Water-based ceramic red dot coating as well as preparation and coating methods thereof

Abstract

The invention discloses a water-based ceramic red dot coating as well as a preparation method and a coating method thereof. The water-based ceramic red dot coating comprises a bottom coating, a first red dot ink layer, a second red dot ink layer and a surface coating which are sequentially coated, the first red dot ink layer and the second red dot ink layer are two kinds of red ink with different color depths; in a normal temperature state, the color of the first red dot ink layer is darker than that of the second red dot ink layer; when the temperature rises, the color of the second red dot ink layer is darkened, and when the set cooking temperature is reached, the color of the second red dot ink layer is overlapped with that of the first red dot ink layer. The invention has the characteristics of high hardness, no ceramic cracking or cracking, lasting non-stickiness, and red dot pattern capable of indicating cooking temperature.

Description

Technical Field

[0001] The invention relates to the technical field of chemical coatings, in particular to a water-based ceramic red dot coating and a preparation and coating method thereof. Background Art

[0002] Water-based non-stick coatings were invented in 1958. The main material is polytetrafluoroethylene. Polytetrafluoroethylene has excellent low surface energy and heat and corrosion resistance. It is widely used in non-stick cookware and has become the core material of non-stick pans. It makes non-stick pans non-stick and easy to clean, and is popular among consumers. Around 2000, as people put forward new requirements for the environmental protection and safety of polytetrafluoroethylene, water-based ceramic non-stick coatings, a substitute for polytetrafluoroethylene, have attracted attention and been applied.

[0003] The technical principle of water-based ceramic non-stick coating is sol-gel technology. The obtained film-forming material is inorganic resin, which has the advantages of high temperature resistance and good hardness. However, due to its excessive hardness, the product is prone to ceramic collapse and cracking. In addition, due to the special nature of ceramic coating materials, it is not easy to blend with other materials, the color is single, and non-stick durability is also a big problem. Therefore, it is urgent to develop a new type of water-based ceramic non-stick coating with high hardness, no ceramic collapse or cracking, long-lasting non-stick properties, and a red dot pattern that can indicate the cooking temperature. Summary of the invention

[0004] The purpose of the present invention is to provide a water-based ceramic red dot paint and a preparation and coating method thereof. The present invention has the characteristics of high hardness, no ceramic collapse and cracking, long-lasting non-stickiness, and a red dot pattern that can indicate cooking temperature.

[0005] The technical solution of the present invention is as follows: a water-based ceramic red dot paint, comprising a primer layer, a first red dot ink layer, a second red dot ink layer and a top coat applied in sequence; the first red dot ink layer and the second red dot ink layer are two red inks with different color depths; at room temperature, the color of the first red dot ink layer is darker than the color of the second red dot ink layer; when the temperature rises, the color of the second red dot ink layer becomes darker, and when the set cooking temperature is reached, the color of the second red dot ink layer will overlap with the first red dot ink layer.

[0006] In the aforementioned water-based ceramic red dot paint, the base coating layer comprises two components, base coating A and base coating B, and the ratio between base coating A and base coating B is 2.0-3.0:1;

[0007] The primer A comprises the following raw materials in percentage by mass: aqueous silica sol: 55.0-75.0%; heat-resistant pigment: 5.0-25.0%; boron nitride whisker: 0-10.0%; quartz powder: 0-15.0%; leveling agent: 0.3-2.0%; balance: deionized water;

[0008] Primer B includes the following raw materials by weight:

[0009] Silane: 90.0-98.0%; Catalyst: 0.2-1.0%; Balance: isopropanol.

[0010] In the aforementioned water-based ceramic red dot paint, the particle size of the water-based silica sol is 10-150nm, the solid content is 20.0-50.0%, and the pH value is 8.5-11.0.

[0011] In the aforementioned water-based ceramic red dot paint, the boron nitride whisker has a particle size of 2000-5000 mesh and an aspect ratio of 10-200:1; and the quartz powder has a particle size of 5-15 um.

[0012] In the aforementioned water-based ceramic red dot paint, the first red dot ink layer includes the following component raw materials in mass percentage: water-based heat-resistant resin: 45.0-75.0%; heat-resistant filler: 0-20.0%; heat-resistant organic red pigment: 2.5-25.0%; heat-resistant coloring pigment: 0.5-5.0%; water-based dispersant: 0.5-2.0%; thickener: 0.5-10.0%; leveling agent: 0.5-1.5%; adhesion promoter: 0.5-5.0%; balance: deionized water; the heat-resistant coloring pigment is copper chrome black pigment or carbon black pigment.

[0013] In the aforementioned water-based ceramic red dot paint, the second red dot ink layer includes the following component raw materials in percentage by mass: water-based heat-resistant resin: 45.0-75.0%; heat-resistant filler: 0-20.0%; heat-resistant iron oxide red pigment: 2.5-25.0%; heat-resistant coloring pigment: 0-2.0%; water-based dispersant: 0.5-2.0%; thickener: 0.5-10.0%; leveling agent: 0.5-1.5%; adhesion promoter: 0.5-5.0%; balance: deionized water; the heat-resistant coloring pigment is copper chrome black pigment or carbon black pigment.

[0014] In the aforementioned water-based ceramic red dot paint, the top coating comprises a top coating A and a top coating B, and the ratio between the top coating A and the top coating B is 1:1;

[0015] The A surface coating includes the following components in percentage by weight: aqueous silica sol: 80.0-99.0%; leveling agent: 0.3-5.0%; balance: deionized water;

[0016] The B-side coating comprises the following components in percentage by mass: silane: 70.0-98.0%; non-sticking agent: 1.0-25.0%; catalyst: 0.2-5.0%; and the balance: isopropanol.

[0017] A method for preparing a water-based ceramic red dot paint comprises the following steps:

[0018] 1) Preparation of primer: Grind primer A to less than 15 μm, then add primer B, roll in a sealed cylinder for 8-12 hours, and filter with 400 mesh;

[0019] 2) Prepare the first red dot ink and the second red dot ink: grind the water-based heat-resistant resin and the heat-resistant red pigment, the heat-resistant filler, the water-based dispersant, the heat-resistant toning pigment, the leveling agent, the adhesion promoter and the deionized water to less than 10 μm, then add the thickener and modulate the viscosity for 90±10 seconds.

[0020] 3) Preparation of topcoat: Mix the A-coat and the B-coat, roll them in a sealed cylinder for 12 hours, and filter them through 400 mesh.

[0021] A method for applying a water-based ceramic red dot paint comprises the following steps:

[0022] 1) Primer coating spraying: preheat the workpiece to 55±10℃, spray the primer, and then dry it at 80±15℃ for 5-10 minutes. The thickness of the primer is 30-40um.

[0023] 2) Printing the first red dot ink layer: printing the first red dot ink layer on the base coating layer by pad printing or silk screen printing, and drying to form the first red dot ink layer;

[0024] 3) Printing the second red dot ink layer: printing the second red dot ink layer on the first red dot ink layer by pad printing or silk screen printing, and drying to form the second red dot ink layer;

[0025] 4) Topcoat spraying: directly spray the topcoat, then sinter at 300-330℃ for 10-15 minutes, and control the topcoat film thickness to 8-15um.

[0026] Compared with the prior art, the present invention is composed of a primer layer, a first red dot ink layer, a second red dot ink layer and a topcoat layer applied in sequence, and has high hardness, no porcelain collapse or cracking, high temperature resistance and excellent non-stick performance, and is a water-based coating, which is environmentally friendly; at the same time, the coating can print a red dot ink pattern to indicate the cooking temperature, prevent the cooking temperature from being too high and affecting health, and give the ceramic red dot coating an artistic appearance, which has good performance and appearance. When applied to non-stick cookware, the non-stick cookware coated with this coating has super wear resistance and scratch resistance, excellent non-stick and has a red dot pattern to indicate the cooking temperature. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0028] Embodiment. A water-based ceramic red dot paint comprises a primer layer, a first red dot ink layer, a second red dot ink layer and a topcoat layer which are applied in sequence; the first red dot ink layer and the second red dot ink layer are red inks of two different color depths; at room temperature, the color of the first red dot ink layer is darker than the color of the second red dot ink layer; when the temperature rises, the color of the second red dot ink layer becomes darker, and when the set cooking temperature is reached, the color of the second red dot ink layer will overlap with the first red dot ink layer.

[0029] The primer layer comprises two components, primer A and primer B, and the ratio between primer A and primer B is 2.0-3.0:1;

[0030] The primer A comprises the following raw materials in percentage by mass: aqueous silica sol: 55.0-75.0%; heat-resistant pigment: 5.0-25.0%; boron nitride whisker: 0-10.0%; quartz powder: 0-15.0%; leveling agent: 0.3-2.0%; balance: deionized water;

[0031] Primer B includes the following raw materials by weight:

[0032] Silane: 90.0-98.0%; Catalyst: 0.2-1.0%; Balance: isopropanol.

[0033] The first red dot ink layer includes the following component raw materials in mass percentage: aqueous heat-resistant resin: 45.0-75.0%; heat-resistant filler: 0-20.0%; heat-resistant organic red pigment: 2.5-25.0%; heat-resistant color-tuning pigment: 0.5-5.0%; aqueous dispersant: 0.5-2.0%; thickener: 0.5-10.0%; leveling agent: 0.5-1.5%; adhesion promoter: 0.5-5.0%; balance: deionized water; the heat-resistant color-tuning pigment is copper chrome black pigment or carbon black pigment.

[0034] The second red dot ink layer includes the following component raw materials in mass percentage: water-based heat-resistant resin: 45.0-75.0%; heat-resistant filler: 0-20.0%; heat-resistant iron oxide red pigment: 2.5-25.0%; heat-resistant color-tuning pigment: 0-2.0%; water-based dispersant: 0.5-2.0%; thickener: 0.5-10.0%; leveling agent: 0.5-1.5%; adhesion promoter: 0.5-5.0%; balance: deionized water; the heat-resistant color-tuning pigment is copper chrome black pigment or carbon black pigment.

[0035] The top coating comprises a top coating A and a top coating B, and the ratio between the top coating A and the top coating B is 1:1;

[0036] The A-side coating includes the following components in percentage by mass: aqueous silica sol: 80.0-99.0%;

[0037] Leveling agent: 0.3-5.0%; balance: deionized water;

[0038] The B-side coating comprises the following components in percentage by mass: silane: 70.0-98.0%; non-sticking agent: 1.0-25.0%; catalyst: 0.2-5.0%; and the balance: isopropanol.

[0039] The water-based silica sol has a particle size of 10-150 nm, a solid content of 20.0-50.0%, and a pH value of 8.5-11.0. Preferably, the silica sol has a solid content of 50% and a particle size of 100 nm. The film thickness and hardness of the coating will be improved.

[0040] The heat-resistant pigment is one or more combinations of titanium white pigment, titanium yellow pigment, carbon black pigment, copper chrome black pigment, iron oxide pigment, ultramarine pigment, cobalt blue pigment, cobalt green pigment, aluminum silver powder, pearlescent powder, etc. The function of the pigment is to provide coloring power, and it is required to be either an inorganic pigment or an organic pigment, and be environmentally friendly, heat-resistant and non-toxic.

[0041] The boron nitride whisker has a particle size of 2000-5000 mesh and an aspect ratio of 10-200:1. Boron nitride whiskers in the coating can improve the hardness and toughness of the coating due to the aspect ratio, and help the coating not to collapse or crack. The optimal amount of addition is about 6%. If the amount is too large, the cost is high and the gloss is reduced. If the amount is too low, the hardness and toughness of the coating are reduced, and it is easy to collapse and crack.

[0042] The quartz powder has a particle size of 5-15 um. The quartz powder is used as a filler in the coating, and can also be other types of inorganic fillers, such as alumina.

[0043] The leveling agent base oil and ink are polyacrylate leveling agents, and the surface oil is low molecular weight hydroxy silicone oil. The base oil and ink leveling agent cannot be silicone-based, which will affect the interlayer adhesion after the ink is applied. The function of the leveling agent is to reduce the surface tension of the coating and improve wettability and flatness.

[0044] The silane is one or a combination of methyltrimethoxysilane, tetramethoxysilane, methyltriethoxysilane, tetraethoxysilane, dimethyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane and the like.

[0045] The non-stick additive is a special reactive silicone oil with a viscosity of 50-2000 mPa.s, such as hydroxyl reactive silicone oil Dow Corning DC-92.

[0046] The catalyst is an organic acid such as formic acid or acetic acid, etc. The pH value is controlled within 3-4, and the main function is to catalyze the hydrolysis of silane.

[0047] The water-based heat-resistant resin is one or a combination of water-based PES resin dispersion, water-based PEEK resin dispersion, etc. Both PES and PEEK have good heat resistance and adhesion.

[0048] The aqueous dispersant is a common aqueous dispersant, such as BYK-190.

[0049] The thickener is an alkali thickener or a polyurethane thickener.

[0050] The adhesion promoter is a silane coupling agent or a titanate coupling agent, which can increase the interlayer adhesion between the ink and the primer layer.

[0051] The heat-resistant red pigment in the first red dot ink layer is an organic red pigment, generally pigment 254 red or other perylene red.

[0052] The heat-resistant coloring pigments in the first red dot ink layer and the second red dot ink layer are copper chrome black pigments or carbon black pigments, etc., and two different red inks are obtained according to the difference in coloring and red pigments. The first red dot ink layer is dark red, and the second red dot ink layer is relatively light red.

[0053] The mechanism of indicating cooking temperature is: the first red dot ink layer is prepared from organic red, and the second red dot ink layer is prepared from iron oxide red. Through color adjustment, when the temperature rises to 150-200 degrees, the iron oxide red of the second red dot ink layer will become darker, and the color overlaps with the first red dot ink layer, and the pattern of the second red dot ink layer cannot be seen, thereby achieving the function of indicating cooking temperature.

[0054] A method for preparing a water-based ceramic red dot paint, the preparation process is as follows:

[0055] 1) Preparation of primer: Grind primer A to less than 15um, then add primer B, roll in a sealed cylinder for 8-12 hours, and filter with 400 mesh.

[0056] 2) Prepare the first red dot ink and the second red dot ink: grind the water-based heat-resistant resin and the heat-resistant red pigment, the heat-resistant filler, the water-based dispersant, the heat-resistant toning pigment, the leveling agent, the adhesion promoter and the deionized water to less than 10 μm, then add the thickener and modulate the viscosity for 90±10 seconds.

[0057] 3) Preparation of topcoat: Mix the A-coat and the B-coat, roll them in a sealed cylinder for 12 hours, and filter them through 400 mesh.

[0058] A method for applying a water-based ceramic red dot paint is as follows:

[0059] 1) Primer coating spraying: preheat the workpiece to 55±10℃, spray the primer, and then dry it at 80±15℃ for 5-10 minutes. The thickness of the primer is 30-40um.

[0060] 2) Printing the first red dot ink layer: printing the first red dot ink layer on the base coating layer by pad printing or silk screen printing, and drying to form the first red dot ink layer;

[0061] 3) Printing the second red dot ink layer: printing the second red dot ink layer on the first red dot ink layer by pad printing or silk screen printing, and drying to form the second red dot ink layer;

[0062] 4) Topcoat spraying: directly spray the topcoat, then sinter at 300-330℃ for 10-15 minutes, and control the topcoat film thickness to 8-15um.

[0063] Embodiment 1-6. The difference from Embodiment 1 is that: the ratio between the primer A and the primer B of the primer layer is 2.5:1; the ratio between the A surface coating and the B surface coating is 1:1;

[0064] The respective component proportions of the primer A, primer B, first red dot ink, second red dot ink, A surface coating and B surface coating in Examples 1-6 are as follows, and the proportions are in mass percentage.

[0065]

[0066]

[0067]

[0068] Specific raw material name:

[0069] Water-soluble silica sol, choose grace AM-30;

[0070] Leveling agent, choose BYK-333;

[0071] The aqueous PES dispersion was made of Sumitomo 4100G, which was ground to obtain a 25% solid dispersion;

[0072] Color pigment: copper chrome black is selected and dispersed and ground to prepare a color paste, and the concentration of the color paste is 20%;

[0073] Thickener: Use alkali thickening Dow ASE60;

[0074] Non-stick additive: Dow Corning DC92 is used;

[0075] Adhesion promoter: Use Momentive wetlink78.

[0076] Test method:

[0077] 1. Wear resistance test: refer to the test method in 4.3.1 of GB / T 32095.2-2015.

[0078] 2. Non-stick test: refer to the test method in 4.2.1 of GB / T 32095.2-2015.

[0079] 3. Hardness test: refer to the test method in 6.2.4 of GB / T 32095.2-2015.

[0080] 4. Thickness test: refer to the test method in 6.2.3 of GB / T 32095.2-2015.

[0081] 5. Adhesion test: refer to the test method of GB / T 1720-1979.

[0082] 6. Gloss test: refer to the test method of GB / T 9754-2007.

[0083] 7. Non-stick durability test:

[0084] Add the test sample into 5% sodium chloride aqueous solution, boil for 2 hours, then wash and test for non-stickiness. During the boiling period, add purified water to maintain two-thirds of the test sample height.

[0085] Hot and cold shock:

[0086] Place the test sample in a 350°C oven for 30 minutes, then take it out with a tool and directly put it in tap water to cool it down, and then use an 80x magnifying glass to observe whether the coating is cracked. Do this for 20 cycles.

[0087] Indication temperature:

[0088] Place the test sample on an induction cooker (ceramic cooker), start heating, visually observe the temperature when the ceramic red dot patterns overlap, and record it.

[0089] The coating was prepared as follows:

[0090] Primer: Grind primer component A to less than 15um, then add primer component B, roll in a sealed cylinder for 12 hours, and filter with 400 mesh.

[0091] 2) The first red dot ink and the second red dot ink: grind the water-based heat-resistant resin, heat-resistant red pigment, heat-resistant filler, water-based dispersant, heat-resistant toning pigment, leveling agent, adhesion promoter and deionized water to less than 10um, then add the thickener and modulate the viscosity for 90±10 seconds.

[0092] 3) Topcoat: Mix the A topcoat component and the B topcoat component, roll them in a sealed cylinder for 12 hours, and filter them through 400 mesh.

[0093] The construction process is as follows:

[0094] 1) Primer spraying: preheat the workpiece to 55±10℃, spray the primer, and then dry it at 80±15℃ for 5-10 minutes. The primer film thickness is 30-40um.

[0095] 2) Printing of the first red dot ink layer: Print the first red dot ink in the middle of the base coating layer by pad printing or silk screen printing, and dry it to form pattern 1. Dry it by surface drying, air drying or drying it at 80±15℃. The oil film thickness (dry film) is 3.5±1um, and there is no specific requirement for the size.

[0096] 3) Printing of the second red dot ink layer: Print the second red dot ink on the first red dot ink layer by pad printing or silk screen printing, and dry to form pattern 2. Dry by surface drying, air drying or drying at 80±15℃. The oil film thickness (dry film) is 3.5±1um, and there is no specific requirement for the size.

[0097] 4) Topcoat spraying: directly spray the topcoat, then sinter at 300-330℃ for 10-15 minutes, and control the topcoat film thickness to 8-15um.

[0098] Example test results

[0099]

[0100]

[0101] From the above table, we can see that Example 4 has the best relative ratio. Boron nitride whiskers can improve the wear resistance and cracking resistance of the coating. The more the amount added, the better the wear resistance and cracking resistance. However, the cost increases and the gloss decreases. We use the optimal ratio of 4-8%. The more the non-stick additive is added, the better the non-stickiness. However, when the amount added exceeds 10%, the non-stickiness is not significantly improved. On the contrary, there is too much silicone oil on the surface of the coating and it is oily. We use the optimal ratio of 6-10%. In addition, we can adjust the clarity of the indicated temperature and pattern by adjusting the color of the ink, and the optimal addition is about 0.6%, so as to achieve the function of indicating the cooking temperature.

[0102] The above is a detailed introduction to a water-based ceramic red dot paint provided by the present invention. This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A water-based ceramic red dot paint, characterized in that: It includes a primer layer, a first red dot ink layer, a second red dot ink layer and a top coat layer which are applied in sequence; the first red dot ink layer and the second red dot ink layer are red inks of two different color depths; at room temperature, the color of the first red dot ink layer is darker than that of the second red dot ink layer; when the temperature rises, the color of the second red dot ink layer becomes darker, and when the set cooking temperature is reached, the color of the second red dot ink layer will overlap with the first red dot ink layer.

2. A water-based ceramic red dot paint according to claim 1, characterized in that: The primer layer comprises two components, primer A and primer B, and the ratio between primer A and primer B is 2.0-3.0:1; The primer A comprises the following raw materials in terms of mass percentage: aqueous silica sol: 55.0-75.0%; heat-resistant pigment: 5.0-25.0%; boron nitride whisker: 0-10.0%; Quartz powder: 0-15.0%; Leveling agent: 0.3-2.0%; Balance: deionized water; Primer B includes the following raw materials by weight: Silane: 90.0-98.0%; Catalyst: 0.2-1.0%; Balance: isopropyl alcohol.

3. A water-based ceramic red dot paint according to claim 2, characterized in that: The aqueous silica sol has a particle size of 10-150 nm, a solid content of 20.0-50.0%, and a pH value of 8.5-11.

0.

4. A water-based ceramic red dot paint according to claim 2, characterized in that: The boron nitride whisker has a particle size of 2000-5000 mesh and an aspect ratio of 10-200:1; the quartz powder has a particle size of 5-15um.

5. A water-based ceramic red dot paint according to claim 1, characterized in that: The first red dot ink layer includes the following component raw materials in mass percentage: aqueous heat-resistant resin: 45.0-75.0%; heat-resistant filler: 0-20.0%; heat-resistant organic red pigment: 2.5-25.0%; heat-resistant color-tuning pigment: 0.5-5.0%; aqueous dispersant: 0.5-2.0%; thickener: 0.5-10.0%; leveling agent: 0.5-1.5%; adhesion promoter: 0.5-5.0%; balance: deionized water; the heat-resistant color-tuning pigment is copper chrome black pigment or carbon black pigment.

6. A water-based ceramic red dot paint according to claim 1, characterized in that: The second red dot ink layer includes the following component raw materials in mass percentage: water-based heat-resistant resin: 45.0-75.0%; heat-resistant filler: 0-20.0%; heat-resistant iron oxide red pigment: 2.5-25.0%; heat-resistant color-tuning pigment: 0-2.0%; water-based dispersant: 0.5-2.0%; thickener: 0.5-10.0%; leveling agent: 0.5-1.5%; adhesion promoter: 0.5-5.0%; balance: deionized water; the heat-resistant color-tuning pigment is copper chrome black pigment or carbon black pigment.

7. A water-based ceramic red dot paint according to claim 1, characterized in that: The top coating comprises a top coating A and a top coating B, and the ratio between the top coating A and the top coating B is 1:1; The A-side coating includes the following components in percentage by mass: aqueous silica sol: 80.0-99.0%; Leveling agent: 0.3-5.0%; Balance: deionized water; The B surface coating includes the following components in percentage by weight: Silane: 70.0-98.0%; Non-stick additive: 1.0-25.0%; Catalyst: 0.2-5.0%; Balance: isopropyl alcohol.

8. A method for preparing a water-based ceramic red dot paint according to any one of claims 1 to 7, characterized in that: The following steps are involved: 1) Preparation of primer: Grind primer A to less than 15 μm, then add primer B, roll in a sealed cylinder for 8-12 hours, and filter with 400 mesh; 2) Prepare the first red dot ink and the second red dot ink: grind the water-based heat-resistant resin and the heat-resistant red pigment, the heat-resistant filler, the water-based dispersant, the heat-resistant toning pigment, the leveling agent, the adhesion promoter and the deionized water to less than 10 μm, then add the thickener and modulate the viscosity for 90±10 seconds. 3) Preparation of topcoat: Mix topcoat A and topcoat B, roll in a sealed cylinder for 12 hours, and filter through 400 mesh.

9. A coating method using a water-based ceramic red dot paint according to any one of claims 1 to 7, characterized in that: The following steps are involved: 1) Primer coating spraying: preheat the workpiece to 55±10℃, spray the primer, and then dry it at 80±15℃ for 5-10 minutes. The thickness of the primer is 30-40um. 2) Printing the first red dot ink layer: printing the first red dot ink layer on the base coating layer by pad printing or silk screen printing, and drying to form the first red dot ink layer; 3) Printing the second red dot ink layer: printing the second red dot ink layer on the first red dot ink layer by pad printing or silk screen printing, and drying to form the second red dot ink layer; 4) Topcoat spraying: directly spray the topcoat, then sinter at 300-330℃ for 10-15 minutes, and control the topcoat film thickness to 8-15um.

Images