Analysis on the influence of spraying parameters of plastic paint for automobile on the directional arrangement of aluminum powder

Sep. 29, 2020

Abstract: This paper briefly introduces the painting process of plastic paint for automobile and the application of aluminum paint in it. Based on the basic formula of two-component automotive interior aluminum paint, the factors influencing the directional arrangement of aluminum powder in the aluminum paint were discussed by changing the spraying conditions, spraying the aluminum paint template, and measuring by visual inspection and colorimeter.

Key words: plastic paint; aluminum powder; coating

Introduction 

Aluminum paint is deeply loved by the majority of users because of its metal color, strong texture and strong decoration. Aluminum paint is widely used in automobiles, especially in interior decoration materials. Aluminum paint is mainly used in automobile gear shift device, air conditioner air outlet, car audio, central console, door armrest and other positions. When aluminum paint is applied to these parts, the paint film usually needs good heterochromatic effect with angle and metal flash appearance, which requires that the aluminum paint has good aluminum powder arrangement effect, and the aluminum powder used is mostly non floating flash aluminum powder.

Analysis on the influence of spraying parameters of plastic paint for automobile on the directional arrangement of aluminum powder

 

Automotive interior materials are mostly plastic parts. Acrylonitrile butadiene styrene terpolymer (ABS) is easy to synthesize, easy to process and shape, can be recycled and has good mechanical properties. Products with different uses and requirements can be obtained by adjusting the different proportions of three components. It is one of the most widely used plastics in automobile industry. In this paper, the effect of spraying conditions on the directional arrangement of aluminum powder was investigated using ABS as substrate. Before spraying, IPA (isopropanol) is generally used to clean the impurities and oil stains on the surface to eliminate the influence of static electricity on the spraying, and then spray. The spraying methods are divided into manual spraying or mechanical hand spraying, and then standing, leveling and drying. The general baking process includes one coating and one drying, two coating and one drying, and two coating and two drying.

1 experimental part

 

1.1 raw materials

 

Toyo aluminum powder, hydroxy acrylic resin A, acrylic resin B, ABS plastic substrate, general color paste, matting powder, wear-resistant additives, etc.

 

1.2 apparatus

 

Fisher electromagnetic film thickness meter, huntlab, spray gun w101, viscosity cup NK-2.

 

1.3 experimental methods

 

The spraying effects under different conditions were compared by the experimental method of combining visual inspection with color measuring instrument in sunlight.

 

1.3.1 inspection method of visual spraying effect

 

In general, under sunlight, the sunlight is directly on the coating surface, and the oriented and uniform aluminum powders are arranged. Most of the non floating flake aluminum powders are parallel or nearly parallel to the substrate. The sunlight is evenly reflected and emits uniform and soft reflected light. Compared with the non-uniform arrangement of aluminum powder, the orientation is good, the side is generally black, and the front whiteness is higher, emitting a stronger sense of metal. When the orientation of the aluminum powder is not good, the aluminum powder is arranged in disorder. Under the sunlight, the stray light in the reflected light is dazzling and uneven. At the same time, the side color is white, the front side is black, and the metal feeling is weak.

There are two different arrangements of aluminum powder. The left side shows that the aluminum powder is parallel to the substrate (ideal state), and the right side is sheet type

 

The irregular arrangement of aluminum powder. It is assumed that the incident light is incident at an angle of 45 ° and there is more stray light reflected when the flake aluminum powder is arranged irregularly, which makes the surface of the paint film more dazzling to the human eye, which is due to the scattering of some light at various angles. When the aluminum powder is arranged in parallel, the color is dark when viewed from the top, but it is very beautiful when viewed from the side. This is caused by the light reflected by the parallel aluminum powder like small mirrors. This difference between light and shade caused by different observation angles is called angular heterochromatic effect. The alignment of aluminum powder can cause the variation of different color effect with angle, and it should be pursued as much as possible in automobile painting.

 

As the saying goes, three coatings, seven construction, coating has a great impact on the orientation of aluminum powder in aluminum paint. The same coating can produce different spraying effects by changing the setting of spray gun. The influence of spray gun setting on aluminum powder orientation is discussed below. In this experiment, the w101 spray gun in Yantian is taken as an example. The spray gun is a low-pressure air spray gun with a diameter of 1.3 mm. During spraying, the amount and amplitude of spraying can be adjusted by adjusting the relevant knobs, and the adjustment range is the number of rotations of the relevant knobs.

 

When the aluminum paint is sprayed on the substrate, the larger the amount of aluminum powder is sprayed on the substrate, the more coating per unit area and the thicker the coating film, the more likely Bernal vortex will be generated, and the more difficult it is to control the directional arrangement of aluminum powder; the smaller the amount of aluminum powder is, the easier the aluminum powder is oriented, and the stronger the flash effect of aluminum powder is. At the same time, considering the efficiency of spraying, it is appropriate to spit out between 1% and 1%.

 

The distance between spray gun and substrate needs to consider the factors of coating appearance and cost. When the distance between the spray gun and the gun is less than 10 cm, the distance of the spray droplet in the air is too short, resulting in a large amount of solvent can not be volatilized, the surface condition is relatively wet, and the aluminum powder can not be well arranged and distributed; when the distance between the spray gun and the gun is more than 40 cm, a large number of spray droplets will be lost in the air, which is easy to produce dry spraying and other defects, and the coating cost per unit area increases. In this experiment, when the gun distance is 15 ~ 20 cm, both the directional arrangement of aluminum powder and the cost are considered, which is the best distance.

 

When the coating viscosity is less than 8s, the viscosity of the system is too low, a large amount of solvent can not be volatilized, the surface condition is relatively wet, aluminum powder is affected by Bernal eddy current, and can not reach a good arrangement distribution; when the coating viscosity is greater than 17s, the system viscosity is high, coating is difficult, and it is easy to produce dry spray and other defects. In this experiment, when the viscosity of the system is between 10 and 13 s, the aluminum powder can achieve a good directional arrangement.


Function of vinyl  resin for plastic paint

 

The silver powder has excellent directional arrangement, stronger metal feeling, better adhesion to substrate, ester soluble and no burning bottom;