Document 2R91p0jnXnLRdgLQOabQ2wan7

I A N OFFICIAL PUBLICATION A Reprint from Materials Performance VOLUME 21 NOVEMBER, 1982 PAGES 9-14 Effect of Anticorrosive Pigmentation on the Performance of Vinyl Coatings Reprinted for: Union Carbide Corporation Specialty Chemicals Division Old Ridgebury Road Danbury, CT. 06817 Copyright 1982 by the National Association of Corrosion Engineers P. o. Box 218340 Houston, Texas 77218 ucc 058258 Effect of Anticorrosive Pigmentation on the Performance of Vinyl Coatings* THOMAS GINSBERG,* JOHN D. KEANE,** and JOSEPH A. BRUNO** Introduction The CORROSION of STEEL requires the presence of both ox ygen end water. It has been long known that coatings which provide an effective barrier to one or both of these 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 lead, 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 particularly 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 ions 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, an 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 were 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 many 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 ft was time to develop data enabling the formulator to select suitable alternative paint Ingredients. The prospect of short ages and regulatory limitations was the basis of the PACE (Performance of Alternate Coatings In the Environment) pro- )ect 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 poten tially 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 series 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 coatings has provided valuable information which is presented here. A small segment ot tnis wont considered the performance of vinyls over hand cleaned, rusty, and Intact millscale 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 oxfdafbarytes. These primers were applied to steel panels blast cleaned to either white metal (SSPG-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, and 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-1141-52) and exposed to salt fog (ASTM B-117), and to a severe industrial atmosphere at 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 3500 hours. 'Voluntary paper submitted for publication February, 1982. 'Union Carbide Corporation, Bound Brook, New Jersey. "Steel Structures Painting Council. Exposure Results 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 Nov mbsr, 1982 UCC 0094-1492/82/00018643.00/0 1982, National Association of Corrosion Engineers 9 058259 TABLE 1 -- Film Thicknaaa Summary: With Prlmar TABLE 2 -- Film Thleknaaa Summary: Waah Frlmar Plua Thraa Prlmar Coala ucc 058260 10 Materials Performance TABLE 3 -- Film Thickna** Summary: Full Syatam (Wash Prlmar Plus Thraa Prlmar Coat* Plu* Topcoat) TABLE 4 -- Fraah and Sait Wstar immersion Oat* Summary (5700 Hours) November, 1982 11 UCC 058261 TABLE S -- Cofct Work* D*t* Summry (24 Month*) TABLE G -- S*lt Fog 0*t* Summlfy ucc 058262 12 Materials Performance TABLE 7 -- Exprfmntil Dtstgn TABLE 8 -- StMl Structures Painting Council Paint Spec. No. 9 Ingredients Pigment Titanium Dioxide, Unextended Ve/t/e/e (88% maximum) Vinyl Resin A (Hydroxyl-Containing) Vinyl Resin B (Carboxyl-Containing) Trfcresyl Phosphate or Dioctyl Phthalate Methyl Isobutyl Ketone Toluene Wt% 12.0 B.O 8.0 3.0 34.3 34.5 100.0 Pounds/100 Gallons 100 66.7 66.7 25.0 286.0 288.0 834.4 Vol.% 2.9 5.9 5.9 2.5 43.0 JSJ 100.0 atmospheres (Table 5) have not shown any signs of rust after two years. However, there are differences In the amount of undercutting at the scribe. Scribe results show essentially no difference between the steel shot and grit abrasives used In blast cleaning. Salt fog exposure performance data are given In Table 6. No signs of rusting were evident after 11,900 hours. Slight blistering was noted only after 6000 hours. After 11,900 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 very well fall within the range of experimental error. A small set of panels was prepared to test tne effect of a thick coat (over 0.9 mils) of wash primer when used with vinyl primers containing both rust-lnhlbltlve and nonlnhlbltive pigments. Standard practice calls for a maximum of 0.9 mils for the wssh primer (SSPC-PT 3). One purpose of this test was to determine If a vlny) coating could be applied successfully November, 1982 over hand-cleaned steei (both intact and partially rusted mlllecale) 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 millscale, and partially rusted millscale. Three exposure environments were chosen: (1) fresh wster immersion; (2) salt fog; and (3) severe industrial. Data for this small side study are given In the last three columns of Tables 1 through 7. The blast-cleaned panels with the thick wash primer re mained in excellent condition after 9700 hours of fresh water Immersion. The hand-cleaned panels, however, started to blis ter, particularly the partially rusted millscale panels. After two years of severe industrial atmospheric ex posure, all panels, including tha hand-cleaned ones, were rustfree. The hand-cleaned panels, on the other hand, showed a 13 ucc 058263 TABLE 9 -- Vinyl Typo Whits (or Gray) Paint Formula V-766* Ingredient* vinyl Resin, Type 3 (Copolymer Resin) Vinyl Resin, Type 4 (Carboxylated Terpolymer Resin) Tltsnlum Dioxide end (for Gray) Carbon Black Diisodecyl Phthalale Methyl Isobutyl Ketone Toluene Orthophosphoric Acid Wt% 5.6 11.6 13.0 2.9 32.0 34.7 p,; 100.0 the formulation of this paint, which was first adopted in 1964. Since this coating contains a carboxylated resin, the paint is suitable for direct application over steel, while it 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 D102-78. In the inside painting system No. 2, this specification indicates that the first coat on the system directly on steel 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 D-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 Cetlosotve Acetate Xylene Toluene VM&P Naphtha Flexol 10-10 UCAR Resin 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 91.78 995.31 Gallons/100 Gallons 7.80 45.17 5.04 7.94 1.66 4.85 19,67 1.08 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 had 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 grit-blasted panels. However, the sand-blasted panels had better scribe performance than either shot- or grit-blasted panels. Even CR-42, which had tha 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 aalt fog tests. After 11,900 hours of salt fog exposure, tha vinyl perfor mance on hand-cleaned steel, coupled with thick wash primer, was comparable to that of blast-cleaned steel- Exp*ri*nc* with Ait*m*tiv* Pigmentation The use of alternative pigmentation In vinyl systems is not new. There are numerous examples of coating systems which have been used for many years and have provided a highly reliable level of performance. One of these la Spec. SSPC:*, which covers a vinyl coating pigmented only with titanium dioxide. Table 8 shows Corps of Engineers has numerous case histories where this type of paint has been applied for over 20 years under condi tions of continuous Immersions such as river locks and dams. A recent example of the use of zinc phosphate as an alter native anticorrosive pigment is illustrated in Formula VP-3639, shown In Table 10. Because of its neutral nature, zinc phos phate can be used in combination with a carboxylated vinyl resin such as VMCA for the formulation of coatings that are applied directly over steel. VP-3639 is one such example; this particular paint with an sntifouling topcoat has been totally Immersed for over S years at a test station in Florida. The results of this test are excellent. Summary In vinyl vehicles, a variety of alternative pigments were at (east equivalent to the established red lead formulations. This conclusion spplies to vinyl systems only. Another portion of the SSPC PACE program dealt with a similar series of ex periments aimed at evaluating alternative pigments in alkyd coatings. Here, the replacement appears to be more difficult, pointing to the fact that permeability of the polymer Itself is an important factor on the allowable formulating latitude. F-48387 14 ucc 058264 Materials Perl rmanee