Studies have shown that when the HPMC content in the blend is less than 24%, the release profile depends on the rate of water penetration into the coating, which in turn becomes a determining factor in selecting the ratio of polymer concentrations in the blend.
Most of the polymers used are available in a wide range of molecular weights, which is a major factor in the choice of coating technology. Molecular weight can have a significant effect on coating properties such as viscosity, mechanical strength, and film elasticity.
Plasticizers. A plasticizer is a liquid or solid with a high boiling point. Examples of plasticizers include glycerin, propylene glycol, polyethylene glycol, triacetin, esters of citric acid (e.g., triethyl citrate), esters of phthalic acid (e.g., triethyl phthalate). The introduction of a plasticizer can improve the elasticity of the coating Cracking the risk of mechanical damage and potentially in the coating improve the adhesion of the film coating to the core.
When the plasticizer interacts with the polymer, the minimum film formation temperature may be reduced. To form a quality film, the plasticizer must have high compatibility with the polymer and be permanently retained in the coating, especially if the main objective of the coating is the stability of the dosage form during storage.

The scientific literature provides numerous examples of the effect of plasticizer concentration on the physicochemical properties of the film coating and on the release of the drug substance from the coated products. For example, high plasticizer content can reduce the release of metoprolol from Eudragit RS coated microspheres and improve the release stability of theophylline from coated microspheres during storage.
Moreover, the release rate of the drug substance has been shown to be influenced by the type of plasticizer. For example, the release of propanolol from microspheres coated with a mixture of ethylcellulose and Eudragit L100-55 is faster when using the hydrophilic plasticizer triethyl citrate than when using the hydrophobic dibutyl sebacinate. Other studies have shown that the plasticizer can leach out of the coating during dissolution, thus affecting both mechanical properties and the release of LVs.
Adhesion of coating substances during film application causes the formation of undesirable aggregates, and the resulting coatings may be damaged when attempts are made to separate adhering parts. This effect can be neutralized by adding anti-adhesion agents to the coating composition or by applying these agents immediately after the spray chamber. Useful anti-adhesion agents include talc, magnesium stearate, kaolin, etc.
Dyes. Dyes are commonly used to improve the appearance of the dosage form.