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Ink Cups vs. Doctor Blades

Differences and uses

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Sealed Cup vs. Doctor Blade System

by Benjamin Adner

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 cup systems over open inkwell doctor blade systems. This is especially true in the US marketplace where sealed cup systems have dominated new pad printing equipment purchases for a number of years; however, open inkwell systems are still popular throughout the world. Both types of inking systems have a great deal of merit and new equipment buyers often inquire regarding the advantages of one system over another. This article discusses the benefits of the two systems.

A doctor blade system has an open reservoir of ink from which a flood bar draws ink onto a printing plate and a sharp blade called a doctor blade wipes the plate clean. With this system the ink is exposed to the air and therefore enables the pad printing solvents to evaporate, slowly changing the ink viscosity. Several pad printing machine types make attempts at creating “covered” inkwells to limit the evaporation, but the ink reservoir is still exposed to the air and ink changes consistency.

A sealed 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. The sealed cup system floods and doctors (wipes) a printing plate in the same motion, dramatically limiting the ink exposure to the air, thereby limiting solvent evaporation and ink viscosity changes.

Doctor blade system

The doctor blade systems have been run very successfully for many years and are still very popular in situation where there are long images, a number of color changes, short print run (less than 500-1000 pieces) and where there are experienced pad printing machine operators who understand the nuances of the pad printing process. You will commonly find open inkwell systems in marketplaces like the plastic housing, golf ball, and promotional products where long images, short runs, and experienced operators are commonplace.

A significant advantage of the doctor blade system over the sealed cup system is that it can easily print long images because there is no major limitation as to how wide a doctor blade of plate can be made. Long images on plastic housings like a television, computer monitor, or vacuum cleaner are primarily done using doctor blade machines.

However, recent equipment developments with ink cup technology have made it possible to enable long image printing with the consistency of a sealed cup. A slide system can be mounted to the pad printing machine that sweeps the cup from side-to-side (instead of front/back) across the length of the image. It works extremely well for mid-quality images and has been the method of choice by the medical field for catheter printing. This technology was actually developed and patented by the author and has become adopted as a standard feature on most ink cups machines offered in the market today.

Sealed cup system

Sealed cup systems have become so popular because of ease of operation. By limiting solvent evaporation from the ink the skill level in maintaining the chemical balance of ink is reduced and the process becomes much more predictable and manageable. Less experienced operators are able to run the pad printing equipment more efficiently.

The two main drawbacks to sealed cup vs. doctor blade systems are the expense of ink cups and doctoring rings and limitation and expense when printing large images.

Many times it is sensible to have extra ink cups and doctoring rings to help improve efficiency when doing ink changes and as spare parts. When used efficiently, one set of ink cups with pre-mixed ink can be ready to be inserted into the pad printing machine for immediate production, while the other ink cups are removed and cleaned on the side. The disadvantage to this arrangement is that the spare ink cups can be very expensive, especially when purchased from the pad printing machine manufacturers. This is why at INKCUPS NOW we have focused on solving this dilemma for the pad printing machine owner by being an alternative source to purchase ink cups from at fair prices. It has proved out to be a powerful value proposition to machine owners.

The largest size ink cups sold on "standard" pad printing machines are generally 135mm or 5" in diameter, which prints about a 4.5" diameter image. If image requirements extend beyond a 5" ink cup, the price of equipment generally goes up significantly and the equipment and ink cups become specialized. To our knowledge the largest ink cups made are roughly 250mm in diameter (10") which could print a 9" diameter image on items like play balls, circular saw blades and satellite dishes, however these machines are very specialized and generally custom made.

The pad printing marketplace has become relatively mature over the last decade and the quality of the products available in the marketplace is very high, so regardless of the type of pad printing machine – Doctor Blade or Sealed Cup – you are bound to have a highly successful experience with pad-transfer printing.

Benjamin Adner, President of Inkcups Now Corp.

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