Controlling Ambient Conditions in Pad Printing

Controlling Temperature and Airflow in Pad Printing

The more stable the environment, the more effectively you can control the process. Although it may seem quite basic, I find that many common problems solve themselves when a few simple rules are followed.

To control temperature, the obvious solution is to operate your press in an air-conditioned room. But other measures to control temperature may not be quite as evident. For example, keep your presses from direct sunlight. Don't put them too close to the entrances or exits of conveyorized dryers. Don't put them in any area of your plant subject to wide swings in temperature, whether or not they are air conditioned.

If a controlled-temperature environment is beyond your reach, other options are available. An essential tool in every experienced pad printer's cupboard is a variable-speed, variable-temperature air blower. (You and I call them hair dryers!) When temperatures are too low and the solvent in the ink is not evaporating quickly enough you'll find that blowing hot or even cold air from the hair dryer onto the pad or substrate wit1 enable printing to take place. By experimenting, you can determine the proper speed, temperature, and direction of the airflow. Normally, you can stop this procedure once ambient temperatures have returned to normal.

Also, consider the role that temperature plays outside of the printing process. For example, storage of

substrates before and after printing is very important prior to printing, substrates are often stored in large warehouses that are very rarely heated and may reach freezing temperatures. When you bring these parts into a heated piant during the winter, the difference in surface temperature is dramatic. On the substrate surface, a very fine film of condensation can form that generally cannot be seen by the naked eye. Under such conditions, you will find it difficult to obtain a good print or acceptable ink adhesion. To prevent this, bring the substrates into the printroom several hours in advance to allow them to reach a stable temperature.

Product storage immediately after printing can also be affected by low temperatures. If you use a two-part ink system, don't let the printed parts drop below 59°F (15O C) until they have fully cured, which can take up to four days or longer if you are air drying them. I f the parts fall below 5g0F (15°C), the ink wil! stop curing and you cannot reverse the problem.

Many of the problems printers experience can be traced back to solvent evaporation in the ink well.

To control airflow, keep the press away from drafts. For example, don't position it underneath an airconditioning duct. Too much air movement around the press will promote faster solvent evaporation. A combination of high temperature and high airflow will increase the effect. The accelerated, irregular ink drying will result in ink remaining in the cliche and/or on the pad, causing inconsistent ink deposits or missed prints.

Not only will drafts or recirculating air cause faster solvent evaporation, but they can also create contamination problems, particularly if you are printing relatively large images or repeating the print stroke several times to increase opacity. Many of the substrates that pad printers use are packed in cardboard containers which, of course generate dust when they are opened and handled. Dust in your shop will be attracted to the tacky surface of the printed parts. The greater the airflow around the press, the greater the chance of dust contamination.

Short of clean-room measures, the only way to overcome this problem is through good housekeeping. Vacuum the floors instead of sweeping them because brooms only recirculate the dust. Do it at night after production has stopped. If possible, avoid bringing cardboard boxes into the production area, or at least line them with polyethylene bags. Wipe down all surfaces using a damp cloth.