The screen department and the process of screen making are, like every stage in the screen-printing process, utterly crucial to the success of quality output and efficiency. However, it is in the screen department where we have seen the greatest improvements in textile screen-printing technology over the past decade. And since we are now a full decade into the new millennium perhaps it is time to review the areas of opportunity for screen making in 2010. In this article I will attempt to provide an overview of the modern screen department and overview what I feel are the key innovations in screen making: thin thread technology and CTS (computer-to-screen) technology.
The benefits of using retensionable frames cannot be overstated. Stabilization, or work-hardening the mesh at 25 Newtons or more, improves registration, image detail, print speeds, and image opacity thus providing greater overall quality and consistency through reduction of variables. The costs of implementing screen retensioning have been reduced significantly as more printers have adopted this technology and new systems have become available. Additionally, thanks to improvements in retensioning systems and mesh technology, screen retensioning has become easier and faster. Maintaining proper tension levels may seem like a daunting task, however there is a simple way to incorporate retensioning into the screen cycle.
At Motion Company, tension level is measured just prior to the coating of each and every screen. We dry and coat screens in batches of 20, otherwise referred to as a “rack” of screens. After reclamation, screens are placed on a rack to dry facing print-side up. Once the screens have thoroughly dried, tension level is measured by sliding a single frame out at a time and placing a properly calibrated tension meter in the center of the screen. This process of measuring tension level on a full rack of screens only takes about two minutes. Screens that are not at the proper tension level (for us, between 25 N/cm and 35 N/cm depending on mesh count) are removed from the rack and placed aside for retensioning. On average only about one-fourth of the screens on a rack will require retensioning. This number will fluctuate based on the number of screens in inventory, turnover frequency, and the number of recently-assembled frames in inventory. Retensioning will take between one and five minutes per frame depending on the retensioning system in place and the skill level of the screen technician. Once this step is incorporated into your screen cycle, the additional time and effort will go virtually unnoticed, while the resulting improvements from working with consistent “plates” will be noticeable, to say the least.
Quality imaging in a modernized screen department is achieved through the combination of a proper exposure system and high-resolution output device. What is a proper exposure system? If you answered “the sun and a pane of glass” it is time to research a new exposure system.
Modern exposure systems will include the following: A high output light source, controller/integrator, blanket, vacuum and glass surface. A high output light source is generally classified as 1,200 watts or higher; the specific technology will vary but the most common, and the one that I recommend, is instant start/metal halide. Whether it is pure lack of knowledge or an attempt to save time, most screen printers are plagued by the on-press consequences of underexposure, namely, screen breakdown. A high output light source will enable the user to achieve complete exposure of the emulsion in a limited amount of time. The controller/integrator serves as the “brains” of the system allowing for storage and adjustment of user-defined exposure settings while maintaining consistent light output throughout the life of the bulb. The vacuum, blanket, and glass combine to achieve constant contact between the film and screen throughout the exposure period. If a CTS system is in place, the blanket, vacuum and glass can be omitted altogether. Such systems are manufactured and sold today, typically marketed as CTS Exposure Systems.
As for high-resolution output devices, we will define as such—any device capable of producing an opaque image onto clear film or, in the case of CTS, onto the screen surface itself (we will not include light-based CTS technology as it is covered later in this article). The two categories of technology include film-based systems and CTS. Although I prefer the benefits of CTS technology, which will eventually become industry standard just as computer-to-plate (CTP) became the standard in the offset printing industry, the majority of printers are still successfully using film-based systems.
Film-based systems can be categorized into three main groups: thermal imagers, inkjet printers and traditional imagesetters. All three have their unique advantages and disadvantages:
• Thermal imaging devices do not require consumables other than the film itself and are typically capable of output resolutions up to 1,200 dpi. The down side is the cost of the device itself, the high cost of film and mis-registration from heat-induced distortion.
• Inkjet printers available for textile application have improved dramatically over the last 10 years. The upfront equipment cost is relatively low, especially when considering the larger format capability (basic units will output film up to 24" wide), film costs are typically lower than that of thermal film, and resolution typically exceeds 1,200 dpi with adequate black ink density. Disadvantages include costs of consumables, including both ink and film, and dealing with clogged inkjet nozzles.
• Traditional imagesetters produce unparalleled film quality with output resolutions upwards of 2,400 dpi, but the downsides are many. Originally the standard output device for offset printers, imagesetters have been almost entirely replaced by CTP technology in that industry. The positive externality of that movement was the plummeting prices of used and refurbished imagesetters which were snatched up by textile screen printers who before could not justify the high costs of such machines. Most detrimental to the future of imagesetters is the reality that as manufacturers abandoned the technology; imagesetters have fast become the dinosaurs of film output devices making service and maintenance of many older units nearly impossible. Another disadvantage of imagesetter output is the use of silver halide coated film and corresponding chemistry which will ultimately end up in a landfill, hardly ideal for the would-be “green” printer.
Overall, I feel the best option in film output for textile printers in today’s market is with inkjet printers, where you will find the best balance of price, quality, and ease of operation. With all that said, I contend that even the highest quality inkjet printer pales in comparison to the superior technology of CTS.
Screen reclamation is quite possibly the ugliest part of the screen-printing process, the black hole in any screen-printing operation. It chills me to think of the many late nights spent reclaiming screens back in the earliest days of my company—no doubt most shop owners can relate. So if for nothing but your own self-interest, some special attention should be placed on the reclamation process and the department as a whole. My approach to screen reclamation is simple, manual and low tech. Though many different automated reclamation units are available, I do not see the benefits outweighing the cost for a typical small-to-medium sized shop (remember, the automation is only partial, human hands are still necessary to card-off excess ink, remove tape, load and unload the machine, etc.). Our process involves the use of three drain-safe chemicals; ink degrader, emulsion remover, degreaser/dehazer as well as scrub pads and a heavy duty pressure washer (2,000 psi / 4.2 GPM). A competent screen reclaim technician should have no problem reclaiming 50 screens per day without any assistance following this formula:
1. Screens are delivered to the reclaim department post-production with all excess ink thoroughly carded off.
2. Block-out tape is removed.
3. Ink degrader is applied to print and squeegee side of the screen, as well as the frame, and thoroughly scrubbed until the ink is degraded.
4. Screen is thoroughly rinsed with high pressure water spray until all ink is removed.
5. Emulsion remover is applied to print and squeegee side of the screen and thoroughly scrubbed until emulsion begins to melt away.
6. Screen is thoroughly rinsed with high-pressure water spray until all emulsion is removed.
7. Combination degreaser/dehazer is applied to print and squeegee side of the screen and thoroughly scrubbed.
8. Screen is thoroughly rinsed with high pressure water spray until all degreaser/dehazer is removed followed by a low-pressure rinse to remove any chemical splash back generated by high-pressure spray.
9. Excess water is removed from mesh with wet/dry shopvac outfitted with custom attachment and screen is placed on rack to dry.
This process can be performed in as little as five minutes per cycle and without the use of reclamation machines, dip tanks or hazardous chemicals. If performed properly, screen mesh will be perfectly primed for coating and frames will look nearly new even after years of use.
Key innovations—thin thread mesh and CTS
The latest and greatest improvement in screen-mesh technology is to be found in so called “thin thread” mesh. The technical advantages in using thin thread mesh are so important that I plan to cover them in a future article. For now I will summarize: Monofilament polyester thread that is thinner and stronger than traditional thread, which provides better memory and a greater percentage of open area at moderate tension levels, resulting in improved image detail, opacity and hand. If you have not researched “thin thread” mesh, now is the time. But beware; if you contact your supplier inquiring about thread diameter and tinsel strength you may get a blank response. I suggest contacting a manufacturer.
In an industry that is hungry for digital progress yet faced with the reality of the craft, computer-to-screen technology represents the greatest technical advance in textile screen printing in the past decade. Although CTS technology has been around for nearly 20 years, only within the last 10 did it become an economically-viable solution for shops of all sizes. As more competitors have entered this market, costs have been driven downward and more printers have adopted CTS technology, further driving costs down. As basic economics works its course, CTS technology will simultaneously improve and become more cost effective. It is for this reason that I feel CTS will remain the dominant technical force in screen printing for the next 10 years.
CTS saves time and money by reducing consumables, reducing setup times (when combined with a registration system), increasing art department and darkroom efficiency and eliminating film handling and storage, all the while increasing the quality of screen image detail over most film systems. And as textile screen printing eventually adopts light-based CTS technology over inkjet technology, image quality will surpass that of any film-based system while increasing efficiency and reducing consumables. At Motion Company, we adopted CTS technology nearly three years ago. Today it remains the single greatest improvement to our workflow since the purchase of our first automated press.
To be sure, we have only scratched the surface of screen making in this article. But I do hope to have inspired you to take a closer look at your screen department and screen-making process. Maybe I’ve simply confirmed that the process and technology you’ve already implemented have put you on the right track to screen-making modernity. I hope you will invest (or continue to invest) both time and money into your screen department, after all, the beneficiary is... you.
A few notes regarding maintaining an eco-conscious approach to the screen making:
Chemicals—I recommend the exclusive use of drain-safe chemicals in the screen-reclamation process. There is a good chance that you are already using drain-safe chemicals. Check the MSDS for each product and/or consult the manufacturer.
Filtration—A simple filtration device can be outfitted to your washout booth for the purpose of removing solids from waste water. Generally these filtration units can be purchased for less than $1,000.
CTS—An ancillary benefit to CTS technology is the reduction of consumables, namely film. The only consumable required by our CTS unit is non-hazardous, water-soluble wax.