Optimizing Your Flexo Printing for Striking Package Graphics
August 1, 2004
Optimizing Your Flexo Printing for Striking Package Graphics
A set of tools is available to measure and control print quality. Insist that your printer use these devices and methods.
by Gennifer Levey
It’s unfortunate that you can put months of planning into your packaging design but still not be certain of what you’re going to produce because it’s a flexographic print job. While printing is usually the wild card, it doesn’t have to be the case.
Many marketers who use flexographic printing are not fully aware of the rich set of tools available to measure and control print quality.
This article will explore what measurements you can insist your printer check with equipment it should already have. You can require your printer to supply data that impels a more efficient, consistent, methodical approach. This will enable you to more effectively control print quality without increasing your budget.
In 1997, the Flexographic Technical Association published a groundbreaking manual called FIRST: Flexographic Image Reproduction Specifications and Tolerances. It is a set of industry guidelines that standardizes printers’ tools and language.
Qualitative vs. Quantitative
Even with quantitative standards, some printers still rely mainly on qualitative methods. If you go to a press check and hear the press operator say, “Looks like it could use some more yellow,” but he has no measurements and gives you a blank stare when you ask him for density readings, your printer is taking a qualitative approach.
It is fine to look at print and think it needs more yellow, but this requires verification with density and dot gain measurements. Perhaps the yellow has plenty of density, but the magenta is too strong, overpowering the yellow.
If you insist that your vendors “print by the numbers,” you are actually supporting your printers in their process improvement initiatives. Among the most important quantitative tools are spectral data, density, dot area, ink trapping and control of the viewing area.
Spectral data. The most accurate way to measure and maintain line colors (also called spot colors) on press is to obtain spectral data with a spectrophotometer. Spectral data is the measure of lightness, saturation and hue of a color. A spectrophotometer measures the reflected three-dimensional color data of print and compares it to a color target or standard.
Your printer should be comparing to either the spectral data of a PMS (Pantone Matching System) color specification or to the spectral data of a pre-approved ink “drawdown.” Your print job might require a drawdown if you want to print with a unique color not specified by PMS.
A spectrophotometer provides a Delta E measurement, which is the cumulative difference between the color target and the print sample. You should request that your printer maintain a color difference of no more than a Delta E of 2. For lighter, subtle colors like grays, tans or pastels, the printer should strive for a Delta E of 1.5 or less. Do not use spectral data alone to sign off on line colors. You must also rely on visual inspection of color.
Density. During a press check, density and dot area are the most important print characteristics to monitor on process printing. They are telltale numbers that can reveal problems in most areas of print quality.
Density is the measurement of the amount of light reflected from the printed sheet. A higher density reading denotes a darker surface that absorbs more light than it reflects.
A press 'fingerprint'
At the proofing stage, you can insist that your separator verify the density of process inks or toners used in your color target proof. A quality separator should attach a sticker to your proof with density measurements of each process color, within acceptable tolerances. It should either be to FIRST target specifications or preferably to your printer’s unique density specifications, as measured on the characterization of the press (also called fingerprint) done beforehand by the separator.
When your job gets to press, you will find that the press check will be shorter and smoother if your printer takes a methodical, numbers-based approach. During set-up, the printer should work to achieve target density on all the process colors.
Once you have achieved the target densities, analyze the print. You might have to make slight adjustments. However, the first step should always be to match the densities of the proof.
Dot area. At the same time your printer is measuring density, he should also be measuring dot area. The two go hand-in-hand. Dot area is the physical size of a dot plus the optical effects that cause it to look larger or smaller.
When a printed dot hits the packaging material in a flexographic press, it spreads, creating a much bigger dot than what was in the negative and on the printing plate. This is called dot gain.
When your job is in press, the printer should measure the printed dot area with a densitometer and compare it to the expected dot area.
If the dot gain and density values for process cyan, magenta, yellow and black are close to the targets used by the separator, then the print job should closely match the target proof. Dot areas that are smaller or larger than characterization numbers indicate that your printer should make adjustments on press. Once you have signed off the job, your printer should take dot area readings on each printed roll.
Ink trapping. One type of ink trapping involves the measurement of how well one ink lays down on top of another ink based on whether the first ink dried enough.
If a layer of ink does not dry enough, the next ink on top may be “eaten” or “picked away,” causing “pinholing” or weakened color intensity. You can see this clearly by looking under a magnifier. You see squiggly, crawl-shaped dots.
If this is visible, ask your printer to take ink trap measurements with either a densitometer or a spectrophotometer. If the trap is less than 80 percent, there might be drying problems on press. Often this is a problem with white because it is so thick and covers so large an area as backup to the main design. You should also watch for this with any large solid area that has overprinted elements.
Viewing area. When you approve either process or line color print jobs, it is essential to have a color-corrected lighting environment.
Keep in mind that your print samples can look quite different once you get them back to the office if the viewing environment there is not the same as your printer’s viewing area. Ideally, you should replicate your printer’s viewing area, especially if you view and measure color away from the printing plant.
When you require your printers to take a methodical, quantitative approach to your jobs, you will certainly see improved, more consistent printing. And your packaging graphics will be the beneficiary. BP
The author, Gennifer Levey, is Graphics Prepress Manager at The Excelsior Packaging Group, Yonkers, N.Y., a printer, laminator and converter of wide web flexible packaging materials. Contact her at 914.968.1300.
Quality every step of the way
Measuring and achieving quality at the printing phase of the process are critical to package success, but flaws at any stage can compromise the effectiveness of your end product.
n Conception. At this point, you must choose the ideal packaging material, with the help of your printer, if necessary. You also have to determine the scope of the project. Is it necessary to print a process image with 10 colors, or will simple, but striking three-color artwork achieve the intended results?
n Printing contract. Along with determining press capabilities and volume capacity, find out if a vendor is committed to quality. This is the best time to negotiate terms of the contract, including numbers-based quality expectations.
n Design. When possible, a designer should work with the separator or printer during the design process. Ask for a preliminary pre-press proof to uncover any potential problem areas.
A flexo-savvy designer should consider choice and size of typeface (including reverse type), registration issues, line color vs. process colors, gradations, images and resolution.
n Pre-press. Depending on complexity of the artwork, you may want to bring the separator and printer together for a structured collaboration. During pre-press, you will receive proofs from the separator. It is essential for the printer to agree that he can achieve the target proofs.
n Conversion or lamination. The best print job means nothing if the converting falls short. You can require your printer, converter or laminator they might all be the same vendor to send you conversion or lamination specifications to approve before the job goes into production. This is usually a sheet with a drawing showing placement of slits, vents, folds, image placement, etc.
Flexography is an excellent choice for process or line printing. Process printing is usually the use of four process colors—yellow, magenta, cyan and black.
Graphics professionals commonly refer to these colors as “CMYK.” When printed on top of one another, the colors produce images. Usually these four colors contain varying sizes of dots—also called screens or halftones—to distinguish light areas from dark areas.
Process printing can also use three or fewer colors, and less frequently involves colors besides CMYK. More recently, flexographers have begun using Hexachrome, Opaltone and other types of expanded gamut printing, which employs six or more process colors, such as orange and green. This produces images with brighter, more vibrant color than can be achieved with standard CMYK process inks.
Flexography uses line printing for simpler artwork not involving process print. It can be a superb choice for high-impact graphics that are easier to print and less costly.
Line colors are solid with no screens. A good example is the Wonder brand bread bag with solid letters and yellow, red and blue circles.
Line colors are usually designated by a Pantone Matching System (PMS) color. For a color not found in the PMS book, printers or ink suppliers can supply a “drawdown” that becomes the color match for a print job.