By Cassandra Balentine
The high-speed inkjet production market supports both dye- and pigment-based inks, which interact differently with paper.
John Crumbaugh, marketing executive, ink and media production print solutions, Canon Solutions America, says on papers designed specifically for dye or pigment inks, the inks will perform in a very similar fashion, producing exceptional results. “Where these ink technologies show their differences is on paper not designed specifically for the ink set. Pigment inks print well on many non-inkjet treated papers such as newsprint and uncoated offset. These types of papers are not ideal for dye,” he explains.
“The main difference is that pigment uses a solid colorant and dye uses a liquid colorant,” says Mike Herold, director of continuous feed inkjet technologies, Ricoh.
Inkjet inks consist of a clear liquid, which Dr. Ross R. Allen, senior technical specialist, Hewlett-Packard (HP) Printing Technology Platforms, says is known as the ink vehicle, and is a colorant based on dyes, pigments, and sometimes a mixture of both. “The ink vehicle carries the colorant to the surface of the print and is an important element of a number of ink characteristics including printhead reliability, dot gain on the media, and drying the print. Colorants work by absorbing specific wavelengths of light and reflecting others. The choice of colorant—as well as ink design—has a significant effect on print durability, color quality, drop ejection reliability, ink cost, ink consumed in servicing cycles, media breadth, and environmental considerations,” he explains.
High-Speed Inkjet: Dye Inks
Dye-based inks were the standard many years ago. However, technologies continue to evolve.
Jennifer Pennington, paper scientists, Eastman Kodak, suggests dye-based inks are not waterfast and therefore require papers that use more expensive chemistries. “For some applications where waterfastness is not required, dye-based inks are still in use. Depending on specific dyes, they can differ greatly in light stability and gamut range.”
Deana Conyard, worldwide marketing manager, high-end inkjet, and Beth Barrese, media manager, inkjet line of business, Xerox Corporation, note that dye inks absorb better into the paper, performing better on coated substrates, but are challenged on gamut and waterfastness. “Dye inks are usually less expensive, but often use more ink in printing,” they explain.
“Dyes are chemical molecules that dissolve in the ink vehicle,” says Allen. He points out that they can have high color strengths, and if they remain at or near the paper’s surface, dyes can be more colorful than pigments. However, on absorbent papers, dye molecules can be carried by the ink vehicle deep into the paper’s structure. When this happens, there may not be enough dye remaining near the surface to produce dense blacks and saturated colors. “Show through can occur on lightweight papers where the image on one side is visible on the other due to migration through the sheet. High dye concentrations can counteract reduced black and color saturation, but this can lead to unreliable drop ejection—especially when the printhead is uncapped for an extended period with nozzles not printing. Frequent service cycles are needed to keep the printhead ejecting drops reliably. A service cycle increases ink consumption and productivity will be reduced when it interrupts printing.”
Mark Schlimme, director of marketing, Americas, Screen, points out that dye-based inks have advanced with the addition of more dye colorant particles in the ink, expanding the color gamut. “Newer dye inks are able to hit colors that have been very hard to achieve in the past,” he points out. However, he adds that dye-based inks are not as durable against sun and moisture compared with pigment-based options.
Bruce Richardson, national sales manager, web presses, and Oliver Baar, head of division business development marketing and digital web presses, KBA, note that dye inks offer compelling pricing. “Therefore, it’s widely used in applications that do not need a high print quality or offset compatibility.”
Dye-based inks are common in transactional applications. “All other markets, like books, magazines, labels, mailings, or even top sheets/corrugated require either a high print quality or a high offset compatibility,” they offer. “Newspaper are special—they have quite a limited lifetime, which might be interesting for dye-based ink. However, we push even this market to pigment ink,” add Richardson and Baar.
High-Speed Inkjet: Pigment Inks
Pigment inks generally perform better on plain, untreated/uncoated paper, maintaining higher optical density, say Conyard and Barrese. “Pigment inks are slightly more expensive, but are more efficient in printing. They also have better light fast and waterfast properties.”
Due to the waterfastness inherent to pigment-based inks, it allows for more economical paper chemistry and a broader range of paper grades, explains Pennington.
Allen explains that pigments are particles that are on the order of 100 nanometers in diameter. “Unlike dyes, pigments do not dissolve in the ink. Pigments are kept in a stable dispersion in the ink vehicle by surface charges that produce repulsive forces between particles. Once on the paper, the chemistry of HP Pigment Inks quickly immobilizes the pigments on or near the paper surface as the ink vehicle is absorbed and evaporates.”
Because pigment inks have more colorant particles compared to dye-based inks, Schlimme says it gives pigment inks better density that will stand up to elements—like sunlight and moisture. “The extra colorant particles also expand the color gamut and generally will allow the press to hit colors not possible with dye inks. Pigment inks are a requirement for text books because of the additional durability the extra colorants provide. However, due to the additional particles in pigment inks, printhead life is reduced, and they also tend to be more expensive compared to dye-based inks.”
“For the markets we serve, KBA clearly sees pigment ink as the best solution,” say Richardson and Baar. “Pigment ink provides a very close offset CMYK compatibility, significantly higher light fastness, as well as better ozone resistance. All of this leads to a higher print quality and closer results to offset printing,” they add.
Applications drive image quality and media compatibility requirements. “Dye versus pigment ink selection is more related to the media requirements and image quality needs versus the specific applications,” say Conyard and Barrese.
Pennington agrees, “both dye and pigment inks can be functional in all markets. It depends on the substrate and specific performance or fitness for use requirements of the application. If anything, pigment inks may have a slight advantage in breadth of applications,” she continues.
Schlimme adds that when permanence and light fastness are more important, typically a pigment ink or UV print process is used, like product labeling applications. He adds that many other applications such as transactional, benefit from the lower cost of dye-based inks.
Crumbaugh points out that as a general trend, book and commercial print providers tend to appreciate pigment, while in-plant operations prefer dye.
When selecting media, it is essential to consider the type of ink the press utilizes to ensure optimum performance. dps