Causes and Countermeasures of Common Faults of Gravure Printing (I)

First, back to stick Plastic film or transparent paper printed surface imprinted with dry artifacts, but in the printed roll or bag after storage in the sense of the phenomenon of back sticky. 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 does not completely evaporate. 1 The plastic film print is dried by evaporation of the solvent. 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 dry too quickly, you can use a little bit of butanol to replace some of the ethanol (butanol has the effect of increasing the ink luster but you must pay attention to the amount of addition should be appropriate, so as not to affect the drying of the print.
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) Poor Ink of Ink The connection material in some plastic gravure inks has a low melting point, and in the case of high ambient temperature and high relative humidity, it tends to adhere.
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) The poor suitability of the film printing: (1) Plastic film formed by non-packaging resin: (2) Insufficient opening agent in the resin. Countermeasure: Replace the plastic film.
(4) Electrostatics Cause: The plastic film products are electrostatic and form films that stick to each other.
Countermeasure: Add antistatic agent to plastic