RAW MATERIAL PROCESSING
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Pharmaceutical Coating Technology: Key Applications and Process Optimization
Pharmaceutical Coating
1. Introduction
2. What Is Pharmaceutical Coating?
3. Coating Types and Functional Applications
3.1 Types and Functions
3.2 Typical Applications
Compressibility describes the ability of a powder to undergo particle rearrangement, plastic deformation, or fracture under applied pressure, ultimately forming a tablet with sufficient mechanical strength.<
Coating Type |
Typical Applications |
Aqueous Film Coating |
General tablets, nutraceuticals, coloring, taste-masking |
Immediate-Release Coating |
Taste-masking, appearance, disintegration control |
Enteric Coating |
Acid protection, GI tolerance, enteric dosage forms |
Sustained/Controlled-Release Coating |
Long-acting tablets, MUPS, pellets |
4. Coating Process Overview and Optimization Strategies
4.1 Process Principles
Most coating polymers are high-molecular-weight materials. Gastric-soluble polymers include HPMC and PVA; enteric polymers include methacrylic acid copolymers (e.g., Eudragit® L30D-55); sustained-release polymers include ethylcellulose (Surelease®, ETHOCEL™, Aquacoat®) and cellulose acetate (CoreleaseCA™).
Because polymers dissolve via a swelling → dissolution process, coating preparation requires adequate hydration and viscosity control (typically 50–150 cP). Proper viscosity ensures stable atomization and uniform film formation.
After the spray gun atomizes the coating suspension onto the tablet surface, moisture evaporates under heated airflow. As the water leaves, the polymer chains move closer, diffuse, and coalesce, ultimately forming a continuous and uniform film. Film-forming mechanisms differ between solution-based systems and dispersion-based systems. Solution systems (e.g., HPMC-based immediate-release coatings) form films through the free movement and interdiffusion of polymer chains. Dispersion systems (e.g., acrylic enteric coatings such as Eudragit® L30D-55) form films by the fusion of latex particles once the temperature is high enough to enable coalescence.
Film quality is governed by the glass transition temperature (Tg) and the minimum film-forming temperature (MFT). The substrate temperature must remain above the MFT; otherwise, the coating may become rough or crack. Plasticizers such as PEG or triacetin help lower the MFT and facilitate film formation. Optimal process temperatures vary by system—for example, HPMC coatings typically run at 38–42°C, while acrylic enteric coatings operate around 28–32°C.
Fill depth determines the theoretical tablet weight and is fundamental to weight consistency. Pre-compression helps remove entrapped air, reducing the risk of capping or lamination during the main compression stage. Main compression force directly affects tablet hardness, density, and internal structure.
These parameters must be optimized in combination rather than individually. By analyzing compression force profiles alongside tablet appearance and physical properties, manufacturers can define a robust process window that ensures consistent quality and stable, continuous production.Traditional sugar-coating pans rely on pan rotation and hot air for drying but tend to generate more dust and have lower efficiency. Modern perforated side-vented coaters use through-air drying, providing faster moisture removal, cleaner operation, and more uniform film quality—making them the standard equipment in today’s pharmaceutical manufacturing.
4.2 Common Coating Problems and Optimization Strategies
4.2.1 Non-uniform Film Thickness
4.2.3 Cracking / Brittle Film
Excess core dust or low surface energy
Insufficient wetting of the first layer
Droplets too fine, inadequate film spreading
Optimization Strategies:
Improve tablet quality: hardness, low friability, thorough dedusting.
Use larger droplets for the first layer to improve wetting and penetration.
Select polymers with stronger adhesion groups (e.g., hydroxyl, carboxyl).
Raise tablet-bed temperature slightly to slow early drying and enhance bonding.
4.2.5 Poor Drying / High Residual Solvent
Low inlet temperature or airflow
Spray–evaporation mismatch
Slow early evaporation in aqueous systems
Optimization Strategies:
Increase inlet air temperature, airflow, and exhaust efficiency.
Adjust spray rate and atomization for better heat and mass transfer.
For aqueous coatings: use high-airflow, low-temperature moisture removal at the final stage.
For organic coatings: enhance solvent recovery and controlled final drying.
5. Conclusion
Coating technology is no longer just a way to improve appearance or protect the drug; it has become a critical step that directly affects stability, release performance, and patient experience.
As manufacturing standards continue to rise, companies must establish a robust process window that balances material selection, spraying parameters, drying efficiency, and equipment control. For manufacturers aiming at high-quality formulations, continuous optimization of the coating process has become a key driver of competitiveness. If you are planning or upgrading your coating line, we are ready to support you with a complete and reliable production solution.
Aligned Machinery is a leading manufacturer of pharmaceutical machinery with over 20 years of experience. Our products are used by pharmaceutical companies worldwide. Recognized for quality, reliability, and compliance with international standards, we are committed to helping partners improve efficiency and achieve sustainable growth.
Aligned Machinery is a leading manufacturer of pharmaceutical machinery with over 20 years of experience. Our products are used by pharmaceutical companies worldwide. Recognized for quality, reliability, and compliance with international standards, we are committed to helping partners improve efficiency and achieve sustainable growth.
To learn more about our solutions or discuss your project needs, please reach us directly at info@aligned-machinery.com / +86 13967712128.
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