Suresh Pareek, Managing Director, Ideal Cures; Dario Luini, Area Manager EMEA & US, Ideal Cures and Sanjay Negi, DGM Film Coatings, Ideal Cures, share more details about Ideal Cures revolutionary product Instacoat 4G
The pharmaceutical industry is witnessing a changeover from conventional batch to automated continuous processing in response to changing marketplace and productivity requirement. In view of this trend, the tablet coating industry has also seen the introduction of numerous types of coating equipment from early batch coating machines having 60 to 72” pan diameter to continuous coating machines, all claiming improved efficiency and productivity. The present study evaluates the coating uniformity and appearance of tablets coated with IDEAL CURES revolutionary product Instacoat 4G (patent pending), high solids coating system of 35 per cent in a continuous mode from start-up to shut-down in a fully perforated continuous coater.Continuous film coating technology is being appreciated widely for improving coating productivity rates; however, it still has to gain acceptability for coating of pharmaceutical products.[1] Advancements in design of continuous coating machines over the years, have allowed the processing by both batch and continuous methods without having to compromise the quality of coated products in terms of colour uniformity and tablet appearance.
It is for the first time, that a coating material at a high solid content of 35 per cent is used for coating of tablets in a continuous coater. Continuous film coating processes are recognised for their high production rates, but have not gained wide acceptance for pharma products due to potential product losses during start-up and shut down. Advancements in continuous coater design over the years, not only allows processing in batch and continuous modes but also ensure uniform and consistent coating for tablets from start to finish.
Materials and methods Materials
Oblong shaped tablets having ‘Instacoat’ embossing were used as a substrate. The coating system used was INSTACOAT 4G (patent pending), a high productivity film coating system by Ideal Cures, reconstituted in water at 35 per cent solids concentration and applied at a target weight gain of 2.5 per cent (see Table 1). This revolutionary coating product provides fast drying of tablets at high spray rates without causing gun blockages.
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Table. 1: Placebo tablets and coating formulation details
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| Placebo tablets details | |
| Placebo tablets dimensions | 19.5 mm long with breadth 9.3 mm and thickness 5.5 mm oblong shaped tablets having monogram (INSTACOAT Logo) on both sides. |
| Coating formulation details | |
| Product name | INSTACOAT 4G |
| Colour | Red |
Equipment
Trials were conducted in a 24 inch fully perforated drum (Drum Diameter) of Thomas Engineering based in Chicago, Illinois, US, continuous coater (Model: Thomas Flex CTC) (see Figure 1), equipped with 22 spray guns (Model: Schlick ABC Technology 940). 22 spray guns were divided into two separate Manifolds (11 Spray Guns per manifold) controls. The continuous coating pan was equipped with an automatic in feed which gently introduces tablets to the bed on a steady basis, weight belt interface permits tablet loading automation with Thomas COMPU-COAT ® controls. The discharge end of the unit contained a pneumatically controlled end plate, which when closed contained all the tablets and when opened, it served to control the flow of tablets in the discharge zone. The individual gun sequencing system ensures less product loss and re-processing during start up and shut down. The absence of baffles in the pan interior is an additional feature that separates this machine from coating machines available earlier. (see Figure 2). Movement of the tablets inside the coating pan is handled by the tablet feed from the hopper. Anti-slide bars inside the coating pan ensure a consistent tablet bed movement.
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Table 2: Coating Suspension Characteristics
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| Parameters | Observations |
| Appearance | Free-flowing, lumps free coating suspension |
| Colour | Red |
| pH (Two per cent w/w at room temperature) | 7 |
| Viscosity (cps) | 210 |
Trial-continuous mode process
The batch was coated using Instacoat 4G, a revolutionary coating material which works efficiently at a high solids content of 35 per cent and provides smooth and elegant coating without gun blockages. Thomas Engineering’s tested coating parameters were used for carrying out continuous coating operation. The tablet container was loaded inside the continuous coater via weigh feed belt. Tablets loaded via bin onto the container of the coating machine feeding zone. Tablets were fed into pan via a tube from the hopper to a total fill of 150 kg. The batch tablets were moved into the waxing /cooling zone after achieving the desired weight gain. Once desired weight gain is achieved machine is tilted and all coated tablets were unloaded in suitable containers. The target process conditions are listed (see Table 3).
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Table 3: Coating process parameters
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| Coating pan details | |
| Pan diameter ( Inches) | 24 |
| Spray gun details | |
| Gun type | Schlick |
| No. of guns | 22 |
| Nozzle diameter (mm) | 1.0 |
| Coating suspension details | |
| Solids content (% w/w) | 35 |
| Solvent | Purified water |
| Stirring time (minutes) | 45 |
| Coating process parameters | |
| Desired weight gain (%) | 2.5 |
| Batch size (Kg.) | 1000 |
| Inlet temp (?C) | 59-64 |
| Bed temp (?C) | 43-45 |
| Exhaust temp. (?C) | 47-48 |
| Airflow (cfm) | 6700 |
| Atomizing air pressure (Psi) | 40-42 |
| Pattern air pressure (Psi) | 30-32 |
| Pan speed (rpm) | 10-12 |
| Spray rate (g/min) | 548-756 |
| Weigh belt feed rate (kg/hr) | 544-635 |
| Environmental equivalence factor | 7.265-11.256 |
Coated tablets obtained the desired weight gain and tablet to tablet color uniformity in continuous mode very quickly as compared to a batch coating machine. This quick rate of attainment color uniformity was due to the combined effect of repeated tablet exposure to spray guns, large spray area, flat tablet bed and also high solids (35% w/w) content of INSTACOAT 4G coating system. INSTACOAT 4G is a revolutionary product which at low viscosity provides easy coating of tablets at high spray rates even in continuous coating operation. The elongated horizontal cylindrical geometry of the continuous coater provided a flat tablet bed and large surface area for the coating of tablets. This coupled with multiple spray guns helped in obtaining desired coating uniformity in less amount of time.
Color development and uniformity testing
Coated tablets samples were collected from the unloading point of the continuous coater once tablets achieved desired weight gain of 2.5 per cent. Tablets were visually tested for appearance, colour uniformity, colour difference, disintegration time and coating defects. Colour difference of the coated tablets was checked using premier colour matching instrument.
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Table 4: Coating process evaluation
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| Parameters | Observations |
| (A) Process feasibility | |
| Ease of operation | No gun choking observed during the coating process |
| Sprayability | Free-flowing, lumps free and grittiness free coating suspension |
| (B) Coating defects | |
| Sticking and picking | |
| Peel off | |
| Logo bridging | No coating defects observed |
| Roughness | |
| Any other | |
| (C) Tablet appearance | |
| Smoothness | Smooth tablet surface |
| Logo clarity | Satisfactory logo clarity |
Results and discussion
The coating trial of Instacoat 4G was successfully executed on a batch size of 1000 Kg using Thomas Engineering Continuous Coater. Coated tablets were evaluated for appearance, colour difference, coating defects and disintegration time at the end of coating process and all the results were found acceptable. The appearance of coated tablet was good. The coated tablets had good colour uniformity and free of any coating defects (Figure 2). Consistent colour uniformity was confirmed with the colour difference results obtained using Premier Colour Matching Instrument
Note: In a continuous coater, colour Uniformity was achieved for the lot in significantly less time (15 minutes) of coating than would be seen in Autocoater (60 Minutes) due to high solids capability of Instacoat 4G and Thomas Engg. Continuous coating technology.
Conclusion
The Instacoat 4G coating formulation is well suited for continuous coating technology due to its low viscosity and high solids capability (35 per cent w/w). As a result target 2.5 per cent coating weight gain could be achieved at a high tablet throughput rates (Feed Rate: 650 Kg/hr) during the continuous mode of operation. Further optimisation of the coating parameters for Instacoat 4G will enable an even higher throughput rate without compromising the quality of the finished product.
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Table 5: Coated tablets characteristics
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| Sampling intervals (Min) | Actual coating weight gain (%) | Parameters | Observations |
| 25 | 2.5 | Appearance | Satisfactory |
| Colour difference (dE) | 1.0 | ||
| Disintegration time (Sec.) | 50 | ||
| Coating Defects | Nil | ||
Instacoat 4G is a highly advanced coating system from Ideal Cures is well suited for all the coating technologies from a conventional to most advanced continuous coaters being used in the pharma industry worldwide.
Reference
1. Porter, SC; “Continuous Film Coating Processes: A Review”, Tablets and Capsules, April 2007.