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Car lights are an indispensable component of the car and are related to the lighting, signaling and decoration of the car. The production of car lights has experienced many years of development, and the degree of plasticization has reached more than 96%.
The main components of automobile lights are composed of reflectors, lenses, casings, light sources, electronic circuits, and installation accessories. At present, the main plastics used in car lights in my country include PC, PP, ABS, PC/ABS, PMMA, PBT, PET, and PA. and a few other plastic materials. Plastic has the advantages of light weight, corrosion resistance, good impact resistance, high transparency, good insulation, low thermal conductivity, good mechanical properties, strong plasticity, molding processing, etc., and is increasingly used in various fields.
1. Polycarbonate (PC)
(1) Introduction to polycarbonate
Polycarbonate, also known as PC. A thermoplastic with excellent comprehensive properties, it has good heat resistance and cold resistance, and maintains high mechanical strength in a wide temperature range (-135℃---+120℃). It has good dimensional stability and the temperature rises to The linear dimension of the material increases by 0.07% at 105°C. It has high impact strength, good ductility, uniform molding shrinkage, and low water absorption. It only gains 0.13% weight when soaked in water for 24 hours, but it is not easy to be machined and injection molded. Molding is the most common method.
PC is an amorphous engineering material with particularly good impact strength, thermal stability, gloss, antibacterial properties, flame retardant properties and anti-pollution properties. The notched impact strength of PC is very high and the shrinkage rate is very low, generally 0.1% to 0.2%. PC has good mechanical properties but poor fluidity, so the injection molding process of PC materials is difficult. When choosing what quality PC material to use, the performance requirements of the product should be used as the benchmark.
(2) Injection molding process conditions
Drying treatment: PC material is hygroscopic and needs drying treatment before processing. Recommended drying conditions are 100°C to 120°C, 3 to 4 hours. Humidity before processing must be less than 0.02%.
Melting temperature: 260~340℃.
Mold temperature: 70~120℃.
Injection pressure: Use as high an injection pressure as possible.
Injection speed: Use low speed injection for smaller gates, medium and high speed injection for other types of gates.
(3) Application of polycarbonate materials in car lights
PC accounts for about 50% of plastic materials in headlights, and is mainly used in reflectors, aluminum-plated decorative parts and masks for headlights and fog lights. The bonding force between PC and aluminum plating layer is very good, and aluminum can be directly plated on PC substrate.
PC reflector
PC aluminum decorative strip
2. Modified polypropylene (PP)
(1) PP chemical and physical properties
PP is a semi-crystalline material that is harder and has a higher melting point than PE.
Since homopolymer PP is very brittle when the temperature is above 0°C, many PP materials are random copolymers with 1% to 4% ethylene added or block copolymers with higher ethylene content.
Copolymer PP materials have a lower heat distortion temperature (100°C), low transparency, low gloss, low rigidity, and stronger impact strength. The strength of PP increases as the ethylene content increases.
The Vicat softening temperature of PP is 150°C.
Due to the high degree of crystallinity, PP materials have good surface stiffness and scratch resistance properties
PP does not have environmental stress cracking problems.
Usually, PP is modified by adding glass fiber, metal additives or thermoplastic rubber.
The flow rate MFR of PP ranges from 1 to 40. Low MFR PP materials have better impact resistance, but lower ductile strength. For materials with the same MFR, the strength of the copolymer type is higher than that of the homopolymer type.
The shrinkage rate of PP is quite high, generally 1.8% to 2.5%. And the directional uniformity of shrinkage is much better than that of PE-HD and other materials. Adding 30% glass additive can reduce the shrinkage to 0.7%.
Both homopolymer and copolymer PP materials have excellent moisture absorption resistance, acid and alkali corrosion resistance, and dissolution resistance. However, it is not resistant to aromatic hydrocarbon (such as benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, etc.
PP also does not have oxidation resistance at high temperatures like PE.
(2) Injection molding process conditions
Drying: Drying is not required if stored properly.
Melting temperature: 220~275℃, be careful not to exceed 275℃.
Mold temperature: 40~80℃, 50℃ is recommended. The degree of crystallization is mainly determined by the mold temperature.
Injection pressure: up to 1800bar.
Injection speed: Using high-speed injection molding can minimize internal pressure. If defects appear on the surface of the product, use low-speed injection molding at a higher plasticizing temperature.
Runners and gates:
For cold runner, the typical runner diameter range is 4 to 7mm.
It is recommended to use round runners, and all types of gates can be used. Typical gate diameters range from 1 to 1.5mm, but gates as small as 0.7mm can also be used.
For edge gates, the minimum gate depth should be half the wall thickness and the minimum gate width should be at least twice the wall thickness.
PP materials can use hot runner systems.
(3) Application of PP materials in car lights
Modified polypropylene is mostly used in automobile lights. Modified PP has strong electrical insulation, chemical corrosion resistance, and fatigue resistance. It has the highest mechanical properties and heat resistance among general plastics, and has obvious price advantages compared to other plastics.
Modified PP accounts for 30% of the plastic materials for car lights, and can be used for the back cover, trim panel and wiring harness guide of the tail light, the lamp body and back cover of the headlight.
Car light housing
3. PMMA
(1) Introduction to PMMA materials
PMMA, commonly known as acrylic or organic glass, is a transparent amorphous plastic. It has good mechanical properties, is strong and rigid at room temperature, and has a light transmittance greater than 92%. It only drops to 89% after 10 years of outdoor use. It still maintains no deformation after being exposed to the outdoors for a long time. It has good weather resistance and mechanical strength. It has excellent properties such as high strength, good machining performance, and can resist erosion by a variety of chemicals. It is mainly used for optically transparent products.
The density of PMMA is 1.19kg/m3, and the average water absorption rate at 20℃*109Pa is 2%. It has the highest water absorption rate among all optical plastics. Its elastic modulus is 3.16*109Pa, Poisson's ratio is 0.32, and tensile strength It is (462---703) *109Pa. The linear expansion coefficient of PMMA is 8.3*10-5 K-1, which is 10 times larger than K9 glass. However, the optical memory of PMMA when cooled from high temperature, that is, the performance of the component in returning to its original size is better than that of glass. Its refractive index changes with The temperature change dn/dt is -8.5*10-5, which is about 30 times larger than K9 glass, but it is a negative value. The thermal conductivity is 0.192W/(m*k), the specific heat capacity is 1465J/(kg*k), its glass transition temperature is 105℃, and its melting temperature is 180℃.
PMMA has excellent resistance to dilute inorganic acid decontamination solutions, grease and weak alkali, moderate resistance to concentrated inorganic acids, is not resistant to alcohols and ketones, is soluble in aromatic hydrocarbons, chlorinated hydrocarbon organic solvents, and is soluble in strong alkali and warm NaOH and KOH. Erodes and does not react with developer. PMMA has excellent weather resistance. It has little change in transparency and color after being exposed to the sun for many years in tropical climates.
(3) Injection molding process conditions
Drying treatment: PMMA is hygroscopic and needs drying treatment before processing. The recommended drying temperature is 80~90℃ and the drying time is 2~4 hours.
Melting temperature: 240~270℃.
Mold temperature: 35~70℃.
Injection speed: medium
(3) Application of PMMA materials in car lights
In the field of automotive lights, it can be used for taillight covers and light guide materials.
4.PC/ABS
(1) Chemical and physical properties
PC/ABS has the comprehensive characteristics of both PC and ABS. For example, the easy processing properties of ABS and the excellent mechanical properties and thermal stability of PC. The ratio of the two will affect the thermal stability of PC/ABS materials. PC/ABS hybrid materials also show excellent flow characteristics.
(2) Injection molding process conditions
Drying treatment: Drying treatment is carried out before processing. The humidity should be less than 0.04%. The recommended drying conditions are 90℃~120℃ for 2 to 4 hours.
Plasticizing temperature: 230℃～300℃.
Mold temperature: 50℃～100℃.
Injection pressure: depends on the plastic part.
Injection speed: as high as possible.
(3) Application of PC/ABS in car lights
In the field of car lights, ABS is generally used after modification with PC materials. Taking into account the respective advantages of the two materials, the long-term heat-resistant temperature can reach 110~120°C. The proportion of PC in ABS can also be adjusted according to the use temperature and impact performance. ABS and PC/ABS alloys are generally used for rear light housings and trim panels.
PC/ABS tail light housing front and back
5. PBT
(1) Introduction to PBT
PBT is commonly known as polybutylene terephthalate. The modified PBT has better mechanical properties (glass fiber reinforced PBT accounts for more than 70% of the market). It is similar to PA and POM. It has a small friction coefficient, good self-lubricating properties, and thermal stability. Good stability and chemical stability, excellent electrical insulation, high rigidity and hardness, good impact, high dimensional stability, and good heat resistance.
PBT is one of the toughest engineering thermoplastic materials. It is a semi-crystalline material with very good chemical stability, mechanical strength, electrical insulation properties and thermal stability. PBT has good stability under environmental conditions. PBT has very weak hygroscopic properties. The tensile strength of non-reinforced PBT is 50MPa, and the tensile strength of glass fiber additive PBT is 170MPa. Too much glass fiber additive will cause the material to become brittle. PBT crystallizes very quickly, and uneven cooling causes bending deformation. For materials with glass fiber additives, the shrinkage in the process direction can be reduced, and the shrinkage in the vertical direction is basically no different from ordinary materials. Generally, the shrinkage rate of PBT materials is between 1.5% and 2.8%. Materials containing 30% glass fiber additives shrink between 0.3% and 1.6%.
(2) Injection molding process conditions
Drying treatment: PBT materials are easily hydrolyzed at high temperatures and require drying before processing. It is recommended to dry in hot air at 120℃ for 6 to 8 hours, or at 150℃ for 2 to 4 hours. Humidity must be less than 0.03%. If a dehumidification dryer is used, the recommended drying temperature is 120°C and the drying time is 4 hours.
Melting temperature: 225℃～275℃, recommended temperature: 250℃.
Mold temperature: 40℃~60℃ for unreinforced materials. The mold cooling must be uniform to reduce the bending deformation of the plastic part. It is recommended that the diameter of the mold cooling cavity is 12mm.
Injection pressure: medium (up to 1500bar).
Injection speed: The fastest possible injection speed should be used (because PBT sets quickly).
Runner and gate: It is recommended to use circular runner to increase pressure transmission (empirical formula: runner diameter = plastic part thickness + 1.5mm). Various types of gates can be used, and hot runners can also be used. The gate diameter should be between 0.8~1.0*t, where t is the thickness of the plastic part. If it is a submersible gate, the recommended minimum diameter is 0.75mm.
(3) Application of PBT in car lights
PBT is generally used in car lights as decorative rings for headlights and brackets in adjustment devices. After PBT and ASA are modified and reinforced with glass fiber, they can be used to make fog lamp casings.
PBT aluminum-plated trim parts
PBT fog light body
6. PET
Commonly known as polyester, and PBT collectively known as thermoplastic polyester, or saturated polyester. The material for car light decorative rings has been mainly heat-resistant PC plastic in the past, but has been gradually replaced by PET in recent years. Compared with heat-resistant PC plastic, the outstanding features of PET car light materials are high heat resistance, good processability and low cost.
The surface gloss of material processing parts is high; it has excellent processing stability and good hydrolysis resistance; it has excellent fluidity and heat resistance; the material price is compared with heat-resistant PC, which can significantly reduce system costs.
PET aluminum-plated car light decorative ring
7. Nylon (PA)
PA polyamide, commonly known as nylon, is a huge variety of plastics. Ordinary screw adjustments or brackets in car lights use glass fiber reinforced nylon 6 or glass fiber reinforced nylon 66.
Aromatic PA is a special nylon with higher heat resistance and strength than PA6 or PA66. It is used in some important adjustment structures and internal brackets in car lights. Use PA+50%GF material for the dimming bracket on the headlight body. There are also PA66 used for dimmer nuts, mounting nuts and ball nuts in headlight internal components.
Aromatic nylon lamp body dimming bracket (+50%GF)
ball nut
8.PEI
(1) Introduction to PEI
PEI, Polyetherimide, PEI for short, is an amber transparent solid. It has inherent flame retardancy and low smoke without adding any additives. The oxygen index is 47% and the combustion grade is UL94-V-0. Density is 1.28~1.42g/cm3.
PEI has strong high-temperature stability, and even non-reinforced PEI still has good toughness and strength. Therefore, PEI's superior thermal stability can be used to make high-temperature and heat-resistant devices.
It has excellent mechanical properties, electrical insulation properties, radiation resistance, high and low temperature resistance and wear resistance, and can transmit microwaves. PEI also has good flame retardancy, resistance to chemical reactions and electrical insulation properties.
PEI has strong high-temperature stability, and even non-reinforced PEI still has good toughness and strength. Therefore, PEI's superior thermal stability can be used to make high-temperature and heat-resistant devices. PEI also has good flame retardancy, resistance to chemical reactions and electrical insulation properties. The glass transition temperature is as high as 215℃. PEI also has very low shrinkage and good isodirectional mechanical properties.
(2) Injection molding process conditions
Drying Processing: PEI has hygroscopic properties and can cause material degradation. The required humidity value should be less than 0.02%. The recommended drying conditions are 150°C and 4 hours of drying.
Melting temperature: 340℃～400℃ for ordinary type materials; 340℃～425℃ for reinforced type materials.
Mold temperature: 107℃~175℃, the recommended mold temperature is 140℃.
Injection pressure: 700~1500bar.
Injection speed: Use the highest possible injection speed.
(3) Application of PEI in car lights
Some newly designed car headlights and reflectors began to use PEI.
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