Newspaper Printing Ink Failure Analysis - Pulling Paper and Sticking Dirty

Pulling paper

During the printing process, the graphic part of the newspaper, especially the high density dark tone area, often appears that some of the paper fibers are pulled up.

Paper-drawing phenomenon and printing paper when the powder off, hair loss phenomenon in the formation of the reasons for the mechanism and solution are fundamentally different. The paper's powder and hair loss are the fibers or filler particles that fall off from the surface of the paper during printing. They are piled up on the blanket's graphic and cause the printed image and headline to appear "snowflake" under the magnifying glass. "Snow" is flat and there is no obvious phenomenon that the fiber is pulled up. The result of pulling the paper is that the fibers on the surface of the paper are pulled up. Its formation is mainly related to the viscosity of the ink and the tightness of the paper.

1. The viscosity of the ink

The viscosity of ink refers to the force that prevents the thin layer of ink from separating when the ink film is separated. The viscosity of the ink is very important to ensure the smoothness of the printing process and the stability of the printing quality. The ink is transferred from the ink roller to the other ink roller on the printing machine, from the ink roller to the printing plate, from the printing plate to the blanket, from the blanket to the paper, and the ink layer needs to peel once during each transfer to strip the ink. The force required for the layer is related to the viscosity of the ink. The greater the viscosity of the ink, the greater the force required to peel the ink layer. Due to the inhomogeneity of the ink transfer, if the ink is too viscous, the surface of the paper is easily peeled off by the ink film at the time of printing, that is, the paper is pulled. Ink mills are generally adjusted by the addition of a diluting solvent or mineral oil; printing plants can be adjusted by adding a suitable amount of viscosifier or No. 6 varnish. In addition, gelation of the ink occurs during the printing process will appear to pull the hair, the ink must be re-dispersed processing can be resolved.

2. The tightness of the paper

Pulling paper is also related to the tightness of the paper itself. In the production of paper, the tightness of the paper and ink absorption are a contradiction. If the tightness of the paper is too large, the ink absorbency will be reduced; if the paper has a loose texture, paper pull-out may occur easily.

In addition, in the printing process, if the temperature of the shop is too low, the viscosity of the ink becomes large, which may cause the paper pulling phenomenon to increase at the time of printing.

Sticky

In the printing process, due to the slow drying of the ink, the ink is too soft, too thin, or the amount of ink to be given is too large, which can cause dirty or dirty images on newspapers. Most of this phenomenon occurs in the field or shaded part where the amount of printed ink is large.

1. Cause

1) The image has a large amount of ink in the field and shadow

Newspaper printing is not like commercial rotary printing. Although the printing speed is very fast, it does not have a drying device. The ink on the solid and dark portions of the freshly printed newspaper is impermeable, passing through the folds of the folds and the clamping of the conveyor belt. Easy to contact with blank parts, resulting in sticky.

2) Large ink droplets cause ink emulsification

During the printing process, large ink droplets cause severe ink emulsification, which slows the drying of the ink and causes the newspaper to become dirty.
3) Slow fixation of the ink If the fixing speed of the ink is slow, the penetrative dryness and coagulability of the ink are poor, and the newspaper can easily become dirty.
4) Surface properties of the paper The surface of the paper is smooth, dense, and poor in ink absorption. After printing, the ink floats on the paper, which cannot be penetrated and dried in a short time, and can also cause stickiness.

2. Solution

In the printing process, if the above problems occur, it is generally necessary to solve from the following aspects.
1) Viscous dirt caused by the machine structure can usually be solved by reducing the force of the carious teeth in the transmission system.
2) Adjust the machine's water transfer mechanism and ink transfer mechanism to ensure that the printing water has good quality, smooth water transfer, uniform ink supply, and moderate ink volume. In the printing process to control the ink balance, reduce the possibility of ink emulsification.
3) Adjust the internal structure of the ink, improve the cohesion of the ink, control the viscosity, use the ink with fast fixing speed and small residual viscosity, and at the same time improve the ink's penetration, drying and fixing properties.

(to be continued)