CN111978527B - High-hardness powder coating with excellent fluorescence performance, preparation method and polyester resin used in preparation method - Google Patents

Abstract

The invention belongs to the technical field of polyester resin, and particularly relates to a high-hardness powder coating with excellent fluorescence performance, a preparation method and the polyester resin. The polyester resin is prepared from melamine, p-methyl benzene sulfonamide, epichlorohydrin, neopentyl glycol diglycidyl ether, N-methyldiethanolamine, octadecanedioic acid, 5-amino isophthalic acid, isobutyric acid and xylene as main materials. The powder coating formula comprises the following components in parts by weight: 550-570 parts of high-fluorescence polyester resin, 40-50 parts of TGIC, 8-10 parts of melamine organic fluorescent pigment, 10-14 parts of brightener and 9-12 parts of flatting agent. The coating film prepared by the powder coating product has the advantages of excellent fluorescence capability, long-time boiling resistance, no obvious brightness reduction, excellent hardness and water resistance and good flame retardant property, can be used for spraying functional plastic devices such as switches of electric lamps, switches of machine equipment, controllers, refrigerators, cabinets and the like, and achieves the effects of corrosion resistance and decoration.

Description

High-hardness powder coating with excellent fluorescence performance, preparation method and polyester resin used in preparation method

Technical Field

The invention belongs to the technical field of polyester resin, and particularly relates to a high-hardness powder coating with excellent fluorescence property, and a polyester resin with high fluorescence property used by the powder coating.

Background

The powder coating does not contain organic solvent, and 100 percent of the powder coating is solid, so compared with the conventional coating, the powder coating has the advantages of no pollution, energy and resource saving, high mechanical strength of the coating film, complete recovery of excessive coating and the like, and is more and more widely applied to coating of building shells of household appliances, automobile industry, outdoor bridges, highway guardrails and the like.

The organic fluorescent pigment is also called daylight fluorescent dye, is prepared by compounding the required fluorescent dye with carrier resin such as melamine resin and the like under certain conditions, mainly comprises the fluorescent dye and the carrier resin, and the carrier resin not only can be used as a fixing agent of the dye, but also endows the dye with stronger fluorescence and fading resistance. The carrier resins generally contain strongly polar groups which, on the one hand, can help to increase the color and fluorescence efficiency of the pigments; on the other hand, the carrier resin is similar to and compatible with the dye, and the dye can be uniformly dispersed in the resin. There are various polymers that can be used as the carrier resin, and para-toluenesulfonamide-formaldehyde-melamine resin (with organic amine type), polyamide resin, etc. can be used as the carrier resin. With the recent increase in the decorative requirements of paints, fluorescent pigments with vivid colors have been widely used in various coated articles.

However, the fluorescent pigment has a large relationship between the color and the carrier resin, and when the fluorescent pigment is used in a coating, especially a powder coating, the fluorescent pigment has the problems of poor compatibility or color compatibility with the existing polyester resin system, and the like, so that the coating is easy to generate pinholes and orange peel, and the coating has the problems of dark color, easy color fading, poor durability and the like.

CN109705701A discloses a fluorescent powder coating and a preparation method thereof, and a preparation method of polyester resin and a fluorescent pigment used by the fluorescent powder coating, wherein the fluorescent powder coating comprises the following raw material components in parts by mass: polyester resin: 280-320 parts of epoxy resin: 280-320 parts of fluorescent pigment: 8-12 parts of titanium dioxide: 6-10 parts of inorganic filler: 300-350 parts of flatting agent: 8-12 parts of benzoin: 2-6 parts of a brightener: 2-6 parts. The patent document uses common polyester resin, and the powder coating has problems of poor compatibility or color compatibility with the existing common polyester resin system, and the like, so that the coating film is easy to have pinholes and orange peel, and the coating film has dark color, easy color fading, poor durability and the like.

Therefore, there is a need to improve the above-mentioned disadvantages, and to invent a novel polyester resin and a powder coating material which can overcome the problems of poor compatibility with the conventional polyester resin systems and poor color compatibility in the powder coating materials.

Disclosure of Invention

Aiming at the defects existing in the application of organic melamine fluorescent pigment with larger dosage in powder coating, the invention provides a high-hardness powder coating which is prepared by taking polyester resin prepared by a specific method as a raw material and has excellent fluorescence property and water resistance, and also provides a preparation method of the powder coating; and the raw materials and the preparation method for the polyester resin are disclosed in detail;

the polyester resin with high fluorescence capability provided by the invention is prepared by high-temperature polycondensation by taking the following raw materials in parts by mole as main materials, wherein the parts by mole of the components are as follows: 3-5 parts of melamine, 5-10 parts of p-methylbenzenesulfonamide, 30-45 parts of epoxy chloropropane, 8-15 parts of neopentyl glycol diglycidyl ether, 3-8 parts of N-methyldiethanolamine, 4-9 parts of octadecanedioic acid, 3-7 parts of 5-amino isophthalic acid, 5-10 parts of isobutyric acid and 15-20 parts of xylene.

In the preparation process of the polyester resin, a first catalyst and a second catalyst are also adopted, wherein the first catalyst is triphenyl methyl phosphonium bromide, and the amount of the first catalyst is 0.05-0.1% of the mass of the raw material of the epichlorohydrin;

the second catalyst is monobutyl tin oxide, and the dosage of the second catalyst is 0.15-0.25 percent of the total mass of the raw materials.

In the preparation process of the polyester resin, an antioxidant of tetra [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid ] pentaerythritol ester is also adopted, and the dosage of the antioxidant is 0.2-0.5 percent of the total mass of the raw materials, namely the antioxidant 1010.

The preparation method of the polyester resin comprises the following steps:

(1) adding the neopentyl glycol diglycidyl ether, epoxy chloropropane and a first catalyst into a reaction kettle according to the formula ratio, adding the melamine and the p-toluenesulfonamide according to the formula ratio, stirring uniformly at room temperature, slowly heating to 70-75 ℃ from room temperature at the heating rate of 8-10 ℃/h, carrying out heat preservation reaction for 1-2h, heating to 100-105 ℃ at the heating rate of 13-15 ℃/h, and carrying out reaction again for 0.5-1 h;

(2) when the viscosity of the system reaches more than 9000mPa & s when detected at 25 ℃, adding N-methyldiethanolamine, octadecanedioic acid and a second catalyst in the formula amount, gradually heating to 210 ℃ at the heating rate of 14-16 ℃, and then continuing the heat preservation polymerization reaction for 1-3 h;

(3) when the acid value of the polymer is lower than 25mgKOH/g, adding antioxidant with the formula amount, starting a vacuum system at the same time, keeping the vacuum degree between-0.098 and-0.095 Mpa, and carrying out vacuum reaction at 210-215 ℃ for 1-2h to promote the further polycondensation of the polyester resin;

(4) stopping vacuumizing when the acid value of the polymer is lower than 12mgKOH/g, adding the 5-amino isophthalic acid with the formula amount, continuing to perform polymerization reaction, heating to 230 ℃ at the heating rate of 5-7 ℃/h, and then performing heat preservation reaction for 2-4 h;

(5) when the acid value of the polymer is 35-42mgKOH/g, cooling to 135-140 ℃, then adding isobutyric acid and xylene with the formula amount for esterification reaction to reduce the number of active hydroxyl groups, carrying out esterification dehydration reaction at 140-145 ℃ for 1-2h, after the system does not have obvious esterification water, starting a vacuum system, heating, removing the solvent, unreacted isobutyric acid and the like by virtue of a decompression system, keeping the vacuum degree between-0.098 and-0.095 MPa, heating to 190-195 ℃, discharging at high temperature when the material is almost not evaporated, cooling the polyester resin, crushing and granulating to obtain the product polyester resin.

When the system is not obviously dehydrated, the esterification water in the system is less than 2 drops in 1 min.

The application of the polyester resin with high fluorescence capability in powder coating.

The formula of the powder coating comprises the following components in parts by weight: 550-570 parts of high-fluorescence polyester resin, 40-50 parts of TGIC, 8-10 parts of melamine organic fluorescent pigment, 10-14 parts of brightener and 9-12 parts of flatting agent.

Among the above raw materials, melamine organic fluorescent pigment was purchased from Huangshan Jiajia fluorescent materials Co., Ltd, red color, model HT-811. The above product preparation scheme corresponds to patent CN102942663B developed by Huangshan Jiajia fluorescent pigment materials, Inc.

The preparation method of the powder coating comprises the following steps:

s1: uniformly mixing the polyester resin and the melamine organic fluorescent pigment according to the formula ratio, and then carrying out melt crosslinking by a double-screw extruder, wherein the screw temperature is controlled to be 160 ℃ and the screw rotating speed is 100 rpm and 150 rpm;

s2: the materials melted and extruded by the double-screw extruder are tabletted by a tablet press with a tap water cooling system and crushed into 2-4mm particles by a crusher;

s3: adding the mixed particles obtained in the step S2, TGIC curing agent, brightener and flatting agent in formula amount into a high-speed mixer, starting mixing equipment, and mixing at high speed for 20-30 min;

s4: after the materials are uniformly mixed, adding the materials into a double-screw extruder for melt extrusion, wherein the temperature of an extrusion section is 135-;

s5: the materials melted and extruded by the double-screw extruder are tabletted and coarsely crushed into granules by a tablet press with a tap water cooling system;

s6: and further grinding the coarse particles by a mill, and screening out the particles with the meshes of 160 and 180 by an induced air system of the mill for collection to obtain the finished product powder coating.

The powder coating of the invention has the following characteristics:

the polyester resin is prepared by reacting raw materials with excellent color development effect in melamine organic fluorescent pigment, such as melamine and p-methyl benzene sulfonamide, and the polar groups of the melamine organic fluorescent pigment, such as amino, sulfonamide and the like ensure the color development capability and color vividness of the organic fluorescent pigment and the excellent fluorescence performance of the final product, namely the powder coating;

epoxy compounds are introduced into the polyester chain segment to participate in reactions such as epichlorohydrin and neopentyl glycol diglycidyl ether so as to improve the adhesive force of the polyester resin and a base material, and long-chain flexible monomers such as octadecanedioic acid and N-methyldiethanolamine are matched, so that the impact resistance of the coating is considered while the hardness of the polyester is realized;

the N-methyldiethanolamine containing polar amino and 5-amino isophthalic acid further enhance the compatibility of polyester resin and melamine organic fluorescent pigment, and are favorable for color;

and isobutyric acid with a branched chain is adopted for carrying out partial esterification end capping so as to further improve the water resistance of the polyester resin.

The polyester resin contains high flame-retardant chlorine and nitrogen elements, the finally obtained polyester resin has high acid value, is matched with a trifunctional nitrogen-containing TGIC curing agent to be cured into a film, and has high crosslinking density and good flame retardant property. The coating film prepared by the final powder coating product has excellent fluorescence property, flame retardant property and higher hardness, and can be used in various fields with higher decorative requirements, such as refrigerators, washing machines, cabinets, guardrails and the like.

The invention has the beneficial effects that:

(1) the polyester resin prepared by the raw materials and the method has high fluorescence capability; after the paint is applied to powder paint, the paint has good compatibility and color compatibility;

(2) the polyester resin produced by adopting specific raw materials and a formula is supplemented with other raw materials, and the prepared powder coating has the advantages of flat and smooth film, bright color, difficult fading and strong durability.

Detailed Description

The present invention will now be further described with reference to specific embodiments in order to enable those skilled in the art to better understand the present invention.

The melamine organic fluorescent pigment used in the following was purchased from Huangshan Jia fluorescent materials, Inc., Red, model HT-811, and the preparation method of the product corresponds to patent CN102942663B developed by Huangshan Jia fluorescent pigments, Inc.

Example 1

A process for the preparation of a powder coating comprising the steps of:

s1: uniformly mixing the polyester resin and the melamine organic fluorescent pigment according to the formula ratio, and then carrying out melt crosslinking by a double-screw extruder, wherein the screw temperature is controlled at 155 ℃, and the screw rotating speed is 140 rpm;

s2: the materials melted and extruded by the double-screw extruder are tabletted by a tablet press with a tap water cooling system and crushed into 3mm particles by a crusher;

s3: adding the mixed particles obtained in the step S2, TGIC curing agent, brightener and flatting agent in formula amount into a high-speed mixer, starting mixing equipment, and mixing at high speed for 25 min;

s4: after the materials are uniformly mixed, adding the materials into a double-screw extruder for melt extrusion, wherein the temperature of an extrusion section is 140 ℃, and the rotating speed of a screw is 480 rpm;

s5: the materials melted and extruded by the double-screw extruder are tabletted and coarsely crushed into granules by a tablet press with a tap water cooling system;

s6: and (3) further grinding the coarse particles by a mill, and screening out 180-mesh particles by an induced air system of the mill for collection to obtain the finished powder coating.

The preparation method of the polyester resin comprises the following steps:

(1) adding the neopentyl glycol diglycidyl ether, epoxy chloropropane and a first catalyst into a reaction kettle according to the formula ratio, adding the melamine and the p-toluenesulfonamide according to the formula ratio, stirring uniformly at room temperature, slowly heating to 75 ℃ from room temperature at a heating rate of about 9 ℃/h, carrying out heat preservation reaction for 1.5h, heating to 105 ℃ at a heating rate of 14 ℃/h, and carrying out reaction again for 0.8 h;

(2) when the viscosity of the system reaches more than 9000mPa & s when detected at 25 ℃, adding N-methyldiethanolamine, octadecanedioic acid and a second catalyst in the formula amount, gradually heating to 210 ℃ at the heating rate of 15 ℃, and then continuing the heat preservation polymerization reaction for 2 hours;

(3) adding antioxidant 1010 with the formula amount when the acid value of the polymer is lower than 25mgKOH/g, starting a vacuum system at the same time, keeping the vacuum degree between-0.098 and-0.095 Mpa, and carrying out vacuum reaction for 1.5h at 212 ℃ to promote the polyester resin to be further polycondensed;

(4) stopping vacuumizing when the acid value of the polymer is lower than 12mgKOH/g, adding the 5-amino isophthalic acid with the formula amount, continuing to perform polymerization reaction, heating to 230 ℃ at the heating rate of 5-7 ℃/h, and then performing heat preservation reaction for 2-4 h;

(5) when the acid value of the polymer is 38mgKOH/g, cooling to 138 ℃, then adding isobutyric acid and xylene with the formula amount for esterification reaction to reduce the number of active hydroxyl groups, carrying out esterification dehydration reaction for 1.5h at 142 ℃, starting a vacuum system after the system does not have obvious esterification water, heating, removing solvent, unreacted isobutyric acid and the like by virtue of the reduced pressure system, keeping the vacuum degree between-0.098 MPa and-0.095 MPa, heating to 193 ℃, discharging at high temperature when the material is almost not evaporated, cooling the polyester resin, crushing and granulating to obtain the product polyester resin.

The indexes of the polyester resin in examples 1 to 4 are: appearance: the colorless transparent particles have an acid value of 35-43mgKOH/g and a softening point of 96-105 ℃. Specific acid values and softening points are shown in Table 3.

The preparation methods of the products in examples 2 to 4 are the same as those in example 1, and they are different only in the amount of the raw materials, which are specifically shown in the following tables 1 and 2:

TABLE 1 raw material amounts of powder coatings in examples 1 to 4

	Example 1	Example 2	Example 3	Example 4
					Polyester resin	560	550	570	555
TGIC	45	40	50	43
					Melamine organic fluorescent pigment	9	8	10	8.5
Brightener	12	14	10	13
					Leveling agent	10	12	9	11

TABLE 2 raw material amounts of polyester resins in examples 1 to 4

	Example 1	Practice ofExample 2	Example 3	Example 4
					Melamine	3	4	5	4.5
Para-methylbenzenesulfonamide	8	8	5	10
					Epichlorohydrin	38	40	30	45
Neopentyl glycol diglycidyl ether	9	12	11	15
					N-methyldiethanolamine	3	5	8	6
Octadecanedioic acid	4	6	8	9
					5-Aminoisophthalic acid	3	5	7	6
Isobutyric acid (Ab)	5	8	10	9
					Xylene	15	18	20	19
First catalyst (%)	0.05	0.08	0.1	0.09
					Second catalyst (%)	0.15	0.2	0.25	0.19
Antioxidant (%)	0.2	0.3	0.5	0.4

Note: in the table 2, the first catalyst is triphenyl methyl phosphonium bromide, and the amount of the first catalyst is the mass percentage of the raw material of the epichlorohydrin;

the second catalyst is monobutyl tin oxide, and the dosage is the percentage of the total mass of the raw materials;

the antioxidant is 1010, namely tetra [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid ] pentaerythritol ester, and the using amount is the percentage of the total mass of the raw materials.

TABLE 3 acid value and softening point of polyester resin in examples 1 to 4

	Example 1	Example 2	Example 3	Example 4
					Acid value (mgKOH/g)	42	36	41	39
Softening Point (. degree. C.)	98	102	100	105

Comparative example 1

A commercially available polyester resin for ordinary HAA, model PH8337, available from new materials gmbh, meijia, anhui, was prepared by the preparation method of example 2;

comparative example 2

The preparation method of the polyester resin and the powder coating in CN109705701A in example 1 is adopted to prepare the fluorescent powder coating, wherein the fluorescent pigment is the organic melamine fluorescent pigment in the product of the invention.

Example 5

Preparing a coating layer: and spraying the prepared powder coating on the galvanized iron substrate subjected to surface treatment by using an electrostatic spray gun, wherein the film thickness is about 70 mu m, and fully curing at 150 ℃/20min to obtain the coating.

The detection of the coating index is based on GB/T21776 2008 'Standard guide for powder coating and coating detection'; the adhesion rating is in accordance with GB/T9286 1998 test of marking test of paint films of colored paint and varnish; the flame retardant property test is carried out according to GB/T2406.2 oxygen index determination combustion behavior, a sample is type I, the higher the oxygen index is, the better the flame retardant property is, generally, the oxygen index is 22-27% of combustible materials, and the oxygen index is more than 27% of flame retardant materials. The pencil hardness test is carried out according to GB/T6739-2006 paint film hardness determination by a color paint and varnish pencil method. The pencil hardness parameter is 5B-4B-3B-2B-B-HB-F-H-2H-3H-4H-5H, and the hardness grade gradually increases from left to right.

Color intensity measurement method: weighing 2g of a sample of the finished powder coating in a 250ml ground bottle, adding 60g of the mixed solvent, covering the bottle cap, soaking and dissolving, slightly stirring by using a glass rod after soaking for 1 hour, continuously dissolving until the sample is completely dissolved, and completely dissolving a standard sample (pure melamine organic fluorescent pigment) by the same method; taking a sample which is slightly completely dissolved and a standard sample, placing the sample and the standard sample on the same A4 paper, and uniformly coating by using an applicator; a light source D65 was selected, and the standard sample was set as a reference (color intensity 100%) on a colorimeter, and then the sample was measured and the color intensity was read.

TABLE 4 test of the properties of the products of the examples and comparative examples after film coating

Note: in the above table, the color intensity of the powder coating refers to the result compared with the standard.

As can be seen from the table above, the coating film of the products in examples 1-4 is excellent in performance, mainly characterized in that the coating film is flat and smooth in appearance, strong in impact resistance, and both positive and negative impacts of 50cm pass through; the gloss (60 degree angle) reaches more than 91.5 percent; the color intensity of the powder coating reaches more than 54 percent, and the coating film has bright color appearance and higher hardness and reaches the standards of 2H and 3H; the color is unchanged when boiling water is boiled, the bright color is still kept, and the oxygen index reaches more than 30 percent;

the product obtained by the preparation is basically flat, but has slight orange peel phenomenon, and positive impact passes through and reverse impact cracks; gloss (60 degree angle) is less than in the examples; color intensity is far less than in the examples; and from the appearance of the coating, the coating shows a dull color, the hardness of the coating is low and only reaches H; the color is darker and the oxygen index is not high, which is obviously lower than that of each example.

In comparative example 2, the polyester resin in example 1 in CN109705701A is used as a raw material, and the prepared fluorescent paint is basically flat, but has obvious pinhole phenomenon, and positive impact passes through and reverse impact cracks; gloss (60 degree angle) is less than in the examples; color intensity is far less than in the examples; and from the appearance of the coating, the coating shows a dull color, the hardness of the coating is lower and only reaches F; the color is darker and the oxygen index is not high, which is obviously lower than that of each example.

Claims (3)

1. The high-hardness powder coating is characterized by comprising the following components in parts by weight: 550-570 parts of polyester resin, 40-50 parts of TGIC curing agent, 8-10 parts of melamine organic fluorescent pigment, 10-14 parts of brightener and 9-12 parts of flatting agent;

the polyester resin is prepared by high-temperature polycondensation by using the following raw materials in parts by mole as main materials, wherein the parts by mole of the raw materials are as follows: 3-5 parts of melamine, 5-10 parts of p-methylbenzenesulfonamide, 30-45 parts of epoxy chloropropane, 8-15 parts of neopentyl glycol diglycidyl ether, 3-8 parts of N-methyldiethanolamine, 4-9 parts of octadecanedioic acid, 3-7 parts of 5-amino isophthalic acid, 5-10 parts of isobutyric acid and 15-20 parts of xylene;

in the preparation process of the polyester resin, a first catalyst and a second catalyst are also adopted, wherein the first catalyst is triphenyl methyl phosphonium bromide, and the amount of the first catalyst is 0.05-0.1% of the mass of the raw material of the epichlorohydrin; the second catalyst is monobutyl tin oxide, and the using amount of the second catalyst is 0.15-0.25% of the total mass of the raw materials;

in the preparation process of the polyester resin, an antioxidant of tetra [ beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid ] pentaerythritol ester is also adopted, and the using amount of the antioxidant is 0.2-0.5 percent of the total mass of the raw materials;

the preparation method of the polyester resin comprises the following steps:

(1) adding the neopentyl glycol diglycidyl ether, epoxy chloropropane and a first catalyst into a reaction kettle according to the formula ratio, adding the melamine and the p-toluenesulfonamide according to the formula ratio, stirring uniformly at room temperature, slowly heating to 70-75 ℃ from room temperature at the heating rate of 8-10 ℃/h, carrying out heat preservation reaction for 1-2h, heating to 100-105 ℃ at the heating rate of 13-15 ℃/h, and carrying out reaction again for 0.5-1 h;

(2) when the viscosity of the system reaches more than 9000mPa & s when detected at 25 ℃, adding N-methyldiethanolamine, octadecanedioic acid and a second catalyst in the formula amount, gradually heating to 210 ℃ at the heating rate of 14-16 ℃, and then continuing the heat preservation polymerization reaction for 1-3 h;

(3) when the acid value of the polymer is lower than 25mgKOH/g, adding antioxidant with the formula amount, starting a vacuum system at the same time, keeping the vacuum degree between-0.098 and-0.095 Mpa, and carrying out vacuum reaction at 210-215 ℃ for 1-2h to promote the further polycondensation of the polyester resin;

(4) stopping vacuumizing when the acid value of the polymer is lower than 12mgKOH/g, adding the 5-amino isophthalic acid with the formula amount, continuing to perform polymerization reaction, heating to 230 ℃ at the heating rate of 5-7 ℃/h, and then performing heat preservation reaction for 2-4 h;

(5) when the acid value of the polymer is 35-42mgKOH/g, cooling to 135-140 ℃, then adding isobutyric acid and xylene with the formula amount to perform esterification reaction to reduce the number of active hydroxyl groups, performing esterification dehydration reaction at 145 ℃ for 1-2h, after the system does not have obvious esterification water, starting a vacuum system, heating, removing the solvent and unreacted isobutyric acid by virtue of a decompression system, keeping the vacuum degree between-0.098 and-0.095 MPa, heating to 195 ℃, discharging at high temperature when the material is almost not evaporated, cooling the polyester resin, crushing and granulating to obtain the product polyester resin.

2. The powder coating of claim 1, wherein (5) when there is no significant removal of the esterification water from the system means that less than 2 drops of esterification water are present in the system for 1 min.

3. The method of preparing a powder coating according to claim 1, comprising the steps of:

s1: uniformly mixing the polyester resin and the melamine organic fluorescent pigment according to the formula ratio, and then carrying out melt crosslinking by a double-screw extruder, wherein the screw temperature is controlled to be 160 ℃ and the screw rotating speed is 100 rpm and 150 rpm;

s2: the materials melted and extruded by the double-screw extruder are tabletted by a tablet press with a tap water cooling system and crushed into 2-4mm particles by a crusher;

s3: adding the mixed particles obtained in the step S2, TGIC curing agent, brightener and flatting agent in formula amount into a high-speed mixer, starting mixing equipment, and mixing at high speed for 20-30 min;

s4: after the materials are uniformly mixed, adding the materials into a double-screw extruder for melt extrusion, wherein the temperature of an extrusion section is 135-;

s5: the materials melted and extruded by the double-screw extruder are tabletted and coarsely crushed into granules by a tablet press with a tap water cooling system;

s6: and further grinding the coarse particles by a mill, and screening out the particles with the meshes of 160 and 180 by an induced air system of the mill for collection to obtain the finished product powder coating.