Common problems in tableting
What are the common problems encountered in tablet manufacturing?
There are many common problems encountered in tablet manufacturing. Some of the most common of these are listed below. Each
of these problem areas may have several potential causes, but brief overviews of the main ones are summarized below:
Tablet weight variation. The most likely cause of this problem is the extensive variation in punch working lengths, which can often be due to worn
punches or sticking/picking that can cause granules to build up on the punch face and result in nonuniform punch lengths.
Picking. Picking refers to when a compressed granule adheres to the detail (i.e., embossing) on the punch face. This problem could
be due to inappropriate embossing design, worn tip faces, insufficient compaction force, or granulation issues such as excessive
moisture or insufficient lubricant.
Sticking. Sticking is defined as general granule adherence to the punch-tip surface. The same causes as for picking may apply. Additionally,
inappropriate tablet profile may have an impact on inadequate tablet hardness and density.
Capping. Capping is the laminar separation of the tablet body or cup and is often caused by air entrapment in the body of the tablet.
Poor tablet definition (embossing). This problem could be attributed to poor embossing design (i.e., too small or too shallow), worn punch faces due to abrasive
formulation, or excessive polishing.
Tablet hardness/breakage issues. These issues are often caused by uneven punch lengths across a set, incorrect binding agents in the formulation, or capping
due to air entrapment.
Other tooling related problems exist such as:
- Tool-handling issues
- Punch-tip breakage
- Punch-head wear
- Punch tightness
- Die-bore wear
- Tip wear by abrasion
- Pitting/impregnation of punch-tip faces
Punch and die manufacturers should be able to provide training on these issues and how to solve them (1).
The seven-step process
PharmTech: What are the solutions to these problems?
I Holland: Depending on the exact causes of each of the problems previously described, there are several potential solutions. As a guide,
following a simple seven-step process for tool care and maintenance can help to minimize the potential occurrence of most
tableting and tooling issues (2). The seven-step process is a logically planned and professional approach to tooling maintenance
and storage as summarized below:
Clean. When tooling is removed from the tablet press, it should be thoroughly cleaned and dried to remove any oil or product residue,
especially from difficult-to-reach areas such as embossing and keyways.
Punches and dies should be visually inspected under magnification for signs of damage, wear, or corrosion, and to validate
the cleaning process. This assessment will establish whether the production process is running well or not, thereby giving
clues to problems with the tablet press or tooling itself and if any tooling maintenance is required.
Light surface wear, corrosion, and damage on tooling can be repaired and polished to a useable condition. Worn tips can result
in poor quality tablets and inferior embossing definition that can lead to picking and sticking. Repair should be carried
out by well-trained and experienced maintenance technicians to ensure that the tooling does not exceed tolerance limits.
Measuring is essential after repair to ensure that critical tooling dimensions have been maintained within an acceptable working
tolerance. Measuring should be carried out at regular intervals even if repair has not been necessary, to check for natural
wear during the compaction process. The essential measurement is the critical working length of the punch as it controls tablet
thickness, weight, and dosage.
Controlled, light polishing on a frequent basis will ensure that tools are maintained to a smooth finish, thereby helping
to maximize tooling life and reduce problems such as sticking and capping.
Lubrication is important to protect, preserve, and aid smooth operation of the tooling. A range of oils and greases can be
recommended for different applications, such as preservatives, or for lubrication purposes.
Store. Tooling storage and transportation should be specifically designed to maximize security and safe handling to minimize damage