The full solution of flexographic printing (2)

(7) Environmental protection characteristics of flexographic printing

Ink is the largest source of pollution in the printing industry. The annual output of ink in the world has reached three million tons. Every year, the global VOC (organic volatiles) pollution caused by ink has reached hundreds of thousands of tons. These organic volatiles can form a greenhouse effect that is more severe than carbon dioxide, and they can form oxides and photochemical smog under the irradiation of sunlight, which seriously pollutes the atmosphere. This has caused widespread concern in various fields. Currently, only environmentally friendly green printing materials—water-based inks, UV inks, and alcohol-soluble inks—have been widely used in various printing methods.

Water-based ink is a world-recognized environmentally-friendly printing material, and is the only non-toxic ink approved by the US Food and Drug Association in all printing inks.

The biggest feature of water-based ink is that it significantly reduces the emission of VOCs (organic volatiles), thereby preventing air pollution, improving the printing operation environment and benefiting the health of workers. It can completely eliminate the harmful effects of some toxic and harmful substances in solvent-based inks on human body and the pollution of packaged products, and improve the overall environmental quality. It is particularly suitable for packaging and printing products that require strict sanitary conditions such as foods, beverages, and medicines. In addition, it not only reduces the risk of fire and hazards caused by static electricity and flammable solvents, but also reduces the residual solvent odor on the print surface.


(8) Analysis of Development of Flexographic Printing and Ink Transfer System

Traditional printing is an industry that reproduces large amounts of text and images on paper, plastics, metals, and other base materials, ranging from a few hundred to as many as tens of thousands. Its quality requirements are uniform ink, consistent depth, clear lines of text, and no flowers. Do not paste. Colorful images, colorful, rich layers, strong sense of three-dimensional. The copy should be faithful to the original or be in conformity with the natural color. Therefore, the traditional printing method has made careful consideration and careful design of the ink transfer system to meet the requirements of ink transfer.

Basic requirements for ink transfer system:

1 There is a reasonable enough amount of ink;

2 ink volume should be uniform;

3 Quantitative supply of ink can be repeated over and over again.

In order to meet the requirements of a large number of reproductions, a deep, shallow, dark ink, and coarse and thin text and lines cannot satisfy quality requirements.

The ink transfer system of early flexo printing has not used anilox roller, so the ink color is very unstable and can only print products with low requirements. The anilox roller is developed through continuous improvement in practice.

The flexographic ink transfer system used rubber rollers, felt rollers, and metal rollers. The rubber roller is made of natural rubber, its mechanical precision is not high, and the ink is difficult to control. Therefore, it was only possible to print some rough and simple paper bags, etc.; the felt roller is a feature that uses felt to absorb and release ink, but the service life of the felt is not long. In the near future, the connecting material in the ink will harden the felt, and the felt loses the characteristics of ink absorption and release, so it is not ideal. Although the metal light roller has a relatively high processing precision, the gap between the two rollers can be used to control the amount of ink. However, due to the tension of the ink, the ink will accumulate together, resulting in a stripe mark, resulting in non-uniform ink transfer, so the printing quality Not too high.

Later, someone used a high-speed shot blasting on the surface of a metal roll to increase the hardness of the metal surface, causing the surface of the metal roll to produce roughening and pitting. Although the nature of the metal roll was changed, the ink was not easy to accumulate, but the spray was Pills do not guarantee the consistency of the depth and each roller; they have also tried firing ceramics on steel rollers to form naturally irregular pits, but they are not well controlled.

In the 1930s, due to the development of photographic and electroplating corrosion techniques, a metal anilox roll was used to plate copper on a steel roll and then print it with a carbon paper or photographic film to corrode the texture. This kind of anilox roller can be controlled due to the network cable and copy processing. Although it has taken a big step forward and laid the foundation for the development of the anilox roller, it is still not ideal:

1 There are seams, uneven ink at seams,

2 The network cable is coarse, about 100l/in or less, and it is not easy to manufacture and corrode. In the early 1980s, when manufacturing laminated flexible printing machines, the imported metal anilox roller was expensive and used an anilox roller that had been corroded.

The development process of things has always been continuously improved and improved. The development of anilox rollers has been improved and improved according to advanced processing technologies at different times. After the anilox roller was corroded, copper rollers were used to plate copper and then mechanically engraved. The electronically-engraved metal mesh roll presents an ideal seamless metal anilox roll. However, the mechanical engraving speed is slow, and the electronic engraving is performed on the steel (Shanghai Printing Technology Research Institute has successfully developed and put into production the metal anilox roller that is directly engraved on the steel roller), and later develops the mechanical extrusion technology directly on the steel. The metal anilox roll machined on the metal anilox roll currently used for electronic engraving and mechanical extrusion is still widely used in corrugated box printing slot machines, laminated flexographic printing machines, and coating equipment.

Regardless of the metal anilox roller processed by electronic engraving or mechanical extrusion, the number of reticulate lines is generally below 3O0l/in, and it can not meet the transmission volume of high-line printing products. It can only print 80l/in, 100l/in. Products, therefore, also limit the improvement and development of flexographic printing quality.

In the mid-1980s, laser technology was used to develop ceramic anilox rollers that were laser-engraved. The ceramic anilox roller was able to process a higher number of lines, had a wear-resistant surface, and could use a squeegee to make the ink transfer system. The amount of ink transferred is more accurate and stable, so the appearance of the ceramic anilox roller not only further improved the ink transfer system of the flexographic printing, but also satisfied the requirements for printing fine products and prompted the development of the flexographic printing.

The anilox roller is often called the heart of a flexographic printing press. As an anilox roller, an ink transfer system cannot be formed in the printing press. The early ink transfer system is composed of two roller pairs, plus an ink tray, one of which is a roller. Contact with the plate, transfer ink to the plate, so it is very simple to form the ink transfer system. Therefore, it is also said that the ink transfer system for flexographic printing is a short ink path, and the ink transfer system for offset printing is a long ink path. This structure has been extended to metal anilox rolls and still remains the same. Therefore, a flexographic printing press usually consists of four rollers (tubes) for each color group (ink fountain roller, metal anilox roller, plate roller, and embossing roller), and is often called a 4-roll type.

Due to the appearance of the metal anilox roll, people naturally contact the gravure printing. The metal anilox roll is very similar to the gravure roll. All are composed of pits, and the surface is also plated with a layer of hard chrome. Gravure printing is more accurate with the scraping method of the scraper than the two-roller, so gravure is precisely the characteristics of scraping ink and is naturally transplanted to the metal. Anilox roller, and ceramic anilox roller with a more rigid surface, more suitable to use a squeegee, so the flexographic printing ink transfer system has no ink fountain roller, only a metal anilox roller or ceramic anilox roller and The ink transfer form of the squeegee, the squeegee is improved from the positive direction to the reversed and bidirectional closed type ink chamber, the ink is supplied by the circulation pump, and the flexographic printing press is reduced from four to three per color group. Roller, it is also called three-roller type.

At this point, the ink-transfer system of the flexographic printing has been practiced-cognition-improvement-improvement, from the development of the kingdom of necessity to the kingdom of freedom. It is simpler, the amount of ink cannot be controlled, the development to advanced and rational is simpler than the original, and the amount of ink can be controlled. . Now it can be handy. According to different printing bases and prints, it is reasonable to dispose anilox roller and become an ideal ink transfer system.

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