Polyurethane (polyurethanes, abbreviated PU) is a kind of polymer with -NHCOO-repeat structural unit as the main chain. Isocyanate (monomer) is polymerized with a hydroxyl compound.Due to the strong polarity of the carbamate group, insoluble in non-polar groups, with good oil resistance, toughness, wear resistance, aging resistance and adhesion. Materials suitable for a wide temperature range (-50 -- 1500℃) can be prepared with different raw materials, including elastomer, thermoplastic resin and thermosetting resin. It is not resistant to hydrolysis or alkaline medium at high temperature.

Adding polyurethane resin to the ink can improve the wettability of the ink to the pigment, and the film is good, the ink film is fast and wear-resistant, and it is used in the manufacturing of offset printing and water-based ink, but the price is higher.

The polyurethane resin used for printing ink is generally made of polyester/polyether polyol and isocyanate reaction, molecular weight of about 20,000 ~ 40,000. Its solvent mainly to benzene, ketone, ester solvent as the main solvent. In the process of research and development according to the ink factory and printing plant environmental protection needs, using ketone ester solvent or alcohol ester solvent to prepare the corresponding benzene free ink resin.

The characteristics of polyurethane resin for printing ink are as follows:

①Excellent yellowing resistance. The polyurethane resin for printing ink is synthesized by aliphatic polyester and aliphatic isocyanate as the main raw materials in the process of preparation. Compared with aromatic polyurethane, it has excellent optical stability, and the film has excellent yellow resistance.

②Excellent adhesion fastness to film substrates. Ink with polyurethane resin molecular chain segment contains carbamate, urea formate, ester bond, ether bond and other polar groups, and a variety of polar substrates PET, PA and other plastic surface polar groups to form hydrogen bonds, and then the formation of a certain connection strength of the joint. The polyurethane resin made of ink, printing on the surface of polar plastic substrate has good adhesion fastness.

③Good affinity and wettability with pigments/dyes. Polyurethane resin for printing ink is generally prepared by polyester or polyether polyols, aliphatic diisocyanate and diamine/diol chain extender. Due to the introduction of urea bond in PU resin, polyurethane monourea resin (PUU) is formed, which makes it have good dispersion wettability for pigments.

④Good resin compatibility. Ink with polyurethane resin and aldehyde-ketone resin, chloro-vinegar resin has a good compatibility, according to the actual situation in their own process formula appropriate to add, in order to improve the comprehensive performance of ink.

⑤Excellent film forming properties. Ink polyurethane resin and other fields of polyurethane resin used in the structure is different, the traditional polyurethane is mainly polyester polyol/polyether polyol and isocyanic acid reaction to generate hydroxy-terminated polyurethane resin, the molecular structure of the polar groups are mainly carbamate, molecular cohesion is not enough to meet the ink resin film performance requirements. Therefore, the ink with polyurethane resin in the traditional polyurethane based on the introduction of urea, in order to greatly improve the cohesion strength of the resin itself and film.

⑥The solubility of organic solvent is widespread and the solvent releability is good. The dissolution of resin by organic solvent is attracted to solute molecules by the polarity of solvent molecules, which is commonly referred to as homogeneous dissolution. Traditional polyurethane resins are soluble in organic solvents widely, and non-alcoholic organic solvents such as ketones, esters and benzenes are excellent solvents. But in the process of making ink, in order to adjust the ink flow performance and viscosity, need to add alcohol organic solvent, so for the traditional polyurethane resin will greatly reduce the stability of the resin system, there will be turbidity, flocculent precipitation and other insoluble phenomenon. But the ink with polyurethane resin due to the existence of urea and alcohol soluble, but pay attention to alcohol solvent is still false solvent, alcohol solvent in the microscopic state of polyurethane resin molecules wrapped, rather than the true solvent as the molecular polarity through the molecules, so that the ink made of polyurethane resin is good fluidity.

In view of the above variety of polyurethane resin application structure, Sinograce Chemical company has developed polyurethane resin series and high-performance polyurethane resin ink series products, which can provide our customers with a variety of ink solutions.