The Right Paper For The Right Job

Why is paper smoothness so important? How do manufacturers test and control paper curl? Is multi-purpose paper really good for everything?

IPG gets to the bottom of it all.

Once upon a time, paper was made of fibers from hemp, rags and mulberry bark, and it wasn't until 1850 that using wood fibers for paper became common practice. Now, at the end of the twentieth century, the paper industry has exploded into a supplier of over 725 pounds of paper and paperboard annually for every man, woman and child in the country.

What does this little history lesson mean for in-plant managers? It means that they have more choices than ever before in paper style, color, weight and application. Those choices are growing even now as paper is refined to match the printing capabilities of the newest hardware.

An example of this is copy, color copy and laser papers, each of which has particular features to optimize the output of the equipment it's used in.

Making the Switch

Let's start with copy paper, the least expensive of the three types of paper. Can an in-plant manager save money by using copy paper for laser or color copies—or produce better black-and-white copies by using the more expensive laser or color copy papers?

"You can exchange them, but it's like the difference between hi-test and regular gas," explains Bob Hieronymus, market manager for Georgia-Pacific Imaging Papers, in Atlanta. "You can run premium gas in a Chevy, and it will work fine—but you don't need it. And you can run regular gas in a Lexus, but you won't get the best performance from the car."

In addition, using copy paper in a color copier can result in the image coming out as a curled-up tube of paper, because thinner paper has a greater tendency to curl towards the toner as it cools.

In any case, it's simply not economical to use cheaper paper in a relatively expensive process such as color copying. Why spend so much money making a color copy and then risk compromising the image to save a few cents?

"The cost of the paper relative to the cost of color copying is small, so you should use the best paper possible," says Ned Spangler, marketing manager for the Merchant Office Papers division of Memphis-based International Paper, which comprises the Hammermill and Springhill brand names.

Aside from price, copy, color copy and laser papers are differentiated by three important features: smoothness, brightness and thickness.

Smooth Sailing

Formation—the evenness and uniformity of the fiber laydown in a paper—is critical in producing fine color and laser images.

"If your paper has a rough surface, your high-dpi equipment's fine printing capabilities will be lost," says Hieronymus. "One dot will be on a hill, another will be on the side of the hill, and a third will be in a valley." With smooth paper, laser and color copying equipment can achieve the print quality that they were designed to achieve.

How smooth is smooth? The measure that mills use to determine smoothness is called a sheffield. The lower the sheffield, the smoother the paper—and the smoother the paper, the sharper the image. Most black-and-white copiers target 160 sheffield, while laser and color copy paper are 50 to 100. Coated papers are even smoother than the sleekest laser and color copy papers, but there's a trade-off: These super-slick papers tend to cause jams in copiers. To get the same print quality without the performance issues of coated paper, manufacturers are now making paper that runs as low as 30 sheffield.

In The Thick Of It

Thickness is another factor that differentiates copy, color copy and laser papers. Thickness adds to the stiffness and opacity of the paper—as well as to the perceived value, since customers tend to associate value with the stiffness of the bulkier papers. Thicker papers also prevent jams and reduce show-through on color copies, which is especially important when the paper is to be printed on both sides.

Bulk is crucial in smooth paper, because the process of making the paper smoother also makes it thinner—which can, again, cause paper jams. So while copy paper is usually between 3.9 and 4.1 mils, robust laser paper requires 4.2 to 4.4 mils of thickness. For color copier paper, the thickness should be at least 4.4 mils. Thicker papers tend to be less transparent. But according to Andrea Day, technical marketing manager of Champion International, in Stamford, Conn., "Paper of any weight can be made more opaque at the mill by adding fillers such as calcium carbonate, titanium dioxide and clays."

Compare a piece of regular copy paper with a piece of paper designed for color copiers, and you'll see a big difference in brightness. The high brightness of color copy paper makes for sharp images and good contrast.

Mills can make paper brighter by adding fillers, dyes and optical brighteners that work on the same principle as brightening laundry detergents. These optical brighteners are fluorescent dyes that are excited by artificial or natural light—so the paper looks even more brilliant when light hits it.

Curl Control

Curl is a big issue for paper manufacturers, and they perform extensive testing and adjustments to make their papers as flat as possible. According to International Paper's Spangler, most companies test at three different points in the process to make sure the product isn't curling.

• In the hanging curl test, paper is cut and hung, then measured for curl.

• The reactive curl test consists of testing the paper after applying heat.

• And finally, in the performance curl test the paper is put through a copier.

All this testing is necessary because paper has a "memory" that's activated by heat. If the paper had excess curl at any point in the manufacturing process, chances are that curl will come back when the paper comes in contact with heat during the printing process.

"Every copier will give paper a little curl because of the heat, but it should be minimal," says Day, of Champion.

Equipment manufacturers are also working to straighten out the curling problem. For example, many hardware manufacturers are changing the way their copiers process duplex printing to keep the sheets as straight as possible between printing the first side and second side.

Older machines had duplex trays that held up to 200 sheets, but fusing and stacking so many sheets within a short time of one another compounds heat-related curl because paper is insulating. Newer high-speed laser printers and copiers have trays that hold only five sheets at a time, so there's no time for the paper to distort with the heat.

Progress In Multi-purpose Paper

The newest development in the paper industry is multi-purpose paper, a hybrid that can be used for color, black-and-white, laser and ink-jet printing. The paper is optimized to work in all equipment without curling or jamming.

"Multi-purpose paper is good for in-plants or anyone who uses many different types of equipment," says Day. "But you'll still probably want to use color copy paper for color copies because of its thickness."

Copier Manufacturers Test Paper

With hardware getting faster by the day, what are paper manufacturers doing to keep up? In two words: not much. This isn't to say that paper manufacturers are unconcerned about their paper's runnability in the newest equipment—but rather, that the responsibility is on the equipment manufacturers to make sure their new machines will work with readily available supplies.

"A lot of improvements are in hardware more than in paper," Hieronymus says. Adds Day, "Equipment makers use generally available paper in their development centers to make sure their equipment will run with the paper that's available on the marketplace today."

At the same time, paper manufacturers test their paper in high-speed copiers; so far, copy papers are feeding through the fastest equipment on the market without any problems.

The paper industry has come a long way from mulberry bark parchment to color copy paper. And as hardware manufacturers create better and faster equipment, the paper industry will keep working to make sure you have just the right paper to go with it.