Offset Blankets — Printers' Security Blanket

BY ERIK CAGLE

The following is an industry service announcement, courtesy of Scott McGowan, product manager, supplies marketing for A.B.Dick-Multigraphics. He offers the following definition of a printing blanket: The medium by which the right reading image on the plate is transferred to become a right reading image on the paper or media being printed. Choosing the correct blanket for your offset printing job, he adds, will yield the highest quality results.

While not the most heralded gun in the offset printing arsenal, blankets play a critical role in the success (or failure) of a client's job and are, ultimately, a deciding factor in whether that client continues patronage. They may not grab headlines at DRUPA or Graph Expo, but choosing the wrong blanket could grab business and send it elsewhere.

Blankets fall into two main classifications:

Compressible blankets contain cushion-like air pockets or layers within the blanket structure that provide them with resiliency and the ability to return to their original dimension after coming into contact with the media being printed. These are ideal for printers whose jobs require a wide range of different weight papers; they can withstand harsh treatment delivered from such substrates as index, envelopes, card and cover stocks, and still be able to print regular bond paper.

Sometimes a low spot or smash will occur in the blanket when it has been pushed beyond its limit, according to McGowan. This limit, however, is greater than when using conventional or hard surface blankets.

Conventional blankets feature a hard, smooth surface and are often used with an under-packer to elevate them to the required thickness for use. They offer excellent ink release from blanket surface to sheet, which makes them the optimal choice for printing higher quality work—fine line screens and halftones.

Decisions, Decisions
McGowan notes that printing envelopes or harder stock with a hard surface blanket can lead to low spots much sooner than if using a compressible blanket, while printing a high screen halftone with a compressible blanket could produce less-than-ideal dots.

"Specialty blankets have come to make the printer's life easier and more productive," he states. "Such blankets would be quick-release style, which have an attached set of aluminum bars, making blanket changes fast and easy."

He adds that the popular two-piece adhesive blankets offer a set of adhesive-back faces and adhesive-back backers. The backer is applied directly onto the blanket cylinder, with the face adhered to the backer. This two-piece system is favored by printers that print on small areas such as business cards or return address envelopes.

A.B.Dick-Multigraphics offers a series featuring the Economy Bronze Conventional, the Popular Silver Compressible and the Premium Gold Conventional products. Both a conventional with under-packer and a compressible are also available for the Itek press series, including quick release for the two-color offset press. Under the Multigraphics product line there are the Multicompressible, Multiconventional, the Multi Premium Plus II (operates like a compressible, but delivers conventional quality), the Multi Select with semi-compressible characteristics and the Multi-quick change adhesive blanket series.

Look At the Issues
According to Brian K. Cosgrove, marketing director for DYC Supply, printers need to weigh a number of issues when selecting a printing blanket. Heading the list is consistency—in the blanket's performance, production and manufacturing process.

"Demand for consistent gauge or thickness has caused manufacturers to continue to process uniform thickness of material from one blanket to the next," Cosgrove adds. "DYC guarantees the gauge of our blankets to be within ±0.0008 from roll to roll."

DYC Supply boasts a wide range of blanket products, featuring the SX-10, Platinum and S7000 models for large commercial, sheetfed and web offset printers.

Ted Miller, North American sales manager for MacDermid Graphic Arts (formerly Polyfibron Technologies), notes that the bevy of products and applications involved is making the printer's decision increasingly difficult. He recommends that printers pay particular attention to the distribution factor—through either a dealer or converter—when buying prominent manufacturer products, as it will impact the level of support they receive.

Caliper control and performance consistency are driving the manufacture of printing blankets, Miller notes. "Because of demands with more sophisticated presses—faster running speeds, shorter makeready times—the expectation is that there is going to be more tighter caliper control on the blanket," he states. "Performance consistency of the product, from lot to lot, is also critical. The printer doesn't want to see any major differences in print quality going from one blanket to the next.

"Printers typically want the optimum in terms of printing quality: good, solid ink density, good laydown and good release," he adds. "The fidelity of the dot that's printed should be very sharp, so they're looking for high quality but, at the same time, they also want longer life and durability. The demands of blankets today are greater than they've ever been before."

MacDermid, which offered a half-dozen blanket products five years ago, now offers 25 to 30. It is unveiling a unique product at Graph Expo this month, and early reports indicate that the blankets will boast a non-rubber surface. Previously offered products, such as the Polyfibron XT750, XT850, XT555 and XT450, head the MacDermid portfolio, along with Highlight Strippable Polyblankets, Highlight Coating Plates and others.

Paper stock; condition and speed of the press; the types of plates (solvent- or aqueous-based); and press chemistry, including fountain solution and washes, are of importance in blanket selection, according to Mike Neroni, national sales director for DAY International. Durability, print quality and productivity play large roles in influencing the manufacture of blankets, he adds.

"The durability issue is addressed through new fabric technology, which addresses gauge stability and registration control. While new compound technology results in resistance to edge cutting, embossing and chemical attack," Neroni states. "New face compounds and surface textures that provide more uniform ink transfer for improved dot reproduction and smoother solids are enhancing print quality, along with a variety of compressible carcass designs that provide quick rebound, uniform print pressure and greater packing latitude."

In terms of productivity, new stable carcass designs that reduce the need for repacking help ensure more press up-time. He adds that less waste at start-up and after blanket washes—due to new solvent-resistant compounds—allows jobs to return quicker to color and register, while new print face compounds reduce paper and ink piling, allowing longer runs between blanket wash cycles.

New fabric-back blankets from the dayGraphica and David M brands highlight the latest offerings from DAY International. The 8300 Static Eliminator from the dayGraphica line is designed for presses utilizing direct-to-plate imaging systems, with the QL Silver from the David M line, designed for high-speed web applications. DAY International also boasts products that address both gapless web press and narrow-gap web press technology.

Kerry Giles, marketing manager for Reeves Brothers, believes printers should concentrate on areas such as printability, durability and release when considering blankets. Also, she says faster press speeds and a variety of substrates wield considerable influence on the manufacturing end. Those factors are addressed via new rubber formulations, uniform thickness, tighter gauge tolerance and maximum release.

To that end, Reeves offers a full line of Vulcan offset printing blankets for the web, sheetfed, newspaper, business forms, packaging, cylindrical and conventional markets. Two new products have been released: the Vulcan Editor newspaper blanket and the Vulcan Alto web blanket.

Among the critical selection factors for printing blankets, according to Billy Bauman, marketing manager for Gans Ink & Supply, are the integrity and smoothness of the blanket surface, its ink-carrying ability, release, longevity and resistance to stretching, smashes and sinking.

Gans Ink & Supply addresses the market with The Edge, which features a super-buffed, defect-free surface and a proprietary sub-face that resists edge cutting and smashing.

"Longevity, dot integrity and ink-carrying ability have emerged as the three most important issues to printers," Bauman states. "Longevity is critical due to the associated costs of downtime necessitated by blanket changes. Dot integrity is a function of the blanket surface's composition and finish. The blanket's ability to minimize dot gain ensures sharp halftones. Ink-carrying ability is crucial for dense solids and, in older designs, was limited due to dot gain issues. These characteristics are designed into the blanket and quality controlled during manufacturing to ensure the level of performance required by today's print buyers."