With the increasingly fierce competition in the printing industry today, the offset printing process technology has become more and more mature. In order to improve the quality of products, it is often necessary to start with the details of printing, careful and thoughtful consideration of its production of auxiliary materials and process technology. Offset printing has the characteristics of low printing pressure, small print distortion value, good manuscript reproduction effect, soft color tone, clear dots, rich printing layers, fast printing, low loss, etc. Therefore, it is widely used in the printing of various products, especially suitable for printing. Transition points, lines, small texts, and more. Now with my many years of work experience, I will discuss with the industry peers about the control of offset printing technology.
1 Design process technology control
1) Printing on-site layouts should avoid the inclusion of fine text, lines, and transitional dots in the same color version, so as to avoid the phenomena of paste, dot expansion, or lack of ink layer due to incompressibility of pressure, ink, etc., and affect product quality.
2) If the overprint exists between the printing plates, the overprinting edge of one of the plates must be appropriately enlarged and contracted to overcome the phenomenon of “whitening†on the edges due to inaccurate overprinting.
3) In four-color printing, the screen angle must be taken into account when the plate is output. Under normal circumstances, the network cable angles Y90°, M 45°, C 75°, and K 15°, and the main color version network line angle is selected to be 45°.
2 Printing Technology Control
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 shop should be kept relatively balanced and the temperature should be kept between 20-25°C, and the humidity should be maintained between 50%-60%.
2) Reasonable selection of offset PS plate. PS version 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 requires the photosensitive layer after exposure to have good oleophilicity, and the printing plate should have good The hydrophilicity. PS version should meet the basic layout, uniform thickness, dimensional stability, not easily deformed, the surface is clean, the dot reducibility is good, the printing rate is high, the printing ink balance is good, not easy to dirt and other basic properties.
3) Reasonable selection of blankets. Blanket used as a medium for blotting transfer has a great influence on the quality of offset printing products. Correct selection of blankets plays an important role in improving product quality. The blanket is composed of synthetic rubber and a woven fabric, and the woven fabric layer is usually formed by attaching 3 to 4 layers of fabric to the synthetic rubber. The selection of blankets should be based on the principle of good appearance quality, high flatness, good elasticity, good ink transfer, small amount of compression 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 balance. There are many factors that affect the offset ink-ink balance, including the thickness of the ink layer, the properties of the printing paper, the ink properties, the temperature and humidity of the workshop, and the fountain solution. Among them, the characteristics of fountain solution have a great influence, especially the pH and conductivity of fountain solution directly affect the quality of printing plate, ink drying speed, interfacial tension and so on. Under normal circumstances, the conductivity of fountain solution should be
800~1200μΩ/cm, preferably between 800~900μΩ/cm. If it is higher than 1200μΩ/cm, the emulsification of the ink will be exacerbated and the dots will be blurred. If it is less than 800μΩ/cm, it will cause dry printing. Make the blank part of the print dirty. The pH of the fountain solution should be kept between 4.5 and 5.5, with the clearest dots. If it is lower than 4.0, it is easy to lose the version, 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 provide as small a fountain solution as possible to allow the ink to adhere to a sufficient amount of ink, and the printing method using the ink-heavy-water balance method should be avoided.
5) Control of the arrangement of color printing in offset printing. At present, the arrangement of printing color sequence is not uniform. In actual production, the color sequence of printing should be determined according to the characteristics of the sample draft, ink, paper, and the specific conditions of the production workshop. Under normal circumstances, the printing color sequence arrangement should follow the following principles: strong ink-covering with high hiding power, high-transparency after-printing, first printing with small ink volume, and large-printing ink;
6) Protection of printed semi-finished products and control of production cycle. A high-quality product, based on the characteristics of its products, often uses a combination of multi-process production methods. In the production process, it is inevitable that there will be multiple printing and combination processes such as bronzing, embossing, and die cutting. If the temperature and humidity of the production workshop are not stable, the semi-finished products should be sealed with plastic film at this time to avoid the telescopic deformation of the printed products, resulting in inaccurate overprinting of subsequent processes. At the same time, according to the production schedule of the product, the production cycle should be reasonably established, the processes should be closely linked, the occupation rate of the production workshop should be reduced, and the production efficiency should be improved.
Source: "Printing World"
Author: Wang Jun
1 Design process technology control
1) Printing on-site layouts should avoid the inclusion of fine text, lines, and transitional dots in the same color version, so as to avoid the phenomena of paste, dot expansion, or lack of ink layer due to incompressibility of pressure, ink, etc., and affect product quality.
2) If the overprint exists between the printing plates, the overprinting edge of one of the plates must be appropriately enlarged and contracted to overcome the phenomenon of “whitening†on the edges due to inaccurate overprinting.
3) In four-color printing, the screen angle must be taken into account when the plate is output. Under normal circumstances, the network cable angles Y90°, M 45°, C 75°, and K 15°, and the main color version network line angle is selected to be 45°.
2 Printing Technology Control
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 shop should be kept relatively balanced and the temperature should be kept between 20-25°C, and the humidity should be maintained between 50%-60%.
2) Reasonable selection of offset PS plate. PS version 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 requires the photosensitive layer after exposure to have good oleophilicity, and the printing plate should have good The hydrophilicity. PS version should meet the basic layout, uniform thickness, dimensional stability, not easily deformed, the surface is clean, the dot reducibility is good, the printing rate is high, the printing ink balance is good, not easy to dirt and other basic properties.
3) Reasonable selection of blankets. Blanket used as a medium for blotting transfer has a great influence on the quality of offset printing products. Correct selection of blankets plays an important role in improving product quality. The blanket is composed of synthetic rubber and a woven fabric, and the woven fabric layer is usually formed by attaching 3 to 4 layers of fabric to the synthetic rubber. The selection of blankets should be based on the principle of good appearance quality, high flatness, good elasticity, good ink transfer, small amount of compression 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 balance. There are many factors that affect the offset ink-ink balance, including the thickness of the ink layer, the properties of the printing paper, the ink properties, the temperature and humidity of the workshop, and the fountain solution. Among them, the characteristics of fountain solution have a great influence, especially the pH and conductivity of fountain solution directly affect the quality of printing plate, ink drying speed, interfacial tension and so on. Under normal circumstances, the conductivity of fountain solution should be
800~1200μΩ/cm, preferably between 800~900μΩ/cm. If it is higher than 1200μΩ/cm, the emulsification of the ink will be exacerbated and the dots will be blurred. If it is less than 800μΩ/cm, it will cause dry printing. Make the blank part of the print dirty. The pH of the fountain solution should be kept between 4.5 and 5.5, with the clearest dots. If it is lower than 4.0, it is easy to lose the version, 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 provide as small a fountain solution as possible to allow the ink to adhere to a sufficient amount of ink, and the printing method using the ink-heavy-water balance method should be avoided.
5) Control of the arrangement of color printing in offset printing. At present, the arrangement of printing color sequence is not uniform. In actual production, the color sequence of printing should be determined according to the characteristics of the sample draft, ink, paper, and the specific conditions of the production workshop. Under normal circumstances, the printing color sequence arrangement should follow the following principles: strong ink-covering with high hiding power, high-transparency after-printing, first printing with small ink volume, and large-printing ink;
6) Protection of printed semi-finished products and control of production cycle. A high-quality product, based on the characteristics of its products, often uses a combination of multi-process production methods. In the production process, it is inevitable that there will be multiple printing and combination processes such as bronzing, embossing, and die cutting. If the temperature and humidity of the production workshop are not stable, the semi-finished products should be sealed with plastic film at this time to avoid the telescopic deformation of the printed products, resulting in inaccurate overprinting of subsequent processes. At the same time, according to the production schedule of the product, the production cycle should be reasonably established, the processes should be closely linked, the occupation rate of the production workshop should be reduced, and the production efficiency should be improved.
Source: "Printing World"
Author: Wang Jun
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