Comprehensive Guide to Heat Sealing Equipment: Methods, Types, and Applications

Introduction

Heat sealing is a vital process in the packaging industry, used to bond plastic films using heat and pressure. Different heat sealing methods offer distinct advantages depending on the type of material and specific packaging needs. Whether you’re sealing polyethylene films, composite materials, or specialized films for sensitive products, choosing the right heat sealing method can ensure strong, durable seals that maintain product integrity. This guide explores the most common heat sealing methods—including plate, roller, pulse, and ultrasonic sealing—along with their applications and benefits in packaging.

Depending on the different heating and pressure methods used, the heat-sealing methods of heat-sealing machines can be classified into the following types.

Heat-sealing the sheet

Plate heat sealing is the most common heat sealing method. In this process, a heating plate is heated intermittently and pressed against the plastic film to create a seal. The heat-sealing principle is illustrated in Figure 6-2. The two layers of film 3 to be sealed are transported between the heating plate 1 and the workbench 5 and then pressed firmly against the non-stick material 4. Heating plate 1 and workbench 5 are heated to a specific temperature (constant temperature control), pressed together under pressure, and then cooled to achieve a tight seal.
Commonly used nonstick materials include heat-resistant polytetrafluoroethylene or fiberglass fabric, primarily to prevent the T-table and the film layer from sticking together, ensuring that the bag opening is sealed cleanly and the workbench is kept clean. The electric heating wire 2 installed in the heating plate 1 heats the heating plate. The heating temperature is typically measured by a resistive temperature sensor and displayed on a temperature indicator. The temperature is adjusted via a voltage regulator or a resistor. To ensure high-quality seal seams, the heat-sealing surface of the heating plate should be flat, and the contact surface should be flat or padded with a heat-resistant rubber cushion. The hot-sealing pressure-application mechanism of the heating plate 1 can be pneumatic, hydraulic, cam-controlled, electromagnetic, etc.

This lamellar hot-melt sealing device is characterized by its simple design and operating principle, as well as its high sealing speed. It is frequently used in intermittent automatic packaging machines. It is primarily used for heat-sealing polyethylene films and polyethylene composite films, but not for heat-sealing films that shrink easily or decompose when exposed to heat.

Roll Heat Sealing

In roller heat sealing, the plastic film is sealed by applying pressure with a continuously rotating roller and heating it with one or two rollers in a roller pair.
The principle of roller heat sealing is illustrated in Figure 6-3. The two layers of film 2 to be sealed are drawn through a pair of heating rollers 1 (or a single heating roller), heated, pressed together, and then cooled to achieve a tight seal. The resistance heater is located inside the heating roller, and electricity is transmitted to the heating wire via wiring (e.g., brushes, slip rings, and wires) that is insulated from the machine. The temperature control system, as well as the device and instrument for measuring and displaying the temperature of the heat-sealing roller, are located externally.
Roll heat sealing is characterized by continuous sealing, which is suitable for heat sealing composite films consisting of a base film (cellophane) and a heat-sealable film (polyethylene). In continuous automatic packaging machines with multiple functions, such as bag making, filling, and sealing, the heat-sealing roller can not only perform the longitudinal sealing of the packaging film material for bag formation but also pull and transport the web of packaging film material. Individual films deform easily when exposed to heat, which compromises the sealing quality and therefore makes them unsuitable for use.

Band Heat Sealing

As shown in Figure 6-4, the two film layers 2 are placed between a pair of thin, circular belts 1 (e.g., polytetraethylene belts, steel bands, stainless steel bands, or nylon textile bands) that rotate in opposite directions, and heated by the heating elements 4 on both sides of the ring band to bond the two film layers together between the ring bands. The film 2 is then cold-pressed against the cooling element 5. Before the seal is fully formed, it is embossed by a pair of embossing wheels at a preset pressure; then the production date is printed by the print coder wheel; and finally, the seal is complete.

This process is suitable for heat-sealing composite film materials. Even films that are easily deformable can be heat-sealed continuously using this machine. The sealing speed is relatively high, making it widely used.

Heat Sealing with Roller Guides

As shown in Figure 6-5, the two overlapping layers of film 1 are fed between heating plates 4 to soften and melt them. As they pass through the closely spaced heat-sealing rollers 3, they are pressed together and sealed. A characteristic feature of this sealing device is that the resistance heater and the heat-sealing roller are independent components, which simplifies the roller’s design. The overall structure is simple and versatile.
This process is suitable for the continuous heat sealing of film packaging materials and can also be used for the continuous heat sealing of films that are prone to significant thermal deformation. In the event of an unexpected machine stoppage, the film material between the electric heating plates overheats and is lost. Therefore, it must be possible to automatically evacuate the heating element to prevent the film from overheating.

Sliding heat sealing

The sliding heat-sealing process is used for packaging (see Figure 6-6). In this process, the object to be packaged 2 is wrapped in a film 3 so that it slides across the heating plate 4. The slight pressure exerted by the object to be packaged and the heat from the heating plate 4 cause the overlapping parts of the two film layers to fuse together.

Pulse Heat Sealing

As shown in Figures 6–7, the nickel-chromium alloy strip 2 presses the film 4 onto the heat-resistant rubber 5. The nickel-chromium alloy strip 2 is rapidly heated by a high current, and the heat is used for heat sealing. A key feature of this process is that the alloy strip 2 does not leave the heat-sealed area until it has cooled, allowing even easily deformable films to be heat-sealed using this method. This method is suitable for sealing products with high requirements for seal strength and sealing integrity, such as liquid packaging and vacuum packaging. This method is generally suitable for intermittent sealing and is frequently used in bag-making machines or automatic packaging machines.

Hot-Melt Cutting and Heat Sealing

As shown in Figures 6–8, the heating blade 5 (or steel wire) is used to melt and cut the film 2 while simultaneously sealing it. This sealing mechanism is simple in design, fast, and allows the film to be melted, cut, and sealed simultaneously. However, due to the limited weld area, the seal strength is relatively low, and the film can be easily opened. It is suitable only for the inner packaging of small quantities of fine powders and granules.

Pulse Melting, Heat Sealing

Fusion welding requires frequent heating of the blade and the steel wire, whereas pulse welding is the opposite (see Figures 6–9). As soon as the pressure plate 6 drives the cast alloy wire 1 and presses the foil 2 onto the heat-resistant rubber 3, the nickel-chromium alloy wire 1 is immediately activated and continues to press the heated and molten sealing part until it is released after cooling. With this method, the melting and sealing of the film can be completed simultaneously.

Hot-melt heat sealing

As shown in Figure 6-10, the heating plate 1 or flame is brought close to one end of the superimposed film 4 to melt and bond it. Using this method, the heat-shrinkable, biaxially oriented polypropylene film achieves high seal strength.

Ultrasonic Heat Sealing

As shown in Figure 6-11, this heat-sealing mechanism consists of a high-frequency oscillator, a magnetostrictive vibrator 1 that converts high-frequency electrical energy into longitudinal vibrations, and an exponential amplitude amplifier 2, which transmits the longitudinal vibrations to the film. During heat sealing, the ultrasonic vibration transmitted by the exponential amplitude amplifier heats up, causing the overlapping surface of the film 4 to melt and bond together.
This sealing process is characterized by heat generation at the center of the film overlap and is therefore suitable for the continuous sealing of films that shrink slightly when heated, such as biaxially oriented films. It can heat-seal a wide variety of plastic film materials (such as polypropylene, nylon, aluminum-plastic composites, polyoxyethylene cans, etc.) and ensures a good seal even if the packaging material is accidentally contaminated by water, oil, etc., during filling. It also provides high-quality sealing for plastics that are prone to deformation due to heat shrinkage or thermal decomposition. It is particularly suitable for heat sealing in the packaging of food, medications, and radio and electronic components that are sensitive to heat radiation, and is frequently used in bag-making machines and automatic packaging machines.

High-Frequency Heat Sealing

As shown in Figure 6-12, high-frequency heat sealing involves pressing the film 4 against a high-frequency electrode 2, applying a high-frequency voltage, and heat sealing it through the dielectric loss of the polymer. The temperature of the sealing section is highest at the sealing surface, ensuring that the film does not overheat and that the seal strength is high.

The heat-sealing time of the heat-sealing machine depends on the heating temperature, the heating method, the film material, the film thickness, and the sealing pressure. For film materials of the same type and thickness, the following applies at a constant sealing pressure: The higher the heating temperature, the shorter the heat-sealing time. The parameters for heat-sealing temperature, pressure, time, and other factors should be determined experimentally based on the mechanical and physical properties of the material being sealed.

Graduation

A heat-sealing machine is a machine that seals packaging containers using heat sealing. It is frequently used to heat-seal various types of plastic bags. Understanding the variety of heat-sealing methods—from simple plate heat sealing to the advanced capabilities of ultrasonic sealing—enables manufacturers to choose the most efficient and appropriate solution for their packaging needs. Each sealing method offers specific advantages, depending on the materials, production speed, and required quality. By choosing the right technique, companies can improve packaging efficiency, reduce waste, and ensure high-quality seals that meet industry standards.