Honeycomb filter

A honeycomb filter comprising:

• partition walls having a porous partition wall base material which separates and forms a plurality of cells functioning as the flow paths of fluid and a surface layer provided on only an inflow side or both the inflow side and an outflow side of the partition wall base material,
• wherein predetermined cells each having an end opened on one side and the other end plugged on the other side and the remaining cells each having an end plugged on one side and the other end opened on the other end are alternately arranged, and
• the following conditions (1) to (5) are satisfied,
• (1) the peak pore diameter of the surface layer is equal to or smaller than the average pore diameter of the partition wall base material, and the porosity of the surface layer is larger than that of the partition wall base material,
• (2) the surface layer has a peak pore diameter of 0.3 μm or more and less than 20 μM and a porosity of 60% or more and less than 95% (measurement method is mercury porosimetry),
• (3) the thickness L1 of the surface layer is 0.5% or more and less than 30% of the thickness L2 of the partition walls,
• (4) the mass of the surface layer per filtration area is 0.01 mg/cm2 or more and less than 6 mg/cm2, and
• (5) the partition wall base material has an average pore diameter of 10 μm or more and less than 60 μm and a porosity of 40% or more and less than 65%.

A manufacturing method of a honeycomb filter comprising the steps of:

• beforehand obtaining a formed honeycomb article which separates and forms a plurality of cells functioning as the flow paths of fluid by forming means;
• mixing the same material as that of the formed honeycomb article, a pore former burnable and flyable at a temperature of 1000° C. or less, having an average pore diameter of less than 10 μm and having a ratio of 60 mass % or more and less than 90 mass % in a material solid content and water to obtain slurry;
• and
• depositing the slurry on only an inflow side or both the inflow side and an outflow side of the formed honeycomb article, and then performing drying or drying and firing to provide a surface layer on only the inflow side or both the inflow side and the outflow side of the formed honeycomb article.

A manufacturing method of a honeycomb filter comprising the steps of:

• beforehand manufacturing, as a fired article, a honeycomb structure provided with a porous partition wall base material which separates and forms a plurality of cells functioning as the flow paths of fluid;
• mixing at least one material selected from the material group consisting of alumina, zirconia, titania, zeolite and ceria, a pore former burnable and flyable at a temperature of 800° C. or less, having an average particle diameter of less than 10 μm and having a ratio of 20 mass % or more and less than 90 mass % in a material solid content and water to obtain slurry;
• and
• depositing the slurry on only an inflow side or both the inflow side and an outflow side of a formed honeycomb article, and then performing drying or drying and firing to provide a surface layer on only the inflow side or both the inflow side and the outflow side of the formed honeycomb article.