ImagesMagUK-Sep18

TIPS & TECHNIQUES step so that every screen will have the perfect coat of emulsion. You can measure the EOM on your screens with a tool called an EOM meter. Your goal should be to get a 12-15% stencil thickness. An easy way to test this is to determine your EOM and set your coating process (1:2 or 2:2) and then see how many screens you get out of a set amount of the emulsion. Let’s say that you get 42 standard-sized screens on average for your target EOM. If you are tracking this with a log, and your screen room coater now shows over 50+ screens for the day, you know the EOM is less than it should be. Predictability and consistency matter. Create your standards. I am far from being a screen-making expert. To really geek out on this stuff, read anything by Dave Dennings with KIWO, or listen to my The Big Idea podcast with Alan Howe with SAATI. Imaging and exposing So let’s assume that your screens are coated and ready to go. The next step in the process is to get the image for the art burned onto the screen. But before we handle that step, ask yourself one question: is my screen dry? Sure, it might be dry to the touch, but so is a tomato… until you slice it open. Your emulsion has to be 100% dry throughout. I’ve been in shops that give little or no thought to the UV sneaking in and pre-exposing the emulsion on screens. “Why do we keep having screen image problems?” they ask. It’s not hard to work out. For lighting, be sure to have the correct UV filter covers. These will cast a yellow glow in your screen room. A good practice also is to paint the screen room a different colour than white. I’ve seen shops use black or even yellow. How you get the image to the screen has a direct impact on the quality of the image to be burned, and its placement on the screen. Currently, the absolute best practice is to use a computer-to-screen (CTS) unit. This piece of equipment is the number one tool to increase efficiency on the production floor. Some CTS units use a water-soluble ink, others use a wax, and SAATI has a new unit that uses a laser to image the screens. These systems are superior because they place the image directly onto the screen. Film or vellum is placed on top of the screen and taped down. During the exposure process light can seep in around the film (or vellum) and erode the quality of the exposure. This directly affects the edges of your image and halftones. With a CTS unit, this doesn’t happen so you create a better channel for your ink to pass through. Also, because the CTS unit locks in each screen frame with three points of contact, the images for a print run are all exactly pre-registered to each other. Duplicating this pre-registration on press with a registration bracket allows your crew to quickly get your screens set up in less time than manually registering them. Finally, CTS units completely eliminate the need for the vacuum table step for exposure and this saves time and rules out the aforementioned pinholes caused by lint on the glass. Some CTS models have an LED exposure system built in, so as the screen frame comes out of the machine it is exposed. The SAATI laser unit exposes and images the screen in one step, without any consumables. Of course, the use of film or vellum will work. Plenty of shops travel down this road every day. However, if you are creating over 40-50 screens a day www.images-magazine.com SEPTEMBER 2018 images 33