Two Main Types of Gelatin Capsules
Common gelatin capsules come in two primary forms: softgels (oval or spherical) and hard capsules (cylindrical tubes). Softgels are specifically designed for liquids. They form a complete sealed unit that fully encloses liquid contents like oils and suspensions, such as fish oil and vitamin E oil. Hard capsules consist of two shell sections fitted together. Due to their brittle material, leak-prone seams, and gelatin solubility, they are rarely used for water or ethanol solutions (which dissolve gelatin). They can be chosen for oil-based or glycerin suspensions but are mostly used for encapsulating powders and granules. Recent technological breakthroughs have enabled liquid filling in hard capsules by modifying shell materials and sealing methods. For liquid filling in hard capsules, it is best to use HPMC (hydroxypropyl methylcellulose) material due to its superior water resistance and stronger liquid erosion resistance.
Filling Methods
There are two approaches to filling capsules with liquid: manual filling and machine filling. You can choose the most suitable method based on your current situation. As professional liquid capsule filling machine manufacturers, we will now detail the capsule filling methods.
Manual Capsule Liquid Filling (Small-Scale Use)
Applicable to: Laboratory trials, R&D batches, or small-scale test runs.
Step-by-step process:
- Separate the capsule cap from the capsule body.
- Use a pipette or syringe to inject liquid into the body, filling to approximately 80–90%.
- Heat the sealing solution to approximately 90 to 110°F and add the sealing solution.
- Connect the cap and body, pressing gently to seal.
- Stand upright and dry under cool ambient conditions for 6-12 hours.
source: capsule connection
Capsule Size Selection and Liquid Fill Capacity
Precise capsule sizing ensures correct dosage delivery and production efficiency. Below are standard sizes and their approximate liquid fill ranges (~1g/ml):
Capsule Size Volume (ml) Liquid Fill (~90%) Approx. Fill Weight
000 1.37 1.0～1.3ml ~1000–1370mg
00 1.00 0.9～1.0ml ~900–1000mg
0 0.90 0.8～0.9ml ~800–900mg
0E 0.78 0.7～0.8ml ~700–800mg
1 0.68 0.6～0.7ml ~600–700mg
2 0.48 0.45–0.5ml ~450–500mg
3 0.36 0.35–0.4ml ~350–400mg
4 0.27 0.25–0.3ml ~250–300mg
5 0.20 0.18–0.2ml ~180–200mg
Select size based on API dosage, fill density, and swallowability. Most semi-automatic/fully-automatic machines support all these sizes with replaceable dies. Manual filling is more suitable for those without capsule filling machines, but pharmaceutical capsules require more precise filling and hygienically safe filling environments. When circumstances permit, using a capsule filling machine is more efficient.
Manual vs. Automatic Method Comparison
Hard Capsule Liquid Filling (Machine Filling)
Applicable to: Medium-high throughput liquid or semi-solid fills.
5 steps:
1. Pre-treatment and Shell Compatibility
Design fill formulation: Oils, suspensions, SEDDS, or thixotropic gels.
Maintain viscosity between ~80–80,000 cP; Keep filling temperature for gelatin shells below 70°C.
When using ethanol or hygroscopic excipients, choose HPMC shells to avoid gelatin shell degradation. When using ethanol or hygroscopic excipients, choose HPMC shells to avoid gelatin shell degradation.
2. Capsule Preparation
Orient and separate capsule bodies and capsule caps for filling. Orient and separate capsule bodies and capsule caps for filling.
3. Filling and Sealing
Filling equipment injects liquid into the body; Typical fill volume is ~80–90% of capacity.
Sealing methods:
- Gelatin tape: Uses colored gelatin strips with tamper-evident function.
- Fusion seal: Sprays hydroalcoholic solution and heats to fuse caps and bodies.
4. Drying
Capsules dry in humidity-controlled rooms for 6-24 hours to achieve equilibrium.
5. Quality Control and Testing
Leak testing, fill weight variation, content uniformity, dissolution/disintegration compliance with pharmacopeial standards.
Soft Gelatin Capsule Filling (Machine Encapsulation)
Ideal for: Oil-based or moisture-sensitive formulations requiring sealing.
Process:
1. Gel Ribbon Preparation and Casting
Melt, degas, and cast shell mixture (gelatin, plasticizer - glycerol or sorbitol, and water) into ribbons with precise thickness.
2. Encapsulation via Rotary Die Process
Two gelatin ribbons pass through rotating die rolls. A heated wedge injects filling material between the gelatin ribbons while simultaneously sealing and cutting capsules. Standard gelatin ribbon sealing temperature is ~37-40°C.
3. Primary Drying (Dynamic)
Softgels are placed in rotary dryers and tumbled at ~35°C for 1-3 hours to remove surface moisture while sealing.
4. Secondary Drying (Static)
Capsules are transferred to trays and placed in controlled tunnels (temperature 21-24°C, relative humidity 20-30%). Drying may take 12 to 72 hours depending on fill type, capsule shell thickness, and humidity.
5. Final Quality Inspection and Packaging
Tests include visual inspection for defects (bubbles, leaks, color), hardness, fill weight, dissolution, and optional printing.
Formulation and Process Best Practices
- Validate the viscosity, density, hygroscopicity, oxidation potential, and uniformity of the filling material.
- Use thixotropic gels or silica-thickened oils to reduce leakage risk.
- Apply inert gas (e.g., nitrogen blanket) to easily oxidizable oil-based fills.
- For softgels, consider using sorbitol-glycerol plasticizer blends to shorten drying time and improve capsule hardness.
Choosing the Right Method for Your Operation
Manual Pipette:
Most suitable for R&D or small-scale experiments.
Hard Shell Liquid Filling:
Efficient and flexible - supports R&D to full-scale production using gelatin or HPMC shells.
Softgel Encapsulation:
Suitable for high-volume oil-based fills requiring sealing and consumer-friendly aesthetics.
Shell Material Decision:
- Gelatin for oil-based fills;
- HPMC when ethanol, water, or hygroscopic excipients are present.
Key Considerations for Manufacturers
- Capsule shell formulation (gelatin bloom and moisture content)
- Fill viscosity and uniformity
- Temperature and humidity control (Optimal ambient temperature: 20–25°C, RH 30–55%)
- Quality control testing: Seal integrity, leakage, content uniformity, dissolution
- CIP (Clean-in-Place) or sterilization protocols for oily or hygiene-sensitive formulations
Equipment Solutions Provided by LTPM CHINA
Hard Shell Liquid Filling Lines:
- Semi-automatic and fully automatic models
- Supports capsule sizes 000 to 5
- Optional vacuum pump, nitrogen inerting, integrated drying and inspection
Softgel Encapsulation Systems:
- Rotary die encapsulation machines, gelatin premixers, drying tunnels, conveyors, CIP/SIP modules
- Custom mold shapes, automatic tray systems, GMP/CE compliant
Additional services: Customized design, turnkey factory layout, and five-year warranty.
Manufacturer FAQs
Gelatin vs. HPMC: Use HPMC for ethanol or moisture-sensitive fills to avoid cross-linking.
Fill Viscosity and Temperature: Hard capsules require viscosity ~80-80,000 cP and temperatures below ~70°C; Softgels require 500-1,000 cP and ribbon temperature ~35-40°C.
Capsule Size Adaptability: Machines support multi-size toolkits for standard sizes 000–5.
Drying Time: Softgel drying time is ~12-72 hours depending on fill and environmental conditions.
Sealing Test Methods: Use leak testing, dissolution analysis, and visual inspection for hard shell and softgel batches.
Summary
This guide thoroughly explains liquid filling methods for gelatin capsules - manual pipetting, hard shell capsule machines, and softgel rotary die systems. It covers capsule size guidance, process steps, equipment considerations, and quality control strategies. Each method has its own advantages and disadvantages in terms of output, seal integrity, and investment. LTPM CHINA provides tailored turnkey equipment and technical support to meet global manufacturers' needs.
Contact LTPM CHINA for free consultations, pilot-scale testing, and custom turnkey capsule filling production lines. Inquire about first-time customer discounts and comprehensive project support with global compliance assurance.