Dirty and dirty oil fault analysis and solution in offset printing production

Dirty plate is a common fault, but in a sense is also a typical failure. In the production process, it is necessary to carry out a detailed analysis according to signs and parts of the layout with dirt, find out the cause of the malfunction, and take effective measures to prevent and solve them. In general, the layout with dirty can be divided into floating dirty, dirty oil, paste version and so on.

First, floating dirty

Dirty refers to the phenomenon that a non-graphic part with a relatively large range and a relatively low density is dirty. Its dirty parts have no fat basis. Because of this, the non-graphical part of the filth, visible on the printed sheet, may be visible on the plate, and may not be visible. Observed from the surface of the printed matter, the dirty spots sometimes float everywhere. It is possible that the locations of the previous and the next dirty spots are different. In addition, generally with a dirty printed matter, the ink is usually dark and faint.

The main cause of buoyancy is ink emulsification caused by ink imbalance. In addition, there are oil paper quality, water, ink roller and printing pressure and other factors.

The specific causes and processing methods are as follows:

(1) Insufficient moisture resistance of the ink is emulsified in the wetting liquid.

Treatment method: To increase the ink consistency for soft or thin ink, add moisture-resistant varnish to the short-ink ink that is easy to soak.

(2) Precipitating the emulsifier from the paper coating and causing it to float.

Treatment method: change paper or harden ink.

(3) In multi-color printing, if the ink of each color is dirty, it may be a paper problem. If only one or two colors of ink are dirty, and other inks are printed clearly, it is an ink or plate problem. Monochromator also has a similar phenomenon.

Processing method: change paper, harden ink or change ink.

A factory uses a four-color offset press to process a batch of 250g/m2 color box. From the point of view of the field prints, the four colors are all dirty and the black spots are the most. After the printer shuts down the plate, it disappears after cleaning the plate, but it appears again after starting the machine.

Similar to the above example, can it be considered a paper problem? Although all four colors are filthy, but the degree is not equal, so we cannot conclude that it is a paper problem. How should we check it?

(1) Check the viscosity, drawability, and ink volume of the ink.

(2) Check the water roller and ink roller pressure.

(3) Check whether the ink-moisture balance is in the best condition (observe whether the layout moisture is too large).

(4) Check whether the parameters of the tank are normal, including temperature, alcohol concentration, conductivity value, pH value, etc.

(5) Clean the water tank and replace the wetting fluid.

Follow the above procedure carefully and then draw a conclusion.

Fouling is often caused by large quantities of printed materials. This type of quality accident happens in packaging and printing, and the operator must pay attention.

The sticky box of a batch of cigarettes printed by a certain factory is printed in red, and the Chinese pinyin is a hollowed out word. In order to highlight the blank after indentation, the white ink is overprinted in the word. When the operator prints red, the layout is printed. The overall production of dingy white words so that the hollow red, and finally make the batch of one-third of the live.

[Expert Tips]: This kind of example is strictly speaking should not happen, this is mainly due to the operator's lack of awareness of quality, that the red version is a little dirty, white ink can cover, but the results prove that mistakes.

Second, the dirty oil

Dirty oil refers to the blank part of the printing plate that is not fat-sensitive, so that the ink adheres to it and forms a dirty plate. The main causes of fat in the blank part of the printing plate are: insufficient amount of water in the blank part or weak acidity of the single wet liquid, or other reasons that damage the hydrophilic salt layer in the blank part of the printing plate.

The biggest feature of the dirty oil is that the dirty parts are relatively fixed, and the dirty parts are not easily wiped off. In addition, the water can be removed by rubbing the syrup and peach gum, but the bad oil can not be eradicated if the sand eyes are damaged.

There was oil in the printed matter. If you look for the reason, it is because the relevant parts of the printing plate and the friction are in doubt. example:

(1) Plate-to-rubber roller pressure is too high.

(2) The ink roller pressure is too high.

(3) The plate is not tightened during loading.

(4) Insufficient lipids and additives.

(5) The pH of the wetting fluid is too large.

(6) Blanket aging, lack of elasticity.

Third, paste version

Paste printing refers to the lines and lines of printed graphics, between dot and dot, and highlights should not be dirty with ink, but sometimes it belongs to the category of dirty, and sometimes belongs to the dirty category.

In the printing process, often judged according to the following conditions:

(1) The location of the dirty area is determined, but the darker ink is definitely dirty.

(2) Dirty positions often change, and the ink is lighter, certainly floating.

If the types of dirt on the layout are sorted out, then the fault can be handled accordingly.

Fourth, dirty, paste, flower version failure analysis

During the printing process, the dirty, paste, and floral prints had the exception of the ink factor. Most of the rest, however, were of varying degrees of damage to the blank part of the printing plate and helped to separate the hydrophilic layer, but the form was different. The specific factors are;

(1) The strength of the wetting fluid is strong. The wetting fluid is too weak in acidity, and the hydrophilic salt layer is generated slowly. The inorganic salt layer of the blank portion cannot be supplied and replenished in time, so that the hydrophilic oleophobicity of the blank portion is reduced. Acidity is too strong, there is corrosion on the printing plateau, destroy the hydrophilic salt layer, easy to make the plate under the pressure friction shine, resulting in dirty, sometimes flower version.

(2) The aging of the ink roller makes the printing plate greasy and the printing plate ink roller aging, the hydrophilic property is strong, and the ink transmission performance is poor. In the mechanical rolling, the water is dispersed in the ink in the form of fine droplets, due to water and ink. The immiscible principle makes the ink on the ink roller emulsified, the viscosity of the ink is reduced, and the adhesive force is reduced. The ink can easily fall from the ink roller onto the blank part of the printing plate, so that the hydrophilic salt layer produces lipophilicity, resulting in the greasy printing plate and Graphic part of the flower version.

(3) The pressure between the water roller and the printing plate is too large, so that the printing plate produces oil dirty and the flower plate contains the acidic wetting liquid. The driving force is driven under the pressure and depends on the surface friction force during the transmission process. Due to the compression and deformation of the water roller and the plate cylinder, there is a certain linear velocity difference, so that the surface of the water roller and the printing plate is rubbed, the sand mesh is destroyed, and the stability of the inorganic salt layer is also destroyed, so that the blank part is easy to feel fat. Produce a dirty version. Therefore, the contact pressure between the water roller and the printing plate must be properly adjusted.

(4) The pressure between the ink roller and the printing plate is so large that the blank part is dirty. The graphic part of the ink roller and the printing plate friction the most times, and the roller has the ink, and some of the ink filler particles play the role of abrasive, resulting in the printing Part of the blank part of the dirty, graphic part of the flowers.

(5) The ink pressure on the printing plate is too small to cause the printing plate. When the printing pressure on the printing roller is too small, the ink transferred to the printing plate is reduced correspondingly, and the ink on the plate graphic part is less, and the printing plate does not get sufficient ink. In the case of layers, the graphic part is subject to wear and tear, and over time the pattern is created.

(6) Excessive pressure between the plate cylinder and the blanket cylinder can cause the plate to be dirty, and increase the pressure between the plate and the plate cylinder and the blanket cylinder when the pressure between the plate cylinder and the blanket cylinder exceeds a specified value. Extrusion force, plate sand gradually flattened to reduce water storage capacity, began to produce stencil, after printing to a certain number, sand polished, the printing plate shines, the foundation of the outlet was also destroyed, and the emergence of the flower version . The shortcomings from the initial paste version to the final version seriously affected the printing quality. At this time, the printing pressure and lining must be readjusted.