NO135095B - - Google Patents

Description

The present invention relates to grease, and more particularly homogeneous grease with improved mechanical properties and improved chemical stability.

In the past, shortening was usually made from

a base lubricating oil or oily carrier and a thickening agent,

which gives the fat the desired consistency. The thickeners are in most cases soaps of fatty acids or inorganic components, such as colloidal silicon oxide and bentonite.

The known shortenings are gels, and the thickener forms

a network in which the oil is incorporated. However, difficulties can be experienced in the production of homogeneous and stable gels, which can be attributed to many factors, such as the type of thickener, the type of base oil, the relative amounts of these components, the method used in the production of shortening fat' °9

the relative effects of these factors are not yet fully understood.

By incorporating polymers into shortenings to enhance some of their properties, further difficulties have arisen. E.g. it has been proposed to use certain olefin polymers as thickeners, namely polyethylene, and more particularly polyethylene with a density higher than 0.94 g/cm at 25°C, as well as copolymers of ethylene and propylene.' However, it has been observed that a slow oxidation and crystallization of these polymers takes place when lubricating grease is subjected to frictional stresses. Oxidized polyethylenes (with 0.2 - 7.5% by weight chemically bound oxygen) have also been proposed, and more particularly complexes of these oxidized polyethylenes with a metal salt where the metal has a valence higher than 2.

Fats containing these complexes are expensive, and they are not satisfactory in terms of good lubricating properties. In general, lubricating greases containing ethylene polymers are not sufficiently stable and exhibit a tendency to break down under mechanical stress with the formation of two liquid products (US patent no. 3,112,270).

Incorporation of polymers into shortening grease introduces a further factor which has an effect on certain properties of these greases.

One purpose of the present invention is to provide new lubricating greases with improved lubricating and anti-wear properties. A further purpose is to provide lubricating greases with improved properties with regard to storage stability, chemical and mechanical stability.

A further purpose is to provide homogeneous and durable shortenings.

According to the present invention, shortening fat consists of: 5 - 25% by weight of thickening soap, calculated on the weight of the fat, 1 - 10% by weight of an anionic emulsion of non-oxidised polyethylene with an average molecular weight higher than 10,000, and where the emulsion has a polyethylene content in the range 35 - 60%, and a content of an anionic emulsifier in the range 8 - 12%, calculated on the weight of the emulsion, and where the average particle size for the polyethylene is in the range 0.02 - 0.5 [ Lm, and where the rest of the composition is made up of an oily carrier containing common" additives for shortening.

It has surprisingly been found that greases containing polyethylene emulsions, as indicated above, have a considerable consistency,

and are particularly stable under mechanical stress.

Such polyethylene emulsions are produced according to methods described in US patents no. 3,296,162 and 3,352,807. These emulsions are produced by a free radical polymerization of ethylene in an aqueous medium containing a mixture of anionic emulsifiers. The emulsion thus obtained is stabilized by a post-treatment which comprises covering essentially 100% of the surfaces of the particles with an anionic emulsifier. For these stabilized polyethylene emulsions, the total content of emulsifiers depends on the particle size of the polymer. E.g. the content of emulsifier can be approx. 10% by weight when the particles contain 40% solids with a particle size of approx. 0.03 µm, while the content of emulsifier is only 8% by weight when the particle size is approx. 0.5|0.m. In general, the content of the emulsifier does not exceed 12% calculated on the weight of the polymeric emulsion, although higher content can be used without any significant improvement in the mechanical properties of these emulsions.

The stabilizing post-treatment is carried out with anionic compounds that are free of acidic groups and results in the stabilized emulsions having a pH higher than 8.

The stabilized polyethylene emulsions, as stated above, are completely different from emulsions made from oxidized polyethylenes, the latter having a relatively low molecular weight, lower than 5000, and usually approx. 3000; this limitation is partly set by the methods by which the emulsions are produced from emulsifiable polyethylene dry substances. The mechanical properties of polymers are generally dependent on their molecular weight. Furthermore, emulsions of oxidized polyethylenes generally do not contain more than 20 - 30% torr toff.

Consequently, emulsions of non-oxidised polyethylenes used in shortening according to the present invention are completely different from emulsions of oxidized polyethylenes, not only because the former have a higher content of polyethylene with a higher molecular weight, higher than 10,000, and in the form of particles with less size, but also because their pH is higher than 8, usually in the range 8.5 - 10. Furthermore, in contrast to non-stabilized emulsions of non-oxidized polyethylenes, their content of anionic emulsifiers is higher than 8%.

By incorporating stabilized emulsions of non-oxidised polyethylene into mixtures of an oily carrier and metallic soap, particularly resistant and smooth greases are obtained as a result of a synergistic effect between the soap and the polyethylene emulsion. Furthermore, this improvement beneficially affects other properties, such as a better water resistance and a significantly reduced tendency to "bleed" or oil separation.

The most used greases will usually contain 1-10% by weight stabilized emulsion of non-oxidized polyethylene in a mixture with 5-25% soap, and the rest of the grease is an oily carrier containing the usual additives for greases.

A significant improvement in the grease's properties is already obtained with a content of polyethylene emulsion as low as 1% by weight, as shown by the results of test methods for evaluating consistency, water resistance and "bleeding" tendency.

In this connection, grease was produced from naphthenic oil (SSU viscosity at 38°C: 500) containing 8.5% by weight (calculated on the grease) lithium 1,2-hydroxystearate, 0.5% of an antioxidant and 0.5% of a rust inhibitor. A comparison grease was prepared without the addition of polyethylene emulsion, while the other greases contain respectively 1%, 2% and 3% stabilized anionic emulsion of non-oxidized polyethylene ('Poly-EM 12', Cosden Oil & Chemical Company). characteristics of this emulsion were:

The following tests were carried out:

Grease consistency by penetration test (ASTM-D 217): Fair tree ring is measured by the length (in 0.1 mm) which a standard cone will penetrate in free fall at 25°C, the surface of grease contained in a co<*>pp. When the grease is introduced into this cup only, the penetration will be reported as "not processed". The "unprocessed" penetration for fat is not always a suitable indication, which is why the test is also carried out on processed fat in the cup (60 strokes in the present case).

Water resistance test (ASTM-D 1264): The fat is washed with water at a controlled temperature and speed, the weight loss of the fat being determined and calculated as weight % loss.

Blood test (IP method no. 121): The fat is subjected to a constant pressure, and the amount of secreted oil is determined (% by weight). The results of these trials are given in the following table:

The improvement in properties is already significant at a content of polyethylene emulsion of 1%, calculated on the total weight of the smb-refett composition, and is particularly remarkable when the content is in the range of 2-3% by weight.

The amount of stabilized emulsion of non-oxidized polyethylene required to improve grease and to provide the desired properties may vary depending on the type of oily carrier, as well as the type and amount of soap added.

With a higher emulsion content than 10%, the effect of these emulsions is already very favorable, and further addition does not provide any significant improvement, and a further addition is therefore not economically justifiable. Taking into account technical and economic conditions, the content of polyethylene content will not usually exceed 10%, and in most cases will be in the range of 1-5% by weight.

The oily carrier is advantageously an aromatic oil or naphthenic oil, more particularly a high naphthenic oil will give fat with better thermal stability. Synthetic lubricating oils containing sebacin or adipine esters of alcohols with 6-12 carbon atoms, such as 2-ethylhexanol, can be used. However, mineral oils or mixtures of mineral oils with smaller amounts of synthetic oil are economically more advantageous.

The amount of soap used as a thickener usually amounts to 5-25% by weight of the fat, this percentage depending on the type of soap, the amount of polyethylene and the desired degree of consistency. The soap is usually made from saturated or unsaturated, higher aliphatic carboxylic acids containing 12 - 18 carbon atoms, for example stearic acid, 1,2-hydroxystearic acid, palmitic acid and oleic acid. Mixed soaps can also be used, as these are mixtures of two different soaps, such as a mixture of alkali metal soap and aluminum soap. Other useful thickeners are complex soaps made from higher aliphatic carboxylic acids and a low molecular weight acid, for example soaps of benzostearic acid, acetopalmitic acid or toluenestearic acid.

Grease according to the present invention also includes common additives, namely antioxidants, rust prevention agents, and additives for extremely high pressures.

Particularly effective antioxidants are N-alkyl-para-phenylenediamines, naphthylamines and di- and tri-alkylphenols. Rust inhibitors often comprise primary amines containing 6-18 carbon atoms or N-heterocyclized derivatives. Additives for extreme pressures include the group of aryl phosphites, aryl phosphates and aryl thiophosphates, aryl sulphides, sulphurised fatty oils, chlorinated naphtha etc.

Anti-wear additives, for example urea or thiourea derivatives or certain polyisobutylenes with a molecular weight higher than 800 which act as a viscosity improver, can also be added to the lubricating grease according to the present invention.

These additives can be used in an amount which will vary in the range of 0.1 - 10% by weight, or more generally between 1 and 5% by weight of the fat.

For the production of lubricating grease according to the present invention, known methods can be used. These consist of forming a homogeneous mixture of the oily carrier and the soap at a relatively high temperature, then adding the stabilized emulsion of polyethylene and cooling the mixture to form a gel and homogenizing this gel to obtain the desired structure. When producing fat containing lithium 1,2-hydroxystearate, it can be advantageous to cool the homogeneous mixture slowly from a temperature of approx. 210°C to a temperature of 120 - 130°C and then carry out an isothermal pre-gelation at this temperature, after which the gel is further cooled.

The following examples illustrate the invention. In these examples, the percentage is percentage by weight.

Example 1

This example illustrates the synergistic effect between soap and polyethylene emulsion.

A grease consisting of 85.5% by weight naphthenic oil (500 SSU at 38°C), 14% by weight sodium soap of stearic acid and 0.5% of an anti-oxidizing agent has a penetration value (60 strokes) of 266.

Another grease consisting of 88% of the same oil, 10% lithium stearate, 0.5% of the same anti-oxidant and 1.5% polyethylene emulsion ("Poly-EM 12") has the same consistency.

These results show that by adding 1.5% of a stabilized emulsion of non-oxidized polyethylene, the amount of soap can be lowered from 14% to 10% without any adverse effect on the consistency of the fat.

On the other hand, to prepare a shortening from an oily carrier and a stabilized emulsion of polyethylene, but without the addition of metal soap, at least 10% by weight of the emulsion is required to obtain a suitable consistency, and furthermore the fat is less stable .

Example 2

A butterfat that contains:

is homogeneous, smooth and hard. Furthermore, the mechanical stability is remarkable, as can be seen from penetration tests where the difference between penetration at 60 blows and 10,000 blows is very

small, respectively 276 and 285. The water loss during washing is 4.5% by weight.

Example 3

A butterfat that contains:

is smooth and the consistency when tested for penetration at 60 blows is 260. Furthermore, this grease has a high mechanical stability, as the penetration after 1O.OO0 blows is 279; i.e. that the difference between penetration at 60 strokes is very small.

Loss by water washing (at 80°C) is 6.5%.

Example 4

Preparation of the fat according to example 3 was repeated, but using a mixed soap. This grease contained 5% lithium 1,2-hydroxystearate and 1.5% aluminum stearate.

The properties of this fat were the same as the properties of the fat according to the previous example.

Example 5

A fat that contains:

has a penetration value of 261 (at 60 hits).

The water resistance of this grease is remarkable, as the loss when washing with water at 80°C is only 0.8% by weight.

In contrast, a corresponding oil containing the same amount of soap, anti-oxidant and rust inhibitor and 87.5% of the same oil, but without the polyethylene emulsion, exhibits a penetration value (at 60 strokes) of 295, and a water wash loss of 18%. This comparative example clearly shows the particularly beneficial effect achieved by adding the stabilized emulsion of non-oxidized polyethylene.

Example 7

A fat containing:

has a penetration value (at 60 blows) of 285 and a loss when washing with water at 80°C of 1.4%.

Example 8

A fat containing:

is particularly durable, the penetration (at 60 strokes) is 207.

Loss by water washing (at 38°C) is 40%, while a similar fat without added polyethylene emulsion shows a loss of 80%.

Example 9

A fat containing:

exhibits a penetration value (at 60 strokes) of 264.

These examples show that greases according to the present invention are durable and mechanically stable, and these improvements are due to the incorporation of stabilized emulsions of non-oxidised polyethylene, as stated above.

For comparison, grease was made from 87.5% mineral oil (500 SSU at 38°C), 8.5% lithium 1,2-hydroxystearate, 1% common additives and 3% of an unstabilized emulsion of polyethylene with a pH of 7.7 and an anionic emulsifier content of 5.21%.

This grease had a penetration value (at 60 strokes) of 312, a bleed (or 61je separation) index of 3.5 and a water wash loss at 80°C of 15%. In comparison with the results obtained for grease C, it can be seen that non-stabilized emulsions of polyethylene, i.e. with a low content of anionic emulsifier, do not lead to any significant improvement for grease.

On the other hand, a grease similar to the aforementioned grease C, but prepared using an emulsion of oxidized polyethylene, showed that the mechanical stability was poor, as lumps were formed as a result of the breakdown of this emulsion and coagulation of the polymer particles.

Claims (2)

1. Spreading fat, characterized in that it comprises 5 - 25%, calculated on the weight of the fat, of a thickening soap, 1-10% by weight of an anionic emulsion of non-oxidised polyethylene, where the polyethylene has an average molecular weight greater than lO .OOO, and the emulsion has a polyethylene content in the range 35 - 60%, an emulsifier content in the range 8 - 12%, calculated on the weight of the emulsion, and where the average density of the polyethylene particles is 0.02-0.5 p-m, as the rest of the fat is made up of an oily carrier containing usual additives for shortening. 2. Grease according to claim 1, characterized in that the content of polyethylene emulsion is 1-5% by weight.