Porous ceramic honeycomb filter and method of producing the same

Abstract

A porous ceramic honeycomb filter having a chemical composition consisting of, as main components, 42-56 wt % SiO.sub.2, 30-45 wt % Al.sub.2 O.sub.3, and 12-16 wt % MgO and containing cordierite as a main component of a crystalline phase. The porous ceramic honeycomb filter has a porosity of at least 40% and not greater than 55%. The volume of pores having a diameter not larger than 2 .mu.m in the filter is not larger than 0.015 cc/g to thereby improve the collecting time with low pressure loss and high collecting efficiency.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a porous ceramic honeycomb filter consisting of a cordierite ceramic. In particular, the invention relates to an improvement of properties of thermal shock resistance and particulate collecting time of the porous ceramic honeycomb filter for collecting particulates, e.g. soots contained in an exhaust gas from a diesel engine for automobiles, and a method of producing the same.

2. Related Art Statement

Recently, ceramic materials having high thermal resistance and thermal shock resistance have been used in various industrial fields with the advance of industrial technology. As an example, a diesel particulate filter having a honeycomb structure consisting of cordierite ceramic is used for collecting particulates contained in exhaust gas from the diesel engine for automobiles.

The diesel particulate filters may be classified broadly into a high collecting efficiency type for big automobiles and a low collecting efficiency type for small automobiles and are used properly corresponding to various purposes.

Japanese patent Application Publication No. 61-54750 is a prior art relating to a filtering performance of a porous honeycomb filter. The publication discloses that porous ceramic honeycomb filters of the high collecting efficiency type and the low collecting efficiency type can be designed by controlling an open porosity and an average diameter of pores. Furthermore, Japanese Patent Application Laid-open No. 58-70814 discloses that the pressure loss can be decreased by providing large pores having a diameter larger than 100 .mu.m.

The porous ceramic honeycomb filter has three properties such as a particulate collecting efficiency, a pressure loss and a particulate collecting time as a filter. The particulate collecting efficiency and the pressure loss are in a relationship of an inverse proportion to each other, that is the higher the collecting efficiency, the greater the pressure loss and conversely the smaller the pressure loss the lower the collecting efficiency. The relationship varies depending on the kinds of engines to be applied.

The most important property of the filter is the particulate collecting time in which the filter can continuously effectively collect the particulates in the gas with a pressure loss not greater than a predetermined value. If the collecting time is short, an interval between regenerating treatments becomes short. Accordingly, there is a problem that the volume of the filter must of necessity be made large since the collecting time is short.

SUMMARY OF THE INVENTION

It is an object of the present invention to eliminate the above mentioned drawbacks, and to provide a porous ceramic honeycomb filter having a property of long collecting time independent of the high collecting efficiency type and the low collecting efficiency type. That is, the collecting time is greatly increased with the same collecting efficiency and pressure loss.

It is another object of the present invention to provide a method of producing such an improved porous ceramic honeycomb filter.

The porous ceramic honeycomb filter according to the present invention has a chemical composition consisting of, as main components, 42-56 wt% SiO.sub.2, 30-45 wt% Al.sub.2 O.sub.3, and 12-16 wt% MgO and contains cordierite as a main component of a crystalline phase, wherein the porous ceramic honeycomb filter has a porosity of at least 40% and not greater than 55%, and the volume of pores having a diameter not larger than 2 .mu.m in the filter is not greater than 0.015 cc/g.

The method of producing the porous ceramic honeycomb filter according to the present invention comprises the steps of:

preparing a mixture by mixing a cordierite raw material having a chemical composition consisting of, as main components, 42-56 wt% SiO.sub.2, 30-45 wt% Al.sub.2 O.sub.3, and 12-16 wt% MgO with a pore forming agent;

adjusting the grain size of fine particles of the raw material such that particles having a diameter not larger than 2 .mu.m are not more than 35 wt% of all of the raw material;

making a batch of mixture by adding a plasticizer and a binder to the adjusted raw material;

manufacturing a ceramic honeycomb filter by extrusion molding the plasticized batch; and

drying and firing the dry ceramic honeycomb filter at a firing temperature in a range of 1350.degree.-1440.degree. C.

According to the present invention, the porous ceramic honeycomb filter has an open porosity of at least 40% and not greater than 55% and the volume of pores having a diameter of not larger than 2 .mu.m is not greater than 0.015 cc/g so as to decrease fine pores to thereby prolong the collecting time, independent of the high collecting efficiency type and the low collecting efficiency type. The fine pores having a diameter not larger than 2 .mu.m do not contribute to the particulate collecting efficiency and are clogged by the particulates to cause premature increase of the pressure loss.

The pores having a diameter larger than 2 .mu.m are effective to the collecting efficiency and the pressure loss. Therefore, the volume of the pores having a diameter larger than 2 .mu.m should be adjusted corresponding to the use. The volume of pores having a diameter not larger than 2 .mu.m is preferably not greater than 0.010 cc/g to further improve the collecting time.

The porous ceramic honeycomb filter wherein the volume of pores having a diameter not larger than 2 .mu.m is not greater than 0.015 cc/g can be produced by adjusting the total amount of fine particles having a grain size not larger than 2 .mu.m so as to decrease it to an amount not more than 35% of the mixture of the cordierite raw material and the pore forming agent. It is preferable to adjust the total amount of fine particles having a grain size not larger than 2 .mu.m so as to decrease it to an amount not more than 15% since the volume of the pores having a diameter not larger than 2 .mu.m can be further decreased.

In a preferred embodiment of the method of producing the porous ceramic honeycomb filter according to the present invention, it is preferable that the amount of the fine particles of silica having a grain size not larger than 2 .mu.m is not more than 20% of the total amount of particles of silica, the amount of the fine particles of alumina having a grain size not larger not more than 70% of the total amount of than 2 .mu.m is not more than 20% of the particles of alumina, the amount of the fine particles of kaolin having a grain size not larger than 2 .mu.m is not more than 60% of the total amount of particles of kaolin, and the amount of the fine particles of the pore forming agent is not more than 10% of the total amount of particles of the pore forming agent.

These and other objects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings; some modifications, variations and changes of the same can be made by the skilled person in the art to which the invention pertains without departing from the spirit of the invention or the scope of claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is made to the attached drawings, wherein:

FIGS. 1A and 1B are a front elevational view and a side elevational view, respectively, with a part being broken away of an embodiment of the porous ceramic honeycomb structural body;

FIGS. 2A and 2B are a front elevational view and a side elevational view, respectively, with a part being broken away of an embodiment of the porous ceramic honeycomb filter;

FIG. 3 is a graph showing a relationship between the pressure loss and the collecting time; and

FIG. 4 is a graph showing a relationship between the volume of pores having a diameter not larger than 2 .mu.m and the collecting time.

DETAILED DESCRIPTION OF THE INVENTION

In a first stage of producing the porous ceramic honeycomb filter according to the present invention, a mixture of a composition of cordierite ceramic consisting of 42-56 wt% SiO.sub.2, 30-45 wt% Al.sub.2 O.sub.3 and 12-16 wt% MgO is prepared by using an amount of each of kaolin, calcined kaolin, alumina, aluminum hydroxide, silica, talc, calcined talc and a pore forming agent such as graphite or the like and is adjusted such that the total amount of fine particles having a grain size not larger than 2 .mu.m is not more than 35% of the starting material. In the next stage, a plasticizer and a binder are added to the mixture to make a deformable batch mixture. The thus plasticized batch mixture is shaped by extrusion molding and dried, which is then fired at a temperature in a range of 1350.degree.-1440.degree. C. to obtain a porous ceramic honeycomb structural body 1, as shown in FIGS. 1A and 1B, having channels 2 extending therethrough and porous ceramic partition walls 3. Finally, the porous ceramic honeycomb structural body 1 is sealed by inserting sealing medium 4 into openings at the opposite ends of the structural body to provide a porous ceramic honeycomb filter 5 as shown in FIGS. 2A and 2B.

In the following, an example of the present invention will be explained.

EXAMPLE 1

Starting materials having chemical compositions and grain sizes shown in Table 1 were mixed to prepare batches of mixture Nos. 1-No. 101 shown in Table 2, to each of which methylcellulose 3.5 parts by weight to 100 parts by weight of the batch mixture and additional water were added. Then each batch mixture was kneaded to make an extrudable molding batch body. Each batch body was extruded to produce a cylindrical honeycomb structural body having an outer diameter of 118 mm, a height of 152 mm and a partition wall thickness of 430 .mu.m with the number of cells being 16/cm.sup.2. Each of the porous ceramic honeycomb structural bodies thus obtained from each batch was dried and then fired in firing conditions shown in Table 2. The properties of the thus fired honeycomb structural bodies, i.e. the coefficient of thermal expansion at a temperature in a range of 40.degree.-800.degree. C., porosity, volume of pores having a diameter not larger than 2 .mu.m and amount of cordierite crystals were determined.

Each porous ceramic honeycomb structural body was sealed by inserting sealants into the openings at the opposite ends of each channel to produce a porous ceramic honeycomb filter. The properties of the filters, i.e., the initial pressure loss and collecting time, were determined. The results of the determination are shown in Table 2.

Furthermore, the relationship between the total volume of pores having a diameter not larger than 2 .mu.m and the collecting time is shown in FIG. 3 and an effect of improving the collecting time is shown in FIG. 4.

TABLE 1__________________________________________________________________________ Amount of particles of not larger than 2.mu. (wt %) Ig .multidot. loss SiO.sub.2 Al.sub.2 O.sub.3 MgO TiO.sub.2 Fe.sub.2 O.sub.3 CaO + Na.sub.2 O + K.sub.2__________________________________________________________________________ OTalc A 2 5.1 59.9 1.5 30.9 -- 1.0 0.5Talc B 1 5.7 60.9 1.2 30.5 -- 1.1 0.6Calcined talc A 2 0.4 64.1 1.3 33.0 0.1 0.1 0.1Kaolin A 12 13.9 45.5 38.8 -- 0.8 0.3 0.2Kaolin B 70 13.9 45.7 38.7 -- 0.8 0.3 0.2Kaolin C 90 13.9 45.5 38.8 -- 1.0 0.4 0.2Calcined kaolin A 50 0.1 53.1 45.1 -- 0.9 0.4 0.2Alumina A 1 0.3 -- 99.2 -- -- -- 0.35Alumina B 70 0.2 -- 99.5 -- -- -- 0.12Alumina C 90 0.2 -- 99.7 -- -- -- 0.10Aluminum hydroxide A 65 34.5 -- 65.0 -- -- -- 0.2Silica A 2 0.1 99.7 0.1 -- -- -- --Silica B 20 0.1 99.7 0.1 -- -- -- --Silica C 50 0.1 99.7 0.1 -- -- -- --Pore forming agent A 10 99.7 -- -- -- -- 0.2 --Pore forming agent B 3 99.7 -- -- -- -- 0.1 --Pore forming agent C 20 99.5 -- -- -- -- 0.3 --__________________________________________________________________________ Note *Measurement for particle size is carried out by Xray sedimentation metho with use of sedigraph manufactured by Micromelitics Co. TABLE 2__________________________________________________________________________ PoreBatch of Mixture (wt %) forming agent Aluminum (Extra addition Amount of Talc Calcined talc Kaolin Calcined kaolin Alumina hydroxide Silica by wt %) particles of (amount of (amount of (amount of (amount of (amount of (amount of (amount of (amount not larger particles of particles of particles of particles of particles of particles of particles of particles than 2 .mu.m not larger not larger not larger not larger not larger not larger not larger not larger in a batchRun than 2 .mu.m, than 2 .mu.m, than 2 .mu.m, than 2 .mu.m, than 2 .mu.m, than 2 .mu.m, than 2 .mu.m, than 2 .mu.m, mixtureNo. wt %) wt %) wt %) wt %) wt %) wt %) wt %) wt %) (wt__________________________________________________________________________ %) 1 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (1) 20.0 (3) 13 2 40.0 (2) 25.5 (70) 20.8 (50) 13.7 (1) 20.0 (3) 25 3 40.0 (2) 25.5 (90) 20.8 (50) 13.7 (1) 20.0 (3) 29 4 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (70) 20.0 (3) 20 5 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (90) 20.0 (3) 23 6 40.0 (2) 25.5 (70) 20.8 (50) 13.7 (70) 20.0 (3) 33 7 40.0 (2) 25.5 (70) 20.8 (50) 13.7 (90) 20.0 (3) 35 8 40.0 (2) 25.5 (90) 20.8 (50) 13.7 (70) 20.0 (3) 37 9 40.0 (2) 25.5 (90) 20.8 (50) 13.7 (90) 20.0 (3) 3910 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (1) 20.0 (10) 1411 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (1) 20.0 (20) 1512 40.0 (2) 25.5 (70) 20.8 (50) 13.7 (1) 20.0 (10) 2613 40.0 (2) 25. (70) 20.8 (50) 13.7 (1) 20.0 (20) 2814 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (70) 20.0 (10) 2215 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (70) 20.0 (20) 2316 40.0 (2) 25.5 (70) 20.8 (50) 13.7 (70) 20.0 (10) 3417 40.0 (2) 25.5 (70) 20.8 (50) 13.7 (70) 20.0 (20) 3618 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (1) 10.0 (3) 1319 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (1) 30.0 (3) 1220 40.0 (2) 25.5 (12) 20.8 (50) 13.7 (1) 35.0 (3) 1121 39.1 (2) 29.1 (12) 16.0 (50) 9.0 (1) 6.8 (65) 20.0 (3) 1422 39.1 (2) 29.1 (70) 16.0 (50) 9.0 (1) 6.8 (65) 20.0 (3) 2923 39.1 (2) 29.1 (90) 16.0 (50) 9.0 (1) 6.8 (65) 20.0 (3) 3324 39.1 (2) 29.1 (12) 16.0 (50) 9.0 (70) 6.8 (65) 20.0 (3) 2025 39.1 (2) 29.1 (12) 16.0 (50) 9.0 (90) 6.8 (65) 20.0 (3) 2126 39.1 (2) 29.1 (70) 16.0 (50) 9.0 (70) 6.8 (65) 20.0 (3) 3427 29.2 (2) 10.0 (2) 30.1 (12) 16.0 (50) 14.7 (1) 20.0 (3) 1128 29.2 (2) 10.0 (2) 30.1 (70) 16.0 (50) 14.7 (70) 20.0 (3) 3429 29.2 (2) 10.0 (2) 30.1 (90) 16.0 (50) 14.7 (70) 20.0 (3) 3930 39.5 (2) 14.0 (12) 9.5 (50) 12.5 (1) 14.5 (65) 10.0 (2) 20.0 (3) 1531 39.5 (2) 14.0 (70) 9.5 (50) 12.5 (1) 14.5 (65) 10.0 (2) 20.0 (3) 2132 39.5 (2) 14.0 (90) 9.5 (50) 12.5 (1) 14.5 (65) 10.0 (2) 20.0 (3) 2433 39.5 (2) 14.0 (12) 9.5 (50) 12.5 (70) 14.5 (65) 10.0 (2) 20.0 (3) 2234 39.5 (2) 14.0 (12) 9.5 (50) 12.5 (90) 14.5 (65) 10.0 (2) 20.0 (3) 2435 39.5 (2) 14.0 (12) 9.5 (50) 12.5 (1) 14.5 (65) 10.0 (20) 20.0 (3) 1636 39.5 (2) 14.0 (12) 9.5 (50) 12.5 (1) 14.5 (65) 10.0 (50) 20.0 (3) 1937 39.5 (2) 14.0 (70) 9.5 (50) 12.5 (70) 14.5 (65) 10.0 (2) 20.0 (3) 2938 39.5 (2) 14.0 (70) 9.5 (50) 12.5 (70) 14.5 (65) 10.0 (20) 20.0 (3) 3039 39.5 (2) 14.0 (70) 9.5 (50) 12.5 (70) 14.5 (65) 10.0 (50) 20.0 (3) 3340 39.5 (2) 14.0 (90) 9.5 (50) 12.5 (70) 14.5 (65) 10.0 (2) 20.0 (3) 3141 39.5 (2) 14.0 (90) 9.5 (50) 12.5 (70) 14.5 (65) 10.0 (20) 20.0 (3) 3242 39.5 (2) 14.0 (90) 9.5 (50) 12.5 (70) 14.5 (65) 10.0 (50) 20.0 (3) 3543 39.5 (2) 14.0 (70) 9.5 (50) 12.5 (90) 14.5 (65) 10.0 (2) 20.0 (3) 3144 39.5 (2) 14.0 (70) 9.5 (50) 12.5 (90) 14.5 (65) 10.0 (20) 20.0 (3) 3245 39.5 (2) 14.0 (70) 9.5 (50) 12.5 (90) 14.5 (65) 10.0 (50) 20.0 (3) 3546 39.5 (2) 14.0 (90) 9.5 (50) 12.5 (90) 14.5 (65) 10.0 (2) 20.0 (3) 3347 39.5 (2) 14.0 (90) 9.5 (50) 12.5 (90) 14.5 (65) 10.0 (20) 20.0 (3) 3548 39.5 (2) 14.0 (90) 9.5 (50) 12.5 (90) 14.5 (65) 10.0 (50) 20.0 (3) 3749 39.5 (2) 14.0 (90) 9.5 (50) 12.5 (90) 14.5 (65) 10.0 (10) 20.0 (20) 3650 39.5 (2) 14.0 (90) 9.5 (50) 12.5 (90) 14.5 (65) 10.0 (20) 20.0 (20) 3751 39.5 (2) 14.0 (70) 9.5 (50) 12.5 (70) 14.5 (65) 10.0 (10) 10.0 (20) 3352 39.5 (2) 14.0 (70) 9.5 (50) 12.5 (70) 14.5 (65) 10.0 (10) 30.0 (20) 3053 29.0 (2) 10.0 (2) 16.0 (12) 17.5 (1) 12.5 (65) 15.0 (2) 20.0 (3) 1054 29.0 (2) 10.0 (2) 16.0 (70) 17.5 (70) 12.5 (65) 15.0 (2) 20.0 (3) 2855 29.0 (2) 10.0 (2) 16.0 (90) 17.5 (70) 12.5 (65) 15.0 (2) 20.0 (3) 3056 29.0 (2) 10.0 (2) 16.0 (70) 17.5 (90) 12.5 (65) 15.0 (2) 20.0 (3) 3157 29.0 (2) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (2) 20.0 (3) 3358 29.0 (2) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (20) 20.0 (3) 3559 29.0 (2) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (50) 20.0 (3) 3960 29.0 (2) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (2) 20.0 (10) 3561 29.0 (2) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (2) 20.0 (20) 3662 29.0 (2) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (50) 20.0 (20) 4263 40.0 (1) 25.5 (12) 20.8 (50) 13.7 (1) 20.0 (3) 1264 40.0 (1) 25.5 (70) 20.8 (50) 13.7 (1) 20.0 (3) 2465 40.0 (1) 25.5 (90) 20.8 (50) 13.7 (1) 20.0 (3) 2966 40.0 (1) 25.5 (12) 20.8 (50) 13.7 (70) 20.0 (3) 2067 40.0 (1) 25.5 (12) 20.8 (50) 13.7 (90) 20.0 (3) 2268 40.0 (1) 25.5 (70) 20.8 (50) 13.7 (70) 20.0 (3) 3269 40.0 (1) 25.5 (70) 20.8 (50) 13.7 (90) 20.0 (3) 3570 40.0 (1) 25.5 (90) 20.8 (50) 13.7 (70) 20.0 (3) 3771 40.0 (1) 25.5 (90) 20.8 (50) 13.7 (90) 20.0 (3) 3972 40.0 (1) 25.5 (12) 20.8 (50) 13.7 (1) 20.0 (10) 1373 40.0 (1) 25.5 (12) 20.8 (50) 13.7 (1) 20.0 (20) 1574 40.0 (1) 25.5 (70) 20.8 (50) 13.7 (70) 20.0 (10) 3475 40.0 (1) 25.5 (70) 20.8 (50) 13.7 (70) 20.0 (20) 3576 40.0 (1) 25.5 (90) 20.8 (50) 13.7 (90) 20.0 (10) 4077 40.0 (1) 25.5 (90) 20.8 (50) 13.7 (90) 20.0 (20) 4278 40.0 (1) 25.5 (12) 20.8 (50) 13.7 (1) 10.0 (3) 1379 40.0 (1) 25.5 (12) 20.8 (50) 13.7 (1) 30.0 (3) 1180 40.0 (1) 25.5 (12) 20.8 (50) 13.7 (1) 35.0 (3) 1181 29.0 (1) 10.0 (2) 16.0 (12) 17.5 (1) 12.5 (65) 15.0 (2) 20.0 (3) 1082 29.0 (1) 10.0 (2) 16.0 (70) 17.5 (1) 12.5 (65) 15.0 (2) 20.0 (3) 1783 29.0 (1) 10.0 (2) 16.0 (90) 17.5 (1) 12.5 (65) 15.0 (2) 20.0 (3) 2084 29.0 (1) 10.0 (2) 16.0 (12) 17.5 (70) 12.5 (65) 15.0 (2) 20.0 (3) 2085 29.0 (1) 10.0 (2) 16.0 (12) 17.5 (90) 12.5 (65) 15.0 (2) 20.0 (3) 2386 29.0 (1) 10.0 (2) 16.0 (12) 17.5 (1) 12.5 (65) 15.0 (20) 20.0 (3) 1287 29.0 (1) 10.0 (2) 16.0 (12) 17.5 (1) 12.5 (65) 15.0 (50) 20.0 (3) 1688 29.0 (1) 10.0 (2) 16.0 (70) 17.5 (70) 12.5 (65) 15.0 (2) 20.0 (3) 2789 29.0 (1) 10.0 (2) 16.0 (70) 17.5 (70) 12.5 (65) 15.0 (20) 20.0 (3) 3090 29.0 (1) 10.0 (2) 16.0 (70) 17.5 (70) 12.5 (65) 15.0 (50) 20.0 (3) 3391 29.0 (1) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (2) 20.0 (3) 3392 29.0 (1) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (20) 20.0 (3) 3593 29.0 (1) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (50) 20.0 (3) 3994 29.0 (1) 10.0 (2) 16.0 (12) 17.5 (1) 12.5 (65) 15.0 (2) 10.0 (3) 1095 29.0 (1) 10.0 (2) 16.0 (12) 17.5 (1) 12.5 (65) 15.0 (2) 30.0 (3) 996 29.0 (1) 10.0 (2) 16.0 (12) 17.5 (1) 12.5 (65) 15.0 (2) 20.0 (10) 1197 29.0 (1) 10.0 (2) 16.0 (12) 17.5 (1) 12.5 (65) 15.0 (2) 20.0 (20) 1398 29.0 (1) 10.0 (2) 16.0 (70) 17.5 (70) 12.5 (65) 15.0 (20) 20.0 (10) 3199 29.0 (1) 10.0 (2) 16.0 (70) 17.5 (70) 12.5 (65) 15.0 (20) 20.0 (20) 33100 29.0 (1) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (50) 20.0 (10) 40101 29.0 (1) 10.0 (2) 16.0 (90) 17.5 (90) 12.5 (65) 15.0 (50) 20.0 (20) 42__________________________________________________________________________ Properties of Fired Body Volume*.sup.3 Amount*.sup.4 Properties of FilterFiring Conditions Coefficient of pores of of Initial*.sup.5 Collect-*.sup.6 Rate of*.sup.1 Maximum Holding of thermal not larger cordierite pressure ingRun heating temperature time expansion Porosity*.sup.2 than 2 .mu.m crystals loss timeNo. (.degree.C./hr) (.degree.C.) (hr) (.times.10.sup.-6 /.degree.C.) (%) (cc/g) (wt %) (mmH.sub.2 O) (min) N__________________________________________________________________________ 1 40 1410 6 0.9 50 0.005 93 120 20 Present invention 2 " " " 0.9 48 0.011 93 132 15 Present invention 3 " " " 0.8 47 0.014 93 137 10 Present invention 4 " " " 0.9 48 0.010 93 131 16 Present invention 5 " " " 0.8 47 0.013 93 138 15 Present invention 6 " " " 0.8 45 0.014 93 140 11 Present invention 7 " " " 0.8 40 0.015 93 142 9 Present invention 8 " " " 0.8 44 0.017 93 133 7 Reference 9 " " " 0.8 40 0.020 93 140 4 "10 " " " 0.9 50 0.007 93 130 20 Present invention11 " " " 0.9 49 0.010 93 132 18 Present invention12 " " " 0.8 45 0.013 93 137 12 Present invention13 " " " 0.8 45 0.013 93 140 10 Present invention14 40 1410 6 0.8 46 0.011 93 135 13 Present invention15 " " " 0.8 46 0.012 93 137 10 Present invention16 " " " 0.8 45 0.014 93 138 10 Present invention17 " " " 0.8 44 0.017 93 138 6 Reference18 " " " 0.8 37 0.004 93 160 10 "19 " " " 0.8 53 0.005 93 124 22 Present invention20 " " " 0.8 55 0.006 93 119 25 Present invention21 50 1420 4 0.8 49 0.008 92 130 18 Present invention22 " " " 0.8 46 0.013 92 137 13 Present invention23 " " " 0.8 45 0.014 93 140 10 Present invention24 " " " 0.8 47 0.012 93 132 15 Present invention25 " " " 0.8 45 0.014 93 135 12 Present invention26 " " " 0.8 44 0.015 93 142 9 Present invention27 45 1410 4 0.9 52 0.006 92 125 22 Present invention28 " " " 0.8 50 0.014 92 137 16 Present invention29 " " " 0.8 49 0.019 92 132 8 Reference30 40 1410 5 0.8 54 0.007 92 130 18 Present invention31 " " " 0.7 52 0.012 92 137 15 Present invention32 " " " 0.7 51 0.014 92 142 12 Present invention33 " " " 0.7 50 0.011 93 135 15 Present invention34 " " " 0.7 49 0.013 93 137 13 Present invention35 " " " 0.8 52 0.010 93 134 14 Present invention36 " " " 0.8 53 0.011 93 140 13 Present invention37 " " " 0.7 51 0.013 93 142 12 Present invention38 " " " 0.7 50 0.012 93 145 12 Present invention39 " " " 0.7 48 0.014 93 146 10 Present invention40 " " " 0.7 48 0.015 93 145 10 Present invention41 40 1410 5 0.7 47 0.015 93 143 9 Present invention42 " " " 0.7 46 0.014 93 145 11 Present invention43 " " " 0.7 48 0.013 93 138 12 Present invention44 " " " 0.7 47 0.014 93 142 12 Present invention45 " " " 0.7 47 0.015 93 140 10 Present invention46 " " " 0.7 46 0.014 93 152 9 Present invention47 " " " 0.7 48 0.014 93 135 13 Present invention48 " " " 0.7 47 0.016 93 135 7 Reference49 " " " 0.7 47 0.016 93 137 7 "50 " " " 0.7 47 0.018 93 131 4 "51 " " " 0.7 40 0.013 92 135 11 Present invention52 " " " 0.7 55 0.012 93 125 18 Present invention53 60 1420 4 0.7 52 0.004 93 120 23 Present invention54 " " " 0.7 50 0.012 93 130 17 Present invention55 " " " 0.6 49 0.013 93 135 13 Present invention56 " " " 0.6 49 0.014 93 134 12 Present invention57 " " " 0.6 49 0.015 93 138 10 Present invention58 " " " 0.6 49 0.014 93 139 11 Present invention59 " " " 0.6 48 0.016 93 137 7 Reference60 " " " 0.6 48 0.015 93 138 11 Present invention61 " " " 0.6 48 0.017 93 139 8 Reference62 " " " 0.6 49 0.019 93 135 4 "63 40 1410 6 1.0 50 0.003 92 89 42 Present invention64 " " " 1.0 49 0.012 92 95 37 Present invention65 40 1410 6 0.9 47 0.014 92 99 35 Present invention66 " " " 1.0 48 0.011 92 94 38 Present invention67 " " " 0.9 46 0.012 92 97 34 Present invention68 " " " 0.9 47 0.013 92 105 30 Present invention69 " " " 0.9 45 0.015 92 110 30 Present invention70 " " " 0.9 45 0.019 92 112 20 Reference71 " " " 0.9 44 0.022 92 109 17 "72 " " " 1.0 49 0.007 92 88 43 Present invention73 " " " 1.0 48 0.010 92 90 40 Present invention74 " " " 0.9 48 0.013 92 107 30 Present invention75 " " " 0.9 48 0.015 92 110 30 Present invention76 " " " 0.9 47 0.021 92 105 21 Reference77 " " " 0.9 47 0.022 92 103 19 "78 40 1410 6 1.0 40 0.004 92 110 32 Present invention79 " " " 1.0 55 0.003 92 75 50 Present invention80 " " " 1.0 58 0.002 92 65 55 Reference81 60 1420 4 0.8 53 0.004 92 85 45 Present invention82 60 1420 4 0.8 52 0.011 93 90 40 Present invention83 " " " 0.7 51 0.013 92 95 37 Present invention84 " " " 0.8 52 0.013 92 90 39 Present invention85 " " " 0.7 51 0.014 92 97 35 Present invention86 " " " 0.9 53 0.007 92 93 42 Present invention87 " " " 0.9 52 0.013 92 105 31 Present invention88 " " " 0.8 51 0.014 92 110 30 Present invention89 " " " 0.8 51 0.014 92 110 30 Present invention90 " " " 0.8 50 0.015 92 113 29 Present invention91 " " " 0.7 48 0.015 92 115 28 Present invention92 60 1420 4 0.7 48 0.015 92 117 28 Present invention93 " " " 0.7 47 0.019 92 110 21 Reference94 " " " 0.9 40 0.003 92 105 25 Present invention95 " " " 1.0 54 0.003 92 90 47 Present invention96 " " " 1.0 49 0.005 93 95 41 Present invention97 " " " 1.0 49 0.006 93 96 40 Present invention98 " " " 0.9 48 0.013 92 105 35 Present invention99 " " " 0.9 48 0.014 92 107 33 Present invention100 " " " 0.8 48 0.019 92 104 25 Reference101 " " " 0.8 48 0.023 92 103 20 "__________________________________________________________________________ *.sup.1 1100.about.1350.degree. C. Average heating rate *.sup.2 Mercury forcing method. Conversion value of volume of pores (for real specific gravity of cordierite: 2.52) *.sup.3 Mercury forcing method. *.sup.4 Amount measured by Xray diffractometer with use of ZnO as interna standard *.sup.5 Room temperature (20.degree. C.) 58.phi. 1 Nm.sup.3 /min *.sup.6 Time spent until a pressure loss reaches to 1600 mmH.sub.2 O when a gas contained soots with a rate of 13 g/hr 2.4 Nm.sup.3 /min at a temperature of 200.degree. C.

In Table 2, the run Nos. 1-62 are of the high collecting efficiency type and the run Nos. 63-101 are of the low collecting efficiency type. It will be understood from the results shown in Table 2 that the collecting time can be more prolonged in the case of the volume of pores having a diameter not larger than 2 .mu.m being not more than 0.015 cc/g, than the case of the total volume of that being more than 0.015 cc/g. If the porosity is less than 40% the initial pressure loss becomes too large to improve the collecting time, while if the porosity is more than 55%, the strength of the honeycomb structural body is decreased.

Claims

1. A method of producing a porous ceramic honeycomb filter, comprising the steps of:

mixing a cordierite raw material consisting essentially of 42-56 wt% SiO.sub.2, 30-45 wt% Al.sub.2 O.sub.3, and 12-16 wt% MgO as main components, with a pore forming agent;

adjusting a grain size of fine particles of the raw material such that a total amount of particles having a grain size not larger than 2 .mu.m is not more than 35% of the entire wt% of the mixture;

adding a plasticizer and a binder to the adjusted raw material to make a batch mixture;

extrusion molding the batch mixture to produce a ceramic honeycomb filter;

drying the extruded ceramic honeycomb filter; and

firing the extruded ceramic honeycomb filter at a firing temperature in a range of 1350.degree.-1440.degree. C.

2. The method of claim 1, wherein the total amount of particles having a grain size not larger than 2 .mu.m in the mixture is not more than 15% of the entire wt% of the mixture.

3. A porous ceramic honeycomb filter produced by the method of claim 1, the ceramic honeycomb filter having a chemical composition consisting essentially of 42-56 wt% SiO.sub.2, 30-45 wt% Al.sub.2 O.sub.3, and 12-16 wt% MgO as main components, and cordierite as a main component of a crystalline phase, wherein the ceramic honeycomb filter has a porosity of at least 40% but not greater than 55%, and a volume of pores in the ceramic honeycomb filter having a diameter not larger than 2 .mu.m is not greater than 0.015 cc/g.

4. The ceramic honeycomb filter of claim 3, wherein the volume of pores in the ceramic honeycomb filter having a diameter not larger than 2 .mu.m is not greater than 0.010 cc/g.