In order to reduce the surface tension of the water-based system grinding base and improve the dispersion effect, it is generally effective to use a dispersing aid. Several wetting and dispersing agents were selected for the initial experiment. Firstly, the HLB value was determined by water dispersion method. A small amount of surfactant was mixed with water to observe the properties of the final dispersion to roughly evaluate the HLB value of a certain surfactant. Among them, insoluble or non-dispersive is 1-4, unstable or poorly dispersed is 5-6, after strong oscillating, milky dispersion is 7-8, stable milky dispersion is 9-10, translucent or gray dispersion For 11 to 13, the clear solution is >13.
Based on YM-3 formula, the effects of different wetting agents on dispersion, gloss, and water resistance were investigated. The formulations are listed in Table 2.
From the results in Table 3, it can be seen that A1, A2, A3, and A4 can significantly reduce the dynamic surface tension of ink, with the formulas A1 and A2 (respectively, sodium polyoxyethylene octylphenol ether sulfate) and Acetylene glycol (EGG) is the most significant, and the lower surface tension has a more pronounced decrease in viscosity. In fact, when designing the ink formulation, the dispersant caused a large drop in viscosity is a very practical indicator of dispersant dispersibility, A3, A4 has a significant role in the stability of the foam, which will inevitably increase the amount of defoamer, and defoaming The increase in dosage may lead to an increase in defects such as fish eyes and shrinkage holes. In addition, the water resistance of A1 and A4 may be decreased due to their high hydrophilicity, which will also affect their drying performance. High dynamic surface tension and stable foaming tendency have a significant effect on the dispersion effect. In addition to the wetting and dispersing agent added, the effect on the film forming performance of the ink should also be considered while improving the dispersion performance.
The experimental results show that when w(A2) = 0.5%, the desired dispersion effect and good film forming performance can only be achieved while the surface tension is significantly reduced. Of course, adjusting the amount of auxiliaries may improve the performance of the auxiliaries.
2.3 Influence of cosolvents
Reducing the viscosity and surface tension of the system can improve the dispersion effect. It was found that when some cosolvents were added, the viscosity of the system was decreased while the initial dryness was increased, thus further examining and comparing the water-water compatibility. Good solvent properties.
The results demonstrate that the co-solvent has good solubility for both R1 and the alcohol solvent for R1. Therefore, YM-3 is still based on the formula, using the common industrial isopropyl alcohol as a co-solvent, with surfactants A2 and A2 mixed with isopropyl alcohol for the comparison test. The test results show that the use of alcohol or A8 alone can reduce the surface tension and achieve similar performance. When w (isopropanol) = 5%, it reduces the surface tension, improves the wetting properties and the printing film. The effect can be the same as when w(A8) = 0.5%, and defects such as pits are not found, providing a basis for reducing costs. For prints with low requirements for VOCs, wetting agents may be partially used in the ink system.
2.4 Effect of grinding temperature
From the process of grinding and dispersing, it was found that for a given system, in the case of different cooling water, a small temperature increase in the grinding will significantly reduce the viscosity of the system. After 10-15 minutes of grinding operation, the color paste viscosity Will be reduced to the system from laminar flow state to turbulent flow, when the dispersion effect is replaced by the mixing effect, it can be observed at this time the sand in the grinding tank is in a sliding state. After discharging, it can be seen that the sand grains have been excessively worn out. .
The other is that in the case of increasing the cooling water, due to the low dispersion power of the test equipment, the abrasive material formula determined by the pour point technology has a high viscosity in the grinding process, hindering the effective movement of the sand, and even causing sand grinding. Blocked. In both cases, the dispersion effect was significantly reduced. From the dispersion of carbon black, it was found that excessively high temperature grinding (above about 60° C.) also caused serious ink loss. After a series of comparative tests, the temperature of the grinder was controlled at 30-50°C by adjusting the amount of cooling water, and the temperature rose to this range. Due to the decrease of viscosity, the dispersion of the pigment-based color paste was allowed to be higher. In addition, from the perspective of diffusion, The higher temperature grinding is more conducive to the wetting of the pigment and allows the paste to have a higher base material fraction.
3 Conclusion
Due to the high surface tension and easy foaming, the dispersion of ink is more difficult than that of solvent-based inks. The use of a mature flow point technique to obtain good results in the dispersion and dispersion of inks shows that higher pigment base ratios can improve dispersion. Effect and dispersion efficiency. At the same time, efficient aqueous wetting and dispersing agents and co-solvents can greatly reduce the surface tension and viscosity of aqueous systems, and improving the wetting performance of pigments by the binder system can increase the dispersion efficiency. In addition, the temperature control when the ink is dispersed is also an important factor that affects the dispersion.
Through the experiment to get the best formula, namely mP1 = 33g, taking into account the stability of the pigment after dispersion, base material mass fraction of 20%, the base ratio of 2.5:1, mR1 = 44g, m water = 20.5g, m isopropanol = 2g, mA2 = 0.3g, mA5 = 0.5g.
Source: China Tobacco Packaging Ink Information Network
