Abstract:
A free-flowing, non-dusting water dispersible granule of an active agricultural chemical having low friability and effective crush strength for delivery to a desired site as a stable suspension in water, without deleterious foaming, which granule includes about 1-25% by weight thereof of a binder which is a copolymer of (a) polyvinylpyrrolidone and (b) a comonomer selected from a C 4  -C 30  alkene and vinyl acetate, and mixtures thereof.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to water dispersible granules (WDG) of active agricultural chemicals, and, more particularly, to free-flowing, non-dusting WDGs of such chemicals, which are characterized by low granule friability and superior granule crush strength, and which granules will form stable suspensions in water, without deleterious foaming; for effective delivery and application of such chemicals at a desired site. 
     2. Description of the Prior Art 
     WDGs are important delivery vehicles for active agricultural chemicals because they are organic solvent-free, unlike emulsion concentrates, do not have dusting problems present with wettable powders, and can be transported more economically than suspension concentrates. WDGs are prepared by water-bonding particles of the active component. However, in the absence of a binder additive in the system, the granules will gradually lose cohesiveness as the water content is reduced by evaporation. An effective binder additive, therefore, must provide for effective granular crush strength and low friability, while enabling the granules to form stable suspensions in water during use, without deleterious foaming as a result thereof, and to quickly dissipate its binding action when immersed in water. 
     Ligninsulfonate has been considered the binder of choice in WDG systems. Polyvinylpyrrolidone, in combination with urea, has been suggested for the same use (Canadian Patent 1,209,363). However, there is a need for new and improved WDG systems in which the binder additive will provide free-flowing, non-dusting granules have low granule friability and superior crush strength, and which granules will form stable suspensions in water, without deleterious foaming, for effective delivery and application of such chemicals at a desired site. 
    
    
     IN THE DRAWINGS 
     FIGS. 1 and 2 are graphs of crush strength vs. granulation moisture for the granules of the invention. 
    
    
     SUMMARY OF THE INVENTION 
     A free-flowing, non-dusting water dispersible granule of an active agricultural chemical having low friability and effective crush strength for delivery to a desired site as a stable suspension in water, without deleterious foaming, which granule includes about 1-25%, preferably 1-6%, and, most preferably, 2-3%, by weight thereof of a binder which preferably is a copolymer of (a) polyvinylpyrrolidone and (b) a comonomer selected from a C 4  -C 30  alkene and vinyl acetate, and mixtures thereof. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The binder component of the composition of the invention suitably is a copolymer of (a) a crosslinked or non-crosslinked N-alkenyl lactam homopolymer or copolymer in which the lactam unit of the polymer is represented by the formula ##STR1## wherein R is C 3  to C 6  alkylene optionally substituted with C 1  to C 20  alkyl; R 1  and R 2  are each independently C 2  to C 20  alkyl or hydrogen and n has a value of from 0 or 2, and mixtures thereof, and (b) a C 2  to C 30  comonomer selected from the group of an alkenoic acid; an alkenyl-anhydride, ester, ether, amino ester or amino amide and an alpha mono- or di-olefin. 
     A preferred binder is a copolymer of (a) polyvinylpyrrolidone and (b) a comonomer selected from a C 4  -C 30  alkene and vinyl acetate, and mixtures thereof. 
     Suitably, the binder is present in an amount of 1-25%, preferably 1-6%, and, most preferably, 2-3%. 
     1. WDG Formulation 
     A representative WDG formulation of the invention is given in Table 1 below. 
     
                       TABLE 1______________________________________         % by Wt.______________________________________Atrazine         92.3Binder Additive  3.0Dispersant       3.0Wetting agent    1.5Defoamer         0.2           100.0______________________________________ 
    
     2. Preparation of WDG (Granulation Procedure) 
     The weighed ingredients of the WDG/simulation (a total of 200 g to 1 kg) were mixed in a V-shell blender for 10 min. and transferred to a 24-inch pan granulator set at an angle of 50° and a speed of 13 r/min. Granulation was effected by spraying the ingredients with tap water. After granulation, the sample was dried in an oven at 40° C. for at least 6 hour to reduce the moisture level from 10-15% to under 1.5%. Finally, the sample was sieved to yield a free-flowing, non-dusting product having a particle size between 10 and 40 mesh (0.425 mm to 2.0 mm). The granules also can be made by extrusion followed by drying of the extruded product. 
     3. Test Procedures 
     Cone Dispersion--15 g. of sample was dispersed in 800 mL of 342 ppm hard water.(hardness equivalent to CaCO 3 ) by stirring with a magnetic stir bar for 2 min. The suspension was poured into a 1 L Imhoff dispersion cone, and allowed to settle for 5 min. The sediment volume was then determined, and a sedimentation index was calculated as follows ##EQU1## 
     Crush Strength--Granules were sieved to provide a sample in the -10+12 mesh range. Granules were placed on balance and crushed firmly with a spatula. The force registered at breakage was recorded as the crush strength. The median of 15 to 20 measurements was reported. 
     Filtration Suspension--A quantity of sample containing 1 g of technical was added to 250 mL of 342 ppm hard water in a Fleaker™. After 5 min, the Fleaker™ was inverted 30 times to disperse the sample. Immediately, the suspension was then poured into an Imhoff dispersion cone. After 30 min, the upper 90% of the suspension was removed by aspiration. The remaining sample was vacuum filtered through a No. 3 Whatman filter paper, dried, and weighed to determine residual solids. The percent suspended was calculated as follows: ##EQU2## where the sample wt consists only of insoluble components of the formulation. 
     Friability--Measurements were carried out on a Vanderkamp® friabilator. 10 g of sample, initially between 10 and 40 mesh in size, was loaded into a Roche drum. 25 PFTE balls of 0.6 cm diameter were also loaded into the drum, which was then attached to the friabilator. The sample was subjected to 400 rotations, where each rotation causes the sample to fall a distance of 15 cm. Afterwards, the sample was sieved through a 40 mesh screen, and the weight of sample remaining above 40 mesh was determined. A friability index was calculated as follows: ##EQU3## 
     Foaming--100 mL of 342 ppm hard water and 5 g of sample were added to a 500 mL fleaker. The suspension was shaken vigorously by hand 60 times, and then allowed to settle for 2 min. The suspension was again shaken 60 times, after which the foam height was measured after 10 s and 2 min. The last step was repeated to produce a second set of values at 10 s and 2 min. A foaming index was calculated as follows: ##EQU4## 
     4. EXAMPLES 
     Example 1 
     Water dispersible granules were prepared with ligninsulfonate binder according to the typical formulation and procedures described previously. Results are plotted in FIGS. 1 and 2 and Tables 2 and 3. 
     * Foam Index as defined above is the average of two readings divided by 10. 
     ** in millimeters 
     Example 2 
     Water dispersible granules were prepared with Agrimer® VA 6, a copolymer of vinyl pyrrolidone and vinyl acetate, as binder according to the typical formulation and procedures described previously. Results are plotted in FIGS. 1 and 2 and Tables 2 and 3. 
     Example 3 
     Water dispersible granules were prepared with Agrimer® AL 10, a polyvinylpyrrolidone grafted with butene, as binder according to the typical formulation and procedures described previously. Results are plotted in FIGS. 1 and 2 and Tables 2 and 3. 
     Example 4 
     Water dispersible granules were prepared with a 1:1 by weight mixture of Agrimer® VA 6 and Agrimer® AL 10 as binder according to the typical formulation and procedures described previously. Results are plotted in FIGS. 1 and 2 and Table 2. 
     5. Discussion of Test Results 
     The data in FIGS. 1 and 2 show that water dispersible granules prepared with Agrimers® VA 6 and AL 10 as binders develop greater hardness and friability resistance at granulation moisture levels below 13% compared to granules prepared with ligninsulfonate. The reduced requirement for granulation moisture decreases energy consumption, and therefore, cost of drying granules. FIG. 2 also demonstrates that the mixture of Agrimers® VA 6 and AL 10 produce a synergistic increase in friability resistance of granules. Such granules will have a reduced tendency to fracture and form hazardous dusts. 
     The data in Table 2 show that water dispersible granules prepared with Agrimers® VA 6 and AL 10 as binders produce less sediment when suspended in water compared to granules prepared with ligninsulfonate. Improvement in dispersion leads to better efficiency in application of the pesticide. Table 2 also shows that Agrimer® AL 10 reduces foaming when used as the sole binder, or in combination with Agrimer® VA 6, compared to ligninsulfonate. Foam is undesirable in pesticide mix tanks because it retards mixing and reduces capacity. 
     The data in Table 3, summarizing the 1 kg scale experiments, is consistent with the other data. Granules with superior dispersion properties can be obtained with less moisture added, and with greater conversion efficiency leading to increased throughput. 
     
                       TABLE 2______________________________________Suspension and Foam Test Results forAtrazine Water Dispersible Granules                            Cone                 Filtration Susp.                            Disp.  FoamBinder       No. Expts.                 % Susp.    Sed. Index                                   Index______________________________________3% Ligninsulfonate        4        86         5      573% Agrimer VA 6        3        86         1      613% Agrimer AL 10        4        87         2      261.5% Agrimer AL 10 +        2        90         2.5    381.5% Agrimer______________________________________ 
    
     
                       TABLE 3______________________________________Granule Conversion and Suspension Propertiesof 1 kg Batch Samples       Granu-  Powder -       lation  Granule       Mois-   Conver-       ture,   sion,    Filtr. Susp                                Cone Disp.Binder      %       %        % suspended                                sed. index______________________________________Ligninsulfonate       15      60       78      13Agrimer ® VA 6       10      84       95      8.0Agrimer ® AL 10       8.0     88       85      6.7______________________________________