IE41629B1 - Synthetic crankcase lubricant - Google Patents

Abstract

The synthetic lubricant preparation contains as the base material a mixture of a liquid polyol ester and a liquid polyalpha -olefin. The polyol ester is derived from an aliphatic monocarboxylic acid and an aliphatic polyol having at least two methylol groups on a quaternary C atom. The preparation is suitable for transmissions and internal-combustion engines.

Description

PATENT APPLICATION BY (71) STAUFFER CHEMICAL COMPANY, A COMPANY ORGANISED UNDER THE LAWS OF THE STATE OF DELAWARE, OF DOBBS FERRY. NEW YORK 10522 UNITED STATES OF AMERICA. ’ Pnct I2|p This invention relates to a ’•synthetic crankcase lubricant.

The use of various diesters, higher polymers and complex esters as lubricating oils is well known to the art and has been described in various patents, e.g. U.S. Patents NOs.2,723,286, 2,743,234 and 2,575,196. Naturally occurring fats and oils, predominantly glyceride esters, have been used as lubricants for many centuries. More recently, synthetic esters or synthetic ester blends prepared from various combinations'of mono- and poly-functional acids and alcohols have been developed for lubricant use.

Synthetic esters have been widely used as turbine engine lubricants, however, there has been little use made of them in piston engines. The reason for their lack of acceptance as piston lubricants has been primarily due to the deleterious effect of excessive swelling that these esters have had upon the elastomer seals used in piston engines.

Seal swell is defined as the amount percent that the volume of elastomer seals expand upon contact with and exposure to the lubricant environment under engine operating conditions. Insufficient or excessive swell causes the seals to lose their ability to retain and confine the engine fluid. Leakage occurs which can cause a high oil consumption. - 3 A controlled seal swell is, therefore, one of the most important characteristics of a crankcase lubricant.

It is essential that the lubricant employed be capable of imparting a controlled swelling of the engine's elastomer seals, sufficient to prevent leakage of lubricant.

The base stock according to the present invention shows excellent properties with elastomer seals, particularly those sold as Buna-N (a copolymer of butadieneacrylonitrile) , (Buna is a Registered Trade Mark).

While the capability of not causing excessive or insufficient elastomer swell is a valuable characteristic, lubricating compositions used in piston-type internal combustion engines, hereinafter referred to as piston engines, must also possess other particular characteristics in order IS to fulfil satisfactorily the particular requirements placed upon lubricants for this type of engine.

It is essential that these lubricants possess sufficient lubricity to permit their use under severe operating conditions. They must also be oxidatively and thermally stable and resistant to the formation of rust, sludge and varnish. The viscosity characteristics must be such that the lubricant can be used over a wide temperature range; that is, adequate viscosity at high temperature, low viscosity at low temperatures and a low rate of change of viscosity with temperature. Its pour point should be low. Its volatility should be low at elevated temperatures of use; that is, selective evaporation or volatilization of any important component should not take place at high temperatures of use.

The wide-spread advance of piston engine powered vehicles has led to the use of piston engine equipment in global areas where ambient temperature conditions are much more severe than the temperature conditions generally encountered in temperate climates. Engine oils must now be sufficiently liquid at temperatures as low as -65°F. to allow the engine to start, yet have volatility properties 416 29 sufficient to preclude evaporation when exposed to temperatures near 35O°F, over prolonged periods of time.

Coupling all these properties with compatibility towards a variety of elastomers is a difficult achievement for such, a fluid. The base stock is generally combined with an additive package designed to maximize the particular characteristics required by the lubricant. In order to accomplish this, the base stock must have additive compatibility.

Additive compatibility is defined as the additive's ability to become homogeneously dissolved or dispersed in the base stock ahd is a measure of the additive's ability to avoid hazing, flocculating or settling out from the base stock fluid.

Petroleum lubricants, which have heretofore been used in piston engines almost exclusively, are generally Incapable of providing both the high and low temperature requirements needed today. Petroleum oils can be modified, for example, by addition of kerosene to provide low temperature starting, but, when this low temperature modification is effected, the lubricants become too volatile for continued high speed, high temperature operation. Conversely, petroleum oils can be modified to provide good high temperature performance, but such compositions generally become so viscous at low temperature that they do not function properly in cold weather.

Conventional synthetic esters commonly used for lubrication of turbine engines, while having better properties than petroleum-based piston engine oils, have generally been found unsuitable for use as piston lubricants. This is due to excessive volatility and inadequate viscosity properties at high temperatures. More importantly, these fluids have a tendency to cause elastomers used as seals in automotive engines to swell excessively, which can result in loss of lubricant by leakage past the engine seals. - 5 British Patent Specification No.1,060,114 relates to synthetic lubricants which are intended for use in high temperatures in systems of consumable lubrication of aeroturbo- jet engines. The lubricating composition comprises at least one ester selected from a sebacate, an adipate or an azelate or a polyester of a polyol, and poly-isobutylene having a molecular weight between 500 and 5000.

British Patent Specification No.1,061,483 relates to functional fluids suitable for use in high speed aircraft. The fluid comprises one or more brominated aryl ethers, a siloxane and at least one hindered ester.

British Patent Specification NO.1,189,541 relates to a fluid for hydraulic transmission. The fluid is characterized in that it comprises at least one fully esterified ester of an aliphatic carboxylic acid and of an alcohol, each having at least 5 carbon atoms, either the acid or the alcohol, but not both, being mono-functional with respect to carboxy and hydroxy groups respectively, and an anti-oxydant association consisting of N-phenyl-1naphthylamine and another arylamine selected from diphenylamine and diphenylamine derivatives.

British Patent Specification No.1,205,274 relates to functional fluid compositions which exhibit improved oxidative stability together with improved resistance to the corrosion of metal surfaces. The fluid comprises an ester base stock and an aromatic compound of a particular type.

British Patent Specification No.1,215,536 relates to functional fluid compositions which have a reduced tendency to cause corrosion of metal surfaces. The fluid comprises an ester base stock containing a pentaerythritol base stock (as therein defined) and an aromatic compound of a particular type.

British Patent Specification No.1,372,375 relates to lubricating compositions usable as base lubricant in lubricating oils for engines operating under severe conditions comprising conventional hydrocarbon oils and derivatives of polyalkyleneglycols.

The present invention provides a crankcase lubricant composition, the base stock of which has a viscosity at 210°F of from 3 to 20 centistokes and which comprises (a) a trimethylolpropane ester or a polytrimethylolpropane ester of an aliphatic hydrocarbyl monocarboxylic acid having an average chain length of from 4 to 12 carbon atoms and, optionally, additionally a dibasic carboxylic acid; and (b) an oligomer selected from oligomers of alpha-decene and mixtures of such oligomers, the relative amounts of component (a) and component (b) being such as to impart a butadiene-acrylonitrile elastomer seal swell of from 4 to 20%.

The aliphatic monocarboxylic acids used in accord15 ance with the present invention are compounds or mixtures of compounds having average chain lengths from 4 to 12 carbon atoms, preferably from 5 to 9 carbon atoms. The individual acids can range in chain length from 2 to 18 carbon atoms. Normal acids are preferred, although branched monocarboxylic acids can also be used, particularly those with no more than two carbon atoms in side chains.

In synthesizing the polyol esters, minor amounts of dibasic acids can be employed as cross-linking agents.

The hydrocarbon portion of the dibasic acid generally ranges .from 2 to 18 carbon atoms, more preferably from 4 to 12 carbon atoms. Particularly preferred dibasic acids include adipic, azelaic, isophthalic and mixtures thereof. Also included for purposes of crosslinking are the dimer and trimer acids, and mixtures thereof.

For spark ignited engine applications, it is particularly preferred to use trimethylolpropane.

Due to its superior additive compatibility, it is especially preferred that the polyol ester be a trimethylolpropane triester.

In those instances where a higher viscosity ester is desirable for use in a diesel engine, then an ester of a higher molecular weight polyol should be employed, preferably a condensed polyol, such as ditrimethylolpropane.

Due to its superior additive compatibility, it is especially preferred that the polyol ester for use in diesel applications be a ditrimethylolpropane tetraester.

The ester-oligomer base stock components are blended in amounts which are effective to impart sufficient swell to the seals. A sufficient amount of elastomer seal swell as contemplated by the present invention is wherein the seal swell is from 4 to 20%, with a seal swell of from 5 to 15% being preferred and a seal swell of from 6 to 9% being especially preferred for an elastomer, such as Buna N, which is commonly employed in automotive crankcases.

Viscosity is another important property. The lubricant must have an acceptable viscosity range to enable it to be liquid at temperatures as low as minus 65°F. to allow the engine to start and yet retain sufficient film strength to adequately lubricate at operating temperatures that can approach 35O°F.

The acceptable viscosity of the lubricant base stock is from 3 to 20 centistokes at 210°F, with a preferred viscosity being from 4 to 12 centistokes at 210°F.

The lubricant should also have volatility properties sufficient to preclude significant evaporation at temperatures of about 35O°F, over extended periods of time.

The most effective blends of ester to oligomer, wherein control of elastomer seal swell is of primary concern, is where the ratio of ester to oligomer is from 35;65 to 80:20,parts, by weight. The preferred weight ratio of ester to oligomer is from 40:60 to 66.7:33.3, with a ratio of about 50:50 parts, by weight, being particularly preferred. The following Table illustrates controlled seal swell resulting from a typical oligomer-ester blend: TABLE I Seal swell characteristics of Buna N with various blends of trimethylolpropane triheptanoate ester and a mixture of decene oligomers: Blend Ester: Oligomer Ratio 40:60 50:50 55:45 60:40 66.7:33.3 80:20 Seal Swell,* 5.20 7.93 8.98 .64 12.53 16.10 TABLE Viscosity and pour from Table I: Viscosity at 210°F. (Centistokes) 100°F 0°F -40°F Pour Point II point for selected blends Ester:Oligomer Ratio 50:50 66.7:33.3 4.40 4.05 21.15 18.79 421 355 4701 3107 -70°F. -75°F For diesel applications, a higher visocsity polyol ester, such as one selected from ditrimethylolpropane tetraesters and mixtures thereof, blended with oligomers, provides an excellent base stock, especially from the standpoint of good viscosity and controlled seal swell characteristics. Table III illustrates these properties.

TABLE XIX 1:1 blend of di-trimethylolpropane tetraheptanoate and mixed decene oligomers.

Properties Viscosity at 210°F 9.5 centistokes Pour Point -40°F Buna N Seal Swell at 300°F. after 70 hours. 7% The ester-synthetic hydrocarbon oligomer base stock system of the present invention has demonstrated excellent additive compatibility without adversely effecting engine elastomeric seals. A typical additive package for the ester-oligomer blend generally comprises those additives which impart anti-corrosion properties, anti-wear properties, load bearing properties, lubricity, viscosity index improvement, detergency, dispersancy, metal deactivation and anti-foam properties.

It is of particular importance that the dispersancy and detergency additives be compatible and effective with the base stock blend. This is due to the fact that acidic engine gases leak through piston rings and can thereby contaminate the crankcase lubricant. The dispersancy and detergency additives prevent corrosion and rust on the bearings and are necessary adjuncts to the base stock by neutralizing, dissolving and dispersing these contaminants, as well as degradation products from fluid oxidation.

The following examples are illustrative of various lubricant compositions incorporating esteroligomer base stocks. (All parts and percentages are by weight, unless otherwise indicated).

Example 1 A lubricant blend having the following composition was prepared and subjected to the Coordinating Research Council's (CRC) L-38 test, also known as Method 3405 of Federal Test Method Standard Number 791a.

Lubricant Composition Component % Hydrogenated mixed decene trimers and tetramers 40 Trimethylolpropane triheptanoate 40 Methacrylate vinyl-pyrrolidone copolymer 9.5 Lubrizol {Registered Trade Mark) 3826A blend of zinc dialkyldithiophosphate, overbase calcium, alkylbenzene-sulfonate, overbase calcium phenate and succinimide) 10.0 Pheny1-alpha-naphthylamine 0.5 Benzotriazole 0.02 Silicone Antifoam 25 ppm The CRC L-38 test is designed to evaluate crankcase lubricating oils for resistance to oxidation, corrosion, sludge and varnish, when subjected to high temperature operation.

The procedure involves the continuous operation of a single cylinder CLR oil evaluation engine under constant speed, air fuel ratio and fuel flow conditions for a total of 40 hrs., subsequent to a break-in period of 4¾ hours, Prior to each run, the engine is thoroughly cleaned, pertinent measurements of engine parts are taken and a new piston, piston rings and new copper-lead connecting rod bearing inserts are installed.

The key operating conditions of the engine of this evaluation are as follows: Duration 40 hours Speed 3150+25 RPM Load Adjusted to provide proper fuel flow at specified airfuel ratio Fuel Flow Air-Fuel Ratio Jacket Out Temperature Difference between jacket in and jacket out temperatures Gallery oil temperature 4.75+ 0.25 lbs./hr 14.0+0.5 200+2°F. +1°F. 290+2°F.

At the conclusion of the run, the engine is disassembled and the performance of the oil is judged by a visual examination of the engine for deposits, by the weight loss of the copper-lead bearing and by comparison of the inspection data on samples of used oil taken at periodic intervals with the inspection data on the new oil.

Test results are tabulated below: Test Results Hour Crankcase Oil Oxidation Evaluation Bearing Weight Loss, mg.

Top 16.6 Bottom 16.7 Total 33.3 A maximum of 40 milligrams (mg.) weight loss is allowed for this test. This test imposes severe corrosion conditions upon the copper-lead connecting rod bearing. Ordinarily with ester-based lubricants, i.e. wherein an ester is the base stock, test failure will occur as mani25 fested by a bearing weight loss in excess of the maximum 40 mg. allowed. The test result of 33.3 mg. weight loss is considered acceptable and indicative of a fluid that will not cause excessive bearing corrosion in actual engine 3θ operation.

Engine Deposit Inspection This is a visual cleanliness inspection wherein a rating of 0 to 10.0 is given. A rating of 10.0 is clean. Varnish is indicative of the degradation tendency , of the lubricant and is manifested by a shellac-like glaze that has formed along the metal parts.

Varnish Deposit Rating Sludge Deposit Rating Piston Skirt 9.8 Rocker Arms 9.9 Rocker Arm Cover 9.9 Rocker Arm Cover 9.9 Push Rod Cover 9.9 Push Rod Cover 9.9 Cylinder Wall, BRT 9.9 Oil Screen 10.0 Oil Pan 9.9 Oil Pan 9.9 Crankcase Cover Plate 9.9 Crankcase Cover Plate 9.9 Varnish Total 59.3 Sludge Total 59.5 Oil Analysis New Oil Used Oil, Hours 10 20 30 40 Neutralization No. 1.87 2.90 3.22 3.57 3.76 Viscosity-SUS at 100°F. 362.4 344. 9 341.4 334.0 330.5 at 21O°F.75.89 73.16 71.47 70.40 69.57 Stripped Viscosity at 210°F. 71.55 % Viscosity increase at 100°F. 4.8 5.8 7.8 8.8 at 210°F. 3.6 5.8 7.2 8.3 Oil Consumption, lb./Hr. 0-10 hours 0.000 10-20 hours 0.015 20-30 hours 0.004 30-40 hours 0.013 Example 2 A lubricant blend identical to the formulation of Example 1 was subjected to a severe wear and high temperature test run at high speed in a 1970 Oldsmobile (Registered Trade Mark), 8 cylinder, 425 cubic inch engine. The duration of the test was 64 hours and the criteria for a test pass are that the viscosity at 40 hours show less than 400% increase and that the cam plus lifter wear be less than 0.002 maximum and less than 0.001 average wear. This test is called the 1970 General Motors (Registered Trade Mark) MS Lubricant Evaluation: Sequence I1IC. A summary of the engine test results appears below: Viscosity Increase Data: Hour Viscosity Change Percent 0 68.OS 8 68.72 0.64 +01 16 69.66 1.58 +02 24 71.79 3.71 +05 32 74.60 6.52 +10 40 76.07 7.99 +12 48 77.44 9.36 +14 56 80.61 12.53 +18 64 82.17 14.09 +21 Comment: The 12% increase in viscosity after 40 hours indicates excellent fluid stability. The maximum allowed is 400%. Sludge Rating: Front Cover Deflector (10.0 is clean) 9.6 Rocker Cover-R 9.5 Rocker Cover-L 9.5 Rocker Cover Baffle-R 9.6 Average 9.6 Oil Screen Plugging (%) 0 Varnish (10.0 Rating: Piston Skirts is clean) Thrust 9.6 Anti-Thrust 9.6 Average 9.6 Sludge and varnish deposits in the critical areas noted were of very low magnitude for the severe operating conditions imposed by this test. In comparison, mineral oil-based lubricants would have a tendency to form much heavier sludge and varnish deposits under equivalent conditions.

Oil Ring Land Faces Rating: Above Below Average 5.9 8.3 7.0 Wear: Cam plus lifter Cin.) Maximum 0.0013 Minimum 0.0003 Average 0.0007 Rod Bearing Wt.Loss (mg.) Rod Number 4 53.1 Rod Number 5 65.1 Average 59.1 Scuffed and/or Worn: Number Scuffed but not Worn Number Worn but not Scuffed Number Worn Scuffed and Worn Cam Lobes 0 0 0 Lifters 0 0 0 Valve Stem Tips 4 2 8 Rocker Arm Pads 3 2 5 Rocker Arm Pivots 3 3 10 Oil Consumption (Qt) 4.53 Ring Area: Oil Ring Plugging (%) 0 Number Stuck Rings None Number Sluggish Rings None Number Stuck Lifters: None Comment: Inspection of the seals showed them to be in good condition, with no evidence of degration. The seals retained their pliability and dimension integrity and no leakage was evident. - 15 " Example 3 A lubricant blend identical to that tested in Example 1 was evaluated in a test method designed to relate particularly to short trip service under typical winter conditions, such as experienced in the upper Mid-Western U.S.

The conditions of this test are most useful in evaluating the rusting characteristics of motor oils due to the fact that test conditions encourage rust formation in critical parts of the engine. This test is called the 1971 General Motors Lubricant Evaluation: Sequence HC and is conducted in a 1971 Oldsmoblle with an 8 cylinder, 425 cubic inch ehgine.

Prior to each test run, the engine is completely disassembled, solvent cleaned, measured and rebuilt in strict accordancd to furnished specifications. Following the preparation, the engine is installed on a dynamometer test stand equipped with the appropriate accessories for controlling speed, load, temperatures and other various engine operating conditions. The engine is operated continuously for 28 hours under conditions of moderate engine speed, partially warmedup- jacket coolant temperature and rich air-fuel ratio. The following is a summary of test operating conditions: Speed, revolutions per minute (rpm) 1500+20 Load, brake horsepower (bhp) 25+2 Oil, to engine, after filter, deg.F. 120+2 Oil pump outlet, psi 50+10 Coolant, jacket out, deg. F 110+1 Coolant, jacket in, deg. F, 105+1 Coolant, jacket flow rate, gpm (U.S. gallons per minute) 60+1 Coolant, crossover out, deg. F 109+2 at at gpm 3.0+5 Coolant, crossover pressure outlet, psi 2.5+0.5 Coolant, breather tube out, deg. F. 60+2 at at gpm 3.0+0.5 Coolant, rocker covers out, deg. F. 6O+2at' at gpm per cover 1.5+0.5 Coolant out, rocker cover pressure psi 13.0+0.5 Air-fuel ratio Carburetor, air temperature, deg.F.

Carburetor, air humidity, grains per lb. of dry air Carburetor, pressure, in.water Blowby rate, ofm at 100 F. and 29.7 in Hg Intake manifold vacuum, in Hg.

Exhaust back pressure, in water Exhaust back pressure max.differential, in water Crankcase oil filter tube .0+0.5 80+2 80+5 0.1 to 0.3 0.8+0.1 18+1.5 4+1 0.2 Removed and plugged Immediately following this 28-hour period of operation, the engine is operated for 2 hours under the same conditions as above, except for the following changes: Coolant, jacket out, deg. F. 120+1 Coolant, jacket in, deg. F. 115+1 Coolant, crossover out, deg. F. 119+2 The engine is then shut down for 30 minutes to change the carburetor, perform an oil level check, change the spark plugs and to make adjustments to the rocker cover coolant system. Following this shutdown and without oil drain the engine is operated for 2 hours under the following hot conditions.

Speed, rpm 3600+20 Load, bhp 100+2 Oil, into engine, after filter, all viscosities, deg. F. 260+2 Coolant, jacket out, deg. F. 200+2 jacket in, deg. F. 190+2 jacket flow rate, gpm. 60+1 intake Crossover out, deg. F. 197+2 Breather tube out, deg. F. at gpm. 3.0+0.5 _ 17 Rocker cover out, deg. F. at gpm. per cover 198+2 at Rocker cover pressure, psi Air-Fuel ratio Carburetor, air temperature, deg. F. air humidity, grains per lb. of dry air pressure, in. water 1.5+0.5 .0+0.5 16.5+0.5 80+2 80+5 0.1 to 0.3 Blowby rate, cfm at 100 deg.F. and 29.7 in Hg.

Intake manifold vacuum, in. Hg. Exhaust back pressure, in. water Crankcase oil filter tube 2.2+ 0.2 11+2.5 30+2 removed and plugged , Inspection On completion of the test, the engine is completely disassembled and, inspected for rusting using the appropriate Coordinating Research Council (CRC) rating techniques. A rating of 10.0 is clean. Parts rated are indicated below: (1) Rust-(CRC) Manual No.7. Engine rust rating is the average of five parts listed below: Valve lifter bodies Valve lifter plungers Valve lifter balls Oil pump relief valve Push rods (2) Others: Oil pump relief valve sticking and valve lifter plunger sticking.

Summary of Engine Test Results Rust Rating: (10,0 is clean) Lifter Bodies Plungers Balls Relief Valve Plunger Push Rods Average 8.9 8.6 8.6 8.8 8.0 8.6 Stuck Lifters: (number) None Stuck Relief Valve: No Oil Consumption: (qts.) 0.25 Comment: An 8.4 average rust rating is considered acceptable in this severe rust promoting test. The 8.6 average rust obtained by the test is especially significant with regard to the lifter bodies, plungers, balls and relief valve plunger due to the fact that the aforesaid parts function within close tolerance restrictions.

Inspection of the seals showed them to be in good condition, with no evidence of degradation. The seals retained their pliability and dimensional integrity and no leakage was evident. The results of this test indicate a crankcase lubricant which has surpassed severe wear and temperature conditions.

Example 4 A lubricant blend identical to the formulation of Example 1 was subjected to the Ford (Registered Trade Mark) Sequence VC Test. This test is designed to evaluate the lubricant's ability to control and disperse harmful contaminants, such as acidic, blowby gases, particularly carbon and highly oxygenated oxidation products. These contaminants cause sludge and varnish deposits that are most likely to occur when the engine is subjected to various intermittent operating cycles whioh include idling, medium speed operation, high speed operation and shutdown.

The Ford Sequence VC Test is conducted on a Ford, 8-cylinder, 302 cubic inch engine. In brief, it consists of four consecutive operating cycles, each having a duration of four hours. In each cycle the engine is subjected to separate periods of idling, medium speed operation and high speed operation.

After the operating sequence of 4 cycles is completed, the engine is shut down for 8 hours, after which the entire operation is repeated. The test lasts for a total of 192 hours of operation.

On completion of the test, the engine is completely disassembled, inspected and rated. A summary of the results is as follows: Results A rating of 10.0 is clean Average Sludge Rating 9.09 (8.5 passes) Piston Skirt Varnish Rating 8.16 (7.9 passes) Average Varnish Rating 8.93 (8.0 passes) Comment: The results evidence the lubricant's ability to disperse harmful contaminants and maintain the engine in a clean operating condition, thereby ensuring good performance under severe operating condition. Inspection of the seals showed them to be in good condition, with no evidence of degradation. The seals retained their pliability and dimensional integrity - no leakage was evidenced.

Claims (12)

1. CLAIMS:1. A crankcase lubricant composition, the base stock of which has a viscosity at 210°F. of from 3 to 20 centistokes and which comprises (a) a trimethylolpropane ester or a polytrimethylolpropane ester of an aliphatic hydrocarbyl monocarboxylic acid having an average chain length of from 4 to 12 carbon atoms and, optionally additionally a dibasic carboxylic acid; and (b) an oligomer selected from oligomers of alpha-decene and mixtures of such oligomers, the relative amounts of component (a) and component (b) being such as to impart a butadiene-acrylonitrile elastomer seal swell of from 4 to 20%.

2. A composition as claimed in claim 1 in which the weight ratio of component (a): component (b) is from 35:65 to 80:20.

3. A composition as claimed in claim 2 in which the ratio is from 40:60 to 66.7:33.3.

4. A composition as olaimed in claim 3 in which the ratio is about.50:50.

5. A composition as claimed in any of claims 1 to 4 in which the relative amounts are such as to impart a seal swell of from 5 to 15%.

6. A composition as olaimed In olaim 5 in which the relative amounts are such as to impart a seal swell of from 6 to 9%.

7. A composition as claimed in any of claims 1 to 6 in which component (a) of the base stock is selected from trimethylolpropane triheptanoate and ditrimethylolpropane tetraheptanoate.

8. 8. Λ composition as claimed in any of claims 1 to 7 in which the base stock has a viscosity of from 4 to 12 centistokes. 5

9. A composition as claimed in any of claims 1 to 8 in which the carboxylic acid of the ester component (a) of the base stock has an average chain length of from 5 to 9 carbon atoms. ; 10 ·( ? *> J . 5 •1

10. A composition as claimed in any of claims 1 to 9 which comprises an anti-corrosion agent and/or an anti-wear agent and/or a lubricity agent and/or a viscosity indeximproving agent and/or a detergent and/or a dispersant and/ or a metal-deactivation agent and/or an antifoaming agent.

11. A composition as claimed in claim 1 substantially as herein described. ί 15 * ί

12. A composition as claimed in claim 1 substantially as herein described with reference to Example 1. F.R.KELLY & CO., AGENTS FOR THE APPLICANTS