GRAPHICS PRO

October '21

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G R A P H I C S - P R O. C O M 2 0 2 1 O C T O B E R G R A P H I C S P R O 3 1 good dehumidifier to keep the room some- where between 35-40% humidity. A lot of people will also set up fans to help circulate air to speed up screen drying. This is not recommended as a fan can blow dust and dirt particles onto your screens and is a primary cause of pinholes and pre- mature emulsion/stencil breakdown dur- ing printing. Ideally, you want to invest in a good screen drying cabinet. These come in different sizes to hold a varying number of screens, but in essence, they are a light safe way to store and dry your screens. These screen drying cabinets circulate hot, filtered air to rapidly dry screens. EMULSION COATING – APPLY CONSTANTLY & STORE PROPERLY Now that you are working in the best screen room environment, you want the proper tools and equipment. The first tool you will use is for coating your screens with emulsion. The most consistent way to do this is with an automatic screen coater. Such automatic pro-coaters can be pro- grammed with virtually unlimited settings regarding the number of coats per side and coating speed so you can specify the exact amount of emulsion you want on your screen (also called EOM - emulsion over mesh). Other options include semi-auto emulsion coaters that move the screen while you hold the emulsion coater and a wall mounted unit that holds the screen in place for you so you can focus on proper coating technique without worrying about holding the screen. No matter how you coat your screens, make sure to store them properly using a screen rack. Dry them print side down (squeegee side up) in a clean and light safe area, as discussed earlier. EXPOSE YOUR SCREENS – LED LIGHT & TIME Once coated with emulsion and dried, you will expose your screens. LED expo- sure units provide the quickest exposure. However, make sure that you get a LED unit with a nanometer range that works with SBQ-photopolymer and dual-cure emulsions. LED exposure units that only work with certain types of emulsion are very limiting. The best exposure units have a solid vacuum to compress your film positive to the frame. Without a vacuum, you will get "light creep" or "light scatter," which is when the UV light bends around the image on your film positive. This can cause "sawtoothing" and non-straight lines on your screen. You might also end up losing halftones and fine print if your exposure unit does not have a vacuum. A proper vacuum motor solves these issues by creat- ing tight contact between your film posi- tive and the screen mesh. Calculating the proper exposure time is key to a good screen. If you underexpose, your emulsion will be soft and too much may wash away during development or lead to pinholes on press. Overexposure will harden the emulsion, causing you to lose fine lines, text, and halftones. Having a wedge test or step calculator helps dial in the right amount of exposure time as it provides real life feedback on your screen so you can see the results. Remember, a change in coating technique, emulsion, and even mesh count can affect your ex- posure time. For this reason, LED units with a programmable touchscreen that can store your settings are ideal. DEVELOP YOUR SCREENS Once exposed, you can develop (wash out) the emulsion so that you are ready to print. One easy way to do this is with a dip tank.

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