KR20080068114A - System for extruding a porous substrate - Google Patents

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

System for Extruding a Porous Substrate

The present invention relates to an extrusion molding method of an extruded porous substrate, and more particularly, to an extrusion molding method of an extrusion molded porous ceramic substrate.

The present application is entitled "System for Extruding a Porous Substrate," US Provisional Application No. 60 / 737,237, filed Nov. 16, 2005; An Extrudable Mixture for Forming a Porous Block, "US Application No. 11 / 323,430, filed December 30, 2005; The invention is entitled "Process for Extruding a Porous Substrate," US Application No. 11 / 322,777, filed December 30, 2005; And the invention entitled "An Extruded Porous Substrate and Products Using the Same," claiming priority over U.S. Application No. 11 / 323,429, filed December 30, 2005. The contents of which are incorporated herein by reference in their entirety.

Many processes require rigid substrates to facilitate and support various processes. For example, the substrate is used for filtration of particulate matter, for the separation of other materials or for the use of filters to remove bacteria or bacteria in the air. Such substrates can be configured to work in air, exhaust gases or liquids and can be made to withstand substantial environmental or chemical stresses. In another example, the catalytic material is disposed on the substrate to facilitate chemical reactions. For example, precious metals can be disposed on a suitable substrate, which can catalytically convert dangerous exhaust gases to less harmful gases. In general, the higher the porosity, the more effective the substrate.

Porosity is generally defined as the property of a solid material that is defined as the percentage of the total volume of material occupied by the open space. For example, a substrate having a porosity of 50% occupies half the substrate volume by open space. Thereby, the highly porous substrate has a lower volume per mass than the substrate of low porosity. In some applications a low mass substrate is advantageous. For example, when the substrate is used to support the catalytic process and the catalytic process proceeds at elevated temperatures, the substrate with low thermal mass can be heated to the reaction temperature faster. Thereby, using a substrate with better porosity and less heat storage property, the time for which the catalyst is heated to the reaction temperature, for example, the light off time can be reduced.

Permeability is also an important property of substrates, in particular filters and catalyst substrates. Permeability is related to porosity. That is, permeability is a measure of how easily a fluid, such as a liquid or gas, can flow through the substrate. Highly permeable substrates are advantageous in most applications. For example, internal combustion engines operate more effectively when an after-treatment filter provides the engine with low back pressure. Low back presses are produced using more permeable substrates. Since permeability is harder to measure than porosity, porosity is sometimes used as a guide to replace the permeability of the substrate. However, if the pores are generally not open but interconnected, the substrate may generally be highly porous but still have limited permeability, which is not a particularly accurate feature. For example, styrofoam beverage cups are highly porous foam materials, but are not permeable to the flow of liquids. Therefore, considering the importance of porosity and permeability, the pore structure of the substrate should also be investigated. In the example of a styrofoam cup, the styrofoam material has a closed pore network. This means that the foam comprises a plurality of pores and / or closed-ended pores that are not connected. Thereby, there are many voids and open spaces in the foam, but because the pores are not connected to each other, fluid or gas cannot flow from one side of the foam to the other. As most of the channels begin to connect, fluid passages begin to form from one side to the other. In this case, the material is said to contain more open pore networks. The more channels formed through the material are connected, the higher the permeability of the material. If all pores are connected with at least one other channel and all pores allow fluid to flow through the entire thickness of the wall formed in the material, the substrate can be defined as having a complete open pore network. It is important to note the difference between the cell and the pores. A cell refers to a channel through a honeycomb substrate (though not necessarily, but each is generally parallel to each other). Usually, honeycomb substrates are referred to as including how many cells per square inch. For example, a substrate having 200 cells per square inch includes 200 channels along the major axis of the substrate. Pores, on the other hand, refer to a gap inside the material itself, such as in the material that constitutes a wall separating two parallel channels or cells in the material. Fully or nearly open pore network substrates are not known in the filter or catalyst industry. Instead, the most extrudable available extrusion substrates are also hybrids of open and closed pore porosity.

Accordingly, it is desirable to form substrates with internal pore structures that enable high porosity and similarly high permeability in various applications. In addition, the substrate should be formed of a sufficiently rigid structure that meets the structural and environmental requirements of a particular application. For example, a filter or catalytic converter attached to an internal combustion engine must be able to withstand environmental shocks, thermal requirements, and manufacturing and use stresses. Finally, the substrate should be manufactured at a price low enough for widespread use. For example, in order to have some impact on global pollution by automobiles, filter substrates are available not only in developed countries but also in developing countries, and must be priced appropriately. Thus, the overall cost structure of the filter and catalytic converter substrate is an essential consideration in the design of the substrate and the selected process.

Extrusion has proven to be an effective and cost effective process for producing rigid substrates of constant cross section. More specifically, extrusion of ceramic powder materials is the most widely used process for producing filter and catalyst substrates of internal combustion engines. Over the years, powder ceramic extrusion processes have evolved to allow extrusion of substrates that currently have about 60% porosity. Such extruded porous substrates have good strength properties, can be manufactured flexibly, can be manufactured in large quantities, can maintain good quality, and are very cost effective. However, extrusion of the powder ceramic material has reached the upper limit of the porosity, and furthermore, the increase in porosity has been shown to result in unacceptably low strength. For example, as the porosity increased above 60%, the extruded ceramic powder substrate was found not to have sufficient strength to operate in the harsh environment of diesel particulate filters. At other limitations of known extrusion processes, an increase in surface area in the substrate is required to enable more efficient catalytic conversion. In order to increase the surface area, the extruded ceramic powder substrate attempted to increase the cell density, but the increase in the cell density resulted in an unacceptable back press in the engine. In addition, the extruded ceramic powder substrate does not have sufficient strength at very high porosity, and also forms an unacceptable back press when there is a need for an increase in surface area. Therefore, the extrusion of the ceramic powder seems to have reached a practical utility limit.

In an effort to achieve high porosity, movement of filter feeds to pleated ceramic paper has been attempted. Using this pleated ceramic paper, about 80% porosity with a low back press was possible. Due to the low back press, these filters have been used in applications such as mining where very low back presses are required. However, the use of pleated ceramic paper filters was short-lived and not widely adopted. For example, pleated ceramic patters have not been used effectively in harsh environments. The manufacture of pleated ceramic paper requires the use of a paper manufacturing process to form a relatively weak ceramic paper structure, which has been found to be less cost effective than extrusion filters. In addition, the formation of pleated ceramic paper allows very low flexibility in cell shape and density. For example, it is difficult to manufacture paper pleated filters with large channel inlets and small channel outlets which may be desirable in some filter applications. Thus, the use of pleated ceramic paper did not meet the needs of high porosity filters and catalyst substrates.

As another example of an effort to increase porosity and overcome the shortcomings of pleat paper, a substrate was formed by forming a ceramic precursor and carefully treating the mass to grow a single crystal whisker in a porous pattern. However, such crystals in-situ require careful and precise control of the curing process, are difficult to bulk up the process, are relatively expensive, and are prone to defects. In addition, this difficult process provides only a few percent increase in porosity. Finally, the process grows only crystal whiskers in the form of mullite, which limits the availability of the substrate. For example, mullite is known to have a high coefficient of thermal expansion, which renders crystalline mullite whiskers undesirable in a variety of applications where undesired wide operating temperature ranges and rapid temperature changes are required. Thus, the industry requires high porosity and associated high permeability rigid substrates. Preferably, the substrate can be formed into a highly desirable open cell network, can be cost effective in manufacturing, and can be manufactured with flexible physical, chemical, and reactive properties.

1 is a block diagram illustrating a system for extruding a porous substrate according to the present invention.

2 is a view illustrating a fibrous extrudable mixture according to the present invention.

3A and 3B illustrate an open pore network in accordance with the present invention.

4 is an electron micrograph of an open pore network according to the present invention and a closed pore network according to the prior art.

5 is a view for explaining a filter block using a porous substrate according to the present invention.

6 are useful fibers, binders, pore formers, fluids and useful rheology tables in accordance with the present invention.

7 is a block diagram illustrating a system for extruding a porous substrate according to the present invention.

8 is a block diagram illustrating a curing system of a porous substrate according to the present invention.

9 is a block diagram illustrating a system for processing fibers of a porous substrate in accordance with the present invention.

10 is a view illustrating extrusion of a porous substrate having a gradient according to the present invention.

11 is a view illustrating extrusion of a porous substrate having a gradient according to the present invention.

12 is a view illustrating extrusion of a porous substrate having a gradient according to the present invention.

In summary, the present invention provides an extrudable mixture that produces a highly porous substrate using an extrusion process. More specifically, the present invention may mix fibers such as organic, inorganic, glass, ceramic, or metal fibers into a mass when extruded or cured to form a highly porous substrate. Depending on the particular mixture, the present invention not only allows for about 60% to about 90% of the porous substrate, but may also favor the process at other porosities. Extrudeable mixtures may use a variety of fibers and additives and may be applied to a variety of operating environments and applications. The fibers have an aspect ratio greater than 1 and are selected according to the requirements of the substrate. The fibers are then mixed with a binder, pore former, extrusion aid and fluid to form a uniform extrudable mass. The uniform mass is extruded into a green substrate. The more volatile material is selectively removed from the intermediate substrate, which allows the fibers to connect and contact. As the curing process proceeds, a fiber to fiber bond is formed to form a structure having a substantially open pore network. The porous substrates formed are useful for a variety of applications, such as filter or catalytic host, or catalytic converter substrates.

As a more specific example, ceramic fibers may be selected from an aspect ratio distribution between about 3 and about 100, although more generally may range from about 3 to about 500. Aspect ratio is the ratio of the length of the fiber divided by the diameter of the fiber. Ceramic fibers are mixed with a binder, pore former, and fluid in a uniform mass. A shear mixing process is used to more evenly distribute the fibers in the mass. The ceramic material may be from about 8% to about 40% by volume of the mass, which forms a substrate having a porosity between about 60% and 92%. The uniform mass is extruded into the intermediate substrate. The binder material is removed from the intermediate substrate, which causes the fibers to overlap and contact each other. As the curing process proceeds, fiber to fiber bonds are formed to form a rigid open cell network. As used herein, "curing" is defined to include two important process steps: 1) binder removal and 2) bond formation. The binder removal process removes free water, removes most of the additives, and enables fiber to fiber contact. The porous substrates formed are useful as substrates for a variety of applications, for example filters or catalytic converters.

In another particular example, the porous substrate can be made without the use of pore formers. In this case, the ceramic material may be from about 40% to about 60% by volume or more of the mass, which forms a substrate having a porosity between about 40% and 60%. Since no pore former is used, the extrusion process is simplified and more cost effective. In addition, the formed structure is a substantially highly preferred open pore network.

Preferably, the disclosed fiber extrusion system process not only has an open pore network that enables high porosity and associated high permeability, but also produces a substrate having sufficient strength, depending on the needs of use. Fiber extrusion systems also produce substrates sufficiently sufficiently cost-effectively to enable widespread use of the formed filters and catalytic converters. Extrusion systems facilitate mass production of products and enable flexible chemical properties and structures to support a variety of applications. The present invention represents a leading use of fiber materials in extrudable mixtures. Fibrous extrudable mixtures enable extrusion of highly porous substrates in mass production and in a cost effective manner. By allowing the fibers to be used in repeatable, powerful extrusion processes, the present invention enables the mass production of filter and catalyst substrates that are widely used throughout the world.

Various features of the invention will be apparent from the following description, and may be understood by means of means and combinations characteristically derived from the claims.

The drawings form part of this specification and include exemplary embodiments of the invention, which may be embodied in various forms. In some embodiments it will be understood that various aspects of the invention may be exaggerated or enlarged for ease of understanding of the invention.

Hereinafter, embodiments of the present invention will be described in detail. However, it will be appreciated that the invention can be illustrated in various forms. Accordingly, the detailed description set forth herein is not intended to limit the invention, but rather as an illustrative basis for teaching one of ordinary skill in the art how to apply the invention to specific systems, structures, or methods. It can be understood.

Referring to FIG. 1, an extrusion molding system of a porous substrate will be described. In general, system 10 uses an extrusion process to extrude an intermediate substrate that can eventually be cured into a highly porous substrate product. System 10 preferably has a substrate having high porosity, having a substantially open pore network that enables associated high permeability, as well as having a sufficient strength depending on the needs of use. In addition, the system 10 allows for the widespread use of filters and catalytic converters formed by making the substrate sufficiently cost-effective. System 10 facilitates mass production and enables flexible chemical properties and structures to support a variety of uses.

System 10 allows for a very flexible extrusion process, which can be applied to a wide range of specific applications. In using the system 10, the substrate designer first identifies the substrate's needs. Such needs may include, for example, size, fluid permeability, desirable porosity, pore size, mechanical strength and shock properties, thermal stability, and chemical reaction limitations. In accordance with these requirements, designers select materials for use in forming extrudable mixtures. Importantly, system 10 allows the use of fibers 12 in the formation of an extruded substrate. Such fibers are, for example, ceramic fibers, organic fibers, inorganic fibers, polymer fibers, oxide fibers, vitreous fibers, glass fibers, amorphous fibers, crystalline fibers, non-oxide fibers, carbides Fibers, metal fibers, other inorganic fiber structures, or combinations thereof. However, although the use of ceramic fibers is described for convenience of description, it will be appreciated that other fibers may be used. It will also be appreciated that although the substrates are generally described as filter substrates or catalyst substrates, they may be used differently within the teachings of the present invention. The designer selects a particular type of fiber according to the specific needs of the application. For example, the ceramic fibers may be selected from mullite fibers, aluminum silicate fibers, or other ceramic fiber materials commonly available. The fibers generally need to be processed in 14 steps to cut the fibers into available lengths, which may include a chopping process prior to mixing the fibers into the additive. In addition, various mixing and forming steps in the extrusion process can further cut the fibers.

Depending on the specific needs, additives 16 are added. Such additives 16 may include binders, dispersants, pore formers, plasticizers, process aids, and reinforcing materials. In addition, the fluid 18, generally water, is mixed with the additive 16 and the fibers 12. Fibers, additives and fluids are mixed into an extrudable rheology 21. Such mixing may include dry mixing, wet mixing, and shear mixing. The fibers, additives, and fluids are mixed until a uniform mass is produced, which evenly distributes and arranges the fibers within the mass. The fibers and the uniform mass are then extruded to form the intermediate substrate 23. The intermediate substrates have sufficient strength and do not fall apart together in subsequent processes.

The intermediate substrate is then cured (25). "Cure" as described herein is defined to include two important process steps: 1) binder removal and 2) bond formation. The binder removal process removes free water, removes most of the additives, and enables fiber to fiber contact. The binder is usually removed using a heating process that burns the binder, although it will be appreciated that other removal processes may be used depending on the particular binder used. For example, some binders may be removed using a vaporization or sublimation process. Some binders and / or other organic compounds may melt before being degraded into the vapor phase. As the curing process proceeds, a fiber to fiber bond is formed. Such bonding not only facilitates the overall structural stiffness, but also forms the desired porosity and permeability of the substrate. The cured substrate 30 is thus a highly porous substrate 30 in which fibers are mostly bonded to an open pore network. The substrate can also be used as a substrate for various applications, including filter applications, catalytic conversion applications, and the like. Preferably, system 10 enables a preferred extrusion process to produce a substrate having a porosity of at least about 90%.

Referring to FIG. 2, an extrudable material 50 is described. The extrudable material 50 is prepared by extruding in an extruder such as a piston or screw extruder. The extrudable mixture 52 is a uniform mass containing fibers, plasticizers and other additives required by the particular application. 2 shows an enlarged portion 54 of a uniform mass. It will be appreciated that the enlarged portion 54 is not shown to scale, for convenience of description. The extrudable mixture 52 includes fibers such as fibers 56, 57, and 58. These fibers are selected to produce a highly porous and rigid final substrate having desirable thermal, chemical, mechanical, and filtration properties. It will be appreciated that the fiber body is not plastic in itself, so that extrusion is not practically possible. However, it can be seen that through the selection of appropriate plasticizers and process control, the extrudable mixture 52 comprising fibers can be extruded. This extends the benefits of cost, scale, and flexibility of extrusion, thereby including the benefits available with the use of fibrous materials.

In general, fibers are considered relatively small diameter materials having an aspect ratio greater than one. Aspect ratio is the ratio of the length of the fiber divided by the diameter of the fiber. In this specification, the 'diameter' of a fiber is simply assumed to be due to the cross sectional area of the fiber, and this simple assumption applies regardless of the shape of the actual cross section of the fiber. For example, fibers of aspect ratio 10 have a length ten times greater than the diameter of the fibers. Although diameters ranging from about 1 micron to about 25 microns are readily available, the diameter of the fibers may be 6 microns. It will be appreciated that fibers of various diameters and aspect ratios can be used successfully in the system 10. There are several other embodiments of selecting the aspect ratio of a fiber, as described in more detail below with reference to other figures. In addition, the shape of the fiber is sharp, unlike the general ceramic powder, it will be understood that the aspect ratio of each ceramic particle is approximately one.

The fibers of the extrudable mixture 52 have been described with reference to ceramic fibers in FIG. 2, but may be metallic (in some cases thin-diameter metallic wires). Ceramic fibers can be in an amorphous state, a glass state, a crystalline state, a poly-crystalline state, a mono-crystalline state, or a glass-ceramic state. In preparing the extrudable mixture 52, a relatively low volume ceramic fiber is used to make the porous substrate. For example, the extrudable mixture 52 may comprise about 10% to 40% by volume of ceramic fiber material. Thereby, after curing, the formed porous substrate may have a porosity of about 60% to about 90%. It will be appreciated that different amounts of ceramic fiber materials may be selected to produce different porosity values.

To produce an extrudable mixture, the fibers are generally mixed with a plasticizer. Accordingly, the fibers are mixed with other selected organic or inorganic additives. These additives provide three key properties of extrusion. First, the additive enables the extrudable mixture to have a rheology suitable for extrusion. Second, the additive provides sufficient strength to the extruded substrate, generally referred to as the intermediate substrate, to maintain the shape of the substrate and the position of the fibers until such additive is removed from the curing process. And thirdly, selecting the additive and burning it in the curing process facilitates the arrangement of the fibers in the overlapped structure, thus not weakening the formation of the rigid structure. In general, the additive includes a binder such as binder 61. The binder 61 acts as a medium to maintain the position of the fibers and provide strength to the intermediate substrate. Fibers and binders can be used to prepare porous substrates having a relatively high porosity. However, to further increase porosity, additional pore formers, such as pore former 63, may be added. Pore formers are added to increase the open space in the final cured substrate. Pore formers may be spherical, elongated, fibrous or irregular. Pore formers are selected according to their ability to form open spaces, their thermal degradation properties as well as their degree of assistance to the arrangement of the fibers. Thereby, the pore former aids in the arrangement of the fibers in the overlapping pattern to facilitate proper bonding between the fibers during subsequent curing steps. In addition, pore formers play an important role in the arrangement of fibers in the preferred direction, which affects the strength and thermal expansion of the extruded material along different axes.

As briefly described above, the compression moldable mixture 52 may use one or more fibers selected from various types of available fibers. In addition, the selected fibers can be mixed with one or more binders selected from various types of binders. It is also possible to add one or more pore formers selected from various types of pore formers. Compression moldable mixtures may use water or other fluids as plasticizers, and other additives may be added. This flexibility in chemical formation allows the extrudable mixture 52 to be usefully used in various types of applications. For example, the combination of mixtures may be selected according to the environmental, temperature, chemical, physical or other necessary needs required. In addition, since the extrudable mixture 52 is produced by extrusion molding, it is possible to flexibly and economically prepare the final compression molded product. Although not shown in FIG. 2, the extrudable mixture 52 is extruded through a screw or piston extruder to form an intermediate substrate, which is then cured into the final porous substrate product.

The present invention discloses the leading use of fiber materials in extrusion molding mixtures or plastic batches. Such fibrous extrudable mixtures enable extrusion of substrates having high porosity in a cost effective manner in mass production. By allowing the fibers to be used in repeatable and powerful extrusion processes, the present invention enables the mass production of filter and catalyst substrates that are used in a wide variety of world wide.

Referring to FIG. 3A, the cured portion of the enlarged porous substrate is described. Substrate portion 100 shows after binder removal 102 and after curing process 110. After binder removal 102, the fibers, such as fibers 103 and 104, initially maintain placement with the binder material and become exposed as the binder material burns into a loose, overlapping structure. In addition, the pore former 105 may be disposed to form additional open spaces as well as to align or arrange the fibers. Since the fibers constitute a relatively small volume in the extrudable mixture, a number of open spaces 107 are present between the fibers. As the binder and pore former are burned, the fibers may be slightly adjusted to contact more of each other. The binder and pore former are selected to combust in a controlled manner so that the substrate does not disintegrate or interfere with the arrangement of the fibers during the combustion process. Generally, binders and pore formers are selected to decompose or burn before the bonds between the fibers are formed. As the curing process proceeds, the overlapped and contacted fibers begin to form bonds. It will be appreciated that the bond can be formed in several ways. For example, the fibers can be heated to form a liquid that assists in sintering bonding at the node or intersection of the fibers. This liquid state sintering can be caused from certain fibers selected, or from additional additives added to the mixture or coated onto the fibers. In other cases, it may be desirable to form a solid state sintered bond. In this case, the crossed bonds form a grain structure that joins the overlapped fibers. In the intermediate state, the fibers do not yet form a physical bond with each other, but may exhibit some degree of green strength due to the tangling of the fibers. The particular type of bond selected may depend on the choice of base material, the desired strength and reaction chemistry, and the environment. In some cases, the bonding may occur in the presence of an inorganic binder that bonds the fibers together to the connected network and is present in the mixture that does not burn during the curing process.

Preferably, the formation of a bond, such as bond 112, facilitates the formation of a substantially rigid structure comprising fibers. The binding also allows the formation of very high porosity open pore networks. For example, open space 116 is naturally formed by the space between the fibers. Open space 114 is formed as pore former 105 decomposes or burns. Accordingly, the fiber bond formation process forms an open pore network having channels that are not terminated or substantially terminated. These open pore networks produce high permeability, high filtration rates and provide a large surface area for catalyst addition, for example. The formation of the bond may depend on the form of the desired bond, such as solid-state or liquid-assisted / liquid-state sintering, and the additives present during the curing process. For example, additives, selection of specific fibers, heating time, degree of heating and reaction environment can all be controlled to form certain types of bonds.

Referring to FIG. 3B, the cured portion of another enlarged porous substrate is described. Substrate portion 120 shows after binder removal 122 and after curing process 124. Since the substrate portion 120 is similar to the substrate portion 100 described with reference to FIG. 3A, detailed description thereof will be omitted. Substrate 120 is formed without the use of specific pore formers, and the entire open pore network is formed from a batch of binder material and fibers. Thereby, a substrate with a moderately high porosity can be formed without the use of specific pore formers, thereby reducing the cost and complexity of producing a substrate with a moderately high porosity. In this way a substrate having a porosity in the range of 40% to 60% can be prepared.

4 shows a set of electron micrographs 150. Photo set 150 first shows an open pore network 152 preferably formed using a fibrous extrudable mixture. As can be seen in the figure, the fibers form bonds at the intersecting fiber nodes, and the pore former and binder are combusted to form a porous open pore network. In contrast, photo 154 shows a typical closed cell network formed using known processes. The partially closed pore network has a relatively high porosity, but at least a portion of the porosity is due to the closed channel. Such closed channels do not contribute to permeability. Thus, even if the closed pore network and the closed pore network have the same porosity, the open pore network can have more desirable permeability characteristics.

A highly effective and highly porous substrate is produced using the extrudable mixtures and processes described above. For example, the porous substrate may be extruded into the filter block substrate 175 shown in FIG. 5. The substrate block 175 is extruded using a piston or screw extruder. The extruder can be adjusted to operate at room temperature, slightly elevated temperature or at a controlled temperature window. In addition, some parts of the extruder may be heated to different temperatures to affect the gelling properties, shear history and slow properties of the extrusion molding mixture. In addition, the size of the extrusion die may vary depending on controlling the expected shrinkage of the substrate during the heating and sintering process. Preferably, the extrudable mixture is a fibrous extrudable mixture comprising sufficient plasticizer and other plasticizers to enable extrusion of the fibrous material. The extruded green state block is cured to remove free water and burn off additives to form structural bonds between the fibers. The formed block 175 has desirable high porosity features as well as good permeability and wide surface area available. In addition, depending on the particular fibers and additives selected, block 175 may be formed into a desired depth filter. Block 176 includes a channel 179 extending longitudinally through the block. The inlet 178 of the block may be open for a flow-through process, or all other openings may be plugged to form a wall flow effect. Although block 175 is shown as including a hexahedral channel in the figure, it will be appreciated that it may be used in other patterns and sizes. For example, the channels may have an evenly sized square, rectangular, or triangular pattern; Octagonal / square or square / rectangular channel patterns with large inlets; Or in other symmetrical or asymmetrical channel patterns. The exact shape and size of the channel or cell can be adjusted by adjusting the design of the die. For example, the square channel may be formed to have curved edges using electronic discharge machining (EDM) with fins formed on the die. Such curved edges can be expected to increase the strength of the final product, despite the slightly higher back press. The die design can also be modified to extrude the honeycomb substrate. Here, the walls have different thicknesses, and the skin has a different thickness than the rest of the wall. Similarly, in some applications, the outer skin can be applied to the final definition of the size, shape, contour and strength of the extruded substrate. When used as a flow device, the high porosity of block 176 allows for an increase in surface area in the use of catalytic materials. Thereby, a highly effective and efficient catalytic converter with low heat storage property can be made. With this low heat storage capability, the formed catalytic converter has good light-off characteristics and uses the catalytic material effectively. When used in wall flow or wall filter examples, the high permeability of the substrate wall allows for a relatively low bag press while facilitating depth filtration action. This depth filtration is not only effective in removing particulates but also facilitates more effective regeneration. In a wall-flow design, fluid flowing through the substrate moves through the wall of the substrate, thereby allowing more direct contact with the fibers that make up the wall. These fibers provide a large surface area where potential reactions occur, such as when a catalyst is present. Since the extrudable mixture can be formed from various kinds of fibers, additives and fluids, the chemical properties of the extrudable mixture can be adjusted to form blocks with specific properties. For example, when the final block is used as a diesel particulate filter, the fibers are selected taking into account that they operate stably even at extreme temperatures where regeneration is not controlled. As another example, when the block is used to filter certain types of exhaust gases, the fibers and bonds are selected to not react with the exhaust gases in the expected operating temperature range. While the advantages of the highly porous substrate have been described above with reference to filtration and catalytic converters, it will be appreciated that the highly porous substrate can be used in a variety of other applications.

The fibrous extrudable mixture described with reference to FIG. 2 may be formed from various kinds of base materials. Selection of the appropriate material may generally be based on chemical, mechanical, and environmental conditions under which the final substrate should operate. Thus, the first step in designing a porous substrate is to understand the end use of the substrate. Depending on these needs, particular fibers, binders, pore formers, fluids and other materials can be selected. It will be appreciated that the process applied to the selected materials may affect the final substrate product. Since fiber is a structurally major material in the final substrate product, the choice of fiber material is very important for the final substrate to work in the desired application. Thus, the fiber is selected according to the desired bonding requirements, and a particular type of bonding process is selected. The bonding process may be liquid state sintering, solid state sintering, or a bond requiring a binder such as glass-forming agent, glass, clay, ceramic, ceramic precursor or colloidal sol. The binder may be part of one of the fiber structures, a coating on the fiber or one of the additives. It will be appreciated that more than one type of fiber may be selected. It will be appreciated that some fibers may be consumed during the curing and bonding process. In the selection of the fiber configuration, the thermal stability of the fiber can be maintained taking into account the final operating temperature. In another example, the fibers are selected to remain chemically stable, unreacted, in the presence of the expected gas, liquid or solid particulate material. Fibers may also be selected according to cost, and some fibers may be considered for their health because of their small size, whereby their use may be avoided. Depending on the mechanical environment, the fibers are chosen not only according to their ability to form a rigid rigid structure, but also to maintain the required mechanical integrity. It will be appreciated that the selection of the appropriate fiber or fiber combination may involve a trade-off of performance and use. Table 1 of FIG. 6A shows some types of fibers used to form a fibrous extrudable mixture. In general, the fibers can be oxide or non-oxide ceramic, glass, organic, inorganic, or metallic. In the case of ceramic materials, the fibers can be in various states such as amorphous, glassy, poly-crystalline or mono-crystalline. Although many available fibers are shown in FIG. 1, it will be appreciated that other types of fibers may be used.

In addition, the binder and pore former may be selected depending on the type of fiber selected as well as other desired properties. As an example, a binder may be selected to facilitate a particular form of liquid state bonding between the selected fibers. More specifically, the binder includes components that react at the bonding temperature to facilitate bonding of the fiber nodes that intersect the flow of the liquid. The binder may also be selected depending on the ability to plasticize the selected fibers as well as the ability to maintain intermediate state strength. In one example, the binder is selected according to the form in which extrusion is used and the required temperature of the extrusion. For example, some binders form gelatinous masses when heated a lot and can therefore only be used in low temperature extrusion processes. In another example, the binder can be selected according to the effect on the shear mixing properties. This facilitates the chopping of the fibers to the desired aspect ratio in the mixing process. The binder may also be selected depending on the decomposition or combustion characteristics. Binders generally require the ability to hold the fiber in position without breaking down the fiber structure formation during the combustion process. For example, if the binder burns too quickly or violently, the exhaust gas can disrupt structure formation. The binder may also be selected according to the amount of residual binder remaining after combustion. Some uses may be very sensitive to these residues.

Pore formers may not be necessary for relatively suitable porosity formation. For example, the natural arrangement and packing of the fibers in the binder may help to allow about 40% to 60% porosity. Thereby, a suitable porous substrate can be formed using an extrusion process without the use of pore formers. In some cases, the removal of pore formers allows for a more economical production of porous substrates compared to known processes. However, if porosity of at least 60% is desired, additional pores can be formed in the substrate after curing using a pore former. Pore formers can also be selected according to their decomposition or combustion characteristics, and according to their size and shape. Pore size is important, for example, to enable trapping of certain types of particulate material, or particularly high permeability. The shape of the pores can also be appropriately adjusted to assist, for example, in the proper arrangement of the fibers. For example, relatively elongated pore shapes can arrange the fibers in a more ordered pattern, while more irregular or spherical shapes can arrange the fibers in a more irregular pattern.

The fibers may be provided in bulk form, which is provided with chopped fibers from the manufacturer and used directly in the process, or which is generally processed prior to use. Either way, a fair consideration should be given to how the fibers are treated with the desired final aspect ratio distribution. In general, the fibers are initially chopped before mixing with other additives and then further chopped at the mixing, shearing and extrusion steps. However, extrusion is carried out with chopped fibers by means of a rheological setting that enables extrusion of the extrusion mixture at the desired extrusion pressure without causing a dealer flow when the extrusion die face is pressurized. It will be appreciated that fiber chopping to an appropriate aspect ratio distribution can be done at various points in the overall process. The fibers are selected and chopped to the available length and then mixed with the binder and the pore former. This mixing can first be carried out in dry form to start the mixing process or in a wet mixing process. Fluid, generally water, is added to the mixture. In order to obtain the required level of homogeneous distribution, the mixture is shear mixed through one or more steps. Shear mixing or dispersion mixing not only provides a highly desirable uniform mixing process for evenly distributing the fibers in the mixture, but also provides for cutting the fibers to the desired aspect ratio.

Table 2 of FIG. 6B shows some binders available for selection. It will be appreciated that one binder or multiple binders may be used. Binders are generally divided into organic and inorganic categories. Organic binders can generally be burned at low temperatures during the curing process, while inorganic binders can generally form part of the final structure at high temperatures. Although some selectable binders are shown in Table 2, it will be appreciated that other binders may be used. Table 3 in FIG. 6C shows a list of available pore formers. Pore formers are generally defined as organic or inorganic, which is generally combusted at lower temperatures than inorganic. Although some pore formers are shown in Table 3, it will be appreciated that other pore formers may be used. Table 4 of FIG. 6D shows various fluids that may be used. Although water is the most economical and commonly available fluid, it will be appreciated that other fluids may be required in some applications. Although Table 4 shows some fluids available, it will be appreciated that other fluids may be selected depending upon the particular application and process requirements.

In general, the mixture can be adjusted to have a rheology suitable for the desired extrusion. In general, suitable rheology can result from the proper selection and mixing of fibers, binders, dispersants, plasticizers, pore formers and fluids. High degree of mixing is necessary to provide sufficient plasticity to the fibers. Once the appropriate fibers, binders and pore formers are selected, the amount of fluid is generally finally adjusted to match the proper rheology. Appropriate rheology can be dictated by one of two tests. The first test is a subjective atypical test in which beads of the mixture are removed and formed between the fingers of a skilled extrusion technician. The technician can know when the mixture slides properly between the fingers, which indicates whether the mixture is suitable for extrusion. A more objective second test relies on measuring the physical properties of the mixture. In general, the compaction pressure relative to shear strength can be measured using a confined (eg high pressure) annular rheometer. The measurement is performed and analyzed according to the comparison of the pressure dependence on the cohesion strength. By measuring the mixture at various levels of mixture and fluids, a rheology chart can be created to identify the rheological point. For example, Table 5 of FIG. 6E shows a rheology diagram of a fibrous ceramic mixture. The axis 232 represents cohesion and the axis 234 represents pressure dependency. Extrudeable region 236 represents an area in which fibrous extrusion can easily occur. Thus, the mixture specified into region 236 by some measurement can be successfully extruded. Of course, it will be appreciated that the rheology plot may vary and that the location of region 236 may vary. In addition, there are several other direct and indirect tests that measure rheology and plasticity, some of which can be used to check whether they have the appropriate rheology that can be extruded into the final form of the desired product.

After reaching the proper rheology, the mixture is extruded through an extruder. The extruder may be a piston extruder, a single screw extruder or a twin screw extruder. The extrusion process may be highly automated, or may require human control. The mixture is extruded through a die having the cross-sectional shape of the desired substrate block. The die is selected to sufficiently form the intermediate substrate. Thereby, a stable intermediate substrate is formed, which can be processed through a curing process while maintaining the fiber arrangement and shape.

The intermediate substrate is then dried and cured. Drying can be done at room temperature, controlled temperature and humidity conditions (eg, controlled oven), micro ovens, RF ovens and convection ovens. Curing generally requires free water removal and dries the intermediate substrate. It is important to dry the intermediate substrate in a controlled manner so that no cracks or structural bonds occur. Thus, the temperature can be raised to burn additives such as binders and pore formers. The additives can be burned in a controlled manner by adjusting the temperature. It will be appreciated that combustion of the additive requires temperature cycling through various time cycles and various heating levels. After the additive is burned off, the substrate is heated to the required desired temperature to form a structural bond at the intersection or node of the fibers. The desired temperature required is selected depending on the type of bond required and the chemistry of the fibers. For example, liquid-assisted sintered bonds are generally formed at lower temperatures than solid state bonds. It will be appreciated that the amount of time at the bonding temperature can be adjusted depending on the type of specific bond formed. The overall thermal cycle can be carried out in the same furnace, different furnaces, batch or continuous processes and at atmospheric or controlled atmospheric conditions. After the fiber bonds are formed, the substrate is slowly cooled to room temperature. It will be appreciated that the curing process may be performed in a single oven or in multiple ovens / furnaces, and may be automated produced in a production oven / furnace, such as tunnel kiln.

Referring to FIG. 7, an extrusion molding system of a porous substrate will be described. System 250 is a very flexible process for producing porous substrates. To design the substrate, the requirements of the substrate are defined as shown in block 252. For example, the end use of a substrate generally defines the requirements of the substrate, which may include size limitations, temperature limitations, strength limitations, and chemical reaction limitations. In addition, the cost and mass productivity of the substrate can determine and drive certain choices. For example, high production rates may involve the generation of relatively high temperatures in the extrusion die, so that binders operating at elevated temperatures without curing or gelling may be selected. In extrusion using a high temperature binder, the die and barrel may need to be maintained at a relatively high temperature, such as 60 ° C to 180 ° C. In such cases, the binder may melt and reduce or eliminate the need for additional fluids. In another example, the filter may be designed to trap particulate matter so that the fibers may be selected to remain unreacted with particulate matter even at elevated temperatures. It will be appreciated that a wide range of possible mixtures and processes can be applied to a variety of applications. Those skilled in the art will be able to consider trade-offs in the selection of fibers, binders, pore formers, fluids and process steps. In addition, one of the important advantages of the system 250 is the flexibility in the selection and process control of the mixture components.

After the requirements of the substrate have been determined, the fibers are selected from Table 1 of FIG. 6A as shown in block 253. The fibers may be in one form or in combination of two or more forms. It will be appreciated that some fibers may be chosen to be consumed during the curing process. Additives may also be added to the fibers, such as coatings on the fibers, to provide other materials to the mixture. For example, a dispersant may be applied to the fibers to facilitate the alignment and separation of the fibers, or a binding aid may be coated on the fibers. In the case of binding aids, when the fibers reach curing temperatures, the binding aids assist in the flow and formation of the liquid state bonds.

80%> General composition for obtaining porosity

Concentration (g / cc) Mass (g) Volume (cc) volume (%) fiber Mullite 2.7 300.0 111.1 9.2 Reinforcement Bentonite 2.6 30.0 11.5 1.0 bookbinder HMPC (hydroxypropylmethylcellulose) 0.5 140.0 280.0 23.1 Plasticizer Propylene glycol 1.1 15.0 13.6 1.1 Pore former PMMA (Polymethylmethacrylate) 1.19 500.0 420.2 34.7 Fluid water One 375.0 375.0 31 Sum 1360.0 1211.5 100.0

And, as shown in block 255, a binder is selected from Table 2 of FIG. 6B. The binder is selected to facilitate combustion control as well as intermediate state strength. The binder is also chosen to form sufficient plasticity in the mixture. If necessary, as shown in block 256, the pore former is selected from Table 3 in FIG. 6C. In some cases, sufficient porosity can be obtained only through the use of fibers and binders. Porosity can be achieved by the natural packing properties of the fibers as well as the space occupied by the binder, solvent and other volatile components released during the debinding and curing steps. In order to achieve high porosity, additional pore formers may be added. Pore formers may also be selected depending on the controlled combustion capacity and may also assist in plasticizing the mixture. As shown in block 257, the fluid, generally water, is selected in Table 4 of FIG. 6D. Other liquid materials can be added, such as dispersants to aid in the arrangement and separation of the fibers, extrusion aids and plasticizers to improve the flow properties of the mixture. Dispersants may also be used to control the surface charge on the fibers. By this, the fibers can control their charge so that each of the individual fibers repel each other. This makes it easier to randomly disperse and homogeneity of the fibers. 80%> The general mixture configuration for forming a substrate having porosity may be as follows. It will be appreciated that the mixture may be adjusted according to the subject porosity, the particular application and the process considerations.

As shown at block 254, the fibers selected at block 252 may be processed to have an appropriate aspect ratio distribution. Such aspect ratios preferably range from 3 to 500, but may have one or more distribution modes. It will be appreciated that other ranges may be selected, for example, an aspect ratio of about 1000. In one example, the distribution of aspect ratios can be arbitrarily distributed within a desired range, while in other examples the aspect ratio can be chosen from mode values more discontinuously. Aspect ratios have been found to be important in defining the packing properties of the fibers. Thus, the aspect ratio and the distribution of aspect ratios can be selected to meet specific strength and porosity requirements. In addition, treatment of the fibers with the desired aspect ratio distribution can be performed at various points in the process. For example, the fibers may be chopped by a third processor to reach a certain aspect ratio distribution. In another example, the fibers are provided in bulk form and can be treated with an appropriate aspect ratio prior to the extrusion process. It will be appreciated that the mixing, shear mixing or dispersion mixing and extrusion aspects of process 250 may also contribute to the chopping and breaking of the fibers. Thus, the original aspect ratio of the fibers introduced into the mixture may differ from the aspect ratio in the final cured substrate. Thus, when selecting 254 an appropriate aspect ratio distribution to be introduced into the process, the chopping and cutting effects of mixing, shear mixing, and extrusion may be considered.

The fibers are treated with an appropriate aspect ratio distribution to mix the fibers, binders, pore formers and fluids into a uniform mass as shown in block 262. The mixing process can include a dry mixing aspect, a wet dry aspect, and a shear mixing aspect. Shear or dispersion mixing has been shown to be desirable to form a high uniform distribution of fibers in the mass. Distribution is particularly important because of the relatively low concentration of ceramic material in the mixture. As the homogeneous mixture is mixed, the rheology of the mixture can be adjusted as shown at block 264. As the mixture is mixed, the rheology changes continuously. Rheology can be subjectively tested or measured to meet the desired area as shown in Table 5 of FIG. 6E. Mixtures in the preferred areas have the potential for proper extrusion. And as shown in block 268, the mixture is extruded into the intermediate substrate. In the case of a screw extruder, the mixture may take place within the extruder itself rather than in a separate mixer. In this case, the shear history of the mixture is carefully managed and controlled. The intermediate substrate has sufficient medium strength and maintains the shape and arrangement of the fibers during the curing process. And the intermediate substrate is cured as shown in block 270. Curing processes include removal of residual water, controlled combustion of most additives, and bond formation of fibers to fibers. During the combustion process, the fibers maintain a tangling and intersecting relationship, and as the hardening process proceeds, bonds are formed at the intersections or nodes. It will be appreciated that the bonding may occur in a liquid or solid-state bonding process. Part of the bond may also be by reaction of an additive provided in a binder, pore former, such as a coating in or on the fiber itself. After the bond is formed, the substrate is slowly cooled to room temperature.

Referring to Figure 8, the curing method of the porous fibrous substrate will be described. Method 275 includes an intermediate substrate comprising a fibrous ceramic content. The curing process first slowly removes residual water from the substrate, as shown in block 277. In general, the removal of water can be carried out at relatively low temperatures in the oven. After the remaining water has been removed, the organic additive can be combusted as shown in block 279. These additives are burned in a controlled manner to facilitate proper alignment of the fibers, to ensure the release of gases, and the residue does not interfere with the fibers and the structure. As the additive burns, the fibers maintain an overlapping arrangement and may further contact at intersections or nodes as shown in block 281. The fibers can be placed in this overlapping arrangement using a binder, and specific patterns can be formed through the use of pore formers. In some cases, inorganic additives may be used, which may bind the fibers and may be consumed during the bond formation process or remain as part of the final substrate structure. The curing process proceeds to form a fiber-to-fiber bond, as shown in block 285. The specific time and temperature required for bond formation depends on the type of fiber used, the type of binding aid or binder used and the type of bond desired. In one example, the bond can be a liquid state sintered bond formed between the fibers as shown in block 286. This bonding is aided by the glass-forming agent, glass, ceramic precursors or inorganic flux present in the system. In another example, the liquid state sintered bond can be formed using a sintering aid or sintering agent, as shown in block 288. Sintering aids may be provided in coatings on fibers, as additives, in binders, pore formers, or chemicals of the fibers themselves. Fiber to fiber bonds can also be formed by solid-state sintering between the fibers as shown in block 291. In this case, the intersecting fibers exhibit grain growth and mass transfer and can cause chemical bonding at the nodes and the entire rigid structure. In the case of liquid state sintering, a mass of bonding material accumulates at the cross nodes of the fibers and forms a rigid structure. It will be appreciated that the curing process may be carried out in one or more ovens and may be automated in an industrial tunnel or kiln type furnace.

With reference to FIG. 9, the process of preparing a fiber is demonstrated. Process 300 indicates that bulk fibers are provided, as shown at block 305. Bulk fibers generally comprise highly elongated fibers in a cohesive and intertwined arrangement. These bulk fibers are treated to sufficiently separate and cut the fibers used in the mixing process. Thus, bulk fibers are mixed with water 307 and a possible dispersant 309 to form slurry 311. Dispersant 309 may be, for example, a pH regulator or a charge regulator to help the fibers repel each other. It will be appreciated that some other form of dispersant may be used. In one example, the bulk fibers are coated with a dispersant prior to introducing the slurry. In another example, simply adding a dispersant to slurry mixture 311. The slurry mixture is mixed vigorously as shown in block 314. This vigorous mixing serves to chop and separate the bulk fibers into an available aspect ratio distribution. As previously described, the aspect ratio of the fibers used initially may differ from the distribution of the final substrate as the mixing and extrusion process chops the fibers.

After chopping the fibers to an appropriate longitudinal distribution, most of the water is removed by using a filter press 316 or by pressing on a filter of other equipment. It will be appreciated that other processes may be used to remove the water, such as freeze drying. The filter press can remove the water using pressure, vacuum or other means. In one example, the chopped fibers may be dried to become dry as shown in block 318. This dried fiber may then be used in a dry mixing process 323 that mixes with other binders and dry pore formers as shown in block 327. Initial dry mixing aids in producing a uniform mass. In another example, the moisture content of the filtered fiber is adjusted to the appropriate moisture content as shown in block 321. More specifically, sufficient water remains in the chopped fiber cake to facilitate wet mixing as shown in block 325. By leaving slurry water on the fibers, further separation and distribution of the fibers can be obtained. It is also possible to add binders and pore formers in the wet mixing step, and to add the corrected rheology by adding water 329. Shear the mass as shown in block 332. Shear mixing may be performed by using a screw extruder, a double screw extruder or a shear mixer (eg, a sigma blade type mixer) to pass the mixture through a die in the form of spaghetti. Shear mixing may also occur inside sigma mixers, high shear mixers, and screw extruders. The shear mixing process is desirable to produce a more uniform mass 335 having the desired plasticity and the extrudable rheology in which the extrusion works. The uniform mass 335 has an even distribution of fibers arranged in an overlapped matrix. Thereby, as the uniform mass is extruded and cured into the substrate block, the fibers enable bonding to the rigid structure. Furthermore, these rigid structures form open pore networks with high porosity, high light transmittance and large surface area.

Referring to FIG. 10, a method of manufacturing a gradient substrate block will be described. Process 350 is designed to enable extrusion and fabrication of substrate blocks having a gradient characteristic. For example, the substrate may be formed to have a first material towards the center of the block and another material toward the outside of the block. In a more specific example, a material with a low coefficient of thermal expansion is used, particularly in the center of a block where high heat is required, while a material with a relatively high coefficient of thermal expansion is used in the outer portion where low heat is required. This allows a more unified expansion characteristic to be maintained in the entire block. In another example, selected regions of the block may include high density ceramic materials that provide increased structural support. Such structural support members may be arranged concentrically or axially in the block. Thus, a particular material can be selected according to the chemical characteristics, pore size or desired gradient of porosity depending on the needs of the application. In addition, the gradient may involve the use of two or more materials.

In one example, the structure having a gradient can be manufactured by providing a cylinder of the first material 351. A sheet of the second material 353 wraps around the cylinder 351 as shown at 355. This causes layer B 353 to be an annular tube around inner cylinder 351. The layered cylinder 355 is then placed in a piston extruder, venting air and extruding the mass through a die. During the extrusion process, the material is mixed at the interface between Material A and Material B, facilitating a seamless interface. This interface allows for the bonding and overlap of fibers between different kinds of materials, thereby facilitating a more rigid structure as a whole. After the material has been extruded, cured and packed, a filter or catalytic converter package 357 having a substrate having a gradient is produced. More specifically, material A forms the center of the substrate, while material B 361 forms the outer portion. It will be appreciated that more than one material can be used, and that pore size, porosity and chemical properties can be adjusted gradient.

Referring to FIG. 11, another process 375 of forming a substrate having a gradient is described. In process 375 the first cylinder 379 is provided at the approximate size of the piston extrusion barrel. In one example, the outer cylinder 379 is a substantial barrel used in the piston extruder. An inner tube 377 of smaller diameter than the outer tube 379 is provided. The tubes are arranged concentrically such that an inner tube 377 is arranged concentrically inside the tube 379. A first extrudable mixture pellet 383 is deposited in the inner tube 377, while a second extrudable mixture pellet 381 is deposited in the ring between the tube 377 and the tube 379. . Carefully removing the inner tube, material A is concentrically surrounded by material 381. The array of materials is then placed on the extrusion piston, the air is removed in vacuo and extruded through the die. After extrusion, curing and packing, a substrate having the gradient described with reference to FIG. 10 is formed. It will be appreciated that two or more concentric rings can be made and that various forms of gradient can be formed.

Another method of manufacturing a substrate having a gradient will be described with reference to FIG. 12. Method 400 includes a column of extrudable mixture 402 that includes a disk of two extrudable materials that intersect. The extrudable mixture 402 includes a first material 403 adjacent to the second material 404. In one example, material A is relatively porous, while material B is less porous. During extrusion, the material flows through the extrusion die to mix in the arrangement where the fibers of the A and B portions overlap. Thereby, the A and B portions are joined together to form a fibrous base block. By curing and packing, the filter 406 is manufactured. The filter 406 includes a first portion 407 having a relatively high porosity and a second portion 408 having a relatively low porosity. As a result, the gas passing through the filter 406 is first filtered through a high porosity region having a large pore size, and then again through a low porosity region having a small pore size. Thereby, large particles are trapped in region 407, while small particles are trapped in region 408. It will be appreciated that the number and size of the disc materials can be adjusted according to the needs of the application.

Fiber extrusion systems provide great flexibility in implementation. For example, a wide range of fibers and additives can be selected to form a mixture. There are several mixing and extrusion linear options as well as options related to curing method, time and temperature. With the scope of the invention disclosed, one skilled in the art of extrusion will appreciate that the invention can be used in various variations. Honeycomb substrates are conventional designs made using the techniques described herein, but other shapes, sizes, contours, designs can be extruded in a variety of applications.

Filter devices (DPF, oil / air filters, hot gas filters, air-filters, water filters) or catalytic devices (e.g. three-way catalytic converters, SCR catalysts, deozonizers, deodorants, biological reactors, chemical reactors, In certain applications, such as those used in oxidation catalysts, etc., the channels of the extruded substrate may need to be plugged. The substrate is plugged using a mixture of materials similar to the extruded substrate. Plugging can be on an intermediate state or on a sintered substrate. Most plugging mixtures require curing heat treatment and bonding with the extruded substrate.

While preferred and alternative embodiments have been disclosed with the intention of the present invention, it will be apparent to those skilled in the art that various modifications and extensions of the above described techniques can be made using the teachings of the invention disclosed herein. Will be obvious. Such modifications and extensions are intended to fall within the spirit and scope of the invention as discussed in the appended claims.

Claims (108)

Ceramic materials mainly composed of elongated fibers; Binder material; And Containing fluids, Wherein said stretched fiber, said binder material and said fluid are uniform masses. The method of claim 1, Wherein said ceramic material is less than about 20 volume percent of a homogeneous mass. The method of claim 1, The extrudable material further comprises an inorganic clay, nanoclay, colloid, glass, or non-fiber ceramic precursor. The method of claim 1, Wherein said ceramic material is less than about 40 volume percent of a uniform mass. The method of claim 1, Wherein said ceramic material ranges from about 15% to about 30% by volume of a uniform mass. The method of claim 1, Substantially all of the stretched fibers have an aspect ratio greater than about 5 and less than about 200. The method of claim 1, Substantially all of the stretched fibers have an aspect ratio in the range of about 10 to about 1000. The method of claim 1, Wherein said ceramic material comprises a ceramic precursor. The method of claim 1, Wherein the stretched fiber is a ceramic fiber selected from the group defined in Table 1 of FIG. 6A. Fibers with aspect ratios greater than one; Binder material; And Containing fluids, Wherein said fiber, said binder material and said fluid are uniform masses. The method of claim 10, Wherein the fiber comprises an aspect ratio distribution in a single mode in a range from about 3 to about 1000. The method of claim 10, Wherein the fiber comprises a multimode aspect ratio having a bilateral mode in a range from about 3 to about 1000. 10. The method of claim 10, Said fiber being a ceramic fiber. The method of claim 10, The fibers are substantially single fibers selected from the group consisting of organic fibers, polymer fibers, inorganic fibers, metal fibers, glass fibers, glass-ceramic fibers, oxide ceramics, non-oxide ceramics, amorphous, polycrystalline, metal alloys. Extrudeable mixture in form. The method of claim 10, The fibers are in the form of a plurality of fibers selected from the group consisting of organic fibers, polymer fibers, inorganic fibers, metal fibers, glass fibers, glass-ceramic fibers, oxide ceramics, non-oxide ceramics, amorphous, polycrystalline, metal alloys. Extrudeable mixtures that are mixtures. The method of claim 10, The fiber is coated extrudable mixture. The method of claim 10, Wherein the fiber is from about 15% to 30% by volume of the extrudable mixture. The method of claim 10, And the fiber is from about 8% to about 40% by volume of the extrudable mixture. The method of claim 10, Wherein said uniform mass comprises a rheological set of regions bounded by points a, b, c, d in Table 5 of FIG. 6E. The method of claim 10, Said fiber is a metal fiber. The method of claim 10, Wherein the fiber is selected from the group defined in Table 1 of FIG. 6A. The method of claim 10, Further includes pore formers, Wherein said inorganic fiber, binder material, pore former and fluid are uniform masses. The method of claim 22, Wherein the pore former is selected from the group defined in Table 3 of FIG. 6C. An extrudable mixture comprising a ceramic material, an organic binder and a fluid, the extrudable mixture comprising a uniform extrudable mass, The ceramic material is less than about 40 volume percent of the mass. The method of claim 24, The ceramic material is about 30% by volume or less of the mass. The method of claim 24, Wherein said ceramic material is a poly-crystalline fiber, a monocrystalline whisker, or an amorphous fiber. Mixing the stretched ceramic-material fiber, binder material and fluid into a uniform mass; Extruding the uniform mass into a green substrate; And Method of producing a porous substrate comprising the step of curing the intermediate substrate to a porous substrate. The method of claim 27, Wherein said mixing comprises using up to about 40% by volume ceramic-material fibers. The method of claim 27, Wherein said mixing comprises using up to about 20% by volume ceramic-material fibers. The method of claim 27, The mixing step comprises the use of a shear mixer. The method of claim 27, The mixing step of forming a uniform mass using a pore-forming agent. The method of claim 27, Further comprising the step of selecting a plurality of binders, Wherein each selected binder has a different thermal decomposition temperature compared to other binders. The method of claim 27, Further comprising selecting a binder that provides sufficient green strength to prevent deformation of the intermediate substrate prior to curing. The method of claim 27, Further comprising selecting the fibers such that substantially all of the fibers have an aspect ratio greater than five by volume. The method of claim 34, Wherein said ceramic-material comprises a fine material or a short material. The method of claim 34, And wherein the ceramic material is substantially free of fine or short materials. The method of claim 27, Wherein the curing step includes forming bonds between the intersecting fibers to form a structure of the porous substrate. The method of claim 37, wherein A method of making a porous substrate wherein substantially all of the intersecting fibers are joined. The method of claim 37, wherein And a portion of the intersecting fibers is unbonded porous substrate. Forming inorganic fibers, binder material and fluid into a uniform mass; Extruding the uniform mass into an intermediate substrate; And Method of producing a porous substrate comprising the step of curing the intermediate substrate to a porous substrate. The method of claim 40, Wherein the curing step includes forming bonds between overlapping inorganic fibers to form a rigid structure of the porous substrate. The method of claim 40, The bond is a sintered bond in the solid state; Liquid-assisted sintering bonds; Or a glass, glass-ceramic or ceramic bond. The method of claim 40, And wherein said curing step comprises burning substantially both said organic material and said fluid. The method of claim 40, The inorganic fiber forms a bond to form an open pore network. The method of claim 40, Wherein said extruding step comprises pushing said extrudable mixture through a die. The method of claim 40, Wherein said extruding step comprises extruding said extrudable mixture through a die using a piston or screw extruder. The method of claim 40, The extrusion molding step is a method for producing a porous substrate operating at room temperature or elevated temperature. Selecting the fiber material in Table 1 of FIG. 6A; Selecting a binder from Table 2 of FIG. 6B; Selecting a fluid from Table 4 of FIG. 6D; Treating the fiber material; Mixing the fibrous material, the binder and the fluid into a uniform mass; Adjusting the uniform mass rheology to be extrudable; Extruding the uniform mass into an intermediate substrate; And Method of producing a porous substrate comprising the step of curing the intermediate substrate into a porous block. The method of claim 48, Wherein said treating step is performed at least in part in said mixing step, wherein said mixing step cuts the stretched fiber into short fibers. The method of claim 48, The processing step further comprises the step of coating the fiber with an organic material to aid in extrusion molding. The method of claim 48, Wherein said treating step comprises forming a slurry of fibrous material and fluid, and strongly stirring said fibrous material to cut the stretched fibers into short fibers. The method of claim 51, The slurry further comprises a dispersion aid, an extrusion aid or a reinforcing aid. The method of claim 48, Selecting an additive selected from the group comprising pore formers, reinforcing agents, opacifiers, extrusion aids, dispersants, pH adjusting agents, inorganic binders, clays, washcoat materials and catalysts; And The method of manufacturing a porous substrate further comprises the step of mixing the additives to the uniform mass. Removing the fluid from the intermediate substrate; Burning organic material; Forming a bond between the fibers; And Forming a fibrous open pore network in the substrate. The method of claim 54, The bond is a solid state sintered bond; Liquid-assisted sintering bonds; Or curing the intermediate substrate, which is a glass, glass-ceramic or ceramic bond, in a porous block. The method of claim 54, As the organic material is burned, the fibers cure the porous substrate in the porous block, which is rearranged into a crossover network. The method of claim 54, A method of curing an intermediate substrate in a porous block further comprising forming a portion of a fibrous open pore network using an inorganic additive material. Forming a first extrudable mixture comprising the first fiber mixture, the additive and the fluid; Forming a second extrudable mixture comprising a second fiber mixture, an additive and a fluid; Arranging the first extrudable mixture adjacent to the second extrudable mixture in an extruder; Extruding the first and second extrudable mixture into an intermediate substrate; And Method for producing a porous substrate having a gradient comprising the step of curing the intermediate substrate. The method of claim 58, Wherein said curing step comprises forming bonds between intersecting fibers to form a porous substrate structure. The method of claim 59, At least a portion of the bond has a gradient formed from one or more fibers of the second extrudable mixture that intersects one or more fibers of the first extrudable mixture. The method of claim 59, The bond is a solid state sintered bond; Liquid-assisted sintering bonds; Or a glass, glass-ceramic or ceramic bond having a gradient. The method of claim 58, The forming and arranging may include forming the first extrudable mixture in the form of a cylinder. And arranging a second extrudable mixture into concentric layers surrounding the cylinder. The method of claim 58, The forming and arranging may include forming an extrudable mixture into first pellets, Forming a second extrudable mixture into second pellets, Filling the tube with the first pellets, Wrapping the tube with the second pellet, The method of manufacturing a porous substrate having a gradient further comprising the step of removing the tube. The method of claim 63, wherein A method of producing a porous substrate having a gradient further comprising evacuating air from the pellets before the extrusion step. The method of claim 58, Forming a first extrudate into a first set of disks; Forming a second extrudate into a second set of disks; And arranging the first and second disks to form an alternating cylinder of the first disk and the second disk. Placing the bulk fibers in a liquid; Strongly mixing the fiber and the liquid to chop the fiber; And A process for producing fibers for use in an extruder comprising extracting most of the water from the mixture. The method of claim 66, The fiber is a ceramic fiber selected from the group listed in Table 1 of FIG. 6A. The method of claim 66, Adding a dispersing agent or a binder to the liquid. The method of claim 66, Wherein said extracting step further comprises pressing said fiber and said liquid into a filter. The method of claim 66, Wherein said extracting step further comprises drying said fibers to remove most of the free water. Comprises porosity in the range from about 60% to about 85%, A porous ceramic substrate comprising a structure formed by bonding ceramic fibers, The substrate blends ceramic material fibers with additives and fluid to form an extrudable mixture; Extruding the extrudable mixture into an intermediate substrate; Porous ceramic substrate formed by an extrusion process comprising curing the intermediate substrate to a porous substrate. The method of claim 71, wherein Porous ceramic substrate further comprising a sintered, crystalline or glass bond between the fibers. The method of claim 71, wherein The cured porous ceramic substrate is a porous ceramic substrate mainly composed of ceramic fibers. The method of claim 71, wherein Wherein said cured porous substrate is comprised primarily of an open-pore network of ceramic fibers. The method of claim 71, wherein Wherein the cured porous ceramic substrate comprises a pore network to which substantially all pores are connected. Comprises porosity in the range of about 60% to 90%, A porous substrate comprising a structure formed by bonding inorganic fibers, The substrate is formed by an extrusion process comprising mixing an inorganic fiber with an additive and a fluid to form an extrudable mixture, extruding the extrudable mixture into an intermediate substrate, and curing the intermediate substrate into a porous substrate. Formed porous substrate. 77. The method of claim 76, Wherein said curing step forms a fiber-to-fiber bond forming said structure. 77. The method of claim 76, The bond is formed by sintering or formed by the formation of glass, glass-ceramic or ceramic bonds. 77. The method of claim 76, Wherein said curing step results in a fiber-to-fiber bond forming an open pore network. 77. The method of claim 76, The inorganic fiber comprises a distributed aspect ratio of a single mode in the range of 3 to 1000. 77. The method of claim 76, The inorganic fiber is a porous substrate selected from Table 1 of Figure 6a. 77. The method of claim 76, And the cured substrate comprises the detectable additive combustion residue. 77. The method of claim 76, At least a portion of the fiber to fiber contact does not form a bond. 77. The method of claim 76, Substantially all of the fiber to fiber contacts form a bond. 77. The method of claim 76, A first substrate portion having a first porosity and A porous substrate further comprising a second substrate portion having a second porosity. 77. The method of claim 76, A first substrate portion having a first density and And a second substrate portion having a second density. 77. The method of claim 76, With a first substrate portion bonded using a fiber-to-fiber bond of type 1 A porous substrate further comprising a second substrate portion that bonds using a fiber to fiber bond of type 2. 77. The method of claim 76, The inorganic fiber comprises a crystalline, amorphous, glass or ceramic material. 77. The method of claim 76, The inorganic fiber is a metal fiber, metal-alloy or ceramic fiber. 77. The method of claim 76, The extrudable mixture further comprises an organic fiber. A porous substrate having from about 40% to about 75% porosity extruded in an extrudable mixture that does not include other functionally efficient pore former components. An extruded porous substrate composed predominantly of bonded fibers. 93. The method of claim 92 wherein The fiber is an extruded porous substrate mainly composed of ceramic fibers. 94. The method of claim 93, An extruded porous substrate further comprising a solid state, crystalline or glass bond between ceramic fibers. 95. The method of claim 94, Wherein said bonded ceramic fibers form an open pore network. 94. The method of claim 93, The ceramic fiber is an extruded porous substrate having a distributed aspect ratio of a single mode in the range of 3 to 1000. 94. The method of claim 93, The ceramic fiber is an extruded porous substrate selected from Table 1 of FIG. 6A. 93. The method of claim 92 wherein An extruded porous substrate further comprising inner and outer channels parallel within the honeycomb pattern. 93. The method of claim 92 wherein Further comprising parallel inner and outer channels, Wherein the inner channel is larger than the outer channel. 93. The method of claim 92 wherein Wherein said porous substrate is a block comprising a random channel. An extruded substrate comprising an open pore network formed by bonded fibers; A housing holding the substrate; An inlet receiving fluid; And A filter product comprising an outlet for providing a filtered fluid. 102. The method of claim 101, wherein Said fluid is an exhaust gas or a liquid. 102. The method of claim 101, wherein The filter product is a vehicle air filter, a vehicle exhaust filter, or a vehicle cabin filter. 102. The method of claim 101, wherein A filter product further comprising a catalyst disposed on the extruded substrate. An extruded substrate comprising an open pore network formed by bonded fibers; A catalyst disposed on the extruded substrate; A housing holding the substrate; An inlet receiving fluid; And A catalytic converter product comprising an outlet for providing a filtered fluid. 105. The method of claim 105, Said fluid is an exhaust gas or a liquid. 105. The method of claim 105, Wherein said filter product is a vehicle air filter, a vehicle exhaust filter, or a vehicle cabin filter. 105. The method of claim 105, A catalytic converter product further comprising a catalyst disposed on the extruded substrate.

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