CA1303600C

CA1303600C - Gear oil composition

Info

Publication number: CA1303600C
Application number: CA000545362A
Authority: CA
Inventors: Kuniaki Suzuki
Original assignee: Toa Nenryo Kogyyo KK
Current assignee: Tonen General Sekiyu KK
Priority date: 1987-08-26
Filing date: 1987-08-26
Publication date: 1992-06-16
Anticipated expiration: 2009-06-16
Also published as: EP0340302A4; WO1989003418A1; JPS62241996A; EP0340302A1

Abstract

ABSTRACT OF THE DISCLOSURE
A gear oil composition comprising as a base oil at least one polyoxyalkylene glycol having a viscosity of from 5 mm2/s at 100° C and derived from at least one monomer comprised of alkylene oxides containing from 2 to 4 carbon atoms.

Description

~ ~o 1 ! , Thi~ inv-ntion r-latos to a g-ar oil composition compri~ing polyoxyalkyl-ne glycol(s) as a ba~- oil More particularly, it relat-s to a goar oil composition whose wear resistanc- and oxidation stability are improved by utilizing polyoxyalkylene glycol(s) having specific vi~co-ity properti-s as a baso oil Mechanical d-vices using goars are well known in the ~art Theso gear`devices aro broadly classified, d~ponding~on th-ir~u~age, into industrial dQvic-s and those for;~ us~ 1n~aueomobil An appropriat- gear oil suitable for th-~partlcular purpose is employod in each cas-A~g~ar oil is~a lubricant oil which reducesfriction~b-tw -n at l-ast one pair of gears transmitting powor~ from a driving device to a driven one~thereby d,ecrea~ing~pow r 108~ ~and inhibiting damage to the gears, t ~ ~prolonging~eh~ lif~ span of the gears Presently ,"~ oii-~ar ~exclu-ively eQloyed as base oils of gear oi~ G ar oll- urth r~co`ntaln;~approximately 0 1 to 10 %
,by~w-ight~of ~variou~ additives such as antioxidants, ~Tt~ pr- ur-~agents, ru-t pr-ventatives and It~ b-co~ing~a usual pract:ice for machines made in;~`Jap~n~,and~xport-d ~to various countries, including the n.s~A~ and~European countries, to supply lubricant-, e g , oils,;~;for~ sù,ch~ export~ ~achines in the manufacturing prior~to~ shipping rher foro, it is nocessary to ~3~3~0 - 2 ~
determine the prop~rties o~ th~- lubrlcants wlth rererence to th- conditlons under which they will be used in the customQr country. Thus, manufacturers Or the machines have re~uested the lubricant oil's manufacturers to supply products of satisfactory properties, depending on the operating conditions of customer countrles. In compl~ance with the wishes of the former, the latter have attempted to develop products satisfying these reguirements.
In Japan, base oils comprising mineral oils are mainly employed in gear oils. When the gears are to be subjected to high temperature or high load, a gear oil composition ccmprising such a base oil, as well as some specific additives such as an extreme-pressure agent or an antioxidant, is usually employed. An example of these gear oils is a lubricant oil composition disclosed in Japanese Patent Laid-Open No. 75995/1984. This invention proposes to improve the wear resistance, extreme-pressure qualities and friction properties of a lubricant oil by introducing an organo molybdenum compound of a specific structural formula and an acid phosphite or an acid phosphate as essential ingredients into, for example, a mineral oil having a lubricant viscosity. These gear oils comprising mineral oils as base oils have been exclusively used in Japan, since mineral oils are relatively inexpensive; and a base oil for a gear oil used in conventional gear devices may be obtained by removing impurities such as unsaturated hydrocarbons and metallic components from a raw mineral oil through solvent-refining or hydrogenation.
Attempts have been made to use synthetic lubricant oils comprising, for example, esters, generally poly-O~ -olefins and polyglycol oils. Generally, a synthetic lubricant oil of the desired lubricant properties may be obtained by controlling the synthesis conditions. Thus it is believed that th- synthetlc lubrlcant olls can exhibit better properties ln the areas o~ inhlblting damage caused by friction and oxidation than mineral oils. Japanese Patent Publication No. 1339/1974 has disclosed a lubricant which is prepared by adding, for example, an aromatic amine, an aliphatic phenol and an organic phosphate to a base oil. This lubricant has improved oxidation stability, load resistance and rust resistance at high working temperatures.
Recently the requirements for the properties, particularly the wear resistance and oxidation stability at a high working temperature, of a gear oil have become more stringent. At present, gear oils comprising mineral oils as a base oil have an overwhelming share in the field of machine industries. However, the gear oils which comprise a mineral oil as a base oil and additives compensating for the aforementioned shortcomings of the base oil are far from satisfactory with respect to the various requirements of the potential future market. Thus, it is impossible to provide excellent gear oils unless the properties of mineral oils, which are contained therein in an amount of 70 to 95 % as base oils, are improved.
Under these circumstances, it is necessary to consider the use of synthetic lubricant oils as base oils for gear oils. However there are presently no commercially available inexpQnsive synthetic lubricant oils which exhibit satisfactory properties. As regards polyglycol oil, the relationship between its properties as a base oil and the its molecular structure is not yet sufficiently under~tood. Thus, present attempts are directed to identifying suitable additives and appropriate effective amounts thereof. In addition, polyglycol gear oil tends to exhibit poor cold viscosity properties when used in a cold environment, thereby resulting in a failure during normal operation of the transmission device.
Accordingly, it is an object of the present invention to provide an inexpensive gear oil comprising a ~303~0 ~, synthetic lubrlcant oll whlch ha- hlgh wear ro-lstance, excellent stablllty at hlgh temperatures and hlgh or mod-rate-speed rotatlon, and hlgh flowability at low temperatures wlthout requiring the use of addltives.
Under these circumstances, we have attempted to overcome the above problems and have consequently found that a gear oll comprising speci~ic polyoxyalkylene gly~ol (Q) as base oils exhibits not only a remarXably improved wear resistance and oxidation stability, even at high temperatures, but also improved viscosity properties at low temperatures.

SUMMARy OF THE INVENTION
A gear oil lubricating composition comprising as a base oil at least one polyoxyalkylene glycol polymer or copolymer having a viscosity of from 5 mm2/s to 20 mm2/s and containing at least one recurring ring-opened alkylene oxide monomer containing 2 to 4 carbon atoms.
DETAILED DESCRIPTION OF THE INVENTION

The present invention resides in a gear oil composition comprising polyoxyalkylene glycol(s) as a base oil wherein said polyoxyalkylene glycol(s) are selected from polymers and copolymers of ring-opened alkylene oxide(s) having two to four carbon atoms and have a viscosity of 5 mm2/s to 20 mm2/s at lOO-C.
The polyalkyleneglycol(s) of the present invention ar- selected from among polymers and copolymers of ring-opened alkylene oxide(s) monomers having two to four carbon atoms, i.e., ethylene oxide, propylene oxide, butylene oxide and isobutylene oxide. Therefore, the polyoxyalkylene glycols include, for example, polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol, polyoxyisobutylene glycol, ethylene oxide/propylene oxide ring-opened copolymer and propylene oxide/butylene oxide ring-opened copolymer. The average molecular weight of these polyalkylene oxides is approx-~D
imately 800 to ~300. For example, polyoxyp~:opyl~nc qlycol of an average molec-llar weight ot' 1000 to 2aoo may ~e employed in the presont inven~ion. It 15 required that sUch a polyoxyalkylene glycol have speci~ic viscosity properties. Namely, the viscoslty thereof at lOo'c should be from 5 to 20centistokes. A polyoxyalkylene glycol having a viscosity lower than S mm2/s at lOO'c is undesirable because of its poor wear resistance and low oxidation stability at high temperatures. on the other hand, one having a viscosity higher than 20 mm2/s is also undesirable because its poor flowability at low temperatures will result in insufficient lubricating effects. A gear oil that is to be used in a machine in a cold area is particularly required to have satisfactory viscosities at low temperatures. It is possible to achieve a good lubricating effect by employing polyoxyalkylene glycol(s) having a viscosity of 6 x 104 mpa.s to 95 x 104 ~pa-.s -at -40-C in the present invention. A
particularly preferred base oil for the gear oil of the present invention comprises polyoxypropylene glycol or poloxyyethylene glycol having a viscosity of 8 mm2~s to 19.8 mm2/s at lOO'C and 10 x 104 mpa.s to 40 x 404 mpa.s at -40-C.
The polyoxyalkylene glycol(s) of the present invention can be produced by known methods. For example, polyoxypropylene glycol can be obtained by polymerizing propylene oxide in the presence of a metal alcoholate as a catalyst and water or an alcohol as an initiator under a pressure of 1 to 10 atm at 100 to lSO-C.
As the polyoxyalkylene glycol~s) of the present invention polyoxypropylene glycol may be used alone.
Alternately a base oil which is a mixture of polyoxy-propylene glycol and poloxyethylene glycol or polyoxy-butylene glycol may be used. It is highly effective to use a base oil comprising such a mixture of polyoxyalkylene glycols for achieving the viscosity properties as described above. That is to say, a polyoxyalkylene glycol base oil ~: B

having appropriate v~scosity propertie- can be readlly obtained by blending polyoxypropyl-n- glycol, whlch has a high molecular weight and a high viscosity at low temperatures , with polyoxyethylene glycol, which has a relatively low molecular weight and is highly flowable at low temperatures. Similarly the polyoxyalkylene glycol~s) of the present invention may be blended with esters.
Example~ of these esters are monoest-rs, dlesters and polyesters, i.e., those having three or more ester bonds.
The monoesters include aliphatic esters having 15 or more carbon atoms: the diesters include those formed by esterifying aliphatic dibasic acids having 4 to 14 carbon atoms with monoalcohols having 4 to 14 carbon atoms; and the polyesters include triesters formed from trihydric alcohol.s having 4 to 13 carbon atoms and fatty acids having 3 to 13 carbon atoms and tetraesters formed from tetra hydric alcohols having 5 to 10 carbon atoms and fatty acids having 5 to 10 carbon atoms. Among these esters diesters such as diisodecyl adipate, dioctyl sebacate and dioctyl azelate, and triesters such as trimethylolpropane trihep tanoate and trimethylolpropane trioctanoate are parti-cularly preferred. These esters enhance the oxidation stability of polyoxyalkylene glycols. In particular, the addition of approximately 10 to 50% by weight of the ester(s) can significantly enhance the lubricant properties of a gear oil comprising polyoxyalkylene glycol(s) of a low viscosity, i.e., 5 to 20 mm2/s at lOO~C as a base oil.
The polyoxyalkylene glycol synthetic lubricant oil of the present invention can be used as a gear oil. It exhibit~ remarkable effects, particularly when used as an industrial gear oil. Namely, it is useful as a gear oil utilized at high temperatures and high load or under unsettled temperature conditions, i.e., widely varying from low temperature to high temperatures. The polyoxyalkylene glycol base oils may further contain conventional additives. Suitable additives include antioxidants such as aromatic amines (0.3 to 5 % by weight); extreme-pressure aqents such as trlcre~yl phw phate (0.3 to 13 % by welght);
metal inactiv~tors (0.01 to 3 ~ by welght); rust inhibitors (0.05 to 2 % by weight); oil improvers (0.01 to 3 % by weight); and anti-foaming agents (0.0005 to 0.02 % by weight). These additives may be added in a total amount of 3 to 15 % by weight. No viscosity index additive is required in the present composition. This is in sharp contrast to mineral base oils wherein a viscosity index additive is required.
Since the polyoxyalkylene glycola are polether(s) wherein oxyalkylene(s) are polymerized through a ring-opening mechanism, the polyoxyalkylene glycol(s) of the present invention have high oxidation stability and flowability even at high temperatures. Furthermore, they can act as a viscosity index improver since they have specific viscosities at both high and low temperatures.
Although the hydroxyl (alcohol) groups present at the ends of the polyoxyalkylene glycol(s) lower the oxidation stability thereof at high temperatures the lubricant properties of the gear oil product are not affected thereby since the base oil shows excellent interaction with antioxidants such as aromatic amine compounds.
The following Examples are provided for illustrative purposes only and are not to be construed as limiting the invention herein described.

Examples 1 to 6 Gear oil compositions (A to F) of the present invention were prepared by using a polyoxyalkylene glycol (polyoxypropylene glycol or polyoxyethylene glycol) as a base oil and adding tricresyl phosphate as an extreme-pressure agent and an aromatic amine antioxidant thereto.
Table 1 shows the composition of each gear oil thus obtained and the viscosity properties thereof at lOO~C and -40-C.
The wear resistance of each gear oil composition of the present invention was determined in the following 13(~3600 manner. A four-ball wear t-ster (Shell type) was operated at an oil temperatur- Or 150'C, at a rate o~ 1800 rpm under a load o~ 25 kg for 30 minutes, and then the wear diameter.
of a roller ~1/2 inch~ was determined. Table 2 shows the results.
Then an IEA gear tester was operated at an oil temperature of 140~C at a gear rate o~ 7000 rpm under a load of 60 lbs for three hours. Subsequently the weight loss in larqe and small gears was determined. Table 2 shows the results.
The oxidation stability of each gear oil composition of the present invention was also determined according to Fed. 791 b. 5308 at an oil temperature of 150-C for 200 hours. The change in viscosity (% per lOO-C), the total acid number gain (mg KOH/g), insoluble matters in oil (% by weight; determined by the pentane-~method) and the change in the weight of metals, i.e., iron and copper (mg/cm2) were determined. Table 2 shows the results.

Comparative gear oils a to d were prepared by adding appropriate amounts of various additives such as a viscosity index improver, an antiwear agent and an antioxidant to commercially available base oils which were ATF-D II, ATF-D II', Gear Oil 75W-90 and a diester oil (DIDA; diisodecyl adipate), although no viscosity index improver was added to the diester oil. Table 1 shows the compo-ition and properties of each gear oil thus obtained.
These comparative gear oils were subjected to the same procedures as those described in Examples 1 to 6 to determine the wear resistances and oxidation stabilities thereof. Table 2 shows the results. -The above Examples 1 to 6 and Comparative Examples 1 to 4 indicate that the polyoxyalkylene glycol gear oils of the present invention have almost the same wear resistances as those of the conventional ATF-D II and Gear Oil 75W-90 but are up-rior to the latter in vlscoslty properti-- and oxldation tabllitl-- It wa~ also ~ound that the polyoxyalkylene glycol gear oils of the present invention had remarkably improved wear resistances and viscosity properties compared with the diester oil (DIDA) .~

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- l2 -The polyoxyalkylene glycol synthetlc lubrlcant oils oS the present inventlon, whlch exhlbit a high oxidation stability and wear reslstancg at high temperatures and high flowability at low temperatures, suffer from less denaturation than conventlonal mineral oil- or ester-based lubricant oil~. Thus, they can be used at low cost with reduced machlnery.

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Claims

1. A gear oil composition comprising: major amount of (A)(i) at least one polyoxyalkylene glycol having a viscosity of from 5 to 20 centistokes at 100°C and 10 x 104 to 40 x 104 mpa.s at -40°C selected from the group consisting of polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol and polyoxyisobutylene glycol; and (ii) at least one ester selected from the group consisting of aliphatic monoesters having at least 15 carbon atoms, diesters of aliphatic dibasic acids having 4 to 14 carbons and monohydric alcohols having 4 to 14 carbon atoms, triesters of trihydric alcohols having 4 to 13 carbon atoms and fatty acids having 3 to 13 carbon atoms, and tetraesters of tetrahydric alcohols having 5 to 10 carbon atoms and fatty acids having 5 to 10 carbon atoms; (B) from 0.3 to 5 weight % antioxidant; and (C) from 0.3 to 13 weight percent extreme pressure agent.

2. The composition of claim 1 wherein said polyoxyalkylene glycol is polyoxypropylene glycol.

3. The composition of claim 1 wherein said polyoxyalkylene glycol is a mixture of polyoxypropylene glycol and at least one polyoxyalkylene glycol selected from polyoxyethylene glycol and polyoxybutylene glycol.

4. The composition of claim 1 wherein said polyoxyalkylene glycol is comprised of the polymerization product of at least one alkylene oxide containing from 2 to 4 carbon atoms obtained via a ring-opening polymerization mechanism.