Electroplating process of ABS, PP, PA, PC and other commonly used automotive plastics

According to statistics from the China Association of Automobile Manufacturers, my country's automobile production and sales in 2022 will complete 27.021 million units and 26.864 million units respectively (ranking first in the world for 14 consecutive years), a year-on-year increase of 3.4% and 2.1%.The automobile industry continues to grow and develop, making outstanding contributions to promoting economic growth, but it also makes energy and environmental problems increasingly severe.Research shows that vehicle lightweighting can effectively reduce fuel consumption and vehicle emissions. For every 10% reduction in vehicle weight, fuel consumption can be reduced by 6% to 8%, and CO2 emissions can be reduced by 5% to 6%.

Automobile lightweight technology can be divided into three aspects: optimized structural design, lightweight material application and advanced manufacturing technology. Among them, the application of lightweight materials is the most direct way to achieve automobile weight reduction.Plastics have good properties such as light weight, low cost, and easy molding. In particular, the application of electroplating technology gives plastics a metallic appearance and luster, which effectively improves the decorative, anti-corrosion, mechanical strength and other properties of plastics, making plastics a popular choice for automobiles. Non-metallic materials are the most used in the lightweight process, and there is a trend of "replacing steel with plastic".

This article introduces the general situation of automotive plastics, summarizes the applications of several plastics such as ABS,  PP, PA, and PC that are widely used in automobiles, and explains their electroplating processes. Provide reference for further research.

1. Overview of the application of plastics in automobiles

Plastic is a polymer material mainly composed of organic synthetic resin, which can be molded under heating and pressure conditions.Because of its excellent properties such as light weight, low cost, easy processing, and various surface treatments, it is widely used in automotive interior parts, exterior parts, structural parts, and functional parts.With the continuous development of automobile lightweight technology, the use of plastics in automobiles has increased sharply.

Among automotive plastics, general-purpose plastics are relatively low-priced and account for more than 50%, followed by engineering plastics, which account for about 15%. Specialty plastics are more expensive and their usage is relatively small.According to research statistics, the automotive plastic varieties that are at the forefront and are suitable for electroplating include ABS, PP, PA, PC, etc.

2. ABS automotive use and its electroplating

1. Application of ABS in automobiles

ABS is a thermoplastic engineering plastic with a wide range of uses.Because ABS plastic has deficiencies such as poor weather resistance, discoloration, and flammability, it is often mixed with other polymers when used in automobiles to prepare more abundant modified products, such as: ABS/PC, ABS/PA, ABS/PVC Plastic alloys, etc. ABS sheet extrusion line

ABS/PC alloy can improve the heat resistance and tensile strength of ABS, reduce PC melt viscosity, improve processing performance, and reduce the sensitivity of product internal stress and impact strength to product thickness. It is mainly used for automotive interior and exterior decoration. , car lights and other parts with high strength and high heat resistance;

ABS/PA alloy has warpage resistance, good fluidity, and unique matte properties, and can be used in parts such as bumpers, instrument panels, and pillar decorative panels.

ABS/PVC alloy not only has heat resistance and impact resistance, but also has flame retardant, self-extinguishing properties and chemical resistance. It is mainly used in automobile dashboards, instrument panel skins and other parts that require flame retardancy.

2. ABS electroplating process

Electroplating grade ABS plastic requires good bonding between the metal coating and the substrate, and the butadiene content should be controlled at 18% to 23%.The ABS plastic electroplating process includes three stages: pretreatment, chemical plating and electroplating,The general main process flow is stress relief →oil removal→ roughening→hexavalent chromium reduction→palladium tin activation→tin hydroxide removal→electroless nickel (or copper) plating→pre-plating→electroplating, among which surface treatment before plating is the most critical.Surface pretreatment, process simplification, environmentally friendly plating solution substitution, etc. have always been hot topics in research.

3. PP automotive use and its electroplating

1. Application of PP in automobiles

PP is an odorless, non-toxic, colorless and translucent thermoplastic lightweight general-purpose plastic with good chemical resistance, heat resistance, electrical insulation and high-strength mechanical properties.Adding reinforcing agents, toughening agents, etc. to the raw materials can change the polymer components and macromolecular structure or crystal configuration of polypropylene to improve its overall performance.

If a certain proportion of glass fiber is added to PP, a glass fiber reinforced PP with higher rigidity and heat resistance can be obtained, which is often used in automobile structural parts and parts with high operating temperatures,such as: intake pipe of engine compartment, air filter housing, radiator fan, etc.Adding an appropriate amount of talc powder and calcium carbonate to PP can also improve the stiffness and heat resistance of PP. This modified PP is often used in automobile bumper frames, instrument panels, deflectors, columns, etc.; adding POE or Toughening agents such as ethylene propylene diene rubber (EPDM) can be used in some structural parts with high toughness requirements in high-end automobiles.

2. PP electroplating process

From the perspective of electroplating process, PP can be divided into ordinary type, electroplating type and conductive type.

Ordinary PP electroplating has poor dimensional accuracy and troublesome roughening. It must be swollen with an organic solvent before etching and roughening. The commonly used organic solvent is xylene.After roughening, it can be processed according to the sensitization, activation and other processes and procedures of ABS plastic;

Electroplating grade PP is made by adding a certain proportion of fillers such as ZnO and TiO2 to polypropylene plastic. These fillers can be dissolved during the chemical etching and roughening process to form a rough surface to improve the bonding strength of the coating.For electroplated PP, it can also be carried out according to the electroplating process of ABS plastic, except that the solution temperature needs to be increased to 70~80℃ during chemical etching;

Conductive PP is obtained by adding graphite powder with a mass fraction of about 30% to polypropylene. It has good electrical conductivity and can be electroplated according to the metal parts process.The development of electroplating-grade PP and the improvement of roughening processes have always been hot topics in PP electroplating process research.

4. PA automotive use and its electroplating

1. Application of PA in automobiles

PA plastic has good mechanical properties, heat resistance, wear resistance, chemical resistance and self-lubrication, low friction coefficient, certain flame retardancy, easy processing, and is suitable for filling with glass fiber and other fillers Enhance modification.

Glass fiber reinforced PA can be used for plastic parts and engine parts in the engine compartment;High heat-resistant PA/ABS alloy, used in automobile rearview mirrors, fuel tank caps, fenders, etc;PA/PPE alloy has excellent heat resistance, strength, flame retardancy, conductivity and other properties, and can be used in automobile central electrical boxes, fenders, large baffles, guard panels, etc.

2. PA electroplating process

The stress of ordinary PA workpieces should be checked before electroplating. The method is to immerse the workpiece in n-heptane. If cracks appear within 5 to 15 seconds, the stress needs to be removed.Stressed workpieces can be placed in cold water and heated to boiling. Keep it for 3 hours and then slowly cool it with water to eliminate internal stress.The pretreatment process before PA electroplating is roughly the same as that of ABS plastic, except for the roughening process.The development of electroplating materials, environmental protection and process improvement are still hot topics in research.

5. PC automotive use and its electroplating

1. Application of PC in automobiles

PC is a high molecular polymer containing carbonate groups in the molecular chain. It has the characteristics of high impact strength, good fatigue resistance, good dimensional stability, transparency and good free dyeability.However, due to its poor scratch resistance and wear resistance, it is often used in the form of plastic alloys for interior and exterior decoration of automobiles.For example, PC/PET and PC/PBT alloys have the high heat resistance and impact resistance of PC and the wear resistance and processing properties of polyester. They are suitable for making automobile body components, side guards, automobile door frames and low-temperature impact properties. high bumper.

2. PC electroplating process

The PC pretreatment process includes internal stress inspection, stress relief, swelling treatment, chemical etching and roughening.The stress inspection is to immerse the workpiece in an aqueous solution with a mass fraction of 70% acetone and leave it at room temperature for 1 minute to observe whether cracks appear.The stress relief method is to slowly raise the temperature to 110~130℃ in the oven, keep it warm for 2~6 hours and then cool slowly;Swelling is to immerse the workpiece in solvents such as methanol, ethanol, phenol and ether until the surface turns slightly white;Chemical etching roughening can use ABS high sulfuric acid chemical roughening solution, but the temperature should be higher. It can also be carried out in roughening liquids such as sodium hydroxide, sodium nitrate, and sodium nitrite.The preparation of alloy materials and the improvement of surface pretreatment processes are hot topics in PC electroplating research.

6. Other plastics for automotive use and their electroplating

In addition to the above four widely used automotive plastics, PE, PET, POM, PPO, PVC, etc. are also widely used in the automotive industry.PE has good insulation and chemical stability and is easy to process. It is often used in automobile interior panels, luggage boxes, fuel tanks, sheaths, fenders, etc;

PET has good creep resistance, fatigue resistance, friction resistance and dimensional stability. Modified PET is often used in automobile reversing mirror frames, audio speakers, sunroof frames, ceilings, etc;POM has higher strength than ABS plastic and is known as "super steel" or "race steel". It has good mechanical properties, insulation, solvent resistance and processability. Modified POM can be used in automotive power valves and universal joints. Bearings, handles, window lifts, etc.

PPO is non-toxic, transparent, has low relative density, and has excellent mechanical strength, creep resistance, heat resistance and dimensional stability. PPO/PS, PPO/PA, PPO/PBT and other alloys are often used in automobile hub covers, car lights Housing, fuse box, large baffle, buffer pad, etc;PVC has good electrical properties, acid and alkali resistance, and good chemical stability. It can be used in automobile anti-collision systems, door interior panel fabrics, instrument panel surfaces and seals, etc.

The main difference in the electroplating process of the above plastics is the pre-treatment and roughening process. As long as the roughening process is suitable to form the best roughened surface, sensitization, activation, electroless plating and electroplating can be smoothly carried out on the surface. , will not be repeated here.

Fiber-reinforced plastics are composite materials made by adding fibrous materials and fabrics to plastics or resins. They have become an important development direction for lightweight automotive materials.Glass fiber reinforced plastic (GFRP), also known as fiberglass, has the advantages of high specific strength, corrosion resistance, good electrical insulation properties, and easy coloring. It is often used in automobile body structural parts, fenders, roofs, bumpers, etc.

Carbon fiber reinforced plastic has the characteristics of high strength, good elasticity, fatigue resistance and wear resistance, and is mostly used in the body, chassis, wheels, etc. of high-end automobiles.Natural fiber plastics use natural plant fibers such as jute and sisal as reinforcing materials. They not only have excellent performance but are also environmentally friendly. They can be used in door interior panels, headliners, seat backs, instrument panels, etc.Fiber-reinforced plastics are based on plastics and resins. The focus of research on its electroplating process is still the preparation of electroplating-grade materials and the improvement of the electroplating process.

7. Conclusion and outlook

With the continuous development of automobile lightweight technology, plastic has become the most widely used lightweight non-metallic material.The wide application of electroplating technology not only gives plastic parts a metallic appearance and texture, improving the aesthetics and comfort of automobile parts, but also improves the mechanical properties and chemical stability of plastic parts, enriching the use of plastics in automobiles application.

Plastic electroplating for automobiles promotes the substitution of metal materials and accelerates the process of automobile lightweighting.Blended modified plastics and fiber-reinforced plastics are increasingly used in automobiles due to their excellent properties. The preparation of electroplating-grade materials and the improvement of electroplating processes will become the key to the development of plastic surface metallization technology.