Field of the Invention This invention relates to rinse aid compositions for machine dishwashing. More specifically, the invention encompasses rinse aid compositions that are for use when no ion exchange replenishing salt is added to the ion exchange mechanism of a dish washing machine.

Background of the Invention For many years, to wash articles in a commercially available dish washing machine has entailed the use of three product types. Ion exchange replenishing salt is added to the salt compartment to enable continued softening of the water by the ion-exchange system in the machine, a dishwashing formulation is used to clean the articles, and a rinse aid is used to reduce the amount of rinse water left on articles after the final rinse, such that residues or streaks, left on articles when dissolved solids precipitate as the residual rinse water evaporates, are minimised.

The salt in the machine does not have to be replaced every wash, as there is usually a salt reservoir in the machine to hold sufficient salt for many wash cycles. However it is inconvenient for consumers replace the salt and machines are frequently operated without salt in the reservoir, leading to non-demineralisation of the rinse water and residues on

articles as a result of this. The present invention relates to a rinse aid that provides good rinsing results from the final rinse in the absence of ion-exchange replenishing salt in the machine.

The machine dishwashing process comprises washing articles in a main wash cycle and rinsing them in one or more rinse cycles. A rinse aid composition is designed for use in the final rinse step of the machine dishwashing operation. The rinse aid's performance is judged particularly by its ability to prevent spot and film formation on washed articles. Rinse aid compositions usually comprise an aqueous liquid containing a low-foaming nonionic surfactant, hydrotropes and an ingredient such as citric acid that can act as a builder and a pH control agent.

EP 0 659,873 describes a Cl to C4 organo diphosphonic acid compound in rinse aid compositions to prevent calcium carbonate scale used in combination with 6.5% Citric acid.

EP 0 197 434 reveals up to 40% of citric acid or 0-10% of threshold-active complexing agents such as 2-phosphonobutane -1,2,4-tricarboxylic acid used in combination with capped alkyl polyethylene glycol ether surfactants to prevent lime deposits when rinsing with non-demineralised water.

Description of the Invention The present invention overcomes the problems in the prior art arising from deposits on items in machine dishwashers arising when the ion-exchange replenishment salt is not

replaced by the user. This is accomplished by using. a specific combination of a minimum level of acid builder with an organic mono or diphosphonic acid.

The present invention provides a A rinse aid composition comprising: a) 0.1 wt% to 5 wt% of a mono or diphosphonic acid or salt thereof and ; b) greater than 20wt% of a water-soluble acid builder or salt thereof other than (a).

Detailed Description of the Invention The invention has as an essential component, mono or di phosphonic acid or salt thereof. Mixtures of these acids and/or salts can also be used.

Preferably the rinse aid comprises a monophosphonic acid or salt thereof, more preferably the mono phosphonic acid or salt thereof is of formula I formula I where n is an integer from 0 to 6 and X1, X2, X3 are independently selected from an alkyl, alkenyl, aryl or

carboxy group with the proviso that at least one of X1, X2, X3 is a carboxy group.

A highly preferred structure is: where n is an integer from 0 to 5.

The most preferred monophosphonic acid is 2-phosphonobutane -1,2,4-tricarboxylic acid.

It is preferred if the level phosphonic acid is from 0.01 to 3wt% of the total composition, more preferably from 0.1 to 2.5 wt% of the total composition, most preferably from 0.5 to 2wt% of the total composition.

An alternative way of assessing the preferred level of phosphonic acid or salt thereof in the composition is to assess the total level of phosphonic acid/salt in solution in the automatic dish washing machine during the rinse cycle. To do this it is assumed that an average rinse cycle has 5 litres of water, so the composition must be capable of providing at least 3ppm of phosphonic acid/salt in the rinse solution.

A second essential feature of the invention is that it

comprises at least 20wt% of a water-soluble acid.

Suitable water soluble acids include inorganic and organic acids such as, carboxylic acids, including citric and succinic acids, polycarboxylic acids, such as polyacrylic acid, and also acetic acid, boric acid, malonic acid, adipic acid, fumaric acid, lactic acid, glycolic acid, tartaric acid, tartronic acid, maleic acid, their derivatives and any mixtures of the foregoing.

It is preferable, if the water-soluble acid is organic, in particular a monomeric, homo or copolymeric polycarboxylic acid in which the polycarboxylic acid comprises at least two carboxylic radicals separated from each other by not more than two carbon atoms.

Suitable water-soluble monomeric or oligomeric carboxylate builders can be selected from a wide range of compounds but such compounds preferably have a first carboxyl logarithmic acidity/constant (pKl) of less than 9, preferably of between 2 and 8.5, more preferably of between 2.5 and 7.5.

Suitable carboxylic acids containing one carboxy group include the water soluble lactic acid, glycolic acid and ether derivatives thereof. Polycarboxylic acids containing two carboxy groups include the water-soluble succinic acid, malonic acid, (ethylenedioxy) diacetic acid, maleic acid, diglycolic acid, tartaric acid, tartronic acid and fumaric acid. Polycarboxylic acids containing three carboxy groups include, in particular, water-soluble citric acid, as well as succinic acids. Polycarboxylates containing four carboxy groups include oxydisuccinic acid, 1, 1,2,2-ethane

tetracarboxylic acid, 1, 1,3,3-propane tetracarboxylic acid and 1, 1,2,3-propane tetracarboxylic acid.

Of the above, the preferred polycarboxylates are hydroxycarboxylates containing up to three carboxy groups per molecules, more particularly citric acid.

The parent acids of the monomeric or oligomeric polycarboxylate chelating agents or mixtures thereof with their salts, e. g. citric acid or citrate/citric acid mixtures are also contemplated as components of builder systems of rinse compositions in accordance with the present invention. However it is preferred if mixtures of acids/salts are not used.

The carboxylate or polycarboxylate builder compounds described above can also have a dual function as pH controlling agents.

The level of water-soluble acid is greater than 20 wt% of the composition, preferably it is greater than 25 wt%, more preferably it is greater than 30 wt%, most preferably it is greater than 35 wt%.

In a preferred aspect of the invention, the compositions have a pH as a 1% solution in distilled water at 20°C of less than 7, preferably from 0.5 to 6.5, more preferably from 0.5 to 4.0, most preferably from 0.6 to 2.

Surfactant System A surfactant system comprising a surfactant selected from nonionic, anionic, cationic, ampholytic and zwitterionic surfactants and mixtures thereof is preferably present in the composition.

The surfactant system most preferably comprises low foaming nonionic surfactant, selected for its wetting ability, preferably selected from ethoxylated and/or propoxylated nonionic surfactants, more preferably selected from nonionic ethoxylated/propoxylated fatty alcohol surfactants.

The alkyl ethoxylate condensation products of aliphatic alcohols with from about 1 to about 25 moles of ethylene oxide are suitable for use herein. The alkyl chain of the aliphatic alcohol can either be straight or branched, primary or secondary, and generally contains from 6 to 22 carbon atoms. Particularly preferred are the condensation products of alcohols having an alkyl group containing from 8 to 20 carbon atoms with from about 2 to about 10 moles of ethylene oxide per mole of alcohol.

The ethoxylated C6-Clg fatty alcohols and C6-Clg mixed ethoxylated/propoxylated fatty alcohols are highly preferred surfactants for use herein, particularly where water soluble. Preferably the ethoxylated fatty alcohols are the Cic-Cis ethoxylated fatty alcohols with a degree of ethoxylation of from 3 to 50, most preferably these are the C12-CI8 ethoxylated fatty alcohols with a degree of

ethoxylation from 3 to 40. Preferably the mixed ethoxylated/propoxylated fatty alcohols have an alkyl chain length of from 10 to 18 carbon atoms, a degree of ethoxylation of from 3 to 30 and a degree of propoxylation of from 1 to 10.

The condensation products of ethylene oxide with a hydrophobic base formed by the condensation of propylene oxide with propylene glycol are suitable for use herein.

The hydrophobic portion of these compounds preferably has a molecular weight of from about 1500 to about 1800 and exhibits water insolubility. Examples of compounds of this type include certain of the commercially-available 'Pluronic'surfactants, marketed by BASF.

The surfactant system is typically present at a level of from 1% to 40% by weight, more preferably 1.5 % to 30% by weight, most preferably from 5% to 20% by weight of the compositions.

Heavy metal ion sequestrants The rinsing compositions herein may also optionally contain further transition metal chelating agents (sequestrants).

These chelating agents may also have calcium and magnesium chelation capacity, but preferentially they bind heavy metal ions such as iron, manganese and copper.

Heavy metal ion sequestrants are preferably present at a level of from 0.005% to 20%, more preferably from 0.1% to

10%, most preferably from 0.2% to 5% by weight of the composition.

Heavy metal ion sequestrants, which are acidic in nature, having for example carboxylic acid functionalities, may be present either in their acid form or as a complex/salt with a suitable counter cation such as an alkali or alkaline metal ion, ammonium, or substituted ammonium ion, or any mixtures thereof. Preferably any salts/complexes are water soluble. The molar ratio of said-counter cation to the heavy metal ion sequestrant is preferably at least 1: 1.

Hydrotropes A highly preferred component of the compositions of the invention is a hydrotrope. The hydrotrope is typically present at levels of from 0.5% to 20%, preferably from 1% to 10%, by weight.

Useful hydrotropes include sodium, potassium, and ammonium xylene sulfonates, sodium, potassium, and ammonium toluene sulfonate, sodium, potassium and ammonium cumene sulfonate, and mixtures thereof.

Other Ingredients Other ingredients that may be present include lime soap dispersing compounds, perfumes and colorants.

Product Form The compositions of the invention can be formulated in any desirable form such as powders, granulates, pastes, liquids and gels. Liquid compositions are most preferred.

Machine dishwashing method The rinse aid compositions in accordance with the present invention may be used in essentially any conventional machine dishwashing method performed using a dishwasher machine, which may be selected from any of those commonly available on the market.

The rinse aid composition is typically employed at levels of from 0.5g to 6g of rinse aid composition rinse dosed into the final rinse cycle.

The invention will now be illustrated by the following non- limiting Examples. Examples of the invention are illustrated by a number. Unless otherwise indicated, all parts, percentages and portions referred to are by weights. ExampleA Example B >. : Example. vl Sodium xylene 5.0 5.0 5.0 sulphonate Citric acid 9. 5 40. 0 40.0 LF 400 14. 5 14. 5 14.5 Cublen P 50 solution--2. 0 Water.............................. to 100 %.............................. Where LF 400S is the trade name for a low-foaming alkyl ethoxylate/propoxylate supplied by BASF and Cublen P50 is

the trade name for a 50% solution of 2-phosphonobutane- 1,2,4-tricarboxylic acid supplied by Zschimmer and Schwarz Mohsdorf GmbH.

The sedimentation was tested by adding 5g of"Sun Sel integre" (Trade mark, as sold in France 2000) in one litre of water (French Hardness 75/50) and heating to 65°C for 15 minutes. The resulting mixture is then diluted 10 times, 3ml of rinse aid added and then left in a graduated test tube for two weeks. The resulting precipitate that has sedimented out is measured. The higher the figure the worse the result. Sedimentation Cm ExampleA 0. 8 ExampleB 0. 7 Example1 0. 6