Fine particle filtration medium including an airlaid composite

Abstract

The present invention pertains to a filter medium including an airlaid composite, which is made of pulp fibers, at least about 2% by weight bicomponent fiber, and moisture. This airlaid composite is unique in that, when used as a filter medium, it exhibits advantageous filtering properties as well as physical strength. The bicomponent fibers of the present invention include a first polymer component and a second polymer component, and the first polymer component melts at a temperature lower than the melting temperature of the second polymer component. Mixing of the pulp fibers with the bicomponent fibers is done in such a way that the fibers are evenly dispersed in the airlaid composite. This airlaid composite is then heated such that at least a portion of the first polymer component of the bicomponent fiber is melted, which bond the bicomponent fibers to many of the pulp and other bicomponent fibers when cooled. Moisture is added to the composite to further facilitate bonding when the composite is subsequently subjected to calendering. Optionally, a support structure may be used to supplement the strength of the airlaid composite. The filter medium of the present invention is characterized by a drape stiffness of at least about 6 cm, and tensile strength of at least about 4 kg. It may also exhibit relatively low average pore size and bubble point.