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Technical Solutions Of HPMC In Film Coating

Views: 6     Author: Site Editor     Publish Time: 2022-01-20      Origin: Site

Using Hydroxypropyl methyl cellulose HPMC as the only polymer, is the most basic film coating, has been widely used in the entire industry for decades, globally acceptable, high IIG inactive ingredient limit, can freely mix plasticizer and colorant, providing different viscosity and film strength;

Hydroxypropyl methyl cellulose HPMC based film coating formulations can improve coating efficiency and reduce costs. Because tablets cannot be exposed to heat and humidity for long periods of time, faster coating speed is required, and the solid content of the coating solution is greater than 15%. Without the use of PVA, the increased carbohydrate can improve the efficiency of the treatment.


In the early 1950s, the first truly thin film coated tablets were born in the United States. Since then, thin-film coating technology has evolved over half a century. However, China started late, in the late 1970s, only a few medical research units and pharmaceutical factories developed a variety of coating liquid and film coating process, and gradually promote the application. Until the mid-1990s, China gradually appeared film coating technology "hot". But overall, the development of this technology in China is still relatively slow. Many pharmaceutical enterprises still have many problems in application due to technical reasons.

On the surface of the core by spraying a layer of relatively stable polymer coating evenly, forming a few micron thick plastic film layer, so as to achieve a certain desired effect, this process is called film coating. The application of film coating technology is the demand and development trend of pharmaceutical industry. Some people think that the film coating tablet is not as good as sugar coated tablets, not as bright as sugar coated tablets, in fact, compared with the traditional coating technology, film coating has many advantages, such as shorter coating time, more moisture-proof, light protection, drug stability, etc..

It is important to change the concept of sugar coating. For a long time, some pharmaceutical companies have regarded film coating technology as simply a separate part of the production of tablets, which are coated like icing. Well, it's not that simple. As a new technology, the requirements of film coating on the core of the sheet are much stricter than that of icing, the hardness of the sheet is higher, and it has requirements on the mutual cooperation between each process, a series of technical indicators in the production process and the adjustment of requirements and mutual matching. Therefore, it is necessary to treat the introduction and application of film coating technology with a scientific and realistic attitude, only in this way, the film can achieve the ideal effect.


Good core quality plays a decisive role in film coating. Sometimes the mechanical quality of the core is so poor that it is impossible to coat the film at all, and even if forced to do so, the quality of the film is difficult to guarantee. Among all the factors that affect the mechanical properties of the core, the hardness and fragility of the core are the most important, and fragility is more prominent than hardness. Generally speaking, the hardness of Chinese medicine tablets suitable for film coating should be 5kg/cm3, and the hardness of Western medicine tablets should be about 4kg/cm3. How do you check? The simplest method is hardness tester test; Or throw a plain sheet vertically up 2 meters, make it fall to the ground freely, more than two times does not break the hardness is qualified. A simple way to check the friability is to scrape the edge or surface of the piece with your finger, preferably without flakes falling off. Another method is to put about 30 plain tablets in a 250ml glass, shake vigorously for about two minutes, with the surface of the piece, the edge of the piece is not worn. For the large hygroscopic plain tablets, the hardness requirements are higher.

The application of film coating technology for coating, whether it is the use of efficient coating machine, fluidized bed coating machine, or the release of sugar coating pan coating, should follow the following principles: first, the hardness of the core should be hard enough, otherwise when the coating begins, the core and the wall of the pot repeated friction, there will be loose, pockskin and other phenomena; Second, the bed temperature should be kept constant; Third, the amount of solvent evaporation in the equipment and the amount of solvent brought into the process of liquid injection should be kept in balance, that is, solvent evaporation and liquid injection rate in a dynamic balance.

The key to one-sided smooth and exquisite is to master the relationship between pot temperature, spray volume and speed in the whole process, which is the most important in the film coating operation. During operation, the degree of atomization of coating liquid directly affects the appearance quality of clothing film, and the atomization effect of spraying liquid is directly determined by atomization pressure and atomization system. At the beginning of spraying, the principle of mastering the spray speed and hot air blowing temperature is to make one side slightly wet, and to prevent one side adhesion, and the temperature should not be too low. If the temperature is too high, the drying is too fast, the film is easy to rough, and the color is uneven; If the temperature is too low, or the spraying speed is too fast, the humidity in the pot will be too high, and soon there will be the phenomenon of adhesion and so on. The relation between the rotation speed of the pot and the coating operation is: low rotation speed, strong adhesion of the coating film; High speed, poor adhesion, easy to peel off.

In the process of coating, if the temperature is too low, the amount of spray is too large, the film flow retention, there may be a sticky film phenomenon. At this time can increase the speed to improve it, if necessary, can also be properly adjusted temperature and spray volume, spray range to overcome.

In the case of the use of coating powder quality unchanged, the problems often occur in the coating operation and the solutions are as follows:

1, stick: mainly because the amount of spray is too fast, in violation of the balance principle of solvent evaporation, so that the pieces adhere to each other. In this case, the amount of coating liquid spray should be appropriately reduced, the temperature of hot air should be increased, and the speed of the pot should be accelerated.

2, the emergence of "orange peel" film: mainly due to improper drying, coating liquid spray pressure is low, so that the spray of liquid droplets heated uneven concentration, resulting in corrugated coating film. In this case, the evaporation rate should be controlled immediately and the spray pressure should be increased.

3, "bridge" : refers to the inscription on the film caused by the logo blurred. The solution is to slow down the coating spraying speed, reduce the drying temperature, and pay attention to the control of hot air temperature.

4, the appearance of color spots: this situation is due to the coating liquid mixing is not uniform or solid character fineness is not enough. The solution is: with coating liquid should be fully stirred evenly.

5. Crack, rupture, peeling or wear of the coating film on the surface or edge of the tablet: If the content of coating liquid and solid is improperly selected, the speed of the coating machine is too fast, or the amount of spraying is too small, the appropriate content of coating liquid and solid should be selected, and the speed and amount of spraying should be properly adjusted; If the hardness of the core is too poor, the formula and process of the core should be improved.

6, the film performance of "frost spraying" : this situation is caused by high humidity of hot air, too long spray, poor atomization effect. At this point, the temperature should be appropriately reduced, the spray distance should be shortened, and the atomization effect should be improved.

7. Color difference between tablets: this situation is caused by uneven jet surface or excessive coating liquid and solid content or slow speed of coating machine. At this time, the Angle of spray gun should be adjusted well, the solid content of coating liquid should be reduced, and the speed of coating machine should be appropriately increased.

8, the surface of the film has pinholes: this situation is caused by the preparation of coating liquid involved in too much air. Therefore, excessive air should be avoided when mixing liquid.


Application of film coating technology in Traditional Chinese medicine

Film coating is a new coating technology, which covers the core with a stable thin layer of polymer coating. Since the 1930s, there has been a series of research guidance on film coating, but because the conditions of film materials, coating technology and equipment can not meet the production requirements, the practical application is limited to some extent. In the 1950s, AbbottLab first produced new film tablets and patented them under the trademark "Filmtab". After nearly 40 years of research and development, production equipment and process of continuous improvement and perfection, the advent of polymer film materials, film coating technology has been rapid development, especially in Japan, film coating technology has developed the fastest, 80% tablets have changed to film coating.

Film coating technology can be widely used in tablets, pellets and granules, especially for traditional Chinese medicine tablets with strong temperature absorption, easy cracking and easy fading. In the 1990s, the film coating technology has developed in the traditional Chinese medicine industry, mainly used for the film coating of tablets. Compared with icing, film coating has the following advantages:

(1) Short time (it only takes about 2 hours to wrap a pot of tablets, while it takes about 16 hours to wrap a pot of sugar-coated tablets), easy to operate, fast drying speed, little influence of heat on drugs, which is conducive to improving the quality of drugs.

(2) The film coating process saves labor (1~2 operators), plant and equipment (only a standard plant and a coating pot), saves materials, so the cost is low, and the early investment is also very limited.

(3) The weight of the core can only be increased by 2%~4% in the film coated tablets, while the weight of the core can be increased by 50%~100% in the sugar-coated tablets (the main excipient is talcum powder which has been eliminated abroad).

(4) Film coating process can reduce the dust in the workplace, is conducive to environmental protection and labor protection, can also save packaging materials.

(5) The mark of the tablet pressed on the tablet by the film coating process is still clearly visible after the film coating, which is convenient for patients to identify and use.


(6) film coated tablets are strong and wear-resistant, not easy to crack; Film coating materials have excellent physical properties, most of the materials can resist heat and humidity, can improve the quality of products, prolong the validity of products.

(7) There are many materials for film coating to choose from. In addition to achieve the general purpose of coating, but also through the selection of film materials and coating prescription design, so that the formation of coating film in a certain pH range of dissolution or disintegration; Also can control the membrane permeability, so that the package of drugs in the body through the diffusion of release, to achieve the purpose of timing, positioning the release of drugs. This is an important reason for the wide development of film coating.

(8) The production process and material consumption can be standardized

Based on the above factors, the international has basically eliminated sugar-coated tablets, instead of film coated tablets, domestic is also accelerating this process. At present, the application of Chinese traditional medicine film coating technology is still in its infancy in China, and Chinese traditional medicine tablets are mainly sugar-coated tablets. The market prospect of film coating is very broad, so the further research and development and improvement of film coating technology should attract our attention.