Liquid Detergent Compositions for Removal of Cooked-on Food Soils

This invention relates to liquid detergent compositions particularly suitable for dishwashing and the use of which facilitates the removal of cooked-on food soils from cooking utensils.

The removal of cooked-on food soils from cooking utensils is one of the more difficult and tedious household tasks and it is common practice to leave such soiled utensils soaking in water or detergent solution for a considerable time before attempting to remove the soil. Even then the use of scouring pads or abrasives is frequently necessary for satisfactory removal of the soil.

It has now been discovered that the task of removing cooked-on food soils from cooking utensils can be facilitated by soaking the soiled utensils in a detergent solution which contains an anionic synthetic detergent and a phosphate builder, at least part of the cations of the synthetic detergent and builder being derived from monoethanolamine, the remaining cations being selected from ammonium, sodium, potassium, calcium and magnesium and the solution optionally also containing free organic base.

Detergent compositions suitable for providing such solutions can be prepared, according to the invention, in the form of single phase liquid detergent compositions.

According to the invention, a clear, single-phase, liquid detergent composition comprises from 26-50% by weight of the composition of anionic detergents selected from the group consisting of linear alkyl benzene sulfonates having from 8-18 carbon atoms in the alkyl radical, alkyl sulfates having from 10 to 20 carbon atoms, paraffin sulfonates having from 10-20 carbon atoms, alkyl polyglycol ether sulfates having from 10-20 carbon atoms in the alkyl group and from 1-6 ethoxy groups in the molecule and mixtures thereof, 0.5-15% by weight of the composition of anion of a condensed phosphoric acid, optionally in admixture with orthophosphoric acid, the composition being solubilized in water with a lower alcohol having from 1-3 carbon atoms, 0-10% by weight of the composition of mono- or di- lower alkyl benzene sulfonate having from 1 to 3 carbon atoms total in the alkyl groups, the cations of the detergent, the phosphoric salts and the optional lower alkyl or dialkyl benzene sulfonate being solely monoethanolammonium (HO.CH.sub.2.CH.sub.2 NH.sub.3.sup.+ ) or a mixture of monoethanolammonium with ammonium (NH.sub.4.sup.+), sodium (Na.sup.+), potassium (K.sup.+), calcium (Ca.sup.++) or magnesium (Mg.sup.++) cations in which not less than 20 mole percent of the total cations are monoethanolammonium. The anionic detergent can be replaced in an amount not greater than 10% by weight of the composition by a suds enhancing agent selected from the group consisting of alkyl glyceryl ether sulfonates in which the alkyl group has 10 to 20 carbon atoms, tertiary amine oxides of the formula R.sub.1 R.sub.2 R.sub.3 N.fwdarw.O in which R.sub.1 is an alkyl group of 10 to 18 carbon atoms and R.sub.2 and R.sub.3 are each alkyl groups of from 1 to 3 carbon atoms, and fatty acid mono- or dialkylolamide in which the fatty acid radical has from 8 to 18 carbon atoms and the alkylol radical has from 1 to 3 carbon atoms. In compositions containing no ammonium cation, the lower alkyl or dialkylbenzene sulfonate can be replaced, wholly or in part, by free monoethanolamine as hereinafter defined.

By free monoethanolamine in the compositions of the invention is meant monoethanolamine which is in excess of that required to adjust the pH of the composition to 7.5.

Preferably, the anionic detergent is a mixture of alkyl sulfate and alkyl polyglycol ether sulfate in a weight ratio of 3:1 to 1:3, preferably substantially 1:1. The total proportion of active detergent is preferably 30-45% by weight of the total composition. When a suds enhancing agent is present, it is preferably a fatty acid mono- or dialkylolamide and is preferably present at a level of 2-8% by weight of the total composition.

Condensed phosphates suitable for use in the compositions are pyrophosphates and the salts of linear polyphosphoric acid which have a mole ratio of H.sub.2 O to P.sub.2 O.sub.5 less than 2:1. Optionally some orthophosphoric acid may also be present. Suitable phosphoric acids are commercial mixtures available under the trade names "Conphos", "Pyrophosphoric acid" and "Tetraphosphoric acid" which have the compositions set out below.

The cations of the detergent, phosphate and optional lower mono- or dialkylbenzene sulfonate may be solely monoethanolammonium or a mixture of monoethanolammmonium with ammonium, sodium, potassium, calcium or magnesium cations. At least 20 mole percent of the cations are monoethanolammonium. In the preferred compositions which contain a mixture of alkyl polyglycol ether sulfate detergent with alkyl sulfate detergent, it is preferred that the monoethanolammonium cation should be equivalent to at least all of the alkyl polyglycol ether sulfate and the phosphate.

Compositions which do not contain ammonium ions may contain free (as defined above) monoethanolamine in place of some or all of the alkyl- or dialkylbenzene sulfonate hydrotropes. This free monoethanolamine serves to solubilize the other ingredients of the composition in the aqueous vehicle, and also at levels of 2 to 10% by weight of the composition it improves the effectiveness of the composition in removing cooked-on food stains. Even if some ammonium ion is present, small proportions of free monoethanolamine (e.g. up to 2% by weight of the composition) can be included provided the amount is not so great as to give rise to an objectionable ammonium odor.

The proportion of lower alcohol is sufficient to solubilize the detergent ingredients and is usually from 3 to 15% by weight of the composition. The preferred alcohol, for reasons of availability, odor and non-toxicity is ethanol in, for example, the form of industrial methylated spirit.

The lower alkyl or dialkyl benzene sulfonate, preferably a toluene sulfonate or xylene sulfonate, serves as a hydrotrope and may be present in an amount up to 10% by weight of the composition. However, as is mentioned above, this hydrotrope ingredient is optional in that it is not necessary in all compositions.

The compositions of the invention may contain minor proportions of the usual additives of dishwashing compositions such as color, perfume, tarnish inhibitor, viscosity control agents, etc.

The products of this invention can be used as conventional dishwashing agents, in which case they are preferably used at a concentration of from 0.05 to 0.5% by weight, preferably about 0.15%. Alternatively, saucepans and like utensils having cooked-on food stains may be left to soak in a somewhat stronger solution, e.g. 0.5 to 2%, preferably 1%, preferably for about 30 minutes to 1 hour, after which they can be washed in the same solution or in a conventional dishwashing solution. In such conditions the cooked-on soil is more easily removed by light rubbing, e.g. with a dishcloth, than is the case if an attempt is made to wash the utensils without a pre-soak or after a pre-soak in a solution of a conventional dishwashing liquid.

The Control Composition is a conventional liquid dishwashing composition included for comparison.

The above three compositions have substantially equal sudsing characteristics.

Aluminum saucepans were used to prepare boiled milk and the milk was then poured out of the pan without scraping the layer of cooked milk adhering to the pan surface. The pans were filled with 1.0% solutions of the test products at room temperature. The pans were left soaking for 30 minutes and the liquid was then poured out. The pans were rinsed for two ten-second periods under a cold running tap.

Four replicate pans were prepared for each product. The treated pans were panelled using a 9-level Scheffe paired comparison technique (H. Scheffe, J. Am. Statist. Ass., 47, 381-400 (1952)).

In this test, Product 1 had a 2.0 panel score unit (psu) advantage over the Control Product and Product 2 had a 4.0 psu advantage over the Control Product. The least significant difference (95% confidence level) was 1.0 psu.

In a similar test using meat and vegetables prepared in pyrex casserole dishes, the same psu advantages over the Control Product were obtained with Products 1 and 2.

In each of the compositions of Example II, of the 6.0% added monoethanolamine, 1.2% is required to neutralize the "Conphos", leaving 4.8% free monoethanolamine. Other effective compositions of the invention which are all clear single phase liquids are: