• The reason why these materials are preferred for car lights?

The Reason Why These Materials Are Preferred for Car Lights

Usually, car lights consist of reflectors, housings, lenses, electronic circuits, and installation accessories. PMMA, PC, ABS, and PP are the main materials used for car lights in China.
1. Why is the lamp housing made of plastic?
There are many reasons for this. Plastic is more elastic than glass. It will not easily break if it is not hit severely. Even if it is broken on the road, it will not cause great harm to passers-by and animals. Plastic has light weights, and the plastic lamp shell is about 0.5 to 1.4 kg lighter than the glass lamp shell. Plastic has advantages of good impact resistance, insulation, plasticity and mechanical properties, corrosion resistance, low thermal conductivity, high transparency, easy forming, and processing.
2. Plastic used in car lights
Polycarbonate or PC is widely used in car lights. PC series account for about 50% of plastic in headlamps. PC is often used in the lens and external lens of headlamps and fog lamps for car lights
Why is the car light made from PC?
PC has great impact resistance, transparency, mechanical properties and electrical insulation properties, dimensional stability, creep resistance, and wide temperature ranges. There will be a certain temperature difference in different parts due to the internal structure of the car lights. PC and PC-HT are generally selected because temperatures of some reflectors and decorative rings can reach 100 to 190℃.
PP used for car lights is modified PP, which accounts for about 30% of plastic for car lights. For instance, shells and rear covers of headlights and rear covers of taillights are generally made from PP. At present, headlamp housings are mainly made from PP.
PP has advantages of good chemical and fatigue resistance, electrical insulation, which has the best heat resistance and mechanical properties among general-purpose plastics. In addition, it is cheaper than other plastics.
PBT is generally used in decorated rings of headlamps and stands of adjustment devices in car lamps. Foglights can be made from modified PBT and ASA and reinforced glass fiber, which have mechanical properties similar to PA and POM. They have advantages of good thermal and chemical stability, self lubricity, dimensional stability, impact resistance, heat resistance, rigidity, hardness, electrical insulation, and low friction coefficient.
The decorative ring is mainly made from heat-resistant PC in the past, but in recent years it has been gradually replaced by PBT or PET. The outstanding features of PBT or PET automotive lamp are good heat resistance, good processability and low costs compared with heat-resistant PC. PBT or PET also has the advantages of excellent processing stability, hydrolysis resistance and surface gloss, heat resistance, and fluidity. Moreover, it has lower prices than heat-resistant PC, which can greatly reduce the system cost. It should be noted that all of the above-mentioned materials for decorative rings need to be metalized by vacuum evaporation technology.
PA plus GF are generally applied to car lights. PA6 plus GF or PA66 plus GF are adopted for ordinary screw adjustment or brackets in car lights. Aromatic PA has higher heat resistance temperature and strength than ordinary PA, and aromatic PA plus glass fiber are applied to some important adjustment structures and internal brackets in car lights.
PMMA is an amorphous thermoplastic material with good transparency, optical performance, weather resistance and overall performance as well as high surface hardness. Its light transmittance can reach 90% to 92% and refractive index 1.49.
Why do we choose PC instead of PMMA for the car's headlight lampshades?
There are some differences between PC and PMMA used for car lights, though they both have good processing characteristics and transparency. First, PC can generally reach 130℃, while PMMA is only about 100℃ in terms of heat-resistant temperature. Second, PC has better toughness than PMMA. PMMA is very brittle, which easily breaks after impact. Third, PMMA has a lower unit price than PC, and forming liquidity of PC is worse than PMMA. Under normal circumstances, the lampshades of the headlights are made from PC mainly due to the high illuminance of the headlights, great heat dissipation, and being in the front of the vehicle. A material with not only heat resistance but also shock resistance is required. PMMA is usually adopted for lampshades of taillights. The tail lamp is often a single-function signal lamp combination, which requires red and transparent colors. PMMA with good fluidity is the best choice.
In the field of car lights, ABS is generally used after modification with PC materials. The proportion of PC content in ABS is determined according to the difference in use temperature and impact performance. ABS and PC/ABS are generally used for taillight housings and trim panels. In the automotive field, ABS is generally used after modification with PC material, depending on the temperature and impact properties of the ABS to determine the proportion of PC content. ABS and PC/ABS are commonly used in taillight housing and trim panels.
The reflector of the car light mainly adopts materials such as BMC and PET. BMC is a new kind of material with the advantages of reinforced engineering plastics and thermosetting plastics. BMC has good rigidity and strength, good molding shrinkage, and good stability for dimensional accuracy. BMC is often adopted for the reflector of the headlight due to the above-mentioned features of BMC. The headlight has the main function of illuminating the road ahead to ensure that the vehicle is running normally. The reflector and the corresponding bulb can emit two types of light shapes, that is, low beam and high beam. The low beam must have a clear dividing line between light and dark and high illuminance, so the above-mentioned features of BMC can meet this requirement. PET, PC, and other materials are often adopted for the rear light. The rear lamp is a combination of signal lamp functions, and its dimensional accuracy is not as high as that of the headlights. However, if the reflector can be directly seen from the lampshade, the reflecting surface on the reflector must be beautifully designed to make sure that the unique light is produced after lighting.


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