GB2193510A - Bleach activators - Google Patents

Abstract

A bleach composition comprises a bleach precursor e.g. a perborate, and a bleach activator which is a mixture of phthalic anhydride and at least one of maleic and succinic anhydrides. The molar ratio of bleach precursor to total anhydride is from 0.75:1 to 20:1 and the molar ratio of phthalic anhydride to maleic and/or succinic anhydride is from 1.5:1 to 20:1. <IMAGE>

Description

SPECIFICATION Bleach activators This invention relates to bleach compositions comprising bleach activators.

Bleaching systems containing a so-called "bleach activator" are known and are used, for example, in laundry detergent powders. Initially a bleach precursor was used on its own, the precursor being a per-salt, e.g. a perborate, which released hydrogen peroxide at the washing temperature. It was found, however, that hydrogen peroxide was only released in quantity at temperatures of 70"C or above, and when the desire to lower washing temperatures to below 60"C became important, bleach activators were added. The bleach activators were compounds capable of reacting with the hydrogen peroxide to form per-carboxylates which are capable of providing a bleaching action at said lower washing temperatures. The bleach activators currently in common use are tetra-acetyl ethylene diamine (TAED) and penta-acetyl glucose (PAG).

Maleic anhydride, succinic anhydride and phthalic anhydride are also known to act as activators of per-salt bleaches, such as perborate. US patent No. 2,362,401 discloses the use of single solid organic acid anhydrides such as succinic anhydride, phthalic anhydride, benzoic anhydride, maleic anhydride, or glutaric anhydride, in a composition with a solid peroxygen bleach precursor compound such as sodium perborate monohydrate, and a water soluble detergent, the anhydrides being employed as bleach activators. These anhydrides, however, have not commonly been used as bleach activators since the activity of most acid anhydrides as bleach activators has been considered insufficient (see UK Patent 907,358). US Patent 3,338,839 discioses a 1:1 mole ratio mixture of phthalic and succinc anhydride and a 1:1 mole ratio mixture of phthalic and maleic anhydride as bleach activators.US 3,338,839 states in column 6 that "aliphatic dibasic anhydrides, such as maleic anhydride or succinic anhydride are not good activators for the peroxygen bleaching compound. Similarly, mixtures of these aliphatic dibasic anhydrides do not show any substantial improvement over the use of these dibasic anhydrides separately".

We have now found that mixes of greater than equimolar ratios of phthalic anhydride to maleic anhydride or succinic anhydride show a synergistic effect in their activity as activators of bleach precursors compared with the individuai anhydrides.

Thus, according to the present invention, a bleach composition comprises a bleach precursor, and a bleach activator, the bleach activator comprising a mixture of phthalic anhydride and at least one of maleic anhydride and succinic anhydride, the molar ratio of bleach precursor to total anhydride being from 0.75:1 to 20:1, and the molar ratio of phthalic anhydride to maleic anhydride and/or succinic anhydride being from 1.5:1 to 20:1.

Preferably, the molar ratio of bleach precursor to total anhydride is from 1.5:1 to 10:1. The most preferred range is 2:1 to 5:1.

It is also preferred that the molar ratio of phthalic anhydride to maleic anhydride and/or succinic anhydride is from 2:1 to 10:1. The most preferred range is 2:1 to 6:1.

The bleach precursor may be a per-salt e.g. an alkali metal perborate (preferably in mono- or tetra-hydrate form), percarbonate or persilicate. Certain clathrates may also be suitable e.g.

4M2SO4:2H202: 1MC1 (where M is an alkali metal) but these may require a separate source of alkalinity.

The bleach compositions of the present invention may be used on their own or in association with or incorporated into detergent compositions.

The bleach activator when used in association with or incorporated into laundry detergents is desirably in the form of granules coated with a material which prevents deterioration of the activator during storage but which releases the activator in the wash cycle. Examples of suitable coatings are soap, polyethyelene glycol, of molecular weight of at least 2000 mole', hydroxye thyl cellulose, carboxymethyl cellulose and hydroxyethylcarboxymethyl cellulose.

When used in a laundry detergent powder the quantity of bleach activator may be from 0.2 to 10% by wt of the powder and the quantity of bleach precursor may be from 5 to 40% wt.

Other components of the powder may be any of those known for use in such powders.

Preliminary experiments have not shown any antagonism between the bleach activators of the present invention and the other components. Such other components may comprise:- Surfactants, which may be anionic, cationic or non-ionic. Normally a mixture of anionic and non-ionic surfactants are used; Inorganic salts as builders and stabilisers e.g. alkali metal or alkaline earth metal phosphates, zeolites, sulphates, silicates or carbonates; Soaps; Chelating agents e.g. ethylene diamine tetra-acetic acid or nitrilotriacetic acid, or an organic phosphonate; Enzymes; Qptical brighteners; Suds suppressing agents; Anti-redeposition agents e.g. carboxy methyl cellulose.

The bleach activators may also be used in association with laundry detergent powders rather than actually incorporated with them. Thus they may be absorbed onto a porous substrate (e.g.

a high wet strength paper or fabric) and introduced into a washing machine in this way. Other methods of introducing the activitors separately into a washing machine may also be used e.g.

sachets.

The bleach precursor will normally remain in the powder.

The invention will now be described by way of example only and with reference to the accompanying drawings, in which Figs. 1 and 2 are representation of a three dimensional graph showing test results obtained with bleach precursor anhydride mole ratios of 1:1 and 2:1 respectively, and to the following experiments in which numbered examples represent examples of the invention while experiments identified as Tests are comparative experiments not according to the invention.

The action of the bleach. activators is illustrated by their oxidation of methylene blue dye in aqueous solution. The dye was present at a level of 5 ppm. The solution also contained sodium hydroxide (8.8x 10-3M) and sodium tetraborate (0.125M) to buffer the system to a pH of 9.5+0.2 at 25"C. Also present were calcium chloride (3 x 10-3M) and magnesium chloride (5 x 10-4M).

At the start of the experiment 200 ml of the above solution was equibrated to the desired test temperature. The absorbance of this solution was measured at 664 nm in a uv/visible spectrophotometer. The bleach precursor and bleach activator mixtue or single bleach activator (a total of 0.1 g) were then added. The absorbance of the solution is then measured again at 5 minute intervais up to 30 minutes. The bleaching activity is expressed as the percentage of methylene blue dye remaining with time.

Comparative Tests A-H The weight of bleach precursor (sodium perborate tetrahydrate) used in tests 1 to 8 below was 0.2 g. The weights of the activator(s) used is given in the following table:-

Test Weight phthalic Weight maleic Mole fraction phthalic anhydride anhydride anhydride in grams in grams in grams A 0 0.127 0 B 0.077 0.076 0.4 C 0.096 0.064 0.5 D 0.116 0.051 0.6 E 0.135 0.038 0.7 F 0.154 0.025 0.8 G 0.173 0.013 0.9 H 0.193 0 1.0 Dye bleaching tests at a constant mole ratio of bleach precursor to bleach activator of 1:1, and at a constant temperature of 60"C yielded the following results.

Comparative Test A Mole ratio of phthalic anhydride to maleic anhydride is 0:1 (mole fraction of phthalic anhydride is 0.0).

Time X methylene blue remaining 0 100 5 74.2 10 69.2 15 68.1 20 - 68.1 25 68.1 30 68.1 Comparative Test B Mole ratio of phthalic anhydride to maleic anhydride is 0.67:1 (mole fraction of phthalic anhydride is 0.4).

Time Z methylene blue remaining 0 100 5 79.1 10 68.7 15 62.6 20 59.3 25 57.7 30 57.1 Comparative Test C Mole ratio of phthalic anhydride to maleic anhydride is 1:1 (mole fraction of phthalic anhydride is 0.5).

Time Z methylene blue remaining 0 100 5 80 10 67.0 15 57.8 20 52.4 25 49.2 30 47.6 Comparative Test D Mole ratio of phthalic anhydride to maleic anhydride is 1.5:1 (mole fraction of phthalic anhydride is 0.6).

Time x methylene blue remaining 0 100 5 80.1 10 64.5 15 53.8 20 47.31 25 43.6 30 40.9 Comparative Test E Mole ratio of phthalic anhydride to maleic anhydride is 2.3:1 (mole fraction of phthalic anhydride is 0.7).

Time Z methylene blue remaining 0 100 5 74.7 10 58.2 15 46.7 20 39.6 25 35.2 30 33.0

Comparative Test F Mole ratio of phthalic anhydride to maleic anhydride is 4:1 (mole fraction of phthalic anhydride is 0.8).

Time Z methylene blue remaining 0 100 5 74.2 10 54.4 15 42.9 20 36.3 25 31.3 30 28.6 Comparative Test G Mole ratio of phthalic anhydride to maleic anhydride is 9:1 (mole fraction of phthalic anhydride is 0.9).

Time Z methylene blue remaining 0 100 5 68.1 10 47.0 15 35.7 20 28.7 25 24.9 30 22.7 Comparative Test H Mole ratio of phthalic anhydride to maleic anhydride is 1:0 (mole fraction of phthalic anhydride is 1.0).

Time Z methylene blue remaining 0 100 5 73.8 10 48.1 15 34.4 20 26.2 25 21.3 30 18.0

Examples 1-5 and Comparative Tests J-L As for Example 1, but 0.4 g of bleach precursor was used.

Dye bleaching tests at a constant mole ratio of bleach precursor to bleach activator of 2:1 and at a constant temperature of 60"C yielded the following results.

Comparative Test J Mole ratio of phthalic anhydride to maleic anhydride is 0:1 (mole fraction of phthalic anhydride is 0.0).

Time Z methylene blue remaining 0 100 5 72.2 10 68.9 15 68.3 20 67.7 25 67.7 30 67.7 Comparative Test K Mole ratio of phthalic anhydride to maleic anhydride is 0.67:1 (mole fraction of phthalic anhydride is 0.4).

Time | X methylene blue remaining 0 100 5 71.0 10 61.2 15 56.3 20 54.6 25 54.1 30 54.1 Comparative Test L Mole ratio of phthalic anhydride to maleic anhydride is 1:1 (mole fraction of phthalic anhydride is 0.5).

Time Z methylene blue remaining 0 100 5 72.8 10 57.8 15 52.2 20 47.8 25 46.7 30 46.1

Example 1 Mole ratio of phthalic anhydride to maleic anhydride is 1.5:1 (mole fraction of phthalic anhydride is 0.6).

Time X methylene blue remaining 0 100 5 72.0 10 57.7 15 50.5 20 46.1 25 44.0 30 42.9 Example 2 Mole ratio of phthalic anhydride to maleic anhydride is 2.3:1 (mole fraction of phthalic anhydride is 0.7).

Time X methylepe blue remaining 0 100 5 62.6 10 44.0 15 36.2 20 33.5 25 33.0 30 33.0 Example 3 Mole ratio of phthalic anhydride to maleic anhydride is 4:1 (mole fraction of phthalic anhydride is 0.8).

Time Z methylene blue remaining 0 100 5 63.2 10 45.1 15 36.8 20 34.1 25 33.0 30 32.4

Example 4 Mole ratio of phthalic anhydride to maleic anhydride is 9:1 (mole fraction of phthalic anhydride is 0.9).

Time X methylene blue remaining 0 100 5 59.8 10 40.2 15 32.6 15 32 6 20 29.9 25 28.3 30 27.7 Example 5 Mole ratio of phthalic anhydride to maleic anhydride is 1:0 (mole fraction of phthalic anhydride is 1.0).

Time X methylene blue remaining 0 100.0 5 67.0 10 45.0 15 33.5 15 33.5 20 27.7 25 25.3 30 24.2 Figs. 1 and 2 show three-dimensional surface graphs of points on a regular grid where the percentage of methylene blue remaining is plotted at 5 minute intervals against mole fraction of phthalic anhydride, for Examples 1 and 2, that is, for bleach precursor to total anhydride ratio of 1:1 and 2:1 respectively. The lines a, b, c, d, e, and f indicate the expected values of methylene blue remaining over time, if the phthalic and maleic anhydrides showed ideal behaviour, i.e. if no antagonism or synergism were shown in a mix upon their bleach activating ability.

The plots show that at molar ratios of phthalic anhydride to maleic anhydride below 1.5:1 (that is where the molar fraction of phthalic an hydride is below 0.6) suggests that there is a tendency to antagonism in the mixed anhydride system (lines a' to f') compared with the expected value (lines a to f) in its bleach activating activity. At molar ratio of phthalic anhydride to maleic anhydride greater than 1.5:1 there is a tendency to synergism in the bleach activating activity of the mixed anhydride system.

Claims (8)

1. A bleach composition which comprises a bleach precursor and a bleach activator, the bleach activator comprising a mixture of phthalic anhydride and at least one of maleic anhydride and succinic anhydride, the molar ratio of bleach precursor to total anhydride being fro 0.75:1 to 20:1 and the molar ratio of phthalic anhydride to maleic anhydride and/or succinic anhydride being from 1.5:1 to 20:1.

2. A bleach composition according to claim 1 wherein the molar ratio of bleach precursor to total anhdyride is from 1.5 to 10:1.

3. A composition according to claim 2 wherein the molar ratio of bleach precursor to total anhydride is from 2:1 to 5:1.

4. A composition according to any one of the preceding claims wherein the molar ratio of phthalic anhydride to maleic anhydride and/or succinic anhydride is from 2:1 to 10:1.

5. A composition according to any one of preceding claims wherein the molar ratio of phthalic anhydride to maleic anhydride and/or succinic anhydride is in the range 2:1 to 6:1.

6. A composition according to any one of the preceding claims wherein the bleach precursor is a salt of a per-acid.

7. A composition according to claim 6 wherein the bleach precursor is an alkali metal perborate.

8. A composition according to any one of the preceding claims which also contains a surfactant and a builder.