Bleaching composition

Abstract: Solutions of hydrogen peroxide which are alkaline, can be thickened with a combination of surfactant and electrolyte without unacceptable loss of stability. Surfactant may be alkyl ether sulphate: R(OC₂H₄) n OSO₃M or a combination of amine oxide R(CH₃)₂NO with alkane sulphonate RSO₃M or alcohol sulphate ROSO₃M where any R is C₈ to C₂₀ alkyl and any M is a solubilising cation and n is 0.5 to 5. Stabiliser is present and may be colloidal hydrous stannic oxide or may be a phosphonate as specified in EP-B-9839.

Description: This invention relates to thickened liquid bleach compositions which may be suitable for sale and use as a domestic bleach. Pourable domestic bleach is frequently thickened by including one or more surfactants which, in the presence of electrolyte, act to thicken the solution rendering it more viscous than water. Thickening of a pourable domestic bleach helps the user to control dispensing of the composition and retards drainage from surfaces to which it is applied. This invention relates to such compositions which include surfactant and electrolyte to increase the viscosity. The compositions of the invention may be pourable or may be even more viscous so as not to be poured easily. A domestic bleach needs to be adequately stable so that a substantial proportion of the bleaching agent survives during storage between manufacture and use. Prior to this invention commercial liquid bleach products have frequently utilised hypochlorite as bleaching agent. It is well known that hydrogen peroxide is unstable unless stabilising agents are present. These counteract decomposition catalysed by transition metal ions. Hydrogen peroxide gives better bleaching action if used under alkaline conditions. However, stabilisation of hydrogen peroxide under alkaline conditions is difficult and in consequence commercial solutions of hydrogen peroxide have generally been acidic for the sake of stability. Certain phosphonates able to stabilise hydrogen peroxide in alkaline solution are disclosed in EP-B-9839 (Unilever). The presence of electrolyte tends to cause decomposition of alkaline hydrogen peroxide solution. For instance, we have found chat a 4% by weight solution of hydrogen peroxide, made alkaline to pH 10 and containing 0.25% of ethylene diamine tetramethylene phosphonic acid as stabiliser (which is not as effective as the phosphonates in accordance with EP-B-9839) was found to retain 95% of its hydrogen peroxide after two weeks storage at 37°C. By contrast, 85% or less of the hydrogen peroxide was retained if the solution also contained 1% by weight of sodium chloride, while only about 50% of the hydrogen peroxide was retained if the solution contained 10% by weight of sodium chloride. Similar results were observed using sodium tripolyphosphate rather than sodium chloride as the added electrolyte. Doubling the quantity of the phosphonate stabiliser had little effect on the rate of decomposition. US 3388069 (Lindner) discloses peroxide based compositions which have surface active properties due to the presence of C10-C24 amine oxides. Amine oxides are amphoteric surfactants and are said to have some stabilizing effect on peroxides at a pH of up to 8.0 (see Lindner col. 2 line 69). It is believed that the compositions will not thicken in the absence of the anionic surfactant. The compositions of Lindner do not have storage stability at higher pH: the compositions of Lindner are often stored at a rather lower pH than they are intended for use at, and an alkali is added before use. Thus, any attempt to make a surfactant-thickened, alkaline domestic liquid bleach product using hydrogen peroxide as the bleaching agent would encounter the potential problem that the thickening of the solution would require the presence of some electrolyte but that this electrolyte would serve to accelerate decomposition of the peroxide. We have now found, however that it is possible to formulate an aqueous alkaline solution of hydrogen peroxide which is thickened with surfactant and electrolyte yet does have sufficient stability to be useful as a commercial product. According to the present invention there is provided a liquid, bleaching composition comprising an aqueous alkaline solution of pH 8.0-10.5, containing: a) 1-15% by weight hydrogen peroxide, b) a stabilizer for hydrogen peroxide, c) 0.05-0.30 Molar electrolyte other than surfactant, and, d) 0.75-3% by weight of a combination of: i) an amphoteric surfactant, and, ii) an anionic surfactant which is either a C8-C20 alkane sulphonate or a C8-C20 alcohol sulphate . We have found that use of a surfactant as specified above is advantageous in achieving thickening with a fairly low electrolyte concentration. This may make it possible for the electrolyte to be provided by ions which are in the composition for other reasons, without deliberate addition of salt for the sole purpose of enhancing ionic strength. Apart from considerations of peroxide stability, a benefit of a low electrolyte concentration is a reduced tendency for the product to leave streaks on a surface which is cleaned with it. A preferred possibility for the amphoteric surfactant is a trialkyl amine oxide with one long chain alkyl of 8 to 20 carbon atoms and two alkyl groups of 1 to 4 carbon atoms. Then, if primary alcohol sulphate is the anionic surfactant the weight ratio of amine oxide:alcohol sulphate is preferably in the range from 82:18 to 65:35, better 80:20 to 65:35, even better 80:20 to 70:30. Alkane sulphonate is preferred over alcohol sulphate because the viscosity is less sensitive to changes in the composition, so making it easier to produce an end product with repeatable viscosity. The weight ratio of amine oxide to alkane sulphonate (when this is used) is preferably in the range from 80:20 to 50:50 or better 65:35, and preferably in the narrower range from 70:30 to 65:35. One or more further surfactants may also be included, within the scope of this invention. Stabiliser for the hydrogen peroxide may be a phosphonate sequestrant in accordance with EP-B-9839, which defines the phosphonate compounds as of the general formula: wherein n = 1-4; and X is H or a water-soluble cation selected from the group consisting of alkali metals, ammonium, substituted ammonium and alkaline earth metals. Such a sequestering agent may be used in an amount from 0,01 to 1% by weight. This is approximately 1.5 x 10⁻⁴ to 2 x 10⁻² molar. These compounds are effective to counter decomposition catalysed by iron but are less effective against manganese. We have found that it may be possible to prevent contamination by traces of manganese (e.g. by use of sufficiently pure raw materials) so that a separate stabiliser against manganese may not be required. However, if required a separate stabilising agent to counteract manganese may be a phosphate salt used in an amount from 0.5% up to 4% by weight, preferably 1 to 3% (reckoned as anhydrous salt). Tetrasodium pyrophosphate may be used as such a salt. Another possible stabilising agent which we have found to be effective in alkaline solution against decomposition caused by transition metals including both iron and manganese, is colloidal hydrous stannic oxide. This stabilising agent is preferably formed in-situ in the solution as the product of hydrolysis of a soluble tin compound. Various tin compounds can be added to the solution to undergo hydrolysis to form the stannic oxide, including tin sulphate, sodium stannate, tin dichloride and tin tetrachloride. Suitable concentrations of tin compound in the composition may lie in the range from 10⁻⁴ molar to 10⁻² molar, preferably 3 x 10⁻³ to 6 x 10⁻³ molar. The quantity of tin compound should not be substantially greater than necessary, since excess of it can itself cause peroxide decomposition. An optimum concentration of the tin compound (or any stabiliser) can be determined by making test solutions with various concentrations of the stabiliser and analytically determining the amount of hydrogen peroxide remaining after a period of storage. An appropriate viscosity for a pourable composition having the appearance of a thick liquid is a dynamic viscosity in the range from 40 to 250 centipoise (0.05 to 0.25 Pa.sec), preferably about 100 centipoise (0.1 Pa.sec). More viscous liquids for example with viscosity in the range from 250 to 1000 centipoise or more are also within the scope of the invention. Since the compositions of this invention are generally aqueous, they will usually have specific gravity close to unity. Consequently values of kinematic viscosities (in stokes) will be numerically approximately the same as values of dynamic viscosity (in poise). Dynamic viscosities expressed in Pascal.sec will be approximately 1000 times kinetic viscosities expressed in m² .sec⁻¹. The pH of the solution is preferably in the range from 8.5 to 9.8 or 10.0. With a phosphonate stabiliser it is further preferred that the pH is in the narrower range from 9.2 to 9.8, while with colloidal stannic oxide as stabiliser it is preferable to use a slightly lower pH in the range from 8.7 to 9.3. A buffer may be included to maintain pH at the desired value, but this may not be necessary. A phosphate, if present, will give a buffering action. Another compound which may be used for this purpose is borax. The concentration of hydrogen peroxide in compositions of this invention, reckoned as pure H₂O₂, desirably lies in the range from 2 to 10% by weight. Example 1 Formulations were prepared containing the constituents set out in Table 1 below. The compositions were stored in plastic bottles at 37°C. At intervals aliquots were removed and titrated with potassium permanganate to determine the level of hydrogen peroxide remaining. Results are included in Table 1. The viscosity of these formulations was measured using a Ubbelohde capillary viscometer and found to be approximately 100cS. Constituent % by weight A B C Hydrogen peroxide (reckoned as anhydrous) 5 5 5 Tallow dimethylamine oxide 1.0 1.0 1.0 Sodium alkane sulphonate 0.5 0.5 0.5 Perfume 1.0 1.0 1.0 Tetrasodium pyrophosphate (reckoned as anhydrous) 1.8 - - Phosphonate stabiliser according to EP 9839 0.15 - - Borax (reckoned as anhydrous) - 1.6 1.6 Sodium stannate trihydrate - 0.5 0.1 Sodium hydroxide to give: pH 9.6 pH 9.6 pH 9.0 Water ----- balance to 100% ----- H₂O₂ remaining after 50 days: 85% 79% H₂O₂ remaining after 100 days: 96% Example 2 The procedure of Example 1 was repeated, using formulations with the same amounts of hydrogen peroxide, surfactant, perfume and dye. Various tin compounds were used at a concentration of 6 x 10⁻³ molar, both with and without 3.0% borax decahydrate. Glass bottles were used, which are somewhat detrimental to stability. In every case pH was 9.6 initially. Proportions of hydrogen peroxide remaining after 28 days were:- SnCl₂ with borax 68% Na₂SnO₃ with borax 47% SnSO₄ with borax 45% Na₂SnO₃ without borax 96% SnCl₄ without borax 68% Example 3 A range of formulations were prepared, all containing: Hydrogen peroxide 5.0% reckoned as anhydrous Tetrasodium pyrophosphate decahydrate 3.0% (approx 1.8% reckoned as anhydrous) Phosphonate stabiliser according to EP 9839 0.3% Perfume 0.1% Sodium hydroxide to pH 9.6 Thickening system variable Water --- balance to 100% --- The thickening systems used various constituents and varied both in the properties and total amounts of materials employed. The thickening systems contained tallow dimethylamine oxide (AO) together with sodium lauryl sulphate (SLS), or sodium alkane sulphonate (SAS), which was a secondary alkane sulphonate derived from an n-alkane mixture which is principally C₁₃ to C₁₈. Viscosities of the formulations were measured using a Ubbelohde capillary viscometer. The results obtained are shown in the accompanying Figures. Figure 1 shows variation in viscosity with the proportion of SLS in an AO/SLS mixture, while the total amount of AO plus SLS is varied from 1.1% to 1.9% by weight of the composition. Figure 2 shows variation in viscosity for AO/SAS mixtures while the total of AO plus SAS is varied from 1.2% to 2.6% of the composition. It can be seen that the viscosity maxima are broader peaks, while the maximum viscosity is less sensitive to variation in the total amount of AO plus SAS. For instance in Figure 1 the concentration of surfactant to give a viscosity of 100cS is 1.2%, and an increase from this of 0.2%, up to 1.4%, would double the viscosity to 200cS. In Figure 2 1.4% total surfactant gives a viscosity of 100cS. Increasing by 0.2% increases the viscosity to 150cS and a larger increase, to 1.8%, is required to achieve 200cS. Example 4 Alkaline solutions of hydrogen peroxide were prepared containing surfactant, sodium chloride and stannic chloride which hydrolysed to colloidal hydrous stannic oxide. The quantities of surfactant and sodium chloride were such as to give viscosities well in excess of that preferred for a pourable "thick liquid" type of bleach product. Smaller quantities could be used to give a "thick liquid" type of bleach product. The initial concentration of hydrogen peroxide, reckoned as anhydrous, was 4% by weight. The solutions were made alkaline to pH 10 with sodium hydroxide. Stannic chloride was used at a concentration of 2.3 x 10⁻³ molar. The surfactant system consisted of 4.5% by weight of C₁₂-C₁₄ alkyl dimethyl amine oxide and 4.5% by weight sodium lauryl sulphate. This was used with a sodium chloride concentration of 95 by weight. The solutions were stored at 40°C and the amount of hydrogen peroxide remaining was determined at intervals. It was found that the amounts of hydrogen peroxide remaining were between 80 and 85%.

Claims: A liquid, bleaching composition comprising an aqueous alkaline solution of pH 8.0-10.5, containing: a) 1-15% by weight hydrogen peroxide, b) a stabilizer for hydrogen peroxide, c) 0.05-0.30 Molar electrolyte other than surfactant, and, d) 0.75-3% by weight of a combination of: i) an amphoteric surfactant, and, ii) an anionic surfactant which is either a C8-C20 alkane sulphonate or a C8-C20 alcohol sulphate . A composition according to claim 1 wherein the surfactant is a combination of (i) a trialkyl amine oxide having one C₈ to C₂₀ alkyl group and two C₁ to C₄ alkyl groups and (ii) a said anionic surfactant. A composition according to claim 1 or 2, wherein the stabiliser is colloidal hydrous stannic oxide. A composition according to claim 1 or 2, wherein the stabiliser is a compound of the formula: wherein n = 1-4; and X is H or a water-soluble cation selected from the group consisting of alkali metals, ammonium, substituted ammonium and alkaline earth metals.

Inventors: CLARKE DAVID ELLIS, CLARKE, DAVID ELLIS
Applicants: UNILEVER NV, UNILEVER PLC, UNILEVER N.V.
Application year: 1989
Main classification: C11D3
IPC codes: C11D10, C11D3, C11D1