Inkjet Coating Formulation Experiment Discussion

2 Results and Discussion

Porous ink-jet paints are mainly composed of an insoluble inorganic pigment particle and some adhesives. It may also contain some special additives to enhance the coating performance. There are more and more reports on new materials used for porous, high-gloss inking coatings.

In this paper, three different SiO2 particles, such as Colloidal SiO2, Sintered SiO2 and SiO2, are studied and their effects on various coating properties and properties are investigated. The average particle sizes of the three SiO2 particles were 95 nm, 278 nm, and 318 nm, respectively.

2.1 Effect on coating formulation

The basic formulation of the paint is polyvinyl alcohol as an adhesive, and the ratio of pigment to adhesive is 80/20. The formulation properties of the coating are shown in Table 1. Colloidal SiO2 and sintered SiO2 have the potential to achieve high solids content at lower Brookfield viscosity.

2.2 Effect on Coating Structure

The final coating structure is changed by changing the particle size of the particles. It is expected that the gloss of the coating will be inversely proportional to the particle size, and the gloss of the coating will decrease as the particle size increases. Calendering can be used to improve gloss and produce high gloss ink jet printing paper.

Figure 1 shows the gloss value of each particle before and after calendering in a hot/soft nip. As can be seen from Figure 1, sintered SiO2 has the highest gloss measurement. Its value is significantly higher than the smoke SiO2 with the same particle size, and it is further increased after calendering.

Inspection of the coated surface using a scanning electron microscope (SEM) was also expected. The surface image is always consistent with the measurement of gloss. The colloidal SiO2-based coated image shows minor cracks.

2.3 Effect on Printing Performance

The performance of an ink jet pigment is good for its printed image. The test pattern was printed on coated and calendered paper. FIG. 2 shows the ink density values ​​of the four colors of blue, red, yellow, and black (CMYB). The performance of all three SiO2 particles was compared. It can be seen from FIG. 2 that the concentration of the colloidal SiO2 and the sintered SiO2 black pigment ink is slightly higher.

In addition to cationic mordants, these pigments showed poor water resistance in the tests. Particle structure and pH have no effect on water resistance, which is controlled by the surface chemistry of SiO2. The addition of a cationic polymer such as poly DADMAC can improve the water resistance of these three particles, however, the colloidal SiO2 and sintered SiO2 particles reduce their surface gloss.

The study of print characteristics by image analysis techniques further illustrates the differences among the three SiO2 particles. Table 2 shows the image analysis results of the Epson printer.

From Table 2, it can be seen that the area of ​​the dot from top to bottom is significantly reduced. The smaller area is better, and the print resolution can be improved without losing the ink density. The test results of the dot roundness values ​​show that the sintered SiO2 coating has a more uniform coating structure. In contrast, the smoke SiO2 has a lower dot area due to its higher porosity, but irregular smoke particles produce a higher dot roundness value resulting in uneven coating.

Figure 3 shows the porosity of the three SiO2 particles. The porosity of colloidal SiO2 and sintered SiO2 is lower than that of smoke SiO2. This data is consistent with the observed dot area results.

The porosity of the colloidal SiO2-based coating is created by the interstitial porosity created by the spherical particles during the filling process. Sintered SiO2 with intercellular particle porosity is expected to have more porosity, but its porosity is only about 10% higher than that of colloidal SiO2. This may be due to the degradation of certain sintered SiO2 to its colloidal raw material. Smoke SiO2 exhibits the highest coating porosity. The final image quality requires a balance between coating porosity and coating uniformity. Although the print quality of colloidal SiO2 and sintered SiO2 coatings is acceptable, their lower porosity limits their effectiveness.

3 Conclusion

Colloidal SiO2 and sintered SiO2 particles have more advantages in the rheology, percentage of solid content, gloss, ink concentration, and dot roundness of the coating formulation than smoke SiO2. However, its coating exhibits a lower porosity. In contrast, smoke SiO2 with a rigid, irregular shape can produce more porous layers. However, it also reduces the gloss and the solids content of the coating formulation. In order to obtain a low-cost, high-gloss ink-jet paint, all factors must be balanced. (MA Yi / Translation)