Application of Polyurethane Resin in Plastic Printing Ink

The liquid portion of the ink composition is referred to as a binder; the solids are pigments (pigments or dyes); and various additives. The binder is a gel-like fluid with a certain viscosity. Its role is first as a carrier of pigments. The powdery pigments and other solid particles are mixed and connected, and the pigment is uniformly dispersed therein, relying on its wetting effect. , It is easier to be finely ground on the grinding machine; secondly as a binder, the pigment can be finally fixed on the surface of the substrate, so as to achieve the purpose of displaying characters, images, marks, decorations, and the like. Also relying on its adhesion, ink can be transferred and transferred on the press. Finally, on the prints, the binder also functions as a protective film and exhibits the necessary gloss and can even have the effect of protecting the substrate.

The quality of the connecting material directly affects the performance of the ink, because the connecting material largely determines the viscosity, viscosity, dryness, and fluidity of the ink. To get high quality inks, you must use high quality binders. The various properties of the ink binder determine the various uses of the printing ink to suit the performance. The resins used for the plastic gravure printing ink generally include chlorinated polypropylene, polyamide, polyurethane and the like. For a long time, chlorinated polypropylene occupies more than half of the market for gravure composite inking ink resins because of its low price and excellent adhesion to OPP. However, the biggest drawback is that the main solvent is toluene, which is usually an environmentally friendly solvent such as an ester. Alcohols and alcohols do not help them. Solvent-based polyurethane ink binders have the advantages of easy use, stable performance, strong adhesion, excellent gloss, and good heat resistance, and can be adapted to various printing methods, especially for screen printing, plastic packaging and laminated films. aspect. Foreign countries have realized industrialization in the 1970s, such as Japan's Toyo Corporation, Daeki Ink Chemical Industry and Takeda Pharmaceutical. The polyurethane ink binders used in China are generally imported from overseas and used for processing. Demand reaches 30,000 tons. In recent years, many domestic production and research institutes have been engaged in the research of polyurethane ink binders and have achieved good results. For example, 121 °C and 135 °C steamed ink binders have been put into production and widely used in the market. , However, the overall performance of the product has a certain gap compared with imported products. Enhancing the overall performance of the product and developing multifunctional products are the focus of domestic research on the connection of polyurethane inks. Beijing Gaomeng Chemical Co., Ltd. has conducted in-depth research on polyurethane ink binders from the structural features and functionalities of polyurethanes, and developed a good glossiness, high cohesive strength, and a good phase with pigments. The polyurethane ink connecting materials with the characteristics of compatibility, good compatibility with alcohol solvents, etc., were put into the market for better response.

The polyurethane resin used in the ink is generally made of a polyester/polyether polyol and an isocyanate, and has a molecular force of about 20,000 to 40,000. Its solvents are mainly benzene, ketone, ester solvents as the main solvent. In the research and development process, according to the environmental requirements of the ink factory and the printing factory, the corresponding benzene-free ink resin can be prepared by using a keto ester solvent or an alcohol ester solvent.

Ink polyurethane resin features

1. Excellent yellowing resistance

In the preparation process, the polyurethane resin for printing ink mainly uses aliphatic polyester and aliphatic isocyanate as the main raw materials for synthesis. Compared with aromatic polyurethane, it has excellent optical stability, and the film has excellent yellowing resistance after film formation.

2. Excellent adhesion fastness to film substrates

Polyurethane resin ink segment contains polar groups such as carbamate, allophanate ester, ester bond, ether bond, and polar groups formed on the surface of many polar substrates such as PET, PA, etc. Hydrogen bonds, in turn, form a linker with a certain degree of linking strength. After the polyurethane resin is made into an ink, it is printed on a polar plastic substrate surface with excellent adhesion fastness.

3. Good affinity and wettability with pigments/dye

Polyurethane resins for inks are generally prepared from polyester or polyether polyols, alicyclic diisocyanates and diamine/diol chain extenders and have a molecular weight of about tens of thousands. Due to the introduction of the urea bond in the PU resin, a polyurethane-urea resin (PUU) is formed so that it has good dispersion wetting properties to the pigment.

4. Good resin compatibility

The polyurethane resin for ink has good compatibility with aldehyde and ketone resin, chloroacetic resin, etc. The user can add it according to the actual situation and his own craft formula to improve the ink's overall performance.

5. Excellent film formation

Ink polyurethane resins are structurally different from polyurethane resins used in other fields. Traditional polyurethanes mainly react with polyester polyols/polyether polyols with isocyanic acid to produce hydroxyl terminated polyurethane resins. The polar groups in the molecular structure are carbamates. Mainly ester, molecular cohesion is insufficient to meet the filming performance requirements of ink resin. Therefore, the use of polyurethane resins for inks to introduce urea groups on the basis of conventional polyurethanes greatly improves the cohesive strength and film-forming properties of the resins themselves.

6. Wide compatibility of organic solvents and good solvent release

Solubility of the organic solvent to the resin is achieved by the polarity of the solvent molecule attracting solute molecules, which is commonly known as the same type of miscibility; traditional polyurethane resin has extensive compatibility with organic solvents, ketones, esters, benzenes, etc. Non-alcoholic organic solvents are excellent solvents. However, in the process of making ink, in order to adjust the ink flowability and viscosity, the addition of alcohol organic solvents is indispensable. For traditional polyurethane resins, the addition of alcohol solvents greatly reduces the stability of the resin system, and often appears turbid, Incompatibility such as flocculation. However, due to the presence of urea groups, polyurethane resins for inks have made their compatibility with alcohols a reality. However, it is worth pointing out that alcohol solvents are still spurious solvents. In the microscopic state, alcohol solvents encapsulate polyurethane resin molecules instead of In the true solvent, the polarity of the molecule penetrates the molecule, making the ink produced from the urethane resin more fluid.