Production technology principle of breathable film

According to the film making process: the manufacture of micro-porous breathable film can be divided into blowing film method and casting method. According to the drawing process: the film can be divided into unidirectional drawing method, bidirectional drawing method and local drawing method. The following aspects need to be paid attention to in the manufacturing process of breathable film:

1. Selection of raw materials

Resin selection

Rigid breathable film needs to choose high density polyethylene. Flexible breathable film needs to choose low density polyethylene. High tensile breathable film needs to choose high strength polyethylene.

Choice of calcium carbonate

Surface treatment of calcium carbonate: fluidity, extrusion stability, die orifice coking, pinhole, film mechanical properties, etc.

Selection of calcium carbonate particle size: tensile property, moisture permeability, uniformity, work-ability.

The choice of raw materials directly affects the work-ability of the breathable film (such as coking time, extrusion stability, thin film work-ability and pinhole defects, etc.) and physical properties (such as air permeability, water resistance, thermal stability and mechanical properties, etc.). Therefore, suitable for the customer's physical requirements for the film and the matching condition with the processing equipment is the first consideration in the selection of breathable materials.

2. Dehumidification system

The high humidity of the raw material is the main reason for the holes in the breathable film and the coking of the T-film, which will seriously affect the production efficiency and product quality of the breathable film. Therefore, the production of breathable film not only requires the dehumidification of raw materials (< 250ppm), but also the transportation of raw materials and flash recovery systems, which should have strict humidity control requirements.

3. Extrusion thickness control

Stretching amplifies the deviation of extrusion thickness, so the control of extrusion thickness is a prerequisite for ensuring the thickness uniformity of the final product.

4. Stretch control

There are two necessary conditions for the manufacture of breathable film, one is calcium carbonate, and the other is stretching. Therefore, drawing is crucial in the manufacturing process of breathable film. Drawing temperature, drawing ratio, drawing rate and drawing gap are the four elements of the drawing process, and its overall balance will have a great impact on the permeability, mechanical properties, consistency and appearance of the breathable film.

5. Heat treatment

The method of heat treatment to restore and relax the rigid polymer chain segment after stretching is a necessary means to improve the stability of the breathable film material in the later process and during use.