Long-term high-temperature-resistant non-stick ceramic coating and preparation method thereof

Abstract

The invention discloses a long-term high-temperature-resistant non-stick ceramic coating and a preparation method thereof. The coating comprises the following components in percentage by weight: 20 to 25 percent of silica sol, 30 to 50 percent of silane, 2.5 to 3 percent of phenyl methyl silicone oil with terminal hydroxyl, 3 to 5 percent of organic solvent, 0.6 to 0.8 percent of 25 percent formic acid, 0.5 to 1 percent of flatting agent and the balance of deionized water. The methyl phenyl silicone oil with terminal hydroxyl groups (the mole fraction of phenyl is 45%-55%) is added into the system, so that on one hand, the phenyl group improves the temperature resistance of the silicone oil, and the coating has the characteristic of non-sticking at high temperature for a long time; on the other hand, the terminal hydroxyl group can be subjected to condensation polymerization with-OH on the surface of silica sol or silanol in a system, so that the silicone oil is connected to a molecular chain of the ceramic coating in a chemical bond form, the service life of the silicone oil is prolonged, and the long-term high-temperature-resistant non-stick durability of the coating is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic coatings and relates to a non-stick ceramic coating with long-term high-temperature resistance and a preparation method thereof. Background Art

[0002] A material's heat resistance and long-term operating temperature are two very different concepts. Heat resistance generally refers to the ability to maintain certain properties of the material after reaching a high temperature state for a certain period of time under standard conditions. Long-term operating temperature, on the other hand, is not time-restricted and requires maintaining certain properties at high temperatures for a long period of time, thus placing higher demands on the material's performance. Common electric ovens are appliances that operate at high temperatures for long periods of time. Since volatile substances such as water and oil often accumulate on their inner walls during operation, these ovens place higher demands on cleanability and non-stick properties, requiring them to maintain non-stick properties even under long-term high temperatures. Household electric ovens typically operate at temperatures below 230°C, while commercial ovens can reach temperatures of up to 300°C.

[0003] Fluorine coatings offer optimal non-stick properties, but they can only operate stably below 250°C. Above this temperature, they begin to decompose, producing fluoride gases that are toxic to the human body. This characteristic of fluorine coatings prevents their application in environments with long-term operating temperatures above 250°C. Ceramic coatings are inorganic, water-based coatings that are safe, healthy, and environmentally friendly. They can withstand temperatures up to 800°C, do not decompose at high temperatures, and do not release toxic substances, making them ideal for use on food contact surfaces. However, the biggest problem with ceramic coatings is that their non-stick properties drop dramatically at high temperatures. This is primarily because ceramic coatings typically use hydroxyl and methyl silicone oils, which typically have a temperature resistance below 250°C. Sustained high temperatures can cause the silicone oil's chemical bonds to continuously break, shorten, and oxidize, resulting in a decrease in the coating's non-stick properties. Therefore, adding silicone oil with better temperature resistance to ceramic coatings is one way to address this loss of non-stick properties at high temperatures. However, silicone oils with high temperature resistance usually have high viscosity and large molecular weight, and are not compatible with ceramic coating systems, and are prone to oil floating and other phenomena. Therefore, it is necessary to optimize the ceramic coating system to improve the compatibility of high-temperature resistant silicone oil with the ceramic coating system. Summary of the Invention

[0004] The present invention aims to address the aforementioned existing art issues: heat-resistant silicone oils typically have high viscosity and molecular weight, resulting in poor compatibility with ceramic coating systems and prone to defects such as oil slicks. The present invention provides a non-stick ceramic coating with long-term high-temperature resistance and a method for its preparation. By optimizing the ceramic coating formulation, the present invention ensures excellent compatibility between the heat-resistant silicone oil and the ceramic coating system, ensuring the ceramic coating maintains excellent non-stick properties at operating temperatures above 250°C, even up to 300°C, while avoiding defects such as oil slicks.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The present invention provides a non-stick ceramic coating composition with long-term high-temperature resistance. The composition comprises the following components in percentages based on 100%: 20-25% silica sol, 30-50% silane, 2.5-3% benzyl silicone oil with terminal hydroxyl groups, 3-5% organic solvent, 0.6-0.8% formic acid, 0.5-1% leveling agent, and the balance deionized water.

[0007] As one embodiment of the present invention, the structural formula of the benzyl silicone oil with terminal hydroxyl groups is: The values of m and n are selected so that the mole fraction of phenyl groups in the phenylmethyl silicone oil is between 45% and 55%. The mole fraction is obtained by liquid chromatography analysis, specifically by first creating a calibration curve using a standard sample and then comparing the liquid chromatography curve of the silicone oil sample to obtain the phenyl content.

[0008] As an embodiment of the present invention, the silane is a combination of methyltrimethoxysilane and ethyl orthosilicate in a mass ratio of 4:1-5:1.

[0009] As an embodiment of the present invention, in the composition, the mass ratio of silica sol to silane is 1:1.5-1:2.

[0010] As an embodiment of the present invention, the organic solvent is one of methanol and ethanol.

[0011] As an embodiment of the present invention, the leveling agent is BYK333.

[0012] The present invention also provides a method for preparing a non-stick ceramic coating composition with long-term high temperature resistance, the method comprising the following steps:

[0013] S1, silane, organic solvent, phenylmethyl silicone oil with terminal hydroxyl groups, and leveling agent are mixed uniformly according to the formula ratio to prepare material 1;

[0014] S2, mixing deionized water and silica sol uniformly to obtain material 2;

[0015] S3. Add 25% formic acid to material 1 and mix evenly. Then immediately add material 2 and mix evenly again. Place on a roller rack for reaction to obtain the non-stick ceramic coating composition.

[0016] As an embodiment of the present invention, in step S3, the reaction temperature is 15-30° C., the rotation speed is 120-180 rpm, and the reaction time is 4-8 hours.

[0017] As an embodiment of the present invention, the pH value of the reaction system in step S3 is controlled at 4.2-4.8.

[0018] The present invention also includes the use of the long-term, high-temperature-resistant non-stick ceramic coating composition in the preparation of the inner wall of kitchen appliances or cookware. The inner wall is required to be resistant to temperatures of at least 230°C to 300°C. Furthermore, the inner wall is required to maintain non-stick properties at temperatures of 230°C to 300°C for extended periods.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) By compounding methyltrimethoxysilane with ethyl orthosilicate, more reactive groups are formed, which can form a denser cross-linking structure and connect more -CH3 groups, thereby improving the long-term high-temperature non-stick durability of the coating; and by adjusting the ratio of silane to silica sol and appropriately increasing the content of organic components, the compatibility of the system with silicone oil is increased, thereby avoiding the defect of oil floating in the coating;

[0021] (2) By adding methylphenyl silicone oil with terminal hydroxyl groups (and the molar fraction of phenyl groups is between 45% and 55%), on the one hand, the phenyl groups improve the temperature resistance of the silicone oil, making the coating non-sticky under long-term high temperature conditions; on the other hand, the terminal hydroxyl groups can undergo a condensation reaction with the -OH groups on the surface of the silica sol or silanol in the system, so that the silicone oil is connected to the molecular chain of the ceramic coating in the form of a chemical bond, thereby extending the service life of the silicone oil and further improving the long-term high-temperature resistance and non-stick durability of the coating.

[0022] (3) By controlling the pH value of the system, the self-condensation reaction of silanols formed after silane hydrolysis is reduced, the compatibility of silicone oil with the system is improved, and the defect of oil floating in the coating is avoided. A non-stick ceramic coating with long-term high temperature resistance is obtained. DETAILED DESCRIPTION

[0023] The present invention is further illustrated by the following examples, but any example or combination thereof should not be construed as limiting the scope or implementation of the present invention. Without departing from the spirit and scope of the present invention, those skilled in the art may make any modifications or changes to the technical solution of the present invention, and such modifications and changes are also included in the scope of the present invention.

[0024] In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer's recommendations. All reagents or instruments that do not specify the manufacturer are conventional products that can be purchased commercially. In order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented equally without certain specific details. In other embodiments, methods, means, equipment and steps well known to those skilled in the art are not described in detail to highlight the gist of the present invention.

[0025] The long-term high-temperature resistant non-stick ceramic coating of the present invention comprises the following components in percentages based on 100%: 20-25% silica sol, 30-50% silane, 2.5-3% benzyl silicone oil with terminal hydroxyl groups, 3-5% organic solvent, 0.6-0.8% formic acid, 0.5-1% leveling agent, and the balance deionized water.

[0026] in:

[0027] Silica sol: the main film-forming substance of ceramic coatings, common commercial products, such as Akzo Nobel's Bindzil2034DI, Nissan Chemical's ST-O-40, Grace HS-40, etc.

[0028] Silane: auxiliary film-forming substance, methyltrimethoxysilane (MTMS): tetraethyl orthosilicate (TEOS) = 4:1-5:1.

[0029] MTMS forms a silanol containing three reactive -OH groups upon acidic hydrolysis, while TEOS forms a silanol containing four reactive -OH groups upon hydrolysis. The combination of these two forms more reactive groups, facilitating the subsequent formation of a denser cross-linked structure and the connection of more -CH3 groups, thereby improving non-stick durability. Due to the silane hydrolysis polymerization reaction, in addition to copolymerization with silica sol, it can also undergo self-polymerization. If the amount of TEOS is too high, its self-condensation reaction can form silica, increasing the hydrophilicity of the system and hindering compatibility with silicone oil, resulting in oil floating. If the amount of TEOS is too low, the improvement in non-stick durability is minimal. Moreover, if MTMS is replaced by methyltriethoxysilane or dimethyldimethoxysilane, since methyltriethoxysilane hydrolyzes slowly and usually requires 14-16 hours of reaction, the sol-gel reaction cannot be completed under the preparation conditions and a dense coating film cannot be formed. Dimethyldimethoxy forms two reactive -OH groups after hydrolysis, which cannot form a cross-linked structure and forms more branched structures, so the coating film is not dense.

[0030] The ratio of silica sol to silane is 1:1.5-1:2. Since silica sol is an inorganic substance with strong hydrophilicity, while silane is rich in -CH3 organic groups and has strong lipophilicity, increasing the silane ratio increases the number of -CH3 organic groups in the system, improving the non-stick properties of the ceramic coating and also enhancing the compatibility of the ceramic coating system with the silicone oil. Too much silica sol can lead to poor compatibility with the silicone oil, and the coating may be prone to oily surface defects after curing. Too high a silane ratio can lead to excessive self-condensation products of the silane, resulting in a loose coating structure, poor wear resistance, and prone to cracking.

[0031] Ceramic coatings for cookware typically require high wear resistance. Since increasing the silica sol ratio improves wear resistance, the silica sol to silane ratio in the formulation is controlled between 1.2:1 and 1:1, resulting in coatings with excellent wear resistance. However, the ceramic coating of the present invention, which requires slightly lower wear resistance, adjusts the silica sol to silane ratio in the formulation, reducing the silica sol content while increasing the silane content. By increasing the organic component content, the system's compatibility with silicone oil is enhanced.

[0032] Organic solvent: Common commercially available products, such as methanol or ethanol, can improve the compatibility of silicone oil with the system. Furthermore, the sol-gel reaction between silica sol and silane produces alcohols such as methanol and ethanol, which are consistent with the added solvent and do not affect the compatibility and stability of the system. Using other organic solvents, such as isopropyl alcohol, will result in slightly lower coating gloss and reduced non-stick durability.

[0033] Non-stick additive: Provides non-stick properties for ceramic coatings. Uses benzyl silicone oil with terminal hydroxyl groups, with a phenyl mole fraction between 45% and 55%. This is a common commercial product, such as IOTA-2207 from Anhui Aiyota Silicone Oil Co., Ltd.

[0034] Benzyl silicone oil, formed by replacing some of the methyl groups in methyl silicone oil with phenyl groups, exhibits superior high-temperature resistance compared to standard methyl and hydroxy silicone oils. The -CH3 group in the silicone oil provides non-stick properties. In the system of the present invention, when the molar fraction of the phenyl group in the silicone oil is ≥45%, the non-stick property can be sustained at temperatures around 300°C. If the molar fraction of the phenyl group in the silicone oil is >55%, too much of the -CH3 group in the silicone oil is replaced by phenyl groups, reducing its non-stick properties and resulting in a decrease in the non-stick properties of the coating. Examples include SF-766 and SF-7673 from Guangzhou Biaomei Silicone Fluorine New Materials Co., Ltd.

[0035] Because the methyl groups in silicone oil are replaced by phenyl groups, the molecular weight and viscosity of the silicone oil increase, reducing its compatibility with water-based ceramic coating systems. Therefore, the dosage in ceramic coatings should not exceed 1.5%. Exceeding this dosage will result in severe oil floating after the coating cures. However, too little silicone oil can result in poor non-stick durability. Using other silicone oils, such as hydroxyl silicone oils or standard methyl silicone oils, will not meet the required temperature resistance, resulting in poor non-stick durability at high temperatures. The terminal hydroxyl groups of phenylmethyl silicone oil can undergo a condensation reaction with the -OH groups on the surface of silica sol or silanols, chemically bonding the silicone oil to the ceramic coating molecular chains, extending the silicone oil's service life and ensuring long-term non-stick properties at high temperatures.

[0036] 25% formic acid solution: A catalyst for the sol-gel reaction of ceramic coatings. Silane hydrolyzes under acidic conditions, undergoing a polycondensation reaction with silica sol to form the ceramic coating. Due to the significant differences in acidity between different acids, other acids, such as acetic acid, citric acid, hydrochloric acid, benzoic acid, and oxalic acid, cannot be used in this invention's formulation. Firstly, at these concentrations and dosages, substituting these acids can significantly alter the coating's pH, potentially causing gelation and rendering it unusable. Secondly, the performance of ceramic coatings is closely linked to their pH; an inappropriate pH value can severely impact the final coating's performance.

[0037] The preparation steps of the ceramic coating are as follows:

[0038] Silane, organic solvent, non-stick additive and leveling agent are mixed evenly according to the formula ratio to prepare a semi-finished product 1;

[0039] Mixing deionized water and silica sol uniformly to obtain a semi-finished product 2;

[0040] Add 25% formic acid to semi-finished product 1 and mix thoroughly. Immediately add semi-finished product 2 and mix thoroughly again. Allow to react on a roller rack for 4-8 hours to obtain a non-stick ceramic coating with a pH of 4.2-4.8. The reaction conditions are as follows: reaction temperature 15-30°C, rotation speed 120-180 rpm.

[0041] The reaction process is as follows: First, silane hydrolyzes in an acidic environment to form silanols (Si-OH). Then, the silanols react with the -OH groups on the surface of the silica sol through condensation to form a ceramic coating. During this reaction, there is also a self-condensation reaction between the silanols. If the pH value of the system is too low, more self-condensation reactions will occur. On the one hand, the silanols formed after the hydrolysis of ethyl orthosilicate may self-condense to form silica. Silica is hydrophilic, affecting the compatibility of the silicone oil with the system and causing the coating to form an oily surface. On the other hand, the resulting coating structure may be loose, with poor wear resistance and poor high-temperature non-stick durability. If the pH value of the system is too high, the high-temperature non-stick durability of the final coating will also be affected.

[0042] Example 1

[0043] This embodiment relates to a non-stick ceramic coating composition with long-term high temperature resistance, the composition of which is shown in Table 1. The coating composition is prepared as follows:

[0044] Silane, organic solvent, non-stick additive and leveling agent are mixed evenly according to the formula ratio to prepare a semi-finished product 1;

[0045] Mixing deionized water and silica sol uniformly to obtain a semi-finished product 2;

[0046] 25% formic acid was added to semi-finished product 1 and mixed thoroughly. Semi-finished product 2 was then immediately added and mixed thoroughly again. The mixture was then placed on a roller rack and reacted at 150 rpm at 25°C for 6 hours to obtain a non-stick ceramic coating. The pH value of the coating in this example was 4.5.

[0047] Examples 2-5

[0048] Examples 2-5 respectively relate to non-stick ceramic coating compositions with long-term high temperature resistance, the compositions of which are shown in Table 1; and the preparation methods are basically the same as those of Example 1.

[0049] Comparative Examples 1-6

[0050] Comparative Examples 1-6 respectively relate to non-stick ceramic coating compositions, the compositions of which are shown in Table 1; and the preparation methods are basically the same as those of Example 1.

[0051] Table 1 Coating composition and dosage of Examples and Comparative Examples (wt.%)

[0052]

[0053]

[0054] Among them, M9660 is a phenylmethyl silicone oil without terminal hydroxyl groups, produced by Guangzhou Chuying New Material Technology Co., Ltd.

[0055] The coatings prepared in the above examples and comparative examples were subjected to main performance tests:

[0056] (1) Test item: Pencil hardness; Test method: Use a Mitsubishi pencil to scratch 10 mm in parallel at a 45° angle with a force of 10 N, and repeat the test 5 times;

[0057] (2) Test item: Adhesion; Test method: 100-grid method, use a single-sided blade to cut parallel and vertical cuts on the coating film, the depth is required to penetrate the entire thickness of the paint film, the cut spacing is 2.0mm, use 3M-898 tape to repeatedly stick and peel 5 times, and check that each scratch has no jagged cracks;

[0058] (3) Test item: gloss; Test method: gloss meter (60°);

[0059] (4) Test item: Salt water resistance; Test method: GB / T 9274-1988, three cycles of testing;

[0060] (5) Test item: Resistance to cold and hot shock; Test method: 300℃×2min, then put into ice-water mixed solution, one cycle;

[0061] (6) Test item: Non-stick durability; Test method: First, heat the pan on the stove to 300-320°C and keep it on for 120 minutes (the normal test is heated for 30 minutes, so one cycle of this test is equivalent to four cycles of the normal test). After cooling naturally, fry eggs without oil at 180-200°C for 90 seconds. Frying 10 eggs constitutes one cycle.

[0062] (7) Test item: Abrasion resistance; Test method: 3.0 kg pressure, 5 cm × 5 cm scouring pad (3M 7447C), soaked in 5 g / L detergent solution, rub back and forth on the coating, one round trip counted as one time, and the scouring pad was replaced every 250 times until three scratches appeared on the coating.

[0063] The main performance tests of the coatings in each embodiment are shown in Table 2:

[0064] Table 2

[0065]

[0066]

[0067] The main performance tests of the comparative coatings are shown in Table 3 and Table 4:

[0068] Table 3

[0069]

[0070]

[0071] Table 4

[0072]

[0073] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A non-stick ceramic coating composition with long-term high temperature resistance, characterized in that: Based on 100%, the percentages of the components are as follows: 20-25% silica sol, 30-50% silane, 2.5-3% benzyl silicone oil with terminal hydroxyl groups, 3-5% organic solvent, 0.6-0.8% 25% formic acid, 0.5-1% leveling agent, and the balance is deionized water.

2. The long-term high-temperature resistant non-stick ceramic coating composition according to claim 1, characterized in that: The structural formula of the benzyl silicone oil with terminal hydroxyl groups is: The values of m and n satisfy that the molar fraction of the phenyl group in the phenylmethyl silicone oil is between 45% and 55%.

3. The long-term high-temperature resistant non-stick ceramic coating composition according to claim 1, characterized in that: The silane is a combination of methyltrimethoxysilane and ethyl orthosilicate in a mass ratio of 4:1-5:

1.

4. The long-term high-temperature resistant non-stick ceramic coating composition according to claim 1 or 3, characterized in that: In the composition, the mass ratio of silica sol to silane is 1:1.5-1:

2.

5. The long-term high-temperature resistant non-stick ceramic coating composition according to claim 1, characterized in that: The organic solvent is one of methanol and ethanol.

6. A method for preparing a long-term high-temperature resistant non-stick ceramic coating composition according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: S1, silane, organic solvent, phenylmethyl silicone oil with terminal hydroxyl groups, and leveling agent are mixed uniformly according to the formula ratio to prepare material 1; S2, mixing deionized water and silica sol uniformly to obtain material 2; S3. Add 25% formic acid to material 1 and mix evenly. Then immediately add material 2 and mix evenly again. Place on a roller rack for reaction to obtain the non-stick ceramic coating composition.

7. The method for preparing the long-term high-temperature resistant non-stick ceramic coating composition according to claim 6, wherein: In step S3, the reaction temperature is 15-30° C., the rotation speed is 120-180 rpm, and the reaction time is 4-8 hours.

8. The method for preparing the long-term high-temperature resistant non-stick ceramic coating composition according to claim 6, wherein: In step S3, the pH value of the reaction system is controlled at 4.2-4.

8.

9. Use of the long-term high-temperature-resistant non-stick ceramic coating composition according to any one of claims 1 to 5 in preparing the inner wall of kitchen appliances or cookware.

10. The use according to claim 9, characterized in that The inner wall is required to maintain non-stickiness at a high temperature of 230-300°C for a long time.

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