Waterproof and waterproof breathable finishing

The waterproofness of a fabric refers to its ability to resist the penetration of water molecules. The traditional treatment method is to apply an impermeable coating on the surface of the fabric, such as polyvinyl chloride resin, polyurethane resin, etc., to eliminate its water permeability. This method has been widely used in the past, but it is not Not a good way to solve the problem, because this kind of coating is not permeable to water vapor, which limits the evaporation of human sweat and causes water vapor to condense on the inner surface of the fabric, making it very uncomfortable to wear.

Waterproofness and moisture permeability may seem contradictory on the surface, but they can be consistent based on the fabric structure and processing methods. The diameter of water vapor molecules is generally 4×10-4µm, and the diameter of raindrops is usually 102µm. Therefore, as long as the diameter of the pores in the fabric is controlled within the range where water vapor molecules can pass but water droplets cannot pass, it can be waterproof and moisture-permeable. The fabric’s ability to prevent water penetration depends on the surface energy of the fabric and the contact angle Q of water droplets on the fabric surface. When Q is greater than or equal to 90, the critical surface tension of the fabric is less than the critical surface tension of water, and the fabric can be wetted by water. However, because the fabric has wicking properties (capillary effect), it cannot prevent the penetration of water droplets, so appropriate waterproofing must be carried out to make the surface energy of the fabric lower than water. At the same time, due to the cohesion of water, the water droplets are in the shape of beads, so that The fabric is water-resistant.

In the system formed by the human body, clothes, and the environment, there is the transfer of moisture and heat. There are two ways of transferring moisture: sweating and dispersion (liquid phase transfer) and insensible evaporation and excretion (vapor phase transfer). The artificial climate that appears around the human skin varies with the human body’s environment, activity status, and clothing.�The relative humidity is 50% and the comfort temperature is 32°C. The moisture permeability of the fabric is closely related to the type of fiber, the structure of the fabric and the finishing of the fabric. When the temperature on the inside of the garment is higher than the outside, there is a pressure gradient on both sides of the fabric. Under its action, water vapor molecules can Heat and moisture exchange with the outside world through the fine channels of the fabric.

The new waterproof and moisture-permeable finishing method is to apply a microporous film on the surface of the fabric or use microfibers to weave a tight fabric, thereby preventing the passage of liquid water and allowing water vapor molecules to pass through, while maintaining a certain degree of breathability of the fabric. And moisture permeability (water vapor) ability, so it is also called waterproof and breathable finishing or waterproof and breathable finishing. There are three main types of waterproof and breathable fabrics of polyester:

Compact waterproof fabrics achieve the purpose of waterproofing and moisture permeability by changing the fabric structure. This type of fabric is the first waterproof and breathable fabric successfully developed. Its mechanism is: simple diffusion of water vapor between yarn gaps; capillary transmission between fiber bundles; diffusion between single fibers. Most of today’s compact waterproof fabrics use ultra-fine polyester fibers as raw materials. In this type of fabric, the fibers and yarns are closely arranged, so that the fabric can withstand water pressure up to 104-104% without water-repellent finishing. 1O5Pa. At the same time, capillaries are formed between fiber yarns, which can transmit water vapor well due to the capillary effect.

The advantage of compact fabrics is that the preparation process is simple, mainly due to changes in yarn and silk fineness, and the clothes made have good drape and good moisture permeability. However, the fabric has low water pressure resistance, which greatly limits its application range.

Laminated fabrics are also called film-type waterproof and breathable fabrics. They are made by pasting functional membranes onto fabrics. Such fabrics can be divided into three categories according to the functional membranes used: microporous membrane type, dense hydrophilic membrane type, and microporous membrane type. Pore ​​hydrophilic binding membrane. Adhesives also play a very important role here. There are two main types of adhesives: moisture-permeable type, which can be continuously coated; moisture-impermeable type, which can only be bonded in a dot-type manner without destroying moisture permeability. The most successful and famous fabric of this type is the Gore-Tex fabric of the American W.L. Gore Company. It is currently recognized as an advanced waterproof and breathable fabric on the market. It is made of polytetrafluoroethylene (PTFE) microporous membrane and fabric composite , Since the preparation of the microporous membrane requires special equipment and technology, the product processing is difficult and costly, the ready-made garments are expensive, and its softness and drape are not satisfactory.

The coating method means that the fabric is coated directly or indirectly to make the fabric waterproof, and the breathability is obtained by creating a microporous structure or making it hydrophilic. It can be divided into three types: microporous coating method, hydrophilic coating method, and microporous hydrophilic bonding method.

The cost of the production process of coated fabrics is low. The hydrophilic coating uses water as the solvent, which has low cost and less pollution. The hydrophilic coating can be carried out according to traditional processes. However, the coating method mainly uses organic solvent systems, and the solvent recovery equipment is expensive and can easily cause environmental pollution. After the fabric coating treatment, the drape and softness become worse, the waterproof durability is poor, and the adhesion fastness is poor.

The waterproofness of a fabric refers to its ability to resist the penetration of water molecules. The traditional treatment method is to apply an impermeable coating on the surface of the fabric, such as polyvinyl chloride resin, polyurethane resin, etc., to eliminate its water permeability. This method has been widely used in the past, but it is not Not a good way to solve the problem, because this kind of coating is not permeable to water vapor, which limits the evaporation of human sweat and causes water vapor to condense on the inner surface of the fabric, making it very uncomfortable to wear.

Waterproofness and moisture permeability may seem contradictory on the surface, but they can be consistent based on the fabric structure and processing methods. The diameter of water vapor molecules is generally 4×10-4µm, and the diameter of raindrops is usually 102µm. Therefore, as long as the diameter of the pores in the fabric is controlled within the range where water vapor molecules can pass but water droplets cannot pass, it can be waterproof and moisture-permeable. The fabric’s ability to prevent water penetration depends on the surface energy of the fabric and the contact angle Q of water droplets on the fabric surface. When Q is greater than or equal to 90, the critical surface tension of the fabric is less than the critical surface tension of water, and the fabric can be wetted by water. However, because the fabric has wicking properties (capillary effect), it cannot prevent the penetration of water droplets, so appropriate waterproofing must be carried out to make the surface energy of the fabric lower than water. At the same time, due to the cohesion of water, the water droplets are in the shape of beads, so that The fabric is water-resistant.

In the system formed by the human body, clothes, and the environment, there is the transfer of moisture and heat. There are two ways of transferring moisture: sweating and dispersion (liquid phase transfer) and insensible evaporation and excretion (vapor phase transfer). The human body varies with the environment, activity status, and clothing. The artificial climate that appears around the human skin has a relative humidity of 50% and a comfortable temperature of 32°C. The moisture permeability of the fabric is closely related to the type of fiber, the structure of the fabric and the finishing of the fabric. When the temperature on the inside of the garment is higher than the outside, there is a pressure gradient on both sides of the fabric. Under its action, water vapor molecules can Heat and moisture exchange with the outside world through the fine channels of the fabric.

The new waterproof and moisture-permeable finishing method is to apply a microporous film on the surface of the fabric or use microfibers to weave a tight fabric, thereby preventing the passage of liquid water and allowing water vapor molecules to pass through, while maintaining a certain degree of breathability of the fabric. And moisture permeability (water vapor) ability, so it is also called waterproof and breathable finishing or waterproof and breathable finishing. There are three main types of waterproof and breathable fabrics of polyester:

Compact waterproof fabrics achieve the purpose of waterproofing and moisture permeability by changing the fabric structure. This type of fabric is the first waterproof and breathable fabric successfully developed. Its mechanism is: simple diffusion of water vapor between yarn gaps; capillary transmission between fiber bundles; diffusion between single fibers. Most of today’s compact waterproof fabrics use ultra-fine polyester fibers as raw materials. In this type of fabric, the fibers and yarns are closely arranged, so that the fabric can withstand water pressure up to 104-104% without water-repellent finishing. 1O5Pa. At the same time, capillaries are formed between fiber yarns, which can transmit water vapor well due to the capillary effect.

The advantage of compact fabrics is that the preparation process is simple, mainly due to changes in yarn and silk fineness, and the clothes made have good drape and good moisture permeability. However, the fabric has low water pressure resistance, which greatly limits its application range.

Laminated fabrics are also called film-type waterproof and breathable fabrics. They are made by pasting functional membranes onto fabrics. Such fabrics can be divided into three categories according to the functional membranes used: microporous membrane type, dense hydrophilic membrane type, and microporous membrane type. Pore ​​hydrophilic binding membrane. Adhesives also play a very important role here. There are two main types of adhesives: moisture-permeable type, which can be continuously coated; moisture-impermeable type, which can only be bonded in a dot-type manner without destroying moisture permeability. The most successful and famous fabric of this type is the Gore-Tex fabric of the American W.L. Gore Company. It is currently recognized as an advanced waterproof and breathable fabric on the market. It is made of polytetrafluoroethylene (PTFE) microporous membrane and fabric composite , Since the preparation of the microporous membrane requires special equipment and technology, the product processing is difficult and costly, the ready-made garments are expensive, and its softness and drape are not satisfactory.

The coating method means that the fabric is coated directly or indirectly to make the fabric waterproof, and the breathability is obtained by creating a microporous structure or making it hydrophilic. It can be divided into three types: microporous coating method, hydrophilic coating method, and microporous hydrophilic bonding method.

The cost of the production process of coated fabrics is low. The hydrophilic coating uses water as the solvent, which has low cost and less pollution. The hydrophilic coating can be carried out according to traditional processes. However, the coating method mainly uses organic solvent systems, and the solvent recovery equipment is expensive and can easily cause environmental pollution. After the fabric coating treatment, the drape and softness become worse, the waterproof durability is poor, and the adhesion fastness is poor.