Title of Invention | HONEYCOMB FILTER FOR CLARIFYING EXHAUST GAS AND METHOD FOR MANUFACTURE THEREOF |
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Abstract | To provide a honeycomb filter for cleaning an exhaust gas, which is excellent in heat resistance and thermal shock resistance and has high thermal decomposition 5 resistance and high mechanical strength and which is thus capable of being used with stability at high and fluctuating temperatures, and a process for its production. A honeycomb filter for removing solid particles 10 containing carbon as the main component in an exhaust gas, characterised m that the material for the honeycomb filter is an aluminum titanate sintered product obtained by firing at from 1,250 to l,700°C a raw material mixture comprising 100 parts by mass of a mixture (component X) 15 comprising TiO2; and A12O3, in a molar ratio of the farmer/the latter being 40 to 6 0/6O tc 40, and from 1 to 10 -parts by mass of an alkali, feldspar represented by the empirical formula {NayKi-y)AlSi3O3 (wherein O<y<l) , an oxide having a spinel structure containing Mg, or MgO or 20 an Mg-containing compound which will be converted to MgO by faring (component Y) |
Full Text | 1 DESCRIPTION HONEYCOMB FILTER FOR CLARIFYING EXHAUST GAS AND METHOD FOR MANUFACTURE THEREOF 5 TECHNICAL FIELD The present invention relates to a honeycomb filter for cleaning an exhaust gas, to capture and remove fine Solid particles (participates) containing carbon as the 10 main component, contained in an exhaust gas from e.g. a Diesel engine, and a process for its production BACKGROUND ART In an exhaust gas from eg a Diesel engine of eg 15 an automobile, participates containing carbon as the main component are contained in a substantial concentration (from 150 to 25 0 mg/Nm3) and thus cause an environmental problem together with nitrogen oxides, etc. Accordingly, it is desired to remove them efficiently and economically 20 Heretofore, various filters have been proposed to capture and remove such fine solid particles contained in exhaust gases For example, JP-A-57-35918 or JP-A-5-214922 discloses an exhaust gas filter wherein a plurality of 25 channels in a honeycomb filter are alternately plugged at the upstream end or the downstream end A honeycomb filter of this type has a structure such that a 2 combustion exhaust gaa to be cleaned, is supplied to openings on the upstream side of the filter and permitted to pass through partition walls of the filter, so that particulates in the exhaust gas are captured and removed 5 by partition walls, and then, the exhaust gas after cleaning is taken out from openings at the downstream side of the filter. On the other hand, the material for such a honeycomb filter is required to have not only high heat reelstance 10 but also a small thermal expansion coefficient and high thermal shock resistance, since it is exposed to a rapidly heated or cooled environment, and. accordingly, silicon carbide or cordiente material has been proposed and practically used However, such, a material still has 15 no adequate properties as an exhaust gas filter. Namely, with an exhaust gas filter, it is likely that when captured non-combustion carbonaceous fine solid particles are abnormally deposited, such carbon will catch-fire and burn, whereby an abrupt tensperature rise 20 will take place so that the temperature locally reaches from 1,400 to l,500 QC. In such a case, a filter made of silicon carbide material will have a temperature distribution at various places of the filter, and the thennal expansion coefficient is about 4.2x10-6K-1 i.e. 25 not so small, whereby cracks are likely to form by the thermal stress or thermal shock exerted to the material, thus leading to partial breakage. On the other hand, in 3 the case of a filter made of cordierite material, the thermal expansion coefficient is small at a level of from 0.6 to 1.2x10-6K-1 whereby the problem of cracks due to thermal shock is less, but the melting point is not so 5 high at a level of from 1,400 to l,450°C, whereby a problem of partial melting due to the above-mentioned abnormal combustion of carbon becomes serious Once defects are formed in the interior of an exhaust gas filter by the breakage or melting of the filter as 10 described above, the efficiency of the filter for capturing carbon decreases, and. at the same time, the pressure of the exhaust gas exerted to the filter will be an excessive load to the defective portions and thus induce new breakage. Consequently, the entire exhaust 15 gas filter will fail to function. As the material for such a honeycomb filter, WOO 1/037971 proposes aluminum titanate as well as silicon carbonate or cordierite. Aluminum titanate is a material having beat resistance at a high temperature exceeding 20 l,700°C and a small thermal expansion coefficient and excellent thermal shock resistance. However, on the other hand, aluminum titanate has a serious problem that since it has a decomposition region usually within a temperature range of from 800 to l,2800 C, it can not be 25 used with, stability within a fluctuated temperature region containing such a temperature range. Further, it has a difficulty each that since the anistropy of its 4 crystal structure is substantial, slippage by a thermal stress is likely to take place, and the mechanical strength is not high enough Accordingly, it still has had a problem in its use for the production of a 5 honeycomb having a thin wall thickness and a high cell density or in its use as an exhaust gas filter to be subjected to a load such as mechanical vibration at a high temperature, as mounted on an automobile or the like 10 DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a honeycomb filter for cleaning an. ejdiaust gas, which is excellent in heat resistance, has a email thermal 15 expansion coefficient and excellent thermal shock resistance, is free from thermal decomposition even at a. high and fluctuating temperature and has high mechanical strength so that it can be used with stability for a long period of time and which is capable of capturing and 20 removing, with high efficiency, particulates such as fine carbon particles contained in an exhaust gas from e.g. a Diesel engine, and a process for its production. As a result of an extensive study to solve the above-mentioned problems, the present invention has been 25 accomplished by paying attention to aluminum titanate, on the basis of a discovery such that a honeycomb filter for cleaning exhaust gas, employing an aluminum titanate 5 sintered product obtainable by firing a mixture having a. specific alkali feldspar, an oxide having a spinel structure containing Mg, or MgO or an Mg-containing compound to be converted to MgO by firing, added in a 5 prescribed ratio to a mixture comprising TiO2 and Al203 in a prescribed ratio to form aluminum titanate, has high mechanical strength and thermal decomposition resistance, as different from conventional aluminum titanate sintered products, while maintaining the excellent heat resistance 10 and high thermal shock resistance due to the small thermal expansion coefficient as inherent properties of conventional aluminum titanate sintered products. Thus, the present invention provides the following: (1) A honeycomb filter for cleaning an exhaust gas which 15 is a honeycomb filter for removing solid particles Containing carbon as their main component in an exhaust gas, characterized in that the material for the honeycomb filter is an aluminum titanate sintered product obtained by firing at from 1,250 to l,700*C a raw material mixture 20 comprising 100 parts by mass of a mixture [component X) comprising T1O2 and AI2O3 in a molar ratio of the former/the latter being 40 to 60/60 to 40, and from 1 to 10 parts by mass of an alkali feldspar 25 represented by the empirical formula [NayKI-V) AlSi3O3 (wherein 0 6 will be converted to MgQ by firing (component Y). (2) The honeycomb filter for cleaning an exhaust gaa according to the above (1), wherein component y is a mature comprising the alkali feldspar represented by 5 (NayK1-Y)AlSi3Oa [wherein O compound which will be converted to MgO by firing, (3] The honeycomb filter for cleaning an exhaust gas according to the above (1}, wherein the honeycomb filter 10 has a wall thickness of from 0,1 to 0 6 mm and a cell density of from 15 to 93 cells/cm2, wherein the porosity of the partition wall is from 30 to 70%, and the thermal expansion coefficient is at most 3.0x10-6K-1. (4} A process for producing a honeycomb filter for 15 cleaning an exhaust gas, characterised by preparing a mixture comprising 100 parts by mass of a mixture (component X] comprising TiO2 and A12O3 in a molar ratio of the former/the latter being 40 to 60/60 to 40, and 20 from 1 to 10 parts by mass of an alkali feldspar represented by the empirical formula (NayKa-y)AlSi3O3 (wherein 0 will be converted to MgO by faring {component Y), adding 25 a molding assistant to the mixture, followed by kneading to plasticine the mixture to make it extrusion- processable, extrusion processing it into a honeycomb 7 structure, followed by firing at from l,250 to l,700°C. (5) The process for producing a honeycomb filter for cleaning an exhaust gas according to the above (4)( wherein component y is a- mixture comprising the alkali. b feldspar represented by (NayKi-y}AlSi3Qs [wherein O MgO or the Mg-containing compound which will be converted to MgO by firing. (6} An apparatus for cleaning an exhaust gas, lo characterised in that the honeycomb filter for cleaning an exhaust gas as defined m any one of the above (1) to (3) is accommodated in a can, (7) The apparatus for cleaning art exhaust gas according to the above (6), which is used for cleaning an exhaust 15 gas of an automobile having a diesel engine mounted The reason as to why the honeycomb filter made of the aluminium titauate sintered produce according to the present invention, has high thermal decomposition 20 resistance and high mechanical strength while maintaining the inherent high heat resistance, small thermal expansion coefficient and excellent thermal shock resistance as described above, is not clearly understood, but may probably be as follows. 25 Namely, by the addition of the alkali feldspar to the mixture to form aluminum titanate, the reaction to farm alumina titanate takes place in a liquid phase, 8 since the alkali feldspar is present which becomes a liquid phase in the vicinity of the temperature at which aluminum titanate will be formed, whereby dense crystals will be formed to improve the mechanical strength. And, 5 the S1 component contained in the alkali feldspar will be solid-solubilized in the crystal lattice of the aluminum titanate and: will be substituted for Al. Si has a smaller ion radius than Al, whereby the bond distance from the surrounding oxygen atoma will be shortened, and 10 the lattice constant tends to have a small value as compared with pure aluminum titanate It is considered that aa a result, "the sintered product thus obtained shows a very high thermal stability as the crystal structure is stabilized, and the thermal decomposition 15 resistance is substantially improved Further, in a case where an oxide having a spinel structure containing Mg, or MgO or an Mg-containing compound which will be converted to MgO by firing, is added to the mixture to form aluminum titanate, it is 20 possible to obtain a dense sintered product and to form a sintered product having a very high mechanical strength as compared with pure aluminum titanate Further, in a case where the alkali feldspar, and the oxide having a spinel structure and/or MgO or the Mg- 25 containing compound which will be converted to MgO by firing, are simultaneously added to the mixture to form an aluminum titanate, S1 contained in the alkali feldspar 9 and Mg contained in the oxide of the spinel structure and/or MgO or the Mg-containing compound which, will be converted to MgO by firing, will be substituted mainly at Al sites in the aluminum titanate if these elements are 5 added alone, a bivalent (Mg} or tetravalent (Si) element would be substituted at Al sites where the balance at electric charge is maintained with trivalency- Accordingly, in order for the sintered product to maintain the balance of electric charge, it as considered 10 that when Mg is added, oxygen is discharged out of the system to create oxygen deficiency to maintain the balance of electric charge, and when S1 is added, since S1 is tetravalent, the tetravalent T1 will he reduced to trivalent to take the balance of electric charge 15 On the other hand, Mg is smaller by 1 in the electric charge than Al, and Si is larger by 1 in. the electric charge than Al. Thus, it ia considered possible to take the balance of electric charge by simultaneously adding the alkali feldspar and the oxide having a spinel 20 structure and/or MgO or the Mg-containing compound which will be converted to MgO by firing, and it will be possible to solid-solubilise them without presenting an influence over other elements constituting the sintered product. 21 It ia considered that especially when the alkali fel&srpar, and the oxicte of spinel structure and/or MgO or the Mg-containing compound which will be converted to MgO 10 by firing, are added in a ratio close to an equitmolar ratio, tine additives can be present more stably as compared With a case where they are added alone. It ie considered that for these reasons, both act 5 synergistically to substantially improve the strength as compared with a case where they are used alone, and it is possible to form an aluminum titanate sintered product which has a high mechanical strength without impairing the low thermal expansion property inherent to aluminum 10 titanate and which at the same time has improved thermal decomposition resistance BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing an. embodiment of 15 a honeycomb filter for cleaning an exhaust gas of the present invention, as partly cut off Fig. 2 is a diagrammatical View shoeing the end face of the honeycomb filter in Fag 1 Fig. 3 is a cross-sectional diagrammatical view along 20 line A-A of the honeycomb filter in Fig. 2. Fig. 4 shows the changes with time of the remaining ratios £ of alummunium titanate with respect to the sintered products in Examples 1 and 2 and Comparative Example 2 25 MEANING OF SYMBOLS 1: honeycomb filter 2: partition wall 3:through-hole 4,5: blockers 11 BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as the material for a honey comb filter, an. aluminum titanate sintered product is used which is obtained by fixing from 1,250 to l,7000C 5 a raw material fixture comprising 100 parts by mass of component X comprising TiO2 and AL2O3- in a molar ratio of the former/the latter being 40 to 60/60 to 40, and from l to 10 parts by mass of component y The above TiO2 and A12O3 to form aluminum titanate may 10 not necessarily be pure TiO2 and AI2O3 respectively, and they are not particularly limited so long as they are components capable of forming aluminum titanate by firing. Usually, they are suitably selected for use among those employed as raw materials for various ceramics, such as 15 alumina ceramics, titania. ceramics and aluminum titanate Ceramics Yor example, double oxides; carbonates, nitrates or sulfates containing Al and Ti as metal components way also be used. TiO2 and Al2O3 are used in a molar ratio of the 20 former/latter being 4 0 to 60/60 to 40, preferably 45 to 5 0/55 to 60. It is possible to avoid the eutectic point of the fired product especially by adjusting the molar ratio of Al2O3/TiO2 to be at least X within the above range. In the present invention, Al2O3 and TiO3 are used 25 as a mixture, and an this invention, such a mixture may sometimes be referred to as component X In the case of the honeycomb filter ot the present 12 invention, it is necessary to add component Y as an additive to the above component X, As the alkali feldspar as one of component Y, one represented by the empirical formula (NayK1-y)AlSi3O8 may be used. In the 5 formula, y satisfies 0≤y≤1, prsferably 0.1≤y≤1 particularly preferably 0 1≤y≤0 85 The alkali feldspar having value y within this range his a low melting point and is particularly effective for acceleration of the sintering of aluminum titanate. 10 As the oxide having a spinel structure containing Mg as another component y, MgAl2O4 or MgTi2O4 may, for example, be used Such an oxide having a spinel structure may be a natural mineral, or a material containing MgO and Al203, a material containing MgO and 15 TiO2, or a spinel-form oxide obtained by firing such a material Further, two or more oxides having different types of spinel structures may be used in combination as a. mixture. Further, as a MgO precursor, any material may be used so long as it is capable of forming MgO by firling 20 and for example, MgCO3, Mg{NO3)2, MgSO4 or a mixture thereof may be mentioned. The ratio of the above components X and y is important, and component Y is from 1 to 10 parts by mass par 100 parts by mass of component x This is a ratio 25 where components X and y are oxides respesctively, and when raw materials other than oxides are used, values calculated as oxides will be employed. If component Y is 13 smaller than 1 part by mass per 100 parts by mass of component X, the effect for improving the properties of the sintered product by the effect of addition of component Y, will be small On the other hand, if it 5 exceeds 10 parts by mass, such will exceeds the solid- solubilization limit of the Si or Mg element in the aluminum titanste crystals, and the excess component added in excess will toe present in an independent oxide an the altered product and tends to increase the thermal 10 expansion coefficient, such being undesirable It is particularly preferred that component 1 ie from 3 to 7 parts by mass per 100 parts by mass of component X Further, in the present invention, it is preferred that as the above component y, the alkali feldspar 15 represented by the empirical formula (NayK1-y)AlSi3O8, and the oxide having a spinel structure containing Mg arid/or MgO or its precursor, are used in. combination as a mixture. When such a, mixture is used, the above mentioned synergistic functional improvement can be 20 obtained, The mixture of the above feldspar (former), and the oxide having a spinel structure containing Mg and/or MgO or its precursor flatter) preferably has a mass ratio of the former/the latter being 2 0 to SO/SO to 40, particularly preferably 35 to 45/65 to 55 In the 25 above range, the ratio of Si/Mg will be equimolar, and j.f the ratio is not within this range, the synergistic effect by the simultaneous solid-solubilizaticn of Si and 14 Mg in aluminum titanate tends to be hardly obtainable, such being undesirable. In the preeent invention, in addition to the above components X and Y, other sintering assistants may be 5 employed as the case requires, whereby the nature of the obtainable sintered product can be improved As such other sintering assistants, SiO2, Zno2, Fe3O3, CaO and Y2O3 may, for example, be mentioned The raw material mixture comprising the above 10 components X and y is sufficiently mixed and pulverised The mixing and pulverization of the raw material mixture is not particularly limited and may be carried out by a known method For example, they may be carried out by irteans of e g. a ball mill or a medium-agitation mill. 15 The degree of pulverization of the raw material mixture is not particularly limited, but the average particle size is preferably at most 3 0 urn, particularly preferably from S to 15 μn. The average particle size should better be small so long as at is within a range where no 20 secondary particles "Will be formed Molding assistant may preferably be incorporated to the raw material mixture. As auch molding assistants, known agents such as a binder, a pore-forming agent, a release agent, a defearning agent and a peptiser may be 25 employed. As the binder, polyvinyl alcohol, microwax emulsion, methyl cellulose or carboxymethyl cellulose may, for example, be preferred. As the pore-forming agent, 15 activated carbon, coke, a polyethylene regin, starch or graphite may, for example, be preferred As the release agents a stearic acad emulsion may, for example, be preferred, as the defoaming agent, n-octyl alcohol or 5 octylphenoxyethanol may, for example, be preferred, and ag the peptizer, diethylamine or triethylanune may, for example, be preferred The amounts o£ the molding assistants are not particularly limited. However, in the case of the 10 present invention, they are preferably within the following ranges, respectively, as calculated as solid contents, per 100 parts by maas o£ the total amount of componetits X and V (as calculated as the respective oxides) to bs used aa the starting waiterials. Namely, it 15 is preferred to use the binder in. an amount of from about 0 2 to 0,6 part by mass, the pore-forming agent in an amount ot from about 40 to 60 parts by mass, the release agent m an amount of from about 0 2 to 0 7 part by mass, the defoaming agent in an amount of from about 0.5 to 1.5 20 parts by mass &nd the peptizer in an amount of from about 0.5 to 1.5 pares by mass. The raw material mixture having such molding assistants incorporated, is mixed, kneaded and plasticized so that it is extruaion-procesgable, followed 25 by extrusion processing to form a honeycomb structure, As the method for extrusion, a known method may be used, and the shape of each cell of the honeycomb may be 15 circular, oval, tetragonal or triangular Further, the entire configuration of the honeycomb molded product may be either cylindrical or square tubular. The molded honeycomb bady is preferably dried and then fired at from 5 1,250 to l,7000C, preferably from 1,300 to l,450°C. The firing atmosphere is not particularly limited and is preferably an oxygen-containing atmosphere such as in the air which is commonly employed The firing time is not particularly limited so long as the firing can be done io until the sintering proceeds sufficiently, and it is usually at a level of from 1 to 20 hours. Also twith respect to the temperature raising rate or the temperature lowering rate at the time of the above firing, there is no particular restriction, and such 15 conditions may the suitably set so that no cracks will be formed in the obtainable sintered product. For example, it is preferred to gradually raise the temperature without rapid rise of the temperatnre to sufficiently remove the molding assistants such. as moisture., a. binder, 20 etc. contained in the raw material mixture, Further, if necessary, prior to heatting at the above-mentioned firing temperature, presintering may be carried out preferably within a. temperature raiyge of from 500 to l,0000C for from 10 to 30 hours by mild temperature raise, whereby 25 the etress in the sintered product which causes cracking during the formation of aluminimum titemate, can be relaxed, and formaticm of cracks in the sinteyed product can be 17 suppressed to obtain a uniform sintered product. The sintered product thus obtainable will be one having, as the basic component, aluminum titanate formed from component X and having a Si component contained in 5 the alkali feldspar and the Mg component derived from the oxide having a spinal structure containing Mg, MgO or the Mg-containing compound which will be converted to MgO by firing, as component Y, solid-solubilized in the crystal lattice of the aluminum titanate Such a sintered 10 product has high mechanical strength and a low thermal expansion coefficient and yet has a crystal structure stabilised, as mentioned above, and will thus be a sintered product having excellent heat decomposition resistance 15 As a result, a honeycomb filter made of such a. sintered product has a thin wall honeycomb structure having a wall thickness of e g from 0.1 to 0.6 mm, preferably from 0-3 to 0 48 mm and a cell density of eg from IS to 93 cells/cm2 And, the porosity of the 20 partition wall is, for example, from 30 to 70%, preferably from 40 to 60%, and the thermal expansion coefficient 19 e.g. at most 3.0xl0-6K-1, preferably at most 1.5xl0-6K-1. Such a honeycomb filter cart be used with stability, from room temperature to l,600°C as the 25 thermal decomposition reaction of aluminum titanate is suppressed even at a high temperature. Fig. 1 is a. perspective view of an embodiment of the 16 honeycomb filter for cleaning an exhaust gas of the present invention Fig. 2 is a diagrammatical view showing the end face of the honeycomb filter in Example 1. Fig. 3 is a diagrammatical view of the cross-section 5 along line A-A of the honeycomb filter in Fig. 2. In these Figs , the honeycomb filter 1 for cleaning an exhaust gas h&a both ends alternately plugged by blockers 4 and 5 at the upstream side and at the downstream side of a honeycomb filter comprising through-holes 3 10 constituted by many partition walls 2. Namely, as shown in Fig. 2, at the upstream or downstream eide end, the throughw holes 3 are plugged with blockers 4 or 5 in a lattice form, and with rfispect to each through-hole 3, either the upstream or downstrearn side end is plugged 15 with a blocker 4 or 5, To such a honeycomb body, an exhaust gas to be cleaned la supplied to through.-holes 3 on the upstream side of the honeycomb body and passed through the partition walls 2 to have particulars in the exhaust gas captured and removed by the partition walls 2, 20 and then, the exhaust gas after the cleaning is taken out from the through-holea 3 on the downstream side. The honeycomb product of the present invention formed as a honeycomb filter for cleaning exhsmet gas is preferably set in a can body by means of a s-uitable 25 supporting material and is "used "to capture and remove fine solid particles (particulates) contaming carbon as the main component, contained in an exhaiist g&s, With 13 respect to the type of the exhaust gas, any gas discharged from a combustion source of either a stationary body or a mobile body may be treated However, as mentioned above, the honeycomb filter is particularly 5 useful for cleaning an exhaust gas from an automobile having a Diesel engine mounted where the severest properties are required 10 Now, the present invention will be described in further detail with reference to Examples. However, it should be understood that the present invention is by no means thereby restricted EXAMPLE 1 15 To 100 parts by mass of a. mixture comprising 56.1 mass% (50 mol%} of easily sinterable α-alumina and 439 mass% (50 nol%) of anatase-type titanium oxide( 4 parts by mass of an alKali feldspar represented by (Na0 6K0 4)AlS1jO8 6 parts by mass of a spinel compound 20 represented by a chemical formula MgAl2O4 0 25 parts by mass of polyvinyl alcohol as a binder, 1 part by mass of diethylamine as a peptizer, 0,5 part by mass of polypropylene glycol as a defoaming agent, and 50 parts by mass of activated carbon having a particle size of 25 from 50 to 80 μm ag a pore-forming agent, were added, mixed for 3 hours in a ball mill and then dried in a dryer at a temperature of 120°C for at least 13 hours to 20 obtain a raw material powder The obtained raw material powder was pulverized to an average particle size of at most 10 ΜM and farmed by a vacuum forming machine (manufactured by Miyazaki Iron 5 Works Co , Ltd ) to obtain a honeycomb formed product. This formed product was dried and then fired in the atmosphere at l,500°C for 2 hours and then left to cool, to obtain a totally cylindrical honeycomb filter having cross-sectionally square cells, as shown in Figs 1 to 3. 10 The honeycomb filter had a wall thickness of 0.38 mm and a cell density of 31 cells/cm2, and the outer diameter o£ tile cylindar was 144 mm and the length. was 152 mm COMPARATIVE EXAMPLE 1 A honeycomb filter made of an aluminum titanate is sintered product, was obtained in the same manner as in Example 1 except that no alkali feldspar was used EXAMPLE 2 To 10 0 parts by mass of a mixture comprising 56,1 mass% {50 mol%) of easily sinterable α-alumina and 43.9 20 mass%- (50 mol%) o£ anatase-type titanium oxide, 4 parts by mass of an alkali feldspar represented by (Na0 6K0 4)AlS1O8 6 parts by mass of a spinel compound represented by a. chemical formula MgAl7O4 0 25 part by tnasa of polyvinyl alcohol as a binder, i part by mass of 25 diethylamine as a peptizer, 0 5 part by mass of polypropylene glycol as a deforming agent, and 50 parts by mass of activated carbon having a particle size of 21 from 50 to 80 yon as a pore-forming agent, were added and mixed for 3 hours in a ball mill and then dried in a dryer at 120°C for at least 13 hours to obtain a raw material powder, 5 Using the obtained raw material powder, pulverisation, forming, drying and firing were carried out in the same manner as in Example 1 to obtain a honeycomb filter EXAMPLE 3 To 100 parts by mass of a mixture comprising 56.1 10 mass% (50 mol%} of easily sinterable α-alumina and 43 9 mass% (50 mol%) of anatase-type titanium oxide, 6 parts by mass of a spinel compound represented by a chemical formula MgAl2Q4 as an additive, 0.25 part by mass of polyvinyl alcohol as a binder, 1 part by mass of 15 diethylamine as a peptizer, 05 part by mass of polypropylene glycol as a defoaming agent, and 50 parts by mass of activated carbon having a particle size of from SO to 80 μm as a pore-forming agent, were added and mixed for 3 hours in a ball mill and then dried, in a 20 dryer at 120°C for at least 12 hours to obtain a raw material powder Using the obtained raw material powder, pulverization, forming, drying and firing were carried out in the same manner as in Exainple 1 to obtain a honeycomb filter. 25 COMPARATIVE EXAMPLES 2 and 3 As materials for honeycomb filters, commercially available silicon carbide powder (tradename SHOCERAM, 22 manufactured by SHOWA DENKO K K) and cordierite powder (2MgO.2Al2O3.5SiO2)) were respectively used, and from these materials, honeycomb filters were obtained by carrying out the conventional methods respectively Here, the s honeycomb made of silicon carhade will be referred to as Comparative Example 2, and the honeycomb made of cordiente as Comparative Example 3 FROPERTY TESTS WITH RESPECT TO HONEYCOMB SINTERED PRODUCTS 10 With respect to the honeycomb filters obtained in the above Examples l, 2 and 3 and Comparetive Examples 1, 2 and 3, the porosity (%), the thermal expansion coefficient (xlO-6K-1) at from room temperature to 800°C, the thermal shock resistance (0C) by art in-water dropping 15 method, the softening temperature {°C) and the compression strength (MPa) were measured, and the results are shown in Table 1 Here, the porosity was measured by a method in accordance with JIS R1634, the thermal expansion coefficient by a method in accordance with JIS 20 R1G18, the thermal shocK resistance by a method in accordance with jIS Rl648f the softening temperature by a method in accordance with JIS R22 09, and the coropression Strength by a method an accordance with JIS R160S. Further, with respect to the compression strength, from 25 each honeycomb filter, a square test specimen having cross-sectionally 5x6 cells and a length of 15 mm, was cut out, and this specimen was measured from three 23 directions i,e. (A) In the lengthwise axial direction (axial) , (B) in the vertical direction (tangential) and (C) in the direction inclined by 45° from the lengthwise axis (diagonal). TABLE 1 Porosity{%) Thermal expansion Thermal shock Softening temperature Compression strength coefficient resistance CO (A) (C) Example 1 43 1.2 950 1570 >5.0 >2.5 >! 2 Example 2 S3 1.5 3SD 1620 >8.3 >5 1 >1 0 Example 3 51 0 9 122 0 1680 >4 1 >1.9 >1 0 Comparativs Example 1 41 0.3 980 1680 >0.4 >0 1 >0 ,1 Comparative Example 2 42 4 0 400 - >6.0 >5 0 >1.5 Comparative Example 3 45 650 650 1320 >10 >1.3 >0.2 25 As is evident from Table l, each of the honeycombs in Examples l) 2 and 3 and Comparative Examples 2 and 3, has a porosity within a. range of from 40 to 60% and a high compression strength sufficient tor mounting 5 Comparative Example 1 is inadequate for mounting However, it is evident that each of the honeycombs in Examples 1, 2 and 3 has a thermal expansion coefficient very much smaller" than that in Comparative Example 2 and has a softening temperature very much higher than that in. 10 Comparative Example 3, Further, it is evident that with, respect to the thermal shock resistance, each of the honeycomb sintered products in Example 1, 2 and 3 has a property very much, higher than that in Comparative Example 2 or 3 15 THERMAL DECOMPOSITION RESISTANCE TEST From each of che honeycomb filters in Examples 1 and 2 and Comparative Example 1, a test specimen of 10 mm x 10 mm * 10 mm was cut out and held in a high temperature atmosphere of l,000°C, whereby the change with time of 20 the remaining ratio 0 (%) of aluminum titanate was investigated to carry out a thermal decomposition resistance test Here, the remaining ratio of aluminum titanate was obtained by the following method from the spectrum of the 25 X-ray diffraction measurement (XRD) Firstly, as A12O3 (corundum) and TiOs (rutile) are formed when aluminum titanate undergoes thermal 26 decomposition, using the integrated intensity (Ifio2(mol) of the diffraction peaK at the {110} face of rutile and the integrated intensity (IAT (0231)) of the diffraction peak at the (023) face of the aluminum titanate, the intensity 5 ratio r of aluminum titanate to rutile was obtained by the following formula: Farther, also with respect to the sintered product before carrying out the thermal treatment at l.000 0C, the 10 intensity ratio r0 of aluminum titanate to rutile was obtained in the same manner Then, uemg r and r0 obtained as described above, the remaining ratio 6(%) of aluminum titanate was obtained by the following formula P=(r/r0) * 100 15 With, respect to the respective honeycomb-shaped sintered products in Examples 1 and 2 and Comparative Example l, the changes with time of the remaining ratios β of the respective crystals are shown by a graph in Fig. 4 As is evident from Fig. 4, Examples 1 and 2 are 20 superior in the thermal decomposition resistance, as the remaining ratios are maintained at high levels over a long time, as compared with Comparative Example 1. Further, it is evident that while the remaining ratio in Example 1 after expiration of 50 hours in. Fig- 4 is 25 slightly low, the remaining ratio in Example 2 is still maintained at a high level and thus shows that the thermal decomposition resistance is further improved over 27 Example 1. INDUSTRIAL APPLICABILITY The honeyscomb filter material made of an aluminum 5 titanate sintered product by the present invention, is excellent in heat resistance and has high heat decomposition resistance and high mechanical strength, while maintaining a small thermal expansion coefficient and heat: shock resistance, and thus has substantially 10 superior properties as compared, with conventional filter materials. As a result, the honeycomb filter for exhaust gas of the present invention is useful to remove fine solid particles is. an exh&ust gae from a combust ion source of either a stationary body or a mobile body, 15 Especially, as mentioned above, it is most suitable for cleaning an exhaust gas froim an automobile having a Diesel engine mounted, where the severest properties are demanded - 28 CLAIMS 1. A honeycomb filter for cleaning an exhaust gas which is a honeycomb filter for removing solid particles containing carbon as their mam component in an exhaust 5 gas, characterised an that the material for the honeycomb filter is an aluminum tita.na.te sintered product obtained by firing at from 1,250 to l,700 0C a raw material mixture comprising- 100 parts by mass of a mixture {component X) 10 comprising TiO2 and Al2O3 m a molar ratio of the former/the latter being 40 to 6O/60 to 40, and from 1 to 10 parts by mass of an alkali feldspar represented by the empirical formula. (Nay K1 4)AlS1jO8 wherein 0 will be converted to MgO by firing [component Y] 2. The honeycomb filter for cleaning an exhaust gas according to Claim 1, wherein component Y is a mixture comprising the alkali feldspar represented by {NayK1. 20 y)AlSi302 (wherein 0 compound which will be converted to MgO by iiring 3 The honeycomb filter for cleaning an exhaust ga.s according to Claim 1, wherein the honeycomb filter has a 25 wall thickness of from 0 1 to o 6 mm and a cell density of from 15 to 93 cells/cm2, wherein the porosicy of Che partition wall 13 from 3 0 to 704, and the thermal 29 expansion coefficient, is at most 3.0 x10-6 K-1, 4. A. process for producing a honeycomb filter for cleaning an exhaust gas, characterized by preparing a mixture comprising: 5 100 parts by iiass of a mixture (component X) comprising TiOz and A12O3 in a, molar ratio of the former/the latter being 40 to 60/60 to 40, and from l to 10 parts by mass of an alkali feldspar- represented by the empirical formula (NayKi-y)AlSi3O3 10 [wherein 0 will be converted to MgO by firing {component Y) , adding molding agsistants to the mixture, followed by kneading to plasticize the mixture to make it extrusion- 15 proceasable, extrusaon processing it into a honeycomb structure, followed by firing at from 1,250 to l,7000C. 5 - The process for producing a honeycomb filter for cleaning an exhaust gas according to Claim 4, wherein component Y is a mixture comprising the alkali feldspar 20 represented by (NayKi-v}AlSi3Os (wherein O the Mg-containing compound which will be converted to MgO by firing 6. An apparatus for clesinang an exhaust gas, 25 characterised in that the honeycomb filter for cleaning an exhaust gas as defined in any one of Claims 1 to 3 is accommodated in a can 30 7 The apparatus for cleaning an exhaust gas according to Claim 6, which is used to cleaning an exhaust gas of an automobile having a diesel engine mounted. To provide a honeycomb filter for cleaning an exhaust gas, which is excellent in heat resistance and thermal shock resistance and has high thermal decomposition 5 resistance and high mechanical strength and which is thus capable of being used with stability at high and fluctuating temperatures, and a process for its production. A honeycomb filter for removing solid particles 10 containing carbon as the main component in an exhaust gas, characterised m that the material for the honeycomb filter is an aluminum titanate sintered product obtained by firing at from 1,250 to l,700°C a raw material mixture comprising 100 parts by mass of a mixture (component X) 15 comprising TiO2; and A12O3, in a molar ratio of the farmer/the latter being 40 to 6 0/6O tc 40, and from 1 to 10 -parts by mass of an alkali, feldspar represented by the empirical formula {NayKi-y)AlSi3O3 (wherein O 20 an Mg-containing compound which will be converted to MgO by faring (component Y) |
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00309-kolnp-2006-description complete.pdf
00309-kolnp-2006-international publication.pdf
309-KOLNP-2006-(13-01-2012)-FORM-27.pdf
309-KOLNP-2006-CORRESPONDENCE.pdf
309-kolnp-2006-granted-abstract.pdf
309-kolnp-2006-granted-assignment.pdf
309-kolnp-2006-granted-claims.pdf
309-kolnp-2006-granted-correspondence.pdf
309-kolnp-2006-granted-description (complete).pdf
309-kolnp-2006-granted-drawings.pdf
309-kolnp-2006-granted-examination report.pdf
309-kolnp-2006-granted-form 1.pdf
309-kolnp-2006-granted-form 18.pdf
309-kolnp-2006-granted-form 3.pdf
309-kolnp-2006-granted-form 5.pdf
309-kolnp-2006-granted-gpa.pdf
309-kolnp-2006-granted-reply to examination report.pdf
309-kolnp-2006-granted-specification.pdf
309-kolnp-2006-granted-translated copy of priority document.pdf
Patent Number | 238262 | ||||||||||||||||||
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Indian Patent Application Number | 309/KOLNP/2006 | ||||||||||||||||||
PG Journal Number | 05/2010 | ||||||||||||||||||
Publication Date | 29-Jan-2010 | ||||||||||||||||||
Grant Date | 28-Jan-2010 | ||||||||||||||||||
Date of Filing | 13-Feb-2006 | ||||||||||||||||||
Name of Patentee | OHCERA CO., LTD. | ||||||||||||||||||
Applicant Address | 1-19, UCHIHONMACHI 2-CHOME, CHUOU-KU, OSAKA-SHI, OSAKA | ||||||||||||||||||
Inventors:
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PCT International Classification Number | B01D 39/20 | ||||||||||||||||||
PCT International Application Number | PCT/JP2004/012312 | ||||||||||||||||||
PCT International Filing date | 2004-08-20 | ||||||||||||||||||
PCT Conventions:
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