二、 the mechanism of TPU film applied to waterproof and moisture permeable fabric
The "pore" between the polymer and the hydrophilic group molecules diffuse through the mechanism of moisture permeability. The principle of non-porous membrane moisture permeability is to introduce a hydrophilic group into a macromolecular chain and form a film which is a block copolymer composed of a single component and a hard segment and a soft segment alternately arranged. Things. In the molecular structure, the hard segment is hydrophobic, and the film itself has continuity and a large membrane surface tension, which can prevent water droplets from passing through, thereby exhibiting excellent wind and water resistance; the soft segments are hydrophilic, and they will be combined with moisture. Interacting, by means of hydrogen bonding and other intermolecular forces, adsorbing water molecules on the high humidity side in the form of "adsorption-diffusion-desorption", and transferring water molecules to low humidity one by one along the molecular chain through hydrophilic groups One side is desorbed to achieve high moisture permeability. The schematic diagram of "adsorption-diffusion-desorption" is shown in Figure 3. In this process, the hydrophilic group is equivalent to the "chemical ladder stone". In actual production, we can generally change the number or relative molecules of soft segments in the macromolecular chain. The mass increases the proportion of hydrophilic groups to make the fabric more permeable to moisture. The formula for moisture permeability is:
WVP = DSΔP / L
Where WVP is the moisture permeability ( g / ( m 2 · 24h )); ΔP is the partial pressure difference of water vapor (Pa ) on both sides of the membrane; D is the diffusion coefficient ( m 2 / s ); S is the solubility parameter; L is the membrane Thickness (cm). As can be seen from the above formula, the moisture permeability of the non-porous hydrophilic film is not only related to the thickness of the polymer film and its own properties, but also depends on the difference in water vapor partial pressure on both sides of the film.
三、the process of forming a waterproof and moisture permeable laminate fabric by TPU film
Suitable lamination techniques are key to producing high quality laminate fabrics. TPU film forming laminated fabric is a hot-melt bonding technology using moisture-curing polyurethane hot melt adhesive. This bonding technology has the advantages of environmental friendliness, low energy consumption, easy control of cross-linking, etc. It is widely used, especially suitable for one.
The combination of some high-grade textile fabrics.
The purpose of the coating transfer is to transfer the wet-cured polyurethane hot melt adhesive from the engraving roll to the film, and after transfer, the film is separated from the engraving roll. During the separation process, the hot melt adhesive must have a low viscosity and good fluidity; if the hot melt adhesive has poor fluidity and high viscosity, it will adhere to the film and the engraving roll, and severe drawing phenomenon occurs during the separation process. Therefore, the transfer efficiency of the coating is lowered, and the separation difficulty is increased. In order to reduce costs and reduce unnecessary waste, this situation is not allowed in actual production.
2. Laminated composite
Good initial bond strength is a key factor in ensuring the combination of fabric and film to form a high quality laminate fabric. When the fabric and the film coated with the moisture-curing polyurethane hot melt adhesive are instantaneously combined under a certain pressure, the hot melt adhesive should have low fluidity and high viscosity; if the fluidity of the hot melt adhesive is too good, the viscosity is too low. On the one hand, because the initial bonding strength is low, the laminated fabric may be separated after leaving the pressing point; on the other hand, due to the good fluidity, the hot melt adhesive may penetrate the fabric to cause the rubber to pass through, thereby affecting the laminated composite fabric. Appearance, feel, adhesion strength and washability.
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