In the packaging and printing process, there are often different materials used to print the same or similar layouts, such as product inner and outer packaging, trademarks, manuals and other serial printed products. Generally, the color design of the printed layout graphics or signs is basically the same, but because of the Due to the differences in the characteristics of substrates, the printing equipment, ink performance and process forms used in some products are not necessarily the same, and customers often require that the printing color requirements of series products are basically consistent, and no obvious color difference can occur. The actual production process shows that there are certain difficulties in controlling the color quality of the series of printed materials of different materials. It is necessary to carefully design the process technology and carefully check the operation technology in order to obtain better print quality effects and meet customer quality requirements.
1. Characteristic analysis and process determination method of serial prints
The so-called series of printed materials refers to the same type of product with different specifications of inner and outer packaging or a set of products with different printing materials, but the graphic structure or color is the same or similar. The adaptability of the printing process is also very different due to differences in material characteristics or specifications of the printing layout. Such as corrugated carton and color box surface packaging materials for outer packaging include whiteboard paper, kraft card or boxboard paper, etc., and carton packaging materials include whiteboard paper, kraft card, white card, glass card, copperplate card, PE coated paper Etc., flexible packaging plastic film, cellophane, tissue paper, glossy paper, copy paper, offset paper, vacuum aluminized paper, laser paper, etc. Corrugated cardboard has a large thickness, surface flatness, and PE printing paper, plastic film, cellophane, tissue paper, and vacuum aluminized paper printing processes. It is suitable for flexographic printing in terms of material characteristics and product packaging safety and sanitary quality. Printing with water-based ink can better guarantee the quality of the product. For pre-printed color box facial paper, color box printed whiteboard paper, kraft paper; vacuum aluminized paper, laser paper and other materials, a large number of gravure or flexographic processes can be used, so that the printing quality and production cost can be obtained Better balance. For whiteboard paper, kraft card, white card, glass card, copperplate card products with a quantity of about 100,000 prints, as well as glossy paper, copy paper, offset paper, vacuum aluminized paper, and laser paper, the offset printing process is more suitable. Among them, the gloss paper and copy paper have a low basis weight and are not suitable for high-speed automatic paper feeding. The low-speed 01 offset printing machine can be used for printing to ensure the product's overprint quality.
Second, we must pay attention to the technical control of pre-press layout design
Many prints are now provided by customers with electronic manuscripts designed or produced by advertising companies. Due to their incomplete understanding of the printing process, the manuscripts produced often cannot be adapted to the requirements of the printing process. Taking a series of printed products with the same mesh structure as an example, due to the different printing materials used, the printing colors will be significantly different. These are the two products of paper plate (whiteboard material) and paper cup (single-sided PE coated paper), which are also printed by the offset printing process. Due to the good surface smoothness of the whiteboard material, the ink absorption is less, while the single-sided PE coated film The surface of the paper is relatively rough, and the amount of ink absorption is larger. If the two materials are used to print the layout with the same mesh structure, the color will be greatly different. The printing color of the single-sided PE coated paper is significantly lighter than that of the whiteboard paper. Ink and pressure adjustments often fail to overcome the chromatic aberration problems that arise from differences in material printing performance. Generally, the main color dot area of ​​the printed single-sided PE coated paper should be properly adjusted through a plate design to make the printing color close. Therefore, when receiving a series of prints with the same screen layout structure but different printing materials, you must first carefully analyze the manuscript layout structure and the characteristics of the substrate materials, and then determine a reasonable plate design plan, that is, based on Material gloss, printing ink absorption performance, reasonable adjustment of the dot area of ​​a certain product layout, to ensure that the colors printed by different materials are close to each other.
3. Pay attention to the process technology control of the imposition direction
Prints with multiple imposition structures usually have several layouts of different varieties on one printed sheet. If the difference in printing colors of different varieties is not taken into account, and different varieties with large color differences are combined in the same vertical direction, then once the vertical layout When the printing color of a certain layout is light or dark, it is difficult to adjust the ink output locally through the ink fountain to achieve the ink color control of a corresponding vertical layout. The ink color adjustment often appears to be inconsistent and impossible Take into account the printing color of the overall vertical layout.
Therefore, for multi-imposed paper plates, paper cups, trademarks and other products, it is best to combine the same variety or varieties with similar colors in each longitudinal position to facilitate the effective adjustment of the ink coating amount. Never squash several products with large color contrast in the same longitudinal direction, because this way, imposition printing is most likely to produce color difference. Even if the printing color can be controlled by adjusting the amount of ink coating, it is easy to produce chain printing quality problems, such as Unfavorable conditions such as paper pulling, pasting, and dirty printing.
Fourth, adjust the size of the control dots through the printing process
The main feature of the series of printed matter is that the graphics are basically the same, but the size is different, and the material characteristics of the substrate are completely different. If the film structure is already the same, you can consider in the process of printing technology, according to the gloss and ink absorption of the printing plate, properly control the exposure time of the main color version of a certain product. To adjust the size of the outlet. Taking the substrates of series products as glass card and offset paper as examples, the offset paper has a relatively rough surface and large ink absorption, which can appropriately shorten the exposure time of the main color plate to achieve the purpose of increasing the dot area. The ink color of the offset printing plate can be close to the ink color of the glass card printing plate, and it is not prone to paste defects. However, it must be pointed out that the adjustment of the dot size by the printing process is limited, and it can only be a small amount of adjustment. If the exposure time is too short, the dark white spots on the layout are prone to stagnation, and the layout is poor. Therefore, the exposure time should be adjusted to a suitable degree. For example, the original normal exposure should be 140S, and the shortened exposure time should be controlled between 110s and 120s. [next]
5. Control the printing color by adjusting the printing pressure
Printing pressure is the medium of imprint transfer. The size of printing pressure is directly reflected in the depth of printing ink color, especially the relief printing process. The size of pressure has a great influence on the color depth of printing ink. When the printing pressure increases, the printing color will appear. Deepen the phenomenon, on the contrary, reduce the printing pressure, the printing color will appear lighter. For a series of printed matter of different substrates, when the surface of the printed material is rough, the printing pressure can be appropriately increased to deepen the printing color, so that the color of the printed matter of different materials is close. However, the adjustment of printing pressure should also be controlled to an appropriate degree. Too much pressure adjustment is easy to accelerate the wear of the printing plate, and it is easy to produce chain quality problems such as paste printing and large deformation of the printing plate surface. This is a problem to be paid attention to during the printing process operation. . The adjustment of general relief printing pressure increase should not exceed 30 silk, otherwise, the printing distortion will directly affect the product's overprint quality.
Sixth, control the printing color through ink hue adjustment
The four-color prints are printed with standard four-color inks according to the conventional process. However, when the color of a certain color is obviously different, the color requirements can not be achieved through the adjustment of the amount of ink. Consider the color of the ink of a certain color Appropriate adjustment to make the ink color of the printed product meet the original color requirements. For example, when we print four-color trademarks at one time, the light orange color of the layout has obvious reddish phase after overprinting, and the yellow hue has a feeling of insufficient, which is quite different from the original color. The increase and adjustment of the Y color are limited and cannot be adjusted to the requirements of the original ink color. In this case, it seems that only by appropriately reducing the dot area of ​​the M version and increasing the dot area of ​​the Y version can it be effective. The effect of adjusting the color, however, is very labor-intensive and time-consuming, and will increase the economic cost, which is undesirable. Through careful analysis and research on the printing samples, the author found that in the entire layout, except for the Y-color part of the flat screen and the M-color plate of the flat screen, there is no overprint relationship between the M-color plate and the single-color color printing. , The author sprouted in the "four-color red" ink, adding part of the "four-color yellow" ink to form a special spot color red ink for overprinting, after this treatment, the light orange yellow overprinting plate, the printing color immediately To achieve a similar effect to the color of the sample, so that the printing color of the product finally meets the customer's requirements. For the same reason, when printing a series of printed materials of different materials, the hue of a main color often appears lighter due to different materials. For this reason, it can be considered to adjust the ink hue of a color appropriately to achieve the printing ink color. Correction, this is also the easiest and fastest way.
Seven, use different printing process characteristics to control printing color
Due to the difference in printing process, the thickness of the ink layer of the printed matter is also significantly different. For a series of printed materials with large material differences, according to the characteristics of the print color and the adaptability of the material to the printing process, selecting the appropriate process for printing is also to control the printing color. An effective way. The thickness of the ink layer for various printing processes is approximately: 3 μm for offset printing; 8 μm for relief printing; 10 μm for flexographic printing; 12 μm for gravure printing; 30 μm for silk printing, according to the basic properties of the substrate, surface gloss, ink absorption, and layout patterns For structure and other situations, consider selecting a printing process suitable for the ink absorption characteristics of the substrate material as appropriate. The offset printing process is limited by the balance of water and ink, and the adjustment range of the ink coating amount is small. It is more suitable for printing substrates with relatively good gloss, such as coated paper, glass card, white card, offset paper, whiteboard paper, kraft card, etc. Napkins are soft in texture, large in ink absorption, poor in tensile strength, and easy to stretch and deform, so they are more suitable for printing with low-viscosity liquid water-based inks to obtain the ideal printing color, and water-based inks have great environmental advantages Therefore, it is the best choice to use a flexographic process to print napkins. The choice of printing process must consider the impact of the printing characteristics of the substrate on the printing color, as well as the cost of printing production, such as high gravure and flexographic process plate making costs, which are more suitable for printing long-term products.
8. Methods of printing quality control of different material series
Due to the limitations of the printing plant's production scale, some factories have only a single flexographic process, and some factories have a single offset printing process or gravure printing process. Many series of printed products, customers often have to send to several factories to print separately . Considering the production cost, some customers do not use the proofing process, and the printed sample of one material is printed first, which is used as the color reference sample of the printed material of another material, such as the flexo napkin used as the offset whiteboard The comparison of the printing colors of paper plates or coated paper cups brings certain difficulties to the control of printing colors. Offset printing is often difficult to keep up with the ink colors of flexo printing. Because, the flexographic ink layer is thick, and the adjustable range of the offset ink layer is relatively smaller than the flexographic printing process. Therefore, when printing a series of prints with different processes, it is advisable to arrange the products that use the offset printing process to be printed first, and then to use flexo, gravure, or silk screen post-printing, which is conducive to the color control of the series of prints. If offset printing is also used to print products of different materials, consideration should be given to printing materials with good gloss first, and materials with poor gloss after printing. Because of the good gloss material, the printing ink volume control is relatively accurate, which can reduce the chance of large deviations in the printing color. It is worth mentioning that the printed manuscript is used as the control sample of the printing color. It is necessary to pay attention to the influence of the light transmission performance of the sample material on the identification of color vision. For example, the transparency of the film print and napkin print is high, and it should be placed side by side with the printed sample to see the sample Discrimination on stage.
In summary, to control the color of a series of printed materials of different materials, it is necessary to pay attention to comprehensive consideration from the aspects of material characteristics, printing process technology and equipment operation adjustment, and through careful technical analysis of the manuscript, and then determine the appropriate production process plan, so Not only can the blindness of the production process be avoided, and the occurrence of printing defects can be reduced, but also the printing quality of the product can be better guaranteed, and the production efficiency can be effectively improved.
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