The quality of the carton printing plate is the key to directly affecting the quality of the carton printing. If the quality of the relevant links is grasped, the printing quality, the life of the printing plate, the loss of the printing plate and the production cost can be improved. In the production of corrugated carton printing, the most commonly used carton printing plates in carton factories are rubber plates and flexographic resin plates. Although the rubber version is cheaper and more frequently used than the flexo resin version, it is performing complex patterns, fine text (such as barcodes, net graphics, and small fonts) and large areas because of its poor printing accuracy and low efficiency. The full version of solid printing requires a photosensitive resin plate to complete the printing process. Of course, the flexographic resin plate also has its disadvantages. The price of the flexographic resin plate is more expensive. The technical content of making and using is higher than that of the hand-engraved rubber plate and the laser-engraved rubber plate. It is particularly important to use methods to extend the life of flexographic resin plates. Only by controlling the quality of the flexographic resin plate of the carton, and mastering its use method, and controlling every link related to the printing plate, can we effectively control the printing quality and produce beautifully printed carton.
Quality factor control related to flexo resin plate
Grasp material quality printing materials
Corrugated cardboard has uneven surface, roughness, and large thickness error (such as A-type corrugated and C-shaped corrugated cardboard, the thickness error is generally 0.5mm or even higher), cardboard warpage, printed surface powder, brushing, paper There are defects such as sand grains, rough calcium carbonate filler made in the cardboard paper, etc., so it is one of the poor quality of paper-based printing materials. In the printing process, these defects are easy to cause the printing plate to paste, crush, or even wear or damage the flexographic resin plate, resulting in shortened service life of the printing plate. Therefore, in the production process of corrugated cardboard, we strictly control from the base paper into the factory, cardboard production technology and other aspects.
Selection and arrangement of flexographic resin plates
The flexographic resin plate used for corrugated carton printing generally selects a plate material with a thickness of 3 mm to 7 mm and a Shore hardness of 25 to 30. In order to overcome the unevenness and roughness of the corrugated cardboard surface, it is necessary to put forward higher requirements for the flexographic resin plate, which requires the printing plate to be wear-resistant, strong impact resistance, moderate hardness, good resilience after compression, uniform ink, Consistent thickness. According to the size of patterns, characters, lines and the material of corrugated cardboard, make corresponding arrangements for the layout design, hardness requirements and production methods of the flexographic printing plate. When the quality of corrugated cardboard is poor and the color of the full solid background is printed, the thicker and softer flexographic version is used; when the corrugated cardboard is of good quality, and the fine patterns, fine prints, and screen versions are printed, the softness with high hardness and low thickness Printed resin version.
When using double-sided adhesive tape and water-free adhesive tape to paste the resin plate to the polyester film, if you find that the double-sided pressure-sensitive adhesive paper and water-free adhesive tape are not strong, they must not be used. Because the resin-resistant plate is not sticky, it can't withstand the pressure and impact of the printing process and the printing plate will bounce off, which will cause the printing plate to be crushed or lost. The defoamer in water ink is recommended to use silicon-based defoamer, do not use hydrocarbon defoamer, because the hydrocarbon defoamer will cause the flexo resin plate to swell (the positive Butanol is a hydrocarbon), which cracks the printing plate and accelerates the damage of the printing plate.
Print content design
The flexographic resin version is not like the PS version. The thickness of the printing plate and the thickness of the printing material are much larger than that of the offset printing. Therefore, when designing thin lines, small text, and patterns with dots, it is not appropriate to arrange it with a large area of ​​the full version on a layout . Because the full version of the solid bottom needs to be printed clearly, the printing pressure needs to be increased, and the printing pressure on the thin lines, small characters, and dotted patterns is easy to cause the thin lines, small characters, and dotted patterns to deform during printing , Resulting in blurred and unclear printing of thin lines, small text and dotted patterns after a period of use of the printing plate, and serious wear and tear or crushing of the printing plate, resulting in printed products with broken lines, font strokes falling off, dot Quality issues such as loss. If it must be designed on a single printing plate, then the full exposure of the full version of the field with thin lines, small text, and dotted patterns cannot be exposed with the same exposure time. For thin lines, small text, and printing plates with dot patterns, the exposure time can be extended to increase the hardness and durability of the printing plate.
Process quality control flexographic resin plate production
The quality of the flexo resin plate is good or bad, the exposure control of plate making is the key. The difference in exposure time will make the produced flexible resin plate have greater differences in hardness, corrosion depth and elasticity. Long exposure time and overexposure will cause the graphics on the printing plate to be lost or not washed out, and the printing plate will also be deformed, hardened and brittle. If the exposure time is too short, that is, underexposure, the photosensitive layer on the surface of the printing plate will be washed away when the plate is washed. In order to avoid underexposure, especially for large-area solid plates and negative plates, the optimal exposure time must be selected to ensure that the resin plate reacts adequately.
Typesetting method
Carton printing generally has more color plates, and the plates cannot be cut too loosely during imposition. It is better to make the same color printing plates into a whole. Care must be taken when pasting unavoidable loose and small editions, otherwise small and fragmented printing plates will not be firmly attached during the production process, causing damage and loss during the printing process. In addition, when pasting, maintaining, and replacing small plates, fine patterns, and text plates, do not pull them too hard to prevent damage and tear the plates.
Printing paste
It is required that the printing plate be pasted flat, and the edge of the printing plate must be sealed firmly with water-free adhesive tape. If the printing plate is not in close contact with the surface of the printing roller, the printing plate will be tilted upward, and the tilted portion is very easy to penetrate the ink and bounce, causing the bounced printing plate to be damaged or lost during the printing process.
Printing process
The production speed of the corrugated board line and the heating area and heating time of the base paper on each preheater are different, which will lead to differences in the produced corrugated cardboard moisture content, cardboard hardness, flatness and cardboard thickness. This is relatively common in the production process, so during the printing process, the relevant gap of the printer should be adjusted at any time to eliminate the impact of the cardboard problem on the printing quality and ensure that the ink color of the printed product is uniform.
Maintenance of flexo resin plate
In order to reduce the friction of the dirt on the resin plate and reduce the chance of abrasion, use a soft brush or soft cotton yarn to dip the resin plate of the printed product with water to remove paper dust, dust, debris, sand particles, and ink residue on the plate Scrub thoroughly until the original color of the printing plate is washed out. If these dirts are not cleaned, it will not be easy to remove them after they are dried. In the next printing, it will cause paste or press into the flexographic resin printing plate, causing partial damage to the printing plate and affecting its use. In addition, during the printing process and after the product is printed, pay attention to whether the edges of the printing plate are warped, the small prints fall off, the tape falls, and the water-free adhesive tape at the edge of the plate is damaged. Exclude to ensure that the printing plate is intact the next time it is used.
Adjusting the operation and debugging gap of printing and slotting machine
The adjustment of the gap between the rollers of the printing machine mainly includes the adjustment of the gap between the feed roller and the bridge roller, the printing roller and the printing roller, especially the adjustment of the gap between the printing roller and the printing roller. This gap includes cardboard thickness + film base (0.1mm) + double-sided tape thickness + resin plate thickness-0.3mm + liner sponge thickness. When adjusting the parallelism of the inking roller, printing roller and embossing roller, make sure that the two ends of each roller are parallel and consistent. This can provide a strong guarantee for the inking of each printing plate uniformly. The small dots are protected from wear and tear, which extends the life of the flexo plate.
Pressure adjustment
The printing pressure here refers to the pressure between the inking roller and the printing plate, the printing plate and the corrugated cardboard during the printing process. Sliding friction causes plate wear. Moreover, the external printing plate will be compressed and deformed due to excessive pressure, resulting in accelerated wear at the edge of the printing plate, deformation of the plate surface, cracks, and off-plate, and wild ink and other failures on the printed matter. In fact, adjust the gap and parallelism between the rollers; control the printing pressure. A good printing pressure can make the printing plate in an ideal state for a long time, and can extend the service life of the printing plate. In addition, under the polyester film affixed to the printing plate, a cushion of sponge is placed to absorb part of the printing pressure, which is also a good way to adjust the pressure of the printing plate.
Speed ​​control
The production speed of corrugated paperboard should be even when printing. If the speed of the machine is too fast or too fast (especially high printing slotting machine with more than 120 sheets / minute), it will cause resin plate and ink roller, resin plate and corrugated cardboard. There will be a large impact between them, and it will also cause the printing plate to hit the roller and jump, especially in the case of uneven corrugated cardboard, the jump of the relevant roller will be more obvious, thus resulting in the gap between the printing plate and the inking roller and corrugated cardboard The resulting speed difference increases the frictional force on the resin plate and accelerates the edge wear of characters and patterns on the plate parallel to the direction of the roller, and even damages by impact.
Storage of the printed version
The original plate material of the unmade flexographic resin plate must be kept away from light. Otherwise, after being irradiated by sunlight and ultraviolet light, the photosensitive material of the flexographic plate will be seriously polymerized and the plate material will be scrapped. The depth of coming out or bump is not enough. In addition, do not place it on a wet floor or a floor with organic chemical solvents to prevent damage to the resin plate.
Please pay attention to the storage of the prepared printing plate and the used printing plate. When stacking up and down between the printing plate and the printing plate, the number of stacks should not be too much. Too much will make the lowermost printing plate under pressure for a long time. The state, especially the printing plate with uneven layout, will be deformed and damaged and scrapped.
Grasp the quality of all links related to flexo printing plates and study their interrelationships. For example, for small batches, multiple specifications and the same type of packaging carton printing plates, when the content is the same, you can adopt a common set of printing plates Methods, only to replace different parts, and formulate corresponding measures, you can ensure the printing quality, reduce the number of re-copying, increase the utilization rate of the printing plate, reduce the number of labor, improve production efficiency, lower the relevant costs, reduce production costs.
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