1. Popularization of theory
Waterproof and breathable coated fabrics are also called “water proof and breathable fabrics” abroad. This kind of fabric is not only rainproof and windproof, but also can evaporate and discharge the sweat produced by the human body, avoiding the formation of a high-humidity space in the clothes and causing a stuffy feeling in the summer. In the winter, it can avoid the condensation of water vapor and freezing, making the wearer more comfortable. Keeps you dry and warm.
The development and application of breathable coated fabrics, as high-tech, high-value-added products abroad, have entered the stage of mass commercial production based on extensive research. The demand in domestic and foreign markets, especially in developed countries, is increasing year by year. According to European market survey statistics, market sales volume in 1986 was 7.35 million square meters. By 1996, sales volume had reached 67 million square meters, an increase of more than 9 times in ten years. The domestic market has also begun to launch in recent years.
UV-resistant fabrics are also one of the hot topics of research and development in recent years. Especially in recent years, the emergence of holes in the ozone layer at the Earth’s two poles has caused a corresponding increase in the proportion of ultraviolet rays reaching the ground. According to reports, the amount of the above-mentioned short-wavelength ultraviolet rays hitting the earth in the early 1990s has increased by 1.5 times compared with the early 1980s. Excessive exposure to ultraviolet rays can cause pigmentation in the human body, aging and dryness of the skin, increased wrinkles, brown spots, and even damage to the deoxyribonucleic acid (DNA) in the cell nucleus, affecting and losing its repair function and causing skin cancer.
The development of a multi-functional, high-tech coated fabric by combining waterproof, moisture-permeable and UV-resistant functions not only conforms to the new development trend of fabric coatings, but also complies with the direction of domestic and foreign market demand, and has broad prospects for economic and social benefits.
2. Technical solution design
In order to produce coated fabrics that are waterproof, breathable and UV radiation resistant, the key technology is to produce coating materials that can impart the above functions to the fabrics. The following technical route has been designed for this purpose:
1. Regarding the waterproof and moisture-permeable mechanism, choose a technical route that combines hydrophilic PU moisture-permeable and dry microporous moisture-permeable (double-solvent method).
2. Use polyester-polyurethane and polyether-polyurethane blending and modification technologies to produce base coating glue and top coating glue with highly uniform waterproofness and moisture permeability respectively.
PU coating agents used for fabric coating can be divided into polyester type and polyether type according to the oligomer diol used. The former has higher strength and hardness, which is attributed to the greater polarity of the ester group (-cooc-) and its cohesive energy (12.2kj/mol) than that of the ether group (-c-o-c-) (4.2kj/mol). mol), so the mechanical strength of polyester PU is high, especially the adhesion to polar substrates is better than that of polyether PU. Polyether PU, especially those containing more polyethylene glycol ethers, not only has better flexibility and hydrolysis resistance, but also has a strong ability to “conduct” water vapor due to its strong hydrophilicity.
If the two are blended and modified in a certain proportion to obtain “PU polymer alloy”, which can be made into base coating and top coating respectively, then the advantages of both can be combined to obtain a coating that has both excellent waterproof performance and Breathable coated fabric with excellent moisture permeability.
3. Inorganic-organic material grafting technology can be used to make coating materials that have both ultraviolet shielding function and moisture permeability function.
Certain inorganic material powders have strong ability to reflect and absorb ultraviolet rays. – Generally, the finer the powder, the better this performance. According to literature reports, the particle diameter is 50-120nm, which has a good shielding effect. Therefore, choose nano- or sub-micron materials and homogenize them carefully. Some organic compounds have the ability to absorb ultraviolet rays and convert them into harmless heat energy. These two types of UV shielding agents are grafted and modified with polymer PU materials through coupling agents, dispersants, etc. to make coating materials with waterproof, breathable and UV protection functions.
At the same time, because this coating material contains tiny particles of inorganic materials, the volume shrinkage effect of the PU polymer during the baking and molding process will cause micro-phase separation, and produce tiny molecular-level pores around the interface of the inorganic particles. A channel for transmitting water vapor molecules, which further helps to improve the moisture permeability of the coated fabric.
3. Process test results and discussion
1. The influence of the blending ratio of polyether PU and polyester PU on the properties of coated fabrics
In order to prepare a fabric coating agent with excellent waterproof and moisture-permeable functions, the effects of different blending ratios on fabric properties were studied. It was observed that as the proportion of polyether PU and polyester PU increased, the static resistance of the coated fabric decreased. The water pressure value shows a slowly decreasing trend, while the moisture permeability shows an increasing trend.
2. Influence of dosage of anti-UV agent
The anti-UV agent, dispersant, and coupling agent were ground into a uniform fine paste through a ball mill three times, and then mixed into the PU coating agent in different proportions. The effect of the added amount of the anti-UV agent on the UV protection performance of the coated fabric was studied.
3. Production process and product test results
The key point of this process is to use copolymer blending modification technology and organic-inorganic coupling grafting technology to prepare base glue and top glue with different compositions. The coating process is to perform one primer, two top coats, drying and baking according to conventional coating methods after waterproofing the base fabric.
4. Discussion on the moisture permeability mechanism of this coated fabric
The moisture permeability mechanism of the coated fabric produced by our factory is a combination of the hydrophilic PU coating method and the dry microporous moisture permeability method. After scanning electron microscopy (SEM) observation of the coating surface of the coated fabric, it was found that there are countless microscopic hole.
The mechanism of micropore formation may be the dual solvent method, that is, the low boiling point solvent as a good solvent for PU is formed with PU macromolecules.A certain amount of high boiling point solvent acts as a poor solvent for PU and is dispersed in the PU solution in a very finely dispersed state. When drying after coating, the low boiling point good solvent evaporates first, and the PU resin concentration increases, gradually condensing around the two-phase interface. When the high boiling point bad solvent evaporates, countless micropores are formed on the coating film. . The drying method can be one-temperature drying (140°C, 3 minutes) or two-temperature drying.
The moisture permeability mechanism of hydrophilic PU coated fabrics is believed to be that the PU macromolecular chain contains more hydrophilic segments and groups. These segments and groups “trap” water vapor molecules emitted by the human body in a way that forms hydrogen bonds. Due to the molecular thermal movement of the soft segments in the amorphous region of PU macromolecules, instantaneous cavities are formed. Driven by the difference in water vapor pressure between the inside and outside of the clothing, the water vapor molecules evaporated from human sweat gradually move from the side with the higher water vapor pressure. “Transmit” to the other side, that is, “transmit” from the side in contact with the skin to the surrounding environment, thereby achieving waterproof and moisture-permeable function.
The combination of the above two moisture permeability methods and mechanisms greatly improves the moisture permeability and breathability function of the coated fabric.
4. Conclusion
This product adopts polymer-blending modification technology and inorganic-organic material grafting technology, and combines two moisture permeability methods: hydrophilic PU moisture permeability method and dry microporous moisture permeability method to produce a product with excellent waterproof properties. The coating material with breathable and anti-UV properties is coated three times on one base and two sides. The fabric obtains high waterproof, moisture-permeable and UV-proof functions.
This product has certain functions of waterproofing, moisture permeability and ultraviolet protection, and has obvious social benefits. Due to the high technical content of the products, the added value of the products is high. The economic benefits are significant. After more than 800,000 meters of trial production and trial sales, the product’s internal indicators and appearance quality are well received by customers, and the market prospect is broad. Further reading: https://www.brandfabric.net/t-c-stretch-interweave-fabric/
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