What materials are best for injection molding?

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Most of the plastic products we see in our lives are completed by injection molding. Different products have different functions and requirements, and the plastic materials used are also different. So, what materials are most suitable for injection molding in injection molding?

To answer this question, we need to understand the usage scenarios and functional requirements of the product, and then select the most suitable plastic material for injection molding within the range that can meet the requirements.

Of course, experienced engineers are required to have a comprehensive understanding of the characteristics of different materials, to make a correct recommendation.

In this article, we will give a detailed introduction to commonly used plastic injection molding materials and their characteristics, so that you can provide some suggestions when choosing the most suitable injection molding materials.

The main raw materials of injection molding products are polystyrene, high-density polyethylene, polypropylene, and ABS4 kinds of resins.

These four plastic resin injection molding plastic products account for more than 80% of the total raw materials of injection molding products. Among them, the application amount of polystyrene, low-density polyethylene, and polypropylene resin accounts for 70% of the total amount of raw materials used.

1. Polystyrene (PS)

Polystyrene, commonly known as hard thermoplastic rubber, is a colorless, transparent, glossy granular material.

Polystyrene has the following properties:

1. Good optical properties

2. Excellent electrical properties

3. The easy injection molding process

4. Good coloring properties

5. The biggest disadvantage is brittleness

6. Low heat resistance temperature (maximum use temperature 60~80 degrees Celsius)

7. Poor acid resistance

Typical application areas:

Product packaging, household products (tableware, trays, etc.), electrical (transparent containers, light scatterers, insulating films, etc.)

2. Polypropylene (PP)

Polypropylene, colorless and transparent or a certain luster of the granular material, referred to as PP, is commonly known as a hundredfold soft rubber. It is a crystalline plastic.

The characteristics of polypropylene are as follows:

1. Good flowability, excellent molding performance

2. Excellent heat resistance can be sterilized by boiling at 100 degrees Celsius 

3. High yield strength

4. Good electrical properties

5. Poor fire safety

6. Poor weather resistance, sensitive to oxygen, susceptible to aging by ultraviolet light

Typical application areas:

Automotive industry (mainly using PP with metal additives: fenders, vent pipes, fans, etc.), apparatus (dishwasher door liners, dryer vent pipes, washing injection molding machine frames, and covers, refrigerator door liners, etc.), consumer goods for daily use (lawn and garden equipment such as lawn mowers and water sprinklers, etc.)

3. Nylon (PA)

Nylon is an engineering plastic, is composed of polyamide resin plastic, referred to as PA, PA6, PA66, PA610, PA1010, etc.

The characteristics of nylon are as follows:

1. Nylon has high crystallinity

2. High mechanical strength and good toughness

3. High tensile and compressive strength

4. Outstanding fatigue resistance, wear resistance, corrosion resistance, heat resistance, non-toxic

5. Excellent electrical properties

6. Poor light resistance, easy to absorb water, not acid resistant

Typical application range:

Widely used for structural components due to good mechanical strength and stiffness. Due to its good wear resistance characteristics, also used in the manufacture of bearings.

4. Polyformaldehyde (POM)

Paraformaldehyde, also known as race steel injection molding material, is an engineering plastic. Formaldehyde has a crystal structure, excellent mechanical properties, high modulus of elasticity, rigidity, and surface hardness, and is also very high, known as the “metal competitor”.

The properties of paraformaldehyde are as follows:

Small coefficient of friction, excellent wear resistance, and self-lubrication, second only to nylon, but cheaper than nylon.

Good solvent resistance, especially organic solvents, but not strong acids, strong alkalis, and oxidizers.

Good dimensional stability can manufacture precision parts.

Large molding shrinkage, poor thermal stability, easy to decompose when heated.

Typical application range:

POM has a very low coefficient of friction and good geometric stability, especially suitable for making gears and bearings.

Because it also has high-temperature resistance, it is also used for pipeline devices (pipe valves, pump housings), lawn equipment, etc.

Typical application range:

POM has a very low coefficient of friction and good geometric stability, especially suitable for making gears and bearings. Because it also has high-temperature resistance, it is also used for pipeline devices (pipe valves, pump housings), lawn equipment, etc.

5. ABS plastic (acrylonitrile-butadiene-styrene)

Paraformaldehyde, also known as race steel material, is an engineering plastic. Formaldehyde has a crystal structure, excellent mechanical properties, high modulus of elasticity, rigidity, and surface hardness, and is also very high, known as the “metal competitor”.

The properties of paraformaldehyde are as follows:

1, ABS is an amorphous, opaque resin, generally light yellow granules or beads. It has good overall performance and is a tough, hard, rigid thermoplastic engineering plastic. (1) Propylene meth gives ABS chemical resistance, oil resistance and a certain degree of rigidity and hardness.

2, butadiene improves the toughness, impact resistance and cold resistance of ABS.

3, Styrene gives ABS good dielectric properties and gloss, good processing fluidity.

In addition, ABS is easy to process and mold. The melting temperature is 217~237℃, and the thermal decomposition temperature is greater than 250℃. Molding shrinkage is small, and the product has good dimensional stability.

4, ABS is non-toxic, odorless, and has low water absorption. Easy to paint, dye, plating and other surface decoration.

5, ABS has the disadvantage of poor weather resistance due to the double bond produced by butadiene, and is prone to aging, discoloration, and even cracking after long-term exposure outdoors, thus reducing impact strength and toughness. ABS is soluble in aldehydes, ketones, esters, and chlorinated hydrocarbons, and is combustible, with a low heat deflection temperature.

6, ABS burns slowly and continues to burn after leaving the fire, with a yellow flame and black smoke. Softening and burning after burning, with special odor and no molten drops.

7, ABS is an amorphous polymer, like polystyrene, with excellent processing properties. It can be injected, extruded, calendered, and thermoformed, and can be subjected to secondary processing such as machining, welding, bonding, painting, and plating. In terms of secondary processing, the surface of ABS can be easily plated with metal, and the adhesion of plating to ABS is 10 to 100 times higher than that of other plastics, which is beautiful and improves the

weather resistance of ABS.

Typical application areas:

1, in the electronics, telecommunications and home appliance industries, widely used in the shells and parts of televisions, radios, tape recorders, washing machines, refrigerators, jukeboxes, telephones, computers, lamps, vacuum cleaners, electric fans, air conditioners, etc.

2, in the light industry, textile and furniture industry, used to manufacture sewing machines, bicycles, light bikes, looms, spinning machines, spindles, office supplies, copiers, cameras, clocks, musical instruments and other parts; in the construction industry, used to manufacture plates, pipes; in agriculture, used to manufacture agricultural tools and sprinkler equipment; in other industries, used to manufacture container packing containers, small boats, sporting goods, suitcases, shoe heels, In other industries, it is used to make container packaging containers, boats, sporting goods, suitcases, shoe heels and baby products; in the aviation industry, it is used to make aircraft parts.

3, ABS is widely used in the machinery and instrumentation industry to manufacture gears, pump impellers, bearings, handles, pipes, motor housings, instrument housings, instrument panels, instrumentation boxes, water tank housings, battery tanks, refrigerator and freezer linings (cold-resistant grade), storage tanks, etc.

4, in the automotive industry, it can be used to make fenders, handrails, hot air conditioning ducts, heaters, etc..

5, in the military and defense facilities also have important uses.

6、ABS can be used to replace metal after plating to make nameplates, decorative parts, etc.

7、ABS can be used for structural foam, flame retardant plastic, and reinforced plastic. It is blended with PVC, PUR, PC, PSU, etc. to make polymer alloy with excellent performance.

6. Polycarbonate (PC)

Commonly known as bulletproof glass, is a non-toxic, tasteless, odorless, transparent material, combustible, but can be self-extinguishing after leaving the fire.

Polycarbonate characteristics

With exceptional toughness and hardness, it has the best impact strength among all thermoplastic materials

Excellent creep resistance, good dimensional stability, high molding accuracy

Good heat resistance (120 degrees)

Disadvantages are low fatigue strength, high internal stress, easy to crack

The wear resistance of plastic parts is poor

Typical application areas:

Electrical and commercial equipment (computer components, connectors, etc.), appliances (food processors, refrigerator drawers, etc.), transportation industry (front and rear lights of vehicles, instrument panels, etc.)

7.PC+ABS (PC+ABS alloy)

Combined PC (engineering plastic) and ABS (general-purpose plastic) are the advantages of both and improve the performance of both. Contains ABS and PC chemical composition, with ABS good fluidity and molding processability, PC impact resistance, and resistance to hot and cold cycle changes.

PC+ABS alloy characteristics

Can be dispensed with glue mouth / large water mouth injection mold design

The surface can be sprayed with oil, plating, metal spray film

Typical application range:

The material is commonly used in hot runner molds and has been used in more and more consumer communication products, such as cell phone cases/computer cases.

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