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Preventing and Removing Haze

(December 2013) posted on Wed Dec 18, 2013

The products and processes that can streamline your screen-reclaiming efforts.

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By Screen Printing's Solution Sourcebook

If you find that time is a factor, or you do not want to use two products for removing haze and are not as concerned about potentially harming the mesh, you should select a caustic haze remover that contains solvent. But ink and emulsion are not always to blame for haze. Other contributing factors, such as process variables, are often overlooked. Process-related variables contribute to the severity of ghost images as much, if not more, than your inks and stencil systems. Since process related variables are often more controllable than the type of ink or emulsion you use, let’s take some time discussing how these variables contribute to ghosting.

Low and unstable screen tension Low and unstable screen tension can contribute to high degrees of ghost haze. Low-tension screens require excessive off-contact on press in order to achieve proper peel/snap-off during printing. High off-contact is how one achieves the proper tension necessary to effectively transfer the ink to the substrate when working with improperly tensioned screens. Unfortunately, excessive off-contact causes inordinate mesh elongation as the squeegee stretches the screen while dropping into printing position. At this point, the ink transfers through the mesh and much of its pigment particles get trapped in the knuckles of the mesh when the screen relaxes to its resting position.

Screens that have high tension initially but are not stabilized properly prior to printing may experience a lot of tension loss, which results in the same pigment-particle entrapment explained above. Some meshes also exhibit lower elongation and relaxation during stretching and printing than others. Thorough in-house testing will prove which ones perform better. Therefore, high tension is good, but high, stable tension is better for reducing ghost haze, as well as print misregistration, distortion, and color shifts.

Unnecessary use of roughening agents Roughening agents, or abraders, improve stencil bonding and durability. These products cost more than concentrated degreasers and microscopically scratch the mesh, which can lead to premature ghosting. These products are beneficial at times, but they should not be used unless absolutely necessary. An alternative to abrading the mesh is a product used as a degreaser/wetting agent that treats and conditions the mesh for improved stencil durability. If used consistently, it may reduce the severity of ghost haze.


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