GRANULAR BUILDER PRODUCT

Abstract: A granular product comprises co-granules of an alkali metal silicate and a builder salt wherein the granules contain an amount of a bicarbonate which is such that when the granular product is dissolved in distilled water as a 1 % solution there is no observable opalescence. The use of bicarbonate allows the incorporation of above 28 %, e.g. above 30 %, silicate (expressed as disilicate) in the granule. The granules may be produced by dry blending the bicarbonate and builder salt, adding to the dry blend a solution of the alkali metal silicate, and effecting agglomeration of the mixture. If necessary the agglomerates are then dried.

Description: GRANULAR BUILDER PRODUCT The present invention relates to a granular product intended for use particularly, but not exclusively, as a builder in a powdered or granular detergent formulation, e.g. of the type used in domestic washing or dishwashing machines. It is well known for powdered and granular detergent products (hereinafter referred to generically as granular detergent products) to incorporate a builder to sequester or precipitate divalent metal ions (e.g. Ca 2+ and Mg 2+ ) so that they do not interfere with the properties of the surfactant. It is also well known that the builder may be provided in the form of a co-granule produced by agglomeration of a solution of an alkali metal silicate (typically sodium silicate) and a builder salt (e.g. sodium carbonate) . Examples of such co-granules are disclosed in U.K. Patent No. 1,396,215 (Diamond Shamrock) and their use as builders is described in European Patent Application No. 91403173.7 (Rhone Poulenc) . An example of a sodium silicate/sodium carbonate co-granule made using this prior process typically contains 27% sodium silicate expressed as disilicate, 54% sodium carbonate of which about is present as monohydrate and about 19% total water. (Unless otherwise stated all percentages referred to herein are by weight). However detergent formulaters would prefer co- granules containing at least 28%, more preferably at least 30%, and most preferably at least 32% of sodium silicate. It has however not hitherto proved possible reliably to increase the silicate content (expressed as disilicate) of the conventional co-granules to at least 28%. If attempts are made to provide such silicate levels by the use of larger amounts of the sodium silicate solution (relative to the carbonate) it is found that agglomeration is limited by the "plastic point" of the mix which prevents increased agglomeration. At this "plastic point" balling of the mix occurs and it becomes noticeably wet. Whilst it might be thought that the use of a sodium silicate solution of higher silicate content would achieve the desired result, this is not a practical possibility. This is because commercially available solutions are constrained by viscosity and gelation points (at low Si0 2 :Na 2 0 ratios) and by gel polymerisation (at high Si0 2 :Na 2 0 ratios). It is therefore an object of the present invention to obviate or mitigate the abovementioned disadvantage. According to the present invention there is provided a granular product comprising co-granules of an alkali metal silicate and a builder salt wherein the granules contain an amount of a bicarbonate which is such that when the granular product is dissolved in distilled water as a 1% solution there is no observable opalescence. The invention has been based on our discovery that the use of the bicarbonate readily allows higher amounts of silicate to be incorporated into the co-granule than can be achieved in prior art processes. In effect the bicarbonate allows greater quantity of sodium silicate solution to be used in the agglomeration process before the plastic point is reached. Thus the invention has the significant advantage that it renders possible the production of granules containing at least 28% of the alkali metal silicate (expressed as disilicate). This is obviously a considerable advance over the prior art processes and meets the needs of detergent for ulaters. It is not however essential that granules in accordance with the invention contain such high loadings of silicate since, even at lower silicate loadings the granules will still have utility as a builder. For all granules of the invention, it is necessary to ensure that the amount of bicarbonate used is such that there is no visually observable opalescence to the naked eye when the granule is dissolved as a 1% solution in distilled water. The test for the presence of observable opalescence (which is caused by formation of silica or silicate) may be carried out by comparing a solution of the granule in distilled water with distilled water per se and comparing the two liquids for the presence of opalescence (e.g. as manifested by "cloudiness") in the former liquid. Preferably granules in accordance with the invention are such that, as a 1% solution of the granule is distilled water, there is no substantial precipitation of silica or silicate, i.e. no visually observable particulate matter formed in the solution (e.g. as a suspended solid). The formation of silica (such as gives rise to opalescence or precipitate formation) can arise as a result of the following reaction which occurs in solution OH " + HC0 3 " = H 2 0 + C0 3 2" The OH " ions are derived from the silicate. In solution, this reaction will go to completion, i.e. up to the point where one of the species on the left hand side of the equation is essentially eliminated. However the sodium silicate relies on the presence of a sufficient level of OH " to remain in solution to avoid Si0 2 precipitation. The precipitation of Si0 2 (or silicate) is obviously undesirable in a domestic laundry or dishwashing operation. Thus at the typical (but not limiting) concentration of 1% in aqueous solution at which the granule will be used in a laundry or dishwashing solution, there should be no opalescence or, more preferably, no substantial precipitation of silica or silicate. The 1% level represents the industry standard. It is however more preferred that the amount of bicarbonate in the granules of the invention is such that there will be no opalescence, or more preferably, no substantial precipitation of silica (or silicate) at a concentration (of the granule) of 2% in aqueous solution. More preferably there should be no opalescence or, more preferably, no substantial precipitation at the 10% level, and even more preferably no precipitation up to the solubility limit of the granule. Subject to the above constraints on bicarbonate content, co-granules in accordance with the invention will typically comprise alkali metal silicate 25-35% (preferably 28-35%) (expressed as disilicate) bicarbonate 0.1-12% (preferably 0.5-8%) builder salt 30-55% (preferably 35-48%) water 10-30% (preferably 13-28%) The invention may be used to produce co-granules having at least 30% alkali metal silicate (expressed as disilicate) The alkali metal silicate of the granules is preferably, but not limited to, sodium silicate. A further example of alkali metal silicate which may be used is potassium silicate. The bicarbonate is most preferably an alkali metal bicarbonate, most preferably sodium bicarbonate. The builder salt is most preferably an alkali metal carbonate (ideally sodium carbonate) but could for example be a phosphate or polyphosphate (e.g. sodium tripolyphosphate or trisodium phosphate), a borate or perborate (e.g. sodium borate or sodium perborate), a percarbonate (e.g. sodium percarbonate) , a metasilicate (e.g. sodium metasilicate) or sodium sulphate. Co-granules in accordance with the invention preferably have a mean particle size of 0.2-2.5 mm, more preferably 0.5-1.4 mm. The granules preferably have a pouring density of 0.6-1.3 g cm "3 , more preferably 0.75-1 g cm "3 . The present invention also provides a method of producing the co-granules comprising the steps of (i) dry blending the bicarbonate and builder salt, (ii) adding to the dry blend a solution of the alkali metal silicate; (iii) effecting agglomeration of the mixture, and (iv) optionally drying the agglomerates, the amount of bicarbonate being such that when the granular product is dissolved in water as a 1% solution in distilled water there is no observable opalescence. The builder salt used in the process is preferably a hydratable salt, most preferably anhydrous sodium carbonate, which becomes at least partially hydrated during the agglomeration. Preferably the builder salt and bicarbonate are of similar particle size. Preferably 75% of these particles have a size less than 180 microns. Typically the builder salt is 'light ash' (sodium carbonate) having a pouring density of 0.4-0.6 g cm -3 and the bicarbonate is sodium bicarbonate. The alkali metal silicate preferably has a solids content of 28-55% (more preferably 45-55%) and a Si0 2 :M 2 0 ratio (where M is an alkali metal) of 1.6-3.5 (more preferably 1.6-2.5). Typically the silicate solution, builder salt and bicarbonate are used in the following relative amounts in the agglomeration process silicate solution 45-60% builder salt 30-50% bicarbonate 0.1-15% Generally, the weight ratio of bicarbonate:silicate (solids) will be less than 1:2.8, more preferably less than 1:3.5 most preferably less than 1:4.5. Any conventional agglomerator may be used for the agglomeration process . Material leaving the agglomeration may be graded through a suitable size mesh sieve to remove fines which are recycled to the agglomeration feed and through a coarser sieve to remove oversize products which can be crushed and recycled through the grading plant. The graded product may then be dried (e.g. in a fluid bed drier, flash drier or similar) in a manner that prevents the solids temperature rising above 60°C. The invention is further illustrated by the following non-limiting Examples. Examples and Comparative Examples Using the abovedescribed procedures, a range of co- granules were produced. Table 1 sets out the amounts of the various components used and the properties of the resultant products. Examples 1-4 all illustrate products of the invention which contain at least 29% of silicate (expressed as disilicate) in the final co-granule. By way of contrast, Comparative Example 1 illustrates a conventional co-granule (i.e. no bicarbonate) in which the amount of silicate (expressed as disilicate) is 26%. The product of Comparative Example 2 contains 28.5% silicate (expressed as disilicate) but the amount of bicarbonate present is such as to cause precipitation of silica when the co-granule is dissolved as a 2% solution. TABLE 1 STARTING MATERIALS j SILICATE IN PHYSICAL PROPERTIES PRODUCT EXAMPLE Na-,C0 3 NaHC0 3 SODIUM DRYING EXPRESSED CLARITY OF FINAL DISS. POURING I SILICATE AS CO Wt. Wt. Wt . Wt . rat. SOLIDS TEMP. DISLICATE A 2% Solut. PH TIME DENSITY (Kg) (Kg) (Kg) Siθ 2 :Na 2 θ (X) (C) (X) (s) (g/cm 3 ) Comp 1 20 0 19 2: 1 53.5 40 26 CLEAR 11.5 160 0.86 m 1 19 1 25.5 2: 1 53.5 40 33 CLEAR 11.34 100 2 18 2 26 2 : 1 53.5 40 32.5 CLEAR 11.13 80 0.87 3 m 3 17.5 2.5 22.7 2 : 1 53.5 40 29.5 CLEAR 4 17 3 24.5 2: 1 53.5 40 29 CLEAR 10.99 110 Ξomp 2 16 4 19.2 2: 1 53.5 40 28.5 PRECIPITATE 10.87 100

Claims: CLAIMS 1. A granular product comprising co-granules of an alkali metal silicate and a builder salt wherein the granules contain an amount of a bicarbonate which is such that when the granular product is dissolved in water as a 1% solution in distilled water there is no observable opalescence. 2. A product as claimed in claim 1 comprising 25-35% alkali metal silicate. 3. A product as claimed in claim 2 comprising 28-35% alkali metal silicate. 4. A product as claimed in any one of claims 1 to 3 wherein the alkali metal silicate is sodium silicate. 5. A product as claimed in any one of claims 1 to 4 comprising 0.1-12% bicarbonate. 6. A product as claimed in claim 5 comprising 0.5-8% bicarbonate. 7. A product as claimed in any one of claims 1 to 6 wherein the bicarbonate is sodium bicarbonate. 8. A product as claimed in any one of claims 1 to 7 comprising 30-55% builder salt. 9. A product as claimed in claim 8 comprising 35-48% builder salt. 10. A product as claimed in any one of claims 1 to 9 wherein the builder salt is sodium carbonate. 11. A product as claimed in any one of claims 1 to 9 wherein the builder salt is a phosphate, polyphosphate, borate, perborate, percarbonate, metasilicate, or sodium sulphate. 12. A product as claimed in any one of claims 1 to 11 comprising 10-30% water. 13. A product as claimed in claim 12 comprising 13-28% water. 14. A product as claimed in any one of claims 1 to 13 which is such that there is no substantial precipitation of silica or silicate at a concentration (of the granule) of 1% in distilled water. 15. A product as claimed in claim 14 which is such that there is no substantial precipitation of silica or silicate at a concentration (of the granule) of 2% in distilled water. 16. A product as claimed in claim 15 such that there is no substantial precipitation of silica or silicate at a concentration (of the granule) of 10% in distilled water. 17. A product as claimed in claim 16 such that there is no substantial precipitation of silica or silicate up to the solubility limit of the granule in distilled water. 18. A product as claimed in any one of claims 1 to 17 having a mean particle size of 0.2-2.5 mm. 19. A product as claimed in claim 18 having a mean particle size of 0.5-1.4 mm. 20. A product as claimed in any one of claims 1 to 19 having a pouring density of 0.6-1.3 g cm -3 . 21. A product as claimed in claim 20 having a pouring density of 0.5-1 g cm '• 3 22. A granular product comprising co-granules of the following composition: alkali metal silicate 28-35% (expressed as disilicate) alkali metal bicarbonate 0.5-8% sodium carbonate 35-48% water 13-28% 23. A method of producing co-granules as claimed in claim 1 comprising the steps of (i) dry blending the bicarbonate and builder salt, (ii) adding to the dry blend a solution of the alkali metal silicate; (iii) effecting agglomeration of the mixture, and (iv) optionally drying the agglomerates, the amount of bicarbonate being such that when the granular product is dissolved in water as a 1% solution in distilled water there is no observable opalescence. 24. A process as claimed in claim 23 wherein 75% of the bicarbonate and builder salt particles have a size less than 180 microns. 25. A process as claimed in claim 23 or 24 wherein the builder salt is sodium carbonate having a pouring density of 0.4-0.6 g cm "3 . 26. A process as claimed in any one of claims 23 to 25 wherein the bicarbonate is sodium bicarbonate. 27. A process as claimed in any one of claims 23 to 26 wherein the alkali metal silicate has a solids content of 28-55% and a Si0 2 :M 2 0 ratio of 1.6-3.5. 28. A process as claimed in claim 27 wherein the alkali metal silicate has a solids content of 45-55% and a Si0 2 :M 2 0 ratio of 1.6-2.5. 29. A process as claimed in any one of claims 23 to 28 wherein the silicate solution, builder salt and bicarbonate are used in the following relative amounts: silicate solution 45-60% builder salt 30-50% bicarbonate 0.1-15% 30. A process as claimed in any one of claims 23 to 29 wherein the weight ratio of bicarbonate:silicate solids is less than 1:2.8. 31. A process as claimed in claim 30 wherein the weight ratio of bicarbonate:silicate solids is less than 1:3.5. 32. A process as claimed in claim 31 wherein the weight ratio of bicarbonate:silicate solids is less than 1:4.5.

Inventors: HUGHES PHILIP GEORGE, MCCLELLAN ALAN KEITH, THORPE MALCOLM JOHN, HUGHES, PHILIP, GEORGE, MCCLELLAN, ALAN, KEITH, THORPE, MALCOLM, JOHN
Applicants: BRUNNER MOND & CO LTD, COLIN STEWART MICHEM LTD, HUGHES PHILIP GEORGE, MCCLELLAN ALAN KEITH, THORPE MALCOLM JOHN, BRUNNER MOND & COMPANY LIMITED, COLIN STEWART MICHEM LIMITED, HUGHES, PHILIP, GEORGE, MCCLELLAN, ALAN, KEITH, THORPE, MALCOLM, JOHN
Application year: 1995
Main classification: C11D7
IPC codes: C11D7, C11D11