Waterproof and oil-proof means that the filter material is not wetted by water or oil to a certain extent. Theoretically, whether liquid B can wet solid A is determined by the surface tension of liquid and the critical surface tension of solid. If the surface tension of the liquid is greater than the critical surface tension of the solid, the liquid cannot penetrate the solid; On the contrary, the critical surface tension of liquids and solids can be wetted by solids.
According to the above analysis, in order to make the filter material waterproof and oil-proof, its surface tension must be reduced to less than that of water and oil, so as to achieve the expected goal. There are two ways to prevent water and oil. One is coating, that is, using layered method to prevent the filter material from being soaked by water or oil. Outside the forest is reactive, even the waterproof oil agent can react with some groups in the fiber macromolecular structure to form macromolecular chains, which changes the affinity of fiber with water and oil and becomes waterproof and oil-proof. The former will generally make the product lose its air permeability, while the latter will only produce water and oil repellency on the fiber surface, and the gaps between fibers will not be blocked, which will not affect the air permeability, which is exactly what the filter material requires. Therefore, the reactive treatment method is generally adopted.
2. Selection of auxiliaries
At present, there are many waterproof and oil-proof additives, such as aluminum soap, silicone, oil wax, rubber, stearic acid cheese, PVC resin, fluoride and so on. Among these auxiliaries, only aluminum soap, silicone, fluoride and stearic acid cheese are suitable for reactive type. Considering the special use of needled felt, additives are needed: ① it can give needled felt waterproof and oil repellent properties; ② High temperature resistance; ③ Corrosion resistance; ④ Durability; (5) that air permeability of the original product is not chan. The surface tension of the above additives is between 10-30dyn/cm, which is much lower than the surface tension of water of 72dyn/cm, and none of them will be wet by back water, so they are waterproof. However, it is quite close to the surface tension of heavy oil (29dyn/cm) and vegetable oil (32dyn/cm), and it is easy to be wetted to some extent. Only fluoride has a surface tension dimension of about 10 dyn/cm, which is lower than that of various liquids, so it has high waterproof and oil-proof performance. Therefore, fluoride is better as an auxiliary material.
3. Characteristics
Compared with traditional needled felt, waterproof and oil-proof filter material has the following characteristics.
1) Oil repellency can avoid the shortcoming that oily dust is easy to stick to the bag and block the filter cloth.
2) Waterproofness can eliminate water-soluble dirt or water droplets that solidify when exposed to cold, and reduce the filtering ability of the filter cloth.
3) Anti-adhesion prevents dust attached to the surface of the filter cloth from infiltrating into the inner layer of the filter cloth, thus improving the filtering performance.
4) In the absence of strong dust removal measures, peeling will make dust leave the filter cloth.
4. Performance of filter materials
The properties of commonly used waterproof and oil-proof needled felt and needled felt which can both prevent water and oil and release static electricity are shown in the following two tables.
4. Needle felt filter felt with high temperature resistance, acid and alkali resistance, water resistance and oil resistance.
PPS fiber, also known as polyphenylene sulfide fiber, has complete strength retention and inherent chemistry, and can maintain good filtration performance in harsh environment and achieve ideal service life. PPS filter felt is an ideal filter material for pulse bag filters such as coal-fired boiler filtration, garbage incineration, power plant dust removal and fly ash treatment.
PPS fiber is produced by only a few large chemical companies in the world. The registered trademarks of Toyo Textile Company of Japan are Pukang and PROCON, Toray Company of Japan is Telitong and TORCON, and Philip Company of the United States is Leiden.
PPS filter is one of the main kinds of high-temperature resistant filter materials, which is made of polyphenylene sulfide (PPS) fiber according to the production process of high-temperature resistant filter felt. Excellent performance in the following applications.
① Working temperature 190℃, short-term working temperature 232℃, melting point 285℃, and limiting oxygen index 34-35.
② The oxygen content is below 15%.
(3) (3) PPS is a kind of fiber with strong acid and alkali corrosion resistance and chemical corrosion resistance, which can be used in fuel or flue gas containing sulfur oxides.
(4) Where the flue contains moisture.
High temperature resistance, acid and alkali resistance, water resistance and oil resistance are shown in table: