Hydrogen peroxide compositions have been the focus of much attention in the patent literature in recent years as replacements for or as alternatives to halogen-containing bleaches, often motivated by environmental considerations. In particular, interest has focused on alkaline hydrogen peroxide bleaches because of their greater reactivity and enhanced bleaching efficacy as compared to acidic hydrogen peroxide compositions.

One of the prime requirements of a bleach intended for domestic use is that the bleaching species remain sufficiently stable to insure good efficacy of the bleach product upon use by the consumer, typically many months after the products manufacture. Hydrogen peroxide solutions are known to provide enhanced bleaching efficacy when used under alkaline conditions. However, stabilization of hydrogen peroxide is particularly troublesome at such alkaline conditions.

Further, the problem of bleach stability is often exacerbated when formulating a thickened bleach product. Thickening of a pourable liquid bleach is intended to provide an enhanced aesthetic appearance of the product as well as assist the consumer to control dispensing of the liquid bleach product. A thickened composition also serves to limit the rate at which the composition flows or drains from the surfaces to which it is applied. However, the use of a thickening agent or thickening system in the bleach composition presents problems in formulation: it is often incompatible with peroxide bleach stabilizers which are otherwise effective in non-thickened compositions, or the thickening agents themselves may provide an uneven viscosity to the liquid bleach product and, in general, adversely affect product appearance and flow characteristics depending on variables such as product pH or the non- bleach ingredients, such as electrolyte, present in the composition.

EP 376 704 describes hydrogen peroxide aqueous solutions which contain a combination of surfactant and electrolyte to provide thickening and bleach stability.

UK patent application GB 2 273 721 describes a thickened bleach composition which comprises an alkaline aqueous solution of hydrogen peroxide containing as the thickening system a mixture of a quaternary long chain alkyl ammonium compound together with a salt of an aromatic sulphonic acid hydrotrope.

U. S. Patent is concerned with alkaline hydrogen peroxide compositions which are thickened with a polymeric thickener having a polyethylene backbone.

U. S. Patent 4,900,469 describes a thickened laundry composition comprising a surfactant thickening system, a hydrogen peroxide bleach and a stabilizing system consisting of a chelating agent and an antioxidant. A C6-Cz8 soap is optionally included to increase viscosity.

Notwithstanding the above-mentioned patent literature and the availability of numerous commercial thickeners intended for liquid compositions, there remains a need in the art for a thickened alkaline liquid bleach composition containing a hydrogen peroxide bleach which is capable of providing long-term bleaching efflcacy, and which also contains an effective, environmentally safe and economical thickening system which does not adversely affect the bleaching performance and stability of hydrogen peroxide.

Summary of the Invention The present invention provides an alkaline thickened liquid bleaching composition comprising, by weight: (a) from about 0.1% to about 10% of hydrogen peroxide ; (b) from about 1.5% to about 8% of a surfactant mixture comprising (i) alkyl dimethylamine oxide; and (ii) soap formed by the in-situ neutralization of a C6-C, 8 fatty acid with an alkali metal hydroxide; the weight ratio of (i) and (ii) being from about 1.5: 1 to about 6: 1; (c) from about 0.5% to about 5% of an electrolyte comprising an alkali metal sulfate; (d) from about 0.4% to about 1% of a phosphonate stabilizer for the hydrogen peroxide; (e) an alkali metal hydroxide in an amount sufficient to effect the in-situ neutralization of the aforesaid C6-Cz8 fatty acid to form the soap defined in (b) (ii), and also provide a pH in the range of from about 8 to about 9.5 for the thickened bleaching composition ;

(f) from about 0% to about 2% of sodium benzoate; and (g) balance water.

In accordance with the method aspect of the invention there is provided a method of bleaching fabrics comprising the step of contacting the fabrics to be bleached with an effective amount of the above-described alkaline thickened liquid bleaching composition.

The present invention is predicated on the discovery that thickening of a hydrogen peroxide bleach solution can be effectively provided with a surfactant mixture of alkyl dimethylamine oxide and soap as herein described in combination with a weak electrolyte such as an alkali metal sulfate, such that a stable commercially desirable viscosity in the range of from about 80 to 500 cps can be readily achieved, preferably from about 100 to 300 cps, without adversely affecting the stability of the peroxide bleach.

Detailed Description of the Invention The amount of hydrogen peroxide bleach present in the composition of the invention may vary from about 0.1% to about 10%, by weight, of the total composition. Preferred compositions comprise from about 2% to about 6%, by weight.

The surfactant mixture which forms part of the thickening system is comprised of an alkyl dimethylamine oxide and a neutralized C6-Cl8 fatty acid, such mixture being present in an amount of from about 1.5 to 8%, by weight, preferably from about 2% to 4%, by weight. The alkyl group in the dimethylamine oxide surfactant contains from about 11 to 16 carbon atoms.

A preferred alkyl group is comprised of a mixture of carbon chain lengths comprising 33% to 43% of C, 2; from 42% to 52% of Cl4; and from 4% to 14% of C16. Lauryl is a particularly preferred alkyl group.

The second component of the surfactant mixture is a C6-C, 8 fatty acid which is neutralized in-situ by the alkali metal hydroxide in the liquid composition to form a C6-Cz8 soap. Typical fatty acids include capric acid, lauric acid, any myristic acid, but most preferred is coconut fatty acid which after neutralization forms the coconut lauryl soap.

The ratio of the described amine oxide surfactant to the fatty acid soap is generally from about 1.5: 1 to about 6: 1, and preferably from about 2: 1 to about 4: 1.

The third component of the thickening system which serves to stabilize the increased viscosity provided by the surfactant mixture is an alkali metal sulfate such as sodium or potassium or magnesium sulfate. Sodium sulfate is preferred as a source of weak electrolyte which serves to stabilize the viscosity of the composition without adversely affecting the

stability of the hydrogen peroxide in solution. It has been found that the presence of strong electrolyte in solution at a level to compliment the surfactant thickening such as Na2CO3, NaOH, NaHCO3 cause decomposition of alkaline hydrogen peroxide solution and is, therefore, to be avoided in the present liquid bleaching compositions.

The peroxide bleach stabilizer used herein is a polyphosphonate sequestrant. Examples of suitable phosphonate stabilizers include sodium or potassium salts of HEDP1 and EDTMP2.

Most preferred is the pentasodium salt of diethylenetriamine penta (methylene phosphonic acid), which is available commercially under the trademark Dequest 2066 from the Monsanto Company.

An essential ingredient in the present bleaching composition is an alkali metal hydroxide such as sodium or potassium hydroxide, in an amount sufficient to neutralize in-situ the fatty acid ingredient present in the surfactant mixture so as to form the soap. The alkali metal hydroxide also serves to provide an alkaline pH in the liquid bleach composition of from 8 to 9.5, and preferably from 8.2 to 9.2. The amount of alkali metal hydroxide in the composition is generally from about 0.10 to 0.5%.

The liquid bleach compositions may preferably include a pH buffer such as sodium benzoate which serves to stabilize the pH of the composition and thereby assists in stabilizing the peroxide bleach.

Other materials, such as colorants, perfumes, germicides may also be added in minor amounts, if desired.

'HEDP = 1,1,1-hydroxyethylenediphosphonic acid 2 EDTMP = ethylene diamine tetramethylenephosphonic acid