Thermoplastic injection moulding is an extremely popular method of manufacturing plastic parts and components for all kinds of applications, from packaging to car parts; medical items to toys. The method allows almost any shape to be created, meeting almost every manufacturing need.
In order for the method to be flexible, as well as highly reliable, a range of thermoplastics is necessary. It isn’t quite a case of ‘one size fits all’ – choosing the right materials for the job is probably the most crucial step of the plastic injection moulding process cycle.
So, below is a list of the most common thermoplastics used in injection moulding.
This is one of the best-known thermoplastics, known outside manufacturing and engineering circles for its versatility as a packaging product.
It has a variable crystalline structure that allows for a vast range of applications. Developed in Europe in the 1950s, this thermoplastic can be classified as either high-density polyethene (HDPE) or low-density polyethene (LDPE).
Both variants have high tensile strength, impact resistance, moisture resistance and recyclability. Higher density versions tend to be more rigid and heat resistant, making it suitable for,
- food containers
while the lower density alternative tends to be used more for,
- plastic bags
- and films.
This thermoplastic comes into its own when a strong, transparent material is required. It also has excellent impact resistance, making it suitable for,
- bullet-proof glass
- reinforced greenhouse panels
It can undergo high levels of stress without cracking or breaking. Other uses for polycarbonate include,
- DVD discs,
- eyewear lenses and
- mobile phone components
Polycarbonate is easily worked, moulded and thermoformed, making it a popular material in the construction industry. They are ideal for,
- greenhouse panels,
- conservatory roofing and
- porch or outhouse windows
Acrylic is popular for its attractive finish and its versatile nature. It can be moulded in a wide variety of colours too. Acrylic is rigid with strong impact resistance. Acrylic sheeting can often be used as an alternative to glass in such applications as,
- fish tanks
- motorcycle helmet visors
It is also frequently used as a material for arts and crafts projects, due to its transparency and aesthetic appeal. Other uses include shop signage and automotive lighting, due to its high resistance to adverse weather conditions and ease of cleaning and maintenance.
Polyamide is better known as nylon and is a common material used in fabrics and sports equipment such as nets. It is extremely tough and resistant to wear and tear. Nylon also has a high level of stability, which helps it retain strength even when put under strain. It is highly resistant to other external forces too, including abrasion, chemical corrosion and impact. As well as clothing, nylon is also used in a wide range of applications, including,
- sports equipment
- medical products
- industrial components and within the automotive sector
High Impact Polystyrene is very popular, thanks to its tough nature and resistance to impacts and heavy knocks. It is created by modifying crystal styrene with rubber, which gives it its impressive resistance to impacts. It is often used to protect assets, such as parcels in transit or valuable machinery and is low cost and easy to produce. It is non-toxic and so can be produced to fit FDA grades and be used as containers for consumable goods. While polystyrene is flammable, flame-0retardant versions can be produced, along with high gloss grades that give a top-quality finish.
Another common thermoplastic, polypropylene (PP) is very flexible, rendering it perfect for such applications as athletic clothing, rugs and car parts that need to be bent into position. It is safe to be used as food containers and does not break down easily when placed in contact with water, acids and detergents. So, it can be reused multiple times, reducing waste and resulting in a more eco-friendly product. Polypropylene has a high melting point and high resistance to cracking and stress. It has been compounded for a wide range of products and is extremely versatile.
Acrylonitrile Butadiene Styrene (ABS)
This opaque thermoplastic is a terpolymer, made up of the three polymers, acrylonitrile, butadiene and styrene. The combination produces a flexible, very light material that can be moulded into a plethora of everyday items and components for use in everyday life. ABS can be modified to produce the exact levels of impact resistance, toughness and heat resistance that the manufacturer needs by moulding it at a high or low temperature. ABS is used commonly in drainpipe systems, automotive parts, musical instruments and sporting equipment, such as,
- golf club heads
- tennis rackets
It is also a key component of the perennial children’s favourite, LEGO.
Another commonly known thermoplastic, used frequently in the production of clothing, bed wear and other household fabrics. However, polyester is also used in electrical, medical, automotive and packaging applications. Industrial uses include,
- conveyor belt fabrics
- seat belts
- coated fabrics
- plastic reinforcements
Polyester offers excellent chemical resistance, dimensional stability and a high toughness-stiffness balance. Polyester fabrics are also highly stain resistant. However, it can also be subject to moisture susceptibility and poor thermal qualities, which can make drying times a critical concern.