While many factors determine the quality of your screen prints, it’s especially important not to overlook the condition of your pallets!
It’s a part of the screen printing press that is known by many names – pallet, platen, shirtboard – to name a few of the more common descriptions. They’ve been manufactured with a variety of bases: wood, plywood, steel, aluminum and various composites. Some of these are honeycombed, and/or covered with a variety of laminates or rubber, and they come in a variety of sizes to handle everything from tees, children’s garments, sleeves and more.
While much attention is paid to mesh, emulsion and squeegees, often overlooked is the critical role of the pallet and leveling in producing a quality print. Too often pallets are treated as if they’re virtually indestructible and level themselves. Pallets must not be warped (a problem usually affecting pallets with wood bases) or bowed/bent (typically affecting metal pallets). The leveled pallet must be strong enough to withstand print head or manual stroke pressure – being flexible in this case is not an advantage, they must be sturdy and able to hold shape regardless of size. Whatever the surface, it must be smooth and even across its plane.
Earlier I had mentioned all the attention given squeegees and mesh. This was not to say these factors aren’t important, but to recognize there are many elements that interact – being cognizant of how one tool or another can affect the outcome of the print is important. You need to use this knowledge to adjust the variables in order to make a print look exceptional. While much of the finesse in screen printing is generally attributed to experience, having a firm grounding in all of the fundamentals is essential.
First of all – discard all warped or bowed screens or pallets. The money you will save in time and labor will more than pay for their replacement and the absence of another headache will be welcomed. Moving on – often when a printing a job that goes askew printers blame a variety of elements; it’s the artwork, the screens weren’t burned correctly, the seps are done wrong…seldom do we address the possibility of a leveling issue. If the job is on deadline, one might crank up the squeegee pressure (which will actually crank the squeegee down). Once on press, if you have registration/accuracy issues that occur every few shirts, it is often a leveling issue. This means that what needs to be corrected are the boards being level to the screens. In order to produce quality prints, the pallet and the screen must not only be centered, they must also share the same plane, i.e. they have to be parallel. The more shirts you print, the more you should be checking this (do it at least weekly to prevent the need for those last minute adjustments).
There are a variety of symptoms to look for. For boards that aren’t level, you may see a slight shift in the print to the left or right on the image. Years back I recall reading an article about the dynamics of ink flow (this is where I learned higher viscosity means “thicker”). While I’m not an engineer, essentially it related that there were many factors to expect and to ensure the accuracy of colors in both spot and process colors, an even flow of ink is required. They added that critical to achieving this was the leveling of all pallets and screens. As the pallets rotate around the press, once noticed this issue could appear to be random when printing. It depends on what pallet (or possibly screen) is the offender, and what was just printed. If it is more than one pallet, this complicates the matter.
A simple way to check to see if your boards are level is to use your on press flash unit as the standard to measure by. Rotate the boards around and note the distance between the bottom of the flash unit and each board with a ruler. Be careful if this is hot (Ouch)! Everything should be the same. If you find one or two that are out of standard, get those adjusted and solve your problem.