The most practical and profitable advice I can give you is to buy the accessories and sundries which are most likely to never slow your press down or compromise the level of quality which supports your corporate image. This treatise is necessary because our customers don’t care about our constraints; they see them as our problems and really don’t want to hear about them!
That agreed upon, if you tell your press operators “print more and faster” and tell your purchasing people “keep the costs down,” bear in mind that these two bits of dogma are nearly always mutually exclusive. Too often you have a group of ill-informed people buying substandard “tools” for frustrated craftsmen in pre-press and on press. Meanwhile, as the industry matures and print buyers become more discriminating, each of the core components becomes proportionally and conspicuously deficient. Here’s the story. . . .
The printing platens on nearly all of the T-shirt presses are too small, too hard, too conductive and too sensitive to attack from solvents and heat. The size is based on making a press which fits into most production floors. If the carousel press’s T-shirt platen was proportionally the same size as a graphics screen and press bed, manuals would take up the floor space of automatics and auto’s would be about 45 feet in diameter. They’d print better and faster but no one could house them.
Most of the surfaces are inelastic (read “unforgiving”) buna-N synthetic rubber and, as far as “cushioning” goes, they might as well be made of granite. The rubber is often glued via two-sided pressure-sensitive tape to an aluminum plate. Well, pressure-sensitive adhesives don’t like three things: heat, wash-up solvent and plasticizer (about 50 percent of our ink). Thus, they tend to delaminate after time, use or abuse.
And those aluminum plates make great cook-wear because they conduct heat very well, they’re relatively lightweight and they’re low in cost. Unfortunately, these characteristics don’t serve us all that well on a T-shirt press. Aluminum conducts all the heat from the flash away from the ink, causing ink penetration and loss of opacity.
If this describes your platen situation, the ideal fix would be to replace them. In lieu of this solution, consider this alternate remedy: Dull one side of higher-durometer squeegee blades, use a lower count mesh with larger mesh openings and face-coat your stencils when you need higher resolution. Set the flash as cool and close to the surface as possible (check with your flash-unit maker) and, once in operation, you may want to speed up the press as the platens heat up.
Printing is accomplished by building force between the blade and the mesh at the point where the T-shirt is compressed to the platen. Any pressure between blade and platen is not only wasted but actually causes problems.
The blades used for T-shirt printing are almost always too long. Likewise, they have to be soft to compensate for the platen. They are too “true” to compensate for the gap between the stencil and the platen on a mesh which has a variable rate of change in tension—lowest at the center and highest at the perimeter.
The ideal blade would be softer at the ends and harder in the middle based on the printing tension of the mesh. This imbalance is why T-shirt printers don’t often sharpen their blades; they don’t use the edge so it never wears out or puts the ink under enough shear-stress to print ideally.
Always minimize both the length and stroke length of the squeegee blade. But when you are maxed-out, be certain the screens are the maximum size your press will permit. Bear in mind that, with an eight-color press, you can run up to four “oversized” screens to accommodate the blade and image.
The ink makers already know (empirically) you’ll need the ink to be much thinner than would be ideal, but a bit of surfactant on hand would be wise. Manufacturers typically overuse reducer and under use wetting agents. (Could be due to the price you’re insisting upon?)
The screens should have the thinnest thread and lowest count possible so they don’t self-destruct on press. Finally, fix those platens! They should be non-conductive and not get hot, and they should be elastic enough to accommodate the inherent flaws in the process (including the oversized, variable-flexing squeegee blade).
Back in the days when we used manly adhesives such as carbon tet, methyline chloride and the like, we were taking the easy way out and making compounds which not only killed people, but ruined the earth for our children and their children. We clearly have been making better choices since, but the transitions between high performance and environmentally responsible are often inconvenient. Contemporary choices of adhesives are too sticky, too wet and melt too easily. As a result, they pull excessive lint from the garment and force clean-up or the use of less costly masking sheets.
Too wet? Note the overspray on your press, in your nostrils, in your hair and, sadly, in your lungs. Too easy to melt is a slight misstatement. Too easily melts too much is more accurate. The temperature in which we are interested causes initial flow or softening; from this point, due to platens which are 150ºF and flash units which are significantly hotter, the malleable adhesive flattens under the excessive pressure of the squeegee. Fluidity and flattening reduce the surface area required to hold the textile substrate in position so the tacky ink doesn’t pry it from the table.
If you’re set on using adhesive at all, reduce the surface tension of the ink (talk to the manufacturer), badger your press manufacturer for a more sensible platen (as described above), calibrate your press first, then set the flash units as close and cool as possible (also detailed above).
I submit that it is not at all obvious exactly how press wash ups are intended to work and even less obvious what they are not supposed to do. If you are using an aerosol ink-clog remover you are in a nasty loop and need to work your way out. The contents of that spray can are absorbed by ink resin (PVC) and causes it to swell; sort of makes your plastisol work like an evaporative ink: when the spray wash evaporates, the resin dries in the screen, the operator uses more spray wash and makes the ink incrementally more evaporative. On and on, ad-infinitum.
The rule of thumb is: “Put the fluid components of the ink into solution and it must wash up.” So the press wash should put the plasticizer into solution. Most wash-ups have a difficult time with the more complex plasticizers (polymeric plasticizers) which are typically used in blacks, blues and whites.
Ever notice which colors typically stain your mesh? Certain dyes (fluorescents and a lot of reds, including magentas) may penetrate the mesh and leave a colored stain; the wash up must, therefore, put the dye into solution to eliminate this type of staining. In addition, the wash up needs to get between the resin and the mesh, even inside the knuckles, to break the temporary adhesion between ink and mesh or stencil.
The wash up should not swell an under-exposed stencil or reclamation will become quite difficult. Finally, the press wash should not leave a residue which can transfer onto the next few printed shirts and prevent tape adhesion. If it was to achieve these goals (and the stencils were adequately hardened) such a press wash would also eliminate the need for haze remover.
Early on I suggested you never purchase materials which retard production or reduce quality. Nowhere is there a greater violator of this recommendation than the low cost “fly-paper” which proliferates in our industry under the pseudonym “tape.” The risk of rejects, the lack of resistance to plasticizer, press wash and heat, and the cost of the protracted removal process makes it the most expensive cheap product in your entire mix! Your tape should be unbreakable, its adhesive resistant to ink and press wash, and it should strip instantly without effort. While the others in our quintet of peripheral equipment and products had alternatives to help mitigate the ill-effects of the wrong choice, not so here. Make your life better; just buy the right tape.
Just-in-time manufacturing is not about inventory as much as a proper chicken-or-egg scenario. I suggest you take a look at your plant and use this list as a guideline to help you fix elements which are troubling your quality or productivity. Eliminate everything in your manufacturing which does not increase the value of your product, as explicitly described by your customer.