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Preventing and Removing Haze

(December 2011) posted on Wed Jan 11, 2012

Ghost haze is a problem you can conquer when you arm yourself with the proper chemicals and use sound techniques.


As the number of products referred to as haze removers continues to grow, so does the confusion over
what classifies as a haze remover. Some degreasers also dehaze, and some dehazers also degrease. There are abraders that dehaze and dehazers that abrade. To simplify matters, let’s organize and define common screen-prep and cleaning products.

Degreasers consist of one or more of the following ingredients: detergents, emulsifiers, surfactants, and wetting agents. They clean the mesh prior to application of emulsion or film and remove most forms of contamination and foreign matter from the screens so a smooth, uniform, blemish-free coating can be achieved. Screens should be degreased just before the mesh is coated. Degreasers are not intended to dehaze.

Abraders scratch the knuckles of the mesh at a microscopic level, which increases the surface area and helps improve stencil adhesion. The active ingredient is silicon carbide, which is a dark, insoluble, crystalline compound used to abrade the mesh. These products are most frequently used to improve the durability of capillary and indirect films when longer production runs are required. Abraders are not intended
to dehaze.

Ink removers consist of various blends of solvents used to dissolve inks for cleanup after printing, or for use while printing. If used after printing, they are classified as ink washes or ink degradants. These ink removers evaporate slowly, contain emulsifiers, and are used during the reclaiming process. Ink removers used while printing are classified as screen openers, press washes, or on-press cleaners. These ink removers are used to open up a clogged screen, to clean excess ink from the substrate side of the screen, and for making color changes at press. They usually evaporate faster than ink washes and preferably leave little to no oily residue so tapes can be used promptly thereafter. Ink removers are not intended to dehaze, but some show promise when used only for removing ink haze.

Haze removers traditionally contain some form of caustic ingredient, such as sodium or potassium hydroxide and/or sodium hypochlorite, and may include a solvent or solvent blend, as in the case of most single-component haze removers. They remove ink and/or emulsion ghost-haze images (stains) that remain in the mesh after removing the ink and emulsion from the screen during the reclaiming process.


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Comments

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