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History of Powder Coating

HomeHistory of Powder Coating

Paint and lacquers

The Stone Age cave paintings at Lascaux in southern France and Altamira in northern Spain are examples of the earliest works of art in human history.

Ceiling painting from the Altamira cave.

Source: www.deutsches-museum.de

The colors made of animal fats and colored earths, as well as lard as a bonding agent and ochre as a pigment used in those days, are in principle similar to today’s methods. Animal products could attain no particular place as a raw lacquer material, although the word “lacquer” is certainly related to shellac, the resinous metabolic product of a scale insect found in India. The word, which comes from the Sanskrit, means “100,000” and represents the large number of animals required for the winning of resin.

The oldest lacquer work from China (500 B.C.) was developed in East Asia to its highest blossoming period and achieved perfection in Japan, are much later than the around 15,000 year old Stone Age paintings. The Japanese made their lacquer from the bark of the lacquer tree, and it was applied in 20 to 30 coats. Works of the highest artistic level were made.

These lacquer wares reached Europe through the Portuguese, who first landed in China in 1515. The Old World began to take an interest in the development of lacquers and by 1610 the “Compagnie van Lackwercken” came into being in Amsterdam. Further lacquer plants followed in other countries.

Knowledge of the then almost 2,000 year old Chinese art reached Europe in the 16th century. The strong demand on the one hand, and the sensitivity of the lacquer tree-which resisted transportation-on the other, soon had a fruitful effect on the development of local lacquers made of easily available raw materials. Plants remained the most important basic raw materials for manufacturing lacquer, which by the beginning of the 20th century demanded quicker processing technologies and raised quality demands for innovative painting materials.

The Modern Era of Powder Coating

The history of powder coating begins in the late 1940s and early 1950s, at a time in which organic polymers were still being spray coated in a powder form on to metallic bases. Dr. Erwin Gemmer, a German scientist, developed in those days the fluidized-bed process for the processing of thermosetting powder coatings, and registered an appropriate process patent in May 1953. Between 1958 and 1965, literally all powder coatings, generally only functional applications with a film thickness of 150 µm to 500 µm, were processed by means of fluidized-bed application. Electric insulation, corrosion and abrasion resistance were in the foreground. The coating materials in those days comprised nylon 11, CAB, polyethylene, plasticized PVC, polyester and chlorinated polyether, among others. At the same time, thermosetting epoxides, e.g. for dishwasher baskets (PVC), for heat insulation (epoxide), for boat accessories (nylon) and metal furniture (PVC, CAB). It was the firm of Bosch that developed the basic type of expoxy resin powder when searching for a suitable electric insulation material.

The high film thicknesses for numerous applications, and the technology of electrostatic processing of powder coating, which was developed shortly after in the U.S.A., and was used commercially between 1962 and 1964 in the U.S.A. and Europe, did not allow the fluidized-bed process to become significant. With the electrostatic spray-guns made by the firm of Sams for electrostatic application and which gave rise to the term “Samesizing”, this hurdle was also overcome. Between 1966 and 1973 the four basic types of thermosetting resins, which are still defining today, were developed and commercially marketed: epoxy, epoxy polyester hybrid, polyurethane and polyester (TGIC). The number of powder-coating plants in Germany alone rose from four in 1966 to 51 in 1970.From the early 1970s, powder coating then began its march of triumph worldwide, even though the growth of the powder coating market was until 1980 initially slight. The plants up to that time were expensive, the film thicknesses too high for commercial use, color-change problems and high curing temperatures greatly limited the color tone, effect and substrate diversity.

From the early 1980s, powder coatings have developed worldwide through continuous growth, which, driven forward by continuous innovations in the raw materials available, improved formulation know-how and advances in application technology and the development of new applications (e.g. MDF and coil coating) and not least due to the increasingly restrictive environmental-protection regulations, will also be constantly continued over the decades to come.

The Modern Powder Coating Process

Application and Equipment

Powder is usually applied with a spray gun. Most guns are similar in their function of spraying the powder. Each gun has a control unit that regulates the voltage being generated and rate at which the powder is delivered from the hopper

Spray Booths and Recovery

Powder booths are very similar, but use two distinct types of recovery equipment, cartridge filters or a cyclone separator. Each style is particularly suitable for a different type of application. To select the appropriate system, you should consider the production size, finish quality of the desired coating, the number of different types or colours of powder being used, and the frequency with which they are changed.

What Type of Powder is Used?

Powder is a dry coating. Instead of being dissolved or suspended in a liquid medium, such as solvent or water, powder is applied in a granular form. Powder coating is created by blending the various components (binders, resins, pigments, fillers and additives) and processing them through an extruder into a continuous mass. This homogenous mass is cooled and broken into small chips, which are then ground into the powder. Each powder particle contains within it the necessary components for reforming into the finished coating. After the powder is applied to the part, typically using an electrostatic spray process, the part passes through an oven and cures, melting into a smooth film on the surface of the part.

How is the Powder Applied?

The application process involves applying a charge to the dry powder particles and spraying them onto a grounded substrate. The substrate, or part, is typically grounded through the conveyor or hanger holding the part. The powder, once attracted to the part, is then held on the surface until it is melted and cured into a smooth coating film in the bake oven. The spray process takes place inside a booth designed to contain the over sprayed powder and makes it possible to collect and reclaim it for re-use. The reclaimed powder is mixed with a proportionate amount of fresh virgin powder for reuse, achieving consistent results and up to 98% material utilization.

Why Powder Coat?

Over the past decade, powder coating has been increasingly accepted as the preferred finishing process.  The reasons for this conversion from wet to dry powder can be attributed to three major forces:

Economy

 1) Material utilization is much higher with powder, making your material costs much lower. 92%-98% of the powder you buy will be applied to the parts you are finishing versus an average of 60% with an electrostatic liquid system (The other 40% is waste and must be disposed of).
2) Since most of the material is used on the part, there is very little waste to be disposed of. Powder is not considered hazardous waste, so the cost of disposal is minimal.
3) Air used to exhaust the powder spray booth is returned directly to the plant, eliminating heating and cooling costs for the make-up air required when air is vented outside the plant.

Excellence

1) The cured powder finish is less susceptible to damage than a liquid finish. There is less need for repair work on the finished item. This results in the need for much less elaborate packaging saving time and cost on re-working and packaging.
2) Epoxy, acrylic, and hybrid powders provide excellent adhesion and harness for improved resistance to chipping, abrasion, corrosion, and chemicals;  Ant it is flexible enough to be formable without cracking
3) Polyester powders provide additional advantages in ultraviolet and weathering resistance.

Ecology

1) Stringent regulations are being aggressively enforced in an effort to control air pollution and hazardous waste disposal.
2) Powder coating eliminate solvent fumes and VOC’s from spray booths and oven exhausts that pollute the air.
3) Potentially toxic sludge and water that can contaminate the earth and must be disposed of as hazardous waste is eliminated.