US1888189A - Coated metal article and method of and composition for producing said article - Google Patents

Description

Patented Nov. 15,1932

PATENT OFFICE ROBERT E. TANNEB, OI HIGHLAND PARK AND VAN M. DABSEY, OI MOBENCI, MICHI- 1 a reunion or ammon a GJATED ARTICLE AND METHOD OF AND COMPOSITION FOR PRODUCING SAID ARTICLE Io Drawing. Application filed larch 29, 1982, Serial No. 601,882, and in New Zealand December 18, 1929.

This invention relates to a composition for coating metals and the method of making and using the same. More particularly, the invention relates to a composition for coat- 5 ing metals, es ecially iron, with phosphate 'coatings suita 1e for bonding to the metal aint, enamel, nickel plating or otherfinish- 1n coats.

e invention has for its object to provide a composition which will coat metal articles, particularly those having surfaces of iron or steel, with a bonding coating which will form a good base for 1paint, enamel or a plating coating and will rmly unite such a coating with the metal articles in such a way as to prevent their pealing.

Another object is to produce articles having surfaces of iron, steel, zinc or their alloys with a bonding coat and a finishing coat, the

bonding coat being of phosphates with particles of accelerating metal firmly embedded 7 therein.

Other features and objects of the invention will appear as the description proceeds.

There will be described first one specific method of carrying out the invention and 'then the principles of the invention and the range of equivalents and approximations will be indicated.

Immersing articles of iron and steel in a heated dilute phosphate solution, and there-- by forming on the surface of the articles substantially integral hosphate coatings, has long been known. 1? properly formed phosphate coating is quite resistant to rust and forms a good base for paint or other finishing coats. The practice for producing phosphate coating that is set forth in the patent to Green et al, No. 1,651,694, has been widely and successfully employed.

Under the most favorable conditions a bath such as described in that patent produe 5 a satisfactory phosphate coat in about onealf hour; but under usual commercial conditions a longer time is required, ,fre-

quently exceeding one hour. Also, difliculty is encountered in making the bath attack and coat iron or steel surfaces which are especially hard or'dense or are otherwise in a condition unfavorable for the formation of the coat and some surfaces are coated part way and left bare in spots.

GAN, ABSIGNOBS TO PARKER BUST PROOF COMPANY, OF DETROIT, MICHIGAN, A 003.-

The addition of a minute amount of copper to the solution greatly speeds up the coating operation and assists in starting the coating action on surfaces which are not readily coated by acopper-free solution.

In a bath produced in accordance with the directions in the above identified patent and having such strength that 10 cc. of the solution is neutralized by about 4-3/4 cc. tenth normal caustic soda solution with methyl orange as the indicator and by about 30 co. with phenolphthalein as the indicator, the presence of from 0.002% to 0.004% copper in the solution accelerates the chemical action so that the solution attacks and coats surfaces ditions similar except for the presence of copper.

Apparently the copper plates out in minute specks on the surface of the iron, in accord ance with well known chemical principles. Whether because of the presenceof these microscopic specks of copper, because of the presence of nascent iron atoms and phosphate radicals released during the plating action, or because of both, the accelerating action of the copper upon the production of the phosphate coating is very marked, so that the resultant coating is not merely the phosphate coating which would be produced otherwise with metallic copper added, but consists chiefly of a phosphate coating produced much more quickly than it would be without the copper present. Nevertheless, the proportion of copper in the coating is greater than it is in the bath, so that the bath becomes deficient in copper long before the phosphate content is seriously depleted. Therefore, 1n order to 5 keep the bath up to proper strength in copabove identi ed patent, copper carbonate in the proportion of about one pound of the carbonate to 30 pounds of the phosphate, or another copper compound, soluble in dilute phosphoric acid, used in an equivalent amount. The copper compound reacts with the phosphates upon standing. If such a mixture is added to the bath as soon as it is depleted to a 28 point strength, as defined in the above said patent, so as to bring the strength back to 30 points, the copper is kept within proper working proportions.

Since the copper works out of the bath more rapidly than the phosphates, much more copper is required in the replenishing powder than in starting the bath. Fairly satisfactory results may be obtained in starting a bath by using one seventh as much of the replenishing powder as is used of the dihydrogen powder with no copper added.

With a bath such as described, the deposited copper is completely embedded in the phosphate coat, so that the coat is as firmly adherent as though no copper was present. However, in a bath such as described, an increase of copper above about 0.004% not only increases the deposition of copper but also interferes with and slows up the formation of the phosphate coat, and there quickly results an excess of copper which is no longer firmly imbedded in phosphate, but creates a smudge on the surface of .the article, and is detrimental in that respect as well as slowing up the formation of the phosphate coating from its rate of production with the best proportion of copper.

The determining factor as to the amount of copper desirable in the bath seems to be the relative rate of deposition of copper and formation of phosphate coat, and, therefore, the percentage given by way of example may be varied with conditions which vary said proportion, either by aifecting the rate of deposition of copper or by affecting the rate of formation of the phosphate coat. For example, an increase of free acid, or the acid indicated by methyl orange indicator, above the proportion given above, expedites the deposition of copper without increasing the formation of the phosphate coat, and therefore anything which increases the free acid, other conditions remaining equal, lessens the percentage of copper desirable in the bath or permissible before a smudge is formed. Reduction of the free acid below that mentioned reduces the rate of deposition of copper, and

renders permissible a higher percentage of copper.- But in a solution neutralized so that little or no free acid is present, there is little or no formation of phosphate coat, so

agent which changes ferrous salts to ferric" salts, throws ferrlc phosphate out of solution and frees acid, which in turn increases the bubbling effect, and retards rather than accelerates the formation of a phosphate coating. These are recently discovered facts, forming no part of the invention claimed herein, and are referred to only to illustrate agencies which affect the permissible percentage of copper. It will be obvious that an oxidizing agent of the first class mentioned, by expediting the formation of the phosphate coat, increases the permissible percentage of copper. For example, sodium nitrate is an oxidizing agent of the first said class, and when the bath is formed by the use of lbs. sodium nitrate to 242 lbs. of the dihydro gen phosphate owder, the copper content may eincrease to .04 percent before smudge results.- However, such a bath. is rapid in its results without the addition of copper, and is very sensitive to a slight amount of copper so far as avoidance of bare spots is concerned. It follows that, with the addition of the sodium nitrate specified above, a copper content of as little as .0001% is effective to avoid bare spots while it does not result in any visible color of copper in the coating. Where a cold solution is used, or otherwise a solution containing little free acid, a still higher content of copper is possible before smudging is caused.

While the coating with copper particles embedded therein forms a very good base for paint or the like, and may even be used as a base for metal plating, it is not as rust-proof as the phosphate coating without the copper present, and so is particularly useful as a base coat rather than as a rust-proof coat per se. However, when used in the manner last specified in connection with an-oxidizing agent, the avoidance of spots is obtained with so little copper present that it has no seriously detrimental effect upon the rust resisting qualities of the coat."

Certain metals other than copper. and less basic than iron may be used to expedite somewhat the formation of the coating, or for other purposes. Silver is the most nearly analagous to copper, but silver works better with higher free acidity than dihydrogen mentioned above. Zinc phosphate normally produces thehigher free acidity desirable "an inhibitor in a phosphate bath, when used required, to

produce thesame result, the amount of silver w:

to produce a y given result being rdughly one-fourth as much as the copper required for an equivalentresult.

Mercury is depositedso very rapidly upon the surface of iron that it acts somewhat as described above in the case of an excessof copper. A minute quantity of mercury might be used in the bathto start a coating operation, but it is obvious that in this case the mercury would be quickl ex austed.

Tungsten has some acce erat g act on, but not as great as that of copper, and it tends to result in a somewhat soft coating. Itmay be used in conjunction with copper to reduce the coloring effect of the copper. Compounds with less accelerating effect.

Lead alone is not a satisfactory ac'celeratpt, but when copper is added the lead is deposited. rapidly and blackens the coat. Lead comof bismuth act somewhat like tungsten, but

2 pounds may be employed for the blackening effect. Two or three times as much lead as copper in the bath produces a fairly black coat. Excess of the copper and lead produces a smudgycoat. v

Molybdenum compounds seem to act as alone, but result in the rapid completion of a very thin hard coat which is not much more than a coloration. When used with an oxidizing agent, lead and copper, a thin hard black coat may be formed. Uranium compounds act somewhat similarly to molybdenum compounds, and are preferable thereto.

. For commercial reasons it is preferable to produce a material in dry or powdered foim which contains the proper constituents for forming the bath. Dihydrogen phosphate of copper might be produced and mixed with such a material, but it is difiicult to form a dry granular or powdered dihydrog'en phosphate of copper, this phosphate of copper having a tendency to remain in a somewhat plastic or jelly-like condition. For this reason, it has been found more feasible to mix with the phosphate powder a composition of copper which will react with the phosphate and produce the phosphate of copper within the powder itself.

1 While reactions have been described above as taking place in connection with phosphate powde'i' such as specified in the above identified patent, it will be readily understood that the same reasoning applies to any other mixture containing phosphates of iron or of other metals more basic than iron.

A phosphate and copper coating prepared as described above, is not as satisfactory for the sole or principle rust-proofing coating as K one free from-the copper, because the presence of copper .expedites the rusting of the i ii on whenever it becomesaccessible to rusting influence. On the other hand, the phosphate and co per coating seems to form fully as good abo particularly applicable topreparing surfaces or paintin or enameling, but is not intended as a su stitute for such a material for nd for a coating of paint or enamel, and in some respects is even superior to the coating as described in the above cited patent,

where that coating is to be depended-upon for the main rust resisting coating on metal.

However, in the example given where sodium nitrate is present, the min e amount ofcopper in the coating does no prevent its being quite rust resistant. With the solution first defined above, with the copper at its upper limit of 004%, or in the proportion of 1 part copper to about 250 parts of the P 0, present, iron articles boiled therein receive a coating containing about one part of metallic copper to 12.5 partsP O This is about the maximum amount of copper which can be used and incorporated in the coating without smudging where no oxidizin agent is used.

When sodium nitrate is adde in the roportion mentioned above, the copper in tiie solution may be increasedto about 04% or to about one part of copper to 25 parts P 0 with a resulting coating having about one part of metallic copper to four parts of P 0 By creasing the amount of oxidizing agent and or reducing the temperature of the bath with a resulting reduction in the proportion of free acid present, a still greater amount of copper may be employed without smudging, but the proportion given is about the upper limit practicable in a hot solution.

When desired, a zinc surface may be coated in accordance with the same principles discussed above in connection with iron.

While some of the possible changes in the preferred embodiment of the invention have been referred to in the above description, it will be readily understood that other variations may be made within the scope of the appended claims.

In the claims, balanced phosphate solution means a solution containing such a proportion of free phosphoric acid and acid phosphate that it will produce a coat on iron or steel of substantially insoluble phosphates.

This application is a continuation in part of group consisting of iron, steel, zinc and their 'alloys, which consists in subjecting the metal to a balanced phosphate solution and including in the solution an amount of metal of the e group consisting of copper, silver and tungsten, regulating the quantity of said metal inversely as to the of the bath its original roportion, and coating other erand directly unto the rate of format on of the hosphate coating so asto expedite the rouctionof a. phosphate coating and wit out deposiging more metal from the solution than is firm y embedded in the phosphate coating. 2. A method in accordance. with claim 1 and in which the accelerating metal is copper.

3. A method in accordance with claim 1 and. in which the acceleratin metal is copper in an. amountnot eater t an 1/25 of the amount of P 0, in t e solution. 4. A method in accordance with claim 1 and in which the solution is used hot, is free from an oxidizing agent, and the accelerating agent in the solution is copper in an amount not great than 1/250 of the P 0. in the solution.

5. A process of coating a metal of the group consisting of iron, steel, zinc and their alloys, which consists in subjecting the metal to an acid phosphate solution having a measured acidity as tested by phenolphthalein indicator at least five times as great as its acidity as tested by methyl orange indicator and containing not more than one part of copper to ten parts of the free acid as indicated by methyl orange indicator.

6. A process in accordance with claim 5 and in which the solution is free from an oxidizing agent and in which there is not more than one part of copper content to 100 parts of the free acid, as indicated by methyl orange" indicator.

7. A method in accordance with claim 1 and in which there is dissolved in the solution a metal of the group consisting of lead, bismuth, molybdenum and uranium.

..ing metal of the group consisting of copper,

silver and tungsten, until a coating is formed,

7 whereby the solution is depleted more in accelerating metal than in phosphates, replenishing the solution with material containin phosphates and accelerating metal with t e metal in greater proportion to the phosphates than it is in the original solution, whereby the solution is restored to its original composition, and treating other articles in the solution.

9. The method of coating articles having surfaces containing iron, which consists in subjecting such articles to a balanced phosphate solution containing not more than one part of copper to 10 parts of the free acid as in the solution as indicated by methyl orange, and thereby forming on the articles coatings relatively richer in copper than is the solution, replenishing the bath by ma terial relatively richer in copper than is the solution and thereby restoring substantially times as .great as its acidity as indicated by 7 methyl orange indicator and the acceleratin metal being present in an amount so sma as related to the free acidity of the solution on the one hand and the capacity of the solution to form a phosphate coat on the other hand, that all of the particles of accelerating metal deposited upon the coated metal are firmly embedded in phosphate formedon the coated metal.

11. A solution for coating a metal of the group consisting of iron, steel, zinc and their alloys, said solution comprising acid phosphates and an accelerating metalof the group consisting of copper, silver and tungsten, and

the acidity of said solution as tested by phenolphthalein indicator being at least five times as great as its acidity as indicated by methyl orange indicator and the accelerating metal being present in an amount less than 1/10 by weight of the free acid indicated by methyl orange indicator.

12. A solution in accordance with claim 10, and in which the accelerating metal is copper. 13. A solution in accordance with claim 11,

and in which the accelerating metal is copper.

14. A solution in accordance with claim 10 and containing dissolved therein a metal of the group comprising lead, bismuth, molybdenum and uranium.

15. A solution for coating metal of the group consisting of iron, steel, zinc and their 'alloys, said solution comprising acid phosphates and copper, the acidity as indicated by the phenolphthalein indicator being at least six times that indieatedby methyl orange, and there being not more than one part of copper to ten parts of free acid as indicated by methyl orange;

16. A solution in accordance with claim 15 and free from an oxidizing agent and in which there is not more than one part of copper to 100 parts of the free acid as indicated by methyl orange.

17. A solution in accordance with claim 15 and containing a metal of the groupco'nsisting of lead, bismuth, uranium and tungsten.

18. An article having a surface containing a metal of the group consisting of iron, steel,

zinc and their alloys, said surface having a bonding coat thereon covered with a finishing coat, the bonding coat comprising phosphates and a metal of the group consisting of copper, silver and tungsten and in an amount not' greater than 1/4 the amount of P 0 in the no coat as calculated from analysis for phosphorus.

19. An article in accordance with claim 18 and in which the metal in the bonding coat is copper.

20. An article in accordance with claim .18 and in which the metal in the bonding coat is copper and in an amount not greater than 1/12 the P 0, in the coat, as calculated from analysis for phosphorus.

In testimony whereof we have hereunto signed our names to this s cification.

ROBER R. TANNER. VAN M. DARSEY.