Offset Printing

Offset printing is an indirect lithographic printing technology. It is so respected among printing service providers as well as end users for the reason that for big amounts, it turns out being less expensive and have absolutely much higher quality in comparison with alternative methods.

The offset printing technology is at the moment the main printing technology. Inside the offset printing process the printing and non printingareas of the plate are basically on one level.The printing fields of the printing plate are oleophilic/ink-accepting as well as water-repellent, that is, hydrophobic.The non-printing areas of the printing plate are hydrophilic,thus oleophobic in behavior. This effect is done 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 obtain good wetting, surface tension is required to be reduced by means of dampening solution additives. In extraordinary instances, reducing the surface tension of the dampening solution too much can result in too great an emulsification of printing ink and dampening solution, leading to a situation where a precise split of printing and non-printing areas on the plate is not really realized when inking.The ideal offset printing process depends on many chemical as well as physical specifics of the materials and components involved in the process. The most important are :
• Influence of the printing plate– surface tension of the ink-accepting zones,– surface tension of the dampening solution accepting areas,– surface roughness, specifically of the ink-free/non-image surface,– production processes in producing the offset plate(mechanical or electrolytic graining, etc.);
• Influence of the inking rollers– qualities 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 acceptance and ink transfer behavior,
• Influence of the ink– surface tension, contact surface tension in relation to the dampening solution,– rheological attributes (viscosity, tack, etc.),– dampening solution absorption/emulsification– running clean behavior in the start-up,– ink composition,– drying behavior;
• Influence of the dampening solution– water hardness/impurities,– dampening solution additives (alcohol, detergents,buffer agents),– pH value, surface tension,– rheological properties (viscosity, tack),– dependence on temperature of the rheological characteristics;
• Influence of the substrate– printability features (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 (effective, stablised,vibration absorbent, etc.),– design of the inking unit (front-heavy, backheavy,free surface, little retroaction),– design of the dampening unit (contact dampening,non-contact dampening),– creation of the ink feed system (ink metering)

Article Tags: Offset Printing, Printing Plate, Non-printing Areas, Dampening Solution, Surface Tension

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