Overview of Application of Platemaking Technology (3)

Third, the gravure plate making technology changes
The gravure plate is divided into two categories: engraved gravure and photographic gravure (also known as photogravure). In the engraving gravure, the engraving method can be divided into hand-carved, mechanically-carved and electronically-engraved.

1. Hand-engraved gravure
Hand-engraving gravure is not so much a process of making plates in the printing industry as it is the re-creation of art in the process of making plates. Gravure gravure does not need to pass through the net screen, is that the sculptors have a certain artistic accomplishment, and they can use the manual knives of the sword freely. They can skillfully use their cutting knives to use their skillful knives, using dotted lines, depth, thickness, and density. , changes in the song, and reproduce the verve of the manuscript. Because it is entirely a manual art creation, even the engraver himself wrote two steel plates with the same manuscript, and it could not be the same. A hand-carved original can no longer be carved out of it. Because of its characteristics, hand-carving is used for security printing of securities or licenses. It is not visible in general printing factories.

2. Mechanical engraving gravure
On the surface of securities or licenses, in addition to hand-carved images of people's landscapes, there are a large number of decorative patterns such as patterns, patterns, shading, etc. These patterns cannot be hand-carved and must be mechanically engraved. At the beginning of this century, the “Universal Engraving Machine” imported from the United States by the printing bureau of the Qing government's branch committee in 1909 was such a mechanical carving tool. As long as the engraver wants to set the relevant parameters of the original pattern mechanically, the engraving machine uses its complex gear transmission system to drive the cutter and the machine to perform complex curve motions, instantly creating a graphic with complex and beautifully shaped patterns.

The engraving machine can be directly sculpted on the metal plate, or it can be engraved on the metal steel plate coated with wax, and the steel plate engraved with the pattern is used as a master plate, and the plate is pressed into a soft plate after quenching and hardening. After being quenched and pressed, the metal gravure printing plate identical to the mechanical engraving pattern is finally printed on the machine.

Machines for engraving patterns, in addition to universal engraving machine, there are scribe engraving machine, relief engraving machine. In the intaglio printing system, several types of engraving methods are often used together, each of which has its own length. The hand-carved figures and landscapes are decorated with mechanically carved patterns to make the picture beautiful and harmonious, and have more anti-counterfeiting capabilities.

3. Photo etching gravure (copy edition)

Although hand-engraved gravure can also print images such as figures and landscapes, it is represented by a combination of dots and lines. It is particularly useful for the reproduction of color-changing manuscripts in a continuous manner. The photographic gravure gravure has the special feature that it can reflect the change of the continuous darkness of the manuscript by the difference in the depth of the etch pit. Even if the color is continuously adjusted, color reproduction can be performed after the color separation.

Photoetching gravure manufacturing process:

(1) First use the camera color separation method to prepare the manuscript and continuously adjust the color separation positive film.

(2) Dry carbon paper. A layer of gelatin solution containing iron oxide is coated on a dedicated carbon paper base, dried and stored for later use. This is carbon paper. When used, the gelatin paper is immersed in a solution of potassium dichromate, and after the potassium dichromate penetrates into the interior of the gelatin layer, the adhesive layer has sensitometric properties, and it is said that this operation is called sensitization treatment. After the dark room is dry, the first exposure is performed with the gravure screen. The purpose is to print the cross transparent screen of the screen onto the carbon paper to form a photo-hardened cross-hair cable. The opaque square holes on the screen are formed on the carbon paper as untouched dots separated by crosshairs.

Take Yangyang continuous adjustment film and carbon paper close together for a second exposure. Since the cross-hairs have been exposed and hardened on the first exposure, the second exposure is mainly performed on the first unexposed separated dots. Also because of the continuous changes in dark shades on the original, the intensity of light transmission is not equal, so the degree of photo hardening of the gelatin layer on the mesh after the second exposure is also different. On the original part of the bright spot, more light transmission, strong photographic network, the gelatin layer of high degree of hardening; the original dark tone on the site, less light transmission, light-sensitive network, the gelatin layer hardening degree is low. In short, corresponding to the different changes in light and darkness of the original plate, after the second exposure, dots corresponding to different hardening degrees have been generated on the carbon paper gelatin layer.

(3) carbon paper overprint. Photographic gravure gravure plates are mostly copper plated drum type. Clean the surface of the copper cylinder before printing, and then double-expose the carbon paper film on the copper surface and tightly wrap it on the copper cylinder. Wet the paper base from the back side to expand the film. After the pressure was applied, the paper base was carefully peeled off in warm water, and the gelatin film was tightly attached to the surface of the copper cylinder from the paper base. When developed in water, the unsensitized gelatin is removed by dissolving water under the effect of water dissolution. Fully photo-cured cross-over wires and dots are left undissolved by water; some of the photosensitive dots exhibit different levels of hardening depending on the amount of light received, and some of them dissolve in developing water and also retain some.

(4) Corrosion layout. A layer of gelatin having a different degree of hardening was adhered to the surface of the copper drum after development, and the copper drum was corroded with a ferric chloride solution. Since the degree of photohardening of the gelatin layer on the surface of the copper drum is different, the speed and depth of corrosion of the surface of the copper drum by ferric chloride are also different. The gelatin layer corresponding to the screen crosshair on the copper drum has the highest degree of photohardening, so it is not corroded by the ferric chloride to form a net wall; the net point corresponding to the net screen depends on the degree of photohardening of the net dot. High light areas, strong light-relief, high degree of hardening, slow penetration of ferric chloride, shallow corrosion of pits, dark shadows, weak light, low degree of hardening, fast penetration of ferric chloride, corrosion of pits Deep. In the continuous change of the dark-and-dark tone on the positive chart, under the effect of the separation of the net wall, a separate pit with a different depth of corrosion is formed on the surface of the copper drum.

The quality of the corrosion of copper drums depends mainly on the experience and methods of the operators. Secondly, the concentration of the ferric chloride solution, the temperature, the photohardening degree of the gelatin layer, and the humidity also affect the quality. Changes in the depth of corrosion directly determine the depth of tone in the printing ink layer. Because there are many factors affecting the change of the depth of corrosion, the technical difficulty of etching the gravure is also relatively large, which is not conducive to the wide application of gravure technology to a certain extent.

4. Enlightenment from gravure network
Traditionally, the screen printing of plain printing and embossing is based on the change in the coverage of the dot area within the unit area, and the photogravure, although it is also screened, is mainly used to form a dividing wall screen. It does not use the dot area size change to express the tone of the tone, but the depth of the pit, corresponding to the thickness of the ink layer in the pit to show the depth of tone. People once thought that we can make the photogravure pit also have a change of depth, but also changes in the coverage of the area, so that its tone changes more expressive? This idea is a certain truth. In 1977, Beijing Xinhua Printing Co., Ltd., in collaboration with the Beijing Institute of Printing Technology, applied Dultgen's screened etching method to create a network of pits with both depth and size. The prints printed with this intaglio print have both the advantages of expressive and bright highlights and the advantages of the gravure prints in deep-adjusting the color of the area, which enhances the appearance of the full tone of gravure printing in the reproduction of the picture. ability. However, although the printing quality of the Durkheim screening method is better, it is a photographic method. After all, the fate of the photogravure is not replaced by the electronic engraving intaglio.

5. Electronic engraving gravure
At the end of the 1970s, a factory was imported from Federal Republic of Germany on a 12/21 mill (later transferred to Beijing Xinhua Printing Factory). Since then, China's gravure platemaking has created a new era of electronic transformation from traditional gravure to electronic engraving intaglio. One of the successful results of the combination of electronic technology and plate-making technology is the electronic color separation machine, and the other is the electronic engraving machine. The former is used for plain printing and the latter is used for gravure printing. In the 1980s, it was the era of gravure printing in packaging printing. Most of the gravure plates use imported electronic engraving machines.

Taking German Hell electronic engraving machine as an example, the manuscript is a continuous color separation negative film or a net color separation positive film (which needs to be processed by a colloidal concave conversion device) obtained by an electronic color separation mechanism. The original is on the scanning roller. On the scan head, the optical signal is converted into an electrical signal, and after analog-digital conversion, it is stored as a digital signal. After the signal is processed and amplified, the diamond carving head is driven to scan on the surface of the copper plate of the printing plate to sculpt a pit. The diamond carving head is in the shape of a quadrangular pyramid with 120°, 130° and 140° included angles. The pits produced by the electric head not only have changes in depth, but also change in size, so the electronic engraving gravure is superior to the traditional gravure in terms of tone expression. Since a large number of electronic engraving gravure plates have been used, photogravure gravure has gradually withdrawn from the stage of history.

Source: China Print History