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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