JP2014055214A - Hydraulic fluid composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic fluid composition which has power saving performance, high shear stability and excellent wear resistance, and is further excellent in thermal oxidation stability and storage stability which are basic performances as an industrial hydraulic fluid.SOLUTION: There is provided a hydraulic fluid composition which comprises: (a) a hydrocarbon base oil having a kinematic viscosity at 40°C of 28 to 51 mm/s; (b) 0.06 to 3 mass% of a polymethacrylate having a weight average molecular weight of 70000 to 200000; (c) 0.1 to 5 mass% of an olefin copolymer having a weight average molecular weight of 5000 to 100000; and (d) 0.2 to 2 mass% of a phosphorus anti-wear agent.

Description

The present invention relates to a hydraulic fluid composition. More specifically, industrial hydraulic fluids used in hydraulic equipment such as construction machines, injection molding machines, and press machines that have power-saving performance, high shear stability, excellent wear resistance, and excellent storage stability. It relates to a composition.

In recent years, as a measure against global warming, reduction of carbon dioxide emissions has become an urgent task, and in the industry, efforts are being made to save energy in industrial machines and transport equipment. In Japan, the Law Concerning Rational Use of Energy and the Law Concerning Promotion of Global Warming Countermeasures were revised and implemented in 2006, and factories, transportation companies, etc. have been required to reduce power consumption more than ever. I came.

One method of reducing power consumption in the industry is to change the hydraulic fluid used in hydraulic equipment such as construction machines, injection molding machines, and press machines to a power-saving type. This method only needs to replace the hydraulic fluid with a power-saving type, and can contribute to power saving without the need for modification of the equipment. At this time, as a power saving by exchanging the hydraulic fluid, for example, it is possible to lower the ISO viscosity grade and change from ISO VG46 to a lower hydraulic fluid such as ISO VG22. If an appropriate viscosity grade is not used in the system, there is a risk of pump and actuator wear, reduced volumetric efficiency, or oil leakage from the seal.

Therefore, as an effective means for imparting power saving performance in hydraulic fluids of the same viscosity grade, for example, the same ISO VG46, a technique for reducing friction and reducing power consumption by blending a friction modifier (for example, patents) Document 1 etc.), a technique (for example, Patent Document 1 etc.) and the like that reduce piping resistance and save power by using low-density base oil are known.

Also, by adding a viscosity index improver such as an olefin copolymer to a low-viscosity base oil, a high-viscosity index hydraulic fluid is produced, and the hydraulic fluid is operated at a low temperature, such as during equipment operation or warm-up operation. A technique for reducing power consumption at the time (for example, Patent Document 2) is known.
Furthermore, among the components of industrial hydraulic equipment, hydraulic fluid flows through very narrow paths inside hydraulic pumps, various control valves such as flow rate, direction and pressure, and actuators such as cylinders and hydraulic motors. From this point of view, it is exposed to high shear conditions, so that the temporary shear viscosity under high shear conditions (hereinafter referred to as “high shear viscosity”) is reduced to save power, and a low viscosity base oil is prescribed. There are also known techniques for blending viscosity index improvers such as olefin copolymers and polymethacrylates having a molecular weight of (for example, Patent Documents 3 to 5).

However, when the viscosity of the base oil is lowered, the oil film cannot be retained, and there is a possibility that the pump and the actuator are worn. In addition, the viscosity index improver may have inferior permanent shear stability, and in that case, viscosity reduction may occur during use of the hydraulic fluid.

By the way, hydraulic fluids generally belong to the dangerous goods class 4 and are subject to regulations of the Fire Service Act for storage and management. However, the Fire Service Act was revised in 2002, and lubricating oils with a flash point of 250 ° C or higher will be classified as “designated combustible flammable liquids” except for a part, and regulations on storage and management. Was greatly relaxed. For this reason, hydraulic fluids with a flash point of 250 ° C or higher are classified as “designated combustible flammable liquids”. Therefore, they are developed and marketed as high-flash point hydraulic fluids with a flash point of 250 ° C or higher. Has been.

Here, in order to provide power saving performance, it was difficult to maintain a flash point of 250 ° C. or higher when a hydraulic fluid was prepared with a combination of a mineral oil-based low viscosity base oil and a viscosity index improver. Conversely, in order to prepare a hydraulic fluid having a flash point of 250 ° C. or higher, a base oil having a 40 ° C. kinematic viscosity of 40 mm ² / s or higher should be used from the balance of distillation properties, kinematic viscosity, and flash point. In many cases, it has been difficult to save power by lowering the viscosity of a base oil and adding a viscosity index improver.

JP 2004-250504 A JP 2008-127426 A JP 2010-215698 A JP 2010-215699 A JP 2011-46900 A

The present invention is a hydraulic fluid composition having power saving performance, high shear stability, excellent wear resistance, and excellent thermal oxidation stability and storage stability, which are basic performances as industrial hydraulic fluids. The purpose is to provide goods. It is another object of the present invention to provide a hydraulic fluid composition that can easily obtain a high flash point while having these performances.

As a result of intensive studies to solve the above problems, the present inventors have found that mineral oil base oils in a specific kinematic viscosity range, polymethacrylates in a specific weight average molecular weight range, and specific weight average molecular weight ranges The present invention was completed by blending a specific amount of the olefin copolymer and a phosphorus wear inhibitor.

That is, the present invention provides (a) a hydrocarbon base oil having a kinematic viscosity at 40 ° C. of 28 to 51 mm ² / s, and (b) a polymethacrylate having a weight average molecular weight of 70,000 to 200,000. (C) 0.1 to 5% by mass of an olefin copolymer having a weight average molecular weight of 5000 to 100,000, and (d) 0.2 to 2% by mass of a phosphorus-based antiwear agent. A hydraulic fluid composition is provided.

In addition, the present invention provides a hydraulic fluid composition further comprising (e) 0.01 to 1% by mass of a dispersant in the above hydraulic fluid composition.
Furthermore, the present invention provides the hydraulic fluid composition as described above, wherein the hydraulic fluid composition has an ISO viscosity grade of ISO VG46 and an absolute viscosity at 40 ° C. of 32 to 39 mPa · s. To do.

According to the present invention, it is possible to realize a hydraulic fluid composition having power saving performance, high permanent shear stability, excellent wear resistance, thermal oxidation stability, and storage stability. Moreover, since it is possible to save power even in a hydraulic fluid composition having a relatively high viscosity, it is easy to obtain a power saving effect even with a hydraulic fluid composition having a flash point of 250 ° C. or higher. Therefore, the hydraulic fluid composition of the present invention can be used as an industrial hydraulic fluid and can be suitably used for hydraulic equipment such as construction machines, injection molding machines, and press machines.

FIG. 1 is a schematic diagram of a power saving evaluation apparatus for evaluating the power saving performance of the hydraulic fluid composition of the present invention.

(A) Base oil The base oil used in the hydraulic fluid composition of the present invention is a hydrocarbon oil whose kinematic viscosity at 40 ° C. measured by JIS K 2283 “Kinematic viscosity test method” is 28 to 51 mm ² / s. A base oil is used, and more preferably 30 to 46 mm ² / s. The kinematic viscosity of the base oil here refers to the kinematic viscosity after mixing when two or more different base oils are mixed. That is, even a base oil having a kinematic viscosity at 40 ° C. outside the range of 28 to 51 mm ² / s is mixed with a base oil having a different kinematic viscosity, and the kinematic viscosity of the mixed base oil is 28 to 51 mm ² / s. If it is in the range of s, it can be suitably used. Hereinafter, the base oil of the present invention that is preferably used alone or in combination is referred to as a “base oil portion”. When the 40 ° C. kinematic viscosity of the base oil part is less than 28 mm ² / s, the flash point is often less than 250 ° C. from the relationship between kinematic viscosity, distillation properties, and flash point, and the volumetric efficiency of the pump is high. If it is lowered or used in a high pressure hydraulic device of 10 MPa or more, it is not preferable because the oil film becomes difficult to hold and wear resistance may be lowered. On the other hand, if the 40 ° C. kinematic viscosity of the base oil portion exceeds 51 mm ² / s, it is not preferable because ISO VG46 grade hydraulic fluid cannot be prepared.

The density of the base oil or base oil part used in the hydraulic fluid composition of the present invention is in the range of a density of 0.8200 to 0.8500 g / cm ³ at 15 ° C. measured by JIS K 2249 “Density Test Method”. And those in the range of 0.8300 to 0.8500 g / cm ³ are more preferred. In the case where the density of the base oil portion is less than 0.8200 g / cm ³ , the flash point tends to be lower than 250 ° C., or almost 100% is a paraffin content like a synthetic hydrocarbon, Since it may be inferior in solubility, it is not preferable. On the other hand, when the density of the base oil portion is larger than 0.8500 g / cm ³ , the absolute viscosity becomes high, so that the power saving performance is lowered, which is not preferable.

The base oil or base oil part used in the hydraulic fluid composition of the present invention is a distillation test (hereinafter referred to as GC) in accordance with “6. Gas chromatographic distillation test method” of JIS K 2254 “Petroleum products-distillation test method”. The initial distillation point is 350 ° C. or higher, and the 5% distillation temperature is preferably 380 ° C. or higher, and the initial distillation point is 370 ° C. or higher and the 5% distillation temperature is 390 ° C. or higher. More preferably. Since the initial boiling point in GC distillation of the base oil portion is 350 ° C. or higher and the 5% distillation temperature is 380 ° C. or higher, the flash point becomes 250 ° C. or higher when the hydraulic fluid composition is prepared. It is suitably used as the base oil part of the invention.

The base oil or base oil part used in the hydraulic fluid composition of the present invention has a percent CP of 72 to 90, a percent CN of 10 to 28, and a percent CA of 2 in ASTM D3238 “ndm ring analysis method”. Preferably,% CP is 75 to 88,% CN is 12 to 25, and% CA is 1 or less. By setting% CP to 72 or more,% CN to 28 or less, and% CA to 2 or less, it is easy to ensure a high viscosity index without increasing the addition amount of the viscosity index improver, and the density tends to decrease. Therefore, it is preferable. Further, it is preferable to set% CP to 90 or less and% CN to 10 or more because it tends to ensure the solubility of the additive.

The base oil or base oil part used in the hydraulic fluid composition of the present invention preferably has a viscosity index of 110 or more, more preferably 120 or more. By setting the viscosity index to 110 or more, the viscosity index when the hydraulic fluid composition is prepared is increased. As a result, the low-temperature viscosity is decreased, so that it is easy to reduce power consumption at low-temperature start. Further, the viscosity index of the composition can be increased as the blending amount of the viscosity index improver that is a component of the present invention is increased. However, if the viscosity index of the base oil is high, the blending amount can be suppressed. The filterability can be improved, the storage stability can be improved, and the cost can be kept low.

The base oil or base oil part used in the hydraulic fluid composition of the present invention is preferably 110 ° C. to 130 ° C., more preferably 120 ° C. to 130 ° C. in JIS K 2256 “aniline point test method”. preferable. An aniline point of 110 ° C. or higher is preferable because it tends to be a high viscosity index and a low density. Moreover, it is preferable to set the aniline point to 130 ° C. or lower because it tends to ensure the solubility of the additive. Also, from the viewpoint of ensuring compatibility with the sealing material, the aniline point needs to be in an appropriate range, and from this viewpoint, it is preferably 110 ° C to 130 ° C.

The base oil contained in the base oil portion of the hydraulic fluid composition of the present invention is not particularly limited as long as it has the above properties when used alone or in combination. As the base oil constituting the base oil portion having the above-mentioned properties, base oils mainly composed of paraffin or isoparaffin such as solvent refined mineral oil, hydrorefined mineral oil, hydrocracked mineral oil, hydrocarbon-based synthetic oil are suitable. Used for. Of these, hydrorefined mineral oil and hydrocracked mineral oil are preferably used, and hydrocracked mineral oil is particularly preferred. Although the manufacturing method of hydrorefining mineral oil and hydrocracked mineral oil is not specifically limited, As a preferable manufacturing method, the following method is mentioned. First, residual oil obtained by atmospheric distillation of crude oil is treated with a vacuum distillation apparatus. The vacuum gas oil thus obtained is hydrotreated and hydrocracked, and then a residue obtained by removing light and fuel components with a vacuum stripper is obtained. This residue is distilled under reduced pressure, and the resulting lubricating oil fraction is subjected to hydrodewaxing treatment or wax isomerization treatment and stabilization treatment. At that time, those having a high viscosity index by wax isomerization are more preferably used.

In the case where a hydrocarbon synthetic oil is used as the base oil contained in the base oil portion of the hydraulic fluid composition of the present invention, a polyα olefin is preferably used. As a suitable production example of poly α-olefin, an α-olefin having 6 to 18 carbon atoms is synthesized by low polymerization of ethylene or thermal decomposition of wax, 2 to 9 units of this α-olefin are polymerized, and hydrogenation reaction is performed. Synthesized by doing. In addition, base oils obtained by hydrocracking and hydroisomerization of raw materials such as slack wax by solvent dewaxing and wax obtained by Fischer-Tropsch synthesis, base oils such as alkylnaphthalene and alkylbenzene, etc. Aromatic hydrocarbon oils can also be suitably used. When using these hydrocarbon synthetic oils, hydroisomerized base oils of wax raw materials, and aromatic hydrocarbon oils, solvent refined mineral oils, hydrogenation to make% CP and% CN within appropriate ranges It is more preferable to use a mixture of refined mineral oil, hydrocracked mineral oil or the like.

The above-mentioned hydrocarbon base oil is used for the base oil portion of the hydraulic fluid composition of the present invention, but other than hydrocarbons such as ester oils and alkylated phenyl ether oils as long as they do not affect the effects of the present invention. These synthetic base oils can also be used. However, since synthetic base oils other than hydrocarbon base oils have a high density, when these base oils are used, it is preferable to mix them at a ratio of 30% or less of the base oil portion, and a ratio of 20% or less. More preferably, a ratio of 10% or less is more preferable, and a ratio of 5% or less is most preferable.

In the hydraulic fluid composition of the present invention, the content of the base oil part is preferably 85 to 98% by mass, more preferably 87 to 99% by mass, more preferably 87% to 99% by mass, based on the total amount of the hydraulic fluid composition. Preferably it is 90-99.5 mass%.

(B) Polymethacrylate Polymethacrylate (hereinafter sometimes referred to as PMA) used in the hydraulic fluid composition of the present invention is specifically at least one selected from compounds represented by formula (1). Copolymerized with one or more monomers selected from non-dispersed PMA or a compound represented by formula (1) and a monomer having a polar group other than an acrylic group. The dispersion type PMA obtained by this is mentioned. These PMAs can be added as a viscosity index improver previously dissolved in a base oil (also referred to as diluent oil) when used in the hydraulic fluid composition of the present invention. A viscosity index improver based on non-dispersed PMA is called a non-dispersed PMA viscosity index improver, a viscosity index improver based on dispersed PMA is called a dispersed PMA viscosity index improver, Either of them can be used, but a non-dispersed PMA viscosity index improver is preferably used.

(R ¹ in Formula (1) represents a hydrogen atom or a methyl group, and may be the same or different. R ² in Formula (1) is a linear or branched chain having 1 to 18 carbon atoms. Represents an alkyl group of
Specific examples of monomers having polar groups other than acrylic groups include nitrogen atom-containing compounds such as alkyl-vinyl pyridine, N-vinyl pyrrolidone and vinyl imidazole, and esters such as polyalkylene glycol esters, maleic esters and fumaric esters. Is mentioned. These may be used alone or in combination of two or more.

The weight average molecular weight of polymethacrylate is 70,000 to 200,000, preferably 100,000 to 180,000, and particularly preferably 120,000 to 160,000. If the weight average molecular weight is less than 70,000, the shear viscosity cannot be sufficiently lowered, and it is difficult to obtain a high power saving effect. On the other hand, if the weight average molecular weight exceeds 200,000, the permanent shear stability decreases, so it is necessary to make it 200,000 or less. The weight average molecular weight is measured by gel permeation chromatography and is a value in terms of polystyrene.

The number average molecular weight of the polymethacrylate is 20,000 to 80,000, preferably 30,000 to 65,000. It is preferable for the number average molecular weight to be 20,000 or more because the high shear viscosity can be lowered and a higher power saving effect can be easily obtained. Moreover, it is preferable for the number average molecular weight to be 80,000 or less because better permanent shear stability can be easily obtained. The number average molecular weight is measured by gel permeation chromatography and is a value in terms of polystyrene.

The above-mentioned polymethacrylate preferably has a ratio of Mw / Mn of 1.5 to 3.5, more preferably 1.9 to 3.0.
The above polymethacrylates may be used alone or in combination of two or more, and when two or more are used in combination, the respective weight average molecular weight and number average molecular weight are within the above ranges. Preferably.

The blending amount of the polymethacrylate with respect to the total amount of the hydraulic fluid composition is preferably 0.06 to 3% by mass, more preferably 0.1 to 2% by mass, and further preferably 0.15 to 1.5% by mass. %. When the blending amount is less than 0.06% by mass, the viscosity index of the hydraulic fluid composition cannot be sufficiently increased, and the temporary shear viscosity under high shear conditions cannot be sufficiently lowered, so that a power saving effect is obtained. It becomes difficult to get. In addition, since polymethacrylate has a relatively high compatibility with additives as compared with olefin copolymers, the blending amount is preferably 0.06% by mass or more from this point. On the other hand, if the blending amount exceeds 3% by mass, the permanent shear stability is deteriorated and it is difficult to ensure the solubility in the base oil.

(C) Olefin Copolymer The c) olefin copolymer (hereinafter sometimes referred to as OCP) used in the present invention is used as a viscosity index improver, and is any copolymer of different olefins. For example, the copolymer of ethylene and monomers other than ethylene is mentioned. Examples of monomers other than ethylene that form a copolymer with ethylene include olefin hydrocarbons, diene hydrocarbons, vinyl aromatics, and the like. These carbon number becomes like this. Preferably it is 3-30, More preferably, it is 3-25, More preferably, it is 3-15, Especially preferably, it is 3-8, Most preferably, it is 3-5. It is preferable for the number of carbon atoms in the monomer to be 30 or less because the molecular weight can be kept relatively low and shear resistance can be improved.

The olefin hydrocarbon used as a monomer other than ethylene may be linear, cyclic, or branched. Specific examples include propylene, n-butene, i-butylene, cyclobutene, n-pentene, i-pentene, cyclopentene, n-hexene, i-hexene, n-heptene, i-heptene and the like. The diene hydrocarbon used as a monomer other than ethylene may be a chain, a ring, or a branched chain. Specific examples include butadiene, cyclobutadiene, pentadiene, cyclopentadiene, hexadiene, heptadiene and the like. Examples of the vinyl aromatic used as the monomer other than ethylene in the olefin copolymer include styrene and divinylbenzene.
Among these, it is particularly preferable to use an ethylene / propylene copolymer as the olefin copolymer of the present invention.

When a copolymer of ethylene and a monomer other than ethylene is used as the olefin copolymer, the molar ratio of the monomer other than ethylene and ethylene is not particularly limited, but is preferably 80:20 to 20:80, more preferably 70: It is 30-30: 70, More preferably, it is 65: 35-35: 65. When the ratio of ethylene exceeds 80, it tends to be difficult to dissolve in the base oil.

Such a copolymer may be any of regular alternating polymers, random polymers, block polymers, or graft polymers, and may be either dispersed or non-dispersed. From the viewpoint of stability, a non-dispersed copolymer is preferable.
These olefin copolymers can also be added as viscosity index improvers previously dissolved in a base oil (also referred to as diluent oil) when used in the hydraulic fluid composition of the present invention, as in PMA. Since the olefin copolymer used in the present invention has a relatively small molecular weight, it is often handled as a viscosity index improver without being dissolved in the base oil.

The weight average molecular weight of the olefin copolymer is 5,000 to 100,000, preferably 8,000 to 80,000, more preferably 10,000 to 50,000, and particularly preferably 10,000 to 20,000. It is. If the weight average molecular weight is less than 5,000, the temporary shear viscosity under high shear conditions cannot be sufficiently lowered, and it is difficult to obtain a power saving effect. If the weight average molecular weight exceeds 100,000, the permanent shear stability is lowered, so it is necessary to set it to 100,000 or less. Here, the weight average molecular weight is measured by gel permeation chromatography and is a value in terms of polystyrene.

The number average molecular weight of the olefin copolymer is 4,000 to 50,000, preferably 6,000 to 30,000. It is preferable for the number average molecular weight to be 4,000 or more because the temporary shear viscosity under high shear conditions can be lowered and the power saving effect can be easily obtained. In addition, it is preferable that the number average molecular weight is 50,000 or less because it tends to easily obtain better permanent shear stability. Here, the number average molecular weight is measured by gel permeation chromatography and is a value in terms of polystyrene.
The olefin copolymer preferably has a Mw / Mn ratio of 1.5 to 3.0, more preferably 1.6 to 2.5.

The above olefin copolymers may be used alone or in combination of two or more, and when two or more are used in combination, the respective weight average molecular weights are within the above range. Is preferred.
The blending amount of the olefin copolymer with respect to the total amount of the hydraulic fluid composition is preferably 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, and still more preferably 0.3 to 2% by mass. is there. A blending amount of 0.1% by mass or more is preferable because the viscosity index of the hydraulic fluid composition can be increased, the temporary shear viscosity under high shear conditions can be lowered, and a power saving effect can be easily obtained. . On the other hand, if the olefin copolymer is too much, the permanent shear stability is lowered, so the blending amount is preferably 5% by mass or less. Also, if there are too many olefin copolymers, the compatibility with other additives, especially phosphorous antiwear agents, will be reduced, especially when the base oil is a paraffinic base oil and the compatibility of the additives will be further reduced. There is. As a result, it may be difficult to sufficiently obtain the effect of the additive. Also in this respect, the blending amount of the olefin copolymer is preferably 5% by mass or less.

In the hydraulic fluid composition of the present invention, as described above, it is important that both the polymethacrylate having a specific weight average molecular weight and the olefin copolymer having a specific weight average molecular weight are contained in a predetermined content. That is, low molecular weight polymethacrylates and olefin copolymers are excellent in permanent shear stability, but are less susceptible to temporary viscosity shearing and are less effective in increasing the viscosity index of hydraulic fluid compositions. The contribution to power performance tends to be low. Conversely, high molecular weight polymethacrylates and olefin copolymers can increase the viscosity index and lower the viscosity with respect to temporary shear, but tend to have poor permanent shear stability.

On the other hand, when comparing polymethacrylates of the same molecular weight with olefin copolymers, polymethacrylates have the advantage of easily increasing the viscosity index, being excellent in compatibility with additives, and being able to sufficiently bring out the effects of additives such as wear resistance. However, it tends to be inferior in permanent shear stability. On the contrary, the olefin copolymer has an advantage of excellent balance between the temporary shear viscosity reduction rate and the permanent shear stability, but tends to be inferior in compatibility with the additive. Therefore, it is difficult to satisfy all of high viscosity index, temporary shear viscosity reduction, permanent shear stability, and compatibility with additives alone, either by polymethacrylate or olefin copolymer. By including both polymethacrylate and an olefin copolymer having a specific weight average molecular weight, all of the required performances can be satisfied.
In order to achieve the above performance, the content ratio of the component (b) and the component (c) is preferably in the range of 10 to 1000 parts by mass of the component (c) with respect to 100 parts by mass of the component (b), and 20 to 500 parts. The range of parts by mass is more preferable.

(D) Phosphorus-based antiwear agent The phosphorus-based antiwear agent used in the hydraulic fluid composition of the present invention is a phosphorus compound that does not contain a metal component, such as phosphate esters and phosphites, and these Derivatives. Those containing metal such as zinc dialkyldithiophosphate may be susceptible to oxidative degradation and hydrolysis under conditions where they are exposed to high temperatures or mixed with water, resulting in sludge containing metal. This is because there is a possibility of generating a large amount. Phosphoric esters and phosphites may be mono-, di- or triesters, but diesters and triesters are preferred. Moreover, as each alcohol residue, C6-C30, such as C4-C30 alkyl groups or alkenyl groups, such as a butyl, an octyl, a lauryl, a stearyl, an oleyl group, a phenyl group, a tolyl group, a xylenyl group Examples thereof include an aryl group and an alkyl-substituted aryl group, but an alkyl-substituted aryl group having 7 to 30 carbon atoms is preferable, and an alkyl-substituted aryl group having 7 to 10 carbon atoms is more preferable.

Specific examples of the phosphorus-based antiwear agent include tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, tripropyl phosphate, tributyl phosphate, dioctyl phosphate, monooleyl phosphate, Examples include rail phosphite, diphenyl phosphite, tricresyl phosphite, and trixylenyl phosphite. These derivatives include amine salts such as stearylamine salts, oleylamine salts, and coconut amine salts. These may be used alone or in combination of two or more.

The blending amount of the phosphorus-based antiwear agent with respect to the total amount of the hydraulic fluid composition is preferably 0.2 to 2% by mass, and more preferably 0.5 to 1.5% by mass. If the blending amount is less than 0.2% by mass, sufficient wear resistance tends to be difficult to obtain. In that case, there is a possibility of metal contact at the sliding portion, and power consumption is reduced due to a reduction in the efficiency of the device. May increase. On the other hand, if the blending amount exceeds 2% by mass, the solubility in the base oil decreases, and the possibility of turbidity and precipitation increases. In addition, this may lead to generation of pressure loss due to clogging of a filter, a control valve, etc. in the hydraulic apparatus and an increase in power consumption. Phosphorous wear inhibitors may be used singly or in combination of two or more, but when combining two or more, the total blending amount needs to be within the above range.
Further, the content ratio (mass ratio) with respect to the total amount of the component (b) and the component (c) of the phosphorus-based antiwear agent of the component (d) is preferably 10: 1 to 1:10, and 5: 1 to 1: 5 is particularly preferred.

(E) Dispersant The hydraulic fluid composition of the present invention preferably contains a dispersant in order to obtain a higher power saving effect. Sludge generated in the hydraulic circuit adheres to various filter parts such as suction filters and line filters, various control valves such as direction control valves and relief valves, piping and tanks, etc., increasing the pressure loss of hydraulic fluid, As a result, the power consumption of the hydraulic equipment is increased. Therefore, by blending the dispersant into the hydraulic fluid composition, the dispersibility of sludge generated in the hydraulic fluid composition can be enhanced, and as a result, the power saving performance can be maintained for a longer period.

Examples of the dispersant used in the hydraulic fluid of the present invention include metal detergents such as Ca sulfonate and ashless dispersants such as succinimide dispersants. Metal-based detergents and ashless dispersants are excellent in the effect of finely dispersing sludge generated when the hydraulic fluid composition is subjected to thermal oxidation or mixed with moisture or wear powder. Furthermore, an ashless dispersant that is less likely to sludge itself due to reaction with moisture or the like is more preferable. Examples of the ashless dispersant include succinimide dispersants, and monotypes and bistypes are preferable, but the bistype is preferable because of good dispersibility of sludge. Further, a boron-modified type and a non-modified type are exemplified, but the non-modified type is preferable because of good dispersibility of sludge.

Moreover, 500-3000 are preferable and, as for the weight average molecular weight of the polybutenyl group of a succinimide type | system | group dispersing agent, 1000-2000 are more preferable. When the molecular weight of the polybutenyl group is smaller than 500 or larger than 3000, the solubility in the base oil may be lowered or the dispersibility of the sludge may be insufficient.

Further, the nitrogen content of the succinimide dispersant is preferably 0.5 to 3% by mass, more preferably 1 to 2% by mass. If the nitrogen content is less than 0.5% by mass, the sludge dispersibility is not sufficient, and it is not preferable if it is more than 3% by mass, since the demulsibility is lowered.
The blending amount of the dispersant with respect to the total amount of the hydraulic fluid composition is preferably 0.01 to 1% by mass, more preferably 0.03 to 0.8% by mass, and still more preferably 0.05 to 0.00%. 5% by mass.

(F) Other Additives Various known additives can be blended with the hydraulic fluid composition of the present invention, if necessary, as long as the object of the present invention is not impaired. Examples thereof include antioxidants, extreme pressure agents, oil agents, detergent dispersants, rust inhibitors, metal deactivators, pour point depressants, antifoaming agents, and demulsifiers.

Antioxidants include monocyclic rings such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, etc. Phenolic antioxidants, 4,4′-bis (2,6-di-t-butylphenol), 4,4′-methylenebis (2,6-di-t-butylphenol), 4,4′-ethylenebis ( 2,6-di-t-butylphenol), 4,4'-butylenebis (2,6-di-t-butylphenol), 6,6'-methylenebis (2-di-t-butyl-4-methylphenol), etc. -Containing bisphenol antioxidants, sulfur content such as 4,4′thiobis- (2,6-di-tert-butyl-phenol), 4,4′thiobis- (2-methyl-6-tert-butyl-phenol) Phenolic antioxidant, Alky Examples thereof include amine-based antioxidants such as diphenylamine and alkylated phenyl-α-naphthylamine, and phosphorus-based antioxidants such as phosphonic acid esters.

Examples of extreme pressure agents include sulfur-based extreme pressure agents such as sulfurized olefins, polysulfides, sulfurized fats and oils, dithiophosphoric acid derivatives, and organometallic extreme pressure agents such as ZnDTP and ZnDTC. Particularly preferred are sulfurized olefins and dithiophosphoric acid derivatives, and specific examples include β-dithiophosphorylated propionic acid.
Examples of the oily agent include higher fatty acids such as oleic acid and stearic acid, higher alcohols such as oleyl alcohol, amines such as oleylamine, and esters such as butyl stearate.
Examples of the cleaning dispersant include alkaline earth metal cleaning dispersants, and specific examples include Ca salicylate, Ca phenate, and Ca sulfonate.

Rust inhibitors include metal soaps such as sulfonate metal salts and naphthenic acid metal salts, alkyl succinic acid derivatives, alkenyl succinic acid derivatives, lanolin compounds, surfactants such as sorbitan monooleate and pentaerythritol monooleate, wax and Oxidized wax, petrolatum, N-oleylsarcosine, rosinamine, alkylated amine compounds such as dodecylamine and octadecylamine, fatty acids such as oleic acid and stearic acid, phosphorus compounds such as phosphite, etc. Acid derivatives, alkenyl succinic acid derivatives, surfactants, and alkylated amine compounds are preferably used, and alkyl succinic acid derivatives and alkenyl succinic acid derivatives are more preferable.

As the metal deactivator, benzotriazole and its derivatives, indazole and its derivatives, benzimidazole and its derivatives, indole and its derivatives, thiadiazole and its derivatives, etc. are used, benzotriazole and its derivatives, thiadiazole and its derivatives Is preferably used. Examples of the pour point depressant include polyalkyl methacrylate, polybutene, polyalkyl styrene, polyvinyl acetate, polyalkyl acrylate and the like.
Examples of the antifoaming agent include silicone-based antifoaming agents such as dimethyl silicone, alkyl-modified silicone, phenyl-modified silicone, and fluorine-modified silicone, and polyacrylate-based antifoaming agents.

Examples of the anti-emulsifier include an anti-emulsifier such as an anionic surfactant, a cationic surfactant, and a nonionic surfactant, and a nonionic surfactant is preferably used. Specifically, polyalkylene glycol is preferably used. As the polyalkylene glycol at this time, a homopolymer obtained by polymerizing ethylene glycol, propylene glycol, and butylene glycol as monomers, and a copolymer obtained by polymerizing each of these alone, or a copolymer obtained by polymerizing each in combination, is used. Each may be used alone or in combination, but a copolymer is preferably used, and an ethylene oxide-propylene oxide copolymer polymerized by combining ethylene glycol and propylene glycol is particularly preferably used.

(G) Property of composition The hydraulic fluid composition of the present invention has a kinematic viscosity at 40 ° C. in accordance with ISO VG32 or ISO VG46 in accordance with JIS K2283 kinematic viscosity test method of 28.8 to 35.2 mm ² / It is preferable that it is s or 41.4-50.6 mm < ² > / s, and in order to have power saving performance, it is preferable that it is 46.0 mm < ² > / s or less. However, when the hydraulic fluid of the present invention is used in a hydraulic system under severe conditions where the oil temperature is as high as 60 ° C. or higher, the volumetric efficiency of the pump or actuator can be prevented. In some cases, a higher viscosity grade is set and used to prevent oil leakage from the connection. In that case, it is preferable to make it a lower kinematic viscosity within the range of each viscosity grade. For example, in the case of ISO VG68, the 40 ° C. kinematic viscosity needs to be 61.2 to 74.8 mm ² / s in the JIS K2283 kinematic viscosity test method, but has power saving performance within the range of ISO VG68. Is preferably 68.0 mm ² / s or less.

The 40 ° C. absolute viscosity of the hydraulic fluid composition of the present invention is preferably 23 to 27 mPa · s in the case of an ISO VG32 compliant product, and 32 to 39 mPa · s in the case of an ISO VG46 compliant product. It is preferably 33 to 38 mPa · s, particularly preferably. Since the absolute viscosity at 40 ° C is calculated as "40 ° C kinematic viscosity x 40 ° C density", if the density is low even at the same kinematic viscosity, the absolute viscosity will be low. . If the absolute viscosity is low, the stirring resistance of the pump and the actuator is reduced, so that the mechanical efficiency is improved and the power saving performance of the hydraulic system is improved. Also, if the absolute viscosity is low, the pressure loss when passing through piping, various control valves, various filters, etc. in the hydraulic fluid flow path is reduced, so the ISO viscosity grade is the same and the value of kinematic viscosity is Even with the same hydraulic fluid, the power saving performance is improved when the density is low, that is, the absolute viscosity is low. Thus, in order to reduce the absolute viscosity with the same ISO viscosity grade, it is necessary to lower the kinematic viscosity within the range specified by the viscosity grade, or to reduce the density, particularly in the ISO VG46 compliant product. In order to make the absolute viscosity at 32 ° C. to 39 mPa · s or less, it is particularly effective to add a specific amount of the base oil having a specific viscosity, the polymethacrylate having a specific molecular weight, and the olefin copolymer, which is the constitution of the present invention. is there.

The viscosity index of the hydraulic fluid composition of the present invention is not particularly limited, but is preferably 135 or more, more preferably 140 or more, and further preferably 145 or more in the JIS K2283 kinematic viscosity test method. By setting the viscosity index to 135 or more, the low-temperature viscosity becomes low, so that it is easy to suppress the power consumption at the time of low-temperature start and it is easy to obtain a higher power saving effect.

The flash point of the hydraulic fluid composition of the present invention is preferably 250 ° C. or higher, more preferably 258 ° C. or higher. A flash point of 250 ° C. or higher is preferred because it is designated as a “flammable liquid” in the dangerous goods classification under the Fire Service Law, and the storage and handling regulations are greatly relaxed. The flash point of the hydraulic fluid composition is such that the initial distillation point in GC distillation of the base oil (or base oil after mixing when a plurality of base oils are used) is 350 ° C. or higher and the 5% distillation temperature is 380 ° C. By setting it as ℃ or more, it is easy to ensure 250 ℃ or more.

Although the hydraulic fluid composition of the present invention can be applied to various industrial hydraulic fluids, it can be preferably used particularly as a hydraulic fluid used in a hydraulic system. Furthermore, in hydraulic systems where wear resistance is required due to high pressure, when hydraulic pipes, various filters, various control valves, etc. cause many pressure losses, hydraulic pumps, hydraulic motors, control valves This is particularly effective in reducing power consumption at locations where the hydraulic oil is exposed to a high shear state.

Next, the present invention will be described more specifically with reference to examples. In addition, this invention is not restrict | limited at all by these examples. The base oil and additive components used in the preparation of the hydraulic fluid composition in each example and comparative example are as follows.

<Base oil>
(1) Hydrocracked mineral oil A: Indonesian paraffinic crude oil is used as a raw material, the residual oil obtained by atmospheric distillation is distilled under reduced pressure, the fraction obtained as a lubricating oil fraction is hydrocracked, and again The mineral oil obtained by distillation under reduced pressure, followed by wax isomerization and hydrofinishing, has the properties shown in Table 1.

(2) Hydrocracked mineral oils B to C: Using a Middle Eastern paraffinic crude as a raw material, the residual oil obtained by atmospheric distillation is distilled under reduced pressure, and then the hydrolyzed fraction obtained as a lubricating oil fraction is hydrocracked. It is a mineral oil obtained by distilling again under reduced pressure, followed by wax isomerization and hydrofinishing, and has the properties shown in Table 1.
(3) Hydrorefined mineral oils A to C: Using a Middle Eastern paraffinic crude oil as a raw material, the residual oil obtained by atmospheric distillation was distilled under reduced pressure, and the fraction obtained as a medium-viscosity lubricating oil fraction was solvent. A mineral oil obtained by a combined process of extraction, solvent dewaxing, press dewaxing, and hydrorefining, and has the properties shown in Table 2.

<Performance additive>
Non-Zn hydraulic oil PKG (package): Contains amine antioxidant, phosphorus-sulfur-containing extreme pressure agent, fatty acid rust inhibitor, thiadiazole derivative.
Dispersant: polybutenyl-bissuccinimide (the weight average molecular weight of the two polybutenyl groups is 1300, and the nitrogen content is 1.8% by mass)
・ Demulsifier: Ethylene oxide-propylene oxide copolymer ・ Phosphoric antiwear agent: tricresyl phosphate ・ Antifoaming agent: Dimethyl silicone ・ Rust inhibitor: Alkenyl succinic acid half ester ・ Phenol antioxidant: Di-t-butyl -P-cresol and pour point depressant: polymethacrylate (Mw: 51,000, Mn: 28,000, Mw / Mn = 1.82)
・ Zn hydraulic oil PKG (package): ZnDTP (zinc dialkyldithiophosphate), Ca salicylate, antioxidant

<Viscosity index improver>
(1) OCP-1: Non-dispersed olefin copolymer (ethylene / propylene copolymer), weight average molecular weight 16,000, number average molecular weight 7000, ethylene / propylene molar ratio: 10/9, active ingredient amount 100% by mass Things.
(2) OCP-2: non-dispersed olefin copolymer (ethylene / propylene copolymer), weight average molecular weight 30,000, number average molecular weight 17,000, ethylene / propylene molar ratio = 10/9, active ingredient amount 100 Mass%.
(3) PMA-1: non-dispersed polymethacrylate viscosity index improver, weight average molecular weight 140,000, number average molecular weight 50,000, active ingredient amount 60 mass%.

(4) PMA-2: non-dispersed polymethacrylate viscosity index improver, weight average molecular weight 130,000, number average molecular weight 62,000, active ingredient amount 55% by mass.
(5) PMA-3: Non-dispersed polymethacrylate viscosity index improver, weight average molecular weight 120,000, number average molecular weight 60,000, active ingredient amount 60% by mass.
(6) PMA-4: Non-dispersed polymethacrylate viscosity index improver, weight average molecular weight 40,000, number average molecular weight 22,000, active ingredient amount 70% by mass.
(7) starPMA: Star-type polymethacrylate viscosity index improver, weight average molecular weight 390,000, number average molecular weight 340,000, active ingredient amount 45% by mass. (Has a “star structure” with multiple arm polymers branched from the central polymethacrylate core)

The physicochemical property tests of the base oils shown in Tables 1 and 2 and the hydraulic fluid compositions shown in Tables 3 to 5 were carried out by the test methods shown below.
·density
: JIS K 2249 “Density Test Method”
・ Kinematic viscosity
: JIS K 2283 "Kinematic viscosity test method"
・ Viscosity index
: JIS K 2283 "Viscosity index calculation method"
・ Pour point
: JIS K 2269 "Pour point test method"
·Flash point
: JIS K 2265-4 "Flash point test method (Cleveland open method)"

・ Residual carbon
: JIS K 2270 “Residual carbon content test method”
・ Acid value
: JIS K 2501 “Neutralization test method”
-ASTM color: JIS K 2580 “ASTM color test method”
・ Sulfur content (ultraviolet fluorescence method): JIS K 2541-6 “Sulfur content test method (ultraviolet fluorescence method)”
・ Nitrogen content: JIS K 2609 “Nitrogen content test method”
・ Ndm
: ASTM 3238-85 "Standard Test Method for Calculation of Carbon Distribution
and Structural Group Analysis of Petroleum Oils By the ndm Method "

-Aniline point: JIS K 2256 "Test method for aniline point and mixed aniline point"
・ Iodine value: JIS K 0070 “Testing methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponified product of chemical products”
GC distillation temperature: JIS K 2254 “Distillation test method (gas chromatography method)”
-About absolute viscosity, it computed with the following formula | equation. In addition, the density and kinematic viscosity in a formula were measured according to the said measuring method.
Absolute viscosity (40 ° C) = density (40 ° C) x kinematic viscosity (40 ° C)

※：括弧内は希釈油を除く有効成分量。

*: Active ingredients excluding diluent oil in parentheses.

※ ：括弧内は希釈油を除く有効成分量。

*: The amount of active ingredients in parentheses excluding diluent oil.

※：括弧内は希釈油を除く有効成分量。

*: Active ingredients excluding diluent oil in parentheses.

The results of performance tests on the hydraulic fluid compositions shown in Tables 3 to 5 are shown in Tables 6 to 8. The performance tests shown in Tables 6 to 8 were performed according to the following test methods, test apparatuses, and test conditions.
High shear viscosity: USV (Ultra Shear Viscometer, manufactured by PCS Instruments) was used to measure the shear viscosity at a temperature of 40 ° C. and a shear rate of 10 ⁶ (S ⁻¹ ).

-Primary shear viscosity reduction rate: High shear viscosity was measured by the above-mentioned apparatus and conditions, and the primary shear viscosity reduction rate was calculated from the following formula.
Primary shear viscosity reduction rate = (high shear viscosity (40 ° C.) − Absolute viscosity (40 ° C.)) / (Absolute viscosity (40 ° C.)) × 100
Storage stability: About 90 ml of the sample was injected into a 100 ml sample tube and stored under the condition of 0 ° C. × 1 week, and the presence or absence of turbidity / precipitation was observed. The observation results were evaluated with the following symbols.
○: No turbidity / precipitation, clear dissolution △: Slight turbidity or precipitation is observed
×: Obvious turbidity or precipitation

SONIC permanent shear viscosity reduction rate: JPI-5S-29-2006, high output method Thermal stability test: 40 ml of sample is placed in a glass container having an inner diameter of 2.5 cm, and a steel and copper catalyst is immersed at 140 ° C. Were left in a constant temperature bath with a rotating plate, and the amount of sludge (using a 0.8 μm millipore filter) after 240 hours was measured.
(Catalyst material / size)
Steel = SPCC-SB, Copper = C1100P,
Both sizes are 1.0mm x 20mm x 50mm

-TOST: Based on JIS K 2514 "turbine oil oxidation stability test method", the acid value increase after 95 ° C x 1000 h and the amount of sludge in 100 ml were measured.
-Vickers 104c pump test: ASTM D 7043-10 “Standard Test Method for Indicating Wear Characteristics of Non-Petoleum and Petroleum Fluid Fluids in a Con V.

-Power-saving evaluation: Evaluation was performed according to the following equipment and test conditions.
<Power saving evaluation device>
(1) Device name: “Energy-saving evaluation device” manufactured by Yuken Kogyo
(2) Equipment overview: Oil tank, electric motor, piston pump, torque meter with tachometer, 10m piping, hydraulic piston motor, dynamometer, suction filter / line filter, relief valve, heat exchanger, wattmeter, inverter, etc. The hydraulic piston motor is rotated by the power of the hydraulic fluid boosted by the piston pump, and the load is applied and the power is absorbed at the same time by the dynamometer directly connected to the hydraulic piston motor. A device that measures with a meter. The hydraulic circuit is shown in FIG.

(3) Equipment specifications:
・ Hydraulic pump: Yuken Kogyo variable displacement piston pump A16
・ Electric motor: Mitsubishi Electric inverter dedicated motor SF-HRCA
Output 18.5kW
・ Hydraulic motor: Piston motor A2FM16 made by Bosch Rexroth
・ Torque meter: Ono Sokki Co., Ltd. SS-101
・ Dynamometer: Takes Co., Ltd. W-100 eddy current dynamometer Maximum absorption power 100kW, Maximum absorption torque 300Nm
-Wattmeter: Hioki Electric Co., Ltd. 3168 Clamp-on-Power HiTester

<Power saving evaluation test conditions>
-Power consumption measurement method: Electric power is continuously measured for 12 minutes each time, and start / stop is repeated every 12 minutes, and the measurement is performed 10 times while stabilizing the oil temperature. The average value of 10 times is taken as the power consumption in the test oil.
Pump discharge pressure: (1) 6.86 Mpa × 6 min
⇒ (2) 13.72 Mpa x 6 min
・ Pump speed: 1500rpm
・ Dynamometer absorption torque: Low pressure: 16 N ・ m, High pressure: 32 N ・ m
·Oil temperature
: 35 ° C, 40 ° C, 45 ° C

According to Tables 3 and 6, Examples 1-4 satisfying the configuration of the present invention have sufficiently low absolute viscosity of 36 mPa · s or less, and a primary shear viscosity reduction rate of −12% to −14% is sufficient. On the other hand, the decrease rate of SONIC permanent shear viscosity is less than −3%, and although the primary shear viscosity is low, it is stable against permanent shear and has good storage stability. . Examples 1 to 4 also have good thermal stability, a small amount of sludge in TOST, and a small amount of wear in the Vickers 104c pump test.
And when the power-saving evaluation of Examples 1-4 was performed with the power-saving evaluation apparatus which can simulate the power-saving effect under conditions close to actual machines, it was compared at all temperatures of 35 ° C, 40 ° C and 45 ° C. Using Example 1 as a reference oil, a power saving effect of 1% or more was obtained. Since Examples 1 to 4 have a high viscosity index, the viscosity is lower than that of Comparative Example 1 at a low temperature, so that the power saving effect tends to increase as the temperature decreases. In addition, it can be seen that each of the examples has a high power saving effect while the flash point is 250 ° C. or higher and the ISO viscosity grade is VG46.

On the other hand, according to Table 4 and Table 7, it turns out that Comparative Examples 1-6 which do not satisfy | fill the structure of this invention do not have the effect of this invention.
First, Comparative Example 1 does not contain polymethacrylate, olefin copolymer and phosphorus-based antiwear agent essential in the present invention, and also has a high absolute viscosity, and this has a low power saving effect as compared with Examples. Recognize. In addition, ZnDTP is blended as an anti-wear agent, and a metal detergent is blended as a dispersant. Although the amount of wear in the pump test is small, a phosphorus anti-wear agent and succinimide are not blended. Is increasing. In addition, this comparative example 1 has implemented the power saving evaluation test as a reference | standard prescription for evaluation of the power saving effect in each Example.

Although the comparative examples 2 and 3 contain the olefin copolymer in this invention, since they do not contain a polymethacrylate, they are inferior in storage stability. Moreover, the amount of sludge in TOST is increasing. Therefore, although a certain power saving effect can be expected from the results of absolute viscosity, high shear viscosity, and primary shear viscosity reduction rate, the basic performance as a hydraulic fluid cannot be secured. Absent.
In Comparative Example 4, a base oil having a kinematic viscosity lower than that specified in the present invention was used as the base oil, and the kinematic viscosity of the composition was adjusted to the same level as in the examples by blending more olefin copolymer. However, it can be seen that this formulation is inferior in wear resistance in the Vickers 104c pump test. Moreover, in this comparative example 4, since the polymethacrylate in this invention is not contained, storage stability is inferior. Furthermore, the amount of sludge in TOST has increased. In this case as well, although a certain power saving effect can be expected from the results of absolute viscosity, high shear viscosity, and primary shear viscosity reduction rate, the basic performance as a hydraulic fluid cannot be secured. Not.

In Comparative Example 5, in place of the polymethacrylate and olefin copolymer in the present invention, a large amount of low molecular weight polymethacrylate was blended to adjust the kinematic viscosity to the same level as in the Examples. -Although high shear viscosity, storage stability, and sludge amount are the level of an Example, it turns out that the sludge amount in a thermal stability test is inferior. Moreover, since the primary shear viscosity reduction rate is not sufficient, a sufficient power saving effect cannot be expected, and thus the power saving effect is not evaluated.
Further, in Comparative Example 6 in which star polymethacrylate was blended instead of polymethacrylate or olefin copolymer in the present invention, absolute viscosity, high shear viscosity, and primary shear viscosity reduction rate were at the example level, but SONIC permanent shear viscosity reduction. It can be seen that the negative value of the rate is large and the shear stability is poor. Therefore, although a certain power saving effect can be expected from the results of absolute viscosity, high shear viscosity, and primary shear viscosity reduction rate, the basic performance as a hydraulic fluid cannot be secured. Absent.

Although the hydraulic fluid composition of the present invention can be applied as various industrial lubricating oils, it can be preferably used particularly as a hydraulic fluid used in a hydraulic system. In particular, among hydraulic systems, hydraulic pumps, hydraulic motors, hydraulic cylinders, etc., equipment that requires wear resistance of hydraulic oil to be used at high pressure, various control valves such as directional control valves, flow control valves, It is preferably used in a device such as a line filter or a suction filter, which has a shear loss or a pressure loss through a minute gap, or a device in which a pressure loss increases by sending oil through an elongated pipe.

Claims (3)

(A) a hydrocarbon base oil having a kinematic viscosity at 40 ° C. of 28 to 51 mm ² / s,
(B) 0.03 to 3 mass% of polymethacrylate having a weight average molecular weight of 70,000 to 200,000,
(C) 0.1 to 5% by mass of an olefin copolymer having a weight average molecular weight of 5,000 to 100,000.
(D) 0.2-2% by mass of a phosphorus-based antiwear agent,
A hydraulic fluid composition containing the hydraulic fluid composition. The hydraulic fluid composition according to claim 1, further comprising (e) 0.01 to 1% by mass of a dispersant. 3. The hydraulic fluid composition according to claim 1, wherein an ISO viscosity grade of the hydraulic fluid composition is ISO VG46, and an absolute viscosity at 40 ° C. is 32 to 39 mPa · s.

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