A primerless thermoset powder coating material and method of coating thereof

Abstract

The application discloses a primerless thermosetting powder coating material and relates to the technical field of abrasion-resistant powder coating preparation. The coating method of the primerless thermosetting powder coating material is as follows: after the surface of a coated part is pretreated, the surface of the part is sprayed with polyester powder coating paint by using an electrostatic spraying process, then the paint room is baked to be heated to 145-150 DEG C, and the heating lasts for 8-10 min, then the temperature is reduced to 125-130 DEG C, and the temperature is kept for 10 min, the part is taken out, and the part is naturally cooled to room temperature, and the polyester powder coating paint is obtained; the polyester powder coating paint contains ZnSt-PPh composite material with a core-shell structure. The coating method is simple and easy to operate, and the energy consumption is low, and the problems of pores and orange peel on the cured surface are solved; the polyester coating has excellent mechanical properties, smoothness and impact resistance, and has excellent weather resistance, corrosion resistance and friction and scratch resistance, and can be applied to the surfaces of high and low temperature substrates such as metals and plastics, and the durability of the coating is prolonged.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of powder coating preparation, and particularly relates to a preparation of a primer-free wear-resistant and scratch-resistant thermosetting powder coating with high adhesion, and a composition of a polyester powder coating material involved in the coating and a coating method of the material on a surface of a metal and heat-sensitive substrate. BACKGROUND

[0002] The thermosetting powder coating is a new type of 100% solid surface decoration and protection material without solvent, which has good adhesion to a metal substrate and outstanding mechanical properties of a coating after film formation, and can meet the needs of different occasions. At present, commonly used thermosetting powder coatings on the market are: epoxy powder coating, epoxy-polyester powder coating and polyester powder coating. The epoxy powder coating has good corrosion resistance, hardness, adhesion and impact strength, but its weather resistance is poor and it is easy to decompose, which is not suitable for outdoor products; the epoxy-polyester powder coating has good impact resistance, leveling property and adhesion, but its yellowing resistance and alkali resistance are general and its weather resistance is relatively poor, which is suitable for indoor use; the polyester powder coating has excellent weather resistance, corrosion resistance and gloss, but different types of curing agents will also cause some problems.

[0003] The curing agents of the polyester powder coating mainly include isocyanuric acid triglycidyl ester (TGIC) type curing agent and hydroxyalkylamide (HAA) type curing agent. TGIC has good stability and outstanding weather resistance, but its curing film formation temperature is generally 180-200℃, which limits its application range and can only be applied to metal substrates with high temperature resistance and consumes more energy. HAA meets the green environmental protection requirements and can be used to replace TGIC, but HAA contains four terminal hydroxyl groups, and small molecule water is generated in the curing process, which leads to poor weather resistance of the cured product, easy occurrence of pores, orange peel and yellowing on the cured surface, etc., which limits its application and promotion.

[0004] However, due to the toxicity of TGIC, its use has been limited in some European countries, and HAA is currently mainly used as a curing agent for polyester resin abroad. We know that the coating film after HAA curing is too thick, which makes the pinhole and shrinkage hole more serious, and the weather resistance is also affected; and the melting point of HAA is relatively high, generally at 120-130℃, and HAA generally starts to cure above 130℃, therefore, the screw temperature needs to be strictly controlled in the melting and extrusion process of the coating to prevent the curing from occurring too early and affecting the performance of the coating film. The polyester-HAA coating is generally cured at above 150℃ (using conventional electrostatic spraying or fluidized bed dipping), so that its smoothness and impact resistance meet the use requirements, but it cannot solve the influence caused by the water produced in the curing, the orange peel is serious, and it is not suitable for the curing of thick coating, which affects the adhesion between the coating and the substrate and the durability is poor.

[0005] In recent years, researchers have studied HAA-type curing agents more, mainly for modification, but the use effect is not good, and the effects such as pinhole, weather resistance, and adhesion are not obviously improved; or the polyester resin is modified, but it is still difficult to achieve industrial production. US6284845 discloses a powder coating composition comprising a carboxyl-terminated polyester, an epoxy compound, and an onium catalyst or a beta-hydroxyalkyl amide. However, due to the presence of linear polyester in the powder coating composition, the impact resistance at low curing temperature is insufficient. CN102365321B discloses a powder coating composition comprising a polyester and a beta-hydroxyalkyl amide as a crosslinking agent, which can be cured at low temperature (140-150℃), and has limited spraying to no spraying, acceptable smoothness and sufficient impact resistance, but the preparation of the polyester resin of the invention requires strict monomers, and the pinhole improvement effect is not good. CN114292567B discloses a powder coating composition and a method for preparing a thickness-controllable electrostatic spray coating, by adding an insulating treated conductive filler and an ionizable group polymer resin to the base layer powder, the base layer coating can be electrostatically adsorbed multiple times, thereby realizing multi-layer electrostatic spraying and adjustable coating thickness, but this method is not suitable for HAA curing, but will make the pinhole of HAA cured coating more and the weather resistance worse.

[0006] At present, for polyester powder coatings used outdoors, in addition to good weather resistance (resistance to ultraviolet light, resistance to acid and alkali, etc.), durability, adhesion and compactness, it must also have excellent wear and scratch resistance, color diversity, especially for the automotive industry. However, researchers in the field have paid less attention to this area, which is the focus of the present invention. SUMMARY

[0007] The purpose of the present application is to provide a method for coating a polyester-type thermosetting powder coating without primer, which is simple and easy to operate, and has low energy consumption, solves the problems of pores and orange peel on the cured surface, and obtains a polyester coating with excellent mechanical properties, smoothness and impact resistance, and excellent weather resistance, corrosion resistance and friction and scratch resistance, which can be applied to metal, plastic and other high and low temperature substrate surfaces, prolonging the durability of the coating.

[0008] In order to achieve the purpose of the present application, the present application provides a method for coating a thermosetting powder coating material without primer, which is electrostatic spraying or fluidized bed dip coating. The steps of electrostatic spraying specifically include:

[0009] P1. The surface of the coated part is pretreated and then placed for standby, and the standby time is generally not more than 24h.

[0010] P2. Open the electrostatic powder spraying cabinet and air tank, vertically hang the pretreated parts in the electrostatic powder spraying cabinet, and uniformly spray the unprimed thermosetting powder coating material through the electrostatic spray gun on the required coating surface of the parts (i.e. the substrate, which can be a metal substrate, a plastic substrate, wood, etc.). The positions of the parts that do not need to be sprayed are shielded and protected by using covering operation and the like.

[0011] P3. Then, the sprayed parts are placed in the baking paint room for staged heating and curing. First, the baking paint room is heated to 145-150°C, heated for 8-10 min, then cooled to 125-130°C, kept for 10 min, taken out, and naturally cooled to room temperature, thereby obtaining the unprimed thermosetting powder coating with the required thickness.

[0012] The curing process of the present application is divided into two stages, first, curing at 145-150°C for 8-10 min, and then curing at low temperature 125-130°C for 10 min, so that the coating can be fully cured at a lower temperature and a shorter time, and better curing effect is achieved. In the conventional electrostatic spraying process, the thermosetting powder coating composition cured at low temperature will have the problems of poor smoothness, spraying frost or insufficient curing, etc., thereby resulting in poor mechanical properties and impact resistance of the coating. However, by using the suitable electrostatic spraying process (the process parameters are described in detail later), the present application can obtain a better coating at a low temperature and a short time, and solve the problems of poor smoothness, spraying frost or insufficient curing, etc., thereby making the coating of the present application have better comprehensive performance.

[0013] Preferably, in step P2, the process parameters of the electrostatic spray gun during spraying are set as follows:

[0014] The atomization pressure is 0.15-0.35 MPa, which can make the coating thickness of the present application uniform, obtain sufficient coating film thickness, and have better coverage ability, which can cover the dead angle. If the atomization pressure is lower than 0.15 MPa, the coating will block the conveying equipment, the coverage rate of the dead angle will be poor, and the coating film thickness will be uneven. If the atomization pressure is higher than 0.35 MPa, the coated parts will be abraded, and the coverage rate of the coating will be reduced.

[0015] The electrostatic current is 20-25 µA. If the electrostatic current is lower than 20 µA, the paint application rate of the coating will be affected, and the coating film thickness will not be enough or uniform. If the electrostatic current is higher than 25 µA, the powder will be easily melted, causing blockage, and the coating layer may be punctured.

[0016] The flow rate pressure is 0.4-0.7 MPa, if the flow rate pressure is too high, the coating consumption is increased, the coating thickness is uneven, and the wear rate of the spray gun is increased; if the flow rate pressure is too low, the coating thickness and the spraying efficiency are affected, and the cost is increased.

[0017] The spraying voltage is 70-80 kV, if the voltage is too low, the painting rate is reduced, and the dead angle coverage is poor; if the voltage is too high, the coating is easily broken down, or the powder adsorption is not good.

[0018] The spraying distance is 20-25 cm, if the spraying distance is too close, the coating is easily broken down by discharge; if the spraying distance is too far, the coating consumption is increased, the production efficiency is affected, and the cost is increased.

[0019] The fluidization pressure of the powder supply tank is 0.06-0.08 MPa, so as to control the powder supply amount, reduce the powder agglomeration, form a dense coating, and improve the production efficiency.

[0020] Preferably, when the coated component is a metal substrate, the pretreatment method is that the metal substrate is first subjected to acetone oil removal, chemical liquid rust removal, then soaked in a silane coupling agent treatment liquid for 15-20 min, taken out, and dried at room temperature for 24 h.

[0021] When the coated component is a heat-sensitive substrate (wood, plastic, etc.), the pretreatment method is that the heat-sensitive substrate is first subjected to surface treatment, then subjected to chemical oil removal, air drying, electric field removal, and dust removal, then the surface of the heat-sensitive substrate is polished or sprayed with a silane coupling agent treatment liquid, taken out, and dried at room temperature for 24 h.

[0022] Since the curing temperature in the coating treatment process is lower than 150℃, and the treatment time at higher than 130℃ is not more than 10 min, the heat-sensitive substrate with small thermal stress can be applied, and the use range of the thermosetting powder coating of the application is expanded.

[0023] Preferably, the silane coupling agent treatment liquid is composed of γ-glycidoxypropyltrimethoxysilane (KH-560), water, ethanol and glycerol in a mass ratio of 1:(2-4):(7-10):(1-2), and the pH value is adjusted to 4-5 by dilute hydrochloric acid.

[0024] The pretreatment liquid of the substrate (i.e. the coated part) is generally treated by a phosphating liquid to improve the adhesion and corrosion resistance of the coating, but the waste liquid is rich in inorganic phosphorus, which increases the environmental burden, and the phosphating treatment liquid contains carcinogenic substances such as nitrous acid phosphorus, which is not suitable for the current domestic environmental protection demand. The silane coupling agent treatment liquid of the present application has good pretreatment effect on the surface of metal substrate and heat-sensitive substrate, which can not only improve the adhesion of the coating to the substrate, but also improve the wear resistance, corrosion resistance and waterproof performance of the substrate surface.

[0025] The silane coupling agent treatment liquid of the present application uses KH-560 containing an epoxy group, which reacts with the coating material components during the warming and curing process, and further has better adhesion effect between the polyester powder coating material of the present application, further improving the waterproofness, wear resistance and corrosion resistance of the coating; using ethanol and glycerol as solvents not only improves the hydrolysis of KH-560, but also improves the stability of the pretreatment liquid.

[0026] Preferably, the particle size distribution of the primerless thermosetting powder coating material is 10-65 µm, which ensures that the coating of the present application has excellent smoothness, dense coating, good impact resistance and toughness, and the coating film has smooth and smooth appearance. If the particle size is too small, the stability is not good, the powder rate is easy to be united, the coating thickness is limited; if the particle size is too large, the powder will fall off before reaching the surface of the part, reducing the powder rate, coating thickness and adhesion.

[0027] Preferably, the polyester powder coating material is composed of the following components by weight: polyester resin 490-520 parts, HAA 31.3-33.2 parts, ZnSt-PPh composite material 5.4-7.2 parts, matt barium 120-145 parts, rutile titanium dioxide 196-226 parts, leveling agent 10.3-12.5 parts, gloss enhancer 8.3-9.4 parts, pure benzoin 3.1-3.5 parts, PTFE modified polyethylene wax 1.14-1.46 parts, anti-yellowing agent 3.9-5.7 parts, electric enhancer 2.56-2.83 parts and pigment 0-0.3 parts; plus 0.08-0.15 wt% of alumina.

[0028] Preferably, the primerless thermosetting powder coating material is a wear-resistant and scratch-resistant polyester powder coating material.

[0029] Preferably, the ZnSt-PPh composite material contains a core containing PPh3 (triphenylphosphine), a polyacrylic acid sodium (PAAS) layer covering the surface of the core, and a coating layer with ZnSt2 (zinc stearate) as the outer shell covering the surface of the polyacrylic acid sodium layer.

[0030] Preferably, the preparation method of the ZnSt-PPh composite material comprises the following steps:

[0031] S1. Slowly add sodium polyacrylate into deionized water at 60-70℃, stir until dissolved, then add PPh3 and stir evenly to obtain suspension A, and then inject suspension A into a spray dryer to obtain pre-coated particles;

[0032] S2. Take an appropriate amount of ZnSt2 and dissolve in 60℃ ethanol, then add the above pre-coated particles and stir for 10-15min, and directly inject into a 120-130℃ spray dryer to process and obtain ZnSt-PPh composite material.

[0033] Preferably, in step S1, the ratio of sodium polyacrylate to deionized water is 0.8-1.0g / L, and the mass ratio of sodium polyacrylate to PPh3 is 0.2-0.3:1;

[0034] In step S2, the ratio of ZnSt2 to ethanol is 0.3-0.5g / 10g, and the mass ratio of ZnSt2 to PPh3 is 0.5-0.6:1.

[0035] The polyester coating obtained by selecting polyester-HAA type thermosetting powder coating and combining with the coating method of phased warming curing has lower curing temperature (not more than 150℃), shorter curing time (not more than 20min), and saves energy consumption; the coating has high flatness, solves the problems of pinholes and yellowing on the surface of the coating, and the thickness can reach 90µm; the polyester coating has excellent weather resistance, impact resistance, corrosion resistance, and friction and scratch resistance; the addition of matt barium further improves the thickness, wear resistance, heat resistance, surface hardness, impact resistance, and weather resistance of the coating; the addition of PTFE modified polyethylene wax improves the scratch resistance and smoothness of the polyester coating; the addition of aluminum oxide C improves the charging capacity of the solid powder, improves the powder coating rate of the polyester coating, and improves the wear resistance of the polyester coating.

[0036] The ZnSt-PPh composite material is a core-shell coated structure composed of ZnSt2-PAAS-PPh3, when heated and cured at 140-150 DEG C, the HAA and polyester resin undergo a curing reaction to produce water molecules, causing pores in the coating, and ZnSt2 and PAAS melt at high temperature, releasing triphenylphosphine in the ZnSt-PPh composite material, under the condition of 125-130 DEG C, the coating curing reaction continues under the promotion of triphenylphosphine, and triphenylphosphine can cause the ester exchange reversible reaction of ester groups, and the surface of the coating undergoes a self-repairing process, the surface pores are continuously reduced until disappearing, the density of the coating is increased, the surface of the coating is smooth, and there are no surface problems such as pores and pinholes, and the weather resistance, impact resistance, corrosion resistance and other properties of the polyester-HAA coating are further improved, and the coating is not prone to yellowing; the addition of ZnSt2 and PAAS improves the flowability of the polyester coating of the application, and improves the impact resistance and wear resistance and scratch resistance of the polyester coating of the application, so that the coating has better smoothness and gloss.

[0037] Preferably, the polyester resin is SJ4868 of Anhui Shenjian New Material; and the HAA is HH8081 of Huaihui.

[0038] The application has the following beneficial effects:

[0039] 1. The thermosetting powder coating (i.e. polyester coating) obtained by the low-temperature curing coating method of the application has low energy consumption, is free of toxicity, solvent and volatile toxic substances, and therefore has no problems such as poisoning, fire, and emission of "three wastes" and other public hazards, and fully meets the requirements of the national environmental protection law.

[0040] 2. The raw materials used in the application are non-toxic and have high utilization rate, and the used powder can be recycled, and the utilization rate is more than 99%.

[0041] 3. The thermosetting powder coating of the application can be applied to the surfaces of different types of substrates such as metals, plastics and wood, and before being coated, the substrates can be pretreated with a self-made silane coupling agent pretreatment liquid, which is simple to operate, only needs one-time construction by spraying, does not need primer, can obtain a coating film with sufficient thickness (up to 90 µm), realizes automatic operation, has high production efficiency, and can reduce costs.

[0042] 4. The polyester coating prepared by the application has good density, adhesion, impact strength and toughness, high corner coverage rate, excellent chemical corrosion resistance, weather resistance, friction resistance and scratch resistance, and electrical insulation performance.

[0043] 5、The present application is mainly used for the surface film coating of outdoor workpieces (or parts), which has outstanding weather resistance, high adhesion to various substrates, outstanding wear resistance, can resist certain mechanical damage, thereby prolonging the durability of the coating and increasing the service life of the outdoor workpiece, and has good storage stability, safe and convenient transportation. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0045] The primerless thermosetting powder coating material and the coating method thereof will be described below in combination with specific embodiments.

[0046] Embodiment 1

[0047] The preparation method of the primerless thermosetting powder coating material in the present embodiment 1 is as follows:

[0048] The raw materials are weighed as follows: 492 Kg of polyester resin, 31.3 Kg of HAA, 5.4 Kg of ZnSt-PPh composite material, 120 Kg of matting barium, 226 Kg of rutile titanium dioxide, 12.5 Kg of leveling agent, 8.3 Kg of gloss enhancer, 3.1 Kg of pure benzoin, 1.46 Kg of PTFE modified polyethylene wax, 3.9 Kg of anti-yellowing agent, 2.83 Kg of electric enhancer, 0.75 Kg of aluminum oxide C, 19.3 g of C311 black, 3.4 g of 122 peach red, and 81 g of ultramarine. After being stirred uniformly, a premix is obtained, which is conveyed to a twin-screw extruder for melt extrusion. The temperature of the screw extruder is set to 110-130 ℃, and the extrusion rate is 50 r / min. Then, the extruded material is pressed and crushed, and is passed through a 200-mesh sieve, to obtain a white and flat color polyester powder.

[0049] The ZnSt-PPh composite material includes a core PPh3 (triphenylphosphine), a polyacrylic acid sodium (PAAS) layer covering the surface of the core, and a coating layer with ZnSt2 (zinc stearate) as the shell covering the surface of the PAAS layer. The preparation method of the ZnSt-PPh composite material is as follows:

[0050] S1. 80 g of polyacrylic acid sodium is slowly added to 100 L of 70 ℃ deionized water, stirred until dissolved, and then 16 g of PPh3 is added and stirred for 30 min to obtain a suspension A. The suspension A is then injected into a spray dryer to dry, to obtain pre-coated particles (i.e., pre-coated powder).

[0051] S2. Take the appropriate amount of 40 g of ZnSt2, dissolve it in 80 g of 60℃ ethanol, then add the above-mentioned pre-coated particles, stir for 15 min, and then directly inject into a 125℃ spray dryer to dry, obtaining a powder-like ZnSt-PPh composite material.

[0052] The above-mentioned polyester resin is selected from the model SJ4868 of Anhui Shenjian New Material;

[0053] The above-mentioned HAA is selected from the model HH8081 of Huangshan Huaihui Technology;

[0054] The above-mentioned sodium polyacrylate is selected from Wanxiang Hongrun Biological Technology, with a molecular weight of 200,000;

[0055] The above-mentioned matting barium is selected from the matt barium sulfate of Yidu Oda Industry, with the model JY-1008 (high-end type);

[0056] The above-mentioned rutile titanium dioxide is selected from Bili Lian R699;

[0057] The above-mentioned leveling agent is selected from Zhanxin ADDITOL P 890 leveling agent;

[0058] The above-mentioned gloss enhancer is selected from the polyester gloss enhancer of Ouming, with the model OM-J-Z-U5-1;

[0059] The above-mentioned pure benzoin is selected from the benzoin of Zaoyang Cixiang;

[0060] The above-mentioned PTFE modified polyethylene wax is selected from Clariant 3940F;

[0061] The above-mentioned anti-yellowing agent is selected from Jetta Tong K7004;

[0062] The above-mentioned electricity increasing agent is selected from the powder coating electricity increasing agent ALBEMAST9100 of acoma;

[0063] The above-mentioned aluminum oxide C is selected from Wacker Degussa AEROSIL Alu C.

[0064] Example 2

[0065] The preparation method of the primerless thermosetting powder coating material of this example 2 is:

[0066] The raw materials are weighed as follows: 518 Kg of polyester resin, 33.2 Kg of HAA, 7.2 Kg of ZnSt-PPh composite material, 145 Kg of matting barium, 196 Kg of rutile titanium dioxide, 10.3 Kg of leveling agent, 9.4 Kg of gloss enhancer, 3.46 Kg of pure benzoin, 1.14 Kg of PTFE modified polyethylene wax, 5.7 Kg of anti-yellowing agent, 2.56 Kg of electric field enhancer, 1.36 Kg of aluminum oxide C, 18.5 g of C311 black, 2.2 g of 122 peach red, and 97 g of ultramarine. After stirring uniformly, a premix is obtained, which is delivered to a twin-screw extruder for melt extrusion. The screw extruder temperature is set to 110-130°C, and the extrusion rate is 50 r / min. Then the extruded material is pressed, crushed, and sieved through a 200-mesh screen to obtain a white, flat, and light-colored polyester powder.

[0067] The core-shell structure of the ZnSt-PPh composite material is the same as in Example 1, and reference is made to Example 1 for details. The ZnSt-PPh composite material is prepared as follows:

[0068] S1. 100 g of sodium polyacrylate is slowly added to 100 L of 70°C deionized water, stirred until dissolved, and then 30 g of PPh3 is added and stirred for 30 min to obtain suspension A. Suspension A is then injected into a spray dryer to obtain pre-coated particles (i.e., pre-coated powder).

[0069] S2. An appropriate amount of 60 g of ZnSt2 is dissolved in 130 g of 60°C ethanol, and then the pre-coated particles are added and stirred for 15 min. The mixture is then directly injected into a 125°C spray dryer to obtain a powder-like ZnSt-PPh composite material.

[0070] In this example 2, the manufacturers and models of various raw materials are the same as in Example 1, and reference is made to Example 1 for details.

[0071] Example 3

[0072] The preparation method of the primerless thermosetting powder coating material in this example 3 is as follows:

[0073] The raw materials are weighed as follows: 504 Kg of polyester resin, 32.4 Kg of HAA, 6.5 Kg of ZnSt-PPh composite material, 135 Kg of matting barium, 216 Kg of rutile titanium dioxide, 11.7 Kg of leveling agent, 9.0 Kg of gloss enhancer, 3.15 Kg of pure benzoin, 1.35 Kg of PTFE modified polyethylene wax, 4.5 Kg of anti-yellowing agent, 2.7 Kg of electric enhancer, 0.93 Kg of aluminum oxide C, 19.8 g of C311 black, 2.7 g of 122 pink, and 90 g of ultramarine. After stirring uniformly, a premix is obtained, which is delivered to a twin-screw extruder for melt extrusion. The screw extruder temperature is set to 110-130°C, and the extrusion rate is 50 r / min. Then, the extruded material is pressed, crushed, and sieved through a 200-mesh sieve to obtain a white, flat, and colorless polyester powder.

[0074] It is detected that the particle size distribution of the white, flat, and colorless polyester powder is as follows: D10: 10-15 µm; D50: 36 µm; D90: 55-65 µm.

[0075] The core-shell structure of the ZnSt-PPh composite material is the same as in Example 1, and specific reference is made to Example 1. The preparation method of the ZnSt-PPh composite material is as follows:

[0076] S1. 90 g of sodium polyacrylate is slowly added to 100 L of 70°C deionized water, stirred until dissolved, then 22 g of PPh3 is added and stirred for 30 min to obtain suspension A. Suspension A is then injected into a spray dryer to obtain pre-coated particles (i.e., pre-coated powder).

[0077] S2. An appropriate amount of 50 g of ZnSt2 is dissolved in 100 g of 60°C ethanol, then the above pre-coated particles are added and stirred for 15 min, and then directly injected into a 125°C spray dryer to obtain a powder-like ZnSt-PPh composite material.

[0078] In this example 3, the manufacturers and models of various raw materials are the same as in Example 1, and specific reference is made to Example 1. The same applies to other examples and comparative examples, which will not be repeated here.

[0079] Comparative Example 1

[0080] The components and preparation method of the primerless thermosetting powder coating material in this comparative example are the same as in Example 3, except that the ZnSt-PPh composite material in this comparative example is a direct mixture of PPh3, ZnSt2, and sodium polyacrylate, and the mass ratio of the three is 11:25:45.

[0081] Comparative Example 2

[0082] The components and preparation method of the primerless thermosetting powder coating material of the present comparative example are the same as in Example 3, except that no ZnSt-PPh composite material is added in the present comparative example, but PPh3 is used instead, i.e. PPh3 is directly added.

[0083] Comparative Example 3

[0084] The components and preparation method of the primerless thermosetting powder coating material of the present comparative example are the same as in Example 3, except that no ZnSt-PPh composite material is added in the present comparative example, but PAAS-PPh composite material is added, which is prepared by slowly adding 90 g of sodium polyacrylate into 100 L of 70 °C deionized water, stirring until dissolved, then adding 22 g of PPh3 and stirring for 30 min to obtain a suspension, and then injecting the suspension into a spray dryer to dry.

[0085] Comparative Example 4

[0086] The components and preparation method of the primerless thermosetting powder coating material of the present comparative example are the same as in Example 3, except that no ZnSt-PPh composite material is added in the present comparative example, and the other components are the same.

[0087] Comparative Example 5

[0088] The components and preparation method of the primerless thermosetting powder coating material of the present comparative example are the same as in Example 3, except that no PTFE modified polyethylene wax is added in the present comparative example, and the other components are the same.

[0089] Example 4

[0090] Preparation method of the primerless thermosetting powder coating based on the surface of a stainless steel substrate:

[0091] P1. A 2 mm stainless steel workpiece was subjected to acetone degreasing and chemical liquid derusting, then immersed in a silane coupling agent treatment liquid for 20 min, and then taken out and dried at room temperature for 24 h.

[0092] P2. The electrostatic powder spraying cabinet and the air compression tank were opened, and the spraying process parameters were set as follows: atomization pressure 0.25 MPa, electrostatic current 25 µA, flow rate pressure 0.6 MPa, spraying voltage 80 kV, spraying distance 200 mm, and powder supply tank fluidization pressure 0.07 MPa. The pretreated stainless steel workpiece was vertically hung in the electrostatic powder spraying cabinet, and the polyester powder prepared in Example 3 was uniformly sprayed onto the coating surface of the stainless steel workpiece through an electrostatic spray gun.

[0093] P3. Subsequently, the sprayed part is placed in a baking booth for staged heat curing. First, the baking booth is heated to 145°C, heated for 10 min, then cooled to 130°C, kept for 10 min, taken out, and naturally cooled to room temperature to obtain a 90 pm polyester powder coating.

[0094] The silane coupling agent treatment liquid is prepared by uniformly mixing KH560, water, ethanol, and glycerol in a mass ratio of 1:4:9:2, and then adjusting the pH value to 4 with dilute hydrochloric acid.

[0095] Example 5

[0096] Method for preparing a primerless thermosetting powder coating on the surface of a plastic substrate:

[0097] P1. The 2 mm ABS workpiece is subjected to surface treatment, then chemical oil removal, air drying, de-electrification, and dust removal, and then the ABS workpiece surface is sprayed with a silane coupling agent treatment liquid, which is taken out and dried at room temperature for 24 h.

[0098] P2. The electrostatic powder spraying cabinet and the air tank are opened, and the spraying process parameters are set: atomization pressure 0.20 MPa, static current 20 pA, flow rate pressure 0.5 MPa, spraying voltage 70 kV, spraying distance 250 mm, and powder supply tank fluidization pressure 0.06 MPa. The pretreated ABS workpiece is vertically hung in the electrostatic powder spraying cabinet, and the polyester powder prepared in Example 3 is uniformly sprayed onto the coating surface of the ABS workpiece by an electrostatic spray gun.

[0099] P3. Subsequently, the sprayed ABS workpiece is placed in a baking booth for staged heat curing. First, the baking booth is heated to 145°C, heated for 10 min, then cooled to 125°C, kept for 10 min, taken out, and naturally cooled to room temperature to obtain a 90 pm polyester powder coating.

[0100] The silane coupling agent treatment liquid is prepared by uniformly mixing KH560, water, ethanol, and glycerol in a mass ratio of 1:2:7:1, and then adjusting the pH value to 5 with dilute hydrochloric acid.

[0101] Comparative Example 6

[0102] The method for preparing a primerless thermosetting powder coating on the surface of a stainless steel substrate in this comparative example is the same as that in Example 4, except that the silane coupling agent treatment liquid used in this comparative example is different from that in Example 4. The silane coupling agent treatment liquid used in this comparative example is prepared by uniformly mixing KH550, water, ethanol, and glycerol in a mass ratio of 1:2:15:0.15, and then adjusting the pH value to 9 with a 10 wt% NaOH solution.

[0103] Comparative Example 7

[0104] The preparation method of the thermosetting powder coating based on the surface of the stainless steel substrate without primer of the present comparative example is the same as that of Example 4, except that the polyester powder used in the present comparative example is the primerless thermosetting powder coating material prepared in Comparative Example 1.

[0105] Comparative Example 8

[0106] The preparation method of the thermosetting powder coating based on the surface of the stainless steel substrate without primer of the present comparative example is the same as that of Example 4, except that the polyester powder used in the present comparative example is the primerless thermosetting powder coating material prepared in Comparative Example 2.

[0107] Comparative Example 9

[0108] The preparation method of the thermosetting powder coating based on the surface of the stainless steel substrate without primer of the present comparative example is the same as that of Example 4, except that the polyester powder used in the present comparative example is the primerless thermosetting powder coating material prepared in Comparative Example 3.

[0109] Comparative Example 10

[0110] The preparation method of the thermosetting powder coating based on the surface of the stainless steel substrate without primer of the present comparative example is the same as that of Example 4, except that the polyester powder used in the present comparative example is the primerless thermosetting powder coating material prepared in Comparative Example 4.

[0111] Comparative Example 11

[0112] The preparation method of the thermosetting powder coating based on the surface of the stainless steel substrate without primer of the present comparative example is the same as that of Example 4, except that the polyester powder used in the present comparative example is the primerless thermosetting powder coating material prepared in Comparative Example 4, and in step P3 of the preparation process of the thermosetting powder coating of the present comparative example, the heating and curing process is modified as follows: the baking oven is heated to 145°C, heated for 20 min, taken out, and naturally cooled to room temperature to obtain a polyester powder coating with a thickness of 50 ± 2 µm.

[0113] Comparative Example 12

[0114] The preparation method of the thermosetting powder coating based on the surface of the stainless steel substrate without primer of the present comparative example is the same as that of Example 4, except that the polyester powder used in the present comparative example is the primerless thermosetting powder coating material prepared in Comparative Example 5.

[0115] The properties of the polyester powder coatings (or primerless thermosetting powder coatings) prepared in Examples 4-5 and Comparative Examples 6-12 were tested, and the coating thickness was 90 ± 2 µm (the polyester powder coating thickness in Comparative Example 11 was 50 ± 2 µm), such as the appearance of the coating, hardness, adhesion, impact strength, flexibility, gloss, wear resistance, etc. The test results are shown in Table 1 and Table 2 below.

[0116] Hardness test: According to GB / T 9754-2007 "Pencil method for the determination of the hardness of paint films" for detection;

[0117] Adhesion test: According to GB / T 9286-1998 "Cross-hatch test for paint films" for detection;

[0118] Impact resistance: According to GB / T 1732-2020 "Paint film impact resistance test method" for detection;

[0119] Gloss: According to GB / T 9754-2007 standard for detection of 60° gloss;

[0120] Abrasion resistance: According to GB / T 1768-2006 "Paint film abrasion resistance test method" for detection;

[0121] Corrosion resistance: According to GB / T 1771-2007 "Determination of the resistance to neutral salt spray of paint and varnish" for detection, the film sample is placed in a salt spray test chamber at 40±2℃, with a salt water concentration of 3.5%, and sprayed with salt mist for 15 minutes every 45 minutes. After 24 hours of testing, the degree of damage to the appearance of the sample was observed, and the grade was evaluated according to GB / T 1740-2007.

[0122] Weather resistance: According to GB / T 14522-2008 detection standard, QUV-B artificial accelerated aging test (gloss retention 50%) / h;

[0123] Color difference ΔE is detected and calculated according to GB / T 11186.2 and GB / T 11186.3.

[0124] Table 1 Test results of appearance, hardness, etc. of polyester coating

[0125]

[0126] From the test results in Table 1, it can be seen that the polyester coating of the application is flat, smooth, has no pinholes and no cracks, and has excellent hardness, adhesion and impact resistance; the use of ZnSt-PPh composite material of the application solves the problems of coating pinholes, smoothness, etc., and significantly improves the hardness, adhesion and impact resistance of the polyester coating; the use of silane coupling agent pretreatment liquid of the application significantly improves the adhesion between the substrate and the coating.

[0127] Table 2 Test results of abrasion and corrosion resistance of polyester coating

[0128]

[0129] It can be seen from the detection results in Table 2 that the polyester coating has excellent gloss, wear resistance, corrosion resistance and aging resistance; the ZnSt-PPh composite material is used to significantly improve the wear resistance and corrosion resistance of the polyester coating; the ZnSt-PPh composite material needs to be combined with the heating curing process to achieve the expected effect; the addition of the PTFE modified polyethylene wax significantly improves the smoothness and wear resistance of the polyester coating.

[0130] It is worth noting that only one specific component of each component is analyzed in the embodiments of the present application, and in fact other components or models not mentioned in the present application can also be selected.

[0131] The technical features of the above-described embodiments can be combined arbitrarily, and in order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present application.

[0132] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A method of applying a primerless thermoset powder coating material, by electrostatic spraying, characterised in that, The electrostatic spraying step specifically comprises: P1. After the surface of the coated component is pretreated, it is placed for standby; P2. Open the electrostatic spraying cabinet and the air compression box, vertically hang the above-mentioned pretreated component in the electrostatic spraying cabinet, and use the electrostatic spraying gun to spray the unprimed thermosetting powder coating material on the required coating surface of the component; The unprimed thermosetting powder coating material is a wear-resistant and scratch-resistant polyester powder coating material; The polyester powder coating material is composed of the following components by weight percentage: polyester resin 490-520 parts, HAA 31.3-33.2 parts, ZnSt-PPh composite material 5.4-7.2 parts, matt barium 120-145 parts, rutile titanium dioxide 196-226 parts, leveling agent 10.3-12.5 parts, gloss enhancer 8.3-9.4 parts, pure benzoin 3.1-3.5 parts, PTFE modified polyethylene wax 1.14-1.46 parts, anti-yellowing agent 3.9-5.7 parts, electric enhancer 2.56-2.83 parts, and pigment 0-0.3 parts; plus 0.08-0.15wt% of alumina; The ZnSt-PPh composite material contains a core containing PPh3, a sodium polyacrylate layer covering the surface of the core, and a coating layer with ZnSt2 as the outer shell covering the surface of the sodium polyacrylate layer; P3. Then place the sprayed component in the baking paint room for stage heating and curing, first heat the baking paint room to 145-150℃, heat for 8-10min, then cool to 125-130℃, keep warm for 10min, take out, and naturally cool to room temperature, to obtain the required thickness of the unprimed thermosetting powder coating.

2. The process for the application of a primerless thermoset powder coating material according to claim 1, characterized in that, In the step P2, the process parameters of the spraying treatment are set as follows: atomization pressure 0.15-0.35MPa; electrostatic current 20-25µA; flow rate pressure 0.4-0.7MPa; spraying voltage 70-80kV; spraying distance 20-25cm; powder supply bucket fluidization pressure 0.06-0.08MPa.

3. The process for the application of a primerless thermoset powder coating material according to claim 1, characterized in that, When the coated component is a metal substrate, the pretreatment method is: first, remove oil from the metal substrate with acetone, then remove rust with chemical liquid, then soak in a silane coupling agent treatment liquid for 15-20min, take out, and dry at room temperature for 24h. When the coated component is a heat-sensitive substrate, the pretreatment method is: first, perform surface treatment on the heat-sensitive substrate, then perform chemical oil removal, air drying, electric field removal, and dust removal, then polish the surface of the heat-sensitive substrate or spray a silane coupling agent treatment liquid, take out, and dry at room temperature for 24h.

4. The process for the application of a primerless thermoset powder coating material according to claim 3, characterized in that, The silane coupling agent treatment liquid is composed of γ-glycidyl ether propyl trimethoxysilane, water, ethanol, and glycerol in a mass ratio of 1:(2-4):(7-10):(1-2), and the pH value is adjusted to 4-5 with dilute hydrochloric acid.

5. The method of coating a primerless thermoset powder coating material according to claim 1, characterized in that, The particle size distribution of the unprimed thermosetting powder coating material is 10-65µm.

6. The method of coating a primerless thermoset powder coating material according to claim 1, characterized in that, The preparation method of the ZnSt-PPh composite material specifically comprises the following steps: S1. Slowly add sodium polyacrylate into deionized water at 60-70℃, stir until dissolved, then add PPh3 and stir to obtain a suspension A, then inject the suspension A into a spray dryer to obtain pre-coated particles; S2. Take an appropriate amount of ZnSt2 and dissolve in 60℃ ethanol, then add the pre-coated particles and stir for 10-15min, then directly inject into a 120-130℃ spray dryer to process and obtain a ZnSt-PPh composite material.

7. The process for the application of a primerless thermoset powder coating material according to claim 6, characterized in that, In the step S1, the ratio of sodium polyacrylate to deionized water is 0.8-1.0g / L, and the mass ratio of sodium polyacrylate to PPh3 is 0.2-0.3:1; In the step S2, the ratio of ZnSt2 to ethanol is 0.3-0.5g / 10g, and the mass ratio of ZnSt2 to PPh3 is 0.5-0.6:1.

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