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Environmental Best Practices, Part 3

(October 2008) posted on Mon Oct 06, 2008

Structuring your company around safe environmental practices is becoming a necessity


By Neil Bolding, Steven Abbott

One issue to be aware of with recirculation systems is that they require low-volatility solvents, otherwise you’ll experience rapid solvent loss within the unit through evaporation during the recirculation and extraction processes. Also, if you don’t get good separation of ink solids from the solvent, the solvent will quickly get too dirty to be useful, and the cost of your system won’t get offset by reduced solvent use and lower BOD/COD. Separation of ink solids and solvent depends on good system design and good control of the chemicals. Even a modest change in the solvent blend can tip the balance away from good separation.

Finally, comprehensive staff training and working practices are essential to ensure you get maximum use out of every drum of solvent and that BOD/COD discharge is minimized. A simple procedure, such as removing excess solvent from the screen with a window cleaning squeegee before rinsing, can offer significant benefits with minimal cost.

 

Controlling pH

Stencil materials are typically acidic and will generate effluent with a pH of approximately 5, which is the low end of most regulatory limits and generally doesn’t create pH-related problems. The area of most interest to printers is at the high end of the pH scale. This is because many haze removers contain high percentages of sodium or potassium hydroxide. These are strong alkalis and will take the pH past 11 very easily.

So what can you do to control high pH? The key is to understand why we use haze removers as much as we do. Some inks are inherently tough and difficult to clean, but much ink haze is created when we use volatile solvents for screen cleaning. These solvents fuse the ink to the mesh. So looking for less aggressive solvents can be part of the cure. Additionally using an effective screen wash at the screen-reclaiming phase may also lighten haze.

Other substitutes for using highly caustic haze removers including using an effective pressure washer that delivers a high-pressure stream of water. Additionally, you may be able to turn to a less caustic haze remover, although using such a product may require you to change reclaiming procedures and will likely add to the time it takes to reclaim the screens.

 

Let sustainability sink in


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