01 Feb The Value of Rubber Tops on Your Platens
Are you still printing on the platens that came with your press and do not have rubber platen tops, then this article will explain how you can benefit from rubber tops and what material you need.
by Bill Hood, ASDPT Fellow
Most manual presses are sold with composition wood platens to lower the cost of the press. Some press manufacturers recycle the sink cutouts from kitchen and bathroom cabinetmakers to further reduce the cost of manufacturing. Some manufacturers of inexpensive semi-automatic presses do not place rubber material on their platens to reduce cost, as well. And all too often screenprinters think that it is perfectly normal to print textile products on these inexpensive platens without realizing the benefits that a rubber platen top can make. If you are a textile printer, and you are not using rubber top platens this article will help you understand how to improve your printing process.
Why You Need Rubber on Your Platens
Composition wood and even metal platens are subjected to uneven print surfaces. Printers will often use platens as shelves, for example, holding cans of ink, tools, and other miscellaneous items, when if dropped can leave a small indentation on the surface. Every small indention is reflected in the print, and each indent can leave a slight, but visible, difference in the ink deposit. Rubber platen tops can rebound to their original smooth surface from these small indentations, where composition wood and metal cannot. The platens are not shelves and the only thing that should be placed on the platens is the substrate to be printed or platen cleaning chemicals. You also should cease placing your hands on the platens, leaning on them, or using your hands to revolve the platens on a carousel press to avoid shifting the plane of the platens, which will result in registration problems and uneven ink deposits across the image.
During the printing process, the mesh is pushed down to the substrate surface. The soft rubber compresses under the squeegee pressure to improve contact between the mesh and the substrate. The result is the ink deposit will be more consistent throughout the image area. At the same time, the compressible surface provides for better penetration of the ink around the threads and improved adherence of the ink deposit when using plastisol inks. Water-based inks will penetrate farther into the substrate and have better opacity and brilliance. The compressible surface allows the press operator to decrease squeegee pressure that lengthens the lifespan of both the mesh and squeegee edge.
If you are still using a flash gel unit and using a print/flash/print technique the heat from the flash gel unit will create problems on both composition wood and metal platens. The composition wood platens will deform as the heat penetrate into them and softens the glue holding the particles together. This softening will create an uneven surface, in which the rubber surface can work in your favor, but only up to a point. Any press will benefit from an investment in aluminum platens. However, aluminum platens dissipate heat quickly. Since platens should be warmed to approximately 120˚F (49˚C) and maintained at that temperature when printing with plastisol ink to help the ink flow into and around the threads of the substrate. Rubber tops increase the heat dispersion time by lowering the loss of heat, as it traps the heat in the aluminum platen. Pre-heated platens are great and keeping the platens warm will reduce the flash gel time, thus there is an energy-saving aspect, as well as reduction of dwell time that increases your production.
What Rubber Material to Buy
What you want is White Buna-Nitrile (some list it as just White Nitrile), 1/8-inch thick, 55 to 60 ShA. You will find it at most industrial rubber suppliers. The material is also used in the medical industry. I buy the white, but there is a black version.
You will also need an adhesive, such as 3M Contact Adhesive 1357, or Lokweld Heat Resistant Contact Adhesive. One pint should be sufficient to cover 1000-square-inches to give you an idea of how much adhesive to buy. Once you open the container it has a very short shelf life, so you do not want to over-purchase.
Be sure to clean the platen completely and sand any nicks or low spots. Heat the platen to approximately 200˚F, then when it is only slightly warm apply the adhesive, then apply the Buna-Nitrile. Let the platen cool completely before cutting. I usually wait overnight. Cut the Buna-Nitrile using the platen as a guide, but do not angle the cut. The Buna-Nitrile will then be about 1/6-inch smaller on each side, which is ideal to help with accidental delamination.
For additional information on how to remove existing rubber and installing rubber tops on your platens see the comprehensive article, “Replacing Rubber Tops on Platens“