Issue link: https://www.e-digitaleditions.com/i/1035980
Tablets & Capsules October 2018 31 expensive system where the marking station itself accounts for only a fraction of the cost. On the other hand, the pharmaceutical industry is already equipped with many thousands of automated lines for sorting, counting, dispensing, and packaging. For example, blister machines have dedicated tablet-han- dling mechanisms coupled with inspection and rejection systems. A modular laser printer can be installed and adapted to work on most existing packaging and encap- sulation lines and could be relatively easily moved from one line to another in accordance with production needs. Another laser marking application is a scaled-down version of an industrial laser printer for use at points of sale such as dispensaries, pharmacies, and health clinics. Specific identifying information (such as names of patients and physicians, prescription number, 2D bar- code, and photo ID) can be imprinted directly onto each tablet or capsule with high resolution. If necessary, the information can be encrypted or imprinted using lines so thin that they are invisible to the naked eye, adding another layer of security and safety. Advantages and limitations The numerous advantages of laser marking compared to conventional printing methods, such as inkjet or offset printing, are summarized in Table 2. The primary limitation for the marking technology described in this article is the requirement of having TiO 2 in the outermost layer of the tablet or capsule. In most applications, TiO 2 is used as a white pigmenting agent and normally turns grayish-blue upon laser irradiation. Table 2 Comparison between ink marking and laser marking of tablets and capsules Ink marking Laser marking • Capsules must be dried and cleaned prior to printing, as ink does not stick to oily surfaces. • Eliminates capsule drying and cleaning stages prior to marking. • Eliminates ink curing and drying stages after marking. • The cleaning process takes time and chemicals, especially for commonly used soft gelatin capsules. • Eliminates chemical waste associated with capsule cleaning. • Eliminates inks, make-up fluids and other consumables associated with ink transfer. • Does not require any additional chemicals or pigments, as TiO 2 is already present in most coating and/or gelatin formulations. • Even after drying and cleaning, the oil from the bulk will diffuse back to the surface in a matter of days, if not hours. This imposes strict timing requirements and reduces marking reliability. • Streamlines the marking process. • The marking does not depend on the capsule surface properties (wet, dry, oily, etc.) or storage conditions. • Inadequate printing results in a huge waste of otherwise legitimate and sometimes quite-expensive product. • The marking is much more accurate, as it is controlled by a precise laser-beam scanning system. • The marking resolution is limited by the size of the nozzle in the case of the non-contact inkjet printing or stencil in the case of direct-contact gravure marking. • The technique can produce high-resolution images, including 2D barcodes, as the laser beam can be focused on a very small area. • The ink marking deteriorates over time depending on the storage and shipping conditions. • The marks are permanent and chemically inert. The marks are contained within a few micron layers "under the skin" and are therefore protected from any mechanical deformations. Figure 6 UV laser marking through blister packaging a. Tablet and chewing gum UV laser marked through blister c. Similar tablet and chewing gum with direct UV marking b. Same tablet and chewing gum removed from blister 2mm 2mm 2mm