Dampening solution and Dampening units_
Offset system
_Dampening Solution
In the standard offset printing procedure the dampening solution is designed to separate the image and no image spots, that is, to stop the transfer of ink to non-image zones of the printing plate. The dampening solution is made primarily of water. Experience has been shown that in conventional offset printing the dampening solution should have a pH value among the 4.8 and 5.5 and the water applied in the dampening solution need to have a hardness level of between 8 and 12° dH. Dampening solution typically has plate preservative ingredients, wetting agent, isopropyl alcohol (IPA), buffer items, and anti-microbe items. Gum Arabic is applied as plate preservative. Wetting ingredients and IPA are used to minimize surface tension. Admixed buffer components are used to stabilize the pH value. Antimicrobial chemicals are absolutely essential if the dampening solution is prepared for a couple offset printing presses in a central chemical metering device. Without these chemicals the pipelines would become blocked as a result of the expansion of algae. Alcohol-free dampening solutions have alcohol substitutes such as glycol, as a substitute for isopropyl alcohol.
Dampening Units
Conventional offset printing needs a dampening device to deliver an extremely thin film of dampening solution (approx. 2 μm) into the non-printing elements of the printing plate. Since part of the dampening solution is printed using the ink, plate, and blanket and another part evaporates, it is essential to have a regular supply of dampening solution. Dampening units have developed from the “dampening roller” used to wet the lithographic stone. Vibrator-type dampening units and non-stop flow dampening systems are systems with contact between the dampening solution pan, the dampening vibrator, and the printing plate. The problem with these dampening units is in the fact that items (e.g., particles of ink, paper dust) may get from the printing plate directly into dampening solution pan and can lead to contamination. This condition does not appear in dampening systems that are contact-free or where there can be no feedback from plate or ink flow. The volume of dampening solution has to be metered very precisely, as excess dampening solution are unable to flow back from the printing plate into the dampening unit with these systems. The units are classified as “brush-type and centrifugal dampening systems” Printing inks absorb dampening solution to a certain point. Printers talk about this as an “emulsion”. In physical/ chemical terms it is an ink/water dispersion. The dampening solution is contained in the ink in the form of droplets while some of it also sits on top of the ink film. If the dampening solution droplets fall below a certain size, the offset printing process immediately breaks down, that is, the transport of ink into the plate is no longer even or in unity with the image. The very small droplets of dampening solution indicate that separation of the printing and non-printing plate elements is no longer possible. Scumming will be the final result, that is, the non-printing spots on the plate also print.
In the standard offset printing procedure the dampening solution is designed to separate the image and no image spots, that is, to stop the transfer of ink to non-image zones of the printing plate. The dampening solution is made primarily of water. Experience has been shown that in conventional offset printing the dampening solution should have a pH value among the 4.8 and 5.5 and the water applied in the dampening solution need to have a hardness level of between 8 and 12° dH. Dampening solution typically has plate preservative ingredients, wetting agent, isopropyl alcohol (IPA), buffer items, and anti-microbe items. Gum Arabic is applied as plate preservative. Wetting ingredients and IPA are used to minimize surface tension. Admixed buffer components are used to stabilize the pH value. Antimicrobial chemicals are absolutely essential if the dampening solution is prepared for a couple offset printing presses in a central chemical metering device. Without these chemicals the pipelines would become blocked as a result of the expansion of algae. Alcohol-free dampening solutions have alcohol substitutes such as glycol, as a substitute for isopropyl alcohol.
Dampening Units
Conventional offset printing needs a dampening device to deliver an extremely thin film of dampening solution (approx. 2 μm) into the non-printing elements of the printing plate. Since part of the dampening solution is printed using the ink, plate, and blanket and another part evaporates, it is essential to have a regular supply of dampening solution. Dampening units have developed from the “dampening roller” used to wet the lithographic stone. Vibrator-type dampening units and non-stop flow dampening systems are systems with contact between the dampening solution pan, the dampening vibrator, and the printing plate. The problem with these dampening units is in the fact that items (e.g., particles of ink, paper dust) may get from the printing plate directly into dampening solution pan and can lead to contamination. This condition does not appear in dampening systems that are contact-free or where there can be no feedback from plate or ink flow. The volume of dampening solution has to be metered very precisely, as excess dampening solution are unable to flow back from the printing plate into the dampening unit with these systems. The units are classified as “brush-type and centrifugal dampening systems” Printing inks absorb dampening solution to a certain point. Printers talk about this as an “emulsion”. In physical/ chemical terms it is an ink/water dispersion. The dampening solution is contained in the ink in the form of droplets while some of it also sits on top of the ink film. If the dampening solution droplets fall below a certain size, the offset printing process immediately breaks down, that is, the transport of ink into the plate is no longer even or in unity with the image. The very small droplets of dampening solution indicate that separation of the printing and non-printing plate elements is no longer possible. Scumming will be the final result, that is, the non-printing spots on the plate also print.