Introduction of computer-to-plate (CTP)
Zheng Shiming, Professor, University of Southern California, USA
President of CPS Technology Development and Investment Company, USA
-
Brief introduction to the development history of CTP technology
CTP (computer-to-plate) technology appeared in 1980s. This period is the primary stage of direct plate making technology research. Therefore, neither the plate-making technology nor the plate-making quality is very mature during this period. In the 1990s, equipment manufacturers cooperated closely with printing manufacturers to speed up the research and development of this technology, and reached the level of maturity and industrial application during this period. Therefore, 42 CTP systems were exhibited at 1995 Druba Printing Exhibition.
This move immediately attracted great attention of the printing industry to this technology. During the period of 1995- 1997, many large printing companies used CTP system to realize the direct plate-making process, but the direct plate-making machine in this period was still very expensive, which limited the use and promotion of this technology in small and medium-sized enterprises. During the period of 1997-1998, the price of direct plate-making machine dropped sharply, and the plates made by direct plate-making began to mature and develop, so a large number of small and medium-sized printing houses began to accept and use CTP technology. According to the situation of the printing factory, the developed machine formats are folio, 8, 16. According to statistics, by 1997 in the United States, 65% of large printing plants (with more than 100 employees) have used CTP technology. According to the survey of GATF, the authoritative organization of printing technology in the United States, from 1995 to 2000, the number of CTP systems installed and expected to be installed in the world is as follows (including CTP systems used in newspaper printing industry, including 8 sets of folio, folio and full boot):
1995 1996 1997 1998 1999 2000
3 1 1 72 1 1686 3 100 6200 12 150
Judging from this set of data, the penetration rate of CTP is more than doubled every year. During the three years from 1995 to 1998, the growth rate was as high as 10 times.
The reason why CTP system can be popularized among users at such an amazing speed is that it has the advantages of good plate-making performance and eliminating film application, and the expansion of CTP technology application scope is also one of the main reasons. At present, the direct plate-making machine on the market can meet the needs of large-format and small-format printing size, single-color printing and four-color printing, newspaper printing and commercial printing. So it is very flexible to use.
Moreover, in recent years, the development and improvement speed of sheet metal is also very fast. The sharp drop in the price of CTP equipment in the past five years has promoted the rise and development of the market. At present, 8-boot has been reduced from the previous $400,000 to150,000-200,000, and the split type has also been reduced to about $400,000.
American media comment: CTP is an inevitable technological revolution, and it will definitely replace imagesetter technology, just as the expansion was replaced by imagesetter five years ago.
1998 At the NEXPO98 exhibition hosted by the American Press Association in June, * *1/manufacturers exhibited their CTP system. However, no influential manufacturer has introduced new laser imagesetter and related technologies. This fully shows that manufacturers are no longer hesitant about CTP technology and have entered the practical stage.
Classification of CTP direct plate making machine
At present, CTP direct plate making machines are generally divided into four categories: inner drum type, outer drum type, flat plate type and curved type. Among these four types, inner cylinder and outer cylinder are the most commonly used; Flat plate is mainly used for large format plates such as newspapers; Curved forms are rarely used. According to statistics, 1997, among the 58 CTP machines provided by 29 manufacturers, there are 24 kinds of inner drums, 6 kinds of outer drums/kloc-0, 9 kinds of flat plates and 9 kinds of curved ones. In these forms, the outer drum gradually presents the mainstream trend.
Layout mode
According to the different degree of automation, the loading methods of plates can be divided into manual and automatic. Manual loading machine is cheap, but it is generally required to operate in a dark room, which is inefficient; Automatic version of the equipment, high efficiency, but the price is more expensive, generally more expensive than manual type 10 million dollars. In addition, when loading plates, the automatic equipment must use a whole box of plates with release paper. The surface of the plate has a light-proof protective film, which can be operated in an open room. During plate loading, the protective film on the surface of the printing plate can be automatically peeled off by the plate feeder, so that the printing plate can participate in plate making.
The fixing methods of the plate on the roller are: full adsorption and intermediate adsorption, and the first part and the second part are fixed by clips. There is no limit to the size of the plate by total adsorption, but the plate format used for clamping must have a fixed size.
30% of CTP equipment is equipped with a punching device, and the punching process is usually carried out after exposure, which can ensure the accurate positioning of the printing plate on the printing press, reduce the prepress preparation time for adjusting the printing roller, and improve the printing quality, overprinter and positioning accuracy.
Print size
According to the requirements of printing format and equipment, the plates used by CTP machines generally have ultra-large format plates with a size of 66*84 inches; Large format printing plate with a size of 55*67 inches; Medium format printing plates with sizes of 4 1 inch, 32 inches and 22 inches; Small format printing plate, the size is less than 18 inch. At present, the most widely used are medium format and small format.
Major equipment suppliers
Most suppliers of CTP equipment come from the United States, as well as companies established in the United States by Germany and Japan. Large format equipment suppliers include Agfa, Barco, Creo, Heidelberg, Garbo, ECRM, Optoelectronic, Sai Angel American prepress company, American screen company, etc. Manufacturers of medium and small formats are: PrintWare Company, DuPont Company, etc. Special equipment for newspapers is provided by Creo Company and Krause Company.
Basic working principle of CTP
CTP direct plate making machine consists of three parts: precise and complex optical system, circuit system and mechanical system.
A single original laser beam generated by a laser is divided into a plurality of ultra-fine laser beams (usually 200-500 beams) through a plurality of optical fibers or a complex high-speed rotating optical beam splitting system, and each beam is modulated by an acousto-optic modulator according to the brightness characteristics of image information in a computer, and then becomes a controlled beam. After focusing, hundreds of miniature laser beams directly hit the surface of the printing plate for engraving, and after scanning and engraving, the latent image of the image is formed on the printing plate. After development, the image information on the computer screen is restored to the printing plate and printed directly by the offset press. The diameter of each micro-laser beam and the light intensity distribution shape of the beam determine the clarity and resolution of the latent image formed on the printing plate. The smaller the microbeam spot, the closer the microbeam light intensity distribution is to the rectangle (ideal case), and the higher the definition of the latent image. The scanning accuracy depends on the mechanical and electronic control parts of the system. The number of laser microbeams determines the scanning time. The more microbeams there are, the shorter the time it takes to etch the printing plate. At present, the beam diameter has developed to 4.6 microns, which is equivalent to the printing accuracy of 600lpi. The number of beams can reach 500. The time for etching the folio can be completed within 3 minutes. On the other hand, the higher the output power and energy density (laser energy per unit area, in Joule/cm2) of the beam, the faster the etching speed. However, too high power will also have negative effects such as shortening the working life of the laser and reducing the beam distribution quality.
The light sources of the plate-making machine include: gas laser (argon ion laser 488nm, power: about 20mw); Solid-state laser (FD YAG 532nm,1100mw or above); Semiconductor laser (LD, infrared semiconductor laser in semiconductor laser has the advantages of low power and long life. )
The direct plate-making system is a comprehensive multidisciplinary technology industry, which includes precision machinery and optics technology, electronic technology, color digital image technology, computer and software technology, new printing plate technology, automation technology and network technology. This is another major technological revolution in the contemporary printing industry.
development trends
The CTP wave is surging. By the end of 1990- 1996, more than 300 patent articles had been published. 1996, among the 65,438+000 largest printing enterprises in the United States, 55.3% adopted CTP system and 28.8% adopted short color digital printing system.
Yangcheng Evening News1April, 1998, the flat CTP plate-making machine of Aikefa Company and the external drum CTP of Fangshi Optoelectronics were tried out in some sections of New Express.
Since 1985, most newspapers and existing printing houses in Chinese mainland have adopted laser phototypesetting and offset printing. The next technological transformation direction of these well-funded newspapers and printing houses is direct plate making, color newspapers and periodicals, high-grade color printing and packaging printing. It is required to expand the scanning format to folio (740*5 10), and the printing resistance of the plate can reach 300,000 ~ 500,000 sheets.
For newspaper printing, CTP saves manpower, improves quality and reduces environmental pollution. The optimized process flow is simplified and it is easy to establish a continuous production line with high automation. In terms of newspapers, domestic national newspapers have a high degree of digitalization and advanced technology and equipment, and there is no obvious gap compared with foreign newspapers. The domestic newspaper industry is facing fierce competition. CTP system can save 30-50 minutes for the whole publishing process, so especially for the publication of evening papers, the deadline for news can be delayed by 30-50 minutes when the opening time is unchanged, which is of great significance to the news of the day.
As a development direction of China's printing and publishing industry, CTP system and technology have been included in the Ninth Five-Year Plan, which is a typical technology-intensive industry with high technology, high growth and high return.
Requirements of CTP system
When using CTP system, we should first pay attention to the interface technology with the front-end system, that is, the improvement of data exchange technology between color prepress systems and data mapping technology of back-end equipment. For large-capacity files, data exchange speed and data transmission speed are very important; Secondly, enterprises are required to establish a new electronic document management system and improve data preservation and retrieval technology; Then, the requirements for color management technology and RIP technology are also very important. Large-capacity files require RIP to have powerful processing power in order to achieve high efficiency. For the consistency of proofing and output, color management technology is needed.
When purchasing CTP, users need to make detailed system demonstration and analysis according to their own needs, and then make a decision. The new technology system should not be required to match the old workflow, but should be considered comprehensively: comprehensive benefits, maintenance workload, consumables price and supply source; The system must be open and the technology used can be upgraded.
Performance description of newspaper CTP printing machine
K & ampf Company and Klaus Company:
LaserExpress direct plate making system is the fastest and most flexible CTP system at present. When the production speed is 10 16dpi, it can reach 200 whole sheets (or 200 double sheets) per hour. At 1270dpi, it can reach 150 sheets/hour. The printing format can consider all the sizes of the current newspaper. Realize the automatic loading and unloading of plates and the automatic removal of plate lining paper. The exposed and developed negatives are sent to K&; F plate is processed online, and the available plate is SilverLith SDB silver salt diffuser made by Aikefa; A photopolymer CTP version can also be used. These two plates are very sensitive to the wavelength of 532nm, but they still have a certain distance from competitors' thermal imaging plates in high-speed production.
Klaus Company:
Star2000 CTP plate-making machine is designed to be used in thermal plate-making mode. Light sources include visible light and infrared laser. Can realize automatic plate loading, and there are five sizes of plates. Equipped with board calibration and punching system, purchase CPI3.
Creo company:
ThermoFlex equipment, large format (VLF) flexographic CTP plate making machine. Manual loading and unloading, the printing plate size can reach 50*67 inches, and it is expected to reach 52*80 inches in the future. It can be directly imaged on flexographic plates and heat-sensitive materials.
Features of TrendSetter 3244F plate-making machine: external drum type, which is difficult to achieve high speed due to the rotation of the drum. Therefore, it is necessary to design multiple beams to scan at the same time, which can shorten the exposure time of the whole layout. The machine can scan as many as 480 beams at the same time. It only takes 5 minutes to scan 813 *118 mm printing plate with a resolution of 3200dp.
The trend-leading plate-making machine can realize multifunctional imaging, integrating plate imaging, film imaging and proofing. For example, you can expose heat-sensitive materials and polaroid dry films. You can also use Imation's Match Print laser printing materials to make contract proofs. Therefore, the tidal current proofing machine can realize three functions of dry film, plate making and color proofing, and has the same screening characteristics. And multi-functional plate making machine is the future development direction.
However, there are the following problems in multi-purpose of one machine: the treatment, requirements, processing methods and outlets of different materials and media are inconsistent, and there are contradictions between labor and productivity. For small manufacturers, it is very popular to use one machine for multiple purposes, but for large printing plants, it is not conducive to the implementation of specialized production and has a great impact on productivity.