POWDERED INSECTICIDAL COMPOSITION CONTAINING SILICA GEL

Abstract: A process for preparing a powdered insecticidal composition comprising the steps of forming a silicic acid and ammonium fluosilicate mix, spraying the mix onto carrier particles of size range 100 to 500 Tyler mesh thereby producing damp sorptive particles coated with the mix in a gel form. The carrier particles are preferably inorganic sorptive particles selected from diatomaceous earth, bentonites, sub-bentonites, montmorillonites, pyrophillite, Fuller's earth, silica flour, carbon or perlite. The damp sorptive particles produced are stabilized with ammonia gas and dried.

Description: POWDERED INSECTICIDAL COMPOSITION CONTAINING SILICA GEL This invention is concerned with non-poisonous insecticides and is more particularly concerned with the production of such insecticides as are described in the specification of Australian Patent No. 476508 the disclosure of which is incorporated herein by reference. BACKGROUND ART The insecticides described and claimed in Australian Patent 476508 have been found to be most effective. However production methods currently employed in the manufacture of such insecticides are somewhat time and energy consuming and it is an advantage of a preferred embodiment of this invention to provide a process for production of non-poisonous insecticides which provide for easier processing. It is a further object of a preferred embodiment to provide a process which is less time and energy consuming than the process described and claimed in Australian Patent 476508. In brief Australian Patent 476508 discloses an insecticidal powdered composition useful as a sorptive dust, insecticide which is effective on contact with the insect's waxy epicuticle. The inorganic sorptive particles are sized in the range of about 100 to about 500 Tyler screen mesh and are selected from such materials as diatomaceous earth, bentonites, sub-bentonites, montmorillonites, pyrophiUite, Fuller's earth, silica flour carbon and perlite. Adhered to the surface of such particles is a coating of sorptive silica gel, this gel ranging from about 0.1% to 10% by weight of the total weight of the coated particles after drying. The composition preferably has a packed bulk density from about 15 to about 100 lbs per cubic foot. Australian Patent 476508 calls for in-situ gelling of the silica gel onto the inert carrier, the inert carriers suitable in the practice of the invention of the said patent being specified in the body and claims thereof. In the preparation of the product of the said patent the silica gel and inert carrier mix must be washed and decanted several times to remove the sodium sulphate produced during the in-situ gellation. After washing, the product is filtered and dried. The water content of a typical formulation, after filtration, is about 70%, that is for each tonne of dry product made, 2.3 or so tonnes of water must be dried off. Obviously the cost of this drying is a significant factor in production costs and any saving in energy costs is advantageous. The disclosure in AU 476508 evolves about the discovery that inorganic particles may be coated with an adherent coating of a sorptive silica gel composition, especially hydrogels, and that the particles thus coated are highly effective as insecticides. As will be described more completely, the particles used preferably should have a sorptive surface, that is the particles themselves should be of a sorptive character. Also, for many uses, a compound such as ammonium fluosilicate is included, which is considered to aid in attracting and/or holding the particles to naturally occurring objects including plants and insects. The preferred particles for use with the present process are diatomaceous earth (diatoraite) , si'rice it has-been found that such particles are quite effective and also are of comparatively low cost and are readily available. However, various other sorptive materials may be used, including various bentonites, sub-bentonites, montmorillonites, pyrophyllite, fuller's earths, silica flour, carbon, perlite, and other natural or synthetic substantial equivalents. The size of the inorganic particles can be varied to a considerable extent, although the size of the particles is important with regard to the ease with which the insecticide can be distributed. In general, the smaller the particles the easier it is to distribute the particles to an operative or intended location as long as size of the particle is sufficiently great that the particles cannot, because of their low weight, be blown about indiscriminately as dust in the air on a normal or "quiet" day. Thus, the particles should be sufficiently large and/or heavy so that they are capable of settling from "normal" or reasonably quiet air, that is at least about 400 mesh (Tyler screen size) or greater. Because the particles must, however, be sufficiently fine so that they can be easily distributed, they should pass a 100 mesh standard Tyler screen and preferably all or substantially all pass a 200 mesh standard Tyler screen. In a composition produced according to the method of AU 476508, the inorganic particles are coated with an adherent coating of a silica gel, normally a hydrogel. Silica aerogels and hydrogels are well known and are used for many purposes such as in the paper and protective coating fields. These aerogels and hydrogels are considered to be highly absorbent for various materials such as water, oils, waxes, and the like. In general, hydrogels tend to be more absorbent toward water and various compositions which are similar to water than aerogels. Conversely, aerogels tend to absorb waxes and various other related compounds characterized by having comparatively long aliphatic hydrocarbon chains to a greater extent than the hydrogels. It is to be noted, however, that the sorptive characteristics of a hydrogel may be changed by various known expedients so as to produce properties which tend to approximate the sorptive properties of an aerogel. • • The thickness of the silica gel coating on the inorganic particles may be varied considerably and may be either a continuous or discontinuous coating, that is, the inorganic particles may or may not be completely coated. The surface of the inorganic particles must have sufficient silica gel coated thereon, however, to impart the necessary sorptive insecticidal properties to the composition. Since the lipid layer of insects is very thin, only a small amount of sorptive silica gel is necessary to kill the insects, and hence only a small quantity of silica gel coating on the inorganic particles is necessary. In general, the silica gel coating will be at least 0.1 percent by weight of the total weight of the dry coated particles, and preferably at least about 0.2 percent. Insofar as the effectiveness of the insecticidal composition is concerned, there does not appear to be an upper limit on the quantity of the silica gel coating. For economic reasons, however, the quantity of such coating will be kept to a inumum, generally not exceeding approximately 10 percent by weight of the total weight of the coated particles. It should also be noted that the silica gel coated inorganic particles, of course, are applied in powder form as a batch of the finely divided coated particles rather than as single particles. Consequently, it is not essential that every particle in such batch have the same quantity of silica gel coating, as it is the effect of the total batch which is significant. In other words, the total batch must contain a sufficient quantity of the sorptive silica gel to provide the necessary insecticidal properties rather than the individual particles. Accordingly, based on the total weight of such a batch, the sorptive silica gel should comprise at least about 0.1 percent by weight and preferably at least 0.2 percent. Depending on the circumstances and nature of the process used to produce the coated particles, individual particles of the composition may contain little or no silica gel coating. Since the coated particles are used as a batch, however, this will not affect the effectiveness of the composition as an insecticide, so long as the composition as a whole contains the indicated minimum quantity of sorptive silica gel. The composition of coated particles, for effective results, will normally have a packed bulk density of about 15 to about 100 pounds/cubic foot, preferably about 20 to about 30 pounds/cubic foot, since the composition may be used in unenclosed areas where the effect of wind must be taken into consideration. The packed bulk density, as is well understood by persons skilled in the art, is the weight/unit volume of the powder when packed in a standard cubic foot container and may be determined simply by filling such a container with the powder and weighing the same. DISCLOSURE OF THE INVENTION It has now been discovered that if the silica gel used in the formulation of the product of Australian Patent 476508 is pre-formed either by ion exchange or by acid treatment of sodium silicate and the thus pre-formed dispersed gel sprayed on to the dry, inert carrier, the need for further washing is eliminated or at least substantially reduced. This clearly permits significant savings in capital cost of manufacturing plant by eliminating the need for filters and decanters and also by reducing the requirement for drying equipment. Further, the requirement for fresh water is reduced from about 16 tonnes per tonne of product to 3 tonnes per tonne of product. The water content of t-he end product, prior to drying is reduced from 2.3 tonnes or so per tonne of product to about 1 tonne per tonne of product. Typically, the drying heat load is reduced from about 10 gigo-joules per tonne of product to about 5 gigo-joules per tonne of product. According to the present invention there is provided a process for preparing a powdered insecticidal composition comprising the steps of: forming a silicic acid mix, spraying said mix onto carrier particles of size range 100 to 500 Tyler mesh thereby producing damp sorptive particles coated with said mix in a gel form. According to a further form of the present invention there is provided an insecticidal composition when prepared by the above process. According to yet another -form of the invention there is provided a method for erradicating insects at a locus by use of an effective amount of an insecticidal composition prepared according to the method above described. It has been found that the sorptive silica gel should be intimately adhered to the inorganic particles as a coating rather than in the form of a mixture of the aerogel or hydrogel and such particles since the degree of adherence produced by mixing is not sufficient because the silica gel and the inorganic particles may be readily separated as, for example, in handling. Further, for reasons which are not clear, the insecticide is not as effective as when a direct, intimate bond is achieved between the silica gel and the inorganic particles. It has been found advantageous to add ammonium fluosilicate to the silicic acid composition prior to dispersal upon the inorganic sorptive particles. This is in contrast with the method of AU 476508 wherein it was disclosed to add the ammonium fluosilicate to the particles after they had been coated with the silica gel. Alternatively, in a preferred form, the ammonium fluosilicate can be sprayed onto the carrier particles prior to spraying the silicic acid mix onto the carrier particles. In a further preferred form, the ammonium fluosilicate can be sprayed onto the damp sorptive particles coated with the silicic acid mix in a gel form. That is, the ammonium fluosilicate can be added after formation of the silicic acid gel coating and prior to the drying step. It is believed that the ammonium fluosilicate reacts in some manner with the sorptive silica gel to provide the desired electrostatic properties to the particles. It should be used in a quantity of at least about 5% by weight based on the weight of the sorptive silica gel. MODES OF CARRYING OUT THE INVENTION By way of example only, two embodiments- of the present invention will now be described. Example 1: A dilute sodium silicate solution (equivalent to a 6% Si0 2 by weight solution) was passed through an ion exchange resin and converted to silicic acid., also of 6% content by weight Si0 2 . Ammonium fluosilicate was dissolved in the silicic acid thus produced at a rate of 13.7g per 400g of silicic acid. The resulting mixture was sprayed onto 302g of dry diatomaceous earth to give a 7% silica gel coating. The resulting damp powder was stabilised with ammonia gas and dried in accordance with the process of Australian Patent No 476508. The damp powder contained only 53% water, i.e. 1.1 tonne of water per tonne of product to be removed. Example 2: 250g of sodium silicate (at a 6% Si0 2 equivalent content in solution) was gelled with sulfuric acid. The resulting gel was cut into small pieces and washed three times using four volumes of water for each wash. After the last decantation, water was added to make up a total weight of 250g. To this was added 13.2g of ammonium fluosilicate and the mixture was dispersed with a high speed mixer then sprayed onto 272g of dry diatomaceous earth to give a 5% silica gel coating. The resulting damp powder contained only 0.75 tonne of water per tonne of product. The damp powder was stabilised and dried as in Example 1. When tested in accordance with the protocol established by the Department of Agriculture of Western Australia in liason with the C.S.I.R.O., the test results were as follows: Days required to achieve 100% mortality of 100 test insects: Example 1 7 days Example 2 7 days

Claims: CLAIMS 1. A process for preparing a powdered insecticidal composition comprising the steps of: forming a silicic acid mix, spraying said mix onto carrier particles of size range 100 to 500 Tyler mesh thereby producing damp sorptive particles coated with said mix in a gel form. 2. The process of claim 1, further comprising the step of stabilising acid damp sorptive particles with ammonia gas and drying the stabilised particles. 3. The process of any preceding claim wherein said mix applied to said carrier particles is in the range of 0.1% to 10% by weight based on the total weight of dried coated particles. 4. The process of any one of claims 1 to 3, wherein the carrier particles are inorganic sorptive particles. 5. The process of claim 4 wherein said inorganic sorptive particles are selected from--one or more of diatomaceous earth, bentonites, sub-bentonites, montmorillonites, pyrophiUite, Fullers earth,- silica flour, carbon or perlite. 6. The process of any preceding claim wherein the silicic acid strength in said mix is in the range of 0.1% to 10% by weight. 7. The process of any previous claim wherein the mix is formed by gelling a solution of an alkali metal silicate, an alkaline earth metal silicate or an ammonium silicate or any combination of two or more thereof with an organic or inorganic acid, cutting said gel into small pieces, washing said gel pieces and adding water and ammonium fluosilicate to said gel pieces. 8. The process of claim 7, wherein the mix is dispersed by means of a mixer prior to spraying onto said carrier particles. 9. The process of claim 7 or claim 8 wherein said organic or inorganic acid is sulfuric acid. 10. The method of any one of claims 1 to 6 wherein the mix is formed by passing a solution of an alkali metal silicate. an alkaline earth metal silicate or an ammonium silicate or any combination of two or more thereof through an ion exchange resin to produce silicic acid and mixing said silicic acid with ammonium fluosilicate. 11. The process of any of claims 7 to 10 wherein said solution of an alkali metal silicate, alkaline earth metal silicate or an ammonium silicate or any combination of two or more thereof comprises approximately 0.5% - 50% by weight of silicon dioxide. 12. The process of any one claims 7, 8 or 9 wherein said solution of an alkali metal silicate, alkaline earth metal silicate or an ammonium silicate or any combination of two or more thereof comprises approximately 10% by weight of silicon dioxide. 13. The process of claim 10 wherein said solution of an alkali metal silicate, alkaline earth metal silicate or an ammonium silicate or any combination of two or more thereof comprises approximately 6 % by weight of silicon dioxide. 14. The process of any preceding claim wherein ammonium fluosilicate is added to said mi* prior to spraying said mix ** onto said carrier particles. 15. The process of any one of claims 1 to 13 wherein a solution of ammonium fluosilicate is sprayed onto said carrier particles prior to spraying said mix onto said carrier particles. 16. The process of any one of claims 1 to 13 wherein a solution of ammonium fluosilicate is sprayed onto said damp sorptive particles coated with said mix in a gel form. 17. The process of any one of claims 14 to 16 wherein the quantity of dried ammonium fluosilicate applied to said carrier particles yields a coating of dried ammonium fluosilicate which is at least 5 % by dried weight based on the weight of the dried sorptive silica gel coating. 18. A process for preparing a powdered insecticidal composition as hereinbefore particularly described with reference to the examples. 19. An insecticidal composition when prepared by the process of any one of the preceding claims. 20. A method for erradicating insects at a locus by application of an effective amount of the insecticidal composition of claim 19 at said locus.

Inventors: HEDGES KENNETH BLAKE, HEDGES, KENNETH, BLAKE
Applicants: AGNEW CLOUGH LTD, DRYACIDE PTY LTD, AGNEW CLOUGH LIMITED, DRYACIDE PTY. LTD.
Application year: 1985
Main classification: A01N59
IPC codes: A01N59