US2579778A - Method of surface lubrication of metal products - Google Patents

Description

W. S. ALLEN Dec. 25, 1951 METHOD OF SURFACE LUBRICATION OF METAL PRODUCTS Original Filed April 6, 1949 1N VEN TOR. U/IM 5, flALf/V,

Patented Dec. 25, 1851 METHOD OF SURFACE LUBRICATION OF METAL PRODUCTS William S. Allen, Pittsburgh, Pa., assignor to United States Steel Company, a corporation of New Jersey Original application April 6, 1949, Serial No. 85,750. Divided and this applicationMay 3, 1951, Serial No. 224,411

4 Claims. 1

This invention relates to improvements in the method of surface lubrication of metal products, such as tin plate and the like.

With the commercial development of electrolytic tin plate, the dry character of such tin plate has caused the container industry difficulty. The industry had adapted their manufacturing methods, machinery and lacquers to accommodate the lubricated tin plate formerly produced by the hot-dip process, and have found that the dry electrolytic tin plate was difiicult to assort and handle, was susceptible to scratches and marking, and provided different enameling and printing characteristics.

Various methods have been tried in an endeavor to supply the desired lubrication to the tin plate, but have proved unsatisfactory for one reason or another. Generally, those methods which have been tried heretofore have been incapable of control and for the most part have produced nonuniform and excessive lubrication which also is highly objectionable.

An object of the present invention is to provide improved methods of applying lubricant coatings to metal surfaces and overcoming the objections of previous coating methods.

A further object of the invention is to provide improved methods of applying to metal surfaces lubricant coatings which are continuous, uniform, non-smeary and the weight of which can be controlled.

A further object of the invention is to provide improved methods of applying lubricant coatings to metal surfaces in which lubricant globules first are deposited on the surface from a lubricantin-water emulsion and subsequently the surface receives a water spray which removes excess emulsion and coalesces the globules that are attached to the surface leaving a uniform lubricant film of controlled weight.

In a lubricant-in-water emulsion, the lubricant globules carry like electric charges and hence repel one another. As hereinafter explained, the

lubricants used in practicing the present invena continuous film since they remain as separate,

droplets. I am aware of previous attempts to apply lubricant coatings to metal surfaces from emulsions in which the water is evaporated after the globules are. deposited, but such attempts have not been successful for the reason that the overlying layer of emulsion also dries and thus the film thickness cannot be controlled.

According to the present invention, after the surface receives the emulsion spray, it receives a water spray which washes away all of the emulsion except the lubricant globules which actually are adhering to this surface. The water spray also unbalances the forces which maintain the globules as separate droplets and thus enables them to coalesce and form a continuous film. I believe their coalescing is due to a breaking of the emulsion, either through removal of the emulsifying agent, or in the case of acid emulsions through dilution of the acid content, or both, but

I do not wish to limit the present invention to any particular theory.

The single figure of the drawing shows diagrammatically one form of apparatus suitable for performing the improved method of the present invention. In this figure tin plate S, in strip form, has been coated and otherwise finished except for the application of a lubricant coating. The strip moves through a series of vertical passes between rolls 2, 3, 4, 5 and 6. In

an upward pass between rolls 3 and 4, emulsion flows onto both sides of the strip from low pressure sprays 1, following which water from low pressure sprays 8 floods the strip during its travel in the downward pass between rolls 4 and 5. The spray pressure must not be so great that it washes away adhered globules. Finally the strip passes upwardly through squeegee rolls 9 and through a drying chamber [0, which may be equipped with steam coils or pipes I I.

The emulsion preferably is homogenized continuously in a homogenizing unit E2 in fluid circuit with a reservoir l3 which contains a supply of the emulsion. Supply and return conduits l4 and I5 connect said reservoir with the homogen izing unit. The emulsion is drawn from the reservoir l3 through a suction conduit l6 and pump 11, and is supplied to the sprays 1 through a conduit l8, the surplus from said sprays and the strip falling into reservoir l3 for reuse.

The emulsion must flow on the strip for a sufficient interval for a complete layer of lubricant globules to adhere thereto. Damming rolls [9 can be employed to prevent drag-out and wastage A lubricant film of about .01 to. .30 gramsof. lubricant per base box, or about .000023 to .00069.

grams per square foot has been found satisfactory for the purposes hereinbefore" stated. Present methods of determining the weights of such lubricant films present some difficulty, but sufficiently accurate Weights and comparisons have been made to fix the foregoinglimitsassatisfactory for the container industry.

The emulsion is of the lubricant-in-water type.

The lubricant mustbe of the class which has a greater affinity for the metal surface than the aqueous "phase of the-emulsion has for this sur-' face. This affinity is an inherent property "of some lubricants, such as those which-"intheir" natural state contain compounds that have free carboxylic groups. The same affinity can be imparted to other lubricants by the addition of substances thathavefree carboxylic groups or 7 their equivalents. Afurtheressential'forlubrieating tin plate which is to be'used'in food cone tainers' isthat the ingredients of the emulsion must be non-poisonous.

Examples of lubricants which I have found satisfactory and whose aflinity 1 is an inherent property are as follows:

Palm oil, cottonseed oil, corn oil, olive oil, coco nut oil, lardoil, tallow, and similar fatty acidesters.

Examples of lubricants which I have found:

otherwise satisfactory and to which the neces: sary afiinity can be imparted by the addition of substances that have free carboxylic groups are as follows:

Dibutyl phthalate, dibutyl sebacate, tributyl citrate, and-similar organic plasticizers.

Additive substances for the second type of lubricants typically-are intermediate and 3 long chain aliphatic carboxylic acids. Specific examples are oleic acid stearic acid, linoleic acid,

myristic. acid and palmitic acid. These-additive substances may, ifdesired, be used with lubri cants of the first type, although ordinarily they" are -not needed since usually they are present,

naturally in sufiicient quantities. The optimum proportion of additive substance may be-deter mined empirically for any particular lubricant and is adjusted to furnish a satisfactory adherence ofthe lubricant globules to a metal surface.

For lubricants of thesecond type, I find 5 to percent of the additive substance in the lubricant ordinarily furnishes satisfactoryglobule a d- Some lubricants of the first type, such herence. V v as'highly refined cottonseed oils, containas-little at'OB to OA percent free acids and yet ordinarily they havesatisfactory globule adherencewithout addition of more acid.

Emulsifying agents can be classifiedas anionic";

cationic, and non-ionic. For forming an emulsion from which an oil film can be deposited on a metal surface, any one of the three classes "ofemulsifying agents is operable.

stabilized with anionic emulsifying agents precipitate insoluble soaps which form scums on the emulsion and smear the metal surface and-also interfere: with subsequent lacquer adhesion-."-'

However, emu1 sions which are formed of hard water and are 4, Therefore the process of the present invention requires that the emulsion be acid. The emulsifying agent can be either cationic or non-ionic, provided it tolerates acidity.

In preparing the acid emulsions, the; emulsifying agentcan beselected from the long chain amines, carboxyl amides, phosphoric acid esters, or fother cationic or non-ionic emulsifying agents. As an example, I have used with particular success Amine 220 which is a commercial productunderstood to be defined by the formula 1 hydroxyethyl 2 'heptadecenyl glyoxalidine. Other specific examples of satisfactory cationic emulsifying agents are:

Oleic amide, .castor amide, coconut amide, coconut amine, oleic amine, n-monododecylamine, and n-monohexadecylamine.

Specific examples of satisfactory non-ionic emulsifying agents are:

Diethylene glycol stearate, mannitan mono palmitate; mannitan -monolaurate-, andsorbitol monopalmitate;

With acid emulsions a weakly ionizable acid, such as acetic, citric'or tartaric is preferable for furnishing the acidity. I have'found that a pI-I f of between 2 and 6 is sufficient-to maintain a stable emulsion-and that acetic acid is particularly suitable for the purpose.

When the emulsion is prepared, the-lubricant and emulsifier, with the additivesubstance if .em-' ployed, are mixed and add'edtothe water and" acid. The water'dilution preferably is such that 1 the resulting emulsion contains from about-3 to 12 ml. of the lubricant per liter. The-concen =tration of the emulsifying agent is sufilcientto I havefound that the weight of depositedlubrie cant-variesinversely with the ratioof emulsifier 1' to lubricant, and that varying either the lubritcant or" the emulsifier content provides aniexe cellent method of controlling the weight of the. lubricant film within the weight ranger hereinbez-x fore stated;

The following are specific examples oftzemule sions which I have found suitable for: producing.

surface lubrication of electrolytic tin platewithinqrr.

the range'of lubricant weights suitable for. such tin plate. The proportionsof lubricant; additive: substance and emulsifying-.agent'arein parts 'by-x volume, and acetic. acid isemployed:tofurnishsthe pH values indicated:

Example .1

Cottonseed oil 10 0 Amine 220' .5; pH .2 ml. oil per liter a 3.8

Example 2 Palm oil i" Amine 220 1.75. pH 2-6 ml. 'oil per liter 4 Example 3 V Palm oil 100* N-monododecyl amine 8.3- pH 2 6- 15 ml. oil per liter 11.4

Example 4 Palm oil 100 Mannitan monopalmitate 8 pH 2-6 ml. oil per liter 12 Example 5 Cottonseed oil 100 Amine 220 1.75 pH 2-6 ml. oil per liter 3.8

Example 6 Dibutyl sebacate 75 Oleic acid 25 Amine 220 3/4 pH 2-6 ml. lubricant per liter 6 Example 7 Dibutyl phthalate 95 Palmitic acid 5 Amine 220 1.2 pH .1--- 2-6 ml. lubricant per liter 5.7

Example 8 Tributyl citrate 77 Stearic acid 23 Amine 220 1.2 pH 26 ml. lubricant per liter 4 After such emulsions are applied to the tin plate in the manner stated, the tin plate is washed to remove substantially all unattached globules of lubricants, leaving only the attached globules which adhere to the surface. The washing step also functions to unbalance those forces which maintain the attached globules of lubricant as individual droplets, whereupon these droplets coalesce and flatten to form a substantially continuous uniform film. Following this washing step, the product is dried by any suitable means.

While my improved method has been shown and described herein in connection with electrolytic tin plate, the same is not to be limited thereto. Since the lubricant-to-metal adhesion tension does not vary in appreciable amount for different metals, obviously the herein described method may be employed for similarly lubricating other metal products.

The present application is a division of my earlier application Serial No. 85,750, filed April 6, 1949. This parent application was a continuation-in-part of my co-pending'application Serial No. 735,637, filed March 19, 1947, now abandoned, and which in turn was a continuation of my application Serial No. 503,723, filed September 24, 1943, also now abandoned.

Various changes and modifications are contemplated within the scope of the following claims.

I claim:

1. The method of surface lubrication of metal strip and the like which comprises applying to the strip surface a lubricant-in-water emulsion having a pH value of 2 to 6 produced by a weakly ionizable organic acid and consisting of 3 to 12 ml. of lubricant per liter of emulsion and 0.5 to 6.0 parts of an emulsifying agent per parts of lubricant by volume, the lubricant being selected from the group which consists of dibutyl phthalate, dibutyl sebacate and tributyl citrate and having incorporated therein a long chain carboxylic acid having from 14 to 18 carbon atoms to furnish free carboxylic groups, the amount of carboxylic acid being 5 to 25 percent of the weight of the lubricant, the emulsifying agent being selected from the group which consists of cationic emulsifying agents and non-ionic emulsifying agents and being an agent which tolerates acidity, the concentration of emulsifying agent being sufficient to stabilize the emulsion without preventing adherence of lubricant globules to the strip surface, lubricant globules thus adhering to the strip surface as separate droplets, washing the emulsion bearing strip with a low pressure water spray, which removes the excess emulsion and coalesces the adhering lubricant droplets into a continuous film, and drying the strip surface.

2. A method as defined in claim 1 in which the lubricant is dibutyl phthalate.

3. A method as defined in claim 1 in which the lubricant is dibutyl sebacate.

4. A method as defined in claim 1 in which the lubricant is tributyl citrate.

WILLIAM S. ALLEN.

N 0 references cited.

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