Thermoset Solution Fluorocarbon Coil Coatings

Article From: Products Finishing, , from Keeler & Long, Inc.

Posted on: 1/1/1998

New coating offers architects and designers more flexibility and color options...

The development of thermoset solution fluorocarbon resins and coil coating paints has been deemed the most significant liquid coil coating development of the past 30 years by the National Coil Coaters Association past president, Dr. Frank Graziano of Material Sciences Corp.

Fluorocarbon resins and paints are not new to the coil coating industry. The older, first-generation thermoplastic dispersion-types have been around for approximately 30 years. They have exemplary performance with respect to exterior weathering properties, specifically color and gloss retention. Because of these properties and performance, these older fluorocarbon coatings have become the choice of architects and specifiers. Therefore, those who came onto the fluorocarbon scene somewhat later with thermoset solution fluorocarbon offerings owe a great debt to the pioneers who established overall fluorocarbon superiority.

A comparison of the composition of the two systems indicates that the older technology is a thermoplastic dispersion that on a coil coating line cures by fusion. That is, under heat, the resin melts and flows uniformly to form a paint film. The most desirable and well-recognized characteristics of fluorocarbon coatings are their excellent weatherability and durability. The primary structures that impart these characteristics in both the PVDF and FEVE chemical structures are essentially the same. In order to obtain the three essential characteristics for a PVDF coating, namely pigment dispersability, adhesion and flexibility, this system requires the addition of an acrylic polymer. There is no crosslinking or chemical reaction taking place, but simply a physical fusing. There is nothing fundamentally lacking in this type of fusion. This type of cure is typical of other thermoplastic dispersions, such as plastisols.

A limitation does exist regarding this type of curing, however, as a result of not being able to make an air-drying equivalent of the coil coating. Since the curing process is limited to heat fusion, this process cannot be duplicated in air-drying fluorocarbon paints used for touch-up or for painting ancillary surfaces on the job site. The air-drying candidates in these older thermoplastic fluorocarbon dispersions must be highly modified with other resins to make them capable of ambient curing. Thus, the air-drying versions, because of their different chemical compositions as compared to the baking versions, have the potential for differential weathering.

The new second-generation thermoset solution fluorocarbon resin and paints (FEVE-based) cure on the coil coating line under heat by a chemical reaction, not simply a heat fusion. Also, in addition to the pigment dispersability, adhesion and flexibility of the PVDF system, these characteristics, along with the other desired properties of solubility, transparency, gloss, hardness and crosslinking, are built into the FEVE resin backbone and thus require no additional modification. Beyond these attributes, if improved pigment dispersability is desired, the basic FEVE resin backbone can be enhanced by incorporating a fourth chain that has carboxyl functionality.

Because of this reaction, air-drying versions can be manufactured using the same resin chemistry. Thus, identical weathering performance is assured between the coil coated surfaces and field-applied touch-up or painted ancillary parts. This advantage removed an impediment to more extensive use of fluorocarbon coil coatings that had existed for 30 years.

There are also some physical appearance differences between the older, thermoplastic dispersion-type coatings and the newer thermoset solution versions. Dispersion resins are typically cloudy in appearance. If one held up a glassful of this resin, you would not be able to see through the glass. This cloudiness, plus the lack of solubility, make it difficult to produce paints with glosses in excess of 40 units on a 60 deg gloss meter (assuming the paint contains the recommended 70 pct level of PVDF resin). This same characteristic limits the color palette available and generally restricts the older fluorocarbon coil coating giant to muted earth tones. Obviously, this limitation has restricted their suitability or desirability for many markets.

Conversely, thermoset solution (FEVE) resins are virtually clear. Through a glassful of the FEVE-type resin, you could clearly read an NCCA "no price discussion" warning. This clarity and solubility make possible a complete gloss range from siding gloss, around 10 units, all the way to full gloss, generally expressed as 80 units and greater. Colors can be bright, clean and vivid. There is a whole new world of opportunities for gloss, color and style with fluorocarbon performance in both bake and air-dry versions. Suddenly, coil coated fluorocarbon performance is available to markets that concentrate on image and want to make dramatic impacts on their customers. Thermoset solution fluorocarbon coil coating paints are quickly establishing an en-viable reputation in serving these new requirements.

Quite often a new and emerging paint technology requires good timing with emerging substrate technologies in order to complement one another. This good timing has definitely been the case in the early successes of the FEVE thermoset solution fluorocarbon paints for coating and field-applied requirements.

The industry most desirous of changing its image and restructuring its total marketing approach has been the oil industry. The oil shocks of 1973 and 1978 were significant factors in reordering the priorities of major oil companies. One of the ways they attempted to control escalating costs was through implementation of self-service stations. This new approach was a great idea, but there was the tremendous number of women drivers who were not keen about self-service and would definitely not go into a dark, dirty, greasy station. This change set the stage for entirely new imaging requirements along with a major shift in marketing opportunities. To attract women, stations must be bright, clean, attractive and safe. If these criteria could be met, the opportunities to sell items other than gasoline were enormous. The results seen today are mini-markets offering an incredible variety of products and services.

In order to make this happen, a new attractive substrate painted with bright, clean long-lasting colors was clearly needed. The new preferred substrate was aluminum composite materials that provided a wonderful appearance by rendering the coil coated surface virtually free of surface waves and oil canning, which often accompany high-gloss coil coating efforts. The coating of choice to provide the required durability and appearance was the second-generation thermoset solution fluorocarbon paints. The oil industry and aluminum composite manufacturers embraced the new fluorocarbon paints, creating an explosion of color, gloss and fabricating opportunities. New, dominant and exciting images were created. Today, every major oil company and many of the smaller players throughout the world are using aluminum composite panels that have been coil coated with FEVE thermoset solution fluorocarbon paints. These companies have also been quick to recognize that, because the ambient cured versions of the solution fluorocarbons use the same resin chemistry, it is now possible that older stations can be resprayed and brought up to future fluorocarbon standards of color, gloss and appearance.

Those who have used and taken advantage of this new technology also take note of two other important characteristics; unlike the older dispersion types of fluorocarbon paints that at best contain 70 pct fluorocarbon resins, the FEVE solution paints can be made using 100 pct of the resin portion as fluorocarbon resin. And the 100 pct resin capability of the FEVE solution system precludes any possible compromise. Also, the less fluorocarbon resin used in a finished paint, the more likely it is to degrade.

Second, the solution fluorocarbon paints can be recoated. Many architects and specifiers view this as an important advantage and are beginning to delineate recoatability as part of their specification.

Where will this new technology be heading? The solution fluorocarbon coating's excellent clarity along with color and gloss retention has not gone unnoticed by the automotive industry. Some of the world's premium luxury cars are using this technology for clear coats. Others are investigating the use of solution fluorocarbon paints for both base and color coats. There is little question that we will witness additional applications in this market.

Of primary interest to coil coating, however, should be the new opportunities in the architectural market. The penetration made in the specialty markets by aluminum composite panels and FEVE solution fluoropolymer paints will carry over into the architectural community. We are already seeing more and more FEVE specified and used. Architects are rushing to confirm their long-standing acceptance and approval of fluorocarbon paints, while opening up their design horizon and showcasing their creativity with a broader palette of colors and glosses. We will see much more of this coating used on aluminum composite panels and more conventional coil coated substrates.

Because of the availability of ambient-cured solution fluorocarbon paints, plastics and other surfaces are now markets for solution fluorocarbon paints. Their design freedom with other surfaces and substrates within the architectural community should expose potential customers to the possibilities and advantage of fluorocarbon paints, creating additional opportunities for coil coating. It is possible that these new opportunities will spark a renewed interest in all fluorocarbon paints, and the FEVE solution types will be able to practically repay the debt of acceptance earned by the earlier thermoplastic dispersions.

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