Gravure printing ink transfer (1)

The shades of the original are reproduced on the gravure printed matter by the thickness of the ink layer. This is the most striking feature of gravure printing that differs from lithographic, letterpress, and stencil printing. Gravure prints are thick, rich in ink and rich in three-dimensional, and are recognized as high-quality prints.

Gravure printing uses hand-engraved intaglio printing plates, electronic engraving gravure plates, and photo-engraving plates (photogravure), which are resistant to printing forces. The lines are delicate and varied in design, and they have high anti-counterfeiting capabilities. Gravure printing has become the main method of printing banknotes, stamps and other securities.

Gravure printing, engraving and printing directly on the plate cylinder, can be seamlessly printed, especially suitable for the printing of building materials and wallpapers.

The gravure printing machine adopts the short ink path ink supply system for ink supply and web printing. The machine structure is simple, and the degree of automation is high. The solvent volatile ink is used, and the ink layer can be quickly dried. Therefore, the general gravure printing machine has a high printing speed, most of which is more than 150m/min. Many of the intaglio printing machines are also equipped with a rolling die-cutting device at the rear end, which can be used for die cutting and creasing, and is conducive to packaging full of prints. The printing.

Compared with gravure printing, flexo printing, flexo printing, and screen printing, the disadvantages include long plate making cycle, high plate making cost, and serious environmental pollution in plate making and printing. With the continuous improvement of gravure printing technology, the above problems will be gradually solved. In a nutshell, gravure printing is a vivid printing method.

One, gravure printing properties can

The gravure is a printing plate whose part is lower than the blank part. When printing, the ink is first filled into the net of the printing plate, and the ink in the net cavity is transferred to the surface of the printing object under the effect of pressure.

Commonly used gravure can be divided into two categories, one is a shadow edition, also called gravure; the other is a gravure gravure, in which manual or mechanical gravure gravure is used to form a print pattern with lines, this gravure is mainly used for printing Money notes (not described in this chapter). A gravure carved with an electronic engraving machine is called an electronic engraving gravure. Regardless of the type of printing plate, the surface structure of the layout, the depth and shape of the cells, are critical to the quality of gravure printing.

1. Shadow Edition. The photocopying edition was named because of the use of negatives that were photographed by the camera. This type of printing plate must first be exposed on the sensitized carbon paper and then continuously adjusted. The film on the carbon paper was then transferred to the surface of a copper plated roller and made by development and etching.

The purpose of the batting cable is to form a “mesh wall” that supports the squeegee on the surface of the printing plate, so as to prevent some of the ink in the stencil from being scraped by the squeegee, and insufficient ink can be obtained on the printed sheet. A gravure screen must be used when drying the cable. The gravure screen is composed of transparent white lines and opaque black ground. The grid shapes are square grid, brick grid, diamond grid, and irregular shape, as shown in Figure 6-1. Usually used more is a grid-like screen, the ratio of the width of the white line and black block is generally 1:3 to 1:2.5 (ie, the ratio of the width of the wall to the width of the hole). When the ratio is small, the net wall is narrow, the net point is large, and the image reproducibility is good. However, the net wall is easily damaged by the squeegee and the print throughput is reduced. On the contrary, if the ratio is large, the net wall is wide, the net hole is small, the net wall is hard-wearing, and the print yield is large. However, the reproducibility of the tone adjustment of the midtone tone and the intermediate tone image is poor.

The depth of photo etching in the shadowing version is related to the density of printing patterns. The density of positive images used in gravure is mostly in the range of 0.3 to 1.7, and the relationship between the corrosion depth of the mesh and the density of positive images is shown in the figure. 6-2) It can be seen that the depth of the cell depth is generally 2 to 40 μm (some prints may reach 60 μm in depth due to special needs), and the depth of the cell site is too dark.

The etching operation of the photocopying version mainly relies on the skilled skill of the operator to carry out step-by-step etching with different concentrations of FeCl3 (ferric chloride) solution, thereby obtaining basin-like mesh holes of different sizes, see Fig. 6-3 ( a).

2. Electronic engraving gravure. Since the 1990s, due to the development of electronics and computer technology, gravure printing mainly uses electronic engraving gravure. This type of printing plate uses a sophisticated electronic engraving machine with a high degree of automation to sculpt a hole in the surface of a copper plated roller. The shape of the carved hole is limited to a reverse taper by the engraving blade. See Figure 6-3(b). , its size and depth are changing. Darkest network points can reach 55-60μm. The grids on the layout are staggered to form a continuous web wall support squeegee.

In multi-color printing, lithography, letterpress, screen printing, in order to avoid the occurrence of "rhizard", the use of different screen angle yellow, magenta, cyan and black four plates overprint reproduction of the tone and color of the original. If the electronically engraved four-color intaglio plate is used with the same cell angle, the printing plate position may shift slightly, and moiré and color cast may also occur. Therefore, the electronic engraving gravure is printed in color using several kinds of cell angles as shown in Figure 6-4 to eliminate moire.

In order to improve the quality of text and eliminate color cast, the angle of the net engraving intaglio is often combined with the number of screen lines. For example, when copying a color image manuscript with text, the Yellow Edition uses the No. 1 net point angle, the Magenta version uses the No. 2 net point angle, and the Qing and Black versions use the No. 3 and No. 4 net point angles respectively (see Figure 6). -5), each block color version can be combined with the corresponding screen line number in Table 6-1. Since the black version selected a fine screen line number, the zigzag shape of the text edge engraving is less obvious, improving the text quality.

Table 6-1 Combination of the network angle and the number of screen lines
Gravure color mesh angle screen screen lines
Yellow No. 1 (Square) 60 lines/cm

Magenta 2 (elongated) 70 lines/cm

Green 3 (flattened) 70 lines / cm

Black 4 (square) 100 lines/cm