Film-tablet adhesion

Adhesion between the polymeric film and substrate is a major concern. Poor adhesion could result in flaking or peeling of the coating from the substrate core. Moisture could accmnulate at the film-substrate interface and compromise the mechanical protection provided by the coating. Polymer adhesion is related to both film-substrate interfacial interactions and internal stresses within the film. Polymer adhesion can be evaluated by peel tests or butt joint tests. Apart from the specific properties of the polymers, excipients used in tablet formulations can influence film-tablet adhesion. Since adhesion between a polymer and the tablet smface is due primarily to hydrogen bond formation, hydrophobic agents may decrease adhesion by... 

EthylceUulose [9004-57-3], a cellulose either (qv), as prepared commercially, ie, of high DS, is thermoplastic and has alow density (1.14 g/cm ). It forms films of good thermostabiUty and excellent flexibiUty and toughness. EthylceUulose is used in lacquers, inks, and adhesives and is combined with waxes and resins in the preparation of hot-melt plastics. It is also used as a pharmaceutical tablet binder. 

Cellulose is also commercially modified by acetylation to produce a material suitable for X-ray and cine film. Commercially cellulose ethers are also prepared, such as methylcellulose. This material is water-soluble and gives a highly viscous solution at very low concentrations. Hence it is widely used as a thickener in latex paints and adhesives, in cosmetics and for coating pharmaceutical tablets. 

Capsule formulations usually require lubricants just as do tablet formulations. Lubricants ease the ejection of plugs, reduce filming on pistons and adhesion of powder to metal surfaces, and reduce friction between sliding surfaces in contact with powder. The same lubricants are used in both tablet and capsule formulations. 

Wetting (velocity at impact can influence the advancing contact angle formed between the tablet surface and the droplet and the degree to which the droplet spreads immediately after contact) and, ultimately, film adhesion... 

The third class of lubricant activity is the antiadherent. Some materials have adhesive properties and can adhere to the punch surfaces during compression. This will induce tablet disorders sticking, with a film forming on the surface of the tablets, or picking, where solid particles from the tablet stick to the punch surface. Most die wall lubricants also have antiadherent actions, and in many formulations, the addition of a specific antiadherent will not be required separately. The antiadherent includes talc, maize starch, and microcrystalline cellulose. 

SEPPIC was the first company to introduce MCC in coating formulations some 20 years ago. The use of MCC allows higher solid content and enhances the adhesion of the film to the tablet core, consequently improving logo definition. Different formulas are provided by Sepifilm, such as SEPIFILM LP, SEPIFILM 003 and 752, and SEPISPERSE Dry. The last one can be provided with SEPIFILM and Kollicoat IR. 

FIGURE 31 (a) Tablet coated with HPMC smooth film, medium discontinuity between film and core. (b) Tablet coated with SEPIFILM 752 white clear edge perfectly coated, good adhesion of film to core and continuity between film and core. 

The surface roughness of the tablet compact and the force of compression used during tableting will affect polymer adhesion, by altering the effective area of contact between the film coating and the surface of the... 

Okhamafe, A.O. York, P. The adhesion characteristics of some pigmented and unpigmented aqueous-based film coatings applied to aspirin tablets. J. Pharm. Pharmacol. 1985, 37, 849-853. 

Rowe, R.C. The adhesion of film coatings to tablet surfaces—the effect of some direct compression excipients... 

J.K. Effect of some excipients and compression pressure 140. on the adhesion of aqueous-based hydroxypropyl methyl-cellulose film coatings to tablet surface. Drug Dev. Ind. 

Effects of surface roughness and coating solvent on film adhesion to tablets. J. Pharm. Sci. 1975, 64, 1554—1557. 142. 

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