For the Business of Apparel Decorating
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96 || P R I N T W E A R M A Y 2 0 1 6 leable and dry to the touch, but there is still free plasticizer between the swollen resin particles so the ink has no durability until it is put through a dryer and reaches between 275 and 330 degrees F exit temperature. At this fusion stage, all of the free plasticizer has been absorbed provided the ink was not overloaded with plasticizer and the operator didn't add curable or other reducers. Such an ink is likely to last the life of the T-shirt. MESH Since plastisol won't dry in the screen and transfers with minimal pressure, we may use as much as four fabrics which deposit 1, 2, 3, and 4 mils respectively. This combina- tion gives the printer the ability to print the widest range of artwork, as well as a variety of garment colors and constructions. These four fabrics will accommodate halftones, print-flash-print, and one-hit whites. Each of the fabrics has balanced stress-strain with a high fill-rate and low capacity. This con- figuration allows us to use minimal pressure and maximum speed and still deposit the minimum quantity of ink on the surface for the best hand and drape. The best "stretch- ing" permits consistent dynamic tension on all points of the screen, from screen- to-screen, and from mesh count to mesh count. With this approach, off-contact and pressure can be standardized so that dimen- sional accuracy is achieved. BLADE Plastisol is not at all chemically aggressive on polyurethane squeegee blades, and with respect to abrasion-resistant plastisol, acts as a lubricant, so blade life is indefinite. The blade must be selected after the ink and mesh, but before the press settings and stencil parameters. The dynamic edge of the blade during the print stroke is based upon minimal drag on the tensioned mesh count, while the cross-sectional profile of the blade is based upon the tack level of the ink and fill-rate and volume requirements of the mesh. The blade, its settings, and press settings are chosen before the stencil because the stencil EOM should always be minimized and it is based on the off-contact distance and the initial blade angle. PRESS Plastisol inks have unparalleled throughput, particularly on non-white garments. They are made to print 900 to 1,200 shirts per hour wet-on-wet, or 700 to 900 shirts per hour print-flash-print. The press should be characterized and calibrated with a nine- zone test image. This fiducial will allow us to quickly op- timize five areas critical to the ink transfer process: parallelism of the carriage/blade/ mesh/platen; off-contact distance; to bal- ance the tonal range; to minimize linear dis- tortion due to blade drag, frame deflection, and tension variance; and to optimize flood and print speeds. Unquestionably, the best white prints will come from the highest stroke speed possi- ble. This does not mean "run at maximum speed," rather, we want to run as fast as is practical. For example, if we are running white at a speed of 2.5 and increase to 5.0, we have increased the shear-rate by more than four times. If we increase from 2.5 to 10, we increase the shear-rate by more than 16 times. With a quality ink and its supporting cast as described herein, we can run at maximum stroke speed and with less pressure for a smoother print. STENCIL Stencil selection and application is simple with plastisol. Although some work bet- ter, most all of them last indefinitely with plastisol inks. The dimensional priorities of a stencil are RzS1 (flatness garment side), EOM (thickness of the garment side), and RzS2 (flatness blade side). To achieve a sharp edge on the image, the garment side of the screen should be suffi- ciently flat. This parameter should be evalu- ated with a flashed underbase print with a 10- to 20-time loupe. The EOM is often thought to be a factor or percentage of the fabric thickness but this is not the best practice. Once the RzS1 is optimal, the EOM needs to only be greater as a result of the blade angle and off-contact distance. The EOM should not be used to increase wet ink film thickness. RzS2 is the buffer used to minimize the volume of ink at the perimeter of the image and to com- pensate for excessive EOM. When working with plastisol, or any ink really, the pertinent question to be answered is, "Do we want to outrun the bear or just to outrun the other guy?" To do the lat- ter, simply find a high quality, solvent-free, phthalate-free, white plastisol and have at it. To outrun the bear, get the same white and follow the prescription herein for effective quality and efficient production. PRINTING WITH PLASTISOL INK Above left: This figure depicts the changes a plastisol undergoes as its core components, resin and plasticizer, are initially blended. Then, the incremental changes in the ink as the free-plasticizer is reduced are due to the flux and absorption at room temperature, then under the printer's flash, and through the printer's dryer. The ink is "cured" once there is no free-plasticizer. (Image courtesy Synergy Inks) Above right: The images above need to be printed and flashed between 700 and 900 pieces per hour. Because the ink on the right was low tack and highly shear thinning, it be- came a smoother surface to hold all of the sim-process colors. (Images courtesy Anderson Studio)