Have you ever observed the structure of capsules? Some gel capsules appear to have no trace of adhesive, yet they are completely leak-proof. How is this achieved?
In the nutritional supplement and pharmaceutical manufacturing industry, capsule sealing plays a crucial role in product quality assurance. Any gap between the capsule cap and the capsule body can cause leakage, significantly reducing the efficacy of the medication. This is especially true for liquid products like omega-3 capsules, where the requirements for capsule sealing are even more stringent. For different contents, capsule sealing methods vary widely. This article will reveal the techniques behind perfectly sealed capsules and will show how capsules are sealed more effectively in real production.
Key Takeaways
● Capsule sealing definition and why it matters
● The differences between hard capsules, softgels, and liquid-filled hard capsules
● Common capsule sealing methods with rationale, pros, and cons
● Step-by-step process of how capsules are sealed in real manufacturing
● Machines used for capsule sealing and how they work
● Key challenges in liquid capsule sealing and how Rich Packing addresses them
Capsule sealing refers to the formation of a strong, closed structure between the capsule cap and the capsule body, acting like a protective shield to prevent external interference with medication or the efficacy of the active ingredient. This basic capsule definition is especially important when the product contains oils, liquids, or moisture-sensitive powders. A good seal helps prevent leakage, oxidation, odor diffusion, and moisture absorption.
When people ask how capsules are sealed, they usually mean one of two things:
Locking and sealing double-layered hard capsules
sealing a one-piece soft capsule, such as a softgel, during or after forming
Two-piece hard capsules, a traditional capsule type, consist of a body and a cap. With records dating back to the mid-19th century, these capsules are commonly seen in medication sold in pharmacies and hospitals like domino seal capsules; other capsules, such as HPMC capsules, also adopt this structure.
As long as the filler is solid, these capsules generally do not require secondary sealing. The cap's structural design allows the capsule to close relatively tightly after passing through the locking station. In some applications, however, manufacturers may still seal hard gelatin capsules to improve tamper evidence or reduce the risk of separation during transport.
Liquid-filled hard capsules are a branch of two-piece capsules. They are widely used to fill oily or water-based health supplements. Supplement products like fish oil capsules, omega-3 capsules, and fat-soluble vitamins use this structure.
Since these capsules contain liquid, they are more prone to leakage compared to powders and granules. Therefore, some liquid capsules undergo a capsule band sealing process, applying a gelatin band around the joint. Other manufacturers use fusion sealing, using alcohol to slightly dissolve the capsule interface, making the cap and body "fuse" together.
There are structural differences between soft capsules and hard capsules, which are closely related to the sealing method. Unlike the separate structure of two-piece capsules, soft capsules:
● Use a one-piece, sealed outer shell
● Usually fill and seal in one step
● Commonly used for oil-based and liquid active ingredients
● Easier to swallow
Soft gel capsules are typically formed by heated gel ribbons on both sides which meet at the forming rollers, filled with liquid and formed in shape by pressure. Therefore, they can achieve good sealing without the need for secondary sealing. This is one reason why how to seal gel capsules depends on whether the product is a softgel or a hard capsule filled with liquid.
This is the heart of the topic. If your audience searches how capsules are sealed, this is the section they really care about.
Below are the most common sealing approaches used in the industry which help boost your understanding of how to seal capsules.
Table 1-Common Capsule Sealing Methods
|
Method |
Principle |
Used For |
|
Capsule Band Sealing |
A gelatin or HPMC band is applied around the seam |
Liquid-filled capsules, fish oil capsules, omega-3 products |
|
Fusion Sealing |
The seam is softened and bonded with heat |
Hard gelatin capsules, some HPMC capsules |
|
Micro-Spray Sealing |
A small amount of sealing solution is sprayed on the joint |
Hard capsules, automated lines |
|
Sealing Fluid / Solvent Sealing |
A sealing fluid helps close the seam after drying |
Some specialty or older processes |
|
Thermal Spot Sealing |
Heat is applied to selected points on the capsule joint |
Certain hard capsule applications |
Capsule Band Sealing
This is one of the most widely used sealing methods in nutraceutical and pharmaceutical production. It is commonly applied to seal oil capsules, as it helps reduce leakage. The colored band also enhances product appearance and brand recognition. As noted in Tablets & Capsules, banding provides benefits such as leak prevention, improved brand visibility, and tamper evidence.
Fusion Sealing
Fusion sealing focuses on bonding the seal itself. It's more like welding the capsule seam rather than adding a sealing strip to the outside. This technique requires more precise control, but the final seal looks cleaner. When comparing band sealing vs fusion sealing, manufacturers usually weigh appearance, compatibility, and leakage risk.
Micro-Spray Sealing
This method uses localized spraying, allowing more precise control over the sealing area. According to CapsCanada’s technical overview, micro-spray sealing lowers the melting point at the joint and promotes bonding. However, such controlled liquid capsule sealing method requires careful monitoring during heating is required to avoid bubbles or deformation.
Solvent Sealing
This is a traditional method once used in the past. The principle is to first soften the capsule joint and then close it after drying. This method is less commonly used today, as modern production lines tend to employ more stable and controllable methods. In some specialty applications, manufacturers still use it to seal hard gelatin capsules.
Thermal Spot Sealing
This method is simple to operate and requires less material. However, the sealing effect is weaker, making it unsuitable for liquid seal products with high sealing performance requirements. It is generally not preferred when manufacturers need a highly reliable sealed capsule.
Band Sealing for Liquid-Filled Hard Capsules
In band sealing, manufacturers first separate and arrange the empty capsules, then fill the capsule body with liquid and close the capsule. After a short resting period to stabilize internal pressure, a sealing band is applied around the cap-body seam. The capsules are then dried, inspected for seal quality, and defective units are rejected before final packaging.
Fusion or Micro-Spray Sealing
In the melt-sealing or micro-spray sealing process, hard gel capsules are first filled and locked, then transferred to a sealing station. Sealing liquid or micro-spray liquid is sprayed at the seam, by localized heating to bond the cap and body together. After drying and cooling, the capsules are inspected for leaks or deformation; only qualified products proceed to the packaging stage.
Softgel Sealing
Softgel sealing follows a different route. The gelatin is prepared first, then formed into ribbons. The filling material is injected during encapsulation, and the softgel is sealed at the same time. After that, the softgels go through drying, inspection and final seal oil capsule packing.
If the process is the recipe, the machine is the kitchen. Different operations need different equipment depending on output, filling type, and required sealing integrity.
Common machines used in capsule sealing include:
Capsule Banding Machine: used to apply a gelatin or HPMC band around the capsule joint part.
Micro-Spray Sealing Machine: sprays sealing liquid on specific position for precise sealing.
Capsule Drying Unit: Used for drying the softgels after they’re formed.
Semi-Automatic Liquid Capsule Filling Machine: suitable for pilot production, testing, and small batches.
Automatic Liquid Capsule Filling Machine: used for large-scale, continuous capsule filling and sealing.
When it comes to actual production, how capsules are sealed perfectly is closely related to the concentricity of the machine's mold, the accuracy of filling, and the precision of the indexing box. Even slight differences can cause solids or liquids to leak from the capsule, or even lead to capsule creases and breakage. Rich Packing, with over 30 years of R&D experience, has a profound understanding of capsule filling, locking, and sealing, and this understanding is fully reflected in its machines.
The following are the common challenges that occur when manufacturers produce capsules and try to handle the sealing.
Leakage at the cap-body joint: oils and liquids can easily escape through small gaps.
Incomplete cap-body separation: Cap and body are not correctly separated that may have a negative impact on filling and sealing.
Inaccurate Filling accuracy: inaccurate dosing may lead to product loss and inconsistency.
Capsule deformation: improper heat or drying conditions can damage the capsule shell.
In practice, good capsule sealing methods depends on the right balance of capsule material, filling accuracy, sealing fluid, and drying control.
No matter it’s a semi-automatic or a fully automatic type, Rich Packing’s NJY Series is designed for manufacturers that need precise filling and perfect sealing with:
● High-precision servo motor for accurate liquid filling
● Matching sealant with the capsule material for perfect sealing
● Real time monitoring system: no liquid filling for the defective ones
And if you are comparing a semi-automatic liquid capsule filling machine for development work with an automatic liquid capsule filling machine for commercial production, the key question is simple: can the system control the details that actually cause leakage? In sealing, details are everything. If you wanto know more details, welcome to reach us.
For manufacturers, how to seal capsules perfectly is a perennial issue. Whether you choose capsule band sealing, fusion sealing, or another capsule sealing method, the goal is always stable and high-quality sealing performance. Of course, if you're looking to upgrade to a new capsule machine, Rich Packing is always there to support you.
Q1: Why Must Capsule Be Sealed?
It’s because a closed capsule can’t be sealed well that makes sealing matter in helping prevent leakage, and moisture ingress.
Q2: What Are The Three Main Kinds Of Capsules?
The three broad types most people talk about are:
● Hard gelatin capsules
● Vegetarian hard capsules (HPMC capsules)
● Softgels
Q3: How To Take Liquid Capsules?
In most cases, you need to take them whole. Do not chew or open them casually, especially with oil-based products.
[1] Grand View Research: Empty Capsules Market Size, Share & Growth Report
https://www.grandviewresearch.com/industry-analysis/empty-capsules-market
[2] Tablets & Capsules: Ask an Expert — Why Use Capsule Banding?
https://www.tabletscapsules.com/3641-Technical-Articles/586241-Ask-an-Expert/
[3] CapsCanada Blog: Types of Sealing for Liquid-Filled Capsules
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