US2080346A - Metallic paint - Google Patents

Description

Patented May 1l, 1937 vPli'rl-:N'r ori-ica METALLIC PAINT UrlynC. Tainton, Baltimore, Md., assignor to Tainton Research Corporation,

of Delaware a corporation Application June 11, 1932, Serial No. 616,730

9 Claims. .(Cl. 134-76) 'I'his invention relates to a new kind of flaked metallic powder having a bright surface, and to the method of manufacture thereof. Metal powders serving as pigment for paint are frequently genericallyreferred to as bronze powders even though made of metals' or alloys of metal which do not have or give what is specifically known as a bronze appearance. The expression bronze powder and the'expression bronze paint" as `10 herein used'are each employed in the broad or generic sense as including any of the metallic powders or metallic paints eventhough the same is used and relied upon to give a golden, yellow, silvery or other metallic appearance to an article or surface coated thereby. The present invention is characterized by being very much more economical, both in raw material and method of manufacture, than the so-called bronze powders now used for paint and similar purposes. At the present time, bronze powders are manufactured eitherfrom alloys of copper, such as brass, in cases where a golden or yellow -tint is required, or from aluminum where the paint is to have a silvery cast. Such present day powders as above mentioned are made by stamping the metal in small hammer mills and subsequently polishing the product so obtained by means of rotating brushes and the addition4 of a small amount of wax. The metals thus far used are relatively expensive and the operation of preparing the same is slow and costly, so that vtheprice of the nished powder is quite high. For example, aluminum powder suitable for paint ordinarily sells'at seventy-ve cents to one 35 dollar per pound.

It is well known that metallic zinc affords unusually good protection especially to surfaces of iron and steel. This fact is made use of in a- .paint which is made by mixing with linseed oilV l0 the material known as "blue powder or zinc dust, which`is obtained as a by-product in l the smelter distillation of zinc ores.

A recent circular, issued by the American Zinc Institute, states with reference to this question: Zinc in thefform of galvanizing is stated by the United States Bureau of Standards, Circular #80, to be by far the best protective metallic coating for the rust-proofing of iron and steel Apparently this characteristic of zinc is 0 equally effective when metallic zinc powder or so-called zinc dust is used in paint as a pigment and applied to metal surfaces -Service tests indicate that metallic zinc paint is outstandingly superior from the standpoint of low 5 cost per year of service.

Zinc dust, as used in the paint above mentioned, is of a. dirty blue-gray color and the resultant paint does not possess an attractive appearance nor good reectivity for light and heat. There would be considerable advantage in producing a metallic powder having the bright appearance like or similar to that of aluminum paint but consisting mainly of zinc and possessing the advantages of low cost and exceptional protection for metal surfaces. Such a bright zinc powder is, however, unobtainable in the market today. Y

Thereason for the above condition is as follows: When ordinary zinc is ground it turns dark and if the grinding is long continued, u1- timately takes on the appearance of soot. Moreover, the cost of grinding by the ordinary methods is very high as the yield in any given time is remarkably small owing to the fact that ordinary zinc, containing impurities, acts asa rather tough material when subjected to sudden impact. 1 p

It has been found that of the disabilities above mentioned, the darkening of the powder is due to e superficial oxidation caused by localv heating at the moment of impact. This condition is very much aggravated if rough surfaces are employed for the hammering action. 'I'he dimculty of grinding the zinc metal may be minimized by the use of certain alloys consisting of pure zinc to which has been added a small amount of one or more other elements. We find that a zinc powder having a bright surface may be obtained if the grinding is carried on with bright or polished surfaces in the presence of a considerable quantity of inert liquid, which prevents the local high temperatures referred to above. Proper means must also be provided for dissipating the heat which is generated by grinding. One of the outstanding advantages of the above method is that it is possible to employ ball mills or similar apparatus of large grinding capacity in the manufacture instead of the small hammer mills normally employed. It has been found that grinding equipment as heretofore employed will not produce satisfactory bronze powders. A recent textbook on the subject, Aluminum Bronze Powder and Aluminum Paint by J. D. Edwards, states, that:

.,There seems to be but one way to make metallic bronze powders, no matter what the specific mechanical arrangement -k employed. By pressure, the metal must be forced to now into ake-like particles. Pressure, such as in .stamping, produces a burnishing action and enhances and conserves metallic luster and brilliancy. abrasion and grinding produce a reduction in size of particle, but the powder so produced is dark in color and granularin nature. It is almost totally lacking in the brilliant ilakes whichl -give bronze powders .their characteristicappearance and value.

Applicant'has discovered and ascertained that in the presence of 'a large volume of inert liquid, it is possible to quite successfully employ standard grinding equipment. v'Io accomplish the desired end, applicant preferably passes a stream of relatively inert liquid through the mill and thereby carries in suspension the metal powder which is undergoing treatment. 'Ihis inert carrying liquid from the mill then passes to and through settling chambers or classifiers, in which the coarser material settles and from which the coarser material is 'returned to the head of the grinding circuit along with the new feed material, while at the same time the fine powder and inert liquid carrying the ilne powder is allowed to overilow and is passed Vto a lter or other suitable separating-out medium, when the iine iiltered out powder or particles are recovered as by filtration, centrifuging or similar treatment and from which the inert liquid freed of the major portion, if not all, of the iine powder is returned to the head f the grinding circuit. In this way, the operation is made continuous and the operating costs are very low.

It is preferred to employ for the lining of the grinding apparatus, to wit, the mill, as it is usually called and the grinding media, hard material capable of taking a high polish. Manganese steel or nickel-chrome alloys provide materials which may be used with advantage. It is also preierable to add to the inert grinding medium, reducing agents such as linseed oil, which will combine with and counteract any oxygen introduced into the circuit; and also sm'all Vamounts of organic acids such as stearic and oleic acid, which will combine with any zinc oxide that may be formed.

There isusually employed as an inert liquid. a light hydrocarbon such as kerosene or benzene. The linseed oil or similar material which is used as a reducing agent is added to this hydrocarbon in appropriate amounts, say ten to twenty per centum of linseed oil to ninety to eighty per centum of the inert light hydrocarbon. It is within the contemplation of this invention that other liquids such as carbon tetrachloride, butyl alcohol, et cetera, may be used to provide the inert liquid.

Before grinding in the'mill, the metal is reduced to the form of sheet, ribbon, granules, shavingaet cetera, and preferably to a thin, nnely divided form and one in which the zinc pieces are clear and bright. 'Ihe operation may be advantageously carried out as a method oijusing scrap zinc foil obtained in connection with `the process described in my Patent No. 1,959,087, dated May 15, 1934, or in my Patent No. 2,011,987, datedAugust 25, 1935, covering joint inventions of myself and Frank W. Harris. I'he zinc foil of these applications-or produced according to either of them-is particularly useful as providing the basic material from which to manufacture a zinc paint pigment according to the present invention. Another suitable method for preliminary preparation of the metal is to melt the metal and allow it to ilow in a molten form onto the periphery of a rapidly revolving metal drum.

By this means, extremely thin sheets or ribbons may be obtained.

However, for eiiective commercial production, it is advisable to have the zinc which is to be ground in relatively thin, slender or finely divided form whereby the grinding operation can be most effectively l'l'ied Out 80 that mQSi 0f the work and energy of grinding is employed-in the actual converting of the fine particles into brightly polished flake-like form.

The grinding operation employed and relied upon for carrying out and realizing the presentl V invention is one in which the application of impact pressure andfrictional rubbing contact is sumcient to break up and flatten. out the metalV -particles and so completely to change their form by pressure applied in a manner sd as to effect a flow of the metal into flake-like particles. In short, the grinding of this invention includes such steps and operations as may be described as grinding, disintegrating and attening out. In other words, the grinding of the invention accomplishes ,a crushing and corresponding spreading or extending of thesurface of the pieces or particles of raw material operated upon in order to produce the desired finished product. Moreover, this type of grinding is carried out in the presence of inert liquids as is herein pointed out.v The grinding of this invention should not be confused with grinding sometimes'so called which may involve nothing more than the introducing of metal pigment into a grinding machine to thereby eifect an intimate mixing of the pigment portions in or with a liquid with which it is being mixed in the grinding machine, and which mixing operation is carried out without disintegrating of the pigment particles and without an extending of the surfaces of the pigment particles.

According to certain broader aspects of the invention, ordinary zinc may serve as the raw material. However, for many purposes, it is especially advantageous to use alloys consisting of high grade zinc and containing a small quantity of another element in solid solution as described in my Patent No. 2,011,987 previously referred to. For example, an alloy which gives exceptionally brilliant paint is one consisting of more than 99.9 percentum of zinc and 0.07 percentum of manganese, other impurities such as cadmium and lead being as small in amount as possible. One purpose of manganese as an alloy is to prevent the recrystallization of the zinc as is described in said Patent No. 2,011,987, and other alloying metals may be used instead of manganese as is described in said patent. It is to be understood, however, that while the process herein described is especially applicable to the production of zinc and zinc alloy powders, it is not to be construed as being limited to this ileld, for the process to which the invention is directed has broad ilelds of application, and, for example, may be applied to the manufacture of powders of other metals such as aluminum, copper, brass, cadmium, lead, nickel, silver, gold, tin, etc. It is of especial value for the production of large tonnages as it permits the use of large grinding equipment and the minimum of supervision. It also obviates the danger of explosion which is a constant hazard when metals are classified in the presence of air as is done at present.

The single sheet of drawings diagrammatically illustrates an arrangement of apparatus by which the desired metallic zinc pigment suitable for paint may be made. 'Ihe apparatus shown emsludge-; and a filter 4 into which there is an ploys a wet grinding process and includes in combination 'and in operative relationship any suitable grinding mill, as, for example, a ball mill I-although any other type of mill such as a tube or rod mill could wellbe employed; a classifier, for example, a. drag classler, 2, into which the pulp from the delivery end of the ball mill ows through suitable pipe line to the classifier; a thickenerl into which there is an overiiow from the delivery end of the classifier through suitable pipe line that carries -fine metallic particles in suspension with the grinding liquid from the classifier to the thickener .wherein the pulp or metallic pigment settles-this settled material is sometimes referred to as the metallic underflow leading through any suitable pipe line from the thickener to the filter. 'I'hese parts are connected so that liquid freed, or freed to a certain extent, from the metallic particles is returned (a) from a portion of the classifier, (b) from an overflow leading from the thickener, and (c) from the lower portion of the filterfrom below or behind the filtering septumback to the entrance end of the ball mill whereby the wet grinding process dan be properly carried out and in a. continuous manner. The apparatus also has any suitable feeding or storage means 5 that delivers the zinc pieces to be ground into the return line leading to the entrance end of the ball mill.

While it is feasible to have all the return lines leading to the ball mill embodied in a single line, still it is possible to have independent lines for any one or more of these returns. In the drawing, as shown, there is provided an independent return line leading from the classifier back to the ball mill whereby the coarser material ls returned and handled through that line and in this return line for this coarse material there is also delivered the material from thelstorage bin preparatory to introduction of material from the storage bin into the ball mill. It will be manifest that in the functioning of this apparatus, the ball mill serves to progressively grind and reduce the metal particles. In this wet grinding, some of the larger particles, as well as the sum- Yciently fine particles, pass from the ball mill to the classifier. This mill is preferably lined with, and the balls or rods used therein are preferably made of, hardened steel, manganese steel or nickel-chrome alloys. The classifier is intended to separate out the coarse material which is not sumciently fine for paint. pigment. Therefore, this material is directly returned from one end of the classifier to the entrance end of the ball mill where the reducing operation is repeated.

The ilne material passes from the delivery end of the classifier through suitable piping into the thickener whereby the operations incident to the thickener take place; namely, the lighter overflow liquid or the overflow liquid to a large extent freed from the metallic particles, pass to an overflow line leading back to the ball mill while from the delivery end of the thickener the ne particles together with a certain amount of the liquid employed in the process, to wit, collectively, the thickened sludge that collects in the bottom of the thickener, are conveyed or conducted to the filter l. While the apparatus l may be referred to as a lter which may more broadly be referred to as a separator, the functioning thereof is definitely tocause a ltering or separating-out of the ne metallic particles from the liquid employed in the process. Afterv this\ operation has been eected, the filtered liquid is returned to the ball mill or lassiiler. The deposited, or concentrated and co ected metallic particles are then removed from the filter or separator. As previously indicated, there is sumcient liquid in the deposited material, however, to prevent oxidation and by the process 'herein described, and due to the retention by the line metallic pigment particles of a certain amount of this liquid vehicle, there is prevented any oxidizing contact which would cause a tarnishing of the metal pigment prior to its introduction into they proper vehicle with which the paint particles are mixed for the formation of paint.

The fine metal particles fromY the filter or lter. press may, if desired, be washed with fresh liquid to separate any dirt or oxide and may then be dried or used in the wet state for mixing with the proper vehicle to form a paint. The dry powder may, if desired, be subjectedv to a polishlng operation but this is usuallyv unnecessary as it will be found that the powder produced in this way already has a brilliant surface similar to the best metallic pigment. When the paint particles have been mixed with this proper vehicle to provide the paint, it is' manifest that they are still retained in such condition and manner that oxidation will not occur so that when` the paint is applied the resulting 'painted article is one having a brilliant, bright metallic surface, and these characteristics are enabled to be realized because the metallic particles are in the form of akes having smooth, bright surfaces. It will also be noted that the ball mill and the grinding operation carried out therein eects not merely a disintegrating of the metallic substances into line powders but it in fact also effects a burnishing and polishing of the metallic Vparticles under conditions where the surface of each particle is rendered smooth and bright and of a character such as to remain so.

The invention hereof relates to the method of making the'zinc particles herein-described, to the zinc particles themselves, to the paint wherein such particles are employed as pigments, and to the apparatus for and process oi' producing such zinc pigment.

What is claimed is: K

1. A metallic powder suitable as a pigment for paint consisting mainly of zinc flakes having smooth, bright surfaces.

2; A metallic powdersuitable for paint consisting mainly of zinc in flake form characterized in that the flakes have smooth, bright surfaces and appearance and are protected by coating substances.

3. A metallic powder suitable for paint consisting mainly of zinc in ilake form having smooth bright surfaces and mixed with a small quantity of an inert material to form a paste.

4. A metallic powder suitable as a pigment for paint consisting mainly of smooth. bright surfaced zinc flakes having a purity of 99.9 percentum and an alloying metal in solid solution therewith.

' 5. A metallic powder suitable as a pigment for paint consisting `mainly of smooth, bright surfaced zinc akes having a purity oi' 99.9 percentum and manganese as an alloying metal in solid solution therewith.

6. A metallic powder suitable as a pigment for paint consisting mainly of smooth, bright surfaced zinc flakes having a purity of 99.9 percentum and nickel as an alloying metal in solid solution therewithq,

7. The method of producing a metallic paint pigment consisting mainly o! zinc particles in the` form oi iiakes'having smooth, bright surfaces, by grinding nnely divided portions o! zinc beneath the surface or a liquid relatively inert to the zinc in a continuous grinding machine, by providing a continuous flow o! such inert liquid into and through the grinding machine and thereby carrying from the grinding machine zinc particles which are in suspension in the inert l liquid to a separating apparatus, by separating the metallic particles in said apparatus and collecting the zinc particles, and byreturning the inert liquid when freed to a large extent from said separated-out particles to the grinding machine.

8. The method of producing a metallic powder o consisting mainly of zinc in iinely comminuted or ake form characterized by the fact that the flakes have smooth, bright surfaces which consists in grinding it in a mill in the presence oi an inert liquid, causing the liquid "to now continuously or intermittently from the mill, thus carrying in suspension from the mill some of the powder resulting from or undergoing treatment, separating the coarser from the nner portions of the powder thus carried from the mill. and returning the coarser portions to the mili for regrinding.

9. The method oi' producing a bright untarnished zinc powder in iiaked form which consists in grinding finely divided portions oi! zinc in 'a ball mill in a liquid grinding medium inert with respect to the zinc and o! low viscosity including a substantial amount of an oleaginous liquid such as linseed oil capable of combining with oxygen at low temperatures such as room temperatures.

. Y URLYN C. TAINTON.

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