Application of plastic plating-Electroplating ABS in Automobile.
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Compared with metal parts, plastic electroplating products can not only achieve a good metal texture, but also reduce the weight of products, effectively improve the appearance and decoration of plastics, but also improve their electrical, thermal and corrosion resistance, and improve their surface mechanical strength. However, the selection of plastic materials for electroplating should comprehensively consider the processing properties, mechanical properties, material cost, electroplating cost, difficulty of electroplating and dimensional accuracy and other factors. Because of its structural advantages, ABS plastic has not only excellent comprehensive properties, easy processing and molding, but also high coating adhesion due to easy erosion on the material surface, so it is widely used in electroplating at present.
From the molecular structure of the material, ABS plastic is a terpolymer of acrylonitrile (A), butadiene (B) and styrene (S). Among them, each monomer can provide different properties for polymers: acrylonitrile can provide high strength, thermal stability and chemical stability; butadiene can provide high toughness and impact resistance; styrene provides easy processing, high finish and high strength properties. Morphologically, ABS is an amorphous material, and three monomers are polymerized to form a ternary copolymer with a two-phase structure: one is the continuous phase of styrene-acrylonitrile (SAN) copolymerization, and the other is the dispersed phase of polybutadiene (PB) rubber. The phase separation diagram and the chemical structure of the molecular chain are shown in figure 1.
Fig. 1 ABS two-phase distribution diagram.
For electroplating grade ABS plastics, the content of each component of the material is very important, in which the content of butadiene has a great influence on electroplating. This is because: ABS is a non-conductor, in order to electroplate it, we must cover a conductive layer on the surface of the material, and the formation of the conductive layer needs to go through the processes of coarsening, neutralization, sensitization, activation and electroless plating, in which coarsening is to etch out butadiene through oxidation reaction and make the parts form an activated hydrophilic surface and anchor structure to improve the adhesion of the coating. Therefore, the higher the butadiene content, the better the adhesion of the coating. At the same time, combined with the characteristics of each monomer, under the premise of ensuring the good properties and fluidity of the material, the butadiene content should be controlled at 18%-23%.
In addition to the content of butadiene, the fluidity and process stability of the material are also the main factors affecting the quality of electroplating. Different from the surface spraying process, the electroplating process will magnify most of the defects on the material surface, that is, the defects will be more obvious after electroplating. Therefore, defects such as flow marks, cold material marks, weld lines (commonly known as "water entrainment"), shrinkage marks, silver wire and sundries on the surface of electroplating materials are not allowed, which requires that the internal stress of the material should be as low as possible. in the molding process, the filling state of each product is basically the same. In a word, electroplating has high requirements for material filling ability and processing stability.
In order to obtain high-quality electroplating products, in addition to higher requirements for materials, mold design and injection molding process also have a great impact on electroplating quality. Therefore, more consideration should be given to mold design, such as minimizing filling resistance, reducing filling pressure and temperature loss, smooth and uniform transition of wall thickness, avoiding sharp edges and right angles, reducing shear, reducing internal stress, improving exhaust, avoiding weld lines and flow lines, etc. In the injection molding process, it is necessary to ensure that the material is fully dried, high mold temperature, high material temperature, low injection pressure and holding pressure, low injection speed, short holding time and appropriate cooling time. Take Jinhu sunny ABS710 as an example, the effect of injection molding process on the adhesion of the coating is shown in figure 2.
Fig. 2 effect of process conditions on coating adhesion.
As reflected in figure 2, the higher the temperature of the mold, the higher the melting temperature, and the slower the injection speed, the higher the orientation ability of the material, the smaller the residual stress, and therefore the higher the adhesion. Jinhu Rili electroplating grade ABS710 has a wide processing window and good production stability. In the actual production, the mold temperature should be controlled at about 80 ℃ and the material temperature should be controlled at about 240 ℃. However, due to the influence of product structure, equipment size and precision, the parameters should be set according to the actual situation.
In a word, the ideal electroplated plastic products can be obtained by selecting electroplating grade ABS with wide processing window, such as Jinhu sunny ABS710, combined with reasonable structural design, injection molding process and basic electroplating process, and various performance tests can fully meet the requirements of the mainframe factory.
Fig. 3 Application of plating grade ABS in heat dissipation grille and decoration signage
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