First, how to achieve positive and negative printing on the gravure printing press
In the field of gravure printing, many printing materials require continuous printing of multiple colors, without any downtime, coating the reverse side of the printing material once in the last printing unit (or full-frame printing). According to the structure of the inline type gravure printing machine itself, if the last color group is to be printed on the reverse side under the condition of feeding, a set of mechanical devices should be placed between the last color group and the previous color group. The device is commonly known as the reprinting frame, which can make the printing material face down to face up, as shown in Figure 1 (front view), where: the two-dot chain line is the running route of the printing material; in addition, if the last This color group does not perform the reverse printing operation, so as long as the running route of the printing material does not pass through the reprinting frame, the color group can be printed on the front side like other color groups.
To achieve this function, the most important component is the printing rack structure that can make the printing material face down.
First, the main functional parts of the reprinting frame structure are as follows:
1. Excessive roller (1) 2. Front plate 3. Reprinting left wallboard 4. Reprinting roller (1) 5. Vortex air pump 6. Inlet tube of reprinting roller 7. Reprinting roller (2) 8. Excessive roller Tube (3) 9, rear plate 10, excessive roller (2) 11, right wall plate
Figure 1 Reprinting frame structure and printing material (plastic film )
Motion circuit schematic (front view)
Figure 2 Reprinting frame structure and printing material (plastic film)
Motion circuit schematic (top view)
Second, the principle of the motion line and the role of the main functional parts
As shown in FIG. 1, the two-dot chain line represents a plastic film, and the plastic film is divided into a front surface and a reverse surface.
The four parallel planes of different horizontal heights in which the plastic film moves on the reprint frame structure are defined as four motion planes A, B, C, and D from low to high. As shown in FIG. 2, two parallel two-dot chain lines represent the edge of the plastic film, and L represents the width of the plastic film. The direction of the arrow closest to each letter is the direction of movement of the plastic film on the moving plane.
As can be seen from the left side of Fig. 1, the printing on the front side of the plastic film against the printing plate roller and the back side against the impression rubber roller is called front side printing. The printing performed by the plate roller and the front surface close to the impression rubber roller is called reverse printing.
The reprinting frame structure is connected by the front panel, the left panel, the back panel, and the right panel to form a solid quadrilateral frame; then all other functional parts and their supporting aids are installed in this quadrilateral frame; therefore the entire reprint The rack structure is a relatively independent structural unit, which can be installed between any two adjacent printing groups. Of course, it is usually installed between the last color group and its previous color group.
In the reprinting frame structure, the excessive roller (1), the excessive roller (2), and the excessive roller (3) are all rotating parts, and the linear speed of the surface of the roller is consistent with the moving speed of the plastic film. The axis of the reprinting roller (1) and reprinting roller (2) is 45 ° with the direction of movement of the plastic film. If it is rotated, the linear speed of the surface of the roller and the direction of movement of the plastic film will be inconsistent, causing the plastic film. Is in an unstable state of motion and cannot be printed.
Therefore, the two reprint rollers must be fixed. Because the plastic film runs around the surface of the printing roller, there must be friction between the film and the surface of the roller. This friction will damage the film surface and cause unstable film tension, which will affect the printing quality. For this reason, the surface of the plastic film and the surface of the printing roller must be brought to a state of zero friction as much as possible in practical applications.
For this reason, two measures should be taken when manufacturing reprinting racks:
First, the surface of the reprinting roller is made as a smooth mirror surface, which can be achieved by surface treatment of parts.
The second is to create an air flow layer on the surface of the printing roller in contact with the plastic film. First, add a vortex air pump and an air inlet tube of the printing roller to the printing frame (shown by the thin solid line in Figure 2); then process the regular distribution of exhaust holes on the surface (semi-cylindrical surface) of the printing roller in contact with the plastic film. See Figure 3P-P for a partial cross-sectional view. The air output by the vortex air pump flows into the inner cavity of the reprinting roller through the intake tube of the reprinting roller, and then becomes an air flow with a relatively large pressure through the exhaust hole. When the roller is under the reaction of the plastic film, an air flow layer will be formed on the surface where the printing roller contacts the plastic film, so that the surface of the plastic film and the surface of the printing roller tend to be in a state of zero friction as much as possible in practical applications.
As can be seen from Figure 1, after the front surface of the plastic film is printed, it first touches the over roller (a) and touches its surface, while driving it to rotate and advance itself. After reaching the highest point of the over roller (a), the plastic film In the plane of movement A, the film is facing down at this time, and the direction of movement is seen to the right as shown in Figure 2. The film continues to move forward, contacts the printing roller (a) and goes around its surface, and reaches the highest point of the printing roller (a). After the point, the plastic film is in the B plane of motion, and the film is facing up at this time, because the angle between the reprinting roller (a) and the transition roller (a) is 45 °, the film bypasses the reprinting roller in the A moving plane The cylinder (1) enters the B plane of movement, and its direction of movement changes by 90 °. Looking at Figure 2 again, after the film movement direction changes by 90 °, it continues to move forward, contacting the excessive roller (II) and driving it around the surface at the same time It rotates and advances on its own. After reaching the highest point of the over roller (II), the plastic film is in the C motion plane. At this time, the front of the film is facing down again, and its motion direction changes by 180 °, which is within the B motion plane. The direction of motion is opposite; continue to look at Figure 2, the plastic film is in C motion Continue to move forward in the plane, contact the printing roller (2) and go around its surface. After reaching the highest point of the printing roller (2), the plastic film is in the D motion plane, and the front side of the film finally faces upward at this time. Because the angle between the printing roller (2) and the transition roller (2) is also 45 °, the film bypasses the printing roller (2) from the C movement plane and enters the D movement plane, and its movement direction also changes by 90 ° At this time, the direction of movement of the plastic film has returned to the direction of movement just after entering the reprinting frame (that is, the A plane of movement); the plastic film continues to advance in the D plane of movement, contacts the excessive roller (three) and drives around the surface at the same time It rotates and advances on its own, and finally leaves the reprinting frame and enters the next printing group.
Figure 3 Partial sectional view of PP
It can be seen from Figure 1 that when the plastic film is in the D motion plane to the transition roller (3) and finally leaves the reprinting frame and enters the next printing group, its front face is always upward, and at this time, the reverse side of the plastic film is tight. The printing plate roller is attached, and the front surface is closely pressed against the embossing rubber roller, and the reverse printing has been formed.
In summary, when feeding, if the operator does not need the last reverse coating, the plastic film can be directly printed on the front of the printing group; if the reverse coating is required, it only needs to pass through the reprinting rack before entering The printing team can realize the reverse printing process.
Third, how to achieve front and back printing on the gravure printing press
In the past ten years or so, a considerable part of the printing materials have been required to continuously print one or more colors on the reverse side of the printing material without stopping the machine after continuous printing of multiple colors. The structure of the linear gravure printing machine itself. If the color group is to be printed on the reverse side when the material is discharged, the rotation direction of the printing plate roller of the color group should be opposite to the rotation direction of the printing plate roller of the previous color group. As shown in Figure a: The thin solid line indicates the running route of the printing material during front printing, and the dashed line indicates the running route of the printing material during reverse printing. In addition, if the color group has not been printed on the reverse side, the color group must also be able to communicate with The other color groups are printed on the front side, which means that the printing plate rollers of the color group can be rotated in the forward direction or the reverse direction. This requires a gear transmission structure with a positive and negative output shaft.
Figure 4 Schematic diagram of forward and reverse gear transmission structure
Among them, 1 is a clutch handwheel, 2 is a clutch push rod, 3 is a reverse gear, 4 is a cover plate, 5 is a clutch gear, 6 is a forward and reverse input shaft, 7 is a driving gear, 8 is a bearing, and 9 is a slave Moving gear, 10 is the forward and reverse rotation box, and 11 is the forward and reverse output shaft.
The entire transmission structure is sealed in a gear box composed of a cover plate and a forward and reverse rotation box. The gear box plays a role of supporting the transmission parts, storing oil, lubricating, and preventing dust.
When the clutch gear is in the position shown in the AA cross-sectional view, the forward and reverse input shaft drives the driving gear to rotate in the positive direction, the driving gear meshes with the clutch gear, and the clutch gear rotates in the opposite direction, and the clutch gear and the reverse gear mesh to achieve the reverse gear positive direction Rotation, the reverse gear meshes with the driven gear to achieve the reverse rotation of the driven gear. Finally, the driven gear drives the forward and reverse output shaft to rotate in the reverse direction, so that the printing plate roller rotates in the reverse direction, which meets the process requirements of reverse printing.
Since the left end of the forward and reverse input shaft is supported by a bearing installed inside the driven gear, the forward and reverse input shaft can rotate relative to the driven gear. When the clutch gear slides to the left from the position shown in the AA cross-sectional view until it disengages from the reverse gear, the forward and reverse input shaft drives the drive gear to rotate in the positive direction, and the drive gear and the clutch gear mesh to realize the reverse rotation of the clutch gear. The driven gear meshes to realize the positive rotation of the driven gear, and finally the driven gear drives the positive and negative output shaft to rotate in the positive direction, so that the printing plate roller rotates forward, which meets the process requirements of front printing.
As can be seen from the KK cross-sectional view in Figure 4, the operator only needs to push and pull the clutch handwheel to move the clutch pusher left and right, thereby causing the clutch gear to slide left and right, and the change in the transmission position of the clutch gear will change the gear The transmission in the box finally achieves that the output shaft can rotate in both directions, so that the printing plate roller can rotate in both directions, which meets the process requirements of front and back printing.