Some ingredients may influence the antibacterial performance
Presence of some ingredients in the formulation may influence the antibacterial performance of silver additives.Some antioxidants, imdidazole derivatives and fillers like calcium carbonate may influence the antibacterial performance of powder.One more suspect is barium sulphate which might spoil the activity of silver because sulphur has a feature which reacts with silver easily. As silver ions have a tendency to react with atmosphere sulphur and exchange the ions it may have some impact. However our present experiments show good performance with optimum proportion of good grade barium sulphate. It may also depend on the dosage and purity of the fillers. In some of the formulations the dosage of antibacterial agent was increased but it didn’t yield the desired result. Scanning electron microscope (SEM) observation had confirmed there were many impurities on the coated panels. So it is necessary to ensure that there is no cross-contamination or absence of contaminants otherwise which may lead to poor antibacterial performance. Some pigments can have detrimental effect on silver for e.g. pigment contains sulphur which will react with silver and spoil its activity.
Recipe of formulation
Recipe of formulation plays a predominant role to get the desired result. For an antibacterial powder coating to be effective requires that silver ions be able to diffuse through the coating to the surface. Matching between a silver additive and recipe of each powder is also important; coarser grade silver additives produce haze and gloss reduction can be noticed. In general it is better to maintain quite good amount of binder in the formulation. There is a correlation between biocide concentration and cross linking density of the powder. Higher cross linking may affect the migration of silver ions to the top surface of the coatings. If the cross linking rate is high then there could be a possibility for silver ions be covered or buried under the coating film it can lead to poor antibacterial performance.