Images_Digital_Edition_August_2019

www.images-magazine.com KB BUSINESS DEVELOPMENT AUGUST 2019 images 63 The higher your tension, the better results you are going to get when printing W hat’s ironic about the ‘screen printing’ industry is that so many shops completely ignore the screen itself. It’s funny because it isn’t like this is some sort of deep, dark, industry secret. Yet, I’ll bet at least half the people reading this article (or who need to read this article) either don’t own a tension meter or never use it. Some time ago I visited a shop to help them out with some process and workflow efficiency points. When I walked through the front door, the production manager was screaming at the artist. You could cut the drama with a knife. “Your separations suck! Nothing ever lines up! Do you even know what you are doing?” But I’d seen this movie before. “Hold on”, I said. “It isn’t the seps. It’s your screens. Do you guys have a tension meter?” They did. It was buried underneath a pile of junk in the back corner on a shelf. The clamshell case was coated with dust and T-shirt lint. Probably like yours. We dug it out, and I calibrated the meter using the thick chunk of glass that comes with the set. The production manager brought the screens over. All were static, aluminium 23” x 31” frames. The table was cleared off and the tension for each of the four screens was measured. The best tension of any screen in the group averaged out to about 16N/cm 2 . The lower left corner of the underbase screen was under 11N/cm 2 . This explained why that job wouldn’t register. It’s like trying to build a house on top of quicksand. There isn’t enough foundational support to do the job right. So, being the curious guy I am, I asked the production manager why they didn’t measure the screen tension. His response: “We don’t have time to measure.” But they did have time to spend over ten minutes per screen per day trying to get jobs to register. Not to mention the previously discussed finger-wagging drama. Screen tension 101 Look, I know this is a fairly boring subject. People in this industry normally want to talk about presses or equipment. Those are sexy. Screen tension? It uses numbers. Maths. It’s a step that’s easily forgotten. But what if I told you that screen tension was a secret way that your shop could make more money? Would the enticement of a truckload of cash make it more interesting? Let’s take that apart for a minute and I’ll explain what I mean. Your screen mesh is comprised of threads that run perpendicular to one another. One set is the warp, and that runs vertically. The other is the weft, and that runs horizontally. Mesh count is the term used to describe the number of threads that are contained in a square inch. A 110-mesh screen has 110 threads per square inch, while a 230-mesh screen has, you guessed it, 230 threads. This is important because the higher the mesh count of the screen, the smaller the openings are between the threads. This factor determines how much ink can pass through the screen and onto the shirt. For static frames, the mesh is pulled in all four directions across the frame and glued down with a special adhesive. Retensionable frames have a built-in system for stretching the mesh using a table jig and special wrench tools to tighten the mesh within the frame without glue. Either way, you want the mesh to be evenly tensioned and locked into place on the frame. Measuring tension A calibrated tension meter is the device used to measure tension. This is a precise instrument and care should be taken to ensure the proper storage and use. The meter measures how much the screen fabric gives way when a downward force is applied to it. The downward force when measuring is gravity, and it uses the weight of the meter to calculate that movement. For an analogy, think about how much a trampoline might give way if you are standing in the middle. For our screens, that deflection is expressed in newtons per square centimetre. Yes, newtons as in Isaac Newton with this whole gravity and apple falling from a tree bit. If you are using static frames, 25N/cm 2 would be an acceptable tension. For retensionable frames, 35N/cm 2 is a good target. To measure tension, first lay the screen on a flat table with the mesh side up. Measure the warp (vertical direction) and then the weft (horizontal direction) in the middle of the screen. Like a tennis racket, the middle of the screen is the sweet spot. It’s not hard to do and only takes a few moments. Then, measure each of the four corners, about a palm’s width away. More expensive tension meters can measure tension bidirectionally – ie they measure the warp and the weft directions simultaneously. Less expensive tension meters only measure tension one way, so you have to rotate the tension meter each time. You want to measure the centre and the corners, and ideally, they will all be about the same in tension. However, it is possible to have good tension with most of the screen but have one area fail due to any number of reasons. Your shop should have a floor limit on what is acceptable for tension. The question that I’m asking right now is, “What is your minimum screen tension for your shop?” Do you even know? My recommendation for shops is that any multicolour job should have tensions for all screens on the print run that are over 20N/cm 2 . And, to ensure easier registration, all of the screens should be within 2N/cm 2 of each other. For any screen that has tension under 20N/cm 2 , they are relegated to only one-colour jobs. I’ve seen shops set their minimum for one-colour screen tension at 16N/ cm 2 , 17N/cm 2 or 18N/cm 2 . It’s up to you… but this needs to be established. Personally, I’m a fan of 18N/cm 2 . Remember, this is the low end. The higher your tension, the better results you are going to get when printing. Let’s examine that next. Have you ever been at a trade show and marvelled at all of those amazing prints on display? The print hand is How much dust is on your tension meter?