Several screen printing facilities have struggled with mesh staining in one way or another. Staining generally occurs in two different forms. One is staining from the emulsion on the screen and the other stems from the type of ink used in the screen printing process.
First, let’s look at the staining of the mesh from the emulsion on the screen. The biggest cause of emulsion staining is due to the under exposure of the screen. When you have emulsion that is not 100% exposed you allow chemicals such as a hot solvent (lacquer thinner, xylol, and screen opener) to crosslink with the emulsion during the printing process. If you allow the emulsion to crosslink with a solvent, you will create a light deposit of emulsion that will be difficult to remove in the reclaiming process. If the light emulsion stain is repeated on a screen, you will likely have to resort to using a ghost and haze remover to remover the staining. As we all know, ghost and haze removers are damaging to screen mesh and shorten the life of a screen.
A couple of general procedures for finding the perfect exposure for a screen are as follows:
1. Perform an exposure test for each mesh count/thread diameter to dial-in the best exposure time for a favorable outcome.
2. Try matching your artwork (halftones, line count) to the proper mesh count, open print area, and thread diameter. Each one of the previous variables will deposit a slightly different ink film.
The second form of staining we commonly run into is the type of ink used in the screen printing process. There are primarily plastisol ink, nylon ink and water based inks for the textile market and solvent, epoxy, enamel, ultraviolet inks for the graphics market. Ink choice sometimes can be an option driven by the substrate we are printing on such as cotton or polyester garments, flat sheet polyester substrates, polycarbonates, vinyl’s, untreated polyesters, etc.
In this case, we need to pay close attention to the products we are applying to our screens as a press wash. Hot solvents have a fast flashpoint and can quickly lock-in an ink stain in the open mesh printing area. In the textile market, PlastiSolv 842 is commonly used for all on-press chemical requirements and will remove most, if not all, of the ink in a screen. If a light stain is still present, the remaining stain can be removed by applying Easisolv 701 screen wash and stain remover. In the case of a graphic ink removing a stain set-in with a hot solvent (like an epoxy or enamel extremely) can be extremely difficult. Be sure to use an on-press solvent formulated for the screen printing industry such as Easisolv 110, Easisolv 120 or Easisolv 140.
Here are a few helpful tips that you can implement to help reduce ink staining during your screen printing process:
1. Use a press wash to clean the image area when your screen is sitting idle for a period of time such as 15 minute breaks, lunch hour, or similar time periods.
2. When your job is complete, be sure to clean out the image area with a press wash so that the remaining ink does not begin to set an ink stain before the reclaiming process. If your screen is not going to be saved for a repeat order and cataloged for future use, another suggestion is to clean the image area with a screen wash such as Easisolv 701.
Written By: Rick Christian | Easiway Systems | Regional Manager East Coast
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