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Cylinder or flatbed: re-evaluate your choices
Choosing between flatbed or cylinder configurations is often a case of company tradition rather than analysis. Some prefer to use higher-priced cylinder screen printing systems for all applications, while others consider this overkill. Whatever the rationale for choosing between flatbed or cylinder configurations in the past, innovation in both systems mean it is timely to re-evaluate the choices.
Improved throughput
Switching from a manually loaded sheet process to an automated web process can speed throughput by 50 per cent or more. The actual speed improvement depends on the size of the job among other factors.
Latest generation flatbed and cylinder screen printing systems are equally suited for high volume workloads and can be expected to increase throughput compared to older screen printing technologies for several reasons.
First, the availability of custom-configurations in both flatbed and cylinder systems means they can be adapted to the job format as opposed to changing job formats to mesh with the dimensions of generic systems. The common 400mm width is no longer a limiting factor and large formats are now achievable as are artwork layouts that maximise yields. It is reasonable to expect that changing printing formats will significantly increase throughput and yields in many applications.
Second, the newer systems, both flatbed and cylinder, bring the advantages of electronic controls to bear on throughput. This is especially important for fast job setup or for fixing fault conditions that previously required a good deal of manual adjustments. All settings in the newer systems can be controlled electronically, including adjustments for material thickness in cylinder systems and pneumatic controls for the screen clamp, squeegee and float bar in flatbed configurations. Best-in-class flatbed systems also feature an automated and synchronised vacuum release on the printing table, which is important for faster throughput on large format jobs.
Lastly, the most dramatic shift in throughput derives from contact drying, which is equally suited to web (flatbed or cylinder) or sheet fed systems (flatbed). This consists of an adjustable heated vacuum plate and conveyor, combined with adjustable hot air from the top, so that wet ink dries upward toward the outside surface of the ink. A substrate that takes two hours to dry with traditional heated air methods now takes 30 seconds. Again, these systems work equally well with sheet or flatbed web or cylinder web systems.
Thinking big
Newer custom-configured flatbed screen printing systems provide for virtually unlimited machine printing size options. They can be configured for maximum job efficiency, even with jobs as large as 2032 by 4191mm.
It should be noted however, that the newer cylinder screen printing systems also have ability to do larger formats compared to their predecessors. Gears and belts have been replaced with compact servo drives, handling wide web widths of 1270mm plus without difficulty.
The basic design of the cylinder system still makes it a better match for ultra-thin substrate applications, with today's electronically controlled cylinder systems handling substrates as thin as 12µm. Electronic controls make it possible to adjust for the actual material thickness as well as any print stretch during operation, which means screen manufacture is also simpler because the electronic cylinder systems can adapt to any screen and material thickness dimensions.
Materials under 50µm thick are not adequately supported by a flat printing table and tend to stretch. They are better suited to a vacuum cylinder design, while thicker substrates greater than 50µm thick can be handled by cylinder or flatbed configurations.
Scratchless results
Those working with sensitive materials or double side printed materials will often find the cylinder configuration better suited to their application. Examples include in-molded faceplates and nameplates for electronic devices or automotive applications.
It is worth noticing that newer flatbed systems use a flat vacuum printing table to hold materials in place, minimising scratching, however when there is a narrow tolerance for scratches in the final product, cylinder configurations remain the better match technology.
Other quality issues centre around screen stretch. In a cylinder design, it is not necessary to stretch the screen as much as in flatbed systems and it is possible to use high tension steel meshes such as those used in the electronics industry.
A flatbed system inherently stretches the screen a bit more when the squeegee is moved to release the mesh from the printed image, however in newer designs this factor is not as pronounced the distance between the screen and the printing table is reduced to less than 1mm. This type of screen holder design minimises screen stretch to the extent that many flatbed systems are now a good match for applications, like electronics, with minimal screen stretch requirements. Newer flatbed technology also delivers better quality with small-sized images with the ability to reduce the gap between first and second prints to only 1mm. This is because newer systems replace traditional motors with electronically controlled servo drives.
There is also considerable difference in the quality that one can achieve with newer cylinder systems compared to earlier cylinder designs. The technology has now advanced to the point where it can reliably be used to screen print pre-printed materials from flexo, digital, or other printing processes. Cylinder technology can also handle wet on wet skip printing applications. The advanced electronics can dynamically position web material 0.1 mm and both shrinking and stretching can be compensated for electronically.
Electronics in the newer cylinder systems also fine tune squeegee pressure, such that there is uniform ink thickness, even with fine-etch designs or thick UV inks.
Modular benefits
Production needs constantly change and evolve, so it is usually better to acquire systems-either flatbed or cylinder-that have a modular design, capable of adding printing heads, additional drying systems, die cutters, laminators or slitting and sheeting systems. By adding a second printing unit one can now add second colours with negligible increase in production time.
With the exception of certain electronics applications, most jobs can be handled by cylinder or flatbed systems. Generic versus custom design is now a far more important purchasing decision and although customisation does cost more, in most cases the throughput advantage soon outweighs initial cost differences.
