EP0117454B1 - Lubricating-grease composition, its preparation and application - Google Patents

Description

The invention relates to a grease composition based on a larger proportion of mineral or synthetic oil as the base oil and a smaller proportion of polyurea as a thickener.

It is known to thicken lubricating mineral or synthetic oils by adding polyureas so that they retain the properties of a grease. The polyureas used in these greases are produced by reacting one or more monoamino and / or diamino components, which can be aliphatic or aromatic, with diisocyanates, which can also be aliphatic or aromatic. Typical examples of this can be found in DE-A-2 540 470, 2 604 342 and 2 604 343 and EP-A 31 179. The lubricating greases obtained in this way are adjusted to the specific uses of the grease by adding additives, high-pressure additives, anti-wear additives and antioxidants are commonly used. In US-A 3 01 625 lubricant additives are described which are obtained by reacting abietylamines with diisocyanates. US Pat. No. 3,015,625 also mentions that triisocyanates are also suitable for the preparation of the additives.

These fats have proven to be well suited for many purposes. In particular, they are suitable for higher continuous operating temperatures than lithium greases, with which most lubrication problems can be solved satisfactorily, but only up to maximum operating temperatures in the region of 135 ° C. With the polyurea-containing greases, this temperature limit could be increased in the range from 150 to 160 ° C.

For application purposes under particularly difficult conditions, however, the long-term operating temperatures that have been achieved so far are not yet sufficient. A further increase would therefore be desirable. In addition, the shelf life of the polyurea thickeners in the presence of the required additives, in particular if they were oil-soluble additives, has proven unsatisfactory in many cases.

The invention has for its object to reduce or eliminate these disadvantages of the previously known oil-based greases with polyureas as thickeners.

This object is achieved according to the invention by a grease composition based on a larger proportion of mineral or synthetic oil as base oil and a smaller proportion of a polyurea compound as a thickener and conventional additives, which is characterized in that, as polyurea, it is the reaction product of an isocyanate with at least 3 isocyanate groups in the Contains molecule with a long-chain, straight-chain or branched aliphatic monoamine. The polyureas used according to the invention are crosslinked high-molecular products which have been mechanically comminuted. The amine component preferably consists predominantly of the monoamines with 16 to 24 carbon atoms, but smaller portions of monoamines with shorter chains down to 10 carbon atoms may also be present, but an amount of 10% of the total amine should not be exceeded . Small amounts of diamines can also be added, an amount of about 5% should not be exceeded.

The term “long-chain aliphatic monoamine” means compounds with more than 14 carbon atoms, preferably those with 16 to 24 carbon atoms, and mixtures thereof. Longer-chain monoamines are also technically useful for the invention, but are currently difficult to obtain economically.

The monoamine can be a saturated fatty amine or contain one or more olefinic double bonds. Straight-chain or branched, aliphatic amines can be used. Particularly preferred for monounsaturated fatty amines are those with 16 to 20 C atoms, more preferably an alkenylamine with 18 C atoms (oleylamine), on the one hand, and for saturated aliphatic alkylamines those with 18 to 24 C atoms, more preferably with 20 up to 22 carbon atoms, on the other hand. Each of these preferred embodiments of the polyurea has special properties with regard to compatibility with additives.

This will be discussed in more detail below.

Commercially available compounds such as Desmodur brands from Bayer AG, Hylene brands from DuPont, Mondur brands from Mobay Chem. Corp. come as the isocyanate component with at least 3 isocyanate groups in the molecule. or Nacconate from Allied Chem. & Dye Corp. are known. Triisocyanates are preferred, but tetraisocyanates and even higher polyisocyanates can also be used, advantageously in a mixture with triisocyanates. In the context of the invention, they are all referred to below as “polyisocyanates”. Both aliphatic polyisocyanates, such as Desmodur N, which contain tri-, tetra- and higher polyisocyanates, and aromatic polyisocyanates, such as Desmodur R, can be used. The latter, which is chemically p, p ', p "-triphenylmethane triisocyanate in the form of a 20% solution in methylene chloride, has been found to be particularly suitable within the scope of the invention. The suitability of a special polyisocyanate within the scope of the invention can be found in the rest can easily be determined by simple preliminary tests.

The grease composition according to the invention contains the polyurea in an amount sufficient to achieve the desired thickening effect. Good results are generally obtained with additions of between 3 and 45% by weight of polyurea, based on the base oil. The best results are generally obtained at levels between 8 and 15%.

As mentioned, mineral oil and synthetic oil come into consideration as base oil. Naphthenic base oils are preferred. Paraffin-based base oils can also be used. In the latter case, polyureas are preferably used as thickeners, in which the monoamine component is as long-chain as possible within the scope taught by the invention.

In the case of synthetic base oils, all the usual classes have proven to be suitable in principle, even if individual members of the respective groups give better results than others with regard to the combination with the polyurea resin. Typical examples of suitable synthetic oils are polyalphaolefins, glycols, esters, alkylbenzenes and silicone oils soluble in organic solvents.

The lubricating grease compositions according to the invention can contain both oil-soluble and non-oil-soluble additives in order, for example, to improve the high-pressure properties, the wear behavior and the oxidation resistance. These lubricant additives are known to the person skilled in the art and do not require any further explanation here unless special considerations in connection with the various possible modification forms of the polyurea used according to the invention need to be taken into account.

Solid additives with high-pressure and / or anti-wear-improving properties are primarily graphite and the lubricating metal sulfides, either alone or in combination with activity enhancers. Among these, graphite and molybdenum disulfide and their mixtures are preferred in the context of the invention. Suitable effect amplifiers are e.g. Metal oxides, hydroxides, phosphates or fluorides. These non-oil-soluble additives are particularly suitable in combination with polyureas, the monoamine component of which is in the longer-chain range, that is to say between about 18 to 24 carbon atoms, preferably 20 to 22 carbon atoms. However, they can be used in all polyureas to be used in the context of the invention. The amount of these non-oil-soluble additives is generally between 0.5 and 10% by weight, based on the total fat composition, an addition of 2 to 6% is particularly preferred. If the specified quantities are exceeded, there is no improvement in the properties which would be adequate for the increased costs; if the limit values are undershot, the desired properties are no longer obtained. From the point of view of the best possible fatigue strength, friction properties and an acceptable price, particularly satisfactory results are obtained with a 2 to 4% addition of non-oil-soluble additive and usually oil-soluble antioxidant.

A particular advantage of the grease composition according to the invention, however, is the excellent compatibility with oil-soluble additives, in particular also oil-soluble high-pressure and anti-wear additives. In the previously known lubricating greases with polyurea additives as thickeners, the highly effective oil-soluble high-pressure and anti-wear additives proved to be unsuitable, since they led to rapid degradation of the polyureas which were prepared with diisocyanates. In this regard, safe oil-soluble additives only gave unsatisfactory properties of the grease composition. In the case of the lubricating grease composition according to the invention, however, the particularly effective oil-soluble additives can also be used without having negative effects on the polyurea component in continuous operation. In the case of oil-soluble additives, the compounds containing phosphorus and sulfur, as well as the replacement products for sulfurized sperm oil that have become known in recent times, are preferred. Particularly good properties are achieved with the additive combinations known from DE-B 1 954 452.

For these oil-soluble additives, those embodiments of the grease composition according to the invention in which the amine component of the polyurea is unsaturated and in the lower range of the chain length in question have proven to be particularly suitable. In this context, an alkenylamine with 18 C atoms, such as oleylamine, is particularly preferred.

The oil-soluble additives are generally used in amounts between 3 and 20% by weight, based on the total grease composition. An addition of between about 5 and 12% by weight is preferred.

Another object of the invention is the method for producing the grease composition described in more detail above. This process is characterized in that a long-chain aliphatic monoamine or a mixture of such amines is dissolved in the base oil, polyisocyanate is added, the mixture is heated to a temperature of at least 160 ° C. until gelation occurs, the gelled product is mechanically minced and the additives and add further base oil if necessary.

The method is based on the mineral or synthetic oil or a mixture of such oils which is to be used as the base oil for the grease composition. If it is a mixture of oils, the process can also be carried out with only one oil component and the further oil component can be added later. It is also possible to use a smaller proportion of base oil in the process than is required for the desired composition with regard to the amount of polyurea. The amount of oil only has to be sufficient to completely dissolve the amine.

The aliphatic monoamine or mixture thereof is expediently introduced into the base oil in the molten state in order to facilitate the dissolution, the dissolution being able to be facilitated by stirring and heating. A suitable amount of the selected triisocyanate is added thereafter or simultaneously. Quantities in which 1/2 to 4 isocyanate groups are available per amine group are generally suitable. In special cases, these conditions can also be exceeded or fallen short of.

The mixture obtained is heated until several recognizable reaction stages are run through and finally gelation occurs. The temperature required depends on the reaction components used and any additives present and is generally above 160 ° C., preferably above 200 ° C. Heating above 240 ° C is generally not required, but can be used.

The gelled mass is then mechanically comminuted, it being possible to use the known comminution methods and devices. The gel is expediently ground in a colloid mill. The additives are then added, and, if appropriate, the remaining amount of base oil.

Preferred amine for the process is oleylamine or a saturated alkylamine or alkylamine mixture having 20 to 22 carbon atoms. The statements made above apply with regard to the preferred polyisocyanate.

The grease composition according to the invention is characterized by improved mechanical stability, in particular in combination with oil-soluble additives, i.e. oil-soluble high-pressure and anti-wear additives. So far, however, it has only been possible to obtain satisfactory lubricating greases based on lubricating oil with polyurea as a thickener with good high-pressure properties when using non-oil-soluble high-pressure additives.

The lubricating grease composition according to the invention is even superior to the best known lithium greases in terms of the achievable high-pressure properties and wear resistance, and at the same time allows the permanent operating temperature, which is in the range from 80 to 110 ° C. and briefly up to 135 ° C. for lithium greases, to be increased to a continuous operating temperature of 150 to 160 ° C, for a short time beyond that too. This corresponds to a very significant improvement in service life and temperature resistance. However, the lubricating grease composition according to the invention is not inferior to the best commercially available lubricating greases even in the low temperature range down to well below minus 30 ° C. It thus has a combination of properties that have not previously been known for commercially available products.

For example, the best known lithium greases can be used to achieve 20 to 25 million rollovers at 50 ° C in particularly difficult conditions, such as those found in homokinetic joints and simulated in cardan shaft test benches. With the lubricating grease compositions according to the invention, at least 30 million rollovers can still be achieved on such cardan shaft test benches at temperatures of 150 to 160 ° C.

The improved properties achieved according to the invention can be illustrated by FIG. 1 of the attached drawing.

1 shows a test sheet which was obtained with the grease composition according to the invention from Example 1 on the commercially available lubricant tester SRV, which is sold by the applicant and which is described in ant «drive technology 19 (1980) No. 1-2. The lubricant composition was subjected to a load increasing from 50 to 1000 Newtons under the specified operating conditions, without the lubricating effectiveness collapsing. This means that the flow limit of the metal is reached in the surface roughness without the lubricating effect of the grease composition according to the invention being lost.

The following examples further illustrate the invention.

example 1

4000 g naphthenic base oil of 100 centistokes (10- ⁴ m ² / sec) at 40 ° C, viscosity index approx. 45, are mixed with 400 g saturated monofatty amine with 20 to 22 C atoms in the molten state and with 1200 g a 20% solution of p, p ', p "-triphenvimethane triisocyanate in methylene chloride, heated with stirring until the methylene chloride has evaporated and then further heated until reached 240 ° C. As soon as the mixture has gelled, it is cooled, comminuted and in Finely ground in a colloid mill, this gives a base fat which is classified as penetration class 3 according to DIN 51818.

2.5% by weight of a mixture of graphite and molybdenum disulfide and 0.5% of a commercially available oil-soluble antioxidant are then added to the base fat thus produced.

The grease obtained in this way is tested in the SRV device. The results are shown in Test Sheet 7922 attached as Fig. 2. It can be seen that at a load of 400 Newton and 80 ° C, a coefficient of friction between 0.093 and 0.110 is reached after one and a half hours of running. The diameter of the wear ball is 0.95 mm. The profilogram of the surface at the friction point shows a very good straight line.

The experiment is repeated with the same basic fat, but without additives. The results are shown in FIG. 3, SRV test sheet 7650. After a test period of 2 hours, the lubricating effect had broken down under a load of 300 Newtons and 50 ° C. and a seizure had occurred. The diameter of the wear ball was 1.35 mm, the profile depth at the friction point 12.0 ₁ 1m compared to 1.0 11m for the additive product. The profilogram shows excessive wear to the point of eating.

Example 2

The procedure was as described in Example 1, but instead of a saturated monofatty amine having 20 to 22 carbon atoms, an equivalent amount of monounsaturated C18 alkenylamine (oleylamine) was used.

As an additive, an oil-soluble additive according to DE-AS 1 954 452 was added, which contained Pb and Mo dialkyldithiophosphate, a metal-free sulfur-phosphorus compound and an epoxide of an ester of an unsaturated fatty acid with an alkanol.

The results of the SRV test are shown in FIG. 4 of the drawing in the form of test sheet 8286. It can be seen from this that a friction coefficient of 0.030 μ is achieved with a load of 300 Newtons and the diameter of the wear ball is only 0.65 mm. The running-in period until the low coefficient of friction is reached is short, the profilogram shows a very good course.

Example 3

The procedure of Example 2 is repeated, but instead of the oil-soluble additives, the additives of Example 1 are added in the amount specified there. 5 of the drawing in the form of test sheet 8254 shows the results of the test on the SRV device. The minimum coefficient of friction is 0.085 μ, the diameter of the wear ball is 0.50 mm at 300 Newton load.

Example 4

As described in Example 1, a grease was produced, but 800 g was used instead of 1200 g of isocyanate solution and 3% was used instead of 0.5% antioxidant.

The grease obtained in this way was examined on a cardan shaft test bench. For this purpose, the joint was heated to an ambient temperature of 75 ° C and then loaded at 1200 revolutions, 8 ° bending angle and 320 Nm. With a rating scale from 1 to 6, in which 1 represents the best and 6 the worst value, the best serial grease based on lithium soap available on the market gave a rating of 4.3 ± 1 and an outside temperature of 103 ± 0 ° C, which corresponds to an internal joint temperature of 15 to 130 ° C.

With the grease according to the invention, a rating of 3.0 ± 1 and an outside temperature of 95 ± 10 ° C were achieved under the same conditions. Alone due to the temperature reduction in the grease according to the invention, a doubling of the life of the joint can be expected, quite apart from the fact that the series grease works at the limit of its permanent temperature stability, while the grease according to the invention is far below such a limit value and thus offers a large safety reserve.

Claims (16)

1. Lubricating grease composition based on a comparatively large proportion of mineral or synthetic oil as base oil and on a comparatively small proportion of a polyurea compound as thickening agent, as well as usual additives, characterised in that, as polyurea, it contains the reaction product of an isocyanate with at least 3 isocyanate groups in the molecule with a longchained, straight-chain or branched aliphatic monoamine.

2. Lubricating grease composition according to claim 1, characterised in that it contains 3 to 45 wt. % of polyurea, referred to the base oil.

3. Lubricating grease composition according to claim 1 or 2, characterised in that the polyurea is based upon triphenylmethane triisocyanate.

4. Lubricating grease composition according to one of the preceding claims, characterised in that it contains a polyurea with an alkenylamine with 18 C-atoms as amine component.

5. Lubricating grease composition according to one of claims 1 to 3, characterised in that it contains a polyurea with a saturated C20 to C22 alkylamine as amine component.

6. Lubricating grease composition according to claim 4 or 5, characterised in that it contains oil-soluble high pressure and/or anti-wear additives.

7. Lubricating grease composition according to claim 6, characterised in that it contains 3 to 20 wt. % of additive.

8. Lubricating grease composition according to claim 4 or 5, characterised in that it contains non-oil-soluble high pressure or anti-wear additives.

9. Lubricating grease composition according to claim 8, characterised in that it contains graphite and/or a lubricant-active metal sulphide as high pressure or anti-wear additive.

10. Lubricating grease composition according to claim 8 or 9, characterised in that it contains 0.5 to 10 wt. % of additive.

11. Lubricating grease composition according to one of the preceding claims, characterised in that it contains 2 to 6 wt. % of non-oil-soluble additive or 3 to 12 wt.% of oil-soluble additive.

12. Process for the production of a lubricating grease composition according to one of claims 1 to 11, characterised in that one dissolves a longchained aliphatic amine or a mixture of such amines in the base oil, adds thereto isocyanate with at least 3 isocyanate groups in the molecule, heats the mixture to such a temperature of at least 1 60°C that a gelling takes place, mechanically finely comminutes the gelled product and adds the additive and possibly further base oil.

13. Process according to claim 12, characterised in that one adds 1/2 to 4 equivalents of isocyanate groups per amine group.

14. Process according to claim 12 or 13, characterised in that, as amine, one uses oleylamine or a saturated alkylamine or alkylamine mixture with 20 to 22 C-atoms.

15. Process according to one of claims 12 to 14, characterised in that, as triisocyanate, one uses triphenylmethane triisocyanate.

16. Use of a lubricant grease composition according to claims 1 to 11 in homokinetic couplings.

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