Chemistry of inorganic compounds – With additive – Coating or binder
Patent
1995-09-28
1997-05-27
Langel, Wayne
Chemistry of inorganic compounds
With additive
Coating or binder
4234152, C01B 3124
Patent
active
056329652
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to a method for the preparation of stabilised sodium percarbonate consisting of a sodium percarbonate core and a coating containing sodium perborate of the formula NaBO.sub.2.H.sub.2 O.sub.2.nH.sub.2 O, wherein n is 0, 1, 2 or 3. The method according to the present invention allows good storage stability to be attained, notwithstanding a small quantity of coating material.
Sodium percarbonate (2 Na.sub.2 CO.sub.3.3 H.sub.2 O.sub.2) is used as an active oxygen component in washing agents, bleaches and cleaning materials. Owing to its unsatisfactory storage stability in a warm, damp environment and in the presence of various washing agent components and cleaning material components, sodium percarbonate must be stabilised. An essential principle of stabilisation is to surround the particles of sodium percarbonate with a coating of stabilising components.
Thus the coating of sodium percarbonate with paraffin or polyethylene glycol is well-known. However adequate long-term stability is not achieved through this and besides the solubility in water is reduced in an undesirable manner. The formation of an alkali silicate coat on the particles of sodium percarbonate, as is proposed in DE-OS 26 52 776, also results in inadequate stabilisation and also to an undesirable proportion of insoluble constituents. According to the methods known from DE-OS 24 17 572 or DE-OS 26 22 610, sodium sulphate and sodium carbonate, or sodium sulphate, sodium carbonate and sodium silicate are used as coating components, wherein the methods are based on spraying a solution of the coating components onto particles of sodium percarbonate in a fluidised bed drier. For stabilisation in practice a quantity of coating material of at least 3% by weight, but in most cases definitely in excess of this, is required.
While the use of a coating material containing at least one boron compound from the group comprising metaboric acid, orthoboric acid and tetraboric acid for the stabilisation of sodium percarbonate is known from DE-PS 28 00 916, the stabilising action attainable thereby is shown in the comparative examples given in DE-OS 33 21 082 to be inadequate and in contrast to that sodium percarbonate with a coating containing sodium borate, in particular sodium metaborate, is presented in that patent as being advantageous. As the inventors of the present application established when reworking the examples from DE-OS 33 21 082, in order to achieve an adequate stability the coating had to contain borate in a quantity such that the boron content of the sodium percarbonate stabilised in this way amounted to at least 0.4% by weight, however the available active oxygen content of the stabilised sodium percarbonate was consequently each time clearly less than 14% by weight. A further development in stabilisation using borates is described in EP-A 0 487 256, however the method disclosed therein is in two steps, with a drying stage being required after each step; hence the method is technically expensive.
Finally, DE-AS 24 58 326 discloses a method for stabilising sodium percarbonate, wherein the storage stability of the pure product, as well as mixed with cleaning materials which accelerate decomposition, is increased. Here the sodium percarbonate is coated with a hydrophobic liquid organic compound to which sodium perborate powder is added.
The disadvantage of this method is the necessity of using a hydrophobic liquid organic compound, which, optionally, for the purpose of better handling must be diluted with a lower alcohol. Moreover the quantities of coating chemicals used, namely 5 to 20% by weight of sodium perborate and 5 to 10% by weight of hydrophobic organic compound, calculated respectively by reference to sodium percarbonate, are very high.
Sodium percarbonate layer particles, which consist of a sodium percarbonate core and a coating of sodium perborate, wherein the sodium perborate contains less than 3 moles of water of crystallisation per mole, are known from DE-PS 26 51 442; according to DE-PS 27 12 139
REFERENCES:
patent: 4194025 (1980-03-01), Klebe et al.
patent: 5366655 (1994-11-01), Yamashita et al.
Bertsch-Frank Birgit
Klasen Claas-Juergen
Lieser Thomas
Mueller Klaus
Schubert Peter
Degussa - Aktiengesellschaft
Langel Wayne
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