ENVELOPE - Printing on envelopes
 

The one thing printing an envelope has in common with printing flat sheets is that both have square corners - or sort of. Envelopes are manufactured on specialty equipment using steel dies and then transferred to high-speed machines that affix glue to the seams, fold and complete the envelope. The very nature of these operations make it extremely difficult to make an envelope that is perfectly square, as is a sheet of paper. And that is the challenge to the printer: printing a ready-made envelope with type and graphics that are straight and true.

Printing on stock envelopes

It is possible to print a considerable variety of single and multiple-color envelopes, including four-color process, on factory-made envelopes. There are some points that should be considered in the design and planning stages.
Limitations on some envelope presses

Many high-speed, two-color "Jet" envelope presses print without gripper; the envelope is literally pushed through each printing cylinder while preserving registration. These presses, however, cannot achieve the quality of a traditional offset press. Newer four-color envelope presses can print process with excellent quality and require gripper margin, however.
Gripper and bleed

Printing a return address—commonly referred to as a corner-card—in the upper left corner or on the back flap is standard procedure. Sometimes small bleed areas are possible, but in almost every instance, allowance must be made for gripper on one of the short sides.

For example, a two-color register envelope that bleeds off the left edge, may have to be gripped on the opposite end. This can be a problem since the envelope may have a tendency to "fish-tail" during printing. This is not a problem, however, on presses with a common printing (blanket) cylinder, since both colors are printed at the same time.
Envelope seams and print quality

Another factor affecting quality are the multi-layers of overlapping seams that double and triple paper thicknesses. Since envelopes, like sheets of paper, must pass through printing and impression cylinders, special make-ready techniques are needed to compensate for these varying paper thicknesses. Choosing an envelope with seams that do not underlie printing areas (especially solids and tints) will often assure better print quality.

When the design is complicated, with heavy solids, such as a flap or side with full bleed printing, or when you require a special grade or a coated paper, then the envelope should be printed flat and converted.
"Made to order" (converted) envelopes
Frequently envelope print jobs are designed with extensive colors and/or graphics that make it necessary and advisable to print the flat sheet and then die cut and fabricate the envelope. Converting an envelope from flat sheets requires machinery that first die cuts the sheets and then, in a separate operation, scores, folds, glues and folds them to their final shape. This equipment normally runs at high speed and the press run requires careful scrutiny by the press operator to maintain quality.
Envelope cutting dies

Converters have on hand hundreds of cutting dies in various styles and sizes. The more common sizes of envelopes exist as stock dies and converting costs are minimal. In some situations, an adjustable die can be used when no stock die is available. A custom die is an expensive proposition and is practical only on very large conversions.

Minimum converting quantities

Envelope conversions usually require minimum runs of 5,000 pieces to be practical. However, you can have as little as 500 envelopes converted, but the unit cost will be high, since final gluing and finishing is frequently done manually.
Custom envelopes for stationery suites

At CJPW, we have converted many types of envelopes, with special flaps, special window positions, including a standard number 10 size envelope with the flap on the short end (open end). Many stationery "suites" contain uniquely designed, printed and configured envelopes. Envelopes that print using two processes, such as offset printing and engraving or blind embossing, are best left to flat sheet conversions. Obviously, one must allow extra time for the conversion process.

Graphic files for conversions are prepared in the same manner, using the final size of the envelope as the document size. When your job goes into production, we configure the printed sheet to the converter's imposition.