Grafica News - Dec 2015
Maximizing Profits with Screen Reclaiming - Part 1
by Dawn M. Hohl-Nowlin
Screen mesh is undeniably one of the most costly materials used in the screen printing process. The larger the screen the greater the material and labor investment. Screen mesh is designed to be used over and over again, and with effective reclaiming you can maximize its investment. Taking the time to clean and reuse screens properly will quickly improve your bottom line, especially if many screens are used on a day to day basis.
As an additional benefit, a properly tensioned screen becomes more stable in tension after the first and second print cycle. Stable screen tension provides superior results on press in all respects. In fact it is better to have a stable lower tensioned screen on press than an unstable high tensioned one.
New screens should not be used on multicolor tight registration jobs until after the first or second print run. Printing forces can cause a new screen to lose an additional 3-5 N/cm in the first 500 impressions. These tensions shifts can cause registration and ink deposit (color shift) changes. Reclaimed screens offer a more consistent tension plate for repeatable printing.
Retensionable frames allow the tension to be readjusted on a reclaimed screen after the first and second print run which stabilizes the mesh in a process known as 'work-hardening'. Work hardened screens will maintain higher consistent and stable tension throughout a print run which ensures registration and color consistency time after time.
There are three main stages to screen reclaiming; ink removal, stencil removal, and if needed ghost/haze stain removal. Degreasing can be considered a fourth and final step to fully prepare the screen for a new stencil.
Basic equipment for reclaiming includes a backlit washout sink, an industrial grade pressure washer, a regular tap pressure garden hose with adjustable nozzle, dedicated reclaiming brushes, and screen drying racks or room. It is best to have a separate washout booth for reclaiming so degreased screens are not contaminated from lingering chemicals and residue (Figure 1). Chemistry selection, especially for ink removal, is very important and should be optimized for the ink type used. In fact, proper chemistry can make or break reclaiming success. There are many safe and effective options designed for screen printing available, so it is essential to do some research and testing to find what works best in your conditions.
Personal safety gear is essential for employee protection during screen reclaiming. It is important to provide gloves, goggles, a particle mask/respirator and a protective smock or overcoat to protect the skin, lungs and eyes of those performing the tasks (Figure 2). Adequate ventilation is also needed. Last but not least, it is necessary to follow all your local waste disposal laws for both the ink and soiled rag/towels, as well as the washout water going into public or ground septic systems.
Another equipment option worth mentioning are dip tanks, typically used for textile size screens (Figure 3). These tanks utilize chemistry that both break down ink (specific chemistry for specific inks) and the stencil at the same time. Once screens sit in the tank for a few minutes they are removed and pressure washed to complete the process. Dip tanks are not appropriate for wood frames and require chemistry replenishment and proper disposal of waste residue collected in the bottom of tank.
Fully automated screen cleaning systems are available for those with high volume processing requirements. They come in a wide variety of configurations and prices and can be custom made to suite a shop's needs (Figure 4). Benefits include reduced labor cost, reclaiming consistency, speed, and safety. It is essential to do a proper cost analysis before purchasing these expensive systems to assure return on investment can be achieved.
In today's market, the successful company must optimize its reclaiming practices to remain competitive. Ineffective methods, inefficient equipment and poor chemical choices can cause screen breakdowns, image flaws, and screen shortages. Giving due attention to this critical area has the potential of lowering costs, improving quality, and ultimately increasing profits. In our next installment we will look closer at each step needed to reclaim a screen and provide practical guidelines for successful results.
Dawn Hohl-Nowlin is a Technical Trainer and Consultant on screen printing. Her industry experience includes 18 years with SPTF/SGIA, USA, overseeing screen printing workshops, developing training resources and conducting process related research. She is a member of the Academy of Screen and Digital Printing Technology (ASDPT). She can be reached at firstname.lastname@example.org