KR20190136281A - Aqueous Polyurethane Dispersion with Improved Cross-linkability and Method For Preparing Same - Google Patents

Abstract

The present invention relates to an aqueous polyurethane dispersion having improved cross-linkability using a polyol compound containing three or more hydroxyl groups as a crosslinking agent and a method for manufacturing the same. The aqueous polyurethane dispersion according to the present invention is in a form of an aqueous dispersion, so that it is environmentally friendly, meets international regulations, and has improved crosslinking properties, thereby having a convenient effect on a process. In addition, it is possible to provide the aqueous polyurethane dispersion having a high solid content and storage stability for long term storage.

Description

Aqueous Polyurethane Dispersion with Improved Cross-linkability and Method For Preparing Same}

The present invention relates to an aqueous polyurethane dispersion having improved crosslinkability and a method for preparing the same, and more particularly, to an aqueous polyurethane dispersion having improved crosslinkability by using a polyol compound containing three or more hydroxyl groups as a crosslinking agent and the same. It relates to a manufacturing method.

Polyurethane (PU) refers to a polymer having a urethane or urea bond in a repeating unit by reacting an isocyanate with a polyol, diol or diamine. Polyurethane has been applied to various fields such as coatings, adhesives, elastomers, fabrics, synthetic leathers, foams, elastomers, fibers, synthetic leathers, waterproofing agents, paints, adhesives and the like due to various physical properties.

Polyurethanes have traditionally been produced oily due to the strong hydrophobicity of the polyols. However, oily oil releases volatile organic compounds in the manufacturing process or use process, resulting in fire hazard and environmental pollution such as air pollution. Therefore, a waterborne polyurethane that does not use an organic solvent for the preservation of the environment or the improvement of the working environment is in the spotlight.

For example, in Korean Patent Publication No. 10-0534152, a urethane-acrylic water-dispersion resin is manufactured, and after urethane resin is prepared, it is mixed with some vinyl monomers, neutralized with trivalent amine, and then water is added to the resin to disperse water. And urethane-acrylic water-dispersion resins prepared by copolymerizing some isocyanates by adding chain extenders and copolymerizing vinyl monomers and initiators without using an emulsifier.

Korean Patent Publication No. 10-0557016 uses a method of preparing a composite binder by mixing a water-dispersed polyurethane resin produced by a polycondensation reaction with a water-dispersible polyacrylic resin prepared by a resin-enhanced polymerization reaction.

In addition, Korean Patent Publication No. 10-0107962 discloses a mono-acrylated diisocyanate compound by reacting a diisocyanate monomer with an active hydrogen-containing acrylic monomer to form a polyol containing active hydrogen and a carbon containing active hydrogen at both ends. A monoacrylated urethane-free polymer is prepared by reacting an acid, and a water-dispersible resin using a monoacrylated urethane-free polymer dispersion prepared using a nonionic or anionic emulsifier and an acrylic monomer and a polymerization initiator. It provides a method for preparing.

Since the polyurethane dispersion obtained by the aforementioned conventional method does not contain an emulsifier, the film has good water resistance, but there is a problem that the chemical resistance and alkali resistance of the film are significantly deteriorated. In addition, since they are easily affected by various salts, they have problems in compatibility with various resins, organic-inorganic pigments, and fillers, and have disadvantages of limited use.

In addition, US Pat. No. 5,137,967 prepared a polyurethane-based aqueous dispersion by neutralizing a prepolymer containing a carboxy group with dimethylaminoethanol, a tertiary amine, and then chain-extending with hydrazine. However, the polyurethane-based water dispersion prepared in this way has a poor storage stability, poor water resistance of the coating, and significantly reduces the overall physical properties of the coating after drying.

Therefore, in the environmentally friendly aqueous polyurethane dispersion, an aqueous polyurethane dispersion having a long-term storage stability, excellent wear resistance, chemical resistance, solvent resistance, and stable coating or film having stability in the external environment can be produced. It is time to develop for.

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous polyurethane dispersion having a long-term storage stability, stable in an external environment when coated, and having an improved crosslinkability.

Still another object of the present invention is to provide a method of preparing the above aqueous polyurethane dispersion.

In order to solve the above problems, one embodiment of the present invention, a polyurethane prepolymer obtained by the reaction of a polyether polyol, a polycarbonate polyol and a polyisocyanate compound; And a crosslinking agent comprising a polyol compound containing three or more hydroxyl groups, an aqueous polyurethane dispersion having improved crosslinkability is provided.

In the present invention, the polyol compound containing three or more hydroxyl groups may be trimethylol propane, glycerol or a mixture thereof.

In the present invention, the polyurethane prepolymer may be characterized in that the chain is extended by an amine compound, the amine compound is ethylenediamine, isophoronediamine (IPDA), 1,4-tetramethylenediamine, 2 -Methyl-1,5-pentanediamine, 1,4-butanediamine, 1,6-hexamethylenediamine, 1,4-hexamethylenediamine, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, 1 1 type selected from the group consisting of, 3-bis (aminomethyl) cyclohexane, xylylenediamine, piperazine, adipoylhydrazide, hydrazine, 2,5-dimethylpiperazine, diethylenetriamine and triethylenetetramine The above compound may be sufficient.

The present invention also provides an aqueous polyurethane dispersion having improved crosslinkability, further comprising a sulfonate group or a carboxyl group-containing compound.

In the present invention, the sulfonate group-containing compound may be diaminosulfonate.

In the present invention, the polyether polyol may be a mixture of two or more polytetramethylene glycols having a number average molecular weight of 1,000 to 2,000 g / mol.

In the present invention, the polyether polyol may further comprise a monofunctional polyether.

The aqueous polyurethane dispersion having improved crosslinkability of the present invention may be characterized in that crosslinking is carried out at 50 to 120 ° C.

Another embodiment of the present invention provides a process for the preparation of an aqueous polyurethane dispersion having improved crosslinkability comprising the following steps:

(a) reacting a polyether polyol, a polycarbonate polyol and a polyisocyanate compound to produce an isocyanate-functional polyurethane prepolymer;

(b) dissolving the isocyanate-functional polyurethane prepolymer and the amine compound in a solvent to increase molecular weight;

(c) adding a sulfonate group or a carboxyl group-containing compound to the mixture and dispersing in water; And

(d) adding a crosslinking agent comprising a polyol compound containing at least three hydroxyl groups.

In the present invention, the polyol compound containing three or more hydroxyl groups may be trimethylol propane, glycerol or a mixture thereof.

The present invention also provides a process for preparing an aqueous polyurethane dispersion having improved crosslinkability, further comprising the step of adding an acid after step (c).

The present invention also provides a method for preparing an aqueous polyurethane dispersion having improved crosslinkability, further comprising the step of removing metal ions after the step (c).

In the present invention, the solvent may be acetone.

Another embodiment of the present invention comprises the steps of: coating an aqueous polyurethane dispersion having improved crosslinkability onto a substrate; And it provides a method of producing an aqueous polyurethane coating comprising the step of heat-treating the substrate to 50 to 120 ℃.

Since the aqueous polyurethane dispersion according to the present invention is in the form of an aqueous dispersion without using an organic solvent, it is environmentally friendly, conforms to the regulations of the international community, and has an improved crosslinking property, thereby having a convenient effect on the process. It is also possible to provide aqueous polyurethane dispersions having a high solids content and having a storage stability against long term storage.

Hereinafter, embodiments of the present invention will be described in detail. The following description is merely to facilitate understanding of the embodiments of the present invention, but is not intended to limit the scope of protection.

The present invention relates to an aqueous polyurethane dispersion with improved crosslinkability. The aqueous polyurethane dispersion of the present invention comprises a polyurethane prepolymer obtained by the reaction of a polyether polyol, a polycarbonate polyol and a polyisocyanate compound, and a crosslinking agent comprising a polyol compound containing three or more hydroxyl groups.

The polyurethane prepolymer may be obtained by increasing the molecular weight by adding an amine compound to an isocyanate-functional polyurethane prepolymer obtained by reacting a polyether polyol, a polycarbonate polyol, and a polyisocyanate compound.

In addition, the isocyanate-functional polyurethane prepolymer may further comprise a sulfonate group or a carboxyl group-containing compound. The sulfonate group or carboxyl group-containing compound acts as a chain termination and / or dispersant.

The aqueous polyurethane dispersion of the present invention can exhibit improved crosslinkability by using a crosslinking agent containing a polyol compound containing three or more hydroxyl groups. The crosslinking agent according to the invention can be added at any time during or after the preparation of the dispersion at room temperature, and the crosslinked polyurethane coating or film is heated when the crosslinking agent-containing aqueous polyurethane dispersion or its coating is heated to 50 to 120 ° C. Can be formed.

Specifically, the components of the aqueous polyurethane dispersion of the present invention in more detail as follows.

(a) polyether polyols

The polyether polyol usable in the present invention preferably has a number average molecular weight of 300 to 4,000 g / mol (hereinafter, unit omitted), and a number average molecular weight of 1,000 to 2,000 is most preferred.

Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, random copolymers or block copolymers of ethylene oxide and propylene oxide, random copolymers or block copolymers of ethylene oxide and butylene oxide, and the like. Can be used. Moreover, polyether polyester polyol etc. which have an ether bond and an ester bond can also be used.

In a preferred embodiment of the present invention, the polyether polyol is preferably a mixture of two or more polytetramethylene glycols having a number average molecular weight of 1,000 to 2,000.

In a preferred embodiment of the present invention, the polyether polyol may further comprise a monofunctional polyether.

(b) polycarbonate polyols

As the polycarbonate polyol that can be used in the present invention, it is preferable to use a polycarbonate polyol having a number average molecular weight of 400 to 3000. When the number average molecular weight of the polycarbonate polyol is less than 400, there may be a problem such as low breaking energy in the tension of the coating obtained, and when the number average molecular weight exceeds 3000, There may be a problem such as poor film forming properties. As for the number average molecular weight of the polycarbonate polyol which can be used by this invention, 800-2500 are more preferable from a film forming property.

It is preferable that the polycarbonate polyol of the number average molecular weights 400-3000 which can be used by this invention contains the polyalicyclic carbonate diol which the some alicyclic diol molecule carbonate-bonded. By containing the polyalicyclic carbonate diol, the tensile strength of the coating or film obtained using the aqueous polyurethane resin dispersion of the present invention can be improved.

The polycarbonate polyol may be obtained by the reaction of a polyol with a carbonic acid derivative such as diphenyl carbonate, dimethyl carbonate, phosgene (COCl), and the like as the polyol, ethylene glycol, 1,3-propanediol, 1,4- Butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-pentanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecane Diol and the like, 1,3-butanediol, 3-methylpentane-1,5-diol, 2-ethylhexane-1,6-diol, 2-methyl-1,3-pentanediol, neopentylglycol, 2-methyl Aliphatic diols such as -1,8-octanediol; Alicyclic diols such as 1,3-cyclohexanediol, 1,4-cyclohexanediol, 2,2'-bis (4-hydroxycyclohexyl) propane, and 1,4-cyclohexanedimethanol; Aromatic diols such as 1,4-benzenedimethanol; And polyfunctional polyols such as trimethylolpropane and pentaerythritol. Using only 1 type, the said polyol may be said polycarbonate polyol, and may use it as a polycarbonate polyol in combination of multiple types.

As said polycarbonate polyol, the polycarbonate polyol containing the said aliphatic diol or alicyclic diol unit is preferable, The polycarbonate polyol containing the said alicyclic diol unit is more preferable, The 1, 4- cyclohexane dimethanol unit Polycarbonate polyols containing are particularly preferred.

In the present invention, it is preferable that the polycarbonate polyol is used from 20 to 70 parts by weight based on 100 parts by weight of the polyether polyol in view of the tensile and breaking energy of the coating.

(c) polyisocyanate compounds

Although the polyisocyanate compound which can be used by this invention is not specifically limited, The diisocyanate compound which has two isocyanate groups per molecule is preferable.

Specifically, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate (TDI), 2,6-tolylene diisocyanate, 4,4'- diphenylene methane diisocyanate ( MDI), 2,4-diphenylmethane diisocyanate, 4,4'- diisocyanate biphenyl, 3,3'-dimethyl-4,4'- diisocyanate biphenyl, 3,3'-dimethyl-4,4 Aromatic polyisocyanate compounds such as' -diisocyanate diphenylmethane, 1,5-naphthylene diisocyanate, m-isocyanatephenylsulfonyl isocyanate and p-isocyanatephenylsulfonyl isocyanate; Ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), dodecamethylene diisocyanate, 1,6,11-undecane triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, Aliphatic polyisocyanate compounds such as 2,6-diisocyanate methyl caproate, bis (2-isocyanate ethyl) fumarate, bis (2-isocyanate ethyl) carbonate, and 2-isocyanate ethyl-2,6-diisocyanate hexanoate; Isophorone diisocyanate (IPDI), 4,4'-dicyclohexyl methane diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), bis (2-isocyanate ethyl) And alicyclic polyisocyanate compounds such as 4-cyclohexene-1,2-dicarboxylate, 2,5-norbornane diisocyanate, and 2,6-norbornane diisocyanate. These polyisocyanate compounds may be used individually by 1 type, and may use multiple types together.

Among the polyisocyanate compounds, alicyclic polyisocyanate compounds are preferred. By using the said alicyclic polyisocyanate compound, the coating film which is hard to yellow can be obtained, and there exists a tendency for the hardness of the obtained coating film to become higher. As an alicyclic polyisocyanate compound, an alicyclic diisocyanate compound is preferable.

Especially, it is especially preferable to use hexamethylene diisocyanate (HDI) and / or isophorone diisocyanate (IPDI) from a viewpoint of the control of reactivity and the high elastic modulus of the coating film obtained.

In the present invention, the polyisocyanate compound is preferably used to include 1 to 5 times, preferably 2 to 2.5 times, isocyanate groups based on the -OH content of the polyol used.

(d) amine compound

In the present invention, the amine compound is a compound having an isocyanate group reactivity, which is used for water dispersion stability and chain extension.

For example, ethylenediamine, isophoronediamine (IPDA), 1,4-tetramethylenediamine, 2-methyl-1,5-pentanediamine, 1,4-butanediamine, 1,6-hexamethylenediamine, 1, 4-hexamethylenediamine, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, 1,3-bis (aminomethyl) cyclohexane, xylylenediamine, piperazine, adipoylhydrazide, hydrazine, 2 Amine compounds such as, 5-dimethylpiperazine, diethylenetriamine and triethylenetetramine can be used.

The amine compound may be used in an amount of 1 to 10 parts by weight, preferably 2 to 6 parts by weight, based on 100 parts by weight of the isocyanate-functional polyurethane prepolymer.

(e) sulfonate groups or carboxyl group-containing compounds

In the present invention, sulfonate groups or carboxyl group-containing compounds act as chain termination and / or dispersants.

As the sulfonate group-containing compound, monoaminosulfonic acid, diaminosulfonic acid, dihydroxysulfonic acid or salts thereof may be used, and diaminosulfonic acid is most preferred.

In addition, the carboxyl group-containing compound may be used dihydroxy carboxylic acid, diamino carboxylic acid or salts thereof, for example, dimethylol propionic acid (DMPA) or dimethylol butyric acid may be used.

The sulfonate group or carboxyl group-containing compound may be used in an amount of 1 to 15 parts by weight, preferably 2 to 10 parts by weight, based on 100 parts by weight of the isocyanate-functional polyurethane prepolymer.

(f) crosslinking agent

The aqueous polyurethane dispersion of the present invention may contain a polyol compound containing three or more hydroxyl groups as a crosslinking agent.

It is preferable to use trimethylol propane, glycerol or a mixture thereof as the polyol compound containing three or more hydroxyl groups.

The crosslinking agent is allowed to react with the sulfonate group- or carboxyl-terminated polyurethane prepolymer by addition of the sulfonate group or carboxyl group-containing compound to form a crosslinked polyurethane.

The crosslinking agent of the present invention also plays a role of a cation forming a salt with the sulfonate group or the carboxy group incorporated to impart the hydrophilic properties required for the polyurethane. This makes it possible to add water to the acetone solution and to stir. As a result, a bluish dispersion can be formed. After removal of the acetone at 45 ° C. under vacuum, a ready to use reactive dispersion is obtained. The use of such crosslinkers as neutralizers for ionic groups can give particularly high grade coagulants or dispersions with particularly good coagulability.

The crosslinking agent may be included in an amount of 1 to 10 parts by weight, preferably 1 to 6 parts by weight, based on the total weight of the dispersion.

The invention also relates to a process for the preparation of an aqueous polyurethane dispersion comprising the following steps:

(a) reacting a polyether polyol, a polycarbonate polyol and a polyisocyanate compound to produce an isocyanate-functional polyurethane prepolymer;

(b) dissolving the isocyanate-functional polyurethane prepolymer and the amine compound in a solvent to increase molecular weight;

(c) adding a sulfonate group or a carboxyl group-containing compound to the mixture and dispersing in water; And

(d) adding a crosslinking agent comprising a polyol compound containing at least three hydroxyl groups.

In the present invention, the step (a) may be prepared without a solvent by reacting the polyether polyol and polycarbonate polyol to the excess polyisocyanate compound.

The polyol component and polyisocyanate component are usually initially introduced for the production of isocyanate-functional polyurethane prepolymers, optionally diluted with a solvent miscible with water but inert to isocyanate groups, and in the range of 50 to 120 ° C. Heated to temperature. In order to accelerate the isocyanate addition reaction, catalysts known in polyurethane chemistry can be used.

Suitable solvents are customary aliphatic keto-functional solvents such as acetone, 2-butanone, which can be added at the start of the preparation as well as if necessary also partially later. Acetone and 2-butanone are preferred.

Other solvents such as xylene, toluene, cyclohexane, butyl acetate, methoxypropyl acetate, N-methylpyrrolidone, N-ethylpyrrolidone, ether or ester units can be further used, these It may be completely or partially distilled off or may remain completely in the dispersion in the case of N-methylpyrrolidone, N-ethylpyrrolidone. However, preferably, no solvent other than conventional aliphatic keto-functional solvents is used.

In the preparation of the polyurethanes essential to the invention, the preparation of isocyanate-functional prepolymers is particularly preferably carried out first, followed by the reaction of the amine-based compound with the isocyanate-functional prepolymers with chain extension. It is also possible to add chain terminators to control the molecular weight.

As a specific example of a chain terminator, For example, monoamines, such as n-butylamine, di-n-butylamine, diethanolamine; Monohydric alcohols such as ethanol, isopropanol, butanol, and the like, and the like, and these chain terminators may be used alone or in combination of two or more thereof.

The conversion to the prepolymer can be carried out partly or completely, and polyurethane prepolymers containing free isocyanate groups are obtained in solid phase or in solution.

The aqueous polyurethane dispersion can be prepared by adding water to the polyurethane prepolymer obtained and stirring. At this time, dispersibility can be improved by adding a sulfonate group or a carboxyl group-containing compound. Solvents still present in the dispersion are usually removed by distillation during or after the dispersion. The residual content of organic solvent in the aqueous polyurethane dispersion is typically less than 1.0% by weight based on the total dispersion.

The method for preparing the aqueous polyurethane dispersion of the present invention may further include adding an acid or removing metal ions after the step (c). If the terminal sulfonate group or carboxyl group of the polyurethane prepolymer is present in the form of a metal salt, it can be converted into a form that can be combined with a crosslinking agent by acid addition or metal ion removal. For example, when the end of the prepolymer is present in the form of -SO ₃ ^- Na ⁺ , the end group may be changed to -SO ₃ H by acid addition, and crosslinked by adding a polyamine compound as a crosslinking agent. Further, after the terminal group is formed in the form of -SO ₃ ^- through metal ion removal, a divalent or higher metal salt can be added as a crosslinking agent. The acid treatment or metal ion removal may use an acid treatment or metal ion removal process generally used in the art.

The pH of the prepared aqueous polyurethane dispersion is preferably 6.0 to 8.0, and the solids content of the aqueous polyurethane dispersion is 40 to 70% by weight, preferably 50 to 65% by weight, particularly preferably 55 to 65% by weight. .

The aqueous polyurethane dispersions according to the invention can be applied onto the substrate, for example, by flow coating, spraying, dipping, kiss rolling, using a film spreader or roller or via a padding machine and the dispersion is liquid or It can be used in the form of a foam.

Typically, after application through one of the above methods, it can be coagulated (crosslinked) by dipping in hot water at 50 ° C. to 120 ° C., preferably 75 ° C. to 98 ° C., using hot steam, and in special cases molding The part is filled with hot water or the molded product is heated to 120 to 130 ° C. or solidified in an oven using irradiation or a high frequency dryer, followed by drying and condensation at 60 to 180 ° C., preferably 100 to 160 ° C. A urethane film can be formed.

As the substrate to which the aqueous polyurethane dispersion of the present invention is applied, various substrates such as textile fabric, flat substrate metal, glass, ceramic, leather, plastic (for example, PVC, polyolefin, polyurethane or the like) can be used. have.

The aqueous polyurethane dispersions according to the invention also contain conventional auxiliary materials and additives such as pigments, flow control agents, UV stabilizers, antioxidants, fillers, plasticizers, carbon blacks and silica sol, so as to be suitable for the substrates used. It may further comprise aluminum, clay, asbestos dispersions or thixotropic agents.

While some embodiments of the present invention have been described above, the present invention is not limited only to the above-described embodiments, but may be modified and modified without departing from the scope of the present invention, and such modifications and variations It is to be understood that this added form also belongs to the technical spirit of the present invention.

Claims (15)

Polyurethane prepolymers obtained by the reaction of polyether polyols, polycarbonate polyols and polyisocyanate compounds, and
Crosslinking agent containing polyol compound containing three or more hydroxyl groups
An aqueous polyurethane dispersion having improved crosslinkability, comprising. The method of claim 1,
An aqueous polyurethane dispersion having improved crosslinkability, characterized in that the polyol compound containing at least three hydroxyl groups is trimethylol propane, glycerol or a mixture thereof. The method of claim 1,
An aqueous polyurethane dispersion having improved crosslinkability, characterized in that the polyurethane prepolymer is chain-extended with an amine compound. The method of claim 3, wherein
The amine compound is ethylenediamine, isophoronediamine (IPDA), 1,4-tetramethylenediamine, 2-methyl-1,5-pentanediamine, 1,4-butanediamine, 1,6-hexamethylenediamine, 1 , 4-hexamethylenediamine, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, 1,3-bis (aminomethyl) cyclohexane, xylylenediamine, piperazine, adipoylhydrazide, hydrazine, An aqueous polyurethane dispersion having improved crosslinkability, characterized in that it is at least one compound selected from the group consisting of 2,5-dimethylpiperazine, diethylenetriamine and triethylenetetramine. The method of claim 1,
An aqueous polyurethane dispersion having improved crosslinkability, further comprising a sulfonate group or a carboxyl group-containing compound. The method of claim 5,
Further comprising a sulfonate group-containing compound,
An aqueous polyurethane dispersion having improved crosslinkability, characterized in that the sulfonate group-containing compound is diaminosulfonate. The method of claim 1,
An aqueous polyurethane dispersion with improved crosslinkability, characterized in that the polyether polyol is a mixture of two or more polytetramethylene glycols having a number average molecular weight of 1,000 to 2,000 g / mol. The method of claim 7, wherein
An aqueous polyurethane dispersion with improved crosslinkability, characterized in that the polyether polyol further comprises a monofunctional polyether. The method of claim 1,
An aqueous polyurethane dispersion having improved crosslinking, characterized in that crosslinking is carried out at 50 to 120 ° C. A process for preparing an aqueous polyurethane dispersion having improved crosslinkability comprising the following steps:
(a) reacting a polyether polyol, a polycarbonate polyol and a polyisocyanate compound to produce an isocyanate-functional polyurethane prepolymer;
(b) dissolving the isocyanate-functional polyurethane prepolymer and the amine compound in a solvent to increase molecular weight;
(c) adding a sulfonate group or a carboxyl group-containing compound to the mixture and dispersing in water; And
(d) adding a crosslinking agent comprising a polyol compound containing at least three hydroxyl groups. The method of claim 10,
The polyol compound containing three or more hydroxyl groups is trimethylol propane, glycerol or a mixture thereof. The method of claim 10,
After step (c), further comprising the step of adding an acid, a method for producing an aqueous polyurethane dispersion having improved crosslinkability. The method of claim 10,
After the step (c), further comprising the step of removing the metal ion, the method of producing an aqueous polyurethane dispersion having an improved crosslinkability. The method of claim 10,
A process for producing an aqueous polyurethane dispersion having improved crosslinkability, characterized in that the solvent is acetone. Coating an aqueous polyurethane dispersion with improved crosslinkability according to any one of claims 1 to 9 on a substrate; And
Heat-treating the substrate to 50 to 120 ° C
Including, a method of producing an aqueous polyurethane coating.