JP4167814B2 - Ceramic filter assembly - Google Patents

Description

従って、本実施形態によれば以下のような効果を得ることができる。
【００８１】
（１）本実施形態では、フィルタ接着構造物の外周面に形成された第２層１６の熱伝導率のほうが、複数のフィルタＦ１の外周面同士を接着する第１層１５の熱伝導率よりも小さくなっている。つまり、第２層１６のほうが第1層１５に比べて相対的に熱抵抗が大きいことになる。ゆえに、従来のものに比べて、フィルタ接着構造物Ｍの外周面９ｃから外部に熱が脱げにくい構造となり、集合体９の当該部分における断熱性が向上する。よって、熱のロスが少なくなり、効率のよい再生を行うことができる。
【００８２】
（２）本実施形態では、第１層１５の熱伝導率に対する第２層１６の熱伝導率の比を０．１〜０．８という好適範囲内にて設定している。従って、第２層１６に必要とされる性能（即ち断熱性、接着性、耐熱性等）が確実に保持されるとともに、セラミックフィルタ集合体９の製造困難化も防止される。
【００８３】
（３）本実施形態では、第１層１５及び第２層１６の熱伝導率を上記好適範囲内にて設定している。このため、第１層１５に必要とされる性能（即ち弾性、接着性、耐熱性等）及び第２層１６に必要とされる性能（即ち断熱性、接着性、耐熱性等）が確実に保持される。それとともに、セラミックフィルタ集合体９の製造困難化も防止される。
【００８４】
（４）本実施形態では、第２層１６は第１層１５よりも厚くなるように形成されている。このため、熱の伝わる距離が長くなり、フィルタ接着構造物Ｍの外周面９ｃから外部に熱がよりいっそう脱げにくい構造となる。従って、再生効率のさらなる向上が図られる。
【００８５】
また、フィルタ接着構造物Ｍの外周面９ｃにある凹凸１７が第２層１６によって埋められることにより、外周面９ｃがフラットな状態になっている。このように凹凸解消が図られる結果、集合体９の収容時にその外周面９ｃに隙間ができにくくなり、その隙間を介した排気ガスのリークが防止される。以上の結果、排気ガスの処理効率に優れたセラミックフィルタ集合体９、ひいては排気ガスの処理効率に優れた排気ガス浄化装置１を実現することができる。
【００８６】
（５）本実施形態では、第１層１５及び第２層１６は、ともに組成中にセラミックファイバを含有しているため、耐熱性に優れたものとなっている。また、第２層１６におけるファイバ含有量は第１層１５におけるファイバ含有量よりも多くなっている。このため、第２層１６のほうが相対的に熱抵抗が大きく、熱が伝わりにくくなっている。
【００８７】
なお、本発明の実施形態は以下のように変更してもよい。
・ フィルタＦ１の組み合わせ数は、前記実施形態のように１６個でなくてもよく、任意の数にすることが可能である。この場合、サイズ・形状等の異なるフィルタＦ１を適宜組み合わせて使用することも勿論可能である。
【００８８】
・ フィルタＦ１は前記実施形態にて示したようなハニカム状構造を有するもののみに限られず、例えば三次元網目構造、フォーム状構造、ヌードル状構造、ファイバ状構造等であってもよい。
【００８９】
・ 外形カット工程前におけるフィルタＦ１の形状は、実施形態のような四角柱状に限定されることはなく、三角柱状や六角柱状等であっても構わない。また、外形カット工程によって集合体９の全体形状を断面円形状に加工するのみならず、例えば断面楕円形状等に加工してもよい。
【００９０】
・ 実施形態においては、本発明のセラミックフィルタ集合体を、ディーゼルエンジン２に取り付けられる排気ガス浄化装置用フィルタとして具体化していた。勿論、本発明のセラミックフィルタ集合体は、排気ガス浄化装置用フィルタ以外のものとして具体化されることができ、例えば熱交換器用部材、高温流体や高温蒸気のための濾過フィルタ等として具体化されることができる。
【００９１】
次に、特許請求の範囲に記載された技術的思想のほかに、前述した実施形態によって把握される技術的思想を以下に列挙する。
（１） 請求項１乃至６のいずれか１項において、前記第１層は固形分で３重量％〜８０重量％の無機粒子を含有するとともに、前記第２層は固形分で０重量％〜２．９重量％の無機粒子を含有すること。
【００９２】
（２） 請求項１乃至６、技術的思想１のいずれか１つにおいて、前記第１層及び第２層は同種の無機繊維を用いて形成されていること。従って、この技術的思想２に記載の発明によれば、第１層と第２層との境界部分の接合強度を向上できる。
【００９３】
【発明の効果】
以上詳述したように、請求項１〜６に記載の発明によれば、フィルタ接着構造物の外周面から外部に熱が脱げにくく、効率のよい再生を行うことが可能なセラミックフィルタ集合体を提供することができる。
【図面の簡単な説明】
【図１】本発明を具体化した一実施形態の排気ガス浄化装置の全体概略図。
【図２】実施形態のセラミックフィルタ集合体の正面図。
【図３】実施形態の排気ガス浄化装置の要部拡大断面図。
【図４】（ａ）〜（ｃ）はセラミックフィルタ集合体の製造手順を説明するための概略斜視図。
【符号の説明】
９…セラミックフィルタ集合体、９ｃ…外周面、１５…第１層、１６…第２層、Ｆ１…フィルタ、Ｍ…（フィルタ接着）構造物。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ceramic filter assembly having a structure in which a plurality of filters made of a ceramic sintered body are bonded and integrated.
[0002]
[Prior art]
The number of automobiles has increased dramatically since the 20th century, and the amount of exhaust gas emitted from the internal combustion engine of the automobile has been increasing rapidly in proportion thereto. In particular, various substances contained in exhaust gas emitted from a diesel engine cause pollution, and are now having a serious impact on the world environment. Recently, research results have reported that particulates (diesel particulates) in exhaust gas sometimes cause allergic disorders and a decrease in the number of sperm. In other words, taking measures to remove particulates in exhaust gas is considered an urgent issue for humanity.
[0003]
Under such circumstances, various types of exhaust gas purification apparatuses have been proposed. A general exhaust gas purifying apparatus has a structure in which a casing is provided in the middle of an exhaust pipe connected to an exhaust manifold of an engine, and a filter having fine holes is disposed therein. As a material for forming the filter, there are ceramics in addition to metals and alloys. As a typical example of a filter made of ceramic, a honeycomb filter made of cordierite is known. Recently, there are advantages such as high heat resistance, mechanical strength, high collection efficiency, chemical stability, low pressure loss, etc., so use porous silicon carbide sintered body as a filter forming material. There are many.
[0004]
The honeycomb filter has a large number of cells extending along its own axial direction. As the exhaust gas passes through the filter, particulates are trapped by the cell walls. As a result, fine particles are removed from the exhaust gas.
[0005]
However, a honeycomb filter made of a porous silicon carbide sintered body is vulnerable to thermal shock. Therefore, the larger the size is, the easier the cracks are generated in the filter. Therefore, as a means for avoiding breakage due to cracks, a technique has recently been proposed in which a plurality of small filter pieces are integrated to produce one large ceramic filter assembly.
[0006]
A general method for manufacturing the above-described assembly will be briefly introduced. First, a rectangular column-shaped honeycomb formed body is formed by continuously extruding a ceramic raw material through a mold of an extruder. After the honeycomb formed body is cut into equal lengths, the cut piece is fired to obtain a filter. After the firing step, the outer peripheral surfaces of the filters are bonded to each other via a ceramic sealing material layer having a thickness of 1 mm to 3 mm, thereby producing a structure in which a plurality of filters are bundled and integrated. And a ceramic layer is formed in the outer peripheral surface of this adhesion structure using the same ceramic material. As a result, a desired ceramic filter assembly is completed.
[0007]
A mat-like heat insulating material made of ceramic fiber or the like is wound around the outer peripheral surface of the ceramic filter assembly. In this state, the assembly is accommodated in a casing provided in the middle of the exhaust pipe.
[0008]
[Problems to be solved by the invention]
By the way, in the prior art, the same ceramic paste as that of the sealing material layer is used to form the ceramic layer on the outer peripheral surface of the filter bonded structure.
[0009]
However, the ceramic material used for forming the sealing material layer basically has a composition for the purpose of bonding the filters and reducing the thermal resistance between the bonded filters. Therefore, the ceramic material for forming the sealing material layer is applied as it is to the ceramic layer on the outer peripheral surface of the filter adhesive structure for the purpose of heat insulation (that is, for the purpose of increasing the thermal resistance). It is impossible. Therefore, in the prior art, heat is easily removed from the outer peripheral surface of the filter adhesive structure to the outside, and efficient regeneration cannot be performed.
[0010]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a ceramic filter assembly capable of efficiently regenerating the heat from the outer peripheral surface of the filter bonded structure and preventing the heat from being removed. There is to do.
[0011]
[Means for Solving the Problems]
In order to solve the above problem, in the invention according to claim 1, the outer periphery of the structure in which the outer peripheral surfaces of a plurality of filters made of a porous ceramic sintered body are bonded together through a first layer made of a ceramic material. On the faceAppliedA ceramic filter assembly in which a second layer made of a ceramic material is formed, wherein the thermal conductivity of the second layer is smaller than the thermal conductivity of the first layer. The gist.
[0012]
According to a second aspect of the present invention, in the first aspect, the ratio of the thermal conductivity of the second layer to the thermal conductivity of the first layer is 0.1 to 0.8.
According to a third aspect of the present invention, in the first aspect, the thermal conductivity of the first layer is 0.1 W / m · K to 10 W / m · K, and the thermal conductivity of the second layer is 0.00. It was assumed that it was 01 W / m · K to 8 W / m · K.
[0013]
According to a fourth aspect of the present invention, in any one of the first to third aspects, the second layer is formed to be thicker than the first layer.
A fifth aspect of the present invention is the method according to any one of the first to fourth aspects, wherein the first layer and the second layer both contain ceramic fibers in the composition, and the second layer contains fibers. The amount was greater than the fiber content in the first layer.
[0014]
  The invention described in claim 6By cutting the outer portion of the structure in which the outer peripheral surfaces of a plurality of honeycomb filters made of porous silicon carbide sintered bodies are bonded together via a ceramic first layer, the cross section is substantially circular or the cross section is substantially oval as a whole. A ceramic filter assembly in which a second layer made of a ceramic material formed on the outer peripheral surface produced by the outer shape cut is formed, wherein the second layer has a thermal conductivity of the first layer The gist of the ceramic filter assembly is that it is smaller than the thermal conductivity.
[0016]
The “action” of the present invention will be described below.
According to invention of Claim 1, 6, the heat conductivity of the 2nd layer formed in the outer peripheral surface of a filter adhesion structure is the heat conductivity of the 1st layer which adhere | attaches the outer peripheral surfaces of several filters. Is smaller than That is, the second layer has a relatively higher thermal resistance than the first layer. Therefore, compared with the conventional one, the structure is such that heat is not easily removed from the outer peripheral surface of the filter adhesive structure to the outside.
[0017]
According to the invention described in claim 2, the performance required for the second layer is ensured by setting the ratio of the thermal conductivity of the second layer to the thermal conductivity of the first layer within the preferred range. And the difficulty in manufacturing the ceramic filter assembly is also prevented.
[0018]
If the ratio is less than 0.1, it is preferable from the viewpoint of increasing thermal resistance, but the performance such as adhesion and heat resistance of the second layer may be impaired. Becomes difficult. On the other hand, if the ratio exceeds 0.8, the thermal resistance cannot be increased sufficiently, and the thermal conductivity is comparable to that of the first layer.
[0019]
According to the invention described in claim 3, by setting the thermal conductivity of the first layer and the second layer within the preferable range, the performance required for the first layer and the second layer is reliably maintained. In addition, the manufacturing difficulty of the ceramic filter assembly is also prevented.
[0020]
When the thermal conductivity of the first layer is less than 0.1 W / m · K, the first layer still has a large thermal resistance, and the thermal conduction between the filters is hindered. On the contrary, if it is intended to obtain a material having a thermal conductivity exceeding 10 W / m · K, the performance such as adhesiveness and heat resistance may be impaired, and if it is attempted to prevent this, the manufacturing becomes practically difficult.
[0021]
When the thermal conductivity of the second layer is less than 0.01 W / m · K, it is preferable from the viewpoint of increasing the thermal resistance, but the performance such as the adhesiveness and heat resistance of the second layer may be impaired. If it is going to prevent this, manufacture will become difficult effectively. On the other hand, when trying to obtain a material having a thermal conductivity exceeding 8 W / m · K, the performance such as adhesiveness and heat resistance may be impaired, which makes it difficult to manufacture.
[0022]
According to the invention described in claim 4, since the second layer is formed so as to be thicker than the first layer, the distance to which heat is transmitted becomes longer, and more heat is transmitted from the outer peripheral surface of the filter adhesive structure to the outside. The structure is even more difficult to remove. Further, for example, when there are some irregularities on the outer peripheral surface of the filter adhesive structure, the irregularities are also filled with the second layer. And as a result of eliminating unevenness in this way, the sealing performance is improved.
[0023]
According to invention of Claim 5, since both the 1st layer and the 2nd layer contain the ceramic fiber in the composition, both layers are excellent in heat resistance. Further, since the fiber content in the second layer is larger than the fiber content in the first layer, the second layer has a relatively higher thermal resistance and heat is less likely to be transmitted.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an exhaust gas purification apparatus 1 for a diesel engine according to an embodiment of the present invention will be described in detail with reference to FIGS.
[0025]
As shown in FIG. 1, this exhaust gas purification device 1 is a device for purifying exhaust gas discharged from a diesel engine 2 as an internal combustion engine. The diesel engine 2 includes a plurality of cylinders (not shown). Each cylinder is connected with a branch portion 4 of an exhaust manifold 3 made of a metal material. Each branch portion 4 is connected to one manifold body 5. Therefore, the exhaust gas discharged from each cylinder is concentrated in one place.
[0026]
A first exhaust pipe 6 and a second exhaust pipe 7 made of a metal material are disposed on the downstream side of the exhaust manifold 3. The upstream end of the first exhaust pipe 6 is connected to the manifold body 5. Between the 1st exhaust pipe 6 and the 2nd exhaust pipe 7, the cylindrical casing 8 which consists of a metal material is arrange | positioned. The upstream end of the casing 8 is connected to the downstream end of the first exhaust pipe 6, and the downstream end of the casing 8 is connected to the upstream end of the second exhaust pipe 7. It can also be understood that the casing 8 is disposed in the middle of the exhaust pipes 6 and 7. As a result, the internal regions of the first exhaust pipe 6, the casing 8, and the second exhaust pipe 7 communicate with each other, and the exhaust gas flows therethrough.
[0027]
As shown in FIG. 1, the casing 8 is formed so that the central portion thereof has a larger diameter than the exhaust pipes 6 and 7. Therefore, the inner area of the casing 8 is wider than the inner areas of the exhaust pipes 6 and 7. A ceramic filter assembly 9 is accommodated in the casing 8.
[0028]
A heat insulating material 10 is disposed between the outer peripheral surface of the assembly 9 and the inner peripheral surface of the casing 8. The heat insulating material 10 is a mat-like material formed including ceramic fibers, and the thickness thereof is several mm to several tens mm. The heat insulating material 10 preferably has a thermal expansibility. The term “thermal expansibility” as used herein means that it has a function of releasing thermal stress because it has an elastic structure. The reason is to minimize energy loss during regeneration by preventing heat from escaping from the outermost periphery of the assembly 9. In addition, the ceramic fiber is expanded by heat at the time of regeneration, thereby preventing the displacement of the ceramic filter assembly 9 caused by exhaust gas pressure or vibration due to running.
[0029]
Since the ceramic filter assembly 9 used in the present embodiment removes diesel particulates as described above, it is generally called a diesel particulate filter (DPF). As shown in FIGS. 2 and 3, the assembly 9 of the present embodiment is formed by bundling and integrating a plurality of filters F1. The filter F1 located in the central portion of the assembly 9 has a quadrangular prism shape, and its outer dimensions are 33 mm × 33 mm × 167 mm. Around the square columnar filter F1, a plurality of non-square columnar filters F1 are arranged. As a result, a cylindrical ceramic filter assembly 9 (diameter around 135 mm) is configured as a whole.
[0030]
These filters F1 are made of a porous silicon carbide sintered body which is a kind of ceramic sintered body. The reason for adopting the silicon carbide sintered body is that it has an advantage of being particularly excellent in heat resistance and thermal conductivity as compared with other ceramics. As a sintered body other than silicon carbide, for example, a sintered body such as silicon nitride, sialon, alumina, cordierite, and mullite can be selected.
[0031]
As shown in FIG. 3 and the like, these filters F1 are so-called honeycomb structures. The reason for adopting the honeycomb structure is that there is an advantage that the pressure loss is small even when the amount of collected fine particles is increased. In each filter F1, a plurality of through holes 12 having a substantially square cross section are regularly formed along the axial direction. Each through hole 12 is partitioned from each other by a thin cell wall 13. On the outer surface of the cell wall 13, an oxidation catalyst composed of a platinum group element (for example, Pt or the like), other metal elements and oxides thereof is supported. The opening of each through-hole 12 is sealed with a sealing body 14 (here, a porous silicon carbide sintered body) on either one of the end faces 9a and 9b side. Accordingly, the end faces 9a and 9b as a whole have a checkered pattern. As a result, a large number of cells having a square cross section are formed in the filter F1. The cell density is set to about 200 cells / inch, the thickness of the cell wall 13 is set to about 0.3 mm, and the cell pitch is set to about 1.8 mm. Of the many cells, about half of the cells open at the upstream end surface 9a, and the remaining cells open at the downstream end surface 9b.
[0032]
The average pore diameter of the filter F1 is preferably 1 μm to 50 μm, more preferably 5 μm to 20 μm. When the average pore diameter is less than 1 μm, clogging of the filter F1 due to accumulation of fine particles becomes significant. On the other hand, if the average pore diameter exceeds 50 μm, fine particles cannot be collected, and the collection efficiency is lowered.
[0033]
The porosity of the filter F1 is preferably 30% to 70%, more preferably 40% to 60%. If the porosity is less than 30%, the filter F1 becomes too dense, and there is a possibility that the exhaust gas cannot be circulated inside. On the other hand, if the porosity exceeds 70%, the filter F1 has too many voids, so that the strength becomes weak and the collection efficiency of fine particles may be reduced.
[0034]
As shown in FIGS. 2 and 3, a total of 16 filters F1 are bonded to each other via a first layer 15 whose outer peripheral surfaces are made of a ceramic material. Further, a second layer 16 made of a ceramic material is formed on the outer peripheral surface 9 c of the ceramic filter assembly 9.
[0035]
Both the first layer 15 and the second layer 16 contain inorganic fibers, specifically ceramic fibers, in the composition. The reason for selecting the ceramic fiber is that since the ceramic fiber is excellent in heat resistance, suitable heat resistance is imparted to the first layer 15 and the second layer 16. Examples of the ceramic fiber include at least one selected from silica-alumina fiber, mullite fiber, alumina fiber, and silica fiber. Among these, it is particularly desirable to select silica-alumina fiber. This is because the silica-alumina fiber has excellent elasticity and absorbs thermal stress. In addition, it is preferable that the 1st layer 15 and the 2nd layer 16 are formed using the same kind of ceramic fiber. That is, when the same kind of ceramic fiber is used, the bonding strength at the boundary between the first layer 15 and the second layer 16 is improved.
[0036]
The fiber content in the second layer 16 is preferably greater than the fiber content in the first layer 15. By doing so, it is possible to relatively increase the thermal resistance of the second layer 16, and it becomes difficult for heat to be transmitted. Specifically, it is preferable that the fiber content in the second layer 16 is 20 wt% to 90 wt% in solid content, and the fiber content in the first layer 15 is 10 wt% to 40 wt% in solid content.
[0037]
The shot content in the ceramic fiber is 1 wt% to 10 wt%, preferably 1 wt% to 5 wt%, more preferably 1 wt% to 3 wt%. This is because it is difficult to make the shot content less than 1% by weight. On the other hand, if the shot content exceeds 50% by weight, the outer peripheral surface of the filter F1 is damaged.
[0038]
The fiber length of the ceramic fiber is 10 μm to 3000 μm, preferably 10 μm to 1500 μm, more preferably 10 μm to 500 μm. This is because the elastic structure cannot be formed when the fiber length is less than 10 μm. This is because if the fiber length exceeds 3000 μm, the fiber becomes like a pill and the dispersibility deteriorates.
[0039]
The first layer 15 and the second layer 16 include at least one selected from an inorganic binder and an organic binder in addition to the inorganic fibers.
As the inorganic binder, at least one colloidal sol selected from silica sol and alumina sol is desirable. Among these, it is desirable to select silica sol. The reason is that silica sol is easy to obtain and can be easily baked to make SiO₂Therefore, it is suitable for the filter F1 exposed to high temperature. Moreover, silica sol is excellent in insulation. In this case, the content of the colloidal sol is preferably set to 1% by weight to 40% by weight in terms of solid content.
[0040]
The organic binder is preferably a hydrophilic organic polymer, more preferably at least one polysaccharide selected from polyvinyl alcohol, methyl cellulose, ethyl cellulose, and carbomethoxy cellulose. Among these, it is desirable to select carboxymethyl cellulose in particular. The reason for this is that carboxymethylcellulose exhibits excellent adhesiveness in the normal temperature region because it contributes to imparting suitable fluidity.
[0041]
The first layer 15 and the second layer 16 may further contain inorganic particles.
Suitable inorganic particles for the first layer 15 include an elastic material using at least one inorganic powder or whisker selected from silicon carbide, silicon nitride, and boron nitride. This is because such carbides and nitrides have a very high thermal conductivity and contribute to the improvement of the thermal conductivity by interposing on the surface of the ceramic fiber and the surface of the colloidal sol and the inside thereof. Among the carbide and nitride inorganic particles, it is particularly preferable to select silicon carbide powder. The reason is that silicon carbide has a property of being easily compatible with ceramic fibers in addition to extremely high thermal conductivity. In addition, in the present embodiment, the filter F1, which is a sealed object, is the same type, that is, made of porous silicon carbide.
[0042]
The content of the inorganic particles in the first layer 15 is 3% by weight to 80% by weight, preferably 10% by weight to 60% by weight, and more preferably 20% by weight to 40% by weight in terms of solid content. This is because if the content is less than 3% by weight, the thermal conductivity of the first layer 15 is lowered. On the other hand, if the content exceeds 80% by weight, the adhesive strength decreases at high temperatures.
[0043]
The particle size of the inorganic particles in the first layer 15 is 0.01 μm to 100 μm, preferably 0.1 μm to 15 μm, more preferably 0.1 μm to 10 μm. This is because if the particle size exceeds 100 μm, the adhesive force and the thermal conductivity are reduced. Conversely, if the particle size is less than 0.01 μm, the cost of the sealing material will increase.
[0044]
On the other hand, the content of the inorganic particles in the second layer 16 is preferably set to be smaller than the content of the inorganic particles in the first layer 15, specifically, 0 wt% to 2.9 wt% in solid content. % Is preferably included. That is, inorganic particles are not necessarily contained in the second layer 16. If the content of inorganic particles such as silicon carbide powder is increased, it is preferable from the viewpoint of improving heat resistance, but it is disadvantageous from the viewpoint of reducing thermal conductivity.
[0045]
In the present embodiment, the heat conductivity of the second layer 16 is set to be smaller than the heat conductivity of the first layer 15 in order to make it difficult for heat to be removed from the outer peripheral surface of the filter adhesive structure. Has been.
[0046]
The ratio of the thermal conductivity of the second layer 16 to the thermal conductivity of the first layer 15 may be 0.1 to 0.8, and preferably 0.2 to 0.7. When the ratio is less than 0.1, it is preferable from the viewpoint of increasing the thermal resistance of the second layer 16, but the performance such as adhesion and heat resistance of the second layer 16 may be impaired. Therefore, if it is going to prevent this, manufacture will become difficult effectively. On the other hand, if the ratio exceeds 0.8, the second layer 16 will not have a sufficient increase in thermal resistance, resulting in a thermal conductivity comparable to that of the first layer 15.
[0047]
More specifically, the thermal conductivity of the first layer 15 is preferably 0.1 W / m · K to 10 W / m · K, and the thermal conductivity of the second layer 16 is 0.01 W / m · K. It is good that it is K-8W / m * K.
[0048]
If the thermal conductivity of the first layer 15 is less than 0.1 W / m · K, the first layer 15 still has a large thermal resistance, and the thermal conduction between the filters F1 is hindered. Conversely, when trying to obtain a material having a thermal conductivity exceeding 10 W / m · K, the performance such as adhesion and heat resistance may be impaired. And if it is going to prevent this, the freedom degree of material and a mixing condition will become small, and manufacture will become difficult effectively.
[0049]
When the thermal conductivity of the second layer 16 is less than 0.01 W / m · K, it is preferable from the viewpoint of increasing the thermal resistance, but there is a risk that the performance of the second layer 16 such as adhesiveness and heat resistance may be impaired. is there. And if it is going to prevent this, the freedom degree of material and a mixing condition will become small, and manufacture will become difficult effectively. On the other hand, when trying to obtain a material having a thermal conductivity exceeding 8 W / m · K, the performance such as adhesiveness and heat resistance may be impaired, which makes it difficult to manufacture.
[0050]
The second layer 16 is preferably formed to be thicker than the first layer 15.
This is because the heat transfer distance of the second layer 16 is longer than that of the first layer 15, and the heat is more difficult to remove from the outer peripheral surface 9 c of the filter adhesive structure M to the outside. Further, when the outer peripheral surface 9 c of the filter bonded structure M has the unevenness 17, the unevenness 17 can also be filled with the second layer 16. And as a result of eliminating the unevenness | corrugation 17 in this way, a sealing performance improves.
[0051]
Specifically, the thickness of the second layer 16 is preferably 0.1 mm to 10 mm, more preferably 0.3 mm to 5 mm, and particularly preferably 0.5 mm to 2 mm. . If the second layer 16 is too thin, it will not be possible to ensure a sufficiently large heat transfer distance, and the unevenness 17 on the outer peripheral surface 9c cannot be completely filled, and there will still be a gap easily left there. Because. On the contrary, if the thickness of the second layer 16 exceeds 10 mm, it is difficult to form a uniform layer or the entire assembly 9 may be increased in diameter.
[0052]
The thickness of the first layer 15 is preferably 0.1 mm to 3 mm, and more preferably 0.3 mm to 1 mm. This is because, by forming the first layer 15 so as to be thinner than the second layer 16, it is possible to prevent a decrease in the filtration capacity and thermal conductivity of the aggregate 9 in advance.
[0053]
Next, a procedure for manufacturing the ceramic filter assembly 9 will be described with reference to FIG.
First, the ceramic raw material slurry used in the extrusion molding process, the sealing paste used in the end face sealing process, the first layer forming paste used in the filter bonding process, and the second layer forming paste used in the unevenness eliminating process Prepare in advance.
[0054]
As the ceramic raw material slurry, a mixture obtained by kneading a silicon carbide powder with an organic binder and water in predetermined amounts and kneading them is used. As the sealing paste, a silicon carbide powder blended with an organic binder, a lubricant, a plasticizer and water and kneaded is used. As the first layer forming paste, a paste obtained by blending and kneading a predetermined amount of inorganic fibers, an inorganic binder, an organic binder, inorganic particles, and water is used. As the paste for forming the second layer, a paste in which inorganic fibers, an inorganic binder, an organic binder, inorganic particles and water are blended in predetermined amounts and kneaded is used. As described above, the inorganic particles may be omitted from the second layer forming paste.
[0055]
Next, the ceramic raw material slurry is put into an extruder and continuously extruded through a mold. Thereafter, the extruded honeycomb formed body is cut into equal lengths to obtain a rectangular pillar-shaped honeycomb formed body cut piece. Further, a predetermined amount of sealing paste is filled into one side opening of each cell of the cut piece, and both end faces of each cut piece are sealed.
[0056]
Subsequently, the main firing is performed by setting the temperature, time, and the like to predetermined conditions, and the honeycomb formed body cut piece and the sealing body 14 are completely sintered. The filter F1 made of a porous silicon carbide sintered body thus obtained is still all in a quadrangular prism shape at this point.
[0057]
In this embodiment, the firing temperature is set to 2100 ° C. to 2300 ° C. in order to set the average pore diameter to 6 μm to 15 μm and the porosity to 35% to 50%. Moreover, the firing time is set to 0.1 hours to 5 hours. Moreover, the atmosphere in the furnace at the time of baking is made into an inert atmosphere, and the pressure of the atmosphere at that time is made into a normal pressure.
[0058]
Next, if necessary, a base layer made of a ceramic material is formed on the outer peripheral surface of the filter F1, and then a first layer forming paste is applied thereon. Then, 16 such filters F1 are used and their outer peripheral surfaces are bonded together to be integrated. At this time, as shown in FIG. 4A, the filter adhesive structure M as a whole has a square cross section.
[0059]
In the subsequent outer shape cutting step, the filter bonding structure M having a square cross section obtained through the filter bonding step is ground, and unnecessary portions on the outer peripheral portion are removed to adjust the outer shape. As a result, as shown in FIG. 4B, a filter bonded structure M having a circular cross section is obtained. Note that the cell wall 13 is partially exposed on the surface newly exposed by the outer shape cut, and as a result, irregularities 17 are formed on the outer peripheral surface 9c. The unevenness 17 that can be formed in the present embodiment is about 0.5 mm to 1 mm, and includes protrusions and grooves extending along the axial direction of the filter bonded structure M (that is, the longitudinal direction of the filter F1).
[0060]
In the subsequent unevenness eliminating step, the second layer forming paste is uniformly applied on the outer peripheral surface 9c of the filter adhesive structure M, and the second layer 16 is formed. As a result, the ceramic filter assembly 9 shown in FIG. 4C is completed.
[0061]
Next, the particulate trap action by the ceramic filter assembly 9 will be briefly described.
Exhaust gas is supplied to the ceramic filter assembly 9 housed in the casing 8 from the upstream end face 9a side. The exhaust gas supplied through the first exhaust pipe 6 first flows into a cell opened at the upstream end face 9a. Next, the exhaust gas passes through the cell wall 13 and reaches the inside of the cell adjacent to the cell wall 13, that is, the cell opened at the downstream end face 9b. Then, the exhaust gas flows out from the downstream end face 9b of the filter F1 through the opening of the cell. However, the fine particles contained in the exhaust gas cannot pass through the cell wall 13 and are trapped there. As a result, the purified exhaust gas is discharged from the downstream end face 9b of the filter F1. The purified exhaust gas further passes through the second exhaust pipe 7 and is finally released into the atmosphere. When fine particles accumulate to some extent, a heater (not shown) is turned on to heat the assembly 9 and burn and remove the fine particles. As a result, the aggregate 9 is regenerated and the particles can be captured again.
[0062]
Next, some examples embodying the present embodiment and comparative examples for them will be introduced.
[0063]
[Examples and Comparative Examples]
Example 1
(1) Wet-mixing 51.5% by weight of α-type silicon carbide powder and 22% by weight of β-type silicon carbide powder, and adding 6.5% by weight and 20% of organic binder (methyl cellulose) and water to the resulting mixture, respectively. It added and knead | mixed by weight%. Next, by adding a small amount of a plasticizer and a lubricant to the kneaded product and further kneading, extrusion-molding was performed to obtain a honeycomb-shaped formed shape.
[0064]
(2) Next, this generated shaped body was dried using a microwave dryer, and then the through hole 12 of the molded body was sealed with a sealing paste made of a porous silicon carbide sintered body. Next, the sealing paste was dried again using a dryer. Following the end face sealing step, the dried body was degreased at 400 ° C., and then further baked at 2200 ° C. for about 3 hours in an atmospheric argon atmosphere. As a result, a porous and honeycomb-like silicon carbide filter F1 was obtained.
[0065]
(3) Ceramic fiber (alumina silicate ceramic fiber, shot content 3%, fiber length 10 μm to 3000 μm) 23.3% by weight, silicon carbide powder having an average particle size of 0.3 μm 30.2% by weight, as an inorganic binder Silica sol (Sol SiO₂The equivalent amount was 30%) and 7% by weight, 0.5% by weight of carboxymethyl cellulose as an organic binder and 39% by weight of water were mixed and kneaded. By adjusting the kneaded product to an appropriate viscosity, a paste used for forming the first layer 15 was produced.
[0066]
Further, ceramic fiber (alumina silicate ceramic fiber, shot content 3%, fiber length 0.1 mm to 100 mm) 53.3% by weight, silicon carbide powder having an average particle size of 0.3 μm, 10.2% by weight, as an inorganic binder Silica sol (sol SiO₂The equivalent amount was 30%) and 7% by weight, 0.5% by weight of carboxymethyl cellulose as an organic binder and 39% by weight of water were mixed and kneaded. By adjusting the kneaded product to an appropriate viscosity, a paste used for forming the second layer 16 was produced.
[0067]
(4) Next, the first layer forming paste is uniformly applied to the outer peripheral surface of the filter F1, and the outer peripheral surfaces of the filter F1 are in close contact with each other, and the conditions are 50 ° C. to 100 ° C. × 1 hour. Dried and cured. As a result, the filters F1 were bonded together via the first layer 15. Here, the thickness of the first layer 15 after drying was set to 1.0 mm.
[0068]
(5) Next, a filter adhesive structure M having a circular cross section was prepared by performing an outer shape cut to adjust the outer shape, and then the second layer paste was uniformly applied to the exposed outer peripheral surface 9c. Then, the second layer 16 having a thickness of 1.0 mm was formed by drying and curing under conditions of 50 ° C. to 150 ° C. × 1 hour, and finally the ceramic filter assembly 9 of Example 1 was completed.
[0069]
The aggregate 9 obtained as described above was measured for the thermal conductivity (W / m · K) of the first layer 15 and the second layer 16 by a conventionally known method. As shown in Table 1. And 0.85 W / m · K and 0.22 W / m · K, respectively.
[0070]
Further, when the various portions of the aggregate 9 were observed with the naked eye, the unevenness 17 of the outer peripheral surface 9c was almost completely filled with the second layer 16, and the outer peripheral surface 9c was in a flat state. In addition, no cracks occurred in any of the boundary portion between the second layer 16 and the filter F1 and the boundary portion between the second layer 16 and the first layer 15. Therefore, it was suggested that high adhesion and sealability were secured at these boundary portions. Of course, no cracks or chips were found in the second layer 16 itself.
[0071]
Subsequently, the thermocouples were embedded in the central portion and the outer peripheral portion of the assembly 9, and then the heat insulating material 10 was wrapped around the casing 8 and accommodated in the casing 8. When exhaust gas was actually supplied in this state, it was found that the exhaust gas did not leak downstream through the gap on the outer peripheral surface 9c.
[0072]
Further, after a predetermined time had elapsed, the heater was heated for regeneration, and the maximum achieved temperatures Ta and Tb (° C.) during regeneration were measured by the thermocouple. Table 1 shows the results of calculating the temperature difference (ΔT = | Ta−Tb | (° C.)).
[0073]
According to Table 1, the temperature difference ΔT was 50 ° C., which was not so large. Therefore, a result suggesting that the structure is such that heat is not easily removed from the outer peripheral surface 9c of the filter bonded structure M to the outside.
[0074]
After completion of the regeneration, the assembly 9 was removed, the assembly 9 was cut along the axial direction, and the cut surface was observed with the naked eye. As a result, no burning residue was observed in the central portion or the outer peripheral portion. Therefore, it was demonstrated that efficient regeneration was performed.
(Examples 2 to 5)
In Examples 2 to 5, the assembly 9 is basically produced in accordance with the method of Example 1, and the thickness and thermal conductivity of the first layer 15 and the second layer 16 are changed as shown in Table 1. did. For those having different thermal conductivities, specifically, the paste of the first layer 15 or the second layer 16 is made by using a paste in which the blending amount of alumina silicate ceramic fiber, silicon carbide powder, silica sol, carboxymethyl cellulose is slightly changed. Formation was performed. Only about Example 5, the 2nd layer 16 was formed using the paste which does not contain the silicon carbide powder which is an inorganic particle at all.
[0075]
When each place of the obtained aggregates 9 was observed with the naked eye, the unevenness 17 of the outer peripheral surface 9c was almost completely filled with the second layer 16, and the outer peripheral surface 9c was in a flat state. In addition, no cracks occurred in any of the boundary portion between the second layer 16 and the filter F1 and the boundary portion between the second layer 16 and the first layer 15. Therefore, it was suggested that high adhesion and sealability were secured at these boundary portions. Of course, no cracks or chips were found in the second layer 16 itself.
[0076]
Then, about Example 2-5, the reproduction | regeneration state quality determination test similar to Example 1 was done, and temperature difference (DELTA) T (degreeC) was calculated | required, respectively. The results are also shown in Table 1. According to this, it was found that substantially the same results as in Example 1 were obtained in Examples 2 to 5. Further, when visual observation of the cut surface of the assembly 9 was performed after completion of the regeneration, no unburned residue was observed in the central portion or the outer peripheral portion.
(Comparative example)
In the comparative example, both the first layer 15 and the second layer 16 were formed using the first layer forming paste. The ceramic filter assembly 9 was manufactured in the same manner as in Example 1 for the other matters. The thickness and thermal conductivity are as shown in Table 1.
[0077]
When each place of the obtained assembly 9 of the comparative example was observed with the naked eye, the unevenness 17 of the outer peripheral surface 9c was almost completely filled with the second layer 16, and the outer peripheral surface 9c was in a flat state. In addition, no cracks occurred in any of the boundary portion between the second layer 16 and the filter F1 and the boundary portion between the second layer 16 and the first layer 15.
[0078]
Subsequently, for the comparative example, a reproduction state pass / fail judgment test similar to that of Example 1 was performed to obtain a temperature difference ΔT (° C.). The results are also shown in Table 1. According to this, it was found that in the comparative example, the value of the temperature difference ΔT (° C.) is larger than the values of the respective examples due to the lowering of the maximum temperature Tb (° C.) at the outer peripheral portion. Therefore, a result suggesting that the structure is such that heat is easily removed from the outer peripheral surface 9c of the filter bonded structure M to the outside.
[0079]
When the cut surface of the assembly 9 was visually observed after the completion of regeneration, it was found that unburned residue was observed on the outer periphery, and that the regeneration efficiency was clearly inferior to each of Examples 1-5. For this reason, in the comparative example, it was necessary to set the regeneration time longer or set the heater heating temperature higher in order to prevent unburned residue.
[0080]
[Table 1]

Therefore, according to the present embodiment, the following effects can be obtained.
[0081]
(1) In this embodiment, the thermal conductivity of the second layer 16 formed on the outer peripheral surface of the filter adhesive structure is more than the thermal conductivity of the first layer 15 that bonds the outer peripheral surfaces of the plurality of filters F1. Is also getting smaller. That is, the second layer 16 has a relatively higher thermal resistance than the first layer 15. Therefore, compared with the conventional one, the structure is such that the heat is less likely to be removed from the outer peripheral surface 9c of the filter bonded structure M, and the heat insulation in the portion of the assembly 9 is improved. Therefore, heat loss is reduced and efficient regeneration can be performed.
[0082]
(2) In this embodiment, the ratio of the thermal conductivity of the second layer 16 to the thermal conductivity of the first layer 15 is set within a preferred range of 0.1 to 0.8. Therefore, the performance required for the second layer 16 (that is, heat insulation, adhesiveness, heat resistance, etc.) is reliably maintained, and manufacturing difficulty of the ceramic filter assembly 9 is also prevented.
[0083]
(3) In the present embodiment, the thermal conductivity of the first layer 15 and the second layer 16 is set within the preferred range. Therefore, the performance required for the first layer 15 (ie, elasticity, adhesiveness, heat resistance, etc.) and the performance required for the second layer 16 (ie, heat insulation, adhesiveness, heat resistance, etc.) are ensured. Retained. At the same time, difficulty in manufacturing the ceramic filter assembly 9 is also prevented.
[0084]
(4) In the present embodiment, the second layer 16 is formed to be thicker than the first layer 15. For this reason, the distance to which heat is transmitted becomes long, and the structure is such that heat is more difficult to remove from the outer peripheral surface 9c of the filter bonded structure M to the outside. Therefore, the reproduction efficiency can be further improved.
[0085]
Moreover, the unevenness | corrugation 17 in the outer peripheral surface 9c of the filter adhesion structure M is filled with the 2nd layer 16, Therefore The outer peripheral surface 9c is in the flat state. As a result of the elimination of the unevenness as described above, it becomes difficult to form a gap in the outer peripheral surface 9c when the assembly 9 is accommodated, and the leakage of the exhaust gas through the gap is prevented. As a result, it is possible to realize the ceramic filter assembly 9 excellent in exhaust gas processing efficiency, and thus the exhaust gas purification device 1 excellent in exhaust gas processing efficiency.
[0086]
(5) In this embodiment, since both the first layer 15 and the second layer 16 contain ceramic fibers in the composition, they are excellent in heat resistance. Further, the fiber content in the second layer 16 is larger than the fiber content in the first layer 15. For this reason, the second layer 16 has a relatively higher thermal resistance and is less likely to transmit heat.
[0087]
In addition, you may change embodiment of this invention as follows.
The number of combinations of the filters F1 does not have to be 16 as in the above-described embodiment, and can be any number. In this case, it is of course possible to use a combination of filters F1 having different sizes and shapes as appropriate.
[0088]
The filter F1 is not limited to the one having the honeycomb structure as shown in the above embodiment, and may be a three-dimensional network structure, a foam structure, a noodle structure, a fiber structure, or the like.
[0089]
The shape of the filter F1 before the outer shape cutting step is not limited to the quadrangular prism shape as in the embodiment, and may be a triangular prism shape, a hexagonal prism shape, or the like. Further, not only the entire shape of the assembly 9 is processed into a circular cross-section by the outer shape cutting process, but it may be processed into an elliptical cross-section, for example.
[0090]
In the embodiment, the ceramic filter assembly of the present invention is embodied as a filter for an exhaust gas purification device attached to the diesel engine 2. Of course, the ceramic filter assembly of the present invention can be embodied as other than a filter for an exhaust gas purification device, for example, a heat exchanger member, a filtration filter for high temperature fluid or high temperature steam, or the like. Can.
[0091]
Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the embodiment described above are listed below.
(1) In any one of Claims 1 thru | or 6, While the said 1st layer contains 3 to 80 weight% of inorganic particles by solid content, the said 2nd layer is 0 weight%-by solid content. Contain 2.9% by weight of inorganic particles.
[0092]
(2) In any one of claims 1 to 6 and technical idea 1, the first layer and the second layer are formed using the same kind of inorganic fibers. Therefore, according to the invention described in this technical idea 2, the bonding strength at the boundary between the first layer and the second layer can be improved.
[0093]
【The invention's effect】
As described above in detail, according to the inventions described in claims 1 to 6, the ceramic filter assembly capable of efficiently regenerating the heat is not easily removed from the outer peripheral surface of the filter adhesive structure. Can be provided.
[Brief description of the drawings]
FIG. 1 is an overall schematic view of an exhaust gas purifying apparatus according to an embodiment embodying the present invention.
FIG. 2 is a front view of the ceramic filter assembly of the embodiment.
FIG. 3 is an enlarged cross-sectional view of a main part of the exhaust gas purification device of the embodiment.
FIGS. 4A to 4C are schematic perspective views for explaining a manufacturing procedure of a ceramic filter assembly. FIGS.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 9 ... Ceramic filter aggregate | assembly, 9c ... Outer peripheral surface, 15 ... 1st layer, 16 ... 2nd layer, F1 ... Filter, M ... (filter adhesion | attachment) structure.

Claims (6)

Ceramic filter in which a second layer made of a ceramic material is formed by applying the outer peripheral surfaces of a plurality of filters made of a porous ceramic sintered body to each other through a first layer made of a ceramic material. A ceramic filter assembly, wherein the thermal conductivity of the second layer is smaller than the thermal conductivity of the first layer. 2. The ceramic filter assembly according to claim 1, wherein a ratio of the thermal conductivity of the second layer to the thermal conductivity of the first layer is 0.1 to 0.8. The thermal conductivity of the first layer is 0.1 W / m · K to 10 W / m · K, and the thermal conductivity of the second layer is 0.01 W / m · K to 8 W / m · K. The ceramic filter assembly according to claim 1. The ceramic filter assembly according to any one of claims 1 to 3, wherein the second layer is formed to be thicker than the first layer. The first layer and the second layer both contain ceramic fibers in the composition, and the fiber content in the second layer is greater than the fiber content in the first layer. The ceramic filter assembly according to any one of claims 1 to 4. By cutting the outer portion of the structure in which the outer peripheral surfaces of a plurality of honeycomb filters made of porous silicon carbide sintered bodies are bonded together via a ceramic first layer, the cross section is substantially circular or the cross section is substantially oval as a whole A ceramic filter assembly in which a second layer made of a ceramic material formed on a peripheral surface produced by the outer shape cut is formed, wherein the second layer has a thermal conductivity of the first layer. A ceramic filter assembly having a thermal conductivity smaller than that of the ceramic filter assembly.

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