Tablet defects are deficiencies that are usually encountered in tablet formulation. Depending on experience, machinery and excipient used, produced or compressed tablets can develop certain defect which may be immediately apparent or appear only after storage.
Listed below are problems associated with tablet manufacturing.
Capping is the removal or separation of the top or the bottom of a compressed tablet from the main body of the tablet. This can occur during ejection from the tablet die or during subsequent operations, such as coating, packing, or shipment.
Lamination on the other hand is the transverse cracking and separation of the compressed tablet into two or more layers. It is when cracks form within the body of the compact, resulting in the tablet splitting apart into layers.
In some instances, a small amount of the compact material may stick to the tooling surfaces’ faces and is referred to as sticking. As compacts are repeatedly made in this station of tooling, the problem gets worse as more and more material gets added to that already stuck to the punch face. The problem tends to be more prevalent on upper punches.
Picking happens when a part of the tablet gets sticks to the punch surface and gets eroded from the tablet surface. It is a more specific term that describes product sticking within the letters, logos, or designs on the punch faces.
This is typically seen with colored granules. Mottling is defined as an unequal distribution of color on a tablet with light and dark areas.
Sometimes compacts after leaving the press, or during subsequent handling and coating operations, are found to have small chips missing from their edges. This fault is described as “chipping” and, in addition to the obvious formulation deficiencies, may be caused by compaction conditions which make too soft (low mechanical strength) or too brittle tablets.
This is characterized by excessive side scraping of the die with the compact ejection forces being high, with the resulting compact edges being rough and scored.
This is the imprint or spur line on the tablet not being clear.
In general, the higher the compaction pressure then the denser the compact will be, and hence the higher the resulting tensile strength of the compact. Consequently, too low a compaction pressure will lead to low tensile strength or “soft” and crumbly compacts. Alternative reasons are excessive coverage of the granulation by a lubricant, such as a stearate, reducing the potential to form strong interparticle bonds. This over lubrication can be caused by:
Over lubrication, particularly during formulation development assessment, can also occur if incomplete sets (for example half sets or singles sets) of tooling are used on rotary presses to conserve granule usage. This will be because of extended residence time in the feeder resulting in overworking of the granule particularly feeders with paddles.
An additional cause can be the weakening of the intergranular bonds by air entrapment, even when this is not sufficient to cause capping.
Poor weight uniformity is usually due to poor die filling. This can be due to either poor flow characteristics of the granule, or due to inadequate filling mechanisms on the compression machine. Granules or powders that are too large, too fine or contain a large proportion of fine material, or are incorrectly lubricated or have components with widely differing densities or sizes, may all contribute to weight variation.
If it is due to poor granule flow then the addition of glidants, such as silica or talc, can be employed. Some particles may acquire a frictional electrostatic charge when handled and this mutual repulsion of the particles and may be sufficient to impede die filling. Talc (at up to 1%) or sodium lauryl sulphate (at up to 2%) are substances which have been used to reduce this charging and which can also have lubricant and anti-adherent properties. Lubricants, such as magnesium stearate, may or may not promote granule flow, depending on the level at which they are used higher levels tending to impede flow.
Occasionally, with high-weight tablets, more uniform weight and improved appearance can be obtained by slowing the machine speed so allowing more time for die-cavity filling.
A double impression involves only lower punches that have a monogram or other engraving on them. The punch can make double impressions on a tablet surface during the ejection process. This can be avoided by incorporating antiturning devices for the punches.