Guangdong Huaping Hygiene Material Industrial Co.,Ltd./about/ main products include PE cast film,breathable membrane,PE perforated film,Multicolor printed film,Nonwoven Laminated film,Anti-counterfeiting Holographic film etc .
When the water vapor concentration on one side of the membrane is greater than the environment on the other side of the membrane, a humidity gradient pressure difference is formed. This provides the basic conditions for gas (steam) convection, and the humidity environment on both sides of the film tends to be relatively balanced due to the formation of convection.
The breathable membrane is used as a water-proof membrane and has a barrier effect on liquids. Because there are many channels in the film, the tortuous channels formed by it have a large “length-to-diameter ratio” (L/D), which can be understood as capillaries. Therefore, under the same liquid (such as water) and the same pressure, as long as the liquid column height of the capillary is smaller than the length of the capillary, the liquid can be guaranteed not to leak out.
Therefore, the water barrier property of the membrane directly depends on the pore size and the channel length of the gas permeable membrane. This performance can usually be measured by water pressure resistance (ΔP). When the water pressure exceeds the water pressure resistance value that the microporous membrane can withstand, water will leak out.
According to the above capillary principle, the water pressure resistance of the pores of the microporous membrane can be replaced by the capillary osmotic pressure ΔP, which can be expressed by the following formula: ΔP=2σcosα/d
ΔP—osmotic pressure (Pa)
σ—surface tension (N/m)
α—contact angle (degrees)
d—capillary diameter
It can be seen that the water pressure resistance requirements (safety requirements) can be met by designing different micropore diameters and film thicknesses; obviously, the WVTR requirements can also be achieved by changing the micropore diameter and micropore density of the film.
Note: For the breathable film used in personal hygiene care products, the principle of improving the breathability of the film under the premise of ensuring safety (ΔP value) must be followed.
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