EP0486575B1 - Basic oil for formulating hydraulic fluids - Google Patents

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

The invention relates to the field of hydraulic fluids, in particular hydraulic oils for hydrostatic power transmission.

In the past, but still today, the majority of hydraulic oils are made from mineral oil. In areas of application in which, for example, leaks that cannot be prevented from escaping the environment are an option, the use of hydraulic oils that contain environmentally friendly ester oils, especially those based on rapeseed oil and / or soybean oil, is increasingly required. Typical areas of application of the area affected here are the machines and implements of forestry, agriculture, excavators and the like. The use of hydraulic oils of water hazard class 0 is required here today. Ester-based hydraulic oils are suitable to meet these requirements.

The ester oils of the aforementioned type which are essential for practical use, i.e. H. However, oils based on purified rapeseed oils and / or soybean oils, which are freed in particular of amylopectins and other mucilaginous oils, show two decisive weaknesses in practical use:

The esterols based on unsaturated fatty acid systems tend to thicken rapidly even at only moderately elevated operating temperatures of, for example, 50 to 80 ° C. Occasion the willingness of the olefinic double bonds of the ester-forming acids of the oil type affected here to react under the influence of atmospheric oxygen, which ultimately leads to an increase in viscosity. Although it is known in principle that such undesirable increases in viscosity can be dampened by adding antioxidants, especially in hydraulic oils, it has been shown that the antioxidants used up to now in hydraulic oils based on mineral oils have only inadequate performance in ester oils of the type concerned here.

Another important limitation for hydraulic oils based on the environmentally friendly ester oils mentioned is the inadequate low-temperature stability. Purified beet oil, for example, has a solidification or pour point of - 16 ° C. Even before the solidification point is reached, there is a remarkable increase in viscosity with falling temperatures. The solidification point of the beet oil, which is comparatively high in winter, for example, poses considerable problems for the practical use of hydraulic oils at low ambient temperatures. Understandably, this problem can be exacerbated dramatically in operation by the fact that an oxidative thickening of the ester oil of the type described above also triggers the considerable increase in the solidification point of the hydraulic oil. The addition of pour point depressants does not solve the technical problem here. It is known that the effect of such pour point depressants disappears when the oil to be treated remains for a long time.

DE-A-34 19 415 describes the production of lubricants, formwork oils and drilling emulsions from environmentally friendly raw materials. For this purpose, vegetable, animal and synthetic esters of polyhydric alcohols, in particular peanut oil, hazelnut oil, cod liver oil, linseed oil, olive oil, castor oil, rape oil, soybean oil and whale oil, are used as the oil base. Easily degradable, harmless auxiliary substances can be considered as additives. For example, products from the wood processing industry (e.g. cellulose derivatives, lignin sulfate) or higher molecular weight substances from the sugar processing industry (e.g. molasses) are used to modify the viscosity, stickiness and adhesiveness of lubricants. In particular, essential oils are added as preservatives. For the stabilization and easier handling of corresponding emulsions, emulsifiers, stabilizers, protective substances, solubilizers, defoamers, antioxidants and preservatives are used. Examples include tocopherol from vegetable oils as an additive.

In contrast, the present invention is based on the object of demonstrating effective remedies for the two main sources of error of the hydraulic oils described above on the basis of environmentally friendly base oils. The aim of the invention is in particular on the one hand the effective stabilization of such ester oils with substantial proportions of highly unsaturated fatty acid in the ester mixture against oxidative Thickening by adding selected antioxidants, on the other hand, the invention also wants to provide mixture components based on environmentally compatible ester oils, the use of which can substantially reduce the solidification point in the hydraulic oil effectively and over any period of use.

• a) gereinigtem Rüböl und/oder Sojaöl als Öl-Hauptkomponente, sowie Antioxidantien und anderen Additiven, welches dadurch gekennzeichnet ist, daß es die folgenden Komponenten enthält:
• b) 0,5 bis 5 Gew.-% - bezogen auf Gesamtgemisch - an Antioxidantien ausgewählt aus der Gruppe Methoxyphenol, Ethoxyphenol, Butylhydroxyanisol, Butylhydroxytoluol, Methoxyhydrochinon, Ethoxyhydrochinon, tert.-Butylhydrochinon und/oder Tocopherol,
• c) Ester des Trimethylolethans, des Trimethylolpropans und/oder des Neopentylglykols mit Monocarbonsäuren der nachfolgenden Unterklassen:
  • c1) gesättigte C₅₋₁₀-Monocarbonsäuren und/oder
  • c2) Fettsäuren auf Basis Rüböl, Sojaöl und/oder technische Ölsäure,
  wobei die Esterkomponenten zu (c) höchstens mengengleich mit der Öl-Hauptkomponente zu (a) vorliegen.

The invention accordingly relates to a first Embodiment a base oil based on natural substances for the formulation of hydraulic oils with viscosity and cold stability based on

• a) purified rapeseed oil and / or soybean oil as the main oil component, as well as antioxidants and other additives, which is characterized in that it contains the following components:
• b) 0.5 to 5% by weight, based on the total mixture, of antioxidants selected from the group consisting of methoxyphenol, ethoxyphenol, butylhydroxyanisole, butylhydroxytoluene, methoxyhydroquinone, ethoxyhydroquinone, tert-butylhydroquinone and / or tocopherol,
• c) esters of trimethylolethane, trimethylolpropane and / or neopentylglycol with monocarboxylic acids of the following subclasses:
  • c1) saturated C₅₋₁₀ monocarboxylic acids and / or
  • c2) fatty acids based on rape oil, soybean oil and / or technical oleic acid,
  the ester components of (c) being at most equal in quantity to the main oil component of (a).

• c1) gesättigte C₅₋₁₀-Monocarbonsäuren und/oder
• c2) Fettsäuren auf Basis Rüböl, Sojaöl und/oder technische Ölsäuren, eingesetzt werden.

In a further embodiment, the invention relates to the use of antioxidants together with other additives for stabilizing the viscosity and lowering the pour point of hydraulic oils based on rapeseed oil and / or soybean oil, characterized in that
b) at least one antioxidant selected from:
Methoxyphenyol, ethoxyphenol, butylhydroxyanisole, butylhydroxytoluene, methoxyhydroquinone, ethoxyhydroquinone, tert-butylhydroquinone and / or tocopherol,
along with
c) esters of trimethylolethane, trimethylolpropane and / or neopentylglycol with monocarboxylic acids of the following subclasses:

• c1) saturated C₅₋₁₀ monocarboxylic acids and / or
• c2) fatty acids based on beet oil, soybean oil and / or technical oleic acids.

If desired, these selected antioxidants are present in solution in a preferably high-boiling solvent, which in turn is soluble in the ester oils which form the main oil component and are based on rapeseed oil and / or soybean oil.

For further details on the composition of the hydraulic oils, reference is first made to the relevant prior art. Special mention should be made here of "Ullmann's Encyclopedia of Technical Chemistry" 4th edition (Verlag Chemie, Weinheim) Volume 13, page 85 ff., Hydraulic fluids, and Dieter Klamann "Lubricants and related products", manufacture, properties, application, (publisher Chemie, Weinheim) 1982, pages 147 / 148-11.9, hydraulic oils.

The mixtures of substances according to the invention differ from the known hydraulic oils based on mineral oil, which are widely used in practice, by the selection of the Environmentally friendly ester oils of the type mentioned as a basic component of the hydraulic oil. The peculiarities of the invention are initially illustrated in the first embodiment of the invention described above, ie using the environmentally friendly base oils based on natural materials for the construction of the hydraulic oils.

Purified and, if necessary, additionally refined by at least partial decolorization, the ester oils forming the main oil component are available inexpensively as commercial products. Suitable rapeseed oils are in particular the erucic acid-free types that are widespread today.

Turnip oil in this category usually has a solidification point at - 16 ° C. By adding the selected esters of trimethylolethane, trimethylolpropane and / or neopentylglycol, the pour point or solidification point is significantly reduced. The ester-forming acids of these mixture components are selected in the two subclasses shown in such a way that they combine the desired viscosity improvement, in particular in the low temperature range, with high environmental compatibility. Accordingly, the use of fatty acids of natural origin in both ester subclasses is preferred in the sense of the inventive action.

The first ester component based on the trimethylol derivatives mentioned uses, as the ester-forming carboxylic acids, comparatively low, in particular saturated, carboxylic acids with a maximum of 10 carbon atoms. A known natural starting material of this type are the so-called preliminary fatty acids, ie straight-chain saturated monocarboxylic acids with 6 to 10 carbon atoms. The esters in this group are characterized by particularly low solidification values and are therefore particularly suitable to improve the cold behavior of the main oil components in the desired sense.

However, the ester-forming carboxylic acids from the second group of the trimethylol derivatives described according to the invention are also suitable for the intended use, depending on the structure. The reason for this is the high concentration of the olefinically mono- and / or polyunsaturated carboxylic acids of rapeseed oil or soybean oil or technical oleic acid.

It is preferred according to the invention to use mixtures of these two subclasses of trimethylolethane, trimethylolpropane or neopentylglycol esters. In a preferred embodiment, the less represented ester component is present in amounts of at least 15% by weight, based on this ester mixture to be added to the main oil component. According to the invention, it can be particularly preferred to use predominant amounts of the trimethyl esters based on the lower fatty acids with a maximum of 10 carbon atoms in this ester mixture. According to the invention, the setting point, for example of rapeseed oil, is thus lowered in the range from -40 to -45 ° C. Due to their high environmental compatibility, these ester mixed components can be added to the main oil component up to the amount of approximately equal proportions of the ester mixture to be added - based on the main oil component - without fear of an undesired restriction of the required environmental compatibility.

The stabilizers proposed according to the invention as antioxidants are known compounds from the class of phenolic inhibitors or corresponding compounds with a hydroquinone basic structure. However, the selection of these stabilizers cannot be taken for granted. It has been shown that by this made according to the invention A surprisingly strong inhibition of the ester oils or ester oil mixtures used according to the invention against the undesirable increase in viscosity due to aging in air can be achieved. The service life and usability of hydraulic oils based on natural materials can thus be extended to a previously unknown extent with largely constant material properties.

As is well known, hydraulic oils are not only supposed to have the previously high stability to low temperatures, but also a change in the viscosity of the base oil that is as small as possible is required immediately after its production on the one hand or after thermal stress in the presence of air on the other hand. The viscosity properties of the hydraulic oils are known to be described in the definition of different viscosity classes according to ISO 3448 or DIN 51519. Here means:

Depending on the mixing ratios of the ester oils used according to the invention and the selection of the inhibitors defined according to the invention, the viscosity classes ISO-VG 22, ISO-VG 32 and ISO-VG 46 can be set with the substance mixtures according to the invention and maintained over long periods of use.

The amount of the inhibitor class according to the invention added to the base oil is in the range from 0.5 to 5% by weight, based on the total ester oil mixture. It may be expedient to provide these inhibitors as an additive, dissolved in a solvent. The requirements for the one selected here Solvents include the solubility of the selected inhibitors over a wide temperature range and the homogeneous miscibility of this solvent in the ester oil mixture. The sufficient low volatility of this solvent is also preferred. Ester oils of various compositions can serve as solvents.

The formulation of the finished hydraulic oil from the base oils formulated according to the invention requires the addition of further components in a known manner. The following additional components can thus be added to the base oils described in accordance with the invention:

High pressure additives

These are, in particular, sulfurized triglycerides, sulfurized fatty acid alkyl esters, sulfurized sperm oils, phosphoric acid esters such as trioleyl alcohol phosphate or triaryl phosphate.

Wear protection additives

Zinc dialkyldithiophosphate compounds such as zinc (di-2-ethylhexyldithiophosphate) are particularly suitable

Pour point lower

For example, the product sold by the applicant under the trade name "Edenor® 2410" is suitable.

For the rest, with regard to the special formulation of hydraulic oils, their additives and the amounts of these additives, reference is made to the detailed, documented prior art relating to this material class.

The following examples describe the effects which can be set according to the invention on main oil components based on rapeseed oil and soybean oil and compare these results with corresponding mixtures of substances which, however, do not correspond to the definition according to the invention.

Examples example 1

A mixture of 69% beet oil, 30% trimethylolpropane tricaprylate and in each case 0.33% butylhydroxyanisole, tert-butylhydroquinone and tocopherol with an initial viscosity of 29 mm² / s at 40 ° C. was stored in an open vessel at 200 ° C. for 106 hours. After this time the mixture had a viscosity of 50 mm² / s at 40 ° C. The mixture is liquid at - 25 ° C.

Comparative Example 1

A mixture of 70% beet oil, 30% trimethylolpropane tricaprylate was stored at 200 ° C for 106 hours. After this time the mixture had a viscosity of 160 mm² / s at 40 ° C. The mixture is solid at - 16 ° C.

Example 2

A mixture of 49% beet oil, 25% trimethylolpropane trioleate, 25% trimethylolpropane tricaprylate and in each case 0.33% butylated hydroxyanisole, tert-butylhydroquinone and tocopherol with an initial viscosity of 33 mm² / s at 40 ° C was in an open vessel at 200 ° C during Stored for 110 hours. After this time the mixture had a viscosity of 52 mm² / s at 40 ° C. The mixture is liquid at - 30 ° C.

Comparative Example 2

A mixture of 50% beet oil, 25% trimethylolpropane trioleate and 25% trimethylolpropane tricaprylate with an initial viscosity of 33 mm² / s at 40 ° C was stored in an open vessel at 200 ° C for 110 hours. After this time the mixture had a viscosity of 130 mm² / s at 40 ° C. The mixture is liquid at - 30 ° C.

Claims (7)

1. A basic oil based on natural materials for the formulation of hydraulic oils having viscosity and low-temperature stability on the basis of
   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, ethoxyhydroquinone, tert. butyl hydroquinone and/or tocopherol,

   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 substantially 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 (cl) 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 (cl) being preferred.
3. The use of antioxidants together with other additives for stabilizing the viscosity and lowering the pour point of hydraulic oils based on rapeseed oil and/or soybean oil, characterized in that
   b) at least one antioxidant selected from:
      methoxyphenol, ethoxyphenol, butyl hydroxyanisole, butyl hydroxytoluene, methoxyhydroquinone, ethoxyhydroquinone, tert. butyl hydroquinone and/or tocopherol,
   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 (cl) 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.