Sofia Martinez
Heat sealing is a process that uses heat to meld plastic films together, creating a protective barrier. The three key elements of heat sealing are heat, pressure, and dwell time. Different plastics have different melting points, and some plastics cannot be heat sealed at all. It is important to use heat seal-approved packaging to ensure safety and the integrity of the seal. Heat sealing machines can be used to seal plastic, but it is also possible to use a curling iron, hair straightener, or butane torch.
| Characteristics | Values |
|---|---|
| Tools | Curling iron, hair straightener, heat sealing machine, heat gun, impulse heat sealer, L-bar and I-bar sealers, constant heat sealer, continuous motion sealer, knife blade, butane torch |
| Plastic type | Poly bags, PE plastic film, polyethylene, polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) |
| Process | Heat and pressure are applied to the plastic, causing it to melt and form a seal. The plastic is then allowed to cool and solidify. |
| Considerations | Melting point of plastic, thickness of material, desired production levels, safety, integrity of packaging, aesthetics |
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What You'll Learn
Using a hair straightener
Sealing plastic with heat from a hair straightener is a simple way to reuse old hair straighteners and obtain hermetically sealed bags. This method does not require the use of a bag-sealing machine. To ensure that the plastic does not stick to the hair straightener, you must use an insulating material that allows heat to pass through, such as parchment paper.
Firstly, place the items inside the bag. Then, place the bag between the heated hair straightener and hold it in place for 5 to 15 seconds, depending on the temperature. Be cautious, as hair straighteners can get extremely hot and may melt the plastic. Therefore, it is recommended to unplug the straightener and let it cool down before using it to seal the plastic.
It is important to note that the type of plastic bag used is crucial. The bag should be made of cellophane, which is stiff and produces a "crackly" sound when placed between your fingers. Soft bags are not suitable for this purpose. Additionally, it is worth mentioning that there are two types of plastic: thermoplastic and thermosetting plastic. Only thermoplastic can be melted and remolded with heat, while thermosetting plastic will not change shape even under extreme heat.
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Heat sealing machines
There are two main types of heat sealing machines: impulse sealers and continuous heat sealers. Impulse sealers, invented by Vertrod around 1950, have become the industry standard for heat sealing plastic films. They work by placing the film between the seal jaws of the machine and applying pressure manually or mechanically. Once the jaws are under pressure, voltage is applied to the heating element for a set amount of time. After the seal time elapses, the voltage is cut off, but the jaws remain under pressure for the cooling phase. Once the cooling time is reached, the jaw pressure is released, and the sealed material is removed. Impulse sealers can produce airtight and watertight seals that are as strong as the material being sealed.
Continuous heat sealers, on the other hand, have been in use longer than impulse sealers. They offer accurate temperature control, allowing for the sealing of heavy materials. However, they can only heat the material under pressure and cannot cool it under pressure. This limitation poses challenges when sealing thinner, more flexible materials, as they may be pulled apart when the seal jaws are released.
Various companies offer a range of heat sealing machines to meet different needs. For example, IMPAK provides sealing equipment for various industries, from tabletop sealers to large-frame freestanding machines. Promarksvac manufactures both impulse and continuous heat sealing machines, including custom-designed machines for specific industries. Nelipak specializes in medical tray and blister heat sealing machines, offering custom-built rotary tray and blister sealers to meet specific packaging requirements.
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Butane torch and knife method
The butane torch and knife method is a great way to seal plastic bags and create your own treat bags or reseal packages. This method is simple and effective, but only if you are confident in using a butane torch safely. Here is a step-by-step guide on how to use the butane torch and knife method to seal plastic:
Firstly, you need to choose the right tools. A butane torch designed for crafting is ideal as it emits a small, precise flame perfect for warming up a knife blade. Look for a torch that stands on its own, as this will make the process safer and easier. For the knife, any metal knife with a non-serrated blade will work. It is recommended to use a knife with an insulated handle to ensure the heat doesn't transfer to your hands.
Once you have your butane torch and knife, it's time to light the torch following the manufacturer's instructions. The method may vary depending on the type of torch you have. Carefully move the knife blade through the flame, ensuring the entire blade is heated evenly. This should only take about five seconds. Be cautious and avoid heating the knife for too long, as you don't want to overheat the blade.
Now that your knife blade is heated, it's time to seal the plastic. Touch the blade to the plastic where you want to create a seal. If the blade doesn't touch the plastic evenly, gently rock the knife from tip to handle. Hold the blade in place for a few seconds, then lift it away and check if a seal has formed. If not, simply heat the blade for a little longer and try again.
When using this method, it is important to work with caution and be mindful of safety. Always enlist the help of a friend to hold the plastic bag and keep the paper or foil in place while you manipulate the hot knife. Additionally, ensure your work area is clear of any flammable materials and have a fire extinguisher or a bowl of water nearby as a safety precaution.
With the butane torch and knife method, you can effectively seal plastic bags and create secure packages. This technique is a great skill to have for various DIY projects and treating yourself to homemade treats.
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Different types of plastics
The heat sealability of plastic refers to the thermal adhesion properties of plastics to themselves or other types of plastics after being heated to a molten state. The three key elements to heat sealing are the film's relaxed state during cooling, the melting point, and the seal time. The degree of heat required depends on the material's thickness and type.
Some of the commonly used plastics for heat sealing include:
Polyethylene (PE)
Polyethylene is a commonly used plastic for heat sealing. It has a low melting point, making it easy to heat, fuse, and cool. Its lightweight material melts at 320 degrees Fahrenheit (160-170 degrees Celsius). When cooled, the poly material contracts, tightening the seal. It is used in bags and pouches to create an airtight seal with a neat, finished edge.
Polypropylene (PP)
Polypropylene is another plastic that can be heat sealed. It has a higher melting point than polyethylene, sealing at roughly 248–253 degrees Fahrenheit (120–123 degrees Celsius). It is also used in bags and pouches to create an airtight seal.
Polystyrene (PS)
Polystyrene is a thermo-reactive plastic that can be heat sealed. It has a melting point of around 140 degrees Fahrenheit. It is used in bags and packaging containers, providing a protective barrier.
Polyvinyl Chloride (PVC)
PVC is a commonly used plastic for heat sealing. It is a thermo-reactive plastic that can be sealed at the right temperature, usually around 140 degrees Fahrenheit. It is used in bags and packaging to create a protective enclosure.
Other plastics that can be heat sealed include polyolefin, LDPE, LLDPE, PLA, and some thinner materials like PE-laminated foil and aluminium foil. However, certain plastics like acetate and PET cannot be heat sealed and require an adhesive layer for lamination.
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Heat sealing for protection
Heat sealing is a process that uses heat to meld together two ends of a thermo-reactive polymer, such as polyethylene, polypropylene (PP), polystyrene (PS), or polyvinyl chloride (PVC). This creates a protective barrier that can provide protection and preservation for various items. The process involves applying heat and pressure to the plastic for a few seconds, either with a heat sealing machine or a handheld device like a hair straightener or curling iron. The plastic melts together and then cools down to form a crystalline structure, creating an airtight seal with a neat, finished edge.
To heat seal effectively, it is important to consider the type and thickness of the plastic, as different plastics have varying melting points and some may not be mendable with heat. It is also crucial to ensure that the plastic is in a relaxed state while cooling down to prevent gaps or pinholes in the seal. Using heat seal-approved packaging and choosing the right tools and materials are essential for achieving a strong and aesthetically pleasing seal.
One commonly used method for heat sealing is the impulse sealing technique, which utilizes an element wire to apply heat and pressure to the plastic for a brief period. This method is suitable for poly bags and can create an airtight seal with a neat finish. Impulse sealing blades, however, may wear out quickly if they are thin, so it is important to consider the quality and durability of the sealing blade.
For sealing smaller projects or individual items, portable heat sealing machines are ideal. Larger sealers are typically used for mid-level sealing, while constant heat sealers, also known as direct heat sealers, are suitable for high-volume projects and can be programmed to pre-heat at different temperatures, accommodating various plastic types. Flat wire seals are commonly used for thicker materials and provide extra flexibility to prevent spills, while round wire seals are thinner and average about one inch in thickness.
Heat sealing is a versatile process that can be adapted to different materials and project sizes. By understanding the characteristics of the plastic and selecting the appropriate tools and techniques, a strong and protective heat seal can be achieved.
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Frequently asked questions
You can use a curling iron, a handheld hair straightener, a butane torch, a knife blade, a vacuum sealer, or a heat sealing machine.
Start with a low to medium heat setting. Fold a piece of foil or thick paper over the top and bottom of the area you want to seal, then run the plastic bag with the paper/foil inside through the hair straightener.
Plastics such as polyethylene, polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) are all thermo-reactive plastics used in bags and other packaging containers that can be heat sealed.
A thinner seal is preferable for shrink wrap, while a flatter seal is better for thicker materials.
Heat sealing can provide protection and preservation for items. It also creates an airtight seal with a neat, finished edge.
