On gravure printing failure: cause and countermeasures of back sticking problem

After the printing of the plastic film or transparent paper, the imprint has dried, but after the printing of the roll or the bag is stored, the back surface becomes dirty. In severe cases, the printed parts cannot be torn apart and the graphic ink is moved. Dyeing, causing the product to be scrapped. This phenomenon is more likely to occur in the hot season, but the high temperature is not the only cause of back tack. It is also closely related to a series of factors such as the plastic, ink, solvent volatilization rate, operating environment, air volume, and illumination.

1. The solvent in the gravure ink failed to completely evaporate after printing.

(1) Plastic Film Printing is drying the ink by solvent evaporation. The volatilization rate is an important factor that determines the drying of the ink layer and affects the printing quality. The slower the volatilization of the solvent, the better the reproducibility of the plate, the more beautiful the color of the print, but easy to adhere; on the contrary, it will produce a white blister and other images. Therefore, the choice of a suitable solvent for evaporation speed is the key to the gravure printing of plastic films. In continuous color printing, the solvent must be completely evaporated after the film is in operation between the two printing stations. Otherwise, the rollers will stick when printing at the next station.

(2) After the film is printed, the organic solvent in the ink is not completely evaporated in the drying system. After the film has been reeled, there is still residual heat, and the solvent remaining in the ink layer brings about the condition of continuing to volatilize and forms the blocking.

(3) In the hot and humid season, the film is wound up tight or under pressure after printing.

Countermeasures: The volatilization rate of the solvent in the ink depends not only on the boiling point of the solvent, vapor pressure, latent heat of the vapor, but also on the conditions of the operating environment such as temperature, humidity, air volume, solute, and ink layer thickness. Therefore, the volatilization rate of the solvent in the ink should be adjusted at any time according to the change of conditions. Under normal temperature, if the ink layer is dried too fast, slow-evaporating solvent (such as Shanghai-made 74-92 type plastic film slow-drying thinning agent) should be added; otherwise, fast-evaporating solvent (such as 74-91 plastic film) should be added. Fast drying thinner). It can 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 to replace some of the ethanol (butanol has the effect of increasing the luster of the ink). However, it must be noted that the amount of addition should be appropriate so as not to affect the drying of the prints.

Solvents for the gravure printing of plastic films, mainly alcohols, together with benzenes. Ethanol and isopropanol are more commonly used for alcohols, and toluene and xylene are more commonly used for benzenes. Due to the requirement of nitrocellulose, esters such as ethyl acetate and butyl acetate are also added. In short, the organic solvent in the ink is sought to completely evaporate before being wound up. Slow down the speed and increase the air volume. After the film is printed, it is loosely placed in a wire woven basket so that the ink layer can continue to be ventilated and dried. After solidification, the film is cut and bagged. After the film is printed and bagged, the film is wrapped and placed in the carton to reduce the film surface. The pressure between.

2. Plastic gravure ink ink is poor. 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.

3. The plastic film is poor in printability and packaging. Reasons: 1 non-packaging resin processed plastic film; 2 resin opening agent is insufficient.

Countermeasure: Replace the plastic film.

4. Electrostatic effects: Causes: Static electricity generated by the plastic film causes the films to adhere to each other.

Solution: Add antistatic stings to the plastic.



Source: China Design Printing Network