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Gel
coat makes fiberglass reinforced products attractive and practical.
Technically, it is a surface coating of pigmented polyester
resin which gels against the mold surface and cures with the
structural laminate. It faithfully reproduces the mold surface,
imparts color, and protects the reinforcing fibers from external
elements. In many cases, the surface treated with gel coat
is the only part of the structure that can be seen. To the
user, it is simply a reinforced plastic. Resins, fillers,
pigments and promoters are carefully selected and formulated
to develop the quality and surface appearance needed to make
the product durable and saleable. Customer acceptance of the
product can depend entirely upon the care and handling of
gel coat.
Several
key points must be considered if the gel coat surface is to
perform to its capabilities:
- Gel
coat make-up and realistic performance expectations.
- Proper
equipment, suitable for the specific application.
- Skill
of the spray operator: proper training and experience.
- General
spray methods.
- Special
spray methods for specific parts according to size and shape.
- Problems
and solutions.
The
various components of the gel coat system influence the quality
and working properties needed to provide the performance characteristics
for the intended end use.
The
Resin: The basic ingredient of gel coat is the polyester
resin system, which provides the chemical composition that
determines the chemical and physical properties of the gel
coat.
Orthophthalic:
Orthophthalic anhydride is used in general purpose resins
where superior (anhydride or acid) resistance to water and
chemicals are not of prime importance. For years it has been
one of the raw materials incorporated into polyester resins
and is still available but is often replaced by the more durable
isophthalic types of resins.
Isophthalic:
Reacted into the resin, isophthalic acid provides greater
levels of water (acid) and chemical resistance than does orthophthalic
anhydride. This is especially important in the manufacture
of boats, shower and bath enclosures. Greater chemical, weather
and corrosion resistance with a higher degree of flexibility
are the immediate benefits when isophthalic acid replaces
orthophthalic acid in the resin.
Neopentyl
Glycol: When the highest possible quality and performance
levels are required, neopentyl glycol is reacted into the
isophthalic resin in the proper mole ratio. This raw material
can produce weathering and chemical resistance capabilities
superior to resins formulated with other common glycols.
Pigments:
Pigments and their quality determine both the color we see
and the color integrity, which simply means the ability of
the color to resist change from exposure to various environments.
Extenders/Fillers:
Extenders provide the gel coat with proper spraying characteristics
and influence the cured physical properties.
Thixotrope:
Most of the viscosity comes from the thixotrope. Its purpose
is to hold the gel coat on a vertical surface, yet allow easy
breakup for good spraying properties.
Accelerators/Promoters:
Regulate gel and cure characteristics of the gel coat. Peroxide
initiates the gel coat cure. Although commonly referred to
as catalysts, peroxides are initiators.
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