Ethan Clarke
Heat sealing is a process that uses heat to seal plastic films together. To heat seal rubberized plastic, you need to understand the interdependent factors of heat, pressure, and dwell time. The plastic film must be melted together and then allowed to cool down and solidify. This process can be done using a heat sealing machine or a heat sealer, also known as an impulse sealer, which uses a resistive heating element to seal plastic bags or sheets. It is important to consider the type of plastic being sealed, as some plastics have lower melting points and can be easily damaged.
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What You'll Learn
Using a heat sealer machine
Firstly, select the appropriate heat sealer machine for your project. There are various types available, such as L-bar and I-bar sealers, which are commonly used for shrink-wrapping. Consider the size and portability, energy usage, volume and durability, and price of the machine to make an informed choice. Impulse sealers, for example, are great for making your own plastic bags as they are easy to use and produce a clean seal.
Next, prepare the plastic film or bag that you will be sealing. Ensure that the plastic is suitable for heat sealing, such as polyethylene, polypropylene, or polyolefin bags. These plastics have a low melting point, making them ideal for the process. Also, consider the thickness of the plastic, as thicker bags may require higher heat settings and longer sealing times.
Now, you can begin the heat sealing process. Feed the plastic film or layflat tubing into the heat sealer machine. If you are creating your own plastic bags, you can heat seal the tubing at the bottom and then cut it to size for a flat-bottomed bag. For a gusseted bag, create a fold in the tubing and heat seal it to form the gusset, allowing the bag to stand up by itself.
At this stage, engage the heat sealer machine. If using an impulse sealer, it will use a timed impulse of heat to seal the plastic. Ensure that the plastic is in a relaxed state during the sealing process to avoid any gaps or pinholes that may form due to stretching. Allow the sealed plastic to cool down enough to become "crystalline" or solid.
Finally, if you have created your own plastic bag, use the built-in heat sealer cutter to separate the bag from the roll. You can now fill the bag with your chosen product, ensuring that it is not perishable if you are not using a vacuum sealer. Seal the remaining open end of the bag using the heat sealer machine, following the manufacturer's instructions for the specific model.
By following these steps, you can effectively use a heat sealer machine to create secure and airtight seals on plastic bags or films, ensuring the protection and preservation of the enclosed items.
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Choosing the right plastic
When choosing the right plastic for heat sealing, there are several factors to consider. Firstly, it is essential to select a plastic that is suitable for heat sealing, as not all plastics are heat-sealable. Some common plastics that can be heat-sealed include polyethylene, polypropylene, PVC, polystyrene, and PETG. These plastics have different melting points and seal initiation temperatures, so it is important to consider the heat source and the thickness of the plastic. For example, polyolefin has a heat-sealing temperature range of 280–350 degrees Fahrenheit (121 degrees Celsius), while polyethylene seals at 140 degrees Fahrenheit (76.6 degrees Celsius).
Another factor to consider is the heat seal strength, which refers to the peel strength of the seal between two layers of the same or different materials. The heat seal strength depends on factors such as the pressure, temperature, and dwell time during the sealing process. It is also influenced by the properties of the resin, the amount and type of additives in the resin, and the degree of oxidation during processing.
The intended use of the heat-sealed plastic is also important to consider. For example, if the plastic needs to be flexible, a thinner seal is preferable, while a flatter seal is better for thicker materials to provide extra flexibility and prevent spilling. Additionally, if the plastic will be used for food packaging, it is essential to consider the food's temperature and the seal's ability to withstand that temperature without compromising the integrity of the seal or the food itself.
It is also worth noting that some plastics can be challenging to work with due to their low melting points and susceptibility to damage. For example, LDPE, LLDPE, and PLA have low melting points and can be easily damaged, so testing is recommended before proceeding with a project. Similarly, polyethylene film has a very low melting point and is prone to damage, making it less common for heat sealing.
Finally, the choice between impulse heat and direct heat sealers is an important consideration. Impulse sealers require no warm-up time and are suitable for thermoplastic materials that require lower seal temperatures, such as polyethylene and polypropylene. On the other hand, direct heat sealers maintain constant heat and are better suited for thicker materials like coated aluminum foil, poly cello films, and gusset bags.
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Applying the right amount of heat
To achieve a strong seal, the plastic must be melted together until the molecules co-mingle, forming a neat seam. This process requires sufficient heat to ensure the plastic reaches a molten state. However, it is important to strike a balance between heat and dwell time. Dwell time refers to the duration the plastic remains in the molten state before cooling. Longer dwell times can lead to stretching and distortion of the plastic, resulting in gaps or pinholes in the seal.
The ideal heat-sealing process involves applying heat for a short duration, just enough to melt the plastic and initiate the seal. This is often achieved using an impulse sealer, which provides a timed impulse of heat rather than continuous heat. The impulse duration can vary depending on the thickness and type of plastic. For example, a half-second impulse is typically sufficient for sealing 4-mil polyethylene bags.
After applying heat, the plastic must be allowed to cool and solidify. This cooling phase is critical, as it allows the molten plastic to crystallize and form a strong, solid seal. During the cooling phase, it is essential to ensure that the plastic is in a relaxed state. Any tension or external forces acting on the plastic during cooling can lead to unwanted distortions or gaps in the seal.
By understanding the properties of the plastic and applying the appropriate amount of heat for the required duration, you can achieve an effective heat seal on rubberized plastic. Remember to consider the melting point, seal initiation temperature, and the cooling process to ensure a strong and intact seal without damaging the material.
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Cooling the plastic
Optimum Cooling Conditions
To achieve optimal results, it is essential to allow the heated plastic sufficient time to cool and solidify. The plastic must be in a relaxed state during cooling to prevent gaps and pinholes caused by stretching the molten plastic. This relaxed state is the reason why bag-making machines are designed to seal the plastic first and then allow a few seconds for cooling.
Cooling Time and Temperature:
The cooling time depends on the plastic type and its melting point. Films with lower melting points and seal initiation temperatures generally require more cooling time. For example, low-density polyethylene, an ideal material for heat sealing, melts at 320 degrees Fahrenheit and can be cooled quickly after removing the heat source.
Contraction During Cooling:
As the poly material cools, it contracts, tightening the seal. This contraction is a natural part of the process and enhances the strength of the seal.
Contaminants and Seal Integrity:
Contaminants, such as blood, fat, and certain powders, can interfere with the heat-sealing process and affect seal integrity. To ensure a strong seal, it is crucial to avoid these contaminants during the cooling stage and consider using sealing layers with multiple resins, each with different sealing temperatures.
Heat Sealing Strength:
The heat-sealing strength of polyethylene is related to its thickness. Increasing the thickness of the heat-sealing resin generally results in a stronger seal. For instance, a higher thickness of 60 to 70 μm in the inner sealing material of a high-temperature cooking bag provides better heat-sealing performance.
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Trimming the material
- Understanding the Material: Before trimming, it is crucial to understand the properties of rubberized plastic. This material typically consists of a layer of thermoplastic polyurethane (TPU) coated onto a woven fabric. The TPU side is smooth and plastic-like, while the uncoated side remains a fabric texture. Identify which side is which, as it will affect how you trim and seal the material.
- Tools for Trimming: You will need sharp cutting tools to trim the material. Scissors or a rotary cutter can be used for straight cuts, while more detailed cuts may require a craft knife or a scalpel. Ensure your tools are sharp to achieve clean cuts and minimize fraying or damage to the fabric.
- Measuring and Marking: Measure the material accurately and mark the cutting lines with a fabric pen or tailor's chalk. If you are joining multiple pieces, account for seam allowances to ensure a precise fit. For intricate shapes, you may consider creating a template from cardboard or paper and tracing it onto the rubberized plastic before cutting.
- Cutting Techniques: When cutting the rubberized plastic, use a steady hand and follow your marked lines closely. Cut in a well-ventilated area to avoid inhaling fumes from the rubberized material. If possible, perform test cuts on scrap pieces to familiarize yourself with the material's behavior when cut and to ensure your cuts are accurate and consistent.
- Seam Considerations: If you are joining multiple pieces of rubberized plastic, consider the type of seam you will create. Straight seams are the simplest and can be easily trimmed and sealed. For curved seams, you may need to trim and shape the fabric pieces accordingly to ensure a precise fit. Overlap seams are another option, where one piece of fabric overlaps the other, which may require less trimming but careful placement during the sealing process.
- Edge Finishing: After trimming, consider the finish of the edges. Some heat sealing machines come with attached cutters that trim the material close to the seal, creating a neat appearance. Alternatively, you can finish the edges manually by folding and sealing, or using binding or trim to create a more refined look, especially if the edges will be visible in the final product.
Remember, trimming the material is a crucial step that requires precision and attention to detail. Take your time and plan each cut to ensure the best results when heat sealing rubberized plastic.
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Frequently asked questions
A heat sealer, also known as an impulse sealer, uses a resistive heating element to seal and/or cut thin plastic bags or sheets.
Many plastics can be heat sealed, including polyethylene, polypropylene, PVC, LDPE, LLDPE, and PLA. Some materials, like PET and HDPE, cannot be heat sealed but can be laminated using an adhesive layer.
The heat sealer melts the plastic material until it blends together, then sets it into a single seam. As it cools, the material contracts, tightening the seal.
It is important to use the correct amount of heat to avoid overcooking the plastic. The film must be in a relaxed state while cooling down to avoid gaps and pinholes. Contaminants such as blood, fat, and powdered milk can interfere with the sealing process.
