Causes of Common Faults of Gravure Printing and Countermeasures (Part One)

First, stick back

After the printing of the plastic film or transparent paper, the imprinted surface had dry artifacts, but it was found that the back surface was dirty during the storage period after the roll or bag was printed. In severe cases, tears do not open between India and India. This phenomenon is more likely to occur in the hot season, but the high temperature is not the only cause of back sticking, and concave sticky also has a close relationship with a series of factors such as plastic, ink, solvent, air volume, light, speed and so on.

(1) The solvent is not completely evaporated

1 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 volatilization of the solvent, the better the reproducibility of the plate, the more beautiful the print color, but easy to stick; the other hand, the phenomenon of whitening and other phenomena. 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 thoroughly evaporated in the drying system. After the film is wound, there is still residual heat, and the solvent remaining in the ink layer brings about the condition of continuing to volatilize, thereby forming blocking.
3 In the hot and humid season, after printing, the film is wound tightly 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, and latent heat of the vapor. It also depends on the conditions of the operating environment such as temperature, humidity, air volume, solute, and ink thickness. Therefore, the volatilization rate of the solvent in the ink should be adjusted at any time according to the change of conditions. Under the general 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. On the contrary, the quick-dissolving solvent (such as 74-91 plastic) should be added. Thin film 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.

Comparison of commonly used solvent volatilization rates:

Solvent name Temperature (°C) Volatilization rate (S)

Toluene 30 31

Xylene 30 70

Isopropanol 30 55

Ethanol 30 47

Butanol 30 147

Ethyl acetate 30 18

Butyl acetate 30 70

In short, the organic solvent in the ink should be exhausted before it is rewinded. After the film is printed, it is loosely put into the wire textile basket so that the ink layer can continue to be ventilated and dried, and then cut and bagged after solidification. After the film is printed and bagged, it is lightly bandaged and placed upright in the carton, reducing the pressure between the film surfaces.

(2) Bad ink and ink

Some plastic gravure inks have a low melting point of the connecting material, and are easily adhered when the operating temperature is high and the relative humidity is high.

Countermeasures: 1, when conditions permit, the operation of the workshop to install air conditioners, the room temperature control between 18 °C -21 °C, relative humidity controlled at 65% or less; 2, replace ink with good ink.

(3) poor film printability

Reasons: 1. Non-packaging resin processed plastic film: 2. Resin opening agent is insufficient. Countermeasure: Replace the plastic film.

(4) Static electricity

Causes: The plastic film products are electrostatic and form films that stick to each other. Countermeasure: Add antistatic agent to the plastic.