The present invention relates to a composite powder comprising a composite prepared from an alkali metal silicate and a water-soluble salt. More specifically, the present invention relates to a composite powder having a low percentage of weight gain during storage and a small change in state, wherein the alkali metal silicate component has high storage stability.
Alkali metal silicates are ion exchange materials having cationic exchange capacity, which have been conventionally utilized for detergent builders, and the like. Distinguishable from zeolites, aluminosilicate detergent builders, a feature of the alkali metal silicates resides in their solubility to water. Therefore, they are excellent in the rinsability after the wash, so that there is an advantage that their remaining property to clothes is low, or the like. They also have an alkaline-buffering ability, the function of which the zeolites do not have. In view of the above facts, recently, there has been an active engagement in the development of the silicates having excellent Ca-ion exchange capacity.
However, while the solubility to water, a feature of the alkali metal silicates, is an advantage of the silicates, the alkali metal silicates absorb moisture in the air or absorb carbon dioxide gas, thereby causing a decrease in the ion exchange capacity. In view of the above, there arises a problem that the performance of the above silicates is apt to decrease by storage.
Therefore, as disclosed, for instance, in Japanese Patent Laid-Open No. Hei 9-208218, it has been proposed to increase the storage stability by surface treatment with an organic substance, or the like to coat crystalline silicates. However, when the surface is coated with an organic substance which does not substantially contain water, there are some cases where such an advantage of the crystalline silicates as solubility is inhibited. In addition, as disclosed in Japanese Patent Laid-Open Nos. Hei 8-143309 and Hei 9-309719, there have been proposed processes of increasing water resistance of an alkali metal silicate by treating an amorphous alkali metal silicate with carbon dioxide gas. When this process is employed, the alkali metal silicates are neutralized with acidic carbon dioxide gas, so that silica is formed locally, thereby causing a disadvantage that water-insoluble components increase. In addition, there is also a defect that the alkaline-buffering ability, one of the advantages of the alkali metal silicates, is lowered by the neutralization. In addition, as disclosed in Japanese Patent Laid-Open No. Hei 8-225317, there has been tried to improve anti-hygroscopicity by forming a solid solution of an alkali sulfate in an amorphous silicate. In order to achieve its purpose, the silicate and the alkali sulfate must be melted at a high temperature of 1000xc2x0 C. or more, which gives rise to such defects that an energy load is high and that it cannot be applied to crystalline silicates, thereby making it poor in the generalized use.
Accordingly, an object of the present invention is to provide a composite powder comprising a composite prepared from an alkali metal silicate and a water-soluble salt, wherein the alkali metal silicate component has high storage stability.
These and other objects of the present invention will be apparent from the following description.
The present invention pertains to:
[1] a composite powder comprising (A) an alkali metal silicate particle having an average particle size of from 1 to 500 xcexcm; and (B) a water-soluble salt particle having an average particle size of from 0.01 to 50 xcexcm, of which solubility to water at 20xc2x0 C. is 1 g/100 g or more, wherein the alkali metal silicate particle has a composition formula in an anhydride form represented by:
xM2O.ySiO2.zMeOxe2x80x83xe2x80x83(I)
wherein M stands for Na and/or K; Me stands for Ca and/or Mg; y/x is from 0.5 to 4.0; z/x is from 0 to 1.0; and Mg/Ca in MeO is from 0 to 10, and
wherein the composite powder has a (A)/(B) weight ratio of from 1/9 to 99/1; and
[2] a detergent composition comprising the composite powder as defined in item [1] above.