The effect of printing speed on printing quality in offset printing (three)
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(4) "One line" problem at the front edge of the paper during the movement of the paper
Sometimes, the teeth are removed due to the individual pieces of paper; after the teeth are worn, they are not adjusted according to the standard; there are dead teeth on the transfer paper, which affects the force and causes the paper to loosen after the paper is fed. These will cause the "one line" state of the front edge of the paper to change.
Due to the small number of teeth of the rotary transfer paper, a part of the paper is out of control, and the external force cannot be withstood during the transfer of the paper by the transfer paper. Therefore, the time for the side gauge to stop pulling the paper must be reasonable (standard time is 10.5 degrees), otherwise the paper feeding paper will grab the paper with the side gauge, so that the front edge of the paper is deformed; the pressure of the paper brush wheel on the paperboard is pressed against the paper. It must be appropriate, otherwise a part of the front edge of the paper will be pulled backwards.
(5) "One line" problem of paper when the transfer paper and the impression cylinder are handed over
1 The delivery time of the transfer paper and the impression cylinder is accurate
The ideal intersection of the transfer paper and the impression cylinder to 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 paper. The midpoint of this handover time is the tangent point of the two rollers. In this interface, the distance between the transfer pad and the impression pad is the closest, and the change is minimal, which can minimize the deformation of the paper during the transfer. The opening time of the transfer paper is (204.9+0.3) degrees, and the closing time of the impression cylinder is (203.9-0.3) degrees. If the handover time is too long or the junction is not based on the tangent point of the roller, the gap between the pads will increase when the transfer is made, and the front edge of the paper will be deformed.
Factors affecting the handover time include: wear of related parts in the transfer paper row; inaccurate opening time of the transfer paper; inaccurate adjustment of the closing time of the impression cylinder row; in the impression cylinder, the dental shaft and the dental shaft There is a “dead tooth” in the copper sleeve, the open ball wear or the tooth row, which changes the tooth sealing time of the impression cylinder or the closing time of some dental caries, and the junction point is uncertain.
2The gap between the paper pad and the impression roller pad is reasonable.
The most reasonable gap is the thickness of the paper to minimize paper distortion. When adjusting the interstitial space, pay attention to the adjustment standard of the height of the dental pad. When printing thin paper, it is recommended to adjust the gap between the transfer pad and the impression pad to 0.15 to 0.20 mm.
There are two factors that affect the gap between the transfer pad and the impression pad. One is the impression cylinder pad. The plane formed by the upper surface of a row of dental pads is the reference plane during the transfer of the printed products. Therefore, the height of the dental pads should be carefully measured before installing the dental pads, and the height error of each row of dental pads should be controlled within 0.02 mm. The second is the transfer paper pad. After the transfer pad is bent, it is difficult to ensure the flatness of the occlusal plane by the adjustment of the operator alone. If the sprayed layer of the individual bite points falls, the gap between the transfer pad and the impression pad is increased. When replacing the transfer pad, the position of the pad must be re-corrected, corrected with the impression roller pad or impression cylinder body or with a special tool.
2. "One line" problem at the front edge of the paper during imprinting
Due to the effects of roller dent, roller body, blanket, printing pressure and dampening solution, the paper undergoes various deformations during the embossing process.
In the Heidelberg 102 series offset press, the impression cylinder has only 14 cavities. When printing positively, there are only 10 crepe papers, the distance between the two fangs is large, and the paper has 45 mm out of control at each of the two front corners.
The deformed part of the paper always starts from both sides of the print mouth and the fangs, so that the image position of the print and the plate cannot be completely coincident or cannot change according to the same law. There is a difference in the location and extent of deformation between printing units due to differences in printing conditions. Due to the wet-wet printing, the deformation of the paper is finally converted into the ghosting and corner failure of the printed product, and the following factors may cause the corner failure of the printed product during the printing process.
(1) The two front corners of the paper are dragged backward by the blanket peeling force, and the paper is not in the "one line" state when the impression cylinder is handed over to the first small transfer cylinder.
(2) Due to the peeling force, the paper is deformed between the two-phase molars, not a line state. Especially when printing longitudinal filament paper, the front edge of the paper is more deformed due to the expansion of the paper fibers.
(3) There is a “dead tooth” on the tooth row, which can not produce enough force on the paper. Under the action of the peeling force, the paper is pulled backwards for a distance in this part, so that the front edge cannot maintain the “one line” state.
(4) Use teeth and pads that do not meet the requirements. The contact between the tooth piece and the tooth pad is in the form of a line contact. Since there is not enough occlusal area, the paper cannot overcome the peeling force between the paper and the blanket cylinder at the nip, and the paper is deformed at the mouth.
(5) If the paper pull is not good, the adhesive is too sticky or the printing pressure is too high, and the paper will also be deformed at 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 not flat, the longitudinal section of the contact area between the impression cylinder and the blanket is not a straight line. When the impression cylinder body is deformed greatly, the printed product will wrinkle, causing partial overprinting or cornering.
4. "One line" problem during paper transfer
(1) The intersection of the tooth row and the common handover time
The ideal intersection point for the transfer of the 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 the rollers (in the single-sided printing state, the common transfer time of the reverse roller to the impression cylinder is 1.0 to 1.8 degrees, and the roller is turned over to the storage roller. The common handover time is 1.0 to 2.0 degrees). The midpoint of the intersection time between all the rows of rollers is the tangent point of the two rollers.
When the outer surface of the roller or the open ball is worn, the transfer time between the rows of the rollers becomes small or there is no handover time, and should be readjusted at this time. If the wear exceeds a certain limit, the joint time of the roller row will not be adjusted. At this time, the tooth piece and the tooth ball must be replaced. When the tooth pad is worn, the paper is wavy on the tooth row. At this time, the roller pad must be replaced. When the roller open ball has obvious gap, the dental shaft and the socket copper sleeve are worn, and the dental shaft bearing is damaged, the opening and closing time of the roller tooth row or a certain tooth decay is uncertain and cannot be adjusted normally. Wear parts in the row.
For large paper rollers and storage rollers, the opening and closing time of the two rows of cavities should be strictly consistent.
Compared with other models, the Heidelberg 102 series offset press has a smaller roller diameter, and the common transfer time between the rows of teeth is not too long (the transfer length is 2.5 to 3.5 mm). Since the roller row has a slope of 2.5 degrees, the deformation of the paper at the intersection is increased, which limits the extension of the time between the rows of the rollers. Therefore, the standard time data must be strictly observed when adjusting the handover time. In particular, when adjusting the opening and closing time of the turning roller, careful operation is required.
(2) interdental space
The most reasonable gap between the roller pads is the thickness of the paper. Pay attention to the adjustment standard 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 rollers, the operator can change the height of the pads to meet the printing needs of different thickness papers. When the equipment is fully maintained and overhauled, the height of the small paper roller pad should be carefully corrected. For the turning roller, the relative position of the molar fixed piece and the turning roller should be carefully adjusted.
When repairing the flipper row, some maintenance personnel can change the front and rear position of the tooth row (without the positioning pin on the tooth row seat) and the positioning position of the gears at both ends of the tooth row in order to increase the force of the flipping tooth row. At the junction, the gap between the pad that flips the roller and the storage roller and the impression pad is seriously deviated from the standard data, and the front edge will be severely deformed during the transfer.
(3) In the process of handing over any two rows of rows of teeth, the "one line" problem of the position of the cusps of the teeth is mutually overlapped.
Due to the slope of the surface of the dental pad, the position of the cusps of the mutually overlapping dental teeth is in a straight line, which can reduce the deformation of the paper. Due to manufacturing, installation and other reasons, it is difficult to strictly do this.
(4) "One line" problem of paper during transmission
The paper should be prevented from deforming at the front edge of the paper during paper transport.
When a "dead tooth" appears in the tooth row, the paper will be out of control at this location, and the two front corners of the paper are generally out of control (the part other than the tooth decay). When the paper encounters an external impact, the uncontrolled portion of the paper is dragged backwards, so that the position of the backing paper is inaccurate, causing the paper to deform.
For the first small transfer roller, the tail of the paper is still between the impression cylinder and the blanket cylinder when the tooth is discharged. If a tooth is a "dead tooth", the paper will be deformed at this location.
(5) "One line" problem with the size of the jaws
Under normal circumstances, the size of the crepe paper of each unit roller should be equal or no significant change. In some machines, the first group of impression cylinders has a size of 6 mm. In the latter unit, the size of the mouth of the impression cylinder is gradually reduced, and the last unit becomes 2 mm, so that the paper is in the mouth. There will be distortion at the place.
This is because the joint time between the rows of the rollers is too long, the teeth of the pickup roller are too early to make the mouth smaller; there is no joint transfer time between the rows, and the whole paper is out of control (handling) when the hand is transferred; The pad gap is not reasonable.
Solve the problem of corners with the "one line" point of view
In order to accurately print, every step of the paper must be ideal during the transfer. However, most maintenance personnel do not understand the corners of the equipment.