A doctor blade system has an open reservoir of ink from which a flood bar draws ink onto a printing plate and a sharp doctor blade wipes the plate clean. With this system the ink is exposed to the air, which enables the solvents to evaporate, slowly changing the ink viscosity. Several machine types make attempts at creating “covered" inkwells but it does not significantly diminish the changes in ink consistency.



Doctor blade systems have been successful and popular where there is short print run (less than 500-1000 pieces), a number of color changes, and experienced machine operators who understand the nuances of ink preparation. These machines are common in plastic housing, golf ball and promotional product marketplace. A significant advantage of the doctor blade system over the sealed ink cup system is that it can easily print long images (for instance on plastic housings like a television, computer monitor, or vacuum cleaner) because there are no major limitations as to how wide a doctor blade of plate can be made.

Sealed Ink Cup System

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. The sealed ink 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. As a result, the process becomes much more predictable and manageable so less experienced operators are able to run the equipment more efficiently.

And with recent developments sealed ink cup machines has become capable of long image printing. A slide system, which can be mounted to a machine, sweeps the cup from side to side 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.

The largest size ink cups for “standard" pad printing machines are generally 135mm or 5" in diameter, which prints about a 4.5" diameter image. Custom ink cups – that cost significantly more than regular ones – can be up to roughly 250mm in diameter (10"), which can print a 9" diameter image on items like play balls, circular saw blades and satellite dishes.

For efficient production it is sensible to use one set of ink cups in immediate production, while the other is removed and cleaned on the side. The disadvantage to this arrangement is that the ink cups can be very expensive, especially when purchased from the machine manufacturers, but there are places to buy ink cups at fair prices if you search.

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 machine – Doctor Blade or Sealed Ink Cup – you are bound to have a highly successful experience with pad-transfer printing.