JP5820558B2 - Lubricating oil composition - Google Patents

Description

  The present invention relates to a lubricating oil composition having effective antifoaming properties. In general, polydimethylsiloxane having excellent antifoaming property is used for lubricating oil in order to impart antifoaming performance. In the present invention, an appropriate amount of polydimethylsiloxane having a specific molecular weight distribution is dispersed in the lubricating oil. The present invention relates to a technique for effectively and stably removing bubbles generated by high-speed stirring.

  Recently, various machines for industrial use including automobiles have become small and highly efficient machines, but the use environment of lubricating oil used in the machines has become severe.

  For example, as machinery becomes more compact, lubricating oil tanks will be smaller and the total amount of oil will be reduced. Further, instead of the gear pump instead of the vane pump, the lubricating oil is likely to be subjected to high shear, and the holding size of the filter tends to be reduced. Especially with the high-speed response control of the hydraulic system, the pore size of the filter used is becoming finer to prevent the foreign matter of the servo valve from getting caught. In addition, low oil viscosity has been introduced to save fuel. As a result, the stress received by the oil is increased, the deterioration rate is increased, and not only the lubrication performance but also the defoaming performance is quickly lost.

  Specifically, unpleasant abnormal noise or the like is generated by blowing bubbles from the oil tank when the oil level rises or by cavitation due to air entrainment in the high-pressure pump. In particular, in the case of an automobile, bubbles generated from the transmission may cause the lubricating oil to be ejected into the engine compartment, resulting in a risk of fire.

  In the field of automobiles, noise reduction has become an important issue as quality is improved. If unpleasant abnormal noise is generated from the transmission as described above, not only the commercial value of the automobile itself decreases. Since the foam is caught in the lubrication part and seizes and may be worn, the oil is required to maintain the defoaming property for a long time from this point.

  Also, in the case of a machine manufacturing factory in the industrial field, from the viewpoint of cost saving, filling oil can be extracted from a product that has been filled when the equipment is assembled and subjected to a completion test, and then returned to the filling tank via a filter for reuse. It is getting done. Under such circumstances, the effect of the dimethylpolysiloxane-based antifoaming agent tends to be difficult to sustain, and further improvement in the performance of the lubricating oil is desired.

  As described above, the defoaming property is increasing in importance. However, under the use conditions of high speed rotation and high temperature, the lubrication judged to be good in the foaming test defined in JIS K2518 in which air is blown and tested. Even with oil, examples of equipment damage due to poor defoaming properties have come to be seen. For example, Patent Document 1 reports that the result of the JIS evaluation does not match the evaluation with the actual machine.

Moreover, since the general knowledge about the defoaming property of lubricating oil is detailed in a nonpatent literature 1 and 2, please refer.
JP-A-10-170506 Mitsuo Okada, “Defoaming of Lubricating Oil”, Oil Chemistry, Vol. 42, No. 10 (1993), pages 807-810 Nobuyuki Takano, “About foaming of lubricating oil”, Lubrication, Vol. 25, No. 4 (1980), pp. 219-223

  The present invention has been made from the above viewpoint, and in a lubricating oil composition, an object of the present invention is to provide a lubricating oil composition capable of maintaining an antifoaming effect and excellent defoaming properties against bubbles on the oil surface generated by high-speed stirring. Is.

  As a result of intensive studies, the present inventors have found that bubbles generated by high-speed stirring can be effectively and stably removed by dispersing an appropriate amount of polydimethylsiloxane having a specific molecular weight distribution in the lubricating oil. Completed the invention.

That is, the present invention is a lubricating oil composition comprising a base oil and polydimethylsiloxane, wherein the molecular weight distribution of the polydimethylsiloxane is measured by gel permeation chromatography (GPC) and log M ≧ 4.2 parts in terms of polystyrene. The lubrication is characterized in that the content of N is 84% or more, the content of log M ≦ 3.1 part is 3% or less, and the kinematic viscosity at 25 ° C. is 10,000 to 60,000 mm ² / s. In the oil composition.

The lubricating oil composition of the present invention has a molecular weight distribution of polydimethylsiloxane having a kinematic viscosity at 25 ° C. of 10,000 to 60,000 mm ² / s in a specific range, and lubricates the polydimethylsiloxane with a specific addition amount. By blending in oil, it has a remarkable effect of exhibiting a stable defoaming property even under severe foaming conditions with high-speed stirring.

In the lubricating oil, the part of the lubricating oil having a viscosity at 25 ° C. of 10,000 to 60,000 mm ² / s and a molecular weight distribution of logM ≧ 4.2 in terms of polystyrene is 84% or more and logM. ≦ 3.1 By blending 3 to 20 mass ppm of polydimethylsiloxane with 3% or less in terms of Si, a lubricating oil composition having defoaming properties that can withstand high-speed stirring is obtained. .

  In addition, for example, the remarkable deterioration phenomenon of the defoaming performance under severe conditions such as automatic transmission oil is considered to be due to the quantitative or qualitative change of the defoaming agent component in the lubricating oil. As such, it is conceivable to collect the antifoaming agent by a strainer (filter) equipped in the lubricating oil circulation line, or to disperse the components by scattering the antifoaming agent by high-speed stirring, but the details are unknown. When this deteriorated lubricating oil is subjected to a foaming test described in JIS K2518, it is evaluated that the defoaming property is rather good and does not reflect the current problem.

  Therefore, a foaming test by a homogenizer method, which will be described later, is devised as a foaming evaluation method in place of JIS K2518, and an evaluation method by passing through a filter is devised and studied as an accelerated test for defoaming agent deterioration of lubricating oil. It was confirmed that the oil composition showed optimum performance even under conditions where high temperature stirring was performed at a high temperature.

  As the base oil in the lubricating oil composition of the present invention, mineral oil, synthetic oil, and appropriate mixtures thereof are used. The mineral oil or synthetic oil is not particularly limited as long as it is generally used as a base oil such as hydraulic oil or ATF.

  Specifically, these mineral oil base oils include the solvent oil removal, solvent extraction, hydrocracking of the lubricating oil fraction obtained by distillation under reduced pressure of the atmospheric residual oil obtained by atmospheric distillation of crude oil. , Manufactured by one or more treatments such as solvent dewaxing, hydrorefining, etc., or by a method of isomerizing GTL WAX (Gas Liquid Wax) produced by wax isomerized mineral oil, Fischer-Tropsch process, etc. Examples thereof include lubricating base oils and the like.

  Synthetic oils include, for example, poly α-olefin (PAO), α-olefin copolymer, polybutene, alkylbenzene, polyol ester, dibasic acid ester, polyoxyalkylene glycol, polyoxyalkylene glycol ester, polyoxyalkylene glycol ether. , Hindered esters, silicone oils and the like. As described above, these synthetic oils can be used alone or in combination of two or more, and further, mineral oil and synthetic oil can be used in combination.

The above base oil is a condition that is stirred at a high speed. From the viewpoint of lowering the stirring resistance, a lubricating oil having a relatively low viscosity is desired, so that the kinematic viscosity at 100 ° C. is usually 1 to 50 mm ² / s. Particularly preferred are those in the range of ^{2 to 10} mm ² / s. Moreover, since the thing with a small viscosity change with respect to a temperature change is desired, 130-200 are desirable for the viscosity index VI.

% C _A of base oil, preferably those from the viewpoint of oxidation stability is 20 or less, preferably not more further 10 or less. The pour point, which is an indicator of low-temperature fluidity, is not particularly limited, but is preferably −10 ° C. or lower, particularly preferably −15 ° C. or lower.

  The anti-foaming agent polydimethylsiloxane constituting the lubricating oil composition of the present invention is represented by the following formula (I).

(In the above formula I, n is a positive integer.)
The polydimethylsiloxane preferably has a kinematic viscosity at 25 ° C. of about 10,000 to 60,000 mm ² / s. Furthermore, when the molecular weight distribution is such that a part with a log M ≧ 4.2 in terms of polystyrene of 84% or more and a part with a log M ≦ 3.1 of 3% or less is used as an antifoaming agent, excellent high-speed stirring can be achieved. Defoaming properties are shown.

  These polydimethylsiloxanes can be used alone or in combination of two or more having different viscosities as long as the above molecular weight distribution can be satisfied.

  About the usage-amount, it mix | blends with base oil in the ratio of about 3-20 mass ppm in Si conversion on the basis of the composition total mass. If the amount is less than 3 ppm by mass, the defoaming effect may not be obtained. If the amount exceeds 20 ppm by mass, the lubricating oil composition may become turbid. More preferably, it is the range of about 6-10 mass ppm.

  The lubricating oil composition of the present invention can be obtained by blending a polydimethylsiloxane component with a base oil as described above, and further, a metal that is usually used for improving its properties depending on the use of the lubricating oil. Well-known additives such as system detergents, ashless dispersants, antioxidants, friction modifiers, metal deactivators, viscosity index improvers, pour point depressants, etc. within a range that does not impair the purpose of the present invention. It can mix | blend suitably.

  These additional additives are usually preferably in the range of about 0.05 to 25% by mass based on the total mass of the composition.

  When the above-mentioned polydimethylsiloxane is blended in a lubricating oil, since the addition amount is extremely small, it is easy to prepare it by diluting and dispersing in a solvent in advance.

  This dilute solution is a solution obtained by adding a necessary amount of solvent to polydimethylsiloxane and stirring it completely with a stirrer.

  The concentration can be easily adjusted by using the solution, and the diluted solution prepared by preventing the concentration of the diluted solution from becoming uneven can be stored.

  The diluting / dispersing solvent is selected so as to dissolve polydimethylsiloxane and dissolve easily, and does not adversely affect the product properties.

  Examples of such a solvent include kerosene defined in JIS K2203.

  In addition, the polydimethylsiloxane can be finely dispersed by increasing the oil temperature and adding the diluted solution little by little at the time of addition.

  The lubricating oil composition produced by such an operation is generated from the lubricating oil composition as a result of an increase in the number of particles even with the same addition amount because the polydimethylsiloxane is finely dispersed in the lubricating oil composition. The probability of coming into contact with the foam is increased, whereby the defoaming effect can be effectively exhibited.

  The lubricating oil composition of the present invention can be used in, for example, gear oil, automatic transmission oil, CVT automatic transmission oil, hydraulic working oil, engine oil, and the like.

<Test by homogenizer method>
As described above, the present inventors have devised a foaming test method based on a homogenizer method as a foaming test method instead of the JIS K2518 foaming test method, and will be described in detail below.

(Test equipment)
FIG. 1 shows an example of a homogenizer test apparatus. Therefore, a device having a similar function can be used to evaluate the lubricating oil of the present invention. The test apparatus will be described with reference to FIG. 1. The test apparatus includes a homogenizer 1 (for example, Ultra-Turaax T25 manufactured by IKA ^(R) Labortechnik, a generator shaft 2 (for example, S-25N- manufactured by IKA ^(R) Labortechnik ^). 25F), thermocouple 3 (K type, etc., capable of measuring up to at least 140 ° C.), cylinder 4 (for example, made of glass with a scale of 20 to 160 mm in height (every 1 mm), inner diameter φ36 mm, thickness 2 mm, height 200 mm. (The reading is not volume (mml).) Clamp 5 (for fixing the cylinder) Heater 6 (When oil is put into the cylinder, the oil temperature is heated to 140 ° C. Lab jack 7 (with the above heater mounted and can be raised and lowered) If the oil temperature is close to the test temperature, it is difficult to make fine adjustments with just the heater output. Adjusting the heater so that it does not come into direct contact with the cylinder, it is composed of stands 8 and 9 (which can fix the homogenizer and cylinder).

(Test procedure)
Sample oil is sampled at a room temperature to a position of 55 mm (corresponding to a volume of 62.5 ml) at room temperature and arranged as shown in FIG. Adjust the position of the homogenizer so that the tip of the generator shaft is at a cylinder scale of 20 mm. At this time, the thermocouple tip is fixed so as to be immersed about 1 cm below the oil surface. In order to raise the temperature of the sample to the measurement temperature, the sample is heated with a heater while stirring the homogenizer at 8000 min ⁻¹ . In addition to electrical control of the heater for fine adjustment of the temperature, the lab jack is raised and lowered to create a gap between the cylinder and the heater, and the distance is adjusted to maintain the target measurement temperature. Stop the homogenizer and record the oil level position at the measurement temperature in mm. Then, stir the homogenizer again at 8000 min ⁻¹ and confirm that it has reached the predetermined measurement temperature. Remove the heater and remove the homogenizer. Stop and read the amount of foam on the oil level in mm, then run at 20000 min ^-1 and stir for 1 minute. Record the position of the foaming surface 3 seconds after stopping. The amount of foam generated by the operation of stirring at 8000 min ⁻¹ for uniforming the temperature usually takes a value of 2 mm or less immediately after stopping the homogenizer, and does not affect the defoaming test result.

  The amount of foaming at the test temperature is

Calculated by

(Measurement conditions and criteria)
Measurement is performed under the temperature conditions of 120 ° C. and 130 ° C. higher than the measurement temperature of 93.5 ° C. in JIS K2518 sequence 2. Defoaming additive-free lubricating oil has the effect of the antifoaming agent when the foaming amount measured by the foaming test method by the homogenizer method is used as a reference value, and an improvement of 20% or more is seen from this reference value. And evaluate.

  Table 1 exemplifies the pass / fail judgment lines at 120 ° C. and 130 ° C. with reference to the antifoam additive-free lubricant shown in Table 4 below. For reference, the measurement results of JIS K2518 Sequence 2 are also included.

  Examples The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

  Molecular weight distribution analysis was performed on six types (A to F) of polydimethylsiloxanes shown in Table 3 using gel permeation chromatography (GPC).

  In the test for gel permeation chromatography (GPC) measurement, a solution obtained by adjusting a sample to a 0.2% solution with a mobile phase (THF) was used as a measurement solution, and the antifoaming agents A to F were measured under the conditions shown in Table 2 below. Went.

  The above antifoaming agents A to F are added to the antifoam additive-free lubricating oil shown in Table 4 below to prepare Examples 1 and 2 and Comparative Examples 1 to 4, and these sample oils are foamed by the homogenizer method. The test and the JIS K2518 foaming test were conducted. The results are shown in Table 5.

  As can be seen from the results of Comparative Example 4 above, it can be seen that there are antifoaming agents that pass in JIS K2518 but fail in the homogenizer test.

    For the accelerated deterioration test of the sample oil, the sample oil was passed through the filter shown below, and the defoaming property was tested for the filtered sample oil.

  Using a filter (mix cellulose cellulose φ47mm retention particle size 0.8μm Advantech product), using JIS B9931 "Measurement method of hydraulic oil contamination by mass method", filter the sample oil and collect the filtrate And it was set as the sample oil after filtration.

  For filtration, 200 ml of sample oil was passed through the above filter for the first time, and the foam was tested (homogenizer method) for the sample oil that was filtered twice with the filter replaced. The results are shown in Table 6.

As can be seen from the results of the homogenizer test, it does not mean that the kinematic viscosity of the antifoaming agent is high. In addition, there is an example in which even if an antifoaming agent is added, it is deteriorated. The result does not correlate with JIS K2518, and even if the lubricating oil is subjected to a filtration treatment, a good result is obtained if an antifoaming agent is added.
The examples showed significantly better defoaming performance at higher temperatures (120 to 130 ° C.) than the comparative examples.

  It can be seen that the anti-foaming agents having the same kinematic viscosity have different effects, and that only the polydimethylsiloxane defoaming agent having the molecular weight distribution of the present invention gives good results.

The homogenizer test apparatus is shown.

Explanation of symbols

1 Homogenizer 2 Generator shaft 3 Thermocouple 4 Cylinder 5 Clamp 6 Heater 7 Lab jack 8, 9 Stand

Claims (1)

It can hold foreign matter up to a particle size of 0.8 μm, including base oil and polydimethylsiloxane added within a range of 3 ppm to 20 ppm by mass in terms of Si based on the total mass of the lubricating oil composition as a defoaming agent. A lubricating oil composition for an automatic transmission having a filter, wherein the molecular weight distribution of polydimethylsiloxane is measured by gel permeation chromatography (GPC) and the content of log ₁₀ M ≧ 4.2 part in terms of polystyrene is 84%. The lubricating oil composition, wherein the content of log ₁₀ M ≦ 3.1 part is 3% or less, and the kinematic viscosity of polydimethylsiloxane at 25 ° C. is 30,000 to 60,000 mm ² / s. cellulose kinematic viscosity at 100 ° C. is 1 to 50 mm ² / s, a viscosity index VI is from 130 to 230, a holding particle diameter 0.8μm said lubricating oil composition Under formula foaming test by homogenizer method scan made filter sample was filtered through a at 120 ° C. and 130 ° C.:

A lubricating oil composition characterized in that the foaming amount calculated by using the above-mentioned foaming amount is 20% or more excellent at 120 ° C. and 130 ° C. based on the lubricating oil composition to which the antifoaming agent is not added.

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