This invention relates to lubricant compositions and a novel ester therefor and to a process for the preparation of the novel ester and other defined esters.

Metal working fluids containing chlorinated paraffin additives have been and are still used because of their good performance as extreme pressure (EP) lubricants. Owing to the chlorine content of the chlorinated paraffin additives, for environmental reasons replacements have been sought for them. Sulphur- containing synthetic, sulphur-containing oleochemical and phosphorus- containing additives have been used successfully as such replacements in many applications.

There are many examples in the literature of esters that are used as lubricants and/or lubricant additives. Some known lubricant and lubricant additives are described below.

US 4113642 discloses high viscosity neutral complex ester lubricants produced from C4-10 branched alkane polyols, dimer and/or trimer fatty acids and alkanoic acids having 6-16 carbon atoms.

JP10231494 discloses a lubricating oil for water dispersion type cold rolling oil, the lubricating oil containing 1) 5-40% by weight of a mineral oil and/or a mono-ester of C12-22 aliphatic carboxylic acid and a C1-12 aliphatic alcohol, 2) 5-70% by weight of oil and fat and 3) 20-90% by weight of composite esters of dimer and/or polymer acid of C16-20 aliphatic unsaturated acid and polyol of which residual COOH or OH are esterified with C12-22 mono-hydric alcohol or mono-basic fatty acid.

JP05043888 discloses a cold rolling oil containing at least 60% by weight of an ester and 1-20% by weight of an organic sulphur compound. The ester has a viscosity at 40°C of 150-350 cSt and consists of higher fatty acids containing 5-60% of C12-22 saturated fatty acids and polyhydric alcohol.

JP01139694, 2028297 and 03097789 disclose lubricating oils containing an ester derived from a di-to hexahydric polyol, a fatty acid and a dibasic acid.

Surprisingly it has now been found that lubricant compositions comprising selected esters exhibit improved performance, the esters having a high viscosity

at 100°C, a high viscosity index and a good compatibility with oils, especially mineral oil.

Especially enhanced properties are obtained in such lubricant compositions when the lubricant is mineral oil containing sulphur-containing synthetic and/or sulphur-containing oleochemical additives and phosphorus- containing additives.

According to one aspect of the present invention, there is provided an lubricant composition suitable for extreme pressure applications comprising : 1) an oil 2) at least one ester selected from a) an ester which is the reaction product of: i) an aliphatic hydrocarbon polyol, ii) a dimer fatty acid and a trimer fatty acid in a weight ratio in the range of 15: 85 to 70: 30 and iii) a monocarboxylic acid having 8-24 carbon atoms wherein at the start of the reaction the ratio of hydroxyl groups to carboxyl groups is in the range of 0.85: 1 to 1.3: 1, and the weight ratio of ii) to iii) is in the range of 50: 50 to 85: 15. and/or b) an ester obtained by reacting a branched saturated alkane diol, a dimer fatty acid and a dicarboxylic acid having 4-10 carbon atoms.

The aliphatic hydrocarbon polyol used for preparing the ester of 2a) has a linear and/or branched hydrocarbon chain. The polyol may be a diol, for example neopentylglycol, a triol, for example trimethylolethane or trimethyolpropane, or a tetraol, for example pentaerythritol. Also the polyol may be a dimer or trimer of pentaerythritol. Preferably the aliphatic hydrocarbon polyol is a diol, more preferably having 2-6 carbon atoms, for example ethylene glycol, propylene glycol, butane diol, pentane diol, neopentyl glycol, hexane diol. Most preferably propylene glycol is used.

The monocarboxylic acid may be selected from linear and/or branched and saturated or unsaturated acids having 8-24, preferably 14-24 and more preferably 16-22 carbon atoms for example palmitic, palmitoleic, margaric,

stearic, isostearic, oleic, linoleic, linolenic, nonadecanoic, arachidic, heneicosanic, behenic, erucic acids and mixtures thereof.

The monocarboxylic acid may be a distillat from the reaction product obtained from dimerisation of an unsaturated fatty acid having 8-24, preferably 14-24 and more preferably 16-22 carbon atoms. This known dimerisation process leads to a mixture comprising: 1) dimer fatty acids containing two carboxylic acids and having 16-48, preferably 28-48, more preferably 32-44, carbon atoms; 2) trimer fatty acids containing three carboxylic acids having 24-72, preferably 42- 72, more preferably 48-66, carbon atoms together with small amounts (less than 5% by weight based on the whole mixture) of higher oligomers and other constituents (tetramer, pentamer, etc.) and 3) monocarboxylic acids having 8-24, preferably 14-24, more preferably 16-22, carbon atoms; such monocarboxylic acids are often referred to as modified fatty acids.

As an example, a typical dimerisation of oleic acid will give 48% by weight dimer dicarboxylic acid with 36 carbon atoms, 40% by weight of monocarboxylic acid and 12% by weight of trimer tricarboxylic acid having 54 carbon atoms together with small amounts of higher oligomers and other constituents. By distillation of the mixture at about 240-270 °C and a pressure of about 0-10bar the monocarboxylic acid is obtained as the distillat and may be used as the monocarboxylic acid of the invention.

The weight ratio of dimer to trimer fatty acid is preferably in the range of 20: 80 to 60: 40. The dimer fatty acid of the invention may be obtained from the dimerisation of the unsaturated fatty acid as described above. It can be separated from the trimer and higher oligomers until the desired ratio of dimer to trimer fatty acid is obtained. Alternatively, fully separated dimer fatty acid and trimer fatty acid may be mixed so as to obtain the desired ratio.

The trimer fatty acid may contain small amounts of higher oligomers.

The ingredients are combined such that at the start of the reaction the weight ratio of the dimer and trimer fatty acid to the monocarboxylic acid is preferably in the range of 60: 40 to 75: 25.

The ingredients are combined such that at the start of the reaction the ratio of hydroxyl groups to carboxyl groups is in the range 0.85: 1 to 1.3: 1. If the range extends beyond 1.3 then the viscosity is too low and the lubricity is reduced to unacceptable levels. Extension of the range below 0.85, conversely leads to a too high viscosity value and the possibility of gelling during production.

The dynamic viscosity at 90°C of the ester product of 2a) obtained is preferably between 700-3000 mPa. s, more preferably 700-1300 mPa. s, and the dynamic viscosity at 40°C is preferably between 9000-40000 mPa. s, more preferably 10000-15000 mPa. s. Furthermore the hydroxyl value of the ester product is below 40, preferably below 20 and more preferably below 10mg KOH/g and the acid value of the ester product is below 20 and preferably below 5 mg KOH/g.

The ester in 2b) is obtained by reacting a branched saturated alkane diol having 3-8 carbon atoms, a dimer fatty acid and a dicarboxylic acid having 4-10 carbon atoms. Preferably the branched saturated alkane diol is neopentyl glycol, the dicarboxylic acid has 4-10 carbon atoms is adipic acid and the dimer fatty acid has 32-44 carbon atoms. The dimer fatty acid preferably comprises at least 95% by weight of dicarboxylic acid dimers, the remainder being higher oligomers and monocarboxylic acids.

Preferably these esters are made by reacting: 70-89% by weight of dimer fatty acid, 10-25% by weight of branched diol and 0.1-5% by weight of dicarboxylic acid having 4-10 carbon atoms, all calculated on the total amount of these three ingredients.

The dynamic viscosity at 90°C preferably is 700-3000 mPa. s, the acid value preferably is below 1 mg KOH/g and the hydroxyl value preferably is below 30 mg KOH/g.

Such esters are known as such; an example is Priolube 3986 ex Uniqema, an ICI Business.

The esters of 2a) and b) show a good solubility/compatibility in the oil.

Oils, which are used in the lubricant compositions, include mineral oils and oils of vegetable or animal origin. Preferably the oil is a mineral oil.

The lubricant compositions according to the invention exhibit an improved load carrying capacity. Preferably the lubricant composition further comprises at least one additive selected from the group consisting of sulphur-containing synthetic additives, sulphur-containing oleochemical additives and phosphorus- containing additives.

A preferred lubricant composition comprises: 80-98% by weight of oil, 1-15% by weight of at least one additive selected from the group consisting of sulphur-containing synthetic additives, sulphur-containing oleochemical additives and phosphorus-containing additives and 1-15% by weight of an ester of 2a) and/or 2b) the amounts being calculated on these three ingredients.

Sulphur-containing synthetic additives include sulphurised olefins, aryl- polysulphides, alkyl-polysulphides, dithiophosphates (organic or metal containing), dithiocarbamates, sulphurised terpenes and aromatic phosphorthionates.

Examples of suitable sulphur-containing olechemical additives include sulphurised natural oils and fats, sulphurised fatty acids and sulphurised esters.

Phosphorus-containing additives, which may be used, include phosphate esters, phosphite esters and amine phosphate esters.

The lubricant compositions may further comprise other ingredients commonly used and known to those skilled in the art and especially those selected from other synthetic esters, surfactants, emulsifiers, corrosion inhibitors, anti-oxidants, anti-wear/EP-agents and anti-foaming agents. The total amount of such other ingredients in general is less than 10% by weight calculated on the total lubricant composition.

According to a second aspect of the present invention there is provided an ester which is the reaction product of: i) an aliphatic hydrocarbon polyol, ii) a dimer fatty acid and a trimer fatty acid in a weight ratio in the range of 15: 85 to 70: 30 and iii) a monocarboxylic acid having 8-24 carbon atoms

wherein at the start of the reaction the ratio of hydroxyl groups to carboxyl groups is in the range of 0.85: 1 to 1.3: 1, and the weight ratio of ii) to iii) is in the range of 50: 50 to 85: 15.

Further, the invention is concerned with a process for preparing the aforementioned ester according to the present invention by mixing and reacting the aforementioned ingredients in the indicated relative amounts, followed, if necessary, by removal and/or by conversion of excess of monocarboxylic acid until the desired acid value is obtained.

To prepare the esters according to the invention, the ingredients are mixed in such relative amounts so as to meet the aforementioned ratios and reacted.

Although the reaction may take place under reduced pressure and slightly elevated temperature, it preferably is conducted at atmospheric pressure and at a temperature in the range of 200 to 250°C.

During the reaction, water and some monocarboxylic acid and polyol are distilled ; the monocarboxyiic acid is fed back into the reaction mixture and the water containing the diol is removed. The reaction is continued until the hydroxyl value of the ester is below 40, preferably below 20 and more preferably below 10 mg KOH/g.

After the reaction, distillation and/or conversion until the acid value is below 20 and preferably below 5 mg KOH/g remove any excess monocarboxylic acid.

The esters according to the present invention find particular utility as additives in lubricants which are used in applications where extremely high pressures are encountered, for example in metal working fluids (drawing, stamping, cutting), rolling oils, greases, hydraulic oils, gear oils (both industrial and automotive), compressor oils and automotive crankcase oils (both 2-stroke and 4-stroke).

According to a third aspect of the present invention there is provided use of an ester in extreme pressure lubricant compositions, wherein said ester comprises at least one ester selected from a) an ester which is the reaction product of: i) an aliphatic hydrocarbon polyol, ii) a dimer fatty acid and a trimer fatty acid in a weight ratio in the range of 15: 85 to 70: 30 and iii) a monocarboxylic acid having 8-24 carbon atoms

wherein at the start of the reaction the ratio of hydroxyl groups to carboxyl groups is in the range of 0.85: 1 to 1.3: 1, and the weight ratio of ii) to iii) is in the range of 50: 50 to 85: 15, and/or b) an ester obtained by reacting a branched saturated alkane diol, a dimer fatty acid and a dicarboxylic acid having 4-10 carbon atoms.

The invention will be further illustrated by reference to the following examples.

Example 1 74.6g of propylene glycol, 328.4g of Trimer 1040, a product commercially obtainable from Uniqema having a weight ratio of dimer fatty acid (derived from oleic acid) to trimer fatty acid (derived from oleic acid) of about 22% to about 78% and 197g of Monomer 7990 (C18 acid), commercially obtainable from Uniqema, where the weight ratio of dimer/trimer to monocarboxylic acid is 62: 38 and the ratio of hydroxyl groups to carboxyl groups at the start of the reaction is approximately 1.05: 1, were reacted at 220°C and atmospheric pressure until the hydroxyl value was 4 mg KOH/g. Then excess of monocarboxylic acid was removed by distillation until the acid value was 0.7 mg KOH/g. The ester obtained (Ester One) was an ester according to 2a) of the present invention having a dynamic viscosity at 40°C of 12000 and a dynamic viscosity at 90°C of 1180 mPa. s. Ester One had a clear appearance.

Example 2 Example 1 was repeated but in the amounts of Trimer 1040-341.5 g and Monomer 7990-183.9 g with a weight ratio of dimer/trimer to monocarboxylic acid of 65: 35 and a ratio of hydroxyl groups to carboxyl groups at the start of the reaction of approximately 1.05: 1. The reaction was conducted till the hydroxyl value was 5 mg KOH/g and the removal of excess monocarboxylic acid was undertaken until the acid value was 0.6 mg KOH/g. The ester obtained (Ester Two) was an ester according to 2a) of the present invention having a dynamic viscosity at 40°C of 29100 and a dynamic viscosity at 90°C of 2660 mPa. s. Ester Two had a clear appearance.

Example 3 Example 1 was repeated but in the amounts of Propylene glycol-76. 2g, Trimer 1040-325.8 g and Monomer 7990-198. Og with a weight ratio of dimer/trimer to monocarboxylic acid of 62: 38 and a ratio of hydroxyl groups to carboxyl groups at the start of the reaction of approximately 1.08: 1. The reaction was conducted till the hydroxyl value was 4 mg KOH/g and the removal of excess monocarboxylic acid was undertaken until the acid value was 1.1 mg KOH/g. The ester obtained (Ester Three) was an ester according to 2a) of the present invention having a dynamic viscosity at 40°C of 10,000 and a dynamic viscosity at 90°C of 985 mPa. s. Ester Three had a clear appearance.

Example 4 10% by weight of each of Esters One and Two were mixed with Vitrea 32 (mineral oil ex Shell) at 80°C and cooled to room temperature. Both mixtures were clear ; the esters showed good solubility in the mineral oil.

Example 5 Priolube 3986 (an ester of the present invention according to 2b)) was used in the following formulation in Table One. The formulation was subjected to the four ball machine test in accordance with ASTM D-2783-88, in order to evaluate its weld load performance. Amounts of each ingredient in the formulation are in parts by weight (pbw).

Table One Formulation1 2 (Comparative) Vitrea32 90 90 Homett Epoil HD17A 1) 10 Priolube 3986 5 Weld load, kg 420 380

1) Sulphur-containing synthetic additive ex Hornett Bros. & Co Limited Formulation 1 demonstrates that the use of esters in lubricant compositions along with the mineral oil and sulphur-containing additive in accordance with the invention have improved load carrying performance with respect to comparative formulation 2 where there are no esters present.

Example 6 Ester Three was used in the following formulations in Table 2. The formulations were subjected to the four ball machine test in accordance with ASTM D 2783-88 , in order to evaluate its weld load performance. Amounts of each ingredient in the formulation are in parts by weight (pbw) Table Two Formulation 3 4 (Comparative) Mineral Oil =9 90 90 Monalube205 3) 5 10 Ester Three 5 Failure Load, 3800 3000 Newton 2) A base oil with kinematic viscosity at 40°C of 10.1, density at 20°C of 0.852 3) A phosphate ester additive ex Uniqema Formulation 3 demonstrates that the use of esters in lubricant compositions in accordance with the invention have improved load carrying performance with

respect to comparative formulation 4 where there is no ester present alongside the mineral oil and phosphate ester additive.

Example 7 Priolube 3986 and Esters One, Two and Three were used in the following formulations in Table Three. The formulations were subjected to the falex machine test in accordance with ASTM D3233-93 method A, in order to evaluate their failure load performance. Amounts of each ingredient in the formulation are in parts by weight (pbw).

Table Three Formulation 5 6 7 8 9 Vitrea 32 90 90 90 90 94 Homett Epoil HD17A 4 4 4 _ Priolube 3986 6--6 Ester One-6-- EsterTwo--6- Ester Three 6 Failure load, >3250 >3250 >3250 >3250 830 lb.

Table Four illustrates falex test results for comparative formulations Table Four Formulation 10 11 (Comparative) (Comparative) Vitrea 32 100 90 Homett Epoil HD17A 10 Failure load, 520 1760 lb.

Formulation 9 demonstrates that the use of esters in lubricant compositions in accordance with the invention have an improved load carrying performance with respect to comparative formulation 10 in which there is no ester present in the mineral oil.

Formulations 5,6,7 and 8 demonstrate that the use of esters in lubricant compositions in accordance with the invention have improved load carrying performance with respect to comparative formulation 11 in which there are no esters present alongside the mineral oil and sulphur-containing synthetic additive.