The research of PTFE microporous film in China is carried out late, lagging behind developed countries such as Europe, America and Japan. At present, the production process of PTFE microporous film has the method of rolling film,

 

Turning film method and stretch film method. Stretch film method can be divided into one-way stretch and two-way stretch, through structural analysis and actual measurement, only two-way stretch film has good micropores.

Structure.

 

The former process of 1. PTFE microporous membrane:

 

The raw material of the PTFE film is a granular PTFE resin, which is a homopolymer of tetrafluoroethylene and cannot be processed by ordinary thermoplastic molding methods. And the use of similar powder metallurgy principle plus.

 

such as suspension method, dispersion method, liquid method and other polymerization methods processing. PTFE resin powder has many products abroad, and there are also a small number of manufacturers in China. Foreign manufacturers

 

Represented by DuPont in the United States and Daikin in Japan.

 

The regular production process is to mix the PTFE dispersion resin with the liquid additive, make the mixture into a sheet by calendering, and then stretch the sheet in both directions by machine to make PTFE micro

 

Pores membrane. The process is as follows: PTFE resin, extrusion aid (material selection)-mixing-calendering-biaxial stretching-coiling.

 

Figure 1: PTFE microporous membrane Source: network

 

Fabrication process

 

(1) Preparation of base film: A good base film must be uniform in thickness, with reasonable crystallinity and density. The quality of the base film directly affects the performance index of the finished product. When preparing the base film, pay attention to the following

Several factors:

 

Selection of raw materials: PTFE resin should be selected with a suitable grade of molecular weight, and its performance can withstand high-speed strain under high-temperature conditions during stretching without breaking; Additives should be selected to make the resin wet.

 

Run, non-toxic, high boiling point, easy to remove and no residual substances.

 

Proportion: according to the resin and extrusion aid brand, according to the appropriate proportion of preparation, extrusion aid general range between 12%-28%.

 

Compression ratio: Compression ratio is also an important parameter that affects product performance indicators. Large compression ratio, high longitudinal fibrosis strength, not easy to break when stretched, easy to continuous production, its product strength is also relatively high.

 

Big. If the compression ratio is too large, the extrudate is too hard, which is not conducive to the normal production of the subsequent process. Therefore, the compression ratio should be reasonably selected according to the resin grade, equipment and production process.

 

(2) Stretching temperature and stretching rate

 

PTFE microporous membrane forming process, in foreign countries to two-way stretching that is extended processing method used more. PTFE can be stretched between room temperature and 327 temperature, that is, below the melting point stage.

 

The stretching is carried out in a high elastic state. Stretching at low temperature will break the film, resulting in stretching can not be carried out, and higher than the 327 temperature, the crystallization state of PTFE molecules changed to amorphous

 

Shape, can get a good network structure, so the general stretching temperature between 40-327.

 

In production, the stretching temperature is related to the stretching rate and speed, and also depends on the strength and size of the product. High temperature, the film is soft and easy to stretch, dimensional stability

 

Good sex, not easy to retract. But the temperature is too high, the strength of the product is reduced, can also lead to fracture. The higher the stretching rate, the higher the temperature required because the lower stretching temperature required

 

The pulling force is large, when the pulling force exceeds the strength that the drawn product can bear, it will break, on the contrary, the stretching rate is small, and the temperature can be lower.

 

The difference in temperature also directly affects the performance indicators of its products. Therefore, it is necessary to find the best range for specific processes and equipment in production. The strength of the product, aperture,

 

The void ratio is an important index to determine the quality of the product, and for different products with different use environments and conditions, the corresponding production process is selected to produce the appropriate aperture.

 

PTFE membrane with small size, uniform distribution, high porosity and small nodules.

 

 

Figure 2: PTFE microporous membrane source: network

 

Effect of 2. operating parameters on the properties of PTFE films

 

The influence factors on the properties of PTFE microporous membrane during biaxial stretching process and its previous process are complex and multifaceted. In addition to the performance of processing equipment, drawing temperature

 

And tensile rate, other factors are: operating temperature, operating humidity.

 

PTFE membranes are particularly sensitive to the effects of temperature, and different operating temperatures can result in different properties of the membrane. This is not only in the stretching process, in the PTFE resin processing and intermediate work

 

process, temperature is a critical operating parameter.

 

Humidity is related to temperature, leaving temperature, humidity from the beginning. Environmental humidity also has a certain effect on the film.

 

 

Figure 3: PTFE microporous membrane Source: network

 

3. PTFE microporous membrane application advantages

 

Filtration characteristics

 

1, from "deep filtration" to "surface filtration";

 

2, high filtering accuracy, the future is very good to deal with the problem of PM2.5;

 

3. The running resistance is low, and the resistance on both sides of the filter bag is 300~500Pa;

 

4. The initial resistance of the mouth is 200~400Pa;

 

5. Low resistance to normal operation of the mouth;

 

6. Easy to clean ash;

 

7, can deal with part of the "wet conditions";

 

8, extreme conditions can be cleaned.

 

Application of 4. PTFE microporous membrane

 

PTFE microporous membrane has many characteristics, such as: no water absorption, high melting point of 327, the use of temperature range of 200-260, that is, thermal stability, friction coefficient of small resistance to many high corrosion

 

medium, weather resistance and electrical resistance, these characteristics determine its application in many fields, we briefly introduce the PTFE microporous membrane in environmental protection, clothing, biological medicine.

The application of the three major areas of medicine.

 

Application of 5. PTFE microporous membrane in the field of environmental protection

 

In the field of environmental protection, PTFE microporous membrane is mainly used in filter material, and the application of bag filter, in the prevention and control of smoke and ultra-fine dust pollution to the atmosphere to obtain a high degree of success.

Work.

 

Application of 6. PTFE microporous membrane in clothing field

 

Polytetrafluoroethylene microporous membrane is a kind of dense and porous film made by mechanical stretching fiber expansion under certain process conditions. The microporous membrane can reach several per square inch.

 

One billion micropores, using this structure can achieve excellent windproof, waterproof and moisture-proof performance. And can filter bacteria, with protective function. Therefore, it can be made into clothing, shoes and hats, tents

Wait.

 

Application of 7. PTFE microporous membrane in biomedical field

 

In the sterile filtration in the field of medicine and biological engineering, PTFE microporous membrane is gaining more and more advantages because of its no phase change, high efficiency, energy saving, simple process and no secondary pollution.

 

The more widely used. Mainly made of membrane separation equipment.

 

At present, most of the protective masks on the market use meltblown non-woven fabrics. The mechanism for filtering PM2.5 and viruses is electrostatic adsorption. Once the mask is stained with water, the filtering function will fail, because

 

This needs to be replaced every 4 hours and has a short service life. Nanomembrane material as a mask filter, its effect is better than meltblown cloth, and can be used repeatedly. After wearing as long as use

 

65-68 warm water soak (not hand rub) for 10 minutes, or use 75% concentration of alcohol evenly spread on the surface of the mask, and then wait for the mask to dry naturally, you can use again.

 

This article is originally created by Teflon's little sister. Welcome to pay attention and take you to grow knowledge together!