JPWO2011161986A1 - Hydraulic fluid composition - Google Patents

Abstract

Provided is a hydraulic fluid having high stick-slip generation suppressing performance and excellent oil / water separation performance. As a lubricating base oil, glycerol stearate, preferably glycerol monoisostearate, based on the total amount of the lubricating oil, 0.01 to 10% by mass and a polyalkylene glycol having a weight average molecular weight of 5,000 to 20,000 is used as the lubricating oil. A hydraulic fluid containing 0.0001 to 0.1% by mass based on the total amount, having a kinematic viscosity at 40 ° C. of 10 to 600 mm 2 / s and a viscosity index of 80 or more.

Description

  The present invention relates to a hydraulic fluid composition having a function of suppressing the occurrence of stick-slip at a sliding portion of a hydraulic cylinder and an excellent oil / water separation performance.

  For systems that require large work energy, such as forklifts, construction machines, various dampers, injection molding machines, machine tools, press machines, and forging press work, pressurization energy of the hydraulic pump is used as kinetic energy (work energy) There are many hydraulic systems that can be converted. In the cylinder portion of such a hydraulic system, various members such as metals or metals and resins and rubber materials slide, and are lubricated with hydraulic fluid in order to perform smooth sliding thereof. In this case, if the sliding speed is extremely slow, the oil film forming capability is insufficient, the oil film breaks, and if the static friction coefficient is significantly larger than the dynamic friction coefficient, stick slip occurs on the sliding surface, and noise and vibration are generated. . This stick slip is likely to occur especially when the sliding speed is 0.01 m / s or less, and among the members, particularly when sliding between metal and rubber material, the adhesion and sliding are repeated between the members. Since this is a forward motion, the increase in the coefficient of friction and the generation of vibration are greater than in sliding between metals.

In order to suppress the occurrence of stick-slip, the oil film holding performance of only the base oil is insufficient, and usually a friction modifier that is chemically adsorbed to the sliding member and has a high effect of forming a lubricating film is added. For example, lubricating oil for internal combustion engines uses a metal-based organic compound such as molybdenum to reduce the friction coefficient, but when this is applied to hydraulic fluid, the metal component becomes sludge insoluble in the lubricating oil and the operating part There is a problem in that the service life of the device itself is shortened.
In addition, forklifts, construction machines, and arm cylinder parts of various dampers used outdoors, there is a problem that rainwater easily enters the sliding part, and the lubricating oil is emulsified to deteriorate the lubricating function.
In general, the friction modifier exerts its effect by adsorbing to the metal surface during the formation of the lubricating coating. However, since the adsorbing group has polarity, it reduces the oil-water separation performance of the lubricating oil, When mixed, it has the property of being easily emulsified.

The present applicant has proposed a lubricating oil composition for machine tools having a stick-slip resistance containing 0.05 to 10% by mass of a polycarboxylate in a lubricating base oil and also having excellent oil / water separation properties ( Patent Document 1). However, this lubricating oil has a problem that stick slip generation cannot be sufficiently suppressed in a hydraulic cylinder having a low sliding speed because the friction modifier is relatively weakly adsorbed on the metal surface.
The inventors of the present invention also use mineral oil and / or poly-α-olefin as a base oil to save energy in the hydraulic system, have a kinematic viscosity at 40 ° C. of 10 to 600 mm ² / s, and a viscosity index of 140 to 200, an olefin copolymer having a viscosity reduction rate of 0.5% or less at high temperature and high shear, a viscosity reduction rate of 0.5% or less in a shear stability test, and a molecular weight of 5000 or less is 0.1 to 10. The hydraulic fluid which mix | blended 0.01 to 10weight% of weight% and glycerol stearate was proposed (patent document 2). However, this hydraulic fluid does not have a function to suppress the occurrence of stick-slip at the sliding portion of the hydraulic cylinder, and the oil / water separation property is not sufficient.

JP 2009-221330 A JP 2008-127426 A

  The problem to be solved by the present invention is to provide a hydraulic fluid composition having high stick-slip generation suppression performance and excellent oil / water separation performance.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have surprisingly found that a lubricant base oil contains glycerol stearate and a small amount of polyalkylene glycol, thereby suppressing stick-slip suppression performance and oil-water separation performance. The inventors have found that it is possible to achieve both, and have arrived at the present invention.

That is, the hydraulic fluid composition of the present invention is a polyalkylene glycol having 0.01 to 10% by mass of glycerol stearate and a weight average molecular weight of 5,000 to 20,000 based on the total amount of lubricating oil. Is contained in an amount of 0.0001 to 0.1% by mass based on the total amount of the lubricating oil, the kinematic viscosity at 40 ° C. is 10 to 600 mm ² / s, and the viscosity index is 80 or more.

  Preferably, glycerol monoisostearate is used as the glycerol stearate, an ethylene oxide-propylene oxide copolymer is used as the polyalkylene glycol, and the polymerization molar ratio of ethylene oxide to propylene oxide (propylene oxide / ethylene oxide) is 0.5 to 0.5. It is to use 3.5.

  The hydraulic fluid of the present invention has a remarkable effect of having high stick-slip generation suppressing performance and excellent oil / water separation performance.

Hereinafter, embodiments of the present invention will be described in detail.
The hydraulic fluid composition of the present invention comprises a lubricating base oil containing specific amounts of glycerol stearate and polyalkylene glycol, and has a kinematic viscosity at 40 ° C. of 10 to 600 mm ² / s and a viscosity index of 80. That's it. The kinematic viscosity is preferably 10~460mm ² / s at this 40 ℃, 10~320mm ² / s is more preferable. When the kinematic viscosity at 40 ° C. is less than 10 mm ² / s, a sufficient oil film is not formed. On the other hand, when the kinematic viscosity exceeds 600 mm ² / s, the viscous resistance becomes too large and the use energy of the hydraulic system increases. Further, the viscosity index is preferably 90 or more, more preferably 100 or more, and the higher the viscosity index, the more preferable, but generally 250 or less is sufficient. If the viscosity index is less than 80, depending on the operating temperature, the driving ability at the time of start-up decreases.

[Lubricant base oil]
The base oil used in the hydraulic fluid of the present invention is the main component of the lubricating oil. If it is used as a normal lubricating base oil, mineral oil, synthetic oil, or a mixture thereof can be used. Either can be used.
The physical properties of the lubricating base oil, kinematic viscosity, pour point, it is important, such as flash point, kinematic viscosity is preferably 10~600mm ² / s at 40 ° C., 20 to 300 mm ² / s is more preferable. The pour point is preferably −5 ° C. or lower, more preferably −10 ° C. or lower. Furthermore, the viscosity index is preferably 80 or more, and more preferably 100 or more.

These physical properties greatly affect the physical properties of the hydraulic fluid as the final product, so that the physical properties required for the use of the final lubricating oil product can be obtained. Since the lubricating base oil is a main component that accounts for 80% or more, and in some cases 90% or more of the hydraulic fluid, it is preferable that the lubricating base oil has physical properties close to those of the desired lubricating oil.
In addition, if the flash point is 250 ° C. or higher, the hydraulic fluid is not a hazardous material but a flammable liquid and is easy to handle under the Fire Service Act. Accordingly, the lubricating base oil that is the main component of the lubricating oil also preferably has a flash point of 250 ° C. or higher.
In the case of a mixture of a plurality of lubricating base oils, as long as the mixture satisfies the above physical properties, it can be used even if the individual base oils before mixing are out of the physical property range.

  Examples of the mineral oil-based lubricating base oil include lubricating oil fractions obtained by purifying distillate obtained by subjecting crude oil to atmospheric distillation or further distillation under reduced pressure by various purification processes. The refining process includes hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, clay treatment, etc., and these can be combined in an appropriate order to obtain the base oil of the present invention. . A mixture of refined oils having different properties, obtained by different crude oils or distillate oils by different process combinations and sequences is also useful. Any method can be preferably used by adjusting the properties of the obtained base oil so as to satisfy the aforementioned viscosity, flash point, pour point and viscosity index.

  As the synthetic base oil, it is preferable to use a base material having excellent hydrolysis stability. For example, polyolefins such as poly-α-olefin, polybutene and copolymers of two or more kinds of olefins, polyester, Examples include alkylene glycol, alkyl benzene, and alkyl naphthalene. Of these, poly-α-olefins are preferable in terms of availability, cost, viscosity characteristics, oxidation stability, and compatibility with system components. The poly-α-olefin is more preferably a polymer such as 1-dodecene or 1-decene in terms of cost.

As the lubricating base oil, the exemplified synthetic oils can be used alone or in admixture of two or more. Furthermore, it can also be used by mixing with the mineral oil.
When using a mixture of a plurality of lubricating base oils, including synthetic base oils, if the base oil mixture satisfies the above physical properties, the individual base oils before mixing have such physical properties. Can be used even if out of range. Accordingly, the individual synthetic base oils do not necessarily satisfy the above physical properties, but are preferably within the above physical properties.

[Glycerol stearate]
The glycerol stearate of the present invention includes glycerol isostearate. That is, it is an ester of glycerol (glycerin) and stearic acid or isostearic acid. These esters include mono-, di- and triesters, and di- and triesters include complex esters of stearic acid and isostearic acid. In the present invention, any of these or a mixture of a plurality of these can be used.
In this glycerol stearate, the oily effect of the lipophilic group due to the fact that the lubricating coating can be chemically ordered is improved because the carbon chain is saturated. In the present invention, it is preferable to use glycerol monoisostearate which has a branched chain and thus improves the solubility in base oil.

  The content of glycerol stearate is 0.01 to 10% by mass, preferably 0.02 to 1% by mass, based on the total amount of the lubricating oil. When the content is less than 0.01% by mass, a sufficient stick-slip suppressing effect cannot be obtained. When the content exceeds 10% by mass, not only the effect is saturated, but also problems such as precipitation occur.

[Polyalkylene glycol]
The polyalkylene glycol of the present invention includes any one of two or more ring-opening polymers or copolymers of alkylene oxides having 2 to 4 carbon atoms, specifically ethylene oxide, propylene oxide, butylene oxide and isobutylene oxide. Can be used, but an ethylene oxide-propylene oxide copolymer is preferable, and a polymerization molar ratio of ethylene oxide to propylene oxide (propylene oxide / ethylene oxide) of 0.5 to 3.5 is more preferable, and 1.0 to 1.0 is preferable. 3.0 is particularly preferred.

The polyalkylene glycol has a weight average molecular weight (MW) of 5,000 to 20,000, preferably 6,000 to 15,000, more preferably 8,000 to 12,000. . When the weight average molecular weight (MW) is out of the range of 5,000 to 20,000, the anti-emulsification performance is not sufficiently secured, and the oil / water separation performance at the time of mixing with water is insufficient.

  The content of the polyalkylene glycol is 0.0001 to 0.1% by mass based on the total amount of the lubricating oil, but preferably 0.001 to 0.05% by mass. If the content is less than 0.0001% by mass, sufficient oil / water separation performance cannot be obtained, and if it exceeds 0.1% by mass, the oil / water separation performance is deteriorated.

In the lubricating oil of the present invention, a viscosity index improver, a pour point depressant, an antioxidant, a rust inhibitor, an antiwear agent, an extreme pressure agent, an antifoaming agent, a metal deactivator, and the like can be appropriately blended. it can.
In particular, the viscosity index improver is preferably added because it can save energy by increasing the viscosity index of the lubricating oil. For example, a PMA polymer, an olefin polymer, or an ethylene-α-olefin polymer can be used. The addition amount is preferably 0.1 to 10% by mass.
The pour point depressant is preferably a polymer having a molecular weight of 400,000 to 600,000 which is effective when added in a small amount, particularly a PMA polymer or polybutene, and its addition amount is preferably in the range of 0.05 to 0.5% by mass, The range of 0.05-0.3 mass% is still more preferable.

In addition, as the antioxidant, a phenolic antioxidant, an amine antioxidant, and the like that are generally used for lubricating oils can be appropriately blended. As the rust preventive agent, generally known additives such as metal salts such as Ca and Ba (such as sulfonates), nonionic compounds (such as sorbitan esters and nonylphenyl ethers), and succinic acid partial esters are appropriately used. Can be blended.
Furthermore, antiwear / extreme pressure agents include sulfur (zirconium disulfide, sulfurized olefin, etc.), phosphorus (tricresyl phosphate, dialkyldithiothiophosphate, etc.), organometallic (zinc dialkyldithiophosphate, etc.) Etc. A sufficient contribution to wear resistance and extreme pressure can be obtained, and it can be blended as appropriate within an economically preferable range. Examples of the antifoaming agent include silicone-based and PMA polymer-based materials, and examples of the metal deactivator include benzotriazole and thiadiazole.

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples.
As a lubricating base oil, mineral oils and synthetic oils having the properties shown in Table 1 and subjected to solvent dewaxing after hydrorefining (poly-α-olefins: mixtures of INEOS DURASYN 168 and 180, fatty acid esters: Croda EMKARATE 1700) was used.

  Glycerol monoisostearate is used as the glycerol stearate. For comparison, friction modifiers such as polycarbonate (Rhein Chemie RC8100), sulfurized ester (Dainippon Ink and Chemicals, Dailube FS-150), molybdenum dithiocarbamate (ADEKA Sakura Rube 165), etc. Was used.

The following four types of polyalkylene glycol were used.
(1) EO-PO copolymer A: ethylene oxide-propylene oxide copolymer; weight average molecular weight = 10,000, EO: PO molar ratio = 1: 2.
(2) PO-BO copolymer: propylene oxide-butylene oxide copolymer; weight average molecular weight = 8,000, molar ratio of EO: PO = 1: 1.5
(3) EO-PO copolymer B: ethylene oxide-propylene oxide copolymer; weight average molecular weight = 25,000, EO: PO molar ratio = 1: 4
(4) EO-PO copolymer C: ethylene oxide-propylene oxide copolymer; weight average molecular weight = 2,000, EO: PO molar ratio = 1: 2.

  For the trial oil, a predetermined amount of the lubricating base oil and additives shown in Table 2 were weighed in a stainless steel container and heated to 60 ° C. to uniformly dissolve the additives. In addition, in order to impart basic performance as a lubricating oil as other additives, in all Examples and Comparative Examples, 0.5% by mass of an antioxidant and 0.5% by mass of an antiwear agent are added to the base oil as basic additives. Were blended to give basic performance (antioxidation, etc.) as a lubricating oil.

<Performance evaluation>
For the prototype oil thus obtained, the kinematic viscosity and the viscosity index are 40 ° C. and 100 ° C. according to JIS K2283, and the oxidation stability is a rotary cylinder type oxidation stability test according to JIS K 2514 ( RBOT), the demulsibility was measured at 54 ° C. according to JIS K2520. Moreover, the friction test was done with the following method.
Friction test: LMW-1 testing machine using block (nitrile rubber) / ring (SUJ-2) as sliding material, load 44N, temperature 70 ° C, sliding speed 5 minutes each, 0.01m / s , 0.1 m / s, 0.6 m / s, and 1 m / s. The coefficient of friction at each speed was used as data. In addition, if chatter or abnormal vibration is observed during the friction test, it is determined that stick-slip is present when the friction coefficient partially increases or decreases when the change in friction coefficient over time is observed on the recording chart. did.
These results are shown in Table 2.

  From the results in Table 2, in Comparative Example 1 in which no friction modifier such as glycerol monoisostearate was added, stick slip occurred at a low speed condition of 0.01 m / s, and the friction coefficient was relatively high. It can be seen that it is big. On the other hand, in Examples 1 to 4 and Comparative Examples 2, 7, 8, and 9 containing glycerol monoisostearate, the friction coefficient in these low speed ranges is decreased, and the effect of stick slip suppression by the friction modifier is observed. It is done. In Comparative Example 5, various precipitation tests were not performed because brown precipitation occurred.

  While Examples 1-4 have good stick-slip suppression performance, oxidation stability performance, and oil-water separation performance, Comparative Example 2 is high in stick-slip suppression performance, but compared with Examples 1-4 in terms of oil-water separation performance. And low. In Comparative Examples 3 and 4, the stickiness lip suppression performance was inferior to that of Examples 1 to 4. Further, Comparative Example 6 has poor oxidation stability as compared with the Examples, and there is a concern that troubles may occur at an early stage in the hydraulic system due to sludge generation due to oxidation degradation during long-term use.

  In Comparative Examples 7 and 8, polyalkylene glycol having a weight average molecular weight of 25,000 or 2,000 was added, but sufficient anti-emulsification performance was not ensured, and oil / water separation performance at the time of water mixing was insufficient. Yes. Further, in Comparative Example 9, when the addition amount of polyalkylene glycol was increased to 0.5%, the oil / water separation property was deteriorated.

  As is clear from the above, by the combined use of glycerol stearate as a friction modifier according to the present invention and a polyalkylene glycol having a specific weight average molecular weight, stick-slip suppression performance, oxidation stability performance, Separation performance can be provided. By reducing the friction coefficient, it is possible to increase the added value of hydraulic fluids such as energy saving, noise, and vibration prevention that have been demanded in recent years.

  The hydraulic fluid composition of the present invention is a hydraulic system capable of converting pressure energy of a hydraulic pump into kinetic energy (work energy), for example, industrial equipment such as an injection molding machine, a machine tool, a press machine, and a forging press machine. It can be used as hydraulic fluid for hydraulic equipment and devices such as machines, construction machines, machine tools, vehicles, ships and aircraft. In particular, since the hydraulic fluid composition of the present invention is excellent in stick-slip generation suppressing performance and oil-water separation performance, it can be used for sliding parts of hydraulic cylinders such as forklifts and construction machines used outdoors or arm cylinders of various dampers. Useful for lubrication of sliding parts.

Claims (3)

To the lubricating base oil, glycerol stearate is 0.01 to 10% by mass or less based on the total amount of lubricating oil and a polyalkylene glycol having a weight average molecular weight of 5,000 to 20,000 is based on the total amount of lubricating oil. A hydraulic fluid composition containing 0.1% by mass, having a kinematic viscosity at 40 ° C. of 10 to 600 mm ² / s and a viscosity index of 80 or more.   The hydraulic fluid composition according to claim 1, wherein the glycerol stearate is glycerol monoisostearate.   The hydraulic fluid composition according to claim 1 or 2, wherein the polyalkylene glycol is an ethylene oxide-propylene oxide copolymer, and a polymerization molar ratio of ethylene oxide to propylene oxide (propylene oxide / ethylene oxide) is 0.5 to 3.5. object.