Treat it Right

The wide range of substrates and ink systems being used makes corona treatment a key tool for package printers.

by Tom Polischuk

PACKAGE PRINTERS ARE dealing with a multitude of market conditions that have them pushing the envelope when it comes to the materials they run. Because of the need to hold onto business, replace lost business, or grow sources of new business, package printers are routinely running a wider variety of substrates, along with new inking systems. This includes a continuing trend toward the use of film substrates (including thinner gauge films and conductive foils) and new inks such as UV and water-based systems.

Not surprisingly, many of these applications have narrower processing windows while quality and productivity demands are higher. However, one of the proven tools in the printing arsenal is the use of corona surface treaters to improve ink adhesion and overall print quality.

Film printing

It is typical for film substrates to be corona treated by the supplier prior to delivery to the printer. There are several reasons why this may not be adequate says Jan Westerheim, president of Solo Systems (Rowlett, Texas).

For starters, the impact of treating dissipates over time, so material sitting in inventory for a number of weeks may not be at acceptable levels for quality printing when it is used. Add to this the variability that comes with different suppliers, some of which may be foreign companies, and Westerheim makes the case for bump treating at the printer's facility. Since bump treating is done to basically even out surface tension and re-establish previous levels, she points out that, many times, corona treaters used in these applications don't require lots of power.

Corotec's (Farmington, Conn.) VP of Sales, Ron Seaman, says that a solid part of its business is in retrofit applications, and these include both materials suppliers and printers. With more use of water-based and UV inks, surface treating is required in more applications. Throw in the wide variety of additives used in film substrates, and the addition of inline bump treating is getting more common. Seaman adds that because of the overall market trends, corona treaters are typically installed on new presses.

Another option that Solo Systems has provided is a corona treater placed on a portable cart. This allows a printer to provide corona-treating at multiple lines, especially when many substrates being run don't need to be treated. Westerheim cautions, however, that care must be taken to not use standard corona treaters in locations using solvent-based inks, as the corona systems are an obvious source of ignition.

Thin film

The trend towards thinner films is one of those issues that is reducing operating windows. Not only does a printer need to deal with the inherent non-porosity of films, but the thinner materials are more susceptible to heat damage, and are prone to wrinkling and other processing problems.

Andy Grzesik, general manager for Tantec (Schaumburg, Ill.) says that running thinner films requires a fine resolution in the control of the power to the corona treater. A film that otherwise treats very well can be overtreated very easily, resulting in material blocking in the rolled material. The objective, says Grzesik, is to get a high level of treatment without blocking.

Shawn Norton, sales engineer for Pillar Technologies (Hartland, Wis.), a division of ITW, says that Pillar provides a power turndown ratio of 20 to 1 to allow printers to handle a variety of different thicknesses. Within this range, everything else is set and the only operator action required is to adjust the dial setting.

There are mechanical limits associated with this ability to adjust power for acceptable treating. According to Norton, the higher power requires a larger discharge area. For printers that are looking to operate outside of the limits provided by the turndown ratio, Pillar has incorporated a modular design that allows for a quick change out to a new electrode assembly with a smaller discharge area.

The proper control of tension is also very important when processing thinner films, says Tom Gilbertson, VP applications engineering for Enercon (Menomonee Falls, Wis.). A printer needs to operate between too little tension that can cause wrinkling and too much tension that can cause breakouts. To help broaden the operating window, Enercon offers its universal ELF (Enercon Low-Friction) roll with a lightweight design to reduce inertia.

For any surface-treating application, Gilbertson points out that the application should ultimately determine the technology to be applied. While corona treaters are a common solution, both flame treating and atmospheric plasma (sidebar, p. 37) can offer valid solutions. Enercon recently added a new web flame treater to its 60˝ wide lab line. With this addition, the company now offers laboratory evaluation of corona, flame, and atmospheric plasma treating.