Grease Composition

In a companion application, Ser. No. 699,853 filed herewith, greases are taught in which polybutene oil is incorporated as a substantial component. That polybutene oil of the companion application however, is lightly hydrogenated whereby the grease formed is substantially saturated for improved color and stability. The present application is directed to ordinary amber color alpha olefinic polybutenes having normal unsaturation and which are unhydrogenated.

Heretofore, most of the lubricating greases have been prepared from a mineral or synthetic oleaginous vehicle or base oil with addition of a thickening agent to obtain the desired consistency. Thickening agents are most often soaps of fatty acids or inorganic agents, such as colloidal silica, bentonite, and the like.

These known greases are gels, the thickening agent forming a network wherein the oil is incorporated. However, difficulties have been encountered in the manufacture of a homogeneous and stable gel. Such difficulties are due to many factors, such as type of thickening agent, type of base oil, amounts of these components, the process for manufacturing the grease, etc. The influence of these factors are not yet well known.

Therefore, by incorporating polymers into lubricating greases to enhance some of their properties, further difficulties are encountered. For example, some olefin polymers, namely polymers of ethylene or propylene or co-polymers of ethylene with higher 1-olefins, have been suggested as thickening agents. However, the gels formed are not sufficiently stable and tend to break down under mechanical stresses with formation of too fluid products (see U.S. Pat. No. 3,112,270). Also, it has been observed that polyisobutylenes produced by low-pressure polymerization are not suitable as thickening agents and attempts to prepare valuable greases from these polymers have failed (German Pat. No. 1,091,683). It also has been proposed to incorporate polymers into lubricating greases in order to avoid bleeding of the greases with separation of the oil from the network formed by the thickening agent. Such compositions generally contain only a small additive quantity of a polyisobutylene having a mean molecular weight much higher than 2500, such as from 10,000 to 11,000, far less than 10%, i.e. less than about 3%.

An object of the present invention is to provide a homogenous, stable and effective lubricating grease.

Another object of the present invention is to provide a simple process for preparing lubricating greases which require smaller amounts of thickening agent and other additives to reach the desired performance.

In fulfillment of these and other objects, the present invention is a lubricating grease comprising 2 to 15% by weight such as 2 to 8% and preferably 3 to 8% of aluminum soap, 25 to 96%, preferably 35 to 97% by weight of a polymer of non-hydrogenated monoolefinic hydrocarbon having 4 carbon atoms and having a mean molecular weight of between 300 and 2500, and 0 to 60%, usually 2 to 60% and preferably at least 10% by weight of lubricating oil such as mineral oil.

The process for preparing these lubricating greases comprises dispersing 2 to 15% by weight, based on the composition, of aluminum soap, first into 10 to 50% by weight of a C.sub.4 olefine hydrocarbon polymer formed by polymerizing a C.sub.4 olefinic gas containing as polymerizable components isobutylene, cis and trans butene-2 and n-butene-1, and usually a refinery gas containing these as a mixture in which the isobutylene content usually exceeds 10%, such gas generally containing substantial quantities of n-butanes. Said polymer has a mean molecular weight between 300 and 2500 and is polymerized with promoted aluminum chloride--anhydrous at a temperature in the range of about 15.degree.-50.degree. C. The soap is dispersed in the polymer at a temperature in the range of 15.degree. to 50.degree. C, the dispersion is effected by progressively heating the dispersion mixture.

In broadest aspect, additional lubricating oil may be omitted. It is preferred, however, to add between 2 and 60% of a lubricating oil, preferably between 5 and 60% of a mineral lubricating oil, but other lubricating oils as listed below may also be used. The important advantages in smooth flow and consistency of the grease are present in the polybutene aluminum soap grease containing at least 2 or 3% and preferably more of the lubricating oil as stated.

In heating to form the grease, when the temperature of the mixture reaches 90.degree. to 110.degree. C, 15 to 48% of additional polybutene polymer oil is added to bring the total polymer content of the grease into the range of 85 to 98%, when no mineral oil is used, the remainder being aluminum soap. The total polymer oil will range from 38 to 96% polymer, 2 to 15 % being soap and 2 to 58% being mineral oil, the preferred oil in mineral oil containing products.

In mixing the components of the grease, the bulk of the mineral oil is added slowly in the mixing when the temperature reaches the range of 150.degree. to 180.degree. C, the grease product is finally cooled to a temperature of 10.degree. to 35.degree. C, and homogenized at that lower temperature.

It has been found that the lubricating greases of the present invention which contain the relatively low molecular weight polymer of butene or isobutylene are smooth, homogeneous and particularly stable, thus making these greases particularly effective. This result is unexpected because according to the prior art, it has been conventional practice to employ polymers having a high molecular weight and to add them in low proportions for preventing any prejudicial action on the stability and the lubricating action of the greases.

The present grease has other most surprising advantages. For instance, a solid grease is available using aluminum soap in the relatively small quantity, for instance, as low as 2%. Greases made with other soaps generally require more soap. Even in the case of aluminum soaps of fatty acids it was thought to require at least 10% of soap used with heavy polymer oil to form a solid grease. The present invention can use much lower quantities of aluminum soap to form a solid grease. Again, it was thought that to make a grease, much working was required for most oils including polymer oils. The present polymeric oil can form a grease with little working having a penetration or consistency index in the range of about 285 to 340 indicating good penetration as compared to other known greases using a comparatively small amount of aluminum soap clearly indicating the superiority of this type of grease. Finally, the grease is a better lubricant with a very low wear index. For instance, grease having a wear index in the range of 0.60 to 0.75 are formed as set forth in the examples below indicating the surprising superiority of the present grease.

The aluminum soap or thickening agent employed in the grease composition of the present invention generally is used in an amount ranging from about 2 to 15%, and more particularly from 3 to 8 % based on the weight of the grease. This aluminum soap is most often a soap of a saturated or unsaturated higher aliphatic carboxylic acid, containing from about 12 to 20 carbon atoms, e.g. stearic, oleic, ricinoleic or palmitic acid. Mixed aluminum soaps, which are soaps obtained from a higher aliphatic carboxylic acid and from a carboxylic acid with a lower molecular weight, may be used. Examples of such aluminum soaps include soaps of benzostearic, acetopalmitic, toluostearic acids, etc.

By substituting an alkali or alkaline earth metal soap for an aluminum soap, the other conditions remaining the same, it has been observed that the lubricating grease is somewhat softer. Therefore, the amount of soap required to prepare a grease having a given consistency is higher with an alkali or alkaline earth metal soap than with an aluminum soap. Thus, the aluminum soaps are economically more advantageous and are preferred.

The lubricating oil employed in the lubricating grease of the present invention is any mineral such as aromatic or naphthenic oil, a highly naphthenic oil being preferably used for the manufacture of greases having a high thermal stability. Synthetic lubricating oils also may be used, e.g. esters of sebacic or adipic acid and of alcohols with 6 to 12 carbon atoms, such as 2-ethylhexanol. The oil is used in an amount not higher than 60% and ranging more often from 10 to 50% by weight of the grease. The consistency of the greases generally increases when the amount of oil decreases. It also is advisable to use oils or mixtures of oils with a viscosity index varying from 10 to 100 or even higher and preferably, between 30 and 70.

The linear polymer of butene or isobutylene most commonly used in the compositions of the present invention is a non hydrogenated liquid homopolymer with a mean molecular weight of between about 300 to 2500. This polymer may be the sole oleaginous component of the grease, the amount by weight in the grease reaching 98%. However, the amount of polymer which is required in preparing a grease with high consistency, stability and performances is at least 25% based on the weight of composition. Mixtures of these polymers may also be used, for example, a blend of two or more of such polymers of different molecular weights or a mixture of non hydrogenated polymer and hydrogenated polymer, etc.

In preparing greases according to the present invention, about 2 to 15%, based on the weight of the grease, of aluminum soap is dispersed into about half of the required amount of polybutene or polyisobutylene. That is to say that such amount is dispersed into about 10 to 50% by weight of polymer. This dispersion is carried out while continuously stirring at a temperature of about 10.degree. to 50.degree. C. The mixture obtained is progressively heated until a temperature of about 110.degree. C is reached and the oil is added. The temperature is further raised to about 150.degree.-180.degree. C and the remaining amount of polymer is progressively added while stirring, the temperature being maintained between the 150.degree.-180.degree. C temperature range. As indicated above, the later added polymer may be different from the polymer used in the first step of the process. The mixture is then cooled and when at room temperature, it is homogenized in a colloidal mill or any known and convenient homogenizer.

Other compounds may be incorporated in the grease. For example, extreme-pressure additives, anti-corrosive agents, colouring agents, high molecular weight polymers improving the adhesiveness of the grease on metallic surfaces, such as polyisobutylene having a molecular weight higher than 100,000 may be added. The amount of these additives generally is not higher than 2 to 3% by weight of the grease.

The components of the grease according to the present invention, that is the aluminum soap, the polymer of C.sub.4 monoolefin and the lubricating oil, when used in the above stated proportions, form unique mixtures, with specific properties. It has been found that the required amount of aluminum soap to be used as thickening agent and the required amount of adhesiveness improver are lower in the greases of the present invention than in conventional greases. The substitution of this soap or of this polymer by another homologue has a detrimental effect on the performance of the grease.

The following examples are given to illustrate the present invention. These examples are not to be construed as limiting the invention however. In these examples, reference is made to the following tests:

Astm d 217-52t or penetration test, which is a measure of consistency and mechanical stability of the grease.

Astm 2266 for testing the wear preventive characteristics of grease (fours balls method, at 1800 r.p.m. 1 h., 75.degree. C and 40 kg/cm.sup.2).

Five parts by weight of aluminum stearate and 42 parts by weight of non hydrogenated polyisobutylene having a mean molecular weight of 460 were blended at room temperature. This mixture was heated as quickly as possible with stirring. When the temperature reached about 120.degree. C, 20 parts by weight of naphthenic oil with a viscosity index of 70 were added. This mixture was further heated and when the temperature reached 170.degree.-180.degree. C, 32.8 parts by weight of non hydrogenated polyisobutylene having a mean molecular weight of 730 and 0.2 parts by weight of polyisobutylene having a mean molecular weight higher than 100,000 were progressively added. The temperature was kept at about 175.degree. C during this addition with stirring. The hot grease was then withdrawn into a cooling vessel. The cooled grease was poured into a mixer and passed through a homogenizer.

The grease was smooth, stringy, homogeneous, sightly coloured but transparent. The hardness was 285 (in tenth of mm. at 25.degree. C: test ASTM 217-T) for the unworked grease and 297 for the 60 strokes worked grease.

The wear index (ASTM 2266) was 0.72.

By way of comparicon, a grease which was free from low molecular weight polyisobutylene rquired a higher amount of aluminum soap (8% by weight instead of 5%) to obtain the same hardness, and a higher quantity of adhesiveness improver (1% by weight instead of 0.2%). On the other hand, the wear index was 1.07 for this grease containing 8% by weight of aluminum soap, 1% of polyisobutylene with a molecular weight higher than 100,000 and 91% of mineral oil.

Thus, it is apparent that by using a polyisobutylene with a molecular weight lower than 2500, the grease requires lower amounts of thickening agents and of additives and has better lubricating and anti-wear properties.

A grease was prepared from the following:

46.8% by weight of non hydrogenated polyisobutylene with a mean molecular weight of 460

48.0% by weight of non hydrogenated polyisobutylene with a maan molecular weight of 730

5.0% by weight of aluminum stearate

0.2% by weight of adhesiveness improver

This grease was smooth, homogeneous, colorless and stringy, with a penetration index of 289 and a wear index of 0.63.

By way of comparison, a grease which was also free from mineral oil but containing lithium soap instead of aluminum soap was prepared. Even with an amount of lithium soap as high as 12% by weight, this grease was less hard, the penetration being 319.

The process of Example I was repeated using 39.8 parts by weight of polyisobutylene, non-hydrogenated with an average molecular weight of 447 and 35.0 parts by weight of polyisobutylene non-hydrogenated having an average molecular weight of 633. After the grease was heated to 120.degree. C, 3% of the same naphthenic oil was added.

By way of comparison, the grease of Example II decomposed on heating to 550.degree. C leaving as residue only molten aluminum stearate, the polybutene decomposing as gases. The grease of Example III however also decomposed, but left a liquid residue of the mineral oil and soap still capable of functioning to a small degree as a lubricant for surfaces so highly heated.

The process of Example I was repeated, but with 74.8 parts by weight of polyisobutylene having a mean molecular weight of 500.

The grease had a good mechanical stability, the penetration being 294 for the unworked grease and 295 for the worked grease (60 strokes).

The anti-wear properties were also good, the wear index being 0.70.

The process of Example I was repeated, but by substituting a synthetic oil (di-2-ethylhexylsebacate) for the naphthenic oil.

The grease also had good anti-wear properties (wear index 0.70) but was somewhat less in consistency (penetration: 340).

Four greases were prepared from naphthenic mineral oils (viscosity index : 70) non-hydrogenated polyisobutylene, aluminum soap and adhesiveness improver (polyisobutylene having a molecular weight higher than 100,000).

The proportions (by weight) of these components in each of the greases and the results of tests are given in the following table. The molecular weight of the polymers is given after the abbreviation PIB.

The primary characteristic of these greases is their consistency and anti-wear power.

By way of comparison, a grease was prepared from 54.8% by weight of mineral lubricating oil, 5% by weight of aluminum stearate, 10% by weight of polyisobutylene with a mean molecular weight of 670 and 30% by weight of polyisobutylene with a mean molecular weight of 3500. Due to the incorporation of this latter polymer, the grease was scarcely workable and mechanically applicable at low temperatures. The same disadvantage appeared with greases containing low molecular weight polyethylene and polyhexane. Also, suitable greases could not be prepared from high molecular weight polyolefins.

The greases of Example VI were duplicated but with calcium stearate instead of aluminum stearate. The grease so produced was of substantially lower consistency.

The above results illustrate that the greases prepared according to the present invention provide substantially improved results.