Flexo printing was first used in newspaper printing in the United States in the mid-1970s. In 1982, the United States introduced a special flexo printing machine for newspapers. Since then, flexo printing has begun to compete with offset printing in the field of newspaper printing. The San Francisco Observer, San Francisco Recorder, News and Observer, etc. all use flexo printing. And achieved good results. Today, about 30% of newspapers in the US use flexo printing; about 14 major newspapers in Europe use flexo printing; and about 25% of newspapers in Italy use flexo printing.
In recent years, flexo printing has also developed rapidly in China, but overall, China's flexo printing technology is still in its infancy. Of the total printing volume, flexo printing accounts for only about 1.5%, and is mainly used for carton and corrugated box printing. Flexo printing has not yet been applied in China's newspaper printing industry.
Problems with offset printing
The basic requirements for newspaper printing are: first, it must be time-sensitive and provide newspapers to the readers at the fastest speed; second, it should meet the quality requirements, with clear graphics, colorful colors, and good visual effects; and third, economy, Under the premise of meeting the basic requirements, the maximum cost is reduced; fourth, it should be environmentally friendly. Under the conditions of increasing international environmental protection requirements, it should meet the environmental protection requirements and should be neglected. The basic conditions of newspaper printing. Below, we make a brief analysis of the offset printing newspaper, and talk about the problem of offset printing newspaper.
1. Adjust the structure of newspaper printing
At present, in China's newspaper printing, offset printing is almost the world, regardless of the size and printing volume, all offset printing is used. In Europe and North America, the single pattern of offset printing was broken in the 1990s, and we should choose the printing method according to the specific situation. For example, the cost of offset printing for newspapers with tens of thousands of copies will be greatly increased. At this time, different printing methods can be selected according to different requirements.
2. The broken paper rate and the high scrap rate are the outstanding problems of offset printing
In offset printing, controlling the water-ink balance is an important issue, and achieving the water-ink balance of offset printing requires a process. Under normal circumstances, it takes about 15-30 minutes from the start-up to the stable working state of the machine adjustment and trial printing stage, which will inevitably increase the paper breakage rate. In the offset printing process, there are many factors that affect the balance of water and ink, and most of these factors change. Even under normal printing conditions, scrap products will occur due to changes in certain conditions. For example, the loss rate of sheet-fed four-color offset presses is generally as high as 7% -15%, and the loss rate of web offset presses is even higher than that of sheet-fed offset presses. Therefore, from the economic point of view, offset printing is not the most ideal.
3. Offset printing newspaper does not have much advantage in printing quality
The high quality of offset printing is premised on many conditions. If the surface performance of the printing material is high, only fine-printed products can be printed when printed on coated paper with higher price and better quality. Printing on newsprint is prone to the following problems: (1) offset printing uses fountain solution, and newsprint is very absorbent, and the whiteness of the paper will decrease after water absorption; (2) because the surface of newsprint is very rough, it will affect the clarity of graphics (3) In the printing process, it is easily affected by external factors, the stability of the printing quality is poor, and the ink color unevenness, dull color and other failures are easy to occur.
4. Offset printing newspaper is at a disadvantage in environmental protection
Offset rotary printing inks are low viscosity solvent-based inks. The solvent content in the ink is high. Without the addition of oxidized conjunctival catalyst, it is directly dried by permeation, absorption and heating. The printed matter is difficult to fully dry in a few hours. Dirty failures occur, and when readers get the newspaper, the wet ink will stick to their hands. In addition, the smell of solvent-based ink is very strong, which is not good for operators and readers. In addition, the volatile organic solvents in the ink pollute the environment. Therefore, the rotary offset printing ink is a polluting ink, and its use should be gradually restricted.
5. Offset printing has certain requirements on paper
The printing speed of offset printing is high, and fountain solution is used. If the paper is too thin, it may cause paper breakage. Therefore, the paper used for offset printing should not be too thin, generally not less than 52g / m2, which will also increase the cost of printed products.
6. Offset printing has higher requirements on the operator's technical level
Due to the relatively complicated structure of offset presses, the adjustment positions are the most among all types of printing presses, and the control of water and ink balance is difficult to master, so there are high requirements on the operator's technical level, basic knowledge and skills. According to reports, less than 1/3 of the basic requirements for offset printing workers among offset printing workers show that it is difficult to cultivate a better offset printing collar machine.
In summary, in the past 10 years, newspaper printing in China has achieved offset printing, and offset printing has played a great role in the development and progress of our newspaper industry. However, with the rapid development of printing technology, newspaper printing only uses offset printing, which is not the best choice. The development trend of newspaper printing in Europe and America has proved this point. In the future, newspaper printing in China should use flexographic printing technology on the basis of continuing to improve printing quality and reduce costs.
Application of flexo printing in newspaper printing
After years of development, flexo technology has made remarkable progress. Especially in recent years, the key technology of flexo has made a major breakthrough, which has created extremely favorable conditions for the application of flexo in the newspaper printing industry. It can be considered that flexo printing technology has been increasingly improved, and has entered the stage of practical promotion in the field of newspaper printing.
1. Application of pre-press digital workflow
The use of digital workflow is an important link to improve timeliness, reduce costs, and improve quality. Its main content and functions include open systems, flexibility in editing and final modification of documents, PDF language format, electronic file exchange, trapping, spelling Large version and digital proofing and RIP output at once. Using this system can not only greatly reduce the process and shorten the working hours, but also exclude the subjective factors of manual operation to ensure the quality of pre-press processing. China ’s newspaper industry already has a good foundation for adopting digital processes. If we further improve and improve its standardization and standardization, we can greatly improve the technical level of China ’s newspaper pre-press digital workflow.
2. Flexo CTP technology has matured
Traditional plate-making technology uses film to print, and it takes about 30 minutes to produce a set of color plates, which is not only time-consuming, but also difficult to guarantee in quality. The use of CTP technology not only greatly simplifies the plate-making process and shortens the plate-making time (the time required to produce a set of color plates is only 1/3 of the traditional plate-making time), but also reduces the phenomenon of dot gain, making highlights and dark parts The number of outlets lost and connected to the network are greatly reduced, improving the copying capacity of the printing plate.
At present, the world-famous prepress equipment and plate material production companies have successively launched practical CTP products. Representative manufacturers include Agfa, Heidelberg, Kriosai Angel, Dupont, Barco, Kodak Polylight, BASF , Hell, etc., the introduction of the flexographic direct plate-making system has provided quality assurance for newspapers using flexographic printing.
3. Flexo printing has advantages
Compared with offset printing, the use of flexo printing technology in newspaper printing has obvious advantages.
(1) The equipment cost is lower than the offset press. Under the condition that the size of the substrate and the printing capacity are the same, the equipment cost of the flexo printing machine is about 1/3 lower than that of the offset printing machine.
(2) The printing speed is higher than that of the offset printing machine. At present, the printing speed of flexo printing machine can be divided into three speeds: low speed (80-150m / min), medium speed (150-300m / min) and high speed (600-700m / min). Because flexo printing is light-pressure printing and sleeve printing plates can be used, the inertial imbalance force is small, the paper is not easy to break, and it has good running stability, so high-speed printing can be achieved.
(3) Low-weight newsprint can be used. Due to the good running stability of the flexo printing machine, and no impact of the dampening solution of the offset press on the performance of the paper, so gram printing can use low-gram weight newsprint (40-45g / m2). If thick paper is changed to thin paper, the average annual national newspaper printing paper can save about 18% (according to the annual printing of 54 billion pairs of opening).
(4) The paper breakage rate of flexo printing is low. The time for adjusting and trial printing of flexo printing is relatively short, so the broken paper rate is low, about 2%, which is nearly 9 percentage points lower than that of offset printing. If the amount of paper saved by using thin newsprint is added, only one item of paper can save about 27% of paper consumption every year. According to reports, the US "San Francisco Observer" uses flexo printing, saving only 41 million US dollars per year on paper alone.
4. The use of ink and short ink system provides a guarantee for the wide application of flexo printing
(1) Ink painting. Ink is an environmentally friendly ink, does not contain volatile organic solvents, can improve the printing environment, which is one of them. Second, the waste water after printing can be recycled after treatment, and all the waste ink can also be recycled into ink color ink for reuse. Third, ink is a quick-drying ink, and there is almost no smearing problem during printing.
(2) Short ink path system. Adopt the closed anilox roller short ink path inking system, which can quantitatively provide stable ink for the printing plate, and the inking performance is obviously improved. By changing the technical parameters of the anilox roller (the number of screen lines and the geometric parameters of the mesh holes), the printed product can get the required amount of ink.
The use of a closed reverse squeegee system not only keeps the ink in a clean state during the printing process, but also keeps the ink performance stable and ensures consistent ink color.
There has been a major breakthrough in the manufacturing technology of ceramic anilox rolls, which can process anilox rolls over 1500 lines / inch, or high line count anilox rolls with 2000 lines / inch or even 2500 lines / inch. This not only greatly improves the service life of the anilox roller, but also creates conditions for high-speed, high-precision flexographic printing.
5. Flexo printing quality is good
The use of flexo printing in newspaper printing has the following characteristics:
(1) Newspaper printing is mainly based on text, lines, and color blocks. Flexo printing has the advantages of embossing. The graphics are clear, the picture is neat and vivid, and the colors are bright. Flexo printing is superior to offset printing in this regard.
(2) It has good printing repeatability and can ensure the consistency of the ink color of the printed products.
(3) The number of screen printing lines can reach 133-150 lines / inch, adopt CTP technology, and its resolution can reach 1270dpi, which can meet the requirements of newspaper printing.
(4) It can easily realize multi-color group printing and give full play to the advantages of spot color printing.
This shows that the quality of flexo printing can fully meet the requirements of newspaper printing.
In short, newspaper printing has taken a gratifying step forward from the era of offset printing, and has begun to enter a new era of flexographic printing. As a major newspaper printing country, China's newspaper printing industry should also make its due contribution to this.
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