Frequently Asked Questions
Q: How can I tell when a printed image fault is caused by the mesh and when it’s caused by something else?
A: Image faults caused by the mesh quality do happen, but they are not as common as those that result from the wrong mesh selection, tensioning or printing parameters. A weaving flaw may leave a thread line in a full coverage of ink, or may be easy to spot on a backlit panel or a job printed with transparent ink.
More likely, image faults such as image distortion, smearing, voids and mesh marks are the result of improper tensioning or another area of the printing process, such as stencil selection and exposure or problems with the artwork.
Q: What is optimum screen tension?
A: For practical purposes, we find that most companies achieve good results printing in the range of 20-25 N/cm. Close tolerance printing jobs may require higher tensions, but when printing on uneven surfaces such as containers, you may want to reduce screen tension.
It’s probably more important to evenly tension sets of screens for accuracy of registration within +/- 1 N/cm. Your stretching equipment, frames and printing equipment will affect how much tension you can apply to your screens, as will the requirements of the job.
Q: Is there such a thing as too much tension?
A: Yes. Excessive tension isn’t the cause of as many problems as insufficient tension, but it can affect your print and ruin the mesh. With increased tension, the mesh count and fabric thickness decrease, and the mesh opening increases. This will affect your ink deposit, but whether this is a good or bad thing is a subjective matter.
Damage to the fabric’s elastic memory is never desirable and can happen when the mesh is tensioned beyond its “yield” or “shoulder” point. The mesh will not tear, but it will lose its ability to snap back to its original tension during printing or retensioning.
Q: How long does a screen need to rest before gluing it down, or locking it into the frame?
A: This will take some experimentation. The low-elongation threads in Monoprint H require less relaxation time. Many printers have found that they don’t need to “stage” their screen tensioning at all. If you are concerned about tension loss after gluing the mesh to the frame, start with this procedure: Tension the mesh slightly, and then soften the corners. Apply tension incrementally, 4-5 times at 1N/cm per second, with a 5 minutes in between. This should take about 30 minutes.
Very large screens may require longer times for the mesh to become stabilized. For extremely close tolerance printing applications, we advise letting the screen relax for a 24-hour period prior to printing, regardless of the type of mesh.
Q: What is “rapid tensioning” and is it recommended for all mesh types?
A: This is a method of taking the fabric up to final tension in one step. The rapid tensioning method should be used under controlled circumstances and should only be used with low-elongation fabric.
Q: What is the formula for selecting mesh counts for halftone printing?
A: This refers to the relationship between halftone line count (or screen ruling) to the mesh count. The higher the line count of your halftone, the smaller your dots will be, especially in the highlight and shadow areas. The minimum mesh count should be 3.5 times the line screen of your artwork. For instance, for a 65 line halftone, your minimum mesh count is 230. Remember to consider the thread diameter and its influence on the printable tonal range. Thinner thread diameters allow for better resolution of highlight and shadow dots.
Q: How can I tell when it’s time to throw out a piece of mesh?
A: Apart from seeing a gaping hole in the mesh, you may not be able to tell when fabric is ready to discard. Haze from ink and unreclaimed emulsion can produce a ghost image in your next print, especially if the haze appears in a large, reversed image. Very long print runs can, over time, deform threads, embossing them into the shape of the substrate or the artwork. Subsequent jobs printed with the mesh might exhibit marks in the print. These image problems are most evident when printing transparent inks or backlit panels.
Q: Do I always need to soften corners?
A: Yes, especially when tensioning to tension levels over 20N/cm, and always with fine meshes (over 305 tpi) or withthin thread diameters. As you increase tension in the print area of the screen, the stress placed on the corners can lead to ripped fabric.
Q: Why are screen fabrics dyed and undyed?
A: Monoprint HT is offered in Golden Yellow and White. Depending on the mesh count, the fabric may be available in one or both colors. Mesh color influences the quality of the stencil resolution as well as the optimum exposure time.
White mesh, just like any white surface, reflects lights, and so reduces exposure time. Dyed mesh will require longer exposure because the yellow color absorbs much of the UV light. This translates to as much as 25% difference in exposure time compared to white fabric, but improves resolution considerably.
For halftone and fine line printing, dyed mesh is always recommended. White mesh is usually found in low mesh counts and is used in non-critical printing applications.
While some printers use different color meshes for easy identification of mesh count, we do not recommend this practice. Because different colors vary in their effect on exposure time, the likelihood of underexposure will increase if you stock several colors of mesh. Instead, label mesh counts clearly and keep the labels readable.
Q: Which is the more important criteria when selecting mesh… mesh count or thread diameter?
A: Always consider every mesh parameter, including fabric thickness. Mesh count is important. This is probably due to the fact that higher mesh counts are typically woven with finer threads than coarse meshes and so provide finer printed detail. While you may be selecting mesh based solely on thread count, the thread diameter invariably has a great impact on the fabric’s performance. The choice may not be entirely up to you. Many inks require the use of specific ranges of mesh counts. As a starting point in mesh selection, follow the ink manufacturer’s guidelines. If the recommended mesh counts are not suitable for the artwork you want to reproduce, you may have a set of incompatible printing parameters, and may be forced to change one or more of them. For instance, you may achieve the desired results only by lowering your halftone line count.
Q: Should I print in the warp direction or the weft direction?
A: Whether you are printing line work or process color, always print all of them in the same direction. We recommend printing in the weft direction whenever possible.
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Jeff Campbell - National Sales Manager
763-234-0040
JCampbell@IFCfabrics.com