The printing industry is becoming more and more competitive, and the offset printing process technology is becoming more and more mature. In order to improve product quality, it is often necessary to start with the printing details and carefully consider its production accessories and process technology. Offset printing has the characteristics of low printing pressure, small printing deformation value, good reproduction effect of original, soft tone, clear dot, rich printing level, fast printing and low loss, so it is widely used in the printing of various products, especially suitable for printing register Transition dot version, lines, fine text, etc. Now, based on my many years of work experience, I will discuss with the industry colleagues on the control of offset printing technology.

1. Technical control of design plate making process

1. The printed solid layout should avoid the small text, lines and transition dots in the same color version, so as to avoid the phenomenon of pasting, expanded dots or insufficient ink layer due to pressure and ink volume, which will affect the quality of the product.

2. There are overprinted parts between the printing plates, and the overprint edge of one of the plates must be properly expanded or contracted to overcome the phenomenon of "whiteness" caused by inaccurate overprint.

3. When printing with four colors, please pay attention to the angle of the screen when outputting the film. Under normal circumstances, the screen angle Y90 °, M45 °, C75 °, K15 °, the general main tone version screen angle selection is 45 °.

2. Process technology control on printing

1. Temperature and humidity control of printing environment.

Controlling the temperature and humidity of the production workshop is an important part of improving the accuracy of product overprinting. The temperature and humidity of the offset printing workshop should be kept relatively balanced and the temperature should be maintained between 20 ° C and 25 ° C, and the humidity should be maintained between 50% and 60% .

2. Reasonable selection of offset PS version. PS plate plays an important role in offset printing. It is mainly composed of two parts: photosensitive layer and plate base. The thickness is generally 0.15mm ~ 0.3mm. The photosensitive layer after exposure needs to have good lipophilicity and the plate base must have Good hydrophilicity. The PS version should meet the basic performances of flat layout, uniform thickness, stable size, not easy to deform, clean surface, good dot reduction, high printing resistance, good ink and water balance during printing, and not easy to get dirty.

3. Reasonable selection of blankets. As a medium for imprinting transfer, blankets have a great influence on the quality of offset printing products. Proper selection of blankets plays an important role in improving product quality. The rubber cloth is composed of synthetic rubber and woven cloth. The woven cloth layer is usually formed by laminating 3 to 4 layers of fabric to the synthetic rubber. The selection of rubber cloth should be based on the principles of good appearance quality, high flatness, good elasticity, good ink transmission, small compression deformation, high tensile strength, small elongation, and good surface rubber characteristics. In addition, different types of blankets should be selected according to different printing materials, inks and graphics.

4. Control of offset ink-water balance. There are many factors that affect the offset ink-water balance, including the thickness of the imprinted ink layer, the nature of the printing paper, the performance of the ink, the temperature and humidity of the workshop, and the fountain solution. Among them, the characteristics of the fountain solution have a great influence, especially the pH value and conductivity of the fountain solution directly affect the quality of the printing plate, the drying speed of the ink, and the interfacial tension. Under normal circumstances, the conductivity of the fountain solution should be between 800μΩ / cm ~ 1200μΩ / cm, preferably between 800μΩ / cm ~ 900μΩ / cm. It will cause blurring of the dots; if it is lower than 800μΩ / cm, it will cause a dry plate and make the blank part of the printed product dirty. The pH of the fountain solution should be maintained between 4.5 and 5.5, at which time the dots are clearest. If it is lower than 4.0, it is easy to fall off, and if it is higher than 5.5, it is easy to paste. Therefore, to control the balance of water and ink, it is necessary to supply the fountain solution with the smallest possible amount of ink, so that the amount of ink attached to the printed product is thick enough.

5. Control of color sequence arrangement of offset printing. At present, the arrangement of the printing color sequence is not uniform. In actual production, the printing color sequence should be determined according to the characteristics of the sample, ink, paper, etc. and the specific conditions of the production workshop. Under normal circumstances, the printing color sequence should follow the following principles: the ink with strong hiding power is printed first, and the transparency is high, and the ink volume is small, and the ink volume is large.

6. Protection of printed semi-finished products and production cycle control. A high-quality product often adopts a combination of multi-process production methods according to its product characteristics. In the production process, it is inevitable that multiple printing and combined processes such as bronzing, bumping, and die cutting will occur. If the temperature and humidity of the production workshop are unstable, plastic films should be used to seal the semi-finished products at this time, so as to avoid expansion and contraction of the printed products, resulting in inaccurate overprinting in the subsequent process. At the same time, the production cycle should be rationally formulated according to the production progress of the product, and the processes should be closely connected to reduce the occupation rate of the production workshop and improve the production efficiency.

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