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、要达到理想的热封强度，热封压力必不可少。对于轻薄包装袋、热封压力少要达到2kg/㎝2，而且随着复合膜总厚度的增加而相应提高；若热封压力不足，两层薄膜之间难以达到真正的熔合，导致局部热封不好或难以夹在焊缝中间的气泡，造成虚焊。但热封压力并非越大越好，应以不损伤焊边为宜，因为在较高的热封温度时，焊边的热封材料已处于半熔融状态，太大的压力易挤走部分热封料，使焊缝边缘形成半切断状态。焊缝发脆，热封强度降低。所以压力的调节非常关键。

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、热封时间主要由制袋机的速度决定。速度快，热封时间就短；速度慢，热封时间就长。热封时间也是影响焊缝封合强度和外观的一个关键因素。相同的热封温度和压力下，热封时间长，则热封层熔合更充分，结合更牢固；但热封时间太长，容易造成焊缝起皱变形，影响平整度和外观。

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.

热封后的焊缝若冷却不好，不但会影响焊疑的外观平整度，而且对热封强度有一定的影响。冷却过程就是通过在一定的压力下，用较低的温度对刚熔融热封后的焊缝进行定形。因此，压力不够，冷却和循环不畅，循环量不够，水温太高或冷却不及时，都会致使冷却不良，热封强度降低。

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、热封次数越多，热封强度越高，纵向热封次数取决于纵向焊棒的有效长度和袋长之比。横向热封次数由机台横向热封装置的组数决定。良好的热封，要求热封次数少达到两次以上。相同结构和厚度的复合膜，复合层间剥离度越高，热封强度越大；对于复合剥离强度低的产品，焊缝破坏往往是焊缝处的复合膜先层间剥离，致使由内面热封层独立承受破坏拉力，而面层材料失去补强作用，致使焊缝的热封强度由此大为降低；若复合层间剥离度强，则不致发生焊边处层间的剥离，所测得的实际热封强度就大得多；在热封内层为PE或OPP时，热封强度就比同样厚度的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、复合袋内容物的影响。有些产品为粉末装，在进行灌装时易沾污封口，例如，当采用LDPE材料作为内层料时，发现封口处易破裂。这是因为LDPE对夹杂物的热封性就不是很好，这时就要更换内层膜材料或增加材料的厚度就可以提高热封强

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