An uv-resistant polyurethane coating and its preparation method and application

Abstract

The application discloses a kind of anti-UV coating bite polyurethane coating and its preparation method and application, including component A, component B and component C, wherein the preparation raw material of the component A includes the following components by weight parts: 40-65 parts of hydroxyl acrylic acid resin, 8-15 parts of cellulose acetate butyrate dissolved in solvent, 2-5 parts of polyaspartic acid ester polyurea resin, 1-3 parts of adhesion promoter and 0.2-0.5 parts of drier;Wherein the component B is curing agent, and the component C is diluent.The polyurethane coating of the application is extremely fast, and the anti-UV bite is excellent, can be directly sprayed on plastic substrate, presents various different colors by adding ordinary color paste, provides the functional requirements of adhesion, a variety of colors.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and particularly relates to a polyurethane coating that resists UV coating biting, its preparation method, and its application. Background Technology

[0002] In the 3C coatings market, primers often use two-component polyurethane coatings (PU coatings, hereinafter the same) paired with UV-cured topcoats (UV coatings, hereinafter the same). This PU+UV combination satisfies both the colorful appearance requirements for plastic substrates and the stringent surface abrasion resistance requirements of the 3C market. This combination has been widely adopted by end-user brands and spray painting plants in recent years. However, with increasingly stringent national environmental protection measures and the promulgation of GB 30981-2020, there are restrictions on VOCs. This has led to the formulation design of PU and UV coatings being limited to high-solids, low-viscosity, low-molecular-weight resins. Low-molecular-weight UV resins easily penetrate into the gaps between the molecules of the underlying PU resin, easily causing "biting" of the primer and substrate, resulting in poor appearance phenomena such as wrinkling, abnormal dullness, cracking, and mottling of the paint film. On the other hand, low-molecular-weight PU resins have a slow drying speed and insufficient strength, making them susceptible to topcoat biting. This results in a double problem: the topcoat is prone to biting the primer (commonly known as "base biting"), while the primer is not resistant to biting.

[0003] However, most coating lines in the 3C industry use spindle lines. To improve production efficiency, the baking time for the primer is relatively short. Therefore, under current conditions, the drying degree of high-solids polyurethane primers cannot meet production requirements, making it very easy for the topcoat to pick up. Therefore, improving the drying speed of low-VOC PU primers is a core issue of great concern to the 3C coating industry. Achieving coating drying at lower temperatures and in shorter times is an urgent need for the 3C coating industry. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a polyurethane coating with fast drying speed and excellent UV erosion resistance, as well as its preparation method and application.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] A polyurethane coating resistant to UV coating biting, comprising component A, component B, and component C.

[0007] The raw materials for preparing component A include the following components by weight: 40-65 parts of hydroxyl acrylic resin, 8-15 parts of cellulose acetate butyrate dissolved in a solvent, 2-5 parts of polyaspartic acid ester polyurea resin, 1-3 parts of adhesion promoter and 0.2-0.5 parts of drying agent.

[0008] The hydroxy acrylic resin has a Tg point of 110-130℃ and an acid value of 5-10 mgKOH / g.

[0009] The cellulose acetate butyrate has a Tg point of 120–130 °C and an acetyl content of 30–35 wt%.

[0010] Component B is a curing agent, and component C is a diluent.

[0011] As a further improvement, component A further includes 0.2 to 0.5 parts of a leveling agent and 4 to 10 parts of an organic solvent.

[0012] As a further improvement, the hydroxyl acrylic resin has a solid content of 60-70 wt% and a viscosity of 1.9-3.8 Pa·s.

[0013] As a further improvement, the hydroxyl acrylic resin is selected from Xinyingyuan's CLP-08 or Jiuwei Dimensions A-2265L; and / or

[0014] The cellulose acetate butyrate used is Eastman's CAB-321-0.1; and / or

[0015] The polyaspartic acid ester polyurea resin is selected from F520 of Feiyang or NH 1520 of Bayer.

[0016] As a further improvement, the adhesion promoter is a polymeric compound that does not contain polysiloxane and contains reactive hydroxyl groups.

[0017] As a further improvement, the drying agent is an organotin drying agent.

[0018] As a further improvement, the curing agent is a mixture of HDI trimer and TDI curing agent, wherein the molar ratio of OH:NCO is <1:1.

[0019] As a further improvement, the weight ratio of component A, component B, and component C is 100:10 to 15:30 to 50.

[0020] The present invention also provides a method for preparing the aforementioned anti-UV coating biting polyurethane coating, comprising:

[0021] The raw materials for preparing component A are mixed and dispersed evenly to obtain component A. Component A, component B and component C are stirred and mixed to obtain the polyurethane coating for resisting UV coating biting.

[0022] The present invention also provides an application of the anti-UV coating biting polyurethane coating in the preparation of 3C products, wherein the anti-UV coating biting polyurethane coating is used to form a primer coating on a substrate, which is dried at a temperature of 45-55°C for 10-15 minutes, and then a UV topcoat coating is formed on the primer.

[0023] This invention aims to broaden the application range of low-VOC PU primers, making them compatible with most low-VOC UV topcoats. Therefore, the most direct and effective method is to maximize the reaction and drying speed of the PU primer while ensuring VOC compliance. This invention achieves this goal through the following three aspects:

[0024] 1. Improve the initial hardness of the coating: Use hydroxyl acrylic resin with a high Tg point and cellulose acetate butyrate.

[0025] The initial hardness of the coating can be measured by the glass transition temperature. Since the solvent evaporates rapidly, the initial coating can be considered as a mixture of resin and curing agent. Therefore, increasing the glass transition temperature of the resin and curing agent can significantly accelerate the drying speed of the coating. The main resin of this invention, hydroxy acrylic acid, has a Tg point as high as 110-130℃, and cellulose acetate butyrate has a Tg point as high as 120-130℃. However, if the resin Tg point is too high, the coating will be relatively brittle, with poor impact resistance and poor adhesion. However, cellulose acetate butyrate has the effect of accelerating the release of solvent from the paint film and accelerating the surface drying speed. When combined with an adhesion promoter, it has a certain effect on improving the flexibility of the paint film and providing adhesion.

[0026] 2. Reduce the activation energy of the curing reaction: Add a drying agent, increase the acid value of the resin, and add polyaspartic acid ester polyurea resin.

[0027] (1) The reaction between a group containing active hydrogen and isocyanate is a nucleophilic addition reaction. The activation energy of the reaction depends on the nucleophilicity of the group containing active hydrogen. For common groups containing active hydrogen, such as amino, hydroxyl and carboxyl, their nucleophilicity decreases in that order, and their activation energy increases in that order. Therefore, adding a small amount of polyaspartic acid ester polyurea resin containing secondary amine groups can significantly accelerate the curing speed of the coating.

[0028] (2) Adding a drying agent can change the chemical reaction process, reduce the activation energy of the reaction, and significantly accelerate the curing reaction. The main component of T-12 added in this embodiment of the invention is dibutyltin dilaurate. The catalytic mechanism is as follows: the carbonyl group in the isocyanate is first polarized by dibutyltin dilaurate, and then the positively charged carbon atom in the isocyanate is attacked by the nucleophile hydroxyl group to complete the reaction.

[0029] (3) The hydroxy acrylic resin of this invention has a high acid value. Since the acid has a catalytic effect on the nucleophilic addition reaction, the increase in the acid value of the resin also reduces the activation energy of the reaction.

[0030] 3. Increase the collision factor of the curing reaction.

[0031] (1) The main factors affecting the collision factor of the curing reaction are: steric hindrance of hydroxyl groups, degree of freedom of hydroxyl groups and molecular shape. The hydroxyl acrylic resin of this invention is a hyperbranched polymer with high surface functional group concentration and less entanglement between molecular chains, making it easier for reactive groups to collide effectively, thus improving the collision factor.

[0032] (2) In some embodiments of the present invention, the curing agent uses a mixture of HDI trimer and TDI. Since TDI is an aromatic isocyanate, its reactivity is significantly higher than that of HDI trimer. The purpose of using a mixed curing agent is to balance reaction rate and adhesion, and to ensure an excess of NCO (when the mass ratio of HDI trimer to TDI is 1:1, the molar ratio of OH to NCO is 1:1.2). This increases the collision probability of the curing reaction and improves the reactivity. Furthermore, with an excess of curing agent (A:B = 100:10-15), the baked two-component polyurethane coating typically exhibits better chemical resistance and resistance to low-VOC UV bleed-off, because urea-formaldehyde bonds are formed during baking. The reaction formula is as follows:

[0033]

[0034] Therefore, the present invention achieves the effect of improving the reaction and drying speed of PU primer through the combined action of the above three aspects and multiple factors.

[0035] Compared with the prior art, the beneficial effects of the anti-UV coating biting polyurethane coating of the present invention are as follows:

[0036] (1) It can be dried quickly at low temperature, and UV topcoat can be sprayed on it after baking at 50℃ for 10 minutes.

[0037] (2) It can resist the biting of various low-VOC UV topcoats and will not cause poor appearance phenomena such as wrinkling, abnormal dullness, cracking, and mottling of the paint film due to biting.

[0038] (3) It is resistant to wiping with solvents such as alcohol and isopropanol, which is beneficial to improving the yield of topcoat spraying;

[0039] (4) It has high solids content and excellent workability. During construction, under the condition that the VOC is controlled within 630g / L, the construction viscosity can reach 9-10s, which is consistent with low solids content products.

[0040] Therefore, the polyurethane coating of this invention dries extremely quickly, exhibits excellent UV resistance, and can be directly sprayed onto plastic substrates. By adding common colorant, it can achieve various colors, providing adhesion and a range of color options. It is suitable for PC plastic substrates and is applicable to 3C product exteriors, such as mobile phone back covers, earphone casings, and laptop casings. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is an image of the appearance after applying a high-solids UV topcoat in Example 1. The paint film has a uniform gloss.

[0043] Figure 2 This is a comparison image showing the appearance of the paint film after spraying a high-solids UV topcoat; wrinkles appear on the paint film.

[0044] Figure 3 This is a picture of the appearance of the paint film after spraying high solids UV topcoat in Comparative Example 2. The paint film shows uneven gloss and matte finish.

[0045] Figure 4 This is a comparison image showing the appearance of the paint film after spraying a high-solids UV topcoat. The paint film shows uneven gloss and matte finishes. Detailed Implementation

[0046] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0047] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0048] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0049] The anti-UV coating of the present invention is a primer used in conjunction with a UV topcoat. The anti-UV coating of the present invention comprises three components: A, B (curing agent), and C (diluent).

[0050] In some specific embodiments, the raw materials for preparing component A include, by weight, the following components: 40-65 parts (preferably 55-65 parts) of hydroxyl acrylic resin, 8-15 parts (preferably 8-10 parts) of cellulose acetate butyrate dissolved in a solvent, 2-5 parts (preferably 3-4 parts) of polyaspartic acid ester polyurea resin, 1-3 parts of adhesion promoter, 0.2-0.5 parts of drying agent, 0.2-0.5 parts of leveling agent, and 4-10 parts of organic solvent. 10-20 parts of colorant may also be added to adjust the color.

[0051] In some specific embodiments, the hydroxyl acrylic resin used in component A has a Tg point (glass transition temperature) of 110-130℃, a hydroxyl value of 20-30 mgKOH / g, a solid content of 60-70 wt%, a viscosity of Z2-Z4 (1.9-3.8 Pa·s (25℃)), and an acid value of 5-10 mgKOH / g. It can be selected from Xinyingyuan's CLP-08 or Jiuwei Dimensions A-2265L. This resin is a hyperbranched medium-low hydroxyl resin with high solids and low viscosity, a high Tg point, fast drying speed, and high hardness after drying. Therefore, it has good solvent resistance and UV erosion resistance, but the paint film is relatively brittle.

[0052] In some specific embodiments, the cellulose acetate butyrate dissolved in the solvent in component A is a 45-55 wt% liquid semi-finished product obtained by dissolving cellulose acetate butyrate powder in an organic solvent. The following Examples 1-2 and comparative examples use a 50 wt% liquid semi-finished product of cellulose acetate dissolved in ethyl acetate.

[0053] The cellulose acetate butyrate used has an acetyl content of 30-35 wt%, a hydroxyl content of 1.1-1.5 wt%, and a Tg point of 120-130℃. In the examples below, the cellulose acetate butyrate has an acetyl content of 32.5 wt%, a hydroxyl content of 1.3 wt%, and a Tg point of 127℃. Eastman's CAB-321-0.1 is selected as a functional modifier for paints. It can resist solvent bleeding in clear varnishes, enhancing solvent release and accelerating the reaction rate; it also improves resin brittleness and enhances film adhesion to the substrate.

[0054] In some specific embodiments, the polyaspartic acid ester polyurea resin used in component A contains secondary amine groups, has a solid content of 94-98 wt%, a viscosity of 900-1300 mPa·s, and a hydroxyl content of 5.5-6 wt%. It can be Feiyang's F520 or Bayer's NH 1520. This resin has a high solid content, low viscosity, and extremely fast reaction speed, which can greatly enhance the reaction speed of the paint film. Therefore, when adding this type of resin, the application life should be evaluated simultaneously.

[0055] In some specific embodiments, the adhesion promoter used in component A is a polysiloxane-free polymer compound with a solid content of 48-52 wt% and containing a small amount of reactive hydroxyl groups. It can be either Deqian's APC or Evonik's LTW. Adding polysiloxanes can have an adverse effect on interlayer adhesion.

[0056] In some specific embodiments, the drying agent used in component A is an organotin drying agent, such as Air Chemical's T-12 or Geistefer's Mittel 6821.

[0057] In some specific embodiments, the leveling agent used in component A is a fluorocarbon leveling agent, such as Efka FL3600.

[0058] In some specific embodiments, the organic solvents used in component A are common ketone and ether solvents on the market, such as PMA, MEK, and MIBK.

[0059] In some specific embodiments, the colorant used in component A is added according to the desired color.

[0060] In some specific embodiments, the production process of component A is as follows: hydroxyl acrylic resin, cellulose acetate butyrate (soluble in solvent), polyaspartic acid ester polyurea resin, adhesion promoter, drying agent, leveling agent, organic solvent, and optionally color paste are added sequentially. The mixture is dispersed at medium speed using a disperser (preferably at 1000-1500 RPM for 15-20 minutes) until fully homogeneous, and then filtered to obtain the final product.

[0061] In some specific embodiments, component B is a polyisocyanate curing agent. In some embodiments, a mixture of aliphatic isocyanate (HDI) trimer and toluene diisocyanate (TDI) can solve the problems of brittle paint film and reduced adhesion. Preferably, the HDI trimer and TDI are mixed in a 1:1 mass ratio. The curing agent used in component B can be an HDI and TDI curing agent from Asahi Kasei or Covestro.

[0062] In some specific implementations, component C is a common diluent, such as a mixture of commonly available solvents, primarily PMA and MEK.

[0063] In some specific embodiments, the application method of the polyurethane coating of the present invention is as follows: the three components A, B and C are diluted in a weight ratio of 100:10-15:30-50 (preferably 100:10:30-50), stirred and mixed (preferably stirred at a speed of about 300 rpm for more than 10 minutes), then filtered, sprayed and applied, and then dried to a dry film thickness of 8-12 μm.

[0064] In some specific embodiments, the drying temperature is 45-55°C (preferably about 50°C), and the drying time is 10-15 minutes.

[0065] The present invention will be described in detail below through specific embodiments and comparative examples.

[0066] Example 1

[0067] The raw materials and their weight parts in component A of the anti-UV biting polyurethane coating of this embodiment are shown in Table 1:

[0068] Table 1

[0069]

[0070] To prepare component A: add novelty CLP-08, Eastman CAB321-0.1 liquid, Feiyang F520, Deqian APC, Air Chemical T-12, Efka FL3600, methyl ethyl ketone (MEK), and color paste in sequence. Disperse the mixture in a disperser at a medium speed of 1000-1500 rpm for 15-20 minutes until fully homogeneous. After dispersion, filter the mixture through a 200-mesh filter cloth.

[0071] Component B is a mixture of Covestro HDI trimer and TDI in a 1:1 ratio.

[0072] The application method of the UV-resistant polyurethane coating in this embodiment includes the following steps:

[0073] 100 parts of component A, 10 parts of component B and 40 parts of component C are physically mixed, filtered through a 200-mesh filter cloth and sprayed onto a primer plate with a film thickness of 10-15 μm. The mixture is then baked at about 50°C for 10-15 minutes to obtain a polyurethane coating that is resistant to UV biting.

[0074] Example 2

[0075] The raw materials and their weight parts in component A of the anti-UV biting polyurethane coating of this embodiment are shown in Table 2:

[0076] Table 2

[0077]

[0078] To prepare component A: add Nine-Dimensional A-2265AL, Eastman CAB321-0.1 liquid, Bayer NH1520, Deqian APC, Air Chemical T-12, Efka FL3600, methyl ethyl ketone (MEK), and color paste in sequence. Disperse the mixture in a disperser at a medium speed of 1000-1500 rpm for 15-20 minutes until fully homogeneous. After dispersion, filter the mixture through a 200-mesh filter cloth.

[0079] Component B is a mixture of Covestro HDI trimer and TDI in a 1:1 ratio.

[0080] The application method of the UV-resistant polyurethane coating in this embodiment includes the following steps:

[0081] 100 parts of component A, 10 parts of component B and 40 parts of component C are physically mixed, filtered through a 200-mesh filter cloth and sprayed onto a primer plate with a film thickness of 10-15 μm. The mixture is then baked at about 50°C for 10-15 minutes to obtain a polyurethane coating that is resistant to UV biting.

[0082] Comparative Example 1

[0083] The raw materials and their weight parts in component A of the polyurethane coating in this comparative example are shown in Table 3:

[0084] Table 3

[0085]

[0086]

[0087] To prepare component A: add Nupes SETAL 189, Eastman CAB321-0.1 liquid, Bayer NH1520, Deqian APC, Air Chemical T-12, Efka FL3600, methyl ethyl ketone (MEK), and color paste in sequence. Disperse the mixture in a disperser at a medium speed of 1000-1500 rpm for 15-20 minutes until fully homogeneous. After dispersion, filter the mixture through a 200-mesh filter cloth.

[0088] Component B is a mixture of Covestro HDI trimer and TDI in a 1:1 ratio.

[0089] The application method of the polyurethane coating in this comparative example includes the following steps:

[0090] 100 parts of component A, 10 parts of component B and 40 parts of component C are physically mixed, filtered through a 200-mesh filter cloth and sprayed onto a primer plate with a film thickness of 10-15 μm. The mixture is then baked at about 50°C for 30 minutes to obtain a polyurethane coating.

[0091] Comparative Example 2

[0092] The raw materials and their weight parts in component A of the polyurethane coating in this comparative example are shown in Table 4:

[0093] Table 4

[0094]

[0095] To prepare component A: add novelty CLP-08, Eastman CAB321-0.1 liquid, Deqian APC, Air Chemical T-12, Efka FL3600, methyl ethyl ketone (MEK), and color paste in sequence. Disperse the mixture in a disperser at a medium speed of 1000-1500 rpm for 15-20 minutes until fully uniform. After dispersion, filter the mixture through a 200-mesh filter cloth.

[0096] Component B is a mixture of Covestro HDI trimer and TDI in a 1:1 ratio.

[0097] The application method of the polyurethane coating in this comparative example includes the following steps:

[0098] 100 parts of component A, 10 parts of component B and 40 parts of component C are physically mixed, filtered through a 200-mesh filter cloth and sprayed onto a primer plate with a film thickness of 10-15 μm. The mixture is then baked at about 50°C for 20 minutes to obtain a polyurethane coating.

[0099] Comparative Example 3

[0100] The raw materials and their weight parts in component A of the polyurethane coating in this comparative example are shown in Table 5:

[0101] Table 5

[0102] Component A Number of weights Hydroxy acrylic resin Novel CLP-08 60 Cellulose acetate butyrate Eastman CAB381-0.1 liquid 10 Polyaspartic acid ester polyurea resin Flying F520 3 Adhesion promoter Deqian APC 2 drying agent Air Chemical T-12 0.2 Leveling agent Evka FL3600 0.3 organic solvents Butanone 4.5 Pigment 20 total- 100

[0103] To prepare component A: add novelty CLP-08, Eastman CAB381-0.1 liquid, Feiyang F520, Deqian APC, Air Chemical T-12, Efka FL3600, methyl ethyl ketone (MEK), and color paste in sequence. Disperse the mixture in a disperser at a medium speed of 1000-1500 rpm for 15-20 minutes until fully homogeneous. After dispersion, filter the mixture through a 200-mesh filter cloth.

[0104] Component B is a mixture of Covestro HDI trimer and TDI in a 1:1 ratio.

[0105] The application method of the polyurethane coating in this comparative example includes the following steps:

[0106] 100 parts of component A, 10 parts of component B and 40 parts of component C are physically mixed, filtered through a 200-mesh filter cloth and sprayed onto a primer plate with a film thickness of 10-15 μm. The mixture is then baked at about 50°C for 10-15 minutes to obtain a polyurethane coating.

[0107] Comparative Example 4

[0108] The raw materials and their weight parts in component A of the polyurethane coating in this comparative example are shown in Table 6:

[0109] Table 6

[0110]

[0111]

[0112] To prepare component A: add DIC ZHL-1063, Deqian APC, Air Chemical T-12, Efka FL3600, methyl ethyl ketone (MEK), and colorant in sequence. Disperse the mixture in a disperser at a medium speed of 1000-1500 rpm for 15-20 minutes until fully uniform. After dispersion, filter the mixture through a 200-mesh filter cloth.

[0113] Component B is a mixture of Covestro HDI trimer and TDI in a 1:1 ratio.

[0114] The application method of the polyurethane coating in this comparative example includes the following steps:

[0115] 100 parts of component A, 10 parts of component B and 40 parts of component C are physically mixed, filtered through a 200-mesh filter cloth and sprayed onto a primer plate with a film thickness of 10-15 μm. The mixture is then baked at about 50°C for 10-15 minutes to obtain a polyurethane coating.

[0116] Comparative Example 5

[0117] The raw materials and their weight parts in component A of the polyurethane coating in this comparative example are shown in Table 7:

[0118] Table 7

[0119]

[0120] To prepare component A: add novelty CLP-08, Eastman CAB321-0.1 liquid, Feiyang F520, Deqian APC, Air Chemical T-12, Efka FL3600, methyl ethyl ketone (MEK), and color paste in sequence. Disperse the mixture in a disperser at a medium speed of 1000-1500 rpm for 15-20 minutes until fully homogeneous. After dispersion, filter the mixture through a 200-mesh filter cloth.

[0121] Component B consists entirely of Covestro's TDI curing agent.

[0122] The application method of the polyurethane coating in this comparative example includes the following steps:

[0123] 100 parts of component A, 10 parts of component B and 40 parts of component C are physically mixed, filtered through a 200-mesh filter cloth and sprayed onto a primer plate with a film thickness of 10-15 μm. The mixture is then baked at about 50°C for 8 minutes to obtain a polyurethane coating.

[0124] Performance testing

[0125] The polyurethane coatings prepared in Examples 1-2 and Comparative Examples 1-5 were each coated with the same high-solids-content matte UV topcoat (VOC below 540 g / L, sprayed solids content exceeding 45%, sprayed viscosity between 9 and 11 s), and then cured under UV light. The performance test results of the high-solids-content polyurethane coatings prepared in Examples 1-2 and Comparative Examples 1-5 are shown in Table 8. The appearance of Examples 1 and Comparative Examples 1-3 after spraying with the high-solids-content UV topcoat is shown in the figure below. Figure 1-4 .

[0126] Table 8

[0127]

[0128] As can be seen from the table above, Examples 1 and 2 of the present invention exhibit excellent performance in terms of appearance, adhesion, application viscosity, surface drying speed, alcohol resistance, and resistance to UV coating adhesion. However, Comparative Example 1, using a common high-solids, low-viscosity resin (Tg point 70-80℃), shows a slow reaction rate, a soft paint film, poor alcohol resistance, and is sprayed with low-VOC... The UV topcoat exhibited severe undercoating and wrinkling of the paint film. In Comparative Example 2, without the addition of polyaspartic acid ester polyurea resin, the reaction speed of the paint film decreased, and slight undercoating was observed, with noticeable uneven gloss and matte finish on the same piece of paint film. In Comparative Example 3, replacing CAB321-0.1 with CAB381-0.1 (CAB381-0.1 acetyl content 10-15% wt%) resulted in decreased alcohol resistance, leading to undercoating and uneven gloss and matte finish. In Comparative Example 4, the absence of a high-solids, low-viscosity resin (solids content 40-50%, viscosity 4.5-8 Pa·s (25℃)) resulted in very high spray viscosity, failing to meet VOC control requirements. In Comparative Example 5, using only TDI curing agent, excellent alcohol resistance was observed, and the reaction speed was actually accelerated, resulting in strong resistance to undercoating, but the paint film was brittle, and adhesion decreased to 2B.

[0129] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A polyurethane coating with anti-UV bite, comprising component A, component B and component C, characterized in that: wherein the raw materials for preparing the component A comprise the following components by weight parts: 40-65 parts of a hydroxyl acrylic resin, 8-15 parts of cellulose acetate butyrate dissolved in a solvent, 2-5 parts of a polyaspartic ester polyurea resin, 1-3 parts of an adhesion promoter and 0.2-0.5 parts of a drier; the hydroxyl acrylic resin has a Tg of 110-130℃, an acid value of 5-10 mgKOH / g, a solid content of 60-70wt%, and a viscosity of 1.9-3.8 Pa·s; the cellulose acetate butyrate has a Tg of 120-130℃ and an acetyl content of 30-35wt%; the drier is an organic tin drier; wherein the component B is a curing agent, the component C is a diluent, and the weight ratio of the component A, the component B and the component C is 100:10-15:30-50; the curing agent is a mixed curing agent of HDI trimer and TDI, wherein the molar ratio of OH:NCO is <1:

1.

2. The UV resistant bite-back polyurethane coating according to claim 1, characterized in that, the component A further comprises 0.2-0.5 parts of a leveling agent and 4-10 parts of an organic solvent.

3. The UV-resistant bite-resistant polyurethane coating according to claim 1 or 2, characterized in that the hydroxyl acrylic resin is selected from CLP-08 of Shin-Etsu or Dimensions A-2265L of Nine Dimensions; and / or the cellulose acetate butyrate is CAB-321-0.1 of Eastman; and / or the polyaspartic ester polyurea resin is selected from F520 of Feiyang or NH 1520 of Bayer.

4. The UV resistant bite-back polyurethane coating according to claim 1 or 2, characterized in that, the adhesion promoter is a high molecular compound containing reactive hydroxyl groups and free of polysiloxane.

5. A process for the preparation of the bite-resistant polyurethane coating of claim 1 to 4, characterized in that comprising: mixing the raw materials for preparing the component A, uniformly dispersing to obtain the component A, and mixing the component A, the component B and the component C to obtain the polyurethane coating with anti-UV bite.

6. Use of the UV-resistant polyurethane coating according to any one of claims 1 to 4 for the production of 3C products, characterized in that, forming a primer coating on a substrate using the polyurethane coating with anti-UV bite, drying at a temperature of 45-55℃ for 10-15min, and then forming a UV topcoat on the primer.

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