Commonly used plastics for interior and exterior automotive parts mainly include PP, PU, ​​ABS (including ABS and PC + ABS), PE, PA and POM, among which PP is the largest amount. The editor will briefly introduce the commonly used plastics and their applications for these types of automotive interior and exterior decorations.

1. PP

      PP Chinese name polypropylene is a polymer made from free radical polymerization of propylene monomer. It is an odorless, side chain-free, high density, high crystallinity milky white linear polymer. It is also the plastic material with the largest amount of interior and exterior parts.

     advantage:

    (1) Small density (lightest plastic) and light weight;

    (2) The water absorption rate is less than 0.02%, and it is almost completely free of water erosion;

    (3) High impact resistance, good processing fluidity, easy to form, and good product appearance quality;

    (4) The source of raw materials is abundant and the price is cheap;

    (5) Good temperature resistance (but poor thermal load deformation ability);

    (6) Good chemical resistance.

     Disadvantages: low temperature environment shows brittleness and poor weathering resistance (can be improved by modification, addition of additives, etc.); crystalline materials, large shrinkage and poor dimensional stability.

     Application: The main components of PP materials are parts body, such as instrument panel body, auxiliary instrument panel body, glove box, storage box, door guard body, upright guard body, sill pressure plate, seat guard, luggage box Guards, passenger armrests, front / rear bumper skins, side skirt guards, decorative panels under the front windshield, fenders, etc. Fiber-reinforced PP materials have high rigidity, especially long glass fiber reinforcement and glass fiber felt modification, which are used more in structural parts.

It is mainly used to replace metals and is used in spare wheel cabins, seat frames, door modules and other components.

2. ABS

      ABS is an amorphous material and is an acrylonitrile-butadiene-styrene copolymer. It combines the excellent properties of three monomers, acrylonitrile (heat resistance, chemical resistance, high rigidity), butadiene (toughness), and styrene (good processability, good dyeability, poor weather resistance, and easy oxidation). The characteristics of ABS mainly depend on the ratio of the three monomers and the molecular structure in the two phases. By changing the ratio of the three components, the compounding method, and the size of the particles, different varieties can be produced.

      Advantages: surface decoration and secondary processing, including painting, electroplating, welding, bonding, etc .; good dimensional stability and creep resistance.

      Disadvantages: Poor chemical resistance, poor UV resistance (butadiene component has), high gloss. The heat resistance is not high, and the heat distortion temperature is low.

      Application: ABS is mainly used for decorative parts using painting, electroplating, water transfer, IMD and other processes on interior and exterior decoration parts, such as painting decorative strips, electroplating bright strips, electroplating grids, electroplating signs, rearview mirror housings, etc. At the same time, because of its good dimensional stability, especially high temperature stability, it is also used in combination instrument cover, steering column shield, door panel middle panel, switch button, air outlet panel, etc. Blow molding grade ABS can also be used for spoilers.

      Note: The temperature requirement of the parts is the main consideration when deciding to choose different heat-resistant ABS. In addition, due to the poor weather resistance of ABS, it is generally not used for exterior leather textures exposed to direct sunlight.

3. PC + ABS

     PC + ABS is an alloy plastic blended with PC and ABS. The blend of PC and ABS can synthesize the excellent performance of PC and ABS.

     advantage:

     (1) Heat resistance, toughness, impact strength (especially suitable for high-strength structural parts) and flame resistance;

     (2) Good workability, apparent quality and low density.

     (3) The unit cost of materials is reduced and the viscosity of the solution is reduced.

     (4) As an alloy of two amorphous plastics, PC + ABS has the advantages of excellent comprehensive performance and no obvious disadvantages.

      application:

      PC + ABS is used in some decorative parts that require certain heat resistance and high impact requirements, such as electroplated door handles, center console decorative boards, etc. Due to its excellent low temperature performance, dimensional stability and excellent adhesion to foam, PC + ABS is also often used in the dashboard body of high-end models.

4. POM

      POM is a semi-crystalline plastic, the Chinese name is polyoxymethylene. POM is divided into two kinds of homopolymerization and copolymerization. Homopolymerized POM is a homopolymer of paraformaldehyde or formaldehyde; copolymerized POM is a copolymer of paraformaldehyde and 1,3-dioxolane. Homo-formaldehyde has high crystallinity, and its mechanical strength, rigidity, heat distortion temperature and other indicators are better than co-formaldehyde. Co-formaldehyde has a low melting point, thermal stability, chemical resistance, flow characteristics, processability, and performance at continuous high temperatures. Higher than homopolyoxymethylene. The end group of POM is hemiacetal (—CH2OH). When the temperature is higher than 100 ℃, the end group is easy to break, and generally needs to be stabilized by the end group treatment to improve its thermal stability and heat-resistant use temperature.

    Advantages: high wear resistance, specific strength and specific rigidity close to metal, and good fatigue resistance.

    Disadvantages: low temperature resistance, poor flame retardancy, and large shrinkage.

    Application: POM is mainly used for components with high creep resistance, fatigue resistance, high wear resistance or self-lubrication requirements, such as bumper mounting brackets, opening handles, buckles, sealing internal mechanism parts, glass lifting systems, etc.

5. HDPE

       HDPE is high-density polyethylene, which is a non-polar thermoplastic resin with high crystallinity. It is an important branch material of PE. Its performance is mainly affected by four factors: density, molecular weight, molecular weight distribution and additives.

      Advantages: excellent cold resistance, environmental stress crack resistance and barrier properties.

      Disadvantages: poor high temperature resistance.

      application:

      HDPE is used for blow molding parts on interior and exterior decoration parts, mainly for the dashboard air duct system. Generally, HDPE with a relatively low melting index is selected, and the melt strength is high. The air duct's main performance requirement for HDPE is temperature resistance, including high temperature, low temperature and temperature alternating stability. Other properties require HDPE to have low emission and low odor.

VI. PA

      PA is commonly known as nylon, and its scientific name is polyamide. It is a general term for thermoplastic resins containing a repeating amide gene— [NHCO] —on the molecular backbone. Aliphatic nylon is the most important variety, its name is determined by the specific number of carbon atoms of the synthetic monomer, the most commonly used are PA6 and PA66.

      Advantages: The main advantages of pure PA6 and PA66 are wear resistance, good self-lubrication, good toughness, the greater the ratio of methylene / amide groups, the better the flexibility.

      Disadvantages: poor water absorption and dimensional stability, the greater the proportion of amide bonds, the higher the water absorption rate.

      Note: PA6 and PA66 are semi-crystalline plastics. After the glass fiber is reinforced, the performance is doubled, especially the rigidity and heat resistance, but the introduction of short glass fiber will also cause orientation warpage and surface float fiber problems.

      application:

      Nylon mainly exerts its advantages of good wear resistance, self-lubricating properties and rigidity in interior and exterior decorative parts. Pure PA66 is widely used in buckles, cable ties and gears, and glass fiber reinforced nylon is mostly used in structural parts, such as outer handles, inner handles, rearview mirror bases, airbag mounting brackets, etc. Considering the ability of nylon materials to withstand high temperatures, most nylon materials are used in the engine compartment field. Fiber grade nylon is called nylon and can be applied to carpets.

7. PVC

      PVC is polyvinyl chloride, which is an amorphous thermoplastic resin made by polymerization of vinyl chloride monomers with certain additives (such as stabilizers, lubricants, fillers, etc.), and its physical appearance is white powder.

      Advantages: After adding additives, it has strong plasticity and good low temperature resistance.

      Disadvantages: Pure PVC has a high softening / melting temperature, is extremely unstable to heat, easily degradable, and easy to age. 

      application:

      PVC plastics are mainly used for instrument panel skins and decorative skins on door panels for interior and exterior trim parts, while some shift lever ball heads use PVC plastics. Need to consider the thermal aging resistance, light fastness and low temperature resistance of PVC.

8. PBT

     PBT is polybutylene terephthalate. It is a semi-crystalline plastic and belongs to the polyester series. Together with PET, it is collectively called thermoplastic polyester, or saturated polyester.

     advantage:

     The best performance of PBT lies in its electrical performance, which is not affected by changes in humidity. After the glass fiber is reinforced, its strength and heat resistance are greatly improved, and it can be used for structural parts.

      Disadvantages:

     The hydrolysis of fat bonds under high-temperature and high-humidity conditions may cause long-term performance degradation. Therefore, the water content must be very low during processing, and some applications should use anti-hydrolysis grades.

      application:

      Pure PBT or low glass fiber content enhanced PBT are mostly used in electrical devices, such as connectors, etc., and high glass fiber content PBT are mostly used in structural parts, such as rearview mirror bases, luggage rack supports, etc. PBT alloy material PC + PBT can be used for bumper energy-absorbing blocks, door handles, fuel filler caps, etc. PBT with high glass fiber content is used as structural parts, because directly replacing metal or glass fiber reinforced nylon, the main performance requirement is mechanical strength.

9. PU

       PU, or polyurethane, is a polymer made of isocyanate reacted with polyol and has a repeating urethane segment structural unit.

      advantage:

      The main advantages of polyurethane foam are its ability to compress deformation, good resilience, and good acoustic performance.

      Disadvantages:

      In view of the environmental protection pressure, polyurethane needs to be improved in terms of environmental protection blowing agent, reducing VOC and intermediate free toluene diisocyanate (TDI) content.

     application:

      Polyurethane is mainly used in car seat foam, soft foam layer of instrument panel, sound absorption layer of carpet / front wall sound insulation pad. In addition, the rigid polyurethane sheet is used in the ceiling base material after a composite sheet composed of glass fiber.