Flexible packaging mainly based on plastic film occupies an important position in various packaging products, and its characteristics are exquisite printing, high transparency, good flexibility, good gas barrier and moisture resistance, and resistance to corrosion of various chemicals. It can meet people's various requirements for packaging - simple, time-saving, labor-saving, fast, fresh, beautiful, resistant to deposit, cheap, etc., throughout every corner of our lives. Due to the high printing speed of the flexo printing (mechanical speed: up to 230 m/min for the unit, up to 250 m/min for the satellite), high efficiency, lower rejection rates than offset and gravure (average cost per unit of unit can be reduced by 20 %, productivity increased by 30% ~ 40%, etc., etc., flexo printing in the plastic film flexible packaging industry, the rapid development. From the perspective of the global market, the annual growth rate of flexographic printing is 6% to 7%, and the proportion of flexo printing in the entire printing industry accounted for only about 5% in the 1980s, and it has now reached 22%.
Figure 1: Flexo Printing Market
Flexographic plastic flexible packaging printing process through a set of more stringent processes in order to get satisfactory results. From the image scanning input, prepress processing, on-machine printing, post-press processing, and final product acquisition, corresponding quality control should be performed to ensure the quality stability.
Figure 2: Example of a superposition angle of a flexographic plate
First, the prepress process points
Good design is the premise to ensure the quality of flexographic printing. The choice of the pattern, text, and color in the manuscript by the process designer must first meet the production requirements for flexo plate making and printing; secondly it should be suitable for the actual level of equipment, materials, and operations of the printing manufacturer; and the specific requirements for the user's product packaging should also be met. Practical standards. Flexo-plastic flexible packaging printing process design points:
â—† Many colors, but less overprinting, more use of spot colors, spot color is the strength of flexographic printing, printing color saturation is good;
â—† Does not require the reproduction of particularly small details;
â—† Original design that adapts to thin, flexible film;
â—† can be online for packaging processing design;
â—† can produce a rich combination of design;
â—† The design of the color printing effect is not too high;
◆ In order to avoid moire, the overlapping angles of different colors should be as far away as possible from the angle of the mesh of the 60° anilox roller;
◆ In the process of color processing, the commonly used screen angle of the flexo is black 7.5°, magenta 37.5°, cyan 67.5°, yellow 82.5° (or 22.5°, black 52.5°);
â—† The design should distinguish between in-print and surface-printing processes, and the dot enlargement value and copy curve are different.
â—† The film will be stretched during the printing process and retracted after cooling. Therefore, the plate bending compensation percentage must be taken into consideration when making the plate, and the error caused by the shrinkage of the material should also be considered.
â—† Flexo-plastic flexible packaging printing is almost indispensable for bar code printing. Because bar code prints require high optical properties and dimensional accuracy, the production process should be strictly controlled. The bar code placement direction should be consistent with the printing direction, so that the bar code distortion occurs at the height of the bar code, this will not affect the bar code width size, in order to ensure the best reading accuracy.
Figure 3: Examples of flexo plates and variations
â—† With the innovation of printing technology, many flexo plastic flexible packaging printing has adopted high-tech laser digital flexo and supporting digital workflow to create a cheap and flexible flexo market. The violet version of the digital flexo is nearly perpendicular to the layout, so that the exposed image dots have steeper edges; in addition, the exposed material in the air will oxidize, which can reduce the diameter of the dot and strengthen the Yin/ The deep groove of whitening greatly improves the resolution of the pattern and the sharpness of the small text. Comparing Fig. 5 with Fig. 6, the digital flexo has a very deep anti-white/negative line. It is not easy to block the ink when printing, and the text details are incomparably clear. Moreover, the dots are finer and the edges are steeper, making the pattern high light and dark tone. The level is clearer and the contrast is stronger.
Figure 4: Barcode placement