyl chloride; long-chain alkyl group-containing amines; long-chain alkyl group-containing alcohols; etc. Among these, from the viewpoints of easy releasability and handleability, long-chain alkyl group-containing isocyanates are preferred, and octadecyl isocyanate is particularly preferred.

[0105] The amount of the alkyl group-containing compound capable of reacting with the reactive group is preferably an appropriate amount that achieves the desired releasability and does not transfer to the adhesive surface, thereby preventing contamination of the adherend. While not particularly limited, it is appropriate to react 100 parts by weight or more (e.g., 200 parts by weight or more, or even 300 parts by weight or more) of the alkyl group-containing compound with 100 parts by weight of the polymer having the reactive group. Furthermore, it is appropriate to use 1000 parts by weight or less (e.g., 800 parts by weight or less, or even 700 parts by weight or less) of the alkyl group-containing compound with 100 parts by weight of the polymer having the reactive group.

[0106] The aliphatic carboxylic acid ester that can be contained in the release treatment agent is obtained by reacting an aliphatic carboxylic acid with an alcohol. The aliphatic carboxylic acid component is preferably a mono- or dicarboxylic acid having 6 to 36 carbon atoms, more preferably a saturated aliphatic monocarboxylic acid having 6 to 36 carbon atoms. Specific examples of the aliphatic carboxylic acid include palmitic acid, stearic acid, valeric acid, caproic acid, capric acid, lauric acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, melissic acid, tetraacontanoic acid, montanic acid, glutaric acid, adipic acid, and azelaic acid. The aliphatic carboxylic acid can be used alone or in combination of two or more. Examples of the alcohol used to produce the aliphatic carboxylic acid ester include saturated or unsaturated monohydric or polyhydric alcohols. The alcohol may have a substituent such as a fluorine atom or an aryl group. For example, saturated alcohols having 30 or less carbon atoms are preferred, and saturated aliphatic alcohols having 30 or less carbon atoms are more preferred. The aliphatic alcohols include alicyclic alcohols. Specific examples of the alcohol include octanol, decanol, dodecanol, stearyl alcohol, behenyl alcohol, ethylene glycol, diethylene glycol, glycerin, pentaerythritol, 2,2-dihydroxyperfluoropropanol, neopentylene glycol, ditrimethylolpropane, dipentaerythritol, etc. The alcohols can be used alone or in combination of two or more.

[0107] Specific examples of the aliphatic carboxylic acid ester include beeswax (a mixture containing myricyl palmitate as a main component), stearyl stearate, behenyl behenate, octyldodecyl behenate, glycerin monopalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, pentaerythritol tetrastearate, etc. The aliphatic carboxylic acid esters can be used alone or in combination of two or more.

[0108] Although not particularly limited, the non-silicone release treatment layer typically contains 70% by weight or more of a release treatment agent such as the long-chain alkyl group-containing compound or aliphatic carboxylic acid ester, and the content of the release treatment agent in the release treatment layer may be 80% by weight or more, or even 90% by weight or more. The upper limit of the content of the release treatment agent may be, for example, 99% by weight or less.

[0109] The release treatment layer may optionally contain known additives such as antistatic agents, colorants, surfactants, plasticizers, tackifiers, low molecular weight polymers, surface lubricants, leveling agents, antioxidants, corrosion inhibitors, light stabilizers, ultraviolet absorbers, polymerization inhibitors, and fillers.

[0110] Non-silicone release sheets can be produced by known methods, or commercially available non-silicone release sheets may be obtained and used. For example, a release sheet having a non-silicone release treatment layer on a release sheet substrate can be produced by applying a solution containing a non-silicone release treatment agent (release treatment agent composition) to the surface of the release sheet substrate using an appropriate coater (such as a gravure roll coater), removing the solvent by drying or the like, and then appropriately curing the film.

[0111] The thickness of the release treatment layer is not particularly limited and is set to an appropriate thickness that provides the desired releasability. The thickness of the release treatment layer is, for example, 1 nm or more, preferably 5 nm or more, more preferably 10 nm or more, and is, for example, about 200 nm or less, preferably 100 nm or less, and may be 50 nm or less.

[0112] The thickness of the entire release sheet is not particularly limited, and from the viewpoint of the strength and dimensional stability of the release sheet, it is suitably 5 μm or more, preferably 10 μm or more, and may be 20 μm or more. By protecting the adhesive surface with a release sheet of sufficient thickness, the smoothness of the adhesive surface is likely to be maintained. Furthermore, from the viewpoint of the handleability of the release sheet (e.g., ease of rolling), the thickness of the release sheet is suitably 300 μm or less, preferably 200 μm or less, more preferably 100 μm or less, and may be 75 μm or less, 50 μm or less, or 35 μm or less. By keeping the thickness of the release sheet at a predetermined value or less, peeling from the adhesive sheet is likely to be smooth.

[0113] <Adhesive sheet characteristics> The release sheet-attached PSA sheet disclosed herein exhibits a release force (release sheet peeling force) when peeling the non-silicone release sheet of the release sheet from the surface of the PSA layer of the PSA sheet, which is comparable to that of a silicone release sheet. While not particularly limited, in some embodiments, the release sheet peeling force is, for example, less than 0.50 N / 50 mm, suitably 0.30 N / 50 mm or less, and may be 0.20 N / 50 mm or less, or even 0.10 N / 50 mm or less. The lower the release sheet peeling force, the more easily the PSA sheet can be peeled. In some preferred embodiments, the release sheet peeling force is less than 0.07 N / 50 mm, more preferably 0.05 N / 50 mm or less, and may be 0.04 N / 50 mm or less, 0.03 N / 50 mm or less, or 0.02 N / 50 mm or less. The technology disclosed herein makes it possible to achieve the above-described easy releasability for non-silicone release sheets. The lower limit of the release sheet peel strength may be, for example, 0.01 N / 50 mm or more. When the release sheet peel strength is equal to or greater than a predetermined value, the adhesive surface can be well protected by the release sheet. The release sheet peel strength is measured under conditions of 23°C, 50% RH, a pulling speed of 0.3 m / min, and a peel angle of 180°. Specifically, it is measured by the method described in the Examples below.

[0114] The adhesive strength of the pressure-sensitive adhesive sheet is not limited to a specific range, as it can be appropriately set depending on the intended use and the application site. In some embodiments, the adhesive sheet (preferably a surface protective film) preferably has an adhesive strength to a glass plate (initial adhesive strength to glass) of 2.0 N / 25 mm or less, measured under conditions of a temperature of 23°C, 50% RH, a peel angle of 180°, and a tensile speed of 0.3 m / min. A pressure-sensitive adhesive sheet (preferably a surface protective film) satisfying these characteristics exhibits a low peel force when peeled from an adherend (e.g., an object to be protected), and is therefore easy to peel. From the viewpoint of peeling workability, the initial adhesive strength to glass is more preferably 1.0 N / 25 mm or less, even more preferably 0.5 N / 25 mm or less, and particularly preferably 0.1 N / 25 mm or less (e.g., less than 0.1 N / 25 mm). From the viewpoint of adhesion to the adherend and protection of the adherend, the initial adhesive strength to glass is suitably 0.01 N / 25 mm or more, may be 0.03 N / 25 mm or more, or may be 0.05 N / 25 mm or more. Specifically, the initial adhesive strength to glass is measured by the method described in the examples below.

[0115] In some embodiments, the pressure-sensitive adhesive sheet preferably has transparency with a total light transmittance of approximately 50% or more. A transparent pressure-sensitive adhesive sheet having a total light transmittance of 80% or more (e.g., 85% or more) is more preferred. The upper limit of the total light transmittance may be approximately 99% or less (e.g., 95% or less) in applications requiring transparency. Pressure-sensitive adhesive sheets with such transparency are preferred because they enable high-precision inspection, for example, when inspecting adherends through the pressure-sensitive adhesive sheet. Such pressure-sensitive adhesive sheets are suitable as optical surface protection films. The total light transmittance value can be a value measured in accordance with JIS K 7361-1.

[0116] <Application> The pressure-sensitive adhesive sheets disclosed herein can be used for a variety of applications. The pressure-sensitive adhesive sheets disclosed herein are suitable, for example, as surface protection films that are attached to an object to be protected and then typically peeled off (removed) from the object once their protective purpose has been achieved. Surface protection films are typically required to prevent deterioration of the object before and after protection. Therefore, the use of non-silicone pressure-sensitive adhesive sheets with release sheets that do not cause contamination of the surface of the object to be protected by silicone materials after peeling and removal can be advantageous. The object to be protected by the surface protection film is not particularly limited, and the film can be used as a protective film for various products, components, and the like. Furthermore, the non-silicone pressure-sensitive adhesive sheets with release sheets disclosed herein do not contaminate the adherend with silicone materials, making them particularly suitable for optical applications requiring specific optical properties. For example, the pressure-sensitive adhesive sheets disclosed herein are particularly suitable as optical surface protection films that protect the surface of optical components (e.g., optical components used as components of liquid crystal display panels, such as polarizing plates and wavelength plates) during processing and transportation of the optical components. More specifically, the surface protective film is suitable for use in protecting optical members used as components of liquid crystal display panels, plasma display panels (PDPs), organic electroluminescence (EL) displays, etc., during production, transportation, etc. In particular, the surface protective film is useful as a surface protective film applied to optical members such as polarizing plates (polarizing films, for example, reflective polarizing films) for liquid crystal display panels, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light diffusion sheets, and reflective sheets.

[0117] Furthermore, in some embodiments, the PSA disclosed herein may contain an acrylic polymer with a high biomass carbon ratio, and therefore may be used as a substitute for conventional, general acrylic PSAs (i.e., acrylic PSAs with a low biomass carbon ratio) in a variety of applications where such acrylic PSAs are used, thereby contributing to reducing dependency on fossil resource-based materials. The PSA sheet disclosed herein may typically be preferably used as a PSA sheet (e.g., a surface protection film) with reduced dependency on fossil resource-based materials.

[0118] The matters disclosed by this specification include the following: [1] A pressure-sensitive adhesive sheet with a release sheet, comprising a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer and a non-silicone release sheet disposed on the surface of the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer contains an acrylic polymer, The acrylic polymer is a polymer of a monomer component containing an alkyl (meth)acrylate (m1) having an alkyl group having 6 to 17 carbon atoms at the ester terminal, wherein the alkyl group having 6 to 17 carbon atoms is a linear alkyl group or a branched alkyl group having one branch carbon atom. [2] The pressure-sensitive adhesive sheet with a release sheet according to the above [1], wherein the alkyl (meth)acrylate (m1) comprises at least one selected from n-heptyl acrylate and n-octyl acrylate. [3] The pressure-sensitive adhesive sheet with a release sheet according to [1] or [2] above, wherein the monomer component includes a monomer (m2) having a hydroxyl group. [4] The pressure-sensitive adhesive sheet with a release sheet according to any one of the above [1] to [3], wherein the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent. [5] The pressure-sensitive adhesive sheet with a release sheet according to any one of the above [1] to [4], wherein the pressure-sensitive adhesive layer contains a zirconium-containing compound. [6] The non-silicone release sheet has a release sheet substrate and a non-silicone release treatment layer provided on at least one surface of the release sheet substrate, The pressure-sensitive adhesive sheet with a release sheet according to any one of [1] to [5] above, wherein the non-silicone release treatment layer is formed from a material containing a long-chain alkyl release treatment agent. [7] The pressure-sensitive adhesive sheet with a release sheet according to any one of [1] to [6] above, which comprises a substrate and the pressure-sensitive adhesive layer disposed on at least one surface of the substrate. [8] The pressure-sensitive adhesive sheet with a release sheet according to any one of [1] to [7] above, wherein the pressure-sensitive adhesive sheet is used by being attached to an optical member. [9] The pressure-sensitive adhesive sheet with a release sheet according to any one of the above [1] to [8], wherein the pressure-sensitive adhesive sheet is used as a surface protection film. [Example]

[0119] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" are by weight unless otherwise specified.

[0120] <Preparation Example> (Preparation of Acrylic Polymer (A1)) A flask equipped with a reflux condenser, stirrer, nitrogen gas inlet tube, and thermometer was charged with 96 parts of n-heptyl acrylate (HpA) and 4 parts of 4-hydroxybutyl acrylate (4HBA) as monomer components, and ethyl acetate (polymerization solvent) to a solids concentration of 36%. 0.3 parts of azobisisobutyronitrile (AIBN) was then added as a polymerization initiator. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 60°C for 4 hours to carry out the polymerization reaction. The mixture was then aged at 70°C for 4 hours to obtain a solution of acrylic polymer (A1). The weight-average molecular weight (Mw) of the resulting acrylic polymer (A1) was 760,000. Note that HpA was synthesized using biomass-derived heptyl alcohol and is a compound with a biomass-derived heptyl group at the ester end.

[0121] (Preparation of Acrylic Polymer (A2)) A flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet tube, and a thermometer was charged with 96 parts of n-lauryl acrylate (LA) and 4 parts of 4HBA as monomer components, and ethyl acetate (polymerization solvent) so that the solids concentration was 30%, and then 0.2 parts of AIBN was added as a polymerization initiator. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 60°C, allowing the polymerization reaction to proceed for 5 hours, and then the mixture was aged at 70°C for 2 hours, yielding a solution of acrylic polymer (A2). The Mw of the resulting acrylic polymer (A2) was 570,000.

[0122] (Preparation of Acrylic Polymer (A3)) A solution of acrylic polymer (A3) was obtained in the same manner as in the preparation of acrylic polymer (A2), except that n-octyl acrylate (n-OcA) was used instead of LA as the monomer component. The Mw of the obtained acrylic polymer (A3) was 800,000.

[0123] (Preparation of acrylic polymer (A4)) A solution of acrylic polymer (A4) was obtained in the same manner as in the preparation of acrylic polymer (A1), except that 2-ethylhexyl acrylate (2EHA) was used instead of HpA as the monomer component. The Mw of the obtained acrylic polymer (A4) was 410,000.

[0124] (Preparation of Acrylic Polymer (A5)) A flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet tube, and a thermometer was charged with 96 parts of n-pentyl acrylate (n-PnA) and 4 parts of 4HBA as monomer components, and ethyl acetate (polymerization solvent) so that the solids concentration was 30%, and then 0.2 parts of AIBN was added as a polymerization initiator. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 60°C, allowing the polymerization reaction to proceed for 6 hours. The mixture was then aged at 70°C for 2 hours, yielding a solution of acrylic polymer (A5). The Mw of the resulting acrylic polymer (A5) was 770,000.

[0125] (Preparation of acrylic polymer (A6)) A solution of acrylic polymer (A6) was obtained in the same manner as in the preparation of acrylic polymer (A2), except that isostearyl acrylate (i-StA) was used instead of LA as the monomer component. The Mw of the obtained acrylic polymer (A6) was 49,000.

[0126] Example 1 (Preparation of Pressure-Sensitive Adhesive Composition) The solution of acrylic polymer (A1) obtained above was diluted with ethyl acetate to a solids concentration of 30%, and to this solution, 3.5 parts (solids) of an isocyanate crosslinking agent (trade name "Coronate HX", an isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh Corporation) and 0.035 parts (solids) of a zirconium catalyst (trade name "ZC-150", zirconium tetraacetylacetonate, manufactured by Matsumoto Fine Chemical Co., Ltd.) were added relative to 100 parts of the solids of the solution, and acetylacetone was further added so that the amount was 8% of the diluted polymer solution, followed by stirring, to obtain an acrylic pressure-sensitive adhesive composition according to this example.

[0127] (Preparation of adhesive sheet) The acrylic pressure-sensitive adhesive composition immediately after blending was applied to a polyethylene terephthalate (PET) film (Mitsubishi Chemical Corporation, product name "Diafoil T100C38", thickness 38 μm) and dried at 130°C for 20 seconds to remove the solvent, forming a pressure-sensitive adhesive layer (thickness 21 μm). The surface of the pressure-sensitive adhesive layer was then covered with a non-silicone release sheet (Mitsubishi Chemical Corporation, product name "Diafoil T100H25[UH18]", thickness 25 μm) and left to stand at room temperature (23°C) for 4 days to obtain a pressure-sensitive adhesive sheet with release sheet according to this example. The non-silicone release sheet has a release treatment layer formed on the surface of a polyester film substrate using a release treatment agent containing a pentaerythritol fatty acid ester and octadecyl isocyanate.

[0128] <Examples 2 to 12 and Comparative Examples 1 to 6> The adhesive sheets with release sheets for each example were obtained in the same manner as in Example 1, except that the type of acrylic polymer, the amount of crosslinking agent used (solid content), the type and amount of catalyst used (solid content), and the type of release sheet were changed as shown in Table 1. In the examples using a tin catalyst, dioctyltin dilaurate (manufactured by Tokyo Fine Chemical Co., Ltd., product name "Envirizer OL-1") was used as the tin catalyst in an amount of 0.015 parts (solid content) per 100 parts solid content of the acrylic polymer solution, and acetylacetone was added so that the amount was 3% of the polymer solution after dilution. The silicone-based release sheet used was prepared by the following method. 3.3 parts of a silicone curing catalyst (CAT-PL-50T, manufactured by Shin-Etsu Chemical Co., Ltd.) was added to 100 parts of a silicone-based release agent (KS-847T, manufactured by Shin-Etsu Chemical Co., Ltd.) and diluted to a concentration of 0.3% with a mixed solvent containing toluene, normal hexane, and methyl ethyl ketone in a weight ratio of 1:2:1 to obtain a silicone-based release treatment composition. This release treatment composition was applied to a 25 μm-thick polyester film (Diafoil T100-25, manufactured by Mitsubishi Chemical Corporation) and dried at 130°C for 1 minute to produce a silicone-based release sheet having a silicone-based release treatment layer on the polyester film with a dry thickness of 20 nm.

[0129] (Initial adhesive strength to glass) The adhesive sheet was cut to a size of 25 mm wide and 80 mm long and pressed against a clean soda glass plate, which had been cleaned by rubbing it back and forth 10 times with an ethanol-soaked clean cloth, using a 2 kg roller to roll it back and forth once to prepare a sample for adhesive strength evaluation. After leaving the evaluation sample at room temperature for 30 minutes, the adhesive strength [N / 25 mm] was measured at 23°C and 50% RH using a tensile tester (Shimadzu Corporation, product name "Autograph AG-50NX") at a peel angle of 180° and a pulling speed of 0.3 m / min. For each example, measurements were performed twice (n = 2), and the average value was used as the initial adhesive strength to glass [N / 25 mm]. The glass plate used as the adherend was a soda glass plate manufactured by Matsunami Glass Co., Ltd. (product number "S200423") or an equivalent.

[0130] (pollution) After measuring the initial adhesive strength to the glass, the adherend surface (the surface of the glass plate from which the adhesive sheet had been removed) was visually observed under reflected fluorescent light in a dark room. If no change in the surface condition of the adherend was observed, it was judged to be pass.

[0131] (Release sheet peel strength) The adhesive sheet was cut to a size of 50 mm wide and 80 mm long, and the back of the adhesive sheet was fixed to an acrylic plate with double-sided tape (Nitto Denko Corporation, product name "No. 5000NS"). The release sheet was peeled from the adhesive surface of the adhesive sheet at a peel angle of 180° and a pulling speed of 0.3 m / min using a tensile tester (Shimadzu Corporation, product name "Autograph AG-50NX") at 23°C and 50% RH, and the peel force [N / 50 mm] was measured. For each example, measurements were performed twice (n=2), and the maximum value was recorded as the release sheet peel force [N / 50 mm].

[0132] (Water contact angle on glass surface after adhesive sheet is peeled off) The adhesive sheet was pressed against a glass slide using a 2 kg roller, rolling it back and forth once to prepare an evaluation sample. After leaving the evaluation sample at room temperature for 30 minutes, the adhesive sheet was peeled off from the glass slide at a constant angle and speed, and the water contact angle (°) of the glass slide surface was measured under an atmosphere of 23°C and 50% RH. The contact angle was measured using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name "CA-X") using the sessile drop method (θ / 2 method). The volume of the distilled water droplet was 2 μL, and the resting time from the time of contact to the time of measurement was 2000 ms. For each example, five measurements (n = 5) were performed, and the average value was used. The glass plate used as the adherend was a soda glass plate (product number "S1214") manufactured by Matsunami Glass Co., Ltd., or an equivalent.

[0133] Table 1 shows the outline of each example and the evaluation results.

[0134] [Table 1]

[0135] As shown in Table 1, when an adhesive containing an acrylic polymer synthesized using 2EHA (branched alkyl group with 8 carbon atoms, branched carbon atoms of 2) as the chain alkyl (meth)acrylate was used, in Comparative Example 1, which used a silicone-based release sheet, the release sheet peel force was low at 0.02 N / 50 mm, and the release sheet releasability was excellent, but in Comparative Example 2, which used a non-silicone-based release sheet, the release sheet peel force increased to 0.07 N / 50 mm, and a tendency for the release sheet releasability to decrease was observed. On the other hand, when HpA (a linear alkyl group with 7 carbon atoms) was used as the monomer component of the acrylic polymer contained in the adhesive, in Comparative Example 4, which used a silicone-based release sheet, the initial adhesive strength to glass was 0.06 N / 25 mm and the release sheet peel strength was 0.02 N / 50 mm, whereas in Example 1, which used a non-silicone release sheet, the initial adhesive strength to glass was 0.05 N / 25 mm and the release sheet peel strength was 0.03 N / 50 mm, confirming that even when a non-silicone release sheet was used, the release sheet releasability was comparable to that when a silicone-based release sheet was used. It was also confirmed that Examples 2 to 4, which used the same acrylic polymer as Example 1 but changed the amount of crosslinker used and the catalyst type, had good release sheet releasability.

[0136] Furthermore, good release sheet releasability was also confirmed in Examples 5 to 12, which used adhesives containing acrylic polymers synthesized using alkyl(meth)acrylates (specifically, LA, n-OcA) as monomer components, in which the alkyl group has a carbon number of 6 to 17 and the alkyl group is either a linear alkyl group or a branched alkyl group with a branch having a carbon number of 1. On the other hand, even if the alkyl group of the alkyl(meth)acrylate used as the monomer component is a linear alkyl group, when the alkyl group has a carbon number of 5 (Comparative Example 5: n-PnA was used), the release sheet peel force tended to be high and good release sheet releasability was not obtained. Furthermore, in Comparative Example 6, in which i-StA, in which an alkyl group with a carbon number of 18, was used as the linear alkyl(meth)acrylate, the viscosity was too low to form a pressure-sensitive adhesive layer with a uniform thickness, and evaluation of the pressure-sensitive adhesive sheet was not possible.

[0137] The water contact angle of the glass plate surface after peeling off the adhesive sheet was measured, and the results were 16° for Example 1, 41° for Comparative Example 1, 43° for Comparative Example 2, and 20° for Comparative Example 4. In Example 1, the water contact angle did not increase before or after application of the adhesive sheet. Furthermore, a comparison between Comparative Examples 1 and 2, and between Example 1 and Comparative Example 4, revealed that in the case of using a silicone-based release sheet, an increase in the water contact angle of the adherend surface was observed after a short application period compared to when a non-silicone-based release sheet was used. This is thought to be due to the silicone material of the release sheet being transferred to the adherend. The difference in water contact angle between Example 1, Comparative Example 4, and Comparative Examples 1 and 2 is thought to be due to the difference in catalyst type. Furthermore, when Examples 1 to 12 and Comparative Examples 1 to 5 were evaluated for fouling, all were found to pass the visual inspection (no change in surface condition was observed).

[0138] The above results show that by using an adhesive containing an acrylic polymer, which is a polymer of a monomer component containing alkyl (meth)acrylate (m1), which has an alkyl group having 6 to 17 carbon atoms at the ester terminal, and the alkyl group having 6 to 17 carbon atoms is either a straight-chain alkyl group or a branched alkyl group with one branched carbon atom, it is possible to achieve release sheet releasability that is comparable to that when a silicone-based release sheet is used, even when a non-silicone-based release sheet is used.

[0139] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0140] 1 adhesive sheet 10 Base material (supporting base material) 10A 1st side 10B 2nd side (back) 21 adhesive layer 21A Adhesive side 31 Release sheet 100 adhesive sheet with release sheet

Claims

1. A pressure-sensitive adhesive sheet with a release sheet, comprising a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer and a non-silicone release sheet disposed on the surface of the pressure-sensitive adhesive layer, the pressure-sensitive adhesive sheet has a substrate and the pressure-sensitive adhesive layer disposed on at least one surface of the substrate, the substrate being a resin film; the pressure-sensitive adhesive layer contains an acrylic polymer, the acrylic polymer is a polymer of a monomer component containing an alkyl(meth)acrylate (m1) having an alkyl group having 6 to 17 carbon atoms at an ester terminal, wherein the alkyl group having 6 to 17 carbon atoms is a linear alkyl group or a branched alkyl group having one branch carbon atom; the alkyl (meth)acrylate (m1) includes at least one selected from n-heptyl acrylate and n-octyl acrylate; The non-silicone release sheet has a release sheet substrate and a non-silicone release treatment layer provided on at least one surface of the release sheet substrate, The pressure-sensitive adhesive sheet with a release sheet, wherein the non-silicone release treatment layer is formed from a material containing a long-chain alkyl release treatment agent.

2. The pressure-sensitive adhesive sheet with a release sheet according to claim 1 , wherein the monomer component comprises a monomer (m2) having a hydroxyl group.

3. The pressure-sensitive adhesive sheet with a release sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent.

4. The pressure-sensitive adhesive sheet with a release sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer contains a zirconium-containing compound.

5. The pressure-sensitive adhesive sheet with a release sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive sheet is used by being attached to an optical member.

6. The pressure-sensitive adhesive sheet with a release sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive sheet is used as a surface protection film.

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