Adhesive sheet and adhesive composition

Abstract

Provided is an adhesive sheet which can be coated and produced with good productivity, while having a good pot life even without using ethyl acetate and toluene. Provided is an adhesive sheet having an adhesive layer containing a polyester, an isocyanate-based crosslinking agent, and a metal catalyst. The adhesive layer does not substantially contain ethyl acetate and toluene. Furthermore, the pressure-sensitive adhesive layer contains 10 [mu] g to 100 [mu] g of a compound having an acetylacetone skeleton per 1 g of the pressure-sensitive adhesive layer.

Description

Technical Field

[0001] This invention relates to an adhesive sheet and an adhesive composition.

[0002] This application claims priority based on Japanese Patent Application No. 2023-051497, filed on March 28, 2023, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Generally, adhesives (also known as pressure-sensitive adhesives, hereinafter the same) are in a soft, solid (viscoelastic) state in a temperature range near room temperature, possessing the property of easily bonding to the adherends under pressure. Taking advantage of this property, adhesives are widely used in the form of adhesive sheets for purposes such as joining components and surface protection. For example, adhesive sheets having an adhesive layer on one surface of a substrate are preferably used as surface protection sheets to prevent damage (scratches, stains, corrosion, etc.) to the surface of various articles during processing or handling. Various adhesives, such as acrylic adhesives, rubber adhesives, and polyester adhesives, are used depending on the intended use, application location, and required characteristics. For example, Patent Documents 1 and 2 disclose prior art regarding polyester adhesives.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2011-236346

[0007] Patent Document 2: Japanese Patent Application Publication No. 2014-129463 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] In recent years, due to environmental concerns and the need to reduce the use of petroleum resources, there has been a demand to reduce the use of organic solvents. For polyester-containing adhesives, research has been conducted on so-called solvent-free adhesives that do not use organic solvents added for dilution purposes (e.g., Patent Document 1). However, if organic solvents are not used in the manufacture of polyester-containing adhesives, the flowability of the adhesive composition cannot be obtained, and the coatability is reduced. Furthermore, solvent-free adhesive compositions have a high concentration of solids, making them prone to crosslinking reactions before application, leading to increased viscosity and difficulty in achieving a sufficient pot life (usable time). Thus, solvent-free polyester-containing adhesives are disadvantageous in terms of productivity compared to solvent-based adhesives. For example, even using polytetramethylene ether glycol (PTMG), which has high room temperature flowability as used in Patent Document 2, the improvement in coatability is limited, making solvent-free production difficult.

[0010] The present invention was made in view of the above circumstances, and its object is to provide an adhesive sheet that, in the formation of a polyester-containing adhesive layer, can be applied with a good pot life even without the use of ethyl acetate and toluene, and can be manufactured with good productivity. A related object is to provide a polyester-containing adhesive composition that, even without the use of the aforementioned organic solvents, has a good pot life and good curing properties.

[0011] Solution for solving the problem

[0012] According to this specification, an adhesive sheet is provided having an adhesive layer comprising a polyester, an isocyanate-based crosslinking agent, and a metal catalyst. The adhesive layer is substantially free of ethyl acetate and toluene. Furthermore, the adhesive layer contains 10 μg to 100 μg of a compound with an acetylacetone backbone per 1g of the adhesive layer. The adhesive layer constructed as described above exhibits a good pot life even without the use of ethyl acetate and toluene, representative examples of organic solvents, and cures well after application. The adhesive sheet having this adhesive layer can be manufactured while simultaneously reducing organic solvent usage and increasing productivity.

[0013] In some preferred embodiments, the glass transition temperature (Tg) of the aforementioned polyester is below -30°C. By using a polyester with a low Tg, there is a tendency to easily obtain good coatability.

[0014] In some preferred embodiments, the weight-average molecular weight (Mw) of the aforementioned polyester is 20,000 or less. By using a polyester with Mw limited to a specified value or less, there is a tendency to easily obtain good coatability.

[0015] In some embodiments, the content of the isocyanate-based crosslinking agent in the adhesive layer is 5 parts by weight or more and 50 parts by weight or less relative to 100 parts by weight of the polyester. By setting the amount of isocyanate-based crosslinking agent used within the above range, a good crosslinking structure is formed in the adhesive layer, and an adhesive with sufficient cohesive strength is easily obtained.

[0016] Furthermore, according to this specification, an adhesive composition is provided comprising a polyester, an isocyanate-based crosslinking agent, and a metal catalyst. The adhesive composition is substantially free of ethyl acetate and toluene. On the other hand, in the adhesive composition, more than 1 part by weight of a compound having an acetylacetone backbone is added relative to 100 parts by weight of the polyester. According to the adhesive composition, since more than 1 part by weight of a compound having an acetylacetone backbone is added relative to 100 parts by weight of the polyester, it can achieve a sufficient pot life and good application even without the use of ethyl acetate and toluene, and the curing properties after application are good, thus enabling efficient formation of the adhesive layer. According to the adhesive composition, an adhesive sheet that balances reduced organic solvent usage and high productivity can be achieved.

[0017] In some preferred embodiments, the content of non-volatile components in the adhesive composition is 90% by weight or more. This adhesive composition sufficiently reduces the content of organic solvents as volatile components, and is therefore preferred.

[0018] In some preferred embodiments, the initial viscosity of the adhesive composition at 25°C is less than 3000 mPa·s. According to the technique disclosed herein, low-viscosity adhesive compositions can be prepared as described above even without the use of ethyl acetate and toluene, thus readily achieving good coatability. Attached Figure Description

[0019] Figure 1 This is a cross-sectional view schematically illustrating the structure of an adhesive sheet according to one embodiment. Detailed Implementation

[0020] The preferred embodiments of the present invention will now be described. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings on carrying out the invention described in this specification and common technical knowledge at the time of application. The present invention can be carried out based on the disclosures in this specification and common technical knowledge in the field.

[0021] It should be noted that in the following figures, sometimes the same reference numerals are used to describe components / parts that perform the same function, and sometimes repeated descriptions are omitted or simplified. Furthermore, the embodiments described in the figures are schematic for the purpose of clearly illustrating the invention and may not accurately represent the dimensions or scale of the adhesive sheet of the invention actually provided as a product.

[0022] <Adhesive Composition>

[0023] (Polyester)

[0024] The adhesive composition disclosed herein comprises polyester (hereinafter, unless otherwise specified, the matters described regarding the adhesive composition, except for those relating to organic solvents and compounds having an acetylacetone backbone, also apply to the adhesive layer described later). The aforementioned polyester is typically contained in the adhesive composition and adhesive (layer) in the form of a base polymer. Here, the base polymer refers to the main component of the rubbery polymer (a polymer exhibiting rubber elasticity in a temperature range near room temperature) contained in the adhesive composition and adhesive (layer). Furthermore, unless otherwise specified, "main component" in this specification refers to a component comprising more than 50% by weight. Additionally, in this specification, polyester refers to a polymer obtained by polycondensation of dicarboxylic acid and diol.

[0025] (Dicarboxylic acid)

[0026] As the dicarboxylic acid used to synthesize the above-mentioned polyester, any one of aliphatic dicarboxylic acids, dimer acids, alicyclic dicarboxylic acids, unsaturated dicarboxylic acids, and aromatic dicarboxylic acids can be used. Specific examples of dicarboxylic acids include: aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, dimethylglutaric acid, adipic acid, trimethyl adipic acid, pimelic acid, octanoic acid, azelaic acid, dodecanoic acid, sebacic acid, thiodipropionic acid, and diethylene glycol; dimer acids formed 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... Alicyclic dicarboxylic acids such as methyl-1,2-cyclohexanedicarboxylic acid, norbornenedicarboxylic acid, and adamantanedicarboxylic acid; unsaturated dicarboxylic acids such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic acid, and dodecenylsuccinic anhydride; aromatic dicarboxylic acids such as isophthalic acid, terephthalic acid, phthalic acid, benzylmalonic acid, 2,2'-biphenyl dicarboxylic acid, 4,4'-biphenyl dicarboxylic acid, 4,4'-dicarboxylic acid diphenyl ether, and naphthalenedicarboxylic acid; their derivatives; etc. It should be noted that the derivatives of the above dicarboxylic acids include carboxylates, carboxylic anhydrides, carboxylic halides, and carboxylic esters. By appropriately selecting and using one or more of these dicarboxylic acids, polyesters that exhibit the desired adhesive properties can be obtained.

[0027] In some preferred embodiments, dimer acids are used as dicarboxylic acids. Polyesters containing dimer acid units readily exhibit low glass transition temperatures and improved hydrolysis resistance. Furthermore, dimer acids are not easily volatile, thus they are also preferred for synthesis under high temperature and high pressure conditions, for example. One dimer acid can be used alone or in combination of two or more. In embodiments using dimer acids as the aforementioned dicarboxylic acids, the weight percentage of the dimer acid used in the synthesis of the polyester in the total amount of dicarboxylic acids (total weight) is not particularly limited, but is appropriately set to about 1% by weight or more, about 10% by weight or more, or about 30% by weight or more. In some preferred embodiments, the weight percentage of the dimer acid in the total amount of dicarboxylic acids is about 50% by weight or more, about 70% by weight or more, about 80% by weight or more, about 90% by weight or more, or about 95% by weight or more (e.g., 95-100% by weight). By setting the amount of dimer acid used to a specified level or higher, polyesters can be designed based on the characteristics of dimer acid (without particular limitation, for example, polyesters with a specified value of Mw and a specified value of Tg below a specified level).

[0028] In some preferred embodiments, biologically derived dicarboxylic acids are preferred as dicarboxylic acids from the viewpoint of reducing dependence on fossil-based materials. Preferred 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. Biologically derived dicarboxylic acids can be used alone or in combination of two or more.

[0029] The molecular weight of the dicarboxylic acid used is not particularly limited, but is appropriately 100 or higher, and can be 150 or higher, 250 or higher, 350 or higher, 450 or higher, or 500 or higher (e.g., 550 or higher). On the other hand, from the viewpoint of monomer availability and synthetic feasibility, the molecular weight of the dicarboxylic acid is appropriately around 1000 or lower, for example, 800 or lower, 700 or lower, or 600 or lower. As a preferred example of a dicarboxylic acid having the above molecular weight, dimer acids can be cited.

[0030] It should be noted that, in this specification, the molecular weight of a dicarboxylic acid can be the molecular weight calculated from its chemical formula or the manufacturer's nominal value (which can be either weight-average molecular weight or number-average molecular weight). Furthermore, in schemes using two or more dicarboxylic acids, the molecular weight of the dicarboxylic acid is the sum of the products of the molecular weight and weight fraction of each dicarboxylic acid (total value).

[0031] (diol)

[0032] As the diol used for synthesizing polyesters, any of the following can be used: (poly)alkylene glycols, aliphatic glycols, dimerized glycols, alicyclic glycols, aromatic glycols, and unsaturated glycols. Specific examples of the aforementioned diols include: ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, and other (poly)alkylene glycols; polytetramethylene ether glycol (PTMG), polytrimethylene ether glycol, copolymers of 3-methyltetrahydrofuran and tetrahydrofuran, copolymers of neopentyl glycol and tetrahydrofuran, and other polyether glycols; 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, 3-methyl-1,5-pentanediol, etc. Aliphatic diols such as 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; dimerized diols (dimerized diols derived from fatty acids such as oleic acid and erucic acid); alicyclic diols such as 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, spirodiol, tricyclodecanediol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol; aromatic diols such as 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, catechol, resorcinol, hydroquinone, 2,5-naphthalenediol, p-xylenediol, and their ethylene oxide and propylene oxide adducts; etc. By appropriately selecting one or more of these diols, polyesters that can exhibit the desired adhesive properties can be obtained.

[0033] In some preferred embodiments, polyether glycols are used as the glycol. Based on polyesters containing polyether glycol units, a low glass transition temperature is readily obtained, which helps improve the flowability and coatability of the substantially solvent-free adhesive composition. As a polyether glycol, polyalkylene ether glycols such as PTMG are preferred. Other examples of polyether glycols include: polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, etc. These can be equivalent to any of the polyalkylene glycols and polyether glycols. For example, polyether glycols containing oxypropylene units can be used as such polyether glycols. Polyether glycols containing oxypropylene units may further contain oxyethylene units or polyoxyethylene units. Examples of such polyether glycols include: polypropylene glycol with at least one end (preferably both ends) modified to (poly)oxyethylene, polyoxyethylene-polyoxypropylene block copolymers having oxyethylene units at at least one end (preferably both ends) and a polyoxyethylene structure, and random copolymers. Examples of polyoxyethylene-polyoxypropylene block copolymers include polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymers. Polyether glycols can be used alone or in combination of two or more. In embodiments using polyether glycols as the aforementioned glycols, the weight percentage of the polyether glycol used to synthesize the polyester in the total amount of glycols (total weight) is not particularly limited, but can be appropriately set to about 1% by weight or more, about 10% by weight or more, or about 30% by weight or more. In some preferred embodiments, the weight percentage of the polyether glycol in the total amount of glycols is about 50% by weight or more, about 70% by weight or more, about 80% by weight or more, about 90% by weight or more, or about 95% by weight or more (e.g., 95 to 100% by weight). By setting the amount of polyether glycol used to a predetermined amount or more, polyesters can be designed based on the characteristics of the polyether glycol (without particular limitation, for example, polyesters with a predetermined Mw value or less and a predetermined Tg value or less).

[0034] In some preferred embodiments, from the viewpoint of reducing dependence on fossil-based materials, bio-derived diols are preferred. Plant-derived polyether diols are a preferred example of such diols. Bio-derived diols can be used alone or in combination of two or more.

[0035] The molecular weight of the diol used is not particularly limited, but is appropriately 100 or higher, and can be 150 or higher, 250 or higher, 350 or higher, 450 or higher, or 550 or higher (e.g., 600 or higher). On the other hand, from the viewpoint of monomer availability and synthetic feasibility, the molecular weight of the diol is appropriately around 5000 or lower, for example, it can be 3500 or lower, 2500 or lower, 1200 or lower, 1000 or lower, 800 or lower, or 700 or lower. As a preferred example of a diol with the above molecular weight, polyether diols can be cited.

[0036] It should be noted that, in this specification, the molecular weight of the diol can be the molecular weight calculated from the chemical formula or the manufacturer's nominal value (which can be weight-average molecular weight or number-average molecular weight). Furthermore, in schemes using two or more diols, the molecular weight of the diol is the sum of the products of the molecular weight and weight fraction of each diol (total value).

[0037] Polyesters can be substantially composed of the aforementioned dicarboxylic acids and diols, but for the purpose of introducing desired functional groups, adjusting molecular weight, etc., other copolymer components besides dicarboxylic acids and diols can also be copolymerized without impairing the effects brought about by the technology disclosed herein. Examples of such other copolymer components include: polycarboxylic acids containing three or four or more carboxyl groups (trimethylammonia, pyromellitic acid, adamantane tricarboxylic acid, pyromellitic acid, trimeric acids, etc., which are ternary or higher polycarboxylic acids); and polyols containing three or four or more hydroxyl groups per molecule (pentaerythritol, dipentaerythritol, tripentaerythritol, glycerol, trimethylolpropane, etc.).

[0038] Trimethylolethane, 1,3,6-hexanetriol, adamantanetriol, etc.), monocarboxylic acids, monools, hydroxycarboxylic acids, lactones, etc. The aforementioned other copolymer components can be used alone or in combination of two or more. The proportion of the aforementioned other copolymer components in the polyester is, for example, appropriately set to less than 10% by weight, less than 3% by weight, typically less than 1% by weight (and further less than 0.1% by weight). The technology disclosed herein can preferably be implemented with a polyester that substantially does not contain the aforementioned other copolymer components.

[0039] In the monomer components used to synthesize polyesters, the total proportion of dicarboxylic acid and diol is appropriately 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 (e.g., 99 to 100% by weight), without particular limitation. The technology disclosed herein is preferably implemented using a scheme that uses polyesters substantially synthesized from dicarboxylic acid and diol.

[0040] In some preferred embodiments, the polyester is a combination of a dimer acid as a dicarboxylic acid and a polyether glycol as a glycol. By combining the dimer acid and the polyether glycol, it is possible, for example, to preferably synthesize a polyester having a Mw value below a specified value and a Tg value below a specified value, without particular limitation. From this viewpoint, in some embodiments, the combined proportion of the dimer acid and the polyether glycol in the total monomer content of the polyester is appropriately about 50% by weight or more, preferably about 60% by weight or more, more preferably about 70% by weight or more, further preferably about 80% by weight or more, and can be about 90% by weight or more, or about 95% by weight or more (for example, 99 to 100% by weight).

[0041] In some embodiments, it is appropriate that, in the synthesis of the polyester, more than 1 mole of diol is incorporated relative to 1 mole of dicarboxylic acid, without particular limitation. The molar ratio of diol to dicarboxylic acid (diol / dicarboxylic acid) is preferably 1.2 or more, more preferably 1.5 or more, and even more preferably 1.8 or more (e.g., 2.0 or more). By increasing the proportion of diol, polyester polyols with hydroxyl groups at the ends (typically both ends) can be obtained, which can preferably be crosslinked with isocyanate-based crosslinking agents described later. Furthermore, by setting the molar ratio (diol / dicarboxylic acid) within the above-mentioned range, polyesters with Mw controlled to a specified value or below are readily obtained. The upper limit of the above molar ratio (diol / dicarboxylic acid) of diol to dicarboxylic acid is not particularly limited. In some embodiments, from the viewpoint of polymerization efficiency, it can be 3.0 or less, 2.5 or less, or 2.2 or less.

[0042] There are no particular limitations on the method for obtaining polyesters, and any polymerization method known as a method for synthesizing polyesters can be appropriately employed. The polyester disclosed herein, like conventional polyesters, can be obtained by the polycondensation of a dicarboxylic acid and a diol. More specifically, the reaction of the carboxyl group of the dicarboxylic acid with the hydroxyl group of the diol occurs simultaneously with the removal of water (product water) typically generated in the above reaction from the reaction system, thereby synthesizing polyesters. Methods for removing the product water from the reaction system include: blowing an inert gas into the reaction system and removing the product water along with the inert gas; azeotropic dehydration by discharging the reaction water in the form of solvents such as toluene or xylene; and distilling the product water from the reaction system under reduced pressure (reduced pressure method), etc.

[0043] The reaction temperature and reaction time for the above reactions (including esterification and polycondensation); the decompression degree (pressure within the reaction system) when using the reduced pressure method can be appropriately set to efficiently obtain polyesters with the target properties (e.g., molecular weight). Typically, the above reaction temperature is appropriately set to about 150°C or higher (e.g., 180°C to 260°C), without particular limitation. By setting the reaction temperature within the above range, a good reaction rate is easily obtained, productivity is increased, and the deterioration of the generated polyester is prevented or suppressed. The reaction time is not particularly limited and can be approximately 1 to 48 hours (e.g., 3 to 10 hours). When using the reduced pressure method, there is no particular limitation, but the above decompression degree is typically appropriately set to below 10 kPa (typically 10 kPa to 0.1 kPa), for example, it can be set to 4 kPa to 0.1 kPa. By setting the pressure within the reaction system within the above range, the water generated during the reaction can be efficiently removed from the system by distillation, and a good reaction rate is easily maintained. Furthermore, at higher reaction temperatures, setting the pressure within the reaction system above the aforementioned lower limit easily prevents the dicarboxylic acid and diol used as raw materials from being distilled away from the system. From the viewpoint of maintaining a stable pressure within the reaction system, the pressure is typically set appropriately above 0.1 kPa.

[0044] In the above reaction, similar to the synthesis of typical polyesters, an appropriate amount of a known or conventional catalyst can be used for esterification and condensation. Examples of such catalysts include various metal compounds such as titanium-based, germanium-based, antimony-based, tin-based, and zinc-based compounds; strong acids such as p-toluenesulfonic acid and sulfuric acid; etc. The amount of catalyst used can be appropriately set according to the reaction rate, etc., therefore, detailed descriptions are omitted here.

[0045] In the above process of synthesizing polyesters via the reaction of dicarboxylic acids and diols, solvents (typically organic solvents) may or may not be used. The above synthesis can be carried out substantially without the use of organic solvents (e.g., excluding the option of intentionally using organic solvents as reaction solvents in the above reaction). Thus, the synthesis of polyesters substantially without the use of organic solvents and the preparation of adhesives using these polyesters are suitable for reducing the amount of organic solvent used, and are therefore preferred.

[0046] The polyester is preferably designed to have a low glass transition temperature (Tg), but there is no particular limitation. In embodiments where organic solvents such as ethyl acetate and toluene are not substantially used, using a polyester with a low Tg can reduce the viscosity of the adhesive composition and improve coatability. In some embodiments, the Tg of the polyester can be below 0°C, below -15°C, or below -25°C. In some preferred embodiments, from the viewpoint of coatability, the Tg of the polyester is below -30°C, below -45°C, below -55°C, below -65°C, or below -70°C (e.g., below -72°C). Furthermore, from the viewpoint of the cohesiveness of the adhesive layer, in some embodiments, the Tg of the polyester is typically above about -85°C, or above about -80°C.

[0047] In this specification, the Tg of the polyester is determined by the following method: A disc-shaped test piece with a thickness of 1 mm and a diameter of 8 mm is prepared using the polyester to be tested. The test piece is clamped with a parallel plate for shear testing, and the peak value of tanδ (loss modulus G” / storage modulus G’) is determined at a frequency of 1 Hz using a measuring device (ARES, manufactured by Rheometric Scientific). The temperature of the peak value is taken as Tg (glass transition temperature) [°C].

[0048] The molecular weight of the polyester is not particularly limited. A polyester with an appropriate molecular weight is used based on the intended use, etc. In some embodiments, the weight-average molecular weight (Mw) of the polyester is about 50,000 or less, and can be 30,000 or less. In some preferred embodiments, the Mw of the polyester is 20,000 or less, and can be 15,000 or less, 12,000 or less, 10,000 or less (e.g., less than 10,000), 8,000 or less, or 7,000 or less (e.g., 6,500 or less). By using a polyester with a Mw limited to a specified value, the viscosity of the adhesive composition can be reduced, and there is a tendency to easily obtain good coatability. The lower limit value of the polyester's Mw can be, for example, 2,000 or more, 4,000 or more, 5,000 or more, or 6,000 or more. By using a polyester with a large Mw, there is a tendency for the cohesiveness of the adhesive layer to increase.

[0049] In this specification, the Mw of polyester refers to the value converted from standard polystyrene obtained by GPC (gel permeation chromatography). For example, a GPC apparatus named "HLC-8320GPC" (column: TSKgelGMH-H(S), manufactured by TOSOH) can be used. More specifically, the GPC determination can be performed under the following conditions. The determination is also performed using the same method in the examples described later.

[0050] [GPC Measurement]

[0051] Column: TSKgelGMH-H(S).

[0052] Column temperature: 40℃.

[0053] Eluent: THF (with 0.1% by weight of amine components added).

[0054] Flow rate: 0.5 mL / min.

[0055] Injection volume: 100μL.

[0056] Detector: Differential refractometer (RI).

[0057] Standard sample: polystyrene (PS).

[0058] (Isocyanate-based crosslinking agent)

[0059] The adhesive composition disclosed herein contains an isocyanate-based crosslinking agent. By using the isocyanate-based crosslinking agent, a high-quality polyester-containing adhesive layer can be formed. The isocyanate-based crosslinking agent can be used alone or in combination of two or more. It should be noted that the aforementioned isocyanate-based crosslinking agent is generally contained primarily in the adhesive layer in its post-crosslinking form. Furthermore, the crosslinking agent used in the crosslinking of the polyester can also function as a chain extender.

[0060] As an isocyanate-based crosslinking agent, a polyisocyanate-based crosslinking agent having two or more isocyanate groups per molecule is preferred. The number of isocyanate groups per molecule of the polyisocyanate-based crosslinking agent is preferably 2 to 10, for example, 2 to 4, typically 2 or 3. Examples of such polyisocyanate-based crosslinking agents include: aromatic polyisocyanates such as toluene diisocyanate and xylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic polyisocyanates such as hexamethylene diisocyanate. More specifically, examples include: 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-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, phenyl diisocyanate, and polymethylene polyphenyl diisocyanate; trimethylolpropane / toluene diisocyanate trimer adducts, trimethylolpropane / hexamethylene diisocyanate trimer adducts (manufactured by TOSOH, trade name "CORONATE HL"), derivatives of hexamethylene diisocyanate (manufactured by Asahi Kasei Corporation, trade name "DURANATE D101"), and isocyanurates of hexamethylene diisocyanate (manufactured by TOSOH, trade name "CORONATE"). Isocyanate adducts such as pentamethylene diisocyanate (manufactured by Mitsui Chemicals, trade name "STABiO D370N"), polyisocyanates such as polyether polyisocyanates and polyester polyisocyanates, adducts of these polyisocyanates with polyols, and polyisocyanates formed by multifunctionalizing these polyisocyanates through isocyanurate bonds, biuret bonds, urethane bonds, etc. For example, in a scheme that substantially does not use organic solvents, from the viewpoint of coating properties, it is preferable to use aliphatic diisocyanates such as pentamethylene diisocyanate and hexamethylene diisocyanate, or isocyanurate forms of such aliphatic diisocyanates. The proportion of aliphatic polyisocyanates (aliphatic diisocyanates, isocyanurates of aliphatic diisocyanates, etc.) in the total amount of isocyanate crosslinking agents is preferably set to more than 50% by weight, or more than 70% by weight, or more than 90% by weight (e.g., 95 to 100% by weight).

[0061] The amount of isocyanate-based crosslinking agent used is not particularly limited. For example, it can be about 0.5 parts by weight or more, about 1 part by weight or more, or about 3 parts by weight or more relative to 100 parts by weight of polyester. By increasing the amount of isocyanate-based crosslinking agent used, good curing properties are easily obtained, and cohesion is also improved. In some embodiments, the amount of isocyanate-based crosslinking agent used relative to 100 parts by weight of polyester is appropriately set to about 5 parts by weight or more, about 10 parts by weight or more, about 12 parts by weight or more, about 16 parts by weight or more, or about 18 parts by weight or more. Furthermore, in some embodiments, the amount of isocyanate-based crosslinking agent used relative to 100 parts by weight of polyester is appropriately set to about 50 parts by weight or less, about 40 parts by weight or less, or about 30 parts by weight or less. By setting the amount of isocyanate-based crosslinking agent used within the above-mentioned range, a structure formed by moderate crosslinking of polyester is preferably formed in the adhesive layer, and an adhesive with sufficient cohesion is easily obtained.

[0062] The adhesive composition disclosed herein may also contain one or more crosslinking agents other than isocyanate-based crosslinking agents (non-isocyanate-based crosslinking agents) without impairing the effects of the invention. Examples of such non-isocyanate-based crosslinking agents include epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, and metal chelate-based crosslinking agents. For example, from the viewpoint of obtaining the effect of containing an isocyanate-based crosslinking agent, the proportion of the isocyanate-based crosslinking agent in the crosslinking agent contained in the adhesive composition is appropriately 50% by weight or more, and may be 70% by weight or more, 90% by weight or more, or 95% by weight or more (e.g., 95 to 100% by weight).

[0063] (Metal catalyst)

[0064] The adhesive composition contains a metal catalyst. By using the metal catalyst, the cross-linking reaction of the isocyanate-based cross-linking agent can be promoted, resulting in efficient curing of the adhesive composition and productive formation of the adhesive layer. This metal catalyst is also called a cross-linking 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). Among these, organometallic catalysts, those having a metal at their active center, are preferred. Titanium-based catalysts are preferred from the perspectives of catalytic activity and transparency. One metal catalyst can be used alone, or two or more can be used in combination.

[0065] Non-limiting specific examples of metal catalysts include: dioctyltin dilaurate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin diacetylacetonate, tetra-n-butyltin, trimethyltin hydroxide, butyltin oxide, etc. (tin-based catalysts); zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium ethyl acetoacetate, zirconium octanoate compounds, etc. (zirconium-based catalysts); tetraisopropyl titanate, tetra-n-butyl titanate, tetrabutyl titanate dimer, tetraoctyl titanate, titanium acetylacetonate, titanium tetraacetylacetonate, titanium ethyl acetoacetate, etc. (titanium-based catalysts); hafnium tetraacetylacetonate, etc. (hafnium-based catalysts); NACEM Iron(III), etc. (iron-based catalysts); aluminum sec-butoxide, aluminum triacetylacetonate, aluminum diacetate, aluminum triacetate, etc. (aluminum-based catalysts); etc.

[0066] In some preferred embodiments, from the viewpoint of environmental impact and safety, the aforementioned metal catalysts are free of tin-containing compounds. By using non-tin compounds as metal catalysts, the amount of tin-based compounds (typically organotin) used in the binder can be reduced. According to the binder compositions disclosed herein, a good cross-linked structure can be formed with good productivity without using tin-based catalysts, which typically exhibit excellent reaction rates. Furthermore, in some embodiments, the metal catalyst is free of iron-based catalysts. For example, in applications requiring transparency and optical properties in the binder, it is ideal to avoid using iron-based compounds that may cause discoloration of the binder.

[0067] There is no particular limitation on the amount of metal catalyst used. In some embodiments, from the viewpoint of enabling the crosslinking reaction to proceed efficiently, the amount of metal catalyst used relative to 100 parts by weight of polyester can be, for example, about 0.01 parts by weight or more, preferably about 0.10 parts by weight or more, and can be about 0.12 parts by weight or more (for example, 0.15 parts by weight or more). Furthermore, the amount of metal catalyst used relative to 100 parts by weight of polyester can be, for example, about 3 parts by weight or less, appropriately about 1 part by weight or less, and can be about 0.3 parts by weight or less.

[0068] In some embodiments, the total content of polyester, isocyanate-based crosslinking agent, and metal catalyst in the adhesive composition can be 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more, without particular limitation. According to the technology disclosed herein, the above configuration can sufficiently reduce the amount of organic solvent used and efficiently form the adhesive layer. The upper limit of the total content of polyester, isocyanate-based crosslinking agent, and metal catalyst in the adhesive composition is, for example, less than 99% by weight, and can be 97% by weight or less.

[0069] (Polyols)

[0070] In some formulations, the adhesive composition preferably includes a polyol. Including a polyol reduces the viscosity of the adhesive composition and improves its spreadability. As the polyol, any type of difunctional polyol having two hydroxyl groups or trifunctional or higher polyol having three or more hydroxyl groups can be used. Furthermore, various polyols such as polyether polyols, polyester polyols, and polycarbonate polyols can be used. One polyol can be used alone, or two or more can be used in combination.

[0071] As the polyol, polyether polyols such as polyalkylene glycols are preferred, but there are no particular limitations. Polyether polyols readily offer good processability and coatability, and are also advantageous in terms of improved wetting and easy peeling properties. Examples of such polyols include: polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polytetramethylene ether glycol, polytrimethylene ether glycol, copolymers of 3-methyltetrahydrofuran and tetrahydrofuran, and copolymers of neopentyl glycol and tetrahydrofuran. Among these, polyether polyols containing oxypropylene units are preferred. Polyether polyols containing oxypropylene units or polyoxypropylene structures have low viscosity due to their amorphous structure, which is advantageous in terms of processability and coatability. Polyether polyols containing oxypropylene units may further contain oxyethylene units or polyoxyethylene units. As such polyols, from the viewpoint of reactivity, for example, polypropylene glycol with at least one end (preferably both ends) modified to (poly)oxyethylidene, polyoxyethylene-polyoxypropylene block copolymers having oxyethylidene units at at least one end (preferably both ends), and random copolymers can be used. Examples of the aforementioned polyoxyethylene-polyoxypropylene block copolymers include polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymers.

[0072] The molecular weight of the polyol is not particularly limited; for example, polyols with a number average molecular weight in the range of 200 to 20,000 can be used. In some embodiments, the number average molecular weight of the polyol can be 300 or more, or 400 or more. In some preferred embodiments, the number average molecular weight of the polyol can be 1,000 or more, or 2,000 or more, or 3,000 or more, or 4,000 or more. By using polyols with high molecular weights, there is a tendency to obtain good wetting properties and light peeling properties. Furthermore, in some embodiments, the number average molecular weight of the polyol can be 15,000 or less, or 13,000 or less. In some preferred embodiments, the number average molecular weight of the polyol can be less than 10,000, less than 8,000, or 7,000 or less, or 5,000 or less. According to the adhesive composition containing polyols with a number average molecular weight below the specified value, it is easy to maintain a low viscosity, which is advantageous from the perspective of coatability.

[0073] It should be noted that, in this specification, the number-average molecular weight of the polyol can be the manufacturer's nominal value. If the nominal value is unclear, the value determined by GPC under known appropriate conditions can be used. Furthermore, in schemes using two or more polyols, the number-average molecular weight of the polyol is the sum of the products of the number-average molecular weight and weight fraction of each polyol (total value).

[0074] In embodiments using polyols, the amount of polyol used is not particularly limited. In some embodiments, the polyol content relative to 100 parts by weight of polyester can be about 0.5 parts by weight or more, about 1 part by weight or more, 2 parts by weight or more, 5 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more. The higher the polyol content, the easier it is to reduce the viscosity of the adhesive composition. In some embodiments, the polyol content relative to 100 parts by weight of polyester can be 30 parts by weight or more, 40 parts by weight or more, or 50 parts by weight or more. Furthermore, from a compatibility point of view, in some embodiments, the polyol content relative to 100 parts by weight of polyester can be about 300 parts by weight or less, about 200 parts by weight or less, or about 150 parts by weight or less. In some preferred embodiments, the polyol content relative to 100 parts by weight of polyester can be 120 parts by weight or less, 100 parts by weight or less, or 80 parts by weight or less.

[0075] (Organic solvents)

[0076] In some preferred embodiments, the adhesive composition is substantially free of organic solvents. According to the technology disclosed herein, an adhesive composition with good pot life and good coatability can be obtained without using organic solvents used for dilution purposes in adjusting the concentration of solid components, viscosity, etc. Thus, the amount of organic solvent used is reduced in the preparation of the adhesive composition, and subsequently in the formation of the adhesive layer and the manufacture of the adhesive sheet. Here, "the adhesive composition is substantially free of organic solvents" means that no organic solvents are intentionally added to the adhesive composition, excluding the possibility of organic solvents unavoidably present in the raw materials of the adhesive composition, or small amounts of organic solvents accidentally mixed in during the preparation of the adhesive composition remaining in the composition. Specifically, the above-mentioned "the adhesive composition is substantially free of organic solvents" can be defined as the content (total) of organic solvents in the adhesive composition being less than 5 parts by weight per 100 parts by weight of polyester. The content of the above-mentioned organic solvents 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). It should be noted that the term "organic solvents" in this specification does not include compounds with an acetylacetone skeleton, as described later.

[0077] The adhesive composition described above is substantially free of ethyl acetate and toluene. The technique disclosed herein can be implemented without using ethyl acetate and toluene, representative examples of organic solvents used for dilution purposes in adjusting solid component concentration, viscosity, etc. By being substantially free of ethyl acetate and toluene, the amount of organic solvent used in the preparation of the adhesive composition is reduced. Here, "the adhesive composition is substantially free of ethyl acetate and toluene" has essentially the same meaning as the description regarding the aforementioned organic solvents; specifically, it is defined as the content (total content) of ethyl acetate and toluene in the adhesive composition being less than 5 parts by weight per 100 parts by weight of polyester. 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).

[0078] Furthermore, typically, the adhesive composition described above may be substantially free of methyl ethyl ketone (MEK). Here, "the adhesive composition is substantially free of MEK" means essentially the same as the description regarding the organic solvents described above; specifically, it can be defined as the MEK content in the adhesive composition being less than 5 parts by weight per 100 parts by weight of polyester. The MEK content 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).

[0079] (Compounds with an acetylacetone skeleton)

[0080] In the adhesive composition disclosed herein, more than 1 part by weight (specifically 1.0 part by weight) of a compound having an acetylacetone backbone is added relative to 100 parts by weight of polyester. The compound having an acetylacetone backbone exhibits keto-enol tautomerism, which, when incorporated into the adhesive composition, extends the pot life. Furthermore, it volatilizes upon heating, such as drying, allowing for rapid curing of the adhesive layer after heating. In addition, the application properties of the adhesive composition are improved by incorporating the compound having an acetylacetone backbone. By incorporating more than 1 part by weight of a compound having an acetylacetone backbone relative to 100 parts by weight of polyester, sufficient pot life and good application are achieved even without the use of ethyl acetate and toluene, representative examples of organic solvents, and good curing properties after application are also achieved, thus enabling efficient and efficient formation of the adhesive layer. By using an appropriate amount of a compound having an acetylacetone backbone, both the amount of organic solvent used and productivity can be balanced. Examples of compounds having an acetylacetone backbone include acetylacetone and acetoacetate esters (methyl acetoacetate, ethyl acetoacetate, etc.). Among these considerations, acetylacetone is preferred, taking into account factors such as coatability and adhesive curing properties.

[0081] In some embodiments, from the viewpoint of obtaining a sufficient pot life and coatability, the content of the compound having an acetylacetone backbone in the adhesive composition may be 2.0 parts by weight or more, appropriately 2.5 parts by weight or more, preferably 3.0 parts by weight or more, more preferably 4.0 parts by weight or more, and even more preferably 4.5 parts by weight or more, and may be 7.0 parts by weight or more, or may be 9.0 parts by weight or more, relative to 100 parts by weight of the polyester. Furthermore, in some embodiments, for example, from the viewpoint of exhibiting the catalytic effect of a metal catalyst, the content of the aforementioned compound having an acetylacetone backbone is appropriately 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. In some preferred embodiments, from the viewpoint of reducing the amount of volatile components used and the adhesive layer formation properties, the content of the aforementioned compound having an acetylacetone backbone is 10 parts by weight or less, more preferably 8.0 parts by weight or less, even more preferably 6.0 parts by weight or less, particularly preferably 5.0 parts by weight or less, and may be 3.5 parts by weight or less, or may be 1.5 parts by weight or less.

[0082] (Other additives)

[0083] In some formulations, the adhesive composition may also include a tackifier. By using an appropriate amount of tackifier, the adhesive strength can be improved. As the aforementioned tackifier, one or more of a variety of known tackifying resins selected from phenolic tackifying resins, terpene tackifying resins, modified terpene tackifying resins, rosin-based tackifying resins, hydrocarbon-based tackifying resins, epoxy-based tackifying resins, polyamide-based tackifying resins, elastic tackifying resins, ketone-based tackifying resins, etc., may be used.

[0084] The content of the tackifier in the adhesive composition is not particularly limited. In some embodiments, the content of the tackifier in the adhesive composition is appropriately set to about 1 to 120 parts by weight relative to 100 parts by weight of polyester, specifically 10 to 100 parts by weight or 20 to 80 parts by weight. In other embodiments, the content of the tackifier in the adhesive composition may be less than 10 parts by weight, less than 3 parts by weight, or less than 1 part by weight relative to 100 parts by weight of polyester, and the adhesive composition may also be substantially free of tackifier. This composition is preferably used, for example, for re-peeling applications such as surface protection.

[0085] Furthermore, the adhesive compositions disclosed herein may also contain a hydrolysis-resistant agent (also known as an anti-hydrolysis agent). By adding a hydrolysis-resistant agent, the hydrolysis reaction in the adhesive is suppressed, and good durability is easily obtained. There are no particular limitations on the hydrolysis-resistant agent; known or conventional hydrolysis-resistant agents can be used. Examples include compounds containing an oxazoline group, compounds containing an epoxy group, and compounds containing a carbodiimide group. Among these, compounds containing a carbodiimide group are preferred. One hydrolysis-resistant agent may be used alone or in combination of two or more.

[0086] Examples of compounds containing a carbodiimide group include: dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, tert-butylisopropylcarbodiimide, diphenylcarbodiimide, ditert-butylcarbodiimide, di-β-naphthylcarbodiimide, polycarbodiimide, and cyclic carbodiimide. The aforementioned polycarbodiimide is a compound formed by the bonding of two or more carbodiimide groups through a bonding group composed of an aliphatic group, an alicyclic group, an aromatic group, or a combination thereof. Furthermore, the aforementioned cyclic carbodiimide is a compound having one or more carbodiimide groups within its molecular structure, wherein the first nitrogen atom and the second nitrogen atom of the carbodiimide group are bonded together through a bonding group composed of an aliphatic group, an alicyclic group, an aromatic group, or a combination thereof to form a ring structure. The aforementioned bonding groups may also have heteroatoms or substituents.

[0087] The amount of hydrolysis-resistant agent (preferably a compound containing a carbodiimide group) used is not particularly limited. However, to preferably achieve the effect of containing the hydrolysis-resistant agent, it is appropriately set to about 0.05 parts by weight or more, preferably about 0.1 parts by weight or more, and for example, about 0.3 parts by weight or more, relative to 100 parts by weight of polyester. The upper limit of the above-mentioned amount of hydrolysis-resistant agent used is, for example, appropriately about 5 parts by weight or less, preferably about 3 parts by weight or less, and for example, about 1 part by weight or less, relative to 100 parts by weight of polyester.

[0088] In addition to the components mentioned above, the adhesive composition may also include, as needed, various additives commonly used in the field of adhesives, such as leveling agents, fillers, plasticizers, softeners, colorants (pigments, dyes, etc.), antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, and light stabilizers. Regarding the various additives mentioned above, conventionally known substances can be used by conventional methods, and since this invention is not specifically characterized, detailed descriptions are omitted.

[0089] (Viscosity)

[0090] In some embodiments, the initial viscosity of the adhesive composition at 25°C is, for example, less than about 10,000 mPa·s, less than about 5,000 mPa·s, or less than about 3,000 mPa·s, without particular limitation. Good coatability is readily obtained with adhesive compositions having viscosities below the specified values ​​as described above. In some preferred embodiments, the initial viscosity of the adhesive composition at 25°C is less than 3,000 mPa·s, less than about 2,500 mPa·s, less than 2,200 mPa·s, or less than 2,000 mPa·s (e.g., less than 1,900 mPa·s). According to the technology disclosed herein, even without the use of organic solvents, adhesive compositions with good coatability can be prepared by having the viscosity described above. Furthermore, in some embodiments, the initial viscosity of the adhesive composition at 25°C is, for example, greater than or equal to about 1,000 mPa·s, more than or equal to about 1,200 mPa·s, or more than or equal to about 1,500 mPa·s. According to the adhesive composition having a viscosity within the above range, it is preferable to balance coatability, workability, and productivity.

[0091] In this specification, the initial viscosity of the adhesive composition at 25°C refers to the viscosity measured within 30 minutes after the preparation of the adhesive composition at 25°C ± 5°C, and can be measured using a commercially available viscometer or rheometer. For example, the rheometer used in the examples described later can be used as the rheometer.

[0092] (Viscosity increase rate)

[0093] The viscosity rise rate of the adhesive composition disclosed herein, as measured by the method described in the examples below, is preferably 10% or less after 6 hours. An adhesive composition with such a suppressed viscosity rise rate has a sufficient pot life and thus maintains good coatability for a long time. In some preferred embodiments, the viscosity rise rate after 6 hours is 7% or less, but can be 5% or less, 3% or less, or 1% or less.

[0094] (Content of non-volatile components)

[0095] Furthermore, in some embodiments, the content of non-volatile components in the adhesive composition is preferably about 90% by weight or more, without particular limitation. This significantly reduces the amount of organic solvents used in the adhesive composition, allowing it to be used as a substantially solvent-free adhesive composition. The content of non-volatile components in the aforementioned adhesive composition can be 92% by weight or more, or 94% by weight or more, or 95% by weight or more, or 96% by weight or more, or 97% by weight or more. Considering the possibility of including volatile organic solvents derived from the materials used, the upper limit of the content of non-volatile components in the aforementioned adhesive composition can be, for example, less than 99% by weight, or less than 97% by weight. It should be noted that, in this specification, the non-volatile components in the adhesive composition refer to components present in the adhesive layer after formation (after drying and curing), typically referring to components present in the formed adhesive layer in solid form (solid components).

[0096] (Initial degree of crosslinking)

[0097] The adhesive composition disclosed herein preferably exhibits an initial crosslinking degree of 40% or higher, as determined by measuring a sample (adhesive) heated at 120°C for 2 minutes. Based on this initial crosslinking degree, the adhesive composition exhibits good curing properties after application, enabling the efficient formation of a high-quality adhesive layer. In some embodiments, from the viewpoint of curability, the aforementioned initial crosslinking degree is preferably 45% or higher, but can be 50% or higher, 55% or higher, 60% or higher, or 65% or higher. In some embodiments, from the viewpoint of balancing sufficient pot life and curability, the aforementioned initial crosslinking degree is preferably around 70% or lower, but can be around 60% or lower, or 50% or lower. Specifically, the aforementioned initial crosslinking degree is determined by the method described in the examples described later.

[0098] (Formation of the adhesive layer)

[0099] The adhesive layer can be formed from the adhesive composition using conventionally known methods. For example, in the case of a substrate-free double-sided adhesive sheet, the adhesive sheet can be formed by applying the adhesive composition to a peelable surface (peel surface) and then curing the adhesive composition, thereby forming an adhesive layer on that surface. Furthermore, in the case of an adhesive sheet with a substrate, a direct method is preferred: the adhesive composition is directly applied (typically coated) to the substrate and cured to form an adhesive layer. Alternatively, a transfer method can be used: the adhesive composition is applied to a peelable surface (peel surface) and cured to form an adhesive layer, which is then transferred to the substrate. The peel surface can be the surface of a release liner, the back side of a peeled substrate, etc. Furthermore, the adhesive composition can be cured by performing curing treatments such as drying, crosslinking, polymerization, or cooling. Two or more curing treatments can be performed simultaneously or in stages. It should be noted that the adhesive layer disclosed herein is typically formed continuously, but is not limited to this form; for example, it can also be formed as a regular or irregular pattern such as dots or stripes.

[0100] The coating of the adhesive composition can be performed using, for example, a gravure roller coater, a reverse roller coater, a roller coater, an immersion roller coater, a die coater, a comma coater, a bar coater, a doctor blade coater, a spray coater, or other known or conventional coating machines. Alternatively, the adhesive composition can also be coated by impregnation, curtain coating, or other methods. The adhesive composition disclosed herein can be readily coated without relying on heating (and thus at a temperature approximately the same as the ambient temperature at which coating is performed, for example, around 10–40°C), in a form substantially free of organic solvents (specifically, ethyl acetate and toluene) added for dilution purposes.

[0101] From the viewpoint of promoting crosslinking reactions and improving manufacturing efficiency, the drying of the adhesive composition is preferably carried out under heating. In some embodiments, the drying temperature is appropriately set to about 80°C or higher, typically preferably around 100°C, and can be 120°C or higher. There is no particular limitation on the upper limit of the heating temperature, which is appropriately set to about 200°C or lower, preferably about 180°C or lower, and can be about 160°C or lower, or about 150°C or lower, or about 130°C or lower. By setting the heating temperature to an appropriate range, for example in the embodiment of drying the adhesive composition on a substrate, it is preferable to prevent thermal degradation of the substrate. After drying the adhesive composition, it is preferable to further cure it for purposes such as adjusting the transfer of components within the adhesive layer, proceeding with the crosslinking reaction, and mitigating any strain that may exist within the substrate or adhesive layer. There is no particular limitation on the curing conditions, which can be, for example, about 70°C or lower (typically about 40 to 70°C) for more than one day (e.g., more than three days).

[0102] <Adhesive Sheet>

[0103] According to this specification, an adhesive sheet is provided, which has an adhesive layer formed from any of the adhesive compositions disclosed herein. The adhesive sheet may be a substrate-supported adhesive sheet having the adhesive layer on one or both sides of a non-peelable substrate (supporting substrate), or a substrate-free adhesive sheet (i.e., an adhesive sheet without a non-peelable substrate) in which the adhesive layer is held in place by a release liner.

[0104] The structure of an adhesive sheet according to one embodiment is schematically shown. Figure 1 The adhesive sheet 1 is configured as a single-sided adhesive sheet with a substrate, comprising: a sheet-like support substrate (e.g., a resin film) 10 having a first side 10A and a second side 10B; and an adhesive layer 21 disposed on the first side 10A. The adhesive layer 21 is fixedly disposed on the first side 10A of the support substrate 10 without the intention of separating the adhesive layer 21 from the support substrate 10. Such a single-sided adhesive sheet 1 is preferably used as a surface protective film for attaching its adhesive side to the surface of an object to be bonded (a protected object, such as an optical component like a polarizing plate), without particular limitation. Figure 1 As shown, the adhesive sheet 1 before use can be a component of an adhesive sheet 100 with a release liner, wherein the adhesive sheet 100 with a release liner is in a form in which the surface (adhesive surface) 21A of the adhesive layer 21 is protected by a release liner 31, which is at least on the side opposite to the adhesive layer 21, serving as the release surface. Alternatively, the release liner 31 can be omitted, and the adhesive sheet 1 can be wound around a support substrate 10, with the second surface 10B serving as the release surface, thereby protecting the adhesive surface 21A against the second surface (back surface) 10B of the support substrate 10 (wound form).

[0105] As the aforementioned release liner (also called release film), release liners with a release layer on the surface of the liner substrate such as resin film or paper, and release liners containing low-adhesion materials such as polyolefin resins (e.g., polyethylene, polypropylene) and fluorine resins can be used. The release layer can be formed, for example, by surface treatment of the liner substrate with release agents such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. As the liner substrate, similar to the substrate of the adhesive sheet described later, materials formed from biological materials or recycled materials (such as recycled membranes) are preferably used.

[0106] It should be noted that the concept of adhesive sheets mentioned here can include items such as adhesive tape, adhesive labels, and adhesive films. Adhesive sheets can be in roll form or in single sheet form. In addition, they can also be adhesive sheets processed into various shapes.

[0107] (Adhesive layer)

[0108] The technology disclosed herein is characterized by the fact that the adhesive layer constituting the adhesive sheet is substantially free of ethyl acetate and toluene. The adhesive layer disclosed herein is substantially free of ethyl acetate and toluene used for dilution purposes in adjusting the concentration of solid components, viscosity, etc., has a good pot life, and cures well after application, thus achieving both reduced organic solvent usage and increased productivity. Here, "the adhesive layer is substantially free of ethyl acetate and toluene" means that the amount of ethyl acetate and toluene is less than 5 μg and less than 1 μg per 1g of adhesive layer, respectively. This means that ethyl acetate and toluene are not intentionally added to the adhesive layer, but does not exclude the unavoidable presence of ethyl acetate and toluene in the raw materials of the adhesive layer; small amounts of ethyl acetate and toluene accidentally introduced during the preparation of the adhesive composition and the manufacture of the adhesive sheet may remain in the adhesive layer.

[0109] Furthermore, the aforementioned adhesive layer is characterized by being substantially free of MEK. Here, "the adhesive layer is substantially free of MEK" has essentially the same technical meaning as the description regarding ethyl acetate and toluene; specifically, it means that the amount of MEK is less than 1 μg per 1g of adhesive layer.

[0110] Furthermore, another feature of the disclosed technology is that the adhesive layer contains 10 μg or more and 100 μg or less of a compound with an acetylacetone skeleton per 1g of the adhesive layer. According to the disclosed technology, by using a predetermined amount of a compound with an acetylacetone skeleton in the formation of the adhesive layer, a good pot life, good coatability during adhesive layer formation, and a well-cured adhesive layer can be obtained. In some preferred embodiments, the amount of the aforementioned compound with an acetylacetone skeleton in the adhesive layer can be 15 μg or more, 20 μg or more, or 25 μg or more per 1g of adhesive layer. The more of the aforementioned compound with an acetylacetone skeleton present, the easier it is to obtain a sufficient pot life and good coatability. Furthermore, in some preferred embodiments, the amount of the aforementioned compound with an acetylacetone skeleton in the adhesive layer can be 50 μg or less, 45 μg or less, 40 μg or less, 35 μg or less, or 30 μg or less per 1g of adhesive layer. Adhesive layers containing compounds with an acetylacetone backbone tend to have a sufficient reduction in the amount of volatile components used and good curing properties when the amount of such compounds is within the above range.

[0111] The amounts of ethyl acetate, toluene, MEK, and compounds with an acetylacetone backbone in the 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 in the examples described later.

[0112] In some embodiments, the degree of crosslinking of the adhesive layer is preferably greater than 70%, without particular limitation. An adhesive layer with a crosslinking degree exceeding 70% is less prone to deformation or damage such as dents caused by external forces during manufacturing, and is less likely to experience changes in appearance. Furthermore, by setting a high degree of crosslinking, it is easier to form an adhesive with excellent re-peelability. From this viewpoint, the aforementioned degree of crosslinking is more preferably greater than 80%, and can be greater than 85%, or greater than 90%, or greater than 95% (e.g., greater than 97%). The aforementioned degree of crosslinking can also be 100%, but from the viewpoint of adhesion to the adhered objects, it can be less than 99%, for example. The aforementioned degree of crosslinking is the gel fraction obtained by measuring the adhesive layer after formation (specifically after drying and curing), and specifically, it is determined by the method for measuring the degree of crosslinking after 3 days as described in the embodiments below.

[0113] The thickness of the adhesive layer is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness of the adhesive layer can be approximately 1 μm or more, or approximately 10 μm or more. In some embodiments, considering the adhesion to the adhered objects, the thickness of the adhesive layer can be 30 μm or more, or 50 μm or more, or for example, 70 μm or more. Furthermore, the thickness of the adhesive layer can be approximately 1000 μm or less, or approximately 500 μm or less, or approximately 300 μm or less. In some embodiments, the thickness of the adhesive layer can be, for example, appropriately 150 μm or less, or 100 μm or less (e.g., less than 100 μm). With adhesive layers whose thickness is limited, it is easy to achieve lightweight, miniaturized, and thin / thin adhesive sheets. In the case of a double-sided adhesive sheet where adhesive layers are provided on both sides of a substrate, the thickness of each adhesive layer can be the same or different.

[0114] (Substrate)

[0115] The material used as the support substrate for the adhesive sheet disclosed herein is not particularly limited, but a resin film is preferred. The resin film can be formed by molding various resin materials into a film shape. Preferably, the resin material is one that exhibits excellent properties in one or more of the following: transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropy. For example, a resin film composed of the following resin materials is preferred as the substrate: a resin material with polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate; celluloses such as cellulose diacetate and cellulose triacetate; polycarbonates; acrylic polymers such as polymethyl methacrylate; etc., as the main component (i.e., containing more than 50% by weight). Other examples of resin materials constituting the above-mentioned resin films include: styrene-based polymers such as polystyrene and acrylonitrile-styrene copolymers; polyolefins such as polyethylene, polypropylene, cyclic or norbornene-containing polyolefins, ethylene-propylene copolymers, etc.; polyvinyl chloride; and polyamides such as nylon 6, nylon 6,6, and aromatic polyamides; etc., as main components. Alternatively, resin films composed of the following resin materials may be used as substrates: resin materials whose main components are polyimides, polysulfones, polyethersulfones, polyetheretherketones, polyphenylene sulfide, fluorinated resins, polyvinyl alcohol, polyvinyl acetate, polyvinylidene chloride, polyvinyl butyral, polyarylates, polyoxymethylene, epoxy resins, etc. The resin materials constituting the above-mentioned resin films can be blends of two or more of these.

[0116] It should be noted that in this specification, "resin membrane" refers to a non-porous structure, typically a resin membrane that is substantially free of air bubbles (pore-free). Therefore, the above-mentioned resin membrane is a concept distinct from foamed membranes, nonwoven fabrics, and woven fabrics.

[0117] Other examples of substrates include: foam sheets formed from polyurethane foam, polyethylene foam, polychloroprene foam, etc.; woven and nonwoven fabrics made from various fibrous materials (such as natural fibers like hemp and cotton; synthetic fibers like polyester and vinylon; semi-synthetic fibers like acetate, etc.) alone or in blends; paper such as Japanese paper, high-grade paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; and glass. Substrates composed of these materials in combination are also possible. Examples of substrates for such composite structures include: substrates with structures formed by laminating metal foil with the aforementioned plastic films; and plastic sheets reinforced with inorganic fibers such as glass cloth.

[0118] The substrate can be formed from biologically derived materials or from non-biologically derived materials. From the viewpoint of producing adhesive sheets that minimize reliance on fossil-derived materials, biologically derived substrate materials (typically resin films) are preferred.

[0119] Furthermore, the substrate can also be formed using recyclable or recycled materials (also known as recycled materials). 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 biologically derived materials are used, continued production is possible by reusing the used resin film, thus reducing environmental impact. Such recyclable or recycled resin films are also called recycled membranes. The aforementioned recycled materials (e.g., recycled membranes) can be formed from biologically derived materials or from non-biologically derived materials.

[0120] In some preferred embodiments, the aforementioned substrate is a resin film (polyester resin film) formed by molding a resin (polyester resin) with polyester as the main component (containing more than 50% by weight) into a film form. For example, the aforementioned resin film (PET film) with PET as the main polyester component or the aforementioned resin film (PEN film) with PEN as the main polyester component can be preferably used.

[0121] The substrate can be a single-layer structure or a multi-layer structure. Therefore, the resin film that can be used as a substrate can be a single-layer structure or a multi-layer structure with two or more layers (e.g., a three-layer structure). It is preferable to use a single-layer resin film as the substrate.

[0122] The aforementioned substrate (typically a resin film) may also contain various additives such as fillers, anti-aging agents, antioxidants, ultraviolet absorbers, antistatic components, plasticizers, and colorants (pigments, dyes, etc.) as needed.

[0123] Surface treatments such as chromic acid treatment, ozone exposure, flame exposure, high-voltage electric shock exposure, and ionizing radiation treatment can also be applied to the adhesive layer side surface of the substrate. Such surface treatments can, for example, improve the adhesion between the substrate and the adhesive layer. In some embodiments, a primer treatment can be applied to the adhesive layer side surface of the substrate. In some embodiments, a hard coating treatment can also be applied to the back side of the substrate. This improves the scratch resistance of the back side of the substrate, providing superior protective performance when the adhesive sheet is used as a protective sheet. Furthermore, in other embodiments, from the viewpoint of suppressing static electricity, the substrate can also be treated with antistatic agents. In addition, the substrate can be treated with various methods such as anti-fouling, anti-fingerprint adhesion, anti-glare, and anti-reflective agents.

[0124] The thickness of the substrate can be appropriately selected considering the purpose, intended use, and application of the adhesive sheet. Typically, the substrate thickness is selected from a range of approximately 1 to 1000 μm. In some designs, considering strength, operability, and other workability factors, a substrate thickness of approximately 10 μm or more is suitable, preferably approximately 30 μm or more, and can be approximately 50 μm or more (e.g., 70 μm or more). Furthermore, in some designs, considering cost, the substrate thickness is appropriately about 500 μm or less, preferably about 300 μm or less, more preferably about 150 μm or less, and can be about 100 μm or less (e.g., less than 100 μm). A substrate with the above-mentioned thickness is preferably used as a substrate for a surface protective film, for example.

[0125] (Total thickness)

[0126] The thickness (total thickness) of the adhesive sheet disclosed herein (including the adhesive layer, and further including the substrate in the case of an adhesive sheet with a substrate, but excluding the release liner) is not particularly limited, and can be set in the range of approximately 2 μm to 1000 μm. In some embodiments, considering adhesive properties, the thickness of the adhesive sheet is preferably set to approximately 5 μm to 500 μm (e.g., 10 μm to 300 μm, typically 15 μm to 200 μm). The lower limit of the thickness of the adhesive sheet is not particularly limited, and can be, for example, approximately 30 μm or more, approximately 50 μm or more, or approximately 100 μm or more.

[0127] <Uses>

[0128] The adhesive sheet disclosed herein can be used for various purposes. For example, it is preferably used as a surface protective film that, after being adhered to a protected object, is typically peeled off (re-peeled) from the protected object when its protective purpose is achieved. The object protected by the aforementioned surface protective film is not particularly limited; it can be used as a protective film for various products, components, etc. For example, the surface protective film is particularly preferred as a surface protective film for protecting the surface of optical components (e.g., polarizing plates, wavelength plates, etc., used as components of liquid crystal display panels) during processing and transportation. More specifically, the surface protective film is suitable for protecting optical components used as components of liquid crystal display panels, plasma display panels (PDP), organic electroluminescent (EL) displays, etc., during manufacturing and transportation. In particular, it is useful as a surface protective film for optical components such as polarizing plates (polarizing films, such as reflective polarizing films), wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light diffusers, and reflective sheets used in liquid crystal display panels. In addition, adhesive sheets can be used, for example, to adhere to components that make up electronic devices or other products, for purposes such as fixing, joining, or reinforcing the components.

[0129] Furthermore, in some embodiments, the adhesive compositions and adhesive sheets disclosed herein can be formed from biologically derived materials, thus helping to reduce dependence on fossil-derived materials. The adhesive sheets disclosed herein are typically preferred as adhesive compositions and adhesive sheets that reduce dependence on fossil-derived materials.

[0130] Example

[0131] The following describes some embodiments related to the present invention, but it is not intended to limit the present invention to the contents shown in these embodiments. It should be noted that in the following description, "parts" and "%" refer to weight unless otherwise specified.

[0132] <Example 1>

[0133] A stirrer, thermometer, and vacuum pump were installed in a separable four-necked flask. 80 g of a dicarboxylic acid dimer (trade name "PRIPOL 1009", manufactured by Cargill, weight-average molecular weight 567, trimeric acid content 1%), 184 g of a polyether glycol (trade name "BioPTMG650", manufactured by Mitsubishi Chemical, number-average molecular weight 650) (molar ratio of dicarboxylic acid to glycol: 1.00:2.00), and 0.26 g of tetrabutyl titanate (trade name "OrgatixTA21", manufactured by Matsumoto Fine Chemical) were added. The mixture was stirred under reduced pressure (0.002 MPa) while heated to 200°C and maintained at this temperature. The reaction was continued for approximately 4 hours to obtain polyester A1. Polyester A1 had a weight-average molecular weight (Mw) of 6260 and a glass transition temperature (Tg) of -74°C.

[0134] To obtain an adhesive composition, 20 parts of a polyisocyanate (trade name "STABiO D370N", manufactured by Mitsui Chemicals) (a derivative of 1,5-pentamethylene diisocyanate, used as an isocyanate-based crosslinking agent C1), 0.15 parts of titanium tetraacetylacetonate (trade name "Orgatix TC401", manufactured by Matsumoto Fine Chemicals), and 3 parts of acetylacetone (manufactured by Fujifilm and Koko Pure Chemicals Co., Ltd.) were added as a metal catalyst. The volatile content of this adhesive composition was 2.5%, and the initial viscosity at 25°C was 2270 mPa·s. It should be noted that the above volatile content was calculated based on the total concentrations of ethyl acetate, toluene, methyl ethyl ketone, acetylacetone, and other volatile organic solvents in the adhesive composition.

[0135] The adhesive composition described above was applied to a polyethylene terephthalate (PET) film substrate (trade name "T100-75S", manufactured by Mitsubishi Chemical Corporation, 75 μm thickness) to a dried thickness of 75 μm, and dried at 130°C for 2 minutes. The peel-treated side of a PET film (trade name "DIAFOIL MRE38", manufactured by Mitsubishi Chemical Corporation) was then laminated onto the substrate. The substrate was left to stand at 22°C and 50% RH for 3 days to obtain the adhesive sheet of this example (an adhesive sheet with a single-sided adhesive layer on the substrate).

[0136] <Examples 2-3 and Comparative Example 1>

[0137] In the preparation of the adhesive composition, the amount of acetylacetone was changed to 5 parts (Example 2), 10 parts (Example 3), or 0 parts (i.e. no addition, Comparative Example 1) relative to 100 parts of polyester. Otherwise, the adhesive compositions of each example were obtained in the same manner as in Example 1, and the adhesive sheets of each example were obtained using the adhesive compositions.

[0138] <Example 4>

[0139] A stirrer, thermometer, and vacuum pump were installed in a separable four-necked flask. 20 g of a dicarboxylic acid dimer (trade name "PRIPOL 1009", manufactured by Cargill Corporation, weight-average molecular weight 567, trimeric acid content 1%), 187 g of a polyether glycol (trade name "SANNIX PL-2100", manufactured by Sanyo Chemical Industry Co., Ltd., number-average molecular weight 2400) (molar ratio of dicarboxylic acid to glycol: 1.00:2.00), and 0.21 g of tetrabutyl titanate (trade name "Orgatix TA21", manufactured by Matsumoto Fine Chemical Co., Ltd.) were added. The mixture was stirred under reduced pressure (0.002 MPa) while heated to 200°C and maintained at this temperature. The reaction was continued for approximately 4 hours to obtain polyester A2. Polyester A2 had a molecular weight of 16500 and a temperature gradient of -58°C.

[0140] In addition to 100 parts of the obtained polyester, 62.5 parts of polyether polyol (trade name "PREMINOL 7012", manufactured by AGC, polypropylene glycol, number average molecular weight 10000), 20.5 parts of polyisocyanate (trade name "DURANATE D101", manufactured by Asahi Kasei Corporation), a derivative of 1,6-hexamethylene diisocyanate as isocyanate crosslinking agent C2, 0.15 parts of tetraacetylacetone titanium (trade name "Orgatix TC401", manufactured by Matsumoto Fine Chemical Co., Ltd.), and 10 parts of acetylacetone (manufactured by Fujifilm and Koichi Pure Chemical Co., Ltd.) were added to obtain an adhesive composition. Using the obtained adhesive composition, except as otherwise provided in Example 1, the adhesive sheet of this example was obtained.

[0141] <Comparative Examples 2-3>

[0142] In the preparation of the adhesive composition, organic solvents (ethyl acetate and toluene) with volatile components as shown in Table 2 were used. Otherwise, the adhesive compositions of each example were obtained in essentially the same manner as in Example 1, and adhesive sheets of each example were obtained using the adhesive compositions.

[0143] <Evaluation>

[0144] (Quantification of residual volatile components)

[0145] Take 10cm 2 The sample (adhesive sheet) was sealed into a 20 mL headspace vial. Using a headspace sampler (HSS: Shimadzu, HS-20), the vial containing the sample was heated at 150°C for 30 minutes, and 1 mL of the heated gas was injected into a GC / MS (Shimadzu QP-2020 instrument) for determination. Using a calibration curve calculated with acetylacetone, the amount of each volatile component per 1 g of adhesive layer was determined [μg / g] (acetylacetone conversion value) based on the peak area obtained from the residual volatile components (toluene, ethyl acetate, methyl ethyl ketone (MEK), and acetylacetone), and this was taken as the content per 1 g of adhesive layer. In the case where the adhesive sheet includes a substrate, the weight of the substrate of the same area was subtracted to determine the amount of residual volatile components per 1 g of adhesive layer. It should be noted that for the substrate used in the above examples and comparative examples, the amount of residual volatile components was confirmed to be negligible. The specific determination conditions for GC / MS are shown in Table 1.

[0146] [Table 1]

[0147]

[0148] (Applicability period evaluation test)

[0149] The adhesive compositions prepared in each example were stored in a sealed container at room temperature (23°C), and their viscosity was measured immediately after mixing (initial) and 6 hours after mixing (at 25°C).

[0150] Substitute the initial viscosity ηa [mPa·s] and the viscosity ηb [mPa·s] after 6 hours into the following formula to calculate the viscosity increase rate A [%) after 6 hours. If the viscosity increase rate A after 6 hours is less than 10%, it is judged as "0" (qualified), and if it exceeds 10%, it is judged as "×" (unqualified).

[0151] A = [(ηb - ηa) / ηa] × 100

[0152] Viscosity was measured using a rheometer (product name "HAAKERheoStress 600") manufactured by Thermo Fisher Scientific at 25°C.

[0153] (Curing properties)

[0154] The curability of the adhesive was evaluated by measuring the degree of crosslinking (initial crosslinking degree) using the method described below.

[0155] The newly formulated adhesive composition was coated onto a PET film (38 μm thick) that had undergone peeling treatment and dried at 130°C for 2 minutes to form an adhesive layer (75 μm thick). A sample was prepared by taking W1 g (approximately 0.1 g of adhesive layer) from the newly formed adhesive layer and encapsulating it in a porous PTFE (polytetrafluoroethylene) sheet. The sample was placed in a glass bottle, immersed in toluene, and left to stand at 23°C for 7 days. The sample was then removed and dried at 130°C for 2 hours. The dried sample was weighed, and the weight of the porous PTFE sheet was subtracted to determine the dried weight of the adhesive, W2 g. The degree of crosslinking (initial degree of crosslinking) [%] was calculated by substituting W1 and W2 into the following formula.

[0156] Degree of crosslinking [%] = (W2 / W1) × 100

[0157] An initial crosslinking degree of 40% or higher is judged as "0" (qualified), and a degree of less than 40% is judged as "×" (unqualified).

[0158] In addition, an adhesive layer that has been held at room temperature (23°C) for 3 days after the adhesive layer is formed was used instead of the adhesive layer that was just formed. Otherwise, the degree of crosslinking (degree of crosslinking after 3 days) [%) was determined by the same method as above.

[0159] It should be noted that, as a porous PTFE sheet, the trade name "TEMISH" or its equivalent, manufactured by Nitto Denko Corporation, can be used.

[0160] Table 2 summarizes the results and evaluations of each example. It should be noted that no evaluation tests were conducted for Comparative Examples 2 and 3.

[0161] [Table 2]

[0162]

[0163] As shown in Table 2, the adhesive layers of Examples 1-4 contain polyester, isocyanate-based crosslinking agents, and metal catalysts, and are substantially free of ethyl acetate and toluene. Each 1g of adhesive layer contains 10μg to 100μg of acetylacetone, and the viscosity increase rate after 6 hours is less than 10%, the initial crosslinking degree is more than 40%, and the evaluation results for pot life and curability are satisfactory. On the other hand, in Comparative Example 1, where the amount of acetylacetone per 1g of adhesive layer is less than 10μg, the viscosity increase is large, and the viscosity after 6 hours cannot be measured. It should be noted that the small amount of acetylacetone contained in the adhesive layer of Comparative Example 1 is believed to originate from the metal catalyst product. Furthermore, in Comparative Examples 2-3, which use organic solvents (ethyl acetate, toluene) to form the adhesive layer, the amount of ethyl acetate in the adhesive layer is more than 8μg / g, and the amount of toluene is more than 4μg / g. It should be noted that the crosslinking degree of the adhesive layers of Examples 1-4 is more than 90% after 3 days.

[0164] The specific examples of the present invention have been described in detail above, but they are merely examples and do not limit the scope of the claims. The technology described in the claims includes solutions derived from various modifications and alterations of the specific examples illustrated above.

[0165] Explanation of reference numerals in the attached figures

[0166] 1: Adhesive sheet; 10: Support substrate; 10A: First side; 10B: Second side (back side); 21: Adhesive layer; 21A: Adhesive surface; 31: Release liner; 100: Adhesive sheet with release liner.

Claims

1. An adhesive sheet having an adhesive layer comprising a polyester, an isocyanate-based crosslinking agent, and a metal catalyst. The adhesive layer is substantially free of ethyl acetate and toluene. The adhesive layer contains 10 μg and 100 μg of a compound with an acetylacetone skeleton per 1g of the adhesive layer.

2. The adhesive sheet according to claim 1, wherein, The glass transition temperature of the polyester is below -30°C.

3. The adhesive sheet according to claim 1 or 2, wherein, The weight-average molecular weight of the polyester is below 20,000.

4. The adhesive sheet according to claim 1 or 2, wherein, The content of the isocyanate-based crosslinking agent in the adhesive layer is 5 parts by weight or more and 50 parts by weight or less relative to 100 parts by weight of the polyester.

5. An adhesive composition comprising a polyester, an isocyanate-based crosslinking agent, and a metal catalyst. The adhesive composition is substantially free of ethyl acetate and toluene. More than 1 part by weight of a compound having an acetylacetone backbone is added relative to 100 parts by weight of the polyester.

6. The adhesive composition according to claim 5, wherein, The content of non-volatile components is 90% or more by weight.

7. The adhesive composition according to claim 5 or 6, wherein, The initial viscosity at 25℃ is less than 3000 mPa·s.

8. The adhesive composition according to claim 5 or 6, wherein, The glass transition temperature of the polyester is below -30°C.

9. The adhesive composition according to claim 5 or 6, wherein, The weight-average molecular weight of the polyester is below 20,000.

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