Mastering High-End Simulated Process Printing - Impressions

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Critical color benefits from professional color separation from companies like Netseps.com or Serichrome Seps. These companies have been producing critical color separations for more than 25 years, and the price today is a fraction of what it used to be. Outputting your digital color separation files is the next step. Using the correct halftone settings is crucial for obtaining the best results. I recommend: • Dot Shape: Elliptical or Diamond • Dot Angle: 22.5° or 67.5° for all colors • Frequency: 55 lpi for automatic printing; 45 lpi for manual Your RIP’s quality and your ink’s opacity are very important. Vellum output is not recommended for halftone printing. The dots are too thin and easily burn through. The inkjet film should be very dense. To quickly check for adequate opacity, hold a piece of film up to an overhead fluorescent light. Look through a solid printed portion of the image. If you can see any of the outline of the overhead tube, the ink is too thin and will burn through. It should be solid black. The correct screen mesh count will make all the difference when it is time to print. Mesh is sold by mesh count, thread diameter and weave type. Underbase for darks can be either 180.48 PW (plain weave) or 225.40 PW. I prefer the latter. Overprint colors are printed with either 280.34 PW or 305.34 PW. Tension on all screens should be 25 N/cm. Tensions below 20 N/cm would yield inconsistent halftone results. Maximum resolution is obtained with a dual-cure diazo/ photo polymer emulsion. The exposure is slower than pure photo polymer, but the dot structure is much better. Coating the screen two passes on the print side followed with two wet-on-wet passes on the squeegee side will give a good stencil profile for the halftones. If your coating is too thin, you risk increased moiré. Dry the screen with the print side down with plenty of filtered air circulation. When it comes to exposure, a UV-rich light source is very important. Use either mercury vapor or metal halide designed for screen printing. The light should look bluish-purple. If it has a yellow cast, or if you can see a filament in the light bulb before you turn it on, you don’t have the right kind of light. Follow the manufacturer’s directions for exposure testing to assure you are not overexposing or underexposing. Washout can make or break your job. After exposure, wet both sides of the screen with water and rub both sides with your hand. Wait at least one minute before you wash out the screen. This step allows the unexposed emulsion to absorb water and soften. After a minute, wash out the screen with a sharp fan spray from a garden hose. Do not use a pressure washer. Wash from the print side, starting at the top and working your way across the screen and down. Always follow the same sequence for consistency. When you’re done, blot the inside of the screen with blank newsprint. You can buy this at a store that sells shipping supplies. Any emulsion color coming off on the paper indicates under-exposure. Allow the screens to dry with cool air blowing across them. A simple box fan works well for this. After block out, pin holing and taping, the screens are ready for the press. PRE-PRODUCTION PRINT A triple durometer 70/90/70 squeegee gives excellent control and print quality. The softer 70 durometer compensates for surface irregularities, while the harder 90 durometer keeps the blade from flexing excessively. Always sharpen your blades before a halftone run. The desired sharpness is reached when you lightly draw your fingertip over the edge of the blade and can feel the individual ridges of your fingerprints. Next, look down the length of the blade. It should be perfectly flat and straight, with absolutely no waviness. The combination of a sharp, flat blade will assure
minimum squeegee pressure and smooth, even printing. The inks you choose for simulated process printing can range from transparent to translucent to opaque. I recommend translucent inks where all the colors have the same level of translucency. The value I recommend is 25%, which means it is ¼ of the way toward opaque. Many printers use opaque inks for simulated process printing because they are easier to print with, but are less accurate in matching with the original art. When an ink is opaque, the physical color blending is poor. The overprint color is shifted toward the color that is more opaque. So mixing red over yellow will give a very strong red-orange color. <strong>Printing</strong> yellow over red will give a very strong yellow-orange. Using a 25% translucent ink for both will give a neutral orange regardless of the print sequence. Finally, the inks you use should be fairly stiff, yet yield under light squeegee pressure. This characteristic is called thixotropy. It’s important because this is what allows us to print sharp, clean, halftone dots that don’t squash when other colors are printed on them. INK TIPS To get great halftones, try applying some sharping base to your ink. This can be accomplished by adding 2% by weight of clear, high-density gel to any ink. A very small addition will dramatically increase halftone sharpness. Another key to achieving maximum image quality is to ensure your inks are at the correct printing temperature. Plastisol inks are made of plastic resins. The colder the temperature, the stiffer the ink. As the ink warms up, it gets softer and thinner. The flow of the ink is continuously changing until the temperature reaches 90°F (32°C). It is impossible to control color accurately with ink temperatures below this point. We use our flash cure units to preheat the shirt platens to 130°F (±55°C). With the print head in auto index, rotate the press until the ink temperature is at the desired point. Use an inexpensive IR digital pyrometer to measure this. With warm platens, the flash time is reduced to less than 1 second using the mesh counts I’ve recommended. All of these preparations are important, but they are of little value unless the garment has enough fiber mass to accept the halftone dots. Most T-shirts are only 65% fiber mass. However, the JERZEES ® 363MR HiDensi-T TM 100% Cotton T-shirt has excellent fiber mass. Having your halftone dot land on the yarn bundle assures minimum dot gain and maximum image sharpness. You also need less ink to achieve greater color and maximum image detail. Careful attention to color separation, prepress and setup will ensure excellent results when printing on an ideal T-shirt surface. The high fiber mass and smooth surface of the JERZEES ® 363MR HiDensi-T TM make it a great destination for your critical color simulated process images. step-by-step to VIew a short VIdeo on the process of creatIng sImulated process prIntIng detaIled In thIs newsletter, please clIck here. step 1 A good 70-90-70 durometer squeegee gives you a perfect blend of conformable edge and controlled blade bend. This allows you to concentrate the squeegee edge on the halftone with minimum squeegee pressure for the sharpest, cleanest print. step 2 After washout, the screens should be blotted with blank newsprint to absorb any water in the mesh. This is a gentle way of making sure all water is removed from the exposed screen without damaging the halftone image. step 3 Here is an excellent example of the fine, smooth surface of the JERZEES ® 363MR HiDensi-T TM . Note the excellent halftone sharpness and how every dot prints perfectly on the garment surface.
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Mastering High-End Simulated Process Printing - Impressions

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