A double-layer protective coating and preparation method thereof

Abstract

The present invention relates to a double-layer protective coating having a low curing temperature. The thermal curing process of the coating does not adversely affect the mechanical properties of the substrate, such as impact strength. The double-layer protective coating is applied to a polycarbonate substrate to enable the substrate to maintain high impact strength. In addition, the present invention also relates to a preparation method of the double-layer protective coating.

Description

Technical Field

[0001] The present invention relates to the technical field of substrate protection, and in particular to a double-layer protective coating and a preparation method thereof. Background Art

[0002] Compared with substrates such as polymethyl methacrylate, PET film, and transparent PU materials, polycarbonate substrates have excellent comprehensive performance, high elastic modulus, high impact strength, and light transmittance, which is also the best among engineering plastics. It is one of the most ideal engineering plastics. However, the wear resistance and solvent resistance of polycarbonate substrates are poor, and they need to be protected by coating and other methods before use. Polycarbonate substrates have high temperature resistance, and the curing temperature of traditional polycarbonate protective materials is high, mostly 120-130°C. However, when the coating is cured, the substrate is heated, and the polycarbonate molecular chains are rearranged, resulting in a decrease in its free volume fraction and void size, and residual stress is generated inside the substrate, which reduces the mechanical properties of the polycarbonate material, such as impact strength.

[0003] Based on the current situation that the impact properties of polycarbonate substrates are contrary to the existing high-temperature curing protective coatings, if a low-temperature curing protective coating can be achieved, the polycarbonate substrate can maintain high mechanical properties such as high impact strength. Therefore, the development of a low-temperature curing protective coating has become an urgent problem to be solved. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems existing in the prior art and provide a double-layer protective coating having a low curing temperature. The thermal curing process of the coating will not have an adverse effect on the mechanical properties of the substrate, such as impact strength. The double-layer protective coating is used on a polycarbonate substrate to enable the substrate to maintain high impact strength.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned double-layer protective coating.

[0006] In order to achieve the above objectives, the present invention provides the following technical solutions.

[0007] A double-layer protective coating comprising:

[0008] a base coating layer, wherein the material of the base coating layer comprises polyurethane; and

[0009] The top coating layer is disposed on the base coating layer, and the material of the top coating layer includes organic silicone resin.

[0010] In some embodiments, the curing temperature of the double-layer protective coating may be 70-90° C. Low temperature curing does not damage the internal microstructure of the substrate, so that the substrate maintains high impact strength. In some specific embodiments, the curing temperature of the double-layer protective coating may be 70° C., 75° C., 80° C., 85° C. or 90° C.

[0011] In some embodiments, the weight average molecular weight of the polyurethane may be 15,000-20,000 Da. The glass transition temperature of the polyurethane may be 75-90° C. The weight average molecular weight of the silicone resin may be 1200-2500 Da. By optimizing the weight average molecular weight and glass transition temperature of the polyurethane and silicone resin, it is beneficial to reduce the curing temperature.

[0012] In some specific embodiments, the weight average molecular weight of the polyurethane may be 16,000-19,000 Da. The glass transition temperature of the polyurethane may be 80-90° C. The weight average molecular weight of the silicone resin may be 1300-2000 Da.

[0013] In some preferred embodiments, the weight average molecular weight of the polyurethane is 18,000 Da. The glass transition temperature of the polyurethane is 85° C. The weight average molecular weight of the silicone resin may be 1700 Da.

[0014] In some embodiments, the double-layer protective coating can be used for a polycarbonate substrate. The polycarbonate substrate coated with the double-layer protective coating can have excellent physical and chemical properties, optical properties, mechanical properties, environmental resistance, etc.

[0015] The present invention also provides a method for preparing the double-layer protective coating, comprising the following steps:

[0016] Applying a polyurethane coating to a substrate;

[0017] After surface drying, applying a silicone resin coating on the formed coating; and

[0018] After the surface is dry, it is cured.

[0019] In some embodiments, the surface drying time may be more than 10 minutes, for example, 10 minutes, 30 minutes, 1 hour, 1.5 hours or 2 hours. The surface drying temperature is generally 18-30°C. In some specific embodiments, the substrate may be tilted to dry the surface, so that the coating on the surface of the substrate is leveled by gravity. In some specific embodiments, the polyurethane coating is applied to the surface of the substrate, and the substrate is tilted to dry the surface, so that the coating on the surface of the substrate is leveled by gravity; thereafter, the silicone resin coating is applied continuously, and the substrate is tilted to dry the surface during coating, so that the resin on the surface of the substrate is leveled by gravity.

[0020] In some embodiments, the curing temperature may be 70-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C. The curing time may be 2-6h, for example, 2h, 3h, 4h, 5h or 6h. Low temperature curing will not destroy the internal microstructure of the substrate, so that the substrate maintains high impact strength. By reducing the curing temperature of the coating and reducing the curing time of the coating, a large amount of economic costs can be saved for the coating users such as manufacturers of vehicles, lenses, helmets, etc.

[0021] In some embodiments, the preparation method of the polyurethane coating comprises: mixing polyol, aliphatic polyisocyanate, a catalyst, a chain extender, a cross-linking agent, a salt-forming agent and a solvent, and reacting them to obtain the polyurethane coating.

[0022] In some specific embodiments, the solid content of the polyurethane coating may be 8%-10%, for example 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9%, 9.1%, 9.2%, 9.3%, 9.4%, 9.5%, 9.6%, 9.7%, 9.8%, 9.9% or 10%.

[0023] In some specific embodiments, the pH value of the polyurethane coating can be 8-10, for example 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9 or 10.

[0024] In some specific embodiments, the polyol includes one or more of polyester polyol and polyether polyol. Preferably, the molecular weight of the polyol may be 500-10000, preferably, the molecular weight of the polyol may be 1000-5000.

[0025] In some specific embodiments, the aliphatic polyisocyanate includes an aliphatic diisocyanate, for example, one or more of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane diisocyanate (HMDI), and HMDI is most preferred.

[0026] In some specific embodiments, the catalyst includes one or more of an organic tin metal catalyst and a tertiary amine catalyst. Preferably, the catalyst includes one or more of dibutyltin dilaurate, stannous octoate, ethylenediamine, and N,N'-dimethylaminopyridine.

[0027] In some specific embodiments, the chain extender includes one or more of a carboxylic acid chain extender, an alcohol chain extender, and an amine chain extender. Preferably, the chain extender includes one or more of dimethylol propionic acid, trimethylol propane, and N,N-dihydroxy (diisopropyl) aniline.

[0028] In some specific embodiments, the salt-forming agent includes one or more of triethylamine, dimethylethanolamine, diethylethanolamine, ammonia water, and sodium hydroxide.

[0029] In some specific embodiments, the solvent may be one or more of methanol, ethanol, isopropanol, ethylene glycol butyl ether, propylene glycol methyl ether, N-methyl pyrrolidone, and water. Most preferably, the solvent may be one or more of isopropanol, propylene glycol methyl ether, N-methyl pyrrolidone and water. The solvent selected in the present invention has weak corrosion ability to the substrate.

[0030] The preparation method of the polyurethane coating is a conventional preparation method of anionic polymerization polyurethane, except that the raw materials used in the synthesis process are slightly different from those in the conventional method, and the crosslinking agent of the present invention uses ethylenediamine and amino resin. Preferably, the amino resin is methyl etherified imino melamine resin; most preferably, the amino resin is hexamethoxymethyl melamine.

[0031] Preferably, the aliphatic polyisocyanate (which is a curing agent) is dicyclohexylmethane diisocyanate, and the mass ratio of dicyclohexylmethane diisocyanate to ethylenediamine is 23: (0.6-1.5); the mass ratio of dicyclohexylmethane diisocyanate to amino resin is 23: (1.0-2.3). If other curing agents are used, the mass ratio needs to be converted according to the -NCO content. After adding an appropriate amount of ethylenediamine and amino resin, the degree of crosslinking after curing of the coating can be effectively controlled. When the addition amount of ethylenediamine and amino resin is within the addition range controlled by this patent, the adhesion of the coating is level 0 after coating. And after various environmental tests, the adhesion does not decrease and no abnormality is found in the surface quality of the film layer.

[0032] In some embodiments, the method for preparing the organic silicone resin coating comprises: adding a silane coupling agent and a catalyst to a methyl silicone resin solution, and preparing the organic silicone resin coating after reaction.

[0033] In some specific embodiments, the mass ratio of methyl silicone resin, silane coupling agent and catalyst is (18-22):(3-5):(2_4), preferably (19-21):(3.5-4.5):(2.5-3.5), and most preferably 20:4:3.

[0034] In some specific embodiments, the silane coupling agent is one or more of epoxy hydrocarbon silane coupling agent, olefin silane coupling agent, and mercapto hydrocarbon silane coupling agent, preferably epoxy hydrocarbon silane coupling agent. Advantages of using the above silane coupling agent: improving the adhesion of polyurethane resin and silicone resin.

[0035] In some specific embodiments, the catalyst is one or more of 1,8-diazabicyclo, undec-7-ene catalyst, 1,4-diazacyclo[2,2,2]octane, and 4-dimethylaminopyridine, preferably 1,8-diazabicyclo. Advantages of using the above catalysts: high catalytic activity at a lower curing temperature, effective control of curing reaction speed and curing time, and improved adhesion of polyurethane resin and silicone resin.

[0036] In a specific embodiment, the method for preparing the organic silicone resin coating comprises: adding an epoxy hydrocarbon silane coupling agent and 1,8-diazabicyclo to a methyl silicone resin solution, and reacting to obtain the organic silicone resin coating.

[0037] In the present invention, coating can be performed by flow coating, dipping coating or spraying.

[0038] In the present invention, the substrate may be a flat plate, a curved surface or other special-shaped surface-made parts.

[0039] In some embodiments, the method for preparing the methyl silicone resin solution includes: adding methyltrichlorosilane to a solvent, and then adding white carbon black and water, and after hydrolysis is completed, obtaining a methyl silicone resin solution.

[0040] In some specific embodiments, the solvent may be one or more of methanol, ethanol, isopropanol, ethylene glycol butyl ether, propylene glycol methyl ether, N-methyl pyrrolidone, and water. Most preferably, the solvent may be one or more of isopropanol, propylene glycol methyl ether, N-methyl pyrrolidone and water. The solvent selected in the present invention has weak corrosion ability to the substrate.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The present invention provides a double-layer protective coating having a low curing temperature. The thermal curing process of the coating will not adversely affect the mechanical properties of the substrate, such as impact strength. The double-layer protective coating applied to a polycarbonate substrate can maintain a high impact strength of the substrate. In addition, the polycarbonate substrate coated with the double-layer protective coating also has excellent physical and chemical properties (such as adhesion and wear resistance), optical properties, environmental resistance (such as moisture and heat resistance, salt spray resistance, temperature shock resistance, solar radiation resistance, and ultraviolet aging resistance), etc., which diversifies the application of the substrate.

[0043] The double-layer protective coating of the present invention has high universality, and has high adhesion matching and good leveling properties with various substrates, such as substrates prepared from thermoplastic polyolefins, acrylonitrile-butadiene-styrene (ABS) copolymers, EPDM rubber, polyurethane, acrylic polymers, polyamides, polyesters, vinyl polymers and copolymers thereof and mixtures thereof. It has a wide range of applications, and is especially suitable for coating on transparent substrates such as polymethyl methacrylate glass, polycarbonate glass, PET film, PU film and other substrates. The film layer has high quality and excellent optical properties. For industries such as automobile manufacturing, it can increase the breadth of substrate and even transparent material selection, which is conducive to achieving vehicle weight reduction.

[0044] The double-layer protective coating of the present invention is formed by successively coating and curing two single-component coatings. No batching is required before coating, which avoids film cracking or delamination problems caused by too fast or insufficient curing of the coating due to inaccurate calculation or weighing. There is no need to use expensive metering equipment and mixing equipment to ensure accurate metering and uniform mixing. The design of the single-component coating is also conducive to "assembly line" operation, and the construction efficiency is high.

[0045] 2. The present invention also provides a method for preparing a double-layer protective coating. After applying the polyurethane coating, it only needs to be surface dried before applying the silicone resin coating. After the surface is dried again, it only needs to be thermally cured once to obtain a double-layer protective coating. The coating and curing process is simple, and the required coating equipment cost is low. It is suitable for "assembly line" operations, has high construction efficiency, and is very valuable for industrial utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the structure of a double-layer protective coating according to an embodiment of the present invention.

[0047] Figure 2 The present invention is a flow chart of the preparation of a double-layer protective coating according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0049] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the raw materials, instruments and equipment used in the following examples, etc., can all be purchased on the market or can be obtained by existing methods; the amounts of the experimental reagents, unless otherwise specified, are the amounts of reagents used in conventional experimental operations; the experimental methods, unless otherwise specified, are all conventional methods.

[0050] The present invention is further described by the following examples. It should be correctly understood that the examples of the present invention are made to illustrate the present invention, rather than to limit the present invention, so simple modifications of the present invention under the premise of the method of the present invention also belong to the scope of the present invention.

[0051] Example 1

[0052] First, prepare the polyurethane coating:

[0053] (1) Nitrogen was passed through a reaction flask to displace the air therein, and 37 g of adipic acid, 23.3 g of hexanediol, 7.65 g of neopentyl glycol, 5 g of polyether diol, 0.6 g of trimethylolpropane and 0.01 g of an organic tin catalyst were added in sequence. The temperature was raised to 140° C. in 1 h, and kept warm for 0.5 h. The temperature was raised to 150° C. in 1 h, and kept warm for 1 h. The temperature was raised to 180° C. in 1 h, and kept warm for 2 h. The temperature was further raised to 220° C., and vacuum distilled for 0.5 h for dehydration. Nitrogen was continuously passed through the flask and kept warm for 1 h. The polyether diol was polyethylene glycol 1000 produced by Jiangsu Hai'an Petrochemical Plant.

[0054] (2) Cool down to 95°C, add 85g N-methylpyrrolidone while stirring, mix and stir for 0.5h. Cool down to 50°C;

[0055] (3) Add 23 g of dicyclohexylmethane diisocyanate dropwise under nitrogen protection and strong stirring, raise the temperature to 80° C. for reaction, keep warm for 1 hour, add 0.02 g of stannous octoate catalyst; continue to keep warm for reaction; test the NCO content of the system at intervals, and stop the reaction when the NCO content drops to 2.5%;

[0056] (4) under high-speed stirring, 6.4 g of a solution of dimethylolpropionic acid in N-methylpyrrolidone (the mass ratio of dimethylolpropionic acid to N-methylpyrrolidone is 1:1) was added for chain extension, and the reaction was continued at 80° C. for 3 h;

[0057] (5) Cooling to 60° C., adding 2.5 g of triethylamine, continuing stirring for 15 min, strengthening stirring, adding 960 g of a mixed solvent (the mixed solvent is a mixture of N-methylpyrrolidone, isopropanol, propylene glycol methyl ether and water, the mass ratio of each component in the mixed solvent is 1:14:28:5) to the reaction bottle, stirring for 5 min, and adjusting the viscosity of the system;

[0058] (6) Cool down to below 20°C, add 0.8 g of ethylenediamine under rapid stirring, stir vigorously for 20 min, and stir slowly for 2 h;

[0059] (7) 1.5 g of hexamethoxymethyl melamine (amino resin) was added dropwise under vigorous stirring, and then slowly stirred for 2 h to obtain a polyurethane coating with a solid content of 8.7%, a pH value of 8.4, and a weight-average molecular weight of 18,000 Da. The glass transition temperature of the polyurethane was 85 °C.

[0060] Then, prepare the silicone resin coating:

[0061] (1) 25 g of methyltrichlorosilane was slowly added to 74 g of a mixed solvent (the mixed solvent was a mixture of methanol, ethanol, isopropanol, butyl acetate, xylene and ethylene glycol butyl ether, and the mass ratio of each component in the mixed solvent was 12:20:25:1:3:13), and white carbon black and water were gradually added. After the hydrolysis was completed, the mixture was allowed to stand at room temperature for 3 hours to obtain a methyl silicone resin solution;

[0062] (2) 4.5 g of silane coupling agent KH560 (epoxy hydrocarbon silane coupling agent) and 3.5 g of 1,8-diazabicyclo (catalyst) were added to the reaction bottle, and the mixture was slowly stirred for 20 min at room temperature to obtain an organic silicon coating, wherein the molecular weight of the organic silicon resin was 1800. The silane coupling agent KH560 was purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0063] Finally, a double layer of protective coating is applied:

[0064] (1) Cleaning the polycarbonate substrate to remove the glue and release agent residues in the substrate coating area;

[0065] (2) using a flow coating method, coating the prepared polyurethane coating on the surface of a polycarbonate substrate, and placing the substrate in an inclined position to dry the surface, so that the coating on the surface of the substrate is leveled under the action of gravity;

[0066] (3) After the primer is dry for about 1 hour, the prepared silicone resin coating is applied by flow coating. During flow coating, the substrate is placed at an angle so that the resin on the substrate surface can flow flat under the action of gravity;

[0067] (4) After the topcoat is dry, it is placed in an oven for curing at 75°C for 2 hours. The resulting double-layer protective coating is as follows: Figure 1 shown.

[0068] Example 2

[0069] First, prepare the polyurethane coating:

[0070] (1) Nitrogen was passed through a reaction flask to displace the air therein, and 37 g of adipic acid, 3.2 g of dimethylolpropionic acid, 23.3 g of hexanediol, 7.65 g of neopentyl glycol, 5 g of polyether diol, 0.6 g of trimethylolpropane and 0.01 g of stannous octoate catalyst were added in sequence, and the temperature was raised to 140° C. in 1 h, and kept warm for 0.5 h, and the temperature was raised to 150° C. in 1 h, and kept warm for 1 h, and the temperature was raised to 180° C. in 1 h, and kept warm for 2 h, and the temperature was further raised to 220° C., and vacuum distilled for 0.5 h for dehydration; nitrogen was continuously passed through and kept warm for 1 h; wherein the polyether diol was polyethylene glycol 1000 produced by Jiangsu Hai'an Petrochemical Plant.

[0071] (2) Cool down to 95°C, add 85g N-methylpyrrolidone while stirring, mix and stir for 0.5h. Cool down to 50°C;

[0072] (3) under nitrogen protection and strong stirring, 23 g of dicyclohexylmethane diisocyanate was added dropwise, the temperature was raised to 80° C. for reaction, and the temperature was kept for 1 h. 0.02 g of stannous octoate catalyst was added; the temperature was kept for reaction; the NCO content of the system was tested at intervals, and the reaction was stopped when the NCO content dropped to 2.0%;

[0073] (4) Cooling to 60° C., adding 2.5 g of triethylamine, stirring for 15 min, strengthening stirring, adding 960 g of a mixed solvent (the mixed solvent is N-methylpyrrolidone, isopropanol, propylene glycol methyl ether and water, and the mass ratio of each component in the mixed solvent is 1:14:28:5) to the reaction bottle, stirring for 5 min, and adjusting the viscosity of the system;

[0074] (5) The temperature was lowered to below 20°C, 0.8 g of ethylenediamine was added under rapid stirring, the mixture was vigorously stirred for 20 min, and then slowly stirred for 2 h to obtain a polyurethane coating with a solid content of 9.2%, a pH value of 8.3, a weight-average molecular weight of 16,000 Da, and a glass transition temperature of 83°C.

[0075] Then, prepare the silicone resin coating:

[0076] (1) 25 g of methyltrichlorosilane was slowly added to 74 g (a mixed solvent was a mixture of methanol, ethanol, isopropanol, butyl acetate, xylene and ethylene glycol butyl ether, and the mass ratio of each component in the mixed solvent was 12:20:25:1:3:13), and white carbon black and water were gradually added. After the hydrolysis was completed, the mixture was allowed to stand at room temperature for 3 hours to obtain a low molecular weight methyl silicone resin solution with a molecular weight of 1800;

[0077] (2) 4.5 g of KH560 and 3.5 g of 1,8-diazabicyclopentane were added to the reaction bottle and stirred slowly for 20 min at room temperature to obtain a silicone resin coating.

[0078] Finally, a double layer of protective coating is applied:

[0079] (1) Cleaning the polycarbonate substrate to remove the glue and release agent residues in the substrate coating area;

[0080] (2) using a spraying method, the prepared polyurethane coating is applied to the surface of a polycarbonate substrate, and the substrate is placed at an angle to dry the surface, so that the resin on the surface of the substrate is leveled by gravity;

[0081] (3) After the primer is dry for about 1 hour, the prepared silicone resin is applied by spraying. During spraying, the substrate is placed at an angle so that the resin on the surface of the substrate can flow level under the action of gravity.

[0082] (4) After the topcoat is dry, place it in an oven for curing at 75°C for 2 hours.

[0083] Example 3

[0084] First, prepare the polyurethane coating:

[0085] (1) Nitrogen was passed through a reaction flask to displace the air therein, and 37 g of adipic acid, 29 g of neopentyl glycol, 0.6 g of trimethylolpropane and 0.01 g of stannous octoate catalyst were added to the reaction flask, and the temperature was raised to 140° C. in 1 h, and kept warm for 0.5 h. The temperature was raised to 150° C. in 1 h, and kept warm for 1 h. The temperature was raised to 180° C. in 1 h, and kept warm for 2 h. The temperature was further raised to 220° C., and vacuum distilled for 0.5 h for dehydration; nitrogen was continuously passed through the flask and kept warm for 1 h.

[0086] (2) Cool down to 95°C, add 85g N-methylpyrrolidone under vigorous stirring, mix and stir for 0.5h. Cool down to 50°C;

[0087] (3) under nitrogen protection and strong stirring, 23 g of dicyclohexylmethane diisocyanate was added dropwise, the temperature was raised to 80° C. for reaction, and the NCO content of the system was tested at intervals. When the NCO content dropped to 2.5%, the reaction was stopped;

[0088] (4) After cooling to 60° C., 2.5 g of triethylamine, a salt-forming agent, was added and stirred for 15 min. Stirring was continued, and 960 g of a mixed solvent (N-methylpyrrolidone, isopropanol, and propylene glycol methyl ether in a mass ratio of 1:14:28) was added to the reaction bottle, the viscosity of the mixed system was adjusted, and stirring was continued for 5 min.

[0089] (5) The temperature was lowered to below 20° C., 0.8 g of ethylenediamine was added under rapid stirring, and the mixture was vigorously stirred for 20 min. After slow stirring for 2 h, a polyurethane coating having a solid content of 9.3%, a pH value of 8.3, a weight-average molecular weight of 14,000 Da, and a glass transition temperature of 87° C. was obtained.

[0090] Then, prepare the silicone resin coating:

[0091] (1) 25 g of methyltrichlorosilane was slowly added to 79 g of a mixed solvent (the mixed solvent was a mixture of methanol, ethanol, isopropanol, butyl acetate, xylene and ethylene glycol butyl ether, and the mass ratio of each component in the mixed solvent was 12:20:25:1:3:13), white carbon black and water were added, and after the hydrolysis was completed, the mixture was allowed to stand at room temperature for 3 hours to obtain a methyl silicone resin solution with a molecular weight of 1800;

[0092] (2) Add 4.5 g of silane coupling agent KH560 and 3.5 g of 1,8-diazabicyclopentane into a reaction bottle and slowly stir at room temperature for 20 min to obtain a silicone resin coating.

[0093] Finally, a double layer of protective coating is applied:

[0094] (1) Cleaning the polycarbonate substrate to remove the glue and release agent residues in the substrate coating area;

[0095] (2) using a dipping method, the prepared polyurethane coating is applied to the surface of a polycarbonate substrate, the substrate is tilted to dry, and the resin on the surface of the substrate is leveled under the action of gravity;

[0096] (3) After the primer is dry for about 1 hour, the prepared silicone resin coating is applied by dipping. During dipping, the substrate is placed at an angle to allow the resin on the substrate surface to flow level under the action of gravity.

[0097] (4) After the topcoat is dry, place it in an oven for curing at 75°C for 2 hours.

[0098] Example 4

[0099] The double-layer protective coating was prepared according to the method of Example 1, except that step 6 was not performed when preparing the polyurethane coating, that is, the cross-linking agent ethylenediamine was not used. The obtained polyurethane coating had a solid content of 9.2%, a pH value of 8.8, a weight average molecular weight of 13,000 Da, and a glass transition temperature of 76°C.

[0100] Example 5

[0101] The double-layer protective coating was prepared according to the method of Example 1, except that step 7 was not performed when preparing the polyurethane coating, that is, the cross-linking agent hexamethoxymethyl melamine (amino resin) was not used. The obtained polyurethane coating had a solid content of 10%, a pH value of 8.3, a polyurethane resin weight average molecular weight of 12,000 Da, and a glass transition temperature of 73°C.

[0102] Example 6

[0103] First, a polyurethane coating was prepared according to the method of Example 1.

[0104] Then, prepare the silicone resin coating:

[0105] (1) 25 g of methyltrichlorosilane was slowly added to 74 g of a mixed solvent (the mixed solvent was a mixture of N-methylpyrrolidone, isopropanol, propylene glycol methyl ether and water, and the mass ratio of each component in the mixed solvent was 1:14:28:5), and white carbon black and water were gradually added. After the hydrolysis was completed, the mixture was allowed to stand at room temperature for 3 hours to obtain a methyl silicone resin solution with a molecular weight of 1800;

[0106] (2) Add 4.5 g of KH560, a silane coupling agent, to the reaction bottle and slowly stir for 20 min at room temperature to obtain an organosilicon coating;

[0107] Finally, coating was performed according to the method of Example 1 to form a double-layer protective coating.

[0108] Example 7

[0109] First, a polyurethane coating was prepared according to the method of Example 1.

[0110] Then, prepare the silicone resin coating:

[0111] (1) 25 g of methyltrichlorosilane was slowly added to 74 g of a mixed solvent (the mixed solvent was a mixture of N-methylpyrrolidone, isopropanol, propylene glycol methyl ether and water, and the mass ratio of each component in the mixed solvent was 1:14:28:5), and white carbon black and water were gradually added. After the hydrolysis was completed, the mixture was allowed to stand at room temperature for 3 hours to obtain a methyl silicone resin solution with a molecular weight of 1800;

[0112] (2) Add 3.8 g of 1,8-diazabicyclopentane to the reaction bottle and stir slowly at room temperature for 20 min to obtain an organosilicon coating;

[0113] Finally, coating was performed according to the method of Example 1 to form a double-layer protective coating.

[0114] Example 8

[0115] A double-layer protective coating was prepared according to the method of Example 1, except that the amount of ethylenediamine added was 0.6 g. The obtained polyurethane coating had a solid content of 9.1%, a pH value of 8.3, a weight average molecular weight of 14,000 Da, and a glass transition temperature of 75°C.

[0116] Example 9

[0117] The double-layer protective coating was prepared according to the method of Example 1, except that the amount of ethylenediamine added was 1.5 g. The obtained polyurethane coating had a solid content of 9.3%, a pH value of 9.2, a weight average molecular weight of 16,000 Da, and a glass transition temperature of 77°C.

[0118] Example 10

[0119] The double-layer protective coating was prepared according to the method of Example 1, except that the amount of amino resin added was 1.0 g. The obtained polyurethane coating had a solid content of 9.1%, a pH value of 8.7, a weight average molecular weight of 12,000 Da, and a glass transition temperature of 73°C.

[0120] Embodiment 11

[0121] The double-layer protective coating was prepared according to the method of Example 1, except that the amount of amino resin added was 2.3 g. The obtained polyurethane coating had a solid content of 9.4%, a pH value of 8.6, a weight average molecular weight of 16,000 Da, and a glass transition temperature of 77°C.

[0122] Example 12

[0123] The double-layer protective coating was prepared according to the method of Example 1, except that the amount of ethylenediamine added was 0.3 g. The obtained polyurethane coating had a solid content of 9.0%, a pH value of 8.0, a weight average molecular weight of 11,000 Da, and a glass transition temperature of 74°C.

[0124] Example 13

[0125] The double-layer protective coating was prepared according to the method of Example 1, except that the amount of ethylenediamine added was 1.8 g. The obtained polyurethane coating had a solid content of 9.8%, a pH value of 9.7, a weight average molecular weight of 17,000 Da, and a glass transition temperature of 78°C.

[0126] Embodiment 14

[0127] The double-layer protective coating was prepared according to the method of Example 1, except that the amount of amino resin added was 0.8 g. The obtained polyurethane coating had a solid content of 9.1%, a pH value of 8.7, a weight average molecular weight of 11,000 Da, and a glass transition temperature of 73°C.

[0128] Embodiment 15

[0129] The double-layer protective coating was prepared according to the method of Example 1, except that the amount of amino resin added was 2.6 g. The obtained polyurethane coating had a solid content of 9.5%, a pH value of 8.6, a weight average molecular weight of 17,000 Da, and a glass transition temperature of 77°C.

[0130] Comparative Example 1

[0131] First, a polyurethane coating was prepared according to the method of Example 1.

[0132] Then, apply:

[0133] (1) Cleaning the polycarbonate substrate to remove the glue and release agent residues in the substrate coating area;

[0134] (2) coating the prepared polyurethane coating on the surface of a polycarbonate substrate by a flow coating method, and placing the substrate in an inclined position to dry the surface, so that the resin on the surface of the substrate is leveled by gravity;

[0135] (3) After the polyurethane coating has dried to form a film for 1 hour, it is placed in an oven for curing at 75°C for 6 hours.

[0136] Comparative Example 2

[0137] First, a silicone resin coating was prepared according to the method of Example 1.

[0138] Then, apply:

[0139] (1) Cleaning the polycarbonate substrate to remove the glue and release agent residues in the substrate coating area;

[0140] (2) coating the prepared silicone resin coating on the surface of a polycarbonate substrate by a flow coating method, and placing the substrate at an angle to dry the surface, so that the resin on the surface of the substrate is leveled by gravity;

[0141] (3) After the silicone resin coating has dried to form a film for 1 hour, it is placed in an oven for curing at 75°C for 6 hours.

[0142] Comparative Example 3

[0143] The method of Comparative Example 2 was followed, except that the curing conditions were 120° C. for 2 h.

[0144] Performance Testing

[0145] The physical and chemical properties, optical properties, mechanical properties and environmental resistance of the substrates modified with coatings prepared in Examples 1-15 and Comparative Examples 1-3 were tested. All tests were conducted in accordance with currently valid standards. The test standards and requirements are as follows:

[0146] (1) The test method of impact test refers to the standard GJB 1043-2006

[0147] (2) Adhesion test reference, GB / T 9286-2021

[0148] (3) Abrasion resistance test reference, ASTM F735-2006, test the change of haze before and after 100 strokes

[0149] (4) Reference standard for damp heat test GB / T 1740-2007, 10d

[0150] (5) Salt spray test reference standard GB / T 1771-2007, 48h

[0151] (6) Solar radiation reference standard GJB 150.7A-2009, light effect, 56 cycles according to procedure 2

[0152] (7) UV performance reference standard, ASTM D4587-2005, UVA-340nm, 0.89W / (m 2 nm), 8h UV ((60±2.5)℃) + 4h condensation ((50±2.5)℃) is one cycle

[0153] (8) Visual inspection of film appearance quality after film formation

[0154] (9) Film quality inspection after environmental testing, GB / T 1766-2008, check the discoloration, powdering, cracking, blistering and peeling of the film

[0155] The test results are shown in the table below:

[0156]

[0157]

[0158]

[0159] “ / ” means not determined.

[0160] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A double-layer protective coating, characterized in that: It comprises a primer layer and a top layer, wherein the top layer is arranged on the primer layer, the primer layer is made of polyurethane, and the top layer is made of silicone resin; the curing temperature of the double-layer protective coating is 70-90°C; the weight average molecular weight of the polyurethane is 18,000 Da, and the glass transition temperature is 85°C; the weight average molecular weight of the silicone resin is 1800 Da; The preparation method of the double-layer protective coating comprises the following steps: Coating a polyurethane coating on a substrate; wherein the pH value of the polyurethane coating is 8.4; and the solid content of the polyurethane coating is 8.7%; After surface drying, applying a silicone resin coating on the formed coating; and After the surface is dry, it is cured at a temperature of 70-90°C and a curing time of 2-6 hours; wherein, the surface drying temperature is 18-30°C and the surface drying time is more than 10 minutes; The preparation method of the polyurethane coating comprises: In a nitrogen atmosphere, 37 g of adipic acid, 23.3 g of hexanediol, 7.65 g of neopentyl glycol, 5 g of polyether diol, 0.6 g of trimethylolpropane and 0.01 g of an organic tin catalyst were added to a reaction bottle in sequence, the temperature was raised to 140°C in 1 h, kept warm for 0.5 h, the temperature was raised to 150°C in 1 h, kept warm for 1 h, the temperature was raised to 180°C in 1 h, kept warm for 2 h, and the temperature was continued to rise to 220°C, and vacuum distilled for 0.5 h for dehydration; nitrogen was continuously passed and kept warm for 1 h; Cool down to 95°C, add 85 g N-methylpyrrolidone under stirring, mix and stir for 0.5 h, and cool down to 50°C; 23 g of dicyclohexylmethane diisocyanate was added dropwise under nitrogen protection and stirring, and the temperature was raised to 80°C for reaction. The temperature was kept for 1 h, and 0.02 g of stannous octoate catalyst was added; the temperature was kept for reaction; the NCO content of the system was tested at intervals, and the reaction was stopped when the NCO content dropped to 2.5%; Under stirring, 6.4 g of N-methylpyrrolidone solution of dimethylolpropionic acid was added for chain extension, and the reaction was continued at 80° C. for 3 h; the mass ratio of the dimethylolpropionic acid to the N-methylpyrrolidone was 1:1; The temperature was lowered to 60°C, 2.5 g of triethylamine was added, stirring was continued for 15 min, 960 g of a mixed solvent was added to the reaction flask, stirring was continued for 5 min, and the viscosity of the system was adjusted; the mixed solvent was a mixture of N-methylpyrrolidone, isopropanol, propylene glycol methyl ether and water; Cool down to below 20°C, add 0.8 g ethylenediamine while stirring, stir vigorously for 20 min, and stir slowly for 2 h; 1.5 g of amino resin was added dropwise under strong stirring, and then slowly stirred for 2 h to obtain the polyurethane coating; the amino resin was hexamethoxymethyl melamine; The preparation method of the silicone resin coating comprises: 25 g of methyltrichlorosilane was added to 74 g of a mixed solvent, and white carbon black and water were added. After the hydrolysis was completed, the mixture was allowed to stand at room temperature for 3 h to obtain a methyl silicone resin solution. 4.5 g of epoxyalkylsilane coupling agent and 3.5 g of 1,8-diazabicyclo were added, and the mixture was slowly stirred at room temperature for 20 min to obtain an organosilicon coating.

2. The double-layer protective coating according to claim 1, characterized in that: The amount of the amino resin added is 2.3 g; The pH value of the polyurethane coating is 8.6, and the solid content of the polyurethane coating is 9.4%; the weight average molecular weight of the polyurethane is 16,000 Da, and the glass transition temperature of the polyurethane is 77°C.

3. The double-layer protective coating according to claim 1, characterized in that: The amount of ethylenediamine added is 0.6 g; The pH value of the polyurethane coating is 8.3, and the solid content of the polyurethane coating is 9.1%; the weight average molecular weight of the polyurethane is 14,000 Da, and the glass transition temperature of the polyurethane is 75°C.

4. The double-layer protective coating according to claim 1, characterized in that: The amount of ethylenediamine added is 1.5 g; The pH value of the polyurethane coating is 9.2, and the solid content of the polyurethane coating is 9.3%; the weight average molecular weight of the polyurethane is 16,000 Da, and the glass transition temperature of the polyurethane is 77° C.

5. The double-layer protective coating according to claim 1, characterized in that: The amount of the amino resin added is 1.0g; The pH value of the polyurethane coating is 8.7, and the solid content of the polyurethane coating is 9.1%; the weight average molecular weight of the polyurethane is 12,000 Da, and the glass transition temperature of the polyurethane is 73°C.

6. The double-layer protective coating according to any one of claims 1 to 5, characterized in that: The dual-layer protective coating is applied to a polycarbonate substrate.

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