Temperature control helps ink customers optimize performance.

Published: December 01, 1996, By Acevedo, Jennifer

Sun Chemical's research and technical facility uses Raytek Raynger PM portable noncontact thermometers to help its customers get the most out of their presses.

Any printing process is difficult to maintain without a good sense of the raw materials and the performance of the equipment involved. But the continuing emergence of four-color process printing and digital control technology is driving what is already a highly competitive industry into almost all-out war. In an effort to help customers remain competitive, many suppliers are offering expert advice on how to use their printing presses in the most efficient manner.

Sun Chemical is known as an industry leader in the manufacture of high quality printing inks. Since the company was founded more than 150 years ago, it has maintained this position through research and technical facilities in the US and Europe. Sun also regularly sends field technicians to customer plants to review and suggest methods of improving the operation of a variety of web presses. The company's Carlstadt, NJ, Technical Center is reported to be the largest research center in the world exclusively devoted to supporting the printing industry.

Realizing that the temperature of its inks is one parameter it can control only with the participation of each customer, Sun has consistently worked to provide teaching tools and expert technical support to its customers.

Temperature is Crucial

When examining the efficiency of the printing process, a number of factors come into play. The better these factors can be isolated and controlled, the more efficient a print run will be.

"Of all the things we have looked at, temperature and residence time in the dryer are probably equally important," says Sun Chemical senior environmental engineer Joe Zborovsky. "You have to control temperature, and you have to control residence time in the dryer in order to optimize the quality of ink drying."

John Callahan, Sun Chemical web offset technical specialist, agrees: "I've been around printing for more than 50 years. There is always a temperature that needs to be measured on the press, whether it's the chill roll surface temperature, the plate cylinder bearers, the fountain solution reservoirs, or the web exit surface temperatures."

"Temperature is a means by which you can watch the entire process," Zborovsky continues. "We look at temperatures as 'events' of printing. They're the prime parameters that tell us what is happening amid the ink and the paper." Ink temperature, paper temperature, and equipment temperature taken together are among the most significant dependent variables in the print equation, he stresses.

Over the past several years, Zborovsky has become the company's mentor on web offset heat-set lithography by studying the way inks set. In addition to his normal duties helping customers understand the formulation of his company's inks and how they can help to comply with clean air regulations, Zborovsky has become increasingly involved in solving the ink drying problems that these customers often encounter.

"What is of primary concern is the amount of heat that is being applied to the printed web to flash off solvents that are used in the construction of heatset inks," Zborovsky explains. "A certain percentage of these solvents has to be flashed off in order to achieve a dry ink film."

Normally, ink should be between 80 and 85 deg F as it enters the vibrator roller, Zborovsky explains. The temperature of the chill rollers is chosen to cool the paper after each dryer to near 70 deg F. The dryer must keep the paper below 400 deg For risk paper decomposition. However, Zborovsky believes the entire printing process is most profitable at the lowest temperature possible.

"Heat is money," he explains. "You really have to look upon it as the relative cost of energy. If you consider operating at a higher temperature versus operating at a lower temperature, your cost of raw materials like natural gas or whatever energy source you're using is going to be higher at the higher energy consumption."

Also, inks not only change viscosity over temperature, but solvent content and trapping values are also affected. And trapping, which is defined as the way the tackiness of one ink will trap another ink that has a lower tack, is critical to multicolor printing.

"You change the tack when you apply heat to the ink during transport. This is why some of our people in the field help our customers out by monitoring what kind of surface temperature of the ink is on the inking train," says Zborovsky. "If you apply heat to the ink, the tack will become lower at higher temperatures, while it will be higher at the lower temperatures."

For example, he says, if the inks become too hot, the tack will change to the point where the first-down ink will not be able to pick up the ink that's printed on top of it. Once the inks' temperature is above the recommended range, you may have a trapping problem. This can also help to identify if there is a problem with the water-cooled ink vibrating rollers.

Taking Control

Four years ago Sun Chemical analyzed the use of portable, noncontact infrared thermometers on the web offset heatset process and decided that all Sun technicians would carry the Raynger PM line of instruments from Raytek.

"I've been using some kind of a heat gun for better than 20 years, and I've been using the Raytek gun for about 3 years," says Callahan. "I like the digital readout and the laser sighting, because it allows me to pinpoint what I'm trying to read. The instrument is excellent for proving what you can't see or touch, and what you can barely reach."

The instrument takes readings in less than a second in cramped locations (between printing units or next to the chill roll stand). All PM models are available with an intrinsic safety rating, which reportedly makes the gun suitable for use in potentially hazardous situations. The PM20 features a temperature range from -18 to 870 deg C; the PM30 offers differential and average temperature readings and analog or digital output. The PM40 adds high and low alarms that alert the user when the temperature strays outside a preset range. And the PM50 incorporates a built-in datalogger that can store up to 64 readings. The cost of a portable IR thermometer is often less than the cost of the paper used to do a major run, reports Callahan.

Callahan says the gun's extensive range makes his job easier and has made him the winner of a few bets to boot. "My gun is accurate within 75 feet, and I've won a few wagers on that. I'd be in a paper warehouse, and someone would want to bet me on the temperature of a roll that was between 50 and 75 feet away," Callahan explains. "Sure enough, we'd climb over to it and find that the gun wasn't even off one degree - it was right on.

The instrument's targeting features have also simplified the process of taking readings in cramped spaces, he adds, such as behind the main units of the web. "It's easier for me to get readings, and I don't have to sight down the barrel of the gun and wonder whether I'm hitting my target or not."

Zborovsky says he has heard similar testimonials from technicians. "People using it in the field have said they enjoy the unit's targeting features, because they know what particular part of the printed web they're measuring. They also like the instrument because it is compact and easy to handle."

In fact, Bill Roberts, Sun Chemical web offset technical specialist, says he advises customers interested in purchasing a heat gun to only consider models with laser-sighted targeting.

A feature that allows technicians to set the emission factor has also proven popular among users, Callahan explains. By setting the gun to the emission factor that the dryer and controls are set to, technicians are able to get the most accurate reading. In this case, Sun Chemical technicians set the emissivity factor at .95 for paper stock.

An Indispensable Tool

The Raytek gun's portability, targeting features, and accurate reading capability have made the instrument indispensable to Sun Chemical technicians and their customers alike. And controlling temperature has meant concrete energy savings in addition to improvements in the performance of the inks that Sun Chemical supplies.

"We've been able to establish curves on how the web is drying as it comes out of the dryer," explains Callahan. "From those curves we've recommended changes in how our customers do things to get the ink to set better on the moving web."

He adds, "Operating at a lower temperature can mean big savings. Customers have been able to use the Raytek sensors to read the web as it comes out of the oven and then use those readings to considerably reduce the cost of operating the dryer."

In addition to establishing excessive efficiency, the gun has become indispensable in situations where a customer is losing jobs because of excessive marking due to an ink that hasn't set properly, Roberts says.

"That's when I get involved, and I go in there with the Raynger and find out exactly what's going on," notes Roberts. By quickly determining if the temperature is too low coming out of the dryer, he can advise his customer to make the necessary adjustments to achieve a hard dry.

All of these benefits became apparent to Callahan when his gun was temporarily out of commission. He says it was then that he realized just how dependent he had become on the instrument.

"I sent the gun to them by an overnight express service, and they got it back to me right away," Callahan says, "because I can't operate without it. I can't be without it for even the shortest period of time."

Supplier Information:

Raytek Inc., Santa Cruz, CA, ph: 408/458-1110; fax: 408/458-1239.