China Suppliers Factory for Industrial Packaging Heat-Shrinkable Bags - Durable & Custom Solutions
What is a hot compressed bag?
Heat shrinkable bags, also known as shrink bags or PVC / POF shrink bags, is a packaging material made of special plastic film. When heated (usually using a hot windmill, syringe, or oven), it contracts evenly in one or both directions, thus tightening the contents of the interior to form a strong, transparent, and aesthetically pleasing protective film.
Working principle
The raw materials of the hot compressed bags have gone through a process of "prestretching" and "cooling and forming" before they leave the factory. This means that the plastic molecules are forcefully stretched and arranged when manufactured, and are cooled to secure in a stretched state. When you heat it again, these "frozen" molecular chains return to their original state of relaxation, causing the film to contract in size and tightly adhere to the product surface.
Main types and materials
1. POF (polyolefin)
- Features: The most mainstream and environmentally friendly option at present.
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Pros:
- High transparency: excellent presentation.
- High toughness: Good tensile resistance and not easy to break.
- Eco-friendly and non-toxic: Carbon dioxide and water are produced after combustion and meet food packaging standards.
- High shrinkage rate: shrinkage is uniform, surface smooth and aesthetically pleasing.
- Disadvantages: The cost is slightly higher than PVC.
- Applications: Widely used in food, pharmaceuticals, cosmetics, stationery, toys, electronics, etc.
2. PVC (polyvinyl chloride)
- Features: Early commonly used materials, now gradually replaced by POF.
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Pros:
- Low cost: the price is relatively cheap.
- Strong contractile force: it binds the product tightly.
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Cons:
- Poor environmental performance: When burned, toxic gases such as hydrogen chloride are produced, which is not conducive to the environment and health.
- Easy to turn yellow: After being stored for a long time or being heated, it may turn yellow, affecting aesthetics.
- Poor resilience: relatively easier to tear.
- Application: It is still used for some industrial products, card cards, etc. packaging that do not have high environmental requirements.
3. PET (Polyethylene Terephthalate) / PETG
- Features: High performance engineering plastics.
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Pros:
- Extremely strong: very strong and shock resistant.
- High transparency: The presentation was excellent.
- Eco-friendly and recyclable.
- Cons: Costs are highest and require higher temperatures to contract.
- Application: mainly used in high-end electronics, batteries, cosmetics, tools and other areas that require high-strength protection.
4. OPS (polystyrene)
- Features: A hard, brittle material.
- Pros: Very high transparency, good gloss, and environmentally friendly.
- Disadvantage: The texture is fragile and easily cracked.
- Applications: Mainly used in food (such as pastries, fruit trays), stationery, toys, etc.
Application Areas
The application of heat-shrinkable bags is extremely widespread, encompassing almost all industries that require packaging:
How to use heat-shrinkable bags?
The size of the bag should be 10-20% larger than the product it will contain, to leave room for shrinkage.
Place the product inside the bag.
Use a specialized L-shaped sealing machine or a cuff-style sealing machine to heat-seal the bag's opening. Manual operation can be performed using a heat sealing rod or the Impulse Sealer.
Frequently Asked Questions (FAQ)
The main materials are POF (polyolefin), PVC (polyvinyl chloride), PET/PETG (polyethylene terephthalate), and OPS (polystyrene). POF is currently the most popular and eco-friendly choice.
You should choose a bag that is 10% to 20% larger than the dimensions of the product itself. This leaves sufficient room for the bag to contract and shrink evenly when heated.
No, you should never use open flames like lighters. Direct flame contact will burn, blacken, and deform the film. Instead, use a heat gun for small batches or a professional thermal shrink tunnel for mass production.
Yes, POF is non-toxic, highly eco-friendly, and meets food packaging standards. It produces only carbon dioxide and water upon combustion, unlike PVC which releases toxic gases.
PVC has lower environmental stability compared to POF or PET. When stored for long periods or exposed to heat, the chemical structure of PVC degrades slightly, causing it to take on a yellowish tint.
Industrial applications use automated thermal shrinkage conveyor tunnels (shrinkers) for high efficiency and uniform heat. DIY or small-batch operations use manual heat guns held 15-20 cm away while moving continuously to prevent localized burning.