Document V4rvaoJ00NLgz9YGB8vjkQbo

Publication A Reprint from Materials Performance VOLUME 21 NOVEMBER. 1982 PAGES 9-14 Effect of Anticorrosive Pigmentation on the Performance of Vinyl Coatings Reprinted tar: Union Carbide Corporation Specialty Chemicals Division Old Ridgebury Road Danbury, CT. 06817 Copyright 1982 by the National Association of Corrosion Engineers P. 0 Bo* 218340 Houston, Texas 77218 ! ICi"' --0157 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 and 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 tas 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 it 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 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 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 this work considered the performance of vinyls over hand cleaned, rusty, and Intact miiiscale 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 S) or near white (SSPC-SP 10) using steel grit or shot abrasives, and primed with wash primer conforming to Mil. Spec. MILP-1S328. The standard United States Navy vinyl aikyd (MIL- P-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 0-1141-52) 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, 1962. `Union Carbide Corporation, Bound Brook. New Jersey. "Steel Structures Painting Council. Exposure Results A$ shown in Table 4, ail 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 November, 1982 0094-1492 '82/000186/J3 00/0 ; 1982. National Association ot Corrosion Engineers 9 TABLE i -- Film Thiekrtstt Summary: Wash Pnmar jIsi fit ft fff1ttt Ii S Ii i j if 4*1 1 ft IIsICnrnrtient P'gment Surface Preparetien a s * iu u u l i i ti ll iz X X * e at u JO e a z cO 3C s u * z San Water Steei Grit T4 '4 :? C4 ` * -, c_: __ . Ct4 t2 j c iSSPC SP s Steei Grit Ci Z * ; * : ; 0*4 j: n ; : ? ffreaft watt' tmnie'aiOn SSPC 1* 1 - 'fttaei MUiacai* SSPC If t - - - :s - - - - - - - 30*. Puaty Mimcai* life if a Pa Sana SSPC SPte _ Steel Grit GH SSPC fp s Steei Snot sw :; a ;; ; 5 ;5 -< :; C 2 s ? G S ; ;; *a : 3 ca : i : ; C3 2 4 ; i i ;; _ _ _ CNe SSPC SP10 Intact Ca va worn* Mltitcal* SSPC SP 1 40** Peaty Minacaia SSPC P 3 ft Sen# :e C0 21 sspc SPio Steal Grit 0* C 3 C a C2 C 4 0 5 :; C 3 C 3 ca : 2 Ota ;t : t : 8 aSSPC SP s Iteat inpt C3 C :3 04 C1 ; 2 a ; * Ca c; zi c: Ca C 3 Z2 _ _ S3I0 IlfMftO _ _ Satt intact p* Mniaetie SSPC S 1 oa C2 07 ; r 30S Swatf Mmieaie SSPC SP 3 Pa Sen# SSPC SPIO Nor# Fitm Thickns mii$ m m<i 25 4 ^mi TABLE 2 -- Film Thlcknaat Summary Wash Prlmor Plus Thro* Prlm#r Coals uco 10 050159 Materials Performance TABLE 3 -- film Thicfcna* Summary Full System 'Wash P'tmar PJu* Thr* Pnmr Coats Plus Topcoat) j Pigment IIfenvironment Surtece r#o*r*|,0r. -! * zX a j j a X a i * 9 f t #e 9 a c Z u i/i c f5 az t s V i U H c n 1s 5? aO i * i $ watt' imnwion f'Hh Co* Mtort* tali *os &ii Gnt ate Sic s i Steel Grit *. 4j _ 5t ` * c1 i _if 4 5- e ' - *- ., * . 4 4 - SSPC S* ft _ 4 __ intact _ .. - - _ - - ' Mmtceie sspc $e 20*. Pyn - - . _- _ae Mmacaie SSPC SP j Pf Sene SSPC 5P10 Steei Gni Gte i ---- - .__ - __- - * ' '` 44 < 2 e 4t -f 4 4 *t SSPC &e & Steot Shet 5260 _ 'b i y e * t 6 - *,,; e, _ 4 OJ _ '< SSPC SPtO *, - - _ -_- Intact _ -- _- -- - c: Wiiteeale SSPC SP t 20*. Putty - - - __- - - -_ - -- - c` Miiifcete SSPCSP 3 - - - _ . - _ - _- - - Pft Sane * ' &SPC SP10 - - - _ - - -- - - - Stee' Grit i9 *; r - 41 3 'c 44 * * 6t 4 4 ; 4 ; C14 SSPC SP 1 - - t1 _ - _ - - - a 4 - Steel Shol e: 6 * 4- 6 e i 5 4 J * a f & S3S0 SSPC SP10 _ - *.e 4 4 _ - ` - - - - intact _---- - - _- -- _ t4 Miiiecata SSPC SP 1 - -- - -_ - --- - - 20*. Putty _ - - - - _ - - - - _ Miitacaie SSPC SP 3 -- -_ - -- _ _- - Pa Sana __-_ __- _,, . _ ** SSPC SPtO - " ' " " - " -" "- -- Note Fum Thinness m?is < t m.l = 2i * umi 5J K ll U Si Z s0 A* : 1 t ` <b ;. e. j e 4 4: j * e* --- -j i ft ft 9 -- -- tins MethoO Putting 4STM O AID uttering PSTM one TABLE 4 * Frtih and Salt Wattr tmmarsion Data Summary (5700 Hours) Ia Pigment 5f * t 1 iI V u Cn.cionmant Sur'ece P'epereiion l9 o X a a X 0 s X Sen *aie> imn>ara>0n pee P|l|r Ifrimef t<on Sen eeeter Immeraion Pr#*h w* ter Immarnon Steal Grit G'4 SSPC SP 6 Stee* G'it G' - SSPC SP ft intact . Miitacaie SSPC SP 1 20*. Putty . - - MHiacalf SSPC SP 2 *e Sene SSPC SP10 Steel Gnt m . Die SSPC SP ft Steel Grit flu r* SSPC SP ft iniact Wiiiecaie SSPC SP i 20*i Putty W'tiaeeie SSPC SP 7 Pa Sane SSPC SPtO l November, 1982 4V 4V ucc 050160 11  ting Method Mvtting l*STM 0iQt Scribe Undercutting 32h4 mth Moment Su*i*ce Porparanon Steel Ont on SSPCSP s Sleet Shot S2M SSPC SP10 tntect wiiiatete SSPC IP ) * Sand SSPC SP10 Sleet Qni 014 SSPC SP ! Sleet Shot S2S0 sspc spia tmeet Mmscate SSPCSP 1 20*. Mutly Mmaeaie SSPC SP 2 * Sand SSPC SPIO TABLE 5 -- Coka Workj Dali Summary (14 Monthll * I l l MD *ot*M E Xe i 0 e 11 * s 1 Hu | 11 2e i 2 C* 1 u (A * u | 5 *& XX z 5 '& - c *0_ - _ - - - - : 'C c - _ 'C _ - - 'r - - _ - - - - - -- - _-- - _---- -- - -- - - 64 2 e --- - i- -- 8 H 4 *> - - - - i -- --- "-- "~ - - - --- --- -- - --- " ---- - " " ~ -" ~ - " i if I*$ o - - - 1. ss c - - - ~ " - s 1 - 4 - - * K i! U 1 KO - * " "" table 6 - Salt Fob Data Summary l*tte'tnf dJTM 07** <1t MS Sd^Se Un0**eul1wig 22nd inch 0*2* *OU>> intact Mitucaie SSPC SP ' JO*. **r Mitiacete S$PC SP 2 * Send lift $P'0 Side' G.t GU SSPC If i Steel Shot S*PC SPiO >itt*Cl M.llatala >PC $* t 20** Musty MinaePM sspc %* i P# Sis pc ip<a Sloe* Grit On UPC if l St**l Shot 1290 SSPC IPtO '{ Mt'ISCSI* ISPCSP I 20*. *uS'v Mxrscfltf SSPC IP 2 Pa Send pc s*'o 12 ucc OT'015^ Materials Performance TABLE ? -- Eip*nmnt>l Q**gn Coe sit P Se"d 5SPC SPiO tlMl Gn( Gn SSC SP i Steel SApt $280 SSPC SPiQ M>II*CI* SSPC SP ' 20* Kuity Mulecete SSPC SP 3 Pa &*ao SSPC SHO Sleei Gri< 014 *C SP 9 Steel Voi S2ao SSPC SP10 impel M<n*ca> SSPC SP ' ID'i ftuliy M.ll*cl SSPC SP 3 Pa S*A SSPC SP'O cpe :i, TABLE 8 -- Steel Structures Painting Council Paint Spec. No. 9 Ingredients Plgmani Titanium Dioxide, Unextended Vahicla (88% maximum) Vinyl Resin A (Hydroxyl-Containing) Vinyl Resin B (Carboxyl-Containing) Trlcresyl Phosphate or Dioctyl Phthalate Methyl Isobutyl Ketone Toluene Wt% 12.0 8.0 8.0 3.0 34.5 34.5 100.0 Pounds/100 Gallons 100 66.7 66.7 25.0 288.0 288.0 834.4 Vol.% 2.9 5.9 5.9 2.5 43.0 JM 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 11,500 hours. Slight blistering was noted only after 6000 hours. After 11,500 hours, there was little difference in blistering among the 12 systems. Aluminum flake 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 preparea to test the effect of a thick coat (over 0.5 mils) of wash primer when used with vinyl primers containing both rust-lnhlbltlve and noninhibitive pigments. Standard practice calls for a maximum of 0.5 mils for the wash primer (SSPC-PT 3). One purpose of this test was to determine If a vinyl coating could be applied successfully November, 1982 over hand-cleaned steei (both intact ana partially rusted miiiscale) 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 miiiscale, and partially rusted miiiscale. Three exposure environments were chosen' (1) fresh water 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 5700 hours of fresh water immersion. The hand-cleaned panels, however, started to blis ter, particularly the partially rusted miiiscale 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 IJ(;0 TABLE 9 -- Vinyl Type White (or Gray) Paint Formula V*766e Ingredients Vinyl Resin, Type 3 (Copolymer Resin) Vinyl Resin. Type 4 (Carboxylated Terpolymer Resmi Titanium Dioxide and (for Gray) Carbon Black Dnsodecyi Ptitnaiate Methyl isobutyl Ketone Toluene Orthophosphoric Acid Wt% 5,6 11,6 130 29 32.0 347 q.2 1000 the `ofmuiation ot this paint wnic* was first adoc'ed - '964 Since this coating contains a carbo*yiatec resin ;ne cai^t s suitable for direct application oxer steel. while it is a'sc seiftopcoatable: 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 m a diff'Cu't 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 coa' on the system directly on steel consists of SSPC Paint No 9 Numerous other examples could be cited. One. mciudeo 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 d'o*-de only This formula is shown in Table 9 The United States Army TABLE 10 -- VP-3639 White High Build Vinyl Anticorrosive Paint Methyl Butyl Ketone Ceiiosoive Acetate Xylene Toluene VM&P Naphtha Flexol 10-10 UCAR Resin VMCA Thixotropic Agent Titanium Dioxide Zinc Phosphate Pounds/100 Gallon* 52.27 365 86 36 57 57.50 10.46 39.00 217 97 9.18 114.72 91 7B 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 TOO.OO Wt% 525 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 (or 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 batter 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 whan applied over a thick wash primer on the sand-blasted panels. However, this surface had poorer performance in the salt fog tests. After 11,500 hours of salt fog exposure, the vinyl perfor mance on hand-cleaned steal, coupled with thick wash primer, was comparable to that of blast-cleaned steel. Experience with Alternative Pigmentation The use of alternative pigmentation In vinyl systems is not new. There ere numerous examples ot costing systems which have been used for many years and have provided a highly reliable level of performance. One ot these ie Spec. SSPC-9, 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 ot continuous immersions such as river locks and dams. A recent example of the use ot zinc phosphate as an alter native anticorrosive pigment is illustrated in Formula vP-3639. shown in Table 10. Because of Its neutral nature, zinc pnosphate can be used m combination witn a carboxyiated vmyi resin such as VMCA tor the formulation of coatings that are applied directly over steel, vp-3639 is one such example, this particular paint with an antifouling topcoat has been totally immersed for over 5 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 least equivalent to the established red lead formulations This conclusion applies 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 aikyd 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 !JCC 05016 Materials Performance