The use of injection molded plastic parts is becoming more and more common. The identification of plastics and selection of raw materials are basis for processing of injection molded parts. This article introduces names, common names, advantages, disadvantages, typical modification methods, and applications for commonly used injection molding plastics.

ABS (styrene-butadiene-propylene)

The starting material is ivory and its density is greater than 1, so it will slowly sink to bottom when placed in water. ABS products immediately turn white when subjected to external force or bending, when tested by combustion, they can burn, flame is yellow, along with flame, traces of black smoke float in air.

Advantage

a. The parts are hard and strong, have a high degree of impact resistance at low temperatures.

b. With low water absorption, it is an excellent insulating material.

c. The parts are shiny, dimensionally stable, have high mold surface reproduction ability, are not easy to wear on surface, and have good electrical properties and fluidity.

d. High mechanical strength, high impact resistance even at low temperature, good notch sensitivity, good creep resistance, low coefficient of friction and little change in temperature and humidity.

Disadvantages

a. Not resistant to organic solvents, it swells and dissolves in polar solvents, has poor weather resistance, oxidizes and decomposes.

b. The viscosity of solution is high.

c. Color quality is relatively sensitive to temperature.

Changed Materials

a. ABS+PC or SAN, increased thermal distortion temperature;

b. ABS+PVC, improve fire performance.

Target

Cases for electrical appliances, daily necessities, expensive toys, furniture, sports equipment, etc.

GPPS (polystyrene)

The material itself is clean and transparent, slowly sinking in water, and product is fragile. When burning, inner flame is yellow and outer flame is black. It will drip, and then there will be a clear smell, fire goes out.

Advantage

a. Good optical performance, light transmission 88-92%, refractive index 1.59-1.60.

b. The electrical characteristics are good, volume resistance is 1018 ohms.

c. Low specific heat capacity, low melt viscosity, strong plasticizing ability, fast heating and molding, short molding cycle, large difference between molding temperature and decomposition temperature, low crystallinity, good dimensional stability.

d. It has good fluidity and thermal stability, low shrinkage and radiation resistance.

d. The plastic itself is clean and transparent, with good coloring properties and is easy to use.

Disadvantages

a. Brittle, with toughnessTew 83.3-98 Pa and poor wear resistance, which leads to high requirements for packaging, storage and transportation.

b. Low temperature heat resistance, highest temperature is 60-80 degrees, hard material, large thermal expansion coefficient, poor heat load.

c. The molding process is highly demanding, aging phenomenon of parts is obvious, and it is very sensitive to heat.

d. Poor acid resistance.

e. Fragile, flammable, high static electricity and easily absorbs dust.

Target

Can be used as a cleaning agent for molding machines without side effects, and for making toys, stationery, daily necessities and containers.

HIPS (modified polystyrene, no adhesive)

HIPS is a modified GPPS product with added rubber materials. Its purpose is to increase impact resistance of material. The material is colorless and transparent, and can be dyed as required.

Advantage

a. It has good fluidity and good impact strength.

b. Easily processed and painted.

Disadvantages

a. The content of rubber material in HIPS is 15%, which affects fluidity to a certain extent, so injection pressure and molding temperature should be slightly higher than that of GPPS, and opening of mold gate should be reasonable. as much as possible.

b. Material cooling is slow. In addition to sufficient holding time and speed, mold must have good heat transfer capacity to reduce localized shrinkage and deformation after demoulding.

c. In actual production, most HIPS and GPPS materials are used in combination. Its characteristics: parts have good gloss, fresh color, good touch and good rigidity. Modified HIPS make up 20-70% of total. ., PS accounted for 80%-30%.

d. Due to inclusion of rubber molecules, internal strength and elasticity of plastic makes edges of product appear white. The solution is to increase temperature of mold at point of whitening, but prerequisite is that there must be a reliable pressing force.

Target

It is mainly used in manufacture of toys, daily necessities, radio housings and TV housings.

PC (bulletproof adhesive)

The raw material is transparent, easy to color, thermal distortion temperature is 135-143 degrees, product can burn, flame is yellow, does not foam, saliva is released, and slowly extinguishes when exposed to an external fire source. removed.

Advantage

a. The mechanical performance is better than any plastic, and heat and weather resistance is very good.

b. High casting precision, good dimensional stability, good optical performance, light transmission 75%-89%.

c. The product is resistant todilute acid.

Disadvantages

A. High water absorption rate, pre-drying during molding, and dried material should not be exposed to air for a long time.

b.The processing requirement of product is high, and machine must have good clamping force. It is best to use a special screw, and fluidity of material is poor.

c. The material is sensitive to loads, and precision of mold must be high. When designing a product, ratio of wall thickness of product should be taken into account.

Target

It is mainly used in production of electric toy enclosures, electric enclosures, safety helmets, bulletproof glass and electrical components.

PP (corrugated adhesive)

Advantage

a. It has good fluidity and good molding characteristics.

b. The surface gloss of workpiece is good, and staining effect and injury marks are better than those of polyethylene.

c. The most heat-resistant plastic among general-purpose plastics.

d. High molecular weight, easy to crystallize, with high tensile yield strength.

e. Good electrical performance, low density and resistance to stress cracking.

Disadvantages

a. The shrinkage rate is large, and workpiece size is not easy to control.

b. The inner wall of slightly larger parts is prone to vacuum.

c. The requirements for mold drawing are high.

d. Printing, bonding, electroplating and other processing difficulties.

e. Poor fire resistance and poor weather resistance.

f. Insufficient rigidity and low notch strength.

Mechanical indicators

a.Heat resistance temperature 135-150 degrees.

b.Resistant to organic acids at 80 degrees.

c. PP+10% talc, heat stabilizer, free flowing, shiny, used for small electrical appliances, auto parts.

d. PP + 20%-40% talc, heat stabilizer, free flowing, stable size, used for making machinery parts.

For example, polypropylene + 40% talc, detergent, light flow, short cycle, used in washing machines, dry cleaning machines.

f. PP+30%-40% chemically bonded glass fiber, heat stabilizer, high rigidity, high strength, low shrinkage for machinery and automobile parts.

g. PP + flame retardant, anti-ultraviolet, easy to flow, weather resistant, mainly used for indoor and outdoor furniture.

Target

Packaging plastic bags, wire drawing, belt ropes, toys, daily necessities, bottles, blue plastic racks, washing machines.

PMMA (plexiglass, acrylic)

Plexiglas is difficult to catch fire, but it can burn slowly. It may ignite spontaneously afterexit from fire. The flame is blue and top is white. The plastic melts and bubbles, giving off a strong smell of flowers and fruits and rotten vegetables.

Advantage

a. Amorphous plastics have best transparency among plastics and can transmit ultraviolet waves with a wavelength of 270 nm, which is similar to optical glass in terms of light transmission.

b. It can withstand non-oxidizing acid, inorganic salt liquid, and has excellent weather resistance.

c. Good electrical properties and relatively stable dimensions.

Disadvantages

a. Fragility, despite high strength of surface, scars remain after rubbing with hard objects.

b. The notched impact strength is low, processing is not easy, and water absorption rate is high.

c. It is heat sensitive and material changes color easily when it dries too long and it is light yellow.

Target

Transparencies, jewelry, sun lenses, stationery, lampshades, camera lenses, fake jewelry, etc.

PA (nylon)

Advantage

a. High mechanical strength, good toughness, high tensile and compressive strength, tensile strength close to yield strength, strong ability to absorb shock and vibration.

b. The fatigue resistance is outstanding, and original mechanical strength can still be maintained after repeated bending.

c. The surface is smooth, coefficient of friction is small, wear-resistant and lubricating.

d. Corrosion resistant, very resistant to alkalis and most acids.

e. Non-toxic, inert to biological erosion, with good resistance to bacteria and mold.

f.Temperature range of heat resistance is -40-100 degrees, can withstand 120-150 degrees for a short time.

Disadvantages

a) Easily absorbs water, unstable in size, not resistant to strong acids and oxidizing agents, cannot be used as acid-resistant materials.

b. Optical rotation resistance is poor, and thermal oxidation by atmospheric oxygen will start to turn brown and then crack after long exposure to high temperature.

c. Injection molding process is strictly required, moisture is harmful to molding, thermal expansion is difficult to control, and inconsistent wall thickness will lead to distortion and deformation of the part, as well as post-processing requirements. high equipment.

Target

Production of drawing wire, toothbrush bristles, fishing wire, packaging film, gears, power tool casings, power accessories, power tools, etc.