Most commonly the term “screen” refers to a frame with screen mesh
attached. There are three options available to screen printers when it
comes to the frames we choose.
Wood Frames
Today, wood frames have glue holding the mesh in place. Most
commonly, mesh is pulled in all directions via a pneumatic device, and
the mesh is then glued across the face of the frame.
While
screen printers in the past stretched their own screens, and some
certainly still do, it is much more common today to buy your screens
already stretched with fabric. The increased cost is nominal
(for frame and mesh), and when you factor in the time involved in
stretching your own screens, it makes more sense to buy frames
pre-stretched. When mesh becomes torn or loses tension, the frames can
be re-stretched with new fabric by most frame suppliers. (Read the
Article: Mesh Tension and the Impact of Your Print)
Static Aluminum Frames
The second frame is static aluminum. Just like the wood frame, static aluminum features mesh that has been stretched and glued in place.
The term “static” refers to the fact, just like wood frames, that the
mesh has been stretched and that same mesh cannot be re-stretched to
maintain tension. In fact, through use, both wood and static aluminum frames will lose tension over time.
The
cost of static aluminum is generally just a few dollars more than wood,
but these frames are lighter to work with in the shop and on the press.
Just as with wood, static aluminum frames are almost always purchased
with mesh attached, and can also be re-stretched as necessary by your
screen supplier.
With pricing of static aluminum frames now more in line with wood frames, the aluminum frame is becoming the industry standard in most shops.
Retensionable Frames
The third option is the retensionable frame. Just as the name infers, these frames can be re-stretched by you as necessary. As you use a screen, whether it be wood, static aluminum or retensionable, it will lose tension as a result of the constant pulling and pushing on the mesh by your squeegee. Wood and static aluminum screens will reach a point where it is not practical to use them any longer because of poor tension.
With retensionable frames, you can tighten the mesh on the frame.
This re-stretching is accomplished by loosening the bolts holding the
frames sides in position and then pulling the mesh taunt with a wrench.
Retensioning occurs only when a screen has been used, then reclaimed (emulsion removed).
Trying to retension a screen with emulsion and an image will result in
distortion of the image and potential cracking of the emulsion on the
mesh. Screens for multi-color work would certainly become difficult to
realign with one another if a retensioning of one or all screens is
attempted.
After you go through this restretching process
approximately five times, you will discover that the screen mesh will no
longer lose its tension. This process of re-stretching and then the mesh maintaining its tension is called “work hardening”.
After stretching and re-stretching a few times, the mesh will reach a
point of work hardening where the mesh will no longer stretch. From this
point forward, if you take care of the screen, you can literally use this stretched screen for years. While a retensionable screen can cost 2-3 times more than a wood or static aluminum frame, in the long run you will have a more economical product.
Here’s the trick though.
In consulting with many screen printing shops, I will ask owners and
managers how often they re-stretch their retensionable frames. The
answer is most often, “We check our mesh tension each time the screen is
reclaimed.” When I then go onto the production floor and ask someone in
the screen prep department the same question, the answer is something
like, “I can tell how tight the screen is just by feeling it.” Then as I
press for an answer, “We’re really busy, so…” Bottom line, in many, many shops, the tension is never checked. If that’s the case, the expensive retensionable frame is no better than a wood or static aluminum frame.
You know who you are.
If you are that person who will check the tension or make sure your
staff checks the tension, these frames will save you money in the long
run. If you treat these frames just like pre-stretched frames, your better off going with the less expensive wood or static aluminum.