KR20090057392A - An extruded porous substrate having inorganic bonds - Google Patents

Abstract

A method is provided for producing a highly porous substrate. More particularly, the present invention enables fibers, such as organic, inorganic, glass, ceramic, polymer, or metal fibers, to be combined with binders and additives, and extruded, to form a porous substrate. Depending on the selection of the constituents used to form an extrudable 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. Additives can be selected that form inorganic bonds between overlapping fibers in the extruded substrate that provide enhanced strength and performance of the porous substrate in a variety of applications, such as, for example, filtration and as a host for catalytic processes, such as catalytic converters.

Description

Extruded Porous Substrate Having Inorganic Bonds

In general, the present invention relates to an extrusion process for extrusion of a porous substrate and, in one particular embodiment, relates to an extrusion process for extrusion of a porous ceramic substrate.

Many processes require reinforcement substrates to smoothly perform and support various processes. For example, substrates are used in the field of filtration of particulate matter, separation of different materials, or filtration to remove bacteria or bacteria in the air. Such substrates can be configured to operate in air, exhaust gases or liquids and can be fabricated to withstand significant environmental or chemical stresses. In another example, a catalyst is deposited on a substrate to promote chemical reactions. For example, depositing a noble metal on a suitable substrate can serve to convert the hazardous emissions into less toxic gases through catalysis. In general, such reinforced substrates operate more efficiently at higher porosities.

Porosity, usually defined as a property of solid materials, refers to the proportion of voids (porosity) in a material's total volume. For example, a substrate with 50% porosity has half the percentage of voids in the substrate. In this way, the higher the porosity of the substrate, the more the mass per volume decreases. In some applications, low mass substrates can have several advantages. For example, if a substrate is used to accelerate the catalytic process and the catalytic reaction takes place at a higher temperature, the substrate with lower thermal mass will heat up more quickly at that operating temperature. In this way, by using a substrate having a high porosity and a low thermal mass, it is possible to reduce the light off time before the catalyst is heated to the operating temperature.

Permeability is also an important property of the substrate, especially for filters and catalyst substrates. Permeability is related to porosity and is a measure of how easily a fluid such as a liquid or gas can pass through a substrate. In most applications, the higher the permeability of the substrate, the greater the benefits. For example, internal combustion engines operate more efficiently when an after-treatment filter provides a lower back pressure to the engine. The lower the back pressure, the higher the permeability of the substrate. Since permeability is more difficult to measure compared to porosity, porosity is often used as a guide in place of substrate permeability. However, if the pores are not generally open or interconnected, accurate methods cannot be measured in this way because the permeability is still limited even if the porosity of the substrate is sufficient. For example, a styrofoam disposable cup consists of a highly porous foam material but does not permeate the liquid. Therefore, the pore structure of the substrate should also be examined in consideration of the importance of porosity and permeability. Taking a styrofoam cup as an example, the strofoam constituent material has closed pore tissue. This means that the foam contained numerous pores that were not connected or closed. In this way, there are many empty or open spaces in the foam, but without these pores connected, fluids or gases cannot pass from one side of the foam to the other. If more channels are interconnected here, a fluid path is formed from one side to the other. In such cases, the material can be said to have more open pore networks. The more connected channels formed throughout the material, the higher the permeability of the substrate. If all pores are connected to at least one channel and fluid can permeate through all of the pores through the entire thickness of the wall formed in the material, the substrate can be defined as having complete open pore tissue. It is also necessary to distinguish the difference between the cell and the pores. A cell refers to a channel through a honeycomb substrate (typically flowing parallel to each other but not required). Often honeycomb substrates are represented by the number of cells contained per square inch. For example, a substrate containing 200 cells per square inch includes 200 channels along the base axis of the substrate. Pores, on the other hand, represent a gap inside the material itself, such as a wall surface separating two parallel channels or cells from the material is formed. Complete or nearly complete open pore tissue substrates are not known in the filtration or catalyst industry. Instead, even the extruded substrate with the highest porosity is a mixture of open and closed porosity.

Accordingly, in most applications, it is desirable to use a substrate having an internal pore structure that has a high porosity and similarly high permeability. In addition, the substrate must be formed of a sufficiently rigid structure to support the structural and environmental requirements of the particular field. For example, filters or catalytic converters attached to internal combustion engines must be able to withstand possible environmental impacts, thermal requirements, and manufacturing and use stresses. Finally, production costs must be low so that the substrate can be used universally. For example, to reduce the level of global pollutants emitted from automobiles, filter substrates must be freely available and available in developing countries as well as developed countries. Therefore, the overall cost structure for the filter and catalytic converter substrate is an important consideration in substrate design and selected processes.

Extrusion has proven to be an effective and cost effective process for producing rigid substrates of constant cross section. In particular, extrusion of ceramic powder materials is the most widely used process for producing filter and catalyst substrates for internal combustion engines. Over the years, the extrusion process of powdered ceramics has advanced to 60% porosity of the substrate. These extruded porous substrates have excellent stiffness characteristics, are flexible and can be manufactured at all scales, maintain high levels of quality and are very cost effective. However, extrusion of powdered ceramic materials has actually reached the upper limit in terms of porosity, and there is an unacceptable stiffness drop problem when the porosity is further increased. For example, as the porosity increases above 60%, the extruded ceramic powder substrate may not maintain sufficient rigidity to operate in harsh environments such as diesel particulate filters. Another limitation known in the extrusion process is to increase the surface area in the substrate for more efficient catalytic conversion. In order to increase the surface area, it is necessary to increase the cell density of the extruded ceramic powder substrate, but as the cell density increases, the back pressure applied to the engine is greatly increased. This results in the extrusion ceramic powder substrate not having sufficient strength at very high porosity and creating unacceptable back pressure when the surface area must be increased. Extrusion of ceramic powders thus reached a practical utility limit.

To achieve higher porosity, filter suppliers are attempting to move to pleated ceramic paper. Using these pleated ceramic papers, a porosity of about 80% can be achieved while maintaining a very low back pressure. Due to their low back pressure characteristics, these filters are used in applications such as mining where very low back pressures are essential. However, the use of pleated ceramic paper filters is extremely rare and is not widely adopted in the industry. For example, pleated ceramic paper cannot be used effectively in extreme environments. In order to manufacture pleated ceramic paper, it is necessary to form a ceramic paper structure that is relatively weaker than an extruded filter, and to use it through an ineffective papermaking process in terms of cost. Even when ceramic fibers were coated with a strong coating such as SiC through an expensive chemical vapor deposition type process, telescoping or unraveling of the pleat paper was observed on site. In addition, the molding of the pleated ceramic paper provides very low flexibility in cell shape and density. For example, it is difficult to fabricate paper pleated filters with wide inlet channels and narrow outlet channels that may be required in some filtration applications. Therefore, the use of pleated ceramic paper does not meet the requirements of high porosity filters and catalyst substrates.

As another example of an effort to increase porosity and avoid the drawbacks of pleat paper, some have used ceramic precursors to form materials, and the materials are carefully treated to grow monocrystalline whiskers in porous patterns to form substrates. Produced. However, growing these ceramics in-situ requires precise and precise control of the hardening process, making the process difficult to scale, relatively expensive, and prone to defects. In addition, the porosity is only a few percent higher than the difficulty of the process. That is, the process grows only the mullite type crystalline whisker, thereby limiting the applicability of the substrate. For example, since mullite is known to have a high coefficient of thermal expansion, crystalline mullite whiskers cannot be used in most applications requiring a wide operating temperature range and rapid transition temperatures.

Thus, there is a need in the industry for rigid substrates with high porosity and associated high permeability. More preferably, the substrate is formed to have a high level of open cell network, and the substrate can be manufactured at low cost and has a great flexibility in physical, chemical and reaction properties.

Invention Summary

In short, the present invention provides a highly porous substrate using an extrusion system. More specifically, the present invention enables the production of highly porous substrates. Depending on the particular mixture, the present invention can achieve a substrate porosity of about 60 to 90%, with the same advantages as other porosities. The extrusion system of the present invention can use various kinds of fibers and additives, and can be applied to a wide range of operating environments and applications. Fibers with an aspect ratio of 1 or more were chosen according to the substrate requirements, and are typically extruded homogeneous by mixing with binders, pore-formers, extrusion aids and fluids. To form. The homogeneous is extruded into a green substrate. The more volatile material is preferentially removed from the green substrate, allowing the fibers to form interconnected tissue. By going through a curing process, inorganic bonds are formed between the fibers, producing a significant amount of open pore tissue. The resulting porous substrate can be usefully used in various applications such as a filter or a catalyst host, a substrate for a catalytic converter.

As a more specific example, aspect ratios use ceramic fibers between about 3 and 1000, but more generally are in the range of about 3 to 500. Aspect ratio is the ratio of fiber length divided by fiber diameter. Ceramic fibers can contain organic binders (weight ratios from 0% to 20%), inorganic binders (weight ratios from 0% to 30%), pore formers (weight ratios from 0% to 60%), fluids (weight ratios from 10% to 40%) Mix with to make homogeneous. Shear mixing and kneading processes are employed to distribute the fibers evenly throughout the material. The ceramic material may be about 8% to 60% by volume of material, resulting in a substrate porosity between about 92% and 60%. The homogeneity is extruded into the green substrate. The binder material is removed from the green substrate, allowing the fibers to overlap and contact. By proceeding with the curing treatment, inorganic bonds are formed between the fibers, forming a robust open cell network. As used in this description, "curing" involves two important process steps. 1) binder removal and 2) bond formation. The binder removal process removes free water and removes additives, allowing the fibers to contact each other. The resulting porous substrate can be usefully used in various applications such as substrates for filters or catalytic converters.

As another specific example, a porous substrate may be created without using a pore former. In this case, the ceramic material may be about 40% to 60% by volume of the material, and may form a substrate having a porosity between about 60% and 40%. Since no pore former is used, the extrusion process is simplified and manufacturing costs can be further reduced. It also creates a fairly high level of open pore tissue structure.

The fiber extrusion system according to the present invention has a high porosity, has open pore structure that can increase the permeability associated therewith, and can produce a substrate having sufficient strength according to the needs of the application. Fiber extrusion systems also create cost-effective substrates for widespread application of the resulting filters and catalytic converters. Extrusion systems are easily scalable for high volume production and can support a wide range of applications by allowing a variety of chemistries and structures. The present invention represents a leading method for using fiber materials in extrudable mixtures. The use of this fibrous extrudable mixture allows for inexpensive, scalable, and highly porous substrate extrusion. Since the fibers can be used in a repeating and robust extrusion process, the present invention enables the mass production of filters and catalyst substrates that can be widely used around the world.

These and other features of the present invention are more clearly shown in the following description, and can be realized in particular by means and combinations specified in the claims.

Detailed description of embodiments of the present invention is provided herein. It should be noted, however, that the present invention can be demonstrated in various forms. Accordingly, the specific details set forth below should be construed as a basis for informing the skilled artisan, and not by way of limitation, the manner in which the present invention may be employed in almost any detail system, structure or manner.

1 shows a system for extrusion of a porous substrate. In general, the system 10 uses an extrusion process to extrude a green substrate that can finally be cured into a highly porous substrate product. System 10 has a high porosity, has a large amount of open pore tissue that can increase the permeability associated with it, and can be useful for producing substrates with sufficient strength, depending on the needs of the application. In addition, the system 10 can create a cost-effective substrate, which can be widely applied to the resulting filter and catalytic converter. System 10 is easily scalable for mass production and can support a variety of applications by allowing a variety of chemistries and structures.

The system 10 allows for a very flexible extrusion process, which can be applied to many types of applications. When using the system 10, the substrate designer first sets the requirements of the substrate. Such requirements may include, for example, size, fluid permeability, desired porosity, pore size, mechanical strength and impact properties, thermal stability, chemical reactivity limits, and the like. Based on these and other requirements, the designer selects the material to be used for the formation of an extrudable mixture. Importantly, the system 10 allows the use of the fibers 12 in the formation of an extruded substrate. Such fibers include, for example, ceramic fibers, organic fibers, inorganic fibers, polymeric fibers, oxide fibers, vitreous fibers, glass fibers, amorphous fibers, crystallone fibers, Monocrystalline fibers, polycrystalline fibers, non-oxide fibers, carbide fibers, metal fibers, other inorganic fiber structures, or combinations of these fibers. However, for convenience of description, the ceramic fiber will be described as an example. However, it is of course not limited to this. In addition, although the substrate mainly describes a filtration substrate or a catalyst substrate, it is of course possible to consider the use of the substrate for other purposes within the scope of the present invention. Designers choose specific types of fibers based on application-specific requirements. For example, mullite fibers, aluminum silicate fibers, or other commonly used ceramic fiber materials may be selected as the ceramic fibers. In general, the fibers must be processed 14 to cut to a suitable size. This may include a cutting process prior to mixing the fiber with the additive. Further fiber cutting takes place in various mixing and molding steps of the extrusion process.

Add additive 16 according to specific requirements. Such additives 16 may include binders, dispersants, pore formers, plasticizers, processing aids, strengthening materials, and the like. In addition, a fluid 18, generally corresponding to water, is mixed with the additive 16 and the fiber 12. Fiber 12, additive 16 and fluid 18 are mixed to form an extrudable flowable material 21. Such mixing may use dry mixing, wet mixing and shear mixing. Fiber 12, additive 16 and fluid 18 are mixed until homogeneity is produced and the fibers are evenly distributed and aligned in the material. The fibrous homogeneous is then extruded to form a green substrate (23). The green substrate has sufficient strength to withstand the rest of the process.

Next, the green substrate is cured 25. As used herein, "curing" involves two important process steps. 1) binder removal and 2) bond formation. In the binder removal process, free water was removed and most of the additives were removed to allow the fibers to contact each other. Often the binder is removed through a heat treatment that burns the binder, although other removal processes may be used depending on the particular binder used. For example, some binders may be removed through an evaporation or sublimation process. Some binders and / or other inorganic components may be dissolved prior to decomposition into the vapor phase. By carrying out the curing treatment, an inorganic bond is formed between the overlapped fibers. This combination not only increases the overall structural strength, but also enables the porosity and permeability of the desired substrate. The cured substrate 30 thus becomes a highly porous substrate with most fibers coupled to an open pore network 30. This substrate can then be used as a substrate for a variety of applications, including substrates for filtration and catalytic conversion. Preferably, the system 10 may produce a substrate having a porosity of up to 90% through an extrusion process.

2 shows an extrudable material 50. The extrudable material 50 is for extruding from an extruder such as a piston or screw extruder. The extrudable mixture 52 is a homogeneous mass that includes the fibers, plasticizers, and other additives required for a particular application. 2 shows an enlarged portion 54 of the homogeneity. The enlarged portion 54 is provided to aid the explanation, not to enlarge the magnification. The extrudable mixture 52 includes fibers such as fibers 56, 57, 58. These fibers are selected to produce a highly porous and rigid final substrate with the desired thermal, chemical, mechanical and filtration properties. Substantially fibrous materials are not plastic in themselves and, therefore, were not considered to be extrudable. However, through appropriate selection of plasticizers and process control, it has been found that the extrudable mixture 52 comprising such fibers can be extruded. In this way, the benefits of the cost, scale and flexibility of the extrusion process can be extended to include the benefits gained from the use of fibrous materials.

Fibers are generally considered to be relatively small diameter materials with one or more aspect ratios. Aspect ratio is the ratio of fiber length divided by fiber diameter. As used herein, the 'diameter' of a fiber simply assumes a circular cross-sectional area of the fiber, and this simple assumption applies to all fibers regardless of the actual cross-sectional shape. For example, a fiber with an aspect ratio of 10 has a length up to ten times the fiber diameter. Fibers with diameters ranging from about 1 micron to 25 microns are readily available, but the fiber diameter can be assumed to be 6 microns. System 10 may be used with fibers of various different diameters and aspect ratios. As will be described in more detail with reference to the following figures, there are several ways to select the aspect ratio for a fiber. Also, the shape of the fiber is clearly distinguished from the general ceramic powder. The aspect ratio of each ceramic particle is about 1.

In FIG. 2, the ceramic fiber is described as an example, but the fiber that can be used for the extrudable mixture 52 may be a metallic material (also referred to as a thin-diameter metallic wire). The ceramic fiber may be in an amorphous state, a vitreous state, a crystalline state, a polycrystalline state, a monocrystalline state or a glass-ceramic state. When making the extrudable mixture 52, a relatively small volume of ceramic fiber is used to fabricate the porous substrate. For example, in the extrudable mixture 52 the ceramic fiber is only about 10-40% by volume. In this way, the resulting porous substrate after curing treatment will have a porosity of about 90 to about 60%. Another amount of ceramic fiber material can be selected to achieve other porosity values.

In order to produce an extrudable mixture, fibers and plasticizers are generally mixed. In this way, the fiber is mixed with other selected organic or inorganic additives 60. These additives provide three main properties for extrudate. First, additives can be used to make the extrudable mixture have a suitable fluidity for extrusion. Secondly, the additive provides sufficient strength to maintain the shape of the substrate and the position of the fiber until the extruded substrate, commonly referred to as the green substrate, is removed during the curing process. Finally, an additive is selected that burns or reacts during the curing process to easily align the fibers in the superimposed structure and to strengthen the porous structure. Inorganic materials comprised as additives 60 of the extruded mixture 52 can bond overlapping fibers by promoting the formation of inorganic bonds in the intersecting fibers or at adjacent locations during reaction curing. In addition, additive 60 generally includes a binder, such as binder 61. The binder 61 serves as a medium for holding the fibers in place and providing rigidity to the green substrate. Fibers and binders can be used to create porous substrates with relatively high porosity. However, pore formers such as pore former 63 may be added to further increase the porosity. Pore formers are added to increase voids in the cured final substrate. Pore formers can be spherical, elongate, fibrous or irregular in shape. Pore formers are selected not only for forming voids based on pyrolytic properties, but also for supporting the orientation of the fibers. In this way, during the post curing step, the pore former helps the fibers to be arranged in an overlapping pattern, facilitating proper bonding between the fibers. The pore former also serves to align the fibers in the primary direction, which affects the thermal expansion of the extruded material and the strength along the different axes.

As outlined above, the extrudable mixture 52 may use one or more fibers selected from the various fiber types available. Furthermore, the selected fiber may be combined with one or more binders of various binders. In addition, one or more pore formers selected from a variety of pore formers may be added. As the plasticizer, water or other fluid may be used in the extrudable mixture, and another additive may be added. Because of the flexibility in this chemical composition, the extrudable mixture 52 can be usefully used for various applications. For example, mixture combinations can be selected according to the environmental, temperature, chemical, physical or other requirements required. In addition, the extrudable mixture 52 can be made to conform to the extrusion process to form the final extruded product in a flexible and economical manner. Although not shown in FIG. The extrudable mixture 52 is extruded through a screw or piston extruder to form a green substrate, which is then cured into a final porous substrate product.

The present invention represents a pioneering method for using fiber materials in plastic batches or mixtures for extrusion processes. The use of this fibrous extrudable mixture enables inexpensive, highly scalable substrate extrusion in a scalable production process. Since the fibers can be used in an iterative and robust extrusion process, the present invention enables the mass production of filters and catalyst substrates that can be widely used around the world.

3A shows an enlarged view of a hardened region in a porous substrate. The substrate portion 100 removes the binder 102 and shows the state after the curing treatment 110. After removing the binder 102, fibers such as fibers 103 and 104 are initially held in place by the binder material, and as the binder material burns, the fibers are exposed and overlapped, resulting in a loose structure. In addition, the pore former 105 may be disposed to create additional voids and to align / arrange the fibers. Because the fibers form a relatively small volume in the extrudable mixture, there are a large number of voids 107 between the fibers. As the binder and pore former burn, the fibers may be slightly adjusted to contact each other. Overlapping fibers 101 can be adjusted to remain in place or to be placed close to adjacent fibers, but do not actually contact 106 as shown in the figure. Binders and pore formers are selected that burn in a controlled manner that does not interfere with the arrangement of the fibers or collapse the substrate upon combustion. In general, the binder and the pore former are selected from materials that decompose or burn before the bonds are formed between the fibers. The inorganic binder 108 contained in the extrudable mixture 52 remains after the binder and the pore former have been burned. As the curing process proceeds, the overlapped and contacted fibers begin to bond, and the inorganic binder 108 flows or reacts to form an inorganic bond 119 to connect the overlapped fibers. Such bonds can be formed in a number of ways. For example, the fibers may be heated to form liquid assisted sintered bonds at the fiber crossover points or nodes. This liquid sintering can be obtained as a result of the particular fiber selected, or it can appear as a result of additives added to the mixture or coated on the fiber. In other cases it may be desirable to form solid phase sintered bonds. In this case, the crosslinks form a particle structure connecting the overlapping fibers. In the green state, the fibers do not yet form a physical bonding structure to each other, but some degree of green strength may occur because the fibers are entangled with each other. The specific bond type is selected according to the base material, the desired strength and the working chemistry and the environment. In some cases, bonding may occur because the inorganic binder 108 is present in the mixture that keeps the fiber in the connected tissue and does not burn during the curing process.

If a bond, such as a bond 112 and an inorganic bond 119 is formed, there is an advantage in that it can form a fiber structure with a significantly higher strength. In addition, overlapping fibers that are not in contact with adjacent fibers are bonded 117 due to the inorganic bonding by the reaction of the inorganic binder 108 during the curing step. These bonds also form open pore tissues with very high porosity. For example, the voids 116 naturally create due to the spacing between the fibers. The voids 114 are made in the process in which the pore former 105 is decomposed or burned. In this way, fiber bond formation results in open pore tissue with no or nearly terminated channels. This open pore tissue produces high permeability, high filtration efficiency and provides a large surface area, for example in addition of catalysts. Bond formation may vary depending on the type of bonding required, such as solid phase sintering or liquid assisted / liquid sintering, additives present during curing treatment, and the like. For example, additives, specific fiber selection, heating time, heating level, and reaction environment can all be adjusted to create specific bond types.

3b shows another view in which the cured area of the porous substrate is enlarged. The substrate portion 120 removes the binder 122 and shows the appearance after the curing treatment 124. The substrate portion 120 is similar to the substrate portion 100 described in FIG. 3A and will not be discussed in detail. The inorganic binder 108 remains intact after the binder burns out, and the superimposed fibers 123 can be adjusted to be in contact with or adjacent to adjacent fibers. The substrate 120 is formed without a specific pore-forming agent. As a result of arranging fibers using a binder material, the entire open pore structure 124 is formed. The strength of the porous structure may be maintained by contacting adjacent fibers to form an inorganic bond 125 between the fibers, or forming a bond 126 between fibers adjacent to the adjacent fiber. Thus, a substrate having a suitable porosity can be formed without using a specific pore-forming agent, thereby reducing cost and manufacturing complexity. Substrates having a porosity of about 40% to 60% can be made in this manner.

4 shows an electron micrograph set 150. Photo set 150 first shows open pore tissue 152 created using a fibrous extrudable mixture. As can be seen in the picture, bonds were formed in the intersecting fiber nodes and the open pore structure remained after the pore former and binder were burned. Inorganic bonding can be confirmed in the portions 151 and 153 connecting the overlapping fibers, and as a result, the strength of the porous substrate is improved. In contrast, photo 154 shows a typical closed cell network fabricated using known prior art processes. Partially closed pore tissue has a relatively high porosity, but some porosity results from at least closed channels. Such closed channels do not provide permeability. As such, when the open pore structure and the closed pore structure have the same porosity, the open pore structure has more excellent permeability.

Using extrudable mixtures and the processes generally described so far, very useful porous substrates are produced. For example, as illustrated in FIG. 5, the porous substrate may be extrusion molded into the filter block substrate 175. The substrate block 175 was extruded using a piston or screw extruder. The extruder can be adjusted to operate at room or slightly higher temperatures or in a controlled temperature range. In addition, some parts of the extruder may be heated to different temperatures, affecting slowing properties, shear history, gelation properties, and the like of the extrusion mixture. In addition, the extrusion size can be modified to adjust the expected degree of shrinkage of the substrate during heating and sintering. Usefully, the extrudable mixture is set up as a fibrous extrudable mixture which adds sufficient plasticizer and other additives for the extrusion of the fibrous material. The extruded green state blocks were cured to remove free water, burn off additives, and form structural bonds between the fibers. As a result, the block 175 exhibited not only high porosity but also excellent permeability and high surface area available. In addition, depending on the particular fiber and additive selected, block 175 can be configured for deep filtration. Block 176 includes a channel 179 extending longitudinally through the block. The inlet of block 178 can be left open for a flow-through process or block the inlet one by one to create a wall pass effect. Although block 175 is shown as a hexagonal channel, other patterns and sizes may be used. For example, the channel may be formed of a square, rectangular, or octagonal channel pattern with a larger inlet channel, or another symmetrical / asymmetric channel pattern, including uniformly sized square, rectangular, or triangular channel patterns. . The precise shape and size of the channel or cell can be adjusted by adjusting the die design. For example, EDM (Electronic Discharge Machining) may be used to form the corners of the square channel to bend to form fins in the die. Such circular edges have slightly higher back pressure, but improve the strength of the final product. In addition, the die design can be modified to extrude a honeycomb substrate with a different wall thickness and a different skin thickness than the rest of the wall surface. Similarly, in some applications, external skins may be applied to the extruded substrate in the final definition of size, shape, contour, and strength.

When using a penetrating device, the high porosity of block 176 creates a large surface area for catalytic material application. In this way, a more effective and efficient catalytic converter with low thermal mass can be made. Through low thermal mass, the resulting catalytic converter has good light off characteristics and can efficiently use the catalytic material. When used in wall passing or wall filtration examples, the high permeability of the substrate wall promotes deep filtration while at the same time lowering back pressure. This depth filtration promotes more effective regeneration, including efficient particulate removal. In some cases, however, most hard precipitates or surface filtration are observed. In a wall pass design, the fluid passing through the substrate travels through the wall of the substrate and thus comes in more direct contact with the fibers forming the wall. Such fibers provide a high surface area where potential reactions can occur, such as when a catalyst is present. Since the extrudable mixture can be formed from a variety of fibers, additives, fluids, and the like, the chemical properties of the extrudable mixture can be adjusted to produce blocks with specific properties. For example, if the final block is a diesel particulate filter, choose a fiber that can operate safely even at extreme temperatures beyond the control of regeneration. As another example, when a block is used to filter a particular type of exhaust gas, a combination with fibers is selected that does not react with the exhaust gas over the expected operating temperature range. Although the advantages of substrates with high porosity have been described here with filters and catalytic converters as examples, many other applications require high porosity substrates as well.

As shown in FIG. 2, the fibrous extrudable mixture may be formed from a variety of base materials. In general, the selection of suitable materials is based on the chemical, mechanical and environmental conditions in which the final substrate is used. Therefore, the first step in designing a porous substrate is to understand the end application of the substrate. These requirements allow the selection of specific fibers, binders, pore formers, fluids and other materials. It should also be noted that the process applied to the selected material may affect the final substrate product. Since fiber is the material that forms the basic structure in the final substrate product, the choice of fiber material is of paramount importance for the final substrate to function smoothly in the intended area. Therefore, fiber should be selected based on the required bonding requirements and the specific bonding process type. The bonding process can be liquid sintering, solid sintering or glass-forming agent, glass, mud, ceramic, ceramic precursors, or a binder requiring a binder such as a colloidal sol and the like. The binder may be part of the fiber structure, a coating of the fiber, or one component of an additive. In addition, more than one fiber type can be selected. It should also be understood that some fibers are consumed during the curing and bonding process. When choosing a fiber composition, the final operating temperature is considered to be an important factor so that the thermal stability of the fiber can be maintained. In another example, select fibers that are chemically inert or do not react in the presence of the expected gas, liquid or solid state material. Fibers can also be selected at a cost, and some fibers can be harmful to the human body because of their small size and should be avoided. Fibers are chosen depending on whether the mechanical environment can form a rigid structure and maintain the required mechanical integrity. When choosing the appropriate fiber or fiber set, trade-offs should be considered in terms of performance and application. 6A and 6B show the various fiber types that can be used to form the fibrous extrudable mixture. In general, the fiber may be an oxidized or non-oxidized ceramic, glass, organic, inorganic or metallic material. In the case of ceramic materials, the fibers can be in various states such as amorphous, glassy, polycrystalline or monocrystalline. Table 1 describes the different fibers available, but other types of fibers can also be used.

The binder and pore former may then be selected, depending on the fiber type selected and other desired properties. As an example, a binder is selected that can promote certain types of liquid sintered bonds between the selected fibers. More specifically, the binder includes a component that reacts at the bonding temperature to promote the liquid bond flow to the node of the cross-fiber. In addition, a binder having the ability to plasticize the selected fiber and maintain the green state strength is selected. As an example, the binder may be selected according to the type of extrusion process to be used and the temperature required for the process. For example, some binders form gelatinous materials when heated too much, and therefore should only be used in low temperature extrusion processes. As another example, the binder may be selected according to the influence on the shear mixing properties. In this way, the binder can promote fiber cutting at the desired aspect ratio during the mixing process. The binder can also be selected depending on the decomposition or combustion characteristics. The binder should generally be able to hold the fibers in place and should not inhibit the formation of the fiber structure during combustion. For example, if the binder burns too quickly or violently, the escape gas may stop the formation of the structure. In addition, the binder may be selected according to the amount of residue remaining after the binder is burned. Some applications may be very sensitive to such residues.

Pore formers may not be required to form relatively moderate porosity. For example, the natural arrangement of the fibers and the packing in the binder can work together to achieve a porosity of about 40-60%. In this way, substrates with moderate porosity can be produced through extrusion processes without pore formers. In some cases, removing the pore former may produce a porous substrate at a lower cost than existing known processes. However, if porosity of 60% or more is required, pore formers may be needed to form additional pores in the substrate after curing. In addition, the pore former may be selected according to decomposition, combustion characteristics, size and shape. For example, pore size can be an important factor in capturing certain types of particulates, especially where high permeability is required. In addition, by adjusting the shape of the pores, for example, the fibers can be properly aligned. For example, if the length of the pore is relatively long, the fibers may be arranged in a more ordered pattern, while if irregular or elliptical, the fibers may be arranged in a random pattern.

Fibers are either cut fibers from the manufacturer and can be used directly in the process, or they can be provided in bulk format, which may normally have to be processed before use. In both cases, the process should be considered in the way the fibers are treated to have the desired final aspect ratio distribution. Generally, the fibers are first cut before mixing with other additives and further cut during the mixing, shearing and extrusion steps. However, it is also possible to extrude the uncut fiber by setting the fluidity so that the extrusion mixture can be extruded when pressure is applied to the extrusion die surface at an appropriate extrusion pressure without causing a volumetric flow to the extrusion mixture. In this case fiber cutting can be made to have an appropriate aspect ratio distribution at various points in the overall process. Once the fibers are selected and cut to the appropriate size, they are mixed with binders and pore formers. This mixing may be carried out in dry form to start the mixing process first, or may be carried out in a wet mixing process. To this mixture a fluid (usually water) is added. In order to obtain the required level of uniform distribution, the mixture is shear mixed in one or more steps. Shear mixing or dispersion mixing is an excellent homogeneous mixing process that allows the fibers to be further cut to an even distribution of fibers and the desired aspect ratio in the mixture.

Table 2 of FIG. 6C shows the various binders available. Only one binder may be used or several binders may be used together. In general, binders are classified into organic and inorganic. Organic binders are usually burned at low temperatures during curing treatment, while inorganic binders generally form part of the final structure at higher temperatures. Although several binders are disclosed in Table 2, other binders may also be used. For example, an inorganic binder may be selected to promote inorganic binding, including colloidal, aluminosilicate, silica, alumina, zirconium dioxide, Titanium dioxide, as well as other compounds including sodium silicate, borosilicate, aluminophosphate, calcium cement, and the like. In addition, a ceramic precursor such as tetraethoxysilane (TEOS) may be added as an inorganic binder to promote inorganic bonding between the fibers. Table 3 in FIG. 6D shows a list of available pore formers. In general, the pore former may be defined as an organic or inorganic agent, and the organic agent has a characteristic of burning at a low temperature than the inorganic agent. Various pore formers are shown in Table 3, but other pore formers may be used. Table 4 of FIG. 6D shows the various fluids available. Water is the most economical and widely used fluid, but other fluids may be needed in some applications. Table 4 lists the different fluids that can be used, but other fluids can be selected depending on the specific application and process requirements.

In general, the mixture may be adjusted to have fluidity suitable for advantageous extrusion techniques. Optimal fluidity is usually achieved through proper selection and mixing of fibers, binders, dispersants, plasticizers, pore formers, and fluids. A high degree of mixing is required to provide adequate plasticity to the fiber. After selecting the appropriate fiber, binder, and pore former, the amount of fluid is usually last adjusted to meet the proper fluidity. Appropriate fluidity can be determined by one of two tests. The first test is a subjective informal test in which a mixture is taken and placed between the fingers of a skilled extrusion technician to make beads. The skilled person will know that the mixture is in a suitable state for the extrusion process when the mixture is properly slipped between the fingers. The second, more objective test is to measure the physical properties of the mixture. In general, shear strength versus compaction pressure can be measured using a defined (eg high pressure) annular rheometer. Collect the measurements and draw a graph to compare the cohesion versus pressure dependencies. By measuring the mixture at various mixing and fluid levels, one can create a flow chart showing the points of flow. For example, Table 5 of FIG. 6E shows a flow chart of the fibrous ceramic mixture. The vertical axis 232 represents adhesion and the horizontal axis 234 represents pressure dependence. Extrudeable region 236 represents an area in which the fibrous material can be extruded. Thus, a mixture with measurements belonging to the extrudable region 236 means that the extrusion is likely to succeed. Of course, various variations may occur in the liquidity chart, so it should be expected that the position of the region 236 will fluctuate to some extent. In addition, there are several direct and indirect tests for measuring fluidity and plasticity, so a number of methods can be used to determine whether the mixture has adequate fluidity to extrude into the desired final product shape.

Once the proper fluidity is reached, the mixture is extruded through an extruder. The extruder can use a piston extruder, a single screw extruder or a twin screw extruder. Most extrusion processes may be highly automated or require operator intervention. The mixture is extruded through a die having the desired cross sectional shape for the substrate block. The die was chosen to be able to form a green substrate. This results in a stable green substrate that can be processed through a curing process while maintaining its shape and fiber arrangement.

The green substrate is then dried and cured. Drying takes place in room conditions, controlled temperature and humidity conditions (eg controlled ovens), microwave ovens, RF ovens, convection ovens, etc. In general, the hardening process requires the removal of free water to dry the green substrate. It is important to dry the green substrate in a controlled manner to prevent cracking or other structural defects in the substrate. The temperature can then be raised to burn the binder and additives such as pore formers. The temperature is adjusted to allow the additive to burn in a controlled manner. Burning the additive may require temperature cycling over several time periods and several heating stages. Once the additive is burned, the substrate is heated to the required temperature to form structural bonds at the fiber crossover points or nodes. The required temperature is selected depending on the type of bond required and the fiber chemistry. For example, liquid assisted sintered bonds are generally formed at lower temperatures compared to solid-state sintered bonds. The application time of the bonding temperature can also be adjusted depending on the specific bonding type to be produced. The entire heat cycle can be carried out in the same furnace or in other furnaces, or in batch or continuous processes, in the atmosphere or in controlled environmental conditions. After the fiber bond is formed, the substrate is slowly cooled to room temperature. The curing process can be carried out in one oven or in several ovens / hot furnaces and can also be automated in production ovens / hot furnaces such as tunnel kilns.

7 shows a system for extrusion of a porous substrate. System 250 represents a very flexible process that can be used to create porous substrates. Substrate requirements for designing the substrate are defined (252) as derived from the block. For example, substrate requirements are typically determined by the end use of the substrate, which may include size constraints, temperature constraints, strength constraints, chemical reaction constraints, and the like. In addition, specific choices can be determined by cost and the feasibility and cost of mass production of the substrate. For example, high production rates can produce relatively high temperatures in the extrusion die, so a binder that can be processed at elevated temperatures without curing or gelling should be selected. In the case of extrusion using a high temperature binder, it may be necessary to maintain the die and barrel at high temperatures ranging from 60 to 180 ° C. In such a case the binder melts and therefore the amount of additional fluid may be reduced or not needed at all. As another example, a filter may be designed to collect particulate matter. In this case, a fiber must be selected that remains unreacted with particulate matter even at elevated temperatures. Many possible mixtures and processes can be used for a wide range of applications. The skilled person should be able to identify the trade-offs involved in the selection of fibers, binders, pore formers, fluids and process steps. Indeed, one of the important advantages of system 250 is its flexibility in mixture selection and process adjustment.

Once the substrate requirements are defined, a fiber is selected from Table 1 of FIGS. 6A and 6B (253). Fiber can be a single type or a combination of two or more. It will also be seen that some fibers may be consumed during the curing process. Additives, such as coatings on fibers, can be added to the fibers to inject other materials into the mixture. For example, a dispersant may be applied or a binding aid may be coated on the fiber to facilitate separation and arrangement of the fiber. In the case of binder aids, when the fiber reaches the curing temperature, the binder aids in the formation and flow of liquid bonds.

Typical composition for obtaining porosity in excess of 80%

Density (g / cc) Mass (g) Volume (cc) volume (%) Fiber Mullite 3.50 300.0 85.74 11.21 Inorganic binder Bentonite Colloidal Silica 2.89 4.40 30.0 120.0 10.38 27.3 1.36 3.57 Organic binder HPMC (hydroxypropyl methyl cellulose) 1.30 96.0 73.86 9.66 Pore former Carbon (graphite) 2.20 390.0 177.30 23.19 Fluid water 1.00 390.0 390.00 51.01 total 1326.0 764.58 100.0

Next, a binder is selected from Table 2 of FIG. 6C (255). Choose a binder that can increase green strength and control combustion. In addition, a binder is selected that can produce sufficient plasticity in the mixture. If necessary, the pore former is selected from Table 3 in FIG. 6D (256). In some cases, sufficient porosity can be achieved by simply using fibers and binders. Porosity is achieved not only by the fiber's original packing properties, but also by the space occupied by the binder and other volatile components released during the releasing and curing steps. Pore formers may be added to achieve higher porosity. Pore formers are selected according to the controlled combustion capacity and can be used to support plasticization of the mixture. A fluid (usually water) is selected from Table 4 in FIG. 6D (257). Inorganic binder is selected in Table 2 of FIG. 6C (259). Dispersants may be added to facilitate fiber separation and alignment, and other liquid materials such as plasticizers or extrusion aids to improve the flow capacity of the mixture. Such dispersants may be used to control the amount of surface charge of the fiber. In this way, the charge can be adjusted so that the individual fibers repel each other. This further promotes uniform and arbitrary distribution of the fibers. The general composition of the mixture for producing substrates with porosities in excess of 80% is shown below. The mixture can be adjusted according to the target porosity, the specific application and the process considerations.

The selected fiber 252 must be processed to have an appropriate aspect ratio (254). Preferred aspect ratios are from about 3 to about 500, and may have one or more distribution modes. Other range aspect ratios may be selected, for example, about 1000. As an example, the aspect ratio distribution is randomly distributed over the desired range, and in other examples an aspect ratio with discrete mode values may be selected. The aspect ratio has been found to be an important factor in defining the packing characteristics of the fiber. Therefore, the aspect ratio and aspect ratio distribution should be chosen to achieve specific strength and porosity requirements. In addition, processing the fibers to a preferred aspect ratio distribution can be performed at various points in the process. For example, a third party can cut the fiber and deliver the fiber with the desired aspect ratio distribution. In another example, fibers can be supplied in large quantities and processed to an appropriate aspect ratio in the preliminary stages of the extrusion process. Mixing, shear mixing or dispersion mixing, and extrusion of process 250 may also affect the cutting and chopping of the fibers. For this reason, the aspect ratio of the fibers originally introduced into the mixture appears different from that of the final substrate cured. Therefore, when selecting the appropriate aspect ratio distribution introduced into the process (254), the chopping and cutting effects of the mixing, shear mixing, and extrusion processes must be considered.

For fibers treated with an appropriate aspect ratio distribution, the fibers, binders, pore formers and fluids are mixed and homogenized (262). This mixing process may include dry mixing, wet mixing, and shear mixing. It is preferable to use shear or dispersion mixing for uniform distribution of the fibers in the material. This distribution is particularly important because the concentration of ceramic material in the mixture is relatively low. When the homogeneous mixture is mixed, the fluidity of the mixture can be adjusted (264). When the mixture is mixed the fluidity continues to change. The fluidity can be tested in a subjective manner or measured to comply with the recommended areas as shown in Table 5 of FIG. 6E. Mixtures belonging to this region are likely to be appropriately extruded. The mixture is then extruded 268 to the green substrate. In the case of a screw extruder, mixing may take place in the extruder itself rather than in a separate mixer. In such cases, the shear history of the mixture should be carefully managed and controlled. The green substrate has sufficient green strength and can maintain the shape and arrangement of the fibers as they are during the curing process. Next, the green substrate is cured 270. Curing processes include removal of residual water, controlled combustion of most additives and the formation of inorganic bonds. During the combustion process, the fibers are connected and remain crossed with each other, and a hardening process is performed, whereby bonds are formed at intersections or nodes. Bonding can be achieved through liquid phase sintering or solid state sintering. Some bonds may also be formed as a binder, pore former, coating of the fiber or by reaction with additives provided within the fiber itself. After the bond is formed, the substrate is slowly cooled to room temperature.

8 illustrates a method of curing a porous substrate. The method 275 includes a green substrate with fibrous ceramic contents. First, the moisture remaining on the substrate is gradually removed through the curing process (277). In general, moisture removal can be performed at a relatively low temperature in the oven. After the residual water is removed, the organic additive is burned (279). These additives are burned in a controlled manner to promote proper alignment of the fibers and to ensure that the escape gases and residues do not damage the fiber structure. As the additive burns, the fiber maintains an overlapping arrangement and may be closer to the intersection or node (281). The binder is used to place the fibers in this overlapping arrangement, and the use of pore formers can form specific patterns. In some cases inorganic additives may be used, which may be combined with the fiber, consumed during the bond formation process, or may remain as part of the final substrate structure. The curing treatment is continued to form an inorganic bond (285). Depending on the fiber type used, the binder or binder used and the type of bond desired, certain times and temperatures are required to form the bond. As an example, a liquid phase sintered bond may be created between the fibers (286). Such bonding is aided by glass-forming agents, glass, ceramic precursors or inorganic fluids present in the system. As another example, the liquid phase sintering bond may be generated using the sintering aid or the sintering agent (288). The sintering aid may be provided as a coating, additive, or from the chemistry of the binder, pore former or the fiber itself. In addition, an inorganic bond may be formed between the fibers through solid state sintering (291). This results in larger particles and mass transfer in the intersecting fibers, resulting in chemical bonds at the nodes and an overall robust structure. In the case of liquid phase sintering, the binder material accumulates at the nodes where the fibers cross, forming a rigid structure. The curing process can be performed in one or more ovens and can be automated in industrial tunnels or kiln type furnaces.

9 illustrates a method 350 of creating a porous substrate. In this case, in block 353, a mullite fiber with ultra-high temperature characteristics such as low coefficient of thermal expansion, good strength and high resistance to thermal shock resulting from interlocking grain structures and thermal stress distribution was selected. Mullite also has a relatively low thermal conductivity and high abrasion resistance. Since such characteristics are not significantly affected even when the temperature rises, a porous substrate can be used even at a high temperature. Mullite is the mineralogy name assigned to the only chemically stable intermediate stage in a SiO ₂ -Al ₂ O ₃ system. Natural minerals are extremely rare and are found on Mule Island on the west coast of Scotland. Often mullite 3Al ₂ O ₃ · SiO ₂ is denoted by (i.e., 60 mol% Al ₂ O ₃ and 40 mol% SiO _2). In practice, however, mullite is misleading because it is a solid solution with an equilibrium composition limit for alumina between about 60 and 63 mol% at less than 1600 degrees Celsius. Fibers are optionally processed 354 for proper aspect ratio distribution. Preferred aspect ratios range from about 3 to 500 and may have one or more distribution modes. Other ranges of aspect ratios may be selected, for example, about 1000. For example, an aspect ratio distribution may be arbitrarily distributed over a desired range, and in another example, an aspect ratio having a discontinuous mode value may be selected. The aspect ratio has been found to be an important factor in defining the packing characteristics of the fiber. Therefore, the aspect ratio and aspect ratio distribution should be chosen to achieve specific strength and porosity requirements. Mullite fibers can also be processed to have the desired aspect ratio distribution at different points in the process, either at the fiber supplier or as a preprocessing step before mixing. Mixing, shear mixing or dispersion mixing, and subsequent extrusion processes during process 350 may also affect the cutting and chopping of the fibers. For this reason, the aspect ratio of the fibers introduced into the mixture appears different from that of the final substrate cured. In addition, optional step 358 is performed to add mullite fibers for surface modification by adding other materials, such as dispersants to promote separation and alignment of the fibers, or plasticizers and extrusion aids to improve the flow characteristics of the mixture. You can do it. Such dispersants can be used to control the amount of surface charge of the fiber. In this way, the charge can be controlled so that the individual fibers can repel each other. This further promotes uniform and arbitrary distribution of the fibers.

In Figure 9 it is recommended to use hydroxypropyl methyl cellulose (HPMC) as a binder (355) to create sufficient plasticity in the mixture. Graphite may be used as a pore former (356) to occupy the pores during the mixing and extrusion process to increase the porosity while decomposing in the presence of oxygen during subsequent curing treatment. Colloidal silica is recommended as an inorganic binder (359). In a practical implementation, a target porosity of 70% can be achieved using a ratio of about 25% mullite fiber, 10% HPMC binder, 30% graphite pore former, 5% collide silica inorganic binder, and 30% water weight. . The mixture composition ratio used in the actual implementation can be proportionally adjusted according to the ratio required to obtain 55 to 85% porosity as shown in FIG.

Fibers, binders, pore formers, inorganic binders and fluids are mixed and homogenized (362). Mixing steps may include dry mixing, wet mixing, and shear mixing. It is preferable to use shear or dispersion mixing for uniform distribution of the fibers in the material. This distribution is particularly important because of the relatively low concentration of ceramic material, in particular the mullite material of the mixture. When the homogeneous mixture is mixed, the fluidity of the mixture can be adjusted (364). When the mixture is mixed the fluidity continues to change. The fluidity can be tested in a subjective manner or measured to comply with the recommended areas as shown in Table 5 of FIG. 6E. The mixture belonging to this region is likely to be appropriately extruded. The mixture is then extruded onto the green substrate (368). In the case of a screw extruder, the mixing may take place in the extruder itself rather than in a separate mixer. In such cases, the shear history of the mixture should be carefully managed and controlled. The green substrate has sufficient green strength to keep the shape and the arrangement of the fibers intact during the curing process. Then, the green substrate is cured (370).

The curing step removes fluid from the green substrate and results in controlled combustion of organic materials such as binders and pore formers (370). If the curing treatment continues, an inorganic bond is formed that connects the overlapping fibers at increased temperature. In practice, the inorganic bonds formed during the curing step 370 may include aluminosilicate bonds, glass bonds, amorphous bonds, crystalline bonds, ceramic bonds, and / or mechanical bonds.

10 illustrates an alternative method 400 for creating a porous substrate. For this implementation, a ceramic or metal fiber has been selected (403) and optionally processed (404) for the aspect ratio distribution, as shown earlier in FIG. Likewise, the fibers can be selectively treated for surface modification by applying dispersants and / or materials that change the amount of charge of the fibers. In order to provide sufficient plasticity during the extrusion and to promote controlled combustion capability during the curing step, including the strength of the green substrate, the binder is selected (405) in Table 2 of FIG. 6C. In this embodiment, only a fiber and a binder (including an inorganic binder) can secure sufficient porosity, so that a pore former is not required to improve the porosity of the porous substrate. Fumed silica was chosen as the inorganic binder (409) and a fluid (usually water) can be selected from Table 4 of FIG. 6D (407). It is found that the mixture can be adjusted according to the target porosity, specific application and process considerations.

Mixing of the fiber, binder, inorganic binder, and fluid is performed (412), and the fluidity is adjusted (414). The extrusion method extrudes the mixture into the green substrate (418, eg, a honeycomb substrate consisting of at least one channel providing an inlet to the porous substrate). Thereafter, the curing step is continued (420). In this embodiment, the hardening treatment removes fluid from the green substrate during the drying process. Since no pore former is used, the organic material which is substantially an organic binder is burned out during the curing treatment. In the next curing step, inorganic bonds are formed that connect the overlapping fibers. Inorganic bonds are formed at interfiber nodes. For example, glass bonds are formed from fumed silica inorganic binders that flow to adjacent fiber nodes. Other inorganic bonds such as aluminosilicate bonds, amorphous bonds, crystalline bonds, ceramic bonds and mechanical bonds are similarly formed.

11 illustrates an alternative method 450 of creating a porous substrate. For this implementation a ceramic or metal fiber was selected (453), and as shown in FIG. 9, the fiber is optionally processed (454) to fit the aspect ratio distribution. Likewise, the fibers can be selectively treated for surface modification by applying dispersants and / or materials that change the amount of charge in the fibers. The binder is selected from Table 2 of FIG. 6C to provide sufficient plasticity during the extrusion and to promote controlled combustion capability during the curing step, including the strength of the green substrate (455). In this embodiment, the pore former is selected from Table 3 of FIG. 6D (456). In some cases, however, fiber and binders alone can provide sufficient porosity. Porosity is achieved by the fiber's inherent packing properties as well as the space occupied by the binder, solvent and other volatile components released during the releasing and curing steps. Pore formers can be added to achieve higher porosity. Pore formers are selected according to the controlled combustion capacity and can be used to support plasticization of the mixture. A fluid (usually water) is selected from Table 4 in FIG. 6D (457). Dispersants may be added to facilitate fiber separation and alignment, and other liquid materials such as plasticizers or extrusion aids may be added to improve the flow characteristics of the mixture.

Mixing of the fiber, the binder, the inorganic binder and the fluid is performed (462) and the fluidity is adjusted (464). The extrusion process extrudes the green substrate to the green substrate (468, eg a honeycomb substrate consisting of at least one channel providing an inlet). In this embodiment the curing process is carried out in two steps. In the first curing step, the fluid is dried and the organic binder and pore former are burned (470). It may be necessary to form sintered bonds between the fibers in contact with each other so that the substrate can have sufficient strength to process before completing the final curing step at this stage. Liquid phase sintered bonds may be formed at elevated sintering temperatures and solid phase sintered bonds may be formed between fibers.

After the first curing step 472, an inorganic binder (eg, colloidal silica) selected from Table 2 of FIG. 6C is applied 456 to the porous substrate. Here, the inorganic binder can be infiltrated into the substrate by immersing the substrate in an inorganic binder solution injected into the liquid, pouring a solvent containing the inorganic binder, or passing a liquid or gas containing a powdery inorganic binder through the substrate. have. The second curing step then continues (474). Herein, the substrate including the inorganic binder is heat-treated to form an inorganic bond connecting the overlapping fibers. Inorganic bonds formed in the second curing step 474 may include aluminosilicate bonds, glass bonds, glass-ceramic bonds, amorphous bonds, crystalline bonds, ceramic bonds, and / or mechanical bonds.

Fiber extrusion systems provide great flexibility in implementation. For example, various types of fibers and additives can be selected when forming the mixture. There are also various mixing and extrusion methods, as well as options related to the curing method, time and temperature. Open training provides the extrusion technician with the understanding that a number of variations are available. Honeycomb substrates are a general design that can be produced using the techniques described herein, but can be extruded in different shapes, sizes, contours, designs, etc. to suit a variety of applications.

In filtration units (DPF, oil / air filters, heating gas filters, air filters, water filters, etc.) or catalytic units (three-way catalytic converters, SCR catalyst units, ozone deodorizers, deodorants, biological reactors, chemical reactors, oxidation catalyst units) For certain applications, such as the use of, it may be necessary to block the channels of the extruded substrate. To fill the substrate, a material of similar composition to the extruded substrate is used. This filling can be carried out in a green state or in a sintered substrate. Most filling compositions require heat treatment to bond with the cured and extruded substrates. Such filtration or catalytic devices may generally be mounted within the housing or with an input / output line connected to the housing. In this way, porous substrates can be applied to a variety of applications, including vehicle air filters, exhaust filters for vehicle exhaust gas treatment, and vehicle cabin filters.

While basic and alternative implementations of the invention have been disclosed, those skilled in the art can implement various extensions and modifications beyond the techniques described using the guidelines for the invention described herein. All such extensions and modifications are included within the true spirit and scope as discussed in the appended claims.

The drawings constitute part of this specification and include representative results of the invention, which can be embodied in various forms. In some instances, various aspects of the invention may be somewhat exaggerated or enlarged to facilitate understanding of the invention.

1 is a block diagram of a system for extrusion of a porous substrate according to the present invention.

2 shows a picture of a fibrous extrudable mixture according to the present invention.

3A and 3B are illustrations of an open cell network according to the present invention.

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

5 shows a picture of a filter block using a porous substrate in accordance with the present invention.

6A-6E are tables for fibers, binders, pore formers, fluids and fluidities useful in the present invention.

7 is a block diagram of a system for extrusion of a porous substrate in accordance with the present invention.

8 is a block diagram of a system for curing a porous substrate in accordance with the present invention.

9 is a block diagram that actually implements a method for producing a porous substrate in accordance with the present invention.

10 is a block diagram embodying a first alternative of a method for producing a porous substrate in accordance with the present invention.

11 is a block diagram embodying a second alternative of a method for producing a porous substrate in accordance with the present invention.

Claims (79)

Superimposed ceramic fibers; An inorganic bond formed between the superimposed ceramic fibers; And Including a substrate produced by the extrusion method, the extrusion method, Ceramic material fibers, additives, and fluids are mixed to form an extrudable mixture, the additives comprising an inorganic binder, Extruding the extrudable mixture into a green substrate, Porous ceramic substrate comprising curing the green substrate to a porous substrate. According to claim 1, The inorganic bond is a glass, amorphous or crystalline porous ceramic substrate. According to claim 1, The cured porous ceramic substrate is a porous ceramic substrate composed of a ceramic fiber and an inorganic bond. The method of claim 1, And the cured porous ceramic substrate comprises about 60 to 95% by weight of ceramic fiber. The method of claim 1, And the cured porous ceramic substrate comprises about 40% by weight of an inorganic binder. The method of claim 1, Wherein the cured porous ceramic substrate comprises about 75% by weight ceramic fiber and about 25% by weight inorganic binder. The method of claim 1, The hardened porous ceramic substrate is a porous ceramic substrate composed of an open pore network of bonded ceramic fibers. The method of claim 1, A portion of the inorganic bond is formed between the superimposed ceramic fibers in contact with each other. The method of claim 1, And a portion of the inorganic bond is formed between the superimposed ceramic fibers that are spaced apart from each other. The method of claim 1, The hardening includes forming the inorganic bond using the inorganic binder. The method of claim 1, The extruding further comprises extruding the extrudable mixture to a green honeycomb substrate. The method of claim 1, The inorganic binder comprises colloidal silica. The method of claim 1, The inorganic binder comprises aluminosilicate glass, colloidal alumina or colloidal zirconia. A porous substrate produced by an extrusion process, having a porosity in the range of about 60-90% and having a structure formed of bonded inorganic fibers, wherein the extrusion process comprises: Inorganic fibers, additives, and fluids are mixed to form an extrudable mixture, the additives comprising an inorganic binder, Extruding the extrudable mixture into a green substrate, Forming a bond between the inorganic fibers using the inorganic binder. The method of claim 14, And the inorganic fiber is substantially one kind of fiber. The method of claim 14, The inorganic fiber comprises a fiber of a plurality of materials. The method of claim 14, Wherein said bond is formed by sintering or by glass, glass-ceramic, or ceramic bonding. The method of claim 14, The inorganic fiber is a porous substrate selected from Table 1 in Figure 6. The method of claim 14, The inorganic fiber is a mullite fiber. The method of claim 14, The inorganic binder comprises a colloidal sol. The method of claim 14, The inorganic binder comprises tetraethoxysilane (TEOS). The method of claim 14, The inorganic binder includes colloidal silica. The method of claim 14, A portion of the bond formed between overlapped inorganic fibers in contact with each other. The method of claim 14, A portion of the bond formed between overlapping inorganic fibers not in contact with each other. The method of claim 14, The inorganic fiber is a metal fiber, a metal alloy or a ceramic fiber. The method of claim 14, The extrudable mixture further comprises an organic fiber. An extruded honeycomb substrate composed of inorganically bonded ceramic fibers. The method of claim 27, The inorganic bond is a crystalline, amorphous or glass bond between overlapping ceramic fibers. The method of claim 27, The porous substrate further comprises an injection and discharge channel parallel to the honeycomb pattern. An extruded honeycomb substrate comprising a glass bonded mullite fiber. An extruded substrate comprising an inorganic bonded fiber; A housing supporting the substrate; And A filter product comprising an inlet for receiving a fluid and an outlet for providing a filtered fluid. The method of claim 31, wherein Said fluid is an exhaust gas or a liquid. The method of claim 31, wherein The filter product is a vehicle air filter, a vehicle exhaust filter or a vehicle cabin filter. The method of claim 31, wherein A filter product further comprising a catalyst disposed on the extruded substrate. An extruded substrate comprising an inorganically bonded fiber; A catalyst disposed on the extruded substrate; A housing holding the substrate; And A catalytic converter product comprising an inlet for receiving a fluid and an outlet for providing a filtered fluid. 36. The method of claim 35 wherein Said fluid is an exhaust gas or a liquid. 36. The method of claim 35 wherein Said filter product is a vehicle air filter, a vehicle exhaust filter or a vehicle cabin filter. 36. The method of claim 35 wherein A catalytic converter product further comprising a catalyst disposed on the extruded substrate. Homogeneously mix ceramic material fibers, organic binders, inorganic binders, pore formers and fluids, Extrude the homogeneous to the green substrate, Forming an inorganic bond between the ceramic material fibers. The method of claim 39, The inorganic binder is a method for producing a porous substrate is a precursor material for inorganic bonding. The method of claim 39, The inorganic binder is a colloidal porous substrate manufacturing method. The method of claim 39, The inorganic binder is a method of producing a porous substrate in the fumed (fumed) or fused (fused) form. The method of claim 39, The inorganic binder is a method for producing a porous substrate containing silica which is a precursor for inorganic bonding. The method of claim 39, Wherein said homogeneous comprises about 10-30% weight of ceramic material fiber. The method of claim 39, Wherein said homogeneous comprises about 5 to 60% of a pore former by weight. The method of claim 39, Wherein said homogeneous comprises about 5 to 20% by weight of an organic binder. The method of claim 39, Wherein said homogeneous comprises about 5-30% by weight of an inorganic binder. The method of claim 39, Wherein said homogeneous comprises about 10 to 30% by weight of fluid. The method of claim 39, wherein the homogeneity is, About 10% to 60% by weight of ceramic material fiber, Up to about 60% by weight of the pore former, Up to about 20% by weight organic binder, Up to about 30% by weight of an inorganic binder, A method of making a porous substrate comprising about 10% to 40% by weight of fluid. The method of claim 39, wherein the homogeneity is, About 10% to 60% by weight of the mullite fiber, About 5% to 60% by weight of the pore formers selected from Table 3 in FIG. About 5% to 20% by weight of the organic binder, About 5% to 30% by weight of colloidal silica, A method of making a porous substrate comprising about 10% to 40% by weight of water. The method of claim 39, And some of the inorganic bonds are formed between overlapping ceramic fibers in contact with each other. The method of claim 39, And some of the inorganic bonds are formed between overlapping ceramic fibers that are not in contact with each other. The method of claim 39, Wherein some of the overlapped fibers are unbonded porous substrate. The method of claim 39, A method of manufacturing a porous substrate comprising sintering the green substrate through the forming step. The method of claim 54, The sintering method of forming a porous substrate by forming a bond between the overlapping ceramic fibers to form a porous substrate. The method of claim 54, The inorganic bond is a glass, glass-ceramic, amorphous or ceramic bond. The method of claim 54, Wherein said inorganic bond comprises a meniscus attachment to a fiber. The method of claim 39, And substantially combusting all of the fluid, the pore former, and the organic binder. The method of claim 39, Forming a bond to the ceramic fiber to produce a porous pore tissue comprising a. Choose the fiber from Table 1 of Figures 6A and 6B, In Table 2 of Figure 6c is selected an inorganic binder, Select a fluid from Table 4 of FIG. Homogeneously mix the fiber, the inorganic binder and the fluid, By adjusting the fluidity of the homogeneous to form an extrudable homogeneous, Extrude the homogeneous to the green substrate, A method of manufacturing a porous substrate comprising forming an inorganic bond between the fibers. The method of claim 60, Selecting an additive selected from pore formers, reinforcing agents, milking agents, extrusion aids, dispersants, pH modifiers, organic binders, clays, washcoat materials, and catalysts, The method of manufacturing a porous substrate further comprising mixing the additive in the homogeneous. The method of claim 60, The extruding further comprises extrusion molding the honeycomb substrate. In the process of curing the green substrate with a porous block containing at least one channel, Remove the fluid from the green substrate, Burning organic materials, Form an inorganic bond to connect the overlapping fibers, Wherein the at least one channel comprises providing an inlet to the porous block. The method of claim 63, wherein Wherein said inorganic bond is a glass, glass-ceramic, amorphous or ceramic bond. The method of claim 63, wherein Curing the inorganic material to form an inorganic bond. The method of claim 63, wherein And curing the inorganic material between the overlapping fibers. The method of claim 63, wherein And curing the inorganic material around the overlapping fibers. The method of claim 63, wherein Coupling the fibers comprises forming an inorganic meniscus. In the process of curing the green substrate with a porous block including a channel, Remove the fluid from the green substrate, Burning organic materials, Form a weapon bond to connect the overlapping fibers, During the forming process, comprising maintaining the structural integrity of the channel. The method of claim 69, wherein Wherein said inorganic bond is a glass, glass-ceramic, amorphous or ceramic bond. The method of claim 69, wherein Curing the inorganic material to form an inorganic bond. The method of claim 69, wherein And curing the inorganic material between the overlapping fibers. The method of claim 69, wherein And curing the inorganic material around the overlapping fibers. The method of claim 69, wherein Joining the fibers comprises forming an inorganic meniscus. Homogeneously mix ceramic material fibers, organic binders, inorganic binders and fluids, Extrude the homogeneous to the green substrate, A method of manufacturing a porous substrate comprising forming an inorganic bond between the ceramic fibers. 76. The method of claim 75, The inorganic binder is a method for producing a porous substrate is a precursor for inorganic bonding. 76. The method of claim 75, The inorganic binder is a colloidal porous substrate manufacturing method. 76. The method of claim 75, The inorganic binder is a method for producing a porous substrate in the fumed or molten form. 76. The method of claim 75, The inorganic binder is a method of manufacturing a porous substrate comprising silica which is a precursor material for inorganic bonding.

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