1. The type, thickness and quality of heat seal material have the most direct influence on the heat seal strength. The common heat sealing materials for composite packaging are CEP, LPPE, CPP, OPP, EVA, hot melt adhesive and some other ionic resin coextrusion or blending modified films. The thickness of heat seal material is generally 20-80 μ M. In special cases, it can reach 100-200 μ For the same heat sealing material, the heat sealing strength increases with the increase of heat sealing thickness. For example, the heat seal strength of cooking bag is generally required to be 40-50n, so the heat seal thickness should be 60-80n μ It is more than 5 m. Temperature is involved in the process of heat sealing bag making, and the temperature control is displayed by the temperature meter.

2、要達到理想的熱封強度，熱封壓力必不可少。對于輕薄包裝袋、熱封壓力至少要達到2kg/㎝2，而且隨著復合膜總厚度的增加而相應提高；若熱封壓力不足，兩層薄膜之間難以達到真正的熔合，導致局部熱封不好或難以消除夾在焊縫中間的氣泡，造成虛焊。但熱封壓力并非越大越好，應以不損傷焊邊為宜，因為在較高的熱封溫度時，焊邊的熱封材料已處于半熔融狀態，太大的壓力易擠走部分熱封料，使焊縫邊緣形成半切斷狀態。焊縫發脆，熱封強度降低。所以壓力的調節非常關鍵。

2. To achieve the ideal heat seal strength, heat seal pressure is essential. For the light and thin packaging bags, the heat sealing pressure should be at least 2kg / cm2, and it increases with the increase of the total thickness of the composite film; If the heat sealing pressure is insufficient, it is difficult to achieve real fusion between the two films, resulting in poor local heat sealing or difficult to eliminate the bubbles in the middle of the weld, resulting in false welding. However, the higher the heat sealing pressure is, the better. It is better not to damage the weld edge, because at a higher heat sealing temperature, the heat sealing material at the weld edge is already in a semi molten state. Too much pressure is easy to squeeze out part of the heat sealing material and make the weld edge form a semi cut-off state. The weld is brittle and the heat seal strength is reduced. So the regulation of pressure is very important.

3、熱封時間主要由制袋機的速度決定。速度快，熱封時間就短；速度慢，熱封時間就長。熱封時間也是影響焊縫封合強度和外觀的一個關鍵因素。相同的熱封溫度和壓力下，熱封時間長，則熱封層熔合更充分，結合更牢固；但熱封時間太長，容易造成焊縫起皺變形，影響平整度和外觀。

3. The heat sealing time is mainly determined by the speed of bag making machine. If the speed is fast, the heat sealing time is short; Slow speed, long heat sealing time. The heat sealing time is also a key factor affecting the weld sealing strength and appearance. Under the same heat sealing temperature and pressure, if the heat sealing time is long, the fusion of the heat sealing layer is more sufficient and the bonding is more firm; However, if the heat sealing time is too long, it is easy to cause weld wrinkling deformation and affect the flatness and appearance.

熱封后的焊縫若冷卻不好，不但會影響焊疑的外觀平整度，而且對熱封強度有一定的影響。冷卻過程就是通過在一定的壓力下，用較低的溫度對剛熔融熱封后的焊縫進行定形。因此，壓力不夠，冷卻和循環不暢，循環量不夠，水溫太高或冷卻不及時，都會致使冷卻不良，熱封強度降低。

If the weld after heat sealing is not cooled well, it will not only affect the appearance flatness of the weld, but also have a certain impact on the heat sealing strength. The cooling process is to fix the weld after the fusion heat seal with a lower temperature under a certain pressure. Therefore, insufficient pressure, poor cooling and circulation, insufficient circulation, too high water temperature or untimely cooling will lead to poor cooling and lower heat seal strength.

4、熱封次數越多，熱封強度越高，縱向熱封次數取決于縱向焊棒的有效長度和袋長之比。橫向熱封次數由機臺橫向熱封裝置的組數決定。良好的熱封，要求熱封次數至少達到兩次以上。相同結構和厚度的復合膜，復合層間剝離度越高，熱封強度越大；對于復合剝離強度低的產品，焊縫破壞往往是焊縫處的復合膜先層間剝離，致使由內面熱封層獨立承受破壞拉力，而面層材料失去補強作用，致使焊縫的熱封強度由此大為降低；若復合層間剝離度強，則不致發生焊邊處層間的剝離，所測得的實際熱封強度就大得多；在熱封內層為PE或OPP時，熱封強度就比同樣厚度的BOPP好得多。

4. The more times of heat sealing, the higher strength of heat sealing. The number of longitudinal heat sealing depends on the ratio of effective length of longitudinal welding rod to bag length. The number of transverse heat sealing is determined by the number of groups of transverse heat sealing devices. Good heat seal, the number of heat seal at least two times. With the same structure and thickness of the composite film, the higher the peeling degree, the greater the heat sealing strength; For products with low composite peel strength, the failure of the weld is usually due to the delamination of the composite film at the weld, which causes the inner heat seal layer to bear the failure tension independently, while the surface material loses its reinforcing effect, which greatly reduces the heat seal strength of the weld; If the delamination degree between the composite layers is strong, the delamination will not occur at the welding edge, and the measured actual heat seal strength is much larger; When the inner layer of heat seal is PE or OPP, the heat seal strength is much better than that of BOPP with the same thickness.

5、復合袋內容物的影響。有些產品為粉末裝，在進行灌裝時易沾污封口，例如，當采用LDPE材料作為內層料時，發現封口處易破裂。這是因為LDPE對夾雜物的熱封性就不是很好，這時就要更換內層膜材料或增加材料的厚度就可以提高熱封強

5. The influence of the contents of the composite bag. Some products are powder packed and easy to contaminate the seal during filling. For example, when LDPE material is used as inner material, it is found that the seal is easy to break. This is because the heat sealing property of LDPE to inclusions is not very good. At this time, it is necessary to replace the inner membrane material or increase the thickness of the material to improve the heat sealing strength