Screen Printing Lines: “Choosing Between Flatbed and Cylinder Screen Print Systems”; SGIA Journal 2nd Quarter 2008

Choosing Between Flatbed vs. Cylinder Screen Print Systems

By Reinhard Zimmermann, Spartanics-Systec

Choosing between flatbed or cylinder configurations for various screen printing applications has traditionally been determined more by the preferences and traditions within a company than by any other factors. In some quarters, the 3 – 4 times higher-priced cylinder screen printing systems are preferred even for simple applications such as standard labels, while others consider this as overkill. Whatever the rationales for choosing between flatbed or cylinder configurations have been in the past, the recent innovations in both flatbed and cylinder screen printing systems suggest that it is timely to revisit the choices between flatbed or cylinder configuration based on the advanced capabilities now available in latest generation systems for both formats.

Here are some factors to consider:

Comparably Improved Throughput

Going from a manually loaded sheet process to an automated web process can speed throughput by 50% or more. The actual speed improvement varies, and is dependent 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 that systems can be adapted to the job format as opposed to needing to change job formats to mesh with the dimensions of generic systems. The common 400 mm width is no longer relevant as a limiting factor, and large formats are now highly doable, as are artwork layouts that will maximize yields. It is reasonable to expect that changing printing formats will significantly increase throughput and yields in a large number of applications.

Second, the newer systems – both flatbed and cylinder—bring the advantages of state-of-art electronic controls to bear on throughput. These electronics are especially important for speeding job setup or for fixing fault conditions during operation with a few keystrokes that previously might have taken a good deal of fussing and manual adjustments. All settings in these newer systems can be controlled electronically, such as adjustments for material thickness in cylinder systems and push button pneumatic controls for the screen clamp, squeegee and float bar in flatbed configurations. The best-in-class flatbed systems now also feature an automated and synchronized vacuum release on the printing table that is especially important to speeding the throughput of large format jobs.

Lastly, THE dramatic shift in throughput in latest generation technology derives mainly from the contact drying innovation that is equally suited for Sheet, flatbed or Cylinder –– websheet`s, Flatbed or cylinder-Web configured systems. For those not familiar with contact drying technology, it consists of an adjustable heated vacuum plate and conveyor carrying the material being dried combined with adjustable hot air from the top. In this type system the wet ink dries upward with the inks. Even for thick coated inks drying times can be expected to be a fraction of that required in conventional heated oven systems. For example, a substrate that takes 2 hours to dry with traditional heated air methods now takes 30 seconds. And again, these systems work equally well with either Sheet, flatbed or cylinder – web systems sheet , Flatbed – or Cylinder web System. Whether the system has a flexible modular design that can easily accommodate these contact drying systems is more relevant.

Large Images

The 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 80” x 165” (2032 mm x 4191 mm).

It should be noted however that the newer cylinder screen printing systems also have ability to do larger formats compared to older cylinder systems. These newer designs do away with gears and belts and replace them with more compact servo drives. Now the better cylinder screen printing systems can handle very wide web widths of more than 1.27 meters (50 inches) without difficulty.

Thinnest Materials Best-Matched with Cylinder

The basic design of cylinder systems still makes it a better match for ultra-thin substrate applications compared to flatbed systems, although today’s fully electronically controlled cylinder systems are much better at handling substrates as thin as 12 microns than earlier generation technology. The electronic controls in the newer systems allow one to adjust for the actual material thickness as well as any print stretch during operation. This also means that screen manufacture is now a simpler process because the improved fully electronic cylinder systems can now adapt to whatever screen and material thickness dimensions are presented.

Thin materials under 50 microns thickness are not adequately supported by a flat printing table design, and tend to stretch; a primary advantage of a cylinder design is that the material is supported on vacuum cylinders. For thicker substrates that are greater than 50 microns thick the need for supporting material is not as relevant and cylinder or flatbed configurations are equally suited to handle them.

Need for Scratchless Results

Those working with sensitive materials or double side printed materials will often find that the cylinder configuration is better suited for their application. For example, in-molded faceplates and nameplates for electronic devices or in automotive applications are most often better served with cylinder systems.

However, it should also be noted that the newer flatbed screen printing systems use flat vacuum printing tables to hold materials in place and that this innovation minimizes any tendencies toward scratching. That said, when there is a narrow tolerance for scratches in the final product, cylinder configurations remain the better match technology.

Quality Issues

Some mistakenly think that cylinder systems are intrinsically better-suited for high quality work as compared to flatbed systems but contrasting the two methods in those terms can lead one to the wrong conclusions, especially when considering the quality improvements in both later generation flatbed and cylinder systems.

In a cylinder design, you do not have to stretch the screen as much as in flatbed systems. Because cylinder systems have less requirement for screen stretch, one can use high tension steel meshes that are often important in the electronics industry, for example.

A flatbed system design inherently stretches the screen a bit more when you move the squeegee to release the mesh from the printed image. However, this factor is not as pronounced in the improved design of newer systems that reduce the distance between the screen and the printing table to less than 1 mm. This type of screen holder design minimizes screen stretch to the extent that many flatbed systems are now also a good match for some electronics applications and similar ones with requirements for minimal screen stretch. Newer flatbed technology designs also deliver better quality with small-sized images and are able to reduce the gap between first and second prints to only 1 mm (0.04 inches). This is because the newer systems replace traditional motors with high precision electronically controlled servo drives.

There is also considerable difference in the quality that one can achieve with the newer cylinder systems compared to earlier cylinder technology. Until recently, cylinder screen print technology had not advanced to the point where one could reliably use them to screen print pre-printed materials from flexo, digital, or other printing processes. This is now doable. Also improvements in cylinder technology now enable them to readily handle wet on wet skip printing applications. The advanced electronics of the newer systems can dynamically position web material total +/-0.1 mm. Both shrinking and stretching can be compensated for electronically. This advance correction capability means, for example, if your print is shrinking on the first run you can compensate for it electronically ensuring maximum quality on subsequent runs. Older types of cylinder systems do not have the complex algorithms that can automatically adjust for image stretch or shrinkage and therefore are not as successful at ensuring registration of multiple print layers.

The newer cylinder systems’ electronics also fine tune squeegee pressure and control it such that there is uniform ink thickness, even with fine-etch designs or thick UV inks. Here too a precisely controlled servo driver keeps the squeegee pressure constant.

Quality in the newer cylinder systems is also improved by using a precisely controlled vacuum to transport materials, thereby relieving stress on the substrate so you can run materials with significantly less web tension. As noted above, this is true even for materials as thin as 12 microns.

Modular Design

Because production needs change and evolve one is usually best-served by acquiring systems—either flatbed or cylinder—that have a modular design that is flexible for adding printing heads drying systems, additional drying systems printing heads, die cutters, laminators, slitting and sheeting systems in the case of cylinder systems, or other modules as needs arise. Consider, for example, that by adding a second printing unit one can now add second colors with negligible increase in production time. Time savings with additional print heads for different colors would be comparable. Clearly those who are able to seamlessly incorporate new printing heads, new dryers or other technologies into their base system will be better able to compete without replacing their entire screen printing system.

Summary — Standard vs. Customized Systems

In summary, with the possible exception of certain electronics applications with the highest requirements for negligible screen stretch, the range of applications served by screen printing technology – graphics, nameplates, textile transfers, RFID, solar panels, etc.—cannot be presumed to be better served by cylinder or flatbed system configurations or vice versa.

Generic vs. custom design is now a far more important purchasing decision. Given the range of screen printing systems one finds in the marketplace, it is now more important to first consider whether an application is well-served by lower cost generic off-the-shelf systems or if the high precision controls and software of custom-built systems are better suited for current or anticipated production requirements. Customization does cost more, but in most situations the throughput advantage of custom-built systems renders these initial cost differences moot in short order. Often, quality requirements alone make the customized software controls of high precision servo drives and similar high quality components one can readily build into customized systems all important.
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Reinhard Zimmermann is General Manager of Systec and a director of the Spartanics/Systec partnership that manufacturers of Spartanics-Systec Fineprint Screen Printing Systems

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