Pad Printing Solutions: Types and Applications of Sealed Ink Cups and Doctoring Rings
When looking at the pad printing equipment market over the past few years, it is apparent that the biggest change in equipment design and implementation has been the widespread use of sealed ink cup systems over open inkwell doctor blade systems. A sealed ink cup system is essentially and inverted cup that is filled with ink and uses the sharp rim of the cup as a printing plate wiping system. As this system floods and doctors (wipes) a printing plate in the same motion, solvent evaporation and ink viscosity changes are much more limited than with doctor blade systems, making the sealed ink cup printing process significantly more predictable and manageable.
In the US marketplace sealed cup systems have dominated new equipment purchases for a number of years. This article discusses the types and applications of sealed ink cups and advantages of ceramic doctoring rings.
Nearly all sealed ink cup types can be broken into two categories, magnetic or non-magnetic. Both cup styles, when integrated into the pad printing machine yield excellent results for clean, properly doctored printing plates.
A magnetic ink cup is basically “self-doctoring unit”. With its extremely powerful magnets, it has all the necessary down-force to clean the plate requiring the machine to simply pull it back and forth. The magnetic ink cup generally has found its strength in multi-color applications because the equipment can generally be of simple construction and the multi-color pad printer more cost effective.
Non-magnetic ink cups are designed to have the pressure applied by the pad printing machine to an outer flange or centering hole in the cup. The pressure is applied by a spring-loaded system geared for one ink cup assembly. The spring-loaded system is compact and very effective, but is not as simple to deploy on a multi-color machines. The non-magnetic cups seem to have their niche in compact or high speed machine applications. In these systems, even at high speeds, the spring loaded hold-down system keeps the ink cup firmly in place while the plate moves in and out.
There has been much debate about which ring material is best for doctoring printing plates. We would guess that the marketplace is evenly divided between the carbide ring and the new generation ceramic doctoring ring. Today, both carbide rings and ceramic rings work extremely well. It is our opinion however, that the ceramic doctoring ring offers some advantages.
One of the primary advantages of the ceramic ring has a “self-lubricating” qualities that make I work equally well on thin steel and thick steel and the softer polymer printing plates. The carbide rings are generally fairly sharp and abrasive and will wear a polymer plate material quickly. Another advantage of the ceramic doctoring ring is that generally thicker, more robust and resistant to damage by during handling. Most ceramic rings taper from the inside and outside diameter to a “point” roughly .006″ leaving plenty of material near the tip. Carbide rings, however, taper from the outside diameter only to a “point” with a cross section of .003″ leaving only a minimum amount of material near the tip resulting in more damage during operator handling. The combination of the ring profile and the brittle nature of carbide make damage to rings fairly frequent during ordinary use.
In general, the quality of the products in pad printing marketplace have become very high, so regardless of the type of sealed ink cup or ring material you are bound to have a highly successful experience.
Benjamin Adner
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