Detergent compositions

Abstract: A liquid detergent composition suitable especially for dishwashing by hand contains four components: (a) any nonionic detergent except alkyl ether sulphate, (b) an alkyl ether sulphate, the ratio of (a) to (b) being 2:1 to 1:10, (c) a lather booster which is a betaine or amine oxide the ratio of (a) to (c) being 3:1 to 1:3 and (d) a nonionic detergent in an amount between 35 and 50 weight %. Compositions of the invention can provide a combination of good performance and good mildness.

Description: The present invention relates to liquid detergent compositions suitable for use especially, but not exclusively, in fabric washing, shampoos, and above all, in manual dishwashing operations in both hard and soft water. The term "dishes" as used herein means any utensils involved in food preparation or consumption which may be required to be washed to free them from food particles and other food residues, greases, proteins, starches, gums, dyes, oils and burnt organic residues. Light-duty liquid detergent compositions such as are suitable for use in washing dishes are well-known. Many of the formulations in commercial use at the present time are based on a sulphonate-type anionic detergent, especially an alkyl benzene sulphonate, in conjunction with an alkyl polyethoxy sulphate (alkyl ether sulphate). The sulphonate-type detergent generally predominates. The use of conventional dishwashing liquids based on alkyl benzene sulphonate (ABS)/alkyl ether sulphate (AES) or on alkyl sulphate (PAS)/alkyl ether sulphate (AES) is seen to have deleterious influence on the hand condition of users. Hence mildness in washing-up liquid is considered a desirable quality, and many specially formulated products on the market make claims for it. Protein denaturation by surfactants is considered to be one of the major causes of skin irritation and skin roughness induced by surfactants (G Imokawa et al. JOACS 52 , 484-489, Dec 1975). The degree of surfactant denaturation of protein depends on the type of surfactants and their concentration. At present, the dishwashing formulations that are on the market which are less interactive with protein and hence considered to be milder are those based on a combination of ether sulphates and amine oxides. See for example US-A-3 928 249 (Procter & Gamble). In place of amine oxides, betaines can also be used. See for example US-A-4 554 098. However, such formulations - particularly with amine oxides - are expensive, not only because the active ingredients are expensive, but also because they require a large amount of expensive hydrotropes such as xylenesulphonate and/or ethanol to produce liquids which are stable and of acceptable viscosity. EP-A-0232153 (Unilever) discloses detergent compositions based upon a mixture of anionic and nonionic surfactants together with lather boosters, at least some of the anionic surfactants being alkyl ether sulphate. Example 9 of EP-A-0036625 relates to a surfactant system comprising 33% of a 9-10EO nonionic in combination with PAS, a specified AES mixture and a betaine. It is preferred to include high amounts of nonionic surfactants in order to produce a mild system because such surfactants are inert towards proteins in the skin and because nonionic-containing formulation require lesser amounts of expensive hydrotropes. Nonionics have also been shown to have a good soil removing potential, particularly of greasy soils often found on dishes. However, nonionics as a class are low foamers and produce unstable lather. GB-A-2 165 855 (Colgate) discloses mild nonionic-based light duty liquid detergents wherein the nonionic component exceeds 50% by weight of the total detergent content. However, for reasons stated above, such high nonionic-based formulations would have foam performance deficiencies. US-A-4 554 098 (Colgate) mentioned above discloses a mild dishwashing formulation based on an alkyl ether sulphate containing-an average of 5 to 12 moles of ethylene oxide in the molecule. However, such ether sulphates are not commercially easily available. Also, it is believed that the dioxane level in ether sulphate raw material increases with the increase in EO content of ether sulphate. Therefore, for ease of commercial exploitation the use of widely used and generally available ether sulphates containing less than 5 EO is preferred. Therefore there is need for the development of more cost-effective mild dishwashing formulations, which are based on relatively less expensive detergent raw materials and which also require lesser amounts of expensive hydrotropes. The present invention is based on the realisation that cost-effective mild liquid dishwashing formulations with adequate performance can be obtained by careful choice of the active ingredients and their preparation, in particular by restricting the main anionic detergent active present and including also selected amounts of alkyl ether sulphate, lather boosters and non-ionic detergent active material. According to a first aspect of the present invention, there is provided a stable detergent composition in liquid or gel form containing from 10 to 80%wt of an active detergent mixture of primary alkyl sulphate (PAS), alkyl ether sulphate (AES), water soluble nonionic detergent active material and betaine and/or amine oxide and also water, CHARACTERISED IN THAT: a) the AES has an average ethoxylation value of between 1 and 5, and weight ratio of PAS:AES is in the range 2:1-1:3; and, b) the molar ratio of PAS to said betaine and/or amine oxide is in the range 3:1-1:3; and, c) the nonionic detergent comprises more than 35%, but less than 50% by weight of the active detergent mixture. Compositions of the invention can give performance in detergency tests as good as those of conventional compositions containing alkyl benzene sulphonate, but are considerably milder. It is particularly surprising that mildness of predominantly nonionic-based formulations can wholly be maintained by substituting a substantial portion of the nonionic with ether sulphates containing less than 5 EO, but enhancing the foam performance significantly and thus improving cost effectiveness. Although in principle the concentration of the active detergent mixture may be as high as desired in the range 10 to 80%, provided that a stable liquid or gel product can be obtained, the range of 5 to 60% by weight is preferred, and aqueous liquid compositions with an active detergent mixture in the range of 5 to 40% by weight are of especial interest. Primary alkyl sulphate (PAS) for use in the invention component is preferably of the formula ROSO₃X where R is a C₈ to C₁₈ primary alkyl group and X is a solubilising cation. Suitable is Dobanol 23A of Shell in which R is predominantly C₁₂ and C₁₃. As will be explained in more detail below alkyl sulphate is a constituent of alkyl ether sulphates. The active detergent mixture may also include one or more other detergent actives used in liquid compositions, for example alkyl glyceryl ether sulphonates, or alkyl sarcosinates. The second essential component of the active detergent mixture is alkyl ether sulphate (sometimes called alcohol ether sulphate or alkyl polyethoxy sulphate) having at least one ethylene oxide residue per molecule. This will normally be provided by incorporating into the composition an alkyl ether sulphate which is a mixture of materials of the general formula: R - (OCH₂CH₂) n - OSO₃X wherein R is a C₁₀ to C₁₈ primary or secondary alkyl group, X is a solubilising cation, and n , the average degree of ethoxylation, is from 1 to 5, preferably from 3 to 4. Particularly preferred values of n are 3 and 4. R₃ is preferably a C₁₀ to C₁₆ alkyl group. In any given alkyl ether sulphate, a range of differently ethoxylated materials, and some unethoxylated material, will be present and the value of n represents an average. The unethoxylated material is, of course, alkyl sulphate and this contributes to the PAS content of the composition. The amount of alkyl sulphate in any alkyl ether sulphate will depend on average degree of ethoxylation n . When n is 3, alkyl sulphate typically constitutes 15 to 20% of the mixture, and less than this when n is 4 or more. When the proportion of alkyl sulphate is low, it may prove convenient to ignore it. Nevertheless, it contributes to the PAS content of the composition. When the average degree of ethoxylation is 2, alkyl sulphate typically constitutes 30% of the mixture provided as "alkyl ether sulphate". Such a mixture can provide both component PAS and AES. We have found that it is not feasible to use alkyl ether sulphate with an average degree of ethoxylation below 1.5. Unless the alkyl sulphate content of the ether sulphate is providing much or the whole of component PAS it is preferred that the alkyl ether sulphate is provided by material with an average of at least 2 or 2.5 ethylene oxide residues per molecule. Alkyl ether sulphate contains molecules with differing numbers of ethylene oxide residues in a statistical distribution. In an alkyl ether sulphate where the average degree of ethoxylation is 1.5 or greater, the proportion of molecules with a single ethylene oxide residue will not be substantially greater than the proportion with two ethylene oxide residues, nor the proportion with the most frequently encountered number of ethylene oxide residues (if this is more than two). Therefore this feature is an observable characteristic of the AES. If the average degree of ethoxylation is 2 or more, as preferred, the proportion of molecules with a single ethylene oxide residue will be less than the proportion with two ethylene oxide residues and the proportion with the most frequently encountered number. Preferred alkyl ether sulphates are mixtures of compounds of the above formula R-(OCH₂CH₂) n - OSO₃X in which n is any positive integer, with the proviso that the average EO value is less than 5. Examples of preferred alkyl ether sulphates for use in the present invention are Dobanol (Trade Mark) 23-3 from Shell in which the degree of ethoxylation (n) is 3 and the equivalent material in which the degree of ethoxylation is 4. These materials are based on C₁₂-C₁₃ (50% of each) primary alcohol (about 75% straight chain, 25% 2-methyl branched). Another preferred material is an alkyl ether sulphate based on Lial (Trade Mark) 123 from Chimica Augusta, which is a branched chain primary alcohol with a degree of ethoxylation of 3 to 4 and with a similar alkyl chain length distribution to Dobanol 23. Also preferred is Empicol MD (Trade Mark) from Albright and Wilson, with degree of ethoxylation of 4 and based on middle-cut coconut alkyl group. A suitable example of a secondary alcohol ether sulphate is a material derived from an alcohol such as Tergitol 15/S/3 (trade mark) of Union Carbide (this material itself is not at present available). The conventional process of manufacture of secondary alkyl ether sulphate is such that there is only a very small quantity of alkyl sulphate in the product. AES generally provides at least 12% of the active detergent mixture, preferably it provides at least 20 or 30%. It preferably provides not more than 40% of the active detergent mixture. The solubilising cations of the anionic detergent actives of the PAS and AES, denoted as X in the formulae above, may be any which provide the desired solubility of the anionic material. Monovalent cations such as alkali metal ions, ammonium and substituted ammonium are typical. Divalent ions giving adequate solubility may be used, and especially magnesium ions may be present to improve soft water performance and can be incorporated as magnesium salt of the anionic actives or as inorganic magnesium salts, or in the hydrotrope system. Betaine and amine oxide can be used as such or in a mixture. It is preferred to avoid using substantial amounts of the betaine or amine oxide, especially amine oxides, for the sake of economy and consequent cost effectiveness. Preferably then the amount of amine oxide is not more than 10% by weight of the active detergent mixture. Preferably the amount of betaine is not more than 30% by weight of this mixture. The total amount of amine oxide and betaine is preferably not more than 30% and more preferably not more than 15% or 10% by weight of the active detergent mixture. It is preferred to use betaines alone. Suitable betaines include simple betaines of formula and amido betaines of formula: In both formulae R is a C₈ to C₁₈ straight or branched alkyl group. It may be a lauryl group or a middle cut coconut alkyl group. R₆ and R₇ are each C₁ to C₃ alkyl or C₁ to C₃ hydroxyalkyl. Examples of sulphobetaines have the above formulae with -CH₂CO - 2 replaced by A suitable simple betaine is Empigen BB (TM) from Albright & Wilson. It has the formula quoted above in which R is C₁₂ to C₁₄ alkyl, derived from coconut, and R₆ and R₇ are both methyl. Also preferred is Tego L7 (TM) from Goldsmidt, which has a whole coconut alkyl group. Suitable amine oxides have the formula R₆ R₇N→O wherein R is a straight or branched chain C₈ to C₁₈ alkyl group and R₆ and R₇ are each C₁ to C₃ alkyl, or C₁ to C₃ hydroxyalkyl. A suitable amine oxide is Empigen OB (TM) from Albright & Wilson. In it R is middle-cut coconut alkyl and R₆ and R₇ are both methyl. The water-soluble non-ionic detergent active materials, are exemplified by materials conventionally used in detergent formulations. The betaines and amine oxides do not form part of the nonionic. The nonionic is preferably a polyalkoxylated material, notably it is one or more ethoxylated non-ionic detergent active materials. It is then desirable that such material should have an HLB value in the range from 12.0 to 16.0. The non-ionic may be a polyethoxylated aliphatic alcohol having an alkyl chain length of from C₈ to C₁₈ preferably C₈ to C₁₆, and an average degree of ethoxylation of from 4 to 14. Suitable nonionic detergents include short-chain high-foaming ethoxylated alcohols of the general formula R - (OCH₂CH₂) m - OH wherein R is an alkyl group, preferably straight-chain, having from 8 to 18, better 8 to 16 and yet more preferably 9 to 12, carbon atoms, and the average degree of ethoxylation m is from 5 to 14, more preferably 6 to 12. An especially preferred nonionic detergent is Dobanol 91-8 from Shell, in which R is C₉-C₁₁ (predominantly straight-chain) and m is 8, or alternatively Lialet C₁₁-10 EO. Alternative suitable materials are those in which R is a secondary alkyl having from 8 to 18, preferably 11-15, carbon atoms and m is from 5 to 14, preferably 6-12. An example is Tergitol (TM) 15/S/12 of Union Carbide (not available at present) or the material of the Softanol (TM) A series (from Japan Catalytic). Preferably the polyethoxylated alcohol mixture is stripped, to reduce odour imparted to the composition. Another possibility for the nonionic is an ethoxylate alkanolamide of the general formula wherein R is a straight or branched alkyl having from 7 to 18 carbon atoms, R₈ is an ethyleneoxy or propyleneoxy group Y is an hydrogen or -R₈(CH₂CH₂O) q H p is 1 or more and q is 0, 1 or more R may be lauryl or coconut alkyl. Examples of ethoxylated alkanolamide are Amidox L5 and Amidox C5 from Stepan Chemical Company. Further possibilities for the nonionic are ethoxylated alkylphenols and ethoxylated fatty acids, ie. polyethyleneglycol esters of fatty acids. The nonionic constitutes more than 35% by weight of the active detergent mixture, but less than 50%. Optionally present within the active detergent mixture of the composition of the invention may be one or more mono- or dialkanolamides, preferably C₈ to C₁₈, more preferably C₁₀-C₁₈ carboxylic acid mono- or di(C₂-C₃) alkanolamides. These have the general formulae R₄ - CO - NHR₅ and R₄ - CO - N(R₅)₂ respectively wherein R₄ is a C₇-C₁₇ aliphatic group, preferably straight- chain and preferably saturated, and R₅ is a hydroxyethyl or hydroxypropyl group. R₅ is preferably a 2-hydroxyethyl group. Materials of this type are generally made from fatty acids of natural origin and contain a range of molecules having R₄ groups of different chain lengths; for example, coconut ethanolamides consist predominantly of C₁₂ and C₁₄ material, with varying amounts of C₈, C₁₀, C₁₆ and C₁₈ material. Preferred are ethanolamides derived from so-called middle cut coconut fatty acid, most preferably from lauric acid. The mono- and di-ethanolamides may range from 5% to 20% of the detergent mixture. As well as the active detergent mixture and water, the liquid detergent compositions of the invention will generally need to contain one or more hydrotropes. Hydrotropes are materials present in a formulation to control solubility, viscosity, clarity and stability but which themselves make no active contribution to the performance of the product. Examples of hydrotropes include lower aliphatic alcohols, especially ethanol; urea; lower alkylbenzene sulphonates such as sodium, toluene and xylene sulphonates and combinations of these. Preferred are alcohol, urea and xylene sulphonate. Hydrotropes are expensive and take up room in a formulation without contributing to its performance, and it is therefore desirable to use as small quantities of them as possible. For example, the use of amine oxides as mentioned above requires a large amount of alcohol as hydrotrope. For this reason and because of expense, it is preferred to avoid the use of a substantial amount of any tertiary amine oxide in the present invention. In preferred forms of this invention the weight of hydrotrope in the composition is not more than 12% of the weight of the active detergent mixture. The compositions of the invention may also contain the usual minor ingredients such as perfume, colour, preservatives and germicides. The stable liquid detergent compositions of the invention may be used for all normal detergent purposes especially where foaming is advantageous, for example, fabric washing products, general purpose domestic and industrial cleaning compositions, carpet shampoos, car wash products, personal washing products, shampoos, foam bath products, and above all, manual dishwashing. The invention is further illustrated by the following nonlimiting Examples. EXAMPLES The foaming performance and mildness of various aqueous formulations were compared. These formulations I and II falling within the scope of the present application were compared with a comparable composition (A) containing over 50% by weight of nonionic active. Foaming performance was assessed by means of a modified Schlachter-Dierkes test based on the principle described in Fetter und Seifen 1951, 53 , 207. A 100 ml aqueous solution of each material tested, having a concentration of 0.04% active detergent in 24°H water (French hardness) at 45°C was rapidly oscillated using a vertically oscillating perforated disc within a graduated cylinder. After the initial generation of foam, increments (0.2 g) of soil (9.5 parts commercial cooking fat, 0.25 parts oleic acid, 0.25 parts stearic acid and 10 parts wheat starch in 120 parts water) were added at 15 second intervals (10 seconds' mild agitation and 5 seconds' rest) until the foam collapsed. The result was recorded as the number of soil increments (NSI score): a score difference of 6 or less is generally regarded as insignificant. Each result was typically the average of 3 or 4 runs. Several in-vitro and in-vivo methods for evaluating protein denaturation potency of surfactants and their mixtures have been reported (see Miyazowa et al, Int J Cos Sci 6 33-46 1984, and the references cited therein). One such method is the study of interaction of detergents with acid phosphatase enzyme either from skin (Prottey et al, Int J Cos Sci 6 263-273 1984) or from wheatgerm (Tanaka et al, Anal Biochem 66 489-498 1975). In vivo mildness of formulations can be assessed using a flex wash test. In this test neat products were rubbed on the forearm of panellists and rinsed. The process was repeated four times a day for five days and the level of erythema developed was assessed by trained assessors. A comparison of wheatgerm acid phosphatase (WGAP) test and flex wash test results indicated that formulations giving less than 50% enzyme inhibition under the test conditions are substantially mild; any mildness differences between products giving <40% inhibition do not show any detectable mildness differences in flex wash test, indicating that the enzyme test is very sensitive and that in a real life situation there is a threshold level of protein denaturation below which all actives and products are indistinguishably mild. The results of the WGAP test are expressed as percentage inhibition (ie 100% minus percentage activity remaining). Water gave no inhibition at all, ie 100% of activity remained. I II A Lialet 123-3S 10 - - Lialet 123-4S - 10 - Dobanol 23-A - - 8 Lialet 123-S 5 5 - Lialet C₁₁ 10EO 15 15 22 Empigen BB 6 6 6 Empigen LME 4 4 4 Plunger Test (0.04% AD) 24°FH 46 46 41 5°FH 45 46 43 % WGAP Inhibition 23 21 12 The Examples show that formulations I and II give a greater foaming performance than A. Although % WGAP inhibition of A is less than I and II, the effective mildness is no different, as explained above. Thus compositions of the present invention give a combination of mildness and performance.

Claims: A stable detergent composition in liquid or gel form containing from 10 to 80%wt of an active detergent mixture of primary alkyl sulphate (PAS), alkyl ether sulphate (AES), water soluble nonionic detergent active material and betaine and/or amine oxide and also water, CHARACTERISED IN THAT: a) the AES has an average ethoxylation value of between 1 and 5, and weight ratio of PAS:AES is in the range 2:1-1:3; and, b) the molar ratio of PAS to said betaine and/or amine oxide is in the range 3:1-1:3; and, c) the nonionic detergent comprises more than 35%, but less than 50% by weight of the active detergent mixture. A composition according to claim 1 wherein the weight ratio of PAS:AES is in the range 2:1 to 1:2. A composition according to any one of the preceding claims wherein the total amount of amine oxide and betaine is not more than 20% by weight of the active detergent mixture. A composition according to any one of the preceding claims which contains substantially no amine oxide. A composition according to any one of the preceding claims wherein the alkyl ether sulphate is provided by a mixture of materials of the general formula: R - (OCH₂CH₂) n - OSO₃X wherein R is a C₁₀ to C₁₈ alkyl group, X is a solubilising cation, and n, the average degree of ethoxylation, if from 2 to 5. A detergent composition according to any one of the preceding claims wherein the alkyl ether sulphate (b) is provided by a primary alkyl ether sulphate in which the alkyl groups R are such that less then 20% of material of alkyl chain length C₁₄ and above is present, and the average degree of ethoxylation n is from 3 to 5. A composition according to any one of the preceding claims wherein the nonionic is a material of chain length less than C₁₂.

Inventors: NAIK APPAYA RAGHUNATH, NAIK, APPAYA RAGHUNATH
Applicants: UNILEVER NV, UNILEVER PLC, UNILEVER N.V.
Application year: 1990
Main classification: C11D1
IPC codes: C11D1, A61K8, A61Q5, A61Q19