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(11) | EP 0 137 871 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Cleaning compositions |
| (57) @ Single phase aqueous liquid detergent compositions having a viscosity of > 180
centipoises at 20 °C are provided by amine oxide - anionic surfactant systems in which
the total surfactant level is not more than 3.0% by weight and in which the proportion
of amine oxide and anionic surfactant is in the range 80:20-99.9:0.1, more preferably
93.5:6.5-99.0:1.0, percent by weight, the compositions also comprising one or more
ionisable non surface active organic or inorganic compound in an amount to give an
ionic strength of at least 3.5 moles/dm3. |
[0001] This invention relates to aqueous liquid detergent compositions and more especially to aqueous liquid detergent compositions of high viscosity. A thick consistency is advantageous for a liquid detergent composition, particularly one employed for cleaning hard surfaces, as the increased viscosity assists the retention of the neat composition on non-horizontal surfaces thereby enhancing the effect of the active ingredient. Viscous liquid detergent compositions are also preferred by the consumer over 'thinner' products, apparently on aesthetic grounds.
[0002] High viscosity aqueous liquids can be produced in a number of ways. High concentrations of dissolved solid materials such as sugars give rise to syrups. The use of polymeric organic compounds such as gums and cellulose derivatives, that swell in aqueous media, is also a common technique used to increase viscosity. Surfactant compounds that interact with each other to produce micellar structures are also recognised as a means of thickening aqueous systems.
[0003] Examples of this surfactant micellar thickening technique, as applied to chlorine-bleach containing liquids, are disclosed in British Patent Specifications Nos. 1,329,086, 1,418,671 and 1,418,672, European Published Applications Nos 0021581 and 0030401, French Patent Applications Nos. 2,355,909 and 2,442,885 and British patent Application No. 2,003,522A. Certain of these prior art disclosures, notably European Patent Applications Nos. 0021581 and 0030401 teach the formation of liquids having viscosities of up to 150 centistokes at 25°C, while British Patent Specification No. 1,418,671 contemplates the preparation of aqueous media having viscosities of from 1 to 60 poise at 20°C as an intermediate step in the formation of a liquid containing a particulate abrasive suspended dispersion of a filamentary network in the aqueous media viscosity disclosed by BP 1,318,671 is about 50 centipoises.
[0004] Amine oxides are well known as components of thickened aqueous detergent compositions and are disclosed for this purpose in the above mentioned prior art. In general, the references in the art are to amine oxides in which the hydrophobic group conferring surface activity is a linear alkyl moiety but certain of the prior art disclosures, notably British Patent Application No. 2,003,522A and European 0021581 disclose the use of amine oxides in which the hydrophobic alkyl group is branched.
[0005] The Applicants have now discovered that clear, physically stable, liquid detergent compositions having low levels of surfactants (i.e.,,< 3%) by weight of the composition, can be formulated to have viscosities in excess of those taught by the prior art, by means of the use of certain amine oxide-anionic surfactant combinations in which the hydrocarbyl-group conferring hydrophobicity on the amine oxide has a specific range of chain length.
[0006] Furthermore, it has been found that a degree of branching of this hydrocarbyl group is desirable and that certain branched chain alkyl amine oxides are more weight effective than the corresponding linear chain alkyl amine oxides in producing clear, stable solutions having the desired rheoiogical properties.
[0007] According to the present invention therefore there is provided an aqueous single phase liquid detergent composition having a viscosity of >180 centipoises at 20°C and comprising not more than 3.0% by weight of a surfactant system consisting of a mixture of from 80% to 99.9% by weight of the system of a tertiary amine oxide having the formula R1R2R3N→0 wherein R1 is a C12-C18 alkyl group which is linear or which contains no more than 70% methyl or ethyl branching, R2 and R3 are C1-C4 alkyl or C1-C4 hydroxy alkyl, and from 0.1% to 20% by weight of the system of an anionic surfactant salt incorporating an aliphatic moiety having an average carbon chain length of more than 12 and less than 18 atoms, said moiety comprising at least 40% by weight of said anionic surfactant, together with at least one ionisable, non surface active organic, or inorganic, compound, said composition having an ionic strength of at least 3.50 moles/dm3.
[0008] In one compositional aspect of the invention the ionic strength is provided by a mixture of alkali metal hypochlorite, alkali metal hydroxide and alkali metal chloride. In a preferred form of this aspect of the invention the surfactant system comprises from 1.0% to 1.5% of a combination of a C14-C16 alkyl dimethyl amine oxide and an alkanoate or alkyl sulphate surfactant, the ratio of the amine oxide to anionic surfactants being within the range 19:1 to 99:1 by weight.
[0009] For the purposes of the present invention 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. v is characterised by the expression v = n/p,where n is the dynamic viscosity in centipoises and P is the density in g/cm3. Compositions in accordance with the present invention have a density in the range from 1.10 to 1.20 g/cm3, typically approximately 1.15 g/cm3, so that the numerical value of the kinematic viscosity in centistokes is very slightly less than that of the dynamic viscosity in centipoises.
[0010] The primary component of the detergent composition of the present invention is a surfactant system comprising a mixture of a C12-C18 amine oxide and a predominantly linear anionic surfactant containing an acyclic moiety of more than 12 and less than 18 carbon atoms.
[0011] Amine oxides suitable for the purposes of the present invention having the general formula
wherein R1 is a C12-C18 alkyl group which can be linear or which can contain up to 70% by weight of the group of methyl or ethyl branching and R2 and R3 are C1-C4 alkyl or C2-C4 hydroxy alkyl groups.
[0012] Preferably the average chain length of R1 is in the range from 13 to 16 carbon atoms and most preferably R1 has an average chain length of from 14 to 16 carbon atoms. The R1 group can be completely linear, as in material derived from natural fats and oils such as coconut and palm kernel oils, or may be branched as in material derived synthetically from petroleum sources. For the purposes of the invention, up to 70% by weight of the alkyl group R1 can contain methyl or ethyl branching, most of which is normally in the 2-position. Suitable sources of this type of alkyl group are alcohols produced by oxo synthesis which have either 40-50% methyl branching or 10-25% methyl branching, dependent on the catalyst employed. Most preferred are alkyl groups having a low level (<25%) of methyl branching.
[0013] The R2 and R3 groups are normally methyl or hydroxyethyl with the former being preferred for embodiments of the invention incorporating hypochlorite bleaches.
[0014] Anionic surfactants useful in the compositions of the present invention are those incorporating an aliphatic hydrocarbyl moiety having an average carbon chain length of more than 12 and less than 18 atoms, said moiety comprising at least 40% by weight of the anionic surfactant. Suitable anionic surfactants satisfying this constraint include alkanoates, C1-C5 alkyl esters of «sulphonated alkanoic acids, olefin sulphonates, alkyl benzene sulphonates in which the alkyl group contains 11-13 carbon atoms, s-alkane sulphonates, alkyl sulphates, certain alkyl polyethoxy sulphates, alkyl phosphates and certain alkyl ether phosphates. Mixtures of any of these surfactants can also be employed if desired. Preferred alkanoates are the C12-C14 alkali metal or alkaline earth metal soaps and mixtures thereof derived from e.g. coconut or palm kernel oils. The preferred α sulphonated alkanoic acid esters are alkali metal sulphonate salts of methyl ethyl propyl and butyl esters of C12-C14 alkanoic acids. Preferred olefin sulphonates are the alkali metal C12-C14 olefin sulphonates and the alkyl benzene sulphonates are preferably those with a linear alkyl chain.
[0015] The alkyl sulphates may be primary or secondary in type, the alkyl group being derived from primary or secondary alcohols. In turn these alcohols may be derived from any of the sources described above in connection with the long chain group of the amine oxide. The average number of ethoxy groups should not exceed 3 per mole where the alkyl chain length is from 12 to 14 carbon atoms and 4 per mole where the alkyl chain length is from 14 to 16 carbon atoms.
[0016] The cation is normally alkali metal, such as sodium, potassium, lithium, or ammonium, although for certain surfactants, alkaline earth metals such as magnesium can also be used.
[0017] Preferred anionic surfactants are primary alkyl sulphates with up to approximately 50% methyl branching, s-alkane sulphonates and alkyl benzene sulphonates. Soaps are also preferred anionic surfactants in mixtures in which the amine oxide:anionic surfactant weight ratio is > 20:1.
[0018] The surfactant system comprises a combination of the amine oxide and anionic surfactants in a mixture composed of from 80% to 99.9% by weight of amine oxide and from 20% to 0.1% by weight of anionic surfactant. In the broadest characterisation of this feature of the invention the surfactant system comprises not more than 3.0% by weight of the composition. Where the R1 alkyl chain length lies in the range of from 13 to 16 carbon atoms, the amount of the surfactant system required to provide a viscosity of 180 centipoises is not more than 2.5% by weight of the composition and the surfactant mixture comprises from 90.5% to 99.9% by weight of amine oxide and from 9.5% to 0.1% by weight of anionic surfactant. In the more preferred embodiments of the invention, the group R1 of the amine oxide has an average chain length of from 14 to 16 carbon atoms and the mixture comprises from 93.5% to 99.5% amine oxide and from 0.5% to 6.5% anionic surfactant. From 1% to 1.5% by weight of the composition of this mixture is sufficient to provide a viscosity of 180 centipoises. In the most preferred embodiments of the invention the surfactant mixture comprises from 95.0% to 99.0% of amine oxide in which R1 has a chain length of 14-16 carbon atoms and from 1.0% to 5% of anionic surfactant. The applicants have found that, in surfactant mixtures containing amine oxide in which the R1 alkyl group has a chain length in the range C14-C16, the use of a C12-C18 saturated or unsaturated fatty acid salt as the anionic surfactant is very effective in producing a viscosity of-7180 centipoises provided that the fatty acid salt comprises no more than approximately 5% of the surfactant mixture. Fatty acid salt levels in excess of approximately 5% by weight of the mixture give rise to the formation of a gel which is difficult to dispense from a container and apply to a non horizontal surface and is less acceptable aesthetically.
[0019] The surfactant systems described above display a viscosity-temperature relationship that has a parabolic profile with the maximum viscosity being exhibited at a temperature in the range from 0°C to 30°C. An increase in chain length of the R1 group increases the temperature at which this peak occurs while a reduction in R1 chain length and/or branching in the R1 group reduces the temperature at which the maximum, viscosity is produced by the system. A similar effect is seen for variations in chain length and linearity of the lipophilic aliphatic group of the anionic surfactant. Ideally, the viscosity of the composition should be independent of the temperature over a temperature range which encompasses the conditions normally encountered in domestic usage ie from 5°C to 25°C. The Applicants have found that this ideal is approached most closely by a surfactant system employing a blend of specific amine oxides as the respective amine oxide-anionic surfactant combinations display a peak viscosity at different temperatures.
[0020] The other essential component of the composition is at least one ionisable non surface-active organic, or inorganic compound which is present in an amount such that the ionic strength of the composition is at least 3.5 moles/dm3.
[0021] 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.
[0022] The ionic strength of the composition is calculated by means of the expression Total Ionic Strength
where C. is the molar concentration of the ionic species in g moles/dm 3
Zi is the valency of the species.
[0023] The function CiZi is calculated for each of the ionic species in solution, these functions are summed and divided by two to give the composition ionic strength.
[0024] 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 3.5 moles/dm where the composition contains only the amine oxide-anionic surfactant mixture would be approximately 8% to 9% 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%.
[0025] In the aspect of the invention directed 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 pyro-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.
[0026] 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 moles/dm 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 R1 alkyl chain length in the range 14 to 16 carbon atoms. This permits the use of low levels of both surfactants and ionisable compounds to obtain the desired viscosity and also minimises the rate of decomposition of the hypochlorite arising from the ionic strength of the solution and from reaction with the surfactant components. These preferred embodiments also utilise the amine oxide component in high weight ratios (20:1 to 40:1) to anionic surfactant components such as alkanoates and alkyl sulphates. In the bleach-containing embodiments it is highly preferred that the anionic surfactant component(s) be free of unsaturation in order to avoid attack by the hypochlorite bleach leading to adverse effects on both bleach level and solution viscosity.
[0027] 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.
[0028] 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 and the anionic surfactant. 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.
[0029] The invention is illustrated in the following examples in which percentages are expressed by weight of the composition unless otherwise stated.
EXAMPLES 1 TO 8
[0032] All of the compositions exhibited viscosities in excess of 200 centipoises at 20°C after 24 hours.
EXAMPLE 9
[0033] A premix was formed by dissolving 4.0g of 50% solution NaOH equivalent to 1% of Finished Product in 67g deionised water. To this preparation was added: 8.7g of 30% (by weight) solution of C14 (myristyl) dimethyl amine oxide, 0.4g of 20% (by weight) solution of sodium C13-C15 Alkyl Sulphate, and 0.1% of bleach stable perfume. This base stock was then agitated to form a homogeneous mixture. Finally, 120g NaOC1 containing 15.0% by weight of available chlorine (supplied by Ellis & Everard) was added to the base stock and agitation continued to give a single phase composition.
[0035] The Ionic strength I was calculated to be 3.69g mol/dm3, and the product viscosity as measured at 20°C by a Brookfield viscometer using a No 3 spindle at 100 rpm was 300 centipoises after 24 hours.
EXAMPLE 10
[0036] The procedure of Example 9 was repeated except that the amine oxide level was 1.1% by weight and the C13-C15 alkyl sulphate surfactant was replaced by sodium laurate at a level to give 0.04% soap in the finished product, the surfactant mixture comprising 96.5% amine oxide and 3.5% soap, an amine oxide:soap ratio of 27.5:1.
1. An aqueous single phase liquid detergent composition having a viscosity of >180
centipoises at 20°C and comprising not more than 3.0% by weight of a surfactant system
consisting of a mixture of:
a) from 80% to 99.9% by weight of the system of a tertiary amine oxide having the formula R1R2R3 N→0 wherein R1 is a C12-C18 alkyl group which is linear or which contains no more than 70% methyl or ethyl branching, R2 and R3 are C1-C4 alkyl or C1-C4 hydroxy alkyl, and from
b) 0.1% to 20% by weight of the system of an anionic surfactant salt incorporating an aliphatic moiety having an average carbon chain length of more than 12 and less than 18 atoms, said moiety comprising at least 40% by weight of said anionic surfactant,
together with at least one ionisable, non surface active organic, or inorganic, compound, said composition having an ionic strength of at least 3.5 moles/dm3.2. An aqueous single phase liquid detergent composition according to claim 1 wherein
the average chain length of R1 is in the range from 13 to 16 carbon atoms.
3. An aqueous single phase liquid detergent composition according to claim 2 wherein
the surfactant system comprises from 90.5% to 99.9%, by weight of amine oxide and
from 0.1% to 9.5%, by weight of anionic surfactant salt.
4. An aqueous single phase liquid detergent composition according to claim 3 wherein
the surfactant system comprises not more than 2.5% by weight of the composition.
5. An aqueous single phase liquid detergent composition according to any one of claims
1 to 4 wherein the average chain length of R1 is in the range from 14 to 16 carbon atoms.
6. An aqueous single phase liquid detergent composition according to claim 5 wherein
the surfactant system comprises from 93.5% to 99.5% by weight of amine oxide and from
0.5% to 6.5% by weight of anionic surfactant salt.
7. An aqueous single phase liquid detergent composition according to either of claims
5 and 6 wherein the surfactant system comprises not more than 1.5% by weight of the
composition.
8. An aqueous single phase liquid detergent composition according to any one of the
preceding claims wherein the anionic surfactant is selected from alkali metal or alkali
earth metal alkanoates, alkyl sulphates, alkane sulphonates, alkyl benzene sulphonates
in which the alkyl portion of the alkyl benzene is a linear C11-C13 moiety, and mixtures of any of the foregoing.
9. An aqueous single phase liquid detergent composition according to any one of claims
1 to 8 wherein the alkyl group R1 incorporates up to 25% methyl branching.
10. An aqueous single phase liquid detergent composition according to any one of claims
5 to 9 wherein the surfactant system constitutes from 1% to 1.5% of the composition
and comprises from 95% to 99.0% amine oxide and from 1.0% to 5% of an alkanoate or
alkyl sulphate surfactant.
11. An aqueous single phase liquid detergent composition according to any one of claims
5 to 10 wherein the at least one ionisable compound comprises a water soluble inorganic
or organic builder and/or sequestrant salt.
12. An aqueous single phase liquid detergent composition according to claim 11 wherein
the water soluble builder or sequestrant salt is selected from alkali metal citrate,
alkali metal amino polycarboxylate and alkali metal aminophosphonate salts.
13. An aqueous single phase liquid detergent composition according to claim 10 wherein
the at least one ionisable non-surface active organic, or inorganic compound, comprises
a mixture of alkali metal hypochlorite, alkali metal hydroxide and alkali metal chloride.