ALUMINIUM TRIHYDRATE MODIFIED ZINC-RICH COATINGS

Abstract: Modifying zinc-rich thermoplastic polyhydroxyether coatings with aluminium trihydrate improves corrosion resistance on unpassivated steel as well as welding prop­ erties.

Description: BACKGROUND OF THE INVENTION This invention pertains to zinc-rich coatings and more particularly to those containing thermoplastic polyhydroxyether and aluminum trihydrate. Zinc-rich thermoplastic polyhydroxyether coatings have been used for corrosion protection particularly in the automobile industry. Such coatings are also electrically conductive and so may be used where welding is used for assembling parts. Electrical spot welding is the preferred method of assembling automotive components. Zinc-rich coatings would be more widely used if certain deficiencies were corrected. These include corrosion resistance on unpassivated steel, welding spark/fume hazards, and poor weld strength. Zinc coatings also tend to coat the electrodes of spot welders so that the number of repetitive welds produced on steel is reduced. Spot welding and arc welding of steel requires temperatures in excess of 1300 C in order to obtain a melt that will flow together to form a bond. The spark temperature developed during arc welding is often 2000 CC or higher, while somewhat lower temperatures are sufficient during spot welding since the electrode pressure aids the flow of the soft steel. In both cases, however, zinc has a tendency to volatilize in the weld area because zinc has a boiling point of 910do. This is encouraged by the nonoxidizing environment, which is produced by the weld flux and the physical protection mechanism of the spot welding electrodes. Welding, therefore, results in an expulsion of zinc vapor which then readily oxidizes to zinc oxide upon leaving the weld area. Aluminum trihydrate has been used in the past to improve the arc and arc track resistance of epoxy compositions intended for electrical applications. Normally, the arc or spark generated during an overvoltage causes carbonization on the surface of the epoxy resulting in a conductive path and producing a short circuit. The presence of aluminum trihydrate in the formulation eliminates the formation of the conductive carbon track. The mechanism postulated is that the water released by the aluminum hydrate at the arc temperature oxidizes the carbon to gaseous components. The actual mechanism has not been defined although it has been discussed in U.S. 2,997,526 and U.S. 2,997,527. The description of the test method for evaluating inclined plane tracking under arc conditions can be found in ASTM D 2303-68. It is an object of this invention to impart such properties as reduced spark spatter, improved weld strength, and reduced electrode fouling in zincrich thermoplastic polyhydroxyether coatings. Other objects will become apparent to those skilled in the art upon a further reading of the specification. SUMSARY OF THE INE 'TION A satisfactory metal-coating composition meeting the above-described electrical criteria has been provided by a composition comprising: (A) a thermoplastic polyhydroxyether reaction product of substantially equimolar amounts of a polynuclear dihydric phenol and epichlorohydrin, said thermoplastic polyhydroxyether having E degree of poly merization of at least about 80; (B) about 350 to about 1350 parts by weight, per hundred parts of polyhydroxy ether, of zinc pigment; (C) about 25 to about 100 parts by weight, per hundred parts of polyhydroxy ether, of aluminum trihydrate; (D) O to about 35 parts by weight, per hundred parts of polyhydroxyether, of a heat hardened resole phenol-aldehyde condensation resin; and (E) 0 to about 15 parts by weight, per hundred parts of polyhydroxyether, of a suspending agent. Figure l-A and B is a Scanning Electron Micrograph of zinc-rich coatings without and with aluminum trihydrate exposed to salt spray for 100 hours. Figure 2-A and B is a Scanning Electron Micro-graph at 1000X magnification of zinc-rich coatings without aluminum trihydrate and containing aluminum trihydrate exposed to salt spray for.100 hours. Figure 3 is a Scanning Electron Micrograph at 600X magnification of a spot welding electrode face which has been exposed to the welding of a zinc-rich coating. The term "thermoplastic polyhydroxyether" herein refers to substantially linear polymers having the general 4. formula: EMI4.1 wherein D is the radical residuum of a dihydric phenol, E is an hydroxyl containing radical residuum of an epoxide and n represents the degree of polymerization and is at least 30 and is preferably 80 or more. The term "thermoplastic polyhydroxyether" is intended to include mixtures of at least two thermoplastic polyhydroxyethers. The thermoplastic poly(hydroxyethers) can be prepared by admixing from about 0.985 to about 1.015 moles of an epihalohydrin with one mole of a dihydric phenol together with from about 0.6 to 1.5 moles of an alkali metal hydroxide, such as, sodium hydroxide or potassium hydroxide generally in an aqueous medium at a temperature of about 100 to about 500C until at least about 60 mole percent of the epihalohydrin has been consumed. The thermoplastic poly(hydroxyethers) thus produced have reduced viscosities of at least 0.43. Reduced viscosity values were computed by use of the equation: EMI4.2 wherein to is the efflux time of the solvent (tetrahydrofuran, ts is the efflux time of the polyChydroxy- ether) solution, c is the concentration of the poly(hydrox ether) solution in terms of grams of poly(hydroxyether) per 100 ml. of tetrahydrofuran. The dihydric phenol contributing the phenol radical residuum, D, can be either a dihydric mononuclear phenol such as those having the general formula: EMI5.1 wherein Ar is an aromatic divalent hydrocarbon such as naphthylene and, preferably, phenylene, Y and Y1 which can be the same or different are alkyl radicals, preferably having from 1 to 4 carbon atoms, halogen atoms, i.e., fluorine, chlorine, bromine and iodine, or alkoxy radicals, preferably having from 1 to 4 carbon atoms, r and z are integers having a value from 0 to a maximum. value corresponding to the number of hydrogen atoms on the aromatic radical (Ar) which can be replaced by substituents and R1 is a bond between adjacent carbon atoms as in dihydroxydiphenyl or is a divalent radical including, for example EMI5.2 -SO-, -SO2- and -S-S-, and divalent hydrocarbon radicals such as alkylene, alkylidene, cycloaliphatic, e.g., cycloalkylidene, halogenated alkoxy or aryloxy substituted alkylene, alkylidene and cycloaliphatic radicals as well as alkarylene and aromatic radicals including halogenated, alkyl, alkoxy or aryloxy su- stituted aromatic radicals and a ring fused to an Ar group; or R1 can be polyalkoxy, or polysilox > , or two or more alkylidene radicals separated by an aromatic ring, a tertiary amino group, an ether linkage, a carbonyl group or a sulfur containing group such as sulfoxide, and the like. Examples of specific dihydric polynuclear pheno's include among others: The bis(hydroxyphenyl) alkanes such as 2,2-bis (4(hydroxyphenol)propane, 2,4'-dihydroxydiphenylmethane, bis (2-hydroxyphenyl)methane, bis (4-hydroxyphenyl)methane, bis(4-hydroxy-2,6-dimethyl-3-Lethoxyphenyl)methane, 1,1-bis-4-hydroxyphenyl ethane, 1,2-bis(4-hydroxyphenyl)ethane, 1,1-bis(4-hydroxy-2-chlorophenyl)ethane, 1,1-bis (3-methyl-4-hydroxyphenyl)ethane, 1,3-bis(3-methyl-4hydroxyphenyl)propane, 2,2-bis(3-phenyl-4-hydroxyphenyl)propane, 2,2 -bis (3-isopropyl-4-hydroxyphenyl)propane, 2,2-bis(2-isopropyl-4-hydroxyphenyl)propane, 2,2-bis (4-hydroxyinaphthyl)propane, 2,2-bis(4-hydroxyphenyl)pentane, 3,3-bis(4-hydroxyphenyl)pentane, 2,2-bis(4hydroxyphenyl)heptane, bis(4-hydroxyphenyl)phenylmethane, bis(4-hydroxyphenyl)cyclohexylmethane, 1,2-bis(4-hydroxyphenyl-1,2-bis(phenyl)propane, 2,2-bis(4-hydroxyphenyl) l-phenyl-propane and the like; Di(hydroxyphenyl)sulfones such as bis(4-hydroxyphenyl)sulfone, 2,4'-dihydroxydiphenyl sulfone, 5' - chloro-2 , 4'-dihydroxydiphenyl sulfone, 5'-chloro-4,4'dihydroxydiphenyl sulfone and the like; ; Di(hydroxyphenyl)ethers such as bis(4-hydroxyphenyl)ether, the 4,3'-, 4,2'-, 2,2'-, 2,3'-, dihydroxydiphenyl ethers, 4,4'-dihydroxy-2,6-dimethyldiphenyl ether, bis(4-hydroxy-3-isobutylphenyl)ether, bis(4-hydroxy 3-isopropyiphenyl) ether, bis(4-hydroxy-3-chlorophenyl)ether, bis(4-hydroxy-3-fluorophenyl)ether, bis (4-hydroxy3-bromophenyl)ether, bis(4-hydroxynaphthyl)ether, bis (4- hydroxy-3-chloronaphthylether, bis (2-hydroxydiphenyl)- ether, 4,4'-dihydroxy-2,6-dimethoxydiphenyl ether, 4,4' dihydroxy-2,3-diethoxydiphenylether, and the like. Also suitable are the bisphenol reaction products of 4-vinylcyclohexene and phenols, e.g., 1,3-bis (p-hydroxyphenyl)-l-ethylcyclohexane and the bisphenol reaction products of dipentene or its isomers and phenols such as 1,2-bis(p-hydroxyphenyl)-l-methyl-4- isopropylcyclohexane as well as bisphenols such as 1,3,3 trimethyl-l- (4-hydroxyphenyl) -6-hydroxyindane, and 2,4bis(4-hydroxyphenyl)-4-methylpentane, and the like. Particularly desirable dihydric polynuclear phenols have the formula EMI7.1 wherein Y and Y1 are as previously defined, r and z have values from O to 4 inclusive and R1 is a divalent saturated aliphatic hydrocarbon radical, particularly alkylene and alkylidene radicals having from 1 to 3 carbon atoms, and cycloalkylene radicals having up to and including 10 carbon atoms. Mixtures of dihydric phenols can also be employed and whenever the term "dihydric phenol" or "dihydric polynuclear phenol" is used herein, mixtures of these compounds are intended to be included. The epoxide contributing the hydroxyl containing radical residuum, E, can be monoepoxide or diepoxide. By "epoxide" is meant a compound containing an oxirane group, i.e., oxygen bonded to two vicinal aliphatic carbon atoms, thus, EMI8.1 A monoepoxide contains one such oxirane group and provides a radical residuum E containing a single hydroxyl group, a diepoxide contains two such oxirane groups and provides a radical residuum E containing two hydroxyl groups. Saturated epoxides, by which term is meant diepoxides free of ethylenic unsaturation, i.e., z C = C < and acetylenic unsaturation, i.e, -CC-, are preferred. Particularly preferred are halogen substituted saturated monoepoxides, i.e., the epihalohydrins and saturated diepoxides which contain solely carbon, hydrogen and oxygen, especially those wherein the vicinal or adjacent carbpn atoms form a part of an aliphatic hydrocarbon chain. Oxygen in such diepoxides can be, in addition to oxirane oxygen, ether oxygen -0-, oxacarbonyl oxygen EMI8.2 carbonyl oxygen EMI8.3 and the like. Specific examples of monoepoxides include epichlorohydrins such as epichlorohydrin, epibromohydrin, 1,2-epoxy-1-methyl-3-chloropropane, 1,2-epoxy-1-butyl-3chloropropane, 1,2-epoxy-2-methyl-3-luoropropane, and the like. Illustrative diepoxides include diethylene glycol bis(3,4-epoxycyclohexane-carboxylate), bis (3,4- epoxycyclohexyl-methyl)adipate, bis (3,4-epoxycyclohexyl- methyl)phtalate, 6-methyl-3,4-epoxycyclohexylmethyl-6methyl-3,4-epoxycyclohexane carboxylate, 2-chloro-3,4 epoxycylohexylmethyl-2-chloro-3,4-epoxycyclohexane carboxylate, diglycidyl ether, bis(2,3-epoxycyclopentyl)ether, 1,5-pentanediol bis (4-methyl-3,4-epoxycyclohexyl- methyl)ether, bis(2 ,3-epoxy-2-ethylhexyl)adipate, diglycidyl maleate, diglycidyl phthalate, 3-oxatetracyclo[4.4.0.17,10.02,4]-undec-8-yl 2,3-epoxypropyl ether, bis(2,3-epoxycyclopentyl)sulfone, bis(3,4-epoxyhexoxypropyl)sulfone, 2,2 -sulfonyldiethyl, bis (2, 3-epoxycyclopentanecarboxylate), 3-oxatetracyclo [4.4.0.17,10.0.2,4]-undec-8-yl 2,3-epoxybutyrate, 4-pentenal-di-(6-methyl-3,4-epoxycyclohexylmethyl)acetal, ethylene glycol bis(9,10-epoxystearate), diglycidyl carbonate, bis(2,3-epoxybutylpenyl)-2-ethylhexyl phosphate, diepoxydioxane, butadiene dioxide, and 2,3-dimethyl butadiene dioxide. The preferred diepoxides are those wherein each of the oxirane groups is connected to an electron donating substituent which is not immediately connected to the carbon atoms of that oxirane group. Such diepoxides having the grouping EMI9.1 wherein A is an electron donating substituent such as --OO-, EMI9.2 and Q is a saturated hydrocarbon radical such as an alkyl, cycloalkyl, aryl or aralkyl radical The zinc pigment used in this invention is commercially available and preferably has a particle size of about 2 to about 15 microns. The resole phenol-aldehyde condensation products which can be used in this invention are produced by the condensation of phenols and aldehydes under alkaline conditions. A resole produced by the condensation of a phenol with formaldehyde-most likely proceeds through an intermediate having the following illustrated type structure: EMI10.1 In a typical synthesis, resoles are prepared by heating one mole of phenol with about 1.5 moles of formaldehyde using sodium or barium hydroxide as a catalyst, although any phenolic compound, or a mixture - of phenolic compounds having two or three reactive aromatic ring hydrogen positions, can be used with an aldehyde or aldehyde-liberating compound capable of undergoing phenol-aldehyde condensation. Illustrative of phenolic compounds are cresol, xylenol, ethylphenol, butylphenol, is opropylmethoxyphenol, chlorophenol, reco rcinol, hydroquinone, naphthol, 2,2-bis(p-hydroxyphenol)propane, and the like. Illustrative of aldehydes are formaldehyde, acetaldehyde, acrolein, crontonaldehyde, furfural, and the like. Illustrative of aldehyde-libera- ting compounds are for example, paraformaldehyde, formal in and 1,3,5-trioxane. Ketones such as acetone are also capable of condensing with the phenolic compounds, as are methylene engendering agents such as hexamethylenetetramine, and are contemplated as useful for preparing the resole resins in this invention. The condensation of phenolic compound and aldehyde, can of course, be conducted in the presence of other alkaline reagents such as sodium carbonate, sodium acetate, potassium hydroxide, ammonium hydroxide and the like, if desired. When the condensation reaction is completed, if desired, the water and other volatile materials can be removed by distillation, and the cathar lyst neutralized. The most suitable resole resins are those which are brought to an advanced state of cure, commonly called the "B" stage, but are still heat-reactive. These resins are insoluble in water, readily soluble in conventional organic solvents such as methyl ethyl ketone, acetone, methanol, ethanol, and the like. Resole resins having a particularly desirable comination of properties are those which have an average molecular weight in the range between about 350 artd 600. Where suspending agents are used their nature is not critical and thus one can employ low molecular weight polyolefins, silane treated pyrogenic silica, quarternary, amine treated hydrous magnesium aluminum silicate, and the like. Suitable solvents are used in applying the coating composition to the particular metallic substrate. The solvents used depend upon the nature of the application method. Thus for example, in spray coating it has been found useful to employ a mixture containing an aliphatic ketone having about 3 to 6 carbons -and aromatic hydrocarbons containing about 7 to 9 carbons plus optional aliphatic alcohols containing about 3 to 5 carbons, and the like. For roller-type applications one can use a mixture of Cellosolve acetate and aromatic hydrocarbons containing 7 to 12 carbons, and the like. It is convenient to use glycol esters such as Cellosolve acetate, (the acetate of a monoalkyl glycol ether sold under the Trademark Cellosolve by Union Carbide Corporation). The preferred polyhydroxyether is available commercially as Bakelite Phenoxy PKHH, a trade designation of Union Carbide Corporation for condensation polymer derived from bisphenoltA (2 ,2-bis (p- hydroxyphenyl)propane and epichlorohydrin having the structural formula: EMI12.1 The phenoxy resin is available as a solution in glycol esters such as Cellosolve acetate (the acetate of a monoalkyl glycol ether sold under the Trademark Cellosolve by Union Carbide Corporation) or in pellet form which is readily soluble in a variety of solvents and solvent blends. The solid phenoxy resin sold under the designation PKDA-8500 by Union Carbide Corporation is soluble in the following solvents: Butyl Carbitol, Butyl Carbitol acetate, Butyl Cellosolve, Carbitol Solvent, Cellosolve acetate, Cellosolve Solvent, Diacetone alcohol, Diethyl Carbitol, Dimethylformamide, Dimethyl sulfoxide, Dioxane, Ethoxy triglycol, Mesityl oxide, Methyl Cellosolve acetate, Methyl ethyl ketone, and Tetrahydrofuran. Carbitol is a Trademark of Union Carbide Corporation for the monoalkyl ether of diethylene glycol. Electrical Properties The electrical conductivities of aluminum trihydrate pigments were measured in order to determine their potential in weldable coatings. The conductance of a composite is dependent upon the electrical conductivity of the bulk material, its surface resistance and the magnitude of the organic insulating layer encapsulating the particles. Shape also is important since it determines the number of current paths. Since the determination of electrical conductivity of a pigment in a coating is subject to the many variables mentioned above, the laboratory measurements were made on dry pigment. The test procedure was as follows. The measurement procedure involved 8 determination of the electrical resistivity of the test powders using a Wheatstone Bridge. The apparatus used included a General Radio 1644 A Megohm Bridge and a test cell made from a polystyrene Petri dish with cover. The top and bottom of the Petri dish are each centrally drilled for a No. 4 brass screw and washer which holds 10 mil copper discs which function as electrodes. The lower dish has an internal diameter of 8.7 cm, a depth of 1.3 cm and a volume of 77.3 cc. The following procedure was used. The lower dish-electrode assembly was filled to over flowing with the powder to be tested. The excess powder was displaced by placing the cover electroded dish over the lower dish. A cork cylinder was placed on top of the cover so that a 500 gram weight could be centrally located on the cell and still permit making electrical contact with leads from the test cell and the megohm bridge. Resistivity measurements were then made using a 20 volt source. The reading in megohms was then converted to ohms/cc. or ohms-cm using the procedure of ASTM D 257. The volume resistivity of various trades of aluminum trihydrate also knows as aluminum hydrate, hydrated alumina or aluminum hydroxide, A1(OH)3 are presented in Table 1 and compared with zinc powder and other typical coating pigments. It may be noted that both 1/2 micron hydrated alumina (Hydral 705) and 1 micron (Hydral 710) have electrical resistivities that are lower than the Zinc Dust Pigment L-15 and therefore will not degrade the electrical conductivity and electrical welding properties of zinc-rich coatings modified with them. Alcoa 2-333 (6-7 micron hydrated alumina pigment), however, has a higher resistivity and is not as desirable. A widely used corrosion inhibitive pigment, zinc phosphate, has a resistivity that is two orders of magnitude higher than zinc. Hydral 710 with its 1 micron particle size was used in the examples because it should provide good particle packing properties with the 6-8 micron zinc dust because a particle diameter ratio of 1 to 5 is considered optimum. TABLE 1 ELECTRICAL PROPERTIES OF PIGMENTS VOLUME (1) (2) RESISTIVITY ALUMINUM TRlHYDRATE - ALCOA 705 5.6 x 105 1.9 x 109 ALUMINUM TRIHYDRATE - ALCOA 710 1.7 x 106 6 x 109 ZINC DUST L-15 5.8 x 106 2.0 x 1010 ALUMINUM TRIHYDRATE - ALCOA 331 6.1 x 107 2.1 x 1011 RED IRON OXIDE 1.5 x 107 5.2 x 1010 MICACEOUS IRON OXIDE 1.7 x 108 5.9 x 1011 ZINC PHOSPHATE 2.1 x 109 7.4 x 1012 TALC > 1012 > 1015 ATOMIZED ALUMINIUM POWDER > 1012 > 1015 (1) OHMS/CM - PETRI DISH TEST CELL AT 20 VOLTS WITH GENERAL RADIO 1644A MEGOHM BRIDGE. (2) ASTM D-257 OHM-CM. The invention is further described in the Examples which follow. All parts and percentages are by weight unless otherwise specified. EXAMPLES 1-6 and CONTROLS A-C Corrosion resistance was demonstrated by using aluminum trihydrate Alcoa 710 to modify zinc-rich phenoxy coatings at three different zinc levels. Twenty volume percent of the hydrated alumina was used to replace an equal volume of zinc or was added to the existing level of zinc in the Controls. The effect of the modification was then determined on salt spray resistance using unpassivated cold-rolled steel panels. Table 2 summarizes the formulations and shows that the substitution or addition of hydrated alumina to the zinc-rich coating results in significant improvements in corrosion resistance. The corrosion resistance improvement was un- expected since aluminum trihydrate is not noted as a corrosion-inhibitive pigment. The prior art contains no explanation of how the hydrated alumina interacts with the zinc to provide good corrosion resistance. Scanning electron micrographs, however, provide some inrorrnation on the physical properties of the corrosion products of the examples containing aluminum trihydrate versus the Control where zinc alone is used. TABLE 2 COMPARISON OF PIGMENT MODIFIED ZINC RICH COATINGS SALT SPRAY RESISTANCE Control Control Control A 1 2 B 3 4 C 5 6 PHENOXY PKHH(1) 25.2 25.2 25.2 25.2 25.2 25.2 25.2 25.2 25.2 PHENOLIC BKR-2620(2) 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 SUSPENDING AGENT &num;1(3) 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 SUSPENDING AGENT &num; ;2(4) .7 .7 .7 .7 .7 .7 .7 .7 .7 ZINC PIGMENT(5) 315 252 315 179 143 179 415 332 415 ALUMINUM TRIHYDRATE(6) - 21.2 21.2 - 12 12 - 27.9 27.9 VOLUME ZINC % 61.5 49.2 54.7 47.6 38.1 43.9 67.8 54.2 59.7 VOLUME ALUMINIUM TRIHYDRATE % - 12.3 10.9 - 9.5 8.7 - 13.6 11.9 PIGMENT VOLUME RATIO - ZINC/ATH 100/0 80/20 100/20 100/0 80/20 100/20 100/0 80/20 100/20 SALT SPRAY RATING(7) EXPOSURE 100 HRS. - BLISTERS 8 MD 8 F 8 F 8 M 8 F 8 M 8 M 8 F CORROSION 6 8 9 7 9 7 7 8 10 250 HRS. - BLISTERS 8 MD 8 F 8 F 8 M 8 F 8 M 8 M 8 F 8 F CORROSION 4 8 8 6 8 6 4 8 9 340 HRS. - BLISTERS 8 MD 8 F 8 F 8 M 8 F 8 M 8 M 8 F 8 F CORROSION 3 7 7 5 7 6 4 7 8 (1) DISSOLVED IN CELLOSOLVE ACETATE (21% SOLIDS). (2) DISSOLVED IN CELLOSOLVE (21% SOLIDS). (3) AEROSIL R-972 - DE GUSSA. (4) MPA-690 NL. INDUSTRIES. (5) L-15 FEDERATED METALS CORP. (6) HYDRAL 710 - 1 MICRON. (7) SALT SPRAY ASTM B-117. (8) APPLIED TO COLD ROLLED STEEL AND BAKED AT 350 F/20 MINS. D. B. 1 MILS (DRY). Examination of Figure 1 shows the presence of thread-like deposits on the surface of the mixtures containing aluminum trihydrate which are absent in formulations containing only zinc. Higher magnification (1000X) in Figure 2 provides more evidence of a multitude of small thread-like structures on the zinc-alumina trihydrate coating. The new surface structure may be expected to have better barrier properties than the formulation containing zinc alone. The thread-like structure seen resembles aluminum hydroxide formed on corroding aluminum. The welding properties of the Examples and Controls were demonstrated by evaluating spark spatter and weld strength of coated steel specimens with a Model CSS-Mark 4, Type OOAH 15 kva spot welder using a 4-cycle welding interval and a 50-cycle hold or cooling period. Water cooled electrodes were used having a 1/4" diameter with an 1/8" tip and a 450 taper. The following conditions were used: Welding Time - 4 cycles of 60 cycle/sec current Phase Shift Heat Control - 60% Hold Time - 50 cycles Gage Clamping Pressure - 75 psi Clamp Force - 100 pounds Electrode Face Pressure - 8150 psi The data in Table 3 demonstrates that spark spatter is decreased and welding strength increased when hydrated alumina is substituted for or added to zinc rich phenoxy coatings. The spark spatter data is the result of visual observations during welding. Weld strength was determined by placing the composites under torsion until broken by hand. These are relative values showing significant differences. The weld nllgget was also examined and found to be cleaner and better shaped when the aluminum trihydrate formulations were used. A similar observation was made on the copper welding electrodes. The aluminum trihydrate formulations provided less buildup or bonding. It may be inferred from this that the zinc oxide formed has less of a tendency to stick to the copper electrodes than due the zinc metal particles which can alloy with the copper. A scanning electron micrograph (Figure 3) shows that the spherical particles of metallic zinc tend to imbed themselves into the face of the copper electrode. TABLE 1 COMPARISON OF PIGMENT MODIFIED ZINC RICH COATINGS SPOT WELDING PROPERTIES (METAL TO METAL) Control Control Control A 1 2 B 3 4 C 5 6 PHENOXY PKHH(1) 25.2 25.2 25.2 25.2 25.2 25.2 25.2 25.2 25.2 PHENOLIC BKR-2620(2) 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 SUSPENDING AGENT &num;1(3) 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 SUSPENDING AGENT &num;2(4) .7 .7 .7 .7 .7 .7 .7 .7 .7 ZINC PIGMENT (5) 315 252 315 179 143 179 415 332 415 ALUMINUM TRIHYDRATE(6) - 21.2 21.2 - 12 12 - 27.9 27.9 VOLUME ZINC % 61.5 49.2 54.7 47.6 38.1 43.9 67.8 54.2 59.7 VOLUME ALUMINUM TRIHYDRATE % - 12.3 10.9 - 9.5 8.7 - 13.6 11.9 PIGMENT VOLUME RATIO - ZINC/ATH 100/0 80/20 100/20 100/0 80/20 100/20 100/0 80/20 100/20 SPARK SPATTER - FEET 4 0 0 3 1 1 2 1 1 WELD STRENGTH M G VG VP M-G VG M-G VG M-G (1) DISSOLVED IN CELLOSOLVE ACETATE (21% SOLIDS). (2) DISSOLVED IN CELLOSOLVE (21% SOLIDS). (3) AEROSIL R-972 - DE GUSSA. (4) MPA-690 NL. INDUSTRIES. (5) L-15 FEDERATED METALS CORP. (6) HYDRAL 710 - 1 MICRON. (7) APPLIED TO COLD ROLLED STEEL AND BAKED AT 350 F/20 MINS. at 0.7'1 MILS DRY. (8) TORSION SHEAR - VP - VERY POOR P - POOR M - MEDIUM G - GOOD VG - VERY GOOD Trade names of the pigments used are tabulated below. Aluminum Trihydrate - Hydral 705 (1/2 micron) Alcoa - Hydral 710 (1 micron) Alcoa - C-331 (6-7 microns) Alcoa Zinc Pigment - L-15 Federated Metals Corp. Zinc Phosphate - Reichard-Coulston, Inc. The following code was used for exposure ratings for coatings in the above-enumerated tests: 10 - No Change 9 - Very Slight Change 8 - Slight Change 7 - Medium + 6 - Medium 5 - Medium 4 - Slightly Bad 3 - Bad 2 - Very Bad 1 - Partial Failure O - Failure Blisters - F I Few M - Medium D - Dense Although the invention has been described with a certain degree of particularity, it will under stood by those skilled in the art that the present disclosure of the preferred forms has been made only by way of example and that numerous changes and modifications can be made without departing from the spirit and the scope of the invention.

Claims: Patent Claims 1. Coating composition comprising: (A) a thermoplastic polyhydroxyether reaction product of substantially equimolar amounts of a polynuclear dihydric phenol and epichlorohydrin, said thermoplastic poly hydroxyether having a degree of polymerization of at least about 80; (B) about 350 to about 1350 parts by weight, per 100 parts of polyhydroxyether, of zinc pigment; (C) about 25 to about 100 parts by weight, per 100 parts of polyhydroxyether, of aluminum trihydrate; (D) O to about 35 parts by weight, per 100 parts of polyhydroxyether, of a heat hardened resole phenol-aldehyde condensation resin; and (E) O to about 15 parts by weight, per 100 parts of polyhydroxyether, of a suspending agent. 2. Composition claimed in claim 1 containing about 35 to about 70 parts by weight of aluminum trihydrate. 3. Composition claimed in claim 1 containing about 20 to about 30 parts by weight of resole phenolaldehyde condensation resin. 4. Composition claimed in claim 1 containing about 4 to about 10 parts by weight of a suspending agent. 5. Composition claimed in claim 1 wherein the polynuclear dihydric phenol is 2,2-bis(4-hydroxyphenyl)propane. 6. Composition claimed in claim 1 dissolved in a glycol ester. 7. Composition claimed in claim 6 wherein the glycol ester is Cellosolve acetate. 8. Composition claimed in claim 1 dissolved in a mixture of Cellosolve acetate and an aromatic hydrocarbon containing about 7 to about 8 carbons. 9. Compositon claimed in claim 1 dissolved in a mixture of an aliphatic ketone containing about 3 to 6 carbons and an aromatic hydrocarbon containing about 7 to 9 carbons. 10. Composition claimed in claim 1 dissolved in a mixture of an aliphatic ketone containing 3 to about 6 carbons, an aromatic hydrocarbon containing 7 to 9 carbons and an aliphatic alcohol containing 3 to about 5 carbons. 11. Corrosion resistant article comprising a metallic substrate and adhering thereto as a coating a composition comprising: (A) a thermoplastic polyhydroxyether reaction product of substantially equimolar amounts of a polynuclear dihydric phenol and epichlorohydrin, said thermoplastic poly hydroxyether having a degree of polymeri zation of-at least about 80; (B) about 350 to about 1350 parts by weight, per 100 parts of polyhydroxyether, of zinc pigment; (C) about 25 to about 100 parts by weight, per 100 parts of polyhydroxyether, of aluminum trihydrate; (D) O to about 35 parts by weight, per 100 parts of polyhydroxyether, of a heat hardened resole phenol-aldehyde condensation resin; and (E) O to about 15 parts by weight, per 100 parts of polyhydroxyether, of a suspending agent. 12. Article claimed in claim 11 wherein the polynuclear dihydric phenol is 2 ,2-bis (4-hydroxyphenyl) - propane.

Inventors: SALENSKY, GEORGE ANTHONY
Applicants: UNION CARBIDE CORPORATION
Application year: 1981
Main classification: C09D5
IPC codes: C08L23, B23K35, C08L71, C08L21, C09D171, C08L7, C09D5, C08L101