Chloe Zhang
Heat sealing is a process that uses heat to melt plastic films together to create a seal. This process is commonly used to seal products for shipping, creating a professional look. To heat seal plastic with a heat gun, the plastic must first be melted together and then allowed to cool and solidify. The heat gun is a tool that applies high, direct heat to quickly melt plastic. It is important to note that hairdryers should not be used as a substitute for heat guns as they do not get as hot and may result in inconsistent seals. When using a heat gun, it is crucial to be cautious and avoid overheating the plastic, which can lead to overcooking and an ineffective seal.
| Characteristics | Values |
|---|---|
| Purpose | To seal plastic by melting it |
| Plastic type | Softer plastics like polyethylene require lower temperatures (around 300°F). Harder plastics like ABS can withstand higher temperatures (around 500°F). |
| Heat settings | Basic heat guns have 2-3 fixed heat settings. Advanced heat guns have adjustable temperatures. |
| Technique | Heat the plastic until it melts and becomes pliable, then join the pieces together, applying gentle pressure. Allow to cool and solidify completely before handling. |
| Nozzle | Look for a nozzle that allows for precise heating. |
| Grip | Choose a heat gun with a comfortable grip that can be held for extended periods. |
| Safety features | Look for a heat gun with an automatic shut-off feature. |
| Performance | Heat guns are designed for long-term performance, maintaining the same quality throughout. |
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What You'll Learn
Heat guns are better than hairdryers
Secondly, heat guns are designed for continual use and long-term performance, maintaining the same quality throughout the process. In contrast, hairdryers are not built for repetitive long-term use, and their performance and quality can diminish with extended use. This makes heat guns more efficient and effective for tasks requiring the sealing of large batches of containers or for crafting projects where consistent heat is required.
Thirdly, heat guns have a more targeted and focused stream of heat compared to hairdryers. Hairdryers are designed to diffuse air outward and spread heat over a large area, which is ideal for drying hair quickly and safely. In contrast, heat guns shoot out a concentrated stream of heat, making them perfect for tasks requiring precision and control, such as moulding shrink bands or removing wallpaper.
Lastly, heat guns are constructed specifically for commercial applications and are therefore better suited for processes that require high and direct heat, such as melting plastic. Hairdryers, on the other hand, dispense gentle heat designed to dry hair without damaging the scalp, and as a result, sealing processes will take longer and may produce an inconsistent finish.
While heat guns offer superior performance in terms of temperature, durability, and precision, it is important to note that they require more frequent cleaning and maintenance compared to hairdryers. Additionally, safety precautions are crucial when using heat guns due to the extremely high temperatures they can reach.
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Seal initiation temperature (SIT)
The seal initiation temperature (SIT) is the minimum temperature at which the maximum heat seal strength is obtained. It is defined as the temperature at which a given seal strength is attained. For instance, a minimum seal initiation temperature of 120°C is identified for OPP/CPP. The SIT can be measured by a number of methods. For instance, the DSC melting behaviour of polyolefins can be correlated with their heat seal strength.
The SIT is influenced by various factors, including the type of sealant used. For example, copolymers such as PEVA lower the melting point and SIT, while some metallocene resins melt and seal much faster than PEVA. The thermal conductivity and thickness of the lidding structure also play a role, with thinner structures sealing faster and at lower temperatures than thicker ones.
Films with a low melting point and SIT seal better with more cooling time, more pressure, and less dwell time, resulting in faster cycle speeds. However, using too much heat can lead to overcooking the film. A sealing temperature of 130°C may be close to causing distortion of the HDPE layer, which has a peak melting point of around 135°C. Therefore, switching to a grade of ionomer with a lower SIT may be advantageous in this case.
The SIT is an important parameter in the heat sealing process, as it determines the minimum temperature required to achieve a strong seal. By understanding the SIT of the materials being used, manufacturers can optimise their sealing processes to achieve consistent and effective seals.
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The importance of cool-down
When heat-sealing plastic with a heat gun, the cooling process is crucial to achieving a strong and long-lasting seal. Here are several reasons why the cool-down phase is essential:
Achieving a Solid State
The primary purpose of the cool-down phase is to allow the melted plastic to solidify and return to a solid state. During the heating process, the plastic becomes pliable and mouldable, but it needs to harden to create a permanent seal. The cooling process enables the plastic molecules to rearrange and form a solid structure, ensuring the joined pieces become securely bonded.
Preventing Gaps and Pinholes
If the plastic is disturbed or stretched while still in its molten state, it can result in gaps or pinholes in the seal. Allowing the plastic to cool down undisturbed is essential to avoid these imperfections. Bag-making machines are designed to maintain the plastic in a relaxed state during cooling to prevent such issues.
Ensuring a Clean Finish
Once the plastic has cooled and solidified, you can trim any excess material or rough edges with a blade or sandpaper. This step gives your project a clean and polished finish. If your heat gun has a fan-only function, you can expedite the cooling process by blowing cool air onto the heated area.
Extending the Lifespan of the Heat Gun
Allowing your heat gun to cool down before storing it is essential for maintaining the tool's performance and longevity. After use, place the heat gun on a heatproof mat or stand to ensure that no other objects come into contact with its hot parts. This cool-down period helps prevent accidental burns and ensures the heat gun is safely stored.
Optimising the Sealing Process
The cooling phase is an integral part of the heat-sealing process and can impact the overall success of the seal. Films with lower melting points often require more cooling time, moderate pressure, and reduced dwell time to achieve a better seal. Allowing the plastic to cool sufficiently helps prevent overcooking the film and ensures a strong and consistent weld.
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The best bags for heat sealing
Heat sealing is a great way to make your packaging tamper-proof and more professional-looking. It is also useful for maintaining the quality and integrity of your product. There are various bags available that are suitable for heat sealing, and the best option for you will depend on your specific needs and requirements.
If you are looking for heat seal bags for food packaging, then flat heat seal bags are a great option. These bags are designed to be a snug fit, ensuring that the contents stay safely in place. They are food-safe, durable, and easy to heat seal with hand or tabletop heat sealers. You can also find eco-friendly options made from materials like kraft paper. These bags can also be customised with your logo or in a special size.
Stand-up pouches are another option for food packaging, especially if you are looking to transition away from traditional rigid packaging like bottles, jars, and tins. These heat seal bags provide a clean, finished look and can be easily filled and sealed with a manual heat sealer machine. They also come with a durable reclosable zipper closure, making it convenient for consumers to open and close the package.
If you are looking to heat seal boxes or containers, then you can use heat shrink bags or shrink wrap foil. This method provides a tamper-evident seal and can be applied to various containers, including glass and plastic bottles, metal containers, and plastic and glass jars. You can find shrink bands made from PVC, which offer grease, oil, and acid resistance, as well as oxygen barriers.
When choosing bags for heat sealing, it is important to consider the type of sealer you will be using. The sealer should be at least 1/2 inch wider than the width of the bag to ensure a proper seal. Additionally, some materials may require specific types of sealers, so it is important to refer to a thickness and material guide to determine the appropriate sealer for your chosen bag.
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Heat guns and shrink bands
Heat guns are an effective tool for applying shrink bands to tin containers and tubs. They are also used for bending plastic, removing paint, curing resins, and heating temperature-sensitive materials.
Heat guns offer adjustable temperature settings, with some models ranging from 250° to 1150° F, and others from 575° to 950° F. The ability to control temperature is crucial when applying heat to plastic, as using too much heat can cause the plastic to melt and become a gooey mess. Different plastics have different melting points and seal initiation temperatures (SIT). For example, films with a low melting point seal better with more cooling time, more pressure, and less dwell time.
When using a heat gun, it is important to consider the three key interdependent factors: heat, pressure, and dwell time. After heating and sealing the plastic, it must be allowed to cool down enough to become "crystalline" or solid. This process is crucial in achieving a strong seal.
To apply a shrink band using a heat gun, follow these general steps:
- Ensure the plastic is in a relaxed state before applying heat.
- Adjust the temperature on the heat gun to the desired setting, typically within the range of 250° to 1150° F.
- Apply heat to the shrink band, moving the heat gun continuously to avoid overheating any specific area.
- Maintain a safe distance from the heat gun to the plastic to prevent melting or damage.
- Once the shrink band has tightened around the container, remove the heat and allow the plastic to cool.
By following these steps and adjusting the temperature and distance as needed, you can effectively use a heat gun to apply shrink bands to containers, creating a secure and tamper-proof seal.
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