Testing the viscosity and drying speed of ink is a key step to ensure the quality and process stability of screen printing. The following are professional test methods and operating points for these two indicators, combined with actual cases and tools for explanation:
1. Ink viscosity test method
Ink viscosity directly affects printing smoothness, wire drawing and transfer effect, and needs to be measured through standardized tools and processes.
1. Test tools and principles
Rotational viscometer (recommended)
Principle: Viscosity is measured by the resistance of the rotor rotating in the ink (unit: Pa·s or cP).
Applicable scenarios: medium and high viscosity inks (such as screen printing inks, UV inks).
Example: NDJ-1 type rotational viscometer, which can measure inks in the range of 10-100,000cP.
Coating 4 cups viscometer (quick test)
Principle: Measure the time required for ink to flow out of the standard aperture (unit: seconds) and convert it into viscosity value.
Applicable scenarios: On-site rapid detection or low viscosity inks (such as water-based inks).
Example: Coating 4 cups with a hole diameter of 4mm, the outflow time of 15-30 seconds is the common ink viscosity range.
2. Test steps
Pre-treatment of ink:
Stir the ink until it is uniform and avoid bubbles.
The test temperature is controlled at 25±1℃ (or the ink use temperature).
Operation of rotational viscometer:
Select a suitable rotor (such as rotor No. 6 for high viscosity ink).
Immerse the rotor in the ink to the scale line, start the instrument and read the data.
Record key points: rotor model, speed, temperature and viscosity value.
Operation of coating 4 cups:
Block the hole at the bottom of the cup and inject ink to the scale line.
Quickly remove your finger and record the time (seconds) for the ink to flow out.
Conversion formula: Viscosity (cP) = Time (s) × Coefficient (adjusted according to the cup type, coating 4 cups coefficient ≈ 1.4).
3. Data analysis and standards
Reference range:
Screen printing ink: 3000-8000cP (high viscosity needs to be diluted).
Water-based ink: 10-25 seconds to apply 4 cups (corresponding to viscosity 10-50cP).
Abnormal handling:
If the viscosity is too high, add a diluent (such as a special solvent for ink) and retest.
If the viscosity is too low, add a thickener or change the ink type.
2. Ink drying speed test method
The drying speed affects production efficiency and finished product quality, and needs to be quantitatively evaluated by physical or instrumental methods.
1. Test tools and principles
Finger touch method (simple and fast)
Principle: Touch the ink surface with your finger to observe whether it is sticky or transferred.
Applicable scenarios: preliminary on-site detection.
Drying time meter (precise measurement)
Principle: Detect the surface drying/actual drying time of the ink through a sensor or mechanical device.
Example: BYK drying time recorder, which can measure surface drying (5-10 seconds) to actual drying (several minutes to several hours).
Weight method (scientific verification)
Principle: Weigh the weight change of the printed sample before and after drying to calculate the solvent volatilization rate.
Applicable scenarios: precise analysis in the laboratory.
2. Test steps
Finger touch method:
Touch the ink surface with your finger every 30 seconds after printing and record the non-stick time (surface drying time).
After complete drying (no fingerprint residue), record the actual drying time.
Drying time meter operation:
Place the sensor or probe on the printed ink surface.
Start the instrument and record the transition time from liquid to solid state of the ink (automatically generate a curve graph).
Weighing method operation:
Weigh immediately after printing (W₁), and weigh again after drying (W₂).
Calculate the drying rate: Drying rate = (W₁ - W₂) / W₁ × 100%.
Example: If W₁=10g, W₂=9g, the drying rate is 10% (solvent volatilization 10%).
3. Data analysis and standards
Reference range:
Surface drying time: UV ink ≤5 seconds, solvent-based ink 30-60 seconds.
Drying time: UV ink ≤ 1 minute, solvent-based ink several hours to 24 hours.
Abnormal handling:
If drying is too fast, add slow-drying agent or lower the ambient temperature.
If drying is too slow, increase ventilation or adjust the UV lamp power (UV ink).
III. Test precautions and optimization suggestions
Environmental control:
Viscosity test temperature 25±1℃, drying test humidity 50%±5%.
Avoid wind speed or light interference (such as UV ink needs to be tested in a dark room).
Repeatability verification:
The same ink sample is tested 3 times and the average value is taken.
Record the test conditions (tools, environment, operator).
Process correlation:
Viscosity and drying speed need to match the printing process: high viscosity ink needs to dry slowly to avoid drawing.
For example: When the viscosity of UV ink is 5000cP, the surface drying time should be ≤3 seconds to prevent clogging of the screen.
4. Comparison of test tools and costs
Tools Accuracy Cost Applicable scenarios
Rotational viscometer High (±1%) Medium (2000-5000 yuan) Laboratory, factory quality inspection
4-cup viscometer Low (±5%) Low (100-300 yuan) On-site rapid detection
Drying time meter High (±0.5 seconds) High (8000-15000 yuan) High-end printing, scientific research
Finger touch method Subjective 0 yuan Worker experience judgment
5. Summary and recommendation
Viscosity test should give priority to rotational viscometer to ensure accurate data.
Drying speed test recommends drying time meter to quantify surface drying/actual drying time.
On-site rapid detection can be combined with 4-cup and finger touch method to reduce testing costs.
Adjust the test frequency according to the ink type: UV ink is tested per batch, and solvent-based ink is tested daily.
The above methods can systematically evaluate the viscosity and drying speed of the ink, providing data support for the optimization of the screen printing process.