generally speaking, the automobile lamp is made up of reflector, lens, shell / light source, electronic circuit, installation parts and so on. the main plastic raw materials for automobile lamps in our country are pc, pp, abs, pmma and a few other plastic materials. but do you know how to choose these materials? today, let me together with you to understand the mystery of the selection of it.
1. why the lamp shell is plastic?
You're reading: Why choose these materials for Automotive lights, you know?
there are many reasons.
a. the elasticity of plastic is stronger than that of glass. not in the case of severe impact will not be easily broken, even if it breaks down on the road, it will not cause great harm to pedestrians or animals.
b. light quality, compared to the glass lamp housing, the plastic lamp housing is lighter about 0.3~1.4 kg
c. with the advantages of good corrosion resistance, good impact resistance, high transparency, good insulation, low thermal conductivity, good mechanical performance, strong plasticity, easy molding and processing.
2. the application of plastics in car lights
according to the relevant data, pc is widely used on car lights, pc series materials in the use of plastic materials in headlight accounted for about 50% (weight ratio), in the automotive lights, the pc is mainly used in headlamps and fog lamps’ lens and external lens．
why choose pc?
pc, polycarbonate, has excellent impact and transparency, good mechanical and electrical insulation properties, wide temperature range, high dimensional stability and high creep resistance.
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the internal structure of the car led to a certain temperature difference in different parts, and the temperature of some part of the reflectors and decorative rings may reach 100 0 ~ 190 0, so pc and pc-ht are usually chosen in the selection of materials.
most of the pp used in car lights are modified pp, accounting for about 30% of the plastic material in the lamp (weight ratio). for example, the rear lamp housing, the trim panel and the wiring harness guide slot (pp-t20), the headlight housing and the back cover, generally use pp. for the moment, the pp is the main material for the headlight housing.
pp has good electrical insulation, chemical corrosion resistance and good fatigue resistance. it has the highest mechanical and thermal resistance in general plastics. besides, it has a price advantage over other plastics.
pbt/pet (polybutylece terephthalate)
the pbt is usually used for the decorated ring and the adjusting brackets in headlights. modified pbt and asa, plus glass fiber reinforcement, can be used to make the shell of fog lamps. mechanical properties similar to those of pa, pom, small friction coefficient, good self-lubrication, good thermal stability and chemical stability, excellent electrical insulation, high rigidity and hardness, good impact, high dimensional stability, good heat resistance.
decorative ring material has been dominated by heat-resistant pc material in past years, gradually replaced by pbt/pet in recent years. compared to the heat-resistant pc, pbi has the prominent features of high heat resistance, good processability, low cost. the material has high surface gloss, excellent in processing stability and good hydrolysis resistance, excellent flowability and heat resistance, material price compared with the heat resistance pc, can greatly reduce the cost of about 40%.
the pa used in the headlights is usually pa+gf, the ordinary adjusted screws or brackets in the headlights, using pa6+gf or pa66+gf.
aromatic pa has higher heat resistance temperature and strength than ordinary pa. some important regulating structures and internal brackets of the lamp will also use some aromatic pa plus glass fiber.
pmma, commonly known as acrylic or plexiglass, is a highly transparent, amorphous thermoplastic material, it has excellent optical performance, light transmittance up to 90%~92%, refractive index 1.49, good weather resistance, high surface hardness and excellent overall performance. it is mainly used for optical transparent products. taillight lens and interior atmosphere lamp optical materials.
well, here comes the question. why does the headlight of the car use pc instead of pmma?
both pc and pmma have high transparency and good processing characteristics, but there are some differences in the use of lights.
firstly, in the heat resistance temperature, pc generally can reach 130 degrees celsius, while pmma is only about 100 degrees celsius.
secondly, the toughness of pc material is better, and pmma material is very crisp, it’s easily broken by impact.
finally, the unit price of pc is higher than pmma, and the liquidity at the time of forming is not better than that of pmma.
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in general, the headlight lamp is pc, which is mainly due to the high brightness and heat of the headlights, and in front of the vehicle, which requires a heat shock resistant material. taillight lampshade is generally pmma, in addition to cheap factors, and the taillights are generally single signal lamp assembly, to red and transparent double color alternating, so the good fluidity pmma is a choice.
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.
bmc, pei, peek, pps, lcp and other materials
lamp reflector mainly adopts the material such as bmc, pet etc.
bmc is a new type of material, which has the advantages of thermosetting plastics and reinforced engineering plastics. when injection molding, it can flow evenly at the same time and can be formed in a very short time. it has high rigidity and high strength, good molding shrinkage and dimensional accuracy stability. on the basis of the characteristics of bmc above, generally headlight reflector adopts the bmc. the main function of the headlight is lighting the road ahead, ensure the vehicle in normal driving, the reflector with the corresponding bulb can shoot two kinds of light beam, near beam and high beam, the near beam should have clear boundaries and high brightness illumination.therefore, bmc’s good molding shrinkage and dimensional accuracy stability can meet this point.
tail lamp generally use the materials such as pet, pc, or directly from the lamp on the hub molding, tail lamp is light function combination, dimensional accuracy is not as high as headlights’ requirements, but if you can see the reflector directly from the lamp-chimney, the reflected surface on the reflector must be beautifully designed, ensure that the light of the unique shape after lighting.
3. the development trend of the automotive light materials
the future lights will develop toward simplicity, light weight, high heat resistance and environmental protection. for the selection of materials for automotive lights, the following 3 points are as the main points to strengthen and breakthroughs in the future:
1. the lens material enables light to be effectively and uniformly scattered, with high light dispersion.
2. heat dissipation, the infrared material can be used as the shell of the headlamp or fog lamp.
3. materials (coatings) are required to have better weather resistance and temperature resistance.
sales & marketing manager at tongjie precision mould limited