Quick Summary
Plastic packaging bag production relies on two key stages: blown film extrusion and bag converting (bag making). In these processes, different types of moulds and tooling systems-especially the extrusion die head (film mould) and cutting die moulds-determine film quality, bag shape, and functional design. Understanding how these moulds work helps buyers and packaging manufacturers choose the right solutions for customized plastic bags with better performance, efficiency, and cost control.
1. Introduction: Why Moulds Matter in Plastic Bag Production
In the flexible packaging industry, plastic bags are not simply "cut and sealed products." Their structure, strength, sealing performance, and even appearance are directly influenced by mould systems used during production.
Two major mould-related systems define the entire process:
Blown film extrusion mould (die head)
Bag making cutting mould (die cutting tools)
Together, they transform raw plastic resin into finished packaging products such as shopping bags, mailing bags, ziplock bags, and food packaging bags.
2. Blown Film Process: The Role of the Extrusion Die Head
2.1 What is a blown film mould?
In the blown film process, plastic raw materials (such as PE, LDPE, or LLDPE) are melted and pushed through an extrusion die head.
This die head is the first "mould system" in plastic packaging production.
2.2 How it works
The process includes:
Plastic pellets are heated and melted
Molten plastic enters the die head
The die head forms the material into a thin tube film
Air is blown inside to expand the tube (bubble formation)
The film is cooled and flattened into rolls
This stage produces plastic film rolls, not finished bags.
2.3 Key functions of the die head mould
Controls film thickness consistency
Determines film width and stability
Ensures smooth surface quality
Affects tensile strength and durability
3. Bag Making Process: Cutting Die Moulds and Forming Tools
After film production, the material enters the bag converting stage, where real bag shapes are formed.
3.1 What is a cutting die mould?
A cutting die mould (knife mould) is used in bag making machines to cut, shape, and seal plastic film into final products.
Unlike the blown film die head, this mould defines:
Bag shape
Handles
Perforation lines
Sealing edges
Functional openings
3.2 How bag moulds work in production
The process typically includes:
Plastic film roll is fed into bag making machine
Film is printed (if required)
Cutting die mould shapes the bag
Heat sealing is applied
Finished bags are collected and packed
3.3 Types of bag mould applications
✔ T-shirt bag mould
Creates handle cut-outs
Used for supermarket shopping bags
✔ Mailing bag mould
Forms flap, adhesive strip area, tear line
Used for e-commerce shipping bags
✔ Ziplock bag mould
Controls sealing edge structure
Ensures zipper alignment
✔ Wicket bag mould
Adds hanging holes and stack alignment
Used for bakery and produce bags
✔ Custom-shaped bag mould
Triangle, oval, or branded design shapes
Used for premium packaging
4. Blown Film vs Bag Making Moulds: Key Differences
| Feature | Blown Film Mould (Die Head) | Bag Making Mould (Cutting Die) |
|---|---|---|
| Production stage | Early stage | Final stage |
| Output | Plastic film rolls | Finished bags |
| Function | Controls film formation | Controls bag shape |
| Main focus | Material quality | Product design & structure |
5. Importance of Mould Design in Custom Packaging
For custom plastic packaging, mould design is critical because it directly affects:
Production efficiency
Bag appearance and branding
Functional performance (tear resistance, sealing, usability)
Material waste reduction
Machine compatibility
A well-designed mould ensures stable mass production and consistent product quality.
6. Industry Trends in Plastic Packaging Mould Technology
Modern packaging manufacturers are increasingly using:
High-precision CNC mould machining
Automated die-cutting systems
Multi-function bag making moulds
Eco-friendly film optimization systems
Custom mould solutions for branding needs
These improvements help reduce cost while improving product consistency and sustainability.
Plastic packaging bag moulds play a crucial role in both the blown film extrusion process and the bag making process. While the die head controls film quality at the early stage, cutting die moulds define the final bag shape and functionality.
Understanding how these moulds work helps businesses choose better packaging solutions, improve product quality, and optimize production efficiency in a highly competitive global packaging market.
