Offset ink balance discussion - ink transfer (2)

Two inks attached

1. The adhesion of ink on paper

The main ingredients of paper are cellulose, rubber, fillers, etc. Cellulose is a long-chain cyclic structure polymer with many hydroxyl groups. The fluid part of the ink is the binder, and the ink is dried and attached to the surface of the paper by the binder. Commonly used binders are dry vegetable oils and various natural or synthetic resins.
The main components of paper and ink are all asymmetric molecules. When their molecules are close to each other, the inherent dipoles repel each other due to homosexuality, and the opposite phase attracts molecules to align the molecules in space in a state of heteropolarity. As a result, the orientation is first generated. Force, then induce force and dispersion force. The secondary binding force between the molecules allows the ink to adhere to the paper, and the greater the secondary binding force, the better the adhesion effect.

On the other hand, the paper is made of fibers intertwined with uneven surface and porosity, and the ink has good flow properties. Therefore, when the ink is transferred to the paper, there is a clear mechanical anchoring effect, which promotes ink on the paper. Attached.

The adhesion of the ink on the paper depends not only on the secondary binding force between the molecules but also on the mechanical anchoring effect of the ink on the paper. For paper with a higher degree of smoothness, the adhesion of the ink depends mainly on the secondary binding force between the molecules; on a rougher paper, the adhesion of the ink is more dependent on the mechanical anchoring effect.

In addition, fillers (calcium oxide, titanium oxide, etc.) and coatings (white clay, calcium carbonate, etc.) contained in paper are mostly inorganic compounds. These inorganic compounds greatly increase the specific surface energy of the paper so that the paper is a high-energy surface. When the low surface tension ink covers the surface of the paper, the surface free energy of the paper is reduced to form a stable system, so the ink can be firmly attached to the surface of the paper.

2. Ink adhesion on metal foil and polymer film

The metal mooring is a printing material with a high degree of smoothness. The adhesion of the ink can only rely on the secondary binding force between the molecules and the interface electrostatic attraction, and there is no mechanical anchoring effect. However, the metal surface is a high-energy surface, and the surface energy is much higher than the surface tension of the ink. When the ink is attached, the surface free energy of the metal can be greatly reduced, so that there is a larger adhesion work and the adhesion effect of the ink is better.

Like metal moorings, polymer film materials with a very high degree of surface smoothness can only adhere to the intermolecular binding forces of the ink. However, the surface of the polymer is a low-energy surface, and the ink can adhere well to a large extent depending on the energy of the polymer surface. In order to improve the adhesion of the ink on the polymer surface, the surface of the polymer must be treated to increase the surface free energy, increase the surface roughness, and improve its wettability with the ink.

In order to make the ink adhere to the surface of metal foil and polymer, UV offset printing developed now has achieved good results.

Three inking device adjustment

The adjustment in the ink transfer process includes adjustment of the ink discharge amount of the ink fountain, adjustment of the contact force of the ink transfer roller, and adjustment of the contact pressure of the ink application roller.

1. Adjustment of the ink fountain ink output The adjustment of the ink fountain ink outlet volume includes two aspects. One is to change the gap adjustment between the ink fountain roller and the ink fountain blade; the other is to change the rotation angle of the ink fountain roller.

The ink fountain roller and ink fountain blade clearance adjustment, there are manual adjustment, electric adjustment two kinds, manual adjustment is to use the screw forward, reverse to change the gap between the ink fountain roller and the blade. The electric adjustment is carried out by a remote control device. The general ink fountain seat is equipped with a piano key iron plate on the surface, and the surface is covered with a hard plastic sheet (some machines do not contain plastic sheets), and the plastic sheet has elasticity to prevent ink In the leakage, the front end of each iron plate is equipped with an eccentric roller, and the supporting ring on both sides of the roller presses the plastic sheet against the ink fountain roller. A total of 30 to 32 eccentric rollers are installed on the ink fountain seat, and the width of each eccentric roller is About 30 ~ 32mm, when the servo motor receives the signal from the console, through the mechanical structure, change the gap between the eccentric roller and the ink roller, so when the ink fountain roller rotates, it drives the ink to squeeze the plastic sheet, forming different ink layers according to the gap size. Thickness, adhered to the ink fountain roller, through the ink transfer roller into the ink distribution mechanism, this structure is characterized by the ability to correctly limit the position of each ink supply area, to prevent the adjustment of an ink area affect the amount of ink supply in the adjacent ink area The plastic sheet is constantly rubbed, easily worn and needs to be replaced regularly.

2. Contact force of the transfer roller The contact force of the transfer roller of the domestic offset press is generally adjusted by the tension spring and cam steering. Changing the size of the spring force is a simple operation, and adjusting the contact pressure according to the steering of the cam conforms to a general regulation rule.

3. Contact pressure adjustment of ink roller

The contact pressure of the ink roller is divided into two parts: one is the pressure adjustment of the ink roller and the ink roller; the other is the pressure adjustment of the ink roller and the plate cylinder. Generally, the pressure adjustment of the ink roller and the ink roller depends on the eccentric mechanism. The ink roller and plate cylinder pressure adjustment is based on the slope principle. Adjusting the contact pressure of the ink roller is usually based on the indentation value of the ink roller on the printing plate or the ink roller. Sometimes, steel is usually used to adjust the accuracy. The film is inserted between the ink roller and the printing plate or the ink roller, and the pressure is judged by the hand feeling. Most imported machines use paper strips to test the size of the contact pressure. The method is the same as that for adjusting the water roller. Then adjust according to the "+/-" mark of the adjustment pressure handle. Turn the handle in the "+" direction to increase the pressure between the ink rollers. Turn the handle in the "-" direction to reduce the pressure. The pressure adjustment of the ink roller is very important, so you must pay attention to the following points:

(1) In the adjusting step, generally, the pressure between the ink form roller and the ink squeezing roller is first adjusted, and the pressure between the ink form roller and the plate cylinder is adjusted later.

(2) When adjusting the ink roller pressure, it can be calibrated on the printing plate that is no longer in use. If it needs to be adjusted during the printing process, it should be measured at both ends of the printing plate or blank part of the trailing edge.
(3) The pad thickness of the printing plate should meet the requirements, so as to avoid the change of the contact pressure between the ink (water) roller and the printing plate due to improper thickness of the pad.

(4) Strict attention must be paid to the symmetry and the consistency of pressure in each adjustment direction to ensure that the tandem roller, the axis between the ink roller and the plate cylinder are parallel, and the pressure is uniform.

(5) The width of the indentation on the printing plate of the J2205 machine with four ink rollers is 6, 5, 4, 3mm or 5, 5, 4 and 4mm in order (this value is for reference only). The indentation on the plate and the indentation on the printing roller of the CD-102 machine with four ink rollers are both 4mm.

4. Adjustment of ink roller lifting mechanism

Inking roller according to process requirements, there are three situations: First, follow the roller away from the pressure, the ink roller automatically with the plate off or contact; the second is when the roller pressure, manually make the ink roller and the plate off; The ink roller is manually brought into contact with the plate after the roller is pressured.

The ink roller automatic lifting mechanism is controlled by a mechanical mechanism and a pneumatic mechanism. No matter which type of mechanism controls, the magnitude of the landing range is basically adjusted by the top screw on the landing gear, and also adjusted by the eccentric mechanism. of.

The contact pressure adjustment of each water roller in the water transfer process is similar to the adjustment method of each ink roller.

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The arrangement of all the ink rollers in the inking device follows the law of alternating soft and hard. This facilitates the transfer of ink (see Figure 6-1). In addition, the basic structure of web offset press is the same as that of sheetfed offset press. In recent years, due to the development of printing technology, the water and ink mechanisms of offset press have been greatly improved, especially the water and ink balance tracking technology. The application has played a significant role in improving the printing quality and production efficiency.