The production process of printing, compounding, slitting, and bag making of plastic flexible packaging is a linkage process, and the design of gravure layout is the first step of the entire plastic composite flexible packaging. The rationality of the layout design is not only a necessary condition for product demand, but also a key issue whether it can improve production efficiency and reduce production costs. Improper layout design will increase the difficulty of printing production, reduce the qualified rate of printed products, and may also cause difficulties in production processes such as compounding, slitting, and bag making, and may even cause the entire batch of products to be scrapped. When designing intaglio layouts, many customers' designers only design from the perspective of decoration art or from the perspective of lithographic printing technology. They have not fully considered the special characteristics of the linkage of the gravure production process, which has led to many design layouts. Can not effectively render the text pattern perfectly.
I. Review work before plate making
Before the layout of the intaglio printing manuscript is confirmed by the customer, before entering the plate making, it is necessary to go through the review of the layout manuscript and determine whether the printed text pattern can be more effective through effective communication between the platemaking manufacturer and the printing manufacturer and effective communication with the customer. To the ground.
During the new layout review process, paper color drafts (or electronic manuscripts), typeset drawings, and physical samples confirmed by customers are required. If there are printing reference samples from other printing manufacturers, you need to retrieve the reference to determine the relevant color sequence and overprinting. If there is no such sample reference before making a plate, and when the actual printing production allows the printing factory to refer to this type of sample, it is very easy to cause inconsistency in hue, or it is difficult to display a certain overlap. Because different printing manufacturers use different ink systems, the printing processes used are not the same. Although these can be adjusted to make the hue close, but when there is a large area of background color, if we use spot color printing, we have made When the overlapping colors are displayed, the hue cannot be followed, which affects the entire production process.
Design and production of electric eye cursor
The electric eye cursor is used to track the fixed length. Generally, only an error of ± 0.5 mm is allowed, so the error between the actual distance and the design value should not be too large. Especially for coils (automatic packaging), the electric eye cursor is particularly important. . The electric eye cursor can be on one side or on both sides of the coil. In general, it is recommended to set two-side electric eye cursors. This method can avoid frequent adjustment of the electric eye cursors when different packaging machinery or post-processed finished products are made. The size of the cursor electric eye also has certain requirements, and there are certain differences in different packaging opportunities. Normally, the cursor width is 2-10 mm. The width of the cursor is less than 2 mm, which may lead to tracking accuracy. After all, the machine has an accuracy error that affects the normal tracking of the device. The cursor width of more than 10 mm is not beautiful, and the accuracy of tracking and positioning will be reduced. The length of the cursor is usually greater than 5 mm. During the automatic packaging process, because the roll film will shake and deviate, the electric eye cursor is too short, which will easily cause the cursor electric eye to deviate from the position of the photoelectric eye, causing tracking failure.
Cursor eyes generally use dark colors that have a large contrast with the background color (usually black). On transparent composite packaging products, the dots should be carved as deep as possible when the cursor is engraved on the plate. Cursor sensors generally do not use red and yellow, nor can they use the same color scale as the light source of the light meter sensor. For example, the light emitted by the photoelectric eye is green, and green or light green cannot be used as the cursor color of the electric eye, otherwise it cannot be recognized. If the background color is a darker color (such as black, dark blue, etc.), the cursor should be designed as a light-colored cursor with hollowed out and white highlighting.
Aluminized film or pure aluminum film has strong specular reflection, which will affect the recognition of the electric eye. It is recommended to print a white base on the composite film cursor. For transparent composite film, as it may be affected by the color of components such as its driving guide rollers, it is also recommended that the cursor be printed with a white background to reduce interference with other background colors.
In addition, when the cursor is set, it is best not to have a different color in the vertical direction of the cursor electric eye of the ordinary automatic packaging roll film, otherwise it will affect the tracking, and even not track. This is related to the cursor electric eye reading program of general packaging machinery. Some automatic packaging machinery has a special cursor recognition program, so this factor will not affect it too much.
Third, the design of the design should consider the post-production process such as printing
Many customers' designers only pursue aesthetics and artistic decoration when designing the layout of manuscripts, and do not consider some situations in the actual printing production. Therefore, it is difficult to perfectly present the text and pattern transfer according to the designer's ideal when printing. How to avoid such situations as much as possible, make design platemaking and printing production more closely, and make production smoother, there are the following suggestions:
1. Shallow net deepening
In the design of gravure printing, if there are red and blue overprint, red and yellow overprint, blue and yellow overprint, black and red overprint, and black, blue, red and yellow overprint, in which the number of dark dots is less than 25%, it is recommended to make it on the printing plate. It will be deepened by 3% to 6% as a whole, especially for overprinting overprints with light screens. When printing on the machine for the first time, the ink used on the deepened plate roller can be diluted with a diluent, under the premise of unchanged hue Try to avoid the phenomenon of "shallow dots missing", commonly known as "dry plate".
In the design of the gravure layout, it should also be noted that if there is a large area of white supporting bottom, the white layout is best to advance in the direction of the scraping plate. As far as possible, do not design particularly light black, blue, red and other hanging nets, otherwise there will be a "dirty ribbon" phenomenon during printing, commonly known as "unclean", and the rendering effect is not ideal.
Gravure overprint accuracy can only reach 0.2 mm, so text and graphics (especially text) smaller than 0.4 mm cannot be printed with multi-color overlay, and can only be printed with a single ink (or spot-color ink), otherwise Can easily cause ghosting. Pay attention to the size of the text and the thickness of the text lines. Too small text and too thin lines may not be printed, and there are often printing failures such as broken lines or lack of pens (similar to the "dry plate" phenomenon). If the text is too small, if there are too many strokes and too dense strokes, and the lines are thick or the printing plate is too dark, the phenomenon of "blurred characters" can easily occur. Monochrome cutouts should be used for small text and pattern cutout printing, and multicolor overlay cutouts should not be used for printing. Nor can the background color of photos be used for hollow out printing. For small text and patterns, it is not suitable to use text pattern cutout overprint text patterns.
In addition, the transfer performance of gravure printing is not as good as that of lithographic printing, and there is a problem of blocking. Generally, it should be avoided to use less than 10% of the dots. Especially for large-area background colors, it is better to avoid too light halftone dots, otherwise the halftone dots are not reproduced well, which may cause uneven color and easy to change color. Even if it can be printed at the beginning, it is too light to affect the hue due to plate roller wear during the printing process. Especially for some composite aluminum-plated or pure aluminum substrates, it is easy to form a "color difference" phenomenon, and the resistance of the printing plate The yield is low. For large area light colors, spot color printing is recommended.
When a text pattern and another text pattern are completely nested and printed, the light-colored text pattern should be expanded to an appropriate size (typically 0.2 to 0.4 mm) so that it overlaps with the darker text pattern, otherwise it is very difficult during the printing process. Easily reveals undertones at the junction. As for how much the lightening is related to the color, if the two colors are complementary colors, the overlapping part will produce black lines, which will affect the appearance, and it should be expanded as little as possible.
5.Setting of spot color printing plate
Trademarks, light screen overprints, transition colors, small print (text below 5), small five-star patterns, large background colors, special effects, etc., many colors have high purity, very bright colors, and some fluorescent colors, are transparent Special colors such as color, gold, and silver must be printed with spot colors. At this time, special color plate rollers must also be made for printing. Due to the fineness of the ink particles and other factors, it is not suitable to use hanging light screen printing for pearlescent inks, golden inks and silver inks.
6, color order arrangement
Generally, the printing is from dark to light, while the surface printing is light and then dark. The two seem to be different. The order in which the actual human eye sees them is exactly the same, that is, the darker ones are seen first. In color printing with photos, the three primary colors should be printed continuously, and do not sandwich other spot colors, otherwise it will not be conducive to the overprinting of the three primary colors, the fusion of the layers of ink, and the effect of the physical image, and the printed picture will be rough. The color sequence of the inner printing process of plastic gravure printing is generally Bk, special 1, special 2, special 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 (other places can be put according to special needs). Spot colors (especially large-area special background colors) are generally placed between black and blue. This allows large-area special background colors to pass through more printing units, ensuring that the ink layer is sufficiently dry, which is conducive to reducing solvent residues. Of course, when there are special needs, it can be placed in other positions. For example, some layouts have dark lines on the special background color, so the special background color must be placed after the C, M, and Y colors.
7. Sharing of printing plates
In order to save costs, most of the same series of products will have a shared version, which layouts can be shared?
Generally speaking, to determine whether the printing plate can be shared, the following factors need to be considered: whether the hollow shape is the same when the white plate is shared, whether the bag-shaped electric eye cursor is white, etc .; when the silver plate is shared, whether there are small silver letters and borders Whether the line shape is consistent and the color sequence of each set is consistent. The shared version also requires the same color serial number. The lower edge of the first color block is aligned with the lower edge of any light spot. The plate circumference and plate length must be consistent. The white and silver plates are placed in the last color, and the color sequence can be disregarded when vertical registration is not involved. For example: variety one is black, blue, red, yellow, silver, and variety two is black, blue, red, yellow, and silver. If the two varieties of silver plate do not involve vertical overprinting, the silver plate can be placed in variety one. In the sixth color, the fifth color can be placed in variety two, but it can be shared.
8.Design principles of vertical and horizontal patterns
Designers often do not consider the errors in the bag making and slitting process, which makes the bag making and slitting difficult. Special attention should be paid to avoid excessively dense patterns and lines at a certain position in the vertical direction, otherwise the position will be violent when printing and rewinding, and the pressure will cause the ink to stick. At this time, a moderate hanging method can be used. Reduce the thickness of the ink layer. The surroundings of the composite bag should be designed to be similar in color or transparent. If the color difference between the top, bottom, left, and right of the packaging bag or roll material is large, after the vertical and horizontal imposition, there will be a clear contrast at the imposition (commonly known as "hard connection"). Since the cutters of bag making machines and automatic packaging machines cannot be absolutely accurate, and generally have a deviation of more than ± 1 mm, the produced bags or cut roll films will have a contrast at the cutting position of the automatic packaging. Larger lines, which can affect aesthetics, or you can only cut off deviations with a double-knife method.
For different bag types, you should carry out typesetting design according to different bag types. For example, three-sided sealing bags can be set up in vertical or horizontal direction. However, for zipper bags, stand-up bags, organs, or mid-sealing bags, etc., It needs to be typeset and designed according to its bag shape. When designing multi-row cut bags, you need to consider the arrangement of patterns, otherwise it will cause greater difficulties when installing heat-sealing knives in the bag making process.
For compound bags that require high compound strength or cooking, in order to improve the strength and protect the ink layer, the surrounding of the compound bag is usually set with transparent edges. If there is a large-area background color, when designing without a transparent edge, the two sides after the imposition must be considered to have a width of 1 to 2 mm wider. In this way, even when there are deviations in bag making or automatic packaging roll film, there will be no transparent edge, aluminum foil, or aluminum plated edge.
9.Slit track line settings
The width of the detection line is generally 2 mm, which is set to black or spot color, and dark color is suitable. Those who have a large area with a lighter background and no obvious vertical contrast edges in the pattern need to add slitting tracking lines, otherwise the semi-finished product rolls cannot be neatly cut.
10, bleeding place and edition week
If the horizontal size of the pattern exceeds 600 mm, the overall bleeding should 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 edges need to consider bleeding. Bleeding of 0.5 to 1 mm (usually added by 1 mm), so as to avoid the white edge of the silver edge due to a slight cut during the slitting process. Similarly, if the electric eye cursor is pressed on a large area background, the large area background must also consider bleeding, which is similar to bleeding of gold and silver edges.
NY film has large shrinkage and easy stretchability. It is necessary to increase each pattern in the direction of the plate by 0.5mm (the plate circumference is 550 ~ 690 mm, and 3 patterns in the direction of the plate circumference). Others such as PET, PE film, PVC, etc. Films need to increase the expansion ratio according to the corresponding shrinkage rate.