How could Polyurethane resin enhance adhesion in plastic printing inks

Polyurethane resin enhances adhesion in plastic inks through its unique chemical structure and physical properties.This process involves multiple aspects, from molecular-level interactions to improvements in macroscopic physical properties. Specifics are as follows:

1. Chemical Bond Formation:
   • Polyurethane resin contains reactive functional groups, such as carbamate and allophanate. These groups can chemically react with corresponding functional groups on the surface of plastic substrates, forming strong chemical bonds. The formation of these chemical bonds directly improves the adhesion of the ink.
   • By introducing urea links, polyurethane-urea resin (PUU) is formed, which not only enhances the dispersion wetting performance to pigments but also strengthens the interaction force with the plastic substrate.
2. Enhancement of Mechanical Keying:
   • Polyurethane binder can endow ink with excellent flexibility. This is particularly important in the field of flexible packaging printing because it ensures that the ink film does not crack or peel off due to bending of the substrate, thereby maintaining good adhesion.
   • By adjusting the ratio and structure of soft and hard segments in the polyurethane formula, polyurethane resins of different hardness can be synthesized. This helps to select the most appropriate ink formula for different plastic substrates to optimize adhesion effects.
3. Compatibility Improvement:
   • Polyurethane resin is compatible with most other resins such as vinyl chloride acetate resin, nitrocellulose resin, etc. This compatibility not only simplifies the design of ink formulas but also improves the overall performance of the final ink product, including adhesion.
   • In ink formulations, polyurethane resin, as a binder, is well-matched and compatible with other ingredients, contributing to the formation of a uniform and stable ink system, which is crucial for achieving good printing results and adhesion.
4. Surface Tension Adjustment:
   • Polyurethane resin can improve the matching of surface tension between ink and plastic substrate. By reducing the surface tension of the ink, it more closely approaches the surface free energy of the plastic substrate, thereby increasing the mutual attraction and adhesion between the two.
5. Enhancement of Water and Chemical Resistance:
   • Water-based polyurethane ink, due to its special chemical structure, not only provides good adhesion to plastic flexible packaging films but also has excellent water resistance. This characteristic allows the ink to maintain strong adhesion even when exposed to water or other liquids, preventing it from being washed off.
   • Due to the chemical resistance of polyurethane resin itself, inks using this resin can also maintain good adhesion and integrity when faced with chemical cleaners or other corrosive substances.

In summary, the application of polyurethane resin in plastic inks enhances the adhesion to plastic substrates through a combination of mechanisms, based not only on its unique chemical structure design but also on its excellent physical properties and good compatibility with other resins.