The most common reclaim chemical in the screen industry is sodium metaperiodate. So there it is: bleach is slower, less green and, most importantly, considerably less reliable than SMP. Certain types of emulsion, such as 925WR, are hard to reclaim with bleach of any concentration. The optimal concentration varies for each emulsion blend. If the concentration is too high, there's danger of a lock-in from an oxidation-reduction reaction too low a concentration, and there's no effect. He says that bleach is both slower than SMP and environmentally harsher.Ĭontrolling the dilution of bleach as it contacts the stencil during decoating is difficult. I've discussed your question about using bleach as stencil remover with our senior chemist. The stencil remover chemical creates another reaction with under-exposed stencil and forms a chemical bond with the mesh that is very difficult to remove. When you spray stencil remover on the stencil, it has to penetrate and attack the chemical crosslinks formed by UV exposure. Many low energy UV lamps may never penetrate a thick stencil. If you double a distance energy has to travel, it takes 4 times the energy - NOT double. The deeper the UV energy has to penetrate, the longer it takes based on the physics rule called the Inverse Square Law. Penetration of UV energy is not 'linear'. This is always on the inside of the stencil because invisible UV energy didn't have enough time to move all the way through the stencil to the inside. Under exposed means some of the sensitizer did not cross link. Under exposed stencils are harder to remove than completely cured/exposed stencils. It locks the stencil in the mesh with a permanent chemical bond. Try switching to one of Franmar's friendly ink cleaners.It is very important to never let the stencil remover dry. Third, some "hot" solvents used in cleaning (paint thinners and mineral spirits, for example) can begin to lock in emulsion. Test to make sure the emulsion is being properly exposed. Second, there may be an under-curing or over-curing problem with the emulsion.
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