The resolution of throwing angles in printing (below)

The fibers in the paper will swell and distort after absorbing water. When the relatively dry paper is printed in the first color group, the amount of water absorbed is relatively large, so the water content of the paper will increase greatly. When the second color is printed, because the moisture content of the paper has been increased a lot, the amount of water that the printing unit can provide does not change significantly. Although the moisture content of the paper will increase further, the relative increase There has been no increase in the relative amount of time when printing in the first color. That is to say, when the paper is printed in the second color, the amount of dimensional change is smaller than the first color. Of course, the relative amount of deformation of the third color of the paper will gradually become smaller.
In the process of imprinting paper, the force deformation is similar to the process of water absorption deformation. Paper deformation can be divided into elastic deformation and plastic deformation. When the first color is printed, the paper will be deformed. At this time, the plastic deformation cannot be recovered, and the elastic deformation of the paper and the sheet is not restored due to the high-speed printing, so that when the second color is printed, the ink is printed. Can only be transferred to the already deformed paper, and at the same time, another plastic deformation will occur on the paper, but at this time the amount of deformation has been reduced due to the deformation of the first color; the same reason, the third color The same as the subsequent color group, that is, the amount of paper deformation is gradually reduced.
2. The rejection angle caused by the adjustment process used by the press itself or the machine.
The manufacture of the machine itself, the structure, and the adjustments to the operation of the printing press can also cause rollover failures. The PZ4880-01A printing press originally produced in China has a much clearer rejection angle. The reason is that the sinking of the tooth pad, uneven bite force, and inconsistency easily lead to the rejection of the printing process. During the printing process, the paper is subjected to the pulling force of the rolling force. If there is not enough force to maintain the stability of the paper, the paper can easily slip relative to the impression roller and the slipping occurs. The shift will also be accumulated and enlarged at the end of the paper, resulting in rejection of the corner.
Third, for the paper deformation and the adjustment of the machine to take measures to make up 1. When selecting the paper, select the appropriate paper according to the requirements of the print job. If printing requires precise overlay, then we must choose paper with low pulp content, high surface sizing, and high mechanical strength when selecting paper. Secondly, before the printing, the paper should be subjected to humidity conditioning (the conditional unit is best to use a forced moisture adjustment method, which can ensure that the paper has a relatively high moisture content), so that the water content of the paper is stable, and the stability is improved during the printing process.
2. For the reasons of the machine itself, the rejection of the corner rejection can be adjusted from the following aspects:
1 Normally bite the teeth of the first color group, and bite teeth at both ends of the impression cylinder of the 2-4 group, and the teeth force is slightly smaller.
2 Add padding of 2-4 sets of blankets (approximately 0.05mm can be reduced). Doing so can bring some convergence to the paper that has already been thrown, but this requires the operator to have a very rich printing experience to master the scale.
3 In addition, the pad at both ends of the impression cylinder can be increased, so that the higher portion can be firstly brought into contact with the pressure, so that the two corners of the paper can be converged in phase so as not to spread.
Fourth, the design of modern printing press to solve the rejection angle 1. China's modern printing press has been able to solve the problem of rejection in the printing process, such as:
1 The use of high-strength alloy steel as the overall structure of the teeth ensures that the paper is stable, avoiding ghosting and rejection;
2 After the version of the card is a segmented type, to solve the phenomenon of "swing angle" appeared in the printing;
3 Use a plurality of support screws on the supporting rod of the impression pad to prevent the roll-off failure caused by sinking of the pad.
2. Several foreign presses also have different solutions. Such as: The roller teether teeth designed to be flexible, before the bite paper has a pre-curved movement, can be adjusted according to need, so that you can avoid the rejection angle failure.