The competitive seas for today's postprint corrugated converters have become rougher in recent years and mandate that the printing "navigator" keep a sharp lookout for safe harbor processes that can maintain or improve their print quality and production efficiencies.

Philadelphia, Pennsylvania based Triangle Container has had a long history of printing excellence. Most recently, it garnered 16 awards, including five Gold Awards at the Point-of-Purchase Advertising Institute's (POPAI) competition, the largest number given any independent converter.

Still, Triangle realizes that its reputation is on the line with every print job it does. Its Superintendent of Flexo Printing, Tom Torrance, explains, "Markets are demanding ever greater graphics capability from post-print corrugated converters. Today's competitive environment virtually dictates expanding graphics capabilities with increasingly faster and greater production output, but makes no allowance for lowered efficiencies that introduce higher production costs." The navigators on these stormy seas, if they fail to keep their hands at the helm, can find themselves amidst rising swells, rocky shoals and the "shipwreck" of falling hopelessly behind their competition.

Leading edge corrugated printers such as Triangle have traditionally fought production problems created by paper lint and dust. Torrance says, "It is difficult to maintain acceptable levels of print quality, while contending with increasing levels of paper dust and high production output demands. Various cleaning and dust collection devices are available that attempt to remove paper dust and lint prior to entry into the print section. While the level of lint and dust may be reduced in this way, it is not eliminated. As these levels increase and mix with ink and accumulate on the printing die, periodic cleaning is usually required to maintain print quality."

The typical scenario is that, following a press set-up, the production run progresses with an initially high level of print quality. But, as Torrance explains, "quality steadily deteriorates as dust, lint and ink slowly accumulate on the plate surfaces that create 'hickeys' on solids and 'print whiskers,' that fill in character bowls and reverses and that plug in the screens areas. Print quality is finally unacceptable, and production is interrupted as corrective measures are taken to restore the print quality through manual plate cleanings."

Attempts to automate the plate cleaning process have led to the development of some mechanical, usually brushing type devices that reduce operator involvement in the plate cleaning, but still require press stoppage, generate print waste upon production restart and still subject plates to an abrasive wearing action in their cleaning. An added problem is that there is often no provision for waste contaminate removal from the area so that contamination often reenters the print screen.

It was during a trip to Clemson University for a printing seminar sponsored by KemiArt that Torrance became aware that there was an alternative. "One of the advantages of Clemson is the networking opportunities it offers participants. I was discussing printing problems with a friend, and he mentioned that a Danish company has a continuous plate cleaning system. I was skeptical, but decided to check it out."

Since there were no installations of the system developed and patented by Tresu, in North American boxplants, Torrance traveled to Denmark Tresu's home country, to see the CycloClean system operating at Danapak on a Bobst 160. "I was immediately sold on its potential," Torrance said. The next step was to try one unit on Triangle's Bobst 200 in cooperation with Tresu and Carol Stream, Illinois based Novaflex, Tresu's North American partner. After a successful trial period, Triangle placed an order for a complete system to be mounted on a new five-color United rotary die cutter, installed in December of 1998.

Continuous Cleaning

Unlike manual or other cleaning systems, the Tresu system operates continuously during print production, cleaning plates without mechanical contact in most cases without disturbing the print. The programmed automatic cleaning operation during print production eliminates the need for the operator to clean plates manually. Fully integrated with the press operation, it operates whenever the press is running and ceases when press operation stops for whatever reason. Integrated with the press operation, there is no operator attendance required following the initial print decks selection during set-up. Operations are automatically controlled through a programmed logic controller.

Cleaning is achieved with the cleaning heads moving back and forth above the plates' surfaces in the region between the board and plate before re-inking by the anilox roll. Since there is no abrasive contact with the printing plate, no wear or damage to the plate occurs as a result of the cleaning process. The plate cleaner is operating continuously during print production, acting more to keep plates clean than to clean plates once they are dirtied with lint and accumulated ink.

The patented design of the cleaning heads marries air and water under high pressure and vacuum technology to provide non-contact cleaning of the printing plates while traversing the plate cylinder as it rotates beneath the cleaning head. Cleaning heads are positioned approximately .080 inches above the plate surface and are designed to approximate the cylinder curvature. Cleaning heads are quickly changed by opening snap locks on either side of the head for cleaning the heads when required.

Micro-nozzles within the cleaning head channel high-pressure air to atomize the cleaning liquid and direct the resulting mist at high pressure against the plate images, dislodging the accumulating paper lint, dirt and ink. Simultaneously, a high vacuum port within the cleaning head is removing the dislodged debris and carrying it through a cyclone separator where moist solids are separated and fine particulates are filtered from the moist air stream, which is vented to the atmosphere.

Sold On The System

"As soon as I saw the system at Danapak and its effect on the high end printing it was doing, I was pretty much sold on it," Torrance remembers. "With a machine that combines rotary die cutting and printing, you're certain that dust will be a by-product."

"Here productivity losses can be even greater owing to the need to open the print units more often to clean the print dies. This is why we chose to put the system on our new five-color United."

"One of the justifications for this system is 'how long can I run without stopping,'" Torrance says. "We've been able to save 1 1/2 to 2 hours a day cleaning plates. It's increased our productivity and reduced start-up waste." The payback period for the unit has been less than six months, adds Torrance.

Increasing demands for higher quality print on corrugated board is spurring greater interest on the part of the industry for a more efficient method of cleaning plates and maintenance of a high level of print quality. Torrance states, "Press operators at our plant have become so dependent on the system that they do not want to operate without it."

- taken from an article by Jim Curley