FLAME RETARDANT HYDRAULIC OIL COMPOSITION
Technical Field

[0001] The present invention relates to a flame retardant hydraulic oil composition, more specifically to such a flame retardant hydraulic oil composition that is most suitably used for applications where it is used under high temperature and pressure conditions with the high risk of fire breakout, such as for use in aluminum die-cast extruding machines or operations in iron mill facilities and that is applicable to a high-pressure pump, excellent in antiwear properties, sludge suppressing properties and in particular zinc elution suppressing properties, making it possible to be used for a long period of time.

Background Art

[0002] Conventionally, as a hydraulic oil that is used at sites with the high risk of fire breakout such as use in aluminum die-cast extruding machines or operations in iron mill facilities, a flame retardant hydraulic oil (fluid) such as water-glycol or a fatty acid ester has been used to maintain safety at the sites. Particularly in sites subject to the regulations of Petroleum No. 4 of the Fire Service Act, a water-glycol fluid has been mainly used but has drawbacks regarding cumbersome storage of the used oil and antiwear properties. However, a revision of the Fire Service Act in 2002 excluded the hydraulic oil having a flash point of 250°C or higher from the Fire Service Act, resulting in the widened applications of a fatty acid ester having a relatively higher flash point. As the result, an ester oil has just become common as a flame retardant hydraulic oil.

[0003] The properties of the fatty acid ester vary on the composition of the fatty acid constituting the ester. An ester of a saturated fatty acid is more excellent in oxidation stability. However, the saturated fatty acid is produced by synthesizing a petroleum raw material or hydrogenating an unsaturated fatty acid derived from an animal or vegetable oil, and thus is an expensive raw material that is not environment friendly. Currently, a natural synthetic ester or fat has also been used, which contains a fatty acid mainly composed of an unsaturated fatty acid, derived from an animal or vegetable oil that is environment friendly and advantageous in cost (see Patent Literatures 1 to 3 below).

Meanwhile, since recent hydraulic systems have been used under higher pressures and become more maintenance-free than ever before, a hydraulic oil used under these circumstances has been required to have long-life properties and excellent antiwear properties. A natural synthetic ester produced from a natural material such as animal or vegetable oils contains a fatty acid mainly composed of an unsaturated fatty acid and thus is friendly in the global environment and advantageous in cost. However, it has a drawback that it is extremely inferior in oxidation stability to synthetic esters of saturated fatty acids or synthetic hydrocarbon oils.

[0004] In principle, since the ester-based hydraulic oil could elude zinc by the remaining fatty acid, zinc had not been used at portions contacting the oil such as piping, valves, joints or the like. However, with the widespread use of the eater-based flame retardant hydraulic oil, the number of cases has been increased, where zinc eluded from galvanized portions of piping, valves, and joints having been conventionally used in a hydraulic system causes problems such as the formation of sludge. In particular, water remaining when a water-glycol hydraulic oil is shifted to an ester-based hydraulic oil facilitates the elution of zinc, and thus problems such as filter clogging have occurred in great numbers. The elution of zinc is also brought about by acid increased as an oil is degraded and thus for measures of zinc elution, the oxidation stability of an oil has also become an important factor.

[0005] For the conventional mineral hydraulic oils or synthetic hydrocarbon hydraulic oils, phenol- or amine-based antioxidants or ZnDTP (zinc dialkyldithiophosphates) have been used. However, an ester-based hydraulic oil containing a saturated or unsaturated fatty acid has a problem that it is difficult to prolong the working life because the antioxidation properties would be insufficient even though such a conventional phenol- or amine-based antioxidant is added.

In particular, this tendency is significant in the case where a synthetic ester produced using an unsaturated fatty acid, which is poor in oxidation stability or an animal or vegetable fat is used as the base oil. Since an additive working effectively for such a synthetic ester produced from an unsaturated fatty acid or an animal or vegetable fat has not been found yet, conventionally there was no alternative but to choose a synthetic ester produced from a saturated fatty acid which adversely affects the global environment and is expensive or a synthetic ester produced from an unsaturated fatty acid or animal or vegetable fat, which is short in intervals for oil change.

[0006] For the conventional mineral hydraulic oil, ZnDTP or an aromatic phosphoric acid ester has also been used as an antiwear additive. However, a problem has been pointed out that for a hydraulic oil containing an ester as the base oil, the additive performs little effect due to the high adsorption activity of the ester itself, comparing with the case where it is used for a mineral hydraulic oil. For example, TCP (tricresyl phosphate), which is a typical phosphorus antiwear additive can exhibit little antiwear effect in a fatty acid ester.

In addition to the above-described problems, a recently arising problem is that zinc plating applied on piping or valves in a hydraulic system is eluded by acid present in an ester hydraulic oil or generated during the use thereof. So far, no technique for suppressing the zinc elution has been created, and the non-use of zinc plating has been regarded as the best measure.

As described above, under the current situations, it has been very difficult to develop a flame retardant hydraulic oil that is excellent in antiwear properties and capable of suppressing zinc elution, consequently prolonging the working life using a synthetic ester which is produced from an environment friendly and relatively inexpensive natural raw material or an animal or vegetable fat,.

Citation List

Patent Literature

[0007]
Patent Literature 1: Japanese Patent Laid-Open Publication No. 2001-214187
Patent Literature 2: Japanese Patent Publication No. 3548591
Patent Literature 3: Japanese Patent Publication No. 2888747

Summary of Invention
Technical Problem [0008] In a synthetic ester, some unreacted fatty acid remains and cause the elution of zinc. When the acid value of the fatty acid is too high, the effect of an additive for suppressing zinc elution is weaken. When a fatty acid forming an ester is a saturated fatty acid, it is poor in dissolubility and thus allows metals such as eluted zinc and degraded products to easily settle and then to be formed into sludge.

Although an extreme pressure additive is added for the purpose of inhibiting wear, a mild extreme pressure additive such as phosphoric acid ester is ineffective in an ester. Whereas, an extreme pressure additive with a strong activity has adverse impacts on oxidation stability and sludge suppression properties and often causes zinc elution.

Furthermore, oxidation stability is also an important matter to suppress the elution of zinc. For a hydraulic oil containing an ester, which is poor in oxidation stability as the base oil, the acid value increases during the use thereof, and thus the elution of zinc is facilitated. However, the conventional phenol- or amine-based antioxidant having been used for mineral oils or synthetic hydrocarbon oils can not provides an ester oil with a sufficient antioxidation effect.

The present invention has been made in view of the above-described circumstances and has an object to provide a longer lasting flame retardant hydraulic oil composition which comprises a unsaturated fatty acid or animal or vegetable fat mainly containing an unsaturated fatty acid and having an acid value of a specific value or less and which has sufficient antioxidation properties and excellent zinc elution inhibiting properties and antiwear properties and responds to the increase in pressure and trend of maintenance-free in the recent hydraulic system.

Solution to Problem

[0009] .As the result of the extensive research and study, the present invention has been accomplished on the basis of the finding that the above problems was solved by adding a specific metal corrosion inhibitor to a base oil that is a synthetic ester and/or a fat containing 20 percent by mole or more of an unsaturated fatty acid derived from a natural raw material particularly in the fatty acid constituting the ester and having an acid value of 1.0 mgKOH/g or less. Furthermore, mixing of a specific amine-based oxidation inhibitor with excellent antioxidation properties and/or a specific nitrogen metal deactivator has lead to the development of an ester-based flame retardant hydraulic oil, which has a further longer service life.

The "acid value" used herein denotes the value measured in accordance with JIS K2501 "Petroleum Products and Lubricating Oils Test Method for Neutralization Number" (potentiometric titration method).

[0010] That is, the present invention relates to a flame retardant hydraulic oil composition comprising (A) at least one type of base oil selected from the group consisting of synthetic esters and fats, containing 20 percent by mole or more of an unsaturated fatty acid in the fatty acid constituting the ester and having an acid value of 1.0 mgKOH/g or less and (B) an alkylthiadiazole in an amount of 0.001 to 1.0 percent by mass on the basis of the total mass of the composition.

[0011] The present invention also relates to the foregoing flame retardant hydraulic oil composition further comprising (C) bis ( 4-dialkylaminophenyl)methane represented by formula (1) below in an amount of 0.001 to 5.0 percent by. mass on the basis of the total mass of the composition:

wherein R1, R2, R3 and R4 may be the same or different from each other and are each independently an alkyl group having 1 to 6 carbon atoms.

[0012] The present invention also relates to the foregoing flame retardant hydraulic oil composition further comprising (D) at least one type of triazole compound selected from the group consisting of triazole derivatives, benzotriazole derivatives and tolutriazole derivatives in an amount of 0.0001 to 1.0 percent by mass on the basis of the total mass of the composition.

Advantageous Effects of Invention

[0013] According to the present invention, a base oil that is an ester oil of a fatty acid containing mainly an unsaturated fatty acid is mixed with a specific metal corrosion inhibitor or further a specific antioxidant and/or a nitrogen-based metal deactivator thereby providing a flame retardant hydraulic oil composition that is not only excellent in oxidation stability and antiwear properties but also capable of suppressing the elution of zinc as well as passing at 10 or higher stages in the FZG gear test.

Best Mode for Carrying Out the Invention

[0014] The present invention will be described in more detail below.

The base oil used in the flame retardant oil composition of the present invention is at least one type of base oil selected from the group consisting of synthetic esters and fats, each containing an unsaturated fatty acid in an amount of 20 percent by mole or more of the fatty acid constituting the ester and having an acid value of 1.0 mgKOH/g or less. Examples of the synthetic esters include fatty acid esters, polyol esters, and complex esters. Examples of the fats include various animal and vegetable fats. Preferred are those with a kinematic viscosity at 40°C of 10 to 200 mm2/s and a flash point of 280°C or higher. [0015] Preferred examples of the fatty acid esters include esters of unsaturated fatty acids such as palmitoleic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, eleostearic acid, and 8,11-eicosadienoic acid and saturated fatty acids having a straight-chain or branched alkyl group having 5 to 19 carbon atoms, such as pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, and nonadecanoic acid and monohydric alcohols having a straight-chain or branched alkyl group having 1 to 15 carbon atoms, such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, and pentadecanol; and mixtures thereof. Specific preferred examples include fatty acid esters such as an ester of a mixed fatty acid of stearic acid and oleic acid and butanol and an ester of a mixed fatty acid of stearic acid and lauric acid and octanol.

[0016] The polyol esters are preferably esters of diols or polyols having 3 to 20 hydroxyl groups and fatty acids having 1 to 24 carbon atoms.

[0017] Specific examples of the diols include ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanedioi1, 1,2-butanediol,

2-methyl-l,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol,
2-ethyl-2-methyl-l,3-propanediol, 1,7-heptanediol, 2-methyl-2-propyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol.

[0018] Specific examples of the polyols include polyhydric alcohols such as trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, di-(pentaerythritol), tri-(pentaerythritol) , glycerin, polyglycerins (dimmer to eicosamer of glycerin) , 1,3,5-pentanetriol, sorbitol, sorbitan, sorbitol-glycerin condensate, adonitol, arabitol, xylitol, and mannitol; saccharide such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, sucrose, raffinose, gentianose, and melezitose; partially eterified products thereof; and methyl glucoside (glycoside). Among these, preferred polyols are hindered alcohols such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane) , tri-(trimethylolpropane), pentaerythritol, and di-(pentaerythritol) because of their excellent hydrolysis stability.

[0019] Examples of the fatty acids of the polyol esters include the unsaturated fatty acids exemplified with respect to the above-described fatty acid esters and saturated fatty acids having a straight-chain or branched alkyl group having 5 to 19 carbon atoms. The unsaturated fatty acids exemplified with respect to the above-described fatty acid esters are particularly preferably used. Neo acid whose a carbon atom is quaternary may also be used. Specific examples of the branched saturated fatty acids include isopentanoic acid (3-methylbutanoic acid), 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid.

[0020] Specific examples of preferred polyol esters include diesters, triesters and tetraesters of one or more fatty acids selected from the group consisting of unsaturated fatty acids such as palmitoleic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, eleostearic acid, and 8,11-eicosadienoic acid and saturated fatty acids having a straight-chain or branched alkyl group having 5 to 19 carbon atoms, such as pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, and nonadecanoic acid and containing an unsaturated fatty acid and a polyol such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, or pentaerythritol.

[0021] Esters of two or more fatty acids may be a mixture of two or more esters of one fatty acid and a polyol or an ester of two or more mixed fatty acids and a polyol.

[0022] Among these polyol esters, preferred are esters of hindered alcohols such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-.( t rimethylolpropane ) , pentaerythritol, di-(pentaerythritol) , and tri-(pentaerythritol) and still more preferred are esters of neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, and pentaerythritol because of their excellent hydrolysis stability. Most preferred are esters of trimethylolpropane and pentaerythritol because of their particularly excellent hydrolysis stability. Specific examples include an ester of a mixed fatty acid of oleic acid and octylic acid and trimethylolpropane, an ester of a mixed fatty acid of oleic acid and pelargonic acid and trimethylolpropane, an ester of a mixed faty acid of oleic acid and octylic acid and pent aery thri tol, and an ester of a mixed fatty acid of oleic acid and pelargonic acid and pentaerythritol.

[0023] The polyol ester may be a partial ester wherein a part of the hydroxyl groups remains unesterified or a full ester wherein all of the hydroxyl groups are esterified. Further, the polyol ester may be a mixture of a partial ester and a full ester but is preferably a full ester.

[0024] The complex ester is an ester of a fatty acid and a dibasic acid and a monohydric alcohol and a polyol. The fatty acid, monohydric alcohol, and polyol may be those exemplified with respect to the above-mentioned polyol esters.

Examples of the dibasic acid include those having 5 to 10 carbon atoms, such as glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

[0025] The ester used in the present invention may be those of one type of ester with a single structure or a mixture of two or more esters with different structures.

Among these synthetic esters, preferred are polyol esters because of their excellent hydrolysis stability.

[0026] Examples of the fats used as the base oil of the flame retardant hydraulic oil composition of the present invention include natural animal or vegetable fats, such as rapeseed oil, sunflower oil, soybean oil, castor oil, coconuts oil, corn oil, cotton seed oil, olive oil, rice bran oil, palm oil, palm kernel oil, peanut oil, tall oil, beef tallow, lard, and hydrogenated products thereof. Among these fats, preferred are high oleic acid type vegetable oils wherein the ratio of the unsaturated fatty acids, particularly oleic acid in the fatty acid constituting the ester is high, such as rapeseed oil, sunflower oil and soybean oil, and more preferred are high oleic fats that are further increased in oleic acid ratio.

[0027] The base oil of the flame retardant hydraulic oil composition of the present invention may be one or more types selected from the group consisting of the above-described synthetic esters and fats.

[0028] In the above-described synthetic esters and/or fats, the ratio of the unsaturated fatty acid in the fatty acid constituting the ester is necessarily 20 percent by mole or more, preferably 50 percent by mole or more, more preferably 70 percent by mole or more. The constituting fatty acids may be selected from saturated fatty acids, unsaturated fatty acids, straight-chain fatty acids and branched fatty acids if the ratio of the unsaturated fatty acid is 20 percent by mole or more but preferably contains a larger amount of unsaturated fatty acids in view of the effect of Component (C), i.e., an amine-based antioxidant, which is bis(4-dialkylaminophenyl)methane represented by formula (1).

If the ratio of the unsaturated fatty acid in the fatty acid constituting the ester is less than 20 percent by mole or less, blending of Component (C) is effective in suppressing the viscosity and acid value from increasing at the initial stage of use of the hydraulic oil but after further progress of the use, deteriorated products tend to become sludge rapidly and cause troubles in a hydraulic system.

In order to further enhance the effect of suppressing the elution of zinc, the acid value of the ester is necessarily 1.0 mgKOH/g or less. If the ester has an acid value of greater than 1.0 mgKOH/g, it inhibits the effects of Component (B), i.e., a metal corrosion inhibitor, which is an alkylthiziazole and Component (D), i.e., a nitrogen-based metal deactivator, which is a triazole compound and will be facilitated in oxidation degradation and thus inhibit the zinc elution preventing properties of the compos it ion.

[0029] No particular limitation is imposed on the kinematic viscosity of these base oils. However, the kinematic viscosity at 40°C is preferably from 10 to 200 mm2/s, more preferably from 15 to 150 mm2/s, more preferably from 20 to 100 mm2/s because the resulting hydraulic composition would be excellent in flame retardant properties, antiwear properties and anti-seizure properties and less in energy loss by stirring resistance. No particular limitation is imposed on the viscosity index of the base oils, either. However, the viscosity index is preferably 80 or greater, more preferably 100 or greater with the objective of maintaining oil film at high temperatures. Furthermore, the pour point is also optional but is preferably -5°C or lower, more preferably -15 ° C or lower with the viewpoint of pump startability during winter.

[0030] The flame retardant hydraulic oil composition of the present invention contains an alkylthiaziazole that is a metal corrosion inhibitor as Component (B).
The alkylthiaziazole is preferably 1, 3 , 4-thiziazole represented by formula (2) below, 1, 2 , 4-thiaziazole represented by formula (3) below or 1, 4 , 5-thiziazole represented by formula (4) below. Alternatively, a mixture of two or more of them is preferably used.

[0031] wherein R5 and R6 may be the same or different from one another and are each independently hydrogen or a hydrocarbon group having 1 to 20 carbon atoms, and a and b may be the same or different from one another and are each independently an integer of 0 to 8.

[0032]

wherein R7 and R8 may be the same or different from one another and are each independently hydrogen or a hydrocarbon group having 1 to 20 carbon atoms, and c and d may be the same or different from one another and are each independently an integer of 0 to 8.

[0033]

wherein R9 and R10 may be the same or different from one another and are each independently hydrogen or a hydrocarbon group having 1 to 20 carbon atoms, and eand f may be the same or different from one another and are each independently an integer of 0 to 8.

[0034] Specific examples of such thiaziazole compounds include

2,5-bis (n-hexyldithio)-1,3,4-thiadiazole,
2,5-bis (n-octyldithio)-1,3,4-thiadiazole,
2,5-bis (2-ethylhexyldithio)-1,3,4-thiaziasole,
2,5-bis (n-nonyldithio)-1,3, 4-thiadiazole,
2,5-bis(l,l,3,3-tetramethylbutyldithio)-1,3,4- thiadiazole,
3,5-bis (n-hexyldithio)-1,2,4-thiadiazole,
3,5-bis (n-octyldithio)-1,2, 4-thiadiazole,
3, 5-bis (n-nonyldithio)-1,2, 4-thidiazole,
3,5-bis(l,l,3,3-tetramethylbutyldithio)-1,2,4-thiadia zole,
4,5-bis(n-hexyldithio)-l,2,3-thiadiazole, 4,5-bis (n-octyldithio)-1,2 ,3-thidiazole, 4,5-bis (n-nonyldithio)-l,2,3-thiadiazole, and 4,5-bis(l,l,3,3-tetramethylbutyldithio)-l,2,3-thiadiazole, and mixtures thereof. [0035] The flame retardant hydraulic oil composition of the present invention contains an alkylthiaziazole that is Component (B) in an amount of 0.001 percent by mass or more, preferably 0.005 percent by mass or more, more preferably 0.01 percent by mass or more on the basis of the total mass of the composition. If the content of Component (B) is less than 0.001 percent by mass, the resulting oil composition fails to obtain zinc elution preventing properties. The flame retardant hydraulic oil composition of the present invention contains Component (B) in an amount of 1.0 percent by mass or less, preferably 0.8 percent by mass or less, more preferably 0.6 percent by mass or less on the basis of the total mass of the composition. If the content of Component (B) is more than 1.0 percent by mass, the resulting oil composition is likely to be sludge due to the decomposition of the alkylthiziazole.

[0036] The flame retardant hydraulic oil composition of the present invention may contain bis(4-dialkylaminopheny1)methane represented by formula (1), which is an amine-based antioxidant as Component (C).

[0037]

[0038] In formula (1), R1, R2, R3 and R4 may be the same or different from each other and are each independently a straight-chain or branched alkyl group having 1 to 6 carbon atoms. If the carbon number of any of R1, R2, R3 and R4 groups is greater than 6, the ratio of the functional group in the molecule would be small, possibly resulting in an adverse affect on antioxidation effect. Examples of the alkyl group represented by R1, R2, R3 and R4 include methyl, ethyl, propyl, butyl, pentyl and hexyl groups (all of which may be straight-chain or branched). [0039] Among the amine-based antioxidants represented by formula (1) , preferred are those wherein R1, R2, R3, and R4 are each independently methyl, ethyl or a branched alkyl group having 3 or 4 carbon atoms, and most preferred are those wherein R1, R2, R3, and R4 are each independently methyl or ethyl.

[0040] The flame retardant hydraulic oil composition of the present invention contains Component (C) that is bis(4-dialkylaminophenyl)methane in an amount of preferably 5.0 percent by mass or less, more preferably 3.0 percent by mass or less, more preferably 1.0 percent by mass or less on the basis of the total mass of the composition . A content of more than 5. 0 percent by mass is not preferable because it causes the formation of sludge.

Whereas, the oil composition contains Component (C) in an amount of 0.001 percent by mass or more, more preferably 0.005 percent by mass or more, more preferably 0.01 percent by mass or more on the basis of the total mass of the composition. A content of less than 0.001 percent by mass is not preferable because the resulting composition can not sufficiently suppress the oxidation degradation of the ester and thus would fail to suppress zinc elution. [0041] The flame retardant hydraulic oil composition of the present invention may contain a triazole compound, which is a nitrogen-based metal deactivator as Component (D) . Component (D) that is a triazole compound is preferably selected from the group consisting of triazole derivatives, benzotriazole derivatives and tolutriazole derivatives. Specific examples of the benzotriazole derivative include N,N-bis (2-ethylhexyl)-4-methyl-lH-benzotriazole-l-methylamine and N,N-bis(2-ethylhexyl)-5-methyl-lH-benzotriazole-l-methyl amine.

[0042] The flame retardant hydraulic oil composition contains Component (D) in an amount of preferably 0.0001 percent by mass or more, more preferably 0.0005 percent by mass or more, more preferably 0.001 percent by mass or more on the basis of the total mass of the composition. A content of less than 0.0001 percent by mass is not preferable the resulting composition would fail to suppress sufficiently zinc elution. Whereas, the oil composition contains Component (D) in an amount of preferably 1.0 percent by mass or less, more preferably 0.8 percent by mass or less, more preferably 0.5 percent by mass, or less on the basis of the total mass of the composition . A content of more than 1. 0 percent by mass is not preferable because Component (D) is hardly dissoluble in the ester base oil and thus is likely to be sludge due to the degradation of additives.

[0043] The flame retardant hydraulic oil composition of the present invention may contain Component (E), which is at least one type of anti-wear additive selected from the group consisting of (El) sulfur-containing phosphoric acid esters, (E2) acidic phosphoric acid esters, (E3) acidic phosphoric acid ester amine salts, and (E4) phosphorus acid esters in order to further enhance the properties of the composition.

[0044] Specific examples of (El) sulfur-containing phosphoric acid esters include trialkyl phosphorothionates whose alkyl group has 4 to 18 carbon atoms, trioleyl phosphorothionate, triphenyl phosphorothionate, tricresyl phosphorothionate, trixylenyl phosphorothionate, cresyldipheny1 phosphorothionate, xylenyldiphenyl phosphorothionate, tris (n-propylphenyl) phosphorothionate., tris(isopropylpheny1) phosphorothionate, tris ( n-butylphenyl) phosphorothionate, tris ( isobutylphenyl) phosphorothionate, tris(s-butylphenyl) phosphorothionate, and tris (t-butylphenyl) phosphorothionate.

[0045] Specific examples of (E2) acidic phosphoric acid esters include alkyl acid phosphates whose alkyl group has 7 to 18 carbon atoms, dialkyl acid phosphates whose alkyl group has 4 to 18 carbon atoms, and dioleyl acid phosphates.

[0046] Specific examples of (E3) acidic phosphoric acid ester amine salts include salts of the aforesaid acidic phosphoric acid esters and amines having an alkyl group of 1 to 8 carbon atoms, amines having two alkyl groups of 1 to 8 carbon atoms, and amines having three alkyl groups of 1 to 8 carbon atoms. [0047] Specific examples of (E4) phosphorus acid esters include dialkyl phosphites having two alkyl groups of 4 to 12 carbon atoms, dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, trialkyl phosphites having three alkyl groups of 4 to 12 carbon atoms, trioleyl phosphite, triphenyl phosphite, and tricresyl phosphite.

[0048] Component (E) is preferably any of (El) sulfur-containing phosphoric acid esters, (E2) acidic phosphoric acid esters, and (E3) acidic phosphoric acid ester amine salts because they exhibit superior effects in combination with a synthetic ester or fat base oil. [0049] When the flame retardant hydraulic oil composition of the present invention is blended with Component (E), the content thereof is preferably 5 percent by mass or less, more preferably 2 percent by mass, more preferably 1.5 percent by mass on the basis of the total mass of the composition. A content of more than 5 percent by mass is not preferable because the resulting composition would be poor in thermal stability and thus cause sludge formation. Whereas, the content of Component (E) is preferably 0.001 percent by mass or more, more preferably 0.005 percent by mass or more, more preferably 0.01 percent by mass or more on the basis of the total mass of the composition A content of less than 0.001 percent by mass is hot preferable because the resulting composition could not be expected to be improved in antiwear properties and anti-seizure properties.

[0050] The use of the phenol-based antioxidant can impart superior antioxiation properties and sludge suppressing properties to the flame retardant hydraulic oil composition. No particular limitation is imposed on the phenol-based antioxidant since any alkylphenol-based compound that has been used as an antioxidant for lubricants may be used. However, the phenol-based antioxidant is preferably of hindered phenol type such as alkylphenols and bisphenols, preferably those containing a sulfide group and an ester bond in the molecule.

[0051] The flame retardant hydraulic oil composition of the present invention contains the phenol-based antioxidant in an amount of preferably 5 percent by mass or less, more preferably 2 percent by mass, more preferably 1.5 percent by mass on the basis of the total mass of the composition. A content of more than 5 percent by mass is not preferable because it causes sludge formation. Whereas, the oil composition contains the phenol-based antioxidant in an amount of preferably 0.01 percent by mass or more, 0.05 percent by mass or more, more preferably 0.1 percent by mass or more on the basis of the total mass of the composition. A content of less than 0.01 percent by mass is not also preferable because the resulting composition would be insufficient in an antioxidation effect. [0052] As described above, in the present invention, at least one base oil selected from synthetic esters and fats is only blended with Components (B) and furthermore one or more types of additives selected from the group consisting of Components (C), (D) and (E) and a phenol-based antioxidant thereby producing a flame retardant hydraulic oil composition that is excellent in antioxidation and antiwear properties. However, if necessary, in order to further enhance these properties, the oil composition may be blended with any one or suitable combinations of various additives such as antioxidants other than those described above, rust inhibitors, metal deactivators other than those described above, antiwear agents other than those described above, viscosity index improvers, pour point depressants, anti-foaming agents, demulsifiers, stickslip preventive agents, and oiliness improvers.

[0053] In addition to Component (C) that is an amine-based antioxidant, other amine-based antioxidant may be used in combination. Typical examples of the amine-based antioxidant include phenyl-a-naphthylamines represented by formula (5) and p,p'-dialkyldiphenylamines represented by formula (6) .

[0054]

wherein R11 is hydrogen or an alkyl group having 1 to 16 carbon atoms.

[0055]

wherein R12 and R13 are each independently a straight-chain or branched alkyl group having 1 to 16 carbon atoms.

[0056] The content of the amine-based antioxidant other than Component (C) is preferably from 0.001 to 2.0 percent by mass on the basis of the total mass of the composition.

[0057] Specific examples of the rust inhibitors include amino acid derivatives; partial esters of polyhydric alcohols; esters such as lanolin fatty acid ester, alkyl succinic acid esters and alkenyl succinic acid esters; sarcosine; polyhydric alcohol partial esters such as sorbitan fatty acid esters; metal soaps such as fatty acid metal salts, lanolin fatty acid metal salts and oxidized wax metal salts; sulfonates such as calcium sulfonate and barium sulfonate; oxidized waxes; amines; phosphorus acid; and phosphorus acid salts. Among these rust inhibitors, amino acid derivatives are preferably used because of their superior rust inhibiting effect.

[0058] Examples of the above-mentioned amino acid derivatives include compounds represented by formula ( 7) below.

[0059]

[0060] In formula (7) above, A is a group represented by formula (8) or (9), B is an alkyl group having 1 to 12 carbon atoms or a residue of a monohydric carboxylic acid ester represented by formula (10) below, R14 is an alkyl group having 4 to 12 carbon atoms, and R15 is an alkyl group having 1 to 10 carbon atoms.

R170-CO-R16- (8)
R190-CO-R18-CO- (9)
-C-CO-O-R20 (10)

wherein R16 is an alkylene group having 1 to 12 carbon atoms, R18 is an alkylene group having 1 to 10 carbon atoms, R17 and R19 are each independently hydrogen or an alkyl group having 1 to 10 carbon atoms, and R20 is an alkyl group having 1 to 10 carbon atoms. [0061] In the present invention, the hydraulic oil composition may be blended with any one or more compound selected from these rust inhibitors in any amount. However, in general the content is preferably from 0.001 to 2.0 percent by mass on the basis of the total mass of the composition.

[0062] Specific examples of the metal deactivators other than Component (D) include imidazole-based compounds. In the present invention, the hydraulic oil composition may be blended with any one or more compound selected from these metal deactivators in any amount. However, in general the content is preferably from 0.0001 to 1 percent by mass on the basis of the total mass of the composition.

[0063] Specific examples of the viscosity index improvers include non-dispersant type viscosity index improvers such as copolymers of one or more monomers selected from various methacrylic acid esters or hydrogenated compounds thereof, ethylene-a-olefin copolymers (a-olefin may be propylene, 1-butene, or 1-pentene) or hydrogenated compounds thereof, polyisobutylenes or hydrogenated compounds thereof; hydrogenated compounds of styrene-diene, and polyalkylstyrenes. In the present invention, the hydraulic oil composition may be blended with any one or more of these viscosity index improvers in any amount. However, in general the content is preferably from 0.01 to 10 percent by mass on the basis of the total mass of the composition.

[0064] Specific examples of the pour point depressants include copolymers of one or more monomers selected from various acrylic acid esters and methacrylic acid esters or hydrogenated compounds thereof. In the present invention, the hydraulic oil composition may be blended with any one or more of these pour point depressants in any amount. However, in general the content is preferably from 0.01 to 5 percent by mass on the basis of the total mass of the compos it ion.

[0065] Specific examples of the anti-foaming agents include silicones such as dimethylsilicone and fluorosilicone. In the present invention, the hydraulic oil composition may be blended with any one or more of these anti-foaming agents in any amount. However, in general the content is preferably from 0.001 to 0.05 percent by mass on the basis of the total mass of the composition.

Examples of the demulsifiers include polyoxyalkyleneglycols, polyoxyalkylenealkylethers, polyoxyalkylenealkylmides, and polyoxyalkylene fatty acid esters.

Specific examples of the stickslip preventive agents include polyhydric alcohol esters (full esters and partial esters).

Specific examples of the oiliness improvers include fatty acids, esters, and alcohols. In general, the content is preferably from 0.01 to 0.5 percent by mass on the basis of the total mass of the hydraulic oil composition.

Examples

[0066] The present invention will be described in more details with reference to the following examples and comparative examples but is not limited thereto. The flash point of and various test for each composition were measured and carried out in accordance with the following methods.

[0067] [Flash Point]
The flash point of each composition was measured in accordance with JIS J 2265 "Crude Oil and Petroleum Products-Determination of flash point (Cleveland open cup method)".

[Four-Ball Test]
This test was carried out at a revolution number of 1200 min"1, a load of 294 N, an oil temperature of 75°C for one hour in accordance with ASTM D 2783-88 "Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Fluids (Four-Ball Method)" to measure the average of scar diameters (mm) of fixed three balls.

[FZG Gear test]
This test is carried out in accordance with ASTM D 5182. The test was started at a revolution number of 1500 min-1 and at an oil temperature of 90°C, and a gear is loaded by applying a certain weight defined in each stage while driven for 15 minute. The anti-seizure properties of each oil was evaluated with the stage where seizure occurs. The stage of load at which the gear seizes is defined as failure.

[Vane Pump Test]
The vane pump test was carried out for 100 hours in accordance with ASTM D 2882. The weights of a vane and a rings were measured before and after the test to determine the wear amount (mg).

[Dry TOST Test]
This test was carried out in accordance with "TOST oxidation stability test" defined in JIS K 2514. The oxidation stability test was carried out by putting 300 ml of a sample oil in a defined vessel and then putting thereinto coil-shaped iron and copper catalysts, and then placing the vessel into a water bath kept at a temperature of 95°C, for 20 days. No water was used. During the test, the sample oil was taken out little by little to measure the acid value increase (mgKOH/g) and the sludge amount (mg/50 ml) (in which a certain amount of the sample oil was filtered with a filter and the weight of the residue was converted to the amount per 50 mL) .

[Zinc Elution Test]
An immersion test was carried out at a temperature of 120°C for 20 days in accordance with JIS B 2301-1976 wherein one defined screwed type malleable cast iron pipe fitting was put in a beaker containing 200 ml of a sample oil. After the test, the amount of zinc eluted in the sample oil (mass ppm) was measured to compare the zinc elution properties for each oil sample .

[0068]

Components used in Examples and Comparative Examples are as follows.
(A) base oil

A1 : ester of t r imethy lolpropane and a mixed fatty acid of oleic acid, otylic acid, and decanoic acid ( 4 0 ° C kinematic viscosity: 47.2mm2/s, viscos ity index: 180, unsaturate ratio: 70 percent by mole, acid value: 0. 5)

A2: ester of trimethylolpropane and a mixed fatty acid of oleic acid, otylic acid, and decanoic acid (40°C kinematic viscosity: 45.2mm2/s, viscosity index: 185, unsaturate ratio: 90 percent by mole, acid value: 2.0)

A3: ester of trimethylolpropane and a mixed fatty acid of oleic acid, otylic acid, and decanoic acid (40°C kinematic viscosity: 34.2 mm2/s, viscosity index: 130, unsaturate ratio: 10 percent by mole, acid value: 0.3)

A4 : ester of pentaerythritol and a mixed fatty acid of oleic acid, otylic acid, and decanoic acid (40 °C kinematic viscosity: 66.2mm2/s, viscosity index: 160, unsaturate ratio: 70 percent by mole, acid value: 1.0)

(B) metal deactivator
Bl: 2,5-bis(2ethylhexyldithio)-l,3,4 thiaziazole
B2: 2,5-bis(n-hexyldithio)-1,3,4 thiziazole

(C) antioxidant
CI: bis(4-dimethylaminophenyl)methane C2: a-naphtylamine C3: 4,4'-methylene bis(2,6-di-tert-butylphenol)

(D) nitrogen-based metal deactivator
Dl: N,N-bis(2-ethylhexyl)-4-methyl-lH- benzotriazole-1-methylamine D2: benzotriazole

(E) antiwear agent
El: 2-ethylhexyl acid phosphate E2 : tricresylphosphate
(F) other additives

E3: sorbitan monooleate

[0069] As shown in Tables 1 and 2, Comparative Example 4 using the base oil where the ratio of the unsaturated fatty acid in the fatty acid constituting the ester is 10 percent by mole was poorer in oxidation stability and in particular formed more sludge than Example 6 although the acid value is low.

Comparative Examples 1 to 3 using base oil A2 whose acid value was 2.0 mgKOH/g were larger in the amount of eluted zinc than Examples 2 and 5 although the ratio of the unsaturated fatty acid in the fatty acid constituting the ester is 90 percent by mole, which is high.

Industrial Applicability
[0072] The flame retardant hydraulic oil composition of the present invention is most suitably used for applications where it is used under high temperature and pressure conditions with the high risk of fire breakout, such as for use in aluminum die-cast extruding machines or operations in iron mill facilities and that is applicable to a high-pressure pump, excellent in antiwear properties, sludge suppressing properties and in particular zinc elution suppressing properties, making it possible to be used for a long period of time. The composition is thus significantly useful in the industry.

CLAIMS
1. A flame retardant hydraulic oil composition comprising:

(A) at least one type of base oil selected from the group consisting of synthetic esters and fats, containing 20 percent by mole or more of an unsaturated fatty acid in the fatty acid constituting the ester and having an acid value of 1.0 mgKOH/g or less and

(B) an alkylthiadiazole in an amount of 0.001 to 1.0 percent by mass on the basis of the total mass of the composition.

2. The flame retardant hydraulic oil composition according to claim 1, further comprising:

(C) bis(4-dialkylaminopheny1)methane represented by formula (1) below in an amount of 0.001 to 5.0 percent by- mass on the basis of the total mass of the composition:

wherein R1, R2, R3 and R4 is the same or different from each other and are each independently an alkyl group having 1 to 6 carbon atoms.

3. The flame retardant hydraulic oil composition according to claim 1 or 2, further comprising (D) at least one type of triazole compound selected from the group consisting of triazole derivatives, benzotriazole derivatives and tolutriazole derivatives in an amount of 0.0001 to 1.0 percent by mass on the basis of the total mass of the compos it ion.