The plastic packaging bags we use are all heat sealed. However, there are many heat sealing methods for plastic packaging bags, including manual heat sealing, high frequency heat sealing, hot plate heat sealing, pulse heat sealing, ultrasonic heat sealing, infrared radiation heat sealing, hot air heat sealing, etc. Each heat sealing method has different advantages and effects. If we want to buy the right plastic packaging bags, we can also master the heat sealing method. Now let's talk about how many kinds of heat sealing methods are there for plastic packaging bags?

　　1.更简单的热封方法手工热封法：常用于PE、PP单一薄膜热封。

　　1. The simplest heat sealing method manual heat sealing method: commonly used in PE, PP single film heat sealing.

　　热封时需要借助于耐热薄膜将普通电烙铁刀口部位弯成“L”形，刀口宽度一般为3mm，再将导线接通在调压器上进行恒温控制。薄膜在封口处留一个边，则热封强度会更大些。实际操作时，更好铺2层细平布，再铺一层不易变形的卡其布，布纹应与热封线呈45°或平直，其作用是使热封部位产生均匀的花纹，以强化花纹(起到筋骨支撑的作用)结构来达到分子间互相渗透的目的，提高封口界面的密封性。

　　During heat sealing, it is necessary to bend the blade of common electric soldering iron into "L" shape with the help of heat-resistant film, and the width of the blade is generally 3mm, and then connect the wire to the voltage regulator for constant temperature control. If the film leaves a side at the sealing place, the heat sealing strength will be higher. In practical operation, it is better to lay two layers of fine flat cloth, and then a layer of khaki cloth which is not easy to deform. The cloth pattern should be 45 ° or straight with the heat sealing line. Its function is to make the heat sealing part produce uniform pattern, so as to strengthen the pattern (playing the role of rib support) structure to achieve the purpose of mutual penetration between molecules and improve the sealing interface.

　　2.高频热封法：利用电子管自激振荡器产生的高频电场，使塑料介质分子产生热量，并施以一定的压力来实现热封。

　　2. High frequency heat sealing method: use the high frequency electric field generated by the self-excited oscillator of the electron tube to make the plastic medium molecules generate heat, and apply certain pressure to realize heat sealing.

　　塑料薄膜在高频电场的作用下，极性分子按照与电极相反的方向排列，分子中的正电荷转向负极，负电荷转向正极。如果电场方向改变，电荷也将改变位置。这种电荷的位移称为“极化”。“极化”就是使分子进行有规则的取向。为此，必须克服摩擦阻力，消耗一定能量，而这种能量的消耗又转化为热的形式放出，这就是发热的原因。发热的薄膜在底板与 模具的适当压力下，两层薄膜就能结合在一起。

　　Under the action of high frequency electric field, the polar molecules are arranged in the opposite direction of the electrode. The positive charge in the molecule turns to the negative and the negative charge turns to the positive. If the direction of the electric field changes, the electric charge will also change its position. The displacement of this charge is called polarization. "Polarization" is the regular orientation of molecules. Therefore, the friction resistance must be overcome and some energy must be consumed, and this energy consumption is transformed into the form of heat to be released, which is the reason of heat generation. Under the proper pressure of the bottom plate and the mold, the two films can be combined.

　　3.依靠外部加热实现热封的热板热封法：先将两层重叠的薄膜放在两块加热(或者其中一块加热)的金属板之间，直到表层熔化，然后在压力下使熔化的表面迅速结合在一起，并保持压力冷却为止。热板热封装置结构简单，成本低，寿命长，且不易损坏。

　　3. Hot plate heat sealing method of heat sealing by external heating: first place two layers of overlapping films between two heated (or one of them heated) metal plates until the surface layer melts, and then rapidly combine the melted surfaces under pressure, and maintain the pressure until it cools down. The hot plate heat sealing device has simple structure, low cost, long service life and is not easy to be damaged.

　　4.脉冲热封法：使被热封件在加压之下热熔，然后冷却并释放压力。通常是用一条镍铬带代替金属板做加热元件，从镍铬带通入瞬时电流而加热。操作时将搭接的塑料薄膜放在工作台上，通过人工或自动控制，使上面的加热元件压紧塑料薄膜，同时电流自动流入镍铬带，于是强热能脉冲作用到热封面上，持续很短时间之后，由时间继电器切断电流，随即加以冷却，然后去除压力，再取出热封件。

　　4. Pulse heat sealing method: first, make the heat sealed parts melt under pressure, then cool and release the pressure. Usually a nickel chromium strip is used instead of the metal plate as the heating element, and the instantaneous current is introduced from the nickel chromium strip for heating. During the operation, the overlapped plastic film is placed on the workbench, and the heating element on it is pressed tightly by manual or automatic control. At the same time, the current automatically flows into the nickel chromium strip, so the strong thermal energy pulse acts on the thermal cover. After a very short time, the current is cut off by the time relay, then it is cooled, then the pressure is removed, and then the thermal seal is taken out.

　　5.超声波热封法：热封机的主要部件是一个换能器，换能器上绕有线圈，线圈连接振荡器，借助磁伸缩效应，把高频电流转换为机械振动，机械能从振动头向外发射，再以一种波的形式传给薄膜，在薄膜内部引起效应力，并在振动的界面上形成两层薄膜的冲突现象。随着发热和升温，使薄膜软化熔融，加之下面支撑台的反作用力及其振动头的夹紧力，使热封合面上的聚合物分子互相扩散。因此，被热封薄膜的分子之间具有较强的结合力。

　　5. Ultrasonic heat sealing method: the main part of the heat sealing machine is a transducer, on which a coil is wound and connected to the oscillator. With the aid of magnetostriction effect, the high-frequency current is converted into mechanical vibration. The mechanical energy is emitted from the vibrating head, and then transmitted to the film in the form of a wave, which causes the effect force inside the film and forms the conflict phenomenon of two layers of film on the vibration interface 。 With the heating and warming up, the film is softened and melted. In addition, the reaction force of the lower support platform and the clamping force of the vibrating head make the polymer molecules on the heat sealing surface diffuse each other. Therefore, there is a strong binding force between the molecules of the heat sealed film.

　　此外，还有一种热空气热封法，这种方法就是借助热气，将其吹向塑料薄膜表面进行热封，此法可应用于重包装的热封。

　　In addition, there is also a hot air heat sealing method, which is to use hot air to blow it to the surface of plastic film for heat sealing. This method can be applied to the heat sealing of heavy packaging.