CA1061689A

CA1061689A - Premix for coating composition for metal substrates

Info

Publication number: CA1061689A
Application number: CA252,507A
Authority: CA
Inventors: Walter H. Gunn
Original assignee: Diamond Shamrock Corp
Current assignee: Diamond Shamrock Corp
Priority date: 1975-05-15
Filing date: 1976-05-13
Publication date: 1979-09-04
Also published as: HK61080A; FR2311074B1; FR2311074A1; AU497016B2; JPS579431B2; MX3433E; NZ180871A; AU1389476A; GB1538892A; DE2620987C3; DE2620987A1; BR7603063A; IT1061287B; JPS51143538A; MY8100223A; DE2620987B2

Abstract

PREMIX FOR COATING COMPOSITION FOR METAL SUBSTRATES

Abstract of the Disclosure An aqueous coating composition is prepared from an anhydrous, storage stable premix component to which there is added additional coating composition ingredients, including water. The premix contains pulverulent metal flake, water-soluble dispersing agent, water-soluble cellulose ether, and water-dispersible organic liquid. The other coating compo-sition ingredients are exemplified by a solution of chromic acid in water.

Description

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Background of the Invention ~ -Pulverulent metal has heretofore been blended, for example in a chromic acid liquid medium, to obtain a coating for application to metal substrates. This can provide corrosion resistance for the substrate as has been disclosed ln U.S. Patent 3,687,738. The coating compositions are typically dispersions of pulverulent metal powder or metal flake in water or t-butanol.
Such compositions that are characterized by being substantially water based and containing metallic flake can be improved through blending with a high boiling organic liquid. This will, for example, enhance coating characteristics.
CQmpositions of typically aluminum flake, a polymeric .
glycol plus wetting agent have been taught in U.S. Patent No.
3,318,716. These concentrates, usually in paste or liquid form, may be used in small amounts as anti-foaming and pigmenting compositions. The paste or liquid is added to coating composi-tions such as dispersions of resin in water. ~dditional pre-packaged admixes that may be useful include ., ,.,~: ,~. , ^'~

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particulate zinc, water-dispersible organic liquid plus thick-ening agent. These admixes are useful in the preparation of ;
coating compositions for metal substrates. These zinc-containing admixes can also be water-based, and have been ;
generally discussed in U.S. Patent 3,849,141.

Summary of the Invention Pigment concentrates such as the above discussed compo-sitions disclosed in U.S. Patent 3,318,716, can be useful to impart minor amounts of pigment to a coating composition.
When the particulate metal is used in the coating composition in heavy doses, as disclosed in U.S. Patent 3,687,738, such particulate metal offers a desirable combination of coating characteristics going beyond pigmentation. To facilitate ease in handling and storage, it is most desirable to pre-package ingredients into only a few, storage stable premix-tures. When the particulate metal is zinc flake, and it -will be used in heavy doses, such prepackaging can become ;
troublesome, often owing to the potential reactivity of pre-blended ingredients.
An improved premix is now provided which may be used in concentrated form and in such form can readily be blended ~;
with other liquid coating composition ingredients while ex-hibiting excellent storage stability before use. Such a premix composition will also provide aqueous-based liquid coating compositions when mixed with substituents that can themselves be prepackaged into a unified, stable blend.
Thus, the premix affords quick coating compositon preparation from only two packages. Unexpectedly, the two package system permits the preparation of liquid coating compositions that exhibit compositional stability themselves, and this stability is substantially extended beyond what has been heretofore acheived.
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Broadly, the present invention relates to a method of preparing a pulverulent-metal-containing coating composition, having enhanced ease of preparation from stable, premixed components. The method involves the blending of a pulverulent-metal-free and water-containing chromate component (A), with an anhydrous and chromate-free pulverulent metal component (B), to thereby prepare a composition adapted for treating metal substrates and providing corrosion resistance thereto.
The method comprises preparing the water-containing chromate component (A) by establishing an aqueous composition containing hexavalent-chromium-providing substance in aqueous solution.
The method also comprises preparing the anhydrous and chro~ate-free pulverulent metal component (B) by blending together water-soluble liquid dispersing agent and water-dispersible organic liquid in amount sufficient to supply the coating composition which above about 0.0005 volume percent of the agent and at least about 5 volume percent of such organic liquid, both basis total volume of the coating composition.
Next the broad method of the invention comprises admixing water-soluble cellulose ether to the resultlng blend of dispersing agent and organic liquid, there being sufficient of such ether to provide between about 0.01-3 weight percent of ether in the pulverulent metal component (B), exclusive of the liquid medium of such component (B); and next this method comprises mixing pulverulent metal flake to the resulting ether-containing admix in amount sufficient to provide a weight ratio of the metal flake to the organic liquid of from about 1:4 to about 4:1 and sufficient to supply above about 50 grams per liter of metal flake to the coating composition. Lastly, the method calls for blending the components (A) and (B) together to prepare the coating composition.

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~ ` ~L069.~`~9 The present invention is further directed to the prepara-tion of coating compositions using the above described anhy-drous and chromate-free premix composition, as well as directed to such premix composition itself.

, Description of the Preferred Embodiments The water-soluble cellulose ethers, and most especially those of commercial importance, can be classified into the ionic type such as sodium carboxymethycellulose, and the ;
anionic. This later includes the hydroxyalkyl ethers as exemplified by hydroxyethylcellulose, as well as the alkyl type as exemplified by methylcellulose. Although the ionic type are the most hydrophylic they may be subject to precipi-tation from solution in the presence of metal ions. Thus, - especially in regard to aqueous coating compositions prepared from chromic acid, the nonionic cellulose ethers are preferred.
Further, the hydroxyalkyl ethers are particularly preferred owing to their more ready solubility in cold, as well as hot water.
For economy, the coating composition preferably contains below about 3 weight percent, based on the total weight of the coating composition, of water-soluble cellulose ether.
To enchance thickening such composition contains the cellulose ether in an amount greater than about 0.01 weight percent, also based on the total weight of the coating composition.
In general then the premix will contain exclusive of its liquid medium, between about 0.01-3 weight percent of the water-soluble cellulose ether. Preferably, for efficiency and economy, the water-soluble cellulose ether is one of -hydroxethylcellulose, methylcellulose, methylhydroxypropyl-cellulose, ethylhydroxyethylcellulose, methylethylcellulose or mixtures of these substances.

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Although the cellulose ether needs to be water soluble to augment coating composition thickening, it need not be soluble in the water-dispersible organic liquid. The ether may be simply dispersed in the liquid, which liquid can contribute substantially to the make up of the premix, since up to 50 volume percent of the coating composition based on the total volume of liquid in the coating composition, can be supplied by such water-dispersible organic liquid. Such organic liquid, when present, also supplies substantially above about 5 volume percent, and advantageously above about 15 volume percent for enhanced coating characteristics, both on the same basis of total liquid volume of the coating composition.
It is most important that the organic liquid be a high boiling organic substance have a boiling point at atmospheric pressure above 100C. The organic liquid should also be easily dispersible in water and preferably water-soluble.
Such organic liquids as are used are those that are retained during baking on the coated substrate in sufficient amount

2~0 and duration to permit participation of the liquid in the formation of a coating. This partlcipation can be exemplified in the coating by reduction of chromium in the coating from hexavalent to the trivalent state.
The organic liquids contain carbon, oxygen and hydrogen and have at least one oxygen-containing constituent that may be hydroxyl, or oxo, or a low molecular weight ether group, i.e., a Cl-C4 ether group. Since water dispersibility and preferably water solubility is sought, polymeric hydro-carbons are not particularly suitable and advantageously serviceable hydrocarbons contain less than about 15 carbon atoms. Particular hydrocaFbons which may be present in the - .

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1~)6~ 39 aqueous coating composition include tri-, and tetraethylene glycol, di- and tripropylene glycol~ the monomethyl, dimethyl, and ethyl ethers of these glycols, as well as diacetone alcohol, the low molecular weight ether of diethylene glycol, - and mixtures of the foregoing.
The pulverulent metal flake, e.g., zinc flake or mixtures ;
therof as with aluminum flake, is most typically such pulveru-lent metal having a thickness on the order of 0.1-0.5 micron and most typically a size in the longest dimension of not substantially above about 150 microns. Aluminum flake, also sometimes termed leafing aluminum pigment, has been discussed, for example, in U.S. Patent 2,312,088. Flake may be blended with pulverulent metal powder, but typically in only minor amounts of the powder, and such powder shauld . . .
have particle size so that all particles pass lO0 mesh and a . .. . .
major amount pass 325 mesh ("mesh" is used herein as U.S. ;~

Standard Sieve Series). The powders are generally spherical as opposed; to the leafing characteristic of the flake.

The coating compositions of particular interest contain 20 an amount of pulverulent metal that does not exceed about :~ ;
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500 grams of metal per liter of coating composition liquid medium. More than this can add expense without a significant ncrease in protection for the coated substrate.~ Advanta-geously, for augmented coating protection, the coatlng com- ;
position contai~s above about 50 grams of metal per liter.
Thus the premix contains sufficient metal flake to supply ;~
above about 50 grams per liter to the coating composition.
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The premix ls prepared to contain a weight ratio of the water-dispersible organic liquid to the pulverulent metal flake of between about 1:4 - 4:1. Within this ratio the premix will exhibit desirable stability whlle providing ready mixing with further compositional constituents to ;
yield the coating composition.

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The premix should contaln some water-soluble liquid dispersing agent. Water-solubillty of the agent provides enhanced stability for the later prepared coating composition.
However, the agent need not be soluble in the water-dispersible organic liquid for such premix to exhibit desirable stability.
Such agent can be present in the premix in amount sufficient to supply the coating composition with as little as about 0.0005 volume percent of agent, basis total coating composition liquid. It is generally contemplated to employ a dispersing agent that is a nonionic surfactant which may be an ethoxylated alkylphenol such as a nonyl or octyl phenol. It is also contemplated to employ the nonionic ethoxylated aliphatic alcohols, representatives of which include the oleyl, lauryl, and stearyl alcohols. Other suitable nonionic surfactants that are also readily commercially available and are contem-plated for use in the present invention include, for example, carboxylic esters that encompass the glycerol esters and the anhydrosorbitol esters, as well as the polyoxyethylene esters of fatty, rosin and tall oil acids. ~It is also further contemplated to use carboxylic amide nonionic surfac-; tants for dispersing the pulverulen~ metal and these are meant herein to include the polyGxyethylene fatty acid amides. The preferred nonionic liquid dispersing agents are - polyethoxy adducts, exemplified by the alkylphenoxypolyethoxy-alkanols, and derivatives thereof, some of which are described , in U.S. Patent 3,281,475. Such agents are nonionic and have between about 7 and 50 oxyethylene units in the molecule.
For economy the agent is generally present in the coating composition in an amount not above 1-2 volume percent, on a total volume of the coating composition.

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The liquid dispersing agent, cellulose ether, pulverulent metal flake, and water-dispersible organic liquid are the key ingredients for the premlx composition. This mixture of ingredients will exhibit extended storage stability. To enhance such stability, the premix should be chromate-free.
Also for best extended stability, the premix composition should be anhydrous. By the use of this term it is meant that the premix may contain some very minor amount of water, as for example, less than 0.5 weight percent water. Water will typically be contributed from commercially available materials used in preparing the premix composition and not from the deliberate addition of water to the premix. For example, commercially available water-dispersible liquids can include very minor amounts of water, generally on the order of a few tenths of a weight percent or less, and it is not meant to exclude the use of such materials in the premix. -The critical components of the premix may be blended -together in any mixing order. Thus it is not critical that -:. . .
the water-soluble liquid dispersing agent and water-dispersible 20 organic liquid be first mixed with one another, although this is preferred for efficiency. After preparation, often followed by storage and/or shipping, the premix is ready for blending with additional ingredients to form an aqueous coating composition. Preferably, this blending will be carried out by simply mixing together the premix composition with an additional package of substituents. Further, this additional package of constituents will typically itself exhibit excellent storage stability. Thus, by means of the premix composition, a coating composition exhibiting excellent coating characteristics including corrosion protection for coated metal substrates, which composition itself further exhibits highly-desirable, extended useful life, will be prepared simply from two packages.

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It is, however, contemplated that the premix composition may be blended with additional coating composition ingredients -that are added individually or in packages other than one packaye. In addition to water, these additional ingredients include a chromate component. Furthermore, for extended storage life, it will be a pulverulent-metal-free component.
By use o the term "chromate component", it is most typically contemplated to use chromic acid. However, it is also contemplated to use its equivalent in aqueous medium, for example, chromium trioxide or chromic acid anhydride. But it is contemplated that the component can be supplied in whole or in part by a salt such as calcium, barium, magnesium, zinc, cadmium or strontium dichromate. Additionally, a minor amount such as 20 percent or less of the component might be a mixed chromium compound, i.e., include trivalent chromium compounds. Although the coating composition might contain only a small amount, e.g., 5 grams per liter of hexavalent chromium, expressed as CrO3, and may contain as much as about l00 grams per liter of composition of hexavalent chromium, expres-sed as CrO3, it will typically contain between about 20-60 grams.
For supplying the liquid medium of the aqueous coating composition, without considering the contribution by the water-dispersible organic liquid, water virtually always supplies the whole amount. Other liquids may possibly be used, but preferably only a very minor amount of the aqueous medium, basis the water content of the medium, is such other liquid material. Such other liquids that might be contem-plated include alcohols, most notably t-butanol, and halo-genated hydrocarbon liquid, some of which have been discussed in U.S. Patents 2,762,732 and 3,437,531. ; ` `-., , ,' '' ' ', . ' - 1 0 ~
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31 ~616~9 .An additional ingredient generally used in preparing the coating composition is an inorganic pH adjustment agent.
Such agent is basic, i.e., will yield a solution pH above 7.0 when dissolved in water alone, and has sufficient solubility in chromic acid solution to provide for pH adjustment. Repre-sentative pH adjusting agents are the inorganic metallic oxide, carbonate and hydroxide of lithium. The higher metals in Group lA, i.e., sodium and potassium, can be initially adequate for pH adjustment. ~owever, the subsequent coatings on metal substrates have been found to be water soluble and thus such agents are not suitable. Other metal oxides, carbonates and hydroxides can be supplied by metals in Group ;
IIA, e.g., calcium oxide or calcium carbonate, or metals in groups above IIA, i.e., to the right of the IIA Group in the ~-periodic table, such as zinc oxide as a represantative of Group IIB.
Other ingredients may be present in the aqueous coating aomposition but, even in combination they are most generally present in very minor amounts. Since the adherence for the particulate metal to the metal substrate might be achieved by the ostensible interaction of the chromate component with the water-dispersible organic liquid during curing of the coating, these coating compositions need not contain resin and are preferably resin-free, and such coatings that will be subsequently topcoated are virtually always pigment~free.
These other ingredients further include inorganic salts and acids as well as organic substances, often typically employed in the metal coating art for imparting some corrosion resis-tance or enhancement in corrosion resistance for metal surfaces. Such materials include zinc chloride, magnesium chloride, molybdates, glutamic acid, succinic acid, zinc -11- '. ' '. .~.
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nitrate, and succinimide and these are all preferably avoided, but if present, are most usually employed in the liquid composition in a total maximum amount of less than 5 grams per liter.
For the metal substrates containing applied coating, the preferred temperature for the subsequent heating, which is also often referred to as curing and which may be preceded by drying such as air drying, is within the range from about 400F. at a pressure of 760 mm. ~g up to not e~sentially above about 1,0~0F. Such an elevated substrate temperature may be attained by preheating the metal prior to application of the liquid composition. However, such curing temperatures do not often exceed a temperature within the range of about 450F-700F. At the elevated curing temperatures the heating can be carried out in as rapidly as about a few seconds but is often conducted for several minutes at a reduced temperature.
Before coating with the aqueous coating composition it is, in most cases advisable to remove foreign mattex from the metal sur~ace by thoroughly cleaning and degreasing.
Degreasing may be accomplished with known agents, for instance, with agents containing sodium metasilicate, caustic soda, carbon tetrachloride, trichlorethylene, and the like. ~ `
Commercial alkaline cleaning compositions which combine washing and mild abrasive treatments can be employed for cleaning, e.g., an aqueous trisodium phosphate-sodium hydro-xide cleaning solution. In addition to cleaning, the sub- ` ~;
strate may undergo cleaning plus etching. i After heating, the resulting coated substrate can be ~; ;
further topcoated with any suitable paint, i.e., a paint, primer, including electrocoating primers, and weldabLe primers such as the zinc-rich primers that can be applied before, typically, electrical resistance welding, and paints . ': -: ', ' ': ' , ,, ' '.' , `, . ' : . .,.';. i ' 1 ' . ' ' ,: ' ' '`, ~: , ' : ,; . ' `

6~9 such as enamel, varnish, or lacquer. Since the coated metal surfaces can exhibit a desirable upgrading in topcoat adhesion when compared, for example, to the uncoated substrate metal, paints are often applied over such coated substrates. Such ;
paints may contain pigment in a binder or can be unpigmented, e.g., generally cellulose lacquers, resin varnishes, and oleo-resinous varnishes, as for example tung oil varnish. The paints can be solvent reduced or they may be water reduced, e.g., latex or water-soluble resins, including modified or soluble alkyds, or the paints can have reactive solvents such as in the polyesters or polyurethanes. Additional suitable paints which can be used include oil paints, including phenolic resin paints, solvent-reduced alkyds, ipoxys, acrylics, vinyl, including polyvinyl butyral and oil-wax-type coatings such as linseed oil-paraffin wax paints. The paints may be applied as mill finishes.
The following examples show ways in which the invention has been practiced but should not be construed as limiting the invention. In the examples the following procedures -have been employed:
Preparatlon of Test Parts Test parts are typically prepared for subsequent treat-ment by immersing in water which has incorporated therein 2-.
5 ounces of cleaning solution per gallon of water. The cleaning solution is typically 75% by weight of potassium .
hydroxide and 25 weight percent tripotassium phosphate. The bath is maintained at a temperature of about 150-180F. ~ ~ `
After the cleaning treatment the parts are rinsed with warm water and may be dried.

Application of Coating to Test Parts and Coating Weight Clean parts are typically coated by placing in a wire basket and dipping the basket into coating composition, -13~

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~)6~16~9 removing the basket and draining excess composition therefrom with a mild shaklng action and then immediately baking or air drying at room temperature until the coating is dry to the touch and then baking. saking proceeds under infrared lamps or in a hot air convection oven, attaining substrate temperatures that can exceed about 450F., with times of several minutes, generally as specified in the examples.
Coating weights for parts, generally expressed as a weight per unit of surface area, are determined by selecting a random sampling of parts of a known surface area and weighing the sample before coating. After the sample has been coated, it is reweighed and the coating weight per selected unit of surface area, most always presented as milligrams per square foot (mgms./sq.ft.), is arrived at by straightforward calculation.
Corrosion Resistance Test (ASTM B-117-64) and Rating Corrosion resistance of coated parts is measured by means of the standard salt spray (fog) test for paints and varnishes ASTM B-117-64. In this test, the parts are placed 20 in a chamber kept at constant temperature where they are ~-exposed to a fine spray (fog) of a 5~ salt solution for ~ ;
speciied periods of time, rinsed in water and dried. The extent of corrosion on the test parts is determined by .
comparing parts one with another, and all by visual inspection.
In the following examples the efficacy of the corrosion ~ ~ ~
resistance obtained on coated parts is, in part, quantatively ;~ -evaluated on a numerical scale from 0 to 10. The parts are visually inspected and compared with one another and the system is used for convenience in the reviewing of results.
30 In the rating system the following numbers are used to cover ~ ;
the following results:

(10) retention of film integrity, no red rust;
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(8) initial coating degradation, pinpoints of red ^
rust;
(6) less than 3~ red rust basis total surface area of the part; ;
(4) 3 to 10% red rust, i.e., a significant amount of rust;
(2) 10 to 25 percent surface area red rust; r, ', (0) greater than 25 percent red rust.

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TO 55 milliliters (mls.) of dipropylene glycol (DPG) there , is blended with moderate hand agitation 0.5 ml. of wetter which .
i5 a nonionic, modified polyethoxy adduct having a viscosity in centipoises at 25C. of 180 and a denslty at 25C. of 8.7 pounds per gallon. The blending is seen to prepare a solution ~;
of the wetter and the DPG. To this solution there is then blended with moderate hand agitation 0.5 gram (gm.) of hydroxyethyl cellulose thickener. The thickener is a cream to white colored powder having a specific gravity of 1.38-1.40 at 2~0/20~C., an apparent density of 22-38 pounds~cu.ft., and all particles paS5 through 80 U. S. mesh. During agitation, ;; -~ -the thickener is seen to readily uniforml~ disperse into the blend of the wetter and DPG. -To this thickener mixture there is then added 84 grams of zinc flake and the addition is accomplished with manual agita- -tion. The zinc flake has particle thickness of about 0.1-0.5 micron and a longest dimension of discrete particles of about ;
80 microns. The resulting dispersion is seen to have a desir~
able uniformity. ~-~
Separately there is added to 88 ml. of deionized water, containing sufficient chromic acid to provide 50 grams per liter (g./l.) of CrO3, an additional 88 ml. of deioni`zed water.
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To this chromic acid solution is added 0.5 gm. of zina oxide.
The resulting chromic acid solution is slowly added to the ' metal flake dispersion to form a coating composition. From observation and analysis, the resulting coating bath is `~
deemed to be a highly acceptable bath, comparing favorably to coating baths prepared by a different, standardized method.
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In the manner of Example 1 the following ingredients, all as described in Example 1, are blended together, with the pro-portions being in grams for a liter of subsequent coating compo-sition: 213 gms. of DPG, 3 gms. of wetter, 3 gms. of cellulose thickener, and 336 gms. of zinc flake; this prepares an admix package. Separately, to prepare an additional package, there ~ -is added to deionized water sufficient chromic acid to provide ~ ~ ;
about 50 g./l. of CrO3 for a subsequent coating composition, and zinc oxide~ to provide 16 g./1. of same for the coating - composition. The metal flake dispers~ion (admix) package is slowly added to the chromic acid solution package to form a i~
coating composition from just the two packages.
~` To prepare a three-package bath, into 216 mls. of DPG
plus 3 mls. of the above described wetter, there is blended ;`
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336 gms. of the above discussed zinc flake. This prepares ~ -the first package. Separately there is added to 355 mls. of ! ' , deionized water, 50 gms. of chromic acid plus 16 gms. of zinc oxide with moderate mechanical sitrring. This formulates the second package.
To the zinc flake slurry (first package) there is slowly ~
added, during maderate mechanical agitation, a third package ~ -that contains 355 mls. of a predissolved solution of water 30 containing 3 gms. of the cellulose thickener. Subsequently, ;

the chromic acid solution (second package) is slowly added ~`

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to the zinc flake/ thickener blend accompanied by moderate mechanical agitation. This prepares a bath from three- `
packages.
The coating composition from the two packages, as well as that from the three packages, are each used to coat ten number 12d mild steel nails and ten 1/4" X 1/2" mild steel bolts. All parts are coated by dipping and draining in the manner described hereinbefore and the coated parts are cured in an oven for 30 minutes at an oven air temperature of 320C. ;
10 This coating process is repeated so that each of the 20 nails ~ ~;
and each of the 20 bolts contains three coatings. All bolts :r are determined to have about 1400 mgms./sq.ft. of coating.
All parts are subjected to the corrosion resistance salt spray test and after 500 hours of such testing, all parts -., . ~
are seen to have the same excellent rating. ~his demonstrates that the two-package coating composition procedure of the present lnvention will provide compositions yielding highly desirable coatings offering excellent corrosion protection equal to that obtained from baths prepared from the three packages.

A similar two-package bath is made in the above described manner, except that the chromic acid solution package is slowly admixed in to the metal flake dispersion package. Next, ~ -using the same substituents and proportions a three-package bath is prepared as discussed hereinabove. In this preparation, and as mentioned above, first a zinc flake/thickener blend is prepared from two packages and then the chromic acid solution is slowly admixed to the zinc flake/thickener blend. All ,. . . .
packages used for the preparation of each bath are formulated -- ~

30 to have excellent shelf stability. In shelf stability testing ~;
for the resulting baths, which can likewise be important, the :., . ~ .
three-package bath is stable for only about 60~ of the shelf life of the two~package bath.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of preparing a pulverulent-metal-containing coating composition, having enhanced ease of preparation from stable, premixed components, wherein said method involves the blending of a pulverulent-metal-free and water-containing chro-mate component (A), with an anhydrous and chromate-free pulveru-lent metal component (B), to thereby prepare a composition adapted for treating metal substrates and providing corrosion resistance thereto, which method comprises:
(I) preparing said water-containing chromate component (A) by establishing an aqueous composition containing hexavalent-chromium-providing substance in aqueous solution;
(II) preparing said anhydrous and chromate-free pulverulent metal component (B) by:
(a) blending together water-soluble liquid dispersing agent and water-dispersible organic liquid in amount suffi-cient to supply said coating composition with above about 0.0005 volume percent of said agent and at least about 5 volume percent of said organic liquid, both basis total volume of said coating composition;
(b) admixing water-soluble cellulose ether to the resulting blend of dispersing agent and organic liquid, there being sufficient of said ether to provide between about 0.01-3 weight percent of ether in said pulverulent metal component (B), exclusive of the liquid medium of said component (B); and (c) mixing pulverulent metal flake to the resulting ether-containing admix in amount sufficient to provide a weight ratio of said metal flake to said organic liquid of from about 1:4 to about 4:1 and sufficient to supply above about 50 grams per liter of metal flake to said coating composition; and (III) blending said components (A) and (s) together to prepare said coating composition.

2. The method of claim 1 wherein said water-soluble liquid dispersing agent is nonionic and the blending of said agent with said water-dispersible organic liquid solubilizes said agent in said liquid.

3. The method of claim 1 wherein said water-soluble liquid dispersing agent is blended with a water-dispersible organic liquid selected from the group consisting of dipropylene glycol, tripropylene glycol monomethyl ether, tetraethylene glycol, diethylene glycol monoethyl ether, dipropylene glycol monomethyl ether, and mixtures of the foregoing, and in an amount sufficient to supply said coating composition with above about 15 volume percent of said organic liquid.

4. The method of claim 1 wherein said hexavalent-chromium-providing substance is supplied by about 80 to 100 weight percent chromic acid and provides not substantially above about 100 grams per liter of chromium, expressed as CrO3.

5. The method of claim 1 wherein the admixing of said cellu-lose ether, to the blend of dispersing agent and organic liquid, disperses solid, particulate ether in said blend and said ether is selected from the group consisting of hydroxy-ethylcellulose, methylcellulose, methylhydroxypropylcellulose, ethylhydroxyethylcellulose, methylethylcellulose and mixtures thereof.

6. The method of claim 1 wherein said water-containing chro-mate component (A) is admixed into said anhydrous and chromate-free pulverulent metal component (B).

7. In the method of preparing a pulverulent-metal-containing and chromate-containing coating composition, wherein said method first involves the preparation of premixed components to thereby prepare a coating composition adapted for treating metal substrates and providing corrosion resistance thereto, the improvement in said method which comprises: preparing an anhydrous, chromate-free and storage-stable premixed pulverulent metal component, adapted for blending with additional coating composition ingredients including water and a chromate substituent, by blending together water-soluble liquid dispersing agent, water-dispersible organic liquid, water-soluble cellulose ether and pulverulent metal flake, with there being in the resulting premixed blend sufficient of said dispersing agent and sufficient of said organic liquid to supply above about 0.0005 volume percent of said dispersing agent and at least about 5 volume percent of said organic liquid to the total volume of said coating composition, and with there being sufficient of said cellulose ether to provide between about 0.01-3 weight percent of ether in said premixed blend, exclusive of the blend liquid medium, and wherein said blend contains a weight ratio of metal flake to water-dispersible organic liquid of from about 1:4 to about 4:1, with the flake being present in an amount sufficient to supply above about 50 grams per liter of metal flake to said coating composition.

8. The method of claim 7 wherein said blending includes dissolving water soluble liquid dispersing agent in said water-dispersible organic liquid as well as dispersing said cellulose ether and said metal flake in said organic liquid.

9. An anhydrous premix composition, formulated for blending with a liquid coating composition precursor that contains water-soluble chromate compound, with said premix providing ease of formulation and excellent stability after blending, and there-after facilitating fast and simple preparation of said liquid coating composition prepared for application to a metal sub-strate, said premix being chromate-free and containing:
(a) pulverulent metal flake;
(b) between about 0.01-3 weight percent, exclusive of premix liquid medium, of water-soluble cellulose ether;
(c) water-dispersible organic liquid providing a weight ratio of said pulverulent metal flake to said organic liquid of from about 1:4 to about 4:1 and with said organic liquid being present in an amount sufficient to supply at least about 5 volume percent of said liquid to the total volume of said coating composition; and, (d) water-soluble liquid dispersing agent in an amount sufficient to supply above about 0.0005 volume percent of said agent, basis total volume of said coating composition.

10. The premix of claim 9 wherein said water-soluble cellulose ether is nonionic and is selected from the group consisting of hydroxyethylcellulose, methylcellulose, methylhydroxypropyl-cellulose, ethylhydroxyethylcellulose, methylethylcellulose and mixtures thereof.

11. The premix of claim 9 wherein the pulverulent metal flake is supplied in major amount by a metal selected from the group consisting of zinc, aluminum, mixtures thereof and alloys of same, and said water-dispersible organic liquid is a compound containing carbon, oxygen and hydrogen and having one or more oxygen-containing constituents selected from the group consisting of hydroxyl, oxo, low molecular weight ether, and mixtures thereof.

12. The premix of claim 9 further characterized by containing said water-dispersible organic liquid in an amount sufficient to supply from about 15, to about 50, volume percent of said liquid to the total volume of said coating composition.

13. The premix of claim 9 further characterized by containing said water-soluble liquid dispersing agent in an amount pro-viding less than about 2 volume percent of said agent, basis total volume of said coating composition.