Uvioresistant modified waterborne polyurethane coating and preparation method thereof

Abstract

The application discloses a kind of UV-resistant modified water-based polyurethane coating and preparation method thereof, belong to coating preparation technical field.Nano titanium dioxide, composite dispersant and buffer are mixed and dispersed to obtain mixed emulsion;Mixed emulsion and modified levodopa are mixed to obtain composite dispersion liquid;Composite dispersion liquid, polyurethane emulsion, diacetone acrylamide and azo catalyst are mixed to obtain modified polyurethane emulsion;Modified polyurethane emulsion and adipic acid dihydrazide are mixed to obtain modified water-based polyurethane coating.Modified water-based polyurethane coating prepared by the application, the protective coating obtained after curing has good anti-ultraviolet performance, adhesion and self-cleaning performance.

Description

Technical Field

[0001] This invention belongs to the field of coating preparation technology, specifically relating to a UV-resistant modified waterborne polyurethane coating and its preparation method. Background Technology

[0002] Polymer coatings are polymer-based coatings widely used in construction, automotive, industrial equipment, furniture, and other fields. Polymer coatings hold an important position in the modern coatings market. Based on different polymer types, polymer coatings can be divided into several categories, including acrylic coatings, polyurethane coatings, epoxy coatings, and fluorocarbon coatings. Acrylic coatings are based on acrylic resins and have good weather resistance, adhesion, and transparency. They are mainly used in building exteriors, furniture, and automobiles. Their advantages include fast drying speed and easy application, but their chemical resistance is relatively weak, and they are susceptible to corrosion from certain solvents. Polyurethane coatings are based on polyurethane resins and have excellent abrasion resistance. They are widely used in floor coatings, automotive coatings, and wood coatings. Their disadvantages include longer curing time and poorer weather resistance. Epoxy coatings are based on epoxy resins and have very good adhesion and chemical resistance. They are widely used in industrial equipment, ship corrosion protection, and floor coatings. Their disadvantages include poor weather resistance; prolonged exposure to sunlight can cause yellowing and loss of gloss. Fluorocarbon coatings are based on fluoropolymers and have excellent weather resistance and stain resistance, making them suitable for exterior wall coatings of high-end buildings. Although fluorocarbon coatings have superior performance, they are expensive and difficult to apply.

[0003] To improve the environmental friendliness of coatings, water-based coatings, which use water as a solvent, have lower volatile organic compound (VOC) content compared to organic solvent-based coatings, and are gradually gaining market favor. Water-based polyurethane coatings, due to their good environmental friendliness, high abrasion resistance, and chemical resistance, are increasingly being used in various fields. However, water-based polyurethane coatings are prone to aging and degradation under light and heat, especially ultraviolet light, which can damage their protective properties.

[0004] Patent CN109897520A discloses a waterborne acrylic polyurethane coating for modified vehicles and its preparation method. This invention improves the acid resistance, alkali resistance and UV resistance of the waterborne acrylic polyurethane coating by adding titanium dioxide to modify nano-graphene in the ingredients and through the synergistic effect between nano-titanium dioxide and nano-graphene.

[0005] Patent CN118374220A discloses a kind of high adhesion weatherable water-based polyurethane coating and its preparation method, the invention uses hydrophilic MDT silicone resin modified polyester polyol, by the branching effect of T chain and using good hydrophilic polyether end-capping, it contains a large number of branched and end-capped hydrophilic polyether chain, improve the water solubility of silicone resin and the compatibility of polyether polyol and polyisocyanate curing agent, then by further copolymerization and curing reaction, make polysiloxane and polyurethane produce chemical connection, realize the effective modification of polysiloxane to water-based polyurethane system, and then make the water-based polyurethane coating prepared has good adhesion, strength and weatherability.

[0006] Patent CN104727150A discloses a kind of waterproof moisture-permeable antibacterial ultraviolet water-based polyurethane material and its preparation method, the invention is prepared by preparing a kind of silver-loaded nanometer titanium dioxide, then mixed with waterproof moisture-permeable polyurethane resin to obtain a kind of water-based polyurethane material with good ultraviolet resistance.

[0007] Titanium dioxide is a kind of inorganic oxide with good ultraviolet resistance, which realizes ultraviolet resistance by scattering and absorption. However, due to the small particle size and large specific surface area of titanium dioxide, it is easy to agglomerate, and the agglomeration is easy to form stress concentration points in the cured coating protective layer, which reduces the mechanical properties of the coating and causes the protective layer to crack and fall off. Therefore, it is of great significance to study a kind of modified titanium dioxide for preparing a kind of water-based polyurethane coating with good ultraviolet resistance for improving the performance and service life of the coating in outdoor applications. SUMMARY

[0008] According to the deficiencies of the prior art, the modified polyurethane emulsion is obtained by mixing and reacting the polyurethane emulsion, the composite dispersion liquid and the diacetone acrylamide; the modified water-based polyurethane coating is formed by mixing the modified polyurethane emulsion and the adipic acid hexahydrate hydrazine, thereby solving the technical problems proposed in the background art. Specifically, the technical scheme of the present application includes the following contents:

[0009] One of the purposes of the present application is to provide a preparation method of a modified water-based polyurethane coating with ultraviolet resistance, which comprises the following steps:

[0010] The nano-titanium dioxide, the composite dispersant and the buffer are mixed and dispersed according to a weight ratio of 3-5:0.5-0.6:80-90 to obtain a mixed emulsion;

[0011] After the mixed emulsion and the modified levodopa are mixed according to a weight ratio of 500-600:5-7, a composite dispersion liquid is obtained by reacting at 30°C for 8-10 hours;

[0012] The modified polyurethane emulsion is obtained by mixing the composite dispersant, the polyurethane emulsion, the diacetone acrylamide and the azo catalyst in a weight ratio of 15-17:20-30:2-4:0.1-0.2, heating to 60-70 DEG C and reacting for 4-6 hours.

[0013] The modified water-based polyurethane coating is obtained by mixing the modified polyurethane emulsion and the adipic acid dihydrazide.

[0014] Further, the nano-titanium dioxide has a particle size of 20-30 nm.

[0015] Further, the composite dispersant is composed of sodium dodecyl benzene sulfonate and triton X-100 in a weight ratio of 1:2.

[0016] Further, the buffer solution comprises a Tris-hydrochloric acid buffer solution with a pH of 8.5-9.0.

[0017] Further, the preparation method of the modified levodopa comprises the following steps:

[0018] The modified levodopa is obtained by mixing levodopa, an enol compound, EDC hydrochloride and 4-dimethylamino pyridine in a molar ratio of 1:2-3:1.5:0.4 and reacting at 25 DEG C for 24-30 hours.

[0019] Further, the enol compound comprises 3-buten-1-ol, and the enol compound is used to introduce the nano-titanium dioxide wrapped by the modified levodopa through the oxidative self-polymerization into the polyurethane structure in a polymer grafting manner.

[0020] Further, the preparation method of the polyurethane emulsion comprises the following steps:

[0021] The polyurethane prepolymer mixed solution is obtained by mixing diisocyanate, mixed dihydric alcohol, chain extender and dibutyl tin dilaurate in a weight ratio of 1:2.3-2.5:0.4-0.6:0.007, heating to 70-80 DEG C and reacting for 2-3 hours;

[0022] The polyurethane emulsion is obtained by mixing the polyurethane prepolymer mixed solution and hydroxyl polydimethyl siloxane in a weight ratio of 1:0.1-0.2, reacting at 70-80 DEG C for 1-1.5 hours, then cooling to 40 DEG C, adding triethylamine and reacting for 25-30 minutes, and finally adding deionized water and stirring.

[0023] Further, the diisocyanate comprises p-phenylene diisocyanate or toluene diisocyanate.

[0024] Further, the mixed dihydric alcohol is composed of 1,6-hexanediol and 1,4-butanediol in a weight ratio of 1:1, and the 1,4-butanediol in the mixed dihydric alcohol functions to graft the modified L-dopa oxidation self-polymerization-wrapped nano-titanium dioxide and the bis-acetone propenamide in the composite dispersion liquid into the polyurethane through a polymerization reaction of a carbon-carbon double bond.

[0025] Further, the chain extender comprises dimethylol propionic acid.

[0026] Further, the triethylamine is used in an amount of 0.8 times to 1 times the weight of the chain extender.

[0027] Further, the deionized water is used in an amount of 8 times to 9 times the weight of the polyurethane prepolymer mixed solution.

[0028] Further, the azo catalyst comprises azobis-isobutyronitrile.

[0029] Further, the adipic acid dihydrazide is used in an amount of 0.6 times to 0.8 times the weight of the bis-acetone propenamide.

[0030] The second object of the present application provides a modified water-based polyurethane coating prepared by a preparation method of a modified water-based polyurethane coating resistant to ultraviolet rays.

[0031] Compared with the prior art, the present application has the following advantages:

[0032] The application firstly obtains a mixed emulsion by treating nano-titanium dioxide through a composite dispersant and then ultrasonic dispersion, and then modifies levodopa, esterifies 3-buten-1-ol through the alcohol hydroxyl group and the carboxyl group on the levodopa, introduces a carbon-carbon double bond into the structure of levodopa, and further obtains modified levodopa. The modified levodopa and the mixed emulsion are stirred and reacted under weak alkaline conditions. The modified levodopa is wrapped around the nano-titanium dioxide in the mixed emulsion by means of oxidative self-polymerization to form a poly-levodopa structure, which weakens the agglomeration of the nano-titanium dioxide, and further obtains a composite dispersion liquid. Then, diisocyanate, mixed diol and chain extender are used as raw materials for preparing polyurethane, and a polyurethane prepolymer mixed liquid is generated under the catalysis of dibutyltin dilaurate. Subsequently, a hydroxyl-terminated polydimethylsiloxane is used for end-capping reaction. The hydroxyl-terminated polydimethylsiloxane has low surface energy and cooperates with the photocatalytic anti-fouling performance of the nano-titanium dioxide to improve the self-cleaning performance of the protective layer after the coating is cured. After neutralization treatment by triethylamine and then high-speed stirring and dispersion with water, a polyurethane emulsion is obtained. After mixing the polyurethane emulsion, the composite dispersion liquid and diacetone acrylamide, the nano-titanium dioxide wrapped by the modified levodopa in the composite dispersion liquid and the diacetone acrylamide are grafted into the polyurethane containing a carbon-carbon double bond through a carbon-carbon double bond polymerization reaction under the catalysis of an azo initiator, to obtain a modified polyurethane emulsion. The modified polyurethane emulsion and adipic acid dihydrazide are mixed to form a modified water-based polyurethane coating. The adhesion performance of the modified water-based polyurethane coating is improved through the synergistic cooperation of the poly-levodopa and ketone hydrazine crosslinking. The prepared modified water-based polyurethane coating not only has good ultraviolet resistance, but also has good mechanical properties and self-cleaning function of the cured protective coating. DETAILED DESCRIPTION

[0033] The technical solutions of the present application will be described clearly and completely through the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0034] Unless otherwise specified, the raw materials and reagents used in the present application are commercially available or can be prepared by known methods.

[0035] The hydroxyl polydimethylsiloxane is purchased from Jiangsu Keying New Material Co., Ltd.

[0036] Preparation Example 1:

[0037] The preparation method of the modified levodopa specifically includes the following processes:

[0038] Take 0.1 mol of levodopa, 0.2 mol of 3-buten-1-ol, 0.15 mol of EDC hydrochloride and 0.04 mol of 4-dimethylaminopyridine together into a flask, then add 150 mL of anhydrous acetone, then place the flask in an ultrasonic cleaner for ultrasonic dispersion mixing treatment at a power of 200 W until completely dispersed and uniform, then introduce nitrogen into the flask as a protective gas, then place it in a temperature environment of 25°C, and stir at a speed of 400 r / min for 24 h. After the reaction is completed, evaporate under reduced pressure, then extract with ethyl acetate to obtain an organic phase, wash the organic phase with deionized water until the washing water is neutral, then remove the ethyl acetate by rotary evaporation and dry at low temperature to obtain modified levodopa.

[0039] Preparation Example 2:

[0040] The preparation method of modified levodopa specifically includes the following processes:

[0041] Take 0.1 mol of levodopa, 0.2 mol of 3-buten-1-ol, 0.15 mol of EDC hydrochloride and 0.04 mol of 4-dimethylaminopyridine together into a flask, then add 150 mL of anhydrous acetone, then place the flask in an ultrasonic cleaner for ultrasonic dispersion mixing treatment at a power of 200 W until completely dispersed and uniform, then introduce nitrogen into the flask as a protective gas, then place it in a temperature environment of 25°C, and stir at a speed of 400 r / min for 24 h. After the reaction is completed, evaporate under reduced pressure, then extract with ethyl acetate to obtain an organic phase, wash the organic phase with deionized water until the washing water is neutral, then remove the ethyl acetate by rotary evaporation and dry at low temperature to obtain modified levodopa.

[0042] Preparation Example 3:

[0043] The preparation method of modified levodopa specifically includes the following processes:

[0044] Take 0.1 mol of levodopa, 0.2 mol of 3-buten-1-ol, 0.15 mol of EDC hydrochloride and 0.04 mol of 4-dimethylaminopyridine together into a flask, then add 150 mL of anhydrous acetone, then place the flask in an ultrasonic cleaner for ultrasonic dispersion mixing treatment at a power of 200 W until completely dispersed and uniform, then introduce nitrogen into the flask as a protective gas, then place it in a temperature environment of 25°C, and stir at a speed of 400 r / min for 24 h. After the reaction is completed, evaporate under reduced pressure, then extract with ethyl acetate to obtain an organic phase, wash the organic phase with deionized water until the washing water is neutral, then remove the ethyl acetate by rotary evaporation and dry at low temperature to obtain modified levodopa.

[0045] Preparation Example 4:

[0046] The preparation method of the polyurethane emulsion specifically includes the following processes:

[0047] 10 parts by weight of p-phenylene diisocyanate, 23 parts by weight of mixed diols (consisting of 1,6-hexanediol and 1,4-butanediol in a weight ratio of 1:1) and 4 parts by weight of chain extender dimethylol propionic acid are weighed into a reactor, and then 0.07 parts by weight of dibutyl tin dilaurate is added. At this time, the reactor is heated to 70°C and timed reaction is carried out for 2 hours. After the reaction is completed, the polyurethane prepolymer mixture obtained is kept warm, and then 0.1 times the weight of the polyurethane prepolymer mixture of hydroxyl polydimethylsiloxane is added as an end-capping agent and the reaction is continued at 70°C for 1 hour. After the reaction is completed, the temperature of the reactor is reduced to 40°C, and then 0.8 times the weight of dimethylol propionic acid of triethylamine is added as a salting agent for neutralization reaction for 25 minutes. After the neutralization reaction is completed, 8 times the weight of the polyurethane prepolymer mixture of deionized water is added, and emulsification treatment is carried out at a high stirring speed of 5000 r / min for 30 minutes to obtain a polyurethane emulsion.

[0048] Preparation Example 5:

[0049] The preparation method of the polyurethane emulsion specifically includes the following processes:

[0050] 10 parts by weight of p-phenylene diisocyanate, 23 parts by weight of mixed diols (consisting of 1,6-hexanediol and 1,4-butanediol in a weight ratio of 1:1) and 4 parts by weight of chain extender dimethylol propionic acid are weighed into a reactor, and then 0.07 parts by weight of dibutyl tin dilaurate is added. At this time, the reactor is heated to 70°C and timed reaction is carried out for 2 hours. After the reaction is completed, the polyurethane prepolymer mixture obtained is kept warm, and then 0.1 times the weight of the polyurethane prepolymer mixture of hydroxyl polydimethylsiloxane is added as an end-capping agent and the reaction is continued at 70°C for 1 hour. After the reaction is completed, the temperature of the reactor is reduced to 40°C, and then 0.8 times the weight of dimethylol propionic acid of triethylamine is added as a salting agent for neutralization reaction for 25 minutes. After the neutralization reaction is completed, 8 times the weight of the polyurethane prepolymer mixture of deionized water is added, and emulsification treatment is carried out at a high stirring speed of 5000 r / min for 30 minutes to obtain a polyurethane emulsion.

[0051] Preparation Example 6:

[0052] The preparation method of the polyurethane emulsion specifically includes the following processes:

[0053] Take 10 parts by weight of toluene diisocyanate, 25 parts by weight of mixed diols (consisting of 1,6-hexanediol and 1,4-butanediol in a weight ratio of 1:1) and 6 parts by weight of chain extender dimethylol propionic acid into the reactor, then add 0.07 parts by weight of dibutyl tin dilaurate, at this time the reactor is heated to 80°C for 3h. After the reaction is completed, the polyurethane prepolymer mixed solution is kept warm, at this time 0.2 times the weight of the polyurethane prepolymer mixed solution of hydroxy polydimethylsiloxane is added as a capping agent and the reaction is continued at 80°C for 1.5h. After the reaction is completed, the temperature of the reactor is reduced to 40°C, at this time 1 times the weight of dimethylol propionic acid of triethylamine is added as a salting agent for neutralization reaction for 30min. After the neutralization reaction is completed, 9 times the weight of the polyurethane prepolymer mixed solution of deionized water is added, and emulsified at a high stirring speed of 5000r / min for 30min to obtain a polyurethane emulsion.

[0054] Preparation Example 7:

[0055] The preparation method of the polyurethane emulsion specifically includes the following process:

[0056] The 1,4-butanediol in the mixed diols in Preparation Example 6 is replaced with 1,4-butanediol, and the rest of the preparation process remains the same as Preparation Example 6.

[0057] Preparation Example 8:

[0058] The preparation method of the polyurethane emulsion specifically includes the following process:

[0059] The toluene diisocyanate in Preparation Example 6 is replaced with hexamethylene diisocyanate, and the rest of the preparation process remains the same as Preparation Example 6.

[0060] Preparation Example 9:

[0061] The preparation method of the polyurethane emulsion specifically includes the following process:

[0062] The 10 parts by weight of toluene diisocyanate in Preparation Example 6 is increased to 20 parts by weight, and the rest of the preparation process remains the same as Preparation Example 6.

[0063] Preparation Example 10:

[0064] The preparation method of the polyurethane emulsion specifically includes the following process:

[0065] The hydroxy polydimethylsiloxane in Preparation Example 6 is replaced with phenol, and the rest of the preparation process remains the same as Preparation Example 6.

[0066] Preparation Example 11:

[0067] The preparation method of the polyurethane emulsion specifically includes the following process:

[0068] The weight of the hydroxyl polydimethylsiloxane is increased to 1 times the weight of the 0.2 times polyurethane prepolymer mixed solution in Preparation Example 6, and the remaining preparation process is consistent with that of Preparation Example 6.

[0069] Example 1:

[0070] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet rays, specifically comprising the following processes:

[0071] 30 parts by weight of nano-titanium dioxide with a particle size of 20 nm, 5 parts by weight of a composite dispersant (composed of sodium dodecyl benzene sulfonate: Triton X-100 according to a weight ratio of 1:2), and 800 parts by weight of Tris-hydrochloric acid buffer with a pH of 8.5 were weighed and added to a container, and then mixed and dispersed by ultrasonic power of 300 W for 15 min to obtain a mixed emulsion;

[0072] Subsequently, 500 parts by weight of the mixed emulsion and 5 parts by weight of the modified levodopa obtained in Preparation Example 1 were mixed, and then placed in a water bath at 30°C, and stirred at a speed of 400 r / min for 8 h to obtain a composite dispersion liquid; an appropriate amount of the composite dispersion liquid was measured by a laser particle size instrument, and the average particle size of the particles wrapped in the composite dispersion liquid was 265.2 nm; the surface tension of the composite dispersion liquid was measured by a surface tension instrument, and the surface tension was 32.1 mN / m, and no demulsification occurred;

[0073] 15 parts by weight of the composite dispersion liquid, 20 parts by weight of the polyurethane emulsion obtained in Preparation Example 4, 2 parts by weight of diacetone acrylamide, and 0.1 part by weight of azobisisobutyronitrile were weighed and added to a reactor, and then nitrogen was introduced to replace the air in the reactor as a protective gas, and then the reactor was heated to 60°C for timed reaction for 4 h. After cooling to room temperature, 0.6 times the weight of diacetone acrylamide was added to the obtained modified polyurethane emulsion, mixed and stirred, and the pH was adjusted to 7.0 to obtain a modified waterborne polyurethane coating.

[0074] Example 2:

[0075] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet rays, specifically comprising the following processes:

[0076] 40 parts by weight of nano-titanium dioxide with a particle size of 30 nm, 5.5 parts by weight of a composite dispersant (composed of sodium dodecyl benzene sulfonate: Triton X-100 according to a weight ratio of 1:2), and 850 parts by weight of Tris-hydrochloric acid buffer with a pH of 8.8 were weighed and added to a container, and then mixed and dispersed by ultrasonic power of 300 W for 15 min to obtain a mixed emulsion;

[0077] Subsequently, 550 parts by weight of the mixed emulsion and 6 parts by weight of the modified levodopa obtained in Preparation Example 2 were mixed, and then placed in a water bath at 30°C and stirred at a rotation speed of 400 r / min for 9 h to obtain a composite dispersion liquid; an appropriate amount of the composite dispersion liquid was taken and measured by a laser particle size instrument to obtain the average particle size of the particles wrapped in the composite dispersion liquid, which was 247.8 nm; and a surface tension instrument was used to measure the surface tension of the composite dispersion liquid, which was 28.3 mN / m, and no demulsification occurred;

[0078] Subsequently, 16 parts by weight of the composite dispersion liquid, 25 parts by weight of the polyurethane emulsion obtained in Preparation Example 5, 3 parts by weight of diacetone acrylamide and 0.15 parts by weight of azobisisobutyronitrile were added into a reactor, and then nitrogen was introduced into the reactor to replace the air therein as a protective gas, and then the reactor was heated to 65°C and reacted for 5 h. After cooling to room temperature, 0.7 times the weight of adipic acid dihydrazide of the diacetone acrylamide was added into the obtained modified polyurethane emulsion, and mixed and stirred to adjust the pH to 7.0 to obtain a modified water-based polyurethane coating.

[0079] Example 3:

[0080] A preparation method of a modified water-based polyurethane coating resistant to ultraviolet rays, specifically comprising the following processes:

[0081] Subsequently, 50 parts by weight of nano-titanium dioxide with a particle size of 30 nm, 6 parts by weight of a composite dispersant (composed of sodium dodecyl benzene sulfonate and triton X-100 at a weight ratio of 1:2) and 900 parts by weight of Tris-hydrochloric acid buffer solution with a pH of 9.0 were added into a container, and then mixed and dispersed by ultrasonic power of 400 W for 20 min to obtain a mixed emulsion;

[0082] Subsequently, 600 parts by weight of the mixed emulsion and 7 parts by weight of the modified levodopa obtained in Preparation Example 3 were mixed, and then placed in a water bath at 30°C and stirred at a rotation speed of 500 r / min for 10 h to obtain a composite dispersion liquid; an appropriate amount of the composite dispersion liquid was taken and measured by a laser particle size instrument to obtain the average particle size of the particles wrapped in the composite dispersion liquid, which was 211.7 nm; and a surface tension instrument was used to measure the surface tension of the composite dispersion liquid, which was 30.5 mN / m, and no demulsification occurred;

[0083] Subsequently, 16 parts by weight of the composite dispersion liquid, 25 parts by weight of the polyurethane emulsion obtained in Preparation Example 5, 3 parts by weight of diacetone acrylamide and 0.15 parts by weight of azobisisobutyronitrile were added into a reactor, and then nitrogen was introduced into the reactor to replace the air therein as a protective gas, and then the reactor was heated to 65°C and reacted for 5 h. After cooling to room temperature, 0.7 times the weight of adipic acid dihydrazide of the diacetone acrylamide was added into the obtained modified polyurethane emulsion, and mixed and stirred to adjust the pH to 7.0 to obtain a modified water-based polyurethane coating.

[0084] Comparative Example 1:

[0085] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet rays, specifically comprising the following processes:

[0086] The polyurethane emulsion in Example 3 is replaced with the polyurethane emulsion obtained in Preparation Example 7, and the remaining preparation process remains consistent with Example 3.

[0087] Comparative Example 2:

[0088] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet rays, specifically comprising the following processes:

[0089] The polyurethane emulsion in Example 3 is replaced with the polyurethane emulsion obtained in Preparation Example 8, and the remaining preparation process remains consistent with Example 3.

[0090] Comparative Example 3:

[0091] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet rays, specifically comprising the following processes:

[0092] The polyurethane emulsion in Example 3 is replaced with the polyurethane emulsion obtained in Preparation Example 9, and the remaining preparation process remains consistent with Example 3.

[0093] Comparative Example 4:

[0094] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet rays, specifically comprising the following processes:

[0095] The polyurethane emulsion in Example 3 is replaced with the polyurethane emulsion obtained in Preparation Example 10, and the remaining preparation process remains consistent with Example 3.

[0096] Comparative Example 5:

[0097] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet rays, specifically comprising the following processes:

[0098] The polyurethane emulsion in Example 3 is replaced with the polyurethane emulsion obtained in Preparation Example 11, and the remaining preparation process remains consistent with Example 3.

[0099] Comparative Example 6:

[0100] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet rays, specifically comprising the following processes:

[0101] The composite dispersant in Example 3 is replaced with sodium dodecyl benzene sulfonate, and the remaining preparation process remains consistent with Example 3.

[0102] Comparative Example 7:

[0103] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet light, specifically comprising the following processes:

[0104] 50 parts by weight of nano-titanium dioxide with a particle size of 100 nm, 6 parts by weight of a composite dispersant (consisting of sodium dodecyl benzene sulfonate: Triton X-100 in a weight ratio of 1:2) and 900 parts by weight of Tris-hydrochloride buffer solution with a pH of 9.0 were weighed into a container, and then mixed and dispersed by ultrasonic power of 400 W for 20 min to obtain a mixed emulsion;

[0105] Then 600 parts by weight of the mixed emulsion and 7 parts by weight of the modified levodopa obtained in Preparation Example 3 were mixed, and then placed in a water bath at 30°C and stirred at a speed of 500 r / min for 10 h to obtain a composite dispersion. It was found that the composite dispersion was demulsified, and the preparation failed. The reason was analyzed: it may be that in this system, the use of nano-titanium dioxide with a large particle size to encapsulate the emulsion is not conducive to the stability of the emulsion system.

[0106] Comparative Example 8:

[0107] A preparation method of a modified waterborne polyurethane coating resistant to ultraviolet light, specifically comprising the following processes:

[0108] 17 parts by weight of the composite dispersion obtained in Example 3, 30 parts by weight of the polyurethane emulsion obtained in Preparation Example 6 and 0.2 parts by weight of azobisisobutyronitrile were weighed into a reactor, and then nitrogen was introduced to replace the air in the reactor as a protective gas. Then the reactor was heated to 70°C and timed for 6 h. After cooling to room temperature, a modified waterborne polyurethane coating was obtained.

[0109] The surface of the tinplate was polished with water sandpaper, and then the impurities generated after polishing were washed off with deionized water and blown dry. The modified waterborne polyurethane coatings prepared in Examples 1-3, Comparative Examples 1-6 and Comparative Example 8 were applied to the tinplate, and then placed in a room temperature environment until the protective coating was formed after solidification. Then they were placed at a high temperature of 200°C for 4 h. After high temperature treatment, the coatings were cooled to room temperature, and the presence or absence of cracking and peeling of the coating film was observed. Then the adhesion grade was tested according to GB / T 9286-2021 Scribed Test for Pigment and Varnish, and the results are shown in Table 1 below.

[0110] Table 1 Adhesion performance

[0111]

[0112]

[0113] The tinplate was polished with water sandpaper, then the impurities generated after polishing were washed with deionized water, and then dried. The modified waterborne polyurethane coating prepared in Examples 1-3, Comparative Examples 1-6 and Comparative Example 8 was applied on the tinplate, and then placed in a room temperature environment until the protective coating was formed. Then, under the irradiation of ultraviolet light at 365 nm, the irradiation intensity was controlled to be 0.5 W / m 2 After the irradiation was completed, the mechanical properties were tested according to the “GB / T 1732-2020 Paint Film Impact Resistance Test Method” and “GB / T 16421-1996 Plastic Tensile Properties Small Sample Test Method”. The results are shown in Table 2 below.

[0114] Table 2 Mechanical properties

[0115]

[0116]

[0117] The tinplate was polished with water sandpaper, then the impurities generated after polishing were washed with deionized water, and then dried. The modified waterborne polyurethane coating prepared in Examples 1-3, Comparative Examples 1-6 and Comparative Example 8 was applied on the tinplate, and then placed in a room temperature environment until the protective coating was formed. Then, under the irradiation of ultraviolet light at 365 nm, the irradiation intensity was controlled to be 0.5 W / m 2 After the irradiation was completed, the mechanical properties were tested according to the “GB / T 1732-2020 Paint Film Impact Resistance Test Method” and “GB / T 16421-1996 Plastic Tensile Properties Small Sample Test Method”. The results are shown in Table 2 below.

[0118] Table 3 Self-cleaning properties

[0119] Material source Protective coating surface with methyl red residue Example 1 No Example 2 No Example 3 No Comparative Example 1 No Comparative Example 2 Yes Comparative Example 3 Yes Comparative Example 4 Yes Comparative Example 5 Yes Comparative Example 6 Yes Comparative Example 8 No

[0120] From the above Tables 1-3, the following conclusions can be drawn:

[0121] (1) It can be found from Examples 1-3 that the protective coating obtained after curing of the modified waterborne polyurethane coating prepared by the present application has good ultraviolet resistance, adhesion and self-cleaning properties.

[0122] (2) It can be found from Comparative Example 1 that the prepared modified waterborne polyurethane coating has poor ultraviolet resistance, resulting in poor mechanical properties, and the adhesion performance is also poor. This may be due to the fact that although 1,4-butanediol can be condensed with isocyanate through hydroxyl groups during the preparation of polyurethane, the prepared polyurethane emulsion does not contain carbon-carbon double bonds. Therefore, the composite dispersion liquid prepared by modifying levodopa oxidation self-polymerization and wrapping nano titanium dioxide and diacetone acrylamide cannot be grafted into the polyurethane structure through polymerization, resulting in that nano titanium dioxide cannot be effectively introduced into the polyurethane, and thus the ultraviolet resistance is poor. In addition, since diacetone acrylamide cannot be introduced into the polyurethane, the lack of ketone hydrazine crosslinking effect leads to poor adhesion.

[0123] (3) It can be found from Comparative Example 2 that the prepared modified waterborne polyurethane coating has poor ultraviolet resistance, resulting in poor mechanical properties, and the adhesion performance and self-cleaning effect are also poor. This may be due to the fact that hexamethylene diisocyanate does not contain a phenyl ring structure with steric hindrance and rigidity compared to toluene diisocyanate during the preparation of polyurethane, and the carbon chain in the mixed diol is long and flexible without the improvement of the phenyl ring. In this system, the nano titanium dioxide used has poor ultraviolet resistance and is not resistant to impact, which finally leads to poor performance of the cured protective coating.

[0124] (4) It can be found from Comparative Example 3 that the prepared modified waterborne polyurethane coating has poor ultraviolet resistance, resulting in poor mechanical properties, and the adhesion performance and self-cleaning effect are also poor. This may be due to the fact that although the rigid phenyl ring has the functions of adjusting the ultraviolet resistance and self-cleaning of the coating after curing, in this system, the content of the rigid phenyl ring in the coating is too high due to the excessive use, which makes the coating brittle after curing, and thus the performance of the modified waterborne polyurethane coating after curing is weakened.

[0125] (5) It can be found from Comparative Example 4 that the prepared modified waterborne polyurethane coating has poor self-cleaning effect. This may be due to the fact that when the capping agent is replaced by phenol, phenol does not have low surface energy performance compared to hydroxyl polydimethylsiloxane. Therefore, only relying on the photocatalytic anti-fouling effect of nano titanium dioxide, the self-cleaning effect is poor.

[0126] (6) It can be found from Comparative Example 5 that the prepared modified waterborne polyurethane coating has poor ultraviolet resistance, and the adhesion and self-cleaning effects are also poor, which may be due to the fact that, in the preparation of polyurethane, although the hydroxyl polydimethylsiloxane can increase the self-cleaning ability of the protective coating after curing of the coating by means of low surface energy, in this system, the amount is too large, which may weaken the polymerization grafting of the polyurethane emulsion, the composite dispersion and the diacetone acrylamide, and thus affect the ketone hydrazine crosslinking process of the modified polyurethane emulsion and adipic acid dihydrazide in the prepared modified waterborne polyurethane coating, and is not conducive to improving the performance of the protective coating after curing of the modified waterborne polyurethane coating.

[0127] (7) It can be found from Comparative Example 6 that the prepared modified waterborne polyurethane coating has poor ultraviolet resistance, and the adhesion and self-cleaning effects are also poor, which may be due to the fact that the composite dispersant plays an important role in the pre-dispersion of the nano-titanium dioxide, and the use of a single emulsifying dispersant may not achieve good dispersion of the nano-titanium dioxide in this system, and thus is not conducive to improving the performance of the protective coating after curing of the modified waterborne polyurethane coating.

[0128] (8) It can be found from Comparative Example 8 that the prepared modified waterborne polyurethane coating has poor adhesion, which may be due to the fact that, in the esterification improvement of levodopa, the introduced structure may have a certain steric hindrance effect on the oxidative self-polymerization of levodopa, resulting in poor oxidative self-polymerization effect, and the adhesion performance relying only on the oxidative self-polymerization of levodopa is not enough to support the adhesion protection of the protective coating obtained after curing of the modified waterborne polyurethane coating to the substrate material.

[0129] The above embodiments have described the technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A method for preparing a UV-resistant modified waterborne polyurethane coating, characterized in that, The preparation method includes the following steps: Nano-titanium dioxide, composite dispersant, and buffer solution are mixed and dispersed in a weight ratio of 3~5:0.5~0.6:80~90 to obtain a mixed emulsion; The mixed emulsion and modified levodopa were mixed at a weight ratio of 500-600:5-7 and reacted at 30°C for 8-10 hours to obtain a composite dispersion. A modified polyurethane emulsion was obtained by mixing a composite dispersion, a polyurethane emulsion, diacetone acrylamide, and an azo catalyst in a weight ratio of 15~17:20~30:2~4:0.1~0.2 and heating the mixture to 60℃~70℃ for 4h~6h. A modified waterborne polyurethane coating is obtained by mixing a modified polyurethane emulsion with adipic acid dihydrazide. The method for preparing the modified levodopa includes the following steps: Modified levodopa was obtained by mixing levodopa, enol compounds, EDC hydrochloride and 4-dimethylaminopyridine in a molar ratio of 1:2~3:1.5:0.4 and reacting at 25℃ for 24h~30h. The enols include 3-buten-1-ol; The particle size of the nano-titanium dioxide is 20nm~30nm; The method for preparing the polyurethane emulsion includes the following steps: Diisocyanate, mixed diol, chain extender and dibutyltin dilaurate are mixed in a weight ratio of 1:2.3~2.5:0.4~0.6:0.007 and heated to 70℃~80℃ for 2h~3h to obtain polyurethane prepolymer mixture; A polyurethane prepolymer mixture and hydroxyl polydimethylsiloxane are mixed at a weight ratio of 1:0.1~0.2 and reacted at 70℃~80℃ for 1h~1.5h. Then, the temperature is lowered to 40℃, triethylamine is added and reacted for 25min~30min. Finally, deionized water is added and stirred to obtain a polyurethane emulsion. The mixed diol is composed of 1,6-hexanediol and 1,4-butenediol in a weight ratio of 1:

1.

2. The method for preparing a UV-resistant modified waterborne polyurethane coating according to claim 1, characterized in that, The composite dispersant is composed of sodium dodecylbenzenesulfonate and Triton X-100 in a weight ratio of 1:

2.

3. The method for preparing a UV-resistant modified waterborne polyurethane coating according to claim 1, characterized in that, The diisocyanate includes terephthalic diisocyanate or toluene diisocyanate.

4. The method for preparing a UV-resistant modified waterborne polyurethane coating according to claim 1, characterized in that, The chain extender includes dimethylolpropionic acid.

5. The method for preparing a UV-resistant modified waterborne polyurethane coating according to claim 1, characterized in that, The amount of adipic acid dihydrazide used is 0.6 to 0.8 times the weight of the diacetone acrylamide.

6. A modified waterborne polyurethane coating prepared by the method for preparing a UV-resistant modified waterborne polyurethane coating according to any one of claims 1 to 5.

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