COATING DEVICE

Abstract: This invention concerns a device for applying a fluid material to a particulate material. In particular to the device suitable for applying pesticides and the like to agricultural and horticultural seeds.

Description: COATING DEVICE This invention concerns a device for smoothing out a fluid coating applied on particulate material, and in particular to a device for smoothing out a fluid coating, for example a pesticide, on seeds. It is increasingly attractive to seed suppliers to apply to agricultural seeds, coatings of various materials, particularly pesticidal materials, which are able to protect the seeds against attack by, for example, fungi and insects, while the seed is dormant in the soil. The application of coating materials to large quantities of seeds present substantial problems. It is important that the seed should be uniformly coated, and in order to ensure that this is achieved, it is conventional to apply pesticidal formulations in liquid form, containing substantial quantities of an inert liquid vehicle (normally water) . The inert liquid vehicle must be removed, generally in a separate drying step, before the treated seed can be bagged and sold. This procedure normally results in the need for a separate drying step, which increases the expense of the overall process. It is, therefore, desirable to be able to apply to the seed the pesticidal substance in a formulation containing very little inert vehicle, so that no separate drying step of the pesticide on the coated product is required, while maintaining substantially even pesticidal distribution. Surprisingly, such a coating device has now been devised. In accordance with a first aspect of this invention a device is provided for applying a fluid coating material to a particulate material, said device having a generally upright circular body, which has an inside wall surface defining a flowpath for passage of the particulate material therethrough, which comprises, a device for making uniform a fluid coating material on a particulate material, said device comprising a generally upright circular body shell, having an inside wall surface defining a flowpath for passage of the particulate material downwardly therethrough, with a) means for feeding the particulate material to the interior of the upper part of the body shell promptly after fluid coating material has been applied thereto, b) a rotatable shaft extending upwardly and axially towards the means for feeding and within and generally along the length of the body shell, c) an array of agitator elements spaced along and affixed to the shaft for rotation therewith, the agitator elements each having a proximal end attached to the shaft and a distal end directed generally radially towards the said inside wall surface, and d) means for rotating the shaft within the body shell at a controllable constant rate, wherein successive agitator elements within said array, are so shaped as to provide decreasing agitation to the particulate material, as the material passes downwardly through the body shell. In particular, the device is suitable for applying a pesticidal material to agricultural seeds, although the device is not limited to such application. The fluid material is preferably a liquid, for example, an aqueous or non-aqueous pesticidal composition which may be of conventional form. The device according to the invention may also be utilized to apply fluid compositions in powder form. However, as is readily apparent, the device of the present invention is not limited to the use of applying pesticides onto seeds, but may advantageously be employed to apply selected fluid coating onto selected particulate material. The device comprises a generally upright circular body shell, having an inside wall surface defining a flowpath for passage of the particulate material therethrough. Means are provided for feeding the particulate material to the interior of the upper part of the body, to cause the particulate material to pass downwardly through the body cavity under gravity. A rotatable shaft extends generally axially within the body, and has a plurality of agitator elements spaced along and affixed to it, for rotation with it. The agitator elements each have a proximal end attached to the shaft, and a distal end directed generally radially towards the inside wall surface of the body. Means are provided for supporting and rotating the shaft within the body at a controllable constant rate. A spray head is preferably provided for applying the fluid coating material (typically, a pesticide) to the particulate material (for example seeds) , prior to contact of the particulate material with the said agitator. The spray head may be provided within the upper part of the body, or externally of the body such that the particulate material may be treated prior to its entry into the body. In the first aspect of the invention the agitator elements are so shaped as to provide a decreasing amount of agitation to the particulate material as it passes downwardly through the body. For example, the agitator elements in the upper part of the body may be generally in the form of plates of blades, angled so as to direct the falling particulate material momentarily generally upwardly against the gravitational flow, whereas the agitator elements in the lower part of the body may be rods or bars or the like. It is desired to produce decreasing agitation as the particular material passes downwardly through the body to ensure even distribution over the particulate material. This result is accomplished when the fluid coating material is applied to particulate material, either immediately before the coated material enters the body, or within the body itself, such that it is distributed to cover all of the available surfaces of the particulate material as soon as possible. For this reason, a relatively large degree of agitation or shear is initially applied, this amount being preferably to provide as high a level of shear as consistent with not damaging the material which is being treated. The lower part of the body functions mainly as a drying chamber. A sufficient amount of drying takes place (particularly in the case of agricultural seeds) so that the material emerging from the coating device can be packed and shipped. Left undisturbed, the fluid coating material distributed in the upper part of the body can tend to cause the material to agglomerate, so that it is not free flowing. In order to prevent possible agglomeration agitation is provided in the lower part of the body, but this agitation is of a much lower degree than is provided in the upper part of the body. In a second aspect of the invention, which is preferably employed in conjunction with the first aspect, but which may be employed separately, the agitator elements are tapered towards their radially extending distal ends in such a manner as to tend to equalize the shear applied to the particulate material over the length of the agitator elements. It has been found that shaping the agitator elements in this way to equalize the shear applied to the particulate material along the length of the agitator elements gives rise to a particularly advantageous distribution of the fluid coating material over the surface of the particulate material. In a third aspect of the invention, which may be employed with either or both of the first and second aspects described above, but which also may be employed alone, a plurality of baffles are mounted on the inside wall of the body. The baffles are so positioned that all of the particulate material passing through the device must necessarily encounter at least one of the baffles, there being no direct downward straight-line path through the body by which the baffles may be avoided. The baffles preferably extend around substantially the entire circumference of the said inside wall. The baffles have a deflecting surface so angled as to face inwardly, so as to deflect downwardly flowing particulate material in a direction generally towards the shaft. When baffles are employed which do not extend around the entire circumference of the inside wall, their leading edges are preferably inclined so as to disrupt plug rotation of the particulate material, for example, they may be inclined at an angle of from 30° to 80° to the vertical, preferably 40° to 70°, most preferably 60°, and so angled as to face uDwardly, and 10 thus deflect particulate material generally upwardly. In this aspect of the invention, the baffles are somewhat interdigitated with the agitator elements, and the clearance between the distal ends of the agitator ..,- elements and the inside wall including the baffles is such that when the shaft is rotated at a constant rate, the shear imparted to the particulate material is from 5 to 50 sec-1. Shear is defined to be the difference in velocity between two layers, divided by the distance 20 between the layers. For the present purposes, the velocity of the layer of particular material adjacent the agitator element, may be considered to be the same as that of the agitator element, and the layer of material adjacent the inside wall surface of the body 25 may be considered to be stationary, and the applied shear may, therefore, be calculated in terms of the relative velocity of the agitator element tips and the inside wall. The rate of shear is from 5 to 50 sec-1, -, Q preferably from 10 to 30 sec- 1 -, more preferably 20 sec-1, although this will depend to some extent on the nature of the particulate material (such as seeds) being treated. Fragile particulate material, for example pea seeds, will require a low shear rate, for examDle, 5 sec-1; whereas cereal seeds such as wheat or other cereal crops will be more suitably treated with a higher shear rate, for example. 20 sec "1 The agitators elements may be of any desired shape, for example they may be circular or square in cross section, but as indicated above, in a preferred embodiment are shaped so as to direct the falling particulate material generally upwardly, against the gravitational flow. For example, they may be triangular in cross section, or may take the form of an angled plate, preferably having a leading surface which forms an angle of from 20° to 75° from the vertical, preferably 60°. It is preferred that the baffles employed in accordance with the third aspect of the invention extend around the entire periphery of inside wall surface of the body, because this configuration results in the best mixing, and allows the shortest possible body length. It is, however, possible to provide short gaps in the baffles, provided that such gaps are not aligned with each other in adjacent baffles so as to provide a direct flow path for the particulate material, without deflection towards the shaft. The deflecting surface of the baffles is preferably at an angle of from 30° to 80° from the vertical, preferably from 40° to 70°, more preferably 60°. The device in accordance with the invention will generally also include measuring means for ensuring that the appropriate dosage of the fluid material is applied. Such measuring means may include means for measuring the flow rate of the incoming particulate material (e.g. , seed) and fluid coating material (e.g., pesticide), and may preferably also include means for weighing treated particulate material, and means for indicating the level of material in the body, for example, a proximity sensor. The device may also include means for indicating the dosage rate applied, in dependence upon the said measuring and sensing means. The invention includes within its scope a method for the application of a fluid coating material (e.g./ pesticidal material) to particulate material (e.g., seeds) employing a device as described above. Also included are particulate materials thus treated. A preferred embodiment of the invention will now be described with reference to the accompanying drawings. Figure 1A is a schematic elevation, partially in section of a device in accordance with the first and second aspects of the invention. Figure IB is a schematic elevation, partially in section of a device in accordance with the first aspect of the invention. Figure 2A is a sectional view of the device of Figure 1A, taken along the line 2-2. Figure 2B is a sectional view of the device of Figure IB, taken along the line 5-5, Figure 3 is a schematic elevation, partially in section of a device in accordance with the first and the third aspects of invention. Referring to Figure 1A, a coating device for applying a fluid coating material (e.g., pesticide) to particulate material (e.g., seeds) is shown, which device comprises a generally upright circular body shell 1, having an inside wall surface 2, defining a flow path for passage of the particulate ^ material. Means not shown are provided for feeding the particulate material to the upper part of the body through the feed opening 3, in direction of arrows 4. Before entering body 1, fluid coating material is applied to the particulate material, using a spray head (not shown) of the conventional "rolling cone" type. The particulate material throughput through opening 3 is such as to maintain the body 1 substantially full of particulate material through the coating process. Thus, the particulate material is allowed to pass the spray head at a convenient rate so that the fluid coating is selectively metered onto it. Centrally located within body 1 is a rotatable shaft 5, extending generally axially within body 1, and journalled for rotation in a bearing (not shown) in the direction of arrow 6. Agitator elements 7 and 8 provided in the upper and lower part of body 1, respectively, are affixed to the shaft 5 for rotation therewith, and have their proximal ends attached to shaft 5, and their distal ends directed generally radially towards surface 2. An electric motor (not shown) is provided for rotating shaft 5 in the direction of arrow 6, at a controllable constant rate. Agitator elements 7 are in the form of angled blades, and are so shaped as to have a maximum cord line or width a., shown in Figure 2A, and to taper from the said maximum chord a both towards shaft 5, and (by virtue of tapered edges 9) towards their distally- directed tips. The tapering edges 9 of agitators 7 tend to ■ equalize the shear applied to the particulate material, over the length of the agitators (i.e. over the radius of body 1). The agitator elements 7 are angled so as to direct the falling particulate material generally upwardly, against their gravitational flow through the body, and serve to distribute the fluid coating material evenly over the surface of the descending particulate material. In the lower part of body 1, paddle-like agitator elements 7 are replaced by smaller agitators 8, in the form of rods that are more or less circular in section. The function of rods 8 is not primarily to further distribute the fluid coating material over the particulate material, but instead to agitate the particulate material continuously, so the agglomerations or clumping of the particulate material does not occur. It has been found that an excess of agitation to the particulate material once the drying process has begun is likely to result in the fluid coating materials being mechanically removed from the particulate material, leading to the formation of dust. The agitator elements 8 are thus shaped to provide a gentle agitation, to minimize such removal. After traversing downwardly through passage through body 1, the treated particulate material emerges passes over a skirt 10 at the bottom of shaft 5, and to a discharge hopper indicated generally at 11, but not shown. Referring now to Figures IB and 2B, a coating device generally similar in form to that of the device of Figures 1A and 2A, respectively is shown, which device has stationary baffles 61 which are similar to the agitator elements 7 of Figures 1A and 2A, except that the baffles 61 are fixed to the wall of the body shell, not to the shaft. The leading edge 60 (Figure 2B) is the edge which first contacts the particulate material if the shaft is rotated in the direction of arrow 6, and the agitator elements 62 form an angle to the horizontal. Referring to Figure 3 of the drawings, a coating device, generally similar in form to that of the device of Figures 1A and 2A, is shown, which device has a body 31, with an inside wall surface 32 defining a flowpath for particulate material 28. Means 29, for example a conveyor belt, are provided for feeding the particulate material to the upper part of the body through the feed opening 33, in direction of arrows 4. The particulate material is fed into the hopper head 46, in either a batch or continuous process. The fluid coating is fed to the spray head 38, and contacts the particulate material within the hopper head (i.e., prior to the particulate material entering the body). Particulate material enters body 31 via opening 33. A shaft 35 is journalled in bearing 36 for rotation about a vertical axis, driven by an electric motor 42. A spray head 45 of the rolling cone type applies fluid coating material 30 to particulate material falling through the hopper 46, in which the spray head 45 is mounted or suspended. A plurality of agitator elements 37 of generally triangular cross-section extend from shafr 35 towards the wall 32. A plurality of baffles 48 are mounted on wall 32, and each extends around the entire circumference of the inside wall. Baffles 48 have a deflecting surface 49 which is angled so as to deflect the particulate material generally inwardly toward the shaft 35. The baffles 48 are interdigitated with agitators 37, and have a clearance such as to provide shear of from 5 to 50 sec~l when the device is in use. As an example, in a device in which the diameter of body 31 is 0.3 meters, and the gap between the tips of agitators 37 and surface 49 is 50 mm, a shear rate of 20 sec-1 will be achieved at a rotational speed of 64 rpm. Generally, it is preferred that the clearance between the agitators and the inside wall surfaces is from 25 to 50 mm and the speed of rotation is such that the distal ends of the agitators have a velocity of from 1 to 2 m/s. Additional agitators 66, in the form of round bars of relatively small diameter, are provided on the lower part of the shaft so as to provide a lesser degree of agitation to the particulate material than it experiences further up the body shell, so as to prevent agglomeration of the seeds without damaging the seeds during drying. Treated particulate material leaves the body 31 via a discharge hopper 41, and is caused to discharge through a gate valve 50a or 50b into a sock 51, which rests on a weighing device 52. A pair of capascitative proximity sensors 53 and 54 detect upper and lower permissible limits of particulate material in body 31, and metering pumps (not shown) are provided for metering the flow of particulate material and fluid material to hopper 46 and spray head 45. Means (not shown) are also provided for producing a visuai display of the said flow rate, weight of material removed, and levels to enable the dosage applied to the particulate material to be accurately monitored and controlled. When the particulate material is seeds, the seeds may then be planted in soil or potting medium, e.g., in a greenhouse or in the field and under ambient normal growth conditions the seeds develop into plants which flower and develop seeds. As used herein the term "plant" includes seed capable of being germinated into a whole fertile plant; plant cells; plant protoplasts; plant cell or tissue cultures from which a plant can be regenerated; plant calli; plant clumps; and plant cells that are intact in a plant or parts of a plant, such as : flowers, kernels, ears, cobs, leaves, husks, stalks, and similar parts or tissues.

Claims: CLAIMS 1. A device for smoothing out a fluid coating material applied to a particulate material, said device comprising a generally upright circular body shell (1) having an inside wall surface (2) defining a flowpath for passage of the particulate material downwardly therethrough, with a) means (46) for feeding to the interior of the upper part of the body shell the particulate material to which fluid coating material has been applied, b) a rotatable shaft (5) extending upwardly and axially towards the means for feeding (46) and within and generally along the length of the body shell (1), c) an array of agitator elements (7, 8), spaced along and affixed to the shaft (5) for rotation therewith, the agitator elements each having a proximal end attached to the shaft (5) and a distal end directed generally radially towards the said inside wall surface (2), and d) means (42) for rotating the shaft within the body shell at a controllable constant rate. wherein successive agitator elements within said array, are so shaped as to provide decreasing agitation to the particulate material, as the material passes downwardly through the body shell. 2. The device of Claim 1, wherein the agitator elements (7) are tapered towards their distal ends in such a manner as to tend to equalize the shear applied to the particulate material over the length of the agitator elements. 3. The device of Claim 1, further comprising a spray head (38) for applying the fluid coating material to the particulate material prior to contact of the particulate material with the said agitators and baffles. 4. The device of Claim 2, having a plurality of baffles (48) mounted on the inside wall surface (32) of the body shell, the said baffles being so positioned that there is no direct straight-line downward flowpath for the particulate material through the body shell by which contact with at least one baffle (48) or agitator elements (37) may be avoided and each baffle having a deflecting surface (49) so angled as to deflect downwardly flowing particulate material generally inwardly towards the said shaft (5). 5. The device of Claim 4, having a spray head (38) for applying the fluid coating material to the particulate material (28) prior to contact of the particulate material with the said agitator elements (37) and baffles (48), wherein the baffles (48) are interdigitated with the agitator elements (37), and wherein the clearance between the distal ends of the said agitator elements (37) and the said inside wall surface is from 25 to 50 mm. 6. The device of Claim 5, wherein the baffles have deflecting surfaces, said deflected surfaces being positioned at an angle of from 30 to 80 to the horizontal. 7. The device of Claim 6, wherein the deflecting surfaces of the baffles are positioned at an angle of from 40 to 70 to the horizontal. The device of Claim 1, wherein the device is adapted to appl1y to tne said particulate material shear from 10 to 9. The device of Claim 1, wherein at least in the upper part of the said body shell, the said agitator elements are so shaped as to direct the falling particulate material generally upwardly against the gravitational flow. 10. The device of Claim 9, wherein the leading surface ooff tthhee aaggitators form an angle of from 20 to 75 with the vertical. 11. The device of Claim 10, wherein the leading surface of the agitators form an angle of 60 with the vertical. 12. A method of applying a fluid coating material onto a particulate material, which method comprises feeding the particulate material to the upper part of the body shell of the device as claimed in Claim 5, feeding the fluid coating material to the said spray head (38) to apply the fluid coating material to the particulate material, and allowing the particulate material to flow through the body shell (1) under gravity while rotating the shaft (5) at a rate such as to impart to the particulate material a shear of from 5 to 50 sec , to relatively uniformly distribute the fluid coating material onto the particulate material. 13. A method as claimed in Claim 12, wherein the shear applied to the said particulate material is from 5 to 50 14. A method as claimed in Claim 12, wherein the clearance between the distal ends of the agitators (7) and the said inside wall surface is from 25 to 50 mm, and wherein the speed of rotation of the rotatable shaft is such that the distal ends of the agitators have a linear velocity of from 1 to 2 m/s. 15. The method of Claim 12, wherein the particulate material is an agricultural seed material, and the fluid coating material is a pesticide. 16. Seeds treated by a method as claimed in Claim 12. 17. A plant or plant part derived from the seed of Claim 16.

Inventors: CLARKE BRIAN, MASON PETER ROBIN, CLARKE, BRIAN, MASON, PETER, ROBIN
Applicants: DOW CHEMICAL CO, DOW CHEMICAL COMPANY LIMITED
Application year: 1990
Main classification: B05C19
IPC codes: A01C1, B02B1