The main functions of waterproof and breathable fabrics are: waterproof, moisture permeable, breathable, insulated, windproof and warm. From the production process, the technical requirements of waterproof and breathable fabrics are much higher than those of ordinary waterproof fabrics. At the same time, from the perspective of quality, waterproof and breathable fabrics also have functional features not available in other waterproof fabrics. The waterproof and breathable fabric enhances the airtightness and watertightness of the fabric, and its unique steam permeability can quickly discharge the water vapor inside the structure, avoiding the structure of mold and mold, and keeping the body always dry, perfectly solving the ventilation and windproof, waterproof, The problem of keeping warm is a new type of fabric that is healthy and environmentally friendly.
The real waterproof fabric can withstand the water seepage pressure and not seep water for a long time in a humid climate. For example, walking for a long time in the wind and rain, walking on the wet ground, will not seep.
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In the state of water vapor, the water particles are very small, and according to the principle of capillary movement, the capillary can be smoothly infiltrated to the other side, thereby causing vapor permeability. When the water vapor condenses into water droplets, the particles become larger. Due to the surface tension of the water droplets (water molecules collide with each other), the water molecules cannot smoothly escape from the water droplets and penetrate into the other side, which is to prevent The penetration of water occurs so that the vapor permeable membrane has a waterproof function.
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1. Young's formula
A drop of liquid is dropped on the solid surface, assuming that the surface is ideally flat, the gravity of the droplet is concentrated at one point, and the amount of the field is ignored. Due to the surface tension (Ys) of the fibers in the fabric, the surface tension of the liquid (YL), and the interfacial tension (YLS) of the firmware, the droplets form a variety of shapes (from cylindrical to fully flattened). ). Except that the night is completely flat, when the droplet is in equilibrium on the solid surface, point A receives the effect of the scattered gravity.
The angle 0 is called the contact angle. When 0=00, the droplet is on the solid surface, which is the limit state where the solid surface is wetted by the field; when 0=1800, the droplet is cylindrical, which is a kind Ideal non-wetting behavior. In the water repellent finishing, the surface tension of the droplet can be regarded as a constant. Therefore, whether the wilderness can wet the solid surface, and the resultant relay tension of the lotus leaf in the bank with the solid surface. From the said requirement, the larger the contact angle 0, the better the rolling loss of water droplets, that is, the smaller the better.
2, fabric adhesion work
Since Ys and YLS are practically impossible to measure directly, the contact angle 0 or cos0 is usually used to directly assess the degree of wetting. However, the contact angle is not the cause of wetting, and the actual result is that there is a relationship between the adhesive work and the interaction, and the degree of wetting.
The YL and cos0 indicating the work of adhesion are all measurable, so the formula has practical significance. In the same way, the work required to divide the liquid bead per unit area on the interface into two liquid beads is 2YL, which can be called the cohesive work of the liquid. It can be seen from the formula that when the adhesion work is increased, the contact angle is reduced. When the adhesion work is equal to the cohesive work, that is, the contact angle is zero, this is that the liquid is completely flattened on the solid surface, and since the cos0 cannot exceed 1, the adhesion work is even Above 2YL, the contact angle remains unchanged. WSL=YL, then 0 is 900. When the contact angle is 180°, WSL=O, indicating that there is no turbidity between the liquid and the solid. However, since there is some sticking effect due to the reduction of the hatchback, the contact angle is equal to 180°, and only a few can be obtained. An approximate situation, such as an angle of 160° or more.
3, the critical surface tension of the fabric
Since the surface tension of the solid is almost impossible to measure, in order to understand the wettability of the solid surface, one has determined his critical surface tension. Although the critical surface tension cannot directly indicate the surface tension of the solid, but indicates the size of the Ys-YLS, it can explain the difficulty of the solid surface being wetted. But should
Note that determining the critical surface tension is an empirical method and the range of measurement is also very narrow.
It can be seen from Table 10-1 that except for cellulose, the critical surface tension of other substances has a small surface tension, so they all have a certain water repellency, of which CF3 is the largest and CH is the smallest. Obviously, those who have a larger contact surface with a smaller critical surface tension can achieve a better water repellency effect.