Principle and method of "waterproof and moisture permeable"

2019-07-03 14:30

What is waterproof and moisture permeable functional fabric? When you go mountaineering, it's cold and rainy. You can't go up the mountain with an umbrella. Mountain climbing is a very physical exercise, producing a lot of sweat. The temperature on the mountain is generally very low, so you can't take off your clothes. So, how can we solve this kind of problem? In fact, people have been studying this problem for a long time, that is to wear a waterproof and moisture permeable clothing（ Usually people often call it breathable fabric, but it is not the gas in the air, but the steam evaporated by sweat.

Specifically, waterproof and moisture permeable fabric is a kind of high-tech and unique functional fabric, which can prevent sweat from accumulating and condensing between the body surface and the fabric in the form of water vapor and can not be immersed in the fabric under certain pressure.

From the literal meaning to understand, waterproof and moisture permeability surface seems to be contradictory, but from the fabric structure and processing methods can be consistent. The main principle that fabric can not only be waterproof, but also be moisture permeable is that according to different states of water material has different diameters, which leads to the possibility of its transmission.

1、 Development of waterproof and moisture permeable technology abroad

The coating with waterproof and moisture permeability as the center is a new technology researched at home and abroad. At the end of 1970s, Gore Rex polytetrafluoroethylene (PTFE) waterproof and moisture permeable membrane of Gore company in the United States was successfully studied abroad.

In the early 1980s, Japan also made micro tex polyurethane waterproof and moisture permeable film.

Dicrylan PC water dispersing microporous acrylate coating agent from Ciba geigy company of Switzerland and impranil DLN water dispersing microporous polyurethane coating agent from Bayer company of Germany are both products with excellent waterproof and moisture permeability.

Raincoats, jackets, ski shirts and sportswear sewn with waterproof and moisture permeable coating fabric are popular in the international market because the rain can not seep in, but the sweat vapor in the body can be emitted, making the clothes very comfortable.

2、 Solution of waterproof and moisture permeable fabric

At present, waterproof and moisture permeable fabrics can be realized by the following methods:

（1） Through the fiber (high density fabric) to achieve moisture permeability

1. High density cotton fabric -- wentaier

The earliest waterproof and moisture permeable fabric is the famous ventile fabric. It was designed by Shirley Research Institute of England in 1940s. It was made of pure cotton yarn with high count and low twist and high density heavy plain weave fabric made of Egyptian long staple cotton. At first, it was mainly used for cold and immersion resistant clothing of British Air Force pilots during World War II.

The principle is that the cross-sectional area of the cotton fiber expands after the fabric is wet, so that the pores between the fibers in the fabric are reduced, so that the penetration of water requires a very high pressure. When the fabric is dry, the gap between warp and weft yarns is large, about 10 microns, which can provide a high moisture permeability structure; When the fabric is drenched with rain or water, the cotton yarn will expand and the gap between the yarns will be reduced to 3-4 microns. This closed cell mechanism is combined with special water repellent finishing to ensure that the fabric will not be further penetrated by rain.

2. Chemical fiber high density fabric -- Coolmax fabric.

DuPont of the United States, Toray of Japan and other companies have researched the way of making channels inside the fiber to discharge sweat out of the body, which is the moisture absorption and perspiration fabric on the market. By using high shrinkage filament of fine and ultra-fine synthetic fiber, combined with super water repellent finishing technology, the waterproof, moisture permeability and wearing comfort of this kind of products have been greatly improved.

For example, the ultra-high shrinkage and high density fabric of Japan Zhongfang company has 30% nylon and 70% polyester as weft and 70D / 72 ordinary polyester as warp. The results show that the yarn fineness is less than 0.2d, the filament density is 68680 pieces / (2.54cm) 2, the moisture permeability is 5000-7000g / m2 · 24h, and the hydrostatic pressure resistance is more than 700mm. It has the properties of heat preservation and expansion.

Trevira and frnasse ultra-fine polyester high density fabric made by Hoechst company in Germany, with warp filament fineness of 1.4dtex, weft filament fineness of < 0.7dtex, single filament warp density of 4800 pieces / cm and single filament weft density of 2680 pieces / cm. After fluorination finishing, the pore size of the final product is 1 / 3000 of the raindrop, the moisture permeability is (20-40) * 103 / g / m2 · 24h, and the hydrostatic pressure resistance is 50cm water column. The rain test shows that the fabric remains dry after 5 hours of artificial rain.

However, this kind of fiber production technology is concentrated in the hands of a few international large companies, and the price is relatively high, so it is difficult to become the mainstream of the market.

The diameter of water vapor molecule is 0.0004 μ m, while the diameter of mist with the smallest diameter in rain water is 20 μ m, and the diameter of drizzle is as high as 400 μ M. if we can make a film with pore diameter between water vapor and rain water, then we can achieve both waterproof and moisture permeability?

There are many ways to produce micropores

Micropores are produced by phase separation (wet process of polyurethane);

Micropores are produced by biaxially stretching the film;

A filler (such as ceramic) is added to the polymer to form pores between the polymer and the filler;

The porous film is mechanically perforated (such as laser) to create voids for air permeability.

The average pore size, distribution, quantity, thickness and water repellency of porous film determine the effect of waterproof and moisture permeable finishing. Generally, water repellent treatment is needed on the surface of coating layer to increase hydrophobic groups on the surface, which makes it more difficult for surface water drops to wet the fabric surface and easy to fall off from the water repellent layer.

The microporous membrane itself has a fine porous structure, and its pore size is very fine (about 0.2-10 μ m. It can only pass through water vapor molecules with particle size of about 0.4 nm, but it can not pass through any raindrop or water drop because of its large particle size. In this way, the water vapor emitted from the human body can effectively diffuse outward through the aperture, while the water droplets can not penetrate inward, so as to achieve the effect of waterproof and moisture permeability; The moisture permeability process is shown in the figure below.

The main fabric products developed by microporous membrane technology abroad are permutexhe and porelle of Stahl / NL company, UCB special chemical / B company of Belgium, etrant of Toray company of Japan, and ultrex of Burlington company of America.

1. Micropores are produced by polyurethane coating

Dry process direct coating, transfer coating, foam coating or wet coating (solidification coating) and so on are applied to coating all kinds of waterproof and moisture permeable coating agents on the surface of the fabric, so that the pores on the surface of the fabric are sealed or reduced to a certain extent by the coating agent, resulting in water repellency.

The moisture permeability of the fabric is obtained by the interaction of the microporous structure formed by special methods on the coating or the hydrophilic groups in the coating agent with water molecules. With the help of hydrogen bonds and other intermolecular forces, water molecules are adsorbed on the high humidity side and then transferred to the low temperature side for resolution. Coated fabric is widely used because of its low price and moisture permeability.

(1) Dry transfer coating: this technology has poor waterproof and moisture permeability performance and unsatisfactory handle, so it has a low market share in waterproof and moisture permeable fabrics.

(2) Wet transfer coating: it not only has high physical properties such as waterproof and moisture permeability, but also can be treated with 100% Teflon, and the washing fastness can reach more than 25 times, and the handle is also very good. The formation of micropores in wet coating mainly depends on the addition of volatile and soluble dimethylformamide (DMF) and carboxymethyl cellulose (CMC) in coating agent, which volatilizes or dissolves during heat treatment or water washing to form microporous network structure film. Its moisture permeability depends on the quality and application process of microporous coating agent. The synthesis process is simple and low cost, The process is easy to operate. The pore diameter is generally between 0.5-2, and the porosity is about 80%.

(3) Mechanical foaming coating

The formation of micropores is mainly through mechanical foaming. Filler, crosslinking agent, stabilizer and foaming agent are added into the coating agent. Foam is applied to the fabric, and then applied to the fabric. After drying, it is rolled and pressed to make the bubbles roll and break and form micropores. This is a stable Foam, and it will not break naturally for a week. It is different from the mechanical foaming of foam finishing, and the latter is broken by drying, which is a sub stable foam (Froth). This method is suitable for mechanical foaming, crushing after rolling. Its moisture permeability depends on the foaming quality. The moisture permeability is acceptable, but the process operation is troublesome. It requires a foaming machine and a reciprocating applicator. The diameter of the micropore is between 5 and 10.

2. Micropores are produced by laminating waterproof and moisture permeable membrane

In this method, a microporous film is first made and then compounded with the fabric. This method is suitable for laminating composite coating film on textiles. Its moisture permeability depends on the quality of the film, which has high moisture permeability and high waterproof performance, but the manufacturing technology of the film is difficult and the cost is expensive.

(1) PTFE film

Gore Tex fabric made by Gore company of America is a typical representative fabric of microporous technology.

Gore Tex film is mainly composed of polytetrafluoroethylene (PTFE) biaxially stretched microporous film with a thickness of about 25 mm μ m. The opening rate is 82%, and the pore size is 0.2 ~ 0.5/ μ m. The moisture permeability is more than 4000g / (M2 · 24h), the air permeability is less than 0.1ml / (cm2 · s), the pore diameter of the micropore is smaller than that of the water drop, which is only 1 / 5000 ~ 1 / 20000 of the water drop diameter, but 700 times of the water vapor molecule, so the smallest raindrop can not pass through, but the water vapor molecule can pass through, which makes the fabric waterproof and moisture permeable.

American Gore company became the first company to produce the membrane by using polytetrafluoroethylene (PTFE). After laminating with fabric, the product name was Gore-Tex. However, due to the strong chemical inertia of PTFE, few materials can laminate it well with other fabrics, and the fastness of the first generation fabrics is very poor.

Later, through continuous efforts, through laminating with other hydrophilic films to form a composite film, and special treatment on the film, the fastness was greatly improved. It is generally believed that the water pressure of Gore Tex fabric can reach 10000 mm, and the water pressure decreases obviously after 6-7 times of washing; The maximum moisture permeability can reach 10000g / sqm * 24hrs, but it is not that the newly made fabric can reach this value. It needs to be washed several times to remove part of the glue, and the available pores will increase and the moisture permeability will increase.

PTFE fabrics are mainly represented by Gore and Donaldson in the United States. Gore produces films and composites by himself. Instead of selling films alone, Gore designates better garment manufacturers to make garments, and has a separate sales staff to cooperate with them. Donaldson only produces thin films and composes them in Japan. The competition between the two companies in the market is also very fierce.

Although the waterproof and moisture permeability of PTFE fabric is better than other fabrics, due to its chemical inertia, the film is difficult to be degraded by nature, and the combustion temperature is as high as 405 ℃. Large scale application makes Gore-Tex gradually become a killer of the environment. Faced with such a problem, Gore company has established a recycling mechanism called balance engineering to reduce its impact on the environment.

The technology has been considered as a high-end product in waterproof and moisture permeable functional fabrics since Gore company of the United States first put it into the market. Domestic PTFE manufacturers are also gradually rising, and many domestic manufacturers have begun to develop and produce this fabric. However, because most of them are single component PTFE films, which are not compounded with hydrophilic films, the washing fastness is generally only about five times. There are some problems such as stratification and poor moisture permeability.

Zhang Hongwei, general manager of Wujiang tutaike textile finishing Co., Ltd., will give a speech on "PTFE microporous membrane waterproof and moisture permeable functional fabric" at the "third textile coating and composite materials forum" (click the link to see the details of the meeting) to be held in Suzhou from August 8 to 9, 2019, and share tutaike's achievements and solutions in waterproof and moisture permeable, We welcome your attention.

The laminating factory of tutek company has introduced five laminating production lines from Taiwan, producing various kinds of laminating production of TPU, PU, PE, PVA and PTFE films. The main products are one-layer, two-and-a-half layer and three-layer laminating, which are used for outdoor assault suits, ski suits, mountaineering suits, etc.

(2) TPU film

TPU is the abbreviation of thermoplastic polyurethane film, which belongs to non porous hydrophilic film. Because the film itself has no pores, the waterproof effect is naturally very good, but also makes the fabric windproof and warm. Moisture permeability is mainly realized through its hydrophilic characteristics. Depending on the difference of vapor pressure inside and outside the clothing, the vapor is transferred from the place with high pressure to the place with low pressure, so as to realize the function of moisture permeability.

Product waiting:

A. Green environmental protection

B. Excellent air and moisture permeability

C. Absolute waterproof, anti bloodstain, antibacterial

D. It is windproof, cold resistant, cashmere proof and smooth

E. Durability, super water splashing finish

F. Easy to clean and wash

Scope of application:

A. Field uniform, fire fighting and special military clothing

B. Protective equipment, military tent, sleeping bag and postal bag

C. Sports clothes for mountaineering, skiing, golf, etc

D. Shoes and hats materials, bags, shading curtains, anti ultraviolet umbrella cloth

E. Rainproof, breathable poncho, casual windbreaker

F. Medical insurance supplies

a. Door width: 1500mm

b. Product thickness: 0.012 ~ 0.025mm

C, low permeable transparent membrane, low permeable mask and low permeability white membrane.

Moisture permeability index: more than 1000g / m2 * 24hrs (astme96bw2000 version)

Hydrostatic pressure resistance index: more than 10000mmh2o (aatcc127)

D, transparent transparent membrane, medium fog mask, and medium permeable white membrane.

Moisture permeability index: more than 3000g / m2 * 24hrs (astme96bw2000 version)

Hydrostatic pressure resistance index: more than 10000mmh2o (aatcc127)

E, transparent transparent membrane, high permeable fog mask and high permeability white film.

Moisture permeability index: more than 5000g / m2 * 24hrs (astme96bw2000 version)

Hydrostatic pressure resistance index: more than 10000mmh2o (aatcc127)

f. Suitable for knitting, woven, non-woven and other different fabrics

The most popular TPU composite fabrics in the market are as follows:

a. Four side bullet + TPU + polar fleece is often called soft shell.

The four side bullet is mainly 75D (for women's wear) and 100D (for men's wear), and the polar fleece is mainly 75D / 72F and 100D / 144f. Can have plain, twill, check and many other styles. The fabric can also be made into ready-made clothes together with knitted composite sweaters such as 30d / 24F, 50D, 75D, etc. Because of its waterproof, moisture permeability, windproof, warm, the scope of use is now not limited to ordinary outdoor sports clothing, many large foreign companies use it as the staff's work clothes. For example, some Japanese companies use it as the work clothes of the noodle shop waiters!

b. Chemical fiber woven fabric + TPU + tricot (warp knitted mesh).

The main woven fabrics are Chunya, Taslon, Oxford, peach skin, Nisi, etc. Common such as 228t Taslon can be used as the main fabric of the garment; The fabric of nylon camouflage printing can be used as military clothing; Fluorescent fabrics can be used for police uniform and other work clothes; wait

3. Chemical moisture permeability through highly hydrophilic groups

This is a non microporous film material. The surface and bulk of the hydrophilic nonporous membrane are homogeneous and dense. The water resistance is determined by the continuity of the material and the large surface tension. This method is suitable for composite coating. Its moisture permeability depends on the number of hydrophilic groups. Its moisture permeability is the highest, which is 50 times higher than that of microporous structure.

Air permeability is due to the fact that polyurethane materials contain a certain amount of hydrophilic groups, which first capture the water vapor molecules emitted by human body in the form of hydrogen bonds. Due to the thermal movement of polyurethane macromolecular chain, the instantaneous gap between the molecular chains is formed, and the pressure difference between the inner and outer sides of the film is promoted, Water vapor molecules are "transferred" from the side with high vapor pressure to the other side along the dense interstices between molecular chains, that is, from the side contacting the skin to the surrounding environment (as shown in the figure below), so as to achieve the purpose of moisture permeability.

This kind of moisture permeability depends on the action of hydrophilic chain segment or hydrophilic group, so it is also called "hydrophilic moisture permeability". Because there are no micropores in the membrane, the waterproof performance is very good, and the external substances can not even pass through the virus, but the air permeability is slightly poor. In addition, when hydrophilic nonporous film is used, the coated fabric surface should be treated with post water repellent treatment, otherwise a water film will be formed on the surface after being wet by rain, which will affect the air permeability. Shirly Institute has developed a new type of polyurethane film and coating with polyethylene glycol as raw material. By adjusting the proportion and relative molecular weight of hydrophilic soft segments, its water vapor permeability can reach the same level as microporous materials, so as to control the moisture and heat balance of the surrounding environment in contact with skin.

Witcoflex STAYCOOL and x-lin of Baxenden chemical company, UK,

UCB special chemicals, Belgium,

Lmparaperm of Bayer company in Germany,

Sympatex of Akzo in the Netherlands,

Hytrel of DuPont and eatane of b.f.goodrich,

"Corplan I" of Asahi Kasei, Bion II of Toho Manufacturing Co., Ltd., Polu SK 111 of teiren, and exception-u of Mitsubishi Kasei Co., Ltd

"Dia. Film" in Taimao, Taiwan Province

It can be seen from the above that in the field of high-end waterproof and moisture permeability, foreign companies have invested a lot and gained a greater leading edge.

Combined with the respective characteristics of hydrophilic membrane and microporous membrane, some enterprises have made more in-depth research, that is, to add a layer of hydrophilic non porous membrane on the microporous membrane and hydrophilic finish the microporous membrane, so as to improve the water resistance of the microporous membrane and ensure that the original moisture permeability is not affected. For example, entrant GLL, which is newly developed by Toray, a Japanese company, composes two kinds of polyurethane materials, and the inner polyurethane contains micropores and supermicropores.

Main uses of waterproof and breathable fabric: racing suit, motorcycle suit, golf suit, waterproof suit, mountaineering shoes, shower curtain, tablecloth, raincoat, baby bib, nautical suit, fishing pants, Snow Jacket, windbreaker, cold jacket, skiing suit, skiing gloves, mountaineering suit, hunting suit, surfing suit, riding suit, assault suit, combat suit, lighting accessories, mobile phone waterproof accessories, etc.