Application of special plastics and engineering plastics in automobile interior and exterior decoration

Posted on : Aug 6 , 2022 By  GREFEE

The plastic used in automotive have advantages than the traditional material, which mainly reflects on light weight, good appearance decoration effect, and multiple actual application functions, so it is quite favored by the automotive plastic parts suppliers. In addition, its good physical and chemical properties make it easy to be formed and save energy, which can be sustained use in different aspects. The main characteristics of polymer automotive materials are as follows:

Light weight: Light weight and high strength, which is only 15-20% of the ordinary steel, even lighter than wood. It promotes the lightweight of vehicles to a large extent.

Good processing performance: good plasticity and good compatibility with other materials, which can process materials in different shapes and colors and materials with different properties and functions. It is also can be used in secondary processing, such as milling, punching, cutting, etc

Excellent comprehensive physical and chemical properties: good insulation performance, corrosion resistance, and anti-aging properties, good wear resistance and washability, good waterproof and mechanical performance, good bonding performance.

Good decoration effect: can be made into products with complex shapes and colors in one time. Sometimes, it still needs printing, printing, coating, embossing, laminating, coloring, processing into very realistic images, patterns. It can imitate natural wood, metal, patterns of animal skin. It can also be bronzed, coated, silvered and inlaid on the surface.

Energy saving and environmental protection: replace large amount of natural material, saving large amount of resources. Good machinability. Saving energy in production. Thermoplastic is largely used. The waste material can be recycled and used for re-produce.

Engineering plastic

The engineering plastic has great comprehensive mechanical properties, which is commonly used in automotive industry. This article will introduce the polyamide (PA), polymethacrylate (PMMA), Polyoxymethylene (POM), polyamide (PU), polycarbonate (PC).

1、PA

Polyamide, also named nylon with a wide varieties in industry. Common used nylon includes  PA6、PA66, and PA610. PA is easily to be printed and coloring. In addition, it also has great electrical properties, and resistance for drug and oil. The similarities in mechanical aspect is the hardness, and high surface stiffness, good tensile strength, impact resistance, fatigue resistance, folding resistance and stress cracking resistance.

The tensile and compressive strength of PA changes with temperature and moisture absorption, so water is the plasticizer of PA. After adding glass fiber, its tensile and compressive strength can be increased to 2 times. Its temperature resistance raises, too. The wear resistance of PA is high, so it can continue to work without the lubricating. The disadvantages of PA is poor acid, light, and pollution resistance. Since the influence of the thermal inflation and water absorption, the stability of the dimension of the parts is poor. The shrinkage is 1~2%. It requires to pay attention to the dimension change after water absorption. Its water absorption is 100%. When the relative moisture absorption is saturated, it can absorb 8%, and the appropriate wall thickness is 2 ~ 3.5mm.

Injection molding performance: due to the existence of acylamino,  PA has strong and firm water absorption. Therefore, it should be fully dried during the injection molding. Generally, it requires to be dried for 3-4 hours under 120 degrees. As the viscosity of PA is low and the flow speed is high, self locking nozzle or nylon special nozzle should be used to avoid the leaking. Meanwhile, the mold accuracy should be paid attention to, too.

PA is mainly used for manufacturing hose (brake hose, fuel pipe), combustion oil filter, air filter, oil filter, water pump housing, water pump impeller, fan, brake fluid tank, power steering fluid tank, white leaf window, front headlight housing, safety belt in automotive industry.

2、PMMA

Polymethacrylate, also known as organic glass, which is resistant to the outdoor aging. It has great light transmission, even under the strong sunlight. After 240 hours of accelerated aging of light, it can still pass through 92% of sunlight, 89% of outdoor ten years, and 78.5% of ultraviolet light. In addition, it has strong mechanical strength and good cold resistance, corrosion resistance, good insulation performance, stable size, easy to form, brittle, fusible in organic solvents, insufficient surface hardness, easy to scratch and fuzz. Appropriate plastic products: transparent structural parts with a certain strength requirements.

Injection molding performance: the hydroscopic ration of PMMA is about 0.3%, which must be dried for 2-4 hours at 80 degrees before injection molding. The molten temperature during the injection molding is 240-270 degrees. The mold temperature should be controlled at 35-70 degrees. Due to the great light transmission of PMMA, it is widely used in the automobile lighting signboard, door glass and lamp glass cover.

Toyota Corolla tail lamp with PMMA

3、POM

Polyoxymethylene, also known as plastic steel, with high tensile strength, impact toughness, rigidity and fatigue strength, high creep resistance, good dimensional stability, small water absorption, small friction number, and excellent friction and wear resistance. In addition, it has great rigidity in high temperature and water. Its chemical corrosion resistance is the same as PA, but cheaper in price. It is resistant to repeated distortion, and it has outstanding resilience, which can be used for a long time between -40 ℃ and -100 ℃. POM is vulnerable to strong acid corrosion, not resistant to high temperature and poor thermal stability. Shrinkage rate is 2-3.5% suitable wall thickness is1.5- 2.5mm.

Injection molding performance: POM has an obvious melting point, which melts at 175 ℃ and decomposes at 240 ℃. The general processing temperature is 190 ℃ ~ 220 ℃, but the processing range is quite limited. As POM does not absorb water, so it does not need to be dried during injection molding. However, products with high quality requirements can be dried at 60 ℃ for 1 ~ 2 hours; The temperature should not be too high, otherwise the color of the no dyed products will change. It has poor acid resistance and cannot be dyed with acid dyes.

POM is used in automobiles to produce instrument panel glove box accessories, various valves (drainage valves, air conditioner valves, etc.), various impellers (water pump impellers, heater impellers, oil pump wheels, etc.), various electrical switches and pinions on electrical instruments, various handles and door pins, etc.

4、PC

Polycarbonate with outstanding impact toughness and creep resistance, good heat resistance, good cold resistance, embrittlement temperature of -100 ℃. Its bending strength is equivalent to nylon, and has high elongation and elastic modulus, but the fatigue strength is less than nylon 66. Its moisture absorption rate and shrinkage are are low, but dimensional stability is good. The wear resistance of PC is equivalent to that of nylon, and it has certain corrosion resistance, but the forming conditions are high. It has good weather resistance and can be used for a long time under high temperature and high load, but it cannot be used under wet temperature because it has poor solvent resistance, stress cracking and poor fatigue strength. The shrinkage rate is 0.5-0.7%, and the appropriate wall thickness is 2-3.5mm. It shows that glass fiber will improve the glass fiber shrinkage, mechanical strength and temperature resistance of PC. The steel will increase after long-term use at about 100 ℃, and the internal stress can be improved by annealing.

Injection molding performance: PC has an obvious melting point, which melts at 220 ℃ and decomposes at 350 ℃. Its general processing temperature is 250℃～320℃. Its moisture absorption amount is low because it just a little amount of water will lead to its decomposition under high temperature. During the injection molding, it must be dried for 4-5 hours under 120 ℃. PC molten has a high viscosity and requires high pressure during the injection molding to reduce the residual stress. Its shrinkage rate is not related to the processing conditions and wall thickness. Its longitudinal and transverse shrinkage rates are relatively close, so it can be used to produce plastic injection molding automotive parts with high accuracy. The shrinkage rate of PC is 0.5%.

Introduction to the main composite pc-abs:

PC-abs is a blend material of PC and ABS, which is general supplied in the shape of pellets after blending. The effect is poor and delimitation will occur if the two materials are simply mixed and injected directly. Its advantage is rigid and tough, while the disadvantages are stress cracking and high viscosity. ABS has the good fluidity but low surface hardness. So, the blended material pc-abs not only has high surface hardness, high rigidity and toughness, but also high stress cracking resistance. Its mechanical properties are between the two.

Automotive plastic parts used PC to manufacture lampshades, left and right wheel guards, instrument baffle body (PC + ABS), left and right wind frame covers, middle wind frame covers (PC + ABS), and rear bumper cushion.

5、PU

Polyurethane, according to the different products of polymerization reaction, it is commonly divided into rigid polyurethane and soft polyurethane. Rigid polyurethane has high strength, good toughness, good heat insulation, good waterproof effect, simple molding process and high production efficiency, whereas soft polyurethane has good elasticity, sound absorption effect, aging resistance, chemical medium resistance, and its comprehensive mechanical properties is much higher than those of PVC and other materials. The polymerization of polyurethane is very convenient, which can not only be polymerized under normal temperature and pressure, but also can be directly foamed, sprayed, repaired and other construction after on-site polymerization.

Polyurethane foam is widely used in automotive interiors and vibration absorbing parts, such as coating materials, polyurethane rigid plastic plates, polyurethane elastomers, soft foam materials for seats, decorative parts, sofa leather, roof accessories. The most widely used are various soft and hard polyurethane foam materials, which have vibration isolation, sound insulation, noise reduction, thermal insulation. PU can also be made into polyurethane coatings, adhesives, sealants, and other components for vehicles. Typical PU made products on the car include instrument panel, rearview mirror, bumper, seat cushion, headrest, steering wheel, instrument panel anti vibration pad, pillar trim, front roof lining, window frame frame, ceiling and side roof frame decoration, door lining, sunshade, rear roof frame decoration, etc.

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