Views:2 Author:Site Editor Publish Time: 2021-10-11 Origin:Site
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.
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.