Key composition of film coating Process robustness: Process robustness means that control parameters can be changed as little as possible from the beginning to the end of the process, with less personnel intervention. This ideal state needs to be excellent in all aspects to achieve. As with continuous process validation, if a prescription is flawed from the beginning of the process, it is difficult for you to make up for it through the coating. The solid preparation process is relatively large, and sometimes there is a kind of dependence. For example, because the nature of the raw materials changes, the particles produced by the granulation are not good. The granulation may hope to adjust the tableting process, and then if the granules are not good due to the bad particles. The core is not good, and the tablet may hope to adjust the coating process. However, the problem is that the coating is not a universal process and cannot cover all the defects. In many cases, the failure of the coating actually fails from granulation. Therefore, process robustness is the foundation, and the rest of the content is optimized on this basis. 2. Product loading: It is generally described that the loading amount is such that the baffle cannot be exposed in the spray area. There is no doubt that the stainless steel piece such as the baffle has a lower temperature and a slower drying, and it is likely to cause adhesion when sprayed on it. In order to improve the coating efficiency, the loading should be as much as possible (as long as the film does not fall out), too little loading will cause uneven sliding coating of the film bed. It should be noted that the loading should ensure that the exhaust chamber can be completely covered after the film bed forms a uniform waterfall, otherwise the reactive hot air will reduce the drying efficiency and prolong the coating time. Of course, there is also a type of "shoe" type coating machine that can adjust the size of the exhaust chamber to solve this problem. 3. Coating pan speed: There is a test to investigate the uniformity of the rotation speed and the coating. In the test, it can be seen that the thickness of the bread is larger than the diameter of the film, and the diameter of the film is larger than the edge of the boundary. Considering that the edges are not easy to observe and select the diameter of the film, it can be seen that increasing the rotation speed reduces the slippage of the bed to improve the uniformity of the coating after the waterfall, but the excessively fast rotation speed leads to increased wear. There are many parameters that affect the setting of the speed, such as: core size, core friability and smoothness, baffle, loading, drying capacity, etc. The size and smoothness of the core, the shape of the baffle have an effect on the formation of the bed waterfall. The flat core is sometimes not bonded in time to form twins or even multiple pieces, of course. Adding a small arc to the core plane will solve it. Core friability is not difficult to understand. If the friability is poor, too fast a speed will cause edge, debris and the like. In order to compensate for the sliding of the bed, the rotation speed can be improved when the loading of the core is small. In addition, the drying speed and drying ability of the coating process also affect the rotation speed. If the drying speed is slow, the drying time can be improved by reducing the spray amount and decreasing the rotation speed. Therefore, the speed selection can make the bed form a low speed of the waterfall. 4. Spray range and spray distribution: The spray range is directly related to the gun design, and the number, mounting angle and installation distance have a direct impact. A relatively good spray gun can generally ensure a uniform distribution of droplets throughout the spray area, and the current domestic effect is slightly worse. For the common multi-gun design coating machine, it should be noted that it is necessary to avoid overlapping or leaking points in the middle of the multi-gun spray area, affecting the uniformity of the coating layer, and of course, preventing spraying onto the wall of the pot. There is no clear value for the height of the spray gun. Generally, the film coat is 30cm on the bed, the enteric coat can be lower, and the angle of the spray gun should be perpendicular to the bed after the waterfall is formed to prevent the coating liquid from rebounding. . There is no clear indication as to whether the spray gun is mounted in the middle or upper 1/3 of the bed. Both positions are acceptable. Relatively speaking, the upper 1/3 can be used for a longer drying time. 5. Coating liquid flow rate: The peristaltic pump is widely used for conveying the coating liquid because of its good flow control ability and non-polluting effect. However, in practical applications, it can be found that the conveying amount of the coating liquid changes relatively large and is not uniform. Ideally, in order to obtain a relatively stable flow rate, the peristaltic pump speed can be set at the middle of the range. For example, for a 0-200 rpm peristaltic pump, a pump speed of about 100 can achieve better flow control effects, such as It is suitable to use a pump head with a small diameter. For the coating machine that delivers the liquid separately for each spray gun, if the rubber hose needs to be replaced, the same one of the pump heads will be replaced. In one case, the effect of the coating machine after the replacement of one of the hoses was reduced. After the investigation, it was found that the flexibility of the new and old hoses caused the flow of the coating liquid to change. 6. Drying: For the drying of the coating process, the air volume is more important than the temperature, which is also the main source of the difference in equipment performance at home and abroad. It should be noted that the negative pressure control for the formation of exhaust air is not the greater the negative pressure, the negative pressure is too large, and the air leakage at the door will affect the spray effect. Therefore, it is recommended to use a small negative pressure or even a negative pressure. In addition, in recent years, with the promotion of water-based coatings, many people mistake the coating temperature as the inlet air temperature. For example, the coating temperature recommended by Kalakang is 40 °C, which means the temperature of the bed is even 70 ° C does not affect, of course, the bed temperature measurement as far as possible to test the middle area of ​​the just sprayed position. For the drying process, preheating can make the coating obtain better drying effect and improve the coating efficiency. The foreign product cores are generally better, and the preheating is beneficial to improve the efficiency. After many cores are preheated, It may cause adverse consequences such as a decrease in friability (such as some Chinese medicines), so whether or not preheating is not mandatory is determined by the ability of the core. 7. Core for coating: For example, the mechanical integrity of the core, film adhesion, marking (scratch), film uniformity, for the core, friability is more important than hardness, the recommended core friability is less than 0.5%, Zui Good not more than 0.1%, hardness 8-10Kp, of course, this is only the ideal recommended value. In fact, many tablets can be coated with 4Kp hardness. The adhesion of the tablet itself depends on the porosity, theoretically microcrystalline cellulose > lactose > sucrose > calcium hydrogen phosphate. (ps: I have seen a prescription, the adhesion of the coating is poor, adding a small amount of sugar to the coating to improve the adhesion) If the mold of the tablet is worn, the core has a groove or flash, when coating The coating liquid is not easy to cover or the falling edge of the coating during the coating process also affects the uniformity of the coating. If it is a scored piece, it is also necessary to combine the shape of the sheet to analyze the easy-wearing position of the Zui, and avoid or adjust it during the scoring. In addition, the formulation of the core has a great influence on the coating effect. For example, magnesium stearate and magnesium stearate are in the form of flakes. The mechanism of lubrication is to wrap the surface of the particles, so the mixing time of magnesium stearate should not be too long. , 1-2min is fine. Too much amount or too long mixing time may cause the core to be soft, the compressibility to decrease, the dissolution to decrease, and the film adhesion to decrease (this has a great influence on the plastic deformation auxiliary materials such as MCC or compressible starch, and the brittle deformation auxiliary materials such as lactose. The effect is slightly smaller, and the brittle fracture is equivalent to an increase in the contact area). In addition, super disintegrants may cause unevenness on the surface of the sheet after coating, because the mechanism of action of the super disintegrant is water swelling and superabsorbent swelling during the coating process.
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