Some Discussions on the "Ghosting" Problem

What is a ghost?
This is a question of defining the norm. If the definition is inaccurate or even wrong, then there is no discussion about ghosting. The concept of ghosts originates from abroad. The English language is GHOST, which means ghosts. It may be that the people who first discovered “ghosts” in prints feel that the ghosts appear to be inconceivable because of the mysteries of ghosts themselves. The meaning is named.

Figure a is the pattern that we want to print when printing. The position of the "ABC" is the direction of the cornice, first touching the ink, and the position of the red solid is in the direction of dragging relative to the character "ABC". When the distance between the text part and the solid part (distance indicated by the blue arrow in figure b) is just within the diameter of the ink roller, it is very likely that the effect of figure b will appear after the printing process, that is, one in the solid part The pale imprint (marked by the green arrow in Figure b), of course, we don't want this imprint, and we call this imprint a ghost.

The emergence of ghosts requires several important preconditions: (1) There is a pattern or text that requires a relatively large amount of ink in the direction of the cornice, which is the basis for the appearance of the ghost; (2) There is a need for ink in the trailing part. The pattern is also very large and has a relatively large area, which is the carrier of the ghost; (3) The distance between the pattern portion of the cornice and the solid portion (or the large area of ​​the ink image) is just a multiple of the diameter of the ink roller. relationship. (4) With the above conditions, there may be ghosting in the printing process, and of course there is a possibility that it does not appear.
How do ghosts come about?
In fact, the reason for the appearance of ghosts is not very complicated. After understanding the causes of ghosts, we will find that the appearance of ghosts is not unthinkable.
The pattern of the rinsing part contacts the ink roller first, that is, the ink roller first supplies the ink to the pattern of the rinsing part. If the ink demand of the gargle part is large, it will leave a deeper impression on the surface of the printing roller. Ink latent image. When the platen roller finishes supplying ink to the image part (such as ABC in figure a) in the direction of the cornice, it turns back and starts to supply the ink from the ink supply ink line, but when the previous ink in the cornice image part is used for ink comparison Large, that is, when the ink layer left on the printing roller has a relatively large shadow, the ink supply at this time sometimes cannot fill up the latent image. Therefore, when the ink roller continues to rotate until the large area of ​​the ink in the direction of the next lap, the latent image is displayed in a shallow shadow.
The same graph as shown in the above figure c is also a kind of ghosting situation. That is, the negative image “ABC” of the mouth part is expressed in the form of a dark pattern to the graphic part of the dragging part.

How to deal with ghosting?
We usually use the following methods on machines without ghost elimination devices:
1. The amount of stringer roller movement increases;
2. Appropriately increase the pressure between the tandem roller and the plate roller;
3. To add some real ground bar to absorb the extra ink in the blank space and solve some problems;
From the above, we can see that the solution to ghosting mainly comes from the improvement of design and ink path. Actually, in many cases ghosts cannot completely solve the adjustment of printing institutions. The more fundamental way is Solve fundamentally from design and platemaking:
4. For some editions, if the mouthpieces are mostly hollowed out drawings, the middle ones will be dragged back to the ground. This version can be used to turn around the sun, dragging slightly on, and solving problems.
5. The person designing must understand the printing and solve it from the design. For example, to avoid the use of relatively large amounts of ink and graphics (especially if the area of ​​the mouth area is relatively small and the size of the relatively large area of ​​the text) on the printing plate above the circumferential correspondence, or design will be smaller at the mouth of the map The text and the tip of the large area of ​​the text and the tone.
6. In addition, when designing the patterns on the printed matter, care should be taken to avoid that the corresponding two pattern spaces are exactly the same as the circumference of the printing roller on the printing roller.

In our actual printing will encounter such problems, the situation shown in Figure d is also exactly the same with the appearance of the ghost, also try to avoid in the design, such as will be shown in the drawing part of the pattern and mouth Part of the pattern block is swapped. The light-colored marks on the pattern appearing on the icon can be effectively avoided. Once the illustrated situation occurs, the solution is the same as the one for ghosting.

Is there any solution to ghosting on modern, more advanced presses?
Heidelberg's presses launched this year have made some effective adjustments to the ghosting problem on the ink path of the press. For example, a separate ink stringing mechanism has been added to the CD102 series of inks produced in recent years. The ink stringing mechanism can be used by the operator (dropping) or not (according to production requirements (mainly for ghosting)). Since), this can make the ink film on the ink path even more smooth in the short term. The agency has a very good effect on the problem of ghosting.
The new commercial rotation produced by Roland Co., Ltd. is based on an edition of ink rollers. The latter two can be axially ganged as required. The amount of movement can be adjusted as required. This device is also very effective in eliminating ghosting.
Domestic printers such as Beiren's N300 and BEIREN 104 series offset presses use pneumatically controlled axial movement of the printing roller to effectively eliminate “ghosting” phenomena.

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