Release coating agent, release sheet, and laminate for polyester substrates

Abstract

To provide a polyester base material release coat agent that has excellent releasability as a release sheet and also has excellent adhesiveness to polyester base materials.SOLUTION: A polyester base material release coat agent according to an embodiment contains a water-based dispersion formed by dispersing a polyurethane resin in a water-based dispersion medium. The water-based dispersion contains a sucrose ester that is produced through the esterification of acetic acid and a fatty acid having 8-25 carbon atoms with sucrose, and exhibits a hydroxyl value of 30 mgKOH / g or less.SELECTED DRAWING: None

Description

Technical Field

[0001] Embodiments of the present invention relate to a release coating agent applied to and used on a polyester substrate, as well as a release sheet and a laminate obtained using the release coating agent.

Background Art

[0002] A release sheet (also referred to as a peel sheet) is known, which is provided with a release layer formed by applying a release coating agent to a polyester substrate such as a polyester film. For example, Patent Document 1 discloses a release agent composition containing a silicone resin, an alkoxy group-containing silane-modified polyurethane resin, and a solvent, as a release coating agent that is applied to the surface of a release base substrate to form a release layer. As such release coating agents, in addition to silicone-based ones, there are also non-silicone-based release coating agents that make it possible to avoid silicone migration.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A release coating agent applied to and used on a polyester substrate is required to be easily peelable from a resin layer such as an adhesive film to be protected as a release sheet or a resin film formed on the release sheet, that is, to have excellent peelability, and is also required to have adhesion to the polyester substrate.

[0005] An embodiment of the present invention aims to provide a release coating agent for polyester substrates, which has excellent peelability and excellent adhesion to polyester substrates.

Means for Solving the Problems

[0006] The present invention includes embodiments shown below. [1] A release coating agent for polyester substrates comprising an aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, wherein the aqueous dispersion comprises a sucrose ester with a hydroxyl value of 30 mgKOH / g or less, which is obtained by esterifying sucrose with a fatty acid having 8 to 25 carbon atoms and acetic acid. [2] The release coating agent for polyester substrates according to [1], wherein the molar ratio of the fatty acid to the acetic acid in the sucrose ester is 3:5 to 7:1. [3] The release coating agent for polyester substrates according to [1] or [2], wherein the content of the sucrose ester per 100 parts by mass of the polyurethane resin is 5 to 80 parts by mass. [4] The release coating agent for polyester substrates according to any one of [1] to [3], wherein the polyol constituting the polyurethane resin is a polyester polyol. [5] The release coating agent for polyester substrates according to any one of [1] to [4], wherein the polyol constituting the polyurethane resin contains an anionic group-containing polyol. [6] A release sheet comprising a polyester substrate and a release layer provided on the polyester substrate, the release coating agent described in any one of [1] to [5]. A laminate comprising a release sheet as described in [7] [6] and a resin layer provided on the release layer of the release sheet in a peelable manner. [Effects of the Invention]

[0007] According to embodiments of the present invention, a release coating agent for polyester substrates can be provided that exhibits excellent peelability and excellent adhesion to polyester substrates. [Modes for carrying out the invention]

[0008] The release coating agent for polyester substrates according to this embodiment (hereinafter also simply referred to as the release coating agent) is a release coating agent comprising an aqueous dispersion of polyurethane resin, wherein the aqueous dispersion contains a specific sucrose ester. Therefore, the release coating agent comprises an aqueous dispersion medium, a polyurethane resin dispersed in the aqueous dispersion medium, and a sucrose ester.

[0009] [Aqueous dispersion medium] The aqueous dispersion medium is a dispersion medium containing water, and includes water or a mixed medium of water and a hydrophilic organic solvent. From the viewpoint of dispersion stability of the aqueous dispersion, the aqueous dispersion medium is preferably water, and although an organic solvent may be included, it is preferable that it be in small amounts. In one embodiment, the aqueous dispersion medium preferably contains 70% by mass or more water, more preferably 80% by mass or more water, more preferably 90% by mass or more water, and may even contain 100% by mass water. That is, in the aqueous dispersion medium, the water / hydrophilic organic solvent ratio is preferably 70 / 30 to 100 / 0 by mass, more preferably 80 / 20 to 100 / 0, and even more preferably 90 / 10 to 100 / 0.

[0010] Examples of hydrophilic organic solvents include lower monohydric alcohols such as methanol, ethanol, and propanol; polyhydric alcohols such as ethylene glycol and glycerin; and aprotic polar solvents such as N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, and acetonitrile.

[0011] [Polyurethane resin] Polyurethane resin is obtained by reacting a polyol with a polyisocyanate and is a polymer having a urethane bond in its molecule. Various water-based polyurethane resins can be used as polyurethane resins, such as anionic polyurethane resins, cationic polyurethane resins, and nonionic polyurethane resins.

[0012] Anionic polyurethane resin is a water-based polyurethane resin having anionic groups. Examples of anionic groups include at least one selected from the group consisting of carboxyl groups, sulfonic acid groups, phosphate groups, and salts thereof. Examples of salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts, ammonium salts, and amine salts such as primary amines, secondary amines, and tertiary amines.

[0013] Cationic polyurethane resins are aqueous polyurethane resins having cationic groups. Examples of cationic groups include quaternary ammonium groups.

[0014] Nonionic polyurethane resins are uncharged, aqueous polyurethane resins that do not have anionic or cationic groups. Examples of nonionic polyurethane resins include polyurethane resins that have hydrophilic segments such as polyoxyethylene groups.

[0015] Examples of polyols that constitute the polyurethane resin include polymer polyols such as polyester polyols (e.g., aliphatic polyester polyols, aromatic polyester polyols), polycarbonate polyols, polyether polyols (e.g., polytetramethylene glycol), and polybutadiene polyols. Any one of these may be used, or two or more may be used in combination. From the viewpoint of water resistance of the release layer, the polymer polyols are preferred in the order of polybutadiene polyol, polycarbonate polyol, polyether polyol, and polyester polyol.

[0016] The molecular weight of the polymer polyol is not particularly limited; for example, the number-average molecular weight (Mn) may be 500 to 5000, 800 to 4000, or 1000 to 3000.

[0017] In this specification, the number-average molecular weight (Mn) is measured by GPC (gel permeation chromatography) and calculated using a calibration curve with standard polystyrene. Specifically, the GPC conditions are as follows: Column: TSKgel G4000HXL + TSKgel G3000HXL + TSKgel G2000HXL + TSKgel G1000HXL + TSKgel G1000HXL (manufactured by Tosoh Corporation), Mobile phase: THF (tetrahydrofuran), Mobile phase flow rate: 1.0 mL / min, Column temperature: 40°C, Sample injection volume: 50 μL, Sample concentration: 0.2% by mass.

[0018] As the polyol constituting the polyurethane resin, in addition to the polymer polyols mentioned above, low molecular weight polyhydric alcohols (preferably dihydric alcohols and trihydric alcohols) such as ethylene glycol, propylene glycol, propanediol, butanediol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, bisphenol A, bisphenol F, bisphenol S, hydrogenated bisphenol A, trimethylolpropane, glycerin, and pentaerythritol may be used. Any one of these may be used, or two or more may be used in combination.

[0019] In one embodiment, the polyol constituting the polyurethane resin preferably contains a polyester polyol to enhance the effect of improving adhesion to the polyester substrate. The amount of polyester polyol in the polyol is not particularly limited, but for example, it is preferably 60% by mass or more, more preferably 70 to 99% by mass, even more preferably 75 to 97% by mass, and may also be 80 to 95% by mass, based on 100% by mass of the polyol.

[0020] In the present specification, with respect to the amount of each component constituting the polyol, the 100% by mass of the reference polyol is calculated by taking the anionic hydrophilic group as an acid form when the polyol contains the anionic hydrophilic group described later. The amount of the anionic group-containing polyol is similarly calculated by taking the anionic group as an acid form.

[0021] In one embodiment, the polyol constituting the polyurethane resin preferably contains a polyol having 3 or more functional groups. Thereby, a crosslinked structure is introduced into the polyurethane resin, and the water resistance of the release layer can be improved. Examples of the polyol having 3 or more functional groups include polyhydric alcohols having 3 or more hydroxy groups such as trimethylolpropane, or alternatively, among the above polymer polyols, those having 3 or more hydroxy groups in the molecule are exemplified.

[0022] Examples of the polyisocyanate constituting the polyurethane resin include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates.

[0023] Examples of the aliphatic polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and the like.

[0024] Examples of the alicyclic polyisocyanate include isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4'-diisocyanate (hydrogenated MDI), hydrogenated xylylene diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and the like.

[0025] Examples of aromatic polyisocyanates include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), and naphthalene diisocyanate.

[0026] Furthermore, isocyanurate, adduct, biuret, allophenate, and carbodiimide forms of these polyisocyanates may also be used. Additionally, one of these polyisocyanates may be used, or two or more may be used in combination.

[0027] In one embodiment, the polyurethane resin (A) is preferably an anionic polyurethane resin obtained by reacting a polyol containing an anionic group-free polyol and an anionic group-containing polyol with a polyisocyanate. Examples of such anionic polyurethane resins are (A1) and (A2) below.

[0028] (A1) An anionic polyurethane resin obtained by synthesizing an isocyanate group-containing urethane prepolymer from an anionic group-free polyol, an anionic group-containing polyol, and polyisocyanate, and then extending the chain of the urethane prepolymer with a chain extender.

[0029] (A2) A hydroxyl group-containing anionic polyurethane resin obtained by reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate.

[0030] The chain extension type described in (A1) offers excellent water resistance in the release layer. On the other hand, the hydroxyl group-containing anionic polyurethane resin described in (A2) is inferior in water resistance, but is advantageous for improving the release properties of the release sheet.

[0031] The various polyols listed above can be used as anionic group-free polyols for synthesizing anionic polyurethane resins.

[0032] As anionic group-containing polyols, carboxyl group-containing polyols having a carboxyl group in the molecule are preferred. Examples include carboxylic acid-containing compounds such as dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dioxymaleic acid, 2,6-dioxybenzoic acid, and 3,4-diaminobenzoic acid, as well as their derivatives and salts. Any one of these may be used, or two or more may be used in combination.

[0033] Here, the concept of anionic groups includes not only acidic forms (in the case of a carboxyl group: -COOH) but also salt forms (in the case of a carboxyl group: carboxylic acid bases represented by -COOX, where X is a cation that forms a salt with a carboxylic acid), and acidic and salt forms may coexist. By neutralizing the anionic group to form a salt, the resulting polyurethane resin can be made water-dispersible. Therefore, in an aqueous dispersion of polyurethane resin, the anionic group may exist in the salt form. On the other hand, in the state of a coating film obtained by drying the aqueous dispersion, if a non-volatile base is used as a neutralizing agent, it may exist in the salt form, and if a volatile base is used, it may exist in the acidic form.

[0034] The chain extender used to extend the chains of the isocyanate group-containing urethane prepolymer is not particularly limited, and examples include water, as well as polyhydric amine compounds such as aliphatic polyamine compounds (e.g., ethylenediamine, trimethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine), aromatic polyamine compounds (e.g., metaxylenediamine, tolylenediamine, diaminodiphenylmethane), alicyclic polyamine compounds (e.g., piperazine, isophoronediamine), and polyhydrazide compounds (e.g., hydrazine, adipic acid dihydrazide).

[0035] In an anionic polyurethane resin, the amount of polyol without anionic groups in the polyol is not particularly limited, and may be 80 to 99% by mass, 85 to 97% by mass, or 90 to 95% by mass, based on 100% by mass of the polyol. In this case, the amount of the polymer polyol (preferably polyester polyol) is not particularly limited, and may be 80 to 99% by mass, 85 to 97% by mass, or 88 to 95% by mass, based on 100% by mass of the polyol.

[0036] In an anionic polyurethane resin, the amount of anionic group-containing polyol in the polyol is not particularly limited, and may be 1 to 20% by mass, 3 to 15% by mass, or 5 to 10% by mass, based on 100% by mass of the polyol.

[0037] In one embodiment, a nonionic polyurethane resin may be used as the polyurethane resin, obtained by reacting a polyol containing hydrophilic segment-containing polyols and hydrophilic segment-free polyols with a polyisocyanate. Examples of such nonionic polyurethane resins include (A3) below.

[0038] (A3) A nonionic polyurethane resin obtained by synthesizing an isocyanate group-containing urethane prepolymer from a hydrophilic segment-containing polyol, a hydrophilic segment-free polyol, and a polyisocyanate, and then extending the chains of the urethane prepolymer with a chain extender.

[0039] Examples of polyols containing hydrophilic segments include polyols having nonionic hydrophilic segments such as polyoxyethylene groups. Examples of polyols without hydrophilic segments include polyols from the list above that do not have anionic groups, cationic groups, or hydrophilic segments.

[0040] In nonionic polyurethane resins, the amount of hydrophilic segment-containing polyol in the polyol is not particularly limited, and may be, for example, 5 to 50% by mass or 10 to 30% by mass based on 100% by mass of polyol. The amount of hydrophilic segment-free polyol is also not particularly limited, and may be, for example, 50 to 95% by mass or 70 to 90% by mass based on 100% by mass of polyol.

[0041] [Sucrose ester] As sucrose esters, ester compounds with a hydroxyl value of 30 mgKOH / g or less are used, which are obtained by esterifying sucrose with a fatty acid having 8 to 25 carbon atoms and acetic acid.

[0042] The sucrose ester is an ester of sucrose with a fatty acid and acetic acid. One molecule of sucrose has eight hydroxyl groups, but the sucrose ester used in this embodiment has a hydroxyl value of 30 mgKOH / g or less, so it can be said that substantially all of the eight hydroxyl groups are ester-bonded to the fatty acid and acetic acid. The hydroxyl value of the sucrose ester is preferably 20 mgKOH / g or less, and more preferably 15 mgKOH / g or less. Since a lower hydroxyl value of the sucrose ester is preferable, the lower limit is not particularly limited and may be 0 mgKOH / g.

[0043] In this specification, the hydroxyl value of sucrose esters is measured in accordance with the Japanese Standards for Ingredients of Quasi-Drugs 2021.

[0044] The fatty acids constituting the sucrose ester are medium-chain or long-chain fatty acids having 8 to 25 carbon atoms, which can impart hydrophobicity to the sucrose ester and improve its affinity with polyurethane resin. The fatty acids may be saturated or unsaturated fatty acids, but saturated fatty acids are preferred. As the fatty acids, one type of saturated and / or unsaturated fatty acid having 8 to 25 carbon atoms may be used, or two or more types may be used in combination. The number of carbon atoms in the fatty acids is preferably 10 to 22, more preferably 12 to 20, and even more preferably 14 to 18.

[0045] The molar ratio of fatty acids to acetic acid constituting the sucrose ester is preferably fatty acid:acetic acid = 3:5 to 7:1. A fatty acid / acetic acid (molar ratio) of 3 / 5 or more further enhances the release properties as a release sheet. The fatty acid:acetic acid (molar ratio) is more preferably 3.5:4.5 to 6:2, and even more preferably 4:4 to 5:3.

[0046] [Aqueous dispersion of polyurethane resin] The aqueous dispersion of polyurethane resin is an aqueous dispersion in which polyurethane resin is dispersed in an aqueous dispersion medium, and contains the sucrose ester described above. By incorporating the sucrose ester into the aqueous dispersion of polyurethane resin in this way, the release properties of the release sheet obtained using the release coating agent made of the aqueous dispersion of polyurethane resin can be improved, and the adhesion to polyester substrates can be improved.

[0047] Since the above-mentioned sucrose ester is hydrophobic, in an aqueous dispersion of polyurethane resin, it is preferable that the sucrose ester does not dissolve in water and is contained within the polyurethane resin particles. Here, "contained within particles" is a concept that includes being present inside the particles and / or on the particle surface. Preferably, at least a portion of the sucrose ester is present inside the polyurethane resin particles, and it is preferable that it is mixed within the particles. As described above, the sucrose ester has a hydroxyl value of 30 mgKOH / g or less and substantially lacks hydroxyl groups, so it is easily incorporated into the polyurethane resin particles when emulsifying and dispersing the polyurethane resin in an aqueous dispersion medium.

[0048] The polyurethane resin content in the aqueous dispersion is not particularly limited and may be, for example, 10 to 50% by mass, 15 to 45% by mass, or 20 to 40% by mass, relative to the total mass of the aqueous dispersion.

[0049] The content of the sucrose ester is preferably 5 to 80 parts by mass, more preferably 7 to 50 parts by mass, even more preferably 8 to 40 parts by mass, even more preferably 10 to 30 parts by mass, and may also be 15 to 25 parts by mass per 100 parts by mass of polyurethane resin.

[0050] The size of the polyurethane resin particles (specifically, resin particles containing sucrose ester) in the aqueous dispersion is not particularly limited, and for example, the average particle diameter may be 0.001 to 0.5 μm. Here, the average particle diameter is the 50% cumulative particle diameter (d50) measured using "Microtrac UPA-UZ152" manufactured by Nikkiso Co., Ltd.

[0051] The aqueous dispersion of polyurethane resin may contain other components, as long as their effectiveness is not impaired. For example, it may contain a crosslinking agent for crosslinking the polyurethane resin.

[0052] Examples of crosslinking agents include compounds having two or more reactive groups in their molecule that can react with at least one active hydrogen-containing group selected from the group consisting of hydroxyl groups, primary amino groups, secondary amino groups, and thiol groups found in polyurethane resins. This improves the water resistance of the release layer formed by the release coating agent. If the polyurethane resin has carboxyl groups, the crosslinking agent can also be used to crosslink those carboxyl groups.

[0053] Examples of crosslinking agents include carbodiimide compounds, oxazoline compounds, blocked isocyanate compounds, and epoxy compounds, and either one of these may be used or two or more may be used in combination.

[0054] Other components may include, for example, a surfactant for dispersing the polyurethane resin in an aqueous dispersion medium. Nonionic surfactants are preferably used as the surfactant. Examples of nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyethylene styrene phenyl ethers, polyoxyethylene phenyl ethers, and polyoxyethylene polyoxypropylene glycol.

[0055] [Method for producing aqueous dispersions] The method for producing an aqueous dispersion of polyurethane resin is not particularly limited, and may be produced by, for example, a method including the following steps (1) to (3).

[0056] Step (1): A step in which the polyol and polyisocyanate are reacted. Step (2): A step of mixing the polyurethane resin obtained in step (1) with sucrose ester. Step (3): A step of dispersing polyurethane resin in an aqueous dispersion medium using the mixture obtained in step (2) and an aqueous dispersion medium.

[0057] By mixing polyurethane resin and sucrose ester in this manner and then dispersing them in an aqueous dispersion medium, the sucrose ester can be efficiently incorporated into the polyurethane resin particles.

[0058] In step (1) above, the reaction between the polyol and the polyisocyanate may be carried out without an organic solvent, or in an organic solvent that does not contain active hydrogen groups, such as methyl ethyl ketone or acetone. The polyurethane resin obtained by the reaction in step (1) is a concept that also includes the urethane prepolymer before chain elongation, etc. Therefore, in step (2), such urethane prepolymer may be mixed with sucrose ester.

[0059] Furthermore, if the polyurethane resin has anionic groups, these anionic groups may be neutralized with a neutralizing agent before or after mixing the polyurethane resin and sucrose ester in step (2).

[0060] Examples of neutralizing agents include non-volatile bases such as sodium hydroxide and potassium hydroxide, tertiary amines such as trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine, and triethanolamine, and volatile bases such as ammonia.

[0061] The method for dispersing the polyurethane resin in the aqueous dispersion medium in step (3) is not particularly limited. Examples include (i) adding the polyurethane resin or its resin solution while stirring the aqueous dispersion medium with a homogenizer or homomixer, and (ii) adding the aqueous dispersion medium while stirring the polyurethane resin or its resin solution with a homogenizer or homomixer. If the polyurethane resin is not self-emulsifying, a surfactant may be added to emulsify and disperse the polyurethane resin in the aqueous dispersion medium.

[0062] If a urethane prepolymer is synthesized in step (1), the urethane prepolymer may be dispersed in an aqueous dispersion medium in step (3) and then chain-extended with a chain-extending agent. Alternatively, if the reaction between the polyol and polyisocyanate in step (1) is carried out in an organic solvent, the polyurethane resin may be dispersed in an aqueous dispersion medium in step (3) and then the organic solvent may be removed.

[0063] In one embodiment, when the anionic polyurethane resin described in (A1) above is used as the polyurethane resin, it may be manufactured by the following steps (a1) to (a5). Step (a1): A step of synthesizing an isocyanate group-containing urethane prepolymer by reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate. Step (a2): A step of neutralizing the anionic groups of the isocyanate group-containing urethane prepolymer. Step (a3): A step of mixing the isocyanate group-containing urethane prepolymer with a sucrose ester. Step (a4): A step of dispersing the isocyanate group-containing urethane prepolymer in an aqueous dispersion medium using the mixture obtained in step (a3) ​​and an aqueous dispersion medium. Step (a5): A step of extending the chains of an isocyanate group-containing urethane prepolymer dispersed in an aqueous dispersion medium using a chain extender.

[0064] Process (a1) corresponds to process (1) above, process (a3) ​​corresponds to process (2) above, process (a4) corresponds to process (3) above, and processes (a2) and (a5) are additional processes.

[0065] In step (a1), the polyisocyanate is used such that the isocyanate groups are stoichiometrically in excess of the hydroxyl groups contained in the polyol, for example, the equivalent ratio of hydroxyl groups to isocyanate groups (NCO / OH) is 1.05 to 1.70 (more preferably 1.10 to 1.60).

[0066] The order of steps (a2) and (a3) ​​does not matter. The anionic group may be neutralized with a neutralizing agent before adding the sucrose ester, or the anionic group may be neutralized after adding the sucrose ester.

[0067] In step (a5), the chain extender may be added either after or during the dispersion of the polyurethane prepolymer in the aqueous dispersion medium in step (a4). As described above, water can also act as a chain extender. When water is used as the chain extender, the water used as the aqueous dispersion medium also functions as the chain extender.

[0068] If the reaction in step (a1) is carried out in an organic solvent, the organic solvent may be removed after chain elongation in step (a5).

[0069] In one embodiment, when the anionic polyurethane resin (A2) described above is used as the polyurethane resin (A), it may be manufactured by the following steps (b1) to (b4). Step (b1): A step of synthesizing a hydroxyl group-containing polyurethane resin by reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate. Step (b2): A step to neutralize the anionic groups of the hydroxyl group-containing polyurethane resin. Step (b3): ​​A step of mixing the hydroxyl group-containing polyurethane resin with a sucrose ester. Step (b4): A step of dispersing the hydroxyl group-containing polyurethane resin in an aqueous dispersion medium using the mixture obtained in step (b3) and an aqueous dispersion medium.

[0070] Process (b1) corresponds to process (1) above, process (b3) corresponds to process (2) above, process (b4) corresponds to process (3) above, and process (b2) is an additional process.

[0071] In step (b1), the polyol is used such that the amount of hydroxyl groups is stoichiometrically in excess of the amount of isocyanate groups contained in the polyisocyanate, for example, the equivalent ratio of hydroxyl groups to isocyanate groups (NCO / OH) is 0.70 to 0.95 (more preferably 0.80 to 0.90).

[0072] The order of steps (b2) and (b3) does not matter. The anionic group may be neutralized with a neutralizing agent before adding the sucrose ester, or the anionic group may be neutralized after adding the sucrose ester.

[0073] If the reaction in step (b1) is carried out in an organic solvent, the organic solvent may be removed after the polyurethane resin is dispersed in an aqueous dispersion medium in step (b4).

[0074] In one embodiment, when the nonionic polyurethane resin (A3) described above is used as the polyurethane resin (A), it may be manufactured by the following steps (c1) to (c4). Step (c1): A step of synthesizing an isocyanate group-containing urethane prepolymer by reacting a hydrophilic segment-containing polyol, a hydrophilic segment-free polyol, and a polyisocyanate. Step (c2): A step of mixing the isocyanate group-containing urethane prepolymer with a sucrose ester. Step (c3): A step of dispersing the isocyanate group-containing urethane prepolymer in an aqueous dispersion medium using the mixture obtained in step (c2) and an aqueous dispersion medium. Step (c4): A step in which an isocyanate group-containing urethane prepolymer dispersed in an aqueous dispersion medium is chain-extended using a chain-extending agent.

[0075] Step (c1) corresponds to step (1) above, step (c2) corresponds to step (2) above, step (c3) corresponds to step (3) above, and step (c4) is an additional step. The equivalent ratio of hydroxyl groups to isocyanate groups in step (c1), the timing of adding the chain extender in step (c4), the case where water is used as the chain extender, and the removal of organic solvents are the same as in steps (a1) and (a5) above.

[0076] [Release agent for polyester substrates] The release coating agent for polyester substrates according to this embodiment contains an aqueous dispersion of the polyurethane resin, and therefore contains an aqueous dispersion medium, a polyurethane resin dispersed in the aqueous dispersion medium, and a sucrose ester. The release coating agent may consist only of the aqueous dispersion of the polyurethane resin, or it may contain various additives such as antioxidants, antistatic agents, surfactants, defoamers, and surface modifiers together with the aqueous dispersion of the polyurethane resin.

[0077] The polyurethane resin content in the release coating agent is not particularly limited and may be, for example, 10 to 50% by mass, 15 to 45% by mass, or 20 to 40% by mass relative to the total mass of the release coating agent.

[0078] [Release sheet] A release sheet according to one embodiment includes a polyester substrate and a release layer provided on the polyester substrate, wherein the release layer is formed by the release coating agent.

[0079] As the polyester substrate, various polyesters comprising dicarboxylic acid and diol as constituent components (monomers) can be used. Examples of polyester substrates include polyethylene terephthalate (PET) substrates, polyethylene naphthalate (PEN) substrates, polyethylene furanoate (PEF) substrates, polytrimethylene terephthalate (PTT) substrates, polybutylene terephthalate (PBT) substrates, and polybutylene naphthalate (PBN) substrates. Among these, polyester substrates formed from polyesters comprising aromatic dicarboxylic acid and ethylene glycol as constituent components, specifically PET substrates, PEN substrates, and PEF substrates, are more preferably used.

[0080] The polyester substrate may be in the form of a film or a plate, and its thickness is not particularly limited. Furthermore, the polyester substrate may be subjected to surface treatments such as corona surface treatment.

[0081] The release layer is a resin layer laminated on at least one side of the polyester substrate, and can be formed by applying a release coating agent to the polyester substrate and drying it. If the release coating agent contains the above-mentioned crosslinking agent, the polyurethane resin is crosslinked by heat treatment such as drying after applying the release coating agent.

[0082] The thickness of the release layer (dry film thickness) is not particularly limited; for example, it may be 0.01 to 50 μm or 0.05 to 10 μm.

[0083] [Laminated structure] A laminate according to one embodiment includes the release sheet and a resin layer that is peelably provided on the release layer. The release sheet is used, for example, (1) as a protective sheet for protecting the adhesive film, or (2) as a support sheet for forming the resin film.

[0084] In the case of the protective sheet described in (1) above, the release sheet is used to protect the adhesive film formed on the surface of a product, and the release sheet is attached to the adhesive surface of the product on which the adhesive film is provided. Therefore, the adhesive film corresponds to the resin layer, and the laminate is formed by the product and the release sheet attached to its adhesive surface. The release sheet is peeled off from the adhesive surface when the product is used. Examples of the product include polarizing plates for liquid crystals.

[0085] In the case of the support sheet described in (2) above, a resin liquid is applied or poured onto the release layer of the release sheet and cured by drying or other means to form a resin film. Therefore, the resin film corresponds to the resin layer, and the release sheet on which the resin film is provided corresponds to the laminate. The release sheet is peeled off from the resin film when the resin film is used. [Examples]

[0086] The present invention will be described in more detail below based on examples and comparative examples, but it is not limited thereto.

[0087] Details of each component used in the examples are as follows.

[0088] [Polyol] • Polyol (1): Aromatic polyester diol (number of functional groups: 2, number average molecular weight: 2000). The synthesis method is as follows. In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, 52.41 parts by mass of isophthalic acid, 8.77 parts by mass of adipic acid, 26.58 parts by mass of 1,6-hexanediol, and 12.24 parts by mass of ethylene glycol were charged, and the mixture was heated to 250°C while stirring under a nitrogen atmosphere. The reaction was continued until the acid value was 5 mg KOH / g or less to obtain an aromatic polyester diol.

[0089] • Polyol (2): Polybutadiene polyol (number of functional groups: 2.4, number average molecular weight: 2700), manufactured by Evonik, "POLYVEST HT" • Polyol (3): Polytetramethylene glycol (PTMG) (Number of functional groups: 2, Number average molecular weight: 2000), manufactured by Mitsubishi Chemical Corporation as "PolyTHF(registered trademark) 2000" • Polyol (4): Nonionic polyol containing polyoxyethylene groups (number of functional groups: 2, number average molecular weight: 600), "Ymer N180" manufactured by Perstorp. • Polyol (5): Polycarbonate diol (number of functional groups: 2, number average molecular weight: 2000), manufactured by Mitsubishi Chemical Corporation, "BENEBiOL® NL2030DB" • Trimethylolpropane: Manufactured by Mitsubishi Gas Chemical Co., Ltd. (Number of functional groups: 3, Molecular weight: 134.2) • Dimethylolpropionic acid: Perstorp's "Bis-MPA (registered trademark)" (Number of functional groups: 2, Molecular weight: 134.1)

[0090] [Polyisocyanate] • IPDI: Isophorone diisocyanate (number of functional groups: 2, molecular weight: 222.3), manufactured by Evonik, "VESTANAT® IPDI" • MDI: 4,4'-diphenylmethane diisocyanate (number of functional groups: 2, molecular weight: 250.3), manufactured by Tosoh Corporation as "Millionate MT-F" • HDI: Hexamethylene diisocyanate (number of functional groups: 2, molecular weight: 168.2), manufactured by Asahi Kasei Corporation, "DULANET® 50M-HDI"

[0091] [Sucrose ester] • Sucrose ester (1): An ester compound of sucrose, a C18 fatty acid, and acetic acid obtained by the synthesis example 1 below (fatty acid:acetic acid = 5:3 (molar ratio), hydroxyl value: 10 mg KOH / g)

[0092] (Synthesis Example 1) <Synthesis of sucrose fatty acid esters> 345.7 parts by mass of dimethyl sulfoxide (DMSO) were charged into a reactor, and the mixture was refluxed under conditions of 90°C and 3.7 kPa until the water content of the DMSO was reduced to 0.06% by mass. 0.26 parts by mass of potassium carbonate, 67.2 parts by mass of sucrose, and 292.53 parts by mass of methyl stearate were added, and the reaction was carried out under conditions of 95°C and 3.7 kPa, with the DMSO being distilled off. After the amount of DMSO distilled off reached 42.9 parts by mass, the reaction was continued under total reflux without further distillation of the DMSO. After a total reaction time of 8 hours, a 90% by mass aqueous lactic acid solution was added to bring the pH to 6.0, and the reaction was stopped. Using a stirred tank, the reaction mixture was concentrated by removing DMSO under reduced pressure until the solid content reached 84.0% by mass. To the obtained concentrate, 240 parts by mass of a 0.1% potassium sulfate aqueous solution and 240 parts by mass of isobutyl alcohol (IBA) were added and the mixture was stirred for 30 minutes. The mixture was allowed to stand to separate into two layers, and the upper layer (IBA phase) was separated. Subsequently, the IBA was removed by distillation under reduced pressure to obtain sucrose fatty acid ester. <Acetylation reaction of sucrose fatty acid esters> 250 parts by mass of the sucrose fatty acid ester and 60 parts by mass of acetic anhydride were charged into a reactor, and the mixture was reacted at 90-100°C for 5-6 hours while bubbling with nitrogen gas at a flow rate of 50 mL / min. Unreacted acetic anhydride and by-product acetic acid were removed under reduced pressure. Next, 1500 parts by mass of toluene and 2250 parts by mass of a 0.5% by mass aqueous solution of sodium bicarbonate were added, and the mixture was stirred at 50°C for 30 minutes. After standing, the toluene was separated. Subsequently, the toluene was removed under reduced pressure to obtain sucrose ester (1).

[0093] • Sucrose ester (2): An ester compound obtained by Synthesis Example 2 below, consisting of sucrose, a C18 fatty acid, and acetic acid (fatty acid:acetic acid = 4:4 (molar ratio), hydroxyl value: 7 mg KOH / g).

[0094] (Synthesis Example 2) In the above Synthesis Example 1, the amount of methyl stearate was 234.4 parts by mass, the amount of acetic anhydride was 90.6 parts by mass, and the rest was carried out in the same manner as in Synthesis Example 1 to obtain sucrose ester (2).

[0095] • Sucrose ester (3) (comparative material): Sucrose benzoate ester (hydroxyl value: 35 mg KOH / g) obtained by synthesis example 3 below.

[0096] (Synthesis Example 3) In a 1 L five-necked flask equipped with a stirring rod, thermometer, cooling condenser, dropping funnel, and pH electrode connected to a pH meter, 34.2 parts by mass of sucrose and 70.0 parts by mass of water were charged and dissolved. Then, while cooling to below 10°C in a water bath, a solution of 106.7 parts by mass of benzoyl chloride dissolved in 100 parts by mass of cyclohexanone was gradually added. Subsequently, while maintaining a temperature below 20°C, 69.0 parts by mass of 48% by mass of caustic soda aqueous solution was added via a dropping funnel at a rate that maintained the pH at 10-11. After removing the water bath, stirring was continued at room temperature (20-30°C) for 1 hour to complete the reaction. A small amount of sodium carbonate was then added and heated to convert the trace amounts of remaining benzoyl chloride to sodium benzoate. After standing for about 30 minutes, the aqueous phase was separated and removed. 70 parts by mass of fresh water were added, the mixture was heated to 40-50°C in a water bath, stirred for 30 minutes, and then allowed to stand for about 30 minutes to separate and remove the aqueous phase. This procedure was repeated three more times (total number of water washes: 4), the mixture was heated to 120°C, and the solvent was removed under reduced pressure to obtain sucrose ester (3).

[0097] • Sucrose ester (4) (comparative material): Sucrose fatty acid ester (hydroxyl value: 120 mg KOH / g) obtained by the synthesis of sucrose fatty acid ester in Synthesis Example 1 above.

[0098] [Surfactants] • Surfactant (1): Nonionic surfactant, "Neugen® EA-157" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0099] [Crosslinking agent] • Crosslinking agent (1): Carbodiimide compound, "V02-L02" manufactured by Nisshinbo Chemical Co., Ltd. (Non-volatile content 40% by mass, NCN equivalent 385)

[0100] The evaluation method for release coating agents is as follows:

[0101] [Adhesiveness] The adhesion between the release coating and the PET substrate was evaluated using the following method. A PET film ("Lumirror T-60," manufactured by Toray Industries, Inc.) was degreased with isopropyl alcohol. Then, the release coating was applied to the PET film using a bar coater to a dry film thickness of 10 μm. The film was dried at 80°C for 10 minutes, and then at 120°C for another 10 minutes to obtain a test piece with a release coating film formed on it. Using this test piece as a sample, a 2 mm grid test in accordance with JIS K5400-8.5:1990 was performed, and the adhesion between the coating and the PET substrate was calculated using the following formula. Adhesion (%) = 100 - (Number of squares that peeled off)

[0102] [Removability 1 (Removability from adhesive tape)] Corona-discharge treated PET substrate ("Lumirror T-60," manufactured by Toray Industries, Inc.) was used as the PET substrate. A release coating agent was applied to the PET substrate using a bar coater to a dry film thickness of 1 μm, dried at 80°C for 10 minutes, and then dried again at 120°C for 10 minutes to obtain a test piece (coated film) with a release coating agent film formed on it. Nitto Denko Corporation's adhesive tape "No. 31B" was applied to the coating film of the test piece using a 2 kg roller, and the peel strength (unit: mN / 25 mm) was measured after 3 hours. The peel strength was measured using a 180° peel test (300 mm / min) in accordance with JIS Z0237:2009. A lower peel strength indicates better peelability. A peel strength of less than 500 mN / 25 mm is preferable, and more preferably less than 300 mN / 25 mm.

[0103] [Removability 2 (Removability from resin coating)] A test specimen was obtained in which a release coating film was formed in the same manner as in release property 1. A rectangular frame measuring 5 cm x 10 cm was made on the coating film of the test specimen using an adhesive backer, and a water-based urethane resin (Superflex 460, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., with a non-volatile content of 38% by mass) was poured in so that the dry film thickness was 250 μm. Next, the specimen was dried at 20°C for 15 hours, at 80°C for 6 hours, and then at 120°C for 30 minutes to create a resin film made of the water-based urethane resin on the test specimen. The ability to peel off the obtained resin film by hand was evaluated, and those that could be peeled off were rated "○", while those that could not be peeled off were rated "×".

[0104] [water resistance] A release agent was poured onto a fluororesin-coated frying pan to a dry thickness of 500 μm. The pan was then dried at 40°C for 15 hours, 80°C for 6 hours, and 120°C for 20 minutes to create a film made of the release agent. This film was used as a test specimen, which was immersed in 40°C water for 24 hours. The mass of the film after immersion was measured. The percentage increase in mass after immersion compared to the initial mass before immersion was calculated. A smaller percentage increase indicates less swelling due to water and superior water resistance.

[0105] [Example 1] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, 68.53 parts by mass of polyol(1), 1.45 parts by mass of trimethylolpropane, 5.50 parts by mass of dimethylolpropionic acid, and 100 parts by mass of methyl ethyl ketone were added and thoroughly stirred until dissolved. Then, 24.52 parts by mass of IPDI were added, and the mixture was reacted at 75°C until the content of free isocyanate groups relative to the solid content reached 1.88% by mass, thereby obtaining a methyl ethyl ketone solution of isocyanate group-containing urethane prepolymer. This prepolymer solution was cooled to 45°C, neutralized by adding 4.15 parts by mass of triethylamine as a neutralizing agent, and then a solution of 20 parts by mass of sucrose ester(1) dissolved in 20 parts by mass of methyl ethyl ketone (heated to 40°C) was added and stirred. While stirring with a homogenizer, 308 parts by mass of distilled water was added as a dispersion medium and the mixture was emulsified and dispersed. Subsequently, the emulsion was stirred at 40°C for 1 hour to complete the chain extension reaction with water. Methyl ethyl ketone was removed by distillation under heating and reduced pressure to obtain a release coating agent consisting of an aqueous dispersion of polyurethane resin with a solid content of 30% by mass.

[0106] [Examples 2, 3, 5-12, Comparative Examples 2, 3] The types and amounts of polyols, polyisocyanates, and sucrose esters were changed as shown in Table 1 below, and the rest of the process was the same as in Example 1 to obtain mold release coating agents consisting of aqueous dispersions of polyurethane resin for Examples 2, 3, 5-12, and Comparative Examples 2 and 3. However, the amount of free isocyanate groups at the end of the urethane reaction when obtaining the isocyanate group-containing urethane prepolymer was 1.61% by mass for Example 2, 1.65% by mass for Example 5, 1.86% by mass for Example 6, 1.93% by mass for Example 7, 4.04% by mass for Example 11, and 1.33% by mass for Example 12. In addition, the amount of distilled water added as a dispersion medium was adjusted so that the solid content concentration of the aqueous dispersion was 30% by mass.

[0107] [Example 4] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, 61.32 parts by mass of polyol(1), 1.45 parts by mass of trimethylolpropane, 17.00 parts by mass of polyol(4), and 100 parts by mass of methyl ethyl ketone were added and thoroughly stirred until dissolved. Then, 20.23 parts by mass of IPDI were added, and the mixture was reacted at 75°C until the content of free isocyanate groups relative to the solid content reached 1.64% by mass, to obtain a methyl ethyl ketone solution of isocyanate group-containing urethane prepolymer. After cooling this prepolymer solution to 45°C, a solution of 20 parts by mass of sucrose ester(1) dissolved in 20 parts by mass of methyl ethyl ketone was added and stirred. While stirring with a homogenizer, 308 parts by mass of distilled water was added as a dispersion medium to emulsify and disperse. The emulsion was then stirred at 40°C for 1 hour to complete the chain extension reaction with water. This was heated under reduced pressure to remove the methyl ethyl ketone, yielding a release coating agent consisting of an aqueous dispersion of polyurethane resin with a solid content of 30% by mass.

[0108] [Example 13] After emulsification and dispersion, 1.21 parts by mass of ethylenediamine as a chain extender was added to the emulsion and stirred at 40°C for 1 hour to complete the chain extension reaction. The rest of the procedure was the same as in Example 1 to obtain the release coating agent consisting of the aqueous dispersion of polyurethane resin of Example 13.

[0109] [Example 14] Instead of 308 parts by mass of distilled water as the dispersion medium, 277 parts by mass of distilled water and 31 parts by mass of N-methylpyrrolidone (NMP) (distilled water / NMP = 90 / 10) were added, and the rest of the procedure was the same as in Example 1 to obtain a release coating agent consisting of the aqueous dispersion of polyurethane resin of Example 14.

[0110] [Example 15] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, 80.25 parts by mass of polyol(1), 1.45 parts by mass of trimethylolpropane, 1.05 parts by mass of dimethylolpropionic acid, and 100 parts by mass of methyl ethyl ketone were added and thoroughly stirred until dissolved. Then, 17.25 parts by mass of IPDI was added, and the mixture was reacted at 75°C until the content of free isocyanate groups relative to the solid content reached 1.43% by mass, to obtain a methyl ethyl ketone solution of isocyanate group-containing urethane prepolymer. This prepolymer solution was cooled to 45°C, neutralized by adding 0.79 parts by mass of triethylamine, and then a solution of 5 parts by mass of surfactant(1) dissolved in 5 parts by mass of methyl ethyl ketone and a solution of 20 parts by mass of sucrose ester(1) dissolved in 20 parts by mass of methyl ethyl ketone were added and stirred. While stirring with a homogenizer, 308 parts by mass of distilled water was added as a dispersion medium to emulsify and disperse the mixture. Subsequently, the emulsion was stirred at 40°C for 1 hour to complete the chain extension reaction with water. Methyl ethyl ketone was removed by distillation under heating and reduced pressure to obtain a release coating agent consisting of an aqueous dispersion of polyurethane resin with a solid content of 30% by mass.

[0111] [Example 16] The amount of distilled water added as a dispersion medium during emulsification and dispersion was 308 parts by mass. After the chain extension reaction with water and the removal of methyl ethyl ketone by distillation, 39.5 parts by mass of crosslinking agent (1) were added, and the rest of the procedure was the same as in Example 1 to obtain the release coating agent of Example 16.

[0112] [Comparative Example 1] A mold release coating agent consisting of an aqueous dispersion of polyurethane resin of Comparative Example 1 was obtained by omitting the addition of sucrose ester (1) and proceeding in the same manner as in Example 1.

[0113] The release coating agents of Examples 1-16 and Comparative Examples 1-3 were evaluated for adhesion, release properties (1), release properties (2), and water resistance. The results are shown in Table 1. In Table 1, "Sucrose ester content (parts by mass)" refers to the parts by mass of sucrose ester per 100 parts by mass of polyurethane resin in the release coating agent (the same applies to Table 2). The index (NCO / OH) is the equivalent ratio of hydroxyl groups to isocyanate groups in the urethane prepolymer (the same applies to Table 2).

[0114] As shown in Table 1, Comparative Example 1, lacking sucrose ester, exhibited poor release properties. Comparative Example 2, which contained sucrose benzoate ester as the sucrose ester, showed improved adhesion but poor release properties. Comparative Example 3, which contained sucrose fatty acid ester as the sucrose ester, resulted in precipitation of the sucrose fatty acid ester, preventing emulsification.

[0115] In contrast, Examples 1-16, which incorporated sucrose esters obtained by esterifying virtually all hydroxyl groups of sucrose with fatty acids and acetic acid, exhibited excellent adhesion and release properties. Furthermore, while Example 4, which contained a nonionic polyurethane resin, and Example 5, which lacked a cross-linked structure, showed poor water resistance, Examples 1-3 and 6-16, which contained anionic polyurethane resins with a cross-linked structure, showed excellent water resistance of the film made from the release coating agent.

[0116] [Table 1]

[0117] [Example 17] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, 79.50 parts by mass of polyol(1), 5.50 parts by mass of dimethylolpropionic acid, and 100 parts by mass of methyl ethyl ketone were added and thoroughly stirred until dissolved. Then, 15.00 parts by mass of IPDI was added, and the mixture was reacted at 75°C until the content of free isocyanate groups relative to the solid content was 0.05% by mass or less to obtain a methyl ethyl ketone solution of hydroxyl group-containing polyurethane resin. This polyurethane resin solution was cooled to 45°C, neutralized by adding 4.15 parts by mass of triethylamine as a neutralizing agent, and then a solution of 20 parts by mass of sucrose ester(1) dissolved in 20 parts by mass of methyl ethyl ketone was added and stirred. While stirring with a homogenizer, 308 parts by mass of distilled water was added as a dispersion medium to emulsify and disperse. The emulsion was then stirred at 40°C for 1 hour. This was heated under reduced pressure to remove the methyl ethyl ketone, yielding a release coating agent consisting of an aqueous dispersion of polyurethane resin with a solid content of 30% by mass.

[0118] [Examples 18, 19] The types and amounts of polyol and polyisocyanate were changed as shown in Table 2 below, and the rest was carried out in the same manner as in Example 17 to obtain the release coating agents consisting of aqueous dispersions of polyurethane resin of Examples 18 and 19.

[0119] [Comparative Example 4] Without adding sucrose ester (1), and otherwise proceeding in the same manner as in Example 17, a mold release coating agent consisting of an aqueous dispersion of polyurethane resin of Comparative Example 4 was obtained.

[0120] The release coatings of Examples 17-19 and Comparative Example 4 were evaluated for adhesion, release properties (1), release properties (2), and water resistance. The results are shown in Table 2.

[0121] [Table 2]

[0122] Furthermore, the various numerical ranges described in this specification can be any combination of their upper and lower limits, and all such combinations are described herein as preferred numerical ranges. Also, the description of a numerical range as "X~Y" means X or greater and Y or less.

[0123] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, and modifications are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

Claims

1. A release coating agent for polyester substrates comprising an aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, The aqueous dispersion contains a sucrose ester with a hydroxyl value of 30 mg KOH / g or less, which is obtained by esterifying sucrose with a fatty acid having 8 to 25 carbon atoms and acetic acid. This is a release coating agent for polyester substrates.

2. The release coating agent for polyester substrates according to claim 1, wherein the molar ratio of the fatty acid to the acetic acid in the sucrose ester is 3:5 to 7:

1.

3. The release coating agent for polyester substrates according to claim 1, wherein the content of the sucrose ester is 5 to 80 parts by mass per 100 parts by mass of the polyurethane resin.

4. The release coating agent for polyester substrates according to claim 1, wherein the polyol constituting the polyurethane resin includes a polyester polyol.

5. The release coating agent for polyester substrates according to claim 1, wherein the polyol constituting the polyurethane resin includes an anionic group-containing polyol.

6. A release sheet comprising a polyester substrate and a release layer provided on the polyester substrate, the release coating agent according to any one of claims 1 to 5.

7. A laminate comprising a release sheet according to claim 6 and a resin layer provided on the release layer of the release sheet in a peelable manner.

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