NO136758B - - Google Patents

Description

The present invention relates to lubricant compositions for use in internal combustion engines. More particularly, they relate to lubricant compositions based on synthetic esters, which can be used in competition engines and other high-performance internal combustion engines.

Modern high compression internal combustion engines, which are subjected to high mechanical stresses at high temperatures and high pressures for extended periods of time as well as frequent starts at high and low temperatures, require lubricants that allow them to operate at a high level of efficiency under these severe conditions. The lubricant's primary function is, of course, to reduce friction and thereby not only reduce wear on pistons, bearings and other moving parts, but also to increase the engine's efficiency. In addition, the lubricant should prevent or inhibit the formation of deposits in the combustion chamber and further remove such deposits from engines that are already coated with such.

Lubricant compositions have been developed which consist wholly or partly of synthetic ingredients in an attempt to

to obtain lubricants suitable for use in internal combustion engines. In general, these have compositions, which contain a synthetic ester as base fluid and a combination of stabilizing

6g other additives, better viscosity properties, lower pour point, lower volatility, better thermal stability, higher specific heat and thermal conductivity and further better resistance to oxidation than petroleum oil-based lubricants with similar viscosity.

A number of types of synthetic esters have been proposed as base fluids for lubricants for internal combustion engines, but none have been found to be entirely satisfactory for this purpose, especially for the more stringent requirements of high-performance engines. Esters of branched-chain polyols and straight-chain fatty acids such as pentaerythritol-tetracaproate do not have the necessary viscosity without the addition of viscosity index improvers or other thickeners, while esters of these polyols and branched-chain fatty acids such as pentaerythritol- tetrapivalate are solid at ambient temperatures and thus difficult to process, and they also have poor properties at low temperatures. Diesters of aliphatic dicarboxylic acids, such as di-(2-ethylhexyl)-sebacate, diisododecyl adipate and diisotridecyl azelate are not suitable for use as lubricants for high-performance internal combustion engines due to their high volatility and insufficient viscosity properties at high temperatures, as well as such as their tendency to cause the elastomers used as seals in engines to swell. Even when mixed with thickeners and other additives, these esters cannot be used successfully under the operating conditions expected of high performance internal combustion engines.

According to the present invention, it has been found that lubricant compositions based on synthetic esters, which comprise a base fluid containing at least one ester derived from an aromatic polycarboxylic acid and an aliphatic or cycloaliphatic monohydroxy alcohol and an additive system as described below, meet the requirements that are set up for motor oils for competition engines. Compared to the previously used petroleum-based competition oils, the use of the lubricant compositions according to the invention results in faster acceleration, reduced engine wear, greater engine cleanliness and a greatly increased service life for the oil.

The synthetic esters which have viscosity, volatility and other properties that make them effective as base fluids for internal combustion engine lubricants have the structural formula:

where R means an alkyl or cycloalkyl group with 5-18 carbon atoms and n is a number in the range 2-4-.

Among the aromatic polycarboxylic acids that can be used in the production of these esters are phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimesic acid, hemimellitic acid, pyromellitic acid, prenic acid, mellophic acid and mixtures thereof. The anhydrides and acid chlorides of these acids can also be used in the preparation of the esters.

The alcohols which are reacted with the aromatic polycarboxylic acids to form the synthetic esters are saturated aliphatic and cycloaliphatic monohydroxy alcohols. 5-1'8 carbon atoms.. Illustrative of these alcohols are the following: n-amyl alcohol, isoamyl alcohol-, neopentyl alcohol., n-:hexanol, .2-methylpentanol, 3-methylpentanol., 2,2-dimethylbutanol-3 ., n-heptanol, 2,4-dimethyl-pentanol-3, n-octanol, 2-ethylhexanol, 2-ethyloctanol, decanol, isodecanol, undecanol, 2-butyl-octanol, n-dodecanol, tridecanol, triispdecanol, cyclohexanol, , cycloheptanol, 2,2-dimethylcycloheptanol and borneol. The branched-chain alcohols with 8-13 carbon atoms are usually preferred, because their use results in the formation of esters with higher viscosities and lower pour points than is obtained when straight-chain alcohols are used. A particularly preferred group of alcohols are the highly branched alcohols produced by the oxo synthesis. This synthesis, described in US Patent No. 2,327,066, entails the catalytic reduction of an olefin with carbon monoxide and hydrogen under special conditions. The most generally available oxo-alcohols and those which are also the most preferred alcohols for use in the preparation of the synthetic esters are those derived from the dimers, trimers and tetramers of propylene and butylene. These oxo-alcohols include isooctanol, 2-ethylhexanol, 3,5>5-trimethylhexanol, isodecanol, 2-ethyldecanol and isotridecanol. It may be desirable to use a mixture of alcohols to obtain mixed esters which have the desired combination of properties.

The esters are produced by methods that are well known in the art. E.g. they can be prepared by direct esterification of the aromatic polycarboxylic acid with a substantially equivalent amount of alcohol in the presence of an acid catalyst such as sulfuric acid or p-toluenesulfonic acid.

Representative of the synthetic esters that can be used as base fluid in the lubricant compositions according to the invention are di-(2£ethylhexyl)-terephthalate, di-(2-ethylbutyl!)~ terephthalate, ditridecyl isophthalate, diundecyl phthalate, undecyl-tridecyl -phthalate, diisotridecyl phthalate, diisooctadecyl phthalate, di-(C^2°xo)-phthalate, di-(C-^^oxo)-phthalate, diundecyl isophthalate, di-(3>5>5~trimethylhexyl) -isophthalate, tri-(2-ethylhexyl)-trimellitate, tridecyl-trimellitate, triundecyl-trimellitate, diiso-nonyl-undecyl-trimellitate, diisotridecyl-trimellitate, triisododecyl-trimellitate, triisotridecyl-trimellitate, triundecyl-trimesate, triisododecyl-trimesate, tetraisodecyl -pyromellitate, diiso-nonyl-diisodecyl-pyromellitate, tetra-{C^QOxo)-pyromellitate and tetra-(C-^2°kso)-pyromellitate. The preferred base fluids are phthalate esters of alcohols with 11-13 carbon atoms, trimellitate esters of alcohols with 8-13 carbon atoms and mixtures of these esters. The best results have been obtained using triisodecyl trimellitate as the base fluid.

The preferred synthetic ester based fluids have combinations of properties that make them useful as competition motor oils. The viscosities at 37>8°C are between 80 and 280 centistokes and at g8.9°c between 5 and 40 centistokes. In most cases, the viscosities at 37.8°C are between 150 and 250 centistokes and at 98.9°C between 10 and 20 centistokes. Their "Dean and Davis" viscosity index is at least $ 0. Flash points are above 204.4°C °g pour points below -28.9°C.

While esters with lower viscosities than those required in competition engine oils can be blended with high molecular weight polymers to form base fluids having viscosities in the desired ranges, modification of the viscosity of the esters in this way is generally undesirable due to excessive volatility for the lower viscosity esters and due to the tendency of most high molecular weight polymers to undergo shear stress under severe operating conditions.

To produce the lubricant compositions according to the invention, the base fluid of synthetic ester is mixed with various additives, each of which is used to achieve a special property in the composition. The additive system used in lubricant compositions intended for use in competition engines and other high-performance internal combustion engines includes antioxidants, metal passivators, rust inhibitors, antifoams and agents to promote resistance to stress in amounts which give the compositions the desired properties.

The present invention thus relates to a lubricant composition for internal combustion engines, and the lubricant composition is characterized by the fact that it comprises

a) .80-96% of a synthetic ester base liquid which

consists of an ester, with the structural formula:

where R denotes an alkyl or a cycloalkyl group with 5-18 carbon atoms and n is an integer in the range 2-4; •b<->) 'O.i^-tO.,^^ of an antioxidant selected tellarite sterically hindered phenols.., aromatic amines with the formula: where Y and Y' are each phenyl, alkylphenyl, naphthyl or alkylnaphthyl, as well as mixtures thereof; c) 0.05-2.0% of a metal passivating compound selected from salicylalaminoguanidine and its fatty acid salts, benzotriazole, methylbenzotriazole, dodecylbenzotriazole, phenothiazine and mixtures thereof; d) 0.1-2.0% of a rust-inhibiting component selected from sorbitan esters of fatty acids.; e) 0.75-5)°% of a ballast-bearing component selected from group-II metal dialkylthiophosphates, group-II metal

diarylthiophosphates, amine salts of partially esterified phosphoric acids, alkylmercaptothiadiazoles, trialkylphosphates with 5-18 carbon atoms and mixtures thereof; .-and

f) .0.0005-0.002% of a foam suppressing ingredient in the form of a polysiloxane

where all percentages are -given on a weight basis by

the lubricant composition.

The antioxidants used in the hitherto unknown lubricant compositions are common antioxidants such as sterically hindered phenols and aromatic amines.

The printable phenolic antioxidants are those in which the substituents ortho to the hydroxyl group are sufficient to block the hydroxyl group by steric hindrance. The preferred sterically hindered phenolic antioxidants include such monocyclic phenols and bisphenols as 2,6-di-tert.butyl-p-cresol, 2,6-di-tert.butyl-4-benzylphenol, 2,6-di -tert .butyl-oc-dimethyl-amino-p-cresol, 2,6-di-tert .butyl-oc-diphenylamino-p-cresol, 4,4,-methylene bis-(2,6-di-tert .butylphenol), 2,2'-methylene bis(4~ ethyl-6-tert.butylphenol), 4>4'-methylene bis(6-tert.butyl-5-indanol) and 1,3» 5_trimethyl-2, 4 > 6-tris-(3 > ^ >- å±- t ert. butyl.-4-hydroxybenzyl) benzene.

As mentioned above, suitable aromatic amino antioxidants include secondary amines with the formula:

where Y and Y' are each phenyl, alkylphenyl, naphthyl or alkylnaphthyl. Illustrative of these compounds are N-phenyl-α-naphthylamine, N-phenyl-(3-naphthylamine, diphenylamine, dinaphthylamine, ditolylamine, phenyltolylamine, p,p'-dioctyldiphenylamine, p,p'-dinonyldinaphthylamine, tolylnaphthylamine, octylphenyl -cc-naphthylamine and p-aminodiphenylamine.

Compositions having the best antioxidant properties are those in which the antioxidant component of the additive system contains from 0.7% to 1.5% of a sterically hindered phenol from 0.3 to 1% of an aromatic amine, calculated on the weight of lubricant composition, or an equivalent amount of a single compound which is both a sterically hindered ■phenol and an aromatic ■amine such as 2,6-di-tert;butyl-oc-diphenylamino-p-cresol. It is particularly preferred that the additive system consists of 4>4'-methyl-bis(2,6-di-tert.butylphenol) and N-phenyl-a-naphthylamine.

Metal passivators are used to reduce the corrosion of engine materials such as copper and lead when these are exposed to the lubricants for longer periods at high temperature and in the presence of air. Among the most effective of the copper passivators are compounds of the azole type, such as imidazole, pyrazole, triazole and their derivatives including benzimidazole, benzotriazole, methylbenzotriazole, dodecylbenzotriazole, . 3-amino-4-anilido-1,2,3-triazole, methylene-bis-benzotriazole and naphthotriazole-salicylaldehyde-semicarbazone and its alkyl derivatives such as isopropyl-salicylaldehyde-semicarbazone; and the condensation product of salicylaldehyde with hydrazine derivatives and ^^_ 2- lQ fatty acid~ salts of such condensation products, e.g. the palmitic acid or oleic acid salt of salicylalaminoguanidine. The preferred copper passivators are benzotriazole, salicylalaminoguanidine monooleate and mixtures thereof. A commercially available source of the latter compound is "Qrtholeum JQO", which contains approx. 10% salicylaminoguanidine monooleate and 90% diphenylamine. Suitable lead passivators include alkyl gallates such as propyl and lauryl gallates; phenothiazine and substituted phenothiazoles; quinizarin; alizarin; dicarboxylic acids such as sebacic acid, azelaic acid and adipic acid; and esters of these acids such as neopentyl glycoisebacate and 2-ethylhexyl acetate. The preferred lead passivator is phenothiazine. The lubricant compositions may also contain compounds that inhibit corrosion of engine components containing silver, iron slag and other metals.

The rust inhibitors present in the system are metal salts from group II, ammonium salts and amine salts of petroleum sulphonic acids, alkylated naphthalenesulphonic acids and alkenyl succinic acids, as well as fatty acid esters of sorbitan. The preferred rust inhibitor is sorbitan monooleate.

Additives that improve the load-carrying capacity and that act as smoothing agents, anti-wear and anti-abrasion compounds and further as agents at extreme pressures are organic compounds containing phosphorus, sulfur and/or chlorine. These include group II metal dialkyl dithiophosphates, group II metal diaryl dithiophosphates, group II metal dicycloalkyl dithiophosphates, group II metal dialkyl thiocarbamates, alkyl mercapt thiodiazbles, phosphate esters, t i o f o s f a t e s t e r e , amine salts of partially esterified phosphoric acids , amine salts of chlorophosphonic acids, chlorinated diphenyls and mixtures thereof. Illustrative of these loading agents are zinc diamyldithiophosphate, zinc di-n-octyldithiophosphate, calcium methylcyclohexyldithiophosphate, calcium methylcyclohexyldithiophosphate, zinc amyldithiocarbamate, tricresyl phosphate, and amine salts of lower alkyl esters of phosphoric acid. The preferred loading agents are zinc dialkyl dithiophosphates and tertiary alkylamine salts of lower alkyl diphosphates. Particularly preferred load-carrying agents are the commercially available products comprising a major proportion of a zinc dialkyldithiophosphate and a minor amount of a petroleum oil and the commercially available products comprising amine salts of the formula:

where R"' denotes a tertiary alkyl group with 8-22 carbon atoms and preferably a tertiary alkyl group with 12-14 carbon atoms.

Polysiloxanes are generally used to reduce the tendency: for the lubricant - to foam and to. support,.. rapid breakdown of any foam that may form. The preferred antifoams are dimethylpolysiloxanes having a nominal viscosity of about 1000 centistokes' at 25°C.

From the preceding description of the additive system, it appears that there are compounds which have properties which make them usable as more than one of the constituents of the additive system. E.g. phenothiazine acts as an antioxidant and as a lead passivator, and a zinc diamyl dithiophosphate acts as an antioxidant and load-carrying agent.

It can be in special cases. advantageous to incorporate other additives such as detergents and dispersants. Suitable detergents and dispersants include neutral and basic alkaline earth metal phenates and sulfonates; reaction products .of copolymers of polyolefins and- maleic anhydride with organic- . polyalkylene pblyamines, e.g. -products of the reaction of poly- / isobutylene maleic anhydride copolymers with tetraethylenepentamine; and copolymers formed' by polymerization of alkyl acrylates and ■ alkyl methacrylates with small amounts of N-vinylpyrrolidone, or hydroxyethyl methacrylates. Methacrylate copolymers are the preferred dispersants. The basic alkaline earth sulfonates. are the preferred detergents. The amount of detergent and/or dispersant, if used within the range from about 0.1% to about- . around 6%, calculated on the weight of the composition.-The curry additives: are added individually or combined in a pre-mixed additive "pack". Such packages frequently contain one or more of each of the above-described additives, which have antioxidant, metal-passivating, rust-inhibiting, load-bearing and detergent-dispersant functions.

Furthermore, it may occasionally be desirable to modify the viscosity and/or viscosity index of the composition. This can be done by mixing in the base fluid from about 0.1% to about 5% by weight of the weight of one or more viscous organic esters to obtain a product, the viscosity of which lies between those of the constituents. The use of from about 2

to about 4% by weight of very high molecular weight polymers usually raises both the viscosity and the viscosity index of the composition significantly. Polymers that can be used for this purpose include polyolefins, polystyrene, acrylate and methacrylate polymers and copolymers as well as polyesters. Methacrylate polymers and copolymers are the preferred viscosity-modifying agents.

While the compositions according to the invention have particular value as lubricants for competition engines, they can also be used as lubricants for other internal combustion engines, including car engines, light aircraft engines, diesel engines and two-stroke engines. They can also be used as bearing lubricants, e.g. for sealing or anti-friction bearings, as a heat transfer fluid, as a vacuum pump oil or as a hydraulic fluid, as a gear oil, as a transformer oil and as a mold release agent. When mixed with other substances, they can be used as transmission fluids and as brake fluids. . The invention shall be illustrated in more detail by the following examples.

Example 1

A competition motor oil was produced by mixing the following substances:

The physical properties of this competition engine oil are listed in Table 1. For the sake of comparison, the properties of a typical petroleum-based competition engine oil ("Sun SAÉ 50") are also included in the table.

Example 2

One competition engine oil suitable for use in "dragster11" cars and "circuit" cars was made by mixing the following substances:

The physical properties of this competing oil are given in Table 1.

Example 3

The products according to examples 1 and 2, as well as the petroleum-based co-current oil, the properties of which are indicated in Table 1, were judged as 'lubricants. Lubricant properties were measured using the "Shell Four Balle" wear test, where the diameter of the wear track on the bearing surface is a measure of lubricity under metal-to-metal conditions. The "Falex Lubricant "Tester" was used to measure the load carrying capacity of the lubricants. The test methods used are described in detail by Currie and Hommel in "Ind. Eng.Chem.", 42, 2452 (1950). The data obtained are given in Table 2.

The data given in table 2 suggest that the competition motor oil according to the invention has significantly better full-load carrying properties than the petroleum-based oil. In addition, the use of the new lubricants results in reduced engine wear.

Claims (3)

1. Lubricant composition for internal combustion engines, characterized in that it comprises a) 80-96% of a synthetic ester base liquid which consists of an ester with the structural formula: where R denotes an alkyl or a cycloalkyl group with 5-18 carbon atoms and n is an integer in the range 2-4; b) 0.5-0.3% of an antioxidant selected from sterically hindered phenols, aromatic amines with the formula: where Y and Y' are each phenyl, alkylphenyl, naphthyl or alkylnaphthyl, as well as mixtures thereof,; c) 0.05-2.0% of a metal passivating compound selected from salicylalaminoguanidine and its fatty acid salts, benzotriazole, methylbenzotriazole, dodecylbenzotriazole, phenothiazine and mixtures thereof; d) 0.1-2.0% of a rust-inhibiting component selected from sorbitan esters of fatty acids; e) 0.75~5>0$ of a load-bearing component selected from group-II metal dialkylthiophosphates, group-II metal diarylthiophosphates, amine salts of partially esterified phosphoric acids, alkylmercaptothiadiazoles, trialkylphosphates with 5_l8 carbon atoms and mixtures thereof; and f) 0.0005-0.002% of a foam suppressant in the form of a polysiloxane where all percentages are given on a weight basis of the butter composition. 2. Lubricant composition according to claim ^characterized in that the synthetic ester base liquid is triisodecyl trimellitate. 3. Lubricant composition according to claim 1, characterized in that it comprises: a) 85-96% triisodecyl trimellitate b-j^) 0.7-1.5% 4,4'-methylene-bis(2,6-di-tert-rbutylphenol) b2) 0.3-1.0% N-phenyl-a-naphthylamine c-^) 0.1-0.2% salicylalaminoguanidine monooleate c2) 0.03-0.2% benzotriazole c,-,) 0.1-0.8% phenothiazine d) 0.3-0.8% sorbitan monooleate e-jj 0.5-2.0% zinc diamylthiophosphate eg) 0.3-0.8% of an amine salt with the formula where each R"' is a tertiary alkyl group of 12-14 carbon atoms, and f) 0.0005-0.002% dimethylpolysiloxane with a nominal viscosity of 1000 centistokes at 25°C where all percentages are given on a weight basis of the weight of the lubricant composition.