We found that sometimes when we peel off the print from the injected resin, ink remains on one side or sometimes on both sides. Why does this occur?

In the case of ink remaining on the substrate, adhesion to the injected resin is poor. When ink remains on the injected resin, the adhesion to the substrate is poor. This is delamination. When ink remains on both sides, adhesion to substrate and injected resin are good, but the cohesion of the ink layer is poor. This is a cohesion failure.