A matte ceramic coating and a method of making the same

Abstract

The application discloses a kind of matte ceramic coating and preparation method thereof;The coating is the double-coating structure of primer+topcoat;Primer includes: 48-52% of silicon-based film-forming material, 4-5% of pH regulator, 10-12% of matt paste, 10-12% of pigment, 6-8% of filler, 1-2% of leveling agent, 4-5% of acetic acid, and the balance of deionized water, with 100% as the basis;Topcoat includes: 68-72% of silicon-based film-forming material, 5-6% of matt paste, 4-5% of non-stick aid, 1.5-2% of leveling agent, 0.5-1% of surfactant, 0.6-0.8% of formic acid, 8-10% of isopropyl alcohol, and the balance of deionized water, with 100% as the basis.The application overcomes the problem that ceramic coating in the prior art cannot consider matte effect and excellent non-stick durability, and a matte ceramic coating with excellent non-stick durability is prepared.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic coatings, and particularly relates to a matte ceramic coating and a preparation method thereof. BACKGROUND

[0002] There are two kinds of non-stick coatings for cookware, namely polytetrafluoroethylene (PTFE) coating and ceramic coating. The polytetrafluoroethylene coating is favored by many consumers due to its excellent non-stick performance, but the polytetrafluoroethylene coating belongs to PFAS substances, which begin to decompose and release a small amount of toxic substances when heated to 250 DEG C, causing harm to the health of users. Due to the strong stability and biological accumulation of polytetrafluoroethylene, the environment is also seriously affected. Therefore, the European Union, the United States and other countries have successively introduced proposals to limit PFAS substances and formulated detailed limitation processes of PFAS substances. Under this background, the polytetrafluoroethylene coating will be gradually eliminated, and the ceramic coating will become the best choice for non-stick coating of cookware due to its environmental protection, health and safety. The traditional PTFE is mostly matte coating, that is, the gloss at an angle of 60 DEG is not more than 20, and the existing ceramic coating product has high gloss, and the gloss at an angle of 60 DEG is about 60. A matte ceramic coating product is needed in the market to meet the needs of consumers for the appearance of the inner coating of cookware.

[0003] The water-based matte coating generally adds matting powder, and the matting powder is arranged irregularly on the surface of the coating to produce diffuse reflection to achieve the matte effect. However, the addition of matting powder will cause problems such as poor wear resistance of the coating and sharp decline in non-stickness. For ceramic coating for cookware, non-stick durability is the most important performance, which is directly related to the use experience of consumers. Therefore, the ceramic coating needs to consider good non-stick durability on the basis of achieving the matte effect. SUMMARY

[0004] The purpose of the present application is to overcome the problem that the ceramic coating in the prior art cannot consider the matte effect and excellent non-stick durability, and to provide a matte ceramic coating and a preparation method thereof.

[0005] The purpose of the present application is achieved by the following technical scheme:

[0006] In a first aspect, the present application relates to a matte ceramic coating, which is a double-coating structure of primer + topcoat. The primer comprises, based on 100%:

[0007] The primer comprises, based on 100%:

[0008]

[0009]

[0010] The pH regulator adjusts the pH value of the primer slurry to be above 9.5;

[0011] The topcoat comprises, by 100%:

[0012]

[0013] In order to ensure that the matting powder can be uniformly dispersed in the coating, the matting powder is made into a matting slurry in advance. Although the matting powder is made into a matting slurry and then added to the coating, the matting effect of the matting powder can be weakened, but a coating with more uniform matting effect and better flatness can be obtained, and the non-stick durability of the coating is better. Especially in the topcoat, if the amount of matting slurry added is too much, the non-stick durability of the coating is not good; if the amount of matting slurry added is too little, the gloss of the coating is high, and the matting effect cannot meet the requirements of a matte finish.

[0014] The matting slurry comprises, by 100%: 20-25% of silica matting powder, 50-60% of isopropyl alcohol, and 20-25% of deionized water. The silica matting powder is gel silica or precipitated silica. For example, OK520 of Degussa, CP4-8991 of Grace, with an average particle size of 4.5-6 μm, can be used in water-based coatings, is easy to disperse, and can balance matting and workability.

[0015] Therefore, the silica matting powder with an average particle size of 4.5-6 μm is further preferred. If the particle size of the matting powder is too small, it cannot play a matting role and the matting effect is not good, and the viscosity of the coating is greatly increased, affecting the dispersion efficiency and the final coating workability; if the particle size is too large, although the matting effect is good, it will cause the surface of the coating to be uneven, affecting the appearance and uniformity of the matting.

[0016] In the primer and the topcoat, the silicon-based film-forming material is selected to be silica sol and methyltrimethoxysilane, respectively, and the mass ratio of silica sol and methyltrimethoxysilane is preferably 1.5-1.8:1. The silica sol is the main film-forming material in the sol-gel reaction, and the methyltrimethoxysilane is the auxiliary film-forming material in the sol-gel reaction. In the sol-gel reaction, the higher the content of silica sol, the lower the gloss of the coating, but too high a content of silica sol will cause poor water resistance and easy cracking of the coating; a low content of silica sol will result in a high gloss of the coating, but too low a content of silica sol will cause low hardness and poor wear resistance of the coating.

[0017] The silica sol is selected to be an alkaline silica sol, such as ST-50-T of Nissan Chemical, TM-50 of Grace, and Bindzil S30 of AkzoNobel. The solid content of the alkaline silica sol is relatively higher under the same particle size, and the wear resistance of the coating is better, and in the system of the present application, the wear resistance and non-stickness are positively correlated, so the alkaline silica sol is selected.

[0018] The pH regulator is selected from 1% NaOH solution, which is used to adjust the pH value of the slurry to be above 9.5.

[0019] The mass ratio of the primer and the topcoat is (3-4):1.

[0020] The filler is selected from one or more of calcined kaolin, heavy calcium, mica powder, silicon powder, nano-aluminum oxide and silicon carbide.

[0021] The pigment is an inorganic pigment, non-toxic, free of heavy metals and good in temperature resistance, which is usually used as the inner coating pigment of cookware and food contact container.

[0022] The leveling agent is selected from a water-based leveling agent, such as BYK333, which can promote the formation of a smooth, smooth and uniform coating film during the drying and film forming process of the coating.

[0023] In the coating system of the present application, acetic acid is used as the catalyst for the sol-gel reaction of the primer. The pH value of the finished product is controlled to be between 4.2 and 5.0 after the preparation of the coating; the weak acidity of acetic acid has a mild catalytic effect, and a small amount of addition error will not cause a large fluctuation of the pH value, which is conducive to the control of the sol-gel reaction process.

[0024] The non-stick agent includes methyl silicone oil and hydroxyl silicone oil, which is used to provide non-stick property for the topcoat. Since the silicone oil has a small density and poor compatibility with the water-based coating, it only floats on the surface of the coating, and after solidification and film formation, the silicone oil is also located on the surface layer of the coating. During use, the -CH3 of the silicone oil is broken due to constant friction, and the non-stick property of the coating is reduced. Therefore, the amount of addition needs to be controlled. If the amount of addition of the silicone oil is too much, the "floating oil" phenomenon will occur on the surface of the coating after solidification.

[0025] The surfactant is a betaine type amphoteric surfactant. The molecular structure of the surfactant has amphiphilic property, one end is a hydrophilic group, and the other end is a lipophilic group, which can increase the compatibility of the non-stick agent with the water-based coating. The betaine type amphoteric surfactant can be easily dissolved in acidic and alkaline solutions, and is not affected by the pH value of the solution, and there is no precipitation at the isoelectric point. Moreover, the surfactant can increase the compatibility of the non-stick agent with the water-based coating, so that the silicone oil is uniformly dispersed in the coating system, which can greatly increase the amount of addition of the silicone oil and improve the non-stick durability of the coating. The amphoteric surfactant and the non-ionic surfactant are not easily affected by pH and electrolyte, and have good stability, but the emulsifying effect of the non-ionic surfactant on the non-stick agent is weak.

[0026] In addition, since the topcoat uses alkaline silica sol and the sol-gel reaction is carried out in an acidic environment, a betaine type amphoteric surfactant is selected, which can be easily dissolved in acidic and alkaline solutions and is not affected by the pH value of the solution, so that the surfactant can play its role to the maximum extent. Other amphoteric surfactants, such as amino acid type, may precipitate in acidic solution.

[0027] In the coating system of the present application, formic acid is used as a sol-gel reaction catalyst in the topcoat, and the pH value of the coating after preparation is controlled between 4.5 and 5.0. The acidity of formic acid is stronger than that of acetic acid, and the catalytic efficiency is high. Since the solid content of the topcoat is low, the sol-gel reaction speed is slower than that of the primer, so a higher catalytic efficiency formic acid is selected to speed up the sol-gel reaction. If acetic acid is used instead of formic acid, the pH value of the coating will reach 6-7, and the coating will gel and cannot be used.

[0028] The present application also relates to a preparation method of a matte ceramic coating, which comprises the following steps:

[0029] S1, preparing a matting paste:

[0030] The matting powder is mixed with isopropyl alcohol and deionized water to prepare a matting paste by dispersion;

[0031] S2, preparation of a ceramic primer:

[0032] S2-1, mixing silica sol, 1% NaOH, fillers, pigments and deionized water, grinding to a fineness of less than 20 microns, and filtering to obtain a color paste;

[0033] S2-2, uniformly mixing methyltrimethoxysilane (MTMS), acetic acid and leveling agent, adding them to the color paste, and then adding the matting paste, and aging to obtain the primer;

[0034] S3, preparation of a topcoat:

[0035] S3-1, uniformly mixing alkaline silica sol, non-stick additives, surfactants and matting paste to obtain a mixed liquid;

[0036] S3-2, uniformly mixing methyltrimethoxysilane (MTMS), formic acid, leveling agent and deionized water, and adding them to the mixed liquid, and aging to obtain the topcoat.

[0037] The content of the extinction powder in the extinction paste in step S1 cannot be too high, because the particle size of the extinction powder is small and the specific surface area is large, and the viscosity of the paste is too high if the content is too high, which leads to low dispersion efficiency or even uneven dispersion. The dispersion efficiency of ultrasonic dispersion is higher than that of stirring dispersion, and the dispersion is more uniform, and the uniformity of the gloss of the final coating is better. If the extinction powder is directly added to the color paste for grinding, the viscosity will increase sharply, a large number of bubbles will be generated, the grinding efficiency will be extremely low, and the final coating film will have many particles and a rough hand feeling, which affects the appearance of the coating film; and the extinction efficiency of the extinction powder will be affected after grinding.

[0038] In step S1, the dispersion is low-speed dispersion at 200-400 r / min for 10-15 minutes, and then ultrasonic dispersion for 30-40 minutes.

[0039] In step S2-1, the filtration is filtration with 300-mesh filter cloth.

[0040] In step S2-2, the aging is rolling aging at 120-150 r / min on a roller stand for 30-40 minutes, and then ultrasonic aging at a power of 400-500 W for 40-60 minutes. The sol-gel reaction process of the ceramic primer is as follows: first, MTMS is hydrolyzed under acidic conditions to generate silicon hydroxyl groups, and then a condensation reaction occurs between the silicon hydroxyl groups and the silica sol in the color paste to generate a ceramic coating with a very stable cross-linked structure of Si-O-Si. Once a certain amount of silicon hydroxyl groups are generated, condensation and hydrolysis occur in parallel. The hydrolysis of MTMS is relatively fast, and it can be completed in about 30 minutes. After hydrolysis, the condensation reaction is dominant. The main hydrolysis process of MTMS needs to be carried out in a rolling manner on a roller stand, because the MTMS and other components are layered during initial mixing, and are located in the upper part of the solution. In order to increase the contact probability and ensure that the MTMS can fully hydrolyze, the rolling aging method is used for the first 30 minutes. When the hydrolysis of MTMS is completed, the solution forms a relatively uniform state, and then the ultrasonic aging method can be used. Otherwise, the coating film is prone to cracking. The ultrasonic aging method can make the extinction paste more uniformly distributed in the coating, and the extinction effect of the coating is more uniform.

[0041] Generally, the non-stick aid can be mixed with the silica sol first, and then the silane is added, or the non-stick aid can be mixed with the silane first, and then the silica sol is added. The present experiment found that in the matte ceramic coating, according to the preparation steps of the topcoat described above, the non-stick aid is mixed with the silica sol first, and then mixed with the silane, and the matte ceramic coating obtained after aging has more excellent non-stick durability.

[0042] In step S3-1, after mixing uniformly, rolling is carried out at 120-150 r / min on a roller stand for 10-20 minutes.

[0043] In step S3-2, the maturing is rolling maturing at 120-150 r / min for 30-40 minutes, followed by ultrasonic maturing for 40-60 minutes.

[0044] The preparation method of the above-mentioned primer and topcoat, the extinction paste is added in the primer and topcoat, the two-layer extinction effects are superimposed, and finally the matt coating with more uniform gloss is obtained. If the primer is sprayed and cured alone, the coating gloss (60°) is 28-35, after the superposition of the topcoat and curing, the coating gloss (60°) is 15-20, the gradual extinction is adopted, and finally the gloss effect of the coating is basically consistent with that of the polytetrafluoroethylene coating. If the extinction paste is only added in the primer and not added in the topcoat, the matt gloss effect cannot be achieved.

[0045] The application also relates to a matting ceramic coating application method, which comprises the following steps

[0046] (1) sand blasting: the substrate is subjected to sand blasting treatment, and the roughness is controlled to be Ra=2.5-5 mu m;

[0047] (2) filtration: the primer and the topcoat are filtered through a 300-mesh silk screen and are ready for use;

[0048] (3) spraying: the substrate is preheated to 45-55 DEG C, the primer is first sprayed, and then the topcoat is sprayed (wet-on-wet mode);

[0049] (4) curing: 80-100 DEG C * 10 min, 200-230 DEG C * 15-20 min, and the performance is tested after natural cooling.

[0050] Compared with the prior art, the application has the following beneficial effects:

[0051] (1) the matting ceramic coating is finally obtained by optimizing the ratio of silica sol and silane, adding the extinction paste in the ceramic primer and topcoat respectively, and superimposing the extinction effects of the primer and the topcoat.

[0052] (2) the compatibility of the non-stick aid and the ceramic coating is improved by adding the betaine amphoteric surfactant in the topcoat, the non-stick durability of the coating is improved by increasing the addition amount of the non-stick aid, and the coating is free of defects such as oil floating; the alkali silica sol is selected, the wear resistance of the coating is improved, and the non-stick durability is improved.

[0053] (3) the matting ceramic coating with excellent non-stick durability is prepared, and the problem that the ceramic coating in the prior art cannot simultaneously have the matt effect and excellent non-stick durability is solved. DETAILED DESCRIPTION

[0054] The application will be described in detail below with reference to the examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the application. These are within the scope of protection of the application.

[0055] In the following examples and comparative examples, the preparation of matting paste A is as follows: matting powder (Gres CP4-8991) 25% is mixed with isopropyl alcohol 55%, deionized water 20%, and dispersed at a low speed of 300 r / min for 12 minutes, and then ultrasonic dispersed at 450 W for 35 minutes to obtain matting paste A. The preparation of matting paste B is as follows: matting powder (Gres CP4-8991) 30% is mixed with isopropyl alcohol 55%, deionized water 15%, and dispersed at a low speed of 300 r / min for 12 minutes, and then ultrasonic dispersed at 450 W for 35 minutes to obtain matting paste B. The preparation of matting paste C is as follows: matting powder (Gres ED2, particle size 2 μm) 25% is mixed with isopropyl alcohol 55%, deionized water 20%, and dispersed at a low speed of 300 r / min for 12 minutes, and then ultrasonic dispersed at 450 W for 35 minutes to obtain matting paste C.

[0056] Examples 1-5

[0057] Examples 1-5 provide a matte ceramic coating, the composition of which is shown in Table 1. The preparation of the matte ceramic coating of the application comprises the following steps:

[0058] 1. Preparation of ceramic primer:

[0059] (1) Mix silica sol, 1% NaOH, filler, pigment, and deionized water, and grind on a grinder to a fineness of less than 20 μm. Filter with a 300-mesh filter cloth to obtain a color paste, and wait for use.

[0060] (3) Mix methyltrimethoxysilane (MTMS), acetic acid, and leveling agent uniformly, and then add the color paste of step (1) and matting paste. Roll on a roller stand at 130 r / min for 35 minutes, and then ultrasonic cure at 450 W for 50 minutes.

[0061] 2. Preparation of ceramic topcoat:

[0062] (1) Mix alkaline silica sol, non-stick aid, surfactant, and matting paste uniformly, and roll on a roller stand at 130 r / min for 15 minutes, and wait for use;

[0063] (2) Mix methyltrimethoxysilane (MTMS), formic acid, leveling agent, deionized water uniformly, then add the solution obtained in step (1), roll curing on the roller stand at 130 r / min for 35 minutes, and then ultrasonic curing at 450 W for 50 minutes.

[0064] Comparative Examples 1-6

[0065] Comparative Examples 1-6 provide a ceramic coating, the composition of which is shown in Table 1; and are prepared as in Example 1.

[0066] Table 1 Coating composition and amount (wt.%) of the examples and comparative examples

[0067]

[0068]

[0069] Comparative Example 7

[0070] Comparative Example 7 provides a ceramic coating, the composition and preparation of which are substantially the same as in Example 5; except that the base paint does not contain the matting paste, and the top paint contains 16% of the matting paste.

[0071] Comparative Example 8

[0072] Comparative Example 8 provides a ceramic coating, the composition and preparation of which are substantially the same as in Example 5; except that the top paint and the base paint are directly ultrasonic cured at 450 W for 85 minutes during preparation.

[0073] Comparative Example 9

[0074] Comparative Example 9 provides a ceramic coating, the composition and preparation of which are substantially the same as in Example 5; except that the base paint is prepared by directly adding the corresponding components to the color paste without first preparing the matting paste, and the top paint is prepared by directly adding the corresponding components to the mixture without first preparing the matting paste.

[0075] Main performance test

[0076] The coatings prepared in the above examples and comparative examples are applied by the following method, and main performance tests are carried out, the test items and methods are shown in Table 2, and the test results are shown in Table 3:

[0077] Application method:

[0078] (1) Sand blasting: the aluminum alloy substrate is subjected to sand blasting treatment, and the roughness is controlled at Ra = 2.5-5 μm;

[0079] (2) Filtration: the base paint and the top paint are filtered with a 300 mesh silk screen before use;

[0080] (3) Spray: the substrate is preheated to 50°C, and then the primer is sprayed, and then the topcoat is sprayed (wet-on-wet method);

[0081] (4) Curing: 90°C x 10 min, 220°C x 15 min, and then the performance is tested after being taken out and naturally cooled.

[0082] Table 2, main performance test method of coating

[0083]

[0084] Table 3, main performance test results of examples and comparative examples

[0085]

[0086] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the above specific embodiments, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application.

Claims

1. A matte ceramic coating, comprising a two-layer structure of primer + topcoat; characterized in that, The primer, calculated at 100%, comprises: Silicon-based film-forming materials: 48-52% pH adjuster 4-5%, Matte paste 10-12%, Pigment 10-12% 6-8% of filler Leveling agent 1-2%, Acetic acid 4-5%, Deionized water balance; The pH adjuster adjusts the pH value of the primer slurry to above 9.5; The topcoat, calculated at 100%, comprises: Silicon-based film-forming materials: 68-72% Matte paste 5-6%, Non-stick additive 4-5%, Leveling agent 1.5-2%, Surfactant 0.5-1%, Formic acid 0.6-0.8%, Isopropanol 8-10%, Deionized water balance; The silicon-based film-forming material is selected from silica sol and methyltrimethoxysilane in a mass ratio of 1.5-1.8:1; The matting paste, calculated at 100%, comprises: 20-25% silica matting powder with an average particle size of 4.5-6μm, 50-60% isopropanol, and 20-25% deionized water; The surfactant used is a betaine-type amphoteric surfactant.

2. The matte ceramic coating according to claim 1, characterized in that, The silica matting agent is either gel-process silica or precipitated silica.

3. The matte ceramic coating according to claim 1, characterized in that, The mass ratio of primer to topcoat is (3-4):

1.

4. The matte ceramic coating according to claim 1, characterized in that, The non-stick additives include methyl silicone oil and hydroxyl silicone oil.

5. A method for preparing a matte ceramic coating according to any one of claims 1-4, characterized in that, The method includes the following steps: S1. Preparation of matte paste: The matting agent was mixed with isopropanol and deionized water and dispersed to prepare a matting paste. S2. Preparation of ceramic primer: S2-1. Mix silica sol, 1% NaOH, filler, pigment and deionized water, grind until the fineness is less than 20μm, and filter to obtain color paste; S2-2. Mix methyltrimethoxysilane, acetic acid, and leveling agent evenly, then add them to the color paste, add matting paste, and cure to obtain the primer. S3. Preparation of topcoat: S3-1. Mix alkaline silica sol, non-stick additive, surfactant, and matting paste evenly to obtain a mixed liquid; S3-2. Mix methyltrimethoxysilane, formic acid, leveling agent, and deionized water evenly, then add the mixture to the prepared liquid and allow it to mature to obtain the topcoat.

6. The method for preparing matte ceramic coating according to claim 5, characterized in that, In step S1, the dispersion is performed at a low speed of 200-400 r / min for 10-15 minutes, followed by ultrasonic dispersion for 30-40 minutes.

7. The method for preparing matte ceramic coating according to claim 5, characterized in that, In steps S2-2 and S3-2, the curing process involves rolling the rollers at 120-150 r / min for 30-40 minutes, followed by ultrasonic curing for 40-60 minutes.

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