F. SCOFIELD
ANNUAL REVIEW
PROTECTIVE COATINGS Better fire retardant paints and electrophoretic application lead developments in paint technology
he production of new and improved coatings
Tusually progresses in small increments. Drying time is improved, durability is enhanced, resistance to various destructive forces is improved, colors are brighter and more permanent, and most strikingly, the tolerance of various coating systems for deviations from ideal conditions of application is improved. These changes take place in nearly all types of coatings, nearly all the time. There are, however, three areas in the coatings field in which striking progress has been made in the last two years. Two-Component Systems
One of the areas of most rapid advance in the field of organic coatings is that of the two-component, catalyzed systems. Conventional coatings dry either by solvent evaporation or by oxidation, but most frequently by some combination of these two phenomena. Twocomponent systems, however, “dry” by a chemical reaction of the two components and require neither solvent evaporation nor oxygen to cure the film. This results in coatings with unique properties and allows the use of organic coatings in areas where previously ceramic or metallic coatings had been required. I n general, three types of resinous binders are used for these coatings-epoxies, urethanes, and polyestersalthough various combinations and other materials are occasionally appearing. The epoxies are characterized by excellent adhesion and good exterior durability, but
some tendency to chalk rather rapidly on the surface. The urethanes are particularly noteworthy for their abrasion resistance and are often recommended for floor and deck enamels. The polyesters have excellent exterior durability and the best color and color retention. Except for these minor differences, there are few differences among the three types of coatings. As a group, these coatings are characterized by very good chemical resistance and a hard, smooth surface, which is easily cleaned. They resist water, acids, steam and detergents well, making them ideal for food processing plants and other areas where frequent disinfection is required. They are also widely used for public spaces in commercial and industrial buildings, where ease of cleaning is required. The coatings may be formulated to give excellent exterior durability, but because of their thickness, as usually applied, they lack flexibility, and their use over wood or metal substrates is questionable. They are, however, excellent over masonry and related materials, and are widely used to give a smooth, hard, and easily cleaned coating to rough surfaces such as concrete or cinder block. These coatings, like all others, also have their drawbacks, which should be considered in deciding on the proper areas of use. Very careful surface preparation is required since the coatings have such a high internal cohesion that they will remove a surface layer from the substrate unless they are firmly bonded. The application of two-component systems, with a limited pot life, presents some pitfalls. Also, the coatings are relatively expensive compared with the traditional paints and, while they can be used to fill and smooth rough surfaces, it is not economical to do so. For this reason, “fillAUTHOR F. Scoj$eld is Technical Director for the National Paint, Varnish and Lacquer Association VOL. 5 6
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coats’’ are often used to smooth the surface first. These must be chosen to be compatible with the particular topcoat to be used, and the manufacturer’s instructions as to surface preparation, application, and curing must be strictly followed. Fire-Retardant Paints
There has been considerable development in the field of fire-retardant paints in recent years. These coatings are designed to insulate combustible surfaces from flame and retard the spread of fire by holding the surface below its ignition temperature for as long a period as possible. This is usually done by means of an intumescent coating which expands on heating to give a porous, insulating coating of substantial thickness. Coatings with flamespread ratings, by the method of the Underwriters’ Laboratories, of less than 25, are now available and permit the use of combustible materials of construction in areas where they would be otherwise barred by safety considerations. In general, fire-retardant paints are likely to be deficient in the standard paint properties of application, moisture resistance, and appearance, and their use is never to be recommended where conventional paints will do the job, but only where the high fire resistance is absolutely necessary. I t must be remembered that nearly all paints contribute significant fire resistance to combustible materials and in many cases fill all requirements.
an operation in which coatings are applied from a dilute emulsion by a process very similar to electroplating of metals. At the present time it is limited to the application of coatings to metals, but is very effective in this area, particularly when unusual or complicated shapes are to be coated. This method, which was developed in Europe, yields uniform coatings even on those areas which are difficult to reach with a spray gun, and unlike dipping processes, gives just as heavy coats on sharp edges as it does on smooth surfaces. Suitable coatings for use with this method are still in the development stage, but it is a method of considerable promise.
B I BLlOG RAPHY Curtain Coating (1) Honigsfeld H. “Finishing Combination Metal and Wood Furniture,” Ind. Finishing (Inkm&lir) 39, No. 7, 62 (1963). (2) Johnson, F. D. “Curtain Coater Potential Yet Untapped,” Can. Paint Varnish 37, No. 8, 26 (19i3). (3) Kitchen J. R. “Formulating Emulsion or Latex-Based Coatings for a Curtain Coating Machink,” Point Technol. 28, No. 4, 1 4 (1964). (4) Willis R. W “Curtain Coating with Polyvinylidene Chloride Dispersions,” Mod. Pimticr 40,’No. 1, 134 (1962). (5) “Method and Apparatus for Curtain Coating,” U. S. Patent 3,067,060 (Dec. 4, 1962). Fire R e t a r d a n t Paint (1) “Fire Retardant Paints-Successful in Some Applications-Largely Unproven in Others,” A m . Paint J. 47, No. 32, 56 (1963). (2) “Fire Retardant Paints-How Good Arc They?,” Am. Painter Decorator 4, No 12, 20 (1962). (3) “Fire and Chemical Resistant Paint,” Japan Patent 2975/62. (4) Building Materials List, January 1964, 35, Underwriters’ Laboratories.
Application Method
Airless Spray
The increasing interest in the application of finishes to building components a t the factory, rather than on the site, has stimulated developments in new and faster methods of application, each of which calls for the development of coatings formulated for the particular production line. I n particular, the factory coating of wood siding has produced many developments in the field of curtain coaters, which lay down a film of controlled thickness at high speed. Factory-coated products are of particular interest because, in general, a better coating may be obtained than can be obtained under any but the most favorable conditions by application after erection. Surfaces are clean and controlled, the application of a uniform film thickness is much easier to achieve, and the operation is not at the mercy of the weather. Also, it is possible in the factory to use curing methods such as baking, which are not practicable in the field. The complete conversion to factory-finished components is delayed by problems of fastening the materials in place since the finish must not be damaged by nails or screws. But problems of repairing damage which occurs during transportation and erection, and color requirements, are much more easily met by field application. For these reasons, many components are primed in the factory and the final coat is applied in the field. One new method of application, electrophoretic coating, has stimulated a great deal of interest. This is
(Indianapolis) 40, No. 2, 46 (1963). ( 2 ) Johnson, F. D. “They Combine Airless and Electrostatic Spray,” Can. Paint Varnish Mag. 36, N o . 10, 28 (1962).
(1) Albrecht, G . “Hot Airless Spray Used in Finishing TV Cabinets,” Ind. Finishing
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(3) Johnson, F. D., “Four Basic Principles Are Used in Spray Equipment,” Ibid., 37, No. 3, 33 (1963). (4) Johnson, F. D., “How Garage Doors are Primed to Weather Well,” Paintindin 12, No. 11, 2 (1963). (5) “New Concept in Low Pressure Spraying,” Prod. Finishing 25, No. 11, 61 (1962). (6) “New Highbuild Airless Spray System,” Ibid., No. 12, p. 48. Factory Coating (1) Carroll, J. W., “How We Finish Steel Store Equipment,” Ind. Finishing (Indianapolis) 39, No. 9, 54 (1963). ( 2 ) Fishlock, D . J., “Applications of Prefinished Metals,” Prod. Finishing (Cinn’nnntt), 26, No. 1, 55 (1963). (3) Icenhower, H. E., “Finishing Slimline Show Cases,” Ind. Finishing (Indianapolis) 39, No. 6 (1963). (4) “Lumber Industry Now Wants to Paint It,” Am. Painter Decorator 40, No. 2, 16 (1963). (5) “Plastic Coated t o Wood Successfully,” Prod. Finishing (Cincinnati) 29, No. 2 , 72 (1963). (6) “New Prefinished Metal Promises Longer Exterior Life,” Ibid., 27, No. 3, 158 (1962). (7) “Newest of Precoaters,” Ibid., 29, No. 6, 50 (1963). Electrophoretic Coatings (1) Berry J. R . “A Beginner’s Guide to Electrophoresis:’ Part 1, Paint Technol. 27, No. 12,’13 (1663). (2) Ibid., Part 2, 28, No. 1, 24 (1964). (3) Ibid.,Part 3, 28, No. 3, 53 (1964). (4) Guilleby P Rotter H. W. “Applying Paint by Electrodeposition,” Coni. Paint Resin”&, 1, N.; 11, 2 (i963). (5) Kumins C. A. “Electrochemical Properties of Protective Coatings,’ Part 1, Paint T c c h h . , 28,’No. 1, 34 (1764). (6) Ibid., Part 2, No. 3, p. 39. (7) Lever R C “The Electrical Analysis of Paints for Electrostatic Deposition,” Paint Tjchnol. $7, No. 2, 35 (1963). (8) Muirhead, J., “Plant Requirements for Electro-Deposition,” Ibid., 28, No. 5, 34 (1 964). (9) Palluel, A. L. L. “Applying Paint by Electrodeposition,” Can. Point Varnish h a g . 38, No. 5, 44 (19d4). (10) Walter, L., “Start Up First Electro-Coat System,” Ibid., p. 43. (11) “Method of Treating Metal Surfaces,” U. S. Patent 3,030,238 (April 17,1962). (12) “Electrophoretic Painting Research,” Cont.Paint R a i n News 2, S o . 5 (1964).
