Characteristics and uses of various plate making techniques in stamp printing
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At present, the printing of stamps is mainly based on gravure printing (partially printed with letterpress and offset printing). This is mainly to ensure its seriousness and accessibility. China's stamps generally use gravure printing. Gravure printing is a printing method that transfers a graphic below the layout onto a substrate. The printed lines printed by the gravure printing method have clear dots, clear layers, thick ink layers, good hand feeling and strong anti-counterfeiting. Therefore, they are mostly used for printing many banknotes, stamps, etc., and their quality is recognized.
There are many kinds of gravure production techniques. In addition to the hand-carving process, there are various engraving methods such as machine engraving, electronic engraving, and laser engraving. These engraving methods each have their own characteristics and uses.
(1) Photopolymerization intaglio. The plate material is composed of a base layer, a photosensitive layer and a protective layer. The first is to place the prepared color separation film on the plate for exposure, which is called color separation exposure. The image is transferred to the plate, and the polymerization reaction in the exposed area becomes an insoluble region. Then, the film was subjected to depth exposure without adding film to control the depth, and then rinsed with water, and the portion where no polymerization occurred was washed away by water. After rinsing, an intermediate exposure is performed to increase the hardness and printing durability of the plate. Finally, no film is added and exposed again to increase stability. This type of printing plate is used on a gravure press consisting of a plate cylinder, a doctor blade assembly and an impression cylinder. It is suitable for printing the base color of gold, silver, Xubu pearl powder or aluminum foil and plastic film.
(2) Hand-engraved gravure. First, the pattern to be printed is drawn into a sketch, and a point, a pattern or a character with a rich layer is engraved on the steel plate according to the sketch. The hand-engraved steel plate is called a small original. The small original is subjected to heat treatment to increase the hardness. The plate on the small original plate is pressed on the steel shaft surface by the plate machine, and the steel shaft is heat treated to increase the hardness, and the pattern on the shaft surface is pressed by the plate press. Turning the picture on the steel plate again, this process is called "over the plate." Thereafter, the image on the steel plate was pressed on a 1 mm thick plastic plate with a hot press. The plastic plate of the single picture is manually modified to make a large version of the plastic plated copper plate, with a copper plated nickel relief, and the nickel relief is turned into a nickel gravure or iron intaglio printed on the machine for use on the machine. . Hand-engraved gravure is mainly used for printing of securities (such as banknotes, stamps, etc.). However, the engraving gravure manufacturing process in stamp printing has now adopted an electronic engraving method.
(3) Photoetching intaglio. First, the color original is color-separated to make a monochrome negative image. After the revision, the negative image is placed on the continuous shooting machine to be photographed into a large Changyang color separation film, and the large Zhangyang picture is used to print on the printing plate. The plate is then etched with a ferric chloride solution and finally plated on the plate to increase the print durability.
Gravure stamps have been used in two platemaking processes, the traditional gravure process and the modern gravure process.
(1) Photographic etching gravure stamp making process. In the traditional gravure stamp making, the original is photo-separated, and the continuous negative shading of several colors is decomposed, and then manually corrected. The corrected negative image is retracted to the photo by the connected camera. The stamps are of the same size and size, and are continuously photographed in tens of thousands or hundreds of editions of the full-page stamps, followed by plate making.
When the plate is made, the grid for gravure printing (also called the network cable) is first exposed to carbon paper, and then the pattern of the stamp (positive image) is also dried onto the carbon paper of the existing grid, and then the carbon is applied. The film with the grid pattern on the paper is transferred to the prepared cylinder, and the surface of the cylinder is deeply corroded with a ferric chloride solution. In order to improve the printing durability of the printing cylinder, a layer of chrome is finally plated on the surface of the printing cylinder for printing on the machine. The traditional gravure plate making process is cumbersome, slow, long production cycle, poor product quality stability, and technically difficult to operate, difficult to master, and is currently not used in stamp printing. As the printing industry entered the era of electronic printing, the plate-making process of gravure stamps was also improved from traditional manual plate making to modern electronic plate making. After the transition of electronic subcontracting and copying the opaque film-electronic engraving, it entered the optical film platemaking stage of the electronic color separation high-end networking system and the electronic engraving workstation.
The stamp original is first separated by an electronic color separation machine, and the image information after color separation is transmitted to the computer for correction and editing. Stamp printing is different from ordinary printed matter. In addition to the use of the three primary colors, it often adds various spot colors. Therefore, it is necessary to correct the layout after the color separation. At the same time, because the stamp face is relatively small, the pattern is exquisite, and the required quality is very high, which brings great difficulty to the printing, especially the high-speed printing. For this reason, special techniques for the printing interface of each color version are also required during plate making. Processing to ensure print quality. In addition, text, border layout, placement, and the like need to be done in the computer. When the layout of a stamp is completed, the operator transmits the electronic data to the electronic engraving workstation. The electronic engraving workstation edits and layouts according to the data and the layout specifications of the full-page stamps and the layout requirements of the printed on the machine. It also needs to smooth the edges of the characters and lines and make the final minor corrections to the patterns. After that, the electronic engraving machine can engrave dozens or even hundreds of stamps of the same color and the same level on the electrolytic copper on the surface of the printing roller. The printing roller can be printed on the machine by chrome plating.
The plate making process of modern gravure stamps uses optical film operation, from high-end electronic color separation system to electronic engraving workstation in one go, improving plate making speed, shortening production cycle, high plate overprinting precision, plate making repeatability, quality Stable, conducive to the process of data, standardization and even standardized management.
(2) The plate making process of engraving gravure stamps. There are various methods for engraving gravure, such as mechanical over-plate method, electroplating plate method, and etching method. China uses the mechanical over-printing method. The method first shrinks the pattern of the stamp original to the flat steel plate according to the size of the stamp. The engraver uses the carving knife to manually pattern the pattern on the copper plate into different shapes, widths, and depths. And lines to show the different levels in the picture. This engraved small steel plate is used as the original version of the engraved gravure (called the original steel plate), and it is used to copy the printing plate. The gravure stamp is printed on the rotary machine. Therefore, when making the printing plate, the original steel plate is first heat-treated to strengthen its hardness, and then placed on a special plate-making machine, and the flat steel plate is pressed by mechanical extrusion. The points of different depths and lines are transferred to another small steel shaft to obtain convex lines and dots; the small steel shaft is also heat-treated and placed on the plate machine, and the economic pressure is to apply the above pattern to the specification of the full-page stamp. One piece is transferred to a printing roller whose surface is coated with an electrolytic copper layer to obtain concave graphic points and lines; after chrome plating, the printing roller can be printed on the machine, and the plate making of the engraved gravure stamp is completed. Engraved gravure stamps have their own unique effects. The lines of the pattern are distinct, the ink layer is thick, and it is slightly convex on the paper surface. The fine points and lines are clearly distinguishable. The color has remained unchanged for a long time, which is conducive to the elimination of the forgery of stamps. Although the engraving gravure plate making and printing technology is very difficult, its anti-counterfeiting performance is good, so most of the world's stamps and the like are printed by engraving gravure.