What are the benefits of the different methods of applying identification to solid dosage drug products?
By Roland Thurston, Ackley Machine Corporation
On-dose marking of solid dosage drug products is critical to identify dosage strengths, active ingredients, brands, and serialization. Each of the various marking methods—rotogravure and pad ink printing and carbon dioxide (CO2) and ultraviolet (UV) laser marking—has its own benefits and drawbacks.
Ink printing offers high throughput speeds and low cost per dose, although temperature and humidity fluctuations can affect the ink’s performance and the mark’s quality. The process also requires a high level of operator interface and monitoring as well as postbatch maintenance and cleanup.
The rotogravure printing process was originally developed in the 1890s, when printing on solid dosage drug products wasn’t even a consideration. Rotogravure printing is still the predominant method for marking solid dosage products today, with speed being its primary benefit.
The process can run as fast as the tablets or capsules can be fed into the system, taking into consideration ink performance and the drug product’s geometry. Because the printing mechanism is a mechanical system, consistency and repeatability is as good as the operator running the system. Due to the continuous nature of this printing method, an experienced operator can usually maintain excellent quality and high throughput in the process.
An inexperienced operator, however, may have difficulty maintaining proper ink conditions, which can lead to unacceptable print quality. This can be due to improper ink-solvent balances, incorrect cleaning, or erroneous setup of the printing mechanism itself. Aged ink can also create difficulties that might not be obvious to an inexperienced operator.
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Pad printing and rotogravure offer similar marking quality, however, rotogravure offers higher speeds due to its continuous process.
Pad ink printing provides quality similar to that of rotogravure printing. Because both methods use ink, issues similar to those for rotogravure printing can arise. While rotogravure is a continuous process, most pad printing systems are indexing systems, which move to a specified position, stop to allow the process to work, and then move to the next position. This type of system can limit the printing speed. Rotogravure and pad printing offer the same marking quality.
Packaging and labeling processes have used laser marking for some time, but the process has been adapted to direct drug-product marking only over the last decade. Laser marking provides consistent quality and indelible marking while requiring minimal operator intervention.
As opposed to ink printing, laser marking isn’t susceptible to environmental fluctuations. Also, laser printing can mark softgel capsules without requiring oils to be removed prior to the process, avoiding the requirement for costly machinery and additional time.
While laser marking requires a lower level of operator interface and monitoring, it’s slower than ink printing. Laser marking is a function of the time and power needed for the laser to react with the drug product’s coating as well as the complexity of the specific logo. For instance, for the outline of a square, laser marking would likely require no more time than ink printing, but for a solid square, a laser system would need to track in a hatching pattern to fill the square. This more complex logo would require more processing time for the laser, while an ink-based system can print logos of any complexity in the same amount of time.
Laser marking systems have virtually no postbatch maintenance or cleanup other than clearing any stray product from the system. With the minimal operator setup; extremely consistent, repeatable quality; and minimal cleanup time, the difference in the time required to mark each dose between ink printing and laser marking may be negligible. Laser marking maintains identical quality from batch to batch or hour to hour, just as ink printing does.
As laser marking has evolved, the process has used two types of lasers.
Laser marking with CO2 uses a galvanometer to direct the laser in a predefined pattern. The laser ablates the coating to a specified depth, which creates an indelible mark on the tablet or capsule. The process is repeatable over any length of time regardless of the operator’s experience, ensuring quality.
UV laser marking is similar to CO2 laser marking in many respects, with the main difference being that CO2 marking removes material from the coating to create the mark, while UV marking changes the coating’s color in a predefined shape. This allows the integrity of the coating to remain intact and allows the use of a lower-power laser.
UV laser marking does require that the tablet coating or capsule shell to be marked contains titanium dioxide (TiO2). While this allows for the creation of an indelible, high-contrast marking, European safety agencies are currently considering banning TiO2 as an additive.
Roland Thurston is service manager at Ackley Machine Corporation, Moorestown, NJ. The company designs and manufactures pharmaceutical tablet printing, laser marking, and laser drilling machines with patented vision inspection.
As appeared in July 20, 2020 Tablets & Capsules Solid Dose Digest E-Newsletter www.tabletscapsules.com
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