WO2014064035A2

WO2014064035A2 - Two-component waterborne polyurethane coating composition

Info

Publication number: WO2014064035A2
Application number: PCT/EP2013/071942
Authority: WO
Inventors: Frank Zhang; Jianping Shen; Ziqi FAN
Original assignee: Bayer Materialscience Ag; Bayer MAterialScience (China) Company Ltd.
Priority date: 2012-10-22
Filing date: 2013-10-21
Publication date: 2014-05-01
Also published as: CN103773210A; WO2014064035A3; CN103773210B

Abstract

The present invention relates to a two-component waterborne polyurethane coating composition, comprising: (a) one or more polyol aqueous dispersion or aqueous emulsion, wherein the polyol has a hydroxyl content of 0.5-5.5 wt.%, based on 100% by weight of the polyol, and the polyol aqueous dispersion or aqueous emulsion has a solid content of 10-70 wt.%, based on 100% by weight of the polyol aqueous dispersion or aqueous emulsion; and (b) one or more hydrophilic modified isophorone diisocyanate polymer or prepolymer, wherein the component (a) and (b) are of such an amount that the ratio of the NCO group to the hydroxyl group in the two-component waterborne polyurethane coating composition is 0.2:1 to 5:1. The two-component waterborne polyurethane coating composition has anti-yellowing property under high temperature, and the coating film prepared from the same has a color difference of less than 3.0 after baking under 150℃ for 1 day.

Description

,

Two-component waterborne polyurethane coating composition

Field

[0001] The present invention relates to a two-component waterborne polyurethane coating composition, particularly to a waterborne polyurethane coating composition including isophorone diisocyanate polymer or prepolymer.

Background

[0002] Generally, two-component polyurethane coating is composed of curing agent containing isocyanate groups and resins containing hydroxyl or amino groups. Two-component polyurethane coatings are usually divided into solvent-based polyurethane coatings and waterborne polyurethane coatings. Waterborne polyurethane coatings, especially two-component waterborne polyurethane coatings, not only retain the excellent performance of solvent-based polyurethane coatings, but also are environmentally friendly. Thus they have wide applications.

[0003] Yellowing, which is an issue for two-component waterborne polyurethane coatings baked under high temperature (>150°C) for a long time (>24h), limits their applications in high temperature situations. In recent years, there have been some studies trying to improve the anti-yellowing property of polyurethane coatings under high temperature. For instance, CN101397475 discloses a preparation method for polyurethane coatings featuring high temperature resistance and long-term corrosion resistance. However, the disclosed polyurethane is solvent-based, and the anti-yellowing property under high temperature was not taken into consideration. CNl 629234 described a silicon modified acrylic polyurethane coating featuring high gloss and high temperature resistance, and its preparation method as well. However, the selected resin was silicone modified acrylic resin, with HDI as its curing agent. In addition, the specific method for improving anti-yellowing property under high temperature was not mentioned in this patent. Other patents, such as CNl 01481578 A, which disclosed a capacitor coating with high impact resistance, good anti-yellowing property under high temperature and a preparation method thereof. However, the polyurethane coating was also solvent-based. Furthermore, because blocked polyisocyanate was used as the curing agent, the capacitor coating falls into the category of baking vanish, which cannot harden to form a film at room temperature.

[0004] In summary, so far, there is no report on two-component waterborne polyurethane coatings with anti-yellowing property under high temperature. Summary

[0005] In one aspect, the present invention provides a two-component waterborne polyurethane coating composition, comprising:

(a) one or more polyol aqueous dispersion or aqueous emulsion, wherein the polyol has a hydroxyl content of 0.5-5.5 wt.%, based on 100% by weight of the polyol, and the polyol aqueous dispersion or aqueous emulsion has a solid content of 10-70 wt.%), based on 100% by weight of the polyol aqueous dispersion or aqueous emulsion;

(b) one or more hydrophilic modified isophorone diisocyanate polymer or prepolymer;

Wherein the component (a) and (b) are of such an amount that the ratio of the NCO group to the hydroxyl group in the two-component waterborne polyurethane coating composition is 0.2: 1 to 5 : 1. In one preferred embodiment of the present invention, the component (a) and (b) are of such an amount that the ratio of the NCO group to the hydroxyl group in the two-component waterborne polyurethane coating composition is 1.2: 1 to 1.5 : 1.

[0006] In one embodiment of the present invention, the hydrophilic modified isophorone diisocyanate polymer or prepolymer has a NCO of 10-14 wt.%, based on 100%) by weight of the hydrophilic modified isophorone diisocyanate polymer or prepolymer.

[0007] In another emb odiment of the present invention, the hydrophilic modified isophorone diisocyanate polymer or prepolymer is the one or more selected from the group consisting of polyether modified isophorone diisocyanate prepolymer, sulphamate modified isophorone diisocyanate polymer or the combination thereof.

[0008] In yet another embodiment of the present invention, the polyol is the one or more selected from the group consisting of polyester modified acrylate polyols, polyester polyols or the combination thereof.

[0009] In still another embodiment of the present invention, the two-component waterborne polyurethane coating composition further comprises: (c) antioxidant. Preferably, the antioxidant is the one or more selected from the group consisting of hindered phenolic antioxidant, organophosphate or the combination thereof. Preferably, the antioxidant has an amount of 0.01 -5 wt.%, based on 100%) by weight of the solid of the two-component waterborne polyurethane coating composition.

[0010] In still another embodiment of the present invention, the two-component waterborne polyurethane coating composition further comprises: (d) waterborne polyurethane dispersion.

[0011] In another aspect, the present invention provides a coating article comprising a substrate and a coating film applied on the substrate, wherein the coating film is prepared from the above two-component waterborne polyurethane coating composition. Preferably, the coating film has a chromatism value of less than 3.0 after baking under 150°C for 1 day, determined and calculated according to GB 11186.2 and GB 11186.3, respectively.

Detailed Description

I. Two-component waterborne polyurethane coating composition

[0012] The present invention provides a two-component waterborne polyurethane coating composition, comprising:

(a) one or more polyol aqueous dispersion or aqueous emulsion, wherein the polyol has a hydroxyl content of 0.5-5.5 wt.%, based on 100% by weight of the polyol, and the polyol aqueous dispersion or aqueous emulsion has a solid content of 10-70 wt.%, based on 100% by weight of the polyol aqueous dispersion or aqueous emulsion;

[0013] As used herein, the term "polyurethane coating" has the meaning as understood by a person skilled in the art and contains pigments and fillers, solvents, catalysts, and additives commonly used in the art in addition to the above component (a) and (b).

(a): polyols

[0014] The polyols suitable for use in the present invention can be those commonly used in the waterborne polyurethane coating field, including those have a molecular weight (Mn) of 400-6000, preferably 400-3000. The polyols may be used in a form of aqueous dispersion or aqueous emulsion, and preferably aqueous emulsion. The preparation of the polyol component a) takes place directly in aqueous phase by the technique of emulsion polymerization, which is known in principle and is summarized, for example, in B. Vollmert, "Grundriss der Makromolekularen Chemie", volume 1 , p.181 ff., Vollmert Verlag 1988, Karlsruhe, or in H. G. Elias, "Makromolekuele", vol. 2, p. 93 ff., Huethig & Wepf Verlag Basel, Heidelberg, N.Y. 1992.

[0015] The examples of the polyol include, but not limited to:

1) polyester polyols, which may be produced from the reaction of organic dicarboxylic acids or dicarboxylic acid anhydrides with polyhydric alcohols. Suitable dicarboxylic acids are preferably aliphatic carboxylic acids containing 2 to 12 carbon atoms, for example, succinic acid, malonic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decane-dicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, and the mixture thereof. Suitable anhydrides are, for example, phthalic anhydride, terachlorophthalic anhydride, and maleic anhydride. Representative polyhydric alcohols include ethanediol, diethylene glycol, 1 ,2- and 1 ,3 -propanediols, dipropylene glycol, 1 ,3-methylpropanediol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, neopentyl glycol, 1 , 10-decanediol, glycerol, trimethylol-propane, or mixtures thereof. The polyester polyol may also be those prepared from lactones, preferably ε-caprolactone;

2) Polycarbonate polyols, which are obtained by reacting carbonic acid derivatives with diols, preferably diols. Suitable example of the carbonic acid derivatives include, but not limited to diphenyl carbonate or dimethyl carbonate or phosgene. Suitable diols include, but not limited to ethylene glycol, 1 ,2- and 1 ,3-propanediol, 1 ,3- and 1 ,4-butanediol, 1 ,6-hexanediol, 1 ,8-octanediol, neopentyl glycol, 1 ,4-bishydroxymethylcyclohexane, 2-methyl-l ,3-propanediol, 2,2,4-trimethylpentane- l ,3-diol, dipropylene glycol, polypropylene glycols, dibutylene glycol, polybutylene glycols, bisphenol A, tetrabromobisphenol A and lactone-modified diols. The diols preferably contains 40-100% by weight of hexanediol, preferably 1 ,6-hexanediol and/or hexanediol derivatives, preferably derivatives which have terminal OH groups and contain ether groups or ester groups. The polycarbonate polyols are preferably substantially linear. As a result of the incorporation of polyfunctional components, however, especially low molecular weight polyols, they may optionally contain a low degree of branching. Examples of compounds suitable for this purpose include glycerol, trimethylolpropane, hexane- l ,2,6-triol, butane- 1 , 2, 4-triol, trimethylolpropane, pentaerythritol, quinitol, mannit o l , s o rb i t o l , m e thy l g lyc o s i d e o r 1 ,3,4,6-dianhydrohexitols;

3) Polyether polyols, which may be produced the reaction of alkylene oxides with

polyhydric alcohol starters in the presence of catalysts. The catalysts are preferably, but not limited to alkali hydroxides, alkali alkoxides, antimony pentachloride, boron fluoride etherate or mixtures thereof. The alkylene oxides are preferably, but not limited to tetrahydrofuran, ethylene oxide, 1,2-propylene oxide, 1,2-and 2,3-butylene oxide, styrene oxide or mixtures thereof. The starter molecules are preferably, but not limited to polyhydric compounds, such as water, ethylene glycol, 1,2-and 1,3-propanediols, 1,4-butanediol, diethylene glycol, trimethylol-propane or mixtures thereof. Vinyl polymers modified polyether polyol may also be used in the present invention, which may be obtained e.g. by polymerisation of styrene and acrylonitrile in the presence of polyethers (U.S. Pat. Nos.3,383,351, 3,304,273, 3,523,093, 3,110,695; DE-A-1,152 ,5369);

4) Polythioethers, which are obtained, for example from thiodiglycol on its own and/or with other glycols, dicarboxylic acids, formaldehyde, aminocarboxylic acids or amino alcohols. The products obtained are either polythio-mixed ethers, polythioether esters or polythioether ester amides, depending on the co-components;

5) Polyacetals, which include those obtained from the above-mentioned polyhydric alcohols, especially diethylene glycol, triethylene glycol, 4,4'-dioxyethoxy-diphenyldimethylene, 1,6-hexanediol and formaldehyde. Polyacetals suitable for use in the invention may also be prepared by the polymerization of cyclic acetals;

6) Polyether esters, which contain isocyanate-reactive groups and known in the art;

7) Polyester amides and polyamides, which include the predominantly linear condensates obtained from polyvalent saturated and unsaturated carboxylic acids or their anhydrides and polyvalent saturated and unsaturated amino alcohols, diamines, polyamines, or mixtures thereof.

[0016] The polyester modified acrylate polyols aqueous dispersions may have a solid content of 30-60 wt.%, and may also 38-45 wt.%, based on 100% by weight of the dispersion; and the aqueous dispersions may have a hydroxyl content of 0.5-5.5 wt.%, and may also 3.5-4.5 wt.%, based on 100%> by weight of the solid content. The examples of the polyester modified acrylate polyols suitable for use in the present invention include, but not limited to, Bayhydrol A 2227/1 and Bayhydrol A 2058 commercial available from Bayer Material Science.

[0017] The polyester polyol aqueous dispersions may have a solid content of 10-70 wt.%, and may also 35-45 wt.%, based on 100%) by weight of the dispersion, and have a hydroxyl content of 0.5-5.5 wt.%, and may also 1.5-4.6 wt.%, based on 100%) by weight of the solid content. The examples of the polyester polyols suitable for use in the present invention include, but not limited to, Bayhydrol U XP 2766 and Bayhydrol U XP 2755commercial available from Bayer Material Science. (b hydrophilic modified isophorone diisocyanate polymer or prepolymer

[0018] As used herein, the term "isophorone diisocyanate polymer" refers to non-blocked IPDI self-polymer, which may be a mixture of isophorone diisocyanate self-polymers with different polymerization degree. Preferably, the IPDI polymer is IPDI trimer. [0019] The isophorone diisocyanate prepolymer can also be used in the present invention.

The isophorone diisocyanate prepolymer refers to a medium molecular weight polymer with a polyurethane chain backbone and terminated with NCO groups and the prepolymer may be obtained by the reaction of isophorone diisocyanate and co-reactant. Suitable co-reactant includes polyamines and polyhydric alcohols. Examples of suitable polyamines include but are not limited to primary and secondary amines, and mixtures thereof, amine terminated polyureas may also be used. Amines comprising tertiary amine functionality can be used provided that the amine further comprises at least two primary and/or secondary amino groups. Examples of suitable polyhydric alcohols include but are not limited to polyether polyols, polyester polyols, polyurea polyols (e.g. the Michael reaction product of an amino function polyurea with a hydroxyl functional

(meth)acrylate), polycaprolactone polyols, polycarbonate polyols, polyurethane polyols, poly vinyl alcohols, addition polymers of unsaturated monomers with pendant hydroxyl groups such as those containing hydroxy functional (meth)acrylates, allyl alcohols and mixtures thereof. Examples of isophorone diisocyanate prepolymer suitable for use in the present invention include, but not limited to Bayhydur® 401 -70.

[0020] The isophorone diisocyanate polymers or prepolymers which can be used in the present invention are hydrophilic modified isophorone diisocyanate polymers or prepolymers. It is well-known to a person skilled in the art the process of hydrophilic modifying isophorone diisocyanate polymers or prepolymers, such as the disclosure in "hydrophilic modified polyisocyanates" (Zhang, Faai et al., Chemistry Online, 2004, vol

67, w002).

[0021] The isophorone diisocyanate polymers or prepolymers may be hydrophilic modified by nonionic and/or anion process. The nonionic hydrophilic modification may be done according to the process disclosed in EP-A0540985 and EP-A0959087. The anion hydrophilic modification may be done by using phosphate, sulphate or sulfonate groups.

In the present invention, the modification is preferably made by sulfonate groups, more preferably sulphamate groups, which present in the isocyanate in the form of chemical bonds.

[0022] In the present invention, the isophorone diisocyanate polymers or prepolymers may also be modified by mixed hydrophilic modification process according to EP-A0510438, i.e. hydrophilic modified by the combination of nonionic polyether groups, and anion or potentially ionic groups.

[0023] In one preferred embodiment of the present invention, the hydrophilic IPDI polymer is selected from sulphamate modified IPDI polymer, the hydrophilic IPDI prepolymer is selected from polyether modified IPDI prepolymer.

[0024] The polyether modified IPDI prepolymer preferably has a solid content of 60- 100 wt.%, more preferably 68-72 wt.%, and a NCO content of 10-20%, more preferably 13- 14%). The sulphamate modified IPDI polymer preferably has a solid content of 60- 100 wt.%), more preferably 68-72 wt.%, and a NCO cotent of 10-20%), more preferably 10- 12%.

(c) waterborne polyurethane dispersion

[0025] As us e d herein, the term "waterb orne p o lyurethane disp ersion" refers to a composition containing at least a polyurethane or polyurethane urea polymer or copolymer dispersed in an aqueous medium,

[0026] The term "aqueous polyurethane dispersion" refers to (such as the polyurethane prepolymer described herein), optionally including a solvent, that has been dispersed in an aqueous medium, such as water, including de-ionized water. The term also comprises the dried composition mentioned above.

[0027] In one embodiment of the present invention, the waterborne polyurethane dispersion has a solid content of 30-70wt.%>, preferably 55-65 wt.%, based on 100%) by weight of the waterborne polyurethane dispersion.

(d antioxidant

[0028] In one embodiment of the present invention, the two-component waterborne polyurethane coating composition further comprises antioxidant. The applicant surprisingly finds that the coating has better anti-yellowing property when comprising antioxidant. The antioxidant may be those commonly used in the coating field, preferably the antioxidant is selected from the group consisting of hindered phenolic antioxidant, organophosphate or the combination thereof. The exemplary hindered phenolic antioxidant is isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, such as Ciba Irganox 1135. The exemplary organophosphate is Ciba IRGAFOS 168.

[0029] The content of the antioxidant may be determined according to the actual usage and requirements by a person skilled in the art, for example 0.01 -5 wt.%, based on 100%) by weight of the two-component waterborne polyurethane coating composition. (e) pigment and filler

[0030] The coating compositions of the present invention may be transparent, translucent or pigment-comprised. Therefore, the coating composition may comprise transparent fillers and pigments that impart color and/or effect to the coating composition. The color and/or effect imparting pigments can be selected from the group consisting of organic and inorganic, coloring, extending, rheology-controlling, optical-effect-imparting, electrically conductive, magnetically shielding, and fluorescent pigments, metallic pigments and metal powders, organic and inorganic, transparent or hiding fillers, and nanoparticles. Examples of the organic and inorganic color pigments include, but not limited to, titanium dioxide, micronised titanium dioxide, iron oxide pigments, carbon black, azo pigments, phthalocyanine pigments, quinacridone or pyrrolopyrrole pigments. Examples of the effect pigments include, but not limited to, metallic pigments, interference pigments, such as such as metal oxide coated with metal, aluminum coated with titanium dioxide, coated mica, such as mica coated with titanium dioxide, graphite effect pigments. Examples of fillers include, but not limited to, alumina trihydrate, silica, aluminum silicate, barium sulfate, calcium carbonate and talc.

[0031 ] The content of the pigments and fillers can be determined by a person skilled in the art according to the actual need and requirements, such as 0-200 wt.%, based on 100% by weight of the coating composition. if) Solvents

[0032] The coating composition of the present invention may contain water as liquid diluents, and optionally organic co-solvents. The content of the co-solvents are maintained at the lowest limit.

[0033] The water used in the coating composition of the present invention is preferably selected from deionized water, and the content may be 1 -90 wt.%, preferably 30-70 wt.%, based on 100% by weight of the coating composition.

[0034] Examples of organic co-solvents that may be mixed with water include glycol ether esters, such as, ethyl glycol acetates, butyl diglycol acetates, methoxypropyl acetates; esters, such as, propylenecarbonate(4-methyl- l ,3 -dioxolan-2-on), ethyl acetate, butyl acetate, isobutyl acetate, amyl acetate; ketones, such as, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diisobutyl ketone, methyl amyl ketone, cyclohexanone, isophorones; aromatic hydrocarbons, such as, toluene, xylenes, Solvessol OO (mixture of aromatic hydrocarbons with a boiling range from 155 to 185°C), Solvesso 150 (mixture of aromatic hydrocarbons with a boiling range from 182 to 202°C), and aliphatic hydrocarbons. The organic co-solvents are contained in the range from 0 to 15 wt. %, preferably in a range of 0 to 5 wt. %, based on 100% by weight of the coating composition.

(s.) Other additives

[0035] In addition to the component (c) antioxidant, the coating composition of the present invention may further comprise at least one additives, which may be those commonly used in the art, for example wetting dispersant, substrate wetting agent, rheological agent, plasticizer, flow agent, defoamer and catalyst. All the terms mentioned above have the definition know to a person skilled in the art.

[0036] The additives may be added into the coating composition before, after or during the process of mixing the composition, or first mixing with the polyol component (a) or the isocyanate component (b) and then mix with other components.

[0037] A person skilled in the art may determine additives and the amount thereof according to the usage and the practical needs, for example the wetting dispersant may have an amount of 0-5wt.%, the substrate wetting agent may have an amount of 0-3 wt.%, the flow agent may have an amount of 0-4.5 wt.%>, the rheological agent may have an amount of 0-4 wt.%>, the amounts above all based on 100 wt.%> by weight of the solid content of the coating composition.

[0038] The coating composition of the present invention may be prepared by mixing and dispersing the respective components of the coating composition, which have been described above, in a water-based medium, making use, for example, of high-speed stirrers or off-line or in-line dissolvers.

II. Coating Article

[0039] In another aspect, the present invention relates to a coating article, which comprises a substrate and a coating film applied on the substrate, wherein the coating film is prepared from the two-component waterborne polyurethane coating composition mentioned above. The two-component waterborne polyurethane coating composition may be applied to the substrate by the way know to a person skilled in the art, including but not limited to, doctor blade coating, rod coating, spraying, rolling, brushing, flow coating, knife coating, and dipping. In one embodiment of the present invention, said coating composition is applied to the substrate by means of doctor blade coating or rod coating. In one embodiment of the present invention, before applying to the substrate, the components of the coating composition of the present invention may be mixed in one container to prepare the coating composition of the present invention. The components of the coating composition of the present invention may also be fed into two or multiple component injection gun respectively, and sprayed onto the substrate to form a coating film before all components are mixed in the injection gun.

[0040] Specifically, a single layer coating film may have a thickness of 1 -500 μιη, preferably 3-150 μηι. The final thickness of a multiple layer coating film may be 10-2000 μιη, preferably 50- 1000 μιη, and may be formed by multiple spraying and a thickness of 10-150 μιη for each spraying according to the practical need.

[0041] The coating process may be applied under room temperature or higher or lower temperature. Before curing under high temperature, there will be an optional flash drying process. The curing temperature may be varied between 5-200°C, preferably 20-150°C, more preferably 100-150°C. The curing time may be, for example, 5 minutes to 24 hours. Preferably, the coating composition of the present invention is cross-linked under a temperature of 20-35°C for 24 hours, or a temperature of 80-150°C for 30-60 minutes.

[0042] The cured coating film may be sand milled and/or polished to obtain a smooth surface with desired thickness. The coated substrate or article may be cutting into desired shape. The coating film of the article provided in the present invention not only has favorable mechanical properties, but also favorable anti-yellowing property. The coating film has a chromatism value of less than 3.0 after baking under 150°C for 1 day, determined according to GB 11186.2 ("the process of determining color", part II, color determination) and calculated according to GB 11186.3 ("the process of determining the color of coating film", part III, chromatism value calculation) respectively.

[0043] The two-component waterborne polyurethane coating composition provided herein may be applied to any substrate, the example of which include but not limited to, woods, plastics, papers, textiles, leathers, glasses, ceramics, gypsums, bricks, concretes, metals (for example, ferrum, steel and aluminum) or coating films. The coating film may be those prepared from the coating composition of the present invention, or other coating compositions.

[0044] In another aspect, the present invention provides a use of the two-component waterborne polyurethane coating composition mentioned above in preparing the said coating article.

[0045] The present invention will be further illustrated in detail by virtue of the following examples. ^

Examples

[0046] The raw materials mentioned in this invention are listed in the following table.

Bayhydrol A 2227/1 Waterborne polyester modified acrylate polyol dispersion, 42 wt.% solid content, 3.8% OH content (supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Bayhydrol U XP 2766 Waterborne polyester polyol dispersion, 40 wt. %> solid content,

4%> OH content (supposing the solid weight is 100%), supplied by Bayer MaterialScience (China) Company Limited.

Bayhydrol A 145 Waterborne acrylic polyol dispersion, 45 wt.%> solid content,

3.3%) OH content (supposing the solid weight is 100%), supplied by Bayer MaterialScience (China) Company Limited.

Bayhydrol A 2470 Waterborne acrylic polyol dispersion, 45 wt.%> solid content,

3.9%) OH content (supposing the solid weight is 100%), supplied by Bayer MaterialScience (China) Company Limited.

Bayhydrol A 2542 Waterborne acrylic polyol dispersion, 50 wt.%> solid content,

3.8%) OH content (supposing the solid weight is 100%), supplied by Bayer MaterialScience (China) Company Limited.

Bayhydrol A 2546 Waterborne acrylic polyol dispersion, 41 wt.%> solid content,

4.1%) OH content (supposing the solid weight is 100%), supplied by Bayer MaterialScience (China) Company Limited.

Bayhydrol A 2646 Waterborne acrylic polyol dispersion, 50 wt.%> solid content,

3.8%o OH content (supposing the solid weight is 100%), supplied by Bayer MaterialScience (China) Company Limited.

Bayhydrol A 2695 Waterborne acrylic polyol dispersion, 41 wt.%> solid content, 5%>

OH content (supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Bayhydrol U XP 2750 Waterborne polycarbonate modified polyester polyol dispersion,

43 wt.%) solid content, 3.6%> OH content (supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Impranil LP RSC 1537 Waterborne polyurethane dispersion, 60 wt. %> solid content, supplied by Bayer MaterialScience(China) Company Limited.

Bayhydur 3100 Polyether modified hexamethylene diisocyanate(HDI) prepolymer, 100% solid content, 17.4% NCO content (supposing th e s o l i d w e i g h t i s 1 0 0 % ) , s up p l i e d b y B ay e r MaterialScience(China) Company Limited.

Bayhydur 304 Polyether modified hexamethylene diisocyanate(HDI) prepolymer, 100wt.%>solid content, 1 8.2% NCO content (supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Bayhydur VP LS 2306 Polyether modifiedhexamethylene diis ocyanate(HDI) prepolymer, 100 wt.%> solid content, 8%>NCO content (supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Bayhydur 401-70 Polyether modifiedisophorone diisocyanate(IPDI) prepolymer,

70 wt.% solid content, 13.4% NCO content (supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Bayhydur XP 2759 Sulphamate modified polyisocyanate based on isophorone diisocyanate (IPDI), 70 wt.% solid content, l l%NCO content (supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Bayhydur XP 2655 Sulphamate modified polyisocyanate based on hexamethylene diisocyanate(HDI), 100 wt.% solid content, 21 .2% NCO content( supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Bayhydur XP 2487/1 Sulphamate modified polyisocyanate based on hexamethylene diisocyanate(HDI), 100 wt.%solid content, 20.5% NCO content( supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Desmodur polyisocyanate based on hexamethylene diisocyanate(HDI), 100 N 3900 wt.%) solid content, 23.5% NCO content(supposing the solid weight is 100%), supplied by Bayer MaterialScience(China) Company Limited.

Ti-pure R960 Rutile titanium dioxide pigment prepared by chlorination process. Ti02 content no less than 89 wt.%, specific gravity about 3.9, oil absorption about 18.7 g/lOOg , pH value about 7.4. Supplied by DuPont Company.

BYK024 Defoaming polymer and polysiloxane mixture. Non-volatile portion > 96%, flash point > 100 °C, density about 1.00 g/cm³ at 20°C. Supplied by BYK Company.„

BYK348 Polyether modified polydimethylsiloxane. Density about

1.05g/ml at 20°C, non-volatile content about 96%>, flash point > 100 °C. Supplied by BYK Company.

Borchi-Gel PW25 Nonionic polyurethane based thickener. Non-volatile content about 24-26%), viscosity greater than 15000 mPa-s at 23°C, flash point > 100 °C, density about 1.00 g/cm³ at 20°C. Supplied by Borchers Company.

TEGO Dispers 752W Aqueous solution of copolymer containing pigment affinity groups. Non-volatile content about 48-52%, viscosity about 150-350mPa-s at 25°C, pH value about 6.0-7.5. Supplied by Evonik Degussa Company.

Texanol 2,2,4-trimethyl- l ,3-pentanediolmono(2-methylpropanoate), content > 99.5%>,density about 0.95g/cm³, vapor pressure about 0.013 mmHg at 20 °C, flash point about 120 °C, boiling point 255 °C, freezing point -50 °C. Supplied by Eastman Company.

Ciba Irganox 1135 H i n d e r e d p h e n o l i c a n t i o x i d a n t s . Octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate. Non- volatile content about 24-26%, viscosity about 220mPa-s at 25°C, flash point 152°C, density about 0.97g/cm³ at 20°C. Supplied by Ciba Company.

Ciba Tinuvin 5060 Composite light stabilizer. Viscosity about 4200 mPa-s at 25°C, density about 0.98 g/cm³ at 20°C, it is miscible with coatings in most of the organic solvents with the miscibility proportion higher than 50%, but its solubility in water is less than 0.01%. Supplied by Ciba Company.

CAB-O-SIL TS 720 A medium surface area gas phase silica, with surface modification by polydimethylsiloxane, supplied by Kabote (china) Investment Co., Ltd.

MPA Solvent: propylene glycol monomethyl ether acetate. Supplied by

Dow Company.

[0047] In various examples of this invention, anti-yellowing property at high temperature and other properties of the coating films prepared from the invention coating combinations were tested and shown in Table 1. Table 1 lists every test item and the corresponding test standard or method, selection and pretreatment of substrate, and preparation of specimen. Among these tests, chromatism (Δ E) was used to evaluate the anti-yellowing property at high temperature.

Table 1 : Test items, test standards or methods, substrate selection and pretreatment, preparation of specimens

Substrates Sample

Test item Test standardor Method Substrates

Pretreatment Preparation

The glass plate

Chromatism meter ( 6835 / was cleaned by M ake fi lms

Chromatism, BYK Gardner ) , conserve at wiping paper with a 120μιη

Glass plate

ΔΕ film maker

23°C, 50 % relative humidity with suitable

for 7 days a m o u n t o f

acetone

Mainly determined by the

change of viscosity. For the

spray co atings , when the

measured viscosity reached

Pot life(min) twice as the initial viscosity, - - - the period can be defined as

their pot life. For the rolK

brush blade coatings, 3-5

times as the measured viscosity reachds the initial viscosity, the

period can be defined as their

pot life.

The glass plate

Drying time, was cleaned by Make films wiping paper with a 120μιη surface drying

GB/T 1728 Glass plate film maker time/hard with suitable

drying time(h) amount of

acetone

The glass plate

was cleaned by Make films

Pendulum wiping paper with a 120μιη

DIN EN ISO 1522 Glass plate film maker hardness (s) with suitable

amount of

acetone

The tin plate

was cleaned by

wiping paper Make films with suitable

Impact with a 120μιη

GB/T 1732 Tin plate anoutn

resistance(cm) rod

ofacetone after

being polished

by a 300 mesh

sandpaper

The tin plate

Chemical was cleaned by

resistance, wiping paper Make films Double rub with suitable with a 120μιη method, Test RJCS 1 kg Load Tin plate anount of rod

solven methyl acetone after

ethyl ketone being polished

by a 300 mesh

sandpaper

[0048] Component A was prepared by water-based polyol dispersion or emulsion, component B was curing agent containing isocyanate groups. Comparing example CI

[0049] In example CI , 9 different types of water-based polyol dispersion and hydrophilic modified polyisocyanate based on hexamethylene diisocyanate(HDI) were used to prepare the coating films . [0050] Take Cl -1 as an example to illustrate the preparation method of the formula. The difference between CI -2 to CI -9 and Cl -1 was the different types of water-based polyol dispersion, but all the formulas shared the same curing agent, additives and preparation method.

Preparation of component A [0051] 50.00g Bayhydrol A145 was added into the blender. 0.10g Borchi-Gel PW25, 0.20g BYK024, 0.70g TEGO Dispers752W, 13.8g R960 and 5.45g deionized water were added slowly in turn under 1200 rpm rotating speed. After that, the rotating speed was accelerated to 3000rpm and kept for 25min or longer until the fineness <15μιη. After reducing the rotating speed to 1000 rpm, 0.6g BYK 348 was added slowly. The mixture was stirred for 5min to finish the preparation of component A.

[0052] Component A was filtered with a 400 mesh filter and stored in a sealed container for 24 hours.

Preparation of component B

[0053] Component B was Bayhydur 2655 diluted with MPA, the dilution ratio was curing agent: MPA = 3 : 1.

Sample preparation and testing

[0054] As shown in Table 2, component A and component B were weighed accurately with mass ratio of 70.85/17.30 and mechanically stirred for 5min until well-mixed to obtain the two-component waterborne polyurethane coatings. The specimens were prepared according to the substrate selection and pretreatment, and sample preparation methods provided in Table 1. The chromatism of the specimens were tested and the test result was presented in Table 3 below.

Table 2 Formulas of comparing examplesCl

Raw Material Weight, g

Cl-1 Cl-2 Cl-3 Cl-4 Cl-5 Cl-6 Cl-7 Cl-8 Cl-9

Component A Bayhydrol Al 45 50 - - - - - - - -

B ayhydrol UXP - 50 - - - - - - - 2750

Bayhydrol - - 50 - - - - - - AXP2695

Bayhydrol - - - 50 - - - - - A2646

Bayhydrol - - - - 50 - - - - A2542

Bayhydrol - - - - - 50 - - - A2546

Bayhydrol - - - - - - 50 - - A2470

Bayhydroal - - - - - - - 50 - A2227/1

Bayhydrol - - - - - - - - 50 UXP2766

Borchi-Gel PW25 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

BYK024 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

TEGO 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7

Dispers752W

R960 13.8 13.8 13.8 13.8 13.8 13.8 13.8 13.8 13.8

Deionized water 5.45 5.45 5.45 5.45 5.45 5.45 5.45 5.45 5.45

BYK 348 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

Component B

B ay h y d u r X P 12.98 13.53 17.92 16.61 16.61 14.69 15.34 13.95 13.98 2655

MPA 4.32 4.51 5.97 5.53 5.53 4.8 5.11 4.65 4.66 - 17 -

Table 3 Test result of anti-yellowing property at high temperature for comparing examples CI

[0055] The test result presented in Table 3 showed that the coating films prepared by various water-based polyol dispersions and hydrophilic modified polyisocyanate based on hexamethylene diisocyanate(HDI) became obviously yellow after being baked at high temperature of 150°Cfor 24h. All chromatism values ΔΕ were over 3, which showed it was difficult to achieve excellent anti-yellowing property at high temperature. The applicants also indicated that different water-based polyol dispersions had different performance on anti-yellowing property at high temperature. Among the formulas in comparing examples CI , Bayhydrol A 2227/1 and Bayhydrol U XP 2766 showed relatively better anti-yellowing property at high temperature.

Comparing example C2

[0056] In C2 comparing examples, BayhydrolA 2227/1 was used as water-based polyol dispersion. Different types of polyisocyanate based on hexamethylene diisocyanate (HDI) suitable for waterborne two-component polyurethane coatings were selected as curing agents.

[0057] Take C2-1 as an example to illustrate the preparation method of the formula. The difference between C2-2 to Cl -6 and C2-1 was the type of polyisocyanate based on hexamethylene diisocyanate (HDI). All the formulas shared the same water-based polyol dispersion, additives and preparation method. Preparation of component A

[0058] 50.00g Bayhydrol A2227/1 was added into the blender. 0.1 Og Borchi-Gel PW25, 0.2g BYK024, 0.7g TEGO Dispers752W, 13.8g R960 and 5.45g deionized water were added slowly in turn under 1200 rpm rotating speed. Then the rotating speed was accelerated to 3000rpm and kept for 25min or longer until the fineness <15μιη. After that, 0.6g BYK 348 was added slowly under l OOOrpm rotating speed. The mixture was stirred for 5min to finish the preparation of component A.

[0059] Component A was filtered with a 400 mesh filter and stored in a sealed container for 24 hours.

Preparation of component B

[0060] Component B was Bayhydur 3100 diluted with MP A, the dilution ratio was curing agent:

MPA = 3:1.

Sample preparation and testing

[0061] Component A and component B were weighted accurately with mass ratio of 70.85/22.67 and mechanically stirred for 5min until well mixed. The mixture was filtered with a 400 mesh filter before using.

[0062] According to the formula shown in Table 4, component A and component B were weighted accurately with mass ratio of 70.85/17.30 and mechanically stirred for 5min until mixed well to obtain two-component waterborne polyurethane coatings. The specimens were prepared according to the substrate selection and pretreatment, sample preparation methods provided in Table 1. The chromatism of the specimens were tested and the test result was presented in Table 5.

Table 4 Formulas of comparing examples C2-1 to C2-6

Material Weight, g

C2-1 C2-2 C2-3 C2-4 C2-5 C2-6

Component A

Bayhydroal 50 50 50 50 50 50

A2227/1

Borchi-Gel PW25 0.1 0.1 0.1 0.1 0.1 0.1

BYK024 0.2 0.2 0.2 0.2 0.2 0.2 TEGO 0.7 0.7 0.7 0.7 0.7 0.7

Dispers752W

R960 13.8 13.8 13.8 13.8 13.8 13.8 deionized water 5.45 5.45 5.45 5.45 5.45 5.45

BYK348 0.6 0.6 0.6 0.6 0.6 0.6

Component B

Bayhydur 3100 17 - - - - -

Bayhydur 304 - 16.25 - - - -

Bayhydur XP - - 14.43 - - - 2487/1

Bayhydur XP - - - 15.34 - - 2655

Bayhydur VP LS - - - - 29.57 - 2306

DesmodurN3900 - - - - - 12.59

MPA 5.67 5.42 4.81 5.11 9.86 4.2

Table 5 Test result of anti-yellowing property at high temperature for comparing examples C2

150°Cfor 1 day 150°C for 2 days

Chromatism ΔΕ Chromatism ΔΕ

C2-1 4.11 5.92

C2-2 4.67 7.01

C2-3 3.82 5.77

C2-4 3.04 5.68

C2-5 3.18 5.58

C2-6 4.11 5.92 [0063] According to the test result presented in Table 5, the coating films prepared by optimized water-based polyol dispersion and various polyisocyanate based on hexamethylene diisocyanate (HDI) that can be dispersed in water became obviously yellow after being baked at high temperature of 150°C for 24h, all chromatism ΔΕ values were larger than 3, which shows the difficulty to achieve excellent anti-yellowing property at high temperature.

Example El

Preparation of component A

[0064] 50.00g Baydrol A2227/1 was added into the blender. 0.10g Borchi-Gel PW25, 0.2g BYK024, 0.7g TEGO Dispers752W, 13.8g R960 and 5.45g deionized water were added slowly in turn under 1200rpm rotating speed. Then the rotating speed was accelerated to 3500rpm and kept for 25min or longer until the fineness <15μιη. After that, 0.6g BYK 348 was added slowly under lOOOrpm rotating speed. The mixture was stirred for 5min to finish the preparation of component A.

[0065] Component A was filtered with a 400 mesh filter and stored in a sealed container for 24 hours.

Preparation of component B

[0066] Component B was Bayhydur XP 2759 (a kind of sulphamate modified polyisocyanate based on isophorone diisocyanate (IPDI)) diluted with MPA, the dilution ratio was curing agent: MPA = 3:1.

Sample preparation and testing

[0067] Component A and component B were weighted accurately with mass ratio of 70.85/51.21 and mechanically stirred for 5min to mix thoroughly. The mixture was filtered with a 400 mesh filter before using.

[0068] The specimens were prepared according to the substrate selection and pretreatment, and sample preparation methods provided in Table 1. The chromatism of the specimens were tested and the test result was presented in Table 6.

Table 6 Test results of anti-yellowing property at high temperature for example El

150°C for 1 day 150°C for 2 days

Chromatism ΔΕ Chromatism ΔΕ

El 1.15 1.36 [0069] In this example, Bayhydur XP 2759 (sulphamate modified polyisocyanate based on isophorone diisocyanate (IPDI) ) was used as the curing agent, the coating films didn't show obviously yellow after being baked at high temperature of 150°Cfor 24h, all the values of chromatism ΔΕ were below 3. That is to say, this formula was obviously better than comparison example CI and C2.

Example E2

Preparation of component A

[0070] 50.00g Baydrol A2227/1 was added into the blender. 0.10g Borchi-Gel PW25, 0.2g BYK024, 0.7g TEGO Dispers752W, 13.8g R960 and 5.45g deionized water were added slowly in turn under 1200rpm rotating speed. Then the rotating speed was accelerated to 3500rpm and kept for 25min or longer until the fineness <15μιη.ΑίΪ6Γ that, 0.6g BYK 348 was added slowly under lOOOrpm rotating speed. The mixture was stirred for 5min to finish the preparation of component A.

[0071] Component A was filtered with a 400 mesh filter and stored in a sealed container for 24 hours.

Preparation of component B

[0072] Component B wasBayhydur XP 401-70 (a kind of polyether modified polyisocyanate based on isophorone diisocyanate(IPDI)) diluted with MPA, the dilution ratio was curing agent: MPA = 3:1.

Sample preparation and testing

[0073] Component A and component B were weighted accurately with mass ratio of 70.85/33.52 and and mechanically stirred for 5min to mix thoroughly. The mixture was filtered with a 400 mesh filter before using.

[0074] According to the items that need to be tested in this example, the specimens were prepared according to the substrate selection and pretreatment, and sample preparation methods provided in Table 1. The specimens were baked at high temperature (150°C) before test and the result of chromatism was showed in Table 7.

Table 7 Test result of anti-yellowing property at high temperature for example E2

150°C for 1 day 150°C for 2 days

Chromatism ΔΕ Chromatism ΔΕ

E2 1.62 2.43 [0075] According to the test results of comparing example C I , BayhydrolA 2227/1 was optimized as water-based polyol dispersion and Bayhydur XP 401-70, the polyether modified polyisocyanate based on isophorone diisocyanate (IPDI) was used separately as curing agent in example E2. As a result, the coating films didn't show obviously yellowing after being baked at high temperature of 150°Cfor 24h, all the chromatism ΔΕ values were b

3. So example E2 was obviously better than the comparing example CI and C2. Therefore, using polyether modified polyisocyanate based on isophorone diisocyanate(IPDI) Bayhydur XP 401-70 separately played a vital role in improving the anti-yellowing property of two-component waterborne polyurethane coatings at high temperature. Example E3

Preparation of component A

[0076] 50.00g Baydrol U XP 2766 was added into the blender. 0.1 Og Borchi-Gel PW25, 0.2g BYK024, 0.7g TEGO Dispers752W, 13.8g R960 and 5.45g deionized water were added slowly in turn under 1200rpm rotating speed. Then the rotating speed was accelerated to 3500rpm and kept for 25min or longer until the fineness <15μιη. After that, 0.6g BYK 348 was added slowly under lOOOrpm rotating speed. The mixture was stirred for 5min to finish the preparation of component A.

[0077] Component A was filtered with a 400 mesh filter and stored in a sealed container for 24 hours. Preparation of component B

[0078] Component B was BayhydurXP 401-70 (a kind of polyether modified polyisocyanate based on isophorone diisocyanate(IPDI)) diluted with MPA, the dilution ratio was curing agent: MPA = 3:1.

Sample preparation and testing [0079] Component A and component B were weighted accurately with mass ratio of 70.85/33.7 and mechanically stirred for 5min to mix thoroughly. The mixture was filtered with a 400 mesh filter before using. According to the items that need to be tested in this example, the specimens were prepared based on the substrate selection and pretreatment, and sample preparation methods provided in Table 1. The specimens were baked at high temperature (150°C) before test and the result of chromatism was showed in Table 8. _

Table 8 Test result of anti-yellowing property at high temperature for example E3

[0080] According to the test results of comparing example CI , Bayhydrol U XP 2766 was optimized as water-based polyol dispersion and Bayhydur XP 401-70, the polyether modified polyisocyanate based on isophorone diisocyanate(IPDI) was used separately as curing agent in example E3. As a result, the coating films didn't show obviously yellowing after being baked at high temperature of 150°Cfor 24h, all the chromatismAE values were below 3, which were obviously better than the comparing example CI and C2. Therefore, using Bayhydur XP 401-70, the polyether modified polyisocyanate based on isophorone diisocyanate(IPDI) separately as the curing agent played an important role in improving the anti-yellowing property of two-component waterborne polyurethane coatings at high temperature.

Example E4

Preparation of component A

[0081] 40.70g Baydrol A2227/1 was added into the blender. 0.1 Og Borchi-Gel PW25, 0.2g BYK024, 0.7g TEGO Dispers752W, 13.8g R960 and 5.45g deionized water were added slowly in turn under 1200rpm rotating speed. Then the rotating speed was accelerated to

3500rpm and kept for 25min. After that, the disc dispersion plate was replaced with a specialized sanding dispersion head, and about 60g sand grinding beads were added under medium-low speed (about 800rpm). The rotating speed was accelerated to 3000 rpm and kept for 60min or longer until the fineness <15μιη. [0082] The mixture was filtered with a 100-200 mesh filter. 0.6g BYK 348,lg Ciba Irganox 1135, 3.39g Texanol and 0.50g Borchi-Gel PW25 were added slowly under lOOOrpm rotating speed and the mixture was stirred for 5min to finish the preparation of component A.

[0083] Component A was filtered with a 400 mesh filter and stored in a sealed container for 24 hours. Preparation of component B

[0084] Component B was Bayhydur XP 2759 (a kinds of sulphamate modified polyisocyanate based on isophorone diisocyanate (IPDI)) diluted with MPA, the dilution ratio was curing agent: MPA = 3:1.

Sample preparation and testing [0085] Component A and component B were weighted accurately with mass ratio of 66.15/33.30 and mechanically stirred for 5min to mix thoroughly. The mixture was filtered with a 400 mesh filter before using. According to the items that need to be tested in this example, the specimens were prepared based on the substrate selection and pretreatment, and sample preparation methods provided in Table l .The specimens were baked at high temperature

(150°C) before test and the result of chromatism was showed in Table 9.

Table 9 Test result of anti-yellowing property at high temperature for example E4

[0086] From above it can be seen that according to the test results of comparing example CI , Bayhydrol A 2227/1 was optimized as water-based polyol dispersion and Bayhydur XP 2759, the sulphamatemodified polyisocyanate based on isophorone diisocyanate (IPDI) was used separately as as the curing agent in example E4. Hindered phenolic antioxidants Irganox 1135 was added in this formula. As a result, the coating films didn't show obviously yellowing after being baked at high temperature of 150°Cfor 96h and all the chromatismAE values were below 3. Example E4 was not only superior to example CI and C2, but also better than example El .

Therefore, the addition of hindered phenolic antioxidants played a certain role in improving the anti-yellowing property of two-component waterborne polyurethane coatings at high temperature.

Example E5 Preparation of component A

[0087] 35.06g Baydrol A2227/1 and 10.52g Impranil LP RSC 1537 were added into the blender.

0.13g Borchi-Gel PW25, 0.2g BYK024, 0.7g TEGO Dispers752 W, 14.45g R960 and 5.02g deionized water were added slowly in turn under 1200rpm rotating speed. Then the rotating speed was accelerated to 3500rpm and kept for 25min. After that, the disc dispersion plate was replaced with a specialized sanding dispersion head, about 60g sand grinding beads were added under medium-low speed(about 800rpm). The rotating speed was accelerated to 3000 rpm and kept for 60min or longer until the fineness <15μιη.

[0088] The mixture was filtered with a 100-200 mesh filter. 0.6g BYK 348,lg Ciba Irganox 1135 and 3.39g Texanol were added slowly under lOOOrpm rotating speed and the mixture was stirred for 5min to finish the preparation of component A. [0089] Component A was filtered with a 400 mesh filter and stored in a sealed container for 24 hours.

Preparation of component B

[0090] Component B was Bayhydur 2759 diluted with MP A, the dilution ratio was curing agent:

MPA = 3:1.

Sample preparation and testing

[0091] Component A and component B were weighted accurately with mass ratio of 71.28/28.73 and mechanically stirred for 5min to mix thoroughly. The mixture was filtered with a 400 mesh filter before using. According to the items that need to be tested in this example, the specimens were prepared based on the substrate selection and pretreatment, and sample preparation methods provided in Table l .The coating films cured at 100°C for lhour. Test items and results of example E5 and Elwere showed in TablelO.

Table 10 Test Items and results of example E5 and example El

[0092] Compared with the formula of example El, water-based polyol dispersion BayhydrolA 2227/1 was mixed with aqueous polyurethane dispersion Impranil LP RSC in proportion of 7/3((solid content) in example E5. TablelO showed that under the premise of inconspicuous reduction in anti-yellowing property at high temperature, the flexibility of the coating film was significantly improved after being baked at high temperature. 3] To sum up, in this invention, water-based acrylic polyol dispersion and polyisocyanate based on isophorone diisocyanate were selected as film formers for preparation of two-component high-temperature resistance water-borne polyurethane coatings, which can greatly improve the anti-yellowing property at high temperature. Adding antioxidants into the formula can further improve the anti-yellowing property of two-component waterborne polyurethane coatings at high temperature. Meanwhile, the addition of the aqueous polyurethane dispersion can effectively enhance the flexibility of the coating system, achieving both good anti-yellowing property and good flexibility . Besides, the coatings have relatively longer pot life, shorter drying time, good hardness and excellent chemical resistance.

Claims

1. A two-component waterborne polyurethane coating composition, comprising:

Wherein the component (a) and (b) are of such an amount that the ratio of the NCO group to the hydroxyl group in the two-component waterborne polyurethane coating composition is 0.2: 1 to 5 : 1.

2. The two-component waterborne polyurethane coating composition according to claim 1 , wherein the hydrophilic modified isophorone diisocyanate polymer or prepolymer has a NCO content of 10-14 wt.%, based on 100% by weight of the hydrophilic modified isophorone diisocyanate polymer or prepolymer.

3. The two-component waterborne polyurethane coating composition according to claim 1 or 2, wherein the hydrophilic modified isophorone diisocyanate polymer or prepolymer is the one or more selected from the group consisting of p olyether modified isophorone diisocyanate prepolymer, sulphamate modified isophorone diisocyanate polymer or the combination thereof.

4. The two-component waterborne polyurethane coating composition according to claim 1 , wherein the polyol is the one or more selected from the group consisting of polyester modified acrylate polyols, polyester polyols or the combination thereof.

5. The two-component waterborne polyurethane coating composition according to claim 1 , wherein the two-component waterborne polyurethane coating composition further comprises :

(c) antioxidant.

6. The two-component waterborne polyurethane coating composition according to claim 5, wherein the antioxidant is the one or more selected from the group consisting of hindered phenolic antioxidant, organophosphate or the combination thereof.

7. The two-component waterborne polyurethane coating composition according to claim 5, wherein the antioxidant has an amount of 0.01 -5 wt.%, based on 100% by weight of the solid of two-component waterborne polyurethane coating composition.

8. The two-component waterborne polyurethane coating composition according to claim 1 , wherein the component (a) and (b) are of such an amount that the ratio of the NCO group to the hydroxyl group in the two-component waterborne polyurethane coating composition is

I .2: 1 to 1.5 : 1

9. The two-component waterborne polyurethane coating composition according to any one of claims 1 -8, wherein the two-component waterborne polyurethane coating composition further comprises: (d) waterborne polyurethane dispersion.

10. A coating article comprising a substrate and a coating film applied on the substrate, wherein the coating film is prepared from the two-component waterborne polyurethane coating composition according to any one of claims 1 -9.

I I . The coating article according to claim 10, wherein the coating film has a chromatism value of less than 3.0 after baking under 150°C for 1 day, determined and calculated according to GB 11186.2 and GB 11186.3 respectively.

12. A use of the two-component waterborne polyurethane coating composition according to any one of claims 1 -9 in preparing the coating article according to claim 10 or 11.