Prassas Metal Products, inc.
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BASICS OF COIL COATING

The paints used for coil coating are made up of pigment, resins, and solvents. Pigments provide the color. The resin binds the coating to substrate metal and provides the paint characteristics, such as durability, weather resistance, flexibility, and is the “glue” holding pigment particles to the substrate. The solvent is evaporated during the curing process.

Resin & PIGMENTS

Resin is a material used to hold pigment particles in suspension and attach them to the painted surface. Degradation of the resin system, characterized by chalking, can be caused by harmful ultraviolet (UV) light rays from the sun, acid rain, pollution, salt spray, and other weather-borne chemicals. When a coating chalks, resin particles at the surface loose adhesion and take on a powdery white, chalky appearance.

Pigment is an insoluble, finely ground material that gives paint its color and its ability to hide irregularities by filling and leveling. Colors can fade or change as a result of the effects of environmental elements, such as UV light and weather.

Solvent is any liquid that can dissolve a resin and make it fluid enough to apply to the steel sheet surface. After paint is applied, the solvent evaporates in the oven, leaving the resin and pigment solids bonded on the painted surface where they can protect it from the environment and give it an attractive appearance.

Polyesters

This resin type has widespread use and is available in a broad spectrum of colors. It can be applied to a wide variety of steel sheet substrates.Polyesters offer a hard, scratch-resistant finish and a wide range of gloss (5 – 80 degree), but are prone to chalking when exposed to UV light. Polyesters are a broad group of chemical compounds and have diverse characteristics and can be tailored to fit many end uses. They can be developed with good weathering properties, but generally not equal to the extended SMP or PVDF coatings. Polyesters in general are cheaper paints, but prices can vary greatly depending on color and the required characteristics. Low-cost polyester resin makes them suitable for partnering with inexpensive organic pigments, thereby offering a wider color spectrum.

Silicon Modified Polyester

Silicon Modified Polyester systems offer a wide range of color, improved color and gloss retention, along with superior weathering resistance to chalking and fading. When several different metal oxides are fused at high temperature, they become a new class of pigments called complex metal oxides or complex inorganic color pigments (CICP), or ceramic pigments. It takes high temperatures to create CICP’s, so it takes a lot of energy to break them down. The UV, heat, moisture, and chemicals (ozone, acid rain, industrial pollutants) that break down organics or in-organic pigments, have little or no effect on them. Some CICP’s have the ability to reflect high percentages of light energy from the non-visible infrared spectrum, leading to development of today’s "Cool Roof" technology. CICP’s with this ability have been developed to make paints that can reflect radiation outside the visible spectrum, allowing darker colored roofs to remain as cool as lighter ones. The main drawback for the CICP’s are their limited color range, largely earth tones, but can be mixed with organics and non-organics to extend their color range.

The 40-year SMP warranty + Cool Roof technology paint systems contain ceramic infrared reflective pigments, special pigments designed to reflect infrared energy, while they absorb visible light energy. They maintain color and stay much cooler, lowering cooling costs, reducing peak energy demand, and helping to relieve the urban heat island effect.

PVDF (KYNAR)

PVDF (Fluropolymers): This paint system combines ceramic pigmentation with polyvinylidene fluoride for superior, long-lasting performance. The PVDF system is respected for its durability and resistance to chalking and fading, chemical resistance, and color retention. The carbon-fluorine bond is one of the strongest chemical bonds known. Key to the chemicals toughness is the bond between carbon and fluorine, the strongest possible polymeric connection. The PVDF resin is similar in respects to Teflon, the popular non-stick coating. This leads to most environmental pollutants washing off in the rain. It is also the reason that adhesives do not stick to it. Paint using this resin is usually offered in a medium or low gloss finish, with excellent weathering and color retention characteristics. The PVDF system meets with both Kynar 500/Hylar 5000 specifications and contains 70% Kynar 500 or Hylar 5000 resins.

PVDF’s are widely used in architectural applications and are more expensive than polyesters and SMP’s. PVDF resin has superior chalk resistance and gloss retention, excellent stain and chemical resistance, with exceptional adhesion and forming characteristics. However, it is softer than both polyesters and SMP’s, so while highly formable, also relatively easy to scratch during transport or installation.