WEB & SHEET STUDIES IN COATING/LAMINATING

Equipment suppliers address coating/laminating material handling issues for both sheet- and web-based applications.

by Jessica Millward, Associate Editor

STUDY #1: Web coating

Registration to a preprinted web (a.k.a. optical registration or dynamic registration) is often used to apply specialty coatings or spot varnishes, and comes in handy for re-running a web through the press for line work. Dri-Tec's Gravure/Flex convertible print station handles such applications with ease, but, as Dri-Tec VP Matt Tielkemeier notes, retrofitting the unit to a geared press may require a little extra attention.

As Tielkemeier explains, dynamic registration is achieved through the use of a high-speed optical sensor, an encoder, and an eye mark on the printed web. To help temper web tension or velocity fluctuations inherent in an older unit's performance, Tielkemeier suggests a dancer be included in retrofit configurations for a geared press. The optical sensor should be located just before or after the print deck or coating station to provide the final control point reference for registration precision.

STUDY #2: Solventless lamination

Controlling web tension in the solventless adhesive lamination process is the key element to avoiding wrinkling, tunneling, and curl. Rick Ruenzel, sales manager for Comexi America, notes "This becomes even more critical when processing a wide range of substrates on the laminator—films, foils, paper, semi-rigid materials."

Effective web tension control is in large part accomplished through the right equipment, Ruenzel insists. A.C. vector drives are now a must. Brakes on the unwinds should not be used because the web tends to stretch in order to overcome the inertia of the non-driven roll. An air dancer is also vital to adjust for any changes or slackness in the web.

The right "hardware" only enhances the abilities of knowledgeable operators, another crucial component of the solventless lamination process. Well-trained personnel should be given a simple way to monitor and control web tension. As Ruenzel maintains, "This includes the use of a touch screen control with readout of tension values throughout all the tension zones ... and the ability to record and save these values for future jobs."

STUDY #3: Sheetfed coating

It was about a decade ago that Heidelberg premiered its first press with two in-line coating towers, and the manufacturer has continued to improve upon in-line, sheetfed coating methodology since. As Packaging and Label Sales/Marketing Manager Achim Schmidt points out, "… since both technologies are attached and integral parts of the press as in-line coaters, there is no sheet alignment whatsoever."

Instead, Heidelberg presses and coaters employ the company's own AirTransfer system for the movement of sheet through the production line. Each sheet is guided contact-free through the press, drawn by suction and borne on air cushions. The requisite blast air is supplied by axial fans located directly on the back of the sheet guide plates. The entire mechanism is controlled by the CP2000 Center, and therefore can be automatically activated when a stock thickness less than 0.3 mm is entered.

Find more information on coating and laminating equipment and suppliers in packagePRINTING's Equipment & Materials Specifier (May '01), p. 23-24, or 2002 Who's Who (Dec. '01), p. 76.