DIE CASTING MOULDING RELEASE AGENTS [0001] FIELD OF THE INVENTION [0002] The present invention relates to a composition based on vegetable unsaturated oils and ethoxylated fatty acids, which is useful, in the form of aqueous emulsion, as die casting moulding release agent. [0003] In particular, the composition of the present invention, beside having good releasing and lubricating properties, has a great ease of use, because it can be easily emulsified and applied, and it allows the reduction of the pollution load of industrial waste water. [0004] "Die casting" is the expression used to define the process whereby a molten metallic alloy is cast into a mould and pressed, in order to fill it perfectly and very rapidly and to obtain, after cooling and removal, metal goods having assumed size and shape. [0005] Die casting is customary employed for the production of the most different non ferrous metal components that are then used in the manufacture of complex equipment and products. [0006] Aluminium and its alloys (AISi, AISiCu, AIMg), zinc and its alloys (Zama), copper and its alloys (brass and bronze), magnesium an its alloys (AZ), tin and its alloys are the materials which are most commonly shaped by means of die casting. [0007] In order to remove the metal components from the moulds without altering their shape it is necessary to apply on the moulds, before casting, a very thin layer of a releasing agent. [0008] Otherwise, due to the combined effect of high filling speed, temperature and pressure, the metal would adhere or even become welded to the mould surface. [0009] A good releasing agent, beside allowing the removal of the metallic components from the moulds, must behave as lubricant for the sliding parts of the moulds and also improve the flow of the molten metal in its core, in order to facilitate complete filling. [0010] Mould release agents are generally applied by automated spray technique; for economical and ecological reasons, die casting plants usually operate with closed circuit, i.e. they recycle for several days the moulding release agent which has not adhered to the moulds. [0011] A good mould release agent, when under recycle, must not leave on the moulds oily residues that would alter the subsequent production of metallic components.

[0012] STATE OF THE ART [0013] Die casting machines have radically changed during the last fifty years, both in pressure and temperature control, in feed system and in the deposition of release agents.

[0014] The most common release agents of the sixties were animal and vegetable oils and graphite; they were applied as such manually or by brush, or by immersion in hydrocarbon based solutions or in aqueous mixtures. [0015] The use of release agents in mixture with water became more and more widespread because it reduces the risk of fire and diminishes the level of harmful emissions in the working place. [0016] Effective changes in the release compositions followed the introduction of their aqueous mixtures. [0017] Natural oils were replaced by synthetic and semi-synthetic products, such as waxes and silicones. [0018] In the 70's, automated spray application systems were introduced for depositing release agents. [0019] The release agents composition also evolved, in order to fit to the changed requirements of the machines for more and more efficient and stable release agents, that did not cause clogging of the nozzle. [0020] Nowadays, the normally employed release agents are complex mixtures of several products, mostly of completely synthetic origin, and usually in the form of aqueous emulsion. [0021] Such synthetic products give good performances and can be recycled many times, but, on the other hand, they have a poor biodegradability. [0022] The more and more felt-need for operating with sustainable environmental impact and for reducing the pollution load of waste water have much increased the importance given in this field to the biodegradability of release agents. [0023] Many attempts have been made to modify natural oils and to adapt them to current die casting machines; some of these attempts are also reported in the patent literature. [0024] For example, US 4634469 describes a release composition comprising glycerol trioleate, up to 35% by weight of castor oil and a corrosion inhibitor. [0025] US 5378270 describes die casting release emulsions obtained from a mineral oil, or a fatty acid, or a fatty ester in the presence of an alkali metal or alkaline earth metal salt of ethylenediaminetetraacetic acid. [0026] SUMMARY OF THE INVENTION [0027] It has now been found that a composition essentially consisting of from 85 to 95% by weight of one or more vegetable unsaturated oil and from 5 to

15% by weight of at least one 4 to 10 moles ethoxylated C16-C22 fatty acid, in the form of a 0.2 to 1.1 % by weight aqueous emulsion, is a good die casting release agent, showing a sustainable environmental impact and not leaving oily residues on the moulds. [0028] It is therefore an object of the invention a composition essentially consisting of from 85 to 95% by weight of one or more vegetable oil

containing at least 70% by weight of triglycerides of monounsaturated or polyunsaturated C16-C22 fatty acids and from 5 to 15% by weight of one or more 4 to 10 moles ethoxylated C16-C22 fatty acid. [0029] It is a further object of the invention the aqueous emulsion comprising from

98.9 to 99.8% by weight of water and from 0.2 to 1.1% by weight of the above described composition. [0030] It is another object of the invention a die casting process comprising the step of lubricating the moulds by automatically spraying on the moulds an aqueous emulsion according to the invention. [0031] DETAILED DESCRIPTION [0032] The preferred composition consists of from 85 to 95% by weight of one or more vegetable oil containing at least 70% by weight of triglycerides of monounsaturated or polyunsaturated C16-C22 fatty acids and from 5 to

15% by weight of one or more 4 to 10 moles ethoxylated C16-C22 fatty acid.

The preferred aqueous emulsion consists of from 98.9 to 99.8% by weight of water and from 0.2 to 1.1 % by weight of the above described composition. [0033] The vegetable oil utilisable for the realisation of the present invention can be technical grade or food grade vegetable oil. [0034] Preferably, the vegetable oil is rape-seed oil, more preferably is food grade rape-seed oil. [0035] The ethoxylated fatty acids useful for the invention are commercially available and are obtainable by ethoxylation of the corresponding saturated or unsaturated, technical grade or purified fatty acids. [0036] According to a preferred embodiment of the invention the ethoxylated C16-

C22 fatty acid is ethoxylated technical grade oleic acid (ethoxylated olein) and more preferably 6 moles ethoxylated technical grade oleic acid. [0037] The composition of the invention is stable at room temperature and homogeneous and can be prepared by mixing at room temperature its ingredients. [0038] The aqueous emulsions of the invention can be prepared by diluting the above described compositions with water, under mechanical stirring. [0039] The emulsions can be prepared short before their use or, preferably, they are prepared in advance and automatically stirred in the die casting plant before use.

[0040] Tab water can be used to prepare the emulsions of the invention. [0041] The die casting process of the invention is suited for the materials which are commonly worked by die casting and, in particular, for aluminium and its alloys. [0042] The releasing and lubricating efficiency of the emulsions of the invention is high; the moulded pieces obtained therewith are easily cleaned up.

[0043] According to a particularly advantageous aspect of the invention, even when recycling for several times the same aqueous emulsion (up to 500 times), the moulds do not show any oily or carbonaceous residue. [0044] Beside being easily biodegraded, the aqueous emulsions of the invention do not generate toxic fumes or unpleasant odours during their use. [0045] EXAMPLE. [0046] A homogeneous composition is prepared by mixing in a large beaker equipped with mechanical stirrer 900 g of food grade rape-seed oil with

100 g of 6 moles ethoxylated technical grade oleic acid (6 moles ethoxylated olein), sold by Lamberti SpA as CHIMIPON OCD(R). [0047] A yellowish pourable composition is obtained having Brookfield viscosity of

65 mPa*s; the composition is stable at room temperature for more than six months. [0048] The thus obtained composition is diluted with tab water to prepared three emulsions, with concentrations of 0.3, 0.5 and 1 % by weight. [0049] Each emulsion is applied on the moulds of two different die casting machines for aluminium, with pressure application time of 5 seconds, moulds at 260 ⁰ C and spraying pressure of 9-10 bar. [0050] The emulsions are applied by automatic spraying; die casting of aluminium is then performed, recycling 500 times the emulsion. Before each application the emulsions are automatically stirred. [0051] All three emulsions allow easy removal of the cast pieces; degradation of the release agent is not observed (absence of fumes and of harsh odour); the moulds do not show oily residue and the little oily traces on the pieces are easily removable with the usual washing step. [0052] [0053]