MDF properties can vary based on the region of the country where it is produced. For best results of powder coating it’s important to select a grade of MDF produced by a given mill that matches the functionality and coatability required by the end product for edge finish, rout quality, face-sanding degree, and screw holding power. The following factors affect these properties.
The internal bond strength of the board must be greater than 130 pounds per square inch (psi). Boards that approach 150 psi perform very well. Boards that machine well have internal bond strengths that work well for powder coating. Within the IR process, the internal bond strength properties are not degraded.
The moisture content of the board should be within 5 percent to 7 percent for optimum coating. Lower than 5 percent requires more preheat temperature, and sharp corners may become difficult to coat.
The average density of MDF should be 45 to 48 pounds per cubic feet (lb/cu ft). The density profile needs to be as flat as possible and not drop below 40 lb/cu ft at the core of the MDF. Sample A, with sharp changes in density profile, will have a greater tendency for the MDF to crack during the heating cycles than sample B that has a more constant density distribution across the board thickness. Lower quality MDF has a large differential between the core density and the face density, causing edge cracking during the heating process. (click image to enlarge). Therefore MDF properties should be carefully considered if a good quality finish is to be achieved.