Causes and countermeasures of common gravure failures (I)

Keywords: plastic film, plastic printing, fastness, overprint accuracy, back to sticky plastic film or transparent paper printed imprinted surface dry artifacts, but in the printed roll or bag after storage in the back of sticky phenomenon. In severe cases, the parts cannot be torn between the prints, and the ink layer of the image is shifted to cause 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 sticking. Back sticking is also closely related to a series of factors such as plastic, ink, solvent, air volume, light, and speed.
(1) The solvent does not completely evaporate. 1 The plastic film print is dried by solvent evaporation. The volatilization rate determines the drying of the ink layer. 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. In 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 other hand, the solvent with fast evaporation (such as 74-91 plastic film) should be added. Fast drying ene 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: (To be continued)