III. Environmental and Durability Testing: Ensuring Quality Throughout the Print Lifespan

1. Temperature Resistance and Freeze-Thaw Testing: Simulating Extreme Environment Stability

• Testing Purpose: Evaluate ink performance changes after high-temperature storage or low-temperature transportation to prevent cracking or delamination.
• Testing Tools: Constant temperature oven (-40°C to 100°C), freezer, cyclic test chamber.
• Testing Procedures:
  ① High-Temperature Resistance Test: Place samples in a 60°C oven for 72 hours, then check for blistering or discoloration of the ink layer after cooling.
  ② Freeze-Thaw Cycle Test: Freeze ink samples at -20°C for 2 hours → stand at 25°C for 2 hours. Repeat 5 cycles, then test viscosity change rate.
• Result Criteria: No abnormalities in the ink layer after temperature resistance testing; viscosity change rate ≤10% after freeze-thaw cycles, with no stratification or sedimentation.

2. Chemical Resistance Testing: Adapting to Packaging Content Contact Requirements

• Testing Purpose: Verify ink resistance to corrosion from contents like food and cosmetics, especially for direct-contact packaging.
• Standard Reference: FDA 21 CFR 175.300 (Food Contact Material Testing).
• Testing Tools: Constant temperature water bath, cotton swabs, alcohol/acetic acid solution (10% concentration).
• Testing Procedures:
  ① Use a cotton swab dipped in 10% acetic acid (simulating acidic food) or 75% alcohol (simulating cosmetics) to rub the ink layer back and forth 50 times.
  ② Observe for ink peeling or discoloration, and test for pigment migration in the solution.
• Result Criteria: No significant damage to the ink layer after rubbing; migrant concentration ≤0.01mg/kg (for food contact scenarios).

3. Rub Resistance and Abrasion Resistance Testing: Ensuring Physical Durability

• Testing Purpose: Evaluate print resistance to damage during folding and transportation, preventing pattern blurring from friction.
• Standard References: ASTM D5264 (Rub Resistance Test), ISO 105-X12 (Color Fastness to Abrasion).
• Testing Tools: Rub tester (e.g., Taber Abraser), gray scale card (for staining grade evaluation).
• Testing Procedures:
  ① Rub Resistance Test: Fold the sample, rub back and forth 100 times under 5N pressure, and check for cracking or peeling of the ink layer.
  ② Abrasion Resistance Test: Use a CS-10 砂轮 under 500g load to rotate and rub 100 cycles, then compare color density changes before and after abrasion.
• Result Criteria: No cracking after rubbing; color density loss rate ≤5% after abrasion testing; staining grade ≥4.

IV. Environmental and Safety Testing

1. VOC Content Testing: Controlling Volatile Organic Compound Emissions

• Testing Purpose: Verify low volatility of inks to meet workshop environmental and packaging safety requirements.
• Standard References: GB 38507-2020 (Limits of Volatile Organic Compounds in Inks), EPA Method 24.
• Testing Tools: Gas chromatograph (GC-FID), constant temperature oven (105°C).
• Testing Procedures:
  ① Weigh 2g of ink sample, heat in a 105°C oven for 3 hours, and calculate mass loss of volatile substances.
  ② Analyze volatile components using a gas chromatograph, then calculate total VOC content after excluding moisture.
• Result Criteria: VOC content of water-based flexographic inks must be ≤50g/L (packaging printing standard), and ≤30g/L for food packaging.

2. Heavy Metal and Hazardous Substance Testing

• Testing Purpose: Detect heavy metals (e.g., lead, cadmium) and harmful additives in inks to avoid endangering human health.
• Standard References: EN 71-3 (Toy Safety), REACH Regulation (211 SVHCs).
• Testing Tools: Inductively coupled plasma mass spectrometer (ICP-MS), high-performance liquid chromatograph (HPLC).
• Testing Procedures:
  ① After microwave digestion of samples, use ICP-MS to detect heavy metal contents (e.g., lead, cadmium, mercury).
  ② Use HPLC to analyze organic hazardous substances such as phthalates and formaldehyde.
• Result Criteria: Heavy metal content ≤0.01ppm; REACH SVHC substances not detected or below limit values.

V. Test Plan Design

1. Targeted Testing Strategies

• New Ink Selection: Comprehensive testing of basic performance + application performance + environmental safety is required, with focus on substrate compatibility.
• Production Process Monitoring: Simplified to hourly testing of viscosity, pH value, and color difference to quickly identify abnormal fluctuations.
• Long-Term Stability Verification: Periodic (monthly) testing of fineness and viscosity changes in stored inks to evaluate performance degradation during shelf life.

2. Data Correlation and Process Optimization

• If adhesion testing fails, adjust substrate corona treatment intensity (increase to ≥38dyn/cm) or switch to inks containing adhesion promoters.
• If dot enlargement rate exceeds standards, reduce ink viscosity (by 5-10cps) or increase anilox roller line count (from 400 to 600 lines).

Conclusion