Grease Compositions Of Polyol Aliphatic Esters

Abstract

Grease compositions comprising (1) as a base fluid a polyol aliphatic ester and (2) as a thickener finely divided sodium montmorillonite clay. The clay may be used as the sole thickener or it may be used in combination with a finely divided fluorinated ethylenepropylene copolymer. Also, molybdenum disulfide or antimony dialkyldithiocarbamate may be added to the compositions. The compositions have both good wear characteristics and good extreme pressure characteristics at temperatures in the -65.degree. F. to 350.degree. F. range. The grease compositions are useful in heavily loaded airframe bearings, screw jack actuators, journal bearings, and in other applications where there is sliding, rolling, oscillating, or other forms of motion where wear and extreme pressure are factors.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is in the field of grease lubricating materials.

2. Description of the Prior Art

With the advent of high-speed aircraft and aerospace vehicles and the increase in their scope of operations under heavy load conditions, serious demands have been made on greases. To meet these demands, the prior art has achieved substantial advancement in the synthesis of a variety of lubricating oils. There are many oils which have desirable lubricating properties and are capable of functioning under moderately heavy loads. Attempts have been made to incorporate these oils into grease formulations capable of preserving their lubricity at the points where originally desired. The prior art has had little success in these attempts. Grease systems which have been used with reasonable degrees of success have involved the complicated, costly, and time consuming addition of many different materials to the basic lubricating oil. Also, while the various additives have provided improvements in one or more areas, they have not provided all the improvements desired and have often subtracted from the potential of the grease system in some areas while they were improving it in others. For example, where a prior art grease formulation might be made capable of withstanding exposure to oxidation or evaporation conditions by an additive, the same additive might also lower the lubricity of the system or make the system unable to prevent excessive wear under heavy load conditions.

Montmorillonite clays are well known as thickeners in the prior art. For example, silicone polymer oils have been thickened with clay to form a grease with the consistency of vaseline. However, despite the contributions of the prior art, the need continues for grease compositions with both good wear properties and good extreme pressure properties over a wide range of temperatures.

SUMMARY OF THE INVENTION

The practice of this invention allows one to formulate a grease composition which has both good wear properties and good extreme pressure properties at temperatures in excess of 350.degree. F. This invention also allows one to incorporate solid lubricants and additives into grease compositions in such manner that the wear and extreme pressure properties of the compositions will be improved. The grease compositions of this invention are useful in heavily loaded airframe bearings, screwjack actuators, journal bearings, and other places where sliding, rolling, oscillating, or other forms of motion take place and wear and extreme pressure are factors.

The invention may be briefly summarized by stating that the grease compositions comprise a polyol aliphatic ester base fluid and a finely divided montmorillonite clay thickener. Finely divided fluorinated ethylenepropylene copolymer and molybdenum disulfide or antimony dialkyldithiocarbamate are also used as additives.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polyol aliphatic ester, which is the base fluid of the grease compositions of this invention, may be characterized by the general formula:

wherein R is a substituted alkane containing one to three carbon atoms, R' is an alkyl group containing three to 12 carbon atoms, and n is an integer having a value of three to four; and wherein the polyol aliphatic ester is further characterized by the following properties.

Viscosity at 100.degree. F. about 25 to 35 centistokes Viscosity at 210.degree. F. about 4 to 6 centistokes Pour point about -70.degree. F. Flashpoint about 450.degree.-525.degree. F.

additives such as molybdenum disulfide and antimony dialkyldithiocarbamate may be used, with advantage, in the compositions of this invention. The antimony dialkyldithiocarbamate may be characterized by the formula:

wherein R is an alkyl selected from the n-butyl, amyl, hexyl, 2-ethylhexyl, and decyl groups with amyl being preferred.

The fluorinated ethylene propylene copolymer is a copolymer of perfluoropropylene and tetrafluoroethylene, preferably of equimolar amounts and characterized by the structure:

wherein n is an integer of sufficient value to give the copolymer an average molecular weight of about 150,000.

The physical characteristics of the thickeners are important. Montmorillonite clay should be finely divided having a surface area of about 15.9 m..sup.2 /gram, a particle size of about 0.75 to 1.0 micron, and a density of about 3.09 grams/cc. If fluorinated ethylenepropylene copolymer is used with the clay, the copolymer should have a surface area of about 1.0 m..sup.2 /gram, a particle size of about 0.15 micron, a density of about 2.18 grams/cc., and an average molecular weight of about 150,000.

The following examples give compositions which were formulated in the percentages indicated. The percentages are by weight unless otherwise specified. Where a percentage range is given a number of compositions were made up in the range specified and the physical characteristics were in the range specified. The ingredients were mixed thoroughly and blended to a grease consistency by passing five times through a three-roll paint mill with the roller opening set at 0.002 inch at room temperature. Other standard grease homogenizing apparatus, however, may be used with equal results. The compositions resulting from the following examples were thermally stable to at least 350.degree. F. and exhibited both good wear and good extreme pressure properties at that temperature. Where molybdenum disulfide or antimony dialkyldithiocarbamate was added, it was added to the oil prior to blending on the three-roll mill. Worked penetration, dropping point, mean Hertz load, and four-ball wear test (steel on steel) mean determined in accordance with Methods 313.2, 1421.1, 6403, and 6514, respectively, of Federal Test Method Standard No. 791a. The oscillating bearing test was conducted in accordance with Military Specification MIL-G-27549.

EXAMPLE I

Composition

78-80% polyol aliphatic ester

7.5-8.5% fluorinated ethylenepropylene

7.5-8.5% sodium montmillonite clay

4.0-6.0% antimony dialkyldithiocarbamate

Test-results

worked penetration 315-320 dropping point 475-490.degree. F. four-ball wear scar (60 kg. load, 1,200 r.p.m. 167.degree. F., 2 hours) 0.9-0.95 mm. oscillating bearing test 300,000 cycles mean Hertz load 90-95

EXAMPLE II

Composition

77-80% polyol aliphatic ester

8-9 % fluorinated ethylenepropylene

8-9 % sodium montmorillonite clay

4-5 % molybdenum disulfide

Test-results

worked penetration 335-345 dropping point 500-515.degree. F. four-ball wear scar (60 kg. load, 1,200 r.p.m. 167.degree. F., 2 hours) 0.95-1.00 mm. oscillating bearing test 250,000-270,000 cycles mean Hertz load 84-89

EXAMPLE III

Composition

84% polyol aliphatic ester 16% sodium montmorillonite clay TEST-RESULTS worked penetration 336 dropping point 562.degree. F. four-ball wear scar (60 kg. load, 1,200 r.p.m., 167.degree. F., 2 hours) 1.10 mm. mean Hertz load 21

The foregoing are three specific examples which serve to indicate to those skilled in the art how the grease compositions were made up. When sodium montmorillonite clay, is used alone as the thickener, it may be present in the amount of about 15-20 weight percent of the composition. When fluorinated ethylenepropylene copolymer is used in conjunction with the clay the two (clay and copolymer) added together should comprise about 15 to 20 weight percent of the composition. If a solid lubricant is used it should comprise about 4 to 5 weight percent of the composition. The base fluid comprises that weight percent of the composition over and above the total of thickener and solid lubricant to make the total weight percent of the composition 100.

Claims

I claim:

1. A grease composition comprising (1) a base fluid, (2) a thickener, and (3) a solid lubricant; said base fluid being a polyol aliphatic ester having a viscosity at 100.degree. F. of from about 25 to 35 centistokes, a viscosity at 210.degree. F. of from about 4 to 6 centistokes, a pour point of about -70.degree. F., a flash point of from about 450.degree. to 525.degree. F. and having the general structural formula:

wherein R is a substituted alkane containing from 1 to 3 carbon atoms, R' is an alkyl group having from three to 12 carbon atoms, and n is an integer having a value of from three to four; said thickener being selected from the group consisting of sodium montmorillonite clay and a mixture of sodium montmorillonite clay and fluorinated ethylenepropylene copolymer characterized by the structure:

wherein n is an integer of sufficient value to give the copolymer an average molecular weight of about 150,000 with said thickener comprising about 15 to 20 weight percent of said composition; and said solid lubricant being selected from the group consisting of

wherein R is selected from the group consisting of n-butyl, amyl, hexyl, 2-ethylhexyl, and decyl and wherein said solid lubricant comprises about 4 to 6 weight percent of said composition.

2. The composition of claim 1 wherein said thickener is sodium montmorillonite clay.

3. The composition according to claim 1 wherein said thickener is a mixture of sodium montmorillonite clay and fluorinated ethylenepropylene copolymer and where said mixture comprises about 8- 9 weight percent of the clay and about 8- 9 weight percent of the copolymer.

4. The composition according to claim 3 wherein the solid lubricant is

5. The composition according to claim 3 wherein the solid lubricant is MoS.sub.2.