How can we optimize our laser marker’s throughput to meet production goals?
By Jonathan Bry, Ackley Machine Corporation
As appeared in March 22, 2021 Tablets & Capsules Solid Dose Digest E-Newsletter www.tabletscapsules.com
For many people, the lightsabers in Star Wars films are their first introduction to lasers. Despite the many liberties the films’ creators take with the physical principles of lasers, lightsabers can help to shed light on laser marking for oral solid dosage formulations (OSDFs). For example, a green or blue lightsaber always outperforms a red one, even if the red one has extra blades. This makes sense because green lasers have a higher frequency and carry more energy than red lasers.
By understanding the way light reacts to different materials, laser suppliers can leverage the photophysical reactions of lasers on pharmaceutical products to allow you to mark them faster and more effectively and to help you make cost-saving decisions in the budgetary stages of development for new products that require marking.
If the marks on your tablets, capsules, or softgels are dull and your lasers aren’t meeting your throughput requirements, increasing the power to your laser isn’t necessarily the best solution. Increased power often leads to larger systems, a larger bill, and an increasingly hazardous environment for employees. You can achieve a more desirable output more efficiently by altering the laser’s wavelength.
From coated tablets to hard-shell capsules to softgels to gummies, each OSDF is different and has unique properties (photo). A laser supplier’s skilled engineers can test each product candidate for absorbance at various wavelengths of the electromagnetic spectrum, from ultraviolet (UV) to visible to infrared ranges, before suggesting the best laser system for that specific product.
The second photo illustrates how laser-marking results differ depending on the laser wavelength. Each sugar-coated tablet was marked using a CO2 laser with identical settings from the same laser manufacturer, but the one on the left used a 9.3-micrometer wavelength, while the one on the right used a 10.6-micrometer wavelength.
A spectrometer directs different wavelengths of light at a target material and measures the energy that returns to the machine’s sensor at each wavelength. The supplier can document the energy difference at each wavelength as the absorbance and use the data to create graphs such as the one in Figure 1. The higher peaks point to wavelengths where energy is absorbed into the target material more efficiently, indicating that the energy from the laser is more effective. The vertical lines in Figure 1 represent three infrared laser wavelengths commonly used in manufacturing.
The figure shows that absorption is best at 9.6 micrometers, but laser manufacturers don’t commonly make lasers in that wavelength at the specified power level. Doing so is more expensive and/or more difficult to maintain in a tablet-marking setting. The figure shows that an easier-to-manufacture laser gain medium provides the laser lines at 9.3, 10.3, and 10.6 micrometers.
Laser gain media are components within a laser processing machine that facilitate the laser beam’s generation, amplify it, and determine its physical characteristics. Pharmaceutical laser processing equipment uses gases, such as CO2 and UV, as their laser gain media. In Star Wars, lightsabers used crystals for their gain media, which possessed unique material and geometric properties to generate lightsaber blades and colors from the same power input. To create a robust OSDF laser marking system that can handle a large amount of power, only a few suitable gain media options are available.
Alternatives, such as tunable lasers, have the ability to vary the wavelength between those indicated by the vertical lines in Figure 1 but are currently cost-prohibitive and either result in lower power levels than the pharmaceutical industry can use or require flowing gas that is difficult to maintain outside of a lab setting.
Narrow-band lasers in precision laser marking systems can provide the energy levels required to mark tablets and capsules. Just as optical systems are optimized for a near-singular primary wavelength to achieve maximum efficiency, narrow-band lasers select a wavelength to meet prerequisite power requirements. It’s critical to select a wavelength that maximizes the photophysical reaction with the material to be marked. You must choose these factors during a project’s design and budgetary stages to be cost-effective because in some scenarios they are unchangeable.
Depending on the laser’s wavelength, you may need to take additional precautions. Laser suppliers’ safety officers carefully evaluate these precautions through calculations approved by the Center for Devices and Radiological Health (CRDH) and the American National Standard Institute (ANSI).
Jonathan Bry is a Mechanical Engineer at Ackley Machine Corporation in Moorestown, NJ.