Offset ghosting fault analysis and exclusion

In our printing process, we often see a light silhouette printer patrolling next to the same color dot or picture, creating a double profile. This is the ghost we often say. Ghosting will seriously affect the quality of the product. This article analyzes the causes of some common faults and proposes corresponding solutions for the reference of their counterparts.

First, the cause of ghosting analysis

The essential cause of ghosting is the instantaneous relative displacement between the cylinder body (plate cylinder, blanket cylinder, impression cylinder), or the instantaneous relative displacement between the printing plate, blanket, and paper, thus making the blanket Several times before and after the image, the blots did not overlap, resulting in a double image upon transfer to the paper.

Second, common ghosting phenomenon and solution

1. Ghosting with wrinkled paper

Analysis of reason: The ghosting detection system and equipment appear on the side of the wrinkled paper in the monochromatic machine, mainly because the paper is thicker at the wrinkled paper. When the embossing is performed, the displacement of the blanket will increase. When the ink is transferred, it cannot be restored to its original shape at once, so that the micro-displacement “China Printing Industry Annual Report” is generated when receiving the imprint from the plate cylinder, forming a ghost image. After the multi-color machine wrinkles, the imprint of the previous color group and the imprint of the previous print left by the post-color blanket cannot overlap, and it also causes ghosting.

Solution: Adjust the paper feeder so that the paper is fed properly. If necessary, knock paper can be used to increase the stiffness of the paper (especially for thin paper, such as laser transfer paper). If this type of faulty special printing still occurs, you will need to check whether your teeth are dead or if the individual teeth are inflexible due to indentation. (You can use the screwdriver to move the teeth to see if they are flexible. Check if the bite force is normal with 0.1mm kraft paper) , otherwise adjust the teeth accordingly. Of course, there may be dirt or crumpled paper on the impression cylinder, resulting in crumpled paper and ghosting. Therefore, it is necessary to remove the dirt or humidity treatment. In short, as long as the problem of wrinkled paper is solved, ghosting will naturally disappear. Ink

2. Longitudinal longitudinal ghosting along with ink bars

Analysis of reason: This fault is mainly caused by wear of other gears or bearings, which results in longitudinal relative slipping of the drum body. The several positions before and after the image footprint do not overlap, resulting in ghosting. At the same time, due to slippage, ink bars will also appear.

Solution: Disassemble the appropriate gear or bearing for appropriate repair or replacement.

Third, a large area of ​​vertical ghosting

Analysis of the causes: This type of failure may be due to a non-clamped plate, insufficient tension in the blanket or insufficient force in the entire row of teeth, or a large viscosity of the ink resulting in a large peel force that causes the paper to slip within the teeth. That is, there is a momentary relative displacement between the paper, printing plate, and blanket, so that the same color image before and after the imprint does not overlap the post-printing process, resulting in longitudinal ghosting. 2 It is also possible that there is relative longitudinal displacement between the three drum bodies. For example, the loosening of the fastening screw between the three-roller transmission gear and its connecting shaft head causes the axial movement of the gear during operation, and the gear axial movement will inevitably lead to the gear circumferential direction. Rotate at an angle, that is, the drum rotates relative to one another, resulting in a ghost with an instantaneous relative displacement. 3 It may also be that the printing pressure is too large for three-dimensional printing, so that the deformation of the blanket cannot be instantaneously restored, and a slight position difference occurs when the blanket is received again from the printing plate to form a ghost image.

Solution: 1 Clamp the plate. 2 Tighten the blanket, especially after the new blanket is pressed for several minutes, tighten it once more, and check the status of the blanket regularly. 3 Check whether the open teeth of the tooth row are worn or whether the two ends of the spring are normal. Otherwise, to repair, replace damaged parts, and adjust the teeth on-demand printing, requires the entire row of teeth bite enough. 4 Add a small amount of detackifier to reduce the viscosity of the ink. 5 Tighten the fastening screws of the roller drive gear. 6 Reduce the printing pressure, reduce the coefficient of expansion and contraction of the blanket. Print inspection

Fourth, unilateral ghosting

Analysis of the reasons: If there is only one side of ghosting and no crumpled paper appears, the blanket may be skewed and skewed. The two sides are loosely inconsistent. As a result, the rubber blanket on one side is not stretched tightly, and the relative displacement occurs locally during operation. Focus on the shadow.

Solution: Re-cut the blanket so that the four corners are all right-angled, and ensure that the direction of the cocoon is consistent with the circumference of the drum, and then tighten on the drum.

V. Several ghosts before press-press printing

Analysis of the reasons: Once the combined pressure is not in place, the "Chinese Blue Print Book" means that the pressure-compressing mechanism is inflexible and has hysteresis. Each time the pressure is built up, there is a certain positional difference.

Solution: Check the pressure-compressing mechanism to see if any part is inflexible. For example, if the valve stem of the cylinder has a resistance glue box, the movement is inflexible and the pressure is not in place, and then the corresponding repair or replacement is performed.

Sixth, large area axial ghost

Analysis of the causes: mainly the axial displacement of the cylinder shafts of the three cylinders or the polychromators has a relative displacement.

Solution: 1 Check whether the corresponding roller shaft end cover or thrust bearing is loose or worn, otherwise, perform corresponding maintenance or replacement. 2 Repair the corresponding bite shaft to prevent it from moving.

The above is a summary of my work experience. If there is any deficiency, please correct me.