DE3876897T2 - LUBRICATING OIL COMPOSITION. - Google Patents

Description

Technological application area

The present invention relates to a lubricating oil composition or, more particularly, to a lubricating oil composition which can be satisfactorily used for the lubrication of wet clutch or wet brake parts such as automatic transmissions, tractors and the like.

Technological background

Lubricating oils used for lubricating parts that are involved in a wet clutch or wet brake, such as automatic transmissions, tractors and the like, require properties that include good friction characteristics, oxidation stability, corrosion resistance and rust prevention, as well as a large torque for power transmission. The friction characteristic that results from this is a ratio of the coefficient of static friction and the coefficient of dynamic friction, and it is required that this ratio be small and little affected by temperature changes or passage of time.

Such a lubricating oil is known from the prior art, which has a high coefficient of static friction and a good torque for power transmission. However, this lubricating oil has the disadvantage that its friction characteristics are not satisfactory, so that a switching shock of the automatic transmission and the like causes a strong shock.

In particular, in recent years there has been a growing trend for automatic transmissions and similar are being built in a reduced size, along with the further spread of compact cars and so-called FF cars (front engine front drive cars). This trend of automatic transmissions toward a compact size increases the adverse influence that the shift shock is sensitively felt by the driver. Accordingly, it is a technical problem to further improve the friction characteristics in order to improve driving comfort by reducing the shift shock.

Therefore, with respect to a lubricating oil, a proposal has been made to improve friction characteristics by using a friction modifier. However, there is a problem that the lubricating oil containing a friction modifier has insufficient friction characteristics when the friction characteristics vary due to a change in oil temperature, and the friction characteristics deteriorate due to deterioration due to oil degradation (changes with the passage of time) in a long-term service.

For example, GB-A-2097813 discloses a lubricating oil composition comprising 0.2% by weight of a glycerol mono-oleate, which may be an ester, prepared from high molecular weight dicarboxylic acids.

Another proposal was made in US-A-4209411, according to which the use of metholol polyester derivatives of C12/C22 hydrocarbon succinic anhydride of the acid as additives for lubricating oils leads to a reduction in friction. However, the results obtained still need to be improved.

Therefore, lubricating oils with good friction characteristics and with small changes in oil temperature and over time as well as with a large transmission torque have not yet been obtained.

The aim of the present invention is to solve the above-described problems of the prior art by a special combination of compounds contained in a base oil, and to provide a lubricating oil composition with a low power impulse and a low transmission torque which can be satisfactorily used for the lubrication of automatic transmissions and the like.

Disclosure of the invention

The present invention therefore relates to a lubricating oil composition characterized by a base oil containing (A) from 0.05 to 5% by weight of an ester of an alkenyl-substituted succinic acid and/or an ester of an alkyl-substituted succinic acid and (B) from 0.005 to 5% by weight of a fatty acid ester of a polyhydric alcohol, wherein the base oil contains 0.5% by weight or less of sulfur.

The lubricating oil composition of the present invention has good friction characteristics, or in particular, a small (coefficient of static friction)/(coefficient of dynamic friction) ratio and gives little shift shock. In addition, the change in friction characteristics depending on oil temperature is small, and the change with time is also small, so that it is fully adaptable to the trend of transmissions and the like toward compact size.

Short description of the drawing

Fig. 1 and Fig. 3 are each a graph showing the change in time of µ₀/µ₁₂₀₀ at each time up to 2000 cycles in the example and the comparative example; and Fig. 2 is a graph showing the temperature change thereof.

Best mode for carrying out the invention

The base oil used in the present invention is the main component of the lubricating oil composition, and various kinds of mineral oils and/or synthetic oils among them as used in conventional lubricating oils can be used.

The base oil should preferably have a viscosity of 1.5 to 30 x 10⁻⁶ m²s⁻¹ (centistokes) at 100ºC, and in particular those with 2 to 20 x 10⊃min;⊃6; m²s⊃min;¹ (centistokes) are preferred when used as an automatic transmission oil and a wet brake oil in agricultural tractors.

To give specific examples of the base oil, the mineral oils include Neutral Oil 60, Neutral Oil 100, Neutral Oil 150, Neutral Oil 300 and Neutral Oil 500 from solvent refining or hydrogenation refining.

On the other hand, synthetic oils include polyolefins, polyglycol esters, esters of dibasic acids, polyol esters, phosphoric acid esters, silicone oils, alkylbenzenes and alkyldiphenyls as well as condensed ring and/or non-condensed ring saturated hydrocarbons, and those mainly composed of these, used as base oil.

As a result, when a mineral oil is used as a base oil in the present invention, various ones can be used provided that the kinematic viscosity at 100°C is in the range of 1.5 to 30 x 10-6 m²s-1 (centistokes), or preferably 2 to 20 x 10-6 m²s-1 (centistokes), and those containing 0.5% by weight or less, or 0.1% by weight or less, or particularly preferably 100 ppm or less of sulfur are to be used.

Due to the reduction in oxidation stability, an excess amount of sulfur above 0.5 wt% is not preferred.

Mineral oils with a low pour point can also be used. It should have a pour point of preferably -15ºC or less, or more preferably -25ºC or less, or most preferably -35ºC or less. This is because the friction characteristics can be further improved at the same time as relaxing the limitation relative to the temperature range for use.

The preferred conditions for the mineral oil are that the aromatic hydrocarbon content (% CA) is 20 or less, or more preferably 10 or less, that the total acid value is 0.1 mg KOH/g or less, preferably 0.05 mg KOH/g or less.

Mineral oils having the properties described above can be obtained by refining a distillate (boiling point under normal pressure about 250 to 450ºC) as obtained by distillation of a paraffin-based crude oil, a mixed-based crude oil or a naphthenic-based crude oil by conventional methods or by deep dewaxing the oil thus obtained.

Distillate is understood to mean an oil obtained either by distillation at normal pressure of a crude oil or by vacuum distillation of a residual oil obtained by the normal pressure distillation of crude oil. The refining method is not critical and any of those described under (1) to (5) below may be used.

(1) The distillate is subjected to a hydrogenation treatment or, alternatively, the distillate is subjected after the hydrogenation treatment to an alkaline distillation or a sulphuric acid wash (treatment).

(2) The distillate is subjected to solvent refining or, alternatively, the distillate is subjected after solvent refining to a hydrogenation treatment, alkaline distillation or sulphuric acid washing (treatment).

(3) The distillate is subjected to a hydrogenation treatment, followed by a second hydrogenation treatment.

(4) The distillate is subjected to a hydrogenation treatment, then to a second hydrogenation treatment and then to a third hydrogenation treatment.

(5) The distillate is subjected to a hydrogenation treatment, followed by a second hydrogenation treatment and further to an alkaline distillation or sulphuric acid wash (treatment).

One of these procedures is explained below.

A starting raw material for a lubricating oil is prepared from a paraffin-based crude oil or a mixed-based crude oil by conventional methods and then subjected to a rigorous hydrogenation treatment. Undesirable components such as aromatics are removed for the lubricating oil fraction or converted into useful components. Almost all sulfur and nitrogen components are removed at the same time.

Such fractional distillation to obtain the required viscosity is carried out by means of vacuum distillation. Then a known solvent dewaxing treatment is carried out to dewax to the pour point that a common paraffin-based oil has, i.e. about -15 to -10ºC.

After the dewaxing treatment, if necessary, hydrogenation is carried out to hydrogenate the majority of the aromatic components into saturated components, thereby increasing the thermal and chemical stability of the base oil. If the mineral oil thus obtained is insufficient because the pour point is still too high, a deep dewaxing treatment can be carried out subsequently. This treatment uses a solvent dewaxing method carried out under strict conditions and a catalytic hydrogenation dewaxing method in which a zeolite catalyst is used, and paraffin (mainly n-paraffin) adsorbed by the fine pores of the catalyst is selectively decomposed under a hydrogen atmosphere to remove components that are converted into paraffin components.

The conditions for the hydrogenation treatment vary with the properties of the oil introduced. Usually, the reaction temperature is 200 to 480°C, and preferably 250 to 480°C, the hydrogen pressure is 4.9 x 10⁵ to 2.94 x 10⁷ Pa (5 to 300 kg/cm²), and preferably 2.94 x 10⁷ to 2.45 x 10⁷ Pa (30 to 250 kg/cm²), and the amount of hydrogen introduced (per kiloliter of distillate introduced) is 30 to 3000 Nm³, and preferably 100 to 2000 Nm³. In this hydrogenation treatment, catalysts are used which are prepared by depositing catalyst components such as metals of Groups VI and VIII, preferably cobalt, Nickel, molybdenum and tungsten on supports such as alumina, silica, silica-alumina, zeolite, activated carbon and bauxite by known methods. It is preferred that the catalyst is preferably subjected to preliminary sulphurisation.

As described above, after the hydrogenation treatment, the distillate is subjected to various treatments. When a second hydrogenation treatment or a further third hydrogenation treatment is applied, the treatment can be carried out under conditions within the ranges as described above. The conditions in the first, second and third stage hydrogenation treatments can be the same or different. Usually, the second hydrogenation treatment is carried out under more severe conditions than the first stage hydrogenation treatment, and the third stage hydrogenation treatment is carried out under even more severe conditions than the second stage hydrogenation treatments.

Alkali distillation is carried out as a step in which small amounts of acidic substances are removed to improve the stability of the distillate. In this alkali distillation, alkalis such as NaOH and KOH are added and vacuum distillation is carried out.

Sulfuric acid washing (treatment) is generally carried out as a finishing step of oil products, whereby aromatic hydrocarbons, particularly polycyclic aromatic hydrocarbons, olefins and sulfur compounds are removed to improve the characteristics of the distillate. In the present invention, 0.5 to 5% by weight of concentrated sulfuric acid is added to the distillate and the treatment is carried out at a temperature in the range between room temperature and 60°C, followed by neutralization using NaOH.

The above-mentioned processes (1) to (5) used in the treatment of a distillate comprise combinations of the processes described above. Of these Methods (1), (3) and (4) are particularly suitable.

The distilled oil obtained by the above treatment has the following properties: kinematic viscosity of 1.5 to 30 x 10-6 m2s-1 (centistokes) (100ºC), sulfur content of 0.5% by weight or less, and pour point of -15ºC or less. Also, the aromatic hydrocarbon content (%CA) is 20% or less, and the total acid value is 0.1 mg KOH/g or less.

The use of such a mineral acid can result in a lubricating oil composition that has a smaller (coefficient of static friction)/(coefficient of dynamic friction) ratio.

Preferred synthetic oils include polyolefins and condensed ring and uncondensed ring saturated hydrocarbons.

Among the various saturated hydrocarbons, preferred are those saturated hydrocarbons which have a cyclohexyl group and/or a decalyl group and have 10 to 20 carbon atoms. The saturated hydrocarbons which have a cyclohexyl group and/or a decalyl group are exemplified below; they are in particular 2-methyl-2,4-dicyclohexylpentane, cyclohexylmethyldecalin, 1-(methyldecalyl)-1-cyclohexylethane, 2,4-dicyclohexylpentane and isododecylcyclohexane.

The base oil can be mixed with a viscosity index improver and a corrosion inhibitor if necessary.

In the present invention, an ester of alkenyl-substituted succinic acid and/or an ester of alkyl-substituted succinic acid are used as component (A). The ester of alkenyl-substituted succinic acid or ester of alkyl-substituted succinic acid can be particularly effective when it is represented by the general formula [I] shown below.

In the above formula [I], R¹ is an alkenyl group or an alkyl group having 6 to 30 carbon atoms or preferably 12 to 24 carbon atoms.

Furthermore, R² and R³ in the above formula [I] are each hydrogen, an alkyl group having 1 to 20 carbon atoms, a hydroxyalkyl group having 1 to 20 carbon atoms or a group of the general formula

-R&sup4; - (OR⁴)n-Sx - R⁵

(wherein in the formula, R⁴ is an alkylene group having 1 to 4 carbon atoms, R⁵ is an alkyl group having 1 to 20 carbon atoms or a hydroxy-substituted group thereof, n is an integer of 0 to 6, and x is 1 or 2).

R² and R³ may be the same or different, except when R² and R³ are both hydrogen.

Specific examples of the ester of alkenyl-substituted succinic acid and the ester of alkyl-substituted succinic acid include monomethyl ester of octadecenylsuccinic acid, dimethyl ester of octadecenylsuccinic acid, monoethyl ester of octadecenylsuccinic acid, diethyl ester of octadecenylsuccinic acid, monooctyl ester of octadecenylsuccinic acid, dioctyl ester of octadecenylsuccinic acid, monononyl ester of octadecenylsuccinic acid, dinonyl ester of octadecenylsuccinic acid, monolauryl ester of octadecenylsuccinic acid, dilauryl ester of octadecenylsuccinic acid, monolauryl ester of dodecylsuccinic acid, dilauryl ester of dodecylsuccinic acid, monomethyl ester of hexadecylsuccinic acid, dimethyl ester of hexadecylsuccinic acid, monoethyl ester of Hexadecylsuccinic acid, diethyl ester of hexadecylsuccinic acid, monomethyl ester of octadecylsuccinic acid, dimethyl ester of octadecylsuccinic acid, monoethyl ester of octadecylsuccinic acid, diethyl ester of octadecylsuccinic acid, monooctyl ester of octadecylsuccinic acid, dioctyl ester of octadecylsuccinic acid, monolauryl ester of octadecylsuccinic acid, dilauryl ester of octadecylsuccinic acid, a reaction product an alkenylsuccinic acid of a propylene oligomer having 18 carbon atoms on average and a propylene glycol, a reaction product of a polybutenylsuccinic acid of a polybutene having an average molecular weight of 400 and a propylene glycol, octylmercaptan ethylene oxide ester of octadecenylsuccinic acid, octylmercaptan propylene oxide ester of octadecenylsuccinic acid, nonylmercaptan ethylene oxide ester of octadecenylsuccinic acid, nonylmercaptan propylene oxide ester of octadecenylsuccinic acid, laurylmercaptan ethylene oxide ester of octadecenylsuccinic acid, laurylmercaptan propylene oxide ester of octadecenylsuccinic acid, 5-hydroxy-3-thiapentyl ester of octadecenylsuccinic acid and 6-hydroxy-3,4-dithiahexyl ester of octadecenylsuccinic acid.

In the present invention, either one of the ester of alkenyl-substituted succinic acid and the ester of alkyl-substituted succinic acid or a mixture thereof is added as the component (A), while the amount of addition depends on the properties of the desired lubricating oil composition and cannot be definitely selected. It is from 0.05 to 5.0% by weight, or preferably from 0.1 to 3.0% by weight. No sufficient effect can be obtained with an amount of addition of less than 0.05% by weight, while an undesirable drop is caused as a concomitant phenomenon in oxidation stability with an addition of over 5.0% by weight.

Next, a fatty acid ester of a polyhydric alcohol is used as component (B) in the present invention. The polyhydric alcohol included here includes glycerin, trimethylolpropane, pentaerythritol and sorbitol, with glycerin being particularly preferred. The fatty acids include those having 8 to 30 carbon atoms, which may be either saturated or unsaturated. Specific examples of the fatty acids are pelargonic acid, lauric acid, palmitic acid, stearic acid, behenic acid, undecylenic acid, oleic acid, linoleic acid and linolenic acid. Examples of the most preferred esters are partial esters of polyhydric Alcohols such as oleic acid monoglyceride, oleic acid diglyceride, stearic acid monoglyceride and stearic acid diglyceride.

The amount of addition of the above-mentioned component (B) is 0.005 to 5% by weight, or preferably 0.01 to 3% by weight. No sufficient improvement in friction characteristics can be obtained with an amount of addition of less than 0.005% by weight. On the other hand, oxidation stability is undesirably adversely affected by addition of more than 5% by weight.

The lubricating oil composition of the present invention can be obtained in principle by mixing the above-described components (A) and (B) with the base oil, but an acid amide or a boron derivative thereof is optionally added with the aim of improving the friction characteristics and at the same time enhancing the physical properties as a lubricating oil. The acid amide is a reaction product of a carboxylic acid having 12 to 30 carbon atoms and an amine compound, and specific examples thereof are the reaction products of isostearic acid or oleic acid with diethylenetriamine, triethylenetetramine, tetramethylenepentamine and hexaethylenepentamine. Examples of the boron-containing derivatives of an acid amide are the reaction products of an acid amide and a boron compound (boric acid, salts of boric acid and esters of boric acid). Specific examples include those obtained by reacting boric acid with the above-mentioned acid amide, e.g. B. the reaction product of isostearic acid and tetraethylenepentamine. The amount of addition is 0.01 to 10% by weight, or preferably 0.05 to 3% by weight. No sufficient effect of improving the friction characteristics and no cleaning and dispersing effect can be obtained with an amount of addition of less than 0.01% by weight, while on the other hand, the addition of more than 10% by weight is undesirable because a drop in the coefficient of static friction occurs with a reduced transmission torque.

To the lubricating oil composition of the present invention If desired, an antioxidant, a detergent dispersant and a viscosity index improver may be added. As the antioxidant, there can be used those which are conventionally used, such as phenol-based compounds, amine-based compounds and zinc dithiophosphate. Representative examples are 2,4-di-tert-butyl-4-methylphenol; 2,6-di-tert-butyl-4-ethylphenol; 4,4'-methylene-bis(2,6-di-tert-butylphenol); phenyl-α-naphthylamine, dialkyldiphenylamine, zinc di-2-ethylhexyldithiophosphate, zinc diamyldithiocarbamate and pinene pentasulfide.

The amount of addition is 0.01 to 3% by weight, or preferably 0.05 to 2% by weight. No effect can be achieved with an amount of less than 0.01% by weight, while no noticeable improvement can be achieved with an amount of more than 3% by weight.

Detergent dispersants that may be used include a low ash base dispersant and a metal-based detergent. For example, alkenyl succinic imides, sulfonates and phenates are preferred. Representative examples of such preferred compounds are polybutenyl succinic imide, calcium sulfonate, barium sulfonate, calcium phenate, barium phenate and calcium salicylate.

The amount of addition is 0.1 to 10% by weight, or preferably 0.5 to 5% by weight. The dispersibility is insufficient at an amount of less than 0.1% by weight, while an amount of more than 10% by weight is undesirable because of the drop in friction characteristics.

Without being particularly limited thereto, polymethacrylates and copolymers of an olefin can be used as viscosity index improvers. Particularly preferred are the polymethacrylates having a molecular weight not exceeding 100,000, or preferably not exceeding 50,000, which have excellent shear stability and are capable of preventing any viscosity changes over a long period of time. The amount of addition is 0.5 to 15% by weight, or preferably 2 to 10% by weight. In the viscosity-temperature Characteristics, no improvement can be achieved with an amount less than 0.5 wt%, while an amount exceeding 15 wt% is undesirable because of the reduction in wear resistance and the like as a result of using a low viscosity oil.

Incidentally, the lubricating oil composition of the present invention may be mixed with a corrosion inhibitor, a rubber swelling agent and a defoamer as necessary.

The present invention will now be explained in more detail with the aid of examples.

Examples 1 and 2 and Comparative Examples 1 and 2

As a base oil, a mineral oil I having a kinematic viscosity of 5 x 10-6 m2s-1 (centistokes) at 100°C and 200 ppm sulfur containing was mixed with 4.0 wt% of a polymethacrylate (molecular weight 42,000), 4 wt% of polybutenylsuccinic acid imide (molecular weight of polybutenyl group 1,000) and 0.5 wt% of an acid amide to obtain a base oil, which was mixed with a compound in an amount shown in Table 1 to obtain a lubricating oil composition.

The lubricating oil composition thus obtained was tested by the following methods.

Friction test SAE No. 2

The friction characteristics were evaluated under the experimental conditions described below using an SAE No. 2 tester manufactured by Greening Co. (USA).

[Test conditions]

Discs: Japanese-made paper-based discs for automatic transmission (2 sheets)

Plates: Japanese-made steel plates for the automatic transmission (4 plates)

Engine speed: 3000 rpm

Thrust pressure on the piston: 3 kg/cm²

Oil temperature: 50º C, 80º C, 100º C and 120º C

The coefficient of dynamic friction at the rotation of 1200 rpm µ₁₂₀₀₀ and the coefficient of static friction at the moment of reaching the rest position µ₀ were determined under the experimental conditions described above, and µ₀/µ₁₂₀₀₀ was calculated. The change in time and the change with temperature in this µ₀/µ₁₂₀₀₀ were determined accordingly to estimate the friction characteristics.

Thus, the change in time of µ₀/µ₁₂₀₀ was determined up to 2000 cycles at an oil temperature of 100ºC. Fig. 1 illustrates the change in time of µ₀/µ₁₂₀₀ at the corresponding moments up to 2000 cycles (100, 200, 300, 400, 500, 1000, 1500 and 2000 cycles). Furthermore, the values of µ₀/µ₁₂₀₀ at 200 cycles and at 2000 cycles are listed in Table 1 as the result of the durability test.

Next, the oil temperature was varied stepwise at 50, 80, 100 and 120ºC after interrupting up to 200 cycles at an oil temperature of 100ºC, and the µ₀/µ₁₂₀₀ was determined at each temperature. The results are shown in Fig. 2. Furthermore, the values of µ₀/µ₁₂₀₀ at 50ºC and 120ºC are shown in Table 1 as the results of the temperature dependence test.

Comparison example 3

A commercial product was subjected to evaluation of friction characteristics in the same manner as in Example 1. The results are shown in Table 1, Fig. 1 and Fig. 2.

Examples 3 and 4 and comparative example 4

The lubricating oil compositions shown in Table 1 were obtained in the same manner as in Examples 1 and 2 and Comparative Examples 1 and 2 except for using a mineral oil II having the following properties as a base oil, and an examination was made. Fig. 3 shows the changes with time of µ₀/µ₁₂₀₀ at the respective moments up to 2000 cycles. Furthermore, Table 1 shows the results of the durability test and the temperature dependency test.

Properties of mineral oil II

Kinematic viscosity (100ºC): 5.0 x 10⊃min;⊃6; m²s⊃min;¹ (centistokes)

Sulfur content (ppm): 1

Pour point: - 45ºC

%CA: 0.1 >

Examples 5 to 10 and Comparative Example 5

For the lubricating oil compositions in Table 1, tests were conducted in the same manner as in Examples 1 and 2 and Comparative Examples 1 and 2. Table 1 shows the results of the durability test and the temperature dependency test. Incidentally, the base oil was blended, in the same manner as in Examples 1 and 2 and Comparative Examples 1 and 2 (in the same manner as in the other Examples and Comparative Examples), with 4.0% by weight of a polymethacrylate (molecular weight 42,000), 4.0% by weight of a polybutenyl succinic acid imide (molecular weight of polybutenyl group 1,000), and 0.5% by weight of an acid amide. Table 1 Base oil Component (wt.%) Resistance test Temp. dependency test Cycles Type*1 Comparative example Example Mineral oil synthetic oil Commercial product*1 Mineral oil I: Kinematic viscosity at 100º C 5 x 10⁻⁶ m²s⁻¹ (centistokes); sulphur content 200 ppm; pour point -17.5 C; and %CA 6 Mineral oil II: Kinematic viscosity at 100º C 5.0 x 10⁻⁶ m²s⁻¹ (centistokes); sulphur content (ppm) 1 >; pour point -45º C; and %CA 0.1 > Synthetic oil III: α-olefin oligomer (kinematic viscosity at 100ºC 4 x 10⊃min;⊃6; m²s⊃min;¹ (centistokes) Synthetic oil IV: 2-methyl-2,4-dicyclohexylpentane (kinematic viscosity at 100ºC 3.7 x 10⊃min;⊃6; m²s⊃min;¹ (centistokes) *2 A⊃1;: monolauryl ester of octadecenylsuccinic acid *3 A⊃2;: octyl mercaptan propylene oxide ester of octadecenylsuccinic acid *4 A⊃3;: 5-hydroxy-3-thiapentenyl ester of octadecenylsuccinic acid *5 B⊃1;: oleic acid monoglyceride *6 B2: Sorbitan monooleate

From Table 1 and Figures 1 to 3, it can be seen that the lubricating oil composition of the present invention has excellent friction characteristics. In particular, from the results of the temperature dependency test, it can be seen that the changes in the friction characteristics depending on the oil temperature are extremely small.

Industrial applicability

Accordingly, the lubricating oil composition of the present invention is very effective as a lubricating oil for automatic transmissions, lubricating oil for parts having a wet clutch or a wet brake in tractors.

Furthermore, the composition having such characteristics is also effective in combination as a lubricating oil in power shock absorbers, power steering, hydraulic suspensions and as a combined oil for a variety of these objects.

Claims (1)

1. Lubricating oil composition, characterized in that the base oil (A) from 0.05 to 5% by weight of an ester of an alkenyl-substituted succinic acid and/or an ester of an alkyl-substituted succinic acid and (B) from 0.05 to 5% by weight of a fatty acid ester of a polyhydric alcohol wherein the base oil contains 0.5% or less by weight sulphur.