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The Secrets of Successful Pad Printing

(February 2003) posted on Wed Mar 12, 2003

This discussion expains how you can make the most of your machine by considering all aspects of production, from climate and press location to substrate readiness and ink preparation.

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By Carol Swift, Peter Kiddell

Radiant heat Dryers based on radiant heat are the type most commonly used to accelerate drying in pad-printing applications. Short-wave infrared (IR) systems are used for applications that require heat exposure for a short duration. In these devices, the heating elements are essentially high-powered light sources using either reflector-based emitters or tube emitters.


Short-wave systems produce very bright visible light along with heat en-ergy they emit. As a result, the performance of these system is color sensitive, meaning that dark colors will absorb the heat energy more readily than light colors. If you were printing white ink onto a black substrate, the substrate would absorb the energy and heat up while the white portion would reflect the energy and remain cool.

Radiant-heat dryers are generally incorporated in conveyorized drying lines. Printed parts are loaded at one end and moved under radiant-heat emitter panels and exit fully dry at the other end. With these systems, maintaining the right conveyor speed is critical if you with to avoid melted parts.


Another way in which short-wave IR emitters may be used for drying is to situate them above one of the stations of indexing conveyors in a multicolor pad-printing system. When a component is presented underneath the emitters, they pulse on for the duration of the print cycle. Afterwards, the part moves on to the next production station.


Medium-wave and long-wave IR emitters are slower in building up their heat. Long wave is the slowest, but it has no light component and its effectiveness is therefore uninfluenced by the color of the ink or substrate. However, long-wave energy is not able to penetrate as far into the substrate as is short-wave IR.


Regardless of what wavelength an IR emitter uses, it's important to make sure that all evaporated solvents are extracted from the drying chamber. If the enclosure becomes saturated with solvent vapors, the system may be unable to dry subsequent prints and the risk of explosion and fire increases, particularly with the hotter-running short-wave systems.


Hot Air Combining high-speed air movement with heat is a very efficient means of drying solvent-based pad-printing inks. For many pad-printing applications, industrial hot-air blowers are ideal drying systems. These devices will generate temperatures up to 1470°F (176°C) and can accelerate drying substantially. However, great care must also be taken to ensure that printed parts aren't damaged by these systems.



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