TABLETING
Particle size of the formulation should
Hartmut vom Bey & Barbara Fretter detail the draw-in capability of press rollers within the roller compaction process
Material is conveyed by the dosing system to the rolls, but the dosing system is not responsible for material movement during densifi cation. T e press rolls draw the material towards the gap (the smallest distance between the press rolls), and the draw-in is based on frictional forces between material and press rolls. As these frictional forces vary due to product properties, Gerteis off ers diff erent press roller surfaces that have diff erent capabilities with respect to draw-in.
DRAW-IN AND FRICTION From the moment the powder is drawn in, the densifi cation process starts. T is area is called the nip area and is defi ned by the nip angle α (Fig. 1). T e nip angle is not constant: it varies due to roller compactor settings and material properties. From this nip angle α onwards, the material is driven by the two press rollers towards the gap. T e frictional force between the surface of the press rollers and the material is responsible for drawing in the powder. Above the nip area, there is a gliding area. If the conditions for draw-in are not met, the press rollers will glide through the material causing slippage and ultimately an increase in the temperature of the product. If a large enough frictional force is achieved however, the material will be drawn in.
50
www.scientistlive.com
PROPERTIES D
PRESS ROLLER
uring the dry granulation process, material is densifi ed between two counter rotating press rolls – the core of a Gerteis roller compactor.
Draw-in problems arise when the nip angle is larger than physically possible (due to settings of the roller compactor, and the densifi cation properties of the material). In other words, the densifi cation process would have to start within the gliding area, but since the material cannot be pulled in by the press rollers in this area, the press rollers cannot densify the material.
INFLUENCES ON DRAW-IN CONDITIONS T e frictional forces between press rollers and the material are based on the material properties of the product. Lubricants have the task of reducing adhesion between tooling surfaces and
material. T ey also reduce the frictional forces between the press rollers and the material. T erefore, lubricants should be used sparingly in roller compaction blends and less than is commonly found in tableting. Depending on the material properties, it is possible to roller compact certain materials without any lubricants. For other materials, some lubricant will be required to prevent too much product sticking to the rolls. Even if there is no lubricant in the product blend, certain excipients (or even the API) may cause low frictional forces with the press rollers. Another infl uence on the frictional
The Mini-Pactor solution
forces is the particle size of the formulation. Coarser particles have less direct contact with the press roller surfaces and therefore create less overall frictional force.
be considered when determining which press rollers are to be used
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
