Mold release coating agent for polyester base materials, mold release sheet, and multilayer body

Abstract

To provide a mold release coating agent for polyester base materials, the mold release coating agent having excellent adhesiveness to a polyester base material and heat-resistant releasability.SOLUTION: A mold release coating agent for polyester base materials according to one embodiment of the present invention contains an aqueous dispersion that is obtained by dispersing a polyurethane resin into an aqueous dispersion medium. The aqueous dispersion contains a (meth)acrylic polymer which contains, as constituent components, a monofunctional alkyl(meth) acrylate that has an alkyl group having 4 to 22 carbon atoms, and a poly (meth)acrylate that has 2 to 6 functional groups.SELECTED DRAWING: None

Description

[Technical field]

[0001] An embodiment of the present invention relates to a release coating agent that is applied to a polyester substrate, and a release sheet and a laminate obtained by using the release coating agent. [Background technology]

[0002] A release sheet (also called a peeling sheet) is 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]

[0003] [Patent Document 1] JP 2011-099095 A Summary of the Invention [Problem to be solved by the invention]

[0004] A release coating agent used by applying it to a polyester substrate is required to have adhesion to the polyester substrate, and is also required to be easily peeled off 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. In this case, since a laminate of a release sheet and a resin layer may be placed in a heated atmosphere, it is desired that the release coating agent can be peeled off even after heat treatment, i.e., has heat resistant peelability.

[0005] An object of an embodiment of the present invention is to provide a release coating agent for polyester substrates that has excellent adhesion to polyester substrates and also has heat-resistant peelability. [Means for solving the problem]

[0006] The present invention includes the embodiments set forth 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, the aqueous dispersion comprising a (meth)acrylic polymer comprising, 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. [2] The release coating agent for polyester substrates according to [1], wherein the (meth)acrylic polymer is contained together with the polyurethane resin in individual resin particles as a dispersoid. [3] The release coating agent for polyester substrates according to [1] or [2], wherein the (meth)acrylic polymer contains 0.3 to 50 parts by mass of the poly(meth)acrylate per 100 parts by mass of the alkyl (meth)acrylate. [4] The release coating agent for polyester substrates according to any one of [1] to [3], wherein the alkyl group of the alkyl (meth)acrylate is a straight-chain alkyl group. [5] The release coating agent for polyester substrates according to any one of [1] to [4], wherein the poly(meth)acrylate has an acrylic equivalent, which is the molecular weight per functional group, of 80 to 150. [6] The release coating agent for polyester substrates 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. [7] The release coating agent for polyester substrates according to any one of [1] to [6], wherein the polyurethane resin contains a polyol including a polyester polyol as a constituent component, and contains the polyester polyol in an amount of 30% by mass or more relative to 100% by mass of the polyol.

[0007] [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 any one of [1] 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.

[0008]

[10] A release coating agent for polyester substrates, comprising an aqueous dispersion obtained by mixing a polyurethane resin having a hydrophilic group, 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, dispersing the mixture in an aqueous dispersion medium, and polymerizing the alkyl (meth)acrylate and the poly(meth)acrylate contained in the mixture.

[0009]

[11] Use of an aqueous dispersion comprising a polyurethane resin dispersed in an aqueous dispersion medium, the aqueous dispersion comprising 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, as a release coating agent for polyester substrates. Effect of the Invention

[0010] According to an embodiment of the present invention, a release coating agent for polyester substrates having excellent adhesion to polyester substrates and heat-resistant peelability can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The release coating agent for polyester substrates according to this embodiment (hereinafter, simply referred to as the release coating agent) is a release coating agent containing an aqueous dispersion of a polyurethane resin, and the aqueous dispersion contains a specific (meth)acrylic polymer. Therefore, the release coating agent contains an aqueous dispersion medium, a polyurethane resin, and a (meth)acrylic polymer.

[0012] In this specification, "(meth)acrylic polymer" means an acrylic polymer and / or a methacrylic polymer. Similarly, "alkyl (meth)acrylate" means an alkyl acrylate and / or an alkyl methacrylate, and "poly(meth)acrylate" means a polyacrylate and / or a polymethacrylate. The same applies to other terms such as "(meth)acrylic" and "(meth)acrylate".

[0013] [Aqueous dispersion medium] The aqueous dispersion medium is a dispersion medium containing water, and may be 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 contains 80% by mass or more of water, more preferably contains 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.

[0014] As the hydrophilic organic solvent, various organic solvents that dissolve 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.

[0015] [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. Here, the phrase "containing a polyol as a constituent component" refers to using the polyol as a raw material (monomer) for synthesizing the polyurethane resin, and the polyurethane resin has a structure derived from the polyol.

[0016] The polyurethane resin may have a hydrophilic group, and may be, for example, various water-based polyurethane resins such as anionic polyurethane resins, cationic polyurethane resins, nonionic polyurethane resins, etc. The hydrophilic group may be an anionic group, a cationic group, or a hydrophilic segment.

[0017] The anionic polyurethane resin is a water-based polyurethane resin having an anionic group. The anionic group may be at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphoric acid group, and salts thereof. The salt may be, for example, an alkali metal salt such as a lithium salt, a sodium salt, or a potassium salt, an ammonium salt, or an amine salt such as a primary amine, a secondary amine, or a tertiary amine.

[0018] The cationic polyurethane resin is a water-based polyurethane resin having a cationic group, such as a quaternary ammonium group.

[0019] The nonionic polyurethane resin is a non-charged water-based polyurethane resin that does not have an anionic group or a cationic group. Examples of the nonionic polyurethane resin include polyurethane resins having hydrophilic segments such as polyoxyethylene groups.

[0020] 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, or two or more of them may be used in combination.

[0021] The molecular weight of the polymer polyol is not particularly limited, and may be, for example, a number average molecular weight (Mn) of 500-5,000, 800-4,000, or 1,000-3,000.

[0022] 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. In detail, 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 amount: 50 μL, sample concentration: 0.2 mass%.

[0023] As the polyol constituting the polyurethane resin, together with or separately from the above polymer polyol, for example, 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 (preferably dihydric alcohols and trihydric alcohols) may be used. Any one of these may be used, or two or more may be used in combination.

[0024] In one embodiment, the polyol constituting the polyurethane resin preferably contains a polyester polyol in order to enhance the effect of improving adhesion to a polyester substrate. That is, the polyurethane resin preferably contains a polyol containing a polyester polyol as a constituent. The amount of the polyester polyol in the polyol is, for example, preferably 30% by mass or more, more preferably 60% by mass or more, further preferably 70 to 99% by mass, and may be 80 to 95% by mass, relative to 100% by mass of the polyol.

[0025] In this specification, the amount of each component constituting the polyol is calculated based on 100% by mass of the polyol when the polyol contains an anionic group described below, with the anionic group being in acid form. The amount of the anionic group-containing polyol is also calculated based on the anionic group being in acid form. When the polyol contains a cationic group described below, the amount of the polyol is calculated based on the cationic group being in acid form. When the polyol contains a cationic group described below, the amount of the polyol is calculated based on the amount of the cationic group before it is neutralized with an acid or quaternized with a quaternizing agent.

[0026] 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, and the water resistance of the release layer can be improved. Examples of polyols having three or more functional groups include polyhydric alcohols having three or more hydroxyl groups, such as trimethylolpropane, or the above-mentioned polymer polyols having three or more hydroxyl groups in the molecule.

[0027] 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.

[0028] Examples of the polyisocyanate constituting the polyurethane resin include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates. Any one of these may be used alone, or two or more of them may be used in combination.

[0029] Examples of the aliphatic polyisocyanate include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0030] 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.

[0031] Examples of aromatic polyisocyanates include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, xylylene diisocyanate (XDI), and naphthalene diisocyanate.

[0032] In addition, isocyanurate, adduct, biuret, allophenate, carbodiimide, etc. of these polyisocyanates may be used. In addition, these polyisocyanates may be used alone or in combination of two or more.

[0033] 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 resin include the following (A) and (B). Among these, the chain-extended type (A) is advantageous in improving the water resistance of the release layer.

[0034] (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 extending the chains of the urethane prepolymer with a chain extender.

[0035] (B) A hydroxy group-containing anionic polyurethane resin obtained by reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate.

[0036] As the anionic group-free polyol used to synthesize the anionic polyurethane resin, a polyol that does not have an anionic group or a cationic group can be used among the various polyols listed above. As the anionic group-containing polyol, a carboxy group-containing polyol having a carboxy group in the molecule is preferable, and examples thereof 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, and derivatives thereof and salts thereof. Any one of these may be used, or two or more may be used in combination.

[0037] Here, the anionic group is a concept including 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 a carboxylic acid), and the acid type and the salt type may be mixed. The anionic group can be neutralized to form a salt to make the finally obtained polyurethane resin water-dispersible. Therefore, in the aqueous dispersion of the polyurethane resin, the anionic group may be present as a salt type. On the other hand, in the state of a coating film obtained by drying the aqueous dispersion, when a non-volatile base is used as a neutralizing agent, the anionic group may be present as a salt type, and when a volatile base is used, the anionic group may be present as an acid type.

[0038] 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.

[0039] In one embodiment, the polyurethane resin may be a cationic polyurethane resin obtained by reacting a polyol containing a cationic group-free polyol and a cationic group-containing polyol with a polyisocyanate. Examples of such cationic polyurethane resins include the following (C).

[0040] (C) A cationic polyurethane resin obtained by synthesizing an isocyanate group-containing urethane prepolymer from a cationic group-free polyol, a cationic group-containing polyol, and a polyisocyanate, and then extending the chain of the urethane prepolymer with a chain extender.

[0041] The cationic group-free polyol used to synthesize the cationic polyurethane resin may be any of the polyols listed above that does not have an anionic group or a cationic group. Examples of cationic group-containing polyols include alkyl dialkanolamines such as N-methyldiethanolamine and N-ethyldiethanolamine, and these may also be quaternized with an acid or a quaternizing agent. Examples of the cationic group include tertiary or quaternary ammonium groups that are obtained by neutralizing a tertiary amino group with an acid or quaternizing with a quaternizing agent. The cationic group-containing polyol may also be a tertiary amine group-containing compound that can form a tertiary or quaternary ammonium group.

[0042] In the cationic polyurethane resin, the amount of the cationic group-free polyol in the polyol is not particularly limited and may be, for example, 75 to 97% by mass or 80 to 95% by mass relative to 100% by mass of the polyol. The amount of the cationic group-containing polyol in the polyol is not particularly limited and may be, for example, 3 to 25% by mass or 5 to 20% by mass relative to 100% by mass of the polyol.

[0043] In one embodiment, the polyurethane resin may be a nonionic polyurethane resin obtained by reacting a polyol containing a hydrophilic segment-containing polyol and a hydrophilic segment-free polyol with a polyisocyanate. Examples of such nonionic polyurethane resins include the following (D).

[0044] (D) 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.

[0045] Examples of the hydrophilic segment-containing polyol include polyols having a nonionic hydrophilic segment such as a polyoxyethylene group. Examples of the hydrophilic segment-free polyol include polyols that do not have an anionic group, a cationic group, or a hydrophilic segment among the various polyols listed above.

[0046] In the nonionic polyurethane resin, the amount of the hydrophilic segment-containing polyol in the polyol is not particularly limited, and may be, for example, 5 to 60 mass% or 10 to 50 mass% relative to 100 mass% of the polyol. The amount of the hydrophilic segment-free polyol is also not particularly limited, and may be, for example, 40 to 95 mass% or 50 to 90 mass% relative to 100 mass% of the polyol.

[0047] The chain extender that extends the chain of the isocyanate group-containing urethane prepolymer is not particularly limited, and examples thereof include water and 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 dihydrazide).

[0048] [(Meth)acrylic polymer] The (meth)acrylic polymer contains, as constituents, a monofunctional alkyl (meth)acrylate (X) having an alkyl group with a carbon number of 4 to 22, and a poly(meth)acrylate (Y) having a functional group number of 2 to 6. Here, with regard to the (meth)acrylic polymer, "containing as a constituent" means that it is used as a raw material (monomer) for synthesizing the polymer, and the (meth)acrylic polymer has a structure derived from this.

[0049] 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 alkyl group preferably has 6 to 20 carbon atoms, 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 carbon numbers.

[0050] The alkyl group of the alkyl (meth)acrylate (X) may be a branched chain, but from the viewpoints of releasability, heat-resistant releasability, and water resistance, it is preferably a straight-chain alkyl group.

[0051] 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 one of these may be used, or two or more may be used in combination.

[0052] Poly(meth)acrylate means an ester compound having two or more (meth)acryloyl groups. Therefore, 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 poly(meth)acrylate (Y), it is possible to improve the heat resistance of peeling.

[0053] In one embodiment, the poly(meth)acrylate (Y) preferably has an acrylic equivalent, which is the molecular weight per functional group, of 80-150, and more preferably has an acrylic equivalent of 90-150.

[0054] 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, and triethylene glycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate, etc. Any one of these may be used alone, or two or more of them may be used in combination.

[0055] Among these, the poly(meth)acrylate (Y) is preferably a (poly)alkylene glycol di(meth)acrylate. Here, "(poly)alkylene glycol" means monoalkylene glycol and / or polyalkylene glycol. The "poly" (repeating bond number) of the polyalkylene glycol is preferably 2 to 3, and the carbon number of the "alkylene" is preferably 2 to 4.

[0056] 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 these (X) and (Y), or may contain other monomers as constituents within a range that does not impair the effects of this embodiment. The total amount of the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in 100% by mass of all the constituents of the (meth)acrylic polymer is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0057] The ratio of the alkyl (meth)acrylate (X) to the poly(meth)acrylate (Y) in the (meth)acrylic polymer is not particularly limited, but the amount of the poly(meth)acrylate (Y) relative to 100 parts by mass of the alkyl (meth)acrylate (X) is preferably 0.3 to 50 parts by mass, more preferably 1 to 30 parts by mass, and even more preferably 5 to 20 parts by mass. By making the amount of the poly(meth)acrylate (Y) 50 parts by mass or less, the initial releasability can be improved, and by making it 0.3 parts by mass or more, the effect of improving the heat resistance releasability can be enhanced.

[0058] Polymerization of the monomer 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 in combination with a peroxide-based initiator such as a persulfate salt, e.g., potassium persulfate, sodium persulfate, or ammonium persulfate, or a peroxide, e.g., hydrogen peroxide, t-butyl hydroperoxide, or cumene hydroperoxide, and a reducing agent such as a sulfite salt, e.g., sodium sulfite, a hydrogen sulfite salt, e.g., sodium hydrogen sulfite, a metal salt, e.g., cuprous sulfate, ferrous sulfate, or an organic reducing agent, e.g., L-ascorbic acid.

[0059] 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).

[0060] [Water-based dispersion of polyurethane resin] The aqueous dispersion of the polyurethane resin is an aqueous dispersion in which the polyurethane resin is dispersed in an aqueous dispersion medium, and contains the above-mentioned (meth)acrylic polymer.

[0061] In the aqueous dispersion, the (meth)acrylic polymer is preferably contained in the polyurethane resin particles. That is, the (meth)acrylic polymer is preferably contained in each resin particle as a dispersoid together with the polyurethane resin. In this case, the (meth)acrylic polymer may be present inside the particle, may be present on the particle surface, or may be present inside and on the particle surface. While the polyurethane resin has a hydrophilic group, the (meth)acrylic polymer is hydrophobic and therefore likely to be present inside the particle. Therefore, it is preferable that the (meth)acrylic polymer is present inside the particle and the polyurethane resin having a hydrophilic group is present on the particle surface so as to cover it, thereby enhancing the effect of this embodiment.

[0062] The content of the polyurethane resin in the aqueous dispersion is not particularly limited, and may be, for example, 10 to 50 mass %, 15 to 45 mass %, or 20 to 40 mass % relative to the total mass of the aqueous dispersion.

[0063] The content of the (meth)acrylic resin is preferably set as the content of the alkyl (meth)acrylate as follows: That is, the amount of the alkyl (meth)acrylate is preferably 40 to 350 parts by mass, more preferably 45 to 300 parts by mass, even more preferably 60 to 200 parts by mass, and even more preferably 70 to 150 parts by mass, relative to 100 parts by mass of the polyurethane resin. By setting the content of the alkyl (meth)acrylate to 40 parts by mass or more, it is possible to improve the releasability and water resistance, and by setting it to 350 parts by mass or less, it is possible to improve the adhesion to polyester substrates.

[0064] 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 "Microtrac UPA-UZ152" manufactured by Nikkiso Co., Ltd.

[0065] The aqueous dispersion of the polyurethane resin may contain other components as long as the effects of the aqueous dispersion are not impaired. For example, a crosslinking agent for crosslinking the polyurethane resin, a surfactant for dispersing the polyurethane resin, the (meth)acrylic resin, or a monomer thereof in an aqueous dispersion medium, a polymerization initiator for polymerizing the (meth)acrylic resin, etc. may be included.

[0066] The crosslinking agent may be a compound 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 hydroxyl groups, primary amino groups, secondary amino groups, and thiol groups in the polyurethane resin. This can improve the water resistance of the release layer formed by the release coating agent. When the polyurethane resin has a carboxyl group, the crosslinking agent can also crosslink with the carboxyl group.

[0067] Examples of the crosslinking agent include carbodiimide compounds, oxazoline compounds, blocked isocyanate compounds, and epoxy compounds. These may be used alone or in combination of two or more.

[0068] 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.

[0069] 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.

[0070] The amount of the 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 the polyurethane resin and the (meth)acrylic polymer.

[0071] [Method of manufacturing aqueous dispersion] The method for producing the aqueous dispersion of the polyurethane resin is not particularly limited, and it may be produced, for example, by a method including the following steps (1) to (4).

[0072] 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), and a poly(meth)acrylate (Y). Step (3): 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.

[0073] In this manner, 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) and then dispersing the mixture in an aqueous dispersion medium, and polymerizing the alkyl (meth)acrylate (X) and poly(meth)acrylate (Y) in the mixture in the dispersed state, the (meth)acrylic polymer can be efficiently incorporated into the polyurethane resin particles.

[0074] 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 having no active hydrogen group, such as methyl ethyl ketone or acetone. The polyurethane resin obtained by the reaction in step (1) is a concept that includes a urethane prepolymer before chain extension, etc. Therefore, in step (2), such a urethane prepolymer may be mixed with an acrylic monomer including the above (X) and (Y).

[0075] In addition, when the polyurethane resin has an anionic group or a cationic group, the anionic group or 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).

[0076] 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.

[0077] 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.

[0078] 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 while stirring the aqueous dispersion medium with a homogenizer, homomixer, etc., and (ii) a method in which the aqueous dispersion medium is added while stirring the mixture or a resin solution thereof with a homogenizer, homomixer, etc. Note that 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.

[0079] When a urethane prepolymer is synthesized in step (1), the chain 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).

[0080] 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.

[0081] In addition, when the reaction between the polyol and the polyisocyanate in the step (1) is carried out in an organic solvent, the organic solvent may be removed after dispersion in an aqueous dispersion medium in the step (3) or after the polymerization reaction in the step (4).

[0082] In one embodiment, when the above 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 reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate to synthesize an isocyanate group-containing urethane prepolymer. 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, an alkyl (meth)acrylate (X), and a poly(meth)acrylate (Y). Step (a4): 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.

[0083] 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.

[0084] In step (a1), the polyisocyanate is used so that the amount of isocyanate groups is stoichiometrically in excess of the amount of hydroxyl groups contained in the polyol, for example, so that the equivalent ratio of hydroxyl groups to isocyanate groups (NCO / OH) is 1.05 to 1.70 (more preferably 1.10 to 1.60).

[0085] 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 can also be a chain extender. When water is used as the chain extender, the water as the aqueous dispersion medium also serves as the chain extender.

[0086] In one embodiment, when the above 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 reacting an anionic group-free polyol, an anionic group-containing polyol, and a polyisocyanate to synthesize a hydroxy group-containing polyurethane resin. 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), and the poly(meth)acrylate (Y). Step (b4): 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.

[0087] 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.

[0088] In step (b1), the polyol is used so that the amount of hydroxyl groups is stoichiometrically excessive relative to the amount of isocyanate groups contained in the polyisocyanate, for example, the equivalent ratio (NCO / OH) of hydroxyl groups to isocyanate groups is 0.70 to 0.95 (more preferably 0.75 to 0.90). The order of steps (b2) and (b3) is not important.

[0089] In one embodiment, when the above cationic polyurethane resin (C) is used as the polyurethane resin, it may be produced by the following steps (c1) to (c6). Step (c1): A step of reacting a cationic group-free polyol, a cationic group-containing polyol, and a polyisocyanate to synthesize an isocyanate group-containing urethane prepolymer. Step (c2): A step of neutralizing the cationic groups of the isocyanate group-containing urethane prepolymer with an acid or quaternizing it with a quaternizing agent. Step (c3): A step of mixing the isocyanate group-containing urethane prepolymer, an alkyl (meth)acrylate (X), and a poly(meth)acrylate (Y). Step (c4): Dispersing the mixture in an aqueous dispersion medium. Step (c5): 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 (c6): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture dispersed in an aqueous dispersion medium.

[0090] Step (c1) corresponds to the above step (1), step (c3) corresponds to the above step (2), step (c4) corresponds to the above step (3), step (c6) corresponds to the above step (4), and steps (c2) and (c5) are additional steps.

[0091] The order of steps (c2) and (c3) does not matter. The equivalent ratio of hydroxyl groups to isocyanate groups in step (c1), and the timing of adding the chain extender in step (c5) and the case where water is used as the chain extender are the same as those in steps (a1) and (a5) above.

[0092] In one embodiment, when the nonionic polyurethane resin (D) is used as the polyurethane resin, it may be produced by the following steps (d1) to (d5). Step (d1): A step of reacting a hydrophilic segment-containing polyol, a hydrophilic segment-free polyol, and a polyisocyanate to synthesize an isocyanate group-containing urethane prepolymer. Step (d2): A step of mixing the isocyanate group-containing urethane prepolymer, the alkyl (meth)acrylate (X), and the poly(meth)acrylate (Y). Step (d3): Dispersing the mixture in an aqueous dispersion medium. Step (d4): A step of extending the chains of the isocyanate group-containing urethane prepolymer dispersed in the aqueous dispersion medium with a chain extender. Step (d5): A step of polymerizing the alkyl (meth)acrylate (X) and the poly(meth)acrylate (Y) in the mixture dispersed in an aqueous dispersion medium.

[0093] Step (d1) corresponds to the above step (1), step (d2) corresponds to the above step (2), step (d3) corresponds to the above step (3), step (d5) corresponds to the above step (4), and step (d4) is an additional step. The equivalent ratio of hydroxyl groups to isocyanate groups in step (d1), and the timing of adding the chain extender and the case where water is used as the chain extender in step (d4) are the same as those in the above steps (a1) and (a5).

[0094] [Release coating agent for polyester substrate] The release coating agent for polyester substrates according to the present embodiment contains the above-mentioned aqueous dispersion, and therefore contains an aqueous dispersion medium, a polyurethane resin, and a (meth)acrylic resin. The release coating agent may be composed of only the above-mentioned aqueous dispersion, or may contain various additives such as an antioxidant, an antistatic agent, a surfactant, an antifoaming agent, and a surface conditioner together with the above-mentioned aqueous dispersion.

[0095] The content of the polyurethane resin in the release coating agent is not particularly limited and may be, for example, 10 to 50 mass %, 15 to 45 mass %, or 20 to 40 mass % relative to the total mass of the release coating agent.

[0096] [Release sheet] The release sheet according to one embodiment includes a polyester substrate and a release layer provided on the polyester substrate, the release layer being formed from the release coating agent.

[0097] The polyester substrate may be formed from various polyesters having dicarboxylic acid and diol as constituents (monomers). Examples of the polyester substrate include polyethylene terephthalate (PET) substrate, polyethylene naphthalate (PEN) substrate, polyethylene furanoate (PEF) substrate, polytrimethylene terephthalate (PTT) substrate, polybutylene terephthalate (PBT) substrate, polybutylene naphthalate (PBN) substrate, etc. Among these, polyester substrates formed from polyesters having aromatic dicarboxylic acid and ethylene glycol as constituents, specifically PET substrate, PEN substrate, PEF substrate, etc., are more preferably used.

[0098] 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.

[0099] 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. When 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.

[0100] 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.

[0101] 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 off release sheet may be discarded.

[0102] [Laminate] The laminate according to one embodiment includes the release sheet and a resin layer releasably provided on the release layer. 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 the resin film.

[0103] In the case of the protective sheet (1) above, the release sheet is used to protect a product having an adhesive film formed on its surface, 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 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 the product include a polarizing plate for liquid crystal.

[0104] 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. EXAMPLES

[0105] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0106] Details of each component used in the examples are as follows.

[0107] [Polyol] Polyester polyol 1: Aromatic polyester diol (functional group number: 2, number average molecular weight: 2000). The synthesis method is as follows. In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube, 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 were charged, and the mixture was heated to 250° C. with stirring under a nitrogen stream. The reaction was continued until the acid value became 5 mgKOH / g or less, and an aromatic polyester diol was obtained.

[0108] 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, a thermometer, a reflux condenser, a dropping tank, and a 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 became 5 mgKOH / g or less, to obtain an aromatic polyester diol.

[0109] Polycarbonate polyol: Polycarbonate diol (functional group number: 2, number average molecular weight: 2000), "UH-200" manufactured by UBE Corporation Bisphenol-type polyol: EO adduct of bisphenol A (functional group number: 2, number average molecular weight: 325), "Newpol BPE-20NK" manufactured by Sanyo Chemical Industries, Ltd. Trifunctional polyol: Trimethylolpropane (functional group number: 3), manufactured by Mitsui Gas Chemicals, Inc. POE-containing polyol: Polyoxyethylene group-containing nonionic polyol (functional group number: 2, number average molecular weight: 600), Perstorp's "Ymer N180" Cationic group-containing polyol: N-methyldiethanolamine, manufactured by Tokyo Chemical Industry Co., Ltd. Dimethylolpropionic acid: Perstorp's "Bis-MPA (registered trademark)" (functional groups: 2)

[0110] [Polyisocyanate] IPDI: Isophorone diisocyanate (functional group number: 2, molecular weight: 222.3), Evonik's "VESTANAT (registered trademark) IPDI" Hydrogenated MDI: Dicyclohexylmethane 4,4'-diisocyanate (functional group number: 2, molecular weight: 262), Evonik's "VESTANAT (registered trademark) H12MDI" HDI: Hexamethylene diisocyanate (functional group number: 2, molecular weight: 168.2), Asahi Kasei Corporation "Duranate (registered trademark) 50M-HDI"

[0111] [(Meth)acrylic acid ester] -n-Butyl acrylate: "Butyl acrylate" manufactured by Mitsubishi Chemical Corporation -n-Octyl acrylate: "NOAA" manufactured by Osaka Organic Chemical Industry Co., Ltd. -n-Dodecyl acrylate: "LA" manufactured by Osaka Organic Chemical Industry Co., Ltd. ·Stearyl acrylate: "STA" manufactured by Osaka Organic Chemical Industry Co., Ltd. n-Dodecyl methacrylate: "Light Ester L" manufactured by Kyoeisha Chemical Co., Ltd. 2-Ethylhexyl acrylate: Mitsubishi Chemical Corporation Ethyl acrylate: Mitsubishi Chemical Corporation

[0112] [Poly(meth)acrylate] Dimethacrylate 1: Ethylene glycol dimethacrylate, "Light Ester EG" manufactured by Kyoeisha Chemical Co., Ltd. Dimethacrylate 2: Triethylene glycol dimethacrylate, "Light Ester 3EG" manufactured by Kyoeisha Chemical Co., Ltd. Hexaacrylate: Dipentaerythritol hexaacrylate (DPHA), "Light Acrylate DPE-6A" manufactured by Kyoeisha Chemical Co., Ltd.

[0113] [Other additives] Surfactant: "Hitenol (registered trademark) LA-12" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Crosslinking agent: Nisshinbo Chemical Co., Ltd.'s "V02-L02" (non-volatile content 40%, NCN equivalent 385) 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.

[0114] The release coating agents were evaluated as follows.

[0115] [Removability 1A (initial peelability against acrylic adhesive)] A 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 with a bar coater to a dry thickness of 1 μm, and the substrate was dried at 160° C. for 1 minute to obtain a test piece (coated film) on which a coating film of the release coating agent was formed. However, in Comparative Example 3, a PP substrate ("Treyfan BO", manufactured by Toray Industries, Inc.) was used instead of the PET substrate. 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 peelability.

[0116] [Removability 1B (heat-resistant peelability against acrylic adhesive, 70℃ x 20 hours)] A Nitto Denko acrylic adhesive tape "No. 31B" was applied to the coating of a test piece prepared in the same manner as for Peelability 1A 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 Peelability 1A. The smaller the peel strength, the better the heat peel resistance. In the peel strength measurement, the case where the coating peeled off was marked "F".

[0117] [1B / 1A] 1B / 1A is the ratio of the peel strength of peelability 1B to that of peelability 1A. The smaller this ratio, the less deterioration of peelability due to heating. In peelability 1B, the coating peeled off together, and was marked with "F."

[0118] [Removability 1C (heat-resistant peelability against acrylic adhesive, 150℃ x 5 minutes)] A Nitto Denko acrylic adhesive tape "No. 31B" was applied to the coating of the test piece prepared in the same manner as in Peelability 1A using a 2 kg roller, and heated at 150°C for 5 minutes. After cooling to room temperature, the peel strength (unit: mN / 25 mm) was measured in the same manner as in Peelability 1A. In the peel strength measurement, the case where the coating peeled off was marked "F".

[0119] [1C / 1A] 1C / 1A is the ratio of the peel strength of peel strength 1C to that of peel strength 1A. The smaller this ratio, the less deterioration of peel strength due to heating. When peel strength 1C was used, the coating peeled off, and the result was marked "F."

[0120] [Removability 2A (initial peelability against silicone-based adhesive)] A silicone adhesive tape "No. 336" manufactured by Nitto Denko Corporation was applied to the coating film of a test piece prepared in the same manner as in Peelability 1A 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. The smaller the peel strength, the better the peelability.

[0121] [Removability 2B (heat-resistant peelability against silicone-based adhesive, 70℃ x 20 hours)] A silicone adhesive tape "No. 336" manufactured by Nitto Denko Corporation was applied to the coating of a test piece prepared in the same manner as for Peelability 1A 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 Peelability 2A. The smaller the peel strength, the better the heat peel resistance. In the peel strength measurement, the case where the coating peeled off was marked "F".

[0122] [2B / 2A] 2B / 2A is the ratio of the peel strength of peelability 2B to that of peelability 2A. The smaller this ratio, the less deterioration of peelability due to heating. When peelability 2B was used, the coating peeled off together, and this was indicated as "F."

[0123] [Removability 2C (heat-resistant peelability against silicone-based adhesive, 150℃ x 5 minutes)] A silicone adhesive tape "No. 336" manufactured by Nitto Denko Corporation was applied to the coating film of the test piece prepared in the same manner as for Peelability 1A using a 2 kg roller, and heated at 150°C for 5 minutes. After cooling to room temperature, the peel strength (unit: mN / 25 mm) was measured in the same manner as for Peelability 2A. In the peel strength measurement, the case where the coating film peeled off was indicated as "F".

[0124] [2C / 2A] 2C / 2A is the ratio of the peel strength of peelability 2C to that of peelability 2A. The smaller this ratio, the less deterioration of peelability due to heating. When peelability 2C was used, the coating peeled off together, and this was indicated as "F."

[0125] [Adhesiveness] A test piece on which a coating film of a release coating agent was formed was obtained in the same manner as in Peelability 1A. The coating surface of the test piece was rubbed with a cotton swab moistened with isopropyl alcohol, and evaluated according to the following criteria. Here, rubbing was performed by lightly pressing the flat surface of the cotton swab against the coating surface and moving it back and forth for about 2 cm (one back and forth for one rub), and the state after the first and second rubs was observed. ◎: No peeling even after the second rubbing ◯: No peeling occurred after the first rubbing, but peeling occurred after the second rubbing. ×: Peeling occurred during the first rubbing.

[0126] [water resistance] A release coating agent was poured onto a fluororesin-coated frying pan so that the dry thickness was 500 μm, and then dried at 40° C. for 15 hours, at 80° C. for 6 hours, and then at 120° C. for 20 minutes to produce a coating made of the release coating agent. The coating was used as a test piece, and the test piece was immersed in 40° C. warm water for 24 hours, and the mass of the coating after immersion was measured. The increase rate (%) of the mass after immersion relative to the initial mass before immersion was calculated. The smaller the increase rate, the smaller the swelling due to water and the better the water resistance.

[0127] [Example 1] In a four-neck flask equipped with a stirrer, reflux condenser, thermometer and nitrogen blowing tube, 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 were added and thoroughly stirred and dissolved, then 34.4 parts by weight of IPDI was added, and the mixture was reacted at 75 ° C until the content of free isocyanate groups relative to the solid content became 2.9% by weight, to obtain a methyl ethyl ketone solution of an isocyanate group-containing urethane prepolymer. This prepolymer solution was cooled to 45 ° C, and neutralized by adding 6.64 parts by weight of triethylamine as a neutralizing agent, and then 100 parts by weight of n-dodecyl acrylate, 10 parts by weight of dimethacrylate 1, 2.2 parts by weight of a surfactant, and 200 parts by weight of methyl ethyl ketone were added and mixed with stirring. Next, while stirring with a homogenizer, 600 parts by mass of distilled water was added as a dispersion medium to emulsify and disperse, and the dispersion was stirred at 40°C for 1 hour to complete the chain extension reaction by water. Then, 0.16 parts by mass of polymerization initiator 1 and 0.15 parts by mass of polymerization initiator 2 were each diluted 10 times with distilled water and added, and reacted at 35°C to 45°C for 3 hours to polymerize a (meth)acrylic polymer. Then, methyl ethyl ketone was distilled off under heating and reduced pressure, and water for adjusting the solid content was added to obtain a release coating agent consisting of an aqueous dispersion with a solid content of 30% by mass.

[0128] [Examples 2 to 18, 20 to 21, and 25, and Comparative Examples 1 to 4] The types and amounts of polyol, polyisocyanate, and acrylic monomer, and the amounts of neutralizer and polymerization initiator 1 and 2 were changed as shown in Tables 1 and 2 below, and the rest was the same as in Example 1 to obtain release coating agents made of aqueous dispersions in Examples 2 to 18, 20 to 21, and 25, and Comparative Examples 1 to 4. However, the amount of free isocyanate groups at the end of the urethane reaction to obtain an isocyanate group-containing urethane prepolymer was 2.9% by mass in Examples 2 to 3, 5 to 18, and Comparative Examples 1 to 4, 3.92% by mass in Example 4, 5.35% by mass in Example 20, 1.8% by mass in Example 21, and 2.3% by mass in Example 25. 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.

[0129] [Example 19] To the dispersion after emulsification and dispersion, 1.87 parts by mass of ethylenediamine was added as a chain extender, and the mixture was 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, and a release coating agent consisting of the aqueous dispersion of Example 19 was obtained.

[0130] [Example 22] Instead of 600 parts by mass of distilled water as a dispersion medium, 550 parts by mass of distilled water and 50 parts by mass of N-methylpyrrolidone (NMP) were added, and after the emulsion dispersion, chain extension reaction, polymerization reaction, and distillation of methyl ethyl ketone, water for adjusting the solid content was added to make the dispersion medium composition distilled water / NMP = 90 / 10 (mass ratio), and the rest was the same as in Example 1, to obtain a release coating agent consisting of the aqueous dispersion of Example 22.

[0131] [Example 23] A release coating agent made of the aqueous dispersion of Example 23 was obtained in the same manner as in Example 1, except that no surfactant was added.

[0132] [Example 24] After the (meth)acrylic polymer was polymerized and the methyl ethyl ketone was distilled off, 18.7 parts by mass of a crosslinking agent was added, and the rest of the procedure was the same as in Example 1, to obtain a release coating agent made of the aqueous dispersion of Example 24.

[0133] [Example 26] In a four-neck flask equipped with a stirrer, reflux condenser, thermometer and nitrogen blowing tube, 65.6 parts by mass of polyester polyol 1, 2.6 parts by mass of trifunctional polyol, 8.8 parts by mass of dimethylolpropionic acid, and 100 parts by mass of methyl ethyl ketone were added and thoroughly stirred and dissolved, then 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 was 0.05% by mass or less, to obtain a methyl ethyl ketone solution of a hydroxyl group-containing polyurethane resin. This prepolymer solution was cooled to 45 ° C, and neutralized by adding 6.64 parts by mass of triethylamine as a neutralizing agent, and then 100 parts by mass of n-dodecyl acrylate, 10 parts by mass of dimethacrylate 1, 2.2 parts by mass of a surfactant, and 200 parts by mass of methyl ethyl ketone were added and mixed with stirring. Subsequently, 600 parts by mass of distilled water was added as a dispersion medium while stirring with a homogenizer to emulsify and disperse. Then, 0.16 parts by mass of polymerization initiator 1 and 0.15 parts by mass of polymerization initiator 2 were each diluted 10 times with distilled water and added, and the mixture was reacted at 35 to 45° C. for 3 hours to polymerize a (meth)acrylic polymer. Then, methyl ethyl ketone was distilled off under heating and reduced pressure, and water for adjusting the solid content was added to obtain a release coating agent consisting of an aqueous dispersion with a solid content of 30% by mass.

[0134] [Example 27] In a four-neck flask equipped with a stirrer, reflux condenser, thermometer and nitrogen blowing tube, 33.0 parts by mass of polyester polyol 1, 35.0 parts by mass of POE-containing polyol, 2.6 parts by mass of trifunctional polyol, and 100 parts by mass of methyl ethyl ketone were added and thoroughly stirred and dissolved, then 29.4 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 became 2.5% by mass, to obtain a methyl ethyl ketone solution of an isocyanate group-containing urethane prepolymer. After cooling this prepolymer solution to 45 ° C, 100 parts by mass of n-dodecyl acrylate, 10 parts by mass of dimethacrylate 1, 2.2 parts by mass of a surfactant, and 200 parts by mass of methyl ethyl ketone were added and mixed with stirring. Next, 600 parts by mass of distilled water was added as a dispersion medium while stirring with a homogenizer to emulsify and disperse, and the dispersion was stirred at 40 ° C for 1 hour to complete the chain extension reaction with water. Then, 0.16 parts by mass of polymerization initiator 1 and 0.15 parts by mass of polymerization initiator 2 were each diluted 10 times with distilled water and added, and the mixture was reacted at 35 to 45° C. for 3 hours to polymerize a (meth)acrylic polymer. Then, methyl ethyl ketone was distilled off under heating and reduced pressure, and water for adjusting the solid content was added to obtain a release coating agent consisting of an aqueous dispersion with a solid content of 30% by mass.

[0135] [Example 28] In a four-neck flask equipped with a stirrer, reflux condenser, thermometer and nitrogen blowing tube, 47.3 parts by weight of polyester polyol 1, 2.6 parts by weight of trifunctional polyol, 10.5 parts by weight of cationic group-containing polyol, and 100 parts by weight of methyl ethyl ketone were added and thoroughly stirred and dissolved, then 39.6 parts by weight 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 3.2% by weight, to obtain a methyl ethyl ketone solution of an isocyanate group-containing urethane prepolymer. This prepolymer solution was cooled to 45 ° C, and 11.11 parts by weight of dimethyl sulfate was added as a quaternizing agent to quaternize it, after which 100 parts by weight of n-dodecyl acrylate, 10 parts by weight of dimethacrylate 1, 2.2 parts by weight of a surfactant, and 200 parts by weight of methyl ethyl ketone were added and stirred and mixed. Next, while stirring with a homogenizer, 600 parts by mass of distilled water was added as a dispersion medium to emulsify and disperse, and the dispersion was stirred at 40°C for 1 hour to complete the chain extension reaction by water. Then, 0.16 parts by mass of polymerization initiator 1 and 0.15 parts by mass of polymerization initiator 2 were each diluted 10 times with distilled water and added, and reacted at 35 to 45°C for 3 hours to polymerize a (meth)acrylic polymer. Then, methyl ethyl ketone was distilled off under heating and reduced pressure, and water for adjusting the solid content was added to obtain a release coating agent consisting of an aqueous dispersion with a solid content of 30% by mass.

[0136] The release coating agents of Examples 1 to 28 and Comparative Examples 1 to 4 were evaluated for releasability 1A, 1B, and 1C, releasability 2A, 2B, and 2C, adhesion, and water resistance. The results are shown in Tables 1 and 2.

[0137] In Tables 1-2, "Water" in the "Chain extender: ethylenediamine" column means that water was used as the chain extender, and "None" means that the chain was not extended. "Amount of polyurethane resin" is the amount of polyurethane resin in the finally obtained aqueous dispersion, and is the part by mass relative to 100 parts by mass of the total of polyol and isocyanate used as raw materials. "Index: NCO / OH" is the equivalent ratio of hydroxyl groups to isocyanate groups in the urethane prepolymer. "Substrate" represents the substrate used in the evaluation of peelability and adhesion, "PET" means PET substrate, and "PP" means PP substrate. The numerical value of the evaluation of peelability is peel strength (unit: mN / 25mm).

[0138] [Table 1]

[0139] [Table 2]

[0140] As shown in Tables 1 and 2, in Comparative Example 1, since no alkyl (meth)acrylate (X) was blended, the initial peelability and heat resistance peelability were poor. In Comparative Example 2, since ethyl acrylate, whose alkyl group has two carbon atoms, was used as the alkyl (meth)acrylate, the initial peelability and heat resistance peelability were poor. In Comparative Example 3, since a PP substrate was used, the adhesion of the release layer to the substrate was poor. In Comparative Example 4, since no poly(meth)acrylate (Y) was blended, the heat resistance adhesion was poor.

[0141] In contrast, in Examples 1 to 28, the adhesiveness to the PET substrate was excellent, and the deterioration of the peelability due to heating was suppressed, and the adhesiveness was heat-resistant. Comparing Examples 1 and 2 with Examples 3 and 4, the initial peelability was improved by using polyester polyol. Comparing Examples 1 and 2 with Examples 5 and 6, it was found that, from the viewpoint of adhesiveness, alicyclic polyisocyanates are preferable to aliphatic polyisocyanates, and IPDI is more preferable. Comparing Examples 1 and 2 with Examples 7 and 8, it is found that the initial peelability and water resistance tend to improve as the number of carbon atoms in the alkyl group of the (meth)acrylate (X) increases, but it is found from Example 9 that the heat-resistant adhesiveness tends to decrease when the number of carbon atoms is too large. In addition, the results of Examples 10 and 11 show that, as the alkyl (meth)acrylate (X), alkyl acrylate has better initial peelability than alkyl methacrylate, and that linear alkyl groups have better initial peelability than branched alkyl groups.

[0142] In Example 23, no surfactant was added to Example 1, and the peelability, adhesion, and heat resistance were equivalent to those of Example 1, but some residue was left on the filter during preparation. In Example 24, a crosslinking agent was added to Example 1, and although the initial peelability tended to decrease slightly, water resistance was improved.

[0143] In addition, the various numerical ranges described in the specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in the specification. In addition, a numerical range described as "X to Y" means from X to Y.

[0144] 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 gist of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included in the scope and gist of the invention as well as the invention and its equivalents described in the claims.

Claims

1. A release coating agent for a polyester substrate, comprising an aqueous dispersion in which a polyurethane resin is dispersed in an aqueous dispersion medium, The aqueous dispersion is a release coating agent for polyester substrates, comprising 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.

2. 2. The release coating agent for polyester substrates according to claim 1, wherein the (meth)acrylic polymer is contained in individual resin particles as a dispersoid together with the polyurethane resin.

3. 2. The release coating agent for polyester substrates according to claim 1, wherein the (meth)acrylic polymer contains 0.3 to 50 parts by mass of the poly(meth)acrylate per 100 parts by mass of the alkyl (meth)acrylate.

4. 2. The release coating agent for polyester substrates according to claim 1, wherein the alkyl group of the alkyl (meth)acrylate is a straight-chain alkyl group.

5. 2. The release coating agent for polyester substrates according to claim 1, wherein the poly(meth)acrylate has an acrylic equivalent, which is the molecular weight per functional group, of 80 to 150.

6. 2. The release coating agent for polyester substrates 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. 2. The release coating agent for polyester substrates according to claim 1, wherein the polyurethane resin contains a polyol including a polyester polyol as a constituent component, and the content of the polyester polyol is 30% by mass or more relative to 100% by mass of the polyol.

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 any one of claims 1 to 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.

10. A release coating agent for polyester substrates, comprising an aqueous dispersion obtained by mixing a polyurethane resin having a hydrophilic group, 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, dispersing the mixture in an aqueous dispersion medium, and polymerizing the alkyl (meth)acrylate and the poly(meth)acrylate contained in the mixture.

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