How to choose plastic materials suitable for car interiors for injection molding?

Examining Plastic Material Characteristics for Automotive Interiors
Low shrinkage rate of 1.8–2.5% and melting point of 173 ℃ have made polypropylene (PP) material the preferred choice for door panels and dashboard frames. Its impact strength can be raised by 30% after modification with 1-4% ethylene; but, low-temperature brittleness (below -20 ℃) should be taken under close consideration. Common uses include PP/EPDM mix bumpers with a notch impact strength ranging up to 50kJ/m ².
Particularly suited for components like instrument panels and switch panels that need surface electroplating, acrylonitrile butadiene styrene copolymer (ABS) material offers a wide melting window of 210-280 ℃ and tensile strength of 135MPa. The distributed structure of butadiene rubber phase helps to achieve its impact resistance; nevertheless, the rubber content must be regulated (15–25%) to balance rigidity and toughness.
Widely used for instrument panel skin and steering wheel wrapping, polyvinyl chloride (PVC) material can reach the adjustment of Shore hardness A50-90 by adding 50 parts of plasticizer. Using a heat stabilizer along with the processing temperature of 140–160 ℃ helps to prevent the breakdown of HCl gas above 180.
Ideal choice for automobile lamp lenses and sunroof frames is polycarbonate (PC), with a glass transition temperature of 150 ℃ and a notch impact strength of 64kJ/m ². But given its 0.6% coefficient of linear thermal expansion (CLTE), which can be lowered to 0.2–0.4% by using 20% glass fiber (GF), one should pay attention to the dimensional stability problem.
Combining SEBS substrate with PP allows thermoplastic elastometers (TPE) material to produce a wide range adjustment of Shore hardness A0-95 and is utilized for soft touch components including dust covers and sealing strips. Its 25 ℃/72h compression permanent deformation rate can be regulated within 20%, so satisfying airbag wrapping sealing requirements.
management of temperature
The recommended melting temperature for PP material is 220–275 ℃; the mold temperature should be under control between 40 and 80 ℃.
ABS material requires a melt temperature of 245 ℃ and a mold temperature of 50-100 ℃ to reduce silver stripe flaws
PC material processing operates within a temperature range of 280–320 ℃, so it is essential to equip the material barrel heating zone control.
managing stress
One should take material fluidity into account while adjusting the injection pressure: PP material uses 500-800 bar, ABS material needs 700-1200 bar
The recommended holding pressure is 60-80% of the injection pressure, and the holding time is varied according to the product wall thickness (2-8mm wall thickness equates to 4-12s)
SPEED CONTROL
Injection speed is controlled in multiple stages: filling stage 30-50mm/s, holding stage 10-20mm/s
High speed injection (>100mm/s) can readily generate tiger skin texture problems, necessitating a gate thickness of 0.7-0.8 times the wall thickness mould design
Gate design: Hot runner method is ideal for large-sized components such as instrument panels, with a gate section ratio of 0.7-0.8
Exhaust system: A 0.05-0.1mm wide exhaust groove is set on the separating surface, with a depth controlled at 0.02-0.03mm
System for Cooling: Adopting a conformal waterway design, the gap between the cooling water and the surface of the product is kept at 10-15mm
Impact strength: evaluated in line with ISO 179, the dashboard material shall be > 20kJ/m Bending modulus: evaluated under ISO 178 criteria, the door panel material must be at least 1800MPa
Hot deformation temperature: PC material must be ≥ 130 ℃ following ISO 75 standard.
Environmental testing for adaptation
High degree of aging from temperature Δ E 1.5 after 80 ℃/72h
Low temperature impact: retention rate of impact strength ≥ 80% at -30 ℃
Chemical corrosion: mass loss 0.5% following 48 hours of soaking in 5% NaCl solution
Analysis of surface quality
glossiness At a 60 degrees angle, the glossiness should reach 80GU or higher.
A haze: Clear 2% material haze.
3D scanner detects leather pattern replication rate: replication accuracy ≥ 95%