How to print a large area of offset field
Time:2023-02-21
Views:1905
The consistency of ink color includes two aspects: one is the consistency of ink color of different printing sheets; The second is the consistency of ink color in different parts of the same sheet. Among them, the ink consistency requirements of different parts of the same sheet are particularly strict, which is the key factor to evaluate the quality of products.
Offset printing ink layer is thin, prone to streaks, dirt on the back, dark ink before and shallow faults, printing a large area of the field is not easy to achieve thick, uniform and consistent ink.
In order to use offset printing process to print a large area of field background color, on the one hand need high precision printing press, on the other hand need to use appropriate process method.
1. Try to avoid fine lines in spot colors
The thickness of the ink layer of color mesh printing is not suitable for printing a large area of background color, especially when the substrate surface is not smooth enough, it will give people the feeling that the ink color is not thick and uneven.
1. Try to avoid fine lines in spot colors
The thickness of the ink layer of color mesh printing is not suitable for printing a large area of background color, especially when the substrate surface is not smooth enough, it will give people the feeling that the ink color is not thick and uneven.
Spot color field background color printing generally needs to increase the amount of ink, the ink layer on the page is thick, will inevitably increase the probability of ink to the blank part of the expansion. So in the prepress design to try to avoid in the field background color has very fine text and fine lines; If there is small print, try to use boldface, because boldface strokes are thicker, not easy paste version.
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2. The secondary overprint results in a better background color
If a page has both a black background color and a color screen image, then the black plate must have a large area of field and screen image, which determines that the black ink can not be printed too thick. In addition to the special production of a black background version of the case, in order to make the black background color to achieve a relatively thick visual effect, you can add about 40% of the corresponding part of the black background in the green version of the flat screen, because the black ink overprint in the blue flat net or black, the result is the ink layer thickened. This method can be used in the case of black ink printing is not very thick, more satisfactory thickening effect.
2. The secondary overprint results in a better background color
If a page has both a black background color and a color screen image, then the black plate must have a large area of field and screen image, which determines that the black ink can not be printed too thick. In addition to the special production of a black background version of the case, in order to make the black background color to achieve a relatively thick visual effect, you can add about 40% of the corresponding part of the black background in the green version of the flat screen, because the black ink overprint in the blue flat net or black, the result is the ink layer thickened. This method can be used in the case of black ink printing is not very thick, more satisfactory thickening effect.
In addition to color images, some products need to be printed with some deep spot color background, such as red background color, dark blue background color, then you can add flat screen printing base on a certain color plate relative to the background color, and then overprint spot color on it.
The advantage of large area of background color from two printing overprinting is: on the one hand, under the condition of controlling the ink layer thickness of the background color plate, the ink layer is thicker; On the other hand, it can greatly reduce the adverse effects of ink, paper powder and streaks on the printing screen.
3. The composition should be as good as possible
To avoid as far as possible in the middle of the field part along the rotating direction of the drum slim blank skylight. Due to the limited ink string capacity of the printing press, the ink at the upper and lower ends of the elongated skylight along the rotating direction of the printing drum will become darker during printing, which seriously affects the appearance of the picture. If the skylight is not in the shape of the finished product, consider filling it into the same field as the surrounding area or, if possible, rotating the entire pattern 90 degrees. In the production of the printing plate of packaging products, because it is often a plurality of patterns together, the joint often appears slender blank part, this blank part should be filled with the same field as the surrounding area as far as possible. Although waste some ink, but conducive to uniform ink color.
4. Printing is the key
High precision printing machine is a prerequisite for printing large area background color. If the printing pressure is lower, you can print a uniform field background color, indicating that the precision of the offset press is higher. The machining accuracy of roller bearing and transmission gear, as well as the reliability of clutch pressure mechanism and ink leveling mechanism are particularly important.
3. The composition should be as good as possible
To avoid as far as possible in the middle of the field part along the rotating direction of the drum slim blank skylight. Due to the limited ink string capacity of the printing press, the ink at the upper and lower ends of the elongated skylight along the rotating direction of the printing drum will become darker during printing, which seriously affects the appearance of the picture. If the skylight is not in the shape of the finished product, consider filling it into the same field as the surrounding area or, if possible, rotating the entire pattern 90 degrees. In the production of the printing plate of packaging products, because it is often a plurality of patterns together, the joint often appears slender blank part, this blank part should be filled with the same field as the surrounding area as far as possible. Although waste some ink, but conducive to uniform ink color.
4. Printing is the key
High precision printing machine is a prerequisite for printing large area background color. If the printing pressure is lower, you can print a uniform field background color, indicating that the precision of the offset press is higher. The machining accuracy of roller bearing and transmission gear, as well as the reliability of clutch pressure mechanism and ink leveling mechanism are particularly important.
- Printing pressure
On the one hand, the printing surface is in full contact with the printing surface, so as to obtain the thick and thick impression. On the other hand can promote the ink on the paper pressure penetration, speed up the ink fixation drying.
- Stability of printing pressure
In the process of rolling plate cylinder and rubber cylinder, rubber cylinder and embossing cylinder for a week, if the printing pressure changes, it will inevitably cause the change of ink transfer rate, and eventually lead to uneven ink color.
- The elasticity of the blanket
Blanket after long-term use will gradually aging, blanket surface ink and paper surface can not fully contact, resulting in poor ink transfer, uneven field, not thick and other ills.
In addition, the tighter the blanket, the thinner the rubber layer, the more serious the elastic loss. For air cushion blanket, even will make the air cushion completely ineffective, not conducive to obtaining even ink color.
- Drum lining
Printing plate drum and rubber drum packaging is improper, will make the impression surface there is a large sliding, the plate surface of the sliding momentum is not consistent, will produce ink bars, affect the uniformity of the field ink layer.
- Printing plate
Printing full plate field, according to the conventional should be exposed to a field plate, but can also use the old plate for full plate printing, this can save production costs, improve efficiency. But the photosensitive resin of the PS layout text part and the alumina of the blank part of the ink adsorption and transfer ability is slightly different, and the ink layer corresponding to the old printing plate graphic part of the printing will be a little darker than the ink layer corresponding to the blank part of the old printing plate. Printing strong colors, such as dark blue, it is best to choose a completely blank plate, or the old plate on the other side (front facing in, reverse facing out) installation for printing; When printing weak colors, such as yellow and glossy oil, it is difficult for the human eye to tell the difference, so you can directly use the old plate left over from the last printing.
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