1.How do you test the hardness of a pencil?
Principle: Using a set of standard drawing pencils from softest to hardest (9B softest → ... → B → HB → F → H → ... → 9H hardest), scratch the coating surface at a specific angle and with specific pressure to find the pencil with the highest hardness that will not scratch the coating.
Common Ranges:
Ordinary Polyester (PE): Typically around H. This is a balanced choice, balancing hardness, flexibility, and cost.
Silicone-Modified Polyester (SMP): Higher hardness, typically 2H to 3H. It sacrifices some flexibility for better hardness, abrasion resistance, and stain resistance.
High Weather-Resistant Polyester (HDP): Hardness similar to or slightly higher than ordinary polyester, approximately H to 2H, but its main advantage lies in excellent weather resistance and gloss and color retention.
Polyvinylidene Fluoride (PVDF): Relatively low hardness, typically F to HB. This is because PVDF resin itself is very soft, and its core advantages are excellent flexibility and unparalleled weather resistance and anti-powdering properties, making it very suitable for deep processing and harsh outdoor environments.
2.How to test the stiffness of a pendulum rod?
Hardness is measured by the time it takes for the amplitude of a pendulum to decay as it swings across the coating surface. The longer the decay time, the higher the hardness.
This method better reflects the internal molecular structure and cross-linking density of the coating, providing more accurate results, but it is not as intuitive as pencil hardness.
3.How is abrasion resistance tested?
Although not directly called "hardness," it is highly correlated with the wear resistance of a coating surface. It is measured by the weight loss of the coating after a certain number of cycles of rotating and rubbing it with a specific grinding wheel. Coatings with higher hardness generally have better wear resistance.
4.What are the key factors affecting coating hardness?
Resin Type: This is the decisive factor. As mentioned above, the molecular structure and properties of different resin systems (polyester, silicone-modified polyester, PVDF) determine the basis of their hardness.
Formulation and Pigments: The proportion and type of pigments and fillers in the coating formulation affect hardness. Generally, the addition of inorganic pigments and fillers can improve hardness.
Curing Conditions: Color-coated coils require high-temperature oven curing during the production process. Sufficient baking temperature and time allow the coating to fully cross-link, thus achieving optimal hardness. Insufficient curing will result in a soft coating.
5.When making a selection, how do you balance hardness, flexibility, and weather resistance?
If your product requires frequent cleaning or contact with friction, choose a higher hardness SMP coating.
If your product requires complex stamping or deep processing, prioritize a lower hardness but more flexible PVDF coating.
For most general applications, PE or HDP coatings offer the best cost-effectiveness and balanced performance.