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An Overview of Frame and Mesh Selection

(November 2008) posted on Wed Nov 05, 2008

Choosing the right frame and mesh is critical to achieving quality prints. This overview looks at different frame types, mesh parameters and performance criteria, screen-preparation tips, and recommendations for ensuring long-lasting screens.


By Andy MacDougall

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Some inks have specific characteristics that put limitations on mesh counts. UV inks require thin ink deposits for proper curing and won’t dry in the screen, so mesh counts above 305 are used. Ceramics printing requires the coarse particles of glass frit that make up the ink to pass through the mesh openings, so meshes in the 110–255 range are used. Other applications and suitable mesh count ranges are listed in the sidebar “Mesh Recommendations by Application” on page 33.

 

Mesh tension

Tension is measured in Newtons/cm, using a device that can be placed on the mesh during tensioning. In general, the higher the tension reading, the easier and better the printing result. A tight screen provides the following advantages:

• It allows the use of less off-contact when printing, which results in better registration, and a sharper print.

• Less pressure is required to print through a tightly stretched screen than a loose one. Although this sounds counterintuitive, it’s because under-tensioned screens require more lift or off-contact in order to print sharply. The increased lift then requires more squeegee pressure, causing folding of the blade, blurring of the print, and stencil breakdown.

• A properly tensioned screen will last longer than an under tensioned one.

• A properly tensioned screen is easier to coat, reclaim, and expose with good stencils.

A hand-stretched and stapled screen can only be tensioned to 1 or 2 N/cm, unevenly. Compare that to some printers using 40-N/cm screens. It’s a safe bet the print quality is reflected in the mesh tension. Can I say enough about this? Do you drive around with underinflated tires? Retensionable screens in the smaller sizes are cheap…do yourself a favor and ditch the cord and stapler!

 

Limitations on stretching

If tighter is better, then why not stretch the screens to 50-100 N/cm?

• The mesh can only take so much ten- sion, and then it rips, delaminates from the frame, or is easily torn during printing.

• Another factor is the frame’s ability to resist bowing or warping because of the tension. This problem increases as the size of the frame increases. Generally, smaller frames can handle high tension (30 N/cm or more). However, once frames reach sizes over 3 feet in any dimension, tensions in the 15–25 N/cm range are common. Extra large frames actually have braces and sup- port structures to stop bowing.


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