Coating is one of the most commonly used technologies in pharmacy, which involves physical chemistry, chemical engineering, liquid mechanics, polymer materials science and other disciplines. In recent decades, with the continuous emergence of new materials, new technologies, and new machinery, coating technology has developed rapidly, forming a relatively complete set of theories and operational experience, which occupies an important position in pharmacy.
Coating is generally applied to solid form preparations. According to different coating materials, it can be powder coating, pellet coating, granule coating, tablet coating, capsule coating; For sugar coating, semi-film coating, film coating (based on a wide variety of polymer materials, including enteric coating), special material coating (such as stearic acid, paraffin, polysaccharide); according to the packaging Coating technologies are divided into spray coating, dip coating, dry pressure coating, electrostatic coating, and lamination coating. Among them, spray coating is the most widely used. Its principle is to spray the coating liquid into mist droplets. Cover the surface of materials (powder, granules, tablets) and dry quickly to form a coating layer; according to the purpose of coating, it is divided into water-soluble coating, gastric-soluble coating, insoluble coating, sustained-release coating, and enteric coating .
The functions of coating include: ① Moisture-proof, light-proof, and air-isolation to increase drug stability; ② Mask bad smell and reduce irritation; ③ Improve appearance and facilitate identification; ④ Control the drug release site, such as Those that are easily destroyed in gastric juice cause it to be released in the intestine; ⑤ control drug diffusion and release speed; ⑥ overcome incompatibility incompatibility, etc. Coating materials should generally have the following requirements: ① non-toxic, non-chemically inert, stable in heat, light, moisture, and air, and do not react with coated drugs; ② capable of being dissolved and evenly dispersed in a dispersion medium suitable for coating Medium; ③ It can form a continuous, strong and smooth coating layer, has crack resistance and has good water, moisture, light-shielding and air-tight functions; ④ Its solubility should meet certain requirements, and sometimes it needs to be unaffected by PH. Sometimes it can only dissolve within a certain pH range. There are not many materials with the above characteristics at the same time, so mixed coating materials are often used to learn from each other's strengths.
Tablet coating is the most widely used. It often uses pot coating and buried tube coating (high-efficiency coating machine coating). The latter is used for film coating and has the best effect. Fluidized bed coating is more suitable for coating materials with smaller particle sizes such as pellets and powders. Film coating has many advantages over sugar coating: ① shortens the time and reduces material costs; ② does not significantly increase the weight; ③ does not require a subcoating layer; ④ is strong and resistant to breakage and cracking; ⑤ can be printed without affecting the tablet core engraving ; ⑥ It can effectively protect the product from light, air and moisture; ⑦ It has no adverse effect on the disintegration time; ⑧ The product is beautiful; ⑨ Provides opportunities for the use of non-aqueous coatings; ⑩ The process and materials can be standardized. The coating of new preparation products currently developed is generally film coating. The basic components of film coating prescriptions include film-forming agents (coating materials), solvents, plasticizers, colorants, and porogens, insoluble fillers, etc. can also be added. . The composition of the film coating formula is critical to the success or failure of the coating. Commonly used film coating materials include hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP). Soluble acrylic resin, hydroxypropyl methylcellulose phthalate (HPMCP), cellulose acetate phthalate (CAP), shellac, insoluble materials include ethyl cellulose (EC), corn protein.
Coating has so many advantages that many pharmaceuticals adopt coating technology. Different coating purposes make coating materials and technologies vary greatly. Research progress and market demand have resulted in the formation of a large market for coating technologies and materials, and the emergence of professional companies that prepare various coating materials and provide technical services. Coating has also become the focus of pharmaceutical researchers when developing new preparations. technical means to consider.