The full name of breathable PE film is "waterproof and breathable microporous membrane", which is breathable and impermeable. It is an international new polymer waterproof material, which is widely used in women's sanitary napkins, pad bottom film, baby diapers and other life fields. This paper introduces the air permeability mechanism, hole making mechanism, process flow and characteristic requirements of PE backsheet film.
(1) Permeability mechanism
The microporous membrane itself has numerous interconnected micropores. Its pore size is very small (about 0.01~10pm), and it can only pass through water vapor molecules with a particle size of about 0.4nm. However, any raindrop or water drop cannot pass through due to its large particle size.
Therefore, the water vapor discharged from the human body can effectively diffuse outward through the aperture, while the water droplets cannot penetrate inward, so as to achieve the effect of waterproof and moisture permeability.
(2) Pore forming mechanism
The main feature is to add inorganic fillers (such as calcium carbonate) to the resin. Based on the principle that micropores are formed at the junction of inorganic filler particles (1~10pm) and the plastic film matrix being shaped during stretching, the size of these micropores is sub nanometer, that is, hundreds of millions of micropores can be distributed on an area of 1 square centimeter. These micropores form a channel that allows gas to pass through, thus realizing the breathable and impermeable characteristics of breathable PE film.
Generally, the method of extruding flat film and then stretching is used for breathable PE film. This process can be divided into three parts: sheet preparation, stretching and forming. The production process is as follows: PE raw material + pore forming agent → extruding sheet → cooling → preheating → stretching → heat setting → cooling → trimming → curling.
(1) Good mechanical strength for longitudinal and transverse stretching
The mechanical strength of the membrane mainly refers to the tensile strength, which refers to the maximum strength that the membrane can bear when it is pulled in a parallel direction, subject to the maximum pull per unit area.
(2) Excellent hydrophobicity
Breathable PE film, also known as "waterproof and breathable microporous membrane", has the characteristics of air permeability and water impermeability. This property is closely related to the adsorption of the film, and mainly depends on the chemical properties and structure of the film material. The hydrophilicity of the film is usually characterized by measuring the contact angle. PE film does not contain hydrophilic groups, so it has strong hydrophobicity and can prevent the leakage and splash of blood, body fluid and urine.
(3) Compare uniform porosity and permeability (determine the permeability by nitrogen oxygen gas exchange test)
Porosity is the ratio of the volume of voids in the whole membrane to the total volume. The microporous membrane itself has numerous interconnected micropores, with a very small pore size (about 0.001~1 micron), which can only pass through water vapor molecules with a particle size of about 0.4nm, while raindrops or water droplets cannot pass through because of their large particle size. Therefore, the water vapor released by the human body can effectively diffuse outward through the aperture, while the water droplets cannot penetrate inward, so as to achieve the role of waterproof and moisture permeability.
(4) Special morphological structure
The morphology of the films can be characterized by electron microscopy.
Breathable PE film, also known as breathing film. Because of its soft skin affinity, relatively high tensile strength and good moisture permeability, it has been more and more widely used in various fields of life. Learn about PE backsheet film to help you use it better.