Printing & Design Tips: APRIL 2006, Issue #57

What is Flexography?

When you pick up a frozen dinner in the grocery store or wrap a birthday present, you are most likely handling a product printed via the flexographic process.

In contrast to offset printing, which is a planographic printing technique in which the image- and non-image areas of a print job are on the same level on a printing plate, flexography is a relief printing process.

That is, the image area is raised above the non-image area. Cutting a relief image in a linoleum block -- or even in a potato, as many of us did as children -- and then pressing the block (or potato) into ink and then onto paper approximates the flexographic process.

The inks can be either water-based or solvent-based, and both sheetfed and web presses can be built for flexographic printing.

Unlike offset printing, flexography does not transfer the image from the printing plate to a blanket and then to the paper. Instead, flexography, like letterpress, transfers the ink directly from the plate to the paper. But whereas letterpress plates are made of metal, flexographic plates are made from a more flexible substance such as rubber or photopolymer materials.

Flexography is most often used for printed products such as envelopes, bags, tags, wrapping paper, corrugated boxes, milk cartons, newspapers, packaging, pressure-sensitive labels, and flexible films.

Why is this process so useful for printing these specific items?

First of all, the ink used in flexography dries very quickly. This makes it perfect for non-porous materials such as plastics and foils. It is also ideal for printing on packaging materials, since the soft rubber plates don’t crush thick, compressible materials like corrugated cardboard.

What is Screen Printing?

Like flexography, silkscreen (or serigraphy) has wide-scale commercial printing applications. It is most useful for apparel, signage, and such specialty products as looseleaf binders. It is, however, better suited to short runs than flexography, which is better suited to long runs of single items. Screen printing can also print on substrates of any thickness and size (a huge banner, for example), whereas flexography is limited to certain sizes.

Screens today are made of nylon, Dacron, and even stainless steel, and the stencils that allow certain portions of the image to print and prevent other portions from printing are produced either mechanically or photomechanically.

Once exclusively a manual process, silkscreen has been mechanized through the use of rotary screen presses. In the past, the drying time of the thick layer of ink limited the usefulness of this technique, but now drying times have been shortened through the use of inks cured with ultraviolet radiation.

Screen printing can lay down very thick ink deposits onto almost any surface, including fabric, plastic, metal, paper, leather, wood, glass, ceramic, or even printed circuit boards used in electronics manufacturing. A screen-printed product can be recognized by its thick, raised ink and, in some cases, even by an impression of the mesh screen on the ink.

Screen printing can be used to print on almost any size or shape of material. Using this process, one can vary the thickness of the ink film and use a high quantity of pigment in the ink, allowing for brilliant colors and durable products that can tolerate everything from harsh weather (signage) to laundering (silk-screened shirts). Equipment costs are also comparatively modest.

[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]