Dingyi
China packaging 200 1 06
Flexographic printing has become the main force in the field of packaging printing. The origin of flexographic printing is still inconclusive. Flexographic printing technology was introduced into China in the early 1970s. After many technical innovations, it has established its position in the field of packaging and printing. This paper analyzes and introduces the current situation and prospect of the popular flexographic printing technology in order to provide dinner for people in the packaging and printing industry.
develop
It is said that in about 1890, the rotary offset printing press began to be used in Britain. At that time, only simple trademarks, paper bags and words were printed on the wrapping paper. Because aniline dye is used to make ink, it is called aniline printing. Soon, it spread to the European continent, and only after World War I did it spread to the United States. After the improvement of ink, printing machine and dryer, cellophane was printed. It was quickly recognized by the society, and then around 1940, the United States invented the anilox roller, thus improving the printing quality.
Gundam 1952 At the printing conference held in Stockholm, Sweden, the name of aniline printing was rejected, and the participants unanimously agreed to change it to flexography. At that time, it was discussed that because photosensitive resin had sprouted, polyethylene and polyester appeared, the carrier of substrate was greatly increased, and the application mode of flexography was flexible, which was suitable for various purposes of printing, so it was named. Without knowing its background, domestic translators literally translated it into flexographic printing and spread it, and the convention has become so far.
In the first half of the 20th century, after being used to print transparent and non-absorbent packaging material cellophane, its application scope expanded rapidly, involving polyethylene and various synthetic resin films. As a packaging material, the printing method has laid a foundation in Europe and America.
Japan only introduced this technology in the early 20th century, and used it to print corrugated paper and paper bags. Different from Europe and America, it was not originally used in the field of flexible packaging materials and cartons for two reasons: first, it was not satisfied with the quality of flexographic printing, and second, gravure printing and offset printing technology had been introduced to meet the demand. Recently, with the flexographic printing technology environment has caught up with gravure printing and offset printing, the expansion speed has been accelerated.
Technical status quo
In recent five or six years, the progress of flexographic printing technology is really enviable. We appreciate it because ① printing machine, ② anilox roller, ③ plate, ④ plate making, and ⑤ ink have all been innovated. The following article focuses on the online flexographic printing machine suitable for narrow web.
(1). Flexographic printing machine
According to the arrangement of flexographic printing machines, they can be divided into three types (see figure 1). In the past, especially in the printing of flexible packaging and other films, taking Flexopak machine produced by COMCO Company in the United States as an example, some measures were taken, such as installing flexible tension regulators at the paper feeding and receiving positions, installing S-shaped overlapping mechanism at the unit position, and installing chilling rollers at the drying position, which achieved the registration accuracy equivalent to that of gravure printing. Compare the Flexopak machine produced by COMCO with the previous printing machine unit, as shown in Figure 2.
In addition, the standard: The drying device, combined with the development of ink, realizes printing that can protect the environment. Furthermore, in order to shorten the preparation time and improve the working performance, the printing plate cylinder, anilox roller and Mo Dou tank can be quickly replaced, and the standard COMCO programming system is installed, which is more conducive to multi-variety and small-batch production activities. According to the latest information, the variable repetition system that can continuously change the perimeter of the garden has been completed, which is closer to gravure printing in structure.
(2) Drum
In the past, the iron core of anilox roller was corroded by chemical means, or the surface was plated with hard chromium after mechanical engraving, and the number of lines was at most 400-500lpi, so the number of printing lines could only be limited to 100- 120lpi. Due to the limited printing resolution and unstable quality, it has never been popularized in the fields of soft packaging and carton printing in Japan. Later, an anilox roller was developed, and the iron core was sprayed with ceramics and then laser carved, and the highest number of lines reached 1200lpi. The arbitrariness of ink hole shape has also expanded. So the number of printed lines can reach 300lpi. At present, the number of gravure lines used in packaging printing in Japan is 1200lpi, and the service life of the roller has also been improved by leaps and bounds, so it is no problem to use it in flexible packaging printing.
(3) Printing plates for flexographic printing
Currently used plates, such as rubber and photosensitive resin (liquid and solid), are the mainstream, especially photosensitive resin solid plates used in high-quality printing for packaging and printing. Photosensitive resin plate was born in the early 1970s. Since then, the printing items have tended to be rationalized, and it can be made into thin printing plates, and the printing quality has also been improved.
The plates used now vary according to their uses. The thickness for packaging and printing is1.14-1.70 mm, and the hardness is generally 50-60 degrees. The surface state of the plate and its resin composition have certain influence on the transfer of ink to the substrate, which is very important for quality. Because of its close relationship with ink, it is also important to develop ink that meets the plate. In view of this, in order to further improve the printing quality, close cooperation between plate manufacturers and ink manufacturers is needed. Recently, developing plates have been gradually adopted abroad, which is beneficial to environmental protection.
(4) plate making and printing
In the past, the negative film made in the process of photography was partially hardened and developed by ultraviolet exposure, and the unhardened non-image part was removed to make a printing plate. Recently, gravure printing and offset printing have introduced this technology. CIP of various specifications developed in Europe and the United States has been introduced to Japan by using a computing mechanism to directly image images onto a board by laser, as shown in the following table. The process comparison between the past method and CIP method is shown in Figure 3-see below. Compared with the previous methods, CIP's direct plate-making does not need film output, so the delivery time is short and the salary is reduced, because it can copy smaller ideas, improve the reproducibility of bright colors, greatly improve the performance of thin lines and characters, and greatly improve the performance range of layout design.
(5) Printing ink
At present, water-based synthetic resin is the main ink used, but solvent-free flexographic ink (UV ink) has been widely used in Europe and America as a solution to limit solvents, and Japanese ink manufacturers have followed suit. Compared with water-based ink, UV ink has higher viscosity (1000-3000cps). The hardened ink film is durable, with good adhesion to various plastic materials and smooth surface. It is expected that there will be better development in the future. The composition of UV ink is shown in Table 2. At present, free radical UV ink is the mainstream. From the perspective of future security, cationic ink will become the mainstream of packaging and printing.
In addition, various flexographic printing machines equipped with UV curing devices have been introduced. Here is a photo of the Flexopak machine produced by COMCO (see Figure 4).
prospect
After entering the 2 1 century, the environmental protection laws and regulations represented by the market environment of printing industry, that is, multi-variety, small batch, individualization and low price, as well as the container packaging reuse law and the chemical substance discharge management law, which are being legalized, will become more and more strict, and become a major issue that must be solved in the early 2 1 century.
In order to solve these problems, we can't make some small reforms in production engineering or simply change the business content of enterprises as in the past, but we must accurately change the production mode and make comprehensive innovations in activating enterprise organizations. We might as well talk about the problems existing in gravure printing and offset printing, and finally describe the prospect of flexographic printing.
① Gravure printing
To meet the needs of the market environment, there is no problem with printing speed, but there are certain restrictions on adapting to small batches, and productivity cannot be improved. At the same time, there are still problems in the handling of delivery time.
As for the legal response, the situation of solvent-based ink requires exhaust (burning, recycling) equipment, because of the initial investment and working capital problems, and the need to consider improving the working environment. Also consider water-based ink, which will slow down the speed and lead to a decline in productivity. In addition, there are many problems in the demand for drainage treatment devices.
②. Offset printing
At present, there is no problem in the handling of laws and regulations, but in the flexible packaging of printed films, it is necessary to develop new inks and drying methods, and there are still many unknown fields, which are not easy to solve immediately. In addition, the carbon dioxide produced by high boiling point solvent treatment is also a problem that must be solved from the perspective of global environmental protection.
③ Flexographic printing
Water-based, solvent-free (UV) and so on are very easy to do, especially UV ink completely meets the needs of environmental protection. In addition, in the case of using a narrow web, the time required for replacement work is very small. On COMCO 16 inch printing machine, each unit can be replaced in 90 seconds, and there are few mistakes. Compared with the above two methods, it has absolute advantages, especially when the batch print work is less than10000m.
At present, the problem is to completely innovate gravure printing for packaging, and what needs to be solved is high investment and heavy operation load. At the same time, there is still a slight quality difference between flexographic printing and the above two methods, which is also a kind of resistance. But from the perspective of environmental protection, priority should be given. Therefore, it is necessary for the packaging and printing industry to launch more narrow flexographic printing machines that can cope with small batch and short delivery time as soon as possible to innovate the packaging and printing industry.
If the flexographic CIP is further improved and the seamless printing plate under development is introduced, it will be not only a small batch but also a large batch of printing work when the quality is not much different from other formats. At that time, it will be there! At the beginning of the # century, flexographic printing with environmental protection, high quality and high productivity will undoubtedly become the mainstream of packaging printing.