CN115121458A

CN115121458A - Automobile exterior trimming part and coating method thereof

Info

Publication number: CN115121458A
Application number: CN202210903207.4A
Authority: CN
Inventors: 周中明; 陈绍木; 王立
Original assignee: Fuyao Technology Development Suzhou Co ltd
Current assignee: Fuyao Technology Development Suzhou Co ltd
Priority date: 2022-07-29
Filing date: 2022-07-29
Publication date: 2022-09-30

Abstract

The invention relates to an automobile exterior trimming part and a coating method thereof. The coating method comprises the following steps: obtaining a workpiece to be processed with a rough surface; treating the rough surface with a silane surface treating agent to form a silane film on the rough surface; spraying powder on the surface of one side of the workpiece to be treated, on which the silane film is formed; and (3) performing infrared curing treatment on the workpiece to be treated after powder spraying, and performing thermal curing treatment to form a powder coating. The coating method of the automobile exterior trimming part is simple in process, causes little pollution to the environment, and can improve corrosion resistance and adhesive force and ensure good appearance.

Description

Automobile exterior trimming part and coating method thereof

Technical Field

The invention relates to the field of powder coating, in particular to an automobile exterior trimming part and a coating method thereof.

Background

In recent years, with the vigorous advocation of the national sustainable development concept, production modes such as energy conservation, emission reduction, environmental protection and the like gradually receive wide attention of various enterprises. The powder coating does not contain organic solvent, has the advantages of near zero VOC (volatile organic compounds) emission, high recycling rate, low production cost and the like, and is rapidly developed and widely applied in the fields of coating, paint and the like. The use of the powder coating not only ensures that the coating process is more environment-friendly, but also ensures that the mechanical strength, adhesive force, ageing resistance and the like of the product are better than those of the original paint coating process.

In the existing powder coating process in the automobile industry, in order to improve the corrosion prevention effect of products, a phosphating or passivation pretreatment process is mostly adopted to form a layer of phosphating film or passivation film with a protection effect on the metal surface. And because the phosphating solution or the passivation solution contains heavy metal ions such as chromium, zinc, manganese, nickel and the like, a large amount of phosphorus, a surfactant and other toxic substances, the production process can cause serious pollution to water, strict equipment for deslagging, purification and the like is required to be arranged subsequently, the process is complex, the operation is required to be carried out under the heating condition, and the production cost is high. In addition, in order to further improve the adhesion between the metal sample and the powder coating, a primer layer is coated in advance through a cathodic electrophoresis process before the powder spraying coating process so as to serve as a transition layer to enhance the bonding force between the metal sample and the coating, but a large number of complicated treatment procedures are undoubtedly increased, and a large amount of energy consumption is caused.

Therefore, researchers gradually replace the phosphating or passivation process with other pretreatment methods, but the defects of poor acid and alkali corrosion resistance, poor adhesion and the like exist, and the product yield is low.

Disclosure of Invention

Therefore, it is necessary to provide an automobile exterior part and a coating method thereof, which have the advantages of simple process, less environmental pollution, and better acid-base corrosion resistance and adhesion.

A coating method of an automobile exterior trimming part comprises the following steps:

obtaining a workpiece to be processed with a rough surface;

treating the rough surface with a silane surface treating agent to form a silane film on the rough surface;

spraying powder on the surface of one side of the workpiece to be treated, on which the silane film is formed; and

and (3) performing infrared curing treatment on the workpiece to be treated after powder spraying, and then performing thermosetting treatment to form a powder coating.

In one embodiment, the roughness of the rough surface is 1 μm to 8 μm.

In one embodiment, the silane surface treatment agent is selected from at least one of KH550, KH560, KH570, Oxsilan9810, Oxsilan9812, Oxsilan9830, and Oxsilan 9832.

In one embodiment, the rough surface is treated by the silane surface treating agent for 1min to 2min, and the thickness of the silane film is 50nm to 100 nm.

In one embodiment, the rough surface is treated by adopting a spraying mode, the spraying flow is 800 mL/min-1000 mL/min, and the spraying pressure is 0.08 MPa-0.12 MPa.

In one embodiment, the process parameters during the infrared curing process satisfy at least one of the following conditions:

(1) the infrared wavelength is 2-4 μm;

(2) the temperature of the infrared curing is 120-160 ℃, and the time is 5-12 min.

In one embodiment, the temperature of the thermal curing is 170-210 ℃ and the time is 10-20 min.

In one embodiment, in the step of spraying the powder on the surface of the side of the workpiece to be processed, where the silane film is formed, an electrostatic powder spraying manner is adopted.

In one embodiment, the process parameter in the electrostatic powder spraying process satisfies at least one of the following conditions:

(1) the spraying voltage is 60kV to 80kV, the pressure of the spray gun is 3.5MPa to 4.5MPa, and the spraying distance is 15cm to 30 cm;

(2) the powder output is 20g/min to 60g/min, and the powder spraying current is 15 muA to 30 muA;

(3) the cleanliness of electrostatic powder spraying is controlled in ten thousand grades, and the air speed of a spray room is controlled in a range of 0.2-0.3 m/s.

In one embodiment, the powder coating used in the dusting process comprises at least one of an acrylic resin, an epoxy resin, and a polyurethane.

In one embodiment, the powder coating used in the dusting process comprises an acrylic resin and the silane surface treatment is selected from at least one of Oxsilan9832, KH560 and Oxsilan 9830.

In one embodiment, the powder coating has a thickness of 90 μm to 120 μm.

An automobile exterior trimming part is obtained after the coating method.

According to the coating method of the automobile exterior trimming part, the workpiece to be treated is provided with the rough surface, so that the contact area and the bonding sites between the powder coating and the workpiece to be treated are improved on the one hand due to the rough surface, and the better combination of the powder coating and the workpiece to be treated is facilitated. On the other hand, the surface of the workpiece to be treated can be activated, and the spreading characteristic of the powder coating on the surface of the workpiece to be treated is improved, so that the bonding strength between the powder coating and the surface of the workpiece to be treated is improved. The rough surface is treated by the silane surface treating agent, one end of the silane surface treating agent can form a hydrogen bond and a Si-O-M covalent bond with the surface of a workpiece to be treated, the adhesion with the workpiece to be treated is improved, the traditional electrophoretic primer pre-coating procedure for improving the adhesion is omitted, the other end of the silane surface treating agent contains carbon functional groups, in the infrared curing process, the infrared curing can be directly radiated into the inner layer of the powder coating to act on the chemical bonds, the silane surface treating agent and each chemical bond of atomic groups in the powder coating can generate resonance through absorbing infrared radiation energy, the molecular internal energy can be rapidly gathered through resonance, the breakage of the chemical bonds in the silane surface treating agent and the powder coating is accelerated, the carbon functional groups of the silane surface treating agent and the molecules in the powder coating are promoted to be better crosslinked, and an interpenetrating network interface layer is formed through a block reaction or a graft reaction, the forms of the interface layer and the powder coating are changed, and the comprehensive performances of acid and alkali corrosion resistance and the like of the powder coating are improved, so that the powder coating has the corrosion prevention effect which is equal to that of the traditional phosphating or passivation process. In the curing process, the infrared curing can promote better crosslinking of the silane surface treating agent and internal molecules of the powder coating, enhance the adhesive force and the corrosion resistance of the powder coating and simultaneously enable the curing process to be faster and more uniform; the thermal curing process can promote the temperature to be further improved, is beneficial to further melting, leveling and curing of the powder coating, and solves the problem of poor appearance caused by difficulty in realizing uniform melting and curing only by adopting an infrared curing method. In addition, the infrared curing and the thermocuring are combined, so that the curing time is greatly shortened, and the defects of workpiece deformation, bubbling and the like caused by long-time high-temperature baking are effectively avoided. Therefore, the coating method of the automobile exterior trimming part is simple in process and small in environmental pollution, and meanwhile, the acid and alkali corrosion resistance and the adhesive force can be improved, and the good appearance is ensured.

Drawings

Fig. 1 is a process flow diagram of a coating method of an automobile exterior trim part according to an embodiment;

FIG. 2 is a schematic view of an embodiment of an exterior trimming part of an automobile;

FIG. 3 is a microscopic morphology diagram of the exterior automotive part treated by the coating method of example 1 after acid and alkali resistance test, neutral salt spray test and high humidity resistance test;

FIG. 4 is a microscopic morphology diagram of the exterior automotive part treated by the coating method of example 2 after acid and alkali resistance test, neutral salt spray test and high humidity resistance test;

FIG. 5 is a microscopic morphology diagram of the exterior automotive part treated by the coating method of example 3 after the acid and alkali resistance test, the neutral salt spray test and the high humidity resistance test;

FIG. 6 is a microscopic morphology diagram of the exterior automotive part treated by the coating method of example 4 after the acid and alkali resistance test, the neutral salt spray test and the high humidity resistance test;

FIG. 7 is a microscopic morphology view of the exterior automotive part after the coating method of comparative example 1, after acid and alkali resistance test, neutral salt spray test and high humidity resistance test;

FIG. 8 is a microscopic morphology view of the exterior automotive part after the coating method of comparative example 2, after acid and alkali resistance test, neutral salt spray test and high humidity resistance test;

fig. 9 is a microscopic sectional view (x 500 times) of bubbles generated during the high humidity resistance test shown in fig. 5;

fig. 10 is a microscopic morphology view of the automobile exterior part treated by the coating method of comparative example 4 after the acid and alkali resistance test, the neutral salt spray test, and the high humidity resistance test.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the following detailed description. The detailed description sets forth the preferred embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Aiming at the problems of complex process, large environmental pollution and the like of the traditional powder coating process of the automobile exterior trimming part, the invention provides the automobile exterior trimming part which has simple process, small environmental pollution and better corrosion resistance, adhesive force and appearance and the coating method thereof.

Specifically, referring to fig. 1, a coating method of an automobile exterior trim according to an embodiment includes steps S110 to S140:

step S110: a workpiece to be treated having a rough surface is obtained.

In some embodiments, the workpiece to be processed is a metal workpiece. For example, the workpiece to be processed is an aluminum alloy workpiece.

In some embodiments, the workpiece to be treated is obtained by means of grinding, with a rough surface. In one particular example, sanding may be performed using tools such as sandpaper and grinding wheels. The oxide layer on the surface of the sample substrate can be removed through polishing, a certain rough structure is formed on the surface of the sample substrate, more 'anchor-breaking' binding sites are provided for subsequent coating powder, a large enough contact area between the coating and the surface of the sample substrate is ensured, and the coating and the sample substrate are promoted to be tightly combined. On the other hand, the roughening treatment can activate the surface of the metal matrix, improve the spreading characteristic of the coating on the metal surface, and improve the bonding strength between the coating and the surface of the substrate.

In some embodiments, the roughness of the rough surface is 1 μm to 8 μm. In a specific example, the roughness of the rough surface is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or a range consisting of any two of these values. The roughness is too low, the surface of the workpiece to be treated is too smooth, a rough surface structure cannot be obtained, the contact area and the combination site of the surface of the workpiece to be treated and a subsequent coating are reduced, and the adhesive force of the coating is reduced; if the roughness is too high, large appearance defects are generated on the surface of the workpiece to be processed, and the mechanical strength of the workpiece to be processed and the appearance and performance of a subsequent coating are influenced.

In the actual process, a corresponding stamping/extruding die can be selected according to the model and the size of a required product, and after a workpiece to be processed is inspected, stamping or extrusion molding processing is carried out, so that the required workpiece to be processed is finally produced. And (4) after the workpiece to be processed after stamping/extrusion molding is inspected to be qualified, polishing the workpiece to be processed to remove an oxide film on the surface, processing scratches, burrs and the like.

In a specific example, the polishing is performed by using a 5-inch disc pneumatic polisher equipped with 3M 400# sandpaper and an air pressure of 0.6MPa to 0.8MPa, so that the surface is clean and free of impurities, pits and pits, scratches, deformation and other defects after polishing.

In some embodiments, after step S110, before step S120, further comprising: degreasing, deoiling and washing the workpiece to be processed. The metal sample is degreased and deoiled to remove oil stains attached to the surface and residues such as waste chips and dust generated in the polishing process, and remove pollutants, loose layers and other substances which influence the binding force on the surface of the substrate.

In some embodiments, degreasing and degreasing are carried out in a spraying mode, and the spraying pressure is 0.08MPa to 0.12 MPa. The temperature of the degreasing agent used for spraying is 40-60 ℃. Compared with impregnation, the spraying treatment can greatly save the equipment space, and the degreasing tank does not need to be frequently salvaged of surface oil stains, so that the operation is convenient.

Specifically, degreasing and oil removing comprise pre-degreasing and main degreasing, degreasing agents used in the two working procedures are mixtures of ParcocCleaner 1507 and Bonderite 125, the pre-degreasing is used for primarily cleaning grease, dust, impurities and the like on the surface of the base material, and then the base material enters the main degreasing for further cleaning so as to ensure that the surface of the base material is cleanly treated. And after a certain production period (generally 2-3 weeks), performing groove inversion, discharging and purifying the pre-degreasing reagent, introducing the main degreasing reagent into the pre-degreasing groove for continuous use, and preparing a new medicament in the main degreasing groove.

In some embodiments, the water wash comprises two steps, the first step has a conductivity of 600 μ s/cm or less and the second step has a conductivity of 50 μ s/cm or less. And (3) removing residual degreasing agents, stains and the like on the surface of the workpiece to be treated in the degreasing process by washing.

In some embodiments, the water washing process adopts a spraying mode, and the spraying pressure is between 0.08 and 0.12 MPa.

In the practical process, the polished workpiece to be treated is fixed on a corresponding tool hanger, and a suspension conveying chain is started to sequentially enter degreasing and washing processes, wherein the chain speed is 0.8-1.2 m/min.

Step S120: and treating the rough surface by using a silane surface treating agent to form a silane film on the rough surface.

And treating the rough surface by using a silane surface treating agent so as to increase the surface active sites of the workpiece to be treated, improve the surface activity of the workpiece to be treated and enhance the adhesive force. The silane surface treatment agent can be used as a bridge for connecting a metal matrix and a powder coating: on one hand, the silane surface treating agent firstly undergoes hydrolysis reaction and then is dehydrated to form oligomer, in the process, the hydrolysate and the oligomer form hydrogen bonds with hydroxyl on the metal surface, and then the dehydration reaction occurs to form Si-O-M covalent bonds (M refers to metal elements on the surface of a metal matrix, such as Al, Fe, Ti, Cu and the like), and finally the metal surface is covered by an organic siloxane film; on the other hand, by utilizing the reactivity of a carbon functional group in the silane surface treating agent, in the infrared curing process, the infrared curing can be directly radiated into the powder coating to act on chemical bonds, and the silane surface treating agent and each chemical bond of an atomic group in the powder coating generate resonance through absorbing infrared radiation energy, so that the molecular internal energy is rapidly gathered through the resonance, the breakage of the chemical bonds in the silane film and the powder coating is accelerated, the silane film and the molecules in the coating are promoted to be better crosslinked, an interpenetrating network interface layer is formed through a block or graft reaction, the forms of the interface layer and the powder coating are changed, and the comprehensive performances of acid-base corrosion resistance and the like of the coating are improved. By combining the two processes, the silane surface treating agent plays a role in bridging between the metal matrix and the coating through chemical bonding, so that the adhesive force between the metal matrix and the coating is enhanced, and the corrosion resistance of the coating is improved. In addition, compared with the phosphating/passivation process, the silane surface treating agent does not contain heavy metal ions such as chromium, zinc, manganese, nickel and the like and a large amount of phosphorus, so that a large amount of pollution to water is avoided, heating treatment is not needed, a surface adjusting procedure is not needed, the process time is short, and the operation is simple.

Taking the workpiece to be treated as the aluminum alloy as an example, the silane surface treating agent can form a hydrogen bond with-OH on the surface of the aluminum alloy and form a Si-O-Al covalent bond with Al on the surface of the aluminum alloy, so that a layer of siloxane film is formed on the surface of the aluminum alloy, and the adhesive force and the corrosion resistance of the surface of the aluminum alloy are improved. The chemical bonding process of the silane surface treating agent and the surface of the workpiece to be treated is as follows: the organosilane surface treating agent is hydrolyzed to obtain a siloxane film which is obtained by dehydrating and condensing a silicon hydroxyl group (-Si-OH) and a hydroxyl group (Al-OH) on the surface of a workpiece to be treated to form a Si-O-Al covalent bond. The reaction involved is as follows:

(1) hydrolysis of siloxane to silicon hydroxyl: -Si-OR + H ₂ O→-Si-OH+ROH；

(2) Dehydration condensation between silicon hydroxyl groups to form oligomers:

(3) silicon hydroxyl is adsorbed on the surface of the metal to form a hydrogen bond: -Si-OH + Al-OH → -Al-O-Si- + H ₂ O；

(4) The silicon hydroxyl generates a cross-linking reaction on the metal surface to form a protective film with a space network structure: -Si-OH + Al-OH → Si-O-Al + H ₂ O。

In some embodiments, the silane surface treatment agent is selected from at least one of KH550, KH560, KH570, Oxsilan9810, Oxsilan9812, Oxsilan9830, and Oxsilan 9832.

The silane surface treating agent has an amphoteric structure, and part of groups in molecules can react with groups on the surface of an inorganic substance to form chemical bonding; the other part of the groups have the property of organic matters and can generate stronger intermolecular action with organic molecules, thereby firmly combining two materials with different properties and improving the mechanical properties such as adhesive force and the like. The reactivity of the silane surface treating agent and the organic polymer in the powder coating is taken from the carbon functional group C-Y, and when the Y group can react with the corresponding matrix resin, a better bridging effect can be achieved, so that the silane surface treating agent is suitable for different powder coatings.

In some embodiments, the powder coating includes an epoxy resin and the silane surface treatment includes CH ₂ –CHCH ₂ O and H ₂ N-is at least one. For example, 3- (glycidoxypropyl) trimethoxysilane, (3-glycidoxypropyl) triethoxysilane, 3-aminopropyltrimethoxysilane and the like can be used as the silane surface treatment agent. In other embodiments, the powder coating comprises an acrylic resin and the silane surface treatment is selected from KH560, Oxsilan9830, Oxsilan9832, and the like. In other embodiments, the powder coating comprises polyurethane and the silane surface treatment may be selected from KH550, KH570, and the like. In other embodiments, the powder coating includes a phenolic resin and the silane surface treatment includes H ₂ N-and H ₂ At least one of NCONH-, for example, the silane surface treatment agent may be Oxsilan9810, Oxsilan9812, etc.

In some embodiments, the rough surface is treated by spraying, the spraying flow rate is 800mL/min to 1000mL/min, and the spraying pressure is 0.08MPa to 0.12 MPa. In a specific example, the flow rate of the spray is 800mL/min, 850mL/min, 900mL/min, 950mL/min, 1000mL/min, or a range of any two of these values. The spraying pressure is 0.08MPa, 0.09MPa, 0.1MPa, 0.11MPa, 0.12MPa or the range formed by any two of the values.

The spraying mode can improve the recycling rate of the medicament. Compared with spraying, firstly, the medicament can more easily permeate into the cavity of the hanger framework through pores such as welding seams and the like, so that rust, stain and the like in the cavity are brought into the medicament tank to pollute the medicament; secondly, the medicament or water and the like which permeate into the cavity are not easy to flow out, so that liquid is accumulated, and the accumulated medicament and water are evaporated and splashed at high temperature in the subsequent coating high-temperature curing process to influence the appearance surface of the paint film; thirdly, a large medicament tank capable of accommodating a hanging tool needs to be prepared for dipping, and equipment space is saved by spraying. Therefore, in the present embodiment, it is preferable to treat the rough surface by spraying.

Further, the temperature of the silane surface treatment agent used for spraying is 25 ℃ to 35 ℃.

In some embodiments, the rough surface is treated with the silane surface treating agent for 1 to 2min, and the thickness of the formed silane film is 50 to 100 nm. In a specific example, the time for treating the rough surface with the silane surface treatment agent is 1min, 1.2min, 1.5min, 1.8min, 2min or a range consisting of any two of these values. The silane film is thin, so that the film thickness is uneven due to too short processing time, and the adhesive force of the coating is obviously influenced; the coating patterns are easily caused by too long treatment time, the appearance is influenced, and the product performance is unqualified.

Further, in some embodiments, after step S120, before step S130, a step of water washing is also included. Residual unreacted medicament on the surface of the workpiece to be treated is removed through water washing, so that the medicament is prevented from being brought into the next procedure.

In one embodiment, the water washing adopts a spraying mode, and the spraying pressure is 0.08MPa to 0.12 MPa.

In one embodiment, the water washing comprises a first water washing and a second water washing. Wherein the conductivity of the first washing and the second washing is respectively less than or equal to 200 mu s/cm and less than or equal to 20 mu s/cm, and the pH value is 6-7.5.

In some embodiments, after the step of washing with water, a step of drying is further included. The surface and internal water is evaporated by drying. In one embodiment, the drying temperature is 110-130 ℃, and the drying time is 20-40 min. In one particular example, drying is performed using a drying oven.

Step S130: and spraying powder on the surface of the side of the workpiece to be treated, on which the silane film is formed.

In some embodiments, electrostatic powder spraying is used in step S130.

The electrostatic powder spraying technology is that based on the principle of high voltage electrostatic corona field, an electrostatic generator discharges high voltage static electricity to the workpiece via the electrode needle or metal flow guiding mark in the mouth of the spray gun. The high voltage static electricity ionizes the mixture of powder and compressed air ejected from the spray gun orifice and the air surrounding the electrodes. A dense charge is generated around it due to corona discharge; the workpiece to be processed is grounded through the hanging tool and the conveying chain to form a positive electrode, so that a strong electrostatic field is formed between the spray gun and the workpiece to be processed. When compressed air as carrier gas is used to convey powder paint from powder supplying barrel to the guide rod of spray gun via powder pipe, the guide rod is connected to corona discharge produced by high voltage negative electricity to produce dense negative charge, so that the powder is charged with negative charge and enters electrostatic field with high electric field strength. Under the double pushing of electric field force and air pressure, the powder is attracted to the surface of the workpiece through electrostatic force, so that a uniform powder layer is formed. The coating of the electrostatic powder spraying process is superior to a paint spraying process in the aspects of mechanical strength, adhesive force, aging resistance and the like, and the powder coating can be recycled, so that the utilization rate of 100 percent can be almost realized, and the cost is lower than that of the paint spraying process with the same effect.

In some embodiments, the cleanliness of electrostatic powder spraying needs to be controlled in ten thousand levels (0.5 mu m dust falling number is less than or equal to 3.50E +05), and the air speed of a spraying room needs to be controlled in a range of 0.2m/s to 0.3 m/s.

In some embodiments, the powder spraying process parameters are controlled as follows: the spraying voltage is 60kV to 80kV, the current is 15 muA to 30 muA, the pressure of a spray gun is 3.5MPa to 4.5MPa, the powder output is 20g/min to 60g/min, the spraying distance is 15cm to 30cm, and four spray guns are adopted for spraying simultaneously.

In a specific example, the spray voltage is 60kV, 62kV, 65kV, 68kV, 70kV, 72kV, 75kV, 78kV, 80kV or a range consisting of any two of these values. The powder spraying voltage is too low, the charging is poor, the powder coating rate of a workpiece to be treated is low, and a sprayed powder layer is thin and is easy to generate bottom exposure defects; the powder spraying voltage is too high, so that the powder layer is too thick, and the powder layer is broken down by the voltage, so that the coating quality is influenced.

In a particular example, the lance pressure is 3.5MPa, 3.6MPa, 3.7MPa, 3.8MPa, 3.9MPa, 4MPa, 4.1MPa, 4.2MPa, 4.3MPa, 4.4MPa, 4.5MPa or a range consisting of any two of these values. The powder coating is unevenly atomized due to the fact that the pressure of the spray gun is too low, a large number of powder coatings are accumulated on the surface of a workpiece to be treated, and appearance defects are formed after the powder coatings are solidified; too high pressure of the spray gun can cause too large airflow to directly impact a powder layer on the surface of a workpiece to be processed, so that the powder layer is uneven, and appearance defects such as orange peel are easily formed.

In a particular example, the lance distance is 15cm, 18cm, 20cm, 22cm, 25cm, 28cm, 30cm, or a range consisting of any two of these values. When the distance of the spray gun is too close, the powder is not fully dispersed, so that poor atomization is caused, powder stacking is easy to generate, and when the distance is too close, sparks are easy to generate due to charge discharge; the distance between the spray guns is too far, so that the powder coating rate is low, the coating efficiency is influenced, and the powder layer is thin and is easy to expose the bottom.

In the practical process, the electrostatic spraying adopts a suspension chain automatic assembly line, the speed of a production chain is 0.8-1.2 m/min, and the spraying time of each workpiece to be processed can be adjusted according to the size of the workpiece to be processed.

In some embodiments, the powder coating is a thermosetting coating. In some embodiments, the powder coating includes at least one of an acrylic resin, an epoxy resin, and a polyurethane. In one embodiment, the powder coating is a Wal Wager W841 or Acksonobel Interpon A2200 type acrylic resin. The powder coating has the advantages of high brightness, black color and good leveling property.

Step S140: and (3) performing infrared curing treatment on the sprayed workpiece to be treated, and performing thermal curing treatment to form a powder coating.

The sprayed workpiece to be treated is firstly subjected to infrared preheating solidification, so that on one hand, the fracture of an internal chemical bond can be accelerated, and the rapid grafting bonding of an organic silicon oxide chain segment in a powder coating and a silane film formed by front-section silanization treatment is realized by combining the silane film formed by front-section silanization treatment, thereby improving the adhesive force between the substrate of the workpiece to be treated and the coating, simultaneously improving the comprehensive performances of the coating, such as physical and chemical corrosion resistance, and the like, on the other hand, the infrared radiation can realize rapid temperature rise, and the rapid melting leveling of the inner-layer powder is promoted.

In some embodiments, the infrared wavelength used during infrared curing is from 2 μm to 4 μm. The infrared curing technology can enable infrared radiation to penetrate through the surface layer of the powder to heat the inner layer, and heat transfer curing from inside to outside is achieved. The corresponding wavelength of the natural oscillation frequency of molecular bonds such as hydroxyl and carboxyl is between 2 mu m and 3.5 mu m. When the intermediate infrared radiation with the wavelength of 2-4 microns is used for preheating and curing, by utilizing the principle that the infrared radiation can directly act on chemical bonds when the infrared spectrum frequency corresponds to the atomic group absorption frequency band, the chemical bonds of atomic groups (such as hydroxyl, carboxyl and the like) in the siloxane film and the powder coating generate resonance through absorbing infrared radiation energy, the resonance enables the molecular internal energy to be rapidly gathered, and the breakage of the chemical bonds in the siloxane film and the powder coating is accelerated, so that the organic polymer powder coating and the organic silicon oxygen chain section in the siloxane film are promoted to be better blocked or grafted and bonded, and fully reacted and crosslinked to form an interpenetrating network interface layer, the combination between the powder coating and the siloxane film is more compact, and the adhesive force and the corrosion resistance are improved. Finally, the powder particle layer which is not adhered to each other forms a firm coating after being heated and melted to be tightly combined with the surface of the workpiece. In addition, infrared curing promotes the rapid and uniform heating of the powder coating from inside to outside, can effectively shorten the curing time, and has low energy consumption and high efficiency.

In some embodiments, the temperature of the infrared curing is 120 ℃ to 160 ℃ for 5min to 12 min. Too long or too short infrared curing time can cause uneven thickness of the coating cambered surface or corner, and defects of cracking, orange peel, color difference and the like occur.

And (4) entering a thermal curing stage after infrared curing, and further melting, leveling, crosslinking and curing the powder on the surface of the metal sample piece by further increasing the curing temperature. In some embodiments, the temperature for thermal curing is 170 ℃ to 210 ℃ for 10min to 20 min. During the curing process, too fast temperature rise, too low curing temperature and poor leveling can also cause orange peel defects, so that the CF value is reduced.

The thermal curing adopts convection heating, so that the coating is heated from outside to inside to raise the temperature. And as the convection heating speed is low, the surface powder layer can be promoted to be uniformly and fully melted, leveled and solidified, so that good glossiness and low chromatic aberration are achieved. In addition, the infrared curing shortens the process time of thermal curing, and avoids the adverse effect on the workpiece to be processed caused by long-time high-temperature baking.

The traditional heat curing technology adopts a heat transfer mode, air is heated through combustion of fuels such as natural gas, and then heat of the air is transferred to the surface of a coating, so that heating and curing from outside to inside are realized, the energy conversion efficiency of the mode is low, generally only 60% -80%, the heating process of the coating is accompanied with evaporation of internal moisture, and the heating mode from outside to inside of heat curing easily causes that the moisture in the inner layer cannot be evaporated after the external coating starts to melt, so that the defects of bubbling and the like are caused. In addition, as the powder coating is mostly made of high polymer materials such as acrylic resin, epoxy resin, polyurethane and the like, a good coating effect can be obtained only by long-time high-temperature curing, so that a very long drying tunnel needs to be arranged, a large amount of production space is occupied, great inconvenience is brought to daily production, management and maintenance, and energy consumption is increased. The long-time high-temperature baking can cause certain influence on some light metal materials such as aluminum alloy and the like, and particularly in the production process of automobile exterior trimming parts, the aluminum alloy trimming parts are thin in matrix, so that the long-time high-temperature baking can easily cause some deformation, and the product yield is influenced. And long-time heat curing is easier to bring pollutants such as dust, particles and the like in the air to the surface of the coating in the hot air circulation convection heating process, thereby causing appearance defects.

The infrared curing only acts on the high molecular powder coating without damaging the base material, and is particularly suitable for light metal base materials such as aluminum alloy and the like, and the infrared curing energy consumption is lower and the production efficiency is high. However, infrared curing makes it difficult to achieve uniform melt curing for some workpieces with complex shapes, recesses, and corners due to heating by infrared radiation.

Therefore, in the embodiment, the infrared preheating curing is combined with the thermosetting process, so that the bonding force between the powder coating and the workpiece to be processed can be improved, and more excellent performance can be obtained. The infrared curing enables the internal coating of the powder coating to absorb a large amount of heat in the infrared radiation stage, and the powder coating is quickly softened into a molten state, so that the powder coating can flow on the surface of a workpiece to be treated to form a film. And the subsequent heat curing stage with higher temperature is carried out, and the curing degree of the coating film is further improved along with the increase of the melting temperature. The higher the melting temperature is, the more beneficial the coating can reach the required minimum curing temperature in a shorter time, and the higher the temperature is quickly raised through the front-stage infrared curing, so that the curing temperature at the initial stage of the thermal curing is relatively higher, and the higher curing temperature can realize the coating film with higher curing degree by needing less curing time, thereby greatly shortening the reaction time of the subsequent thermal curing and avoiding the adverse effect of the long-time high-temperature thermal curing on the sample piece. In addition, in the practical process, only two rows of infrared radiation lamps are needed to be installed on the front section of the thermosetting lamp, and the large production space cannot be occupied.

In addition, the thermal curing is from outside to inside, the infrared curing is from inside to outside, the thermal curing is carried out firstly, the outer part of the powder layer is melted and leveled preferentially, and the inner layer coating layer adjacent to the silane film is still in a powder state, so that the outer powder layer can sag under the action of melting gravity; and because the inner layer does not have enough temperature to be crosslinked with the silane film or the crosslinking is too slow, the melted coating on the surface layer can not be adhered, and the paint is easy to drop. Therefore, in the present embodiment, the infrared curing is performed first, and then the thermal curing is performed.

Automobile exterior trimming parts are mostly small-size spare part that contains many orientations, different radian curved surfaces, turning, because "edge effect" among the electrostatic spraying, deposit lacquer easily at radian, corner, easily cause the membrane thickness uneven to change appearance defects such as sagging, orange peel to appear in follow-up curing process, and more planar structure is higher to the requirement of electrostatic spraying and solidification. In the embodiment, by adjusting the process parameters in the electrostatic spraying and curing processes, better corrosion resistance and adhesion can be ensured, and better appearance can be ensured.

The coating method of the automobile exterior trimming part at least has the following advantages:

according to the coating method of the automobile exterior trimming part, the workpiece to be processed is provided with the rough surface, and the rough surface improves the contact area and the bonding site between the powder coating and the substrate of the workpiece to be processed, so that the powder coating and the substrate of the workpiece to be processed can be better combined. On the other hand, the surface of the workpiece substrate to be treated can be activated, and the spreading characteristic of the coating on the metal surface is improved, so that the bonding strength between the coating and the surface of the substrate is improved. The silanization treatment is used for replacing the traditional complex phosphating/passivation process with large pollution, one end of the silane surface treating agent and the surface of a sample form a hydrogen bond and a Si-O-M covalent bond, the adhesive force with the sample matrix is improved, the traditional electrophoretic primer pre-coating process for improving the adhesive force is omitted, the other end of the silane surface treating agent can directly radiate into the powder inner layer to act on the chemical bond due to the infrared curing in the infrared curing process through the reactivity of the carbon functional group in the silane surface treating agent, each chemical bond of the atomic group in the silane surface treating agent and the powder coating can generate resonance through absorbing the infrared radiation energy, the molecular internal energy can be rapidly gathered through resonance, the fracture of the chemical bond in the silane film and the powder coating is accelerated, the better crosslinking of the molecules in the silane film and the powder coating is promoted, and an interpenetrating network interface layer is formed through the block or graft reaction, the forms of the interface layer and the powder coating are changed, and the comprehensive performances of acid and alkali corrosion resistance and the like of the powder coating are improved, so that the powder coating has an anti-corrosion effect which is equal to that of the traditional phosphating/passivation process. In the curing process, infrared curing can promote better crosslinking of the silane film and internal molecules of the powder coating, so that the adhesive force and the corrosion resistance of the coating are enhanced, and the curing process can be quicker and more uniform; the heat curing process promotes the temperature to be further improved, the further melting, leveling and curing of the powder are facilitated, and the problem of appearance defects caused by the fact that the uniform melting and curing are difficult to realize only by adopting an infrared curing method is solved. The infrared curing and the thermocuring are combined, so that the curing time is greatly shortened, the workpiece deformation and appearance defects caused by long-time high-temperature baking are effectively avoided, the energy is saved, the consumption is reduced, and the production efficiency is improved.

In addition, the coating method of the automobile exterior trimming part can improve the salt mist resistance, high humidity resistance and other performances, and enables the workpiece to be treated to have no obvious appearance defects such as orange peel, bubbles, impurities and the like.

The invention also provides the automobile exterior trimming part of the embodiment, which is obtained after the coating method is used for treatment.

Referring to fig. 2, the aluminum alloy exterior trimming part for an automobile includes: metal substrate 1, silane film 2 and powder coating 3. The metal substrate 1 has a rough surface, the silane film 2 is arranged on the rough surface of the metal substrate 1, and the powder coating 3 is arranged on the surface of the silane film 2 far away from the metal substrate 1.

The automobile exterior trimming part has good corrosion resistance, adhesive force and appearance.

In order to make the objects and advantages of the present invention more apparent, the method for coating an exterior automotive part and the effects thereof according to the present invention will be described in detail with reference to the following specific examples, which should be construed as merely illustrative and not limitative of the present invention. The following examples are not particularly specified, and do not include other components except inevitable impurities. The examples, which are not specifically illustrated, employ drugs and equipment, all of which are conventional in the art. The experimental procedures without specifying the specific conditions in the examples were carried out under the conventional conditions such as those described in the literature, in books, or as recommended by the manufacturer.

Example 1

The embodiment provides a coating method of an aluminum alloy exterior trimming part for an automobile, which specifically comprises the following steps:

(1) polishing: and (3) polishing the aluminum alloy workpiece to be treated by using a 5-inch disc pneumatic polisher, preparing 3M 400# abrasive paper and preparing air pressure of 0.65MPa to remove an oxide film, machining scratches, burrs and the like on the surface of the formed aluminum alloy sample, so that the surface roughness of the polished aluminum alloy workpiece is 3.2 mu M. And (3) fixing the polished aluminum alloy workpiece on a corresponding tool hanger, starting a hanging conveying chain, and sequentially performing degreasing, washing, silanization and pure water washing processes at a chain speed of 0.8 m/min.

(2) Degreasing: the samples were spray degreased using ParcoCleaner 1507 and Bonderite 125 degreasers formulated at 50 ℃ respectively, with a spray pressure of 0.1 MPa.

(3) Washing with water: and (3) flowing the degreased workpiece into the next washing procedure, wherein the washing comprises two procedures, the first washing procedure ensures that the conductivity is less than or equal to 600 mu s/cm, and the second washing procedure ensures that the conductivity is less than or equal to 50 mu s/cm. The water washing adopts a spraying mode, and the spraying pressure is 0.1 MPa.

(4) Silanization treatment: and (3) performing silanization treatment on the aluminum alloy workpiece after washing by adopting a silane surface treating agent Oxsilan9832 in a spraying mode to form a silane film with the thickness of 80nm on the rough surface. The temperature of the silane tank is 28 ℃, the spraying flow is 900mL/min, the spraying pressure is 0.1MPa, and the time is 1.5 min.

(5) Pure water washing: and (3) carrying out pure water spraying cleaning on the silanized aluminum alloy workpiece, wherein the spraying pressure is 0.1MPa, and the steps comprise a first pure water washing step and a second pure water washing step. The electric conductivities of the first pure water washing and the second pure water washing are respectively less than or equal to 200 mu s/cm and less than or equal to 20 mu s/cm, and the pH value is 7.2.

(6) Drying: and (3) drying the aluminum alloy workpiece subjected to the pure water washing by using a drying furnace, wherein the temperature of the drying furnace is 120 ℃, and the drying time is 30 min.

(7) Electrostatic powder spraying: and (3) cooling the surface of the dried aluminum alloy workpiece through a cooling area, and then flowing into a powder spraying room for electrostatic powder spraying, wherein the powder coating is acrylic resin of Volverger W841 type, the cleanliness of electrostatic powder spraying is controlled to be ten thousand levels (the dust falling number is less than or equal to 3.50E +05) and the air speed of the powder spraying room is 0.25 m/s. The technological parameters of powder spraying are as follows: the spraying voltage is 70KV, the current is 25 muA, the pressure of the spray gun is 4.0MPa, the powder output is 45g/min, the spraying distance is 25cm, and four spray guns are adopted for spraying simultaneously.

(8) Infrared preheating: and (3) the aluminum alloy workpiece after electrostatic powder spraying enters a preheating section of a curing furnace to be subjected to infrared preheating curing. The infrared preheating adopts a medium-wavelength infrared radiation lamp tube, the wavelength is 2-4 mu m, the heating temperature is 140 ℃, and the heating time is 6 min.

(9) Thermal curing: and (4) carrying out thermocuring on the aluminum alloy workpiece subjected to infrared preheating and curing. The thermosetting temperature is 195 ℃, the curing time is 15min, and a powder coating with the thickness of 95 μm is formed on the surface of the aluminum alloy workpiece.

The aluminum alloy workpieces obtained in the above examples were subjected to adhesion, acid and alkali resistance, corrosion resistance and other related performance tests, and the results are shown in table 1. The powder coating has the adhesion test grade of 0 grade, the pH 13.5 alkali-resistant immersion test is more than 3h, the pH 1.0 acid-resistant immersion test is more than 72h, the neutral salt spray test (NSS) test is more than 1680h, and the high-humidity test is 360h, so that no change occurs, the requirement on the test performance is far higher, and the powder coating has excellent adhesion and corrosion resistance.

Fig. 3 is a surface topography of the automobile exterior part treated by the coating method of example 1, which was observed under a magnification of 100 times using an optical microscope after the test. In FIG. 3, a is an appearance pattern after 3h of pH 13.5 alkali resistance test and no change in appearance, b is an appearance pattern after 72h of pH 1.0 acid resistance test and no change in appearance, c is an appearance pattern after 1680h of neutral salt spray test (NSS) test and no change in appearance, and d is an appearance pattern after 360h of high humidity test and no change in appearance. As can be seen from FIG. 3, the surface morphology after the test does not have any defects such as corrosion, bubbles and the like.

TABLE 1 Performance test results for the aluminum alloy workpiece of example 1

Example 2

This example provides a method for coating an aluminum alloy exterior part for an automobile, which comprises the steps similar to those of example 1, except that the time for the silylation treatment in step (4) of this example is 5 min.

The aluminum alloy workpieces obtained in the above examples were subjected to adhesion, acid and alkali resistance, corrosion resistance and other related performance tests, and compared with example 1, the adhesion was not changed by prolonging the silylation time, but the corrosion resistance and the high humidity resistance were deteriorated. The main reasons are that the silanization treatment time is too long, a large amount of silane groups are enriched due to the fact that a silane film is too thick, the silane groups are used as a blocking agent of the acrylic resin coating, the reaction activity in the coating is reduced, the crosslinking density is greatly reduced, the film layer is not compact, and therefore the silane coating is more easily corroded by external water vapor and corrosive liquid, and performance is reduced. Specific results and morphology analysis are shown in table 2 and fig. 4. In fig. 4, a is an appearance diagram after 10min of a pH 13.5 alkali resistance test, the appearance is unchanged, b is an appearance diagram after 24h of a pH 1.0 acid resistance test, the surface has a small amount of corrosion points, c is an appearance diagram after 480h of a neutral salt spray test (NSS), the surface has a small amount of corrosion points, d is an appearance diagram after 240h of a high humidity test, and a large amount of bubbles appear on the film layer.

Table 2 results of performance testing of the aluminum alloy workpiece of example 2

Example 3

This example provides a method for coating an aluminum alloy exterior part for an automobile, which comprises the steps similar to those of example 1, except that in step (7) of this example, the pressure of the spray gun is 2.5 MPa.

The aluminum alloy workpieces obtained in the above embodiments were subjected to adhesion, acid and alkali resistance, corrosivity, and other related performance tests, and specific results and morphology analysis are shown in table 3 and fig. 5. In FIG. 5, a is an appearance diagram after 10min of pH 13.5 alkali resistance test and no change in appearance, b is an appearance diagram after 24h of pH 1.0 acid resistance test and no change in appearance, c is an appearance diagram after 480h of neutral salt spray test (NSS) test and no change in appearance, and d is an appearance diagram after 240h of high humidity test and no change in appearance. However, as is apparent from fig. 5, the appearance of the prepared workpiece is very poor, the thickness of the cured film layer is severely uneven, and the defects such as bulges appear in partial areas. Too low a spray gun pressure can result in uneven atomization of the powder coating, resulting in build-up of powder and thus severe cosmetic defects after curing.

TABLE 3 Performance test results for the aluminum alloy workpiece of example 3

Example 4

The present example provides a coating method for an aluminum alloy exterior trimming part for an automobile, which comprises the following steps similar to those of example 1, except that in step (8) of the present example, the infrared preheating curing time is 3 min.

The aluminum alloy workpieces obtained in the above embodiments were subjected to adhesion, acid and alkali resistance, corrosion resistance and other related performance tests, and the specific results and morphology analysis are shown in table 4 and fig. 6. In FIG. 6, a is an appearance diagram after 10min of pH 13.5 alkali resistance test, the appearance is unchanged, b is an appearance diagram after 24h of pH 1.0 acid resistance test, the surface has a plurality of corrosion points, c is an appearance diagram after 480h of neutral salt spray test (NSS), the surface has a small number of corrosion points, d is an appearance diagram after 240h of high humidity test, and the surface has more bubbles.

Table 4 performance test results for the aluminum alloy workpiece of example 4

Example 5

This example provides a method for coating an aluminum alloy exterior part for an automobile, which comprises the steps similar to those of example 1, except that in step (9) of this example, the time for thermosetting is 8 min. Due to the fact that the thermosetting time is too short, the powder layer is too thick, the film layer cannot be cured uniformly, particularly in the grooves, corners and other areas, the viscosity is high, the surface layer is slightly sticky after being touched lightly, and fingerprints are remained. Since the film layer was not fully cured, no relevant performance tests were performed.

Comparative example 1

Comparative example 1 provides a method for coating an aluminum alloy exterior member for an automobile, which comprises the steps similar to those of example 1, except that the polishing treatment of step (1) is not performed in comparative example 1, and the surface roughness of the aluminum alloy test piece is 0.8 μm.

The aluminum alloy exterior trimming part treated by the method of comparative example 1 has reduced adhesion, coating adhesion of level 1, no change in appearance after an alkali resistance test, a small number of black corrosion points on the surface after an acid resistance test, partial corrosion of the surface film layer after a neutral salt spray test, a large number of bubbles on the surface of the film layer after a high humidity test, and the specific results and the morphological analysis are shown in table 5 and fig. 7. In FIG. 7, a is an appearance diagram after 10min of a pH 13.5 alkali resistance test, the appearance is unchanged, b is an appearance diagram after 24h of a pH 1.0 acid resistance test, the surface has few corrosion points, c is an appearance diagram after 480h of a neutral salt spray test (NSS) test, the film layer is corroded, d is an appearance diagram after 240h of a high humidity test, and the film layer is bubbled.

Table 5 results of performance test of the aluminum alloy workpiece of comparative example 1

Comparative example 2

Comparative example 2 provides a coating method of an aluminum alloy exterior member for an automobile, which is similar to example 1 except that the silanization treatment of step (4) is not performed in comparative example 2.

The aluminum alloy exterior trimming part treated by the method of the comparative example 2 has extremely poor adhesive force and corrosion resistance, the adhesive force of the coating is 2-level, a large number of black corrosion points appear after an alkali resistance test, the film layer bubbles and the surface is seriously corroded after an acid resistance test, the surface bubbles and the large corrosion appears after a salt spray test, and the film layer seriously bubbles and cracks after a high humidity test. The main reasons are that the base material is not subjected to electrophoresis or silanization treatment, the adhesion between the coating and the base material is poor, so that the film layer is loose and not compact, and liquid permeates between the base material and the coating in the test process to cause defects of foaming, corrosion and the like. The specific test results are shown in table 6 and fig. 8. In fig. 8, a is an appearance diagram after 10min of a pH 13.5 alkali resistance test, the surface has a large number of corrosion points, b is an appearance diagram after 24h of a pH 1.0 acid resistance test, the surface has bubbles and a large number of corrosion points, c is an appearance diagram after 480h of a neutral salt spray test (NSS) test, the film layer is seriously corroded, d is an appearance diagram after 240h of a high humidity test, and the film layer is seriously foamed and cracked.

As shown in fig. 9, the bubbles generated after the high humidity test in fig. 8 were analyzed in cross section, and as is apparent from fig. 9, the bubbling was caused by the formation of a hollow cavity between the coating and the substrate, and since the high humidity test was always performed at 40 ℃ and 100% RH, the bonding force between the coating and the substrate was weak, which caused the permeation of water vapor, and the bubbles were formed between the two, and after the experiment, the water vapor slowly evaporated to form the cavity shown in fig. 9. The importance of the silanization treatment was thus also confirmed.

TABLE 6 results of Performance test of the aluminum alloy workpiece of comparative example 2

Comparative example 3

Comparative example 3 provides a coating method of an aluminum alloy exterior member for an automobile, which is similar to example 1 except that the heat curing treatment of step (9) is not performed in comparative example 3 while the infrared curing treatment time of step (8) is increased to 25 min.

The aluminum alloy exterior trimming parts treated by the method of comparative example 3 had severe curing unevenness: the areas such as grooves and corners which cannot be irradiated by infrared rays cannot be completely cured, and the curing degree of each area of the coating is extremely uneven. Because the curing was not uniform, the appearance of the sample was very poor and no relevant tests were performed.

Comparative example 4

Comparative example 4 provides a coating method of an aluminum alloy exterior member for an automobile, which is similar to example 1 except that the infrared curing treatment of step (8) is not performed in comparative example 4 while the heat curing treatment time of step (9) is increased to 45 min.

The aluminum alloy exterior trim treated by the method of comparative example 4 has serious orange peel appearance defects, and has defects of bubbling, impurities and the like on the surface. The appearance has no obvious change after the alkali resistance test, the surface of the sample piece has impurity particle point defects, and the surface has defects of corrosion, bubbles and the like after the acid resistance, neutral salt fog and high humidity test, and the defects of corrosion, bubbles and the like are presumed to be caused by the fact that steam under the test condition permeates into the film layer through surface impurities. The specific test results are shown in table 7 and fig. 10. In fig. 10, a is an appearance diagram after 10min of a pH 13.5 alkali resistance test, and the appearance is not changed, b is an appearance diagram after 24h of a pH 1.0 acid resistance test, and the surface has a large number of small corrosion points, c is an appearance diagram after 480h of a neutral salt spray test (NSS) test, and the film layer erodes and foams, d is an appearance diagram after 240h of a high humidity test, and the surface has a large number of foams.

TABLE 7 Performance test results for the aluminum alloy workpiece of comparative example 4

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, which is convenient for specific and detailed understanding of the technical solutions of the present invention, but the present invention should not be construed as being limited to the scope of the invention. It should be noted that various changes and modifications can be made by those skilled in the art without departing from the spirit of the invention, and these changes and modifications are all within the scope of the invention. It should be understood that the technical solutions provided by the present invention, which are obtained by logical analysis, reasoning or limited experiments, are within the scope of the present invention as set forth in the appended claims. Therefore, the protection scope of the present invention should be subject to the content of the appended claims, and the description and the drawings can be used for explaining the content of the claims.

Claims

1. A coating method of an automobile exterior trimming part is characterized by comprising the following steps:

obtaining a workpiece to be processed with a rough surface;

and performing infrared curing treatment on the workpiece to be treated after powder spraying, and then performing thermosetting treatment to form a powder coating.

2. The coating method of the automobile exterior trim according to claim 1, wherein the roughness of the rough surface is 1 μm to 8 μm.

3. The coating method of the automobile exterior trim according to claim 1, wherein the time for treating the rough surface with the silane surface treating agent is 1 to 2min, and the thickness of the silane film is 50 to 100 nm.

4. The coating method of the automobile exterior trim according to claim 1, wherein the rough surface is treated by spraying at a flow rate of 800 to 1000mL/min and a spray pressure of 0.08 to 0.12 MPa.

5. The method for coating exterior automotive trims as claimed in any one of claims 1 to 4, wherein said silane surface treatment agent is at least one selected from the group consisting of KH550, KH560, KH570, Oxsilan9810, Oxsilan9812, Oxsilan9830 and Oxsilan 9832.

6. The method of coating exterior automotive trims as claimed in claim 1, wherein the powder coating used in the powder spraying process comprises at least one of acrylic resin, epoxy resin and polyurethane.

7. The method of coating exterior automotive trims as claimed in claim 6, wherein the powder coating used in the powder spraying process comprises an acrylic resin, and the silane surface treatment agent is at least one selected from the group consisting of Oxsilan9832, KH560 and Oxsilan 9830.

8. The coating method of the automobile exterior trim part according to claim 1, wherein the process parameters in the infrared curing process satisfy at least one of the following conditions:

(1) the infrared wavelength is 2-4 μm;

9. The coating method of the automobile exterior trim according to claim 1, wherein the heat curing is performed at a temperature of 170 ℃ to 210 ℃ for 10min to 20 min.

10. The method for coating an exterior automotive trim according to claim 1, wherein in the step of spraying the powder onto the surface of the workpiece to be treated on which the silane film is formed, an electrostatic powder spraying method is used.

11. The coating method of automobile exterior parts according to claim 10, wherein the process parameters in the electrostatic powder spraying process satisfy at least one of the following conditions:

(2) the powder spraying amount is 20 g/min-60 g/min, and the powder spraying current is 15 muA-30 muA;

(3) the cleanliness is controlled at ten thousand levels, and the air speed of the spray room is controlled at 0.2-0.3 m/s.

12. The method for coating an exterior automotive trim according to any one of claims 1 and 8 to 11, wherein the thickness of the powder coating layer is 90 to 120 μm.

13. An automobile exterior part, characterized by being obtained by the coating method according to any one of claims 1 to 12.