Tablet Coating Process
The distribution of the coating is refined by the movement of the tablet in the coating pan and air suspension coater either perpendicular or vertically for the application of the coating composition. The tablet coating process is often the last step in the tablet manufacturing cycle.The application of the coating solution on a tablet provides visual characteristics to a tablet. Hence, the quality of the product may be determined in this final production step.
The selection of different types of tablet coating that is to be applied as per the durability means toughness of the tablet core, and also depends upon that how economical the process is.
As increasing the cost of labor and energy, the cost of organic solvents as well as an environmental compulsion, the economics of the process gets increases.
The sugar coating process because of achieving excellent tablet appearance is a very widely used technique.
Read More - Why coat tablets?
Essentially there are four major techniques used for the application of a coating of pharmaceutical dosage forms;
1) Sugar coating
2) Film coating
3) Microencapsulation
4) Compression coating
This process includes the application of an aqueous solution of sugar mainly sucrose as well as sorbitol.
1) Sugar coating
2) Film coating
3) Microencapsulation
4) Compression coating
This process includes the application of an aqueous solution of sugar mainly sucrose as well as sorbitol.
Anciently, the sugar coating involved a large number of individuals in the application of most of the coating formations, and this employing technique required highly-skilled people. Because of this reason, a batch of tablets takes at least five days for coating. (In recent advances it takes less than one day to complete)
The film coating involved the application of thin polymeric film that contains polymers, plasticizers, coloring agents, and flavoring agents onto the dosage forms in the form of a solution, originally based on organic solvent, but that is now more dependent upon water as a prime solvent.
The majority of film coating formulations are designed for immediate release. It can also be used for modifying drug release from the final dosage forms.
The polymer that is used to modify drug release, is not soluble in water and hence, these systems are commonly formulated as aqueous-based suspensions.
Microencapsulation is an advanced or modified form of film coating. The main differences are only in the size of particles that are to be coated and the methods through which it is finished.
The Microencapsulation process is based on mechanical methods that involved air suspension technique, multi-orifice centrifugal technique, pan coating, and modified spray-drying techniques.
The physicochemical methods involved coacervation-phase separation, in which the material that is to be coated is suspended in the solution of the polymer. The phase separation is carried out by the addition of incompatible polymer or inorganic salts, nonsolvent.
Compression coating comprises the use of modified tablet machines that allows the compaction of dry coating around a tablet core exhibited by that same tablet machine.
Necessarily, the tablet core produced on one side of the tablet machine is transferred into the large die, which is partially filled with coating power and additional coating power is filled on the top of the core tablet and finally, the powdered coating material is compacted into a layer that surrounds the core tablet.
The advantage of the compression coating process is that it eliminates the use of any of the solvents whether it is organic or aqueous.
Although, the compression coating is very complex and not used vary commonly. But nowadays, there are some modifications found in this process and this process is used in a special type of coating formation the novel drug delivery system.
Sugar Coating of Compressed Tablets
Sucrose is a commonly used material in the sugar coating of tablets because it produces smooth and high-quality coatings.Although the popularity of this process has declined the sugar-coating technique is still used by many companies.
The sugar coating technique is a multistep process, where the aesthetics of the final coated product is an important characteristic. It is depending upon the highly skilled operators.
The sugar coating technique is mainly a manual process, where coating materials either in the form of liquid or solids are applied by the hand to the surface of the rotating bed of tablets.
The sugar-coating process is commonly distributed into six main steps:
(1) Sealing(2) Sub coating
(3) Smoothing
(4) Color coating
(5) Polishing
(6) Printing
Sealing:
In this step, a specialized polymer coating is directly applied to the tablet core for separating the tablet ingredients (drug) from the water for achieving good product stability.It also provides strength to the tablet core. Usually, the sealing coats contain approximately 10% to 30% of alcoholic solutions of resins such as cellulose acetate phthalate, polyvinyl acetate phthalate, shellac, and zein.
Generally. shellac is a popular choice of material in the step of sealing. Although, this natural polymer can undergo further polymerization on the storage due to which the seal coat becomes completely insoluble and because of this reason, the bioavailability of the active pharmaceutical ingredients may be compromised.
This problem may be minimized by adding polyvinylpyrrolidone (PVP) into the shellac-based seal coating formulations.
The quantity for the application of the sealing coat depends on the batch size of the tablet. The porosity is also an important factor because highly porous tablets may tend to soak up the first application of the solution. It is also very important for preventing the uniform spreading of solution on the surface of the tablet batch.
It can be minimized by the application of resin solution to ensure that the tablet cores are seasonally sealed completely.
Many sealing coats develop stickiness during the drying process so it is important to apply dusting power for the prevention of tablet sticking.
The excessive use of talc may cause problems like tablets becoming more slippery. To minimize it, the rolling of tablets should be in the proper manner in the pan.
If there is a requirement of preparation of delayed-release that enteric coated tablet then it can be obtained by making additional application of seal coat solution.
Subcoating:
In this step of the sugar-coating process, the tablet gained almost 50% of the final coating weight.When there is difficulty in covering the edges of the tablets, a lumpy sub-coat can be the result, especially if care is not taken during the application of the alternate layers. Then, this is a very effective step in the sugar-coating process.
If the amount of dusting powder applied is not matched to the binding capacity of the gum solution, the final coating become hard and dust will also collect on the backside of the coating pan and stick again to the tablet surface while following the application of gum solution that may cause roughness to the tablet.
Smoothing:
Smoothing can be instructed by the application of simple syrup solution (approximately 60-70% of sugar solids). Smoothing syrups consist of a low percentage (1-5%) of titanium dioxide as an opacifier. This is useful when the following color coating formulation uses water-soluble dyes as a colorant.Color Coating:
This is the most critical step in the sugar-coating process because it has the greatest impact on the final visual effect of the tablet. It contains multiple applications of syrup solution that contains proper coloring materials.Two types of coloring material are used: ed, water-soluble dyes, and water-insoluble pigments. The selection of the colorants depends on the type of coating procedure.
The water-soluble dyes produce the most elegant sugar-coated tablets. The water-soluble dyes are migratory colorants because of this great care must be taken.
The water-insoluble pigments have significant advantages, as pigments are insoluble in water during the drying step color migration is eliminated.
water-insoluble pigment (e.g., titanium dioxide, iron oxides) based color coatings are easier to use by less skilled coating operators.
Polishing:
As sugar-coating tablets are very dull in appearance so, it needs to be polished for getting a glossy finish.Polishing is achieved by applying a wax mixture like beeswax, candelilla wax, carnauba wax, or hard paraffin wax to the tablets in a polishing pan. This wax mixture is applied as powder or solutions in various organic solvents.
Printing:
In addition to the shape, size, and color, to identify the sugar-coated tablets it is very important to print them either before or after polishing by using the inks of pharmaceutical branding.Sugar-Coating Problems
During the sugar coating of tablets, there are various problems may be encountered. If the tablets are not strong enough to withstand the applied stress, any process in which tablets fall over constantly can cause this problem.
Using lots of dusting power may cause cracking of the coated tablets.
When water-soluble dyes are used then during drying color migration may occur.
The rough surface of tablets shows a marbled appearance during the polishing of tablets.
The traditional sugar-coating pans show poor mixing characteristics. Due to this if care is not taken during the coating process then the distribution of coating materials throughout the batch can be nonuniform and will create finished tablets of varying sizes.
Read more - Common tablet defects appear in the manufacturing of tablets
I hope you like my article Tablet Coating Process in Pharmaceutical Industry. I give up the information about tablet coating critical process parameters after compression. If you have any questions or queries related to the article then feel free to ask in the comment section.
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Read more - Physical evaluation of a tablet after post-compression
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