Topcoats are generally a transparent or translucent or opaque layer of paint applied over the primer or intermediate coat. This is the coat that is directly exposed to various environmental conditions and factors such as sunlight, water, chemicals, pollutants, microbial, and the wear and tear due to particulate abrasion from the air. For this reason, topcoats need to be very robust with high impermeability and a very compact structure.
The choice of chemistry of topcoat is guided by the following factors:
- Exposure conditions
- The substrate to be coated
- Cost economics
Exposure conditions greatly influence the choice of chemistry of the topcoats. The Major Categories of topcoat chemistries are:
- Alkyd: These are topcoats based on alkyd resin. Generally these topcoats are moderate in chemical, mechanical, UV resistance.
- QD/Modified Alkyd: These are topcoats based on quick-drying modified alkyd resin. Generally they perform better than alkyd topcoats.
- TPA (Thermoplastic Acrylic): These topcoats are quick-drying, semi-glossy in finish, and better in performance compared to QD / Modified Alkyd.
- Chlorinated Rubber: These topcoats provide excellent chemical resistance.
- Silicon: These topcoats are for excellent heat resistance properties.
- Acrylic Polyurethane: These topcoats are cross-linked products, the extent of cross-linking can be varied to offer various levels of resistance for: chemical, mechanical, abrasion and UV resistance.
- Polyester Polyurethane: These topcoats offer excellent acid resistance and UV resistance.
- Epoxy: These topcoats offer excellent chemical, mechanical, and abrasion resistance. The degree of resistance can be varied by the choice of hardener ranging from polyamide, polyamide amine, polyamine, phenylamine, phenylalanine, and also cycloaliphaticamine. Other, high functional epoxies can also be chosen such as Novolac epoxies for even better chemical resistance usually required for tank lining coatings.
- Vinyl Esters: These topcoats offer excellent chemical resistance. It is generally used for vessel lining or for structures that are exposed to aggressive chemical environments.
How does topcoat benefit your paint?
Topcoats are the topmost layer of paints that not only provide the protection against various substances in the air, but also provide the appeal to the surface. It provides a barrier to entry to corrosion causing factors like water and oxygen and also to manual abuses from handling. Additionally, it reflects the sun rays, thus providing extended retention of appeal to the surface. The extent depends upon the type of topcoat and area of exposure. Topcoats provide mechanical strength to the coating but also provide excellent resistance to loss in gloss, UV, water, chemicals.
Is a topcoat always required?
In the Unicoat Paint system, the paint acts as a primer as well as a topcoat. In the case of a multi-coat system, a topcoat is essential as each topcoat has a specific function.
Does topcoat benefit the paint to be waterproof?
Yes, to some extent topcoats offer water resistance properties. But, for complete waterproofing various factors are involved such as the surface preparation, substrate, primer, type of topcoat, the thickness of paint, amount of dampness or water exposure, type of finish required, etc. GP has specific products that have been designed for the purpose of waterproofing.
Can topcoats be used as base coats?
No, topcoat and basecoat should not be used interchangeably as both have different properties and offer different advantages to the paint and the surfaces.
Monocoat, Unicoat: This is the latest trend in industrial paint applications where performance requirements of both primer and topcoat are provided through a single robust coating. This coating offers corrosion protection, condensation resistance along with gloss & color retention as well as chemical resistance. To combine these properties, these products use very special resin technologies that are developed in house at GP’s lab. For more information, please contact the nearest Grand Polycoats sales office.