Most of the carton printing adopts rubber engraving layout. The birth of laser engraving machine replaced manual engraving. This is a qualitative leap for carton printing, but it is powerless for the printing of light and dark gradient patterns and small text, although its fineness is not high. Can only consider offset printing, otherwise it can not meet customer requirements, so the entire production process had to be adjusted. Of course, it is not difficult for producers with offset presses and laminating machines. Corrugated cardboard has been produced. What if there is no offset press or laminating machine?
The use of flexographic printing can only use existing resources to find a way. In fact, the working principle of flexo printing machine and ordinary watermarking machine is the same, the difference is its core component-anilox roller. The flexo printing machine is a laser engraved ceramic anilox roller with deep mesh holes, and the mesh line is more than 300 per square centimeter. The ink printing machine is a steel anilox roller with only 40 ~ 65 lines per square centimeter and the mesh holes are shallow , The mesh structure is different. We understand these and think of ways in process and operation skills.
1. Plate making
A. Design
To obtain high-quality prints using resin plates, you must have excellent design drafts and high-quality film. A good design draft is the basis of high-quality printed matter, to ensure good reproducibility, you should pay attention to when designing:
1. If a photo-engraving is used, all lines and text in the ink manuscript must be of the same ink level, otherwise it will lead to unnecessary photo correction and manual modification to produce a satisfactory film.
2. In the case of satisfying the requirements of customers, try to make the strokes of the positive characters thinner and the strokes of the negative characters thicker, so that the interval between the strokes is increased, and it is not easy to cause printing paste.
3. As far as possible, avoid printing dots and large area color block patterns on the same plate. If large area color block patterns and thin line patterns are printed separately, pressure adjustment and color control are much simpler.
4. If another color is overprinted in one color, and no gap is required between the colors, the accuracy of the printing machine must be considered in the design, so that the two-color layouts are superimposed and the width of the superimposed part is the printing deviation of the printer.
5. The design draft must consider the elongation of the resin version. During plate making, the plate will not shrink and stretch, and when the plate is mounted on the plate roller, the plate will extend in the direction around the plate roller, and the resin plate elongation can be calculated: resin plate elongation = plate roller + Double-sided tape and liner thickness ÷ (plate roller + double-sided tape thickness + resin plate thickness) × 10%
The actual size required for design multiplied by the elongation of the resin version is the size of the design draft.
B. Film
High-quality film is critical to the production of resin plates, and the film used must be carefully checked:
1. The density of the light-transmitting area should be less than 0.05, so as to ensure that the film meets the requirements of plate-making, has a strong subtle pattern and clear negative characters
2. The density of the opaque area is greater than 4.0. Too low a density will cause the pattern to not be deep enough or undesirable patterns appear.
3. Films must have the correct pattern direction, that is, the positive film and text when the drug film is upward, which is very important, so as to ensure that the film and the surface of the plate are in good contact during plate making
4. Film should be clean, free of stains and wrinkles. Otherwise, the wrinkles of the pattern part will be reflected on the plate. Holding the film diagonally can reduce the wrinkles.
5. The number of screen lines must not be higher than the number of screen lines of the anilox roller. Generally, the number of screen lines should be about 1/3 of the number of lines of the anilox roller. The ink is transferred by the roller, and the ink hole of the anilox roller is engraved at a certain angle. It is easy to interfere with the angle of the screen and produce a "moire". Therefore, pay attention to avoid moire during plate making. Since most anilox rollers usually engrave ink holes at a 45 ° angle, the screen angle should try to avoid 45 °, generally Y90 °, M15 °, K30 °, C60 °, or Y82.5 °, M67.5 °, BK37.5 °, C97.5 °. At present, there are many new anilox roller ink hole engraving angles are no longer 45 °, but 60 ° or other angles are used for engraving, which is very beneficial to avoid moire. [next]
D. Plate making
The design draft can be plated after being photographed or photographed into a film, which can be divided into six steps: back exposure, main exposure, processing, drying, debonding and post-processing. During the actual operation, special attention should be paid to the following issues:
1. The base layer of the plate can be established by back exposure to obtain the desired relief and strengthen the adhesion between the polyester support film and the photosensitive resin layer. The correct back exposure is from the direction of the polyester support film, which can protect the fine pattern of the plate during the rinsing process and prevent the relief from collapsing.
2. The main exposure should be performed immediately after the back exposure, because the photosensitive activity will gradually disappear, resulting in a longer main exposure time and poorer exposure latitude.
3. When the guarantee layer of the resin plate is torn off, the photosensitive speed of the plate is rapidly attenuated. The film should be placed on the plate immediately or the main exposure should be performed within 10 minutes to obtain the best results.
4. The main exposure time can be determined by the main exposure test. The photosensitive resin becomes insoluble by the polymerization reaction, and the printing plate can reproduce the fine patterns on the film. Before performing the main exposure, the vacuum film must be wiped by hand to expel the air so that the plate and the negative film are closely attached.
5. The printing plate must be dry, otherwise it will affect the thickness uniformity of the printing plate. After drying, do not let the printing plate surface contact with the surface of other objects, and do not touch the printing surface with your fingers, otherwise it will leave traces. But before removing the tack, be sure to remove any spots on the surface of the printing plate. After debonding, you should clean the remaining spots on the back of the resin plate. If you do not clean these things, it will affect the uniformity of the thickness of the printing plate and the adhesion of the mounting tape.
When making a resin plate, it often happens that the thin line part is washed out or the relief of the negative picture part is shallow, then a special process is needed to achieve the desired effect:
Using "separate back exposure" process. Corrugated carton industry generally adopts a flexible resin plate with a thickness of 3.94mm. The depth of the graphic is 1.52 ～ 2.00mm. The base layer is thin. The very fine parts of the printed pattern cannot withstand conventional exposure. Separate back exposure "process. First confirm the very thin line points and text areas in the film, use the mask to cut into an area outline model, first establish the entire base layer for the back exposure of the plate, and then accurately position the mask on the surface of the polyester support film according to the film instructions Then, back exposure is performed to establish the base layer in the desired area, and the time of the two back exposures is determined according to the required base layer thickness.
Using the "main exposure mask" process. If the design draft contains thin lines of text and a negative image that is easy to paste, then the masking process can be used to achieve the desired effect. The mask should be made of a material that does not transmit ultraviolet light. First use a shorter main exposure time to ensure the depth of the negative image to expose the plate, and then use a mask to cover the negative image part and add exposure to the thin line part. [next]
Second, adjust the equipment
Check whether the electrical control device of the ink-printing machine is sensitive, whether the air valve of each trachea leaks, and add lubricating oil to each lubricating part. Clean the inking roller thoroughly (it is best to clean the anilox roller with detergent or detergent, if necessary, you can use a brush dipped in detergent to clean it, and do not use a metal brush to avoid damage to the anilox.), Adjustment roller and Plate cylinder, adjust paper feeding device, paper guide wheel spacing, printing pressure, slot size and phase. Correct the parallel rotation of the rollers.
Start the main motor of the watermarking machine, run slowly and at a constant speed, and the plate can be installed without any abnormal rotation.
3. Selection of ink
Generally, field products use water-based inks with a viscosity of 45 to 60 ° (coating 4 cups). The ink leveling and hiding power of this viscosity range are both. The ink has good hiding power and is solid on the ground; the ink has good leveling property and is fine and shiny on the ground. The viscosity of the ink used in the network cable product is 30-40 ° (coating 4 cups). The ink transfer performance of this viscosity range is good, and the reproducibility of the dot is strong. The printed product has clear dots, small deformation, and is not easy to paste and dirty. Version.
4. Operation
Everything is ready, stick the dried resin plate to the 4mm liner, and then paste it on the plate cylinder according to the specified size, then adjust the viscosity of the water-based ink with industrial ethanol at a ratio of 1: 1, and then start the ink pump Ink, rotate the inking roller until the amount of ink is uniform, check the amount of ink, it is better to distribute the ink evenly on the inking roller and loosing the net pattern. At this time, start the trial printing, as the picture is not clear and the bottom phenomenon can be adjusted The printing pressure should not be too large to prevent the deformation of the printing plate; if the picture is blurred, the ink line can be reduced to reduce the amount of ink until the picture and text are clear, the network line is defensible, and the dots are not deformed.
The first print can be printed in batches after confirmation. The speed of normal printing should be balanced and maintained at 900 ~ 1000r? Min. The printing process should pay attention to the amount of ink, whether the dots are deformed, and whether there are dirty spots. It must be as strict as offset printing. Achieve "Sanping (ink roller flat, plate roller flat, pressure roller flat), two small (small ink volume, low pressure), four hard (look at proofs, stir ink tanks, check ink volume, wipe frequently) Version). It must be noted here that the wiping version can be scrubbed with a soft cloth dipped in absolute ethanol. It is strictly forbidden to use gasoline, otherwise the resin version is very easy to corrode and deform. Rotate two times in a row, and then send the board for printing after the printing plate is evenly coated with ink.
V. Analysis and summary
Practiced according to the above method, we printed seven wolf clothing outer boxes with good results, clear patterns and clear layers. Especially the background and close-range gradual effects of the seven wolves are excellent. The unwillingness of backward wolf has truly restored the connotation and corporate philosophy of the "seven wolves" trademark, and the batch of carton boxes has been well received by customers. Since then, we have received gratifying rewards for other customers' packaging.
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