Printing balance of offset fountain solution (below)

The surface failures of the printing plate, which are common due to the unfavorable acidity of the fountain solution and the unbalanced printing plate, are summarized as follows:

It is generally considered that the pH of the PS plate fountain solution is preferably between 4.5 and 5.5.

3) Factors affecting the balance between printing plate and fountain solution

1 Blanket

Commonly used in the production of air-cushion blankets and ordinary blanket two, when pressed into contact with the plate, due to the surface of the blanket has a certain degree of adsorption, the printing plate surface of a portion of the fountain solution transferred to the blanket surface. Loss of some of the fountain solution on the surface requires timely replenishment. The amount of replenishment will cause problems with balance and imbalance.
2 water roller

The water roller is the main component that directly contacts the printing plate and supplies the fountain solution at the same time. The excessive contact pressure with the printing plate will damage the image part, and the fountain solution cannot uniformly coat the printing plate. ". If the contact pressure is too light, the fountain solution on the surface of the printing plate will not be properly coated, resulting in a similar coating condition, and the “plate” phenomenon will appear on the surface of the printing plate.

3 plate area

The amount of fountain solution required on the surface of the printing plate is directly related to the area of ​​the graphic. The area of ​​the map is large, the area of ​​relative blank is small; the area of ​​the picture is small, and the area of ​​relative blank is large. Under normal circumstances, the printing plate with a large area requires less amount of fountain solution, whereas the amount of fountain solution is more.

4 ink thickness

The ink layer thickness of the print has a certain relationship with the size of the fountain solution on the surface of the printing plate. There are two ways to increase the thickness of the printing ink layer. First, the volume of the fountain solution is constant and the amount of ink is increased. First, the amount of ink is constant and the amount of fountain solution is reduced. The reason for these two approaches is the same. They both increase the ink content under "oil-in-water" conditions and reduce the content of fine water droplets in the ink on the plate surface, thereby achieving the purpose of increasing the ink layer thickness.

4 Balance between fountain solution and paper

In the lithographic printing process, after the fountain solution is transferred by printing plates and blankets, a certain amount of fountain solution must be transferred to the paper. After absorbing the dampening solution, the paper will have a telescopic deformation, which will affect the quality of overprinting. Therefore, when we understand their balance problems, we should first clarify the following relationships:

1) Relationship between paper deformation and water content

Paper is a thin layer of material that is intertwined with natural plant fibers. Plant fibers include components such as cellulose, hemicellulose, and lignin. Due to the special structure of the paper, the paper not only absorbs water when in contact with the paper, but also has the ability to absorb moisture from the moist air and to dehumidify the dry air.
After a dry fiber is completely wet, the increase in diameter is about 30%, and the increase in length is about 1% to 2%. Since there is such a difference in the increase in diameter and length after the paper fibers absorb water, the deformation must be different in length and width depending on the direction of the paper fibers. In the printing process, the image size of the plate or blanket along the axial surface of the drum is difficult to adjust, but the size of the image along the circumferential direction of the drum, ie the printing direction, can be adjusted by adding a pad of paper under the plate or blanket. Therefore, the wide side of the paper and the printing direction are often taken as parallel in the printing, that is, the printing is performed using a longitudinal wire and a paper without affecting the printing performance of the paper.

2) The relationship between the acidity of fountain solution and paper

Paper is generally weakly acidic, and a few coated papers (such as coated paper) are weakly alkaline. The relationship between the fountain solution and the paper is mainly the effect of the acidity of the fountain solution on the paper. When the dampening solution is too acidic, some components of the paper surface coating and filler will seep out of the fountain solution, and some will accumulate on the surface of the blanket. This phenomenon will not only cause dirty printing and dirty blankets. The paper structure and printing ink absorption, ink drying will have a negative impact. The disadvantages caused by the strong acidity of the dampening solution are similar to those of the acid paper and the alkaline paper. When the fountain solution is too weak, the effect on the paper is much smaller.

3) The relationship between the amount of fountain solution and the paper

The amount of fountain solution directly changes the amount of water in the paper, which in turn affects the degree of paper stretching and the accuracy of product overprinting.

If the amount of fountain solution is too large, it is easy to change the ink absorption performance of the paper surface, the paper surface coating and adhesive will also be affected, resulting in paper lint, powder off phenomenon, delay the ink drying time. In addition, excessive water content of the paper will cause the paper to stretch and affect the quality of overprinting.

If the amount of fountain solution is too small, there will be no obvious impact on the paper, but the paper will appear dirty, and the tone level is fuzzy and other ills.

Water resistance is an important technical indicator in the performance of offset printing paper. The water absorption performance is also different for different types of paper. Compared with the smoothness of the paper surface, a smoother surface has a smaller water absorbency, and a smoother surface has a higher water absorbency. The surface of the coated paper is smoother than that of the offset paper, and the water absorbency is smaller than that of the offset paper; and the degree of sizing is compared with that of the surface of the paper. When the gel size is large, the absorbency is small, and when the size is small, the absorbency is large. The sizing degree of the offset paper is larger than that of the sticker and the writing paper, and the water absorbency is smaller than the size of the sticker and the writing paper; and the structure is compact when compared to the paper structure. The paper has low water absorbency, loose structure of the paper and high water absorption.

In the offset printing process, the most obvious problem is the relationship between the fountain solution and the ink and the printing plate. The amount of the fountain solution is determined by the amount of ink and printing plate, not the water content of the paper. . In order to achieve as much as possible the paper content does not exceed the allowable amount, in order to meet the requirements of the ink and printing plate, while trying to balance the fountain solution and the paper. (Finish)