Offset plate and its process control considerations
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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 details of the printing, careful and thoughtful consideration of its production accessories and process technology. Offset printing has the characteristics of small printing pressure, small printing deformation value, good original rendering effect, soft color tone, clear dot, rich printing layer, fast printing and low loss. It is widely used in the printing of various products, especially suitable for printing color. Transition dot version, lines, small text, etc. Now combined with my many years of work experience, for the control of offset printing technology, and colleagues in the industry to discuss.
First, design plate technology technology control
1. The printed solid layout should avoid the use of small characters, lines and transitional dots in the same color version, so as to avoid the phenomenon that the pressure, the amount of ink can not be balanced, the paste is enlarged, the dot is enlarged or the ink layer is not thick enough, which affects the product quality.
2. There are overprinting parts between the printing plates. The overprinting edge of one of the plates must be properly expanded to overcome the phenomenon of “whitening” of the edges due to inaccurate overprinting.
3. When printing in four colors, pay attention to the angle of the cable when making the film. Normally, the cable angles are Y90°, M45°, C75°, and K15°. Generally, the angle of the main tone screen is 45°.
Second, the process technology control on printing
1. Temperature and humidity control of the 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 relatively balanced and the temperature should be kept between 20~25°C, and the humidity should be kept between 50%~60%.
2. Reasonable selection of offset PS version. PS plate plays an important role in offset printing. It is mainly composed of two layers of photosensitive layer and plate base. The thickness is generally 0.15~0.3mm. It is required that the photosensitive layer after exposure should have good lipophilicity and the base should be good. Hydrophilicity. PS plate should meet the basic performances such as flat layout, uniform thickness, stable size, not easy to deform, clean surface, good dot reduction, high printing durability, good ink balance during printing, and not easy to get dirty.
3. Reasonable selection of blankets. As the medium of imprint transfer, the blanket has a great influence on the quality of offset printing products. The correct selection of blankets plays an important role in improving product quality. The blanket is composed of synthetic rubber and woven fabric, and the woven fabric layer is usually formed by laminating 3 to 4 layers of fabric onto synthetic rubber. The selection of the blanket should be based on the principle of good appearance quality, high flatness, good elasticity, good ink transfer, small compressive deformation, high tensile strength, small elongation and good surface rubber properties. In addition, different types of blankets should be selected according to different printing substrates, inks and graphics.
4. Control of offset ink and wash balance. There are many factors affecting the balance of offset ink, including the thickness of the imprinted ink layer, the properties of the printing paper, the performance of the ink, the temperature and humidity of the workshop, and the dampening solution. The characteristics of the dampening solution have a great influence, especially the pH value and conductivity of the dampening solution directly affect the printing plate quality, ink drying speed and interfacial tension. Under normal circumstances, the conductivity of the dampening solution should be between 800 and 1200 μΩ/cm, preferably between 800 and 900 μΩ/cm. If it is higher than 1200 μΩ/cm, the emulsification of the ink is intensified, resulting in blurring of the dots; If it is less than 800μΩ/cm, it will cause a dry plate, which will make the blank part of the print dirty. The pH of the dampening solution should be kept between 4.5 and 5.5, when the dots are the clearest. If it is lower than 4.0, it is easy to lose the plate, and if it is higher than 5.5, it is easy to paste. Therefore, to control the balance of ink and water, it is necessary to use a supply of fountain solution as small as possible to make a sufficient amount of ink adhered to the printed product, and to avoid the use of the "ink and water" balance method printing.
5, the control of offset printing color sequence arrangement. 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 arrangement should follow the following principles: the ink with strong hiding power is printed first, and the printing with high transparency; the printing with small ink volume and the printing with large ink volume;
6. Protection of printed semi-finished products and control of production cycle. A high-quality product, according to its product characteristics, often uses a combination of multi-process production methods, in the production process will inevitably appear multiple printing and bronzing, bump, die-cutting and other combined processes. If the temperature and humidity of the production workshop are unstable, the semi-finished product should be sealed with a plastic film at this time to prevent the printed product from being deformed and deformed, resulting in inaccurate overprinting of the subsequent process. At the same time, according to the production progress of the product, the production cycle should be reasonably established, and the processes should be closely connected to reduce the occupation rate of the production workshop and improve the production efficiency.