WO2001004240A1

WO2001004240A1 - Hydraulic oil

Info

Publication number: WO2001004240A1
Application number: PCT/SE2000/001493
Authority: WO
Inventors: Anders RANTÉN
Original assignee: Canadian Oil Co Sweden Ab
Priority date: 1999-07-13
Filing date: 2000-07-13
Publication date: 2001-01-18
Also published as: AU6330400A; SE9902681D0

Abstract

The invention refers to a readily biodegradable hydraulic oil which comprises a mixture of a mineral oil and an ester, the viscosity of the mineral oil being lower than the viscosity of the ester.

Description

Hydraulic Oil

The present invention refers to a lubricant. More specifically, the present invention refers to a lubricant composition in the form of a hydraulic oil which is readily biodegradable and is intended to be used in an equipment which works within a broad temperature range and at high pressures.

In this connection a hydraulic oil (hydraulic liquid) refers to a medium for pressure transmission in hydraulic servo means or pressure transmission in motor vehicles or machine tools. Thus, a hydraulic oil does not refer to a lubricating oil which is a shock absorbing medium in a hydraulic shock absorber, a so-called shock absorber oil. It is well known that oil-containing liquids are released into the environment on many occasions. For example, it is inevitably that the environment will be exposed to lubricating oils intended for power saws. Motor oils and hydraulic oils also frequently leach and contam- inate land and sea. In Sweden, the contaminating amount is estimated to be 10-12 thousand tons per year. Therefore, increasingly far-reaching demands are raised on products used in for example forests, sources of water supply and other sensitive environments. The need of pro-environment lubricant products has thus increased.

The most pro-environment lubricants have been those in the form of vegetable and animal oils. However, many of these oils are impaired by the drawback of having an insufficient technical function in the equipment to be used. Furthermore, vegetable and animal oils have a lower oxidation stability than mineral oils, an evil smelling precipitate being formed in the equipment, which has a further negative effect on the same.

Different types of oils have been developed in the form of synthetic esters with the purpose of increasing the functioning. Several of these products have drawbacks with reference to such properties as oxidation stability, especially at high temperatures, hydrolytic resistance, filter- ability, and separation power when water is absorbed. It is nowadays important that the lubricants are classified with reference to the environment. The requirement for such a product as a lubricant is that it must be readily biodegradable in order to be consistent with the environment. In this connection, different countries have different requirements for the product, in Germany, the product must be degraded to 70 % after 21 days. According to Swedish standard, the product must in Sweden be naturally biodegraded to >60 % within 28 days. The degradability is preferably determined according to OECD or ISO methods. In the debate on emissions of oleaginous substances in nature, the environment considered has only been the outer environment. However, the working environment has not been sufficiently considered, i.e. if the product in question is nasty smelling, irritating for the skin and mucous membranes etc. Especially important in this connection is the partial neglectance to establish if the final product is allergenic, toxic or carcinogenic. Above all, this concerns used lubricants, which have been utilized for a long time.

According to governmental rules, hydraulic oils must not be considered or classified as injurious to health or worse. In order to be able to label a hydraulic oil as adapted to the environment, all the ingredients present in the oil must be decomposable according to OECD 301 A-F and fulfil SS 155434 (the environmental part) . Thus, chemical substances with allergenic properties must not be present at a concentration of ≥l wt%. Substances with allergenic properties must be specified if the concentration is ≥O.OI wt%. This also applies if the complex product or additive mixtures in the product have not been evaluated as aller- genie when tested according to OECD 406. Chemical substances present in concentrations of ≥5 wt% must for each chemical substance have an acute aquatic toxicity with a value for EC_S0/LC_5fl/IC₅₀ of >100 mg/1. Chemical substances with a value for EC_S0/LC₅₀/lC_5β of _<1 mg/1 have a maximum permissible concentration of 1 wt% in total.

Chemical substances in the middle range, i.e. with a value for EC_S0/LC_5O/IC_S0 from 1 mg/1 to 100 mg/1, have a maximum permissible concentration of 5 wt% in total.

With reference to the biodegradability, chemical substances with a solubility in water of ≤IOO mg/1 at 20 °C shall at concentrations of ≥5 wt% have a biodegradability for each chemical substance, which is ≥60% within 28 days. The test shall preferably be carried out according to ISO 9439.

At concentrations of >5 wt% chemical substances with a solubility in water of ≥IOO mg/1 at 20 °C must have a biodegradability for each chemical substance which is ≥70 % within 28 days. The tests must be performed according to one of the methods OECD 301 A or E.

Thus, according to OECD 301 or ISO 9439 these requirements concern all the components present in a product at a concentration of >1 %. Hydraulic oils are subjected to extremely high as well as extremely low temperatures in different hydraulic systems. For example, at temperatures of 80-90 °C viscosity improving polymers in the oil will be rapidly degraded by the heat (disintegrated by boiling) as well as the sheer forces, which they are subjected to when working in mobile hydraulics. Furthermore, this degradation will increase when the oil is worn out, i.e. after about 2-500 working hours. Thus, these products with viscosity improving additives have a viscosity which is drastically deteriorated with time. This degradation also results in harmful deposits on hydraulic valves and systems with accompanying wear, which reduces the reliability in operation and increases operation as well as maintenance costs. Furthermore, the de- gradation results in a reduction in oil viscosity, less exact hydraulic movements being obtained with an increased risk of pump cavitation.

Neither can plastic-like viscosity improving polymer additives be degraded according to all the criteria of the OΞCD (especially OECD 301 B) and the ISO standards.

It is thus an object of the present invention to provide improved hydraulic oils which do not have the drawbacks according to the state of the art, the above-mentioned problems being eliminated. The object of the invention is particularly to provide a hydraulic oil which fulfils the environment requirements according to OECD 301 B and which fulfils Swedish standards .

Another object of the invention is to provide a hydraulic oil which can be used around the year under extreme temperature differences from about -40 to about 100 ^βc.

Yet another object of the invention is to provide a hydraulic oil with improved oxidation and thermal stability in comparison with esters and normally refined products of today .

These objects are achieved by the hydraulic oil according to claim 1.

The invention offers biodegradable hydraulic oils which are intended to be used around the year in piston, vane and gear pumps in industrial plants, within shipping as well as in forest, mining, contracting, and other mobile equipment. Furthermore, there is no risk of additive losses or clogging of filters when the inventive oils are used in hydraulic systems equipped with fine filters (down to 3 μm) .

The inventive oils are unique pro-environmental biodegradable hydraulic oils which have good wear preventing properties and a long service life. They are intended to be used around the year in heavy-duty hydraulic systems which are subjected to large temperature differences. Thus, they are ideal for different high-pressure systems in forest, contracting, and mining machinery as well as other mobile equipmen .

According to the invention a hydraulic oil is thus achieved, which does not have any effect on the user, which does not have any effect on the environment, and which is technically compatible with the equipment to be used. Furthermore, the hydraulic oil according to the invention is especially resistant to water aβ well as resistant to both high and low temperatures. This is achieved by the oil being composed of a mixture of a mineral oil - which is readily biodegradable according to OECD 301 B - and an ester.

A useful mineral oil according to the invention is any such oil which can be used in hydraulic oils, provided that it is readily biodegradable and/or fulfils the technical requirements for a mineral oil in the form of a hydraulic oil. The mineral oil provides for the majority of those technical effects which are of importance for the functional properties of the hydraulic oil.

In this connection a mineral oil means an oil which consists of a mixture of hydrocarbons, either naturally occurring or obtained by the treatment of materials of natural mineral origin. Preferably, mineral oils are used in the form of stable straight saturated hydrocarbons. The number of carbon atoms is preferably 12-30, most preferred It is also preferred that sulphur, nitrogen, oxygen as well as cyclic aromatics have been removed from the mineral oils. A so-called white oil is obtained when these components are eliminated, which is a pure paraffin oil. This results in that the hydraulic oil will be very stable in the equipment to be used, and it will at the same time be sufficiently biodegradable in nature. The removal of sulphur and nitrogen eliminates any acid and toxic fallout in the environment, and the removal of oxygen reduces the oxidation of the machinery parts. Cyclic aromatics are irritating for the skin as well as mucous membranes and can in addition be carcinogenic. Thus, the exclusion of these substances from a hydraulic oil represents a considerable improvement of the working environment. Preferably, saturated esters are used in the hydraulic oils according to the invention. The esters can be synthesized from linear acids as well as linear alcohols. Such suitable esters comprise the esters of dicarboxylic acids (e.g. phthalic acid, succinic acid, alkyl succinic acids, alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleiα acid dimer, malonic acid, alkyl malonic acids, alkenyl malonic acids, etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2- ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol, etc) .

Since a certain branching is required in order to increase the viscosity of the hydraulic oil while attaining good flow properties, esters are, however, preferred which are synthesized from linear acids and branched alcohols, such as polyol esters of linear acids. These are high viscosity esters. Suitable esters are those which are synthesized from C5 to C12 onocarboxylic acids and polyols and polyol ethers, such as neopentyl glycol, trimethylol pro- pane, pentaerythritol, dipentaerythritol, tripentaerythritol, etc. However, esters should not be used in which both the acid and the alcohol portions are highly branched since such esters exhibit inferior biodegradability. Useful esters in the inventive hydraulic oil are complex esters of aliphatic, σyσloaliphatic or aromatic dicar- boxylic acids with 2 till 36 carbon atoms as well as aliphatic dicarboxylic acids with 6 to 22 carbon atoms.

Other useful esters in the hydraulic oil according to the invention are also polymers, copolymers and derivatives thereof, such as alkylene oxide polymers, in which the terminal hydroxyl groups have besn modified by means of esterification. Likewise, mono- or polycarboxylic esters of ethylene glycols can be used. In the inventive hydraulic oil the viscosity of the mineral oil is lower than the viscosity of the ester. A viscosity value is given at 40 and 100 °C as well as -20 or -30 ^βC in dependence on the ISO number 22, 32, 46 or 68, respectively. Each number then represents the viscosity at 40 °C. Thus, when producing a hydraulic oil according to the invention a very thin mineral oil can be mixed with a very thick ester. The viscosity values of the components are given according to the recommendations of the national association of Swedish Mechanical Engineers (SMR) and classified according to a standardized ISO VG grade, for example VG 22, VG 32, VG 46, VG 68, and VG 100. Thus, the mineral oil and the ester are mixed in such a ratio that accepted ISO grades are obtained. This is demonstrated in Table 1 below. No viscosity improving agents, polymers or friction modifiers at all are included in the inventive hydraulic oil. However, an environmentally friendly friction improving additive package can be added to the hydraulic oil. Such an additive package or an anti-wear inhibiting effect should contain phosphorous and should be ashless. Thus, it should not contain any metals and be of low viscosity and of low density. Preferably, the additive package also contains antioxidants and corrosion inhibitors as well as about 2.7 wt% nitrogen and 0.5 wt% phosphorous.

Those polymers, which according to the state of the art bring about an increased viscosity in oils, are according to the invention compensated for by a thick mineral oil. The effect can be enhanced by means of a thick complex ester with a high viscosity number for the ester, a hydraulic oil with a viscosity of 9-12 being obtained.

Table 1 shows the proportions required for mixing an ester and a mineral oil of dif erent specified viscosities at 40 °C in order to obtain complete hydraulic oils according to the invention with accepted standards according to ISO VG

Table 1

For example, the mineral oil can have a viscosity ISO VG of less than 20, whereas the ester can have a viscosity ISO VG which is as large as 500 or more. Preferably, the mineral oil has a viscosity ISO VG of 10-15.

Table 2 below shows technical data which have been obtained for inventive hydraulic oils with ISO VG 22, ISO VG 32, ISO VG 46 and ISO VG 68, respectively.

Furthermore, by using an extremely highly viscous ester in the hydraulic oil according to the invention, a very thin mineral oil of- low viscosity can be used. Thus, the ester can represent more than 50 wt% of the total weight of the hydraulic oil.

Recoverable hydraulic oils are obtained according to the invention, which can sustain heavy loads and which have very good intrinsic technical properties, above all with reference to cold/heat, water-repelling capacity, lubricating properties and shear stability. Thus, the hydraulic oils can work within a wide temperature range, including temperatures down to -50°C, good fluidity properties at low temperatures being retained and cold start-ups being allowed down to -40°C. The products fulfil the requirements made on the influence of substantial mechanical shear under given prerequisities . They have good heat stability and good oxidation stability.

According to the invention, an oil is obtained which fulfils the high technical requirements raised upon prolonged shear. In this connection the extreme shear stability of the hydraulic oil is due to a very high intrinsic viscosity index (_>180) . (The viscosity index is a number which characterizes the variation in viscosity of a petroleum product with temperature; a high viscosity index indicates a relative small change of viscosity with temperature and vice versa) , Extreme water-repelling hydraulic oils are provided by the invention, which do not bind and absorb water. This means that they provide excellent protection against rust, corrosion and ice formation. They also have excellent properties with reference to water separation as well as hydro- lytic stability in comparison with simple vegetable oils or ester-based oils.

Furthermore, the inventive oils are compatible with sealings in the equipment used and they have good ant -wear properties, which prolongs the operation time of the eguip- ment. Due to the mineral oil base, an excellent lubrication of the hydraulic components is obtained at high operation temperatures. After any leakage that may occur the product is not oxidized, which means that it does not become tacky or sticky and is thus easy to remove during decontamina- tion.

Hydraulic oils according to the invention are readily biodegradable, which protects the environment. The requirement of biodegradation according to Swedish standard (SS155434) is fulfilled by all the components being de- graded, which are present in the hydraulic oil at a concentration of more than 1 wt%.

Above all, degradable hydraulic oils according to the invention are completely harmless to man by being non- toxic, non-allergenic as well as non-carcinogenic. Neither do these oils irritate the eyes or the skin. In addition, they have a low vapour pressure which, results in that they do not represent a danger when inhaled at normal room temperature .

Table 2

Claims

1. Readily biodegradable hydraulic oil, c h a r a c t e r i z e d in that it comprises a mixture of a mineral oil and an ester, the viscosity of the mineral oil being lower than the viscosity of the ester.

2. Readily biodegradable hydraulic oil as in claim

1, c h a r a c t e r i z e d in that the mineral oil comprises straight saturated hydrocarbons and that sulphur, nitrogen, oxygen, and cyclic aromatics are removed from the same .

3. Readily biodegradable hydraulic oil as in claim

2, c h a r a c t e r i z e d in that the mineral oil is a pure paraffin oil, a so called white oil.

4. Readily biodegradable hydraulic oil as in claim 1, c h a r a c t e r i z e d in that the ester is a saturated ester. . Readily biodegradable hydraulic oil as in claim 1, c h a r a c t e r i z e d in that the ester is synthesized from linear acids and branched alcohols. 6. Readily biodegradable hydraulic oil as in claim l, c h a r a c t e r i z e d in that the mineral oil has a viscosity ISO VG of less than 20.