Impact of Ink Composition and Parameters on Inkjet Printing Systems
From the perspectives of pigment–resin interactions, substrate/nozzle plate interfaces, and ink chemical properties, ink-related issues in inkjet printing systems can be summarized into the following key areas:
I. Compatibility Issues in Pigment–Resin Systems
1. Resin Binder Selection
Pigments must be chemically compatible with the resin binder (such as acrylic or polyurethane resins).
If resin polarity is mismatched, pigments may disperse unevenly, leading to sedimentation or color deviation.
Example:
- Acrylic pigments are well suited to acrylic resin systems, but when applied to polyolefin substrates, phase separation is likely to occur.
In two-component inks, resin crosslinking reactions after mixing may accelerate pigment precipitation, making strict ratio control essential.
2. pH Sensitivity
In water-based inks, pH fluctuations (especially outside the pH 8–10 range) can cause anionic pigment flocculation, resulting in:
- Deposits forming on the nozzle plate surface, leading to clogging
- Batch-to-batch color inconsistency during printing
II. Substrate–Nozzle Plate Interface Effects
1. Surface Tension Matching
The substrate surface energy should be greater than 38 mN/m (often achieved through corona treatment).
Insufficient surface energy leads to poor ink wetting, which can cause:
- Droplet retraction during jetting, forming satellite dots
- Pigment accumulation along the edges of the nozzle plate
2. Pigment Particle Size Control
For ceramic printheads, pigment particle size must be below 200 nm. Otherwise:
- Oversized pigment particles may abrade the micro-nozzles
- Ink supply system pressure abnormalities may occur
III. Mixing Risks in Two-Component Ink Systems
1. Reactive Compatibility Conflicts
Exothermic reactions between curing agents (such as isocyanates) and resins may:
- Trigger thermal degradation and discoloration of pigments
- Generate gas bubbles, leading to jetting interruptions
2. Storage Stability Control
Reaction inhibitors must be added to slow down reaction rates. Without proper stabilization:
- Ink viscosity may increase sharply within 24 hours after mixing
- Ink supply lines and channels may become blocked
Characteristics and Application Analysis of Oil-Based Inks
Oil-based inks exhibit the following key characteristics and application scenarios:
1. Application Scenarios
Suitability for Porous Substrates
Oil-based inks are well suited for coding, marking, and high-speed printing applications (such as Riso printing), as well as for ceramic tiles and other substrates that require rapid ink absorption.
Compatibility with Piezoelectric Printheads
These inks are specifically formulated for piezoelectric inkjet printheads. They do not contain the highly volatile components required for thermal inkjet (TIJ) systems, making them more suitable for industrial-grade, stable output.
2. Material Composition
Solvent System
Oil-based inks typically use long-chain glycols, hydrocarbons, and vegetable oils as base solvents. These components provide excellent fluidity, adhesion, and print stability.
Environmental Considerations
Vegetable-oil-based solvents may reduce VOC emissions compared with traditional oil-based inks. However, the overall environmental performance depends on the specific ink formulation.
3. Drying and Penetration Performance
Fast Drying Behavior
Oil-based inks achieve rapid drying through capillary absorption into porous substrates, significantly reducing drying time and making them ideal for high-speed printing applications.
Droplet Control
By adjusting solvent ratios and additives (such as resins), droplet spreading and penetration can be optimized, improving print sharpness, edge definition, and overall clarity.
4. Comparison with Other Ink Types
Compared with Water-Based Inks
Oil-based inks offer stronger adhesion and better weather resistance on non-absorbent substrates such as plastics and metals. However, their environmental performance is generally inferior to water-based inks.
Compared with Neutral Inks
Oil-based inks dry faster, but their color vibrancy may be slightly lower than that of neutral inks.
5. Areas for Improvement and Future Development
Environmental Upgrades
Further development of low-VOC, vegetable-oil-based formulations can help balance performance requirements with environmental regulations.
Substrate Adaptation
For special substrates such as ceramic tiles, further optimization of ink penetration and abrasion resistance is required.