Roger L. Jennings

Every shop faces the same problems that are seldom solved, but can be solved at no expense. Seven of those problems are described, and the solutions will save a lot of time and avoid a lot of aggravation and expense. See if they work for you.

#1. Plexiglas set up. Screen printers know that the best quality registrations are achieved when the screen is actually touching the positive, but the best quality printing is achieved when the screen is off-contact from the garment being printed. Turning the off-contact bolt in the registration gate to achieve off-contact for a screen that was registered on-contact introduces a pitch to the screen and will probably result in images being out of registration.

The problem gets worse when the screen printer has a multi-color press with multiple print stations each with its own off-contact bolt, because each off-contact bolt will be turned slightly differently. The pitch of the screen at each printing station is therefore different.

Some presses are offered with a pitch adjustment to compensate for the pitch problem. The theory is to compensate for the pitch that was created with the off-contact bolt by adjusting the pitch of the screen. In theory the screen will then be level and parallel to the platen. In practice getting each screen to be parallel to the platen is nearly impossible. On a 6-color, 4-station press, for example, the practice of turning 4 off-contact bolts and the pitch on 6 color arms is time consuming. Then after the job has been printed, all of the off-contact bolts and color arm pitches need to be set to their former height and angle. Again, as a practical matter, getting the screens flush on the platen and the color arms on the off-contact bolts is difficult and time consuming at best.

The solution is simple. A sheet of plexiglas 1/8" x say 17" x 17" is laid on the platen. The height and angle of the screen must be adjusted so that the screen is flush on the plexiglas at the four corners of the platen and the color arm must be resting on the off-contact bolt. The screen used to make the adjustment should first be checked for flatness. If a screen is laid on glass, e.g. part of the exposure unit, and the screen when pushed on the four corners does not rock, then the screen is flat.

The positives can be laid on top of the plexiglas and used to register the screens on-contact. After all of the screens have been registered, the plexiglas and positives are removed from the platen. Now when the screen is brought down towards the platen, the color arm of the press will bottom out on the off-contact bolt before the screen touches the platen. The screen will be parallel to the platen, which is critical for quality printing, and be off-contact by the thickness of the plexiglas. T-shirts are typically 1/32". So the off-contact for Ts would be 3/32".

Setting up jobs is now easy and quick, and the printing results are better than when moving off-contact bolts or changing the pitch in the color arms. No tools are required. Put the plexiglas on the platen to set up a job, register the screens, and remove the Plexiglas when all done. Now the benefits of a micro registration adjustment will not lost by changing the pitch of a color arm.

#2. Add a piece of cardboard to the neck of the platen. Screen printers know that the mesh needs to pull away from the ink on the garment. Tight screens work better than screens with little or low tension, because mesh in tight screens snaps off of the printed image. However, ink is adhesive, and can prevent the mesh from snapping off of the ink.

Retensionable screens where the mesh has been retensioned regularly to remove the slack in mesh offer the best opportunity for the mesh to snap off of the printed image. However, when printing on retensionable screens the mesh is so tight that when the screen printer pushes down on the squeegee the frame is pushed down onto the garment, and the mesh does not have an opportunity to snap off of the garment.

Again, the solution is simple. Just cut a piece of cardboard maybe 3" by 3" from a carton and tape that to the neck of the platen. When printing and pushing down on the mesh with the squeegee the frame and mesh will rest on the cardboard preventing the frame from bending downward, and the mesh then will be able to snap off the garment.

This piece of cardboard pays big dividends when printing on dark garments. Opaque inks printed through 110 or more coarse mesh in a retensionable frame coated with 50 micron capillary film can be laid down on a garment in sufficient thickness to leave a bright image without having to flash cure and print again. Printing without flash curing can increase productivity 300-400%. For example, a light colored shirt printed with one color dark ink at 100-120 shirts per hour in many shops would be only 30 shirts per hour when a light colored ink is printed on a dark shirt, flash cured and then printed again. The cardboard, retensionable screen and capillary film can eliminate the need for the flash cure and second print.

#3. Adjusting to thickness of garment without tools. When printing Ts, fleece, jackets, totes, towels and more, the thickness of the substrate changes. If the machine is adjusted with tools, that effort is time consuming and difficult to get the screen absolutely parallel to the platen for quality printing.

The simple solution is to put a shim like a ruler in the channel clamp where the screen goes in the press, and then lay the screen on top of the shim. The thickness of the shim should equal the additional thickness of the substrate so that the off-contact distance is maintained regardless of thickness of substrate.

Adjusting a press so that the screen is absolutely parallel and on-contact while the color arm of the press is resting on the off-contact bolt takes time. Once that effort has been completed successfully, you will not want to use any tools on the press. When the job is over the shim can be removed and the screen will be parallel to the platen without spending any time and without using any tools.

#4. Home made squeegee sharpener. Sharp knives work better in the kitchen than dull knives. A blade that is sharp cuts cleaner and faster. Ink needs to be cut from the screen to be deposited on the garment.

The problem is almost no screen printer sharpens a squeegee before each use. Scraping the squeegee across the coarse mesh quickly dulls the squeegee blade. Just compare the edge of a new blade to an old blade, and the difference is immediately apparent.

When men go to the barber shop, the barber polishes the blade of the razor on a leather strap before shaving the side burns of the customer. When that customer gets out of the barber’s chair, and another customer gets in the chair, the barber goes through the same routine of sharpening the blade on the leather strap. Actually, the blade is already sharp. The barber is actually polishing the blade, because he knows the blade will work better.

A screen printer is cutting ink and also needs a blade that has been polished to peak sharpness. A squeegee sharpener to polish the blade can be made by laying 200 grit sandpaper on a smooth surface, and by supporting the squeegee in a vertical position with supports on both sides of the blade. The supports are screwed into the board supporting the sandpaper. Then all the screen printer needs to do is draw the squeegee down the slot a few times before each use to keep the square edge of the blade polished sharp.

Old, dull blades cannot be sharpened by this method. If the blade can be removed from the handle, then by inverting the blade a screen printer might get a sharp blade. Old blades can be squared off by an amateur carpenter so that the home made squeegee sharpener is only used to polish the blade.

#5. Images are exposed high, low, crooked in the screen. Have you ever had a perfect screen that you could not use, because the image was exposed too high, low, or crooked? A lot of time can be spent measuring the location of the positive on the screen, and still the image requires putting the screen in the press crooked to compensate for a crooked image in the screen. Sometimes there is no choice, except to spend the time and use more materials to make a new screen.

With a Screen Registration Guide, this problem will never occur again. A Screen Registration Guide is something anyone can make in 10 minutes. All you need to do is to screw a strip of wood on a flat sheet of plywood or particle board. Then push a screen against this strip of wood, and use the side of the screen to locate a second strip of wood that is also screwed to the plywood or particle board. The center lines vertically and horizontally are measured and drawn with a pen inside a screen. A similar cross is draw on lined paper, such as graph paper or paper from a flip chart.

The paper is slipped between the screen and Screen Registration Guide while the screen is pushed against the two strips of wood. Once the cross on the paper is registered to the cross in the mesh while the screen is being pushed against the strips of wood, the paper should be taped to the plywood or particle board. Then remove the screen and lay a clear plastic sheet over the graph paper and tape the clear plastic sheet in place.

A positive is laid on the plastic sheet using the graph under the plastic to locate the positive making sure the image is centered and parallel to the lines. This positive is then affixed to the plastic with one or two short pieces of cellophane tape. The next positive is then laid on top of the first in registration and affixed to the plastic sheet. Any number of positives can be stacked up in registration with each independently taped to the plastic sheet.

Now, one inch strips of double sided adhesive tape are put in the four corners of the top positive. A coated screen is pushed against the two wood strips and lowered down on top of the positives. The mesh should be rubbed where the four pieces of double sided tape are so that the screen picks the positive up off of the pile when the screen is picked up. The positive is still affixed to the plastic sheet, and so it is necessary to reach under the screen to separate the cellophane tape from the plastic sheet. The screen can be exposed.

Again, double sided adhesive tape is applied to the four corners of the next positive, and the process is repeated. All the images will be located on their screens at exactly the same distance from the outside edges of the frames. Later when registering screens, none of the images will be high, low or crooked, and registering should require only moving the screen left or right in the press. If the channel clamps that hold the screen are all the same distance from the center of the press, then screens only need to be moved laterally to register colors, and set up time is reduced. Best of all, screens never have to be made a second time to solve image placement mistakes.

The Screen Registration Guide will work even better, if made from plexiglas rather than plywood. Then the image area can be back lighted with a low wattage light so you can see the registration of images better.

Jobs can be set up on a press faster, if one of the platens is modified to provide location or pin points on two sides of one platen. A screen is placed against the pin points much like you did with the two wood strips on the Screen Registration Guide. If the screen butts against the pin points on the platen while the screen is being seated in the channel clamp of the color arm, then all screens can be seated exactly in the same place by placing each screen against the same two pin points. Now you effectively have a home-made pin registration system.

#6. Avoid ghost images. Almost every shop has those annoying ghost images, and some shops spend money on ghost removers or toxic dehazers. The solution to the problem is to not get the ghost images in the first place.

Ghost images can come from a variety of sources. The most common is the emulsion locking up in the mesh with ink in the emulsion. Another source is emulsion baked into the mesh from the glass on the exposure unit getting too hot. Exposing with moisture in the emulsion can also be the reason emulsion locks up.

The solutions are simple. To avoid having the emulsion lock up in the mesh, use the following procedure. First, scrape as much ink from the screen using the squeegee as possible. Then, second, lay the screen in a horizontal position with the print side up and ink side down. Spray the emulsion with stencil remover, and let the stencil remover sit on the stencil for about two minutes. Never let the stencil remover dry, or the emulsion might never come out of the mesh.

The stencil remover will melt the emulsion. Now scrub the emulsion lightly with a plastic bristle brush to loosen the emulsion on the print side of the screen. Stand the screen up vertically in the sink, and run water down the print side of the screen. The emulsion goes down the drain, and the ink on the ink side of the screen remains in place. No water pressure should be used. Then remove the ink with a chemical like a citrus or soy product, and you will have a clean screen without a ghost image.

Almost every shop uses some chemical to remove ink before attempting to remove the emulsion, and those chemicals used on ink lock up the emulsion material in the mesh. By changing the procedure to remove the emulsion before the ink, there is no emulsion left in the mesh to lock up. Capillary films that are applied to screens with only water and without squeegeeing the capillary film into the mesh can be removed faster and more easily than liquid emulsions.

If the glass on the exposure unit gets hot, then a household fan should be directed at the glass to keep it cool. Emulsion and the stencil material from capillary film must be absolutely dry before being exposed to avoid staining the mesh.

#7. Improve the flash curing and cut the electric bill. If the ink in the center of the image cures before the ink around the edges, or scorching is a problem during curing, the flash cure heater is probably 4-6" above the garment and very hot. Many flash units are made without temperature control.

In studies of how power is used in shops large and small we found consistently that 50% of the total electric bill in shops with screen printing and even embroidery comes from one source - the flash dryer. So the opportunity here is to cut the electric bill, avoid scorching of shirts, and flash cure ink consistently across the entire image.

A temperature control is simply a rheostat switch as used on the kitchen oven. Such a switch can be put in an electric box with a cover. Installing such a switch is similar to installing a light fixture or light switch in a house. Once the temperature control switch is installed, the flash dryer can be run at a lower temperature to save money and to get the surface of the flash dryer 1.5 – 2" above the garment. When the heater is closer than 4-6", the heat will be more evenly distributed and the risk of scorching can be reduced.

Conclusion. Problems that continue to annoy screen printers and cost them money often can be solved with simple solutions that don’t cost a significant amount of money.