The technical problems produced by offset printing in production and use mainly have the following three points:
1. Master the exposure time and development time in offset printing
Control of offset printing mastering the ratio of exposure time, development time, developer humidity, and concentration is one of the ways to reduce the expansion and shrinkage of the dot. The four-color film separated by color transfers the graphic dots to the printing plate through the printing process, requiring the expansion and loss of dots as little as possible, 3% to 5% dots are not lost, 5% dots are not expanded, 95 % ~ 98% of the dots are not paste version, the dots are strong, the particles are round and neat, the dots have no white dots, burrs, and the levels are rich, complete and clear.
This requires accurate preparation of the ps version of the developer, according to the formula ratio of the developer's instructions. Do not add more or less. The exposure time is controlled by the gray scale and the signal plate for printing. The printing plate is used after it is exposed. The magnifying glass inspection of 5 to 10 times is lost at the level of the ladder and signal bar, and the paste version and the network point are expanded.
2. Reasonably select the offset printing liner material to adjust the printing pressure
Offset printing has three forms of hard, neutral and soft liner, which is the best? It can be said that each has its own characteristics. Offset printing is an indirect printing method. It requires an elastic body in the middle of the rubber cylinder to transfer the graphic dots of the printing plate to the surface of the paper. The rubber patch and its lining material are the middle of the graphic transfer in offset printing. There is no printing pressure for the media, and there is no indirect printing and no offset printing.
By adjusting the thickness of the liner of the offset printing machine, you can get a reasonable and optimal printing pressure, enhance the uniformity of the ink density of the printed product and the clarity of the dots. In addition, the reasonable installation of the liner reduces the dot expansion and improves The durability of the printing plate is very beneficial.
The printing pressure is obtained by two methods of adjusting the thickness of the lining and the center distance of the cylinder. In general, the appropriateness of the printing pressure is often expressed by the quality of the printed matter.
The pressure should be based on the premise that the printed product has strong dots, clear graphics, bright colors and shades, and the smaller the applied, the better. It is critical to control the expansion of the dots and adjust the accurate printing pressure. The printing pressure is large, and the dots are expand.
Accurately calculate and use a micrometer to measure the thickness of the rubber roller lining in the work, adjust the center distance between the two rollers, and use the minimum printing pressure evenly on the basis that the footprint is sufficiently strong within the allowable range of the dot expansion.
3. Offset printing controls the balance of water and ink, reducing the expansion of the network
Offset printing must be controlled to control the water and ink balance to improve the quality of the printed product. It is recommended to use as little water as possible on the premise of not dirty plates and paste plates, so as to compare with the emulsification of ink and the expansion and contraction of paper. The operator's technical level is high, only when the ink and water balance is reached, the paper has small expansion and deformation, high overprint accuracy, bright colors, and colors and hues can meet the proofs. A batch of printed inks have the same color depth, and the printed dot particles are round and strong. The network cable is uniform, and it also reduces the expansion of the network.
When offset printing, avoid the large dots of water and ink, the dots of the ink layer spreading outwards are too thick, control the small dots of 3% to 5% of the bright tone area, do not lose, the 5% of the intermediate tone dots do not expand, do not stretch, dark tone area 95% to 97% of the large dots are not confused. The control standard for the amount of ink is: the graphic dots are strong and clear, and the color and hue of the printed ink are accurate. Use as little ink as possible.
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