In offset printing, there are many reasons for the scaling of the ink layer, but the main ones are as follows: too high dry oil content in offset printing ink leads to scaling; Excessive temperature causes the scaling of offset printing ink; The surface layer of offset printing ink and air contact for a long time, resulting in scaling.
Generally, such mistakes may occur in the process of manufacturing offset printing ink or printing. When adding desiccant, be sure to add it properly according to the printing conditions and ambient temperature, otherwise the offset printing ink will dry (scaling) when you do not want to dry.
Offset ink scaling due to high temperature
The scaling of offset printing ink caused by temperature is mainly caused by high temperature. When the temperature is too high, the activity of unsaturated molecules in the offset printing ink is enhanced, especially the part of the surface contacting with air is easier to be oxidized under the action of oxygen.
A. The ambient temperature is too high. According to our experience, the peeling phenomenon of offset printing ink is much more obvious in summer than in winter. If there is no air conditioner in the workshop, it will be more obvious. It is necessary to control the temperature of the working environment reasonably. Generally speaking, it is an ideal temperature to control the temperature of the workshop at about 20 ℃, which can ensure the good fluidity and transfer performance of the offset ink, and can control the scale of the offset ink at a relatively low level.
B. When the temperature on the machine (such as between the ink rollers) is too high, the offset ink will also skin during the printing process. When the contact pressure between the ink rollers is too high, the temperature rises obviously, and at this time, the offset printing ink is easy to scale on the ink bucket and the ink roller. Accurate adjustment and control of the pressure between the ink rollers is of great significance to prevent the scaling of offset printing ink in the printing process.
C. The air leaked from the dryer dried the surface of the offset printing ink, or the hot air blew the offset printing ink in the ink bucket.
Offset printing ink skin-003.jpg3, the surface layer of offset printing ink and air contact for a long time, resulting in scaling
Binder components in offset printing ink can react with oxygen in the air for oxidation-reduction reaction. If exposed to the air for a long time, they will be oxidized and crusted. Generally, there are the following types of crusts:
A. The offset printing ink that is not used temporarily will be exposed in the air, and a thick oxide film will appear on the surface for a long time. The printing factory will have the experience that when the ink is filled out from the ink cartridge or the ink bucket, the surface of the offset printing ink should be kept as flat as possible. The reason for doing this is to minimize the contact area between the ink and the air, so that the waste of the ink will be as small as possible even after the ink film is formed. Then cover the remaining offset ink with a protective film to block the contact with the air, which can also effectively prevent the scaling of the offset ink.
B. When the printer is shut down for a long time, the ink path is not cleaned, resulting in the scaling of the offset ink in the ink roller and ink bucket. During work, pay attention to clean the offset ink path when the machine is shut down for a long time. When the machine is not shut down for a long time, you can choose to spray ink anti-scaling agent on the ink path.
C. If the offset printing ink is not stirred for a long time in the ink bucket, it will be skinned. In the process of printing, we often talk about "three diligence", in which the frequent stirring of the ink in the ink bucket is a very important one. First, it can maintain the good fluidity of the offset ink in the ink bucket. Second, it can make the surface ink and the internal ink exchange frequently, and the ink that avoids contact with the air is always the same part. Standardized operation of ink supply adjustment. The basic principle of ink supply adjustment is: the gap between the ink bucket blade and the ink bucket roll should be as small as possible, and the angle of the ink bucket roll should be as large as possible. This is partly due to the above considerations.
D. The structure of the ink roller is not good, resulting in stagnant parts.
How to effectively deal with and solve the problem of offset ink scaling in printing?
1. Do not use offset printing ink that dries too fast;
2. Add slowly drying solvent and other additives;
3. Replace the deteriorated offset printing ink;
4. Stir constantly in the ink bucket;
5. A closed top cover is arranged on the ink bucket;
6. Adjust the angle of hot air blowing. People with a little common sense of printing know that when the drying is too fast, the ink concentration is too weak, the flow is poor, the ink thixotropy is large or the ink is static, the speed of the printing machine is adjusted to speed up, which prevents the offset printing ink from drying on the printing plate in advance, overcomes the skin formed by the ink formation of the packaging printing ink, and also eliminates the speckle fault of the image and text.