Development of low resistance antibacterial air filter

Abstract: the two problems of air filter, resistance and secondary pollution, are analyzed The main characteristics of electret electrosynthetic fiber, photocatalysis nano titanium oxide and nano silver are introduced The test results of the synthesized nano titanium oxide and nano silver electret electrostatic air filter are reported The test results show that 62 PA has low resistance, 99.99% rate and low cost The price has greatly expanded the application range of air filter, providing a practical product for improving indoor air quality and preventing the spread of diseases Key words: air filter nano titanium oxide nano silver electret 1 Introduction the SARS epidemic that swept the world in the spring of 2003 left people with not only lessons and warnings, but also more about how to prevent diseases, how to prevent, and how to treat these diseases that are harmful to human health and survival Today, the concept of "health" has entered all aspects of human life Natural "health" has also become the focus of HVAC research, development and manufacturing, and air purification technology has received special attention Among many air purification technologies, air filter is the most widely used, mature and no objection Whether abroad or at home, the air filter has developed to a very high level, enough to meet all kinds of needs In many cases, the air filter has become a safe and effective defense means for * Zui, which can be clearly seen from the spread of SARS and a series of documents, measures and standards issued later However, in the process of using air filter, people have to pay a certain price to deal with a series of problems brought by high resistance, such as energy consumption, noise, fan selection and so on On the other hand, the rate of air filter intercepts the dust, bacteria, viruses and microorganisms in the air However, if the microorganisms deposited on the filter are not treated in time, it will cause serious secondary pollution, so other measures have to be taken, resulting in a series of new problems The focus of this paper is trying to select some mature, effective and cheap technologies from many air purification technologies that have entered the market at home and abroad to form a new type of air filter material, so as to solve the above problems 2 Resistance of air filter: according to two national standards of air filter [1, 2], see Table 1 [3] for classification of air filter in China Table 1 shows the initial resistance of various air filters In practical application, the final resistance of air filters must be considered The so-called final resistance means that the resistance of air filters rises and reaches the specified value due to dust accumulation under the rated air volume It's usually twice the initial resistance " [4] Table 2 gives the recommended final resistance of the air filter [5] Table 1 Classification of air filter in China efficiency at rated air volume (%) initial resistance at rated air volume (PA) note Coarse, medium and high efficiency sub particle size ≥ 5 μ m, 80 < η ≥ 20 particle size ≥ 1 μ m, 70 < η ≥ 20 particle size ≥ 1 μ m, 99 < η ≥ 70 particle size ≥ 1 μ m, 99.9 < η ≥ 95 ≤ 50 ≤ 80 100 ≤ 120 efficiency is the counting efficiency of air dust a B C D η ≥ 99.9 η ≥ 99.99 η ≥ 99.999 particle size ≥ 0.1 μ m, η ≥ 99.999 The efficiency of ≤ 190 ≤ 220 ≤ 250 ≤ 280 a, B and C is sodium flame method; the efficiency of D is the recommended value of final resistance of air filter in Table 2 It is suggested that the final resistance (PA) should be between 100-200250-300-400400-450400-600 In order to prolong the service life of air filter with high and medium efficiency, pre coarse and medium efficiency filters are generally required From table 1 and table 2, it can be seen that the resistance of air filter is considerable when three-stage air filter is used in series If the air filter is used in the air conditioning system, plus the resistance of the surface cooler, heater, humidifier and other air treatment equipment and air duct, not only leads to high energy consumption and noise, but also many times it is difficult to select the fan Therefore, the resistance of air filter is always a problem faced by air conditioning designers 3 Air filter pollution Without considering the above resistance and other problems caused by high resistance, the current air filter can intercept almost all substances in the air, including dust, bacteria, viruses and microorganisms During the anti SARS epidemic period, the anti SARS air filter introduced by the United States can completely filter out bacteria and viruses of 0.025-0.027 μ M the filtration efficiency is as high as 99.9% [6] In recent years, in the process of indoor air quality research, researchers in the United States have found that microorganisms deposited on the filter will produce serious secondary pollution if they are not treated in time Figure 1 shows the air filter pollution in the air conditioning unit reported by the air Bioengineering Institute of the University of Pennsylvania in the United States [7] At present, auxiliary measures are basically adopted to prevent air filter from being polluted Among them, ultraviolet lamp is a widely used and mature measure [7] However, a series of problems arise as follows: ① the increase of primary investment; ② the need for adequate installation space; ③ the design and calculation method must be correct; ④ the life problems (the life of domestic tubes is only 2000 hours, and that of imported tubes is 4000 hours) all affect the wide use of ultraviolet lamps Zui near-low temperature plasma has also begun to be used with air filter in air-conditioning system, but the actual effect has yet to be verified by engineering At present, the high price seriously affects the promotion of this advanced technology in air-conditioning system Therefore, it is a subject worthy of further study to find out measures to prevent secondary pollution of air filter and to kill harmful microorganisms deposited on the filter 4 Electret electrostatic filter material the electret electrostatic synthetic fiber filter material is used to charge the polypropylene fiber in the process of melt blown manufacturing, making it an electrostatic electret melt blown nonwovens (filter paper), with a fiber diameter of 2-5 μ M In addition to the filtration mechanism of traditional air filter materials, this kind of filter material uses the Coulomb force of charged fiber to capture particles, so the efficiency increases and the resistance decreases [8] At present, this kind of filter material is used in surgical masks (N95, N97, n99) with virus prevention function (including SARS virus) in the world, and it is also used in the anti SARS air filter launched in April 2003 in the United States [7]     Because of the high efficiency, low resistance and low price of this filter material, the author first used this material in the air filter for general air conditioning and ventilation When the wind speed on the windward side is 0.5m/s, the filter efficiency for dust of 0.5 μ M can reach more than 95%, and the air resistance is only 40Pa, which is incomparable to the air filter of traditional cabinet air conditioning unit (generally nylon mesh) This air filter has been used in large shopping malls, supermarkets and hospital air conditioning systems for nearly 10 years, and has achieved good air purification effect [8] The production process has been improved comprehensively At present, the electret electrostatic filter material with the efficiency of 99.9999% by sodium flame method has been produced At the same time, the shortcomings of poor uniformity and low strength of this filter material have been solved, which provides an ideal filter material for air filter The production of electret electrosynthetic fiber filter material solves the contradiction between efficiency and resistance of air filter to a great extent.