NO172354B - BLEACH MIXING - Google Patents

Abstract

Solutions of hydrogen peroxide which are alkaline and which are thickened with a combination of surfactant and electrolyte can be stabilized with colloidal aqueous tin (IV) oxide.

Description

This invention relates to liquid bleach mixtures which may be thickened liquids suitable for sale and use as household bleach. The mixtures according to the invention may be pourable liquids, although they are more viscous than water, or they may be even more viscous mixtures which cannot be easily poured. Thickening a pourable household bleach helps the user control the distribution of the mixture and delays runoff from surfaces to which it is applied.

It is necessary for a household bleach to be suitably stable, so that a substantial proportion of the bleach remains during storage between manufacture and use. Prior to the present invention, commercial liquid bleach products often used hypochlorite as a bleaching agent.

It is well known that hydrogen peroxide is unstable if no stabilizers are present. These counteract decomposition catalyzed by transition metal ions. Hydrogen peroxide gives a better bleaching effect if used under alkaline conditions. However, stabilization of hydrogen peroxide under alkaline conditions is difficult, and consequently commercial solutions of hydrogen peroxide have usually been acidic for reasons of stability.

EP-B-9839 describes that the stabilization of hydrogen peroxide under alkaline conditions can take place using certain specified phosphonate compounds. It also contains comparative results testing the effectiveness of different materials and stabilizers under alkaline conditions. These comparative results show that many materials known to stabilize acidic hydrogen peroxide have very little effect under alkaline conditions.

One material that has been described as a stabilizer for hydrogen peroxide in acidic solution is colloidal hydrous tin(IV) oxide. US 3781409 and US 3607053 are examples of descriptions of the use of sodium stannate as a stabilizer for acidic hydrogen peroxide solution. In these US patents, the sodium stannate is dissolved in an alkaline but peroxide-free solution, which is then added as a stabilizer to much larger volumes of acidic hydrogen peroxide solution. The sodium stannate will undergo hydrolysis to colloidal aqueous tin(IV) oxide in the solution. The alkaline solution contains other salts in addition to sodium stannate, but these are diluted to a very low electrolyte level when added to the acidic hydrogen peroxide solution.

Pourable liquid household bleach is often thickened by incorporating one or more surfactants, which in the presence of electrolyte thicken the solution so that it becomes more viscous than water.

The presence of electrolyte tends to cause decomposition of alkaline hydrogen peroxide solution. For example, we have found that a 4% by weight solution of hydrogen peroxide, made alkaline to pH 10 and containing 0.25% ethylenediaminetetramethylenephosphonic acid as a stabilizer (which is not as effective as phosphonates according to EP-B-9839), preserves 95 % of its hydrogen peroxide after two weeks of storage at 37°C. In contrast, 85% or less of the hydrogen peroxide was retained if the solution also contained 1% by weight 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 instead of sodium chloride as the added electrolyte. Doubling the amount of the phosphonate stabilizer had little effect on the rate of decomposition.

Thus, any attempt to produce an alkaline, liquid household bleach product thickened by surfactants, using hydrogen peroxide as a bleaching agent, will encounter the potential problem that thickening the solution would require the presence of an electrolyte, but that this electrolyte would serve to accelerate decomposition of the peroxide.

A further potential problem arises because an electrolyte itself tends to cause flocculation of colloidal suspensions. Accordingly, the presence of electrolyte also has the potential to produce a reduction in the effectiveness of any stabilizer that is in the form of a colloidal suspension.

It is surprising that - as we have now found - colloidal aqueous tin(IV) oxide can act as a very effective stabilizer for alkaline hydrogen peroxide solutions. It is also surprising that colloidal aqueous tin(IV) oxide will tolerate the incorporation of surfactant and electrolyte in amounts sufficient to effect thickening.

Accordingly, the present invention provides a liquid bleach mixture which is an alkaline, aqueous solution containing hydrogen peroxide and also containing colloidal aqueous tin (IV) oxide, see claim 1.

Preferably, the mixture also contains a viscosity-increasing agent which is one or more surfactants in the presence of electrolyte. Preferably, therefore, a mixture according to the invention also contains an electrolyte other than surfactant, together with at least one surfactant which, in the presence of electrolyte, serves to increase the viscosity of the solution.

The colloidal, hydrous tin (IV) oxide used as stabilizer is preferably formed in situ in the solution as the hydrolysis product of a soluble tin compound. A method for the production of such a liquid bleach mixture comprises incorporating into the mixture, successively or together, hydrogen peroxide, sufficient alkaline material to give the solution an alkaline pH, and a tin compound which can be hydrolysed to tin (IV) oxide, so that the tin compound is hydrolyzed in the solution to colloidal, aqueous tin(IV) oxide. The hydrolysis may take place in a solution already thickened by the presence of surfactant, although the peroxide may not have been added to the solution yet. Various tin compounds which undergo hydrolysis to form the tin(IV) oxide can be added to the solution.

The preferred ones are stannous sulfate and sodium stannate. Other stannous compounds may be used, including stannous dichloride and stannous tetrachloride.

The concentrations of tin compound incorporated into the mixture will lie in the range from 10"<4> molar to 10"<2> molar, preferably from 3 x 10"<3> to 6 x 10"<3> molar. The amount of tin compound should not be significantly greater than necessary, since an excess of it in itself can cause peroxide decomposition. An optimal concentration of the tin compound can be determined by preparing test solutions with different concentrations of the tin compound and analytical determination of the amount of peroxide retained during storage.

The mixtures according to this invention must have a pH in the range from 8.5 to 9.3. A buffer can be incorporated to determine the pH.

As already mentioned above, it is preferred to incorporate at least one surfactant to increase the viscosity of the mixture. It is desirable that this surface-active agent or surface-active agents have the ability to thicken a solution in the presence of a fairly low electrolyte concentration.

This may allow the electrolyte to be provided by salts which are in the mixture for another purpose, without the intentional addition of a salt for the sole purpose of increasing the ionic strength. Since electrolytes are known to be detrimental to the stability of hydrogen peroxide, it is desirable to keep the electrolyte concentration low. A further advantage of a low electrolyte concentration is a reduced tendency for the mixture to leave streaks on a surface cleaned with it.

One surfactant suitable for effecting thickening is alkyl ether sulfate of the formula:

R(OC 2 H 4 ) n OSO 3 M

where R is an alkyl group, preferably straight chain alkyl, containing 8-20 carbon atoms, n has an average value in the range from 0.5 to 12, preferably from 1 to 6, and M is a solubilizing cation, preferably an alkali metal such as sodium.

A pair of surfactants used to effect thickening may be a combination of a nonionic or amphoteric surfactant together with an anionic surfactant. Two specific possibilities are the combinations of: i) an amine oxide surfactant, preferably a trialkylamine oxide with one long-chain alkyl group of 8-20

carbon atoms, and two alkyl groups of 1-4 carbon atoms and

ii) an anionic surfactant which is either primary alcohol sulfate with 8-20 carbon atoms in the alkyl group, or

alkane sulfonate derived from alkane with 8-20 carbon atoms.

Additional surfactants may also be present. The total amount of surfactant(s) incorporated may be a small proportion of the mixture; more specifically, the thickening surfactant(s) will comprise from 0.75 to 3% of the mixture.

When primarily alcohol sulfate is used, the weight ratio between amine oxide and alcohol sulfate is preferably in the range from 82:18 or 80:20 to 65:35, better from 80:20 to 70:30.

Alkanesulfonate is preferred over alcohol sulfate, because the viscosity is less sensitive to changes in the mixture, making it easier to produce a final product with repeatable viscosity. The weight ratio between amine oxide and alkanesulfonate is preferably in the range from 80:20 to 50:50 or 65:35, better from 70:30 to 65:35.

The electrolyte concentration in a mixture according to this invention must be such that the total amount of inorganic salts, apart from the surfactant, is not greater than 5% by weight. The electrolyte level can be such that a concentration of electrolyte is obtained in the range from 0.05 to 0.30 molar, preferably from 0.1 to 0.2 molar. Higher concentrations can be used, but this is less preferred.

It is required that the concentration of hydrogen peroxide in mixtures according to this invention, calculated as pure H 2 O 2 , lies in the range from 1 to 15% by weight, preferably from 2 to 10% by weight.

A suitable viscosity for a pourable mixture with the appearance of a thick liquid is a dynamic viscosity in the range from 50 to 250 centipoise (0.05-0.25 Pa.sec), preferably approx. 100 centipoise (0.1 Pa.sec). More viscous liquids, for example with viscosities in the range of 250 to 1000 centipoise or more, are also within the scope of the invention.

Since the compositions of this invention are usually aqueous, they will usually have a specific gravity close to 1. Consequently, values for kinematic viscosities (in stokes) will numerically be approximately the same as values for dynamic viscosities (in poise). Dynamic viscosities expressed in Pascal.sec will be approximately 1000 times kinetic viscosities expressed in m<2>.sec"<1>.

Example 1

Preparations containing the components were produced

listed in Table 1 below. The mixtures were stored in plastic

bottles at 37°C. At intervals, aliquots were removed and titrated with potassium permanganate to determine the level of residual hydrogen peroxide. The results are included in table 1.

The viscosity of these preparations was measured using

a capillary viscometer of the Ubbelohde type and found to be approx. 100 cS.

The stabilizer according to EP 9839 was

diethylenetriaminepenta(methylenephosphonic acid).

Example 2

The procedure according to example 1 was repeated using preparations 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, but with and without 3.0% borax decahydrate. Glass bottles were used, which is somewhat detrimental to stability. In each case the initial pH was 9.6. Proportions of hydrogen peroxide that remained after 28 days was:

Example 3

The procedure according to example 1 was repeated using a different surface-active agent and with stannous chloride as stannous salt. The surfactant used was a straight-chain alkyl ether sulfate with the general formula: where the alkyl group R was straight-chain C12 and C13 alkyl groups, and n had an average value of 3. A comparative experiment replaced the stannous chloride with the same phosphonate stabilizer according to EP 9839 as used in Example 1. The compositions and results are listed in the following table. The viscosities were determined using a roto-viscometer of the Haake type and were approx. 100 cP at a shear speed of 21 sec"<1>.

Example 4

An alkaline solution of hydrogen peroxide was prepared, containing 4% by weight of hydrogen peroxide (calculated as anhydrous) and sodium hydroxide to achieve a pH of 10, and a 5.7 x 10"<3 >molar amount of stannous chloride which was hydrolyzed to colloidal aqueous tin(IV) oxide.

The mixture was stored at 40°C, and the amount of residual hydrogen peroxide was determined analytically at intervals. It was found that 75% of the hydrogen peroxide remained after 3 weeks.

Although this test was performed without surfactant or much electrolyte present, it confirms the effectiveness of colloidal tin(IV) oxide as a stabilizer in alkaline solution.

Example 5

Alkaline solutions of hydrogen peroxide were prepared containing surfactant, sodium chloride and tin(IV) chloride, which were hydrolysed to colloidal aqueous tin(IV) oxide. Two combinations of surfactant were used.

The amounts of surfactant and sodium chloride were such that viscosities were obtained that were far greater than that preferred for a pourable type of bleach product. Smaller amounts could be used to obtain a "thick liquid" type bleach product.

In each case, the concentration of hydrogen peroxide, calculated as anhydrous, was 4% by weight. The solutions were made alkaline to pH 10 with sodium hydroxide.

Tin (IV) chloride was used at a concentration of 2.3 x 10"<3 >molar.

One surfactant system consisted of 4.5 wt% C12-C14 alkyldimethylamine oxide and 4.5 wt% sodium lauryl sulfate. This was used with a sodium chloride concentration of 9% by weight.

The second surfactant system consisted of 5% by weight of C₁-C₂-sec alcohol ethoxylated with an average of 3 ethylene oxide residues, and 5% by weight of sodium lauryl sulfate. This combination was used with 3.37% by weight of sodium chloride.

The solutions were stored at 40°C, and the amount of residual hydrogen peroxide was determined at intervals. The amounts of hydrogen peroxide remaining were found to be between 80 and 85% with each of the surfactant combinations.

Example 6

A base solution was prepared containing tallow dimethylamine oxide, sodium alkanesulfonate and borax. This was used to form solutions containing hydrogen peroxide and colloidal tin (IV) oxide, but two methods were used.

In one method, stannous chloride dihydrate was added to the base solution and stirred until completely dissolved or dispersed, after which hydrogen peroxide solution was added. The solution pH at this stage was 6.5. It was adjusted to pH 9.9 by the addition of 20% w/v sodium hydroxide solution and a portion of distilled water.

The amounts used were such that the mixture contained:

In the alternative method, a suspension of tin (IV) oxide was prepared by dissolving 5 g of tin (II) chloride dihydrate in approx. 115 g of distilled water, and then addition of sodium hydroxide solution, achieving a pH of 9.7. The resulting tin(IV) oxide suspension was stored overnight.

Hydrogen peroxide was added to the base solution, followed by sodium hydroxide solution and a portion of distilled water, achieving a pH of 9.9. A small amount of suspension was then added. This was calculated to be the amount of suspension formed by 0.14 g of SnCl2.2H20. Other amounts were as in the first procedure.

The solutions were both stored at 37°C (for accelerated aging) and the concentration of residual hydrogen peroxide was determined by analysis after 48 and 120 hours. The results were as follows:

Claims (3)

1. Liquid bleach mixture, characterized in that it comprises an aqueous alkaline solution with a pH in the range from 8.5 to 9.3 and which contains hydrogen peroxide,' calculated as pure H202, in the range from 1 to 15% by weight, based on the mixture, of an electrolyte other than surfactant agent, the amount of electrolyte in solution being such that the total amount of inorganic salts in the mixture does not exceed 5% by weight, based on the entire mixture, at least one surface-active agent which, in the presence of electrolyte, serves to increase the viscosity of the solution, and which is a combination of a nonionic or amphoteric surfactant and an anionic surfactant, the amount of surfactant present being in the range of 0.75 to 3% by weight, based on the total composition, and also containing colloidal aqueous tin ( IV)-oxide, the concentration of tin compound being in the range from 10"<4> to 10"<2> molar. 2. Mixture according to claim 1, characterized in that the surfactant is an alkyl ether sulfate with the formula N where R is an alkyl group containing 8-20 carbon atoms, n has an average value in the range from 0.5 to 12 and M is a solubilizing cation. 3. Mixture according to claim 1, characterized in that the surface-active agent is a combination of (i) a trialkylamine oxide with one C8-C20 alkyl group and two q-C4-alkyl groups and (ii) either a C8-C20 alkane sulfonate or a C8-C20 alcohol sulfate.