Ink Printing Common Failure Analysis - Ink Emulsification

6. Ink emulsion

Phenomenon and Cause: The separation of water into tiny droplets dispersed in the ink is called emulsification. In the printing process, the oil and water are not absolutely incoherent, due to the constant contact of ink and moisture, and the role of mechanical forces and other factors. There will be different degrees of emulsification involved. When printing yellow ink and pale blue ink, this phenomenon often occurs, and most of them are produced on both ends of the ink roller. The emulsification of ink has a great harm to printing, diluting the ink and affecting the drying of the imprint, creating a dingy, the ink becoming “defective”, the ink roller deinking, the imprinting color discoloration, the paper turning yellow or blue, affecting the product quality and other defects as a result of. Caused by ink emulsification is mainly due to the surface tension between the oil and water is reduced, in addition to the layout of water is too large, the water bucket syrup is too acidic, the resin content is too much, the active material on the surface of the paper off and other factors, the common ink The reasons for emulsification are:

1) The acid value of the ink is too high. The surface tension at the interface between ink and water depends on their polarity. The polarity of the ink is usually measured by the acid value. The more free fatty acid in the ink, the higher the acid value. The stronger the polarity, the greater the possibility of emulsification. A certain acid value can ensure the dispersion of the pigment in the ink and the adhesion of the ink in the transfer process, but the high acid value is the biggest cause of ink emulsification.
2) The poor water resistance of ink pigments, especially those of inks for offset printing, are not only soluble in water and acid, but also have water-resistance properties, as the common lake pigments are often hydrophilic powders. When the dye components in the pigment are soaked in acidic water, the dye will quickly precipitate out of the dissolved water, causing emulsification failure. If the pigment of the ink pigment is coarse, the viscosity is not enough, and the binding with the binder is not strong enough during the rolling process, and after the contact with the acid during the printing process, the moisture is easily absorbed and expands by itself, and gradually detaches from the binder to generate emulsification.
3) There are no graphics on both sides of the plate, and the water content is large, which promotes emulsification at both ends.
4) Add too much diluting agent in the ink, commonly used accessories from the oil composition is carbonic acid, Wei Li oil composition is aluminum hydroxide, wood is emulsifier, so the more the addition and release of accessories, the more will promote ink emulsification . Too much of the driers in the ink, the printing process is bound to increase the acidity of the water bucket syrup, the acidity is too strong to easily cause ink emulsification, in addition to the driers wooden body is a strong oxidant, so the driers in the ink plus the more More, the more can cause the ink to emulsify failure.

Treatment method: It is impossible to completely solve the problem of ink emulsification because the oil and water will produce emulsification under the action of the machine. The slight emulsification has little effect on printing. If the emulsification is serious, it must be solved.

1) Exchange new ink
2) Add concentrated oil to the ink to reduce the acidity of the medicine and the amount of gum arabic.
3) Add less oleic acid, oil and Weili oil.
4) Reduce the amount of driers.