Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Patent
1991-12-31
1994-02-15
Breneman, R. Bruce
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
252135, 23293R, C01B 3332
Patent
active
052864707
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to solid silicate products intended for use in particulate detergent compositions. These silicate products act as a source of alkalinity for the detergent powder when in use. Thus, in common with the other components of the detergent composition, the silicate product is required to have acceptable water solubility, be non-caking and not provide fines by attrition when subjected to handling or while in the detergent powder.
BACKGROUND OF THE INVENTION
Detergent compositions intended for mechanical dishwashing will usually require a component capable of providing a considerable alkalinity in the wash liquor. Sodium silicates having a SiO.sub.2 /Na.sub.2 O mole ratio from about 1.5:1, preferably from 1.8:1 to about 3.3:1, preferably to 2.2:1 are particularly suitable for this purpose and also they protect glassware from corrosion. There is a general movement towards providing detergent compositions with increased bulk densities i.e. above about 700 g/l, preferably above 800 g/l. Sodium silicates within the mole ratio 1.8 to 2.2:1 range will be referred to herein as sodium disilicates, although strictly this term is applicable only to those silicates having a mole ratio of about 2:1. Disilicates and other silicates can be formed into a product of the desired bulk density by compacting the appropriate feedstock, which may be spray-dried material, between rollers to provide a compacted sheet-like product which is subsequently broken up and sieved to provide the desired particle size range. Examples of procedures which provide these compacted materials will be found in US 3875282 (Stauffer Chemical Co.) and US 3931036 (Philadelphia Quartz Co.).
GENERAL DESCRIPTION OF THE INVENTION
The sodium disilicate or other silicate product obtained by compaction displays the desired bulk density but demonstrates a relatively high loss of material as fines by virtue of the attrition the product undergoes when handled and incorporated in the product. A particular source of attrition comes from the pneumatic handling devices commonly used in transporting the raw materials before preparing the detergent composition by mixing the desired ingredients. The particle size of the desired silicate granules will preferably be in the range 0.4 to about 0.75 mm, but the process of the invention is applicable to materials having particle sizes in the range 0.3 to 2 mm.
The applicants have found that the attrition of compacted sodium silicate can be reduced by treating the compacted silicate with added moisture preferably at elevated temperatures, i.e. above 80.degree. C., in an agitated bed. Usually the moisture treatment will be achieved by introducing steam into the vessel containing the agitated bed. The use of steam to introduce the added water is preferred because better distribution is provided The device in which the silicate is treated may be, as examples, a rotating drum, cement mixer, Eirich-type open pan, or Lodige mixer. The agitated bed can be formed in free fall/tumbling mixer, fluidised bed or paddle mixer as examples. These provide a rapid renewal of exposed surfaces and application of shear to round off the particle edges.
The moisture as liquid water or water vapour, e.g. steam, will be applied at a rate and for a time to ensure the moisture content of the disilicate is not increased by more than about 1% by weight. Increasing the water content by more than this amount may lead to caking of the product in the absence of an additional drying step.
The treated product may be cooled in an air stream or other cooling gas.
The invention provides a method of treating compacted sodium silicate granules, having a molar ratio SiO.sub.2 /Na.sub.2 O of from about 1.5:1, preferably from about 1.8:1, to about 3.3:1, preferably to about 2.2:1, and an average particle size in the range from about 0.3 mm to about 2 mm, wherein the granules are contacted with moisture preferably at elevated temperatures above 80.degree. C. in an agitated bed. Preferably the particles are contacted with
REFERENCES:
patent: 3687640 (1972-08-01), Sams et al.
patent: 3782906 (1974-01-01), Pierce
patent: 3868227 (1975-02-01), Gericke et al.
patent: 3875282 (1973-04-01), Steinreich
patent: 3918921 (1975-11-01), Pierce
patent: 3931036 (1976-01-01), Pierce
patent: 4126423 (1978-11-01), Kongsgaarden
patent: 4834902 (1989-05-01), Pioch et al.
Breneman R. Bruce
Unilever Patent Holdings B.V.
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