Coil Paint and Metal Embossing
Coil Paint and Metal Embossing and ‘special additives’ in the paint are finishes that are becoming increasing popular in the coil coating industry as they:
- Provide interesting effects instead of just a plain painted surface
- Provide extra character to the finished product to make the product more visually appealing
- Impart special properties to allow the painted steel / aluminium to be used in a wider range of applications
These finishes can require extra equipment; such is needed to apply a pattern (metal embossing), or simply paint with special additives to give a different appearance, like metallic pigments.
Quite a number of systems, primers and top coats, have been developed that result in appealing visual effects or differing properties. Unlike pattern coating where special rolls are needed, these systems can be applied using the normal coater head equipment included on coil lines.
- Metallic Paints – these are especially visibly appealing. Special pigments, using aluminium powders or mica flakes are added which give this metallic appearance.
- Wrinkle Finish Paints – These are again especially formulated by the paint companies but are readily applied in normal 2 roll coater heads. The wrinkled surface has the effect of increasing the coefficient of friction, making it safer for roofing contractors. Two levels of ‘wrinkle’ can be supplied; one at a coarse wrinkle, the other a micro wrinkle. The coarse wrinkle has the additional effect of increasing the surface hardness so that damage resistance is improved. The micro wrinkle has a side effect of giving a low gloss (matte) finish and is often used instead of controlling gloss with other matting agents in the formulation.
- High Build Primers – These systems are used where extra corrosion resistance is needed. Instead of the 5um applied, normally extra resistance can be achieved by applying 25um of primer. These primers are commonly polyurethane based. The polyurethane top coat is also an excellent performer with respect to colour and gloss retention externally. Another high performing coating, PVDF, is also used in conjunction with high build primers. Logically, if a coating is to perform for a long time as a barrier it also needs to retain its appearance over that time.
- Plastisol – This is liquid polyvinylchloride (PVC). This is another means of achieving higher corrosion resistance through increasing the film thickness. As with high build primers the extra thickness forms a barrier to the environment. The thicker dry film thickness is always embossed at the exit of the oven with water cooled rolls, while the film is still approximately 180 degrees C. Embossing is used here to guarantee that the surface is uniform. The embossing is usually a leathergrain pattern.
Unlike the embossing carried out on plastisols, the base metal is embossed completely. (The metal is actually deformed). The purpose of this embossing is less about visual appearance and is more about increasing the strength and stiffness of the base metal, such that lighter gauge material can be used. The most frequent pattern used for metal embossing is a stucco pattern which in addition to adding strength and stiffness reduces reflectivity. Other patterns like diamonds or leathergrain can be used.
Coil coating provides an opportunity to produce a wide range of different visual effects.
These effects can be used by producers to differentiate their product offer within the market to win and maintain market share.
Although some of these effects can be achieved by utilising specialty paints, others require special equipment to be incorporated into the line. It is important when designing a line that consideration be given to the products that are to be offered so that this equipment, or provision for it, is made at installation.