Lubricating esters with reduced elastomer swelling

Abstract

 The present invention relates to a lubricant composition comprising an amount of at least one ester, characterised in that the ester is an ester of (a) at least one organic carboxylic acid comprising at least one carboxylic acid group with (b) at least one mono- or polyfunctional alcohol comprising a first alcohol of which at least one OH group is coupled to an epoxide.

Description

[0001] The present invention relates to a lubricant composition comprising an amount of at least one ester as described in the preamble of the first claim.

[0002] The use of esters of fatty acids as performance lubricants in automotive and industrial applications, both as basic oil or additive to a lubricant composition or a hydraulic oil composition is well known in the art. The better intrinsic lubricity of fatty acid esters as compared to their equivalents of mineral origin, renders them particularly suitable for use in lubricant compositions where specifically reduction of friction and reduced fuel consumption is aimed at. Ideally, a lubricant should be made exclusively of fatty acid esters. The better intrinsic lubricity thereof is attributed to the polar character of the fatty acid ester.

[0003] However, when contacting the polymer material used in joints, gaskets or seals, with esters of short chain fatty acids, like esters of octanoic or decanoic acid, the occurrence of a swelling of these materials has been observed. This polymer swelling is a problem in industrial applications, like e.g. hydraulic devices which should be pressure tight as often high pressures are generated therein.

[0004] There is thus a need to a lubricant composition with which the above described swelling may be minimised.

[0005] It is therefore the object of the present invention to provide a lubricant composition with which swelling of the polymer materials used in joints, gaskets or seals, which contact the composition may be minimised.

[0006] This is achieved with the technical features of the characterising part of the first claim.

[0007] It has been found with the present invention that the swelling of polymer material may be minimized, provided the lubricant composition comprises an ester of:

(I) at least one organic carboxylic acid comprising at least one carboxylic acid group
with

(II) at least one mono- or polyfunctional alcohol comprising a first alcohol of which at least one OH group is coupled to an epoxide.

[0008] The ester according to the invention can comprise different organic carboxylic acids and different alcohols.

[0009] Without wanting to be limited thereto, the inventors are of the opinion that the reduced swelling properties of the ester of the present invention can be explained by the fact that when a mono- or polyfunctional alcohol comprising a first alcohol of which at least one OH group is coupled to an an epoxide is used for the ester, an additional branching is added to the ester, thereby increasing the steric hindrance. With 'epoxide', a three-membered cyclic ether is meant, having a general formula

[0010] R1 and R2 being indepently from each other H, a hydrocarbon chain being aliphatic or aromatic, saturated or unsaturated, branched, linear, or cyclic, including polycyclic, and containing one or more functional groups.

[0011] It is believed that the increased steric hindrance counteracts interaction of the polar group of the ester with the polymer material thus reducing the risk to swelling thereof. Besides this, it has been found that the esters of the present invention show improved lubricating properties, which are believed to be related to the higher polarity of the esters of this invention when compared to the known materials.

[0012] The organic carboxylic acid may contain one or more carboxylic acid groups. Preferably, the extent of esterification of the carboxylic acid groups is as high as possible to have an acid number that is as low as possible and to minimise the risk to corrosion of the equipment.

[0013] The organic carboxylic acid used in the ester of the present invention comprises at least one COOH group and a hydrocarbon chain having 1-54 carbon atoms, the hydrocarbon chain being aliphatic or aromatic, saturated or unsaturated, branched, linear, or cyclic, including polycyclic, and containing one or more functional groups. Preferably, the organic carboxylic acid is selected from the group of acids comprising 2-24 carbon atoms, more preferably 8-12 carbon atoms, including the so-called short chain fatty acids.

[0014] Short chain fatty acids like octanoic and decanoic acid are preferred, because they are liquid and saturated at room temperature and allow obtaining lubricants with improved cold stability and improved oxidation resistance. Although the esters of these short chain carboxylic acids would be suspected to involve polymer swelling because of their polar character, this swelling has been observed to be of minimal extent with esters made from the above described alcohol. Accordingly, this will allow using the short chain fatty acids as the carboxylic acid component of the ester.

[0015] Other organic carboxylic acids suitable for use with the present invention include synthetic mono-, di- or polycarboxylic acids and dimers or polymers of the above described organic carboxylic acids.

[0016] The first alcohol used in the ester of the present invention contains at least one OH group and a hydrocarbon chain having 1-54 carbon atoms, the hydrocarbon chain being aliphatic or aromatic, saturated or unsaturated, branched, linear, or cyclic, including polycyclic, and containing one or more functional groups. Preferably, the alcohol contains 2-15 OH groups. More preferably, the alcohol corresponds to the following formula:

   with R1 and R2 being independently of each other a C1-C4 linear or branched alkyl or alkylol, and R3 and R4 being independently of each other a C1-C4 linear or branched chain alkylol. Even more preferably, the first alcohol is selected from the group comprising trimethylolpropane, pentaerytritol and neopentylglycol. Whereas an ester of such a polyol with an organic carboxylic acid would be suspected to cause polymer swelling because of its polar character, the swelling appears to be minimal when at least one OH group of the first alcohol is coupled to an epoxide. Other suitable first alcohols for the present invention include condensation products of two or more of the above described alcohol monomers.

[0017] The epoxide to which at least one OH group of the first alcohol is coupled, is preferably an epoxide having 2-20 carbon atoms. The epoxide may be a mono- or polyepoxide, the hydrocarbon chain of the epoxide being aliphatic or aromatic, saturated or unsaturated, and being a branched, linear, or cyclic, including polycyclic, structure and containing one or more functional groups.

[0018] Preferably, the epoxide is selected from the group comprising propyleneoxide, butyleneoxide, dodecene oxide, styrene oxide, isoamylene oxide. With increasing chain length of the linear monoepoxide namely a reduced tendency to involve polymer swelling has been observed. The larger the length of the epoxide hydrocarbon chain, the larger the steric hindrance will be, and the lower the tendency to close interaction of the polar ester group with the polymer will be. This results in a lubricant composition with a decreased tendency to polymer swelling.

[0019] The extent to which the OH group(s) of the first alcohol are coupled to epoxides, will be adapted by the man skilled in the art depending on the properties of the lubricant composition aimed at. The lower limit of the extent to which the OH group(s) of the first alcohol are coupled to epoxides is determined by the viscosity of the resulting ester which increases with increasing degree of epoxidation. The upper limit of the extent to which the OH group(s) of the first alcohol are coupled to epoxides is determined by the emulsion-forming tendency of the ester. For instance, for propoxylated tri octanoate/decanoate esters of trimethylolpropane, a propoxylation degree of 7 moles propyleneoxide per mole of trimethylolpropane results in a viscosity at 40°C of 42.1 centistokes, which is a viscosity suitable for hydraulic oils.

[0020] Examples of esters suitable for use in the lubricant composition of this invention are tri octanoate/decanoate esters of propoxylated trimethylolpropane, tri octanoate/decanoate ester of butoxylated trimethylolpropane, tetra octanoate/decanoate ester of propoxylated pentaerytritol, tetra octanoate/decanoate ester of butoxylated pentaerytritol, di octanoate/decanoate ester of propoxylated neopentylglycol, di octanoate/decanoate ester of butoxylated neopentylglycol.

[0021] The lubricant composition may also comprise a mixture of two or more different esters according to the present invention so as to allow adjusting the viscosity and polarity of the lubricant composition.

[0022] The lubricant composition of the present invention preferably comprises the above described ester in an amount which can vary depending on the application and the properties of the ester. Because of the reduced tendency to involve polymer swelling, an increased amount of ester may be incorporated in the lubricant composition, thus allowing to obtain a lubricant composition with enhanced performance. Consequently, a lubricant composition may contain 100% of the above described ester. On the other hand, the above described ester can also be present as an additive in a very low amount in the lubricant composition.

[0023] The invention is further elucidated in the following examples.

[0024] The Comparative Examples I-III and Examples 1-9 describe experiments in which different esters were tested for the swelling they cause when they are contacted with different polymers. In the comparative examples, esters not according to the invention were tested, whereas in the examples esters according to the invention were tested. The percent of swelling of the different polymers has been determined according to method ISO6072.

Comparative Examples I-II.

[0025] A series of swelling tests were done with esters not according to the invention and different polymers.

Table 1

Comparative Examples	Lubricating ester of	% swelling of acrylonitrile butadiene rubber	% swelling of ethylene-propylene rubber	% swelling of fluorcarbon rubber
I	TMP	24.3	44.7	2.1
II	Penta	17.53	-	-

[0026] In Comparative Example I, the tri octanoate/decanoate ester of trimethylolpropane (TMP) was contacted with either acrylonitrile butadiene rubber, ethylene-propylene rubber or with fluorcarbon rubber and the % swelling of the respective materials was measured according to method ISO6072.

[0027] In Comparative Example II, the experiment of Comparative Example II was repeated, however, with the tetra octanoate/decanoate ester of pentaerytritol (Penta).

Examples 1-7.

[0028] A series of swelling tests were done with esters according to the invention and different polymers.

[0029] In Example 1, the tri octanoate/decanoate ester of ethoxylated trimethylolpropane (20EO TMP) having 20 moles ethyleneoxide per mole trimethylolpropane, was contacted with acrylonitrile butadiene rubber rubber and the % swelling of acrylonitrile butadiene rubber was measured according to method ISO6072.

[0030] In Example 2, the tri octanoate/decanoate ester of propoxylated trimethylolpropane (3PO TMP) having 3 moles propyleneoxide per mole trimethylolpropane, was contacted with either acrylonitrile butadiene rubber, ethylene-propylene rubber or with fluorcarbon rubber and the % swelling of the respective materials was measured according to method ISO6072.

[0031] Example 3 was conducted similar to Example 2, however using the tri octanoate/decanoate ester of propoxylated trimethylolpropane (4PO TMP) having 4 moles propyleneoxide per mole trimethylolpropane.

[0032] Example 4 was carried out similar to Example 1, however with the tri octanoate/decanoate ester of propoxylated trimethylolpropane (5PO TMP), having 5 moles propyleneoxide per mole trimethylolpropane.

[0033] Example 5 was carried out similar to Example 2, using the tri octanoate/decanoate ester of propoxylated trimethylolpropane (7PO TMP), having 7 moles propyleneoxide per mole trimethylolpropane.

[0034] Example 6 was carried out similar to Example 1, using the tetra octanoate/decanoate ester of propoxylated pentaerytritol (5PO Penta), having 5 moles propyleneoxide per mole Penta.

[0035] In Example 7, use was made of the tetra octanoate/decanoate ester of propoxylated pentaerytritol (8.5PO Penta), having 8.5 moles propyleneoxide per mole Penta.

Table 2

Examples	Lubricating ester of	% swelling of acrylonitrile butadiene rubber	% swelling of ethylene-propylene rubber	% swelling of fluorcarbon rubber
1	20EO TMP	19.4	-	-
2	3PO TMP	19	22.5	0.31
3	4PO TMP	18.4	-	-
4	5PO TMP	15.5	-	-
5	7PO TMP	9.8	10.6	0.007
6	5PO Penta	15.06	-	-
7	8.5PO Penta	11.11	-	-

[0036] Table 2 shows that the swelling caused by tri octanoate/decanoate ester of ethoxylated trimethylolpropane having 20 moles ethyleneoxide per mole trimethylolpropane (20EO TMP) of Example 1 is inferior to the swelling caused by the non-ethoxylated tri octanoate/decanoate ester of trimethylolpropane (TMP) of comparative example I. This is attributed to a dilution effect of the polar ester groups in Example 1.

[0037] Table 2 further shows that the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 3 moles propyleneoxide per mole trimethylolpropane (3PO TMP) of Example 2 causes a reduced swelling of acrylonitrile butadiene rubber, ethylene-propylene rubber and fluorcarbon rubber as compared to the non-ethoxylated tri octanoate/decanoate ester of trimethylolpropane (TMP) of comparative example I.

[0038] Table 2 further shows that that the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 4 moles propyleneoxide per mole trimethylolpropane (4PO TMP) of Example 3 causes a reduced swelling of acrylonitrile butadiene rubber as compared to the non-ethoxylated tri octanoate/decanoate ester of trimethylolpropane (TMP) of comparative example I or as compared to the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 3 moles propyleneoxide per mole trimethylolpropane (3PO TMP) of Example 2.

[0039] Further, the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 5 moles propyleneoxide per mole trimethylolpropane (5PO TMP) of Example 4 causes a reduced swelling of acrylonitrile butadiene rubber as compared to the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 4 moles propyleneoxide per mole trimethylolpropane (4PO TMP) of Example 3, and consequently also as compared to the esters with a lower degree of propoxylation of examples 2 and 3 and as compared to the ester without propoxylation of Comparative Example I.

[0040] Further, the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 7 moles propyleneoxide per mole trimethylolpropane (7PO TMP) of Example 5 causes a reduced swelling of acrylonitrile butadiene rubber as compared to the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 5 moles propyleneoxide per mole trimethylolpropane (5PO TMP) of Example 4, and consequently also as compared to the esters with a lower degree of propoxylation of examples 2 and 3 and as compared to the ester without propoxylation of Comparative Example I.

[0041] Further, the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 7 moles propyleneoxide per mole trimethylolpropane (7PO TMP) of Example 5 causes a reduced swelling of ethylene-propylene rubber and of fluorcarbon rubber as compared to the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 3 moles ethyleneoxide per mole trimethylolpropane (3PO TMP) of Example 2, and as compared to the ester without propoxylation of Comparative Example I.

[0042] The previous examples 2-5 all demonstrate the same principle, being that the propoxylation of trimethylolpropane adds an additional branching in the resulting esters, thereby increasing the steric hindrance of the ester. This steric hindrance prevents close interaction of the polar ester groups with the polymers, thereby avoiding the swelling of the polymers. Thus, the higher the degree of propoxylation of the tri octanoate/decanoate ester of trimethylolpropane (examples 2 throughout 5), the lesser the resulting swelling of the polymers.

[0043] Table 2 further shows that the tetra octanoate/decanoate ester of propoxylated pentaerytritol having 5 moles propyleneoxide per mole pentaerytritol (5PO Penta) of Example 6 causes a reduced swelling of acrylonitrile butadiene rubber as compared to the non-ethoxylated tetra octanoate/decanoate ester of pentaerytritol (Penta) of comparative example II.

[0044] Similarly, the tetra octanoate/decanoate ester of propoxylated pentaerytritol having 8.5 moles propyleneoxide per mole pentaerytritol (8.5PO Penta) of Example 7 causes a reduced swelling of acrylonitrile butadiene rubber as compared to the tetra octanoate/decanoate ester of propoxylated pentaerytritol having 5 moles propyleneoxide per mole pentaerytritol (5PO Penta) of Example 6, and consequently also as compared to the non-ethoxylated tetra octanoate/decanoate ester of pentaerytritol (Penta) of comparative example II.

[0045] For Examples 7 and 8 again the same principle applies, being that the propoxylation of pentaerytritol adds an additional branching in the resulting esters, thereby increasing the steric hindrance of the ester. This steric hindrance prevents close interaction of the polar ester groups with the polymers, thereby avoiding the swelling of the polymers. Thus, the higher the degree of propoxylation of the tetra octanoate/decanoate ester of pentaerytritol (examples 6 and 7), the lesser the resulting swelling of the polymers.

Comparative Example III and Examples 8-9.

[0046] A series of swelling tests were done with esters not according and according to the invention and acrylonitrile butadiene rubber.

[0047] In Comparative Example III, the tri octanoate/decanoate ester of glycerol was contacted with acrylonitrile butadiene rubber and the % swelling of acrylonitrile butadiene rubber was measured according to method ISO6072.

[0048] Example 8 was carried out similar to Comparative Example III, using the tri octanoate/ decanoate ester of propoxylated glycerol having 8 moles propyleneoxide per mole glycerol (8PO).

[0049] Example 9 was carried out similar to Comparative Example III, using the tri octanoate/ decanoate ester of ethoxylated glycerol having 9 moles ethyleneoxide per mole glycerol (9EO).

[0050] Table 3 shows that the tri octanoate/decanoate ester of propoxylated glycerol having 8 moles propyleneoxide per mole glycerol (8PO) of Example 8 causes a reduced swelling of acrylonitrile butadiene rubber as compared to the non-propoxylated tri octanoate/decanoate ester of glycerol of Comparative Example III. This can be explained by the fact that the propoxylation of glycerol adds an additional branching in the resulting ester, thereby increasing the steric hindrance of the ester. This steric hindrance prevents close interaction of the polar ester groups with the polymers, thereby avoiding the swelling of the polymers.

Table 3

	Lubricating ester	% swelling of acrylonitrile butadiene rubber
Comparative Example III	Triglyceride C8/C10	28.8
Example 8	Triglyceride C8/C10 8PO	10.8
Example 9	Triglyceride C8/C10 9EO	21.1

[0051] Further, table 3 shows that the tri octanoate/decanoate ester of ethoxylated glycerol having 9 moles ethyleneoxide per mole glycerol (9EO) of Example 9 causes a reduced swelling of acrylonitrile butadiene rubber as compared to the non-ethoxylated tri octanoate/decanoate ester of glycerol of Comparative Example III. This can be attributed to a dilution effect of the polar ester groups in Example 9.

[0052] Examples 10-14 describe experiments in which esters according to the invention were tested for various parameters such as viscosity at 40°C and the extent to which they form an emulsion.

Examples 10-14.

[0053] In Example 10, the viscosity at 40°C and the tendency for the formation of an emulsion of the tri octanoate/decanoate ester of ethoxylated trimethylolpropane (20EO TMP) having 20 moles ethyleneoxide per mole trimethylolpropane was tested.

[0054] Example 11 was carried out similar to Example 10 using the tri octanoate/decanoate ester of propoxylated trimethylolpropane (3PO TMP) having 3 moles propyleneoxide per mole trimethylolpropane.

[0055] In Example 12, the viscosity at 40°C of the tri octanoate/decanoate ester of propoxylated trimethylolpropane (4PO TMP) having 4 moles propyleneoxide per mole trimethylolpropane was tested.

[0056] Example 13 was carried out similar to Example 12 using the tri octanoate/decanoate ester of propoxylated trimethylolpropane (5PO TMP), having 5 moles propyleneoxide per mole trimethylolpropane.

[0057] Example 14 was carried out similar to Example 10 using the tri octanoate/decanoate ester of propoxylated trimethylolpropane (7PO TMP), having 7 moles propyleneoxide per mole trimethylolpropane.

[0058] The tri octanoate/decanoate ester of ethoxylated trimethylolpropane having 20 moles ethyleneoxide per mole trimethylolpropane (20EO TMP) of Example 10, the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 3 moles propyleneoxide per mole trimethylolpropane (3PO TMP) of Example 11, and the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 7 moles propyleneoxide per mole trimethylolpropane (7PO TMP) of Example 14 show a low tendency to form an emulsion.

[0059] The tri octanoate/decanoate ester of propoxylated trimethylolpropane having 7 moles propyleneoxide per mole trimethylolpropane (7PO TMP) of Example 14 has a higher viscosity as compared to the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 5 moles propyleneoxide per mole trimethylolpropane (5PO TMP) of Example 13, the latter having a higher viscosity than the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 4 moles propyleneoxide per mole trimethylolpropane (4PO TMP) of Example 12, in its turn having a higher viscosity than the tri octanoate/decanoate ester of propoxylated trimethylolpropane having 3 moles propyleneoxide per mole trimethylolpropane (3PO TMP) of Example 11. Apparently, the viscosity increases as the degree of propoxylation increases.

Table 4

	Lubricating ester of	Viscosity (cSt)	Emulsion test (oil/water/emulsion)
Example 10	20EO TMP	71.4	24/0/56
Example 11	3PO TMP	28.9	39/38/3
Example 12	4PO TMP	30.9	-
Example 13	5PO TMP	34.8	-
Example 14	7PO TMP	42.1	42/37/0

Claims

1. A lubricant composition comprising an amount of at least one ester, characterised in that the ester is an ester of

(a) an organic carboxylic acid comprising at least one carboxylic acid group with

(b) at least one mono- or polyfunctional alcohol comprising a first alcohol of which at least one OH group is coupled to an epoxide.

2. A lubricant composition comprising an ester as claimed in claim 1, characterised in that the organic carboxylic acid comprises at least one COOH group and a hydrocarbon chain having 1-54 carbon atoms, the hydrocarbon being aliphatic or aromatic, saturated or unsaturated, branched, linear, or cyclic, including polycyclic, and containing one or more functional groups.

3. A lubricant composition comprising an ester as claimed in claim 1-2, characterised in that the organic carboxylic acid is a polymer of two or more organic carboxylic acids.

4. A lubricant composition comprising an ester as claimed in claim 1-3, characterised in that the organic carboxylic acid comprises 2-24 carbon atoms, preferably 8-12 carbon atoms.

5. A lubricant composition comprising an ester as claimed in claim 1-4, characterised in that the first alcohol contains at least one OH group and a hydrocarbon chain having 1-54 carbon atoms, the hydrocarbon chain being aliphatic or aromatic, saturated or unsaturated, branched, linear, or cyclic, including polycyclic, and containing one or more functional groups.

6. A lubricant composition comprising an ester as claimed in claim 1-5, characterised in that the first alcohol is a condensation product of two or more alcohol monomers.

7. A lubricant composition comprising an ester as claimed in claim 1-6, characterised in that the first alcohol preferably contains 2-15 OH groups.

8. A lubricant composition comprising an ester as claimed in claim 1-7, characterised in that the first alcohol preferably has the following structure:

with R1 and R2 being independently of each other a C1-C4 linear or branched alkyl or alkylol, and R3 and R4 being independently of each other a linear or branched chain alkylol.

9. A lubricant composition comprising an ester as claimed in claim 1-8, characterised in that the first alcohol preferably is selected from the group comprising of trimethylolpropane, pentaerytritol and neopentylglycol.

10. A lubricant composition comprising an ester as claimed in claim 1-9, characterised in that the epoxide contains 2-20 carbon atoms and is a mono- or polyepoxide, the hydrocarbon chain of the epoxide being aliphatic or aromatic, saturated or unsaturated, and being a branched, linear, or cyclic, including polycyclic, structure and containing one or more functional groups.

11. A lubricant composition comprising an ester as claimed in claim 1-10, characterised in that the epoxide preferably is selected from the group comprising propyleneoxide, butyleneoxide, dodeceneoxide, styrene oxide, isoamylene oxide.

12. A lubricant composition comprising an ester as claimed in claim 1-11, characterised in that the composition comprises a mixture of two or more different esters of any one of claims 1-11.