WO2008055998A1

WO2008055998A1 - Lubricating oil composition

Info

Publication number: WO2008055998A1
Application number: PCT/EP2007/062193
Authority: WO
Inventors: Yoshitomo Fujimaki; Ryuji Maruyama; Hiroyuki Tazaki; Tetsuo Wakizono
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2006-11-10
Filing date: 2007-11-12
Publication date: 2008-05-15
Also published as: JP5820558B2; JP2008120889A

Abstract

The present invention aims to offer a lubricating oil composition which is able to maintain in the lubricating oil composition a defoaming effect and excellent defoaming properties with regard to the foam on the surface of the oil which occurs because of high-speed churning. To this end the present invention provides a lubricating oil composition comprising a base oil and polydimethylsiloxanes wherein the molecular weight distribution of the polydimethylsiloxanes as measured by gel permeation chromatography (GPC) is such that the content of the log M ≥ 4.2 portion converted to polystyrene is not less than 84 % and the content of the log M ≤ 3.1 portion is not more than 3 %, and wherein kinetic viscosity at 25 °C is from 10,000 to 60,000 mm2/s.

Description

_ _

LUBRICATING OIL COMPOSITION

This invention relates to a lubricating oil composition having effective defoaming qualities.

In order to impart the ability to prevent foaming in the lubricating oil, polydimethylsiloxanes, which have excellent defoaming properties, are normally used.

The present invention relates to a .technology for effectively and stably removing the foam that occurs due to high-speed churning by dispersing a suitable amount of polydimethylsiloxanes having a specified molecular weight distribution in the lubricating oil composition.

Recently, not only cars but various kinds of machinery in industrial use have become more compact and more highly mechanised, and in tandem with that the environment in which the lubricating oils used in these machines has become more severe.

For example, as machines have become ever more compact, the lubricating oil tanks have ^'also become more compact, and the amount of oil supplied has also diminished. In addition, the trend has been that the circulating pumps have changed from gear pumps to vane pumps, and the lubricating oil has become prone to be being subject to high shear and the hold-back size of filters has become of even smaller diameter. In particular, the pore size of filters has become increasingly fine when using hydraulic high-speed response controls, in order to avoid ingress of foreign bodies from servo pumps. Further, lower viscosities have been adopted for oils with a view to economising on fuel consumption. As a result, the stresses to which oils are subject to have become greater, and the rates at which they deteriorate have increased, and so not only lubricating performance but also defoaming performance may be lost early. Specifically, unpleasant and abnormal sounds may occur because of foam being blown out of the oil tank as the oil surface rises, or cavitation due to air ingress in the high-pressure pumps. In particular, in the case of cars, with foam emanating from transmissions as the basic cause, lubricating oil may be sprayed into the engine chamber and there is a risk of fires occurring.

According to examples in the field of cars, as quality of the product increases, so increasing quietness becomes an important attribute, and, as mentioned above, if unpleasant and abnormal noises occur in transmissions, not only does the commercial value of the car itself decrease, but also foam gets into the lubricated parts and causes scorching and wear, and so from this point of view too it has become a requirement of lubricating oils that they maintain defoaming properties over a long period.

Further, according to examples in the industrial field, with a view to reducing costs, the procedure is that installations are pre-filled with oil at assembly and thoroughly tested, the oil then being tapped off from the finished .product and returned to filling tanks via filters for re-use. Under such conditions, the tendency is that it becomes harder to maintain the effect of the dimethylpolysiloxane-based anti-foaming agent, and so yet more improvement of the lubricating oil's performance is desirable .

The defoaming properties have thus increased in importance, but, under conditions of use with high speeds and high temperatures, instances have been seen where damage occurs to machinery because of unsatisfactory defoaming properties even when the lubricating oil has been assessed as satisfactory in foaming tests as stipulated in JIS K2518, which tests for foaming by blowing in air. This mismatch between the results of JIS evaluations and evaluations in actual machines has been reported, for example, in Japanese Laid-open Patent 10- 170506 (1998) . Reference should also be made to the details in

Okada Mitsuo, "Junkatsuyu no shoho" (De-foaming of lubricating oils), Abura Kagaku, Vol. 42 No. 10 (1993) pages 807-810 and Takano Nobuyuki , "Junkatsuyu no awadachi ni tsuite) " (On the foaming of lubricating oils), Junkatsu, Vol. 25 No. 4 (1980), pages 219-223 concerning general knowledge as regards defoaming properties in lubricating oils.

This invention has been based on the aforementioned considerations and offers a lubricating oil composition which is able to maintain in the lubricating oil composition a defoaming effect and excellent defoaming properties with regard to the foam on the surface of the oil which occurs because of high-speed churning.

By dint of intensive research, the inventors have discovered that dispersing a suitable amount of polydimethylsiloxanes having a specified molecular weight distribution in the lubricating oil effectively and stably removes the foam that occurs due to high-speed churning, and so have been able to perfect this invention.

In other words, this invention provides a lubricating oil composition comprising a base oil and one ore more polydimethylsiloxanes wherein the molecular weight distribution of the polydimethylsiloxanes as measured by gel permeation chromatography (GPC) is such that the content of the log M ≥ 4.2 portion converted to polystyrene is not less than 84% and the content of the log M ≤ 3.1 portion is not more than 3%, and wherein kinetic viscosity at 25⁰C is from 10,000 to 60,000 mm²/s (according to ASTM D 445, Appendix C) .

By making the molecular weight distribution of the polydimethylsiloxanes be in the range where the kinetic viscosity at 25°C is from 10,000 to 60,000 mm²/s and blending said polydimethylsiloxanes in the lubricating oil in the specified additive amount, the lubricating oil composition of this invention has a considerable effect in demonstrating stable defoaming properties even under conditions of severe foaming caused by high-speed churning .

This invention provides a lubricating oil composition which adds defoaming properties capable of resisting even high-speed churning by incorporating as a defoaming agent in the lubricating oil composition in an amount of from 3 to 20 ppm by mass, converted to Si, of polydimethylsiloxanes wherein the viscosity at 25⁰C is from 10,000 to 60,000 mm²/s and the molecular weight distribution is such the log M ≥ 4.2 portion converted to polystyrene is not less than 84% and the log M £ 3.1 portion is not more than 3%.

Also, the phenomenon of considerable deterioration of defoaming performance under severe conditions such as experienced, for example, in car transmission fluids is thought to be due to qualitative or quantitative changes in the constituents of the anti- foaming agent in the lubricating oil, and the root cause of these is thought to be increasing maldistribution of the constituents due _

to fly-off of the anti- foaming agent caused by high-speed churning, but the details are not known. Even when the foaming tests specified in JIS K2518 have been carried out on lubricating oils subject to this deterioration, they have been assessed as relatively satisfactory, and so the current problems are not reflected.

Consequently, the investigations were carried out by giving consideration to a foaming evaluation test using the undermentioned homogeniser process in place of JIS K2518, and also giving consideration to an evaluation method which accelerates deterioration of the anti- foaming agent in the lubricating oil by passing it through a filter, and it was confirmed that the lubricating oil composition of this invention exhibits ideal performance even under conditions of high temperatures and high-speed churning.

For the base oils in the lubricating oil composition of this invention mineral oils, synthetic oils and suitable mixtures thereof may be used. These mineral oils and synthetic oils are not specially limited and may be those generally used as base oils in hydraulic oils and ATFs (Automatic Transmission Fluids) .

Examples of such mineral-oil type base oils include, specifically, those where a lubricating oil fraction obtained by vacuum distillation of an atmospheric residue obtained by atmospheric distillation of crude oil is refined by carrying out one or more treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing and hydrofinishing, or wax isomerised mineral oils and lubricating oil base oils manufactured by the procedure of isomerising GTL (gas-to-liquid) waxes manufactured by methods such as the Fischer-Tropsch method. _r

- 6 -

As examples of synthetic oils, mention may be made of poly-α-olefins (PAO), α-olefin copolymers, polybutenes, alkylbenzenes, polyol esters, dibasic acid esters, polyoxyalkylene glycols, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, hindered esters and silicone , oils . As mentioned above, these synthetic oils may be used alone or in mixtures of two or more kinds, and it is also possible to use synthetic oils in combination with mineral oils. The aforementioned base oils are used under conditions where churning occurs at high speeds, and because it is desirable, from the standpoint of reducing churning resistance, to have lubricating oils with a relatively low viscosity, the ideal ones are normally those where the kinetic viscosity at 100⁰C is in the range of from 1 to 50 mm²/s, and particularly 2 to 10 mm²/s (according to ASTM D 445) . Also, since those that have small viscosity changes in respect of temperature changes are preferred, the viscosity index (VI) is preferably from 130 to 200 (according to ASTM D2270) .

From the standpoint of oxidative stability, the %C_A of these base oils is preferably not more than 20, and more preferably not more than 10. Also, whilst there is no special restriction on the pour point, which is a measure of low-temperature flow characteristics, those with -1O⁰C and below are preferred, and particularly preferred are those of -15⁰C and below.

The polydimethylsiloxane anti-foaming agents which are constituted in the lubricating oil composition of this invention are expressed by the following Formula (I) . Formula 1

C H ₃ C H :, C H s

1 1 1 .

C H J - S i - 0 '(- S i - O -)- S i - C H . ^{• • • (} I )

I I . t

C H ₃ C H ₃ C H ,

(In the aforementioned formula, n is a positive integer . )

The aforementioned polydimethylsiloxanes preferably have a kinetic viscosity at 25°C of from 10,000 to 60,000 mm²/s. Further, if those where the molecular weight distribution is such that the log M ≥ 4.2 portion converted to polystyrene is not less than 84% and the log M ≤_ 3.1 portion is not more than 3% are used as the defoaming agent, excellent defoaming properties are exhibited even in respect of high-speed churning.

These polydimethylsiloxanes may be used singly or in combinations of two or more kinds having different viscosities provided the aforementioned molecular weight distribution can be satisfied. As to the amount used thereof, they are blended into the base oils in the proportion of from 3 to 20 ppm by mass, converted to Si, taking the total mass of the composition as the criterion. If the amount is less than 3 ppm by mass, there may be no defoaming effect, and if it exceeds 20 ppm by mass there may instead be deleterious effects on the defoaming effect such as clouding of the lubricating oil composition. The range of from 6 to 10 ppm by mass is even more preferred.

The lubricating oil composition of .this invention is obtained, as mentioned above, by blending polydimethylsiloxanes with the base oils, but it is also possible, depending on the application of the lubricating oil, to incorporate, as appropriate and within a range that will not impair the objective of this invention, already known additives such as metallic detergents, ashless dispersants, anti-oxidants, friction modifiers, metal deactivators, viscosity index improvers and pour- point depressants normally used in order to improve other characteristics .

These further additives are preferably used normally within the range of from 0.05 to 25% by mass based on the total mass of the composition. When blending the polydimethylsiloxanes with the lubricating oil, it is easier to make adjustments if they are incorporated after having first been diluted and dispersed in a solvent, so reducing the amounts added to the minimum. The diluting solvent is used by adding the necessary amount of solvent to the polydimethylsiloxanes and dissolving completely by stirring with a mixer.

Adjustment of the concentration is easier by using the solutions, and it is possible to store the dilutions made subject 'to preventing dehomogenisation of the concentrations of these dilutions.

The aforementioned solvents used for dilution and dispersion dissolve the polydimethylsiloxanes and are selected so that they readily do the dissolving while not having any detrimental effect on the characteristics of the finished product.

As examples of these solvents mention may be made of the kerosenes stipulated in JIS K2203.

It is also possible to disperse the polydimethylsiloxanes more finely by raising the oil temperature when adding, and by adding small amounts of diluted solution at a time under a suitable stirring regime . ^

A lubricating oil composition prepared by such means is able to exhibit a defoaming effect effectively because the polydimethylsiloxanes are more finely dispersed in the lubricating oil composition, and even where the same amount is added the number of particles increases, with the result that the probability they will come into contact with foam emanating from the lubricating oil composition increases.

The lubricating oil composition of this invention may be used for example in gear oils, automatic transmission fluids, CTV automatic transmission fluids, hydraulic oils and engine oils. Tests using the homogeniser process

As mentioned above, the inventors have conceived a method for a foaming test using a homogeniser process in place of the foaming test of JIS K2518. It is explained in detail below. Test apparatus

Figure 1 shows an example of the test apparatus for the homogeniser process. In consequence, any apparatus having similar functions can be used in order to evaluate the lubricating oil of this invention. Referring to Figure 1 in order to explain the test apparatus, the test apparatus comprises a homogeniser 1 (for example, Ultra- Turaax T25 manufactured by IKA^® Labortechnik Co. Ltd.), a generator shaft 2 (for example, S-25N-25F manufactured by IKA^® Labortechnik Co. Ltd.), a thermocouple 3 (K type and so on, capable of measuring up to at least 140⁰C) , a cylinder 4 (for example, of glass, calibrated (at each lmm) at heights 20 ~ 160 mm, internal diameter 0 36 mm, thickness 2 mm, height 200 mm; calibration measures height of liquid level (mm) , readings are not volume (mml) ) , a clamp 5 (for fixing the cylinder) , a heater 6 (having sufficient electrical capacity so that when oil is fed into the aforementioned cylinder it is heated to a temperature of 14O⁰C), a laboratory jack 7 (supports the aforementioned heater and is capable of being raised and lowered; when the oil temperature is close to the test temperature, since fine control is difficult by means of the heater output alone, control is effected by raising or lowering the heater but in such manner that it does not come into direct contact with the cylinder; at the moment of measurement, the heater is lowered in order to ascertain the amount of heat generated by churning) , and stands 8, 9 (capable of fixing the homogeniser and cylinder) . Experimental procedure Specimen oil is drawn into the cylinder at room temperature up to a calibration level of 55 mm (corresponding to a volume of 62.5 ml) , with the disposition as shown in Figure 1. The position of the homogeniser is set so that the tip of the generator shaft is at a calibration level of 20 mm. The tip of the thermocouple is then fixed so that it is immersed to approximately 1 cm below the oil surface. In order to raise the temperature of the specimen to the measurement temperature, , the homogeniser is made to churn at 8000 min^"1 while heating by means of the heater. For fine control of the temperature, apart from the electrical controls of the heater the laboratory jack is raised and lowered to create a gap between cylinder and heater, and the specified target measurement temperature is maintained by regulating that distance. The homogeniser is shut down, and the oil level at that measurement temperature is recorded in mm units, and then the homogeniser is run again at 8000 min^"1. Once it is ^

confirmed that the specified measurement temperature has been reached, the heater is taken away, the homogeniser is temporarily shut down, and the amount of foam on the surface of the oil is read off in mm units. The speed is then adjusted to 20000 min^"1 and the homogeniser is allowed to churn for 1 minute. The position of the foaming level three seconds after shutdown is read off. Because of the uniformity of the temperature, the amount of foaming generated by the procedure of churning at 8000 min^"1 is normally a value of 2 mm or less immediately after shutdown of the homogeniser, and so there is no impact on the results of the foaming test.

The amount of foaming is calculated by means of the following formula. Mathematical Formula 1

Reading of foaming level after churning (mm) - reading of oil level before churning (mm) = amount of foaming (mm) Measurement conditions and evaluation criteria Measurement was under the temperature conditions of

12O⁰C and 130⁰C, higher than the measurement temperature of 93.5°C in JIS K2518 Sequence 2. Taking as the criterion the value when the amount of foaming is measured by means of the foaming test method using this homogeniser process for a lubricating oil with no anti- foaming agent added, the evaluation was that there was a defoaming effect when an improvement of 20% or more than this criterion was observed.

Table 1 shows the pass-fail evaluation lines at 120⁰C and 130⁰C taking as a criterion the lubricating oil with no anti-foaming agent added as given in the undermentioned Table 4. For reference, the measurement values of JIS K2518 Sequence 2 are appended. Table 1 : Evaluation lines for defoaming effect at 120⁰C and 130⁰C

Examples

The invention is further explained in detail below by means of examples of embodiment, but the invention is in no way limited to these examples.

A molecular weight distribution analysis using gel permeation chromatography (GPC) was effected for the six kinds (A-F) of polydimethylsiloxane shown in Table 3.

In the gel permeation chromatography (GPC) test, measurements were carried out for the anti-foaming agents A-F under the conditions show in Table 2 below, taking as the measurement liquid a liquid with the specimen adjusted to a 0.2% solution with the mobile phase (THF) . - -

Table 2: GPC measurement conditions

Table 3 : Molecular weight distributions

Molecular weight is polystyrene-conversion value

The aforementioned anti-foaming agents A-F were added to the lubricating oil without anti- foaming agent as specified in Table 4 below, to prepare Examples 1 and 2 and Comparative Examples 1-4. A foaming test using the homogeniser process and the foaming test of JIS K2518 were carried out on these specimen oils. The results are given in Table 5. Table 4 : Composition and properties of lubricating oil with no anti-foaming agent added

Table 5 : Results of evaluation of specimen oils

Ul

Note: The entries for the JIS foaming test are the reading (ml) immediately after completion of the test and the reading (ml) 10 minutes later, in the form 50-0. The criterion is set at a value of 20% improvement over the results of the tests for the lubricating oil without anti-foaming agent.

As can be seen from the results given above, Comparative Example 4 is a pass as an anti-foaming agent in JIS K2518 but a fail as an anti-foaming agent in the homogeniser test.

In order to carry out an accelerated deterioration test on the specimen oils, they were passed through the filter described below, and a test of their defoaming properties was carried out after filtering. Using a filter (made of mix cellulose, 0 47 mm, particle retention size 0.8 μm, diameter, Advantek product) and using the apparatus of JIS B9931 "Procedure for measuring operating oil contamination by the weighing method", the specimens oils were filtered and the filtered liquid collected to give the specimen oil after filtering.

After the first filtering in which 200 ml of specimen oil was passed through the aforementioned filter, the filter was changed and a second filtering was carried out, then a foaming test (homogeniser process) was carried out on the specimen oils. The results are given in Table 6. Table 6 : Results for specimen oils after filtering

(JIS K2518 foaming test Sequence 2, homogeniser process)

As can be seen from the results of the homogeniser test, it does not mean it is all right just because the kinetic viscosity of the anti-foaming agent is high. Also, there are cases where there is a detrimental effect even when an anti-foaming agent is added. The results have no correlation with JIS K2518, and the results are good if an anti-foaming agent is added even in lubricating oils treated by filtering.

The examples of embodiment exhibited extremely good defoaming performance in comparison with the comparative examples at high temperatures (120-130⁰C) .

The effect may vary even with anti-foaming agents of the same kinetic viscosity, and it can be seen that only polydimethylsiloxane anti-foaming agents having the molecular weight distribution of this invention exhibit good results. Brief Explanation of Drawings

Figure 1 shows the experimental apparatus in the homogeniser test. Explanation of Symbols

1 Homogeniser

2 Generator shaft

3 Thermocouple

4 Cylinder 5 Clamp

6 Heater

7 Laboratory jack 8, 9 Stands

Claims

C L A I M S

1. A lubricating oil composition comprising a base oil and one or more polydimethylsiloxanes, wherein the molecular weight distribution of the polydimethylsiloxanes as measured by gel permeation chromatography (GPC) is such that the content of the log M ≥ 4.2 portion converted to polystyrene is not less than 84% and the content of the log M ≤ 3.1 portion is not more than 3%, and wherein kinetic viscosity at 25°C is from 10,000 to 60,000 mm²/s.

2. A lubricating oil composition according to Claim 1 wherein the one or more polydimethylsiloxanes are used as an anti-foaming agent and are present in an amount of from 3 to 20 ppm by mass, as converted to Si, based on the total mass of the lubricating oil composition.

3. A lubricating oil composition according to Claim 1 or 2 wherein the kinetic viscosity at 100⁰C is from 1 to 50 mm²/s

4. A lubricating oil composition according to any of the Claims 1-3, wherein the viscosity index (VI) is from 130 to 230.

5. Use of the lubricating oil composition according to any of Claims 1-4 as a gear oil, automatic transmission fluid, CVT automatic transmission fluid, hydraulic oil or engine oil .

6. Method of improving defoaming properties by using the lubricating oil composition according to any one of Claims 1-4.