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.
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.
Classifying ghost images
The two basic types of ghost haze are stains left by the printing ink and those left by the emulsion. The one not so basic form of ghosting is referred to as latent or phantom haze. We’ll talk about that at the end of this article.
The first thing we think about when discussing ghost images is a stain of the printed image that remains in the mesh after reclaiming. 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 (Figure 1).
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