Detailed explanation of offset printing - ghosting failure (2)

(C). A, B ghosting

A, B ghosting is a typical failure of multi-color offset printing presses. It directly affects the reproduction of gradations and colors of printed products, reduces the image resolution, reduces the image layer, and blurs the text.

1, the basic concept of A, B ghosting

Most modern multi-color offset presses use double-diameter impression cylinders and transfer cylinders. There are two sets of enamel teeth on the cylinder. These two cavities are called A molars (axis) and B molars (axis). (See Figure 8-3). If the machine's jaw shaft is manufactured and installed with high precision, the ideal state is achieved, ie aa=0 bb=0 cc=0

There will be no ghosting. On the contrary, when the three sets of data are greater than zero or less than zero, the dots on the two sets of paper on A and B cannot be completely overlapped on the post-printing rubber, which inevitably produces ghost images. The ghost caused by the double-diameter cylinder cavities is called "A, B" ghost.

2. A, B ghosting is a double-ghost theater in which the multi-color offset printing machine in the wet-type superimposition double-deck roller is operated continuously, and this ghosting is regular. It refers to the failure of a certain set of tusks on the double-diameter cylinder of the previous unit, which caused the paper to slip during the printing process or the paper to be transferred inaccurately. The print of the previous unit will not overlap on the subsequent sets of blankets. , it has produced A, B ghosting.

For example, the first set of impression cylinder A sets of tusks work well, and the marks it left on the second set of blankets are at point A, and the first set B sets of buckling devices are defective, causing the paper to slide back during printing. Moving, it stays on the blanket of the second unit, underneath point A, and says A. At this time, the ghost of point A appears above A. When the third sheet of paper is again a set of gingival gums, the marks it left on the second set of blankets coincide with point A, so that under point A, the marks of A remaining on the blanket coincide with point A. In this way, A appears at the bottom of point A, a transfer print left on the blanket, so that the ghosting occurs continuously. In general, printing thick paper is less obvious, and printing thin paper (below 100 g/m2) - it is easy to see.

The causes of the A, B ghost theater are mainly due to the periodic printing of different thickness papers to wear the tooth pads, or due to the inconsistent speed of the machine, the lubrication is not in place, and the wear accuracy of the dental shaft is reduced.

Based on the above reasoning, ghosts corresponding to ghosts above the normal footprint (pulling direction) have a fault, and ghosts are normal underneath a normal footprint (a fistula direction). .



Figure 8-3 Accuracy of A and B jaw axes and carious teeth


AB ghost detection and exclusion

In the high-speed operation situation, how to determine which of the two AB gears have failed?
The first method is a group-by-group test, that is, the first and second units are used for printing. The purpose is to check whether the prints on the first group of papers can be overlapped on the blankets of the second unit. If they are coincident, the first units are proved. The embossing and transfer cylinders have been working properly; if they are not coincident, it is proved that the first group embossing and the transfer cylinder tooth removal device is faulty and needs to be eliminated. Then use the second and third units to print to determine if the second unit's dental caries work properly, and so on.

The second method is to print the four units at the same time, observe the color mark, and set the printing sequence to black, cyan, magenta, and yellow (ie, B, C, M, Y). For example, BK and C color labels simultaneously generate ghost images. If the M and Y color marks are clear, then it can be proved that the marks of BK and C can not be overlapped on the M and Y blankets, and it can be judged that there is a fault in the C group's embossing or transfer cylinder with a set of tooth decay devices, and the M color set The two sets of dental caries working properly, because the M color mark can be completely overlapped on the blanket of the Y color group, so the M and Y color marks are clear.

Based on the above introduction, we have been able to quickly determine which unit and which gearing device has failed and we can troubleshoot which set of teething devices.

The exclusion method is as follows:

(1) First check whether the open roller is excessively worn;
(2) Check the acetabular shaft bearing and whether the shaft seat is worn out;
(3) To clean the cavities, teeth and pads, and to adjust the force, Komori, KBA, Mitsubishi, and Roland have forced tooth closing devices. First, the open and closed teeth are transferred to the small face, and then one by one. Loosen the tooth chip and clean the tooth chip and the tooth pad, and then close the tooth chip on the tooth pad. Finally, turn the open tooth roller to the big surface (forced) to close the teeth and adjust the force and the closing force. In the above operations, the power must be turned off to prevent damage to the device due to incorrect operation.

Source: Ke Yin Network

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