What are the factors that affect the heat seal strength of composite film bag making?

Some common factors that affect the heat-sealing strength of composite film bags are heat-sealing pressure, heat-sealing time, heat-sealing speed, bag contents, etc.

The purpose of the heat-sealing pressure is to make the heat-sealing layer of the composite film flow in a viscous state, so that there is effective molecular mutual penetration and diffusion between the heat-sealing interfaces at the heat-sealing temperature. The heat-sealing pressure also helps the gas escape from the surface of the film, shortens the distance between molecules on the surface of the heat-sealing material, increases the force between molecules, and makes the heat-sealing property stronger. In order to obtain better heat seal strength, the right amount of pressure needs to be used. The heat sealing pressure depends on the working condition of the composite film, its thickness and the width of the heat seal.

The speed of heat sealing indicates the quality of the bag making machine, and is also an important factor affecting the strength and appearance of heat sealing. The faster the heat-sealing speed, the higher the heat-sealing temperature should be to ensure that the heat-sealing strength and heat-sealing state reach a suitable level. Under the same heat-sealing temperature and pressure, the slower the heat-sealing speed, the more fully and firmly the heat-sealing material will be fused, but it will not cause root breakage.

Influence of compound bag contents

Some products come in powder form, which makes it easy for the seal to get dirty when the product is filled. For example, when LDPE is used as the inner layer, the seal is easily broken. This is because LDPE does not do a good job of preventing the contents inside from moving when it gets hot. The heat seal strength needs to be improved by changing the inner film material or thickening the inner film.

Also important is how long the heat seal film stays in place and how effective the seal is. If the heat-sealing temperature and pressure are the same and the heat-sealing time is long, the heat-sealing layer will be more fully and firmly fused and bonded. However, if the heat-sealing time is too long, the heat-sealing joint is easy to wrinkle and deform, thereby changing its flatness and aesthetics. At the same time, if the heat sealing time is too long, the plastic will decompose, and the sealing performance of the sealing interface will deteriorate.