Both the high impact, medium impact and crystal versions of polystyrene are injection molded at Rebling for a variety of applications. Typical uses for this versatile material are compact disc cases, packaging applications and household appliances. Like other amorphous thermoplastics, Polystyrene has predictable and uniform material shrinkage in all directions which minimizes warpage of plastic injection molded parts. Another benefit of this uniform shrinkage characteristic is that it enables the molder and mold maker to more accurately predict the final dimensions of the molded part.
In the natural state, Polystyrene is a clear transparent material. The term "crystal styrene" is generally used to describe this transparent grade which has light transmission properties approaching 90 percent. In this state, polystyrene is somewhat brittle, but with the addition of rubber compounds, the impact resistance is dramatically improved while tensile strength and stiffness are reduced. This blended material is commonly referred to as High Impact Polystyrene or HIPS. The HIPS material however is no longer clear and transparent.
Flame retardant grades and high gloss grades of polystyrene are also molded at Rebling. The choice of available color concentrates for this material is almost limitless. The resin identification code for Polystyrene is:
Properties of Polystyrene plastic
Although polystyrene can be supplied with UV inhibitors and colored to minimize UV absorption, this plastic injection molding material is not recommended for continuous outdoor use. Intermittent and short term outdoor usage is acceptable, but the material is best suited for indoor applications.
Polystyrene is chemically resistant to water, alkalis and dilute mineral acids, but is attacked by organic solvents such as esters, ethers and ketones.
Crystal polystyrenes typically have heat deflection temperatures at 264 psi in the range of 155°F to 200°F while specialty grades of this material can be up to 210°F. The tensile strength of the crystal grade material ranges from 5000 to 7000 psi while the impact grades range from 3000 to 4000 psi. The rubber impact modifier is responsible for this tensile strength reduction. However, the notched impact strength for the HIPS material is typically 2.5 ft-lbs./inch; a factor seven times higher than the crystal version.
The flexural modulus of the crystal grades is generally 450,000 psi dropping to 250,000 psi for the high impact grades. The flexural modulus term is an indication of the stiffness of the material, with higher numbers indicating higher stiffness.
Secondary Operations for Polystyrene plastic parts
Polystyrene is readily decorated using the pad printing and hot stamping processes at Rebling. Vacuum metallizing, wherein a thin layer of aluminum is applied, can also be provided. Post molding machining operations including drilling, tapping, turning and milling of the high impact grade version is also routinely handled by Rebling.
Polystyrenes are ultrasonically welded at Rebling. Excellent joint strength is achieved when both parts to be welded are made from polystyrene.