Patent ID: 8343431

Claim:
A honeycomb filter structured to have a large number of cells parted by porous partition walls, where the large number of cells include (i) inlet opening cells that extend along a length of the honeycomb filter and have open inlets on an inlet side of the honeycomb filter and closed outlets on an outlet side of the honeycomb filter that are sealed with outlet sealing members, and (ii) outlet opening cells that extend along the length of the honeycomb filter and have closed inlets on the inlet side of the honeycomb filter sealed with inlet sealing members and open outlets on the outlet side of the honeycomb filter, the inlet opening cells and the outlet opening cells are arranged alternately to be adjacent to each other, and each of the inlet opening cells has an inner surface covered with a surface layer having smaller pores than pores of the porous partition walls, wherein the surface layer has zero film thickness in an inlet peripheral region that represents an area extended from the open inlet of the opening cell to a specific depth corresponding to a length of the inlet sealing members of adjacent outlet opening cells opposite to the inner surface of the inlet opening cell, and then extends along the entire length of the inlet opening cell, wherein the surface layer has a tapered section where a film thickness gradually increases from a terminal end of the inlet peripheral region for a predetermined length, shorter than the entire length of the inlet opening cell, toward the outlet side of the inlet opening, and wherein, aside from the tapered region section, the surface layer has a constant thickness.