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[Ije-qMaterials of Construction Review
Protective Coatings by FRANCIS SCOFIELD, National Paint, Varnish and Lacquer Association, Washington, D. C.
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Organic coatings with increasing resistance to chemicals, abrasion, and corrosion continue to appear
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N e w coatings for structural steel increase the protection afforded
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THE past year there have been relatively few developments or products in the protective coatings industry that are really new. While the industry is active in all areas all the time, the most recent period has been devoted more to determining the place of the numerous film-forming materials introduced since World War I1 than to introducing more new materials. In particular, the catalyzed finishesepoxy, urethane, and polyester-which have been known for some years, attracted much attention as more was learned about their possibilities and some of the problems of application were smoothed out. Also, water-thinned, or latex, coatings, with many years of successful use for interior finishes and exterior masonry, continued to expand as coatings for exterior wood and for industrial finishing processes. Not all of the problems associated with the use of latex coatings in these fields have been solved, but many cases of successful employment have been reported, and most of the problems are gradually being brought under control. Simultaneously, much new interest is being shown in the protection of metals, particularly steel, from corrosion. T o some extent this interest is stimulated by the use of newer products, but much arises from a growing realization of the economics of using high quality materials and careful surface preparation.
Newer Materials
The various types of coatings available have been reviewed, and the outstanding merits of each indicated (7A). Others (ZA, 77A) covered the various types of epoxy coatings. Glaser and Floyd (6A) discussed the formulation and properties of amine-cured epoxies, and Naumann (77A) and Somerville (76A)emphasized the value of the heavy coatings obtain-
able in maintenance painting. The chemical and abrasion resistance of epoxies makes them useful in bakeries (70A). The growth of urethane coatings was reviewed (8A), and the numerous types were classified (73A)with suggestions for their use. Norden (7.23) stressed the chemical resistance of properly formulated urethane coatings. The properties and uses of vinyl plasticizers and organosols were described (74A),with particular stress on their abrasion resistance, toughness, and electrical properties. A committee report (4A) covers the properties of polyethylene coatings applied as powders by a fluidized bed process. Frederick (5A) described some of the newer types of aluminum paints and outlined their uses. The present state of latex paints was reviewed (75A),and the improvements in latexes for industrial finishing were surveyed ( 7 4 78A). Carpenter (3A) emphasized uses of automotive primers and tank car linings where extreme alkali resistance is required. Johnson (9A) pointed out the problems in obtaining a satisfactory gloss latex for industrial finishing. Metal Protection
The old question of whether it is more economical to paint steel than to let it rust was discussed by Wiscombe (36B). He favors painting. Bosch (4B) reported on the minimum thickness of various coatings on hot rolled steel which give satisfactory protection. As yet, the report is only preliminary. A number of corrosion failures were investigated by White and Chandler (34B),who suggested suitable preventative measures. Bigos (ZB)reported on the relation of steel surface roughness to the performance of a coating. If the profile is less than 4 mils, it does not
affect performance. Stephenson (30B) described techniques for obtaining very thick (10- to 15-mil) films in one coat with conventional coatings. The troubles encountered in painting over rust were attributed by Mayne (74B)to iron(I1) sulfate entrapped in the rust; he showed that performance is related to iron(I1) sulfate content. Copson and Larrabee (6B)discussed the relation between steel composition and paint performance. Certain low-alloy steels gave much better performance than standard carbon steel. I n the continuing study of surface preparation, Bley ( 3 8 ) reviewed various methods with particular emphasis on sandblasting. Other types of preparation studied included phosphate processes (33B), chromate conversion processes (8B),wash primers (35B), and fillers and primer-surfacers for low-grade castings
(78B). Although many discussions deal with newer materials, one report of British and Swedish experience (278) still recommends red lead in linseed oil, particularly if thixotropic paints, which allow the application of thicker coatings, are used. Much interest is evinced in paints containing metallic zinc. Anderson (7B)showed that zinc, particularly in a silicate binder, gives as good protection as hot-dip galvanizing in sea water. Other reports (75B,2223) also emphasize the performance of zinc-rich paints for marine use. Paints made with stainless steel powder were described by Higgins ( 70B); as topcoats over a n anticorrosive primer, they give excellent service in extremely corrosive areas. Ramanan (26B)urged the use of composite aluminum-zinc oxide primers. The performance of vinyl (79B)and epoxy (ZOB)coatings has also been described. For coating of aluminum, Thake (32B) stressed the importance of getting a clean surface. Among the specific problems reviewed VOL. 52, NO. 10
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Materials of Construction Review
are the coating of containers (37B), the protection of oil refineries (13B), and methods used for the control of internal corrosion in tankers ( 7 7B). Recent improvements in automotive coatings were outlined (28B), and the problems of corrosion prevention on railways were reviewed (27B). In the always active field of marine paints, methods of evaluation were described (5B), a number of tests were reported (76B), and paints with and without zinc oxide were compared (24B). I n the field of coating underground pipes, conventional methods, based on asphalt and coal tar, were compared with newer methods using plastic and elastomeric coatings ( 2 3 4 29B). Edwards and others (7B) suggested a pickling bath inhibited with an acetylenic alcohol, followed by an epoxy-phenolic coating for pipes used for potable water. Graham (9B) recommended glass fibers to reinforce pipe coatings. According to Pemberton (25B), economic considerations favor reconditioning rather than replacing corroded pipes; he suggested appropriate steps. Koenecke ( I 2 B ) has investigated the performance of various coatings when used with cathodic protection and recommended either epoxy or butoxy coatings. Morgan (178) also urged the use of coatings to supplement cathodic protection, especially for pipes carrying sea water. Miscellaneous
As usual, because coatings impinge on almost every aspect of life. a variety of subjects were covered by useful discussions. Several workers (8C, IOC, 73C, 74C) discussed the testing and use of fire-retardant paints and their place in the prevention of fire. The Southern Production Club (77C) reported on the correlation between laboratory and field tests on traffic paints. In general, it is not very good. Johnson (9C) suggested the use of a coating on road surfaces to improve their wear resistance. The newer floor coatings were described ( 7 IC), with particular emphasis on urethane and latex finishes. Talley ( 78C) covered multicolor lacquers. In the field of specialties, coatings were described ( 4 C ) which enable carbon steel to withstand steam sterilization in hospitals; a paint for high-temperature service was also reported (7C). I n the field of exterior finishes, clear coatings for exterior wood were reviewed (6C), exterior masonry coatings, with particular emphasis on latex paints were surveyed (ZC), and the results of tests on more than 350 coatings in five tropical environments were reported ( I C ) . Finally, on the general subject of the maintenance of structures, Moore (72C)
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showed the influence of construction details on the durability of coatings, and Prather (15C) outlined the advantages of having a coatings engineer work with designers to ensure ease of maintenance. Others (3C, 5C, 76C)outlined the necessary steps to set u p a good maintenance painting program. literature Cited Newer Materials (1A) Bress, J., Feld, I., Paint Znd. M a g . 75, NO. 3, 13-4 (1960). (2A) Buegc, F. J., Drubel, A. C., Modern Plastics 36, No. 11, 80-1 (1959). (3A) Carpenter, M. C., Prods. Finishing (Cincinnati) 23, No. 6, 28-33 (1959). (4A) Corrosion 15, No. 3, 33-6 (1959). (5A) Frederick, R . H., A m . Paint &? W a l l pafier Dealer 51, No. 11, 26-7, 68 (1959). (6A) Glascr, D., Floyd, D. E., Ofic. Di
