English
日本語
한국어
français
Deutsch
Español
italiano
русский
العربية
ไทย
हिंदी
Selecting the appropriate resin to enhance ink adhesion requires a comprehensive consideration of factors such as substrate characteristics, ink drying methods, and application scenario requirements. Key dimensions to evaluate include the resin’s polarity, film-forming properties, molecular weight, crosslinking characteristics, and compatibility. The specific methods are as follows:
The foundation of adhesion lies in the interfacial forces between the resin and the substrate. The resin’s polarity should align with that of the substrate:
Polar substrates (e.g., paper, metal, glass, PET/PA plastics): Prioritize resins containing polar groups (e.g., hydroxyl, carboxyl, amino, epoxy groups), such as alkyd resins, polyurethane resins, epoxy resins, and polyamide resins. For example, paper fibers contain abundant hydroxyl groups, and polar resins can form hydrogen bonds with them to enhance adhesion. Metal surface oxide layers (polar) can chemically adsorb with epoxy groups in epoxy resins, resulting in stronger adhesion.
Non-polar substrates (e.g., PE, PP plastics): Opt for low-polarity or modified resins (e.g., chlorinated polypropylene, polyolefin graft resins). Their molecular structure is more similar to that of non-polar substrates, enhancing adhesion through van der Waals forces. Avoid using polar resins on non-polar substrates, as this may cause ink rejection and detachment.
The continuity of resin film formation and drying speed directly impact adhesion effectiveness:
Film-forming properties:
Choose resins with uniform molecular weight distribution and a moderate glass transition temperature (Tg). Excessively low molecular weight may result in weak film strength, while excessively high molecular weight can lead to poor flow and inadequate substrate wetting. A Tg that is too high may cause film brittleness and cracking, while a Tg that is too low may result in a soft film with poor abrasion resistance (e.g., low-Tg resins for soft PVC printing, medium-to-high-Tg resins for rigid substrates).
Drying method compatibility:
—Solvent-based inks: Select resins compatible with solvent evaporation rates (e.g., fast-drying solvents paired with fast-dissolving resins) to avoid issues like "surface drying too quickly leading to incomplete internal curing" (false drying) or "drying too slowly causing smudging."
—UV/EB-curable inks: Prioritize resins with high unsaturated double-bond content (e.g., acrylate resins) to ensure rapid crosslinking and film formation under radiation, locking pigments into a three-dimensional network structure.
—Oxidative drying inks (e.g., alkyd resins): Ensure the resin contains an appropriate proportion of unsaturated fatty acid chains to facilitate sufficient oxidative crosslinking and form a tough film.
Crosslinking resins form a three-dimensional network after curing, significantly improving adhesion and resistance properties. They are suitable for demanding applications (e.g., outdoor, abrasion-resistant printing):
Chemically crosslinking resins: Examples include epoxy resins (requiring amine-based hardeners) and polyurethane resins (containing isocyanate groups that react with substrate hydroxyl groups). After crosslinking, the film exhibits greatly enhanced water and abrasion resistance, making it ideal for hard substrates like metal and plastics.
Self-crosslinking resins: Examples include acrylic resins containing hydroxyl/carboxyl groups (self-crosslinking at high temperatures). These do not require additional hardeners, making them suitable for applications where process simplicity is prioritized (e.g., paper, wood printing).
Note: Crosslinking density should be moderate, as excessive crosslinking may cause film brittleness and reduce adhesion durability.
The resin must mix uniformly with pigments, solvents, and additives to avoid adhesion defects caused by poor compatibility:
Compatibility with pigments: Choose resins with good pigment wetting properties (e.g., amine-containing polyamide resins for organic pigments) to ensure the resin encapsulates pigment particles and anchors them to the substrate surface. Poor compatibility may lead to pigment flocculation or precipitation, causing "powdering."
Solvent compatibility: The solvent must fully dissolve or disperse the resin (e.g., polar solvents for polar resins, non-polar solvents for non-polar resins) to avoid resin precipitation and uneven film formation. For example, acrylic resins require medium-polarity solvents like esters or ketones, while chlorinated polypropylene requires non-polar solvents like toluene.
Synergy with additives: When using adhesion promoters (e.g., silane coupling agents), ensure compatibility with the resin to avoid disruptions in film formation.
Outdoor weather resistance: Choose resins resistant to UV light, acids, and alkalis (e.g., fluorocarbon resins, silicone-modified acrylic resins) to prevent resin degradation and adhesion failure in long-term outdoor environments.
Food contact applications: Select resins compliant with food safety standards (e.g., water-based polyurethane, modified polyester resins) to ensure no migration of harmful substances while maintaining adhesion to packaging substrates (e.g., PE, aluminum foil).
High-speed printing processes: Opt for low-viscosity, high-fluidity resins (e.g., low-molecular-weight acrylic resins) to ensure sufficient substrate wetting and rapid adhesion during fast printing, avoiding smudging.
The core logic for resin selection is: "Match polarity with the substrate, align film-forming properties with drying methods, enhance strength through crosslinking, and ensure uniformity through compatibility." Additionally, consider the specific application scenario’s resistance and processability requirements. Validate adhesion effectiveness through small-scale tests (e.g., cross-hatch adhesion test, friction test) to ultimately determine the optimal resin type.
