Printing ink is a mixture formed by the uniform dispersion of components such as resin binder, pigment (filler), additives and solvents. Resin binder, as the "heart" of ink, mainly plays the role of dispersing pigments and connecting substrates.
Polyurethane Resin as an
Ink Binder has the following advantages:
(1) Flexibility
In the field of flexible packaging printing, as the printing substrate is flexible materials such as PE, OPP, and PET, the ink film should not be too brittle after formation. Polyurethane resin can endow the ink with excellent flexibility. In fact, by adjusting the proportion and structure of soft and hard segments in the polyurethane formula, polyurethane resins of different hardness can be synthesized to meet the requirements of various types of inks.
(2) Resin compatibility
To achieve the optimization of ink performance, the resin binders in most ink formulations are often composed of a mixture of several resins, which requires good matching and compatibility among different resins. Polyurethane resin is compatible with most resins such as chlorinated vinyl acetate resin, nitrocellulose resin, acrylic resin, polyketone resin, chlorinated polypropylene resin, etc., thus enabling the preparation of different types of polyurethane inks.
(3) Adhesion
Due to the presence of polar groups such as carbamate (-NH-COO-) and ester group (-COO) in the molecular structure of polyurethane, it has good adhesion to the surfaces of paper, plastic and metal. As a polyurethane binder for ink, it usually increases the molecular weight of the resin (about tens of thousands) and polar groups, thereby enhancing the adhesion of the resin to the substrate.
(4) Pigment dispersibility
Pigments are insoluble in the ink medium. The finer the pigments are dispersed, the better the tinting strength of the ink will be. This requires that the resin has good dispersibility for pigments. Generally, introducing urea groups into polyurethane molecules to form polyurethane-polyurea resin (PUU) can significantly enhance the resin's wetting and dispersing properties for pigments.
(5) Low odor
For some special packaging, the printing ink is required to have a low odor. However, for some products such as acrylic resin and maleic acid resin, which have a strong odor themselves, it is difficult to meet the customer's requirements after being made into ink. Polyurethane ink binder is a low-odor resin and can meet the requirements of low-odor ink.
