US 3042621 A
Description (OCR text may contain errors)
3,942,521 Tatented July 3, 1962 3,042,621 DETERGENT COMPOSITION Hans George Kirschenhauer, Allendale, N.J., assignor to Colgate-Palmolive Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 1, 1957, Ser. No; 693,801 14 Claims. (Cl. 252-99) The present invention relates to an essentially nonabrasive detergent composition exhibiting substantially non-acidic and acidic pH conditions in a predetermined order of succession in water, and to a process of preparing the same, as hereinafter described and claimed.
The optimum effectiveness of detergent compositions for different functions or properties may occur at different pH ranges in water. For example, it is believed that a detergent composition exhibiting an alkaline pH in water may be preferable for various cleaning operations whereas a composition exhibiting an acidic pH may be desired for other cleaning or related operations or for conditioning of the cleaned material. It would be desirable in some instances to employ several such processing steps successively which operate initially at a pH range suitable for a particular function and then at a distinctly different pH range which is desired for a different function. Such practice could be utilized in many fields of application including commercial laundry, textile-treating and hair-treating operations and the like.
' In accordance with the present invention, it has been discovered that there can be'prepared a detergent composition exhibiting'variable and controlled pH conditions in water which comprises 'an ingredient yielding in solution an alkaline or substantially neutral pH condition, and an ingredient adapted to convert the solution to an acidic pH condition after elapse of a predetermined time. More particularly, it relates to a non-abrasive cleaning composition in particulate form which upon admixture with water is adapted to yield an alkaline or neutral pH condition and an acidic pH condition successively to the resulting cleaning solution which comprises essentially a mixture of a Water-soluble organic neutral or alkaline detergent, and a water-soluble acidic ingredient which is adapted to dissolve in' an amount sufficient to subsequently convert said cleaning solution to an acidic pH condition, said acidic ingredient having a coating of a water-dispersible material to retard its rate of solubility. A preferred embodiment comprises a particulate mixture of an organic detergent, a water-soluble alkaline builder salt and a normally solid water-soluble acid having a coating of a water-dispersible material on the acid particles. Various other preferred embodiments will be apparent in the following description. V
For convenience of illustration, the invention will be described most particularly with respect to the composition yielding successive alkaline and acidic pH conditions though it is to be understood that compositions exhibiting a different order such as successive neutral and acidic conditions are Within the scope of the invention. Where reference is made to pH conditions in the specification and claims, it is intended that such condition be illustrated by a 0.25% solution position in water. n
The composition should contain a water-soluble organic substantially neutral or alkaline detergent. Such compositions are known and are disclosed in Us. Patent of the detergent com- :No. 2,625,513, issued January .13, 1953. It is highly advantageous to incorporate an organic detergent material such as the organic anionic and non-ionic surface-active agents for a variety of effects including detergency, foaming, and surface tension and wetting effects so as tofacilitate removal of the dispersible coating on the acidic par- -to 50 alkylene oxide groups.
The soaps are generally the water-soluble salts of higher fatty acids (including rosin acids) which are derived usually from fats, oils and waxes of animal, vegetable or marine origin, e.g. tallow, coconut oil, tall oil, palm kernel oil soaps and the like. It is preferred to employ a higher alkyl aryl sulfonate such as an alkyl benzene sulfonate detergent wherein the alkyl group has about 8 to 16 carbon atoms. Suitable examples are sodium decyl benzene sulfonate, sodium dodecyl and pentadecyl sulfonates wherein the dodecyl and pentadecyl groups are derived from a propylene polymer, and sodium keryl benzene sulfonate. Other suitable agents are the surface-active sulfated or sulfonated aliphatic compounds, preferably having 8 to 22 carbon atoms. Examples thereof are sulfuric acid esters of polyhydric alcohols incompletely esterified with higher fatty acids (e.g. sodium coconut oil monoglyceride monosulfate); the long-chain pure or mixed higher alkyl sulfates (e.g. sodium lauryl sulfate and coconut fatty alcohol sulfate); the higher fatty acid ethanolamide sulfates (e.g. sodium coconut fatty acid ethanolamide sulfate); the higher fatty acid amides of amino alkyl sulfonic acids (eg sodium lauric acid amide of taurine); the higher fatty acid esters of isethionic acid; and the like. These anionic surface-active agents are used generally in the form of their water-soluble salts, such as the alkali metal (e.g. sodium, potassium), though other soluble salts such as ammonium, alkylolamine and alkaline earth metal salts may be used if desired depending upon the particular detergent.
Various non-ionic agents may be employed also, such as the non-ionic polyalkylene oxide condensates with an aliphatic or aromatic hydrophobic group. The hydrophobic organic group contains usually at least about 8 carbons condensed with at least about 5 and usually up Examples are the polyethylene oxide condensates with alkyl phenols having 6 to 20 carbons in the alkyl group such as Igepal CA and CO; the polyethylene oxide esters with higher fatty acids such as tall oil acids or lauric acid condensed with about 16 or 20 ethylene oxide groups; the polyethylene oxide condensates with higher aliphatic alcohols such as lauryl, myristyl, oleyl or stearyl alcohol with 6 to 30 moles ethylene oxide; the polyoxyethylene oxide condensates with higher fatty acid amides such as coconut fatty acid amide containing about 10 to 50 moles ethylene oxide. The water-soluble polyoxyethylene condensates With hydrophobic polyoxypropylene glycols may be employed also.
Any Water-soluble ingredient which yields an alkaline pH of above "7, preferably a pH of 8 to 12, to the aqueous solution may be employed in the composition also. The alkaline organic detergents such as the water-soluble soaps and the like described above may be employed but it is' preferred to use the water-soluble inorganic alkaline builder salts, such as the alkali metal carbonates (e.g. sodium carbonate), the alkali metal phosphates (e.g. trisodium phosphate, tetrasodium pyrophosphate, sodium tripolyphosphate), the alkali metal silicates (eg. sodium metasilicate) and the alkali metal borates (e.g. sodium borate). Any suitable base such as sodium and potassium hydroxide, and tetramethylammonium hydroxide may be employed also. Generally, it is preferred to use the normally solid organic detergent and alkaline builder salts and bases but, if desired, 'a normally'liquid mate rial may be employed by suitable combination with a Solid carrier such as by adsorption of a liquid. detergent upon a solid alkaline builder, and the like. V
The concentration of these active ingredients and mixtures thereof in the detergent compositions of the present invention vary widely according to the contemplated field of application and any amount of the detersive material may be employed which does not substantially adversely affect the desired characteristics of the product. In general, the neutral or alkaline detergent may be present in amounts from about /2 to about 99%, and preferably from about 1 to 75 by weight of total solids. With regard to detersive compositions designed primarily for comparatively light-duty cleansing purposes such as dishwashing, shampoos and the like, the composition may be free from alkaline inorganic builder salts if desired. For compositions designed for heavy-duty cleansing purposes, there is present usually at least about 5% of Water-soluble alkaline inorganic salt and about /2 to 95% detergent. A preferred formulation comprises a mixture of about 5 to 50% neutral or alkaline organic detergent with the balance of total solids being primarily water-soluble inorganic salts, preferably containing about 5 to 75% alkaline builders such as phosphates, which is admixed With a sufficient amount of an acidic ingredient as hereinafter described.
The neutral and alkaline detersive materials may be employed in the form of solid particles of any suitable size. The particle size is not critical but will vary usually from about to 400 mesh as determined on a U.S. standard sieve. The organic detergent and alkaline builder salts and the like may be in individual particulate form or they may be admixed in any suitable way to prepare mixed granules. Thus, the organic detergent and alkaline salts in the form of an aqueous slurry may be subjected to the usual drying procedures in order to obtain a relatively dry, homogeneous granular product, such as by heat-drying (e.g. drum-drying or spray-drying) of the mixture in known manner. 7
Any water-soluble acidic ingredient which will dissolve in the cleansing solution to yield an acidic pH of below 7, preferably a pH from 2 to 7, to the aqueous solution may be employed in the product. In general, it is preferred to employ a normally solid acid or acid salt in particulate form. If desired, a normally liquid material may be employed by suitable combination with a solid carrier in particulate form, such as diatomaceous earth or bentonite. The particle size of the acidic material is not critical and it may be employed in any suitable size as illustrated for the detersive materials above. Examples of suitable materials are the organic acids such as tartaric acid, maleic acid, boric acid, glutamic acid, citric acid, acetic acid, oxalic acid, gluconic acid and its lactone, and the like. Suitable inorganic acids and acid salts such as sulfamic and phosphoric acids and sodium bisulfate may be employed also.
The acidic ingredient should be used in any amount sufficient to convert the substantially neutral or alkaline solution to an acidic solution of less than 7 and preferably to a pH from about 2 to 5, when the quantity of acid has been dissolved or otherwise released in the cleansing solution. In general, it is preferred that the amount of acid be from about /2 to 50% and preferably from about 1 to by weight.
If a mixture containing alkaline and acidic ingredients in powdered form are added to water, the two materials tend to neutralize one another such that the cleansing solution will have either an alkaline or an acidic pH condition depending upon the proportion and strentgh of the different ingredients. In the case of a neutral detergent containing the acidic ingredient, the composition would yield initially an acidic condition. In order to obtain successive action of separate and distinct pH effects, it is necessary to defer or retard the rate of solubility of the acidic ingredient. This deferred acidification permits the user to utilize initially the alkaline or neutral properties of the product for optimum foaming and cleaning effects in many cases followed by use of the acidic properties of the product for other optimum effects in rinsing, dyeing, bleaching and conditioning of the cleansed material. Ac-
cordingly, the rate of solution of the acidic constituent is to be sufiiciently depressed to permit the neutral or alkaline detersive materials to dissolve first and thereby permit utilization of these properties. The acidic constituent must then be present in sufiicient amount or in stoichiometric excess over the alkaline ingredient so that when it is dissolved or released after a predetermined time the pH of the cleansing solution is reduced to the desired acidic level.
The rate of solubility of the acidic constituent may be reduced in any suitable manner. It is preferred to coat the normally solid acid particles with a solution inhibitor such as a water-dispersible coating agent. The presence of such a film or coating upon the particles of the acid will inhibit and retard the solubility of the acid when the composition is admixed with water initially. The amount of the coating is not critical and may vary from a monomolecular film to a coating of any particular size depending upon the specific coating agent, its water-dispersibility, the contemplated conditions of use, and the particular time interval which is desired before the change in the pH condition of the aqueous cleaning solution. For example, where it is contemplated to use detergent baths at relatively higher temperatures, it is desirable to employ coatings having a relatively high melting point or poor solubility in water. Thus, the predetermined time interval for the pH change may be controlled so as to be a few seconds up to any point desired in the use of the product such as up to about 30 minutes. It is preferred that the change in pH occur from about 15 seconds to 15 minutes after the product is admixed in water.
Any suitable material may be used as the coating agent such as the higher fatty alcohols, preferably having 12 to 18 carbon atoms (e.g. lauryl alcohol, coconut fatty alcohol, cetyl alcohol, stearyl alcohol), mineral oil, the higher fatty acid amide compounds, preferably having 12 to 18 carbon atoms in the acyl radical (lauric acid, coconut acid and myristic acid primary amides and the corresponding monoethanolamides, isopropanolamides and diethanolamides) and their ethylene oxide reaction products having up to about 5 moles of ethylene oxide, the higher fatty acids, preferably having 12 to 18 carbons, such as stearic acid, palmitic acid, tallow fatty acids and the like. Other coating materials are the waxlike polymers of ethylene glycol such as Oarbowax 1500, 2025 and 4000, the soluble starches and dextrins and the like. These materials may have highly limited solubility in water to extreme solubility but are effective to delay the solubility or release of the acid in the cleansing solution. The term waterdispersi ble coating agent or equivalent as used herein refers to agents of varying water solubility or dispersibility but which have been found to be dispersed or dissolve under conditions of use of the product. For example, organic materials such as lauryl alcohol and lauric acid amides and alkylol-amides have limited water solubility but in the presence of organic detergent material tend to dissolve in the cleansing solution.
The coating agent may be applied to the particles of the acid in any suitable manner. It is preferred that the coating agent be dissolved, suspended or dispersed in an appropriate solvent or heated to molten form and then sprayed or atomized on the individual acid particles to form the desired coating. Any suitable solvent may be employed, such as a normally gaseous propellant in a pressure container. Examples are the normally gaseous low-molecular weight hydrocarbon and halogenated hydrocarbon propellants, such as propane, butane, halogenated ethanes and methanes. The propellants known as the Freons and Genetrons are suitable, examples being dichlorodifluoromethane and monochlorodifluoroethane. Other solvents or dispersing mediums such as ethanol, isopropanol and aqueous alcohol mixtures may be suitably employed also. In this manner there is obtained the desired coating or film on the surface of the minor proportion usually such as from about A acid particles. Where the coating agent is normally solid it will dry to a film, and where it is normally liquid it will be adsorbed or absorbed upon the surfaces of the particles. The coating material may be applied also in solid form to the surfaces of the acid particles by mixing the coating agent in powdered form with the acid particles by suitable means for mechanical admixture including tumbling in a rotary drum. The various ingredients such as the detergent, alkaline builder salt and the coated acidic ingredient are mixed in particulate form to produce a dry, uniform granular mixture. The ingredients are admixed mechanically by tumbling, fluidizing or the like in conventional soap powder mixers known in the art or by any other suitable means for mechanical admixture.
When the final composition is added to water to form a washing solution, the organic detergent and watersoluble alkaline ingredients dissolve to form a non-acidic solution. Since the acid particles are coated with higher fatty acid amide or any other suitable coating as indicated, its rate of solution is sufficiently depressed to permit the alkaline builder to dissolve first. After a predetermined time, which may be controlled as desired by selection of the particular coating agent, the coating material disperses in the aqueous medium whereupon the acid is released and dissolves so that the pH is reduced to the desired acidic condition.
The product may contain a bleaching agent which results in effective bleaching action during use of the product. The bleaching agent may be incorporated into the product in any suitable manner, such as during or after the mixing of the essential ingredients. In general, bleaching agents are more effective in one pH condition than another. Since the product during use will form a plurality of controlled pH conditions, there can be obtained at some stage optimum conditions for a particular bleaching agent. The bleaching agent may be incorporated into the detergent composition in known manner, such as by dry mixing of the powdered materials or in any other suitable manner. If desired, the bleaching agent may be coated with any suitable material such as the coating agents previously described so that the bleaching agent is released in the same manner. Examples of suitable bleaching agents are the known oxygen and chlorine-releasing substances, such as sodium perborate, sodium, calcium and lithium hypochlorites, dichlorocyanuric acid, trichlorocyanuric acid,
Chloramine T, diohlorodimethyl hydantoin and the like.
The amount of bleaching agent is not critical but will he usually from about 0.01 to 50% of the product (e.g.
A cationic surface-active agent may be incorporated in the product also. It may be admixed in powdered or liquid form with the ingredients in any suitable manner. Vfnere it is desired to use a cationic agent, it is preferred to admix it with the acidic ingredient and coatthis mixture with the coating agent. Suitable cationic detergents are the higher alkyl quaternary ammonium compounds such as the cetyl quaternary ammonium salts. Specific examples of such materials are cetyl trimethy-l ammonium chloride, cetyl pyridinium chloride, and the like. These materials are employed in to 25% of the composition.
A suitable color indicator which would demonstrate to the consumer'whenthe change from one pH condition to the other pH condition occurs or when a particular pH level is obtained during use may be incorpoorated in the product also. The quantity of indicator is not critical except that it should be capable of producing a detectable coloration to the cleansing solution. in general, the amount of color indicator vary with the type of indicator but is usually from about 5' parts per million to 3% of the product. If methyl orange is employed, the color of the aqueous solution is yellow when the alkaline ingredient dissolves initially and the acid is coated, but the cleaning solution turns red when the acid dissolves in a stoichiometric excess after elapse of a predetermined time. Another suitable color indicator is bromo t-hymol blue which changes color from blue to yellow on conversion of the washing solution from an alkaline to an acidic condition. The color in dicator may be incorporated in any suitable manner such as by spraying it directly upon the particles at any suitable stage in the mixing operation. If the indicator is solid, it may be dissolved or dispersed in a suitable aqueous or alcoholic solution in order to form a liquid solution for ease of application to the particles. Other suitable dyes are phenol red, t-hymol blue, metacresol purple, etc.
Various known materials may he incorporated in the product also as desired. Suitable examples are minor amounts of ant-caking agents such as hydra ed magnesium trisilicate, sodium carboxymethyl'cellulose, perfume, antiseptics, germicides, skin emollient materials and the like.
The following examples are illustrative of the present invention and it will be understood that the invention is not limited thereto. All proportions indicated are by weight unless otherwise specified.
EXAMPLE I Part A Sulfamic acid in the form of a powder is pretreated to apply a coating to the particles as follows: 35 parts of the sulfamic acid particles are tumbled in a Mason jar. Through an opening in the cover of the jar, a spray of a lauric acid monoethanolamide solution is introduced until 4 parts of the lauric acid monoethanolamide are deposited on the surfaces of the sulfamic acid powder. The spraying composition contains 30% lauric monoethanolamide dissolved in of a 1:1 mixture of Freon-l1 and Freon- 12 in a pressure resistant container.
Part B An alkaline detergent composition is prepared in known manner by spray-drying an aqueous slurry of about 60% solids to obtain a spray-dried granular product containing 10 parts sodium dodecyl benzene sulfonate and 5 parts sodium lauryl sulfate detergents, 15 parts sodium tripolyphosphate, 4 parts sodium silicate, 5 parts sodium perborate, 6 parts moisture, and 53.7 parts sodium sulfate, with the balance of 100 parts being small amounts of perfume, fluorescent dye, and the like.
The above coated sulfamic acid particles (Part A) are tumbled with the granular alkaline detergent composition (Part B) until the product is a uniform homogeneous mixture. When this mixture is added to warm water in about 0.25% concentration with mild agitation, the resulting solution is alkaline initially and after a few minutes the solution is converted to an acidic pH. The final composition shows effective cleaning, laundering and bleaching properties during use of the product on soiled textiles and the like.
EXAMPLE II lowing ingredients as Parts A and B to obtain a uniform product exhibiting successively alkaline and acidic prop- 7 Part B Parts Sodium metasilicate Sodium tripolyphosphate Sodium perborate 5 Sodium dodecyl benzene sulfonate 2 Non-ionic detergent 1 Sodium sulfate 77 Ethylene oxide condensation product of polypropylene glycol with average M.W. of about 7500, ethylene oxide con tent of about 80 to 90% and M.P. of 51 to 54 C.
EXAMPLE III The procedure of Example I is repeated with the following formulation to obtain a uniform mixture exhibiting a neutral pH condition initially in water which is converted to an acidic pH condition subsequently:
Part A Parts Sulfamic acid powder 5.0 Laurie acid amide as coating agent 1.5
Part B Sodium lauryl sulfate 28.0 Sodium sulfate 71.8
EXAMPLE IV The procedure and formulation of Example III is repeated using 6 parts of sodium bisulfate in place of the 5 parts of sulfamic acid with similar results.
EXAMPLE V The procedure of Example I is repeated with the following ingredients to prepare a product suitable as a dry shampoo and exhibiting neutral and acidic properties successively in water:
Part A Parts Boric acid powder 4.0 Cationic detergent powder 1.0 Lauric acid amide as coating agent 1.5
Part B Sodium coconut monoglyceride monosulfate 30.0 Sodium sulfate 69.6 Perfume 0.4
1 Cetyl pyridinium chloride.
EXAMPLE VI The same procedure is followed to prepare a powdered bleaching composition exhibiting successive alkaline and acidic reactions in water:
The following coating materials are employed in the same proportions in place of the coating agents in Examples I to VI, with equivalent results: coconut fatty acid diethanolarnide, stearic acid monoethanolamide, cetyl alcohol, stearyl alcohol, Carbowax 1500, and commercial stearic acid.
Although the present invention has been described with reference to particular embodiments and examples, it will be apparent to those skilled in the art that variations and 8 modifications of this invention can be made and that equivalents can be substituted therefor without departing from the principles and true spirit of the invention.
What is claimed is:
1. A detergent composition which upon admixture with water is adapted to yield a non-acidic pH condition and an acidic pH condition successively to the resulting cleaning solution which comprises about /2 to 99% by weight of a water-soluble detergent selected from the group consisting of water-soluble organic neutral and alkaline anionic and non-ionic detergents, and a water-soluble acidic compound having a coating of a water-dispersible material resulting in a retarded rate of solubility, said acidic compound being present in excess so that it renders the solution acidic when dissolved, said composition dissolving sufiiciently upon admixture with water so that the resulting cleaning solution initially exhibits a non-acidic pH condition which is converted to an acidic pH condition upon dissolving of said water-soluble acidic compound after a predetermined time.
2. A detergent composition in accordance with claim 1 wherein said acidic ingredient is a normally solid acid.
3. A detergent composition in accordance with claim 1 wherein said coating is a higher fatty acid amide compound selected from the group consisting of primary amides, monoethanolamides, isopropanolamides and diethanolamidcs of fatty acids of 12 to 18 carbon atoms.
4. A detergent composition in accordance with claim 1 which contains about 5 to 75% by weight of water-soluble inorganic phosphate.
5. A detergent composition in accordance with claim 2 wherein said acidic ingredient is sulfamic acid.
6. A detergent composition which upon admixture with water is adapted to yield an alkaline pH condition and an acidic pH condition successively to the resulting cleaning solution which comprises a mixture of about /2 to by weight of a water-soluble detergent selected from the group consisting of organic neutral and alkaline anionic and non-ionic detergents, at least about 5% by weight of a water-soluble alkaline inorganic salt which upon contact with water renders the solution alkaline, and a minor proportion of a water-soluble acidic ingredient which upon contact with water renders the solution acidic, said alkaline ingredient dissolving sufficiently upon admixture of said composition with water so that the resulting cleaning solution intially has an alkaline pH condition and said acidic ingredient having a coating of a water-dispersible material to retard its initial solubility but being present in a stoichiometric excess so that it subsequently converts said cleaning solution to said acidic pH condition.
7. A detergent composition in accordance with claim 6 wherein said acidic ingredient is a normally solid acid.
8. A detergent composition in accordance with claim 6 wherein said detergent is a water-soluble anionic organic sulfonated detergent.
9. A detergent composition in accordance with claim 6 which contains a color indicator to indicate by color change when the cleaning solution is converted from said alkaline to said acidic pH condition.
10. A detergent composition in particulate form which upon admixture with water is adapted to yield an alkaline pH condition and an acidic pH condition successively to the resulting cleaning solution which comprises a mixture of about 5 to 50% by weight of a water-soluble detergent selected from the group consisting of organic neutral and alkaline anionic and non-ionic detergents, and the balance of total solids being primarily water-soluble inorganic salts containing at least about 5% water-soluble alkaline builder salts which upon contact with water renders it alkaline, and having admixed therewith particles of a Water-soluble normally solid acid which upon contact with Water renders it acidic, said acid having a coating of a Water-dispersible material, and said composition upon admixture with water yielding an alkaline pH condition in Water which is subsequently converted to an acidic pH condition.
11. A detergent composition in accordance with claim 10 which contains particles of sulfamic acid coated with said material.
12. A detergent composition in accordance with claim 10 which contains about /2 to 25% by weight of sodium perborate.
13. A method of preparing a detergent composition which upon admixture with Water is adapted to exhibit a substantially non-acidic pH condition and an acidic pH condition to the resulting cleaning solution successively which comprises coating With a Water-dispersible compound an acidic ingredient to retard its rate of solution in water, admixing the resulting coated material with a Water-soluble detergent selected from the group consisting of the organic neutral and alkaline anionic and non-ionic detergents, and forming a homogeneous mixture.
14. A method of preparing a detergent composition characterized by a mixture of Water-soluble detergent selected from the group consisting of organic neutral. and alkaline anionic and non-ionic detergents, a Water-soluble alkaline inorganic salt and a water-soluble normally solid acidic ingredient adapted to yield an alkaline pH condition and an acidic pH condition successively upon admixture with Water which comprises treating said acidic ingredient to apply a coating of a water-dispersible material, and admixing the coated acidic material with said detergent and alkaline salt to form a homogeneous mixture.
References Cited in the file of this patent UNITED STATES PATENTS 284,464 Michaelis Sept. 4, 1883 856,672 Best et a1 June 11, 1907 871,612 Nesfield Nov. 19, 1907 980,936 Federer Jan. 10, 1911 1,075,663 Meerbott Oct. 14, 1913 1,854,235 Stoddard Apr. 19, 1932 1,966,203 Gravell July 10, 1934 1,989,765 Moss et al Feb. 5, 1935 2,196,901 Ham et al. Apr. 9, 1940 2,228,483 Raeke Jan. 14, 1941 2,308,992 Mertens Jan. 19, 1943 2,430,233 Magill Nov. 4, 1947 2,497,057 Pape et al. Feb. 7, 1950 2,498,344 Rider et a1 Feb. 21, 1950 2,540,253 Gakenheimer Feb. 6, 1951 2,578,270 Strain Dec. 11, 1951 2,763,618 Hendrix Sept. 18, 1956 FOREIGN PATENTS 749,857 Great Britain June 6, 1956