**2.1.1 Film formation facilitated by plasticizer**

The film-formation mechanism from the coating dispersions is a complex process influenced mainly with the type and also with the quantity of plasticizer. The temperature below which a coating will not form a continuous, cohesive film is called the minimum film forming temperature; it is the minimum temperature above the Tg of the polymer. In order to ensure the optimum conditions for film formation, the really used coating temperature during the application process should be 10-20 °C above the minimum film forming temperature (Lehmann, 1992). Since plasticizer addition to film coating formulation reduces the Tg of the polymer, as a result the temperature required for film coating is reduced by plasticization (Zhu et al., 2002).

pharmaceutical compositions of two kinds of coated beads were patented. The polymer coatings of the beads differed in water solubility. This pharmaceutical composition comprised phtalates, trimellitates, adipates, sebacates, glycols, polyethers and alkyl citrates

Cellulose acetate phthalate (CAP), widely used in enteric film coating, is available as a white powder or also as a 30 % solid nanodispersion (pseudolatex) (Aquacoat® CPD). Polyvinyl acetate phthalate is less susceptible to hydrolysis, which minimizes or limits the content of

Cellulose acetate trimellitate (CAT) has three carboxylic groups on the aromatic ring and dissolves at a pH of 5.5. The plasticizers as triacetin, acetylated monoglyceride, diethyl phthalate are recommended, and to obtain the best enteric coating results from aqueous

Hydroxypropyl methylcellulose phthalate (HPMCP) characteristics, particularly at the pH where dissolution occurs, are determined by the degree of substitution of the three kinds of substituent groups (i.e. methoxy, hydroxypropoxy, and carboxybenzoyl). Valuable

Acrylic polymers as a group of various synthetic polymers, methacrylic amino ester copolymers, have diverse functionality in film coating. They can be used for rapidly disintegrating coatings, taste and odour masking, coloured or transparent coatings, etc., and

Methacrylic acid copolymers contain free carboxylic acid groups, and therefore can be used for enteric coating purposes by forming salts with alkalis. Methacrylic acid copolymers are soluble at pH values higher than 5.5. The addition of a plasticizer in these polymers is necessary. Methacrylic acid copolymers are available as various grades of Eudragit®

The plasticizer plays the major role in the all process of the oral dosage form coating, and significantly influences the quality of the coatings, particularly the release of incorporated

The film-formation mechanism from the coating dispersions is a complex process influenced mainly with the type and also with the quantity of plasticizer. The temperature below which a coating will not form a continuous, cohesive film is called the minimum film forming temperature; it is the minimum temperature above the Tg of the polymer. In order to ensure the optimum conditions for film formation, the really used coating temperature during the application process should be 10-20 °C above the minimum film forming temperature (Lehmann, 1992). Since plasticizer addition to film coating formulation reduces the Tg of the polymer, as a result the temperature required for film

processing, ammoniated solutions of CAT in water are the best choice.

plasticizers include triacetin, acetylated monoglyceride and diethyl phthalate.

as the plasticizers (Paborji & Flugel 2011).

free phthalic acid and other free acids.

are available mainly as the Eudragit® products.

**2.1 The role of the plasticizer in the film coating** 

**2.1.1 Film formation facilitated by plasticizer** 

coating is reduced by plasticization (Zhu et al., 2002).

products.

drugs.

A sufficient amount of time should be allowed for the plasticizer uptake to ensure a homogeneous distribution of the plasticizer in the coating film. The time between the addition of the plasticizer to the polymer dispersion and the coating step is usually called as the plasticization time and presents a critical process variable, especially when waterinsoluble plasticizers are used. Water insoluble plasticizers have to be emulsified in the aqueous phase of the polymer dispersions. During plasticization of the polymer dispersions, the plasticizer partitions into the colloidal polymer particles and softens them thus promoting particle deformation and coalescence into a film upon drying. Commercial suppliers of polymer dispersions often recommend a relatively short plasticization time of 30 - 60 minutes irrespective of the solubility of the plasticizer. Plasticizers are incorporated in the amorphous parts of polymers while the structure and size of any crystalline part remains unaffected (Fedorko et al., 2003). The thermal treatment following the application of the coat is known as curing. During this stage of coating, the coated dosage form is subjected to temperatures higher than the Tg, which facilitates uniform distribution of plasticizers. During curing of the coatings, plasticizers could also redistribute in the polymeric film.

Controlled released pharmaceutical formulations comprising pseudoephedrine embedded in core and coating shell made from mixture of two different polymers were approved. One of the used polymers was water soluble, the second one water insoluble. The water insoluble plasticizer ranged from 0.1 to 15.0 % by weight in this composition (Nair et al., 2010).
