Inconsistent substrates like pique shirts, 6-panel and corduroy caps, and twill weaves on aprons, jackets and bags can now be printed with an inexpensive press using line art to produce highly opaque and sharp images that look die cut.
The inconsistency of the substrate does not affect the printed image. New interesting effects can be created, such as 3 dimensional prints, layers of colors, textures on top of flat prints, faux embroidery, fine details and stipple effects that cannot be duplicated with much more expensive embroidery equipment. Hi-Square can be used as a first layer with high resolution, and other inks like puff printed through a half-tone screen to create a convex shaped image such as a golf ball.
This paper will provide instructions so you can print successfully with Hi-Square inks and create new sales opportunities while enjoying the economic and technical advantages of screen printing.
What is Hi-Square?
Hi-Square is a plastisol ink that holds sharp, square edges created by thick stencils between 150 and 700 microns of thickness. The ink, mesh size and emulsion thickness all contribute to achieve the high deposit of ink and the sharp, defined edges. The ink must be heat cured, but is not a puff ink.
What Garments Can Be Printed?
Any textile product that can be laid flat and which fuses to plastisol inks can be printed. The ink lays down like asphalt being paved on the highway as it fills in cracks and potholes but still leaves a smooth exterior surface. Inconsistencies like seams, stitching, the wale of the corduroy, and twills are filled with ink leaving a smooth top surface. The ink is forgiving by allowing misprints to be flash cured and printed a second time to achieve a consistent surface.
What Are The Advantages Of Printing Hi-Square Versus Standard Plastisol Inks?
Inconsistent substrates like twills fuse with standard inks at the high points of the printed surface, but leave the low points as unprinted voids. Such prints may not be opaque and may show saw-toothed edges. Many fabrics like pique knit shirts and 6-panel caps have been embroidered rather than printed to produce opaque images that are not influenced by the surface conditions of the textile. Now that Hi-Square inks are available, the resolution of the image is defined by the stencil and is much sharper than embroidery. Inks can be printed in thick deposits and bury any inconsistencies of the fabric in the ink. Even though the inks are extremely opaque, Hi-Square inks offer easy printability.
Mesh And Screen Preparation
Coarser meshes such as 60s, 86s and 110s are typically used to transfer large quantities of ink from the screen to the substrate. A coarse mesh will allow tensioning on a retensionable frame to very high levels, such as 55 N/cm with a 60 mesh screen on a small cap frame. The high tension is important so that no deflection or bow occurs in the mesh during printing that would leave an image of inconsistent thickness. The stencil material is thick in order to create the thick ink deposit needed to produce the 3D print. Stencil material in a dry film form greatly reduces the stencil making process and is recommended over liquid emulsions which would require the
screen maker to coat/dry/coat approximately 25 times in order to produce the same film thickness. Even if the screen maker had both the time and patience to coat/dry/coat 25 times, it would not reproduce the sharply defined images achieved with thick, stencil films.A stencil of 150-200 microns is recommended for printers who have never printed high-density inks. This will help develop the technique of high-density printing before working with thicker stencils. Also, images which are open such as a ball rather than fine details are a better place to start so that the screen washes out more easily. A thicker stencil in the 400-700 micron range requires longer exposure times and some experimenting will be required to find the times that work best for different stencil thicknesses and the available exposure unit.
Under exposed film will peel off the mesh. Squeegeeing the wet, soft film of emulsion into the mesh will help, but a thorough exposure is still required. Thick stencils can be created by using a thinner stencil, like 50 or 90 microns first, exposing and washing out, and then laying thicker stencil material like 200 microns on the wet 50 micron material. After drying, the positive will have to be mounted in exactly the same location as previously. A pin registration system makes the process easier. Using this technique, washing out the 200-micron film will be easier because there is no mesh supporting the stencil in the image area.The laminating technique will be useful to screen printers with weaker light sources, such as fluorescent bulbs, halogen lights and similar light sources that are less than 1000 watts of metal halide or mercury vapor.
The screen should be minimally off-contact, such as the thickness of several pieces of paper. This is so no ink seeps between the stencil and substrate. Holding the screen down on contact during the flood stroke will provide insurance that the image will be defined by the stencil. More than one flood stroke may be necessary to fill a thick stencil with ink. A low squeegee angle like 30-35 degrees will fill the stencil more quickly than a higher angle. No pressure on the squeegee should be necessary. Pressure could cause the image to lose the desired definition.
The print stroke, by contrast, should be at a very high angle like 75-80 degrees, but again with no pressure on the squeegee. If the screen was held down on the flood stroke, it can be released on the print stroke. The ink is already in the ink well. So the objective with the print stroke is to scrape the ink off the ink side of the mesh leaving only the side walls of the stencil to hold the ink. Then lift the screen, slowly at first, to allow the ink to drop out of the image area.
If the image does not meet your quality specifications, flash the image, and slide the stencil over the printed image to print a corrective top coat.
Curing The Ink
These prints are thicker deposits of ink that require more dwell time in the dryer. Until a dryer has been tested, the temperature should be turned down to avoid scorching during the longer periods the ink is exposed to heat. The actual time required will increase with the thickness of ink, and decrease when forced air is used to promote curing.
The completeness of cure can be checked by stretching the print. Cracks indicate that further curing is necessary. If ink can be picked off, the image should be cured further.
Environmental, Health and Safety
Hi-Square inks are plastisol inks and should be handled like any other plastisol. If you did not receive a MSDS on this product please call 1-800-526-0455 or visit the Union web site at www.unionink.com.
Residue ink should be scraped out of the screen and returned to the container or discarded as solid waste. Any screen cleaner compatible with plastisol inks may be used to further clean the screen.
Customer testing is required and should be mandatory with this product or any new product or process before running production. Our technical advice and recommendations given verbally, in writing, or by trials are believed to be correct. They are not binding also with regard to the possible rights of third parties and do not exempt you from your task of examining the suitability of our products for the intended use. We cannot accept any responsibility for application and processing methods which are beyond our control, nor can we accept responsibility for misuse by you of the products or use by you of the products outside the specified written instructions given with the products. User must protect sensitive skin, exposed wounds and eyes from contact with products.