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AN OFFICIAL PUBLICATION A Reprint from Materials Performance VOLUME 21 NOVEMBER, 1982 PAGES 9-14 Effect of Anticorrosive Pigmentation on the Performance of Vinyi Coatings Reprinted for: Union Carbide Corporation Specialty Chemicals Division Old Ridgebury Road Danbury, CT. 06817 Copyright 1982 by th National Association of Corrosion Enginear* P. 0. Box 218340 a Houtton, Taxas 77218 occ S8258 Effect of Anticorrosive Pigmentation on the Performance of Vinyl Coatings* THOMAS QINSBERQ, * JOHN D. KEANE, * * and JOSEPH A. BRUNO* * Introduction ThE CORROSION of STEEL requires the presence of both ox ygon and water. It haa boon long known that coatings which provide an effoctivo barrier to one or both of those elements will effectively reduce corrosion. Tar and grease are welldocumented examples of such coatings. As coatings tech nology developed, it was discovered that certain compounds provided additional anticorrosive properties. Thus, when dry ing oils began to be used, the technique of incorporating cer tain pigments, particularly derivatives of toad, became popular because of the additional protection they provided. With the advent of synthetic resins, technologists continue to use those formulating principles. While the mechanism by which anticorrosive pigments provide a corrosion retarding effect to coatings is not entirely understood, it has been shown empirically that compounds of lead and zinc are perticulerly effective for this purpose. The corrosion protection afforded by these two pigment types is quite different. While lead pigments are believed to retard cor rosion primarily through the generation of an alkaline environ ment, zinc pigments are thought to be effective primarily through metal passivation caused by the slow release of zinc or chromate ions. While the presence of lone has been dem onstrated to be of considerable help in reducing corrosion, it has also been demonstrated that a salt of high solubility such as sodium chromate does not protect the substrate, and can actually be harmful. Therefore, en effective anticorrosive pig ment should have proper balance between solubility and in solubility. The development of highly hydrophobic and chemically Insensitive high performance polymers in the last few decades has provided a level of resistance properties unknown in earlier types of coatings. However, the earlier principles of for mulation wore so deeply entrenched that many of these newer high performance binders were formulated Into coatings ac cording to established pigmentation rules. However, new forces in technical and regulatory areas foster change con stantly. There is considerable stimulus to eliminate the presence of heavy metals such as lead and chromium (as chrome) from paint formulations. Vinyl coatings have been used for meny years with and without anticorrosive pigments both in government paint specifications and proprietary com positions. Methodology The severe raw material shortages following the oil em bargo of 1973 convinced many researchers and engineers that it was time to develop data enabling the formutator to select suitable alternative paint Ingredients. The prospect of short ages end regulatory limitations was the basis of the PACE (Performance of Alternate Coatings In the Environment) pro ject at the Steel Structures Painting Council In Pittsburgh, Pennsylvania. After an industry-wide search, a critical survey of alter natives, and selection of the most promising candidates, a broad range of products was evaluated. Some of these were: free of pigments, resins, and solvents which could be potentlelly hazardous during application, use, and removal; pro ducts low in volatile organic pollutants; surface preparation methods that are safe and nonpolluting; and improved primers and pretreatments. These coatings were exposed in five typical environments In a statistically designed experiment in which they were directly compared with reproducible standard products, the performance of which had been documented over many years. The program was administered by a balanced committee of producers and users who selected promising products for evaluation. The evaluation of a variety of anticorrosive pigments In vinyl coatings was one of the earliest aeries started. Thanks to the early initiation of tests, panels In this particular series have logged a substantial length of exposure, and have reached a point where the results yield valid conclusions. While the PACE program continues to evaluate a variety of coatings, the branch on pigmentation of vinyl eoatinga has provided valuable Information which Is presented here. A small segment ot tnls work considered the performance of vinyls over hand cleaned, rusty, and Intact mlllscale sur faces with a thick coat of wash primer. Three primer formula tions were exposed in three environments. The vinyl formulation described In Mil. Spec. MIL-P-15929 was chosen. A variety of pigments were substituted for red lead at a constant pigment volume concentration: aluminum flake, calcium boro silicate, zinc molybdate, barium meta borate, zinc sulfo oxide complex, micaceous Iron oxide, and red Iron oxide/barytes. These primers were applied to steel panels blast cleaned to either white metal (SSPC-SP 5) or near white (SSPC-SP 10) using steel grit or shot abrasives, and primed with wash primer conforming to Mil. Spec. MILP-15328. The standard United States Navy vinyl alkyd (MILP-16188) was used as topcoat. Film thicknesses were well-controlled (Tables 1,2, snd 3) to minimize the thickness-related effects. Ten percent of the panels were selected randomly and replicated to establish a statistical measure of precision. Panels were immersed at room temperature in fresh (dis tilled) and synthetic sea water (ASTM D-1141-92) and exposed to salt fog (ASTM B-l 17). and to a severe industrial atmosphere st a coke works. Initially, only the panels exposed at the In dustrial site were scribed. The salt fog panels were still In ex cellent condition after 8000 hours exposure. At this point, they were scribed and reexposed for an additional 3600 hours. * Voluntary paper submitted for publication February, 1062. `Union Carbide Corporation, Bound Brook, New Jersey. "Steel Structures Painting Council. Exposure Rbsult* As shown In Table 4, all but one of the panels were still perfect after 5700 hours of fresh or salt water immersion. Similarly, the panel surfaces exposed in the severe industrial N v mber, 1982 UCC 0094-1492/82/000186(33.00(0 1982, National Association of Corrosion Engineers 9 058259 TABLE 1 -- Film Thicfcnaa* Summary wth Artmuf TABLE 1 -- FMm TMcknaaa Summary. Wih Artmar Alu* Thraa Artmar CAita Nora: Film Tiucltnaa*: mna n mil 25.4 /un). 10 ucc 058260 Materials Performance Not* FHm ThicKfus*. mils (i mil 25 4 f*m) TABLf 4 -- Froth and Silt Wator Immortlofl Data Summary <5700 Hours) November, 1982 11 UCC 058261 > TABLE 5 -- CaM Woriti Data Summary 04 Month*) TABLE -- Salt Fo Data Summary ucc 058262 12 Materials Parformance TABLE 7 -- Expwtmtmal Datlgfl TABLE -- StMl Structures Painting Council Paint Spec. No. 9 lngndlntt Pigment Titanium Dioxide, Unextended Vahlela (89% maximum) Vinyl Resin A (Hydroxyl-Containing) Vinyl Resin B (Carboxyl-Containing) Trieresyl Phosphate or Dloctyl Phthalate Methyl Isobutyl Ketone Toluene Wt% 12.0 6.0 6.0 3.0 34.5 34.5 100.0 Potmda/100 Gallons 100 66.7 66.7 25.0 286.0 266.0 834.4 Vol.% 2.0 5.9 5.9 2.5 43.0 J3 100.0 atmosphere* (TsNe 5) have not mown any signs of rust after two yaara. However, there are differences In the amount of undercutting at the scribe. Scribe results show essentially no difference between the steal shot and grit abrasives used in blast cleaning. Salt fog exposure performance data are given in Table 6i No signs of rusting were evident after Ti.500 hours. Slight blistering was noted only after 6000 hours. After 11,500 hours, there was little difference In blistering among the 12 systems. Aluminum flaks and iron oxide were slightly better than the rest. These small differences, however, may vary well fall within the range of experimental error. A small set of panels was prepareo to test tne effect of a thick coat (over 0.5 mils) of wash primer when used with vinyl primers containing both rusMnhlbltlve and noninhlbitive pigments. Standard practice calls for a maximum of 0.5 mils for the wash primer fSSPC-PT 3). One purpose of this test was to determine If a \rtny| coating could be applied successfully N winter, 1982 over hand-cleaned steal (both Intact and partially rusted mlllscale) if a thick coat of wash primer Is applied. It is impor tant to note that no controls were Included to establish the performance of a thin coat. Except for the thick wash primer, the vinyl systems used here were identical to those used in the main vinyl pigmentation study. Four surfaces were used: sand blasted, grit-blasted. Intact mlllscale, and partially rusted mlllscale. Three exposure environments were chosen: (i) fresh water Immersion; (2) salt fog; and (3) severe industrial. Oats for this small side study are given In the last three columns ol Tables i through 7. The blast-cleaned panels with the thick wash primer re mained In excellent condition after 5700 hours of fresh water Immersion. The hand-cleaned panels, however, started to blis ter, particularly the partially rusted mlllscale panels. After two years of severe industrial atmospheric ex posure, all panels, Including the hand-cleaned ones, were rustfree. The hand-cleaned panels, on the other hand, showed a 13 UCC 058263 TABLE 9 -- Vinyl Type Whit* (or Or*y) Paint Formula V-7Ma Ingredients Wt% Vinyl Resin, Type 3 (Copolymer Resin) Vinyl Rasta, Typa 4 (Carboxylatsd Terpolymer Rasta) Titanium Dioxide and (ter Gray) Carbon Black Dlisodscy! Phthalate Mathyl Isobutyl Katona Toluana Orthophosphoric Acid 5.6 11.6 13.0 29 32.0 34.7 0.2 Too!5 tbs formulation ot this paint, which was first adoptad m 1964. Since this coating contains a carboxylatsd rasm, the paint is suitable for direct application over steel, while il is also selftopcoatable; therefore, an entire system can be based on it. One such system Is described in SSPC paint system # 4. An example of the use of paint SSPC-9 in a difficult en vironment is that defined by the American water Works Association in Spec. AWWA 0102-78. In the Inside painting system No. 2, this specification Indicates that the first coat on the system directly on steal consists of SSPC Paint No. 9 Numerous other examples could be cited. One. included In the United States Army Corps of Engineers Spec. CW-09940. System No. 3, is a 4 coat system in which the primer consists of Formula 0-766, which is pigmented with titanium dioxide only. This formula is shown in Table 9. The United States Army TABLE 10 - VP-3639 Whit* High Build Vinyl Anticorrosive Paint Methyl Butyl Ketone Cellosolve Acetate Xylene Toluene VMAP Naphtha Flaxol 10-10 UCAR Rasta VMCA Thixotropic Agent Titanium Dioxide Zinc Phosphate Pounds/100 Gallons 52.27 365.86 36.57 57.50 10.46 39.00 217.97 9.18 114.72 91.78 "5533T Gsllona/100 Gallons 7.80 45.17 5.04 7.94 1.66 4.85 19.67 1.06 3.45 3.34 100.00 Wt% 5.25 36.76 3.67 5.78 1.05 3.92 21.90 0.92 11.53 9.22 100.00 large area of scribe undercutting. Thick wash primer bed no noticeable effect on scribe undercutting for blast-cleaned steel. There was no difference In scribe ratings at the Industrial site between the shot* and grlt-blaated panels. However, the sand-blasted panels had better scribe performance than either shot* or grit-blasted panels. Even CR-42, which had the most scribe undercutting In the pigment section Of this branch study had an excellent scribe rating when applied over a thick wash primer on the sand-blasted panels. However, this surface had poorer performance In the salt fog tests. After 11,600 hours of salt fog exposure, the vinyl perfor mance on hand-cleaned steel, coupled with thick wash primer, was comparable to that of blast-cleaned steel. Experience with Attemetlv* Pigmentation The use ol alternative pigmentation In vinyl systems Is not new. There ere numerous examples of coating systems which have been used for many years and have provided e highly reliable level of performance. One of these le Spec. SSPC*, which covers e vinyl coating pigmented only with titanium dioxide. Table 8 shows Corps of Enginsers has numarous casa historias whers this typa of paint haa baen appliad for ovar 20 yaars undar condi tions ot continuous immersions such as river locks snd dsms. A rsctnt sxsmpis of ths uss of zinc phosphats ss an alter native anticorrosive pigment is iliustratsd in Formula vp-3639, shown in Table 10. Because of its neutral natura, zinc phos phate can be used In combination with a carboxylatsd vinyl resin such as VMCA for the formulation of coatings that ara applied directly over steel. VP-3639 Is ona such example; this particular paint with an antifouling topcoat has baen totally Immersed for over 5 years at a test station in Florida. The results of this test art excellent. Summary in vinyl vehicles, a variety of alternative pigments were at least equivalent to the established red lead formulations. This conclusion applies to vinyl systems only. Another portion ol the SSPC PACE program dealt with a similar aeries of expertments aimed at evaluating alternative pigments in sikyd coatings. Hers, the replacement appears to be more difficult, pointing to ths fact that permeability of the polymer itself is an Important factor on the allowable formulating latitude. F-48387 14 ucc 058264 Materials Performance