Thermoplastic resin is a polymer compound that becomes soft or fluid when heated and then returns to its original solid state when cooled. This compound is used in molding processes like injection molding, which requires the raw material to be in a liquid or plastic state to fill the mold completely. When cooled, the resin or polymer solidifies to form the finished product, which is then ejected or dropped out of the mold. The resin is used to manufacture many consumer products.
The use of thermoplastic resin dates back to the mid 1800s, with celluloid being the first commercial example. The most commonly used contemporary compounds are polyethylene, polypropylene, polyvinyl chloride, polyester, polystyrene, and polycarbonate. All these raw materials share the common characteristic of a long chain molecular structure with no cross-links. This unique molecular feature of thermoplastics allows the resin to become fluid when heated and reform to its original state when cooled.
Injection molding is the most common use for heat activated resins and is the production process of choice for mass-quantity products that feature intricate detail and produced. The molding process makes use of precision-machined molds with very small internal tolerances and requires the raw material to be in a very plastic or fluid state to correctly fill the mold. Thermoplastic is ideal for this application, as it may be completely liquefied when heated to the correct temperature. This allows for the mold cavity to be completely filled to correctly form any intricate detail incorporated in the product design.
Thermoplastic resin and its associated molding processes are the most common means of mass producing polymer products such as sound system cabinets, toys, kitchen appliance casings, wrapping film, automotive parts, and computer cabinets. One of the best examples of a mass produced product are Lego® blocks, which are turned out in production runs often numbering several hundred thousand units. The audio cassette was another example.
The use of this resin is not limited to high-pressure injection molding processes; several common household products are produced by extrusion or blow molding techniques. These include food wrapping films, stretch fabric used in clothing, and drinking bottles. All of these processes are, however, perfectly suited to producing high volumes and levels of uniformity at low costs and all employ the heat softening characteristics of thermoplastic.
The compound is also particularly well suited to encapsulation processes due to its excellent flow characteristics. These processes are commonly used to enclose or encapsulate the windings of electrical equipment where no air pockets or areas of non-adhesion can be tolerated. The resins have been designed to expand at the same rate as the steel or copper components they enclose to maintain the structural integrity of the encapsulation.