Control of dot size during printing

The change in dot size during the printing process is the most important factor affecting the printing quality. Bright tuning refers to bright tonality on the screen. It is generally expressed as a dot area. Brightness out of small dots means that the image transitions from a meshed dot to a dot and can be printed. If the hue begins to change, if it is printed out, If you do not print it out, the image will be bright and hard; if you should not print it out, the image will be light and gray. Both affect the three-dimensional, spatial and texture of the image. Therefore, you must strictly control the minimum dot of the printing. However, due to the independent coloring of dots, the dot area difference of 1% in normal time will affect the color tone, so it is more difficult to control.

Dot gains are divided into increasing dot geometry and dot optics. The increase in the geometry of the dots refers to the fact that the actual inked area of ​​the dot in the unit area of ​​the substrate is larger than the corresponding dot area of ​​the film, which is due to the force, and the dot size expands. The optical enlargement of the dot means that the visual perception of the dot on the dot is a larger point than the actual geometric area due to the light penetration phenomenon of the sheet. This extra volume is called optical enlargement.

The main factors affecting the increase of the dot geometry are the following:

1 ink layer thickness. The geometric increase is caused by the expansion of the ink around the dots under pressure during the normal printing process. The thicker the ink layer, the more serious the dot gain.

2 ink properties. The greater the fluidity of the ink, the greater the possibility of dot gain.

3 embossing surface sliding amount. The lithographic embossing surface has an unavoidable slide, and the slippage causes the dot deformation to increase. When a common blanket or a soft lining is used, the embossing surface has a large amount of sliding, and the dot gain is increased. When the lining plate cylinder is rewound When the ratio of the radius of the squeegee and the squeegee does not correspond to the rolling ratio, the larger the deviation from the synchronizing rolling, the larger the squeezing amount of the embossing surface is, and the more dots are increased.

4 printing pressure. The greater the pressure, the more ink spreads and the more serious the dot growth.

5 plate wear. The brightening part of the printing plate graphics and texts, the area coverage of the dots is small, and the hydrophilic area is larger than the lipophilic area, which is beneficial to the expansion of the wetting fluid. Once the high-profile part of the dot foundation is worn out, it is instantly encroached by the wetting fluid and becomes the basis of hydrophobes and oleophobicity, making the high-profile spots even smaller or incomplete. The dark tone of the printing plate graphic, the coverage area of ​​the dot area is large, and the lipophilic area is larger than the hydrophilic area, which is beneficial to the expansion of the ink. After the blank part around the dot is worn out, it is easily spread by the ink and makes the dot enlarged. , Or even produce paste version.
6 Effect of paper types on the increase of dot geometry. Theoretically speaking, under the same printing conditions, the dot gain of different papers is the same, but in the actual production, if non-coating is used, due to the poor smoothness of the non-coated paper and the good ink absorption, the ink supply must be increased. , increase the ink layer thickness on the paper, in order to achieve sufficient saturation; must increase the printing pressure in order to make full contact with the ink, there is enough ink to transfer to the paper; must reduce the viscosity of the ink in order to use the fluidity of the ink , get uniform ink effect. The ink with low viscosity and high ink volume is transferred to the PS plate, and is transferred to the blanket under relatively greater printing pressure. When the final ink reaches the paper, it will cause larger dot area.

7 Miscellaneous distortion caused by various printing defects increases.

In actual production, as long as we prepare to do a good job, understand and master the characteristics and printing requirements of the prints before printing, and do more detailed operations, it will reduce the amount of deformation of the dots. In the offset printing process, ink transfer is accomplished in three steps. The first step is the wetting and inking of the printing plate. The second step is to transfer the ink of the printing plate to the blanket. The third step is to transfer the ink from the eraser. When the cloth is transferred to the paper, the size and shape of the screen are prone to change in these several steps. Therefore, when printing a dot print, according to the printing requirements of the print, the elasticity of the rubber blanket of the machine must be checked first. Whether it is appropriate, whether the surface of the blanket is clean and smooth, whether the pressure of each impression cylinder is moderate, and whether the dot on the printing plate is real with the magnifying glass, whether there is deformation, etc., adjust the printing ink, and control the amount of ink in the printing, so that It will greatly reduce the amount of deformation of the dots, so that the correct reduction of the tone can be guaranteed and the color reproduction of the printed product can be guaranteed.