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Profitable plastics

Jun 1, 2007 12:00 AM


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Sixty years ago, James Wolff entered the printing industry as an apprentice. Today, Wolff is president of General Press Inc. (Natrona, PA). As with all journeys of this magnitude, Wolff has faced many challenges along the way. In recent years, faced with a marketplace rife with plant closings and consolidations, Wolff recognized the survival of his employee-owned company would be based on its ability to expand its product offerings.

A steadfast commitment to that goal ultimately set General Press apart. “We were prepared to make the capital investments required, we knew we wouldn't be successful overnight and we knew we'd have to absorb losses along the way,” says Wolff.

Specifically, Wolff was interested in developing printing capabilities for in-mold labeling. “In-mold labeling has been prominent in Europe for many years, and there was growing demand in the United States,” he says. “We wanted to offer North American customers a domestic supplier as well as enter the market as an international supplier.”

A custom fit

The company partnered with MAN Roland (Westmont, IL) to develop a modified press design that would allow them to handle very thin synthetic labels. The result was an eight-color ROLAND 700 perfector with a label printing package and inline coater. It includes the printnet/PECOM press control, as well as automatic plate loading and washup. In addition to an infrared dryer and IR thermal air dryer, the press features interdeck UV and end-of-press UV dryers. For printing synthetic substrates, there is an ionized air system in the delivery and anti-static on each printing unit.

Although General Press had specified nearly every detail of the equipment, printing on plastics would provide new challenges and a steep learning curve.

Surface treating bumps up business

The shop quickly identified surface energy as one variable where greater control was needed. General Press found that many polymer films have chemically inert and non-porous surfaces with low surface tensions (measured as dyne level) causing them to be non-receptive to printing inks.

Wolff explains, “To ensure substrates were at optimal dyne levels, we added an Enercon corona treater to bump treat materials prior to printing.” Enercon Industries Corp. (Menomonee Falls, WI) supplied a 40-inch Universal roll treater with ceramic electrodes and a 3kW power supply. The surface treater is mounted between the unwind and the Mabeg (Mörfelden-Walldorf, Germany) sheeter (see diagram).

The corona treating system consists of two major components: the power supply and the treater station. The power supply converts standard 50/60 Hz utility electrical power into single phase, higher frequency power that is supplied to the treater station. The station applies this power to the surface of the material through an air gap via a pair of ceramic electrodes at high potential and a roll at ground potential that supports the material.

The surface treater allows General Press to eliminate surface energy as one of their printing variables. According to Wolff, not all substrates require surface treatment, but having the treater has proved fortuitous.

“Dyne levels can degrade over time and get too low for printing,” says Wolff. “We recently received a call from one of our material suppliers who had some older material in their warehouse. None of their other customers could print on the material, but because we had the treater online, we were able to bump treat the material to make it suitable for printing.”

Integrating the corona treater has been one of the easier line modifications General Press has made. The Enercon treater fit seamlessly into its production line and the shop reports its performance has been reliable.

OPP success story

A large water bottling company came to General Press with an identity problem. Its paper labels were dissolving in the ice water baths used to cool its product in stores during the summer months. The printer suggested switching from paper to oriented polypropylene (OPP) film labels, which are waterproof.

OPP film is a synthetic material that is impervious to water and has a surface that suggests high quality and value. Material costs are higher than C1S paper, but the enhanced look and performance of the material offset the higher cost, for this customer.

Typically, this type of film is run roll-to-roll on flexographic presses. With General Press' new MAN Roland 700 series offset press, the company is able to feed sheeted film stock, print it, cure the ink and deliver flat-stacked labels. The bonus for the customer is its ability to continue to use its existing labeling equipment.

Initial tests performed on a 75-micron opaque film met with great success. Later, a 57-micron clear film was tested, and it performed even better.

“Imagine a sheetfed offset printer feeding, printing and delivering a 57-micron clear OPP film,” Wolff says. “Our film supplier tells us we might be the only offset printer in the United States with the capability to print on such a lightweight, cost-effective film.”

Expanding capabilities

The success of its first ROLAND printing press has led General Press to the purchase of two more new systems from MAN Roland: a seven-color ROLAND 700 and a six-color ROLAND 500, both with inline coating.

In addition to plastic labels, the company is planning to run high-end commercial work and credit card applications on the new presses. Wolff explains, “That's the range of thicknesses our current ROLAND 700 handles now, so the new presses will fit right in.”

Job changeovers aren't expected to be a problem, thanks to printnet/PECOM connectivity throughout the pressroom. It will automate a variety of makeready steps and provide other computer integrated manufacturing (CIM) benefits over time.

And when it comes to surface treating, Wolff is confident the company will be ready to handle its next challenge. “There's no telling what type of new substrates will be engineered over the next several years,” he notes. With inline surface treatment, General Press is well prepared to pioneer offset printing on next-generation materials.

Improving plastics printing

Rory A. Wolf, Enercon Industries Corp., shares the following tips for printing on plastics:

Printing on plastics can be an unforgiving process.

Controlling printing variables is imperative and requires you to finely tune your offset press for the application. In addition to a complete and detailed makeready, it is important to ensure that rollers are set and striped properly as well as checked for the correct durometer. Blankets should be packed accurately and in good condition. Critical components such as rollers and ink fountains must be free of contamination from previous print jobs. Fountain solution should be clean and adjusted to the right pH and conductivity. Dampners and plates must be in good condition, as well.

Substrates, ink & adhesion

Unlike paper, plastics tend to be nonabsorptive. Offset printers without printing experience on nonabsorptive substrates will find it challenging to produce high-resolution printing. These plastics have chemically inert and nonporous surfaces with low surface tensions, causing them to be non-receptive to bonding with many printing inks. For a liquid to wet a surface properly, the surface energy of the plastic must be higher than the surface tension of the liquid. Surface energy is measured in dynes per centimeter. Ideally, the surface energy of the plastic should be 7 to 10 dynes/cm higher than the surface tension of the ink.

For example, a printing ink having a surface tension of 30 dynes/cm would not adequately wet or bond to a material having a surface energy of less than 37 to 40 dynes/cm. Properly formulated inks are one of the keys to success for printing on nonabsorptive surfaces. Ink film thickness is another critical variable. Heavy ink film can result in drying problems. Light ink film will create an ink/water imbalance and destroy the ink's resin system. Fountain solutions should be clean, free of silicone and adjusted to the right pH and conductivity. Because the substrate will not absorb water, the minimum water and minimum ink combination will provide the optimum print quality and drying characteristics. To keep the water film thin, it's advised to keep five to 10 percent of alcohol, if possible.

Hybrid inks offer users the ability to take advantage of some UV benefits without making a significant capital investment to convert their presses to UV. These inks are similar to conventional inks but replace some of the oil and solvent components with UV-curable materials.

Regardless of the type of ink used, the surface energy relationship between the ink and the substrate is critical. In other words, UV inks, hybrid UV inks and conventional inks all require substrate surface tension levels to be high enough to effect surface adhesion.

Corona treatment approach

Plastic substrate surface treatment usually is accomplished with an appropriate corona discharge device (bare roll, covered roll or universal roll), or by applying a suitable primer coating. Corona treatment is fast and relatively inexpensive compared to primers, typically applied as a pretreatment by the material supplier. There has been one major issue with this approach, however. Surface dyne levels on plastics are susceptible to loss or decay during prolonged storage at the manufacturer, primarily due to atmospheric effects and processing additive migration. To control and maintain a uniform surface energy level that is not too high or low across the sheet, pretreat (“bump-treat”) these substrate surfaces at the press.

Retrofitting corona treating components into existing sheetfed offset presses is nearly impossible, given space constraints. Enercon has developed a solution to this issue that augments the construction of roll-to-sheet sheeting systems. This corona treating system is designed and installed on offline and inline roll sheeting systems.

For inline applications, it is designed to mount directly to Heidelberg Speedmaster CutStar units, Komori Lithrone Magnum sheeters and other inline roll-to-sheet feeding systems. Enercon also is developing an integrated corona treating station for new sheetfed offset presses.

Market opportunities in plastic printing

Embarking on plastics printing can take sheetfed printers into the production of a diverse array of value-added products, including promotional cards, promotional plastic key fobs, luggage tags, gift cards with magnetic stripes, postcards and specialty items such as plastic rulers. UV printing can incorporate inks formulated for sheetfed printing of RFID tags, plastic cards and smart cards.

Knowing the requirements to bond your inks to these nonporous surfaces first and foremost means understanding and creating the requisite surface tension on your substrate. Taking control of this variable by considering ways to bring corona surface pretreatment in-house can be an effective method for accelerating entry and penetration into value-adding plastic product markets.

AMERICAN PRINTER and sister publication PFFC (Paper, Film & Foil CONVERTER) offer a wide range topics and information for the print and converting expert.