CN113831831B

CN113831831B - Waterborne polyurethane coating suitable for winter and preparation method thereof

Info

Publication number: CN113831831B
Application number: CN202111273151.0A
Authority: CN
Inventors: 朱作元
Original assignee: Jiangsu Dowill Paints Co ltd
Current assignee: Jiangsu Dowill Paints Co ltd
Priority date: 2021-10-29
Filing date: 2021-10-29
Publication date: 2022-05-17
Anticipated expiration: 2041-10-29
Also published as: CN113831831A

Abstract

The invention discloses a water-based polyurethane coating suitable for winter, which comprises the following raw material components in percentage by mass: a water-based hydroxy acrylic resin; a polyaspartic acid ester resin; water; water-oil universal dispersants; defoaming agents; white carbon black; a pigment; barium sulfate; a pH adjusting agent; a rheological aid; an emulsifier; an accelerator; an ultraviolet absorber; a cosolvent; HDI curing agent; PMA; the method comprises the following steps: 1) placing polyaspartic acid ester resin under pressure and heating; 2) adding the water-based hydroxyl acrylic resin, water, a water-oil universal dispersant and a defoaming agent into a tank, and stirring; 3) putting the accelerant into a tank; 4) adding pigment, barium sulfate and white carbon black; 5) feeding the slurry into a grinder; 6) adding polyaspartic acid ester resin into the slurry; 7) a PH regulator, a cosolvent, an ultraviolet absorbent and a rheological additive are sequentially arranged in the tank; adding PMA into the HDI curing agent while stirring, separately packaging, and introducing nitrogen. The reduction of the system viscosity is beneficial to the drying of a paint film and prevents whitening and falling off.

Description

Waterborne polyurethane coating suitable for winter and preparation method thereof

Technical Field

The invention relates to the field of paint production, in particular to a waterborne polyurethane paint suitable for winter and a preparation method thereof.

Background

With the deepening of environment-friendly society of national construction and the stricter national requirements on VOC emission, the water-based paint instead of solvent-based paint is a necessary trend. However, the water-based paint has the disadvantage of poor water resistance compared with natural water, so that the popularization of the water-based paint in a certain field is slow. After 10 months in the north, the lowest temperature can be reduced to below 10 ℃, and rainfall weather appears from time to time; in the south, the temperature is generally below 10 ℃ in winter, and rainfall is more frequent than in the north. Along with the reduction of the temperature, the reactivity of the polyurethane coating is reduced, the polyurethane coating is difficult to be cured, and in addition, the phenomena of whitening, rusting, falling off and the like easily occur due to the poor water resistance of the waterborne polyurethane coating under the condition of incomplete curing.

For small parts, the temperature can be raised by baking and the like to accelerate curing, and for large equipment such as wind power blades and steel structures, baking conditions are not available, so that the waterborne polyurethane coating is difficult to popularize and apply in the field.

Traditionally, in order to solve this problem, a drier is added to the polyurethane system to improve the reactivity. Most of the common driers are organic tin and amine driers, but the organic tin is oxidized into 4-valent tin in water and oxygen, and the drying effect is lost. The amine drier has a more obvious effect of promoting the reaction of-NCO and water while promoting the reaction of-NCO and-OH, so that the paint film has the undesirable phenomena of foaming, light loss and the like.

In the published document CN 201910809324-a new use of aqueous polyurethane, an aqueous polyurethane cooling coating and a preparation method thereof, the aqueous polyurethane cooling coating comprises the following components in parts by weight: 90-95 parts of aqueous polyurethane emulsion, 0.1-0.5 part of ammonia water, 0-1 part of color paste, 30-50 parts of filler, 0.5-0.8 part of defoaming agent, 0.5-1.0 part of dispersing agent, 0.2-0.6 part of thickening agent, 1.0-2.0 parts of flatting agent and 6-15 parts of dipropylene glycol methyl ether; the filler is a non-heat reflective filler. Although the effect of reducing the temperature can be achieved, foaming and light loss are easy to occur in the using process.

Disclosure of Invention

In order to solve the problems, the invention discloses a waterborne polyurethane coating suitable for winter and a preparation method thereof, which can reduce the viscosity of a system, facilitate the drying of a paint film and prevent whitening and falling.

The technical scheme of the invention is as follows: the waterborne polyurethane coating suitable for winter comprises the following raw material components in percentage by mass:

a main agent:

45-60 percent of water-based hydroxyl acrylic resin

5 to 10 percent of polyaspartic acid ester resin

5 to 7 percent of water

2 to 3 percent of water-oil universal dispersant

0.1 to 0.2 percent of defoaming agent

0 to 3 percent of white carbon black

5 to 20 percent of pigment

5 to 20 percent of barium sulfate

0.1 to 0.2 percent of pH regulator

0.2 to 0.5 percent of rheological additive

0.5 to 2 percent of emulsifier

0.5 to 1 percent of accelerant

0.5 percent of ultraviolet absorbent

5 to 6 percent of cosolvent

Curing agent:

60 percent of HDI curing agent

PMA 40%

A method of preparing an aqueous polyurethane coating suitable for use in winter comprising the steps of:

the main agent part:

1) placing the polyaspartic ester resin in a pressure-resistant tank with a heating device, adding an emulsifier under the stirring state, stirring within a certain time, heating, introducing nitrogen into the tank for pressurization, increasing the pressure, stopping stirring after maintaining for a period of time, reducing the pressure in the tank for deaeration, maintaining the pressure in the tank for deaeration for a certain time, cooling the emulsified polyaspartic ester resin to room temperature, and standing for later use;

2) sequentially adding the water-based hydroxyl acrylic resin, water, the water-oil universal dispersant and the defoaming agent into a tank, and stirring;

3) adding the accelerant into the tank under the stirring state, and stirring for a certain time;

4) adding the pigment, the barium sulfate and the white carbon black in sequence under a stirring state, and stirring within a certain time;

5) the slurry enters a grinder to be ground to a certain fineness;

6) adding the emulsified polyaspartic ester resin into the ground slurry;

7) sequentially stirring a pH regulator, a cosolvent, an ultraviolet absorbent and a rheological additive in the tank for a certain time;

curing agent part:

adding PMA into HDI curing agent while stirring, stirring for a certain period, separately packaging, and introducing nitrogen.

Further, the rotation speed of stirring in the step 1) is 300-500r/min, the stirring time is 10-15min, the heating temperature is controlled at 60-65 ℃, the pressure is increased to 130-150 kPa, and the pressurizing and stirring process lasts 60-70 min. The pressure in the defoaming process is reduced to 85-90kPa, and the defoaming process is maintained for 60-70 min.

Further, the stirring speed in the step 2) is 300-500 r/min.

Further, the stirring time in the step 3) is 5-10min, and the stirring rotation speed is 300-400 r/min.

Further, the stirring time in the step 4) is 10-20min, and the rotation speed is 500-600 r/min.

Further, the fineness of grinding in step 5) is 30 μm or less.

Further, the stirring time in the step 7) is 20-30min, and the stirring rotation speed is 300-500 r/min.

Further, the stirring time of the curing part is 15-20min, and the stirring speed is 300-500 r/min.

The invention has the advantages that: 1. the invention uses non-tin organic metal accelerant, in order to ensure that the accelerant can effectively contact with the resin curing agent, the emulsifier and the accelerant are co-ground with the resin; the water-oil universal dispersant is used for ensuring that the water-based resin can be effectively embedded with the accelerant, so that the catalytic efficiency of the accelerant is improved; meanwhile, the dispersant is required to effectively reduce the viscosity of the dispersion slurry and the water content of the system, the added water amount is only about 5 percent of the mass of the main agent in the construction process, and the phenomenon that a paint film is slowly dried due to low water volatilization rate in the construction process in winter is avoided; the cosolvent is a solvent with high hydrophilic volatilization rate, so that the viscosity of the system is reduced, and the water consumption in the construction process is reduced; on the other hand, the solvent with high volatilization rate is also beneficial to drying the paint film.

2. The polyaspartic ester resin is added into the system according to a certain proportion, the curing rate of the polyaspartic ester resin is less influenced by temperature, and the curing rate of the polyaspartic ester resin is mainly influenced by the structure of the polyaspartic ester resin; therefore, the proper polyaspartic ester resin is selected to ensure drying in winter, and a polyurea structure formed by the polyaspartic ester resin and isocyanate has strong water resistance, so that the bad phenomenon that a paint film turns white and falls off after being soaked in rain and water is prevented; polyurea structures themselves suffer from poor weatherability and are therefore not suitable for use alone in topcoats.

3. The polyaspartic ester resin disclosed by the invention does not have water solubility, so that the polyaspartic ester resin cannot be directly added into an aqueous system and needs to be emulsified; the conventional emulsification method is not ideal in emulsification effect through testing, is difficult to be organically combined with an aqueous system, is poor in product performance, and is easy to coarsen in the storage process; tests show that the emulsification effect is obviously improved by heating and pressurizing in the resin emulsification process, the product is still stable after being stored for 6 months, and adverse phenomena such as coarsening, layering and the like do not occur.

Detailed Description

For the purpose of enhancing understanding of the present invention, the following detailed description is given in conjunction with the accompanying drawings, which are included for the purpose of illustration only and are not intended to limit the scope of the present invention.

Example 1:

a waterborne polyurethane coating suitable for winter comprises a component A: 47% of water-based hydroxyl acrylic resin, 9% of polyaspartic acid ester resin, 3% of dispersing agent, 0.2% of defoaming agent, 2.5% of white carbon black, 15% of titanium dioxide, 0.1% of carbon black, 10% of barium sulfate, 5% of cosolvent, 0.1% of pH regulator, 0.2% of rheological additive, 1% of emulsifier, 1% of accelerator, 0.5% of ultraviolet absorbent and 5.4% of water.

And B component: HDI60% and PMA 40%.

Component a/component B =3.5/1

The component A comprises: the water-based hydroxy acrylic acid adopts quick-drying resin with the solid content of 42 percent (New Union solid material (Guangzhou) company 2125H); the polyaspartic ester resin is high in reactivity and has a secondary amino group (Shenzhen flying jun research new material, Inc. F421); the dispersant is a high molecular block polymer (BYK 185 chemical) containing pigment-philic groups; the defoaming agent is selected from organosilicon defoaming agent (TEGOFoamex 810, the best creation); the white carbon black is hydrophobic silicon dioxide (Cabot M-5) by a gas phase method; the titanium dioxide is selected from DuPont R706; the carbon black is selected from Mitsubishi MA-100; the barium sulfate is 2500 meshes of ultrafine barium sulfate (ultrafine barium sulfate of Yangzhou conglomeration gold) with the water content of less than 1 percent; the cosolvent is ethylene glycol butyl ether (DOW); the pH regulator is 2-amino-2-methyl-1-propanol (Angus AMP-95); the rheology adjuvant is low shear thickener (moderate chemical (Shanghai) Co., Ltd. WT-102); the emulsifier is nonionic emulsifier (Craine LCN 407); the ultraviolet absorbent adopts AQ-1 (Taiwan permanent photochemical); the promoter is K-KAT4205 (King chemical, USA).

And B component: the HDI is selected from 2655 isocyanurate curing agent (Corcission chemical), and the PMA is selected from Dow chemical.

The method comprises the following steps:

the main agent part:

1) putting the polyaspartic ester resin into a pressure-resistant tank with a heating device, adding an emulsifier under the stirring state, controlling the rotating speed at 300r/min, stirring for 10min, controlling the heating temperature at 60 ℃, simultaneously introducing nitrogen into the tank to pressurize, and increasing the pressure to 130kPa, wherein in the process, the stirring is continuously carried out, the rotating speed is maintained at 300r/min, the process is maintained for 70min after pressurization, then the pressure in the tank is reduced to 85kPa, the stirring is stopped for deaeration, the process is continued for 60min, and the temperature of the emulsified polyaspartic ester resin is reduced to the room temperature and is placed for standby;

2) sequentially adding the water-based hydroxyl acrylic resin, water, the water-oil universal dispersant and the defoaming agent into a tank, and starting stirring at the stirring speed of 300 r/min;

3) putting the accelerant into a tank under a stirring state, wherein the stirring time is 5min, and the stirring speed is 300 r/min;

4) adding the pigment, the barium sulfate and the white carbon black in sequence under a stirring state, wherein the stirring time is 10min and the rotating speed is 500 r/min;

5) grinding the slurry in a grinder until the fineness is 25 μm;

6) adding the emulsified polyaspartic ester resin into the ground slurry;

7) sequentially adding a pH regulator, a cosolvent, an ultraviolet absorbent and a rheological additive into the tank, stirring for 20min at a stirring speed of 300 r/min;

curing agent part:

adding PMA into the HDI curing agent while stirring, rotating at 300r/min, and stirring for 15 min. Separately, and separately filled with nitrogen.

Example 2:

a waterborne polyurethane coating suitable for winter comprises a component A: 52% of water-based hydroxyl acrylic resin, 10% of polyaspartic acid ester resin, 2% of dispersing agent, 0.1% of defoaming agent, 15% of titanium dioxide, 0.1% of carbon black, 6.5% of barium sulfate, 6% of cosolvent, 0.1% of pH regulator, 0.2% of rheological additive, 1% of emulsifier, 1% of accelerator, 0.5% of ultraviolet absorbent and 5.5% of water.

And B component: 60% of HDI and 40% of PMA.

Component a/component B =3.3/1

The component A comprises: the water-based hydroxy acrylic acid adopts quick-drying resin with the solid content of 42 percent (New Union solid material (Guangzhou) company 2125H); the polyaspartic ester resin is selected from polyaspartic ester resin with high reaction activity and a secondary amino group (Shenzhen Feiyang Jun research New Material F421); the dispersant is a high molecular block polymer (BYK 185 chemical) containing pigment-philic groups; the defoamer is selected from a silicone defoamer (TEGOFoamex 810, the Wobo); the titanium dioxide is selected from DuPont R706; the carbon black is selected from Mitsubishi MA-100; the barium sulfate is 2500 meshes of ultrafine barium sulfate (ultrafine barium sulfate of Yangzhou conglomeration gold) with the water content of less than 1 percent; the cosolvent is ethylene glycol butyl ether (DOW); the pH regulator is 2-amino-2-methyl-1-propanol (Angus AMP-95); the rheology adjuvant was a low shear thickener (modesty, chemical (shanghai) ltd WT-102); the emulsifier is nonionic emulsifier (Craine LCN 407); the ultraviolet absorbent adopts AQ-1 (Taiwan permanent photochemical); the promoter is Kat4205, King's chemical.

The method comprises the following steps:

the main agent part:

1) placing the polyaspartic ester resin in a pressure-resistant tank with a heating device, adding an emulsifier under stirring, wherein the rotating speed is 500r/min, the stirring time is 15min, the heating temperature is controlled at 65 ℃, simultaneously introducing nitrogen into the tank for pressurizing, increasing the pressure to 150kPa, continuously stirring in the process, maintaining the rotating speed at 500r/min, maintaining the process for 60min after pressurizing, then reducing the pressure in the tank to 90kPa, stopping stirring for defoaming, continuing the process for 70min, and reducing the temperature of the emulsified polyaspartic ester resin to room temperature for standby;

2) sequentially adding the water-based hydroxyl acrylic resin, water, the water-oil universal dispersant and the defoaming agent into a tank, and starting stirring at the stirring speed of 500 r/min;

3) putting the accelerant into a tank under a stirring state, wherein the stirring time is 10min, and the stirring speed is 400 r/min;

4) adding the pigment, the barium sulfate and the white carbon black in sequence under a stirring state, wherein the stirring time is 20min and the rotating speed is 600 r/min;

5) grinding the slurry in a grinder until the fineness is 20 μm;

6) adding the emulsified polyaspartic ester resin into the ground slurry;

7) sequentially adding a pH regulator, a cosolvent, an ultraviolet absorbent and a rheological additive into the tank, stirring for 30min at a stirring speed of 500 r/min;

curing agent part:

adding PMA into the HDI curing agent while stirring, rotating at 500r/min, and stirring for 20 min. Separately, and separately filled with nitrogen.

Example 3:

a waterborne polyurethane coating suitable for winter comprises a component A: 48% of water-based hydroxyl acrylic resin A, 7% of polyaspartic acid ester resin, 3% of dispersing agent, 0.2% of defoaming agent, 2% of white carbon black, 6% of titanium dioxide, 3% of pigment yellow, 15.5% of barium sulfate, 6% of cosolvent, 0.1% of PH regulator, 0.2% of rheological additive, 1% of emulsifier, 0.7% of accelerant, 0.5% of ultraviolet absorbent and 6.8% of water.

And B component: 60% of HDI and 40% of PMA.

Component a/component B =3.5/1

And (2) component A: the water-based hydroxy acrylic acid adopts quick-drying resin with the solid content of 40% (2 AH0501W of Fushan Gaoming and chemical Co., Ltd.); the polyaspartic ester resin is high in reactivity and has a secondary amino group (Shenzhen flying jun research new material, Inc. F421); the dispersant is a high molecular polyurethane dispersant (Pickering chemical DISPBYK 2013) containing pigment affinity groups; the defoaming agent is an organic silicon defoaming agent (ByK 024 Germany); the white carbon black is hydrophobic silicon dioxide (Cabot M-5) by a gas phase method; the titanium dioxide is selected from DuPont R706; the pigment yellow is PY139 (pigment yellow SY3C of Nike chemical engineering (Shanghai) Co., Ltd.); the barium sulfate is 2500 meshes of ultrafine barium sulfate (ultrafine barium sulfate of Yangzhou conglomeration gold) with the water content of less than 1 percent; the cosolvent is ethylene glycol butyl ether (DOW); the pH regulator is 2-amino-2-methyl-1-propanol (Angus AMP-95); the rheological aid is low shear thickening agent (Basff chemical Rheovis 1191); the emulsifier is nonionic emulsifier (Craine LCN 407); the ultraviolet absorbent adopts AQ-1 (Taiwan permanent photochemical); the promoter is American King's chemical K-KAT6212

And B component: 2655 isocyanurate curing agent (Corsai chemical) is used for HDI, and Dow chemical is used for PMA.

The method comprises the following steps:

the main agent part:

1) placing the polyaspartic ester resin in a pressure-resistant tank with a heating device, adding an emulsifier under stirring, wherein the rotating speed is 400r/min, the stirring time is 12min, the heating temperature is controlled at62 ℃, simultaneously introducing nitrogen into the tank for pressurizing, increasing the pressure to 140kPa, continuously stirring in the process, maintaining the rotating speed at 400r/min, maintaining the process for 60min after pressurizing, then reducing the pressure in the tank to 85kPa, stopping stirring for defoaming, continuing the process for 70min, and reducing the temperature of the emulsified polyaspartic ester resin to room temperature for standby;

2) sequentially adding the water-based hydroxyl acrylic resin, water, the water-oil universal dispersant and the defoaming agent into a tank, and starting stirring at the stirring speed of 400 r/min;

3) putting the accelerant into a tank under a stirring state, wherein the stirring time is 6min, and the stirring speed is 350 r/min;

4) adding the pigment, the barium sulfate and the white carbon black in sequence under a stirring state, wherein the stirring time is 15min, and the rotating speed is 550 r/min;

5) grinding the slurry in a grinder until the fineness is 25 μm;

6) adding the emulsified polyaspartic ester resin into the ground slurry;

7) sequentially adding a pH regulator, a cosolvent, an ultraviolet absorbent and a rheological additive into the tank, stirring for 25min at a stirring speed of 400 r/min;

curing agent part:

adding PMA into the HDI curing agent while stirring, rotating at 400r/min, and stirring for 18 min. Separately, and separately filled with nitrogen.

Example 4:

a waterborne polyurethane coating suitable for winter comprises a component A: 50% of water-based hydroxyl acrylic resin A, 10% of polyaspartic acid ester resin, 2.5% of dispersing agent, 0.2% of defoaming agent, 7% of titanium dioxide, 3% of pigment yellow, 12.5% of barium sulfate, 6% of cosolvent, 0.1% of pH regulator, 0.2% of rheological additive, 1% of emulsifier, 0.8% of accelerator, 0.5% of ultraviolet absorbent and 6.2% of water.

And B component: 60% of HDI and 40% of PMA.

Fraction a/fraction B = 2.5/1.

The component A comprises: the water-based hydroxy acrylic acid adopts quick-drying resin with the solid content of 40% (2 AH0501W of Fushan Gaoming and chemical Co., Ltd.); the polyaspartic ester resin is high in reactivity and has a secondary amino group (Shenzhen flying jun research new material, Inc. F421); the dispersant is a high molecular polyurethane dispersant (Pickering chemical DISPBYK 2013) containing pigment affinity groups; the defoaming agent is an organic silicon defoaming agent (ByK 024 Germany); the titanium dioxide is selected from DuPont R706; the pigment yellow is PY139 (pigment yellow SY3C of Nike chemical engineering (Shanghai) Co., Ltd.); the barium sulfate is 2500 meshes of ultrafine barium sulfate (ultrafine barium sulfate of Yangzhou conglomeration gold) with the water content of less than 1 percent; the cosolvent is ethylene glycol butyl ether (DOW); the pH regulator is 2-amino-2-methyl-1-propanol (Angus AMP-95); the rheological aid is low shear thickening agent (Basff chemical Rheovis 1191); the emulsifier is nonionic emulsifier (Craine LCN 407); the ultraviolet absorbent adopts AQ-1 (Taiwan permanent photochemical); the promoter is American King's chemical K-KAT 6212.

And the component B comprises: the HDI is selected from 2655 isocyanurate curing agent (Corcission chemical), and the PMA is selected from Dow chemical.

The method comprises the following steps:

the main agent part:

1) placing the polyaspartic ester resin in a pressure-resistant tank with a heating device, adding an emulsifier under stirring, wherein the rotating speed is 380r/min, the stirring time is 15min, the heating temperature is controlled at 65 ℃, simultaneously introducing nitrogen into the tank for pressurizing, increasing the pressure to 140kPa, continuously stirring in the process, maintaining the rotating speed at 380r/min, maintaining the process for 60min after pressurizing, then reducing the pressure in the tank to 85kPa, stopping stirring for defoaming, continuing the process for 70min, and reducing the temperature of the emulsified polyaspartic ester resin to room temperature for standby;

3) putting the accelerant into a tank under a stirring state, wherein the stirring time is 8min, and the stirring speed is 350 r/min;

5) grinding the slurry in a grinder until the fineness is 25 μm;

6) adding the emulsified polyaspartic ester resin into the ground slurry;

7) sequentially adding a pH regulator, a cosolvent, an ultraviolet absorbent and a rheological additive into the tank, stirring for 25min at the stirring speed of 350 r/min;

curing agent part:

Comparative example

A main agent:

curing agent

Proportioning: main agent/curing agent =3.5/1

Test data

Storage stability test:

according to the test results, compared with the traditional waterborne polyurethane coating, the waterborne polyurethane coating has the advantages that the drying rate is obviously improved in a low-temperature environment, the initial water resistance is excellent in a low-temperature environment in winter, and the waterborne polyurethane coating can be used in winter. Experiments prove that the product of the invention has stable performance and can be stored for more than 6 months.

Claims

1. The water-based polyurethane coating suitable for winter is characterized by comprising the following raw material components in percentage by mass:

a main agent:

45-60 percent of water-based hydroxyl acrylic resin

5 to 10 percent of polyaspartic acid ester resin

5 to 7 percent of water

2 to 3 percent of water-oil universal dispersant

0.1 to 0.2 percent of defoaming agent

0 to 3 percent of white carbon black

5 to 20 percent of pigment

5 to 20 percent of barium sulfate

0.1 to 0.2 percent of pH regulator

0.2 to 0.5 percent of rheological additive

0.5 to 2 percent of emulsifier

0.5 to 1 percent of accelerant

0.5 percent of ultraviolet absorbent

5 to 6 percent of cosolvent

Curing agent:

60 percent of HDI curing agent

PMA40％

The method for preparing the waterborne polyurethane coating suitable for the winter comprises the following steps:

the main agent part:

3) adding the accelerant into the tank in a stirring state, and stirring within a certain time;

5) the slurry enters a grinder to be ground to a certain fineness;

6) adding the emulsified polyaspartic ester resin into the ground slurry;

7) stirring the pH regulator, the cosolvent, the ultraviolet absorbent and the rheological additive in the tank in sequence for a certain time;

curing agent part:

adding PMA into HDI curing agent while stirring, separately packaging, and introducing nitrogen.

2. The waterborne polyurethane coating suitable for winter season as claimed in claim 1, wherein: the stirring speed in the step 1) is 300-500r/min, the stirring time is 10-15min, the heating temperature is controlled at 60-65 ℃, the pressure is increased to 130-150 kPa, and the pressurizing and stirring process lasts 60-70 min.

3. The waterborne polyurethane coating suitable for winter season as claimed in claim 1, wherein: and (3) reducing the pressure in the defoaming process in the step 1) to 85-90kPa, and maintaining the defoaming process for 60-70 min.

4. The waterborne polyurethane coating suitable for use in winter as claimed in claim 1, wherein: the stirring speed in the step 2) is 300-500 r/min.

5. The waterborne polyurethane coating suitable for winter season as claimed in claim 1, wherein: the stirring time in the step 3) is 5-10min, and the stirring speed is 300-400 r/min.

6. The waterborne polyurethane coating suitable for winter season as claimed in claim 1, wherein: the stirring time in the step 4) is 10-20min, and the rotation speed is 500-600 r/min.

7. The waterborne polyurethane coating suitable for winter season as claimed in claim 1, wherein: the grinding fineness in the step 5) is below 30 mu m.

8. The waterborne polyurethane coating suitable for winter season as claimed in claim 1, wherein: the stirring time in the step 7) is 20-30min, and the stirring rotating speed is 300-500 r/min.

9. The waterborne polyurethane coating suitable for winter season as claimed in claim 1, wherein: the stirring time of the curing agent part is 15-20min, and the stirring speed is 300-500 r/min.