WO 2011/138620 PCT/GB2011/050886 Aerosol Compositions The present invention relates to household aerosol compositions using a compressed gas propellant that are free of hydrocarbon propellants, and particularly the use of such 5 compositions with metal aerosol canister that are capable of corrosion. Many household products designed for use in domestic applications, on hard surfaces, for fabric care, as carpet cleaners are sold in aerosol containers. A few aerosol products are sold in glass or plastic containers. Most containers are metal canisters, most canisters are 10 steel, usually tinplated (tin coated), others are aluminium (which are the most expensive financially and environmentally). Tinplated metal canisters may also be lacquered with a resin on the inside to provide additional protection. Examples of household aerosol products are air fresheners, car products, household 15 products, fabric care, waxes, polishes, insecticides, ironing aids, fabric refreshers, and carpet cleaners. Tinplating protects the metal canisters against rapid corrosion, but tends itself to dissolve in aqueous based formulations. With aerosol formulations containing less than 50 ppm of water, 20 corrosion of tinplated canisters is not generally a serious problem. However, if the water content of an aerosol product is more than 50 ppm (and particularly when greater than 150 ppm), problems due to corrosion are more likely to occur. The world market trend is to move towards water-based aerosol formulations. This is due 25 mainly to a regulatory issue; the reductions of the volatile organic content (VOC) levels in aerosol product has involved the reduction of the solvent level in many products and an increase of the water content. Currently it is desirable to have a VOC propellant level of below 30% w/w not only to reduce cost but also to comply with increasingly stringent regulatory limits (e.g. a maximum of 24.5% w/w in the USA for air freshener products). 30 Whilst not presently driven by regulatory concerns, it is desirable to use non-VOC propellant such as compressed gas (compressed gas referring to compressed air, compressed nitrogen or mixtures thereof) since this is of less impact to the environment, less expensive than VOC propellant and safer to handle from a manufacturing perspective as well as a consumer 35 perspective due to the likely reduction in flammability. Although compressed gas propellant aerosols have well documented performance drawbacks, such as poor particle break up, risk of propellant discharge, etc, there is a further problem of corrosion due to the presence of large quantities of water in the formulation. 40 Indeed, many producers of commercially available household compressed gas aerosol 1 WO 2011/138620 PCT/GB2011/050886 products use an aerosol canister made of aluminium rather than tin-plated steel canisters that are more commonly used for household aerosol products. Whilst aluminium canisters are resistant to corrosion they suffer from two significant drawbacks, firstly, the production of virgin aluminium sheets is considered in some circles to be environmentally costly and, 5 secondly, aluminium is a significantly more expensive raw material than a standard tin-plated steel canister. Many corrosion inhibitor systems have been developed for low VOC market requirements in aerosol products, especially for tin-plated canisters. Examples of these products are borates, 10 benzoates, molybdates, and anionic surfactants (such as sodium lauroyl sarcosinate). Historically the common 'wet' (i.e. water rather than solvent based) air freshener aerosol compositions using VOC propellants typically contain nitrite as a corrosion inhibitor and sorbitan monooleate as an emulsifier to ensure uniform emulsification of water soluble and 15 oily components such as water insoluble fragrance. The best recognised inhibitor system for tin-plated canisters is sodium nitrite and morpholine. Morpholine is a volatile base that helps to preserve the vapour phase in the aerosol containers and gives an alkaline pH to the formula. This system can involve the formation of nitrosamines that are very carcinogenic. 20 In addition, even sodium nitrite and morpholine are not generally able to prevent the dissolution of the tin coating, but to reduce the rate of dissolution of the tin coating to an acceptable level in VOC propellant systems. The amount of morpholine, sodium nitrite and thickness of tin plate are designed for around the required shelf life, for example two years. The dissolution of the tin plate to form a tin hydroxyl-oxide complex has been shown to have a 25 negative effect on cleaning performances. The tin complex generally gives a pale yellow to an intense yellow colour when deposited, especially when sprayed onto a white surface. White fabrics or carpets can remain coloured by the liquids of aged aerosol products. Other considerations relate to certain stains like coffee, tea and wine that contain cationic metals. These metals can form brown coloured complex with tin hydroxyl-oxide complex, causing an 30 evident negative effect of the cleaning formulation and its overall cleaning performance. Even resin lacquered tin-plated canisters generally need an effective corrosion system when used with a VOC propellant system. Possible defects on the lacquer layer are the cause of pit corrosion: where a galvanic potential is discharged in a limited area, involving a quick and 35 deep corrosion. Even sodium nitrite and morpholine cannot prevent dissolution of the lacquer and tin plate, whereupon the liquid becomes yellowish and the interior can darken. This system is in addition to be avoided for nitrosamine formation during the product life. Furthermore it is desirable to replace nitrite corrosion inhibitors due to these health concerns 40 and performance issues. One solution to this has been to replace nitrite corrosion inhibitors 2 WO 2011/138620 PCT/GB2011/050886 with phosphate corrosion inhibitors but these carry the financial penalty of requiring internally lacquered cans to obtain satisfactory storage/corrosion performance. Many corrosion inhibitors have been identified in the prior are for use with VOC propellant 5 systems, but little is known about the production and/or use of corrosion inhibitors in a compressed gas propellant system. It has been found that a borate salt (such as sodium borate) is particularly effective. 10 However when using sodium borate as a corrosion inibitor it has been discovered that standard emulsifiers such as sorbitan monooleate used in combination with sodium borate at propellant (butane/propane) levels of below 30% w/w results in very coarse particle sizes and excessive foaming, making the product unsuitable as an aerosol air freshener. 15 According to a first aspect of the present invention, there is provided an aerosol composition with compressed gas propellant that is free of hydrocarbon propellants, wherein the composition comprises: 85.Owt% to 98.Owt% water; 0.Olwt% to 10.00wt% low MW alcohol; 20 0.001wt to 5.00wt% surfactant; 0.001wt to 5.00wt% fragrance; 0.001wt to 5.00wt% borate salt; 0.001wt to 5.00wt% preservative. 25 Preferably the composition is an air freshening composition. Preferably the composition further comprises 0.00wt% to 0.Swt% sodium molybdate, and even more preferably comprises 0.Owt% to O.lwt% sodium molybdate. 30 Preferably the composition comprises: 90.Owt% to 95.Owt% water; 1.00wt% to 7.00wt% low MW alcohol; 0.01wt to 3.00wt% surfactant; 0.005wt to 3.00wt% fragrance; 35 0.005wt to 1.00wt% borate salt; 0.00wt% to 0.5wt% sodium molybdate; 0.001wt to 1.00wt% preservative. Preferably the composition consists essentially of: 40 90.Owt% to 95.Owt% water; 3 WO 2011/138620 PCT/GB2011/050886 1.00wt% to 7.00wt% low MW alcohol; 0.01wt to 3.00wt% surfactant; 0.005wt to 3.00wt% fragrance; 0.005wt to 1.00wt% borate salt; 5 0.00wt% to 0.5wt% sodium molybdate; O.ODlwt to 1.00wt% preservative; wherein the wt% of the composition adds up to exactly 100wt%. Even more preferably the composition consists essentially of: 10 92.Owt% to 94.5wt% water, and most preferably 93.1wt% to 93.6wt%; 3.5wt% to 6.5wt% low MW alcohol, and most preferably substantially 5.Owt% ethanol; 0.3wt to 1.Owt% surfactant, and most preferably 1.Owt% to 0.5wt%; .1wt to 1.Owt% fragrance, and most preferably substantially 0.25wt%; .1wt to 1.00wt% borate salt, and most preferably substantially 0.4wt% sodium borate; 15 0.00wt% to 0.5wt% sodium molybdate, and most preferably substantially O.Owt%; .1wt to 0.5wt% preservative, and most preferably substantially 0.25wt%; wherein the wt% of the composition adds up to exactly 100wt%. The compressed gas propellant used with the composition is preferably compressed air or 20 compressed nitrogen or a mixture thereof. The borate salt for use in the compositions of the present invention is preferably sodium borate, although other commercially available borate salts may be used either alone or in combination with sodium borate. 25 The low MW alcohol for use in the compositions of the present invention is preferably ethanol, although other commercially available low MW alcohols may be used either alone or in combination with ethanol. 30 Composition to be used with steel aerosol canisters, tin-plated steel canisters or other metal canisters that are capable of rusting - ie - not aluminium canisters, galvanised canisters etc According to a second aspect of the present invention, there is provided an aerosol dispenser wherein the dispenser is a steel aerosol canister, tin-plated steel canister or other metal 35 canister capable of corrosion and wherein the composition is an air freshener propelled, in use, by compressed gas propellant that is free of hydrocarbon propellants, the air freshener composition comprising: 85.Owt% to 98.Owt% water; 0.01wt% to 10.00wt% low MW alcohol; 40 0.001wt to 5.00wt% surfactant; 41 WO 2011/138620 PCT/GB2011/050886 0.001wt to 5.00wt% fragrance; 0.001wt to 5.00wt% sodium borate; 0.001wt to 5.00wt% preservative. 5 For the avoidance of doubt, corrosion is understood in the context of the present invention to refer to the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings, in particular in the context of metal canisters corrosion means electrochemical oxidation of the metal canister in reaction with an oxidant such as oxygen. 10 Preferably the dispenser is a steel aerosol canister or a tin-plate steel aerosol canister. Preferably the composition further comprises 0.00wt% to 0.5wt% sodium molybdate, and even more preferably comprises O.Owt% to O.lwt% sodium molybdate. 15 According to a third aspect of the present invention, there is provided an anti-corrosion air freshening composition for use with a compressed gas propellant in a steel aerosol canister, tin-plated steel canister or other metal canister capable of corrosion wherein the composition comprises: 85.Owt% to 98.Owt% water; 20 O.Olwt% to 10.00wt% low MW alcohol; 0.001wt to 5.00wt% surfactant; 0.001wt to 5.00wt% fragrance; 0.001wt to 5.00wt% sodium borate; 0.001wt to 5.00wt% preservative. 25 Preferably the dispenser is a steel aerosol canister or a tin-plate steel aerosol canister. Preferably the composition further comprises 0.00wt% to 0.5wt% sodium molybdate, and even more preferably comprises O.Owt% to O.lwt% sodium molybdate. 30 The surfactant(s) used in the composition(s) of the present invention are preferably a non ionic surfactant. More preferably the non-ionic surfactant(s) are ethoxylates of fatty alcohols, most preferably saturated C 820 alcohols and the like, and most preferably saturated iso-C 13 alcohols such as those available from BASF under their LUTENSOL@ brand of surfactants. 35 The preservative(s) used in the composition(s) of the present invention are preferably formed from lox toxicity biocides suitable for use in water-based canister systems such as NIPACIDE@ available from CLARIANT or PROXEL@ available from ARCH. 5 WO 2011/138620 PCT/GB2011/050886 According to a fourth aspect of the present invention, there is provided a method of preventing corrosion of a metal aerosol canister capable of corrosion wherein the method involves the step of introducing a composition according to the first or third aspect of the present invention into said aerosol container along with a compressed gas propellant that is 5 free of hydrocarbon propellants. The following description and examples are intended merely to illustrate the invention and are not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention 10 should be construed to include everything within the scope of the appended claims and equivalents thereof. Two example formulations were prepared as set out below. 15 Exam ple 1 250ml of composition were made according to the following proportions: 93.1wt% water; 5.Owt% ethanol; 1.Owt% LUTENSOL@ T089; 20 0.25wt% fragrance; 0.4wt% sodium borate; 0.25wt% NIPACIDE@ BIT 20; wherein the wt% of the composition adds up to exactly 100wt%. 25 Example 2 250ml of composition were made according to the following proportions: 93.6wt% water; 5.Owt% ethanol; 0.5wt% LUTENSOL@ T089; 30 0.25wt% fragrance; 0.4wt% sodium borate; 0.25wt% preservative; wherein the wt% of the composition adds up to exactly 1 00wt%. 35 Each sample was then loaded into a tin-plated steel aerosol canister having a 15 bar pressure rating and filled with compressed air until the internal pressure within the canister reached 9.0 bar @ 20 0 C. 6 WO 2011/138620 PCT/GB2011/050886 Samples of examples 1 & 2 were then held in a secure storage container at respective constant temperatures of 20"C, 30*C and 40 0 C for a period of 10 weeks and then tested for spray performance and, once exhausted, corrosion. 5 All samples of examples 1 & 2 at all temperatures showed no signs of impairment after the storage, they all sprayed within consumer acceptable spray performance parameters and no canisters showed any signs of corrosion therein. All of the features disclosed in this specification (including any accompanying claims, abstract 10 and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and 15 drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention 20 extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 7