A polyurethane dispersion and a method for its preparation

Abstract

The application discloses a polyurethane dispersion and a preparation method thereof, and relates to the field of high molecular compounds. The polyurethane dispersion comprises the following components in percentage by weight: 8.0-30% of polymeric polyol, 0.1-2.0% of low molecular weight polyol, 0.1-5.0% of hyperbranched hydroxyl compound, 0.5-5.0% of ion, latent ion or non-ion compound with hydrophilicity, 10-25% of polyisocyanate, 0.5-5% of salt-forming aid, 0.1-3.0% of chain extender and 55-70% of deionized water. The paint film prepared from the polyurethane dispersion not only has good hardness, weather resistance and salt spray resistance, but also has good flexibility, and can effectively reduce cracking.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high molecular compounds, in particular to a polyurethane dispersion and a preparation method thereof. BACKGROUND

[0002] Aluminum profile is a kind of metal material widely used, in the use environment, it mainly plays the role of support or decoration. In order to prolong the service life of aluminum profile, the surface of aluminum profile is generally coated. There are many methods for coating aluminum profile, such as electrophoretic coating, powder coating and organic polymer coating.

[0003] The above coating is to provide a paint film with good weather resistance, water resistance or corrosion resistance, but the paint film prepared by the existing method generally has the problem of insufficient flexibility. The aluminum profile often has a small angle of the corner, when the flexibility of the paint film is insufficient, the paint film coated at the corner will be easy to crack.

[0004] In addition, the existing coating often uses a large amount of solvent as viscosity reducer in production, the VOCs content is high, and does not meet the requirements of environmental protection and emission reduction.

[0005] It can be seen that the prior art still needs to be improved and improved. SUMMARY

[0006] In view of the above shortcomings of the prior art, the purpose of the present application is to provide a polyurethane dispersion and a preparation method thereof, which aims to solve the technical problems of insufficient flexibility of the paint film and high VOCs in the prior art.

[0007] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0008] A polyurethane dispersion, by weight percentage, comprises the following components: 8.0% to 30% of polymeric polyol, 0.1% to 2.0% of low molecular weight polyol, 0.1% to 5.0% of hyperbranched hydroxyl compound, 0.5% to 5.0% of ion, potential ion or non-ionic compound with hydrophilicity, 10% to 25% of polyisocyanate, 0.5% to 5% of salt forming aid, 0.1% to 3.0% of chain extender and 55% to 70% of deionized water.

[0009] The polyurethane dispersion, wherein the hyperbranched hydroxyl compound is prepared from trihydroxypropane and dihydroxymethylpropionic acid with a molar mass ratio of 1:6.

[0010] The polyurethane dispersion, wherein the preparation method of the hyperbranched hydroxyl compound comprises the following steps: dissolving trimethylolpropane and dimethylolpropionic acid in a solvent, adding p-toluenesulfonic acid and a catalyst, heating to 110℃, reacting for 3-6 hours until the acid value is less than 5 mgKOH / g and does not decrease any more, removing the solvent by distillation under reduced pressure to obtain the hyperbranched hydroxyl compound.

[0011] The polyurethane dispersion, wherein the polymeric polyol comprises one or more of a polyether polyol, a polycaprolactone polyol, and a polycarbonate polyol.

[0012] The polyurethane dispersion, wherein the polymeric polyol is a polytetrahydrofuran polyol.

[0013] The polyurethane dispersion, wherein the low molecular weight polyol has a number average molecular weight of 62-500 g / mol.

[0014] The polyurethane dispersion, wherein the ionic or potentially ionic hydrophilic compound having isocyanate activity comprises at least one of a mono- or dihydroxycarboxylic acid, or a mono- or diamino sulfonic acid.

[0015] The polyurethane dispersion, wherein the polyisocyanate is an aliphatic isocyanate.

[0016] The polyurethane dispersion, wherein the salt forming aid comprises at least one of an aqueous ammonia solution, sodium hydroxide, potassium hydroxide, and a trialkyl amine having 2-3 carbon atoms.

[0017] The polyurethane dispersion, wherein the chain extender is at least one of ethylenediamine, or sodium 2-(2-aminoethylamino)ethanesulfonate.

[0018] A method for preparing a polyurethane dispersion, for preparing the polyurethane dispersion as described above, comprising the following steps:

[0019] S1. adding a polymeric polyol, a low molecular weight polyol, a hyperbranched hydroxyl compound, an ionic, potentially ionic, or non-ionic hydrophilic compound having isocyanate activity, a solvent into a reactor, heating to 60℃, and stirring;

[0020] S2. adding a polyisocyanate, and increasing the temperature of the reactor to 70℃, and stirring until the NCO content in the system reaches 1.2%-3.5%;

[0021] S3. cooling to 50℃, adding a salt forming aid, stirring for 30 min, and forming a prepolymer;

[0022] S4. The prepolymer is dispersed in water at 0 DEG C under vigorous stirring to obtain a dispersion, and the mass percentage of the prepolymer in the dispersion is controlled to be 30-45%; after the dispersion, the stirring is continued for 10 minutes;

[0023] S5. The solvent is removed by vacuum distillation to obtain the product.

[0024] Beneficial effects:

[0025] The polyurethane dispersion is prepared by combining and matching the polymeric polyol, the low-molecular-weight polyol, the hyperbranched hydroxyl compound, the hydrophilic ion, latent ion or non-ion compound and the polyisocyanate, and has excellent weather resistance, salt spray resistance and good flexibility, and the paint film formed after the paint is dried is not easy to crack.

[0026] The application further provides a preparation method of the polyurethane dispersion, which is used for preparing the polyurethane dispersion as described above, can be carried out at a lower temperature, has low energy consumption, uses less solvent, can effectively reduce the content of VOCs and achieves the purpose of energy saving and emission reduction. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The synthesis route of the hyperbranched hydroxyl compound provided by the application is shown in the figure. DETAILED DESCRIPTION

[0028] The application provides a polyurethane dispersion and a preparation method thereof, in order to make the purpose, technical scheme and effect of the application more clear and explicit, the application is further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0029] The application provides a polyurethane dispersion, which comprises the following components in percentage by weight: 8.0-30% of polymeric polyol, 0.1-2.0% of low-molecular-weight polyol, 0.1-5.0% of hyperbranched hydroxyl compound, 0.5-5.0% of hydrophilic ion, latent ion or non-ion compound, 10-25% of polyisocyanate, 0.5-5% of salt-forming aid, 0.1-3.0% of chain extender and 55-70% of deionized water.

[0030] The low-molecular-weight polymeric polyol is used to harden or branch the polymer chain;

[0031] The polymeric polyol is a soft segment in the polyurethane molecular main chain segment, and endows the resin with flexibility, adhesion and the like.

[0032] The hyperbranched hydroxyl compound has multiple hydroxyl reactive groups, which can provide more reaction crosslinking points for the synthesis of the polyurethane resin, thereby increasing the crosslinking density, and further improving the hardness and adhesion, wear resistance of the resin.

[0033] The ion, potential ion or non-ion hydrophilic compound is used to make the polyurethane molecular chain segment contain a hydrophilic segment, which can be hydrophilic after ionization, complete the dispersion process of the oil-in-water phase inversion, and make the dispersion stable and not layered.

[0034] The polyisocyanate is used as a hard segment in the polyurethane molecular main segment, which gives the resin hardness and tensile strength.

[0035] Preferably, the polyurethane dispersion is an aliphatic isocyanate. The polyisocyanate can be one or more of 4,4'-diisocyanate dicyclohexyl methane (H 12 MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI).

[0036] The number average molecular weight (Mn) of the polymeric polyol is 500-3500 g / mol.

[0037] The polymeric polyol includes one or more of a polyether polyol, a polycaprolactone polyol and a polycarbonate polyol. Among them, the polyether polyol is preferably polytetrahydrofuran polyol.

[0038] The polymeric polyol is a polyether polyol, which is less prone to hydrolysis and has better weather resistance than polycaprolactone polyol and polycarbonate polyol.

[0039] The number average molecular weight (Mn) of the low molecular weight polyol is 62-500 g / mol.

[0040] The low molecular weight polyol includes at least one of 1,4-butanediol and 1,6-hexanediol.

[0041] The ion or potential ion hydrophilic compound includes at least one of mono- or dihydroxy carboxylic acid, mono- or diaminosulfonic acid.

[0042] Preferably, the mono- or dihydroxy carboxylic acid includes at least one of dimethylol propanoic acid, dimethylol butanoic acid and their salts. The mono- or diaminosulfonic acid includes at least one of 2-(2-aminoethylamino)ethanesulfonic acid and its salts.

[0043] The salt-forming aid includes at least one of aqueous ammonia, sodium hydroxide, potassium hydroxide and trialkylamine containing 2-3 carbon atoms. The trialkylamine containing 2-3 carbon atoms includes at least one of trimethylamine, triethylamine, methyldiethylamine, tripropylamine, N-methylmorpholine, methyldiisopropylamine and diisopropylethylamine.

[0044] The hyperbranched hydroxyl compound is prepared from trihydroxypropane and dihydroxymethylpropionic acid with a molar mass ratio of 1:6. Figure 1 The synthesis route of the hyperbranched hydroxyl compound is shown in the figure, and the preparation method of the hyperbranched hydroxyl compound comprises the following steps: trihydroxymethylpropane and dihydroxymethylpropionic acid are dissolved in toluene, p-toluenesulfonic acid and a catalyst are added, the temperature is raised to 110℃, and the reaction is carried out for 3-6 hours until the acid value is less than 5mgKOH / g and does not decrease any more, and then toluene is removed by vacuum distillation to obtain the hyperbranched hydroxyl compound.

[0045] Preferably, the chain extender is at least one of ethylenediamine and 2-(2-aminoethylamino)ethanesulfonic acid sodium.

[0046] Preferably, in the preparation of the polyurethane dispersion, a catalyst can also be added, and the catalyst is an organic zinc catalyst, and the amount of the catalyst is 0.01%-1.0%.

[0047] The reaction temperature of the preparation method of the hyperbranched hydroxyl compound is low, only 110℃, which is very energy-saving and can effectively reduce carbon emissions.

[0048] The preparation method of the polyurethane dispersion comprises the following steps:

[0049] S1. The polymeric polyol, low molecular weight polyol, hyperbranched hydroxyl compound, ion, latent ion or non-ionic hydrophilic compound with isocyanate activity, solvent are added to the reactor, and heated to 60℃ and stirred;

[0050] S2. The polyisocyanate is added, and the temperature of the reactor is raised to 70℃, and stirring is carried out until the NCO content in the system reaches 1.2%-3.5%;

[0051] S3. Cooling to 50℃, adding a salt-forming aid, stirring for 30min, and forming a prepolymer;

[0052] S4. The prepolymer is dispersed in water at 0℃ under vigorous stirring to obtain a dispersion, and the mass percentage of the prepolymer in the dispersion is controlled to be 30%-45%, and after dispersion, stirring is carried out for 10min;

[0053] S5. The solvent is removed by vacuum distillation to obtain the product.

[0054] The solvent can be acetone, butanone, dimethylbenzene, toluene, cyclohexane, ethyl acetate, methoxypropyl acetate, N-methylpyrrolidone.

[0055] The synthesis of the prepolymer can be realized without using a catalyst. When needed, the reaction can also be accelerated by adding a catalyst.

[0056] S4. After the prepolymer is dispersed in water, chain extender is added during stirring, and after the chain extender is completely added, stirring is performed at 30°C for 15 min.

[0057] The application is further described below with specific examples.

[0058] Example 1

[0059] A polyurethane dispersion is prepared by the following steps:

[0060] Synthesis of hyperbranched hydroxyl compound: trimethylolpropane 13.4 g and dimethylolpropionic acid 81 g (molar ratio 1:6) are dissolved in toluene, p-toluenesulfonic acid 0.82 g and TMG634 environmentally friendly catalyst are added, the temperature is raised to 110°C, and the reaction is performed until the acid value is less than 5 mgKOH / g and no longer decreases, and then hyperbranched hydroxyl compound is obtained by distillation under reduced pressure.

[0061] Synthesis of polyurethane dispersion:

[0062] S1. The polymeric polyol, low molecular weight polyol, hyperbranched hydroxyl compound, hydrophilic ionic or potentially ionic compound, and solvent are added to the reactor, and heated to 60°C and stirred;

[0063] S2. The polyisocyanate is added, and the temperature of the reactor is raised to 70°C, and stirring is performed until the NCO content in the system reaches 1.32%;

[0064] S3. Cooling to 50°C, adding a salt-forming aid, stirring for 30 min, and forming a prepolymer;

[0065] S4. The prepolymer is dispersed in water at 0°C under vigorous stirring, and after dispersion, stirring is performed for 10 min, and chain extender is added during stirring, and after the chain extender is completely added, stirring is performed at 30°C for 15 min;

[0066] S5. The solvent is removed by vacuum distillation at 40°C to obtain the product.

[0067] In S1, the polymeric polyol is polytetrahydrofuran polyol (Mn = 1000), and the amount used is 300 g;

[0068] The low molecular weight polyol is 1,4-butanediol, and the amount used is 6 g;

[0069] The hydrophilic ionic or potentially ionic compound is dimethylolpropionic acid, and the amount used is 20 g;

[0070] The amount of hyperbranched hydroxyl compound used is 5 g;

[0071] The solvent is acetone, and the amount used is 200 g;

[0072] In S2, the polyisocyanate is 4,4'-diisocyanate dicyclohexyl methane (H 12 MDI), and the amount is 165 g;

[0073] In S3, the salt forming aid is triethylamine, and the amount is 13.7 g;

[0074] In S4, the amount of water is 870 g; and the chain extender is ethylenediamine, and the amount is 15 g, wherein the ethylenediamine is first prepared into a 60 g aqueous solution and then added.

[0075] Example 2

[0076] A polyurethane dispersion, the preparation method of which is different from that of Example 1 in that:

[0077] In S1, the polymeric polyol is polytetrahydrofuran polyol (Mn=2000), and the amount is 340 g;

[0078] The low molecular weight polyol is 1,4-butanediol, and the amount is 8 g;

[0079] The compound having hydrophilic ions or latent ions is dimethylol propionic acid, and the amount is 22 g;

[0080] The amount of the hyperbranched hydroxyl compound is 15 g;

[0081] The solvent is acetone, and the amount is 150 g;

[0082] In S2, the polyisocyanate is isophorone diisocyanate (IPDI), and the amount is 160 g; and the NCO content in the system is controlled to reach 3.2%.

[0083] In S3, the salt forming aid is triethylamine, and the amount is 16.6 g;

[0084] In S4, the amount of water is 755 g; and the chain extender is ethylenediamine, and the amount is 15 g, wherein the ethylenediamine is first prepared into a 80 g aqueous solution and then added.

[0085] Example 3

[0086] A polyurethane dispersion, the preparation method of which is different from that of Example 1 in that:

[0087] In S1, the polymeric polyol is polytetrahydrofuran polyol (Mn=1000), and the amount is 230 g;

[0088] The low molecular weight polyol is 1,4-butanediol, and the amount is 6 g;

[0089] The hydrophilic ionic or potentially ionic compound is dimethylol butanoic acid, and the amount is 17.6g;

[0090] The amount of the hyperbranched hydroxyl compound is 25g;

[0091] The solvent is acetone, and the amount is 150g;

[0092] In the S2, the polyisocyanate includes 80g of hexamethylene diisocyanate (HDI) and 70g of isophorone diisocyanate (IPDI); and the NCO content in the system is controlled to reach 3.3%.

[0093] In the S3, the salt forming aid is triethylamine, and the amount is 13.2g;

[0094] In the S4, the amount of water is 740g; and the chain extender is ethylenediamine, and the amount is 13g, wherein the ethylenediamine is first prepared into a 60g aqueous solution and then added.

[0095] Example 4

[0096] A polyurethane dispersion, the preparation method of which is different from that of Example 1.

[0097] In the S1, the polymeric polyol is polycarbonate polyol (Mn=2000), and the amount is 250g;

[0098] The hydrophilic ionic or potentially ionic compound is dimethylol butanoic acid, and the amount is 25g;

[0099] The amount of the hyperbranched hydroxyl compound is 25g;

[0100] The low molecular weight polyol is 1,6-hexanediol, and the amount is 12g;

[0101] The solvent is acetone, and the amount is 300g;

[0102] In the S2, the polyisocyanate includes 20g of hexamethylene diisocyanate (HDI) and 110g of isophorone diisocyanate (IPDI); and the NCO content in the system is controlled to reach 1.45%.

[0103] In the S3, the salt forming aid is triethylamine, and the amount is 17g;

[0104] In the S4, the amount of water is 740g; and the chain extender is 2-(2-aminoethylamino)ethanesulfonic acid sodium, and the amount is 21g, wherein the 2-(2-aminoethylamino)ethanesulfonic acid sodium is first prepared into a 60g aqueous solution and then added.

[0105] Example 5

[0106] A polyurethane dispersion, the preparation method of which is different from that of Example 1 in that:

[0107] In the S1, the polymeric polyol is a polycaprolactone polyol (Mn = 1000) and the amount used is 100 g;

[0108] The hydrophilic ionic or potentially ionic compound is dimethylol butyric acid and the amount used is 10 g;

[0109] The amount of the hyperbranched hydroxyl compound used is 60 g;

[0110] The low molecular weight polyol is 1,6-hexanediol and the amount used is 2 g;

[0111] The solvent is acetone and the amount used is 300 g;

[0112] In the S2, the polyisocyanate includes 100 g of 4,4'-diisocyanate dicyclohexyl methane (H 12 MDI) and 40 g of isophorone diisocyanate (IPDI); and the NCO content in the system is controlled to reach 2.19%;

[0113] In the S3, the salt-forming aid is triethylamine and the amount used is 7 g;

[0114] In the S4, the amount of water used is 740 g; the chain extender is ethylenediamine and the amount used is 9.6 g, wherein the ethylenediamine is first prepared into a 60 g aqueous solution and then added.

[0115] Example 6

[0116] A polyurethane dispersion, the preparation method of which is different from that of Example 1 in that:

[0117] In the S1, the polymeric polyol is a polycaprolactone polyol (Mn = 1000) and the amount used is 110 g;

[0118] The hydrophilic ionic or potentially ionic compound is dimethylol butyric acid and the amount used is 15 g;

[0119] The amount of the hyperbranched hydroxyl compound used is 50 g;

[0120] The low molecular weight polyol is 1,6-hexanediol and the amount used is 4 g

[0121] The solvent is acetone and the amount used is 300 g;

[0122] In the S2, the polyisocyanate includes 20 g of hexamethylene diisocyanate (HDI) and 100 g of isophorone diisocyanate (IPDI); and the NCO content in the system is controlled to reach 1.91%.

[0123] In the S3, the salt forming aid is triethylamine, and the amount is 11 g;

[0124] In the S4, the amount of water is 680 g; the chain extender is 2-(2-aminoethylamino) ethanesulfonic acid sodium, and the amount is 25 g, wherein the 2-(2-aminoethylamino) ethanesulfonic acid sodium is first prepared into a 60 g aqueous solution and then added.

[0125] Comparative Example 1

[0126] A polyurethane dispersion, the preparation method thereof comprising the following steps:

[0127] S1. Polymeric polyol, low molecular weight polyol, ion or potential ion compound with hydrophilic, solvent are added into the reactor, heated to 60℃, stirring;

[0128] S2. Polyisocyanate is added, and the temperature of the reactor is raised to 70℃, stirring is carried out until the NCO content in the system reaches 1.55%;

[0129] S3. Cooling to 50℃, adding salt forming aid, stirring for 30 min, forming prepolymer;

[0130] S4. The prepolymer is dispersed in water at 0℃ under vigorous stirring, after dispersion, stirring for 10 min, chain extender is added during stirring, after the chain extender is completely added, stirring at 30℃ for 15 min;

[0131] S5. The solvent is removed by vacuum distillation at 40℃ to obtain the product.

[0132] In the S1, the polymeric polyol is polytetrahydrofuran polyol (Mn = 1000), and the amount is 300 g;

[0133] The low molecular weight polyol is 1,4-butanediol, and the amount is 6 g;

[0134] The ion or potential ion compound with hydrophilic is dimethylol propionic acid, and the amount is 20 g;

[0135] The solvent is acetone, and the amount is 200 g;

[0136] In the S2, the polyisocyanate is 4,4'-diisocyanate dicyclohexyl methane (H 12 MDI), and the amount is 165 g;

[0137] In the S3, the salt forming aid is triethylamine, and the amount is 14 g;

[0138] The water is used in an amount of 840 g in the S4; the chain extender is ethylenediamine, which is used in an amount of 8 g, wherein the ethylenediamine is first prepared into a 60 g aqueous solution and then added.

[0139] Comparative Example 2

[0140] A polyurethane dispersion, the preparation method of which is different from that of Example 1 in that:

[0141] The polymeric polyol is a polycaprolactone polyol (Mn = 1000) in the S1, which is used in an amount of 100 g;

[0142] The hydrophilic ionic or potentially ionic compound is dimethylol butyric acid, which is used in an amount of 10 g;

[0143] The hyperbranched hydroxyl compound is used in an amount of 70 g;

[0144] The low-molecular-weight polyol is 1,6-hexanediol, which is used in an amount of 2 g;

[0145] The solvent is acetone, which is used in an amount of 300 g;

[0146] The polyisocyanate in the S2 includes 100 g of 4,4'-diisocyanate dicyclohexyl methane (H 12 MDI) and 40 g of isophorone diisocyanate (IPDI); and the NCO content in the system is controlled to reach 1.67%;

[0147] The salt-forming aid in the S3 is triethylamine, which is used in an amount of 7 g;

[0148] The water is used in an amount of 740 g in the S4; the chain extender is ethylenediamine, which is used in an amount of 7.5 g, wherein the ethylenediamine is first prepared into a 60 g aqueous solution and then added.

[0149] Comparative Example 3

[0150] A polyurethane dispersion, the preparation method of which is different from that of Example 1 in that:

[0151] The polyisocyanate in the S2 is an aromatic isocyanate: diphenyl methane diisocyanate (MDI); and the NCO content in the system is controlled to reach 3.3%;

[0152] When the prepolymer is dispersed in water, slagging, caking, gel foaming, and the like occur, and the dispersion cannot be obtained.

[0153] Due to the very active reactivity of the aromatic NCO groups, a large amount of polyurea and carbon dioxide is generated by the reaction of the aromatic NCO groups with water in the water dispersion process, which causes foaming, and thus leads to the occurrence of slagging and the like when the prepolymer is dispersed in water. Therefore, an aliphatic isocyanate is selected as the raw material.

[0154] The average particle size (LCS), pH value and solid content of the polyurethane dispersions of Examples 1-6 and Comparative Examples 1-2 were determined, and the corresponding test results are shown in Table 1:

[0155] Table 1

[0156] Average particle size (nm) pH Solids content Example 1 110 8 35％ Example 2 90 7.5 40％ Example 3 88 7.5 35％ Example 4 60 8 35％ Example 5 150 8 30％ Example 6 80 8 30％ Comparative Example 1 120 7.5 35％ Comparative Example 2 160 7.5 29％ Comparative Example 3 No finished product, clogging - -

[0157] The polyurethane dispersions of Examples 1-6 and Comparative Examples 1-2 were formulated into coatings and sprayed onto aluminum profiles, and then the various properties thereof were determined.

[0158] The raw materials for formulating the coatings were as follows:

[0159] Raw material Manufacturer Mass fraction / % Aqueous polyurethane dispersion Self-made 60 Aqueous pigment DIC 19 Aqueous defoamer BYK 0.2 Aqueous leveling agent BYK 0.2 Wetting agent TEGO 0.5 Dispersant TEGO 0.1 Deionized water 20

[0160] The adhesion of the coatings was tested in accordance with GB / T 9286-1998;

[0161] The impact resistance was tested in accordance with GB / T 1732-1993;

[0162] The flexibility was tested in accordance with GB / T 1731-1993;

[0163] The hardness was tested in accordance with GB / T 6739-1996;

[0164] The gloss was tested in accordance with GB / T 9754-1988;

[0165] The salt spray resistance was tested in accordance with GB / T 1771-1991;

[0166] The acid resistance and alkali resistance were tested in accordance with GB / T 9274-88;

[0167] The weather resistance was tested in accordance with GB / T 1865-1997.

[0168] The corresponding test results are shown in Table 2:

[0169] Table 2

[0170]

[0171] As can be seen from the results in Table 2, the polyurethane dispersion of Comparative Example 1 did not include a hyperbranched hydroxyl compound, and the hardness, acid resistance, alkali resistance, weather resistance and flexibility of the paint film prepared therefrom were all inferior to those of Examples 1-6. The content of the hyperbranched hydroxyl compound in the polyurethane dispersion of Comparative Example 2 was 6.5%, and the paint film prepared therefrom had good flexibility and hardness, but the acid resistance, alkali resistance and weather resistance were significantly decreased.

[0172] It can be understood that, for those ordinary skilled in the art, equivalent replacements or changes can be made according to the technical solutions and the inventive concept of the present application, and all the changes or replacements shall fall within the protection scope of the appended claims of the present application.

Claims

1. A polyurethane dispersion, characterized in that, By weight parts, consisting of: 250 parts of polycarbonate polyols, 12 parts of 1,6-hexanediol, 25 parts of hyperbranched hydroxyl compound, 25 parts of dimethylol butyric acid, 20 parts of hexamethylene diisocyanate, 110 parts of isophorone diisocyanate, 17 parts of triethylamine, 21 parts of 2- (2-aminoethylamino) sodium ethanesulfonate and 740 parts of deionized water; the hyperbranched hydroxyl compound is prepared from trimethylolpropane and dihydroxymethylpropionic acid with a molar ratio of 1:

6.

2. The polyurethane dispersion according to claim 1, characterized in that, The preparation method of the hyperbranched hydroxyl compound comprises the following steps: dissolving trimethylolpropane and dihydroxymethylpropionic acid in a solvent, adding p-toluenesulfonic acid and a catalyst, heating to 110℃, reacting for 3-6 hours until the acid value is less than 5mgKOH / g and no longer decreases, removing the solvent by reduced pressure distillation to obtain the hyperbranched hydroxyl compound.

3. A process for the preparation of a polyurethane dispersion, characterized in that, The polyurethane dispersion of claim 1 or 2, comprising the following steps: S1. Put polycarbonate polyols, 1,6-hexanediol, hyperbranched hydroxyl compound, dimethylol butyric acid, acetone into the reactor, heat to 60℃, stir; S2. Add hexamethylene diisocyanate and isophorone diisocyanate, and increase the temperature of the reactor to 70℃, stir until the NCO content in the system reaches 1.2%-3.5%; S3. Cool to 50℃, add salt-forming aid triethylamine, stir for 30min to form a prepolymer; S4. Disperse the prepolymer in water at 0℃ under vigorous stirring, after dispersion, stir for another 10min, add chain extender 2- (2-aminoethylamino) sodium ethanesulfonate while stirring, after the chain extender is completely added, stir at 30℃ for 15min; S5. Remove the solvent by vacuum distillation to obtain the product.

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