Processing Technology Affecting the Morphological Structure of Waterproof and Breathable Membrane

1. Effect of longitudinal stretch

The resin passes through the process of compounding, extrusion and calendering, exhibiting a partial thinning of the film due to the formation of fibrillation characteristics during the calendering process. During longitudinal stretching, polycrystalline aggregates begin to elongate to form fibrils, which are parallel to the stretching direction. The cross-section of the fibrils is wide and thin, and its maximum width is about 100nm, while the small fibrils are 0. 5 ~ 1. 0nm.

2. The influence of horizontal expansion multiple

The transverse stretching stage is to control the microporous structure and thickness of the film. In the process of transverse stretching, the transverse stretching of each part of the film along the transverse stretching direction is uneven, and transverse stretching is a non-uniform stretching process. Compared with the two sides of the film, the stretching ratio of the middle part is smaller, and the non-uniform transverse stretching forms a small pore size and low porosity in the middle part of the film in the transverse stretching direction, while the pore size and porosity of the two sides are large. The difference in the microporous structure in the transverse stretching direction of the film will affect the waterproof and moisture permeability of the waterproof breathable membrane and its laminated fabric.
Fix the process conditions such as longitudinal stretching ratio and stretching temperature, and change the transverse stretching ratio. The film porosity and uniform pore size increase with increasing transverse stretch ratio. At the same time, fibrils parallel to this direction also appeared in the transverse stretching direction.

3. Influence of lateral expansion speed

The lateral expansion speed also affects the film structure, the higher the lateral expansion speed, the larger the porosity, while the average pore size decreases slightly. The length of the thicker area of the film is small during rapid stretching, while the edge of the film is excessively elongated by low-speed stretching, which cannot effectively stretch the central area of the base tape, so the length of the thicker area is large. Under different stretching rates, the stretching rate affects the transfer of stress. When stretching at high speed, due to strain hardening and rate-sensitive effects, the thickness of the thinned area will increase, and the stress caused by continuous deformation will increase, and the stress will be quickly transmitted to the center of the base belt, making the The thickness and microporous structure tend to be consistent in the transverse direction of the film;

Stretching at low speed forms a film with large apertures on both sides and thin thickness. Therefore, in order to obtain a waterproof and breathable membrane with high porosity, uniform porosity and thickness, and stable dimensions, stretching speed is one of the key factors.