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Trouble Shooting Tips For Direct Emulsions
When coating your own screens with direct liquid emulsions, it is necessary to easily identify the cause of common problems. And of course it would then be important to understand how to solve them as well. Some of the most common direct emulsion problems can be directly related to screen making. Some problems are as easy to identify. Check out this briefing on the most common issues with direct emulsions.
Formation of fish-eyes, crescents, half moons - This could be the result of inefficient mesh prep procedures. It is very important to remove all of the grease and dust. Any dirt or debris will cause emulsion problems. These problems may be easily avoided with proper mesh prep. Poorly mixed sensitizers and photopolymer emulsions that have been sitting for long periods of time and not mixed before use may also cause these symptoms.
Pinholes and/or air bubbles - Pinholes are often caused by dust or debris on the screen or in the emulsion during coating. But, pinholes may also be produced by air bubbles being left in the screen due to rapid coating passes. It is best to use a slow pass when coating the mesh with emulsion. Also, after mixing the emulsion, it is recommended to allow it to sit for some time so that all of the air bubbles introduced during mixing may settle.
Poor emulsion adhesion - This too is can be caused by improper mesh preparation. But it is a problem that may occur if the screen is exposed before it is completely dry. That is to say that if there are still high amounts of humidity in the emulsion, it can affect adhesion. This should be kept in mind if you work quickly and especially in high humidity regions. Another cause of this may be incompletely dissolved sensitizers. Make sure your emulsion is well mixed when using two part diazo or dual cure emulsions.Undercutting or loss of detail - White mesh may produce this problem by halation. This is light scatter caused by light passing through the clear film base on its way to the emulsion. This can be minimized by making sure your film positive comes in contact with the emulsion on the same side that the image was applied to the clear film base. Over exposure can also cause undercutting. Be careful to expose the emulsion just enough to thoroughly cure it.
Saw tooth effect - Poorly coated screens can be the direct cause of this all to common result. Saw tooth effect happens when the emulsion cannot bridge the gap between mesh openings especially in diagonal directions from corner to corner. It may also occur if the emulsion coating is too thin and forms to the geometry of the mesh surface. Using High quality emulsions with good bridging characteristics and creating a smooth, thick emulsion surface on the substrate side will help reduce or eliminate this.
Emulsion is difficult to reclaim - Leaving ink or tape adhesives on emulsion after using a screen for long periods of time may cause the emulsion to become permanently hardened. This may also happen with other chemicals or ink removers. Leaving excessive ink wash on a screen directly prior to reclaiming may too cause difficulty. And never spray any stencil remover onto emulsion and let the screen dry. That will harden the emulsion beyond reclaiming especially if it is allowed to sit a long time. Finally, make sure your stencil remover is compatible with your brand of emulsion. Not all emulsion removers are suitable for some emulsions.
A little bit of knowledge and some precautionary measures can save you a lot of time and wasted emulsion. Coating your screens properly will take some experience. Work with liquid and unexposed emulsion in subdued red or yellow light. And always keep your emulsion covered when not in use.