Lubricant compositions

Description

This invention relates to novel lubricant compositions that are useful as lubricants in high load carrying oils, e.g. metal working fluids, gear oils, extreme pressure turbine oils and hydraulic oils. The lubricant compositions of the invention are especially useful in metal working fluids.

The cutting of metal involves the expenditure of significant amounts of energy and the development of high temperatures as the cutting tool removes metal from the workpiece. In order to reduce the energy consumed, obtain a long life for the cutting tool and a high surface finish on the workpiece, it is essential that the lubricant used is able to operate efficiently under the conditions of operation. This means essentially that it is capable of working at very high loads and quickly removing the heat generated by the cutting process. Mineral oil alone does not have sufficient lubricity to perform this function and it is necessary to incorporate additives to enhance this aspect of the oil's performance.

In the past the most common extreme pressure additives have been those containing chlorine (for example C14-17 chlorinated paraffins), phosphorus containing additives in the form of neutral triaryl phosphates, alkyl or alkylaryl acid phosphates and alkylpolyalkoxy or alkylarylpolyalkoxy acid phosphates and sulphur carriers (for example sulphurised olefins, sulphurised esters, and sulphurised fats). The level of performance offered by the different additives varies depending on the temperatures at which the active species are released to form a salt layer at the metal surface. This in turn depends on the speed and feed rate of the cutting tool, the type and hardness of the alloy being machined and the specific machining operation.

The severity of the application would largely determine the chemical nature of the selected extreme pressure additive, the level of use and whether a combination of additives might be preferable. For example, if the application was not too heavy duty it might use a low concentration of an extreme pressure additive (such as a chlorinated paraffin or a phosphate ester). While for heavier duty applications, higher concentrations of the different types of extreme pressure additives or mixtures of these additives are utilised by the formulator.

None of the commonly used extreme pressure additives is without its disadvantages. Sulphur can produce staining of workpieces derived from non-ferrous alloys at high concentrations and also an unattractive odour as the carrier decomposes to release the sulphur. Problems associated with the usage of chlorine stem from concerns about disposal of the cutting fluid These compounds can also produce hydrochloric acid on decomposition which can cause corrosion of the workpiece and equipment in the environment of the machining operation.

In addition to mineral oil as the “carrier” for the extreme pressure/antiwear additives, and usually for applications which are more severe, oil in water emulsions and water based solutions are also commonly used in applications which require less lubricity. However in all these fluids, additives are required to improve the lubrication performance of the fluid.

The type of phosphorus-containing additives which are found in metal working fluids are typically alkyl or alkylaryl acid phosphates and alkylpolyalkoxy or alkylarylpolyalkoxy acid phosphates used either as the free acid or neutralised with basic materials such as alkanolamines and caustic soda e.g. products sold under the trade marks of Lubrhophos and Rhodafac; neutral triaryl phosphates e.g. synthetic isopropylated phenyl phosphates such as are available commercially under the Durad trde mark.

Concern has been expressed regarding the use of neutral or acid aryl and acid alkylaryl phosphates lest the used fluid containing phenolic compounds (arising largely from the hydrolysis of the phosphates) should escape into the environment and contaminate water courses. Acid phosphate esters can also become less effective as extreme pressure additives when neutralised and are also unstable when subjected to hard water.

One objective of the present invention is to provide a novel lubricant composition which improves the cutting performance of both neat oil and water based cutting fluids. Another objective of the present invention is to replace acid phosphates as extreme pressure/anti wear additives in metal working applications. This objective has been achieved by the combination of certain neutral alkyl phosphorus compounds with certain sulphur carriers.

According to the present invention, there is provided a lubricant composition for a high load carrying oil said lubricating composition comprising:

• (a) a neutral alkyl phosphorus compound selected from those corresponding to the following general formulae:
• (i) neutral alkyl phosphates
•  wherein R₁, R₂ and R₃ are the same or different and are alkyl groups with 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms.
• (ii) neutral alkyl phosphonates
•  wherein R₁, R₁ and R₃ have the same meaning as in I above.
• (iii) neutral alkyl phosphinates
•  wherein R₁, R₂ and R₃ have the same meaning as in I above.
• (iv) neutral alkoxyalkyl phosphates
•  wherein R₄, R₆ and R₈ are —C₂H₄ or C₃H₈ and R₅, R₇ and R₉ are the same or different and are alkyl groups with 1 to 8 carbon atoms and n is 1 to 6.
• (v) neutral alkoxyalkyl phosphonates
•  wherein R₄, R₅, R₆, R₇, R₈ and R₉ and n have the same meanings as in IV above.
• (vi) neutral alkoxyalkyl phosphinates
•  wherein R₄, R₅, R₆, R₇, R₈ and R₉ and n have the same meanings as in IV above.
• (vii) neutral alkyldialkoxyalkyl phosphonates
•  wherein R₄, R₅, R₆, R₇ and n have the same meanings as in IV above and R₁₀ is an alkyl group with 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms.
• (viii) neutral dialkylalkoxyalkyl phosphinates
•  wherein R₄, R₅ and n have the same meanings as in IV above and R₁₀ and R₁₁ are the same or different and are alkyl groups with 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms.
• (ix) neutral alkoxyalkyl dialkyl phosphonates
•  wherein R₆, R₇ and n have the same meanings as in IV above and R₁₂ and R₁₃ are the same or different and are alkyl groups with 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms.
• (x) neutral dialkoxyalkylalkyl phosphinates
•  wherein R₆, R₇, R₈, R₉ and n have the same meanings as in IV above and R₁₂ is an alkyl group with 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms.
• (xi) neutral dialkylalkoxyalkyl phosphates
•  wherein R₂ and R₃ are the same as in I above and R₄ and R₅ are the same as in IV above.
• (xii) neutral alkyl phosphites
•  wherein R₁, R₂, R₃ have the same meaning as in I above.
• (xiii) neutral alkoxyalkyl phosphites
•  wherein R₄, R₅, R₆, R₇, R₈, R₉ and n have the same meanings as in IV above.
• and (b) a sulphur carrier containing active or inactive sulphur.

The lubricant composition of the invention can comprise one or more of the compounds of general formulae I to XIII.

Advantageously, the neutral alkyl phosphorus compound and the sulphur carrier are utilised in a weight ratio of P to S content from 1:50 to 1:1, preferably a weight ratio of 1:1 to 1:30.

Examples of compounds of the general formulae I to XIII are as follows:

• I—triisobutyl phosphate, tributyl phosphate, triisopropyl phosphate, trioctyl phosphate and tri-2-ethylhexyl phosphate
• II—butyl dibutyl phosphonate and octyl dioctyl phosphonate
• III—dioctyl octyl phosphinate
• IV—tributoxyethyl phosphate
• V—butoxyethyl dibutoxyethyl phosphonate
• VI—dibutoxyethyl butoxyethyl phosphinate
• VII—octyl dibutoxyethyl phosphonate
• VIII—dioctyl butoxyethyl phosphinate
• IX—butoxyethyl dioctyl phosphonate
• X—dibutoxyethyl octyl phosphinate
• XI—butoxyethyl dioctyl phosphate
• XII—trilauryl phosphite, trioleyl phosphite, trioctyl phosphite and tributyl phosphite
• XIII—tributoxyethyl phosphite

Preferred sulphur carriers are selected from at least one of sulphurised synthetic esters, sulphurised hydrocarbons (e.g. sulphurised olefins), sulphurised vegetable oils and fats, metal sulphonates, metal dialkyldithiophosphates and triaryl phosphorothionates.

The sulphur carriers serve to release sulphur at the cutting face of the workpiece where it reacts to form a lubricating film at relatively high temperatures.

The present invention is also a high load carrying oil which contains a lubricant composition as described above.

The high load carrying oil may be a metal working fluid, a gear oil, an extreme pressure turbine oil or a hydraulic oil.

From another aspect, the present invention is also a method for working metal comprising (a) contacting a metal workpiece with a lubricant composition as described above and (b) working the metal workpiece.

The lubricant composition of the invention can include other components conventional in the art, e.g. surfactants, non-ionic alcohols.

Embodiments of the invention will now be described simply by way of example:

• 1) As sulphur carriers, Rhein Chemie products RC 2526 (a sulphurised fatty acid ester with 26% total sulphur of which 15% is active) and RC 2540 (a dialkylpentasulphide with 40% total sulphur of which 36% is active).
• 2) As an alkylpolyalkoxy acid phosphate, (mixed mono- and di-), Lubrhophos LB400 ex Rhodia Chemicals which is based on oleyl alcohol reacted with ethylene oxide and then the product is reacted with phosphorus pentoxide. This product is oil soluble and recommended as an EP additive for cutting oils.
• 3) Durad TiBP which is tri-isobutyl phosphate
• 4) Durad TBEP which is tributoxyethyl phosphate

Durad is a registered trade mark of Great Lakes Chemical Corporation.

In the following tests, an automatic drilling machine is used to drill holes in metal discs 40 mm thick. The holes are 18 mm deep while, for oil-based cutting fluids, the drill feeds and speeds were 0.13 mm/rev (or 156 mm/min) and 1200 rpm respectively. Tests were carried out until the drill failed either due to breakage or to excessive wear. The average of at least duplicate test results are quoted.

(A) Drill Life Test Data on Mild Steel Using Neat Oil: Durad TiBP/Sulphur Carriers as Replacements for Chlorparaffins

The metal used was EN24T carbon steel; the drill feeds and speeds were as indicated below and the base stock was an ISO VG 22 paraffinic oil. In this case the S/P ratio was 13:1. The formulation containing Durad TiBP is seen to be significantly more active than the chlorparaffin.

	Formulation (w/w)

	1	2	3

TiBP	0.6	—
Sulphur carrier (36.7% sulphur - all active)	2.5	—	4.3
Chlorparaffin (40% chlorine)	—	8.0	—
ISO VG 22 paraffinic oil	96.9	92.0	95.7
Holes drilled to failure	280	140	100

(B) Drill Life Tests on Stainless Steel Using Neat Oil: A Comparison with Acid Phosphates

Stainless steel type 304 was used for this study. The sulphur carriers used were a 4:1 mix of a sulphurised fatty acid ester (26% total sulphur of which 15% is active) and a dialkyl polysulphide (40% total sulphur of which 36% is active). The levels of sulphur and phosphorus used were 1.5% and 0.5% respectively giving an S/P ratio of 3:1. As for previous tests the oil used was an ISO VG 22 Group 1 base.

	Formulations (w/w)

		4	5	6	7

	Sulphur carriers	5.2	5.2	5.2	5.2
	Durad TiBP	—	4.17	—	—
	Durad TBEP	—	—	6.4	—
	Oleyl acid phosphate	—	—	—	10.0
	Neat Oil	94.8	90.63	68.4	84.8
	Holes drilled to failure	84	432	>>500	18

The quality of swarf associated with Durad TBEP in the above test was regarded as excellent throughout. In fact no drill failures occurred with this formulation.

(C) Performance of S/P Combinations on Stainless Steel Using Macro-Emulsions

The conditions for this test were somewhat different. In order to satisfactorily machine the stainless steel with the emulsion the conditions were modified to a feed rate of 70 mm/min and a speed of 700 rpm-slightly more severe conditions than were recommended by the drill manufacturers. The same sulphur carriers were used as in the previous test on stainless. A concentrate of the phosphate and sulphur carriers with emulsifiers, corrosion inhibitors, antifoams etc was first prepared in aqueous solution with the part addition of the triethanolamine base. This concentrate was subsequently added to a 60 solvent pale oil (naphthenic type) containing a further small amount of emulsifier and triethanolamine to produce an emulsion concentrate. This emulsion concentrate was then diluted to 4% to produce the working fluid. Tap water with a hardness of 160 ppm calcium carbonate was used throughout. In this test, the concentration of the sulphur and phosphorus in the final emulsion were 0.36% sulphur and 0.012% phosphorus (a 30:1 ratio). The table below gives the approximate formulation of the concentrate before dilution.

	Formulation (%)

	8	9

	Sulphur carriers	3.12	3.12
	Durad TiBP	—	0.25
	Emulsifier/inhibitor mixture	2.84	4.99
	Triethanolamine	3.04	3.04
	Mineral oil	46.0	46.0
	Water	45.0	42.6
	Holes drilled to failure	214	>>500

In this test Durad TiBP is seen to be a most effective additive which in combination with the sulphur carriers shows a significant improvement over the sulphur carriers alone.

(D) Drill Life Test Data on Stainless Steel Using Neat Oil: A Comparison of Tributoxyethyl phosphate (TBEP) with Dioctyl octyl phosphonate

The sulphur carriers used RC2526 and RC2540 were the same as used in the previous Examples.

Concentrations used were 1.5% sulphur and 0.5% phosphorus in an ISO VG 22 paraffinic type neat oil (i.e. the same as before).

Stainless steel type 304 was used for this study.

The drill feed rate was 150 mm/min and the speed was 1500 rpm. The depth of hole was 18 mm.

Formulation (w/w)	Holes drilled to failure
Sulphur carriers alone	56
Sulphur carriers plus Dioctyl octyl phosphonate	336
Sulphur carriers plus TBEP	500+

The above results show that although both phosphorus additives showed enhanced activity, TBEP was the higher of the two.

N.B. In the above tests, an automatic drilling machine is used to drill holes in metal discs 40 mm thick. The holes are 18 mm deep, while drill feeds and speeds are normally 0.13 mm/rev (or 156 mm/min) and 1200 rpm respectively. Tests were carried out until the drill failed either due to breakage or to excessive wear. The average of at least duplicate test results are quoted.

Although lubricity additives such as fatty oils and long chain esters can be used in cutting fluids, these were not included in the formulations shown above.

CONCLUSIONS

A major benefit of the present invention is that neutral alkyl phosphorus compounds provide a synergistic performance with sulphur carriers in both neat oil and aqueous cutting fluids on both mild steel and stainless steel. Such a synergistic combination enables the formulation of cutting fluids with the following properties:

• (a) no chlorine present;
• (b) the elimination of the production of phenolic degradation products;
• (c) a possible reduction in the level of sulphur in the oil;
• (d) improved lubrication performance; and
• (e) extended drill life in metal cutting applications.

The use of neutral alkyl phosphorus compounds also allows higher levels of phosphorus to be used when necessary. Where acid phosphates are used, the acidity effectively limits the level of phosphorus that can be used because the acid can become corrosive at high levels. This allows for more flexibility in formulating mixtures of P/S and higher levels where necessary depending on the severity of the worling process.

Benefits from the use of the synergistic combination of the invention in applications other than metal cutting processes include:

• (i) An increase in the level of performance without substantially increasing the level of the sulphur carriers. These can adversely affect the oxidation stability and corrosive tendencies of the formulation.
• (ii) Alternatively, for the same level of performance, it is possible to lower the sulphur carrier level thereby favourably impacting the stability/corrosivity of the formulation.