Tension of your mesh is measured in “Newtons”, or more specifically, Newtons per centimeter. To measure tension, a weighted Tension Meter is rested on the fabric and the deflection (how much the fabric “gives”) is denoted by number. For example, 25 Newtons is a good tension for garment printing.
To determine the tension of a particular screen,
lay the screen on a flat surface with the print side (mesh side) up.
Looking at the screen from the top (the narrow side), place the meter in
the center of the screen so that you can see the face of the meter. The
needle will point to the number that will correspond to the tension of
the mesh from side to side.
Now, move to the side of the screen
(long side) and place the meter so you can see the face. This will tell
you the tension of the mesh from top to bottom.
The ideal tension will be in the 25 and up to the 35 Newton range.
There are special high tension mesh products available, but for garment
printing, I personally feel these higher tensions are a bit of overkill
and unnecessary. And, high tension mesh is very difficult to use when
printing by hand on a manual press.
As a rule of thumb:
- 25 Newton mesh will give you an excellent tension for all types of printing
- 10 Newtons and below, your screen should be re-stretched
A tension meter will cost approximately $500.00 and it is not a required product when you are first getting started, but should be on your wish list. If you opt to use retensionable frames, a tension meter is absolutely necessary to achieve proper mesh tension during the stretching process.
Low Tension
So
what’s the big deal about having screens with proper tension? There are
two issues that may occur when you use screens with too soft mesh.
These are (1) fabric wave, and (2) mesh release.
Fabric wave
means, as you apply pressure and pull or push the squeegee across the
screen and shirt, a small wave of screen mesh may form in front of the
squeegee blade. On the bottom side of the screen, this wave of
fabric may fill with ink as it passes over the image, and then smear ink
onto the garment when the squeegee reaches the edge of the graphic.
The more common issue is mesh release.
Printing with the preferred method of off contact, the only place the
screen physically comes into contact with the garment is along the sharp
edge of the squeegee blade. If your screen mesh is too soft, the mesh will not release from the garment as you pull or push the squeegee across the image.
When the mesh does release, often when you lift the screen, the ink on
the shirt will try to hold onto the screen mesh, causing a rough finish
to your print.
On a multi-color job, soft mesh will stick to the previous colors on the shirt,
and the ink picked up will begin to build up on the backs of your
subsequent screens. In short order, your prints will start to appear
muddy around the edges and where colors touch within your image.
When printing dark garments, poor screen tension can be doubly troublesome. The ink from the white underbase print is pulled up with the screen, and then flash cured
into that position. My best analogy is seeing a thousand little
mountain peaks standing up on the shirt. Under a microscope, the surface
would look like the Alps. When colors are printed on top, the print
feels very rough, or worse, hundreds of tiny white specks show
throughout the print area where the white underbase peeks through the
colors.
To recap, when a print feels rough, it is almost always caused by a screen with poor tension.
(I get this phone call from screen printers all the time!) A tight
screen will give you a crisp, sharp image. And on a manual press, a
tight screen will cause far less printing fatigue during the process.