The importance of haze removal:
Most ghost images are made up of microscopic residues on the mesh left over from the previous job. These residues not only prevent the stencil from adhering properly, they can even affect the way in which the ink flows through the mesh to cause a latent ‘ghost’ image in the print. Therefore it is very important that these residues are removed from the mesh during the cleaning process.
Prevention is better than cure
Before going into detail about haze removal it is worth stating that a few simple steps can be taken to reduce, or even eliminate, the formation of screen haze and stains. Exposing screens correctly, cleaning them as soon as possible after printing and using the right Screen Wash, can minimise and even eliminate the need for an additional haze removal process, saving time and money.
Identifying the type of stain
Typically ghost images come from one or more of the following: fused Acetate (‘locked-in screens’) or Diazo from the stencil, ink that has dried-in, ink staining of the mesh fibres, or even mechanical abrasion of the mesh itself. Knowing the root cause of the stain will then help you choose the ideal haze remover to clean it.#ScreenPrinitngTopTip: As a simple guide if the stain is the same as the print, then it has come from the ink and if it is a negative of the print, it has come from the stencil.
Haze removers are powerful chemicals and must be handled carefully. Always read the Safety Data Sheet before use and wear PPE when handling them. It is very important to always rinse off any haze remover with a low pressure spray before using the High Pressure Gun, otherwise you will atomise the chemical and expose the operator to this mist. Did you know, when atomised caustic lands on screens that have already been cleaned they will produce pinholes the next time they are used?
All caustics react with aluminium, so take care when applying the low viscosity haze removers to aluminium frames and do not leave in an aluminium scoop coater overnight.
#ScreenPrinintgTopTip: A High Pressure Gun should be classed as an essential piece of screen making equipment as it will save you time, money and materials in cleaning screens. A good quality industrial High Pressure Gun producing at least 75 BAR will clean screens quicker and outlast the cheaper alternatives.