Brief introduction of production process and principle of micro-tie breathable waterproof film

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In the late 1980s S, building waterproof breathable membrane was vigorously promoted in developed countries in Europe and America. However, micro-prick breathable waterproof film technology has only entered the domestic market for a few short years and is still in the promotion stage. Some domestic enterprises are also in the research and production stage. With the improvement of China's requirements for building energy conservation, the formulation of relevant engineering technical specifications and product standards will soon be promoted and applied in the domestic market.

classification and production process of waterproof and breathable membranes

waterproof and breathable membranes are generally divided into microporous membranes, hydrophilic membranes and microporous hydrophilic membranes. The microporous membrane is a very thin polymer membrane with a large amount of direct less than 2μ on the surface. Micropores of m; Droplet diameter 100 μAbout m, the diameter of water vapor is 0. 0004 muM, so it can be effectively waterproof and breathable. The hydrophilic membrane has no physical micropores. The membrane is a group of copolymers consisting of soft segments and hard segments. The hard segments can prevent water droplets from passing through and play a waterproof role, the soft segment is composed of hydrophilic components and can play a role in ventilation. Microporous hydrophilic membrane is composed of microporous membrane and hydrophilic membrane. Building waterproof and breathable membrane is a new type of polymer waterproof material. Most of the waterproof and breathable membranes used in buildings are microporous membranes. Products produced by a company in the United States adopt flash evaporation process, A domestic company adopts thermoplastic blown film extrusion composite process. We will focus on the advanced flash evaporation process. Flash evaporation, also known as instantaneous solvent volatilization method, does not use melt spinning, but uses dry spinning technology. The polymer solution is made into a spinning solution in a certain solvent, and then sprayed out from a spinneret hole. The polymer is resolidified into a fiber due to the sharp volatilization of the solvent. At the same time, the dry spinning technology adopted by the flash method is different from the common spinning technology, which is mainly reflected in the low viscosity of the spinning solution adopted by the flash process, however, it is sprayed out of the spinneret hole at extremely high pressure and speed. Due to the low viscosity and good fluidity of the solution, the liquid wire strips are solidified in high-speed motion to form extremely fine fiber strips, which are finally adsorbed on the net curtain to directly form a fiber net. The spinning solution of flash method consists of fiber-forming polymer, main solvent, secondary solvent and some additives. The fiber diameter of flash nonwoven fabric is very thin, so it has excellent waterproof and air permeability.

Functional principle of waterproof and breathable film

Air permeability is that the structure of the fabric allows moisture to pass through the body of the fabric, at the same time, it prevents external liquid from penetrating into the fabric. At present, there are two kinds of air permeability Technologies, one is microporous air permeability technology and the other is molecular air permeability technology. The structure of microporous thin films is formed by drafting two incompatible components, such as adding inorganic particles into polymers, and there are many micropores like capillaries in its structure. These micropores form a channel that allows gas to pass through, but cannot pass through because the diameter of external liquid droplets is larger than the diameter of micropores. The permeability of gas through the film depends on the size of micropores. The water transmission rate is proportional to the surface area and concentration driving force of the film. The physical structure of the film in The microporous film is the decisive factor of the permeability. Molecular films are dense microporous-free films produced by simple extrusion or other processes and then attached to fabrics. The permeation process of water vapor on molecular films can be called'Active diffusion process'. The penetrant is attached to one side of the high concentration and diffuses to penetrate to the other side of the film using the existing pressure difference. The chemical structure of the molecular film polymer and the thickness of the film are the main factors that determine the penetration force.

The Micro-prick breathable waterproof film can not only be waterproof, but also ensure that the water vapor inside the enclosure structure can be effectively discharged, and can certainly be popularized in the field of building energy conservation.