Offset cylinder printing pressure and ink transfer

Printing pressure and ink transfer

When the ink touches the paper, under the effect of a certain pressure between the rollers, the molecules of the linking material are forcibly pressed into the fiber gaps on the surface of the paper, and then there is a gap free capillary phenomenon in the paper layer. Therefore, the pressure is an important condition for the drying and permeability drying of the binder on the paper surface.

When the printing pressure exceeds a certain value, due to excessive printing pressure, the amount of ink on the printing plate graphic begins to spread to the blank portion, the ink transfer rate begins to decline, the printed network of the printed matter is enlarged, and the graphic picture is obviously distorted. Therefore, it exceeds the determination. The value of printing pressure is not suitable for printing.

The size of the printing pressure has a great influence on the degree of transfer of ink from the printing plate to the paper. When the printing pressure is insufficient, the ink is not transferred enough and is not suitable for printing; when the printing pressure is excessive, due to the printing plate The spread of ink to blank parts other than those in the graphic and graphic text shows that the ink transfer rate has not been improved, and it has also brought other ills. It is also not suitable for printing. Only in the appropriate range of printing pressure can print thick prints, clear images, and good reproducibility of prints.

1 roller lining impact on the printing pressure

The blanket cylinder of an offset press is named after a metal blanket wrapped with a blanket. A blanket made of paper, wool, etc. is also lined between the blanket and the cylinder, and the blanket and the gasket are together. The lining of the blanket cylinder of the offset printing press is formed. Similarly, the printing plate and the liner on the plate cylinder also constitute the plate cylinder liner, and the impression cylinder liner is the printed paper. Roller lining is the basic source of printing pressure and has a great influence on the printing pressure.

Offset materials used in offset printing include liners, plastic films, worsted fabrics, blankets, and the like.

Combine blankets and various cushioning materials into soft, inner, and hard packs, based on their modulus of elasticity.

Hard lining has large printing pressure, narrow nip, soft lining, low printing pressure, and wide imprinting line. It can be seen that the hard lining has better reproducibility than the soft lining, but the soft lining With good elasticity, the advantages of "ink streak" are not easy to appear in the printing. Therefore, the soft lining is often used in offset printing machines where the printing precision is not high and the printing surface is worn more seriously. The hard lining has a smaller amount of compression deformation, the dots on the printed material are bright and clear, and the image is clear. Therefore, it is particularly suitable for printed materials with a high dot number of lines, but the hard lining is prone to “ink streaks” and must be used in high-precision offset printing. on board.

The printing pressure is also affected by the printing speed. With the increase of the printing speed, the contact time between the printing surfaces will be shortened, the dots will be made empty, and the printing quality will be reduced. In order to ensure the full contact of the printing surface and improve the printing quality, it is required to control the printing speed under a certain printing pressure.

The performance of the neutral lining is between the rigid lining and the soft lining and can be further subdivided into a neutral lining and a neutral lining. Neutral liner lining often has the advantages of both rigid liner and soft liner. Therefore, it has strong adaptability and wide application, and it is the lining form commonly used on offset presses. The use of a neutral lining and dot reproducibility is good, and the accuracy of the offset press is not too demanding.

To sum up, different offset linings are selected for different offset presses. Whether the lining selection is reasonable or not affects not only the printing quality but also the service life of the offset printing press.

[Case 6-5]

A printing factory uses a J2205 printer to print a batch of cartons with a white paper thickness of 300 g/m2. The captain only adjusts the center distance between the rubber and the press rolls. As a result, the machine noise during formal printing is very high.

[case analysis]

From the processing method point of view, this case does not seem to be a big problem, but further analysis, or feel that something is wrong, as we all know, J2205-type machine blanket roller shaft end with a pair of sets of eccentric bearings, in which the outer eccentric bearing control the rubber ~ pressure center distance If the rubber-to-pressure center distance is adjusted to the limit, the unbalance of the variable load of the drum is caused, thereby generating an inertial force, so that the roller gear receives an impact load and noise occurs.

[Expert Tips]

When increasing the center distance, you can consider reducing the thickness of the lining.

The basic principle of rational lining is: in the case of a certain deformation of the printing surface, the minimum pressure should be evenly used on the basis that the printing is sufficiently strong and the dots are well reproduced, so as to increase the printing plate resistance and reduce the load of the roller gear.

The specific steps are:

(1) Accurately measure and correct the center distance of the roller.
(2) Accurately calculate and measure the thickness of cylinder liners.
(3) Select the ideal liner and increase the minimum liner thickness within the limit to achieve optimal contact pressure.
(4) Correctly check the unevenness of the printing plate and the blanket under printing pressure that will come in contact without contact.
(5) Effectively fill unevenness of the blanket.