Effect of Printing Speed ​​on Print Quality in Offset Printing (Part 2)

(4) "One line" problem of the front edge of the paper during the movement of the paper feed teeth

Sometimes, the dental plaque is removed due to the individual tooth chipping. After the tooth chip is worn, it is not adjusted according to the standard. There are dead teeth on the transfer tooth, which affects the force, causing the paper to be loose after the paper is pulled. These will cause the "line" status of the front edge of the paper to change.

Due to the small number of dental pieces of the rotary transfer paper, part of the paper is out of control, and it cannot withstand large external forces during the transfer of the paper. Therefore, the time required for the lateral stop to pull the paper must be reasonable (standard time is 10.5 degrees). Otherwise, the paper feed teeth will grab the paper with the side guide, causing the front edge of the paper to be deformed; the paper pressure on the paper press roller will stress the paper. Must be appropriate, otherwise, some part of the front edge of the paper will be pulled back.

(5) "One line" problem of paper when transferring paper and impression cylinder

1The delivery time of the paper handing tooth and the impression cylinder is accurate

The ideal point of contact between the paper feed and the impression cylinder on the paper should be at the tangent point of the two rollers. In order to ensure the stability of the transfer process, there must be a common transfer time of 1.0 to 1.6 degrees between the impression cylinder and the transfer teeth. The midpoint of this transfer time is the cut point of the two rollers. In this transfer interval, the distance between the transfer pad and the impression pad is the shortest and the change is minimal, which can minimize the deformation of the paper during the transfer. The opening time of the delivery tooth was (204.9+0.3) degrees, and the closing time of the impression cylinder was (203.9-0.3) degrees. If the transfer time is too long or the transfer point is not based on the tangent point of the roller, the gap between the pads will increase at the time of transfer, and the front edge of the paper will be deformed.

Factors influencing the handover time include: wear of the relevant parts in the paper transfer tooth row; inaccurate opening time of the paper feed teeth; inaccurate adjustment of the closed tooth time of the impression cylinder; the tooth axis and the tooth shaft in the impression cylinder row There is a "dead tooth" in the wear of copper sleeves, open teeth, or in the tooth row, which changes the time of closing the teeth of the impression cylinder or the closing time of a certain number of teeth, and the contact point is indeterminate.


2 The gap between the paper handing pad and the embossing roller tooth pad is reasonable

The most reasonable gap is the thickness of the paper, so as to minimize the deformation of the paper. When adjusting the gap between the pads, you should pay attention to the adjustment of the height of the pad. When printing thin paper, it is recommended that the gap between the transfer tooth pad and the impression pad be adjusted to 0.15 to 0.20 mm.
There are two factors that affect the gap between the transfer paper pad and the impression pad. One is the embossing roller pad. The plane formed by the upper surface of a row of dental pads is the reference plane during the transfer process of the printed products. Therefore, the height of the dental pads must be carefully measured before installing the dental pads, and the height error of each row of dental pads is controlled within 0.02 mm. The second is a paper pad. After the paper pad is bent, it is difficult to ensure the flatness of the occlusal plane only by the adjustment of the operator. If the sprayed layer of an individual bite falls, the gap between the transfer pad and the impression pad increases. When replacing the transfer pad, the position of the pad must be recalibrated, calibrated against the impression pad or impression cylinder or calibrated using a special tool.

2. The "line" problem of the front edge of the paper in the imprinting process

Due to the effects of roller dents, drums, blankets, printing pressure, and fountain solution, various conditions of paper deformation occur during the imprinting process.

In the Heidelberg 102 series offset press, the impression cylinder row only has 14 teeth. When printing positively on the paper, there were only 10 gingiva crepe papers, and the distance between the two cavities was relatively large. The paper had 45 mm out of control positions at both front corners.

The position where the paper is deformed always starts from the two sides of the print mouth and the cavities, so that the image position of the print and the plate cannot be completely coincident or cannot be changed according to the same rule. Between printing units, there are differences in the locations and degree of deformation due to differences in printing conditions. Due to wet and wet printing, the deformation of the paper eventually translates into ghosting and throw-off failures of the printed product. The following factors in the imprinting process can cause roll-off failure of the printed product.

(1) The two front corners of the paper are dragged back by the release force of the blanket. When the impression cylinder is in contact with the first small transfer cylinder, the paper is not in a "one line" state.

(2) Due to the peeling force, the paper is deformed between the two phases of caries and is not a line state. Especially when printing longitudinal warp and paper, the front edge of the paper is more deformed due to the expansion of the paper fibers.

(3) The "dental teeth" appear on the tooth row and cannot exert sufficient force on the paper. Under the action of the peeling force, the paper is dragged backward at this position for a certain distance so that the front mouth cannot maintain the "one line" state.

(4) Use dental plaques and dental pads that do not meet the requirements. The contact form between the dental piece and the dental pad is line contact. Because there is not enough nip area, the paper cannot overcome the peeling force between the paper and the squeegee at the occlusal position, resulting in the deformation of the paper at the gargle.

(5) If the paper tension is not good, the blanket is too viscous or the printing pressure is too high, the paper will also be deformed in the mouth.

3. One line problem in the embossed area

If the impression cylinder is deformed, the quality of the blanket is not good or the blanket is uneven, the longitudinal section of the contact area between the impression cylinder and the blanket is not a straight line. When the deformation of the impression cylinder body is large, the printing product will wrinkle, causing partial overprinting or rejection.

4. One Line Problem in Paper Transfer

(1) The transfer point and common handover time of the tooth row

The ideal point of transfer of the roller tooth between the two rollers should be at the tangent point of the two rollers. In order to ensure the stability of the transfer process, there must be a common transfer time of 1.0 to 1.6 degrees between the rows of drums (in the single-sided printing state, the common transfer time of the inverting cylinder to the impression cylinder is 1.0 to 1.8 degrees, and the roller is reversed to the storage roller. The common handover time is 1.0 to 2.0 degrees. The midpoint of the transfer time between all the roller rows is the tangential position of the two rollers.

When the outer surface of the drum tooth or the open tooth is worn, the transfer time between the teeth of the drum will become smaller or there will be no transfer time, and at this time, it should be readjusted. If the abrasion exceeds a certain limit, the common time for feeding the drum teeth will not be adjusted. At this time, the tooth chip and the open tooth must be replaced. When the tooth pad wears, the paper appears wavy on the tooth row. At this time, the tooth pad must be replaced. When the open teeth of the roller have obvious gaps, the wear of the copper shaft of the tooth shaft and the tooth base, and the damage of the bearing of the tooth shaft, the opening and closing teeth of the roller tooth or a certain tooth become indefinite and cannot be adjusted normally. At this time, the tooth should be changed. The worn parts in the row.

For large transfer drums and storage rollers, the open and close teeth of two rows of cavities should be strictly identical.

Compared with other models, the cylinder diameter of the Heidelberg 102 series offset press is small, and the common transfer time between the rows of teeth cannot be too long (the transfer length is 2.5 to 3.5 mm). Since the drum row has a slope of 2.5 degrees, the deformation of the paper at the junction point is increased, which limits the extension of the transfer time between the rows of drum teeth. Therefore, it is necessary to strictly follow the standard data when adjusting the hand-over time. Especially when adjusting the opening and closing time of the tumbler drum, careful operation is required.

(2) Pad gap

The most reasonable gap between roller pads is the thickness of the paper. Pay attention to the adjustment of the height of the dental pad. When printing thin paper, it is recommended to adjust the gap between the rollers to 0.15 to 0.20 mm.

For small transfer drums, the operator can change the height of the pad to meet the printing needs of different thicknesses of paper. When the equipment is under full maintenance and overhaul, the height of the pad of the small transfer roller should be carefully adjusted. For the tumbler, the relative position of the tuck flap and the tumbler should be carefully adjusted.

When repairing the roll row, some maintenance personnel arbitrarily change the front-to-rear position of the tooth row (positioning pins on the tooth row seat is not installed) and the positioning positions of the gears at both ends of the row in order to increase the force of turning the row of teeth. At the point of intersection, the gap between the gasket of the flipping cylinder and the storage pad and the pad of the impression cylinder is seriously deviated from the standard data, and the front side of the paper will undergo severe deformation during the transfer process.

(3) In the process of the transfer of any two rows of teeth, the "one line" problem of arranging the cusps of the teeth row is mutually transmitted.

Because there is a slope on the surface of the tooth pad, the cusps of the tooth rows intersecting each other are in a straight line, which can reduce the deformation of the paper. Due to manufacturing, installation and other reasons, it is difficult to do this strictly.

(4) "One Line" Problem in Paper Transfer

Prevent deformation of the front edge of the paper during paper transport.

When "dental teeth" appear in the teeth row, the paper will be out of control in this area, and the two front corners of the paper are generally out of control (parts that are outside the tusks). When the paper encounters an external impact, the uncontrolled portion of the paper is dragged backwards, causing the position of the rear tooth row to be inaccurate, causing the paper to deform.

For the first small transfer drum, the end of the stack is still between the impression cylinder and the blanket cylinder when the row of teeth is creped. If a tooth decayed is "dead tooth," the paper will be deformed at this point.

(5) "One line" problem of rinsing teeth

Under normal circumstances, the crepe size of each unit drum tooth should be equal or no significant change. For some machines, the size of the first group of impression cylinders is 6mm. In the following group, the size of the jaws of the impression cylinder gradually decreases, and the last unit becomes 2mm. Department will be deformed.

This is due to the fact that the common time between drum teething is too long, the teeth of the pick-up drums are too early to make the mussels smaller; there is no common hand-off time between the rows, and the entire paper is in an out of control state (paper throw) at the time of hand-over; The pad gap is unreasonable.

Solving the problems of rejection with "one line"

In order to accurately print, every link in the paper must be in perfect condition. However, most maintenance personnel do not understand the device's throwing angle.