How to use this guide
This page is a practical decision aid for ink and coatings teams who need stable dispersion and predictable rheology from production to end-use. Use it to align formulation, process, QC, procurement, and EHS on:
- Dispersion success criteria (fineness, color strength, gloss, no flocculation)
- Stability success criteria (no hard-settle, minimal viscosity drift, no syneresis)
- Production robustness (reproducible grind time, heat management, filterability)
- Commercial readiness (COA limits, packaging, shelf life, change control)
Fast route to a stable ink system
If you share (1) ink type (waterborne/solvent/UV), (2) pigment(s), (3) resin/binder family, (4) target viscosity window, (5) application (flexo/gravure/screen/digital) and (6) storage conditions, we can propose dispersants, wetting agents, rheology modifiers, and defoamers with a trial plan and procurement-ready specs.
Where dispersion & stability fit in ink performance
Ink stability is not one parameter — it is the outcome of wetting, deagglomeration, surface stabilization, and rheology control across your full use-case: manufacturing, pumping, filtration, printing, drying/curing, and shelf storage.
What you optimize
- Consistent color strength and shade
- Stable viscosity window (printability)
- No hard-settle; easy remixing
- Filterability (no gel/fish-eyes)
- Uptime (less cleaning, less scrap)
What typically fails
- Settling / hard pack / sediment
- Viscosity drift (up or down)
- Flocculation → shade shift, poor gloss
- Foam / pinholes / craters
- Flooding/floating or rub-off
Four stages of a “good” dispersion
- Wetting: the vehicle/dispersant replaces air and liquid interfaces on pigment surfaces.
- Deagglomeration: milling/shear breaks pigment agglomerates to a controlled particle size distribution.
- Stabilization: dispersant prevents re-agglomeration via electrostatic and/or steric repulsion.
- Rheology control: yield stress and viscosity profile prevent settling without harming printability.
Commercial reality: Many stability failures are caused by “minor” raw material changes: pigment surface treatment, resin acid value, solvent blend, or dispersant molecular weight distribution. Procurement needs change control and measurable COA limits, not just a product name.
Ink families: what changes with waterborne, solvent, UV
| Ink system | Typical challenges | Common levers | Watch-outs |
|---|---|---|---|
| Waterborne | Foam, pH sensitivity, electrolyte effects, microbial risk, freeze/thaw | pH control, dispersant selection (ionic/steric), defoamer compatibility, biocide plan | Hard water, amine neutralization shifts, surfactant-driven foam |
| Solvent-based | Solvent power balance, resin compatibility, evaporation concentration changes | Solvent blend tuning, resin choice, dispersant polarity match | Flammability/VOC constraints; thickening from evaporation |
| UV/EB | High viscosity, oxygen inhibition (for some), cure interaction, photoinitiator compatibility | Low-viscosity oligomers/monomers, dispersants built for UV, controlled milling heat | Viscosity drift via post-reaction; pigment inhibiting cure |
Key additive roles (what to specify and why)
| Additive | Main job | Symptoms when wrong | Selection notes |
|---|---|---|---|
| Dispersant | Stabilize pigment; prevent flocculation and viscosity drift | Shade shift, loss of gloss, thickening, hard-settle | Match to pigment + binder; define dosage window; check compatibility with let-down |
| Wetting agent | Improve wetting on pigment/substrate; reduce craters | Poor wetting, fish-eyes, pinholes, poor transfer | Overuse can destabilize foam or reduce intercoat adhesion |
| Rheology modifier | Create yield stress to resist settling; control flow | Settling, sagging, poor leveling, stringiness | Choose based on system (water vs solvent vs UV) and shear profile |
| Defoamer | Control foam without craters | Foam, pinholes, craters, haze | Must be compatible; wrong defoamer can cause surface defects and separation |
| Biocide / preservative (waterborne) | Prevent microbial growth → viscosity drift/odor | Odor, gas, pH drift, viscosity change, spoilage | Use a program aligned to regulations and storage conditions |
Dispersion workflow (repeatable production method)
Most stability issues can be traced to inconsistent grind and poor let-down compatibility. Use the structured workflow below.
1) Premix (wetting & dispersion resin)
- Order of addition: vehicle/resin → dispersant → wetting agent → pigment under controlled agitation.
- Pre-wet: allow time for pigment wetting before applying high shear (reduces micro-foam and dry clumps).
- Temperature control: manage heat early; many dispersants and resins change viscosity with temperature.
2) Milling / deagglomeration
- Equipment: bead mill, triple-roll, high-speed disperser—each produces different PSD and heat profile.
- Targets: set a fineness-of-grind target (e.g., Hegman) suitable for your print method and nozzle/plate.
- Do not over-mill: too fine or too hot can increase viscosity, destabilize, or create unwanted surface area demand.
3) Let-down (compatibility check)
- Binder compatibility: add let-down resin slowly; incompatibility causes flocculation and instant viscosity jumps.
- Solvent/water balance: sudden polarity shift can crash dispersions (especially in mixed cosolvent waterborne systems).
- Filtration: define filter mesh and pressure drop limits; gels are early warning for instability.
4) Final adjustment
- Viscosity window: adjust with controlled diluent; avoid chasing viscosity without diagnosing cause.
- Defoamer: tune after milling (many systems foam more during high shear).
- Preservation: finalize pH and biocide plan for waterborne systems.
QC tests that predict storage stability
Stability is best controlled by a small set of repeatable QC tests. Below is a practical core package for plant labs.
| Test | What it tells you | Typical acceptance approach |
|---|---|---|
| Fineness of grind (Hegman / grind gauge) | Particle size control; predicts nozzle/plate issues | Set max speck size and a target range per product |
| Viscosity @ defined shear & temperature | Printability; drift detection | Measure at fixed temperature; define window and drift limit after aging |
| Density / solids | Batch consistency and dilution control | Define range aligned to process capability |
| Color strength / ΔE | Shade repeatability; flocculation indicator | Compare to retained standard; define ΔE limits |
| Filterability (time/pressure trend) | Gel/seed formation; dispersion crash risk | Define maximum filtration time or pressure rise |
| pH (waterborne) | Stability and microbial risk | Set pH window and monitor drift on aging |
Storage stability tests (fast screening)
To predict months of shelf life quickly, use accelerated screening. Always compare to a retained control batch.
- Heat aging: store at elevated temperature (e.g., 40–50°C) and track viscosity, ΔE, and sedimentation weekly.
- Cold storage / freeze-thaw: critical for waterborne shipments; check for separation and re-dispersibility.
- Centrifuge screening: fast indication of settling tendency and phase separation.
- Vibration/transport simulation: reveals foam sensitivity and separation during logistics.
- Re-dispersibility test: define “easy remix” criteria (time to homogenize, no hard cake).
Dispersant dosage estimator (starting point)
For estimation only: calculates dispersant mass based on pigment loading. Always optimize experimentally—too little causes flocculation; too much can reduce water resistance or increase foam.
Troubleshooting: symptoms → likely causes → first actions
- Likely causes: insufficient yield stress; pigment not fully stabilized; PSD too coarse; density mismatch.
- First actions: verify fineness-of-grind; adjust rheology modifier to introduce yield stress; optimize dispersant dose.
- Process fix: control milling time/energy and heat; confirm let-down compatibility (avoid crash).
- Likely causes: flocculation; resin incompatibility; waterborne pH drift; microbial growth; solvent loss.
- First actions: check ΔE and gloss for flocculation; verify pH and preservation; confirm container seal and solvent balance.
- Prevention: define pH window; specify compatible dispersant; include change control and preservative plan.
- Likely causes: shear breakdown of rheology; incompatible solvent/cosolvent; phase separation; over-wetting agents.
- First actions: compare viscosity at same temperature; review shear exposure; check for syneresis or clear layer.
- Prevention: select rheology modifier for shear profile; validate under pumping/filtration conditions.
- Likely causes: pigment flocculation; surface tension gradients; incompatible additive package.
- First actions: verify dispersion quality; reduce surface-active additives; adjust dispersant/wetting balance.
- Prevention: define a controlled additive order-of-addition and keep supplier changes documented.
- Likely causes: high-foam surfactants; wrong defoamer; air entrainment in high shear; contamination.
- First actions: tune defoamer type and dose; reduce foam-generating wetting agents; improve mixing geometry.
- Prevention: specify foam behavior and surface defect checks in QC/approval.
Procurement specs (COA fields you can enforce)
If you buy inks, dispersants, or concentrated pigment pastes, define measurable limits so substitutions don’t drift performance.
| Spec item | Why it matters | Practical guidance |
|---|---|---|
| Batch/lot traceability | Root-cause analysis and containment | Require lot number on label + COA |
| Viscosity window (method & temp defined) | Printability and stability | Specify instrument/method and temperature; define allowable drift after aging |
| Fineness of grind | Nozzle/plate performance; gloss & color strength | Set max speck size; record and trend |
| Solids / non-volatiles | Consistency, drying/curing behavior | Define range; check on receipt for concentrates |
| Color strength / ΔE | Repeatability and flocculation indicator | Define standard drawdown method and ΔE limit |
| pH (waterborne) | Stability and microbial risk | Define pH window and acceptable drift |
| Shelf life & storage | Risk of separation and drift in warehouse | Specify minimum remaining shelf life on delivery; add freeze protection if needed |
| Change control | Prevents “silent” formulation drift | Request notification for raw material, site, or process changes |
Handling & storage (what prevents drift)
- Temperature control: avoid freeze damage for waterborne systems; avoid high heat that accelerates drift.
- Headspace & sealing: solvent loss changes viscosity and resin solvency; keep containers sealed.
- Mixing SOP: define remix procedure and maximum allowed sediment; record deviations.
- Contamination control: dedicated tools and clean transfer lines prevent gels and surface defects.
- FIFO and labeling: manage by lot and retest date; store away from incompatible materials.
EHS notes (safety-first)
Always follow your site EHS rules and the supplier SDS. Typical EHS considerations in ink operations include:
- Solvents: ventilation, ignition control, and static grounding in handling areas.
- Powder pigments: dust control and appropriate respiratory protection where required.
- UV systems: skin/eye protection and safe handling of reactive monomers/photoinitiators.
- Waste: manage rags/filters and dispose per local regulations and site procedures.
RFQ notes (copy/paste)
- Ink type: waterborne / solvent / UV; application method (flexo/gravure/screen/digital).
- Pigment(s): type and loading, surface treatment if known (esp. carbon black and organics).
- Binder/resin: family and key constraints (VOC, food-contact requirements, cure method).
- Process: milling equipment, typical temperature rise, filtration mesh/pressure limits.
- Targets: viscosity window at defined method/temp; fineness-of-grind target; ΔE limit; storage time.
- Stability needs: heat aging, freeze-thaw (if relevant), “no hard settle” requirement.
- Logistics: monthly volume, packaging (pail/drum/IBC), delivery country/city, incoterms.
- Documentation: SDS, COA, compliance statements required by your customers.
Need a stable additive package or second source?
Send your resin system, pigment list, viscosity target, and storage conditions. We’ll propose a shortlist with expected COA fields, trial plan, and procurement-ready logistics.
Educational content only. Always follow site EHS rules and the supplier SDS for safe use. Validate on your process before full-scale production.