Key points for design and printing of plastic gravure printing patterns

Manuscript design of composite flexible packaging is the first step in the design and manufacture of composite flexible packaging. Unreasonable document design will increase the difficulty of printing and reduce the pass rate of printed products. It may also cause difficulties in slitting, bag making and other processes, or even a whole batch. Product scrapped. Therefore, when designing platemaking and printing, many designers engaged in fine arts only design from the perspective of art or lithography process when designing intaglio documents, without fully considering the particularities of gravure printing technology. Many beautiful and moving pictures of the designed manuscript cannot be printed ideally. From the perspective of gravure printing technology, what issues should be paid attention to in the manuscript of composite flexible packaging? You can pay attention to whether the design manuscript can meet the printing requirements from the following aspects:

1. Printing review work before design manuscript making

After the gravure manuscript is confirmed by the customer before entering the plate making, it must go through the evaluation of the layout. That is, the plate-making manufacturer and the printing manufacturer communicate effectively to determine whether the printed manuscript can be effectively printed by the printing manufacturer.

During the evaluation of the new layout, there must be a paper color manuscript confirmed by the customer (the electronic manuscript can only be used as a reference), a layout drawing, and a review form; if there are printing reference samples from other printing manufacturers, it must be brought to determine the relevant color sequence In the case of overprinting, if there is no such sample before making a plate, and the actual manuscript is printed according to this type of manuscript, it is easy to cause the hue to not be printed. Because different printing companies use different inks and different printing processes, these can be adjusted to make the hue close, but if it is the same large area special green background color, if the customer's printing reference samples from other manufacturers are special Color, and when we have made blue and yellow overprints, there may be a phenomenon that the hue is out of touch, which affects the production efficiency and misses the time and time.

2. Design and manufacture of electric eye cursor

The electric eye cursor can be on one side of the coil or on both sides. However, it is recommended to have both sides, so as to avoid the use of some coiled electric eye cursors on the left and some stored on the right. It is necessary to constantly adjust the position of the photoelectric eye. The size of the cursor also has certain requirements, and different packaging opportunities have certain differences. Under normal circumstances: 2mm <width of cursor < 10mm , length greater than 5mm . The width of the cursor ( less than 2mm) may affect the normal tracking of the device due to the weak signal. The cursor is too wide ( greater than 10mm) , which is not beautiful. On the other hand, the tracking and positioning accuracy will be reduced. The length of the cursor should generally be greater than 5mm . During the packaging process, the roll film will be shaken and deviated. If the cursor is too short, the cursor may deviate from the position of the photoelectric eye, resulting in inability to track.

The cursor generally chooses a dark color with a large contrast to the background color, preferably black. On transparent composite packaging products, the cursor should be carved as deep as possible when engraving the plate. Electric eye cursors cannot generally use red and yellow as cursors, nor can they use the same color code as the photoelectric eye for the cursor color. If the light emission of the photoelectric eye is green, the light green color cannot be used as the color of the electric eye cursor. The eye cannot recognize the green color. If the background color is a darker color, then the cursor should be designed as a hollow light-colored cursor.

The spacing between the cursors is used to fix the length, so the error between the actual spacing and the design value should not be too large, generally only an error of ± 0.5mm is allowed .

Aluminum-plated films or pure aluminum films have strong specular reflection, which will affect the identification of electric eyes. It is recommended to print a white background on the composite film cursor. For the transparent composite film, because it will be affected by the color of the items in contact with it, it is also recommended that the cursor be printed on a white background to reduce the interference of other background colors.

3. Design and printing of patterns

Many designers do not understand the technical principles of gravure printing and the difficulties in actual printing. They only pursue aesthetics and artistry in the design of manuscripts, but do not consider the difficulties in actual printing. Therefore, they cannot follow the designer ’s ideals when printing. The perfect picture is printed, so how to reduce the occurrence of this situation and make the design plate making and printing more closely? The author sums up the following experiences from actual work:

1. Deepen the shallow net

In the gravure printing layout design, if there is red and blue overprint, red and yellow overprint, blue and red overprint, black and red overprint, or black, blue, red and yellow overprint, the dark dots are less than 25% . During the production process, the whole is deepened by 3 ~ 5% . When the machine is printed for the first time, the ink used on the deepened plate roller can be diluted with a diluent. Under the premise that the hue is unchanged, it can be guaranteed that there will be no "shallow dot leakage. "The phenomenon is also called" dry plate "in the printing industry.

2. Dirty version

When designing the gravure printing layout, you should also note that if there is a large area of ​​white bottoming, it is best not to design a particularly light black, blue, red, etc. hanging screen before or after the white layout follows the scratch direction, otherwise it will be The phenomenon of "white belt dirty" appears, which is also called "scratching" in the printing industry.

3. Overprint accuracy

The overprinting accuracy of gravure printing can only reach 0.2mm , so text and graphics ( especially text ) with strokes less than 0.4mm cannot be printed by multi-color overlay, and can only be printed with a single ink, otherwise it will easily cause ghosting (overprinting) Not allowed) phenomenon. For small text and pattern hollow printing, monochromatic hollowing should be used, multi-color superimposed hollow printing should not be used, and the background color of the photo should not be used for direct hollow printing. For small text and patterns, it is also inappropriate to use text pattern hollow overprint text patterns. Pay attention to the size of the text and the thickness of the strokes. Text that is too small and strokes that are too thin may not be printed, and printing failures often occur when the pen is broken or even missing. Too small text, if the strokes are too many and too dense and the lines are thick or the printing plate is too dark, it is easy to appear "paste characters". The transfer performance of gravure printing is not as good as that of lithographic printing. There is a problem of blocking the plate. Generally, you should avoid using dots below 10 %. Especially for large-area background colors, too light dots should be avoided, otherwise the dots will not be reproduced well, which will easily cause uneven color and easy to change color. Even if it is printed at the beginning, because it is too light, it is easy to affect the hue due to the abrasion of the plate roller during the printing process, and the number of printing plates is low. Spot color printing is recommended for large areas of light colors.

4. Shallow

When a character pattern and a character pattern exactly another printing nest, the expansion should be appropriately sized character pattern light (typically 0.2 - 0.4mm), so that the darker character pattern overlaps with, or is in the printing process It is easy to reveal the background color at the joint. As for how much the lightening is related to the color, if the two colors are opposite colors, the overlapping part produces a black line, which affects the appearance and should be minimized.

5. Setting of spot color printing plate

Trademarks, light-screen overprint , excessive colors , small characters ( text under 5 characters ), small five-star patterns , large-area background colors , special effects, etc. There are many colors with high purity, very bright colors, and some fluorescent colors and transparent Special colors, such as color, gold, silver, etc., must be printed with a spot color. At this time, a spot color plate roller must also be produced for printing. Due to coarse particles and other reasons, the general pearlescent ink, golden ink and silver ink should not be used for hanging shallow screen printing.

6. Arrangement in color sequence

In general, the printing is from dark to light, while the surface printing is usually printed in light and then dark. The two seem to be different. In fact, the human eye sees that the sequence is exactly the same, that is, the dark color is the first to be seen. For color printing with photos, the three primary colors should be printed continuously, and no other spot colors should be sandwiched between them. Otherwise, it is not conducive to the overprinting of the three primary colors and the fusion of various layers of ink, and the printed photos will be less effective. Plastics generally intaglio printing color sequence K, specifically 1, 2 special, specifically 3, C, M, Y, W. Special products can be treated specially , gold is usually put in the first or second color, silver is usually put in the last color (it can be put in other places according to special needs). Spot colors (especially large-area spot background colors) are generally placed between black and blue, so that large-area spot background colors can pass through more printing units to ensure that the ink layer is fully dried, which is helpful to reduce the amount of residual solvent. Of course, special needs can be placed in other places. For example, some layouts are designed with dark lines on the background color, so the background color must be placed after the C (blue), M (red), and Y (yellow) colors.

7. Sharing of printing plates

In order to save costs, most products of the same series will have a common version. Which pages can be shared? Generally speaking, the following factors should be considered to determine whether the printing plate can be shared:

When the white version is shared, consider whether the shape of the hollow is the same , whether the bag is white under the light spot, etc.

When the silver version is shared, it depends on whether there is a small silver word , the shape of the border line is consistent , and the color sequence of each set is consistent. Common version also requires consistent color number, the lower edge of a first color block any of the light spot is aligned lower edge, the circumferential version, long version, the pattern must be consistent. (The white version and the silver version are placed in the last color, and the color sequence may not be considered when vertical overprint is not involved. For example: the first variety is black, special, blue, red, yellow, and silver. The second variety is black, blue, red, Yellow and silver. If the two types of silver plates do not involve vertical overprinting, the silver plates can be placed in the sixth color in variety one and in the fifth color in variety two, but they can be shared.)

8. Design principles of horizontal and vertical patterns

Special care should be taken not to have too dense patterns and lines at a certain position in the vertical direction, otherwise the position will produce strong tendons during printing and winding, and the pressure will cause the ink to stick back. At this time, a moderate hanging method can be used to reduce The thickness of the ink layer. The art designer did not consider the errors in the bag making and slitting process, which made the bag making and slitting difficult.

The surroundings of the compound packaging bag should be designed with similar colors or transparent. If the color contrast of the packaging bag or roll material is large, the vertical and horizontal imposition will have obvious contrast. Since the cutting of the bag making machine, slitting machine and automatic packaging machine is impossible to be absolutely accurate, generally there is a deviation of more than ± 1mm , so the bag or the rolled film produced by the slitting will be cut at the cutting place. There is a line with a large contrast, which affects the appearance. For high-strength composite products and high-temperature cooking bags , in order to improve strength and protect the ink layer, it is recommended that no color be printed around the composite product. For a large background area, in the absence of the side of the transparent design, plate making process imposition must consider both sides of the widening 1 - 2mm. In this way, in the slitting and bag making process, even if there are deviations, there will be no transparent edges or aluminum foil, aluminum-plated edges.

9. Setting of cutting track

Detecting a line width of 2mm is generally appropriate, generally set to black or spot color, preferably dark.

Large areas with lighter backgrounds, flavoured text or patterns without obvious vertical contrast edges need to be added with a slit tracking line, otherwise it will cause the semi-finished rolls to be unclear and neatly cut.

10. Bleeding and weekly release

If the horizontal size of the pattern exceeds 600mm , the overall bleeding needs to be considered . In addition, the white and coated products are printed with gold and silver edges (the electric eye cursor is pressed on the gold and silver edges). The gold and silver patterns need to consider bleeding and bleeding on both sides. 0.5 - 1mm (typically 1mm according added), thus avoiding the cutting process due to a slightly off-cut edge exposed silver resulting white edge. Similarly, if the electric eye cursor is pressed against a large area of ​​background color, the large area of ​​the background color should also consider bleeding. The bleeding situation is similar to gold and silver edge bleeding.

Extinction BOPP film shrinkage greater need circumferential direction of each of the pattern on the plate increases 1mm (Version periphery 550 - 690mm, the circumferential direction of the plate 3 patterns)

Others such as: PET , PE film, PVC and other films need to be considered in addition.

The above is some shallow understanding of my actual work. I hope that it will be helpful in the actual work of the peers. It is our ultimate desire to organically combine design, plate making and plastic gravure to make the design more perfect and printed. More ideal is also our expectation. Plastic gravure belongs to the sunrise industry. Many problems need to be continuously summarized in practical work. I believe that if everyone goes to research and development together, the plastic gravure industry will definitely flourish!

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