Substantially Neutral Aqueous Lubricant

The invention relates to aqueous gel lubricants used in a variety of applications such as the installation of electrical or telephone cable in conduit.

In lubricating the interface between two relatively moving surfaces a number of requirements must be met. The lubricant must be essentially chemically and physically inert with respect to the surfaces. The lubricant must reduce the force required to move one surface over the other. Lastly the lubricant must be in a form that permits the easy application of the lubricant to one or both surfaces.

Historically, lubricants were first prepared by thickening natural fats and oils with clay or chalk in order to provide sufficient lubrication for primitive wheels and axles. Upon the advent of the petroleum industry lubricant oils and greases were prepared from heavy petroleum oil fractions. In many applications petroleum lubricants are undesirable. Petroleum lubricants can interreact with many organic and inorganic substances such as plastics and rubbers, can be difficult to clean up after application, can remain in place well after application and can be unpleasant to workmen.

In view of the serious drawbacks that petroleum lubricants can have in certain applications, water based lubricants were developed. The use of many different water based lubricants is well known. More specifically, aqueous based compositions of high molecular weight polyalkylene oxide polymers have been prepared for a variety of applications including lubrication. Many other compounds have been used in preparing aqueous lubricants such as various fatty acid soaps, acrylate polymers, waxes, alkylene glycols, guar gum, Irish moss, carboxymethyl cellulose, phenolic and amineformaldehyde resins, hydrocarbon sulfonic acid, gelatin, polyurethanes, and others. See for example U.S. Pat. Nos. 3,227,652 and 3,699,057. Aqueous based lubricants are commonly more easily cleaned, more easily applied and are more agreeable to use.

To the best of my knowledge aqueous based lubricants containing many of the above mentioned compounds can suffer certain disadvantages. The lubricant compositions can be stiff, can be nonthixotropic, can be hard to handle and apply to the surfaces, the lubricant can fail to reduce the coefficient of friction under a broad load range or can be expensive.

Clearly a need exists for an inexpensive substantially inert aqueous lubricant that can be easily handled, easily applied to surfaces, having a low coefficient of friction under heavy or light load.

I have found an inexpensive gel lubricant that has the ability to lubricate surfaces in contact under a variety of loads by reducing the coefficient of friction to an acceptable level. The lubricant has the advantages that it is an aqueous gel that is easy to apply and easily cleaned, provides lubrication under both high and low load condition, is essentially inert to most lubricated surfaces, leaves little residue upon evaporation of the liquid phase, is easy to handle, and is slow in evaporating. The gel is substantially freeze-thaw stable, is agreeable to workmen, can be pumped, has long-time shelf stability, is substantially nonflammable, and can be used in water filled conduit. The improved lubricant is an aqueous gel comprising a major proportion of water, an effective gelling amount of an acrylate polyelectrolyte compound, an effective lubricating amount of a fatty acid salt compound, an effective lubricating amount of a polyalkylene oxide compound, and an effective solubilizing, antioxidant preservative amount of a C.sub.1-6 alkanol, wherein sufficient fatty acid salt compound is added to titrate the acrylate polyelectrolyte to substantial neutrality.

The preparation of the gel lubricant can be difficult. The solubilities of certain of the components can be low, the kinetics of solution formation can be slow, and the individual components can interact in ways that prevent the rapid formation, under certain conditions of a single phase composition or a stable suspension. Accordingly, we have found that the gelled lubricant of the invention is most advantageously prepared by first forming (1) an aqueous solution or suspension of the acrylate polyelectrolyte compound, (2) a solution or suspension of the fatty acid compound in water or in a C.sub.1-6 alcohol, and (3) a suspension of the polyalkylene oxide in a C.sub.1-6 alcohol, and second intimately combining each of the resulting compositions with mixing until the component parts have formed a stable, intimately blended, apparently single phase gel.

While I do not wish to be held to a theory of action of the gel preparation, it appears that titrating the acrylate polyelectrolyte compound with the basic salt of the fatty acid results in the formation of a stable gel without breaking the suspension of the fatty acid salt compound. We have found that at substantially more basic pH than neutrality, the gel tends to be loose, less thixotropic, and has reduced lubricant properties. At pH's substantially more acid than neutrality, the lubricant becomes more stiff and more difficult to handle. Accordingly, pH control during the formation of the lubricant compositions is critical in obtaining adequate lubricating properties.

Acrylate polyelectrolyte gelling compounds that can be used in forming the novel lubricant compositions of the invention include polyelectrolyte polymers and copolymers having a molecular weight in excess of about 1,000, and preferably about 20,000 to 10,000,000.

The preferred polymers are derived from the polymerization of at least one polymerizable acrylate monomer having ethylenically unsaturated group and a hydrophilic acidic group, that can maintain an ionized electrical charge in solution, selected from the class consisting of carboxylic acid, carboxylic acid anhydride, carboxylic acid halide, or mixtures thereof. Preferred organic polymeric acrylate-type polymers are made from carboxylic acid containing monomers, forming polyelectrolyte organic polymers which are anionic in nature. Useful monomers include acrylic acid, acrylic acid esters and salts, methacrylic acid and methacrylic acid ester salts, alpha-beta unsaturated dicarboxylic anhydride compounds such as maleic anhydride, itaconic acid, citriconic acid, and others. Along with the acidic carboxyl containing monomer other monomers can be used in preparing the polymers which do not detract from the polyelectrolyte or carboxylic acid nature of the polymer. Such comonomers can include styrene, vinyl acetate, vinyl chloride, vinyl ethers, ethylene, isobutylene, and others.

The most preferred gelling agent comprises polyacrylic acid having a molecular weight of at least about 3,000, which comprises the following formulae: ##STR1##

Polyacrylic acid polymers can be efficient gelling agents for aqueous solutions, are low in toxicity, do not increase frictional force and are compatible in aqueous solution with other components.

Polyalkylene oxide compounds that can be used in the novel gel lubricants of the invention are well known polymeric and copolymeric compounds formed by polymerizing alkylene oxide compounds including ethylene oxide, propylene oxide, butylene oxide, etc. Preferred polyalkylene oxide compounds comprise polyethylene oxide, polypropylene oxide, polyalkylene glycol, polypropylene glycol, etc. A more preferred compound comprises a polyethylene oxide compound having a molecular weight from about 3.times.10.sup.5 to about 4.times.10.sup.6, which compound has the following formula: ##STR2## wherein y is 1.times.10.sup.4 to 3.times.10.sup.5. Most preferred are polyethylene oxide compounds having a molecular weight of about 2.times.10.sup.6 to 6.times.10.sup.6. Polyethylene oxide polymers can reduce friction at concentrations as little as 0.003%. Aqueous solution can produce significant reductions in frictional force needed to move surfaces past one another. Polyethylene oxides provide lubricity and a "silky" feel to aqueous solution. Polyethylene oxides are tolerant of electrolytes and can be combined with many other types of compounds. Polyethylene oxide has low toxicity.

Basic salts formed from an alkali metal, alkaline earth metal or ammonia and aliphatic saturated or unsaturated fatty acid having from about 8 to 25 carbon atoms can be used in the novel aqueous gel lubricant of this invention. Examples of suitable acids include lauric acid, dodecenoic acid, myristic acid, myristoleic acid, palmitoleic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolinic acid, arachidonic acid, behenic acid, lignoceric acid, eicosenoic acid, pentacosenoic acid and others. These acids can be derived from both natural and synthetic sources. Natural sources include animal and vegetable fats or oils which can be partially or fully hydrogenated if desired. Synthetic acids can be produced by the oxidation of petroleum wax, for example synthetic acids commercially available from Sun Oil Company. Preferred fatty acids compounds are the alkali metal salts of C.sub.16-20 carboxylic acids. The most preferred fatty acid compound comprises the potassium salt of C.sub.16-20 fatty acid which is commercially available as "Flaxoap".

Hydroxy compounds (hydroxy substituted aliphatic compounds) that can be used as antioxidant, preservative, solvating or suspending agents in preparing the lubricants of the invention include compounds having from 1 to 3 hydroxy groups and from 1 to 6 carbon atoms. The hydroxy compounds can be essentially straight or branched chain compounds. Examples of suitable hydroxy compounds include methanol, ethanol, ethylene glycol, propanol, isopropyl alcohol, propylene glycol, glycerine, n-butanol, isobutanol, tertiary butanol, amyl alcohol, isoamyl alcohol, n-hexanol, t-hexanol, cyclohexanol, etc. Preferred hydroxy compounds include methanol, ethanol isopropanol and propylene glycol. Most preferred hydroxy compounds are isopropanol and propylene glycol for reasons of availability and solvent power.

The lubricant of the invention comprising a major portion of water, the acrylate polyelectrolyte compound, the fatty acid salt compound, the polyalkylene oxide compound, and the hydroxy compound requires some care in blending. While the lubricant of the invention can be prepared by blending the components in any order, the results can be unreliable. Blending the lubricant can take an inordinate amount of time and the components can interact or fail to solvate resulting in multiphase compositions. In other words, each of the individual components has its own particular solubility, solvation kinetics, and interaction characteristics which can result in formulation problems. Further, the pH of the final composition must be closely controlled to insure success in formulation.

I have found a unique, successful method for combining the ingredients into a stable, apparently single phase composition that provides the desired lubricating characteristics. The method comprises first forming (1) a solution or suspension of the acrylate compound in water, (2) a solution or suspension of the fatty acid salt compound in water or in the hydroxy compound, (3) a solution or suspension of the polyalkylene oxide in the hydroxy compound and combining the above compositions with agitation resulting in a smooth, apparently single phase clean gel lubricant composition.

In order to form the aqueous acrylic compound suspension, about 0.1 to 50 parts by weight of acrylic polymer is blended with about 1,000 parts by weight of water and the resulting mixture is agitated until solution is complete. Preferably, for reasons of economy and lubricating performance, about 1 to 10 parts by weight of the acrylate compound is dissolved in 1,000 parts of water.

The solution of the fatty acid salt compound in water or hydroxy compound is formed by adding about 10 to 100 parts by weight of the fatty acid salt compound to about 10 parts of water or hydroxy compound and agitating the resulting mixture until solution is complete. For reasons of economy and optimized lubricating properties, about 10 to 50 parts of the fatty acid salt compound is used per 10 parts of water or hydroxy compound.

Similarly, the suspension of polyalkylene oxide in the hydroxy compound is prepared by adding about 1 to 10 parts of the polyalkylene oxide in a finely divided state to about 10 parts of hydroxy compound with vigorous stirring in order to form a slurry of the polyalkylene oxide. A preferred suspension contains about 1 to 5 parts of the polyalkylene oxide per 10 parts of hydroxy compound.

The acrylate solution, the fatty acid solution, and the polyalkylene oxide suspension are combined in a mixer at a volume ratio such that the final lubricant composition contains a major proportion of water, the acrylic polyelectrolyte polymer, about 1 to 10 parts by weight of the fatty acid compound, about 0.05 to 10 parts by weight of the polyalkyleneoxide compound, about 0 to 30 parts by weight of hydroxy compound each per part of the acrylate polyelectrolyte compound and has a pH of about neutrality, preferably about 6.4 to 7.0. Additional water or hydroxy compound can be added until the lubricant composition comprises about 0.5 to 10 wt-% total solids and about 0 to 15 wt-% hydroxy compound, the balance being water and optionally emulsifying agents or suspending agents or other beneficial additives.

A preferred method for distributing the lubricant in a conduit and an article for providing an even distribution of the lubricant is disclosed in U.S. Ser. No. 445,469, filed Nov. 30, 1982.

The aqueous gel lubricant may be applied to surfaces requiring lubrication using various means such as roller application, flow coating, spraying, or by immersing the surface in the lubricant. In such applications lubricant temperature may vary widely from about ambient (27.degree. C.) up to about 70.degree. or 80.degree. C. Typical temperatures for application by immersion are commonly within the range of about ambient to 50.degree. C. Using roller applications, we have found that the lubricant can be applied to the metal surface or can be applied to the roller before the lubricant is evenly distributed over the surface. In the case of lubricating conduit and cable, we have found that the lubricant can be evenly distributed on the inside surface of the conduit using a variety of methods. Alternatively the lubricant can be applied to the electrical or telephone cable by hand or by automatic machines prior to installation.

After application and installation of cable and conduit, we have found that the water and/or hydroxy compound present in the cable lubricant compound slowly evaporates, leaving a residue comprising acrylate polyelectrolyte, fatty soap and ethylene oxide. One advantage of the invention is that the residue maintains substantial lubricating properties which can be very useful in maintenance of cable installations a while after installation is complete. Further, the evaporation of the liquids from the lubricant is slow even in environments where ambient temperature is high and in the range between 30.degree. and 40.degree. C. Many lubricating compositions tend to evaporate at a rate such that before installation is complete aqueous solvents have been removed by evaporation and residue of the lubricant fails to provide any substantial lubricating properties.

I have found that using the lubricant compositions of this invention surface lubricating operations are easily and economically performed. I have also found that little or no problems with respect to separation or phase changes between the components of the lubricant occur. In addition to the components which have been set forth above, the lubricant compositions of the present invention may also contain a variety of additives, agitants, dyes, colorants, perfumes, or corrosion inhibitors well known in the art. When used these additives are chemically present in amounts within the range of about 0.1 to 5 wt-% of the composition and are preferably present in amounts within the range of about 0.1 to about 3 wt-% of the composition.

The following Example discloses the preparation of the novel lubricant composition of the invention and includes a best mode.

Into a one liter glass beaker was placed 883.5 grams of water maintained at ambient temperature and 6.0 grams of polyacrylic acid having a molecular weight of about 4000 (CARBOPOL 940, B. F. Goodrich Co.) was slowly added. The mixture was stirred at ambient until an smooth viscous mixture was obtained. Into a separate 200 ml beaker was placed 20 milliliters of isopropyl alcohol, and 80 grams of the potassium salt of a mixture of C.sub.16-20 fatty acid (Flaxoap, Sherwin-Williams Company). The mixture was agitated until the Flaxoap was completely solubilized. Into a separate 100 ml beaker containing 10 grams of isopropanol was slowly added 3 grams of polyethylene oxide (Polyox WSR-310, Union Carbide Company, having a molecular weight of about 4,000,000). The mixture was stirred until a stable slurry was formed. Into the beaker containing the CARBOPOL solution was placed the Flaxoap solution and the Polyox slurry which were intimately combined with vigorous agitation until a smooth white stringy gel having a pH of 6.5 was obtained.

The results in Table I and II show that the lubricant of this invention provides substantially equivalent lubricating properties to current commercial lubricant #2, substantially better performance than aqueous lubricant #1. Surprisingly the lubricant of the invention containing about 12% wt. Flaxoap provides essentially equivalent performance to Flaxoap under high loadings.

The foregoing discussion, Examples and data are illustrative of the invention. However, since many variations can be made without departing from the spirit and scope of the invention, the invention resides wholly in the claims hereinafter appended.