Imagine standing on the production floor to witness your staff at the very onset of a press run, only to get called back to your office for a phone call. Later that day, you return to find they haven’t printed a single shirt yet! You don’t know how this can possibly be so you look at the facts as you know them—it is a work day, there were no power outages, you trust your crew, there were two or three of them press-side when you last left the floor and you bought them that register gizmo when the press was new.
So what gives?
If the crew spends too much time on setup, there are three areas that bear investigation and may serve to explain their periodic (or perennial) lack of progress:
1) Poor clearing
2) Misaligned image
3) Color variance
Printing systems must be characterized in this sequence or the results will be unpredictable and inconsistent, no matter the registration system.
Pre-cal the press
Press calibration means there are four planes on which the press needs to be parallel—the carriages, blades, screens and platens. Each carriage on each head must be parallel to the platens, often gauged by pushing a flood-bar across the platen while inspecting for light leaks or binding. Each blade should apply consistent pressure side-to-side on all platens as based on a feeler gauge between blade and bed. Finally, each screen should be parallel to each of the platens at all points of the image area.
Even if only for the calibration process, it’s recommended to use a variable-hinge printing blade. Traditional blades buckle and force the operator to use excessive pressure, creating a few problems in turn—excessive pressure is required to make up for the excess angle; the ink transfers before the edge of the blade arrives to make a seal; the speed must be slowed, preventing matte down and leaving a very rough print surface; and these blades drag the mesh in the stroke direction causing shape-distortion that cannot be “put into register.” In addition, traditional (single-axis) blades tend to rip screens as they are insensitive to the elasticity of the mesh. Bi-axial blades accommodate the resistance-differential of the mesh even when printing close to the edge in the case of oversized-images.
Those who think they have “the guy with the eye” for register are wasting a lot of time and missing the point. Misalignment could be due to the blade. The shape of the image can change if a blade buckles, if it requires a lot of angle or pressure or if it is necessary to print slowly. The key, then, to predictable and consistent T-shirt printing is in using a variable-hinged-blade running at or near zero degrees, with minimum pressure at maximum stroke speed.
Getting close to alignment takes no time at all; it’s the last little bit that holds one’s feet to the fire. Try the following to get there:
1) Build a test grid with 1-point lines, 1/4" squares the maximum size your press will handle.
2) At the four image corners, put 2" solid squares of color and center a gradient from 0 to 100 percent in both north-south and east-west directions. (If unable to output a 0.007" gauge polyester film with this image, have a service bureau output the film for you.)
3) Begin press characterization by putting the test image on the highest tension of screen you would take to press to print white ink.
4) Load it in head one, put a medium-value shirt (gray, medium green, tan, etc.) on platen number one. Make certain the screen is parallel to the platen.
5) Using a bi-axel blade (described above), make a test print with your tackiest white, then gently flash the image.
Ensure the ink is transferring through the mesh, leaving it clean at all points of the image. If it does not, use the troubleshooting guide below to rectify the situation.
IF: The screen and platen are not parallel front to back...
THEN: Level the screen to the platen and reprint.
• If it is still out, level the platen to the carriage, then level the screen to the platen.
IF: The blade and platen are not parallel side-to-side...
THEN: Always adjust the blade to minimize pressure.
• Raise pressure on the side of blade that cleared and reprint.
IF: Both edges do not clear...
THEN: There is excess blade angle; minimize angle and reprint.
• Reduce blade pressure much as possible.
IF: Center does not clear...
THEN: Minimize blade angle and reprint.
• If still poor, off-contact gap is too low; raise in 1/8" increments and reprint each time.
IF: Localized portions do not clear...
THEN: There is a flaw in the platen; swap out for a flat-surface platen and reprint.
• There is a low tension spot in screen; swap out for a consistent screen and reprint.
• Blade is flawed; dress the edge or swap out the blade and reprint.
Once the ink is clearing the mesh at all points, flash the printed ink very gently, then lay the master positive over the top of the dry ink to scrutinize the image alignment. Note that most registration systems will not work unless the shapes of the image are maintained. Following are various distorted shapes common to T-shirt printing which cannot be aligned and ways to correct them.
1. Stretched in the stroke direction:
• Reduce blade angle and blade pressure.
• Increase off-contact distance by 1/8" increments.
• Reprint and check for clearing.
2. Crowned (stretched more in the center and less at the edges):
• Increase off-contact distance by 1/8" increments.
• Reduce blade angle and blade pressure
• Reprint and check for clearing.
3. Convex sides (narrowest at mid-stroke; top and bottom are square):
• Frame is deflecting during printing tension—reduce blade angle and reprint.
• Reduce off-contact gap, reprint and check for clearing.
4. Skewed (longer on one side):
• Reduce squeegee pressure on long side and reprint.
• Reduce angle if necessary, reprint and check for clearing.
5. Re-proportioned (larger on all four sides):
• Reduce the off-contact gap, reprint and check for clearing.
• Gear future artwork to adapt for this level of dimensional error.
If your press is calibrated and you are using a variable-hinged blade, there are only four possibilities for color quality at this stage—the color is perfect without variance; the color is blotchy; there are wet artifacts or there are dry artifacts.
1. Perfect color:
• Congratulations, go directly to the last paragraph; proceed until complete.
2. Blotchy color (single print has a thin, smooth fluid aspect and a stucco aspect):
• Low volume mesh is filtering the ink during transfer; increase flood and squeegee speeds.
• If no improvement, swap out for a high-volume mesh (lower count and/or thinner thread).
3. Wet artifacts/system running “rich” (blurring, filling, sagging, etc.):
• Minimize blade angle, reprint and recheck dimensional accuracy.
• Or, if needed, increase off-contact gap, reprint and recheck dimensional accuracy.
4. Dry artifacts/system running “lean” (streaks, line or dot loss, piling, etc.):
• Increase squeegee speed by 30 percent increments and recheck each time.
• If color becomes blotchy, with increased speed, return to #2 above.
Swap the screen in head number one for the lowest tension screen you would ever use for white ink. Leave all other settings the same and print with the same tacky white ink. Odds are, this low-tension mesh won’t clear very well. Increased squeegee pressure will not help, but one of the following two options will. Use whichever you prefer.
1. Increase the off-contact gap… a lot.
Since the press is in calibration (right?!), don’t mess around with settings. Use a 1/8" shim stock temporarily positioned between the underside of the screen frame and the screen clamps at each end to suit the added gap required for your tension range. Then, take the off-contact distance up in 1/8" increments. But, before you reprint, realize that elevating the screen ultimately re-proportions the image (i.e. makes it larger on all four sides). This is another shape change that cannot be fitted to a different shape with use of micro-register.
2. Increase the minimum screen tension and use this elevated level. Test the screen as indicated above and if the result is acceptable, use it as your new standard minimum tension to take to press. The maximum acceptable tension for your press was already established with the first (highest tension) screen.
Once your blade is at or near zero degrees, with minimum pressure and maximum speed, the ink is completely clearing the screen, you have eliminated shape-shifting (dimensional error), minimized any color variance and established the permissible range of screen tension, you are ready to finish the job.
Since your press is calibrated (right?!) and you are using a variable-hinge blade, it shouldn’t take much time at all to perform the same characterization on each of the heads and each of the platens. Most press manufacturers have some sort of calibration process. To determine whether theirs is better than yours, characterize the press as described above first. Otherwise, you may want to hang out in your office more often.