How to Test Water-Based Flexo Ink Performance(Part 1)

I. Basic Performance Testing

1. Color and Color Difference Testing: Ensuring Color Consistency

• Testing Purpose: Verify color stability between ink batches and after printing, preventing color differences caused by uneven pigment dispersion.
• Standard References: ASTM D2244, ISO 11664-4.
• Testing Tools: Spectrophotometer, standard light source box.
• Testing Procedures:
  ① Take undiluted ink samples and print 10×10cm color blocks on standard white paper (wet film thickness: 5-10μm).
  ② After 24 hours of drying, measure L* (lightness), a* (red-green value), and b* (yellow-blue value) using a spectrophotometer under D65 light source and 10° observation angle.
  ③ Calculate the color difference ΔE from the standard sample and average results from 3 repeated tests.
• Result Criteria: Qualified standards require inter-batch ΔE ≤1.0; post-printing ΔE ≤1.5 compared to the standard sample (≤1.0 for high-precision scenarios like food packaging).

2. Fineness and Dispersibility Testing

• Testing Purpose: Check the uniformity of pigment dispersion in water, avoiding issues like plate clogging and color spots caused by coarse particles.
• Standard Reference: GB/T 13217.3 (Ink Fineness Testing Method).
• Testing Tools: Scraper fineness gauge (range: 0-50μm), 10x magnifying glass.
• Testing Procedures:
  ① Drop ink samples into the bottom of the fineness gauge groove and scrape vertically with a blade to fill the scale range with ink.
  ② Observe the scale value at the area with dense particles using a magnifying glass within 30 seconds, repeating 3 times.
• Result Criteria: Water-based inks for flexographic printing require fineness ≤5μm; for fine printing (e.g., 600-line anilox rollers), fineness ≤3μm.

3. Viscosity and pH Value Testing

• Testing Purpose: Ensure stable ink fluidity during printing, preventing uneven ink transfer caused by viscosity or pH fluctuations.
• Standard References: ASTM D2196 (Rotational Viscometer Method), GB/T 13217.4 (Ink pH Value Testing Method).
• Testing Tools: Rotational viscometer (e.g., Brookfield DV2T), portable pH meter (accuracy: ±0.01).
• Testing Procedures:
  ① Viscosity Test: Adjust ink temperature to 25°C, select a suitable rotor (e.g., No. 63) at 60rpm, and record cps values after stabilization.
  ② pH Value Test: Insert the pH meter probe into the ink, stir for 30 seconds, and read the value. Calibrate with standard buffer solution before testing.
• Result Criteria: Viscosity for conventional flexographic printing should be controlled at 25-40cps; pH value must remain 8.0-8.5 (alkaline environment prevents resin precipitation).

II. Application Performance Testing: Practical Verification Simulating Printing Scenarios

1. Adhesion Testing: Evaluating Ink-Substrate Bond Strength

• Testing Purpose: Verify ink adhesion to the target substrate, preventing ink peeling during subsequent processing.
• Standard References: ASTM D3359 (Cross-Cut Method), GB/T 9286 (Cross-Cut Test for Paints and Varnishes).
• Testing Tools: Cross-cut knife (blade spacing: 1mm), 3M 610 tape, eraser.
• Testing Procedures:
  ① Use a cross-cut knife to score a 10×10 grid (area: 1cm²) on printed samples, with depth penetrating the ink layer to the substrate.
  ② Firmly apply tape to the grid area, peel it off vertically quickly, remove residual ink with an eraser, and observe grid peeling.
• Result Criteria: Ratings range from 0 to 5B (5B is best); film substrates require ≥4B, and paper substrates require ≥5B.

2. Drying Speed Testing: Optimizing Efficiency and Anti-Smudging

• Testing Purpose: Determine ink drying time under specific process conditions, preventing smudging and sticking caused by insufficient drying.
• Standard References: TAPPI T559 (Paper Ink Drying Test), custom drying simulator (temperature control: 60-80°C).
• Testing Tools: Finger-touch drying test pen, drying time recorder, friction tester.
• Testing Procedures:
  ① Surface Drying Test: Lightly touch the ink layer with clean filter paper every 10 seconds after printing until no ink transfers, and record surface drying time.
  ② Complete Drying Test: Place samples in a 60°C oven for varying durations, rub 30 times under 500g load, and check for ink peeling.
• Result Criteria: Surface drying time must be ≤2 seconds (to adapt to 300m/min printing speed); complete drying time ≤10 seconds, with no significant color loss after friction.

3. Dot Reproduction and Enlargement Rate Testing: Evaluating Fine Printing Capability

• Testing Purpose: Verify ink transfer precision under high-line anilox rollers, ensuring clarity of fine patterns like small text and gradients.
• Standard Reference: ISO 12647-6 (Process Control for Flexographic Printing).
• Testing Tools: Dot measuring instrument, 50x magnifying glass.
• Testing Procedures:
  ① Print standard step wedges (containing 10%-90% dots) and use a measuring instrument to read the actual area of 50% dots.
  ② Calculate dot enlargement rate: [(Actual dot area - Nominal dot area) / Nominal dot area] × 100%.
• Result Criteria: For 600-line anilox rollers, 50% dot enlargement rate must be ≤15%; for 800-line rollers, ≤12%, with no blurred edges.