Gravure printing ink transfer (5)

Fifth, the gravure ink drying

The ink used in gravure printing contains a high proportion of volatile solvents. In order to increase the drying speed of the ink, electric heating and vapor heating methods are generally used to accelerate solvent evaporation and the ink layer is dried in a timely manner.

1. Gravure ink drying speed adjustment. The drying speed of gravure printing ink depends not only on the boiling point of the solvent, vapor pressure, latent heat of evaporation, but also on the temperature, humidity, air volume, and ink layer thickness of the operating environment. Therefore, the evaporation rate of the solvent in the ink should be adjusted according to the specific conditions of the printing process.

At room temperature, if the ink layer dries too slowly, an appropriate amount of solvent with a high volatilization rate can be added. On the contrary, you can add a suitable amount of slow evaporation solvent. It can also be adjusted with a mixed solvent. For example, diluting the ink with a mixed solvent of xylene, ethanol, and isopropyl alcohol is more advantageous for the adjustment of the volatilization rate. If the drying rate is too fast, a small amount of butanol can be used instead of a part of the ethanol. Butanol Improve the effect of ink luster, printing better. The volatilization rates of commonly used solvents are listed in Table 6-4.

Table 6-4 Volatilization rate of commonly used solvents (30 °C)

Solvent Name Ethyl Acetate Toluene Alcohol Isopropionic Acid Xylene Butyl Butyl Butanol
Volatilization speed (s) 18 31 47 55 70 70 147

The temperature has a great influence on the drying of gravure printing inks. Generally, it adjusts according to the printing materials, printing speed, and the area of ​​printing graphics. For example, the printing material is paper, the color sequence is yellow, magenta, cyan, black solid version printing, the first color temperature should not be too high, controlled at about 80 °C, too low ink drying bad, too high caused by paper shrinkage, Two-color overprint is not allowed. After that, the drying temperature of each color gradually increases, and the maximum temperature shall not exceed 120°C.

Plastic films are softened by heat and easily stretched under tension. Therefore, the drying temperature must be strictly controlled. Polypropylene, polyethylene, nylon and other easily stretchable films, the best drying temperature should not exceed 70 °C. The more suitable drying rates provided by the production site are listed in Table 6-5 for reference.

Table 6-5 Drying Speed ​​and Temperature of Plastic Film Inks

Temperature graphic area printing rate 0 to 20% 30% to 70% 80% to 100%

80m/min 40±10°C 50±10°C 60±10°C

120m/min 40±10°C 60±10°C 70±10°Cb

160m/min 45±10°C 60±10°C 75±10°C

200m/min 45±10°C 60±10°C 80±10°C

2. Dryer ventilation and environmental protection. In the drying process of gravure printing inks, solvent gases that are volatilized out are mostly flammable. When they are mixed with air to a certain percentage, they are in a deflagrable state. Table 6-6 lists the deflagration ranges for several common solvents.

In order to avoid deflagration, the recirculation air is used to continuously send air to the drying device of the gravure printing machine, and the amount of combustible gas is controlled to be less than 1/2 of the lower limit of the explosion.

Exhaust from the dryer, containing a large number of toxic gases, such as benzene, xylene, etc., harm personal health and cause environmental pollution. Therefore, the gas discharged from the dryer should be sent to a solvent recovery device, which will recover both organic solvents and atmospheric pollution.

Table 6-6 Deflagration range of common solvents

Solvent Name Upper Limit Lower Toluene 6.8% 1.4%
Xylene 6.0% 1.0%
Methanol 36.5% 6.0%
Ethanol 19.0% 3.28%
Ethyl acetate 11.4% 2.2%
Methyl ethyl ketone 11.5% 1.8%