As long as flexography has been a printing process, matching proofs from the press to proofs approved by the customer has been a challenge. The reason: Most of the current proofing methods were really designed for the offset litho printing process.

Fortunately, in the last few years the mindset has changed. From trying to match the proof to the flexo press, printers instead have moved to matching the proof to the capabilities of the press. There are several types of proofing methods available, and each has its plusses and minuses. In the end, what is most important is that the proofing method chosen be mutually agreed on by both the printer and the customer.

There are basically two types of proofing available: analog and digital.

Analog proofs are made from films. They can be on a color overlay or on a single layer (laminate). Typically standard dot gains are built into these proofs, but they are usually for SWOP (Standard Web Offset Press) using a standard process-ink set.

Therein lies the problem. The built-in dot gain is for SWOP and not a typical flexo-press application. Expense is added with the need for films and assembly. Another drawback is that line work is not always adequately color managed. Neither are these proofs capable of reproducing some print attributes such as ink overprints, color sequence and ink deficiencies.

On the upside, these proofs do show dots and these dots can be "pushed" to more accurately reflect some of the gain characteristics of flexo—especially in the highlights. Images can be color managed, as some of these systems can match spot and PMS colors well.

The three types of analog proofs are Dylux (also called Blueline), Color Overlay, and Laminate.

Dylux: The proof is made from output films and is best suited to check copy, register, moiré and defects. Dyluxes are typically used for quality control.

Pros—They are inexpensive if made from final films, there are no chemicals to handle and they are easily stored.

Cons—They are not for color and are unstable for size.

Color Overlay: The proof is made from working or final films and can be processed dry or by using a de-veloper. It is a favorite of the press operator because it shows how each individual color looks, which is helpful to press setup.

Pros—Separations can be seen along with traps and plate breaks. These can be laid over art to check copy and can be mounted on the customer's substrate.

Cons—They are not for color because they are made to SWOP standards.

Laminate: Proofs are again made from working film negatives. Successive layers of colored dyes are imaged and laminated to a carrier base sheet.

Pros—They can be mounted on the customer substrate, can be color managed, and some systems can match the customer process-ink set.

Cons—They have built-in dot gain for SWOP standards.

The common characteristic of all digital proofs is that they don't require the use of film negatives and can help to eliminate some of the steps in the reproduction process. Digital proofs are usually color-managed and are often "pushed" for color. Some of these systems can show dots on the proof (laser ablation), while others use continuous dots for color (inkjet, continuous inkjet). Digital proofing is obviously the method of choice when working with the newer digital-plate technologies, and will be explained in depth in Part 2.

Proofing for the flexo process will continue to be a challenge because of all its printing variables. One of flexography's chief advantages—its ability to print on almost any substrate, with inks having just about any combination of properties—can lead to dramatic variables in print-job appearance. Therefore, the best "proof" for flexo would be one that is generated from the actual press, using the proper inks and substrates, approved by the customer. As long as proper documentation is used to accomplish this, matching should be relatively easy. Because this isn't always possible or realistic, other proofing methods need exploration.

Steve Utschig, Consulting Technical Editor 920/735-4882 utschig@foxvalleytech.com