Principles and New Trends of Flexo Printing Technology (I)

The first flexo printing press was born in 1905 in the United Kingdom. In the 50s and 60s of the last century, flexo printing was valued by people. In 1984, laser-engraved anilox rollers were officially adopted for flexo printing due to the maturity of laser technology and their wide application in various industries. Since then flexo printing technology has achieved rapid development in Europe and the United States. According to statistics, in the European packaging printing method in 2000, offset printing accounted for 8% and flexo printing accounted for 32%; in the United States, more than 70% of packaging products were printed by flexo printing.

At the 6th Beijing International Printing Technology Exhibition “2005 International Flexographic Technology Development Summit Forum & Technology Exchange Conference”, some experts analyzed and forecasted: In the next five years, the European and American flexo printing market will continue to maintain 1% to 3% of the Growth rate; The growth rate of China's flexo printing market is surprising. It may maintain an annual growth rate of 8%, which is equal to or faster than that of the national economy.

At present, the composition of the printing industry in China and developed countries in Europe and the United States is very different. For example, in the United States, offset printing, flexo printing, and gravure printing have their own world. Flexographic printing accounts for a high percentage of flexible packaging printing, but in China this proportion is less than 8%; The per capita annual consumption of self-adhesive labels in developed countries is 14 m2, in the United States is 16 m2, while in China it is only 0.5 m2, and the gap is close to 30 times. China has a large population. DuPont predicted at the China Print 2005 exhibition that China will have 100 million middle-class consumers in 2010. This means that the purchasing power and spending power of the Chinese will be greatly enhanced. The growth of the Chinese print market is immeasurable. . The most suitable range for flexographic printing is flexible packaging printing, as well as packaging and printing of food, medicine, cosmetics, toiletries, etc. The application of flexographic printing in these areas in China has just started and the share is very small, so it can be foreseen that flexo printing in our country The future will be very good.

First, the advantages of flexographic technology and

Core competitiveness

Flexographic printing has the advantages of wide printing materials, fast printing speed, high printing rate, easy operation, printing and post-press processing can form linkage production lines, short production cycle and pollution-free pollution, etc. It has been considered as a The "best and most promising printing methods" are widely used in many aspects. At present, China's packaging and printing companies are also constantly introducing flexographic printing production lines to improve their competitiveness. To sum up, flexo has the following advantages:

1. The widespread use of non-toxic water-based inks and UV inks helps protect the health of operators and protect the environment. It shows strong advantages in the areas of food packaging and daily necessities packaging.

2. Wide range of printing media. Flexo printing can be widely used to print all kinds of packaging products. The thickness of the substrate can range from 0.012 mm to 0.6 mm. It can be printed on various types of paper, plastic film, glass bottles, hoses, metal cards and other media. Post-processing; widely used in printing and producing various types of goods paper packaging, folding cartons, paper bags, paper cups, paper cutlery, wallpaper; and all kinds of plastic film, vacuum aluminized film, pure aluminum foil packaging products printing, such as food packaging, beverages Packaging, daily cleaning supplies and medical packaging products printing.

3. Equipment comprehensive processing ability. Almost all narrow-width unit type flexographic printing presses can perform printing and post-press processing such as front and back printing, coating, laminating, die cutting, cross cutting, slitting, punching, fan folding, automatic ejection, etc. It is even possible to add numbers, bronzing or screen printing units to the printing unit. Therefore, it is not unreasonable to call a flexographic printing press a print processing line. In the United States, due to the use of automatic labeling machines and numerous applications of stickers, flexo printing presses have become the main production method.

4. Small investment in production. Because of the relatively simple structure of the flexographic printing press, the equipment investment is lower than offset presses or gravure presses of the same scale, which can generally be as low as 30% to 40%.

5. Short production cycle. With the use of flexographic technology, especially the use of computer-to-plate, sleeve technology, shaftless transmission technology and UV technology, while the quality of printed products has been significantly improved, the production cycle has been further shortened, making it more suitable for short-run printing and on-demand printing. print.

Second, the basic principles of flexo and "heart"


The oil pump sprays the flexo ink on the surface of the anilox roller at the ink inlet and holds it in the F roller by its tension. After the scraper scrapes off excess ink, the ink is transferred to the resin plate when the F roller and the plate on the C roller contact. The graphic text (ie, the protruding dot) portion is then rotated and pressed by the C roller and the D roller onto the substrate H to complete a single color printing.

In the ink chamber system, two blades function differently. One is a reverse scraper, which is used to scrape off the excess ink on the anilox roller. The other is a positive seal blade and plays a sealing role. The scraped ink can continue to be recycled, which saves a lot of ink.

The core part here is the anilox roller and the printing plate; the anilox roller is called the heart of the flexographic printing machine, the depth (the amount of ink storage) and the shape of the cell site directly affect the quality of the printing product; the printing plate is directly In contact with substrates, the photosensitive resin plates used today are mostly laser-engraved. The resolution can reach up to 200 lines/inch. Some fine prints can be made. The quality of printed products can be comparable to offset printing and gravure printing.

As the "heart" part of the anilox roller, arranged above the same size, uniform location, the same depth of the depression, we call it a net. The network points have the shape specifications shown in Figure 2 respectively:

At present, the most used and best is a 60° honeycomb type cell. According to calculations, in the case of the same area and the same network cable, the cell area reached by the honeycomb type cell site is 1.155 times that of the diamond type. That is, in the same area, the hexagonal occupied area is approximately smaller than the diamond shape. 15% more, so hexagonal cells on the anilox roll means that it can reduce the depth of the hole by about 15% without affecting its original capacity. Obviously, when using hexagonal cells, the depth is comparable to that of diamond eagles. It is lighter, so it achieves a higher resolution.

At present, many domestic and foreign flexographic presses are equipped with ceramic anilox rollers. The production process of ceramic anilox rollers is quite complicated. The two most important parameters are the number of screen lines and the amount of ink transmitted through the mesh. The number of lines of the anilox roller is generally determined according to the special proportional relationship between the number of printed lines and the number of anilox rollers. At present, the network cable that can be engraved with advanced laser engraving equipment can reach 2 000 lines/inch, but this kind of high cable will not be applied to practical flexo printing in a short period of time, even if the 200 lines/inch prints are equipped with anilox rollers. Will exceed 1 400 lines/inch. Due to the small mesh opening of the anilox roller of the ultra-high cable, the network wall is too thin, the wear resistance is poor, and the service life is also reduced; in addition, the anilox roller of the ultra-high cable can increase the difficulty of cleaning the anilox roller. . Taking all factors into consideration, the printing factory uses a low number of anilox rollers as much as possible under the conditions of the printing permission.
Another important parameter of the anilox roller production is the amount of ink transmitted by the mesh. The unit is expressed by BCM (ie, the volume of the cell per square inch) and is the standard unit of measure for the volume of the mesh. The thickness of the ink layer transferred by the laser-engraved anilox roller depends on the volume of the cell. For example, comparing an anilox roller with a 500-line 6.00 BCM volume and an 800-line 2.00 BCM volume anilox roller, it is clear that the 800 line Since the anilox roller has a small capacity, its ink layer is thinner and the ink layer is thinner, so that the printing effect of the high light dot network can be controlled more.