Views:1 Author:Site Editor Publish Time: 2021-10-13 Origin:Site
HEPA (High Efficiency Particulate Airfilter) filters have been used for approximately 40 years. First developed in North America for the nuclear industry, such filters play an important role in many manufacturing processes in the health care, hospital and pharmaceutical industry, in biotechnology, and most importantly in the electronic and computer related industries to manufacture chips and other electronic parts very sensitive to any particulate contamination.
Virtually all currently used HEPA filters worldwide are based on microglass, wet laid paper with minimum efficiencies according to the DOP test (dioctyl phthalate liquid) of 9.95% for 0.3 micron particles. The next generation of filters are referred to as ULPA (ultra low penetration airfilter) with required efficiencies of 99.9995% for particles 0.1 micron. Such efficiencies can be obtained; however, this is normally at the expense of relatively high differential pressure.
It was, therefore, natural that companies that manufacture microfiber and in most cases electrostatically charged materials investigated the potential to replace microglass, wet laid paper with such new materials.
Most of the activity in such developments can be observed in Japan. Two companies, Toray Industries and Toyobo, seem to be in the forefront.
Worldwide in electret nonwovens, two companies - Freudenberg and 3M - are currently market leaders; both have manufacturing facilities in Europe, North America and Japan.
Additional companies active in producing electret nonwovens located in Japan include Asahi Chemical, Mitsui Sekka, Toray and Toyobo; in Europe, Hepworth is also major companies, while in North America, other companies involved include Fiberweb and Hollingsworth & Vose.
Electret nonwovens can be divided into different fields of manufacturing: electrostatically from a polymer solution, split fiber corona charged and post media charged materials.
Toyobo has introduced a special electret nonwoven, "Elitolon Super," for HEPA filtration. Elitolon-SP is manufactured in different weight ranges and thickness and consequently, different efficiencies up to 99.9996% according to DOP conditions 0.1 micron at air flow rates of 5.3 cm/sec. This product is still under development, however, and not yet commercially available.
Synthetic microfiber developments for HEPA and possibly ULPA filtration look very promising. However, it will take some time for these filters to penetrate the industry. Much has to do with well established specifications in different industries. Secondly, these filters are significantly more expensive than wet laid microglass papers; therefore, superior performance would have to justify the significantly higher price. If these filters turn out to provide greater air flow, existing filter units could either handle a much greater air flow or new units could be designed significantly smaller, saving installation cost.
Other companies are expected to follow in this field. Freudenberg, for instance, developed a synthetic microfiber HEPA filter many years ago for one particular application in the nuclear industry. This filter, however, was never sold on a commercial basis, but because of Freudenberg's strong filtration background, it would be no surprise if the company offers a synthetic microfiber based HEPA filter construction as well.