Over the years, the printing of corrugated board is merely to apply functional marks on the packaging box of corrugated cardboard, or to simply print in lines and words in monochrome, and the process is backward, inefficient, and costly. With the development of market economy, people's demands for packaging products have been continuously improved. Corrugated cartons and special-shaped corrugated cartons of various colors and designs have emerged, which have not only increased the added value of products, but also increased the competitiveness of products. Adapt to the development of the international packaging market.
Corrugated cardboard structure shown in Figure 1, the inner layer is a special wavy structure, buffering the vibration and enhance the impact ability. It is mainly used in the outer packaging of goods. With the appearance of waterproof corrugated cardboard and reinforced corrugated board, corrugated board can also be made into special liquid packaging containers, which expands the application of corrugated cardboard. With the continuous improvement of flexo printing technology, more and more flexo printing methods are used on corrugated paper. According to statistics, the color printing of corrugated boxes mainly uses flexographic printing technology. The United States accounts for 98%, Western Europe accounts for 85%, China's corrugated board printing area for packaging exceeds 10 billion m2 per year, facing such a huge market. We need to further improve the lack of printing of corrugated paper, improve the quality of printing, and meet the needs of market development in the region.
Fig.1 Corrugated cardboard structure
1. Color printing of corrugated cardboard
1.1 Advantages of Flexo Printing on Corrugated Paperboard
When the corrugated paperboard is using the flexo printing technology, due to the elastic deformation of the flexographic printing plate, it can make up for the errors in the printing thickness and the unevenness of the surface, so that the printing ink color is uniform; the color printing of corrugated cardboard in foreign countries tends to white E-type corrugated cardboard, high grade The number of printing screens is up to 120 lines/in. Both the field version and the cable version can be printed, and four color printing can be realized. The flexo printing is light pressure printing, and the printing pressure is small, and the thickness of the corrugated paper is not uniform. The resulting imprinting or imprinting of the imprint is not true; the sang yin has used water-based ink, so the metal anilox roller can be used to transfer the ink, and the printing plate only needs to gently touch the corrugated cardboard, and the water-based ink is completely absorbed; the structure of the flexo printing machine is simple The four rollers form a color group, which is very convenient for loading, adjusting, and cleaning. The flexographic printing press can also be linked to other processes, such as indentation, slotting, die cutting, gluing, box making, and counting. Linkage production line.
1.2 Color Flexo Printing Process for Corrugated Cardboard
Corrugated cardboard painting process is:
Graphic design → image processing → plate making → printing → die cutting → box making
Manuscript drawings and design and image processing must fully consider the characteristics of corrugated paper, to avoid full-page printing and band-shaped graphics in the same direction as the corrugated file, the text should not be too small, the ink color should be eye-catching, choose strong coloring, high saturation ink The number of screens for coloring pictures is generally 60 lines/in, the number of high-grade prints is 100-120 lines/in, the number of colors is 3-4 colors, there are also 5-6 colors, and only 2% of the dots can be printed. In the separation of color separation, comprehensive consideration of the actual ink parameters, dot gain and other parameters, the preparation of outstanding balance and gray balance procedures, and draw the C, M, Y and BK tone reproduction curve. In addition, we must fully consider the different number of lines, the width of the flexo printer, and the printing slot machine, as well as the influence of different materials and pressures. In the plate making process, a thicker photosensitive resin plate is selected for the flexographic plate, which has a thickness of about 3-7 mm and a hardness of 25-50 Shore Hardness (HS). When the quality of corrugated paper is poor, thicker and lower hardness plates are used. When the quality of corrugated paper is better and small prints and screen printing are required, a plate with a higher hardness is used. When printing with a thick plate, as shown in Fig. 2, the printing pressure is too small, the printing substrate is liable to produce corrugated and "sawboard"-like patterns, affecting the quality of printed matter with high field and screen number; when the printing pressure is too high, printing The substrate is easily deformed and even damaged, causing deformation and dot enlargement of the resin plate. At the same plate thickness and speed, the printing plate with higher hardness has no obvious enlargement of the imprinting, but the imprinting on the edge parallel to the corrugated fiber is less realistic, the soft plate with lower hardness has strong print, but the edge parallel to the corrugated fiber expands. .
Figure 2 Schematic diagram of the effect of printing pressure
Figure 3 H/bak pad technology pad absorbs greater compression
The US R/bak air-cushion lining technology is currently used in more pad technology, as shown in Figure 3. It can effectively prevent the deformation of the printing plate and the destruction of the corrugated paper, make the ink layer more uniform, and have better printing tone levels and sharpness. When used, it is only necessary to place the liner containing the microbubbles on the back of the flexographic plate and attach it to the cylinder. During the printing, the air cushion has the function of cushioning pressure and absorbs the printing substrate, the printing plate and the plate roller. The resulting pressure is shown in Figure 4. The dot enlargement caused by excessive or small printing pressure and the deformation and damage of corrugated paper can all be reduced or even eliminated. It also has a unique compensating effect on the oversized plate roll and has good adaptability to various corrugated papers. Sex. Therefore, air-cushion lining technology gradually replaces traditional thick-type printing plates.
The main feature of the flexographic printing press is that the ink path is short, and the anilox roller is the key component of ink transfer and ink distribution. The structure and line number of the ink hole on the anilox roller determine the ink transfer performance and application range of the anilox roller. In the flexo printing of corrugated board, the number of anilox roller lines is often 180-300 lines/in, and the ratio of line number of screen dots to that of anilox rollers is 1:4-1:5. In addition, the majority of corrugated board flexographic printing presses have a drum arrangement in which an impression cylinder is on top and a printing plate cylinder is on the bottom, and the bottom surface of the cardboard is printed so that dust and shredded paper on the printing surface can be naturally dropped.
Figure 4 H/bak pad technology pad absorbs greater compression
After the corrugated board is printed, according to the design requirements of various packaging boxes and boxes, the corresponding die-cutting methods and box making equipment are used for die-cutting, and finally the desired products are produced. (to be continued)