Orthophthalic Is also referred to as ortho or General Purpose Polyester (GP) was the original
polyester developed. It has the lowest cost and is still very widely used in FRP industry.
It is commonly used
applications where high mechanical properties, corrosion resistance, and thermal stability
are not required.
Although the upper temperature limit is only 50oC, it performs satisfactory in water and sea
water. It is
normally not recommended for use in contact with chemicals.
Main Applications are hand lay up, RTM, putties, roofing sheets, etc.
Often referred to as ISO, it is improved polyester. It has a slightly higher cost, improved strength, thermal stability(55oC) and mild resistance to corrosion conditions. Improved resistance to water permeation has prompted its use as a gel barrier coat in marine applications. Improved chemical resistance has led them to extensive use in underground petroleum tanks (in gas stations) with satisfactory service life. They are also used in salts and mild acids and in automobile and marine applications, corrosion resistant tanks, etc.
Even further improved polyester, it is bisphenol chlorinated, or a combination of polyester and epoxy. Its curing, handling and processing characteristics are those of polyester, and it exhibits higher test results in corrosion temperature resistance and strength and has higher cost. Modifications of the molecule have produced even higher properties.
Gel coats are prepared from a base resin and additives. The base resin can be polyester,
vinyl ester, phenolic
or epoxy. Additives are thixotropic agents, fillers, pigments and other. The gel coat, as
the name implies, has a
gel texture. This makes the gel coat capable to “stay” on vertical surfaces of moulds
without draping. It is
placed first in the mold, so it becomes the outer surface of the construction. It is used to
replace paint, for
cosmetic purposes, and to protect from the environment.
Gelcoats have a good gloss, resistance to cracking during re-molding and have low porosity finish Gelcoats are used in automobile and marine applications, sanitary wares, etc.