HPMC for Film Coating

HPMC for Film coating is the technique of forming a thin film of a polymer over a solid preparation. For example, a layer of stable polymer material is sprayed uniformly on the surface of plain sheet by spraying method to form a plastic film layer several microns thick, so as to achieve the desired effect. The formation of this layer of film outside the tablet is that a single tablet adheres to the polymer coating material after passing through the spray area, and then receives the next part of coating material after drying. After repeated adhesion and drying, the coating is completed until the entire surface of the preparation is completely covered. Film coating is a continuous film, thickness mostly between 8 to 100 microns, a certain degree of elasticity and flexibility, tightly adhere to the surface of the core.

In 1954, Abbott produced the first batch of commercially available film sheets, since then, with the continuous improvement and perfection of production equipment and technology, polymer film materials have been released, so that film coating technology has been rapidly developed. Not only the variety, quantity and quality of color coating agents have increased rapidly, but also the kinds, forms and characteristics of coating technology, coating equipment and coating film as well as the coating of TCM pills have been greatly developed. Therefore, the application of film coating technology has become the need and development trend of pharmaceutical enterprises to improve product quality.

Early use in film coating film forming materials, there are still a large number of products using HPMC hydroxypropyl methylcellulose as Membrane materials. It is the purification HPMC cellulose from cotton lint or wood pulp, and sodium hydroxide solution to reflect the swelling of the alkali cellulose, and then with chloromethane and propylene oxide treatment to get methyl hydroxypropyl cellulose ether HPMC, the product to remove impurities after drying, crushing, packaging. Generally, low viscosity HPMC is used as film coating material, and 2% ~ 10% solution is used as coating solution. The disadvantage is that the viscosity is too large and the expansion is too strong.

The second generation of film forming material is polyvinyl alcohol (PVA). Polyvinyl alcohol is formed by alcoholysis of polyvinyl acetate. Vinyl alcohol repeat units cannot be used as reactants because they do not meet the quantity and purity required for polymerization. In methanol, ethanol or ethanol and methyl acetate mixed solution with alkali metal or inorganic acid as catalyst, hydrolysis is rapid.

PVA is widely used in film coating. Because it is insoluble in water at room temperature, it is generally coated with about 20% water dispersion. The water vapor and oxygen permeability of PVA is lower than HPMC and EC, so the blocking ability of water vapor and oxygen is stronger, which can better protect the chip core.

Plasticizer refers to a material that can increase the plasticity of film forming materials. Some film forming materials change their physical properties after the temperature is reduced, and the mobility of their macromolecules becomes smaller, making the coating hard and brittle, lacking the necessary flexibility, and thus easy to break. Plasticizer was added to reduce glass transition temperature (Tg) and increase coating flexibility. Commonly used plasticizers are amorphous polymers with relatively large molecular weight and strong affinity with film-forming materials. The insoluble plasticizer helps to reduce the permeability of the coating, thus increasing the stability of the preparation.

It is generally believed that the mechanism of plasticizer is that plasticizer molecules are embedded in the polymer chain, which blocks the interaction between polymer molecules to a large extent. The interaction is easier when the polymer-plasticizer interaction is stronger than the polymer-plasticizer interaction. Thus, the opportunities for the polymer segments to move are increased.

The third generation of film forming materials is the plasticizer by chemical method grafted in the film forming material polymer

For example, THE innovative film forming material Kollicoat® IR introduced by BASF is that PEG is chemically grafted to the long chain of PVA polymer without adding plasticizer, so it can avoid the migration of lake after coating