Question

We were told that stretching our screen mesh onto the frame at an angle, instead of square, would improve our print quality. Is this true, and if so what is the best angle?

Solution

The advice you received was partly correct, in that under some circumstances it can improve print quality some of the time. However, it offers little if any benefit for most types of printing, and requires a different, (and probably more costly approach) in your methods of stretching screens.

The types of printing that benefit from angling the mesh on the frame include those where the artwork consists mostly of thin, straight parallel and perpendicular lines, such as those in circuitry, nameplates or panels. In these cases, the lines print better because they are at an angle to the mesh threads.

Some other types of printing benefit from angling the mesh on the frame because the squeegee then runs at an angle to the mesh threads. For instance, this is the case with the very fast printing speeds involved when decorating compact discs. Angling the mesh in relation to the squeegee results in improved flow and transfer of the UV-cured inks.

These benefits, although substantial for some types of printing, and maybe even critical for success in the above-mentioned applications, will not be realized with most types of printing. In fact, most of the time the drawbacks associated with angling the mesh on the frame will more than offset any perceived benefits.

It's not just a question of increased cost, where you need to use a longer and wider piece of fabric to accommodate a frame at an angle, there are also some technical arguments for why it's not a good idea.

You may suffer some unexpected distortion of the printed image, which will be especially exaggerated if you use an oversized squeegee, or excessive off-contact, in conjunction with too much squeegee pressure. This can also show up as increased difficulty in achieving registration when printing multi-color images, particularly in larger formats.

If you use self-tensioning frames, then stretching at an angle, or on the bias as it is sometimes referred to, is definitely not recommended. Although not impossible, it is very difficult, and there are severe limitations on how much of an angle you can achieve, and the tension level that can be reached. First of all, there is a tendency to pull the mesh openings out of square, due to initial tensioning and pre-softening of the corners, and this can have an effect on ink deposit, or even cause moiré.

The amount of distortion increases as the angle is raised or as the tension level is increased, and in addition to this, it is very difficult during stretching to achieve an even tension over the whole print area.

If you stretch and glue, even though you keep the mesh openings nice and square, and the tension even, the screen mesh seems to be more fragile at the upper end of the recommended tension range because the mesh is stretched square with the frame angled underneath. Things that you would normally get away with, such as scraping some emulsion on the screen with an old nicked-up scoop coater, or leaving haze-remover on for too long, will suddenly start to split the mesh for no apparent reason.

Now, having considered the possible benefits, and also the drawbacks, if you still want to try printing with your screen mesh stretched at an angle, then we would recommend using 22.5 degrees. This angle has been proven to work, and is used successfully to overcome problems in the types of printing mentioned at the beginning. If you don't have a protractor to measure angles, then you can use a ruler on a straight edge to measure ten inches along and 4.1 inches out. When you join the starting and finishing points, the angle of the line will be 22.5 degrees from your straight edge.

One last thing: if you print halftones or four-color process, don't forget that you may also have to adjust the angles of the dots on your positives in order to avoid the formation of moiré when exposing screens with your newly angled mesh.