CA2065011A1

CA2065011A1 - Environment-friendly basic oil for formulation hydraulic fluids

Info

Publication number: CA2065011A1
Application number: CA002065011A
Authority: CA
Inventors: Frank Bongardt; Karl Schmid; Reinhold Wuest
Original assignee: Individual
Current assignee: Henkel AG and Co KGaA
Priority date: 1989-08-17
Filing date: 1990-08-08
Publication date: 1991-02-18
Also published as: DE3927155A1; WO1991002784A1; JPH05503949A; BR9007600A; EP0486575B1; US5451334A; DE59003632D1; EP0486575A1; ES2060193T3

Abstract

The invention relates to an environment-friendly naturally-based raw oil for formulating hydraulic fluids with improved viscosity and/or cold stability in use, in which the main components are refined rapeseed and/or soya oil to which selected esters based on trimethylol ethane, trimethylol propane and/or neopentene glycol are added in at the most the same quantities as those of the raw oil. The invention also includes an additive of this kind to stabilise the viscosity of hydraulic fluids based on rapeseed and/or soya oil and the use of selected esters of trimethylol ethane, trimethylol propane and/or neopentene glycol with monocarbonic acids in environment-friendly hydraulic fluids based on rapeseed and/or soya oil to improve their cold stability.

Description

j 2065011 wo 91/02784 PCT/EP90/01296 An environment-friendly basic oil for the formulation of hydraulic oils This invention relates generally to hydraulic fluids `~ and, more particularly, to hydraulic oils for hydrostatic power transmission.
Hitherto, most hydraulic oils have been made from mineral oil. In applications where the escape of oil into the environment is a possibility, for example through unavoidable leakages, there is an increasing demand for hydraulic oils which contain environment-friendly ester oils, particularly those based on rapeseed oil and/or soybean oil, as the oil base. Typical applications of the type in question are forestry and agricultural machinery and equipment, dredgers and the like. Applications such as these now require the use of hydraulic oils of water hazard class 0. Ester-based hydraulic oils are capable of satis-fying these requirements.
However, the above-mentioned ester oils essential for , practical application, i.e. rapeseed oils and/or soybean ; oils which have been purified and, in particular, freed from amylopectins and other mucilaginous substances, have two crucial weaknesses in practical application, namely:
Ester oils based on unsaturated fatty acid systems tend to thicken rapidly, even at only moderately elevated operating temperatures of, for example, 50 to 80C. This is attributable to the readiness of the olefinic double bonds of the ester-forming acids of the type of oil in question to enter under the effect of atmospheric oxygen into reactions which ultimately lead to an increase in vis-cosity. Although it is basically known that unwanted ; increases in viscosity can be counteracted by addition of antioxidants, it has been found that the antioxidants hitherto preferably used in hydraulic oils based on mineral oils do not perform satisfactorily in ester oils of the . A ~ .
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Another important limitation for hydraulic oils based on the environment-friendly ester oils mentioned above is their inadequate stabilitv at low temperatures. Purified rapeseed oil, for example, has a solidification point or pour point of -16C. Even before the solidification point is reached, the oil undergoes a significant increase in viscosity with falling temperatures. The comparatively high solidification point of rapeseed oil, for example in winter conditions, presents considerable problems for the practical application of the hydraulic oils at low ambient temperatures. In practical application, these problems can of course be dramatically aggravated by the fact that oxidative thickening of an ester oil of the above-mentioned type is accompanied by a considerable reduction in the solidification point of the hydraulic oil. The addition of pour point depressants does not solve the technical problem involved. It is known that the effect of pour point depressants disappears in the event of prolonged residence in the oil to be treated.
The problem addressed by the present invention was to provide effective remedies for the two above-described principal error sources of hydraulic oils based on environ-i ment-friendly basic oils. More particularly, the object of the invention on the one hand was effectively to stabilize i ester oils containing substantial proportions of highly , unsaturated fatty acids in the ester mixture against oxidative thickening by addition of selected antioxidants and, on the other hand, to provide mixture components, again based on ecologically safe ester oils, with which a substantial reduction in the solidification point in the hydraulic oil could be effectively achieved over indefinite periods of use.
In a first embodiment, therefore, the present inven-tion relates to an environment-friendly basic oil based on ' :; :
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~ 2~6~û11 ., natural materials for the formulation of hydraulic oils having improved viscosity and/or low-temperatuxe stability in practical application containing a) purified rapeseed oil and/or soybean oil as the main oil component, b) 0.5 to 5~ by weight, based on the mixture as a whole, - of antioxidants selected from the group consisting of methoxyphenol, ethoxyphenol, butyl hydroxyanisole, butyl hydroxytoluene, methoxyhydroquinone, ethoxy-hydroquinone, tert. butyl hydroquinone and/or toco-pherol.
If desired, these ester oils to which the antioxidants selected in accordance with the invention are added contain as an additional mixture component c) esters of trimethylol ethane, trimethylol propane and/or neopentyl glycol with monocarboxylic acids of the following subclasses cl) saturated CslO monocarboxylic acids and/or c2) fatty acids based on rapeseed oil, soybean oil and/or I 20 technical oleic acid, `, the ester components (c) being present in at most substan-tially equal quantities to the main oil component (a).
In another embodiment, the present invention relates to an additive containing antioxidants for stabilizing the , 25 viscosity of hydraulic oils based on rapeseed oil and/or , soybean oil, characterized in that it contains one or more of the following antioxidants: methoxyphenol, ethoxyphenol, butyl hydroxyanisole, butyl hydroxytoluene, methoxyhydro-quinone, ethoxyhydroquinone, tert. butyl hydroquinone and/or tocopherol.
. If desired, these selected antioxidants are present in ~ solution in a preferably high-boiling solvent which, in -~ turn, is soluble in the ester oils based on rapeseed oil ;, and/or soybean oil forming the principal oil component.
~ 35 Finally, another embodiment of the invention relates :;

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to the use of esters of trimethylol ethane, trimethylol propane and neopentyl glycol with monocarboxylic acids of the following subclasses cl) saturated C51~ monocarboxylic acids and/or ; 5 ` c2) fatty acids based on rapeseed oil, soybean oil and/or technical oleic acid for mixing with environment-friendly hydraulic oils based on rapeseed oil and/or soybean oil, the outcome being a reduction in the pour point and an improvement in the low-~: 10 temperature stability of the ester-based hydraulic oil.
Further particulars of the composition of the hydraul-ic oils can be found in the relevant prior art, cf. in particular "Ullmanns Enzyklopadie der technischen Chemie", 4th Edition (Verlag Chemie, Weinheim), Vol. 13, pages 85 et seq., "Hydraulikflussigkeiten (Hydraulic Fluids)" and also , Dieter Klamann "Schmierstoffe und verwandte Produkte, Herstellung, Eigenschaften, Anwendung (Lubricants and ¦ Related Products, Production, Properties, Uses)", Verlag ;~I Chemie, Weinheim, 1982, pages 147/148, 11.9 Hydraulikole (Hydraulic Oils).
The mixtures according to the invention differ from the known mineral-oil-based hydraulic oils widely used in ~ practice in the choice of the environment-friendly ester ;~ oils of the above-mentioned type as the basic component of ,~ 25 the hydraulic oil. The particular features of the inven-tion will now be described with reference to the above-mentioned first embodiment of the invention, i.e. with reference to the ecologically safe basic oils based on natural materials for the formulation of the hydraulic oils.
Purified ester oils which form the main oil component and which may optionally have been additionally refined by 3 at least partial decoloration are inexpensively available as commercial products. Particularly suitable rapeseed , 35 oils are the types free from erucic acid which are now . , .
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widely used.
Rapeseed oil of this category typically has a solidi-fication point of -16C. A distinct reduction in the pour point or solidification point can be obtained by addition of the selected esters of trimethylol ethane, trimethylol propane and/or neopentyl glycol. In the two subclasses mentioned, the ester-forming acids of these mixture com-i ponents are selected so that they combine the desired improvement in viscosity, particularly at low temperatures, with high environmental compatibility. Accordingly, it is preferred in accordance with the invention to use fatty acids of natural origin in both ester subclasses.
The first ester component based on the trimethylol derivatives mentioned uses comparatively low, more par-lS ticularly saturated, carboxylic acids containing at most 10 carbon atoms as the ester-forming carboxylic acids. One known natural starting material of this type are the so-i called head-fractionated fatty acids, i.e. linear saturated monocarboxylic acids containing 6 to 10 carbon atoms. The esters of this groups are distinguished by particularly low solidification points and, accordingly, are particularly suitable for improving the low-temperature behavior of the main oil components in the desired sense.
However, the ester-forming carboxylic acids from the ;~ 25 second group of trimethylol derivatives described in accordance with the invention are also structurally suit-able for the intended application by virtue of the high concentration of olefinically mono- and/or polyunsaturated carboxylic acids of rapeseed oil or soybean oil or of technical oleic acid.
Mixtures of these two subclasses of trimethylol . ethane, trimethylol propane or neopentyl glycol esters are preferably used in accordance with the invention. In one . preferred embodiment, the lesser represented ester com-ponent is present in quantities of at least about 20% by i '' ,~ . .. .
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I- 20~011 Wo 91/02784 6 pcT/Epso/ol2s6 weight, based on the ester mixture to be added to the main oil component. According to the invention, it can be particularly preferred to use predominant quantities of the trimethylol esters based on lower fatty acids containing at most 10 carbon atoms in the ester mixture. According to the invention, it is thus possible to reduce the solidifi-cation point of rapeseed oil, for example, to -40 to -45C.
By virtue of their high environmental compatibility, these - ester components may safely be added to the main oil component in up to substantially equal proportions of the ester mixture to be added, based on the main oil component, ' without any danger of an unwanted reduction in the required ,, environmental compatibility.
The stabilizers proposed in accordance with the invention as antioxidants are compounds known per se from s, the class of phenolic inhibitors or corresponding compounds having a basic hydroquinone structure. Nevertheless, the ~ choice of these particular stabilizers is not an obvious s choice. It has been found that the choice made in accord-ance with the invention enables the ester oils or ester oil mixtures used in accordance with the invention to be inhi-bited surprisingly effectively against unwanted increases in viscosity by ageing in air. Accordingly, the life and usefulness of the hydraulic oils based on natural materials ~ 25 can be prolonged to a hitherto unknown extent for substan-tially constant material properties.
~, It is known that hydraulic oils are not only required to show the high low-temperature stability mentioned above, the basic oil is also required to undergo only a minimal change in viscosity immediately after its production on the ' one hand and after exposure to heat in the presence of air on the other hand. The viscosity properties of hydraulic oils are described in the definition of different viscosity ~3 classes in IS0 3448 or DIN 51519. Under this definition, 'l 35 the following meanings apply:

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~ 2~6~011 Wo 91/02784 7 pcT/Epso/ol2s6 Viscosity (mm2/s) at 40~C
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IS0-VG 22 19.8 24.2 IS0-VG 32 28.8 3S.2 IS0-VG 46 41.4 50.6 IS0-VG 68 61.2 74.8 .
Depending on the ratios in which the ester oils are mixed in accordance with the invention and on the choice of - 10 the inhibitors defined in accordance with the invention, viscosity classes IS0-VG 22, IS0-VG 32 and IS0-VG 46 can be established and maintained over long periods of use with the mixtures according to the invention.
The quantity in which the inhibitor class according to : 15 the invention is added to the basic oil is in the range , from 0.5 to 5% by weight, based on the ester oil mixture as a whole. It may be advisable in this regard to make the inhibitors available as an additive in solution in a , solvent. The requirements which the solvent selected has to satisfy include the solubility of the inhibitors selec-ted over a wide temperature range and the homogeneous ~ miscibility even of this solvent in the ester oil mixture.
.~. In addition, the solvent selected should show sufficiently low volatility. Ester oils of diverse composition may be used as the solvent.
The formulation of a hydraulic oil from the basic oils formulated in accordance with the invention requires the addition of further components in known manner. Thus, the following further components in particular may be added to the basic oils described in accordance with the invention:

High-pressure additives These additives are, in particular, sulfurized tri-glycerides, sulfurized fatty acid alkyl esters, sulfurized sperm oils, phosphoric acid esters, such as trioleyl alco-: ~

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, ~ 2Q~3Qll Wo 91/02784 8 pcT/spso/ol296 hol phosphate or triaryl phosphate.

Anti-wear additives - Suitable anti-wear additives are, in particular, zincdialkyl dithiophosphate compounds, such as zinc-(di-2-ethylhexyldithiophosphate) ~R ~ ~ ~ 5 1 lR ~ ~ \ 5 2 Pour point depressants One example of a suitable pour point depressant is the product marketed by applicants under the trade name of "Edenor 2410".
Further particulars of the special formulation of q hydraulic oils, their additives and the quantities in which ~ these additives are used can be found in the prior publica-;~ tions on this class of materials cited in detail in the foregoing.
The following Examples describe the effects obtainable in accordance with the invention with main oil components based on rapeseed oil and soybean oil and compare these I results with corresponding mixtures which do not correspond to the definition accordance with the invention.

~, E x a m p 1 e 8 ;' Ex~mple 1 A mixture of 99~ rapeseed oil and 0.33% butyl hydroxy-anisole, tert. butyl hydroquinone and tocopherol having an initial viscosity of 36 mm2/s at 40-C was stored for 112 hours at 200 C in an open vessel. Thereafter, the mixture had a viscosity of 69 mm2/s at 40-C. The oil is liquid at -15'C.

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- 2~ ~011 . ' ,.. -....... -Wo 91/02784 9 PCT/EP90/01296 Comparison Example 1 Rapeseed oil having a viscosity of 36 mm2~s was stored for 112 hours at 200~C in an open vessel. Thereafter, the mixture had a viscosity of 200 mm2/s at 40~c.

Example 2 A mixture of 69~ rapeseed oil, 30% trimethylol propane tricaprylate and 0.33% each of butyl hydroxyanisole, tert.
butyl hydroquinone and tocopherol having an initial vis-cosity of 29 mm2/s at 40C was stored for 106 hours at 200C in an open vessel. Thereafter the mixture had a viscosity of 50 mm2/s at 40C. The mixture is liquid at -25~C.

Compari~on Example 2 A mixture of 70% rapeseed oil and 30% trimethylol ' propane tricaprylate was stored for 106 hours at 200C.
' Thereafter the mixture has a viscosity of 160 mm2/s at 40C. The mixture is solid at -16C.
, 20 ,~ Example 3 A mixture of 50% rapeseed oil, 25% trimethylol propane trioleate, 25% trimethylol propane tricaprylate and 0.33~
) each of butyl hydroxyanisole, tert. butyl hydroquinone and tocopherol having an initial viscosity of 33 mm2/s was stered for llO hours at 200-C in an open vessel. There-after the mixture had a viscosity of 52 mm2/s at 40 C. The mixture is liquid at -30-C.

- 30 Comparison Example 3 A mixture of 50% rapeseed oil, 25% trimethylol propane trioleate and 25% trimethylol propane tricaprylate having an initial viscosity of 33 mm2/s at 40-C was stored for 110 i hours at 200-C in an open vessel. Thereafter the mixture had a viscosity of 130 mm2/s at 40 C. The mixture is liquid at -30C.

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Claims

Translation of Claims as amended under Article 34 6/17/91.

New Claims

1. An environment-friendly basic oil based on natural materials for the formulation of hydraulic oils having improved viscosity and low-temperature stability based on a) purified rapeseed oil and/or soybean oil as the main oil component and also antioxidants and other additives, characterized in that it contains the following components:
b) 0.5 to 5% by weight, based on the mixture as a whole, of antioxidants selected from the group consisting of methoxyphenol, ethoxyphenol, butyl hydroxyanisole, butyl hydroxytoluene, methoxyhydroquinone, ethoxy-hydroquinone, tert. butyl hydroquinone and/or toco-pherol, c) esters of trimethylol ethane, trimethylol propane and/or neopentyl glycol with monocarboxylic acids of the following subclasses c1) saturated C5-10 monocarboxylic acids and/or c2) fatty acids based on rapeseed oil, soybean oil and/or technical oleic acid, the ester components (c) being present in at most substan-tially equal quantities to the main oil component (a).

2. A basic oil as claimed in claim 1, characterized in that mixture component (c) is present in the form of an ester mixture of the carboxylic acids of subclasses (c1) and (c2) which consists of at least about 15% by weight, based on the ester mixture, of one ester subclass and, for the rest, of esters of the other subclass, predominant quantities of ester subclass (c1) being preferred.

3. The use of antioxidants together with other additives for stabilizing the viscosity, lowering the pour point and improving the low-temperature stability of hydraulic oils based on rapeseed oil and/or soybean oil, characterizedin that b) at least one antioxidant selected from:

methoxyphenol, ethoxyphenol, butyl hydroxyanisole, butyl hydroxytoluene, methoxyhydroquinone, ethoxy-hydroquinone, tert. butyl hydroquinone and/or toco-pherol, together with c) esters of trimethylol ethane, trimethylol propane and/or neopentyl glycol with monocarboxylic acids of the following subclasses:
c1) saturated C5-10 monocarboxylic acids and/or c2) fatty acids based on rapeseed oil, soybean oil and/or technical oleic acids, are used.

4. The use claimed in claim 3, characterized in that the trimethylol ethane, trimethylol propane and/or neopentyl glycol esters are added to the hydraulic oil in at most substantially equal quantities to the rapeseed oil and/or soybean oil.

5. The use claimed in claims 3 and 4, characterized in that trimethylol ethane/trimethylol propane ester mixtures containing a relatively high percentage of esters of acids of subclass (c1) and, for the rest, esters of acids of subclass (c2) are added.

6. The use claimed in claims 3 to 5, characterized in that esters or ester mixtures of acids of subclass (c1) of which the acid components are of natural origin and, more particularly, are corresponding head-fractionated fatty acids are used.

7. The use claimed in claim 3, characterized in that the antioxidants (b) are present in solution in a preferably high-boiling solvent soluble in ester oils.