3 Factors for Heat Sealing

Heat sealing is a critical process that involves the application of heat and pressure to thermoplastic materials in order to join or seal them together. The effect of heat sealing is influenced by several key factors, namely heat sealing temperature, heat sealing time, and heat sealing pressure.

Heat Sealing Temperature

The heat sealing temperature refers to the temperature at which the thermoplastic materials reach a suitable viscous state for bonding. Thermoplastics have a range between solid and liquid phases where they become molten and can bond. The temperature range for heat sealing is determined by the polymer’s melting point, viscous temperature, and decomposition temperature. The smaller the difference between the viscous temperature and decomposition temperature, the more complex the heat sealing process.
The heat sealing temperature directly affects the heat sealing strength. As the temperature increases within the appropriate range, the strength of the seal generally increases. However, there is a limit to this relationship, and beyond a certain temperature, the heat sealing strength may plateau or even decrease.

Setting the appropriate heat sealing temperature depends on various factors such as the properties of the materials, film thickness, frequency of heat application, and heat sealing area. Increasing the frequency of heat application in the same area can lower the required temperature. It is important to note that the actual heat sealing temperature in production is often higher than the melting temperature of the materials due to the impact of heat sealing pressure, machine speed, and film thickness. If the heat sealing temperature is too low, the materials may not properly fuse, resulting in weak or incomplete seals. Conversely, excessively high temperatures can lead to material degradation, discoloration, or even burning of the thermoplastic materials. It can also cause the formation of “root cutting” phenomena, where the molten material cuts through the seal, resulting in weakened strength and reduced impact resistance of the sealed product. Meawhile, different thermoplastic materials have different ideal heat sealing temperatures, and it is important to consider the specific properties and melting points of the materials being sealed.

Heat Sealing Dwell Time

Heat sealing dwell time refers to the duration for which the materials are subjected to heat and pressure. It plays a crucial role in determining the strength and performance of the seal. The heat sealing time determines the duration for which the heat and pressure are applied to the materials. It directly affects the level of fusion and bonding between the thermoplastic layers.
A longer heat sealing time allows for a more complete fusion of the heat sealing layer, resulting in a stronger bond, as they allow for more complete intermolecular diffusion and fusion of the materials. However, excessively long heat sealing times can lead to material degradation, loss of seal performance, and deformation of the seal area and cause wrinkling and deformation at the seal, affecting the flatness and performance of the sealed product. Prolonged heat sealing times can also lead to macromolecule decomposition, resulting in deteriorated sealing performance at the interface.

It is crucial to find the right balance in heat sealing time to ensure a strong seal without compromising the quality and integrity of the sealed product.

Heat Sealing Pressure

Heat sealing pressure is the force applied to the thermoplastic materials during the sealing process, it plays a vital role in achieving proper interpenetration and diffusion of the polymer molecules, leading to a strong and reliable seal. The appropriate heat sealing pressure depends on factors such as the type and thickness of the thermoplastic materials, the size of the sealing area, and the desired seal strength. The pressure facilitates molecular interpenetration and diffusion between the heat sealing interfaces, ensuring a proper seal. The ideal pressure must be applied to achieve optimal heat sealing strength. For lightweight pouch bags, such as those used in the medical industry, a heat sealing pressure of at least 20N/cm² is recommended. As the thickness of the film and the width of the heat sealing area increase, the pressure should be adjusted accordingly.
Insufficient heat sealing pressure can result in incomplete melting and bonding of the plastic films, leading to areas without proper sealing and potential air entrapment, which can compromise the seal integrity and flatness. On the other hand, excessive pressure can cause material extrusion and squeezing, resulting in brittle welds and reduced seal strength. Generally, the heat sealing strength should not experience a loss of more than 10% to 15% after the sealing process.

Changes in pressure can affect heat sealing properties. Higher pressure generally leads to shorter heat sealing times, lower temperatures, and narrower heat sealing ranges. Adjusting the heat sealing pressure during production is possible, but it requires careful consideration to avoid negative effects.

Finding the optimal heat sealing pressure requires considering the specific materials and adjusting it accordingly to achieve the desired seal strength and integrity.

In conclusion, achieving optimal heat sealing performance requires careful consideration of the heat sealing temperature, heat sealing dwell time, and heat sealing pressure. These factors must be carefully adjusted and controlled to ensure strong and reliable seals.

It is important to note that the optimal heat sealing parameters may vary depending on the specific materials, equipment, and application requirements. It is advisable to conduct thorough testing and optimization to determine the precise heat sealing temperature, time, and pressure for a given sealing process and ensure consistent, high-quality seals.

Conclusion

In conclusion, achieving optimal heat sealing performance requires careful consideration of the heat sealing temperature, heat sealing dwell time, and heat sealing pressure. These factors must be carefully adjusted and controlled to ensure strong and reliable seals.

It is important to note that the optimal heat sealing parameters may vary depending on the specific materials, equipment, and application requirements. It is advisable to conduct thorough testing and optimization to determine the precise heat sealing temperature, time, and pressure for a given sealing process and ensure consistent, high-quality seals.