Special Treatment

Surface treating technology makes printing on plastic substrates possible, but not just any off-the-shelf equipment will do.

PRINTING ON FILMS without first treating the substrate surface is a lot like skydiving without a parachute. It's possible, but the result is going to be a mess.

Luckily, there are several surface treating options, each with advantages for different applications. Of the three main kinds of treaters, corona treaters are the most common, according Tom Gilbertson, Enercon Industries Corp.'s vice president of applications engineering. They are used for most applications and are less expensive alternatives compared to atmospheric plasma and flame treaters.

Atmospheric plasma treaters, however, are good for hard-to-treat substrates, and have the advantage of having no environmentally-harmful emissions and low degrees of dyne level degradation—which also goes for flame treaters. Flame treaters also are excellent options for high-speed applications where high treatment levels are required.

"Surface treatment helps printers avoid [problems with wettability and adhesion of inks, coatings, and adhesives] by ensuring consistent surface energy throughout the substrate surface," Gilbertson said. "The biggest challenge facing printers is controlling the process, including the interaction of ink and the substrate surface. Surface treatment is a simple and inexpensive way to eliminate (or control) one of the key variables in the process."

Surface treaters have become a vital part of package printers' day-to-day operations, especially in light of the growing popularity of films. And while the treating systems have evolved into advanced forms, costly problems can still arise.

The ins and outs

First of all, really knowing what you are buying and how to get the most out of your purchase is one of the most important things a printer can do prior to finalizing a purchasing decision, according to Bruce Stobbe, president of Corotec. That's elementary. But printers need to know more than how to use the equipment—cost of operation and the treater's efficiency are just as important.

"An introduction and good basic understanding of the technical elements of the process is very important when it comes to day-to-day operations, especially when things aren't going as expected," Stobbe said. "Another area that is often overlooked is the daily cost of operation of the equipment, not only from a maintenance standpoint, but from a power consumption standpoint. There can be vast differences in the efficiency of the system from one supplier to another, so it is important to consider this when comparing equipment, because a savings in the purchase price could be lost in additional power consumption costs over the course of the first year of operation."

All of the systems differ from each other in chemistry and application, but there are certain features each should have. According to Todd Guzzardo of Erhardt + Leimer's Inspection Technologies/Converting Division, to fend off basic problems like lack of adhesion, printers need to "treat properly with a state-of-the-art treater specially designed for its purpose and incorporation of all technology."

In this case, Guzzardo said, state-of-the-art means:

• "Compact design, as printing machines do not offer much space for a treater;

• "Dynamically balanced rollers for web speeds up to 1,200 feet per minute (fpm);

• "Big discharge area for handling high power leaves without saturation effects; and

• "Very powerful ozone extraction, as fast webs transport ozone out of the treater box easily."

Accessories are also essential for trouble-free operation, Guzzardo said. He suggests:

• "Automatic power-speed matching, as line speeds and substrates often vary, which makes a power adjustment necessary;

• "Electronic skip treatment control, synchronized with the printed image by a print mark reader or a pulse; and

• "Remote control via factory [communication] bus for easy settings from the operator's panel."

Beyond a quality treater, installation is another important aspect to consider. Stobbe says, printers have to think about the ease of installation, which can be a substantial expenditure depending on the equipment.

He said, "Some systems are much more difficult to install than others, or the installation location or method makes using and maintaining the systems properly very difficult. Some systems are supplied as pre-wired modules, greatly simplifying the installation process, while others consist of multiple separate enclosures that must be interconnected properly on-site in order to function as a system. Off-the-shelf systems may not always be the best choice because installation compromises may be necessary, and these compromises affect how easy the system is to use and maintain over the entire lifetime of the equipment."

The nitty-gritty

Problem solving is part of a production line operator's job. But manufacturers of surface treating systems can make that job easier by helping troubleshoot issues like insufficient dyne level and blocking.

Problem: Insufficient dyne level

Solution: If a printer is treating a material to no avail, the problem may lie in the equipment or power supply sizing being used more than the actual process of surface treatment itself, said Rob Hablewitz, sales manager, Pillar Technologies. "The only way to remedy this problem of insufficient dyne level or dyne level degradation may be to have appropriately sized or specified equipment. This needs to be done in the first place, not after the fact."

In order to provide equipment suited to the application, a relationship must be established between the manufacturer and the end user. "Proper power requirements, ground roll diameter, dielectric materials, and electrode sizing and type are all derived and/or dependent on data received from the customer," Hablewitz said. Pillar provides an application data sheet that asks questions affecting equipment and sizing choices of surface treating equipment. It's up to the end user to assure proper answers to these questions.

According to Hablewitz, the application data sheet asks questions like what is the customer's process; type of materials or substrate to be treated; dyne level required; identify additives or slip, and at what quantities; maximum speed; maximum web width; is back-side treat a concern; and is the substrate conductive or non-conductive—this information determines the kind of equipment that will work best. If unclear at any point, Pillar requests a sample for treatment tests. This assists Pillar in providing the customer with the optimum equipment choice—a common practice with all surface treating system makers.

"When a sample product or substrate comes in, we measure the dyne level untreated, then we determine what watt density it takes to get to the customers requirement, or if we can get any higher in dyne level. The watt density is determined by the power used, speed of the line, the web width, and one side or two sides to be treated. Once known, consistent dyne levels should be generated on a day to day basis. That's where the additives and slip agent amounts and types come into play when mixed in with a specific customer's resins. After receiving correct and consistent customer application info, we can begin our testing protocol in our lab to determine the watt density that ultimately determines a consistent treat or dyne level. The better the information, the better the product or equipment sized specifically for the application."

Problem: Blocking

Solution: Blocking, or when a roll cannot be unwound easily or at all, is often caused by reverse treatment issues, according to Guzzardo.

The solution lies in a properly laid-out machine, Guzzardo said. Three things to consider are:

1) Be sure there's "enough electrode surface to avoid local overheating of web material, which creates reverse treatment; 2) "Incorporate a pressure roller, as entrapped air between the film and treatment roller creates reverse treatment; and

3) "Having a nip (pressure) roll makes it often necessary to drive the treatment roller in order to maintain the correct web tension."