Talking about the PH value of water-based ink

Water-based inks are mainly scientifically processed with water as the solvent. In the printing process, the inks are dried with the evaporation of water. They are non-pollution to the environment, are non-toxic to the human body, are not easy to burn, and have good safety. In practical production applications, the pH value of water-based inks will have an important influence on the print quality.

First, the relationship between aqueous ink PH value and viscosity

Viscosity is closely related to the fluidity of aqueous inks. The decrease of PH value of the water-based ink directly affects the ink activity, causing the decrease of the solubility of the resin, resulting in the increase of the viscosity of the ink, which may cause the printing plate to dry up, thereby causing problems such as dry plate, drop point, and the like. Conversely, if the pH value of water-based ink is high, the alkalinity is strong, and the resin dissolves too much, the pigment and the binder may separate, the ink fluidity will increase, causing the printing dots to be unclear, and causing problems such as agglomeration, and the ink will not dry easily (rotary printing The machine easily sticks the paper guide roller).

In actual printing, when the PH value is between 6.0 and 7.0, the ink will have a delamination phenomenon, and a print plate will be produced during printing. When the pH is between 7.0 and 8.5, the ink system becomes unstable and the viscosity of the ink increases, resulting in poor transfer, dry printing, and dropping, and the color intensity of the printed matter decreases (black ink is the most obvious). When the PH value is between 8.5 and 9.1, the water-based ink has good fluidity, the ink viscosity is suitable for printing needs, has good wettability and spreadability to the substrate, and the ink layer also has good drying properties. PH value of 9.1 ~ 11.5, a large number of foam in the ink tank, the ink viscosity has a significant reduction, resulting in slow drying rate, water resistance becomes worse, the dot gain rate increases, the footprint is not clear, agglomerate, trademark The standard barcode bar increases. At the same time, due to the strong alkaline ink, the properties of the pigment may be damaged. Therefore, the pH of water-based ink should generally be controlled between 8.5 and 9.1.

Second, the relationship between aqueous ink hue and PH value

Pigment is the main factor that determines the color of ink. It is an inert substance. Its chemical stability determines the color rendering of the pigment. The chemicals that the ink is usually exposed to are nothing more than acids, alkalis, salts, water, corrosive gases, organic solvents (the ink tank is not clean), and these factors can affect the hue of the ink. Although the pigments used in water-based inks all have good alkali resistance, generally speaking, regardless of the choice of pigments, if the pH value of the ink is too high and the alkalinity is too strong, it will have more or less influence on the pigments and thus affect the pigments. The hue of the ink, so should try to avoid the PH value of the ink is too high. If the PH value is too high, the color will become lighter, and poor transfer will occur. Conversely, the solubility of the alkali-soluble resin will decrease, the viscosity of the ink will increase, the printing ink film will be thicker, and the color density of the ink layer will also be high. . Of course, if the pH value of the ink is properly controlled (between 8.5 and 9.1), the pigment will be thoroughly dissolved, the dispersibility will be good, and the hue will remain normal.

Third, the relationship between water-based ink gloss and PH value

The glossiness of water-based ink is mainly related to the thickness of the ink film, the glossiness of the linking material, the transparency and fluidity of the ink, the particle size of the pigment, the resin content, and the drying speed of the ink. The change of ink PH value will affect the ink layer thickness, fluidity, and drying speed, thus affecting the gloss of the ink. In addition, the solubility of the alkali-soluble and dispersion-type resins in the aqueous ink, the size of the pigment particles, and the degree of polymerization are also related to the pH of the ink.

Fourth, water-based ink printing environment and solutions

In the actual production, the working environment of the printing shop has relatively strict requirements on temperature and humidity. When the temperature is higher than 26.5°C, the volatilization of ammonia in the ink is accelerated and the PH value will decrease. If the PH value is lower than 8.5, the pH adjustment solution may be added in an appropriate amount. When the pH value is higher than 9.1, hot air and hot water may be suitably used to heat the ink, so that the alkaline substance in the ink is volatilized, thereby lowering the PH value of the ink. Do not reduce the pH by adding acidic substances. Doing so may cause deterioration of the ink. It is generally believed that the ambient temperature of the workshop is maintained at 19°C to 25°C and the relative humidity is controlled at 55% to 65%.

Reprinted from: NPES International Printing Business Network