Factors affecting solvent volatilization

The volatility of the solvent is suitable for multi-color printingprovides the possibility, and affects the residue of the printed solvent and the fundamental impact of the solvent volatility The factors are the vapor pressure of the solvent at a certain temperature, as well as the molecular weight and latent heat of evaporation of the solvent.

Boiling point versus solvent volatility The impact

Generally has a boiling point of 60~150℃ of solvents can be used in gravure printing inks. Generally, the lower the boiling point of the solvent, the faster it evaporates. However, there are exceptions. For example, ethyl acetate and ethanol have similar boiling points, but the volatilization rate of ethyl acetate is almost twice that of ethanol. Therefore, ethyl acetate is often used to replace ethanol in plastic gravure inks with fast printing speeds. In summer, the temperature is high, the solvent evaporates quickly, and the price of ethanol is low. Ethanol is often used instead of ethyl acetate.

The release effect of resin

The situation of solvent volatilization in ink is more complicated. When the resin is dissolved in the solvent, the molecules of the two substances are closely combined with each other. At this time, the volatilization speed of the solvent is lower than the volatilization speed of the solvent itself. For liquid ink with a certain viscosity, the attached solvent evaporates during the drying process, the resin content increases, and the evaporation rate of the solvent also slows down. In particular, alcoholic solvents have greater polarity and are more attractive to polar polyamide resins. Especially alcohols with slightly higher boiling points are not easy to volatilize, which increases the amount of solvent in the remaining ink film and causes pollution. Packaging, therefore, when choosing ink, you should try to use ink with resin that has better solvent release properties.

The influence of mixed solvents

Plastic gravure inks generally use mixed solvents. The volatilization speed of the mixed solvents is not only related to the boiling point of each solvent itself, but also the interaction between solvent molecules. The volatilization speed is not the average volatilization speed of each mixed solvent. When selecting a solvent, two pros and cons must be considered at the same time: it must not only meet the printing requirements, but also ensure that the residual amount of solvent is as small as possible.

The influence of temperature and air volume in the drying oven

The faster the temperature in the drying oven is, the faster the solvent will evaporate. However, if the temperature is too high, it will easily cause the printing film to stretch. Therefore, for layered printing, the temperature is generally set to 45~65°C. ; For large-area printing, the temperature is generally controlled at 75~90℃. The air inlet pressure and exhaust pressure of the drying box are not as high as possible, but require a balance between the air inlet volume and the exhaust air volume. If the exhaust air volume is too large, it will cause the film to break or scratch the ink layer. Generally, the air inlet pressure of the drying box is better. The air pressure is 80~90H2O, and the exhaust pressure is 40~50H2O.

The impact of printing speed

The faster the printing speed, the shorter the time it takes for the printed matter to pass through the drying box, which is more detrimental to the drying of the ink. Appropriately reducing the vehicle speed is also a way to solve the problem of residual solvent.

Environmental impact

The higher the ambient temperature, the faster the solvent evaporates. The faster the air flows in the workshop, the faster the solvent evaporates, and vice versa.

Pigment particle condition

When making ink, when pigments, fillers and other materials are added, the evaporation rate of the solvent is greatly reduced. The finer the pigment particles and the larger the surface area, the slower the evaporation rate of the solvent.