New Generation Aqueous Ink Base Material for Packaging Film and Paper (3)

Reversibility

The polymer particles were mixed at different ratios (large/small, mass ratios) and the reversibility was measured when they contained no or 10% and 30% hard or soft oligomers. The results are shown in Table 4.

The results showed that all the samples had poor reversibility and were irreversible when no oligomer was added, indicating that the polymer had started to coalesce after being dried at room temperature for 1 h. However, most samples showed good reversibility when containing oligomers. This oligomer is adsorbed on the surface of the particles, providing the particles with additional static and steric stabilizing properties, thus delaying the coalescence stage during film formation. In addition, due to its hydrophilic nature, water layers remain around the particles. It was found that slightly better reversibility can be obtained when using more hydrophilic high Tg oligomers, thus further confirming the above viewpoint. Especially at low oligomer content, there is a clear correspondence between total surface area SA (particle size and mixing ratio) and reversibility. This shows that the reversibility is not a surface feature as much as the system's identity, which is consistent with the fact that oligomers are attracted to the surface of the particles to provide static electricity and partially sterically hindered repulsive forces.

From the results in Table 4, it can also be found that at low surface areas (ie, high ratios of large/small particle sizes), the reversibility seems to be independent of the surface area, so that the correspondence can be divided into two different parts. The most important conclusion that can be obtained from the above example is that the reversibility is greatly affected by the total surface area (such as particle size and particle size distribution), and the reduced surface area (more large particles or larger particles) can be better reversible Sex, especially at low oligomer levels. In some literature it is recommended to use a small particle size latex to obtain the best ink base properties. This result, however, shows that the use of two sizes of base material can reduce the amount of oligomer needed to obtain good reversibility. Reducing the amount of water-sensitive oligomers can improve the durability of the film.

In addition to the addition of 10% oligomers, the lowest turning point was found at the L/S of 80/20 on the curve, and in the absence of oligomers, there was a double continuous phase and the smallest void volume ( See Figure 7). With the addition of 30% oligomers, the lowest point of the curve is also present at the size ratio 80/20. This phenomenon can be explained by the fact that at low oligomer levels, the surface of the particles may not be fully covered with oligomers, which may cause bridging flocculation, causing a change in particle packing.

Film formation Measure MFFT with a mixture of large and small particles and mixed systems containing 0, 10%, or 30% hard or soft oligomers, respectively. The results are shown in Figure 6.

At higher oligomer concentrations, the particles are completely covered by oligomers, which prevent the formation of bridge flocculation. This also has good particle filling characteristics, and low concentration oligomers have no major effect on the absolute value of MFFT. In the presence of high Tg oligomers in the presence of high concentrations of oligomers, all MFFT values ​​increase (however MFFT increase is still not much), whereas in the case of low Tg oligomers, they have With the same particle Tg, MFFT decreases. Although the oligomers have the same Tg as the polymer particles, they can still reduce the MFFT because the oligomers have lower relative molecular mass and higher acid content, which leads to greater water plasticity of the polymer particles. Thereby, the film forming property is better.

Fig. 7 shows that when the Tg and composition of the large and small particles are different, different surface and host compositions can be obtained. Therefore, when the small particles are hard and the large particles are soft, the coating shows a low MFFT (subjects with low Tg size particles). In the main, it still has good anti-adhesion (rich in small high Tg particles on the membrane surface). A good example of such a polymer is NeoCry A-1110, an ink base containing two forms of PSD (50% solids) for low quality substrates. Figure 8 shows the model of NeoCry A-1110.

Figure 5 Solid content versus time for oligomers/polymer systems and pure oligomers containing single and large PSDs