Water tolerant lubricant composition

Abstract

 Lubricants are provided which are capable of tolerating substantial amounts of dissolved water without significant loss of lubricating and load-bearing properties. These lubricants comprise water-soluble polymers and copolymers of alkylene oxides, i.e., polyoxyalkylene glycols, typically containing at least about 20% by weight of ethylene oxide.

Description

BACKGROUND OF THE INVENTION

[0001] This invention relates to water-tolerant organic lubricants for use in the lubrication of close-fitting moving parts, such as in gear boxes.

[0002] Petroleum-based lubricants are well known. Similarly, water-soluble poly (alkylene oxide) polymers are known for use as thickeners in aqueous hydraulic fluids. See, for example, U.S. Pat. Nos. 2,602,780 and 2,768,141. While such aqueous hydraulic fluids have certain desirable properties, such as non-flammability, good temperature stability and relatively low cost, their lubrication characteristics are often inferior to those of petroleum-based products. Efforts have often been made to improve the lubrication properties of water-soluble organic materials by the use of various additives. See, for example, co-pending U.S. Ser. No. 221,503, filed December 30, 1980. Water insoluble poly(alkylene oxide) polymers have also been known for some years as gear box lubricants but, like petroleum-based lubricants, they do not perform satisfactorily when contaminated with water.

[0003] Many uses for lubricants involve requirements for the lubricity of petroleum products, but yet require a high level of tolerance for water as an impurity since the uses unavoidably expose the lubricant to contamination by water. Unfortunately, even a small amount of water, e.g., 5% or less, by weight, and even as little as about 900 ppm in some high-pressure uses, causes severe detrimental effects, such as viscosity change and substantial loss of load-carrying ability of petroleum lubricants. An effective lubricant capable of dissolving a substantial amount of water without sacrificing significant levels of important properties would clearly be very desirable.

SUMMARY OF THE INVENTION .

[0004] It has now been discovered that certain polyoxyalkylene glycols which are water-soluble make excellent lubricants for close-fitting moving parts. Because of their water-solubility, they are able to take up substantial amounts of ambient water without significant loss of their lubricity and load-bearing properties.

[0005] The polyoxyalkylene glycols useful in this invention are the water-soluble reaction products of an alkanol having up to 4 carbon atoms with ethylene oxide or mixtures of ethylene oxide and higher alkylene oxide. The concentration of the ethylene oxide moiety can be as much as 100% of the total alkylene oxide content. ,The lower limit of ethylene oxide is that concentration which renders the polyoxyalkylene glycol soluble in water, usually about 20% by weight.

[0006] Accordingly, this invention provides a lubricant for close-fitting, moving parts which comprises a water-soluble polyoxyalkylene glycol capable of dissolving 20% or more, by weight of the solution, of ambient water without losing more than about 40% of its water-free viscosity and without significant loss of its load-carrying ability, as measured by the "Falex" test, ASTM D-3704. In addition, this invention provides a method for lubrication of close-fitting, moving parts exposed to ambient moisture comprising using as the lubricant for such moving parts the polyoxyalkylene glycols disclosed herein. The lubricants of this invention are particularly suitable for moving parts subject to close tolerances, high shear and high pressure, such as occur in gear boxes.

DETAILED DESCRIPTION OF THE INVENTION

[0007] Poly(alkylene oxide) polymers useful in this invention are those which are water-soluble and thus are capable of themselves dissolving a substantial quantity of water. In general, these polymers will contain oxyethylene groups or both oxyethylene groups and higher oxyalkylene groups, such as oxypropylene and oxybutylene groups, either in random or block distribution in their molecules, and will have average molecular weights from 400 to 40,000, or even higher. Preferably, the average molecular weight ranges from 400 to 4,000. The amount of oxyethylene groups in the molecule is such that the poly(alkylene oxide) polymers are soluble in water at ordinary temperatures, and the amount of oxypropylene or higher oxyalkylene groups is such that the poly(alkylene oxide) remains liquid at ordinary temperatures up to an average molecular weight of 40,000 and higher. The oxypropylene/oxyethylene ratio may vary from zero to about unity. Preferably, the ethylene oxide content will be at least about 20% by weight of the polymer. These poly(alkylene oxide) polymers may be made by processes well known in the art by reacting ethylene oxide or mixtures of ethylene oxide and propylene oxide or higher alkylene oxide with a compound, known as a "starter," having at least one active hydrogen atom up to as many as six such active hydrogen atoms including, for example, water, monohydroxylic alcohols such as ethanol and propanol, dihydroxylic alcohols such as ethylene glycol, trihydroxylic alcohols such as glycerine and trimethylolpropane, tetrahydroxylic alcohols such as pentaerythritol, hexahydroxylic alcohols such as sorbitol, and mono- or poly- functional amines such as butylamine and ethylene diamine. The poly(alkylene oxide) products of such reaction will have linear or branched oxyethylene or oxyethylene-higher oxyalkylene chains and such chains will terminate with hydroxyl groups. Some or all of these hydroxyl groups may be etherified by reaction with a dialkyl sulfate such as diethyl sulfate.

[0008] Mixtures of alkylene oxide homopolymers and copolymers can also be used, provided that such mixtures are water-soluble.

[0009] The preferred polymers are copolymers of ethylene oxide and propylene oxide. In order to be rendered water-soluble, such copolymers will ordinarily contain at least about 20% by weight ethylene oxide. The most preferred copolymers are those containing about 50% ethylene oxide and about 50% propylene oxide and having viscosities ranging 21-1100 mm²/s 38°C from 100 SUS to 5,000 SUS at 100°F. Useful copolymers meeting these criteria include those sold by Union Carbide Corporation under the trademark UCON fluids, as the series 50 HB.

[0010] It will be appreciated by those skilled in the art that one of the primary criteria for specifying lubricants, especially gear lubricants, for which this invention is particularly suited, is viscosity. Typically, the viscosity requirements are stated, at a given temperature, in terms of a test known in the industry as ASTM D-2270. For convenience in the industry, viscosity is often expressed in "SUS" units, stated at 100°F. It has been found that the-viscosity specifications for any given use can be met either by selecting a polyalkylene glycol inherently having the required viscosity, or by mixing two or more polyalkylene glycols having different viscosities. Useful polyalkylene glycols will have SUS viscosities at 38°C 21 mm²/s 100°F ranging from 100 to . 90,002, and 1100 mm²/s preferably from 15₀ and 5,000 SUS units.

[0011] It will also be understood that the lubricants of this invention can be formulated, within the skill of the art, to include corrosion inhibitors, antioxidants, viscosity control agents, extreme pressure additives, anti-wear additives, freezing point depressants, pH conditioners, anti-foaming agents, and the like.

[0012] The invention is demonstrated in the following examples which are offered for illustration only and are not intended to impose any necessary limitations on the invention.

EXAMPLES

Example 1

[0013] A polyalkylene glycol lubricant mixture was prepared containing the following, in parts by weight:

68.6 parts glycol I

30.3 parts glycol II

0.5 part antioxidant

0.2 part solvent

0.4 part corrosion inhibitors

[0014] Glycols I and II are butanol - started, random copolymers containing about 50% by weight ethylene oxide and about 50% by weight propylene oxide and 430 36,5 mm²/s having nominal viscosities of 2000 and 176, respectively, as determined by ASTM D-2270. This mixture was divided into a control and 6 samples to which were added various amounts of deionized 38°C water. SUS viscosity was measured at 100°F, with the following results:

Although the viscosity did decrease upon addition of large amounts of water, it will be seen that the viscosity with as much as 20% water is still quite serviceable.

Example 2

[0015] The compositions of Example 1 were subjected to a procedure known as a "Falex" test (ASTM D-3233) to measure their load-carrying capacity. The results were as follows:

It will be seen from Table II that load-bearing ability, as evidenced by psi load to break, is retained throughout a broad range of pressure, even for materials containing as much as 20% water (Sample G).

Example 3.

[0016] A polyalkylene glycol lubricant mixture was prepared containing the following, in parts by weight:

97.65 parts glycol III

2.0 parts antioxidant

0.35 part corrosion inhibitors

Glycol III is a butanol - started, random copolymer containing about 50% by weight ethylene oxide and about 50% by weight propylene oxide and having a nominal viscosity of 660 SUS as determined by ASTM D-2270.

[0017] This mixture was found to have a _SUS 144 mm²/s 38°C viscosity of 664 at 100°F. Its performance, without water, in the Falex test was as follows:

[0018] This lubricant was not evaluated with water contaminant in the Falex test; however, its performance leads to the expectation that the addition of substantial amounts of water would not significantly degrade performance.

Example 4.

[0019] The lubricant mixture of Example 3 was used to replace the normal petroleum lubricant in the gear box of a "Lightnin'" mixer which tends to absorb a substantial quantity of ambient moisture through "breathers." Typical petroleum oil service life in this gear box is three months or less, at which time the lubricant is changed because its performance has been substantially degraded by water contamination. In contrast, the lubricant of ) Example 3 showed no degration after four months of service even though water content had risen to 2-3% by weight. After eight months of service, performance remained normal.

Example 5.

[0020] The lubricant mixture of Example 3 was used to replace the petroleum lubricant in a gear box in a can drawing system subject to extensive contamination by water. The lubricant of this invention operated well for several weeks, thereby substantially out-performing petroleum-based lubricants. When it did fail, it was found to have a water content of more than 30%. It was also observed that the operating temperature of this gear 40°C 65,5°C box dropped to 105°F from 150°F, thus evidencing the excellent lubricating qualities of this composition.

Claims

1. A lubricant for close-fitting, moving parts which comprises a water-soluble polyoxyalkylene glycol capable of dissolving at least about 20% by weight of the solution, of ambient water without losing more than about 40% of its water-free viscosity and without significant loss of its load-carrying ability.

2. A lubricant of claim 1 wherein the polyoxyalkylene glycol is a polyoxyethylene glycol or copolymer of ethylene oxide and propylene oxide.

3. A lubricant of claim 2 wherein the copolymer contains at least about 20 % by eight ethylene oxide preferably about 50 % by weight ethylene oxide.

4. A lubricant of claim 1 having an vis-21 mm²/s 38°C cosity of 100 to 90,000 SUS at 100°C.

5. A method for improving the performance of a gear box exposed to ambient moisture comprising using as the lubricant in such gear box the lubricant of claim 1 to 4.