Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – With oxygen or halogen containing chemical bleach or oxidant...
Patent
1995-06-21
1996-09-17
Albrecht, Dennis
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
With oxygen or halogen containing chemical bleach or oxidant...
4234152, 427213, 427215, 510108, 510441, 510442, 510509, 510510, 510511, 25218626, C01B 1510, C11D 704, C11D 714, C11D 718
Patent
active
055568343
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for stabilising alkali metal percarbonates by coating particles of alkali metal percarbonates, the coated alkali metal percarbonates thus obtained and washing or bleaching compositions containing such particles.
It is well known that percarbonates can be used as bleaching compounds in detergent powder mixtures. Compared with perborate tetrahydrate, they have the advantage of dissolving more rapidly at 20.degree. C. Another advantage of the percarbonates is that they are environmentally friendly. However, the said percarbonates have the drawback of decomposing in the powdered state, particularly if stored in a damp atmosphere. Moreover, the other constituents of washing compositions can accelerate their decomposition.
In order to improve the stability of percarbonates, it has been proposed to coat the percarbonate particles with different types of coating agents. Organic and/or polymer compounds such as paraffins, polyols, vinyl resins etc. and inorganic compounds such as silicates, borates, perborates, boric acids etc. have been proposed as coating agent.
French patent published under number 2 528 447 describes coating the surface of sodium percarbonate with sodium borate. A process for coating sodium percarbonate consists of wetting the sodium percarbonate with water, mixing the damp sodium percarbonate with sodium borate in powder form and then drying them at a temperature above the melting temperature of the sodium borate used. This process requires a substantial amount of energy because of the high temperature required to melt sodium borates. In addition, the fact that the sodium percarbonate needs to be wetted requires strict control of its water content to prevent its decomposition.
Another coating method is described in British patent 1 575 792. This patent describes spraying boric acid solutions onto percarbonate particles or otherwise bringing them into contact. However, the solubility of boric acids in water is limited, particularly at ambient temperatures. Such low concentrations are disadvantageous for industrial use from the economic point of view because a large input of thermal energy is necessary to dry the percarbonate particles after spraying and because of the prolonged drying periods which cause a reduction in the active oxygen content of the percarbonate as a result of its decomposition.
European patent application 0 459 625 describes coating sodium percarbonate particles by spraying them with two distinct solutions, one comprising an aqueous solution of boric acid and the other a solution of an alkali metal silicate. According to this document, the simultaneous dissolution of boric acid and an alkali metal silicate in water is alleged to cause precipitation of a gel. Moreover, in this method of operation, the quantities of water to be eliminated are substantial on the one hand due to the fact that the solubility of boric acid in water is limited and, on the other hand, because two separate solutions are introduced. Furthermore, the homogeneity of the coating is not necessarily guaranteed. In addition, this technique is relatively complex due to the double introduction of solutions of coating agents.
It is an object of the present invention to provide a process for stabilizing percarbonate particles which ameliorates or overcomes the disadvantages of the above-mentioned processes. It is an object of at least some embodiments of the present invention to obtain a homogeneous coating of the percarbonate particles and to obtain in this way an alkali metal percarbonate which is particularly stable in the presence of the other constituents of detergent powders without, however, reducing to a substantial or significant extent its active oxygen content.
It is a further object of some or further embodiments of the present invention to enable the use of aqueous mixed solutions of boric acid and an alkali metal silicate which are sufficiently concentrated to encourage industrial interest, but in which gel formation does not take place at all or at most t
REFERENCES:
patent: 4194025 (1980-03-01), Klebe
patent: 4321301 (1982-03-01), Brichard
patent: 4526698 (1985-07-01), Kuroda
patent: 5194176 (1993-03-01), Copenhafer
patent: 5219549 (1993-06-01), Onda
patent: 5332518 (1994-07-01), Kuroda
Horne Graham R.
James Alun P.
Albrecht Dennis
Solvay Interox Limited
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