Solution for Irregular Ripple Patterns in CMYK Solid Color Blocks

I. Core Cause Analysis

(1) Underlying Logic of Ripples Caused by Abnormal Ink Viscosity

1. Issues with Low-Viscosity Ink

When the ink viscosity falls below the standard range, intermolecular cohesion becomes insufficient, leading to “tailing” and “ink bleeding diffusion” after ejection:

• During printhead movement, low-viscosity ink cannot stabilize quickly. As adjacent droplets merge, irregular ripple patterns resembling water waves are formed.
• At the same time, low viscosity increases the number of satellite droplets (＞3 per 1,000 drops). These tiny droplets randomly attach to the color block surface, further intensifying the ripple effect.

Main causes of low viscosity include:

• Temperature increase (viscosity decreases by ~0.25 cP per 1°C rise)
• Excess solvent
• Overuse of surfactants

2. Issues with High-Viscosity Ink

When viscosity exceeds the standard range, ink fluidity decreases, and the piezoelectric actuator must provide greater driving force:

• Uneven droplet velocity (CV ＞ 8%) leads to inaccurate landing positions, forming “accumulation ripples.”
• High viscosity prolongs the decay time of nozzle pressure oscillation. In multi-pulse printing, residual vibrations from the previous waveform overlap with subsequent pulses, causing droplet deviation (phase deviation ＞ 5°) and resulting in periodic ripples.

Main causes of high viscosity include:

• Excess pigment concentration (volume fraction φ ＞ 0.2)
• Overuse of thickeners
• Pigment flocculation due to long-term storage

3. Impact of Poor Viscosity Stability

Environmental fluctuations (e.g., RH ＞ 70% causing moisture absorption in water-based inks) or failure in temperature control of the ink circulation system lead to real-time viscosity variations (＞ ±1 cP).

• This dynamic instability prevents the printhead from maintaining a stable jetting state.
• Droplet volume deviation exceeds ±3%, resulting in random ripple defects.

A4 Print Result — Before Optimization

A4 Print Result — After Optimization

(2) Key Issues of Waveform Parameter Mismatch

1. Imbalance Between Pulse Width and Viscosity

The waveform pulse width (t₍fire₎) is the key parameter controlling droplet volume:

• For low-viscosity ink, if pulse width is not reduced (still using standard 3.5 μs), droplet volume becomes too large (＞10 pL), causing uneven spreading.
• For high-viscosity ink, if pulse width is not increased (＜5 μs), droplet ejection becomes insufficient, resulting in “intermittent jetting ripples.”

2. Conflict Between Pulse Interval and Residual Vibration

In multi-pulse printing, waveform intervals must be adjusted according to viscosity:

• Low-viscosity ink: requires longer intervals (+15–25 μs) to avoid droplet overlap
• High-viscosity ink: requires shorter intervals (−30–50 μs) to utilize residual pressure

If not properly adjusted:

• Pressure oscillations at the nozzle surface do not decay to zero
• Subsequent pulses are disturbed
• Droplet roundness decreases (aspect ratio ＜ 0.95), forming ripples

3. Improper Waveform Type Selection

• Basic single-pulse waveforms cannot suppress residual vibration or satellite droplet generation
• Droplet roundness is only ~0.85
• Unoptimized multi-pulse waveforms can cause pulse interference, resulting in droplet velocity fluctuation ＞ 0.5 m/s, further aggravating ripple defects

II. Targeted Solutions

(1) Ink Viscosity Optimization

1. Precise Viscosity Calibration

• Low-viscosity ink:
  • Add 0.1–0.3% thickener (e.g., Hydroxyethyl Cellulose, HEC)
  • Supplement high-viscosity base ink
  • Adjust viscosity to 8–10 cP
  • Reduce surfactant dosage and control solvent ratio
• High-viscosity ink:
  • Add appropriate diluents (e.g., ethanol)
  • Adjust viscosity to 10–12 cP
  • Filter out pigment flocculation
  • Control pigment volume fraction φ ＜ 0.18
• Calibration tool:
  • Use a rotational rheometer (shear rate 10⁴ s⁻¹)
  • Ensure viscosity deviation ≤ ±0.5 cP

2. Viscosity Stability Control

• Environmental control:
  • Temperature: 23 ± 2°C
  • Humidity: 50 ± 10% RH
• Equipment optimization:
  • Use multi-tank ink circulation systems (e.g., Keyence MK-G series)
  • Real-time viscosity sensors (±0.1 cP accuracy)
  • Heating/cooling modules for automatic compensation
  • Enable automatic nozzle cleaning
• Ink management:
  • Use within 3 months after opening
  • Shake before use to ensure uniform dispersion

(2) Waveform Parameter Optimization

1. Viscosity-Based Waveform Adjustment

2. Waveform Type Optimization

• Recommended: Trailing-edge W-type waveform
  • Suppresses residual vibration
  • Droplet roundness ≈ 1 (optimal 0.997)
  • Satellite droplets ≤ 1 per 1,000
  • Significantly reduces ripple defects
• Multi-pulse printing:
  • Use phase synchronization correction technology
  • Prevent waveform interference

3. Dynamic Adjustment Mechanism

• Establish a viscosity–waveform linkage model based on real-time feedback:
  • When viscosity changes by ±0.5 cP:
    • Pulse width ±0.3 μs
    • Voltage ±1 V

Example:

• Using 15 cP ink
• Droplet velocity CV reduced from 8.7% → 2.3%
• Ripple defects completely eliminated

III. Verification and Debugging Process

1. Basic Testing
   • Measure viscosity with viscometer
   • Observe droplets using high-speed camera (＞1000 fps)
   • Requirements:
     • Roundness ≥ 0.98
     • Satellite droplets ≤ 1 per 1,000
2. Sample Printing
   • Print 10 cm × 10 cm solid color block
   • Inspect under microscope (50×)
   • Requirement:
     • ＜ 2 ripple lines per cm
     • No visible defects
3. Stability Testing
   • Continuous printing for 1 hour
   • Measure every 10 minutes
   • Requirements:
     • Viscosity fluctuation ≤ ±0.3 cP
     • Droplet volume deviation ≤ ±2%
4. Final Verification
   • Use spectrophotometer to measure uniformity
   • Requirement:
     • ΔE ＜ 1.5 (lower = better uniformity)