Patent Application
20200277543
This application is based on and claims priority from Korean Patent Application No. 10-2019-0023681, filed on Feb. 28, 2019 with the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
The present invention relates to a lubricant composition, and more particularly to a lubricant composition, which has superior oxidation stability and friction characteristics even under harsh conditions of high temperature and high pressure and is thus suitable for use in hydraulic oil.
A lubricant is an oily material used to reduce the generation of frictional force on the friction surface of a machine or to dissipate frictional heat generated from the friction surface. Because of the wide variety of machinery that requires lubrication and the wide variety of conditions under which such machinery works, lubricants vary in type and quality. Depending on the application thereof, different types of base oil must be used. In particular, when a lubricant is used for an airplane or an advanced hydraulic system, hydraulic oil having a strong flame-retarding effect is required.
Any type of hydraulic oil used in industrial fields is a medium of power transmission and plays roles in lubrication, rust prevention, sealing and cooling of respective parts of hydraulic equipment. The hydraulic oil is manufactured by adding additives to base oil, and is largely classified into mineral hydraulic oil (petroleum-based hydraulic oil) and synthetic hydraulic oil depending on the type of base oil, synthetic hydraulic oil being classified into polyalphaolefin-based hydraulic oil and ester-based hydraulic oil.
Meanwhile, the operating temperature range of hydraulic oil varies, and especially in the summer, may be 75 to 850 or higher. At such temperatures, however, mineral hydraulic oil and polyalphaolefin-based hydraulic oil generate a lot of oil vapor. The occurrence of such oil vapor causes a problem of increasing the evaporation loss of hydraulic oil, and also promotes the oxidation of hydraulic oil. Hence, it is necessary to minimize the generation of oil vapor. In particular, mineral hydraulic oil, which accounts for most hydraulic oil, requires additional measures to improve oxidation stability due to the characteristics of the base feedstock oil. Moreover, since hydraulic systems are recently becoming more and more sophisticated, hydraulic oil is required to have superior friction characteristics.
Therefore, the present inventors have developed a lubricant composition for hydraulic oil, which has superior thermal and oxidation stability and is capable of reducing mechanical wear of hydraulic equipment.
(Patent Document 0001) Korean Patent No. 10-0201759
(Patent Document 0002) Korean Patent Application Publication No. 10-2008-0109015
Accordingly, the present invention has been made keeping in mind the problems encountered in the related art, and an objective of the present invention is to provide a lubricant composition, in which a functional additive for friction reduction and an ethylene-alphaolefin liquid random copolymer having a high viscosity index are mixed, thereby exhibiting superior friction characteristics, thermal stability and oxidation stability.
Another objective of the present invention is to provide a lubricant composition for hydraulic oil, which is capable of reducing the mechanical wear of hydraulic equipment and energy consumption when applied to hydraulic equipment and of decreasing evaporation loss due to low changes in the physical properties of hydraulic oil, and thus may be used for a long period of time.
In order to accomplish the above objectives, the present invention provides a lubricant composition, comprising a base oil, a liquid olefin copolymer, a phosphorothioate compound, and phosphonium phosphate.
The base oil may be at least one selected from the group consisting of mineral oil, polyalphaolefin (PAO) and ester.
The liquid olefin copolymer may be prepared by copolymerizing ethylene and alphaolefin in the presence of a single-site catalyst system, and the single-site catalyst system preferably includes a metallocene catalyst, an organometallic compound and an ionic compound.
The liquid olefin copolymer may have a coefficient of thermal expansion of 3.0 to 4.0.
The liquid olefin copolymer may be included in an amount of 0.5 to 30 wt %, and preferably 0.5 to 25 wt %, in the lubricant composition of the present invention.
The phosphorothioate compound may be included in an amount of 0.1 to 5.0 wt %, and preferably 0.1 to 3.0 wt %, in the lubricant composition.
The phosphonium phosphate may be included in an amount of 0.05 to 3.0 wt %, and preferably 0.1 to 1.5 wt %, in the lubricant composition.
The lubricant composition may have an SRV friction coefficient of 0.1 to 0.35 and a traction coefficient of 0.15 to 0.3.
According to the present invention, a lubricant composition includes phosphorothioate, phosphonium phosphate, and an ethylene-alphaolefin liquid random copolymer having a high viscosity index, which are mixed together, thereby improving friction characteristics and thermal and oxidation stability, and is capable of reducing the mechanical wear of hydraulic equipment and energy consumption when applied to hydraulic equipment, thereby maximizing energy-saving effects.
Also, according to the present invention, the lubricant composition has low changes in the physical properties of hydraulic oil, thus decreasing evaporation loss, and can endure 1000 min or more, and preferably 1200 min or more, in an RBOT oxidation stability test (ASTM D2271), thereby enabling the long-term use thereof as hydraulic oil.
Hereinafter, a detailed description will be given of the present invention.
The present invention relates to a lubricant composition, which has superior oxidation stability and friction characteristics and is thus suitable for use in hydraulic oil. Hence, the lubricant composition of the present invention includes a base oil, a liquid olefin copolymer, a phosphorothioate compound, and phosphonium phosphate.
Here, the base oil varies from the aspects of viscosity, heat resistance, oxidation stability and the like depending on the manufacturing method or refining method, but is generally classified into mineral oil and synthetic oil. The API (American Petroleum Institute) classifies base oil into five types, namely Group I, II, III, IV and V. These types, based on API ranges, are defined in API Publication 1509, 15th Edition, Appendix E, April 2002, and are shown in Table 1 below.
In the lubricant composition of the present invention, the base oil may be at least one selected from the group consisting of mineral oil, polyalphaolefin (PAO) and ester, and may be any type among Groups I to V based on the API ranges.
More specifically, mineral oil belongs to Groups I to III based on the API ranges, and mineral oil may include oil resulting from subjecting a lubricant distillate fraction, obtained through atmospheric distillation and/or vacuum distillation of crude oil, to at least one refining process of solvent deasphalting, solvent extraction, hydrogenolysis, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid cleaning, and white clay treatment; wax isomerized mineral oil; or a gas-to-liquid (GLT) oil obtained via the Fischer-Tropsch process.
The synthetic oil belongs to Group IV or V based on the API ranges, and polyalphaolefin belonging to Group IV may be obtained through oligomerization of a higher alphaolefin using an acid catalyst, as disclosed in U.S. Pat. Nos. 3,780,128, 4,032,591, Japanese Patent Application Publication No. Hei. 1-163136, and the like, but the present invention is not limited thereto.
Examples of the synthetic oil belonging to Group V include alkyl benzenes, alkyl naphthalenes, isobutene oligomers or hydrides thereof, paraffins, polyoxy alkylene glycol, dialkyl diphenyl ether, polyphenyl ether, ester, and the like.
Here, the alkyl benzenes and alkyl naphthalenes are usually dialkylbenzene or dialkylnaphthalene having an alkyl chain length of 6 to 14 carbon atoms, and the alkyl benzenes or alkyl naphthalenes are prepared through Friedel-Crafts alkylation of benzene or naphthalene with olefin. The alkylated olefin used in the preparation of alkyl benzenes or alkyl naphthalenes may be linear or branched olefins or combinations thereof.
Also, examples of the ester include, but are not limited to, ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, tridecyl pelargonate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, trimethylolpropane caprylate, trimethylolpropane pelargonate, trimethylolpropane triheptanoate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, pentaerythritol tetraheptanoate, and the like.
In the lubricant composition of the present invention, the liquid olefin copolymer is prepared by copolymerizing ethylene and alphaolefin monomers in the presence of a single-site catalyst system in order to uniformly distribute alphaolefin units in the copolymer chain. Preferably, the liquid olefin copolymer is prepared by reacting ethylene and alphaolefin monomers in the presence of a single-site catalyst system including a crosslinked metallocene compound, an organometallic compound, and an ionic compound for forming an ion pair through reaction with the crosslinked metallocene compound.
Here, the metallocene compound included in the single-site catalyst system may be at least one selected from the group consisting of Chemical Formulas 1 to 6 below.
In Chemical Formulas 1 to 4,
M is a transition metal selected from the group consisting of titanium, zirconium, and hafnium,
B is absent or is a linking group including a C1-C20 alkylene group, a C6-C20 arylene group, C1-C20 dialkyl silicon, C1-C20 dialkyl germanium, a C1-C20 alkylphosphine group or a C1-C20 alkylamine group,
X1 and X2, which are the same as or different from each other, are each independently a halogen atom, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C7-C40 alkylaryl group, a C7-C40 arylalkyl group, a C1-C20 alkylamido group, a C6-C20 arylamido group, a C1-C20 alkylidene group or a C1-C20 alkoxy group, and
R1 to R10, which are the same as or different from each other, are each independently hydrogen, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C6-C20 aryl group, a C7-C20 alkylaryl group, a C7-C20 arylalkyl group, a C5-C60 cycloalkyl group, a C4-C20 heterocyclic group, a C1-C20 alkynyl group, a C6-C20-aryl-containing hetero group or a silyl group.
In Chemical Formulas 5 and 6,
M is a transition metal selected from the group consisting of titanium, zirconium, and hafnium,
B is absent or is a linking group including a C1-C20 alkylene group, a C6-C20 arylene group, a C1-C20 dialkyl silicon, a C1-C20 dialkyl germanium, a C1-C20 alkylphosphine group or a C1-C20 alkylamine group,
X1 and X2, which are the same as or different from each other, are each independently a halogen atom, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C7-C40 alkylaryl group, a C7-C40 arylalkyl group, a C1-C20 alkylamido group, a C6-C20 arylamido group, a C1-C20 alkylidene group or a C1-C20 alkoxy group, and
R1 to R10, which are the same as or different from each other, are each independently hydrogen, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C6-C20 aryl group, a C7-C20 alkylaryl group, a C7-C20 arylalkyl group, a C5-C60 cycloalkyl group, a C4-C20 heterocyclic group, a C1-C20 alkynyl group, a C6-C20-aryl-containing hetero group or a silyl group.
Furthermore, all of R11, R13 and R14 are hydrogen, and each of R12 radicals, which are the same as or different from each other, may independently be hydrogen, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C6-C20 aryl group, a C7-C20 alkylaryl group, a C7-C20 arylalkyl group, a C5-C60 cycloalkyl group, a C4-C20 heterocyclic group, a C1-C20 alkynyl group, a C6-C20-aryl-containing hetero group or a silyl group.
Also, the metallocene compound of Chemical Formulas 2 to 6 may include a compound substituted through a hydroaddition reaction, and a preferred example thereof includes dimethylsilyl bis(tetrahydroindenyl) zirconium dichloride.
The organometallic compound included in the single-site catalyst system may be at least one selected from the group consisting of an organoaluminum compound, an organomagnesium compound, an organozinc compound and an organolithium compound, and is preferably an organoaluminum compound. The organoaluminum compound may be at least one selected from the group consisting of, for example, trimethylaluminum, triethylaluminum, triisobutylaluminum, tripropylaluminum, tributylaluminum, dimethylchloroaluminum, dimethylisobutylaluminum, dimethylethylaluminum, diethylchloroaluminum, triisopropylaluminum, triisobutylaluminum, tricyclopentylaluminum, tripentylaluminum, triisopentylaluminum, ethyldimethylaluminum, methyldiethylaluminum, triphenylaluminum, methylaluminoxane, ethylaluminoxane, isobutylaluminoxane and butylaluminoxane, and is preferably triisobutylaluminum.
The ionic compound included in the single-site catalyst system may be at least one selected from the group consisting of organoboron compounds such as dimethylanilinium tetrakis(perfluorophenyl)borate, triphenylcarbenium tetrakis(perfluorophenyl)borate, and the like.
The component ratio of the single-site catalyst system may be determined in consideration of catalytic activity, and the molar ratio of metallocene catalyst:ionic compound:organometallic compound is preferably adjusted in the range of 1:1:5 to 1:10:1000 in order to ensure desired catalytic activity.
Furthermore, the components of the single-site catalyst system may be added at the same time or in any sequence to an appropriate solvent and may thus function as an active catalyst system. Here, the solvent may include, but is not limited to, a hydrocarbon solvent such as pentane, hexane, heptane, etc., or an aromatic solvent such as benzene, toluene, xylene, etc., and any solvent usable in the preparation may be used.
Also, the alphaolefin monomer used in the preparation of the liquid olefin copolymer includes a C2-C20 aliphatic olefin, and may specifically be at least one selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-octene, 1-decene, 1-dodecene and 1-tetradecene, and may include isomeric forms, but the present invention is not limited thereto. In the copolymerization, the monomer content is 1 to 95 mol %, preferably 5 to 90 mol %.
The liquid olefin copolymer required in the present invention has a coefficient of thermal expansion of 3.0 to 4.0 and a bromine number of 0.1 or less.
The liquid olefin copolymer may be included in an amount of 0.5 to 30 wt %, and preferably 0.5 to 25 wt %, based on 100 wt % of the lubricant composition. If the amount of the liquid olefin copolymer is less than 0.5 wt % based on 100 wt % of the lubricant composition, stability may deteriorate. On the other hand, if the amount thereof exceeds 30 wt %, application of the resulting composition to hydraulic oil becomes difficult, which is undesirable.
The phosphorothioate compound, serving as a friction-reducing agent, may be at least one selected from the group consisting of monophosphorothioate, diphosphorothioate, triphosphorothioate, methylphosphorothioate, ethylphosphorothioate and sulfonylphosphorothioate. When the phosphorothioate compound is included in the lubricant composition, it may exhibit synergistic effects with an existing wear-resistant agent and friction reduction effects, and additionally, energy-saving effects may be achieved through friction reduction.
The phosphorothioate compound may be included in an amount of 0.1 to 5.0 wt %, and preferably 0.1 to 3.0 wt %, based on 100 wt % of the lubricant composition. If the amount of the phosphorothioate compound is less than 0.1 wt % based on 100 wt % of the lubricant composition, the friction reduction effect is insignificant. On the other hand, if the amount thereof exceeds 5.0 wt %, the additional reduction effect is insignificant despite the excessive addition thereof, which is undesirable.
The phosphonium phosphate is a material having the structure of Chemical Formula 7 below, and is used as a friction/wear-reducing agent. In particular, when it is used together with the phosphorothioate compound, the effects thereof may be maximized.
The phosphonium phosphate exists in the form of an ionic liquid having both a phosphonium anion and a phosphate cation, and, among various phosphonium compounds, exhibits a characteristic friction/wear reduction effect.
Also, the phosphonium phosphate may be included in an amount of 0.05 to 3.0 wt %, and preferably 0.1 to 1.5 wt %, based on 100 wt % of the lubricant composition. If the amount of the phosphonium phosphate is less than 0.05 wt % based on 100 wt % of the lubricant composition, the friction/wear reduction effect may be insignificant. On the other hand, if the amount thereof exceeds 3.0 wt %, there is no synergistic effect thereof with the phosphorothioate compound, and wear may increase, which is undesirable.
The lubricant composition of the present invention may further include an additive selected from the group consisting of an antioxidant, a metal cleaner, an anticorrosive agent, a foam inhibitor, a pour-point depressant, a viscosity modifier, a wear-resistant agent and combinations thereof.
The antioxidant may be included in an amount of 0.01 to 5.0 wt % based on 100 wt % of the lubricant composition, and is preferably used in the form of a mixture of a phenolic antioxidant and an aminic antioxidant, more preferably a mixture of 0.01 to 3.0 wt % of the phenolic antioxidant and 0.01 to 3.0 wt % of the aminic antioxidant.
The phenolic antioxidant may be any one selected from the group consisting of 2,6-dibutylphenol, hindered bisphenol, high-molecular-weight hindered phenol, and hindered phenol with thioether.
The aminic antioxidant may be any one selected from the group consisting of diphenylamine, alkylated diphenylamine and naphthylamine, and preferably, the alkylated diphenylamine is dioctyldiphenylamine, octylated diphenylamine, or butylated diphenylamine.
The metal cleaner may be at least one selected from the group consisting of metallic phenate, metallic sulfonate, and metallic salicylate, and preferably, the metal cleaner is included in an amount of 0.1 to 10.0 wt % based on 100 wt % of the lubricant composition.
The anticorrosive agent may be a benzotriazole derivative, and is preferably any one selected from the group consisting of benzotriazole, 2-methylbenzotriazole, 2-phenylbenzotriazole, 2-ethylbenzotriazole and 2-propylbenzotriazole. The anticorrosive agent may be included in an amount of 0 to 4.0 wt % based on 100 wt % of the lubricant composition.
The foam inhibitor may be polyoxyalkylene polyol, and preferably, the foam inhibitor is included in an amount of 0 to 4.0 wt % based on 100 wt % of the lubricant composition.
The pour-point depressant may be poly(methacrylate), and preferably, the pour-point depressant is included in an amount of 0.01 to 5.0 wt % based on 100 wt % of the lubricant composition.
The viscosity modifier may be polyisobutylene or polymethacrylate, and preferably, the viscosity modifier is included in an amount of 0 to 15 wt % based on 100 wt % of the lubricant composition.
The wear-resistant agent may be at least one selected from the group consisting of organic borates, organic phosphites, organic sulfur-containing compounds, zinc dialkyl dithiophosphate, zinc diaryl dithiophosphate and phosphosulfurized hydrocarbon, and preferably, the wear-resistant agent is included in an amount of 0.01 to 3.0 wt %.
The lubricant composition of the present invention has an SRV friction coefficient of 0.1 to 0.35. Moreover, the lubricant composition has a traction coefficient of 0.15 to 0.3.
A better understanding of the present invention through the following examples. However, the present invention is not limited to these examples, but may be embodied in other forms. These examples are provided to thoroughly explain the invention and to sufficiently transfer the spirit of the present invention to those skilled in the art.
1. Preparation of Additive Composition
An additive composition for use in the lubricant composition of the present invention was prepared as shown in Table 2 below.
2. Preparation of Liquid Olefin Copolymer
A liquid olefin copolymer was prepared using an oligomerization method through a catalytic reaction process. Depending on the reaction time and conditions, which follow, liquid olefin copolymers having different molecular weights were prepared, and the properties thereof are shown in Table 3 below.
The reaction time and conditions were increased by 4 hr each from 20 hr. Here, the amounts of hydrogen and comonomer C3, which were added thereto, were increased by 10% each, and polymerization was performed under individual conditions, and the resulting polymers were classified depending on the molecular weight thereof.
3. Preparation of Lubricant Composition for Hydraulic Oil
A lubricant composition was prepared by mixing a base oil, the liquid olefin copolymer, a phosphorothioate compound, phosphonium phosphate and the additive prepared above, as shown in Tables 4 and 5 below. Here, the base oil was polyalphaolefin (PAO 4 cSt, available from Chevron Philips) having kinematic viscosity of 4 cSt at 1000, and the phosphorothioate compound was monophosphorothioate.
4. Evaluation of Properties
The properties of the lubricant compositions prepared in Preparation Examples and Comparative Examples were measured as follows. The results are shown in Tables 6 and 7 below.
Friction Coefficient
In the ball-on-disc mode, friction performance was evaluated by sequentially elevating the temperature in increments of 100 from 40 to 120□ at 50 Hz and comparing the average friction coefficients at individual temperatures.
Here, the friction coefficient value decreases with an increase in effectiveness.
Traction Coefficient
The traction coefficient was measured using an MTM instrument made by PCS Instruments. Here, the measurement conditions were fixed at 50N and SRR 50%, and friction and traction were observed depending on changes in temperature. The temperature was varied from 40 to 120□, and the average values were compared.
Wear Resistance
Four steel balls were subjected to friction with the lubricant composition for 60 min under conditions of 20 kg load, 1200 rpm, and 540, the sizes of wear scars were compared, and evaluation was carried out in accordance with ASTM D4172. Here, the wear scar (average wear scar diameter, μm) value decreases with an increase in effectiveness.
Oxidation Stability
Oxidation stability was measured using an RBOT (Rotational Bomb Oxidation Test) meter in accordance with ASTM D2271.
As is apparent from Tables 6 and 7, the lubricant compositions including the liquid ethylene alphaolefin copolymer, the phosphorothioate compound and the phosphonium phosphate within the amount ranges of the present invention were significantly reduced in wear scar and friction coefficient compared to the lubricant compositions of Comparative Examples, and also exhibited superior oxidation stability. Therefore, it is concluded that the lubricant composition of the present invention is improved from the aspects of friction characteristics and stability and thus is suitable for use in hydraulic oil.
Although the embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2019-0023681 | Feb 2019 | KR | national |
