Screen Savers

With good reason, many converters see the rotary screen printing method as a way to enter the high-end label and package markets. Screen printing provides a solution to create raised or tactile features; print rich, brilliant and opaque colors for the no-label look; and decorate with numerous varnish effects. Screen-printed metallic and conductive inks offer value-added possibilities.

Competing in these markets — and maximizing profits — will depend on keeping the consumable and labor costs as low as possible. This is especially true since today's end-user demands a higher level of service and flexible deliveries without having to pay extra. Short-run, repeat jobs are becoming increasingly common for converters. Delivering on a just-in-time basis means producing smaller and more frequent orders. A typical day for many screen printers could involve up to five job changeovers per day.

A rotary screen printing system that allows you to reuse and re-image your screens is a great way to maintain competitiveness and reduce consumable costs. Following are variables that determine how the screen printing system's consumables contribute to the profitability of a specific job.

  • The cost of the screen.
  • The screen's durability (number of impressions).
  • The costs of the prepress and post-press operations.

The ability to reuse a screen will reduce your costs per job significantly, since the initial screen cost can be amortized over the number of jobs for which it is used.

Re-Imaging Screens

The re-imageable screen for the narrow and mid-web markets was pioneered in the 1980s. Its mesh is a nonwoven, pure nickel material, and it's manufactured using an electroforming process. The nonwoven mesh and hexagonal hole structure give the screens strength to withstand the rigors of the pressroom environment and print at speeds of 500 fpm. The durable screen provides in-press stability and does not contribute to press downtime due to screen breakage. No press downtime due to screen damage is also a significant cost savings.

It is the prepress and post-press operations that enable the screens to be used so many times. To start, the end rings are mounted in the screens with a two-part epoxy glue. Then the screen is coated with a light-sensitive emulsion. After drying the emulsion, the screen is wrapped with an undistorted film positive and then exposed to UV light. After exposing, the film positive is removed, and the unexposed areas are washed out and developed with water. Then the screen's image is inspected and ready for press.

After printing, the ink is cleaned from the screen with an automatic screen washer. At this point, the printer has a choice, either to put the screen into storage until the same job repeats or remove the existing image. A screen stripping unit can remove the existing image and make the screen ready for re-imaging with a new design.

If the converter relies on screen printing on a frequent basis — and fast turnaround is an important consideration — then it is advantageous to perform the screen prepress operations in-house. The complete prepress system includes an end-ring gluing and coating unit, drying cabinet, exposure unit, a developer and stripping unit, and an inspection wash-out booth.

In-house prepress gives you much greater freedom in your job planning and thus flexibility. The other option is to let your screen supplier provide the screen prepress service.

Reuse of screens is an efficient process, whether a printer uses the same screen for a repeat job or re-images it for a different job. The time required for a screen to be re-imaged does not vary significantly from the time and labor costs associated with imaging a one-way, disposable rotary screen.

Boosting Your Profits

Figure 1 illustrates how the costs of each screen print job decline with the number of times a screen is re-imaged.

By the third re-image operation, the re-imageable screen clearly is providing a cost savings. When the screen is used for the tenth different design, the converter has saved significantly.

Figure 2 shows what happens to the costs of the screen when it is used to print the same design on repeat jobs. The savings are even more pronounced than in the first graph because the labor costs associated with re-imaging are now eliminated. In the case of a repeat job, the screen only requires cleaning after printing.

Industry surveys show a distinct decline in average run lengths in the labelling industry and projections indicate this trend will continue. This makes low consumable printing solutions even more important. Working with re-imageable nonwoven nickel screens is certainly one way to reduce consumable and production costs.

John Costenoble is sales manager, rotary screen products, for Stork Prints America, Charlotte, NC. He's worked at Stork for 17 years as technical applications manager and sales engineer. Contact him at 704/921-5300; john.costenoble@stork.com; storkprints.com.

The views and opinions expressed in Technical Reports are those of the author(s), not those of the editors of PFFC. Please address comments to author(s).


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