The quality of offset printing products is inseparable from the consistency of ink and water. In the printing process, the amount of water supplied too much or too small is often easy to occur, because the amount of moisture in the printing plate is manifested from the dirty surface of the printing plate. However, the so-called dirty is not only caused by the small amount of water, the operator often mistakes the water supply amount to cause the ink and water to lose balance and form a vicious circle. What kind of printing consequences are caused by excessive moisture?
Alkali resistance of pigments: Pigments are materials that impart color characteristics to the ink and meet the color requirements of printing. Since the resin of the aqueous ink is mostly alkali-soluble, the viscosity and pH of the ink are precisely controlled, and the pH is generally controlled between 8.0 and 9.5. When the pH is higher than 9.5, the alkalinity is too strong, the viscosity of the ink will decrease, the monotonic speed will be slow, and the water resistance will be deteriorated; when the pH is lower than 8.0, the alkalinity will be too weak, and the viscosity of the ink will rise. The ink is easy to monotonous and will form defects such as dirty plate, paste and blistering. Therefore, pigments with excellent alkali resistance must be used when selecting pigments.
Relative density of pigments: When the relative densities of pigments for aqueous inks are very different from each other, pigments with relatively low density are simply floating on them. For example, ink-green inks are often co-colored with pigments such as carbon black and phthalocyanine blue lead chrome. The phenomenon of floating color, hair flowering, sedimentation, etc.; when the relative density of the pigment is too large, the stability of the aqueous ink is damaged due to its simple deposition and agglomeration, such as iron red, chrome yellow, etc., often because the agglomeration cannot be stirred.
On the other hand, it is necessary to add a stabilizer in a quantitative manner. Generally, the pH value of the water-based ink should be kept between 8.0 and 9.5. If the pH value is too high or too low, the printing quality will be affected. When the pH value is too low, the printing performance of the acrylic resin will be affected. When the pH value is too high, the ink will dry slowly. It is prone to the problem of dirty and poor water resistance on the back of the printed product.
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