Research on the performance of new waterproof and breathable PTFE composite fabrics

Research on the performance of new waterproof and breathable PTFE composite fabrics, the principle of waterproof and breathable functional fabrics, the function and use of waterproof and breathable functional fabrics, the price of waterproof and breathable functional fabrics

Waterproof and moisture-permeable functional fabrics have broad market prospects. Based on the bidirectional stretching properties of microporous polytetrafluoroethylene (PTFE) film composite fabrics, new waterproof and moisture-permeable composite fabrics are developed. The products are waterproof, moisture-permeable, breathable, windproof, New high-end textiles that combine warmth and warmth.

In recent years, the use of composite fabrics with breathing functions (such as knitted or woven fabrics bonded with films) has increased significantly in domestic casual wear and casual wear fabrics. For this reason, this article intends to make a relevant analysis of the performance of such fabrics.

1 Overview of waterproof and breathable composite fabrics
Waterproof and breathable functional fabrics include: high-density fabrics, coated fabrics, and composite fabrics. Gore-tex is a waterproof and breathable fabric product on the market. It is a microporous polytetrafluoroethylene (PTFE) film. Gore-tex material not only has good water repellency, but also has excellent moisture permeability. It is a polytetrafluoroethylene (PTFE) film with approximately 9 billion micropores per square inch (6.25cm2). These micropores The diameter of the pore is one-twentieth-thousandth that of a water droplet, but about 700 times larger than the size of a water molecule. Therefore, water droplets cannot pass through these micropores, but water vapor molecules can. Among them, biaxially stretched microporous PTFE film composite fabric occupies an important position.

In 1969 by R. W. Gore developed the epoch-making microporous PTFE film, and the composite (or composite) fabric named Gore-tex came out in 1971. This was an important progress in the development of waterproof and breathable fabrics. Its substitute products are in It was introduced to the market in 1976. Soon after, based on market feedback, the improved second-generation product was put on the market in 1978. After that, two series of elastic and thermal insulation products were successively developed. In recent years, a new generation of Gore-windstopper products has appeared on the market. Subsequently, relevant companies in the Netherlands, Japan, the United Kingdom and other countries also developed microporous or non-porous polyurethane films and non-porous copolyester film composite fabrics. Composite fabrics have become the main force in waterproof and breathable functional products.

2 Research on the performance of new waterproof and breathable composite fabrics
2.1 Basic properties of PTFE microporous membrane
As clothing fabrics, textiles are not only popular for their beauty and fashion, but also their wearing comfort is very important. Waterproof, breathable and soft to the touch are important aspects of comfort. Waterproof and moisture-permeable films and their composite fabrics are called “breathable fabrics” because they have successfully solved the long-standing problem of being unable to achieve both waterproofing and moisture-permeable properties. Made of PTFE biaxially stretched microporous film, with a thickness of about 20 to 70 μm, a porosity of 25 to 96%, and an average pore diameter of 0.18 to 1.3 μm, which is about 1/20000 of a water droplet and 700 times larger than a water vapor molecule. Its resistance The hydrostatic pressure is 90~170kP, the moisture permeability is 4000~17000 kg/cm2·24h, and the air permeability is less than 0.3 ml/m2·s. Therefore, it has good waterproof, moisture-permeable and windproof functions.
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PTFE film microporous film has good thermal stability and a wide operating temperature. It can work continuously at a low temperature of minus 200℃ to a high temperature of above zero 260℃. The melting point is as high as 327℃. It is non-flammable and has excellent chemical stability. It has good acid and alkali resistance, can withstand many highly corrosive media, has a small friction coefficient and strong hydrophobicity.

2.2 Waterproof and breathable mechanism of PTFE microporous film
Waterproof and moisture-permeable means that water will not invade the fabric under a certain pressure, but the sweat vapor emitted by the human body can diffuse or be conducted to the outside through the fabric, without accumulating and condensing between the body surface and the fabric, making the human body feel stuffy. . The waterproof and breathable performance of PTFE microporous film depends on the structure and surface wettability of the film. The morphological structure of the film has a great influence on the waterproof and breathable performance. It uses composite technology to combine the excellent properties of ordinary textile fabrics and high-tech microporous film products, learn from each other’s strengths and fully demonstrate the characteristics of the times of differentiation and functionality. It is the main development direction of waterproof and breathable fabrics at present.

As long as the diameter of the microporous film is controlled within the range of 0.2 to 20μ, the diameter of water vapor molecules emitted by the human body is 0.0004μ. The diameters of various rain and fog are: light fog 20μ, fog 200μ, drizzle 400μ, light rain 900μ, moderate rain 2000μ, heavy rain 3000~4000μ, and heavy rain 6000~10000μ.

(1) Waterproofness of PTFE waterproof and breathable composite fabric.

Water resistance refers to the fabric’s resistance to the relative penetration of liquids. The ability of a fabric to resist the osmotic pressure experienced by rain or exposure to water. The film has countless micropores with a pore size of 0.2 to 10 μm, which is much smaller than the diameter of raindrops (100 to 6000 μm), but much larger than the diameter of water vapor (0.0004 μm), so water vapor can pass through, but water due to a certain For this reason, the impedance of surface tension cannot pass. In order to improve the waterproofness of the fabric, waterproof (water-repellent) finishing must be carried out.

(2) Moisture permeability of PTFE waterproof and breathable composite fabric.

Moisture permeability refers to the ability of a fabric to pass through water vapor. Moisture permeability is usually expressed by the amount of moisture that passes through a unit area of a fabric sample in a unit time due to the unit water vapor pressure difference on both sides of the fabric at a certain temperature. It reflects the fabric’s resistance to water vapor transmission, that is, vapor resistance. Moisture permeability is an important factor when wearing clothing. The amount of water vapor evaporation (without sweating) of the human body varies from person to person.Normally, it is 350-600 g/m2·24h, and can reach 12,000 g/m2·24h during heavy physical labor, so its minimum moisture permeability must also reach 2500 g/m2·24h. The PTFE film microporous film has good moisture permeability.

3 PTFE microporous film production process

PTFE film processes mainly include calendering film, turning film and stretching film. According to relevant literature and tests, only stretch film has a good microporous structure. The production process of bidirectionally stretched PTFE microporous film is: PTFE resin + liquid lubricant → mixing → pressing into a blank → pushing and extruding → calendering → drying → longitudinal drawing → transverse drawing → shaping → finished film.

The microporous membrane is composed of many nodes, and there are many fibrils connecting the nodes. The width of the fibril can be as large as 0.1μm and as small as only 1 to 2 knots of steam molecules. The size of the nodes can be from 1μm to 20μm according to the stretching process. At this time, the water pressure resistance value is high and the moisture permeability is good, ensuring At the same time, it achieves waterproof and moisture-permeable effect.

3.1 Wet process of PTFE waterproof and breathable composite fabric

Fabric water repellent treatment→Corona discharge→Rotary web gluing→PTFE film unwinding, corona treatment, lamination→Drying and hot pressing lamination→PTFE film surface treatment→(gluing→composite lining→) trimming→rolling→ Inspection → packaging → finished product. The water-repellent finishing of the fabric can be carried out by applying liquid on one side after compounding if necessary. The use of corona treatment is very effective in improving the bonding strength of the composite.

3.2 Main process requirements for PTFE waterproof and breathable composite fabric

Requirements: Fabrics and linings are appropriately selected according to user requirements. Water-repellent finishing: According to user requirements, organic fluorine or silicone waterproof finishing agents can be used. Corona discharge: voltage 5~25KV, spacing 2~20 mm. Adhesive coating: For wet method, you can choose to use organic glue or PU glue according to your needs. The amount of glue applied is 10~20g/m2, and the vehicle speed is 8~10m/min. Bake
Dry or dry: temperature 90~150℃. Hot pressing compound: temperature 150~165℃, pressure 4~6bar, time 15~20s.

4 Finishing of PTFE waterproof and breathable composite fabric

PTFE membrane has the characteristics of high hydrophobicity, heat resistance, excellent chemical resistance and insulation. It is combined with fabric through point bonding to form the famous Gore-tex fabric. Its second-generation product has a durable water-repellent finish. It is a composite fabric composed of the original hydrophobic multi-micro PTFE membrane and an organic fluorine oil-repellent finish. It can prevent the passage of all other liquid and gaseous substances except water vapor molecules. The waterproof polymer membrane can overcome body fat pollution and deterioration in water resistance caused by washing surfactants, thus improving the waterproof and moisture permeability and durability of use, and correspondingly improving the resistance to hydrostatic pressure.

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