Thickened acidic cleaning products have been commercially available for many years. Typically they are used in the field of toilet bowl cleaning where the viscosity gives the product extended contact time as it runs down the vertical walls of the toilet bowl. Generally, toilet bowl cleaners contain in the region of 10% acid, usually made up of either a mineral acid, such as hydrochloric, sulphamic or phosphoric acid; or an organic acid such as citric, oxalic, lactic or maleic acid.

Thickened acidic cleaning products have also found utility as all purpose washroom cleaners which are milder in pH than the aforesaid toilet cleaning products, typically buffered to between pH 2. 0 and pH 5. 5, and often containing a biocide for general disinfection.

Furthermore, thickened acidic cleaning products have been used for derusting vertical surfaces or cleaning areas with a high level of metallic soiling such as removing brake dust from wheels or railway carriages.

In any of the aforesaid applications the thickened acidic products are typically applied as a thick liquid or as a foam via an aerosol device with or without dilution or a foaming lance.

Traditionally the thickening agent of the aforesaid cleaning products have been alkyl phenyl ethoxylates (APE's), whilst these afford suitable viscosity and detergency to the products their use has been recently restricted, particularly in Europe, due to their detrimental effects on the environment so much so that OSPAR (the Oslo and Paris Convention) has recommended a ban on their use.

Consequently, the industry has sought less damaging alternatives although there has proven to be a very limited supply of suitable agents.

The most common-replacements for APE's in other cleaning applications are alcohol ethoxylates but these have insufficient thickening properties to make them a commercially viable alternative. Naturally derived polymers such as xanthan gum and hydroxy ethyl cellulose (HEC) have been used but are limited by their relative instability in acidic conditions leading to a drop in viscosity over time, and their cost, since the formulated product still requires additional agents for detergency and perfume solubility. A good review of surfactant based thickening systems is given by Ben Milwidsky in the April 1990 edition of HAPPI. One of the more successful systems mentioned in this review is using a C, 8 alkyl amine ethoxylate in combination with an alcohol ethoxylate and cumene sulphonate. This gives a viscous stable product but suffers from a poor odour due to the requirement to use a relatively long chain amine.

A similar system is mentioned in EP 0265979 which uses a long chain (Ci6 or greater) alkyl amine derivative, such as tallow trimethyl ammonium chloride in combination with an organic aryl sulphonate, such as sodium xylene sulphonate. Again this system can be limited by poor odour and pseudoplastic rheology which gives undesirable product aesthetics. Similar results can be achieved using other long chain amine derivatives such alkyl amine oxide ethoxylates, for example Aromox T12 produced by Akzo Nobel, or amphoteric surfactants derived from long chain amines such as Mona AT1200 produced by Uniqema. However, these systems based on longer chain amines suffer the same problems of poor odour and, when used alone, pseudoplastic rheology.

Other disadvantages of using the long chain amine derivatives is the frequent need to add an organic aryl sulphate. Whilst this material is suitable for use in normal toilet

bowl cleaning it is not suitable for use with certain cationic additives such as quaternary ammonium biocides. This limits the use of these systems in milder washroom cleaners where the addition of a biocide is desirable.

Medium chain length alkyl amine oxides (typically Clo-Ci4) have been used predominantly for thickening hypochlorite containing cleaning solutions for many years. Although these alkyl amine oxides and their ethoxylates have been shown to exhibit thickening effects in acidic conditions, the amounts required to achieve this effect are uneconomical for such a competitive market as toilet bowl cleaning due to the relatively high market price of the said alkyl amine oxides and their ethoxylates.

It has been shown that amphoteric surfactants exhibit synergistic thickening effects in conjunction with anionic surfactants in neutral or alkaline pH. However, the more commonly used and economical anionic surfactants such as sodium lauryl sulphate and sodium lauryl ether sulphate, are unstable in acidic conditions and so are not suitable for use as thickening agents in acids.

It is desirable therefore to produce a stable, economical, odourless thickened acidic cleaning product with good detergency containing an environmentally acceptable thickening agent. In particular, such a system should perform well over a wide range of acidic conditions and be suitable for use in conjunction with other cationic active ingredients to widen the range of formulated products available.

According to the present invention there is provided a thickened acidic cleaning composition comprising an acidic component, at least one amine oxide of general formula 1 and at least one amphoteric surfactant General Formula 1 wherein Ri, R2 and R3 are any alkyl, alkoxylated or aryl group.

It has been found that suitable amine oxides and amphoteric surfactants exhibit synergistic thickening properties in a wide range of acidic conditions.

Advantageously, the synergistic thickening enables shorter chain amine oxides to be used than in the aforementioned prior art systems, typically a Cl4 amine oxide can be used. Since C14 amine oxides have no appreciable odour their use does not restrict the fragrance of the product as masking of the amine oxide odour is not a consideration.

Furthermore, the use of these materials does not interfere with the addition of other cationic additives such as biocides, corrosion inhibitors and water displacing agents.

A surprising additional benefit of this system is that in more acidic conditions, for example below pH 5, the formulation exhibits some biocidal properties such that the addition of further biocide (s) is not always required.

Conveniently, the composition of the present invention may be supplied as a concentrated liquid requiring dilution prior to use, a dilute ready to use liquid, an aerosol product or otherwise.

The composition of the present invention is suitable for use in a wide variety of applications for example, descaling and derusting products general washroom and toilet bowl cleaning products. The thickness and acidity of the composition can be adjusted

to suit the application of the composition, but will typically range from lOCps to 3000Cps. (viscosity is measured at 20°C using a Brookfield viscometer).

The amine oxide shall preferably comprise alkyl groups whereiIl Rl=Cl to C22 and R2=R3=Me.

More preferably, the amine oxide shall comprise alkyl groups wherein Rl=Clo to Cis and R2=R3=Me.

Most preferably the amine oxide shall comprise alkyl groups wherein R, =Cl4 and R2=R3=Me, that is myristyl amine oxide.

The amine oxide shall constitute from 0.2 to 20% by weight, and preferably from 0.2 to 10% by weight of the total composition. However, in order to achieve sufficient thickening of the composition the amine oxide preferably constitutes from 0.5 to 5% by weight of the total composition of the present invention.

Typically, an amine oxide content of greater than 5% by weight of the composition is needed where viscosity upon dilution is required.

Suitable amphoteric surfactants are typically derived from secondary and/or tertiary amines where the alkyl groups can be straight or branched alkyl chains bearing between 1 and 22 carbon atoms. Furthermore, the alkyl chains may also bear additional functional groups, for example amido groups.

The nitrogen of the amphoteric surfactant is preferably in a cationic state although there is'no limit to the number of cationic charges the said amphoteric surfactant may bear.

At least one of the said alkyl groups must contain an ionisable head group which may adopt a negative charge. Suitable examples include carboxylate, sulphate, sulphonate, phosphate, phosphonate, succinate or sulphosuccinate.

The amphoteric surfactant shall preferably, be chosen from betaines, sultaines, hydroxysultaines, iminopropionates and iminodipropionates. The most preferred amphoteric surfactant being an alkylamidopropyl betaine, for example cocamidopropyl betaine.

The amphoteric surfactant shall constitute from 0. 1 to 15% by weight of the total composition, preferably from 0.1 to 10% by weight and most preferably from 0.2 to 5% by weight of the total composition.

The acidic component comprises at least one mineral acid and/or at least one organic acid, and/or at least one buffer and mixtures thereof.

Suitable mineral acids, which may be used alone or in combination, include nitric, phosphoric, sulphamic, sulphuric and hydrochloric acid.

Suitable organic acids, which may be used alone or in combination, include citric, formic, lactic and maleic acid.

Where a buffer is used, the buffer is prepared from one or more mineral and/or organic acids or any acidic product which is partially neutralised using an alkali, examples of which include, sodium hydroxide, tetrasodium nitrilo triacetate and tetra sodium ethylene diamine tetraacetate. Preferred sources of alkali are mono-, di-and tri-alkanolamine.

Where an acid is used in preference to a buffer, a milder mineral acid is preferred, for example, sulphamic and/or phosphoric acid.

Generally, the acidic component shall constitute from 0. 1 to 75% by weight of the total composition of the present invention.

However, the level at which the acidic component is included in the composition depends upon the use to which the composition is to be put.

Where the composition is to be applied as a descaling product, the acidic component shall preferably constitute more than 1% by weight of the total composition of the present invention.

Where the composition is to be applied as a toilet cleaning product, the acidic component shall preferably constitute from 0.4 to 40% by weight and more preferably from 5 to 20% by weight of the total composition of the present invention.

Where the composition is to be used for derusting purposes, the acidic component shall preferably constitute about 30% by weight of the total composition of the present invention.

Where a buffer is used in preference to an acid, said buffer preferably constitutes from 0.5 to 5% by weight and more preferably around 2% by weight of the total composition of the present invention.

The pH of the composition differs depending on the use to which the composition is to be put, but typically does not exceed 5.5.

Alternatively, where a particularly mild formulation is required the natural acidity of one or more of the components may be sufficient to lower the pH below 7 i. e. acidic. For example, where the product is being used for general hard surface washing it may be preferable to have a pH closer to neutral so further addition of acid may not be required if the formula naturally has a pH below 7.

Electrolyte is often added to raise the viscosity of the formulation. There are several sources of electrolyte. Organic electrolytes, such as the anionic aryl sulphonates used by Akzo, raise the viscosity at relatively low addition rates. Inorganic electrolytes such as sodium chloride, are also suitable and have the benefit of being

economical and compatible with optional additional cationic ingredients. Other electrolytes can be prepared in situ, examples of which include aforementioned buffers.

Inclusion rates of the electrolyte are only limited by the solubility of the electrolyte. Some formulations may naturally contain a sufficient amount and not require any further additions.

Where the biocidal efficacy resulting from the synergistic interaction of the amine oxide and the amphoteric surfactant is insufficient for the use to which the composition is to be put, biocides may be optionally added.

Typically suitable biocides are those of the quaternary ammonium type. Since such biocides enhance the existing biocidal nature of the composition only small quantities are required, preferably, less than 3% by weight of the total composition.

Any cationic biocide is suitable for inclusion into the composition, but benzalkonium chloride is the biocide of choice.

Furthermore, additional constituents may be added to the composition of the present invention in order to improve the cleaning or foaming properties of the composition, to deposit an active ingredient onto the surface such as a water displacing agent or to adjust the rheological characteristics of the composition. These include dyes, perfumes, corrosion inhibitors, solvents, surfactants, biocides, associative thickeners and mixtures thereof. Careful selection of these ingredients is required since their inclusion is limited only by their compatability with the essential features of the composition.

Acid stable dyes are added to the composition at levels not exceeding 0.5% by weight of the total composition. Perfumes are added to the composition at levels not exceeding 2% by weight of the total composition. Suitable corrosion inhibitors are

those of the Armohib (RTM) range available from Akzo Nobel Chemicals and are added to the composition at levels not exceeding 1.0% by weight of the total composition.

Additional surfactants may be added in order to boost the detergency, alter the foaming properties and alter the rheology of the composition. Typically additional surfactants are of a non-ionic type although other types of surfactants are equally suitable. Examples of suitable additional surfactants include alcohol ethoxylates, alkyl polyglucosides and alkyl amides and their ethoxylates.

Solvents may be added in order to enhance the degreasing properties of the composition, for example glycol ethers and terpenes.

It is to be understood that all percentage values are measured by weight, and are relative to the total composition whether the composition is in a concentrated form or a dilute ready-to-use form.

The invention will now be described further by reference to the following specific examples- Compound Class of Amount Added (% w/w) Compound A B G D E Myristyl amine oxide Amine oxide 0.9 0.9 1.26 2.37 15.0 3.38 Cocamidopropyl betaine Amphoteric 0.6 - 0.29 1.42 5.0 1.13 surfactant Tallowamphopoly-carboxy Amphoteric-0. 6---- glycinate surfactant Phosphoric acid Mineral ACid 30 - - - 70 - Sulphamic acid Mineral Acid-10-0. 95-- Citric acid Organic acid-9. 5 0. 95 MonoethanolamineAlkali0. 51 Perfume Perfume---0. 38-- Sodium Xylene Sulphonate Organic 1.6 1.5 1. 8-5- electrolyte Sodium chloride Inorganic-----10 electrolyte Benzalkonium Chloride Biocide 0. 48 0. 3 Didecyl dimethyl ammonium Biocide-----0. 48 chloride Water Solvent 66. 9 87 82.14 92.94 5 62. 81 CAP 70 (proprietary blend of Propellant--5 propane and butane)

NB: Monoethanolamine is added to the formulation D as a neutralising agent in a amount to make the pH of the formulation pH 4.0.

Formulation C is an example of an aerosol product.

Formulation E is an example of a concentrated liquid product which is diluted in the ratio 1 part product to 20 parts water prior to use.

Formulation F has a natural pH of 6.9.