8 factors affecting the quality of color box printing
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1. The effect of film film on the quality of color box printing
The development and fixing process of film film after exposure is directly related to the sharpness and contrast of the image on the film. Therefore, for plate-making film, the key is to see the density of the graphic part and the contrast between the graphic part and the non-image part. The higher the density, the greater the contrast, the better the quality of the plate-making film, and the quality of the plate printing produced by it can be guaranteed. In addition, the thickness of the plate-making film base also has an effect on the quality of the plate making. Generally, the film has a better effect than the thick film.
2. The effect of printing on the quality of color box printing
In the process of printing, the intensity of the light source, the distance between the light source and the plate, and the length of the exposure time will affect the quality of the printing plate. The light source is strong, the distance is short, and the exposure time is relatively short; the light source is weak, the distance is long, and the exposure time is relatively long. Under a certain light source and distance, as the exposure time increases, the decomposition of the film in the plate sees light is intensified until the film surface is completely decomposed. If the exposure time continues to increase, the edge of the film surface is not visible due to the radiation of strong light, and the photosensitive film begins to gradually decompose, so that the printed graphic lines will become thinner, even broken, and molded. . If the exposure time is insufficient, the non-image part will not completely decompose the film surface, and there will still be a film in the non-image part after the printing plate is developed, and it will be dirty when printed on the machine. In addition, the exposure time required for different brands of plates is different, which must be noticed.
In addition, when the vacuum is applied to the printing plate, the degree of close contact between the film and the printing plate also affects the quality of the printing plate. If the sticker is not applied, the printed printing plate may have problems such as ghosting and unclearness.
3. The effect of development on the quality of color box printing
3.1 developer concentration
The developer concentration is too large, the development is too fast, it is easy to cause excessive development of the printing plate, the lines of the graphic are thinner, the small dots are lost or the graphics are faint, which affects the printing quality of the color box; the developer concentration is too small, see the photolysis drug The film surface is not easy to clean, and it is easy to get dirty when printing on the machine.
3.2 development time
If the development time is too long, the film surface of the printing plate that is not visible will be easily dissolved, and the printing plate will become lighter and thinner, resulting in imprinting and unclear printing. The development time is too short, and the photolysis film is seen. The surface is not easy to remove completely, and it is easy to get dirty when printing. A suitable development time is when the printing plate is developed and rinsed, and the photodecomposed film surface is just rinsed out. If the concentration of the liquid is relatively large, the development time should be shortened accordingly; conversely, the development time should be extended accordingly.
4. The effect of ink transfer on the quality of color box printing
The printing process is actually the process of ink transfer. Generally speaking, the ink transfer rate of offset printing is relatively low, about 38%. After the printing plate is in contact with the blanket, the ink transfer rate is about 50%, and the blanket is in contact with the paper, and the ink transfer rate is about 76%. Therefore, controlling the transfer rate of ink is critical. Ink suitability, ink balance, plate, blanket performance, paper, printing press, etc. all affect the transfer of ink.
4.1 Effect of ink properties on ink delivery
Ink with low viscosity and high fluidity is easy to transfer, and the transfer rate is high; the ink with high viscosity and low fluidity has a low transfer rate. To increase the ink transfer rate, the viscosity and fluidity of the ink must be controlled. The performance of the ink also changes with the environment. When the temperature is high, the viscosity of the ink is low, and when the temperature is low, the viscosity of the ink is high. In actual production, inks of different types, types and different drying methods should be selected according to actual conditions. In addition, by adding an appropriate amount of varnish to the ink, the performance of the ink can be adjusted, which is advantageous for controlling the dot gain and increasing the ink transfer rate.
4.2 The effect of blanket performance on ink delivery
The rubber cloth must have good ink absorption and ink transmission properties, and must also have the characteristics of oil resistance, acid resistance, alkali resistance and elasticity. If the blanket is not thoroughly cleaned after printing, the ink retained in the fluff will slowly harden the conjunctiva, which will damage the villus-like structure of the rubber surface, directly affecting the ink receiving rate of the blanket, thereby reducing the ink transfer rate of the blanket. Therefore, after the printing is completed, the blanket should be thoroughly cleaned. If the downtime is relatively long, a layer of pumice powder can be rubbed on the surface to keep the original fluffy structure of the blanket surface, and the blanket has good ink absorption and ink transfer.
5. The influence of paper suitability on the quality of color box printing
The suitability of paper is mainly reflected in smoothness, whiteness and stiffness. Paper with a high smoothness requires a relatively small amount of ink; paper with a poor smoothness requires a relatively large amount of ink. In the printing process, different papers vary according to their surface conditions, and the amount of ink required changes accordingly. Under the same variety, same quantitative, and the same price, the paper with higher smoothness and whiteness is better than the paper with lower smoothness and whiteness.
6. The influence of plate suitability on the quality of color box printing
The quality of the base plate of the plate, the hydrophilicity of the metal plate and the lipophilicity of the surface of the coated polymer resin are related to the suitability of the plate, affecting the ink transfer and the balance of the ink on the plate. In the process of plate making, the quality of exposure and development will also affect the performance of the plate.
7. Influence of ink balance on the quality of color box printing
Ink balance is a relative balance, not an absolute balance. During the high-speed operation of the equipment, the graphic part and the non-image part of the printing plate are both inked, watered and infiltrated, so ink emulsification will inevitably occur on the printing plate. If the amount of water and ink is not well controlled, it will inevitably deepen the emulsification of the ink, resulting in the occurrence of stencils and dirty plates in printing. Printing is usually done by reducing the amount of water and increasing the amount of ink, but sometimes it also reduces the amount of ink. In addition, the ink emulsification will change with the change of environmental conditions. In the actual printing production, the ink viscosity and the pH value of the fountain solution should be well controlled according to the actual situation, and the ink volume and water volume should be controlled. The 煳 version and the non-dirty version are the benchmarks.
8. Influence of printing pressure on the quality of color box printing
The printing pressure refers to the interaction force between the plate cylinder and the blanket cylinder, and between the blanket cylinder and the impression cylinder, which is a necessary condition for ink transfer. The printing pressure is too small, the ink is not easy to transfer, the ink is light and faint; the printing pressure is too large, and the ink volume expands to the non-image part, which makes the dot increase serious, the image is distorted, and the printing plate and the blanket are easy to resist. decline. Therefore, the mechanical pressure must be properly adjusted. Different quantitative papers require different printing pressures, and only the proper printing pressure can ensure uniform ink color and uniformity.