2.2 description of bumper spray process:

Plastic bumper spraying as a relatively high-grade surface coating process means, the quality requirements of the whole process are extremely strict, with the coating manufacturers of the entire surface treatment process, including pretreatment process, spraying process to the curing process, all need to have strict quality control to ensure the quality of bumper coating.

Bumper spraying process mostly adopts multi-layer spraying, this paper adopts the "three spraying and two drying" process, in order to give full play to the advantages of durability and weatherability of the paint. Spraying equipment must ensure excellent atomization effect, ensure the uniformity of spraying coating, the distribution of metal particles in the coating, directly affect the appearance of the coating effect. The coating is uniform, and the coating with excellent quality has metallic luster, bright color and obvious three-dimensional sense. The use of inappropriate spraying equipment spraying coating, will produce uneven color, surface shadows or coating is not strong. The decorative effect of bumpers is greatly affected.

The following is a detailed description of the painting process for plastic bumpers:

2.2.1 surface treatment:

Pretreatment is the basis of painting operation, is an indispensable important process, is the key link to improve the adhesion and corrosion resistance of bumper coating, so the quality of pre-treatment is directly related to the quality of bumper spraying. On the one hand, the surface treatment can improve the anti-corrosion and anti-rust performance of the coating, prolong the service life of the coating, on the other hand, improve the adhesion of the coating to the bumper, on the other hand, can make the bumper get a uniform coating performance.

Surface treatment mainly includes three aspects:

(1) remove dirt from the bumper surface. For example, degreasing (also known as degreasing) ensures the physical and chemical properties of the coating and the quality of the product. Common dirt is: dust, oil, old coating, etc.

(2) The surface of the washed bumper is chemically treated to improve the corrosion resistance of the coating and the adhesion between the coating and the surface of the workpiece.

(3) Adopt mechanical method to eliminate the processing defects of bumper, adjust the surface roughness of the matrix to improve the appearance quality and adhesion of the product.

2.2.2 water drying:

The purpose of drying is to make the chemical conversion film formed on the bumper surface dehydrate sufficiently to obtain the best adhesion and corrosion resistance. However, the drying temperature should not be too high, otherwise excessive dehydration will lead to a significant decrease in coating performance.

2.2.3 surface spraying:

Usually, the surface layer of bumper is composed of different coatings. At present, wet spraying is often used in spraying process, which can not only save energy, simplify the process, but also meet the needs of mass production line.

At present, the more advanced painting line is composed of spraying robot, two-component paint supply, automatic color change, workpiece identification, synchronization, general control and other subsystems, with automatic color change, automatic identification, synchronous movement, off-line simulation and other functions. Several robots move in turn to finish polishing, flame treatment, electrostatic precipitation, primer, topcoat and varnish spraying at one time. Of course, it is relatively expensive to invest and operate in each process by robots, which is a fully automatic operation mode. At present, it has not been applied to this field in most domestic enterprises.

(1) polishing and cleaning:

Bumper after surface treatment, the first process is grinding clean, this process can be based on the surface of the actual situation of the workpiece can be saved, but there are uneven or other damage to the surface of the workpiece, the operation of this process must be carried out, and then surface cleaning.

(2) flame treatment:

The flame treatment method uses high temperature (3000 degree F or more) gas flame to oxidize the surface of the plastic. Flames activate oxygen molecules in the air, causing them to form polar groups with carbon molecules on the surface of the material. The surface tension of plastics is reduced and the adsorptive force of the base material to the paint is increased with the increase of surface grouping polarity and oxidation.

Maintaining a certain flame temperature and distance is a kind of pre-spraying treatment to the workpiece surface at a proper moving speed, in order to reduce the surface stress of the workpiece, improve the adhesion of the workpiece surface and improve the quality of spraying.

(3) electrostatic precipitator:

It can remove burrs on the surface of the workpiece due to electrostatic adsorption, ensure the cleanliness of the workpiece before spraying, and help to improve the yield of the spraying process. The main equipment can use electrostatic precipitator gun, electrostatic precipitator ion blower, electrostatic precipitator ion dust rod and so on.

(4) priming:

The purpose of primer coating is to improve the anti-permeability of the coating, enhance the protection of the substrate, conceal the micro-defects on the metal surface, strengthen the adhesion between the top coat and the metal surface, and ensure the color uniformity of the top coat. The thickness of the paint layer is usually 5~8 m.

(5) topcoat:

The bumper is coated with primer and primer after leveling, which is the key stage in finishing the painting process. The function of topcoat is to provide the required decorative colors, make the appearance meet the design requirements, and protect the metal surface from the external environment atmosphere, acid rain pollution, prevent ultraviolet light penetration, greatly increase the anti-aging ability. The top coat is the thickest coating in multi-layer spray, usually 30~35 m.

(6) coated varnish:

The function of coated varnish is to enhance the anti-corrosion ability of the top coat, protect the top coat from oxidation, increase the metallic luster of the top coat color, and make the appearance of the product more bright. The thickness of the paint layer is usually 10~15 m.

(7) flat air drying:

Leveling and drying is a process of evaporation of solvent or water in a coating, allowing the coating to be touchable or dry.