Main composite film substrate moisture permeability and gas permeation amount and heat sealing performance and method

Barrier property is the main performance of the film, after the moisture permeability and gas permeability of various films are finished.
It is seen that the gas barrier properties are preferably EVOH, PVA, and K-OPP; the moisture resistance is preferably PVDC or PP; the transparent film having the same water vapor transmission rate and gas permeation amount, but the permeability is not good. The same, the opposite is also quite a lot.
The mechanism by which the gas permeates the film shows that the gas is first adsorbed on the surface of the film and then transmitted through the film through the diffusion process. However, the basic factors for the polymer of the film having high gas barrier properties are as follows:
1) Crystallinity: The crystallinity is high, and the bonding strength between the polymer chains is large.
2) Orientation: The degree of orientation is high and the barrier property is high.
3) The rigidity of the polymer chain: the polymer has a high glass transition temperature and high rigidity
4) Gap between polymers: as small as possible, the filling degree of the polymer chain is dense.
5) Aggregation energy density: a polymer having a high polarity (having an OH group and a CN group) has a high binding force (aggregation power) and is difficult to diffuse a gas.
6) Sensitivity to water vapor, after absorbing water vapor, plasticizing, the bonding force is weakened, and the gas is not easily transmitted.
The above is a rule that is generalized by gas permeation mechanism and polymer characteristics.
Heat sealing performance of heat seal film
The plastic packaging film, in most cases, is also heat-sealed to form a bag, or on an automatic packaging machine, heat sealing → filling → bag making, in order to achieve the basic purpose of packaging. Therefore, the performance of the heat-sealing layer as a dry composite, or the heat-sealing layer of the extrusion-coated composite and co-extruded composite film is a very important basic property of the packaging film.
Heat sealing method
There are many heat sealing methods, which are mainly divided into four types, namely, ordinary electric heat sealing method and pulse.
Heat sealing method, ultrasonic heat sealing method, high frequency heat sealing method