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
1997-09-23
Albrecht, Dennis
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
With oxygen or halogen containing chemical bleach or oxidant...
423271, 4234152, 427212, 427213, 427215, C01B 1510, C11D 306, C11D 339, C11D 1706
Patent
active
056704704
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for stabilising alkali metal percarbonates by coating particles of alkali metal percarbonates, 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 paraffin's, polyols, vinyl resins etc. and inorganic compounds such as silicates, borates, perborates, boric acids etc. have been proposed as coating agent.
A 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.
It is an object of the present invention to provide a process for stabilising 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 a phosphate which are sufficiently concentrated to encourage industrial application.
The present invention relates to a process for stabilising particles of alkali metal percarbonate by coating by means of a coating agent, characterised in that the percarbonate particles are brought into contact with a concentrated aqueous solution of the coating agent containing at least one boron compound selected among the meta and orthoboric acids and at least one phosphate and thereafter dried or permitted to dry.
The proportion of boron compound used in the coating agent is generally 5 to 85% by weight calculated as H.sub.3 BO.sub.3, based on the total weight of the coating agent. The best results are obtained when the proportion of boron compound is 30 to 80% by weight. Preferably, a proportion selected in the range of 50 to 80% by weight, based on the weight of the coating agent, are used.
The best results are obtained when the coating agent contains at least one boron compound selecte
REFERENCES:
patent: 4179394 (1979-12-01), Dillenburg
patent: 4321301 (1982-03-01), Brichard
patent: 5366655 (1994-11-01), Yamashita
Horne Graham Robert
James Alun Pryce
Albrecht Dennis
Solvay Interox Limited
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