What are they and how do you get rid of them?
A ghost image is a stain the mesh of the screen. This can occur from either the ink used or the emulsion used to create the image. Most printers experience both types of ghost images.
-Solvent or catalyzed inks can create staining of the mesh by penetrating the mesh usually due to reacting with the “hot” solvents required for cleaning.
-Emulsion created ghost images are created by partially unexposed emulsion reacting with the ink and solvents used in cleanup.
There are several causes for ghosting :
- Screen tension- low tension screens require more off contact to get the ink to the garment. This excessive pressure can trap pigments into the mesh.
- Abraders during screen prep. These can scratch the surface of the mesh creating areas for pigments to settle.
- Humidity – improper drying of the mesh does not allow the emulsion to cross-link to the mesh. This will create emulsion ghosting.
- Underexposure – under exposure leaves parts of the emulsion soft and they cannot cross link with the mesh. This makes the emulsion difficult to remove in the reclaim process and can leave behind thin layers around the image area.
- Improper clean-up -
- cleaning from only one side of the screen can create issues by pushing chemical or unexposed emulsions to the opposite side of the screen. All cleaning and rinsing should be done on both sides of the screen
- Hot solvents - such as lacquer thinner can cause emulsions to swell and trap pigments in the weave.
- Ink removal delay- waiting to remove inks, especially solvent based inks, makes removing the stains even more difficult.
Follow instruction on haze removal products. Most chemicals require a 3-30 minutes wait time for the chemical to work.
Making sure that your stencil preparation, exposure and screen tension are correct will help to reduce ghost images in your screens.