Printer's Guidebook, Part XI

On Press, continued

43. Peel-off adjustment
That which controls the rate at which the mesh peels off the substrate, following the blade stroke.

With fixed off-contact, this space is used to keep the screen and substrate separated except where the edge of the blade brings the mesh in momentary contact with the substrate. After the blade passes, the mesh must peel smoothly away from the substrate. This peeling away is affected by screen tension and off-contact, and must be adjusted so as not to occur too quickly or too slowly. Manual printers develop the bad habit of printing and peeling more slowly when they have low-tension screens and poor off-contact. With automatic presses, the sudden snapping of the mesh, all at once, can cause terrible image resolution and sharpness because ink spits around during the snap. So, while there should be no delay as the mesh smoothly pulls itself from the ink deposit-directly behind the blade-this peel shouldn't be forced by an overeager automatic. Since the ink acts like an adhesive between the mesh and the substrate, the larger the printed area is, the harder it is to pull the mesh out of the ink film. Smaller images don't have as much trouble pulling themselves out of the ink film. Automatic peel uses a mechanism to lift the screen away from the substrate during the print stroke, continuously changing the angle between screen and platen. The advantage of automatic peel is that it separates the mesh from the ink film with more control than mesh tension alone. Automatic peel is a necessary evil for huge screens. Its disadvantage is that changing the off-contact of the screen changes the size of the image, which can blur the print. Often, we can't count on all the conditions of an ink to be the same; thus, the extra control of the separating force is an advantage. In fact, the ink is never the same, so the peel is never the same. This has made peel adjustment a standard feature on graphic flat-bed presses, large long-stroke presses and belt printers for textiles. Distortion Unfortunately, there is more distortion with automatic peel than fixed off-contact which is why we rarely see it on smaller presses. Fixed off-contact has smaller and more predictable distortions and the introduction of higher and higher mesh tensions has created less demand for automatic peel. If you remember your geometry from high school, you'll remember the Pythagorean Theorem (the square of the hypotenuse of a right triangle is equal to the sum of the squares of the other sides) which proves that, if you change the off-contact, you will change the length of the mesh ... thereby distorting it.

44. Press bed evenness
Aids in the creation and maintenance of the gasket-like seal between stencil and substrate.

The best printing is done on a perfectly flat surface. To print, the blade brings the mesh into momentary contact with the substrate. The screen must be suspended above the substrate to aid ink and stencil separation; this distance adds to the blade's main task of moving ink. It is more important that platens be parallel to the screens than, necessarily, "level" (as in exactly 90° off vertical), although it is recommended that all parts of a press be level and square whenever possible. (It is possible to print on a rocking boat, but you wouldn't do it if you had the choice.) We use flexible blades that can bend and absorb irregularities in the substrate, or to compensate for the variable resistance of screens. For a continuous print, we must have consistent blade pressure, creating a seal between the stencil and substrate; if not, the ink won't transfer through the mesh. We can't print a hole or shallow area. The ink won't transfer to air. For the same reason nicked blades don't print where there is no contact, if, for any reason, the blade lifts off the substrate, ink won't transfer through the mesh. If that happens, we often resort to adding more blade pressure (which bends the blade and changes its tip angle) until those voids are filled. But areas that had sufficient contact now have too much angle and the image changes. Some areas now get too much ink and it begins to build up. You have to stop regularly to clean up the mess. Damage Platens can become warped from too much flash heat, dented from being dropped or having something dropped on them. Everything that damages the flatness of a platen will slow down your set-up time and press speed, as you are forced to compensate. Rubber or plastic surfaces may need to be replaced if they get damaged. This is usually a simple procedure, but take care that the surface is flat when finished. Textile adhesives and lint build-up can also affect the finished print if the blade has to ride over it. Process prints are susceptible to changes even from a shirt tail folded over at the end of the platen as it's loaded. Multiple platens that can be removed will always go back on at a different elevation or flatness (see variables 45: PLATEN-TO-PLATEN PLANE and 46: PLATEN-TO-SCREEN PARALLELISM). The best you can do is to keep their supports clean and smooth. Label each platen and platen support so you can return each to the same place. Belt printers have extra trouble. Yes, they use a laminated synthetic belt which is as flat as it can be, but the combination of big screens and lots of ink make this printing a little harder than finished-shirt printing on a conventional press. Graphic or flat-stock presses are usually larger and, thus, harder to keep flat, especially honeycomb style press beds that are very susceptible to dents from dropping things on them. Sometimes, dents can be fixed with automotive body filler, then ground to a nice flat finish. Check your platens using a straightedge with a fluorescent (diffused) light behind it to look for gaps. And use the same dial indicator you use to measure off-contact distance, except check the platen for parallelism in various locations (instead of shirt-to-stencil distance).

45. Platen-to-platen plane
For multi-color work, all platens must be in the same plane.

In order that every screen/platen combination has the same off-contact distance, multiple platens on a press must be set at he same elevation. If such is not the case, blade pressure will be different for every platen-a disaster because you are printing on many platens under each head and you can't rely on any single setting. What's more, it is impossible to change the off-contact for each platen; they must, therefore, all be the same distance from each head when in a neutral position. On a multihead press, the entire press must be leveled for the best results. To accomplish this, start by leveling the press legs or center shaft. You should only have to do this once, as it rarely changes (unless you are on a wooden floor). Next, level and square head number one. Neutralize the off-contact adjustments and put in a reliable frame (square and flat) without mesh. Clamp it in place in the usual manner. This is your benchmark, the head against which all others will be measured. Establish platen number one Most presses have platens that can be adjusted up or down. Because they can be moved, employees like to move them. If you don't bring them back to the same "neutral" position every time you start a job, set-up will take longer. So identify one platen as platen number one and label it accordingly. Bring it under the frame in head number one and bring the two together as if you were printing. Use a straight edge and dial indicator to measure the distances from the frame to the platen. Adjust the platen until you have an off-contact distance for your typical printing (including the substrate), and write the measurement down. Now it's time to transfer this measurement to the other heads and platens. Move platen number one under head number two and adjust the head so the screen is level to it. Next adjust platen number two, which is now under head number one. Continue around your press, adjusting all your heads to platen number one and all your platens to head number one. At some point, you may find you want to change the base elevation of the platens to make changes from sweatshirts to T-shirts easier. Start this procedure by changing your initial distance.

46. Platen-to-screen parallelism
For an even ink deposit, screens and platens must be parallel to each other.

This is certainly a function of off-contact. If you aren't parallel from platen to screen, your off-contact is unbalanced and you will get an uneven print. For off-contact to stay constant, at all points between the bottom of the screen and the top of the platen, the distance must be equal. Measure this with a straight edge and dial indicator as described in Variable 42: OFF-CONTACT DISTANCE.The final print is tremendously affected by the order in which you print the different colors of a multi-color design. All the other variables can and do affect the print but, because we typically print wet-on-wet, color order adds to the complexity of a design. If the separator or illustrator is able to visualize the finished product (yes, product) and design and engineer the art, screens and ink with that conclusion in mind, the printer's job is greatly simplified. So think of your art department as your engineering department; everyone there should have printed at one time or other (or at least experienced how their art can change under the influence of each variable). Art mandates order There are fascinating methods to increase the number of colors you print, such as overlapping transparent or even semi-opaque inks, effectively creating new colors. Transparent inks on a colored shirt will also create new colors. Ink opacity and alterations in print sequence can alter the resultant color as well. (But you should experiment before you try these techniques with real work. Only through testing can you train yourself to predict what an overlapping color will look like, and it may not be practical to experiment during actual production.) At any rate, start by knowing the number of colors you can print. The number of possible colors is determined by the number of heads on your press, less those dedicated to flash and cooling stations. Next determine what type of shirt you're printing. The big question is: light or dark? This determines what kind of ink should be used: wet-on-wet inks (that stain a light garment) or any of the variety of dark systems we've developed over the last 20 years to defeat the "evil" dark shirt (by sitting on top of, rather than staining, it). Before you start separating, choose the colors you'll use so your separations reflect trapping, overlays and, finally, print order. As you look over the design, write down every color you see on a 3X5 index card. If there are more colors than you can print, you have to eliminate or create some. Once you have done this a few times, print order becomes easier to predict.

47. Color sequence
A variety of factors dictates the order in which the colors of a multi-color job will be printed.

The final print is tremendously affected by the order in which you print the different colors of a multi-color design. All the other variables can and do affect the print but, because we typically print wet-on-wet, color order adds to the complexity of a design. If the separator or illustrator is able to visualize the finished product (yes, product) and design and engineer the art, screens and ink with that conclusion in mind, the printer's job is greatly simplified. So think of your art department as your engineering department; everyone there should have printed at one time or other (or at least experienced how their art can change under the influence of each variable). Art mandates order There are fascinating methods to increase the number of colors you print, such as overlapping transparent or even semi-opaque inks, effectively creating new colors. Transparent inks on a colored shirt will also create new colors. Ink opacity and alterations in print sequence can alter the resultant color as well. (But you should experiment before you try these techniques with real work. Only through testing can you train yourself to predict what an overlapping color will look like, and it may not be practical to experiment during actual production.) At any rate, start by knowing the number of colors you can print. The number of possible colors is determined by the number of heads on your press, less those dedicated to flash and cooling stations. Next determine what type of shirt you're printing. The big question is: light or dark? This determines what kind of ink should be used: wet-on-wet inks (that stain a light garment) or any of the variety of dark systems we've developed over the last 20 years to defeat the "evil" dark shirt (by sitting on top of, rather than staining, it). Before you start separating, choose the colors you'll use so your separations reflect trapping, overlays and, finally, print order. As you look over the design, write down every color you see on a 3X5 index card. If there are more colors than you can print, you have to eliminate or create some. Once you have done this a few times, print order becomes easier to predict. Finally, establish the order Look at the design and pick which elements you would print first and last. These will usually stick out with the last being the most prominent. There are no hard and fast rules about this, though. You should keep an open mind because going against these suggestions could give you fabulous results. Keylines (the outline around a cartoon figure like a bunny or a tractor), novelty inks like puff, glitter, white or other high-opacity colors, fine details, very large areas and, of course, copy or company logos are usually printed last. Tiny areas, light colors, backgrounds, colors that fill in the key line or cartoon can go first. Small areas go first because they're picked up less on successive screens, which reduces build-up. Light colors and background colors can be liquid inks that penetrate into the substrate (staining or wet-on-wet) without trouble. Even dark colors like black can be early in the sequence if they're filler, because they stain so well and don't build up. Process printing The typical print order for process is WYMCKT which stands for: white, yellow, magenta, cyan, black and touchplate. (This, too, is not a law, but just the way things usually work best.) Yellow is the brightest color of the spectrum but also the worst color for contrast, so it holds up well against the other colors but you can't see it on a white shirt. A non-opaque white is sometimes used as a sizing agent to surround the transparent process colors so they don't gain as much. This was developed as a litho-printing method for newsprint which is very absorbent. Printers would print a clear varnish first, then print on top of the varnish. This is also the inspiration for our sealing and flashing of dark shirts, then printing on top of the sealer (or underbase). It's also useful to pre-print white when you're printing pastel rather than white shirts. The white color has to come from somewhere. A touchplate or spot printer is used in addition to the four process colors to enhance parts of the design that don't reproduce well because of the limitations of process inks. Favorite colors are reds, violets, fluorescents and the like, which are hard to simulate with process inks. Printers have had good results changing the print order to enhance dominant colors in the design. This is an acquired technique and should be tested. Otherwise, stick to WYMCKT. It also follows the scheme of light colors to dark colors.

General rules A lot of judgement and experience contributes to picking first and last elements of a design. Here are some general guidelines, though, that will help you gain that experience.
Early in order	Late in order
Least important	Most important
Small image element	Large image element
Small ink area	Large ink area
Light color	Dark color
Background element	Foreground element
Undefined area	Fine detail
Standard colors	Novelty inks
Standard colors	Copy
Standard color	Company logos

Note: Obviously, everything can't be last; that's where judgment comes in.

1997 National Business Media, Inc.