Automotive plastic has many advantages that traditional materials do not have. This is mainly manifested in light weight, good external decorative effect, various practical application functions, good physical and chemical properties, easy processing and molding, energy saving, sustainable use and other aspects.

The main characteristics of polymer automotive materials are as follows:

Light weight:

Light weight, high strength, only 15-20% of the share of ordinary steel, lighter than wood, greatly contributes to reducing the weight of cars.

Good machinability:

Good ductility and good compatibility with other materials allow different processes to process materials with different shapes, different properties, different colors and different functions; secondary processing such as turning, stamping, cutting, etc. can also be performed.

Excellent complex physical and chemical properties:

Good insulation performance, corrosion resistance, aging resistance, good wear and abrasion resistance, good waterproof and mechanical properties, good adhesion performance.

Nice decorative effect:

It can be processed into complex shapes and multiple colors at the same time, and sometimes requires printing, filming, embossing, layering and coloring to turn them into very realistic images, designs and patterns that can mimic natural wood. , The texture of metal and animal skin can also be bronzed, captivated, silvered, inlaid, etc.

Energy saving and environmental protection:

Replacing a large number of natural materials, saving a large amount of resources; good machinability, saving energy in the production process; the use of a large number of thermoplastics, the waste can be easily recycled and directly used for re-production.

Technical plastics

Technical plastics are also widely used in the automotive industry due to their good complex mechanical properties. This article mainly features polyamide (PA), polymethacrylate (PMMA), polyoxymethylene (POM), polyamide (PU), polycarbonate (PC). .

PA

Polyamide, commonly known as nylon, has many types of polyamide used in the industry, and the most commonly used are polyamide 6, PA66 and PA610. Polyamide is easy to print, easy to dye, has excellent electrical properties, and is resistant to chemicals and oil corrosion. Common in mechanical aspects is toughness, all of which have high surface hardness, good tensile strength, good impact resistance, fatigue resistance, folding resistance and stress cracking resistance. The tensile and compressive strength of PA varies with temperature and absorption.moisture removal, so water is a relatively plasticizer for PA. After adding glass fiber, its tensile and compressive strength can be increased by about 2 times, and the heat resistance can be improved accordingly. PA itself wear resistance is very high, so it can work continuously without lubrication. The disadvantages of PA are poor acid resistance, poor light resistance, and poor soil resistance. Due to the influence of thermal expansion and water absorption, the dimensional stability of the part is low, and the shrinkage rate is 1-2%. Note the change in moisture absorption dimensions after molding. The water absorption rate is 100%, and it can absorb 8% when the relative moisture absorption reaches saturation. Suitable wall thickness is 2-3.5mm.

Injection molding performance: Due to the presence of amide groups, PA has strong water absorption and strong water absorption. Therefore, it should be completely dried during injection molding, generally at 120°C for 3-4 hours; PA has a low viscosity and a high flow rate. Self-locking nozzles or special nylon nozzles should be used to prevent flow through the nozzle. At the same time, pay attention to the accuracy of the mold.

PA is mainly used in the automotive industry for the production of hoses (brake hoses, fuel pipes), oil filters, air filters, oil filters, water pump housings, water pump impellers, fans, brake fluid tanks, power steering tanks, white curtains , headlight housings, seat belts.

PMMA

Polymethacrylate, commonly known as plexiglass, is resistant to outdoor aging and has excellent light transmission. Exposure to sunlight does not affect its transparency. After 240 hours of accelerated aging, it can still pass through 92% of sunlight. Sunlight , 89% of them are still outdoors for ten years, and 78.5% are ultraviolet rays. High mechanical strength, certain cold resistance, corrosion resistance, good insulation performance, stable size, easy to form, relatively brittle, easy to melt in organic solvents, insufficient surface hardness, easy to scratch and fluff. Suitable plastic products: transparent structural parts with specific strength requirements.

Injection molding performance: PMMA's moisture absorption rate is 0.3%, and it must be dried before injection molding, generally at about 80 ° C for 2 to 4 hours; the melt temperature during injection molding is 240-270°C, and the mold temperature should be controlled at 35-70°C.

Because of its good light transmission, polymethyl methacrylate is widely used in automotive light panels, door glass and glass lamp covers.

Toyota Corolla taillight using PMMA

POM

Polyoxymethylene, commonly known as ductile steel, has high tensile strength, toughness, stiffness and fatigue strength, high creep resistance, good dimensional stability, low water absorption, low coefficient of friction, as well as excellent friction and wear resistance. high rigidity at high temperature and water, and its chemical corrosion resistance is the same as that of polyamide, but its price is lower, it is resistant to repeated twisting, and it has outstanding resilience. It can be used for a long time at -40 to 100 degrees Celsius. The disadvantages of POM are: easy attack by strong acid, high temperature instability and poor thermal stability. Shrinkage rate 2-3.5% Corresponding wall thickness: 1.5-2.5 mm.

Injection molding characteristics: POM has an obvious melting point, which melts at 175°C and decomposes at 240°C. The general processing temperature is from 190°C to 220°C, and its processing range is very narrow; POM does not absorb water and does not absorb water at all when injection molded. Items requiring drying but requiring high quality can be dried at 60°C for 1-2 hours, the temperature should not be too high, otherwise unpainted items will change color ; its acid resistance is poor, so it cannot be dyed with acid dyes.

POM is used in automobiles to make accessories for dashboard gloves, various valves (drain valves, air conditioning valves, etc.), various impellers (water pump impellers, heater impellers, oil pump wheels, etc.), various electrical switches and small gears, various handles and door pins on electrical appliances.

PC

Polycarbonate has outstanding toughness and creep resistance, good heat and cold resistance, embrittlement temperature reaches -100°C, bending strength is equivalent to nylon, it has high elongation and elastic modulus, but fatigue strength is less than nylon 66. Low water absorption, low shrinkage, good dimensional stability. The wear resistance is similar to nylon, and it has a certain corrosion resistance, but the molding conditions are high. It has good weather resistance and can be used for a long time at high temperatures and high loads, but it cannot be used at humid temperatures, it has poor solvent resistance, stress cracking phenomenon and low fatigue strength. The shrinkage ratio is 0.5-0.7% and the suitable wall thickness is 2-3.5mm. Adding fiberglass to polycarbonate can improve its shrinkage, mechanical strength, and heat resistance. Long-term use at around 100°C will increase stiffness, and annealing can be used to reduce internal stress.

Injection molding performance: PC has an obvious melting point, which melts at 220 ° C and decomposes at 350 ° C. The general processing temperature is between 250 ° C and 320 ° C, it absorbs water and a small amount of water. may cause it to decompose at high temperatures. Drying is necessary, and the drying temperature can be dried at 120 ° C for 4-5 hours; the melt viscosity of PC material is high, and high pressure is required during injection molding; when PC is processed, if conditions permit, mold temperature can be used. The machine raises the mold temperature to reduce the residual stress of the product; PC shrinkage rate has nothing to do with processing conditions and product wall thickness, and its vertical and horizontal shrinkage ratios relatively close, so it can be processed into products with high precision, its shrinkage rate is 0.5%.

Introduction to the main synthetic plastic PC-ABS:

PC-ABS is a mixture of PC and ABS, which after mixing is usually supplied in the form of granules. If you simply mix the two materials and inject them directly, the effect will be poor and delamination will occur; the advantage of polycarbonate in rigidity and strength, but the disadvantage is stress cracking and high viscosity; The advantage of ABS is good fluidity, but the surface is low hardness; PC-ABS mixed material retains the advantages of both; PC-ABS has high surface hardness, high rigidity and toughness, and high resistance to stress cracking; its mechanical properties are in between.

PC is mainly used to make lampshades, protect left and right wheel covers, dashboard shell (PC+ABS), left and right frame coverswe, mid-frame covers (PC+ABS) and rear bumper cushions. in the automotive field.

PU

Polyurethane, according to different polymerization products, is generally divided into rigid polyurethane and soft polyurethane. Hard polyurethane has high strength, good toughness, good thermal insulation, good waterproof effect, simple molding process and high production efficiency, soft polyurethane has good elasticity, good sound absorption effect, aging resistance, chemical resistance, etc. The comprehensive mechanical properties are much superior to PVC and other materials. The polymerization of polyurethane is very convenient. The polymerization reaction can not only be carried out under normal temperature and pressure conditions, but even directly foamed or sprayed and repaired after polymerization in situ.

Polyurethane foam is widely used in automotive interiors and vibration-absorbing parts, such as coating materials, polyurethane rigid plastic sheets, polyurethane elastomers, seat soft foam materials, decorative parts, leather sofa and car roof accessories. various soft and hard polyurethane foam materials that have vibration, sound, noise, heat insulation properties, as well as polyurethane coatings for cars, adhesives, sealants, etc. Representative parts of polyurethane for cars include dashboards, rear-view mirrors, bumpers, seat cushions, head restraints, steering wheels, dashboard anti-vibration pads, pillar trim, front roof lining, window frames, roofs and side roofs. rear top shelf trim, etc.

Fiberglass-reinforced plastic is based on the original pure plastic with the addition of fiberglass and other additives to expand the range of use of the material. Generally speaking, most glass fiber reinforced materials are mainly used in the structural parts of the product, which is a kind of structural engineering material, such as: PP, ABS, PA66, PA6, PC, POM.

Benefits:

①After the fiberglass is reinforced, the fiberglass becomes a high temperature resistant material, so the heat resistance temperature of the reinforced plastic is much higher than before without fiberglass, especially nylon plastic;

②Limits the mutual movement between the polymer chains of the plastic, so the shrinkage rate of the reinforced plastic is greatly reduced, and the rigidity is also greatly increased;

③Reinforced plastics do not crack under stress, and the impact resistance of plastics is greatly improved;

④Glass fiber is a high-strength material that significantly increases the strength of plastics (significantly improves tensile strength, compressive strength and bending strength);

⑤ Due to the addition of fiberglass and other additives, the combustion performance of reinforced plastics has been greatly reduced, and most materials cannot be ignited.

Weaknesses:

①It is transparent until fiberglass is added and it will become opaque;

② The strength of the plastic decreases and the brittleness increases;

③The melt viscosity of all materials increases, the fluidity becomes poor, and the injection pressure is much higher than without fiberglass;

④Poor fluidity. For normal injection molding, the injection temperature of all reinforced plastics must be increased by 10-30 °C than before adding fiberglass;

⑤The hygroscopic performance of reinforced plastics is greatly improved, and even pure plastics that do not absorb water become water absorbent, so they need to be dried during injection molding;

⑥During the injection molding process, glass fiber may get on the surface of the plastic product, which will make the surface of the product rough and mottled (in order to get a better surface quality, it is best to use a mold heating machine). mold by injection molding, so that the plastic resin hits the surface of the product, but the appearance quality of pure plastic cannot be achieved);

⑦ Glass fiber is a material with high hardness. After the additive evaporates at high temperature, it will be a very corrosive gas, which will cause severe wear and corrosion of the screw of the injection molding machine and injection mold. Therefore, mold making using this material. When using and injection molding machine, attention should be paid to anti-corrosion surface treatment and processingtke equipment surface hardness.

Representative material for fiberglass reinforcement, FRP/composite applications in the automotive industry:

Body parts: including bodyshells, hardtops, sunroofs, doors, grilles, headlight reflectors, front and rear bumpers, and interior parts. This is the main application of FRP/composite materials in automobiles. It is mainly aimed at meeting the requirements of streamlined body structure and high-quality appearance. At present, there is a huge potential for development and application. The material of this part is mainly glass fiber reinforced thermosetting plastic, and the typical molding processes include: SMC/BMC, RTM, hand laid/sprayed, etc.

Structural parts: including front brackets, bumper frames, seat frames, floors, etc. The goal is to improve design freedom, versatility and part integrity. Mainly use high strength SMC, GMT, LFT and other materials.

Functional parts: Its main feature is that it requires high temperature resistance and oil corrosion resistance, mainly of the engine and its peripheral parts. For example: engine valve cover, intake manifold, oil pan, air filter cover, gear chamber cover, air duct cover, intake pipe guard, fan blade, fan air duct ring, heater cover, water tank parts, water outlet housing, water pump. turbine, engine soundproofing plate, etc. Main process materials: SMC/BMC, RTM, GMT and fiberglass reinforced nylon, etc.

Representatives of car companies and models:

Varieties of plastic and examples of application in car structural elements, as well as in interior and exterior trim elements: