Aqueous dispersion, and release coating agent for polyester base material using the same, release sheet, and laminate

Abstract

To provide an aqueous dispersion exhibiting superior adhesion to polyester base materials and having heat-resistant peelability.SOLUTION: An aqueous dispersion according to an embodiment is an aqueous dispersion having a polyurethane resin dispersed in an aqueous dispersion medium, wherein a (meth)acrylic polymer containing, as its constituents, a monofunctional (meth)acrylic acid alkyl having an alkyl group with 4 to 22 carbon atoms and a poly(meth)acrylate having a functionality of 2 to 6 is contained, together with the polyurethane resin, in resin particles as a dispersed phase. The aqueous dispersion further contains an ionic liquid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, and also to a release coating agent for polyester substrates containing the aqueous dispersion, as well as a release sheet and a laminate obtained by using the release coating agent. [Background technology]

[0002] BACKGROUND ART Aqueous dispersions of polyurethane resins obtained by dispersing a polyurethane resin in an aqueous dispersion medium are widely used in paints, inks, adhesives, and the like.

[0003] On the other hand, release sheets (also called release sheets) are known in which a release layer is provided 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. Such release coating agents include not only silicone-based but also non-silicone-based release coating agents that make it possible to avoid silicone migration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-099095 Summary of the Invention [Problem to be solved by the invention]

[0005] A release coating agent that is applied to a polyester substrate is required to have adhesive properties to the polyester substrate. Furthermore, the release coating agent is required to be easily peeled from a resin layer, such as a pressure-sensitive adhesive film to be protected as a release sheet or a resin film formed on the release sheet, i.e., to have peelability from the resin layer. Since a laminate of a release sheet and a resin layer may be placed in a heated atmosphere, it is desirable for the release coating agent to be peelable even after heat treatment, i.e., to have heat-resistant peelability. If an aqueous dispersion of the polyurethane resin described above having such properties can be provided, it can be advantageously used as a release coating agent.

[0006] An object of an embodiment of the present invention is to provide an aqueous dispersion that has excellent adhesion to polyester substrates and heat-resistant peelability. [Means for solving the problem]

[0007] The present invention includes the embodiments shown below. [1] An aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, wherein a (meth)acrylic polymer containing, as constituent components, a monofunctional alkyl (meth)acrylate having an alkyl group with 4 to 22 carbon atoms and a poly(meth)acrylate having 2 to 6 functional groups is contained in resin particles as a dispersoid together with the polyurethane resin, and further containing an ionic liquid. [2] The aqueous dispersion according to [1], wherein the amount of the poly(meth)acrylate is 0.3 to 100 parts by mass per 100 parts by mass of the alkyl (meth)acrylate. [3] The aqueous dispersion according to [1] or [2], wherein the alkyl (meth)acrylate contains an alkyl (meth)acrylate having a linear alkyl group as the alkyl group. [4] The aqueous dispersion according to any one of [1] to [3], wherein the poly(meth)acrylate contains a (poly)alkylene glycol di(meth)acrylate. [5] The aqueous dispersion according to any one of [1] to [4], wherein the amount of the ionic liquid is 0.1 to 5 parts by mass per 100 parts by mass of the total amount of the polyurethane resin and the (meth)acrylic polymer. [6] The aqueous dispersion according to any one of [1] to [5], wherein the amount of the alkyl (meth)acrylate is 40 to 350 parts by mass per 100 parts by mass of the polyurethane resin.

[0008] [7] A release coating agent for polyester substrates, comprising the aqueous dispersion according to any one of [1] to [6]. [8] A release sheet comprising a polyester substrate and a release layer formed on the polyester substrate and comprising the release coating agent according to [7]. [9] A laminate comprising the release sheet according to [8] and a resin layer releasably provided on the release layer of the release sheet.

[10] Use of the aqueous dispersion according to any one of [1] to [6] as a release coating agent for polyester substrates. [Effects of the Invention]

[0009] According to an embodiment of the present invention, it is possible to provide an aqueous dispersion that has excellent adhesion to polyester substrates and heat-resistant peelability. DETAILED DESCRIPTION OF THE INVENTION

[0010] The aqueous dispersion according to this embodiment is an aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, and contains an ionic liquid together with a specific (meth)acrylic polymer. Therefore, the aqueous dispersion contains an aqueous dispersion medium, a polyurethane resin, a (meth)acrylic polymer, and an ionic liquid.

[0011] In this specification, "(meth)acrylic polymer" means an acrylic polymer and / or a methacrylic polymer. Similarly, "alkyl (meth)acrylate" means alkyl acrylate and / or alkyl methacrylate, and "poly(meth)acrylate" means polyacrylate and / or polymethacrylate. The same applies to other terms such as "(meth)acrylic" and "(meth)acrylate."

[0012] [Aqueous dispersion medium] The aqueous dispersion medium is a dispersion medium containing water, and examples thereof include 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 an organic solvent may be contained, but preferably in a small amount. In one embodiment, the aqueous dispersion medium preferably contains 70% by mass or more of water, more preferably 80% by mass or more of water, more preferably 90% by mass or more of water, and may be 100% by mass of water. That is, in the aqueous dispersion medium, the mass ratio of water / hydrophilic organic solvent is preferably 70 / 30 to 100 / 0, more preferably 80 / 20 to 100 / 0, and even more preferably 90 / 10 to 100 / 0.

[0013] As the hydrophilic organic solvent, various organic solvents that are soluble in water can be used, and examples thereof 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.

[0014] [Polyurethane resin] A polyurethane resin is obtained by reacting a polyol with a polyisocyanate, and is a polymer having a urethane bond in the molecule. That is, a polyurethane resin contains a polyol and a polyisocyanate as its constituent components. In this specification, "containing a constituent component" in a polyurethane resin means that the polyurethane resin is used as a raw material (monomer) for synthesizing the polyurethane resin, and the polyurethane resin has a structure derived from this.

[0015] The polyurethane resin may have a hydrophilic group, and various water-based polyurethane resins such as anionic polyurethane resins, cationic polyurethane resins, and nonionic polyurethane resins may be used. The hydrophilic group may be an anionic group, a cationic group, or a hydrophilic segment.

[0016] The anionic polyurethane resin is a water-based polyurethane resin having an anionic group. Examples of the anionic group include at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphoric acid group, and salts thereof. Examples of the salt 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.

[0017] The cationic polyurethane resin is a water-based polyurethane resin having cationic groups, such as quaternary ammonium groups.

[0018] Nonionic polyurethane resins are non-charged water-based polyurethane resins that do not have anionic or cationic groups, such as polyurethane resins having hydrophilic segments such as polyoxyethylene groups.

[0019] Examples of polyols constituting 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), polybutadiene polyols, etc. Any one of these may be used alone, or two or more may be used in combination.

[0020] The molecular weight of the polymer polyol is not particularly limited, and may be, for example, 500 to 5,000 in number average molecular weight (Mn), 800 to 4,000, or 1,000 to 3,000.

[0021] In this specification, the number average molecular weight (Mn) is a value measured by GPC (gel permeation chromatography) and calculated using a calibration curve of standard polystyrene. Specifically, the GPC conditions are as follows: columns: "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, and sample concentration: 0.2% by mass.

[0022] As the polyol constituting the polyurethane resin, low molecular weight polyhydric 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 in addition to or separately from the above polymer polyols. Dihydric alcohols and / or trihydric alcohols are preferably used. These may be used alone or in combination of two or more.

[0023] In one embodiment, the polyol constituting the polyurethane resin preferably contains a polyester polyol to enhance the effect of improving adhesion to polyester substrates. That is, the polyurethane resin preferably contains a polyol containing a polyester polyol as a constituent component. The amount of polyester polyol in the polyol is, for example, preferably 30% by mass or more, more preferably 60% by mass or more, still more preferably 70 to 99% by mass, and may be 80 to 95% by mass, relative to 100% by mass of the polyol.

[0024] In this specification, when the amount of each component constituting a polyol is calculated based on 100% by mass of the polyol, if the polyol contains an anionic group, the anionic group is considered to be in the acid form. The amount of the anionic group-containing polyol is also calculated based on the anionic group in the acid form. Furthermore, if the polyol contains a cationic group, the amount is calculated using the amount of the polyol before the cationic group is neutralized with an acid or quaternized with a quaternizing agent.

[0025] In one embodiment, the polyol constituting the polyurethane resin preferably contains a polyol having three or more functional groups. This introduces a crosslinked structure into the polyurethane resin. Examples of polyols having three or more functional groups include polyhydric alcohols having three or more hydroxy groups, such as trimethylolpropane, and also include the above-mentioned polymer polyols having three or more hydroxy groups in the molecule.

[0026] The amount of the polyol having three or more functional groups in the polyol is not particularly limited, and may be, for example, 0.1 to 10 mass %, 0.5 to 8 mass %, or 1 to 5 mass % relative to 100 mass % of the polyol.

[0027] Examples of polyisocyanates that constitute the polyurethane resin include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates, any one of which may be used alone or in combination of two or more.

[0028] Examples of the aliphatic polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0029] Examples of alicyclic polyisocyanates include isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4'-diisocyanate (hydrogenated MDI), hydrogenated xylylene diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatemethyl)cyclohexane.

[0030] Examples of aromatic polyisocyanates include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), and naphthalene diisocyanate.

[0031] Furthermore, isocyanurates, adducts, biurets, allophenates, carbodiimides, etc. of these polyisocyanates may also be used. These polyisocyanates may be used alone or in combination of two or more.

[0032] In one embodiment, the polyurethane resin 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 include the following (A) and (B). Of these, the chain-extended type (A) is advantageous in improving the water resistance of the coating film.

[0033] (A) 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 a polyisocyanate, and then chain-extending the urethane prepolymer with a chain extender.

[0034] (B) A hydroxy group-containing anionic polyurethane resin obtained by reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate.

[0035] The anionic group-free polyol used to synthesize the anionic polyurethane resin can be any of the various polyols listed above that does not have an anionic group or a cationic group. The anionic group-containing polyol is preferably a carboxyl group-containing polyol having a carboxyl group in the molecule, such as dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dihydroxymaleic acid, 2,6-dihydroxybenzoic acid, or tartaric acid, as well as derivatives and salts thereof. These compounds may be used alone or in combination.

[0036] Here, the anionic group is a concept that includes not only the acid type (in the case of a carboxy group: -COOH) but also the salt type (in the case of a carboxy group: a carboxylate group represented by -COOX, where X is a cation that forms a salt with the carboxylic acid), and the acid type and the salt type may be mixed. The anionic group can be neutralized to form a salt, making the final polyurethane resin water-dispersible. Therefore, in an aqueous dispersion of polyurethane resin, the anionic group may exist as a salt type. 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, the anionic group may exist as a salt type, and if a volatile base is used as a neutralizing agent, the anionic group may exist as an acid type.

[0037] In the anionic polyurethane resin, the amount of the anionic group-free polyol in the polyol is not particularly limited and may be, for example, 75 to 99 mass%, 80 to 97 mass%, or 85 to 95 mass% relative to 100 mass% of the polyol. The amount of the anionic group-containing polyol in the polyol is not particularly limited and may be, for example, 1 to 25 mass%, 3 to 20 mass%, or 5 to 15 mass% relative to 100 mass% of the polyol.

[0038] The chain extender that extends the chain of the isocyanate group-containing urethane prepolymer is not particularly limited, and examples thereof include water, and also polyvalent 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).

[0039] [(Meth)acrylic polymer] The (meth)acrylic polymer contains, as constituent components, a monofunctional alkyl (meth)acrylate (X) having an alkyl group with 4 to 22 carbon atoms and a poly(meth)acrylate (Y) having functional groups of 2 to 6. In this specification, with regard to the (meth)acrylic polymer, "containing as a constituent component" means that the (meth)acrylic polymer is used as a raw material (monomer) for synthesizing the polymer, and the (meth)acrylic polymer has a structure derived from this.

[0040] When the alkyl group of the alkyl (meth)acrylate (X) has 4 or more carbon atoms, the initial releasability can be improved, and when the alkyl group has 22 or less carbon atoms, the deterioration of the releasability due to heating can be suppressed. The number of carbon atoms in the alkyl is preferably 6 to 20, more preferably 8 to 18, and even more preferably 10 to 16. The alkyl (meth)acrylate (X) may be a mixture of alkyl groups having different numbers of carbon atoms.

[0041] The alkyl group of the alkyl (meth)acrylate (X) may be branched, but is preferably a linear alkyl group from the viewpoints of releasability and heat releasability. The amount of alkyl (meth)acrylate having a linear alkyl group in 100% by mass of the alkyl (meth)acrylate (X) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass.

[0042] Specific examples of the alkyl (meth)acrylate (X) include n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, n-icosyl (meth)acrylate, and n-docosyl (meth)acrylate. Any of these may be used alone, or two or more may be used in combination.

[0043] Poly(meth)acrylate refers to an ester compound having two or more (meth)acryloyl groups. Therefore, a poly(meth)acrylate (Y) having 2 to 6 functional groups is a (meth)acrylic acid ester having 2 to 6 (meth)acryloyl groups in one molecule. By using such a poly(meth)acrylate (Y), it is possible to improve heat-resistance peelability.

[0044] In one embodiment, the poly(meth)acrylate (Y) preferably has an acrylic equivalent, which is the molecular weight per functional group, of 80 to 150, and more preferably has an acrylic equivalent of 90 to 150.

[0045] Specific examples of the poly(meth)acrylate (Y) include (poly)alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Any of these may be used alone or in combination of two or more.

[0046] Among these, (poly)alkylene glycol di(meth)acrylate is preferred as the poly(meth)acrylate (Y). The amount of (poly)alkylene glycol di(meth)acrylate in 100% by mass of poly(meth)acrylate (Y) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass. Here, "(poly)alkylene glycol" means monoalkylene glycol and / or polyalkylene glycol. The "poly" (number of repeating bonds) of the polyalkylene glycol is preferably 2 to 4, and the number of carbon atoms in the "alkylene" is preferably 2 to 4. Use of such a bifunctional poly(meth)acrylate can improve releasability and heat releasability.

[0047] The (meth)acrylic polymer is a copolymer of an alkyl (meth)acrylate (X) and a poly(meth)acrylate (Y), and may be composed of only (X) and (Y), or may contain other monomers as constituent components as long as the effects of this embodiment are not impaired. The total amount of the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in 100% by mass of all constituent components of the (meth)acrylic polymer is preferably 80% by mass or more, more preferably 90% by mass or more, and may even be 100% by mass.

[0048] The ratio of alkyl (meth)acrylate (X) to poly(meth)acrylate (Y) in the (meth)acrylic polymer is not particularly limited, but the amount of poly(meth)acrylate (Y) per 100 parts by mass of alkyl (meth)acrylate (X) is preferably 0.3 to 100 parts by mass, more preferably 0.5 to 50 parts by mass, more preferably 1 to 40 parts by mass, more preferably 5 to 30 parts by mass, and even more preferably 10 to 25 parts by mass. When the amount of poly(meth)acrylate (Y) is 100 parts by mass or less, initial releasability can be improved, and when it is 0.3 parts by mass or more, the effect of improving heat releasability can be enhanced.

[0049] Polymerization of the monomers containing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) may be carried out by adding a known polymerization initiator. Examples of the polymerization initiator include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine), and substituted ethane initiators such as phenyl-substituted ethane. Alternatively, a redox initiator may be used which is a combination of a peroxide-based initiator such as a persulfate such as potassium persulfate, sodium persulfate, or ammonium persulfate, or a peroxide such as hydrogen peroxide, t-butyl hydroperoxide, or cumene hydroperoxide, and a reducing agent such as a sulfite such as sodium sulfite, a hydrogen sulfite such as sodium hydrogen sulfite, a metal salt such as cuprous sulfate or ferrous sulfate, or an organic reducing agent such as L-ascorbic acid.

[0050] The amount of the polymerization initiator is not particularly limited, and may be, for example, 0.005 to 1 part by mass relative to 100 parts by mass of all monomers including the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y).

[0051] [Ionic liquid] The aqueous dispersion according to this embodiment contains an ionic liquid. By incorporating an ionic liquid together with the specific (meth)acrylic polymer, it is possible to improve the heat-resistant peelability.

[0052] Ionic liquids are liquids that consist of cationic and anionic components and have a melting point of 100°C or less. Examples of anionic components include BF4 - , PF6 - , SbF6 - , NO3 - , CF3SO3 - , (FSO2)2N - (i.e., FSI anion), (CF3SO2)2N -(i.e., TFSI anion), (C2F5SO2)2N - , (CF3SO2)3C - , CF3CO2 - , C3F7CO2 - , CH3CO2 - , (CN)2N - These may be used alone or in combination of two or more. Among these, it is preferable to use bis(fluorosulfonyl)imide anion (FSI anion) and / or bis(fluoromethanesulfonyl)imide anion (TFSI anion) as the anion component.

[0053] Examples of cationic components include compounds containing elements such as N, P, S, O, C, and Si, and cations having a chain structure or a cyclic structure such as a five-membered ring or a six-membered ring as a skeleton. Examples of cyclic structures such as a five-membered ring or a six-membered ring include heterocyclic structures such as a furan ring, a thiophene ring, a pyrrole ring, a pyridine ring, an oxazole ring, an isoxazole ring, a thiazole ring, an isothiazole ring, a furazan ring, an imidazole ring, a pyrazole ring, a pyrazine ring, a pyrimidine ring, a pyridazine ring, a pyrrolidine ring, a piperidine ring, a benzofuran ring, an isobenzofuran ring, an indole ring, an isoindole ring, an indolizine ring, and a carbazole ring. These may be used alone or in combination of two or more. Among these, the cationic component is preferably a chain or cyclic compound containing a nitrogen element, for example, alkylammonium such as triethylammonium, 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-methyl-1-propyl-pyrrolidinium, methylpropylpiperidinium, 1-octyl-4-methylpyridinium, etc.

[0054] [Aqueous dispersion] The aqueous dispersion according to this embodiment is a liquid aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, and contains the above-mentioned (meth)acrylic polymer and ionic liquid.

[0055] In the aqueous dispersion, the (meth)acrylic polymer is contained in polyurethane resin particles. That is, the (meth)acrylic polymer is contained in resin particles as a dispersoid together with the polyurethane resin. The (meth)acrylic polymer may be present inside the particles, on the particle surface, or both inside and on the particle surface. While polyurethane resin has hydrophilic groups, the (meth)acrylic polymer is hydrophobic and therefore likely to be present inside the particles. Therefore, it is preferable that the (meth)acrylic polymer is present inside the particles and that the polyurethane resin having hydrophilic groups is present on the particle surface so as to cover it, thereby enhancing the effects of this embodiment.

[0056] The ionic liquid may or may not be contained in the resin particles as a dispersoid. For example, an ionic liquid that is insoluble in water may be contained in the resin particles together with a polyurethane resin, similar to a (meth)acrylic polymer. In this case, the resin particles contain a polyurethane resin, a (meth)acrylic polymer, and an ionic liquid.

[0057] The content of the polyurethane resin in the aqueous dispersion is not particularly limited, and may be, for example, 3 to 50 mass %, 5 to 30 mass %, or 10 to 20 mass % relative to the total mass of the aqueous dispersion.

[0058] The content of the (meth)acrylic resin is preferably set as follows in terms of the content of alkyl (meth)acrylate: That is, the amount of alkyl (meth)acrylate is preferably 40 to 350 parts by mass, more preferably 45 to 320 parts by mass, even more preferably 60 to 200 parts by mass, and even more preferably 70 to 150 parts by mass, per 100 parts by mass of polyurethane resin. By setting the content of alkyl (meth)acrylate to 40 parts by mass or more, the effect of improving releasability can be enhanced, and by setting it to 350 parts by mass or less, the effect of improving adhesion to polyester substrates can be enhanced.

[0059] The content of the ionic liquid is preferably 0.1 to 5 parts by mass, more preferably 0.3 to 4 parts by mass, more preferably 0.5 to 3.5 parts by mass, and even more preferably 1.0 to 3.0 parts by mass, relative to 100 parts by mass of the total amount of the polyurethane resin and the (meth)acrylic polymer. When the content of the ionic liquid is 0.1 part by mass or more, the effect of improving the releasability and heat-resistant releasability can be enhanced. When the content of the ionic liquid is 5 parts by mass or less, the effect of improving the adhesion to polyester substrates can be enhanced.

[0060] The size of the resin particles in the aqueous dispersion is not particularly limited, and may be, for example, an average particle size of 0.001 to 0.5 μm. Here, the average particle size is the 50% cumulative particle size (d50) measured using a "Microtrac UPA-UZ152" manufactured by Nikkiso Co., Ltd.

[0061] The aqueous dispersion of polyurethane resin may contain other components as long as the effects of the aqueous dispersion are not impaired, such as a crosslinking agent for crosslinking the polyurethane resin, a surfactant for dispersing the polyurethane resin, a (meth)acrylic polymer or its monomer, or an ionic liquid in an aqueous dispersion medium, and a polymerization initiator for polymerizing the (meth)acrylic polymer.

[0062] Examples of the crosslinking agent include compounds having two or more reactive groups in the molecule that can react with at least one active hydrogen-containing group selected from the group consisting of a hydroxy group, a primary amino group, a secondary amino group, and a thiol group contained in the polyurethane resin. When the polyurethane resin has a carboxy group, the crosslinking agent can also undergo a crosslinking reaction with the carboxy group.

[0063] Examples of the crosslinking agent include carbodiimide compounds, oxazoline compounds, blocked isocyanate compounds, and epoxy compounds, and any one of these may be used alone or in combination of two or more.

[0064] The amount of the crosslinking agent is not particularly limited, and may be, for example, 1.0 to 20 parts by mass per 100 parts by mass of the polyurethane resin.

[0065] The surfactant is not particularly limited, and anionic surfactants and nonionic surfactants are preferably used. Examples of anionic surfactants include polyoxyalkylene alkyl ether sulfates, polyoxyalkylene styrenated phenyl ether sulfates, and polyoxyalkylene alkyl ether phosphates. Examples of nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyethylene styrenated phenyl ethers, polyoxyethylene phenyl ethers, and polyoxyethylene polyoxypropylene glycols.

[0066] The amount of surfactant is not particularly limited, and may be, for example, 0.1 to 5.0 parts by mass per 100 parts by mass of the total amount of polyurethane resin and (meth)acrylic polymer.

[0067] [Method for producing aqueous dispersion] The method for producing the aqueous dispersion of polyurethane resin is not particularly limited, and it may be produced, for example, by a method including the following steps (1) to (4).

[0068] Step (1): A step of reacting a polyol with a polyisocyanate. Step (2): A step of mixing the polyurethane resin having a hydrophilic group obtained in step (1), an alkyl (meth)acrylate (X), a poly(meth)acrylate (Y), and an ionic liquid. Step (3): A step of dispersing the mixture in an aqueous dispersion medium. Step (4): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) contained in the mixture dispersed in an aqueous dispersion medium.

[0069] In this way, it is believed that by mixing a polyurethane resin having a hydrophilic group with an alkyl (meth)acrylate (X) and a poly(meth)acrylate (Y), dispersing the mixture in an aqueous dispersion medium, and polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture in the dispersed state, the (meth)acrylic polymer can be efficiently incorporated into the interior of the polyurethane resin particles.

[0070] In the above step (1), the reaction between the polyol and the polyisocyanate may be carried out without an organic solvent, or may be carried out in an organic solvent that does not have an active hydrogen group, such as methyl ethyl ketone or acetone. The polyurethane resin obtained by the reaction in step (1) also encompasses the urethane prepolymer before chain extension, etc. Therefore, in step (2), the urethane prepolymer may be mixed with the acrylic monomers containing the above (X) and (Y) and an ionic liquid.

[0071] Furthermore, when the polyurethane resin has an anionic group or a cationic group, the anionic group or the cationic group may be neutralized with a neutralizing agent or the cationic group may be quaternized with a quaternizing agent before or after mixing the polyurethane resin with the acrylic monomer in step (2).

[0072] Examples of bases that neutralize the anionic group 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.

[0073] Examples of acids that neutralize cationic groups include inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as formic acid, acetic acid, propionic acid, butyric acid, lactic acid, malic acid, and malonic acid. Examples of quaternizing agents that quaternize cationic groups include alkyl halides such as methyl chloride and methyl bromide, and dialkyl sulfates such as dimethyl sulfate and diethyl sulfate.

[0074] The method for dispersing the mixture in the aqueous dispersion medium in step (3) is not particularly limited, and examples thereof include (i) a method in which the mixture or a resin solution thereof is added to the aqueous dispersion medium while stirring it with a homogenizer, homomixer, etc., and (ii) a method in which the aqueous dispersion medium is added to the mixture or a resin solution thereof while stirring it with a homogenizer, homomixer, etc. A surfactant may be added to facilitate emulsification and dispersion of the mixture containing the polyurethane resin and the acrylic monomer in the aqueous dispersion medium.

[0075] When a urethane prepolymer is synthesized in step (1), the chains of the urethane prepolymer may be extended with a chain extender after or during dispersion in step (3). The chain extension reaction may be carried out simultaneously with or before the polymerization reaction in step (4).

[0076] The polymerization in step (4) may be thermal polymerization, but is preferably carried out by adding a polymerization initiator. The polymerization temperature is adjusted depending on the type of polymerization initiator, and may be, for example, 20°C to 100°C.

[0077] When the reaction between the polyol and the polyisocyanate is carried out in an organic solvent in step (1), the organic solvent may be removed after dispersion in an aqueous dispersion medium in step (3) or after the polymerization reaction in step (4).

[0078] In one embodiment, when the anionic polyurethane resin (A) is used as the polyurethane resin, it may be produced by the following steps (a1) to (a6). 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, the alkyl (meth)acrylate (X), the poly(meth)acrylate (Y), and an ionic liquid. Step (a4): A step of dispersing the mixture in an aqueous dispersion medium. Step (a5): A step of extending the chains of the isocyanate group-containing urethane prepolymer in the mixture dispersed in the aqueous dispersion medium with a chain extender. Step (a6): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture dispersed in an aqueous dispersion medium.

[0079] Step (a1) corresponds to the above step (1), step (a3) ​​corresponds to the above step (2), step (a4) corresponds to the above step (3), step (a6) corresponds to the above step (4), and steps (a2) and (a5) are additional steps.

[0080] In step (a1), the polyisocyanate is used so that the amount of isocyanate groups is stoichiometrically in excess of the amount of hydroxy groups contained in the polyol, for example, so that the equivalent ratio of hydroxy groups to isocyanate groups (NCO / OH) is 1.05 to 1.70 (more preferably 1.10 to 1.60).

[0081] The order of steps (a2) and (a3) ​​does not matter. In step (a5), the chain extender may be added after or during the dispersion of the polyurethane prepolymer in the aqueous dispersion medium in step (a4). The chain extender is as described above, and water also serves as a chain extender. When water is used as the chain extender, the water in the aqueous dispersion medium also serves as the chain extender.

[0082] In one embodiment, when the anionic polyurethane resin (B) is used as the polyurethane resin, it may be produced by the following steps (b1) to (b5). Step (b1): A step of synthesizing a hydroxy group-containing polyurethane resin by reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate. Step (b2): A step of neutralizing the anionic groups of the hydroxy group-containing polyurethane resin. Step (b3): ​​A step of mixing the hydroxy group-containing polyurethane resin, the alkyl (meth)acrylate (X), the poly(meth)acrylate (Y), and an ionic liquid. Step (b4): A step of dispersing the mixture in an aqueous dispersion medium. Step (b5): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture dispersed in an aqueous dispersion medium.

[0083] Step (b1) corresponds to the above step (1), step (b3) corresponds to the above step (2), step (b4) corresponds to the above step (3), step (b5) corresponds to the above step (4), and step (b2) is an additional step.

[0084] In step (b1), the polyol is used so that the amount of hydroxy groups is stoichiometrically in excess of the amount of isocyanate groups contained in the polyisocyanate, for example, so that the equivalent ratio of hydroxy groups to isocyanate groups (NCO / OH) is 0.70 to 0.95 (more preferably 0.75 to 0.90). The order of steps (b2) and (b3) is not important.

[0085] [Release coating agent for polyester substrates] The release coating agent for polyester substrates according to this embodiment contains the aqueous dispersion, and therefore contains an aqueous dispersion medium, a polyurethane resin, a (meth)acrylic resin, and an ionic liquid. The release coating agent may consist solely of the aqueous dispersion, or may contain various additives, such as an antioxidant, an antistatic agent, a surfactant, an antifoaming agent, and a surface conditioner, in addition to the aqueous dispersion.

[0086] The content of the polyurethane resin in the release coating agent is not particularly limited and may be, for example, 3 to 50 mass %, 5 to 30 mass %, or 10 to 20 mass % relative to the total mass of the release coating agent.

[0087] [Release sheet] A release sheet according to one embodiment includes a polyester substrate and a release layer provided on the polyester substrate, and the release layer is formed from the release coating agent.

[0088] The polyester substrate can be formed from various polyesters containing dicarboxylic acid and diol as constituent components (monomers). 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 containing aromatic dicarboxylic acid and ethylene glycol as constituent components, specifically PET substrates, PEN substrates, and PEF substrates, are more preferably used.

[0089] The polyester substrate may be in the form of a film or a plate, and the thickness is not particularly limited. The polyester substrate may be subjected to a surface treatment such as a corona surface treatment.

[0090] The release layer is a resin layer laminated on at least one of the front and back surfaces 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 applying the release coating agent and then performing a heat treatment such as drying.

[0091] The thickness (dry film thickness) of the release layer is not particularly limited, and may be, for example, 0.01 to 50 μm, or 0.05 to 10 μm.

[0092] The release sheet can be used, for example, as a process protection film, and is attached to an adhesive or non-adhesive object to protect the object. When the object to which the release sheet is attached is used, the release sheet is peeled off. The peeled release sheet may be discarded.

[0093] [Laminate] The laminate according to one embodiment includes the release sheet and a resin layer releasably provided on the release layer. The resin forming the resin layer is not particularly limited, and examples thereof include acrylic resins, silicone resins, and aminoalkyd resins.

[0094] The release sheet is used, for example, as (1) a protective sheet for protecting the pressure-sensitive adhesive film, or as (2) a support sheet for forming a resin film.

[0095] In the case of the protective sheet (1) above, the release sheet is used to protect a product having a pressure-sensitive adhesive film formed on its surface, and the release sheet is attached to the adhesive surface of the product on which the pressure-sensitive adhesive film is formed. Therefore, the pressure-sensitive adhesive film corresponds to the resin layer, and the product and the release sheet attached to its adhesive surface constitute the laminate. The release sheet is peeled off from the adhesive surface when the product is used. Examples of such products include liquid crystal polarizing plates.

[0096] In the case of the support sheet (2) above, a resin liquid is applied or poured onto the release layer of the release sheet and cured by drying or the like 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 to be used. [Example]

[0097] The present invention will be explained in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0098] Details of each component used in the examples are as follows:

[0099] [Polyol] Polyester polyol 1: Aromatic polyester diol (functional group number: 2, number average molecular weight: 2000). The synthesis method is as follows: A reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube was charged with 54.72 parts by mass of isophthalic acid, 8.63 parts by mass of adipic acid, 23.89 parts by mass of neopentyl glycol, and 12.76 parts by mass of ethylene glycol, and the mixture was heated to 250° C. with stirring under a nitrogen stream. The reaction was continued until the acid value reached 5 mgKOH / g or less, yielding an aromatic polyester diol.

[0100] Polyester polyol 2: Aromatic polyester diol (functional group number: 2, number average molecular weight: 2000). The synthesis method is as follows. A reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube was charged with 52.41 parts by mass of terephthalic 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, and the mixture was heated to 250° C. with stirring under a nitrogen stream. The reaction was continued until the acid value reached 5 mgKOH / g or less, yielding an aromatic polyester diol.

[0101] Polycarbonate polyol: Polycarbonate diol (functional group number: 2, number average molecular weight: 2000), "UH-200" manufactured by UBE Corporation Trifunctional polyol: Trimethylolpropane (functionality: 3), manufactured by Mitsui Gas Chemicals, Inc. Dimethylolpropionic acid: Perstorp's "Bis-MPA (registered trademark)" (number of functional groups: 2)

[0102] [Polyisocyanate] IPDI: Isophorone diisocyanate (functional groups: 2, molecular weight: 222.3), Evonik "VESTANAT (registered trademark) IPDI" TDI: Tolylene diisocyanate (functional groups: 2, molecular weight: 174.2), "Cosmonate T100" manufactured by Mitsui Chemicals Fine Co., Ltd.

[0103] [(Meth)acrylic acid ester] n-Dodecyl acrylate: "LA" (linear C12) manufactured by Osaka Organic Chemical Industry Co., Ltd. n-Dodecyl methacrylate: "Light Ester L" (linear C12) manufactured by Kyoeisha Chemical Co., Ltd. n-Octyl acrylate: "NOAA" (linear C8) manufactured by Osaka Organic Chemical Industry Co., Ltd. Stearyl acrylate: "STA" (linear C18) manufactured by Osaka Organic Chemical Industry Co., Ltd. 2-Ethylhexyl acrylate: Mitsubishi Chemical Corporation (branched C8) Ethyl acrylate: Mitsubishi Chemical Corporation (C2)

[0104] [Poly(meth)acrylate] Dimethacrylate: Ethylene glycol dimethacrylate, "Light Ester EG" manufactured by Kyoeisha Chemical Co., Ltd. Tetraacrylate: Pentaerythritol tetraacrylate, "Light Acrylate PE-4A" manufactured by Kyoeisha Chemical Co., Ltd.

[0105] [Ionic liquid] Ionic liquid 1: 1-octyl-4-methylpyridinium bis(trifluoromethanesulfonyl)imide, CAS RN: 712355-04-9, Fujifilm Wako Pure Chemical Industries, Ltd. Ionic liquid 2: 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, CAS RN: 235789-75-0, manufactured by Kishida Chemical Co., Ltd.

[0106] [Other additives] Polymerization initiator 1: tert-butyl hydroperoxide (70% aqueous solution), manufactured by Tokyo Chemical Industry Co., Ltd. Polymerization initiator 2: sodium sulfite, manufactured by Nacalai Tesque, Inc.

[0107] The release coating agents were evaluated as follows.

[0108] [Initial peelability] A corona-discharge-treated PET substrate ("Lumirror T-60" manufactured by Toray Industries, Inc.) was used as the polyester substrate. A release coating agent was applied to the PET substrate using a bar coater to a dry film thickness of 1 μm, and the PET substrate was dried at 160°C for 1 minute to obtain a test piece (coated film) with a coating film of the release coating agent. An acrylic adhesive tape "No. 31B" manufactured by Nitto Denko Corporation was attached to the coating film of the test piece using a 2 kg roller, and the peel strength (unit: mN / 25 mm) after 3 hours was measured. The peel strength was measured using a 180° peel test (300 mm / min) in accordance with JIS Z0237:2009. The smaller the peel strength, the better the releasability. In the peel strength measurement, if the coating peeled off, the measurement was not possible and the sample was marked "F."

[0109] [Heat-resistant peeling] Nitto Denko Corporation's acrylic adhesive tape "No. 31B" was applied to the coating film of a test piece prepared in the same manner as for initial peelability using a 2 kg roller, and heated at 70°C for 20 hours. After cooling to room temperature, the peel strength (unit: mN / 25 mm) was measured in the same manner as for initial peelability. The smaller the peel strength, the better the heat peel resistance. In the peel strength measurement, if the coating peeled off, it was deemed unmeasurable and was marked "F."

[0110] [Heat resistance / initial peelability] The ratio of the heat-resistant peel strength to the initial peel strength was calculated. The smaller this ratio, the less deterioration of peel strength due to heating. If the coating peeled off during the initial or heat-resistant peel test, it was marked "F."

[0111] [Adhesiveness] Test pieces with a release coating film formed thereon were obtained in the same manner as for initial releasability. The coating surface of the test piece was rubbed with a cotton swab moistened with isopropyl alcohol, and the test piece was evaluated according to the following criteria. Rubbing was performed by lightly pressing the flat side of the cotton swab against the coating surface and moving it back and forth for approximately 2 cm (one back and forth stroke), and the condition was observed after the first and second rubbing. A: No peeling even after the second rub B: No peeling occurred after the first rubbing, but peeling occurred after the second rubbing. C: Peeled off at the first rubbing.

[0112] [Example 1] A four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 54.2 parts by weight of polyester polyol 1, 2.6 parts by weight of trifunctional polyol, 8.8 parts by weight of dimethylolpropionic acid, and 100 parts by weight of methyl ethyl ketone. The mixture was thoroughly stirred and dissolved, and then 34.4 parts by weight of IPDI was added. The mixture was allowed to react at 75 ° C until the content of free isocyanate groups relative to the solids content reached 2.9% by weight. A methyl ethyl ketone solution of an isocyanate group-containing urethane prepolymer was obtained. This prepolymer solution was cooled to 45 ° C. and neutralized by adding 6.64 parts by weight of triethylamine as a neutralizing agent. Then, 100 parts by weight of n-dodecyl acrylate, 20 parts by weight of dimethacrylate 1, 3.0 parts by weight of ionic liquid 1, and 200 parts by weight of methyl ethyl ketone were added and stirred. Subsequently, while stirring with a homogenizer, 600 parts by weight of distilled water was added as a dispersion medium to emulsify and disperse the mixture. An aqueous solution of an extender prepared by diluting 1.87 parts of ethylenediamine with 20 parts of water was added to the dispersion and stirred at 40°C for 1 hour. Then, 0.17 parts by mass of polymerization initiator 1 and 0.17 parts by mass of polymerization initiator 2 were each diluted 10-fold with distilled water and added, and the mixture was allowed to react at 35°C to 45°C for 3 hours to polymerize a (meth)acrylic polymer. Then, the methyl ethyl ketone was distilled off under heating and reduced pressure, and water was added to adjust the solids content, yielding a release coating agent consisting of an aqueous dispersion with a solids content of 30% by mass.

[0113] [Examples 2 to 16 and Comparative Examples 1 to 4] The types and amounts of polyol, polyisocyanate, acrylic monomer, and ionic liquid, as well as the amounts of neutralizer, chain extender, and polymerization initiators 1 and 2, were changed as shown in Tables 1 to 3 below, and the rest of the procedure was the same as in Example 1 to obtain release coating agents composed of aqueous dispersions in Examples 2 to 16 and Comparative Examples 1 to 4. However, the amount of distilled water added as a dispersion medium was adjusted so that the solids concentration of the aqueous dispersion became 30% by mass. In Example 16, ethylenediamine was not used as a chain extender, and chain extension was performed with water.

[0114] The release coating agents of Examples 1 to 16 and Comparative Examples 1 to 4 were evaluated for initial releasability, heat-resistant releasability, and adhesion. The results are shown in Tables 1 to 3.

[0115] In Tables 1 to 3, "amount of polyurethane resin" refers to the amount of polyurethane resin in the final aqueous dispersion, expressed in parts by mass relative to 100 parts by mass of the total of the polyol and isocyanate used as raw materials. "Index: NCO / OH" refers to the equivalent ratio of hydroxyl groups to isocyanate groups in the urethane prepolymer.

[0116] [Table 1]

[0117] [Table 2]

[0118] [Table 3]

[0119] As shown in Table 3, Comparative Example 1, which did not contain any alkyl (meth)acrylate (X), exhibited poor releasability. Comparative Example 2, which did not contain any poly(meth)acrylate (Y), exhibited excellent initial releasability but poor heat-resistant releasability. Comparative Example 3, which did not contain any ionic liquid, exhibited poor heat-resistant releasability. Comparative Example 4, which used ethyl acrylate, whose alkyl group had two carbon atoms, as the alkyl (meth)acrylate (X), exhibited poor initial releasability and poor heat-resistant releasability.

[0120] In contrast, Examples 1 to 16 exhibited excellent adhesion to PET substrates, excellent initial releasability, and little deterioration of releasability due to heating, resulting in excellent heat-resistance releasability. Comparing Examples 1 and 2 with Example 3, the initial releasability was improved by using polyester polyol. The results of Examples 1, 5, and 6 indicate that increasing the number of carbon atoms in the alkyl group of the alkyl (meth)acrylate (X) tends to improve initial releasability, but too many carbon atoms tends to decrease heat-resistant adhesion. Furthermore, the results of Examples 1 and 4 indicate that alkyl acrylates, as the alkyl (meth)acrylate (X), provide better initial releasability than alkyl methacrylates. Furthermore, the results of Examples 5 and 7 indicate that linear alkyl groups provide better releasability than branched alkyl groups.

[0121] The various numerical ranges described in this specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

[0122] 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, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

Claims

1. An aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, a (meth)acrylic polymer containing, as constituent components, a monofunctional alkyl (meth)acrylate having an alkyl group having 4 to 22 carbon atoms and a poly(meth)acrylate having 2 to 6 functional groups is contained in resin particles as a dispersoid together with the polyurethane resin; Further containing an ionic liquid, Aqueous dispersion.

2. 2. The aqueous dispersion according to claim 1, wherein the amount of the poly(meth)acrylate is 0.3 to 100 parts by mass per 100 parts by mass of the alkyl (meth)acrylate.

3. The aqueous dispersion according to claim 1 , wherein the alkyl (meth)acrylate comprises an alkyl (meth)acrylate having a linear alkyl group as the alkyl group.

4. The aqueous dispersion of claim 1 , wherein the poly(meth)acrylate comprises a (poly)alkylene glycol di(meth)acrylate.

5. 2. The aqueous dispersion according to claim 1, wherein the amount of the ionic liquid is 0.1 to 5 parts by mass per 100 parts by mass of the total amount of the polyurethane resin and the (meth)acrylic polymer.

6. 2. The aqueous dispersion according to claim 1, wherein the amount of the alkyl (meth)acrylate is 40 to 350 parts by mass per 100 parts by mass of the polyurethane resin.

7. A release coating agent for polyester substrates, comprising the aqueous dispersion according to any one of claims 1 to 6.

8. A release sheet comprising a polyester substrate and a release layer formed on the polyester substrate, the release layer comprising the release coating agent according to claim 7.

9. A laminate comprising the release sheet according to claim 8 and a resin layer releasably provided on the release layer of the release sheet.

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