Extrudable mixture for forming a porous block

Abstract

An extrudable mixture is provided for producing a highly porous substrate using an extrusion process. More particularly, the present invention enables fibers, such as organic, inorganic, glass, ceramic or metal fibers, to be mixed into a mass that when extruded and cured, forms a highly porous substrate. Depending on the particular mixture, the present invention enables substrate porosities of about 60% to about 90%, and enables process advantages at other porosities, as well. The extrudable mixture may use a wide variety of fibers and additives, and is adaptable to a wide variety of operating environments and applications. Fibers, which have an aspect ratio greater than 1, are selected according to substrate requirements, and are mixed with binders, pore-formers, extrusion aids, and fluid to form a homogeneous extrudable mass. The homogeneous mass is extruded into a green substrate. The more volatile material is preferentially removed from the green substrate, which allows the fibers to interconnect and contact. As the curing process continues, fiber to fiber bonds are formed to produce a structure having a substantially open pore network. The resulting porous substrate is useful in many applications, for example, as a substrate for a filter or catalyst host, or catalytic converter.

Description

RELATED APPLICATIONS [0001] This application claims priority to U.S. provisional patent application No. 60 / 737,237, filed Nov. 16, 2005, and entitled “System for Extruding a Porous Substrate”, which is incorporated herein in its entirety.BACKGROUND [0002] 1. Field [0003] The present invention relates generally to an extrusion processes for extruding a porous substrate, and in one particular implementation to an extrusion process for extruding a porous ceramic substrate. [0004] 2. Description of Related Art [0005] Many processes require rigid substrates for facilitating and supporting various processes. For example, substrates are used in filtering applications to filter particulate matter, separate different substances, or remove bacteria or germs from air. These substrates may be constructed to operate in air, exhaust gases or liquids, and may be manufactured to endure substantial environmental or chemical stresses. In another example, catalytic materials are deposited on the subst...

AI Technical Summary

Benefits of technology

[0013] Briefly, the present invention provides an extrudable mixture for producing a highly porous substrate using an extrusion process. More particularly, the present invention enables fibers, such as organic, inorganic, glass, ceramic or metal fibers, to be mixed into a mass that when extruded and cured, forms a highly porous substrate. Depending on the particular mixture, the present invention enables substrate porosities of about 60% to about 90%, and enables process advantages at other porosities, as well. The extrudable mixture may use a wide variety of fibers and additives, and is adaptable to a wide variety of operating environments and applications. Fi

Problems solved by technology

However, this is not a particularly accurate characterization, as a substrate may be quite porous but still have limited permeability if the pores are not generally open and interconnected.

In this way, there are many voids and open spaces within the foam, but since the pores are not connected, the fluid or gas cannot flow from one side of the foam to the other.

However, extrusion of powdered ceramic material has reached a practical upper limit of porosity, and further increases in porosity appear to result in an unacceptably low strength.

For example, as porosity is increased beyond 60%, the extruded ceramic powder substrate has not proven strong enough to operate in the harsh environment of a diesel particulate filter.

In order to increase surface area, extruded ceramic powder substrates have tried to increase cell density, but the increase in cell density has resulted in an unacceptable back pressure to the engine.

Thus, the extruded ceramic powder substrate does not have sufficient strength at very high porosities, and also produces unacceptable back pressure when there is a need for increased surface area.

Accordingly, the extrusion of ceramic powder appears to have reached its practical utility limits.

However, the use of the pleated ceramic paper filters has been sporadic, and has not been widely adopted.

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