Printing on Exotic Substrates

No one said print has to reside on paper. The packaging world thrives on flexible films and foils, rigid plastics, metals, and a host of other media. The commercial offset print world also has exotic options that are outside the tree-based cellulose products. We’ll examine these alternatives while avoiding the uncharted territory that is the nightmare of productivity.

A substrate is any surface onto which you can apply a printed image. Some call it material; others media. To the average printer, it is paper or board. The main differentiator is the finish—gloss or matte. Offset inks are not compatible with a broad range of substrates, although choices do exist. These options appeal especially to environmental groups in search of what appears to be a greener alternative. Today’s exotic choices fall into just a few categories.

Options Free of Tree

Tree-free paper based on plants, one alternative to destroying old-growth forests, intrigues the marketplace. The substrates look and feel like normal papers but the base sheet uses cellulose from plants other than trees. Botanically, these plants are grasses or bushes.

One choice is papyrus, a reed that grows along the banks of the Nile River and was used by the ancient Egyptians. The center of the reed was sliced into strips, laid in a crosshatch pattern, and pounded into a flat sheet. Although it is sparsely available today, it is still unique in that it can be folded in both directions without cracking.

Other naturally occurring wild plants include bamboo, straw, and switchgrass. Bamboo, a high-yielding perennial, is used extensively in India to make paper. Typically blended with tree fibers, bamboo paper is readily printable. The gallery invitation depicted on our front cover was printed on a 150-lb., uncoated cover sheet made with 90 percent bamboo fibers from GPA Specialty Substrate Solutions.

Switchgrass is a component of Western prairie grass. It has been studied since the 1990s with positive results. In appropriate climates, switchgrass is an economical substitute for wood pulp. The substrates manufactured by blending these quick-growing crops with slower-growing wood pulps are a safer choice in American printing systems.

More broadly available cellulose-based, tree-free paper falls into two additional categories: agricultural wastes and agricultural crops.

Agricultural wastes left over from food production are at the top of the second list. Making use of waste products instead of finding ways to dispose of them has appeal for obvious reasons. The best-known agricultural waste is bagasse, the fibrous biomass left after juices have been extracted from sugar cane. Bagasse is harvested within a year or two of its planting, requires minimal bleaching, and is plentiful. Sugar cane is widely produced, and the use of its leftovers for paper is desirable. New capacity for pulping bagasse is already coming on line in India.

Printers must use caution: The bagasse fibers are short, and the strength of papers can be variable. Choose your supplier with care, and ask for referrals.

Leftovers from the cotton crop find their way into our money as well as top-of-the-line printing papers. Runnability, printability, and durability of the finished papers are superb. Most of the pulp comes from cotton linters—those short fine silky fibers that adhere to cotton plant seeds after ginning. The longer fibers are removed for use in fabric but the shorter fibers are still up to ten times stronger than wood pulp fibers. Rags or cotton clippings left over from clothing manufacture are an additional source of fiber for these papers.

Crops grown specifically for paper manufacture such as hemp, kenaf, and jute round out the list. Kenaf, a long-fiber plant that originated in the East Indies, is now grown in the US. A relative of okra and cotton, kenaf was determined by the USDA to be “the best option for tree-free papermaking.” Pioneering Vision Paper perseveres as the lone US company with a stated objective of growing and pulping kenaf for use in paper products. Unfortuantely, many of the smaller mills that experimented with kenaf have closed, so kenaf paper is not currently available. Look to the future for this paper type to reappear.