Offset Printing - The Basic Introduction

Offset printing is an indirect lithographic printing technology. It is so very respected between printing service agencies and clients because for big amounts, it turns out being less expensive and still have much better quality compared to alternative technologies. The offset printing technology is currently the main printing technology. In the offset printing process the printing and non-printing areas of the plate are basically on one level.The printing areas of the printing plate are oleophilic/ink-accepting as well as water-repellent, that is, hydrophobic.The non-printing regions in the printing plate are hydrophilic,thence oleo-phobic in behavior. This effect is generated by physical phenomena at the contact surfaces. The dampening system covers the non-printing areas of the printing plate with a thin film of dampening solution.This dampening solution (water plus additives)spreads over the non-printing areas. To achieve good wetting, surface tension is required to be reduced by means of dampening solution additives. In extraordinary situations, reducing the surface tension of the dampening solution too much may end up in too great an emulsification of printing ink and also dampening solution, leading to a situation where an explicit spiting up of printing and non-printing areas on the plate is not achieved when inking. The perfect offset printing process is dependent upon many chemical together with physical details of the materials and components associated with the process. The most important are : • Influence of the printing plate– surface tension of the ink-accepting spots,– surface tension of the dampening solution accepting areas,– surface roughness, primarily of the ink-free/non-image surface,– construction technologies in making the offset plate(mechanical or electrolytic graining, etc.); • Influence of the inking rollers– characteristics of the roller coverings,– surface tension of the roller material,– surface roughness,– concentric running; • Influence of the blanket– surface tension of the blanket,– surface roughness,– compressibility,– ink acclaim and ink transport behavior, • Influence of the printing ink– surface tension, contact surface tension in relation to the dampening solution,– rheological properties (viscosity, tack, etc.),– dampening solution absorption/emulsification– running clean behavior at the time of start-up,– ink composition,– drying behavior; • Influence of the dampening solution– water hardness/impurities,– dampening solution components (alcohol, detergents,buffer agents),– pH value, surface tension,– rheological features (viscosity, tack),– dependence on temperature of the rheological characteristics; • Influence of the substrate– printability capabilities (smoothness, absorption capacity, wettability),– pH value of the substrate,– workability properties (tension/stretch behavior,picking, tearing); • Influence of the printing press (on print quality and process stability)– design of the printing unit (accurate, steady,vibration absorbent, etc.),– design of the inking component (front-heavy, back-heavy,free surface, little retro-action),– design of the dampening equipment (contact dampening,non-contact dampening),– creation of the ink feed system (ink metering)