Eliminating Tablet Spots and Specks

Manufacturers of tablets have long battled a host of occasional but common issues, one of which is spots or specks, which are undesirable visual flaws that can be superficial and/or embedded within a tablet. Commonly referred to by the over-generalizing term “black spots,” these unsightly blemishes or foreign substances should more appropriately be categorized as any spots or specks that are not supposed to appear in the first place, but that in most cases are easily (and visually) detectable. Spots are generally those imperfections that reside on the surface of the tablet only, while specks can be present throughout a tablet. Specks are sometimes visible on the surface, sometimes hidden inside, or both. It is important to note that undesirable spots or specks can be gray, black, or almost any other color, even white.

Possible causes of spots and specks

Although it often proves true that an oil-based issue on the tablet press is the culprit, the following are other potential sources:

• Over-lubricated upper punches

• Worn, faulty, or missing dust cups

• Sloppy, worn upper-punch bores

• Reactions between incompatible material combinations (e.g., certain active ingredients will turn darker when subjected to high heat or when mixed with particular tooling lubricants)

• A “slinging” effect at excessively high turret speeds, where an accumulated product–lubricant mix is thrown from the punch barrel

• Poor or inadequate cleaning procedures, especially between product changes

• Upstream origins (e.g., contaminated raw materials, blending issues, dislodging of grease and lubricants on mixers or granulators)

• Improper product-specific gaps between feeder base plates and the turret surface; too-tight gaps can cause some particle sizes to “roll” and ultimately change color

• Poor punch quality and/or maintenance.

Potential solutions

The best possible solution for an issue with spots on tablets is to consistently employ methods for avoiding them in the first place. This may appear obvious, but in reality, tablet press operators often deviate from GMP methodology, especially in terms of following recommended guidelines for cleaning and set-up as provided by original equipment manufacturers (OEMs). If not already in possession of such procedures, every company should poll their suppliers for them and implement their contents into a cohesive and all-encompassing set of standard operating procedures (SOPs).

Having stated the above as a best line of first defense, strict adherence to good SOPs cannot supersede all potential issues. Some suggested guidelines for eliminating spots when they do appear, or for helping to prevent their occurrence at all, include:

• Optimizing lubrication settings, including dose rate, interval, and duration, especially for upper punches; documents and suggestions from the OEM should help here

• Regular use, and replacement of, quality dust cups; they are easy to install and are disposable

• Regular use, and replacement of, upper punch seals (on presses that offer them as an option)

• Use of punch bellows, especially for particularly dirty products or those necessitating the use of maximum upper lubrication; bellows can actually prevent the mixing of lubricant and dust in the first place, greatly reducing the likelihood of eventual spots

• Strict adherence to SOPs for cleaning and set-up

• The use of equipment manufacturer-recommended vacuum settings

• Judicious inspection and replacement of “contact” parts, such as feeder base plate seals and “tail-over-die” scrapers

• Regular inspection of seals and/or gaskets located within mechanical feeders

• A systematic inspection of all product-contact areas within the entire manufacturing line where an oil or other lubricant may be used.

If, indeed, raw material issues are ruled out and a press manufacturer is asked to recommend a first place to look, most will generally suggest the bottom of the barrels on the upper punches, where the punches protrude from the upper punch ring. A quick visual inspection can detect any unusual build-up of material and excessive lubricant that may be contributing to a problem. If present, it should then prove easier to put a stop to the offense.

Depending on the severity of the issue and the company experiencing it, some will seek independent analysis from a third-party laboratory in an effort to determine the source and composition of the spots. It is, however, important to note that the success of such an investigation can vary considerably. Certainly there are times where the lab can shine the brightest light on a shadowy issue, while just as frequently the offending contaminant is identified and confirmed locally, at the floor level.

For further suggestions and to read how a mysterious problem of blue spots was solved, read the full article in the December issue of Pharmaceutical Technology. 

Matt Bundenthal is direct sales and communications manager at Fette Compacting America.