process-related factors contribute to coating separation:

1.1 Poor Adhesion Between Core and Coating

Causes:

• Low surface roughness of the tablet core, reducing mechanical bonding.
• Incompatible coating polymer with tablet excipients.
• Residual moisture in the tablet affecting adhesion.

Solution:

• Use pre-coating treatments such as sub-coating or priming layers to improve adhesion.
• Ensure the tablet core has slight surface porosity to enhance mechanical interlocking.

1.2 Inadequate Coating Solution Composition

Causes:

• Incorrect polymer-to-plasticizer ratio affecting film flexibility.
• Use of high-viscosity coating dispersions leading to uneven layer formation.

Solution:

• Use optimized plasticizer levels (10-20%) for flexibility.
• Ensure coating dispersion is well mixed and free of agglomerates.

1.3 Improper Drying Conditions

Causes:

• Excessive drying leads to rapid shrinkage, causing cracks and delamination.
• Insufficient drying results in high residual solvent levels, weakening adhesion.

Solution:

• Maintain controlled inlet air temperature (50-60°C) to allow gradual solvent evaporation.
• Ensure post-coating curing at 40°C for 24 hours to stabilize the polymer film.

Step 2: Optimizing Tablet Core Properties

The mechanical properties of the tablet core influence coating adhesion.

2.1 Controlling Tablet Hardness

Solution:

• Maintain an optimal hardness range of 5-8 kg/cm² to avoid excessive surface smoothness.
• Avoid over-lubrication with magnesium stearate, which can hinder coating adhesion.

2.2 Ensuring Uniform Tablet Surface

Solution:

• Use pre-compression dust removal to eliminate fine powder from the tablet surface.
• Perform tablet dedusting before coating.

Step 3: Improving Coating Application Parameters

Proper spray settings ensure even coating deposition and adhesion.

3.1 Adjusting Spray Rate and Nozzle Position

Solution:

• Use a moderate spray rate (5-10 g/min) to prevent over-wetting.
• Maintain a nozzle-to-tablet bed distance of 10-15 cm for uniform film formation.

3.2 Controlling Atomization Pressure

Solution:

• Set spray pressure between 1.5-2.5 bar to achieve fine droplet formation.
• Prevent excessive air turbulence inside the coating pan.

Step 4: Enhancing Polymer Film Flexibility

Flexible coatings are less prone to cracking and delamination.

4.1 Using the Right Plasticizer

Solution:

• Incorporate triethyl citrate (TEC) or polyethylene glycol (PEG) to improve film strength.
• Ensure plasticizer-polymer compatibility to avoid phase separation.

4.2 Post-Coating Curing

Solution:

• Apply a controlled curing step (40°C, 24 hours) to enhance film integrity.

Step 5: Quality Control and Process Monitoring

Regular quality checks prevent coating defects during production.

5.1 Film Adhesion Testing

Solution:

• Perform tape adhesion tests to evaluate coating integrity.
• Use scanning electron microscopy (SEM) for detailed film analysis.

5.2 Stability Testing

Solution:

• Conduct accelerated stability studies (40°C/75% RH) to assess long-term adhesion.

Step 6: Advanced Technologies to Improve Coating Adhesion

New coating technologies are helping minimize delamination risks.

6.1 Electrostatic Spray Coating

Electrostatic-assisted spraying enhances film adhesion by improving polymer deposition.

6.2 AI-Optimized Coating Process

Machine learning models analyze coating data to recommend optimal process settings.

6.3 3D-Printed Enteric Coatings

Layer-by-layer coating using 3D printing ensures precise polymer adhesion.

Regulatory Considerations for Enteric Coated Tablets

Ensuring compliance with regulatory guidelines is crucial for formulation approval.

7.1 USP and EP Coating Standards

Solution:

• Ensure compliance with USP General Chapter <711> Dissolution for enteric-coated tablets.
• Follow ICH Q6A guidelines for quality attributes of polymer coatings.

7.2 In-Vitro Dissolution Testing

Solution:

• Perform two-stage dissolution testing to confirm acid resistance and intestinal release.
• Ensure no drug release in pH 1.2 gastric fluid and complete release in pH 6.8 buffer.

Conclusion:

Coating layer delamination in enteric-coated tablets can be prevented by optimizing tablet core properties, coating solution composition, drying conditions, and adhesion-enhancing strategies. Implementing plasticizer optimization, post-coating curing, and AI-driven process control will ensure robust enteric coatings, minimizing product defects and improving patient outcomes. Emerging technologies like electrostatic spray coating and 3D-printed coatings offer exciting advancements in enteric coating uniformity and performance.