Ceramic honeycomb structure and its production method

1. A ceramic honeycomb structure having pluralities of flow paths partitioned by porous cell walls,

(a) said cell walls having porosity of 50-60%; and

(b) in a pore diameter distribution in said cell walls measured by mercury porosimetry,

(i) a pore diameter d5 at a cumulative pore volume corresponding to 5% of the total pore volume being 22 μm or more and less than 55 μm,

a pore diameter d10 at 10% being 15-35 μm,

a pore diameter (median pore diameter) d50 at 50% being 10-20 μm,

a pore diameter d85 at 85% being 5-9 μm,

a pore diameter d90 at 90% being 3-8 μm,

a pore diameter d98 at 98% being 2.5 μm or less,

(d10−d90)/d50 being 1.3-1.8,

(d50−d90)/d50 being 0.45-0.75, and

(d10−d50)/d50 being 0.75-1.1; and

(ii) σ[=log d20−log d80] being 0.39 or less, wherein σ represents the difference between a logarithm of the pore diameter d20 at a cumulative pore volume corresponding to 20% of the total pore volume and a logarithm of the pore diameter d80 at 80%.

2. The ceramic honeycomb structure according to claim 1 , wherein a pore diameter d2 at a cumulative pore volume corresponding to 2% of the total pore volume is 75-250 μm, and the volume of pores of 20 μm or more is 0.12 cm 3 /g or less.

3. The ceramic honeycomb structure according to claim 1 , wherein said porosity is 52-60%.

4. The ceramic honeycomb structure according to claim 1 , wherein said median pore diameter d50 is 10-18 μm.

5. The ceramic honeycomb structure according to claim 1 , wherein said σ is 0.3 or less.