US2078917A - Method of attaching rubber to metal and articles produced thereby - Google Patents

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P 2 3 J.'IG..\MALONE- I 2,078,917

METHOD OF ATTACXflNG RUBBER TO METAL ARTICLES PRODUCED THEREBY Filed Aug. 24, v19:54

ATI'ORNEY Patented Apr. 27, 1937- UNITED STATES" mm QFFICE METHOD ons'rmcnmc nnnnan T METAL gun ARTICLES rnonncm THE John Gilbert Malone, Detroit, Mich. assignor, by

mesne assignments, -to-United States Rubber Company, New York, N. 12., a corporation of New Jersey- Application August 24, 1934, Serial No. 141,200 '1 (or. 18-59) proper adhesion of the rubber to such a plating, it

is necessary for the copper and zinc to'be deposited in definite proportions, about a 75% .cop-' per and 25% mm combination producing optimum results. The proportions of copper and zinc, however, can only be controlled in an electro plating operation when the metal surface to be treated is comparatively uniform in plane and is located in the bath ata definite relative position to the anode. Where the article to be rubber quality for a 75% coppergand 25% zinc com- 35 'ing an 'the elevated portions and on the edges than in coated is uneven and irregular in shape, the composition of the copper and in adeposit on the base is not maintained uniform, nor for that matter, is the thickness of the deposit. In platuneven surface more metal deposits on the depressions. This variation of thickness caused by directional effect may be as much as 1 to for diflerent parts of the surface. Also, a greater percentage of copper is deposited in the depressions or hollow portions andva higher percentage of zinc is deposited alongthe projections or edges of the article. Thimportance of obtaining a uniformly proportionate deposit of the c pperand zinc is exemplified when it is considered that on the basis of 100% adhesion bination, a "100% copper plating produces an ad-v hesion quality of about 50%, and where the copper content drops to about 60% with about 40% zinc content, the adhesion quality of the rubber to the copper-zinc plating is v practically nil. It has long since been suggested that rubber be adhered to metal by first dip-coating the metal with copper from a copper sulphate solution, but

as seen in the figures above, such a coating on I the base metal provides an adhesion quality only half that obtainable with a 75% copper and mnc coating. According to the present invention, high quality adhesion of'rubber to metal may be obtained by means of an alloy surface which may be deposited by a so-called dip-coating: methodn' By dip-coating" a metal base is meant the treatment of. thebase with a solution of the metals desired to be plated by a dipping, spraying,

spreading or other operation and allowing the plating operation to proceed merely by contact of the liquid with the base without the aid of an external electric current as in an electro plating operatio'nq The metal surface to which the rubber may be adhered according to the present invention is a bronze surface, that is, an alloy 5 comprising a major proportion of copper and a minor proportion of tin, with or without small amounts of other metals, as is well known in her is to be secured, is provided. with a bronze surface preferably by a dip-coating method, al-N though an electro plating method or a melting of the alloy directly on the surface of the base 25 1 i may be employed.

The following example of coating 0. steel base. with rubber by first dip-coating" the base with bronze is included merely. as an illustration of the present invention and is not to be consldered as limiting the same. The steel base was one designated in the trade as a 10-10 carbon steel, hot rolled. vIt contains about .02% sulphur,

1 .00'7% phosphorus, 437% manganese, and .06%

carbon. The micro structure is considered ferrite with minute pearlite areas with no evidence of deformation due to cold working. This is merely illustrative of the type of material which in large quantities is coated with a rubber composition in commercial practice: The constituents of the 40 plating solution were Sn, which may be added as such; Cu, which maybe added as CuSCn; and oxalate, which may be added as -potassium, 'sodium or ammonium oxalate, or as oxalic acid which is preferably almost completely neutralized by hydroxide. An example of a satisfactory solutioncontains 2 to 3 ounces of oxalate per gallon prepared by neutralizing all but about .5 oz. per gallon of the oxalic acid with potassium, sodium, or ammonium hydroxide to a phenolphthalein endpoint; .05'to .15 oz. pergallon oi'Bn as SnChZHzO: .002 paper gallon ofcopper as disodium (or ammonium) dlaquo dioxalate cupriate prepared by adding copper sulphate toa hot solution ofsodlum oxalate, as for example,

by adding a saturated copper sulphate solution to a solution containing about 5 oz. of sodium oxalate per gallon until turbidity appears. The disodium (or ammonium) diaquc dioxalate may be prepared as described by Fink and Wong Trans. Electrochem. 800., Vol. 63, pages 67-68, (1933) The coating solution should at all times be kept acid and it is preferable to apply the solution at a temperature between 50 and 60 C. A nve minute-treatment with the solution at such temperature is satisfactorybut a longer treatment is not detrimental. The surfacemay be coated by dipping into the solution or by spraying the solution on to the surface, using'a compressed air operated spray jet. The metal and the spray gun, however, should be free from oil andgrease or a uniform plating cannot be attained. A so-called rubber adhesion stock containing a vulcanizing agent was brought into contact with the dried bronze-coated steel base and vulcanized to the bronze coating by a heating operation as in present practice. An ad:-

hesion stock which is satisfactory .ona bronzed surface is set forth below, but many other different adhesion stocks may be used and these are well known in the art of adhering rubber to metal surfaces:

' The above composition may be vulcanized to the metal by heating for one-half hour at 148 C.

A bronze coating plated on a metal by a dipcoating method, unlike brass coated on a metal by an electroplating method, is of uniform thickness even over irregular portions of the article, and is of uniform composition at the same depth of the coating throughout the article. However, a dip-coating of bronze unlike the usual :clectroplated coatings gives a great variation in composition in the various layers of the coating itself, and a bulk analysis of the coatings is not a fair guide in determining the analysis of the coating for the best adhesion to a particular stock. The bulk analysis of, satisfactory coatings shows generally about 20% tin and over, but

the color of the. outer layers of the plating is a 55 much better guide than bulk analysis and should be gold when deposited from an oxalate-coppertin solution. The proportion of copper to tin increases as the deposition continues and is materially greater on the outer surface of'the coatings than adjacent the base. Analysis of the best coatings for adhesion show as a rule less than 15% tin in the outer coating layers, but with some stocks satisfactory adhesion may be obtained on a surface having as high a tin content as 30%, which is considerably more than the usualrun'of commercial bronzes. It is considered that this variation in the proportion of the diifereht ingredients of the alloy between the outer surface of the coating and' the surface ad- Jacent the base may be a cpnsiderable factorin .the production of successful coatings by the present invention. 7

The example above shows a dip-coating of bronze on ferrous metal for adhesion of rubber to ferrous metal, but the bronze may be coated on any-metal to which a is desired :8 aidhere -the rubber-"stock. As above stated, the

bronze may, if ,desired, be coated on the metal 7 stock bymelting-the same on to a clean surface of the stock, or, by-an electroplating, as well as by a dip-coating'process, as above described. If

it is desired to. adhere a rubber composition to a bronze base and the base isof a proper composition forsecuring the desired rubber combronze is too high in tin, it maybe dip-coated with an axalato-copper-tin solution as above'described. If, however, the bronze is of too high a copper content, or if, for example, it is desired to secure rubber, directly to a copper surface, then it is necessary to first plate the high-copper bronze or the copper base with a metal, such as tinfto'whlch both the base and the desired dipcoated bronze surface will adhere. For example, in dip-coating a copper surface, the cleaned copper surface may be coated with SnCh and water in the form of a paste which is then rubbed well with a wire brush to producea tinned'surface to which after washing the bronze may be applied by the dip-coating method as above. The samemethod is applicable in the case of a highcopper bronze where it is desired to ,plate a bronze coating of lower copper content for the desiredadhesion.

By dip-coating the base with ari acid aqueous oxalate solution containing copper and tin, coatings having less tendency to stain spotting" than coatings from alkaline cyanide solutions as in brass electro-plating are obtained. since it is known that alkaline compounds are more likely to cause this spotting out than acid substances. This spotting out is believed to'deleteriously affect the adhesion of the rubber, and experiments have shown that a small amount of residual oxalic acid on the metal coating does not impair adhesion of the rubber composition while smallamounts of residual cyanide do.

at various temperatures and for different periods of time depending on the composition of the same as is well-known in the art. Various modincations of the invention will occur to those skilled in the art and it is not intended to limit the invention other than as set forth in the appended claims.

Having thus described my invention, what I claim and desire to protect by Letters Patent is: 1. A new article of manufacture comprising a rrous base, a bronze coating comprising a major proportion of copper and a minor proportion of tin on said base, the proportion of copper to tin in said bronze being materially greater on the I outer surface of said coatingJghan adjacent the said base, the tin content of said outer surface being up to 15; percent and arubber'layer vulcanized on said coating.

2. A new article of manufacture a metallic base, a bronze coating comprising a major proportion of copper and a minor proportion of tin on said base, the proportion of copper to tin in said bronze being materially greater on the outer surface of said coating than adjacent the said base, analysis of the outer surface of the analysis of the entire thickness of coating showing at least 20% tin, and a rubber layer vulcanized on said coating.

5 3. A new article of manufacture comprising aferrous base, a bronze coating comprising a major v proportion of copper and a minor proportion of tin on said base, the proportion of copper to tin in said bronze being materially greater onthe' in outer surface of said coating than adjacent the said base.. analysis .ofthe outer surface of the coating showing at the most 15% tin and bulk 1 analysis of the entire thickness of coating showing at least 20% tin, and a rubber layer vulcanized 15 on said coating. 1 e

'4. The methodof attaching-rubber to metal which comprises dip-coating a bronze containing up to15 percent tin in the outer layers upon the metal from a solution containing copper and tin, 2 0 bringing rubber containing a vulcanizing agent into engagement with the coated surface, and

vulcaiilizing the rubber onto said Surface.

5.: The-method of-attaching' rubber to ferrous metal which comprises dip-coating a bronze con- 25taining u'p'to 15 percent tin in the outer layers ame'pr: j I 3 coating showing at the most 15% tin and bulk;

upon the ferrous metal from an aqueous solution containing'copper and tin, bri ein rubber cona vulcanizing agent into engagement with 1 the coated surface, and vuleanizing the rubber onto said surface.

6. The method of attaching rubber to metal which comprises dip-coating a bronze containing up to 15 percent tin in the outer layers andwith a bulk analysis of the entire thickness of the coating showing at least 20 percent tin upon the metal 10 from an aqueous solution containing copper and 'tin, bringing rubber'containing a vulcanizing .coated surface, and vulcanizing the rubber onto said surface. r

. JOHN GILBERT MALONE 25

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