Polyurethane
Ink Binder is a key component of the ink system, and its performance directly determines the final quality and applicability of the ink. It plays multiple core roles in ink, and its specific functions can be summarized as follows:
1. Bearing and connection function (core function)
Binder, as the name suggests, its most fundamental function is to serve as the "carrier" and "connector" of pigments. It evenly encapsulates and disperses tiny, solid powder-like pigment particles, forming a stable fluid system suitable for printing. During the printing and drying process, the binder firmly adheres the pigment to the surface of the substrate through physical or chemical changes, forming a solid ink film. Without a binder, the pigment will not be able to adhere, and the ink will lose its function as a medium for transferring graphics and text.
2. Determine the adhesion of the ink
Polyurethane binders, through the polar groups in their molecular structure, can generate strong intermolecular forces with the surfaces of various substrates (such as plastic films, metals, paper, etc.), including van der Waals forces, hydrogen bonds, etc., thereby achieving excellent adhesion. Especially for non-absorbent and hard-to-adhere plastic substrates (such as PET, BOPP, NY, etc.), through formula design, polyurethane binators can provide targeted and strong bonding effects, preventing printed patterns from falling off during subsequent processing or use.
3. Provide excellent wear resistance and flexibility
The polyurethane molecular chain is composed of soft segments and hard segments. This special microphase separation structure endows its polymer material with unique properties. The soft segments provide elasticity and flexibility, enabling the dried ink film to withstand deformations such as bending, folding, and squeezing without cracking. Hard segments provide strength and wear resistance, enabling printed matter to withstand external friction and scratches, thereby ensuring the integrity and durability of the pattern during transportation, packaging and use. This is crucial for packaging products that require subsequent processing, such as bag-making and lamination.
4. Regulate the rheological properties and printability of the ink
The rheological properties of the binder, such as viscosity, stickiness and fluidity, directly affect the transfer, transfer and leveling behavior of the ink on the printing press. Polyurethane binders can precisely control the rheological properties of the ink by adjusting the molecular weight and solid content of the resin, enabling it to adapt to different printing speeds and plate depths. This ensures that the ink can be evenly and smoothly transferred onto the substrate, forming exquisite patterns with clear Outlines and complete dots.
5. Endow with resistance
Depending on the final use, packaging materials may need to be resistant to water, grease, chemicals or high temperatures, etc. After complete reaction and curing, polyurethane binder can form a three-dimensional network structure with high crosslinking density and stable chemical properties, thereby providing excellent water resistance, oil resistance, chemical solvent resistance and anti-sticking property for the ink. Through special modification, high performance such as resistance to boiling and steaming can also be achieved.
6. Participate in curing as a reaction component
In two-component polyurethane inks, the binder itself usually contains hydroxyl groups, which act as the main agent and need to be mixed with the isocyanate component as the curing agent. After mixing, the two undergo cross-linking and curing reactions, generating a network polyurethane structure. This chemical reaction greatly enhances the mechanical strength, resistance and adhesion of the ink film, and is a key approach to obtaining high-performance ink.
