Honeycomb structure

A honeycomb structure comprising a honeycomb structure body having partition walls to define and form a plurality of cells extending from a first end surface as one end surface to a second end surface as the other end surface to become through channels of a fluid,

• wherein in a cross section perpendicular to an extending direction of the cells, the honeycomb structure body is constituted of a first region which is an inside region and a second region which is an outside region surrounding a periphery of the first region, and
• in the cross section perpendicular to the cell extending direction, the cells of a part positioned in the outermost periphery of the honeycomb structure body among the plurality of cells are incomplete cells in which a part of an outer periphery of a cross section of each of the cells has a shape along an outer peripheral shape of the honeycomb structure body,
• the cells other than the incomplete cells among the plurality of cells are complete cells having a polygonal sectional shape in the cross section perpendicular to the cell extending direction,
• the second region is from a region having a width corresponding to three cells in terms of the number of the complete cells from the outermost periphery of the honeycomb structure body toward a center thereof to a region having a width corresponding to 20 cells in terms of the number of the complete cells from the outermost periphery toward the center,
• an open area ratio in the first region of the honeycomb structure body is 83% or more,
• a porosity of the partition walls is from 20 to 60%,
• a thickness t1 of the partition walls constituting the first region is 0.11 mm or less,
• a thickness t2 of the partition walls constituting the second region is larger than the thickness t1 of the partition walls,
• a value (t3/t1) of a ratio between a thickness t3 of the partition walls forming the first complete cells from the outermost periphery of the honeycomb structure body toward the center thereof in the second region and the thickness t1 of the partition walls is from 1.2 to 1.4,
• a partition wall strength index A represented by Equation (1) described in the following in the first region is 4.0 or more,
• A=t12/Ls2×1000 Equation (1):
• where A is the partition wall strength index, and Ls is a partition wall central portion length (mm), and
• when intersecting portions of the partition walls are rounded intersecting portions having a round shape, Ls is calculated in accordance with Equation (2),
• Ls=p−t1−(Is−21/2t1)/(21/2−1) Equation (2):
• where p is a cell pitch (mm), and Is is a diagonal width (mm) in each of the rounded intersecting portions.