Research on Polyurethane Adhesives for Plastic Printing Ink (Part Two)

2.2 Viscosity Control

The viscosity of the adhesive has a certain influence on the manufacturing process and performance of the ink. We controlled the viscosity of NCO and OH and NH2 in raw materials by controlling the molar ratio of NCO to OH and NH2 in the raw material (this can control the molecular weight of the finally obtained binder within a certain range). On the other hand, the viscosity is close to the late stage of the synthesis reaction. When the desired value is reached, a monofunctional amine reaction terminator is added to stop the reaction quickly, and the viscosity of the product can be effectively controlled within a certain range.

2.3 Storage stability

Regardless of the ink or the adhesive used, their storage stability is of significant importance. Therefore, we conducted a storage stability test on the obtained adhesive and ink samples. The method is as follows: Take a certain weight of the adhesive and ink sample in a metal container, keep it tightly at room temperature, observe its appearance, and measure its viscosity change over time. After three months of storage under the above conditions, the adhesive sample we prepared and the resulting ink exhibited a large change in appearance and viscosity, and it was considered that the storage stability was satisfactory.

2.4 Adhesion test

A white ink made of a binder with different proportions of PPG and PVHA copolymers was printed on a base film such as OPP, PET, and NYLON with a corona-treated surface, and the adhesion between the ink and the base film was tested. The specific test method is as follows: After printing, the sample is fully dried at 40-50° C. and left for 24 hours. Then the adhesive tape is applied on the printing surface, and the sample is rapidly peeled after being fastened. The surface state of the printed film after peeling was observed. Visual measurement standards: ○: 90% or more of printed film residues; □: 60-90% of printed film residues; △: 60% or less of printed film residues. The observations are as follows:

It can be seen from Table 2 that the ink made of pure polyurethane adhesive (ie, 100/0 sample of PPG/PVHA) has poor adhesion to the OPP film; after introducing a certain proportion of PVHA segments into the molecular chain, the ink The base films listed in the table all have good adhesion; however, if the proportion of PVHA segments is too high, the adhesion of the ink to the PET film may be degraded. In summary, we chose PPG/PVHA ratio around 70/30 in the synthesis.

3 Conclusion

A novel urethane adhesive for inks is produced by introducing a certain proportion of hydroxyl group-containing vinyl chloride-hydroxyethyl acrylate copolymer segments into the polyurethane molecular chain. The inks prepared therefrom have good adhesion to base films such as OPP, PET, NYLON, etc., making their use more extensive than the original, thereby effectively improving the quality of the ink.


Source: Print Chemicals Network