How much is the packaging offset? (53-60)

The choice of overprinting or trapping should be considered from the following perspective: Is it conducive to registration? Is it conducive to drying? Is it conducive to the color sequence arrangement? Is the printing effect good?

53. How to use trapping and overprinting in offset printing?

Overprinting here refers to the adhesion of the latter color ink to the previous color ink film layer during the printing process.

Trapping refers to the printing of a color ink in an image that is hollowed out at a corresponding position in another different color ink.

From the color point of view, it is generally necessary to superimpose several colors to obtain the color desired by the customer. For example, if a large red is reproduced by a four-color printing process, it must be overprinted with magenta ink and yellow ink. However, some colors do not look too similar to those obtained by overprinting and trapping. Overprinting or trapping like black, gold, silver, and other colors results in a difference that is not very great; dark colors are similar to light colors The results obtained with trapping are similar.

The choice of overprinting or trapping in actual production requires comprehensive consideration of the relevant issues and the selection of suitable processes.

1 Consider from the perspective of registration and drying

Overprinting Even if overprinting is inaccurate, there will be no problem of missing white, but it is easy to cause back rubbing because the ink layer is too thick. Trap trapping is not easy to appear on the back, but if overprinting is not allowed, it will easily dew white and affect the appearance.

For a monochrome machine, the previous color is dried and printed one after the other, which is beneficial to the drying of the ink, but it is prone to overprinting due to the overprinting of the paper due to water expansion and elongation.

For multi-color machines, multi-color printing is completed in an instant. Basically, there is no problem of overprinting due to water absorption elongation. The registration is improved, but the ink layer that is too thick is accumulated in a wet manner. It is prone to dry defects and tends to use trapping.

2 consider from printing color sequence

Wet overprinting must take into account the nature of the ink. The viscosity and adhesiveness of the first printed ink must be greater than that of the later printed ink. Otherwise, the reversed overprinting phenomenon will occur in the printed ink. Post-printing inks must also have a high degree of transparency. Trapping on the arrangement of the color sequence is not limited by the nature of the ink, and it is more favorable for selecting the most suitable printing sequence according to other factors.

3 consider from the color effect

When gold and silver inks are printed on coated paper, the colors obtained by printing gold ink and silver ink on white paper by trapping are more thick and pure than those obtained on other background colors.

When printing black, if there is only a larger solid image on the black plate, use the trapping method to increase the ink volume of the black plate to print thicker on the white paper than on the other solid ground. But when printing only words and lines, because the human eye does not have a strong ability to discriminate the fine line density, printing small texts and lines does not need to be printed too heavily, and thin lines will be trapped if trapping is used. It is difficult to overprint accurately, therefore, the printing of small lines generally uses overprinting.

54. For the prints that need to be glued, how should the position of the life and the flip cover be kept in a corresponding relationship?

Special care should be taken to avoid sticking the box tongue at the edge of the socket at the point of application. In that case, when the flip cover is inserted into the socket edge, the flip cover can easily be caught by the tongue of the hole. When the box is small and the number is large, the paper tray will be fed. The use of it brings great inconvenience.

55. Why do some of the glazing folding cartons require partial printing of the gloss oil?

Considering the carton forming process, some cartons need to stick one side of the carton after the printing and die-cutting. If the carton is full of printing glossy oil, it is difficult for the adhesive to penetrate the light oil layer to reach the paper. The bond is not strong. In order to ensure the firmness of the adhesive box, some gluing machines are equipped with edging devices, which will break the surface of the paper tongue of the adhesive, but this has some difficulties in the process. Therefore, many people like to print bright oil only on the part of the carton product, and the paper tongue of the adhesive is no longer printed with bright oil.

56. What method is used to print partial gloss oil?

One way to print glossy oil on the surface of a cassette is to burn a plate that prints bright oil and print bright oil like a printing ink. But doing so increases the cost of production.

For some hard-to-finish plates, the paper pad under the blanket corresponding to the paper tongue of the bond can be partially cut off, so that the printing pressure of that part is insufficient to transfer the light oil to the paper, so that no other Partial gloss oil printing is completed in the case of printing plates.

57. What is hi-fi printing?

Since existing papers and inks cannot yet fully reproduce the color gamut of natural color originals, in order to improve the saturation of certain colors on prints, the pure color is added on the basis of the four colors of C, M, Y, and K. The bright red, green, and blue-purple colors allow the printed image to produce a more natural contrast and a fresher color sense. This printing method is called high-fidelity printing. For example, when printing a picture with strawberries, the red and green versions can be added, making the red and green leaves of the strawberry fruit appear more pure and lifelike, and the whole picture appears vivid and vivid.

The use of high-fidelity printing increases the production costs and the technical requirements for the production process are also high. At present, high-fidelity printing is still at the research and experimental stage in China, and it is rarely used for commercial printing.

58. Why use waterless offset printing?

Ordinary offset printing must use dampening solution to moisten the layout, and the intervention of water reduces the saturation of the ink and makes the color not bright. It also complicates the printing process and the printing quality is difficult to control.

Waterless offset printing adopts an offset printing plate without fountain solution, which eliminates the need for fountain solution intervention. It only needs to supply ink to the plate, and the image can be finished by selectively adsorbing the ink using the printing plate itself. The correct transfer allows printing to proceed smoothly.

59. What is the principle of waterless offset printing?

Waterless offset printing plates are available in both positive and negative formats. Currently, the positive type waterless offset printing plate is used more often.

Taking a positive-type waterless offset printing plate as an example, it is composed of an aluminum plate base layer, a bottom layer, a photosensitive resin layer, a silicone layer, and a cover film. After the exposure, the silica gel layer of the light part (blank portion) on the printing plate undergoes a bridging reaction to perform photocrosslinking; and the silicone layer without the light part (image part) is removed under the action of the developer to expose The photosensitive resin layer below. Since the photosensitive resin layer is ink-receptive, and the non-graphical portion of the silicone layer repels ink, the need for fountain solution intervention eliminates the need for selective ink adsorption.

60. What are the advantages of waterless offset printing?

1 Since there is no intervention of fountain solution, dot reproducibility is good. The dot reproduction range is 2% to 98%, which is larger than the reproduction range of the ordinary PS version (about 5% to 95%); the dot gain value is small, and the enlarged dot value of the intermediate dot network is about 7% to 8%, which is higher than that of the ordinary PS plate. The dot enlargement value (around 15%) is much smaller. Therefore, the waterless offset printing layer has less loss, and the reduction of color and tone is better than ordinary offset printing.

2 Because there is no involvement of the fountain solution, the ink will not reduce the color saturation due to emulsification, making the waterless offset printing color more vivid. Because of the emulsification, the phenomenon that the ink drying speed becomes slower does not exist, and it is less likely that the backside of the printed product will be dirty.

3 Ordinary offset printing In the test printing stage, since the ink has not reached equilibrium, the ink keeps changing, and it is not easy to identify the ink color. At the same time, due to the involvement of the fountain solution, the paper absorbs water and stretches, which also brings adjustments to the adjustment of various color versions. difficult. Waterless offset printing has no ink color change and paper stretching problems caused by the fountain solution, which can save the trial printing time, reduce the trial printing paper loss, and improve the working efficiency and economic efficiency.

Monochrome wet-dry printing tends to use overprinting, multicolor wet-wet printing tends to use trapping

How to maintain the relationship between life and cover position

What method to print local bright oil

What is high fidelity printing

What is the principle of waterless offset printing?

What are the advantages and disadvantages of waterless offset?

Which prints are suitable for waterless offset printing

What are the basic principles of lithographic offset?

What is the principle of similar dissolution

(Qufu Normal University, Yu Tianjian, Tian Peijuan)