Offset plate layout problem

Dirty dirt refers to the lack or incompleteness of the water film on the surface of the blank part of the printing plate, and the improvement of the oleophilic properties caused by other original difficulties. The ink layer on the surface of the ink roller is in direct contact with the printing plate surface, and the ink layer breaks and the dirtiness caused by the ink transfer occurs. Commonly known as "dry version." The outstanding feature of this dirty plate phenomenon is that the upper dirt position is fixed with the basis for adsorbing the ink. This kind of process failure is easier to find on the printed matter. The key is to find out the cause of the failure and quickly find a reasonable solution.

1 plate problem

The printing plate has not been printed yet, and the layout is greasy, mainly due to improper printing. If the greasy heavier is for the PS plate because the underexposure of the blank part is not completely decomposed, or if it is underdeveloped, the photosensitive layer of the blank part is not washed. If the oiliness is only a few parts, it may be due to the following reasons:

(1) The old pictures and traces remain on the original plate;

(2) The tanning factor is generally caused by improper operation during exposure. The large glass or film of the printing machine is stained with dirt, stains, underexposure, and imperfections.

(3) The front surface of the baking plate is not thoroughly cleaned or the coating of the protective agent is not uniform;

(4) Dirty rubber or dirty ink.

To overcome the method: If the plate is greasy, it must be reprinted. If the plate is greasy to produce individual parts, the PS plate must be reduced in fat, and some arabic resin must be added to the fountain solution.

2 The pH of the fountain solution is not properly controlled

The fountain solution has a large pH value, the hydrophilic colloid layer is generated slowly, and the inorganic salt layer of the blank part cannot be supplied and replenished in time, and the blank is divided into hydrophilic oleophobicity; the pH value is too small and there is anodic corrosion on the printing plate I mesh. Therefore, the amount of water on the surface of the blank cannot be sufficient to cause dirty oil.

Ways to overcome: When adjusting the dampening, we must strictly control the PH value, according to the type of printing plate, the thickness of the printing ink layer, the amount of drying economy, the nature of the paper, and the workshop temperature, temperature and other actual conditions to grasp. Generally, the pH of the dampening solution is normally 4.5 to 6 for the PS plate.

3 Ink roller aging

The ink roller is prone to heat aging due to rolling for a long time under the heated state and contact with the fountain solution and ink, the surface is dry and conjunctiva, the hydrophilicity is enhanced, the ink transfer performance and the adsorption performance are weakened, and the ink on the printing surface is not ink, and the greasy ink cannot Adsorption in time, resulting in greasy plate;

To overcome the method: The ink roller is often removed, scrubbed, polished, and prevented from aging to maintain its ink-receptive properties.

4 The pressure between the roller and plate is too great

The pressure between the water roller and the printing plate is too large, the elasticity of the velvet cloth loses its elasticity, and the friction increases. As a result, the sand of the plate wears, and the stability of the inorganic salt layer is destroyed, and the blank part is liable to produce oil dirty;

To overcome the method: reasonably adjust the pressure between the water roller and the printing plate, use a thin steel plate with a thickness of about 0.15 to 0.2mm and a width of about 20 to 30mm to insert between the water rollers or between the water roller and the plate at both ends and in the middle. There is friction resistance, and feel that the steel sheet can be smoothly pulled out. In addition, it is necessary to frequently scrub the water roller, and the water roller flannel should be promptly replaced after losing its elasticity.

5 improper use of water roller

The flannel cover of the water roll has better hydrophilicity though degreasing treatment. However, due to improper use, the surface of the water roller cover is in contact with the ink or the large amount of oil adsorbed on the surface of the water roller is not washed in a timely manner and dried. The suede gradually loses its original hydrophilicity, and the water absorbency and water transfer ability also gradually weaken, resulting in layout water. The ink balance is destroyed, resulting in greasy;

Overcome the method: Pay attention to the large water content in the control panel to prevent the water roller from sticking ink due to the small water. In time, pour pumice powder with concentrated water to remove the dirty ink on the surface of the water roller, and often clean the water roller to ensure good hydrophilic performance;

6 The pressure between the plate and the blanket cylinder is too great

Printing can not be separated from the pressure, but the pressure between the printing plate and the blanket cylinder is too large, it will produce friction, make the sand eyes wear, the layout of the shiny, damaged the layout of the hydrophilic layer produces greasy. This kind of grinding friction generally comes from two aspects. On the one hand, the lining distribution is unreasonable, resulting in a large amount of slippage between the rollers; on the other hand, it is the compression theory.

Ways to overcome: On the basis of ensuring that the prints are strong enough without laminating, evenly use the minimum pressure, calculate and measure the initial thickness of the pad correctly, and at the same time, determine the amount of compression according to the properties of the pad.

7 The pressure between the printing plate and the ink roller is too great

The ink roller has the most friction and there is ink on the roller surface. Some of the ink filler particles play the role of abrasive. In particular, the particles of the chrome yellow ink are relatively coarse. When the pressure between the printing plate and the ink roller is large, large friction occurs and the sand self He was worn out and he was sometimes worn out.

To overcome the method: to correct the pressure between the printing plate and the ink roller, the steel roller can be used to adjust the pressure of the ink roller by the root of the roller and make the pressure on both sides of the ink roller consistent. Can also see the width of the ink stick: general ink roller and plate pressure should be adjusted to 5 ~ 6mm.

8 Paper factors

Due to the composition of the paper: fibers, fillers and sizing, etc., the organization is not dredged, and the surface strength of the paper is poor. In the printing process, the paper is subjected to a peeling force, and the surface is easily peeled off and fluffed, forming a buildup layer on the surface of the blanket. , And through the blanket into the ink roller, water roller to the plate, a long time, the accumulation of paper hair, silty and filler and other impurities, exacerbated the friction between the rollers, so that the fuzzy imprint of the imprint, the plate surface trachoma Wear destroys the hydrophilic layer and causes oil.

Ways to overcome: Add 6# varnish and detackifying agent in an appropriate amount, but the varnish is easy to dilute the ink, increase the fluidity, and must be used with caution. In order to prevent the floating ink oil dirty, it can be properly moistened with the fluid, and the blanket and printing plate should be cleaned frequently.