Novel Granule composition of Alphamethrin and a process for its manufacture

Background of the invention

Alphamethrin belongs to a class of compounds known as "Pyrethroids ". Pyrethroids are synthetic third generation insecticides. They are considerably toxic and instantly kill insects by nerve shock effect and are effective even at very low doses. The advantage of these compounds is that they are deemed to have low toxicity to humans and hence are given the highest safety factor among the chemical insecticides. Another advantage is that these compounds are biodegradable and do not persist in the environment. However these compounds are toxic to certain aquatic organisms and bees.

Alphamethrin is a 1:1 mixture of the IR-cis S and IS - cis R isomers of α -cyano-3-phenoxybenzyl-2,2-dimethyl-3-(2,2-dichlorovinyl)-cyclopropanecarboxylate. The compound has the following structure:

Alphamethrin is used to protect crops like rice, maize, cotton, tobacco, soybeans, sugar beet, sugar cane, feed crops, grapes, apples, pears, citrus fruits, tea, coffee against pests like leafroller, borer, black tail leafhoppers, planthopper, aphids, corn borer and cotton bollworm, cabbage moth and many other pests.

Alphamethrin is currently available as emulsion concentrates (EC), wettable powders (WP), suspension concentrates (SC) & ultra-low volume liquid (ULV). Emulsion concentrates & ultra low volume formulations consist of phyto-toxic organic solvents. The suspension concentrate, while generally giving satisfactory performance, may settle out of suspension during storage and may need vigorous agitation to re-suspend. More over since the water quantity is high (more than 50%), it needs special leak proof packing during transportation, resulting an increase in packaging and transportation cost.
Wettable powder is generally produced by blending Alphamethrin technical with wetting and dispersing agents along with inert carrier and is passed through an air jet mill to produce an intimate mixture of ingredients. The resultant wettable powder formulation is generally very bulky and becomes air borne very readily. This poses high danger to the users and the environment.

Hence there exists a need for novel formulations of Alphamethrin that will help in overcoming the aforesaid disadvantages and offer environment friendly applications and reduced human exposure. Further, since the formulation is a water dispersible granule, it contains minimum dust (5% maximum) and easily disperses in water increasing the efficacy of the product.

The granules may be packed in water soluble pouches and may be directly employed during dilution which minimizes the user's exposure to the pesticide and eliminate the container disposal problem.

Summary of the invention

The inventors have found a novel granule formulation of Alphamethrin that demonstrates good dispersibility in water and excellent storage stability.

In a preferred embodiment of the invention, the granules have a uniform shape and a specific size distribution.

In another preferred embodiment, the active is uniformly distributed in the granules thereby providing good content uniformity.

In another preferred embodiment of the invention, the granules comprise active ingredient along with dispersants, wetting agents, defoamers, fillers etc.

The inventors have also found a novel process for the manufacture of the granules which is environment friendly and is capable of producing high yields. Another embodiment of the invention relates to the manufacturing process of the said granules. A preferred embodiment of the invention relates to an extrusion process to produce the granules.

Detailed description of the invention

During the development of the current formulations, the inventors found that water dispersible granule (WDG) formulations of Alphamethrin have better efficacy and better tolerance as compared to the active ingredient or application thereof. Another advantage is that the granules easily disperse in water without any suspended remnants. This prevents unwarranted exposure which can happen by three different routes - dermal absorption, ingestion and inhalation.

Alphamethrin is highly toxic when improperly handled, and has a LD50 value of 57mg/kg for rats. The LD50 value refers to the dose of a chemical that kills 50% population of test animals. Due to its toxic nature, it is preferred to apply Alphamethrin using a formulation which would minimise the exposure levels. The granule formulations of the instant invention satisfy this requirement too.

Formulation compositions

The Alphamethrin granules of the present invention comprise the active ingredient, inert substances such as carriers, dispersing agents, wetting agents, disintegrating agents, etc. The inert substances help to disperse the active ingredient, improve effectiveness, reduce toxicity, or break the active ingredient down into smaller parts, making the resulting formulation diluted, and easier to apply.

Typically, Alphamethrin comprises 2 to 80% and preferably from 10 to 70% by weight of the dry weight of the composition. The dispersing agent generally comprises 1 to 25% and preferably from 4 to 15% by weight of the dry weight of the composition. Dispersing agents described in this process include naphthalene condensates, lignosulfonates, poly acrylates and phosphate esters, wherein the preferred dispersants are poly acrylates and phosphate esters.

The filler component generally comprises 0 to 95% and preferably 1 to 80% by weight of the dry weight of the composition. Fillers described in this process include lactose, sucrose, saccharides, cellulose, china clay, talc, starch, maize, diatomaceous earth, atapulgite, kielserghur, calcium carbonate, magnesium carbonate, silica etc. The preferred fillers are silica, china clay and lactose as filler.

The wetting agent generally comprises 0.1 to 20% and preferably from 1 to 10% by weight of the dry weight of the composition. Wetting agents described in this process include alkyl naphthalene sulfonates, lauryl sulfates, sulfosuccinates, phosphate esters and ethoxylates. Preferred wetting agents are alkyl naphthalene sulfonates and ethoxylates.

The defoaming agent comprises 0 to 10% and preferably 0.1 to 4% by weight of the dry weight of the composition. Defoamers described in this inventioninclude silica activated poly siloxane emulsion, blend of fatty esters emulsified in water, mineral oil based defoamer etc, with silica activated polysiloxane emulsion being most preferred.

The disintegrating agent component generally comprises 0 to 10% and preferably 0 to 2% by weight of the dry weight of the composition. Disintegrants described in this process include starch, sodium glycolate, silica etc.

Water is preferably present in the wet mixing step of the process in a controlled amount to obtain required consistency to facilitate the extrusion process. The quantity of water may vary but will be generally in the range of 1 to 50%, preferably 3 to 20% of the dry weight of the composition.

Manufacturing process

The present invention also encompasses a novel process for manufacturing Alphamethrin water dispersible granules. The process involves:
(i) Dry mixing the active and inactive ingredients

(ii) Adding water to form an extrudable mixture

(iii) Passing the mixture through an extruder to get the desired size range

(iv) Drying the granules in a fluid bed dryer or hot air dryer

(v) Optionally, sieving the granules

The first step in the manufacturing process is intended to improve the physical properties of the active ingredient to facilitate its handling in the subsequent steps of the process. The premix of step 1 contains the active ingredient, dispersant, wetting agents, fillers and are premixed in suitable mixers like ribbon blender, blade mixer and the like. The order of addition of ingredients is not critical.

Step 2 comprises the milling of the pre-milled solid mix of active ingredient, dispersants, wetting agents, disintegrants and filler in air jet mill or air classified mill.

Step 3 of the process of manufacturing process is designed to get a wet paste suitable for extrusion by mixing the dry solid mix with water and defoamer in a planetary mixer.

Step 4 of the process consists of the extrusion of the wet paste through an extruder to give elongated wet granules.

The size range of the granules obtained at this stage may vary from 0.8mm to 2mm in diameter, more preferably between 0.8mm - 1mm in diameter.

Step 5 comprises the drying of wet granules in a fluidized bed drier or hot air dryer to form extrusion granules. The drying process will preferably eliminate maximum amount of water in order to provide good stability to the granular product in a dry flowable state.

Drying in a fluid bed dryer can be carried out at an inlet temperature of 50 - 60° for 30 - 60 minutes. Drying will be complete when the product achieves a moisture content of less than 3%. The moisture content of the granules can be determined by KF apparatus or by LODmethod. The granules thus obtained have high dispersion and suspensibility when compared to granules obtained in pan granulator.

The step of sieving the granules reduces the amount of oversized and undersized materials and results in a product of uniform size distribution. The granule end product has a size distribution 0.8 - 1mm diameter depending upon the requirement.

As the granules prepared have uniform size and shape, quantities for end use can be conveniently and accurately measured. The granules prepared from this process have a lower tendency to powder and form dust than granules prepared by the conventional pan-granulation process. The suspensibility and dispersion properties are also far superior from that of conventional pan-granulation process.

Example 1:

The active ingredient, Alphamethrin (25.5%), wetting agent, polyalkoxy alkyl ether phosphate ester (5%), dispersing agent, anionic styrene acrylate (8%), defoamer, silica activated polysiloxane emulsion (3%) & inert filler (58.5%) were pre-mixed and milled in air jet mill. The milled powder was wetted with water (10%) and extruded in extruder to form wet extrusion granules. The wet granules were dried in a hot air dryer at 50 - 60°C for 2 hours to obtain free flowing uniform granules having a suspensibility of minimum 85%.

Example 2:

The active ingredient, Alphamethrin (10.2%), wetting agent, lauryl sulfate (5%), dispersant, naphthalene-formaldehyde condensate (10%), defoamer, silica activated polysiloxane emulsion (4%) & inert filler (70.8%) were pre-mixed and milled in air jet mill. The milled powder was wetted with water (12%) and extruded in extruder to form wet extrusion granules. The wet granules were dried in a hot air dryer at 50 - 60°C for 2 hours to obtain free flowing uniform granules having a suspensibility of minimum 80%.

We claim

1. A granule composition of Alphamethrin comprising active ingredient, dispersants, wetting agents, fillers and defoamers.

2. A granule composition of Alphamethrin comprising granules in 0.8mm to 2mm in diameter.

3. A process for the manufacture of Alphamethrin granules comprising the following steps:

(i) Dry mixing of active and inactive ingredients

(ii) Addition of water to form an extrudable mixture

(iii) Extruding the mixture to desired size range of granules.

4. The process of claim 3 comprising an additional drying step