JPH078727A - Collection material for exhaustion of diesel engine and production thereof - Google Patents

Abstract

PURPOSE:To provide a fine particle collection material for the exhaustion of a diesel engine low in pressure loss and high in collection efficiency. CONSTITUTION:A collection material for the exhaustion of a diesel engine is constituted of a three-dimensional porous structure composed of a hollow skeleton having fine pores and produced by making the parts forming the fine pores 2 of the surface of the skeleton 1 of the three-dimensional porous structure non-conductive and subsequently applying electroplating to the non-conductive parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel diesel engine exhaust trapping material having a three-dimensional porous structure having a hollow skeleton with fine pores and a method for producing the same.

[0002]

2. Description of the Related Art Exhaust gas from an automobile is one of the major causes of air pollution, and a technique for removing harmful components contained in the exhaust gas is extremely important. Particularly in diesel engine vehicles, the removal of soot-like fine particles (particulates) mainly composed of NOx and carbon is an important issue. In order to remove these harmful components, supercharging, improvement of the fuel injection system and improvement of the shape of the combustion chamber have been made, and efforts have been made on the engine side, but there is no definitive decisive factor and the aftertreatment Removal by is essential.

Among exhaust gas harmful components, fine particles consist of solid carbon and a soluble organic substance dissolved in an organic solvent, and it is considered that the method of collecting and removing them by a filter trap is the most practical. It is necessary for the trapping material of this filter trap to satisfy the following performances under the conditions of use. First, it is necessary to have a collection efficiency for fine particles that can satisfy the required cleanliness of exhaust gas. Secondly, the engine exhaust is exhausted through this trap, so that the ventilation pressure loss during exhaust gas flow must be small in order to prevent excessive back pressure on the engine. It is required that the initial pressure loss is small and that the pressure loss is hard to increase even if fine particles are trapped. Third, if particulates are collected and accumulated to a certain extent or more, the pressure loss when passing through the exhaust gas becomes large, and back pressure is applied to the engine, so trapped particulates are removed and regenerated to collect. Need to recover. As the method of this regeneration treatment, it is considered that the method of burning and removing fine particles by electric heating or burner heating is the most effective method. Therefore, the trapping material must withstand this recycling process.

At present, as the trapping material, the honeycomb porous body of cordierite ceramics is said to be the most practical material from the viewpoints of corrosion resistance against exhaust gas, heat resistance, trapping material performance and durability against regeneration. There is. However,
When cordierite ceramics is used as the trapping material, local temperature distribution tends to occur in the trapping material due to combustion of fine particles during regeneration, and in order to prevent cracking due to thermal stress, control of regeneration conditions is extremely important. There is a problem that it is difficult. In order to solve these problems, it has been proposed to use a three-dimensional network structure porous body made of a heat-resistant alloy as a collector (Japanese Patent Laid-Open No. 4-86313).
Issue).

[0005]

However, it is desired to further improve the performance of the three-dimensional network structure porous body made of this heat resistant alloy. The present invention has been completed by finding that these problems can be solved by imparting a novel microstructure in which fine pores are formed to the hollow skeleton of a porous body.

[0006]

That is, the present invention is a diesel engine exhaust trapping material characterized by using a three-dimensional porous structure comprising a hollow skeleton having fine pores, and a porous base material. The method for producing a diesel engine exhaust trapping material is characterized in that a portion of the skeleton surface of the porous structure that forms fine pores is made non-conductive and then electroplated. Furthermore, the three-dimensional porous structure is a heat-resistant alloy, which is a collector for a diesel engine exhaust.

The trapping material for diesel engine exhaust of the present invention will be described below. FIG. 1 is a diagram schematically showing a portion where the hollow skeletons of a three-dimensional porous structure constituting the trapping material for exhaust of a diesel engine of the present invention intersect. The hollow skeleton 1 has fine pores 2, and a continuous hollow portion 3 exists inside the skeleton, which communicates with the outside through the fine pores 2.

FIG. 2 shows the appearance of the diesel engine exhaust gas collecting material of the present invention having a three-dimensional mesh structure. There is a gap portion 5 surrounded by a hollow skeleton 1 having fine pores 2.

A heat-resistant alloy is preferred as the material forming the hollow skeleton of the diesel engine exhaust gas collecting material of the present invention. Especially nickel-chromium alloy, nickel-chromium-iron alloy,
An iron-chromium-aluminum alloy or an alloy obtained by adding a trace amount of a rare earth element such as aluminum, yttrium or cerium to these alloys is preferable. Further, it is also preferable to coat these alloys with a heat-resistant ceramic layer by a sol-gel method or the like. These materials have excellent heat resistance and high temperature corrosion resistance.

The smaller the size of the gap surrounded by the skeleton of the three-dimensional porous structure, the greater the collection efficiency but the pressure loss, and the larger the size, the smaller the pressure loss but the collection efficiency. . Therefore, the size of the gap surrounded by the skeleton is appropriately selected from the balance of increased collection efficiency and reduced pressure loss, but a range of about 0.1 to 0.5 mm is preferable.

The size of the fine pores of the skeleton is preferably several μm to several tens of μm from the viewpoint of improving the collection efficiency, but the size of the skeleton is also taken into consideration. When the size of the fine pores is close to the thickness of the skeleton, the strength may decrease, which is not preferable.
The shape of the micropores can be various shapes, but from the viewpoint of strength, a round shape such as a circle or an ellipse is preferable.

As a method for producing the diesel engine exhaust gas trapping material of the present invention, a method of applying electroplating after making the portions of the skeleton surface of the substrate porous structure forming the fine pores non-conductive is applied. It Depending on the application, it is also applicable to further remove the substrate porous structure after electroplating. Hereinafter, the three-dimensional porous structure of the present invention will be described by taking a three-dimensional network structure or a cloth-like structure as an example. However, these are one example of producing the diesel engine exhaust gas trapping material of the present invention. It is not limited.

A synthetic resin foam is preferably used as the three-dimensional network-structured substrate porous structure used in the present invention. Specific examples thereof include synthetic resin foams having three-dimensional continuous ventilation holes such as polyurethane foam, polystyrene foam, epoxy foam, polyvinyl chloride foam, phenol resin foam, silicone foam, and polyacrylic foam. Of these, urethane foam is preferable, and particularly flexible polyurethane foam having no cell membrane is preferable. As a method for producing a flexible polyurethane foam having no cell membrane, there is a method of eliminating the cell membrane by controlling foaming, or a method of removing the cell membrane by alkali treatment, heat treatment, hydraulic treatment, etc. The method is preferable in terms of completeness of cell film removal. The size of the bubbles of the flexible urethane foam varies depending on the purpose of use of the diesel engine exhaust trapping material and is not particularly limited.

The case where the substrate porous structure used in the present invention has a cloth-like structure will be described. The cloth is roughly classified into a non-woven fabric, a woven fabric and a knitted fabric. Nonwoven fabrics are fiber aggregates, felts, mats, papers, etc., and woven fabrics use substrates in the form of two-dimensional and three-dimensional woven fabrics, knits, sheets and the like. Examples of the fiber that constitutes the substrate porous structure having the cloth-like structure include conductive or non-conductive fiber.

As the conductive fibers, fibers made of materials such as conductive carbon fibers and graphite fibers, which are easily removed after electroplating, are preferably used. Carbon fibers having a low conductivity to a high conductivity having a high graphitization rate can be used, but a carbon fiber having a high conductivity is preferable because plating can be uniformly performed in the electroplating process.

The fibers constituting the non-conductive fiber substrate are, for example, polyethylene, polyethylene terephthalate, polypropylene, polyester, polyamide, polystyrene, polyacrylonitrile, polyvinyl alcohol, cellulose, lignin, polyvinylidene chloride, polybutadiene, polyacetylene, nylon. Organic fibers such as various synthetic fibers made of acrylic resin, acrylic resin, polyurethane, epoxy resin, phenol resin, polyvinyl chloride, or various natural fibers are suitable for use because they are easy to remove after electroplating.

As a method for producing the non-woven fabric, a general production method is applied and is not particularly limited, but for example, 2 to 10 cm.
A method for producing a dry non-woven fabric, in which the fiber length of the fiber is opened with a textile card or the fibers are randomly collected by an air flow, or 1
Any method such as a method of manufacturing a wet non-woven fabric by meshing after dispersing fibers having a size of not more than cm and a spun bond manufacturing method of spinning a melted resin and directly spraying it directly onto a support may be used. . A method for producing a two-dimensional or three-dimensional woven fabric is generally applicable to the method for producing a fiber woven fabric used in the present invention and is not particularly limited.

The portions of the skeleton surface of these base porous structures which form fine pores are made non-conductive and then electroplated. At this time, when the substrate is non-conductive, an operation is performed to make the portion of the skeleton surface where the fine pores are formed non-conductive during the conductive treatment. Further, if necessary, the substrate is removed after electroplating. The case of using a conductive substrate porous structure made of conductive carbon or the like will be described below. In this case, it is possible to apply a method in which the portions where the fine pores are formed as they are without conducting treatment on the skeleton surface are made non-conductive. Of course, even if it has conductivity, it may be subjected to a conductive treatment.

The method of forming the non-conductive portion on the portion of the skeleton surface where the fine pores are formed is not particularly limited, but a method of applying a non-conductive substance to the portion where the fine pores are formed in spots is preferably applied. it can. The non-conductive substance to be attached is preferably one that can be easily decomposed and removed after the electroplating treatment,
Organic substances such as synthetic resins are preferred. In addition, it may be preferable that it does not contain metal impurities, although it varies depending on the use conditions. The shape of the non-conductive portion is also related to the shape of the fine pores to be formed, but in consideration of the strength of the obtained diesel engine exhaust gas trapping material, a rounded shape such as a spherical shape is preferable. Therefore, the non-conductive substance is preferably in the form of particles.

Examples of the non-conductive substance in the form of particles include various synthetic resin beads, various latex particles, and various emulsion particles. In practice, emulsion particles may aggregate from the particle form into a film of various shapes and attach to the skeleton surface in spots. In addition to the case of attachment, it attaches to the skeleton surface in various shapes such as a film and hemisphere.
In any case, it is desirable to form the non-conductive portion without forming the connecting portion in which the spot-like, that is, non-conductive portion extends over a wide range. Further, the shape and size of the non-conductive particles are appropriately selected according to the shape and size of the micropores determined by the application.

As a specific method of forming the non-conductive portion, there is a method of immersing the porous structure of the substrate in a liquid containing the above-mentioned various non-conductive substances and adhering it to the surface of the skeleton. For example, it is a method in which the base porous structure is dipped in a dispersion liquid of synthetic resin beads. At this time, it is preferable to appropriately add additives such as a pressure-sensitive adhesive component and a dispersant, which aid adhesion of the synthetic resin beads to the skeleton surface. Properties of non-conductive materials,
In particular, the state of adhesion to the skeleton surface differs depending on the mutual relationship between the surface property and the skeleton surface property, so it may be necessary to adjust the surface property of the non-conductive substance or skeleton by methods such as surface modification. .

By adjusting the kind and amount of the non-conductive substance and the kind and amount of the additive in the dispersion, the spot-like non-conductive portion formed on the surface of the skeleton occupies the shape, size and surface of the skeleton. The ratio can be adjusted appropriately. Further, when the shape of the base porous structure is simple, a method of spraying a liquid containing a non-conductive substance to attach the liquid droplets to the surface of the skeleton is also applicable.

Next, the case of using a non-conductive substrate porous structure such as an organic substance will be described below. In this case, it is necessary to make the portion of the skeleton surface where the fine pores are formed in the conductive treatment non-conductive. Specific examples of the method of conductive treatment include a method of forming a film with a conductive paste prepared by dispersing powder of a conductive substance such as carbon, graphite or metal, or a metal salt solution such as electroless plating or silver mirror reaction. A chemical method utilizing a reduction reaction can be mentioned.
In the present invention, the non-conductive portion is formed in spots in the portion where the fine pores are formed during the conductive treatment. The procedure is to perform a conductive treatment on the surface of the non-conductive skeleton, and then form a non-conductive portion by depositing a non-conductive substance in spots and a method of introducing the non-conductive portion at the same time as the conductive treatment. There is.

Specifically, a conductive treatment film is formed by using particles of a non-conductive substance dispersed in a conductive paste, and at the same time, the non-conductive substance is attached to the skeleton surface to remove the non-conductive portion. The forming method may be used. At this time, the shape, size, and amount of the non-conductive substance in the paste are appropriately adjusted according to the application. In addition, it is necessary to pay attention to the points such as surface modification so that the surface of the non-conductive substance is not covered with the conductive substance or a non-conductive substance having a thickness larger than the thickness of the conductive film is used.

A usual method is applied to electroplating. The thickness of the metal layer formed by electroplating is several μm to several hundred μm, although it varies depending on the usage conditions and use of the collecting material.
It is also possible to form a multi-layered structure composed of various kinds of metals by sequentially changing the plating composition during electroplating. Further, as a method for removing the base porous structure and / or the non-conductive portion after electroplating, a method such as thermal decomposition, dissolution with a solvent or melting can be applied.

[0026]

Since the skeletal portion of the trapping material of the present invention has fine pores, when exhaust gas passes through, the process of collision and adhesion of fine particles to the skeleton due to inertial force and gravity is promoted and the trapping efficiency is high. Conceivable.

[0027]

EXAMPLES Examples of the present invention will be specifically described below. [Example] As a substrate porous structure having a three-dimensional network structure,
A conductive polyurethane treatment was applied to the surface of the skeleton by electroless nickel plating on a soft polyurethane foam without a cell film having a gap size of about 0.3 mm surrounded by the skeleton. This was immersed in a dispersion liquid containing polystyrene resin particles (particle diameter 4 to 5 μm) and an organic additive and then dried. This is followed by electroplating to form a nickel-chromium-iron-based metal film (composition nickel 42-48%, chromium 25-31%, iron 24-30%).
To form a porous structure having a three-dimensional network structure. The obtained porous structure was heat-treated in air at a temperature of about 600 ° C. to thermally decompose and remove the base resin portion to obtain a collecting material. When the obtained trapping material was observed with an electron microscope, it was found that 4
There were micropores of about 5 μm, and the amount of the micropores was about 15% of the entire skeleton surface. It was also confirmed that the polyurethane resin of the substrate was decomposed and removed to form a hollow skeleton, and the outside and inside of the hollow skeleton communicated with each other through the fine pores in the skeleton.

In order to evaluate the performance of this trapping material, the particulate reduction effect was measured by using the exhaust gas of a diesel engine. As a result, the trapping efficiency was 95.000 at a pressure loss of 0.01 kg / cm 2.
It was 4%. Moreover, in order to evaluate the durability at the time of regeneration, the trapping material that trapped the fine particles was heat-treated in air at 700 ° C., but no melting, cracking, or excessive oxidative corrosion was observed.

[Comparative Example] The same procedure as in Example was carried out except that the treatment with the dispersion liquid of polyethylene resin particles was not carried out. A porous structure having a three-dimensional network structure without fine pores in the skeleton was obtained. When this was subjected to the same exhaust gas collection test as in the example, the pressure loss was 0.01 kg / cm.
2 was similar to that of the example, but the collection efficiency was 89.3%, which was lower than that of the example. Also, regarding the durability during reproduction, the same favorable results as in the example were obtained.

[0030]

EFFECTS OF THE INVENTION Since the diesel engine exhaust gas collecting material of the present invention is a three-dimensional porous structure having fine pores in the hollow skeleton, it exhibits the effect of high collection efficiency and small pressure loss. Further, according to the method of the present invention, it is possible to produce the diesel engine exhaust gas trapping material of the present invention with high productivity.

[0031]

[Brief description of drawings]

FIG. 1 is a cross-sectional perspective view of a portion where hollow skeletons of a diesel engine exhaust collecting material of the present invention intersect with each other.

FIG. 2 is a partially enlarged view showing a typical structure of the diesel engine exhaust gas collecting material of the present invention having a three-dimensional mesh structure.

[Explanation of symbols]

 1 Skeleton 2 Micropores 3 Hollow part 4 Crossing part 5 Gap part surrounded by skeleton

Claims (3)

[Claims] 1. A collection material for diesel engine exhaust, comprising a three-dimensional porous structure comprising a hollow skeleton having fine pores. 2. The method for producing a diesel engine exhaust gas collecting material according to claim 1, wherein the portion of the skeleton surface of the base porous structure that forms fine pores is made non-conductive and then electroplated. Method. 3. The diesel engine exhaust gas collecting material according to claim 1, wherein the three-dimensional porous structure is a heat-resistant alloy.