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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.


Classifying ghost images
The two basic types of ghost haze are stains left by the printing ink and those left by the emulsion. The severity of ghosting often depends on the type of ink used. For example, catalyzed inks contain solvents that react with low-surface-energy substrates to improve ink adhesion. These types of inks can create ghost haze that is difficult to remove. Inks also contain pigments that get trapped in between the knuckles of the mesh, bond to the mesh, or become partially dissolved by hot solvents and slightly penetrate the mesh.

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.

Other considerations
Underexposure prevents the emulsion that encapsulates the mesh from the squeegee side from absorbing enough UV light to become anchored firmly 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 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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Comments

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