The honeycomb structure body has a dense part having a change ratio of porosity calculated by the following Expression (1) that is 1 to 5%. The honeycomb structure body also has an outside-diameter decreasing part in which the outside diameter decreases from the inflow end face to the outflow end face. The honeycomb structure body has a change ratio of average diameter calculated by the following Expression (2) that is 0.2 to 3%.
(1P.sub.x/P.sub.y)100,Expression (1): in Expression (1), P.sub.x denotes the porosity (%) at the center region of the outflow end face, and Py denotes the porosity (%) of a circumferential region of the outflow end face other than the center region.
(1D.sub.x/D.sub.y)100,Expression (2): in Expression (2), D.sub.x denotes the average diameter (mm) of the outflow end face, and D.sub.y denotes the average diameter (mm) of the inflow end face.

A honeycomb structure including prismatic columnar honeycomb segments and a bonding layer, wherein the bonding layer has rows in each of which bonding layer portions each disposed between two honeycomb segments arranged to face each other are arranged to extend from one point of a peripheral edge of a bonded body of the honeycomb segments to the other point thereof, in a cross section, the bonding layer of each of the-rows is disposed so that among the bonding layer portions arranged in one direction, an outermost circumference bonding layer portion and at least one of the other bonding layer portions are not superimposed on each other on an extension line of the one direction, and a ratio of shift of side surfaces of adjacent honeycomb segments to a length of one side of a side surface of honeycomb segments having the same cross-sectional shape is 10% or less.

A honeycomb filter includes a pillar-shaped honeycomb substrate including a porous partition wall that defines a plurality of cells extending from an inflow end face to an outflow end face, an inflow side plugging portion disposed at the inflow end face of the honeycomb substrate to plug open ends of outflow cells and an outflow side plugging portion disposed at the outflow end face of the honeycomb substrate to plug open ends of inflow cells other than the outflow cells. The honeycomb substrate includes the partition wall that defines two of the inflow cells by division. An average of the plugging length L.sub.IN of the inflow side plugging portions disposed in the outflow cells of the honeycomb substrate is larger than an average of the plugging length L.sub.OUT of the outflow side plugging portions disposed in the inflow cells of the honeycomb substrate.

A method for producing a honeycomb structure for fine particle collection filters, the honeycomb structure including a plurality of porous honeycomb structure segments. The method includes joining each of the porous honeycomb segments via a joining material layers by applying a joining material between joining surfaces of each of the porous honeycomb structure segments, through a nozzle portion of a joining material applicator. The nozzle portion of the joining material applicator includes: a joining material introduction port; a joining material discharge space; and a joining material flow path having a bent portion, through which the joining material passes from the joining material introduction port to the joining material discharge space. The joining material flow path of the nozzle portion includes a buffer space configured such that a flow path cross section gradually expands toward the joining material discharge space on a downstream side of the bent portion.

A honeycomb filter includes a pillar-shaped honeycomb substrate including a porous partition wall that defines a plurality of cells extending from an inflow end face to an outflow end face, an inflow side plugging portion disposed at the inflow end face of the honeycomb substrate to plug open ends of outflow cells; and an outflow side plugging portion disposed at the outflow end face of the honeycomb substrate to plug open ends of inflow cells other than the outflow cells. The honeycomb substrate includes the partition wall that defines two of the inflow cells by division. An average of the plugging length L.sub.OUT of the outflow side plugging portions disposed in the inflow cells of the honeycomb substrate is larger than an average of the plugging length L.sub.IN of the inflow side plugging portions disposed in the outflow cells of the honeycomb substrate.

A honeycomb structure includes honeycomb segments, bonding layers and a circumferential wall. The bonding layers include bottomed-hollow voids which extend toward an internal side in an axial direction from an end face of the honeycomb structure and which are formed at at least one of intersections, and a ratio of a depth of each void in the axial direction to a length of each honeycomb segment in the axial direction is 5% or more.

A honeycomb structure includes plugged honeycomb segments, bonding layers and a circumferential wall. The bonding layers includes bottomed-hollow unbonded portions, which extend toward an internal side in an axial direction from an end face of the honeycomb structure, in portions of circumferential bonding layers bonding the honeycomb segments on an outermost circumference. The unbonded portions exist on respective extended lines extending from an intersection of the bonding layers which is closest to a centroid of the end face. An opening length of the unbonded portion is 1 to 10 mm, a ratio of an opening depth of the unbonded portion to a length of the honeycomb segment is 10 to 45%, and a ratio of a distance from the circumferential wall to a point at which an open end of the unbonded portion ends to a length of the circumferential bonding layer is 5 to 100%.

A honeycomb segment joined body includes a plurality of honeycomb segments; and joining layers for bonding side surfaces of the plurality of honeycomb segments. Each of the joining layers is a cured product of a pasty joining material, and has a standard deviation of joined widths of 0.30 or less. The honeycomb segment joined body is produced by applying pressurization with vibration when joining side surfaces of a plurality of honeycomb segments using a pasty joining material.

Provided is a honeycomb fired body in which the pressure loss in the initial state where PM has not accumulated is sufficiently low, the strength is sufficiently high, and the heat capacity is not small. The honeycomb fired body of the present invention is a honeycomb fired body including a plurality of cells in each of which one end is plugged and which serve as channels of exhaust gas, and porous cell partition walls that define the cells, wherein the honeycomb fired body is formed of SiC, the plurality of cells include peripheral cells located at an outermost peripheral region of the honeycomb fired body and inner cells located more inward than the peripheral cells, all the inner cells have the same cross-sectional shape that is a rectangle in a plane perpendicular to the longitudinal direction thereof, each peripheral cell is defined by the cell partition walls and an outer wall forming a periphery of the honeycomb fired body, the cell partition walls in contact with the outer wall each have a thick wall region where the wall thickness gradually increases toward the outer wall, the cross-sectional shape of the peripheral cells in a plane perpendicular to the longitudinal direction thereof is a shape formed by reducing the rectangular cross-sectional shape of the inner cells to obtain a reduced rectangle and chamfering or rounding two corners of the reduced rectangle, the cross-sectional area of each peripheral cell in a plane perpendicular to the longitudinal direction thereof is 60 to 80% of the cross-sectional area of each inner cell in a plane perpendicular to the longitudinal direction thereof, the cell partition walls include inter-peripheral-cell cell partition walls each located between the peripheral cells and inter-inner-cell cell partition walls each located between the inner cells, and the minimum thickness of the inter-peripheral-cell cell partition walls is greater than the thickness of the inter-inner-cell cell partition walls.

The present invention provides a honeycomb filter including a honeycomb fired body including porous cell partition walls, exhaust gas introduction cells each having an open end at an exhaust gas inlet side and a plugged end at an exhaust gas outlet side, exhaust gas emission cells each having an open end at the exhaust gas outlet side and a plugged end at the exhaust gas inlet side, and an outer wall on the periphery thereof. The cross-sectional shape of each exhaust gas introduction cell in a plane perpendicular to the longitudinal direction thereof is entirely uniform from the end at the exhaust gas inlet side to the end at the exhaust gas outlet side excluding the plugged portion. The cross-sectional shape of each exhaust gas emission cell in a plane perpendicular to the longitudinal direction thereof is entirely uniform from the end at the exhaust gas inlet side to the end at the exhaust gas outlet side excluding the plugged portion. The exhaust gas emission cells, except for the cells adjacent to the outer wall, are each adjacently surrounded fully by the exhaust gas introduction cells across the porous cell partition walls. The cells adjacent to the outer wall include the exhaust gas introduction cells and the exhaust gas emission cells. A substantial ratio of the number of the exhaust gas introduction cells to the number of the exhaust gas emission cells (exhaust gas introduction cells:exhaust gas emission cells) is 4:1. All the exhaust gas introduction cells, except for the cells adjacent to the outer wall, have the same cross-sectional area in a plane perpendicular to the longitudinal direction thereof, the cross-sectional area of each exhaust gas introduction cell being smaller than that of each exhaust gas emission cell in a plane perpendicular to the longitudinal direction thereof.