Non-Toxic Antimicrobial Lubricant

1. Field of the Invention

This invention relates to lubricants containing an antimicrobial compound.

2. Brief Description of the Prior Art

Lubricants containing an antimicrobial compound have been generally known. Commonly, such lubricants include an antimicrobial compound for one or more of a number of reasons, including preservation of the lubricant from deterioration or contamination, and protection of those coming in contact with the lubricant from a condition known as contact dermatitis. For these and similar reasons for the use of an antimicrobial compound, the antimicrobial compound must be active in the presence of the lubricant's substituents and strong enough to perform the function for which it is used. In the typical instances of preserving the lubricant or preventing contact dermatitis, the antimicrobial compounds heretofore proposed for use have been toxic to humans if ingested. Consequently, antimicrobial compound--containing lubricants have been limited to certain applications in which human ingestion is unlikely because they are too aggressive for human ingestion.

Moreover, certain applications for lubricants require the use of a special class of lubricants called boundary lubricants. Such applications often pose moderate to severe loading, high speed, or moderate to high temperature conditions that non-boundary lubricants cannot adequately tolerate. Consequently, extreme pressure (EP) additives have been developed that, when added to a base lubricant, produce a boundary lubricant for these severe applications. The presence of EP additives in lubricants is very important if a lubricant is to perform favorably under heavily loaded, high speed, or high temperature conditions. Typical of such an application are dental tools such as dental hand pieces, and some medical devices as well as food, pharmaceutical and cosmetics manufacturing, processing or packaging equipment, where boundary lubrication is essential in cage/ball and cage/race bearing contacts, bushings, slides, cams, gears etc. In the absence of a suitable boundary lubricant, such devices wear out much too soon because metal to metal contact and/or metal to ceramic contact, and/or metal to other composite material contact, and/or composite material to composite material contact creates unacceptable wear and surface distress.

Dental tools and some medical devices as well as food, pharmaceutical, and cosmetic manufacturing processing or packaging equipment, in which use of a boundary lubricant would be highly desirable, are designed and/or required to come into contact with the human body and/or it's internal parts or have a high probability of incidental contact with the body or food/pharmaceutical products that are ingested. However, extreme pressure additives used in boundary lubricants are so highly toxic that they are unsuitable for use in devices that may come into contact with the human body and/or it's internal parts, including the oral cavity in the case of dental tools or food/pharmaceutical machinery in the case of incidental product contact that may be ingested. Furthermore, known antimicrobial compounds used in lubricants are also too aggressive for such uses.

It is a primary object of the present invention to provide a non-toxic boundary lubricant that contains an antimicrobial compound so that devices employing such a lubricant can safely come into contact with internal or external parts of the human body, such as the oral cavity or by ingestion.

This and other objects and advantages will become apparent from the following description of the invention.

In accordance with these objects and advantages, the invention comprises:

The lubricant of the present invention is a non-aqueous lubricant having a major part comprising a suitable animal, vegetable or petroleum-based lubricant, either individually or in various blended combinations. A suitable stock base lubricant is a U.S. Government approved lubricant for safe use in external or internal contact with the human body. Such lubricants may include; U.S.P. Grade oil; U.S.D.A Grade oil, (H1) or (H2) or (H3); or F.D.A. Grade oil. U.S.P. Grade mineral oil (CAS# 8012-95-1) is a suitable stock base lubricant product for use in the present invention. The lubricant has a minor part of an extreme pressure additive, such as, but not limited to, a phosphate ester oil additive, the resulting boundary lubricant composition being a base fluid to which the herein below-identified substituents are added. Of this base fluid, the blended combination of mineral oil component preferably constitutes between about 75% and 99.99% by volume, and the extreme pressure additive preferably constitutes between about 0.01% and 25.00% by volume.

As such, the boundary lubricant composition base fluid of the present invention fits within the overall class of lubricants known as fluid boundary lubricants, having capability of boundary film lubrication where a eutectic film is formed between opposing contacting surfaces under the extreme operating conditions to which the lubricated opposing surfaces are exposed.

To the boundary lubricant base fluid, a suitable non-toxic antioxidant is added to de-toxify the EP additive. A suitable antioxidant would be a biological antioxidant such as DL-alpha-Tocopherol, U.S.P./N.F. (CAS# 59-02-9), of the vitamin E group. Only a very small amount of antioxidant is required, in the case of DL-alpha-Tocopherol about 26.0 grams per 54.0 gallons of the base fluid.

The boundary lubricant and antioxidant are blended together with a suitable non-toxic emulsifier, such as polyoxypropylene 15 stearyl ether (CFTA name: PPG-15 Stearyl Ether). A suitable emulsifier is ARLAMOL E Emollient-Solvent, available from ICI Surfactants, in an amount sufficient to completely emulsify the mixture. Other U.S.P./N.F. Grade emulsifying agents could be selected from the following group: Acacia (CAS# 9000-01-5); 2-Aminoethanol (CAS# 141-43-5); Cholesterol (CAS# 57-88-5); Octadecanoic Acid (CAS# 57-11-4); lecithin; 9-Octadecanoic Acid (CAS# 112-80-1); Polyethylene-Polypropylene Glycol (CAS# 9003-11-6); Polyoxyl 20Cetostearyl Ester (CAS#9005-00-9); Polyoxyl 40 Stearyl (CAS# 9004-99-3); Polysorbate 20(CAS# 9005-64-5); Polysorbate 40(CAS# 9005-66-7); Polysorbate 60 (CAS# 9005-67-8); Polysorbate 80(CAS# 9005-65-8); Sodium Lauryl Sulfate (CAS# 151-21-3); Sodium Stearate (CAS# 882-162); Sorbitan Monooleate (CAS# 1338-43-8); Sorbitan Monopalmitate (CAS# 26266-57-9); Sorbitan Monostearate (CAS# 1338-41-6); Triethanolamine (CAS# 102-71-6).

Following the blending of the antioxidant and emulsifier substituents into the base fluid, the mixture is buffered so as to be physiologically neutral, pH 7.3-7.48. A suitable buffering agent is acetic acid, 36% (w/w), U.S.P./N.F. (CAS# 64-19-7). Then, an appropriate non-toxic antimicrobial compound is added in an appropriate efficacious amount to produce the final mixture, between about 0.01% and 25.00% by volume of the final mixture. A suitable antimicrobial compound could be selected from the following group: Chlorhexidine gluconate (CAS# 18472-51-0); Cetylpyridinium chloride (CAS# 123-03-5); Sanguinarine (CAS# 244754-3); Sodium fluoride (CAS# 7681-49-4); Thymol (CAS# 89-83-8); and equal parts of: (a) Alkyl dimethyl betaine (CAS# 693-33-4) and (b) N,N-dimethyl alkylamine-N-oxide (CAS# 3332-27-2). Of these antimicrobial compounds, chlorhexidine gluconate is preferred because of its 50 year safety record. The type and amount of the non-toxic antimicrobial compound to be added would depend on the variety of microorganisms to be controlled, such as fungus, bacteria, algae, viruses and yeast, but not necessarily limited to these varieties. The relative amounts of antimicrobial compounds to be added to the final mixture will depend on the application and the useful antimicrobial dosage range for a particular application. Typical such applications would include equipment used in the processing and/or manufacturing of health care products, dental instruments and/or the processing and/or manufacturing of dental care products, equipment used in and/or manufacturing of food processing systems, equipment used in the processing and/or manufacturing of cosmetic and/or pharmaceutical products and any other of the like.

The blending of a preferred non-toxic antimicrobial boundary lubricant would be as follows;

1. Blending the Base Fluid

Stage one begins with a stock base lubricant such as U.S.P. Grade mineral oil. To this base lubricant, an EP additive is blended until a mixture of between 75% and 99.99% by volume mineral oil with the EP additive part being between 25% and 0.01%.

2. Blending the Second Stage Fluid

After stabilizing a 54.0 gallon quantity of base oil at 32.degree. C., 26.0 grams of DL-alpha-Tocopherol, preheated to 55.degree. C. is added. The addition of this hydrophilic polymer is used to form the anti-corrosive element so useful for sterilizing, disinfecting and cleaning devices generally including medical and dental devices where the efficacy of cleaning and sterilizing requires severe treatment. Using a paddle mixer, the entire solution is mixed for 60 minutes. While continuing to mix the heated solution, a small amount such as 50 cc may be removed, being careful to observe sterile sampling techniques, and emulsified using the standard Hydrophile-Lipophile-Balance system technique using a ARLAMOL E Emollient-Solvent preheated to 60.degree. C. to establish the proportion of emulsifier required to balance the solution. During the balancing process, care should be taken to maintain both the second stage sample and the emulsifier at their respective temperatures of 55.degree. C. and 60.degree. C., and to accurately account for the volume of emulsifying agent required to achieve balance. Once the amount of emulsifier is known, a proportionate amount must be added to the bulk second stage oil. While maintaining the 55.degree. C. temperature, continue mixing with the paddle mixer for 90 minutes, whereupon this stage is complete. While not required, a biological microscope will assist the technician to balance the solution.

3. Blending the Final Stage Fluid

Using ASTM test method D-2896 (88),Standard Test Method for Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration), adjust the solution using the acetic acid buffer to a pH range of 7.4-7.48. Depending on the desired end use of the product, the amount of the final stage product will vary from 75.00% to 99.99% by volume. The remainder volume will be a combination of emulsifier, added in stage 2, and the antimicrobial compound. The preferred antimicrobial composition, chlorhexidine gluconate may be used in an amount up to 24.0%, with 0.12% being preferred. The amount of emulsifier used in stage 2 may comprise up to 25% by volume of the final stage product.

The physical data of a commercial version of the final stage product, containing 0.12% chlorhexidine gluconate are:

Contrary to the general class of boundary lubricants, the boundary lubricant of this invention is non-toxic and suitable for human contact. The general class of boundary lubricants have, as one of their greatest drawbacks, the general toxic nature of their elementary components which are unsuitable for human contact and have borne the appropriate label warning, "Harmful or fatal if swallowed." The boundary lubricant of this invention is non-toxic and thus set apart from the general class of boundary lubricants.

While the preferred embodiment of the invention has been described herein, variations in the design may be made in order to properly adapt the finished product to the cosmetic, pharmaceutical and/or food processing, manufacturing and/or equipment industry. The scope of the invention, therefore, is only to be limited by the claims appended hereto.

The embodiments of the invention in which an exclusive property is claimed are defined as follows: