Second, the development of lithographic plate technology
For more than 40 years, with the development and popularization of lithographic printing technology, lithographic plate making technology has made great progress. It has undergone fifties lithographs, protein plates, flat intaglio plates from the sixties to the seventies, multi-layered metal plates. Pre-coated version (PS version) since the 1980s.
Lithographic plate
Plain printing was developed from lithographs. Lithographic plate was originally called "painted stone". It was the plate-making staff who used the fatty substances to directly depict the graphic on the stone plate surface. Later, with the progress of the transfer method, the plate-making staff first attached the graphic containing the fat-transfer ink to the pasted paper, and then transferred the transferred ink on the pasted paper onto the stencil under the pressure. Lithographic version. Stones are heavy and neither easy to use nor easy to use. Second, this type of lithographic material is a natural marble that has been milled and has a limited source.
Due to these shortcomings of the lithographs, many printing factories in the 1950s gradually switched to the lithographed version of the zinc-coated leather plate. The printed version is lighter, but the principle of plate making is the same as that of the stone making version, and there is also a saying that this type of printing plate is a paste version. Slurry transfer ink transfer under the pressure effect, to expand outwards, so that the graphic thicker, so this version can only be applied to some thick lines, text printing.
2. Minami plate making process
In the lithographic plate family, there is also a version that is very old and has a small amount of usage, but is quite distinctive. It is said that it is a long-lived person who has been in Europe since the 1850s. In 1907, the Commercial Press formally established the Feiluo workshop. It is said that its small amount is due to the fact that the output of the Minami version print is minimal in the entire print product. But it is quite distinctive. It can copy continuous originals without going through the net.
The Feiluo version also belongs to photolithography. The process is as follows: 10 mm thick glass plate is used as a base plate, and a photosensitive solution of ammonium dichromate gelatin is coated on the plate, and after drying, the negative film is successively adjusted to the negative film for close exposure. Develop with water. Since the tone on the negative film is continuously changed, the exposure amount of the photosensitive film is also continuously changed, and the degree of hardening of the photosensitive film after exposure is changed accordingly. When the amount of light on the cloudy film passes through many places, the film hardens the wrinkles and absorbs ink, and its water repellent ability is weak. The printing ink layer is thick and has a dark hue; the light quantity passes through a small area, the film hardens the wrinkles, and the ink absorbing ability is weak, and the water absorption ability is strong. The printing ink is thin and light in color. Where no light is received, no hardened wrinkles are generated, completely hydrophilic, and no ink is absorbed. The Jurassic version does not require screening, and it can still print continuous-tone images with bright and dark effects at the light and dark levels. This is where the Jurassic printing is uniquely attractive. This is also not possible with other printing methods.
The graphic version of the Milo Edition is based on a film of different degree of hardening. Under the constant infiltration of water during the printing process, the wrinkles in the graphic area gradually lose their ability to attract ink or fall off. Therefore, the number of imprints of the Milo version is very low, generally around 500 impressions. Although the images are printed beautifully, the print resistance is too low, and the consistency of the printed products is poor, which greatly limits its application.
After the public-private partnership in the Shanghai printing industry in the 1950s, part of the Jurassic printing factory was relocated to Beijing, and Shanghai retained part of it as a laboratory for Shanghai printing companies. I moved this part of Beijing to the Printing House of the Palace Museum and later changed its name to the printing house of the Cultural Relics Publishing House. In the past decades, the Milon Edition technology has not changed substantially and its scale has not developed. However, its unique continuous replication effect proves its survival value, making it a unique and never-fading flower in the Print Garden. .
3. Protein version
Protein version of the sensitizing gel is formulated with ammonium dichromate and protein gel, so this name. Due to the simple production process of the proteoplasty and low cost, it can be printed on the typographical machine. It is a more popular typographic version in the fifties.
The plate-making process of the protein plate is: Dissolve the protein powder in water (if it can not buy protein powder, use egg white can also), add ammonia, increase the ammonium chromate solution, formulated as a protein photographic solution. The protein photosensitive liquid is applied to a roughened zinc plate, dried, and the photosensitive adhesive is brought into close contact with the negative film, exposed, wiped and developed, and developed under clean water. The non-photosensitive part of the protein gel was washed away in water to expose the zinc plate; the photo-sensitive part of the image produced a solidified protein film showing a graphic, and the Arabic gum solution could be printed on the machine.
Although the production of the protein version is convenient, it also has its disadvantages. First, the use of negative plates for protein plates is inconvenient for observation; second, the loss of overtones through the network negative film is large; and third, the protein version is low against the printing force, and is generally printed around 5000 lines. From 12,000 to 12,000, it is not appropriate to print a long version.
4. Intaglio
Printing expert Liu Yuqing promoted the use of flat intaglio printing in the People's Printing Factory in Beijing in the 1950s. In the late 1950s, the Beijing Institute of Printing Technology launched a new process of “dry and wet†with two inverted positive figures. Compared with the proteotype, there can be less than one negative in the photographic stage.
The photoinitiator is made of ammonium dichromate and gum arabic. Due to the need for imports of gum arabic, after the 1970s, domestic polyvinyl alcohol was gradually used instead of gum arabic.
The process is as follows: the sensitized film is coated on the roughened zinc leather plate surface, and the film is sealed and exposed with a positive image, and the film is rinsed with clean water. The image area is not photosensitive, and the photosensitive adhesive is dissolved to expose the metal during development; the photosensitive resist in the blank area remains in the blank area due to the photohardenable development to form a hardened photosensitive protective film. Slightly corrode the exposed image area with ferric chloride solution to make it 5-10 μm concave, wash it off immediately, dry it, wipe the base paint and developing ink, and lightly recess the metal surface on the graphic area. Attach a layer of solid ink-resistant ink paint. Finally, remove the hardened photoresist from the blank area and wipe with gum arabic to print on the machine.
Compared with the albumin, the intaglio plate is not only concave in the image area, but also has a thick ink layer, good ink-transmitting properties, and high resistance to printing. It is about 5 to 10 times more than the plate version.
For publications with large circulation such as banknotes and books, of course, it is hoped that the higher the printing plate resistance, the better. For this reason, Beijing Xinhua Printing Co., Ltd. and Beijing People's Printing Co., Ltd. and other large-scale printing factories use multi-layered metal plates on the basis of the plane and gravure plates. In terms of plate making process, this multi-layered metal plate is also an intaglio plate. The difference is that the multi-layered metal plate is composed of iron, copper, chromium, or copper, chromium multi-layer metal. Regardless of two or three layers, the surface layer is chromium, and the chromium layer is under the copper.
The plate making process is as follows: coating the same sensitized photoresist on the chrome layer, exposing and developing the positive film, etching the chromium layer with a hydrochloric acid solution, and exposing the graphic region to the copper layer. After rubbing the developing ink, the blank area is removed to harden the photosensitive adhesive and rubbed with gum arabic to print on the machine.
The characteristic of the multi-layer metal plate is that the graphic area is based on the copper metal with good oleophilicity; the blank area is established on the hydrophilic chromium. Therefore, the multi-layer metal plate has stable ink and ink balance performance in the graphic area and blank area, and has high resistance to printing force, which can reach 100 to 2 million printed pages, which is more than 10 times that of the flat and concave plate.
5. Pre-coated version (PS version)
From the platen to the plano-gravure, to the multi-layer metal plate, although there has been great progress, but these several plate-making techniques, the coated photoresist contain dichromate, chromium is a harmful heavy metal to the human body, not with the human body Long-term exposure. Secondly, this kind of sensitized adhesive can only be used with the device, and it cannot be stored for a long time. When it is used, it is greatly affected by the environment temperature and humidity, and it cannot achieve industrial mass production.
In the mid-1970s, the Institute of Printing Science and Technology in China first developed a pre-coated sensitized plate (PS plate). This is to apply a synthetic polymer photopolymer to an aluminum plate base surface-treated in advance and dried for packaging. The sensitization performance of the pre-coated version is not affected by long-term storage, so that it is possible to achieve centralized mass production at the plate material factory, ready for use by the printing plant.
Pre-coated version of the plate making process is: the positive film with the pre-coated version of the photosensitive adhesive surface, exposure. Under the effect of light, the photosensitive resin in the blank area of ​​the plate undergoes photodecomposition reaction, and the organic acid that is soluble in hydrophobic water is generated. The graphic and text area is not sensitive to light, and it is still oleophilic and constitutes a graphic basis. Developing, rinsing, drying, wiping arabic gum, printing on the machine after inking.
Pre-coated version of the plate making process is simpler than the gravure, easy to use. Its printing graphic is based on the unsensitized macromolecular finger, which is good in ink affinity, and its resistance to printing force is higher than that of the plano-gravure. If it is necessary to further improve the resistance to printing, it can be baked at a high temperature of 220°C to further cross-link the photosensitive resin molecules in the graphic area to form a network structure and completely lose the photosensitivity to enhance film formation and lipophilicity. The baked preprinted plate can withstand more than 300,000 impressions.
In 1977, the printing factory in Beijing applied the scientific research results of the Institute of Printing Science and Technology of China to start mass production of a single-sheet coated PS version, which was generally better reflected by the printing plant. In the early 1980s, pre-coating was also started in Shanghai, Shaanxi, Sichuan, and Guangdong. In the future, several precoating aluminum coil continuous coating lines, such as the China Institute of Printing Science and Technology and the second film factory of the Ministry of Chemical Industry, were put into production. Since the 1990s, with the large supply of pre-coated plates, the flat intaglio plates that have been used for more than 30 years have finally been replaced by advanced pre-coated plates.
(to be continued)
Overview of Application of Platemaking Technology (2)
February 21 09:10:01, 2024
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