Plastic gravure plate making is more complicated than paper gravure plate making, and there are many influencing factors. Designers should have certain color knowledge, understand the printing process, and grasp the characteristics of plate making in order to design high-quality product packaging quickly and well.
Plate making requirements for different types of packaging bags
According to the bag making method, plastic packaging bags can be divided into four categories: three-side sealing, middle bottom sealing, three-dimensional middle sealing and sheet material.
The three-side seal is sealed around the packaging bag. The front and back dimensions are the finished product size, with a certain sense of integrity, the design is not constrained, and the front and rear designs have a certain coherence. Since the dimensions of the front and back are the same, the front can be designed first so that the back echoes the front. When making plates, the front and back should be arranged on the same set of plate cylinders.
The middle bottom seal is sealed on the back, the front size is the finished product size, the back is divided into two equal parts, and the sum of their widths is equal to the width of the front, usually in the design, the front and the back are unfolded to carry out an integrated design, and the left and right are Add 25px for each edge, and the front and back are also on the same set of rollers.
The three-dimensional middle seal is based on the middle bottom seal, and three-dimensional edges are added on both sides, and the front, back and side three sides are also on the same set of plate cylinders.
Due to the limitation of printing materials, the front and back sides of the sheet must be designed separately and plate-making separately, and cannot appear on the same set of plate cylinders at the same time.
Color Handling Points for Line Version and Halftone Version
1. Line version
A considerable part of gravure printing is line version printing. The line version is composed of lines and solid color blocks. The shape wins, and the solid (special version spot color) is used to create a visual impact to highlight the advantages of the line version. According to the characteristics of the gravure printing machine, the printing plate generally does not exceed 6 colors, and try to use the spot color as much as possible, and should be equipped with a color code to facilitate the color matching during printing.
A set of line version can be combined to form a series of products. When designing, a color matching scheme can be designed for users to choose. Since the line version has no sense of hierarchy, attention should be paid to overlapping color processing between colors to meet the overprinting requirements caused by the expansion and contraction of the substrate.
2. Net mesh version
The mesh tone version has extremely rich layers and ever-changing colors, but no matter how complex the layers are, they are composed of cyan, magenta, yellow, and black (special colors need to be added). Highlights, shadows, and midtones are 3 parts.
Therefore, first of all, it is necessary to know the gray balance data of the four-color ink and the printing suitability of each level segment, master the change rule of the dots, and summarize the image level processing method, so that the product can achieve the best visual effect.
①Gray balance adjustment
②Highlight, bright tone area tone value setting
For the highlight part, one is to adjust the three primary colors of the extremely high light to 0, as the brightest part of the image tone, and if necessary, the range of the highlight part can be increased; the other is to adjust the highlight white area that needs to be layered to the minimum printable tone. The value is determined according to multiple testing and proofing, and the minimum dot value is C6%, M5%, Y5%.
③ Midtone layer processing
Midtones are the top priority of the entire image. The level of midtones should achieve the best visual brightness. For this reason, the overall saturation can be deepened or the saturation can be reduced according to the situation, but try not to affect the gray balance of the image, and only make local adjustments to the image. For example, a plate of brightly colored fruits can be handled by grasping the main colors of different fruits, appropriately reducing the green leaves to red, adding red appropriately to red fruits, and reducing blue and red to yellow fruits. However, after locking the local area, micro-adjustment of the level and color should be carried out to make the color of the product cleaner, brighter and more pleasing to the eye.
④Dark tone level processing
In general, gravure has poor level restoration for more than 80% of the dot area. In this way, it is necessary to open the layers of the darkest part and the sub-deep part, and reduce the layer of the sub-deep part to about 60%.
Overprint processing between color plates
Since plastic film materials are more flexible than paper, the overprint processing between color plates is a link that must be considered in the front-end production of gravure. The standards for overprint processing are as follows.
1. The text version is usually black. When doing overprint processing, hollowing is not allowed. If the text version is in other colors, such as magenta, it can be considered whether it is overprinted with the background color according to the size of the text. When the word is less than 12 points, it must be overprinted with the background color, but it is still necessary to consider whether the color of the overlaid text is eye-catching. If it affects the recognition effect, consider changing the color.
2. When the light color is connected with the dark color, the edge expansion value of the light color is generally set to 1~2PIXS. For larger layouts, the value can be appropriately increased.
3. When the spot color plate is connected to the picture, without affecting the edge pixels of the picture, the edge of the spot color plate can be enlarged, and the value of the edge expansion is usually 1 to 2 PIXS.
4. If printing opaque ink, such as gold ink, the printing order of the ink should be considered first, otherwise the gold ink will cover the relevant colors. If you have to do overprinting, you should also consider the problem that gold ink and other color inks will become dark and not bright when overprinted.
5. Silver ink is also a special ink, light silver has a certain transparency. Therefore, when using silver ink, it must be determined by design according to customer requirements whether it is overprinted or hollowed out with the background color or related color.
