US2763054A - Coating compositions and methods of coating metal products - Google Patents

Description

nited States Patent COATING COMPOSITIONS AND METHODS OF COATING METAL PRODUCTS Wesley J. Wojtowicz, Detroit, -Mich., assignor to The H. A. Montgomery Company, a corporation of Michigan No Drawing. Application March 5, 1952, Serial No. 275,030

7 Claims. (Cl. 29-424) This invention relates to coating compositions and methods of coating metal products for cold working, for example by deep drawing, shearing, form rolling and the like.

Before a metal workpiece can be worked, it is usually necessary to lubricate its surface. Whenever a lustrous surface is sought in the finished product, itis desirable to finish the surface prior to the .cold working operation. Protective coating materials are known which when used in conjunction with a lubricant rendera finished surface mar-proof during the working operation. Howevenmost of the mar-proof coatings with which I amfamiliar have disadvantages, such as causing coated workpiecesto stick together (blocking effect) or being corrosive to some metals. It would be desirable to apply the mar-proof coating material to the metal as the latter is finished in a continuous strip or sheet mill, but the foregoing disadvantages have prevented this practice.

An object of the present invention is to provide improved methods of preparing 'metalproducts for cold working in which the metal surfaces can be finished to a suitable luster and coated, the coated product can be coiled or stacked without the contacting surfaces sticking together, and subsequently the product can be cold worked with the coating protecting its surfaces against marring.

A further object is to provide improved coating compositions which eifectively protect metal surfaces against marring during cold working, possess good adhesion to metal surfaces, show no tackiness or blocking effect, and are nonhygroscopic, noncorrosive, impervious to ordinary lubricants, yet are easily removed from a workpiece after the latter has been cold worked.

Further objects are to provide coating compositions which have the foregoing improved properties and can be applied to continuous lengths of metal in a strip or sheet mill, and to provide coatingmethods wherein the metal is coated in the strip or sheet mill, whereby the metal can be delivered in coiled or stacked form to a fabricator already coated for subsequent working.

A further object is to provide as an improved article of manufacture a metal product coated with a composition which protects it during cold working and yet is not tacky.

Coating compositions of the present invention consist essentially of dewaxed shellac dispersed by. means of an alkali in aqueous glycol. They contain suflicient volatile alkali to neutralize the shellac, and advantageously can contain a wetting agent and a dye. The basic formulation by weight is as'fol-lows:

Dewaxed shellac .10 to 1.8.percent. Glycol to 25 percent of the weight of dewaxed. shellac. Volatile alkali "sufficient to new .tralize. the acidity ofthesshellac.

ous alkaline solutions.

Wetting agent 0 to 0.5 percent. Dye 0 to 0.04.percent. Water remainder.

KOH necessary to neutralize 1 gr.) and is thermoplastic,

having a tack point of about 205 F. When simply heated to 400 F. for 2-hours, dewaxed shellac undergoes a molecular rearrangement whereby its acid number drops to about 50 and it becomes tack-free at 250 F., but it remains thermoplastic. When dewaxed shellac is similarly heated in the presence of a suitable glycol, the acid numberdrops to about 15 and on prolonged heating the product becomes thermosetting. This reaction product forms the basis of the coating material used in the present invention, but, because of difficulties in obtaining a suitable solvent, I prefer to apply these ingredients 'to the workpiece in unreacted form and to produce .a

thermosetting coating .film .by subsequent heating. Shellac is used in the dispersion in an amount of l0:to 18 *percent by weight, since greater concentrations become shellac content with certain natural or synthetic resins.

Such resins should have an acid number of at least and are furthercharacterized by their solubility in aque- Examples of suitable resins are Manilla- DEB, a natural resin, "Ambero1 750, manufactured by.Rohm and Haas, and Arochem 450, manufactured by U. S. Industrial Chemicals, Inc. I prefer the straight shellac, but in the event of a scarcity, such replacement extends the, supply.

The glycols I have found particularly useful for the present invention are ethylene glycol, hexylene glycol and glycerin. They are usedin an amount equal to about 5 to 25 percent of the weight of dewaxed shellac. .Coatings produced with lessthan 5 percent glycol tend tobe brittle, whilethose produced with more than 25 percent tend to be tacky. The optimum proportion varies slightly with different glycols, being about 20 percent for hexylene glycol and 15 percentfor ethylene glycol and glycerin.

The volatile alkali canbe ammonia or morpholine or other equivalents. It is used in an amount sufiicient to neutralize the :acid content of the dewaxed shellac, preferably with a'reasonable excess. The alkali is removed when the coating is heated, so that the exact amount of excess is not critical. About 2.0 to 3.6 percent bywei'ght of the solution either ofammonium hydroxide (28 percent NHs) or morpholine furnishes satisfactory results.

The wetting agent used optionally conveniently can be Aerosol GT or other known equivalents for increasing the wetting action of the solution .on metal surfaces. The dye also used optionally conveniently can be basic fuchsine and furnishes a ready indication as to whenthe coating is cured properly, as hereinafter explained.

The preferred procedure in making up compositions .of the present invention is ,first to grind the dewaxedshellac and disperse it in' water andvolatilealkali at a temper- .ature of about F. After the shellacziszcompletely .troduced.

ireceived sufficient heating.

heating step and allowing it to cool slowly in air. coiled strip retains its heat long enough to accomplish the necessary cure.

Specific examples of compositions contemplated by the present invention follow. In each example the proportions are by weight.

Example I Percent Dewaxed shellac 13.0 Hexylene glycol 2.6 Morpholine 2.7 Aerosol OT (25% aqueous) 2.0 Water 79.7

Example ll Percent Dewaxed shellac 18.0 Ethylene glycol 2.7 Ammonium hydroxide (28% NHs) 3.6 Aerosol OT (25% aqueous) 2.0

Water 73 .7

Example 111 Coating compositions of the present invention are applied to the surface of a metal workpiece after the surface has been cleaned thoroughly. The workpiece can be of various metals, such as plain carbon steel, stainless or other alloy steel, aluminum, magnesium and numerous others. If desired, the surface can be polished to a high luster while the workpiece still is fiat before the coating is applied. Any usual procedure can be employed for applying the coating. For example, I have applied coatings successfully by dipping, spraying, spreading the composition with a roller or knife, and by flowing the composition over the metal.

After receiving its coating, the workpiece is heated to dry and set the coating. Preferably the heating is performed at 350 to 400 F. for about a half minute to a minute, although temperatures up to 450 F. can be used but are not preferred since the resulting coating is more ditlicult to remove. Equivalent results can also be obtained by heating to lower temperatures for longer intervals, for example, by heating to 300 for about 10 minutes. A dye incorporated in the composition furnishes a convenient means for indicating when the coating has In the example of basic fuchsine dye, the coating is blue as deposited. On heating the dye decomposes and becomes successively green, golden and brown. The coating should be heated until the coating attains a golden or a brown color. After this initial heating, the workpieces are cured by holding them at a temperature of 200 to 300 F. for about two hours. When the coating is applied to strip material, it can be cured simply by coiling the strip immediately after the The Coatings applied in accordance with the present invention, after curing are exceeding thin.

4 Their thickness should be within the range of 20 to millionths of an inch.

After the coating has been cured, the workpiece can be cold worked in any desired way, such as deep drawing, shearing, form rolling and the like. The coating is nonlubricating so that for more diflicult operations a lubricant should be supplied. The coating is impervious to all the common lubricants of which I am aware so that any standard lubricant can be used for this purpose. The coating effectively protects the surface of the workpiece against marring, so that if this surface has been polished it retains its lustre even after severe working and is free of scratches or mars. For shearing workpieces, which I define as including blanking, piercing, cutting and perforating, the coatings have special value in their ability to protect the dies.

After the cold working operation, the coating can be removed either mechanically by bufling or chemically by dissolving the coating material in an alkaline solution. Any of the commercial balanced industrial alkali cleaners at concentrations of about 4 ounces per gallon appear suitable. For example, I have used successfully a cleaner which consists by weight of the following:

Caustic soda percent 20 Water glass do 15 Trisodium phosphate do 15 Rosin soap do 10 Sodium carbonate balance The workpiece is immersed in the cleaner solution for about 2 minutes at B, after which the coating easily is removed with a water spray.

From the foregoing description it is seen that the present invention furnishes coating compositions which effectively protect metal surfaces during cold working and at the same time do not have the undesirable properties of being corrosive or hygroscopic or exhibiting or blocking effect. According to the cold working method of the invention, the coating can be applied well in advance of the working operation and the workpiece first can be polished to a high luster. Very conveniently the coating can be applied to metal strip in a finishing mill and the strip can be heated and then coiled all in a continuous operation.

While I have described only certain preferred embodiments of the invention, it is apparent other alternatives may arise. Therefore I do not wish to be limited by the disclosure, but only by the scope and obvious equivalents of the appended claims.

I claim:

1. A method of cold Working a metal workpiece comprising cleaning and finishing the surface of a workpiece, applying to the surface a single coating which has a thickness of 20 to 150 millionths of an inch and is of a thermosetting composition consisting by weight of the following:

dewaxed shellac 10 to 18 percent,

glycol 5 to 25 percent of the weight of dewaxed shellac,

volatile alkali sufiicient to neutralize the acidity of the shellac,

Water remainder,

the glycol being of the class which consist of hexylene glycol, ethylene glycol and glycerin, said composition being in the form of an unreacted aqueous dispersion when it is applied to the surface of the workpiece, heating the coated surface to a temperature of 350 to 450 F. for a half minute to a minute to dry and set the coating, curing the resulting thermally set coating by retaining this surface at a temperature of 200 to 300 F. for about two hours, cold working the coated workpiece with the coating protecting its surface against marring, and removing the coating by washing with a water solution of a balanced industrial alkali cleaner.

2. A method as defined in claim 1 in which the coating is applied to the workpiece while the latter is in continuous strip form, and the coa ing is cured by coiling the strip immediately after the first heating step, the contacting coated surfaces remaining free of cohesion for subsequent uncoiling.

3. A method of preparing a thermosetting coating composition which is adapted to be applied to metal products to enable them to be cold worked comprising dispersing ground dewaxed shellac in water and volatile alkali at a temperature of about 175 F., the resultant dispersion containing about 10 to 18 percent by weight of dewaxed shellac and sufiicient alkali to neutralize the acidity of said shellac, and adding to said dispersion at said temperature a glycol of the group consisting of hexylene glycol, ethylene glycol and glycerin, the glycol being present in an amount equivalent to 5 to 25 percent of the weight of deWaXed shellac, said dewaxed shellac and said glycol remaining unreacted in said dispersion but forming a thermosetting coating when applied to the surface of a workpiece, dried and heated at 350 to 450 F. for about half a minute to a minute.

4. A method of preparing metal products for cold working comprising coating the surface thereof with a thermosetting composition which consists by weight of the following:

dewaxed shellac to 18 percent glycol 5 to 25 percent of the weight of dewaxed shellac volatile alkali sufricient to neutralize the acidity of the shellac water remainder,

the glycol being of the group which consists of hexylene glycol, ethylene glycol and glycerin, said composition being in the form of an unreacted aqueous dispersion when it is applied to the surface of the workpiece, heating the coated surface to a temperature of 350 to 450 F. for half a minute to a minute to dry and set the coating, and curing the resulting thermally set coating by retaining the workpiece at a temperature of 200 to 300 F. for about two hours.

5. A method of preparing continuous lengths of metal strip for cold working comprising coating the surface thereof with a thermosetting composition which consists by weight of the following:

dewaxed shellac 10 to 18 percent glycol 5 to 25 percent of the weight of dewaxed shellac,

volatile alkali sufiicient to neutralize the acidity of the shellac water remainder,

the glycol being of the group which consists of hexylene glycol, ethylene glycol, and glycerin, said composition being in the form of an unreac'ted aqueous dispersion when it is applied to the strip surface, heating the coated surface to a temperature of 350 to 450 F. for half a minute to a minute to dry and set the coating, and immediately thereafter coiling the metal strip and thus retaining the strip at a temperature of 200 to 300 F. for about two hours to cure the coating, the contacting coated surfaces of the strip remaining free of cohesion for subsequent uncoiling.

6. An reacted aqueous dispersion for coating metal workpieces for cold working consisting by weight of the following:

dewaxed shellac 10 to 18 percent glycol 5 to 25 percent of the weight of dewaXed shellac,

volatile alkali sufiicient to neutralize the acidity of the shellac water remainder,

the glycol being of the group which consists of hexylene glycol, ethylene glycol and glycerin, the shellac and glycol having been dispersed in the water at a temperature of about F. to avoid reaction between them, said composition forming a thermosetting coating when applied to the surface of a workpiece, dried and heated to a temperature of 350 to 450 F. for half a minute to a minute.

7. A metal workpiece having on its surface a thermally set coating formed of a dispersion as defined in claim 6.

References Cited in the file of this patent UNITED STATES PATENTS 2,165,056 Kalischer July 4, 1939 2,166,179 Rubin July 18, 1939 2,166,180 Rubin July 18, 1939 2,245,100 Bernstein June 10, 1941 2,300,907 Bronson Nov. 3, 1942 2,363,540 McVey Nov. 28, 1944 2,365,959 Horwedel Dec. 26, 1944 2,386,421 Bassford Oct. 9, 1945 2,387,388 Gardner Oct. 23, 1945 2,425,023 Bassford Aug. 5, 1947 FOREIGN PATENTS 410,503 Great Britain May 14, 1934 515,000 Great Britain Nov. 23, 1939 OTHER REFERENCES Warren, Electrical Insulating Materials, 1931, London, pages 138 and 418.

Claims (1)

1. A METHOD OF COLD WORKING A METAL WORKPIECE COMPRISING CLEANING AND FINISHING THE SURFACE OF A WORKPIECE, APPLYING TO THE SURFACE A SINGLE COATING WHICH HAS A THICKNESS OF 20 TO 150 MILLIONTHS OF AN INCH AND IS OF A THERMOSETTING COMPOSITION CONSISTING BY WEIGHT OF THE FOLLOWING: