CA2156775A1

CA2156775A1 - Lubricant composition

Info

Publication number: CA2156775A1
Application number: CA002156775A
Authority: CA
Inventors: David Gary Lawton Holt; Patrick Desmond Fraser Vernon
Original assignee: Individual
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1994-08-26
Filing date: 1995-08-23
Publication date: 1996-02-27
Also published as: GB2292747B; GB2292747A; GB9417220D0

Abstract

A lubricant composition, more particularly an automotive crankcase lubricant formulation containing a polar dispersant, e.g. having amide, imide oramine groups, is rendered compatible with fluorocarbon and nitrile material usedin engine seals by the addition to the base oil of from 2 to 50 % by weight, based on the weight of base oil, of a copolymer of a one or more C10 -C16 .alpha.-olefins and one or more dicarboxylic acid esters of C3 to C8 monoalkyl alcohols, the copolymer having a weight average molecular weight (Mw) from 500 to 3,000 and a kinematic viscosity from 3 to 100 cSt (mm/s) at 100°C.

Description

. ~ -1- 21~677~
Lubricant Composition The present invention relates to lubricant compositions, rnore especially automotive crank case lubricant formulations, employing polar dispersants.
Slud3e forms in working lubricants when insoluble oil de3radation products fall out of solution and cover the machine parts with heavy black sticky deposits. Additive packages are included in lubricant oil formulations, especially crank case lubricants, with components designed to reduce the problems arising. Detergents such as calcium and magnesium sulphonates have the purpose of cleaning the machine surfaces affected. However in order to keep the degradation products in suspension and prevent their deposition it is necessary to include a dispersant. The dispersant usually consists of a compound (or compounds) with a polar head and an inert, oleophilic tail. The polar head, which often contains nitrogen atoms, binds to insoluble particles and the tail, usually including a long chain hydrocarbyl group, maintains the resulting agglomerate suspended in the oil, preventing further agglomeration and deposition. Generally the more active is the polar head, the more effective is the dispe,~a"L.
Unfortunately the active polar compounds tend to attack flurocarbon and nitrile elastomers that are used as seals in many types of machinery, especiallyin crankshafts and inlet valves of automobile engines. Therefore the formulator has to compromise between achieving good sludge control and passing elastomer ..c",pa~iL,ilily tests. One attempted solution has been to reduce the 25 activity of the (normally amine) dispersant by capping a part of the amine groups, e.g. with boron, until acceptable compatibility is achieved. Otherwise less aggressive dispersants can be used. However both attemp~ed solutions result in poorer dispersion properties.
Another problem lies in an interaction that occurs between the 30 dispersant additive and ZDDP (zinc dialkyldithiophosphate) which is often included in oil formulations as an antiwear additive. It also has other properties, e.g. as an antioxidant. A complex tends to form between the amine nitrogen and the ZDDP having two implications. Firstly the nitrogen is further capped andtherefore cannot be useful as dispersant or aggressive towards seal material.
35 Secondly the additive properties of the ZDDP, e.g. as antiwear agent, are reduced. Complications arise as the drive towards lower phosphorus and ash levels increases. Levels of ZDDP are being reduced by the alternative incorporation of ashless antiwear additives. As this occurs, a formulation 2- 2~5~77~
previously known to pass the seal c~r"p ' ' :' 'y tests fails to do so because the dispersant nitrogen is no longer capped by ZDDP.
The invention is aimed primarily at relieving these problems.
It has now been found that the inclusion in a lubricant co",~osilion of a S particular copolymer containing ester groups and of ap~rup,idLe molecular weight and viscosity, i.e. which conforms generally to a synthetic oil has the unexpected benefit of improving the cor"p ' ' .' :y of the resulting cui,,pûsiLiûl~ to both fluorocarbon and nitrile elastomers.
Numerous types of synthetic oils are now available, including polyethers, 10 ester oils (monomeric esters of mono- and polybasic acids having suitable viscosities), esters of phosphoric and phosphonic acids, silicones, polyûlefins and alkylaromatics. Among these, polyalphaolefin oligomers (PAO) and ester oils (EO) are well known and are often blended with mineral oils to improve performance, e.g. in thermal and oxidative stability and sludge dispersion.
It is suggested in EP-A-471 266 that mixtures of PAO and EO have good compatibility with rubber based materials and good miscibility wi~h polar additives. It describes a synthetic oil comprising from 5 to 1ûû wt.% of homopolymers of (meth)acrylic esters or copolymers of these with 1-alkenes.
One example describes a blend of a copolymer of C12-C15 alkylmethacrylate 20 and 1-decene with TMA (trimethylolpropane adipate), blended in turn with a ~enerally equal part of PAO. The synthetic oils are said to give rise to fewer problems e.g. with seals.
Copolymers of a"~-unsaturated dicarboxylic acid esters and a-olefins are known in a number of ~F'~ 5, notably as pour point depressants for 25 petroleum fuels. Such additives are generally formed from long chain (C10+) alcohols as well as long chain olefins, and are generally waxy solids.
CA-A-1,238,448 (DE-A-3223694) describes copolymers of a,~-unsaturated dicarboxylic acid esters of C3 to C10 strai~ht chain and/or branchedmonoalcohols and C10 to C16 a-olefins. The cûpolymers have optionally a 30 degree of crosslinking. These are proposed as synthetic oils ûf low pour point and high viscosity index.
According to one aspect the invention provides a lubricant composition comprising in percent by weight of total weight from 70 to 95% of a base oil andfrom 5 to 30% of additives, wherein the base oil is wholly or partly composed of35 synthetic oil, the balance, if any, being mineral oil characterised in that:
(i) the additives include from 1 to 10 wt.% of total composition weight of a polar dispersant, and 93EPE002 lS108/94 3 21~677~
the base oil comprises from 2 to 50 % by weight, based on the weight of base oil, of a copolymer of a one or more C10 -C16 a-olefins and one or more dicarboxylic acid esters of C3 to C~ monoalkyl alcohols, the copolymer having a weight average molecular weight (M_) from 500 to 3,000 and a kinematic viscosity from 3 to 100 cSt (mm2/s) at 100C.
It is possible to utilise the copolymeric oil to constitute the whole of the base oil. However it will normally be blended with poly-a-olefin (PAO) and/or mineral oil. In general, amounts from 10 to 30 wt.% are preferred, based on the weight of base oil. Preferably the base oil comprises at least 10 wt % based on the weight of base oil of PAO oil. Thus a preferred base oil comprises, in weight per cent of total weight of base oil:
from 10 to 30% of the said copolymer from 20 to 70% of PAO oil, and from 0 to 70% of mineral oil.
The dispersant, which forms an essential additive component of the inventive composition, may include any of the known polar dispersants, e.g.
di~,ue,~a,~l~ based on polar oxygen atoms such as polyalkylene glycol ethers, but the invention is more particularly concerned with more active dispersants cor' ,i"g polar nitrogen atoms, e.g. amide, imide and/or amine groups, notably those based on polyamines and their reaction products.
Particularly active dispersants are those comprlsing one or more reaction products of hydrocarbyl-substituted mono- or disubstituted acids or a"l"/~,ides wlth one or more polyamines.
The expression "hydrocarbyl" is intended to include hydrocarbon groups and groups which may contain non-hydrocarbon moieties such as sub-groups having oxygen, sulphur or nitrogen atoms which are generally inert in context and not present in amounts which would detract from the generally hydrocarbon nature of the hydrocarbyl group. Thus In the present context the hydrocarbyl groups are oleophilic groups easily miscible with the base oll for the purpose of distributing sludge partlcles bonded to the polar component of the dlspe,:,a"~.
The hydrocarbyl group may be a polyalphaolefin, e.g. polyisobutylene (Pl) which may have a number average molecular weight (MQ) from 700 to 5,000, a preferred ~i~pe,~a,~ containing mixtures of Pl of MQ 1,500-5,000 and 700-1,500.
The hydrocarbyl groups may be attached as substituents to carboxyllc groups derived from mono- or dicarboxylic acids or anhydrides, particularly preferred being succinic anhydride (SA) which may be reacted with amines to form the final dispersant. The preferred amines for reaction with such acids or 93EPE002 1510r~/94 ~ 21~77~
anhydrides are polyamines (PAM) such as TEPA (tetraethylene pentamine) and PEHA (pentaethylene hexamine). Polyalkylene polyamines can also be utilised.
A particularly preferred dispersant is a PIBSA/PAM dispersant, i.e. a reaction product of polyisobutenyl succinic anhydride and polyamine.
Copolymer oils suitable for use in the invention are available commercially or may be made as described in CA-A-1,238,448. Dicarboxylic esters and a-olefins may also be obtained commercially and copolymerised.
C~ iricd(io,1 procedures are well known. The acid component e.g. as anhydride may be reacted with the alcohol in the presence of acid, e.g. p-toluene sulphonic acid at boilin3 point, normally with the alcohol in excess, residual alcohol being later distilled off.
The ratio of a-olefin to dicarboxylic ester may vary generally from 0.5:1 to 4:1, a 1:1 ratio being preferred, more especially if the base oil contains PAO.
Conditions for copolymerisation are also well known. The a-olefin may be copolymerised with the dicarboxylic ester at temperatures generally around 150-200C in the presence of a peroxide catalyst such as t-butyl hydroperoxide which may be added gradually to the reactants.
The a"3-unsaturated dicarboxylic acid is preferably unsubstituted, examples being maleic, fumaric, itaconic and citraconic acids. Maleic and fumaric acids are generally preferred.
The alcohol component of the ester should have from 3 to 8 carbon atoms, 2 to 6 being preferred. The preferred alcohol is n-butanol.
The a-olefin should have from 10 to 16 carbon atoms, 10 to 12 being preferred, e.g. 1-decene. Mixtures of a-olefins may be used, e.g. mixtures of 1-decene and 1-dodecene.
The resulting copolymer should have a weight average molecular weight (M~ from 500-3,000, more preferably from 600 to 1,500, for example in the case of crank case lubricants. The viscosity should be suitable for the purpose intended. In general the kinematic viscosity should be from 3 to 100 cSt (mm2/s) at 100C. In the case of automotive crank case lubricants a range of 3 to 20 cSt (mm2/s) at 100C is preferred.
According to a second aspect, the invention provides a fully formulated automotive crank case lubricant composition having a fluorocarbon l,-,r,,p ' ' :' 'y passing VW PV 3334 and a nitrile compatibility passing CCMC RE4, said composition comprising in percent by weight of total weight from 70 to 95% of a base oil and from 5 to 30% of additiYes, wherein (i) the additives include from 3 to 10 wt.% of total composition weight of a dispersant containing amide, imide or amine groups, and 93EPE002 ~5108/94 5 21~677~
~ii) the base oil comprises in weight per cent of total weight of base oil:
(a) From 10 to 30% of a copolymer of one or more C10 -C16 a-olefins and one or more dicarboxylic acid esters of C3 to Cg monoalkyl alcohols, the copolymer having a wei3ht average molecular weight ~M~) from 500 to 3,000 and a kinematic viscosity from 3 to 20 cSt (mm2/s) at 100C.
(b) `from 20 to 70% of PAO oil, and (c) from 0 to 70% of mineral oil.
The preferred features of the first aspect, already described, apply also to this aspect, e.g. the most preferred dispersant comprises a PIBSA/PAM
dispersant.
A preferred base oil comprises:
from 20 to 30% of the said copolymer from 15 to 25% of PAO oil, and from 45 to 65% of mineral oil.
The additives included in the lubricant composition, e.g. the fully formulated crank case lubricant outlined above, may be added as a package or "Adpack". This preferably comprises from 5 to 10 wt.% of total composition weight of detergent, e.g. a calcium and/or magnesium arylsulphonate detergent.
It may also include other additives conventional in lubricant formulations such as the following:
A viscosity index (Vl) improver, e.g. an olefin/methacrylate copolymer.
An antioxidant, preferably an ashless antioxidant e.g. a phenolic or amine antioxidant. However ZDDP (zinc dialkyldithiophosphate) sometimes added as an antiwear agent can be added for this purpose also.
A friction modifier, antifoam agent and corrosion inhibitor may also be included.
In the examples which follow standard fluorocarbon and nitrile degradation tests were carried out on base oils (A1 and A2) in accordance with the invention and compared to a base oil (O) without any added ester oil and four base oils (B), (C) (D) and E in which the copolymer of A was replaced by different ester oils. Two additive packages were used differing by the addition of ZDDP antiwear agent.
The following table gives the composition of the base oils in wt.% of total weight of base oil, together with viscosity (V) in mm2/s at 100C and molecularweight (M_y) (where dpplUplidl~l and available).

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Table 1 5V Mw O A(1,21 B,D C E
A1 15 1,200 19 (15) A2 6 800 [ " I
lO DITA 6 19 (1s) DIDAZ 6 19 (15) TMPPE 4 ~9 (15) PAO6 6 44 (35) 25 (20) 25 (20) 25 (20) 25 (20) NS 150 15 56 (44.8) 56 (44.8) 56 (44.8) 56 (44.8) 56 (44.8) Notes Figures in brackets denote content in terms of total composition wei~ht.
DITA: diisotetradecyl adipate (B and D were from different co,11."v.-.ial sources) 20 DIDAZ: di-2-isodecyl azelate TMPPE: ester of decanoic acid and trimethylolpropane polyol NS 150: a neutral solvent (mineral) oil of stated viscosity PAO6: a polyalphaolefin oil of stated viscosity A1 and A2 are copolymers (differing in molecular weight and viscosity) of n-butanol esters of a"~-unsaturated dicarboxylic acid and o-olefin of chain length falling with the range of 10 to 16 carbon atoms.
The following table shows typical additives and their contents in wt.% of total composition weight in terms of a broad range, a narrow, preferred range and as used in the examples to follow.

93EPE002 ~s~oal94 '~ '~ 7 21~677~
Table 2 Additive Broad Preferred Examples Content s Dispersant 1-10 4-7 6 non-borated PIBSA/PAM
Vl improver 0-12 3-8 6.2 poly-olefin/methacrylate Antioxidant 0-5 1-2 1.5 sub. aromatic amine+
nonylphenyl sulphide +
sulphurised phenolic Deter3ent 0-10 3-8 6.3 overbased detergents +
neutral Ca detergent +
overbased Mg detergent Friction modifier 0-5 0.05-0.5 0.1 glycerol monooleate 15 Corrosion inhibitor 0-1 0.01-0.3 0.1 copper complex Antifoam agent 0-0.1 (polysiloxane) Antiwear agent 0-3 0-1.5 1 2inc dialkyldithiophosphate Totals <45 11-26 20.2 ZDDP was added to one series of examples only. The detergent, antioxidant, corrosion inhibitor and friction modifier in the examples were added as part of an 8% additive package so that the overall additive content of the composition was 25 20.2 wt,%.
The following test procedures were used.
Fluorocarbon (Viton(D type AK-6) compatibility was tested according to Volkswa3en test VW PV 3334 and nitrile (CCMC Reference Elastomer RE4) 30 compatibility according to CEC L/39-T-87.
Volkswagen Test VW PV 3334 This test sets out PASS and FAIL limits under standard testing 35 conditions for fluorocarbon material used in engine seals and has been adopted as an industry standard.
Six test samples of "dumbbell" shaped material are prepared from the same sheet of fluorocarbon (e,g, Viton(~) material, s3EPEoo2 15108/94 . . 21~77~
Three samples to be used as controls are tested untreated for tensile strength, elongation at break and cracking.
Tensile strength and elongation at break are determined according to the ISO 37 method. Cracks are determined visually after stretching the samples 5 to 100% elongation.
The tests are repeated on the three remaining test samples after suspension in the oil to be evaluated at 150C for four days.
The limits are based on the percentage change in the properties tested, relative to the control samples.
CCMC RE4 Nitrile Test This test generally follows the VW test above, but changes in hardness and volume are also measured, and the three test samples are suspended in the 15 oil at 1 00C for one week.
Hardness is measured in IRHD units.
The results obtained on the described lubricant compositions were as shown in the following Tables 3 and 4, in which:
20 TS = Percentage change in tensile strength at break EAB = Percentage change in elongation at break Hard = Change in IRHD hardness units Vol = Percentage change in volume It will be observed that fails were obtained with all comparative formulations B, C, D and E on fluorocarbon samples except where ZDDP was present to cap the dispersant amine groups. Passes were obtained on all fluorocarbon samples with formulations A1 and A2 in accordance with the invention, whether or not ZDDP was present.
In the nitrile tests, fails were obtained on all comparative formulations B, C, and D and passes obtained on the inventive formulation A1 whether or not ZDDP was present. One of the control formulations without added ester obtained a pass but there was a significant improvement in elongation at break with the co-tested formulation with added copolymer A1.

93EPE002 15/Oa/94 21~677~

Table 3 Fluorocarbon (Viton~) Tests Test Limits -TS -201~20 EAB -25/125 Crack 0/C
s Ex/test O B C D E A1 A2 No ZDDP added 1 Crack 0 0 0 0 fail fail fail pass 15 No ZDDP added 2 Crack 0 0 0 0 fail fail fail pass No ZDDP added 3 crack C 0 fail pass -ZDDP added to all formulations 304 crack 0 0 0 o 0 pass pass pass pass pass 93E~E002 15/08~94 ~ -10- 2~775 Table 4 Nitrile Tests Test Limits -TS -20/0 EAB -50/0 Hard -5/+5 Vol -5/+5 --s Ex/test O B C D E A1 No ZDDP added 3 Hard +2 +2 3 Vol +1 +1 pass pass ZDDP added to all formulations 4 Hard +3 +1 0 0 0 204 Vol +4 +4 +1 +3 +3 fail fail fail fail pass 93EPE002 15/Or5194

Claims

1. A lubricant composition comprising in percent by weight of total weight from 70 to 95% of a base oil and from 5 to 30% of additives, wherein the base oil is wholly or partly composed of synthetic oil, the balance, if any, being mineral oil characterised in that:
(i) the additives include from 1 to 10 wt.% of total composition weight of a polar dispersant, and (ii) the base oil comprises from 2 to 50 % by weight, based on the weight of base oil, of a copolymer of a one or more C10 -C16 .alpha.-olefins and one or more dicarboxylic acid esters of C3 to C8 monoalkyl alcohols, the copolymer having a weight average molecular weight (Mw) from 500 to 3,000 and a kinematic viscosity from 3 to 100 cSt (mm2/s) at 100°C.

2. A composition according to claim 1 wherein the base oil comprises at least 10 wt.% based on the weight of base oil of poly-.alpha.-olefin (PAO) oil.

3. A composition according to any preceding claim wherein the base oil comprises in weight per cent of total weight of base oil:
from 10 to 30% of said copolymer from 20 to 70% of PAO oil, and from 0 to 70% of mineral oil.

4. A composition according to any preceding claim wherein said dispersant comprises one or more reaction products of hydrocarbyl-substituted mono- or disubstituted acids or anhydrides with one or more polyamines.

5. A composition according to any preceding claim wherein said copolymer is derived from one or more said .alpha.-olefins of 10 to 12 carbon atoms.

6. A composition according to any preceding claim wherein said copolymer is derived from butanol.

7. A composition according to any preceding claim wherein the composition is an automotive crank case lubricant composition and said base oil has a kinematic viscosity from 3 to 20 cSt (mm2/s) at 100° C.

8. A fully formulated automotive crank case lubricant composition having a fluorocarbon compatibility passing VW PV 3334 and a nitrile compatibility passing CCMC RE4, said composition comprising in percent by weight of total weight from 70 to 95% of a base oil and from 5 to 30% of additives,-wherein (i) the additives include from 3 to 10 wt.% of total composition weight of a dispersant containing amide, imide or amine groups, and (ii) the base oil comprises in weight per cent of total weight of base oil:
(a) from 10 to 30% of a copolymer of one or more C10 -C16 .alpha.-olefins and one or more dicarboxylic acid esters of C3 to C8 monoalkyl alcohols, the copolymer having a weight average molecular weight (Mw) from 500 to 3,000 and a kinematic viscosity from 3 to 20 cSt (mm2/s) at 100°C.(b) from 20 to 70% of PAO oil, and (c) from 0 to 70% of mineral oil.

9. Use of a copolymer of one or more C10 -C16 .alpha.-olefins and one or more dicarboxylic acid esters of C3 to C8 monoalkyl alcohols, the copolymer having a weight average molecular weight (Mw) from 500 to 3,000 and a kinematic viscosity from 3 to 20 cSt (mm2/s) at 100°C for addition to a lubricant composition containing a polar dispersant as a preventative against degradation of fluorocarbons and nitriles.

10. Use according to claim 9 wherein the copolymer is added in an amount not less than 2 wt.% based on the weight of the composition.