1.What is the core of the pollution resistance assessment?
The core of the pollution resistance assessment is to simulate the pollutants that may be encountered in actual use (such as dust, oil, atmospheric pollutants, etc.), and verify the anti-pollution and easy-to-clean capabilities of the coating through the "pollution-cleaning-evaluation" process.
2.What are the steps in stain resistance assessment?
Sample preparation
Select representative color-coated coil samples to ensure that there are no defects on the coating surface (such as scratches and bubbles). Before testing, pretreatment is required according to standard requirements (such as placing in a constant temperature and humidity environment for 24 hours).
Pollutant selection
Typical pollutants are selected according to the application scenario. Common types include:
Solid particle pollutants: such as carbon black, fly ash, quartz sand, etc., usually made into a suspension of a certain concentration.
Liquid pollutants: such as motor oil, soy sauce/vinegar, sulfate solution, ink, etc.
Biological pollutants: such as mold spore suspension.
Pollution application and standing
Use uniform smearing, spraying or immersion to cover the pollutant on the sample surface.
Stand for a certain period of time in a specific environment according to standard requirements to allow the pollutant to fully adhere or interact with the coating.
Cleaning treatment
Simulate actual cleaning methods, such as rinsing with deionized water, wiping with a soft cloth dipped in clean water (5-10 times back and forth), or wiping with a neutral detergent for oily contaminants and then rinsing.
After cleaning, place the sample in a standard environment to dry (usually 24 hours).
3.What are the evaluation metrics?
Visual appearance rating, color difference change (ΔE), gloss retention, residual contamination area ratio, coating performance change
4.What are the rating criteria?
Visual appearance rating: Level 1 (no residual stains); Level 2 (very slight residue, only visible at close range); Level 3 (obvious residue, but area <10%); Level 4 (residue area 10%-30%); Level 5 (residue area >30% or coating discoloration/damage).
Color difference change (ΔE)
Use a colorimeter to measure the color difference ΔE between the cleaned sample and the uncontaminated area (or the original sample) (ΔE=√[(ΔL*)²+(Δa*)²+(Δb*)²], where L is lightness and a/b* is color coordinate).
Gloss retention rate
Use a gloss meter to measure the 60° gloss value (G1) and the original gloss value (G0) of the cleaned sample, and calculate the retention rate (G1/G0×100%).
A retention rate of ≥90% is "excellent", 70%-90% is "good", and <50% is "poor" (obvious loss of gloss due to contamination).
Residual contamination area ratio
Use image processing software (such as Photoshop) to calculate the ratio of the residual stain area to the total contaminated area. ≤5% is "excellent", 5%-15% is "good", and >30% is "poor".
Changes in coating performance
If contamination causes damage to the coating, additional adhesion testing is required (such as the cross-cut method GB/T 9286). If the adhesion decreases by ≥1 level (such as from level 0 to level 2), the stain resistance rating is reduced.
5.What other factors need to be considered in practical applications?
Accelerated aging synergistic test: Pollution resistance may be affected by long-term ultraviolet rays, high temperature, and humidity. Therefore, it is necessary to combine accelerated aging tests (such as testing pollution resistance after 1000 hours of ultraviolet aging) to evaluate the anti-pollution ability of the coating after aging.
Self-cleaning performance auxiliary evaluation: For color-coated coils that emphasize "self-cleaning" (such as fluorine-containing coatings), contact angle tests (water contact angles > 110° are usually considered super-hydrophobic and have good self-cleaning properties) can be used to assist in judgment - the larger the contact angle, the easier it is for pollutants to be washed away by rainwater, and the better the pollution resistance.
Field exposure test: Place samples in actual application scenarios (such as industrial areas and coastal areas) for 6-12 months, and regularly observe surface pollution and cleaning difficulty as a supplementary verification of laboratory tests.