Powder Coating Properties Problems

Issues with appearance and film formation can reveal issues with equipment, powders and techniques. Employing a host of quality control tests will help to analyse the powder coating problem.

POWDER COATING PROPERTIES	CAUSE	SolUTION
The cured film has poor adhesion	Unsatisfactory cleaning or pre-treatment Possible change to substrate Under curing	Check cleaning conditions and chemical for cleaning, rinse, and pre-treatment stages Contact the substrate suppliers to check if any alterations have been made Modify cure conditions through increasing oven temperature and dwell time
Pinholes form in the surface of the coating	Coating is contaminated by an incompatible powder Pinholes produced from outgassing Unsatisfactory rinse stages Vapours in the curing oven	Make sure to clean equipment when changing from one powder to the next Determine metal porosity and adjust processing accordingly. Ensure no moisture is on part. Reduce film thickness. Note oven temperatures to check for excessive temperature issues. Check rinse stage conditions to ensure no chemical residues are drying on the surface of the substrate Vapours can be produced by masking products in an oven. Monitor ovens and maintain air exchange procedures
Gloss levels do not match the standard	Under cured films will vary in their gloss levels Pinholes will reduce gloss	Modify cure conditions through oven temperature and dwell time See ‘pinholes’, above
Too much orange peel	Film thickness may be too thick or thin	Increase or decrease film thickness accordingly
Poor corrosion resistance	Unsatisfactory cleaning and/or pretreatment	Check the cleaning, rinse, and pre-treatment chemicals and conditions
Low flexibility and impact resistance	A change has been made to the substrate without a corresponding change in the process Film thickness may be too thick Under curing	Contact suppliers to ensure no changes to the substrate have been made Reduce film thickness Modify cure conditions
The film has poor hardness	Under curing	Modify cure conditions with oven temperature and dwell time
Coating colour drifts from the standard	Oven air is not exchanged enough to eliminate combustion by-products Oven temperature is too high Coating formulation may not have sufficient pigment opacity Film thickness may be too thick or thin	Adjust the air exchange rate to reduce the concentration of by-products. With light colors the oven volume must be exchanged several times more often than with dark colors to minimize discoloration and haze. Reduce oven temperature. Know oven profile and set temperature and dwell to match the cure schedule. Find hot spots in the oven. If an infrared oven is used, vary the energy density and the line speed. Increase coating thickness to provide coverage. The pigment opacity dictates the required thickness for proper color. Adjust for proper coverage. This is most predominant in metallic finishes.