Following up on the last blog post.

Today we introduce three injection molding plastics: PC, PE, POM

PC (Polycarbonate)

Polycarbonate is a naturally transparent, strong, and resilient material. Its characteristics are similar to PMMA,

but PC maintains its physical properties over a wider temperature range. After coloring, PC retains its color and strength over time.

Advantages and Disadvantages of PC

PC is highly durable, being 250 times stronger than glass.

With its predictable and uniform mold shrinkage rate, this injection molding material offers precise dimensional control.

PC plastic is also lightweight and possesses excellent optical properties to support light transmission.

Because it contains BPA, injection molded PC is not recommended for food preparation or storage.

It also requires higher processing temperatures, which can increase molding costs. PC is also not scratch-resistant.

Applications and Grades of PC

PC is used in mechanical protective devices, transparent or colored windows, diffusers, light tubes for Light Emitting Diodes (LEDs), and transparent tubes.

This material can also be used to produce transparent molds for polyurethane and silicone castings.

PC can be filled with glass and compounded with ABS to improve impact resistance.

Some grades contain relatively small percentages of stainless steel fibers.

PE (Polyethylene)

PE is the most commonly used plastic in the world and primarily comes in three types:

• High Density (HDPE)
• Low Density (LDPE)
• Polyethylene Terephthalate (PET)

PE is the only commercially available polymer that can be selected based on its density, which controls other material properties, making this measurement significant.

HDPE and LDPE both have useful properties like chemical resistance, but they differ in hardness, flexibility, melting point, and optical transparency.

PET plastic is not defined by density.

Advantages and Disadvantages of PE

HDPE, LDPE, and PET are all low-cost plastics resistant to moisture and chemicals.

LDPE is softer and more flexible than HDPE, while HDPE is an opaque material. PET, like LDPE, can be transparent like glass.

Engineers and designers appreciate these materials because they offer various choices in optical clarity and other characteristics.

PE plastics are limited by poor UV resistance and cannot withstand high operating temperatures.

HDPE parts thinner than 0.020 inches are difficult to mold. Achieving tight tolerances is challenging for injection molded LDPE.

PET absorbs moisture extensively and requires resin drying, increasing production costs.

Applications and Grades of PE

PE plastics are known for their use in milk bottles (HDPE), plastic films (LDPE), and water bottles (PET), but these products are not injection molded.

They are made using a different type of molding called blow molding. 

Examples of injection molded PE include children's toys, toolboxes, wire and cable insulation, and medical device components.

PE plastics have numbered grades, with higher numbers typically indicating higher density.

For example, HDPE 500 has a higher density than HDPE 300. Both grades have higher densities than LDPE, which also uses a numerical grading system.

POM (Polyoxymethylene)

POM is an engineering plastic, also known as acetal.

It can be injection molded into parts requiring low friction, high stiffness, and excellent dimensional stability.

POM plastics are naturally opaque and white due to their highly crystalline structure.

Advantages and Disadvantages of POM

Injection molded POM combines excellent rigidity, thermal stability, and a low friction coefficient.

It also has low water absorption and good chemical resistance.

There are two main types of POM plastics to choose from: homopolymers and copolymers.

This allows engineers and designers to select acetal materials with different characteristics.

POM, in its pure form, has low impact strength and a very high coefficient of thermal expansion.

Mold shrinkage rates are relatively high, and acetal does not resist UV rays. Homopolymer POM plastics offer higher hardness and tensile strength.

However, all POM plastics (homopolymers and copolymers) do not meet fire resistance standards like UL 94.

Applications and Grades of POM

Due to its low friction coefficient, injection molded POM is suitable for bearings, gears, conveyor belts, and pulleys.

Other applications include fasteners, eyeglass frames, cutting tools and firearm parts, locking systems, and high-performance engineering components.

POM is available in grades reinforced with glass fiber or mineral to enhance strength and stiffness.

Compounds enhanced with both materials provide an excellent balance of mechanical properties.