Causes and countermeasures of back tack problem in gravure printing
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After printing on plastic film or transparent paper, the print has a dry illusion, but the back side is dirty during storage after printing the roll or bag. In severe cases, the print can not be peeled off between the prints. Dyeing, resulting in product scrapping. This phenomenon is more likely to occur during the hot season, but high temperature is not the only cause of back tack. It is also closely related to a series of factors such as plastics, inks, solvent evaporation rate, air volume in the operating environment, and illumination.
1. The solvent in the gravure ink did not completely evaporate after printing.
(1) Plastic film printing is to dry the ink by solvent evaporation. Its volatilization speed is an important factor that determines the drying of the ink layer and affects the printing quality. The slower the solvent evaporates, the better the reproducibility of the plate, the more beautiful the color of the print, but it is easy to stick; on the contrary, it will produce a white appearance such as blotting. Therefore, choosing the solvent with the proper volatilization speed is the key to gravure printing of plastic film. In continuous color printing, the film must be completely evaporated during the running time between the two printing stations. Otherwise, the roller will stick when printing at the next station.
(2) After the film printing, the organic solvent in the ink is not completely volatilized in the drying system, and there is still residual heat after the film is wound, and the solvent remaining in the ink layer is brought to a condition of continued volatilization to form blocking.
(3) During the hot and humid season, the film is too tight or compressed after printing.
Countermeasure: The evaporation rate of the solvent in the ink depends not only on the boiling point of the solvent, vapor pressure, latent heat of vapor, but also on the temperature, humidity, air volume, solute and thickness of the ink layer in the operating environment. Therefore, the evaporation rate of the solvent in the ink should be adjusted at any time according to the change of the conditions. At normal temperature, if the ink layer is too fast, add a slow-releasing solvent (such as Shanghai 74-92 plastic film slow-drying thinner); otherwise, add a volatile solvent (such as 74-91 plastic film). Quick dry thinner). It may also be diluted with a mixed solvent of xylene, ethanol and isopropanol (the three solvents are each mixed in a ratio of 1/3, and it is better to use a single solvent than the mixed solvent). If you feel too dry, you can use a little bit of butanol instead of some ethanol (butanol has the effect of increasing the gloss of the ink). But be sure to pay attention to the amount of addition, so as not to affect the drying of the print.
The solvent for the gravure printing of the plastic film is mainly composed of an alcohol and a benzene. The alcohols are mostly ethanol and isopropyl alcohol, and the benzenes are mostly toluene and xylene. Due to the need of nitrocellulose, esters such as ethyl acetate and butyl acetate are also added. In short, the organic solvent in the ink is required to be completely volatilized before winding. Appropriately slow down the speed and increase the air volume. After the film is printed, it is loosely placed in the wire woven basket, so that the ink layer can be continuously ventilated and dried, and then cut and bagged after curing. After film printing, the bag is wrapped and placed vertically in the carton to reduce the film surface. The pressure between.
2. Poor ink in plastic gravure ink. The binder in some plastic gravure inks has a low melting point and is easy to stick when the operating environment temperature is high and the relative humidity is large.
Countermeasures: 1 When the conditions permit, install the air conditioner in the operation workshop, control the room temperature between 18 °C and 20 °C, and control the relative humidity to less than 65%; 2 Replace the ink with good ink.
3. Plastic film thin printing package is not suitable. Reasons: 1 Plastic film processed from non-packaging resin; 2 insufficient opening agent in resin.
Countermeasure: Replace the plastic film.
4. Electrostatic effect: Cause: The plastic film generates static electricity and forms a film to adhere to each other.
Countermeasure: Add antistatic thorns to the plastic.