A dark grid writing color coated plate and a preparation method thereof

Abstract

The application discloses a dark grid writing color-coated plate and a preparation method thereof, and relates to the field of color-coated plates. The dark grid writing color-coated plate comprises a galvanized steel plate or a cold-rolled steel plate, a primer layer, a dark grid layer and a green plate topcoat layer, the dark grid layer is obtained by printing dark grid paint, the dark grid paint is composed of 14-18 wt% fluorescent pigments, 30-35 wt% polyester resins, 10-12.5 wt% amino resins, 0.1-0.3 wt% acid catalysts, 0.5-0.7 wt% defoaming agents, 0.5-0.7 wt% leveling agents, 0.5-0.7 wt% wetting dispersants and a residual solvent; and the solvent is a mixed solvent with an ethyl acetate, isobutyl alcohol and butyl ether weight ratio of (4-5): (2-3): 3. The dark grid writing color-coated plate has a long service life and is not prone to wear and tear, the dark grid layer can only be displayed at a close distance, and the dark grid layer cannot be clearly seen at a distance of more than 2 meters, so that the aesthetic appearance is not affected, and the dark grid writing color-coated plate is widely applied to teaching in kindergartens and primary schools.

Description

Technical Field

[0001] This application relates to the field of color-coated plates, and in particular to a color-coated plate with a hidden grid for writing and a method for preparing the same. Background Technology

[0002] Writing boards, as common writing materials, are widely used in offices, classrooms, and other settings. In teaching, writing boards with grid patterns are often needed to guide young students in writing neatly. However, existing writing boards have some shortcomings. For example, grid writing boards have the grid printed on the surface, and over time, the printed grid is prone to wear and fading, significantly shortening their lifespan. Summary of the Invention

[0003] In order to improve the problems of grid-patterned writing color-coated boards being prone to wear and having a short service life in related technologies, the present invention provides a grid-patterned writing color-coated board and its preparation method.

[0004] Firstly, the hidden-grid writing color-coated plate provided in this application adopts the following solution:

[0005] A color-coated board with a hidden grid for writing includes a galvanized steel plate or cold-rolled steel plate, a primer layer, a hidden grid layer, and a green board topcoat layer arranged sequentially. The hidden grid layer is obtained by printing with a hidden grid paint composed of 14-18 wt% fluorescent pigment, 30-35 wt% polyester resin, 10-12.5 wt% amino resin, 0.1-0.3 wt% acid catalyst, 0.5-0.7 wt% defoamer, 0.5-0.7 wt% leveling agent, 0.5-0.7 wt% wetting and dispersing agent, and the balance solvent. The solvent is a mixed solvent of ethyl acetate, isobutanol, and butyl ether in a weight ratio of (4-5):(2-3):3.

[0006] Addressing the issue that existing hidden grid layers, located above the green board surface coating, suffer wear and tear after prolonged use, this application's hidden grid writing color-coated board places the hidden grid layer beneath the green board surface coating. Protected by the green board surface coating, the hidden grid layer is not subject to wear and tear over time, effectively maintaining its integrity and extending the lifespan of the board. Furthermore, the hidden grid layer is only visible at close range; it becomes invisible at distances exceeding 2 meters, thus achieving an invisible effect and preserving the aesthetic appeal.

[0007] Secondly, in this application, the grid layer uses polyester resin as the film-forming material and amino resin as the crosslinking agent and curing agent. Under the action of an acid catalyst, the amino resin reacts with the hydroxyl groups in the polyester resin, promoting film formation and increasing the hardness and wear resistance of the paint film. The defoamer effectively eliminates bubbles generated during the preparation and use of the grid paint, avoiding paint film defects caused by bubbles and ensuring the smoothness and quality of the grid layer. The fluorescent pigment mainly serves to facilitate the display of the grid layer; any fluorescent pigment that can penetrate the green board surface paint layer and be clearly displayed can be used. The leveling agent reduces the surface tension of the grid paint, assisting in achieving uniform spreading after printing. The wetting and dispersing agent improves the dispersibility of the components in the grid paint, allowing the fluorescent pigment to be uniformly dispersed in the solvent, avoiding agglomeration and ensuring the color uniformity of the grid layer. The solvent is a mixture of ethyl acetate, isobutanol and butyl ether in a specific ratio. The specific mixed solvent of this application, together with leveling agents, wetting and dispersing agents, defoamers, etc., is conducive to the formation of clear, uniform, complete and continuous dark grid layers in the dark grid paint. It is especially suitable for processing dark grid layers with a line width of less than 1mm, and will not cause problems such as jagged edges, broken lines or ink clumps at the intersection of dark grids, thereby improving the appearance quality of the dark grid layer.

[0008] In addition, in this application, the topcoat layer of the dark grid writing color-coated board is a green board topcoat layer. Compared with the conventional white board topcoat layer or black board topcoat layer, the green board topcoat layer is the gentlest to the eyes and is less likely to cause glare or fatigue after prolonged viewing.

[0009] In some preferred embodiments, the fluorescent pigment is PanaxVIOLET FL605, a purple fluorescent pigment from Asusung Corporation of South Korea.

[0010] In this application, the fluorescent pigment is preferably a purple fluorescent pigment. The dark grid layer presented by the purple fluorescent pigment is combined with the green board paint layer. The dark grid layer can be clearly presented through the green board paint layer without being too eye-catching, which is gentler on the eyes and less likely to cause eye fatigue.

[0011] In some specific embodiments, the polyester resin is polyester resin a, which has a number average molecular weight of 3000-3500 g / mol, a weight average molecular weight of 15000-20000 g / mol, a hydroxyl value of 80-90 mg KOH / g, and an acid value of 10-15 mg KOH / g.

[0012] In this application, when polyester resin a is used, during the printing of the grid layer, if the conveying speed of the galvanized steel plate or cold-rolled steel plate does not exceed 40m / min, the grid layer is not easily worn, and the resulting grid writing color-coated board can withstand 5T (180° bending) without paint peeling.

[0013] In some preferred embodiments, the polyester resin comprises polyester resin a and polyester resin b in a weight ratio of (8-8.5):(1.5-2), wherein the number average molecular weight of polyester resin a is 3000-3500 g / mol, the weight average molecular weight is 15000-20000 g / mol, the hydroxyl value is 80-90 mgKOH / g, and the acid value is 10-15 mgKOH / g; and the number average molecular weight of polyester resin b is 1800-2200 g / mol, the weight average molecular weight is 5000-5500 g / mol, the hydroxyl value is 105-115 mgKOH / g, and the acid value is 5-8 mgKOH / g.

[0014] In this application, two polyester resins, a and b, with different molecular weight distributions and hydroxyl values, are used together as polyester resins. This allows the grid layer to have both excellent wear resistance and toughness. During the printing process of the grid layer, when the conveying speed of the galvanized steel plate or cold-rolled steel plate does not exceed 60m / min, the grid layer is not easily worn. At the same time, the resulting grid writing color-coated board can withstand 3T (180° bend) without paint peeling, and the grid layer has good structural stability.

[0015] It should be noted that the amount of polyester resin b should not be excessive. Too much resin can cause the interlayer to become too hard and brittle, which will reduce the wear resistance and bending resistance.

[0016] In some preferred embodiments, the amino resin is at least one of hexamethoxymethyl melamine resin, n-butanol etherified melamine-formaldehyde resin, isobutanol etherified melamine-formaldehyde resin, imino-containing n-butanol etherified melamine-formaldehyde resin, and imino-containing methanol etherified melamine-formaldehyde resin.

[0017] In some preferred embodiments, the acid catalyst is at least one selected from p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, blocked p-toluenesulfonic acid, blocked dodecylbenzenesulfonic acid, and blocked dinonylnaphthalenedisulfonic acid.

[0018] In some preferred embodiments, the defoamer is an acrylate defoamer or a modified silicone defoamer.

[0019] In some preferred embodiments, the leveling agent is an acrylate leveling agent.

[0020] In some preferred embodiments, the wetting and dispersing agent is a polymer-modified polyester wetting and dispersing agent.

[0021] In some specific embodiments, the thickness of the galvanized steel sheet or cold-rolled steel sheet is 0.2-0.4 mm, the thickness of the primer layer is 4-5 μm, the thickness of the dark grid layer is 5-8 μm, and the thickness of the green plate topcoat layer is 28-33 μm.

[0022] In some specific embodiments, the dark-grid writing color-coated plate further includes a back paint layer, which is located on the side of the galvanized steel plate or cold-rolled steel plate away from the primer layer, and the thickness of the back paint layer is 7-10μm.

[0023] Secondly, the method for preparing a hidden-grid writing color-coated plate provided in this application adopts the following technical solution:

[0024] A method for preparing a color-coated writing board with hidden grids includes the following steps:

[0025] A primer is uniformly applied to one surface of a galvanized steel sheet or a cold-rolled steel sheet and then dried to obtain a primer layer.

[0026] A grid pattern is printed on the surface of the dried primer layer using grid paint, and then dried to obtain the grid layer.

[0027] Green board paint is uniformly coated onto the surface of the dark grid layer and dried to obtain a green board paint layer.

[0028] In some specific embodiments, the drying of the dark compartment sequentially passes through a drying zone one at 60-80°C and a drying zone two at 140-150°C.

[0029] In this application, the drying of the dark grid passes through a drying zone 1 at 60-80℃ and a drying zone 2 at 140-150℃. First, it passes through the lower temperature drying zone 1, which is beneficial to obtain a dark grid layer with uniform seam width and no broken lines or ink clumps at the intersection of dark grids. At the same time, the temperature of the drying zone 2 is controlled at 140-150℃, so that the dark grid layer will not wear during the transmission due to insufficient hardness, nor will it become brittle due to excessive temperature, affecting the integrity of the dark grid layer and the adhesion of the green board paint layer.

[0030] In some specific embodiments, the following steps are also included: applying a back paint to the side of the galvanized steel sheet or cold-rolled steel sheet away from the primer layer, and drying it to obtain a back paint layer.

[0031] In summary, this application includes at least the following beneficial technical effects:

[0032] (1) The hidden grid writing color-coated board of this application sets the hidden grid layer under the green board topcoat layer. Under the protection of the green board topcoat layer, the hidden grid layer will not be worn due to long-term use, which can effectively maintain the integrity of the hidden grid layer and extend the service life of the hidden grid writing color-coated board. In addition, the hidden grid layer can only be seen at close range. At a distance of more than 2 meters, the hidden grid layer cannot be seen, so the hidden grid layer has an invisible effect and does not affect the aesthetics.

[0033] (2) The specific mixed solvent of this application, combined with leveling agent, wetting and dispersing agent, defoamer, etc., is conducive to the formation of clear, uniform, complete and continuous dark grid layer of dark grid paint. It is especially suitable for processing dark grid layer with line width of less than 1 mm. It will not cause problems such as jaggedness, broken lines or ink accumulation at the intersection of dark grids, and can improve the appearance quality of dark grid layer.

[0034] (3) In this application, two polyester resins a and b with different molecular weight distributions and hydroxyl values ​​are used together as polyester resins, which can make the grid layer have both excellent wear resistance and toughness, so that the grid layer is not easily worn at higher conveying speeds. At the same time, the resulting grid writing color-coated board can withstand 3T (180° bending) without paint peeling, and the grid layer has good structural stability. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the color-coated plate for writing in the hidden grid of this application;

[0036] Figure 2 This is a product image of the color-coated board with hidden grid writing in this application.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. Back paint layer; 2. Galvanized steel sheet or cold-rolled steel sheet; 3. Primer layer; 4. Hidden grid layer; 5. Green board topcoat layer. Detailed Implementation

[0039] The following detailed experiments further illustrate this application. In the embodiments and comparative examples below, the primer used is the off-white polyester primer DB-14-3337-7-B from Qingyuan Huigu New Materials; the green board topcoat is the green polyester topcoat DJ-14-866791 from Qingyuan Huigu New Materials; and the back coat is the light gray polyester back coat IH-14-7147 from Qingyuan Huigu New Materials.

[0040] Example of polyester resin preparation

[0041]

Preparation Example 1-1

[0042] A polyester resin a is prepared from raw materials including 21 kg neopentyl glycol, 7 kg trimethylolpropane, 18 kg hexahydrophthalic anhydride, 9 kg phthalic anhydride, 9 kg adipic acid, and 36 kg xylene. The specific preparation steps are as follows:

[0043] Neopentyl glycol, trimethylolpropane, hexahydrophthalic anhydride, phthalic anhydride, and adipic acid were added to a reaction vessel. Under a nitrogen atmosphere, the mixture was stirred and heated to 160°C. The temperature was then increased to 230°C over 3 hours and maintained at a constant temperature. The acid value of the reaction system was measured periodically, and the water generated in the reaction was removed. When the acid value dropped to 10-15 mg KOH / g, the temperature was lowered to below 100°C, and xylene was slowly added and stirred until homogeneous to obtain polyester resin a. In this preparation example, the number average molecular weight of polyester resin a was 3048 g / mol, the weight average molecular weight was 16852 g / mol, the hydroxyl value was 83 mg KOH / g, and the acid value was 12 mg KOH / g.

[0044]

Preparation Examples 1-2

[0045] A polyester resin b is prepared by diluting 24 kg of neopentyl glycol, 8 kg of trimethylolpropane, 6.5 kg of hexahydrophthalic anhydride, 17 kg of phthalic anhydride, 14 kg of adipic acid, 0.008 kg of dibutyltin dilaurate, and 32 kg of xylene. The specific preparation steps are as follows:

[0046] Neopentyl glycol, trimethylolpropane, hexahydrophthalic anhydride, phthalic anhydride, adipic acid, and dibutyltin dilaurate were added to a reaction vessel. Under a nitrogen atmosphere, the mixture was stirred and heated to 160°C. The temperature was then increased to 200°C over 3 hours and maintained at a constant temperature. The acid value of the reaction system was periodically measured, and the water generated in the reaction was removed. When the acid value dropped to 5-8 mg KOH / g, the temperature was lowered to below 100°C, and xylene was slowly added and stirred until homogeneous to obtain polyester resin b. In this preparation example, the number average molecular weight of polyester resin b was 2000 g / mol, the weight average molecular weight was 5200 g / mol, the hydroxyl value was 110 mg KOH / g, and the acid value was 6 mg KOH / g.

[0047] Example of preparation of dark grid paint

[0048]

Preparation Example 2-1

[0049] A type of grid paint is prepared by uniformly mixing 14wt% fluorescent pigment, 30wt% polyester resin, 10wt% amino resin, 0.1wt% acid catalyst, 0.5wt% defoamer, 0.5wt% leveling agent, 0.5wt% wetting and dispersing agent, and the balance solvent.

[0050] Among them, the fluorescent pigment used is the purple fluorescent pigment Panax VIOLET FL605;

[0051] The polyester resin includes polyester resin a from [Preparation Example 1-1] and polyester resin b from [Preparation Example 1-2], with a weight ratio of polyester resin a to polyester resin b of 8.5:1.5.

[0052] The amino resin used is hexamethoxymethyl melamine resin (CYMEL 303) from Cytec Corporation.

[0053] The acid catalyst used is p-toluenesulfonic acid;

[0054] The defoamer used is BYK-057 from BYK.

[0055] The leveling agent used is BYK-358N from BYK.

[0056] The wetting and dispersing agent used is KEPERDISP-6517;

[0057] The solvent used is a mixed solvent composed of ethyl acetate, isobutanol and butyl ether, with a weight ratio of 5:2:3.

[0058]

Preparation Example 2-2

[0059] A type of grid paint is prepared by uniformly mixing 18wt% fluorescent pigment, 35wt% polyester resin, 12.5wt% amino resin, 0.3wt% acid catalyst, 0.7wt% defoamer, 0.7wt% leveling agent, 0.7wt% wetting and dispersing agent, and the balance solvent.

[0060] Among them, the fluorescent pigment used is the purple fluorescent pigment Panax VIOLET FL605;

[0061] The polyester resin includes polyester resin a from [Preparation Example 1-1] and polyester resin b from [Preparation Example 1-2], with a weight ratio of polyester resin a to polyester resin b of 8:2.

[0062] The amino resin used is CYMEL 325, a methanol-etherified melamine-formaldehyde resin containing imine groups from Cytec.

[0063] The acid catalyst used is dodecylbenzenesulfonic acid;

[0064] The defoamer used is BYK-022 from BYK.

[0065] The leveling agent used is BYK-361N leveling agent;

[0066] The wetting and dispersing agent used is KEPERDISP-6517;

[0067] The solvent used is a mixed solvent composed of ethyl acetate, isobutanol and butyl ether, with a weight ratio of 4:3:3.

[0068]

Preparation Examples 2-3

[0069] A type of guilloché varnish, which differs from [Preparation Example 2-1] in that polyester resin b is replaced by an equal mass of polyester resin a.

[0070]

Preparation Examples 2-4

[0071] A type of guilloché varnish, which differs from [Preparation Example 2-1] in that the weight ratio of polyester resin a to polyester resin b is 5:5.

[0072]

Preparation Examples 2-5

[0073] A type of grid paint, which differs from [Preparation Example 2-1] in that the solvent is different. In this preparation example, the solvent is a mixed solvent composed of ethyl acetate and butyl ether, with a weight ratio of ethyl acetate to butyl ether of 5:5.

[0074]

Preparation Examples 2-6

[0075] A type of grid paint, which differs from [Preparation Example 2-1] in that the solvent is different. In this preparation example, the solvent is a mixed solvent composed of isobutanol and butyl ether, with a weight ratio of isobutanol to butyl ether of 7:3.

[0076]

Preparation Examples 2-7

[0077] A type of grid paint, which differs from [Preparation Example 2-1] in that the solvent is different. In this preparation example, the solvent is a mixture of ethyl acetate and isobutanol, with a weight ratio of 5:5 between ethyl acetate and isobutanol. Example

[0078]

Example 1

[0079] A type of color-coated writing board with hidden grids, as shown in the reference. Figure 1 The process includes, in sequence, a back paint layer 1, a galvanized steel plate 2, a primer layer 3, a grid layer 4, and a green topcoat layer 5. The grid layer 4 consists of multiple grids formed by crisscrossing lines. In this embodiment, the preparation process of the grid writing color-coated board includes the following steps:

[0080] S1. Apply primer evenly to one surface of a galvanized steel sheet with a thickness of 0.2 mm, dry and cure at 220℃, with a drying zone length of 15 m and a galvanized steel sheet conveying speed of 60 m / min to obtain a primer layer with a dry thickness of 5 μm.

[0081] S2. Apply back paint to the side of the galvanized steel sheet away from the primer layer, and dry and cure it at 230℃. The length of the drying zone is 15m and the conveying speed of the galvanized steel sheet is 60m / min to obtain the back paint layer with a dry thickness of 8μm.

[0082] S3. Using the grid paint from Preparation Example 2-1, print grid lines with a width of 0.5 mm on the surface of the dried primer layer. The size of each grid is 50 mm * 50 mm. Dry the grid layer to obtain a grid layer. The grid layer is dried sequentially through a drying zone 1 at 80°C and a drying zone 2 at 140°C. The length of both drying zones 1 and 2 is 15 m. The conveying speed of the galvanized steel plate is 60 m / min. The dry thickness of the grid layer is 8 μm.

[0083] S4. Apply green board topcoat evenly to the surface of the dark grid layer, and dry and cure at 240℃ to obtain a green board topcoat layer with a dry thickness of 30μm.

[0084]

Example 2

[0085] A type of color-coated writing board with hidden grids, as shown in the reference. Figure 1 The process includes, in sequence, a back paint layer 1, a galvanized steel plate 2, a primer layer 3, a grid layer 4, and a green topcoat layer 5. The grid layer 4 consists of multiple grids formed by crisscrossing lines. In this embodiment, the preparation process of the grid writing color-coated board includes the following steps:

[0086] S1. Apply primer evenly to one surface of a galvanized steel sheet with a thickness of 0.2 mm, dry and cure at 220℃, with a drying zone length of 15 m and a galvanized steel sheet conveying speed of 60 m / min to obtain a primer layer with a dry thickness of 5 μm.

[0087] S2. Apply back paint to the side of the galvanized steel sheet or cold-rolled steel sheet away from the primer layer, and dry and cure it at 230℃. The length of the drying zone is 15m and the conveying speed of the galvanized steel sheet is 60m / min to obtain the back paint layer with a dry thickness of 8μm.

[0088] S3. Using the grid paint from [Preparation Example 2-2], print grid lines with a width of 0.5 mm on the surface of the dried primer layer. The size of each grid is 50 mm * 50 mm. Dry the primer layer to obtain a grid layer. The grid layer is dried sequentially through a drying zone 1 at 60°C and a drying zone 2 at 150°C. The length of both drying zones 1 and 2 is 15 m. The conveying speed of the galvanized steel plate is 60 m / min. The dry thickness of the grid layer is 8 μm.

[0089] S4. Apply green board topcoat evenly to the surface of the dark grid layer, and dry and cure at 240℃ to obtain a green board topcoat layer with a dry thickness of 30μm.

[0090]

Example 3

[0091] A type of color-coated writing board with a hidden grid, which differs from [Example 1] in that: in S3, the hidden grid paint used is the hidden grid paint of [Preparation Examples 2-3], and in step S3 of this example, the conveying speed of the galvanized steel plate is 40m / min.

[0092] Comparative Example

[0093] Comparative Example 1

[0094] A type of dark grid writing color-coated board, which differs from [Example 1] in that: in S3, the dark grid paint is the dark grid paint of [Preparation Examples 2-4].

[0095] Comparative Example 2

[0096] A type of dark grid writing color-coated board, which differs from [Example 1] in that: in S3, the dark grid paint is the dark grid paint of [Preparation Examples 2-5].

[0097] Comparative Example 3

[0098] A type of dark grid writing color-coated board, which differs from [Example 1] in that: in S3, the dark grid paint is the dark grid paint of [Preparation Examples 2-6].

[0099] Comparative Example 4

[0100] A type of dark grid writing color-coated board, which differs from [Example 1] in that: in S3, the dark grid paint is the dark grid paint of [Preparation Examples 2-7].

[0101] Comparative Example 5

[0102] A type of color-coated board with a hidden grid for writing, which differs from [Example 1] in that the temperature of the second drying zone is 220°C.

[0103] Performance testing

[0104] (1) Quality of the dark grid layer: Visually inspect whether the dark grid layer of the dark grid writing color plate is continuous and complete, and whether there is ink accumulation or clumping at the intersection of the dark grids.

[0105] (2) Cross-cut test: Refer to Section 13 of GB / T 13448-2019 to conduct a cross-cut test on the color-coated board with a grid writing surface, and classify the adhesion of the green board topcoat layer of the color-coated board with a grid writing surface according to Table 1 in GB / T 13448-2019 13.6. The lower the grade, the better the adhesion.

[0106] (3) Bending test: Refer to section 7.5.1 of GB / T 13448-2019 to bend the dark grid writing color-coated board 180°, use tape to test peeling, and record the minimum T-bend value when the paint layer does not peel off or crack.

[0107] Table 1

[0108]

[0109] Based on the test data in Examples 1, 3, Comparative Example 1, and Table 1, it can be seen that when polyester resin is used in a specific ratio of polyester resin a and polyester resin b, combined with other raw materials, the grid layer can be adapted to the high-speed production scenario of grid writing color-coated board. A continuous, complete grid layer with no ink accumulation or clumping at the grid intersections can be obtained. At the same time, the paint layer of the grid writing color-coated board has high adhesion strength. In the cross-cut test, the adhesion strength grade is 0. In addition, the grid writing color-coated board can withstand 3T (180° bend) without paint peeling, and the grid layer has good structural stability.

[0110] Based on the detection data from Example 1 and Comparative Examples 2-4, it can be seen that the composition of the solvent also plays an important role in forming a continuous and complete dark grid layer. The preferred solvent is a mixed solvent of ethyl acetate, isobutanol and butyl ether in a weight ratio of (4-5):(2-3):3.

[0111] Based on the test data in Example 1, Comparative Example 5, and Table 1, it can be seen that if the temperature in the second drying zone of the dark grid layer is too high, it will easily affect the integrity of the dark grid layer and the adhesion of the green board paint layer. At the same time, the bending resistance of the dark grid writing color-coated board will also decrease.

[0112] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this specific embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A color-coated writing board with hidden grids, characterized in that: The coating comprises, in sequence, a galvanized steel sheet or cold-rolled steel sheet, a primer layer, a grid layer, and a green topcoat layer. The grid layer is formed by printing a grid paint composed of 14-18 wt% fluorescent pigment, 30-35 wt% polyester resin, 10-12.5 wt% amino resin, 0.1-0.3 wt% acid catalyst, 0.5-0.7 wt% defoamer, 0.5-0.7 wt% leveling agent, 0.5-0.7 wt% wetting and dispersing agent, and the balance solvent. The solvent is a mixed solvent of ethyl acetate, isobutanol, and butyl ether in a weight ratio of (4-5):(2-3):

3. The polyester resin is polyester resin a or a combination of polyester resin a and polyester resin b in a weight ratio of (8-8.5):(1.5-2). The number average molecular weight of polyester resin a is 3000-3500 g / mol, the weight average molecular weight is 15000-20000 g / mol, the hydroxyl value is 80-90 mgKOH / g, and the acid value is 10-15 mgKOH / g. The number average molecular weight of polyester resin b is 1800-2200 g / mol, the weight average molecular weight is 5000-5500 g / mol, the hydroxyl value is 105-115 mgKOH / g, and the acid value is 5-8 mgKOH / g.

2. The color-coated writing board with hidden grids according to claim 1, characterized in that: The amino resin is at least one of the following: hexamethoxymethyl melamine resin, n-butanol etherified melamine-formaldehyde resin, isobutanol etherified melamine-formaldehyde resin, n-butanol etherified melamine-formaldehyde resin containing imine groups, and methanol etherified melamine-formaldehyde resin containing imine groups.

3. The color-coated writing board with hidden grids according to claim 1, characterized in that: The acid catalyst is at least one of p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, blocked p-toluenesulfonic acid, blocked dodecylbenzenesulfonic acid, and blocked dinonylnaphthalenedisulfonic acid.

4. The color-coated writing board with hidden grids according to claim 1, characterized in that: The defoamer is an acrylate defoamer or a modified silicone defoamer, the leveling agent is an acrylate leveling agent, and the wetting and dispersing agent is a polymer-modified polyester wetting and dispersing agent.

5. A color-coated writing board with a hidden grid according to claim 1, characterized in that: The thickness of the galvanized steel sheet or cold-rolled steel sheet is 0.2-0.4 mm, the thickness of the primer layer is 4-5 μm, the thickness of the dark grid layer is 5-8 μm, and the thickness of the green plate topcoat layer is 28-33 μm.

6. A color-coated writing board with a hidden grid according to claim 1, characterized in that: The dark-grid writing color-coated board also includes a back paint layer, which is located on the side of the galvanized steel plate or cold-rolled steel plate away from the primer layer, and the thickness of the back paint layer is 7-10μm.

7. A method for preparing a grid-style writing color-coated plate as described in any one of claims 1-6, characterized in that, Includes the following steps: A primer is uniformly applied to one surface of a galvanized steel sheet or a cold-rolled steel sheet and then dried to obtain a primer layer. An invisible grid is printed on the surface of the dried primer layer using an invisible grid paint, and then dried to obtain an invisible grid layer; wherein the drying of the invisible grid passes through a drying zone one at 60-80℃ and a drying zone two at 140-150℃ in sequence. Green board paint is uniformly coated onto the surface of the dark grid layer and dried to obtain a green board paint layer.

8. The method for preparing a grid-writing colored plate according to claim 7, characterized in that: It also includes the following steps: A back paint is applied to the side of the galvanized steel sheet or cold-rolled steel sheet that is away from the primer layer, and then dried to obtain a back paint layer.

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