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State of the art dryers

Today's top concerns in the converting industry are precise coating application with consistent quality and higher speed

Coatings and substrates are getting more and more sophisticated. While there are a number of reasons for this, for example, more value added, reduced use of energy, water and solvent, states Fribourg, Switzerland, based Polytype Converting, the result is a greater strain on drying systems.

Main issue for converters today is the ability to control precision coatings. Second is the ability to repeat that coating in a narrow window of operation. If someone wants to put down a coating that is a couple of microns thick, they want to do it not only once, but also again and again.

Tighter tolerances, both in machinery and in the coated product, are the key to today’s drying systems. The market asks for open-ended drying systems designed for future products as well as providing the ability to run laboratory trials to determine specifications and drying methods.

Coping with today’s trend of shorter run lengths and hence faster change-over times has meant that automatic settings for dryer systems are needed.

Polytype Converting says it has continued to invest in technological innovations in anticipation of these trends. Constant development, especially in the field of flotation drying with its new Euro, as well as an extended range in winding and coating technology, is claimed to ensure cutting edge safety and efficiency features are built into the designs.

Goal of an “optimized” dryer design is to minimize operating costs, provide good web handling and stability, maximize heat and mass transfer, and minimize dryer length and associated capital costs. And all this while delivering a high quality end product.

Polytype dryer technology can be demonstrated on its in-house pilot lines. A flotation dryer with different nozzles, as well as the roller system, are available for trials in combination with IR, UV or EB curing.

The company’s new Euro flotation dryer has a very small footprint. Air handling equipment is integrated in the enclosure with a vertical fan arrangement.

The model is a self contained unit, available in three standard lengths and in web widths up to 2,400mm. A combination of high heat transfer values, uniform airflow at air bars and “superb web stability with proven air bar systems” is a result of the sophisticated air handling concept.

There is easy access to the inside of the dryer module for cleaning and maintenance through sealed doors. And access to web and air bars from both sides of the dryer unit simplifies webbing up, cleaning and maintenance.

The necessary air temperature control can be combined with control of humidity, web temperature, box pressure, solvent concentration monitoring and exhaust rate.

Performance depends mainly on the nozzle system used, its choice depending on the coated web characteristics at the specific machine speed. To obtain the best result, dryer characteristics have to match coating and substrate specifications.

Available are:

2 slot impingement flotation nozzle up to 40m/s

idem for cooling sections up to 50m/s

air foil nozzles for single side web heating

parallel flow system for extreme sensitive evaporation

dilution nozzles for high solvent loads

nozzle pitch standard 250 and 500mm

combination of roll support and air foil nozzles

integration of UV or IR beams

The impingement nozzle systems generally show the best heat exchange combined with minimum risk of web disturbance and dryer contamination, especially when comparing to airflow nozzles, says Polytype. Web tension is not affected so allowing efficient drying of even very thin PET films of less than 4 micon.

To support high speed lacquering and laminating projects, Polytype has added new modules to the Polynorm dryer system. It claims that with the new design of the support roller dryer system and the availability of 3m and 4m Polynorm dryer modules, the price performance value per module has significantly improved.

This system is said to show an outstandingly high drying efficiency. Special nozzle concepts have been developed for heavy coatings. And the accurate support roller drive concept is claimed to guarantee perfect web handling, even with the lowest gauge substrates. No tension variations are observed for any kind of production conditions, says the company. Hoods tilt back and enable free access over the entire length of the dryer, making for easy operation and maintenance.


Polytype Converting
Tel: +41 (0) 79 342 2527

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Polytype Converting