Troubleshooting 5 Common Tablet Coating Defects: Bridging, Cratering, and Orange Peel

Introduction

Achieving a smooth, consistent finish on tablets isn’t always easy, even with a high-quality tablet coating machine. Common defects such as bridging, cratering, orange peel, peeling, and sticking can appear unexpectedly, affecting tablet appearance, quality, and downstream processes.

The good news is that most defects can be prevented or corrected if you understand their causes and know the right adjustments to make. In this guide, we explore the five most common tablet coating defects and provide practical solutions that production managers and operators can apply immediately.

Bridging: Coating Filling the Gaps

What Is Bridging?
Bridging occurs when coating material accumulates in the concave areas of a tablet, forming a “bridge” over these indentations instead of coating evenly. This results in uneven tablet surfaces and can affect both appearance and function.

Common Causes:

• High viscosity coatings that do not level properly

• Slow drying or inadequate airflow

• Incorrect spray rate or pan speed

Practical Solutions:

• Reduce the flow rate of the coating solution and increase pan rotation speed to improve tablet movement

• Adjust coating viscosity or improve drying conditions

• Using a tablet film coating machine with better airflow can significantly reduce bridging

Cratering: Small Pits on Tablet Surfaces

What Causes Cratering?
Cratering appears as tiny pits or holes in the tablet surface. It often happens when air or moisture escapes from the tablet during drying, or when the coating formulation is incompatible with the tablet core.

Key Factors:

• Spray rate that is too fast

• High drying temperature

• Thick or uneven coating solution

• Poor tablet surface quality

Troubleshooting Tips:

• Slow down the spray rate and optimize drying temperature for better leveling

• Consider using a thinner coating solution or adding plasticizers for smoother film formation

• Ensure tablets are properly dried and cured before coating

Orange Peel: Rough, Uneven Texture

Understanding Orange Peel Defect
Orange peel refers to a bumpy, rough tablet surface that resembles the skin of an orange. While often cosmetic, it can also indicate problems with coating adhesion or formulation.

Main Causes:

• Improper atomization of the spray

• High spray rates or low pan speeds

• Inadequate drying conditions

Solutions:

• Adjust nozzle pressure and angle for better atomization

• Balance pan speed and spray rate for proper tablet tumbling

• Control drying temperature and humidity

• In some cases, minor reformulation of the coating solution can improve surface smoothness

Peeling and Flaking: When Coating Detaches

Why It Happens:
Peeling or flaking occurs when the coating layer separates from the tablet surface. This can compromise product quality and shelf life.

Common Causes:

• Incompatible coating materials

• Over-drying or rapid temperature changes

• Contaminated tablet surfaces

Preventive Measures:

• Ensure coating and tablet core are compatible

• Use controlled drying cycles to prevent thermal shock

• Maintain clean tablet surfaces prior to coating

• Employ a sugar coating pan or fluid bed coater with precise environmental controls for sensitive formulations

Sticking and Picking: Tablets Adhering to Surfaces

What Are Sticking and Picking?

• Sticking: Tablets adhere to the pan or each other

• Picking: Coating is pulled off the tablet surface

Causes:

• High moisture content or tacky coatings

• Insufficient drying

• Poor pan design

Remedies:

• Optimize drying conditions to reduce surface moisture

• Adjust coating formulation to reduce tackiness

• Use tablet coating machines with non-stick or perforated pans for improved airflow

• Regular equipment cleaning prevents buildup

Quick Comparison Table: Common Tablet Coating Defects

Conclusion

Defects like bridging, cratering, and orange peel don’t have to slow down your production. By understanding the root causes and applying targeted fixes, you can:

• Improve product appearance and quality

• Reduce material waste and downtime

• Maximize the efficiency of your tablet coating machine

Choosing the right equipment—such as a tablet film coating machine, sugar coating pan, or perforated coating pan from trusted manufacturers like JIANPAI—can prevent many common defects and enhance overall production performance.

Frequently Asked Questions

Q1: What causes bridging in tablet coating?
A1: Bridging usually happens when the coating is too thick or slow to dry, causing accumulation in tablet indentations.

Q2: How can cratering be minimized?
A2: Reduce spray rate, optimize drying temperature, and ensure proper tablet curing.

Q3: Why does orange peel occur?
A3: It’s often due to poor atomization, high spray rates, or incorrect drying conditions.

Q4: How can sticking and picking be prevented?
A4: Use non-stick or perforated pans, control moisture, and maintain proper drying.

Q5: Can coating defects affect drug efficacy?
A5: Yes. Peeling, cratering, or uneven coating may compromise drug release and shelf life.