Main properties of PVDF KYNAR® 500:
• Mechanical strength
• High durability
• High thermal stability
• Hot-melt roller application processability
• Resistance to most chemicals and solvents
• Resistance to UV and radioactive radiation
• Remarkable resistance to weathering
• Excellent reliability for exterior application
• Good color retention
• Stains resistance, "anti-graffiti effect" (paints do not stick on PVDF)
• Self-cleaning from dust due to low surface energy
• Flexibility and elasticity (ability to stretch)
• Biological resistance to mould, fungi, bacteria
• Low permeability for most gases and liquids
• Low flammability and combustibility (does not burn itself), low smoke characteristics.
To create metallic tone of the coating, a fine aluminium-based metal powder is added to the polymeric coating. Good quality facing coat usually consists of three layers: primer, a colored layer and a transparent protective layer. Total thickness is approximately 30 μm. Without primer, polymeric layer cannot stick to the surface firmly enough. Lack of lacquering affects resistance to abrasion.
The process of application of polyester coating to rolled aluminium sheet differs from that of PVDF-coating. For polyester coating application, a polymer solution in a solvent is applied by roller method. This coating can be re-painted. PVDF coating cannot be painted because the adhesive force between a polar polymer and other substances is very weak. By the way, that's what self-cleaning property is explained by: no dirt can stick onto the surface. PVDF coat application process consists of several stages. First, PVDF polymer is heated to molten condition, then it is applied onto the surface painted by primer, and evenly spread by roller all over the surface with an uninterrupted broach of aluminium coil. Then, a procedure of thermal polymerization at high temperatures follows. Each further layer out of three-layered PVDF coating is applied at a lower temperature than a previous one. Elasticity and strength properties of the coating may be affected by "overheating" the polymer, i.e. exceeding the time or temperature of thermal processing. That is why in line production the process of rolled aluminium coating is supported by precise control of broaching speed and temperature at all application stages.
Application of advanced painting technology Kynar 500® makes it possible to increase the warranty life of ECOBOND® Plus panels up to 25 years.
How to check the quality of aluminium composite panel coating?
PVDF face coating differs from polyester coating by a better abrasion resistance and can be easily checked by harrowing, as well as grinding by felt disk or fine emery cloth. For example, you can harrow the panel coat by scraper with 1mm-thick blade, pushing it with 1 Kg force. If after 100 times harrowing the same place the aluminium becomes visible, it means that coating consists of polyester. If in some harrowed places you see a different color coating – primer, then the panel is coated by PVDF.
Good quality coating should neither whiten in the bending edges, nor crack when bent, nor peel-off from aluminium skin if ACP pre-grooved on the back side is bent and unbent for several times.
A kind of coating can be identified by chemical solubility. Xylene, an organic solvent, dissolves polyester to aluminium skin, but it cannot dissolve PVDF. Exposure time depends on coating thickness.
Quality of polyester coating, for instance, can be evaluated with the help of methyl ethyl ketone (MEK) that cannot dissolve two-and three-layered polymeric structure of coating, but disrupts it by penetrating into its pores. MEK exposure time is 8 to 24 hours. Painted coating layer can be then removed from aluminium surface by a piece of cloth, wiping it with a certain effort. Good quality coating resists to such process even in 24 hours after MEK solvent exposure.