Application of polyurethane binder in film printing ink

The liquid part of the ink component is called the binder; the solid component is the color material (pigment or dye); and various additives.The connecting material is a colloidal fluid with a certain viscosity. Its function is first to serve as a carrier for pigments, mixing and connecting solid particles such as powdered pigments. The pigments are evenly dispersed in it, relying on its wetting effect. , it is easier to be ground finely on the grinding machine; secondly, it serves as a binder to enable the pigment to be finally fixed on the surface of the substrate to achieve the purpose of displaying text, images, marks, decoration, etc.It is also relying on its adhesion function that the ink can be transferred and delivered on the printing press.Finally, on the printed matter, the connecting material also plays the role of a protective film, presents the necessary gloss, and can even protect the substrate.

The quality of the connecting material directly affects the performance of the ink, because the connecting material determines the viscosity, stickiness, dryness, fluidity and other properties of the ink to a large extent.If you want to get high-quality ink, you must use high-quality connecting materials.The various properties of the ink binder determine the various adaptability of the printing ink. The resins used in plastic gravure printing inks generally include chlorinated polypropylene, polyamide, polyurethane, etc.For a long time, chlorinated polypropylene has occupied most of the resin market for gravure composite back printing inks due to its low price and excellent adhesion to OPP. However, its biggest shortcoming is that its main solvent is toluene, and environmentally friendly solvents such as ester are usually used. Alcohol-based solvents are ineffective. Solvent-based polyurethane binder for ink has the advantages of easy use, stable performance, strong adhesion, excellent gloss, and good heat resistance. It can meet the requirements of various printing methods, especially suitable for screen printing, plastic packaging, and composite films. aspect.Industrialization has been achieved in foreign countries in the 1970s, such as Toyo Corporation of Japan, Dainippon Ink Chemical Industries, and Takeda Pharmaceuticals. The polyurethane ink connecting materials used in China are generally polyurethane rubber particles imported from abroad, and then processed and used. The demand reaches 30,000 tons.In recent years, many domestic production and scientific research units have been engaged in the research of polyurethane ink connectors, and have achieved good results. For example, units that can withstand 121°C and 135°C cooking ink connectors have been put into production and are widely promoted and used in the market. , but there is a certain gap between the comprehensive performance of the product and imported products. Improving the comprehensive performance of the product and developing multi-functional products are the focus of domestic research on polyurethane ink connecting materials.

The polyurethane resin used in ink is generally formed by the reaction of polyester/polyether polyol and isocyanate, with a molecular force of about 20,000 to 40,000.The solvents are mainly benzene, ketone and ester solvents.During the research and development process, ketone ester solvents or alcohol ester solvents can be used to prepare corresponding benzene-free ink resins according to the environmental protection needs of ink factories and printing factories.

Characteristics of polyurethane resin for ink

1. Excellent yellowing resistance

Polyurethane resin for ink is mainly synthesized from aliphatic polyester and aliphatic isocyanate as the main raw materials during the preparation process. It has excellent optical stability compared to aromatic polyurethane, and the film has excellent yellowing resistance after film formation.

2. Excellent adhesion fastness to film substrates

The molecular segments of polyurethane resin for ink contain polar groups such as urethane, allophanate, ester bond, and ether bond, which form with the polar groups on the surface of various polar base materials such as PET and PA. Hydrogen bonds, thereby forming joints with a certain connection strength.After the polyurethane resin is made into ink, it has excellent adhesion fastness when printed on the surface of polar plastic substrates.

3. Good affinity and wettability with pigments/dyes

Polyurethane resin for ink is generally prepared from polyester or polyether polyol, alicyclic diisocyanate and diamine/diol chain extender, with a molecular weight of approximately tens of thousands.Due to the introduction of urea bonds in PU resin, polyurethane-urea resin (PUU) is formed, which has good dispersion and wetting properties for pigments.

4.Good resin compatibility

Polyurethane resin for ink has good compatibility with aldehyde-ketone resin, chlorine-vinegar resin, etc. Users can add it appropriately according to the actual situation and their own process formula to improve the overall performance of the ink.

5．Excellent film forming properties

Ink polyurethane resin is structurally different from polyurethane resins used in other fields. Traditional polyurethane mainly reacts with polyester polyol/polyether polyol and isocyanic acid to form hydroxyl-terminated polyurethane resin. The polar group in the molecular structure is carbamic acid. Mainly ester, the molecular cohesion is not enough to meet the film-forming performance requirements of resin for ink.Therefore, polyurethane resin for ink introduces urea group on the basis of traditional polyurethane, which greatly improves the cohesive strength and film-forming properties of the resin itself.

6. Wide compatibility with organic solvents and good solvent release

The dissolving effect of organic solvents on resin is to attract solute molecules through the polarity of solvent molecules, which is commonly known as like miscibility; traditional polyurethane resin has a wide range of compatibility with organic solvents, such as ketones, esters, benzene, etc. Non-alcoholic organic solvents are excellent solvents.However, in the process of making ink, in order to adjust the flow performance and viscosity of the ink, the addition of alcoholic organic solvents is essential. For traditional polyurethane resins, the addition of alcoholic solvents greatly reduces the stability of the resin system, often causing turbidity, Incompatibility phenomena such as flocculent precipitation.However, the presence of urea groups in polyurethane resin for ink makes its compatibility with alcohol a reality. However, it is worth pointing out that alcohol solvents are still pseudo-solvents. In the microscopic state, alcohol solvents wrap the polyurethane resin molecules instead of Like a true solvent, the ink made from polyurethane resin has good fluidity due to the molecular polarity running through the molecule.

Applications of polyurethane ink resin

①Selection of solvent

During the ink manufacturing process, considering the volatilization gradient of the overall solvent system of the ink, to improve the solvent release of the printing ink and reduce the organic solvent residue of the printed product solvent, the solvents used are often several mixed solvents with different volatilities.The main organic solvents used in the ink manufacturing process include toluene, methyl ethyl ketone, cyclohexanone, ethyl acetate, butyl acetate, n-propyl acetate, isopropyl alcohol, etc. Customers can adjust the volatility of the ink according to seasonal changes. adjust.

②Selection of pigments

Due to the large differences in pigment grades on the market today, the dispersion and ink stability of the same pigment from different manufacturers of the same resin often vary greatly in polyurethane inks. Therefore, it is recommended that users base their actual needs on their own. Customers need to choose pigments carefully.

③Selection of additives

Wax powder: The wax powder used in the production of polyurethane ink is often low molecular weight polyethylene wax, with a relative molecular weight of generally 1000 to 6000. It has good solubility in the organic solvents in the ink and has affinity with the polyurethane resin itself. Better and has good chemical stability.It mainly serves to increase the friction resistance of the ink film surface, and at the same time, it can appropriately alleviate the anti-stick resistance of the ink itself.

Dispersant: A type of surfactant, mainly used to moisten the surface of the pigment, shorten the ink manufacturing time, facilitate the dispersion of the pigment, and sometimes appropriately reduce the oil absorption of the pigment.When manufacturing high-concentration ink, it can reduce the yield value of the ink and prevent the aggregation and precipitation of pigment particles in the ink.

Adhesion promoter: The polyurethane resin used for ink contains a large number of polar groups. Even if the surface of non-polar substrates such as BOPP and PE is treated with surface corona, the surface tension is generally between 38 and 42 dynes. To improve the adhesion of polyurethane ink, The adhesion fastness on the surface of this type of substrate often requires the appropriate addition of titanate coupling agents or chlorinated polypropylene adhesion accelerators.

Ink binder resin is an extremely critical raw material in the production of ink. It not only serves as a bridge between the color material and the base material, but also gives the ink various excellent physical properties.In ink production, choosing the right resin connecting material directly affects the performance of the ink on various substrates and the process adaptability during the printing process.When selecting resin, the physical properties of the resin must be fully considered to match the performance that the ink needs to achieve.

Polyurethane resin is a versatile material that can be used in the preparation of gravure printing ink for film. Gravure printing is a method of printing that uses engraved cylinders to transfer ink onto a substrate, and it is commonly used for high-volume printing applications such as packaging and labeling.

as a binder to provide adhesion and durability to the ink. It can also be used to adjust the viscosity and flow properties of the ink, which is important for ensuring consistent print quality and optimal ink transfer to the substrate.

We could provide solvent based polyurethane resin, polyurethane emulsion, acrylic resin, waterborne polyurethane dispersion to meet diversified requirement.

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