POURABLE AQUEOUS BORON-CONTAINING COMPOSITIONS AND THEIR PREPARATION

Abstract: The invention relates to a pourable aqueous borate-containing suspension which suspension in water contains 8 to 13 % by weight boron as sodium pentaborate, 0.1 to 3 % by weight, based on the total weight of a composition, of a swellable clay, and 0.05 to 0.2 % by weight, based on the total weight of the composition, of a polysaccharide. The aqueous compositions according to the invention are readily handled. They may be used directly or, if appropriate, diluted for use.

Description: POURABLE AQUEOUS BORON-CONTAINING COMPOSITIONS AND THEIR PREPARATION This invention relates to pourable aqueous boron- containing compositions, particularly pourable aqueous borate-containing compositions having a high boron content, and to their preparation. It is known to prepare borate solutions with a high boron content using organic solvents. Thus US Patent Specification 4332609 describes a method of fertilising plants in which the reaction product of a boric acid compound with an alkanolamine or aliphatic polyamine, in particular monoethanolamine, is applied to plants. The reaction products are water-soluble and thus can be dissolved in water for application to crops. The production of the monoethanolamine reaction products for example, adds to the cost of the boron to be applied to the crops. Using an alternative organic solvent, US Patent Specification 4572733 describes a so-called storage- stable concentrate formed by making a solution of a first boron compound in a water-miscible glycol solvent and then dispersing fine particles of a second boron compound in the solution. For use, the storage-stable concentrate is diluted with water and applied to crops. Aqueous borate suspension formulations have been proposed for the treatment of timber. Thus AU-A-574389 proposes the use of a preservative composition comprising a colloidal micro-crystalline suspension of boron salts and a thickening agent, which serves to maintain the stability of the suspension. Similarly EP-A-0289317 describes timber preservative compositions comprising a boron-containing preservative, which may be a micro- crystalline suspension, e.g. 10 to 30 microns, and a thickening agent such as the polysaccharide xanthan gum in a preferred amount of 0.25 to 3.0% by weight. These compositions are obtained by forming, with heating, a borate solution, cooling rapidly to obtain crystals and adding thickening agent to maintain the crystals in suspension. Such compositions are stiff and pasty. We have now found that pourable aqueous borate-containing formulations having a high boron content can be prepared using an anti-settling system comprising a swellable clay and a polysaccharide. According to one aspect of the present invention, there is provided a pourable aqueous borate-containing suspension which suspension in water contains 8 to 13% by weight boron as sodium pentaborate, 0.1 to 3% by weight, based on the total weight of the composition, of a swellable clay, and 0.05 to 0.2% by weight, based on the total weight of the composition, of a polysaccharide. It has surprisingly been found that the presence of the specified amounts of clay and polysaccharide in an aqueous suspension have a significant viscosity-reducing effect rather than a thickening effect. At concentrations above these levels, both the clay and polysaccharide will contribute to undesired thickening of the suspensions. There may readily be obtained according to the invention aqueous borate-containing suspensions which on the one hand have a high boron content and on the other hand are pourable making them capable of being easily handleable by users. Thus the compositions according to the present invention may be sprayed directly or, alternatively poured for dilution by water or aqueous systems for application, e.g. onto crops, or for other applications where there is a need for aqueous soluble borate suspensions . The compositions according to the invention are pourable and, at the same time, physically stable, that is the compositions have: (a) a sufficiently high viscosity at low stresses (shear rates) e.g under stable storage and transport conditions so as to prevent particle sedimentation or significant separation; and (b) a sufficiently rapid decrease in viscosity at a particular stress (depending on the application) e.g under pouring, pumping or spraying conditions that ensures the pourability of the product on application. Thus the suspensions according to the invention do not separate when stored or when subjected to minor vibration e.g when transported. Typically under such conditions the suspensions are subjected to shear rates below 1 sec "1 , e.g 0.001 to 0.1 sec _1 for storage. At higher shear rates, the compositions are capable of being poured, pumped or sprayed. The pourable aqueous borate-containing compositions according to the present invention may contain from 8 to 13% by weight boron as sodium pentaborate, generally 9.5 to 12.5% by weight boron as sodium pentaborate, preferably 10 to 12% by weight boron as sodium pentaborate. Suitable swellable clays which may be used in the suspensions according to the present invention include the montmorillonite group of clays particularly sodium enriched montmorillonite clays and sodium montmorillonite clays, some of which are known commercially as bentonite, minerals analogous to montmorillonite such as hectorite, and sepiolite. Suitably the amount of swellable clay employed in the suspensions according to the present invention is 0.5 to 1.5% (e.g. approximately 1%) by weight, based on the total weight of the composition. Generally the composition would contain between 1 and 1.5% by weight of montmorillonite clays such as IGB clay minerals available from IMV Nevada. When other clays are used, such as sodium enriched calcium bentonite, e.g. Bentonite MB 300S from Fordamin Company Limited, the amount of clay required may be up to 3% by weight, preferably approximately 2.5% by weight. Polysaccharides which may be used include those already known as gelling or thickening agents in other applications. Particularly preferred in the compositions according to the invention is xanthan gum. The amount of polysaccharide, e.g. xanthan gum, used may be e.g. 0.05 to 0.2%, preferably 0.05 to 0.16%, more preferably 0.08 to 0.15% or 0.08 to 0.14%, most preferably about 0.1% or 0.12%, based on the total weight of the composition. Optionally a dispersant, for example an acrylic polymer, or water soluble polymeric dispersants such as polyethylene oxide, hydrolysed polyvinyl acetates, polyvinyl pyrrolidone, polyacrylamide and polyvinyl alcohol, may be added prior to the polysaccharide during the manufacture of the suspension according to the invention. This aids the dispersion of the polysaccharide in water. The amount of dispersant may be small. For example 0.05 to 1%, generally about 0.1% by weight, of a polyacrylate dispersant may be used. Preferred suspensions according to the present invention contain, based on the total weight of the composition: 10 to 12% by weight boron as sodium pentaborate; 0.5 to 1.5% by weight of IGB; 0.05 to 0.16, e.g. to 0.15% by weight xanthan gum; 0.00 to 0.5% by weight polyacrylate dispersant; the remainder being water. The amount of the anti-settling system incorporated obviously depends on the size and concentration of the resulting suspended particles. Generally speaking the suspension comprises particles predominantly less than 10 microns in size, e.g. in the range 0.1 to 10 microns, and more preferably below 5 microns (e.g. 0.1 to 5 microns) in size. The nature of the interaction between the sodium pentaborate and clay and polysaccharide, leading to reduced viscosity, is not fully understood. The reduced viscosity observed with the addition of ingredients which would normally be expected to result in a thickening effect is regarded as most surprising. The suspensions according to the present invention may be prepared by any suitable route. Suitably the sodium pentaborate may be prepared in suspension, with agitation, in situ by reaction in water of boric acid and a hydrated sodium tetraborate, preferably sodium tetraborate pentahydrate, with the other ingredients premixed in water being added before, during or after the reaction. According to the present invention, there is provided a process for preparing a suspension, which process comprises, in aqueous suspension, allowing boric acid and a sodium tetraborate, generally in substantially stoichiometric amounts for sodium pentaborate, to react under agitation, and before, during or after the reaction, adding to the suspension or adding the suspension to the clay, polysaccharide and any other ingredients, themselves also being dispersed in water. According to one embodiment, there is provided a process for preparing a suspension according to the invention which process comprises forming a mixture of the clay, polysaccharide and any other ingredients with water, adding boric acid and a hydrated sodium tetraborate in substantially stoichiometric amounts for sodium pentaborate and allowing to react under agitation. The particle sizes of the borate feed stocks are not critical. They may be in granular, crystalline or finely divided forms. Alternatively, they may be added as wet cakes or slurries. In one aspect of the invention, the water can be derived from plant liquors obtained from processes well known to the art for manufacture of boric acid or sodium tetraborates, that are saturated with the respective boric acid or sodium tetraborate. Preferably the clay is dispersed in water (optionally containing a dispersant) according to the manufacturers recommendations (about 10 minutes). The polysaccharide is then added to the suspension and dissolved according to the manufacturers recommendations (about 50 minutes) . This results in hydration of the clay. After this period the mixture may optionally be heated, e.g. up to about 50°C, e.g. to 35 to 40°C, suitably about 38 °C. Boric acid and sodium tetraborate are then added and the mixture is allowed to react, with agitation, generally for about one half to one and a half hours, preferably about forty five minutes, i.e. until coarse particles are essentially all reacted, e.g. after 1 hour. At no time should there be complete solution of the borate ingredients and sodium borate reaction product. The mixture may then be discharged to a holding vessel or packed. Generally speaking the reaction may continue on standing with any coarse particles remaining disappearing on standing e.g. overnight. The reaction is endothermic leading to an initial drop in temperature. The reaction may be carried out at 20°C with the endotherm leading to a cooling to about 12°C after 5 to 10 minutes while the exotherm leads to a temperature rise to about 20 °C when the crystallisation is all but complete i.e. after about 30 minutes. A temperature of 20°C, i.e. no external heating is required, is preferred, for the purpose of dispersing the clay and polysaccharide. However it may be desired to heat the clay and polysaccharide dispersion prior to addition of the boric acid and sodium tetraborate. If the temperature is allowed to become too high, e.g. up to 80°C, crystal sizes may become unacceptably high. However temperatures of up to 50°C e.g. 35 to 40°C, suitably about 38 °C, may generally be used with advantage and without adverse effect on particle size. The particle size of the crystals making up the suspension are predominantly in the range of 0.1 to 10 microns. When the reaction is carried out with heating, the reaction times are generally shortened. The boric acid and sodium tetraborate react with the formation of sodium pentaborate. The reactants will normally be used in their stoichiometric ratio of Na 2 0:5B 2 0 3 . Any excess boric acid or sodium tetraborate will remain unreacted and may contribute to coarser crystals in the final products. In some applications excess boric acid may be desired. In this case, when fine boric acid is required, the suspension may be wet milled. In a modification finely divided boric acid may be added to the formed suspension. Unexpectedly this results in a product having substantially the same flow properties as product without boric acid addition. This is the case for example when the amount of boric acid present increases the overall boron content from 10 to 11%. The compositions according to the invention may be used as fertilisers. When used for the application of boron to crops, the composition according to the present invention is compatible with and may be used together with other plant fertilisers for simultaneous spraying. However, with the well established nitrogen fertiliser N39, to ensure compatibility, the clay selected is suitably IGB and this is used with xanthan gum and an acrylic polymer dispersant that assists the dispersion of the ingredients of the composition in N39. It may also be convenient in some applications to incorporate small amounts of other micronutrients, herbicides, fungicides or insecticides. According to the invention, there is provided a method of treating crops, e.g as a fertiliser which method comprises: (a) diluting with water a suspension according to the invention, optionally in the presence of another treatment agent; and (b) applying the diluted composition to a crop or to a location in which crops are growing or are intended to grow. Also there is provided a method of treating crops e.g as a fertiliser which method comprises applying a suspension according to the invention optionally in the presence of another treatment agent, to a crop or to a location in which crops are growing or are intended to grow. The invention is further illustrated with reference to the following Examples: EXAMPLE 1 A pourable aqueous borate-containing suspension was prepared as follows: Water (4698g) at 20°C was added to a 5 litre reaction vessel and stirred at 500 rpm. 12g of Dispex N40 acrylic polymer dispersant (ex Allied Colloids) was added followed by 123g IGB montmorillonite clay (ex IMV Nevada) . Stirring was continued for 10 minutes and then 12g of Kelzan xanthan gum (ex Kelco Industrial Biopolymers) were added and stirring was continued for a further 50 minutes. The mixture was transferred to a 10 litre reaction vessel and stirred at 1000 rpm using a saw-toothed stirring disc to ensure constant agitation of all of the composition. 4200g of Optibor TG boric acid (ex US Borax Inc.) was added and this was immediately followed by 3300g of Neobor borax pentahydrate (ex U.S. Borax Inc.). Agitation was continued for a further 60 minutes. The product was a pourable suspension containing 10% by weight boron as sodium pentaborate with the suspended particles having a particle size less than 10 microns. EXAMPLES 2 TO 6 The method of Example 1 was followed and the ingredients were added in the amounts shown in Table I below. A pourable stable composition was obtained in each case. TABLE I BA - boric acid %B represents the percentage boron as sodium pentaborate, EXAMPLE 7 247g (2% by weight) bentonite were dispersed in water (4585g) at 40°C with stirring over 10 minutes. 12g (0.1% by weight) of Kelzan xanthan gum was added and the stirring was continued for a further 50 minutes. Boric acid (4200g) and borax pentahydrate (3300g)were added to the mixture obtained. The resulting mixture was stirred at 850 rpm for 45 minutes using a saw toothed blade . The product was a pourable and stable suspension containing 10% by weight boron as sodium pentaborate, with the suspended particles having a particle size less than 10 microns . EXAMPLE 8 Water (132.5 kg) at 20°C was poured into a 200 litre tank stirred at 200 rpm using a 10 cm diameter saw toothed head. 0.35 kg (0.1% by weight) of Dispex dispersant were added followed by 3.5 kg (1% by weight) IGB clay. Stirring was continued for 10 minutes and then 0.35 kg (0.1% by weight) Kelzan xanthan gum was added and stirring was continued for a further 50 minutes. The mixture was transferred into a jacketed 500 litre tank and stirred using dual high efficiency hydrofoil propellors 25cm in diameter. The mixture was then heated to 38 °C by pumping steam through the heating jacket. Boric acid (119.5 kg) and borax pentahydrate (94 kg) were added to the tank and stirring was carried out for 75 minutes at 100 rpm. The product was a pourable and stable suspension containing 10% by weight boron as sodium pentaborate.

Claims: CLAIMS 1. A pourable aqueous borate-containing suspension which suspension in water contains 8 to 13% by weight boron as sodium pentaborate, 0.1 to 3% by weight, based on the total weight of the composition, of a swellable clay, and 0.05 to 0.2% by weight, based on the total weight of the composition, of a polysaccharide. 2. A suspension according to claim 1 which contains 9.5 to 12.5% by weight boron as sodium pentaborate. 3. A suspension according to claim 1 which contains 10 to 12% by weight boron as sodium pentaborate. 4. A suspension according to any preceding claim which contains 0.5 to 1.5% by weight, based on the total weight of the composition, of the swellable clay. 5. A suspension according to claim 4 which contains approximately 1% by weight, based on the total weight of the composition, of the swellable clay. 6. A suspension according to any preceding claim wherein the swellable clay is a montmorillonite clay, a mineral analogous to montmorillonite, or sepiolite. 7. A suspension according to claim 6 wherein the swellable clay is a sodium enriched montmorillonite clay, a sodium montmorillonite clay, hectorite or sepiolite. 8. A suspension according to any preceding claim having a particle size of 0.1 to 10 microns. 9. A suspension according to any preceding claim wherein the polysaccharide used is xanthan gum. 10. A suspension according to any preceding claim which also contains a dispersant. 11. A suspension according to claim 10 wherein the dispersant is a polyacrylate. 12. A suspension according to any preceding claim which also contains boric acid particles. 13. A suspension according to claim 1 substantially as described in any of Examples 1 to 8. 14. A process for preparing a suspension as claimed in any preceding claim which process comprises, in aqueous suspension, allowing boric acid and a sodium tetraborate to react under agitation to form sodium pentaborate in the presence of the clay, polysaccharide and any other ingredients . 15. A process according to claim 14, in which there is formed a mixture of the clay, polysaccharide and any other ingredients with water, and boric acid and a hydrated sodium tetraborate are added in substantially stoichiometric amounts for sodium pentaborate and allowed to react under agitation. 16. A suspension according to claim 1 prepared by the process claimed in claim 14 or 15. 17. A method of treating crops which method comprises (a) diluting with water a suspension as claimed in any of claims 1 to 13, optionally in the presence of another treatment agent; and (b) applying the diluted composition to a crop or to a location in which crops are growing or are intended to grow. 18. A method of treating crops which method comprises applying a suspension as claimed in any of claims 1 to 13, optionally in the presence of another treatment agent, to a crop or to a location in which crops are growing or are intended to grow.

Inventors: CAMPBELL COLIN WILLIAM, HAYATI IGAN, CAMPBELL, COLIN, WILLIAM, HAYATI, IGAN
Applicants: CAMPBELL COLIN WILLIAM, HAYATI IGAN, UNITED STATES BORAX INC, CAMPBELL, COLIN, WILLIAM, HAYATI, IGAN, U.S. BORAX INC.
Application year: 1999
Main classification: C05D9
IPC codes: C01B35, C05D9, C05G3