By Annette M. Sharon
At the dawn of commercial pad print history, 1950s Swiss watch manufacturers used a crude form of pad printing to mark their watch dialsreplacing laborious hand painting. But it wasn’t until the early 1970s that the world got its first glimpse of pad printing at an international trade fair, and the technology picked up speed with automation through the 1990s.
In that span of time, pad printing has become a favorite for surfaces that challenge traditional “flat” printers:
Sticky SituationsApplying adhesives is considered by many manufacturers to be a time-consuming and labor-intensive process. Small or translucent parts need precision application, which often drives up the bottom line.
When factored in with waste and clean up, alternative methods of adhesive application are much sought after. Adhesive film is one method, but also results in waste materials.
|The pad can be |
over the surface
to which an adhesive
or other fluid is to be applied.
|The pad is lowered |
surface to ensure a
uniform application across
As part of an in-line automated process, the finished partfor example, a beveled cell phone lenscan be fed into a custom machined shuttle fixture that holds the part in place while glue is applied to its edge. The lens is then conveyed to a pick-n-place robot arm that sets the cell phone body onto the glued area. Further automation can transfer the joined parts onto another conveyor that transports them through a drying tunnel or further down the assembly line.
Ultraviolet or heat-cured adhesives are useable with this process, as are many solvent-based glues that aren’t too aqueous or hydrophilic.
Smooth MovingAnother exacting and hands-off use for the pad printing of fluids is in the realm of lubricants. Again, this is an area where precision can be challenging, and waste is costly and messy.
Without re-inventing the manufacturing process by integrating new and different materials such as powdered or dry film lubricants (and their associated unknown problems, costs, and technologies), pad printing provides a simple, proven mechanical solution. Whether it’s an oil, grease, or other substance that reduces friction, if it can stick to a silicon pad and can be transferred to another substrate, it can be pad printed.
Since pad printing is well suited for use on three-dimensional objectssuch as hinges, bearings, threaded parts, and housingsany production line that manufactures similar components can integrate this technology into the process. In particular, where misapplication can cause catastrophic failure of adjacent mechanisms, precise lubricant application can be achieved with pad printingwhether it be miniscule dots, fine lines and squiggles, or exact angular confinement.
Better LivingThe increasing sophistication of pharmaceutical formulationssuch as multiple-use base tablets with a variety of custom additivesalso lends itself to pad printing. From applying micro-amounts of a specific chemical onto a supplement or analgesic pill to creating made-to-order combinations of drugs, pad printing can open new avenues of marketing and solve perennial problems of mass manufacturing.
| Pads can be positioned to provide different fluid materials as needed in a specific application. |
Automating such a deposition process involves existing technology, including feeder bins and chutes, custom machined fixtures that hold many pieces, robot arms, and conveyors.
Speed can be less of a concern with pad printing as well, since some electro-mechanical machines can print up to 4,000 strikes per hour. Multiply that by the number of spots for substrate in a fixture and pad printing can be a viable part of an in-line solution.
It’s ElectrifyingAdvances in conductive ink technologyincluding ethyl-cellulose polymers, carbon/graphite, silver, or UV curable dielectric inksallow for pad printing circuit boards, multilayer membrane switches, and touch-key applications, among other uses.
Benefits include savings in process and materials cost, such as doing away with etched copper, gold plating, or soldered wire. For example, replacing gold plating with a carbon ink has proven greater robustness over the extremely expensive metal. It also offers a lower electrical resistance than copper.
A growing economic sector is using conductive inks for radio frequency identification (RFID), which is rapidly streamlining inventory and shipping in the global marketplace.
Other applications for conductive inks include medical sensors, transistors, antennas, and electrodes; shielding against electro-magnetic and radio-frequency interference, and dissipating or eliminating static.
Once again, pad printing’s ability to print on uneven, curved, or recessed surfaces gives the technology an advantage over standard flatbed methods of materials deposition. As with printing adhesives, however, conductive inks must be solvent based and neither too aqueous nor too hydrophilic to be effectively transferred with pad printing.
Beyond the HorizonWith the fast pace of medical and technological design advances, finding a tool that bridges the past and future is critical, both on the manufacturing floor and in budget meetings. Pad printing is a tried and true technology that is flexible enough to adapt to a vast variety of substrates and substances. The need to customize materials deposition will only increase as market niches continue to increase and narrow. Designers, manufacturers, engineers and managers would be well served to explore the ways pad printing can be used for non-decorating, non-identifying purposes. It’s proven that the best tool is one with many uses and ideal for turning a problem into a solutionjust add a full measure of creativity and a spark of imagination.
ONLINEFor additional information on the technologies and products discussed in this article, visit Pad Print Machinery of Vermont at www.padprintmachinery.com .
Annette M. Sharon earned her BA in Science Journalism from the University of Minnesota and works as lead technical writer at Pad Print Machinery of Vermont. She can be reached at 802-362-0844 or email@example.com.