Cast Polymer

While sports parts, yacht hulls and bridge decks can be the centerpieces of the composites industry, the fabrication of cast polymer bath and kitchen fixtures is a vital and lucrative segment. For over half a century, kitchen and bath manufacturers have been combining resins with a variety of fillers, additives, pigments and performance enhancers to create glossy, gorgeous products in many colors and patterns. The new home and remodeling markets depend on the variety of vanity tops, bathtubs, shower stalls, kitchen countertops and other components produced with composites.

Achieving the Certified Composites Technician (CCT) designation helps industry professionals markettheir knowledge and expertise. The Fall 1020 issue of MasterCast Connection included three technical questions for cast polymer professionals as part of its “Ask the Experts” column. Professionals who’ve earned their CCT-Cast Polymer designation should be able to answer these questions. 

Why is the temperature of the raw materials important to matrix performance?

Temperature can be your best friend or worst enemy. Temperature of the raw materials used to make a matrix affects the gel time, cure time, de-mold time, viscosity, volume, and filler loading of the system. Every 10° C can significantly affect the resin performance.

High temperature shortens the gel time, cure time and de-mold time. It lowers the viscosity, increases the filler loading and volume. Lower temperature lengthens the gel, cure and de-mold time, makes a thicker mix, and decreases the volume and amount of filler that can be used to give the same veining aesthetics. -- Contributed by Ken Lipovsky, Reichhold

What is the effect of particle packing on filled polyester matrix?

Proper particle packing in a matrix can lead to a reduction in viscosity (increased matrix flowability) and decreased resin demand.

Coarse fraction weight % range of 50-70%
Median particle size ratio range of 3.5- 9.0
> 150 phr level of ATH (40/60 ratio - resin/ATH)
Increased FR resistance with increased fine fraction

In solid surface applications, as fine fraction increases settling, resistance increases. Translucency decreases as fine fraction increases (more opaque). -- Contributed by Gary Rex, Huber Corp.

What is crazing?

Crazing creates stress in the gel coat, which in turn causes cracking. Crazing occurs when a gel coat film is too thick or cures too slowly, or if a mold-release agent is defective. An improperly prepared mold surface brought about by such actions as waiting too long between re-waxing can also create this problem.  -- Contributed by Glenn Wigington, HK Research