In the actual production process, due to the influence of heat sealing pressure, bag making machine speed and composite substrate thickness, the actual heat sealing temperature is often higher than the melting temperature of heat sealing materials. The smaller the pressure of heat seal, the higher the temperature of heat seal, the faster the machine speed, and the thicker the surface material of composite film, the higher the temperature of heat seal.

热封温度若低于热封材料的软化点，则无论怎样加大压力或延热封时间，均不能使热封层真正封合。但是，如果热封温度过高，又极易损伤焊边处的热封材料，熔融挤出产生“根切”现象，大大降低了封口的热封强度和复合袋子的耐冲击性能。在实际制袋热封过程中，热封刀具的压力常采用可旋转弹簧来调整，调整过程一般刀具由两个弹簧组成，分左、右两边，如果压力影响热封强度。、

If the heat sealing temperature is lower than the softening point of the heat sealing material, no matter how to increase the pressure or extend the heat sealing time, the heat sealing layer can not be really sealed. However, if the heat sealing temperature is too high, it is easy to damage the heat sealing material at the welding edge, resulting in "undercutting" phenomenon during melt extrusion, which greatly reduces the heat sealing strength of the seal and the impact resistance of the composite bag. In the actual bag making and heat sealing process, the pressure of the heat sealing tool is often adjusted by a rotatable spring. In the adjustment process, the tool is generally composed of two springs, which are divided into left and right sides. If the pressure affects the heat sealing strength. 

检测方法则是：取一只正加工的复合袋仔细观察缝迹，如果压力均匀是不会产生气泡等现象；另一种方法是，用长500px、宽75px、厚5000px专用光滑竹块进行试验，由于压力不够，强度低，往往出现漏破现象，所以均匀的压力与温度是降低强度低、分层现象的基本之一。

The detection method is: take a composite bag that is being processed and carefully observe the seam. If the pressure is uniform, there will be no bubbles; another method is to use a special smooth bamboo block with a length of 500px, a width of 75px and a thickness of 5000px for test. Due to insufficient pressure and low strength, leakage often occurs. Therefore, uniform pressure and temperature are one of the basic factors to reduce the phenomenon of low strength and delamination .

对于轻薄包装袋、热封压力少要达到2kg/cm2，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。

For the light and thin packaging bags, the heat sealing pressure should be at least 2kg / cm2, and it should be increased 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 local poor heat sealing or difficult to eliminate the gas 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.