Application of CTP Direct Plate Making in Packaging Printing

The printing technology method and its quality are critical to the market popularity of flexible packaging products. In recent years, the infiltration of information technology and computer technology in printing engineering has been very rapid, and the traditional printing process has been changed to some extent.

Direct Plate Technology (CTP) refers to Computer to Plate technology, which does not include film in traditional lithography. It is currently one of the fastest-growing and most influential high-tech industries in the prepress industry. It has developed rapidly in the field of publishing and printing in China, especially in the newspaper industry, and it has become quite popular.

It is not common to apply CTP technology in lithographic offset printing in the packaging and printing industry. There are only a handful of manufacturers that have CTP systems in Shanghai. In fact, in the packaging and printing, there are a considerable number of lithographic offset products, short-lived, plate-making workload, the application of CTP technology has obvious advantages.

Due to the development of new technologies and the continuous improvement of user requirements, the steps between prepress and printing have been gradually reduced. With the development of CTP system technology, digital processes from design to final printing have become a reality. Digital technology has greatly shortened the printing cycle, reduced manual operations, improved product quality, and increased the degree of automation. This allows printers to provide customers with a full range of services with shorter cycle times and lower prices. Computer-to-plate technology will bring significant social and economic benefits. Therefore, it is imperative to promote the use of CTP technology by drawing heavily on foreign advanced technologies.

1. The basic working principle of CTP technology

The CTP plate making machine consists of three parts: precise and complex optical system, circuit system, and mechanical system.

The single-beam original laser generated by the laser is split into multi-beams of ultra-fine laser beams by multiple optical fibers or a complex high-speed rotating optical splitting beam system. The acousto-optic modulator is characterized by the brightness and darkness of the image information in the computer. The light and dark changes of the laser beam are modulated. After focusing, several hundred micro lasers are directly shot on the surface of the printing plate to form a latent image. After development, the image information on the computer screen is restored on the plate for direct printing by the offset press. The diameter of each micro laser beam and the light intensity distribution of the beam determine the sharpness and resolution of the latent image formed on the plate. The smaller the beam spot, the closer the light intensity distribution of the beam is to the rectangle (ideal case), the higher the clarity 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 length of the scan time. The greater the number of microbeams, the shorter the time for etching one plate. On the other hand, the output power and energy density of the engraved beam also have an effect on the etching speed. At present, the beam diameter has been developed to 4.6 micrometers, which is equivalent to the printing accuracy of 600lpi. The number of beams can reach 500. The time to etch a split printing plate can be completed within 3 minutes.

2. Computer-to-plate (CTP) technology key

The CTP system is a high-tech product that integrates a variety of new technologies. Its structure is mainly composed of mechanical systems, optical systems, and circuit systems. One of the key technologies of computer-to-platemaking is the matching of printing plates and imaging systems. Its technology is summarized as: working mode, laser technology and media technology.

(1) Working methods

The working mode of the direct plate making equipment refers to the exposure mode of the layout recorder, which can be divided into inner drum exposure mode, outer drum exposure mode and flat bench exposure mode.

The advantages of the inner drum type are the fast scanning speed and high precision. The single beam laser head is used. The price is relatively cheap. The upper and lower versions are simple and convenient, and they can support a variety of punching specifications at the same time. The disadvantage is that it is not suitable for large format.

The advantages of the external drum type are that it is suitable for large format, suitable for thermal plates, and uses multi-beam laser heads. Due to the large amount of heat required for the thermal plate, the light source must have large power, and the external drum plate is used. The machine can position the light source close to the plate. The disadvantage is that the applicable plate has less specifications, the drum cannot rotate at a high speed, the upper and lower versions are slow, and the mechanical failure is relatively large.

The advantage of the platform type is that the mechanical structure is simple and stable, the scanning speed is high, the price is relatively cheap, the upper and lower versions are simple and convenient, and can support a variety of punching specifications at the same time, using a single beam laser head. The disadvantage is that it has a large area and is not suitable for large format.
(2) Laser technology

Light sources of the computer-to-platemaker include: gas lasers (such as argon ion lasers), solid-state lasers (such as FD YAG), and semiconductor lasers (LD). The laser light source used by CTP can be divided into visible light source, infrared light source, and ultraviolet light source according to its spectral characteristics. Early computer-based platemaking equipment used blue (488nm), green (532nm), and red (633nm) visible lasers, and is now being replaced by infrared (830nm, 1064nm) and violet (400nm, 410nm) technologies.
(3) Plate material technology

Different from the film used in the imagesetter, CTP media is directly printed on the machine. Its accuracy and integrity are the key to the final product, and it is also one of the key factors restricting the development of CTP. Due to the high price of the plate, the cost of CTP is high.

At present, the types of plates can be divided into metal plates and polyester plates if they are divided by plate base.

Metal plate is mainly referred to as aluminum plate. The market share of aluminum plate in the United States accounts for about 90% of the total market. The main advantage is the high resistance to printing, a wide range of applications, and better graphic quality, especially for long-run printing.
With the rapid development of digital technology, on-demand printing, short lived more and more, the use of polyester version allows the printing factory to better meet customer needs.

There are two commonly used CTP plates that are divided by coating: photosensitive resin plates and thermal plates.

Photosensitive resin plates are imaged with light and therefore require processing under darkroom conditions. It is most suitable for medium-to-long version of color commercial printing, the output line is 175Ipi, the plate making speed is fast, the stability of the printing on the machine is good, so it can make up for the inconvenience it requires in the darkroom version.

Thermal plates are based on thermal imaging technology and can therefore be processed in yellow light or ultraviolet light. The thermal CTP system has good platemaking quality and can restore 200Ipi, 1% to 99% of the dot. Thermal imaging is also expected to achieve non-chemical processing of plate technology, but its speed is not the fastest. In the CTP plate, the sensitivity of the CTM plate was the highest, followed by the photopolymer plate, and finally the thermal plate.

3. CPT related equipment and its suppliers

According to the above working methods, the computer-to-platemaking machine can be divided into: inner drum type platemaking machine, outer drum type plate making machine, and platform type plate making machine. The most used ones are inner drum type and outer drum type. Internal drum direct plate-making machines are mainly used for large-format plates such as newspapers. They mainly include Agfa's Galileo VS/VXT system, ECRM's Wildcat/Tigercat system, and Baoluode. Purop-Eskofot's DMX/ImageMaker system, etc. The external drum type plate making machine is suitable for use with a thermal plate, mainly including Lotem 400VA/Letem 800V/Letem XL from Creoscites, and Plate Rite 4000/Plate Rite 8000 from Screen. Platform-type computer platesetters are particularly suitable for aluminum plate bases, and they include Barco's Mondrian systems. The printing plates used by CTP machines are generally large-format printing plates with dimensions of 66*84 inches according to the printing format and equipment requirements; large-format printing plates with dimensions of 55*67 inches; medium-format printing plates with sizes of 41 inches. 32-inch, 22-inch three; small format plate, size less than 18 inches. The most used ones are medium format and small format.

The suppliers of CTP equipment are mostly from the United States, as well as companies established by Germany and Japan in the United States. The suppliers of large-format equipment include Agfa, Barco, Creo, Heidelberg, Gerber, ECRM, Optronics, Saiten U.S. Prepress, U.S. Screen, etc.; medium and small format manufacturers include: PrintWare, DuPont, etc. Many.

The current production of CTP plates include: Agfa-Dupont's aluminum-based Silverlith and Lithostar CTP, Mitsubishi Chemical's polyester film-based CTP, Mitsubishi Paper's polyester film base, and paper-based SDP and Silver. The Master CTP version is compatible with various models.

The thermal plate includes Kodak Polystar's 830nm thermal plate, Agile's Galileo VLF-Thermalstar P970 thermal plate, Fujifilm's LH-NI and LH-PI thermal plates, and Mitsubishi Chemical's LT- 1 (830nm) and LT-G (1064nm) thermal plates.

The photosensitive resin plate mainly includes Agfa's N91 photosensitive resin plate. Fujifilm's thermal plates include Brillia LH-PI (Bright Pattern Thermal Plate), Brillia LH-NI (Negative Pattern Thermal Plate), Brillia LP-NS and Brillia LP-NN, etc. produced by Mitsubishi Chemical Corporation of Japan. High-sensitivity photosensitive resin plates, such as LA-S and LY-S plates. 4. Basic requirements for using CTP systems

With the CTP system, it is necessary to improve the interface technology of the front-end system and the data and technology of the back-end equipment. Enterprises must establish a complete set of electronic document management systems, improve data preservation and retrieval technologies, and apply color management techniques to solve the problem of consistency in digital proofing and output.

When purchasing CTP, users can consider comprehensive benefits, maintenance workload, consumables prices and supply sources according to their own needs.

Source: Packaging Expo