The Causes and Countermeasures of Sticking Back in Plastic Film Gravure

After the printing of the plastic film, the imprint of the printed film has appeared dry, but the phenomenon of back-surface stickiness occurs during the storage of the roll or bag after printing. In severe cases, the printed parts cannot be torn apart, and the ink layer of the image is shifted to cause a stain. Product is scrapped. This phenomenon is more likely to occur in the hot season.

However, high temperature is not the only cause of back-tacking. It is also closely related to a series of factors such as plastic, ink, solvent volatilization speed, operating environment air volume, and illumination. The specific causes and solutions are as follows:

First, the solvent in the gravure ink has not been completely evaporated after printing

(a) Plastic film printing is the drying of 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 solvent volatilization, the better the reproducibility of the plate, the more beautiful the print color, but easy to stick; 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 printing of the thin film, the organic solvent in the ink is not completely evaporated in the drying system. After the film is wound, there is still waste heat, and the solvent remaining in the ink layer is brought into a condition of continuing to volatilize to form a blocking.

(C) In the hot and humid season, after the printing, the film was over-tightened or under pressure.

Countermeasures:

The volatilization rate of the solvent in the ink depends not only on the boiling point of the solvent, vapor pressure, vapor latent heat, etc., 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.

Second, plastic gravure ink bad ink

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 conditions permit, the operation workshop installs air conditioners, controls the room temperature between 18°C ​​and 20°C, and controls the relative humidity below 65%;

(b) Replace ink with good ink.

Third, poor suitability of plastic film printing and packaging

(1) Plastic film processed from non-packaging resin;

(b) Insufficient opening agent in the resin.

Countermeasures:

Replace plastic film.

Fourth, electrostatic effects

The plastic film generates static electricity, forming films that stick to each other.
Countermeasures:

Add antistatic stings to the plastic.