Compositions – Oxidative bleachant – oxidant containing – or generative – Free halogen or oxy-halogen acid type
Patent
1997-11-17
1999-07-27
Anthony, Joseph D.
Compositions
Oxidative bleachant, oxidant containing, or generative
Free halogen or oxy-halogen acid type
25218724, 25218726, 423473, 423 34, 423 50, 423 55, 423140, C01B 1106
Patent
active
059285591
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for the manufacture of a liquid bleaching composition which is suitable for laundry applications including handwashing as well as washing with automatic washing machines.
BACKGROUND OF THE INVENTION
Liquid bleaching compositions are well known in the art. Amongst the different bleaching compositions available, those relying on bleaching by hypochlorite are often preferred. Representative of the art is, for example, WO-88-05461 which discloses an aqueous composition comprising hypochlorite, sodium carbonate and sodium hydroxide and the use of said composition for removing stains from the fabrics.
However, the drawbacks associated with the use of chlorine-based compositions are that said compositions may both damage and yellow fabrics.
We have now found that the whiteness performance and/or the fabric safety performance of a liquid aqueous hypochlorite-containing composition is mainly dependent on two factors: the pH of the bleaching environment and the presence of heavy metal ions in said bleaching environment.
It is believed that higher pH of the bleaching environment is beneficial for the whiteness and fabric safety performance because it shifts the chemical equilibrium between hypochlorite and hypochlorous acid to reduce the level of hypochlorous acid, the species which we have found to be the most responsible for the yellowing and the fabric damage.
The presence of heavy metal ions such as Ni, Co, Cu, Mn, Cr, and Fe adversely affects the hypochlorite bleaching performance. It is believed that in the washing environment said heavy metal ions catalyze the attack of hypochlorous acid on fabrics with the generation of yellow oxidized species. Said heavy metal ions also lead to reduced tensile strength of the fabrics, thereby reducing fabric resistance. It is further believed that said heavy metal ions are adsorbed per se on oxidized fabrics as colored species and catalyze the degradation of the brighteners adsorbed on fabrics generating thereby highly colored species on fabrics. Also, said heavy metal ions stabilize colored pigments of enzymatic stains such as blood or grass. Furthermore, it is believed that said heavy metal ions are detrimental for the performance of a hypochlorite composition as they tend to react with the hypochlorite present in said composition and thereby catalyze the decomposition of said hypochlorite.
In the current industrial manufacturing processes, liquid aqueous compositions comprising hypochlorite and a source of alkalinity, such as sodium hydroxide, are prepared by using the cheapest and most commonly available raw materials. Such commercially available raw materials are usually contaminated by impurities like heavy metal ions. For example, the commercially available hypochlorite used may contain proportions of other materials such as sodium carbonate and/or caustic soda and/or heavy metal ions. Also, the current caustic soda is commonly contaminated by heavy metal ions such as iron.
More particularly, in the current industrial manufacturing processes, such liquid aqueous compositions comprising hypochlorite are prepared by diluting a concentrated hypochlorite solution with tap water, i.e. non-demineralized water, in presence of said source of alkalinity, allowing precipitation of insoluble salts, such as metal hydroxides and metal carbonates, and finally removing said insoluble salts from said compositions. However, the compositions obtained are not satisfactory as regard their purity, because they still contain a certain level of heavy metal ions which have not been retained/eliminated by conventional separation means like filtration with a decantation filter. The amount of heavy metal ions in the finished composition is even higher when manufacturing a liquid aqueous composition comprising hypochlorite at high pH values such as 13 and above. Indeed, the solubility of most of the heavy metal ions that should be eliminated in order to ensure good whiteness and/or fabric safety performance, increases with the pH of
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Marchesini Mauririo
Trigiante Giuseppe
Anthony Joseph D.
Echler Richard S.
Rasser Jacobus C.
The Procter & Gamble & Company
Zerby Kim William
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