The present invention relates to an aqueous bleaching composition suitable for laundry and general domestic bleaching and disinfecting purposes. More particularly, it relates to an aqueous bleaching composition which also contains a synthetic detergent which is soluble in the composition thereby to impart a foaming capacity to the composition. The preferred bleaching agent is alkali metal hypochlorite.
Such an aqueous alkali metal hypochlorite composition comprising a foam-imparting synthetic detergent is known in the art, e.g. from British Patent Specification 886,084. This specification describes inter alia the use of betaine-type quaternary ammonium detergent surfactants in aqueous alkali metal hypochlorite compositions. Another suitable type of foam-imparting synthetic detergents are the trialkylamine oxides, containing one C₁₂-C₁₈ alkyl group and two C₁-C₃ alkyl groups.
Such compositions, while having the required foaming characteristics, present a problem, however, in that, during manufacture and packing of the composition the foaming of the composition makes it difficult to fill the containers properly; the composition foams out of the bottle, resulting in messy bottles which are not filled with the proper filling weight.
We have now found that this problem can be overcome by adding a suitable foam-depressing agent to the composition. We have found that if a foam-depressing agent is added which is not stable in the aqueous bleaching composition, the foam produced during manufacture and packing of the composition is significantly reduced. It may be reduced to an almost negligible level. However, the foaming capacity of the composition is restored upon storage of the packed composition owing to the instability of the foam-depressing agent in the composition, thus resulting in a foaming composition after storage thereof.
The features of this invention can be stated in several ways. In a first aspect the invention provides an aqueous bleaching composition alkali metal hypochlorite composition comprising a foaming synthetic detergent with a controlled foaming behaviour, characterised in that it has been obtained by the addition thereto of a foam-depressing agent which is not stable in the composition.
In a second aspect the invention provides a process for the production of an aqueous bleaching composition comprising an aqueous mixture of a bleaching agent and a foaming synthetic detergent, characterised by including a foam-depressing agent which is not stable in the mixture, packing the composition in containers while the foam-depressing agent remains effective, and optionally then storing the containers.
In another aspect the invention provides a bleaching composition obtained by including a foam-depressing agent in an aqueous mixture of a bleaching agent and a foaming synthetic detergent, which foam-depressing agent is not stable therein, packing the composition in containers while the said foam-depressing agent remains effective, and optionally then storing the containers.
The composition in the containers will change during storage. Initially it will be temporarily low-foaming or non-foaming, with a latent foaming property. As time passes the foam-depressing agent is replaced by products of its decomposition and the foaming property will appear.
The invention extends of course to containers with the bleaching composition therein. A preferred feature made possible by this invention is that the containers are filled substantially full with the composition.
The foam-depressing agent must be unstable in the composition. Foam-depressing agents which have been found very effective are silicones (more correctly polysiloxanes). These may be used in an amount which is at least 0.001% by weight of the composition. Amounts greater than 0.01% by weight will normally not be necessary, although amounts somewhat in excess of this may be used if desired, for instance up to 0.5% by weight of the composition.
Polysiloxanes which can be employed as antifoam agents have the structure:
wherein R and R', which may be the same or different, are alkyl or aryl groups having from 1 to 6 carbon atoms; and x is an integer of at least 20.
The preferred polysiloxanes are polydimethylsiloxanes where both R and R' are methyl groups. Usually the molecular weight is from 500 to 200 000.
Examples of suitable commercially available polydimethylsiloxanes are the "Silicone 200 Fluids", available from Dow Corning.
The composition will generally contain from 1 to 15% by weight of the bleaching agent. As mentioned, the preferred bleaching agent is alkali metal hypochlorite, for example sodium hypochlorite. Other bleaching agents may be used, for example hydrogen peroxide. The time taken for the composition to regain its foaming properties will of course depend on the rate of reaction between the bleaching agent and the silicone. Thus, hydrogen peroxide would take somewhat longer than a like amount of hypochlorite to degrade the silicone but this merely necessitates some increase in the time for which the composition is stored after packing.
Various foam-imparting detergents are available. Synthetic detergents are described in "Surface Active Agents" by Schwartz and Perry (Interscience 1949) and Volume II by Schwartz, Perry and Berch (Interscience 1958).
The synthetic detergents preferably used in this invention are amine oxides, more preferably trialkyl amine oxides in which one alkyl group has from 8 to 20 carbon atoms while the other two have from 1 to 4 carbon atoms. An example is lauryl dimethyl amine oxide.
The amount of surfactant included in the composition typically lies in the range from 0.05 to 1.5% by weight of the composition. Amounts somewhat greater than 1.5% by weight may be used if desired, for instance up to 5% by weight.
Usually the composition also contains free alkali to provide a desired alkaline pH. Other additives can be included, such as perfumes and colouring agents.
The following Example illustrates the invention.
Four bleaching compositions as set out in the Table below were prepared. The proportions stated in this Table are percentages by weight based on the whole composition as prepared.
The foaming characteristics of the compositions were assessed by shaking a quantity of each composition in accordance with a standardised procedure and then observing the height of foam generated. The compositions were analysed for residual bleaching agent after a period of storage. These test results are included in the Table below.
This example shows that the initial foaming is significantly reduced, but that the foaming characteristics reappear after 1-2 weeks storage, while there is no substantial loss of bleaching agent.