Surface protection sheet

Abstract

The purpose of the present invention is to provide a surface protection sheet exhibiting both improved anchoring properties and good removal properties. The provided surface protection sheet includes a base material and an adhesive layer. The adhesive layer contains a polyester. In the adhesive layer, the ratio (F1 / F2) of the interfacial adhesion force F1 (kN / m) with the base material to the shear stress F2 (N) is 0.6-3.0, inclusive.

Description

Surface protection sheet

[0001] The present invention relates to a surface protection sheet. This application claims priority to Japanese Patent Application No. 2024-051944 filed on March 27, 2024, Japanese Patent Application No. 2024-051945 filed on March 27, 2024, and Japanese Patent Application No. 2024-077496 filed on May 10, 2024, the entire contents of which are incorporated herein by reference.

[0002] Generally, adhesives (also referred to as pressure-sensitive adhesives; the same applies hereinafter) are soft solids (viscoelastic bodies) at temperatures near room temperature and have the property of easily adhering to adherends under pressure. Taking advantage of 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 surfaces of various items when they are processed or transported. For such applications, for example, acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, etc. are used. Patent Document 1, for example, is an example of a document disclosing prior art related to adhesive sheets using polyester adhesives.

[0003] Japanese Patent Application Publication No. 2014-129463

[0004] After achieving its protective purpose, the surface protection sheet is peeled off and removed from the adherend (object to be protected) at an appropriate time. In this case, a surface protection sheet with removability that allows it to be easily peeled off from the adherend while minimizing adhesive residue (adhesive residue) on the adherend is desirable. For example, if the cohesive strength of the adhesive constituting the adhesive layer is insufficient, the adhesive layer will undergo cohesive failure upon peeling from the adherend, resulting in adhesive residue. On the other hand, if the cohesive strength of the adhesive is increased in an attempt to avoid cohesive failure, the adhesive layer will be less anchored to the substrate, making it more likely to lift or peel off from the substrate, which could lead to poor appearance or reduced performance due to chipping of the adhesive layer.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a surface protection sheet that combines improved anchoring properties with good removability.

[0006] According to the present specification, there is provided a surface protection sheet comprising a substrate and a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer comprises polyester. The pressure-sensitive adhesive layer has a ratio (F1 / F2) of the interfacial adhesion strength F1 [kN / m] with the substrate to the shear stress F2 [N] of 0.6 or more and 3.0 or less. A surface protection sheet satisfying the above characteristics can achieve both improved anchoring properties and good removability. A surface protection sheet in which the ratio (F1 / F2) is 1.0 or more and 3.0 or less is more preferred.

[0007] In some embodiments, the PSA layer is substantially free of ethyl acetate and toluene. According to the present specification, a surface protection sheet that combines improved anchoring properties and good removability can be achieved by using a PSA layer that is substantially free of ethyl acetate and toluene, which are typical examples of organic solvents.

[0008] In some preferred embodiments, the surface protection sheet has a peel strength from a glass plate of 1.0 N / 25 mm or less. A surface protection sheet with such a low peel strength can be easily peeled from an adherend (object to be protected) (easy releasability), which is advantageous from the standpoints of ease of peeling and reduced load on the adherend during peeling.

[0009] In some embodiments, the polyester contained in the pressure-sensitive adhesive layer preferably has a weight average molecular weight (Mw) of 3,000 or more and 30,000 or less. A polyester having an Mw within the above range makes it easier to obtain a pressure-sensitive adhesive layer having adhesive properties suitable for use as a pressure-sensitive adhesive sheet for surface protection (surface protection sheet).

[0010] Appropriate combinations of the elements described in this specification may also be included within the scope of the invention for which patent protection is sought by this patent application.

[0011] 1 is a cross-sectional view schematically illustrating the configuration of a surface protection sheet according to one embodiment.

[0012] Preferred embodiments of the present invention are described below. Matters necessary for implementing 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 implementing the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be implemented 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 that perform the same function may be described using the same reference numerals, and duplicated descriptions may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic to clearly explain the present invention and do not necessarily accurately represent the size and scale of the surface protection sheet of the present invention that is actually provided as a product.

[0013] In this specification, "weight" may be read as "mass." For example, "wt%" may be read as "mass%," "parts by weight" may be read as "parts by mass," and "weight average molecular weight" may be read as "mass average molecular weight."

[0014] <Configuration Example of Surface Protective Sheet> The surface protective sheet disclosed herein includes a substrate and a pressure-sensitive adhesive layer. The structure of a surface protective sheet according to one embodiment is shown schematically in FIG. 1 . This surface protective sheet 1 is configured as a substrate-attached single-sided PSA sheet including a sheet-like substrate (e.g., a resin film) 10 having a first side 10A and a second side 10B, and a pressure-sensitive adhesive layer 21 provided on the first side 10A. The pressure-sensitive adhesive layer 21 is fixedly provided on the first side 10A of the substrate 10, i.e., without any intention of separating the pressure-sensitive adhesive layer 21 from the substrate 10. The surface protective sheet 1 is used by attaching its adhesive surface to the surface of an adherend (a target to be protected, for example, an optical component such as a polarizing plate). Before use, the surface protective sheet 1 can be a component of a release-liner-attached surface protective sheet 100, in which the surface (adhesive surface) 21A of the pressure-sensitive adhesive layer 21 is protected by a release liner 31, at least the side facing the pressure-sensitive adhesive layer 21 serving as a release surface, as shown in FIG. 1 . Alternatively, the release liner 31 may be omitted, and a substrate 10 having a second surface 10B as the release surface may be used, and the surface protection sheet 1 may be rolled up so that the adhesive surface 21A is in contact with the second surface (back surface) 10B of the substrate 10 and protected (in roll form).

[0015] The release liner (also referred to as a release film) may be a release liner having a release layer on the surface of a liner substrate such as a resin film or paper, or a release liner made of a low-adhesion material such as a polyolefin resin (e.g., polyethylene or polypropylene) or a fluorine-based resin. The release layer may be formed by surface treating the liner substrate with a release treating agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. As with the substrate of the surface protection sheet described below, a liner substrate made from a biological material or a recycled material (e.g., recycled film) may be preferably used.

[0016] The surface protection sheet disclosed herein is configured to include a substrate and a pressure-sensitive adhesive layer as described above, and is used by attaching the pressure-sensitive adhesive surface to an adherend. Therefore, the surface protection sheet can also be understood as a pressure-sensitive adhesive sheet with a substrate. In the following description, the surface protection sheet may be referred to as a pressure-sensitive adhesive sheet.

[0017] <Pressure-Sensitive Adhesive Layer> (Ratio (F1 / F2)) The surface protection sheet disclosed herein includes a pressure-sensitive adhesive layer containing polyester, and is characterized in that the ratio (F1 / F2) of the interfacial adhesion strength F1 [kN / m] of the pressure-sensitive adhesive layer with a substrate to the shear stress F2 [N] is 0.6 or more and 3.0 or less. Here, in the ratio (F1 / F2), F1 is the numerical portion when the interfacial adhesion strength measured by the method described below is expressed in units of "kN / m", and F2 is the numerical portion when the shear stress measured by the method described below is expressed in units of "N", and both F1 and F2 are dimensionless numbers. The interfacial adhesion strength makes it possible to determine the degree of releasability of the pressure-sensitive adhesive layer from the substrate. Furthermore, the shear stress makes it possible to determine the hardness and degree of stress relaxation of the pressure-sensitive adhesive layer. If the ratio (F1 / F2) determined from these properties is too small below the above range, the anchoring property decreases. Furthermore, if the ratio (F1 / F2) is too much greater than the above range, it becomes difficult to obtain the removability required of a surface protection sheet due to adhesive residue caused by insufficient cohesive strength, reduced easy removability from the adherend, etc. By ensuring that the ratio (F1 / F2) is within the above range, it is possible to improve the anchoring properties of the PSA layer to the substrate while ensuring the good removability required of a surface protection sheet.

[0018] In some embodiments, from the viewpoint of improving anchoring ability, etc., the ratio (F1 / F2) is preferably 0.7 or more, more preferably 0.8 or more, even more preferably 0.85 or more, and may be 0.9 or more, or may be 0.95 or more. In some preferred embodiments, the ratio (F1 / F2) may be 1.0 or more, or may be 1.1 or more (e.g., 1.15 or more). Furthermore, in some embodiments, from the viewpoint of removability, etc., the ratio (F1 / F2) is suitably 2.5 or less, for example, preferably 2.0 or less, more preferably 1.8 or less, may be 1.6 or less, may be 1.4 or less, or may be 1.2 or less.

[0019] The interfacial adhesion strength is appropriately set so that the ratio (F1 / F2) can be within the above-mentioned numerical range. In some embodiments, the interfacial adhesion strength is suitably 0.1 kN / m or more, preferably 0.13 kN / m or more, more preferably 0.15 kN / m or more, even more preferably 0.17 kN / m or more, and may be 0.18 kN / m or more, 0.19 kN / m or more, or even 0.20 kN / m. In some embodiments, from the viewpoint of easily obtaining easy releasability from the adherend, the interfacial adhesion strength is suitably less than 0.3 kN / m, preferably 0.28 kN / m or less, more preferably 0.26 kN / m or less, may be 0.25 kN / m or less, or may be 0.24 kN / m or less.

[0020] The shear stress is appropriately set so that the ratio (F1 / F2) falls within the above-mentioned numerical range. In some embodiments, the shear stress is suitably 0.10 N or more (e.g., greater than 0.10 N) from the viewpoint of avoiding adhesive residue due to cohesive failure when peeling from an adherend, and is preferably 0.15 N or more, more preferably 0.17 N or more, and may be 0.19 N or more, or may be 0.20 N or more. Furthermore, when the shear stress exceeds a certain level, the value of the interfacial adhesion force F1 [kN / m] required to keep the ratio (F1 / F2) within the above-mentioned range in relation to the value of the shear stress F2 [N] increases, which tends to make it difficult to achieve easy peelability from the adherend. From this viewpoint, in some embodiments, the shear stress is suitably less than 0.70 N, preferably 0.60 N or less, more preferably 0.50 N or less, and may be 0.40 N or less, 0.30 N or less, or 0.25 N or less.

[0021] The interfacial adhesion and shear stress are measured by the methods described in the Examples below. The interfacial adhesion and shear stress can be adjusted by the design of the polyester contained in the pressure-sensitive adhesive layer (material used, weight average molecular weight, glass transition temperature (Tg), number of functional groups (e.g., number of hydroxyl groups), etc.), the crosslinking structure (e.g., type of crosslinking agent, number and amount of crosslinkable functional groups), the use, type, amount, and number of functional groups (e.g., number of hydroxyl groups in polyol, etc.) of additives (e.g., polyol, plasticizer, etc.).

[0022] (Gel Fraction) While not particularly limited, in some embodiments, the gel fraction of the PSA layer may be, for example, approximately 60% or more, or may be 65% or more. In some preferred embodiments, the gel fraction is 70% or more. According to the technology disclosed herein, a high gel fraction of 70% or more and an improved anchoring effect to the substrate can be preferably achieved at the same time. A PSA layer having a gel fraction of 70% or more tends to have good cohesion, is less likely to leave adhesive residue, and has good releasability from the adherend. Furthermore, a PSA layer having 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 experience changes in appearance, making it suitable for surface protection applications. From the viewpoints of easy releasability, prevention of adhesive residue, etc., the gel fraction is more preferably 75% or more, may be 80% or more, may be 85% or more, or may be 90% or more. The gel fraction may be 100%, but from the viewpoint of adhesion to the adherend, it may be, for example, less than 99% or less than 95%. The gel fraction is a gel fraction measured for the pressure-sensitive adhesive layer after formation (specifically, after drying and aging), and is specifically determined by the measurement method described in the Examples below.

[0023] (Glass Transition Temperature (Tg)) Although not particularly limited, the pressure-sensitive adhesive layer is preferably designed to have a low glass transition temperature (Tg). For example, in embodiments in which organic solvents such as ethyl acetate and toluene are not substantially used, the viscosity of the pressure-sensitive adhesive composition can be reduced by using a material with a low Tg (e.g., polyester), thereby improving coatability. In some embodiments, the Tg of the pressure-sensitive adhesive layer may be 0°C or lower, -15°C or lower, or -25°C or lower. In some preferred embodiments, from the viewpoint of coatability of the pressure-sensitive adhesive composition, the Tg of the pressure-sensitive adhesive layer may be, for example, -30°C or lower, -45°C or lower, -50°C or lower, or -55°C or lower. Furthermore, from the viewpoint of cohesive strength, in some embodiments, the Tg of the pressure-sensitive adhesive layer is usually about -75°C or higher, or may be about -65°C or higher. The Tg of the pressure-sensitive adhesive layer is determined by the measurement method described in the Examples below.

[0024] (Thickness) The thickness of the pressure-sensitive adhesive layer is not particularly limited and can be appropriately selected depending on the purpose. The thickness of the pressure-sensitive adhesive layer is, for example, suitably about 1 μm or more, and may be about 10 μm or more. In some embodiments, from the viewpoint of improving the stress relaxation property within the pressure-sensitive adhesive layer and thereby dispersing the stress that may be applied to the interface with the substrate, the thickness of the pressure-sensitive adhesive layer may be 30 μm or more, 50 μm or more, for example, 70 μm or more. Furthermore, the thickness of the pressure-sensitive adhesive layer may be about 1000 μm or less, about 500 μm or less, or about 300 μm or less. In some embodiments, the thickness of the pressure-sensitive adhesive layer is suitably, for example, 150 μm or less, and may be 100 μm or less (e.g., less than 100 μm). A pressure-sensitive adhesive layer with a limited thickness makes it easier to achieve a lighter, smaller, and thinner surface protection sheet.

[0025] (Amount of Organic Solvent) In some embodiments of the surface protection sheet disclosed herein, the PSA layer preferably contains substantially no ethyl acetate or toluene. Such a PSA layer can be formed by coating and then curing a PSA composition that is substantially free of ethyl acetate and toluene, which are used for dilution purposes to adjust the solid content concentration and viscosity, etc., thereby reducing the amount of organic solvent used. Here, "the PSA layer contains substantially no ethyl acetate or toluene" means that the amounts of ethyl acetate and toluene are less than 5 μg and less than 1 μg, respectively, per gram of PSA layer. This means that ethyl acetate or toluene is not intentionally added to the PSA layer, but does not exclude small amounts of ethyl acetate or toluene that are unavoidably present in the raw materials for the PSA layer or that are unintentionally mixed in during the preparation of the PSA composition or the production of the surface protection sheet.

[0026] In some embodiments, the PSA layer is substantially free of methyl ethyl ketone (MEK). Here, the technical meaning of "the PSA layer is substantially free of MEK" is basically the same as that explained for ethyl acetate and toluene, and specifically means that the amount of MEK is less than 1 μg per 1 g of the PSA layer.

[0027] The pressure-sensitive adhesive layer may contain a compound having an acetylacetone skeleton (e.g., acetylacetone). While not particularly limited, in some embodiments, the pressure-sensitive adhesive layer may contain approximately 100 μg or less of the compound having an acetylacetone skeleton per gram of the pressure-sensitive adhesive layer. In some preferred embodiments, the amount of the compound having an acetylacetone skeleton in the pressure-sensitive adhesive layer may be 50 μg or less, 45 μg or less, 40 μg or less, 35 μg or less, or 30 μg or less per gram of the pressure-sensitive adhesive layer.

[0028] In this specification, the amounts of ethyl acetate, toluene, MEK, and compounds having an acetylacetone skeleton in the pressure-sensitive adhesive layer can be quantified by GC / MS. More specifically, they can be quantified by the method described in the quantification of residual volatile components below. [Quantification of residual volatile components] Sample (pressure-sensitive adhesive sheet) 10 cm ２ The sample is collected and sealed in a 20 mL headspace vial. The vial containing the sample is heated at 150°C for 30 minutes using a headspace sampler (HSS: Shimadzu Corporation, HS-20), and 1 mL of the heated gas is injected into a GC / MS (Shimadzu Corporation, "QP-2020" instrument) for measurement. Using a calibration curve calculated for one appropriate volatile component (acetylacetone in the examples described below), the detected amount [μg / g] of each volatile component per 1 g of adhesive layer is determined from the peak area obtained for the residual volatile components (toluene, ethyl acetate, MEK, and acetylacetone) (in the examples described below, this is the acetylacetone equivalent value), and this is taken as the content per 1 g of adhesive layer. If the adhesive sheet contains a substrate, the weight of the substrate for the same area is subtracted to determine the amount of residual volatile components per 1 g of adhesive layer. Note that it has been confirmed that the amount of residual volatile components is negligible for the substrate used in the examples described below. Specific measurement conditions for GC / MS are shown in Table 1.

[0029]

[0030] (Composition of adhesive layer) As the adhesive constituting the adhesive layer, an adhesive containing polyester and capable of forming an adhesive layer satisfying the above ratio (F1 / F2) can be used. The composition of the adhesive layer that can be employed in the surface protection sheet disclosed herein is as described below for the adhesive composition, except for the volatile component. Therefore, the matters described for the adhesive composition can also be applied to the adhesive layer, except for the matters related to the volatile component.

[0031] (Polyester) In the surface protection sheet disclosed herein, the pressure-sensitive adhesive layer and the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer contain polyester. In this specification, polyester refers to a polymer obtained by polycondensation of a dicarboxylic acid and a diol. A pressure-sensitive adhesive containing polyester can effectively achieve adhesive properties, properties required for surface protection applications such as easy peelability and adhesive transfer resistance, and properties required for optical applications such as transparency. In addition, polyester is preferable because it can be synthesized primarily from plant-derived materials, which has the advantage of reducing dependence on fossil resource-based materials.

[0032] The dicarboxylic acid used in the synthesis of the polyester may be any of aliphatic dicarboxylic acids, dimer acids, alicyclic dicarboxylic acids, unsaturated dicarboxylic acids, and aromatic dicarboxylic acids. Specific examples of the dicarboxylic acid include aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, dimethylglutaric acid, adipic acid, trimethyladipic acid, pimelic acid, suberic acid, azelaic acid, dodecanedioic acid, sebacic acid, thiodipropionic acid, and diglycolic acid; dimer acids obtained by dimerizing fatty acids such as oleic acid and erucic acid; 1,2-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and 4-methyl-1,2 Examples of suitable dicarboxylic acids include alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, norbornanedicarboxylic acid, and adamantanedicarboxylic acid; unsaturated dicarboxylic acids such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic acid, and dodecenyl succinic anhydride; aromatic dicarboxylic acids such as isophthalic acid, terephthalic acid, orthophthalic acid, benzylmalonic acid, 2,2'-biphenyldicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-dicarboxydiphenyl ether, and naphthalenedicarboxylic acid; and derivatives thereof. Derivatives of the dicarboxylic acids include derivatives such as carboxylic acid salts, carboxylic acid anhydrides, carboxylic acid halides, and carboxylic acid esters. By appropriately selecting and using one or more of these dicarboxylic acids, a polyester exhibiting the desired adhesive properties can be obtained.

[0033] In some preferred embodiments, a dimer acid is used as the dicarboxylic acid. Polyesters containing dimer acid units tend to have a low glass transition temperature and improved hydrolysis resistance. Furthermore, because dimer acids are less volatile, they can be preferably used in synthesis, for example, under high-temperature and highly reduced-pressure conditions. Dimer acids can be used alone or in combination. In embodiments where a dimer acid is used as the dicarboxylic acid, the weight ratio of the dimer acid to the total amount (total weight) of dicarboxylic acids used in the synthesis of the polyester is not particularly limited, and is suitably approximately 1 wt % or more, and may be approximately 10 wt % or more, or even approximately 30 wt % or more. In some preferred embodiments, the weight ratio of the dimer acid to the total amount of dicarboxylic acids is approximately 50 wt % or more, approximately 70 wt % or more, approximately 80 wt % or more, approximately 90 wt % or more, or approximately 95 wt % or more (e.g., 95 to 100 wt %). By using a dimer acid in a predetermined amount or more, a polyester (for example, but not limited to, a polyester having a Mw within a predetermined range and a low Tg) can be designed based on the properties of the dimer acid.

[0034] In some preferred embodiments, it is preferable to use a dicarboxylic acid derived from a biological source, in order to reduce dependence on fossil resource materials. Suitable examples of such dicarboxylic acids include sebacic acid derived from plants (e.g., castor oil) and dimer acids derived from fatty acids such as oleic acid and erucic acid. The biologically derived dicarboxylic acids may be used alone or in combination of two or more.

[0035] The molecular weight of the dicarboxylic acid used is not particularly limited, and is suitably 100 or more, and may be 150 or more, 250 or more, 350 or more, 450 or more, or 500 or more (for example, 550 or more). On the other hand, from the viewpoint of monomer availability, ease of synthesis, etc., the molecular weight of the dicarboxylic acid is suitably about 1000 or less, and may be, for example, 800 or less, 700 or less, or 600 or less. Suitable examples of dicarboxylic acids having the above molecular weight include dimer acids.

[0036] In this specification, the molecular weight of a dicarboxylic acid may be the molecular weight calculated from the chemical formula, or the manufacturer's nominal value (which may be a weight-average molecular weight or a number-average molecular weight). In an embodiment in which two or more dicarboxylic acids are used, the molecular weight of the dicarboxylic acid is the sum (total value) of the products of the molecular weights and weight fractions of the respective dicarboxylic acids.

[0037] As the diol used in the synthesis of the polyester, any of ethylene glycols, propylene glycols, polyether diols, aliphatic diols, dimer diols, alicyclic diols, aromatic diols, and unsaturated diols can be used. Specific examples of the diol include ethylene glycols such as ethylene glycol and diethylene glycol; propylene glycols such as propylene glycol and dipropylene glycol; polyether diols such as triethylene glycol, polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polytetramethylene ether glycol, polytrimethylene ether glycol, a copolymer of 3-methyltetrahydrofuran and tetrahydrofuran, and a copolymer of neopentyl glycol and tetrahydrofuran; 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 3-methyl-1,5-pentanediol. aliphatic diols such as 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,3-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; dimer diols (e.g., dimer diols derived from fatty acids such as oleic acid and erucic acid); 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,5-cyclohexanediol, 1,6-hexanediol, 2-methyl-1,3-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; Alicyclic diols such as methanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol; and aromatic diols such as 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, o-, m-, and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and ethylene oxide and propylene oxide adducts thereof.By appropriately selecting and using one or more of these diols, a polyester that can exhibit desired adhesive properties can be obtained.

[0038] In some preferred embodiments, a polyether diol is used as the diol. Polyesters containing polyether diol units are likely to achieve a low Tg, which can contribute to improving the fluidity and coatability of pressure-sensitive adhesive compositions that are substantially free of organic solvents. The use of polyether diols is also advantageous in terms of improving wettability and easy peelability when attached to an adherend (object to be protected). Preferred polyether diols include polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, and polytetramethylene ether glycol, with polyoxyethylene polyoxypropylene glycol being more preferred. Among these, polyether diols containing oxypropylene units are preferably used. Polyesters synthesized using polyether diols containing oxypropylene units or polyoxypropylene structures have low viscosity due to their amorphous structure, and are advantageous in terms of handleability and coatability. The polyether diols containing oxypropylene units may further contain oxyethylene units or polyoxyethylene units. Preferred examples of such polyether diols include polypropylene glycols modified with (poly)oxyethylene at least at one end (preferably both ends), and polyoxyethylene-polyoxypropylene block copolymers or random copolymers having an oxyethylene unit or polyoxyethylene structure at at least at one end (preferably both ends). Polyether diols having such structures allow for the efficient incorporation of oxypropylene units into polyesters. A suitable example of the polyoxyethylene-polyoxypropylene block copolymer is a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer. One type of polyether diol can be used alone, or two or more types can be used in combination. In this specification, (poly)oxyethylene comprehensively refers to oxyethylene and polyoxyethylene (i.e., a structure in which two or more oxyethylene units are consecutive).

[0039] In embodiments in which a polyether diol is used as the diol, the weight proportion of the polyether diol relative to the total amount (total weight) of diols used in the synthesis of the polyester is not particularly limited, and is suitably approximately 1 wt % or more, and may be approximately 10 wt % or more, or approximately 30 wt % or more. In some preferred embodiments, the weight proportion of the polyether diol relative to the total amount of diols is approximately 50 wt % or more, approximately 70 wt % or more, approximately 80 wt % or more, approximately 90 wt % or more, or approximately 95 wt % or more (e.g., 95 to 100 wt %). By using a predetermined amount or more of polyether diol, it is possible to design a polyester (e.g., a polyester having a Mw within a predetermined range and a low Tg) based on the properties of the polyether diol, although this is not particularly limited.

[0040] The molecular weight of the diol used is not particularly limited, and is suitably 100 or more, and may be 150 or more, 250 or more, 350 or more, 450 or more, 550 or more, 650 or more, or 750 or more. In some preferred embodiments, the molecular weight of the diol may be 1000 or more, 1250 or more, 1500 or more, 1750 or more, 2000 or more, or 2250 or more. Using a diol with a high molecular weight tends to facilitate good wettability and easy release properties. On the other hand, in some embodiments, from the viewpoint of, for example, monomer availability and ease of synthesis, the molecular weight of the diol is suitably about 6000 or less, preferably 5000 or less, more preferably 4500 or less, even more preferably 4000 or less, even more preferably 3000 or less, and particularly preferably 2800 or less. A suitable example of a diol having the above molecular weight is polyether diol.

[0041] In this specification, the molecular weight of a diol may be the molecular weight calculated from the chemical formula, or the manufacturer's nominal value (which may be a weight average molecular weight or a number average molecular weight). In an embodiment in which two or more diols are used, the molecular weight of the diol is the sum (total value) of the products of the molecular weights and weight fractions of the respective diols.

[0042] The polyester may be substantially composed of the dicarboxylic acid and diol described above. However, for purposes such as introducing desired functional groups or adjusting molecular weight, other copolymerization components other than the dicarboxylic acid and diol may be copolymerized within a range that does not impair the effects of the technology disclosed herein. Examples of such other copolymerization components include polycarboxylic acids containing three or four or more carboxy groups (trivalent or higher polycarboxylic acids such as trimellitic acid, pyromellitic acid, adamantanetricarboxylic acid, trimesic acid, and trimer acid), polyols containing three or four or more hydroxyl groups per molecule (pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, trimethylolpropane, trimethylolethane, 1,3,6-hexanetriol, and adamantanetriol), monocarboxylic acids, monoalcohols, hydroxycarboxylic acids, and lactones. The above-mentioned other copolymerization components may be used alone or in combination of two or more. The proportion of the other copolymerization component in the polyester is suitably, for example, less than 10% by weight, and may be less than 3% by weight, typically less than 1% by weight (or even less than 0.1% by weight). The technology disclosed herein can also be preferably implemented in an embodiment in which the polyester is substantially free of the other copolymerization component.

[0043] Although there are no particular limitations on the monomer components used in the synthesis of the polyester, the total proportion of dicarboxylic acid and diol is suitably about 90% by weight or more, preferably about 95% by weight or more, more preferably about 98% by weight or more, and even more preferably about 99% by weight or more (for example, 99 to 100% by weight). The technology disclosed herein is preferably carried out in an embodiment using a polyester synthesized substantially from a dicarboxylic acid and a diol.

[0044] In some preferred embodiments, the polyester is prepared by combining a dimer acid as the dicarboxylic acid with a polyether diol as the diol. The combined use of a dimer acid and a polyether diol allows, without limitation, the synthesis of a polyester having a Mw within a specific range and a low Tg. From this perspective, in some embodiments, the combined proportion of the dimer acid and the polyether diol relative to the total monomer components of the polyester is suitably approximately 50% by weight or more, preferably approximately 60% by weight or more, more preferably approximately 70% by weight or more, and even more preferably approximately 80% by weight or more. It may also be approximately 90% by weight or more, or even approximately 95% by weight or more (e.g., 99 to 100% by weight).

[0045] Although not particularly limited, in some embodiments, in the synthesis of a polyester, it is appropriate to blend more than 1 mole of diol per mole of dicarboxylic acid, and the molar ratio of diol to dicarboxylic acid (diol / dicarboxylic acid) is preferably 1.2 or more, more preferably 1.5 or more. By increasing the proportion of diol, a polyester polyol having hydroxyl groups at its terminals (typically both terminals) can be obtained. This allows for favorable crosslinking with, for example, a crosslinking agent (e.g., an isocyanate-based crosslinking agent) described below. Furthermore, by maintaining the molar ratio (diol / dicarboxylic acid) within the above range, a polyester with a Mw controlled within a predetermined range is easily obtained. The upper limit of the molar ratio of diol to dicarboxylic acid (diol / dicarboxylic acid) is not particularly limited, and in some embodiments, from the viewpoint of polymerization efficiency, etc., it may be 3.0 or less, 2.5 or less, 2.2 or less, or 2.0 or less.

[0046] The method for obtaining the polyester is not particularly limited, and any polymerization method known as a polyester synthesis method can be appropriately adopted. The polyester disclosed herein can be obtained by polycondensation of a dicarboxylic acid and a diol, similar to general polyesters. More specifically, the polyester can be synthesized by proceeding with the reaction between a carboxy group of the dicarboxylic acid and a hydroxyl group of the diol, typically while removing water (produced water) produced by the reaction from the reaction system. Methods for removing the produced water from the reaction system include a method of blowing an inert gas into the reaction system and removing the produced water together with the inert gas from the reaction system, a method of azeotropic dehydration using a reaction water discharge solvent such as toluene or xylene, and a method of distilling the produced water from the reaction system under reduced pressure (decompression method).

[0047] The reaction temperature and reaction time during the above reaction (including esterification and polycondensation), and the degree of vacuum (pressure within the reaction system) when a reduced pressure method is used, can be appropriately set so as to efficiently obtain a polyester with the desired properties (e.g., molecular weight). While not particularly limited, the reaction temperature is typically set to approximately 150°C or higher (e.g., 180°C to 260°C). Setting the reaction temperature within the above range results in a good reaction rate, improved productivity, and facilitates the prevention or suppression of deterioration of the polyester produced. The reaction time is also not particularly limited and can be approximately 1 to 48 hours (e.g., 3 to 10 hours). When a reduced pressure method is used, although not particularly limited, the degree of vacuum is typically set to 10 kPa or less (typically 10 kPa to 0.1 kPa), for example, 4 kPa to 0.1 kPa. Setting the pressure within the reaction system within the above range allows the water produced by the reaction to be efficiently distilled out of the system, making it easier to maintain a good reaction rate. Furthermore, when the reaction temperature is relatively high, by setting the pressure in the reaction system to the above-mentioned lower limit or higher, it is easy to prevent the distillation of the raw materials, dicarboxylic acid and diol, outside the system. From the viewpoint of maintaining a stable pressure in the reaction system, it is usually appropriate to set the pressure in the reaction system to 0.1 kPa or higher.

[0048] In the above reaction, a known or conventional catalyst can be used in an appropriate amount for esterification and condensation, as in the synthesis of general polyesters. Examples of such catalysts include various metal compounds such as titanium-based, germanium-based, antimony-based, tin-based, and zinc-based compounds; and strong acids such as p-toluenesulfonic acid and sulfuric acid. The amount of catalyst used can be appropriately determined depending on the reaction rate, etc., and therefore, a detailed description thereof will be omitted here.

[0049] In the above process of synthesizing polyester by the reaction of dicarboxylic acid and diol, a solvent (typically an organic solvent) may or may not be used.The above synthesis can be carried out without substantially using an organic solvent (for example, this means excluding the case where an organic solvent is intentionally used as a reaction solvent during the above reaction).Synthesizing polyester without substantially using an organic solvent in this way and preparing a pressure-sensitive adhesive using such polyester are preferable because they are suitable for reducing the amount of organic solvent used.

[0050] Although not particularly limited, the polyester is preferably designed to have a low glass transition temperature (Tg). In embodiments in which organic solvents such as ethyl acetate and toluene are not substantially used, the use of a polyester with a low Tg can reduce the viscosity of the PSA composition and improve coatability. In some embodiments, the Tg of the polyester may be 0°C or lower, -15°C or lower, or -25°C or lower. In some preferred embodiments, from the viewpoint of coatability, the Tg of the polyester is, for example, -30°C or lower, -35°C or lower, -40°C or lower, -45°C or lower, -50°C or lower, -55°C or lower, -60°C or lower, or -65°C or lower. Furthermore, from the viewpoint of the cohesive strength of the PSA layer, in some embodiments, the Tg of the polyester is typically about -85°C or higher, may be about -80°C or higher, or may be about -75°C or higher.

[0051] In this specification, the Tg of a polyester can be determined by taking about 5 mg of a sample, subjecting it to DSC (differential scanning calorimetry) measurement under the following conditions, and calculating the midpoint Tg from the measurement results. [Measurement conditions] Measurement device: TA Instruments, product name "Q-2000" Temperature program: 50°C → -90°C → 50°C Measurement rate: 10°C / min Atmospheric gas: N ２ (50 mL / min) Measurement container: Aluminum airtight container

[0052] The molecular weight of the polyester is not particularly limited. A polyester having an appropriate molecular weight is used depending on the intended use, etc. In some embodiments, the weight-average molecular weight (Mw) of the polyester may be, for example, 2,000 or more, 4,000 or more, 5,000 or more, or 6,000 or more. In some preferred embodiments, the Mw of the polyester is 8,000 or more, more preferably 10,000 or more (e.g., greater than 10,000), even more preferably 12,000 or more, even more preferably 14,000 or more, and particularly preferably 15,000 or more. By using a polyester with a high Mw, the cohesive strength of the pressure-sensitive adhesive layer is increased, making it easier to obtain better adhesive performance. In addition, in some embodiments, the weight-average molecular weight (Mw) of the polyester is approximately 50,000 or less, or may be 40,000 or less. In some preferred embodiments, the Mw of the polyester is 35,000 or less, 30,000 or less, 25,000 or less, or 23,000 or less. By using a polyester whose Mw is limited to a predetermined value or less, the viscosity of the pressure-sensitive adhesive composition can be reduced, and good coatability tends to be easily obtained.

[0053] In this specification, the Mw of a polyester refers to a value calculated in terms of standard polystyrene obtained by GPC (gel permeation chromatography). As a GPC device, for example, a model "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) can be used. More specifically, GPC measurement can be performed under the following conditions. Measurements are also performed in the examples described below using a similar method. [GPC Measurement] Column: TSKgel GMH-H(S) Column temperature: 40°C Eluent: THF (0.1 wt% amine component added) Flow rate: 0.5 mL / min Injection volume: 100 μL Detector: differential refractometer (RI) Standard sample: polystyrene (PS)

[0054] The polyester is used in an appropriate amount to exhibit its function as a pressure-sensitive adhesive. In some embodiments, the content of the polyester in the pressure-sensitive adhesive composition and the pressure-sensitive adhesive layer can be approximately 25% by weight or more. By including a predetermined amount or more of polyester in a composition in which the amount of organic solvent used is sufficiently reduced, the effects of including the polyester can be preferably exhibited. From this perspective, in some preferred embodiments, the content of the polyester in the pressure-sensitive adhesive composition and the pressure-sensitive adhesive layer is approximately 30% by weight or more, more preferably approximately 35% by weight or more, even more preferably approximately 40% by weight or more, particularly preferably approximately 45% by weight or more, and may be, for example, approximately 50% by weight or more (e.g., more than 50% by weight). In other preferred embodiments, the content of the polyester in the pressure-sensitive adhesive composition and the pressure-sensitive adhesive layer may be approximately 55% by weight or more, approximately 60% by weight or more, approximately 65% ​​by weight or more, approximately 70% by weight or more, or approximately 75% by weight or more. In addition, from the viewpoint of obtaining the effects of containing other components (e.g., polyols and crosslinking agents described below), in some embodiments, the content of polyester in the PSA composition is suitably about 90% by weight or less, preferably about 80% by weight or less, or may be about 70% by weight or less, about 65% by weight or less, about 60% by weight or less, or may be about 55% by weight or less. The content of polyester in the PSA layer formed from the PSA composition is suitably about 95% by weight or less, preferably about 85% by weight or less, or may be about 75% by weight or less, about 65% by weight or less, or may be about 60% by weight or less.

[0055] (Polyol) In some embodiments, the pressure-sensitive adhesive composition may contain a polyol in addition to the polyester. In a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition containing a polyester and a polyol, the polyol may be contained in a form chemically bonded to the polyester, or the polyols may be contained in a form chemically bonded to each other. The chemical bond may be, for example, a chemical bond via a crosslinking agent described below. By incorporating the polyol into the pressure-sensitive adhesive in any of the above forms, it can contribute to improving the interfacial adhesion with the substrate and suppressing the peel force from the adherend (making peeling easier). The polyols may be used alone or in combination of two or more.

[0056] As the polyol, either a bifunctional polyol having two hydroxyl groups or a trifunctional or higher polyol having three or more hydroxyl groups can be used. Various polyols such as polyether polyols, polyester polyols, and polycarbonate polyols can also be used. While not particularly limited, polyether polyols such as polyalkylene glycols are preferably used as the polyol. Polyether polyols tend to provide good handling and coating properties, and are also advantageous in terms of improving wettability and easy release properties. Examples of such polyols include polyethylene glycol, polypropylene glycol (PPG), polyoxyethylene polyoxypropylene glycol, polytetramethylene ether glycol (PTMG), polytrimethylene ether glycol, a copolymer of 3-methyltetrahydrofuran and tetrahydrofuran, and a copolymer of neopentyl glycol and tetrahydrofuran. Among these, polyether polyols containing oxypropylene units are preferably used. Polyether polyols containing oxypropylene units or polyoxypropylene structures have low viscosity due to their amorphous structure, and are advantageous in terms of handleability and coatability. Polyether polyols containing oxypropylene units may further contain oxyethylene units or polyoxyethylene units. From the standpoint of reactivity, for example, such polyols may include polypropylene glycols modified with (poly)oxyethylene at least at one end (preferably both ends), or polyoxyethylene-polyoxypropylene block copolymers or random copolymers having oxyethylene units or polyoxyethylene structures at at least at one end (preferably both ends). An example of the polyoxyethylene-polyoxypropylene block copolymer is a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer. These may be used alone or in combination of two or more.

[0057] The molecular weight of the polyol is not particularly limited, and for example, a polyol having a number average molecular weight (Mn) in the range of 200 to 20,000 can be used. In some embodiments, the number average molecular weight of the polyol may be 300 or more or 400 or more. In some preferred embodiments, the number average molecular weight of the polyol may be 1,000 or more, 2,000 or more, 3,000 or more, or 4,000 or more. The use of a polyol with a high molecular weight tends to make it easier to achieve good wettability and easy releasability. In some embodiments, the number average molecular weight of the polyol may be 15,000 or less or 13,000 or less. In some preferred embodiments, the number average molecular weight of the polyol may be less than 10,000, less than 8,000, 7,000 or less, or 5,000 or less. A pressure-sensitive adhesive composition containing a polyol having a number average molecular weight of a predetermined value or less is advantageous in terms of coatability, as it is easier to maintain a low viscosity.

[0058] In this specification, the number average molecular weight of a polyol (including a trifunctional or higher polyol, as described below) can be the manufacturer's nominal value. If the nominal value is unknown, the number average molecular weight (Mn) obtained by GPC measurement under conditions similar to those for the Mw of the polyester can be used. In addition, in an embodiment in which two or more polyols are used, the number average molecular weight of the polyol is the sum (total value) of the products of the number average molecular weights and weight fractions of the polyols. The same applies to an embodiment in which two or more trifunctional or higher polyols are used.

[0059] In embodiments in which the PSA composition contains a polyol, the polyol is used in an appropriate amount depending on the purpose. In some embodiments, the content of the polyol in the PSA composition and the PSA layer may be 0.1 wt% or more, 1 wt% or more, 2 wt% or more, 5 wt% or more, or 10 wt% or more. In some preferred embodiments, the content of the polyol in the PSA composition and the PSA layer may be 15 wt% or more, 20 wt% or more, 25 wt% or more, or 30 wt% or more. By using a predetermined amount or more of polyol, the effects of containing the polyol can be effectively exerted. In other embodiments, the content of the polyol (e.g., bifunctional polyol) in the PSA composition and the PSA layer may be approximately 40 wt% or more, or approximately 50 wt% or more (e.g., more than 50 wt%). The content of polyol in the pressure-sensitive adhesive composition and the pressure-sensitive adhesive layer may be, for example, 90% by weight or less, approximately 70% by weight or less, approximately 60% by weight or less, approximately 50% by weight or less (e.g., less than 50% by weight), approximately 40% by weight or less, approximately 30% by weight or less, approximately 20% by weight or less, or approximately 10% by weight or less.

[0060] In some preferred embodiments, the PSA composition contains a trifunctional or higher polyol. By using the trifunctional or higher polyol in combination with a suitable crosslinking agent, such as a bifunctional isocyanate-based crosslinking agent described below, it is possible to more effectively achieve good anchoring properties to the substrate and easy releasability from the adherend. The reason for this is thought to be that by including a polyester, a predetermined amount of a trifunctional or higher polyol, and the crosslinking agent, a loose crosslinked structure with good extensibility is obtained, and the stress relaxation properties of this crosslinked structure result in good anchoring properties and easy releasability. The technology disclosed herein is not limited to the above considerations. The trifunctional or higher polyol can be used alone or in combination of two or more.

[0061] The number of hydroxyl groups possessed by the tri- or higher functional polyol is 3 or 4 or more, and the upper limit is not particularly limited, but is, for example, preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. When the number of hydroxyl groups in the tri- or higher functional polyol is within the specified range, a crosslinked structure suitable for achieving both good anchoring properties and easy releasability tends to be easily obtained.

[0062] Furthermore, it is preferable to use a trifunctional or higher polyol having a number-average molecular weight in the range of 200 to 20,000. By using an appropriate amount of a trifunctional or higher polyol having such a number-average molecular weight relative to the polyester, a crosslinked structure suitable for achieving both good anchoring properties and easy releasability is easily obtained. Furthermore, a PSA composition containing a trifunctional or higher polyol having a number-average molecular weight of a predetermined value or less is likely to maintain a low viscosity and is advantageous in terms of coatability. From the viewpoint of improving anchoring properties, the number-average molecular weight of the trifunctional or higher polyol is preferably 300 or more, more preferably 400 or more. In some embodiments, the number-average molecular weight of the trifunctional or higher polyol may be 1,000 or more, 2,000 or more, 3,000 or more, 4,000 or more, 5,000 or more (e.g., greater than 5,000), or 6,000 or more. Furthermore, the number-average molecular weight of the trifunctional or higher polyol is preferably 15,000 or less, more preferably 13,000 or less. By using a tri- or higher functional polyol with a relatively low molecular weight within a predetermined range, a crosslinked structure based on the tri- or higher functional polyol can be formed with a relatively small amount of use. This can be useful for effectively exhibiting adhesive properties based on polymers such as polyester. In some embodiments, the number average molecular weight of the tri- or higher functional polyol may be less than 10,000, less than 8,000, 7,000 or less, 5,000 or less, or 3,000 or less.

[0063] In some preferred embodiments, the tri- or higher functional polyol used has a number average molecular weight in the range of 8,000 to 20,000. In such embodiments, the number average molecular weight of the tri- or higher functional polyol is preferably 15,000 or less, and more preferably 13,000 or less. In other preferred embodiments, the tri- or higher functional polyol used has a number average molecular weight in the range of 200 or more and less than 8,000. In such embodiments, the number average molecular weight of the tri- or higher functional polyol is preferably 7,000 or less, and may be 5,000 or less, 3,000 or less, 1,500 or less, or 1,000 or less (for example, less than 1,000).

[0064] As the trifunctional or higher functional polyol, any polyol having three or more hydroxyl groups and a predetermined number-average molecular weight can be used without particular limitation. For example, from the viewpoint of anchoring properties, trifunctional or higher functional polyether polyols are preferably used. The use of polyether polyols is also advantageous in terms of improving wettability and easy release properties. As the trifunctional or higher functional polyether polyol, for example, a trifunctional or higher functional polyol can be selected from polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polytetramethylene ether glycol, polytrimethylene ether glycol, a copolymer of 3-methyltetrahydrofuran and tetrahydrofuran, a copolymer of neopentyl glycol and tetrahydrofuran, and the like. Such trifunctional or higher functional polyether polyols may contain units derived from glycerin, trimethylolpropane, or pentaerythritol (glycerin units, trimethylolpropane units, pentaerythritol units). Other examples of trifunctional polyols include dipentaerythritol and tripentaerythritol. These may be used alone or in combination of two or more.

[0065] As the tri- or higher functional polyol, one containing an oxypropylene unit is preferably used. Tri- or higher functional polyols containing an oxypropylene unit or a polyoxypropylene structure have low viscosity due to their amorphous structure, and are advantageous in terms of handleability and coatability. Tri- or higher functional polyols containing an oxypropylene unit may further contain an oxyethylene unit or a polyoxyethylene unit. From the standpoint of reactivity, for example, the tri- or higher functional polyol may be a polypropylene glycol in which at least one end (e.g., both ends) is modified with (poly)oxyethylene, or a polyoxyethylene-polyoxypropylene block copolymer or random copolymer having an oxyethylene unit or a polyoxyethylene structure at at least one end (e.g., both ends).

[0066] In some embodiments in which the PSA composition contains a polyester and a tri- or higher functional polyol, the content of the tri- or higher functional polyol in the PSA composition is the amount of hydroxyl groups A ＯＨ Amount of hydroxyl groups contained in trifunctional or higher polyol relative to [mol] B ＯＨ Ratio of [mol] (B ＯＨ / A ＯＨ It is preferable that the ratio (B) is set to be in the range of 0.5 to 10. ＯＨ / A ＯＨ When the amount A of hydroxyl groups contained in the polyester is within the above range, the PSA formed into a sheet with a suitable cohesive strength can preferably have good anchoring properties and easy releasability. ＯＨ is represented by the formula: A ＯＨ Amount B of hydroxyl groups contained in tri- or higher functional polyol is calculated by: Polyester content (parts by weight) × Number of hydroxyl groups in one polyester molecule / Weight average molecular weight of polyester. ＯＨ is represented by the formula: B ＯＨ = content (parts by weight) of tri- or higher functional polyol × number of hydroxyl groups in one molecule of tri- or higher functional polyol / number average molecular weight of tri- or higher functional polyol. ＯＨ / A ＯＨ) is preferably 8.0 or less, more preferably 6.0 or less, even more preferably 5.0 or less, and may be 4.5 or less, 3.5 or less, 2.5 or less, or 2.0 or less. ＯＨ / A ＯＨ By using a tri- or higher functional polyol in a ratio that is appropriately limited to the polyester based on the amount of hydroxyl groups within the range of (B), excellent anchoring properties tend to be easily obtained. ＯＨ / A ＯＨ The ratio (B) is preferably 1.0 or more, and more preferably 1.4 or more. ＯＨ / A ＯＨ By using a polyol having a functionality of 3 or more in a predetermined amount relative to the polyester in terms of the amount of hydroxyl groups within the range of the above ratio (B), the pressure-sensitive adhesive can preferably have an appropriate cohesive strength. ＯＨ / A ＯＨ ) can preferably provide a surface protection sheet that combines improved anchoring properties and good removability.

[0067] In an embodiment in which a tri- or higher functional polyol is used, the amount of the tri- or higher functional polyol used is not particularly limited. In some embodiments, the amount of the tri- or higher functional polyol used is, for example, ＯＨ / A ＯＨ) is preferably used in an amount within a range that satisfies the above condition. In some embodiments, the content of the tri- or higher functional polyol may be approximately 0.5 parts by weight or more, approximately 1 part by weight or more, 2 parts by weight or more, 5 parts by weight or more, or 10 parts by weight or more, relative to 100 parts by weight of the polyester contained in the PSA composition. From the viewpoint of improving cohesive strength, in some preferred embodiments, the content of the tri- or higher functional polyol relative to 100 parts by weight of the polyester may be 15 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, 40 parts by weight or more, 50 parts by weight or more, 55 parts by weight or more, or 60 parts by weight or more. In embodiments in which a predetermined amount or more of a tri- or higher functional polyol is used, good coatability tends to be easily obtained even in PSA compositions that are substantially free of ethyl acetate and toluene used for dilution purposes. In such embodiments, there is also the advantage that the Mw and Tg of the polymer, which tend to be limited due to coatability, can be more flexibly designed. In some embodiments, the content of the tri- or higher functional polyol relative to 100 parts by weight of the polyester may be 80 parts by weight or more, 90 parts by weight or more, 100 parts by weight or more, or 110 parts by weight or more. Furthermore, in some embodiments, the content of the tri- or higher functional polyol relative to 100 parts by weight of the polyester may be approximately 200 parts by weight or less, or approximately 150 parts by weight or less. Limiting the content of the tri- or higher functional polyol is also preferable from the viewpoint of reducing contamination of the adherend caused by the tri- or higher functional polyol. In some embodiments, the content of the tri- or higher functional polyol relative to 100 parts by weight of the polyester may be 120 parts by weight or less, 100 parts by weight or less, or 80 parts by weight or less.

[0068] The range of the amount of trifunctional or higher polyol used may vary depending on the molecular weight of the trifunctional or higher polyol used. Specifically, in an embodiment using a trifunctional or higher polyol having a number average molecular weight in the range of 8,000 to 20,000, the content of the trifunctional or higher polyol is, for example, about 15 parts by weight or more, preferably about 20 parts by weight or more, more preferably about 30 parts by weight or more, even more preferably about 40 parts by weight or more, particularly preferably about 50 parts by weight or more (e.g., more than 50 parts by weight), and may be 60 parts by weight or more, 80 parts by weight or more, or 100 parts by weight or more, relative to 100 parts by weight of polyester contained in the pressure-sensitive adhesive composition. In such an embodiment, the content of the trifunctional or higher polyol relative to 100 parts by weight of polyester may be about 200 parts by weight or less, suitably about 150 parts by weight or less, preferably 120 parts by weight or less, or may be 100 parts by weight or less, or may be 80 parts by weight or less.

[0069] In an embodiment using a tri- or higher functional polyol having a number average molecular weight in the range of 200 or more but less than 8000, the content of the tri- or higher functional polyol is, for example, about 0.5 parts by weight or more, or may be about 1 part by weight or more, and in some preferred embodiments, 1.5 parts by weight or more, more preferably 2 parts by weight or more, or may be 5 parts by weight or more, or may be 10 parts by weight or more, or may be 15 parts by weight or more, or may be 20 parts by weight or more, relative to 100 parts by weight of the polyester contained in the PSA composition. In such an embodiment, the content of the tri- or higher functional polyol relative to 100 parts by weight of the polyester may be about 100 parts by weight or less, and is suitably about 80 parts by weight or less, and in some preferred embodiments, it is 60 parts by weight or less, more preferably 50 parts by weight or less, even more preferably 40 parts by weight or less, or may be 30 parts by weight or less, or may be 25 parts by weight or less.

[0070] In an embodiment using a polyester and a tri- or higher functional polyol, the PSA composition may or may not contain a bifunctional polyol. In such an embodiment, the content of the bifunctional polyol in the PSA composition may be, for example, less than 30 parts by weight, less than 10 parts by weight, less than 3 parts by weight, or less than 1 part by weight per 100 parts by weight of the tri- or higher functional polyol. The technology disclosed herein can be preferably implemented in an embodiment in which the PSA composition contains a polyester and a tri- or higher functional polyol and is substantially free of a bi- or higher functional polyol.

[0071] (Crosslinking Agent) In some embodiments, the pressure-sensitive adhesive composition preferably 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, hydrazine-based crosslinking agents, and amine-based crosslinking agents. The crosslinking agents can be used alone or in combination of two or more. The above-mentioned crosslinking agents are usually contained in the pressure-sensitive adhesive layer exclusively in the form after the crosslinking reaction. In addition, crosslinking agents used for crosslinking polyesters or polyols can also function as chain extenders.

[0072] The number of crosslinkable functional groups in the crosslinking agent is not particularly limited, and typically, those having 2 to 10, preferably 2 to 6, for example, 2 or 3 crosslinkable functional groups can be used. Therefore, any of bifunctional crosslinking agents having two crosslinkable functional groups, trifunctional crosslinking agents having three crosslinkable functional groups, and tetrafunctional or higher crosslinking agents having four or more crosslinkable functional groups can be used. Furthermore, the crosslinking agent may be derived from biomass or non-biomass. From the perspective of producing a PSA that takes into consideration reduced dependence on fossil resource-based materials, the use of a biomass-derived crosslinking agent is preferred.

[0073] 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 50 parts by weight relative to 100 parts by weight of the polyester contained in the pressure-sensitive adhesive composition. From the viewpoint of achieving a good balance between improved cohesive strength and adhesion to the adherend, the amount of crosslinking agent used relative to 100 parts by weight of the polyester is usually preferably 40 parts by weight or less, may be 30 parts by weight or less, or may be 25 parts by weight or less, and is suitably 1 part by weight or more, or may be 3 parts 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.

[0074] In some embodiments, the pressure-sensitive adhesive composition preferably contains an isocyanate-based crosslinking agent. The use of an isocyanate-based crosslinking agent allows the formation of a high-quality pressure-sensitive adhesive layer. The isocyanate-based crosslinking agents can be used alone or in combination of two or more.

[0075] 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, trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Co Examples of suitable polyisocyanates include isocyanate adducts such as derivatives of hexamethylene diisocyanate (manufactured by Asahi Kasei Corporation under the trade name "Duranate D101"), an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation under the trade name "Coronate HX"), and an isocyanurate of pentamethylene diisocyanate (manufactured by Mitsui Chemicals, Inc. under the 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 embodiments in which ethyl acetate and toluene are not substantially used, or in embodiments in which organic solvents are not substantially used, from the viewpoint of coatability, it is preferable to use aliphatic diisocyanates such as pentamethylene diisocyanate and hexamethylene diisocyanate, or isocyanurates of such aliphatic diisocyanates, etc. The proportion of aliphatic polyisocyanates (aliphatic diisocyanates, isocyanurates of aliphatic diisocyanates, etc.) in the total amount of isocyanate-based crosslinking agent is, for example, preferably more than 50% by weight, and may be 70% by weight or more, or may be 90% by weight or more (e.g., 95 to 100% by weight).

[0076] In some preferred embodiments, the PSA composition contains an isocyanate-based crosslinking agent having two isocyanate groups (bifunctional isocyanate-based crosslinking agent). The bifunctional isocyanate-based crosslinking agent is likely to improve anchoring properties even in PSA compositions that are substantially free of ethyl acetate and toluene. PSA compositions that do not use organic solvents for dilution use a relatively low-molecular-weight polyester to achieve coatability, and the resulting reduced cohesive strength is typically addressed by a multifunctional crosslinking agent with three or more functional groups. However, such a dense crosslinked structure can impair anchoring properties through factors such as a reduction in stress relaxation performance within the PSA layer. By using a bifunctional isocyanate-based crosslinking agent rather than a trifunctional or higher functional crosslinking agent as the crosslinking agent, a loose crosslinked structure with good extensibility can be formed, thereby enhancing the interfacial adhesion of the PSA layer to the substrate. Although not particularly limited, for example, by combining a trifunctional or higher polyol with a bifunctional isocyanate crosslinking agent to form a loose crosslinked structure with good extensibility, it is possible to suitably achieve both good interfacial adhesion and easy releasability. As the bifunctional isocyanate crosslinking agent, a bifunctional one (i.e., one having two isocyanate groups) from the materials exemplified above as the isocyanate crosslinking agent can be used. The bifunctional isocyanate crosslinking agent can be used alone or in combination of two or more.

[0077] In embodiments using a bifunctional isocyanate crosslinking agent, the amount of the bifunctional isocyanate crosslinking agent used is not particularly limited and may be, for example, about 1 part by weight or more, or about 3 parts by weight or more, relative to 100 parts by weight of the polyester contained in the pressure-sensitive adhesive composition. In some preferred embodiments, the amount of the bifunctional isocyanate crosslinking agent used relative to 100 parts by weight of the polyester is about 5 parts by weight or more, more preferably about 10 parts by weight or more, even more preferably about 15 parts by weight or more, particularly preferably about 18 parts by weight or more, or even about 20 parts by weight or more. In some embodiments, the amount of the bifunctional isocyanate crosslinking agent used relative to 100 parts by weight of the polyester is suitably about 50 parts by weight or less, may be about 40 parts by weight or less, may be about 30 parts by weight or less (e.g., less than 30 parts by weight), may be about 25 parts by weight or less, or may be about 22 parts by weight or less. By setting the amount of the bifunctional isocyanate crosslinking agent used within the above range, it is possible to preferably achieve both good anchoring properties and easy releasability.

[0078] In addition, in an embodiment in which the pressure-sensitive adhesive composition contains a polyester and a bifunctional isocyanate-based crosslinking agent and may further contain a trifunctional or higher polyol as an optional component, the amount of the bifunctional isocyanate-based crosslinking agent used is not particularly limited, and may be, for example, approximately 1 part by weight or more, or approximately 3 parts by weight or more, per 100 parts by weight of the polyester and the trifunctional or higher polyol combined. By increasing the amount of the bifunctional isocyanate-based crosslinking agent used, good curing properties are more likely to be obtained and cohesive strength can be improved. In some preferred embodiments, the amount of the bifunctional isocyanate-based crosslinking agent used per 100 parts by weight of the polyester and the trifunctional or higher polyol combined is approximately 5 parts by weight or more, more preferably approximately 8 parts by weight or more, and may be approximately 10 parts by weight or more, or may be approximately 12 parts by weight or more. In some embodiments, the amount of bifunctional isocyanate crosslinking agent used per 100 parts by weight of the polyester and tri- or higher functional polyol combined is suitably about 50 parts by weight or less, and may be about 30 parts by weight or less, about 25 parts by weight or less, about 20 parts by weight or less, about 18 parts by weight or less, about 16 parts by weight or less, or about 14 parts by weight or less. By setting the amount of bifunctional isocyanate crosslinking agent used within the above range, good anchoring properties and easy releasability can be preferably achieved at the same time.

[0079] In some embodiments, the pressure-sensitive adhesive composition may contain a trifunctional or higher isocyanate-based crosslinking agent. As the trifunctional or higher isocyanate-based crosslinking agent, a trifunctional or higher isocyanate-based crosslinking agent (i.e., having three or more isocyanate groups) can be used among the materials exemplified above as the isocyanate-based crosslinking agent. The trifunctional or higher isocyanate-based crosslinking agent can be used alone or in combination of two or more. The pressure-sensitive adhesive composition may contain a bifunctional isocyanate-based crosslinking agent and a trifunctional or higher isocyanate-based crosslinking agent.

[0080] Although not particularly limited, in embodiments in which the pressure-sensitive adhesive composition contains an isocyanate-based crosslinking agent, the proportion of the bifunctional isocyanate-based crosslinking agent in the total isocyanate-based crosslinking agents contained in the pressure-sensitive adhesive composition may be 10% by weight or more, suitably 25% by weight or more, or even 30% by weight or more, from the viewpoint of obtaining the effect of containing the bifunctional isocyanate-based crosslinking agent. In some preferred embodiments, the proportion of the bifunctional isocyanate-based crosslinking agent in the total isocyanate-based crosslinking agents is 50% by weight or more (e.g., more than 50% by weight), may be 70% by weight or more, may be 90% by weight or more, or may be 95% by weight or more (e.g., 99 to 100% by weight). The technology disclosed herein can be preferably implemented in embodiments in which the pressure-sensitive adhesive composition uses only a bifunctional isocyanate-based crosslinking agent as the isocyanate-based crosslinking agent. In addition, in an embodiment in which a bifunctional isocyanate-based crosslinking agent and a trifunctional or higher isocyanate-based crosslinking agent are used in combination, the proportion of the bifunctional isocyanate-based crosslinking agent in the entire isocyanate-based crosslinking agent may be 90% by weight or less, 70% by weight or less, 50% by weight or less (for example, less than 50% by weight), or 40% by weight or less.

[0081] In embodiments using an isocyanate-based crosslinking agent, the amount of the isocyanate-based crosslinking agent used is not particularly limited, and may be, for example, approximately 0.5 parts by weight or more, approximately 1 part by weight or more, or even 3 parts by weight or more, relative to 100 parts by weight of the polyester contained in the pressure-sensitive adhesive composition. Increasing the amount of the isocyanate-based crosslinking agent used makes it easier to obtain good curing properties and improve cohesive strength. In some embodiments, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the polyester is suitably approximately 5 parts by weight or more, or may be approximately 10 parts by weight or more, or may be approximately 12 parts by weight or more, or may be approximately 16 parts by weight or more, or may be approximately 18 parts by weight or more. Furthermore, in some embodiments, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the polyester is suitably approximately 50 parts by weight or less, or may be approximately 40 parts by weight or less, or may be approximately 30 parts by weight or less. By setting the amount of isocyanate-based crosslinking agent used within the above range, a suitably crosslinked structure is preferably formed in the pressure-sensitive adhesive layer, and a pressure-sensitive adhesive having sufficient cohesive strength is easily obtained.

[0082] In embodiments using an isocyanate-based crosslinking agent, the pressure-sensitive adhesive composition may contain one or more crosslinking agents other than the isocyanate-based crosslinking agent (non-isocyanate-based crosslinking agent). Examples of such non-isocyanate-based crosslinking agents include the crosslinking agents exemplified above, other than the isocyanate-based crosslinking agents. For example, from the viewpoint of obtaining the effects of using the isocyanate-based crosslinking agent, the proportion of the isocyanate-based crosslinking agent in the crosslinking agent contained in the pressure-sensitive adhesive composition may be 10% by weight or more, suitably 30% by weight or more, 50% by weight or more (e.g., more than 50% by weight), 70% by weight or more, 90% by weight or more, or 95% by weight or more (e.g., 99 to 100% by weight). The technology disclosed herein is preferably implemented in an embodiment using only an isocyanate-based crosslinking agent as the crosslinking agent.

[0083] Although not particularly limited, in an embodiment in which the pressure-sensitive adhesive composition contains a polyester and a crosslinking agent and may further contain a polyol as an optional component, the total content of the polyester, polyol, and crosslinking agent contained in the pressure-sensitive adhesive composition may be 80 wt% or more, 85 wt% or more, 90 wt% or more, or even 95 wt% or more of the entire pressure-sensitive adhesive composition. According to the technology disclosed herein, the above configuration makes it possible to form a pressure-sensitive adhesive layer that can exhibit desired performance with good productivity while sufficiently reducing the amount of organic solvent used. The upper limit of the total content of the polyester, polyol, and crosslinking agent contained in the pressure-sensitive adhesive composition may be, for example, less than 99 wt% and 97 wt% or less.

[0084] (Metal Catalyst) In some embodiments, the pressure-sensitive adhesive composition preferably contains a metal catalyst. The use of a metal catalyst promotes the crosslinking reaction, efficiently curing the pressure-sensitive adhesive composition, and enables the pressure-sensitive adhesive layer to be formed with high productivity. The metal catalyst is also referred to as a crosslinking catalyst. Examples of metal 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). Organic compounds having a metal in the active center, i.e., organometallic catalysts, are preferably used as the metal catalyst. Metal catalysts can be used alone or in combination of two or more.

[0085] Non-limiting specific examples of metal catalysts include dioctyltin dilaurate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin diacetylacetonate, tetra-n-butyltin, trimethyltin hydroxide, butyltin oxide, and the like (tin-based catalysts); zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium ethylacetoacetate, zirconium octylate compounds, and the like (zirconium-based catalysts); tetraisopropyl titanate, tetra-n-butyl titanate, titanium acetylacetonate, butyl titanate dimer, tetraoctyl titanate, titanium acetylacetonate, titanium tetraacetylacetonate, titanium ethylacetoacetate, etc. (titanium-based catalysts); hafnium tetraacetylacetonate, etc. (hafnium-based catalysts); nursem ferric acetonate, etc. (iron-based catalysts); aluminum sec-butoxide, aluminum trisacetylacetonate, aluminum bisethylacetoacetate, aluminum trisethylacetoacetate, etc. (aluminum-based catalysts);

[0086] In some preferred embodiments, a compound containing a Group 4 element is used as the metal catalyst from the viewpoints of catalytic activity and transparency. As the Group 4 element-containing compound, a zirconium-containing compound (zirconium-based catalyst) or a titanium-containing compound (titanium-based catalyst) is preferred. The Group 4 element-containing compound may be used alone or in combination of two or more.

[0087] In some preferred embodiments, the metal catalyst does not contain a tin-containing compound from the viewpoints of environmental impact and safety. By using a non-tin-based compound as the metal catalyst, the amount of tin-based compounds (typically organotin compounds) used in the PSA can be reduced. The PSA composition disclosed herein can form a good crosslinked structure with high productivity without using a tin-based catalyst, which generally tends to have a superior reaction rate. Furthermore, in some embodiments, the metal catalyst does not contain an iron-based catalyst. For example, in applications where the PSA requires transparency and optical properties, it is desirable to avoid the use of iron-based compounds, which may discolor the PSA.

[0088] In the embodiment of using a metal catalyst, the amount of the metal catalyst is not particularly limited.In some embodiments, from the viewpoint of efficiently proceeding with the crosslinking reaction, the amount of the metal catalyst can be, for example, about 0.01 parts by weight or more, preferably about 0.10 parts by weight or more, and may be about 0.12 parts by weight or more (for example, 0.15 parts by weight or more) relative to 100 parts by weight of the polyester contained in the pressure-sensitive adhesive composition.In addition, the amount of the metal catalyst can be, for example, about 3 parts by weight or less, preferably about 1 part by weight or less, and may be about 0.3 parts by weight or less relative to 100 parts by weight of the polyester.

[0089] (Organic Solvent) In some preferred embodiments, the PSA composition is substantially free of organic solvents. According to the technology disclosed herein, a PSA composition having a good pot life and excellent coatability can be obtained without using organic solvents that may be added for dilution purposes, such as to adjust the solid content or viscosity. This reduces the amount of organic solvent used in the preparation of the PSA composition, and ultimately in the formation of the PSA layer and the production of the surface protection sheet. Here, "the PSA composition is substantially free of organic solvents" refers to the absence of intentional addition of organic solvents to the PSA composition. However, this does not exclude the possibility of small amounts of organic solvents inevitably present in the raw materials of the PSA composition or unintentionally mixed in during the preparation of the PSA composition remaining in the composition. Specifically, "the PSA composition is substantially free of organic solvents" can be defined as the content (total amount) of organic solvents in the PSA composition being less than 5 parts by weight per 100 parts by weight of the polyester contained in the PSA composition. The content of the organic solvent is preferably less than 3 parts by weight, more preferably less than 1 part by weight, and even more preferably less than 0.3 parts by weight (e.g., less than 0.1 parts by weight). Note that the term "organic solvent" in this specification does not include compounds having an acetylacetone skeleton, which will be described later.

[0090] Typically, the PSA composition is substantially free of ethyl acetate and toluene. The technology disclosed herein is implemented without using ethyl acetate and toluene, which are typical organic solvents added for dilution purposes. By substantially freeing the PSA composition from ethyl acetate and toluene, the amount of organic solvent used in preparing the PSA composition can be reduced. Here, the meaning of "the PSA composition is substantially free of ethyl acetate and toluene" is basically the same as that described above for organic solvents. Specifically, it is defined as the content (total content) of ethyl acetate and toluene in the PSA composition being less than 5 parts by weight per 100 parts by weight of the polyester contained in the PSA composition. The content of ethyl acetate and toluene is preferably less than 3 parts by weight, more preferably less than 1 part by weight, and even more preferably less than 0.3 parts by weight (e.g., less than 0.1 parts by weight).

[0091] Furthermore, the PSA composition may typically be substantially free of MEK. Here, the meaning of "the PSA composition is substantially free of MEK" is basically the same as that of the organic solvent described above, and specifically, it may be defined as the content of MEK in the PSA composition being less than 5 parts by weight per 100 parts by weight of the polyester contained in the PSA composition. The content of MEK is preferably less than 3 parts by weight, more preferably less than 1 part by weight, and even more preferably less than 0.3 parts by weight (e.g., less than 0.1 parts by weight).

[0092] (Compound Having an Acetylacetone Skeleton) In some embodiments, the PSA composition preferably contains a compound having an acetylacetone skeleton. Compounds having an acetylacetone skeleton exhibit keto-enol tautomerism, and when incorporated into the PSA composition, they exhibit the effect of extending the pot life. Furthermore, since they volatilize upon heating, such as drying, they allow the PSA layer to rapidly cure after heating. Furthermore, incorporating a compound having an acetylacetone skeleton can improve the coatability of the PSA composition. By using an appropriate amount of a compound having an acetylacetone skeleton, it is possible to achieve both a reduction in the amount of organic solvent used and productivity. Examples of compounds having an acetylacetone skeleton include acetylacetone and acetoacetic esters (e.g., methyl acetoacetate, ethyl acetoacetate, etc.). Among these, acetylacetone is preferred from the viewpoints of coatability, PSA curability, etc.

[0093] Although not particularly limited, in some embodiments, from the viewpoint of obtaining sufficient pot life and coatability while reducing the amount of organic solvent used, the content of the compound having an acetylacetone skeleton in the pressure-sensitive adhesive composition is preferably more than 1 part by weight (specifically 1.0 part by weight) relative to 100 parts by weight of the polyester contained in the pressure-sensitive adhesive composition, more preferably 3.0 parts by weight or more, even more preferably 5.0 parts by weight or more, even more preferably 7.0 parts by weight or more, and particularly preferably 9.0 parts by weight or more. Furthermore, in some embodiments, from the viewpoint of, for example, exhibiting the catalytic action of the metal catalyst, the content of the compound having an acetylacetone skeleton is suitably about 15 parts by weight or less, and may be 12 parts by weight or less, relative to 100 parts by weight of the polyester contained in the pressure-sensitive adhesive composition.

[0094] (Other Additives) In some embodiments, the PSA composition may contain a tackifier. The use of an appropriate amount of tackifier can improve adhesive strength. The tackifier may be one or more selected from various known tackifier resins, such as phenolic tackifier resins, terpene tackifier resins, modified terpene tackifier resins, rosin tackifier resins, hydrocarbon tackifier resins, epoxy tackifier resins, polyamide tackifier resins, elastomer tackifier resins, and ketone tackifier resins.

[0095] The content of the tackifier in the PSA composition is not particularly limited. In some embodiments, the content of the tackifier in the PSA composition is suitably about 1 to 120 parts by weight, or may be 10 to 100 parts by weight, or may be 20 to 80 parts by weight, per 100 parts by weight of the polyester contained in the PSA composition. In other embodiments, the content of the tackifier in the PSA composition may be less than 10 parts by weight, less than 3 parts by weight, or less than 1 part by weight, per 100 parts by weight of the polyester contained in the PSA composition. The PSA composition may be substantially free of tackifier. Such a composition may be preferably applied to applications that require removability, such as surface protection.

[0096] The adhesive composition disclosed herein may contain a hydrolysis stabilizer (also referred to as a hydrolysis inhibitor). Addition of a hydrolysis stabilizer inhibits hydrolysis reactions in the adhesive, making it easier to achieve good durability. The hydrolysis stabilizer is not particularly limited, and known or conventional hydrolysis stabilizers can be used. Examples include oxazoline group-containing compounds, epoxy group-containing compounds, and carbodiimide group-containing compounds. Of these, carbodiimide group-containing compounds are preferred. One hydrolysis stabilizer can be used alone, or two or more can be used in combination.

[0097] Examples of carbodiimide group-containing compounds include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide, di-β-naphthylcarbodiimide, polycarbodiimide, and cyclic carbodiimides. The polycarbodiimide is a compound in which two or more carbodiimide groups are bonded together via a linking group composed of an aliphatic group, an alicyclic group, an aromatic group, or a combination thereof. The cyclic carbodiimide is a compound in which one or more carbodiimide groups are bonded together via a linking group composed of an aliphatic group, an alicyclic group, an aromatic group, or a combination thereof to form a ring structure, whereby the first and second nitrogen atoms of the carbodiimide groups are bonded together via a linking group composed of an aliphatic group, an alicyclic group, an aromatic group, or a combination thereof. The linking group may have a heteroatom or a substituent.

[0098] The amount of hydrolysis stabilizer (preferably a carbodiimide group-containing compound) used is not particularly limited, and is suitably about 0.05 parts by weight or more, preferably about 0.1 parts by weight or more, for example, about 0.3 parts by weight or more, per 100 parts by weight of the polyester contained in the pressure-sensitive adhesive composition so that the effect of the hydrolysis stabilizer is preferably exhibited. The upper limit of the amount of the hydrolysis stabilizer used is, for example, about 5 parts by weight or less, preferably about 3 parts by weight or less, for example, 1 part by weight or less, per 100 parts by weight of the polyester.

[0099] In addition to the above-mentioned components, the pressure-sensitive adhesive composition may contain, as necessary, various additives commonly used in the field of pressure-sensitive adhesives, such as leveling agents, fillers, plasticizers, softeners, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, etc. As for the above-mentioned various additives, conventionally known ones can be used in the usual manner, and they do not particularly characterize the present invention, so detailed description thereof will be omitted.

[0100] (Non-volatile Component Content) Although not particularly limited, in some embodiments, the content of non-volatile components in the PSA composition is preferably approximately 90% by weight or more. A PSA composition with such a low content of volatile components, such as organic solvents, uses a sufficiently reduced amount of organic solvent, and can be used as a substantially solvent-free PSA composition. The content of non-volatile components in the PSA composition may be 92% by weight or more, or may be 94% by weight or more. The upper limit of the content of non-volatile components in the PSA composition may be, for example, less than 99% by weight or 97% by weight or less, since volatile organic solvents may be contained in the PSA composition due to the products of the materials used. In this specification, the non-volatile components in the PSA composition refer to components present in the PSA layer after formation (after drying and aging), typically components present in the PSA layer as solids (solid content) after formation.

[0101] (Formation of Pressure-Sensitive Adhesive Layer) The pressure-sensitive adhesive layer can be formed from the pressure-sensitive adhesive composition by a conventionally known method. For example, a method (direct method) in which a pressure-sensitive adhesive composition is directly applied (typically coated) to a 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 the pressure-sensitive adhesive layer is then transferred to a substrate can be employed. The release surface can be the surface of a release liner or the back surface of a release-treated substrate. 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 performed simultaneously or in stages. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form. For example, the pressure-sensitive adhesive layer may be formed in a regular or random pattern such as a dotted or striped pattern.

[0102] The PSA composition can be applied using a known or conventional coater, such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, die coater, comma coater, bar coater, knife coater, or spray coater. Alternatively, the PSA composition may be applied by impregnation, curtain coating, or the like. In some preferred embodiments of the PSA composition disclosed herein, the PSA composition can be applied satisfactorily without relying on heating (i.e., at a temperature roughly similar to the ambient temperature at which the application is performed, for example, about 10 to 40°C), in a form that is substantially free of organic solvents (specifically, ethyl acetate and toluene) added for dilution purposes.

[0103] The drying of the PSA composition is preferably carried out under heating from the viewpoints of promoting the crosslinking reaction, improving production efficiency, etc. In some embodiments, the drying temperature is suitably, for example, about 80°C or higher, usually preferably about 100°C, and may be 120°C or higher. The upper limit of the heating temperature is not particularly limited, but is suitably about 200°C or lower, preferably about 180°C or lower, and may be about 160°C or lower, about 150°C or lower, or about 130°C or lower. By setting the heating temperature within an appropriate range, for example, in embodiments in which the PSA composition is dried on a substrate, thermal degradation of the substrate can be prevented, which is preferable. After drying the PSA composition, it is preferable to further perform aging for the purposes of adjusting component migration within the PSA layer, promoting the crosslinking reaction, and alleviating distortion that may exist in the substrate or PSA layer. The aging conditions are not particularly limited, and can be, for example, about 70°C or lower (typically about 20 to 70°C) for one day or more (e.g., three days or more).

[0104] <Substrate> The substrate constituting the surface protection sheet disclosed herein is not particularly limited, and for example, a resin film can be preferably used. Hereinafter, a surface protection sheet having a substrate including a resin film may be referred to as a "surface protection film." The resin film may be formed from various resin materials in a film shape. The resin material is preferably one that can form a resin film having one or more excellent properties, such as transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropy. For example, a resin film composed of a resin material whose main component (i.e., a component contained in an amount greater than 50% by weight) 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; or the like 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, ethylene-propylene copolymer, etc.; 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.

[0105] 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.

[0106] 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; paper such as Japanese paper, fine paper, kraft paper, and crepe paper; metal foil 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.

[0107] The substrate may be formed from a material of biological origin or a material of non-biological origin. From the viewpoint of producing a surface protection sheet that takes into consideration reduced dependence on fossil resource-derived materials, a substrate material of biological origin (typically a resin film) is preferably used.

[0108] 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 (e.g., polyester films such as PET films) are recyclable, so regardless of whether or not they use biologically derived materials, by reusing used resin films, sustainable reproduction is possible and the environmental burden can be reduced. Such recyclable resin films and recycled resin films are also referred to as recycled films. The recycled materials (e.g., recycled films) may be formed from biologically derived materials or non-biologically derived materials.

[0109] 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.

[0110] 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.

[0111] The substrate (typically a resin film) may contain various additives, such as a filler, an antioxidant, an antioxidant, an ultraviolet absorber, an antistatic component, a plasticizer, and a colorant (pigment, dye, etc.), as needed.

[0112] 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 can provide 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.

[0113] The thickness of the substrate can be appropriately selected taking into consideration the application, purpose, and usage form of the surface protective sheet. Typically, the thickness of the substrate is selected from a range of about 1 to 1,000 μm. In some embodiments, from the viewpoint of workability such as strength and handleability, a substrate having a thickness of about 10 μm or more is appropriate, and this thickness is preferably about 30 μm or more, and may be about 50 μm or more (e.g., 70 μm or more). Furthermore, in some embodiments, from the viewpoint of cost, etc., the thickness of the substrate is appropriately about 500 μm or less, preferably about 300 μm or less, more preferably about 150 μm or less, and may be about 100 μm or less (e.g., less than 100 μm).

[0114] <Total Thickness> The thickness (total thickness) of the surface protection sheet disclosed herein (including a pressure-sensitive adhesive layer, and in a surface protection sheet with a substrate, further including a substrate but excluding a release liner) is not particularly limited and can be, for example, in the range of approximately 2 μm to 1000 μm. In some embodiments, the thickness of the surface protection sheet is preferably about 5 μm to 500 μm (e.g., 10 μm to 300 μm, typically 15 μm to 200 μm), taking into account adhesive properties and the like. The lower limit of the thickness of the surface protection sheet is not particularly limited and may be, for example, approximately 30 μm or more, approximately 50 μm or more, or approximately 100 μm or more.

[0115] <Adhesive Properties> In some embodiments of the surface protection sheet disclosed herein, the surface protection sheet preferably has a peel strength (glass peel strength) from a glass plate measured under conditions of a temperature of 23°C, a peel angle of 180°, and a tensile speed of 300 mm / min of 1.0 N / 25 mm or less. A surface protection sheet that satisfies this property has a low peel strength (easy peelability) when peeled from an adherend (e.g., an object to be protected), and is therefore preferred from the standpoints of ease of peeling and reduced load on the adherend during peeling. The glass peel strength is more preferably less than 1.0 N / 25 mm, 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). It may also be 0.07 N / 25 mm or less, 0.05 N / 25 mm or less, or less than 0.05 N / 25 mm (e.g., 0.04 N / 25 mm or less). Furthermore, from the viewpoint of adhesion to the adherend and protection of the adherend, the glass peel strength is suitably 0.005 N / 25 mm or more, and may be 0.01 N / 25 mm or more, or may be 0.02 N / 25 mm or more. Specifically, the glass peel strength is measured by the method described in the Examples below. When a surface protection sheet is produced and the glass peel strength is evaluated, the surface protection sheet is produced, and then left to stand in an environment of 22°C and 50% RH for 3 days, and then the measurement is performed.

[0116] <Applications> The surface protective sheet disclosed herein has good anchoring properties and removability, making it suitable as a surface protective sheet that is attached to various objects to be protected and, after achieving its protective purpose, is peeled off (removed) from the object to be protected. The object to be protected by the surface protective sheet (e.g., a surface protective film) is not particularly limited, and the surface protective sheet can be used as a protective film for various products, parts, etc. For example, the surface protective sheet is particularly suitable as a surface protective sheet that protects 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.

[0117] Furthermore, the surface protective sheet disclosed herein has transparency while exhibiting good anchoring properties and removability, and is therefore useful as a surface protective film for optical applications requiring transparency in inspecting adherends. More specifically, the surface protective film is suitable for protecting optical components 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 components such as polarizing plates (polarizing films, e.g., reflective polarizing films) for liquid crystal display panels, wave plates, retardation plates, optical compensation films, brightness enhancement films, light diffusion sheets, and reflective sheets.

[0118] Furthermore, in some embodiments, the surface protection sheet disclosed herein can be formed from biologically derived materials, thereby contributing to reduced dependency on fossil resource-derived materials. The surface protection sheet disclosed herein can typically be preferably used as a surface protection sheet with reduced dependency on fossil resource-derived materials.

[0119] The matters disclosed in this specification include the following. [1] A surface protection sheet including a substrate and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer contains a polyester, and the pressure-sensitive adhesive layer has a ratio (F1 / F2) of the interfacial adhesion strength F1 with the substrate to the shear stress F2 of 0.6 or more and 3.0 or less. [2] The surface protection sheet according to [1] above, wherein the pressure-sensitive adhesive layer is substantially free of ethyl acetate and toluene. [3] The surface protection sheet according to [1] or [2] above, wherein the peel strength from a glass plate is 1.0 N / 25 mm or less. [4] The surface protection sheet according to any of [1] to [3] above, wherein the ratio (F1 / F2) is 1.0 or more and 3.0 or less. [5] The surface protection sheet according to any of [1] to [4] above, wherein the weight-average molecular weight of the polyester is 3,000 or more and 30,000 or less. [6] The surface protection sheet according to any of [1] to [5] above, wherein the substrate is a resin film.

[0120] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0121] Example 1 A four-neck separable flask was equipped with a stirrer, a thermometer, and a vacuum pump. 28 g of dimer acid (trade name "PRIPOL 1009", manufactured by Cargill, weight average molecular weight 567, trimer acid content 1%; in Table 2, it is indicated as "DA") as a dicarboxylic acid, 233 g of polyether diol (trade name "SANNICS PL-2100", manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight 2400; in Table 2, it is indicated as "DOL1") as a diol (molar ratio of the diol / dicarboxylic acid: 1.8 / 1.0), and 0.25 g of tetra normal butyl titanate (trade name "Orgatix TA21", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a polymerization catalyst were charged, and the mixture was stirred in a reduced pressure atmosphere (0.002 MPa), heated to 200 ° C., and maintained at this temperature. The reaction was continued for about 4 hours to obtain a polyester. The weight average molecular weight (Mw) of this polyester was 17,000 and the glass transition temperature (Tg) was -69°C.

[0122] A pressure-sensitive adhesive composition was obtained by blending 100 parts of the obtained polyester with 7.0 parts of a trifunctional isocyanate compound (trade name "STABIO D-370N", manufactured by Mitsui Chemicals, Inc., a derivative of 1,5-pentamethylene diisocyanate) as crosslinking agent C1, 3.2 parts of a bifunctional isocyanate compound (trade name "DURANATE D101", manufactured by Asahi Kasei Corporation, a derivative of 1,6-hexamethylene diisocyanate) as crosslinking agent C3, 0.1 parts of zirconium tetraacetylacetonate (trade name "ORGATIX ZC-150", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 10 parts of acetylacetone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0123] The pressure-sensitive adhesive composition was applied to a polyethylene terephthalate (PET) film (trade name "T100-75S", manufactured by Mitsubishi Chemical Corporation, thickness 75 μm) as a substrate so that the thickness after drying would be 75 μm, and the coating was dried for 2 minutes at 130° C. The release-treated surface of a release-treated PET film (trade name "Diafoil MRE38", manufactured by Mitsubishi Chemical Corporation) was then attached thereto, and the coating was allowed to stand in an environment of 22° C. and 50% RH for 3 days to obtain a pressure-sensitive adhesive sheet according to this example (a surface protection sheet in the form of a single-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on a substrate).

[0124] Examples 2 to 4 and Comparative Examples 1 to 3 In preparing the pressure-sensitive adhesive compositions, the type and amount of diol used in polyester synthesis, the presence or absence, type and amount of polyol used, and the type and amount of crosslinking agent were changed as shown in Table 2. Pressure-sensitive adhesive compositions of each example were obtained in the same manner as in Example 1, except that the obtained pressure-sensitive adhesive compositions were used. Pressure-sensitive adhesive sheets of each example were obtained in the same manner as in Example 1. The materials shown in Table 2 are as follows. DOL2: Polyether polyol manufactured by AGC (trade name "PREMINOL5005", number average molecular weight 4000, number of functional groups 2) DOL3: Polyether glycol manufactured by Mitsubishi Chemical Corporation (trade name "PTMG250", number average molecular weight 225, number of functional groups 2) DOL4: Polyether glycol manufactured by Mitsubishi Chemical Corporation (trade name "BioPTMG650", number average molecular weight 650, number of functional groups 2) Polyol A1: Polyether polyol manufactured by AGC (trade name "PREMINOL7012", polypropylene glycol, number average molecular weight 10000, number of functional groups 3) Polyol A2: Polyether polyol manufactured by AGC (trade name "EXCENOL230", polypropylene glycol, number average molecular weight 3000, number of functional groups 3) Crosslinking agent C2: Trifunctional isocyanate compound manufactured by Tosoh Corporation (trade name "Coronate HX", isocyanurate of hexamethylene diisocyanate)

[0125] <Measurement and Evaluation> (Gel Fraction) A 38 μm thick PET film (trade name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side was prepared. The pressure-sensitive adhesive composition immediately after blending was applied to the release-treated surface and dried at 130°C for 2 minutes to form a 75 μm thick pressure-sensitive adhesive layer. The surface of the resulting pressure-sensitive adhesive layer was covered with a 38 μm thick PET film (trade name "Diafoil MRE38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side, with the release-treated surface facing the pressure-sensitive adhesive layer. The film was then left to stand at 22°C and 50% RH for 3 days. Next, W1 g of pressure-sensitive adhesive was collected from the pressure-sensitive adhesive layer (adhesive amount: approximately 0.1 g) and wrapped in a porous PTFE (polytetrafluoroethylene) sheet to prepare a sample. The sample was placed in a glass bottle, immersed in toluene, and left to stand at 23°C for 7 days, after which the sample was removed and dried at 130°C for 2 hours. The dried sample was weighed, and the weight of the porous PTFE sheet was subtracted from it to determine the weight of the adhesive after drying, W2g. W1 and W2 were substituted into the following formula to calculate the gel fraction [%]: Gel fraction [%] = (W2 / W1) x 100. Note that the porous PTFE sheet may be a product manufactured by Nitto Denko Corporation under the trade name "TEMISH" or an equivalent product.

[0126] (Interfacial Adhesion) Using the pressure-sensitive adhesive composition according to each example, pressure-sensitive adhesive sheets were prepared in the same manner as in Example 1, except that the coating amount was adjusted so that the thickness of the pressure-sensitive adhesive layer was 25 μm, 50 μm, or 100 μm. The release-treated PET film was removed from the obtained pressure-sensitive adhesive sheet to expose the surface of the pressure-sensitive adhesive layer. Using a surface and interface analyzer (Surface and Interfacial Cutting Analysis System: SAICAS), oblique cutting was performed from the surface side of the exposed pressure-sensitive adhesive layer under the following test conditions. When the indentation depth by the oblique cutting reached the thickness of the pressure-sensitive adhesive layer, horizontal cutting was performed at that thickness to scrape off the pressure-sensitive adhesive layer from the substrate (PET film). The interfacial adhesion was calculated from the average horizontal load and blade width at this time using the following formula. Interfacial adhesion force [kN / m] = average value of horizontal load [N] / blade width [mm] The interfacial adhesion force was calculated by the above method for three types of pressure-sensitive adhesive sheets with different thicknesses of the adhesive layer, and an approximate formula was determined from the interfacial adhesion force and the thickness of the adhesive layer. Based on the approximate formula, the interfacial adhesion force F1 [kN / m] when the thickness of the adhesive layer was 0 μm was calculated. [Test conditions] - Apparatus: SAICAS EN-WA type (manufactured by Daipla Wintes) - Blade width: 1 mm (single crystal diamond) - Rake angle: 10° - Clearance angle: 10° - Cutting speed: horizontal 10 μm / sec, vertical 0.5 μm / sec

[0127] (Shear stress) The release-treated PET film was removed from the pressure-sensitive adhesive sheet (adhesive layer thickness: 75 μm) according to each example to expose the surface of the pressure-sensitive adhesive layer. Using a surface and interface analyzer (Surface and Interfacial Cutting Analysis System: SAICAS), oblique cutting was performed from the surface side of the exposed pressure-sensitive adhesive layer under the same test conditions as in the measurement of the interfacial adhesion force. When the indentation depth reached the thickness of the pressure-sensitive adhesive layer, horizontal cutting was performed at that thickness. The horizontal load when the indentation depth reached the thickness of the pressure-sensitive adhesive layer was taken as the shear stress F2 [N] of the pressure-sensitive adhesive layer.

[0128] (Ratio (F1 / F2)) The ratio (F1 / F2) was calculated from the interfacial adhesion strength F1 [kN / m] and the shear stress F2 [N].

[0129] (Anchoring ability) The release-treated PET film was removed from the PSA sheet (adhesive layer thickness: 75 μm) according to each example to expose the surface of the PSA layer. The surface of the exposed PSA layer was rubbed strongly with a finger, and if the PSA layer did not peel off from the substrate (PET film), it was evaluated as "○" (good anchoring ability), and if it peeled off, it was evaluated as "×" (insufficient anchoring ability).

[0130] (Glass peeling force) At an ambient temperature of 23 ° C., the release-treated PET film was peeled from the surface of the adhesive layer of a pressure-sensitive adhesive sheet cut to a size of 25 mm wide x 140 mm long, and the sheet was attached to a glass plate (soda-lime glass, manufactured by Matsunami Glass Industry Co., Ltd.) as an adherend by rolling a 2 kg hand roller back and forth once to obtain an evaluation sample. After leaving the sheet at the same ambient temperature for 30 minutes, the evaluation sample was placed in a tensile tester (manufactured by Kyowa Interface Science Co., Ltd., trade name "VPA-H200") under the same environment, and the load when the pressure-sensitive adhesive sheet was peeled from the glass plate under conditions of a peel angle of 180 degrees and a tensile speed of 300 mm / min was measured, and the average load was taken as the glass peeling force [N / 25 mm].

[0131] (Cohesive Strength) At an ambient temperature of 23°C, the adhesive surface of a measurement sample was exposed by cutting the pressure-sensitive adhesive sheet into a size of 25 mm wide x 100 mm long, and the sample was pressed against a glass plate (soda-lime glass, manufactured by Matsunami Glass Industry Co., Ltd.) as an adherend by rolling a 2 kg hand roller back and forth once. The measurement sample thus pressed against the adherend was then left at the same ambient temperature for 30 minutes, and then the pressure-sensitive adhesive sheet was peeled from the adherend using a tensile tester (manufactured by Kyowa Interface Science Co., Ltd., trade name "VPA-H200") at a peel angle of 180° and a tensile speed of 300 mm / min. At this time, it was visually confirmed whether the pressure-sensitive adhesive layer underwent cohesive failure, and the cohesive strength was evaluated according to the following criteria: ○: No cohesive failure was observed. ×: Cohesive failure was observed.

[0132] (Tg of Pressure-Sensitive Adhesive Layer) A 38 μm thick PET film (trade name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side was prepared, and the pressure-sensitive adhesive composition immediately after blending was applied to the release-treated surface. The adhesive composition was then dried at 130 ° C. for 2 minutes to form a 75 μm thick pressure-sensitive adhesive layer. The surface of the resulting pressure-sensitive adhesive layer was covered with a 38 μm thick PET film (trade name "Diafoil MRE38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side, with the release-treated surface facing the pressure-sensitive adhesive layer, and the film was left standing in an environment of 22 ° C. and 50% RH for 3 days. The pressure-sensitive adhesive layer was then cut into a size of 5 mm × 50 mm, and the release-treated PET film was peeled off to prepare a 50 mm long strip sample. Using a dynamic viscoelasticity measuring device (trade name "RSA-G2", manufactured by TA Instruments), the storage modulus E', loss modulus E" and loss tangent tan δ (loss modulus E" / storage modulus E') were measured under the following conditions, and the temperature at the peak top of the loss tangent tan δ was taken as the glass transition temperature [°C]. Loading mode: tension Loading gap: 20 mm Temperature range: -80°C to 100°C Heating rate: 5°C / min Frequency: 1 Hz Initial strain: 0.1%

[0133] The outline and evaluation results of each example are shown in Table 2. The Tg of the polyester was determined by the method described above. In Examples 3 and 4 containing a polyester and a tri- or higher functional polyol, the amount of hydroxyl groups A contained in the polyester was 0.01. ＯＨ Amount of hydroxyl groups contained in trifunctional or higher polyol relative to [mol] B ＯＨ Ratio of [mol] (B ＯＨ / A ＯＨ ) was 1.6 in Example 2 and 4.4 in Example 3. Furthermore, when the residual volatile components were quantified by the above-mentioned method for the PSA layers according to each of the Examples and Comparative Examples, the amount of ethyl acetate was less than 5 μg / g, the amount of toluene was less than 1 μg / g, and the amount of MEK was less than 1 μg / g in all cases.

[0134]

[0135] As shown in Table 2, the PSA sheets (surface protection sheets) of Examples 1 to 4, in which the ratio (F1 / F2) was in the range of 0.6 or more and 3.0 or less, exhibited good anchoring properties and removability (easy removability and resistance to adhesive residue) in configurations having PSA layers that were substantially free of ethyl acetate and toluene. The PSA sheet of Example 3, in which the ratio (F1 / F2) was 1.0 or more, was particularly excellent in easy removability. On the other hand, the PSA sheets of Comparative Examples 1 to 3, in which the ratio (F1 / F2) was less than 0.6, all exhibited poor anchoring properties, and the PSA sheet of Comparative Example 3 was also poor in easy removability.

[0136] 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.

[0137] REFERENCE SIGNS LIST 1 surface protection sheet 10 substrate 10A first surface 10B second surface (rear surface) 21 adhesive layer 21A adhesive surface 31 release liner 100 surface protection sheet with release liner

Claims

1. A surface protection sheet comprising a substrate and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer comprises polyester, and the ratio (F1 / F2) of the interfacial adhesion strength F1 [kN / m] with the substrate to the shear stress F2 [N] is 0.6 or more and 3.0 or less.

2. The surface protection sheet according to claim 1, wherein the pressure-sensitive adhesive layer is substantially free of ethyl acetate and toluene.

3. The surface protection sheet according to claim 1 or 2, which has a peel strength from a glass plate of 1.0 N / 25 mm or less.

4. The surface protection sheet according to claim 1 or 2, wherein the ratio (F1 / F2) is 1.0 or more and 3.0 or less.

5. The surface protection sheet according to claim 1 or 2, wherein the weight average molecular weight of the polyester is 3,000 or more and 30,000 or less.

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