Presentation is everything—up to a point and down to a dot.
WITH RESPECT TO proofing, package printers must be prepared to be all things to all customers, or nearly so, and still be able to assure their customers that the proof they receive will reproduce accurately and consistently on both plates and press. To accomplish this, the printer will choose the technology or technologies that will provide him the tools to keep that promise.
Few would argue that packagers have special proofing needs. These include:
• Ability to proof on a wide range of packaging substrates, whether coated or uncoated, glossy or flat, smooth or rough, including metallics, plastics, and white-behind-color;
• Ability to accurately predict a wide gamut of custom process colors and Pantone spot colors;
• Ability to represent the three-dimensional characteristics of the finished package;
• Ability to accurately show trap and overprint characteristics;
• Ability to produce cost savings; and
• Ability to produce high-quality proofs for a range of uses.
Variability in any of these areas is anathema in brand-intensive, color-critical package converting; consequently, effective proofing solutions are designed to remove it from the process. As the graphics industry moves toward 100 percent digital workflows, including computer-to-plate (CtP), digital proofing technologies are replacing time- and labor-intensive film-based modalities with accurate, reliable digital proofing equipment that integrates easily with digital workflows. Installation of digital proofing systems in packaging environments is accelerating as flexographers also transition to CtP.
In digital proofing, the output device is still the center of attention, although inks or dyes, media, RIPs, and color management tools play critical supporting roles, and no discussion of the hardware should exclude them. Proofing technologies used in contemporary packaging applications belong in one of two broad categories: digital halftone and inkjet, specifically, piezo-electric drop-on-demand (DOD).
Advantage: Digital halftone
Digital halftone proofers use screening and high resolution to match screening and resolution on press. Typically, halftone devices offer colors that are said to accurately reflect press capabilities, including CMYK and Pantone specialty colors, but also 6-color processes (e.g., Hexachrome), gold and silver metallics, etc. Specialized prepress features may include halftone patterns, calibrated inks, and built-in press profiles. On the downside, halftone devices are considerably more expensive than inkjet printers, and use proprietary rather than off-the-shelf consumables.
According to Richard Deroo, director of marketing and strategic partnerships, Latran Technologies LLC, digital halftone technology inherently contains the promise of consistent, repeatable, and accurate color reproduction. Inkjet, he explains, contains some inherent drawbacks such as limited substrate capabilities, inability to provide a "true dot" proof, and the need to apply color management techniques to simulate color.
"The dot or screening is a critical component in creative design, by which we mean that it is necessary to be able to accurately predict the color dot," Deroo says. Not surprisingly, Latran emphasizes that "the digital integrity of the file (the dot), substrate independence, and accurate color reproduction are three critical areas where digital halftone proofing demonstrates clear superiority as an accurate, achievable, and cost-effective predictor of final press quality."
Latran Technologies' Prediction family of 4-up digital halftone proofing systems is based on its patented Laser Ablation Transfer (LAT) technology. The line includes several partly or fully automated imagers, from the entry level model 1420 to the high-end, fully automated Prediction 4600, ranging in format sizes from 14˝ x 20˝ to 22˝ x 30˝.
Advantage: Inkjet
Inkjet solutions are digital proofing devices that spray CMYK-based dyes or pigment-based inks as droplets onto the proofing media. They are fast, affordable, capable, flexible, easy to use, easily supported, and produce near photographic quality. Lower-cost inkjet supplies—including specialized inkjet transfer media—may be proprietary or off-the-shelf.
Skeptics observe that there is still a tradeoff in terms of the color management and specialized media needed to prevent dot gain. Moiré patterns also can be more difficult to spot in inkjet proofs, and light pastels and metallics can be difficult to represent accurately. For fine lines and text, it's also easy to overdo overprint trapping, producing effects on press that inkjet would not be able to predict.
Nevertheless, the introduction of new pigment-based inks and more capable media play into the improved quality and growing popularity of digital inkjet proofing, especially piezo-electric DOD. As a result, inkjet proofs have advanced from low-end preproof and comp work into wide acceptance as a legal contract proof.
Currently, inkjet may be the most widely installed of proofing technologies. Where there is a critical need and/or a customer's strong preference for a so-called "true dot" proof, digital halftone technologies are preferred; however, for many printers and their customers, inkjet's improved quality and affordability compensate for the lingering drawbacks. Many believe that inkjet eventually will render digital halftone technologies obsolete.
Inkjet 101
Frances Cicogna, packaging segment manager, North America, Agfa Corp., says that the inkjet market has been evolving rapidly. According to Cicogna, Agfa has found a way to produce a true color halftone dot using variable piezo inkjet DOD technology. (A word of explanation: Inkjet can be piezo electric drop-on-demand (DOD) or thermal. In piezo DOD, a piezo element (crystal) deforms in a chamber under an electric charge, mechanically pushing out the ink. By permitting larger and smaller drops to form, piezo inkjet provides better control of ink delivery and gray scale elements. Piezo heads are also more durable than thermal heads, which wear out with repeated heating of nozzles.)
For inkjet proofing in most packaging applications, Cicogna says, dye inks are recommended, since they have a much greater gamut than pigmented inks and can better match Pantone and other spot colors.
Packaging has broad requirements for reproducing color, from "pleasing color" on up; this is the primary reason, in addition to cost, that inkjet proofing is appropriate for a variety of interim proofing needs that fall short of the contract stage.
Inkjet does have limitations as to substrate, especially if it's going to be used to make a contract proof, Cicogna says. For this reason, she says, Agfa has developed a special transfer material that encapsulates the ink and prevents dot gain, "which you can't control and can't predict." Inkjet is fine for most packaging substrates, "as long as you have this inkjet layer—and this includes metal, label stocks, plastic," Cicogna says.
The biggest differences between most digital halftone systems and their inkjet counterparts relate to speed and cost. "It's time-consuming to do a proof for a brand," Cicogna explains. "If you think about the cost of inkjet vs. the cost of thermal halftone proofing in this light," she says, the inkjet advantage is clear. Size is also a factor. The modest footprint of most inkjet proofing devices makes the presence of multiple devices in a single shop feasible.
Worldwide, Agfa claims more than 7,000 installations of its Sherpa piezo inkjet proofers, three-quarters in contract proofing environments, including packaging, Cicogna says.
You get what you pay for
"It's crystal clear," says Jerry Willer, worldwide product marketing manager, thermal proofing systems, Kodak, "that thermal costs more than inkjet. In fact, inkjet is roughly 20 percent of the cost of a thermal system." You get what you pay for, Willer suggests: a thermal proof that is specifically designed to emulate the printing press in every dimension in terms of ink density, image structure, substrate, overprint trapping, correct gamut, and special plates such as metallics or white. Because the aim is to emulate the press as nearly as possible, Willer says, it is the halftone proof's ability to match the "nuances" that commands the premium price.
Because the price of a digital halftone system from Kodak ranges from $150,000 to $195,000, Kodak finds greatest success among what he terms "high-value brandowners," for whom it's worth the premium price to mitigate any risk of error, Willer says.
Love all
Practically speaking, many packaging workflows use a mix of both proofing technologies. "Inkjet and digital halftone technologies can, do, and probably should co-exist within a single workflow," says Deroo. Depending on the stage in the workflow or the client whose job is being produced, low-cost inkjet can be used legitimately and cost-effectively for concept and/or imposition proofing, color checks and quality control, where cost savings count, reserving the more expensive digital halftone output for the "contract proof" that receives the customer's signature. "When screening is important and/or the actual substrate matters, then digital halftone is a requirement," says Deroo.
What lies beneath:
Substrate considerations
Whereas commercial offset printers can either use commercial grade paper stocks or simulate them on high-grade proofing papers, flexographers must deal with a virtually unlimited range of substrates. In general, digital halftone proofing systems place a premium (and justify their premium price, in part) on their ability to limit dot gain and achieve high repeatability by proofing directly on the press stock or flexo substrate.
"The biggest issues in proofing for packaging relate to variability of substrates," confirms Latran's Deroo, adding, "When you image, you want to ensure 100 percent pigment transfer to the substrate." Latran Technologies claims its patented LAT technology limits troublesome dot gain and achieves high repeatability by transferring pigmented inks directly to the substrate, thereby eliminating the variability of stock color without resorting to intermediate processing or color management. Thermal proofing is fine for most substrates, Deroo says, including board and foil-faced, embossed and refractive surfaces, making it a reliable, capable tool for packaging applications. Exceptions include some plastics and polyesters that can't survive the temperatures.
Color, a key differentiator
Inkjet evangelists insist that the primary purpose of a digital proof is to match color, not dots. They also accept that color management is an integral part of proofing. Unlike the four process colors that dominate offset, the spot colors prevalent in packaging applications are printed with special ink or combination of inks. Because all proofing is based on CMYK, spot colors have to be simulated. Inkjet is useful for simulating some—but not all—spot colors and for reproducing the extended gamut of flexo presses: Pantone, Hexachrome, Opaltone, Ultratone, etc. Color management employs a technique known as "dithering" to simulate colors that are unavailable within the inkjet printer's recognized color gamut.
For the makers of digital halftone proofers, this is where the rubber meets the road. As Deroo explains, "With digital halftone technology, you don't need color management expertise because it's built into the proofer and into the pigmented ink sheets. It doesn't move."
Willer takes a slightly different tack: "Kodak has stressed for a long time that you don't need color management, but we're extending that functionality now, based on our recognition that presses, substrates, and inks exhibit subtle differences most easily accommodated through color management. What our Approval system alone does, is to create a real spot color from within the Approval itself, using color 'donors' that can be mixed inside the machine to create the exact colors needed. This enables Approval to reproduce spot colors with exactly the fine lines and text for which color-managed inkjet uses dithering, as well as true overprints and vignettes. We take the guesswork and risk out of fine line and fine text and detail work with non-traditional inks (important in labels, for example). There's no way you can do this in an inkjet machine."
The ICC difference
Others see inkjet's reliance on color management not as a weakness but as one of its greatest strengths. Says Ray Cassino, director of product management, prepress, for Heidelberg USA, "Inkjet isn't the next big thing. It's here." Lingering skepticism about what inkjet proofing technology can and cannot do is a function, Cassino says, of what the customer's customer is most comfortable with. "In the broadest terms, it comes down to educating the customer's perception and preference—of looking at the color and not the dot."
Beyond this, Cassino says, inkjet has an inherent ability to make a proof match the press more closely than any other device because of its ability to move through three-dimensional color space changes. "Pressmen want and trust an ICC-profiled proof," Cassino says.
As to substrate, he adds, ICC profiling also takes care of trap, dot gain, saturation, and "paper white" considerations, based on the inkjet proofer's color-managed ability to simulate background color on stock that is brighter and whiter than the stock that will be used for the job. Cassino does acknowledge that, in packaging, with the absence of a "true" halftone dot, "you do worry about moiré." However, he explains, stochastic screening and dithering can ameliorate these concerns.
Rising to the challenge
"Proofing is a little more challenging in flexographic printing, but it's not a matter of hitting the precise process dot," says Dan Bowen, global product manager, color proofing, DuPont.
"What makes inkjet so well-suited for packaging applications is the color gamut. This is where the technology shines," he says, explaining that flexographic printing's aggressive dot gain curve requires color management. In addition, he says, the extended inkjet color gamut is better suited to specialty packaging needs than the more limited gamut of most digital halftone equipment. Consequently, "Inkjet is the system of choice for proofing in a packaging environment," Bowen says. To those who point out that at the current time only 30 percent of the Pantone cannot be reproduced with inkjet, Bowen says simply, "That is changing."
Despite Bowen's endorsement of inkjet proofing technology, DuPont continues to serve all segments of the marketplace, but watches for and supports advances in color management, as well as standards work by CIE, CGATS, SWOP, GRACOL, and FIRST. DuPont chemists are continually working to improve the interactions of inks and substrates.
With a spectrophotometer and RIP on board the proofer, DuPont's self-calibrating Cromalin B-series two-page inkjet proofer is targeted to integration-fatigued customers that want a turnkey solution from a single vendor, Bowen says.
Eventually, inkjet will replace digital halftone proofing, Bowen predicts. The combination of attractive pricing, improved ink sets, expanded color gamuts, better resolution, and more durable print head technologies will obsolete the costly halftone proof. "Inkjet resolutions are already at 100-133 linescreen, and will certainly improve," Bowen says. "It's a matter of time."
By Jean-Marie Hershey
Prepress Editor