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Melt blown nonwovens in filtration.

Melt Blown Nonwovens In Filtration

a look at the use of melt blown nonwovens, specifically synthetic microfibers, in high efficiency HVAC and HEPA filtration.

Melt blown nonwovens belong to one of the fastest growing nonwovens groups with total worldwide production of melt blown products at approximately 110-115 million pounds (50,000 tons). Of this total, approximately 18-19 million pounds (8500 tons) are represented by filtration products; therefore, filtration is one of the largest segments within melt blown nonwovens.

Filtration applications include HVAC filtration, HEPA filtration, face masks and respiratory protection, liquid disposable pleated cartridges, melt blown sprayspun cartridges, micron rated liquid vessel bags, coolant filtration and cigarette filters.

HVAC Filtration

Heating, ventilation, air conditioning (HVAC) filters with regard to different efficiencies are regulated through Ashrae in North America and under the designation Eurovent 4/5 in Europe.

Melt blown and microfiber nonwovens are used primarily in the higher efficiency Ashrae and Eurovent classes with efficiencies predominantly between 80-95%. This development did not come overnight, however. The market leader throughout Europe, Freudenberg, Weinheim, Germany, introduced such filters probably as early as 8-10 years ago using their proprietary electrostatic spinning process.

Many melt blown microfiber nonwovens currently used in high efficiency Ashrae/Eurovent filtration are often electrostatically charged and referred to as electret nonwovens. An electret in contrast to the field of a magnetic body is a solid die electric processing, long term electric polarization, forming an electric field in the environment. An electret is a non-conductive polymeric material that maintains a long-lived electrostatic charge. Such media combine mechanical removal of particles and electrostatic forces responsibles for the removal of very fine, mostly submicron, particles.

Filter configurations vary and can be divided into four basic shapes - panel filter, roll band filter, rigid filter cassette and extended surface/pocket filter. For the high efficiency HVAC/Eurovent filtration segment, extended surface/pocket filters are the most common filter configuration currently being used.

Historically, microglass blanket filter media has been used throughout the world and is still the predominant filter medium worldwide. Although microfiber melt blown materials have grown very dramatically within the last couple of years, the total worldwide market of approximately 23-25 million sq. yards of microglass blanket media represents a huge potential.

There is ongoing discussion as to what extent fiber breakage influences the performance of such filters. Synthetic filter media has a proven record of significantly less fiber breakage, particularly over a longer period of usage. The debate is ongoing and naturally divides different manufacturers depending on their raw material basis.

Melt blown materials are combined with high loft, dry laid nonwovens and needled felts and sometimes microfiber layers are attached to a backing material to obtain the required efficiencies.

Popular applications include the very critical paint spray booth use in the automotive industry, health care and critical hospital usage, food processing and the pharmaceutical industry.

In virtually all cases in which HEPA filters are being used, high efficiency HVAC filters can be found upstream to protect HEPA and ULPA filters to obtain longer life.

Gas Turbine Application

Another filtration application is the use of filters for intake air filtration in gas turbine installation. The gas turbine consists of a compressor section, combustion section and the turbine, which in turn produces shaft horsepower.

Atmospheric air is drawn through the compressor into the combustor where fuel is added and burned. The heat expansion turns the turbine blades, which creates shaft output to turn an electric generator. Huge amounts of air are used and naturally contain any size and concentration of particulate contaminant. If not properly filtered, erosion, fouling or soiling and corrosion are the results of inefficient filter systems. Filter cartridges are being used; however, extended surface filters offer an increased filter area, necessary structural integrity and moisture resistance required in such systems.

The use of high efficiency, extended surface/pocket filters-manufactured from melt blown and other microfiber products will sharply increase. They are currently more expensive than microglass blanket filter elements, but their superior performance guarantees further penetration in this very demanding filtration application.

HEPA/ULPA Filtration

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.

Electret Nonwovens

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.

For The Future

HVAC microfiber melt blown media may represent currently $15-16 million worldwide; the largest market currently existing in Europe, followed by North America and Japan.

With growth expected throughout Europe in the 10-12% range, in North America at a 20-25% range and growth of about 15% in the rest of the world, total media in 1995 is expected to grow to $30-35 million.

The growth in HEPA filters based on synthetic media will be much more modest. The total in 1991 is expected to reach approximately $1.2 million for all HEPA filters produced worldwide. Even in China, electrostatically charged melt blown media is currently produced into HEPA filters. Although prices vary widely, the forecast is based on approximately $12/lb. of such media. The total market for such materials, therefore, is forecast to reach $4 million by 1995.

As can be seen, melt blown and microfiber synthetic products for these selected filtration segments show a great opportunity for new developments. The penetration of certain products, however, is 100% dependent on marketing efforts. If a company with an interesting and challenging product does not find an effective way to market and sell its filter material, its participation will be insignificant.

PHOTO : Freudenberg's "Viledon MF 90" pocket filtration media
COPYRIGHT 1992 Rodman Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Title Annotation:synthetic microfiber applications
Author:Bergman, Lutz
Publication:Nonwovens Industry
Date:Feb 1, 1992
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