Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – Inorganic silicon containing component
Reexamination Certificate
1998-05-05
2001-05-01
Hendrickson, Stuart L. (Department: 1754)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
Inorganic silicon containing component
C423S332000
Reexamination Certificate
active
06225280
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compacted sodium silicate, a method for the preparation of said silicate and its use in cleaning compositions.
BACKGROUND OF THE INVENTION
Sodium metasilicate, i.e., sodium silicate having a molar ratio SiO
2
:Na
2
O of about 1, is frequently used in cleaning products such as detergents and dishwashing agents. The silicate inhibits corrosion on glass, glazing, and metal parts, and also functions as an alkali generating agent. Generally, granules of pentahydrate are used, which granules dissolve quickly in water. However, many products contain metasilicate in such a high amount that a very high alkalinity is obtained, which renders the products corrosive and unpleasant to handle.
Accordingly, the first requirement for products containing sodium silicate is to lower their alkalinity. Lower alkalinity but the same protection against corrosion can be obtained by the use of sodium silicates having a higher molar ratio SiO
2
:Na
2
O, for example disilicates with a ratio of about 2. However, higher ratios also can be employed, i.e., up to a ratio of 3.3.
Preference is also given to an amorphous product over a crystalline product. The preparation process for crystalline products is more elaborate than for amorphous products, in view of the extra high temperature treating step which has to be applied. Also, it is more difficult to compact crystalline sodium silicate, and the resulting product has a high amount of dust.
Furthermore, a compacted sodium silicate is required for ease of handling of the product by producers and detergent manufacturers. Powders are more difficult to handle, in view of dust.
For use in highly concentrated cleaning products it also is highly desirable for the silicate to have the highest possible bulk density. However, this bulk density should not have an adverse effect on the dissolution of the compacted sodium silicate in water.
In addition to the above, the compacted sodium silicate serves as a carrier for, e.g., surfactants and other washing aids, such as polycarboxylates. This requires a high porosity of the compacted silicate, to give a high loading capacity.
Finally, the compacted sodium silicate is required to have a high mechanical strength. As used herein, mechanical strength is defined as the inverse of the weight percentage of dust with a particle size below 400 &mgr;m, resulting from a milling operation of compacted silicate with a particle size between 400 and 1000 &mgr;m, as will be described hereinafter. A high mechanical strength, therefore, results in a low percentage of dust, which is an advantage when handling the product after preparation but especially avoids dust problems during various after treatments, such as adsorption of the above-mentioned washing aids, and introduction into the cleaning composition.
Compacted sodium silicate is known from U.S. Pat. No. 3,931,036. However, the disclosed product lacks the required porosity and mechanical strength. Furthermore, it is prepared according to a spray-drying technique known in the art. Accordingly, the outlet temperature required in the process of the present invention has not been applied in the process of this disclosure.
Compacted sodium silicate is also known from EP-A-0 486 078 and EP-A-0 486 079. Again, the products disclosed do not have the required porosity and mechanical strength. Also, as mentioned above, a normal sprayrying technique is applied, requiring an outlet temperature substantially lower than that of the process of the present invention.
The object of the present invention is to provide a compacted amorphous sodium silicate having the above-mentioned properties. More particularly, the invention concerns compacted sodium silicate having a molar ratio SiO
2
:Na
2
O from 1.6 to 3.3, characterized in that the silicate has the following properties:
a bulk density of above 500 g/l,
a porosity of above 190 ml/kg, and
a dust percentage of below 40 wt %.
SUMMARY OF THE INVENTION
The present invention generally relates to compacted sodium silicate having a molar ratio SiO
2
:Na
2
O from 1.6 to 3.3, wherein the silicate has the following properties:
a bulk density of above 500 g/l,
a porosity of above 190 ml/kg, and
a mechanical strength such that the dust percentage is below 40 wt %.
The invention also relates to process for the preparation of compacted sodium silicate described above, said process comprising the steps of:
spray-drying an aqueous solution of sodium silicate with a molar ratio SiO
2
:Na
2
O from 1.6 to 3.3,
applying a water glass solution to the spray-dried powder,
subjecting the water glass treated powder to a compacting step, applying a pressure below 100 bar, and
crushing the resulting flakes having a thickness of above 4 mm to obtain the compacted sodium silicate,
wherein during the spray drying step an outlet temperature above 114° C. is applied.
Finally, the invention discloses the use of the compacted sodium silicate in a cleaning composition.
DETAILED DESCRIPTION OF THE INVENTION
As described above, the present invention relates to compacted sodium silicate having a molar ratio SiO
2
:Na
2
O from 1.6 to 3.3, wherein the silicate has the following properties a bulk density of above 500 g/l, a porosity of above 190 ml/kg, and a mechanical strength such that the dust percentage is below 40 wt %; and to a process for the preparation of same. In the compacted sodium silicate of the invention also small amounts of potassium oxide and/or soda ash may be present. Preferably, up to 5 wt % potassium oxide, more preferably 1 to 5 wt %, and/or up to 10 wt % soda ash, more preferably 5 to 10 wt %, are present in the sodium silicate.
It is preferred that the compacted sodium silicate have a bulk density which ranges from 600 to 1000 g/l.
It is also preferred that the compacted sodium silicate have a porosity of above 200 ml/kg, preferably from 200 to 300 ml/kg. By porosity is meant the porosity of the compacted sodium silicate, not the internal porosity of sodium silicate powder.
Furthermore, it is preferred that the mechanical strength of the compacted sodium silicate is such that the dust percentage is below 35 wt %. The dust percentage is measured by subjecting compacted sodium silicate having a certain particle size distribution to milling in the presence of stainless steel balls.
The compacted sodium silicate of the present invention is preferably prepared in the form of granules. It is also preferred that 96-100 wt % of these granules have a particle size above 250 &mgr;m and 0-20 wt % of these granules have a particle size above 1000 &mgr;m.
Finally, it is preferred that the molar ratio of SiO
2
:Na
2
O of the compacted solid sodium silicate ranges from 2 to 3.3. More preferably the molar ratio of SiO
2
:Na
2
O of the silicate is between 2.6 and 3.3, since under government regulations labels of cleaning compositions comprising sodium silicates having a molar ratio equal to or below 2.6 have to show a black cross, indicating that the composition may be injurious to eyes. With a molar ratio of SiO
2
:Na
2
O greater than 2.6, such a label is no longer required.
The water content of the granule may be between 10 and 30 wt %, preferably 10 to 20 wt %.
A preferred compacted sodium silicate is amorphous and has a molar ratio of SiO
2
:Na
2
O of about 2.65, a bulk density of about 630 g/l, a porosity of about 225 ml/kg, a mechanical strength corresponding to a dust percentage of about 31 wt %, and a water content of 18 wt %. Surprisingly, it has been found that although the water content is fairly high, the porosity remains high too.
The present invention also relates to a method for preparing the compacted sodium silicate according to the above description by:
spray-drying an aqueous solution of sodium silicate with a molar ratio SiO
2
:Na
2
O from 1.6 to 3.3, applying an outlet temperature above 114° C.,
applying a water glass solution to the spray-dried powder,
subjecting the water glass treated powder to a compacting step, applying a pressure below 100 bar, and
crushing the resulting flakes having a thickness
De Koning Hubertus Josephus Maria
Dokter Willem Hendrik
Akzo-PQ Silica Vof
Hendrickson Stuart L.
Mancini Ralph J.
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