Discussion on the application of offset printing t

2022-09-19
  • Detail

Discussion on the application of paper packaging offset printing technology II

2.2 computer direct plate making

computer direct plate making is called CTP (compmertoplate), which is a high-tech plate making method and is used more and more widely

2.2.1 process flow

manuscript, mixed layout of graphics and texts, and zigzag proofing, laser plate making machine plate, development and plate forming before and after aging because the internal stress of aluminum alloy profile cannot be completely eliminated

2.2.2 features

(1) graphic information is stored digitally in various memories, which is convenient to save and modify

(2) omit the film production process

(3) simplify the plate making process

(4) high plate making accuracy

(5) high printing resistance of printing plate

(6) high plate cost

(7) the investment of plate making machine is high

2.2.3 CTP plate making machine

ctp plate making machine has inner drum type, outer drum type and platform type, and the light source is laser

2.2.4 plate

ctp plate includes metal plate and polyester plate

("photosensitive type (photosensitive version) CTP version: the new energy vehicle version is also vigorously trying and promoting spray free materials. There is a photosensitive coating on the surface of the material, which uses laser imaging and operates in the dark room, and the plate making speed is fast

(2) heat sensitive (thermal version) CTP version: there is a thermal coating on the surface of the plate. Using thermal imaging technology, it is operated in the open room, and the plate making quality is good

2.3 wetting

at present, China's offset printing industry is still dominated by water offset printing, and wetting is an indispensable process

2.3.1 wetting principle

surface free energy wetting liquid surface tension of blank part of printing plate surface free energy ink surface tension of image and text part of printing plate surface free energy ink surface tension, ink and image and text part of printing plate are similar and mutually soluble, liquid with low surface tension can be wetted on high-energy surface, otherwise it cannot. Wetting liquid can only be wetted in the blank part of the printing plate, not in the graphic part. After the printing plate is wetted, the ink and the wetting liquid are immiscible with each other and cannot be attached to the blank part, but only to the graphic part

2.3.2 function of wetting liquid

(1) wetting the printing plate to prevent dirty plates. The wetting liquid forms a water film that repels ink in the blank part of the printing plate and resists the expansion of ink to the blank part

(2) add hydrophilic layer, the printing plate is worn by friction, the hydrophilic layer is destroyed, and the electrolyte in the wetting solution reacts with the plate base to form a new hydrophilic layer

(3) reduce the surface temperature of the printing plate, the ink roller runs at high speed, the temperature increases, the ink viscosity decreases, and the dot expands. The wetting liquid can reduce the surface temperature of the printing plate

2.3.3 types of wetting liquid

2.3.3.1 ordinary wetting liquid

ordinary wetting liquid is mainly composed of phosphoric acid, ammonium nitrate, hydrophilic colloid, surfactant, etc. surfactant is used to reduce the surface tension of wetting liquid and improve the wetting effect

ordinary wet liquid self-adhesive mechanical testing machine has good wetting effect and low cost. The general dosage of surfactant is 0.1%. Too much will seriously emulsify the ink

2.3.3.2 alcohol wetting liquid

the main raw material of alcohol wetting liquid is ethanol or isopropanol, and the volume in the wetting liquid is 8% - 25%

alcohol wetting solution can reduce the surface tension of wetting solution, improve the film-forming condition, and the wetting effect is very good; Less liquid, less ink emulsification; Good printing quality. Alcohol wetting liquid is volatile and its concentration is unstable; Higher price; inflammable and explosive; Special wetting device and liquid volume compensation device are required

2.3.4 pH value of wetting solution

the pH value of wetting solution should be 5..0. The pH value is too small and the acidity is too large, which will corrode the plate base and slow the drying of the ink; The pH value is too large and alkaline, which destroys the hydrophilic layer and seriously emulsifies the ink. (to be continued)

Copyright © 2011 JIN SHI