Interpretation of Stamp Printing Technology and Anti-counterfeiting Technology (II)

Gravure stamps are printed using a dedicated gravure rotary press. There are four-color, five-color, six-color stamp printing machines, one-color engraving gravure printing, and five-color or four-color gravure printing. These special stamp presses are equipped with counting numbers, perforations, and cutting devices. Stamps can be counted, punched, and full-size stamps cut to size. The ink used for gravure printing is a solvent-based liquid ink. When the printing plate is immersed in the ink fountain, the ink on the non-graphic part of the plate is scraped off by the squeegee, and the graphic part is the concave part of the printing plate. The ink is just stored. After being imprinted on the impression cylinder, this part of the ink is transferred to the paper. After multi-color overprinting, an exquisite stamp is transferred onto the paper. The printing ink used for the engraved stamps is a viscous resin ink. Its ink transfer form is similar to that of the emboss, but since the graphic part of the engraving intaglio is concave, the non-graphic part (flat) ink on the plate is printed. It depends on a special wiping device to wipe off. At present, there are roughly four types of ink wipes for engraving and printing: cloth wiper, trichloroethylene wiper, water wiper, and paper eraser. Rubbing the ink with a cloth, the three-dimensional impression and gloss of the printed ink layer are better, but the printing speed is slower; Trichloroethylene wiper printing speed is faster, but toxic, harmful to the human body; water wipe ink is a More advanced methods of wiping ink, but there are also problems of waste water treatment and pollution; paper wiping ink is suitable for small paper printing, and is not suitable for such large-volume stamp printing in China. China's engraving stamp printers are equipped with cloth rubbing devices.

In addition to the single photo ticket or the single carved ticket mentioned above, the intaglio stamp also includes a postage stamp that has been overprinted and embossed, known as the shadow carving stamp. It is a favorite of philatelists. The printing of shadow carving stamps overprints the combination of two different printing methods: gravure and engraving gravure. Although engraving and gravure is an ideal process for printing valuable securities, it is difficult to express rich colors and delicate levels. Photogravure also has its disadvantages. Because some stamps have a darker color and require more ink for printing, gravure ink is a fluid with very low viscosity. Therefore, irregular watermarks often appear in deep-adjusted areas and the stamps are damaged. In addition, since the gravure printing patterns are all composed of dots of different depths and different sizes, zigzag slivers will appear at the edges of the thin lines or characters, which will affect the smoothness of printing. In order to make stamps more perfect, the method of engraved intaglio and photogravure mixed overprinting is usually used to exert the respective advantages of the two printing methods so as to obtain more ideal printing effects, such as the famous “Landscape of Huangshan Mountain” and “Landscape of Mount Lushan”. The "Zodiac" stamps and "China Ancient Pagoda", "Lushan" and "Rare Bird" stamps issued in recent years have all been printed in this way.

Combining two different printing methods with different properties, the process is particularly difficult to overprint accuracy, their respective needs of the printing pressure is completely different, the ink properties are not the same, and there are different requirements for the printability of the paper Therefore, the mechanical error in printing is large, and the rejection rate is also higher than other printing methods. When designing the printing process of such stamps, it is necessary to fully understand and utilize the characteristics of these two printing methods, and to avoid weaknesses in order to obtain better printing results. This type of overprinted version of the stamp is generally based on the engraving version, to make the screen pattern of the sketch effect, and then lined with the color of the gravure smudge. Therefore, the main lines and ideas of the engravings should be emphasized and real, and the contours and outlines of the motifs should be made. The inset color of the photogravure can be shallow and imaginary, supplemented by the detailed changes of colors and levels, so that even mechanical errors exist. It will not affect the clear and complete contours of the theme scenes. The printed stamp lines are solemn and straight, with prominent theme scenes, strong three-dimensional sense, and magnificent colors, with very unique artistic effects, especially worth collecting by stamp collectors. At present, international stamps are mostly printed on engraving and offset printing. Modern offset printing technology greatly enhances the ability to express color and levels. Offset printing has clear and smooth text and lines, a uniform and thick background, elegant and harmonious pattern colors, and overprinting of engraving lines and ideas. The artistic effects of stamps are reflected. More perfect.

3. Application of spot color in printing

Stamps are very small printed materials, but the printing volume is very large. Not only do we need to arrange dozens or even hundreds of patterns on a printing plate, but it requires that the color and level of each pattern are completely consistent; and the same pattern of stamps should be printed repeatedly. Tens of millions of pieces, the printing cycle is sometimes several months. In this way, printing the same product for a long time and in large quantities also meets the very high quality requirements of stamp collectors and consumers. Not only must each overprint in the full-page stamp be accurate, but also the color of the face pattern printed in the front and post printing stamps. The level is the same. This requires taking into account its characteristics during the pre-press process design to ensure that the print repeatability is better. For this reason, in addition to the use of conventional yellow, magenta, cyan, and black four-color inks, the application of spot color inks is also indispensable. According to the characteristics of the manuscript, different spot color inks are used for printing. The printed stamps can achieve satisfactory artistic effects and higher passing rates. Therefore, spot colors are often used in stamp printing. It is mainly used in the following aspects.

(1) Background color. In the printing of the stamps, the background has two different manifestations. One is the background often appearing on the stamps as the background of the theme pattern. Although it is not the subject of the screen, it plays a very important role in the whole picture. The important contrasting effect directly affects the artistic effect of the stamps. In order to make the stamp color of the finished product after printing in large quantities basically the same, there is no obvious color cast phenomenon, can perfectly reproduce the designer's artistic conception, this kind of background color generally adopts trapping printing. When encountering a background with a dark background or a large stamp area (such as a small sheet), it is also necessary to design two color shades, dark and light, that are similar to the color to be printed. Consistent with the original color, the ink layer is thick, flat, does not spend, does not leak white point, can truly reproduce the artistic effect of the original. There is also a background color in the pre-press design, in order to facilitate the printing control of hue and to make up for the color difference between the printed matter and the draft, the stamp color part of the artificially added background, it is also the use of spot color printing. This is because the manuscripts of the stamp designs are often selected from Chinese paintings, gouache paintings, and oil paintings. The recent works of art are very beautifully designed, with rich colors and vivid changes in levels. If you choose to use this kind of transcript to copy the stamp, if you simply use the three primary colors plus black overlay to reproduce the picture, the color of the stamp picture will appear monotonous and much thinner than the original, often giving people a feeling of lack of color, which is inferior to the color of the manuscript. Rich and thick, the changes between colors are also more rigid and uncoordinated. The scenes on the screen are also plain and rough, and the artistic effects of copying are not ideal. On the other hand, from a printing point of view, if the postage stamps completely rely on the superposition of the three primary colors to produce a change in color, it is difficult to make the face-to-face hues of large-volume prints consistent. In this case, in order to be able to perfectly reproduce the artistic charm of the manuscript and obtain a high-quality stamp product, the process design is based on the main colors of the original picture, and one or two spot colors are used as the background color of the pattern portion. Pavement, which is the complement of color, such as: dark, light gray, dark, light yellow, purple, etc., plus the three primary colors. In such large-volume printing, the main color of the ticket surface is fixed and fixed, and the ink color can be relatively uniform, ensuring the printing quality. At the same time, the artistic effect of the stamps has been greatly improved, making the tone basically the same as the original. It also reproduces the blooming effect of the original color. The color is rich and soft. The color changes naturally and harmoniously. The whole picture is smooth and delicate.

(2) The color of the character. The skin color of the character, especially the color of the face, is an important part of the character pattern, and is also the main rendering part of the art design. This is also crucial in the printing of other books and advertisements. And it is even more prominent in the imprint of the stamp. As the area of ​​the stamp is small, the area of ​​the face complexion is even smaller. If three primary colors are used for overlay printing, it will bring certain difficulties for overprinting and ink control. After mass printing, the face color of finished stamps often appears color cast, some reddish, some yellowish, and inaccurate overprinting, facial contours will also be deformed. In particular, stamps on the subject matter of characters, if the subject person's facial skin color is inconsistent, or the outline is unclear, it will affect the image of the character, directly affect the artistic effect of the stamp, of course, has greatly affected the quality of the stamp. Therefore, in the process of design, according to the skin color hue of the manuscript, a spot color is generally used as the main color of the skin color, and then the three primary colors are added to set the level, so that the color of the printed skin color of the stamp part does not change much, overprinting is accurate, and the facial contours are clear. The transition of levels is natural and soft.

(3) Neutral gray. Neutral gray is a sign of testing the balance of three primary colors ink in printing, so the reproduction of neutral gray has certain technical difficulty in printing, especially light gray neutral gray, its color change is visually more sensitive, the ratio of three primary colors Slight deviations, the hue will be very different. In high-volume batch printing of stamps, if three primary colors are used to reproduce neutral grey, the technical difficulty and labor intensity will be high, and the final product pass rate will be low; the neutral gray color will be on the face of the ticket. Color cast. If the standard of finished product quality inspection is not properly grasped, it will cause confusion to the philatelic market. In order to avoid the above phenomenon, in the process design, the neutral gray part of the ticket is generally printed with a spot color gray. Such stamp products printed in batches before and after batch printing will not have any difference in the hue, which can greatly improve the qualification rate of finished products, at the same time shorten the production cycle and save raw materials.