Factors affecting the expansion of outlets and the expansion of outlets

The expansion of outlets is affected by many factors, such as ink, blankets, printing pressure, and paper, etc. The effects of these factors are specifically discussed below.

1. The relationship between ink and dot gain The effect of ink transfer on dot gain is achieved through the ink roller. The ink is transferred from the ink fountain to the uniform ink roller via the transfer roller. Under the shearing action of the uniform ink roller, the thixotropic phenomenon occurs, the structure is destroyed, and the film is extended into a uniform film, which is transferred to the surface of the printing plate through the ink roller. Only the ink system guarantees high-precision ink supply to transfer ink evenly to the plate. The ink is squeezed between the printing plate and the blanket, and then squeezed between the blanket and the paper to form a thin ink layer. If the ink layer is thicker, the dot expansion will occur. At the same time, the hardness of the rubber roller must meet the requirements. The surface of the rubber roller must not have the vitrification phenomenon, and it must have good ink transmission performance so that the printing plate dot has sufficient ink absorption capacity.

2. The relationship between blankets and dot enlargement In offset printing, blankets are used to transfer ink dots, and under the pressure of printing, the ink spreads around the dots. At the same time, due to the elastic deformation of the blanket, relative slippage occurs between the printing plate and the blanket, and between the blanket and the paper. This is an important factor that causes dot expansion in lithography.
In order to keep the dot gain value within the minimum range, the correct printing pressure should be debugged, and a printable rubber blanket should be selected. Blanket is divided into air blanket and ordinary blanket. The air-cushioned blanket has excellent printability on the structure, and has a large printing capacity and a small amount of deformation. When the same amount of compression occurs, the pressure of the air-cushion blanket is lower than that of the ordinary blanket cylinder, and the dot enlargement value is also small. With good printing blankets and correct liners, care must be taken to keep the blanket surface clean.
In the printing process, the surface of the blanket is covered by paper fluff, paper powder, residual particles in the ink, adherence of fountain solution, dusting, and friction during high-speed operation, greatly reducing the spread of the blanket. Ink, which causes blurring of dots and floating in the field, directly affects the quality of printed matter. Therefore, it must be cleaned frequently to keep the surface of the blanket clean.

3. The relationship between printing pressure and dot gain is very important to correctly adjust the working pressure of the printing press. When the pressure is small, each printing surface cannot be fully contacted, and the molecular force between the ink and the paper is very small. Only a small amount of ink is transferred to the paper. , The printed product is pale in color and even the artwork is incomplete. If the pressure is too high, the ink will be squeezed into the blank space outside the picture, causing the dots to expand and level, the image is blurred; the ink transfer will also drop, leaving prints appear unclear, and the spot and dot can not reproduce the original color.
High-quality prints can only be obtained with proper printing pressure. The determination of printing pressure, in addition to the structural performance of the machine itself, is also related to ink, paper, dampening fluid, blanket, ink roller, printing speed and other factors used in the printing process, so in the printing process, it must be based on the actual The printing conditions are adjusted to get the desired printing pressure.

4. The relationship between paper and dot gain The printability of paper depends on the surface characteristics of the paper, such as the amount of ink absorbed and accepted. Absorption rate is fast, and the degree of expansion of the printing outlets is large. The absorption rate of ink for paper plays a key role in the expansion of outlets. The higher the paper smoothness, the smaller the dot gain value. In printing paper, the absorptivity of the coated paper is lower than that of the non-coated paper, and the non-coated paper has high absorbency, with the result that the percentage of dot gain is high. Even with the same coated paper, the smoothness of the paper varies greatly from place to place. The quality problems that can be solved by this difference can only be achieved by adjusting the printing pressure.

5. The relationship between printing speed and dot gain The change in printing speed directly affects product quality. When the printing pressure is set at certain data, the printing speed is slowed down, the contact time of the printing surface becomes longer, the ink transfer rate is high, the dots are full of ink, and the ink of the image is bright. When the printing speed increases, the contact time with respect to the printing surface becomes shorter, the printing surface is not sufficiently contacted, the ink transfer rate becomes low, the ink absorption of the dots is insufficient, and the image is pale. If the printing speed is not stable in a batch of printed products, it will cause inconsistencies in the ink before and after.

Source: PACK.CN