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.更簡單的熱封方法手工熱封法：常用于PE、PP單一薄膜熱封。

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

　　熱封時需要借助于耐熱薄膜將普通電烙鐵刀口部位彎成“L”形，刀口寬度一般為3mm，再將導線接通在調壓器上進行恒溫控制。薄膜在封口處留一個邊，則熱封強度會更大些。實際操作時，更好鋪2層細平布，再鋪一層不易變形的卡其布，布紋應與熱封線呈45°或平直，其作用是使熱封部位產生均勻的花紋，以強化花紋(起到筋骨支撐的作用)結構來達到分子間互相滲透的目的，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.高頻熱封法：利用電子管自激振蕩器產生的高頻電場，使塑料介質分子產生熱量，并施以一定的壓力來實現熱封。

　　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.

　　塑料薄膜在高頻電場的作用下，極性分子按照與電極相反的方向排列，分子中的正電荷轉向負極，負電荷轉向正極。如果電場方向改變，電荷也將改變位置。這種電荷的位移稱為“極化”。“極化”就是使分子進行有規則的取向。為此，必須克服摩擦阻力，消耗一定能量，而這種能量的消耗又轉化為熱的形式放出，這就是發熱的原因。發熱的薄膜在底板與 模具的適當壓力下，兩層薄膜就能結合在一起。

　　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.依靠外部加熱實現熱封的熱板熱封法：先將兩層重疊的薄膜放在兩塊加熱(或者其中一塊加熱)的金屬板之間，直到表層熔化，然后在壓力下使熔化的表面迅速結合在一起，并保持壓力至冷卻為止。熱板熱封裝置結構簡單，成本低，壽命長，且不易損壞。

　　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.脈沖熱封法：首先使被熱封件在加壓之下熱熔，然后冷卻并釋放壓力。通常是用一條鎳鉻帶代替金屬板做加熱元件，從鎳鉻帶通入瞬時電流而加熱。操作時將搭接的塑料薄膜放在工作臺上，通過人工或自動控制，使上面的加熱元件壓緊塑料薄膜，同時電流自動流入鎳鉻帶，于是強熱能脈沖作用到熱封面上，持續很短時間之后，由時間繼電器切斷電流，隨即加以冷卻，然后去除壓力，再取出熱封件。

　　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.超聲波熱封法：熱封機的主要部件是一個換能器，換能器上繞有線圈，線圈連接振蕩器，借助磁伸縮效應，把高頻電流轉換為機械振動，機械能從振動頭向外發射，再以一種波的形式傳給薄膜，在薄膜內部引起效應力，并在振動的界面上形成兩層薄膜的沖突現象。隨著發熱和升溫，使薄膜軟化熔融，加之下面支撐臺的反作用力及其振動頭的夾緊力，使熱封合面上的聚合物分子互相擴散。因此，被熱封薄膜的分子之間具有較強的結合力。

　　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，還有一種熱空氣熱封法，這種方法就是借助熱氣，將其吹向塑料薄膜表面進行熱封，此法可應用于重包裝的熱封。

　　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.