Patent Application
20070014865
1. Field of the Invention
The present invention relates to chemically stable, dry-flow, low compact, dust free, soluble granules of phosphoroamidothioate prepared by a substantially dry granulation process including an agitative balling process. This dry granulation process preferably produces spherical granules of phosphoroamidothioate without using substantial amounts of water, liquid, solvent or binder. The granules are preferably characterized as having a spherical shape with a low bulk density, narrow particle size distribution, least crushing strength, proportionate pore size distribution, uniform surface area and a low angle of repose which are responsible for their dust free nature and high flowability.
2. Description of Related Art
In recent years, agricultural chemicals have been most preferably formulated in the form of dusts, wettable powders, soluble powders, emulsifiable concentrates, soluble liquid/concentrates, granules, coated granules, water dispersible granules, suspension concentrates, and solutions. Occasionally, when dusts are produced by absorbing or mixing active ingredients with a finely divided inert carrier material, for example China Clay or the like, drift problems occur. With wettable powders and soluble powders the problems faced at the time of dilution are not only drift, but the final disposal of containers, for dust particles tend to stick to sides of the containers. The left over materials within the containers pose great problems to the environment, operators and users.
Dust emission from granular pesticides has, in recent years, been an increasing concern because of the growing reliance on bulk handling of pesticides, in preference to bags, and because of the heightened awareness of the potential health hazards of airborne dust. Dustiness, in large part, is due to inefficient removal of fines during manufacture, poor granule strength, abrasion of fine surface crystals, and poorly adherent anti-caking additives. As a consequence, a substantial amount of dust is created during handling and transportation of granular pesticides.
Dust control is in most cases a superficial and temporary remediation. Road and/or soil stabilization are more aggressive techniques that involve forming a longer-lasting structure, which incorporates subsurface matter to some depth in combination with an externally applied binder. The binders used for dust control and for road or soil stabilization serve a similar function, with the binding ability or amount of the binder varying across a spectrum.
The processing, packing, storage, handling and applying of such compositions can have attending complications and problems. Such problems can require improvements in production methods to reduce attrition and undersizing of particles leading to dustiness and product loss. It can require mechanical methods to assist in formulating and handling the products.
The processing of such compositions comprise an active substance by using an effective amount of moisture content to enhance the flowability of the particulate composition, reduce the dustiness of the composition to some extent, increase the bulk density of the composition. Another method for producing such pesticidal particulate compositions is controlled slurry production and spray-drying effective in producing such compositions with enhanced properties. More preferably, the amount of moisture content is optionally effective to reduce the dustiness of the composition, increase the bulk density of the composition only when the active substance is stable and not degraded in the presence of moisture. Also, in some literature references, the volume percent amount of dry particles greater than about 20 micrometers is at least about 50 percent of the volume percent amount of dry particles present when said composition is dried to 1 percent moisture content.
Of the current products that provide effective dust suppression, certain drawbacks exist, namely poor longevity, environmental toxicity and cost. Many such products that have a desirable useful life are generally considered to be environmentally unsafe. Other products that are more environmentally friendly have a shorter useful life. Synthetic binders that possess a favorable useful life and that do not have serious environmental problems are available, but such products are costly. Oils and oil emulsions are costly, have stickiness concerns and are not environmentally friendly.
Generally non dusty materials derive their effectiveness from the hygroscopicity of one of the components of the formulation. Although generally effective in drawing enough moisture from the air to immobilize dust particles, the highly soluble nature of the agents causes them to be easily washed away.
Although dusts are undesirable because of airborne contamination and handling difficulties, liquid spray formulations have not provided an acceptable alternative, for they involve solvents and packaging expenses, along with container disposal requirements that detract from their commercial desirability.
Water dispersible granules produced by fluidized bed spray dryers overcome the problems associated with wettable powders and soluble powders, but have high processing costs and require high value capital investment, as well as requiring highly skilled staff. These problems impose a significant barrier in widening the market acceptance of these compounds.
Certain phosphoroamidothioates and phosphoroamidodithioates, collectively referred to as phosphoroamidothioates, are known to have excellent insecticidal activity against a variety of insects and in a variety of environments. Acephate, one of the important commercial insecticides within this class of compounds, is a systemic and contact insecticide of moderate persistence with residual activity lasting about 10-15 days. It is effective against a wide range of aphids, leaf-miners, lepidopterous, larvae, sawflies and thrips and it is also a non-phytotoxic on many crop plants.
Phosphoroamidothioate containing pellets have been proposed in the past, but difficulties have been encountered in pelletizing acephate technical, the preferred insecticide within the class of phosphoroamidothioates. Attempts to manufacture acephate technical pellets from acephate technical powders have been proposed and have several disadvantages. As disclosed below, prior extrusion processes include the addition of costly surfactants, the combination of phosphoroamidothioate with a second active ingredient, or the creation of a mixture of the active ingredient with a solvent in an amount of from 3-25% by weight before extrusion.
One formulation of acephate presently in use is acephate 75% soluble powder having acephate active ingredient (a.i.) 75% (w/w), surfactant 1 to 2% (w/w), inert filler (precipitated silica) to make 100% (w/w). Acephate 75% soluble powder poses several problems including the production of dust, low pourability of the powder, high transportation costs, high capital manufacturing investment, measurement difficulties, difficulties in packing, material disposal, handling problems, high risk of caking and others.
A previous process for preparing pellets comprising insecticidal N-hydrocarboyl phosphoroamidothioates and/or phosphoroamidodithioates includes the extrusion of a solid composition. The concentration of the active ingredient in the pellets prepared is in the range of about 2 to 80% a.i., with the most likely concentration of 70% a.i. The process comprises (i) forming an extrudable mixture comprising the active ingredient; (ii) forming said pellets by extrusion of the mixture and cutting the extrudate. Another similar method comprises (i) forming a suspension or solution containing said active ingredient and a dispersant, wetting agent and/or surfactant; (ii) evaporating the solvent from said solution or dispersion; (iii) dividing the remaining solids into particles; and (iv) forming the resultant mixture into pellets. These processes experience several limitations and difficulties. First, the amount of active ingredient is in the range of about 2 to 80%, preferable being 70% so the process does not produce pellets having a concentration of active ingredient above 80%. Second, the process envisions two active ingredients namely N-hydrocarboyl phosphoroamidothioates and phosphoroamidodithioates in a single product. The selection of the combination of ingredients is important so that the product does not deteriorate in a few days to a few months. Third, the process involves forming a suspension or solution of the active ingredient and a dispersant, wetting agent and/or surfactant, and evaporating the solvent which are complicated processes and make the manufacturing process cumbersome and uneconomical.
In another previously used process for pelletizing insecticidal N-hydrocarboyl phosphoroamidothioates and phosphoroamidodithioates, the insecticidal ingredient in the pellets formed is in the range of about 50 to 95% preferably about 90%. This process involved mixing technical grade insecticide in a dry form with one or a mixture of surfactants (10% by weight of total dry composition) preferably containing an inert diluents ammonium sulfate (<40% of total pellet composition preferably 2% or less); solid additive (up to about 40% anhydrous Magnesium sulphate) and small amounts of deodorants and antifoam agents. The dry ingredients are ground to powdered form. Currently available pelletized acephate, known commercially as ORTHENE, requires the use of an anticaking agent, such as fumed silica. This process also has various limitations and difficulties. The amount of insecticidal ingredient present in these pellets is in the range of about 50 to 95%, preferably about only 90%. The final product may also contain inert diluents ammonium sulfate (<40% of total pellet composition preferably 2% or less) by weight of the total pellet composition. The presence of this agent is not desirable in the final product as it adds to the cost and imparts hardness to the granule when the active ingredient in the granule is in low concentration. The product may also include up to about 40% anhydrous magnesium sulphate, preferably 2% or less by weight of the total pellet composition, as a dehydrating agent to absorb trace amounts of the water present in the pellets to prevent hydrolysis of the insecticide. The presence of this agent is not desirable in the final product because it adds insoluble matter into the granules which causes problems in the application of the product.
In yet another previous process for forming pelletized insecticidal N-Hydrocarboyl phosphoroamidothioates and phosphoroamidodithioates, extrusion of a damp sandy loam of a dry mixture of the active ingredient and a solvent is formed. Several limitations and difficulties are associated with this process. First, the process involves mixing of active ingredient in a solvent to form a consistency of damp sandy loam and then pellets are formed by extrusion. Second, the process involves passing the mixture of active ingredient and the solvent in molten form through an orifice to form molten pellet-sized drops of said active ingredient and solidifying the said drops. These steps increase the processing costs of making the pellets because of the addition of costly solvents and the additional drying steps to remove the solvent and/or moisture.
One rapidly expanding field used in a variety of chemical processes is an agitative balling process for the formation of granules. Current processes used for making granules using the agitative balling process produce agglomerations and the resulting granules by admixing fine powder with binders, water or other types of liquids. The addition of binders, waters and other liquids increases the processing costs in formulating the granules.
Because of the problems associated with producing granular forms of phosphoroamidothioates, such as the preferred acephate, there is a need in the art for a process for preparing chemically stable, dry flow, low compact, dust free, insecticidally active soluble granules of phosphoroamidothioate which are useful from a practical stand point, as well as for a low cost, practical manufacturing technique which can be practiced on a commercial scale without requiring expensive additives or solvents. There is also a need for a non-dusty, freely flowable granule which characteristics have not been achieved to a maximum extent in any product known so far.
The problems associated with previous method for making chemically stable, dry flow, low compact, dust free, insecticidally active soluble granules of phosphoroamidothioate may be overcome by a substantially dry granulation process which uses an agitative balling process preferably producing spherical granules. Additional ingredients, such as specified adjuvants and other inert ingredients may be included in the dry granulation process and are preferably added as solids forming a dry pre-mix. The dry granulation process is performed without employing substantial amounts of water and/or solvent. In a preferred embodiment, no water and/or solvents are intentionally added at any stage of the process. The concentration of phosphoroamidothioate present in the resulting granules preferably varies from 75-99 wt. % phosphoroamidothioate. Acephate is the preferred phosphoroamidothioate.
The dry pre-mix is ground in a microniser and then the dry pre-mix is granulated using the agitative balling process through a granulator. The granulator is preferably provided with an external jacket heater to attain and maintain a processing temperature of preferably 115-145° F. The product is further passed through an air chamber to condition the granules for good surface finish. The conditioned product is then sieved for removal of fines, which are later recycled, resulting in chemically stable, dry flow, low compact, dust free, soluble granules of phosphoroamidothioate, preferably acephate. No sizing operation is required, which helps to avoid exposure and handling of dust.
In a preferred embodiment, the dry granulation process produces a spherical granule of phosphoroamidothioate without the intentional addition of water or any solvent in any step of the process. Since the dry granulation process avoids the use of water and/or solvent, the process is a free flowing process. Additionally, the dry granulation process avoids compacting or extruding of the material used to make the granules. By avoiding compaction and/or extrusion, the resulting granules have low compact and are readily soluble in water. Water soluble and insoluble powder can be mixed together in the absence of water to produce uniformly blended water dispersible granules.
The dry granulation process includes an agitative balling process, which utilizes a heat and balling conditioning of powder material. The present dry granulation process is a blend of technology relating to particle size enlargement and balling. The agitative balling process produces an agglomeration using binding force to achieve the granular shape by combining a brute force of agitation and a softening point of the material. The dry granulation process recognizes the distinct difference between forming pellets from powder and producing granules by an agitative balling process. More specifically, the agitative balling process described herein consolidates particles to produce a granular shape using external heat. The present dry granulation process shows that binding of dust particles can be achieved on account of the “binding tendency” induced in the dust particle at the softening point due to gentle heating. In one embodiment of the present invention, the phosphoroamidothioate used for the dry granulation process may have a trace concentration of process solvents, up to 1.0 wt. % max, preferably 0.5% max., which adds in attaining the softening of the material at lower temperature and enhances the compacting tendency to form granules.
The preferred granules produced using the process of the present invention are characterized by a lower angle of repose, preferably lower than 25, which is responsible for their increased flowability resulting in minimum dustiness.
In the present invention the particle size and distribution is such that the embodied composition has a significantly reduced dustiness, that is, reduced volume of particles with particle diameters. The granules resulting from the present invention exhibit excellent mechanical stability when dry so that dustiness is minimized during handling an application in conventional distribution equipment. Yet, after such particles are placed in contact with soil and contacted with water, they rapidly solubilize and/or disintegrate to substantially their original ungranulated, fine particle-size distribution for realizing and effecting maximum pest control.
The features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawing, in which:
The process of the present invention is best described by referring to the flow chart in
wherein R and R1 individually are an alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, R2 is hydrogen, an alkyl group containing 1 to 18 carbon atoms, a cycloalkyl group containing 3 to 8 carbon atoms, an alkenyl group containing 2 to 18 carbon atoms or an alkynyl group containing 3 to 18 carbon atoms, R3 is hydrogen or an alkyl group containing 1 to 6 carbon atoms, and Y is oxygen or sulfur. All of the ingredients are preferably solids and in a powder form. In a preferred embodiment, the preferred dry pre-mix contains 75.0-99 wt. % phosphoroamidothioate 2, 0.1-3.0 wt. % wetting agent 6 and a filler 16 to make 100 wt. %. The preferred phosphoroamidothioate is acephate. In a preferred embodiment of the present invention the wetting agent 6 is a calcium or sodium salt of alkyl aryl sulphonate; the dispersing agent 4 is a derivative of sulfonated fatty alcohol; the disintegrating agent 12 is selected from swelling type clays like bentonite, zeolite; the antifoaming agent 10 may be a silicon oil derivative; the stabilizer 14 is selected from salts of higher fatty acids; and the filler 16 is selected from precipitated silica, kaoline, bentonite, dolomite and the like. In a preferred embodiment, no water and/or solvents are intentionally added during the dry granulation process. However, if the processing temperature is low, a small amount of processing solvent, preferably 1.0 wt. %, may be added to enhance compaction.
The essentially dry pre-mix is subjected to pre-mixing 18 by charging the essentially dry pre-mix into a premixer and mixing to get a homogeneous pre-mixture 20. Grinding 22 of the pre-mix 20 is then conducted, preferably in a microniser to get a ground product 24 with particle size of 5 microns to 10 microns. The ground product 24 is subjected to post-mixing 26 to form a mixture 28 which is then made into granules 36 having the same amounts of constituents as the dry pre-mix by preferably charging 30, by way of a rotary feeder, a feeding hopper which supplies the mixture 28 to a granulator for granulation 34.
The resulting granules 36 are subjected to a conditioning process 38, preferably by passing the granules 36 through an air chamber, producing conditioned granules 40. The conditioned granules are then subjected to sieving 46 to separate fines 50 from desired dust free soluble granules 51.
The fines 50 from the sieving 46 process may be collected and recycled at the charging 30 stage of the process to obtain a minimum yield of 99.0% dry flowable, low compact, dust free, soluble granules 54 of phosphoroamidothioates, preferably acephate.
The granules of phosphoroamidothioate prepared by the process of the invention are useful as they have odor control, good pourability, high a.i., low capital investment, easy to handle, limited risk of caking, good dispersibility, easily reproducible during processing, very high degree of flowability, easy to measure, and a uniform size. Since the granules undergo agitative balling in repetitive manner-till acquiring size and load, before they leave the trough a layering type of granulation are attained forming well rounded granules of excellent dispersibility.
The following examples are presented to illustrate but not to restrict the present invention. Parts and percentage are by weight unless otherwise specified.
Acephate 97% Granules can be prepared as follows:—
The constituents of the above composition are mixed in a pre-mixer, then micronised and ground in a microniser to the required size of 5 to 50 microns homogeneous mixture. This mixture is then fed through a feeder into a granulator and agglomerated for 1 to 1.5 hour using the agitative balling process. The granulator has a cylindrical trough having an interior lining made of rubber/PV sheet, where the material fills ⅓rd of the trough. The clearance between the paddles and the trough wall is 1.5-2.0 mm. The trough has an external jacket heater to attain and maintain a processing temperature of 115-125° F. The paddles are rotated at 250-300 RPMs. The acephate granules are further conditioned using an air chamber and are collected after sieving. The fines generated during the process are recharged to get the conversion yield of 99 percent.
Acephate 90% Granules can be prepared as follows:—
Acephate 90% granules with above composition can be prepared by following the process described in EXAMPLE-1.
Acephate 85% granules can be prepared as follows:—
Acephate 85% granules with above composition can be prepared by following the process described in EXAMPLE-1 with the proviso that the process temperature is 145° F., the RPM is 350-400, the clearance between the paddles and the trough wall is 1.25-1.75 mm, and the processing time is 2.5-3 hours.
Acephate 75% Granules can be prepared as follows:—
Acephate 75% Granules with above composition can be prepared by following the process described in EXAMPLE-3.
The physical properties of Acephate granules prepared by the dry granulation process of the present invention were determined before and after aging at 45° C. for 500 hrs. Tests performed included flowability, wetting time, attrition test, disintegration rate, tap density, suspensibility, sedimentation and persistent foam. The dynamic wetting time and solubility test were measured as per MT-167 of CIPAC. The flowability was measured as per MT-172 of CIPAC. The dry sieve analysis was measured as per MT-170 of CIPAC. The sedimentation was measured as per MT-15.1 of CIPAC. Dustiness of granules was measured as per MT-171 of CIPAC. The tap density was measured as per MT-58.4 and MT-33 of CIPAC. The Acephate technical content was determined by GLC method published in AOAC. No noticeable problems relating to the properties of the granules were observed in the above-listed tests.
Acephate was prepared by the following processes and the products were compared to test flowability and the angle of repose which affect the dustiness.
a. Crushing process
b. Shattering or compact Formulation
c. Extrusion
d. Agitative balling.
Acephate 97% Granules can be prepared by a crushing process for granulation as follows:
The constituents of the above composition are mixed in a pre-mixer, then micronised and ground in a microniser to the required size of 5 to 50 microns homogeneous mixture. Thereafter, the homogeneous mixture is post-mixed to ground the product to produce a mixture. The mixture is then fed into a mixer. Thereafter a sufficient quantity of solvent (methanol/ethanol/dichloromethane) is added and homogenously mixed to obtain the big lumps. These lumps are then dried. The dried lumps are then charged into a crusher to get irregular shaped particles. These particles are then conditioned and sieved to obtain the granules in the desired size range.
Granules obtained by the crushing process have the practical advantages of eliminating dust problems as compared to powder forms, reducing offensive odors in comparison to powder forms because of a reduced surface area to weight ratio. These granules have sluggish flowability but are better than the powder forms and have a high angle of repose in the range of 40-44 radians.
Acephate 97% Granules can be prepared by a compacting and shattering process for granulation as follows:
The constituents of the above composition are mixed in a pre-mixer, then micronised and ground in a microniser to the required size of 5 to 50 microns homogeneous mixture. Thereafter, the homogeneous mixture is post-mixed to ground the product to produce a mixture. The mixture is then fed through a feeder into a compactor. The compacted formulation is shattered to form irregularly shaped compacted particles. The irregularly shaped compacted particles are conditioned and then fed for screening through a screen to separate oversized particles and fine particles from particles having a desired particle size. The fines, which are less than a predetermined granular size, generated during the process are recharged to get the conversion yield of 99 percent.
Granules obtained by the shattering and compaction process have the practical advantages of eliminating dust problems as compared to powder forms as well as granules obtained due to crushing. They have average flowability but are better than the powder forms and have a high angle of repose in the range of 30-35 radians.
Acephate 97% Granules can be prepared by an extrusion process for granulation as follows:
The constituents of the above composition are mixed in a pre-mixer, then micronised and ground in a microniser to the required size of 5 to 50 microns homogeneous mixture. Thereafter, the homogeneous mixture is post-mixed to ground the product to produce a mixture. The mixture is then fed through a feeder into an extruder and water is fed to the extruder. A flow regulator was installed in the line which allowed regulation and monitoring of the water feed. The point at which the water contacted the powder in the extruder was about six inches downstream from where the powder entered the extruder. The water contacting the powder to form a mixture, extruding an extrusion product while controlling the temperature within the extruder and the rate and quantity of water fed to the extruder to minimize tackiness and clumping together of the extrusion product, and forming granules. Drying/conditioning the pellets/granule to a required moisture content. The granules are rolled to break them down into granules of desired size.
Granules obtained by the extrusion process have the practical advantages of eliminating dust problems as compared to powder forms as well as granules obtained due to crushing. They have an average flowability, but are better than the powder forms and have a high angle of repose in the range of 30-35 radians.
The extruder used may be a low pressure basket extruder or high pressure extruder.
The process involved when using a low pressure basket extrusion process includes providing a post-mixed powder, contacting the powder with water to form a damp or wet mixture, and thereafter extruding an extrusion product of predetermined diameter from the damp or wet mixture, forming pellets/granules from the extrusion product, and drying the pellets/granule to a moisture content of less than about 0.5% by weight. The pellets can contain small amounts of a processing aid to enhance the ability of extrusion. Extruded into pellets using only water as a processing aid in small quantities of processing aids other than water admixed with the active ingredient prior to extrusion without such processing aids, as long as the addition of such materials did not conflict with or adversely affect the basic characteristics of the pellets formed.
The product commercially has satisfactory shelf life on the order of about 2-4 years, during which time they generally remain free-flowing and avoid the raw powder's tendency to agglomerate. As discussed further below, it has now been discovered that excellent flowability can be maintained over time when the pellets are produced so as to have angle of repose of less than 20 and/or a moisture content of about 0.5 wt % or less.
The granules generally have off-white to white appearance but may have a yellowish tint, and are able to avoid creation of significant quantities of dust during packing, handling, storage and transport due to product crumbling and the like.
High Pressure Extrusion—The constituents of the above composition are mixed in a pre-mixer, then micronised for delumping in a conventional mill or the like, if necessary to reduce or eliminate clumps of material that may have formed due to the material's agglomeration tendency. Delumping of pre-mix powder is done for better flowability during extrusion and ground in a microniser to the required size of 5 to 50 microns homogeneous mixture. Thereafter, the homogeneous mixture is post-mixed to ground the product to produce a mixture. The mixture is then fed through a feeder into a high pressure extruder. Next, the delumped mixture, if needed, is blended with a small quantity of a processing aid (other than water). The powder mixture is then placed into a suitable apparatus for supplying the powder to the extruder. The supply can either be continuous over the course of a desired production run, or alternatively, measured batches can be supplied. The extruder is preferably an axial extruder. The provided extrudate is in the form of “noodles” or cylindrical pellets depending on their length. Both the temperature of the extruder barrel during extrusion as well as the rate of water flow are key factors which determine whether commercially viable, high strength acephate pellets can be produced. At higher temperatures within the extruder, the extruded noodles have a tendency to become too mushy and tacky, and thus stick and clump together. Also, an extrudate which is too wet due to excessive water addition is not preferred because it can lead to stickiness and/or a requirement for excessive drying of the extrudate for a period sufficient to achieve the target moisture level.
Acephate 97% Granules can be prepared by agitative balling granulation process as follows:
The constituents of the above composition are mixed in a pre-mixer, then micronised and ground in a microniser to the required size of 5 to 50 microns homogeneous mixture. Thereafter, the homogeneous mixture is post-mixed to ground the product to produce a mixture. This mixture is then fed through a feeder into a granulator and agglomerated for 1 to 1.5 hour using the agitative balling process to produce granules. The granulator has a cylindrical trough having an interior lining made of rubber/PV sheet, where the material fills ⅓rd of the trough. The clearance between the paddles and the trough wall is 1.5-2.0 mm. The trough has an external jacket heater to attain and maintain a processing temperature of 115-125° F. The paddles are rotated at 250-300 RPMs. The acephate granules are further conditioned using an air chamber and are collected after sieving. The fines, which are less than a predetermined granular size, generated during the process are recharged to get the conversion yield of 99 percent.
Granules obtained due to the agitative balling process eliminate dust problems to the maximum amount due to very good flowability and have a low angle of repose in the range of 16-18 radians.
The products manufactured by different process were measured for the angle of repose. Different testing methods are known for finding out the angle of repose. One method of measurement is discussed in The Standards Direct Glossary of European/EN Standards wherein EN 12047:1997 discloses a testing method for measurement of static angle of repose for solid fertilizers. The ASTM C1444-00 is a standard method for Standard Test Method for measuring the Angle of Repose of Free-Flowing Mold Powders. ISO 8398:1989 is a measurement of static angle of repose of solid fertilizers wherein the method is suitable for free flowing materials for measuring angles of repose, but not for those which contain a large proportion of particles exceeding 5 mm in diameter. The method consists in measuring of the height and diameter of the base of the cone, obtained by allowing a sample to fall through a fixed distance from a defined funnel onto a horizontal base plate. Another standard testing Method of the International Organization for Standardization ISO 4324:1977, is a measurement of angle of repose of powders or granules. Determination of the base angle of the cone obtained by passing a given volume of the product in the form of powder or granules through a special funnel placed at a fixed height above a completely flat and level plate.
The measurement of the angle of repose of the product of the present invention has the angle of repose less than 25 and the measurement has been done using the method disclosed in ISO 4324:1977.
The apparatus for the measurement of the angle of repose is shown in
The results are calculated as follows:
The angle of repose (φ) of the sample is given, in radians by the formula
φ=Arctan 2 h/100=Arctan h/50
where h is the height, in millimeters of the cone formed by the test material.
A uniform volume (200 cc) of granules of the product acephate 97% prepared by different processes of crushing, shattering, extrusion and agitative balling is passed through a special funnel 104 whose stem has been previously blocked and placed at a fixed height above a completely flat plate. The stem of the funnel 104 is then unblocked and the test material was allowed to fall into the transparent vessel 109 with continued agitation by the use of agitator rods 106 and form cone. The base angle of the cone is measured as the angle of repose.
The angle of repose of the product of the present invention in relation to the products obtained by different process is compared in Table 1.
The relation between the angle of repose and flowability is given in the following Table 2 which has been cited in the C.E.M.A. Handbook, UNIROYAL Conveyor Belt Selection Guide, PROK Handbook.
**As per die.net online dictionary the term sluggish has been defined as slow or having little motion.
As per the literature sources, a high flowability powder has a lower angle of repose than a poor flowability powder. Angle of repose usually increases as flowability decreases with increasing moisture content.
It is clear from the above data that the product of the present invention has a lower angle of repose, preferably less than 25, than the products obtained by any other process. Table 1 clearly indicates the comparative differences in the angle of repose and flowability of the claimed product with earlier known products.
The particle size and its distribution for all samples were measured in a sizer as follows.
Aproximately 5 mL of granules were used for each measurement. The air pressure was set at 2.0 bar, and the feed rate was set at 50%. The mass median diameter (particle size at which 50% by volume of the sample is smaller and 50% by volume is larger) and particle size distribution were recorded. Fine particles are the ones which are below the required size and results in dusts. Generally, granules that contain more fine particles will result in low flowability while with granules with less fine particles exhibit good flowability.
In particular cases, the granules produced by crushing, shattering and compaction and extrusion exhibit more fine particles leading to poor to average flowability in comparison to the product of the present invention which shows excellent flowability and negligible dusting. As the temperature and humidity conditions were held constant for all the tests, the improved flowability of the product of the present invention indicates that it has a different particle morphology. The particle size of the product obtained by each of the different processes were as follows in the following Table 3.
The bulk and tap density of the granules was determined according to the following method:
A 50-mL glass cylinder was weighed and filled with 30 mL of granules and reweighed. The opening was secured with parafilm. The cylinder was gently reversed once, and the granules were carefully leveled without compacting. Bulk volume was determined after 1 mechanical tap on a tap density tester. Tap volume was measured after 2000 taps.
As shown in Table 4, the densities of the granules produced by crushing, shattering and compaction and extrusion exhibit particles of high bulk density leading to poor to average flowability in comparison to the product of the present invention which shows excellent flowability and negligible dusting due to the low bulk density.
The crushing strength of a granule was determined by compressing a granule diametrically on a granule tester. The results are shown in Table 5. The greater the crushing strength, the greater is the percentage of fines produced and less is the flowability
Note*
A = Highest
B = High
C = Less
D = least
The bulk densities for the Acephate DF of different percentages and the relative comparison with the flowability is as given in the following tables.
Handling, storage and transport of granules is known to offer considerable flow problems due to inter-particulate adhesive-cohesive forces resulting in poor flowability and dusty characteristics.
The specific function of better flowability and non dusty nature is due to the effect of the preferred spherical nature of the product of the present invention complemented by specific characteristics like low bulk density, narrow particle size distribution, least crushing strength, proportionate pore size distribution, uniform surface area and low angle of repose. Thus the preferred product of the present invention is characterised by a low angle of repose and spherical size leading to a free flowing, dust free product.
The dry granulation process of the present process wherein the preferred embodiment has no water added at any stage is an important characteristics since the quality, flowability, and dust free property of the product may vary with the moisture content.
Although the present invention has been disclosed in terms of a preferred embodiment, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention as defined by the following claims:
This application is a continuation-in-part of U.S. patent application Ser. No. 10/652,567 filed on Sep. 2, 2003, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10652567 | Sep 2003 | US |
| Child | 11483201 | Jul 2006 | US |
