CN113481567B - Powder coating method for automobile body - Google Patents

Powder coating method for automobile body Download PDF

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Publication number
CN113481567B
CN113481567B CN202110713054.2A CN202110713054A CN113481567B CN 113481567 B CN113481567 B CN 113481567B CN 202110713054 A CN202110713054 A CN 202110713054A CN 113481567 B CN113481567 B CN 113481567B
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automobile body
spraying
powder
powder coating
electrophoresis
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CN113481567A (en
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李庆华
殷坤
张丽桂
王文文
苏军
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Dongfeng Motor Corp
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Dongfeng Motor Corp
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/12—Electrophoretic coating characterised by the process characterised by the article coated
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B16/00—Spray booths
    • B05B16/60—Ventilation arrangements specially adapted therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/02—Processes for applying liquids or other fluent materials performed by spraying
    • B05D1/04—Processes for applying liquids or other fluent materials performed by spraying involving the use of an electrostatic field
    • B05D1/06—Applying particulate materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/002—Pretreatement
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/10—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by other chemical means
    • B05D3/102—Pretreatment of metallic substrates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
    • B05D5/06—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects
    • B05D5/065—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects having colour interferences or colour shifts or opalescent looking, flip-flop, two tones
    • B05D5/066—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects having colour interferences or colour shifts or opalescent looking, flip-flop, two tones achieved by multilayers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/20—Pretreatment
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/22—Servicing or operating apparatus or multistep processes

Abstract

The application relates to the technical field of automobile coating, in particular to a powder coating method for an automobile body. The powder coating method provided by the application comprises the following steps: pretreatment, electrophoresis, powder coating spraying, coating drying and offline fine finishing, wherein the powder coating spraying comprises the following processes: cleaning a powder spraying room: the dust in the powder spraying room is cleaned, and the dust in each cubic foot of air is ensured to be as follows: the dust particle with the particle size of more than or equal to 5 mu m is not contained, and the number of the dust particles with the particle size range of 0.5 to 5 mu m is not more than 30000; setting the wind direction, the wind speed and the temperature and humidity of the powder spraying room: setting the wind direction of the powder spraying room to be vertical downward, setting the wind speed to be 0.3-0.5 m/s, setting the temperature to be 20-30 ℃ and setting the humidity to be 50-70%; spraying: conveying the automobile body to be treated into a powder spraying room, and spraying the powder coating on the surface of the automobile body under the condition that the electrostatic voltage is-70 to-60 kV. The coating process provided by the application can realize zero discharge of VOC in the finish coating process.

Description

Powder coating method for automobile body
Technical Field
The application relates to the technical field of automobile coating, in particular to a powder coating method for an automobile body.
Background
Automobile coating, namely surface treatment of automobile metal plates, can directly influence the service life, the attractive appearance and the whole automobile value of an automobile. With the improvement of environmental protection requirements, the requirements on pollutant emission and energy consumption of automobile coating technology are more and more strict.
The VOC discharge is one of important indexes for measuring the coating environmental protection, and relevant environmental protection regulations clearly require that the VOC discharge of each unit coating area of an automobile is not more than 20g/m2. The control of VOC emissions is mainly carried out from three aspects: firstly, source control, namely, a coating material with low VOC content is adopted; the second process control, namely, a high-efficiency spraying technology is adopted, so that ineffective discharge is reduced; and thirdly, treating the tail end, namely configuring a waste gas purification facility. In order to solve the problem of VOC emission, in recent years, a newly built or modified automobile coating production line generally adopts a water-based coating process and an exhaust gas incineration technology in a combined manner, and the VOC emission can be greatly reduced, but about 12g/m still exists in comparison with the traditional solvent-based coating process2The discharge problem cannot be thoroughly eliminated.
The powder coating is a solid powder synthetic resin coating composed of solid resin, pigment, filler, auxiliary agent and the like, and is different from common solvent-based coatings and water-based coatings, the dispersion medium of the powder coating is not solvent and water but air, and the powder coating has the characteristics of no solvent pollution, 100% film forming and low energy consumption. Therefore, the development of the automobile coating process of the powder coating is expected to solve the VOC emission problem from the source.
Disclosure of Invention
The embodiment of the application provides a powder coating method of an automobile body, which aims to solve the problem of VOC emission in the related technology.
In a first aspect, the present application provides a method of powder coating an automotive body, comprising the steps of: sequentially carrying out pretreatment, electrophoresis, powder coating spraying, coating drying and fine trimming and off-line treatment on an automobile body to form an automobile body coating structure which is sequentially provided with an electrophoresis coating and a powder coating from inside to outside; wherein, the powder coating spraying comprises the following processes:
cleaning a powder spraying room: the dust in the powder spraying room is cleaned, and the dust in each cubic foot of air is ensured to be as follows: the dust particle with the particle size of more than or equal to 5 mu m is not contained, and the number of the dust particles with the particle size range of 0.5 to 5 mu m is not more than 30000;
setting the wind direction, the wind speed and the temperature and humidity of the powder spraying room: setting the wind direction of the powder spraying room to be vertical downward, setting the wind speed to be 0.3-0.5 m/s, setting the temperature to be 20-30 ℃ and setting the humidity to be 50-70%;
spraying: conveying the automobile body to be treated into a powder spraying room, and spraying powder coating on the surface of the automobile body under the condition that the electrostatic voltage is-70 to-60 kV, wherein the film forming thickness is 40-60 mu m.
In some embodiments, the temperature for drying the coating is 160-180 ℃ for 20-30 min.
In some embodiments, the distance between the spray guns is 15-25 cm and the speed of the spray guns is 400-600 mm/s during the powder coating spraying process.
In some embodiments, the pretreatment is performed by a phosphating pretreatment or a film pretreatment.
In some embodiments, the pre-phosphating treatment comprises the following processes:
(1) pre-washing: spraying industrial water at the temperature of 30-50 ℃ on the automobile body, wherein the spraying time is 20-30 s, and the spraying pressure is 0.05-0.15 MPa;
(2) pre-degreasing: spraying the automobile body with pre-degreasing bath solution for 30-60 s, wherein the spraying pressure is 0.2-0.3 MPa, the temperature of the pre-degreasing bath solution is 40-50 ℃, and the pH value of the pre-degreasing bath solution is 12-14;
(3) degreasing: immersing the automobile body into degreasing bath solution with the pH value of 12-14, wherein the immersion time is 180-240 s, the surface flow circulation pressure is 0.08-0.12 MPa, and the temperature of the degreasing bath solution is 40-50 ℃;
(4) first water washing: immersing the automobile body into industrial water for 120-150 s, wherein the spraying pressure during the immersion of the automobile body and the spraying pressure during the immersion of the automobile body are both 0.23-0.27 MPa;
(5) and (3) second water washing: spraying industrial water on the automobile body for 20-30 s at a spraying pressure of 0.23-0.31 MPa;
(6) surface conditioning: immersing the automobile body into surface conditioning bath solution with the pH value of 9.5-10.5, wherein the soaking time is 60-120 s, and the temperature of the surface conditioning bath solution is 25-35 ℃;
(7) phosphorization: immersing an automobile body into phosphating tank liquor with the ratio of total acid to free acid of 21-23, wherein the immersion time is 180-240 s, the surface flow spraying pressure of the phosphating tank liquor is 0.02-0.06 MPa, and the temperature of the phosphating tank liquor is 40-45 ℃; the phosphated automobile body needs to be ensured: the size of phosphorization crystal is less than or equal to 10 mu m, the zinc-iron phosphate content in the phosphorization film is more than or equal to 90 percent, and the weight of the phosphorization film on the surface of the cold-rolled steel plate is 2-3 g/m2The weight of the phosphating film on the surface of the galvanized steel sheet is 2-4 g/m2；
(8) And (3) washing for the third time: immersing the automobile body into industrial water for 120-150 s, wherein the spraying pressure during the immersion of the automobile body and the spraying pressure during the immersion of the automobile body are both 0.13-0.21 MPa;
(9) fourth water washing: spraying industrial water on the automobile body for 20-30 s at a spraying pressure of 0.13-0.17 MPa;
(10) and (3) circulating pure water washing: immersing the automobile body into pure water with the conductivity less than or equal to 20 mu s/cm, wherein the immersion time is 120-150 s, and the spraying pressure during the immersion of the automobile body and the spraying pressure during the leaching of the automobile body are both 0.13-0.31 MPa;
(11) fresh pure water washing: pure water with the conductivity less than or equal to 5 mu s/cm is adopted to spray the automobile body, the spraying time is 20-30 s, the spraying pressure is 0.15-0.25 MPa, the spraying flow is 70-130L/min, and the water dropping conductivity of the automobile body is less than or equal to 50 mu s/cm.
In some embodiments, both the pre-degreasing bath and the degreasing bath employ an alkaline surfactant.
In some embodiments, both the surface conditioning bath and the phosphating bath employ zinc-based phosphating solutions.
In some embodiments, the film pre-treatment comprises the following processes:
(1) pre-washing: spraying industrial water at the temperature of 30-50 ℃ on the automobile body, wherein the spraying time is 20-30 s, and the spraying pressure is 0.05-0.15 MPa;
(2) pre-degreasing: spraying the automobile body with pre-degreasing bath solution for 30-60 s at a spraying pressure of 0.2-0.3 MPa at a temperature of 40-50 ℃ and a pH value of less than 12.5;
(3) degreasing: immersing the automobile body into degreasing bath liquid for 180-240 s, wherein the surface flow circulation pressure of the degreasing bath liquid is 0.08-0.12 MPa, the temperature of the degreasing bath liquid is 40-50 ℃, and the pH value of the degreasing bath liquid is less than 12;
(4) first water washing: immersing the automobile body into industrial water with the pH value less than or equal to 11.8 and the conductivity less than or equal to 3000 mu s/cm, wherein the immersion time is 120-150 s, and the spraying pressure during the immersion of the automobile body are both 0.1-0.18 MPa;
(5) and (3) second water washing: spraying industrial water with the pH value of less than or equal to 9.5 and the conductivity of less than or equal to 1000 mu s/cm on the automobile body, wherein the spraying time is 20-30 s, and the spraying pressure is 0.1-0.18 MPa;
(6) and (3) washing for the third time: immersing the automobile body into pure water with the pH value of less than or equal to 8.9 and the conductivity of less than or equal to 300 mu s/cm, wherein the immersion time is 120-150 s, the spraying pressure during the immersion of the automobile body and the spraying pressure during the immersion of the automobile body are both 0.1-0.18 MPa, and the pure water replenishing flow is 30-70L/min;
(7) silane treatment: immersing an automobile body into silane tank liquid with the pH value of 4.2-5.5 and the conductivity of less than 4000 mu s/cm, wherein the immersion time is 120-180 s, the temperature of the silane tank liquid is 27-38 ℃, the stirring pressure in the silane tank liquid is 0.1-0.2 MPa, the Zr content in the silane tank liquid is 100-300 mg/L, Cu content, the Zr content in the silane tank liquid is 0.5-3 mg/L, Si content in the silane tank liquid is 25-55 mg/L, and the free fluorine content in the silane tank liquid is 20-52 mg/L; the silane treated automobile body needs to guarantee: the weight of the silane film on the surface of the galvanized steel sheet is 70-180 mg/m2The weight of the silane film on the surface of the cold-rolled steel plate is 30-100 mg/m2；
(8) Fourth water washing: spraying pure water with the pH value of 6-9 and the conductivity of less than or equal to 600 mu s/cm on the automobile body for 20-30 s, wherein the spraying pressure is 0.1-0.18 MPa;
(9) and (3) circulating pure water washing: immersing the automobile body into pure water with the pH value of 5.5-8 and the conductivity of less than or equal to 60 mu s/cm, wherein the immersion time is 120-150 s, and the spraying pressure during immersion and leaching of the automobile body is 0.1-0.18 MPa;
(10) fresh pure water washing: pure water with the conductivity less than or equal to 5 mu s/cm is adopted to spray the automobile body, the spraying time is 20-30 s, the spraying pressure is 0.1-0.18 MPa, the spraying flow is 50-80L/min, and the water dropping conductivity of the automobile body is less than or equal to 50 mu s/cm.
In some embodiments, both the pre-degreasing bath and the degreasing bath employ an alkaline surfactant.
In some embodiments, electrophoresis comprises the following processes:
(1) electrophoresis: immersing an automobile body into an electrophoresis tank liquid with the pH value of 5.8-6.5, the conductivity of 1300-2200 mu s/cm, the throwing power of more than or equal to 60 percent and the solvent content of less than or equal to 2 percent, wherein the temperature of the electrophoresis tank liquid is 28-32 ℃, the solid content of the electrophoresis tank liquid is 19-22 percent, the ash content is 15-20 percent, the electrophoresis process adopts two-stage voltage step control, the first-stage voltage is 160-250V, the second-stage voltage is 200-300V, and the electrifying time of the electrophoresis process is more than or equal to 180 s;
(2) first ultrafiltration water washing: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 20-30 s at a spraying pressure of 0.05-0.15 MPa;
(3) and (3) ultrafiltration washing for the second time: immersing an automobile body into the electrophoresis ultrafiltration washing tank liquor for 120-180 s, wherein the spraying pressure during the immersion of the automobile body and the leaching of the automobile body is 0.05-0.15 MPa, and the solid content of the electrophoresis ultrafiltration washing tank liquor is less than or equal to 2%;
(4) and (3) ultrafiltration washing for the third time: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 20-30 s at a spraying pressure of 0.05-0.15 MPa;
(5) pure water washing is circulated for the first time: spraying pure water with the solid content of less than or equal to 0.5% on an automobile body for 20-30 s, wherein the spraying pressure is 0.05-0.12 MPa;
(6) and (3) circulating pure water for the second time: immersing the automobile body into pure water with the solid content of less than or equal to 0.5%, wherein the immersion time is 120-180 s, and the spraying pressure during the immersion of the automobile body and the leaching of the automobile body are both 0.05-0.12 MPa;
(7) fresh pure water washing: pure water is adopted to spray the automobile body, the spraying time is 20-30 s, the spraying pressure is 0.05-0.12 MPa, and the spraying flow is 70-130L/min.
In some embodiments, the thickness of the electrophoretic coating after electrophoresis is: the thickness of the electrophoretic coating on the outer surface of the vehicle body is more than or equal to 15 microns, and the thickness of the electrophoretic coating on the inner cavity of the vehicle body is more than or equal to 10 microns.
In some embodiments, the electrophoresis is followed by flash drying at a temperature of 100-120 ℃ for 8-12 min. The flash drying temperature and time are both less than the drying temperature and time, and compared with the drying solidification film forming after electrophoresis, the length of the flash drying furnace is shorter than that of the drying furnace, the furnace temperature of the flash drying furnace is set to be lower than that of the drying furnace, and the electrophoresis flash drying is more energy-saving than the drying; and secondly, compared with electrophoretic drying, electrophoretic flash drying is directly carried out by spraying powder coating after electrophoretic flash drying, an electrophoretic polishing procedure is not carried out in the middle, the process length is shortened, manual polishing operation is not carried out, and energy consumption and labor cost are further saved.
In some embodiments, the flash-dried electrocoat has a dehydration rate of 95% or more.
In some embodiments, the electrophoresis is sequentially dried and polished at 160-180 ℃ for 20-30 min.
In some embodiments, the hardness of the dried electrophoretic coating is more than or equal to H, and the adhesive force of the electrophoretic coating is less than or equal to 0 grade measured by a Baige method.
In some embodiments, the process of refining the offline is: and inspecting the vehicle body after the powder coating is dried, marking defects, and modifying the defects by adopting methods such as grinding, polishing and the like to prevent the defects of the paint film from flowing out.
In some embodiments, the hardness of a paint film after the powder coating is dried is more than or equal to HB, and the adhesive force of the paint film measured by a Baige method is less than or equal to 0 grade.
In a second aspect, the present application further provides a method for coating by using the cooperation of three powder spray rooms, specifically: spraying a main color (such as a color with a color scheduling ratio of more than or equal to 30%) by using the powder spraying room A, spraying an auxiliary color 1 by using the powder spraying room B, and spraying an auxiliary color 2 by using the powder spraying room C; when the main color needs to be sprayed in the production process, the automobile body is directly sent into a powder spraying room A for spraying; when colour 1 and supplementary colour 2 are assisted in the needs spraying, spout the room B by the powder and spout the room C and trade the colour spraying in turn by the powder, when the room B spraying of powder is assisted colour 1, the room C is spouted to the powder trades the colour and prepares the supplementary colour 2 of spraying, when the room C spraying is assisted colour 2 to the powder, the room B is spouted to the powder trades the colour and prepares the supplementary colour 3 of spraying, analogizes in proper order and accomplishes the spraying of all colours. The problem of low production efficiency of a coating production line caused by powder coating color changing waiting can be solved by using three parallel powder spraying rooms in a matched mode.
The beneficial effect that technical scheme that this application provided brought includes: according to the method, the powder coating without VOC is used for replacing a washing coating or a solvent type coating used in the traditional coating process, so that the zero emission of VOC in the finish coating process of the automobile body can be realized, dust in a powder spraying room is cleaned before the powder coating is sprayed, and the wind direction, the wind speed and the temperature and humidity are set, so that the powder spraying process can be effectively prevented from being interfered; meanwhile, the vehicle body coating obtained by the powder coating method is of a two-coating structure, so that the coating process route is greatly simplified, and the energy consumption can be reduced by 30-40%.
Drawings
FIG. 1 is a schematic flow chart illustrating a powder coating method for an automobile body according to an embodiment of the present application;
FIG. 2 is a schematic structural diagram of an automotive body coating sprayed by the powder coating method provided by the embodiment of the application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The embodiment of the application provides a powder coating method of an automobile body, which aims to solve the problem of VOC emission in the related technology.
Fig. 1 is a schematic flow chart of a powder coating method for an automobile body provided by the present application, and referring to fig. 1, the powder coating method for an automobile body of the present application comprises the following steps:
the method comprises the following steps of firstly, preprocessing, wherein the preprocessing mode adopts phosphating preprocessing or film preprocessing, wherein the phosphating preprocessing comprises the following processes:
(1) pre-washing: spraying industrial water at the temperature of 30-50 ℃ on the automobile body, wherein the spraying time is 20-30 s, and the spraying pressure is 0.05-0.15 MPa;
(2) pre-degreasing: spraying the automobile body with pre-degreasing bath solution for 30-60 s, wherein the spraying pressure is 0.2-0.3 MPa, the temperature of the pre-degreasing bath solution is 40-50 ℃, and the pH value of the pre-degreasing bath solution is 12-14; the pre-degreasing bath solution is an alkaline surfactant;
(3) degreasing: immersing the automobile body into degreasing bath solution with the pH value of 12-14, wherein the immersion time is 180-240 s, the surface flow circulation pressure is 0.08-0.12 MPa, and the temperature of the degreasing bath solution is 40-50 ℃; degreasing bath solution is alkaline surfactant;
(4) first water washing: immersing the automobile body into industrial water for 120-150 s, wherein the spraying pressure during the immersion of the automobile body and the spraying pressure during the immersion of the automobile body are both 0.23-0.27 MPa;
(5) and (3) second water washing: spraying industrial water on the automobile body for 20-30 s at a spraying pressure of 0.23-0.31 MPa;
(6) surface conditioning: immersing the automobile body into surface conditioning bath solution with the pH value of 9.5-10.5, wherein the soaking time is 60-120 s, and the temperature of the surface conditioning bath solution is 25-35 ℃; the surface conditioning bath solution is zinc phosphating solution;
(7) phosphorization: immersing an automobile body into phosphating tank liquor with the ratio of total acid to free acid of 21-23, wherein the immersion time is 180-240 s, the surface flow spraying pressure of the phosphating tank liquor is 0.02-0.06 MPa, and the temperature of the phosphating tank liquor is 40-45 ℃; the phosphated automobile body needs to be ensured: the size of phosphorization crystal is less than or equal to 10 mu m, the zinc-iron phosphate content in the phosphorization film is more than or equal to 90 percent, and the weight of the phosphorization film on the surface of the cold-rolled steel plate is 2-3 g/m2The weight of the phosphating film on the surface of the galvanized steel sheet is 2-4 g/m2(ii) a The phosphating tank solution is zinc phosphating solution;
(8) and (3) washing for the third time: immersing the automobile body into industrial water for 120-150 s, wherein the spraying pressure during the immersion of the automobile body and the spraying pressure during the immersion of the automobile body are both 0.13-0.21 MPa;
(9) fourth water washing: spraying industrial water on the automobile body for 20-30 s at a spraying pressure of 0.13-0.17 MPa;
(10) and (3) circulating pure water washing: immersing the automobile body into pure water with the conductivity less than or equal to 20 mu s/cm, wherein the immersion time is 120-150 s, and the spraying pressure during the immersion of the automobile body and the spraying pressure during the leaching of the automobile body are both 0.13-0.31 MPa;
(11) fresh pure water washing: spraying the automobile body with pure water with the conductivity of less than or equal to 5 mu s/cm for 20-30 s, spraying pressure of 0.15-0.25 MPa, spraying flow of 70-130L/min, and automobile body water drop conductivity of less than or equal to 50 mu s/cm;
the film pretreatment comprises the following processes:
(1) pre-washing: spraying industrial water at the temperature of 30-50 ℃ on the automobile body, wherein the spraying time is 20-30 s, and the spraying pressure is 0.05-0.15 MPa;
(2) pre-degreasing: spraying the automobile body with pre-degreasing bath solution for 30-60 s at a spraying pressure of 0.2-0.3 MPa at a temperature of 40-50 ℃ and a pH value of less than 12.5; the pre-degreasing bath solution selects an alkaline surfactant;
(3) degreasing: immersing the automobile body into degreasing bath liquid for 180-240 s, wherein the surface flow circulation pressure of the degreasing bath liquid is 0.08-0.12 MPa, the temperature of the degreasing bath liquid is 40-50 ℃, and the pH value of the degreasing bath liquid is less than 12; the degreasing bath solution selects an alkaline surfactant;
(4) first water washing: immersing the automobile body into industrial water with the pH value less than or equal to 11.8 and the conductivity less than or equal to 3000 mu s/cm, wherein the immersion time is 120-150 s, and the spraying pressure during the immersion of the automobile body are both 0.1-0.18 MPa;
(5) and (3) second water washing: spraying industrial water with the pH value of less than or equal to 9.5 and the conductivity of less than or equal to 1000 mu s/cm on the automobile body, wherein the spraying time is 20-30 s, and the spraying pressure is 0.1-0.18 MPa;
(6) and (3) washing for the third time: immersing the automobile body into pure water with the pH value of less than or equal to 8.9 and the conductivity of less than or equal to 300 mu s/cm, wherein the immersion time is 120-150 s, the spraying pressure during the immersion of the automobile body and the spraying pressure during the immersion of the automobile body are both 0.1-0.18 MPa, and the pure water replenishing flow is 30-70L/min;
(7) silane treatment: immersing the automobile body into silane tank liquid with the pH value of 4.2-5.5 and the conductivity of less than 4000 mu s/cm, wherein the immersion time is 120-180 s, the temperature of the silane tank liquid is 27-38 ℃, the stirring pressure in the silane tank liquid is 0.1-0.2 MPa, and siliconThe alkane tank solution contains 100-300 mg/L, Cu of Zr content, 0.5-3 mg/L, Si of Zr content, 25-55 mg/L of free fluorine content and 20-52 mg/L of free fluorine content; the silane treated automobile body needs to guarantee: the weight of the silane film on the surface of the galvanized steel sheet is 70-180 mg/m2The weight of the silane film on the surface of the cold-rolled steel plate is 30-100 mg/m2；
(8) Fourth water washing: spraying pure water with the pH value of 6-9 and the conductivity of less than or equal to 600 mu s/cm on the automobile body for 20-30 s, wherein the spraying pressure is 0.1-0.18 MPa;
(9) and (3) circulating pure water washing: immersing the automobile body into pure water with the pH value of 5.5-8 and the conductivity of less than or equal to 60 mu s/cm, wherein the immersion time is 120-150 s, and the spraying pressure during immersion and leaching of the automobile body is 0.1-0.18 MPa;
(10) fresh pure water washing: spraying the automobile body with pure water with the conductivity less than or equal to 5 mu s/cm for 20-30 s, spraying pressure of 0.1-0.18 MPa, spraying flow of 50-80L/min, and automobile body water drop conductivity less than or equal to 50 mu s/cm;
second, electrophoresis, specifically:
(1) electrophoresis: immersing an automobile body into an electrophoresis tank liquid with the pH value of 5.8-6.5, the conductivity of 1300-2200 mu s/cm, the throwing power of more than or equal to 60 percent and the solvent content of less than or equal to 2 percent, wherein the temperature of the electrophoresis tank liquid is 28-32 ℃, the solid content of the electrophoresis tank liquid is 19-22 percent, the ash content is 15-20 percent, the electrophoresis process adopts two-stage voltage step control, the first-stage voltage is 160-250V, the second-stage voltage is 200-300V, and the electrifying time of the electrophoresis process is more than or equal to 180 s;
(2) first ultrafiltration water washing: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 20-30 s at a spraying pressure of 0.05-0.15 MPa;
(3) and (3) ultrafiltration washing for the second time: immersing an automobile body into the electrophoresis ultrafiltration washing tank liquor for 120-180 s, wherein the spraying pressure during the immersion of the automobile body and the leaching of the automobile body is 0.05-0.15 MPa, and the solid content of the electrophoresis ultrafiltration washing tank liquor is less than or equal to 2%;
(4) and (3) ultrafiltration washing for the third time: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 20-30 s at a spraying pressure of 0.05-0.15 MPa;
(5) pure water washing is circulated for the first time: spraying pure water with the solid content of less than or equal to 0.5% on an automobile body for 20-30 s, wherein the spraying pressure is 0.05-0.12 MPa;
(6) and (3) circulating pure water for the second time: immersing the automobile body into pure water with the solid content of less than or equal to 0.5%, wherein the immersion time is 120-180 s, and the spraying pressure during the immersion of the automobile body and the leaching of the automobile body are both 0.05-0.12 MPa;
(7) fresh pure water washing: spraying the automobile body with pure water for 20-30 s, wherein the spraying pressure is 0.05-0.12 MPa, and the spraying flow is 70-130L/min; the thickness of the electrophoretic coating after electrophoresis satisfies the following conditions: the thickness of the electrophoretic coating on the outer surface of the vehicle body is more than or equal to 15 microns, and the thickness of the electrophoretic coating on the inner cavity of the vehicle body is more than or equal to 10 microns;
thirdly, spraying powder coating, which specifically comprises the following steps:
(1) cleaning a powder spraying room: the dust in the powder spraying room is cleaned, and the dust in each cubic foot of air is ensured to be as follows: the dust particle with the particle size of more than or equal to 5 mu m is not contained, and the number of the dust particles with the particle size range of 0.5 to 5 mu m is not more than 30000;
(2) setting the wind direction, the wind speed and the temperature and humidity of the powder spraying room: setting the wind direction of the powder spraying room to be vertical downward, setting the wind speed to be 0.3-0.5 m/s, setting the temperature to be 20-30 ℃ and setting the humidity to be 50-70%;
(3) spraying: conveying the automobile body to be treated into a powder spraying room, and spraying powder coating on the surface of the automobile body under the condition that the electrostatic voltage is-70 to-60 kV, wherein the film forming thickness is 40-60 mu m; the distance between the spraying guns is 15-25 cm, and the speed of the spraying guns is 400-600 mm/s;
fourthly, drying the coating: baking the automobile body for 20-30 min at 160-180 ℃;
fifthly, fine trimming and offline: and inspecting the vehicle body after the powder coating is dried, marking defects, and modifying the defects by adopting methods such as grinding, polishing and the like to prevent the defects of the paint film from flowing out.
In the steps, after electrophoresis, flashing off for 8-12 min at 100-120 ℃, and then spraying powder coating; or drying for 20-30 min at 160-180 ℃ after electrophoresis, polishing and spraying the powder coating.
Fig. 2 is a schematic structural diagram of an automotive body coating obtained by spraying by using the powder coating method, wherein 1 represents an electrophoretic coating, and 2 represents a powder coating, and as can be seen from fig. 2, the automotive body coating obtained by using the powder coating method is a two-coating structure in which the electrophoretic coating and the powder coating are sequentially arranged from inside to outside, and the process route is greatly simplified.
The following describes the powder coating method for automobile bodies in detail with reference to examples.
Example 1:
embodiment 1 of the present application provides an automobile body powder coating method, including the steps of:
firstly, phosphating pretreatment:
(1) pre-washing: spraying industrial water at 35 ℃ on the automobile body for 25s at the spraying pressure of 0.08 MPa;
(2) pre-degreasing: spraying the automobile body with pre-degreasing bath solution for 50s at a spraying pressure of 0.25MPa at 45 deg.C and a pH of 13; the pre-degreasing bath solution adopts an alkaline surfactant;
(3) degreasing: immersing the automobile body into degreasing bath solution with the pH value of 13, wherein the immersion time is 200s, the surface flow circulation pressure is 0.09MPa, and the temperature of the degreasing bath solution is 45 ℃; the degreasing bath solution adopts an alkaline surfactant;
(4) first water washing: immersing the automobile body in industrial water for 130s, wherein the spraying pressure during the immersion of the automobile body and the spraying pressure during the immersion of the automobile body are both 0.25 MPa;
(5) and (3) second water washing: spraying industrial water to the automobile body for 25s under 0.28 MPa;
(6) surface conditioning: immersing the automobile body into surface adjustment tank liquid with the pH value of 10, wherein the immersion time is 80s, and the temperature of the surface adjustment tank liquid is 30 ℃; the surface conditioning bath solution adopts zinc phosphating solution;
(7) phosphorization: immersing the automobile body into phosphating tank liquor with the ratio of total acid to free acid of 22, wherein the immersion time is 200s, the surface flow spraying pressure of the phosphating tank liquor is 0.04MPa, and the phosphating tankThe temperature of the liquid is 42 ℃; the phosphated automobile body needs to be ensured: the size of phosphorization crystal is less than or equal to 10 mu m, the zinc-iron phosphate content in the phosphorization film is more than or equal to 90 percent, and the weight of the phosphorization film on the surface of the cold-rolled steel plate is 2-3 g/m2The weight of the phosphating film on the surface of the galvanized steel sheet is 2-4 g/m2(ii) a The phosphating tank solution adopts zinc phosphating solution;
(8) and (3) washing for the third time: immersing the automobile body in industrial water for 130s, wherein the spraying pressure during the immersion of the automobile body and the spraying pressure during the immersion of the automobile body are both 0.15 MPa;
(9) fourth water washing: spraying industrial water to the automobile body for 25s under 0.16 MPa;
(10) and (3) circulating pure water washing: immersing the automobile body into pure water with the conductivity of 16 mu s/cm for 140s, wherein the spraying pressure during the immersion of the automobile body and the spraying pressure during the immersion of the automobile body are both 0.2 MPa;
(11) fresh pure water washing: spraying the automobile body with pure water with the conductivity of 4 mus/cm for 25s, spraying pressure of 0.24MPa, spraying flow of 80L/min, and automobile body water drop conductivity of less than or equal to 50 mus/cm;
II, electrophoresis:
(1) electrophoresis: immersing an automobile body into an electrophoresis tank liquid with the pH value of 6, the conductivity of 1500 mu s/cm, the throwing power of more than or equal to 60 percent and the solvent content of less than or equal to 2 percent, wherein the temperature of the electrophoresis tank liquid is 30 ℃, the solid content and the ash content of the electrophoresis tank liquid are 21 percent and 16 percent respectively, the electrophoresis process adopts two-stage voltage step control, the first-stage voltage is 200V, the second-stage voltage is 245V, and the electrifying time of the electrophoresis process is 220 s;
(2) first ultrafiltration water washing: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 25s at a spraying pressure of 0.08 MPa;
(3) and (3) ultrafiltration washing for the second time: immersing the automobile body into the electrophoresis ultrafiltration washing tank liquor for 150s, wherein the spraying pressure during the immersion of the automobile body and the leaching of the automobile body are both 0.08MPa, and the solid content of the electrophoresis ultrafiltration washing tank liquor is less than or equal to 2%;
(4) and (3) ultrafiltration washing for the third time: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 25s at a spraying pressure of 0.1 MPa;
(5) pure water washing is circulated for the first time: spraying pure water with the solid content of less than or equal to 0.5 percent on the automobile body for 25s at the spraying pressure of 0.09 MPa;
(6) and (3) circulating pure water for the second time: immersing the automobile body into pure water with the solid content of less than or equal to 0.5%, wherein the immersion time is 160s, and the spraying pressure during the immersion of the automobile body are both 0.08 MPa;
(7) fresh pure water washing: spraying pure water on the automobile body for 25s, wherein the spraying pressure is 0.09MPa, and the spraying flow is 85L/min;
thirdly, flash drying: flashing the automobile body for 9min at the temperature of 110 ℃, wherein the thickness of the electrophoretic coating on the outer surface of the automobile body is 20 microns, and the thickness of the electrophoretic coating in the inner cavity of the automobile body is 12 microns; the dehydration rate of the electrophoretic coating is more than or equal to 95 percent;
fourthly, spraying powder coating:
(1) cleaning a powder spraying room: the dust in the powder spraying room is cleaned, and the dust in each cubic foot of air is ensured to be as follows: the dust particle with the particle size of more than or equal to 5 mu m is not contained, and the number of the dust particles with the particle size range of 0.5 to 5 mu m is not more than 30000;
(2) setting the wind direction, the wind speed and the temperature and humidity of the powder spraying room: setting the wind direction of the powder spraying room to be vertical and downward, setting the wind speed to be 0.4m/s, setting the temperature to be 25 ℃ and setting the humidity to be 65 percent;
(3) spraying: conveying the automobile body to be treated into a powder spraying room, and spraying powder coating on the surface of the automobile body under the condition that the electrostatic voltage is-62 kV; the distance between the spraying guns is 18cm, and the speed of the spraying guns is 450 mm/s; the film forming mode is one-stop spraying film forming; the film thickness is 45 μm;
fifthly, drying the coating: baking the automobile body for 25min at the temperature of 165 ℃; the hardness of the dried paint film is more than or equal to HB, and the adhesive force of the paint film measured by a Baige method is less than or equal to 0 grade;
sixthly, fine trimming and inserting the wire: and inspecting the vehicle body after the powder coating is dried, marking defects, and modifying the defects by adopting methods such as grinding, polishing and the like to prevent the defects of the paint film from flowing out.
The paint film of the paint of example 1 after drying was tested for properties and the results are shown in table 1.
Table 1: results of testing the Properties of the paint film of example 1 after drying
Figure BDA0003134396790000151
Figure BDA0003134396790000161
As can be seen from Table 1, the appearance, mechanical properties, resistance to humidity and heat, water resistance, chemical reagents resistance, resistance to cold and heat cycling, and xenon lamp aging properties of the paint film formed by spraying the powder coating on the automobile body all meet the technical requirements of passenger cars.
Example 2:
embodiment 2 of the present application provides an automobile body powder coating method, including the steps of:
firstly, pretreatment of a film:
(1) pre-washing: spraying industrial water at 45 ℃ on the automobile body for 25s at the spraying pressure of 0.12 MPa;
(2) pre-degreasing: spraying the automobile body with pre-degreasing bath solution for 50s at a spraying pressure of 0.25MPa at 45 deg.C and a pH of 11.5; the pre-degreasing bath solution adopts an alkaline surfactant;
(3) degreasing: immersing the automobile body into degreasing bath liquid for 200s, wherein the surface flow circulation pressure of the degreasing bath liquid is 0.09MPa, the temperature of the degreasing bath liquid is 45 ℃, and the pH value of the degreasing bath liquid is 11; the degreasing bath solution adopts an alkaline surfactant;
(4) first water washing: immersing the automobile body into industrial water with the pH value of 10 and the conductivity of 2800 mu s/cm, wherein the immersion time is 140s, and the spraying pressure during the immersion of the automobile body are both 0.12 MPa;
(5) and (3) second water washing: spraying industrial water with pH value of 9 and conductivity of 800 μ s/cm for 25s under 0.16 MPa;
(6) and (3) washing for the third time: immersing the automobile body into pure water with the pH value of 8 and the conductivity of 250 mu s/cm, wherein the immersion time is 130s, the spraying pressure during the immersion of the automobile body and the spraying pressure during the leaching of the automobile body are both 0.15MPa, and the pure water replenishing flow is 45L/min;
(7) silane treatment: immersing the automobile body into silane tank liquid with the pH value of 5 and the conductivity of 3500 mu s/cm, wherein the immersion time is 150s, the temperature of the silane tank liquid is 35 ℃, the stirring pressure in the silane tank liquid is 0.15MPa, the Zr content in the silane tank liquid is 150mg/L, Cu content and 1.5mg/L, Si content and the free fluorine content is 45 mg/L; the silane treated automobile body needs to guarantee: the weight of the silane film on the surface of the galvanized steel sheet is 70-180 mg/m2The weight of the silane film on the surface of the cold-rolled steel plate is 30-100 mg/m2；
(8) Fourth water washing: spraying pure water with the pH value of 8 and the conductivity of 450 mu s/cm on the automobile body for 25s at the spraying pressure of 0.15 MPa;
(9) and (3) circulating pure water washing: immersing the automobile body into pure water with the pH value of 8 and the conductivity of 50 mu s/cm, wherein the immersion time is 130s, and the spraying pressure of the automobile body during immersion and leaching is 0.5 MPa;
(10) fresh pure water washing: spraying the automobile body with pure water with the conductivity of 3 mus/cm for 25s, spraying pressure of 0.15MPa, spraying flow of 60L/min, and automobile body water drop conductivity less than or equal to 50 mus/cm;
II, electrophoresis:
(1) electrophoresis: immersing an automobile body into an electrophoresis tank liquid with the pH value of 6, the conductivity of 1600 mu s/cm, the throwing power of more than or equal to 60 percent and the solvent content of less than or equal to 2 percent, wherein the temperature of the electrophoresis tank liquid is 29 ℃, the solid content and the ash content of the electrophoresis tank liquid are 20 percent and 17 percent, the electrophoresis process adopts two-stage voltage step control, the first-stage voltage is 210V, the second-stage voltage is 250V, and the electrifying time of the electrophoresis process is 200 s;
(2) first ultrafiltration water washing: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 25s at a spraying pressure of 0.12 MPa;
(3) and (3) ultrafiltration washing for the second time: immersing the automobile body into the electrophoresis ultrafiltration washing tank liquor for 160s, wherein the spraying pressure during the immersion of the automobile body and the leaching of the automobile body are both 0.12MPa, and the solid content of the electrophoresis ultrafiltration washing tank liquor is less than or equal to 2%;
(4) and (3) ultrafiltration washing for the third time: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 25s at a spraying pressure of 0.08 MPa;
(5) pure water washing is circulated for the first time: spraying pure water with the solid content of less than or equal to 0.5 percent on the automobile body for 25s at the spraying pressure of 0.08 MPa;
(6) and (3) circulating pure water for the second time: immersing the automobile body into pure water with the solid content of less than or equal to 0.5%, wherein the immersion time is 150s, and the spraying pressure during the immersion of the automobile body and the leaching of the automobile body are both 0.08 MPa;
(7) fresh pure water washing: spraying pure water on the automobile body for 25s, wherein the spraying pressure is 0.09MPa, and the spraying flow is 85L/min;
thirdly, drying: baking the automobile body for 25min at 165 ℃, wherein the hardness of the electrophoretic coating is more than or equal to H after baking, and the adhesive force of the electrophoretic coating is less than or equal to 0 grade measured by a Baige method; the thickness of the electrophoretic coating on the outer surface of the vehicle body is 25 micrometers, and the thickness of the electrophoretic coating in the inner cavity of the vehicle body is 16 micrometers;
fourthly, electrophoretic polishing: polishing the electrophoresis defects by using sand paper;
fifthly, powder coating spraying:
(1) cleaning a powder spraying room: the dust in the powder spraying room is cleaned, and the dust in each cubic foot of air is ensured to be as follows: the dust particle with the particle size of more than or equal to 5 mu m is not contained, and the number of the dust particles with the particle size range of 0.5 to 5 mu m is not more than 30000;
(2) setting the wind direction, the wind speed and the temperature and humidity of the powder spraying room: setting the wind direction of the powder spraying room to be vertical and downward, setting the wind speed to be 0.4m/s, setting the temperature to be 25 ℃ and setting the humidity to be 65 percent;
(3) spraying: conveying the automobile body to be treated into a powder spraying room, and spraying powder coating on the surface of the automobile body under the condition that the electrostatic voltage is-62 kV; the distance between the spraying guns is 20cm, and the speed of the spraying guns is 550 mm/s; the film forming mode is one-stop spraying film forming; the film thickness is 50 μm;
sixthly, drying the coating: baking the automobile body for 25min at the temperature of 175 ℃; the hardness of the dried paint film is more than or equal to HB, and the adhesive force of the paint film measured by a Baige method is less than or equal to 0 grade;
seventhly, fine trimming and inserting the wire: and inspecting the vehicle body after the powder coating is dried, marking defects, and modifying the defects by adopting methods such as grinding, polishing and the like to prevent the defects of the paint film from flowing out.
Example 3:
example 3 of the present application provides an automotive body powder coating method, and the coating process of example 3 differs from that of example 1 in that: the pretreatment mode of the coating process of example 3 is film pretreatment; the rest of the procedure is basically the same as in example 1.
Example 4:
embodiment 4 of the present application provides an automobile body powder coating method, and the coating process of embodiment 4 is different from that of embodiment 2 in that: the pretreatment mode of the coating process of example 4 is phosphating pretreatment; the rest of the procedure is basically the same as in example 2.
The powder coating used in the examples of the present application is not particularly limited, and the powder coatings suitable for spraying on automobile bodies in the prior art are all specific embodiments of the powder coating of the present application.
It is noted that, in the present application, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The above description is merely exemplary of the present application and is presented to enable those skilled in the art to understand and practice the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A method of powder coating an automotive body, comprising the steps of: sequentially carrying out pretreatment, electrophoresis, powder coating spraying, coating drying and fine trimming and off-line treatment on an automobile body to form an automobile body coating structure which is sequentially provided with an electrophoresis coating and a powder coating from inside to outside; wherein, the powder coating spraying comprises the following processes:
cleaning a powder spraying room: the dust in the powder spraying room is cleaned, and the dust in each cubic foot of air is ensured to be as follows: the dust particle with the particle size of more than or equal to 5 mu m is not contained, and the number of the dust particles with the particle size range of 0.5 to 5 mu m is not more than 30000;
setting the wind direction, the wind speed and the temperature and humidity of the powder spraying room: setting the wind direction of the powder spraying room to be vertical downward, setting the wind speed to be 0.3-0.5 m/s, setting the temperature to be 20-30 ℃ and setting the humidity to be 50-70%;
spraying: conveying the automobile body to be treated into a powder spraying room, and spraying the powder coating on the surface of the automobile body under the condition that the electrostatic voltage is-70 to-60 kV.
2. The powder coating method for an automobile body according to claim 1, wherein the powder coating has a film thickness of 40 to 60 μm.
3. The method for powder coating an automobile body according to claim 1, wherein the temperature for drying the paint is 160 to 180 ℃ for 20 to 30 min.
4. The powder coating method for an automobile body according to claim 1, wherein the pretreatment is a phosphating pretreatment or a film pretreatment.
5. The powder coating method for an automobile body according to claim 1, wherein the electrodeposition comprises the following processes:
(1) electrophoresis: immersing an automobile body into an electrophoresis tank liquid with the pH value of 5.8-6.5 and the conductivity of 1300-2200 mu s/cm, wherein the temperature of the electrophoresis tank liquid is 28-32 ℃, the electrophoresis process adopts two-stage voltage step control, the voltage of one stage is 160-250V, the voltage of the second stage is 200-300V, and the electrifying time of the electrophoresis process is more than or equal to 180 s;
(2) first ultrafiltration water washing: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 20-30 s at a spraying pressure of 0.05-0.15 MPa;
(3) and (3) ultrafiltration washing for the second time: immersing an automobile body into the electrophoresis ultrafiltration washing tank liquor for 120-180 s, wherein the spraying pressure during the immersion of the automobile body and the leaching of the automobile body is 0.05-0.15 MPa, and the solid content of the electrophoresis ultrafiltration washing tank liquor is less than or equal to 2%;
(4) and (3) ultrafiltration washing for the third time: spraying the automobile body with the electrophoretic ultrafiltration water washing tank liquor for 20-30 s at a spraying pressure of 0.05-0.15 MPa;
(5) pure water washing is circulated for the first time: spraying pure water with the solid content of less than or equal to 0.5% on an automobile body for 20-30 s, wherein the spraying pressure is 0.05-0.12 MPa;
(6) and (3) circulating pure water for the second time: immersing the automobile body into pure water with the solid content of less than or equal to 0.5%, wherein the immersion time is 120-180 s, and the spraying pressure during the immersion of the automobile body and the leaching of the automobile body are both 0.05-0.12 MPa;
(7) fresh pure water washing: pure water is adopted to spray the automobile body, the spraying time is 20-30 s, the spraying pressure is 0.05-0.12 MPa, and the spraying flow is 70-130L/min.
6. The method for powder coating an automobile body according to claim 5, wherein the throwing power of the bath solution is not less than 60%, the solvent content is not more than 2%, the solid content is 19 to 22%, and the ash content is 15 to 20%.
7. The method for powder coating an automobile body according to claim 1, wherein the electrophoresis is followed by flash drying at a temperature of 100 to 120 ℃ for 8 to 12 minutes.
8. The powder coating method of an automobile body according to claim 1, wherein the electrophoresis is followed by drying and polishing in sequence, wherein the drying temperature is 160 to 180 ℃ and the time is 20 to 30 min.
9. The powder coating method for automobile bodies according to claim 1, wherein the paint film hardness after the paint is dried is not less than HB, and the paint film adhesion is not more than 0 grade.
10. The powder coating method for an automobile body according to claim 1, wherein the thickness of the electrophoretic coating layer after electrophoresis satisfies: the thickness of the electrophoretic coating on the outer surface of the vehicle body is more than or equal to 15 microns, and the thickness of the electrophoretic coating on the inner cavity of the vehicle body is more than or equal to 10 microns.
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