After corona discharge treatment, surface tension test pen or surface tension test can be used to determine the effect of plastic film pretreatment. The ratio of the surface tension test solution is shown in Table 6-3. During the test, the known surface tension measuring solution is applied on the surface of the treated film with a cotton wool ball. The coated surface is approximately 30 mm2. If it shrinks into a water particle shape within 2 s, the film surface tension is lower than that of the test liquid. Surface tension, need to improve the corona strength before processing. If the test solution does not shrink within 2 seconds, the film has reached the treatment effect. Under normal circumstances, the surface tension of the plastic film can reach 3.8×10-2N/m, which can be used for printing. When it reaches 4.0-4.2×10-2N/m, it can meet the compounding requirements.

Table 6-3 Surface Tension Determination Liquid Proportioning Table

Formic acid amine (%) Ethylene glycol ether (%) Surface tension (10-2N/m) Formamine (%) Glycol Ethyl ether (%) Surface tension (10-2N/m)
0 100 3.0 67.5 32.5 4.1
2.5 97.5 3.1 71.5 28.5 4.2
10.5 89.5 3.2 74.5 25.3 4.3
19.0 1.0 3.3 78.0 22.0 4.4
26.5 73.5 3.4 80.3 19.7 4.5
35.0 65.0 3.5 83.0 17.0 4.6
42.5 57.5 3.6 87.0 13.0 4.8
48.5 51.5 37 90.7 9.3 5.0
54.0 40.0 3.8 93.7 6.3 5.2
59.9 41.0 3.9 96.5 3.5 5.4
63.5 36.5 4.0 99.0 1.0 5.6

4. Electrostatic blotting. Ink in the gravure network must be under greater pressure before it can be transferred to printing materials. Therefore, the load of the gravure printing press is greater than the load of the letterpress lithography printing press. In spite of this, when the surface of the paper is rough, the ink in the cells is also difficult to fully contact with the paper, and the ink does not transfer well to the substrate, resulting in a white dot in the printed graphic, which is commonly referred to as "frost." For the engraving intaglio, the ink transfer effect stored at the bottom of the cone tip is even worse. This is particularly noticeable in the highlight portion, so the subtle level of the highlight portion of the intaglio print is generally not reproducible. Although increasing the pressure can improve the transferability of the ink, the increase in the pressure has a certain limit, otherwise it is easy to burst the adhesive layer of the impression cylinder, or to extend the substrate. In order to increase the ink transfer rate of gravure printing, an electrostatic ink-absorbing device is installed on the gravure printing machine, and the ink on the printing plate is sucked onto the printing material by the principle of positive and negative charges attracting each other.

Figure 6-10 is a schematic diagram of an electrostatic ink-absorbing device. The imprinting cylinder of the printing press is conductive. When printing, an electrostatic high-voltage generator is used to generate an electric field between the printing plate or the embossing cylinder, and the ink in the printing plate cell is sucked onto the substrate by electrostatic attraction.

In designing and manufacturing an electrostatic ink-absorbing device, a voltage of 200 to 1000 V is applied to a sufficient amount of paper, and a voltage of 500 to 5000 V is applied to the printed thick paper.

The application of electrostatic ink-absorbing device will increase the ink transfer rate of gravure printing by 15% to 20% compared with that under normal pressure. This not only enables the reproduction of subtle levels of prints, but also reduces the printing pressure and prolongs the printing press. life span. However, in the printing process, it is necessary to keep the environment clean, to prevent the conductive rubber on the surface of the impression roller from adhering to the dust, and to prevent the uneven voltage from occurring at various parts of the impression cylinder, resulting in the problem of reduced ink absorption.

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