EP0079697A1

EP0079697A1 - Cleaning compositions

Info

Publication number: EP0079697A1
Application number: EP82305666A
Authority: EP
Inventors: Anthony Francis Martin
Original assignee: Procter and Gamble Ltd; Procter and Gamble Co
Current assignee: Procter and Gamble Ltd; Procter and Gamble Co
Priority date: 1981-11-07
Filing date: 1982-10-26
Publication date: 1983-05-25
Anticipated expiration: 2002-10-26
Also published as: DE3268705D1; EP0079697B2; EP0079697B1; CA1202853A; ATE17595T1

Abstract

Aqueous cleaning compositions of viscosity >180 centipoises at 20°C are provided containing a trialkyl amine oxide of formula R₁R₂R₃N→O, where 13 < R₁ ≤ 18 and R₂ and R₃ are C₁-C₄ alkyl, as the sole surfactant at a level of 0.5% to 5.0% by weight of the composition. The compositions also incorporate one or more ionisable water soluble compounds to provide an ionic strength of 3.0 g molesldm³ minimum, and in preferred embodiments this is provided by an alkali metal hypochlorite bleach component.

Description

This invention relates to aqueous cleaning compositions and especially to chlorine bleach-containing aqueous cleaning compositions useful for the removal of oxidisable stains from and the disinfection of hard surfaces. Compositions in accordance with the invention find particular utility in the cleaning of sanitary fittings such as toilets, bidets, sinks, baths and shower units in addition to the disinfection of drains and the washing of tiled surfaces.
Aqueous chlorine bleaching products are well known in the art and have been used for many years in a variety of bleaching and disinfecting applications. The active component of a product of this type is normally an alkali metal hypochlorite, usually at a level of from 1 to 15% by weight, and the physical characteristics of the product are those of a dilute salt solution with a viscosity less than 20 centistokes.
In recent years, interest has developed in chlorine bleach products of higher viscosity, in order to provide longer lasting adherence to vertical surfaces and hence greater efficacy, and a number of compositions have been disclosed that are stated to be both chemically stable and physically stable over an extended period of time.
Examples of such compositions are disclosed by British Patent No. 1329086, European Published Patent Applications Nos. 0021581, 0030401, French Published Patent Application No. 2355909 and British,Patent Application No. 2003522A.
These thickened compositions incorporate one or more bleach stable surfactants as an aid in increasing viscosity and a preferred example of such a surfactant is an amine oxide containing one C₁₀-C₁₈ alkyl group and two lower alkyl, usually _Cl-_C4 alkyl groups. The compositions also contain a source of alkalinity and alkali metal salts of various kinds.
In order to achieve a significant enhancement of viscosity the prior art has employed other surfactants in admixture with the amine oxide such as alkali metal fatty acid salts, alkali metal alkyl sulphate salts and saccharose esters and viscosities of up to 150 centistokes at 25°C are stated to be obtainable by this technique.
It has now surprisingly been found that stable aqueous chlorine bleach-containing compositions having viscosities appreciably in excess of 150 centistokes can be achieved without the necessity of employing the surfactant mixtures taught as necessary by the prior art.
This finding has also simplified the formulation of a thickened chlorine bleach composition insofar as it lowers- the level of organic components in the formulation and thereby lessens the problem of ensuring chemical stability as well as reducing the cost of the composition.
It has also been found that compositions in accordance with the invention display cleaning advantages relative to commercially available chlorine bleach compositicns embodying the prior art.
According to the present invention there is provided a stable single phase aqueous detergent composition incorporating an amine oxide of formula R₁R₂R₃N→O wherein R₁ is an alkyl group in which the average number of carbon atoms is such that 13 <R₁≤18 and R₂and R₃ are C_l-C₄ alkyl groups or C₂-C₄ hydroxy alkyl groups together with at least one ionisable water soluble compound wherein the amine oxide comprises the sole surfactant and is present in an amount of not more than 2.5% by weight of the composition and in that the at least one water soluble inorganic salt is present in an amount to provide a total ionic strength of the composition of at least 3.0 g moles/dm³, such that said composition has a viscosity of at least 180 cp at 20°C.
In one aspect of the invention the alkyl group R₁ comprises a mixture of groups containing 13 and 15 carbon atoms and comprising a mixture of moieties of structure,
and
the group P₄being predominantly methyl, the composition also being characterised by a total ionic strength of at least 4.7 g moles/dm³.
In a preferred aspect of the invention in which the composition incorporates a hypochlorite bleach, R₁contains an average of from 14 to 16 carbon atoms and is selected from linear moieties and moieties containing no more than 25% methyl branching.
In this specification fluid viscosity is expressed as the dynamic viscosity _n in centipoises. The dynamic viscosity is measured by a Brookfield RVT viscometer and for the purposes of this specification measurements are made with Spindle No. 3 at 100 rpm and a liquid temperature of 20°C. Fluid viscosity can also be expressed as the kinematic viscosity v in centistokes as measured by an Ostwald viscometer and is characterised by the expression v = n/p where _n is the dynamic viscosity in centipoises and α is the density in g/cm³. Compositions in accordance with the present invention have a density in the range from 1,10 to 1.25 g/cm³, typically approximately 1.15 g/cm³; so that the numerical value of the kinematic viscosity in centistokes is slightly less than that of the dynamic viscosity in centipoises.
The invention will be described primarily with reference to an aqueous composition containing an alkali metal hypochlorite bleach, the latter providing the majority, and preferably substantially all, of the ionic strength requirement. However, the invention also embraces non-bleach compositions in which the ionic strength is provided by any ionisable alkali or alkali earth metal compound.
Bleach composition embodiments of the present invention therefore comprise an amine oxide of defined structure and an alkali metal hypochlorite there being sufficient ionisable inorganic salt present to provide an ionic strength of at least 3.0 g moles/dm .
The alkali metal hypochlorite may be a lithium, potassium or sodium hypochlorite and the level of hypochlorite in the composition is normally arranged to lie in the range 1-12%, preferably 5-10% by weight. Customarily hypochlorite bleach compositions contain approximately 6% or 9% hypochlorite by weight. However, the activity of chlorine bleaching compositions is conventionally expressed in terms of the weight percentage of available chlorine in the composition, and the actual weight percentage of bleaching species is arranged to provide the desired level of 'available chlorine'. The preferred hypochlorite species is sodium hypochlorite which contains 95.3% available chlorine.
Alkali metal hypochlorites are commercially available as aqueous solutions containing 10-15% by weight 'available chlorine' and the bulk suppliers normally produce material having available chlorine contents towards the upper end of this range viz. 12-14% by weight. These commercially available hypochlorite solutions contain other salts as byproducts or contaminants, more specifically free alkalinity in the form of alkali metal hydroxide and alkali metal carbonate, and alkali metal chloride. Low levels of other species such as sodium chlorate are also believed to be formed during hypochlorite manufacture but their chemical stability is sufficiently low that they have largely decomposed by the time the hypochlorite is employed in product formulations. The levels of the byproduct materials depend on the processing conditions employed in the manufacture of the hypochlorite but in general they fall within the ranges
expressed as a weight percentage of the hypochlorite solution as supplied.
Amine oxides useful in the present invention have the formula R₁R₂R₃N→O wherein R₁is an alkyl group in which the number of carbon atoms is 13 ^< R₁≤18 and R₂ and _R3 are _Cl-_C4 alkyl groups or C₂-C₄ hydroxy alkyl groups. The amine oxide is present in an amount of from 0.5% to 5%, more preferably from 0.5% to 2.5% and,in preferred embodiments of the invention in which the R₁ average chain length ≥14 carbon atoms, from 1% to 1.5% by weight of the composition. The R₁ group may be linear or branched and may be derived from natural or synthetic hydrocarbon sources. For the purposes of the present invention linear groups are defined as including moieties incorporating up to 25% methyl branching, predominantly in the 2-position relative to the nitrogen atom of the amine oxide.
Methyl branching on the alkyl chain also predominates in those amine oxides useful in the present invention in which the R₁ group is branched, rather than linear in nature.
Commercially available sources of these amine oxides are normally a mixture of

which arises as a result of the processing route used to form the precursor alcohol or aldehyde. This route involves carbonylating or hydroformylating an olefin, preferably a linearorα-olefin and leads to a mixture of the desired branched chain aldehyde or alcohol of the same carbon number. For olefin starting materials having a range of carbon chain length, the resultant alcohol or aldehyde mixture contains compounds of different carbon number and isomers containing straight chain and 2-alkyl branched chain alkyl groups. A typical mixture useful in the present invention comprises 65 to 75% by weight C₁₃ and 35 to 25% by weight _C15 amine oxides with approximately 50% by weight- straight chain and 50% by weight 2-alkyl branched chain where the 2-alkyl group is predominantly methyl. These are available from ICI under the trade name Synprolam 35 DMO as a 30% aqueous solution. The branched chain amine oxides and mixtures thereof with linear chain amine oxides are used at levels towards the upper end of the range viz. > 2% by weight of the composition and typically from 2.0% to 2.5% by weight.
Although the above-described mixture of straight chain and branched chain alkyl dimethyl amine oxides has been found to provide the benefits of the invention, their use does not constitute the most preferred execution of the hypochlorite bleach aspect of the invention. This is because an ionic strength of at least 4.7 g moles/dm³ is required to achieve the target viscosity and this level of ionic strength is believed to make the storage stability of the hypochlorite bleach less than that which is considered desirable for the expected shelf life of the product. For the hypochlorite bleach aspect of the composition, the preferred amine oxide structure is one in which R₁ has an average chain length in the range C₁₄-C₁₆ and is a linear group, linear being defined as including moieties containing up to 25% 2-methyl branching. Compositions containing these preferred amine oxides require a lower amine oxide level viz.< 2.0%, more typically 1.0-1.5% and also a lower ionic strength viz. 3.0 g moles/dm minimum in order to achieve target viscosity. Both of these reductions. in ingredient level lead to improved storage stability and also lower the cost of the product.
The ionisable water soluble compound which forms the other major component of the compositions of the invention is a non surface active organic, or inorganic, compound which must be present in an amount to provide an ionic strength of at least 3.0 g moles/dm³.
The ionisable compound(s) can be inorganic in nature eg. hydroxide sulphate, halide (particularly chloride) carbonate, nitrate, orthophosphate, pyrophosphate, polyphosphate or silicate, or organic such as citrate, formate, acetate or succinate. In a preferred aspect of the invention in which sodium hypochlorite bleach is incorporated, the hypochlorite itself, together with the sodium hydroxide, chloride and chlorate associated with the bleach provides the, or a major proportion of the ionisable compounds required by the invention. In the preferred hypochlorite bleach-containing embodiments of the invention, certain inorganic compounds such as silicates, and organic compounds incorporating oxidisable groups are unstable and should be avoided.
The ionic strength of the composition is calculated by means of the expression

where C_i is the molar concentration of the ionic species in g moles/dm 3
Z_i is the valency of the species.

The ionisable alkali metal compound normally comprises a caustic alkali such as sodium or potassium hydroxide either alone or in admixture with alkali metal salts. The level of sodium hydroxide necessary to provide a total composition ionic strength of 3.0 g moles/dm where the composition contains only the amine oxide would be approximately 11% to 12% by weight of the composition dependent on the density of the solution. More preferably, for product safety reasons, the at least one ionisable compound comprises a mixture of a caustic alkali in an amount of from 0.5% to 2% by weight of the composition together with one or more alkali metal salts in an amount of at least 10% by weight, more usually at least 15-20%.
In that aspect of the invention airectea to liquid detergent compositions suitable for cleaning hard surfaces such as walls and windows, the ionisable compound can include any of the water soluble inorganic and organic builder and sequestrant salts normally incorporated in such products. Compounds classifiable and well-known in the art as detergent builder salts include the nitrilotriacetates, polycarboxylates, citrates, ortho- and pyre-phosphates, and mixtures of any of these. Metal ion sequestrants include all of the above, plus materials like ethylenediaminetetraacetate, the amino-polyphosphonates and phosphates (DEQUEST). A wide variety of poly-functional organic acids and salts is disclosed in European Patent Application Publication No 0040882 which contains examples of the use of such materials in various cleaning compositions. In general the builder/sequestrant will comprise from 1% to 25% of the composition. Citric acid (2%-20% as sodium citrate) is a preferred builder.
In the aspect of the invention in which a hypochlorite bleach is incorporated the bleach itself, containing the range of by-product materials previously mentioned, provides a major portion of the ionic strength requirement, viz at least 3.0 g moles/dm³ assuming an available chlorine level of 9% in the composition. In practice therefore it is usually only necessary to add alkali metal hydroxide on a total composition basis. In this aspect of the invention it is particularly preferred that the, or the major part of the, amine oxide should have an R_l alkyl chain length in the range 14 to 16 carbon atoms. A desirable optional component of compositions in accordance with the invention is a perfume which is present at a level of from 0.01% to 0.5% preferably from 0.05% to 0.25% by weight of the composition.
The compositions are made by conventional mixing techniques. Although any order of mixing can be used, presolution of the alkali metal hydroxide and any alkali metal salt is desirable and these are normally added to a solution of the amine oxide. Perfume is then added under high shear agitation together with any additional water to provide the desired product concentration. In the aspect of the invention in which an alkali metal hypochlorite bleach is included, this component is added last.
The invention is illustrated in the following examples in which percentages are expressed by weight of the composition unless otherwise stated.
In the examples reference to ingredients have been abbreviated as follows:

EXAMPLE 1

l.Og of pelleted sodium hydroxide, equivalent to 0.5% of the finished product composition, was dissolved in 7.4 ml soft water and 8.0 g anhydrous sodium carbonate was added to the solution. This solution was then added to 16.6 g of a 30% by weight solution of C_13-15 alkyl dimethyl amine oxide (available from ICI as Synprolam 35DMO). Finally this mixture was blended with high shear agitation into 167g of a sodium hypochlorite solution^* containing 11.5% by weight of available chlorine.
^*Supplied by British Drug Houses Ltd as GPR hypochlorite
This composition had the following analysis, in percent by weight and had a density of 1.25 g/cm².
This product was a single phase solution having a dynamic viscosity as measured at 20°C with a Brookfield viscometer using the No. 3 spindle at 100 rpm was 165 cp fresh and 180 cp after 24 hours.
The ionic strength of this composition was as calculated

EXAMPLE 2

20 g powdered anhydrous sodium carbonate and 20 g pelleted sodium hydroxide were dissolved in 200 ml soft water. 66.6 g of a 30% solution of a C_13/15 alkyl dimethyl amine oxide sold under the trade name Synprolam 35 DMO by ICI Ltd, was added to the alkaline salt solution with high shear agitation. The mixture was then added to 720 g of a sodium hypochlorite solution containing 10% available chlorine sold by British Drug Houses Ltd and further soft water was added provide a final composition containing:
The ionic strength I of this composition was found to be 5.61 moles/dm³ and the dynamic viscosity, measured by means of a Brookfield RVT viscometer (Spindle No. 3 at 100 rpm) at 20°C was 220 cp as measured 24 hours after the solution was prepared. The density of the solution was 1.25 g/cm³ so that the calculated kinematic viscosity v was 215.6 centistokes.

EXAMPLE 3

The following composition was prepared using the technique employed in Example 2.
The density of this solution was 1.25 g/cm and on this basis the ionic strength of the composition was calculated to be 5.50 g moles/dm3. Its viscosity (after 24 hours) was 220 centipoises.

EXAMPLE 4

The following compositions, prepared according to the technique of Example 1 illustrate the criticality of the various features of the invention.
Composition (a) is in accordance with the present invention whilst compositions (b), (c) and (d) are illustrative of prior art products. Comparison of compositions (a) and (b) demonstrates the different viscosity behaviour of products containing a) amine oxides of average chain length < C₁₃ and b) amine oxide of average chain length > C₁₃ both products being at the same ionic strength. Comparison of compositions (a) and (c) illustrates the role of ionic strength in providing the product viscosities of the present invention. In particular it should be noted that, for amine oxides having a chain length at the lower end of the range found to be useful in the invention, an ionic strength > 5.0 g moles/dm³ is required i.e. appreciably higher than the recited minimum of 3.0 g moles/dm³. Comparison of compositions (c) and (d) shows that for this amine oxide chain length, increasing amine oxide concentration does not compensate for the shortfall in ionic strength displayed by these compositions.

HXAHPLE 5

-- The composition set out in Example 4(a) and designated I was tested for its hard surface cleaning ability relative to a commercially available chlorine bleach product designated II and_having the following approximate analysis:
A synthetic soil was made up comprising by volume 8 parts ground garden soil, 4 parts roast lamb fat and 1 part milk. The soil was made up by mixing the fat and garden soil, heating and stirring to melt the fat and then dispersing the milk in the mixture.
15 cm square ceramic tiles were each soiled with 10 ml of the above soil, which was applied by pad and then allowed to dry for one hour or overnight (18 hours).
A soiled tile was then clamped with the soiled surface uppermost at an angle of 30° to the vertical and the soiled surface was divided equally into Left hand and Right hand areas. 14 ml of Product I was applied by syringe on to the Left Hand area and the same volume of Product II was applied to the Right Hand area, each application being arranged to cover the whole surface of the respective area. The areas were then left to drain for 10 minutes or overnight (18 hours) before being rinsed for 10 seconds with water at a rate of 8.5 litres/minute and a temperature of 20°C using a split rinsing head to treat both LH and RH areas simultaneously. Four replicate tests were carried out in two of which the tile areas to which the products were applied were also reversed.
Assessment of cleaning differences between LH and RH areas was carried out by visual grading using a 1-4 scale, higher values denoting enhanced cleaning. Results are given below in which the cleaning performance of Product I is expressed as a difference relative to that of Product II.
Time elapsed after
It can be seen that Product I provides significantly better soil cleaning than Product II under the conditions of the Test.

Example 6

The following composition was prepared according to the technique of Example 1:
The density of each of these compositions was 1.15 g/ml and the ionic strength for each composition was calculated to 3 be 3.5 g moles/dm³. The product viscosity was measured at 20°C using the technique of Example 1.
It can be seen that an amine oxide alkyl chain length of > C₁₃ is required in order to achieve the recited viscosity minimum of 180 centipoises. An increase in the level of C₁₃ DMAO to 5% by weight of the composition did not produce the desired viscosity increase.

EXAMPLE 7

The following compositions are in accordance with the invention.
All of the compositions exhibit viscosities in excess of 200 centipoises at 20°C after 24 hours.

Claims

1. A stable single phase aqueous detergent composition incorporating an amine oxide of formula R₁R₂R₃N→O wherein R₁ is an alkyl group in which the average number of carbon atoms is such that 13 < R₁ ≤ 18 and R₂ and R₃ are C₁-C₄ alkyl groups or C₂-C₄ hydroxy alkyl groups together with at least one ionisable water soluble compound characterised in that the amine oxide comprises the sole surfactant and is present in an amount of not more than 2.5% by weight of the composition and in that the at least one water soluble inorganic salt is present in an amount to provide a total ionic strength of the composition of at least 3.0 g moles/dm³, such that said composition has a viscosity of at least 180 cp at 20°C.

2. An aqueous detergent composition according to Claim 1 characterised in that the alkyl group R₁ comprises a mixture of groups containing 13 and 15 carbon atoms and comprising a mixture of moieties of structure,

and

the group R₄ being predominantly methyl, the composition also being characterised by a total ionic strength of at least 4.7 g moles/dm .

3. An aqueous detergent composition according to Claim 2 wherein a) and b) are present in approximately equal proportions by weight.

4. An aqueous detergent composition according to Claim 1 wherein R₁ contains an average of from 14 to 16 carbon atoms and is selected from linear moieties and moieties containing no more than 25% methyl branching.

5. An aqueous detergent composition according to any one of Claims 1-4 characterised in that the ionisable water soluble compound is an organic or inorganic builder or sequestrant salts.

6. An aqueous detergent composition according to-Claim 5 wherein the water soluble compound is selected from alkali metal carbonates, citrates, pyrophosphates, amino polyacetates and amino polyphosphonates.

7. An aqueous detergent composition according to any one of Claims 1-4 characterised in that substantially all of the ionic strength is provided by a mixture of alkali metal hypochlorite, alkali metal chloride and alkali metal hydroxide.

8. An aqueous detergent composition according to Claim 7 characterised in that it comprises from 1% to 1.5% C₁₄ linear alkyl dimethyl amine oxide, from 9.0% to 9.5% sodium hypochlorite, from 9.0% to 9.5% sodium chloride and from 0.5 to 1.5% sodium hydroxide.

9. An aqueous detergent composition according to either one of the claims 7 and 8 wherein the composition incorporates a bleach stable perfume.