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(11) | EP 0 184 888 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Coloured bleaching compositions |
| (57) The invention provides an aqueous, coloured bleaching composition, particularly a
thickened chlorine bleaching composition, in which as colouring agent a colloidally
stable, coated pigment is used which has been coated with a bleach-resistant polymer,
e.g. polystyrene. These coated pigments are colloidally stable in the bleaching composition,
in many cases more stable than uncoated pigments. |
[0001] The present invention relates to aqueous, coloured, bleaching compositions, particularly alkali metal hypochlorite compositions.
[0002] By bleaching compositions are meant aqueous compositions comprising an oxygen or chlorine bleaching agent, such as hydrogen peroxide, organic or inorganic persalts (with or without a bleach precursor), organic or inorganic peracids, and alkali metal hypochlorites.
[0003] Hereinafter the invention will be described and exemplified with particular reference to alkali metal hypochlorite compositions, but it is to be understood that the present invention is also applicable to the above other bleaching compositions..
[0004] Aqueous solutions of alkali metal hypochlorites have been known and used since ages unknown. Normally, they consist of an alkali metal hypochlorite, dissolved in water, and are used for general bleaching and disinfecting purposes. Such solutions are normally straw-coloured, and in order to make them more attractive and more distinguishable from other household products, attempts have been made to impart to them a more distinguishable, aesthetically attractive colour.
[0005] These hypochlorite solutions, however, form a strongly oxidizing environment, and consequently the choice of a colouring additive is very limited, restricted to only such colouring additives that are stable in these strongly oxidizing media. Potassium permanganate and potassium dichromate are such colouring agents, but they impart aesthetically less attractive colours (purple and yellow). Ultramarine Blue has also been proposed, but this pigment tends to settle out from the compositions during storage.
[0006] During the last decade, thickened aqueous hypochlorite solutions have become known and marketed. These are aqueous solutions of an alkali metal hypochlorite which have been thickened by the inclusion therein of a mixture of two different detergent surfactants. The above problems accompanying colouring aqueous hypochlorite solutions also occur on colouring such thickened compositions, but the problem of storage stability arises even with such thickened compositions. Unless major changes are made in the thickening system, the pigment particles tend to settle out, and if major changes are made, this setding out can be reduced, but the thickening effect is significantly impaired.
[0007] It has also been proposed to use a floc.system in such thickened hypochlorite compositions to prevent the particulate colouring agent from settling out, such a floc system comprising, inter alia, a polymer latex. Although such a polymer latex may provide an improved physical stability of the particulate colouring agent in the hypochlorite compositions, it does not provide coloured products which are chemically stable over longer periods.
[0008] It has now been found that the chemical and physical stability of pigments as colouring agents in aqueous alkali metal hypochlorite compositions can be improved by coating the pigments with a coating of a bleach-resistant polymer.
[0009] It has already been proposed in US Patent Specifications 3,666,680 (Briggs) and 3,655,566 (Robinson) to include optical brighteners in liquid hypochlorite compositions, whereby these optical brighteners are protectively enclosed in the inner portion of a two-layer synthetic polymer particle.
[0010] This is achieved by dissolving the optical brightener in the oil-soluble monomer, copolymerizing the monomer- brightener solution with a vinyl acid, and subsequently performing a second polymerization with the hydrophobic monomer, whereby an impermeable film is formed around the previously obtained polymer-brightener particles. Although this prior proposal also mentions the possibility of using dyes and pigments such as Ultramarine Blue, Monastral Fast Green GWD, etc., it is primarily directed to optical brightening agents.
[0011] These polymer particles, however, contain a hydrophilic monomer as well, and in thickened liquid hypochlorite compositions they do not give a satisfactorily stable colour. Furthermore, these particles have an average particle size in the range of 0.1-2 micron or 0.5-2 micron, which is not suitable to produce compositions which are physically stable without the need of a suspending agent.
[0012] Recently, it has been described in GB-A1-2100307 to include a hypochlorite solution stable, suspendable dye particle in a liquid bleaching and dyeing composition. These particles contain a dye which is resistant to attack by hypochlorous acid, which dye is incorporated in a hydrophobic latex. The dye is incorporated or "embedded" in a highly hydrophobic matrix, thus shielding it from actual contact with the hypochlorite.
[0013] Dyes, however, are discrete molecular units, whereas pigments are agglomerations of molecules into particles of microscopic rather'than molecular (5-50 Angstroms) dimensions. The dyes of the above proposal must be soluble in the organic/monomeric phase. In addition, low chromophore to polymer ratios are required to get a high proportion of the finished particles to be polymer to get some effective physical entrapment.
[0014] We have now found that pigments, i.e. colourants which are insoluble in the organic and aqueous phase, which have been coated with a protective coating in a single-stage process have an improved stability against attack by hypochlorite and do not cause any significant physical storage stability problems when used in an aqueous bleaching composition.
[0015] In its broadest aspect, therefore, the present invention relates to coloured aqueous alkali metal hypochlorite compositions, comprising as colouring agent a colloidally stable, coated pigment which has been coated with a bleach-resistant polymer.
[0016] Surprisingly, these coated pigments are colloidally at least as stable, or in many cases more stable than the uncoated pigments. In addition, often less coated pigment particles than dyed latices are required to colour the aqueous hypochlorite solution to the same intensity.
[0018] The pigments which can be used in the present invention can be of any type, as long as they are insoluble in the organic and aqueous phase and are of a relatively small average particle size (e.g. - 1000 A). They can include metallated and non-metallated synthetic pigments as well as organic and inorganic pigments.
[0021] Mixtures of various pigments can equally be used. Preferably, non-metallated pigments are used in bleaching compositions which are susceptible to decomposition by metal ion catalysis, but metallated pigments when used according to the present invention show already a significant improvement in this respect in comparison with the uncoated pigments, without any significant physical stability problem. Thus it has been found that a copper-containing halogenated phthalocyanine, when used according to the present invention, causes substantially less decomposition of the bleaching composition than the same uncoated pigment, and less settling out of the pigment particles. When metallated pigments are used, it is sometimes advantageous to use a metal sequestering agent in the composition, such as a periodate or other suitable metal-chelating agent which is stable in the bleaching composition in amounts of up to about 5% by weight of the coated pigment added, to reduce the decomposition even further.
The Coating
[0022] The coating material to be used in the present invention should be bleach-resistant. Any organic material can be used, as long as the pigment is not soluble therein. Preferably, organic materials are used in which the pigment is readily dispersible. Suitable materials are (co)polymers prepared from a hydrophobic monomer which is capable of undergoing emulsion polymerization.
[0023] Typical examples are styrene, alkyl styrenes with one to four carbon atoms in the alkyl group, monohalogenated styrenes, acrylates, methacrylates, vinylesters, ethylene and vinylchloride. A particularly suitable material is polystyrene.
[0024] The coating process is carried out in a manner known per ss, by introducing the pigment particles into an aqueous emulsion polymerization of styrene, using a common initiator such as potassium persulphate, azobis-(isobutyramidine hydrochloride) or 4,4'-azobis-(4-cyanovaleric acid). It has been found that higher concentrations of initiator than are usual for conventional emulsion polymerization favour the coating of the pigment particles.
[0025] The concentration ratio of monomer to pigment should be such that there is sufficient monomer present to just coat all the particles to avoid the formation of un-coloured polymeric latices. For e.g. styrene and Pigment Green 7 (C.I. N° 74260), the most effective styrene/pigment ratio was found to be 5:1.
[0026] To aid the dispersal of the pigment in the polymerization reaction mixture, a suitable surfactant, such as a nonionic or an anionic synthetic detergent, can be advantageously added.
The composition
[0027] The coated pigments of the present invention are suitable for colouring aqueous bleaching compositions, both thickened and non-thickened ones. These compositions may contain other ingredients, which are governed by the purpose for which these compositions are used, such as heavy-duty liquid fabric-bleaching and -washing compositions, liquid fabric-softening compositions, hair-bleaching compositions, hygienic cleaning compositions, hard- surface-cleaning compositions, etc. Thus, they preferably contain one or more detergent-active compounds. Further ingredients commonly encountered in such products may be included in the compositions of the invention. As said before, the bleaching agent can comprise both oxygen and chlorine bleaching agents, as well as reducing bleaches.
[0028] The coated pigments of the present invention are particularly suitable for thickened aqueous alkali hypochlorite compositions such as described in GB-A-1329086, EP-A1-0030401, GB-A-1548379, GB-A-1466560, GB-A1-2003522, GB-A1-2041162, GB-A1-2076010 and GB-A1-2046321.
[0029] The amount of coated pigments used in the bleach composition varies from 0.0005 to 10% by weight, preferably from 0.001 to 1 % by weight
[0031] In the following examples, the bleaching composition was a current commercial thickened hypochlorite bleaching composition, Domestos, manufactured and sold by Lever Brothers Ltd. This product is a product according to GB Patent 1329086.
[0032] The colour and physical stability were assessed spectrophotometrically and visually, respectively, and the hypochlorite decomposition ("gassing") was measured by collecting the volume of gas evolved.
Example 1 - Coated Colanyl Green GG
[0034] Colanyl Green GG was dispersed in water (970 g) and heated to 82°C. The dispersion was purged with nitrogen for 15 minutes and styrene was added with vigorous stirring. 4,4'-azobis-(4-cyanovaleric acid) was slurried in the remaining water and added to the reactants. Polymerization was continued for 6 hours at 82°C. The latex was steam- stripped to remove any unconverted monomer and filtered through glass wool.
[0035] Transmission Electron Microscopy showed that the pigment particies were encapsulated within a sheath of polystyrene, and that the average size of these particles was 900 Å.
[0037] A sample of the above dispersion was added to Domestos at 200 ppm to give a clear, green colouration. Both colour and colloidal stability were maintained for 8 weeks at 37°C. In gassing studies hypochlorite containing polymer-protected pigment showed dramatically less gassing than a sample containing Colanyl Green (order 100 times less gassing).
[0042] A sample of the above dispersion was added to Domestos at 200 ppm to give a clear, green colouration. The product retained a colour and colloidal stability for greater than 60 days.
Styrene
Colanyl Green GG
Potassium persulphate
Distilled water
Method
[0047] A sample of the above dispersion was added to Domestos at 150 ppm to give a translucent green colouration. The product remained coloured after 60 days storage at 37 °C.
[0049] The sodium dodecyl sulphate was dissolved in the water and the encapsulation effected as in Example 1.
[0051] A sample of the above dispersion was added to Domestos at 150 ppm to give a translucent green colouration. The product remained coloured after 60 days storage at 25°C.
[0057] The Arylan SNS solution was mixed with the pigment and the encapsulation effected as in Example 1.
[0059] A sample of the above dispersion was added to Domestos at 550 ppm to give a clear blue colouration. Encapsulation enhanced the colour stability eightfold over that of the untreated pigment (120 min. vs 15 min.).
[0063] A sample of the above dispersion was added to Domestos at 500 ppm to give a clear violet colouration. Encapsulation enhanced the colour stability threefold over that of the untreated pigment (15 min. vs 5 min.).
[0069] A sample of the above dispersion was added to Domestos at 500 ppm to give a blue colouration. Encapsulation enhanced the colour stability of the pigment (up to 1 hour).
[0073] A sample of the above dispersion was added to Domestos at 500 ppm to give a green colouration. Encapsulation enhanced the colour stability of the pigment (up to 20 minutes).
[0078] A sample of the above dispersion was added to Domestos at 500 ppm to give a blue colouration. Colour was retained for 1 week (cf. unencapsulated pigment 3 days).
[0083] A sample of the dispersion was added to Domestos at 500 ppm to give a brown colouration. Colour was retained for 5 hours at room temperature (cf. 5 minutes for the uncoated pigment).
[0090] A sample of the dispersion was added to Domestos at 500 ppm to give a brown colouration. Colour was retained for 45 minutes at room temperature.
[0094] The vinyl sulphone derivative of Remazol Brilliant Green was generated by treating the - sulphatoethyl-sulphone form of the dye with 2M aq. sodium hydroxide [e.g. see Robinson, C. et al., Proc. R. Soc. (A) 31, 576, (1931)]. The dye and surfactant were dissolved in the water, and concentrated hydrochloric acid was added until the pH of the aqueous phase was less than 1. The resulting precipitated pigment was coated as in Example 4.
1. An aqueous, coloured bleaching composition comprising a bleaching agent and a particulate,
polymer-coated colouring agent, characterised in that the colouring agent is a colloidally
stable, coated pigment which has been coated with a bleach-resistant polymer.
2. A composition according to claim 1, characterised in that the pigment is a metallated
pigment.
3. A composition according to claim 1 or 2, characterised in that the bleach-resistant
polymer is prepared from a hydrophobic monomer.
4. A composition according to claim 3, characterised in that the bleach-resistant
polymer is polystyrene.
5. A thickened, aqueous coloured bleaching composition, comprising a colloidally stable,
coated pigment which has been coated with a bleach-resistant polymer according to
any one of claims 1-4.