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Giving up the Ghost: Tips for Preventing and Removing Haze

(July 2007) posted on Wed Jul 11, 2007

Ghost haze is a problem you can conquer when you arm yourself with the proper chemicals and employ sound techniques. This article examines products that help remove ghost images as well as methods you can use to reduce or prevent their occurrence.

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By Dave Dennings

Another area we think about is the negative image created by the stenciled parts of the screen. Here, the emulsion or film used to define the customer’s artwork most often causes the ghost haze; however, the ghosting can be attributed to a combination of the emulsion and the ink staining the mesh in these areas (Figure 2).

Other considerations regarding haze

Underexposure prevents the emulsion that encapsulates the mesh from the squeegee side from absorbing enough UV light to become firmly anchored to the screen. When developed, most of this emulsion rinses away along with the unexposed emulsion from the image area. The only firmly anchored emulsion resides on the side closest to the light source—the substrate side. This leaves mesh threads on the squeegee side exposed and susceptible to staining from ink and emulsion. Additionally, a reaction may occur between partially hardened emulsion, which may remain on the squeegee side of the screen, and the ink. This reaction makes reclaiming difficult and often results in excessive ghosting.

When deciding which haze remover will best meet your needs, you want to consider which type of haze is most prevalent in your shop. If it’s ink haze, which ink formulation is the cause? Is it plastisol, UV, solvent, aqueous, conductive, ceramic? And if it’s an emulsion haze, take stock of the emulsions you use. Do you apply an SBQ pure photopolymer emulsion or a diazo, or diazo-photopolymer dual-cure product? Diazo sensitized emulsions generally have a propensity for staining mesh more often than SBQ emulsions. Water-resistant emulsions are prone to staining more often than solvent- resistant emulsions.

If you determine that ink is the only cause of your haze, you may be able to remove it by using a highly effective ink remover, sparing your screens the damage caused by unnecessarily using aggressive and caustic haze removers, thus extending the screens’ useful life. If, on the other hand, you’ve determined that emulsion is the only cause of your haze, you may not need to use a solvent activator with your haze remover in the case where two-part haze removers are used, thereby saving you time and money.


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