Quality control during corrugated box printing
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Corrugated boxes are printed in a special way. There are many quality problems in the printing process. In order to ensure the quality of printing, strict quality control is required. This article describes the following aspects.
First, the use of printing plates
In the printing production of corrugated boxes, the carton printing plates commonly used in most carton factories mainly include rubber plates and flexo resin plates. Although the rubber version is cheaper and more frequently used than the flexographic resin version, it has complex printing patterns, fine text (such as barcodes, web graphics, and small fonts) and large areas because of its poor printing accuracy and low efficiency. When printing in the full version, it is necessary to use a photosensitive resin plate to complete the printing work. Of course, the flexographic resin version also has its disadvantages: the flexographic resin version is more expensive, and the technical content of the production and use is higher than that of the hand-carved rubber plate and the laser-engraved rubber plate, so it is trying to improve the printing durability of the flexo plate and adopt the best. It is especially important to use the method to extend the life of the flexo resin. Only by controlling the quality of the carton flexographic resin plate, and mastering the method of use, and controlling each link related to the plate, can effectively control the printing quality and produce a beautifully printed carton.
Flexo resin plates for corrugated box printing generally use plates with a thickness of 3 to 7 mm and a Shore hardness of 25 to 30. In order to overcome the unevenness and rough surface of the corrugated board, it is necessary to put forward higher requirements on the flexographic resin plate, which requires the printing plate to be wear-resistant, strong in impact resistance, moderate in hardness, good in resilience after compression, and uniform in ink. The thickness is the same. According to the pattern, the size of the lines, and the material of the corrugated board, the layout of the flexo plate, the hardness requirements, and the production method are arranged accordingly. When the quality of corrugated board is poor and the full-color color is printed, a thicker and softer flexo plate is used; when the quality of the corrugated board is good, and the fine pattern, small-word and screen version are printed, the flexo with high hardness and low thickness is selected. Resin version.
Second, the selection and correct use of water-based ink
The advantages and disadvantages of water-based inks are related to whether the color of the carton printing is pure and bright, so pay great attention to the selection. There is no obvious difference between high-quality ink and color standard. The hand feel is fine and viscous. The concentration is suitable for adding water or alcohol solvent to dilute without precipitation and agglomeration. It is stirred with wood stick and no foam is produced. It is mixed with other inks, and the affinity is good. Dissolved phenomenon, the ink color is pure, no abnormal reflection, and vice versa.
1. Requirements for water-based ink performance
After long-term storage of the precipitate, it should be easily redispersed after stirring; it should have good flow properties and viscosity; have good storage stability; dry performance should be fast and appropriate; it can not have any adverse effect on the printing plate and printing machine; There is too much pungent odor.
2. Selected water-based ink technical parameters
Color: Approximate to the standard pattern (Note: compare the sample and the standard sample without using the manual color wheel to compare the color);
Fineness: less than 20 microns, instrument: 0-50 micron scraper fineness meter; viscosity: 20 seconds ± 5 seconds, instrument: RIGOSHA4 # cup (25 ° C); PH value: 8.0-9.5, instrument: portable pH meter ( PHB-2 type); Heavy metal content: in line with the world packaging green environmental standards; various tolerance: meet the requirements.
3. The correct use of water-based inks
Stir well before use to keep the ink composition uniform; after the use, the ink should be sealed and sealed, so that the dust can be dropped and the skin can be dried; if the ink contains impurities, it should be filtered first, then used with new ink. During storage, please avoid near high temperature or hot sun exposure. Under normal conditions, it can be stored for one year without deterioration. If the viscosity of applied ink is found to be slightly larger, an appropriate amount of water can be added for adjustment.
Third, the process design should be reasonable.
1. Guarantee print clarity
Firstly, the printing plate should be made of materials with good wear resistance, moderate elasticity and high quality. The thickness of the same plate should be the same. The thickness of the resin plate should be no less than 4mm, and the rubber plate should be 6-7mm. Whether it is printed with a negative film or a hand-cut, the layout must be flat. The depth of the line of the handwriting is not less than 3mm. The arrangement of the characters should not be overcrowded, the arc should be smooth, the thickness should be uniform, and the straight line should be straight and smooth. The ink should be properly lightened during printing. The ink layer of the ink roller should not be too thick, and the pressure of the roller should be moderate. The ink is evenly printed, and the surface of the box is not obviously dent. It is forbidden to increase the ink concentration and increase the pressure of the applicator roller to improve the printing effect. This will not achieve the desired effect, but will result in the printing paste ink, the printing quality is even worse, especially the text is small, the pattern is complicated, the lines are delicate, and the overprinting precision is required. The high layout, the disadvantage is more obvious; the speed of the printing machine can not be lower than 800 rev / min, the speed is too fast, the surface of the box is uneven, and there is a bottom phenomenon. Too slow ink is too thick, the plate is easy to paste, and at the same time, it is necessary to prevent paper wool, paper scraps, etc. from entering the printing machine and sticking to the printing plate. If it is found that there is paper scraping, stop it immediately, wipe it with a rag and alcohol.
2. Prevent overprinting and ghosting when printing whiteboard carton
When the coated whiteboard paper is manufactured, the coating liquid for coating the whiteboard contains glue, and the surface of the high-grade whiteboard is coated with a small amount of light wax, so when the paperboard of the whiteboard is used for printing, the printing plate is in contact with the whiteboard paper. There is a slip phenomenon at the moment. In addition, the pressure of the printing plate is too heavy, the water-based ink is not easy to permeate, the printing of the carton ink is slow, the printing is continuous, the printing products are stacked one on top of the other, and the overprinting ghost formed by the scratches appears on the surface of the box.
To solve this problem, the ink should be diluted with ethanol, not water, because it is not volatile, it is not conducive to the drying of the ink; the printing pressure should be appropriately reduced, the printing speed should not be too fast, not more than 600 rev / min. Add the exhaust fan or the hot air drying box ink before the stacking of the printing machine.
3. Ensure overprint accuracy
The accuracy of overprinting depends first on the precision of the equipment and whether the adjustment of the paper-feeding board is parallel, and the layout, assembly and calibration. Let's talk about the overprint accuracy in terms of layout collage.
After the printing plate is completed, take a 0.5mm thick transparent polypropylene plate base, draw a vertical line at the center of its length, and then press the size of the carton to be printed, draw the long and wide high side lines with a small stroke, and then press the sample or sample box. Production notices specify imposition. After the position of the layout is positioned, draw the line with the water pen according to the edge of the plate, and then cover the same size plate prepared in advance on the plate of the drawn line, and accurately trace all the edges (such as the imprinting three colors can draw a plate base) Finally, according to the overprint color, the corresponding printing plate is firmly glued to the painted position with neoprene. Then, the printing plate is attached to the roller of the printing machine by double-sided tape, and the center line of the plate is aligned with the center line of the printing plate of the printing machine. As long as the position of the imposition is accurate, other objective conditions are satisfied, and the overprinting is accurate.
4. Note the effect of full-page printing on the strength of the carton
We know that when printing, corrugated cardboard is formed by the various paper guide rollers and printing rollers of the printing press and is transferred to the grooved part. After the paperboard is subjected to the pressure of the roller during the transfer process, its physical shape changes to varying degrees, which will inevitably affect. The strength to the carton. The full-page printing is particularly prominent. The strength of the carton of the same material is reduced by about 30% compared with the non-printing. Therefore, the production process should be very careful, and the following measures can be taken to alleviate:
First, the gap between the paper guide rollers of the printing press should be properly adjusted, so that the inconvenient behavior of the printed paperboard should be smoothly passed (slightly less than the thickness of the cardboard 0.1-0.15mm);
Second, the plate pressure is adjusted to meet the clear printing, and the handle of the box has no depression and flatness;
Third, properly increase the speed of the printing press (1000 rev / min or more), so that the cardboard passes through the printing machine as soon as possible, reducing the compression time of the cardboard.
Fourth, the printing operation process
1. Clearance adjustment between rollers of the printing press
It mainly includes the gap adjustment of the paper feed roller and the bridge roller, the printing roller and the printing roller, especially the gap between the printing roller and the printing roller. This gap includes cardboard thickness + film base (0.1 mm) + double-sided tape thickness + resin plate thickness - 0.3 mm + pad sponge thickness. When adjusting the parallelism of the ink roller, printing roller and embossing roller, make sure that the ends of each roller are parallel and consistent, which can provide a strong guarantee for the uniform printing of each plate, and can also make fine text, Small dots are less protected from wear and tear, extending the life of the flexo plate.
2. 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, and the pressure between them is too large, and the printing plate is compressed to generate a certain amount with the anilox roller. Sliding friction causes the plate to wear. Moreover, the outer printing plate is compressed and deformed due to excessive pressure, resulting in accelerated wear at the edge of the printing plate, deformation of the plate, cracking, severing of the plate, and occurrence of problems such as wild ink on the printed matter. In fact, the gap and parallelism between the rolls are adjusted; the printing pressure is controlled. Good printing pressure can make the printing plate under ideal pressure for a long time, which can extend the service life of the printing plate. In addition, under the printing of the polyester film, a layer of cushioned sponge is applied to absorb part of the printing pressure, which is also a good way to adjust the plate pressure.
3. Machine speed control
Corrugated paperboard should be produced at a uniform speed when printing. If the machine speed is too fast or the speed is too fast (especially the high printing slotting machine of 120 pieces/min or more), it will cause the resin plate and the inking roller, the resin plate and the corrugated cardboard. A large impact between the two causes the plate to hit the roller and bounces, especially in the case of uneven corrugated cardboard, the beating of the associated roller is more pronounced, resulting in a difference between the printing plate and the inking roller and corrugated cardboard. The speed difference is generated to increase the friction of the resin plate, and the edge of the text and the pattern parallel to the direction of the roller on the plate is accelerated and even damaged by the impact.
4. Keeping the printed version
The original material of the unprinted flexographic resin plate must be stored in the dark, otherwise it will seriously cause the flexographic photosensitive material to polymerize and cause the plate to be scrapped after being irradiated by sunlight and ultraviolet light. The lighter will cause pattern, text and line washing. Out or the depth of the convex and concave is not enough. Also, do not place it on wet ground or organic chemical solvents to prevent damage to the resin plate. Note that the prepared printing plate and the used printing plate should be stored. When the printing plate and the printing plate are stacked up and down, the stacking quantity should not be too much. Too much will make the lowermost printing plate under pressure for a long time. The state, especially the uneven printing plate, will be deformed and scrapped.
The above mentioned aspects, although not very comprehensive, can give the peer a little reference.