The present invention concerns a lubricant, and in particular a lubricant for use in a metal forming process such as an aluminium fin stamping or cutting operation.

Aluminium fins are used in air conditioning, refrigeration and engine cooling equipment to improve thermal performance. The fins are stamped or cut from aluminium sheet that is covered in lubricant. The use of a lubricant increases production output, improves the quality of the fins and increases the tool life of the stamping and cutting equipment.

EP 0 690 121 discloses a lubricant for use in a metal forming process. The lubricant comprises a mixture of mineral spirits and one or more compounds selected from the group consisting of polyisobutenes having a molecular weight of from 320 to 460 and alkylene glycols having one terminal hydroxyl group and a viscosity in the range of from 65 to 1715 Saybolt Universal Seconds (SUS) at 100 °C. We are told that the selected organic compounds evaporate leaving a small trace of residue that may be removed using water based cleaning agents.

EP 0 690 121 acknowledges prior art lubricants made of mineral oil that have excellent lubricating properties. The mineral oil remains as a residual coating on the fins after the fin stamping operation and it needs to be removed before subsequent manufacturing operations.

EP 0690 121 also acknowledges prior art lubricants comprising mineral spirits with small amounts of surfactants and lubricity enhancement agents. Although these lubricants evaporate without leaving a residue, their lubricating performance is very poor. These lubricants are also volatile organic compounds.

Construction costs of air conditioning equipment can be reduced if the lubricant is left on the fins after the stamping operation. In order for the lubricant to be left on the fins, it must be: compatible with new hydrofluorocarbon ('HFC') refrigerants and hydrochlorofluorocarbon (ΗCFC) refrigerants, in particular, refrigerants classed as R134A (chemical formula CF ₃ CH ₂ F) and R22 (chemical formula CHF ₂ CI), and also those classed as R407C (23% CH ₂ F ₂ , 25% C ₂ HF ₅ and 52% CF ₃ CH ₂ F) and R410A (50% CH ₂ F ₂ and 50% C ₂ HF ₅ ); compatible with conventional and new synthetic compressor oils used in air conditioning equipment; and compatible with polystyrene and ABS plastics used in air conditioning equipment to restrict movement of the fins.

The lubricant should be capable of showing good performance in the ANSI-ASHF*AE 97/1989 sealed tube test, a copper stain test, a rinsability test and a friction test. The ANSI-ASHRAE 97/1989 sealed tube test is a well known test in the art that involves placing clean metal specimens, such as steel, aluminium and copper, in a refrigerant in a sealed tube; placing the tube in an oven, for example, at 175 °C for 14 days; removing the tube from the oven and allowing the tube to warm to room temperature; examining the metal specimens for corrosion and analysing the lubricant for, for example, Total Acid Number and Wear Metals.

The copper stain test involves immersing a copper strip in a solution of lubricant and 1 % water. This test is used to check whether the lubricant would stain copper tubes if contact is made between the lubricant and copper tubes in the air conditioning equipment. The rinsability test investigates the effect of condensation on fins covered in lubricant. This test is used to imitate the effect of condensation on fins covered in lubricant during initial use of the air conditioning equipment. The friction test is a scaled down version of an aluminium fin stamping operation and is used to check the lubricity of the lubricant.

It is desirable that a die using the environmentally friendly lubricant has a die life that is comparable to the die life exhibited by a die using current environmentally unfriendly lubricants.

It is, also desirable that the lubricant has a low viscosity, for example less than 100 SUS at 100 °C, so that it does not interfere with the punch step of the stamping operation. Low odour is also desirable by the operators assembling the air conditioning equipment.

The aim of the present invention is to provide a lubricant for use in a metal forming process such as an aluminium fin stamping or cutting operation that overcomes the disadvantages of the prior art lubricants. In particular, the aim of the present invention is to provide a lubricant having a reduced VOC content, e.g. less than 10%, without a reduction in performance. In particular, it is also the aim of the present invention to provide a lubricant that is compatible with materials used in air conditioning equipment, for example, HFC and HCFC refrigerants, so that it may be left on the fins after the stamping or cutting operation.

In accordance with the present invention there is provided a lubricant for a metal forming process such as an aluminium fin stamping or cutting operation, the lubricant comprising an alcohol having a carbon chain length of at least 12 and being branched or unbranched, an olefin having a carbon chain length of 12 to 20, preferaby 14 to 18, and a triazole that is soluble in the lubricant.

The inventors have found that a lubricant falling within the above definition is capable of passing the ANSI-ASH FIAE 97/1989 sealed tube test, a copper stain test, a rinsability test and a friction test. The lubricant has also been found to be compatible with new HFC and HCFC refrigerants, conventional and new synthetic compressor oil and polystyrene and ABS plastics.

The alcohol is preferably isocetyl alcohol. The alcohol may be present in an amount ranging from 50 to 90%. The lubricant preferably comprises approximately 60% by weight of isocetyl alcohol.

The olefin is preferably a C ₁₄ - C ₁₈ olefin, more preferably a C ₁₆ -C ₁₈ olefin. The olefin is preferably an alpha olefin. The olefin may be present in an amount ranging from 10 to 50%. The lubricant preferably comprises approximately 40% by weight of C ₁₆ -C ₁₆ alpha olefin.

The triazole is preferably tolytriazole or benzotriazole. The triazole may be present in an amount ranging from 0.01% to 1%. The lubricant preferably comprises approximately 0.2% triazole. Heat may be required to make the triazole soluble in the lubricant.

The lubricant preferably has a VOC content of less than 10%.

The lubricant preferably has a solidification temperature of approximately lower than 0 °C, even more preferably lower than -20 °C, so that the lubricant does not solidify in cold climates or in winter.

The invention will now be described with reference to the following examples:

Example 1

The following lubricant was prepared:

isocetyl alcohol 60.0%

C ₁₆ -C ₁₈ alpha alcohol 39.8% tolyttriazole 0.2%

A third of the isocetyl alcohol was added to the triazole and heat was used to dissolve the triazole. The remaining isocetyl alcohol and the alpha olefin were added to the mixture.

The lubricant had a viscosity of 67 SUS at 100 °C.

Tests

The lubricant was subjected to the following tests:

The ANSI-ASHRAE 97/1989 Test

This test involves the following steps: a) pipetting a desired amount of lubricant, for example, 0.7g, into a clean glass tube; recording the mass of lubricant added to the glass tube; and adding clean metal specimens, such as steel, aluminium and copper, to the tube; b) sealing the tube; c) placing the tube in an aluminium block, a small quantity of glass wool being used to 'cushion' the tube; d) placing the aluminium block in an oven for a required period of time, for example, 14 days at 175 °C; e) removing the tube from the oven and allowing it to warm to room temperature. During this time refrigerant gas will evaporate from the lubricant; f) removing the metal specimens from the tube, cleaning them and then examining them for signs of corrosion; and g) analysing the lubricant for, for example, Total Acid Number and Wear Metals.

The Copper Stain Test

The copper stain test involves the following steps:

a) half immersing a small copper strip in a closed test tube containing the lubricant contaminated with 1% of water; b) placing the test tube in an oven at 175 °C for 2 weeks; and c) removing the copper strip from the test tube and examining it for signs of corrosion.

The Rinsability Test

The rinsability test involves the following steps: a) coating test panels in the lubricant and allowing them to air dry overnight; b) subjecting the panels to a very fine water spray using an air brush placed one foot away from the panels; c) checking to see whether the lubricant produces a water break free surface, i.e. one that does not allow water to separate into beads, after approximately 90 seconds.

The Friction Test

The friction test simulates a fin stamping operation.

Results

The lubricant made in the above Example passed the above mentioned tests.