Thermoclad Duravin Vinyl PVC Coatings

Duravin Powder Coatings for Corrosion Protection of Metallic Surfaces

Available in an almost unlimited range of colors, DURAVIN Vinyl Powders are dry, free-flowing, specially formulated resins for application by the fluidized-bed, electrostatic, rotational moulding, flock or 'slush' coating processes. These powders fuse with the application of heat to form smooth, glossy, resilient plastic coatings. These coatings generally exhibit outstanding impact resistance, chemical resistance, outdoor durability, color uniformity, and toughness, developing excellent adhesion to various substrates when applied over DURAVIN Vinyl Primer.

Properly applied DURAVIN powder coatings produce uniform finishes that are free from sag, tears or runs in a practical range of thicknesses from 7 to 30 mils with a single application. Thinner or heavier coatings are often possible by employing special coating techniques. During the fusion or melting process, DURAVIN vinyls develop a high degree of surface tension to smooth out relatively rough surfaces such as castings, welds, and forming imperfections, however, their thixotropic properties offer a remarkable degree of edge coverage at metal edges, and cut wire ends. These characteristics allow minimum surface preparation, aside from normal chemical pretreatment, which reduces substratepreparation costs required for painted or other thin film powder coated surfaces.

PROPERTIES

As a family of coatings, DURAVIN PVC Vinyl powders offer certain common predictable properties that remain reasonably unchanged in spite of modification of the variable properties. Corrosion and Chemical resistance, insulating properties, both Thermal and Electrical, Salt Spray, as well as some physical properties will exhibit remarkable similarity compound to compound, whereas Hardness, Tensile and Tear Strength, Resistance to Ultraviolet Light (Outdoor Durability), Volatility and Compatibility properties must be formulated for to attain the desired results.

Vinyl coatings, as a rule, exhibit excellent chemical resistance to acids, alkalies, aqueous salt solutions, alcohols, gasoline, and aliphatic hydrocarbons, although concentration, temperature, and the nature of the chemical does have a bearing on the degree of the coating's inertness. Vinyls are not recommended for contact with aromatic hydrocarbons, chlorinated solvents, or ketones.

Except for specifically designed, high temperature formulations, with equivalence to as high as a 105º C Underwriters Laboratory rating, such as our specially stabilized Low Volatile DURAVIN products, vinyl coatings are not recommended for continuous use above 180º F, and preferably below 160º F. Some intermittent use at temperatures as high as 325º F (163º C) may be tolerated in certain applications.

Powder coated DURAVIN vinyl films exhibit dielectric properties from 600 to more than 1000 volts per mil, depending on the coating thickness and to some degree, formulation.

Salt spray resistance of all properly applied and primed DURAVIN Vinyls is excellent; a zinc or iron phosphated substrate, primed with the recommended DURAVIN primer, and suitably coated, will provide a durable finish showing little or no effect in 5,000 hours of Salt Spray exposure; less than 1/16" undercutting will be observed on a scored panel exposed for 2,000 hours.

PRODUCT CATEGORIES

Certain DURAVIN Vinyl powder series have dominated the bulk of Thermoclad Company's customer demands, either because of environmentalrequirements or the test of time. Three such product categories should be mentioned, although within each group, a number of finite modifications are possible for adaptation to individual customer use.

The Low Volatile DURAVIN formulations were introduced in the fall of 1969 and constitute our largest sales volume. At application temperatures these materials will lose only a small fraction of a percent of volatile organic matter, resulting in very, very little smoke evolution in the plant area. Regular volatility formulations, on the other hand, will lose as much as 4 to 8% by weight during the fusion process at temperatures as high as 450º to 550º F (232º - 288º C). This weight percentage of the low specific gravity organic material lost during the fusion step extrapolates to a thickness (volume) loss of as much as 5 to 10% - which may readily justify the consideration of the Low Volatile product. The coater can benefit several ways: compliance with clean air environmental regulations, attainment of a more compatible plan environment, and in many instances a cost saving is realized.

The second product category is Thermoclad's Appliance Grade DURAVIN vinyl powder. With only minor modification this product series has competed in the dishwasher basket coating market for over 30 years, and has been accepted by every major appliance manufacturer in the United States and Canada.

The third substantial product group in the DURAVIN powder series is aimed at demanding Outdoor and Corrosive uses such as chain link fence wire, fence posts and hardware, electrical conduit, and electrical underground and pole transformer coatings.

APPLICATION PARAMETERS

The fusion of flexible PVC powder formulations normally starts at about 400º F (205º C) when the powder begins to coalesce and continues to 'flow-out' into a uniform film as the temperature of the material is increased. When the coating has achieved the desired degree of smoothness, further exposure to heat should be terminated and the coated part cooled by forced air or a water quench. DURAVIN Vinyl Powder formulations have been designed to resist a reasonable amount of over-bake or extended exposure to high temperatures, however, it is good practice to minimize such exposure in order to achieve and retain the optimum coating integrity.

Application temperatures may vary depending on the idiosyncrasies of the specific DURAVIN compound, the substrate and often equipment. Minimum part temperatures for dip or hot spray electrostatic applications should exceed 450º F (232º C) to realize practical production cycles. For wire goods, a 5 to 10 minute preheat at 550º to 650º F (288º - 343º C) may suffice to achieve the proper temperature, whereas lower and longer preheat would be called for when coating heavier parts, or parts having substantial mass differential, such as large springs, castings, or complex parts combining tubular and wire goods, where 10 to 30 minutes at 475º to 550º F may be more suitable.

To obtain the optimum bond to a cold or cool, electrostatically sprayed part, it should be first cleaned, the primer applied and cured at 350º - 450º F (177º - 233º C); the substrate should be 'cool' by the time it reaches the spray booth to allow uniform powder application. Very hot parts may result in rough and non-uniform coatings. The parts may be postheated at 410º - 450º F (210º - 232º C) until complete fusion is achieved. A lesser chemical bond will be achieved if the primer is not pre-cured prior to powder spray.

ECONOMICS

The marriage of plastic to metal has been considered the ideal partnership - combining the strength of the metal with corrosion resistance of plastic, however, the proper choice of a protective or decorative coating is crucial in how well it performs at the job for which it is intended.

A premature failure, be it the fault of the structural part, of the coating, defeats the economic purpose of design. The planned longevity of a coating system depends as much on the choice of the correct DURAVIN product as it does on the metal surface preparation and selection of a primer or adhesive.

Once the correct system has been determined, a cost analysis must be performed to determine whether the proposed project is economically feasible. Certain exotic plastics may carry a price tab five to ten times that of vinyl, but may have to be considered as the logical engineering choice, if it offers the only desired solution.

DURAVIN Vinyl Coatings, on the average, have a specific gravity of 1.28, which extrapolates to a coverage factor of .1 lb. vinyl per square foot at 15 mils. To estimate the cost per square foot, the following formula may be used for all plastic coatings:

Cost per square foot = 5.21 X Price Per Pound X Thickness in Mils X Specific Gravity ÷ 1000
Powder coverage per pound =192.3÷Specific Gravity = Coverage @ 1 mil