The relationship between gravure printing ink and tackiness and its countermeasures (2)

Third, the adhesion of the printing ink layer

The fastness of adhesion of printing ink layers is also closely related to adhesion. When the adhesion fastness of the printing ink layer is poor, it is easy to transfer the printing ink film under pressure to another film in contact with it, thereby causing blocking. Therefore, good ink adhesion must be ensured. The following are the causes of poor ink fastness.

1. Whether ink was misused or mixed with different types of ink.

2, plastic film corona treatment or excessive moisture absorption.

3. The additive in the plastic film is precipitated, or the air is adsorbed on the film by the dust, thus affecting the adhesion of the ink.

4, ink bleaching and deterioration.

5, poor drying.

Fourth, some other major issues

1, plastic gravure ink ink is bad. Some plastic gravure inks have a low melting point of the linking material and are prone to sticking when the operating temperature is high and the relative humidity is high.

Countermeasures: 1 When the conditions permit, the operation of the workshop to install air conditioners, the room temperature control between 18 °C -20 °C, relative humidity controlled at 65% or less; 2 replace ink with good ink.

2, poor plastic film packaging and poor suitability

Reasons: 1 non-packaging resin processed plastic film; 2 resin opening agent is insufficient.

Countermeasure: Replace the plastic film.

3, electrostatic effects

Cause: The plastic film generates static electricity, forming a film that sticks to each other. Countermeasure: Add antistatic agent to the plastic.

4, cooling conditions and storage environment

The printed matter has a high heat after passing through the drying oven. The film coming out of the drying system still has a certain amount of waste heat. If it is not cooled back, it will cause waste heat accumulation inside the rolled semi-finished product, and then increase due to ink softening. The possibility of adhesion. Therefore, the printed film must be cooled before rewinding.

Cooling rollers are now commonly used for cooling. Cooling roll temperature running smoothness, printing line speed, etc. are the main factors affecting the cooling effect. If you forget to use tap water for cooling during operation, the cooling roller loses its cooling effect. After the plastic film has been completely printed and the roll is closed, the heat will accumulate in the film roll and the temperature will rise to 50-60°C. There are many examples of this causing adhesion.

In addition, during storage and handling, too high temperatures or poor ventilation may cause blocking.

5, winding tension is too large. Too much tension in the winding can directly increase the transfer tendency between the printing ink layer and the contact surface. Therefore, under the premise of ensuring that the winding is neat, the winding tension should be reduced as much as possible, and the winding diameter should not be too large.

6. When the cohesion of the ink layer is very weak (when the cohesive force is extremely poor), when the cohesion of the ink film is weak, the separation of the ink film occurs under a small pressure, resulting in blocking.

7, excessive pressure on the membrane roll over the pressure on the membrane roll will increase the tendency of the ink layer to the contact surface. The rigid storage of the film roll can effectively reduce the pressure between the ink film and the contact layer.

8. If the affinity of the printing surface and the contact surface is too strong, if the affinity of the printing surface and the contact surface is too strong, part (or all) of the ink layer can be easily transferred to the contact surface under pressure and cause blocking.

Fifth, to solve the adhesion failure methods and precautions

By analyzing the above factors that affect adhesion, we can summarize the solutions and precautions for plastic gravure adhesion failure.

1. Addition of additives in the resin can effectively prevent the internal adhesion, and the trial results are good. The specific methods are as follows. Oleic acid amide was selected and its chemical structure was C17H33CONH2, iodine value ≤86g iodine/100g, acid value ≤0.8mgKOH/g, melting point 72~76°C, white or yellow wax. It is a kind of slip agent. It is added into PE resin, heated and mixed by screw, melted and evenly dispersed in plastic at about 50°C. After high temperature extrusion, part of oleic acid amide oozes out of the surface to form a The thin layer of wax film makes the film layer and layer not directly contact and incompatibility, so it can play anti-blocking effect.

The operation method is as follows: first, the oleic acid amide is finely ground, or added into a crusher to crush. Because the incoming material is not uniform at the beginning, it will cause local concentration of additives without crushing. After smashing, sieve with a 50 mesh screen to remove coarse chips and add LDPE pellets. Add 100 parts of resin and add 0.1 part of oleic acid amide. Stir briefly, add the hopper, and blow directly. The other operating process does not change.

Effect: After adding additives, it not only effectively prevents the adhesion of the inner layer of the film, but also because the film forms a uniform and extremely thin layer of wax, which improves the smoothness and transparency of the film.

After gravure printing, the brightness of the ink is greatly improved, and it has no effect on the ink property. Only after the amount exceeds 0.3%, the surface tension of the film is difficult to control and the ink receptivity decreases. Therefore, the amount should be controlled below 0.3%, and the film should be corona treated after blowing, so that the surface tension of the film is controlled at 38 × 10-5N/cm2 or more. When the content of the formula is 0.2%, the screw and the head can be easily removed and washed, and at the same time, the lubricity protects the screw, the barrel and the head. Oleamide also has a certain antistatic effect in plastics. Blowing a color film and adding oleic acid amide can improve the coloration and dispersibility, eliminate the phenomenon of masterbatch accumulation, and have no adverse effect on color. In addition, there is no impact on the processes of heat-sealing, bag making, slitting and cutting.

2. Control the use of slow-drying solvents and residual solvents. Try to improve the performance of the oven so that it can supply sufficient heat and weight. When the chill roll is rotated smoothly and the rewinder is rewinded, the temperature rise caused by the slippage of the paper tube and the roll is noticed. When printing or recoiling, special attention is paid to thin films such as PET and NY. During transport and handling, the printed film should be kept upright and not tipped over. Otherwise, the local pressure of the film roll will be too large and cause blocking. Print patterns should not be concentrated on specific areas. For multi-color printing, it should be considered in the design of the pattern can not be too much overlap, if possible, you can use spot color ink printing to prevent the local ink layer is too thick.

3. In the case where the printed pattern on the plastic film is deviated toward one side, the pressure on the side of the rolled-up film on which the printed pattern is printed must be relatively large and it is very likely to cause blocking. Therefore, especially for this type of printed matter, it is not too tight in the roll. Take appropriate measures to improve the adhesion of the ink layer. The ink containing the metal powder in the plastic film gravure ink has weak ink layer cohesion and poor adhesion, and it is very easy to cause adhesion under very small pressure, and it must be fully noted.

4. The corrugated film on cellophane, nylon, or both sides has strong affinity for contact with the ink layer after rewinding, and there is a high risk of blocking. Therefore, appropriate measures should be taken before printing. . When only one-side printing is performed, the corona treatment device should be adjusted to perform only one-side processing. Slow down the printing speed. When the temperature of the drying oven is increased, the printed film must be fully cooled by the cooling roll before being wound up. For films such as polyolefin films that are easily stretched, care must be taken not to over-tighten them.

5, prints should be kept in a cool place. During the storage, it should be ventilated and dry, and the storage time should not be too long. It should be avoided to store the printed matter under direct sunlight or near the heat source. The warehouse should take ventilation and cooling measures when the climate is hot.

Sixth, summary

Plastic film gravure printing is a comprehensive technology. There are many problems that easily arise in the printing process. Sticking is one of the most common problems. In the high-temperature, high-humidity rainy season, adhesions are particularly prone to occur. Because adhesion is not immediately noticeable (unintuitive), it often causes great losses.

Summarizing the experience of some seniors, whether it is for our ink manufacturer or for the printing industry, is of great benefit. This is also the original intention of this little thing.