How does "offset printing technology" print off a large area of offset printing?
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
To print a large area of the ground color with an offset printing process. On the one hand, high-precision printing presses are required, and on the other hand, appropriate process methods are required.
First, try to avoid thin lines in the background color of the spot color
The color of the ink layer printed by the color mesh is not suitable for printing a large area of the background color, especially when the surface of the substrate is not smooth enough, it will give the impression that the ink color is not thick and uneven.
Spot color solid background printing generally needs to increase the amount of ink supply. The thickness of the ink layer on the plate is thick, which will increase the probability of the ink expanding to the blank. Therefore, it is necessary to avoid the fineness of the ground color in the prepress design. The text and the dash line; if there is a small word, try to use the black body, because the strokes of the black body are thicker and not easy to paste.
Second, the second overprinted background color is better
If there is a black background and a color mesh image on a layout, then the black version must have both a large area and a mesh image, which determines that the black ink cannot be printed too thick. In the case of not making a black background, in order to make the black background achieve a thicker visual effect, you can add about 40% of the flat net to the black background of the blue version, because the black ink is overlaid in cyan. The flat screen is still black, and the result is that the ink layer is thicker. In this way, a relatively satisfactory thick effect can be obtained in the case where the black ink is not printed very thickly.
In addition to color images, some product prints also need to print some deep spot color backgrounds, such as a red background, a dark blue background, etc., at this time, you can add a flat screen printing on the corresponding part of the color background. Make a base and then overprint the spot color on it. For example, if you print a red background, you can add a suitable number of flat nets to the corresponding parts of the magenta plate on the reddish background; if you print a dark blue background, you can add appropriate numbers to the corresponding parts of the cyan plate on the dark blue background. Flat net.
The advantage of the large-area background color being overprinted by two printings is that, on the one hand, in the case of controlling the thickness of the ink layer of the ground color plate, the overprinted ink layer is thicker; on the other hand, the ink skin and paper powder can be greatly reduced. , streaks, etc. have an adverse effect on the printed image. For example, when only a black background is printed on a white paper, due to the influence of paper dust, ink on the printing process, or other reasons affecting the ink transfer, very obvious spots and blisters appear on the black background. If the black background is overprinted on the cyan flat screen, even if the black ink layer has blisters, since the exposed paper base is no longer white, but the cyan flat mesh layer, compared to the black contrast, the black and blue contrast It is not so obvious.
Third, the typesetting is as beneficial as possible to even ink
Try to avoid having a slim, blank skylight in the middle of the solid section along the direction of rotation of the drum. Because the ink splicing ability of the printing machine is limited, the elongated sunroof along the rotation direction of the printing cylinder will appear darker at the upper and lower ends of the skylight during printing, which seriously affects the appearance of the picture. If the sunroof is not within the shape of the finished product, consider replenishing it to the same ground as the perimeter, or if possible, rotating the entire pattern 90 degrees. When making a printing plate of a packaged product, since a plurality of patterns are often joined together at the intersection, a blank portion of the elongated portion tends to appear at the place where the contact is made, and the blank portion should be filled with the same field as the periphery as much as possible. Although some ink is wasted, it is advantageous for uniform ink color.
Fourth, printing is the most critical
The high precision of the press is a prerequisite for printing a large background. If a uniform solid background is printed at a lower printing pressure, the accuracy of the offset press is higher. The machining accuracy of the roller bearing, the transmission gear, etc., and the reliability of the clutch pressure mechanism and the ink distribution mechanism are particularly important.
1, printing pressure size
Large printing pressure is used when printing on the ground, which is beneficial to the printing surface to fully contact to obtain a thick and thick imprint; on the other hand, it can promote the pressure penetration of the ink on the paper and accelerate the fixing and drying of the ink.
2, the stability of printing pressure
During the rolling process of the plate cylinder and the blanket cylinder, the blanket cylinder and the impression cylinder, if the printing pressure changes, the ink transfer rate will inevitably change, eventually resulting in uneven ink color on the ground.
3, the elasticity of the blanket
After long-term use, the blanket will gradually age, and the ink on the surface of the blanket and the surface of the paper will not be in full contact, resulting in poor ink transfer, unevenness in the field, and no thickness.
In addition, the tighter the blanket is stretched, the more the rubber layer is thinned, and the more elastic loss is. For air-cushion blankets, even the air cushion layer is completely ineffective, which is not conducive to obtaining a uniform ink color.
4, roller lining
Improper lining of the plate cylinder and the blanket cylinder will cause a large sliding of the embossed surface, and the sliding amount of the surface of the printing plate is inconsistent, and a ink stick is generated, which affects the uniformity of the ink layer in the ground.
5, printing plate
Print a full version of the field, as usual, should be a solid plate, but you can also use the old plate for full-page printing, which can save production costs and improve efficiency. However, the photosensitive resin in the PS version and the alumina in the blank portion have a slight difference in the ability to adsorb and transfer the ink. The ink layer on the printed product corresponding to the old printing image will be blanker than the old printing plate. Some of the corresponding ink layers are slightly darker in color. For printing strong colors, such as dark blue, it is best to use a completely blank plate, or to turn the old plate in reverse (front facing, back facing outward) for printing; printing weak colors, such as printing yellow and printing varnish, due to It is difficult for the human eye to distinguish this small difference, and the old printing plate left after the last printing can be used directly.
6, ink blending
Ink for printing on the ground, the fluidity is slightly larger than the image of the printed mesh. The fluidity of the ink is too small to spread evenly between the ink rollers, which may cause the ink to be deep before and after. The fluidity is larger, and after the ink is printed on the paper, it can be quickly leveled before drying, which is beneficial to increase the coverage of the ground to obtain a uniform and thick ink effect. The worse the paper, the more it is necessary to increase the fluidity of the ink when printing on the ground.
The fluidity of the ink is adjusted to adjust the viscosity of the ink. Generally add a low viscosity No. 6 varnish to dilute the ink, but also strictly control the dosage. Because the viscosity is too low, the ink is easily emulsified.
When printing coated paper, in order to prevent smudging on the back side, it is necessary to add a small amount of desiccant or viscous agent to the ink.
7. Ink transfer of ink roller
The ink roller becomes smooth due to aging or improper cleaning, and the ability to adsorb and transfer ink is reduced. In particular, the inking roller, if it can not absorb enough ink, after the first transfer of ink after contact with the printing plate, due to the small amount of ink stored, the darkness of the image on the printing plate and the ink on the surface of the printing plate have been sucked. Most of them, but the ink roller can not get enough ink to supplement immediately, so in the second transfer of ink, the image is darkly adjusted or the ink obtained in the field is much less than the first turn. Although there are 4 ink rollers that transfer ink, there will still be a dark and dark phenomenon before the ink color. Therefore, the inking roller, especially the first two inking rollers, must use a rubber roller with good surface transfer performance.
8. Pressure regulation of the ink roller
The pressure between the ink roller and the ink roller, between the ink roller and the printing plate should be adjusted appropriately. The pressure is too small, the ink transfer is poor, especially the contact pressure between the inking roller and the tandem roller is too light, so that the ink roller does not get enough ink, and the ink will be light and heavy before the printing surface; Accelerate the aging of the ink roller, especially if the pressure between the ink roller and the printing plate is too large, and an impact jump will occur at the cornice, and a ink stick will appear. The pressure between the same inking roller and the inking roller is slightly less than the contact pressure with the printing plate. This is to ensure that the inking roller can be pressed with pressure when the surface linear velocity of the inking roller is inconsistent with the surface speed of the printing plate. One side of the plate is synchronized, so that the ink roller and the surface of the printing plate are not slipped as much as possible.
9, pressure adjustment of the water roller
Too little or too much pressure between the water roll and the water roll, between the water roll and the printing plate can result in poor water transfer, which can cause the plate to get dirty. The pressure between the water roller and the printing plate is too large, and the pressure between the water roller and the water roller is too large, which may cause a white bar.
10, the adjustment of the ink roller
In order to achieve the best ink leveling effect, the axial movement amount of the squeezing roller is generally at the maximum traverse amount position, and at this position also facilitates the operator to quickly adjust the axial amount of the printing plate evenly. In some printing machines, the inking roller can also be strung after being adjusted. In order to achieve a better ink mixing effect, the inking roller can be properly synchronized. The circumferential distribution of the ink can be changed by adjusting the starting point of the stringer. It is difficult to determine which step position must be the optimal starting position. Generally, it is only possible to determine the position that is most favorable for the uniformity of the ink by gradually adjusting the starting position of the string.
11. Control the effect of emulsification on ink color
When printing the ground color, the emulsification consumes a lot of water and the water supply is large. The axial ends of the solid ground part, especially when the ground part is close to or reaches the edge of the paper, the area other than the paper is neither emulsified by ink and water, nor the blank part of the paper absorbs moisture, and the excess moisture will follow The striking of the water roller enters the bottom color portion of the axial ends of the paper, causing the underlying ink layer at both ends of the paper to be excessively emulsified, the ink color becomes shallow, and the back surface smudging may be caused. It is reasonable to use the water pipe blowing device or the sticker on the water roller to reduce the water supply at the axial ends of the printing plate and control the degree of emulsification of the entire layout.