Moisture permeability and gas permeability of main composite film substrates and heat sealing properties and methods

Barrier property is the main performance of the film, after sorting the moisture permeability and gas permeability of various films

It can be seen that EVOH, PVA, and K-OPP are the best gas barrier properties; PVDC and PP are the best moisture resistance; there are permeable films with the same good water vapor transmission and gas transmission, but their permeability is not good. Similarly, there are many opposites between the two.

From the mechanism of gas permeation film, it can be seen that the gas is first adsorbed on the surface of the film, and then passes through the film through the process of diffusion. However, for polymers with high gas barrier properties, the basic factors are as follows:

1) Crystallinity: high crystallinity, strong bonding strength between polymer chains.

2) Orientation: High degree of orientation and high barrier properties.

3) The rigidity of the polymer chain: the glass transition temperature of the polymer is high and the rigidity is strong

4) The gap between the polymers: as small as possible, the filling degree of the polymer chain is dense.

5) Coagulation energy density: polymers with high polarity (with OH and CN groups) have high binding force (cohesion force), and the diffusion of gas is difficult.

6) Sensitivity to water vapor, after absorbing water vapor, it becomes plasticized, the binding force is weakened, and the gas is not easy to pass through.

The above are the rules summarized by the gas permeation mechanism and polymer properties.

Heat-sealing performance of heat-sealing film

In most cases, the plastic packaging film needs to be heat-sealed to form a bag, or on an automatic packaging machine, heat-sealed → filled → bag-made, in order to achieve the basic purpose of packaging. Therefore, the performance of the heat-sealing layer film as a dry compound, or the heat-sealing layer of extrusion-coated compound and co-extruded compound films is a very important basic property of packaging films

heat sealing method

There are many heat sealing methods, which are mainly divided into four types, namely, ordinary electric heat sealing method, pulse sealing method

Heat sealing method, ultrasonic heat sealing method, high frequency heat sealing method