POP (Plating On Plastic) was developed in the 1960s and gradually realized industrialization. Compared with metal, plastic is not only light in weight, but also easy to process and shape. Electroplating not only improves the appearance and decoration of the plastic, but also improves its surface impact resistance, heat resistance, abrasion resistance and mechanical strength. Therefore, plastic electroplating is increasingly favored by automotive engineers. The article combines the characteristics of plastic electroplating, introduces the application of plastic electroplating Cu/Ni/Cr in automobiles and common defects in the market, and analyzes the future of automobile plastic electroplating Cu/Ni/Cr from the perspective of the needs of the automobile industry and social development. Development trend.
1 Plastic electroplating Cu/Ni/Cr application in automobiles
With the continuous pursuit of luxury, beauty and light weight in modern automobiles, plastic electroplating Cu/Ni/Cr has many advantages such as its metallic appearance, easy processing, weight reduction, excellent performance and low cost, and it is increasingly replacing metal applications. Used in the manufacture and design of automobiles.
01 Application in automotive exterior parts
Plastic electroplating Cu/Ni/Cr not only adds a sense of fashion to the exterior of the car, but also makes the car full of high-end sense, so it is widely used in car logos, door handles, rearview mirrors, wheel housings, license plates, insurance Bar trim, radiator grille, anti-scratch strip, rearview mirror, roof rack, door handle trim and other exterior trims.
Automotive exterior parts are usually exposed to the outdoors, and have to undergo various environmental tests such as severe cold, exposure, heat, corrosion, acid rain, mud, stone and scratches. Therefore, automotive exterior plastic electroplated parts have very strict quality requirements. .
02 Application in automotive interior parts
Car interiors have the closest relationship with drivers and passengers, not only affecting customer comfort and vision, but also directly affecting brand image and customers' purchase intentions.
Compared with exterior decoration, automobile interior parts have more parts, and their shapes and functions are relatively complicated. Therefore, automobile interior parts not only require high appearance and performance, but also are particularly important in terms of assembly and size control. Plastic electroplating Cu/Ni/Cr is not only easy to shape, easy to control in size, and can be made into more complex and diverse parts, and the surface can present a variety of advanced metal textures, so more and more automotive interior parts, such as air outlets Trim frames, dashboard trim strips, door opening handles, steering wheel trim, shift handball, gear shift covers and door trim strips are all made of plastic plating Cu/Ni/Cr technology.
03 Application in automotive electronic parts
The miniaturization and light weight of plastic electroplating Cu/Ni/Cr is very suitable for electronic products. Its chrome-plated surface is very smooth, has very good visibility and feel. It is also widely used in automotive electronic parts. The main application is currently Used on electronic components such as buttons, switches, lamps, and dial decorations.
04 Application in automotive engine compartment parts
Due to its poor temperature resistance, plastics generally cannot be used directly in the engine compartment. Electroplating can improve the temperature resistance, creep resistance, chemical resistance and mechanical strength of plastic parts. The engine compartment is also a part of the car that customers often open. Therefore, many parts of the engine compartment also require visibility. The stable and shiny appearance of plastic plating Cu/Ni/Cr makes the car look more luxurious and is loved by customers. It has been successfully used. On engine compartment parts such as engine hoods, badges and nameplates.
2 Common defects of plastic plating Cu/Ni/Cr in automotive applications
The production process of plastic electroplated parts is relatively complicated, involving design, raw materials, injection molding, electroplating process and assembly, and the use environment of automobiles is also relatively harsh, so defects are more prone to defects. Common defects in the market can be summarized as follows.
01 Coating peeling off bubble crack
Coating shedding, bubbles and cracks are the most common failure modes of plastic electroplating Cu/Ni/Cr. There are two typical failure modes: the separation of the coating from the substrate and the separation of the coating from the coating.
The main reasons for the separation of the coating and the substrate are as follows: 1) The internal stress of the substrate is too large. When the temperature of the part changes, the internal stress is released, resulting in the separation of the coating and the substrate. At present, the residual stress caused by injection molding can be evaluated through the glacial acetic acid immersion experiment and the red dye experiment. Such defects mainly reduce or eliminate the internal stress of the substrate by improving the injection molding process (such as injection temperature, injection pressure, holding pressure time, cooling rate, etc.). 2) Insufficient coarsening or excessive coarsening. Insufficient roughening causes the surface to not be effectively bitten, and excessive roughening causes insufficient palladium to be adsorbed normally, neither can provide a good anchor point for the subsequent electroless plating layer, resulting in poor bonding between the metal plating layer and the plastic substrate. 3) The copper layer is too thin. The copper layer has good ductility, can improve the thermal shock resistance and mechanical shock performance of the coating, and has a certain buffer effect on residual stress, thermal expansion and contraction of the substrate, and assembly stress. However, a too thin copper layer will It can't play a relevant role, and eventually the coating is easy to fall off, produce bubbles, and even cracks.
The main reasons for the separation of the plating layer and the plating layer are: 1) bath contamination; 2) insufficient washing or activation; 3) midway power failure or too long production line, resulting in excessive exposure of the parts; 4) improper composition of the plating solution causes the internal stress of the plating layer is too big. The defect of separation of plating and plating can be solved by optimizing the electroplating and production control process. In order to prevent the defects of coating shedding, bubbles and cracks in the market, many automobile companies have designed high and low temperature impact tests, high temperature storage tests, cross-cutting tests, coating peeling tests and sawing tests and other strict test standards for verification.
At present, the corrosion forms in the market are mainly pits and yellow corrosion spots, and the pits often evolve into yellow corrosion deposits after further corrosion. The corrosion process generally starts along the micropores and corrodes the nickel layer, and the resulting corrosion products gradually accumulate under the chromium layer. When the accumulation reaches a certain level, the chromium layer will crack and fall off. The main reasons for corrosion are: 1) The number of micropores is too small, generally requiring ≥8 000 holes/cm2; 2) The chromium layer is too thin or thick, generally requiring 0.3~0.5 μm; 3) The potential difference is too high or too low , The gap between the nickel seal and the bright nickel is controlled at 20-40 mV; the bright nickel and semi-bright nickel are controlled at 100-200 mV, and the corrosion resistance is better. Different automobile companies have also formulated their own corrosion testing standards, which are mainly evaluated through CASS experiments and neutral salt spray experiments.
03 Depressed coating surface
Plastic plating Cu/Ni/Cr is deeply loved by customers for its mirror metal texture. One of the most intuitive ways to evaluate the quality of chrome plating on the market is the mirror image effect on the surface. When there are defects in the plastic substrate or the plating process, the parts are exposed to the sun. Under the impact of temperature and temperature, the surface is prone to dents, destroying the mirror effect and affecting the appearance of the car. The main reasons for this kind of defects are: 1) poor temperature resistance of the base material, the base material softens at high temperatures, resulting in surface deformation and depression; 2) the base material has stress, and when the temperature changes, the stress is released, resulting in depression; 3) Design defects, such as the thickness of the main surface of the workpiece is too low, the width of the skeleton is too large, it is easy to produce depressions; 4) improper injection molding process parameters, injection molding is not full. As customers pay more and more attention to car details, many car companies are paying more and more attention to such defects, and they have also formulated strict visual inspection standards to control environmental storage tests.
3 development trend
01Development of trivalent chromium plating
The main component of the chromium plating bath is oxychromic acid. Hexavalent chromium is widely used in the automobile industry due to its stable performance and low cost. But hexavalent chromium is highly toxic and carcinogenic. Although most of the hexavalent chromium is reduced to metallic chromium after electroplating, there is still a very small amount of hexavalent chromium remaining on the surface of the coating, and the hexavalent chromium used in the electroplating process The chromium plating solution also causes great pollution to the environment. In this context, automobile companies and electroplating manufacturers in various countries are committed to the research and development of trivalent chromium electroplating on the basis of hexavalent chromium electroplating technology. The main research directions at present are chlorinated and sulfuric acid types. Although some research results have been obtained abroad and have been promoted in a small range on some models, trivalent chromium is not as stable as hexavalent chromium, the color is not easy to control, and the CASS experiment is prone to failure, etc., so far it has not been fully promoted. The popularization and application of trivalent chromium electroplating will be an environmental protection revolution in the Cu/Ni/Cr electroplating technology of automotive plastic parts.
02 Chromium-free roughening process
Plastic electroplating Cu/Ni/Cr In addition to hexavalent chromium electroplating solution, hexavalent chromium coarsening is also one of the biggest hazards on the electroplating line. The research and development of chromium-free coarsening has always been a research hotspot in plastic electroplating Cu/Ni/Cr. Chromium-free coarsening has the advantages of low pollution, environmental friendliness, low waste water treatment cost, and safe operation of employees. It can also reduce defective products due to chromium fog, increase product qualification rate, and reduce production costs. At present, the most researched technology is potassium permanganate technology, but there are still some limitations such as longer coarsening time (generally 2~3 times of coarsening of hexavalent chromium), unstable chemical properties, and flammability of the product.
03Environmental protection alternative process
At present, all Cu/Ni/Cr electroplating on plastics is water electroplating, which belongs to a highly polluting industry. Looking for alternative water electroplating is also one of the research directions in the future. At present, there are more researches on vacuum sputtering, nano-mirror spraying and hot stamping film technology. Vacuum sputtering evaporates metal chromium or aluminum into atoms or molecules, and condenses to form a coating on the surface of the part, producing a decorative effect similar to plastic electroplating Cu/Ni/Cr. Nano-mirror spraying technology mainly applies the principle of chemical reaction, and uses direct spraying to make the surface of the part show a chrome-plated mirror metal effect. The hot stamping film technology transfers the hot stamping film to the plastic by heating and pressing. The hot stamping technology has been applied to some parts of BMW and Volkswagen due to the advantages of convenient processing and low cost, but the hot stamping The film cannot fully reach the mirror metal texture of electroplated Cu/Ni/Cr, which limits its large-scale promotion. The alternative process is environmentally friendly, safe to operate, stable in performance, more diverse in color, and not limited by volume. However, due to the diversity and functional complexity of the use of auto parts, some environmentally friendly alternative processes have performance, color, appearance and other problems. If you want to completely replace it Plastic plating Cu/Ni/Cr still has a long way to go.
04Post-treatment and composite coating process
In order to further enrich the appearance and function of plastic electroplating Cu/Ni/Cr and make it more widely used in automobiles, the combination of electroplating and painting, printing, laser and laser engraving is also one of the research focuses of automobile plastic electroplating. Some researches have been successfully applied, such as electroplating and spray painting decorative grilles and nameplates, which not only have the appearance of metal but also enrich the color of the parts. The laser engraving treatment of the electroplated parts not only satisfies the decoration, but also satisfies the light transmission. Such functional requirements have been successfully applied to the one-button start switch, but the smooth surface of electroplating can easily lead to poor paint adhesion, causing paint to fall off, and the laser engraving process makes the metal coating discontinuous, causing the coating to shell and other defects. Problems to be solved in the composite process.