January 2017
e-VIBES
January 2017
0.05 second!) THE DAMPENIONG SOLUTION HAS WETTING AGENTS TO ACHIEVE THIS FEAT. To keep the non-printing surface from getting sensitized, de-sensitizers are provided in the fount solution. Another important function of the water and fount solution is the lubrication and anti piling. Fountain solution concentrates should contain lubricants and“ release” agents for blankets. The film of water on the plate slows down the wear due to friction, thus increasing plate life. Also this reduction in the friction prevents the ink train and plate surface from overheating! Further during the printing the paper lint and dried ink resin do build up on the blanket and this is called piling or linting. The release agents in the fount solution help to prevent the blanket from becoming“ sticky”, thereby avoiding excessive paper linting. Another important function of dampening is to prevent excessive emulsification of water in the ink. The tiny ink or pigment particles floating in the water can stain the non printing areas or print as light tone- this defect is called tinting. An overall understanding of the ingredients used in the fountain solution may help. The essential ones are:
Water soluble gums
pH buffer system
Desensitizing salts
Acids and their salts
Wetting agents
Solvents
Non-piling and lubricating agents
Emulsion control agents
Viscosity builders
Biocides to prevent fungus, bacteria and moulds
Deforming agents It is necessary to keep the non image areas from getting sensitized to ink. As the plate wears and is constantly getting exposed to ink and dirt, the tendency of the plate is to get sensitized. Hence there must be a continual desensitization process. Gum Arabic, the dried sap of acacia tree is water soluble and has high affinity for aluminum metal. This is the best de-sensitizer.( This works better at water pH near four). Other water soluble starches and acrylic polymers are also used in the solution. These chemicals, a small amount of them adheres to the non printing areas providing a thin protective film. Also when the press is stopped for any length of time or for the plates stored for a re-run, it is very important that gum is applied. Acids, such as phosphoric are used for metal cleaning and brighten the surface. This is called“ etching. A very thin layer of the metal, only a few molecules thick, is continually dissolved off the plate, continually exposing a fresh surface. It is necessary to know pH and conductivity, which are deeply associated with water and dampening: pH. The gum Arabic, the great de-sensitizer works the best in a controlled pH value. The best water is with neutral pH at 7. However it is preferred to keep the water in the acidic side at 4.5 pH to start with. The water chemistry will change depending on the source. The quality will also change between seasons. It is essential to control the fresh input water quality. In the absence it is difficult to control their properties even by using the best of dampening concentrate. Conductivity control is being considered as an important element in quality management, as the commercial concentrates are buffered for sustaining a definite pH even for any long run printing. To say the truth, the water and dampening are the least understood area in the printing.
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