Method of making granules and the granulator

Details Method of making granules and the granulator Method of making granules and the granulator

2000-11-09

2003-06-24

Lechert, Jr., Stephen J. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Forming articles by uniting randomly associated particles

With subsequent cutting, grooving, breaking, or comminuting

C264S119000, C264S176100, C264S210100, C264S210100, C425S331000

Reexamination Certificate

active

06582638

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
This invention relates to granulators used for or as part of a process for reducing the size of materials to form granules. Granules are widely used in the food, cleaning detergent, mineral processing, agrochemical and pharmaceutical industries. In many applications they offer significant advantages over other types of formulations. For example, they are typically low dusting and also offer advantages of ease of clean up of spills.
Granules may be prepared using a number of methods including agglomeration, spray drying and size reduction.
The term granulator is applied generally to equipment that may be used to produce granules. However, more particularly it is usually used to refer to special equipment specifically designed or modified for producing granules.
In the pharmaceutical industry granulation is a standard step that precedes tabletting. In practice in the pharmaceutical industry, it has been found that it is difficult to obtain accurately metered amounts of finely divided materials into a tablet die, because of the inconsistent flow characteristics of finely divided materials. To overcome this problem the finely divided materials are first converted to granules. Forming tablets from granules also tends to improve the integrity of the tablets. One method of forming granules that can be used is first to form a wet mix of the finely divided materials with water and then to extrude this damp plastic wet mix using an extruder. The extrudate is then dried to form a friable dry extrudate which can then be reduced to the final granule size by cutting or fragmentation. Equipment that can be used for both the extrusion stage and the cutting or fragmentation stage are the Manesty Rotorgran or the Jackson-Crockatt granulators.
The granules thus formed are then fed to the tablet die, enabling tablets of uniform mass to be prepared because of the more accurate metering and flow characteristics of granules. These tablets also exhibit improved integrity.
In the pharmaceutical industry granules may also be prepared by a size enlargement process whereby finely divided materials are agglomerated by tumbling the materials in the presence of a mist of water and optional binders. This process can be carried out using a pan granulator, fluidised bed apparatus or a tumbler. More recently new methods have been proposed for forming drug containing pellets. In U.S. Pat. No. 5,709,885 a method of preparing pellets is proposed that involves aggregation of finely divided materials to form a granulate, extrusion of the granulate into strands and then spheronization of these strands.
Granulation processes suitable for the pharmaceutical industry may also be used in the agrochemical industry to prepare granules containing pesticides or other agrochemical active ingredients. Agrochemical granules are usually used by the farmer by adding the granules to water allowing dissolution/dispersion of the granule to enable application of the active ingredient to target species by spray application. This class of granules is usually referred to as water dispersible granules (WG) but can be regarded as including water soluble granules as well as granules intended for direct application to soil or other loci.
In the agrochemical industry such granules have represented a major formulation breakthrough allowing easier handling, metering and clean-up of spillage.
One method of preparing WG granules is described in Australian Patent Application No. 606,719 where a wet mix is first formed with defined ingredients. The wet mix is then extruded, typically using a Manesty Rotorgran or Jackson-Crockatt type granulator having a woven wire mesh screen or a punched plate screen made out of stainless steel. The aperture size of the screen may be varied but is typically in the range of 0.5-2.0 mm. The damp extrudate that emerges from the screen has a diameter similar to that of the screen aperture size. This damp extrudate is then broken down in size to granules by a tumbling action. The tumbling action may be imparted to the extrudate using a tumbler rotating about its usual horizontal or inclined axis or by using a fluidised bed apparatus. The tumbling action causes a cascading motion resulting in shear mixing as extrudate cascades over other extrudate, resulting in the break down of extrudate to form granules. These granules typically have low compactness and redisperse readily. While WG granules prepared using the above described process have been successfully commercialized, the rate limiting step in the production process has been found to be the extrusion stage.
The Manesty Rotorgran includes a curved grid or screen of aperture size that may be varied but which is typically approximately 1 mm. Mounted above and in close proximity to the surface of this screen are reciprocating blades attached to a rotor assembly. They are arranged and operate so that the edges of the blades sweep in a reciprocating scraping action against the tensioned screen as the rotor assembly rotates backwards and forwards. In operation, material is placed into the Manesty Rotorgran from above to contact the screen and is swept by the blades. When the material is friable the sweeping action of the blades over the screen causes the material to be fractured and broken down in size. This size reduction process continues until the broken down material is small enough to pass through the screen apertures. Accordingly, this apparatus when used with coarse friable material provides a material size reduction process as well as a sizing process. This granulator may also be used for size reduction when the material is deformable or plastic. In this case the sweeping scraping action of the blade causes the plastic material to be compressed and forced through the screen, thus forming extrudate strands of approximately the same diameter as the screen openings. This latter process with plastic materials can also be described as an extrusion process and such a process is regarded as a size reduction process as the plastic material is reduced in size to extrudate. Usually the extrudate is further reduced in size to form granules. This can be done by first drying the extrudate or by size reduction while the extrudate is still damp and plastic.
An alternative granulator to the Manesty Rotorgran is the Jackson-Crockatt granulator. This apparatus operates on a similar principle to the Manesty Rotorgran but instead of using a sweeping blade action over a curved screen uses a reciprocating rotational action applied to the blade so that the blade rotates about a vertical axis at the mid point of the length of the blades. The blades are arranged to be in close proximity to a flat horizontal screen. In the Jackson-Crockatt equipment the effective speed of the blade increases as the distance from the rotational axis increases. In common with the Manesty Rotorgran the material has a sweeping action applied by the blades.
In both the Manesty Rotorgran and the Jackson-Crockatt granulators, in use, pressure is applied between blade edge and the screen. In practice, in combination with the sweeping action, this causes frictional wear on the screen and the blade edge. This is particularly the case when used with damp plastic materials that contain abrasive mineral extenders. This is often the case with agrochemical WG formulations. This pressure requirement also means adjustment to provide uniform pressure across the working area is difficult as the characteristics of the plastic material may change from batch to batch and also with temperature. In the case of the Jackson-Crockatt apparatus with the reciprocating rotating blade, if the diameter of the screen and area of the working surface is increased to increase productivity, the tip speed of the blade is increased which can lead to difficulties in satisfactory operation. For example, it is more difficult to achieve satisfactory alignment of the blade and screen. Furthermore, because of higher tip speeds heat build up can cause problems. Accordingly it is not practical to increase the dia

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