Coating Choices in Coated Grades

The old classifications of coated paper are fading fast. In this global marketplace, the archaic system of grading paper by numbers is nearly obsolete as sources, materials, and prices blur in appeals to purchasing agents and designers.

Today, procuring paper is about where to add value, and in the end, its specification boils down to choosing brands.

A few decades ago, specifiers and production managers would buy paper based on a graduated list of coating specifications in a numbered system. The dividing line was a difference of pulps or wood fiber: groundwood coated (mechanically ground) and coated freesheet ("free" of mechanical pulp; made with longer, stronger chemical pulp). Luckily for buyers, papermakers are moving away from these classic labels and branding products with recognizable properties based on post-print performance.

Optical properties like brightness, whiteness, and gloss remain key competitive specifications between mills, but achieving superiority and distinction in a cost-focused manufacturing environment is no easy task. At one time, paper engineers would rely on fiber cost and efficiency, but today the focus is on coatings. Coating materials are cheaper than fibers, and easier to vary in integrated mills.

In this column, GAM asked leading coated paper companies to comment on marketing coating technologies to buyers, as well as on trends developing in coated paper applications in commercial printing plants.

Before all of the global paper consolidation activity, European mills marketed double- and triple-coated papers as an adjunct to quality distinction. It was a clever ploy to link gloss with coatings, while U.S. mills were using fiber types to sell stiffness and throughput.

Producers on both sides of the Atlantic were playing to their strengths–-Europe with its shortage of fiber and massive research efforts in coatings, and America with its abundance of fiber and cost fixation. Unfortunately, global economic factors pushed the market to great depths for traditional suppliers, and massive restructuring ensued.

"For Stora Enso North America, our foray into double- and triple-coated papers began in the mid-1980s as a response to a European brand that attracted our customers' attention," says Rick Merdan, Stora Enso North America Fine Papers project manager. "Since that time, many coated paper companies have taken advantage of the economics of additional coating application. It is definitely not a flash in the pan. For many high-end paper grades, double and triple coating is merely 'table stakes.' "

Stora Enso's premier product line, Centura, is the heavyweight multi-coated substrate in its portfolio, though Merdan urges customers to specify weight, finish, and printing application before ordering.

Bryan Ortman, global graphics product manager for MeadWestvaco, sees a change taking place regarding gloss in the minds of print buyers and commercial printers.

"The market once wanted the maximum possible paper gloss, which is a function of the coating pigments," he relates. "Today, buyers and specifiers are becoming more savvy and are looking for more choices, a trend reflected in the increasing interest in alternative finishes [silk and dull, most recently].

"The perception still exists that more coating realizes better gloss," Ortman continues. "The reality is that a finished piece with 'snap' can be achieved through paper or printing techniques. In paper, one or two coatings can provide outstanding gloss, while UV inks, varnishes, and aqueous coatings can be applied on press to improve after-print gloss. The result is that reliance on additional coating layers can be reduced if the printer chooses."

Even the terminology of double and triple coating can be deceiving. Explains Ortman, "Manufacturers define coatings differently. Some products are single-coated but have a 'wash coating,' which is really a starch-based surface treatment, rather than a full blade or precision metered coating." Mills can use all kinds of materials at the newly designed "size press," says Ortman, including high brightness minerals and pigmented coatings.

MeadWestvaco offers its Tango line as a double-coated stock (C2S) for heavyweight applications like covers, cards, folders, and much more. As an economic alternative, Tango Performance Plus, a new-generation C11¼2S, fits in a high-quality graphic side with an improved, lightly coated backside, says Ortman.

Tango Again is a recycled-content option. MeadWestvaco has a variety of other well-known products, including Sterling and Signature.

Uniform quality of the printing surface is the key factor in performance. Since coating formulations are designed not only for optics but surface strength as well, more coatings on the rough paper surface increase smoothness.

"Multi coatings provide a far superior and smoother printing surface," states Stora Enso's Merdan. "They reduce surface anomalies and enhance gloss. However, at a given basis weight, additional coating may mean less fiber, and perhaps less stiffness and press stability."

Ortman concurs. "Coatings fill in the low areas, resulting in a smoother sheet with better dot reproduction, higher gloss, and increased brightness–-all of which leads to superior print quality," he says. "This needs to be balanced with over-coating problems such as scratching, cracking, less stiffness, and press reliability. A superior sheet also requires a smoother base sheet with superior fibers, high-quality coating materials, and high-quality processing, including calendering."

Ortman adds that paper mills are using more solid-pigment binders and less water, which inhibits absorption and keeps the coating on the surface. Fillers, much improved and engineered specifically for paper, are an inexpensive way to add bulk and smooth out the base sheet, he offers.

"High-quality, high-gloss paper probably has a smoother, tighter surface that would lead to less ink absorption, sharper dots, more uniform ink laydown, and an overall better printed piece," concludes Ortman.