US3249447A - Coating compositions - Google Patents

Description

United States Patent 3,249,447 CGATIYG COMPfiSlTlUNS William A. Higgins, Cleveland, Ohio, assignor to The Lnbrizol Corporation, Wickliife, Ohio, a corporation of Ohio No Drawing. Filed Jan. 23, B62, Ser. No. 168,234 7 Claims. (Cl. 106-14) The present invention relates, as indicated, to improved coating compositions. In a more particular sense, it relates to improved protective coating compositions for metals, which compositions contain certain metal di-(aromatic) phosphinates.

The corrosion of metal surfaces is of obvious economic significance in many industrial applications and, as a consequence, the inhibition of such corrosion is a matter of prime consideration. It is particularly significant to users of steel and other ferrous alloys. The corrosion of such ferrous metal alloys is largely a matter of rust formation, which in turn involves the overall conversion of the free metal to its oxide.

The theory which best explains such oxidation of ferrous metal surfaces postulates the essential presence of both Water and oxygen. Even minute traces of moisture are sufficient, according to this theory, to induce the dissolution of iron therein and the formation of ferrous hydroxide until the water becomes saturated with ferrous ions. The presence of oxygen causes the oxidation of the resulting ferrous hydroxide to ferric hydroxide, which then settles out of solution and is ultimately converted to ferric oxide or rust. I

The above sequence of reactions can be prevented, or at least in large measure inhibited, by relatively impermeable coatings which have the effect of excluding moisture and/ or oxygen from contact with the ferrous metal surface. Such coatings are, of course, subject to abrasion, flexing, and other forms of physical deformation and to the extent that these coatings are penetrated or otherwise destroyed by such influences they become ineffective for the desired purpose. It is important that such coatings provide protection for all of the ferrous metal surface. A satisfactory protective coating composition, then, should have the ability to withstand corrosive, humid atmospheres, undercutting, and abrasion so that the protective film is maintained on the metal surface. Undercutting is a term commonly used in the protective coating art to indicate the separation of a protective coating from the metal substrate in areas adjacent to a scratch or score, causing a progressive flaking of the coating from the substrate. In severe cases, the undercutting may extend an inch-or more from each side of the scratch or score, causing the separation and subsequent flaking of the coating from a substantial portion, if not all, of the metal substrate.

Although known, siccative, organic coating compositions such as paint, lacquers, varnishes, synthetic resins, primers, enamels, etc., have been useful in protecting metal articles against corrosion, the degree of protection in many instances has been less than desired. In humid, corrosive environments, films of such known coating compositions generally exhibit a tendency to separate from the metal substrate and thus expose such substrate to corrosion. In an effort to improve the adhesion and corrosion resistance of known, siccative, organic coating compositions, workers in the field of protective coatings have investigated various chemical pretreatments of the metal article with metal-passivating solutions, aqueous phosphat- "ice ing solutions, and the like. Although such pretreatments have been effective in improving the adhesion of protective coatings to the metal substrate and in extending the useful life of such coatings in humid, corrosive environments, they have added. substantially to the cost of providing the desired degree of protection.

It is, accordingly, an object of the present invention to provide an improved protective coating composition for metal articles, especially ferrous metal articles.

Another object is to provide an economical method for protecting metal articles against the ravages of corrosion.

Still another object is to improve the corrosion resistance and bonding characteristics of known, siccative, organic coating compositions.

These and other objects of the invention are realized by means of an improved protective coating composition for metals which comprises (A) a major proportion of a siccative organic coating composition and (B) a minor proportion of a polyvalent metal di-(aromatic)phosphinate. The polyvalent metal may be any one of the various light or heavy metals such as, e.g., aluminum, copper, chromium, magnesium, calcium, zinc, strontium, barium, tin, lead, iron, cobalt, nickel, molybdenum, titanium, manganese, etc. In most instances, it will be a metal selected from Groups II, III, IV, VI, and VIII of the Periodic Table.

Thin films, generally from about 0.1 to about 10 mils and preferably 0.3-5 mils dry thickness, of the improved protective coating compositions of this invention are remarkably effective in protecting metal surfaces, especially ferrous metal surfaces, against the ravages of corrosion. Their effectiveness is believed to be due at least in part to their superior bonding or adhesion characteristics.

INGREDIENT A This ingredient, the siccative organic coating composition, may be any one of the various known paints, varnishes, lacquers, synthetic resins, primers, enamels, e-tc. Generally this ingredient will comprise from about to about 99.9 percent, more often from about to about 99.5 percent, of the improved protective coating composition of the present invention, including any additional solvent or solvents which may be added to thin the composition so that it can be suitably applied to a metal article. Solvents useful for the purpose of thinning include those generally employed in the protective coating industry such as benzene, toluene, xylene, mesitylene, ethylene dichloride, trichloroethylene, diisopropyl ether, aromatic petroleum spirits, turpentine, dipentene, amyl acetate, methyl isobutyl ketone, etc.

This ingredient may also be a water base or emulsion paint such as synthetic latex paints derived from acrylic resins, polyvinyl alcohol resins, alkyd resins, etc., by emulsification thereof with water, as well as Water-soluble paints derived from Water-soluble alkyd resins, acrylic resins, and the like.

Ingredient A may also contain conventional improving agents such as pigment extenders, anti-skinning agents, driers, gloss agents, color stabilizers, etc.

Ar OM wherein Ar and Ar are the same or different aromatic radicals and M is one equivalent of a polyvalent metal.

Ar and Ar are exemplified by phenyl; alkyl-substituted phenyl such as, e.g., methylphenyl, ethylphenyl, isopropylphenyl, n-butylphenyl, isobutylphenyl, hexylphenyl, octylphenyl, dodecylphenyl, hexadecylphenyl, wax-substituted phenyl, polyisobutene-substituted phenyl wherein the polyisobutene substituent contains from about 20 to about 100 or more carbon atoms, dimethylphenyl, trimethylphenyl, diethylphenyl, dihexylphenyl, etc.; alkoxy-substituted phenyl such as, e.g., methoxyphenyl, ethoxyphenyl, isopropoxyphenyl, lauroxyphenyl, etc.; and polynuclear aryl radicals such as naphthyl, substituted naphthyl, xenyl, substituted xenyl, phenoxyphenyl, substituted phenoxyphenyl, phenanthryl, substituted phenanthryl, and the like. Ar and/or Ar may also contain inorganic substitutents such as chloro, bromo, fluoro, nitro, nitroso, ether, sulfide, etc. In most'instances, however, Ar and Ar will be aryl or alkaryl radicals, generally the phenyl radical or lower alkylphenyl radicals in which the alkyl group or groups contain a total from one to about 6 carbon atoms. Although any polyvinyl metal is useful as the metal component of ingredient B of this invention, some are more effective than others. Particularly excellent results are obtained when the polyvinyl metal of ingredient B is lead, chromium, or calcium and, therefore, a preference is expressed for these metals. In some instances it is desirable to use more than one polyvalent metal. For example, a mixed lead-chromium salt or a mixed calciummagnesium salt is eifective as ingredient B.

Ingredient B can be prepared by any one of the several conventional methods available for the preparation of a salt of an organic acid such as, for example, the saponification of the di-(aromatic)phosphinic acid or ester thereof with a polyvalent metal oxide, hydroxide, carbonate, hydride, alcoholate, etc., or the metathesis of a monovalent metal or ammonium di-(armatic)phosphinate with a nitrate, chloride, acetate, etc., of the polyvalent metal desired in the final salt.

The di-(aromatic)phosphinic acid starting material may likewise be prepared by known methods, a number of which are described in chapter 7 of Organo-Phosphorus Compounds, by G. Kosolapoff (1950), John Wiley & Sons, New York, N.Y.

Such known methods include, for example, the following:

( Ar Ar 0 PCI 21120 1? 31101 Ar Ar OH (II) Ar 0 Ar 0 P 1120 --r P HCI A14 Cl Ar 011 (III) Ar Ar 0 PH l- 02 P Ar Ar OH The di-(aromatic)trichlorophosphorane and di-(aromatic)phosphinic chloride starting materials required for methods I and II are conveniently and economically prepared by methods disclosed, respectively, in US. Patents Nos. 2,727,073 and 2,724,726.

Examples of polyvalent metal di-(aromatic)phostheir efficacy as protective coatings.

phenyl phosphinate, zinc diphenyl phosphinate, cadmium di-(methylphenyl)phosphinate, barium di-(chlorophenyl) phosphinate, strontium di-(isopropylphenyl)phosphinate, nickel dixenyl phosphinate, calcium di-(ethylphenyl) phosphinate, calcium di (ethoxyphenyl)phosphinate, chromic dinaphthyl phosphinate, plumbous di-(phenoxyphenyl)phosphinate, aluminum diphenyl phosphinate, stannic diphenyl phosphinate, etc.

Specific techniques for the preparation of a number of polyvalent metal diphenyl phosphinates suitable as ingredient B of this invention are described below.

436 grams of diphenyl phosphinic acid (cf. Journal of the American Chemical Society, vol. 64 I942), pp. 2982 2983) is slurried in 365 ml. of Water and neutralized with 50 percent aqueous sodium hydroxide solution until the whole is just basic to a strip of pH 7 indicator paper. The crude, aqueous sodium diphenyl phosphinate is then filtered to yield a clear, amber solution. In separate vessels, -gram portions of 35 percent aqueous solutions of magnesium nitrate, calcium nitrate, cobaltous nitrate, cupric nitrate, chromic nitrate, ferric nitrate, plumbic nitrate, aluminum nitrate, stannic nitrate, and zinc nitrate are prepared. Each'of these ten metal nitrate solutions is then added dropwise slowly to a like number of 100-gram portions of the aqueous sodium diphenyl phosphinate solution until no further precipitation occurs. The precipitated polyvalent metal diphenyl phosphinate in each instance is collected on filter paper, washedwell with cold water, and dried under an infra-red lamp.

The magnesium, calcium, ferric, plumbic, aluminum, stannic, and zinc diphenyl phosphinates are white powders. Some of the polyvalent metal diphenyl phosphinates are highly colored, for example, the cobaltous salt is a dark blue powder, the cupric salt a light green powder, and the chromic salt a vivid green powder. For best yields in the case of the chromic and calcium salts, the aqueous sodium diphenyl phosphinate solution and the chromic and calcium nitrate solutions should be cooled to about 40 F. before they are mixed.

Generally ingredient B will comprise from about 0.1 to about 25 percent, more often from about 0.5 to about 15 percent, of the improved protective coating composition of the present invention, including any additional sol vent or solvents which may be added, as indicated earlier, to thin the composition so that it can be suitably applied to a metal article.

Ingredients A and B may be mixed-or blended in any one of several Ways such as, for example, the desired amount of the polyvalent metal di-(aromatic)phosphinate may be added to' the siccative organic coating composition and the whole then thoroughly mixed by means of a conventional paint mill or paint-shaking machine; In other instances, it may be more convenient to mix the polyvalent metal di-(aromatic)phosphinate with one or more of the components of the siccative organic coating compositions such as the vehicle, pigment, or. solvent thereof, and then to add the remaining components and mix them thoroughly by conventional means.

The improved protective coating compositions of this invention may be applied to a metal article by any one of several ordinary techniques such as brushing, sprayi 8, dipping, roller-coating, flow-coating, etc. Thereafter, the coated article is dried in the manner best suited for the siccative organic coating composition present therein such as air-drying at ambient temperature, drying in a current of hot air, baking in an oven, or baking under a battery of infra-red lamps. As noted earlier, the thickness of the dried film should generally be within the range from about 0.1 to about 10 mils, preferably 0.3-5 mils.

The following examples are presented to illustrate specific modes of preparing compositions of this inventlon, applying them to metal articles, and determining These examples in a laboratory paint-milling machine manufactured by are intended for purposes of illustration only and are not to be construed as limiting the scope of the invention, except as the latter is defined by the appended claims. Unless otherwise indicated, all parts and percentages are by weight and are based on the total composition.

Example A Eleven pairs of 4-inch x 8-inch panels of clean, degreased, ZO-gauge SAE 1020 cold-rolled steel were brushcoated, respectively, with 11 samples of a commercial, clear alkyd resin solution containing an anti-skinning agent and metallic naphthenate driers. The first sample contained no additional improving agent; the remaining samples had been blended, respectively, with 10 different polyvalent metal di-(aromatic)phosphinates.

The coated panels were allowed to air-dry and then they were subjected to rigorous Salt Fog Corrosion Test. The apparatus used for this test is described in ASTM procedure B117-57T. It consists of a chamber in which a mist or fog of 5 percent aqueous sodium chloride is maintained in contact with the test panels for a predetermined time at 95 *:2 F. In the present instance, the panels were placed at a 15 angle in the chamber, allowed to remain there for 96 hours, and then removed for inspection. The percent of the upper-face area of each pairof panels which was still covered with an intact film (i.e., a film which shows no rust and which is free from blisters, pinholes, etc.) was measured and reported as average percent of film intact.

The results obtained in this test are shown in Table 1.

TABLE 1 Salt Fog Corrosion Test,

Protective coating composition,

average percent of Each of the polyvalent metal diphenyl phosphinates was blended with the alkyd resin solution over a 15-minute perioid ar nor Laboratory, Inc. The alkyd resin solution contains 480 parts of a commercial alkyd resin, 120 parts of xylene, 6 parts of a 1% solution of cobalt naphthenate in aromatic petroleum spirits, 6 parts of a 4% solution of lead naphthenate in aromatic petroleum spirits, and 10 parts of a 10% solution of a proprietary anti-skinning agent in aromatic petroleum spirits.

It will be noted that each of the polyvalent metal diphenyl phosphinates measurably improved the corrosion inhibiting'properties of the alkyd resin. The most substantial improvement was realized, however, in those instances where a calcium, chromium, or lead diphenyl phosphinate was employed.

Example B Four pairs of 4-inch x 8-inch panels of clean, degreased, ZO-guage, SAE 1020 cold-rolled steel were brushcoated, respectively, with a commercial, titanium dioxidepigmented alkyd resin enamel and 3 coating compositions of this invention derived from said enamel. After the coating had air-dried, they were found to have a thickness of 15:0.1 mil.

The four pairs of coated panels were then subjected to the Salt Fog Corrosion Test described in Example A. In the present instance, however, the test period was 120 hours instead of 96 hours. The test results are given in Table 2.

TABLE 2 Protective coating composition: film intact Commercial TiO igmented alkyd resin enamel 1 60 Commercial TiO -pigmented alkyd resin enamel plus 2.7% of calcium diphenyl phosphinate 92 Commercial TiO -pigmented alkyd resin enamel plus 2.7% of chromic diphenyl phosphinate 92 Commercial TiO -pigmented alkyd resin enamel plus 2.7% of plumbous diphenyl phosphinate 91 Contains 2,384 parts of an alkyd resin, 1,200 parts of rutile (T102). 43 parts of castor wax, 36 parts of a 1% solution of cobalt naphthenate in aromatic petroleum spirits, parts of a 4% solution of lead naphthenate in aromatic petroleum spirits, parts of a 10% solution of a proprietary anti-skinning agent in aromatic petroleum spirits, and 716 parts of aromatic petroleum spirits.

The superiority of each of the three compositions of this invention over the siccative organic coating composition from which each was derived is clearly shown by the above test results.

Example C Four steel panels of the type previously described were brush-coated, respectively, with a commercial alkyd resin (described in Example A) and with 3 compositions of the invention derived therefrom. After the coatings on the panels had air-dried, they were found to have a thickness of 05:0.1 mil.

The coating on each panel was pierced with a pointed instrument to yield a vertical scribe beginning one inch from the top of the panel and extending one inch from the bottom thereof. The panels were then subjected for hours to the Salt Fog Corrosion Test described in Example A. After removal from the test chamber, each panel was inspected to determine the extent of undercutting. The undercut rating given in Table 3 is the average loss of coating from each side of the scribe expressed as an integer which represents the number of thirty-seconds of an inch of such loss.

TABLE 3 Salt llog Protective coating composition, com- 0011981011 Test, underrnercial alkyd resin plus: cut rating Control 15 0.78% of chromic diphenyl phosphinate 2 1.95% of chromic diphenal phosphinate 2 3.9% of chromic diphenyl phosphinate 1 The test results indicate that the coating compositions of this invention are remarkably resistant to unde-rcutting when conacted with a highly corrosive, salty atmosphere.

Example D Two steel panels of the type previously described were brush-coated, respectively, with a commercial, clear acrylic resin and a coatingcornpoistion of the present invention derived from said acrylic resin. After the coatings on the panels had air-dried, they were found to have a thickness of 04:0.05 mil. The coated panels were scribed and tested in the same manner set forth in Example C. The test results are given in Table 4.

TABLE 4 Salt Fog Corrosion Test, under- Protectlve coating composition: cut rating Commercial acrylic resin 10 Commercial acrylic resin plus 2% of chromic diphenyl phosphinate 3 The test data indicate that compositions of this invention derived from acrylic resins are highly resistant to undercutting.

Example E TABLE Protective Coating Composition Water Immersion Test,

Inspectors Remarks Strontium chromate wash primer 1 A number of small (ca. Mrs-inch (top-coated with a bake/enamel).

diameter) blisters scattered over the panel.

Completely free from blisters or pinholes.

1 Contains 150 parts of a commercial polyvinyl butyral resin, 18 parts of strontium chromate, 3 parts of magnesium silicate, 5 parts of 85% phosphoric acid, and 5 parts of water.

In addition to their utility as protective coating materials for ferrous metals, the compositions of this invention are useful in protecting non-ferrous metals and alloys thereof such as aluminum, magnesium, zinc, cadmium, Magnalium, copper, brass, brone, white metal, Dowmetal, etc., against corrosion. They are also useful as protective coating materials on galvanized ferrous surfaces, on plated metal surfaces such as copper-plated, nickel-plated, and cadmium-plated ferrous surfaces, and on phosphated metal surfaces. They are also useful as protective coating materials on chromated aluminum or chromated zinc surfaces, i.e., aluminum or zinc surfaces which have been treated with an aqueous solution of ch-romic acid or a derivative thereof such as a metal chromate or dichromate, an amine chromate, ammonium chromate, etc. Particularly fine results are obtained when the coating compositions of the present invention are applied to a metal article which has been phosphated by means of a novel aqueous phosphating solution containing as essential ingredients zinc ion, phosphate ion, nitrate ion, and a cation selected from the group consisting of lithium, beryllium, magnesium, calcium, strontium, cadmium, and barium.

What is claimed is:

1. A method for protecting a metal article against cor rosion which comprises applying thereto a thin film of a coating composition consisting essentially of (A) from about 75 to about 99.9% of a siccative organic coating composition selected from the group consisting of paints, lacquers, varnishes, synthetic resins, primers, and enamels,

and (B) from about 0.1 to about 25% of a polyvalent metal di-(aromatic) phosphinate.

2. A method in accordance with claim 1 wherein the polyvalent metal of (B) is chromium.

3. A method in accordance with claim 1 wherein the polyvalent metal of (B) is calcium.

4. A method in accordance with claim 1 wherein the polyvalent metal of (B) is lead.

5. A method in accordance with claim 1 wherein the aromatic radicals of the polyvalent metal di-(arornatic) phosphinate of (B) are phenyl radicals.

6. A method in accordance with claim 1 characterized further in that the metal article is a ferrous metal article.

7. A metal article which has been protected against corrosion in accordance with the method of claim 1.

References Cited by the Examiner UNITED STATES PATENTS 2,174,019 9/1939 Sullivan 260O 2,671,758 3/1954 Vinograd et al 10614 2,724,718 11/1955 Stiles et al 2605OO ALEXANDER H. BRODMERKEL, Primary Examiner.

MORRIS LIEBMAN, Examiner.

J. E. CARSON, L. HAYES, Assistant Examiners.

Claims (1)

1. A METHOD FOR PROTECTING A METAL ARTICLE AGAINST CORROSION WHICH COMPRISES APPLYING THERETO A THIN FILM OF A COATING COMPOSITION CONSISTING ESSENTIALLY OF (A) FROM ABOUT 75 TO ABOUT 99.9% OF A SICCATIVE ORGANIC COATING COMPOSITION SELECTED FROM THE GROUP CONSISTING OF PAINTS, LACQUERS, VARNISHES, SYNTHETIC RESINS, PRIMERS, AND ENAMELS, AND (B) FROM ABOUT 0.1 TO ABOUT 25% OF A POLYVALENT METAL-DI(AROMATIC) PHOSPHINATE.