JP5577954B2 - Lubricating oil composition - Google Patents

Description

  The present invention relates to a lubricating oil composition used for lubricating oil for automobiles and the like.

  Lubricating oil used in devices such as automobiles is required to maintain high performance over a long period of time even with a small amount of oil as the device becomes smaller and has higher performance. As the performance of the lubricating oil, not only the lubricating performance but also the defoaming performance is important. The generation of bubbles not only makes the hydraulic control in the apparatus unstable, but also causes the generation of abnormal noise due to the blowing of bubbles from the oil tank and the occurrence of cavitation due to air entrainment. For example, when lubricating oil is used in a transmission of an automobile, the risk of fire is increased if the lubricating oil is ejected into the engine compartment due to the generation of bubbles. For this reason, the lubricating oil which can maintain a defoaming performance over a long term is calculated | required.

Patent Document 1 describes that (a) a polydimethylsiloxane having a kinematic viscosity at 25 ° C. of 300,000 to 1,500,000 mm ² / s and (b) a fluorination having a kinematic viscosity at 25 ° C. of 500 to 9,000 mm ² / s. A lubricating oil composition comprising polysiloxane is disclosed. This document provides a lubricating oil composition capable of maintaining excellent antifoaming properties from low to high temperatures by using a specific polydimethylsiloxane and a specific fluorinated polysiloxane in combination as an antifoaming agent for the lubricating oil composition. It will be described.

Patent Document 2 is a lubricating oil composition containing a base oil and polydimethylsiloxane, and the molecular weight distribution of polydimethylsiloxane is measured by gel permeation chromatography (GPC) and contains a log M ≧ 4.2 portion in terms of polystyrene. Disclosed is a lubricating oil composition characterized in that the amount 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 . The document includes an antifoaming effect on bubbles on the oil surface generated by high-speed stirring by including polydimethylsiloxane having a specific molecular weight distribution at a specific addition amount as an antifoaming agent for a lubricating oil composition. It is described that the defoaming property can be maintained.

Patent Document 3 describes mineral oil and / or synthetic oil, polydimethylsiloxane having a kinematic viscosity at 25 ° C. of 10,000 to 60,000 mm ² / s, 0.1 to 30 ppm in terms of Si, and a weight average molecular weight of 4,000 to 150,000. Disclosed is a lubricating oil composition containing a system antifoaming agent 60 times or more the Si equivalent amount (ppm) of the polydimethylsiloxane. In this document, the polydimethylsiloxane is diluted with kerosene, light oil or other organic solvent, and the diluted solution is stirred with a stirrer for 1 minute or more at 8,000 revolutions / minute or more than 5 minutes at 20,000 revolutions / minute or more. The above lubricating oil composition in which the average particle size of dimethylsiloxane is 0.1 μm or less is also disclosed. This document describes the defoaming and foaming in the oil by adding a constant viscosity polydimethylsiloxane and a constant molecular weight polyacrylate antifoaming agent in a certain ratio to the lubricating oil. It describes that both of defoaming can be effectively performed. Moreover, it describes that the antifoaming effect can be maintained over a long period of time by mixing polydimethylsiloxane with a diluent at high speed to make fine particles and mixing with polyacrylate antifoaming agent.

JP 2000-87065 A JP2008-120889 JP 2008-120996 A

  Usually, polydimethylsiloxane is used as an antifoaming agent for lubricating oil. Polydimethylsiloxane is insoluble in lubricating base oils such as mineral or synthetic oils. For this reason, at the time of manufacture of lubricating oil, after mixing base oil and an antifoamer, it stirs at high rotation speed using a stirrer (homogenizer), and an antifoamer is disperse | distributed in lubricating oil. (Patent Documents 1 to 3).

However, the density of the lubricating oil is generally in the range of 0.85 to 0.92 g / cm ³ , whereas the density of polydimethylsiloxane is in the range of 0.94 to 0.97 g / cm ³ , and the polydimethylsiloxane is in the lubricating oil. On the other hand, it has a high specific gravity. For this reason, even if polydimethylsiloxane is homogeneously dispersed in the lubricating oil using a homogenizer, the polydimethylsiloxane precipitates with time. Since the precipitated polydimethylsiloxane is difficult to come into contact with bubbles generated in the lubricating oil, the defoaming effect cannot be exhibited.

  As described above, the conventional lubricating oil has a problem that the defoaming effect decreases with time. Therefore, an object of the present invention is to provide a lubricating oil composition that can exhibit high defoaming performance over a long period of time.

  As a result of various studies on means for solving the above-mentioned problems, the present inventor, when producing a lubricating oil composition containing an antifoaming agent and a base oil, erased by shearing at a lower shear rate than in the prior art. By dispersing the foaming agent, it was found that the defoaming performance was improved with time, and the present invention was completed.

That is, the gist of the present invention is as follows.
(1) A lubricating oil composition containing an antifoaming agent having a kinematic viscosity at 25 ° C. of 1,000 cSt or more and a base oil, wherein a mixture containing the antifoaming agent and the base oil is 4.8 × 10 ^{3 to} 8.0 × 10 ^{3. The} lubricating oil composition, wherein the antifoaming agent is dispersed by shearing at a shear rate in the range of ³ 1 / second.
(2) The lubricating oil composition according to (1), wherein the antifoaming agent is silicone oil.
(3) The lubricating oil composition according to (2), wherein the antifoaming agent is polydimethylsiloxane.
(4) A method for producing a lubricating oil composition comprising an antifoaming agent having a kinematic viscosity at 25 ° C. of 1,000 cSt or more and a base oil,
A dispersion step of dispersing the antifoaming agent by shearing a mixture comprising the antifoaming agent and the base oil at a shear rate in the range of 4.8 × 10 ^{3 to} 8.0 × 10 ³ 1 / second;
The manufacturing method of the said lubricating oil composition containing this.
(5) The method according to (4) above, wherein the antifoaming agent is silicone oil.
(6) The method according to (5) above, wherein the antifoaming agent is polydimethylsiloxane.
(7) Before the dispersion process,
A diluting liquid preparation step for mixing a defoaming agent and a solvent to prepare a diluting liquid for the defoaming agent; and a diluting liquid for the defoaming agent and the base oil are mixed to contain the defoaming agent and the base oil. A mixture preparation step for preparing the mixture;
The method according to any one of (4) to (6), comprising:
(8) The method according to (7) above, wherein the solvent is kerosene.

  By this invention, it becomes possible to obtain the lubricating oil composition which can exhibit high defoaming performance over a long period of time.

FIG. 4 is a graph showing changes over time in foaming degree and silicon amount of the lubricating oil composition (Example 1) of the present invention. It is a figure which shows a time-dependent change of the foaming degree of a lubricating oil composition (comparative example 1) of a prior art, and the amount of silicon.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

1. Lubricating oil composition The lubricating oil composition of the present invention comprises an antifoaming agent and a base oil.
In the present specification, the “antifoaming agent” means a component having an effect of destroying (defoaming) foam generated when the lubricating oil composition is used. The antifoaming agent used in the lubricating oil composition of the present invention is preferably silicone oil, and more preferably polydimethylsiloxane. The antifoaming agent preferably has a kinematic viscosity at 25 ° C. of 1,000 cSt or more, and more preferably in the range of 1,000 to 100,000 cSt. When it is less than 1,000 cSt, aggregation of the antifoaming agent described below does not occur, and the desired defoaming effect cannot be exhibited. Therefore, by adding an antifoaming agent having a kinematic viscosity in the above range to the lubricating oil composition, it is possible to obtain a lubricating oil composition that exhibits high antifoaming performance over a long period of time.

  The kinematic viscosity of the antifoaming agent can be determined by a method defined in JIS K2283, for example.

  The antifoaming agent used in the lubricating oil composition of the present invention preferably has a concentration in the range of 10 to 30 ppm in terms of silicon (Si) mass relative to the total mass of the lubricating oil composition. If it is less than 10 ppm, the antifoaming agent is insufficient and the desired defoaming effect cannot be exhibited, which is not preferable. On the other hand, if it exceeds 30 ppm, it is not preferable because it becomes difficult to disperse it in the lubricating oil composition. By adding an antifoaming agent to the lubricating oil composition at a concentration in the above range, it is possible to obtain a lubricating oil composition that exhibits high antifoaming performance over a long period of time.

  The concentration of the antifoaming agent in terms of Si can be calculated by measuring the amount of silicon contained in the lubricating oil composition using, for example, a high frequency plasma emission spectroscopic analyzer (ICP).

In the production method described below, the antifoaming agent used in the lubricating oil composition of the present invention is a mixture containing the antifoaming agent and the base oil in the range of 4.8 × 10 ^{3 to} 8.0 × 10 ³ 1 / sec. It is preferably dispersed in the lubricating oil composition by shearing at a shear rate. By mixing under the above conditions, a lubricating oil composition that exhibits high defoaming performance can be obtained.

  In this specification, “base oil” means a component used as a main component of a lubricating oil composition. For the lubricating oil composition of the present invention, any of ordinary mineral oils, synthetic oils or mixtures thereof commonly used in the art can be used. Examples of such mineral oils include paraffinic mineral oils classified into groups 1, 2, 3 or 4 of the American Petroleum Institute (API) group category. It is preferred to use group 1 paraffinic mineral oils. Moreover, as said synthetic oil, the synthetic oil containing polyolefin, alkylbenzene, alkylnaphthalene, or organic acid, phosphoric acid, or silicate ester can be mentioned. It is preferable to use a synthetic oil containing polyolefin. By using the above base oil in the lubricating oil composition of the present invention, it is possible to obtain a lubricating oil composition that maintains lubricating performance over a long period of time.

  The lubricating oil composition of the present invention may contain various performance additives conventionally used in the art as desired. Examples of performance additives used in the lubricating oil composition of the present invention include, but are not limited to, metal detergents, dispersants, antiwear agents, pour point depressants and antioxidants. .

  In the present specification, the “metal detergent” refers to a sludge precursor that removes sludge generated when a device using a lubricating oil composition is operated at a high temperature from the surface of a metal member inside the device and is a source of sludge. Means a component that neutralizes and cleans the inside of the apparatus. In the lubricating oil composition of the present invention, an ordinary metal detergent commonly used in the art such as a metal salt of an organic acid can be used. Examples of such metal detergents include, but are not limited to, sulfonates such as Ba, Ca, and Mg, phenates, and salicylates.

  In the present specification, the “dispersant” means a component having a function of dispersing sludge and soot in the lubricating oil when the apparatus using the lubricating oil composition is operated at a low temperature. In the lubricating oil composition of the present invention, an ordinary dispersant commonly used in the art can be used. Examples of such dispersants include, but are not limited to, succinimides, succinates, and benzylamines. By using the above metal detergent and dispersant in the lubricating oil composition of the present invention, it is possible to remove or disperse sludge and soot to obtain a lubricating oil composition that maintains high lubricating performance over a long period of time. It becomes possible.

  In the present specification, the “pour point depressant” means a component that lowers the pour point of the lubricating oil composition by preventing the wax contained in the lubricating oil composition from crystallizing at a low temperature. To do. In the lubricating oil composition of the present invention, a usual pour point depressant commonly used in the art can be used. Examples of such pour point depressants include, but are not limited to, polymethacrylates, alkylated aromatic compounds, and fumarate. By using the above pour point depressant in the lubricating oil composition of the present invention, it is possible to obtain a lubricating oil composition that exhibits stable lubricating performance even at low temperatures.

  The lubricating oil composition of the present invention can be used as, but not limited to, a lubricating oil for devices such as automobile engines and automatic transmissions. Since the lubricating oil composition of the present invention exhibits a high defoaming performance over a long period of time, the use of the lubricating oil composition of the present invention in the above-described apparatus makes it possible to improve the performance and quietness of the apparatus. Can contribute.

2. Method for Producing Lubricating Oil Composition The lubricating oil composition of the present invention includes a dispersion step in which a mixture containing an antifoaming agent and a base oil is sheared to disperse the antifoaming agent in the lubricating oil composition. Can be manufactured.

  The antifoaming agent and base oil described above can be used in the production method of the present invention. Also, if desired, the various performance additives described above may be used as additional components. When using the performance additive, it may be added to the mixture containing the antifoaming agent and the base oil in the mixture preparation step or dispersion step described below. By using the above components, it is possible to produce a lubricating oil composition that exhibits high defoaming performance over a long period of time.

2-1. Diluent Preparation Process The antifoaming agent used in the production method of the present invention may be used as it is, but is diluted in advance to a desired concentration with a solvent selected from kerosene, toluene and xylene. It may be used in the form of a diluted solution. It is preferable to use kerosene. In this case, the production method of the present invention includes a dilution liquid preparation step in which the antifoaming agent and the solvent are mixed to prepare the antifoaming agent dilution before the dispersion step.

  In this step, the antifoaming agent is preferably diluted with the above solvent so that the mass ratio is 10 to 20 times the mass of the antifoaming agent. By using the diluted solution prepared under the above conditions as an antifoaming agent, the affinity for the base oil is improved, and the mixing with the base oil can be performed more uniformly.

  In this step, examples of the means for mixing the antifoaming agent and the solvent include a stirring device. Such a stirring device is not limited, but for example, a propeller mixer having a stirring blade or a homogenizer having a rotary inner blade and a fixed outer blade is preferable. In this case, the stirring speed is preferably in the range of 500 to 1,000 rpm. The stirring time is preferably 30 minutes or longer. The stirring temperature is preferably room temperature, and more preferably in the range of 10 to 30 ° C. By carrying out this step under the above conditions, it is possible to obtain a diluted solution in which the antifoaming agent is uniformly dispersed.

2-2. Mixture preparation step This step is intended to prepare a mixture containing an antifoaming agent and a base oil by mixing the antifoaming agent dilution obtained in the diluent preparation step and the base oil. To do.

  The base oil demonstrated above can be used for this process. In addition, when using the performance additive described above as an additional component, by mixing together with the antifoaming agent and the base oil, a mixture further containing the performance additive in addition to the antifoaming agent and the base oil. Can be prepared.

  This step can be carried out by mixing each component under the same conditions as in the diluent preparation step. By carrying out this step under the above conditions, a mixture containing an antifoaming agent and a base oil can be obtained.

2-3. Dispersing step The purpose of this step is to shear the mixture containing the antifoaming agent and the base oil so that the antifoaming agents are aggregated and dispersed in the lubricating oil composition.

  In the production method of the present invention, when the antifoaming agent is used in the form of a diluent, in this step, the mixture obtained in the diluent preparation step and the mixture preparation step described above can be used.

  Moreover, when using an antifoamer as it is, the mixture containing an antifoamer and base oil used at this process is prepared by mixing an antifoamer and base oil on the conditions demonstrated below. can do. In this case, in this step, the performance additive described above is mixed with the antifoaming agent and the base oil to prepare a mixture further containing the performance additive in addition to the antifoaming agent and the base oil. Can do.

  Prior art lubricating oil compositions are typically produced by shearing or stirring at high shear rates (eg, Patent Document 3). Patent Document 3 discloses that the antifoaming agent that is insoluble in the base oil is uniformly dispersed in the lubricating oil composition, thereby improving the contact probability with the foam and more effectively expressing the defoaming effect. Describe.

  However, in a lubricating oil composition produced by shearing or stirring at a high shear rate, the antifoaming agent settles and the amount of silicon in the lubricating oil composition decreases as time elapses after production. Foam performance is reduced. Antifoaming agents have a high specific gravity and are insoluble in the base oil, so they settle over time, while polar substances such as metal detergents and dispersants that cause foaming are lubricated without settling. The cause is considered to be dispersed in the oil composition.

  When the present inventor shears a mixture containing an antifoaming agent and a base oil at a lower shear rate compared to the prior art, the amount of silicon in the lubricating oil composition decreases with time, but the antifoaming We have found that the performance is rather improved. Antifoams in lubricating oil compositions are believed to be present in a cohesive form when sheared at a low shear rate. The anti-foaming agent in the form of agglomerated with each other has a strong adsorptive power to polar substances such as metal detergents and dispersants, and because of its high specific gravity with respect to the base oil, it easily settles while adsorbing polar substances. . Thus, the lubricating oil composition of the present invention, together with the antifoaming agent, polar substances that cause foaming settle together, so that the antifoaming performance does not decrease over time, but rather significantly improves. Conceivable.

In this step, the means for shearing the mixture containing the antifoaming agent and the base oil is not limited, and examples thereof include a stirring device. Such a stirring device is preferably a homogenizer having a rotary inner blade and a fixed outer blade. In this case, the shear rate is preferably in the range of 4.8 × 10 ^{3 to} 8.0 × 10 ³ 1 / second. For example, when a homogenizer having an inner blade with a radius of 30 mm and an outer blade with a radius of 30.98 mm is used, the stirring speed is preferably in the range of 1,500 to 2,500 rpm. The stirring time is preferably 5 minutes or more, and more preferably in the range of 5 to 15 minutes. The stirring temperature is preferably room temperature, and more preferably in the range of 10 to 30 ° C.

  In this specification, the “shear rate” means that when the fluid moves through the flow path, the moving speed of the fluid differs between the vicinity of the wall surface and the central portion due to frictional force with the wall surface of the flow path. It means the velocity gradient in the resulting fluid. When stirring is performed using a homogenizer having a rotary inner blade and a fixed outer blade, the shear rate can be calculated by the following calculation formula.

When the radius r (mm) of the inner blade of the homogenizer; the radius r '(mm) of the outer blade; and the rotation speed n (rpm):
Inner blade circumference a = 2πr (mm);
Gap length between inner and outer blades d = r'-r (mm);
Inner blade peripheral speed v = a × n (mm / sec);
Shear rate t = v / d (1 / second)

  By shearing the mixture containing the antifoaming agent and the base oil under the above conditions, it is possible to obtain a lubricating oil composition in which the antifoaming agent is dispersed in the lubricating oil composition in an aggregated state.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
[material]
Base oil: Group 1 mineral oil in API group category Defoamer: Polydimethylsiloxane (Kinematic viscosity at 25 ° C: 1,000 cSt or more) Diluted liquid Performance additive: Metal detergent, dispersant, antiwear agent, pour point Depressant

[Preparation of lubricating oil composition]
Example 1
After diluting polydimethylsiloxane 16 times (mass ratio) with kerosene, the mixture was stirred at 25 ° C. for 30 minutes at 500 to 1,000 rpm using a propeller mixer having a stirring blade.

  The resulting polydimethylsiloxane kerosene dilution was mixed with the base oil and performance additives. The kerosene dilution of polydimethylsiloxane was mixed so as to have a concentration of 12 ppm in terms of Si with respect to the total mass of the lubricating oil composition.

Stir the above mixture with a homogenizer (inner blade radius r: 30 mm; outer blade radius r ': 30.98 mm) at room temperature (25 ° C) for at least 5 minutes at 1,500-2,500 rpm. Thus, the lubricating oil composition of Example 1 was prepared. In this case, the shear rate is in the range of 4.8 × 10 ^{3 to} 8.0 × 10 ³ 1 / second. The shear rate is calculated as follows.

When the rotation speed is n = 1,500 rpm The peripheral speed of the inner blade v: a x n = 188.4 x 1,500 / 60 = 4,710 mm / sec Shear speed t: v / d = 4,710 / 0.98 = 4.8 x 10 ³ 1 / sec When n = 2,500 rpm Peripheral speed of inner blade v: a x n = 188.4 x 2,500 / 60 = 7,850 mm / sec Shear speed t: v / d = 7,850 / 0.98 = 8.0 x 10 ³ 1 / sec

Comparative Example 1
In the same manner as in Example 1, a kerosene dilution of polydimethylsiloxane was prepared and mixed with the base oil and performance additives. The kerosene dilution of polydimethylsiloxane was mixed so as to have a concentration of 12 ppm in terms of Si with respect to the total mass of the lubricating oil composition.

Stir the above mixture with a homogenizer (inner blade radius r: 30 mm; outer blade radius r ': 30.98 mm) at room temperature (25 ° C) for 5 minutes or more and 10,000 rpm or more. A lubricating oil composition of Comparative Example 1 was prepared. In this case, the shear rate is in the range of 3.2 × 10 ⁴ 1 / sec. The shear rate is calculated as follows.

When the rotation speed is n = 10,000 rpm The peripheral speed of the inner blade v: a x n = 188.4 x 10,000 / 60 = 31,400 mm / sec Shear speed t: v / d = 31,400 / 0.98 = 3.2 x 10 ⁴ 1 / sec

[Test 1: Foaming test of lubricating oil composition]
Measures the foaming degree of the lubricating oil compositions of Example 1 and Comparative Example 1 after standing at room temperature for a predetermined time by a foaming degree test of Sequence II (93 ± 1 ° C) defined by ASTM D892 or JIS K2518 did.

[Test 2: Silicon content measurement of lubricating oil composition]
The amount of silicon in the lubricating oil compositions of Example 1 and Comparative Example 1 after being allowed to stand at room temperature for a predetermined time was quantified using a high-frequency plasma emission spectrometer (ICP).

[Test results]
The results of Tests 1 and 2 are shown in FIG. 1 (Example 1) and FIG. 2 (Comparative Example 1), respectively.
As shown in FIG. 1, in the lubricating oil composition of the present invention (Example 1), the amount of silicon decreased with time, but the foaming degree also decreased. On the other hand, the lubricating oil composition of the prior art (Comparative Example 1) showed a decrease in the amount of silicon with the passage of time and an increase in the degree of foaming.

  Consider the above results. Prior art lubricating oil compositions are prepared by shearing at a high shear rate. For this reason, while polydimethylsiloxane does not aggregate each other and gradually settles, polar substances such as metal detergents and dispersants that cause foaming are uniformly dispersed without sedimentation. Therefore, it is considered that the antifoaming performance of the conventional lubricating oil composition has decreased with time.

  In contrast, the lubricating oil composition of the present invention is prepared by shearing at a lower shear rate compared to the prior art. For this reason, it is thought that the polydimethylsiloxane in a lubricating oil composition exists in the form aggregated mutually. Thus, the mutually agglomerated polydimethylsiloxane has a strong adsorptive power to polar substances such as metal detergents and dispersants, and easily settles in a state where the polar substances are adsorbed. Therefore, it is considered that the antifoaming performance of the lubricating oil composition of the present invention is remarkably improved even though the polydimethylsiloxane is precipitated with time.

  In the lubricating oil composition of the present invention, the antifoaming performance is remarkably improved even if polydimethylsiloxane settles with time after preparation. This makes it possible to produce a lubricating oil composition that exhibits high defoaming performance over a long period of time.

Claims (3)

Lubricating oil composition comprising an antifoaming agent which is a polydimethylsiloxane having a kinematic viscosity at 25 ° C. of 1,000 cSt or more and a base oil which is a paraffinic mineral oil classified as Group 1 of the American Petroleum Institute (API) group category A manufacturing method of
A dispersion step of dispersing the antifoaming agent by shearing a mixture comprising the antifoaming agent and the base oil at a shear rate in the range of 4.8 × 10 ^{3 to} 8.0 × 10 ³ 1 / second;
The manufacturing method of the said lubricating oil composition containing this. Before the dispersion process,
A diluting liquid preparation step for mixing a defoaming agent and a solvent to prepare a diluting liquid for the defoaming agent; and a diluting liquid for the defoaming agent and the base oil are mixed to contain the defoaming agent and the base oil. A mixture preparation step for preparing the mixture;
Including method of claim 1. 3. The method of claim 2 , wherein the solvent is kerosene.

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